Yukihiro Nomura

Profile of urinary bile acids in infants and children : developmental pattern of excretion of unsaturated ketonic bile acids and 7β-hydroxylated bile acids

Unusual bile acids, such as unsaturated ketonic and 7β-hydroxylated bile acids, have been detected in urine early in life. To elucidate the normal profiles of usual and unusual urinary bile acids in the neonatal and pediatric periods, we measured the concentrations of 28 kinds in urine from normal newborns, infants, and children by gas chromatography-mass spectrometry. The mean total bile acid/Cr ratio in 7-d-old infants was significantly higher than in subjects of other age groups (birth, 2-4 mo, 5-7 mo, 11-12 mo, 2-3 y, 9-14 y, and adult) (p < 0.05). Relatively large amounts of unusual bile acids were detected during infancy, especially during the period up to 1 mo of age. At that time, 1β,3α,7α,12α-tetrahydroxy-5β-cholan-24-oic, 7α,12α-dihydroxy-3-oxo-5β-chol-1-en-24-oic, and 7α,12α-dihydroxy-3-oxo-4-cholen-24-oic acids were predominant among the unusual urinary bile acids present. Moreover, the levels of 3α,7β,12α-trihydroxy-5β-cholan-24-oic acid increased significantly after 2-4 mo of age. These results indicate that bile acid synthesis and metabolism in the liver of developing infants are significantly different from that occurring in the liver of adults. Significant amounts of urinary isomerized 7β-hydroxylated bile acids were detected after late infancy, probably because of changes in the intestinal bacterial flora response to a change in nutrition. We describe, for the first time, evidence of the epimerization of the 7α-hydroxyl group of cholic acid, which may be unique to human development.

Prediction of human pharmacokinetics of typical compounds by a physiologically based method using chimeric mice with humanized liver

Abstract In this study, total body clearance (CLt), volume of distribution at steady state (Vss) and plasma concentration–time profiles in humans of model compounds were predicted using chimeric mice with humanized livers. On the basis of assumption that unbound intrinsic clearance (CLUint) per liver weight in chimeric mice was equal to those in humans, CLt were predicted by substituting human liver blood flow and liver weights in well-stirred model. Vss were predicted by Rodgers equation using scaling factors of tissue-plasma concentration ratios (SFKp) in chimeric mice estimated from a difference between the observed and predicted Vss. These physiological approaches showed high prediction accuracy for CLt and Vss values in humans. We compared the predictability of CLt and Vss determined by the physiologically based predictive approach using chimeric mice with those from predictive methods reported by Pharmaceutical Research Manufacturers of America. The physiological approach using chimeric mice indicated the best prediction accuracy in each predictive method. Simulation of human plasma concentration–time profiles were generally successful with physiologically based pharmacokinetic (PBPK) model incorporating CLUint and SFKp obtained from chimeric mice. Combined application of chimeric mice and PBPK modeling is effective for prediction of human PK in various compounds.

Studies on the Unusual 1β-Hydroxylated Bile Acid Biosynthesis in Infants

Unusual bile acids (1β-hydroxylated bile acids), particularly 1β-hydroxyl-cholic acid (CA-1β-ol) and 1β-hydroxyl-chenodeoxycholic acid (CDCA-1β-ol), have been detected in the urine of infants. These acids are conjugated with amino acids, such as taurine, and are then excreted mainly via the urine. CA-1β-ol and CDCA-1β-ol are the predominant bile acids during infancy and are present in relatively large amounts in the urine. However, the biosynthetic pathway of 1β-hydroxylated bile acids in infants remains unclear. To investigate the biosynthetic pathway of 1β-hydroxylated bile acids during infancy, we performed a metabolic reaction using infant hepatocytes at 3 months after delivery. Glyco- and tauro-CA-1β-ol were identified by LC/tandem mass spectrometry (MS/MS) analysis of the extracted culture medium incubated with cholic acids (CAs). Further, we identified that ketoconazole suppressed CA 1β-hydroxylation and that the CYP3A subfamily was the primary group of enzymes responsible for CA-1β-ol formation. The present study provides new information about the biosynthetic pathway of 1β-hydroxylated bile acids during infancy.