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In order to study the glycosidic conjugation of chenodeoxycholic, hyodeoxycholic, and ursodeoxycholic acids in patients with cholestasis after oral administration of pharmacological amounts of the respective bile acids avoiding the application of radioactive tracers we synthesized [24-13C]chenodeoxycholic, [24-13C]hyodeoxycholic, and [24-13C]ursodeoxycholic acids. The reaction intermediates of the bile acid syntheses were characterized by infrared spectroscopy. Purity was confirmed using thin-layer chromatography as well as gas chromatography-mass spectrometry. The 13C atom excess of approximately 90% of the synthesized bile acids was the same as the 13C atom excess of the sodium [13C]cyanide used for the labeling reaction confirming the successful synthesis. After oral administration of 0.5 g of [24-13C]ursodeoxycholic acid to a healthy volunteer, 13C label was detected in the nonamidated and glycine- or taurine conjugated glucosides and the N-acetylglucosaminide of ursodeoxycholic acid in urine. This establishes ursodeoxycholic acid as the first bile acid so far known to undergo both of the recently described glycosidic conjugation reactions in humans.

A stable isotope dilution assay using D3-mevalonic acid was developed and applied to the study of mevalonic aciduria. The method also appears to be suitable for the evaluation of different therapeutic regimens in patients with hypercholesterolemia. Mevalonic acid was isolated by liquid partition chromatography and quantified as the underivatized lactone by means of ammonia chemical ionization selected ion monitoring capillary gas chromatography-mass spectrometry. In heterozygotes there was significantly greater urinary excretion of mevalonic acid, while the range of enzymatic activity of mevalonate kinase showed an overlap with that of controls. The analysis of amniotic fluids of two pregnancies at risk for mevalonic aciduria showed a 3277-fold elevation as compared to controls in the first case, diagnostic of an affected fetus, and a normal value in the second one. Mevalonic acid concentration was much increased in tissues of the affected and aborted fetus. Concentrations ranged from 840 to 1120 mumol/kg in various tissues and were as high as 1810 mumol/kg in brain. Concentrations in control fetal tissues were approximately 1 mumol/kg.