Fructose Promotes Leaky Gut, Endotoxemia, and Liver Fibrosis Through Ethanol‐Inducible Cytochrome P450‐2E1–Mediated Oxidative and Nitrative Stress

Abstract

Fructose intake is known to induce obesity, insulin resistance, metabolic syndrome and non-alcoholic fatty liver disease (NAFLD). We aimed to evaluate the effects of fructose drinking on gut leakiness, endotoxemia, and NAFLD and study the underlying mechanisms in rats, mice, and T84 colon cells. The levels of ileum junctional proteins, oxidative stress markers and apoptosis-related proteins in rodents, T84 colonic cells and human ileums were determined by immunoblot, immunoprecipitation, and immunofluorescence analyses. Fructose drinking caused microbiome change, leaky gut, and hepatic inflammation/fibrosis with increased levels of nitroxidative stress marker proteins cytochrome P450–2E1 (CYP2E1), inducible nitric oxide synthase, and nitrated proteins in small intestine and liver of rodents. Fructose drinking significantly elevated plasma bacterial endotoxin levels likely resulting from decreased levels of intestinal tight junction (TJ) proteins (ZO-1, occludin, claudin-1, and claudin-4), adherent junction (AJ) proteins (β-catenin and E-cadherin), and desmosome plakoglobin along with α-tubulin in wild-type rodents but not in the fructose-exposed Cyp2e1 -null mice. Consistently, decreased intestinal TJ/AJ proteins and increased hepatic inflammation with fibrosis were observed in autopsied obese people compared to lean individuals. Furthermore, histological and biochemical analyses showed markedly elevated hepatic fibrosis markers proteins in fructose-exposed rats compared to controls. Immunoprecipitation followed by immunoblot analyses revealed that intestinal TJ proteins were nitrated and ubiquitinated, leading to their decreased levels in the fructose-exposed rats. Conclusion: These results showed for the first time that fructose intake causes protein nitration of intestinal TJ and AJ proteins, resulting in increased gut leakiness, endotoxemia and steatohepatitis with liver fibrosis, at least partly, through a CYP2E1-dependent manner.