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.

Grant Number: 1R03ES037466-01
NIH Institute/Center: NIH
Principal Investigator: Dhimiter Bello