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Background: Alterations in factors involved in cholesterol homeostasis are critical in Alzheimer's disease (AD), but the stage of occurrence, their specific association, and a possible relationship with the APOE4 genotype are not clarified. Objective: We aimed to quantify and correlate specific lipid factors in patients with different degrees of cognitive decline, namely patients with AD and patients with mild cognitive impairment due to AD (MCI-AD), carriers or non-carriers of the APOE4 genotype. Methods: We evaluated Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9), cholesterol and the oxidative metabolites 24-, 25-, 27-hydroxycholesterol (HC) in the cerebrospinal fluid (CSF) and serum of AD (n = 28) and MCI-AD (n = 27) patients. Results: CSF and serum PCSK9 and lipids were similar, except for higher serum PCSK9 and triglycerides in MCI-AD compared to AD. In CSF, AD APOE4 carriers showed higher PCSK9 and 24-HC (+61.3%, p = 0.027 and +32.7%, p = 0.037), compared to non-carriers. There was a negative association between CSF PCSK9 and 27-HC in AD (r = −0.444, p = 0.049) and, exclusively among AD APOE4 carriers, a negative association between CSF PCSK9 and 24-HC (r = −0.786, p = 0.028). A positive correlation was observed between CSF and serum PCSK9 in AD (r = 0.520, p = 0.004), driven by APOE4 carriers (r = 0.544, p = 0.038), suggesting PCSK9 exchange between brain and periphery. A positive correlation was detected between serum and CSF 27-HC (r = 0.465, p = 0.039) in AD. None of these results were found in MCI-AD patients. Conclusions: PCSK9 and 24-HC might be specific markers of ApoE4-associated lipid alterations in AD, possibly contributing to clinical progression in the AD continuum. [ABSTRACT FROM AUTHOR]

Cholesterol is an essential element for the development and normal function of the central nervous system. While peripheral cholesterol is influenced by liver metabolism and diet, brain cholesterol metabolism takes place in an isolated system due to the impermeability of the blood–brain barrier (BBB). However, cross-talk occurs between the brain and periphery, specifically through metabolites such as oxysterols that play key roles in regulating cholesterol balance. Several neurodegenerative conditions such as Alzheimer’s disease or Parkinson’s disease are considered to be affected by the loss of this balance. Also, the treatment of hypercholesterolemia needs to consider these discrete interferences between brain and peripheral cholesterol and the possible implications of each therapeutic approach. This is particularly important because of 27-hydroxycholesterol and 24-hydroxycholesterol, which can cross the BBB and are involved in cholesterol metabolism. This paper examines the metabolic pathways of cholesterol metabolism in the brain and periphery and focuses on the complex cross-talk between these metabolisms. Also, we emphasize the regulatory role of the BBB and the need for an integrated approach to cholesterol management.

Objective: The aim of this study was to investigate the role of cholesterol metabolism disorders in the etiopathogenesis of Autism Spectrum Disorder (ASD) through the analysis of central and peripheral oxysterol levels (24-hydroxycholesterol, 25-hydroxycholesterol, 27-hydroxycholesterol). These compounds, found in the cholesterol excretion pathways, are considered potential biomarkers for diagnosing and monitoring various neuropsychiatric disorders. Materials and Methods: This study included 42 children diagnosed with ASD, aged between 1 and 6 years, who had no additional psychiatric or medical illnesses other than cognitive delay/intellectual disability and were not on medication, along with 38 age-matched typically developing children. After comprehensive mental health assessments, the symptom severity in children with ASD was evaluated using the Childhood Autism Rating Scale, Autism Behavior Checklist, and Repetitive Behavior Scale-Revised Form. After the clinical evaluation, peripheral blood samples were obtained from all children. Oxysterol levels were assessed using liquid chromatography coupled with tandem mass spectrometry. Results: In the ASD group, levels of 24-hydroxycholesterol and 25-hydroxycholesterol were significantly higher compared to the control group, while 27-R-hydroxycholesterol levels were lower. The ratio of 24-hydroxycholesterol (µg/L) to 27-hydroxycholesterol (µg/L) was notably higher in the autism group. The receiver operating characteristic (ROC) analysis indicated that this ratio was statistically significant and could discriminate between ASD and non-ASD diagnoses with "acceptable discrimination potential." Conclusion: Our findings suggest that alterations in oxysterol levels, commonly associated with neurodegenerative processes, can also be observed in ASD and may serve as a potential candidate biomarker for the disorder. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Apolipoprotein E4 (APOE4) carriers' tendency toward hypercholesterolemia may contribute to Alzheimer's disease (AD) risk through oxysterols, which traverse the blood‐brain barrier. METHODS: Relationships between baseline plasma oxysterols, APOE status, serum lipids, and cognitive impairment risk were examined in 328 postmenopausal women from the Women's Health Initiative Memory Study. Women were followed for 25 years or until incident dementia or cognitive impairment. RESULTS: Levels of 24(S)‐hydroxycholesterol (24‐OHC), 27‐hydroxycholesterol (27‐OHC), and 24‐OHC/27‐OHC ratio did not differ by APOE status (p's > 0.05). Higher 24‐OHC and 27‐OHC were associated with higher total, low density lipoprotein (LDL), non‐high density lipoprotein (HDL), remnant, LDL/HDL, and total/HDL cholesterol and triglycerides (p's < 0.05). Higher 24‐OHC/27‐OHC was associated with greater dementia risk (hazard ratio = 1.51, 95% confidence interval:1.02‐2.22), which interaction analyses revealed as significant for APOE3 and APOE4+, but not APOE2+ carriers. DISCUSSION: Less favorable lipid profiles were associated with higher oxysterol levels. A higher ratio of 24‐OHC/27‐OHC may contribute to dementia risk in APOE3 and APOE4+ carriers. [ABSTRACT FROM AUTHOR]

Objective: Disruption of cholesterol homeostasis in Alzheimer’s disease (AD) plays a crucial role in diseasepathogenesis, making it a potential therapeutic target. Mesenchymal stem cells (MSCs) show promise in treatingcognitive impairment and provide a novel therapeutic approach. This study aims to investigate the effects of MSCs onspecific metabolites associated with brain cholesterol homeostasis in an AD rat model.Materials and Methods: In this experimental study, animals were divided into three groups: control, AD, andAD+MSCs. AD was induced using amyloid beta (Aβ) and confirmed through the Morris water maze (MWM) behaviouraltest and Congo red staining. MSCs were extracted, characterised via flow cytometry, subjected to osteoblast andadipose differentiation, and injected intraventricularly. The cholesterol metabolite levels were measured using gaschromatography-mass spectrometry (GC)-MS and compared among the groups.Results: Treatment with MSCs significantly improved memory function in the AD+MSCs group compared to theAD group and the number of beta-amyloid plaques decreased according to histological assessment. Disturbancesin the brain cholesterol metabolites that included desmosterol, 7-dehydrocholesterol, 24S-hydroxycholesterol,27-hydroxycholesterol and cholesterol were observed in the AD group compared to the control group. Treatment withMSCs resulted in significant alterations in the levels of these metabolites.Conclusion: The findings indicate that MSC therapy has the potential to improve AD by modulating brain cholesterolhomeostasis and promoting the differentiation of stem cells into nerve cells. The results emphasize the importance ofinvestigating the role of cholesterol metabolites in the context of MSC therapy to gain deeper insights into underlyingmechanisms of the therapeutic efficacy of MSCs in AD.

Apolipoprotein J (APOJ) is a multifunctional protein with genetic evidence suggesting an association between APOJ polymorphisms and Alzheimer’s disease as well as exfoliation glaucoma. Herein we conducted ocular characterizations of Apoj−/− mice and found that their retinal cholesterol levels were decreased and that this genotype had several risk factors for glaucoma: increased intraocular pressure and cup-to-disk ratio and impaired retinal ganglion cell (RGC) function. The latter was not due to RGC degeneration or activation of retinal Muller cells and microglia/macrophages. There was also a decrease in retinal levels of 24-hydroxycholesterol, a suggested neuroprotectant under glaucomatous conditions and a positive allosteric modulator of N-methyl-d-aspartate receptors mediating the light-evoked response of the RGC. Therefore, Apoj−/− mice were treated with low-dose efavirenz, an allosteric activator of CYP46A1 which converts cholesterol into 24-hydroxycholesterol. Efavirenz treatment increased retinal cholesterol and 24-hydroxycholesterol levels, normalized intraocular pressure and cup-to-disk ratio, and rescued in part RGC function. Retinal expression of Abcg1 (a cholesterol efflux transporter), Apoa1 (a constituent of lipoprotein particles), and Scarb1 (a lipoprotein particle receptor) was increased in EVF-treated Apoj−/− mice, indicating increased retinal cholesterol transport on lipoprotein particles. Ocular characterizations of Cyp46a1−/− mice supported the beneficial efavirenz treatment effects via CYP46A1 activation. The data obtained demonstrate an important APOJ role in retinal cholesterol homeostasis and link this apolipoprotein to the glaucoma risk factors and retinal 24-hydroxycholesterol production by CYP46A1. As the CYP46A1 activator efavirenz is an FDA-approved anti-HIV drug, our studies suggest a new therapeutic approach for treatment of glaucomatous conditions. [ABSTRACT FROM AUTHOR]

Abstract Background Efavirenz is an anti-HIV drug, and cytochrome P450 46A1 (CYP46A1) is a CNS-specific enzyme that metabolizes cholesterol to 24-hydroxycholesterol (24HC). We have previously shown that allosteric CYP46A1 activation by low-dose efavirenz in a transgenic mouse model of Alzheimer’s disease (AD) enhanced both cholesterol elimination and turnover in the brain and improved animal performance in memory tests. Here, we sought to determine whether CYP46A1 could be similarly activated by a low-dose efavirenz in human subjects. Methods This pilot study enrolled 5 subjects with early AD. Participants were randomized to placebo (n = 1) or two daily efavirenz doses (50 mg and 200 mg, n = 2 for each) for 20 weeks and evaluated for safety and CYP46A1 target engagement (plasma 24HC levels). A longitudinal mixed model was used to ascertain the statistical significance of target engagement. We also measured 24HC in CSF and conducted a unique stable isotope labeling kinetics (SILK) study with deuterated water to directly measure CYP46A1 activity changes in the brain. Results In subjects receiving efavirenz, there was a statistically significant within-group increase (P ≤ 0.001) in the levels of plasma 24HC from baseline. The levels of 24HC in the CSF of subjects on the 200-mg dose of efavirenz were also increased. Target engagement was further supported by the labeling kinetics of 24HC by deuterated water in the SILK study. There were no serious adverse effects in any subjects. Conclusions Our findings suggest efavirenz target engagement in human subjects with early AD. This supports the pursuit of a larger trial for further determination and confirmation of the efavirenz dose that exerts maximal enzyme activation, as well as evaluation of this drug’s effects on AD biomarkers and clinical symptomatology. Trial registration ClinicalTrials.gov, NCT03706885.

The retina and brain are separated from the systemic circulation by the anatomical barriers, which are permeable (the outer blood-retinal barrier) and impermeable (the blood-brain and inner blood-retina barriers) to cholesterol. Herein we investigated whether whole-body cholesterol maintenance affects cholesterol homeostasis in the retina and brain. We used hamsters, whose whole-body cholesterol handling is more similar to those in humans than in mice, and conducted separate administrations of deuterated water and deuterated cholesterol. We assessed the quantitative significance of the retinal and brain pathways of cholesterol input and compared the results with those from our previous studies in mice. The utility of the measurements in the plasma of deuterated 24-hydroxycholesterol, the major cholesterol elimination product from the brain, was investigated as well. We established that despite a sevenfold higher serum LDL to HDL ratio and other cholesterol-related differences, in situ biosynthesis remained the major source of cholesterol for hamster retina, although its quantitative significance was reduced to 53% as compared to 72%–78% in the mouse retina. In the brain, the principal pathway of cholesterol input was also the same, in situ biosynthesis, accounting for 94% of the total brain cholesterol input (96% in mice); the interspecies differences pertained to the absolute rates of the total cholesterol input and turnover. We documented the correlations between deuterium enrichments of the brain 24-hydroxycholesterol, brain cholesterol, and plasma 24-hydroxycholesterol, which suggested that deuterium enrichment of plasma 24-hydroxycholesteol could be an in vivo marker of cholesterol elimination and turnover in the brain.

Considerable evidence indicates that cholesterol oxidation products, named oxysterols, play a key role in several events involved in Alzheimer's disease (AD) pathogenesis. Although the majority of oxysterols causes neuron dysfunction and degeneration, 24-hydroxycholesterol (24-OHC) has recently been thought to be neuroprotective also. The present study aimed at supporting this concept by exploring, in SK-N-BE neuroblastoma cells, whether 24-OHC affected the neuroprotective SIRT1/PGC1α/Nrf2 axis. We demonstrated that 24-OHC, through the up-regulation of the deacetylase SIRT1, was able to increase both PGC1α and Nrf2 expression and protein levels, as well as Nrf2 nuclear translocation. By acting on this neuroprotective pathway, 24-OHC favors tau protein clearance by triggering tau ubiquitination and subsequently its degradation through the ubiquitin–proteasome system. We also observed a modulation of SIRT1, PGC1α, and Nrf2 expression and synthesis in the brain of AD patients with the progression of the disease, suggesting their potential role in neuroprotection. These findings suggest that 24-OHC contributes to tau degradation through the up-regulation of the SIRT1/PGC1α/Nrf2 axis. Overall, the evidence points out the importance of avoiding 24-OHC loss, which can occur in the AD brain, and of limiting SIRT1, PGC1α, and Nrf2 deregulation in order to prevent the neurotoxic accumulation of hyperphosphorylated tau and counteract neurodegeneration. [ABSTRACT FROM AUTHOR]

CYP46A1 is a CNS-specific enzyme, which eliminates cholesterol from the brain and retina by metabolism to 24-hydroxycholesterol, thus contributing to cholesterol homeostasis in both organs. 2-Hydroxypropyl-β-cyclodextrin (HPCD), a Food and Drug Administration-approved formulation vehicle, is currently being investigated off-label for treatment of various diseases, including retinal diseases. HPCD was shown to lower retinal cholesterol content in mice but had not yet been evaluated for its therapeutic benefits. Herein, we put Cyp46a1−/− mice on high fat cholesterol-enriched diet from 1 to 14 months of age (control group) and at 12 months of age, started to treat a group of these animals with HPCD until the age of 14 months. We found that as compared with mature and regular chow-fed Cyp46a1−/− mice, control group had about 6-fold increase in the retinal total cholesterol content, focal cholesterol and lipid deposition in the photoreceptor-Bruch’s membrane region, and retinal macrophage activation. In addition, aged animals had cholesterol crystals at the photoreceptor-retinal pigment epithelium interface and changes in the Bruch’s membrane ultrastructure. HPCD treatment mitigated all these manifestations of retinal cholesterol dyshomeostasis and altered the abundance of six groups of proteins (genetic information transfer, vesicular transport, and cytoskeletal organization, endocytosis and lysosomal processing, unfolded protein removal, lipid homeostasis, and Wnt signaling). Thus, aged Cyp46a1−/− mice on high fat cholesterol-enriched diet revealed pathological changes secondary to retinal cholesterol overload and supported further studies of HPCD as a potential therapeutic for age-related macular degeneration and diabetic retinopathy associated with retinal cholesterol dyshomeostasis.

Background: Efavirenz is an anti-HIV drug, and cytochrome P450 46A1 (CYP46A1) is a CNS-specific enzyme that metabolizes cholesterol to 24-hydroxycholesterol (24HC). We have previously shown that allosteric CYP46A1 activation by low-dose efavirenz in a transgenic mouse model of Alzheimer’s disease (AD) enhanced both cholesterol elimination and turnover in the brain and improved animal performance in memory tests. Here, we sought to determine whether CYP46A1 could be similarly activated by a low-dose efavirenz in human subjects. Methods: This pilot study enrolled 5 subjects with early AD. Participants were randomized to placebo (n = 1) or two daily efavirenz doses (50 mg and 200 mg, n = 2 for each) for 20 weeks and evaluated for safety and CYP46A1 target engagement (plasma 24HC levels). A longitudinal mixed model was used to ascertain the statistical significance of target engagement. We also measured 24HC in CSF and conducted a unique stable isotope labeling kinetics (SILK) study with deuterated water to directly measure CYP46A1 activity changes in the brain. Results: In subjects receiving efavirenz, there was a statistically significant within-group increase (P ≤ 0.001) in the levels of plasma 24HC from baseline. The levels of 24HC in the CSF of subjects on the 200-mg dose of efavirenz were also increased. Target engagement was further supported by the labeling kinetics of 24HC by deuterated water in the SILK study. There were no serious adverse effects in any subjects. Conclusions: Our findings suggest efavirenz target engagement in human subjects with early AD. This supports the pursuit of a larger trial for further determination and confirmation of the efavirenz dose that exerts maximal enzyme activation, as well as evaluation of this drug’s effects on AD biomarkers and clinical symptomatology. Trial registration: ClinicalTrials.gov, NCT03706885. [ABSTRACT FROM AUTHOR]

The brain cholesterol content is determined by the balance between the pathways of in situ biosynthesis and cholesterol elimination via 24-hydroxylation catalyzed by cytochrome P450 46A1 (CYP46A1). Both pathways are tightly coupled and determine the rate of brain cholesterol turnover. Evidence is accumulating that modulation of CYP46A1 activity by gene therapy or pharmacologic means could be beneficial in the case of neurodegenerative and other brain diseases and affect brain processes other than cholesterol biosynthesis and elimination. This minireview summarizes these other processes, most common of which include abnormal protein accumulation, memory, and cognition, motor behavior, gene transcription, protein phosphorylation as well as autophagy and lysosomal processing. The unifying mechanisms, by which these processes could be affected by CYP46A targeting are also discussed.

Cytochrome P450 46A1 (CYP46A1 or cholesterol 24-hydroxylase) controls cholesterol elimination from the brain and plays a role in higher order brain functions. Genetically enhanced CYP46A1 expression in mouse models of Alzheimer's disease mitigates the manifestations of this disease. We enhanced CYP46A1 activity pharmacologically by treating 5XFAD mice, a model of rapid amyloidogenesis, with a low dose of the anti-HIV medication efavirenz. Efavirenz was administered from 1 to 9 months of age, and mice were evaluated at specific time points. At one month of age, cholesterol homeostasis was already disturbed in the brain of 5XFAD mice. Nevertheless, efavirenz activated CYP46A1 and mouse cerebral cholesterol turnover during the first four months of administration. This treatment time also reduced amyloid burden and microglia activation in the cortex and subiculum of 5XFAD mice as well as protein levels of amyloid precursor protein and the expression of several genes involved in inflammatory response. However, mouse short-term memory and long-term spatial memory were impaired, whereas learning in the context-dependent fear test was improved. Additional four months of drug administration (a total of eight months of treatment) improved long-term spatial memory in the treated as compared to the untreated mice, further decreased amyloid-β content in 5XFAD brain, and also decreased the mortality rate among male mice. We propose a mechanistic model unifying the observed efavirenz effects. We suggest that CYP46A1 activation by efavirenz could be a new anti-Alzheimer's disease treatment and a tool to study and identify normal and pathological brain processes affected by cholesterol maintenance.

Background: For several decades, it has been recognized that overactivation of the glutamate-gated N-methyl-D-aspartate receptors (NMDARs) and subsequent Ca 2+ toxicity play a critical role in ischemic brain injury. 24S-hydroxycholesterol (24S-HC) is a major cholesterol metabolite in the brain, which has been identified as a potent positive allosteric modulator of NMDAR in rat hippocampal neurons. We hypothesize that 24S-HC worsens ischemic brain injury via its potentiation of the NMDAR, and reducing the production of 24S-HC by targeting its synthetic enzyme CYP46A1 provides neuroprotection., Methods: We tested this hypothesis using electrophysiological, pharmacological, and transgenic approaches and in vitro and in vivo cerebral ischemia models., Results: Our data show that 24S-HC potentiates NMDAR activation in primary cultured mouse cortical neurons in a concentration-dependent manner. At 10 µmol/L, it dramatically increases the steady-state currents by 51% and slightly increases the peak currents by 20%. Furthermore, 24S-HC increases NMDA and oxygen-glucose deprivation-induced cortical neuronal injury. The increased neuronal injury is largely abolished by NMDAR channel blocker MK-801, suggesting an NMDAR-dependent mechanism. Pharmacological inhibition of CYP46A1 by voriconazole or gene knockout of Cyp46a1 dramatically reduces ischemic brain injury., Conclusions: These results identify a new mechanism and signaling cascade that critically impacts stroke outcome: CYP46A1 → 24S-HC → NMDAR → ischemic brain injury. They offer proof of principle for further development of new strategies for stroke intervention by targeting CYP46A1 or its metabolite 24S-HC., Competing Interests: Dr Leng discloses the pending patent US Application No. 18/527,676. The other authors report no conflicts.

Non-cholesterol sterols are transported in plasma lipoproteins and are consequently important in cholesterol metabolism. We investigated the distribution of non-cholesterol sterol precursors of cholesterol synthesis (NCSPCS), oxysterols, and phytosterols in lipoproteins of healthy subjects differing according to HDL-Cholesterol (HDL-C) plasma levels. Elevated NCSPCS (desmosterol, lathosterol) in the High HDL group suggests that HDL exports these sterols from cells, but not the cholesterol metabolite 24-OHC which was higher in the Low HDL group than in the High HDL group. 27-hydroxycholesterol (27OH-C) plasma levels did not differ between groups. Percentage of NCSPCS and phytosterols predominates in LDL, but did not differ between groups. Thirty percent of desmosterol and lathosterol are present in HDL, with the High HDL group carrying higher percentage of these sterols. A high percentage of campesterol and sitosterol in HDL suggests that phytosterols are absorbed by enterocytes, and that HDL could be a marker of the ABCA1/ApoA1 intestinal activity.

Cytochrome P450 46A1 (CYP46A1) is a key enzyme responsible for metabolizing cholesterol to 24‐hydroxycholesterol in the brain, and thus might serve as a therapeutic target for several neurodegenerative disorders including Parkinson's disease, Alzheimer's disease and Huntington's disease. However, an applicable, sensitive and reliable method for the precise measurement of CYP46A1 activities in complex biological samples remains limited. In this study, a novel ultra‐high‐performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method for highly sensitive and selective determination of 24‐hydroxycholesterol was developed to characterize CYP46A1 activity. The mass spectrometric detection was performed using multiple reaction monitoring for 24‐hydroxcholesterol at m/z 385.2 → 367.2. The limit of quantification for 24‐hydroxycholesterol using this UPLC–MS/MS method was as low as 10 nM, which is lower than those reported previously. The method also showed favorable accuracy and precision. Meanwhile, the short‐ and long‐term stability of this method was fully validated. In addition, the method was successfully applied to investigate the kinetic properties of 24‐hydroxycholesterol formation by CYP46A1. [ABSTRACT FROM AUTHOR]

Considerable evidence indicates that cholesterol oxidation products, named oxysterols, play a key role in several events involved in Alzheimer’s disease (AD) pathogenesis. Although the majority of oxysterols causes neuron dysfunction and degeneration, 24-hydroxycholesterol (24-OHC) has recently been thought to be neuroprotective also. The present study aimed at supporting this concept by exploring, in SK-N-BE neuroblastoma cells, whether 24-OHC affected the neuroprotective SIRT1/PGC1α/Nrf2 axis. We demonstrated that 24-OHC, through the up-regulation of the deacetylase SIRT1, was able to increase both PGC1α and Nrf2 expression and protein levels, as well as Nrf2 nuclear translocation. By acting on this neuroprotective pathway, 24-OHC favors tau protein clearance by triggering tau ubiquitination and subsequently its degradation through the ubiquitin–proteasome system. We also observed a modulation of SIRT1, PGC1α, and Nrf2 expression and synthesis in the brain of AD patients with the progression of the disease, suggesting their potential role in neuroprotection. These findings suggest that 24-OHC contributes to tau degradation through the up-regulation of the SIRT1/PGC1α/Nrf2 axis. Overall, the evidence points out the importance of avoiding 24-OHC loss, which can occur in the AD brain, and of limiting SIRT1, PGC1α, and Nrf2 deregulation in order to prevent the neurotoxic accumulation of hyperphosphorylated tau and counteract neurodegeneration.

Abstract Objective This study measured and analyzed the serum levels of 24‐hydroxycholesterol in patients with probable Alzheimer's disease (AD) and age‐/sex‐matched controls. Methods A case‐control study involving 40 AD patients and 40 controls was performed at a tertiary neurological teaching hospital in eastern India. Blood and serum samples were collected for APOE genotyping and 24‐hydroxycholesterol levels, respectively. Results Serum 24‐hydroxycholesterol was significantly lower in AD patients compared to controls (median concentration: controls, 47.14 ng/mL (interquartile range, 16.34); AD patients, 32.93 ng/mL (interquartile range, 9.45); P

Cholesterol, an essential component of the brain, and its local metabolism are involved in many neurodegenerative diseases. The blood-brain barrier is impermeable to cholesterol; hence, cholesterol homeostasis in the central nervous system represents a balance between in situ biosynthesis and elimination. Cytochrome P450 46A1 (CYP46A1), a central nervous system-specific enzyme, converts cholesterol to 24-hydroxycholesterol, which can freely cross the blood-brain barrier and be degraded in the liver. By the dual action of initiating cholesterol efflux and activating the cholesterol synthesis pathway, CYP46A1 is the key enzyme that ensures brain cholesterol turnover. In humans and mouse models, CYP46A1 activity is altered in Alzheimer’s and Huntington’s diseases, spinocerebellar ataxias, glioblastoma, and autism spectrum disorders. In mouse models, modulations of CYP46A1 activity mitigate the manifestations of Alzheimer’s, Huntington’s, Nieman-Pick type C, and Machao-Joseph (spinocerebellar ataxia type 3) diseases as well as amyotrophic lateral sclerosis, epilepsy, glioblastoma, and prion infection. Animal studies revealed that the CYP46A1 activity effects are not limited to cholesterol maintenance but also involve critical cellular pathways, like gene transcription, endocytosis, misfolded protein clearance, vesicular transport, and synaptic transmission. How CYP46A1 can exert central control of such essential brain functions is a pressing question under investigation. The potential therapeutic role of CYP46A1, demonstrated in numerous models of brain disorders, is currently being evaluated in early clinical trials. This review summarizes the past 70 years of research that has led to the identification of CYP46A1 and brain cholesterol homeostasis as powerful therapeutic targets for severe pathologies of the CNS.

The understanding of the excitotoxic processes associated with a severe status epilepticus (SE) is of major importance.Changes of brain cholesterol homeostasis is an emerging candidate for excitotoxicity. We conducted an overall analysis of the cholesterol homeostasis both (i) in fluids and tissues from patients with SE: blood (n = 63, n = 87 controls), CSF (n = 32, n = 60 controls), and post-mortem brain tissues (n = 8, n = 8 controls) and (ii) in a mouse model of SE induced by an intrahippocampal injection of kainic acid.24-hydroxycholesterol levels were decreased in kainic acid mouse hippocampus and in human plasma and post-mortem brain tissues of patients with SE when compared with controls. The decrease of 24-hydroxycholesterol levels was followed by increased cholesterol levels and by an increase of the cholesterol synthesis. Desmosterol levels were higher in human CSF and in mice and human hippocampus after SE. Lanosterol and dihydrolanosterol levels were higher in plasma from SE patients.Our results suggest that a CYP46A1 inhibition could occur after SE and is followed by a brain cholesterol accumulation. The excess of cholesterol is known to be excitotoxic for neuronal cells and may participate to neurological sequelae observed after SE. This study highlights a new pathophysiological pathway involved in SE excitotoxicity.

Cholesterol, an essential component of the brain, and its local metabolism are involved in many neurodegenerative diseases. The blood-brain barrier is impermeable to cholesterol; hence, cholesterol homeostasis in the central nervous system represents a balance between in situ biosynthesis and elimination. Cytochrome P450 46A1 (CYP46A1), a central nervous system-specific enzyme, converts cholesterol to 24-hydroxycholesterol, which can freely cross the blood-brain barrier and be degraded in the liver. By the dual action of initiating cholesterol efflux and activating the cholesterol synthesis pathway, CYP46A1 is the key enzyme that ensures brain cholesterol turnover. In humans and mouse models, CYP46A1 activity is altered in Alzheimer's and Huntington's diseases, spinocerebellar ataxias, glioblastoma, and autism spectrum disorders. In mouse models, modulations of CYP46A1 activity mitigate the manifestations of Alzheimer's, Huntington's, Nieman-Pick type C, and Machao-Joseph (spinocerebellar ataxia type 3) diseases as well as amyotrophic lateral sclerosis, epilepsy, glioblastoma, and prion infection. Animal studies revealed that the CYP46A1 activity effects are not limited to cholesterol maintenance but also involve critical cellular pathways, like gene transcription, endocytosis, misfolded protein clearance, vesicular transport, and synaptic transmission. How CYP46A1 can exert central control of such essential brain functions is a pressing question under investigation. The potential therapeutic role of CYP46A1, demonstrated in numerous models of brain disorders, is currently being evaluated in early clinical trials. This review summarizes the past 70 years of research that has led to the identification of CYP46A1 and brain cholesterol homeostasis as powerful therapeutic targets for severe pathologies of the CNS. [ABSTRACT FROM AUTHOR]

Introduction: Apolipoprotein E4 (APOE4) carriers' tendency toward hypercholesterolemia may contribute to Alzheimer's disease (AD) risk through oxysterols, which traverse the blood-brain barrier., Methods: Relationships between baseline plasma oxysterols, APOE status, serum lipids, and cognitive impairment risk were examined in 328 postmenopausal women from the Women's Health Initiative Memory Study. Women were followed for 25 years or until incident dementia or cognitive impairment., Results: Levels of 24(S)-hydroxycholesterol (24-OHC), 27-hydroxycholesterol (27-OHC), and 24-OHC/27-OHC ratio did not differ by APOE status (p's > 0.05). Higher 24-OHC and 27-OHC were associated with higher total, low density lipoprotein (LDL), non-high density lipoprotein (HDL), remnant, LDL/HDL, and total/HDL cholesterol and triglycerides (p's < 0.05). Higher 24-OHC/27-OHC was associated with greater dementia risk (hazard ratio = 1.51, 95% confidence interval:1.02-2.22), which interaction analyses revealed as significant for APOE3 and APOE4+, but not APOE2+ carriers., Discussion: Less favorable lipid profiles were associated with higher oxysterol levels. A higher ratio of 24-OHC/27-OHC may contribute to dementia risk in APOE3 and APOE4+ carriers., (© 2024 The Authors. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Efavirenz (EFV) is an anti-HIV drug, and cytochrome P450 46A1 (CYP46A1) is the major brain cholesterol hydroxylase. Previously, we discovered that EFV activates CYP46A1 and improves behavioral performance in 5XFAD mice, an Alzheimer's disease model. Herein, the unbiased omics and other approaches were used to study 5XFAD mice in the amyloid-decreasing paradigm of CYP46A1 activation by EFV. These approaches revealed increases in the brain levels of postsynaptic density protein 95, gephyrin, synaptophysin, synapsin, glial fibrillary acidic protein, and CYP46A1 and documented altered expression and phosphorylation of 66 genes and 77 proteins, respectively. The data obtained pointed to EFV effects at the synaptic level, plasmin-depended amyloid clearance, inflammation and microglia phenotype, oxidative stress and cellular hypoxia, autophagy and ubiquitin-proteasome systems as well as apoptosis. These effects could be realized in part via changes in the Ca2+-, small GTPase, and catenin signaling. A model is proposed, in which CYP46A1-dependent lipid raft rearrangement and subsequent decrease of protein phosphorylation are central in EFV effects and explain behavioral improvements in EFV-treated 5XFAD mice. [ABSTRACT FROM AUTHOR]

Efavirenz, the FDA-approved anti-retroviral medication, is evaluated in the clinical trial in patients with mild cognitive impairment or early dementia due to Alzheimer's disease. Efavirenz is assessed for activation of cytochrome P450 46A1 (CYP46A1), a CNS-specific enzyme that converts cholesterol to 24-hydroxycholesterol. Cholesterol 24-hydroxylation is the major pathway for brain cholesterol removal, and a mechanism that controls brain cholesterol turnover. The present study tested efavirenz on 5XFAD mice (an Alzheimer's model) at a very low daily dose of 0.1 mg/kg body weight. Efavirenz treatment started from three months of age, after amyloid plague appearance, and continued for 6 months. This treatment led to CYP46A1 activation in the brain, enhancement of brain cholesterol turnover, behavioral improvements, reduction in microglia activation but increased astrocyte reactivity. The levels of the soluble and insoluble amyloid 40 and 42 peptides were unchanged while the number and area of the dense core amyloid plaques were slightly decreased. The measurements of the brain levels of several pre- and post-synaptic proteins (Munc13-1, PSD-95, gephyrin, synaptophysin, synapsin-1, and calbindin-D28k) suggested efavirenz effect at the synaptic level. Efavirenz treatment in the present work seems to represent a model of behavioral and other improvements independent of the levels of the amyloid peptides and provides insight into potential outcomes of the future clinical trial. [ABSTRACT FROM AUTHOR]

Cholesterol 24-hydroxylation is the major mechanism for cholesterol removal from the brain and the reaction catalyzed by cytochrome P450 46A1 (CYP46A1), a CNS-specific enzyme. This review describes CYP46A1 in the context of cholesterol homeostasis in the brain and summarizes available experimental data on CYP46A1 association with different neurologic diseases, including the mechanisms by which changes in the CYP46A1 activity in the brain could be beneficial for these diseases. The modulation of CYP46A1 activity by genetic and pharmacologic means is also presented along with a brief synopsis of the two clinical trials that evaluate CYP46A1 as a therapeutic target for Alzheimer's disease as well as Dravet and Lennox-Gastaut syndromes. [ABSTRACT FROM AUTHOR]

Objective: This study measured and analyzed the serum levels of 24‐hydroxycholesterol in patients with probable Alzheimer's disease (AD) and age‐/sex‐matched controls. Methods: A case‐control study involving 40 AD patients and 40 controls was performed at a tertiary neurological teaching hospital in eastern India. Blood and serum samples were collected for APOE genotyping and 24‐hydroxycholesterol levels, respectively. Results: Serum 24‐hydroxycholesterol was significantly lower in AD patients compared to controls (median concentration: controls, 47.14 ng/mL (interquartile range, 16.34); AD patients, 32.93 ng/mL (interquartile range, 9.45); P < 0.001) but showed no significant correlation with Mini Mental State Examination (MMSE) score in AD cases (r = −0.169, P = 0.298) or in controls (r = 0.18, P = 0.26). No statistically significant difference was observed between serum 24‐hydroxycholesterol levels of the APOE4‐positive and ‐negative subgroups in AD patients (P = 0.79). Findings were consistent and unchanged even when the ratio of serum 24‐hydroxycholesterol to serum total cholesterol was considered. Conclusion: The decreased 24‐hydroxycholesterol level in peripheral circulation in AD cases observed in the present study may suggest its role in AD pathogenesis. The lack of a clear correlation between serum levels of 24‐hydroxycholesterol and MMSE score—a surrogate marker of AD severity—raises the question as to whether 24‐hydroxycholesterol level declines with decreasing neuronal mass or whether the steroid continues to play a protective role. [ABSTRACT FROM AUTHOR]

Abstract Aims 24-Hydroxycholesterol (24HC) is the main brain cholesterol metabolite, which level in the circulation is significantly changed under physiological and pathological conditions. Here, we have studied the effect of 24HC on the inotropic responses to β-adrenoceptor (AR) stimulation. Main methods Electrical stimulation-evoked contractions were recorded in isolated atria from mice. Fluorescent dyes, Fluo-4 and DAF-FM, were used for estimation of Ca2+ transient and NO production, respectively. Key findings We revealed that 24HC in the submicromolar range attenuated β-AR-induced positive inotropy in isolated atria. This was accompanied by a decrease in Ca2+ transient and unchanged nitric oxide (NO) production. However, β1-AR-induced positive inotropy and enhancement of Ca2+ transient were increased by 24HC due to suppression of NO production. Only β2-AR-dependent inotropy and enhancement of Ca2+ transient were decreased by 24HC in a NO-independent manner. Inhibition of phosphodiesterase (PDE) suppressed effect of 24HC on β2-AR-dependent contractility as well as on non-subtype specific β-AR activation. Moreover, 24HC counteracted positive inopropic action of PDE inhibitors, IBMX and rolipam. Thus, 24HC modulates the effects of β1- and β2-AR stimulation via different mechanisms linked with change in activity of NO synthase or PDE, respectively. Under conditions of non-selective activation of β-ARs, the depressant effect of 24HC related with β2-AR-dependent signaling dominates. Significance We suggest that 24HC could serve as a modulator of atrial β-AR signaling, contributing to regulation of contractility. Graphical abstract Unlabelled Image Highlights • We studied alteration in responses to β-adrenoceptor stimulation in the mice atria. • 24-Hydroxycholesterol suppressed effects of β-adrenoceptors on contractility and [Ca2+] in. • The oxysterol affected responses to β1 and β2-adrenoceptor activation in different ways. • The mechanisms of oxysterol effects were dependent on NO synthase and phosphodiesterase. • 24-Hydroxycholesterol is a potential modulator of β-adrenoceptor dependent signaling. [ABSTRACT FROM AUTHOR]

Abstract Cholesterol and its oxygenated metabolites, such as oxysterols, are intensively investigated as potential players in the pathophysiology of brain disorder. Altered oxysterol levels have been described in patients with numerous neuropsychiatric disorders, including Alzheimer's disease, Amyotrophic Lateral Sclerosis, Parkinson's disease, X-linked adrenoleukodystrophy, and Smith-Lemli-Opitz Syndrome. Recent studies have shown that Autism Spectrum Disorders are associated with disruption of cholesterol metabolism. The present study aimed at investigating the profile of oxysterols in plasma and their association with clinical parameters in patients with Autism Spectrum Disorders. Thirty-six children with Autism Spectrum Disorders and thirty-eight healthy children, from Sfax (a southern area of Tunisia) matched for age and sex, were included in the study. The severity of Autism Spectrum Disorders was evaluated using the childhood autism rating scale. Standard lipid profile (total cholesterol, triglycerides, and high-density lipoprotein-cholesterol), serum glucose, high-sensitive C-reactive protein and orosomucoid levels were measured utilizing standard techniques. Oxysterol levels were measured by isotope-dilution gas chromatography/mass spectrometry. Standard lipid profile, serum glucose, high-sensitive C-reactive protein and orosomucoid levels were similar between the two studied populations. Compared to the control group, children with Autism Spectrum Disorders showed a significant higher plasma level of 24-hydroxycholesterol, while borderline significance was observed for 7α-hydroxycholesterol, and 25-hydroxycholersterol. In patients, 24-hydroxycholesterol was inversely correlated with age. Multivariate analysis showed that high plasma levels of 24-hydroxycholesterol are independent risk factors for Autism Spectrum Disorders. On the other hand, an analysis of the receiver's operating characteristics proved that the measured parameters recorded satisfactory levels of specificity and sensitivity. The present study provides evidence that Autism Spectrum Disorders are associated with altered levels in circulating oxysterols. The finding that 24-hydroxycholesterol is an independent risk factor for the disease and suggests the use of this oxysterol as a diagnostic tool in Autism Spectrum Disorders. Highlights • Altered profile of oxysterols inASD. • 24-hydroxycholesterol is an independent risk factor and a predictive marker for ASD. [ABSTRACT FROM AUTHOR]

Cytochromes P450 (CYPs) constitute a family of enzymes that can be found in the endoplasmic reticulum (ER), mitochondria or the cell surface of the cells. CYPs are characterized by carrying out the oxidation of organic compounds and they are mainly recognized as mediators of the biotransformation of xenobiotics to polar hydrophilic metabolites that can be eliminated from the organism. However, these enzymes play a key role in many other physiological processes, being involved in diverse indispensable metabolic pathways since they metabolize many endogenous substrates. Various CYP isoforms are expressed in the brain, and it is believed that this could be in part due to the particular function of brain CYPs. In the brain, CYPs are involved in the cholesterol turnover, the biosynthesis of dopamine, serotonin, morphine, hormones, and protective lipid mediators (epoxyeicosatrienoic acids), in addition to their already recognized role in xenobiotics detoxification and psychotropic drug metabolism. Increasing evidence suggests that this group of enzymes is fundamental for the normal functioning and maintenance of brain homeostasis. This review is focused on highlighting the importance of CYP-mediated endogenous metabolism in the central nervous system (CNS) and its relationship with recent findings regarding CYP involvement in neurodegenerative diseases. Some therapeutic approaches focused on CYP regulation are also discussed. [ABSTRACT FROM AUTHOR]

The potential use of cholesterol esterases was tested to avoid alkaline hydrolysis for cleavage of plasma esterified oxysterols. The enzymatic hydrolysis was optimized by testing two sources of enzyme— Pseudomonas and bovine pancreas, presence of surfactants, incubation time and amount of enzyme. Free forms of 4β-, 7-, 24-, 25- and 27-hydroxycholesterol (HC) as well 7-ketocholesterol (7-KC) were analyzed by liquid chromatography and mass-spectrometry using the deuterated internal standard, 25-HC(d6). Enzymatic hydrolysis was more effective using the Pseudomonas enzyme and in presence of surfactants. Compared to alkaline hydrolysis, it generated a cleaner chromatographic baseline and better recovery of the internal standard. Oxysterols were assayed with detection limits between 7 and 31 pg/mL. Interassay coefficients of variation were lower than 10% and extraction recovery efficiencies, higher than 90%. The procedure was used to characterize plasma levels of Cyp7b1- deficient rat, where it showed increased plasma levels of 7, 24 and 25-HC. Due to the low volume of sample required, it may be used in other animal models, particularly rodents, as well as in pediatric samples where sample amount is always a problem. Thus, the proposed new method offers mild enzymatic processing that greatly facilitates oxysterol determinations to delineate their role in physiopathology. [ABSTRACT FROM AUTHOR]

In mice, dietary cuprizone causes brain demyelination with subsequent spontaneous remyelination upon return to normal chow. Heavy water (2H 2 O) labeling with mass spectrometric analysis can be used to measure brain de novo synthesis of several myelin components including cholesterol, phospholipids, galactocereboside (GalC) and myelin-associated proteins. 24-hydroxycholesterol (24-OHC), the major metabolite of brain cholesterol, is detected in blood and is believed to be specifically derived from CNS cholesterol metabolism. We assessed changes in syntheses of myelin components in brain and of blood sterols during cuprizone-induced experimental demyelination and remyelination, with and without thyroid hormone (T3) treatment. Mice were fed cuprizone for 4 weeks, then returned to control diet and treated with either placebo or T3 (0.005 mg/day). 2H 2 O was administered for the last 14 days of cuprizone diet, and for either 6, 12 or 19 days of treatment during recovery from cuprizone, after which blood and corpus callosum (CC) samples were collected (n = 5/time point/treatment). 2H incorporation into cholesterol and 24-OHC in blood and CC, and incorporation into phospholipid (PL)-palmitate, GalC, myelin basic protein (MBP) and 2′,3′-cyclic-nucleotide 3′-phosphodiesterase (CNPase) in CC were measured. Cuprizone significantly (p < 0.05) decreased syntheses of cholesterol, 24-OHC, GalC, MBP, CNPase and PL-palmitate in the CC and these effects were all reversed during recovery. T3 treatment significantly (p < 0.05) increased syntheses of cholesterol, 24-OHC and palmitate compared to placebo. 24-OHC and cholesterol turnover rates in brain and blood were nearly identical and 24-OHC rates in blood paralleled rates in CC, indicating that blood 24-OHC derives primarily from the brain and reflects oligodendrocyte function. In summary, changes in synthesis of several lipid and protein components in brain during cuprizone-induced demyelination and remyelination are measurable through stable isotope labeling. Blood 24-OHC turnover rates closely reflect flux rates of brain cholesterol in response to cuprizone and T3, which alter oligodendrocyte function. Labeling of blood 24-OHC has potential as a non-invasive marker of brain de novo cholesterol synthesis and breakdown rates in demyelinating conditions. • Deuterated water labeling measures synthesis of brain myelin lipids and proteins. • Myelin lipid and protein synthesis are altered by cuprizone and during recovery. • Brain and blood 24-OHC turnover reflects changes in brain cholesterol turnover. • Thyroid hormone increases myelin lipid synthesis during recovery from cuprizone. [ABSTRACT FROM AUTHOR]

Abnormal cholesterol metabolism is an established feature of Alzheimer's disease (AD). Cerebrospinal fluid (CSF) is the fluid surrounding the central nervous system, and the protein and lipid content alterations in the CSF could be biomarkers for degenerative changes in the brain. The laboratory diagnosis of AD is limited to the analysis of three biomarkers in CSF: Aβ42, total tau, and phospho-tau. The purpose of this analysis is to systematically analyze the available data describing the biomarkers of cholesterol and its metabolites in the CSF of subjects with AD. MEDLINE, EMBASE, and the Cochrane Central database were systematically queried to collect studies that have evaluated the markers of cholesterol and its metabolites in the CSF of subjects with mild cognitive impairment (MCI) or AD and age-matched controls. Analysis of the published data shows that the levels of cholesterol are increased in MCI subjects; 24-hydroxycholesterol and 27-hydroxycholesterol are elevated in AD and MCI subjects compared to controls. There is a significant dysfunction of cholesterol metabolism in the CSF of AD subjects. This analysis indicates that in addition to the available biomarkers in the CSF, such as Aβ42, total tau, and phospho-tau, 24-hydroxycholesterol, 27-hydroxycholesterol, and cholesterol appear to be sensitive biomarkers for the evaluation of MCI and AD. [ABSTRACT FROM AUTHOR]

24-Hydroxycholesterol (24OH-C) is esterified by the enzyme lecithin-cholesterol acyltransferase (LCAT) in the cerebrospinal fluid (CSF). We report here that the level of 24OH-C esters was lower in CSF of patients with amyotrophic lateral sclerosis than in healthy subjects (54% vs 68% of total 24OH-C, p = 0.0005; n = 8). Similarly, the level of 24OH-C esters in plasma was lower in patients than in controls (62% vs 77% of total 24OH-C; p = 0.0076). The enzyme amount in CSF, as measured by densitometry of the protein band revealed by immunoblotting, was about 4-fold higher in patients than in controls ( p = 0.0085). As differences in the concentration of the LCAT stimulator Apolipoprotein E were not found, we hypothesized that the reduced 24OH-C esterification in CSF of patients might depend on oxidative stress. We actually found that oxidative stress reduced LCAT activity in vitro, and 24OH-C effectively stimulated the enzyme secretion from astrocytoma cells in culture. Enhanced LCAT secretion from astrocytes might represent an adaptive response to the increase of non-esterified 24OH-C percentage, aimed to avoid the accumulation of this neurotoxic compound. The low degree of 24OH-C esterification in CSF or plasma might reflect reduced activity of LCAT during neurodegeneration. [ABSTRACT FROM AUTHOR]

Objective of this work was to evaluate the protective effect of vitamin E on the cooked ham. Ninety-six pigs (LW X L X P), forty-eight barrows and forty-eight gilts were divided in four randomized blocks. Each block received four treatments: a control diet, diets formulated with 100 mg, with 200 mg and with 400 mg of vitamin E/kg diet. The average cholesterol values in cooked ham were 46.53 ± 0.47 mg/100g. However, a reduction of 30% was observed in samples of supplemented diets with 400 mg of vitamin E/kg. During shelf-life of the cooked ham was observed a reduction in the cholesterol levels, with the associated production of cholesterol oxides. The cholesterol oxides observed were: cholesta-4,6-dien-3-one; 20alpha-hydroxycolesterol; 24-hydroxycholesterol, and 25-hidroxycholesterol. Supplementation of 200 mg of vitamin E/kg or more maintained the cholesterol oxides values below 10 µg/g during the 116 days before slaughter.O objetivo deste trabalho foi avaliar o efeito protetor da vitamina E no presunto cozido. Noventa e seis suínos (LW X L X P), 48 machos castrados e 48 fêmeas foram divididos aleatoriamente em 4 blocos. Cada bloco recebeu 4 tratamentos: dieta controle, dietas formuladas com 100 mg, com 200 mg e com 400 mg de vitamina E/kg de ração. O período de fornecimento da dieta foi de 116 dias antes do abate, quando os suínos atingiram uma média de peso de 110 kg. O presunto cozido foi produzido em um frigorífico, e estocado a 5,0 ± 0,2°C para as análises químicas. Análise de colesterol e óxidos de colesterol foram feitas em amostras de presunto cozido com 0, 30 e 60 dias de armazenamento. O colesterol e os óxidos de colesterol foram determinados por cromatografia líquida. A média para os níveis de colesterol foi de 46,53 ± 0,47 mg/100g. Entretanto, foi observada uma redução de 30% nos níveis de colesterol das amostras que receberam suplementação de 400 mg de vitamina E/kg. Durante o armazenamento do presunto cozido foi observado uma redução nos níveis de colesterol, associada a um aumento nos níveis de óxido de colesterol. Os óxidos de colesterol observados foram: cholesta-4,6-dien-3-one; 20alfa-hydroxycolesterol; 24-hydroxycholesterol e 25-hidroxycholesterol. Níveis de suplementação de 200 mg de vitamina E/kg ou mais, fornecidos durante 116 dias antes do abate, mantiveram os teores de óxidos de colesterol abaixo de 10 µg/g.

The accumulation and aggregation of the amyloid-β peptide (Aβ) in the brain are important contributing factors to Alzheimer's disease (AD). Consequently, blocking the generation of Aβ is a potentially important treatment strategy. Recent work on the metabolism of Aβ has identified several cellular proteins and proteases that collectively promote or prevent the generation of Aβ.In addition, accumulating in vitro and in vivo evidence suggests a role for cholesterol in modulating the cellular processing of Aβ with the potential to affect AD.

Multiple sclerosis (MS) is a chronic central nervous system disease that is associated with progressive loss of myelin and subsequent axonal degeneration. Cholesterol is an essential component of mammalian cellular and myelin membranes. In this systematic review, we examined the relationship between levels of cholesterol and markers of cholesterol turnover in circulation and/or cerebrospinal fluid (CSF) and disease outcomes in adults with clinically isolated syndrome (CIS) or confirmed MS. Studies suggest that elevated levels of circulating low density lipoprotein cholesterol (LDL), total cholesterol, and particularly, apolipoprotein B and oxidized LDL are associated with adverse clinical and MRI outcomes in MS. These relationships were observed as early as CIS. The studies also suggest that oxysterols, cholesterol precursors, and apolipoprotein E may be markers of specific disease processes in MS, but more research is required to elucidate these processes and relationships. Taken together, the data indicate that cholesterol and markers of cholesterol turnover have potential to be used clinically as biomarkers of disease activity and may even be implicated in the pathogenesis of MS. [ABSTRACT FROM AUTHOR]

Background: Cholesterol has essential functions in neurological processes that require tight regulation of synthesis and metabolism. Perturbed cholesterol homeostasis has been demonstrated in Huntington's disease, however the exact role of these changes in disease pathogenesis is not fully understood. Objective: This study aimed to comprehensively examine changes in cholesterol biosynthetic precursors, metabolites and oxidation products in the striatum and cortex of the R6/1 transgenic mouse model of Huntington's disease. We also aimed to characterise the progression of the physical phenotype in these mice. Methods: GC-MS/MS was used to quantify a broad range of sterols in the striatum and cortex of R6/1 and wild type mice at 6, 12, 20, 24 and 28 weeks of age. Motor dysfunction was assessed over 28 weeks using the RotaRod and the hind-paw clasping tests. Results: 24(S)-Hydroxycholesterol and 27-hydroxycholesterol were the major cholesterol metabolites that significantly changed in R6/1 mice. These changes were specifically localised to the striatum and were detected at the end stages of the disease. Cholesterol synthetic precursors (lathosterol and lanosterol) were significantly reduced in the cortex and striatum by 6 weeks of age, prior to the onset of motor dysfunction, as well as the cognitive and affective abnormalities previously reported. Elevated levels of desmosterol, a substrate of delta(24)-sterol reductase (DHCR24), were also detected in R6/1 mice at the end time-point. Female R6/1 mice exhibited a milder weight loss and hind paw clasping phenotype compared to male R6/1 mice, however, no difference in the brain sterol profile was detected between sexes. Conclusion: Several steps in cholesterol biosynthetic and metabolic pathways are differentially altered in the R6/1 mouse brain as the disease progresses and this is most severe in the striatum. This provides further insights into early molecular mediators of HD onset and disease progression and identifies candidate molecular targets for novel therapeutic approaches. [ABSTRACT FROM AUTHOR]

Ageing accompanied by a decline in cognitive performance may be a result of the long-term effects of oxidative stress on neurologic processes. It has been shown that high-cholesterol contents in the blood and brain may lead to the deposition of the β-amyloid (Aβ) protein in the brain, which damages brain cells. The present study was designed to observe the effect of polyphenol-rich Oriental plums on cognitive function and cerebral neurodegeneration-related protein expression in mice that were fed a high-cholesterol diet for 5 months. The study consisted of four groups: the control (Ctrl) group, which was fed the American Institute of Nutrition (AIN)-93M diet; the high cholesterol (HC) group, which was fed the AIN-93M diet with 5 % cholesterol; the high cholesterol+low Oriental plum (LOP) group, which was fed the AIN-93M diet with 5 % cholesterol and 2 % Oriental plum powder; and the high cholesterol+high Oriental plum (HOP) group, which was fed the AIN-93M diet with 5 % cholesterol and 5 % Oriental plum powder. Measurements of cognitive function were assessed using the Morris water maze, and the mRNA expression of cholesterol hydroxylase (Cyp46), Aβ and β-secretase 1 (BACE1) were analysed. The results showed that cholesterol concentrations in both the blood and the brain were significantly higher in the HC group than in the Ctrl and HOP groups at the end of the trial. The high-cholesterol diet per se produced significant cognitive deficits, which were accompanied by a significantly increased mRNA expression of Cyp46, BACE1, Aβ and 24-hydroxycholesterol in the brain cortex and hippocampus. However, all of these variables were non-significantly increased in the HOP group as compared to the Ctrl group. In conclusion, incorporating polyphenol-enriched Oriental plum into a high-cholesterol diet can ameliorate some of the symptoms of neurodegenerative conditions. [ABSTRACT FROM PUBLISHER]

Abstract: Background: HDL is considered the most important mechanism for the excretion of intracellular cholesterol. The liver is the only organ capable to metabolize cholesterol into bile acid. The enzymatic conversion of cholesterol to bile acid is dependent on the cytochrome P450 microsomal system which is also responsible for the generation of oxysterols. The latter's plasma concentrations may reflect the metabolic processes of specific tissues where they are generated. The objective of this study was to investigate in healthy individuals who differ according to their HDL levels the concentration of oxysterols and relate it to the HDL-dependent cell cholesterol efflux rate. Methods: 24-Hydroxycholesterol, 25-hydroxycholesterol, 27-hydroxycholesterol were determined in plasma by GLC/mass spectrometry in 107 healthy subjects with low HDL (HDL-C<1.03mmol/l) and high HDL cholesterol (HDL-C>1.55mmol/l). HDL-dependent in vitro cell cholesterol efflux rate was measured in 29 cases. Results: No differences were found in plasma oxysterol concentrations between the Low HDL and High HDL groups. There was a significant negative correlation between HDL-C and 27-hydroxycholesterol. Plasma oxysterol concentrations were significantly lower in female than in male subjects. The Low HDL male group had higher 27-hydroxycholesterol than the High HDL male group. Cell cholesterol efflux rate was lower in Low HDL than in High HDL and related inversely with 27-hydroxycholesterol. Conclusion: As compared to High HDL, Low HDL men have increased 27-hydroxycholesterol plasma level that may circumvent their reduced cell cholesterol efflux rate. [Copyright &y& Elsevier]

An abnormal accumulation of cholesterol oxidation products in the brain of patients with Alzheimer's disease ( AD) would further link an impaired cholesterol metabolism in the pathogenesis of the disease. The first evidence stemming from the content of oxysterols in autopsy samples from AD and normal brains points to an increase in both 27-hydroxycholesterol (27- OH) and 24-hydroxycholesterol (24- OH) in the frontal cortex of AD brains, with a trend that appears related to the disease severity. The challenge of differentiated SK-N- BE human neuroblastoma cells with patho-physiologically relevant amounts of 27- OH and 24- OH showed that both oxysterols induce a net synthesis of Aβ1-42 by up-regulating expression levels of amyloid precursor protein and β-secretase, as well as the β-secretase activity. Interestingly, cell pretreatment with N-acetyl-cysteine ( NAC) fully prevented the enhancement of β-amyloidogenesis induced by the two oxysterols. The reported findings link an impaired cholesterol oxidative metabolism to an excessive β-amyloidogenesis and point to NAC as an efficient inhibitor of oxysterols-induced Aβ toxic peptide accumulation in the brain. [ABSTRACT FROM AUTHOR]

• Oxidized cholesterol molecules (oxysterols) have been implicated in multiple sclerosis (MS). • The relationship between oxysterol and vascular pathology was investigated in 99 MS patients and 38 healthy controls. • Higher 24-hydroxycholesterol (HC) levels are associated with smaller lumen of the common carotid artery (CCA) in relapsing-remitting MS patients. • Higher 24HC levels were also associated with greater time-averaged and peak diastolic velocities. • Potent anti-inflammatory therapy may decrease the oxysterol levels in MS patients. Multiple sclerosis (MS) studies suggest greater cardiovascular disease burden and disturbances in the cholesterol pathways. The potential impact of oxidized cholesterol molecules on MS is emerging. To determine the relationship between multiple oxysterol molecules and atherosclerosis burden in MS patients. A total of 99 MS patients (61 relapsing-remitting MS(RRMS) and 38 progressive MS (PMS)) patients and 38 healthy controls (HCs) underwent magnetic resonance angiography (MRA) and the cross-sectional area (CSA) of the common carotid artery (CCA) was determined at three different levels before the bifurcation (C7, C6 and C5). Additionally, an echo-color Doppler ultrasound was performed and measures of blood flow velocities were derived. Blood samples acquired at the time of the imaging examinations were analyzed and 24-, 25-, 27-hydroxycholesterol (24HC, 25HC, 27HC) and 7-ketocholesterol (7KC) were quantified in ng/mL In the MS patients, higher levels of 24HC were significantly associated with smaller CCA CSA measured at all three cervical levels (r =-0.201, p = 0.046; r =-0.228, p = 0.023, and r =-0.215, p = 0.032, for C7, C6 and C5, respectively). These associations were driven by the RRMS group only (r =-0.407, p = 0.002 for C7; r =-0.414, p = 0.002, for C6; and r =-0.368, p = 0.006 for C5). No associations were seen in the HCs. Despite adjusting for the significant age effect (B = 0.445, p = 0.004), higher 24HC levels were independently associated with smaller CCA CSA (B =-0.20, p = 0.045). 24HC was additionally associated with greater time-averaged and peak diastolic CCA velocities. RRMS patients treated with potent anti-inflammatory therapies had lower oxysterol levels (p = 0.019). Greater 24HC levels are associated with smaller CSA CCA and greater flow velocities in RRMS patients. [ABSTRACT FROM AUTHOR]

High cholesterol turnover catalyzed by cholesterol 24-hydroxylase is essential for neural functions, especially learning. Because 24(S)-hydroxycholesterol (24- OHC), produced by 24-hydroxylase, induces apoptosis of neuronal cells, it is vital to eliminate it rapidly from cells. Here, using differentiated SH- SY5Y neuron-like cells as a model, we examined whether 24- OHC is actively eliminated via transporters induced by its accumulation. The expression of ABCA1 and ABCG1 was induced by 24- OHC, as well as TO901317 and retinoic acid, which are ligands of the nuclear receptors liver X receptor/retinoid X receptor ( LXR/ RXR). When the expression of ABCA1 and ABCG1 was induced, 24- OHC efflux was stimulated in the presence of high-density lipoprotein ( HDL), whereas apolipoprotein A-I was not an efficient acceptor. The efflux was suppressed by the addition of si RNA against ABCA1, but not by ABCG1 si RNA. To confirm the role of each transporter, we analyzed human embryonic kidney 293 cells stably expressing human ABCA1 or ABCG1; we clearly observed 24- OHC efflux in the presence of HDL, whereas efflux in the presence of apolipoprotein A-I was marginal. Furthermore, the treatment of primary cerebral neurons with LXR/ RXR ligands suppressed the toxicity of 24- OHC. These results suggest that ABCA1 actively eliminates 24- OHC in the presence of HDL as a lipid acceptor and protects neuronal cells. [ABSTRACT FROM AUTHOR]

Cholesterol metabolism is implicated in the etiology of Alzheimer's disease (AD) and amyloid production in the brain. While brain cholesterol cannot be measured directly in vivo, the oxysterol, 24S-hydroxycholesterol (24-OHC), is the predominant metabolite of brain cholesterol and can be measured in the blood. The aim of this review is to evaluate plasma 24-OHC as a potential biomarker of AD risk and discuss factors related to its levels in the brain and blood. This systematic review examines studies published between 1950 and June 2012 that examined the relationship between plasma 24-OHC, cognition, brain structure, and dementia using the following key words ('24S-hydroxycholesterol' or '24-hydroxycholesterol') and ('Brain' or 'Cognitive'). We found a total of 28 studies of plasma 24-OHC and neurodegenerative disease, including a subset of 12 that used dementia as a clinical endpoint. These studies vary in the direction of the observed associations. Results suggest plasma 24-OHC may be higher in the early stages of cognitive impairment and lower in more advanced stages of AD when compared to cognitively normal controls. Measures of 24-OHC in the blood may be an important potential marker for cholesterol metabolism in the brain and risk of AD. Further studies of plasma 24-OHC and dementia must account for the stage of disease, establish the temporal trends in oxysterol concentrations, and employ neuroimaging modalities to assess the structural and metabolic changes occurring in the brain prior to the onset of cognitive impairment. [ABSTRACT FROM AUTHOR]

In spite of the fact that cholesterol does not pass the blood-brain barrier, hypercholesterolemia has been linked to increase Alzheimer's disease (AD) risk. Hypertension is another risk factor and angiotensin converting enzyme (ACE) activity is known to be increased in AD. Furthermore, a lower incidence of AD has been reported in patients taking anti-hypertensive drugs. Here we show that the levels of angiotensinogen (AGT) and ACE are increased in the cerebrospinal fluid (CSF) of patients with mild cognitive impairment and AD. Moreover, we show ACE activity in the CSF to be positively correlated with both plasma and CSF levels of 27-hydroxycholesterol (27-OH), an oxysterol known to pass through the BBB and taken up from the circulation by the brain. In addition, treatment of rat primary neurons, astrocytes, and human neuroblastoma cells with 27-OH resulted in increased production of AGT. Our results demonstrate that upregulation of renin-angiotensin system (RAS) in AD brains occurs not only at the enzymatic level (ACE) but also at the substrate level (AGT). The possibility that 27-OH is part of a mechanism linking hypercholesterolemia with increased brain RAS activity and increased AD risk is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Despite apolipoprotein E''s important role in cholesterol transport and metabolism in the brain as well as its influence on Alzheimer''s disease, the impact of the human APOE genotype on cholesterol metabolism in brain has not been fully examined. This study was carried out to investigate APOE genotype effects on oxysterols measured. In this study the measurement of cholesterol and several oxysterols in the brains of human APOE ε2, ε3 and ε4 knock-in mice at 8 weeks and 1 year of age using gas chromatography mass spectrometry (GC–MS) demonstrated no APOE genotype or age effect on total brain cholesterol and the oxysterol 24-hydroxycholesterol. The level of 27-hydroxycholesterol was elevated in 1 year old animals for all APOE genotypes. Interestingly, lathosterol an indicator of cholesterol synthesis was significantly reduced in the 1 year old animals for all APOE genotypes. APOE ε4 expressing mice exhibited statistically lower levels of lathosterol compared to APOE ε2 in both the young and old mice. Oxidized cholesterol metabolites were significantly lower in APOE ε2 mice compared to other genotypes at 8 weeks old. Although minimal differences were observed between APOE E3 and E4 knock-in (KI) mice, these findings indicate that there are some clear APOE genotype specific effects on brain cholesterol synthesis and associated metabolic pathways, particularly in APOE ε2 KI mice. [Copyright &y& Elsevier]