NPC1L1 Deficiency Suppresses Ileal Fibroblast Growth Factor 15 Expression and Increases Bile Acid Pool Size in High-Fat-Diet-Fed Mice

Niemann–Pick C1-like 1 (NPC1L1) mediates intestinal uptake of dietary and biliary cholesterol and is the target of ezetimibe, a cholesterol absorption inhibitor used to treat hypercholesterolemia. Genetic deletion of NPC1L1 or ezetimibe treatment protects mice from high-fat diet (HFD)-induced obesity; however, the molecular mechanisms responsible for this therapeutic benefit remain unknown. A major metabolic fate of cholesterol is its conversion to bile acids. We found that NPC1L1 knockout (L1-KO) mice fed an HFD had increased energy expenditure, bile acid pool size, and fecal bile acid excretion rates. The elevated bile acid pool in the HFD-fed L1-KO mice was enriched with tauro-β-muricholic acid. These changes in the L1-KO mice were associated with reduced ileal mRNA expression of fibroblast growth factor 15 (FGF15) and increased hepatic mRNA expression of cholesterol 7α-hydroxylase (Cyp7A1) and mitochondrial sterol 27-hydroxylase (Cyp27A1). In addition, mRNA expression of the membrane bile acid receptor Takeda G protein-coupled receptor 5 (TGR5) and type 2 iodothyronine deiodinase (Dio2) were elevated in brown adipose tissue of L1-KO mice, which is known to promote energy expenditure. Thus, altered bile acid homeostasis and signaling may play a role in protecting L1-KO mice against HFD-induced obesity.

Bile Acids, Liver Cirrhosis, and Extrahepatic Vascular Dysfunction

The bile acid pool with its individual bile acids (BA) is modulated in the enterohepatic circulation by the liver as the primary site of synthesis, the motility of the gallbladder and of the intestinal tract, as well as by bacterial enzymes in the intestine. The nuclear receptor farnesoid X receptor (FXR) and Gpbar1 (TGR5) are important set screws in this process. Bile acids have a vasodilatory effect, at least according to in vitro studies. The present review examines the question of the extent to which the increase in bile acids in plasma could be responsible for the hyperdynamic circulatory disturbance of liver cirrhosis and whether modulation of the bile acid pool, for example, via administration of ursodeoxycholic acid (UDCA) or via modulation of the dysbiosis present in liver cirrhosis could influence the hemodynamic disorder of liver cirrhosis. According to our analysis, the evidence for this is limited. Long-term studies on this question are lacking.

Blood serum amino acid pool violation of in patients with liver cirrhosis

Objective. To investigate serum amino acid pool changes in patients with liver cirrhosis. Materials and methods. 95 patients with liver cirrhosis were participated in the study. In the 1st group (class A disease severity according to Child- Pugh score) there were 18 (18.95%) patients, in the 2nd group (class B) - 25 (26.3%), in the 3rd groups (class C) - 52 (54.7%) patients. The amount of free amino acids in blood serum was determined by reversed-phase high-performance liquid chromatography in isocratic elution mode with electrochemical detection. Results. Violations of free amino acid reserves were revealed in patients with cirrhosis of the liver with a predominant accumulation of aromatic amino acids: phenylalanine - (162.45 ± 14.12) nmol/ml, tyrosine - (99.05 ± 10.07) nmol/ml, tryptophan - (76.10 ± 12.40) nmol/ml, as well as an increase in the content of proline, lysine, cysteine (p <0.05) . In parallel, the decreasing of free serum amino acids with branched side chain levels were observed: valine - up (150.10 ± 8.92) nmol/ml leucine - up (75.14 ± 5.12) nmol/ml (p < 0.05) and isoleucine - up to (80.40 ± 8.01) nmol/ml. Conclusions. The correlation between the second degree of thick guts dysbiosis and increased levels of tryptophan was determined (r = 0.77; p <0.01). III degree thick dysbiosis was correlated with increasing levels of phenylalanine (r = 0.71; p <0.01). In patients of 2nd group the correlations between levels of tryptophan and II degree of intestinal dysbiosis (r = 0.58; p <0.01) and the levels of tyrosine in phenylalanine in III stage intestinal dysbiosis were detected.

Secondary bile acid ursodeoxycholic acid alters weight, the gut microbiota, and the bile acid pool in conventional mice

Ursodeoxycholic acid (commercially available as ursodiol) is a naturally occurring bile acid that is used to treat a variety of hepatic and gastrointestinal diseases. Ursodiol can modulate bile acid pools, which have the potential to alter the gut microbiota community structure. In turn, the gut microbial community can modulate bile acid pools, thus highlighting the interconnectedness of the gut microbiota-bile acid-host axis. Despite these interactions, it remains unclear if and how exogenously administered ursodiol shapes the gut microbial community structure and bile acid pool in conventional mice. This study aims to characterize how ursodiol alters the gastrointestinal ecosystem in conventional mice. C57BL/6J wildtype mice were given one of three doses of ursodiol (50, 150, or 450 mg/kg/day) by oral gavage for 21 days. Alterations in the gut microbiota and bile acids were examined including stool, ileal, and cecal content. Bile acids were also measured in serum. Significant weight loss was seen in mice treated with the low and high dose of ursodiol. Alterations in the microbial community structure and bile acid pool were seen in ileal and cecal content compared to pretreatment, and longitudinally in feces following the 21-day ursodiol treatment. In both ileal and cecal content, members of the Lachnospiraceae Family significantly contributed to the changes observed. This study is the first to provide a comprehensive view of how exogenously administered ursodiol shapes the healthy gastrointestinal ecosystem in conventional mice. Further studies to investigate how these changes in turn modify the host physiologic response are important.

Bile Acids in Control of the Gut-Liver-Axis

The liver and gut share an intimate relationship whose communication relies heavily on metabolites, among which bile acids play a major role. Beyond their function as emulsifiers, bile acids have been recognized for their influence on metabolism of glucose and lipids as well as for their impact on immune responses. Therefore, changes to the composition of the bile acid pool can be consequential to liver and to gut physiology. By metabolizing primary bile acids to secondary bile acids, the bacterial gut microbiome modifies how bile acids exert influence. An altered ratio of secondary to primary bile acids is found to be substantial in many studies. Thus, disease pathogenesis and progression could be changed by gut microbiome modification which influences the bile acid pool.

Antibiotic-Induced Changes in Microbiome-Related Metabolites and Bile Acids in Rat Plasma

Various environmental factors can alter the gut microbiome’s composition and functionality, and modulate host health. In this study, the effects of oral and parenteral administration of two poorly bioavailable antibiotics (i.e., vancomycin and streptomycin) on male Wistar Crl/Wi(Han) rats for 28 days were compared to distinguish between microbiome-derived or -associated and systemic changes in the plasma metabolome. The resulting changes in the plasma metabolome were compared to the effects of a third reference compound, roxithromycin, which is readily bioavailable. A community analysis revealed that the oral administration of vancomycin and roxithromycin in particular leads to an altered microbial population. Antibiotic-induced changes depending on the administration routes were observed in plasma metabolite levels. Indole-3-acetic acid (IAA) and hippuric acid (HA) were identified as key metabolites of microbiome modulation, with HA being the most sensitive. Even though large variations in the plasma bile acid pool between and within rats were observed, the change in microbiome community was observed to alter the composition of the bile acid pool, especially by an accumulation of taurine-conjugated primary bile acids. In-depth investigation of the relationship between microbiome variability and their functionality, with emphasis on the bile acid pool, will be necessary to better assess the potential adverseness of environmentally induced microbiome changes.

Bile Acid pool composition and Gallbladder function are controlled by TGR5 to protect the liver against Bile Acid overload

Backgrounds & AimsAs the bile acid (BA) pool composition is of major impact on liver pathophysiology, we studied its regulation by the BA receptor TGR5, promoting hepatoprotection against BA overload.MethodsWT, total and hepato-specific TGR5-KO, and TGR5-overexpressing mice were used in: partial and 90% extended hepatectomies (EH) upon normal, ursodeoxycholic acid (UDCA)- or cholestyramine (CT)-enriched diet, bile duct ligation (BDL), cholic acid (1%)-enriched diet, and TGR5 agonist (RO) treatments. We thereby studied TGR5 impact on: BA pool composition, liver injury, regeneration and survival. Particular focus was made on gut microbiota (GM) and gallbladder (GB) function analysis. BA pool composition was analyzed in patients undergoing major hepatectomy.ResultsThe TGR5-KO hyperhydrophobic BA pool was not related to BA synthesis alteration, nor to the TGR5-KO GM dysbiosis, as supported by hepatocyte-specific KO mice and cohousing experiments. The TGR5-dependent control of GB dilatation was crucial for BA pool composition, as determined by experiments including RO treatment +/− cholecystectomy. The poor TGR5-KO post-EH survival rate, related with exacerbated peribiliary necrosis and BA overload, was improved by shifting the BA pool towards a more hydrophilic composition (CT and UDCA treatments). After either BDL or CA-enriched diet +/− cholecystectomy, we found that GB dilatation had strong TGR5-dependent hepatoprotective properties. In patients, a more hydrophobic BA pool was correlated with an unfavorable outcome after hepatectomy.ConclusionBA pool composition is crucial for hepatoprotection in mice and humans. We point TGR5 as a key regulator of BA profile and thereby as a potential hepatoprotective target under BA overload conditions.Lay summaryThrough multiple in vivo experimental approaches in mice, together with a patients study, this work brings some new light on the relationships between biliary homeostasis, gallbladder function and liver protection. We showed that the bile acid pool composition is crucial for optimal liver repair, not only in mice but also in human patients undergoing major hepatectomy.

Hypoxic Adaptation of Mitochondrial Metabolism in Rat Cerebellum Decreases in Pregnancy

Function of brain amino acids as neurotransmitters or their precursors implies changes in the amino acid levels and/or metabolism in response to physiological and environmental challenges. Modelling such challenges by pregnancy and/or hypoxia, we characterize the amino acid pool in the rat cerebellum, quantifying the levels and correlations of 15 amino acids and activity of 2-oxoglutarate dehydrogenase complex (OGDHC). The parameters are systemic indicators of metabolism because OGDHC limits the flux through mitochondrial TCA cycle, where amino acids are degraded and their precursors synthesized. Compared to non-pregnant state, pregnancy increases the cerebellar content of glutamate and tryptophan, decreasing interdependence between the quantified components of amino acid metabolism. In response to hypoxia, the dependence of cerebellar amino acid pool on OGDHC and the average levels of arginine, glutamate, lysine, methionine, serine, phenylalanine, and tryptophan increase in non-pregnant rats only. This is accompanied by a higher hypoxic resistance of the non-pregnant vs. pregnant rats, pointing to adaptive significance of the hypoxia-induced changes in the cerebellar amino acid metabolism. These adaptive mechanisms are not effective in the pregnancy-changed metabolic network. Thus, the cerebellar amino acid levels and OGDHC activity provide sensitive markers of the physiology-dependent organization of metabolic network and its stress adaptations.