PROJECT SUMMARY/ABSTRACT – PROJECT 3 MECHANISMS Project 3 (P3–Mechanisms) is a biomedical project utilizing expertise in pharmacy and chemical engineering to elucidate mechanisms that underlie per- and polyfluorinated alkyl substances (PFAS) absorption, distribution, and excretion (ADE). PFAS have been detected in human serum and excreta. Since the inception of STEEP I, it has become evident that PFAS contamination is global, exposure is ubiquitous, and the need to understand PFAS properties is urgent. There is a large gap in knowledge regarding the mechanisms by which the ~7000 PFAS that are on the commercial market are absorbed, retained, and are eliminated by the living system, with very little understood about the mechanisms that dictate PFAS ADE. Cell-based studies suggest both protein binding (i.e., Serum Albumin and Fatty Acid Binding Proteins) and xenobiotic/drug transporters (i.e., Organic Anion Transporting Polypeptide (OATP2B1) and ATP-Binding Cassette Subfamily G Member 2 (ABCG2)) are potential mechanisms that dictate PFAS absorption, distribution, and excretion in vivo. P3–Mechanisms will use mouse knock-out models and cell-based assays to test the hypothesis that protein transporters and protein binding are critical factors for PFAS ADE and tissue distribution through accomplishing the following three aims: Aim 1: Determine the contribution of OATP2B1 as a critical uptake mechanism for cellular PFAS uptake, tissue distribution and elimination; Aim 2: Determine the contribution of Serum Albumin and Fatty Acid Binding Proteins as critical mechanisms for PFAS uptake, tissue retention, and elimination; and Aim 3: Determine the contribution of ABCG2 as a critical efflux mechanism that influences PFAS ADE. The outcome of the proposed work will be the validation of critical mechanisms using in vivo, rodent based tools and in vitro humanized tools. The findings of the project will help guide the prioritization and selection of key toxicological mechanisms that can be targeted in larger screening efforts. Key mechanisms identified by P3–Mechanisms will inform P1–Exposure, P2– Critical Effects, and P4–Detection and will be incorporated into bioaccumulation modeling. Projects 1, 2, and 4 will inform P3–Mechanisms about new PFAS to characterize in the proposed in vitro models. P3– Mechanisms will provide an interdisciplinary training experience through STEEP’s RETCC and will support the Community Engagement Core (CEC) through participation in bidirectional communications about findings and PFAS science. This work will significantly advance our mechanistic understanding of PFAS ADE, especially in relationship to predicative physiochemical properties of emerging PFAS, which addresses SRP Mandate #2 (techniques of assessing the effects of hazardous substances on human health). It uses a mechanistic approach to identify underlying genetic risk or dietary factors that modulate PFAS ADE, which addresses the broad SRP Mandate # 3 (development of metho...