Effect of subchronic 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure on immune system and target gene responses in mice: calculation of benchmark doses for CYP1A1 and CYP1A2 related enzyme activities.
The dose-effect relationships were analysed for several noncarcinogenic endpoints, such as immunological and biochemical responses at subchronic, low dose exposure of female C57BL/6 mice to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The animals were treated i.p. with TCDD according to the initial- and maintenance-dose principal for a period of 135 days. The initial doses were 1, 10 and 100 ng TCDD/kg, the weekly maintenance doses were 0.2, 2 and 20 ng TCDD/kg, respectively. At days 23, 79 and 135 of TCDD/kg, treatment 10 animals of each dose group were killed. As immunological parameters the number of thymocytes and the pattern of thymocyte subpopulations were determined. In liver, lung and thymus, mRNA expression of TGF-alpha, TGF-beta(1), TGF-beta(2), TGF-beta(3), TNF-alpha, IL-1 beta and different CYP1 isoforms (CYP1A1, CYP1A2, CYP1B1) was analysed. In the livers, activities of 7-ethoxyresorufin-O-deethylase (EROD) and 7-methoxyresorufin-O-demethylase (MROD) were measured. TCDD content in the liver was determined. The main results are summarized as follows: (1) The TCDD doses were not sufficient to elicit dose-dependent changes of pattern of thymocyte subpopulation. (2) TCDD failed to change the mRNA expression of TGF-alpha, TGF-beta and TNF-alpha, but led to an increase of IL-1 beta mRNA expression in liver, lung and thymus. The results show that the TCDD induced IL-1 beta mRNA increase is at least as sensitive a marker as the induction of CYP1A isoforms. (3) The expression of CYP1B1 mRNA remained unchanged at the doses tested, while CYP1A1 and CYP1A2 mRNA expression was dose-dependently enhanced. EROD and MROD activities in the liver paralleled the increases of CYP1A1 and CYP1A2 mRNA expression. (4) Regression analysis of the data showed that most of the parameters tested fit a linear model. (5) From the data, a benchmark dose for EROD/MROD activities in the livers of female C57BL/6 mice of about 0.03 ng TCDD/kg per day was calculated.
Vogel
C
C
Medical Institute of Environmental Hygiene, Heinrich Heine University of Düsseldorf, Germany.
Donat
S
S
Döhr
O
O
Kremer
J
J
Esser
C
C
Roller
M
M
Abel
J
J
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001835:Body Weight / Q000187:drug effects; D002452:Cell Count / Q000187:drug effects; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism*; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism*; D065633:Cytochrome P-450 CYP1B1; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics; D007274:Injections, Intraperitoneal; D007375:Interleukin-1 / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D008168:Lung / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009929:Organ Size / Q000187:drug effects; D000072317:Polychlorinated Dibenzodioxins / Q000008:administration & dosage / Q000378:metabolism / Q000633:toxicity*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012044:Regression Analysis; D013950:Thymus Gland / Q000166:cytology / Q000187:drug effects*; D016211:Transforming Growth Factor alpha / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
D007375:Interleukin-1; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D016211:Transforming Growth Factor alpha; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585498:Cyp1b1 protein, mouse; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D065633:Cytochrome P-450 CYP1B1