Molecular level insights into the direct health impacts of some organic aerosol components†
Organic aerosols (OAs) comprise 20–90 w% of atmospheric aerosols. While they have some positive impacts (e.g. acting as precipitation nuclei), they can pose some negative impacts on human health. The health impacts range from pulmonary inflammation to suppression of defense mechanisms, cancer and death. To understand how OA components can affect human body, this study employed a combination of in silico techniques: molecular docking, quantum chemical analysis of interactions, thermodynamics and kinetics of the reaction of OA components with DNA and oxidative stress mechanism, in addition to theoretical evaluation of their absorption, distribution, metabolism and excretion (ADME) properties. As OAs contain many components, this study just focused on benzo[a]pyrene (BaP), benzo[a]pyrene diol epoxide (BPDE), the cyclopentanoperhydrophenanthrene (CPPP) sterane, 2,6-dimethyl-1,4-benzoquinone (DMBQ), hopane (HOP), 9,10-phenanthrenequinone (PQ), and an OA model (fulvic acid; FA), which are all known for their negative health impacts. According to the ADME predictions, the low bioavailability of FA would limit its negative impacts. However, the ADME estimations and docking simulations suggested that BPDE, DMBQ and PQ have significant impact in affecting human health negatively: they can be feasibly distributed throughout human body by human serum albumin, they can likely permeate cell membranes, the blood–brain barrier and the gastrointestinal tract, and they show higher DNA binding efficiencies compared to the other OA components. Based on the quantum chemical calculations, BPDE, DMBQ and PQ can interact with the adenosine nucleobases of DNA, but they cannot directly form DNA adducts because of the nonspontaneous and kinetically infeasible nature of the corresponding reaction routes. Similarly, they cannot directly cause oxidative stress. However, in reference to the experimental evidence offered by earlier studies, their metabolites can result in both oxidative stress and carcinogenicity.