Jk. Bielicki et al., COPPER AND GAS-PHASE CIGARETTE-SMOKE INHIBIT PLASMA LECITHIN-CHOLESTEROL ACYLTRANSFERASE ACTIVITY BY DIFFERENT MECHANISMS, Journal of lipid research, 36(2), 1995, pp. 322-331
Cigarette smokers have reduced levels of plasma high density lipoprote
in (HDL) compared to nonsmokers and are at risk of premature cardiovas
cular disease. Previous work from this laboratory has shown that expos
ure of human plasma to gas phase cigarette smoke (CS) inhibited the ac
tivity of lecithin:cholesterol acyltransferase (LCAT), the enzyme that
catalyzes the formation of cholesteryl ester in HDL and thereby promo
tes HDL maturation. As CS contains free radicals that could potentiall
y oxidize plasma lipoproteins, we examined the involvement of lipid pe
roxidation in LCAT inhibition. Results obtained with CS were compared
with those obtained by initiating lipid peroxidation with copper ions.
Exposure of dialyzed human plasma to an equivalent of one-eighth of a
cigarette at 15-min intervals resulted in a progressive loss of LCAT
activity (50 and 90% reductions by 1 and 6 h, respectively). A similar
pattern of LCAT inhibition was produced with copper (0.5 mM) where 50
and 97% reductions were observed at 1 and 6 h, respectively. To deter
mine whether LCAT inhibition was related to lipid peroxidation, lipopr
otein fractions corresponding to VLDL-IDL, LDL, and HDL were isolated
from plasma exposed to CS or copper and analyzed for changes in TBARS,
the polyunsatu rated fatty acid arachidonate relative to palmitate (2
0:4/16:0 ratio), and vitamin E concentrations. Exposure of plasma for
6 h to CS had no effect on the levels of TBARS and 20:4/16:0 ratio; ho
wever, 6 h copper treatment (0.5 mM) caused a 3.0-, 4.0-, and 1.4-fold
increase in TBARS and a 17, 25, and 13% reduction in the 20:4/16:0 ra
tio in VLDL-IDL, LDL, and HDL fractions, respectively. In addition, a
complete depletion of lipoprotein vitamin E was observed with CS, wher
eas copper decreased vitamin E levels by approximately 50% in each fra
ction. Supplementation of plasma with either vitamin C (85 mu M) or bu
tylated hydroxytoluene (BHT, 0.45 mM) was unable to protect LCAT from
CS. In contrast, BHT completely protected LCAT activity from inhibitio
n by copper. We conclude that unlike copper, CS-induced inhibition of
plasma LCAT activity was unrelated to free radical-induced lipid perox
idation. The inhibition of LCAT activity by cigarette smoke may contri
bute to the development of atherosclerosis by impairing HDL metabolism
and the reverse cholesterol transport process.,