Niacin: a re-emerging pharmaceutical for the treatment of dyslipidaemia

Structural insights into ligand recognition and selectivity of the human hydroxycarboxylic acid receptor HCAR2

Hydroxycarboxylic acid receptor 2 (HCAR2) belongs to the family of class A G protein-coupled receptors with key roles in regulating lipolysis and free fatty acid formation in humans. It is deeply involved in many pathophysiological processes and serves as an attractive target for the treatment of cardiovascular, neoplastic, autoimmune, neurodegenerative, inflammatory, and metabolic diseases. Here, we report four cryo-EM structures of human HCAR2-Gi1 complexes with or without agonists, including the drugs niacin (2.69 Å) and acipimox (3.23 Å), the highly subtype-specific agonist MK-6892 (3.25 Å), and apo form (3.28 Å). Combined with molecular dynamics simulation and functional analysis, we have revealed the recognition mechanism of HCAR2 for different agonists and summarized the general pharmacophore features of HCAR2 agonists, which are based on three key residues R1113.36, S17945.52, and Y2847.43. Notably, the MK-6892-HCAR2 structure shows an extended binding pocket relative to other agonist-bound HCAR2 complexes. In addition, the key residues that determine the ligand selectivity between the HCAR2 and HCAR3 are also illuminated. Our findings provide structural insights into the ligand recognition, selectivity, activation, and G protein coupling mechanism of HCAR2, which shed light on the design of new HCAR2-targeting drugs for greater efficacy, higher selectivity, and fewer or no side effects.

Orthosteric ligand selectivity and allosteric probe dependence at Hydroxycarboxylic acid receptor HCAR2

Hydroxycarboxylic acid receptor 2 (HCAR2), a member of Class A G-protein-coupled receptor (GPCR) family, plays a pivotal role in anti-lipolytic and anti-inflammatory effects, establishing it as a significant therapeutic target for treating dyslipidemia and inflammatory diseases. However, the mechanism underlying the signaling of HCAR2 induced by various types of ligands remains elusive. In this study, we elucidate the cryo-electron microscopy (cryo-EM) structure of Gi-coupled HCAR2 in complex with a selective agonist, MK-6892, resolved to a resolution of 2.60 Å. Our structural analysis reveals that MK-6892 occupies not only the orthosteric binding pocket (OBP) but also an extended binding pocket (EBP) within HCAR2. Pharmacological assays conducted in this study demonstrate that the OBP is a critical determinant for ligand selectivity among the HCARs subfamily. Moreover, we investigate the pharmacological properties of the allosteric modulator compound 9n, revealing its probe-dependent behavior on HCAR2 in response to varying orthosteric agonists. Collectively, our findings provide invaluable structural insights that contribute to a deeper understanding of the regulatory mechanisms governing HCAR2 signaling transduction mediated by both orthosteric and allosteric ligands.

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.

Imaging niacin trafficking with positron emission tomography reveals in vivo monocarboxylate transporter distribution

Introduction

A sufficient dietary intake of the vitamin niacin is essential for normal cellular function. Niacin is transported into the cells by the monocarboxylate transporters: sodium-dependent monocarboxylate transporter (SMCT1 and SMCT2) and monocarboxylate transporter (MCT1). Despite the importance of niacin in biological systems, surprisingly, its in vivo biodistribution and trafficking in living organisms has not been reported. The availability of niacin radiolabelled with the short-lived positron emitting radionuclide carbon-11 ([¹¹C]niacin) would enable the quantitative in vivo study of this endogenous micronutrient trafficking using in vivo PET molecular imaging.

Methods

[¹¹C]Niacin was synthesised via a simple one-step, one-pot reaction in a fully automated system using cyclotron-produced carbon dioxide ([¹¹C]CO₂) and 3-pyridineboronic acid ester via a copper-mediated reaction. [¹¹C]Niacin was administered intravenously in healthy anaesthetised mice placed in a high-resolution nanoScan PET/CT scanner. To further characterize in vivo [¹¹C]niacin distribution in vivo, mice were challenged with either niacin or AZD3965, a potent and selective MCT1 inhibitor. To examine niacin gastrointestinal absorption and body distribution in vivo, no-carrier-added (NCA) and carrier-added (CA) [¹¹C]niacin formulations were administered orally.

Results

Total synthesis time including HPLC purification was 25 ± 1 min from end of [¹¹C]CO₂ delivery. [¹¹C]Niacin was obtained with a decay corrected radiochemical yield of 17 ± 2%.

We report a rapid radioactivity accumulation in the kidney, heart, eyes and liver of intravenously administered [¹¹C]niacin which is consistent with the known in vivo SMCTs and MCT1 transporter tissue expression. Pre-administration of non-radioactive niacin decreased kidney-, heart-, ocular- and liver-uptake and increased urinary excretion of [¹¹C]niacin. Pre-administration of AZD3965 selectively decreased [¹¹C]niacin uptake in MCT1-expressing organs such as heart and retina.

Following oral administration of NCA [¹¹C]niacin, a high level of radioactivity accumulated in the intestines. CA abolished the intestinal accumulation of [¹¹C]niacin resulting in a preferential distribution to all tissues expressing niacin transporters and the excretory organs.

Conclusions

Here, we describe the efficient preparation of [¹¹C]niacin as PET imaging agent for probing the trafficking of nutrient demand in healthy rodents by intravenous and oral administration, providing a translatable technique to enable the future exploration of niacin trafficking in humans and to assess its application as a research tool for metabolic disorders (dyslipidaemia) and cancer.

Niacin Cures Systemic NAD+ Deficiency and Improves Muscle Performance in Adult-Onset Mitochondrial Myopathy

NAD⁺ is a redox-active metabolite, the depletion of which has been proposed to promote aging and degenerative diseases in rodents. However, whether NAD⁺ depletion occurs in patients with degenerative disorders and whether NAD⁺ repletion improves their symptoms has remained open. Here, we report systemic NAD⁺ deficiency in adult-onset mitochondrial myopathy patients. We administered an increasing dose of NAD⁺-booster niacin, a vitamin B3 form (to 750-1,000 mg/day; clinicaltrials.govNCT03973203) for patients and their matched controls for 10 or 4 months, respectively. Blood NAD⁺ increased in all subjects, up to 8-fold, and muscle NAD⁺ of patients reached the level of their controls. Some patients showed anemia tendency, while muscle strength and mitochondrial biogenesis increased in all subjects. In patients, muscle metabolome shifted toward controls and liver fat decreased even 50%. Our evidence indicates that blood analysis is useful in identifying NAD⁺ deficiency and points niacin to be an efficient NAD⁺ booster for treating mitochondrial myopathy.

NLRP3 inflammasome as a treatment target in atherosclerosis: A focus on statin therapy

Activation of NOD-like receptor (NLR) family and pyrin domain containing 3 (NLRP3) inflammasome contributes to inflammation and may lead to atherosclerosis. The NLRP3 inflammasome as a molecular platform regulates the activation of ATP signaling, K⁺ efflux, cathepsin-B activity, lysosomal function and pro-inflammatory cytokines (i.e. IL-1β and IL-18). Statins has been widely prescribed for the treatment of hyperlipidemia and cardiovascular diseases. In addition to lipid-lowering effect, statins have immunomodulatory, anti-inflammatory, antioxidant and antiapoptotic functions. An increasing number of studies indicated NLRP3 inflammasome and their downstream mediators as important targets for statin drugs in inflammatory diseases. In this review, we discussed different aspect of the NLRP3 inflammasome signaling pathways and focused on the effect of statin drugs on NLRP3 inflammasomes in association to atherosclerosis in order to elucidate possible targets for future research and clinical settings.

Niacin and olive oil promote skewing to the M2 phenotype in bone marrow-derived macrophages of mice with metabolic syndrome

Metabolic syndrome (MetS) is associated with obesity, dyslipemia, type 2 diabetes and chronic low-grade inflammation.

Effects of Biotin Supplementation in the Diet on Adipose Tissue cGMP Concentrations, AMPK Activation, Lipolysis, and Serum-Free Fatty Acid Levels

Several studies have shown that pharmacological concentrations of biotin decrease hyperlipidemia. The molecular mechanisms by which pharmacological concentrations of biotin modify lipid metabolism are largely unknown. Adipose tissue plays a central role in lipid homeostasis. In the present study, we analyzed the effects of biotin supplementation in adipose tissue on signaling pathways and critical proteins that regulate lipid metabolism, as well as on lipolysis. In addition, we assessed serum fatty acid concentrations. Male BALB/cAnN Hsd mice were fed a control or a biotin-supplemented diet (control: 1.76 mg biotin/kg; supplemented: 97.7 mg biotin/kg diet) over 8 weeks postweaning. Compared with the control group, biotin-supplemented mice showed an increase in the levels of adipose guanosine 3',5'-cyclic monophosphate (cGMP) (control: 30.3±3.27 pmol/g wet tissue; supplemented: 49.5±3.44 pmol/g wet tissue) and of phosphorylated forms of adenosine 5'-monophosphate-activated protein kinase (AMPK; 65.2%±1.06%), acetyl-coenzyme A (CoA), carboxylase-1 (196%±68%), and acetyl-CoA carboxylase-2 (78.1%±18%). Serum fatty acid concentrations were decreased (control: 1.12±0.04 mM; supplemented: 0.91±0.03 mM), and no change in lipolysis was found (control: 0.29±0.05 μmol/mL; supplemented: 0.33±0.08 μmol/mL). In conclusion, 8 weeks of dietary biotin supplementation increased adipose tissue cGMP content and protein expression of the active form of AMPK and of the inactive forms of acetyl-CoA carboxylase-1 and acetyl-CoA carboxylase-2. Serum fatty acid levels fell, and no change in lipolysis was observed. These findings provide insight into the effects of biotin supplementation on adipose tissue and support its use in the treatment of dyslipidemia.

Niacin-induced hyperglycemia is partially mediated via niacin receptor GPR109a in pancreatic islets

The widely used lipid-lowering drug niacin is reported to induce hyperglycemia during chronic and high-dose treatments, but the mechanism is poorly understood. Recently, the niacin receptor [G-protein-coupled receptor, (GPR) 109a], has been localized to islet cells while its potential role therein remains unclear. We, therefore, aimed at investigating how GPR109a regulates islet beta-cell function and its downstream signaling using high-fat diet-induced obese mice and INS-1E beta cells. Eight-week niacin treatment elevated blood glucose concentration in obese mice with increased areas under the curve at oral glucose and intraperitoneal insulin tolerance tests. Additionally, niacin treatment significantly decreased glucose-stimulated insulin secretion (GSIS) but induced peroxisome proliferator-activated receptor gamma (Pparg) and GPR109a expression in isolated pancreatic islets; concomitantly, reactive oxygen species (ROS) were transiently increased, with decreases in GSIS, intracellular cyclic adenosine monophosphate (cAMP) accumulation and mitochondrial membrane potential (ΔΨm), but with increased expression of uncoupling protein 2 (Ucp2), Pparg and Gpr109a in INS-1E cells. Corroborating these findings, the decreases in GSIS, ΔΨm and cAMP production and increases in ROS, Pparg and GPR109a expression were abolished in INS-1E cells by GPR109a knockdown. Our data indicate that niacin-induced pancreatic islet dysfunction is probably modulated through activation of the islet beta-cell GPR109a-induced ROS-PPARγ-UCP2 pathways.

Nicotinic acid is a common regulator of heat-sensing TRPV1-4 ion channels

Nicotinic acid (NA, a.k.a. vitamin B3 or niacin) can reduce blood cholesterol and low-density lipoproteins whereas increase high-density lipoproteins. However, when NA is used to treat dyslipidemias, it causes a strong side effect of cutaneous vasodilation, commonly called flushing. A recent study showed that NA may cause flushing by lowering activation threshold temperature of the heat-sensitive capsaicin receptor TRPV1 ion channel, leading to its activation at body temperature. The finding calls into question whether NA might also interact with the homologous heat-sensitive TRPV2–4 channels, particularly given that TRPV3 and TRPV4 are abundantly expressed in keratinocytes of the skin where much of the flushing response occurs. We found that NA indeed potentiated TRPV3 while inhibited TRPV2 and TRPV4. Consistent with these gating effects, NA lowered the heat-activation threshold of TRPV3 but elevated that of TRPV4. We further found that activity of TRPV1 was substantially prolonged by extracellular NA, which may further enhance the direct activation effect. Consistent with the broad gating effect on TRPV1–4 channels, evidence from the present study hints that NA may share the same activation pathway as 2-aminoethoxydiphenyl borate (2-APB), a common agonist for these TRPV channels. These findings shed new light on the molecular mechanism underlying NA regulation of TRPV channels.

Treatment of dyslipidemia in allogeneic hematopoietic stem cell transplant patients

As survival rates in allogeneic hematopoietic stem cell transplantation (HSCT) continue to improve, attention to long-term complications, including cardiovascular disease, becomes a major concern. Cardiovascular disease and dyslipidemia are a common, yet often overlooked occurrence post-HSCT that results in significant morbidity and mortality. Also, increasing evidence shows that several anti-hyperlipidemia medications, the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in particular, may have a role in modulating graft-versus-host disease (GVHD). However, factors such as drug-drug interactions, adverse effect profiles, and the relative efficacy in lowering cholesterol and triglyceride levels must be taken into account when choosing safe and effective lipid-lowering therapy in this setting. This review seeks to provide guidance to the clinician in the management of dyslipidemia in the allogeneic HSCT population, taking into account the recently published American College of Cardiology/American Heart Association guidelines on hyperlipidemia management, special considerations in this challenging population, and the evidence for each agent's potential role in modulating GVHD.

Nicotinic acid activates the capsaicin receptor TRPV1: Potential mechanism for cutaneous flushing

OBJECTIVE

Nicotinic acid (also known as niacin or vitamin B3), widely used to treat dyslipidemias, represents an effective and safe means to reduce the risk of mortality from cardiovascular disease. Nonetheless, a substantial fraction of patients discontinue treatment because of a strong side effect of cutaneous vasodilation, commonly termed flushing. In the present study, we tested the hypothesis that nicotinic acid causes flushing partially by activating the capsaicin receptor TRPV1, a polymodal cellular sensor that mediates the flushing response on consumption of spicy food.

APPROACH AND RESULTS

We observed that the nicotinic acid-induced increase in blood flow was substantially reduced in Trpv1(-/-) knockout mice, indicating involvement of the channel in flushing response. Using exogenously expressed TRPV1, we confirmed that nicotinic acid at submillimolar to millimolar concentrations directly and potently activates TRPV1 from the intracellular side. Binding of nicotinic acid to TRPV1 lowers its activation threshold for heat, causing channel opening at physiological temperatures. The activation of TRPV1 by voltage or ligands (capsaicin and 2-aminoethoxydiphenyl borate) is also potentiated by nicotinic acid. We further demonstrated that nicotinic acid does not compete directly with capsaicin but may activate TRPV1 through the 2-aminoethoxydiphenyl borate activation pathway. Using live-cell fluorescence imaging, we observed that nicotinic acid can quickly enter the cell through a transporter-mediated pathway to activate TRPV1.

CONCLUSIONS

Direct activation of TRPV1 by nicotinic acid may lead to cutaneous vasodilation that contributes to flushing, suggesting a potential novel pathway to inhibit flushing and to improve compliance.

New compounds able to control hepatic cholesterol metabolism: Is it possible to avoid statin treatment in aged people?

Aging is characterized by the loss of homeostasis that leads to changes in the biochemical composition of tissues, reduced ability to respond adaptively to environmental stimuli, and increased susceptibility and vulnerability to diseases including coronary artery diseases, carotid artery disease and brain vessel disease. Hypercholesterolemia is one of the primary risk factors for these pathologies, whose incidence is highly related to aging. Almost 25% of men and 42% of women older than 65 years have a serum total cholesterol level greater than 240 mg/dL. The mechanisms behind this age-related increase in plasma cholesterol are still incompletely understood, thus, the control of plasma cholesterol content in aged people is more challenging than in adults. In this review the different pharmacological approaches to reduce plasma cholesterol levels, particularly in aged people, will be discussed. In brief, current therapies are mostly based on the prescription of statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) that are pretty effective but that exert several side effects. More attention should be given to potential drug interactions, potential age-related changes in drug pharmacokinetics, adverse effects such as myopathy and competing risks when statins are prescribed to old patients. In combination or in alternative to statin therapy, other agents might be required to reduce low density lipoprotein (LDL) cholesterol levels. Among the available drugs, the most commonly prescribed are those addressed to reduce cholesterol absorption, to modulate lipoprotein lipase activity and bile acid sequestrants: even these pharmacological interventions are not exempt from side effects. The use of antioxidants or organoselenium compounds and the discovery of new proteins able to modulate exclusively LDL receptor recycling such as Proprotein convertase subtilisin kexin 9 and SEC24 offer new pharmacological approaches to selectively reduce the main causes of dyslipidemia.

GSK256073, a selective agonist of G-protein coupled receptor 109A (GPR109A) reduces serum glucose in subjects with type 2 diabetes mellitus

AIMS

This clinical trial assessed whether a potent, selective GPR109A agonist, GSK256073, could, through inhibition of lipolysis, acutely improve glucose homeostasis in subjects with type 2 diabetes mellitus.

METHODS

Thirty-nine diabetic subjects were enrolled in the randomized, single-blind, placebo-controlled, three-period crossover trial. Each subject received placebo and two of four regimens of GSK256073 for 2 days. GSK256073 was dosed 5 mg every 12 h before breakfast and supper (BID), 10 mg every 24 h before breakfast (QD), 25 mg BID and 50 mg QD.

RESULTS

The change from baseline weighted mean glucose concentration for an interval from 24 to 48 h after the initial drug dose was significantly reduced for all GSK256073 regimens, reaching a maximum of -0.87 mmol/l (-1.20, -0.52) with the 25 mg BID dose. Sustained suppression of non-esterified fatty acid (NEFA) and glycerol concentrations was observed with all GSK256073 doses throughout the 48-h dosing period. Serum insulin and C-peptide concentrations fell in concert with glucose concentrations and calculated HOMA-IR scores decreased 27-47%, consistent with insulin sensitization. No marked differences were evident between either 10 and 50 mg total daily doses or QD versus BID dosing.

CONCLUSIONS

Administration of a GPR109A agonist for 2 days significantly decreased serum NEFA and glucose concentrations in diabetic subjects. Glucose improvements were associated with decreased insulin concentrations and measures of enhanced insulin sensitivity. Improved glucose control occurred with GSK256073 doses that were generally safe and not associated with events of flushing or gastrointestinal disturbances.

Endothelial dysfunction in diabetes: pathogenesis, significance, and treatment

Type 2 diabetes (T2D) markedly increases the risk of cardiovascular disease. Endothelial dysfunction (ED), an early indicator of diabetic vascular disease, is common in T2D and independently predicts cardiovascular risk. Although the precise pathogenic mechanisms for ED in T2D remain unclear, at inception they probably involve uncoupling of both endothelial nitric oxide synthase activity and mitochondrial oxidative phosphorylation, as well as the activation of vascular nicotinamide adenine dinucleotide phosphate oxidase. The major contributing factors include dyslipoproteinemia, oxidative stress, and inflammation. Therapeutic interventions are designed to target these pathophysiological factors that underlie ED. Therapeutic interventions, including lifestyle changes, antiglycemic agents and lipid-regulating therapies, aim to correct hyperglycemia and atherogenic dyslipidemia and to improve ED. However, high residual cardiovascular risk is seen in both research and clinical practice settings. Well-designed studies of endothelial function in appropriately selected volunteers afford a good opportunity to test new therapeutic interventions, paving the way for clinical trials and utilization in the care of the diabetic patient. However, based on the results from a recent clinical trial, niacin should not be added to a statin in individuals with low high-density lipoprotein cholesterol and very well controlled low-density lipoprotein cholesterol.

Atherogenic dyslipidemia and combination pharmacotherapy in diabetes: recent clinical trials

Patients with type 2 diabetes (T2D) are at a markedly increased risk of cardiovascular disease (CVD). Dyslipidemia is a common risk factor and a strong predictor of CVD in T2D patients. Although statins decrease the incidence of CVD in T2D, residual cardiovascular risk remains high despite the achievement of optimal or near-optimal plasma low-density lipoprotein (LDL) cholesterol concentrations. This may, in part, be due to uncorrected atherogenic dyslipidemia. Hypertriglyceridemia, the driving force behind diabetic dyslipidemia, results from hepatic overproduction and/or delayed clearance of triglyceride-rich lipoproteins. In patients treated with a statin to LDL-cholesterol goals, the addition of ezetimibe, fenofibrate, niacin, or n-3 fatty acid ethyl esters may be required to correct the persistent atherogenic dyslipidemia. Clinical trial evidence describing best practice is limited, but recent data supports the strategy of adding fenofibrate to a statin, and suggests specific benefits in dyslipidemic patients and in the improvement of diabetic retinopathy. However, based on results from a recent clinical trial, niacin should not be added to a statin in individuals with low high-density lipoprotein cholesterol and very well controlled LDL-cholesterol. Further evidence is required to support the role of ezetimibe and n-3 fatty acids in treating residual CVD risk in statin-treated T2D patients.

Atherogenic dyslipidemia and combination pharmacotherapy in diabetes: recent clinical trials

Patients with type 2 diabetes (T2D) are at a markedly increased risk of cardiovascular disease (CVD). Dyslipidemia is a common risk factor and a strong predictor of CVD in T2D patients. Although statins decrease the incidence of CVD in T2D, residual cardiovascular risk remains high despite the achievement of optimal or near-optimal plasma low-density lipoprotein (LDL) cholesterol concentrations. This may, in part, be due to uncorrected atherogenic dyslipidemia. Hypertriglyceridemia, the driving force behind diabetic dyslipidemia, results from hepatic overproduction and/or delayed clearance of triglyceride-rich lipoproteins. In patients treated with a statin to LDL-cholesterol goals, the addition of ezetimibe, fenofibrate, niacin, or n-3 fatty acid ethyl esters may be required to correct the persistent atherogenic dyslipidemia. Clinical trial evidence describing best practice is limited, but recent data supports the strategy of adding fenofibrate to a statin, and suggests specific benefits in dyslipidemic patients and in the improvement of diabetic retinopathy. However, based on results from a recent clinical trial, niacin should not be added to a statin in individuals with low high-density lipoprotein cholesterol and very well controlled LDL-cholesterol. Further evidence is required to support the role of ezetimibe and n-3 fatty acids in treating residual CVD risk in statin-treated T2D patients.

Adherence, Persistence, and Predictors Associated with Early Niacin Termination

Background:

Niacin is the most effective therapy currently available to increase high-density lipoprotein cholesterol. However, adherence to niacin may be limited by a number of factors and it is important to characterize who is likely to discontinue the medicine.

Objective:

To measure adherence and persistence to niacin, estimate the influence of niacin dose on adherence, and identify factors associated with early termination of niacin.

Methods:

This retrospective study estimated adherence to niacin by calculating the medication possession ratio, persistence, number of refills, and termination proportion in a large, deidentified US health claims database consisting of 42,685 insurance-carrying adults who were new users of niacin.

Results:

We identified 29,801 new users of niacin who were not taking statins or fibric acid, 12,298 new users of niacin plus statin, 441 new users of niacin plus fibric acid, and 145 new users who initiated all 3 agents. Persistence was lowest among individuals taking less than 1 g/day and was highest among those taking niacin plus fibric acid plus statin (5.10 vs 7.17 months, respectively). However, lower niacin dose was associated with greater adherence, regardless of statin use. Termination of niacin within 1 year of initiation was significantly associated with being female or having 1 of the following conditions: peripheral vascular disease, chronic pulmonary disease, diabetes mellitus, rheumatic disease, or liver disease. Increased age, taking niacin in combination with a statin, or taking drugs from 2 or more concomitant prescription medication classes were significantly associated with a reduced likelihood of termination within 1 year.

Conclusions:

We observed relatively high adherence rates to niacin; however, most patients failed to persist with use of the drug beyond 7 months.

Cardiovascular disease risk reduction by raising HDL cholesterol--current therapies and future opportunities

Since the first discovery of an inverse correlation between high-density lipoprotein-cholesterol (HDL-C) levels and coronary heart disease in the 1950s the life cycle of HDL, its role in atherosclerosis and the therapeutic modification of HDL-C levels have been major research topics. The Framingham study and others that followed could show that HDL-C is an independent cardiovascular risk factor and that the increase of HDL-C of only 10 mg·L(-1) leads to a risk reduction of 2-3%. While statin therapy and therefore low-density lipoprotein-cholesterol (LDL-C) reduction could lower coronary heart disease considerably; cardiovascular morbidity and mortality still occur in a significant portion of subjects already receiving therapy. Therefore, new strategies and therapies are needed to further reduce the risk. Raising HDL-C was thought to achieve this goal. However, established drug therapies resulting in substantial HDL-C increase are scarce and their effect is controversial. Furthermore, it is becoming increasingly evident that HDL particle functionality is at least as important as HDL-C levels since HDL particles not only promote reverse cholesterol transport from the periphery (mainly macrophages) to the liver but also exert pleiotropic effects on inflammation, haemostasis and apoptosis. This review deals with the biology of HDL particles, the established and future therapeutic options to increase HDL-C and discusses the results and conclusions of the most important studies published in the last years. Finally, an outlook on future diagnostic tools and therapeutic opportunities regarding coronary artery disease is given.

The hypotriglyceridemic effect of biotin supplementation involves increased levels of cGMP and AMPK activation

In addition to its role as a carboxylase cofactor, biotin modifies gene expression and has manifold effects on systemic processes. Several studies have shown that biotin supplementation reduces hypertriglyceridemia. We have previously reported that this effect is related to decreased expression of lipogenic genes. In the present work, we analyzed signaling pathways and posttranscriptional mechanisms involved in the hypotriglyceridemic effects of biotin. Male BALB/cAnN Hsd mice were fed a control or a biotin-supplemented diet (1.76 or 97.7 mg of free biotin/kg diet, respectively for 8 weeks after weaning. The abundance of mature sterol regulatory element-binding protein (SREBP-1c), fatty-acid synthase (FAS), total acetyl-CoA carboxylase-1 (ACC-1) and its phosphorylated form, and AMP-activated protein kinase (AMPK) were evaluated in the liver. We also determined the serum triglyceride concentrations and the hepatic levels of triglycerides and cyclic GMP (cGMP). Compared to the control group, biotin-supplemented mice had lower serum and hepatic triglyceride concentrations. Biotin supplementation increased the levels of cGMP and the phosphorylated forms of AMPK and ACC-1 and decreased the abundance of the mature form of SREBP-1c and FAS. These data provide evidence that the mechanisms by which biotin supplementation reduces lipogenesis involve increased cGMP content and AMPK activation. In turn, these changes lead to augmented ACC-1 phosphorylation and decreased expression of both the mature form of SREBP-1c and FAS. Our results demonstrate for the first time that AMPK is involved in the effects of biotin supplementation and offer new insights into the mechanisms of biotin-mediated hypotriglyceridemic effects.

Statins as anti-inflammatory agents in atherogenesis: molecular mechanisms and lessons from the recent clinical trials

Ample evidence exists in support of the potent anti-inflammatory properties of statins. In cell studies and animal models statins exert beneficial cardiovascular effects. By inhibiting intracellular isoprenoids formation, statins suppress vascular and myocardial inflammation, favorably modulate vascular and myocardial redox state and improve nitric oxide bioavailability. Randomized clinical trials have demonstrated that further to their lipid lowering effects, statins are useful in the primary and secondary prevention of coronary heart disease (CHD) due to their anti-inflammatory potential. The landmark JUPITER trial suggested that in subjects without CHD, suppression of low-grade inflammation by statins improves clinical outcome. However, recent trials have failed to document any clinical benefit with statins in high risk groups, such in heart failure or chronic kidney disease patients. In this review, we aim to summarize the existing evidence on statins as an anti-inflammatory agent in atherogenesis. We describe the molecular mechanisms responsible for the anti-inflammatory effects of statins, as well as clinical data on the non lipid-lowering, anti-inflammatory effects of statins on cardiovascular outcomes. Lastly, the controversy of the recent large randomized clinical trials and the issue of statin withdrawal are also discussed.

Effects of biotin supplementation in the diet on insulin secretion, islet gene expression, glucose homeostasis and beta-cell proportion

Besides its role as a carboxylase cofactor, biotin has a wide repertoire of effects on gene expression, development and metabolism. Pharmacological concentrations of biotin enhance insulin secretion and the expression of genes and signaling pathways that favor islet function in vitro. However, the in vivo effects of biotin supplementation on pancreatic islet function are largely unknown. In the present study, we investigated whether in vivo biotin supplementation in the diet has positive effects in rodent pancreatic islets. Male BALB/cAnN Hsd mice were fed a control or a biotin-supplemented diet over 8 weeks postweaning and tested for glucose homeostasis, insulin secretion, islet gene expression and pancreatic morphometry. Insulin secretion increased from the islets of biotin-supplemented mice, together with the messenger RNA (mRNA) expression of several transcription factors regulating insulin expression and secretion, including forkhead box A2, pancreatic and duodenal homeobox 1 and hepatocyte nuclear factor 4α. The mRNA abundance of glucokinase, Cacna1d, acetyl-CoA carboxylase, and insulin also increased. Consistent with these effects, glucose tolerance improved, and glucose-stimulated serum insulin levels increased in biotin-supplemented mice, without changes in fasting glucose levels or insulin tolerance. Biotin supplementation augmented the proportion of beta cells by enlarging islet size and, unexpectedly, also increased the percentage of islets with alpha cells at the islet core. mRNA expression of neural cell adhesion molecule 1, an adhesion protein participating in the maintenance of islet architecture, decreased in biotin-supplemented islets. These findings provide, for the first time, insight into how biotin supplementation exerts its effects on function and proportion of beta cells, suggesting a role for biotin in the prevention and treatment of diabetes.

Blood lipids and stroke: what more can we do besides reducing low-density lipoprotein cholesterol?

Statin therapy has became the most important advance in stroke prevention since the introduction of aspirin and blood pressure-lowering therapies. Other lipid-modifying drugs have been less successful in reducing the incidence of stroke, but because of evidence for the use of triglyceride-lowering drugs and treatments that raise concentrations of high-density lipoprotein (HDL) cholesterol, further investigations are needed, particularly in patients with an atherogenic dyslipidemia profile (high triglycerides and low HDL cholesterol levels). Furthermore, beyond reducing low-density lipoprotein cholesterol and possibly improving other lipids fractions in patients who are at high risk of stroke, the present review shoes that lipid-modifying drugs might have neuroprotective effects that should also be further explored.

Nicotinamide phosphoribosyltransferase (Nampt) affects the lineage fate determination of mesenchymal stem cells: a possible cause for reduced osteogenesis and increased adipogenesis in older individuals

Human aging is associated with a progressive decline in bone mass and an accumulation of marrow fat. We found that osteoblast differentiation was reduced and adipocyte formation increased in bone marrow stromal cells derived from aged mice compared with young controls. The increased adipogenesis correlated with a relatively lower Sirt1 activity and a lower intracellular NAD(+) concentration. We suppose that these effects were caused by age-related reduction of nicotinamide phosphoribosyltransferase (Nampt), the enzyme catalyzing NAD resynthesis from nicotinamide (NAM). In support of this hypothesis, treatment with Nampt inhibitor FK866 increased adipocyte formation and reduced mineralization in primary cultured bone marrow stromal cells. In addition, knockdown of Nampt in the mouse mesenchymal cell line C3H10T1/2 cells resulted in decreased Sirt1 activity and enhanced adipogenesis. Interestingly, although Nampt deficiency resulted in both decreased intracellular NAD(+) and increased NAM, the cell differentiation could be controlled only by regulation of NAM. These results indicate that the lineage fate determination of mesenchymal stem cells (MSCs) is influenced by cell energy metabolism and points to a possible mechanism for the development of senile osteoporosis. Furthermore, we suggest that side effects on bone should be considered when evaluating the long-term safety of NAD-interfering pharmaceuticals.

Extended release niacin-laropiprant in patients with hypercholesterolemia or mixed dyslipidemias improves clinical parameters

The progression of atherosclerosis remains a major cause of morbidity and mortality. Plaque formation is an immunological response driven by a number of risk factors, and reduction of risk is the primary goal of treatment. The role of LDL-C is well established and statins have proved effective drugs, although the relative risk reduction is only around 30%. The importance of other factors-notably low HDL-C and high TGs-has become increasingly clear and the search for alternative strategies continues. Niacin is particularly effective in achieving normalization of HDL-C but is clinically underutilized due to the side effect of cutaneous flushing. The discovery that flushing is mediated by mechanisms distinct from the lipid-lowering effects has led to the development of combination drugs with reduced side effects. This review considers the evidence regarding the clinical efficacy of extended-release niacin and the DP1 antagonist laropiprant in the treatment of hypercholesterolemia and mixed dyslipidemias.

High dietary niacin may increase prostaglandin formation but does not increase tumor formation in ApcMin/+ mice

High doses of niacin (nicotinic acid) used to treat dyslipidemias cause flushing, due to high levels of prostaglandin D(2) (PGD(2)). GPR109A, a G-protein coupled receptor, triggers the flushing in the skin. In addition to boosting PGD(2), niacin binding to GPR109A activates the entire prostanoid cascade. We found that GPR109A occurs throughout the gastrointestinal tract. Mice that alternated between a 1% niacin diet and a control diet had higher urinary prostaglandin E(2) (PGE(2)) metabolite levels when on niacin (2.8-fold increase; 95% confidence interval, 1.8-3.9). PGE(2) promotes tumors in the intestines, whereas PGD(2) may have an opposite effect, on the basis of our report showing that transgenic hematopoietic prostaglandin D synthase suppresses intestinal adenomas in Apc(Min/+) mice. To determine if either tumor growth or tumor suppression prevails, we fed Apc(Min/+) mice a 1% niacin diet and assessed tumor development. A 1% niacin diet did not affect the number of tumors scored histologically in Apc(Min/+) mice at 14 wk (33 mice on niacin, 33 controls). Although niacin stimulates production of various prostaglandins, our results support an interpretation that very high intakes of niacin are safe in relation to intestinal tumors in this model.

Niacin and its metabolites: role of LC-MS/MS bioanalytical methods and update on clinical pharmacology. An overview

Niacin (nicotinic acid), although an old drug, has seen a sudden surge in popularity for treatment of lipid disorders and other associated clinical conditions for the prevention of cardiovascular risk. Also, there has been considerable interest in clarifying the role of metabolic pathways of niacin in explaining the tolerability/adverse affect profile of the agent. Hence, it has become very important to quantify/monitor the levels of niacin and its metabolites in various clinical studies. This review describes the recent trends in the bioanalysis of niacin and its metabolites, where HPLC and LC-MS/MS assays have been successfully employed to measure the drug levels in various biological matrices arising from preclinical and clinical studies. In addition, this review encompass various considerations such as internal standard selection, extraction schemes, matrix effect, selectivity evaluation and optimization of mass spectral conditions to enable the development of sound bioanalytical methods for niacin alone or niacin along with its metabolites. Recent updates pertaining to the clinical pharmacology of niacin and ongoing debate for the clarification of adverse effects are also provided. Overall LC-MS/MS methods have proven to be choice of bioanalytical method for the quantification of niacin alone or with its metabolites in both preclinical and clinical studies.

Niacin improves small artery vasodilatory function and compliance in statin-treated type 2 diabetic patients

We investigated the effect of niacin (nicotinic acid prolonged release) on forearm vasodilatory function and arterial compliance in statin-treated type 2 diabetic patients with endothelial dysfunction. In a parallel group study, we randomised 15 subjects, with LDL-cholesterol ≤2.5 mmol/L, to niacin (dose titrated to 1500 mg/day over 8 weeks, then maintained for a further 12 weeks) or no additional treatment. Niacin increased maximal post-ischaemic forearm blood flow (mean ± SEM 6.4±2.4 vs. -2.3±1.2 ml/100 ml/min, p = 0.001) and small artery compliance (1.3±0.8 vs. -2.3±1.1 ml/mmHg, p = 0.01) compared with no additional treatment, but did not alter large artery compliance, blood pressure nor heart rate. Niacin decreased serum triglycerides by 47% (p = 0.04), with no change in LDL-cholesterol, HDL-cholesterol, apolipoprotein (Apo) B-100 nor ApoA-I (p > 0.05). Adding niacin to statin therapy improves small artery vasodilatory function and compliance in type 2 diabetes. This may relate to a decrease in serum triglycerides and/or a direct benefit of niacin on vascular biology.

Niacin as potential treatment for dyslipidemia and hyperphosphatemia associated with chronic renal failure: the need for clinical trials

Niacin has profound and unique effects on lipid metabolism. In addition to increasing high-density lipoprotein cholesterol, it is also known to decrease total cholesterol, low-density lipoprotein cholesterol, and triglyceride. Interestingly, the plasma concentration of lipoprotein(a) [Lp(a)], which has been suggested to play a role as an independent risk factor for coronary heart disease, is also decreased by niacin. Therefore, it is not surprising that in the literature it was given unique description as broad-spectrum lipid drug. Its impact is referred to as desirable normalization of a range of cardiovascular risk factors. However, its clinical use is limited due to harmless but unpleasant unique side effect of cutaneous flushing. Interestingly, recent experimental and clinical studies suggest the potential benefit of niacin as a treatment of dyslipidemia and high plasma phosphate associated with chronic kidney disease (CKD). Both dyslipidemia and high serum phosphate levels are shown to be associated with higher cardiovascular mortality. Furthermore, niacin administration improves renal tissue lipid metabolism, renal function and structure, hypertension, proteinuria, and histological tubulointerstitial injury. Further studies are required before the use of niacin for the treatment of both dyslipidemia and hyperphosphatemia with CKD advocated.

Association between change in plasma triglyceride levels and risk of stroke and carotid atherosclerosis: systematic review and meta-regression analysis

BACKGROUND AND PURPOSE

The contribution of modifying non-low-density lipoprotein cholesterol (LDL-C) levels to reduce stroke risk remains uncertain. The aim of this study was to investigate the association between treatment-induced change in plasma triglyceride levels and risk of stroke and progression of carotid intima-media thickness (CIMT).

METHODS

We performed a systematic review and meta-regression analyses of randomized controlled trials of lipid-modifying treatments selected from a PubMed search on literature published from 1966 to 2008.

RESULTS

We identified 64 randomized controlled trials (active groups, n=96,807; control groups, n=98,681) that tested lipid-modifying drugs and reported triglyceride levels and stroke outcome. Extracting data from placebo groups, we found a statistically significant association between baseline triglyceride levels and stroke risk (adjusted relative risk [RR], 1.05 per 10-mg/dL increase; 95% CI, 1.03-1.07). Except for a trend in fibrate and niacin trials, there was no evidence of any relationship between degree of triglyceride change and stroke incidence. In multivariable meta-regression analysis including baseline and change in LDL-C, only change in LDL-C was associated with log risk ratio of all strokes (RR reduction, 4.5% per 10-mg/dL reduction; 95% CI, 1.7-7.2; P=.003). Similarly, taking into account 26 randomized controlled trials reporting CIMT outcome, LDL-C reduction was associated with reduced CIMT progression (-3.0 microm/y per 10-mg/dL reduction; 95% CI, -5.5 to -0.4; P=.03).

CONCLUSIONS

In view of the limitations of meta-regression analysis and CIMT measures as surrogate endpoints in lipid-lowering drugs trials, additional studies are needed to more precisely quantify the detrimental effect of triglyceride levels on stroke risk and to establish the efficacy of triglyceride-lowering therapy in addition to LDL-C reduction.

Nicotinamide-rich diet protects the heart against ischaemia-reperfusion in mice: a crucial role for cardiac SUR2A

It is a consensus view that a strategy to increase heart resistance to ischaemia-reperfusion is a warranted. Here, based on our previous study, we have hypothesized that a nicotinamide-rich diet could increase myocardial resistance to ischaemia-reperfusion. Therefore, the purpose of this study was to determine whether nicotinamide-rich diet would increase heart resistance to ischaemia-reperfusion and what is the underlying mechanism. Experiments have been done on mice on control and nicotinamide-rich diet (mice were a week on nicotinamide-rich diet) as well as on transgenic mice overexpressing SUR2A (SUR2A mice), a regulatory subunit of cardioprotective ATP-sensitive K(+) (K(ATP)) channels and their littermate controls (WT). The levels of mRNA in heart tissue were measured by real-time RT-PCR, whole heart and single cell resistance to ischaemia-reperfusion and severe hypoxia was measured by TTC staining and laser confocal microscopy, respectively. Nicotinamide-rich diet significantly decreased the size of myocardial infarction induced by ischaemia-reperfusion (from 42.5+/-4.6% of the area at risk zone in mice on control diet to 26.8+/-1.8% in mice on nicotinamide-rich diet, n=6-12, P=0.031). The cardioprotective effect of nicotinamide-rich diet was associated with 11.46+/-1.22 times (n=6) increased mRNA levels of SUR2A in the heart. HMR1098, a selective inhibitor of the sarcolemmal K(ATP) channels opening, abolished cardioprotection afforded by nicotinamide-rich diet. Transgenic mice with a sole increase in SUR2A expression had also increased cardiac resistance to ischaemia-reperfusion. We conclude that nicotinamide-rich diet up-regulate SUR2A and increases heart resistance to ischaemia-reperfusion.

Themed section: Advances in nutritional pharmacology. Editorial

A themed section in this issue of Br J Pharmacol, on 'Advances in Nutritional Pharmacology', provides a valuable and timely update on progress in this area. The value of dietary components to improvement in health and, particularly, to prevention of cardiovascular disease and cancer, is frequently reported in the media and therefore often captures the attention of the wider public. Understanding the pharmacological mechanisms by which nutritional elements confer their health benefits enables us to keep the public informed, but also aids in the identification of new targets for drug development. In recent years there has been significant progress in this field. Four rapidly developing areas are reviewed. Vosper (2009) covers the identification of a receptor for niacin and the subsequent development of selective agonists as lipid lowering agents. Wu-Wong (2009) describes the development of new Vitamin D analogues for the treatment of cardiovascular disease. de Roos et al. (2009) provide detailed insight into how omega-3 fatty acids, also known as longchain n-3 polyunsaturated fatty acids (PUFAs) protect against cardiovascular disease. Zhou et al. (2009) cover the mechanisms underlying the beneficial effects of resveretrol in protection against cancer. These reviews are complimented by three key original articles focusing on endogenous mechanisms of weight control involving endocannabinoids (Izzo et al., 2009), a circulating protein, the soluble leptin receptor (Zhang & Scarpace, 2009) and a treatment, zinc plus cyclo-(His-Pro) (CHP), known to increase insulin metabolism (Song et al., 2009).