N-nitrosodiethylamine initiation of carcinogenesis in Japanese medaka (Oryzias latipes): hepatocellular proliferation, toxicity, and neoplastic lesions resulting from short term, low level exposure.
To investigate relationships among carcinogen exposure, cell proliferation, and carcinogenesis, 14-day post-hatch Japanese medaka (Oryzias latipes) were exposed to 0, 10, 25, 50, or 100 ppm N-nitrosodiethylamine (DEN) for 48 h under static renewal conditions. They were then held in clean water until sampling at 3 and 6 months. The frequencies of hepatic lesions and neoplasms were determined from hematoxylin/eosin-stained paraffin sections. A significant (p < 0.0001) concentration-related increase in hepatic vacuolated foci occurred in 3- and 6-month samples, with males having a significantly (p = 0.02) higher incidence than females. Concentration-related increases in degenerative lesions were documented for spongiosis hepatis at 3 months (p = 0.053) and hepatic vacuoles at 6 months (p = 0.005). There was a significant (p = 0.0001) concentration-related increase in macrophage aggregates at 6 months. Basophilic foci were significantly related (p < 0.0001) to DEN concentration at 3 months post-exposure and were unaffected by gender or age. At both 3 and 6 months, there were significant concentration-related increases in hepatocellular carcinoma (p < or = 0.02). Hepatocyte proliferation in 3-month whole specimens was quantified using an immunohistochemical assay for proliferating-cell nuclear antigen. Trend tests and a probit dose-response model showed a significantly positive correlation (p = 0.015) between proliferating hepatocytes and DEN concentrations. These results confirm that short-term exposure to low and moderate levels of DEN initiates concentration-dependent carcinogenic effects in medaka that are apparent at 3 months postexposure. DEN could be an effective initiator in an initiation/promotion assay for medaka using a 48-h exposure period, DEN concentrations < or = 10 ppm, and a 6-month sampling period.
Brown-Peterson
N J
NJ
Department of Coastal Sciences, The University of Southern Mississippi, Ocean Springs 39566-7000, USA.
Krol
R M
RM
Zhu
Y
Y
Hawkins
W E
WE
D000367:Age Factors; D000818:Animals; D015197:Carcinogenicity Tests / Q000379:methods; D002273:Carcinogens / Q000633:toxicity*; D002455:Cell Division / Q000187:drug effects; D056486:Chemical and Drug Induced Liver Injury; D004052:Diethylnitrosamine / Q000008:administration & dosage / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D005399:Fishes; D007150:Immunohistochemistry; D008107:Liver Diseases / Q000473:pathology; D008113:Liver Neoplasms / Q000139:chemically induced* / Q000473:pathology; D008264:Macrophages / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis; D011897:Random Allocation; D012737:Sex Factors; D015996:Survival Rate; D013997:Time Factors
D002273:Carcinogens; D018809:Proliferating Cell Nuclear Antigen; D004052:Diethylnitrosamine