The disposition of acrylic acid in the male Sprague-Dawley rat following oral or topical administration

Comprehensive analysis of chronic rodent inhalation toxicity studies for methyl acrylate with attention to test conditions exceeding a maximum tolerated concentration

MA is a chemical intermediate, manufactured and processed within closed systems. While so far available subacute to chronic inhalation toxicity studies performed in compliance with OECD TG principles gave no indication of any carcinogenic potential for MA, a recent 2-year inhalation study with F344/DuCrlCrlj rats published in 2017 by the JBRC showed a statistically significant increase of squamous cell carcinoma in the nasal cavity of male rats at the highest tested concentration of 160 ppm. However, the results of the different studies in total indicate that this high concentration exceeded the MTC. As MA has a low potential for genotoxic and mutagenic activity, the increased tumour incidence can be attributed to a non-genotoxic mechanism, namely to a strong inflammatory response observed in this study. Together with mechanistic and epidemiologic data for other compounds related to nasal carcinogenesis via this mode of action, it can be concluded that the relevance of this increased tumour incidence in male rats for humans is questionable. Also, a long-term exposure to higher concentrations of MA is highly unlikely to be reached in the environment or at workplaces. Therefore, a risk for humans including cancer hazard is considered implausible.

Estimation of tetrabromobisphenol A (TBBPA) percutaneous uptake in humans using the parallelogram method

Tetrabromobisphenol A (TBBPA) is currently the world's highest production volume brominated flame retardant. Humans are frequently exposed to TBBPA by the dermal route. In the present study, a parallelogram approach was used to make predictions of internal dose in exposed humans. Human and rat skin samples received 100 nmol of TBBPA/cm(2) skin and absorption and penetrance were determined using a flow-through in vitro system. TBBPA-derived [(14)C]-radioactivity was determined at 6h intervals in the media and at 24h post-dosing in the skin. The human skin and media contained an average of 3.4% and 0.2% of the total dose at the terminal time point, respectively, while the rat skin and media contained 9.3% and 3.5%, respectively. In the intact rat, 14% of a dermally-administered dose of ~100 nmol/cm(2) remained in the skin at the dosing site, with an additional 8% reaching systemic circulation by 24h post-dosing. Relative absorption and penetrance were less (10% total) at 24h following dermal administration of a ten-fold higher dose (~1000 nmol/cm(2)) to rats. However, by 72 h, 70% of this dose was either absorbed into the dosing-site skin or had reached systemic circulation. It is clear from these results that TBBPA can be absorbed by the skin and dermal contact with TBBPA may represent a small but important route of exposure. Together, these in vitro data in human and rat skin and in vivo data from rats may be used to predict TBBPA absorption in humans following dermal exposure. Based on this parallelogram calculation, up to 6% of dermally applied TBBPA may be bioavailable to humans exposed to TBBPA.

Effects of dose and route on the disposition and kinetics of 1-butyl-1-methylpyrrolidinium chloride in male F-344 rats

Studies were conducted to characterize the effects of dose and route of administration on the disposition of 1-butyl-1-methylpyrrolidinium (BmPy-Cl) in male Fischer-344 rats. After a single oral administration of [(14)C]BmPy-Cl (50 mg/kg), BmPy-Cl in the blood decreased rapidly after C(max) of 89.1 min with a distribution half-life (t(1/2)(alpha)) of 21 min, an elimination half-life (t(1/2)(beta)) of 5.6 h, and a total body clearance of 7.6 ml/min. After oral administration (50, 5, and 0.5 mg/kg), 50 to 70% of the administered radioactivity was recovered in the feces, with the remainder recovered in the urine. Serial daily oral administrations of [(14)C]BmPy-Cl (50 mg/kg/day for 5 days) did not result in a notable alteration in disposition or elimination. After each administration, 88 to 94% of the dose was eliminated in a 24-h period, with 63 to 76% of dose recovered in the feces. Intravenous administration of [(14)C]BmPy-Cl (5 mg/kg) resulted in biphasic elimination. Oral systemic bioavailability was 43.4%, approximately equal to the dose recovered in urine after oral administration (29-38%). Total dermal absorption of [(14)C]BmPy-Cl (5 mg/kg) was moderate when it was applied in dimethylformamide-water (34 + or - 13%), variable in water (22 + or - 8%), or minimal in ethanol-water (13 + or - 1%) vehicles. Urine was the predominant route of elimination regardless of vehicle. Only parent [(14)C]BmPy-Cl was detected in the urine after all doses and routes of administration. BmPy-Cl was found to be a substrate for (K(t) = 37 microM) and inhibitor of (IC(50/tetraethylammonium) = 0.5 microM) human organic cation transporter 2. In summary, BmPy-Cl is moderately absorbed, extracted by the kidney, and eliminated in the urine as parent compound, independent of dose, number, or route of administration.

Characterization of the disposition and toxicokinetics of N-butylpyridinium chloride in male F-344 rats and female B6C3F1 mice and its transport by organic cation transporter 2

Studies were conducted to characterize the effect of dose and route of administration on the disposition of N-butylpyridinium chloride (NBuPy-Cl), an ionic liquid with solvent properties. Urine was the major route of NBuPy-Cl excretion after intravenous (5 mg/kg), single oral (0.5, 5, or 50 mg/kg), or repeated oral (50 mg/kg/day, 5 days) administration to male F-344 rats and single oral (50 mg/kg) administration to female B6C3F1 mice. Depending on the vehicle, absorption after dermal application (5 mg/kg, 125 microg/cm(2)) was 10 to 35% at 96 h. After the single intravenous dose, the blood concentration of NBuPy-Cl decreased in a biphasic manner with an elimination half-life of 2.2 h and a clearance of 7 ml/min. After single oral administration of NBuPy-Cl (50 mg/kg), maximum blood concentration was reached at 1.3 h, and the bioavailability was determined to be 47% at 6 h based on the blood toxicokinetics and 67% at 72 h based on urinary excretion. In all the urine and blood samples, only the parent compound was detected. Coadministration of NBuPy-Cl and inulin (by intravenous injection) revealed that the clearance of NBuPy-Cl exceeded the rat glomerular filtration rate. After incubation with Chinese hamster ovary cells expressing human organic cation transporter 2 (hOCT2), NBuPy-Cl was transported effectively (K(t) = 18 microM), and also a potent inhibitor of hOCT2 mediated tetraethylammonium transport (IC(50) = 2.3 microM). In summary, NBuPy-Cl is partially absorbed from the gastrointestinal tract and eliminated rapidly in the urine as parent compound most likely by renal glomerular filtration and OCT2-mediated secretion.

The effects of dose and route on the toxicokinetics and disposition of 1-butyl-3-methylimidazolium chloride in male F-344 rats and female B6C3F1 mice

These studies characterize the effect of dose and route of administration on the disposition and elimination of the ionic liquid, 1-butyl-3-methylimidazolium chloride (Bmim-Cl). After i.v. (5 mg/kg) or oral (50 mg/kg) administration to male F-344 rats [(14)C]Bmim-Cl detected in blood decreased rapidly. Clearance rates from the blood after i.v. and oral administration were similar (7.4 and 11.9 ml/min, respectively). Systemic bioavailability was determined to be 62.1% of a 50 mg/kg dose in rats. Urinary excretion of the parent compound by rats was the major route of elimination (i.v.: 91% in 24 h; oral: 55-74% in 24 h). The rates and routes of elimination were not affected by escalation of dose (0.5-50 mg/kg) or repeated oral administration (five daily administrations, 50 mg/kg) and were similar in male rats and B6C3F1 female mice (86-95% of dose eliminated in 24 h). Apparent systemic exposure to Bmim-Cl after dermal administration was dependent upon vehicle, as assessed by the percentage of dose eliminated in urine after application in a particular vehicle (water: 1%; ethanol/water: 3%; and dimethylformamide/water: 13% of dose). Regardless of gender, species, dose, route, or number of exposures, high-pressure liquid chromatography-UV/visible-radiometric analyses of urine samples showed a single peak that coeluted with the Bmim-Cl standard. These studies illustrate that systemic bioavailability of Bmim-Cl is high, tissue disposition and metabolism are negligible, and absorbed compound is extensively extracted by the kidney and eliminated in the urine as the parent compound.

Final report on the safety assessment of Acrylates Copolymer and 33 related cosmetic ingredients

Ingredients in the Acrylates Copolymer group all contain the monomers acrylic acid or methacrylic acid or one of their salts or esters. These ingredients are considered similar in that they are uniformly produced in chemical reactions that leave very little residual monomer. Although residual acrylic acid may be as high as 1500 ppm, typical levels are 10 to 1000 ppm. There is sufficient odor if residual monomers are present to cause producers to keep levels as low as possible. These ingredients function in cosmetics as binders, film formers, hair fixatives, suspending agents, viscosity-increasing agents, and emulsion stabilizers. Concentrations may be as high as 25% if used as a binder, film former, or fixative; or as low as 0.5% if used as a viscosity-increasing agent, suspending agent, or emulsion stabilizer. These very large polymers exhibit little toxicity. In rabbits and guinea pigs, Acrylates Copolymer did produce irritation, but no evidence of sensitization was found. The principle concern regarding the use of these polymer ingredients is the presence of toxic residual monomers. In particular, although 2-ethylhexyl acrylate was not genotoxic, it was carcinogenic when applied at a concentration of 21% to the skin of C3H mice. Lower concentrations (2.5%) and stop-dose studies at high concentrations (43%) were not carcinogenic. 2-Ethylhexyl acrylate was not carcinogenic in studies using NMRI mice. Whether an increase in carcinogenesis was seen or not, there was evidence of severe dermal irritation in these 2-ethylhexyl acrylate studies. Another concern regarding residual monomers was inhalation toxicity. Although the acrylic acid monomer is a nasal irritant, exposure to the monomer from use of these polymers in cosmetic formulations would always be less than the established occupational exposure limits for nasal irritation. Although there appears to be a huge variation in the mix of monomers used in the synthesis of these polymers, they are similar in that the polymers, except for dermal irritation, are not significantly toxic, and residual monomer levels are kept as low as possible. Although the monomers may be toxic, the levels that would be found in cosmetic formulations are not considered to present a safety risk. Accordingly, these Acrylate Copolymers are considered safe for use in cosmetic formulations when formulated to avoid irritation.

Measurement of bioavailability: measuring absorption through skin in vivo in rats and humans

Absorption through the skin is a route of exposure to a wide variety of therapeutic and/or environmental compounds. In vivo assays are advantageous in that they retain intact epidermal and dermal structures and thus reflect a more normal situation. The test compound is applied to the skin in a protected area for a specified period of time. At the end of the incubation, skin, tissues, and excreta are assessed for the presence of the test compound. The assay can also be performed with volatile compounds. When performed using laboratory animals, it is possible to assess the distribution of the compound throughout the body. If human volunteers are studied such analysis is limited to the skin, blood, and excreta.

Developmental toxicity study of inhaled acrylic acid in New Zealand White rabbits

In range-finding and definitive developmental toxicity studies, timed pregnant New Zealand White rabbits were exposed to acrylic acid (CAS No. 79-10-7) vapour for 13 consecutive days during pregnancy. In the range-finding study, eight pregnant does/group were exposed to 30, 60, 125 or 250 ppm acrylic acid vapour on gestation days (gd) 10-22 of pregnancy. Monitors of toxicity included body weight measurements, daily food consumption measurements and clinical observations. Three of the eight does/group were killed on the day following the last exposure (gd 23), and the remaining does were killed and autopsied on gd 29. At autopsy, special attention was given to gross observation of maternal nasal turbinates, and nasal turbinates from all does were evaluated histologically. No evaluation of foetuses was performed in the range-finding study. In the definitive study, 16 does/group were exposed to concentrations of 25, 75 or 225 ppm acrylic acid vapour from gd 6 to 18, the major period of organogenesis. Monitors of maternal toxicity included clinical observations and measurements of body weight and daily food consumption measurements. Does were killed and autopsied on gd 29. Maternal liver and kidney weights were measured and external, visceral and skeletal evaluations of foetuses were conducted. Maternal nasal turbinates were not evaluated histologically in the definitive study. Effects in does from both studies included consistent concentration-related reductions in food consumption and body weight gains throughout the exposure period at concentrations of acrylic acid vapour above 60 ppm. Characteristic clinical signs of sensory irritation, including perinasal and perioral wetness and severe nasal congestion, were noted in does from both studies at or above vapour concentrations of 75 ppm. Gross observation of nasal turbinates immediately following exposures in the range-finding study indicated colour changes in the nasal turbinates of does in the 60 and 250 ppm groups. Colour changes in the nasal turbinates were noted in one doe from the 250 ppm exposure group killed on gd 29. Pertinent autopsy findings in the does from the definitive study included ulceration of the nasal turbinates of a single doe in the 225 ppm group. Histological evaluation of turbinates from does killed the day following exposures in the range-finding study revealed lesions in the nasal epithelium in all acrylic acid-exposed groups. The severity of the lesions was concentration related. Microscopic evaluation of turbinates from does killed on gd 29 showed the presence of nasal lesions in the 60, 125 and 250 ppm groups. However, the nasal tissues had recovered considerably during the post-exposure interval. Despite the severe effects on the nasal mucosa of does in both studies, there was no evidence of developmental toxicity including teratogenicity at any exposure concentration used in the definitive study.

Disposition and metabolism of acrylic acid in C3H mice and Fischer 344 rats after oral or cutaneous administration

Acrylic acid (AA) is used in large amounts to produce acrylic esters and polymers. Here we report on the disposition and metabolism of [1-14C]AA in male C3H mice and Fischer 344 (F344) rats after oral (40 and 150) mg/kg) or cutaneous (10 and 40 mg/kg) administration. Although these and other strains of rodents have been used frequently in toxicity studies of AA, results of pharmacokinetic studies are available for only the Sprague-Dawley rat. In the current study, C3H mice rapidly absorbed and metabolized orally administered AA, with about 80% of the dose exhaled as 14CO2 within 24 h. Excretion in urine and feces accounted for approximately 3% and 1% of the dose, respectively. Elimination of 14C from plasma, liver, and kidney was rapid but was slower from fat. The disposition of orally administered AA in F344 rats was similar to the results obtained from mice. After cutaneous administration to C3H mice, about 12% of the dose was absorbed, while the remainder apparently evaporated. Approximately 80% of the absorbed fraction of the dose was metabolized to 14CO2 within 24 h. Excretion in urine and feces each accounted for less than 0.5% of the dose. Elimination of radioactivity from plasma, liver, and kidney was rapid; however, levels in fat were higher at 72 h than at 1 or 8 h. After cutaneous administration to F344 rats, 19-26% of the dose was absorbed, and the rest apparently evaporated. Disposition of the absorbed fraction of the dose was similar to results found in mice. Results from an in vitro experiment with rat skin showed that at least 60% of the applied dose evaporated and about 25% was absorbed, confirming the in vivo results. High-performance liquid chromatography (HPLC) analysis of rat urine and rat and mouse tissues indicated that absorbed AA was rapidly metabolized by the beta-oxidation pathway of propionate catabolism. In summary, rapid detoxification of systemically absorbed AA, as observed here in C3H mice and F344 rats, can explain findings that AA causes minimal systemic toxicity despite its causing irritation at portal-of-entry tissues.

Acrylic acid oxidation and tissue-to-blood partition coefficients in rat tissues

We report rates of acrylic acid (AA) oxidation and tissue/blood partition coefficients in rat tissues. AA oxidation in Fischer 344 rat kidney and liver slices was described by saturable kinetics with maximal velocities of about 4 and 2 mumol/h/g, respectively. AA oxidation rates in 11 additional tissues were 40% or less than in liver. AA oxidation rates in Sprague-Dawley rat liver and kidney were similar to those in Fischer rats. Partition coefficients varied within a narrow range, suggesting that a tissue's contribution to systemic detoxification of AA will depend much more strongly on its rate of AA oxidation and the proportion of the cardiac output that it receives.