title: Measurement of parameters of cholic acid kinetics in plasma using a microscale stable isotope dilution technique: application to rodents and humans.
abstract: A stable isotope dilution method is described that allows measurement of cholic acid (CA) kinetics, that is, pool size, fractional turnover rate (FTR), and synthesis rate in mice, rats, and humans. Decay of administered [2,2,4,4-2H4]CA enrichment was measured in time in 50-microl plasma samples by gas-liquid chromatography/electron capture negative chemical ionization-mass spectrometry, applying the pentafluorobenzyl-trimethylsilyl derivative. The kinetic data expressed species-dependent differences. The CA pool sizes were 16.8 +/- 2.1, 10.6 +/- 1.2, and 2.4 +/- 0.7 micromol/100 g body weight for mice, rats, and humans, respectively. The FTR values were 0.44 +/- 0.03, 0.88 +/- 0.10, and 0.46 +/- 0.14 per day for mice, rats, and humans. The corresponding synthesis rates were 7.3 +/- 1.6, 9.3 +/- 0.1, and 1.0 +/- 0.2 micromol/100 g body weight per day. The human data agreed well with literature data obtained by conventional isotope dilution techniques. For rats and mice these are the first reported isotope dilution data. The method was validated by confirmation of isotopic equilibrium between biliary CA and plasma CA in the rat. Its applicability was demonstrated by the observation of increased CA FTR and CA synthesis rate in rats fed cholestyramine, which is known to increase fecal bile acid excretion. The presented stable isotope dilution method enables the determination of CA kinetic parameters in small plasma samples. The method can be applied in unanesthetized rodents with an intact enterohepatic circulation and may also be valuable when studying the development of human neonatal bile acid kinetics.
authors.affiliation: Groningen University Institute for Drug Exploration, Center for Liver, Digestive, and Metabolic Diseases, Laboratory of Pediatrics, University Hospital Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands.
authors.forename: C V
authors.initials: CV
authors.lastname: Hulzebos
authors.forename: L
authors.initials: L
authors.lastname: Renfurm
authors.forename: R H
authors.initials: RH
authors.lastname: Bandsma
authors.forename: H J
authors.initials: HJ
authors.lastname: Verkade
authors.forename: T
authors.initials: T
authors.lastname: Boer
authors.forename: R
authors.initials: R
authors.lastname: Boverhof
authors.forename: H
authors.initials: H
authors.lastname: Tanaka
authors.forename: I
authors.initials: I
authors.lastname: Mierau
authors.forename: P J
authors.initials: PJ
authors.lastname: Sauer
authors.forename: F
authors.initials: F
authors.lastname: Kuipers
authors.forename: F
authors.initials: F
authors.lastname: Stellaard
mesh_terms: D000328:Adult; D000818:Animals; D001646:Bile / Q000378:metabolism; D002792:Cholestyramine Resin / Q000008:administration & dosage; D019826:Cholic Acid / Q000008:administration & dosage / Q000097:blood* / Q000493:pharmacokinetics*; D003903:Deuterium; D004032:Diet; D005243:Feces / Q000737:chemistry; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007201:Indicator Dilution Techniques; D007700:Kinetics; D016014:Linear Models; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged; D051381:Rats; D017208:Rats, Wistar; D012680:Sensitivity and Specificity
chemical_list: D002792:Cholestyramine Resin; D003903:Deuterium; D019826:Cholic Acid