1842-P: Modeling Nonalcoholic Steatohepatitis in Aged C57BL/6J Mice

Nonalcoholic steatohepatitis (NASH) is usually diagnosed in 40-60 year old patients with metabolic syndrome, but many common mouse models involve dietary or chemical interventions that begin at young ages. We established 3 NASH models using year-old C57BL/6J (B6J) males with approximate human age equivalence of 40 years. In one model, aged mice ate Gubra Amylin NASH (GAN) diet (40 kcal% fat with 18 kcal% palm oil; 20% fructose; 2% cholesterol; N=12) or chow diet (6% fat by weight; N=10) for 5 months. Aged mice fed GAN had rapid signs of liver damage: by 1 month, serum alanine aminotransferase (ALT) rose from 53 ± 20 to 309 ± 188 IU/L (Repeated measures ANOVA; P < 0.0001) and aspartate aminotransferase (AST) increased from 77 ± 33 to 399 ± 420 IU/L (P < 0.0001); values were stable in aged B6J fed chow. In contrast, liver damage progressed more slowly when B6J were started on GAN as young adults (6 weeks old; N=11); ALT increased from 27 ± 5 to 231 ± 96 IU/L and AST from 53 ± 18 to 177 ± 88 IU/L after 5 months. After 1 month, GAN-fed aged B6J serum cholesterol rose from 166 ± 24 to 290 ± 65 mg/dL (P < 0.0001) but not in aged B6J fed chow or young B6J fed GAN. Triglycerides and glucose did not change after 5 months in any group, while ALT, AST and cholesterol remained high in aged GAN mice throughout. Histopathology of aged B6J fed GAN for 5 months showed severe submassive to diffuse steatosis; perivascular, bridging, and perisinusoidal fibrosis; necrosis and hepatocyte degeneration. A second model was created by treating year-old B6J mice with 3 daily doses of 50 mg/kg streptozotocin (STZ) and 60 kcal% high fat diet (STZ-HFD). Serum glucose, ALT, AST and cholesterol rose in STZ-HFD mice. Steatosis and fibrosis were less severe in STZ-HFD mice compared to aged mice fed GAN. In a third model, young and aged B6J responded similarly to a choline-deficient, reduced-methionine diet with elevated ALT and AST; reduced glucose, cholesterol and body weight; and comparable histopathology scores. The results show the value of studying mice at a life stage that more closely resembles age of clinical diagnosis.