Langmuir Monolayers as Effective Models of Apical Epithelial Cell Membranes: Studies on the Effects of Phthalate Incorporation

Phthalates are the most common plasticizers on the market, produced in megaton quantities. Phthalates can be released from plastics and enter the human body, primarily through ingestion or inhalation. The phthalate used in the largest quantities is di(2-ethylhexyl) phthalate, DEHP. However, this compound is toxic: mutagenic, carcinogenic, and endocrine-disrupting. Therefore, DEHP is gradually being replaced by other phthalates, primarily diesters with longer, unbranched, or iso-branched chains. Upon entering the human body, phthalates first interact with epithelial cells, primarily their apical membrane. Our research aimed to develop models of apical membranes and to examine the effects of DEHP and its substitutes on their physical properties. In the research, the fact that the apical membrane contains raft and nonraft regions was considered, so two different membrane models were created and studied. Lipid Langmuir monolayers were used as membrane models. The effects of phthalate incorporation on the mechanical properties of these membranes, their morphology (Brewster angle microscopy), and their crystal structure (grazing incidence X-ray diffraction) were studied. Studies have shown that phthalates primarily disrupt the raft regions of the apical membrane. It was demonstrated that replacing DEHP with phthalates with long, unbranched chains is a poor option because their impact on the model membranes is more unfavorable than DEHP itself. However, using phthalates with iso-branched chains seems reasonable. These compounds have a lesser effect on the properties of the model membranes, and given their significantly lower toxicity, their use seems to be a suitable direction for the development of plasticizer chemistry.