Background and aims: Despite recent improvements, an optimal model that reflects all features of human non-alcoholic steatohepatitis (NASH) is needed. We developed a NASH model that combines a high-fructose/high fat diet with low dose Streptozotocin (STZ) to induce hyperglycemia with hyperinsulinemia but relative insulin resistance.
Methods: Six week old female C57BL/6 mice were randomly 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; Surwit: 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 STZ i.p. (HF/HC/STZ group; 65mg STZ/kg; four weeks before sacrifice on two consecutive days) to induce relative insulin deficiency despite hyperinsulinemia, as found in type 2 diabetes. Parameters of insulin resistance and liver function, intrahepatic lipid, inflammation, fibrosis (hydroxyproline, Sirius red morphometry) and transcript levels related to fibrogenesis and fibrolysis (qPCR) were determined at sacrifice.
Results: Compared to animals on normal chow, mice on HF/HC and HF/HC/STZ showed significantly more weight gain (up to 15 g at 18 w) and significantly higher serum markers of insulin resistance compared with normal chow (HOMA score, elevated 1.6-fold at 12 w). While the HF/HC and the HF/HC/STZ groups developed comparable increases of liver weight (1.5-fold) and fat (29%) compared with normal chow, collagen content of the HF/HC/STZ group was significantly higher than in the HF/HC group at week 12 (1.8-fold). Interestingly, HF/HC/STZ mice at week 12 showed a more impressive NASH-like phenotype than at 18 weeks, with comparable levels of fibrosis. In line, transcripts which are relevant to fibrosis such as procollagen α1(I), α-SMA, TGFβ1, MMP-2, 9, 13 and TIMP-1 were highest at 12 weeks compared to 18 weeks.
Conclusions: We describe a NASH model that combines dietary factors implicated in human NASH with high insulin but low level exhaustion of insulin production, mimicking type 2 diabetes. This model produces robust inflammation and fibrosis, which level off after 12 weeks, indicating adaptive processes.
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