Paul H. Lieder

A comparison of the pharmacokinetics of perfluorobutanesulfonate (PFBS) in rats, monkeys, and humans.

Materials derived from perfluorobutanesulfonyl fluoride (PBSF, C(4)F(9)SO(2)F) have been introduced as replacements for eight-carbon homolog products that were manufactured from perfluorooctanesulfonyl fluoride (POSF, C(8)F(17)SO(2)F). Perfluorobutanesulfonate (PFBS, C(4)F(9)SO(3)(-)) is a surfactant and potential degradation product of PBSF-derived materials. The purpose of this series of studies was to evaluate the pharmacokinetics of PFBS in rats, monkeys, and humans, thereby providing critical information for human health risk assessment. Studies included: (1) intravenous (i.v.) elimination studies in rats and monkeys; (2) oral uptake and elimination studies in rats; and (3) human serum PFBS elimination in a group of workers with occupational exposure to potassium PFBS (K(+)PFBS). PFBS concentrations were determined in serum (all species), liver (rats), urine (all species), and feces (rats). In rats, the mean terminal serum PFBS elimination half-lives, after i.v. administration of 30mg/kg PFBS, were: males 4.51+/-2.22h (standard error) and females 3.96+/-0.21h. In monkeys, the mean terminal serum PFBS elimination half-lives, after i.v. administration of 10mg/kg PFBS, were: males 95.2+/-27.1h and females 83.2+/-41.9h. Although terminal serum half-lives in male and female rats were similar, without statistical significance, clearance (CL) was significantly greater in female rats (469+/-40mL/h) than male rats (119+/-34mL/h) with the area under the curve (AUC) significantly larger in male rats (294+/-77microg.h/mL) than female rats (65+/-5microg.h/mL). These differences were not observed in male and female monkeys. Volume of distribution estimates suggested distribution was primarily extracellular in both rats and monkeys, regardless of sex, and urine appeared to be a major route of elimination. Among 6 human subjects (5 male, 1 female) followed up to 180 days, the geometric mean serum elimination half-life for PFBS was 25.8 days (95% confidence interval 16.6-40.2). Urine was observed to be a pathway of elimination in the human. Although species-specific differences exist, these findings demonstrate that PFBS is eliminated at a greater rate from human serum than the higher chain homologs of perfluorooctanesulfonate (PFOS) and perfluorohexanesulfonate (PFHxS). Thus, compared to PFOS and PFHxS, PFBS has a much lower potential for accumulation in human serum after repeated occupational, non-occupational (e.g., consumer), or environmental exposures.

Comparative Pharmacokinetics of Perfluorobutyrate in Rats, Mice, Monkeys, and Humans and Relevance to Human Exposure via Drinking Water

Perfluorobutyrate (PFBA) has been detected in precipitation, surface waters, water treatment effluent, and in public and private wells in Minnesota at up to low microg/l concentrations. We evaluated the pharmacokinetics of PFBA in rats, mice, monkeys, and humans to provide a rational basis for dose selection in toxicological studies and to aid in human-health-risk assessment. Studies included (1) rats--iv and oral; (2) mice--oral; (3) monkeys--iv; and (4) humans--occupationally exposed volunteers. PFBA was determined in serum (all species), liver (rats and mice), urine (rats, mice, and monkeys), and feces (rats and mice). In addition, we characterized serum PFBA concentrations in 177 individuals with potential exposure to PFBA through drinking water. Mean terminal serum PFBA elimination half-lives for males (M) and females (F), respectively, in h were (1) for rats given 30 mg/kg, 9.22 and 1.76 (oral), and 6.38 and 1.03 (iv); (2) for mice given oral doses of 10, 30, or 100 mg/kg ammonium PFBA, 13.34 and 2.87 at 10 mg/kg, 16.25 and 3.08 at 30 mg/kg; and 5.22 and 2.79 at 100 mg/kg; (3) for monkeys given 10 mg/kg iv, 40.32 and 41.04; and (4) for humans, 72.16 and 87.00 (74.63 combined). Volume of distribution estimates indicated primarily extracellular distribution. Among individuals with plausible exposure via drinking water, 96% of serum PFBA concentrations were < 2 ng/ml (maximum 6 ng/ml). These findings demonstrate that PFBA is eliminated efficiently from serum with a low potential for accumulation from repeated exposure.

Toxicological evaluation of potassium perfluorobutanesulfonate in a 90-day oral gavage study with Sprague-Dawley rats.

Perfluorobutanesulfonate (PFBS) is a surfactant and degradation product of substances synthesized using perfluorobutanesulfonyl fluoride. A 90-day rat oral gavage study has been conducted with potassium PFBS (K+PFBS). Rats were dosed with K+PFBS at doses of 60, 200, and 600mg/kg-day body weight. The following endpoints were evaluated: clinical observations, food consumption, body weight, gross and microscopic pathology, clinical chemistry, and hematology. In addition, functional observation battery and motor activity assessments were made. Histological examination included tissues in control and 600 mg/kg-day groups. Additional histological examinations were performed on nasal cavities and turbinates, stomachs, and kidneys in the 60 and 200 mg/kg-day groups. No treatment-related mortality, body weight, or neurological effects were noted. Chromorhinorrhea (perioral) and urine-stained abdominal fur were observed in males at 600mg/kg-day. Red blood cell counts, hemoglobin, and hematocrit values were reduced in males receiving 200 and 600mg/kg-day; however, there were no adverse histopathological findings in bone marrow. Total protein and albumin were lower in females at 600mg/kg-day. There were no significant changes in clinical chemistry in either sex. All rats appeared normal at sacrifice. Microscopic changes were observed only at the highest dose in the stomach. These changes consisted of hyperplasia with some necrosis of the mucosa with some squamous metaplasia. These effects likely were due to a cumulative direct irritation effect resulting from oral dosing with K+PFBS. Histopathological changes were also observed in the kidneys. The changes observed were minimal-to-mild hyperplasia of the epithelial cells of the medullary and papillary tubules and the ducts in the inner medullary region. There were no corresponding changes in kidney weights. Clinical chemistry parameters related to kidney function were unchanged. These kidney findings are likely due to a response to high concentration of K+PFBS in tubules and ducts and represent a minimal-to-mild effect. Microscopic changes of an equivocal and uncertain nature were observed in the nasal mucosa and were likely attributable to the route of dosing (oral gavage). The NOAEL for the female rat in this study was 600 mg/kg-day (highest dose of study). The NOAEL for the male rat was 60 mg/kg-day based on hematological effects.

A two-generation oral gavage reproduction study with potassium perfluorobutanesulfonate (K+PFBS) in Sprague Dawley rats.

Perfluorobutanesulfonate (PFBS) is a surfactant and degradation product of substances based on perfluorobutanesulfonyl fluoride. A two-generation reproductive rat study has been conducted with potassium PFBS (K(+)PFBS). Parental-generation (P) rats were dosed orally by gavage with 0, 30, 100, 300 and 1000mg K(+)PFBS/kg/day for 10 weeks prior to and through mating (males and females), as well as during gestation and lactation (females only). First generation (F1) pups were dosed similarly, beginning at weaning. Second generation (F2) pups were not directly dosed but potentially exposed to PFBS through placental transfer and nursing, and the study was terminated 3 weeks after their birth. Endpoints evaluated included body weight, food consumption, clinical signs, estrus cycling, sperm quality, pregnancy, natural delivery, litter outcomes, and developmental landmarks. The no-observable-adverse effect dose level (NOAEL) in the parental generations (P and F1) was 100mg/kg/day. In the 300 and 1000mg/kg/day dose group rats, there were (1) increased liver weight (absolute or relative) and corresponding increased incidence of adaptive hepatocellular hypertrophy (male only) and (2) increased incidence of minimal to mild microscopic findings in the medulla and papilla of the kidneys (male and female). There were no K(+)PFBS treatment-related effects on fertility or reproduction among the P or the F1 rats. There were no microscopic changes in male or female reproductive organs, and no biologically relevant effects on sperm parameters, mating, estrous cycles, pregnancy, and natural delivery in the P- or F1-generations. There were no K(+)PFBS treatment-related effects on survival of pups in the two-generation study. Litter size and average pup birth weight per litter were not statistically significantly different from controls in any dose group. In the F1-generation, terminal body weight was reduced in males at 1000mg/kg/day. Preputial separation was slightly delayed (approximately 2 days) at this dose, a finding consistent with the body weight reduction. Essentially no effects were observed in the F1 females. F2 pups had normal body weights. The reproductive NOAEL was >1000mg/kg/day in both generations.

Fluoroacetate-Mediated Toxicity of Fluorinated Ethanes

A series of 1-(di)halo-2-fluoroethanes reported in the literature to be nontoxic or of low toxicity were found to be highly toxic by the inhalation route. Experiments were performed that showed the compounds, 1,2-difluoroethane, 1-chloro-2-fluoroethane, 1-chloro-1,2-difluoroethane, and 1-bromo-2-fluoroethane to be highly toxic to rats upon inhalation for 4 hr. All four compounds had 4-hr approximate lethal concentrations of < or = 100 ppm in rats. In contrast, 1,1-difluoroethane (commonly referred to as HFC-152a) has very low acute toxicity with a 4-hr LC50 of > 400,000 ppm in rats. Rats exposed to the selected toxic fluoroethanes showed clinical signs of fluoroacetate toxicity (lethargy, hunched posture, convulsions). 1,2-Difluoroethane, 1-chloro-2-fluoroethane, 1-chloro-1,2-difluoroethane, and 1-bromo-2-fluoroethane were shown to increase concentrations of citrate in serum and heart tissue, a hallmark of fluoroacetate intoxication. 19F NMR analysis confirmed that fluoroacetate was present in the urine of rats exposed to each toxic compound. Fluorocitrate, a condensation product of fluoroacetate and oxaloacetate, was identified in the kidney of rats exposed to 1,2-difluoroethane. There was a concentration-related elevation of serum and heart citrate in rats exposed to 0-1000 ppm 1,2-fluoroethane. Serum citrate was increased up to 5-fold and heart citrate was increased up to 11-fold over control citrate levels. Metabolism of 1,2-difluoroethane by cytochrome P450 (most likely CYP2E1) is suspected because pretreatment of rats or mice with SKF-525F, disulfiram, or dimethyl sulfoxide prevented or delayed the toxicity observed in rats not pretreated. Experimental evidence indicates that the metabolism of the toxic fluoroethanes is initiated at the carbon-hydrogen bond, with metabolism to fluoroacetate via an aldehyde or an acyl fluoride. The results of these studies show that 1-(di)halo-2-fluoroethanes are highly toxic to rats and should be considered a hazard to humans unless demonstrated otherwise.

Hepatic macromolecular binding and tissue distribution of ortho- and para-toluidine in rats

The in vivo covalent binding of ortho- and para-toluidine (OT and PT) to rat hepatic macromolecules was investigated to determine if a relationship exists between the degree of binding for each isomer and its carcinogenic potency. The ortho-isomer has been shown to be a more potent hepatocarcinogen than the para-isomer. In addition to the macromolecular binding, the tissue distribution of each isomer was also measured. The degree of binding to hepatic macromolecules appeared to be at maximum for both at 24 28 h following dosing. At 24 h following dosing, the level of DNA binding of OT was approximately 1.2-fold lower than that of PT. The binding to RNA and protein was also lower for OT than PT, although the differences were not as great as that observed for DNA binding. There were subtle differences in tissue distribution for each isomer. However, in contrast to the macromolecular binding data, the area under the plasma concentration curve for OT was approximately 1.8-fold greater than that for PT. Based on the results of these studies, there was no direct correlation between the degree of macromolecular binding and carcinogenic potency.

Dimethylacetamide pharmacokinetics following inhalation exposures to rats and mice

Whole-body inhalation exposures to N,N-dimethylacetamide (DMAC) were conducted with male rats (Crl:CD BR) and mice (Crl:CD-1 (ICR)BR). Exposure concentrations were 50, 150, 300 and 500 ppm. The exposure routines consisted of single 1-, 3-, or 6-h exposures and ten 6-h exposures (10 exposure days in 2 weeks). Area under the plasma concentration curve (AUC) values were determined for DMAC and its metabolite N-methylacetamide (NMAC), following 6-h exposures (single exposure or last in a series of 10 exposures). The range of exposures was chosen to assess the exposure-dependent nature of DMAC pharmacokinetics in rats and mice. Plasma profiles indicated mice metabolized DMAC rapidly with plasma half-lives from 0.3 to 0.5 h for DMAC. The DMAC AUC values from mice were underestimated due to the required time (< 30 min) between termination of exposure and the initial blood sample. DMAC plasma half-life in rats ranged from 0.6 to 1.5 h. The AUC values for DMAC in rats increased approximately 5-fold and 3-fold as exposure concentrations increased from 150 to 300 ppm and 300 to 500 ppm, respectively. NMAC persisted in plasma for at least 24 h after the 150, 300 and 500 ppm exposures to rats. NMAC was not detected in plasma from mice beyond the 12-h post-exposure timepoint for the 300 and 500 ppm exposures. Regardless of exposure level, repeated DMAC exposures to both rats and mice resulted in plasma profiles of DMAC and NMAC similar to those from a single exposure. The dose-dependent nature of the DMAC AUC data and the absence of effects of repeated 300 and 500 ppm DMAC exposures supported a toxicity-driven upper limit of 350 ppm for a chronic inhalation study.

1,1,1-Trifluoro-2,2-dichloroethane (HCFC-123) and 1,1,1-Trifluoro-2-bromo-2-chloroethane (Halothane) Cause Similar Biochemical Effects in Rats Exposed by Inhalation for Five Days

1,1,1-Trifluoro-2,2-dichloroethane (HCFC-123) and 1,1,1-trifluoro-2-bromo-2 chloroethane (halothane) are gases with anesthetic properties. HCFC-123 is used as a refrigerant, fire extinquishing agent, and solvent, while halothane is a clinical anesthetic. Much information is available on chronic toxicity of HCFC-123 in animals, while the information available for halothane is from short-term animal exposures or chronic, low level human exposures. Thus, there is little biochemical information available on similar endpoints for these two chemicals, which share common metabolites. In the present study, male rats were exposed to 5000 ppm HCFC-123, 5000 ppm halothane, or room air for 6 hr per day for 5 consecutive days. Rats exposed to both test compounds gained little or no weight during the study. Liver weights were slightly decreased in the rats exposed to HCFC-123 and halothane compared to controls. The serum triglycerides were decreased to approximately 20% of control level in rats exposed to both HCFC-123 and halothane, and serum cholesterol was decreased to less than 80% of control by both compounds. Both test compounds increased hepatic beta-oxidation by approximately 3-fold over control, and HCFC-123 caused a significant increase in hepatic cytochrome P450 content, while the increase in cytochrome P450 was not statistically significant in the halothane-treated rats. The results indicate that HCFC-123 and halothane share not only common metabolic pathways, but also several common biological effects, specifically those associated with peroxisome proliferation. These data indicate that human experience with halothane may be useful in the risk assessment of HCFC-123.