Identification of bile alcohols in urine from healthy humans.

Abstract

Bile alcohols present in urine from healthy adults were studied. Urine was extracted with octadecylsilane-bonded silica gel, and a neutral fraction and a glucuronide fraction were isolated by ion exchange chromatography on piperidinohydroxypropyl Sephadex LH-20. Following hydrolysis of the glucuronide fraction with beta-glucuronidase and purification by silica gel column chromatography, the bile alcohols were analyzed by a combined gas-liquid chromatography-mass spectrometry. By direct comparison with reference standards, the structures of four major bile alcohols were elucidated as follows: 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25- pentol ; 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24, 25- pentol ; 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26- pentol ; and 5 beta-cholestane-3 alpha,7 alpha,12 alpha,26,27- pentol . The daily excretion of these four bile alcohols in urine was 0.5-1.0 mumoles. After purification by silica gel column chromatography, the neutral fraction was analyzed by a combined gas-liquid chromatography-mass spectrometry. The major bile alcohol excreted in urine as the unconjugated form was 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25- pentol . The daily excretion of the unconjugated C26 pentol (0.02-0.05 mumoles) was far lower than that of the conjugated C26 pentol (0.34-0.86 mumoles).