Microsomal expoxide hydrolase is required for 7,12-dimethylbenz[a]anthracene (DMBA)-induced immunotoxicity in mice.
Microsomal epoxide hydrolase (mEH, EPHX1) is involved in the metabolism of chemicals to generate dihydrodiol intermediates in the presence of the cytochrome P450. We have previously shown that 7,12-dimethylbenz[a]anthracene (DMBA) can suppress both cell-mediated and humoral immune responses in wild-type (WT) C57BL/6N mice but not in CYP1B1 null mice. In the present studies, we hypothesized the critical metabolite responsible for DMBA-induced immunotoxicity is likely to be the 3,4-dihydrodiol-1,2-epoxide metabolite of DMBA, which requires mEH for formation. Mice were gavaged orally with DMBA (0, 17, 50, and 150 mg/kg) once a day for 5 days. Immune function and other assays were performed on day 7. Our data showed that unlike WT mice, DMBA treatment of mEH null mice produced no alterations in the body weight, spleen weight, or spleen cellularity. Similarly, DMBA treatments did not affect the PFC response in mEH null mice. Natural killer activity was not altered by DMBA treatment in mEH null mice. T-cell mitogenesis was partially suppressed by 50 and 150 mg/kg DMBA treatments of mEH null mice, but B-cell mitogenesis was not affected. Finally, we assessed the biodistribution of DMBA in both C57BL/6N WT and mEH null mice in spleen, thymus, and liver after 24 h and 7 days oral gavage. The concentrations of DMBA in each organ were not significantly different in WT and in mEH null mice. Collectively, these results demonstrate that mEH (EPHX1 gene) is a crucial enzyme for metabolic activation of DMBA in vivo leading to immunosuppression of spleen cells.
Gao
Jun
J
The University of New Mexico College of Pharmacy Toxicology Program, Albuquerque, New Mexico 87131-0001, USA.
Lauer
Fredine T
FT
Mitchell
Leah A
LA
Burchiel
Scott W
SW
D015127:9,10-Dimethyl-1,2-benzanthracene / Q000633:toxicity*; D000818:Animals; D000917:Antibody Formation / Q000187:drug effects*; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology; D002851:Chromatography, High Pressure Liquid; D002860:Chromium Radioisotopes; D004851:Epoxide Hydrolases / Q000378:metabolism*; D005260:Female; D005434:Flow Cytometry; D006462:Hemolytic Plaque Technique; D007111:Immunity, Cellular / Q000187:drug effects*; D007114:Immunization; D007166:Immunosuppressive Agents; D007202:Indicators and Reagents; D007694:Killer Cells, Natural / Q000187:drug effects; D008099:Liver / Q000166:cytology / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008862:Microsomes, Liver / Q000201:enzymology*; D012015:Reference Standards; D012756:Sheep / Q000276:immunology; D013154:Spleen / Q000166:cytology / Q000276:immunology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D013936:Thymidine / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology
D002860:Chromium Radioisotopes; D007166:Immunosuppressive Agents; D007202:Indicators and Reagents; D015127:9,10-Dimethyl-1,2-benzanthracene; D004851:Epoxide Hydrolases; D013936:Thymidine