Impaired intestinal defensin production leads to bacterial translocation and subsequently aggravates hepatic inflammation and fibrogenesis in an experimental NASH model – a new second hit

Aims: Increased intestinal permeability and bacterial overgrowth and are pathophysiological factors of NASH in patients and in experimental models. Recently, we developed a new experimental setting combining a dietary NASH model with a model of chronic colitis, induced by application of dextran sulphate sodium (DSS), in order to study the liver-gut axis.

Aim: The aim of the current study was to investigate the mechanism of bacterial translocation in our model, i.e. whether expression of intestinal antimicrobial peptides was altered.

Methods and Results: Male C57bl/6 mice (n=6) were randomly allocated into four experimental groups receiving ether (I) standard chow (SC), (II) a high fat (HF) diet, (III) SC+DSS (1% in the drinking water), and (IV) HF+DSS for 12 weeks. Chronic DSS treatment caused intestinal inflammation, which was absent in SC mice and HF treated mice. Expression of intestinal IL-1 beta- and TNF-mRNA was significantly elevated in both DSS groups. Also expression of intestinal antimicrobial peptides Cramp and mBD3 was increased in SC+DSS mice. In contrast Cramp expression was blocked in the HF+DSS group. LPS serum concentration was augmented in HF mice, which was further enhanced by DSS addition. In line with these findings we found increased hepatic TLR4- and TLR9-mRNA expression in HF+DSS treated mice, accompanied by NF-kappa B activation. HF diet lead to hepatic inflammation that was more severe in HF+DSS mice as reflected by liver histology and analysis of TNF- and MCP-1-mRNA expression. Moreover, HF+DSS mice showed extracellular matrix deposition and had significantly elevated hepatic TIMP-1-, TGF beta-, Pai-1- and alpha-SMA-mRNA expression.

Summary and Conclusions: Intestinal defensin generation is inhibited in experimental NASH, thereby facilitating bacterial translocation. This leads to up regulation of TLR expression and increased hepatic inflammation and fibrogenesis. Therefore we propose lack of intestinal defensins as new second hit in NASH.