Plasticizers and Inhibition of Leukocyte Function in Vitro

Abstract

To evaluate the influence of the plasticizer metabolites of di(2-ethylhexyl)phthalate (DEHP), mono(2-ethylhexyl)phthalate (MEHP), 2-ethylhexanol (2-EH), and phthalic acid (PA) on various immune functions of polymorphonuclear blood leukocytes (PMNL) and monocytes (MN). MEHP, 2-EH, and PA are the main hydrolysis products of DEHP. Since DEHP is leached out of the plastic matrix, patients on hemodialysis and continuous ambulatory peritoneal dialysis are exposed to considerable amounts of DEHP and its metabolites. Teaching hospital, Department of Nephrology. Ten healthy volunteers. After incubation of leukocytes in solutions with different plasticizer concentrations, oxidative respiratory metabolism was determined by luminol-enhanced chemiluminescence (CL) after stimulation with phorbol myristate acetate (PMA). Furthermore, superoxide (O2-) generation was measured by cytochrome c reduction. At pH 5.4, a dose-dependent decrease of luminol-enhanced CL response was found in all assays. For MEHP and PA the level of significance was reached at 10 mg/L and 1 mg/L, respectively. Superoxide generation by PMNL and MN at pH 5.4 was also suppressed by MEHP and PA. At pH 7.4, only a slight suppression of oxidative metabolism at higher concentrations was observed. After incubation of the cells in a solution containing all DEHP metabolites (MEHP, PA, and 2-EH), a significant suppressive effect of CL at pH 5.4 could be observed at final plasticizer concentrations of 0.5 mg/L. A dose-dependent impairment of leukocyte oxidative metabolism at a low pH could be demonstrated. The suppressive effect was particularly marked after incubation of the cells in solutions containing a mixture of the main plasticizers. At pH 5.4, we observed a slight alteration even at concentrations very close to those that could be found in commercially available peritoneal dialysis fluids. These results might point toward a possible synergistic detrimental effect of the different DEHP metabolites on leukocyte function, with possible clinical relevance.