Aim: To evaluate the potential of S-nitroso-N-acetyl-cysteine (SNAC) in inhibition of lipid peroxidation and the effect of oral SNAC administration in the prevention of nonalcoholic fatty liver disease (NAFLD) in an animal model. Methods: NAFLD was induced in Wistar male r ats by choline-deficient diet for 4 wk. SNAC-treated animals (n=6) (1.4 mg/kg/day of SNAC, orally) were compared to 2 control groups: one (n=6) received PBS solution and the other (n=6) received NAC solution (7 mg/kg/d). Histological variables were semiquantitated with respect to macro and microvacuolar fat changes, its zonal distribution, foci of necrosis, portal and perivenular fibrosis, and inflammatory infiltrate with zonal distribution. LOOHs from samples of liver homogenates were quantified by HPLC. Nitrate levels in plasma of portal vein were assessed by chemiluminescence. Aqueous low-density lipoprotein (LDL) suspensions (200 μg protein/mL) were incubated with CUCl2 (300 μmol/L) in the absence and presence of SNAC (300 μmol/L) for 15 h at 37 °C. Extent of LDL oxidation was assessed by fluorimetry. Linoleic acid (LA) (18.8 μmol/L) oxidation was induced by soybean lipoxygenase (SLO) (0.056 μmol/L at 37 °C in the presence and absence of N-acetylcysteine (NAQ and SNAC (56 and 560 μmol/L) and monitored at 234 nm. Results: Animals in the control group developed moderate macro and microvesicular fatty changes in periportal area. SNAC-treated animals displayed only discrete histological alterations with absence of fatty changes and did not develop liver steatosis. The absence of NAFLD in the SNAC-treated group was positively correlated with a decrease in the concentration of LOOH in liver homogenate, compared to the control group (0.7±0.2 nmol/mg vs 3.2±0.4 nmol/mg protein, respectively, P<0.05), while serum levels of aminotransferases were unaltered. The ability of SNAC in preventing lipid peroxidation was confirmed in in vitro experiments using LA and LDL as model substrates. Conclusion: Oral admi nistration of SNAC prevents the onset of NAFLD in Wistar rats fed with choline-deficient diet. This effect is correlated with the ability of SNAC to block the propagation of lipid peroxidation in vitro and in vitro. © 2006 The WJG Press. 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