Protein Information

ID 450
Name demethylase
Synonyms DMTase; Demethylase; MBD 2; MBD2; Methyl CpG binding domain protein 2; Methyl CpG binding protein MBD2; NY CO 41; Demethylases…

Compound Information

ID 182
Name endosulfan
CAS 6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin 3-oxide

Reference

PubMed Abstract RScore(About this table)
16855053 Casabar RC, Wallace AD, Hodgson E, Rose RL: Metabolism of endosulfan-alpha by human liver microsomes and its utility as a simultaneous in vitro probe for CYP2B6 and CYP3A4. Drug Metab Dispos. 2006 Oct;34(10):1779-85. Epub 2006 Jul 19.
Endosulfan-alpha is metabolized to a single metabolite, endosulfan sulfate, in pooled human liver microsomes (Km = 9.8 microM, Vmax = 178.5 pmol/mg/min). With the use of recombinant cytochrome P450 (P450) isoforms, we identified CYP2B6 (Km = 16.2 microM, Vmax = 11.4 nmol/nmol P450/min) and CYP3A4 (Km = 14.4 microM, Vmax = 1.3 nmol/nmol P450/min) as the primary enzymes catalyzing the metabolism of endosulfan-alpha, although CYP2B6 had an 8-fold higher intrinsic clearance rate (CL (int) = 0.70 microl/min/pmol P450) than CYP3A4 (CL (int) = 0.09 microl/min/pmol P450). Using 16 individual human liver microsomes (HLMs), a strong correlation was observed with endosulfan sulfate formation and S-mephenytoin N-demethylase activity of CYP2B6 (r (2) = 0.79), whereas a moderate correlation with testosterone 6 beta-hydroxylase activity of CYP3A4 (r (2) = 0.54) was observed. Ticlopidine (5 microM), a potent CYP2B6 inhibitor, and ketoconazole (10 microM), a selective CYP3A4 inhibitor, together inhibited approximately 90% of endosulfan-alpha metabolism in HLMs. Using six HLM samples, the percentage total normalized rate (% TNR) was calculated to estimate the contribution of each P450 in the total metabolism of endosulfan-alpha. In five of the six HLMs used, the percentage inhibition with ticlopidine and ketoconazole in the same incubation correlated with the combined % TNRs for CYP2B6 and CYP3A4. This study shows that endosulfan-alpha is metabolized by HLMs to a single metabolite, endosulfan sulfate, and that it has potential use, in combination with inhibitors, as an in vitro probe for CYP2B6 and 3A4 catalytic activities.
6(0,0,1,1)