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Reference
Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 417 (Toxicokinetics)
Version / remarks:
parts of the guidelines are taken
Qualifier:
equivalent or similar to
Guideline:
EPA OPPTS 870.7485 (Metabolism and Pharmacokinetics)
GLP compliance:
yes (incl. certificate)
Radiolabelling:
no
Species:
rat
Strain:
Wistar
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Laboratories, Sulzfeld, Germany
- Age at study initiation: 6-12 weeks
- Weight at study initiation: 250 - 350 g prior to dosing
- Housing: During acclimatization animals were housed in groups in Polysulfonate cages (2000P; H Temp (PSU), 2065 qcm, Tecniplast). During plasmakinetic experiments animals were kept individually. in Polycarbonate cages (1291H; PC, 820 cm2, Tecniplast) for experiments 1 and 2 and in Polycarbonate cages III (800 cm2, Tecniplast) for experiments 3 – 6.
- Diet (e.g. ad libitum): Kliba lab diet (mouse/rat "GLP"); Provimi Kliba SA, Kaiseraugst, Switzerland (ad libitum)
- Water (e.g. ad libitum): tap water (ad libitum)
- Acclimation period: at least 7 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 24
- Humidity (%): 30 - 70
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:
oral: gavage
Vehicle:
water
Details on exposure:
PREPARATION OF DOSING SOLUTIONS:
The test substances were weighed in, filled up with tap water to an appropriate weight and were solved by stirring at room temperature on a magnetic stirrer for about 5 min. The resulted solutions with defined concentrations were used for the test-substance administrations. 10 mL/kg bw of test-substance preparation was dosed orally by gavage.
Duration and frequency of treatment / exposure:
once
Dose / conc.:
200 mg/kg bw/day (nominal)
Remarks:
Hydroxypropylacrylate
Dose / conc.:
117 mg/kg bw/day (nominal)
Remarks:
Propylene glycol
No. of animals per sex per dose:
4
Control animals:
no
Details on study design:
- Dose selection rationale:
By request of the sponsor the following dose levels were selected:
dose 1 with Hydroxypropylacrylate: 250 mg/kg body weight, (p.o.), (1.92 mmol/kg body weight)
dose 2 with Propylene glycol: 146 mg/kg body weight (p.o.), (1.92 mmol/kg body weight)
Based on the unforeseen toxicity of HPA at a dose level of 250 mg/kg bw under the test conditions used, the experiment was repeated with two dose groups at lower dose levels. Additionally, conditions were optimized to reduce potential stress during blood sampling. In agreement with the sponsor the additional dose levels were tested:
dose 3, Hydroxypropylacrylate: 200 mg/kg body weight, (p.o.), (1.54 mmol/kg body weight)
dose 4, Propylene glycol: 117 mg/kg body weight (p.o.), (1.54 mmol/kg body weight)
dose 5, Hydroxypropylacrylate: 50 mg/kg body weight, (p.o.), (0.38 mmol/kg body weight)
dose 6, Propylene glycol: 29 mg/kg body weight (p.o.), (0.38 mmol/kg body weight)
Details on dosing and sampling:
TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: blood, plasma
- Time and frequency of sampling: blood samples 10 and 30 min, 1, 2, 4, 8, 24, 48, 72, 96 hours

Plasma kinetics were investigated in order to determine the pharmacokinetic parameters of the test substances in rats. It was of special interest to demonstrate the absence of HPA in the systemic circulation and to investigate the internal doses of PG (quantified as AUC) for equimolar oral doses of HPA and PG. The hypothesis of comparable internal doses of PG after oral equimolar dosings of HPA and PG is based on the assumption of a complete first pass effect of HPA by hydrolysis and its quantitative conversion into the corresponding glycol derivative.

The plasma concentrations of individual animals and thereof derived mean values after single oral administrations of HPA and PG to male Wistar rats at target dose levels of 200 and 117 mg/kg bw (corresponding to 1.54 mmol/kg bw for both test substances) . Kinetic results of dose groups 1 and 2 are not determined based on observed, unexpected toxicities of HPA at a target dose of 250 mg/kg bw under the applied test conditions. Plasma samples of these dose groups were not analysed. Kinetic results of dose groups 5 and 6 are not evaluated because these dose groups were foreseen as simultaneous back up groups in case of unexpected toxicities of HPA at a target dose of 200 mg/kg bw (dose group 3). Since dose groups 3 and 4 are assessed to be valid, plasma samples of dose groups 5 and 6 were not analysed and no kinetic results were generated.

Hydroxypropylacrylate: target dose of 200 mg/kg bw: In male Wistar rats exposed to a single oral target dose of 200 mg HPA/kg bw (corresponding to 1.54 mmol/kg bw), the mean actual nominal dose of 206.2 mg/kg bw was administered. In plasma samples taken before, and from 0.17 hours post dosing up to 96 hours post dosing, no HPA could be detected in plasma. For the analyte PG, the maximum mean plasma concentration of 22.5 μg/mL occurred 1 hour post dosing, declined to 3.7 μg/mL at 8 hours, to 0.5 μg/mL at 24 hours and was negligible at later sampling time points. The individual maximum mean plasma concentrations for PG ranged from 14.0 to 28.0 μgmL. The terminal half-lifes ranged from 1.4 to 3.8 hours. The mean terminal half life was 2.7 hours. For the analyte PG, the calculated values for the area under the plasma concentration time curve AUD ranged for individual animals from 90 to 157 [μg x h/mL]. For rat 12, the AUD was calculated to be 57 [μg x h/mL]. However, since there were no quantitative values for the plasma samples at 4 and 8 hours, this AUD is assessed to be underpredictive and was not included into the statistics of this pharmacokinetic parameter. The calculated mean AUD for rats 9 to 11 was 125±33 [μg x h/mL]. The data of this dose group demonstrate a fast absorption of HPA after oral dosing in the rat and its metabolic first pass effect. PG could be identified as a major systemic metabolite of Hydroxypropylacrylate.

Propylene glycol: target dose of 117 mg/kg bw: In male Wistar rats exposed to a single oral target dose of 117 mg PG/kg bw (corresponding to 1.54 mmol/kg bw), the mean actual nominal dose of 116.9 mg/kg bw was administered. PG was not detected in plasma samples taken before dosing but was present in plasma samples taken between 0.17 hours to 8 hours post dosing. The maximum mean plasma concentration of 66.8 μg/mL occurred 0.5 hours post dosing, declined to 1.1 μg/mL at 8 hours and was negligible at later sampling time points. The individual maximum mean plasma concentrations for PG ranged from 61.0 to 72.0 μgmL. The terminal half-lifes ranged from 1.2 to 1.6 hours. The mean terminal half life was 1.3 hours. For the analyte PG, the calculated values for the area under the plasma concentration time curve AUD ranged for individual animals from 169 to 198 [μg x h/mL]. The calculated mean AUD was 182±12 [μg x h/mL]. The data of this dose group demonstrate a fast absorption of PG after oral dosing to rats. The measured plasma concentrations and the calculated AUD outline that unmetabolized PG is the major component of its systemic dose. In the current experiments, the calculated maximum plasma concentrations as well as the AUDs for equimolar oral doses of 1.54 mmol/kg bw of HPA and PG resulted in values of 22.5 and 66.8 [μg/mL] as well as 125 and 182 [μg x h/mL], respectively. These results demonstrate that the maximum plasma concentrations of PG is about 3-fold higher for and equimolar dose of PG compared to HPA. The corresponding internal dose of PG is 47% higher for an equimolar oral dose of PG compared to dosed HPA. It may be assumed that this observation is based on potential direct reaction of the monomer in the stomach, i.e. with glutathion or stomach content, which is known for this chemistry.

Conclusions:
Overall, the data of the current study demonstrate that HPA and PG are fast metabolized when dosed orally to male Wistar rats. After one oral dose of HPA, the acrylate itself could not be determined in rat plasma, demonstrating a complete metabolic first pass effect. Consequently, for orally dosed HPA as well as for orally dosed PG, PG is the major entitiy in the systemic circulation. When the plasma concentrations of PG are compared quantitatively for an equimolar target dose of the test substances of 1.54 mmol/kg bw, the maximum plasma concentration was about 3-fold and the internal dose about 50% higher for administered PG compared to HPA.

Description of key information

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

A toxicokinetic study with hydroxypropyl acrylate (HPA) showed a fast metabolism in Wistar rats. After one oral dose of HPA, the acrylate itself could not be determined in rat plasma at any time, demonstrating a complete metabolic first pass effect. Consequently, for orally dosed HPA as well as for orally dosed PG, PG is the major entitiy in the systemic circulation. When the plasma concentrations of PG are compared quantitatively for an equimolar target dose of the test substances of 1.54 mmol/kg bw, the maximum plasma concentration was about 3-fold and the internal dose about 50% higher for administered PG compared to HPA.

After oral HPA gavage the propylene glycol amount could be reduced compared to the equimolar dose of propylene glycol based lower systemic uptake, on direct reaction of the monomer in the stomach, i.e. with glutathion or stomach content, which is known for this chemistry.

 

In addition the structural analogue 2-hydroxyethyl acrylate (HEA) was investigated in rats using several routes of exposure.

The metabolism, distribution and excretion of uniformly labelled 14C-2-hydroxyethyl acrylate was examined in male Fischer 344 rats using oral, intraperitoneal, dermal and inhalation routes of exposure (BAMM 1992). The results of the study indicate that once the chemical becomes systemically available, it is rapidly metabolized and eliminated from the body as either CO2in the expired air or urinary metabolites. Greater than 70 % of the administered dose of HEA-derived14C was excreted by 12 hr post-dosing or post-exposure as urinary metabolites and as14CO2in the expired air for the oral, ip, and inhalation routes.

No qualitative differences in urinary metabolites between routes were observed, indicating no marked route-dependent differences in the metabolic fate of HEA.

According to the metabolic scheme proposed by BAMM (1992) metabolism occurs by two primary routes, hydrolysis of the ester linkage by carboxylesterase to acrylic acid and ethylene glycol, and conjugation with glutathione (GSH). Both pathways serve to detoxify 2-hydroxyethyl acrylate. In rats, the metabolism of ethylene glycol proceeds via the alcohol and aldehyd dehydrogenase pathway finally resulting in the formation of CO2 and acrylic acid is rapidly incorporated into the normal cellular metabolism via the propionate degradative pathway. Conjugation of 2-HEA with GSH can occur spontaneously by a Michael addition or can be mediated by GSH transferase. The conjugated form is rapidly excreted by the kidney.

Based on the structural similarity of HEA and HPA and the oral toxicokinetic study with HPA, similar kinetics for both acrylates are anticipated.

 

Discussion on bioaccumulation potential result:

After oral gavage HPA is rapidly metabolised. Also, the structural analogue 2-hydroxyethyl acrylate was investigated in rats using several routes of exposure.

In vitro Studies

To determine the in vitro rate of degradation or metabolism of 2-HEA in rat blood, male Fischer 344 rats were anesthetized, exsanguinated via cardiac puncture and their blood obtained. Triplicate samples (along with corresponding blank) were prepared at three concentration levels (100, 10 and 1 µg 2-HEA/mL) for each time point selected. In addition to the 2-HEA spiking solutions, an internal standard (2-hydroxyethyl methacrylate, 2-HEMA at a concentration of 0.5 µg/mL) was added at 15 seconds, 30 seconds, 1 min, 2 min and 5 min after spiking. Quantification of 2-HEA in the blood extracts by gas chromatography-mass spectrometrywas based on comparison of the extract response to the external standard response taking into account the ratio of the 2-HEA response to that of the internal standard (2-HEMA).

 

The in vitro half-life of 2-hydroxyethyl acrylate in rat blood was approx. 100 sec (BAMM 1992).

In vivo Studies

The metabolism, distribution and excretion of uniformly labelled14C-2-hydroxyethyl acrylate was examined in male Fischer 344 rats using oral, intraperitoneal, dermal and inhalation routes of exposure (BAMM 1992). For the oral and intraperitoneal routes of exposure rats (4 animals/dose level/route of exposure) received a single dose of 2.5 or 50 mg/kg body weight (approximately 20μCi), respectively. For the inhalation exposure six rats were exposed to a target vapour concentration of 8 ppm (corresponding to approx. 0.0385 mg/L and to approx. 0.2 µCi/L)14C-HEA for 6 hours nose only under dynamic flow-through conditions. For the dermal exposure 4 rats were treated under occlusive conditions with14C-HEA at a dose of 12.5 mg/kg body weight (approximately 15-20μCi).

The results of the study indicate that once the chemical becomes systemically available it is rapidly metabolized and eliminated from the body as either CO2 in the expired air or urinary metabolites. Greater than 70 % of the administered dose of HEA-derived14C was excreted by 12 hr post-dosing or post-exposure as urinary metabolites and as14CO2in the expired air for the oral, ip, and inhalation routes.

For the oral and intraperitoneal routes (2.5 mg/kg bw) 35-36 % of the administered dose was expired as14CO2and 43 - 47 % of the dose excreted via urine by 48 hours post-dosing. At 50 mg/kg bw following oral and ip administration, there was some evidence of saturation kinetics, with 40 – 45 % of the dose expired as14CO2and 33 – 36 % of the dose excreted in the urine. The rate of absorption of HEA appeared to be route-dependent and was complete within 4 hr or less when HEA was given by the oral or ip routes of administration.

Following dermal administration 66 % of the dose was slowly absorbed within 48 hours of the application with the remaining 33 % being associated with the application site. Of the absorbed dose 27 % was excreted in the urine as metabolites of HEA and 27 % was excreted in the expired air as14CO2.

For inhalation 39 % of the 14C-activity recovered at 48 hr was eliminated in the urine and 41 % was expired as14CO2.

For all routes, 9 – 16 % of the dose or recovered activity was found in the tissues and carcass and less than 3 % in the faeces.

The half-lives of elimination of radioactivity in the urine and for expired 14CO2 were 14 h and 17 h, respectively. The half-life of elimination of radioactivity in the plasma was determined to be 26 hr and did not represent parent chemical.

No qualitative differences in urinary metabolites between routes were observed, indicating no marked route-dependent differences in the metabolic fate of HEA. HPLC analyses were performed on pooled urine specimens from all treatment groups and exposure routes. Radiochromatograms of the urinary metabolites contained four major peaks or peak groups of radioactivity. One metabolite could be identified as N-acetyl-S-(carboxylethyl)cysteine by GC/EI/MS. No attempts were made to identify the other three major14C peaks, however, none of the three peaks were found to correspond to the retention times of HEA or acrylic acid.

The available metabolic data on HEA is consistent with information on other acrylates where hydrolysis of the ester functionality is the primary metabolic pathway. By analogy with e.g. ethyl acrylate or acrylic acid it is expected that a minor metabolic pathway for HEA will be via conjugation with glutathione with the resulting mercapturic acid derivatives being excreted in the urine. This is supported by the identity of one of the major urinary metabolites of HEA.

 

Conclusion:

Animal studies indicated rapid metabolism of HPA and HEA via hydrolysis of the ester functionality with the subsequent rapid metabolism of the hydrolysis products to produce exhaled CO2 or urinary metabolites (mercapturic acid derivatives). There were no marked route-dependent differences in the metabolic fate of HEA when administered by the oral, intraperitoneal, dermal or inhalation routes of exposure.

Based on the similarity of the results for HEA with other acrylic acid esters, similar kinetics of 2-hydroxypropyl acrylate are anticipated.

 

Discussion on absorption rate:

No reliable studies concerning dermal absorption were identified for hydroxypropyl acrylate. However, the structural analogue 2-hydroxyethyl acrylate was investigated in rats by the dermal route of exposure.

Dermal absorption:

The metabolism, distribution and excretion of uniformly labelled14C-2-hydroxyethyl acrylate was examined in male Fischer 344 rats using dermal application (BAMM 1992). 4 rats were treated under occlusive conditions with14C-HEA at a dose of 12.5 mg/kg body weight (approximately 15-20μCi).

Following dermal administration 66 % of the dose was slowly absorbed within 48 hours of the application with the remaining 33 % being associated with the application site. Of the absorbed dose 27 % was excreted in the urine as metabolites of HEA and 27 % was excreted in the expired air as14CO2. HPLC analyses were performed on pooled urine specimens. Radiochromatograms of the urinary metabolites contained four major peaks or peak groups of radioactivity. One metabolite could be identified as N-acetyl-S-(carboxylethyl)cysteine by GC/EI/MS.

The dermal absorption of HEA was relatively slow with a half-life in the order of 24 hr or greater, which was confirmed by plasma and red blood cell radioactivity concentration-time curves, amount remaining on the skin at sacrifice, and the lag time in peak urinary and CO2 excretion.

Based on the structural similarity of HEA and HPA, similar adsorption kinetics of hydroxypropyl acrylate are anticipated.