Optimal therapy of low levels of high density lipoprotein-cholesterol

Chronic use of pravastatin reduces insulin exocytosis and increases β-cell death in hypercholesterolemic mice

We have previously demonstrated that hypercholesterolemic LDL receptor knockout (LDLr(-/-)) mice secrete less insulin than wild-type mice. Removing cholesterol from isolated islets using methyl-beta-cyclodextrin reversed this defect. In this study, we hypothesized that in vivo treatment of LDLr(-/-) mice with the HMGCoA reductase inhibitor pravastatin would improve glucose-stimulated insulin secretion. Female LDLr(-/-) mice were treated with pravastatin (400mg/L) for 1-3 months. Isolated pancreatic islets were assayed for insulin secretion rates, intracellular calcium oscillations, cholesterol levels, NAD(P)H and SNARE protein levels, apoptosis indicators and lipidomic profile. Two months pravastatin treatment reduced cholesterol levels in plasma, liver and islets by 35%, 25% and 50%, respectively. Contrary to our hypothesis, pravastatin treatment increased fasting and fed plasma levels of glucose and decreased markedly (40%) fed plasma levels of insulin. In addition, ex vivo glucose stimulated insulin secretion was significantly reduced after two and three months (36-48%, p<0.05) of pravastatin treatment. Although reducing insulin secretion and insulinemia, two months pravastatin treatment did not affect glucose tolerance because it improved global insulin sensitivity. Pravastatin induced islet dysfunction was associated with marked reductions of exocytosis-related SNARE proteins (SNAP25, Syntaxin 1A, VAMP2) and increased apoptosis markers (Bax/Bcl2 protein ratio, cleaved caspase-3 and lower NAD(P)H production rates) observed in pancreatic islets from treated mice. In addition, several oxidized phospholipids, tri- and diacylglycerols and the proapoptotic lipid molecule ceramide were identified as markers of pravastatin-treated islets. Cell death and oxidative stress (H2O2 production) were confirmed in insulin secreting INS-1E cells treated with pravastatin. These results indicate that chronic treatment with pravastatin impairs the insulin exocytosis machinery and increases β-cell death. These findings suggest that prolonged use of statins may have a diabetogenic effect.

Taking aim at HDL-C

Although statin therapy has revolutionized management of coronary heart disease (CHD), the lowering of low-density lipoprotein cholesterol (LDL-C) levels is not the whole story. Increased plasma concentrations of high-density lipoprotein cholesterol (HDL-C) have a cardioprotective effect that is just as important for reducing risk of heart attack and stroke. In this article, Dr McGovern examines the evidence that provides the rationale for HDL-C as a therapeutic target for cardiovascular risk reduction.

The prevalence of dyslipidemia in patients with spinal cord lesion in Thailand

Objective. To assess the prevalence of dyslipidemia in 90 patients with spinal cord lesion (SCL) of duration greater than 2 years. The study was carried out from November 2007 to September 2008. Methods. Clinical history, physical examination, and lipid profiles were recorded and analyzed. Dyslipidemia was assessed using guidelines from the National Cholesterol Education Project Adult Treatment Panel III (ATP III). Results. The prevalence of dyslipidemia in at least one lipid parameter was 76.7%. The most frequent finding was low HDL-C (58.9%). Hypertriglyceridemia, hypercholesterolemia and high LDL-C were found in 28.9%, 26.7% and 21.1% of patients, respectively. The factors sex = male and age ≥45 years were associated with high LDL-C (P < 0.05 and P < 0.01). Patients who exercised less than 30 minutes per day had associated hypercholesterolemia (P < 0.01), hypertriglyceridemia (P < 0.01), and higher LDL-C (P < 0.05). Patients with BMI ≥23 kg/m² had associated hypercholesterolemia and high LDL-C. Age was a significant determinant of high LDL-C. BMI was the most powerful and significant determinant of hypercholesterolemia and high LDL-C. Conclusion. SCL patients should have a regular lipid checkup, especially those patients having the following risk factors: males, age ≥45 years, BMI ≥23 kg/m² and exercise duration <30 minutes per day.

Cloning and characterization of the hamster and guinea pig nicotinic acid receptors

In this study, we present the identification and characterization of hamster and guinea pig nicotinic acid receptors. The hamster receptor shares approximately 80-90% identity with the nucleotide and amino acid sequences of human, mouse, and rat receptors. The guinea pig receptor shares 76-80% identity with the nucleotide and amino acid sequences of these other species. [(3)H]nicotinic acid binding affinity at guinea pig and hamster receptors is similar to that in human (dissociation constant = 121 nM for guinea pig, 72 nM for hamster, and 74 nM for human), as are potencies of nicotinic acid analogs in competition binding studies. Inhibition of forskolin-stimulated cAMP production by nicotinic acid and related analogs is also similar to the activity in the human receptor. Analysis of mRNA tissue distribution for the hamster and guinea pig nicotinic acid receptors shows expression across a number of tissues, with higher expression in adipose, lung, skeletal muscle, spleen, testis, and ovary.

HDL Cholesterol: Physiology, Pathophysiology, and Management

Numerous epidemiological studies have identified high-density lipoprotein cholesterol (HDL) to be an independent risk factor for coronary heart disease (CHD). HDL is an emerging therapeutic target that could rival the impact of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitors (statins) on LDL and CHD risk reduction. HDL metabolism, HDL kinetics, the concentration of various HDL subclasses, and other genetic factors affecting HDL functionality may all contribute to the anti-atherogenic properties of HDL; thus, standard plasma measurement may not capture the full range of HDL effects. Algorithms have been suggested to treat low HDL levels in subgroups of patients; however, no formal HDL target goals or treatment guidelines have been implemented as there is a lack of strong clinical evidence to support effective pharmacologic therapy for primary risk reduction. Available therapies have a modest impact on serum HDL levels; however, emerging therapies could have a more significant influence.

An update on alcohol and atherosclerosis

PURPOSE OF REVIEW

Epidemiological studies consistently link moderate alcohol use with a lower risk of cardiovascular disease, but a number of important issues remain controversial. These include the putative impact of non-alcoholic constituents of some alcoholic beverages, the role of genetic factors, potential mechanisms for this association, and confirmation of the relationship in experimental models.

RECENT FINDINGS

Although high-density lipoprotein cholesterol (HDL-C) is considered the primary mediator of the cardiovascular effects of moderate drinking, recent evidence has shown the alcohol-HDL-C relation is not linear beyond the range of moderate drinking. Moderate alcohol use also has important inverse relations with inflammatory factors. Some, but not all, animal models confirm the anti-atherogenic effects of ethanol and highlight inflammatory factors as one possible mechanism. The non-alcoholic constituents of red wine also have anti-atherogenic and perhaps even life-extending properties in vitro, but their relevance to humans remains uncertain. Genetic variants of the apolipoprotein E and interleukin 6 genes in humans may modify how alcohol influences atherosclerosis, further emphasizing the importance of HDL-C and inflammatory factors as mediators.

SUMMARY

The robust relationship between moderate drinking and lower risk of cardiovascular disease remains an intriguing area of investigation. Clarifying potential gene-environment interactions and translational research into uses for non-alcoholic components will be important areas for future investigation.

Multivariate Assessment of Lipid Parameters as Predictors of Coronary Heart Disease Among Postmenopausal Women

Background— Over the past decade, lipid measurements have been significantly improved and standardized. We evaluated the usefulness of multiple plasma lipid parameters in predicting coronary heart diseases (CHD) among women.

Methods and Results— Among 32 826 women from the Nurses’ Health Study who provided blood samples at baseline, 234 CHD events were documented during 8 years of follow-up. In a nested study, these cases were matched to controls (1:2) for age, smoking, fasting status, and month of blood draw. We estimated the relative risk (RR) for each lipid parameter, adjusted for C-reactive protein, homocysteine, body mass index, family history, hypertension, diabetes, postmenopausal hormone use, physical activity, alcohol intake, and blood draw parameters. The RRs associated with an increase of ≈1 SD (mg/dL) were as follows: HDL cholesterol (HDL-C) (RR=0.6 [0.5 to 0.8], SD=17), apolipoprotein B 100 (apoB 100 ) (RR=1.7 [1.4 to 2.1], SD=32), LDL cholesterol (LDL-C) (RR=1.4 [1.1 to 1.7], SD=36), total cholesterol (TC) (RR=1.4 [1.1 to 1.6], SD=40), and triglycerides (RR=1.3 [1.0 to 1.5], SD=80). Among the lipid indexes, the RRs were: apoB 100 /HDL-C (RR=1.7 [1.4 to 2.1], SD=1.0), TC/HDL-C (RR=1.6 [1.3 to 1.9], SD=1.3), LDL-C/HDL-C (RR=1.5 [1.3 to 1.9], SD=1.0), and non–HDL-C (RR=1.6 [1.3 to 1.9], SD=42 mg/dL). After simultaneous control for several lipid biomarkers, HDL-C was the primary contributor of the variation in multivariate models ( P =0.01), followed by LDL-C ( P =0.01), whereas triglycerides and apoB 100 did not contribute further information. HDL-C–related ratios were the strongest contributors to predicting CHD ( P <0.0001).

Conclusions— Lower levels of HDL-C may be a key discriminator of higher CHD events among postmenopausal women. HDL-C–related ratios (such as TC/HDL-C) provide a powerful predictive tool independently of other known CHD risk factors.

Pharmacologic elevation of high-density lipoproteins: recent insights on mechanism of action and atherosclerosis protection

PURPOSE OF REVIEW

Despite the best efforts in reduction of low-density lipoprotein cholesterol, most cardiovascular events are not being prevented. Because high-density lipoprotein (HDL) promotes reverse cholesterol transport and other antiatherogenic effects, interventions aimed at raising HDL cholesterol or mimicking its beneficial effects may greatly improve treatment and prevention of cardiovascular disease. This article reviews the antiatherogenic effects of HDL, recent insights into the mechanisms of action of currently available, and emerging HDL-based therapies.

RECENT FINDINGS

New insights into the basic science of HDL function and metabolism (such as the discovery of beta-chain ATP synthase as a hepatic catabolic HDL receptor) are further characterizing the importance of HDL in atheroprotection and identifying novel targets of drug development. Nicotinic acid, fibrates, statins, and thiazolidinediones not only increase HDL cholesterol but also alter HDL subpopulation size and composition. Furthermore, these drugs promote direct antiatherogenic effects of HDL (antioxidation, anti-inflammation, antithrombotic effects, endothelial stabilization). Emerging HDL-raising therapies (such as cholesteryl ester transfer protein inhibitors and 1,2-dimyristoyl-sn-glycero-phosphocholine) and novel interventions that mimic HDL's beneficial effects (such as apolipoprotein AImilano and apolipoprotein AI mimetic peptides) are proving beneficial in animal and human studies.

SUMMARY

An understanding of the atheroprotective mechanisms of HDL is essential for the rational use of currently available drugs and directed development of new drugs. Increasing total HDL cholesterol may not be as important as increasing the functional properties of HDL. Cardiovascular disease treatment and prevention can be improved by combining current low-density lipoprotein-based strategies with effective HDL-based interventions.