Chemopreventive Effects of Taurine on Diethylnitrosamine and Phenobarbitalinduced Hepatocarcinogenesis in Male F344 Rats

Modifying effects of taurine, a naturally occurring organosulfur compound, on diethylnitrosamine (DEN) and phenobarbital (PB)‐induced hepatocarcinogenesis were examined in rats. Male F344 rats, 5 weeks old, were divided into 8 groups. Rats of groups 1 through 5 were given i.p. injections of DEN (100 mgAg body weight) once a week for 3 weeks from one week after the start of the experiment. Of them, animals of group 2 received taurine mixed in a basal diet at a concentration of 2000 ppm for the initial 4 weeks, and those of groups 3 and 5 were given the agent starting 4 weeks after the beginning of experiment until the end (24 weeks). Rats in groups 1, 4, 7 and 8 were kept on the basal diet throughout the experiment (24 weeks). Group 6 was given taurine throughout the experiment and group 8 was treated as a vehicle control. Animals of groups 1,2, 3 and 7 received PB in drinking water at a dose of 500 ppm from one week after the end of carcinogen or vehicle treatment. Liver neoplasms were recognized only in DEN‐treated groups. The incidence and average number of liver neoplasms of group 3 were significantly lower than those of group 1. The number of glutathione S‐transferase placenta! form (GST‐P)‐positive foci of group 2 or 3 was significantly smaller than that of group 1 (P < 0.01 or P < 0,005). The average and unit areas of GST‐P‐positive foci in groups 2 and 3 were also significantly smaller than those in group 1 (P< 0.005 and P< 0.0001, P< 0.0001 and P< 0.001, respectively). In this study, the level of ornithine decarboxylase activity in non‐neoplastic liver tissue was reduced by taurine treatment in both the initiation and postinitiation phases. These results suggest that taurine could be a chemopreventive agent for liver neoplasia.