Low density lipoprotein (LDL) particles are heterogenous with respect to their size, density and lipid composition. Among LDL particles, the smaller and denser LDL particles [small dense (sd) LDL] are more atherogenic and the sd LDL phenotype is strongly associated with development of coronary heart disease. Here we will review various methods for measurement of sd LDL. Although ultracentrifugation, nuclear magnetic resonance (NMR) spectroscopy and gradient-gel electrophoresis (GGE) are usually employed for the measurement of sd LDL, such methods are either too laborious or expensive for general clinical use. We recently established a simple precipitation method for the quantification of sd LDL. This method is applicable to routine clinical use and allows the rapid measurement of a large number of samples.
Recent clinical studies have revealed that increased serum triglyceride (TG) levels are closely related to atherosclerosis, independently of serum levels of high-density lipoproteins (HDL) and low-density lipoproteins (LDL). Among triglyceride-rich lipoproteins (TRLs), remnant lipoproteins (RLPs) are considered to be atherogenic and an independent coronary risk factor. We previously reported that monocytes cultured in the presence of RLPs increased their adhesion to vascular endothelial cells. The underlying mechanism involved activation of RhoA, a member of small GTP binding proteins, resulting in activation of focal adhesion kinase (FAK) and s1-integrin. It is also known that RLPs enter vessel walls. In another study, we reported that RLPs induced smooth muscle cell (SMC) proliferation, independently of oxidative stress. Recently, we identified the molecular mechanisms, in which RLPs from hypertriglyceridemic patients stimulated SMC proliferation via epidermal growth factor (EGF) receptor transactivation and heparin-binding EGF-like growth factor (HB-EGF) shedding. More recently, we reported that apoB48 receptor was involved in RLP-induced foam cell formation in macrophages. The current review focused on the molecular mechanisms for the atherogenicity of RLPs.
Insulin resistance plays an important role not only in the development and progression of diabetes mellitus but also in the establishment of metabolic syndrome. Improvement of insulin resistance is thus of great importance both in improving glucose metabolism and preventing atherosclerosis. Although HMG-CoA reductase inhibitors appear to favorably affect glucose metabolism, as indicated by the results of a subanalysis in the West of Scotland Coronary Prevention Study (WOSCOPS), their effects on glucose metabolism and insulin resistance have not been thoroughly investigated in animal models. In this study, the effects of atorvastatin on the glucose metabolism and insulin resistance of KK/Ay mice, an animal model of type II diabetes, were investigated. Atorvastatin significantly decreased the non-HDL-cholesterol level in the oral glucose tolerance test, inhibited increase in the 30-min glucose level, decreased plasma insulin levels before and 30 and 60 minutes after glucose loading, and decreased the insulin resistance index, compared with corresponding values in controls, indicating that atorvastatin appeared to improve glucose metabolism by improving insulin resistance. Northern blot analysis revealed decreases in levels of mRNA of sterol regulatory element binding protein-1 (SREBP-1) and glucose-6-phosphatase (G6Pase), and it may play a role in the improvement of glucose metabolism and insulin resistance.
We tried to investigate whether accumulation of visceral fat, assessed by a simple but widely used ultrasonographic method, was associated with common carotid atherosclerosis in non-obese men ranging from 16 to 79 years old. The subjects were consecutive 297 male in-patients whose body mass index ranged from 18.5 kg/m2 to 25 kg/m2. An ultrasonographic evaluation using a 7.5 MHz linear type B-mode probe was performed by a specialist to determine the intima-media thickness (IMT) of the common carotid artery and the maximal thickness of peritoneal fat (Pmax) at the anterior surface of the liver and the minimal thickness of subcutaneous fat (Smin) of the abdomen. The Pmax/Smin ratio, which was termed the abdominal wall fat index (AFI), was then calculated. The mean age ± standard deviation in this series was 65 ± 13 (range, 15−79) years. Multiple regression analysis using IMT as an objective variable, adjusted by various risk factors as explanatory variables, showed that AFI [β, 0.0538; 95% confidence interval (CI), 0.0116-0.0960] was a significant independent contributing factor along with known risk factors such as age, smoking status, systolic blood pressure, HDL-cholesterol and LDL-cholesterol. We found that AFI was useful in evaluating disorders of metabolism and atherosclerosis in non-obese men.
To clarify whether an increased proliferative potential of vascular smooth muscle cells (SMC) under diabetic conditions augments the susceptibility of the cells to 7-ketocholesterol-induced apoptosis, we investigated the difference in sensitivity to 7-ketocholesterol between SMC obtained from diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats and the control Long-Evans Tokushima Otsuka (LETO) rats. The outgrowth rate from aortic wall explants and cell proliferation were higher in SMC derived from OLETF rats (OLETF-derived SMC) compared to those from LETO rats (LETO-derived SMC). When 7-ketocholesterol was added to SMC, the amount of fragmented DNA increased significantly in OLETF-derived compared to LETO-derived SMC. The amount of fragmented DNA induced by 7-ketocholeaterol decreased significantly in both OLETF- and LETO-derived SMC when they were incubated without fetal bovine serum. By adding PDGF-BB to LETO-derived SMC, the amount of fragmented DNA induced by 7-ketocholesterol increased significantly. These results suggest that apoptosis of SMC induced by 7-ketocholesterol may be accelerated when SMC acquire a high proliferative potential by prolonged exposure to diabetic condition.
To determine the recent serum lipid levels and other serum variables in the general Japanese population and trends in their changes over the past 40 years, a nationwide survey of serum lipid levels was conducted in 36 institutes from various districts around Japan in 2000. The total number of subjects was 12,839, aged 4 through 99 years. The mean total cholesterol level was 201 mg/dl; 202 mg/dl in men and 200 mg/dl in women. The mean HDL-cholesterol level was 59 mg/dl; 55 mg/dl in men and 65 mg/dl in women. The mean LDL-cholesterol level was 118 mg/dl; 121 mg/dl in men and 115 mg/dl in women. The mean triglyceride level was 118 mg/dl; 136 mg/dl in men and 92 mg/dl in women. The total cholesterol level slightly increased by 5 mg/dl in 10 years. Although the triglyceride level in women did not change, the triglyceride level in men increased over 10 years, especially in the 30s through 70s age bracket, indicating a possible increase in metabolic syndromes in the future. The present results will become the standard serum lipid level data for the Japanese people, and succeeding 10-year surveys will clarify the trends of lipid levels in this country.
Plasma non-HDL cholesterol (HDL-C) concentration that is simply estimated from plasma total cholesterol and HDL-C concentrations, without the influence of plasma triglyceride concentration, has been included as a therapeutic target for hypertrigly-ceridemic patients in the most recent National Cholesterol Education Program (NCEP) recommendations. In the present study, we estimated plasma non-HDL-C concentration in Japanese subjects to clarify the correlation of plasma non-HDL-C to other plasma lipid concentrations, and to evaluate the NCEP recommendation. Plasma non-HDL-C concentration has a positive correlation with low-density lipoprotein cholesterol (LDL-C) and triglyceride concentrations. From our analysis, 140 mg/dl of plasma LDL-C concentration, which is the level for the diagnosis of hyper-LDL cholesterolemia, corresponds to 169 mg/dl of non HDL-C concentration. The relationship between plasma non-HDL-C and LDL-C concentrations in Japanese subjects is quite similar to that described in the NCEP guideline. Thus, we suggest that non-HDL-C is a useful risk marker in Japan, as recommended by the NCEP.
Reduction of serum cholesterol levels with statin therapy decreases the risk of coronary heart disease. Inhibition of HMG-CoA reductase by statin results in decreased synthesis of cholesterol and other products downstream of mevalonate, which may produce adverse effects in statin therapy. We studied the reductions of serum ubiquinol-10 and ubiquinone-10 levels in hypercholesterolemic patients treated with atorvastatin. Fourteen patients were treated with 10 mg/day of atorvastatin, and serum lipid, ubiquinol-10 and ubiquinone-10 levels were measured before and after 8 weeks of treatment. Serum total cholesterol and LDL-cholesterol levels decreased significantly. All patients showed definite reductions of serum ubiquinol-10 and ubiquinone-10 levels, and mean levels of serum ubiquinol-10 and ubiquinone-10 levels decreased significantly from 0.81 ± 0.21 to 0.46 ± 0.10 μg/ml (p < 0.0001), and from 0.10 ± 0.06 to 0.06 ± 0.02 μg/ml (p = 0.0008), respectively. Percent reductions of ubiquinol-10 and those of total cholesterol showed a positive correlation (r = 0.627, p = 0.0165). As atorvastatin reduces serum ubiquinol-10 as well as serum cholesterol levels in all patients, it is imperative that physicians are forewarned about the risks associated with ubiquinol-10 depletion.