The Role of Plasma Proteins in Low Density Lipoprotein

• Main Authors: Tsai-Mu Cheng, 鄭財木
• Other Authors: An-Na Chiang
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/08108713286533442723

碩士 === 國立陽明大學 === 生物化學研究所 === 87 === Abstract Lipoproteins and apolipoproteins are known to play a central role in lipid transport and metabolism. Abnormal changes in plasma lipid and lipoprotein levels are usually the intervening variables predisposing to atherosclerosis. Numerous studies have shown that oxidized lipids and proteins, as well as oxidatively modified low-density lipoprotein (LDL), are potentially atherogenic. The objectives of the present studies were to determine the association between lipid and apolipoprotein levels in subjects with dyslipoproteinemia, and to determine the biochemical nature of the adduct formed during LDL oxidation.The results showed that abnormal lipoprotein metabolism interfered with most of the levels of plasma lipids and apolipoproteins. As compared with control groups, subjects with hypoalphalipoproteinemia had higher levels of total cholesterol (TC), LDL-cholesterol (LDL-C), triglyceride (TG) and apoB-100 but lower levels of apoA-I, A-II and E. Subjects with hyperbetalipoproteinemia had higher levels of TC, TG and apoB-100 but lower levels of high density lipoprotein (HDL)-cholesterol (HDL-C) and apoE. Hypertriglyceridemia group had higher levels of TC, LDL-C and apoB-100 but lower levels of HDL-C and apoA-I.A 14.4 kDa protein of hemoglobin (Hb) subunit was differentially expressed in a lot of subjects with dyslipoproteinemia. The increased expression of plasma 14.4 kDa protein seemed to be associated with elevated plasma levels of TC, LDL-C, TG and apoB-100 and decreased levels of HDL-C and apoA-I. The results suggest that beside apolipoproteins, hemoglobin may also intervene lipid and lipoprotein metabolism. However, the effect of these plasma proteins on LDL oxidation was unclear. Another aim of this study is therefore to assess the roles of apolipoproteins (apoA-I, AII, B, E3, E4 and H) and plasma proteins (Hb and haptoglobin) in the oxidative modification of LDL.Upon incubation of LDL with various concentrations of apolipoproteins, Hb and haptoglobin (Hp) in the presence of 5uM CuSO4, changes in Cu2+ or Hb-mediated LDL oxidation were demonstrated by monitoring conjugated diene formation at OD234nm. Pretreatment of LDL with apoA-I, apoH or Hp inhibited Cu2+-mediated LDL oxidation in a concentration-dependent manner. However, apoE4 resulted in the induction Cu2+-mediated LDL oxidation. Results from the analyses of Western blotting and immunoprecipitation indicated that LDL oxidation was accompanied by the formation of apoB fragmentation and protein-protein interaction adduct. ApoB, the major protein of LDL, seemed to be degraded and modified by apoA-I, AII, E and H protein residues during Cu2+-mediated LDL oxidation.The present studies provide preliminary characterization of protein products that can react with LDL during LDL oxidation. Complete purification and analyses of these protein adduct should lead to a fuller understanding of the physiologic role of these protein-protein interactions.