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Chemicals/CAS: cholesterol, 57-88-5; cholic acid, 32500-01-9, 361-09-1, 81-25-4; colestyramine, 11041-12-6, 58391-37-0; compactin, 73573-88-3; lipid, 66455-18-3; tritium oxide, 14940-65-9; Bile Acids and Salts; Cholesterol, 57-88-5; Cholestyramine, 11041-12-6; compactin, 73573-88-3; Lipids; Naphthalenes; Tritium, 10028-17-8

In previous work we have demonstrated suppression of cholesterol 7α-hydroxylase by bile acids at the level of mRNA and transcription, resulting in a similar decline in bile acid synthesis in cultured rat hepatocytes. In view of the substantial contribution of the 'alternative' or '27-hydroxylase' route to total bile acid synthesis, as demonstrated in cultured rat hepatocytes and in vivo in humans, we here evaluate the effects of various bile acids commonly found in bile of rats on the regulation of sterol 27-hydroxylase in cultured rat hepatocytes. Addition of taurocholic acid, the predominant bile acid in rat bile, to the culture medium of rat hepatocytes resulted in a 72% inhibition of sterol 27-hydroxylase activity. The effect was exerted at the level of sterol 27-hydroxylase mRNA, showing a time- and dose-dependent decline with a maximal suppression (-75%) at 50 μM taurocholic acid after 24 h of culture. The decline in mRNA followed first-order kinetics with an apparent half-life of 13 h. Under these conditions cholesterol 7α-hydroxylase mRNA (-91%) and bile acid synthesis (i.e. chenodeoxycholic and β-muricholic acid, -81%) were also maximally suppressed. In contrast, no change was found in the level of lithocholic acid 6β-hydroxylase mRNA. Assessment of the transcriptional activity of a number of genes involved in routing of cholesterol towards bile acids showed similar suppressive effects of taurocholate on expression of the sterol 27-hydroxylase and cholesterol 7α-hydroxylase genes (-43% and -42% respectively), whereas expression of the lithocholic 6β-hydroxylase gene was not affected. Taurocholic acid and unconjugated cholic acid were equally as effective in suppressing sterol 27-hydroxylase mRNA. The more hydrophobic bile acids, chenodeoxycholic acid and deoxycholic acid also produced a strong inhibition of 57% and 76% respectively whereas the hydrophilic β-muricholic acid was not active. We conclude that (1) a number of bile acids, at physiological concentrations, suppress sterol 27-hydroxylase by down-regulation of sterol 27-hydroxylase mRNA and transcriptional activity and (2) co-ordinated suppression of both sterol 27-hydroxylase and cholesterol 7α-hydroxylase results in inhibition of bile acid synthesis in cultured rat hepatocytes. Chemicals/CAS: chenodeoxycholic acid, 474-25-9; cholesterol 7alpha monooxygenase, 9037-53-0; cholic acid, 32500-01-9, 361-09-1, 81-25-4; deoxycholic acid, 83-44-3; lithocholic acid, 434-13-9; oxygenase, 9037-29-0, 9046-59-7; taurocholic acid, 145-42-6, 59005-70-8, 81-24-3; Adenosine Triphosphate, 56-65-5; Bile Acids and Salts; Cholesterol 7-alpha-Hydroxylase, EC 1.14.13.17; Cytochrome P-450 Enzyme System, 9035-51-2; cytochrome P-450C27/25, EC 1.14.-; Oxidoreductases, EC 1.; RNA, Messenger; Steroid Hydroxylases, EC 1.14.-; Taurocholic Acid, 81-24-3

We have used primary monolayer cultures of rat hepatocytes to study the effects of physiological concentrations of various bile acids, commonly found in bile of normal rats, on the mechanism of regulation of cholesterol 7α-hydroxylase and bile acid synthesis. Addition of taurocholic acid, the most predominant bile acid in rat bile, to the culture medium suppressed cholesterol 7α-hydroxylase activity and mRNA time- and dose-dependently. The decrease in enzyme activity paralleled the changes in mRNA. Maximal suppression of cholesterol 7α-hydroxylase mRNA (-91%) and enzyme activity (-89%) was observed after a 16 h incubation period with 50 uM taurocholic acid. The declines in mRNA and enzyme caused by taurocholic acid were tightly coupled and followed first-order kinetics with a half-life of 4 h. Transcriptional activity, as assessed with nuclear run-on assays, was decreased by 44% at 50 μM taurocholic acid. Mass production of bile acids (chenodeoxycholic acid and β-muricholic acid) was inhibited to a similar extent as the cholesterol 7α-hydroxylase when different concentrations of taurocholic acid were used, giving maximal inhibition (-81%) at 50 μM taurocholic acid. Glycocholic acid and unconjugated cholic acid were equally effective as taurocholic acid in suppressing cholesterol 7α-hydroxylase mRNA. The more hydrophobic bile acids (chenodeoxycholic acid and deoxycholic acid) showed profound suppression of the cholesterol 7α-hydroxylase mRNA by 85% and 75% respectively, whereas the other trihydroxy bile acids in rat bile, α- and β-muricholic acid, were not or only marginally active. We conclude that rat bile acids, in particular the more hydrophobic ones, in concentrations commonly observed in portal blood, exert negative feedback control at the level of cholesterol 7α-hydroxylase mRNA in cultured rat hepatocytes through a direct effect on the hepatocytes, and that down-regulation of transcription is only one of the mechanisms involved in this regulation. Chemicals/CAS: chenodeoxycholic acid, 474-25-9; cholesterol 7alpha monooxygenase, 9037-53-0; cholic acid, 32500-01-9, 361-09-1, 81-25-4; deoxycholic acid, 83-44-3; glycocholic acid, 475-31-0; taurocholic acid, 145-42-6, 59005-70-8, 81-24-3; Bile Acids and Salts; Chenodeoxycholic Acid, 474-25-9; Cholesterol 7-alpha-Hydroxylase, EC 1.14.13.17; Cholic Acid, 81-25-4; Cholic Acids; Glycocholic Acid, 475-31-0; muricholic acid, 39016-49-4; RNA, Messenger; Taurocholic Acid, 81-24-3

Bile acids (BA) are signaling molecules with a wide range of biological effects, also identified among the most responsive plasma metabolites in the postprandial state. We here describe this response to different dietary challenges and report on key determinants linked to its interindividual variability. Healthy men and women (n = 72, 62 ± 8 yr, mean ± SE) were enrolled into a 12-wk weight loss intervention. All subjects underwent an oral glucose tolerance test and a mixed-meal tolerance test before and after the intervention. BA were quantified in plasma by liquid chromatography-tandem mass spectrometry combined with whole genome exome sequencing and fecal microbiota profiling. Considering the average response of all 72 subjects, no effect of the successful weight loss intervention was found on plasma BA profiles. Fasting and postprandial BA profiles revealed high interindividual variability, and three main patterns in postprandial BA response were identified using multivariate analysis. Although the women enrolled were postmeno-pausal, effects of sex difference in BA response were evident. Exome data revealed the contribution of preselected genes to the observed interindividual variability. In particular, a variant in the SLCO1A2 gene, encoding the small intestinal BA transporter organic anion-transporting polypeptide-1A2 (OATP1A2), was associated with delayed postprandial BA increases. Fecal microbiota analysis did not reveal evidence for a significant influence of bacterial diversity and/or composition on plasma BA profiles. The analysis of plasma BA profiles in response to two different dietary challenges revealed a high interindividual variability, which was mainly determined by genetics and sex difference of host with minimal effects of the microbiota. NEW & NOTEWORTHY Considering the average response of all 72 subjects, no effect of the successful weight loss intervention was found on plasma bile acid (BA) profiles. Despite high interindividual variability, three main patterns in postprandial BA response were identified using multivariate analysis. A variant in the SLCO1A2 gene, encoding the small intestinal BA transporter organic anion-transporting polypeptide-1A2 (OATP1A2), was associated with delayed postprandial BA increases in response to both the oral glucose tolerance test and the mixed-meal tolerance test. © 2017, American Physiological Society. All rights reserved. Chemicals/CAS: chenodeoxycholic acid, 474-25-9; cholic acid, 32500-01-9, 361-09-1, 81-25-4; deoxycholic acid, 83-44-3; glycine, 56-40-6, 6000-43-7, 6000-44-8; glycochenodeoxycholic acid, 640-79-9; glycocholic acid, 475-31-0; glycodeoxycholic acid, 16409-34-0, 360-65-6; taurine, 107-35-7; taurochenodeoxycholic acid, 516-35-8; taurocholic acid, 145-42-6, 59005-70-8, 81-24-3; taurodeoxycholic acid, 1180-95-6, 516-50-7; tauroursodeoxycholic acid, 14605-22-2; ursodeoxycholic acid, 128-13-2, 2898-95-5; Bile Acids and Salts

Background/Aims: Bile flow consists of bile salt-dependent bile flow (BSDF), generated by canalicular secretion of bile salts, and bile salt-independent flow (BSIF), probably of combined canalicular and ductular origin. Bile salt transport proteins have been identified in cholangiocytes, suggesting a role in control of BSDF and/or in control of bile salt synthesis through cholehepatic shunting. Methods: We studied effects of bile duct proliferation under non-cholestatic conditions in multidrug resistance-2 P-glycoprotein (Abcb4)-deficient multidrug resistance gene-2 (Mdr2(-/-)) mice. BSDF and BSIF were determined in wild-type and Mdr2(-/-) mice during infusion of step-wise increasing dosages of tauroursodeoxycholate (TUDC). Cholate synthesis rate was determined by 2H4-cholate dilution. Results were related to expression of transport proteins in liver and intestine. Results: During TUDC infusion, BSDF was increased by ∼ 50% and BSIF by ∼ 100% in Mdr2(-/-) mice compared with controls. Cholate synthesis rate was unaffected in Mdr2(-/-) mice. Hepatic expression of the apical sodium-dependent bile salt transporter (Asbt), its truncated form (tAsbt) and the multidrug resistance-related protein 3 were upregulated in Mdr2(-/-) mice. Conclusions: Bile duct proliferation in Mdr2(-/-) mice enhances cholehepatic shunting of bile salts, which is associated with a disproportionally high bile flow but does not affect bile salt synthesis. © Blackwell Munksgaard 2005. Chemicals / CAS: carrier protein, 80700-39-6; chenodeoxycholic acid, 474-25-9; cholic acid, 32500-01-9, 361-09-1, 81-25-4; deoxycholic acid, 83-44-3; lithocholic acid, 434-13-9; multidrug resistance protein 2, 256503-65-8; multidrug resistance protein 3, 231947-64-1; muricholic acid, 39016-49-4; tauroursodeoxycholic acid, 14605-22-2; bile acid binding proteins; Bile Acids and Salts; Carrier Proteins; Cholates; Deuterium, 7782-39-0; Membrane Glycoproteins; Organic Anion Transporters, Sodium-Dependent; P-glycoprotein 2; P-Glycoproteins; Phospholipids; RNA, Messenger; sodium-bile acid cotransporter, 145420-23-1; Symporters