Gas-phase cigarette smoke inhibits plasma lecithin-cholesterol acyltransferase activity by modification of the enzyme's free thiols

• Published in: Biochimica et biophysica acta Vol. 1258; no. 1; pp. 35 - 40
• Main Authors: Bielicki, John K., Forte, Trudy M., McCall, Mark R.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 24.08.1995
• Subjects: Acetylcysteine - pharmacology; Binding Sites; Cross-Linking Reagents; Dithionitrobenzoic Acid - pharmacology; Gas-phase cigarette smoke; Glutathione - pharmacology; Humans; Lecithin-cholesterol acyltransferase; Lipoproteins, HDL - blood; Nicotiana; Phosphatidylcholine-Sterol O-Acyltransferase - antagonists & inhibitors; Phosphatidylcholine-Sterol O-Acyltransferase - blood; Phosphatidylcholine-Sterol O-Acyltransferase - chemistry; Plants, Toxic; Reverse cholesterol transport; Smoke; Smoking - adverse effects; Sulfhydryl Compounds - chemistry; Lecithin-cholesterol acyltransferase; CS; GSSG; DTNB; Reverse cholesterol transport; LCAT; Gas-phase cigarette smoke; GSH
• ISSN: 0005-2760; 0006-3002; 1879-145X
• DOI: 10.1016/0005-2760(95)00092-Q

Cigarette smoking is associated with an increased risk of premature atherosclerosis. The underlying mechanisms responsible for this association are unknown. Recent work from this laboratory has shown that ex vivo exposure of plasma to gas-phase cigarette smoke (CS) produces a rapid inhibition of lecithin-cholesterol acyltransferase (LCAT) activity and crosslinking of HDL-apolipoproteins. The goal of the present study was to investigate the mechanism(s) by which CS inhibited LCAT and modified HDL. When dialyzed human plasma (12 ml) was exposed to the gas-phase of an equivalent of l 8 of a cigarette (one ‘puff’) at 15 min intervals for 3 h, LCAT activity was reduced by 76 ± 1% compared to controls; supplementation of plasma with glutathione produced a dose-dependent protection of LCAT activity where at the highest concentration (l mM) 78% protection was observed. A similar protection was obtained with N-acetyl cysteine (l mM). In addition to LCAT inhibition, HDL-apolipoproteins were crosslinked after 3 h exposure of plasma to CS; crosslinking was reduced by the addition of either glutathione or N-acetyl cysteine to plasma. The amino compounds N-acetyl lysine, N-acetyl arginine, and aminoguanidine failed to protect LCAT and HDL indicating a specificity with regard to the ability of free thiols to buffer the deleterious components of CS which inhibited LCAT and crosslinked HDL-apolipoproteins. Since LCAT contains two free cysteine residues (Cys-31 and -184) near the active site of the enzyme, we tested whether pretreatment of plasma with the reversible sulfhydryl modifying compound, 5,5′-dithiobis-2-nitrobenzoic acid (DTNB), could protect LCAT from CS-induced inhibition. Plasma pretreated with DTNB prior to CS exposure retained an additional 50% of LCAT activity compared to CS treatment in the absence of DTNB. These results indicate that covalent modification of free cysteine residues of LCAT was, in part, responsible for the inhibition of plasma LCAT activity by CS.