Evaluation of 14 PFAS for permeability and organic anion transporter interactions: Implications for renal clearance in humans

Abstract

Per- and polyfluoroalkyl substances (PFAS) encompass a diverse group of synthetic fluorinated chemicals known to elicit adverse health effects in animals and humans. However, only a few studies investigated the mechanisms underlying clearance of PFAS. Herein, the relevance of human renal transporters and permeability to clearance and bioaccumulation for 14 PFAS containing three to eleven perfluorinated carbon atoms (η_pfc = 3-11) and several functional head-groups was investigated. Apparent permeabilities and interactions with human transporters were measured using in vitro cell-based assays, including the MDCK-LE cell line, and HEK293 stable transfected cell lines expressing organic anion transporter (OAT) 1-4 and organic cation transporter (OCT) 2. The results generated align with the Extended Clearance Classification System (ECCS), affirming that permeability, molecular weight, and ionization serve as robust predictors of clearance and renal transporter engagement. Notably, PFAS with low permeability (ECCS 3A and 3B) exhibited substantial substrate activity for OAT1 and OAT3, indicative of active renal secretion. Furthermore, we highlight the potential contribution of OAT4-mediated reabsorption to the renal clearance of PFAS with short η_pfc, such as perfluorohexane sulfonate (PFHxS). Our data advance our mechanistic understanding of renal clearance of PFAS in humans, provide useful input parameters for toxicokinetic models, and have broad implications for toxicological evaluation and regulatory considerations.

Keywords: Ion transporters; PFAS; Permeability; Renal clearance.

Figure 1:

LogD (A) and molecular weight (B) plotted against apparent permeability ${\mathrm{P}}_{\mathrm{a}\mathrm{p}\mathrm{p}}$ of PFAS at pH 7.4. PFAS were grouped into carboxylic and sulfonic acids and PFOSA (sulfonamide). PFOSA and PFOS is highlighted due to their high permeability. 6:2 FTS is highlighted for its low permeability. The solid blue lines are exponential growth fits for the carboxylic acids, and the goodness-of-fit is reported (r²). The dotted line is the permeability cut-off of 5 × 10⁻⁶ as applied in the ECCS framework (Varma et al., 2015).

Figure 2:

Heat map of PFAS substrate activity of PFAS against human OAT1, OAT2, OAT3, and OAT4 expressed in human kidney proximal tubules. The color code indicates uptake ratios (transfected vs. wild-type cells) from 1 (baseline, white) to 11.9 (highest value, dark blue).

Figure 3:

Substrate uptake ratios of PFAS against human (A) OAT1, (B) OAT3, and (C) OAT4, with (w/) and without (w/o) OAT-specific inhibitor probenecid [1mM]. Significant inhibition was shown against all PFAS transporter combination (t-test, ***: p<0.001, **: p <0.01), except for PFHxS and OAT4.

Figure 4:

Reciprocals of 50% inhibitory concentrations (IC50, 1/μM) for the study PFAS against hOAT1, hOAT3, and hOCT2 mediated uptake of prototypical substrates. Probenecid and quinidine were tested as control inhibitors for OATs and OCT, respectively. IC50 of >300 μM were set to 1/300 μM in the graph to indicate the baseline.