Organic sunscreens and their environmental degradation products: an in silico study of interactions with enzymatic antioxidant systems in the human placenta

The main function of the placenta is to facilitate and regulate the mother-to-fetus transport of oxygen and nutrients. The placenta is also responsible, due to some enzymes present within it, for protecting the fetus against harmful xenobiotics. One of the protective mechanisms of the placenta is linked to the antioxidant enzyme glutathione S-transferase. Enzymes from this family can detoxify many endogenous compounds and break down xenobiotics through the conjugation of various substrates with reduced glutathione.

Organic sunscreens are expected to protect the skin, hair, and materials such as cosmetics or fabrics against the harmful effects of UV radiation. Unfortunately, many compounds from this group are known to cross biological barriers; they are found in the mother’s milk, umbilical cord blood, or placental tissues. Some organic sunscreens are able to cross the placenta and to interfere with fetal development; they are known or suspected to be endocrine disruptors or neurotoxins.

In this study, 16 organic sunscreens and over 100 products of sunscreen degradation in biotic and abiotic conditions were investigated in the context of their interactions with the enzyme gluthatione S-transferase present in the human placenta. Molecular docking analysis proved that several compounds from the studied group show stronger affinity for glutathione S-transferase that glutathione; it is therefore possible that they are able to reduce the enzyme’s antioxidant activity. It was established that sunscreens and their degradation products bind to glutathione S-transferase mainly by hydrogen bonds, but there are also van der Waals, pi-pi, pi-alkyl, and pi-sulfur interactions that contribute to the stability of enzyme—ligand complexes.

To conclude, due to the complexity of sunscreens’ degradation pathways and he abundance of both parent sunscreens and their degradation products in the environment, a relatively small group of popular cosmetic ingredients may be a source of a considerable number of stressors affecting individuals at different stages of development.