Arteriosclerosis and thrombosis : a journal of vascular biology最新文献

The impact of apolipoprotein (apo) E polymorphism on interindividual variation in plasma lipid, lipoprotein, and apolipoprotein levels was studied in a sample of familial hypercholesterolemic (FH) patients (147 women, 116 men) with the same mutation, a > 10-kilobase deletion of the low-density lipoprotein (LDL) receptor gene. Each trait was adjusted for concomitants (age, age squared, height, weight, weight squared) for each sex separately before the apoE genotypic effects were estimated. The relative contribution of concomitants to sample variability was found to be very different in women and in men. Allelic variation in the apoE gene was shown to explain a statistically significant portion of the variability in adjusted lipid traits. Moreover, the contribution of apoE polymorphism was different between sexes. In women, there was significant variability (P < .01) among apoE genotypes for total cholesterol, LDL cholesterol, and total and LDL apoB. In men, significant variability (P < .01) was observed among apoE genotypes in very-low-density lipoprotein (VLDL) cholesterol and triglyceride levels. Women with the epsilon 3/2 genotype had significantly lower means for total cholesterol, LDL cholesterol, and LDL apoB than women with the epsilon 3/3 genotype (P < .05). In men, the mean VLDL cholesterol was significantly higher for the epsilon 2/2 genotype and was significantly lower for the epsilon 4/2 genotype than the mean for the epsilon 3/3 genotype (P < .05). Overall, the greatest influence was associated with the epsilon 2 allele, and the LDL cholesterol-lowering effect of this allele was present only in FH women. No statistically significant apoE effect was shown on lipoprotein(a) levels in either sex.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined hyperlipidemia may result from the interaction of several metabolic and environmental factors. We explored to what extent fasting insulin concentration, apolipoprotein (apo) E2 frequency, and cigarette smoking explained the serum levels of triglyceride and high-density lipoprotein cholesterol (HDL-C) in patients with combined hyperlipidemia. Forty-nine untreated patients with combined hyperlipidemia were compared with 49 hypercholesterolemic patients who were matched for gender, age, and body mass index. All laboratory values were obtained after 9 weeks of standardized dietary intake and after an overnight fast. The patients with combined hyperlipidemia had a significantly higher (33 pmol/L, 50%) mean insulin concentration than matched hypercholesterolemic control subjects, indicating that the combined hyperlipidemic patients were more insulin resistant. However, the differences in the fasting insulin and triglyceride concentrations within the pairs were only slightly correlated (adjusted r = .29). The combined hyperlipidemic patients were also characterized by a higher frequency of apoE2 alleles (25% versus 6%) and smokers (41% versus 16%). In a matched multiple linear regression model, the differences in insulin concentration, apoE2 allele frequency, and smoking explained 12%, 8%, and 9%, respectively, of the mean paired difference in triglyceride concentration. The differences in insulin concentration or apoE2 allele frequency did not significantly explain the mean paired difference in HDL-C concentration, whereas smoking explained 17% of the difference. In conclusion, fasting insulin concentration, the presence of the apoE2 allele, and smoking may explain 30% of the hypertriglyceridemia and the low levels of HDL-C in nonobese patients with combined hyperlipidemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelets are capable of producing nitric oxide (NO) through the L-arginine-NO synthase pathway. Acute exposure to supraphysiological concentrations of L-arginine in vitro increases the production of NO by platelets and is associated with an increase in platelet cyclic GMP (cGMP) levels and a reduction in platelet aggregation. The purpose of this study was to determine if chronic oral administration of L-arginine decreases platelet aggregation in hypercholesterolemic animals and to determine if this effect is mediated by the metabolism of L-arginine to NO. Male New Zealand White rabbits were fed normal chow (Con), a 1% cholesterol diet (Chol), or a 1% cholesterol diet supplemented with a sixfold enrichment of dietary L-arginine (Arg) or L-methionine (Met). After 10 weeks, cholesterol levels were equally increased in Chol and Arg animals, whereas plasma arginine levels were doubled in the Arg group. There was no difference in maximum aggregation initiated by ADP (100 mumol/L) between washed platelets from Con, Met, and Chol animals, but aggregation of platelets from Arg animals was significantly decreased (P < .05). In aggregating platelets from Arg animals, cGMP levels were significantly higher than the other groups (P < .05). When platelets were incubated ex vivo with the NO synthase inhibitor NG-monomethyl-L-arginine, the effects of dietary L-arginine were reversed. Chronic dietary supplementation of L-arginine decreases platelet aggregation in hypercholesterolemic rabbits. This effect appears to be due to the metabolism of L-arginine to NO.

Women have significantly higher plasma concentrations of high-density lipoprotein (HDL) and apolipoprotein (apo) A-I than men. Human HDL consists of two major species of apoA-I-containing lipoproteins: LpA-I (lipoprotein containing apoA-I but not apoA-II) and LpA-I:A-II (lipoprotein containing both apoA-I and apoA-II). LpA-I is itself heterogeneous and contains several subclasses of different size and composition. We analyzed LpA-I subclasses in 12 male and 12 female healthy normolipidemic adults. LpA-I concentrations were significantly higher in women (72.4 +/- 5.6 mg/dL) than in men (50.2 +/- 2.2 mg/dL) (P < .05). LpA-I was preparatively isolated from fasting plasma by immunoaffinity chromatography. Gel filtration chromatography was then used to isolate LpA-I subclasses based on size. Three major subclasses were eluted: large, medium, and small LpA-I. No differences between men and women in the size or composition of individual LpA-I subclasses were observed. In contrast, the distribution and plasma concentration of LpA-I subclasses were significantly different between men and women. As a fraction of total LpA-I, the large LpA-I was significantly higher (68.0% to 48.4%) and the medium LpA-I was significantly lower (26.4% to 44.9%) in women than in men. The fraction of small LpA-I was not significantly different. Plasma concentrations of large LpA-I in women (49.2 mg/dL) were twice that in men (24.3 mg/dL), whereas plasma concentrations of medium LpA-I (19.1 mg/dL versus 22.5 mg/dL) and small LpA-I (4.0 mg/dL versus 3.0 mg/dL) were similar in women and men.(ABSTRACT TRUNCATED AT 250 WORDS)

We studied the relation between the concentration of lipoprotein(a) [Lp(a)] in plasma, apolipoprotein (a) [apo(a)] phenotype, and the clinical expression of coronary artery disease (CAD) in a previously described cohort of patients with familial hypercholesterolemia (FH) and an appropriate population of control subjects. The plasma concentration of Lp(a) was markedly skewed in both the FH and control populations; however, the distribution was less skewed in FH (50% greater than 300 mg/L) compared with control subjects (27% greater than 300 mg/L). Patients with FH had significantly higher median and mean log Lp(a) levels compared with control subjects. There was no difference in the level of Lp(a) between men and women in both the control and FH groups. Frequency distribution analysis of the major apo(a) isoform size for each subject showed that, in contrast to the near-normal distribution seen in control subjects, two major subpopulations were apparent in the FH cohort, based on apo(a) isoform size > 700 kD or < or = 700 kD. There was no correlation between Lp(a) plasma concentration and apo(a) isoform size in either population. FH subjects with smaller apo(a) isoforms were more likely to have a history of signs of, or symptoms of CAD than those with larger isoforms. These data illustrate that on the basis of Lp(a) plasma concentration alone, there is no significant difference between FH patients with and without signs or symptoms of CAD. In the control population the smaller apo(a) isoforms were associated with higher Lp(a) levels, whereas in the FH population both small and large apo(a) isoforms were associated with higher Lp(a) levels.(ABSTRACT TRUNCATED AT 250 WORDS)

We hypothesized that the formation of foam cells and fatty streaks requires a postsecretory oxidative modification of lipoproteins that targets them for rapid uptake by macrophages. Lipid peroxidation may in part depend on the concentration of tissue iron, one of the major oxidants in vivo. We analyzed the relation between sonographically assessed carotid atherosclerosis and body iron stores in a population sample of 847 men and women aged 40 to 79 years. In a logistic regression analysis adjusting for age, sex, and all major vascular risk markers, ferritin emerged as one of the strongest indicators of carotid artery disease in both sexes (40 to 59 years; odds ratio, 1.54 per 100 micrograms/L; P < .001). The predictive significance of ferritin was found to be synergistic with that of hypercholesterolemia. Variations in body iron stores between sexes may partly explain evident sex differences in the expression of carotid atherosclerosis. In the elderly (> or = 60 years) the predictive significance of ferritin was found to decrease parallel to that of apolipoprotein B. The current study suggests a possible role of body iron in early atherogenesis.

Advanced glycation end products (AGEs) form by the interaction of aldoses with proteins and the subsequent molecular rearrangements of the covalently linked sugars, eventuating in a diverse group of fluorescent compounds of yellow-brown color. This heterogeneous class of nonenzymatically glycated proteins or lipids is found in the plasma and accumulates in the vessel wall and tissues even in normal aging. As a consequence of hyperglycemia, AGE formation and deposition are much enhanced in diabetes, in which their presence has been linked to secondary complications, especially microvascular disease. This review summarizes the cellular interactions of AGEs and describes the central role of a novel receptor for AGE (RAGE). RAGE, an immunoglobulin superfamily member, mediates the binding of AGEs to endothelial cells and mononuclear phagocytes, interacts with a lactoferrin-like polypeptide that also binds AGEs, and appears to activate intracellular signal transduction mechanisms consequent to its interaction with the glycated ligand. RAGE is expressed by ECs, mononuclear phagocytes, smooth muscle cells, mesangial cells, and neurons, indicating a potential role in the regulation of their properties in homeostasis and/or their dysfunction in the development of diabetic complications. Since AGEs have been shown to generate reactive oxygen intermediates, tethering of AGEs to the cell surface by their receptors focuses oxidant stress on cellular targets, resulting in changes in gene expression and the cellular phenotype. The discovery of RAGE and development of reagents to block its interaction with AGEs should provide insights into the role of this ligand-receptor interaction in the pathogenesis of diabetic complications and, potentially, atherosclerosis.

Cell adhesion to endothelial cells stimulated by tumor necrosis factor-alpha (TNF) is due to induction of surface receptors, such as vascular cell adhesion molecule-1 (VCAM-1). The antioxidant pyrrolidine dithiocarbamate (PDTC) specifically inhibits activation of nuclear factor-kappa B (NF-kappa B). Since kappa B motifs are present in VCAM-1 and intercellular adhesion molecule-1 (ICAM-1) promoters, we used PDTC to study the regulatory mechanisms of VCAM-1 and ICAM-1 induction and subsequent monocyte adhesion in TNF-treated human umbilical vein endothelial cells (HUVECs). PDTC or N-acetylcysteine dose dependently reduced TNF-induced VCAM-1 but not ICAM-1 surface protein (also in human umbilical arterial endothelial cells) and mRNA expression (by 70% at 100 mumol/L PDTC) in HUVECs as assessed by flow cytometry and polymerase chain reaction. Gel-shift analysis in HUVECs demonstrated that PDTC prevented NF-kappa B mobilization by TNF, suggesting that only VCAM-1 induction was controlled by NF-kappa B. Since HUVECs released superoxide anions in response to TNF, and H2O2 induces VCAM-1, PDTC may act as a radical scavenger. Although ICAM-1 induction was unaffected, inhibitors of NADPH oxidase (apocynin) or cytochrome P-450 (SKF525a) suppressed VCAM-1 induction by TNF, revealing that several radical-generating systems are involved in its regulation. PDTC, apocynin, or SKF525a decreased adhesion of monocytic U937 cells to TNF-treated HUVECs (by 75% at 100 mumol/L PDTC). Inhibition by anti-VCAM-1 monoclonal antibody 1G11 indicated that U937 adhesion was VCAM-1 dependent and suppression by antioxidants was due to reduced VCAM-1 induction.(ABSTRACT TRUNCATED AT 250 WORDS)

Due to the great length of apolipoprotein (apo) B-100, the localization of lipid-associating domains in this protein has been difficult. To address this question, we developed a computer program called Locate that searches amino acid sequences to identify potential amphipathic alpha-helixes and beta-strands by using sets of rules for helix and strand termination. A series of model chimeric protein test datasets were created by tandem linking of amino acid sequences of multiple proteins containing four different secondary structural motifs: motif A (exchangeable plasma apolipoproteins); motif G (globular alpha-helical proteins); motif C (coiled-coil alpha-helical proteins); and motif B (beta pleated-sheet proteins). These four test datasets, as well as randomly scrambled sequences of each dataset, were analyzed by Locate using increasingly stringent parameters. Using intermediately stringent parameters under which significant numbers of amphipathic helixes were found only in the unscrambled motif A, two dense clusters of putative lipid-associating amphipathic helixes were located precisely in the middle and at the C-terminal end of apoB-100 (a sparse cluster of class G* helixes is located at the N-terminus). The dense clusters are located between residues 2103 through 2560 and 4061 through 4338 and have densities of 2.4 and 2.2 amphipathic helixes per 100 residues, respectively; under these conditions, motif A has a density of 1.4 amphipathic helixes per 100 residues. These two domains correspond closely to the two major apoB-100 lipid-associated domains at residues 2100 through 2700 and 4100 through 4500 using the principle of releasability of tryptic peptides from trypsin-treated intact low-density lipoprotein. The classes of amphipathic helixes identified within these two putative lipid-associating domains are considerably more diverse than those found in the exchangeable plasma apolipoproteins. Interestingly, apoB-48 terminates at the N-terminal edge of the middle cluster. By using a similar strategy for analysis of amphipathic beta-strands, we discovered that the two gap regions between the three amphipathic helix clusters are highly enriched in putative amphipathic beta-strands, while the three amphipathic helical domains are essentially devoid of this putative lipid-associating motif. We propose, therefore, that apoB-100 has a pentapartite structure, NH2-alpha 1-beta 1-alpha 2-beta 2-alpha 3-COOH, with alpha 1 representing a globular domain.

The mechanism by which granulocyte-macrophage colony-stimulating factor (GM-CSF) lowers plasma cholesterol levels is not well understood. We tested recombinant human GM-CSF (rhGM-CSF) on plasma cholesterol and triglycerides in rabbits and attempted to determine the mechanisms of the cholesterol-lowering effect. rhGM-CSF (20 micrograms.kg-1.d-1) was administered to normal and cholesterol-fed rabbits for 2 weeks and to Watanabe heritable hyperlipidemic (WHHL) rabbits for 1 week. The administration of rhGM-CSF markedly lowered cholesterol and triglycerides, an effect that persisted in normal and cholesterol-fed rabbits even after termination of treatment. The cholesterol-lowering effect of rhGM-CSF was also observed in WHHL rabbits. rhGM-CSF was capable of stimulating granulocyte-macrophage colony formation in vitro in rabbits with an effect comparable to that in humans. Northern blot analysis with rabbit very-low-density-lipoprotein (VLDL) receptor cDNA revealed that rhGM-CSF increased the levels of VLDL receptor mRNA in muscle of rabbits after only 1.5 hours of treatment compared with control (2.6-fold), with the 1.5-fold increase following a 5-day administration. No changes in the levels of LDL receptor mRNA in liver, spleen, and bone marrow were observed in the treated rabbits. These findings suggest that the cholesterol-lowering effect of rhGM-CSF may be mediated by enhancement of macrophage functions in lipid metabolism and the increase in mRNA for VLDL receptor in rabbits.