A medium-term rat liver bioassay for rapid in vivo detection of carcinogenic potential of chemicals.
A reliable medium-term bioassay system for rapid detection of carcinogenic potential of chemicals in the human environment has been developed. The 8-week-protocol consists of 2 stages; male F344 rats are given a single intraperitoneal injection of diethylnitrosamine (200 mg/kg) for initiation of liver carcinogenesis, followed by a 6-week test chemical treatment starting 2 weeks thereafter. Test chemicals are usually given in the diet or the drinking water and in the 2nd week of test chemical treatment, all rats are subjected to two-thirds partial hepatectomy in order to induce regenerative cell replication. The end-point marker is the glutathione S-transferase placental form (GST-P)-positive hepatic focus, the numbers and sizes of which are analyzed using an image-analyzer and expressed as values per unit liver section (1 cm2). When the yield of GST-P-positive foci is significantly enhanced (P<0.05) over the control value, a chemical is judged to possess carcinogenic or promotion potential for the liver. Among 313 chemicals already tested in this system in our laboratory, 30/31 (97%) mutagenic hepatocarcinogens and 29/33 (88%) non-mutagenic hepatocarcinogens gave positive results. Ten out of 43 (23%) agents known to be carcinogenic in organs other than the liver were also positive. It is particularly important that only one of 48 non-carcinogens gave a very weak positive result, so that the system has a very low false-positivity rate. It is now well documented that the assay system is highly effective for detecting hepatocarcinogens, bridging the gap between traditional long-term carcinogenicity tests and short-term screening assays. At the Fourth International Conference on Harmonization, our medium-term liver bioassay based on an initiation and promotion protocol was recommended in the guidelines as an acceptable alternative to the long-term rodent carcinogenicity test.
Ito
Nobuyuki
N
Nagoya City University, 1 Kawasumi, Mizuho-ku, Nagoya 467-8601.
Tamano
Seiko
S
Shirai
Tomoyuki
T
D000284:Administration, Oral; D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology / Q000627:therapeutic use; D001681:Biological Assay / Q000379:methods*; D014408:Biomarkers, Tumor / Q000032:analysis; D015197:Carcinogenicity Tests / Q000379:methods*; D002273:Carcinogens / Q000008:administration & dosage / Q000633:toxicity; D003043:Cocarcinogenesis; D004052:Diethylnitrosamine / Q000008:administration & dosage / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005189:False Positive Reactions; D005982:Glutathione Transferase / Q000032:analysis; D006498:Hepatectomy; D022781:Hepatocytes / Q000187:drug effects; D007091:Image Processing, Computer-Assisted; D007274:Injections, Intraperitoneal; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced* / Q000209:etiology; D008115:Liver Regeneration; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344
D016588:Anticarcinogenic Agents; D014408:Biomarkers, Tumor; D002273:Carcinogens; D004052:Diethylnitrosamine; D005982:Glutathione Transferase