IN-VITRO METABOLISM OF CHLORO-2-METHYLPHENYL)-N'-(2-METHYLPROPYL)THIOUREA - SPECIES COMPARISON AND IDENTIFICATION OF A NOVEL THIOCARBAMIDE-GLUTATHIONE ADDUCT
Gj. Stevens et al., IN-VITRO METABOLISM OF CHLORO-2-METHYLPHENYL)-N'-(2-METHYLPROPYL)THIOUREA - SPECIES COMPARISON AND IDENTIFICATION OF A NOVEL THIOCARBAMIDE-GLUTATHIONE ADDUCT, Chemical research in toxicology, 10(7), 1997, pp. 733-741
The in. vitro metabolism of SDZ HDL 376, a thiocarbamide developed for
the treatment of atherosclerosis, was investigated in rat, dog, monke
y, and human liver microsomes, as well as in rat and human liver slice
s. [C-14]SDZ HDL 376 was extensively metabolized in all the species ex
cept human. In rat liver microsomes an S-oxide was the major metabolit
e. In human and monkey microsomes, carbon hydroxylation was favored; T
he NADPH-dependent oxidation of SDZ HDL 376 resulted in covalent bindi
ng to microsomal protein. Addition of GSH to the incubations decreased
protein binding in a concentration-dependent manner and resulted in a
novel SDZ HDL 376-GSH adduct. Adduct formation required NADPH and was
mediated predominately by cytochrome P450. Inhibition of cytochrome P
450 by 1-aminobenzotriazole resulted in a 95% decrease in adduct forma
tion, while heat inactivation of flavin-containing monooxygenases resu
lted in a 10% decrease. Unlike other thiocarbamides which form disulfi
de adducts with GSH, the SDZ HDL 376 adduct contained a thioether link
age as characterized by LC/MS/MS and reference to a synthetic standard
. Reactions performed with [S-35]GSH resulted in a [S-35]SDZ HDL 376-G
SH adduct, demonstrating the sulfur was derived from GSH. Adduct forma
tion was faster in rat microsomal reactions compared to human microsom
es. Other structurally unrelated thiocarbamides (phenylthiourea, methi
mazole, 2-mercaptobenzimidazole, 2-mercaptoquinazoline, and 2-propyl-6
-thiouracil) did not form similar adducts in rat liver microsomes supp
lemented with GSH. Therefore, the GSH adduct of SDZ HDL 376 is unique
fdr this type of thiocarbamide. These results suggest that the bioacti
vation and detoxification bf SDZ HDL 316 differ significantly from oth
er thiocarbamides. Furthermore, the in vitro formation of S-oxides and
GSH adducts in rat hepatic tissue, and ring hydroxylation and glucuro
nidation in human hepatic tissue, suggests rats may be more susceptibl
e to the toxicity of SDZ HDL 376 compared to humans.