Inhibition of lecithin:cholesterol acyltransferase by lipid peroxidation products
详细信息 查看全文
文摘
The oxidation of lipoproteins has been implicated in the inhibition of lecithin-cholesterol acyl-transferase (LCAT) activity. However, the oxidation products which inhibit LCAT and are recovered within the polar lipid fraction, have not been well identified (Bielicki et al., JLR, 1996). In an attempt to gain insight into the nature of the LCAT-inhibitory factor(s), isolated LDL and HDL were oxidized with lipoxygenase treatment and were, in a first experience, separately incubated with a LCAT-containing d > 1.210 g/ml fraction of plasma. The LCAT activity was measured on the d > 1.210 g/ml fraction after separation from LDL and HDL by using exogenous substrate. After incubation with oxidized LDL and HDL, we observed respectively 70 % and 30 % reduction of LCAT activity compared to unoxidized lipoproteins. In a second experiment, the lipid oxidation products from oxidized lipoproteins were separated using an high performance liquid chromatography (HPLC) procedure. Four fractions from phospholipids were collected and identified using UV and chemiluminescence detections: fraction 1 corresponds to fatty acid hydroperoxide, fraction 2 to short chain oxidized PC, fraction 3 to hydroperoxides from phosphatidylcholine (PC) 16:0/22:6 or 20:4 or 18:2 molecular species and fraction 4 to hydroperoxides from PC 18:0/22:6 or 20:4 or 18:2 molecular species. Cholesterol extract gave rise to 2 fractions (fraction 1: oxidized cholesterol, fraction 2: hydroperoxide from cholesterol ester). Each fraction was incubated with a d > 1.210 g/ml fraction and LCAT activity was assessed. Neither the fractions obtained from cholesterol extracts, nor fractions 1 and 2 from PL extracts, produced reduction of LCAT activity. Fractions 3 from oxidized HDL and LDL produced respectively 47 % and 52 % reduction of LCAT activity and fractions 4 from oxidized HDL and LDL produced respectively 29 % and 36 % reduction of LCAT activity. The lowest reduction of LCAT activity obtained by this latter fraction may be due to the lowest concentration of PC hydroperoxides produced from PC 18:0 molecular species.