CHARACTERIZATION OF 1-HYDROXYPYRENE AS A NOVEL MARKER SUBSTRATE OF 3-METHYLCHOLANTHRENE-INDUCIBLE PHENOL UDP-GLUCURONOSYLTRANSFERASE(S)

Rats were treated with acetone, pyrazole, phenobarbital, 4,4'-methylen ebis-(2-chloroaniline) (MOCA), 3- methylcholanthrene, creosote oil, or a mixture of polychlorinated biphenyls (Aroclor 1254) to study the in ducibility and enzyme kinetics of UDP-glucuronosyltransferases towards 1-hydroxypyrene, which is a human metabolite and a urinary biomarker of exposure to pyrene. The rate of 1-hydroxypyrene glucuronidation was analysed in rat liver microsomes by a fluorometric HPLC assay of the formed glucuronide. The apparent K-m and V-max values in untreated con trols (K-m = 0.27 mM; V-max = 31 nmol/min./mg protein) did not differ markedly from those in rats treated with acetone, pyrazole or phenobar bital, whereas the significantly decreased K-m and increased V-max val ues of the rats treated with the carcinogenic chemicals, MOCA (0.11; 5 1), creosote (0.06; 137), 3-methylcholanthrene (0.07; 141) or the Aroc lor-1254 polychlorinated biphenyl (PCB) mixture (0.08; 226), implicate d major changes in the hepatic expression of UDP-giucuronosyltransfera ses. 1-Hydroxypyrene proved to be a high affinity substrate and a sens itive marker of the polycyclic aromatic hydrocarbon (PAH) metabolizing UDP-glucuronosyltransferase(s). Catalytically, the most efficient iso forms were induced in creosote, 3-methylcholanthrene and PCB-treated r ats showing V-max/K-m ratios which were 22-27 times greater than in un treated controls. Our findings suggest the existence of a 3-methylchol anthrene type inducible and a functionally efficient low-K-m/ high-V-m ax form(s) of UDP-glucuronosyltransferase (s) that detoxify 1-hydroxyp yrene a nd probably other polycyclic aromatic hydrocarbons as well.