Enhancing effect of various hepatocarcinogens on induction of preneoplastic glutathione S-transferase placental form positive foci in rats—an approach for a new medium-term bioassay system

Abstract

A large series of assays of the hepatocarcinogenic potential of 112 different compounds were carried out using a rapid bioassay system developed in this laboratory based on the two-step concept of hepatocarcinogenesis. Rats were initially given a single dose (200 mg/kg) of diethylnitrosamine (DEN) i.p. and starting 2 weeks later were treated with test compounds for 6 weeks and then killed, all rats being subjected to two-thirds partial hepatectomy (PH) at week 3. Carcinogenic potential was scored by comparing the number and area per cm2 of induced glutathione S-transferase placental form-positive (GST-P+) foci in the liver with those of the corresponding control group given DEN alone. Positive was scored for a significant increase in the value of GST-P+ foci, negative for no change or a decrease. Results were compared to reported Salmonella/microsome and long-term carcinogenicity test findings. Of the liver carcinogens, 10 out of 11 (90.9%) mutagenic, and 11 out of 13 (84.6%) non-mutagenic compounds gave positive results (mean, 87.5%). Carcinogens other than the hepatocarcinogens gave less positive results (two out of 17, 11.8%). None of the compounds reported as non-carcinogenic demonstrated positivity suggesting that the assay system does not suffer from the disadvantage of false-positive results. The protocol system also provided information concerning the inhibitory potential of compounds such as anti-oxidants. It is concluded that the present experimental protocol which requires far fewer animals and shorter duration than a long-term carcinogenicity test has practical applications for the rapid and economical screening of environmental hepatocarcinogens and their inhibitory agents.

Anticarcinogenic Effect and Modification of Cytochrome P450 2E1 by Dietary Garlic Powder in Diethylnitrosamine-Initiated Rat Hepatocarcinogenesis

“…In this study, we examined the effects of dietary garlic powder at various levels on the formation of preneoplastic foci, and the modification of CYP 2E1 in rat livers using a modified method of the medium term bioassay system of Ito et al (1988). The medium term bioassay system, which involves the GST-P form as an enzyme marker, was used as the assay method, since it is a specific assay system for preneoplastic lesions that occur during hepatocarcinogenesis (Ito et al, 1988;Satoh et al, 1989).…”

“…Therefore, in this study, we investigated the effects of dietary garlic powder at various levels on DENinitiated hepatocarcinogenesis and the hepatic microsomal CYP P450 2E1 and P450 2B1 in rats. We used a modified method of the medium-term bioassay system of Ito et al (1988). The glutathione S-transferase placental (GST-P) form was used as an enzyme marker of hepatocarcinogenesis (Satoh et al, 1989).…”

Potential effect of Nigella sativa against Diethylnitrosamine-induced hepatocarcinogenesis in rats

“…Therefore, this enzyme has been used as a reliable tumor marker for both chemically induced and spontaneously arising precancerous lesions and hepatomas in experimental carcinogenesis studies. In the present investigation, the method of the medium-term bioassay proposed by Ito et al based on the two-step model of hepatocarcinogenesis was used (Ito et al, 1988), modified appropriately. This system was initially introduced in order to screen environmental and naturally occurring carcinogens and was later used successfully for identifying different anticarcinogens (Ito et al, 1989;Ogiso et al, 1990).…”

“…Diethylnitrosamine (DEN) was dissolved in normal saline (1 g in 25 mL). A single dose of 200 mg/ kg-body weight was given to each animal to initiate hepatocarcinogenesis (Ito et al, 1988).…”

“…The DEN-partial hepatectomy model has been proven to be a consistent bioassay for the detection of chemical hepatocarcinogenesis and for the assessment of the beneficial potential of chemopreventive agents (Ito et al, 1988;Moore et al, 1999). All animals were euthanized at the end of the experiments and subjected to full necropsy.…”