Protection of Progression of Nonalcoholic Steatohepatitis in Diet-Induced Obese Mice by a Low-Iron Diet

Iron is a risk factor for type 2 diabetes, but its relationship to other aspects of metabolic syndrome is less clear. To investigate iron’s relation to nonalcoholic steatohepatitis (NASH), mice were fed a “fast food” (FF)-diet (40% energy as fat, 12% SFA, 0.2% cholesterol, and 18.9 g/L glucose and 23.1 g/L fructose in their drinking water) for 10 or 24 weeks. The diets contained either 4 (low iron, LI), 35 (normal iron, NI) or 2000mg iron/kg chow (high iron, HI). HOMA-IR values were 2.2-fold higher (p<0.001) in the FF-groups at 10 weeks, but did not increase further with HI (1.48-fold, p=0.5). At 10 weeks all groups had similar glucose excursions during glucose and pyruvate tolerance testing. There was no significant difference in IP-GTT or IP-PTT area under the glucose curve. Liver triglycerides (TG) were significantly increased by FF (4.2-fold, p<0.01) but not iron at 10 weeks. The effect of FF was greater at 24 weeks (22.4 fold p<0.001), and at 24 weeks iron further increased liver TG (3.3 fold HIFF vs. LIFF, p<0.001). A marker of liver injury (ALT) increased 10.3-fold (p<0.001) on the HIFF diet compared to LI normal chow, but only 3.2-fold (p<0.05) on LIFF. The fibrotic gene collagen1alpha increased 14.3-fold (p<0.001) in HIFF but not at all (0.8-fold) on LIFF compared to LI normal chow. Similar protection was afforded by the LI diet to increases in expression of the inflammatory genes TGF-beta and TNF-alpha seen in HIFF. RNA sequencing data revealed transcriptional regulation of a large family of fat metabolic genes by FF, whereas only the TGF-beta signaling pathway was significantly altered by iron content. We conclude that dietary iron restriction can protect from NASH induced by a high-fat and -carbohydrate diet. A likely candidate mechanism is through a known mediator of hepatic fibrosis, TGF-beta.