This study investigated the effects of copper-zinc type superoxide dismutase (Cu-Zn·SOD) on the oxidation of low density lipoprotein (LDL), using cultured vascular smooth muscle cells (SMC) and endothelial cells (EC). In this study, we produced endothelial cell-induced oxidized LDL (EC-OxLDL) and minimally oxidized LDL (MmLDL). And we investigated 1) the effect of EC-OxLDL on SMC, 2) the effect of MmLDL on EC and 3) effect of Cu-Zn·SOD on both EC-OxLDL and MmLDL. The value of LDL oxidation was expressed as the equivalent of thiobarbituric acid-like substance (TBARS) production.
EC-OxLDL induced the SMC proliferation and migration, greater than the reactions by MmLDL. MmLDL evoked EC injury, characterized by EC number reduction along with vascular cell adhesion molecule-1 (VCAM-1) expression. Cu-Zn·SOD inhibited TBARS production by endothelium-derived oxidation. Cu-Zn·SOD suppressed the reactions caused by both EC-OxLDL and MmLDL, except for the induction of VCAM-1 expression on EC by MmLDL. We concluded superoxide was involved the biochemical reaction caused by endothelial cell-derived LDL oxidation and minimally oxidation of LDL. Cu-Zn·SOD exhibited the possibility of anti-atherosclerotic material due to inhibition of oxidized LDL.

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Acyl-coenzyme A: cholesterol acyltransferase (ACAT), an integral membrane protein located in the endoplasmic reticulum, catalyzes the intracellular formation of cholesteryl esters (CE) from cholesterol and long-chain fatty acyl-coenzyme A. Pathologically, this enzyme is expected to play an important role in foam cell formation in atherosclerotic lesions. Cytoplasmic CE accumulated in foam cells undergo a continual shuttle between hydrolysis to free cholesterol by neutral cholesteryl ester hydrase and re-esterification to CE by ACAT. This CE turnover is known as CE cycle. Since the turnover rate of CE cycle serves as a regulatory step of high density lipoprotein (HDL)-induced cholesterol efflux from cells, the molecular mechanism for the regulation of ACAT activityis to be elucidated.
To clarify the ACAT regulatory mechanism during foam cell formation, we first cloned rat ACAT cDNA and examined effects of acetylated low density lipoprotein (acetyl-LDL) on ACAT in rat peritoneal macrophages. Rat ACAT cDNA consisted of an open reading frame of 1, 635 bp with its deduced protein sequence of 545 amino acids. When resident peritoneal macrophages were incubated with 50μg/ml of acetyl-LDL for 16 hours (CE accumulation at this stage was 35nmol/mg cell protein), the ACAT activity of these cell homogenate was increased 7-fold when determined by the reconstituted assay using cholesterol/phosphatidylcholine liposomes. The ACAT protein of these cell homogenates determined by Western blot with an anti-ACAT antibody (DM10) was also increased 4-fold above control. However, a corresponding increase in their mRNA level determined by Northern blot using rat ACAT cDNA (300-1, 300 of its open reading frame) as a probe was relatively low (1-2-folds). These results suggest that ACAT activation by acetyl-LDL occurs not only at a transcriptional level but also at a posttranscriptional level.

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Preβ-high-density lipoprotein (HDL) is a minor HDL subfraction with a preβ-electrophoretic mobility. Preβ1-HDL, the smallest preβ-HDL, is the initial acceptor of cell-derived free cholesterol (FC). FC on preβ1-HDL is immediately transferred to preβ2-HDL, and then esterified on preβ3-HDL, the biggest preβ3-HDL, by lecithin: cholesterol acyltransferase (LCAT). Preβ1-HDL decreased during 37°C-incubation by the action of LCAT, but this decrease is completely blocked by a LCAT inhibitor, or anti-human LCAT antibodies. This decrease in preβ1-HDL is also blocked when plasma was incubated with fibroblasts, smooth muscle cells, or macrophages but not with red blood cells.
We recently demonstrated that preβ1-HDL levels increase in coronary artery disease, hypercholesterolemia, and hypertriglyceridemia. Preβ1-HDL levels are also affected by lipid-lowering agents. The relative concentration of preβ1-HDL is normal in CETP deficiency, but the decreasing rate of preβ1-HDL during 37°C-incubation is significantly slower in CETP deficiency than in normal controls. Preβ-HDL/LpA-I ratio is not constant in various disorders, although preβ1-HDL belongs to LpA-I. In summary, preβ-HDL plays an important role in the metabolism of cell-derived cholesterol, and its plasma level changes in various disorders. More study is needed to elucidate the clinical significance of plasma preβ-HDL levels.

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Glucocorticoid-induced alterations of blood lipoprotein metabolism were analyzed in patients with various collagen diseases. Serum triglyceride concentration was rapidly and transiently increased by prednisolone treatment; it reached the maximal level after 2 weeks, and then gradually decreased to the initial level. On the other hand, serum total cholesterol concentration was slowly increased to the maximal level by 8 weeks and, thereafter, remained constant. Mathematical analysis has revealed that the average prednisolone-induced increase was about 2.5mg/dl/mg prednisolone for both serum total cholesterol and triglyceride levels. Ultracentrifugation analysis showed that not only low density but also very low density and high density lipoproteins were increased by prednisolone treatment. In a female patient with angina pectoris and xanthelasma, probucol treatment effectively normalyzed her glucocorticoid-induced hypercholesterolemia and, furthermore, the effective lowering of serum cholesterol level was also followed by successful cessation of angina attack and healing of xanthelasma. The data suggest the possible importance of glucocorticoid-induced hyperlipidemia in the development of atherosclerosis.

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