In vitro metabolism of 8-2 fluorotelomer alcohol: interspecies comparisons and metabolic pathway refinement.

The detection of perfluorinated organic compounds in the environment has generated interest in their biological fate. 8-2 Fluorotelomer alcohol (8-2 FTOH, C(7)F(15)CF(2)CH(2)CH(2)OH), a raw material used in the manufacture of fluorotelomer-based products, has been identified in the environment and has been implicated as a potential source for perfluorooctanoic acid (PFOA) in the environment. In this study, the in vitro metabolism of [3-(14)C] 8-2 FTOH and selected acid metabolites by rat, mouse, trout, and human hepatocytes and by rat, mouse, and human liver microsomes and cytosol were investigated. Clearance rates of 8-2 FTOH in hepatocytes indicated rat > mouse > human >/= trout. A number of metabolites not previously reported were identified, adding further understanding to the pathway for 8-2 FTOH metabolism. Neither perfluorooctanoate nor perfluorononanoate was detected from incubations with human microsomes. To further elucidate the steps in the metabolic pathway, hepatocytes were incubated with 8-2 fluorotelomer acid, 8-2 fluorotelomer unsaturated acid, 7-3 acid, 7-3 unsaturated acid, and 7-2 secondary fluorotelomer alcohol. Shorter chain perfluorinated acids were only observed in hepatocyte and microsome incubations of the 8-2 acids but not from the 7-3 acids. Overall, the results indicate that 8-2 FTOH is extensively metabolized in rats and mice and to a lesser extent in humans and trout. Metabolism of 8-2 FTOH to perfluorinated acids was extremely small and likely mediated by enzymes in the microsomal fraction. These results suggest that human exposure to 8-2 FTOH is not expected to be a significant source of PFOA or any other perfluorocarboxylic acids.

Absorption, distribution, metabolism, and elimination of 8-2 fluorotelomer alcohol in the rat.

The absorption, distribution, metabolism, and elimination of [3-14C] 8-2 fluorotelomer alcohol (8-2 FTOH, C7F1514CF2CH2CH2OH) following a single oral dose at 5 and 125 mg/kg in male and female rats have been determined. Following oral dosing, the maximum concentration of 8-2 FTOH in plasma occurred by 1 h postdose and cleared rapidly with a half-life of less than 5 h. The internal dose to 8-2 FTOH, as measured by area under the concentration-time curve to infinity, was similar for male and female rats and was observed to increase in a dose-dependent fashion. The majority of the 14C 8-2 FTOH (> 70%) was excreted in feces, and 37-55% was identified as parent. Less than 4% of the administered dose was excreted in urine, which contained low concentrations of perfluorooctanoate (approximately 1% of total 14C). Metabolites identified in bile were principally composed of glucuronide and glutathione conjugates, and perfluorohexanoate was identified in excreta and plasma, demonstrating the metabolism of the parent FTOH by sequential removal of multiple CF2 groups. At 7 days postdose, 4-7% of the administered radioactivity was present in tissues, and for the majority, 14C concentrations were greater than whole blood with the highest concentration in fat, liver, thyroid, and adrenals. Distribution and excretion of a single 125-mg/kg [3-14C] 8-2 FTOH dermal dose following a 6-h exposure in rats was also determined. The majority of the dermal dose either volatilized from the skin (37%) or was removed by washing (29%). Following a 6-h dermal exposure and a 7-day collection period, excretion of total radioactivity via urine (< 0.1%) and feces (< 0.2%) was minor, and radioactivity concentrations in most tissues were below the limit of detection. Systemic availability of 8-2 FTOH following dermal exposure was negligible.

Absorption, distribution, metabolism, excretion, and kinetics of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoic acid ammonium salt following a single dose in rat, mouse, and cynomolgus monkey.

Ammonium, 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate has been developed as a processing aid used in the manufacture of fluoropolymers. The absorption, distribution, elimination, and distribution (ADME) and kinetic behavior of this substance has been evaluated in rats, mice, and cynomolgus monkeys by oral and intravenous routes of exposure and studied in both plasma and urine. The test substance is rapidly and completely absorbed in both rats and mice and both in vivo and in vitro experiments indicate that it is not metabolized. The test substance is rapidly eliminated exclusively in the urine in both rats and mice, with rats eliminating it more quickly than mice (approximately 5h elimination half-life in rats, 20 h half-life in mice). Pharmacokinetic analysis in monkeys, rats, and mice indicate rapid, biphasic elimination characterized by a very fast alpha phase and a slower beta phase. The beta phase does not contribute to potential accumulation after multiple dosing in rats or monkeys. Comparative pharmacokinetics in rats, mice, and monkeys indicates that the rat is more similar to the monkey and is therefore a more appropriate rodent model for pharmacokinetics in primates.

Dermal penetration of propylene glycols: measured absorption across human abdominal skin in vitro and comparison with a QSAR model.

The dermal penetration of undiluted monopropylene glycol (MPG) and dipropylene glycol (DPG) has been measured in vitro using human abdominal skin under conditions of infinite dose application, and the results compared with predictions from the SKINPERM QSAR model (ten Berge, 2009). The measured steady-state penetration rates (Jss) for MPG and DPG were 97.6 and 39.3 µg/cm2/h, respectively, and the permeability coefficients (Kp) were 9.48×10(-5) cm/h for MPG and 3.85×10(-5) cm/h for DPG. In comparison, the SKINPERM model slightly over-predicted Jss and Kp for MPG and DPG by between 2.6- and 5.1-fold, respectively. The model predictions of 254 µg/cm2/h and 24.6×10(-5) cm/h for MPG, and 202 µg/cm2/h and 19.8×10(-5) cm/h for DPG were in fairly good agreement with the measured values. Further, the model predicted a Jss of 101 µg/cm2/h and a Kp of 9.9×10(-5) cm/h for the homologue tripropylene glycol. Assuming that the measured Jss was the same under conditions of finite dose application (taken to be 10 µL/ cm2) and was maintained over a 24-h period (both conservative assumptions), the relative dermal absorption of the applied dose was estimated to be 23% (0.96%/h) for MPG and 9% (0.39%/h) for DPG. However, the extrapolation for MPG may be further overestimated due to possible residence in the stratum corneum under infinite conditions of exposure that would not be applicable to a finite loading dose.

Kinetics of 8-2 fluorotelomer alcohol and its metabolites, and liver glutathione status following daily oral dosing for 45 days in male and female rats.

Fluorotelomer alcohols (FTOHs) are raw materials used in the manufacture of polymeric and surfactant products. Based on previous findings from single oral dosing in rats with radiolabeled 8-2 FTOH, glutathione (GSH) depletion and/or the presence of perfluorinated/polyfluorinated acids and aldehyde metabolites was hypothesized to account for the hepatocellular lesions observed in male rats from a 90-day subchronic oral dosing study. Further, the reported nephropathy in female rats from the subchronic experiment was hypothesized to have been initiated by a thiol metabolite produced by degradation of GSH conjugates. In the current investigation, the kinetics of 8-2 FTOH and its metabolites along with liver GSH status were evaluated in the rat following daily oral dosing with 8-2 FTOH for 45 days at 5 and 125 mg/kg/day. Liver GSH stores 1-2h after dosing were unaffected, suggesting that GSH depletion is not likely a relevant mode of action in the liver. The tissue metabolite data indicate that the liver toxicity mode of action is likely associated with elevated levels of perfluoroalkyl acids found in males, since other polyfluorinated metabolites and 8-2 FTOH were present in livers from female rats at comparable or higher levels. Detection of the N-acetyl cysteine conjugate of the unsaturated parent telomer alcohol in urine from female rats and not male rats provides some evidence to support the mechanistic basis for the observed kidney effects. Further, the increasing levels of perfluorooctanoic acid (PFOA) in plasma from female rats over the 45-day dosing phase, while unexpected, may reflect an increased net absorption of 8-2 FTOH, slow elimination of intermediates in the metabolic pathway between 8-2 FTOH and PFOA, or altered kidney clearance. The results of this study have enhanced our understanding of 8-2 FTOH kinetics and metabolism and potential modes of action in the rat, which will guide the design of future studies for FTOHs and our need to define the mechanistic basis for the observed effects.

In vitro dermal absorption rate testing of certain chemicals of interest to the Occupational Safety and Health Administration: summary and evaluation of USEPA's mandated testing.

In 2004, the United States Environmental Protection Agency (USEPA) published a final test rule in the US Federal Register requiring in vitro dermal penetration rate testing for selected industrial chemicals. The test rule described procedures for determining a permeability coefficient (Kp) and two short-term dermal absorption rates at 10 and 60min using human cadaver skin mounted in an in vitro diffusion cell model. According to the USEPA announcement, the selected chemicals were to be spiked with their radiolabeled form and tested in either water, isopropyl myristate (IPM) or neat depending on their physical character at room temperature, their aqueous solubility, their potential to damage the skin and their ability to achieve the study endpoints as prescribed. Overall, and for the majority of chemicals, the short-term absorption rates were higher at 10min than at 60min and the portion of applied dose remaining in the skin at the end of the exposure period was greater than the portion of dose that had penetrated through the skin and was detected in the receptor solution. In contrast to this, the amount of chemical in the receptor solution at study termination for the Kp (steady-state) experiments was greater than the amount remaining in the skin. For the Kp experiments, which lasted from 2 to 48h, a majority of skins exposed to neat chemical exhibited a reduced barrier function. However, integrity was mostly unaltered for skins from the short-term experiments and Kp experiments using chemicals applied either in water or IPM. Quantitative structure activity relationship (QSAR) model-predicted Kp values were in fair agreement with experimental data for those chemicals that were applied in a water vehicle when the integrity of the skin was not compromised. However, QSAR-derived Kp values were not predictive for those chemicals when applied in IPM vehicle or neat. Absorption predictions, based on the measured Kp and steady-state flux data for chemicals applied in water or neat, respectively, were comparable to measured values at both 10 and 60min. Kp data for chemicals applied in water and the flux values for neat chemicals will be useful for making estimates of skin absorption in occupational settings. Kp measurements for chemicals applied in IPM vehicle are not envisioned to provide useful data for estimating the risk from dermal exposure to chemicals in the workplace. When available, in vitro dermal flux measurements should be combined with toxicity information in order to improve the utility of chemical skin notations.

The in vitro permeability coefficient and short-term absorption rates for vinyl toluene using human cadaver skin mounted in a static diffusion cell model.

Vinyl toluene is one of several methylstyrene monomers that provide improved performance in resins for specialty paints, hydrocarbon resins for adhesives, specialty polymers, and unsaturated polyester resins. The purpose of this study was to determine a permeability coefficient (Kp) and short-term absorption rate for vinyl toluene using human cadaver skin mounted in an in vitro static diffusion cell model with an exposure area of 0.64 cm2. For the Kp determination, vinyl toluene was applied at a rate of 100 microL/cm2 to 6 skin replicates representing 4 human subjects. Serial receptor fluid samples were collected at 1, 2, 4, 8, 12, 24, 36, and 48 h postapplication and analyzed for vinyl toluene by HPLC-UV. Based on the slope at steady-state (203.3 microg cm(-2) h(-1) +/- 120.0 microg cm(-2) h(-1)) and the concentration of the applied dose of vinyl toluene, taken as its density (894,600 microg/cm3), the Kp was calculated to be 2.27 x 10(-4) cm/h (+/-1.34 x 10(-4) cm/h). For the short-term absorption experiments, 12 skin replicates representing 3 human subjects were employed. Following 10- and 60-min exposures to a finite dose of vinyl toluene (10 microL/cm2), the respective short-term absorption rates were calculated to be 66.0 (+/-29.9) and 104.2 (+/-63.0) microg cm(-2) h(-1). These data provide industrial hygienists and safety personnel values to estimate the amount of vinyl toluene that may be absorbed via the dermal exposure route, given a variety of exposure scenarios, and the time it takes (skin absorption time) to reach a body burden equal to the Occupational Safety and Health Administrative permissible exposure level (OSHA PEL) or ACGIH TLV.