NIEHS Report on the in vivo repeat dose biological potency study of perfluorohexanesulfonamide (CASRN 41997-13-1) in Sprague Dawley (Hsd:Sprague Dawley® SD®) rats (Gavage Studies)

Abstract

Background: Perfluorohexanesulfonamide (PFHxSAm) is a member of the per- and polyfluoroalkyl class of compounds to which humans are widely exposed. Toxicological information on this class of chemicals is sparse. A short-term, in vivo transcriptomic study was used to assess the biological potency of PFHxSAm.

Methods: A short-term in vivo biological potency study on PFHxSAm in adult male and female Sprague Dawley (Hsd:Sprague Dawley® SD®) rats was conducted. PFHxSAm was formulated in acetone:corn oil (1:99) and administered once daily for 5 consecutive days by gavage (study days 0–4). PFHxSAm was administered at 10 doses (0, 0.15, 0.5, 1.4, 4, 12, 37, 111, 333, and 1,000 mg/kg body weight [mg/kg]). Blood was collected from animals dedicated for internal dose assessment in the 4 and 37 mg/kg groups. On study day 5, the day after the final dose was administered, animals were euthanized, standard toxicological measures were assessed, and the liver and kidney were assayed in gene expression studies using the TempO-Seq assay. Modeling was conducted to identify the benchmark doses (BMDs) associated with apical toxicological endpoints and transcriptional changes in the liver and kidney. A benchmark response of one standard deviation was used to model all endpoints.

Results: Several clinical pathology and organ weight measurements showed dose-related changes from which BMD values were calculated. In male rats, the effects included significantly decreased total thyroxine concentration, increased absolute liver weight, increased relative liver weight, and decreased total triiodothyronine concentration. The BMDs and benchmark dose lower confidence limits (BMDLs) were 7.264 (5.024), 8.492 (5.426), 16.251 (8.358), and 19.107 (7.426), respectively. In female rats, there were no apical endpoints for which a BMD value could be reliably estimated. Average PFHxSAm plasma concentrations at 2 and 24 hours postdose were lower in male rats than in female rats. Half-lives estimated using the two time points were longer in female rats (78.2 and 25.6 hours for the 4 and 37 mg/kg groups, respectively) than in male rats (40.1 and 15.1 hours for the 4 and 37 mg/kg groups, respectively).

In the liver of male and female rats, no Gene Ontology biological process or individual genes had BMD median values below the lower limit of extrapolation (<0.050 mg/kg). The most sensitive gene sets in male rats for which a reliable estimate of the BMD could be made were negative regulation of myeloid cell differentiation and regulation of cytokine production with median BMDs of 0.520 and 0.750 mg/kg and median BMDLs of 0.160 and 0.186 mg/kg, respectively. The most sensitive gene sets in female rats for which a reliable estimate of the BMD could be made were phenol-containing compound metabolic process and carboxylic acid catabolic process with median BMDs of 11.677 and 12.316 mg/kg and median BMDLs of 5.931and 8.410 mg/kg, respectively. The most sensitive upregulated genes in male rats with reliable BMD estimates included Gsta2, Gsta5, Crot, Slc27a2, Acaa1a, and Acaa1b with BMDs (BMDLs) of 5.725 (1.686), 5.725 (1.686), 7.423 (5.757), 7.622 (5.499), 8.417 (7.129), and 8.417 (7.129) mg/kg, respectively. The most sensitive downregulated genes in male rats with reliable BMD estimates were Egr1, Zfp354a, Tsku, and Cyp7a1 with BMDs (BMDLs) of 0.750 (0.186), 0.835 (0.271), 1.384 (0.541), and 5.721 (0.985) mg/kg, respectively. In female rats, the most sensitive upregulated genes with reliable BMD estimates included Dao, Ephx2, Ehhadh, Cyp2b1, Loc108348266/Cyp2b1, Cyp2c6v1, Loc100911718, and Ech1 with BMDs (BMDLs) of 6.134 (2.436), 6.441 (2.664), 7.300 (5.266), 7.456 (5.106), 7.456 (5.106), 9.829 (7.252), 9.829 (7.252), and 9.874 (6.591) mg/kg, respectively. The most sensitive downregulated genes in female rats with reliable BMD estimates were A2m and Loc100911545/A2m, both with a BMD (BMDL) of 1.163 (0.179) mg/kg.

In the kidney of male and female rats, no Gene Ontology biological process or individual genes had BMD median values below the lower limit of extrapolation (<0.050 mg/kg). The most sensitive gene sets in male rats for which a reliable estimate of the BMD could be made were fat cell differentiation and ER-nucleus signaling pathway, both with a median BMD of 8.745 mg/kg and with median BMDLs of 5.224 and 5.589 mg/kg, respectively. The most sensitive gene sets in female rats for which a reliable estimate of the BMD could be made were regulation of cell division, chromosome segregation, and cell division with median BMDs of 10.324, 11.921, and 11.921 mg/kg and median BMDLs of 7.461, 8.348, and 8.348 mg/kg, respectively. The most sensitive upregulated genes in male rats with reliable BMD estimates included Insig1, Srebf1, Fads1, Ppard, Decr1, Acot2, Acaa1a, Acaa1b, and Fasn with BMDs (BMDLs) of 7.612 (5.589), 8.745 (5.224), 9.357 (6.123), 9.934 (5.754), 12.862 (10.721), 13.201 (10.994), 13.398 (11.228), 13.398 (11.228), and 13.486 (11.223) mg/kg, respectively. One gene, Loc100911814/Spink1l, was downregulated with a BMD (BMDL) of 0.510 (0.212) mg/kg. In female rats, the most sensitive upregulated genes with reliable BMD estimates included Cdca3, Pck1, Ube2t, Srebf1, Ckap2, Lilra3, Lilrb3l, and Acaa1a with BMDs (BMDLs) of 2.619 (0.978), 5.515 (1.341), 10.991 (7.866), 11.236 (4.944), 12.122 (8.470), 17.020 (10.650), 17.020 (10.650), and 17.682 (14.617) mg/kg, respectively. The most sensitive downregulated genes in female rats with reliable BMD estimates were Slc10a1 and Cyp2c24 with BMDs (BMDLs) of 7.968 (6.075) and 10.565 (7.636) mg/kg, respectively.

Summary: Taken together, in male rats, the most sensitive gene set BMD (BMDL) median, individual gene BMD (BMDL), and apical endpoint BMD (BMDL) values that could be reliably determined occurred at 0.520 (0.160), 0.510 (0.212), and 7.264 (5.024) mg/kg, respectively. In female rats, the most sensitive gene set BMD (BMDL) median and individual gene BMD (BMDL) values that could be reliably determined occurred at 10.324 (7.461) and 1.163 (0.179) mg/kg, respectively. There were no apical endpoints in female rats for which a BMD value could be reliably estimated.