DEVELOPMENTAL TOXICITY AND STRUCTURE-ACTIVITY-RELATIONSHIPS OF CHLOROPHENOLS USING HUMAN EMBRYONIC PALATAL MESENCHYMAL CELLS

The chlorophenols (CPs) comprise a major class of widely distributed a nd frequently occurring environmental contaminants. Previous studies h ave demonstrated the adverse effects of CPs on embryonic and fetal dev elopment. HEPM (human embryonic palatal mesenchymal) and MOT (mouse ov arian tumor) cell lines have been utilized in complementary bioassays for the detection of teratogens, but not the CPs. In this study, our o bjectives were 2-fold: (1) to determine if the HEPM assay could be use d to complement other bioassay systems of nonhuman origin, i.e., Hydra attenuata (HA) and rat whole embryo culture (WEC), in the evaluation of the developmental toxicity of CPs, and (2) to delineate the ability of the HEPM assay to evaluate structure-activity relationships of pen tachlorophenol (C5P), 2,3,4,5-tetrachlorophenol (C4P), 2,3,5-trichloro phenol (C3P), 3,5-dichlorophenol (C2P), 4-monochlorophenol (CP), pheno l, and CP derivatives (i.e., acetates, sodium phenates and anisoles). HEPM cells were seeded into each well of a 24-well plate and cultivate d for 24 h. The medium was replaced with fresh medium containing vario us concentrations of test chemicals dissolved in dimethyl sulfoxide (D MSO, 0.1%). After culturing for 72 h, the medium was removed, cells we re trypsinized, and cell number determined. The HEPM cell growth inhib ition assay demonstrated a linear relationship between the IC50 values of the CPs and degree of chlorine substitution. The IC50 values of C5 P, C4P, C3P, C2P, CP, and phenol were 18.8, 21.5, 27.5, 63.0, 150.0 an d 470.0 mu M, respectively. A clear structure-activity relationship wa s observed between toxicity of CPs and the degree of chlorine substitu tion. The rank order of CP toxicity from the HEPM assay (i.e., C5P > C 4P > C3P > C2P > CP > phenol) is in excellent agreement with previous, in vitro and in vivo studies. However, contrary to published reports, the HEPM assay predicted that all CPs were teratogenic (false positiv es). These findings suggest that the HEPM cell growth inhibition bioas say may be useful to discriminate between subtle differences in struct ure-activity and, in combination with other bioassays, might facilitat e the rapid detection and prioritization of diverse cytotoxins, includ ing various developmental toxicants. Importantly, conclusions about th e teratogenicity of a test chemical (via HEPM testing) should be appro ached with caution and confirmed with other teratogen-sensitive system s.