Anti-inflammatory effect is an important property of niacin on atherosclerosis beyond its lipid-altering effects

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

PURPOSE

Niacin (nicotinic acid), known for its lipid-modifying effects, has been explored for its potential anti-inflammatory properties and potential to affect adipokines secretion from adipose tissue. The aim of this systematic review and meta-analysis was to assess the effects of niacin on inflammatory markers and adipokines.

METHODS

A comprehensive search was conducted across five databases: PubMed, Scopus, Cochrane Library, Embase, and ISI Web of Science. Randomized controlled trials exploring the effects of niacin on inflammatory markers (CRP, IL-6, TNF-α) and adipokines (Adiponectin, Leptin) were included. Pooled effect sizes were analysed using a random-effects model, and additional procedures including subgroup analyses, sensitivity analysis and dose-response analysis were also performed.

RESULTS

From an initial 1279 articles, fifteen randomized controlled trials (RCTs) were included. Niacin administration demonstrated a notable reduction in CRP levels (SMD: -0.88, 95% CI: -1.46 to -0.30, p = 0.003). Subgroup analyses confirmed CRP reductions in trials with intervention durations ≤ 24 weeks, doses ≤ 1000 mg/day, and elevated baseline CRP levels (> 3 mg/l). The meta-analysis of IL-6 and TNF-α revealed significant TNF-α reductions, while IL-6 reduction did not reach statistical significance. Niacin administration also substantially elevated Adiponectin (SMD: 3.52, 95% CI: 0.95 to 6.1, p = 0.007) and Leptin (SMD: 1.90, 95% CI: 0.03 to 3.77, p = 0.04) levels.

CONCLUSION

Niacin treatment is associated with significant reductions in CRP and TNF-α levels, suggesting potential anti-inflammatory effects. Additionally, niacin positively influences adipokines, increasing Adiponectin and Leptin levels. These findings provide insights for future research and clinical applications targeting inflammation and metabolic dysregulation.

Is Niacine a Potential Agent to Decrease Dyslipidemia Risk?

Cardiovascular diseases are the most common non-communicable diseases with the highest prevalence and mortality rate in the all around the world. There are some risk factors -such as modifiable and non-modifiable- which are effective on the development of these diseases. Modifiable risk factors are closely related to dyslipidemia, which forms the basis of cardiovascular diseases. Dyslipidemia is characterized by high triacylglycerol (TAG) and free fatty acids, decreased high density lipoprotein (HDL) level and function, increased low density lipoprotein (LDL) level and apolipoprotein B (Apo B) production. There is a relation between dyslipidemia with nutritional and physical activity behaviors. In particular, adherence to the Mediterranean diet and lifestyle behaviors instead of the Western diet can potentially decrease dyslipidemia risk. On the other hand, some of micronutrients such as niacin can potentially decrease dyslipidemia risk as a nutritional supplement. Niacin -which is a water-soluble, B group vitamin- can potentially decrease TAG, free fatty acids, Apo B, very low density lipoprotein (VLDL) and LDL levels and increase HDL and apolipoprotein A (Apo A) levels in plasma. Due to these potential beneficial effects, niacin acts a pharmacological agent to decrease both of dyslipidemia risk and symptoms. However, niacin is used more than tolerable upper intake level (35 mg/day) to show these potential effects (1-3 g). This situation may cause to ‘niacin flush’ symptom. In addition, there is a need for the studies which aim to determine the negative effects of high dose niacin intake on human’s health in long-term. In this review article, potential effects of the niacin on dyslipidemia are examined within the current literature.

Macrophages in tumor: An inflammatory perspective

Inflammation is a part of carefully co-ordinated healing immune exercise to eliminate injurious stimuli. However, in substantial number of cancer types, it contributes in shaping up of robust tumor microenvironment (TME). Solid TME promotes infiltration of tumor associated macrophages (TAMs) that contributes to cancer promotion. TAMs are functionally heterogeneous and display an extraordinary degree of plasticity, which allow 'Switching' of macrophages into an 'M2', phenotype, linked with immunosuppression, advancement of tumor angiogenesis with metastatic consequences. In contrary to the classical M1 macrophages, these M2 TAMs are high-IL-10, TGF-β secreting-'anti-inflammatory'. In this review, we will discuss the modes of infiltration and switching of TAMs into M2 anti-inflammatory state in the TME to promote immunosuppression and inflammation-driven cancer.

Niacin ameliorates ulcerative colitis via prostaglandin D2-mediated D prostanoid receptor 1 activation

Niacin, as an antidyslipidemic drug, elicits a strong flushing response by release of prostaglandin (PG) D₂. However, whether niacin is beneficial for inflammatory bowel disease (IBD) remains unclear. Here, we observed niacin administration‐enhanced PGD₂ production in colon tissues in dextran sulfate sodium (DSS)‐challenged mice, and protected mice against DSS or 2,4,6‐trinitrobenzene sulfonic acid (TNBS)‐induced colitis in D prostanoid receptor 1 (DP1)‐dependent manner. Specific ablation of DP1 receptor in vascular endothelial cells, colonic epithelium, and myeloid cells augmented DSS/TNBS‐induced colitis in mice through increasing vascular permeability, promoting apoptosis of epithelial cells, and stimulating pro‐inflammatory cytokine secretion of macrophages, respectively. Niacin treatment improved vascular permeability, reduced apoptotic epithelial cells, promoted epithelial cell update, and suppressed pro‐inflammatory gene expression of macrophages. Moreover, treatment with niacin‐containing retention enema effectively promoted UC clinical remission and mucosal healing in patients with moderately active disease. Therefore, niacin displayed multiple beneficial effects on DSS/TNBS‐induced colitis in mice by activation of PGD₂/DP1 axis. The potential efficacy of niacin in management of IBD warrants further investigation.

The role of HDL in plaque stabilization and regression: basic mechanisms and clinical implications

On the basis of studies that extend back to the early 1900s, regression and stabilization of atherosclerosis in humans has progressed from being a concept to one that is achievable. Successful attempts at regression generally applied robust measures to improve plasma lipoprotein profiles. Possible mechanisms responsible for lesion shrinkage include decreased retention of atherogenic apolipoprotein B within the arterial wall, efflux of cholesterol and other toxic lipids from plaques, emigration of lesional foam cells out of the arterial wall, and influx of healthy phagocytes that remove necrotic debris as well as other components of the plaque. Currently available clinical agents, however, still fail to stop most cardiovascular events. For years, HDL has been considered the 'good cholesterol.' Clinical intervention studies to causally link plasma HDL-C levels to decreased progression or to the regression of atherosclerotic plaques are relatively few because of the lack of therapeutic agents that can selectively and potently increase HDL-C. The negative results of studies that were carried out have led to uncertainty as to the role that HDL plays in atherosclerosis. It is becoming clearer, however, that HDL function rather than quantity is most crucial and, therefore, discovery of agents that enhance the quality of HDL should be the goal.

Hazelnut and neuroprotection: Improved memory and hindered anxiety in response to intra-hippocampal Aβ injection

OBJECTIVES

Corylus avellana L. (hazelnut) is known to be a delicious and nutritious food. This study was carried out to evaluate the use of hazelnut as a therapy for memory impairment because in Iranian traditional medicine, it is recommended for those suffering from a particular type of dementia, with symptoms of Alzheimer's disease.

METHODS

In this study, rats were fed with hazelnut kernel [(without skin) 800 mg/kg/day] during 1 week before stereotaxic surgery to 24 hours before behavioral testing (in general, for 16 consecutive days) and the effect of hazelnut eating on memory, anxiety, neuroinflammation and apoptosis was assessed in the amyloid beta-injected rat.

RESULTS

The results of this study showed that feeding with hazelnut improved memory, (which was examined by using Y-maze test and shuttle box apparatus), and reduced anxiety-related behavior, that was evaluated using elevated plus maze. Also, western blotting analysis of cyclooxygenase-2, interleukin-1β, tumor necrosis factor-α, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein, and caspase-3 showed that hazelnut has an ameliorating effect on the neuroinflammation and apoptosis caused by Aβ.

DISCUSSION

These findings suggest that hazelnut, as a dietary supplement, improves healthy aging and could be a beneficial diet for the treatment of AD.

Regression of atherosclerosis: insights from animal and clinical studies

BACKGROUND

Based on studies that date back to the 1920s, regression and stabilization of atherosclerosis in humans has gone from just a dream to one that is achievable. Review of the literature indicates that the successful attempts at regression generally applied robust measures to improve plasma lipoprotein profiles. Examples include extensive lowering of plasma concentrations of atherogenic apolipoprotein B and enhancement of reverse cholesterol transport from atheromata to the liver.

FINDINGS

Possible mechanisms responsible for lesion shrinkage include decreased retention of atherogenic apolipoprotein B within the arterial wall, efflux of cholesterol and other toxic lipids from plaques, emigration of lesional foam cells out of the arterial wall, and influx of healthy phagocytes that remove necrotic debris as well as other components of the plaque. This review will highlight the role key players such as LXR, HDL and CCR7 have in mediating regression.

CONCLUSION

Although much progress has been made, there are many unanswered questions. There is, therefore, a clear need for preclinical and clinical testing of new agents expected to facilitate atherosclerosis regression with the hope that additional mechanistic insights will allow further progress.

Niacin, an old drug with a new twist

Niacin (nicotinic acid) has been used for decades as a lipid-lowering drug. The clinical use of niacin to treat dyslipidemic conditions is limited by its side effects. Niacin, along with fibrates, are the only approved drugs which elevate high density lipoprotein cholesterol (HDLc) along with its effects on low density lipoprotein cholesterol (LDLc) and triglycerides. Whether niacin has a beneficial role in lowering cardiovascular risk on the background of well-controlled LDLc has not been established. In fact, it remains unclear whether niacin, either in the setting of well-controlled LDLc or in combination with other lipid-lowering agents, confers any therapeutic benefit and if so, by which mechanism. The results of recent trials reject the hypothesis that simply raising HDLc is cardioprotective. However, in the case of the clinical trials, structural limitations of trial design complicate their interpretation. This is also true of the most recent Heart Protection Study 2-Treatment of HDLc to Reduce the Incidence of Vascular Events (HPS2-THRIVE) trial in which niacin is combined with an antagonist of the D prostanoid (DP) receptor. Human genetic studies have also questioned the relationship between cardiovascular benefit and HDLc. It remains to be determined whether niacin may have clinical utility in particular subgroups, such as statin intolerant patients with hypercholesterolemia or those who cannot achieve a sufficient reduction in LDLc. It also is unclear whether a potentially beneficial effect of niacin is confounded by DP antagonism in HPS2-THRIVE.

Evidence for constitutive dimerization of niacin receptor subtypes

The recently deorphanized niacin receptor subtypes NIACR1 (GPR109A) and NIACR2 (GPR109B) play an essential role in the regulation of metabolic processes and immune reactions. Both receptors belong to the G-protein-coupled receptor (GPCR) family, whose members have traditionally been treated as monomeric entities, but now appear to exist and function as both homodimers and heterodimers. In this study, a close physical interaction is shown between the highly homologous niacin receptor subtypes, NIACR1 and NIACR2, using bioluminescence resonance energy transfer (BRET(2)) in living cells. The extent of homo- and hetero-dimerization of the niacin receptors did not vary after activation of the receptors with selective agonists, indicating that the dimerization state of NIACR1 and NIACR2 is not regulated by ligand binding. Moreover, detection of niacin receptor dimers in both plasma membrane- and endoplasmic reticulum-enriched fractions suggests that they are formed early in the biosynthetic pathway. Taken together, these results demonstrate that niacin receptor dimerization is a constitutive process occurring early during biosynthesis.