Background: The role of dichloromethane (DCM) and 1,2,3-trichloropropane (1,2,3-TCP) in occupational cholangiocarcinoma, first reported in 2012, remains a subject of ongoing debate.
Objectives: The aim of this study was to determine the potential of 1,2-dichloropropane (1,2-DCP), DCM, and 1,2,3-TCP to induce DNA damage—a hallmark of carcinogenicity—in human cholangiocytes.
Methods: Mono-cultures of human MMNK-1 cholangiocytes and co-cultures of MMNK-1 cholangiocytes-human THP-1 monocyte-derived macrophages were exposed to 1,2-DCP, DCM or 1,2,3-TCP at 0, 0.1, and 0.4 mM for 24 hours. DNA double-strand break marker γ-H2AX positive foci and γ-H2AX pan-nuclear positive cholangiocytes were counted in 100 and 200 cholangiocytes, respectively. Apoptosis was evaluated by TUNEL staining.
Results: The percentage of cholangiocytes exhibiting moderate (5-54) and dense (≥55) γ-H2AX immunostaining was significantly greater in all co-cultures than in monocultures, suggesting that the DNA damage in cholangiocytes induced by all three chemicals was enhanced by macrophages. However, only 1,2-DCP decreased the number of γ-H2AX pan-nuclear-positive cholangiocyte-macrophage co-cultures.  Co-treatment with pan-caspase inhibitor decreased the number of γ-H2AX pan-nuclear-positive cholangiocytes in each group by about 50%, suggesting the involvement of apoptotic signal pathway in the induction of γ-H2AX pan-nuclear-positive cholangiocytes. Furthermore, 1,2-DCP reduced TUNEL-positive cells in the co-cultures, but not in the monocultured cholangiocytes, suggesting anti-apoptotic effect of 1,2-DCP in cholangiocytes co-cultured with macrophages.
Conclusion: Our study showed that 1,2,3-TCP is the strongest inducer of DNA damage, while only 1,2-DCP showed proliferative and anti-apoptotic effects, which are also recognized as key characteristics of carcinogens, thus distinguishing 1,2-DCP from DCM or 1,2,3-TCP.