(735d) Effect of Di(2-ethylhexyl) Phthalate and Mono(2-ethylhexyl) Phthalate Interactions with a Lipid Membrane

Di(2-ethylhexyl) phthalate (DEHP), a common plasticizer, is present in many household products posing potential environmental exposure issues as it easily leaches from surfaces. DEHP most commonly metabolizes in the body in the presence of lipases into monoesters, such as mono(2-ethylhexyl) phthalate (MEHP). While previous studies have focused on its role as an endocrine disruptor, with major concerns of exposure to newborns and those undergoing medical procedures, DEHP and MEHP have yet to be studied for their physical and chemical interaction with lipid bilayers. These studies would provide critical information on phthalate adsorption mechanisms, potential pore formations, and compromises to the membrane structure. Previous work has investigated nanoparticle, peptide, polymer, and small molecule interactions with lipid bilayers for understanding possible toxic effects of these substances to human cells. In this work, we examined the effects of DEHP and MEHP on adsorption and permeability within a model lipid bilayer.

In our study we investigated changes occurring with vesicle and lipid bilayer structures due to the presence of various concentrations of DEHP and MEHP. We observed statistically significant changes in the size and polydispersity of L-α-phosphatidylcholine (egg PC) vesicles with the presence of 100 and 200 μM DEHP using dynamic light scattering. We then developed egg PC supported lipid bilayers (SLBs) on silica surfaces using quartz crystal microbalance with dissipation (QCM-D) monitoring. Based on frequency and dissipation changes occurring on the lipid bilayer surface, we observed mass removal or adsorption due to the presence of phthalate at concentrations of 5-200 μM, based on physiologically relevant values. With DEHP incubation, we observed lipid removal at 5 and 100 μM DEHP concentrations and significant adsorption of DEHP with 50 and 200 μM concentrations. With MEHP, we observed relatively identical lipid removal for all concentrations tested. From dynamic light scattering results of DEHP and MEHP aggregates, we hypothesize that the size of the phthalate aggregate can influence its interaction with a SLB, with larger aggregates causing adsorption to the SLB and smaller aggregates causing lipid removal. Following QCM-D studies, we performed parallel artificial permeability assay (PAMPA) by forming a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid bilayer across a polyvinylidene fluoride permeable support. We observed permeability differences between DEHP and MEHP with this bilayer structure and observed differences in small molecule (including caffeine, carbamazepine, warfarin, furosemide, folic acid, and methotrexate) interaction with the DOPC membrane following incubation with DEHP and MEHP. Specifically, we observed more interaction of DEHP with the DOPC bilayer compared to MEHP. We also observed that DEHP incubation caused higher molecular weight and more negative logP small molecules to interact more with the bilayer. The opposite trend was observed after MEHP incubation. Finally, we investigated the influence of adsorption of 200 μM DEHP to 1 μm chitosan particles on egg PC vesicle size. Before chitosan adsorption, egg PC vesicle size was significantly increased due to introduction and interaction with DEHP (200 μM). However, after the chitosan adsorption, there was no statistically significant change in the size of egg PC vesicles. Ultimately, this work demonstrates the physical changes DEHP and MEHP can have on lipid vesicles and bilayer structures, which can better inform exposure toxicity of phthalates.