Biased allosteric activation of ketone body receptor HCAR2 suppresses inflammation.

Hydroxycarboxylic acid receptor 2 (HCAR2), modulated by endogenous ketone body ß-hydroxybutyrate and exogenous niacin, is a promising therapeutic target for inflammation-related diseases. HCAR2 mediates distinct pathophysiological events by activating Gi/o protein or ß-arrestin effectors. Here, we characterize compound 9n as a Gi-biased allosteric modulator (BAM) of HCAR2 and exhibit anti-inflammatory efficacy in RAW264.7 macrophages via a specific HCAR2-Gi pathway. Furthermore, four structures of HCAR2-Gi complex bound to orthosteric agonists (niacin or monomethyl fumarate), compound 9n, and niacin together with compound 9n simultaneously reveal a common orthosteric site and a unique allosteric site. Combined with functional studies, we decipher the action framework of biased allosteric modulation of compound 9n on the orthosteric site. Moreover, co-administration of compound 9n with orthosteric agonists could enhance anti-inflammatory effects in the mouse model of colitis. Together, our study provides insight to understand the molecular pharmacology of the BAM and facilitates exploring the therapeutic potential of the BAM with orthosteric drugs.

Butyrate, Valerate, and Niacin Ameliorate Anaphylaxis by Suppressing IgE-Dependent Mast Cell Activation: Roles of GPR109A, PGE2, and Epigenetic Regulation.

Short-chain fatty acids (SCFAs) are produced by the intestinal microbiota during the fermentation of dietary fibers as secondary metabolites. Several recent studies reported that SCFAs modulate the development and function of immune-related cells. However, the molecular mechanisms by which SCFAs regulate mast cells (MCs) remain unclear. In the current study, we analyzed the function and gene expression of mouse MCs in the presence of SCFAs in vitro and in vivo. We found that the oral administration of valerate or butyrate ameliorated passive systemic anaphylaxis and passive cutaneous anaphylaxis in mice. The majority of SCFAs, particularly propionate, butyrate, valerate, and isovalerate, suppressed the IgE-mediated degranulation of bone marrow-derived MCs, which were eliminated by the Gi protein inhibitor pertussis toxin and by the knockdown of Gpr109a. A treatment with the HDAC inhibitor trichostatin A also suppressed IgE-mediated MC activation and reduced the surface expression level of FcεRI on MCs. Acetylsalicylic acid and indomethacin attenuated the suppressive effects of SCFAs on degranulation. The degranulation degree was significantly reduced by PGE2 but not by PGD2. Furthermore, SCFAs enhanced PGE2 release from stimulated MCs. The SCFA-mediated amelioration of anaphylaxis was exacerbated by COX inhibitors and an EP3 antagonist, but not by an EP4 antagonist. The administration of niacin, a ligand of GPR109A, alleviated the symptoms of passive cutaneous anaphylaxis, which was inhibited by cyclooxygenase inhibitors and the EP3 antagonist. We conclude that SCFAs suppress IgE-mediated activation of MCs in vivo and in vitro involving GPR109A, PGE2, and epigenetic regulation.

Optimizing Biocompatibility and Gene Delivery with DMAEA and DMAEAm: A Niacin-Derived Copolymer Approach.

Gene therapy is pivotal in nanomedicine, offering a versatile approach to disease treatment. This study aims to achieve an optimal balance between biocompatibility and efficacy, which is a common challenge in the field. A copolymer library is synthesized, incorporating niacin-derived monomers 2-acrylamidoethyl nicotinate (AAEN) or 2-(acryloyloxy)ethyl nicotinate (AEN) with N,N-(dimethylamino)ethyl acrylamide (DMAEAm) or hydrolysis-labile N,N-(dimethylamino)ethyl acrylate (DMAEA). Evaluation of the polymers' cytotoxicity profiles reveals that an increase in AAEN or DMAEA molar ratios correlates with improved biocompatibility. Remarkably, an increase in AAEN in both DMAEA and DMAEAm copolymers demonstrated enhanced transfection efficiencies of plasmid DNA in HEK293T cells. Additionally, the top-performing polymers demonstrate promising gene expression in challenging-to-transfect cells (THP-1 and Jurkat cells) and show no significant effect on modulating immune response induction in ex vivo treated murine monocytes. Overall, the best performing candidates exhibit an optimal balance between biocompatibility and efficacy, showcasing potential advancements in gene therapy.

Effects of niacin on apo A1 and B levels: a systematic review and meta-analysis of randomised controlled trials.

Niacin has been investigated for its potential impact on lipid metabolism and cardiovascular health. This meta-analysis aims to systematically evaluate the effects of niacin interventions on apo A1 and apo B levels, key regulators of lipoprotein metabolism and markers of cardiovascular risk. A comprehensive search of the literature was performed on five databases of PubMed, Scopus, Web of Science, Embase and Cochrane library, from inception up to 15 July 2023. This search identified 1452 publications, from which twelve randomised controlled trials met the inclusion criteria. The intervention dosages ranged from 500 to 3000 mg/d, and the study durations spanned from 6 to 102·8 weeks. The niacin intervention demonstrated a significant reduction in apo B levels (weighted mean differences (WMD): -24·37 mg/dl, P = 0·01). Subgroup analyses indicated that intervention duration played a role, with trials of ≤ 16 weeks showing a greater reduction in apo B. Regarding apo A1, niacin significantly increased its levels (WMD: 8·23 mg/dl, P < 0·001). Subgroup analyses revealed that the beneficial effects of niacin on apo A1 were observed at a dosage of > 1500 mg/d (P < 0·001), and extended-release niacin was more effective compared with other forms (P < 0·001). According to the Begg's regression test, no publication bias was observed in this systematic review and meta-analysis. This meta-analysis highlights niacin's potential role in improving lipid profiles and cardiovascular health. Further well-designed clinical trials are needed to elucidate and confirm optimal dosages and durations of niacin interventions for influencing apo A1 and B.

The effect of niacin on inflammatory markers and adipokines: a systematic review and meta-analysis of interventional studies.

PURPOSE: Niacin (nicotinic acid), known for its lipid-modifying effects, has been explored for its potential anti-inflammatory properties and potential to affect adipokines secretion from adipose tissue. The aim of this systematic review and meta-analysis was to assess the effects of niacin on inflammatory markers and adipokines. METHODS: A comprehensive search was conducted across five databases: PubMed, Scopus, Cochrane Library, Embase, and ISI Web of Science. Randomized controlled trials exploring the effects of niacin on inflammatory markers (CRP, IL-6, TNF-α) and adipokines (Adiponectin, Leptin) were included. Pooled effect sizes were analysed using a random-effects model, and additional procedures including subgroup analyses, sensitivity analysis and dose-response analysis were also performed. RESULTS: From an initial 1279 articles, fifteen randomized controlled trials (RCTs) were included. Niacin administration demonstrated a notable reduction in CRP levels (SMD: -0.88, 95% CI: -1.46 to -0.30, p = 0.003). Subgroup analyses confirmed CRP reductions in trials with intervention durations ≤ 24 weeks, doses ≤ 1000 mg/day, and elevated baseline CRP levels (> 3 mg/l). The meta-analysis of IL-6 and TNF-α revealed significant TNF-α reductions, while IL-6 reduction did not reach statistical significance. Niacin administration also substantially elevated Adiponectin (SMD: 3.52, 95% CI: 0.95 to 6.1, p = 0.007) and Leptin (SMD: 1.90, 95% CI: 0.03 to 3.77, p = 0.04) levels. CONCLUSION: Niacin treatment is associated with significant reductions in CRP and TNF-α levels, suggesting potential anti-inflammatory effects. Additionally, niacin positively influences adipokines, increasing Adiponectin and Leptin levels. These findings provide insights for future research and clinical applications targeting inflammation and metabolic dysregulation.

Effects of rumen-protected niacin on inflammatory response to repeated intramammary lipopolysaccharide challenges.

Nutritional strategies that improve an animal's resilience to various challenges may improve animal health and welfare. One such nutrient is niacin, which has reduced inflammation in mice, humans, and swine; however, niacin's anti-inflammatory effects have not been investigated in cattle. Our objective was to determine whether rumen-protected niacin (RPN) alters lactating dairy cows' inflammatory response to intramammary LPS challenges, whether RPN resulted in any carryover effects, and whether repeated LPS challenges result in signs of immune tolerance or innate immune training. Twenty healthy, late-lactation Holstein cows (232 ± 65 DIM; 39 ± 5.8 kg/d of milk) were enrolled in a randomized complete block experiment that lasted 70 d. Cows received 26 g/d of RPN or no top-dress (CON) for the first 42 d of the experiment. During the final milking of d 27 and 55, cows were challenged in their rear right (RR) mammary gland with 100 µg of LPS suspended in 5 mL of PBS. Milk yield, milk conductivity, and feed intake were measured daily. Milk composition was measured on d 14, 23, 24, 30, 37, 45, and 52. Blood samples were collected at 0, 8, 12, 24, 48, 72, 96, and 120 h after each LPS challenge, whereas RR quarter milk samples were collected at 0, 8, 16, 24, 48, 72, 96, 120, 144, and 168 h after each LPS challenge. Body temperature was measured continuously during each challenge with an intravaginal thermometer. Linear mixed models with repeated measures were used to analyze the results. Before LPS challenge, RPN did not affect feed intake or milk production, but it reduced SCS (1.24 ± 0.41 [SE] vs. 0.05 ± 0.45). After challenge, RPN did not affect feed intake, milk production, milk composition, SCS, body temperature, plasma glucose, or plasma insulin concentrations. Our results suggest RPN reduced peak plasma haptoglobin and lipopolysaccharide binding protein during the first LPS challenge. Plasma haptoglobin tended to be less after the second challenge for cows previously supplemented RPN, and lipopolysaccharide binding protein was similar for each treatment group after the second challenge. The second LPS challenge resulted in decreased plasma haptoglobin compared with the first LPS challenge, suggestive of tolerance, but it also induced a greater peak SCS than the first LPS challenge. Our results suggest that repeated LPS challenges promote a systemic tolerance but heightened local response to LPS-induced mastitis. Feeding RPN reduced SCS before challenge and reduced plasma acute phase proteins after challenge, suggesting that RPN may reduce systemic inflammation without altering the local inflammatory responses.

Lipolysis inhibition as a treatment of clinical ketosis in dairy cows: Effects on adipose tissue metabolic and immune responses.

Dairy cows with clinical ketosis (CK) exhibit excessive adipose tissue (AT) lipolysis and systemic inflammation. Lipolysis in cows can be induced by the canonical (hormonally induced) and inflammatory lipolytic pathways. Currently, the most common treatment for CK is oral propylene glycol (PG); however, PG does not reduce lipolysis or inflammation. Niacin (NIA) can reduce the activation of canonical lipolysis, whereas cyclooxygenase inhibitors such as flunixin meglumine (FM) can limit inflammation and inhibit the inflammatory lipolytic pathway. The objective of this study was to determine the effects of including NIA and FM in the standard PG treatment for postpartum CK on AT function. Multiparous Jersey cows (n = 18; 7.1 ± 3.8 DIM) were selected from a commercial dairy. Inclusion criteria were CK symptoms (lethargy, depressed appetite, and drop in milk yield) and high blood levels of BHB (≥1.2 mmol/L). Cows with CK were randomly assigned to one of 3 treatments: (1) PG: 310 g administered orally once per day for 5 d, (2) PG+NIA: 24 g administered orally once per day for 3 d, and (3) PG+NIA+FM: 1.1 mg/kg administered IV once per day for 3 d. Healthy control cows (HC; n = 6) matched by lactation and DIM (±2 d) were sampled. Subcutaneous AT explants were collected at d 0 and d 7 relative to enrollment. To assess AT insulin sensitivity, explants were treated with insulin (1 µL/L) during lipolysis stimulation with a ß-adrenergic receptor agonist (isoproterenol, 1 µM). Lipolysis was quantified by glycerol release in the media. Lipid mobilization and inflammatory gene networks were evaluated using quantitative PCR. Protein biomarkers of lipolysis, insulin signaling, and AT inflammation, including hormone-sensitive lipase, protein kinase B (Akt), and ERK1/2, were quantified by capillary immunoassays. Flow cytometry of AT cellular components was used to characterize macrophage inflammatory phenotypes. Statistical significance was determined by a nonparametric t-test when 2 groups (HC vs. CK) were analyzed and an ANOVA test with Tukey adjustment when 3 treatment groups (PG vs. PG+NIA vs. PG+NIA+FM) were evaluated. At d 0, AT from CK cows showed higher mRNA expression of lipolytic enzymes ABHD5, LIPE, and LPL, as well as increased phosphorylation of hormone-sensitive lipase compared with HC. At d 0, insulin reduced lipolysis by 41% ± 8% in AT from HC, but CK cows were unresponsive (-2.9 ± 4%). Adipose tissue from CK cows exhibited reduced Akt phosphorylation compared with HC. Cows with CK had increased AT expression of inflammatory gene markers, including CCL2, IL8, IL10, TLR4, and TNF, along with ERK1/2 phosphorylation. Adipose tissue from CK cows showed increased macrophage infiltration compared with HC. By d 7, AT from PG+NIA+FM cows had a more robust response to insulin, as evidenced by reduced glycerol release (36.5% ± 8% compared with PG at 26.9% ± 7% and PG+NIA at 7.4% ± 8%) and enhanced phosphorylation of Akt. By d 7, PG+NIA+FM cows presented lower inflammatory markers, including ERK1/2 phosphorylation, and reduced macrophage infiltration, compared with PG and PG+NIA. These data suggest that including NIA and FM in CK treatment improves AT insulin sensitivity and reduces AT inflammation and macrophage infiltration.

Effect of nicotinic acid supplementation on digestion, metabolism, microbiome, and production in late-lactation Holstein cows.

The purpose of this experiment was to determine if nicotinic acid (NA) effects on dairy cows and rumen microbial characteristics are forage-type dependent (corn silage, CS; grass silage, GS). Four late-lactation (DIM = 225 ± 12 d) Holstein cows were used in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. The main effects were a CS (66.10% CS) based diet or a GS (79.59%) based diet with or without 12 g/d NA. Each experimental period lasted for 28 d. Milk production and milk components, blood metabolites, apparent total-tract nutrient digestibilities, minutes rumen pH were below 5.8 as an indicator of ruminal acidosis, and body temperature changes were analyzed as indicators of heat stress. Nicotinic acid supplementation did not improve apparent total-tract nutrient digestibility. Feeding a GS-based diet improved NDF and hemicellulose digestibility. Feeding a CS-based diet increased the apparent total-tract digestibility of fat, and minutes rumen pH below 5.8 for a greater proportion of the time. The CS-based diet also improved milk yield, milk fat and protein yields, and ECM yield; however, somatic cell count and BHB were also increased. Supplementing NA tended to decrease nonesterified fatty acids, especially when combined with GS where DMI was low. There was a trend for the total protozoa population to increase when GS and NA were fed but decreased when CS and NA were fed. Nicotinic acid tended to decrease rumen protozoal populations of Dasytricha, but increased populations of Ophryoscolex and Diplodiniinae with GS diets and decreased with CS diets. Entodiniinae were increased with CS but NA had no effect. Body temperature was increased when a CS-based diet was fed when compared with a GS-based diet. More research is needed to determine how NA can affect rumen microbial protein synthesis and what kind of diets will provide the optimum effect.

Altered HCAR3 expression may underlying the blunted niacin responses of the psychiatric disorders and the risk of schizophrenia.

AIM: Blunted niacin response (BNR) was an endophenotype of schizophrenia, but the underlying mechanism remains unclarified. The objective of this study was to verify whether genes associated with BNR pathway constitute the genetic basis and the pathological mechanism of BNR phenotypic psychiatric patients. METHODS: Two independent sample sets consisting of 971 subjects were enrolled in this study. A total of 62 variants were genotyped in the discovery set, then the related variants were verified in the verification set. The published PGC GWAS data were used to validate the associations between the variants and psychiatry disorders. RT-PCR analysis, eQTL data, and Dual-Luciferase Reporter experiment were used to investigate the potential molecular mechanisms of the variants underlying BNR. RESULTS: The results showed that two SNPs, rs56959712 in HCAR2 and rs2454721 in HCAR3 were significantly associated with niacin response. The risk allele T of rs2454721 could affect the niacin responses of psychiatric patients through elevated HCAR3 gene expression. These two genes, especially HCAR3, were significantly associated with the risk of schizophrenia, as identified in this study and verified using the published GWAS data. CONCLUSION: HCAR3 is a novel schizophrenia susceptibility gene which is significantly associated with blunted niacin response in schizophrenia. In-depth investigation of HCAR3 is of great significance for uncovering the pathogenesis and propose new therapeutic targets for psychiatric disorders, especially for the BNR subgroup patients.

Transdermal Delivery of Niacin Through Polysaccharide Films Ameliorates Cutaneous Flushing in Experimental Wistar Rats.

BACKGROUND: Niacin, an established therapeutic for dyslipidemia, is hindered by its propensity to induce significant cutaneous flushing when administered orally in its unmodified state, thereby constraining its clinical utility. OBJECTIVE: This study aimed to fabricate, characterize, and assess the in-vitro and in-vivo effectiveness of niacin-loaded polymeric films (NLPFs) comprised of carboxymethyl tamarind seed polysaccharide. The primary objective was to mitigate the flushing-related side effects associated with oral niacin administration. METHODS: NLPFs were synthesized using the solvent casting method and subsequently subjected to characterization, including assessments of tensile strength, moisture uptake, thickness, and folding endurance. Surface characteristics were analyzed using a surface profiler and scanning electron microscopy (SEM). Potential interactions between niacin and the polysaccharide core were investigated through X-ray diffraction experiments (XRD) and Fourier transform infrared spectroscopy (FTIR). The viscoelastic properties of the films were explored using a Rheometer. In-vitro assessments included drug release studies, swelling behavior assays, and antioxidant assays. In-vivo efficacy was evaluated through skin permeation assays, skin irritation assays, and histopathological analyses. RESULTS: NLPFs exhibited a smooth texture with favorable tensile strength and moisture absorption capabilities. Niacin demonstrated interaction with the polysaccharide core, rendering the films amorphous. The films displayed slow and sustained drug release, exceptional antioxidant properties, optimal swelling behavior, and viscoelastic characteristics. Furthermore, the films exhibited biocompatibility and non-toxicity towards skin cells. CONCLUSION: NLPFs emerged as promising carrier systems for the therapeutic transdermal delivery of niacin, effectively mitigating its flushing-associated adverse effects.