γH2AX is immunohistochemically detectable until 7 days after exposure of N-bis (2-hydroxypropyl) nitrosamine (DHPN) in rat lung carcinogenesis

It is known that γH2AX, which is formed when there is a double-strand break in DNA, can act as a sensitive marker of genomic instability. In this experiment, the time-course manner of the expression of γH2AX in the lung was examined in the early phase after treatment with a lung carcinogen, N-bis (2-hydroxypropyl) nitrosamine (DHPN). The expression of γH2AX is expected to be one of the useful markers for lung carcinogenesis in early stages. Rats were separated into 10 groups of 5 rats. The DHPN groups were administered 0.1% DHPN in drinking tap water for two weeks, while the control group received drinking tap water. At 0, 1, 3, 7, and 14 days after finishing DHPN treatment, one group each from the DHPN and control groups was sacrificed. The removed lung tissues were examined for immunostaining of γH2AX and PCNA, and positive cells were counted. The γH2AX levels of the DHPN-treated groups were found to be increased significantly at 0, 1, 3, and 7 days (4.4 ± 1.4, 5.1 ± 2.7, 3.3 ± 1.0, and 4.1 ± 1.3%, respectively), and they dropped significantly on day 14 (1.1 ± 0.4%). The experiment showed that the γH2AX-positive score could be effectively measured for up to 7 days after exposure, as a significance difference was observed between the treated group and the control group. It can be deduced that γH2AX is an effective marker for DHPN-induced double-strand breaks in pulmonary epithelial cells.