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Methionine is converted by the transmethylation/transsulfuration pathway to homocysteine which may exert atherogenic effects by several mechanisms, including lipid peroxidation. Therefore, the excessive dietary methionine may induce the development of atherosclerosis. To test this hypothesis, plasma and aortic thiobarbituric acid reactive substances (TBARS), as well as activities of aortic and erythrocyte superoxide dismutase (SOD), catalase and selenium-dependent glutathione peroxidase (GPX) were measured in rabbits fed a diet enriched with 0.3% methionine for 6 or 9 months. Histological examinations of aortas also were performed. Feeding rabbits a methionine-enriched diet for 6 or 9 months resulted in significant increases in plasma and aortic TBARS levels and aortic antioxidant enzyme activities. However, a decrease in plasma antioxidant activity (AOA) was observed. In erythrocytes, SOD activity increased, catalase remained normal and GPX decreased in the treated animals. Histological examination of aortas showed typical atherosclerotic changes, such as intimal thickening, deposition of cholesterol, and calcification in methionine-fed rabbits. These results confirm that high-methionine diet may induce atherosclerosis in rabbits and indicate disturbances in lipid peroxidation and antioxidant processes as possible mechanisms of its atherogenic influence.

Markers of elastin metabolism were estimated in sera of children from families with a high risk of atherosclerosis (ATH). There was no statistically significant difference in the serum elastase-like activity between the groups studied. The concentration of elastin-derived peptides was statistically significantly elevated in the ATH group. Anti-elastin antibodies were found to be present in 73% of ATH children, while they circulated in 5% of control subjects only. Antibodies observed in the youngest ATH children were of the IgM type, suggesting the initial stage of the autoimmunization to elastin. The data obtained in this study may indicate an enhanced metabolism of elastin in ATH children.

Anti-elastin antibodies which seem to play an important role in atherogenesis were studied in serum of rabbits fed with a cholesterol-rich diet using the dot-immunobinding assay. These antibodies appeared only in rabbits of the experimental group after the sixth week of the experiment and a progressive rise in their titer was observed. The concentration of total serum cholesterol and the elastase-like activity in aorta which were determined additionally showed a statistically significant increase of both analyzed parameters in animals from the experimental group when compared to the controls. Anti-elastin antibodies seem to reflect an increased elastin turnover during the induction of experimental atherosclerosis.

Immunological factors seem to play an important role in the pathogenesis of atherosclerosis, which is a multifactorial chronic disease. It was demonstrated on animals that antibodies, immune complexes and cells may be the reason why the immunological damage in the vascular wall appears and may lead in consequence to the development of atherosclerotic changes. Immunological mechanisms of atherosclerosis are discussed.

Proteoglycans (PG) from normal and atherosclerotic rabbits aortas were extracted with 4 M guanidine hydrochloride and digested with collagenase in the presence of protease inhibitors. The contents of uronic acid and hexosamine from PG fractions purified by isopycnic CsCl gradient ultracentrifugation under associative and dissociative conditions were significantly higher in the atherosclerotic aortas (up to 40%) than in the control tissue. The uronic acid/protein ratio increased from 0.7 to 1.3 in the monomers PG fraction of atherosclerotic aortas. Chromatographic separation and electrophoretic analysis of PG monomers indicated the presence of three different subfractions PGI, PGII and PGIII in both groups of animals. The uronic acid/protein ratio in PGI from experimental aorta was increased whereas this ratio in PGIII was decreased compared to contrast tissue. The observed increase of sugar component in the core proteins suggests their over glycosylation.

In rabbits with experimental atherosclerosis induced by a cholesterol-rich diet, alpha 1-antitrypsin concentration was decreased as compared with control, by 34%, whereas alpha 2-macroglobulin concentration was increased by 86%. In animals fed a methionine-rich diet changes in concentration of both inhibitors involved in elastase metabolism were but slight, if any.