Relative sensitivities of plasma lecithin : cholesterol acyltransferase, platelet-activating factor acetylhydrolase, and paraoxonase to in vitro gas-phase cigarette smoke exposure
Jk. Bielicki et al., Relative sensitivities of plasma lecithin : cholesterol acyltransferase, platelet-activating factor acetylhydrolase, and paraoxonase to in vitro gas-phase cigarette smoke exposure, ATHEROSCLER, 155(1), 2001, pp. 71-78
Citations number
32
Categorie Soggetti
Cardiovascular & Respiratory Systems","Cardiovascular & Hematology Research
In order to identify potential atherogenic properties of gas-phase cigarett
e smoke, we utilized an in vitro exposure model to determine whether the ac
tivities of several putative anti-atherogenic enzymes associated with plasm
a lipoproteins were compromised. Exposure of heparinized human plasma to ga
s-phase cigarette smoke produced a dose-dependent reduction in the activity
of platelet-activating factor acetylhydrolase (PAF-AH). Reductions of near
ly 50% in PAF-AH activity were observed following exposure to gas-phase smo
ke from four cigarettes over an 8-h period. During this time of exposure, l
ecithin:cholesterol acyltransferase (LCAT) was rendered almost completely i
nactive (> 80%). In contrast, paraoxonase was totally unaffected by cigaret
te smoke. Supplementation of plasma with 1 mM reduced glutathione was found
to protect both PAF-AH and LCAT from cigarette smoke, suggesting that cyst
eine modifications may have contributed to the inhibition of these two enzy
mes. To evaluate this possibility, we blocked the free cysteine residues of
these enzymes with the reversible thiol-modifying reagent dithiobisnitrobe
nzoic acid (DTNB). Reversal of the DTNB-cysteine adducts following cigarett
e smoke exposures revealed that LCAT, but not PAF-AH, was protected. Moreov
er, high doses (1.0-10 mM) of acrolein and 4-hydroxynonenal, reactive aldeh
ydic species associated with cigarette smoke, completely inhibited plasma L
CAT activity, whereas PAF-AH was resistant to such exposures. Taken togethe
r, these results indicate a divergence regarding the underlying mechanism o
f PAF-AH and LCAT inhibition upon exposure to gas-phase cigarette smoke. Wh
ile LCAT was sensitive to exposure to volatile aldehydic products involving
, in part, cysteine and/or active site modifications, the enzyme PAF-AH exh
ibited an apparent resistance. The latter suggests that the active site of
PAF-AH is in a microenvironment that lacks free cysteine residues and/or is
shielded from volatile aldehydic combustion products. Based on these resul
ts, we propose that cigarette smoke may contribute to atherogenesis by inhi
biting the activities of plasma PAF-AH and LCAT, but the nature of this inh
ibition differs for the enzymes. (C) 2001 Elsevier Science Ireland Ltd. All
rights reserved.