Defining the Urinary, Biliary and Fecal Excretion of Diverse PFAS and the Impact of Dietary Fiber - Project Summary Per- and polyfluoroalkyl substances (PFAS) are now a part of the everyday lives of most Americans. PFAS are strongly associated with adverse human health effects including, increased serum low density lipoprotein cholesterol, reduced antibody responses to vaccination, altered liver serum biomarkers, pregnancy-induced hypertension, and decreased birth weight. An important toxicokinetic feature of PFAS is their long half-lives of elimination in humans, which contributes to bioaccumulation and increased risk of adverse health outcomes. It is hypothesized that differences in biliary/fecal or urinary elimination between humans and other species are driving the long human PFAS half-lives. What we do not know is the extent to which reuptake of PFAS in the gut prevents PFAS from being eliminated in feces. PFAS are amphipathic, and the majority of molecules are ionic at physiological pH. As such, PFAS are absorbed/reabsorbed by enterocytes and secreted by and reabsorbed by renal epithelial cells via the action of transporter proteins. The balance of uptake and efflux transport of PFAS in the gut and kidney will dictate the overall rate of elimination from the body in feces and urine. PFAS have been measured in urine and bile of people, but not feces. In animal models, PFAS are typically measured in urine and feces, but not bile. A critical gap in our ability to assess the extent of enterohepatic recirculation of PFAS is the lack of data on matched PFAS concentrations in urine, bile and feces. Here, we propose to test the overarching hypotheses that, in addition to slow urinary elimination, enterohepatic recirculation of PFAS is a driving factor in maintaining PFAS body burdens. We will take advantage of samples that have been generated in a mouse study designed to test the hypothesis that consumption of gel-forming natural dietary fibers will reduce PFAS absorption and reabsorption in the gut and increase PFAS elimination (TX220007, PI: Schlezinger, Co-I: Bello). To establish proof of principle that enterohepatic recirculation is critical to maintaining high body burdens of PFAS, we propose the following Specific Aims: Aim 1. To define the urinary, biliary and fecal excretion of PFAS in tandem in the context of different dietary conditions and Aim 2. To define the effect of PFAS on transporter expression that could modify PFAS toxicokinetics. We will achieve these aims by analyzing samples collected from humanized PPARα mice that were exposed in drinking water to seven PFAS commonly measured in people and fed diets based on the What We Eat In America analysis in NHANES for 6 weeks. The diets were supplemented with dietary fibers with different characteristics or cholestyramine. We will test the hypotheses that a) excretion of PFAS in bile is equal to or greater than excretion in urine but that reuptake in the gut is a major limiting factor in PFAS leaving the body in feces and b) the balance of excretion of PFAS in urine and bile is influenced by changes in transporter gene expression induced by PFAS and dietary fiber. The coordinated analyses of our TERP grant and this R03 proposal will generate the toxicokinetic, physiological and molecular evidence needed to define the role of enterohepatic recirculation in PFAS toxicity.
