Effects of chlorinated phenols on rat embryonic and hepatic mitochondrial oxidative phosphorylation

Chlorinated phenols (CPs), including pentachlorophenol, selected positional isomers from each major group of CPs, and phenol were previously selected from 38 possible compounds and ranked according to developmental toxicity. The present study was designed to utilize these compounds (and a variety of chemical derivatives) to elucidate the mechanism(s) of developmental toxicity of the chlorinated phenols. Mitochondria were isolated by differential centrifugation from rat embryos (REM) and maternal liver (MLM) on day 15 of gestation. The higher CPs, i.e., pentachlorophenol (C₅P), 2,3,4,5‐tetrachlorophenol (2,3,4,5‐C₄P), and 2,3,5‐trichlorophenol (2,3,5‐C₃P) at concentrations > 1.33 μM, inhibited ADP phosphorylation and state 4 respiration in the presence of either glutamate plus malate or α‐ketoglutarate or succinate. These compounds also exerted a significant uncoupling activity at a concentration of 1.33 μM, with C₅P > 2,3,4,5‐C₄P > 2,3,5‐C₃P. The lower CPs, i.e., 3,5‐dichlorophenol (3,5‐C₂P), 4‐chlorophenol (4‐CP), and phenol, produced comparable mitochondrial effects, but only at a higher concentration (20 μM). Enhanced mitochondrial ATPase activity (with and without Mg²⁺) was induced by C₅P, 2,3,4,5‐C₄P and 2,3,5‐C₃P at concentrations that exhibited maximum uncoupling activity. The CPs (except for the derivative C₅P‐anisole) caused significant mitochondrial swelling. The reversal of oligomycin‐inhibited respiration by C₅P from REM or MLM was also reproducible in the intact Hydra attenuata. A correlation of 0.9 (p = 0.0151) between CP‐induced uncoupling activity and the reciprocal of the minimal affective concentration in the Hydra developmental assay was observed. These findings suggest that CPs may elicit their effects by interacting with target cell mitochondria.