Gut microbial composition can differentially regulate bile acid synthesis in humanized mice

Abstract

We previously reported that alcohol drinkers with and without cirrhosis showed a significant increase in fecal bile acid secretion compared to nondrinkers. We hypothesized this may be due to activation by alcohol of hepatic cyclic adenosine monophosphate responsive element‐binding protein 3‐like protein 3 (CREBH), which induces cholesterol 7α‐hydroxylase (Cyp7a1). Alternatively, the gut microbiota composition in the absence of alcohol might increase bile acid synthesis by up‐regulating Cyp7a1. To test this hypothesis, we humanized germ‐free (GF) mice with stool from healthy human subjects (Ctrl‐Hum), human subjects with cirrhosis (Cirr‐Hum), and human subjects with cirrhosis and active alcoholism (Alc‐Hum). All animals were fed a normal chow diet, and none demonstrated cirrhosis. Both hepatic Cyp7a1 and sterol 12α‐hydroxylase (Cyp8b1) messenger RNA (mRNA) levels were significantly induced in the Alc‐Hum and Ctrl‐Hum mice but not in the Cirr‐Hum mice or GF mice. Liver bile acid concentration was correspondingly increased in the Alc‐Hum mice despite fibroblast growth factor 15, fibroblast growth receptor 4, and small heterodimer partner mRNA levels being significantly induced in the large bowel and liver of the Ctrl‐Hum mice and Alc‐Hum mice but not in the Cirr‐Hum mice or GF mice. This suggests that the normal pathways of Cyp7a1 repression were activated in the Alc‐Hum mice and Ctrl‐Hum mice. CREBH mRNA was significantly induced only in the Ctrl‐Hum mice and Alc‐Hum mice, possibly indicating that the gut microbiota up‐regulate CREBH and induce bile acid synthesis genes. Analysis of stool bile acids showed that the microbiota of the Cirr‐Hum and Alc‐Hum mice had a greater ability to deconjugate and 7α‐dehydroxylate primary bile acids compared to the microbiota of the Cirr‐Hum mice. 16S ribosomal RNA gene sequencing of the gut microbiota showed that the relative abundance of taxa that 7‐α dehydroxylate primary bile acids was higher in the Ctrl‐Hum and Alc‐Hum groups. Conclusion: The composition of gut microbiota influences the regulation of the rate‐limiting enzymes in bile acid synthesis in the liver. (Hepatology Communications 2017;1:61–70)

Modulation of the intestinal bile acid/farnesoid X receptor/fibroblast growth factor 15 axis improves alcoholic liver disease in mice

“…The initiating/central role of the intestinal microbiome in alcohol‐related disturbances of bile acid homeostasis has been demonstrated using humanized gnotobiotic mice . Germ‐free mice transplanted with stool from patients with cirrhosis with active alcoholism showed a higher ability to deconjugate and produce secondary bile acids in the stool with subsequent derangements of the bile acid homeostasis in several organs than germ‐free mice transplanted with stool from healthy subjects, similar to the human subjects themselves . This supports the importance of the deconjugating choloylglycine hydrolase family in the development of ALD.…”

“…Alcoholics with cirrhosis have also been found to have higher fecal concentrations of hepatotoxic DCA and increased secondary to primary bile acid ratios in relation to healthy controls . The initiating/central role of the intestinal microbiome in alcohol‐related disturbances of bile acid homeostasis has been demonstrated using humanized gnotobiotic mice . Germ‐free mice transplanted with stool from patients with cirrhosis with active alcoholism showed a higher ability to deconjugate and produce secondary bile acids in the stool with subsequent derangements of the bile acid homeostasis in several organs than germ‐free mice transplanted with stool from healthy subjects, similar to the human subjects themselves .…”

Gut–liver axis alterations in alcoholic liver disease: Are bile acids the answer?

“…This increase in secondary BAs is purported to be toxic to the intestinal barrier and could perpetuate alcoholic liver disease. Prior work has also shown that microbiota from an actively drinking human can replicate this BA profile after humanization of germ‐free mice who were not fed alcohol …”

Neuroinflammation in Murine Cirrhosis Is Dependent on the Gut Microbiome and Is Attenuated by Fecal Transplant

“…Before colonization, these were thawed, resuspended in 1.5 mL of sterile PBS per tube/pellet, and then gavaged 0.2 mL per mouse per day. In our prior studies, stool treated in this manner, once thawed and inoculated, could effectively colonize GF mice without complications and with good retention of bacterial profiles …”

“…Using established protocols that the NGRRC has developed and published, intact fecal material was transferred to 10‐15‐week‐old GF C57BL/6 mice (both male and female) by daily gavage for 3 days (6‐8 mice/group) . The mice were observed in sterile individually filtered cages for 15 days, after which they were harvested.…”