Critical evaluation of the existence of so-called tissue-bound lithocholate in human liver tissue by selected ion monitoring.

Monohydroxy bile acids in liver tissue may be of importance because of their hepatotoxicity and strong cholestatic effects. Recently, the existence of lithocholate in liver tissue in two forms was suggested by Nair et al. (Lipids. 1977. 12: 922-929) i.e., either in free form or as so-called tissue-bound lithocholate released exclusively by cholylglycine hydrolase treatment. The presence of the latter aroused much interest in relation to its hepatotoxicity and possible role in tumor induction. In the present investigation lithocholyl-epsilon-L-lysine, proposed as the predominant tissue-bound bile acid, was synthesized and its metabolic behavior was tested. Lithocholyl-epsilon-lysine was not deconjugated by cholylglycine hydrolase treatment but only by alkaline hydrolysis. Bile acids in seven cirrhotic and three noncirrhotic liver samples were extracted with 95% ethanol-0.1% ammonium hydroxide. The bile acids in the extract and residue were quantified by glass capillary gas-liquid chromatography using selected ion monitoring. The presence of so-called tissue-bound lithocholate could not be substantiated in either cirrhotic or noncirrhotic liver tissues. Nearly complete extraction of lithocholate was achieved by the use of organic solvent alone. Therefore, tissue-bound lithocholate, if it exists at all, may be attached to tissue by a physical linkage which can be disrupted by the use of conventional organic solvent.