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High serum low density lipoprotein (LDL) level is known injurious to endothelial cell (EC) and that high density lipoprotein (HDL) protects EC from such injury. The protective effect of HDL and apolipoprotein C1 (apo C1) on the endothelial cells (EC) isolated originally from human umbilical vein and injured by LDL was studied morphologically with phase-contrast and transmission electron microscope. Additionally, their functional changes were detected by measuring the amount of lactate dehydrogenase (LDH) and 6-keto-prostaglandin F1 alpha (PGF1 alpha) released. The EC were divided into four groups: control, HDL+LDL, apo C1 + IDL and LDL group. EC after being injured by LDL showed cell contraction, increased release of LDH and decreased secretion of PGF1. Anyhow, they would be left normal on morphology, LDH release and PGF1 alpha synthesis if HDL or apo C1 had been added to the culture media before LDL injury. The results indicated that both HDL and apo C1 can resist the injurious effect of LDL on the cultured EC.

Effects of purified human apolipoproteins AI, CI, CII, CIII-1, Cs and E on the binding of 125I-labeled apo E-deficient HDL3 to isolated rat liver plasma membranes were investigated. Unlabeled apo AI, CI, CII, CIII-1 and apo Cs, but not apo E, could effectively inhibit 125I-labeled HDL3 binding to liver membranes, apoCIII-1, was the strongest among the apoC subclasses and the inhibition curve of apoCIII-1 was similar to that of apo AI. This result indicates that apo C, especially apo CIII, may be another specific ligand of HDL receptor, and it plays an important role in regulation of HDL receptor activity in liver.

Serum triglycerides, cholesterol, HDL-cholesterol and apolipoproteins (apo) AI, B100. CI and CII were determined and analyzed in 72 apoplectic patients and 64 age-matched normal subjects. Significantly increased triglycerides, low HDL-C and slightly decreased cholesterol levels were found in the apoplectics. Apo AI was slightly decreased and apo B100 slightly increased in the apoplectics compared with normal subjects. Apo CI and CII levels were significantly decreased in the apoplectics. The results are discussed.

Serum triglycerides (TG), cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and apolipoproteins AI, B100, CI, CII and CIII were analyzed in 142 patients with coronary heart disease (CHD) and 64 age-matched healthy subjects in the Chengdu area. Significantly increased TG and decreased HDL-C were found in the CHD patients (P less than 0.001). Serum apo AI and CII were significantly decreased in the CHD patients compared with the normal subjects (P less than 0.01 or P less than 0.001). Serum apo B100 and CIII were slightly higher in the CHD group than in the normal group (P less than 0.001 or P less than 0.05). No significant differences were observed in apo CI levels in the CHD patients when compared with the normal subjects. The results were discussed.