Activation of PPAR and PPAR by Environmental Phthalate Monoesters

Phthalate esters are widely used as plasticizers in the manufacture of products made of polyvinyl chloride. Mono-(2-ethylhexyl)phthalate (MEHP) induces rodent hepatocarcinogenesis by a mechanism that involves activation of the nuclear transcription factor peroxisome proliferator-activated receptor-alpha (PPAR ). MEHP also activates PPAR-gamma (PPAR ), which contributes to adipocyte differentiation and insulin sensitization. Human exposure to other phthalate monoesters, including metabolites of di-n-butyl phthalate and butyl benzyl phthalate, is substantially higher than that of MEHP, prompting this investigation of their potential for PPAR activation, assayed in COS cells and in PPARresponsive liver (PPAR ) and adipocyte (PPAR ) cell lines. Monobenzyl phthalate (MBzP) and mono-sec-butyl phthalate (MBuP) both increased the COS cell transcriptional activity of mouse PPAR , with effective concentration for half-maximal response (EC50) values of 21 and 63 M, respectively. MBzP also activated human PPAR (EC50 30 M) and mouse and human PPAR (EC50 75–100 M). MEHP was a more potent PPAR activator than MBzP or MBuP, with mouse PPAR more sensitive to MEHP (EC50 0.6 M) than human PPAR (EC50 3.2 M). MEHP activation of PPAR required somewhat higher concentrations, EC50 10.1 M (mouse PPAR ) and 6.2 M (human PPAR ). No significant PPAR activation was observed with the monomethyl, mono-n-butyl, dimethyl, or diethyl esters of phthalic acid. PPAR activation was verified in FAO rat liver cells stably transfected with PPAR , where expression of several endogenous PPAR target genes was induced by MBzP, MBuP, and MEHP. Similarly, activation of endogenous PPAR target genes was evidenced for all three phthalates by the stimulation of PPAR dependent adipogenesis in the 3T3-L1 cell differentiation model. These findings demonstrate the potential of environmental phthalate monoesters for activation of rodent and human PPARs and may help to elucidate the molecular basis for the adverse health effects proposed to be associated with human phthalate exposure.