Gut microbiota depletion aggravates bile acid-induced liver pathology in mice with a human-like bile acid composition.

Cyp2c70-deficient mice have a human-like bile acid (BA) composition due to their inability to convert chenodeoxycholic acid (CDCA) into rodent-specific muricholic acids (MCAs). However, the hydrophobic BA composition in these animals is associated with liver pathology. Although Cyp2c70-ablation has been shown to alter gut microbiome composition, the impact of gut bacteria on liver pathology in Cyp2c70-/- mice remains to be established. Therefore, we treated young-adult male and female wild-type (WT) and Cyp2c70-/- mice with antibiotics (AB) with broad specificity to deplete the gut microbiota and assessed the consequences on BA metabolism and liver pathology. Female Cyp2c70-/- mice did not tolerate AB treatment, necessitating premature termination of the experiment. Male Cyp2c70-/- mice did tolerate AB but showed markedly augmented liver pathology after 6 weeks of treatment. Dramatic downregulation of hepatic Cyp8b1 expression (-99%) caused a reduction in the proportions of 12α-hydroxylated BAs in the circulating BA pools of AB-treated male Cyp2c70-/- mice. Interestingly, the resulting increased BA hydrophobicity strongly correlated with various indicators of liver pathology. Moreover, genetic inactivation of Cyp8b1 in livers of male Cyp2c70-/- mice increased liver pathology, while addition of ursodeoxycholic acid to the diet prevented weight loss and liver pathology in AB-treated female Cyp2c70-/- mice. In conclusion, depletion of gut microbiota in Cyp2c70-/- mice aggravates liver pathology at least in part by increasing the hydrophobicity of the circulating BA pool. These findings highlight that the potential implications of AB administration to cholestatic patients should be evaluated in a systematic manner.

A human-like bile acid pool induced by deletion of hepatic Cyp2c70 modulates effects of FXR activation in mice.

Bile acids (BAs) facilitate intestinal absorption of lipid-soluble nutrients and modulate various metabolic pathways through the farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5. These receptors are targets for therapy in cholestatic and metabolic diseases. However, dissimilarities in BA metabolism between humans and mice complicate translation of preclinical data. Cytochrome P450 family 2 subfamily c polypeptide 70 (CYP2C70) was recently proposed to catalyze the formation of rodent-specific muricholic acids (MCAs). With CRISPR/Cas9-mediated somatic genome editing, we generated an acute hepatic Cyp2c70 knockout mouse model (Cyp2c70ako) to clarify the role of CYP2C70 in BA metabolism in vivo and evaluate whether its activity modulates effects of pharmacologic FXR activation on cholesterol homeostasis. In Cyp2c70ako mice, chenodeoxycholic acid (CDCA) increased at the expense of ßMCA, resulting in a more hydrophobic human-like BA pool. Tracer studies demonstrated that, in vivo, CYP2C70 catalyzes the formation of ßMCA primarily by sequential 6ß-hydroxylation and C7-epimerization of CDCA, generating αMCA as an intermediate metabolite. Physiologically, the humanized BA composition in Cyp2c70ako mice blunted the stimulation of fecal cholesterol disposal in response to FXR activation compared with WT mice, predominantly due to reduced stimulation of transintestinal cholesterol excretion. Thus, deletion of hepatic Cyp2c70 in adult mice translates into a human-like BA pool composition and impacts the response to pharmacologic FXR activation. This Cyp2c70ako mouse model may be a useful tool for future studies of BA signaling and metabolism that informs human disease development and treatment.

New insights in the multiple roles of bile acids and their signaling pathways in metabolic control.

PURPOSE OF REVIEW: There is a growing awareness that individual bile acid species exert different physiological functions, beyond their classical roles in bile formation and fat absorption, due to differential stimulatory effects on the bile-acid-activated receptors farnesoid X receptor (FXR) and takeda G receptor 5 (TGR5). This review integrates recent findings on the role of individual bile acids and their receptors in metabolic control, with special emphasis on cholesterol homeostasis. RECENT FINDINGS: The consequences of altered bile acid metabolism, for example, in type 2 diabetes and during aging, on metabolic control is increasingly recognized but full impact hereof remains to be elucidated. These effects interact with those of newly developed pharmacological FXR and TGR5 modulators that aim to improve metabolic health. Studies in genetically modified mice have provided important new insights, for example, establishment of the role of intestinal FXR in control of the transintestinal cholesterol excretion pathway. However, translation from mice to men is hampered by the presence of rodent-specific bile acid species with special features. SUMMARY: Specific bile acids and their signaling pathways play important roles in control of (cholesterol) metabolism. Deeper insight into the interactions between endogenous (i.e., bile acids) and pharmacological modulators of FXR and TGR5 is needed to optimize therapeutic benefit of the latter. The recent identification of cytochrome P450 2C70 as key enzyme in the formation of rodent-specific hydrophilic muricholic acids allows for the development of adequate mouse models for this purpose.

Bile Acid Sequestration via Colesevelam Reduces Bile Acid Hydrophobicity and Improves Liver Pathology in Cyp2c70-/- Mice with a Human-like Bile Acid Composition.

Bile acids (BAs) and their signaling pathways have been identified as therapeutic targets for liver and metabolic diseases. We generated Cyp2c70-/- (KO) mice that were not able to convert chenodeoxycholic acid into rodent-specific muricholic acids (MCAs) and, hence, possessed a more hydrophobic, human-like BA pool. Recently, we have shown that KO mice display cholangiopathic features with the development of liver fibrosis. The aim of this study was to determine whether BA sequestration modulates liver pathology in Western type-diet (WTD)-fed KO mice. The BA sequestrant colesevelam was mixed into the WTD (2% w/w) of male Cyp2c70+/+ (WT) and KO mice and the effects were evaluated after 3 weeks of treatment. Colesevelam increased fecal BA excretion in WT and KO mice and reduced the hydrophobicity of biliary BAs in KO mice. Colesevelam ameliorated diet-induced hepatic steatosis in WT mice, whereas KO mice were resistant to diet-induced steatosis and BA sequestration had no additional effects on liver fat content. Total cholesterol concentrations in livers of colesevelam-treated WT and KO mice were significantly lower than those of untreated controls. Of particular note, colesevelam treatment normalized plasma levels of liver damage markers in KO mice and markedly decreased hepatic mRNA levels of fibrogenesis-related genes in KO mice. Lastly, colesevelam did not affect glucose excursions and insulin sensitivity in WT or KO mice. Our data show that BA sequestration ameliorates liver pathology in Cyp2c70-/- mice with a human-like bile acid composition without affecting insulin sensitivity.

Role of bile acids in inflammatory liver diseases.

Bile acids and their signaling pathways are increasingly recognized as potential therapeutic targets for cholestatic and metabolic liver diseases. This review summarizes new insights in bile acid physiology, focusing on regulatory roles of bile acids in the control of immune regulation and on effects of pharmacological modulators of bile acid signaling pathways in human liver disease. Recent mouse studies have highlighted the importance of the interactions between bile acids and gut microbiome. Interfering with microbiome composition may be beneficial for cholestatic and metabolic liver diseases by modulating formation of secondary bile acids, as different bile acid species have different signaling functions. Bile acid receptors such as FXR, VDR, and TGR5 are expressed in a variety of cells involved in innate as well as adaptive immunity, and specific microbial bile acid metabolites positively modulate immune responses of the host. Identification of Cyp2c70 as the enzyme responsible for the generation of hydrophilic mouse/rat-specific muricholic acids has allowed the generation of murine models with a human-like bile acid composition. These novel mouse models will aid to accelerate translational research on the (patho)physiological roles of bile acids in human liver diseases .

Targeting senescent cells alleviates obesity-induced metabolic dysfunction.

Adipose tissue inflammation and dysfunction are associated with obesity-related insulin resistance and diabetes, but mechanisms underlying this relationship are unclear. Although senescent cells accumulate in adipose tissue of obese humans and rodents, a direct pathogenic role for these cells in the development of diabetes remains to be demonstrated. Here, we show that reducing senescent cell burden in obese mice, either by activating drug-inducible "suicide" genes driven by the p16Ink4a promoter or by treatment with senolytic agents, alleviates metabolic and adipose tissue dysfunction. These senolytic interventions improved glucose tolerance, enhanced insulin sensitivity, lowered circulating inflammatory mediators, and promoted adipogenesis in obese mice. Elimination of senescent cells also prevented the migration of transplanted monocytes into intra-abdominal adipose tissue and reduced the number of macrophages in this tissue. In addition, microalbuminuria, renal podocyte function, and cardiac diastolic function improved with senolytic therapy. Our results implicate cellular senescence as a causal factor in obesity-related inflammation and metabolic derangements and show that emerging senolytic agents hold promise for treating obesity-related metabolic dysfunction and its complications.