Advanced glycation end products (AGE) -modified proteins behave as active ligands for several receptors belonging to the scavenger receptor family. Scavenger receptor class B type I (SR-BI) was identified as the first high density lipoprotein (HDL) receptor that mediates selective uptake of HDL-cholesteryl esters (HDL-CE). This study investigated whether AGE proteins serve as ligands for SR-BI and affect SR-BI-mediated cholesterol transport using Chinese hamster ovary (CHO) cells overexpressing hamster SR-BI (CHO-SR-BI cells). [125I] AGE-bovine serum albumin (AGE-BSA) underwent active endocytosis and subsequent lysosomal degradation by CHO-SR-BI cells, indicating that SR-BI serves as an AGE receptor. SR-BI-mediated selective uptake of HDL-CE by CHO-SR-BI cells was efficiently inhibited by AGE-BSA although AGE-BSA had no effect on HDL binding to CHO-SR-BI cells. In addition, AGE-BSA significantly inhibited the efflux of [3H] cholesterol from CHO-SR-BI cells to HDL. These findings suggest the possibility that AGE proteins in the circulation interfere with the functions of SR-BI in reverse cholesterol transport by inhibiting the selective uptake of HDL-CE, as well as cholesterol efflux from peripheral cells to HDL, thereby accelerating diabetes-induced atherosclerosis.
Although ascorbic acid (ASA) is known as a water-soluble antioxidant, we found that it accelerated the cytotoxicity induced by oxidized low-density lipoprotein (OxLDL) in vitro. This suggests that ASA may enhance the oxidation of LDL to augment the atherogenic activities of OxLDL under certain conditions. Thus, this study was designed to investigate the underlying mechanism that ASA enhances OxLDL-induced cytotoxicity. ASA enhanced the cytotoxicity of macrophage cell line (J774) induced by OxLDL in a dose-dependent manner, whose effect was more apparent in high glucose concentration in the medium. The ASA-induced enhancement in cytotoxicity was inhibited by the presence of lipid-soluble antioxidants, such as α-tocopherol and probucol, suggesting that the pro-cytotoxic effect by ASA is likely due to its pro-oxidant property. We also investigated the effects of ASA at different time points on the Cu2+-mediated oxidation of LDL. ASA decreased the rate of conjugated dienes formation when added at the early phase of oxidation, whereas it increased when added at the late phase of oxidation. These data suggest that ASA may act as a pro-oxidant under the condition of extensive LDL oxidation. To prevent oxidation stress, ASA would be better used together with lipid-soluble antioxidants for antioxidant therapies.
To clarify current changes in the patterns of carotid atherosclerosis in Japan, carotid ultrasonographic findings in Japanese male patients with aortic aneurysm were compared between two groups examined in different periods. The first group was recruited from 42 consecutively examined patients in 1997, while the second group consisted of 40 consecutive patients from September, 2001 to January, 2002. Carotid lesions were analyzed by computer, and classified into three types based on the texture: echolucent, hyperechoic, and heterogeneous types. The mean age of the first group was 72 years, similar to that of the second group. In the first group, cigarette smoking was frequently noted, while the mean BMI was greater and IHD and CVD were frequent in the second group. Fifty carotid lesions were seen in each group. Severe stenosis and hypoechoic type lesions were more frequent in the second group than in the first group. These findings indicated that hypoechoic-type lesions, which are considered to be lipid deposition, hemorrhage, or loose fibrous tissue, and severe stenosis, were increased in the more recent group. This predicted that circulatory disturbance due to unstable atherosclerotic lesions may increase in the future among the elderly because carotid lesions reflect vascular change in other organs.
The aim of this study was to observe the efficacy of atorvastatin and the related factors of meeting the National Cholesterol Education Program (NCEP)-recommended low-density lipoprotein (LDL) cholesterol levels in patients with hypercholesterolemia. A total of 107 patients were treated with atorvastatin 10 mg/day for 12 weeks. Eighty % of the patients achieved the target goals. There was a significant difference in the initial body mass index (BMI) between patients achieving the target goals and those not achieving the target goals (p < 0.05). In multiple stepwise logistic regression analysis, initial BMI and complications correlated with reaching the NCEP-recommended target goals (p < 0.05). A great number of patients treated with atorvastatin, including those previously poorly controlled with other therapies, reached the target goals at the starting dose 10 mg/day. BMI may be a useful index of achieving the NCEP-recommended target goals with atorvastatin.
We conducted a prospective study to investigate the relationship between the decrease of serum lipid levels during pravastatin therapy and changes of coronary angiography parameters in Japanese patients with coronary atherosclerosis. The patients were predominantly male, aged between 18 and 75 years (mean: 58 years), had at least 25% stenosis of one or more major coronary arteries, and had a serum total cholesterol ( TC) level ≥ 200 mg/dl (5.18 mM/l). Treatment with pravastatin (10 mg/day) was continued for 3 years. Coronary angiography was performed before and 3 years after the start of pravastatin therapy to assess the relationship between the mean segment diameter (MSD), the minimal lumen diameter (MLD), and the annual changes of percent stenosis and TC levels. of 265 patients who were initially registered, 129 were followed for an average of 35 months. Consequently, second angiograms were only obtained in 68 patients for various reasons, so this group was used for analysis. During pravastatin therapy, the TC level significantly decreased from 239 mg/dl (6.19 mM/l) to 210 mg/dl (5.44 mM/l) (a 12% reduction; p<0.001). In addition, HDL-cholesterol increased by 5% (p=0.007), but the triglyceride level did not show a significant change. Both MSD and MLD were significantly improved on follow-up angiography, increasing from 2.67 mm to 2.76 mm and from 2.09 mm to 2.13 mm, respectively. However, no change of percent stenosis was observed. The mean TC level during treatment did not show any significant correlation with the changes of angiography parameters. However, a significant correlation was observed between the percent reduction of TC and the annual change of MSD (r=−0.272, p=0.027). A similar relationship was also found between the change of MLD and the percent reduction of TC (r=−0.260, p=0.035). In conclusion, the percent decrease of serum cholesterol may be a better indicator of clinical efficacy than the absolute cholesterol level during pravastatin therapy.
Acyl-CoA:cholesterol acyltransferase (ACAT) catalyzes cholesterol esterification in mammalian cells. Two isoforms of ACAT have been reported to date (ACAT-1 and ACAT-2). ACAT-1 protein is ubiquitously expressed in tissues, including macrophages, hepatocytes, adrenal glands, and intestines. In contrast, ACAT-2 is expressed mainly in the intestine in humans. However, the roles of ACAT-1 and ACAT-2 in lipoprotein metabolism in humans have not yet been reported. This study was carried out to clarify the relationship between ACAT-2 gene mutations and hyperlipidemia in humans. To identify gene mutations, we screened 30 subjects with hyperlipidemia (TC > 220 mg/dl or TG >150 mg/dl) by direct sequencing. As a result, we found a new single-nucleotide polymorphism (SNP; a point mutation in intron 1, IVS1 −8 G→C) in the ACAT-2 gene. To investigate the relationship between this SNP and both plasma lipids and apolipoproteins, 91 unrelated hyperlipidemic subjects (40 males and 51 females), and 92 unrelated normolipidemic subjects (46 males and 46 females) were screened by direct sequencing. The frequencies of the IVS1 −8G→C allele in normolipidemic and hyperlipidemic subjects were 0.131 and 0.125, respectively. IVS1 −8 G→C did not affect plasma concentrations of lipids or apolipoproteins in either normolipidemic or hyperlipidemic subjects. Although further studies are needed, our data suggest that the ACAT-2 gene may not affect lipid levels in humans.
We recently reported that lysophosphatidylcholine (lysoPC) acts on vascular smooth muscle cells ( VSMCs ) to produce a mitogenic response through the activation of extracellular signal-regulated kinases 1/2 (ERK1/2). In this study, we examined the role of HMG-CoA reductase inhibitors on lysoPC-induced VSMC proliferation. Pitavastatin, a new HMG-CoA reductase inhibitor, suppressed lysoPC-induced DNA synthesis in primary cultured rat VSMCs. Since lysoPC-induced ERK1/2 activation contributes to smooth muscle cell proliferation, we explored the effect of pitavastatin on ERK1/2 activation. Pitavastatin inhibited lysoPC-induced ERK1/2 phosphorylation and ERK1/2 activation. The other HMG-CoA reductase inhibitors, atrovastatin and fluvastatin, also inhibited lysoPC-induced ERK1/2 phosphorylation. Pitavastatin also inhibited lysoPC-induced c-fos mRNA expression. To gain insight into the mechanism of the inhibitory effect of pitavastatin on ERK1/2 activation by lysoPC, we examined the role of the mevalonate pathways. Mevalonate and farnesylpyrophosphate reduced the inhibition of ERK1/2 phosphorylation by pitavastatin. These studies demonstrate that pitavastatin may inhibit lysoPC-induced VSMC proliferation, at least in part, by inactivating ERK1/2, which is linked to mevalonate metabolism.
Nitric oxide (NO) regulates endothelial function and is believed to prevent atherogenesis. In endothelial cells, endothelial nitric oxide synthase (eNOS) is expressed constitutively, and regulates NO synthesis. A mutation of the eNOS gene has been associated with the development of coronary artery disease (CAD). The development of CAD is also influenced by insulin resistance, and recent studies suggest that NO might affect cellular insulin activity. We investigated the association between eNOS polymorphisms and insulin resistance in patients with CAD. We screened 45 patients with a history of myocardial infarction (MI), angina pectoris (AP), or coronary spasm. Genotypes were determined by polymerase chain reaction-restriction fragment-length polymorphism analysis. We examined two polymorphisms of the eNOS gene (The T-786→C variant and the missense Glu298Asp variant). Insulin resistance was measured by determining the plasma immunoreactive insulin concentration at the 120 min time point (IRI 120) of a 75 g oral glucose tolerance test. The IRI 120 of the T-786→C variant group was higher than that for the control group (p<0.05). This finding demonstrates that the T-786→C mutation in the eNOS gene decreases insulin sensitivity.
Little is known about the relationship at the molecular and cellular levels between vascular calcification and elastic fibers essential for elasticity. To gain a better understanding of the physiological function of elastin in vascular calcification, we developed a calcification model on cultured bovine retinal-pigmented-epithelial cells (RPEs) that do not express endogenous tropoelastin. The addition of inorganic phosphate (NaH2PO4; Pi) induced calcium deposition in RPEs. The Pi-induced calcification, as assessed by the o-cresolphthalein complexone method, Goldenberg’s method, and von Kossa staining, was completely inhibited by treatment with clodronate (DMDP) and phosphonoformic acid (PFA) and was weakly suppressed by treatment with levamisole. Moreover, the osteopontin mRNA expression was upregulated in the Pi-induced calcification of RPEs. These reactions in RPEs were characteristically consistent with those already established in cultured bovine aortic smooth muscle cells (BASMCs). Furthermore, bacterially expressed tropoelastin inhibited calcium deposition in RPEs as well as in BASMCs. Finally, Pi-induced calcification was partially suppressed after the addition of tropoelastin due to elastic fiber formation. In conclusion, we suggest that this calcification model in RPEs is useful for analyzing the relation between elastic fibers and vascular calcification, and that tropoelastin and elastic fibers may contribute to the inhibition of vascular calcification.
Paraoxonase (PON), an HDL- associated enzyme, may protect against the development of atherosclerosis. Single nucleotide polymorphisms of PON have been reported to be associated with an incidence of coronary heart diseases. We investigated the effect of PON R192Q variants on serum lipid profile after caloric restriction in nondiabetic healthy males. After caloric restriction for 12 weeks, the levels of high-density lipoprotein cholesterol (HDL-C) increased in the subjects carrying RR genotype, but not in the QR and QQ genotypes. The changes in HDL-C from the baseline values in the RR genotype were significantly different from those in the QR and QQ genotypes. Although the changes in lipoprotein lipase activity were not different among three genotypes, we observed a significant difference in the changes in hepatic lipase (HL) activity after caloric restriction, namely, a decrease in the RR genotype and an increase in the subjects carrying the Q allele. In addition, the changes in fasting insulin levels significantly correlated with those in HDL-C levels in the RR genotype, not in the QR and QQ genotypes. PON R192Q polymorphism could affect HDL-C levels after caloric restriction presumably due to decreased HL activity and altered insulin resistance.