Background:

6:1 Fluorotelomer alcohol (6:1 FTOH) 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 6:1 FTOH.

Methods:

A short-term in vivo biological potency study on 6:1 FTOH in adult male and female Sprague Dawley (Hsd:Sprague Dawley^® SD^®) rats was conducted. 6:1 FTOH was formulated in corn oil and administered once daily for 5 consecutive days by gavage (study days 0–4). 6:1 FTOH 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 relative liver weight, increased albumin concentration, increased relative left kidney weight, increased aspartate aminotransferase activity, increased absolute liver weight, increased alanine aminotransferase activity, increased alkaline phosphatase activity, and increased creatinine concentration. The BMDs and benchmark dose lower confidence limits (BMD_Ls) were 3.19 (1.774), 12.122 (9.527), 13.365 (4.084), 20.907 (4.272), 28.117 (19.352), 28.507 (15.286), 36.116 (21.468), 89.383 (74.114), and 97.38 (32.365) mg/kg, respectively. In female rats, the effects included significantly decreased reticulocyte count, increased large unstained cell count, decreased total triiodothyronine concentration, increased monocyte count, increased thyroid stimulating hormone concentration, and increased aspartate aminotransferase activity. The BMDs (BMD_Ls) were 15.578 (3.622), 54.339 (15.759), 161.48 (122.215), 257.111 (160.613), 356.61 (268.917), and 497.046 (340.458) mg/kg, respectively. Average 6:1 FTOH plasma concentrations at 2 hours postdose were lower in female rats than in male rats. At 24 hours postdose, the concentration fell below the limit of detection of the analytical method in both male and female rats, suggesting short plasma half-lives of 6:1 FTOH in rats.

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 cellular response to epidermal growth factor stimulus and response to epidermal growth factor with median BMDs of 0.368 and 0.690 mg/kg and median BMD_Ls of 0.103 and 0.456 mg/kg, respectively. The most sensitive gene sets in female rats for which a reliable estimate of the BMD could be made were positive regulation of phagocytosis and regulation of phagocytosis with median BMDs of 44.730 and 48.555 mg/kg and median BMD_Ls of 22.260 and 27.154 mg/kg, respectively. The most sensitive upregulated genes in male rats with reliable BMD estimates included Acot2, Eci1, Loc100911558/Spink1l, Spink1, Ehhadh, Crot, Acaa1a, and Acaa1b with BMDs (BMD_Ls) of 1.012 (0.809), 1.013 (0.769), 1.270 (0.542), 1.270 (0.542), 1.280 (1.047), 1.411 (1.092), 1.874 (1.524), and 1.874 (1.524) mg/kg, respectively. The most sensitive downregulated genes in male rats with reliable BMD estimates were Myc and Zfp36 with BMDs (BMD_Ls) of 0.186 (0.103) and 0.368 (0.097) mg/kg, respectively. In female rats, the top 10 most sensitive individual genes were upregulated. These genes were Gdf15, Igfbp1, Eci1, Etfdh, Cyp2b1, Loc108348266/Cyp2b1, Dhrs7, Dhrs7l1, Slc27a2, and Vnn1 with BMDs (BMD_Ls) of 17.724 (8.696), 18.792 (7.230), 32.546 (27.162), 34.846 (26.297), 35.483 (29.479), 35.483 (29.479), 35.986 (10.630), 35.986 (10.630), 36.103 (26.571), and 37.026 (30.688) mg/kg, respectively.

In the kidney of male rats, two Gene Ontology biological processes had BMD median values <0.050 mg/kg, which relate to astrocyte activation and negative regulation of response to biotic stimulus. The most sensitive gene sets in male rats for which a reliable estimate of the BMD could be made were acetyl-CoA metabolic process and acyl-CoA metabolic process with median BMDs of 1.346 and 1.928 mg/kg and median BMD_Ls of 0.541 and 1.305 mg/kg, respectively. No gene sets in the kidney of female rats had estimated BMD median values <0.050 mg/kg. The most sensitive gene sets in female rats for which a reliable estimate of the BMD could be made were fatty acid beta-oxidation and fatty acid oxidation with median BMDs of 21.079 and 27.058 mg/kg and median BMD_Ls of 13.312 and 13.877 mg/kg, respectively. No individual kidney genes in male rats had median BMD values <0.050 mg/kg. The most sensitive upregulated genes in male rats with reliable BMD estimates included Decr1, Vnn1, Hmgcs2, Ehhadh, Eci2, Acaa2, Acot1, Cyp4a1, and Ech1 with BMDs (BMD_Ls) of 0.680 (0.505), 0.705 (0.488), 0.804 (0.541), 0.953 (0.671), 0.989 (0.643), 1.346 (0.539), 1.363 (0.938), 1.593 (1.021), and 2.055 (1.124) mg/kg, respectively. One gene, Acmsd, was downregulated with a BMD (BMD_L) of 0.775 (0.183) mg/kg. In female rats, the top 10 most sensitive individual genes were upregulated. One individual gene, Plod3, had a BMD value <0.050 mg/kg. The next most sensitive upregulated genes with reliable BMD estimates included Eci1, Vnn1, Hmgcs2, Ehhadh, Eci2, Acaa1a, Acaa1b, Ech1, and Acaa2 with BMDs (BMD_Ls) of 9.486 (7.353), 10.025 (7.993), 11.644 (9.266), 12.212 (9.437), 12.789 (9.488), 13.850 (11.009), 13.850 (11.009), 19.820 (14.141), and 22.339 (13.614) mg/kg, respectively.

Summary:

Taken together, in male rats, the most sensitive gene set BMD (BMD_L) median, individual gene BMD (BMD_L), and apical endpoint BMD (BMD_L) values that could be reliably determined occurred at 0.368 (0.103), 0.186 (0.103), and 3.19 (1.774) mg/kg, respectively. The BMDs (BMD_Ls) could not be determined for two gene sets and were estimated to be <0.050 mg/kg. In female rats, the most sensitive gene set BMD (BMD_L) median, individual gene BMD (BMD_L), and apical endpoint BMD (BMD_L) values that could be reliably determined occurred at 21.079 (13.312), 9.486 (7.353), and 15.578 (3.622) mg/kg, respectively. The BMD (BMD_L) could not be determined for one individual gene and was estimated to be <0.050 mg/kg. Future studies investigating lower doses would be helpful to obtain more accurate estimates of BMD values for the most sensitive gene sets.