Abstract: Objective To investigate the effects and mechanism of plasma cysteine/cystine redox potential (Eh Cys/CySS) on hepatic steatosis in mice with NAFLD. Methods 64 ICR mice were randomly divided into 4 groups with 16 mice in each group, respectively the control, model, NAC-L and NAC-H group. The mice in the control group were fed with a normal chow diet while in the model group, the NAC-L group, and the NAC-H group were fed with a high-fat diet. The mice in the NAC-L and NAC-H groups received NAC daily by oral gavage at doses of 100 mg/kg and 300 mg/kg, respectively. After 10 weeks, body weight change, liver weight and hepatic histopathological examination by oil red O staining were observed. The level of alanine aminotransferase (ALT) , aspartate aminotransferase (AST), triglyceride (TG) and total cholesterol (TC) in serum were measured by biochemical method. The levels of the oxidative product malondialdehyde (MDA) and the antioxidant substances superoxide dismutase (SOD) and glutathione (GSH) in liver tissue homogenate were measured by biochemical method. The plasma levels of cysteine (Cys) and cystine (CySS) were analyzed and calculated using the Nernst equation. The level of SREBP1 and PPARα protein were tested by western blot analysis. Results The NAFLD mice model was successfully established. Compared with control group, the model group mice showed significant increases in body weight change, liver weight, and liver index [(8.49(7.36,11.19) g/10w vs. 15.2(14.52,17.95) g/10w, (1.33±0.05) g vs. (1.69±0.06) g, (4.20±0.30) % vs. (4.42±0.33) %](all P<0.05). The liver lobes in model group appeared paler and greasier, liver sections stained with oil red O showed a marked increase in red lipid droplets. Compared with control group, levels of ALT, AST, TG and TC were significantly elevated (P<0.01 for all); the increase in MDA and the decrease in SOD and GSH were significant (P<0.01 for all); expression of SREBP1 was significantly increased [(0.732±0.010) vs. (1.872±0.058)](P<0.01), while the expression of PPARα was significantly decreased [(1.836±0.039) vs. (1.216±0.059)](P<0.01); Eh Cys/CySS in model group was significantly elevated [(-85.10±5.65) mV vs. (-74.02±11.75) mV](P<0.05). The NAC intervention results showed that, compared with the Model group, Eh Cys/CySS was significantly decreased [(-74.02±11.75) mV vs. (-86.85±8.30) mV, (-74.02±11.75) mV vs. (-105.83±4.10) mV](P<0.05); the liver lobes of mice in the NAC-H group appeared closer to the normal control group, with a significant reduction in red lipid droplets in oil red O staining. Compared with the model group, body weight change and liver weight were reduced significantly [15.20(14.52,17.95) g/10w vs. 13.90(12.60,15.94) g/10w, (1.69±0.06) g vs. (1.57±0.07) g](P<0.05), and the levels of ALT, AST, TG and TC in the NAC-H group were reduced significantly (P<0.05). No significant changes were observed in the NAC-L group. Compared with model group, the decrease in MDA and the increase in SOD and GSH in the NAC-L were significant (P<0.01 for all), which in the NAC-H were also significant (P<0.01 for all). SREBP1 expression was significantly decreased in the NAC-L and NAC-H groups, respectively [(1.872±0.058) vs. (1.218±0.007), (1.872±0.058) vs. (0.744±0.016)] (all P<0.01), and expressions of PPARα in NAC-L and NAC-H groups were significantly increased [(1.216±0.059) vs. (1.491±0.047), (1.216±0.059) vs. (1.617±0.034)](all P<0.01) compared with the model group. Conclusion A high-fat diet induces NAFLD in mice and oxidizes Eh Cys/CySS in plasma. NAC reduces plasma Eh Cys/CySS and affects hepatocellular lipid metabolism by modulating the expression of SREBP1 and PPARα proteins, thereby ameliorating NAFLD-related hepatic steatosis in mice.

Key words: Non-alcoholic fatty liver disease, Cysteine/cystine redox potential, High-fat diet, N-acetylcysteine