Niacin: An old drug rejuvenated

Effect of Different Levels of Niacin on Serum Biochemical Parameters, Antioxidant Status, Cytokine Levels, Inflammatory Gene Expression and Colonic Microbial Composition in Weaned Piglets

Niacin plays an important role in regulating the gut health of weaned piglets. In this study, 48 25-day-old weaned piglets (7.9 ± 0.20 kg) produced by 14 sows (3 to 4 piglets per sow) were randomly divided into 4 groups with 6 replicates in each group and 2 piglets in each replicate. Each group was fed diets supplemented with 22.5 (N1), 30 (N2), 45 (N3), and 75 (N4) mg/kg of niacin, respectively. Samples were taken at 7 and 14 d, respectively. The study shows that changes in niacin levels significantly affected the content of IgG and IgM in the serum (p < 0.05). Niacin had a significant effect on antioxidant parameters such as MDA, T-SOD, and CuZn-SOD in the jejunal mucosa of weaned piglets (p < 0.05). Moreover, significant differences were observed in the expression of cytokines such as TGF-β, TNF-α, and COX2 in the jejunal mucosa (p < 0.05). The 16S rRNA sequencing analysis showed that there were significant differences in the colonic species composition, which were also accompanied by changes in the isovaleric acid content (p < 0.05). In conclusion, an appropriate increase in niacin dose based on NRC (2012) has an important role in improving the antioxidant status of weaned piglets, alleviating intestinal inflammation in piglets, improving immunity, and regulating the structure of the microbiota.

Anti-Atherosclerotic Action of Agmatine in ApoE-Knockout Mice

Atherosclerosis is an inflammatory disease in which dysfunction of mitochondria play an important role, and disorders of lipid management intensify this process. Agmatine, an endogenous polyamine formed by decarboxylation of arginine, exerts a protective effect on mitochondria and modulates fatty acid metabolism. We investigated the effect of exogenous agmatine on the development of atherosclerosis and changes in lipid profile in apolipoprotein E knockout (apoE-/-) mice. Agmatine caused an approximate 40% decrease of atherosclerotic lesions, as estimated by en face and cross-section methods with an influence on macrophage but not on smooth muscle content in the plaques. Agmatine treatment did not changed gelatinase activity within the plaque area. What is more, the action of agmatine was associated with an increase in the number of high density lipoproteins (HDL) in blood. Real-Time PCR analysis showed that agmatine modulates liver mRNA levels of many factors involved in oxidation of fatty acid and cholesterol biosynthesis. Two-dimensional electrophoresis coupled with mass spectrometry identified 27 differentially expressed mitochondrial proteins upon agmatine treatment in the liver of apoE-/- mice, mostly proteins related to metabolism and apoptosis. In conclusion, prolonged administration of agmatine inhibits atherosclerosis in apoE-/- mice; however, the exact mechanisms linking observed changes and elevations of HDL plasma require further investigation.

Pharmacogenomics in the development and characterization of atheroprotective drugs

Atherosclerosis is the main cause of cardiovascular disease (CVD) and can lead to stroke, myocardial infarction, and death. The clinically available atheroprotective drugs aim mainly at reducing the levels of circulating low-density lipoprotein (LDL), increasing high-density lipoprotein (HDL), and attenuating inflammation. However, the cardiovascular risk remains high, along with morbidity, mortality, and incidence of adverse drug events. Pharmacogenomics is increasingly contributing towards the characterization of existing atheroprotective drugs, the evaluation of novel ones, and the identification of promising, unexplored therapeutic targets, at the global molecular pathway level. This chapter presents highlights of pharmacogenomics investigations and discoveries that have contributed towards the elucidation of pharmacological atheroprotection, while opening the way to new therapeutic approaches.

Clinical relevance of target identity and biology: implications for drug discovery and development

Many of the most commonly used drugs precede techniques for target identification and drug specificity and were developed on the basis of efficacy and safety, an approach referred to as classical pharmacology and, more recently, phenotypic drug discovery. Although substantial gains have been made during the period of focus on target-based approaches, particularly in oncology, these approaches have suffered a high overall failure rate and lower productivity in terms of new drugs when compared with phenotypic approaches. This review considers the importance of target identity and biology in clinical practice from the prescriber's viewpoint. In evaluating influences on prescribing behavior, studies suggest that target identity and mechanism of action are not significant factors in drug choice. Rather, patients and providers consistently value efficacy, safety, and tolerability. Similarly, the Food and Drug Administration requires evidence of safety and efficacy for new drugs but does not require knowledge of drug target identity or target biology. Prescribers do favor drugs with novel mechanisms, but this preference is limited to diseases for which treatments are either not available or suboptimal. Thus, while understanding of drug target and target biology is important from a scientific perspective, it is not particularly important to prescribers, who prioritize efficacy and safety.

It ain't over 'til the fat lady sings

The antiatherogenic drug nicotinic acid (niacin) has antidyslipidemic effects independent of free fatty acid suppression mediated by its receptor HCA₂ (GPR109A) (Lauring et al., this issue).

Endogenous metabolites as ligands for G protein-coupled receptors modulating risk factors for metabolic and cardiovascular disease

During the last decade, several G protein-coupled receptors activated by endogenous metabolites have been described. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Receptors of endogenous metabolites are expressed in taste cells, the gastrointestinal tract, adipose tissue, endocrine glands, immune cells, or the kidney and are therefore in a position to sense food intake in the gastrointestinal tract or to link metabolite levels to the appropriate responses of metabolic organs. Some of the receptors appear to provide a link between metabolic and neuronal or immune functions. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.

Niacin in cardiovascular disease: recent preclinical and clinical developments

Niacin has been used for more than 50 years in the treatment of cardiovascular disease, although its use has largely been superseded by better-tolerated lipid-modulating interventions. There has been a renewed interest in the HDL-cholesterol raising properties of niacin, with the appreciation that substantial cardiovascular risk remains despite effective treatment of LDL-cholesterol. This coincides with increasing evidence that the complex functional properties of HDL are not well reflected by measurement of HDL-cholesterol alone. In addition to favorable actions on lipoproteins, it is becoming apparent that niacin may also possess lipoprotein independent or pleiotropic effects including the inhibition of inflammatory pathways mediated by its receptor GPR109A, which is expressed by adipocytes and some leukocytes. In this article we consider emerging and prior clinical trial data relating to niacin. We review recent data in respect of mechanisms of action on lipoproteins, which remain complex and incompletely understood. We discuss the recent reports of anti-inflammatory effects of niacin in adipocytes and through bone marrow derived cells and vascular endothelium. These novel observations come at an interesting time, with current imaging and outcome studies leaving outstanding questions on niacin efficacy in statin-treated patients.

Nicotinic acid (niacin): new lipid-independent mechanisms of action and therapeutic potentials

Nicotinic acid (niacin) has been used for decades to prevent and treat atherosclerosis. The well-documented antiatherogenic activity is believed to result from its antidyslipidemic effects, which are accompanied by unwanted effects, especially a flush. There has been renewed interest in nicotinic acid owing to the need for improved prevention of atherosclerosis in patients already taking statins. In addition, the identification of a nicotinic acid receptor expressed in adipocytes and immune cells has helped to elucidate the mechanisms underlying the antiatherosclerotic as well as the unwanted effects of this drug. Nicotinic acid exerts its antiatherosclerotic effects at least in part independently of its antidyslipidemic effects through mechanisms involving its receptor on immune cells as well as through direct and indirect effects on the vascular endothelium. Here, we review recent data on the pharmacological effects of nicotinic acid and discuss how they might be harnessed to treat other inflammatory diseases such as multiple sclerosis or psoriasis.

Evolving concepts on benefits and risks associated with therapeutic strategies to raise HDL

PURPOSE OF REVIEW

To provide an update on high-density lipoprotein (HDL) biology and emerging new HDL-based therapies for athero-thrombosis.

RECENT FINDINGS

Atherosclerotic cardiovascular disease remains a major public health threat despite a significant decline over the past three decades. Although current medical therapies, specifically low-density lipoprotein lowering with statins, reduce cardiovascular events by about 25-35%, a substantial residual risk remains, leading to a search for additional therapeutic interventions. In this regard, HDL has emerged as one important target because of epidemiologic evidence linking HDL levels inversely to cardiovascular events, known vascular protective actions of HDL and experimental and clinical research supporting athero-protective actions of HDL. However, complexities of HDL composition, particle size, and metabolism have suggested that HDL functionality, and how HDL is increased, may be important determinants of its protective effects.

SUMMARY

Thus the possibility that HDL modification could address the residual risk has brought renewed focus on an old HDL-raising drug, niacin, and a number of newer strategies to exploit the vascular benefits of HDL.

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.

Low HDL Cholesterol is Associated with Lower Gray Matter Volume in Cognitively Healthy Adults

Dyslipidemia is common in adults and contributes to high rates of cardiovascular disease and may be linked to subsequent neurodegenerative and neurovascular diseases. This study examined whether lower brain volumes and cognition associated with dyslipidemia could be observed in cognitively healthy adults, and whether apolipoprotein E (APOE) genotype or family history of Alzheimer's disease (FHAD) alters this effect. T1-weighted magnetic resonance imaging was used to examine regional brain gray matter (GM) and white matter (WM) in 183 individuals (58.4 ± 8.0 years) using voxel-based morphometry. A non-parametric multiple linear regression model was used to assess the effect of high-density lipoprotein (HDL) and non-HDL cholesterol, APOE, and FHAD on regional GM and WM volume. A post hoc analysis was used to assess whether any significant correlations found within the volumetric analysis had an effect on cognition. HDL was positively correlated with GM volume in the bilateral temporal poles, middle temporal gyri, temporo-occipital gyri, and left superior temporal gyrus and parahippocampal region. This effect was independent of APOE and FHAD. A significant association between HDL and the Brief Visuospatial Memory Test was found. Additionally, GM volume within the right middle temporal gyrus, the region most affected by HDL, was significantly associated with the Controlled Oral Word Association Test and the Center for Epidemiological Studies Depression Scale. These findings suggest that adults with decreased levels of HDL cholesterol may be experiencing cognitive changes and GM reductions in regions associated with neurodegenerative disease and therefore, may be at greater risk for future cognitive decline.

Adipose tissue lipolysis

PURPOSE OF REVIEW

Adipose tissue lipolysis is a critical pathway for the maintenance of energy homeostasis through the degradation of triglycerides and the release of fatty acids into the circulation. The understanding of the cellular factors regulating triglyceride hydrolysis and the metabolic function of lipases has considerably expanded in the last few years, revealing an unexpected complexity. This review aims at describing recent discoveries related to the lipolytic pathway and its regulatory mechanisms.

RECENT FINDINGS

Considerable progress has been made in understanding the role and the mechanisms of activation of the lipolytic enzymes. Recent discoveries have dramatically altered the view of adipose tissue lipolysis and highlighted the importance of additional molecular actors in regulating this process. Catecholamines, natriuretic peptides, and insulin are considered to be the major regulators of lipolysis in humans. However, autocrine/paracrine factors such as metabolites and prostaglandins may also participate in its regulation.

SUMMARY

The manipulation of lipolysis has therapeutic potential in the metabolic disorders frequently associated with obesity. Unraveling the molecular events occurring during regulation of lipolysis may lead to novel therapeutic targets.

The effect of body mass index on fasting blood glucose and development of diabetes mellitus after initiation of extended-release niacin

BACKGROUND

Niacin increases blood glucose, but whether the degree of increase is associated with increasing body mass index (BMI) is unknown. We evaluated the effect of extended-release niacin initiation on fasting plasma glucose (FPG) and the development of new-onset diabetes mellitus (DM) in relation to body mass index (kg/m(2)) in nondiabetic patients.

METHODS

This retrospective observational study used data from six facilities within a geographical region of the Department of Veterans Affairs (VA). Patients included were 18 years of age or older and on a stable extended-release niacin dose (minimum 100 days) of at least 250 mg/day between January, 2001, and April, 2007. Patients were excluded if they were new to the VA, on corticosteroids or insulin, if medication adherence was <80%, or if they met criteria for DM.

RESULTS

A total of 811 nondiabetic patients taking extended-release niacin initiation were studied. FPG after niacin initiation was stastically significantly correlated with increasing BMI (P < 0.001, R = 0.144 Pearson correlation coefficient). Factors independently associated with change in FPG using multiple linear regression were BMI (P = 0.043), baseline average glucose (P < 0.001), and baseline average triglycerides (P = 0.037). Of all patients started on niacin, 220 (27.1%) patients developed DM after niacin initiation. BMI, (P = 0.002) and baseline average glucose (P < 0.001) were independent predictors of the development of new-onset DM (logistic regression analysis).

CONCLUSIONS

We found an association between increasing BMI and increasing FPG and diagnosis of new-onset DM after initiation of extended-release niacin initiation. This suggests that extended-release niacin may increase FPG into the diabetic range, especially for obese patients.

Safety and efficacy of laropiprant and extended-release niacin combination in the management of mixed dyslipidemias and primary hypercholesterolemia

Statins form the cornerstone of pharmaceutical cardiovascular disease prevention. However, despite very effective statin intervention, the majority of events remain unpreventable. In some cases statin therapy alone is insufficient to achieve adequate lipid levels whereas other patients are unable to tolerate statins. This calls for additional treatment options. Niacin has a long history of success in reducing low-density lipoprotein cholesterol and triglycerides, and increasing high-density lipoprotein cholesterol. It was the first lipid-lowering drug to demonstrate a reduction in cardiovascular events, and remains the only one that has consistently shown benefits on surrogate outcomes when added to background therapies of other lipid-lowering drugs, including statins. Niacin’s uptake in clinical practice has been less successful due to its side-effect profile, most notable being flushing. The uncovering of the mechanism by which flushing is induced, together with the development of a prostaglandin D₂ receptor inhibitor (laropiprant) which reduces this downstream flushing effect of niacin, has sparked new promise in therapeutic lipid management. It provides an additional treatment option into managing lipid abnormalities. The uptake in clinical practice of the niacin–laropiprant combination will depend on the relative improvements experienced by the patient in the side-effect profile compared to other treatment options, as well as on the the keenly-awaited outcome studies currently underway. Until these data become available guidelines and recommendations are unlikely to change and niacin’s position in therapeutic cardiovascular risk prevention will be determined by clinician opinion and experience, and patient preferences.

Meta-analysis of the effect of nicotinic acid alone or in combination on cardiovascular events and atherosclerosis

OBJECTIVE

High-density lipoprotein cholesterol (HDL-C) concentration is a strong predictor of cardiovascular events in both naïve and statin-treated patients. Nicotinic acid is an attractive option for decreasing residual risk in statin-treated or statin-intolerant patients since it increases HDL-C by up to 20% and decreases low-density lipoprotein cholesterol and lipoprotein(a) plasma concentrations.

METHODS

We performed a computerized PubMed literature search that focused on clinical trials evaluating niacin, alone or in combination with other lipid-lowering drugs, published between January 1966 and August 2008.

RESULTS

Among 587 citations, 29 full articles were read and 14 were eligible for inclusion. Overall 11 randomized controlled trials enrolled 2682 patients in the active group and 3934 in the control group. In primary analysis, niacin significantly reduced major coronary events (relative odds reduction=25%, 95% CI 13, 35), stroke (26%, 95% CI=8, 41) and any cardiovascular events (27%, 95% CI=15, 37). Except for stroke, the pooled between-group difference remained significant in sensitivity analysis excluding the largest trial. In comparison with the non-niacin group, more patients in the niacin group had regression of coronary atherosclerosis (relative increase=92%, 95% CI=39, 67) whereas the rate of patients with progression decreased by 41%, 95% CI=25, 53. Similar effects of niacin were found on carotid intima thickness with a weighted mean difference in annual change of -17 microm/year (95% CI=-22, -12).

CONCLUSIONS

Although the studies were conducted before statin therapy become standard care, and mostly in patients in secondary prevention, with various dosages of nicotinic acid 1-3g/day, this meta-analysis found positive effects of niacin alone or in combination on all cardiovascular events and on atherosclerosis evolution.

Low levels of high-density lipoprotein cholesterol: an independent risk factor for late adverse cardiovascular events in renal transplant recipients

Long-term kidney transplant graft and patient survival is often limited by cardiovascular (CV) disease. Risk factors for CV disease such as diabetes, hypertension and elevated low-density lipoprotein levels are well documented; however, the impact of low levels of high-density lipoprotein (HDL) has not been defined. We performed a retrospective chart review of 324 consecutive renal transplant recipients from 2001 to 2007 to correlate baseline HDL levels with major adverse cardiovascular events (MACEs) defined as a composite of new onset CV illness, cerebral vascular events and peripheral vascular disease. A total of 92 MACEs occurred over a total of 1913 patient years of follow-up. Low HDL cholesterol levels were noted in 58.3% of patients. Compared with those with normal HDL levels, a greater percentage of patients with low HDL levels had post-transplant MACEs (20% vs. 60% respectively) and experienced an increased rate of all cause mortality. Sixty-two percent of all MACEs occurred in patients with low HDL levels. In the low HDL group, the odds ratio for experiencing a MACE was 1.92. Therefore, HDL cholesterol may provide an important new therapeutic target to prevent vascular morbidity and mortality following renal transplantation.

Review of extended-release niacin/laropiprant fixed combination in the treatment of mixed dyslipidemia and primary hypercholesterolemia

Although statins reduce cardiovascular morbidity and mortality further risk reduction is needed. In this respect low HDL-cholesterol concentrations and/or elevated triglyceride concentrations may be potential treatment targets. Niacin (nicotinic acid) is an effective drug which increases the plasma concentration of high-density lipoprotein (HDL)-cholesterol and decreases the concentration of low-density lipoprotein (LDL)-cholesterol, triglycerides and lipoprotein(a). Clinical studies indicate that niacin can significantly reduce the risk for cardiovascular events. However, niacin is not very commonly used because of significant side effects (especially flushing). Laropiprant is a potent selective antagonist of PGD2-receptor subtype-1 and can thus reduce niacin-induced flushing. Although the addition of laropiprant will reduce the frequency of flushing, it will not completely eliminate this side effect. Laropiprant does not change the effect of niacin on lipids or other side effects of niacin (ie, gastro-intestinal problems, glucose elevation). The combination of niacin with laropiprant may therefore enable use of niacin at higher doses and therefore exploit the full potential of the drug. Endpoint studies that will be published over the next few years will show whether this treatment modality also translates into clinical effect in patients treated with statins. Until publication of these studies niacin/laropiprant should be used only in high-risk patients not achieving lipid goals on statins.

New insights and therapies for the metabolic consequences of Alström syndrome

PURPOSE OF REVIEW

Recent studies have begun to evaluate the heterogeneity of insulin resistance in syndromes associated with type 2 diabetes, dyslipidaemia and associated cardiac, renal and hepatic consequences. These insights are of particular importance in Alström syndrome in which all of these conditions coexist from a young age with considerable morbidity and reduction in life expectancy. Clear definition of the phenotype in the syndrome may clarify biochemical pathways of crucial importance in propensity to diabetic complications and heart disease in the general population. This review will focus on ways in which more effective treatments can be put in place for Alström families from childhood and adolescence.

RECENT FINDINGS

Studies of body fat distribution, insulin resistance, glucose metabolism and dyslipidaemia in Alström syndrome will be discussed as well as genotypic and phenotypic variation in the syndrome in the context of recent metabolic studies in insulin resistance. Potential therapies including low-carbohydrate diet, niaspan and incretins will be considered.

SUMMARY

These new insights will encourage early introduction of protective nutrition, exercise and drug therapies in Alström syndrome and suggest novel approaches to understanding diabetes mellitus, hyperlipidaemias and heart disease in the general population.