In previous studies, we detected the photoinitiators 1-hydroxycyclohexyl phenyl ketone (1-HCHPK) and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone (MTMP) in an intravenous injection solution. Importantly, 1-HCHPK and MTMP have been demonstrated to be cytotoxic to normal human peripheral blood (PB) mononuclear cells (MNC). Cell death (apoptosis) pathways can be classified into two modes, caspase-dependent and -independent pathways. However, it is unclear whether methyl 2-benzoylbenzoate (MBB) induces the caspase-dependent and/or -independent pathway in normal human PBMNC. In the present in vitro study, we examined the levels of MBB in a solution from an intravenous fluid bag and the cytotoxicity of MBB towards normal human PBMNC via the caspase-8-, caspase-9-, or apoptosis-inducing factor (AIF)-mediated apoptosis pathways. We found that extracts from the injection solution had been contaminated with approximately 80 μM of the photoinitiator MBB. In addition, MBB induced apoptosis in the high concentration range in normal human PBMNC in vitro. Moreover, we found that MBB-induced apoptosis occurs via the caspase-9 pathway, but not the AIF pathway. In conclusion, we suggest that MBB has cytotoxic effects on normal human PBMNC in vitro, which are mediated via the caspase-dependent pathway.
Keywords: Apoptosis; Apoptosis-inducing factor; Caspase-9; Injection; Methyl 2-benzoylbenzoate; Photoinitiator.