Previous evidence suggests that the content of polyphenols in alcoholic beverages are responsible for their beneficial effects in cardiovascular diseases such as atherosclerosis (1) characrterised by increased oxidative stress (2). The aim of the present study was to examine the effects of wine polyphenols on the production reactive oxygen radicals and the expression of antioxidant enzymes in vascular tissue in atherosclerosis. ApoE-deficient mice, that spontaneously develop atherosclerosis were fed a control diet or diets containing dealcoholized white (DWW) or red wine (DRW) (25 ml wine/ kg body weight/day) for 12 and 20 weeks. Other groups of mice received L-NAME (50 mg/kg body weight/day) in their diet for 20 weeks. At the end of the treatment mice were anesthetized with 150 mg/kg ketamin: 10 mg/kg xilacin and thoracic aorta was opened lenghtwise to atherome plaque quantification. Expression of endothelial (eNOS) and inducible (iNOS) nitric oxide synthases and p22phox (subunit of the NADPH oxidase) were then probed in the aortic root sections by immunofluorescence. Generation of superoxide anion (O2.-) in thoracic aorta rings was determined by lucigenin chemiluminiscence and nitrotyrosine compounds by immunofluorescence in aortic root. Furthermore, human umbilical vein endothelial cells (HUVEC) were incubated with 1% and 3% DWW or DRW for 4, 8 and 12 h, and expression of the antioxidant enzymes heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase 1 (NQO1) determined by immunoblotting. A decreased formation of lesions was detected after 20 weeks dietary treatment with wine polyphenols (23 and 62%, n=8 for DWW and DRW, respectively), yet this was prevented in mice treated with L-NAME. Although expression of eNOS, iNOS and p22phox were not changed, the production of O2.- was increased in groups treated with DWW and DRW for 12 weeks (83 ± 10, 122 ± 10 and 125 ± 18 light units/mg protein/min for control, DWW- and DRW-treated mice, respectively, n=8, S.E.). The presence of nitrotyrosine compounds in aortic tissue was decreased in mice treated with DRW for 20 weeks (76%, n=6). HO-1 expression was increased in HUVEC incubated with 1% and 3% DRW for 8 h (197 and 684% for 1% and 3% DRW, respectively, n=3). The present findings suggest that physiological levels of endogenous NO and O2.- production may be involved in the protection afforded by wine polyphenols against the progression of atherosclerosis via their ability to upregulate expression of the antioxidant enzyme HO-1.