Search

Patients with systemic lupus erythematosus (SLE) frequently experience chronic pain due to the limited effectiveness and safety profiles of current analgesics. Understanding the molecular and synaptic mechanisms underlying abnormal neuronal activation along the pain signaling pathway is essential for developing new analgesics to address SLE-induced chronic pain. Recent studies, including those conducted by our team and others using the SLE animal model (MRL/lpr lupus-prone mice), have unveiled heightened excitability in nociceptive primary sensory neurons within the dorsal root ganglia and increased glutamatergic synaptic activity in spinal dorsal horn neurons, contributing to the development of chronic pain in mice with SLE. Nociceptive primary sensory neurons in lupus animals exhibit elevated resting membrane potentials, and reduced thresholds and rheobases of action potentials. These changes coincide with the elevated production of TNFα and IL-1β, as well as increased ERK activity in the dorsal root ganglion, coupled with decreased AMPK activity in the same region. Dysregulated AMPK activity is linked to heightened excitability in nociceptive sensory neurons in lupus animals. Additionally, the increased glutamatergic synaptic activity in the spinal dorsal horn in lupus mice with chronic pain is characterized by enhanced presynaptic glutamate release and postsynaptic AMPA receptor activation, alongside the reduced activity of glial glutamate transporters. These alterations are caused by the elevated activities of IL-1β, IL-18, CSF-1, and thrombin, and reduced AMPK activities in the dorsal horn. Furthermore, the pharmacological activation of spinal GPR109A receptors in microglia in lupus mice suppresses chronic pain by inhibiting p38 MAPK activity and the production of both IL-1β and IL-18, as well as reducing glutamatergic synaptic activity in the spinal dorsal horn. These findings collectively unveil crucial signaling molecular and synaptic targets for modulating abnormal neuronal activation in both the periphery and spinal dorsal horn, offering insights into the development of analgesics for managing SLE-induced chronic pain. [ABSTRACT FROM AUTHOR]

Abstract Background Previous studies have shown a close association between an altered immune system and Parkinson's disease (PD). Neuroinflammation inhibition may be an effective measure to prevent PD. Recently, numerous reports have highlighted the potential of hydroxy-carboxylic acid receptor 2 (HCA2) in inflammation-related diseases. Notably, the role of HCA2 in neurodegenerative diseases is also becoming more widely known. However, its role and exact mechanism in PD remain to be investigated. Nicotinic acid (NA) is one of the crucial ligands of HCA2, activating it. Based on such findings, this study aimed to examine the effect of HCA2 on neuroinflammation and the role of NA-activated HCA2 in PD and its underlying mechanisms. Methods For in vivo studies, 10-week-old male C57BL/6 and HCA2−/− mice were injected with LPS in the substantia nigra (SN) to construct a PD model. The motor behavior of mice was detected using open field, pole-climbing and rotor experiment. The damage to the mice's dopaminergic neurons was detected using immunohistochemical staining and western blotting methods. In vitro, inflammatory mediators (IL-6, TNF-α, iNOS and COX-2) and anti-inflammatory factors (Arg-1, Ym-1, CD206 and IL-10) were detected using RT-PCR, ELISA and immunofluorescence. Inflammatory pathways (AKT, PPARγ and NF-κB) were delineated by RT-PCR and western blotting. Neuronal damage was detected using CCK8, LDH, and flow cytometry assays. Results HCA2−/− increases mice susceptibility to dopaminergic neuronal injury, motor deficits, and inflammatory responses. Mechanistically, HCA2 activation in microglia promotes anti-inflammatory microglia and inhibits pro-inflammatory microglia by activating AKT/PPARγ and inhibiting NF-κB signaling pathways. Further, HCA2 activation in microglia attenuates microglial activation-mediated neuronal injury. Moreover, nicotinic acid (NA), a specific agonist of HCA2, alleviated dopaminergic neuronal injury and motor deficits in PD mice by activating HCA2 in microglia in vivo. Conclusions Niacin receptor HCA2 modulates microglial phenotype to inhibit neurodegeneration in LPS-induced in vivo and in vitro models.

Patients with systemic lupus erythematosus (SLE) frequently experience chronic pain due to the limited effectiveness and safety profiles of current analgesics. Understanding the molecular and synaptic mechanisms underlying abnormal neuronal activation along the pain signaling pathway is essential for developing new analgesics to address SLE-induced chronic pain. Recent studies, including those conducted by our team and others using the SLE animal model (MRL/lpr lupus-prone mice), have unveiled heightened excitability in nociceptive primary sensory neurons within the dorsal root ganglia and increased glutamatergic synaptic activity in spinal dorsal horn neurons, contributing to the development of chronic pain in mice with SLE. Nociceptive primary sensory neurons in lupus animals exhibit elevated resting membrane potentials, and reduced thresholds and rheobases of action potentials. These changes coincide with the elevated production of TNFα and IL-1β, as well as increased ERK activity in the dorsal root ganglion, coupled with decreased AMPK activity in the same region. Dysregulated AMPK activity is linked to heightened excitability in nociceptive sensory neurons in lupus animals. Additionally, the increased glutamatergic synaptic activity in the spinal dorsal horn in lupus mice with chronic pain is characterized by enhanced presynaptic glutamate release and postsynaptic AMPA receptor activation, alongside the reduced activity of glial glutamate transporters. These alterations are caused by the elevated activities of IL-1β, IL-18, CSF-1, and thrombin, and reduced AMPK activities in the dorsal horn. Furthermore, the pharmacological activation of spinal GPR109A receptors in microglia in lupus mice suppresses chronic pain by inhibiting p38 MAPK activity and the production of both IL-1β and IL-18, as well as reducing glutamatergic synaptic activity in the spinal dorsal horn. These findings collectively unveil crucial signaling molecular and synaptic targets for modulating abnormal neuronal activation in both the periphery and spinal dorsal horn, offering insights into the development of analgesics for managing SLE-induced chronic pain.

Background: Previous studies have shown a close association between an altered immune system and Parkinson's disease (PD). Neuroinflammation inhibition may be an effective measure to prevent PD. Recently, numerous reports have highlighted the potential of hydroxy-carboxylic acid receptor 2 (HCA2) in inflammation-related diseases. Notably, the role of HCA2 in neurodegenerative diseases is also becoming more widely known. However, its role and exact mechanism in PD remain to be investigated. Nicotinic acid (NA) is one of the crucial ligands of HCA2, activating it. Based on such findings, this study aimed to examine the effect of HCA2 on neuroinflammation and the role of NA-activated HCA2 in PD and its underlying mechanisms. Methods: For in vivo studies, 10-week-old male C57BL/6 and HCA2−/− mice were injected with LPS in the substantia nigra (SN) to construct a PD model. The motor behavior of mice was detected using open field, pole-climbing and rotor experiment. The damage to the mice's dopaminergic neurons was detected using immunohistochemical staining and western blotting methods. In vitro, inflammatory mediators (IL-6, TNF-α, iNOS and COX-2) and anti-inflammatory factors (Arg-1, Ym-1, CD206 and IL-10) were detected using RT-PCR, ELISA and immunofluorescence. Inflammatory pathways (AKT, PPARγ and NF-κB) were delineated by RT-PCR and western blotting. Neuronal damage was detected using CCK8, LDH, and flow cytometry assays. Results: HCA2−/− increases mice susceptibility to dopaminergic neuronal injury, motor deficits, and inflammatory responses. Mechanistically, HCA2 activation in microglia promotes anti-inflammatory microglia and inhibits pro-inflammatory microglia by activating AKT/PPARγ and inhibiting NF-κB signaling pathways. Further, HCA2 activation in microglia attenuates microglial activation-mediated neuronal injury. Moreover, nicotinic acid (NA), a specific agonist of HCA2, alleviated dopaminergic neuronal injury and motor deficits in PD mice by activating HCA2 in microglia in vivo. Conclusions: Niacin receptor HCA2 modulates microglial phenotype to inhibit neurodegeneration in LPS-induced in vivo and in vitro models. [ABSTRACT FROM AUTHOR]

Abstract Background The adaptation of cellular metabolism is considered a hallmark of cancer. Oncogenic signaling pathways support tumorigenesis and cancer progression through the induction of certain metabolic phenotypes associated with altered regulation of key metabolic enzymes. Hydroxycarboxylic acid receptor 2 (HCA2) is a G protein-coupled receptor previously shown to act as a tumor suppressor. Here, we aimed to unveil the connection between cellular metabolism and HCA2 in BT-474 cells. Moreover, we intend to clarify how well this metabolic phenotype is reflected in transcriptional changes and metabolite levels as determined by global metabolomics analyses. Methods We performed both, siRNA mediated knockdown of HCA2 and stimulation with the HCA2-specific agonist monomethyl fumarate. Seahorse technology was used to determine the role of HCA2 in BT-474 breast cancer cell metabolism and its potential to induce a switch in the metabolic phenotype in the presence of different energy substrates. Changes in the mRNA expression of metabolic enzymes were detected with real-time quantitative PCR (RT-qPCR). Untargeted liquid chromatography-mass spectrometry (LC-MS) metabolic profiling was used to determine changes in metabolite levels. Results Knockdown or stimulation of HCA2 induced changes in the metabolic phenotype of BT474 cells dependent on the availability of energy substrates. The presence of HCA2 was associated with increased glycolytic flux with no fatty acids available. This was reflected in the increased mRNA expression of the glycolytic enzymes PFKFB4 and PKM2, which are known to promote the Warburg effect and have been described as prognostic markers in different types of cancer. With exogenous palmitate present, HCA2 caused elevated fatty acid oxidation and likely lipolysis. The increase in lipolysis was also detectable at the transcriptional level of ATGL and the metabolite levels of palmitic and stearic acid. Conclusions We combined metabolic phenotype determination with metabolomics and transcriptional analyses and identified HCA2 as a regulator of glycolytic flux and fatty acid metabolism in BT-474 breast cancer cells. Thus, HCA2, for which agonists are already widely used to treat diseases such as psoriasis or hyperlipidemia, may prove useful as a target in combination cancer therapy.

Endogenous ligands for alicarboxylic acid receptors are important metabolic intermediates that play a significant role in regulating body energy and maintaining homeostasis. However, the molecular mechanism of alicarboxylate ligand-mediated counterpart receptors is currently unclear. We resolve the active state structure of HCA2-niacin, and the structural analysis explains the mechanism of niacin selectivity in the alicarboxylic acid receptors family. Homology modeling, molecular dynamics simulation and mutagenesis experiments reveal different ligand recognition modes and activation mechanisms of the alicarboxylic acid receptors, analyze the flexibility of the binding pocket and elucidate the important role of disulfide bonds on receptor activation and ligand binding. These more detailed molecular mechanisms further elucidate the relevant mechanisms of human metabolism and provide key clues for subsequent drug development of alicarboxylic acid receptors., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

One third of epilepsy patients are resistant to treatment with current anti-seizure medications. The ketogenic diet is used to treat some forms of refractory epilepsy, but the mechanism of its action has not yet been elucidated. In this study, we aimed to investigate whether the hydroxycarboxylic acid receptor 2 (HCA2), a known immunomodulatory receptor, plays a role in mediating the protective effect of this diet. We demonstrate for the first time that selective agonists at this receptor can directly reduce seizures in animal models. Agonists also reduce network activity in rodent and human brain slices. Ketogenic diet is known to increase circulating levels of endogenous HCA2 agonists, and we show that the effect of ketogenic diet in reducing seizures in the 6 Hz seizure model is negated in HCA2-deficient mice. Our data support the potential of HCA2 as a target for the treatment of epilepsy and potentially for neurodegenerative diseases., (© 2024 GSK. Pharmacology Research & Perspectives published by British Pharmacological Society and American Society for Pharmacology and Experimental Therapeutics and John Wiley & Sons Ltd.)

Aim: Dimethyl fumarate and nicotinic acid activate the hydroxy‐carboxylic acid receptor 2 (HCA2) and induce flushing. It is not known whether HCA2 mediates other adverse drug reactions (ADRs) to these two substances. This study aims to compare ADRs associated with dimethyl fumarate and nicotinic acid, and to discuss whether they are HCA2‐mediated. Methods: We identified spontaneous reports of suspected ADRs to dimethyl fumarate and nicotinic acid in the European Adverse Drug Reaction Database (EudraVigilance). These reports were analysed at different hierarchical levels of the Medical Dictionary for Regulatory Activities (MedDRA). In addition, we screened murine organs for HCA2 expression. Results: Similarities in the ADR profile of dimethyl fumarate and nicotinic acid included "gastrointestinal signs and symptoms" (odds ratio [OR] 0.8 [0.6‐1.1]), "hepatobiliary investigations" (OR 1.3 [0.7‐2.5]) and "anxiety disorders and symptoms" (OR 0.9 [0.3‐2.2]) in High Level Group Terms; "diarrhoea (excluding infective)" (OR 1.2 [0.7‐1.8]) and "liver function analyses" (OR 1.3 [0.7‐2.6]) in High Level Terms; and "diarrhoea" (OR 1.2 [0.7‐2.0]) and "vomiting" (OR 0.9 [0.4‐1.7]) in Preferred Terms. In analogy, HCA2 was expressed in the gastrointestinal tract, liver and central nervous system (CNS) of murine organs. A discrepant ADR profile was seen for "lymphopenia" (n = 777) at the preferred term level (only reported for dimethyl fumarate) and "blood glucose increased" (more often reported for nicotinic acid; OR 0.1 [0.0‐0.5]). Conclusion: The gastrointestinal ADRs common to both substances may be mediated by HCA2. Other ADRs not common to both substances are compound or indication‐specific reactions and likely do not involve HCA2. [ABSTRACT FROM AUTHOR]

Hydroxycarboxylic acid receptor 2 (HCA2) is vital for sensing intermediates of metabolism, including β-hydroxybutyrate and butyrate. It also regulates profound anti-inflammatory effects in various tissues, indicating that HCA2 may serve as an essential therapeutic target for mediating inflammation-associated diseases. Butyrate and niacin, endogenous and exogenous ligands of HCA2, have been reported to play an essential role in maintaining intestinal homeostasis. HCA2, predominantly expressed in diverse immune cells, is also present in intestinal epithelial cells (IECs), where it regulates the intricate communication network between diet, microbiota, and immune cells. This review summarizes the physiological role of HCA2 in intestinal homeostasis and its pathological role in intestinal inflammation and cancer.

Hydroxycarboxylic acid receptor 2 (HCA2) is vital for sensing intermediates of metabolism, including β-hydroxybutyrate and butyrate. It also regulates profound anti-inflammatory effects in various tissues, indicating that HCA2 may serve as an essential therapeutic target for mediating inflammation-associated diseases. Butyrate and niacin, endogenous and exogenous ligands of HCA2, have been reported to play an essential role in maintaining intestinal homeostasis. HCA2, predominantly expressed in diverse immune cells, is also present in intestinal epithelial cells (IECs), where it regulates the intricate communication network between diet, microbiota, and immune cells. This review summarizes the physiological role of HCA2 in intestinal homeostasis and its pathological role in intestinal inflammation and cancer. [ABSTRACT FROM AUTHOR]

Post-sepsis cognitive impairment is one of the major sequelae in sepsis survivors. Its prevention remains clinically challenging. Here we tested the effects and underlying mechanisms of exogenous β-hydroxybutyrate (BHB) on post-sepsis cognitive impairment. We found that subcutaneous administration of BHB increased survival and body weight recovery of sepsis mice and improved learning and memory of sepsis surviving mice in a cecal ligation and perforation-induced sepsis model. Additionally, the improvement of learning and memory of sepsis surviving mice was still detected even if BHB was administrated at the late stage of sepsis. In contrast, glucose solution did not show similar effects. Mechanistically, subcutaneous administration of BHB increased the BHB level of hippocampus, and limited neuroinflammation and neuroplasticity damage in sepsis mice. Intracerebroventricular administration of BHB also alleviated neuroinflammation and cognitive impairment of sepsis surviving mice. In the coculture of neurons, astrocytes, and BV2 cells (a microglial cell line), knocking down the expression of microglial HCA2 (BHB receptor) via a specific shRNA reduced the protection of BHB to lipopolysaccharide-induced inflammatory response and neuron damage more significantly than knocking down neuronal MCT2 (BHB transporter). These data showed that (1) BHB was a potential pharmacological adjunct treatment for prevention of post-sepsis cognitive impairment and (2) inhibiting neuroinflammation via HCA2 was an important mechanism. [ABSTRACT FROM AUTHOR]

Objective: Dimethyl fumarate (DMF) is prescribed against relapsing-remitting multiple sclerosis (MS). Here, we investigated the effects of DMF and monomethyl fumarate (MMF), its metabolite in vivo, at the (inflamed) blood–brain barrier (BBB). Methods: Effects of fumaric acid esters were analyzed using primary human brain–derived microvascular endothelial cells (HBMECs) in combination with peripheral blood mononuclear cells (PBMCs) derived from DMF-treated MS patients. Results: MMF-binding to brain endothelium cells leads to activation of nuclear factor (erythroid-derived 2)–related factor 2 (Nrf2)–induced downregulation of vascular cell adhesion molecule 1 (VCAM-1). This might be mediated via the G-protein-coupled receptor (GPCR) hydroxycarboxylic acid receptor 2 (HCA2), a known molecular target of MMF, as we could demonstrate its expression and regulation on HBMECs. DMF treatment in vivo led to a strongly reduced expression of VCAM-1's ligand very late antigen 4 (VLA-4) by selectively reducing integrin high-expressing memory T cells of MS patients, potentially due to inhibition of their maturation by reduced trans-localization of NFκB. Conclusion: DMF-mediated VCAM-1 downregulation on the endothelial side and reduction in T cells with a migratory phenotype on the lymphocyte side result in a synergistic reduction in T-cell adhesion to activated endothelium and, therefore, to reduced BBB transmigration in the setting of MS. [ABSTRACT FROM AUTHOR]

Novel series of compounds consisting of 2-amidocyclohex-1-ene carboxylate and phenyl parts which are connected by enyne (compounds 2a – f ), but-1-yne (compounds 4a – j ), and phenylethylene (compounds 5a – f ) linkers as HCA2 full agonists were designed and their functional activity using cAMP assay and binding affinity using radioligand ( 3 H-niacin) binding assay were evaluated. In general, compounds of all three series exhibit similar HCA2 binding and activation profile. However, the activity is strongly dependent on the substituent at the aromatic part of the structure. Among the structures evaluated, the highest affinity and potency in all series were exhibited by compounds containing 4-hydroxy and/or 2-chloro or 2-fluoro substituents. The most active compounds in the enyne and but-1-yne series in the cAMP assay are 2-fluoro,4-hydroxy and 2-chloro,4-hydroxy phenyl derivatives 2f , 4f , and 4g showing potency similar to the previously described 4-hydroxy-biphenyl analogue 5c . [ABSTRACT FROM AUTHOR]

Periparturient cows are commonly fed diets supplemented with Niacin (nicotinic acid, NA) because of its anti-lipolytic properties. NA confers its anti-lipolytic effects by activating the hydroxycarboxylic acid 2 receptor (HCA2). HCA2 is also activated by the ketone body beta-hydroxybutyrate (BHB) and circulating BHB levels are elevated in postpartum dairy cows. The HCA2 receptor is highly expressed in bovine polymorphonuclear leukocytes (PMN) and could link metabolic and innate immune responses in cattle. We investigated how HCA2 agonists affected bovine PMN function in vitro. We studied different PMN responses, such as granule release, surface expression of CD11b and CD47, generation of neutrophil extracellular traps (NETs), and apoptosis. NA, BHB, and 4,4aR,5,5aR-tetrahydro-1H-cyclopropa [4,5] cyclopenta [1,2-c] pyrazole-3-carboxylic acid (MK-1903) treatment triggered the release of matrix metalloproteinase 9 (MMP-9), a component of the tertiary granule, from neutrophils. Additionally, all HCA2 agonists induced NETs formation but did not affect surface expression of CD11b and CD47. Finally, none of the HCA2 agonists triggered apoptosis in bovine PMN. This information will give new insights into the potential role of the HCA2 receptor in the bovine innate immune response. [Display omitted] • Ligands of HCA2 receptor, including beta-hydroxybutyrate, nicotinic acid and MK-1903, induce NETs formation in bovine PMN. • Nicotinic acid and MK-1903 induce metalloproteinase 9 release in bovine PMN. • HCA2 receptor agonists do not affect CD11b or CD47 expression or apoptosis in bovine PMN. [ABSTRACT FROM AUTHOR]

Niacin has been reported to have potent anti-inflammatory effects in LPS-induced acute lung injury. However, the molecular mechanism of niacin has not been fully understood. The aim of the present study was to investigate the effects of niacin on the production of pro-inflammatory cytokines TNF-α, IL-6 and IL-1β in LPS-induced mouse alveolar macrophages and explore its underlying mechanism. Mouse alveolar macrophages were incubated in the presence or absence of various concentrations of niacin (1, 10, 100 μmol/l) 1 h before LPS (1 μg/ml) challenge. The results showed that niacin reduced the levels of TNF- α , IL-6 and IL-1β in LPS-challenged alveolar macrophages. Furthermore, NF-κB activation was inhibited by niacin through blocking the phosphorylation of NF-κB p65 and IκBα. In addition, silencing HCA2 abrogated the effect of niacin on the production of pro-inflammatory cytokines. These findings suggested that niacin attenuated the LPS-induced pro-inflammatory cytokines possibly mediated by HCA2 in LPS-challenged alveolar macrophages. [ABSTRACT FROM AUTHOR]

Abstract: 2-(3-(Naphthalen-2-yl)propanamido)cyclohex-1-enecarboxylic acid and its 6-hydroxynaphthalen-2-yl analogue are well-known hydroxyl-carboxylic acid (HCA) receptor HCA2 agonists. A series of novel aryl derivatives of 2-amidocyclohex-1-ene carboxylic acid that contained rigidity elements, such as an E-double bond, triple bond, and trans or cis-substituted cyclopropane rings, instead of the saturated ethane linker in the amide part of the molecules were designed and synthesized, and the derivatives’ potency for the activation of HCA1, HCA2, and HCA3 receptors by 3′–5′-cyclic adenosine monophosphate (cAMP) assay were evaluated. The SAR studies revealed that the rigidifying of appropriate molecules enabled modulation of the potency and selectivity of the HCA2 receptor activation. [Copyright &y& Elsevier]

BACKGROUND AND PURPOSE Niacin can effectively treat dyslipidaemic disorders. However, its clinical use is limited due to the cutaneous flushing mediated by the nicotinic acid receptor HCA2. In the current study, we evaluated two partial agonists for HCA2, LUF6281 and LUF6283, with respect to their anti-dyslipidaemic potential and cutaneous flushing effect. EXPERIMENTAL APPROACH In vitro potency and efficacy studies with niacin and the two HCA2 partial agonists were performed using HEK293T cells stably expressing human HCA2. Normolipidaemic C57BL/6 mice received either niacin or the HCA2 partial agonists (400 mg·kg−1·day−1) once a day for 4 weeks for evaluation of their effects in vivo. KEY RESULTS Radioligand competitive binding assay showed Ki values for LUF6281 and LUF6283 of 3 and 0.55 µM. [35S]-GTPγS binding revealed the rank order of their potency as niacin > LUF6283 > LUF6281. All three compounds reduced plasma VLDL-triglyceride concentrations similarly, while LUF6281 and LUF6283, in contrast to niacin, did not also exhibit the unwanted flushing side effect in C57BL/6 mice. Niacin reduced the expression of lipolytic genes HSL and ATGL in adipose tissue by 50%, whereas LUF6281 and LUF6283 unexpectedly did not. In contrast, the decrease in VLDL-triglyceride concentration induced by LUF6281 and LUF6283 was associated with a parallel >40% reduced expression of APOB within the liver. CONCLUSIONS AND IMPLICATIONS The current study identifies LUF6281 and LUF6283, two HCA2 partial agonists of the pyrazole class, as promising drug candidates to achieve the beneficial lipid lowering effect of niacin without producing the unwanted flushing side effect. [ABSTRACT FROM AUTHOR]

Abstract: Nicotinic acid (NA) and fumaric acid esters (FAE) such as monomethyl fumarate or dimethyl fumarate are drugs that elicit a cutaneous reaction called flushing as a side effect. NA is used to reduce progression of atherosclerosis through its anti-dyslipidemic activity and lipid-independent mechanisms involving immune cells, whereas FAE are used to treat psoriasis via largely unknown mechanisms. Both, NA and FAE, induce flushing by the activation of the G-protein-coupled receptor (GPCR) Hydroxy-carboxylic acid receptor 2 (HCA2, GPR109A) in cells of the epidermis. While the wanted effects of NA are at least in part also mediated by HCA2, it is currently not clear whether this receptor is also involved in the anti-psoriatic effects of FAE. The HCA2‐mediated flushing response to these drugs involves the formation of prostaglandins D2 and E2 by Langerhans cells and keratinocytes via COX-1 in Langerhans cells and COX-2 in keratinocytes. This review summarizes recent progress in the understanding of the mechanisms underlying HCA2-mediated flushing, describes strategies to mitigate it and discusses the potential link between flushing, HCA2 and the anti-psoriatic effects of FAE. [Copyright &y& Elsevier]

Abstract: GPR109A (PUMA-G, NIACR1, HCA2) and GPR81 (HCA1) are G protein-coupled receptors located predominantly on adipocytes that mediate anti-lipolytic effects. These cell surface receptors give the adipocyte the ability to “sense” metabolic changes in the environment and respond through lipolytic regulation and release of products including free fatty acids and pro- or anti-inflammatory adipokines. The endogenous ligands for GPR109A and GPR81 are β-hydroxybutyrate and lactate, respectively, both of which are hydroxycarboxylic acids and intermediates of energy metabolism. Circulating β-hydroxybutyrate levels are increased during a 2–3day fast and prolonged starvation, while lactate levels are elevated during times of intense exercise. Therefore, regulation of expression of these receptors is crucial for the metabolic sensing ability of the adipocyte and ultimately whole body energy homeostasis. We investigated the effects of high fat diet-induced obesity on expression of GPR109A and GPR81. Sixteen male C57BL/6 mice were placed on a control (10% kcal fat; n =8) or a high fat (60% kcal fat; n =8) diet for 11weeks. Diet-induced obesity significantly reduced GPR109A and GPR81 gene expression in epididymal fat pads. This decrease in GPR109A and GPR81 gene expression was positively correlated with a decrease in adipose tissue PPARγ gene expression. In contrast, acute treatment of both 3T3-L1 adipocytes and RAW 264.7 macrophages with lipopolysaccharide significantly increased GPR109A gene expression, but had no effect on GPR81 expression in 3T3-L1 adipocytes. In conclusion, chronic obesity reduces GPR109A and GPR81 expression in the adipose tissue, while acute in vitro LPS treatment increases expression of GPR109A in adipocytes and macrophages. [Copyright &y& Elsevier]

BACKGROUND AND PURPOSE 3-Hydroxy-octanoate, recently identified as a ligand for, the orphan GPCR, HCA3, is of particular interest given its ability to treat lipid disorders and atherosclerosis. Here we demonstrate the pathway of HCA3-mediated activation of ERK1/2. EXPERIMENTAL APPROACH Using CHO-K1 cells stably expressing HCA3 receptors and A431 cells, a human epidermoid cell line with high levels of endogenous expression of functional HCA3 receptors, HCA3-mediated activation of ERK1/2 was measured by Western blot. KEY RESULTS HCA3-mediated activation of ERK1/2 was rapid, peaking at 5 min, and was Pertussis toxin sensitive. Our data, obtained by time course analyses in combination with different kinase inhibitors, demonstrated that on agonist stimulation, HCA3 receptors evoked ERK1/2 activation via two distinct pathways, the PLC/PKC pathway at early time points (≤2 min) and the MMP/ epidermal growth factor receptor (EGFR) transactivation pathway with a maximum response at 5 min. Furthermore, our present results also indicated that the βγ-subunits of the Gi protein play a critical role in HCA3-activated ERK1/2 phosphorylation, whereas β-arrestins and Src were not required for ERK1/2 activation. CONCLUSIONS AND IMPLICATIONS We have described the molecular mechanisms underlying the coupling of human HCA3 receptors to the ERK1/2 MAP kinase pathway in CHO-K1 and A431 cells, which implicate the Gi protein-initiated, PLC/PKC- and platelet-derived growth factor receptor/EGFR transactivation-dependent pathways. These observations may provide new insights into the pharmacological effects and the physiological functions modulated by the HCA3-mediated activation of ERK1/2. [ABSTRACT FROM AUTHOR]

Resveratrol, trans-3,5,4′-trihydroxystilbene, is a polyphenolic compound which has been reported to mimic the gene expression patterns seen in whole animals undergoing dietary restriction. The mechanism of action of resveratrol remains poorly understood, but modulation of both cellular proliferation and apoptosis has been proposed as important routes by which the molecule may exert its effects. This study reports the effects of both resveratrol and dihydroresveratrol (a primary in vivo metabolite) on the proliferative capacity of human primary fibroblasts. No generalised reduction in the growth fraction was observed when fibroblasts derived from three different tissues were treated with resveratrol at concentrations of 10 μm or less. However, concentrations above 25 μm produced a dose-dependent reduction in proliferation. This loss of the growth fraction was paralleled by an increase in the senescent fraction as determined by staining for senescence associated beta galactosidase and dose recovery studies conducted over a 7-day period. Entry into senescence in response to treatment with resveratrol could be blocked by a 30-min preincubation with the p38 MAP kinase inhibitor SB203580. No effects on proliferation were observed when cells were treated with dihydroresveratrol at concentrations of up to 100 μm. [ABSTRACT FROM AUTHOR]

Aim: Dimethyl fumarate and nicotinic acid activate the hydroxy-carboxylic acid receptor 2 (HCA 2 ) and induce flushing. It is not known whether HCA 2 mediates other adverse drug reactions (ADRs) to these two substances. This study aims to compare ADRs associated with dimethyl fumarate and nicotinic acid, and to discuss whether they are HCA 2 -mediated., Methods: We identified spontaneous reports of suspected ADRs to dimethyl fumarate and nicotinic acid in the European Adverse Drug Reaction Database (EudraVigilance). These reports were analysed at different hierarchical levels of the Medical Dictionary for Regulatory Activities (MedDRA). In addition, we screened murine organs for HCA 2 expression., Results: Similarities in the ADR profile of dimethyl fumarate and nicotinic acid included "gastrointestinal signs and symptoms" (odds ratio [OR] 0.8 [0.6-1.1]), "hepatobiliary investigations" (OR 1.3 [0.7-2.5]) and "anxiety disorders and symptoms" (OR 0.9 [0.3-2.2]) in High Level Group Terms; "diarrhoea (excluding infective)" (OR 1.2 [0.7-1.8]) and "liver function analyses" (OR 1.3 [0.7-2.6]) in High Level Terms; and "diarrhoea" (OR 1.2 [0.7-2.0]) and "vomiting" (OR 0.9 [0.4-1.7]) in Preferred Terms. In analogy, HCA 2 was expressed in the gastrointestinal tract, liver and central nervous system (CNS) of murine organs. A discrepant ADR profile was seen for "lymphopenia" (n = 777) at the preferred term level (only reported for dimethyl fumarate) and "blood glucose increased" (more often reported for nicotinic acid; OR 0.1 [0.0-0.5])., Conclusion: The gastrointestinal ADRs common to both substances may be mediated by HCA 2 . Other ADRs not common to both substances are compound or indication-specific reactions and likely do not involve HCA 2 ., (© 2021 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Hydroxycarboxylic acid receptor 2 (HCA 2 ) is vital for sensing intermediates of metabolism, including β-hydroxybutyrate and butyrate. It also regulates profound anti-inflammatory effects in various tissues, indicating that HCA 2 may serve as an essential therapeutic target for mediating inflammation-associated diseases. Butyrate and niacin, endogenous and exogenous ligands of HCA 2 , have been reported to play an essential role in maintaining intestinal homeostasis. HCA 2 , predominantly expressed in diverse immune cells, is also present in intestinal epithelial cells (IECs), where it regulates the intricate communication network between diet, microbiota, and immune cells. This review summarizes the physiological role of HCA 2 in intestinal homeostasis and its pathological role in intestinal inflammation and cancer., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Li, McCafferty and Judd.)