Effect of niacin on preβ-1 high-density lipoprotein levels in diabetes

Dyslipidemia and diabetes mellitus: Role of lipoprotein species and interrelated pathways of lipid metabolism in diabetes mellitus

Diabetes mellitus is a complex disease. We are increasingly gaining a better understanding of its mechanisms at the molecular level. From these new insights, better therapeutic approaches should emerge. Diabetes mellitus is a syndrome with many associated subphenotypes. These include mitochondrial disorders, lipodystrophies, and inflammatory disorders involving cytokines. Levels of sphingosine-1-phosphate, which has recently been shown to play a role in glucose homeostasis, are low in diabetics, whereas levels of ceramides are increased. Major phenotypes associated with diabetes mellitus are dyslipidemias, notably hypertriglyceridemia and low high-density lipoprotein cholesterol levels. Both diabetes and dyslipidemia are strongly associated with increased risk for atherosclerotic vascular disease.

Pre-β1 HDL in type 2 diabetes mellitus

BACKGROUND AND AIMS

Pre-β1 HDL, being a major acceptor of free cholesterol from cells, plays an important role in reverse cholesterol transport. This study was performed to determine whether abnormalities in pre-β1 HDL concentration were present in type 2 diabetes irrespective of their HDL-cholesterol levels, and the impact on cholesterol efflux.

METHODS

640 type 2 diabetic patients with or without cardiovascular disease (CVD) and 360 non-diabetic controls matched for serum HDL-cholesterol levels were recruited. Plasma pre-β1 HDL was measured by ELISA, and cholesterol efflux to serum, mediated by ATP-binding cassette transporter A1 (ABCA1), was determined by measuring the transfer of [3H]cholesterol from cultured cells expressing ABCA1 to the medium containing the tested serum.

RESULTS

Despite the diabetic subjects having matched HDL-cholesterol and total apoA1 as controls, plasma pre-β1 HDL was significantly reduced in both male (p < 0.01) and female diabetic patients (p < 0.05), and patients with CVD had the lowest pre-β1 HDL level. Serum capacity to induce ABCA1-mediated cholesterol efflux was impaired in the diabetic group (p < 0.01) and cholesterol efflux correlated with pre-β1 HDL (Pearson's r = 0.38, p < 0.01), and this association remained significantly even after controlling for age, gender, body mass index, diabetes status, smoking, apoA1, triglyceride and LDL.

CONCLUSIONS

Plasma pre-β1 HDL level was significantly decreased in type 2 diabetes and was associated with a reduction in cholesterol efflux mediated by ABCA1. Our data would suggest that low pre-β1 HDL might cause impairment in reverse cholesterol transport in type 2 diabetes.

Effects of Rosuvastatin Versus Atorvastatin, Alone or in Combination, on Lipoprotein (a)

Background: There are little evidences about the therapeutic efficacy of different lipid-lowering agents in the reduction of elevated lipoprotein(a) [Lp(a)]. Objective: testing the effect of different lipid-lowering agents on elevated Lp(a). Methods: prospective interventional study performed in patients with CAD, or high CAD risk, with Lp(a), >50 mg/dL. Lp(a), total cholesterol (C), HDL-C, LDL-C, triglycerides (TGs), apolipoprotein (Apo) A1, Apo B, enzymes of myocyte and hepatic injury were comparatively analyzed between 4 lipid-lowering strategies: rosuvastatin (R group) 40 mg, atorvastatin (A group) 80 mg, atorvastatin 40 mg add-on micronized fenofibrate (A+F group), and atorvastatin 40 mg add-on 1 g extended-release niacin (A+ERN group). Comparison was made for their therapeutic efficacy on Lp(a), and safety. Results: 87 patients with mean Lp(a) 94.6 ± 39.6 mg/dL were analyzed. Groups: 25 patients in the R, 22 in the A, 20 in the A+F and 20 in A+ERN group. Significant reduction in all lipid fractions in all treatment groups was reported after 6 months. The average reduction of Lp(a) was 15.9 ± 21.0 mg/dL, with: 18.2 ± 24.8 ( P = 0.001) in the R group, 17.3 ± 10.4 (P = 0.001) in A+F, 19.5 ± 10.9 (P = 0.001) in A+ERN and the lowest in the A group (11.24 ± 22.91, P = 0.032). No adverse effects were observed in any of the treatment groups. Conclusions: When compared with atorvastatin, it seems that rosuvastatin can achieve more significant decrease of Lp(a).The efficacy of the second one can be increased by adding fibrate or ERN.

High-density lipoprotein subfractions--what the clinicians need to know

Although the inverse relationship between plasma levels of high-density lipoprotein (HDL) and cardiovascular disease has been largely demonstrated, many observations have suggested that the assessment of HDL functionality might be more informative than a simple measurement of HDL-cholesterol plasma levels. HDLs are a class of structurally and functionally heterogeneous particles; in atherosclerosis-related diseases, changes in HDL subfraction levels and functions are frequently observed. Circulating levels of large HDL particles are decreased in dyslipidaemic conditions, while levels of small dense HDL particles are increased in patients with coronary heart disease. Furthermore, specific genetic defects in proteins involved in HDL metabolism significantly impact the distribution of HDL subpopulations. Finally, many drugs used for dyslipidaemia induce changes in HDL subfractions strictly related to cardiovascular disease. Although several methods exist to evaluate HDL subclass levels, most of them are not easily applicable in clinical practice, due to the costs and high variability. However, the possibility to measure the levels of specific HDL subfractions in patients with atherosclerosis-related diseases might help to better define their cardiovascular risk.

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.

Different effects of compounds decreasing cholesteryl ester transfer protein activity on lipoprotein metabolism

PURPOSE OF REVIEW

Review literature on the effect of decreasing cholesteryl ester transfer protein (CETP) activity through pharmacological inhibition or modulation in preclinical and clinical settings compared to human CETP deficiency on lipoprotein characteristics, HDL remodelling and function.

RECENT FINDINGS

Torcetrapib, anacetrapib and dalcetrapib inhibited the heterotypic transfer of cholesteryl ester from HDL to LDL and/or VLDL with similar potency, although the potency of dalcetrapib was time dependent. Homotypic transfer of cholesteryl ester from HDL3 to HDL2 via recombinant human CETP was inhibited by torcetrapib and anacetrapib (CETP inhibitors, CETPi) but not by dalcetrapib (CETP modulator, CETPm). In a hamster model of reverse cholesterol transport, only dalcetrapib increased efflux of fecal sterols from macrophages to feces. In clinical studies, dose-responses of CETPi and CETPm demonstrate qualitative and quantitative changes in HDL and LDL particle composition and distribution.

SUMMARY

Recent studies of the CETPi torcetrapib and anacetrapib and the CETPm dalcetrapib have shown differences in the resulting increase in HDL-cholesterol and in the level of HDL remodelling and potential for effective reverse cholesterol transport. Results from ongoing clinical outcomes studies with anacetrapib and dalcetrapib will clarify the relevance of CETP inhibition versus modulation towards HDL remodelling in the treatment of cardiovascular diseases.