Disturbed bile acid metabolism as a cause of intestinal failure-associated liver disease in a piglet model of short bowel syndrome.

Abstract

Introduction: The most common cause of death in patients with short bowel syndrome (SBS) is sepsis in the setting of severe intestinal (Figure Presented) failure-associated liver disease (IFALD). However the cause and complex mechanisms underlying the development of IFALD are poorly understood. Small bowel resection (SBR) is the only proven independent risk factor for the development of IFALD. We hypothesised that SBR-related alterations in the gut microbiota will have a significant impact on bile acid metabolism and may contribute to the development of IFALD in a piglet SBS model via increased delivery of potentially hepatotoxic primary bile acids to the liver. Method(s): 4-week old piglets underwent 75% small bowel resection (SBR) or sham operation and were fed a polymeric infant formula diet for six weeks (n = 5 - 6/group). Histological evidence of liver damage was confirmed with Sirius red and Oil Red O staining. High throughput sequencing of colonic content was performed to identify changes in bacteria with bile salt hydrolysing activity or 7alpha-dehydroxylation ability. UPLC-MS was used to determine bile acid composition in end-point bile and portal serum samples. Result(s): At six weeks post-SBR, SBS piglets exhibited decreased weight gain (P < 0.001), persistent diarrhoea (P < 0.001), and increased stool fat (P < 0.01) when compared with sham controls. Consistent with the development of IFALD we observed hepatic fibrosis (P < 0.01) and fat accumulation (P = 0.007). Hepatic bile acid synthesis, as indicated by the biliary bile acid composition, was disturbed in SBS piglets: unconjugated and conjugated CDCA (P < 0.01) and conjugated HCA (P < 0.0001) levels were increased in bile samples whilst levels of unconjugated HDCA (P < 0.0001) and DCA (P < 0.05) were decreased compared with sham controls. Portal serum bile acid composition reflects the bile acid species delivered to the liver: unconjugated CA and DCA were not detected in portal serum samples. Unconjugated and conjugated forms of the primary bile acids CDCA (P < 0.0001) and HCA (P < 0.0001, P < 0.05) were elevated in SBS piglets whilst unconjugated levels of the secondary bile acid LCA were decreased (P < 0.0001) together with unconjugated and conjugated secondary HDCA (P < 0.0001), and conjugated DCA (P < 0.0001). High throughout sequencing of the colonic content was used to assess if changes in the microbiota contribute to changes in portal bile acid composition (Figure 1). We observed a 10-fold decrease in Clostridium (P = 0.06) and two-fold decrease in Bacteroides (P < 0.05) in SBS piglets. The minor bacteria Eubacterium was increased following SBR (P < 0.05). Conclusion(s): In the piglet SBS-ALD model, we have observed a significant increase in free and conjugated primary BA levels that occurs concurrent with a significant decrease in free and conjugated secondary bile acids level. Furthermore we have observed a decrease in Clostridium and Bacteroides, two of the main bacteria responsible for both deconjugation of bile acids and transformation of primary bile acids into secondary bile acids. The results of our study are in accordance with studies performed on other liver diseases including cirrhosis, alcoholic liver disease and cholestasis in which secondary bile acid levels are reduced concomitant with a dominance of the primary bile acid CDCA. We conclude that significant microbial dysbiosis and consequent bile acid dysmetabolsim contribute to the development of liver disease in a piglet model of SBS.