Species differences in response to the phthalate plasticizer monoisononylphthalate (MINP) in vitro: a comparison of rat and human hepatocytes

Diisononylphthalate (DINP) is one of the group of dialkyl phthalate esters used widely to impart flexibility to polyvinyl chloride (PVC) products. However, DINP and other phthalates are rodent peroxisome proliferators (PPs), a class of compounds that cause rodent hepatic peroxisome proliferation, induction of DNA synthesis and suppression of apoptosis leading to liver tumours. Despite these adverse effects in rodent liver, humans appear to be nonresponsive to the adverse effects of PPs. Here, we have examined species differences in the response of rat and human hepatocytes to MINP, a principle metabolite of DINP and the proximal peroxisome proliferator. In rat hepatocytes in vitro, MINP caused a concentration-dependent induction of peroxisomal beta-oxidation. Similarly, MINP caused a concentration-dependent suppression of apoptosis and induction of DNA synthesis. In contrast to the pleiotropic response noted in rat hepatocytes, MINP did not cause induction of beta-oxidation, stimulation of DNA synthesis or suppression of apoptosis in human hepatocytes. These data provide evidence for species differences in the hepatic response to the phthalate ester DINP, confirming that human hepatocytes are refractory to the adverse effects noted in rodents.