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Polyunsaturated fatty acids (PUFA) are fundamental building materials for cells and play crucial function as signaling molecules. When PUFA are used as substrates for non-enzymatic or enzymatic reactions and gut microbiota metabolism, they can generate electrophilic derivatives (called Reactive Lipid Species, RLS) that promptly form adducts with nucleophilic molecules. RLS participate in several signaling pathways, including the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, which is the key mechanism in the maintenance of redox, metabolic and protein homeostasis, as well as the regulation of inflammation. Recent studies have provided insights on the localization of enzymes that synthesise reactive oxygen or nitrogen species (ROS or RNS respectively) in plasma membrane compartments (raft/caveolae) which also harbour PUFA esters, from which free acid forms can be released by phospholipase A2 activity (PLA 2), and the complex of Nrf2 with the inhibitory protein Kelch-like ECH-associated Protein 1(Keap1). Additional investigations have indicated that dietary PUFA insertion into specific plasma membrane microdomains may alter the lipid environment and thereby influence caveolar composition and cell signaling. Given that PUFA-originated RLS attack such a complex and promote the release of active Nrf2, it cannot be excluded that all the biochemical machinery for Nrf2 activation is present in caveolae, where it triggers the Nrf2-mediated adaptive response for rescuing or maintaining cellular redox homeostasis. Here, we specifically aimed to summarize current information with regard to the roles of dietary PUFA and RLS in Nrf2-mediated redox homeostasis, namely 1) their role as Nrf2 activators, 2) the significance of the in vivo conversion of PUFA into RLS and 3) the caveolar involvement in cell signaling for redox homeostasis. [ABSTRACT FROM AUTHOR]

24-hydroxycholesterol (24OH-C) is synthesized almost exclusively in neurons. This oxysterol is mostly present as ester form in both cerebrospinal fluid and plasma. The enzyme lecithin-cholesterol acyltransferase esterifies 24OH-C in the brain, and the level of 24OH-C esters in cerebrospinal fluid was found to be correlated with the level of 24OH-C esters in plasma. Decreased levels of 24OH-C esters levels were previously found in Alzheimer’s disease and Amyotrophic Lateral Sclerosis. This finding was attributed to the inhibitory effect of oxidative stress on lecithin-cholesterol acyltransferase activity in neurodegenerative conditions. Data reported here show that the plasma level of 24OH-C esters is decreased also in Parkinson’s disease. ROC analysis identified 69.0% of 24OH-C esterification as the threshold (AUC = 0.98) discriminating patients (N = 19) from healthy subjects (N = 19) with 100% specificity vs controls, 89.5% sensitivity, 94.7% accuracy, and 100% precision. The level of 24OH-C esters was not correlated with UPDRS I or UPDRS III when evaluated at the time of blood sampling. By contrast, it was negatively correlated with UPDRS I (r = −0.4984, p = 0.0299) after one year of follow up. Therefore, this level might represent a novel biomarker of neurodegeneration in Parkinson’s disease. The biomarker level is here proposed as a measure to evaluate the severity of disease, as well as to monitor the progression of this pathology. [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]

Abstract: Oxidative stress is caused by imbalance between the production of reactive oxygen species (ROS) and biological system ability to readily detoxify the reactive intermediates or repair the resulting damage. 2-deoxy-D-ribose (dRib) is known to induce apoptosis by provoking an oxidative stress by depleting glutathione (GSH). In this paper, we elucidate the mechanisms underlying GSH depletion in response to dRib treatment. We demonstrated that the observed GSH depletion is not only due to inhibition of synthesis, by inhibiting gamma-glutamyl-cysteine synthetase, but also due to its increased efflux, by the activity of multidrug resistance associated proteins transporters. We conclude that dRib interferes with GSH homeostasis and that likely cellular oxidative stress is a consequence of GSH depletion. Various GSH fates, such as direct oxidation, lack of synthesis or of storage, characterize different kinds of oxidative stress. In the light of our observations we conclude that dRib does not induce GSH oxidation but interferes with GSH synthesis and storage. Lack of GSH allows accumulation of ROS and cells, disarmed against oxidative insults, undergo apoptosis. [Copyright &y& Elsevier]

Abstract: Growing evidence suggests that atherogenesis is associated with inflammation or defective removal of cholesterol excess from peripheral cells. Apolipoprotein A-I [ApoA-I] activates the enzyme Lecithin-Cholesterol Acyl-Transferase to esterify cell cholesterol for transport to liver. Haptoglobin [Hpt] was previously found able to bind ApoA-I, and suggested to reduce the enzyme activation. The aim of this study was to demonstrate that enhanced levels of Hpt, as present during inflammation, are associated with low enzyme activity and increased thickness of the arterial wall. Enzyme activity and Hpt concentration were analysed in patients with rheumatoid arthritis having the same plasma levels of antioxidants (ascorbate, urate, alpha-tocopherol, retinol) or oxidation markers (nitrotyrosine, lipoperoxide) of healthy subjects. Cholesterol esterification, determined as ratio of cholesteryl esters with cholesterol in high-density lipoproteins, was lower in patients than in controls, and negatively correlated with the intima-media wall thickness of the common carotid. The ratio of Hpt with ApoA-I was negatively correlated with the enzyme activity, while positively correlated with intima-media wall thickness. The results suggest that high Hpt levels might severely impair the enzyme activity, thus contributing to cholesterol accumulation in vascular cells, and lesion formation in the endothelium. [Copyright &y& Elsevier]

Haptoglobin (Hpt) was previously found to bind the high density lipoprotein (HDL) apolipoprotein A-I (ApoA-I) and able to inhibit the ApoA-I-dependent activity of the enzyme lecithin:cholesterol acyltransferase (LCAT), which plays a major role in the reverse cholesterol transport. The ApoA-I structure was analyzed to detect the site bound by Hpt. ApoA-I was treated by cyanogen bromide or hydroxylamine; the resulting fragments, separated by electrophoresis or gel filtration, were tested by Western blotting or enzyme-linked immunosorbent assay for their ability to bind Hpt. The ApoA-I sequence from Glu113 to Asn184 harbored the binding site for Hpt. Biotinylated peptides were synthesized overlapping such a sequence, and their Hpt binding activity was determined by avidin-linked peroxidase. The highest activity was exhibited by the peptide P2a, containing the ApoA-I sequence from Leu141 to Ala164. Such a sequence contains an ApoA-I domain required for binding cells, promoting cholesterol efflux, and stimulating LCAT. The peptide P2a effectively prevented both binding of Hpt to HDL-coated plastic wells and Hpt-dependent inhibition of LCAT, measured by anti-Hpt antibodies and cholesterol esterification activity, respectively. The enzyme activity was not influenced, in the absence of Hpt, by P2a. Differently from ApoA-I or HDL, the peptide did not compete with hemoglobin for Hpt binding in enzyme-linked immunosorbent assay experiments. The results suggest that Hpt might mask the ApoA-I domain required for LCAT stimulation, thus impairing the HDL function. Synthetic peptides, able to displace Hpt from ApoA-I without altering its property of binding hemoglobin, might be used for treatment of diseases associated with defective LCAT function. [ABSTRACT FROM AUTHOR]

Technological processes are the main sources of protein and lipid oxidation in food. The oxidative status was determined in a soft Italian cheese, namely mozzarella, produced from water buffalo or bovine milk. The amount of protein-bound carbonyls, dityrosine and α-lactalbumin aggregates were measured to evaluate the extent of protein oxidation. The α-tocopherylquinone/α-tocopherol ratio and the trolox-equivalent antioxidant capacity were used as redox markers in the fat fraction. The levels of protein-bound carbonyls and α-lactalbumin aggregates were found significantly higher in bovine mozzarella than in buffalo mozzarella. On the other hand, higher amounts of redox markers were found in buffalo mozzarella. The levels of dityrosine aggregates were similar in the two types of cheese. The data suggest that protein and fat are more protected against oxidative structure alterations in buffalo mozzarella than in bovine mozzarella. [Copyright &y& Elsevier]