Mice on a high-fat, high-fructose diet and treated with low dose streptozotocin develop features of human NASH

Introduction: An improved model of human non-alcoholic steatohepatitis (NASH) is needed. To this aim we combined a recent model of a high-fructose/high fat diet with low dose Streptozotocin (STZ) to induce hyperglycemia with hyperinsulinemia but relative insulin resistance (IR).

Methods: Six week old female C57BL/6 mice were assigned to standard chow (13% kcal from fat; 65% kcal from complex carbohydrates, n=10), or to a high-fat and high-carbohydrate diet (HF/HC; 59% kcal fat; 26% kcal complex carbohydrates, plus 55% fructose and 45% sucrose in drinking water; n=20) for 6, 12 and 18 weeks. 10/20 mice on the HF/HC diet received low dose (65mg/kg) STZ i.p. (HF/HC/STZ group) four weeks before sacrifice on two consecutive days, to induce relative insulin deficiency despite hyperinsulinemia, as found in type 2 diabetes. Parameters of IR and liver function, intrahepatic lipid, inflammation, fibrosis and transcript levels related to fibrogenesis and fibrolysis (qPCR) were determined at sacrifice.

Results: Mice on HF/HC and HF/HC/STZ gained significantly more weight (up to 35.1g vs. 33.1g at 18 w) and significantly higher serum markers of IR compared to mice on normal chow (1.6-fold vs. 1.5-fold increased HOMA score at 12 and 18 w). The HF/HC and the HF/HC/STZ groups developed comparable increases of liver weight (1.5-fold) and fat (29%) compared with mice on normal chow, but collagen content of the HF/HC/STZ group was significantly (1.8-fold) higher than in the HF/HC group at week 12. The HF/HC/STZ mice at week 12 showed more severe NASH than at 18 weeks. Accordingly, procollagen α1(I), α-SMA, TGFβ1, MMP-2, -9, -13 and TIMP-1 mRNA expression was significantly higher at 12 compared to 18 weeks. Expression of CCL22, which plays a role in alternative macrophage activation, cells that are implicated in fibrogenesis and beneficial modulation of IR, was significantly up-regulated at week 12.

Conclusions: We describe a NASH model that combines dietary factors relevant to human NASH with high but mitigated insulin secretion which does not match insulin requirements, similiar to type 2 diabetes. The observed steatosis, inflammation and fibrosis level off after 12 weeks, indicating late metabolic adaptation which may also occur in patients.