Toxicoproteomics, from finding molecular targets to evaluating the impact on human health

Abstract: The exposome refers to all exposures, including exposures to chemicals, that an individual may encounter over the whole life, from conception to death, that influence the individual’s health. To date, over 200,000 chemicals have been registered under the legislative framework of the European Union. Exposomics studies have revealed that individuals are exposed to chemical mixtures consisting of hundreds of compounds simultaneously. The risks to human health posed by many of these chemicals and chemical mixtures are still unknown and require evaluation. Traditional methods for assessing chemicals and chemical mixtures have been inadequate in addressing the increasing number of potentially toxic compounds in the environment. Current high-throughput toxicology methods, which involve the application of batteries of in vitro bioassays, can reduce the time and costs of analysis. However, these methods evaluate the impact on well-established pathways that have already been identified as being affected by exposure, making it difficult to discover new modes of action. The goal of this thesis is to provide a method to unravel the targets of chemicals for a better understanding of the mechanisms of action of chemicals and chemical mixtures under the scenario of the exposome. The proteome integral solubility alteration (PISA) assay is a proteome-wide approach for drug-target identification. However, implementing the PISA assay to address toxicological challenges requires different experimental considerations from chemical properties and toxicology principles. Moreover, it is necessary to translate the data from target identification to an understanding of the potential impact on human health. Therefore, three steps were followed to implement the PISA method in the field of toxicology: i) experimental considerations of the method for toxicology and chemical assessment purposes, ii) analysis of the method capability in the field of toxicology, and iii) development of pipelines from the target identification to the understanding of potential impact on human health. The results showed the capability of the PISA assay to identify the protein targets of single chemicals and chemical mixtures, extending, in an unbiased manner, the list of evaluated biological pathways in current available methodologies. The approach presented here reduces the time and cost associated with experimental and data analysis work, which could aid in the chemical risk assessment process in the context of the exposome.