Dietary wheat amylase trypsin inhibitors worsen chronic liver disease in preclinical models of non-alcoholic fatty liver disease and liver fibrosis
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Abstract
A Westernized diet and sedentary life style are the main contributing factors triggering the onset of obesity and non-alcoholic fatty liver disease. However, general dietary components that have low nutritional value and have the potential to trigger inflammatory responses may also be of great importance. In this respect, a common dietary component, wheat amylase trypsin inhibitors (ATI) that have a negligible nutritional value were shown to activate intestinal macrophages and dendritic cells via toll like receptor 4. Importantly, once activated by nutritional ATI, these cells leave the gut to the surrounding mesenteric lymph nodes and likely other sites, potentially promoting intestinal as well as extra-intestinal inflammation. The liver is particularly prone to such effects, according to the postulated immunological gut-liver axis, with anticipated effects of such signals on the course of chronic liver disease, such as non-alcoholic fatty liver disease (NAFLD) and its severe form NASH (non-alcoholic steatohepatitis), and liver fibrosis in general. I therefore studied how far nutritional ATI may affect the severity of liver fibrosis and non-alcoholic fatty liver disease (NAFLD), obesity and the metabolic syndrome upon feeding mice with experimental liver fibrosis or NAFLD ATI-enriched vs ATI-free diets. For liver fibrosis, Mdr2-/- FVB mice that develop spontaneous secondary biliary fibrosis resembling human primary sclerosing cholangitis received a carbohydrate and protein (zein from corn) defined and vitamin/mineral/essential amino acid supplemented control diet, or 0.7% of the zein being replaced by purified ATI for 6 weeks. For NAFLD/NASH, male C57BI6J mice received the zein-based diet with or without the carbohydrates replaced by 53% of calories by defined fats (high fat diet, HFD), with or without 30% of the zein being replaced by wheat gluten (G, containing about 0.15g ATI per 10g; HFD/G/ATI), or 0.7% of the zein being replaced by purified ATI (HFD/ATI) for 8 weeks. At sacrifice blood, liver and peripheral adipose tissues (in the NAFLD mice) were collected for biochemical, immunological and histological analysis. In the NAFLD mice, insulin resistance (IR) was assessed by an intraperitoneal glucose tolerance test (IPGTT). Mice on the high fat diet (HFD) gained significant weight and developed IR. Compared to the HFD alone, mice fed the HFD/G/ATI, or the HFD/ATI diets dose-dependently gained significantly more weight and displayed significantly higher serum transaminases and triglycerides, epididymal, mesenteric and inguinal fat, and a higher insulin resistance. ATI feeding induced enhanced liver and adipose tissue inflammation, with an increased M1-type macrophage polarization and infiltration, and a significantly increased fibrogenic response in the liver compared to HFD mice on the ATI-free diet. Mdr2-/- mice on the ATI containing diet developed a significantly more severe liver fibrosis than their ATI-free controls. Therefore, in mice wheat ATI when ingested in quantities comparable to human average consumption exacerbate all features of NAFLD/NASH, the metabolic syndrome and biliary fibrosis despite their irrelevant caloric value. These findings underline the detrimental effects of wheat ATI on ongoing peripheral chronic diseases, especially liver inflammation and fibrosis, and NAFLD/NASH related adipose tissue inflammation and insulin resistance. They are currently tested in clinical studies, also in view of consumption and finally the production of healthier (ATI-reduced wheat) products.