Overproduction of very low-density lipoproteins is the hallmark of the dyslipidemia in the metabolic syndrome

Effect of chronic ethanol exposure on the liver of Clock-mutant mice

In humans, chronic ethanol consumption leads to a characteristic set of changes to the metabolism of lipids in the liver that is referred to as an "alcoholic fatty liver (AFL)". In severe cases, these metabolic changes result in the enlargement and fibrillization of the liver and are considered risk factors for cirrhosis and liver cancer. Clock-mutant mice have been shown to display abnormal lipid metabolism and alcohol preferences. To further understand the potential interactions between ethanol consumption, lipid metabolism, and the circadian clock, we investigated the effect of chronic ethanol intake on the lipid metabolism of Clock-mutant mice. We found that ethanol treatment produced a number of changes in the liver of Clock-mutant mice without impacting the wild-type controls. First, we found that 8 weeks of exposure to ethanol in the drinking water increased the weight of the liver in Clock-mutant mice. Ethanol treatment also increased triglyceride content of liver in Clock-mutant and wild-type mice. This increase was larger in the mutant mice. Finally, ethanol treatment altered the expression of a number of genes related to lipid metabolism in the Clock-mutant mice. Interestingly, this treatment did not impact circadian clock gene expression in the liver of either genotype. Thus, ethanol produces a number of changes in the liver of Clock-mutant mice that are not seen in the wild-type mice. These changes are consistent with the possibility that disturbance of circadian rhythmicity associated with the Clock mutation could be a risk factor for the development of an alcoholic fatty liver.

Small and dense LDL in familial combined hyperlipidemia and N291S polymorphism of the lipoprotein lipase gene

There is a predominance of small and dense LDL cholesterol particles in familial combined hyperlipidemia (FCH). The lipoprotein lipase gene could exert an influence in these circumstances.

To study the relationship of pattern B LDL and lipids with N291S polymorphism of lipoprotein lipase (LPL) in FCH patients.

Lipid profile, apolipoproteins, diameter of LDL and N291S polymorphism were determined in 93 patients with FCH and 286 individuals from the general population.

FCH patients with N291S polymorphism showed a lower mean diameter of LDL. FCH patients with pattern B LDL showed higher concentrations of triglycerides, VLDLc, non-HDLc and apo B100 and lower levels of HDLc than those with pattern A. Of FCH patients with polymorphism 87.5% presented pattern B and 12.5% pattern A, while patients without polymorphism presented pattern A in 69.2% cases and pattern B in 30.8% cases, with differences being statistically significant (p < 0.004). The prevalence of this mutation in our FCH patients was 9.7%.

The prevalence of N291S mutation in our FCH patients was similar to the 9.3% described in Dutch FCHL patients but clearly higher than the 2–5% described for other Caucasian populations. No polymorphism was found in our general population sample. FCH patients with phenotype B of LDL possessed an atherogenic lipid profile. The relationship between small and dense LDL and the presence of the N291S mutation may identify patients with high cardiovascular risk.

Very low density lipoprotein metabolism and plasma adiponectin as predictors of high-density lipoprotein apolipoprotein A-I kinetics in obese and nonobese men

CONTEXT

Hypercatabolism of high-density lipoprotein (HDL) apolipoprotein (apo) A-I results in low plasma apoA-I concentration. The mechanisms regulating apoA-I catabolism may relate to alterations in very low density lipoprotein (VLDL) metabolism and plasma adiponectin and serum amyloid A protein (SAA) concentrations.

OBJECTIVE

We examined the associations between the fractional catabolic rate (FCR) of HDL-apoA-I and VLDL kinetics, plasma adiponectin, and SAA concentrations.

STUDY DESIGN

The kinetics of HDL-apoA-I and VLDL-apoB were measured in 50 obese and 37 nonobese men using stable isotopic techniques.

RESULTS

In the obese group, HDL-apoA-I FCR was positively correlated with insulin, homeostasis model of assessment for insulin resistance (HOMA-IR) score, triglycerides, VLDL-apoB, and VLDL-apoB production rate (PR). In the nonobese group, HDL-apoA-I FCR was positively correlated with triglycerides, apoC-III, VLDL-apoB, and VLDL-apoB PR and negatively correlated with plasma adiponectin. Plasma SAA was not associated with HDL-apoA-I FCR in either group. In multiple regression analyses, VLDL-apoB PR and HOMA-IR score, and VLDL-apoB PR and adiponectin were independently predictive of HDL-apoA-I FCR in the obese and nonobese groups, respectively. HDL-apoA-I FCR was positively and strongly associated with HDL-apoA-I PR in both groups.

CONCLUSIONS

Variation in VLDL-apoB production, and hence plasma triglyceride concentrations, exerts a major effect on the catabolism of HDL-apoA-I. Insulin resistance and adiponectin may also contribute to the variation in HDL-apoA-I catabolism in obese and nonobese subjects, respectively. We also hypothesize that apoA-I PR determines a steady-state, lowered plasma of apoA-I, which may reflect a compensatory response to a primary defect in the catabolism of HDL-apoA-I due to altered VLDL metabolism.

Differential influence of different dietary fatty acids on very low-density lipoprotein secretion when delivered to hepatocytes in chylomicron remnants

The influence of dietary fats carried in chylomicron remnants on the hepatic secretion of very low-density lipoprotein (VLDL) was investigated using chylomicron remnant-like particles (CRLPs) and cultured rat hepatocytes as the experimental model. Chylomicron remnant-like particles containing triacylglycerol (TG) from palm, olive, or corn (enriched in saturated, monounsaturated, or n-6 polyunsaturated fatty acids) oil, respectively, were incubated with cultured hepatocytes for 5 hours. The medium was then removed and replaced with medium without CRLPs; and the secretion of TG, cholesterol, and apolipoprotein B48 during the following 16 hours was determined. Secretion of TG into the d less than 1.050-g/mL fraction containing VLDL was unaffected by olive CRLPs, but was significantly increased in cells exposed to palm or corn CRLPs in comparison with both olive CRLPs and control incubations without CRLPs. Secretion of apolipoprotein B48, however, was not changed by any of the CRLP types. Apolipoprotein B messenger RNA levels were decreased by olive and corn CRLPs, and 3-hydroxy-3-methylglutaryl coenzyme A reductase messenger RNA abundance was increased by palm CRLPs; but expression of other genes involved in the regulation of VLDL secretion was unaffected. These findings demonstrate that CRLPs enriched in saturated fatty acids or n-6 polyunsaturated fatty acids increase the secretion of TG in VLDL, possibly because of the secretion of larger particles, whereas those enriched in monounsaturated fatty acids have no effect. Thus, different dietary fats have differential effects on VLDL secretion directly when delivered to the liver in chylomicron remnants.

The relationship of body fat to metabolic disease: influence of sex and ethnicity

Clinical investigations designed to determine risk profiles for the development of cardiovascular disease (CVD) and type 2 diabetes mellitus (DM) are usually performed in homogenous populations and often focus on body mass index (BMI), waist circumference (WC), and fasting triglyceride (TG) levels. However, there are major ethnic differences in the relationship of these risk factors to outcomes. For example, the BMI risk threshold may be higher in blacks than in whites and higher in women than in men. Furthermore, a WC that predicts an obese BMI in white women only predicts a BMI in the overweight category in black women. In addition, overweight black men have a greater risk of developing type 2 DM than do overweight black women. Although TG levels are excellent predictors of insulin resistance in whites, they are not effective markers of insulin resistance in blacks. Among the criteria sets currently available to predict the development of CVD and type 2 DM, the most well known is the metabolic syndrome. The metabolic syndrome has 5 criteria: central obesity, hypertriglyceridemia, low high-density lipoprotein (HDL) levels, fasting hyperglycemia, and hypertension. To make the diagnosis of the metabolic syndrome, 3 of the 5 factors must be present. For central obesity and low HDL, the metabolic syndrome guidelines are sex specific. Diagnostic guidelines should also take ethnic differences into account, particularly in the diagnosis of central obesity and hypertriglyceridemia.

Molecular processes that handle -- and mishandle -- dietary lipids

Overconsumption of lipid-rich diets, in conjunction with physical inactivity, disables and kills staggering numbers of people worldwide. Recent advances in our molecular understanding of cholesterol and triglyceride transport from the small intestine to the rest of the body provide a detailed picture of the fed/fasted and active/sedentary states. Key surprises include the unexpected nature of many pivotal molecular mediators, as well as their dysregulation - but possible reversibility - in obesity, diabetes, inactivity, and related conditions. These mechanistic insights provide new opportunities to correct dyslipoproteinemia, accelerated atherosclerosis, insulin resistance, and other deadly sequelae of overnutrition and underexertion.

Metabolic syndrome: from epidemiology to systems biology

Metabolic syndrome (MetSyn) is a group of metabolic conditions that occur together and promote the development of cardiovascular disease (CVD) and diabetes. Recent genome-wide association studies have identified several novel susceptibility genes for MetSyn traits, and studies in rodent models have provided important molecular insights. However, as yet, only a small fraction of the genetic component is known. Systems-based approaches that integrate genomic, molecular and physiological data are complementing traditional genetic and biochemical approaches to more fully address the complexity of MetSyn.