Enhancement of rat liver cell foci development by combined treatment with heterocyclic amines at low doses.

Potential synergism between 5 or 10 carcinogenic heterocyclic amines (Trp-P-1, Trp-P-2, Glu-P-1, Glu-P-2, IQ, MeIQ, MeIQx, MeA alpha C, A alpha C and PhIP) acting at low doses was examined in a medium-term liver bioassay system for carcinogens. Immunohistochemically-demonstrated glutathione S-transferase placental form (GST-P) positive foci were assessed as the endpoint marker lesions. Male F344 rats were initially given diethylnitrosamine (DEN, 200mg/kg, ip) and beginning 2 weeks later received heterocyclic amines individually or in combination for 6 weeks. All animals were subjected to partial hepatectomy at week 3 and killed at week 8. A clear dose response relationship was observed for all heterocyclic amines, except for the nonhepatocarcinogen PhIP, with the dose used in earlier carcinogenicity assays and 1/5, 1/10, 1/25 and 1/100 of these levels. Carcinogenicity could be predicted for all compounds at the highest dose or lower dose levels except for PhIP. With combined administration of 5 or 10 chemicals, foci induction significantly exceeded the sums of 5 or 10 individual data for the 1/5, 1/10 and 1/25 dose levels, but not for the 1/100 case. The findings are of particular significance since several heterocyclic amines and other carcinogenic agents might be simultaneously generated during cooking, although each at very low concentration.