ENHANCED MODIFICATIONS OF LOW-DENSITY LIPOPROTEINS (LDL) BY ENDOTHELIAL-CELLS FROM SMOKERS - A POSSIBLE MECHANISM OF SMOKING-RELATED ATHEROSCLEROSIS

Objective: The aim of the study was to investigate LDL modifications b y cultured human umbilical vein endothelial cells (HUVEC) from women s mokers and non-smokers, Methods: Modifications of LDL by HUVEC were st udied by determining the values of thiobarbituric acid-reactive substa nces (TEARS) and the percentage of the most electronegative oxidized L DL fraction (fraction C) by using an ion-exchange chromatographic meth od based on fast protein liquid chromatography (FPLC), We also studied the cellular production of superoxide anion, the effect of various in hibitors and cysteine, and determined total intracellular glutathione content and cell growth. Results: LDL exposed to HUVEC from smokers fo r 48 h showed significantly greater modifications than LDL exposed to HUVEC from non-smokers, as assessed by TEARS determination (19.4+/-1.2 , mean+/-s.e.m., n=20 versus 15.4+/-0.7 nmol/mg LDL, n=19; P<0.01) and by FPLC (percentage of fraction C: 39+/-7, n=29 versus 14+/-3, n=34; P<0.001), Moreover, HUVEC from smokers produced significantly more sup eroxide anion than those from non-smokers (0.46+/-0.13 nmol/10(5) cell /min, n=9 versus 0.22+/-0.05, n=10; P<0.05). Superoxide production, li ke cell-induced modification of LDL, was strongly dependent on the pre sence of cysteine in the medium. Furthermore, HUVEC from smokers had a significantly (P<0.05) higher total intracellular glutathione content than those from non-smokers (39.9+/-3.1 nmol/mg, n=9 versus 31.8+/-2. 2, n=7), Finally, HUVEC from smokers and non-smokers showed similar gr owth at 48 h, Conclusion: HUVEC from smokers converted significantly m ore LDL into an atherogenic form than HUVEC from non-smokers, a phenom enon that was not due to altered cell growth, HUVEC-mediated LDL modif ications were strongly thiol-dependent, as both LDL modifications and superoxide anion production were inhibited in cysteine-free medium, St imulation of cystine uptake by HUVEC, reflected by the enhanced total glutathione content, could account for the enhanced superoxide anion p roduction. All these observations may be relevant to the pathophysiolo gy of smoking-related cardiovascular disease.