Peroxisomal effects of phthalate esters in primary cultures of rat hepatocytes

Primary rat hepatocyte cultures were used to compare the effects of some alkylphthalate esters on peroxisomal enzyme activities and morphology. Linear diesters from methyl to n-octyl and their constituent monoesters and alcohols were compared with the branched chain 2-ethylhexyl derivatives. Carnitine acetyltransferase activity was increased 9.5-fold by mono-2-ethylhexylphthalate (MEHP) and 5.5- and 7-fold by mono-n-pentyl- and mono-n-octylphthalate (MNOP), the 2 most potent of the linear monoesters. Activity of the specific peroxisomal marker, cyanide-insensitive palmitoyl-CoA oxidation decreased with time in control cultures. Whereas MEHP produced a time related increase over the initial level of palmitoyl-CoA oxidation, MNOP treatment only maintained the initial level of activity. The peroxisome proliferation-associated 80 000 mol. wt polypeptide was induced by MEHP but not MNOP. Similarly, MEHP produced increased numbers of peroxisomes, many without a nucleoid, whereas MNOP and mono-n-pentylphthalate had no such effect. 2-Ethylhexanol was less potent as an inducer of carnitine acetyltransferase than MEHP and the linear alcohols had no effect on this enzyme. Studies with diesters indicated that induction of carnitine acetyltransferase required hydrolysis of the diester. It is concluded that the straight-chain phthalates studied have little effect on hepatic peroxisomes compared with the 2-ethylhexyl ester and that hepatocyte cultures provide a rapid means of comparing the peroxisomal effects of different phthalates.