OP79 ADIPOKINES MEDIATE THE RELATIONSHIPS BETWEEN ABDOMINAL ADIPOSITY AND INSULIN RESISTANCE IN ASIAN ETHNIC GROUPS: SINGAPORE ADULT METABOLISM STUDY (SAMS)

Abstract

Background: Nonalcoholic steatohepatitis (NASH) and insulin resistance frequently coexists in subjects with obesity and type 2 diabetes. NASH can be defined as a lipotoxic liver injury caused by excess body adiposity. Hepatic inflammation and/or fibrosis could be caused by lipid peroxidation preceded by excessive hepatic lipid accumulation. In our previous study, we developed a cholesteroland saturated fatty acid-induced model of lipotoxic NASH and revealed that hepatic oxidative stress and insulin resistance promotes hepatic inflammation and fibrosis [1,2]. Astaxanthin is a carotenoid compound that is known to be approximately 500 times more potent in inhibiting lipid peroxidation than vitamin E in vitro . In the present study, we examined the inhibitory effect of astaxanthin against the progression of NASH to clarify the significance of lipid peroxidation-mediated lipotoxicity and insulin resistance in the pathogenesis of NASH. Method: 7-week-old C57BL/6 mice were fed on a highcholesterol/high-fat diet (CL) or a CL diet containing 0.02% astaxanthin (CL + Ax), for a total of 12 weeks. The lipid peroxidation, insulin sensitivity, and inflammatory/stress signal were evaluated. Result: After 8 weeks of feeding, the levels of thiobarbituric acid reactive substances (TBARS) in liver were significantly increased and histological examination revealed hepatic steatosis and inflammation. At week 12, hepatic fibrosis was observed in mice fed CL diet. They showed hyperinsulinemia (CL1.4±0.3 vs normal chow (NC) 0.3±0.1ng/ml, p< 0.05) and glucose intolerance even though weight and adiposity were similar, indicating that mice fed on a CL diet developed NASH associated with insulin resistance. Astaxanthin administration markedly reduced lipid peroxidation and improved glucose intolerance and insulin sensitivity in CL group. CL group had 2.5-fold and 4.1-fold increases in hepatic triglyceride (TG) and total cholesterol (TC) levels compared to NC group; astaxanthin decreased hepatic TG and TC levels by 38% and 46%, respectively (all p< 0.05). The a-SMA positive cell, as an index of activated stellate cells, increased in CL group, but decreased significantly in CL+Ax group. Furthermore, CL treatment led to 1.5-fold and 6-fold increase in TGF-b and collagen I mRNA expression, and 4.3-fold increase in hydroxyproline content, whereas astaxanthin administration inhibited fibrosis, lowering the TGF-b and collagen I mRNA expression, and hydroxyproline content by 28%, 35%, and 24%, respectively (all p< 0.05). Astaxanthin administration in CL-fed mice led to enhanced insulin signal assessed by IRb and Akt phosphorylation in the liver. These findings were associated with reduction of ER stress (CHOP/GRP78), attenuation of MAPK (JNK/p38MAPK) and NF-kB activation in liver. Astaxanthin, however, showed little effect on insulin resistance and stress response in the adipose tissue in the CL-treated mice. Conclusion: Hepatic cholesterol and TG accumulation causes excessive lipid peroxidation and the development of insulin resistance, leading to hepatic inflammation and fibrosis. Astaxanthin, a potent antioxidant, inhibits the progression of NASH by attenuating lipid accumulation, lipid peroxidation, and insulin resistance. Reference(s) [1] Matsuzawa N et al, Lipid-induced oxidative stress causes steatohepatitis in mice fed an atherogenic diet. Hepatology 46: 1392–1403, 2007. [2] Ota T et al., Insulin resistance accelerates a dietary rat model of nonalcoholic steatohepatitis. Gastroenterology 132:282–293, 2007.