Modulation of endocrine pathways by 4,4'-DDE in the deer mouse Peromyscus maniculatus.
4,4'-DDT and 4,4'-DDE are widespread environmental contaminants that cause eggshell thinning in birds, altered sex ratios in the American alligator, and changes in the anal-genital distance in rodents. These contaminants are known to cause some of their toxicity by altering steroid receptor-mediated mechanisms. However, chemical-specific alterations in the expression of hormone-metabolizing enzymes may also be a mechanism for endocrine disruption, by altering the half-life of hormones in critical tissues. Previously, we showed that 4,4'-DDE causes a dose-dependent increase in ethoxyresorufin-O-deethylase (EROD) activity, but not pentoxyresorufin-O-dealkylase (PROD) activity, in the deer mouse. In this study, we demonstrated that 4,4'-DDE elicited a corresponding increase in CYP1A protein expression but not CYP2B using Western blotting and immunoprecipitation. 4,4'-DDE-mediated changes in phase II conjugating enzymes; UDP-glucuronosyltransferase (UGT) and phenolsulfotransferase (ST), were also investigated for the first time. Prepubescent female deer mice were dosed with 4,4'-DDE by gavage on days 1 and 2, then euthanized on day 4. As anticipated, dose-dependent increases in hepatic EROD and MROD activities, but not PROD or BROD, were observed. UGT activity was monitored by incubating liver microsomes and 14C-UDP-GA with potential substrates and measuring incorporation of radioactivity into TLC-resolved glucuronides. Dose-dependent increases in conjugation were observed with p-nitrophenol (a general UGT substrate) but not testosterone. Interestingly, a biphasic dose-response curve was observed for ST activity, with a peak at the 3 mg/kg dose. Dose-dependent increases in CYP1A1 and UGT-specific immunoreactive proteins were observed, suggesting de novo synthesis as a consequence of 4,4'-DDE exposure. We also measured Phase I and II enzymes in deer mouse platelets. Preliminary results indicate that the 4,4'-DDE-induced changes in liver Phase I and II enzyme activity were similar, but not identical, to those found in platelets. These results indicate that environmentally-relevant levels of 4,4'-DDE modulate the activity and expression of CYP1A1 and phase II enzymes in the deer mouse and that certain changes may be measured non-lethally.
Dickerson
R L
RL
Texas Tech University/Texas Tech University Health Sciences Center, Lubbock 79430, USA. phrrld@ttuhsc.edu
McMurry
C S
CS
Smith
E E
EE
Taylor
M D
MD
Nowell
S A
SA
Frame
L T
LT
D000818:Animals; D001792:Blood Platelets / Q000201:enzymology; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D019362:Cytochrome P-450 CYP2B1 / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003633:Dichlorodiphenyl Dichloroethylene / Q000633:toxicity*; D004702:Endocrine Glands / Q000187:drug effects*; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000633:toxicity*; D004958:Estradiol / Q000097:blood; D005260:Female; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D010088:Oxidoreductases / Q000378:metabolism; D010542:Peromyscus / Q000378:metabolism*; D013739:Testosterone / Q000097:blood
D004785:Environmental Pollutants; D013739:Testosterone; D003633:Dichlorodiphenyl Dichloroethylene; D004958:Estradiol; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; C076307:methoxyresorufin-O-demethylase; D019363:Cytochrome P-450 CYP1A1; D019362:Cytochrome P-450 CYP2B1