4‐chloro‐1,2‐phenylenediamine Induces Apoptosis in Mardin–Darby canine kidney cells via activation of caspases

4‐Chloro‐1,2‐phenylenediamine (4‐Cl‐ o ‐PD) is a halogenated aromatic diamine that was used as a precursor for manufacturing permanent hair dyes. Despite its well‐documented mutagenic and carcinogenic effects in a number of in vitro and in vivo models, its cytotoxicity and mode of action have not received similar attention. Here, we investigated the effect of 4‐Cl‐ o ‐PD on Mardin–Darby canine kidney cells. It induced apoptosis and the evidence suggests its initiation by reactive oxygen species (ROS). The results of various assays used show a dose‐dependent (i) decrease in cell viability, (ii) increase in cells at sub‐G1 phase and the G0/G1 phase arrested in cell cycle, (iii) increase in intracellular ROS accompanied by depletion of glutathione, and (iv) that apoptotic cell death probably involves activation of both intrinsic and extrinsic pathways. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 655–664, 2014.