Biotransformation of lifibrol (U-83860) to mixed glyceride metabolites by rat and human hepatocytes in primary culture.
Lifibrol (U-83860), K12.148) is a lipid-lowering drug that has the potential to accumulate in the liver and induce hepatic peroxisome proliferation. To investigate the identity and potential human relevance of persistent lifibrol-related residues in rat liver, rat and human hepatocyte primary cultures were treated with 30 microM of [14C]lifibrol. After a steady uptake for 24 hr, cellular levels of radioactivity became stable for the next 24-48 hr. A nonradioactive lifibrol chase caused an efflux of intracellular radioactivity. Cellular autoradiography revealed the association of radioactivity with small lipid drops at 6 hr exposure and with large lipid drops at 24 hr exposure. HPLC analysis of media revealed that lifibrol acyl glucuronide and a t-butylcarboxylic acid metabolite (U-94613) were the major metabolites of rat and human hepatocytes, respectively. Using an HPLC method suitable for nonpolar metabolites, the analysis of rat and human cell extracts revealed a broad band of multiple, radioactive peaks that had a similar retention and UV spectrum to a synthetic standard of lifibrol cholesterol ester. Folch extracts of liver from rats treated with [14C]lifibrol or unlabeled lifibrol and [14C]acetate had a unique radioactive TLC band that had similar HPLC retention to hepatocyte residues. The group of nonpolar peaks from the hepatocytes was purified by HPLC. Conversion of the lifibrol sec-hydroxy group to a nicotinate ester afforded particle beam-electron impact mass spectra of the cholesterol ester standard and hepatocyte residues. The derivatized rat hepatocyte residue did not contain detectable lifibrol cholesterol ester (M+.816), but did contain molecular ion clusters corresponding to a mixed triglyceride of lifibrol and two fatty acids. Lifibrol-specific product ions of molecular ion clusters centered at M+.1021, 1047, and 1073 were observed at m/z 448, 430, and 310. The major lifibrol-containing triglycerides had a fatty acid composition of C16-C20 with 0-6 unsaturations.
Sun
E L
EL
Investigative Toxicology, Pharmacia and Upjohn, Inc., Kalamazoo, MI 49007, USA.
Feenstra
K L
KL
Bell
F P
FP
Sanders
P E
PE
Slatter
J G
JG
Ulrich
R G
RG
D000818:Animals; D000924:Anticholesteremic Agents / Q000493:pharmacokinetics*; D001711:Biotransformation; D000440:Butanols / Q000493:pharmacokinetics*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003470:Culture Media; D005989:Glycerides / Q000378:metabolism*; D006801:Humans; D062385:Hydroxybenzoates / Q000493:pharmacokinetics*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D015394:Molecular Structure; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar
D000924:Anticholesteremic Agents; D000440:Butanols; D003470:Culture Media; D005989:Glycerides; D062385:Hydroxybenzoates; C059343:lifibrol