Chemopreventive activity of very low dose dietary tannic acid administration in hepatoma bearing C3H male mice.

Tannins are plant polyphenols comprising a heterogeneous group of compounds. Tannic acid is a common tannin found in tea, coffee, immature fruits, etc. and it has also been used as a food additive. An increasing body of experimental evidence supports the hypothesis that tannins exert anticarcinogenic activity in chemically induced cancers in animal models. In the present study, tannic acid was administered in very low doses in the drinking water of C3H male mice divided into three groups (75 mg/l, 150 mg/l and 300 mg/l). These animals carry a genetic defect and show a high incidence of spontaneous liver tumors (> 50%) at an age older than 12 months. The results showed a decrease in the overall incidence of hepatic neoplasms (adenomas plus carcinomas): 53.3% of animals in the control group developed hepatic neoplasms versus 33.3% in the group given a low dose of tannic acid, 26.6% in the group given a medium dose and 13.3% in the high dosage group. The difference was more pronounced in the animals with carcinomas: 4.44% of mice who received tannic acid developed carcinomas versus 33.3% of those in the control group. Tannic acid administration did not affect the PCNA labeling index of normal hepatocytes. It is concluded that tannic acid dietary intake in low doses can exert a strong dose-dependent chemoprotective activity against spontaneous hepatic neoplasm development in C3H male mice, most probably through antipromoting mechanisms.

Ribonucleases protect RNA from acid precipitation.

Four, widely used, ribonucleases were found to protect their substrates from acid precipitation by causing, evidently, a modification of their physicochemical properties. The protection was dependent on the kind of substrate while the ratio of protective to nucleolytic activity varied widely between the four enzymes. The protection was enhanced by some nucleotides like UMP, CMP and IMP and decreased in the presence of several bivalent ions like Zn++, Co++ and Cu++. It was completely abolished when the substrates were hybridized with their complementary ribohomopolymers. In the case of bovine pancreatic ribonuclease, the part of the molecule which was responsible for the protective activity was localized on the enzyme domain characterized as S-protein, which lacks nucleolytic activity. The observed property of ribonucleases could lead to false data when the measurement of TCA-soluble material is the method used to follow the purification of ribonucleases or to study their activity. It was also found that ribonuclease S-protein enhances the catalytic activity of B. Cereus RNAse. S-protein could potentiate other RNAses activity like onconase, which has recently been used as an anticancer agent.