主催: 日本毒性学会
Many studies have shown that lipoxygenase (LOX) can mediate the co-oxidation and activation of xenobiotics including carcinogens in vitro enzyme system. To the authors' knowledge, however, there is almost no evidence that the oxidation can be conducted in cells, tissues and mammals. It has also been unclear whether 4-aminobiphenyl (4-ABP) can be activated by LOX in living organisms. This study was carried out to provide the evidence that LOX is a metabolic pathway of activation of precarcinogen. 4-ABP reacted with soybean lipoxygenase (SLO) in vitro enzyme system and the products were tested by spectrophotometry. The livability of human bronchial epithelial (HBE) cells was tested by MTT assay, the protein expression of 5-lipoxygenase (5-LOX) by western blot and DNA damage by single cell gel electrophoresis. Results showed that SLO could oxidize 4-ABP in the presence of hydrogen peroxide. A LOX inhibitor nordihydroguaiaretic acid could suppress the oxidation. The expression of 5-LOX in HBE cells was strengthened by 4-ABP but not affected by AA-861. The DNA of HBE cells treated by 400μmol•L-1 4-ABP was obviously damaged and 47.7% of the cells displayed a comet shape. AA-861 and naproxen inhibited the DNA damage and the maximum protection rates were 58.1% and 21.7% respectively. These results suggest that the expression of 5-LOX can be influenced by 4-ABP, and the co-oxidation of 4-ABP by 5-LOX in the cells may produce electrophilic free radicals which can combine with DNA, thus causing DNA damage. This may be one of the carcinogenic mechanism of 4-ABP.
KEY WORDS: 5-lipoxygenase; co-oxidation; 4-aminobiphenyl; protein expression; DNA damage
