Species differences in bile acids II. Bile acid metabolism

Abstract

One of the mechanisms of drug-induced liver injury (DILI) involves alterations in bile acid (BA) homeostasis and elimination, which encompass several metabolic pathways including hydroxylation, amidation, sulfation, glucuronidation and glutathione conjugation. Species differences in BA metabolism may play a major role in the failure of currently used in vitro and in vivo models to predict reliably the DILI during the early stages of drug discovery and development. We developed an in vitro cofactor-fortified liver S9 fraction model to compare the metabolic profiles of the four major BAs (cholic acid, chenodeoxycholic acid, lithocholic acid and ursodeoxycholic acid) between humans and several animal species. High- and low-resolution liquid chromatography-tandem mass spectrometry and nuclear magnetic resonance imaging were used for the qualitative and quantitative analysis of BAs and their metabolites. Major species differences were found in the metabolism of BAs. Sulfation into 3-O-sulfates was a major pathway in human and chimpanzee (4.8%-52%) and it was a minor pathway in all other species (0.02%-14%). Amidation was primarily with glycine (62%-95%) in minipig and rabbit and it was primarily with taurine (43%-81%) in human, chimpanzee, dog, hamster, rat and mice. Hydroxylation was highest (13%-80%) in rat and mice followed by hamster, while it was lowest (1.6%-22%) in human, chimpanzee and minipig. C6-β hydroxylation was predominant (65%-95%) in rat and mice, while it was at C6-α position in minipig (36%-97%). Glucuronidation was highest in dog (10%-56%), while it was a minor pathway in all other species (<12%). The relative contribution of the various pathways involved in BA metabolism in vitro were in agreement with the observed plasma and urinary BA profiles in vivo and were able to predict and quantify the species differences in BA metabolism. In general, overall, BA metabolism in chimpanzee is most similar to human, while BA metabolism in rats and mice is most dissimilar from human.

Quantification of common and planar bile acids in tissues and cultured cells

“…S3A). These results conform with previous studies indicating the prevalence of unconjugated BAs in rhesus macaque plasma; however, they disagree with previous studies regarding individual BAs, finding a higher percentage of unconjugated CDCA instead of DCA (46,47,72). Circulating TBA concentration in NHP plasma proved comparable to that in human plasma as reported in scientific literature, i.e.…”

“…Additionally, though this study did not evaluate sulfated BAs, at least one previous study has reported marked differences between the extent of this BA elimination pathway in NHP versus humans (46,47). Overall, however, this laboratory animal represents a highly relevant model for the study of BA synthesis, metabolism, and pharmacology with relatively minor disparities in comparison to other models.…”

“…Murine BA metabolism is well studied and known to have several discrepancies when compared to that of humans, but mouse and rat models are still used most often (5,(38)(39)(40)(41)(42)(43)(44)(45). Nonhuman primate (NHP) models represent an attractive alternative because of their increased genetic resemblance to man; however, BA metabolism in NHPs has not been as well characterized (46,47).…”

Optimization of Experimental Conditions of Automated Glucuronidation Assays in Human Liver Microsomes Using a Cocktail Approach and Ultra-High Performance Liquid Chromatography–Tandem Mass Spectrometry

“…The relative activity of recombinantly expressed UGT1A1 and UGT2B7 isoforms was less than 1.5% of UGT1A3 activity in chenodeoxycholic acid glucuronidation (in-house data), indicating a good selectivity of chenodeoxycholic acid for UGT1A3. However, chenodeoxycholic acid would not be a useful UGT1A3 probe substrate in a more complex system such as hepatocytes, due to very high taurine and glycine conjugation rates (Thakare et al, 2018). Raloxifene, considered as a partial substrate of UGT1A8 and UGT1A10 (Kemp et al, 2002), was not included in our report, as neither UGT isoform was detected in HLMs (Fallon et al, 2013;Margaillan et al, 2015).…”

Species Differences of Bile Acid Redox Metabolism: Tertiary Oxidation of Deoxycholate is Conserved in Preclinical Animals

“…The BAs in humans, minipigs, and hamsters conjugate mainly with glycine, while taurine amidation is predominant in mice, rat and dogs. It has been also discovered that less sulfation occurs in rat and mice compared to human and chimpanzee (Thakare et al, 2018b;Thakare et al, 2018a).…”