Detailed low-dose study of 1,1-bis(p-chlorophenyl)-2,2,2- trichloroethane carcinogenesis suggests the possibility of a hormetic effect.
To obtain information on the effects of nongenotoxic carcinogens at low doses for human cancer risk assessment, the carcinogenic potential of the organochlorine insecticide, 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), in the liver was assessed in F344 rats. In experiment 1, 240 male animals, 21 days old, were administered 0, 0.5, 1.0, 2.0, 5.0, 20, 100 and 500 ppm DDT in the diet for 16 weeks. Experiment 2 was conducted to elucidate the carcinogenic potential of DDT at lower levels using 180 rats given doses of 0, 0.005, 0.01, 0.1, 0.2 and 0.5 ppm. The livers of all animals were immunohistochemically examined for expression of glutathione S-transferase placental form (GST-P), putative preneoplastic lesions. Quantitative values for GST-P-positive foci in the liver were increased dose-dependently in rats given 20 ppm DDT and above with statistical significance as compared with the concurrent control value. In contrast, doses of 0.005 and 0.01 ppm were associated with a tendency for decrease below the control value, although not significantly. Western blotting analysis show that cytochrome P-450 3A2 (CYP3A2) protein expression tended to decrease at 0.005 and 0.01 ppm, a good correlation being observed with the change in the number of GST-P-positive foci. These findings suggest that a DDT hepatocarcinogenicity may show nonlinear response, that is, hormetic response at low doses. Furthermore, since CYP3A2 protein expression appears to be important for the effects of phenobarbital and the alpha-isomer of benzene hexachloride, mRNAs for IL-1 receptor type 1 (IL-1R1) and TNF-alpha receptor type 1 (TNFR1) whose ligands have roles not only in downregulating CYP3A2 expression but also in inducing antiproliferative effect or apoptosis in hepatocyte were examined. Increase was observed at low doses of DDT. Oxidative stress in liver DNA, assessed in terms of 8-hydroxydeoxyguanosine as a marker, was also decreased. These findings suggest that the possible hormetic effect that was observed in our detailed low-dose study of DDT carcinogenesis, although not statistically significant, may be linked to levels of oxidative stress and proinflammatory cytokines.
Sukata
Tokuo
T
Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., Osaka, Japan. sukata@sc.sumitomo-chem.co.jp
Uwagawa
Satoshi
S
Ozaki
Keisuke
K
Ogawa
Motome
M
Nishikawa
Takayuki
T
Iwai
Syuji
S
Kinoshita
Anna
A
Wanibuchi
Hideki
H
Imaoka
Susumu
S
Funae
Yoshihiko
Y
Okuno
Yasuyoshi
Y
Fukushima
Shoji
S
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D001835:Body Weight / Q000187:drug effects; D002273:Carcinogens / Q000633:toxicity*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003634:DDT / Q000633:toxicity*; D017931:DNA Primers / Q000737:chemistry; D043382:DNA-Formamidopyrimidine Glycosylase; D004032:Diet; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase / Q000378:metabolism; D007124:Immunoenzyme Techniques; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced* / Q000201:enzymology; D008297:Male; D009699:N-Glycosyl Hydrolases / Q000378:metabolism; D009929:Organ Size / Q000187:drug effects; D018384:Oxidative Stress; D051381:Rats; D011916:Rats, Inbred F344; D017472:Receptors, Interleukin-1 / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D047888:Receptors, Tumor Necrosis Factor, Type I; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013250:Steroid Hydroxylases / Q000378:metabolism
D015703:Antigens, CD; D002273:Carcinogens; D017931:DNA Primers; D007527:Isoenzymes; D017472:Receptors, Interleukin-1; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; D003577:Cytochrome P-450 Enzyme System; D003634:DDT; D013250:Steroid Hydroxylases; C022657:steroid hormone 6-beta-hydroxylase; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase; C496558:Gstp1 protein, rat; D009699:N-Glycosyl Hydrolases; D043382:DNA-Formamidopyrimidine Glycosylase