RT Journal Article
SR Electronic
T1 Glucuronidation of all-<em>trans</em>-Retinoic Acid and 5,6-Epoxy-all-<em>trans</em>-retinoic Acid
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 5
OP 11
VO 25
IS 1
A1 Little, Joanna M.
A1 Lehman, Paul A.
A1 Nowell, Susan
A1 Samokyszyn, Victor
A1 Radominska, Anna
YR 1997
UL http://dmd.aspetjournals.org/content/25/1/5.abstract
AB The effects of detergent, alamethicin (a channel-forming peptide), and the inducers phenobarbital and 3-methylcholanthrene on glucuronidation of all-trans-retinoic acid (atRA) and 5,6-epoxy-atRA have been investigated using liver microsomes from Sprague-Dawley and Fischer 344 rats. Conditions for enzymatic glucuronidation were optimized for substrate concentration, protein, and time by using atRA and Sprague-Dawley microsomes. With detergent-activated Sprague-Dawley microsomes, 5,6-epoxy-atRA was shown to be a significantly better substrate than atRA for microsomal glucuronidation (263 vs. 116 pmol/mg/min for 5,6-epoxy-atRA and atRA, respectively). The product of incubation of microsomes with atRA and UDP-glucuronic acid was identified as a glucuronide by β-glucuronidase hydrolysis and by HPLC analysis. Alamethicin was shown to be a highly effective activator of glucuronidation activity; atRA and 5,6-epoxy-atRA glucuronidation rates were increased 2- and 3-fold, respectively, compared with detergent activation. Alamethicin (but not detergent) significantly increased retinoid glucuronidation by microsomes from Fischer 344 rats treated with phenobarbital and 3-methylcholanthrene, compared with untreated controls. The two compounds were equally effective inducers of activity, although 5,6-epoxy-atRA was again the better substrate. The same control and induced Fischer rat microsomes were photolabeled with [32P]5-azido-UDP-glucuronic acid in the absence or presence of detergent, two concentrations of alamethicin, and a 10-fold molar excess of unlabeled UDP-glucuronic acid. Photoincorporation into microsomal proteins from detergent-disrupted induced microsomes was 2–3 times greater than that of controls. Alamethicin increased photoincorporation of the probe into UDP-glucuronosyltransferase proteins an additional 1.5–2-fold in control and induced microsomes, compared with the respective detergent-activated samples. The American Society for Pharmacology and Experimental Therapeutics