Relative sensitivities of plasma lecithin : cholesterol acyltransferase, platelet-activating factor acetylhydrolase, and paraoxonase to in vitro gas-phase cigarette smoke exposure

Citation
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
Journal title
ATHEROSCLEROSIS
ISSN journal
00219150 → ACNP
Volume
155
Issue
1
Year of publication
2001
Pages
71 - 78
Database
ISI
SICI code
0021-9150(200103)155:1<71:RSOPL:>2.0.ZU;2-J
Abstract
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.