The modifying effects of dietary administration of dried Chlorella pyrenoidosa powder (C. pyrenoidosa) on the development of glutathione S-transferase placental form-positive foci (GST-P-positive foci), which are putative preneoplastic lesions, in male F344 rats were investigated using a medium-term liver bioassay system. In rats given 10% C. pyrenoidosa in a basal diet, the number and area of GST-P-positive foci in the rat livers, which diethylnitrosamine (DEN) initiated and 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx) promoted, were significantly decreased compared with those fed a basal diet not containing C. pyrenoidosa. The inhibition percentage of the number and area of GST-P-positive foci ≥0.2 mm in diameter was 67.6 and 74.2%, respectively (p<0.01). Furthermore, C. pyrenoidosa significantly decreased the number of GST-P-positive foci induced by MeIQx alone. The inhibition percentage of the number of GST-P-positive foci <0.2 mm in diameter was 52% (p<0.01). These results suggest that C. pyrenoidosa has chemopreventive effects against hepatocarcinogenesis in rats. C. pyrenoidosa appears to be a promising chemopreventive agent for human liver neoplasia and carcinogenesis induced by heterocyclic amines such as MeIQx.

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