Mechanism of action of niacin

Effects of low-dose niacin on dyslipidemia and serum phosphorus in patients with chronic kidney disease

BACKGROUND

Niacin supplementation improves dyslipidemia and lowers serum phosphorus levels in patients with chronic kidney disease (CKD). We evaluated whether low-dose niacin supplementation can improve dyslipidemia, lower serum phosphorus levels, and be administered with a low frequency of adverse effects in patients with CKD.

METHODS

We retrospectively analyzed the clinical records of patients with CKD who had taken niacin from January 2009 to June 2011. We excluded patients with CKD stage 1 and 5. We then enrolled 31 patients with CKD who had taken niacin at a fixed dose of 500 mg/day for 6 months. We also randomly selected 30 patients with CKD who had been taking statin for 9 months as a control group.

RESULTS

Among the 34 patients with CKD who were prescribed niacin, five (14%) complained of adverse effects, and three (8%) discontinued niacin. The proportion of patients in the niacin group who had been taking a statin or omega-3 fatty acids was 67.7% and 48.8%, respectively. In the niacin group, high-density lipoprotein cholesterol level was significantly increased and triglyceride level was significantly decreased at 12 and 24 weeks compared with baseline levels (P<0.05). In the niacin group, phosphorous level (P<0.05) was significantly decreased, and glomerular filtration rate (GFR) was significantly increased (P<0.05) at 24 weeks compared with baseline values.

CONCLUSION

Low-dose niacin had a low frequency of adverse effects and also improved dyslipidemia, lowered serum phosphorus level, and increased GFR in patients with CKD. Further studies are needed to evaluate the long-term effects of low-dose niacin for renal progression of CKD.

The current state of niacin in cardiovascular disease prevention: a systematic review and meta-regression

OBJECTIVES

This study sought to assess the efficacy of niacin for reducing cardiovascular disease (CVD) events, as indicated by the aggregate body of clinical trial evidence including data from the recently published AIM-HIGH (Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglycerides: Impact on Global Health Outcomes) trial.

BACKGROUND

Previously available randomized clinical trial data assessing the clinical efficacy of niacin has been challenged by results from AIM-HIGH, which failed to demonstrate a reduction in CVD event incidence in patients with established CVD treated with niacin as an adjunct to intensive simvastatin therapy.

METHODS

Clinical trials of niacin, alone or combined with other lipid-altering therapy, were identified via MEDLINE. Odds ratios (ORs) for CVD endpoints were calculated with a random-effects meta-analyses. Meta-regression modeled the relationship of differences in on-treatment high-density lipoprotein cholesterol with the magnitude of effect of niacin on CVD events.

RESULTS

Eleven eligible trials including 9,959 subjects were identified. Niacin use was associated with a significant reduction in the composite endpoints of any CVD event (OR: 0.66; 95% confidence interval [CI]: 0.49 to 0.89; p = 0.007) and major coronary heart disease event (OR: 0.75; 95% CI: 0.59 to 0.96; p = 0.02). No significant association was observed between niacin therapy and stroke incidence (OR: 0.88; 95% CI: 0.5 to 1.54; p = 0.65). The magnitude of on-treatment high-density lipoprotein cholesterol difference between treatment arms was not significantly associated with the magnitude of the effect of niacin on outcomes.

CONCLUSIONS

The consensus perspective derived from available clinical data supports that niacin reduces CVD events and, further, that this may occur through a mechanism not reflected by changes in high-density lipoprotein cholesterol concentration.

Niacin improves lipid profile but not endothelial function in patients with coronary artery disease on high dose statin therapy

AIMS

To determine the effect of extended release (ER) niacin on endothelial and vascular function assessed by brachial flow-mediated dilatation (FMD), peak hyperemic velocity (VTiRH) and pulse arterial tonometry (PAT) in patients with established coronary artery disease (CAD), already treated with high dose statins. Endothelial dysfunction is common in patients with established coronary artery disease (CAD) and has prognostic implications. Niacin has proven clinical benefit in patients with CAD, but its additive effect in patients on statin therapy is being evaluated. The effect of niacin on endothelial function, in the presence of optimal LDL cholesterol is unclear.

METHODS AND RESULTS

Sixty-six patients with CAD (mean age 57.9 ± 8.5 yrs) received ER niacin (1500 mg per day) and placebo in a randomized crossover fashion for 3 months of each therapy. All patients received atorvastatin 80 mg per day. FMD, VTiRH and PAT measurements were performed at baseline and after each treatment period. Treatment with niacin improved dyslipidemia parameters (LDL placebo 1.52 ± 0.51 vs. niacin 1.30 ± 0.43; p = 0.004; HDL placebo 0.95 ± 0.16 vs. niacin 1.11 ± 0.22; p < 0.001). However, there was no observed improvement in endothelial function as assessed by FMD (placebo 6.1 ± 4.9 vs. niacin 6.6 ± 4.8%; p = 0.48), VTiRH (placebo 75 ± 28 vs. niacin 78 ± 26 cm; p = 0.23) or PAT (placebo 1.8 ± 0.42 vs. niacin 1.79 ± 0.5; p = 0.43).

CONCLUSION

Niacin as add-on treatment to high dose statins in patients with established CAD significantly improves lipid profile. However, these changes were not associated with improved endothelial or microvascular function. Registered clinical trial with clinicaltrials.gov: NCT00150722.

Nicotinic acid inhibits hepatic APOA gene expression: studies in humans and in transgenic mice

Elevated plasma lipoprotein(a) (LPA) levels are recognized as an independent risk factor for cardiovascular diseases. Our knowledge on LPA metabolism is incomplete, which makes it difficult to develop LPA-lowering medications. Nicotinic acid (NA) is the main drug recommended for the treatment of patients with increased plasma LPA concentrations. The mechanism of NA in lowering LPA is virtually unknown. To study this mechanism, we treated transgenic (tg) APOA mice with NA and measured plasma APOA and hepatic mRNA levels. In addition, mouse and human primary hepatocytes were incubated with NA, and the expression of APOA was followed. Feeding 1% NA reduced plasma APOA and hepatic expression of APOA in tg-APOA mice. Experiments with cultured human and mouse primary hepatocytes in addition to reporter assays performed in HepG2 cells revealed that NA suppresses APOA transcription. The region between -1446 and -857 of the human APOA promoter harboring several cAMP response element binding sites conferred the negative effect of NA. In accordance, cAMP stimulated APOA transcription, and NA reduced hepatic cAMP levels. It is suggested that cAMP signaling might be involved in reducing APOA transcription, which leads to the lowering of plasma LPA.

Diagnosis and treatment of severe hypertriglyceridemia

Severe hypertriglyceridemia is associated with acute pancreatitis and can be a manifestation of lipoprotein lipase (LPL) deficiency. It is associated with a spectrum of disorders, ranging from heterozygous LPL deficiency allied with environmental factors to rare severe cases of homozygous LPL deficiency. The genes associated with reduced LPL activity include LPL, its cofactor apoC-2, a controlling protein apoA-5 and the LPL receptor GPI-HBP1. The effects of mutations are exacerbated by environmental factors such as diet, pregnancy and insulin resistance. Treatment of clinical LPL deficiency is by ultra-low-fat diet along with the use of fibrates, omega-3 fatty acids, niacin, statins and insulin-sensitizing therapies, depending on the extent of residual LPL activity. Novel therapies that target lipoprotein particle assembly through the antisense oligonucleotides or by interference with triglyceride-loading microsomal transport protein inhibitors offer new potential options for treating hypertriglyceridemia.

G protein-coupled receptors for energy metabolites as new therapeutic targets

Several G protein-coupled receptors (GPCRs) that are activated by intermediates of energy metabolism - such as fatty acids, saccharides, lactate and ketone bodies - have recently been discovered. These receptors are able to sense metabolic activity or levels of energy substrates and use this information to control the secretion of metabolic hormones or to regulate the metabolic activity of particular cells. Moreover, most of these receptors appear to be involved in the pathophysiology of metabolic diseases such as diabetes, dyslipidaemia and obesity. This Review summarizes the functions of these metabolite-sensing GPCRs in physiology and disease, and discusses the emerging pharmacological agents that are being developed to target these GPCRs for the treatment of metabolic disorders.

Colesevelam hydrochloride: evidence for its use in the treatment of hypercholesterolemia and type 2 diabetes mellitus with insights into mechanism of action

Colesevelam hydrochloride is a molecularly engineered, second-generation bile acid sequestrant demonstrating enhanced specificity for bile acids which has been approved for use as adjunctive therapy to diet and exercise as monotherapy or in combination with a β-hydroxymethylglutaryl-coenzyme A reductase inhibitor for the reduction of elevated low-density lipoprotein cholesterol in patients with primary hypercholesterolemia. It is also the only lipid-lowering agent currently available in the United States which has been approved for use as adjunctive therapy in patients with type 2 diabetes mellitus whose glycemia remains inadequately controlled on therapy with metformin, sulfonylurea, or insulin. With the recent emphasis upon drug safety by the Food and Drug Administration and various consumer agencies, it is fitting that the role of nonsystemic lipid-lowering therapies such as bile acid sequestrants – with nearly 90 years of in-class, clinically safe experience – should be reexamined. This paper presents information on the major pharmacologic effects of colesevelam, including a discussion of recent data derived from both in vitro and in vivo rodent and human studies, which shed light on the putative mechanisms involved.

Triglyceride, nonesterified fatty acids, and prediabetic neuropathy: role for oxidative-nitrosative stress

Peripheral neuropathy develops in human subjects with prediabetes and metabolic syndrome before overt hyperglycemia. The contributions of impaired glucose tolerance and insulin signaling, hypertriglyceridemia and/or increased nonesterified fatty acids (NEFA), and hypercholesterolemia to this condition remain unknown. Niacin and its derivatives alleviate dyslipidemia with a minor effect on glucose homeostasis. This study evaluated the roles of impaired glucose tolerance versus dyslipidemia in prediabetic neuropathy using Zucker fatty (fa/fa) rats and the niacin derivative acipimox, as well as the interplay of hypertriglyceridemia, increased NEFA, and oxidative-nitrosative stress. Sixteen-week-old Zucker fatty rats with impaired glucose tolerance, obesity, hyperinsulinemia, hypertriglyceridemia, hypercholesterolemia, and increased NEFA displayed sensory nerve conduction velocity deficit, thermal and mechanical hypoalgesia, and tactile allodynia. Acipimox (100 mg kg(-1) day(-1), 4 weeks) reduced serum insulin, NEFA, and triglyceride concentrations without affecting glucose tolerance and hypercholesterolemia. It alleviated sensory nerve conduction velocity deficit and changes in behavioral measures of sensory function and corrected oxidative-nitrosative stress, but not impaired insulin signaling, in peripheral nerve. Elevated NEFA increased total and mitochondrial superoxide production and NAD(P)H oxidase activity in cultured human Schwann cells. In conclusion, hypertriglyceridemia and/or increased NEFA concentrations cause prediabetic neuropathy through oxidative-nitrosative stress. Lipid-lowering agents and antioxidants may find a use in the management of this condition.

Treatment options for the management of hypertriglyceridemia: strategies based on the best-available evidence

A severe elevation in triglycerides (TG; ≥500 mg/dL) increases the risk for pancreatitis. TG levels ≥200 mg/dL are associated with a greater risk of atherosclerotic coronary heart disease (CHD). However, no outcomes trials exist to assess the efficacy of TG lowering for preventing pancreatitis in patients with severe hypertriglyceridemia. Similarly, no completed prospective outcomes trial exists to support or refute a reduction in CHD risk resulting from lipid-altering therapy in patients specifically selected for the presence of hypertriglyceridemia. This review examines the available evidence for the use of statins, omega-3 fatty acids, fibrates, and niacin in the management of hypertriglyceridemic patients. Results from CHD outcomes trials support statins as the first-line lipid-altering drug therapy to reduce CHD in hypercholesterolemic patients, and subgroup analyses suggest statins are efficacious in hypertriglyceridemic patients with fasting TG levels <500 mg/dL. Omega-3 fatty acids and fibrates are reasonable first drug options for patients with TG ≥500 mg/dL and often are used to lower TG levels with the objective of reducing pancreatitis risk, although a statin or niacin may also be reasonable options. Combination lipid drug therapy may be needed to achieve both low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol treatment goals for CHD prevention in patients with elevated TG levels, particularly those with TG ≥500 mg/dL. Additional clinical outcomes data are needed to provide a more evidence-based rationale for clinical lipid management of hypertriglyceridemic patients.

Niacin increases HDL biogenesis by enhancing DR4-dependent transcription of ABCA1 and lipidation of apolipoprotein A-I in HepG2 cells

The lipidation of apoA-I in liver greatly influences HDL biogenesis and plasma HDL levels by stabilizing the secreted apoA-I. Niacin is the most effective lipid-regulating agent clinically available to raise HDL. This study was undertaken to identify regulatory mechanisms of niacin action in hepatic lipidation of apoA-I, a critical event involved in HDL biogenesis. In cultured human hepatocytes (HepG2), niacin increased: association of apoA-I with phospholipids and cholesterol by 46% and 23% respectively, formation of lipid-poor single apoA-I molecule-containing particles up to ~2.4-fold, and pre β 1 and α migrating HDL particles. Niacin dose-dependently stimulated the cell efflux of phospholipid and cholesterol and increased transcription of ABCA1 gene and ABCA1 protein. Mutated DR4, a binding site for nuclear factor liver X receptor alpha (LXR α ) in the ABCA1 promoter, abolished niacin stimulatory effect. Further, knocking down LXR α or ABCA1 by RNA interference eliminated niacin-stimulated apoA-I lipidation. Niacin treatment did not change apoA-I gene expression. The present data indicate that niacin increases apoA-I lipidation by enhancing lipid efflux through a DR4-dependent transcription of ABCA1 gene in HepG2 cells. A stimulatory role of niacin in early hepatic formation of HDL particles suggests a new mechanism that contributes to niacin action to increase the stability of newly synthesized circulating HDL.

The role of triglycerides in atherosclerosis

Hypertriglyceridemia is a prevalent risk factor for cardiovascular disease (CVD) and increasingly important in the setting of current obesity and insulin resistance epidemics. High triglyceride (TG) levels are markers for several types of atherogenic lipoproteins. Patients who have hypertriglyceridemia may be at significant risk for CVD even if low-density lipoprotein cholesterol levels are at goal, and therefore warrant treatment that optimizes diet, reduces overweight, and promotes regular exercise. High-risk patients with hypertriglyceridemia, such as those with diabetes, CVD, or metabolic syndrome, may benefit from additional drug treatment aside from a statin to address other lipid abnormalities. In this discussion, we review the role of hypertriglyceridemia and its associated atherogenic lipoproteins in the pathogenesis of atherosclerosis, the relevance of a high TG level as a predictor of CVD, the cardiovascular outcomes from TG-lowering intervention trials, and the current guidelines for treating hypertriglyceridemia.

Targeting sirtuin 1 to improve metabolism: all you need is NAD(+)?

Sirtuin 1 (SIRT1) is an evolutionarily conserved NAD(+)-dependent deacetylase that is at the pinnacle of metabolic control, all the way from yeast to humans. SIRT1 senses changes in intracellular NAD(+) levels, which reflect energy level, and uses this information to adapt the cellular energy output such that it matches cellular energy requirements. The changes induced by SIRT1 activation are generally (but not exclusively) transcriptional in nature and are related to an increase in mitochondrial metabolism and antioxidant protection. These attractive features have validated SIRT1 as a therapeutic target in the management of metabolic disease and prompted an intensive search to identify pharmacological SIRT1 activators. In this review, we first give an overview of the SIRT1 biology with a particular focus on its role in metabolic control. We then analyze the pros and cons of the current strategies used to activate SIRT1 and explore the emerging evidence indicating that modulation of NAD(+) levels could provide an effective way to achieve such goals.

Optimal pharmacotherapy to combat the atherogenic lipid triad

PURPOSE OF REVIEW

A lipid triad involving an atherogenic dyslipidemia characterized by moderate/high LDL-C, low HDL-C, and elevated triglyceride (TG) occurs in numerous clinical settings associated with high cardiovascular risk. This article focuses on optimizing treatment of atherogenic dyslipidemias involving this lipid triad, emphasizing niacin-based or fibrate-based therapies.

RECENT FINDINGS

Niacin-based therapies comprehensively improve the atherogenic lipid profile, lead to atherosclerosis regression, and exert benefits across a spectrum of cardiovascular endpoints in studies based on limited patient numbers. Fibrates impact TG, HDL-C, and LDL-C according to lipid phenotype and underlying metabolic abnormality. In a recent meta-analysis, fibrates significantly reduced major cardiovascular events (-10%) and coronary events (-13%) across a wide range of lipid phenotypes, but had no impact on stroke, sudden death, or mortality. The Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial in type 2 diabetic patients similarly showed no significant effect of fenofibrate + simvastatin (vs. simvastatin) on nonfatal myocardial infarction, nonfatal stroke, or cardiovascular death; a subgroup (17%) with marked atherogenic dyslipidemia trended toward benefit. Both niacin and fibrates attenuate vascular inflammation but the potential clinical relevance is indeterminate.

SUMMARY

Optimal cardiovascular risk reduction in patients exhibiting the lipid triad requires integrated pharmacotherapy to normalize LDL-C, HDL-C, TGs, and potentially lipoprotein(a). Ongoing studies may provide definitive evidence of the impact of niacin plus statins on cardiovascular outcomes.

The association of lipoprotein lipase PvuII polymorphism and niacin intake in the prevalence of metabolic syndrome: a KMSRI-Seoul study

Lipoprotein lipase (LPL) polymorphism correlated with LPL activity is associated with plasma lipid and lipoprotein levels. We aimed to investigate the frequency of LPL PvuII polymorphism and effects of LPL PvuII polymorphism and niacin intake on the prevalence of metabolic syndrome (MetSyn) in Koreans. Lifestyle questionnaires, anthropometry, and dietary records were completed, and LPL PvuII polymorphism, LPL mass, and lipid profiles were determined in 548 Koreans (MetSyn: 278, Non-MetSyn: 270). The MetSyn group showed a significantly lower frequency of P1P1 (wild type) and a higher frequency of P1P2 (hetero type) than the non-MetSyn group. The P2P2 (mutant type) group significantly showed lower levels of HDLc and LPL mass and a higher level of TG than the P1P1 group. As niacin intake increased, LPL mass decreased in the P2P2 group (r (2) = 0.07). In particular, the lowest niacin intake group (≤14.82 mg/day) increased more than 3 times with regard to a higher risk of MetSyn than the others in the P2P2 mutant groups. However, the MetSyn risk declined 74% at the optimal levels of niacin intake (14.83-17.80 mg/day) in the P2P2 group compared to those of the P1 allele group. The findings indicate that optimal levels of niacin intake effectively decreased Korean MetSyn prevalence in the P2P2 mutant group.

Effects of nicotinic acid on gene expression: potential mechanisms and implications for wanted and unwanted effects of the lipid-lowering drug

CONTEXT

Nicotinic acid (NA), or niacin, lowers circulating levels of lipids, including triglycerides, very low-density lipoprotein-cholesterol, and low-density lipoprotein-cholesterol. The lipid-lowering effects have been attributed to its effect to inhibit lipolysis in adipocytes and thus lower plasma free fatty acid (FFA) level. However, evidence accumulates that the FFA-lowering effect may account for only a fraction of NA effects on plasma lipids, and other mechanisms may be involved. Recent studies have reported NA effects on gene expression in various tissues in vivo and in cultured cells in vitro.

EVIDENCE ACQUISITION

We reviewed articles reporting NA effects on gene expression, identified by searching PubMed, focusing on potential underlying mechanisms and implications for unexplained NA effects.

CONCLUSION

The effects of NA on gene expression may be mediated directly via the NA receptor in the affected cells, indirectly via changes in circulating FFA or hormone levels induced by NA, or by activating the transcription factor FOXO1 in insulin-sensitive tissues. NA effects on gene expression provide new insights into previously unexplained NA effects, such as FFA-independent lipid-lowering effects, FFA rebound, and insulin resistance observed in clinics during NA treatment.

The effect of hepatic lipase on coronary artery disease in humans is influenced by the underlying lipoprotein phenotype

Increased or decreased hepatic lipase (HL) activity has been associated with coronary artery disease (CAD). This is consistent with the findings that gene variants that influence HL activity were associated with increased CAD risk in some population studies but not in others. In this review, we will explain the conditions that influence the effects of HL on CAD. Increased HL is associated with smaller and denser LDL (sdLDL) and HDL (HDL(3)) particles, while decreased HL is associated with larger and more buoyant LDL and HDL particles. The effect of HL activity on CAD risk is dependent on the underlying lipoprotein phenotype or disorder. Central obesity with hypertriglyceridemia (HTG) is associated with high HL activity that leads to the formation of sdLDL that is pro-atherogenic. In the absence of HTG, where large buoyant cholesteryl ester-enriched LDL is prominent, elevation of HL does not raise the risk for CAD. In HTG patients, drug therapy that decreases HL activity selectively decreases sdLDL particles, an anti-atherogenic effect. Drug therapy that raises HDL(2) cholesterol has not decreased the risk for CAD. In trials where inhibition of cholesterol ester transfer protein (CETP) or HL occurs, the increase in HDL(2) most likely is due to inhibition of catabolism of HDL(2) and impairment of reverse cholesterol transport (RCT). In patients with isolated hypercholesterolemia, but with normal triglyceride levels and big-buoyant LDL particles, an increase in HL activity is beneficial; possibly because it increases RCT. Drugs that lower HL activity might decrease the risk for CAD only in hypertriglyceridemic patients with sdLDL by selectively clearing sdLDL particles from plasma, which would override the potentially pro-atherogenic effect on RCT. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Future of GPR109A agonists in the treatment of dyslipidaemia

Abnormal blood lipids are the major modifiable risk factor underlying the development of cardiovascular disease. Niacin has a profound ability to reduce low-density lipoprotein-C, very low-density lipoprotein-C and triglycerides and is the most effective pharmacological agent to increase high-density lipoprotein-C. Recently, the receptor for niacin, GPR109A, was discovered. GPR109A in the adipocyte mediates a niacin-induced inhibition of lipolysis, which could play a crucial part in its role as a lipid-modifying drug. GPR109A in epidermal Langerhans cells mediates flushing, an unwanted side effect of niacin therapy. For the past decade, the functions of GPR109A have been studied and full or partial agonists have been developed in an attempt to achieve the beneficial effects of niacin while avoiding the unwanted flushing side effect. This review presents what is known to date about GPR109A biology and function and the future of GPR109A as a pharmacological target.

Polycystic ovary syndrome: a common endocrine disorder and risk factor for vascular disease

OPINION STATEMENT

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy among women of reproductive age, impacting 5-10% of premenopausal American women. During the reproductive years, women with PCOS seek medical attention related to infertility, hirsutism, and acne. About 60% of women with PCOS are obese and insulin resistant. Up to 40% of women with PCOS will develop diabetes by the age of 50 and many are dyslipidemic. In addition to treating the cosmetic and fertility issues associated with PCOS, health care providers must educate patients regarding the long-term cardiovascular consequences associated the this disorder. At menopause, a woman with PCOS is likely to have had multiple cardiac risk factors for several decades. Postmenopausal women with a history of PCOS, especially those with established diabetes and/or dyslipidemia, should be considered at high risk for the development of clinical cardiac disease. Exercise and a prudent calorie-restricted diet aimed at weight loss must be stressed early. Pharmacologic therapy for diabetes and hyperlipidemia should be used when appropriate. Bariatric surgery, known to positively impact all the aforementioned cardiac risk factors, may also be of benefit.

High-density lipoprotein therapy: is there hope?

OPINION STATEMENT

The treatment of lipid abnormalities generally has focused on low-density lipoprotein cholesterol (LDL-C) reduction based on extensive clinical trials and the National Cholesterol Education Program Adult Treatment Panel III guidelines. Unfortunately, it has become increasingly clear that a significant percentage of patients continue to have cardiovascular events despite being on LDL-C-lowering medications and having LDL-C levels below 100 mg/dL. Numerous epidemiologic studies have associated low high-density lipoprotein cholesterol (HDL-C) levels with increased risk of cardiovascular disease (CVD). Furthermore, recent data show that up to 55% of patients hospitalized for CVD have low HDL-C levels (<40 mg/dL) on admission, suggesting a possible target for further reducing CVD. Low HDL-C also is part of the atherogenic phenotype associated with obesity, glucose intolerance, and hypertension, termed the metabolic syndrome, and often is seen in patients with insulin resistance states. In general, the first line of therapy for increasing HDL-C in patients with levels below 40 mg/dL is lifestyle modification with smoking cessation, exercise, weight loss, and diet modifications. The pharmacologic treatment of isolated low HDL-C in patients without coronary disease is controversial but should be considered in those with a strong family history of CVD. In patients with coronary artery disease and isolated low HDL-C, statins remain the first-line therapy and should be instituted after lifestyle modifications, with the goal of increasing HDL-C above 40 mg/dL. If concomitant hypertriglyceridemia is present, a fibrate or niacin should be considered. Although statins do offer some HDL-C-raising properties, they tend to have modest effects. If treatment goals have not been achieved with either lifestyle changes or statin therapy, then the next agent of choice is niacin. Among the various HDL-C-raising therapies, niacin continues to be the most potent therapeutic option available. There are several novel HDL-C therapies in the research pipeline; however, only one class of medications is relatively close to clinical use, the cholesteryl ester transferase protein (CETP) inhibitors. Although one of the CETP inhibitors, torcetrapib, has received much negative attention from a large randomized trial showing increased mortality associated with its use, the overall class of therapeutic agents may still hold some benefit. Currently, two new CETP inhibitors without the off-target effects of torcetrapib are undergoing clinical research. Overall, the use of HDL-C-modifying agents likely will increase over the next decade.

International Union of Basic and Clinical Pharmacology. LXXXII: Nomenclature and Classification of Hydroxy-carboxylic Acid Receptors (GPR81, GPR109A, and GPR109B)

The G-protein-coupled receptors GPR81, GPR109A, and GPR109B share significant sequence homology and form a small group of receptors, each of which is encoded by clustered genes. In recent years, endogenous ligands for all three receptors have been described. These endogenous ligands have in common that they are hydroxy-carboxylic acid metabolites, and we therefore have proposed that this receptor family be named hydroxy-carboxylic acid (HCA) receptors. The HCA(1) receptor (GPR81) is activated by 2-hydroxy-propanoic acid (lactate), the HCA(2) receptor (GPR109A) is a receptor for the ketone body 3-hydroxy-butyric acid, and the HCA(3) receptor (GPR109B) is activated by the β-oxidation intermediate 3-hydroxy-octanoic acid. HCA(1) and HCA(2) receptors are found in most mammalian species, whereas the HCA(3) receptor is present only in higher primates. The three receptors have in common that they are expressed in adipocytes and are coupled to G(i)-type G-proteins mediating antilipolytic effects in fat cells. HCA(2) and HCA(3) receptors are also expressed in a variety of immune cells. HCA(2) is a receptor for the antidyslipidemic drug nicotinic acid (niacin) and related compounds, and there is an increasing number of synthetic ligands mainly targeted at HCA(2) and HCA(3) receptors. The aim of this article is to give an overview on the discovery and pharmacological characterization of HCAs, and to introduce an International Union of Basic and Clinical Pharmacology (IUPHAR)-recommended nomenclature. We will also discuss open questions regarding this receptor family as well as their physiological role and therapeutic potential.

Continuous 24-h nicotinic acid infusion in rats causes FFA rebound and insulin resistance by altering gene expression and basal lipolysis in adipose tissue

Nicotinic acid (NA) has been used as a lipid drug for five decades. The lipid-lowering effects of NA are attributed to its ability to suppress lipolysis in adipocytes and lower plasma FFA levels. However, plasma FFA levels often rebound during NA treatment, offsetting some of the lipid-lowering effects of NA and/or causing insulin resistance, but the underlying mechanisms are unclear. The present study was designed to determine whether a prolonged, continuous NA infusion in rats produces a FFA rebound and/or insulin resistance. NA infusion rapidly lowered plasma FFA levels (>60%, P < 0.01), and this effect was maintained for ≥5 h. However, when this infusion was extended to 24 h, plasma FFA levels rebounded to the levels of saline-infused control rats. This was not due to a downregulation of NA action, because when the NA infusion was stopped, plasma FFA levels rapidly increased more than twofold (P < 0.01), indicating that basal lipolysis was increased. Microarray analysis revealed many changes in gene expression in adipose tissue, which would contribute to the increase in basal lipolysis. In particular, phosphodiesterase-3B gene expression decreased significantly, which would increase cAMP levels and thus lipolysis. Hyperinsulinemic glucose clamps showed that insulin's action on glucose metabolism was improved during 24-h NA infusion but became impaired with increased plasma FFA levels after cessation of NA infusion. In conclusion, a 24-h continuous NA infusion in rats resulted in an FFA rebound, which appeared to be due to altered gene expression and increased basal lipolysis in adipose tissue. In addition, our data support a previous suggestion that insulin resistance develops as a result of FFA rebound during NA treatment. Thus, the present study provides an animal model and potential molecular mechanisms of FFA rebound and insulin resistance, observed in clinical studies with chronic NA treatment.

Apolipoprotein E genotype as a most significant predictor of lipid response at lipid-lowering therapy: mechanistic and clinical studies

APOE alleles and apolipoprotein E isoforms control plasma cholesterol level on population level. Among three ɛ2, ɛ3, ɛ4 alleles, ɛ4 allele is associated with the increase in cholesterol level, risk of atherosclerosis and Alzheimer disease, while ɛ2 allele is associated with the decrease in cholesterol level and risk of atherosclerosis. The increase in plasma triglyceride is an independent risk factor of atherosclerosis and triglyceride-high density lipoprotein coupling determines the efficiency of reverse cholesterol transport. The impairment of this coupling specifically at hypertriglyceridemia may be followed by specific lipoprotein markers. The influence of major lipid-lowering drugs on lipoprotein metabolism and association of apoE isoforms with the efficiency of therapy by statins and fibrates are summarized both at isolated and combined increase in plasma triglyceride and cholesterol. APOE polymorphism seems to be a single genetic variant with a confirmed stratification both at candidate gene and at wide genome analyses.

Triglyceride-rich lipoproteins and high-density lipoprotein cholesterol in patients at high risk of cardiovascular disease: evidence and guidance for management

Even at low-density lipoprotein cholesterol (LDL-C) goal, patients with cardiometabolic abnormalities remain at high risk of cardiovascular events. This paper aims (i) to critically appraise evidence for elevated levels of triglyceride-rich lipoproteins (TRLs) and low levels of high-density lipoprotein cholesterol (HDL-C) as cardiovascular risk factors, and (ii) to advise on therapeutic strategies for management. Current evidence supports a causal association between elevated TRL and their remnants, low HDL-C, and cardiovascular risk. This interpretation is based on mechanistic and genetic studies for TRL and remnants, together with the epidemiological data suggestive of the association for circulating triglycerides and cardiovascular disease. For HDL, epidemiological, mechanistic, and clinical intervention data are consistent with the view that low HDL-C contributes to elevated cardiovascular risk; genetic evidence is unclear however, potentially reflecting the complexity of HDL metabolism. The Panel believes that therapeutic targeting of elevated triglycerides (≥ 1.7 mmol/L or 150 mg/dL), a marker of TRL and their remnants, and/or low HDL-C (<1.0 mmol/L or 40 mg/dL) may provide further benefit. The first step should be lifestyle interventions together with consideration of compliance with pharmacotherapy and secondary causes of dyslipidaemia. If inadequately corrected, adding niacin or a fibrate, or intensifying LDL-C lowering therapy may be considered. Treatment decisions regarding statin combination therapy should take into account relevant safety concerns, i.e. the risk of elevation of blood glucose, uric acid or liver enzymes with niacin, and myopathy, increased serum creatinine and cholelithiasis with fibrates. These recommendations will facilitate reduction in the substantial cardiovascular risk that persists in patients with cardiometabolic abnormalities at LDL-C goal.

Triglyceride-rich lipoproteins and high-density lipoprotein cholesterol in patients at high risk of cardiovascular disease: evidence and guidance for management

Even at low-density lipoprotein cholesterol (LDL-C) goal, patients with cardiometabolic abnormalities remain at high risk of cardiovascular events. This paper aims (i) to critically appraise evidence for elevated levels of triglyceride-rich lipoproteins (TRLs) and low levels of high-density lipoprotein cholesterol (HDL-C) as cardiovascular risk factors, and (ii) to advise on therapeutic strategies for management. Current evidence supports a causal association between elevated TRL and their remnants, low HDL-C, and cardiovascular risk. This interpretation is based on mechanistic and genetic studies for TRL and remnants, together with the epidemiological data suggestive of the association for circulating triglycerides and cardiovascular disease. For HDL, epidemiological, mechanistic, and clinical intervention data are consistent with the view that low HDL-C contributes to elevated cardiovascular risk; genetic evidence is unclear however, potentially reflecting the complexity of HDL metabolism. The Panel believes that therapeutic targeting of elevated triglycerides (≥1.7 mmol/L or 150 mg/dL), a marker of TRL and their remnants, and/or low HDL-C (<1.0 mmol/L or 40 mg/dL) may provide further benefit. The first step should be lifestyle interventions together with consideration of compliance with pharmacotherapy and secondary causes of dyslipidaemia. If inadequately corrected, adding niacin or a fibrate, or intensifying LDL-C lowering therapy may be considered. Treatment decisions regarding statin combination therapy should take into account relevant safety concerns, i.e. the risk of elevation of blood glucose, uric acid or liver enzymes with niacin, and myopathy, increased serum creatinine and cholelithiasis with fibrates. These recommendations will facilitate reduction in the substantial cardiovascular risk that persists in patients with cardiometabolic abnormalities at LDL-C goal.

Triglycerides and heart disease: still a hypothesis?

The purpose of this article is to review the basic and clinical science relating plasma triglycerides and cardiovascular disease. Although many aspects of the basic physiology of triglyceride production, its plasma transport, and its tissue uptake have been known for several decades, the relationship of plasma triglyceride levels to vascular disease is uncertain. Are triglyceride-rich lipoproteins, their influence on high-density lipoprotein and low-density lipoprotein, or the underlying diseases that lead to defects in triglyceride metabolism the culprit? Animal models have failed to confirm that anything other than early fatty lesions can be produced by triglyceride-rich lipoproteins. Metabolic products of triglyceride metabolism can be toxic to arterial cells; however, these studies are primarily in vitro. Correlative studies of fasting and postprandial triglycerides and genetic diseases implicate very-low-density lipoprotein and their remnants and chylomicron remnants in atherosclerosis development, but the concomitant alterations in other lipoproteins and other risk factors obscure any conclusions about direct relationships between disease and triglycerides. Genes that regulate triglyceride levels also correlate with vascular disease. Human intervention trials, however, have lacked an appropriately defined population and have produced outcomes without definitive conclusions. The time is more than ripe for new and creative approaches to understanding the relationship of triglycerides and heart disease.

Secreted dengue virus nonstructural protein NS1 is an atypical barrel-shaped high-density lipoprotein

Dengue virus (DENV) causes the major arboviral disease of the tropics, characterized in its severe forms by signs of hemorrhage and plasma leakage. DENV encodes a nonstructural glycoprotein, NS1, that associates with intracellular membranes and the cell surface. NS1 is eventually secreted as a soluble hexamer from DENV-infected cells and circulates in the bloodstream of infected patients. Extracellular NS1 has been shown to modulate the complement system and to enhance DENV infection, yet its structure and function remain essentially unknown. By combining cryoelectron microscopy analysis with a characterization of NS1 amphipathic properties, we show that the secreted NS1 hexamer forms a lipoprotein particle with an open-barrel protein shell and a prominent central channel rich in lipids. Biochemical and NMR analyses of the NS1 lipid cargo reveal the presence of triglycerides, bound at an equimolar ratio to the NS1 protomer, as well as cholesteryl esters and phospholipids, a composition evocative of the plasma lipoproteins involved in vascular homeostasis. This study suggests that DENV NS1, by mimicking or hijacking lipid metabolic pathways, contributes to endothelium dysfunction, a key feature of severe dengue disease.

Carotid artery atherosclerosis: effect of intensive lipid therapy on the vasa vasorum--evaluation by using dynamic contrast-enhanced MR imaging

PURPOSE

To investigate whether short-term, intensive lipid therapy leads to changes in microvascular characteristics, as measured by using dynamic contrast material-enhanced (DCE) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained for this HIPAA-compatible study. Subjects with established coronary artery disease or carotid artery stenosis of 15% or greater determined by using ultrasonography and with levels of apolipoprotein B of 120 mg/dL (1.2 g/L) or greater were enrolled in an ongoing study (clinical trial NCT00715273). All received intensive lipid therapy to achieve targeted high- and low-density lipoprotein cholesterol levels and underwent serial serum monitoring including high-sensitivity C-reactive protein (HsCRP) level measurements. Carotid artery MR imaging examinations including morphologic and DCE MR images were obtained at baseline and 1 year after treatment. In subjects with advanced lesions (>2 mm thick), MR image analysis was performed, including measurement of lipid-rich necrotic core size and kinetic modeling of DCE MR images to assess changes in the transfer constant (K(trans)). The differences in K(trans) between baseline and 1-year follow-up were compared by using the Wilcoxon signed rank test, and associations were assessed by using the Spearman rank correlation coefficient.

RESULTS

Twenty-eight subjects with interpretable DCE MR imaging results at both baseline and 1-year follow-up were included. After 1 year of treatment, a significant reduction was found in mean K(trans) (0.085 min(-1) ± 0.037 [standard deviation] to 0.067 min(-1) ± 0.028, P = .02). Reduction in K(trans) was not significantly correlated with observed reductions in lipid-rich necrotic core size or reductions in HsCRP level.

CONCLUSION

These findings suggest that DCE MR imaging may be a useful imaging method for the assessment of the therapeutic response of the vasa vasorum in patients with atherosclerotic plaque.

The role of niacin in raising high-density lipoprotein cholesterol to reduce cardiovascular events in patients with atherosclerotic cardiovascular disease and optimally treated low-density lipoprotein cholesterol Rationale and study design. The Atherothrombosis Intervention in Metabolic syndrome with low HDL/high triglycerides: Impact on Global Health outcomes (AIM-HIGH)

BACKGROUND

The aim of this study was to test the hypothesis that patients with atherosclerotic cardiovascular (CV) disease optimally treated on a statin but with residual atherogenic dyslipidemia (low high-density lipoprotein cholesterol [HDL-C] and high triglycerides) will benefit from addition of niacin with fewer CV events compared with placebo. Statin monotherapy trials have found 25%-35% CV risk reduction relative to placebo, leaving significant residual risk. Patients with atherogenic dyslipidemia have substantially increased CV risk.

METHODS

Participants were men and women with established CV disease and atherogenic dyslipidemia. Lipid entry criteria varied by gender and statin dose at screening. All participants received simvastatin (or simvastatin plus ezetimibe) at a dose sufficient to maintain low-density lipoprotein cholesterol (LDL-C) 40-80 mg/dL (1.03-2.07 mmol/L). Participants were randomized to extended-release niacin or matching placebo. The primary end point was time to occurrence of the first of the following: coronary heart disease death, nonfatal myocardial infarction, ischemic stroke, hospitalization for acute coronary syndrome, or symptom-driven coronary or cerebral revascularization. This event-driven trial will have 85% power to show a 25% reduction in primary event frequency after 850 patients have experienced a primary outcome event.

RESULTS

AIM-HIGH completed enrollment in April 2010. Follow-up is expected to continue through 2012.

SUMMARY

AIM-HIGH was designed to determine whether treating residual dyslipidemia with niacin further reduces cardiovascular events in patients with CV disease on a statin at target levels of low-density lipoprotein cholesterol.

Nicotinic acid inhibits progression of atherosclerosis in mice through its receptor GPR109A expressed by immune cells

Nicotinic acid (niacin) is a drug used to reduce the progression of atherosclerosis. Its antiatherosclerotic activity is believed to result from lipid-modifying effects, including its ability to decrease LDL cholesterol and increase HDL cholesterol levels in plasma. Here, we report that in a mouse model of atherosclerosis, we found that nicotinic acid inhibited disease progression under conditions that left total cholesterol and HDL cholesterol plasma levels unaffected. The antiatherosclerotic effect was not seen in mice lacking the receptor for nicotinic acid GPR109A. Surprisingly, transplantation of bone marrow from GPR109A-deficient mice into atherosclerosis-prone animals also abrogated the beneficial effect of nicotinic acid. We detected expression of GPR109A in macrophages in atherosclerotic plaques. In macrophages from WT mice, but not from GPR109A-deficient animals, nicotinic acid induced expression of the cholesterol transporter ABCG1 and promoted cholesterol efflux. Furthermore, activation of GPR109A by nicotinic acid inhibited MCP-1-induced recruitment of macrophages into the peritoneal cavity and impaired macrophage recruitment to atherosclerotic plaques. In contrast with current models, our data show that nicotinic acid can reduce the progression of atherosclerosis independently of its lipid-modifying effects through the activation of GPR109A on immune cells. We conclude therefore that GPR109A mediates antiinflammatory effects, which may be useful for treating atherosclerosis and other diseases.

Optimal therapy for reduction of lipoprotein(a)

WHAT IS KNOWN AND OBJECTIVE

There is a growing body of experimental and clinical evidence for the atherogenic and pro-thrombotic potential of Lipoprotein(a) [Lp(a)], as well as for its causative role in coronary heart disease and stroke. We comment on novel strategies for reducing Lp(a) levels.

COMMENT

Irrespective of the underlying biological mechanisms explaining the athero-thrombotic potential of this lipoprotein, most work has focused on the identification of suitable therapies for hyperlipoproteinemia(a). These include apheresis techniques, nicotinic acid and statins. None of these strategies have been shown to be definitely effective or convenient for the patient and new strategies are being attempted. Promising results are emerging with therapeutic interventions targeting the 'inflammatory pathways' by inhibition of Interleukin-6 (IL-6) signalling with natural compounds (e.g., Ginko biloba) or the IL-6 receptor antibody Tocilizumab. These may both lower Lp(a) and cardiovascular risk of the patients. Besides inhibiting platelet function, antiplatelet therapy with aspirin may also decrease the plasma concentration of Lp(a) and modulate its influence on platelets.

WHAT IS NEW AND CONCLUSION

We highlight the inadequacy of current approaches for lowering Lp(a) and draw attention to novel insights that may lead to better treatment.

Biological and pharmacological roles of HCA receptors

The hydroxy-carboxylic acid (HCA) receptors HCA(1), HCA(2), and HCA(3) were previously known as GPR81, GPR109A, and GPR109B, respectively, or as the nicotinic acid receptor family. They form a cluster of G protein-coupled receptors with high sequence homology. Recently, intermediates of energy metabolism, all HCAs, have been reported as endogenous ligands for each of these receptors. The HCA receptors are predominantly expressed on adipocytes and mediate the inhibition of lipolysis by coupling to G(i)-type proteins. HCA(1) is activated by lactate, HCA(2) by the ketone body 3-hydroxy-butyrate, and HCA(3) by hydroxylated β-oxidation intermediates, especially 3-hydroxy-octanoic acid. Both HCA(2) and HCA(3) are part of a negative feedback loop which keeps the release of fat stores in check under starvation conditions, whereas HCA(1) plays a role in the antilipolytic (fat-conserving) effect of insulin. HCA(2) was first discovered as the molecular target of the antidyslipidemic drug nicotinic acid (or niacin). Many synthetic agonists have since been designed for HCA(2) and HCA(3), but the development of a new, improved HCA-targeted drug has not been successful so far, despite a number of clinical studies. Recently, it has been shown that the major side effect of nicotinic acid, skin flushing, is mediated by HCA(2) receptors on keratinocytes, as well as on Langerhans cells in the skin. In this chapter, we summarize the latest developments in the field of HCA receptor research, with emphasis on (patho)physiology, receptor pharmacology, major ligand classes, and the therapeutic potential of HCA ligands.

High-density lipoprotein (HDL) cholesterol: leveraging practice-based biobank cohorts to characterize clinical and genetic predictors of treatment outcome

Over the past decade, large multicenter trials have unequivocally demonstrated that decreasing low-density lipoprotein (LDL) cholesterol can reduce both primary and secondary cardiovascular events in patients at risk. However, even in the context of maximal LDL lowering, there remains considerable residual cardiovascular risk. Some of this risk can be attributed to variability in high-density lipoprotein (HDL) cholesterol. As such, there is tremendous interest in defining determinants of HDL homeostasis. Risk prediction models are being constructed based upon (1) clinical contributors, (2) known molecular determinants and (3) the genetic architecture underlying HDL cholesterol levels. To date, however, no single resource has combined these factors within the context of a practice-based data set. Recently, a number of academic medical centers have begun constructing DNA biobanks linked to secure encrypted versions of their respective electronic medical record. As these biobanks combine resources, the clinical community is in a position to characterize lipid-related treatment outcome on an unprecedented scale.