Innovative analytical techniques for identifying metabolites of the UV filter homosalate through UPLC-MS:...

Homosalate (HMS), a widely used sunscreen ingredient, functions as a UVB absorber, protecting against harmful ultraviolet radiation. Nevertheless, laboratory investigations have prompted concerns regarding its potential to disrupt endocrine function, given that HMS demonstrates both estrogenic and anti-androgenic properties. These effects could be shaped by its metabolic byproducts. Certain HMS metabolites may carry toxicological implications. To date, no research has applied an untargeted metabolomics methodology to comprehensively explore HMS metabolism using high-resolution mass spectrometry. In this study, we used three advanced metabolomics-based data-processing approaches to comprehensively identify HMS metabolites from human liver enzyme incubation samples including two-dose difference coupled with stable isotope tracing, dose-response relationship coupled with stable isotope tracing, and mass defect filter coupled with stable isotope tracing. We identified nine peaks with the proposed structures as potential HMS metabolites. Previously reported HMS metabolites, including salicylic acid, HMS-carboxylic acid, aryl-alkyl-dihydroxylated HMS, and aryl-hydroxylated HMS-carboxylic acid, were confirmed in this study. We confirmed the proposed salicylic acid by comparison with an authentic standard. Salicylic acid may be the major HMS metabolite, showing significantly higher abundance compared with the other identified metabolites. However, salicylic acid originates from various sources, making it difficult to determine its origin. In addition, we identified two novel metabolites: M4 and M14/M15. M4 was proposed to be a hydroxylated salicylic acid; therefore, it was not an HMS structure-specific metabolite and could not serve as an exposure biomarker. In contrast, M14 and M15-identified as isomers-were proposed to be aryl-monohydroxylated-alkyl-dihydroxylated HMS and are considered HMS structure-specific metabolites. The potential of these two isomers as exposure biomarkers should be further validated in future studies.