Niacin Receptor Research Articles

The Nicotinic Acid Receptor HCA2 Regulates Progression of AKI and Development of CKD in Mouse Models of Sepsis and Postischemic Kidney Injury

The Nicotinic Acid Receptor HCA2 Regulates Progression of AKI and Development of CKD in Mouse Models of Sepsis and Postischemic Kidney Injury

Abstract 3022: GPR109A activation limits cell growth by inducing p53 and its targets in human colon cancer cells

Abstract Chemical carcinogens or xenobiotics present in the diet play a significant role in colon cancer (CC) formation. p53, a tumor suppressor and multi-functional protein, provides an important barrier against the initiation and maintenance of CC. p53 mutation or inactivation is observed in about 60% of CCs and about 90% of all cancers. Therefore, therapeutic avenues that will rejuvenate wild-type p53 or target mutant p53 should have a significant impact on the prevention and treatment of CC. GPR109A, a G-protein coupled receptor for the FDA-approved lipid-lowering drug Niacin (NA), bacterial metabolite Butyrate (BTR), and ketone body β-hydroxybutyrate (BHB), functions as a novel tumor suppressor in the colon by providing the molecular link between colonic bacteria and p53 function. GPR109A activation limits cAMP by inhibiting adenylate cyclase (AC), which induces RAS and its downstream growth-promoting signaling. cAMP also enhances the binding of MDM2 to p53 and induces the proteasomal degradation of p53. p53 is an NAD+-dependent molecule and deficiency of NA, the precursor of NAD+, impairs p53 function. We tested the role of GPR109A and its agonists (NA, BTR, and BHB) in normal immortalized colon epithelial cell lines (CCD33 and CCD81) and various CC lines such as HCT116-p53+/+, HCT116-p53−/−, DLD1 (p53 point mutation), VACO4A (p53 insertion mutation), and SW498 (p53 deletion) and measured cell proliferation, cell cycle, apoptosis, and analyzed the expression of GPR109A and p53 (total, phosphorylated, and acetylated), MDM2, p21, Bax, and Puma in the presence and absence of GPR109109 agonists. We found that GPR109A expression is significantly reduced in CC cell lines, especially in p53 mutant cell lines, when compared to normal immortalized colonic epithelial cell lines. Treatment of CC cell lines with GPR109A agonists-induced apoptosis in wild-type p53 expressing CC by activating p53 and its targets. However, some lesser extent in p53 mutant or p53 null cell lines. Lentiviral-mediated GPR109A expression in CC cell lines itself induced apoptosis in both wild-type and mutant p53 expressing CC cell lines and GPR109A agonists treatment induced further. Interestingly, GPR109A agonists BTR and BHB significantly increased apoptosis in p53 mutant and p53 null CC cell lines in a p53-independent manner. Overall, our results provide evidence that GPR109A activation can be used as an effective therapeutic strategy for the treatment of CC. Citation Format: Muthusamy Thangaraju, Nanditi N. Thangaraju, Lauren Gilstrap, Madison Chimenti, Tulshi Patel, Sathish Sivaprakasam, Nikhil Patel, Santhakumar Manicassamy, Puttur D. Prasad, Vadivel Ganapathy. GPR109A activation limits cell growth by inducing p53 and its targets in human colon cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3022.

Structure-guided engineering of biased-agonism in the human niacin receptor via single amino acid substitution

The Hydroxycarboxylic acid receptor 2 (HCA2), also known as the niacin receptor or GPR109A, is a prototypical GPCR that plays a central role in the inhibition of lipolytic and atherogenic activities. Its activation also results in vasodilation that is linked to the side-effect of flushing associated with dyslipidemia drugs such as niacin. GPR109A continues to be a target for developing potential therapeutics in dyslipidemia with minimized flushing response. Here, we present cryo-EM structures of the GPR109A in complex with dyslipidemia drugs, niacin or acipimox, non-flushing agonists, MK6892 or GSK256073, and recently approved psoriasis drug, monomethyl fumarate (MMF). These structures elucidate the binding mechanism of agonists, molecular basis of receptor activation, and insights into biased signaling elicited by some of the agonists. The structural framework also allows us to engineer receptor mutants that exhibit G-protein signaling bias, and therefore, our study may help in structure-guided drug discovery efforts targeting this receptor.

Tuning the Reactivity of Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) Activators for Optimal in Vivo Efficacy.

Dimethyl fumarate 1 is approved for the treatment of multiple sclerosis but is also associated with off-target activation of the niacin receptor. By using a tetrazolone or triazolone bioisostere approach to the fumarate and vinyl sulfone series of Nrf2 activators, we have optimized the electrophilicity of the double bond to tune the on-target Nrf2 activation with PK properties to achieve efficacy in animal models of multiple sclerosis. The study linked highly potent, highly electrophilic molecules to low plasma stability and, subsequently, limited efficacy. By contrast, a sulfonylvinyltriazolone 17 retains on-target potency but shows much weaker electrophilic potential. As a consequence, in vivo high exposures of 17 are obtained, resulting in efficacy in the EAE model similar to that observed for DMF. 17 (R079) is Ames negative, is not cytotoxic to cells, and shows little inhibition of either the niacin receptor or a panel of off-target receptors.

The niacin receptor HCAR2 induces a protective response of microglia to amyloid pathology.

AbstractBackgroundDietary intake of niacin correlates with reduced risk of Alzheimer´s disease (AD). Niacin is a ligand for the niacin receptor HCAR2, which, in the brain, is expressed by microglia. HCAR2 ligands have been shown to modulate microglia functions and exert neuroprotective effects in different models of neuronal injury. Therefore, we hypothesized that HCAR2 modulates a protective microglial phenotype in AD, which can be stimulated by HCAR2 agonists.MethodTo assess the role of HCAR2 in amyloid pathology, the brains of the AD animal model 5xFAD and 5xFAD mice lacking Hcar2 gene (5xFAD‐KO) were subjected to transcriptomic, immunohistochemistry and biochemical analysis. Furthermore, to activate HCAR2, 5 month‐old 5xFAD mice were treated with a FDA‐approved formulation of niacin (Niaspan®) daily, by oral gavage for 30 days with 100 mg niacin/kg. Treated animals were sacrificed and the brains were collected for immunohistochemistry and biochemical analysis. To validate that Niaspan® effects were dependent on HCAR2, we performed the same treatment paradigm and analysis using 5xFAD‐KO mice.ResultOur results indicate that microglia significantly induce HCAR2 expression in the AD brain. Lack of Hcar2 in the 5xFAD mice leads to a deficient response of microglia to amyloid pathology, which is accompanied by an increase in plaque load and exacerbation of the amyloid‐associated neuropathology. Niaspan® treatment increased the response of microglia to amyloid pathology, decreased plaque burden in 5xFAD, and exerted a neuroprotective effect evidenced by reduced neuronal loss in the subiculum, accompanied by a rescue of working memory deficits. Niaspan® did not induce these beneficial effects in 5xFAD‐KO mice.ConclusionThese data suggest that HCAR2 induces a protective microglial phenotype in AD. Furthermore, activation of HCAR2 by Niaspan® treatment has neuroprotective effects in AD, even after the onset of severe amyloid pathology, possibly through the stimulation of a protective microglia response. Niaspan® is a FDA‐approved drug, thus there is a translational potential of this strategy into clinical practice, supporting further study of this therapeutic approach.

Hydroxycarboxylic acid receptors in GtoPdb v.2023.1

The hydroxycarboxylic acid family of receptors (ENSFM00500000271913, nomenclature as agreed by the NC-IUPHAR Subcommittee on Hydroxycarboxylic acid receptors [36, 12]) respond to organic acids, including the endogenous hydroxy carboxylic acids 3-hydroxy butyric acid and L-lactic acid, as well as the lipid lowering agents nicotinic acid (niacin), acipimox and acifran [53, 60, 65]. These receptors were provisionally described as nicotinic acid receptors, although nicotinic acid shows submicromolar potency at HCA2 receptors only and is unlikely to be the natural ligand [60, 65].

Structural insights into the human niacin receptor HCA2-Gi signalling complex

The hydroxycarboxylic acid receptor 2 (HCA2) agonist niacin has been used as treatment for dyslipidemia for several decades albeit with skin flushing as a common side-effect in treated individuals. Extensive efforts have been made to identify HCA2 targeting lipid lowering agents with fewer adverse effects, despite little being known about the molecular basis of HCA2 mediated signalling. Here, we report the cryo-electron microscopy structure of the HCA2-Gi signalling complex with the potent agonist MK-6892, along with crystal structures of HCA2 in inactive state. These structures, together with comprehensive pharmacological analysis, reveal the ligand binding mode and activation and signalling mechanisms of HCA2. This study elucidates the structural determinants essential for HCA2 mediated signalling and provides insights into ligand discovery for HCA2 and related receptors.

Niacin exacerbates β cell lipotoxicity in diet-induced obesity mice through upregulation of GPR109A and PPARγ2: Inhibition by incretin drugs.

The widely used lipid-lowering drug niacin was reported to increase blood glucose in diabetes. How does niacin regulate β Cell function in diabetic patients remains unclear. This study aimed to investigate the effect of niacin on β cell lipotoxicity in vitro and in vivo. Niacin treatment sensitized the palmitate-induced cytotoxicity and apoptosis in INS-1 cells. In addition, palmitate significantly increased the niacin receptor GPR109A and PPARγ2 levels, which could be further boosted by niacin co-treatment, creating a vicious cycle. In contrast, knocking down of GPR109A could reverse both PPARγ2 expression and niacin toxicity in the INS-1 cells. Interestingly, we found that GLP-1 receptor agonist exendin-4 showed similar inhibitive effects on the GPR109A/PPARγ2 axis and was able to reverse niacin induced lipotoxicity in INS-1 cells. In diet-induced obesity (DIO) mouse model, niacin treatment resulted in elevated blood glucose, impaired glucose tolerance and insulin secretion, accompanied by the change of islets morphology and the decrease of β cell mass. The combination of niacin and DPP-4 inhibitor sitagliptin can improve glucose tolerance, insulin secretion and islet morphology and β cell mass, even better than sitagliptin alone. Our results show that niacin increased β cell lipotoxicity partially through upregulation of GPR109A and PPARγ2, which can be alleviated by incretin drugs. We provide a new mechanism of niacin toxicity, and suggest that the combination of niacin and incretin may have better blood glucose and lipid control effect in clinical practice.

GPR109a Regulates Phenotypic and Functional Alterations in Macrophages and the Progression of Type 1 Diabetes.

Dietary fibers can alter gut microbiota and microbial metabolite profiles. SCFAs are produced by bacterial fermentation of fiber, mediating immune homeostasis through G-protein-coupled receptors (GPCRs). GPR109a, a receptor for niacin and butyrate, expressed by immune cells and non-immune cells, is a key factor regulating immune responses. However, the role and underlying mechanisms of GPR109a in type 1 diabetes (T1D) remain unclear. Experimental T1D was induced by streptozotocin in GPR109a-deficient (Gpr109a-/- ) and wild type mice. The study found that Gpr109a-/- mice were more susceptible to T1D with dysregulated immune responses, along with increased M1 macrophage polarization (from 10.55% to 21.48%). Further, an adoptive transfer experiment demonstrated that GPR109a-deficient macrophages promoted the homing of intestine-derived type 1 cytotoxic Tcells to pancreas (from 18.91% to 24.24%), thus disturbing the pancreatic immune homeostasis in non-obese diabetic mice. Mechanistically, GPR109a deficiency promoted M1 macrophage polarization associated with the activation of suppressor of cytokine signaling 3-signal transducer and activator of transcription 1 signaling pathway. The findings reveal that macrophage GPR109a deficiency accelerates the development of T1D. Activation of GPR109a on macrophage by dietary components may provide a new strategy for preventing or treating T1D.

The niacin receptor HCAR2 modulates microglial response and limits disease progression in a mouse model of Alzheimer's disease.

Increased dietary intake of niacin has been correlated with reduced risk of Alzheimer's disease (AD). Niacin serves as a high-affinity ligand for the receptor HCAR2 (GPR109A). In the brain, HCAR2 is expressed selectively by microglia and is robustly induced by amyloid pathology in AD. The genetic inactivation of Hcar2 in 5xFAD mice, a model of AD, results in impairment of the microglial response to amyloid deposition, including deficits in gene expression, proliferation, envelopment of amyloid plaques, and uptake of amyloid-β (Aβ), ultimately leading to exacerbation of amyloid burden, neuronal loss, and cognitive deficits. In contrast, activation of HCAR2 with an FDA-approved formulation of niacin (Niaspan) in 5xFAD mice leads to reduced plaque burden and neuronal dystrophy, attenuation of neuronal loss, and rescue of working memory deficits. These data provide direct evidence that HCAR2 is required for an efficient and neuroprotective response of microglia to amyloid pathology. Administration of Niaspan potentiates the HCAR2-mediated microglial protective response and consequently attenuates amyloid-induced pathology, suggesting that its use may be a promising therapeutic approach to AD that specifically targets the neuroimmune response.

The role of microglia niacin receptor (HCAR2) in Alzheimer's disease.

Dietary intake of niacin reduces the risk of Alzheimer´s disease (AD) and protects against age-related cognitive decline. Niacin is a ligand for the niacin receptor (HCAR2), which, in the brain, is selectively expressed by microglia. HCAR2 is significantly increased in the AD brain, and activation of this receptor has been shown to be neuroprotective in stroke and demyelination models. Thus, we hypothesized that microglial HCAR2 plays a protective role in AD. To understand the role of HCAR2 in AD, we compared disease progression of the AD mouse model 5xFAD lacking the Hcar2 gene (5xFAD;Hcar2 -/- ) with 5xFAD;Hcar2 +/+ . Plaque burden, neuronal loss, microglial function, cognition and gene expression were analyzed in both genotypes at 4 and 6 months of age. Furthermore, 5 month-old 5xFAD mice were treated with a FDA-approved formulation of niacin (Niaspan®) daily, by oral gavage for 30 days with 100 mg niacin/kg to assess the effects of pharmacological activation of HCAR2 on disease progression in these mice. Our results show a dramatic increase of microglial HCAR2 expression in the AD brain. In 5xFAD mice, the induction of Hcar2 is selective for microglia associated with amyloid plaques. 5xFAD;Hcar2 -/- exhibit a more severe amyloid pathology compared to controls, increased plaque load and neuronal loss, decreased Aβ phagocytosis by microglia and accelerated onset of cognitive deficits. On the other hand, activation of HCAR2 in 5xFAD with niacin treatment reduces neuronal loss and plaque burden, increases Aβ phagocytosis and rescues working memory deficits. Our data suggest the microglia receptor HCAR2 plays a protective role in AD, and is part of an endogenous response from microglia to tackle the disease. HCAR2 is a potential therapeutic target to modulate microglia phenotype towards beneficial outcomes in AD. Our results indicate that the activation of HCAR2 with the FDA-approved formulation of niacin, Niaspan®, leads to neuroprotective effects in AD, even after the onset of severe amyloid pathology, highlighting the translational potential of this strategy into clinical practice, supporting further study of this therapeutic approach.

Effect of Niacin on Growth Performance, Intestinal Morphology, Mucosal Immunity and Microbiota Composition in Weaned Piglets.

Simple SummaryThe protective effect of niacin on growth performance and gut health of weaned piglets and the underlying mechanism remains unclear despite it being a common additive in pig diets. The present study aimed to investigate the effect of niacin on growth performance, intestinal morphology, intestinal mucosal immunity, and colonic microbiota in weaned piglets. Our results show that niacin supplementation significantly improved the growth performance in piglets as compared with those given a niacin receptor antagonist. Niacin also significantly improved the relative abundance of beneficial bacteria in the colon and alleviate the inflammatory response in the intestinal mucosa as compared with control piglets and those given a niacin receptor antagonist. These results provide new insight into the beneficial effects of niacin on growth performance and gut health in weaned piglets.This study aimed to investigate the effects of niacin on growth performance, intestinal morphology, intestinal mucosal immunity, and colonic microbiota in weaned piglets. A total of 96 weaned piglets (Duroc × (Landrace × Yorkshire), 21-d old, 6.65 ± 0.02 kg body weight (BW)) were randomly allocated into 3 treatment groups (8 replicate pens per treatment, each pen containing 4 males; n = 32/treatment) for 14 d. Piglets were fed a control diet (CON) or the CON diet supplemented with 20.4 mg/kg niacin (NA) or an antagonist for the niacin receptor GPR109A (MPN). The results showed that NA or MPN had no effect on ADG, ADFI, G/F or diarrhea incidence compared with the CON diet. However, compared with piglets in the NA group, piglets in the MPN group had lower ADG (p = 0.042) and G/F (p = 0.055). In comparison with the control and MPN group, niacin supplementation increased the villus height and the ratio of villus height to crypt depth (p < 0.05), while decreasing the crypt depth in the duodenum (p < 0.05). Proteomics analysis of cytokines showed that niacin supplementation increased the expression of duodenal transforming growth factor-β (TGF-β), jejunal interleukin-10 (IL-10) and ileal interleukin-6 (IL-6) (p < 0.05), and reduced the expression of ileal interleukin-8 (IL-8) (p < 0.05) compared with the control diet. Piglets in the MPN group had significantly increased expression of ileal IL-6, and jejunal IL-8 and interleukin-1β (IL-1β) (p < 0.05) compared with those in the control group. Piglets in the MPN group had lower jejunal IL-10 level and higher jejunal IL-8 level than those in the NA group (p < 0.05). The mRNA abundance of duodenal IL-8 and ileal granulocyte-macrophage colony-stimulating factor (GM-CSF) genes were increased (p < 0.05), and that of ileal IL-10 transcript was decreased (p < 0.05) in the MPN group compared with both the control and NA groups. Additionally, niacin increased the relative abundance of Dorea in the colon as compared with the control and MPN group (p < 0.05), while decreasing that of Peptococcus compared with the control group (p < 0.05) and increasing that of Lactobacillus compared with MPN supplementation (p < 0.05). Collectively, the results indicated that niacin supplementation efficiently ensured intestinal morphology and attenuated intestinal inflammation of weaned piglets. The protective effects of niacin on gut health may be associated with increased Lactobacillus and Dorea abundance and butyrate content and decreased abundances of Peptococcus.

Novel Niacin Receptor Agonists: A Promising Strategy for the Treatment of Dyslipidemia

Background: Hyperlipidemia is characterized by high level of cholesterol and triglycerides in blood. Various classes of drugs like statins, fibrates, niacin etc. are used for treatment of hyperlipidaemia. Objective: Niacin, which is one of the beneficial anti-hyperlipidemic agents, helps to lower LDL cholesterol by 20 to 40% and causes increase of HDL cholesterol by 20 to 35%. However cutaneous flushing, loss of glucose tolerance, liver toxicity are the reported side effects of niacin therapy responsible for decreased patient compliance. Very recently, the G protein coupled receptor (GPCR); GPR109A located on the adipocytes has been identified as the receptor for activation of niacin. Method: In-vitro studies have demonstrated that GPR109A receptor having high affinity for niacin. The present review attempts to provide a systematic presentation of the various chemical classes of compounds that have been reported as novel niacin receptor agonists including pyrazole-3-carboxylic acids, urea derivatives, anthranilic acids, biaryl anthranilides, tetrahydro anthranilic acid, xanthines, barbituric acid, bicyclic pyrazole carboxylic acids, pyrido pyrimidinones, pyrazolyl propionyl cyclohexenamides, pyrazole acids etc. Results: As the design of GPR109A receptor agonists offers a promising solution for treatment of dyslipidemia, this review will be beneficial for medicinal and drug discovery chemists to expediate the process of discovery of new class of antihyperlipidemic agent with favorable lipid lowering profile with increase in HDL levels. Conclusion: This review explains about novel GPR109A receptor agonist for the treatment of dyslipidemia.

Structural and Energetic Insights Into the Interaction of Niacin With the GPR109A Receptor.

The transmembrane G-protein coupled receptor GPR109A has been previously shown to function as a receptor for niacin in mediating antilipolytic effects. Although administration of high doses of niacin has shown beneficial effects on lipid metabolism, however, it is often accompanied by disturbing side effects such as flushing, liver damage, glucose intolerance, or gastrointestinal problems. Thus, it is important to understand niacin-GPR109A interactions, which can be beneficial for the development of alternate drugs having antilipolytic effects with less or no side effects. To get into the structural insights on niacin binding to GPR109A, we have performed 100 nanoseconds long all-atom MD simulations of five niacin-GPR109A complexes (automatically docked pose 0, and randomly placed niacin in poses 1 to 4 in the receptor crevice) and analyzed using binding free energy calculations and H-bond analysis. Steered MD simulations were used to get an average force for niacin translocation between the bulk and the external crevice of the wild type and mutant (N86Y, W91 S, S178I, and triple mutant of all three residues) GPR109A receptors, as well as GPR109B (as a control that does not bind niacin). The H-bond analysis revealed that TMH3 residue R111 interacts with niacin in a total of 4 (poses 0 to 3) complexes, while residues C177, S178, and S179 contact niacin in complex pose 4, and all these complexes were energetically stable. According to steered MD simulations, all the GPR109A mutants and GPR109B required greater force than that of wild-type GPR109A to translocate in the external crevice, suggesting increased sterical obstacles. Thus, the residues N86 (at the junction of TMH2/ECL2), W91 (ECL2), R111 (TMH3), and ECL3 residues (C177, S178, S179) play an important role for optimal routing of niacin entry and to bind GPR109A.

Therapeutic potential of niacin in Alzheimer's disease

AbstractBackgroundDietary intake of niacin reduces the risk of Alzheimer's disease (AD) and protects against age‐related cognitive decline. Niacin is a ligand for the niacin receptor HCAR2, which, in the brain, is selectively expressed by microglia. HCAR2 activation has been shown to be neuroprotective in stroke and demyelination models. Therefore, we hypothesized that niacin administration could have beneficial effects in AD pathology.Method5 month‐old 5xFAD mice, an animal model of AD, were treated with a FDA‐approved formulation of niacin (Niaspan®) daily, by oral gavage for 30 days with 100 mg niacin/kg. After treatment, the animals were sacrificed and the brains were collected for immunohistochemistry and biochemical analysis. Gene expression and Aβ uptake efficiency were analyzed in primary cultures of microglia incubated with 1.25 nM of Niaspan®.ResultOur results indicate there is an induction of HCAR2 expression in the AD brain, prominently in activated microglia. Niaspan® treatment significantly reduced Aβ burden and number of compact plaques in 5xFAD brain. Accordingly, Niaspan® induced phagocytic genes and Aβ uptake in primary cultures of microglia. Importantly, Niaspan® exerted a neuroprotective effect evidenced by reduced neuronal loss in the subiculum and cortical layer 5 of Niaspan®‐treated mice, accompanied by a rescue of working memory deficits.ConclusionThese preliminary data suggest that Niaspan® treatment has neuroprotective effects in AD, even after the onset of severe amyloid pathology, through an induction of Aβ cleareance by microglia. Niaspan® is a FDA‐approved drug, thus there is a translational potential of this strategy into clinical practice, supporting further study of this therapeutic approach.

Nicotinamide inhibits melanoma in vitro and in vivo

BackgroundEven though new therapies are available against melanoma, novel approaches are needed to overcome resistance and high-toxicity issues. In the present study the anti-melanoma activity of Nicotinamide (NAM), the amide form of Niacin, was assessed in vitro and in vivo.MethodsHuman (A375, SK-MEL-28) and mouse (B16-F10) melanoma cell lines were used for in vitro investigations. Viability, cell-death, cell-cycle distribution, apoptosis, Nicotinamide Adenine Dinucleotide+ (NAD+), Adenosine Triphosphate (ATP), and Reactive Oxygen Species (ROS) levels were measured after NAM treatment. NAM anti-SIRT2 activity was tested in vitro; SIRT2 expression level was investigated by in silico transcriptomic analyses. Melanoma growth in vivo was measured in thirty-five C57BL/6 mice injected subcutaneously with B16-F10 melanoma cells and treated intraperitoneally with NAM. Interferon (IFN)-γ-secreting murine cells were counted with ELISPOT assay. Cytokine/chemokine plasmatic levels were measured by xMAP technology. Niacin receptors expression in human melanoma samples was also investigated by in silico transcriptomic analyses.ResultsNAM reduced up to 90% melanoma cell number and induced: i) accumulation in G1-phase (40% increase), ii) reduction in S- and G2-phase (about 50% decrease), iii) a 10-fold increase of cell-death and 2.5-fold increase of apoptosis in sub-G1 phase, iv) a significant increase of NAD+, ATP, and ROS levels, v) a strong inhibition of SIRT2 activity in vitro. NAM significantly delayed tumor growth in vivo (p ≤ 0.0005) and improved survival of melanoma-bearing mice (p ≤ 0.0001). About 3-fold increase (p ≤ 0.05) of Interferon-gamma (IFN-γ) producing cells was observed in NAM treated mice. The plasmatic expression levels of 6 cytokines (namely: Interleukin 5 (IL-5), Eotaxin, Interleukin 12 (p40) (IL12(p40)), Interleukin 3 (IL-3), Interleukin 10 (IL-10) and Regulated on Activation Normal T Expressed and Secreted (RANTES) were significantly changed in the blood of NAM treated mice, suggesting a key role of the immune response. The observed inhibitory effect of NAM on SIRT2 enzymatic activity confirmed previous evidence; we show here that SIRT2 expression is significantly increased in melanoma and inversely related to melanoma-patients survival. Finally, we show for the first time that the expression levels of Niacin receptors HCAR2 and HCAR3 is almost abolished in human melanoma samples.ConclusionNAM shows a relevant anti-melanoma activity in vitro and in vivo and is a suitable candidate for further clinical investigations.

Nicotinic acid receptor agonists impair myocardial contractility by energy starvation.

Nicotinic acid receptor agonists have previously been shown to cause acute reductions in cardiac contractility. We sought to uncover the changes in cardiac metabolism underlying these alterations in function. In nine humans, we recorded cardiac energetics and function before and after a single oral dose of nicotinic acid using cardiac MRI to demonstrate contractile function and Phosphorus-31 (31 P) magnetic resonance spectroscopy to demonstrate myocardial energetics. Nicotinic Acid 400mg lowered ejection fraction by 4% (64±8% to 60±7%, P=.03), and was accompanied by a fall in phosphocreatine/ATP ratio by 0.4 (2.2±0.4 to 1.8±0.1, P=.04). In four groups of eight Wistar rats, we used pyruvate dehydrogenase (PDH) flux studies to demonstrate changes in carbohydrate metabolism induced by the nicotinic acid receptor agonist, Acipimox, using hyperpolarized Carbon-13 (13 C) magnetic resonance spectroscopy. In rats which had been starved overnight, Acipimox caused a fall in ejection fraction by 7.8% (67.5±8.9 to 60±3.1, P=.03) and a nearly threefold rise in flux through PDH (from 0.182±0.114 to 0.486±0.139, P=.002), though this rise did not match pyruvate dehydrogenase flux observed in rats fed carbohydrate rich chow (0.726±0.201). In fed rats, Acipimox decreased pyruvate dehydrogenase flux (to 0.512±0.13, P=.04). Concentration of plasma insulin fell by two-thirds in fed rats administered Acipimox (from 1695±891ng/L to 550±222ng/L, P=.005) in spite of glucose concentrations remaining the same. In conclusion, we demonstrate that nicotinic acid receptor agonists impair cardiac contractility associated with a decline in cardiac energetics and show that the mechanism is likely a combination of reduced fatty acid availability and a failure to upregulate carbohydrate metabolism, essentially starving the heart of fuel.

Discovery of novel pyrrole derivatives as potent agonists for the niacin receptor GPR109A

Novel pyrrole derivatives were discovered as potent agonists of the niacin receptor, GPR109A. During the derivatization, compound 16 was found to be effective both in vitro and in vivo. The compound 16 exhibited a significant reduction of the non-esterified fatty acid in human GPR109A transgenic rats, and the duration of its in vivo efficacy was much longer than niacin.

Niacin-mediated rejuvenation of macrophage/microglia enhances remyelination of the aging central nervous system

Remyelination following CNS demyelination restores rapid signal propagation and protects axons; however, its efficiency declines with increasing age. Both intrinsic changes in the oligodendrocyte progenitor cell population and extrinsic factors in the lesion microenvironment of older subjects contribute to this decline. Microglia and monocyte-derived macrophages are critical for successful remyelination, releasing growth factors and clearing inhibitory myelin debris. Several studies have implicated delayed recruitment of macrophages/microglia into lesions as a key contributor to the decline in remyelination observed in older subjects. Here we show that the decreased expression of the scavenger receptor CD36 of aging mouse microglia and human microglia in culture underlies their reduced phagocytic activity. Overexpression of CD36 in cultured microglia rescues the deficit in phagocytosis of myelin debris. By screening for clinically approved agents that stimulate macrophages/microglia, we have found that niacin (vitamin B3) upregulates CD36 expression and enhances myelin phagocytosis by microglia in culture. This increase in myelin phagocytosis is mediated through the niacin receptor (hydroxycarboxylic acid receptor 2). Genetic fate mapping and multiphoton live imaging show that systemic treatment of 9–12-month-old demyelinated mice with therapeutically relevant doses of niacin promotes myelin debris clearance in lesions by both peripherally derived macrophages and microglia. This is accompanied by enhancement of oligodendrocyte progenitor cell numbers and by improved remyelination in the treated mice. Niacin represents a safe and translationally amenable regenerative therapy for chronic demyelinating diseases such as multiple sclerosis.

Discovery of a novel niacin-lipoic acid dimer N2L attenuating atherosclerosis and dyslipidemia with non-flushing effects

Niacin has been widely used as an antihyperlipidemic drug, but the flushing effect restricted its clinical application. Here, we developed novel niacin-lipoic acid dimers which lead to better lipid modulation, higher synergistic effects and less side effects. We utilized molecular docking simulation to design a novel series of niacin-lipoic acid dimers. The compound N-(2-(5-(1,2-dithiolan-3-yl)pentanamido)ethyl)nicotinamide (N2L) was selected for the in vitro and in vivo evaluation, including the agonist activity in CHO-hGPR109A cells, cell protective effects in HT22 and HUVECs cells, flushing effect in guinea pigs and rats, lipid modulation in C57BL/6 mice and high fat diet-rats and atherosclerotic lesions regulation in apolipoprotein E null mice. N2L worked as potent and selective agonists for the high affinity niacin receptor GPR109A. N2L retained antioxidation and cytoprotection of lipoic acid. In addition, N2L displayed a good therapeutic index regarding lipid modulation and atherosclerotic lesions regulation, and minimized niacin-induced vasodilation (flushing) effect in vivo. N2L showed effective treatment regarding to lipid regulation and atherosclerosis inhibition effects, also with excellent antioxidant effects, safety profiles and non-flushing. All these results suggest N2L promising application prospects in the drug development for the treatment of atherosclerosis.