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Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable, well documented publication based on scientific principles, part of a comprehensive test programme (Rohm & Haas)
Objective of study:
metabolism
Principles of method if other than guideline:
Metabolic in-vitro studies on tissue slices and homogenates from rats (F344 and Sprague Dawley), using 1-14C-labelled AA. The rate of oxidation [expressed as nmol CO2/h per g tissue or mg protein and kinetic parameters (pseudo-Km and Vmax) were determined.
GLP compliance:
not specified
Specific details on test material used for the study:
- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: 98 %
- Supplier: Rohm and Haas Company

- Radiochemical purity (if radiolabelling): > 98 % and 95 %, respectively
- Specific activity (if radiolabelling): 0.1-0.5 mCi/mmol and 1.44 mCi/mmol, respectively
- Locations of the label (if radiolabelling): [1-14C]Acrylic acid
- Supplier: Sigma Chemical Co. (St. Louis, MO) and Chemsyn Science Laboratories (Lenexa, KS), respectively
Radiolabelling:
yes
Species:
rat
Strain:
other: Fischer 344 and Sprague Dawley
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories (Wilmington, MA)
- Weight at study initiation: 249 ± 50 g (Fischer 344); 386 ± 120 g (Sprague-Dawley)
- Housing: 1-2 per cage
- Diet (ad libitum): Purina Certified Lab Chow Checkers (Purina, St. Louis, MO)
- Water: ad libitum
Toxicokinetic parameters:
other: The kidney and liver were the organs showing the highest oxidation rates. All tissues were able to oxidize AA to a certain extent. Lung, glandular stomach, heart, spleen, small and large intestine oxidized AA at rates that were between 10 and 40 %.
Toxicokinetic parameters:
other: Oxidation of AA in Fischer 344 rat kidney and liver slices were described by pseudo MIchaelis-Menten kinetics. The pseudo Km value did not vary between kidney and liver: ca. 0.5 mM. However, the pseudo Vmax in kidney was approx. twice the value in liver.

The kidney and liver were the organs showing the highest oxidation rates, with maximal velocities of 4 and 2 µmol/h/g, respectively. The metabolic conversion rate was similar in both strains with no difference between slice model and homogenate. All tissues were able to oxidize AA to a certain extent, but with considerable variation. Lung, glandular stomach, heart, spleen, small intestine and large intestine oxidized AA at rates that were between 10 and 40 % of the rate measured in liver. The remaining tissues (forestomach, brain, skin, fat, and muscle) oxidized AA at less than 10 % of the rate observed in the liver.

Compared to the mouse (see Black et al., 1993), the absolute rates per g tissue in the rat are 2 - 3 x higher than in the mouse.

Oxidation of AA in Fischer 344 rat kidney and liver slices were described by pseudo MIchaelis-Menten kinetics. The pseudo Km value did not vary between kidney and liver: approx. 0.5 mM. However, the pseudo Vmax in kidney was approx. twice the value in liver. At relatively low concentrations, i.e. well below km, AA oxidation would follow apparent first-order kinetics, and the half-life of AA in liver and kidney would be approx. 10 min or less.

AA tissue-to-blood partition coefficients were measured in homogenates by micropartitioning. Relatively little variation between tissues in the partition coefficient was observed, with values ranging between 0.9 (fat) and 2.1 (brain).

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented, acceptable publication
Objective of study:
metabolism
Qualifier:
no guideline followed
GLP compliance:
not specified
Specific details on test material used for the study:
- Name of test material (as cited in study report): Acrylic acid
- Radiochemical purity (if radiolabelling): > 98 %
- Specific activity (if radiolabelling): 0.1 - 0.5 mCi/mmol
- Locations of the label (if radiolabelling): 1. [1-14C]AA; 2. [2,3-14C]AA (radiochemical purity and specific activity identical for both species)
- Supplier: Sigma Chemical Co., St. Louis, MO
Radiolabelling:
yes
Species:
mouse
Strain:
other: C3H/HeNCrlBR
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories (Wilmingtob, MA)
- Age at study initiation: 1.5 to 4.5 months
- Housing: 6/cage
- Diet (ad libitum): Purina certified Lab Chow Checkers
- Water (ad libitum): tap water
Metabolites identified:
yes
Details on metabolites:
HPLC analysis of incubation medium following metabolism of [1 -14C]AA by mouse kidney:
Kidney slices formed a metabolite that coeluted with a 3-hydroxypropionic acid standard. No other metabolites were found in this analysis. Samples from incubations of [1-14C]AA with either mouse liver, skin, or small intestine were also analyzed by HPLC, and a peak that coeluted with 3-hydroxypropionic acid was found in each.

Kinetic parameters for AA oxidation in mouse liver, kidney and skin were determined. Oxidation of [1-14C]AA to 14CO2 by liver, kidney and skin slices followed pseudo-Michaelis-Menten kinetics. Marked differences between these tissues in the pseudo-Vmax existed. The rate in the kidney was about 5-fold higher than the rate in the liver which, in turn, was about 12-fold higher than the rate in the skin.

Kinetic constants for acrylic acid metabolism in mouse tissue slices:

Tissue

Pseudo-Km [mM]

Pseudo-Vmax [nmol/hr/g]

Half-life [hr]

Kidney

0.558 ± 0.068

2890 ± 436

0.139 ± 0.026

Liver

0.759 ± 0.032

616 ± 62

0.867 ± 0.069

Skin

0.694 ± 0.058

47.9 ± 5.8

10.2 ± 0.6

The rate of AA oxidation in 10 additional tissues was measured at 1 and 5 mM AA. All tissues studied oxidized [1 -14C]AA; however, the rate varied considerably between tissues. The kidney, by far, was the most active tissue, oxidizing AA at a rate about five fold higher than in the liver, which was the next most active tissue. The other tissues oxidized AA at relatively low rates. Lung, glandular stomach, heart, spleen, fat, and large intestine oxidized AA at rates that were between 10 and 40 % of the rate measured in liver. The remaining tissues, forestomach, small intestine, brain, skin, and muscle oxidized AA at less than 10 % of the rates observed in liver. The rate of oxidation at 5 mM AA was l.5 to 3 times higher than the rate measured at 1 mM AA except for the fat, in which the rates were similar at these concentrations. Rates of AA oxidation in tissues from male and female mice were similar.

Oxidation of [2,3 -14C]AA in kidney and liver slices:

Endproducts of acrylic acid metabolism are CO2 and Acetyl-CoA which is derived from carbons 2 and 3 of AA. Acetyl-CoA generated from AA in this manner could then enter the TCA cycle to provide for the complete oxidation of AA carbons to CO2. In both liver and kidney, the rate of 14CO2 formation from [2,3-14C]AA was about two-thirds of the rate from [1 -14C]AA.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Objective of study:
toxicokinetics
Principles of method if other than guideline:
Disposition and metabolism of Acrylic acid (AA) in C3H mice after single cutaneous administration.
GLP compliance:
yes
Specific details on test material used for the study:
- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 98 % (unlabeled AA)
- Supplier: Union Carbide Corporation

- Radiochemical purity (if radiolabelling): >= 98.6 %
- Specific activity (if radiolabelling): 0.14 - 0.4 mCi/mmol
- Locations of the label (if radiolabelling): [1-14C]AA
- Supplier: Sigma Chemical Co. (St. Louis, Mo.)
Radiolabelling:
yes
Species:
mouse
Strain:
C3H
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY)
- Substrain: C3H/HeNCrlBR
- Age at study initiation: approx. 35 d old
- Weight at study initiation: 21 g
- Diet (ad libitum): Agway Prolab Diet Mouse, Agway Inc., Syracuse, NY
- Water (ad libitum)
Route of administration:
dermal
Vehicle:
acetone
Details on exposure:
TEST SITE
- Area of exposure: 1.0 X 1.0 cm
- Type of wrap if used: nonocclusive dose containment devices constructed from Stomahesive and cemented to the skin with Skin-Bond
- Time intervals for shavings or clipplings: prior to application


REMOVAL OF TEST SUBSTANCE
- Washing (if done): at the end of experiment to remove the unabsorbed portion of the dose


TEST MATERIAL
- concentration (if solution): 1 mL test AA/100 mL acetone


VEHICLE
- Amount(s) applied (volume or weight with unit): 0.95 and 3.8 mL/kg bw, respectively

Duration and frequency of treatment / exposure:
72 hrs
Dose / conc.:
10 mg/kg bw/day (actual dose received)
Dose / conc.:
40 mg/kg bw/day (actual dose received)
No. of animals per sex per dose:
15
Control animals:
no
Details on study design:
- Dose selection rationale: The cutaneous dose levels were selected based on previous work on the cutaneous toxicity of AA in several strains of mice (DePass et al. 1984, Tegeris et al. 1988).
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, stomach contents (after sacrifice)
- Time and frequency of sampling: Urine was collected under dry ice and faeces were collected at room temperature at 8, 24, 48, and 72 h. At 1 and 8 hrs, 5 animals from ech group were sacrificed and blood samples collected. Tissues were sampled at termination (liver, kidney, fat, stomach).
- Traps for volatile compounds:
Room air was drawn through the metabolism cages at a rate of approximately 350 mL/min. Expired 14CO2 was collected in traps containing a solution of 2-methoxyethanol : ethanolamine (7:3, v/v), which was replaced with fresh solution at regular intervals. Other exhaled volatile 14C-labeled organic compounds were collected onto activated charcoal traps (approximately 4 g) placed in series ahead of the 14CO2 traps. In addition to the in-line volatile organics trap, the dose-containment device was modified by cementing activated charcoal-impregnated filter paper sheets to the top of the frame in order to trap the volatile fraction of the applied dose at the dosing site.
Details on absorption:
After cutaneous administration of single doses (40 or 10 mg/kg bw) to C3H mice, the processes of AA absorption and elimination were rapid and nearly complete within 8 h. Evaporation from the dosing site accounted for the largest fraction of the applied dose, although total recovery of the dose was variable. After 40 mg/kg bw, 11.4 ± 1.7% (mean t ± SD, n= 5) of the dose was absorbed (sum of cumulative proportions exhaled as 14CO2 or excreted in urine or faeces and the proportions found in dosing site skin, tissues, and carcass at 72 h), and after 10 mg/kg bw, 12.4 ± 3.3% was absorbed. Metabolism to 14CO2 was the major route of elimination, accounting for 83.5 ± 8.4% and 77.7 ± 10.4% of the absorbed dose after the high and low dose, respectively. Elimination via other routes was minor.
Details on distribution in tissues:
At the end of the experiment, 0.2-1.5% of the dose was found in the dosing site skin, and about 1% was found in tissues and carcass. Exhalation of volatile organic compounds other than 14CO2 was not quantified separately but was presumed to be negligible based on the results from orally dosed animals. Elimination of radioactivity from the dosing site skin, plasma, liver, and kidney was rapid. The concentration of radioactivity found in fat at 72 h was greater than that found at 1 or 8 h.
Metabolites identified:
no
Details on metabolites:
Neither AA nor its metabolites were detected in livers from mice at any time after cutaneous administration of 40 mg/kg bw.

Disposition of radioactivity in C3H mice after cutaneous administration of [1 -14C]AA:

Dose

40 mg/kg bw

10 mg/kg bw

14CO2

9.6 ± 2.2

9.3 ± 1.2

Volatilized dose

49.9 ± 12.6

70.9 ± 9.6

Urine

0.4 ± 0.1

0.3 ± 0.1

Faeces

0.2 ± 0.1

0.4 ± 0.1

Cage wash

0.2 ± 0.1

0.2 ± 0.1

Tissues

0.0 ± 0.0

0.2 ± 0.1

Carcass

0.8 ± 0.8

0.5 ± 0.1

Dosing-site skin

0.2 ± 0.1

1.5 ± 2.3

Skin rinse

0.2 ± 0.1

0.6 ± 0.3

Total recovery

61.5 ± 14.0

84.0 ± 10.5

The less than complete recovery of the administered doses is probably explained by the volatile nature of acrylic acid and its propensity to bind to materials such as plastic and glass, properties that may also be shared by some of the metabolites of acrylic acid.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented, acceptable publication
Objective of study:
toxicokinetics
Principles of method if other than guideline:
Disposition and metabolism of Acrylic acid (AA) in Fischer 344 rats after single cutaneous administration.
GLP compliance:
yes
Specific details on test material used for the study:
- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 98 % (unlabeled AA)
- Supplier: Union Carbide Corporation

- Radiochemical purity (if radiolabelling): >= 98.6 %
- Specific activity (if radiolabelling): 0.14 - 0.4 mCi/mmol
- Locations of the label (if radiolabelling): [1-14C]AA
- Supplier: Sigma Chemical Co. (St. Louis, Mo.)
Radiolabelling:
yes
Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY)
- Substrain: F344/NHsd
- Age at study initiation: approx. 7 wk old
- Weight at study initiation: 210 g
- Diet (ad libitum): Agway Prolab Diet Rat, Agway Inc., Syracuse, NY
- Water (ad libitum)

Route of administration:
dermal
Vehicle:
acetone
Details on exposure:
TEST SITE
- Area of exposure: 2.5 X 4.0 cm (high dose), 1.0 X 2.5 cm (low dose)
- Type of wrap if used: nonocclusive dose containment devices constructed from Stomahesive and cemented to the skin with Skin-Bond
- Time intervals for shavings or clipplings: prior to application


REMOVAL OF TEST SUBSTANCE
- Washing (if done): at the end of experiment to remove the unabsorbed portion of the dose


TEST MATERIAL
- concentration (if solution): 1 mL test AA/100 mL acetone


VEHICLE
- Amount(s) applied (volume or weight with unit): 0.95 and 3.8 mL/kg bw, respectively

Duration and frequency of treatment / exposure:
72 hrs
Remarks:
Doses / Concentrations:
10 and 40 mg/kg bw
No. of animals per sex per dose:
15
Control animals:
no
Details on study design:
- Dose selection rationale: The cutaneous dose levels were selected based on previous work on the cutaneous toxicity of AA in several strains of mice (DePass et al. 1984, Tegeris et al. 1988).
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, stomach contents (after sacrifice)
- Time and frequency of sampling: Urine was collected under dry ice and faeces were collected at room temperature at 8, 24, 48, and 72 h. At 1 and 8 hrs, 5 animals from ech group were sacrificed and blood samples collected. Tissues were sampled at termination (liver, kidney, fat, stomach).
- Traps for volatile compounds:
Room air was drawn through the metabolism cages at a rate of approximately 500 mL/min. Expired 14CO2 was collected in traps containing a solution of 2-methoxyethanol : ethanolamine (7:3, v/v), which was replaced with fresh solution at regular intervals. Other exhaled volatile 14C-labeled organic compounds were collected onto activated charcoal traps (approximately 4 g) placed in series ahead of the 14CO2 traps. In addition to the in-line volatile organics trap, the dose-containment device of the low-dose animals was modified by cementing activated charcoal-impregnated filter paper sheets to the top of the frame in order to trap the volatile fraction of the applied dose at the dosing site.
Details on absorption:
After cutaneous administration of single doses (40 or 10 mg/kg bw) to Fischer 344 rats, AA absorption and elimination were rapid and nearly complete within 8 h after either dose. Evaporation accounted for the largest fraction of the applied dose, although total recovery of the applied dose was only about 50-60%. After application of 40 mg/kg, 25.6 ± 1.5% (mean ± SD, n= 5) of the dose was absorbed. After 10 mg/kg, 19.4 ± 1.3% of the dose was absorbed. The major route of elimination of the absorbed dose was via exhalation of 14CO2, which accounted for 77.0 ± 5.5 and 69.5 ± 1.3% of the absorbed dose after the 40 and 10 mg/kg doses, respectively. Approximately 1% of the dose remained in the dosing site skin after either dose.
Details on distribution in tissues:
Elimination of radioactivity from plasma and tissues was rapid except for fat, where concentrations measured at 72 h were higher than those measured at earlier times.
Details on excretion:
Urinary excretion accounted for 1-2% of the dose, with most occurring within the first 24 h. Excretion in faeces accounted for less than 1%, and approximately 2-3% of the dose was found in peripheral tissues and the carcass at the end of theexperiment.
Metabolites identified:
yes
Details on metabolites:
Urine collected from rats after the cutaneous routes was analyzed by HPLC for AA and metabolites. After cutaneous dosing, a peak that coeluted with AA was detected in urine along with the polar major metabolite which was also found after oral dosing. A trace amount of one other metabolite was detected in urine from the 40 mg/kg bw cutaneous dose group but not after 10 mg/kg bw.

Disposition of radioactivity in Fischer 344 rats after cutaneous administration of [1 -14C]AA:

Dose

40 mg/kg bw

10 mg/kg bw

14CO2

19.7 ± 2.2

13.5 ± 1.0

Volatilized dose

26.5 ± 6.9

41.3 ± 5.8

Urine

2.0 ± 0.7

0.8 ± 0.1

Faeces

0.8 ± 0.1

0.5 ± 0.2

Cage wash

0.5 ± 0.1

0.3 ± 0.0

Tissues

0.1 ± 0.0

0.2 ± 0.0

Carcass

1.7 ± 0.5

2.8 ± 0.9

Dosing-site skin

1.0 ± 0.3

1.4 ± 0.6

Skin rinse

0.2 ± 0.1

0.4 ± 0.1

Total recovery

52.2 ± 7.6

61.1 ± 5.3

The less than complete recovery of the administered doses is probably explained by the volatile nature of acrylic acid and its propensity to bind to materials such as plastic and glass, properties that may also be shared by some of the metabolites of acrylic acid.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Objective of study:
toxicokinetics
Principles of method if other than guideline:
Disposition and metabolism of Acrylic acid (AA) in C3H mice after single oral administration.
GLP compliance:
yes
Specific details on test material used for the study:
- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 98 % (unlabeled AA)
- Supplier: Union Carbide Corporation

- Radiochemical purity (if radiolabelling): >= 98.6 %
- Specific activity (if radiolabelling): 0.14 - 0.4 mCi/mmol
- Locations of the label (if radiolabelling): [1-14C]AA
- Supplier: Sigma Chemical Co. (St. Louis, Mo.)
Radiolabelling:
yes
Species:
mouse
Strain:
C3H
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY)
- Substrain: C3H/HeNCrlBR
- Age at study initiation: approx. 35 d old
- Weight at study initiation: 21 g
- Diet (ad libitum): Agway Prolab Diet Mouse, Agway Inc., Syracuse, NY
- Water (ad libitum)

Route of administration:
oral: gavage
Vehicle:
water
Details on exposure:
- Vehicle: Milli-Q filtered water at a final concentration of 4 or 15 mg/mL
- Dosing volume: 10 mL/kg bw
Duration and frequency of treatment / exposure:
once
Dose / conc.:
40 mg/kg bw/day (actual dose received)
Dose / conc.:
150 mg/kg bw/day (actual dose received)
No. of animals per sex per dose:
15
Control animals:
no
Details on study design:
- Dose selection rationale: The oral dose of 40 mg/kg bw was selected for comparison to previous work on the disposition of [2,3-14C]AA in Sprague-Dawley rats (de Bethizy et al. 1987) and the 150 mg/kg bw dose was selected since a similar oral dose induced slight, acute gastric irritation in Fischer 344 rats (Ghanayem et al. 1985).
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, stomach contents (after sacrifice)
- Time and frequency of sampling: Urine was collected under dry ice and faeces were collected at room temperature at 8, 24, 48, and 72 h. At 1 and 8 hrs, 5 animals from ech group were sacrificed and blood samples collected. Tissues were sampled at termination (liver, kidney, fat, stomach).
- Traps for volatile compounds:
Room air was drawn through the metabolism cages at a rate of approximately 350 mL/min. Expired 14CO2 was collected in traps containing a solution of 2-methoxyethanol : ethanolamine (7:3, v/v), which was replaced with fresh solution at regular intervals. Other exhaled volatile 14C-labeled organic compounds were collected onto activated charcoal traps (approximately 4 g) placed in series ahead of the 14CO2 traps.
Details on absorption:
Absorption and elimination of AA were rapid and nearly complete within 24 h after administration of single oral doses of either 150 or 40 mg/kg bw to C3H mice. Metabolism to 14CO2 was the major route of elimination, accounting for about 80% of the administered dose (92% of recovered radioactivity).
Details on distribution in tissues:
Approximately 1% or less of the dose remained in the tissues and carcass at the end of the experiment. Elimination of radioactivity from stomach tissue, plasma, liver and kidney was rapid, but it was somewhat slower from fat.
Details on excretion:
Urinary excretion accounted for about 3% of the dose, with most occurring during the first 24 h. Excretion in faeces accounted for about 1% of the dose. Only trace amounts of exhaled volatiles other than 14CO2 were detected.
Metabolites identified:
yes
Details on metabolites:
Livers collected from orally dosed mice were analyzed by HPLC for AA and metabolites. Unchanged AA was not detected 1 h after oral administration; however, several metabolites that were more polar than AA were detected, including 3-hydroxypropionate and peak 1, the metabolite that was also the major urinary metabolite in rats. Neither AA nor its metabolites were detected at later times after oral administration.

The less than complete recovery of the administered doses is probably explained by the volatile nature of acrylic acid and its propensity to bind to materials such as plastic and glass, properties that may also be shared by some of the metabolites of acrylic acid.

Disposition of radioactivity in C3H mice after oral administration of [1 -14C]AA:

Dose

150 mg/kg bw

40 mg/kg bw

Exhaled 14CO2

80.0 ± 4.1

76.8 ± 2.8

Exhaled volatiles

0.1 ± 0.0

0.1 ± 0.0

Urine

3.4 ± 1.3

3.0 ± 1.4

Faeces

1.2 ± 1.2

1.2 ± 0.4

Cage wash

1.9 ± 2.2

0.5 ± 0.3

Tissues

0.1 ± 0.1

0.3 ± 0.0

Carcass

0.3 ± 0.1

0.8 ± 0.1

Total recovery

86.9 ± 6.1

82.5 ± 2.1

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented, acceptable publication
Objective of study:
toxicokinetics
Principles of method if other than guideline:
Disposition and metabolism of Acrylic acid (AA) in Fischer 344 rats after single oral administration.
GLP compliance:
yes
Specific details on test material used for the study:
- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 98 % (unlabeled AA)
- Supplier: Union Carbide Corporation

- Radiochemical purity (if radiolabelling): >= 98.6 %
- Specific activity (if radiolabelling): 0.14 - 0.4 mCi/mmol
- Locations of the label (if radiolabelling): [1-14C]AA
- Supplier: Sigma Chemical Co. (St. Louis, Mo.)
Radiolabelling:
yes
Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY)
- Substrain: F344/NHsd
- Age at study initiation: approx. 7 wk old
- Weight at study initiation: 210 g
- Diet (ad libitum): Agway Prolab Diet Rat, Agway Inc., Syracuse, NY
- Water (ad libitum)

- Individual metabolism cages: no
Route of administration:
oral: gavage
Vehicle:
water
Details on exposure:
- Vehicle: Milli-Q filtered water at a final concentration of 4 or 15 mg/mL
- Dosing volume: 10 mL/kg bw
Duration and frequency of treatment / exposure:
once
Dose / conc.:
40 mg/kg bw/day (actual dose received)
Dose / conc.:
150 mg/kg bw/day (actual dose received)
No. of animals per sex per dose:
15
Control animals:
no
Details on study design:
- Dose selection rationale: The oral dose of 40 mg/kg bw was selected for comparison to previous work on the disposition of [2,3-14C]AA in Sprague-Dawley rats (de Bethizy et al. 1987) and the 150 mg/kg bw dose was selected since a similar oral dose induced slight, acute gastric irritation in Fischer 344 rats (Ghanayem et al. 1985).
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, stomach contents (after sacrifice)
- Time and frequency of sampling: Urine was collected under dry ice and faeces were collected at room temperature at 8, 24, 48, and 72 h. At 1 and 8 hrs, 5 animals from ech group were sacrificed and blood samples collected. Tissues were sampled at termination (liver, kidney, fat, stomach).
- Traps for volatile compounds:
Room air was drawn through the metabolism cages at a rate of approximately 500 mL/min. Expired 14CO2 was collected in traps containing a solution of 2-methoxyethanol : ethanolamine (7:3, v/v), which was replaced with fresh solution at regular intervals. Other exhaled volatile 14C-labeled organic compounds were collected onto activated charcoal traps (approximately 4 g) placed in series ahead of the 14CO2 traps.







Details on absorption:
In Fischer 344 rats, AA was rapidly absorbed and eliminated after single oral doses of either 150 or 40 mg/kg bw. Exhalation of 14CO2 was the major route of elimination, accounting for approximately 80-90% of the administered dose (94% of recovered radioactivity) after either dose level. This process was rapid and nearly complete within 8 h after administration of 40 mg/kg and within 24 h after 150 mg/kg. The somewhat slower rate of 14CO2 exhalation after the latter dose appeared to reflect slower absorption of the bolus dose.
Details on distribution in tissues:
AA-derived radioactivity was rapidly eliminated from stomach tissue, plasma, liver, and kidney, while elimination of radioactivity from fat was somewhat slower. Less than 2% of the dose remained in tissues or carcass 72 h after dosing.
Details on excretion:
Urinary excretion accounted for about 3-4% of the dose, with most occurring over the first 24 h. Excretion in faeces accounted for less than 0.2% of the dose. Only trace amounts of exhaled organic volatile compounds other than 14CO2 were detected.
Metabolites identified:
yes
Details on metabolites:
Urine collected from rats after the oral route was analyzed by HPLC for AA and metabolites. Several peaks of radioactivity were detected by HPLC and were designated according to their order of elution in urine samples from rats dosed orally with 40 mg/kg bw. Trace amounts of material that coeluted with AA were detected in urine of orally dosed rats. The major metabolite eluted early in the gradient and accounted for about 2-3% of the oral dose (identy unknown). A metabolite that coeluted with 3-hydroxypropionic acid was also detected. Small amounts of several other metabolites more polar than AA were detected, as well as small amounts of two metabolites that were less polar than AA.
Plasma and liver from orally dosed rats were also analyzed for AA and metabolites by HPLC. One hour after dosing, a metabolite in plasma that coeluted with 3-hydroxypropionic acid accounted for about 0.5% of the dose after 40 mg/kg. This metabolite was also detected in plasma after the high dose, but the levels were variable. The polar metabolite, which was also the major urinary metabolite, was the major metabolite found in the liver 1 h after 150 mg/kg and was the only metabolite in liver after 40 mg/kg. After the high dose, peaks corresponding to 3-hydroxypropionate and a small amount of AA were detected. Neither AA nor metabolites were detected in plasma or liver at times later than 1 h, nor were they detected in kidney at any time after administration.

Disposition of radioactivity in Fischer 344 rats after oral administration of [1 -14C]AA:

Dose

150 mg/kg bw

40 mg/kg bw

Exhaled 14CO2

81.6 ± 1.8

90.3 ± 1.0

Exhaled volatiles

0.2 ± 0.4

0.1 ± 0.2

Urine

4.2 ± 1.0

2.9 ± 0.2

Faeces

0.6 ± 0.1

0.7 ± 0.0

Cage wash

0.2 ± 0.2

0.2 ± 0.1

Tissues

0.3 ± 0.1

0.3 ± 0.2

Carcass

1.0 ± 0.2

0.8 ± 0.1

Total recovery

88.1 ± 2.0

95.2 ± 0.9

The less than complete recovery of the administered doses is probably explained by the volatile nature of acrylic acid and its propensity to bind to materials such as plastic and glass, properties that may also be shared by some of the metabolites of acrylic acid.

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
Flowthrough in vitro skin penetration chamber method according to Frantz et el. (1990).
GLP compliance:
not specified
Specific details on test material used for the study:
- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 98 % (unlabeled AA)
- Supplier: Union Carbide Corporation

- Radiochemical purity (if radiolabelling): >= 98.6 %
- Specific activity (if radiolabelling): 0.14 - 0.4 mCi/mmol
- Locations of the label (if radiolabelling): [1-14C]AA
- Supplier: Sigma Chemical Co. (St. Louis, Mo.)
Radiolabelling:
yes
Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY)
- Substrain: F344/NHsd
- Age at study initiation: approx. 7 wk old
- Weight at study initiation: 210 g
- Diet (ad libitum): Agway Prolab Diet Rat, Agway Inc., Syracuse, NY
- Water (ad libitum)
Vehicle:
acetone
Duration of exposure:
6 hrs
Control animals:
no
Details on in vitro test system (if applicable):
SKIN PREPARATION
- Source of skin: dorsal skin from male rats (hair clipped)


PRINCIPLES OF ASSAY
- Diffusion cell: flow-through diffusion cell (Frantz cell)
- Flow-through system: yes
- Test temperature: 32 °C
- Occlusion: no

Absorption in different matrices:
Over a 6-h period, 23.9 ± 5.4% (mean ± SD, n= 3) of the dose was absorbed into the effluent or was found in the skin. At least 60% of the dose evaporated, and total recovery of the applied dose was about 85%.
Total recovery:
85 %

The results from the in vitro experiment supported those of the in vivo study (see 7.1.1).

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented, acceptable publication
Objective of study:
metabolism
Principles of method if other than guideline:
Investigation of the pathway of acrylic acid metabolism to CO2 in rats.
GLP compliance:
not specified
Specific details on test material used for the study:
- Name of test material (as cited in study report): Acrylic acid
- Radiochemical purity (if radiolabelling): > 95 %
- Supplier: Sigma Chemical Co.

- Locations of the label (if radiolabelling): [1-14C]AA
- Specific activity (if radiolabelling): 0.1 - 0.43 mCi/mmol

- Locations of the label (if radiolabelling): [2,3-14C]AA
- Specific activity (if radiolabelling): 0.4 - 1.0 mCi/mmol
Radiolabelling:
yes
Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Laboratories, Inc. (Kingston, NY)
- Weight at study initiation: 150 - 300 g
- Housing: 2/cage
- Diet (ad libitum): Purina Mills Inc., St. Louis, MO
- Water: ad libitum
Metabolites identified:
yes
Details on metabolites:
Major intermediate: 3 -hydroxypropionic acid

The rate of 14CO2 formation from [14C]AA was measured in vitro with three different preparations from rat liver. Rat liver hepatocytes metabolized AA to CO2 at a rate of approximately 40 nmol/hr/mg protein. Disruption of the cells and reconstitution of the homogenate with buffers and cofactors resulted in a substantial loss of enzyme activity to approximately 5% of the whole cell rate. Isolation of the mitochondria from the tissue homogenate resulted in an 21 - fold increase in the specific enzyme activity responsible for 14CO2 production. These results suggest that the metabolism of AA to CO2 occurs primarily in the mitochondria. To determine if the mitochondrial oxidation of AA could be augmented by other hepatic fractions, [1 -14C]AA and mitochondria were incubated in the presence of various amounts of either 12500g supernatant (homogenate depleted of mitochondria), microsomes or cytosol. The rate of mitochondrial metabolism of AA was not affected by the addition of other subcellular fractions. In addition, neither 12500g supernatant, microsomes nor cytosol oxidized [1 -14C]AA significantly by themselves, further supporting the conclusion that the mitochondrion is the site of metabolism of AA.

The rate of 14CO2 formation by hepatic homogenates or mitochondria from AA radiolabeled at the olefinic carbons, [2,3 -14C]AA, was significantly less than AA radiolabeled at the carboxyl carbon, [1 -14C]AA, suggesting that not all the carbons of AA are metabolized to CO2 with equal efficiency and that the olefinic carbons may instead be bioincorporated into other molecules.

The metabolism of AA to CO2 was characterized further by examining the kinetics of the reaction. A plot of the rate of metabolism of [1 -14C]AA in liver homogenate versus AA concentration was consistent with apparent Michaelis-Menten kinetics. The metabolism observed with mitochondria and hepatocytes also followed apparent Michaelis-Menten kinetics. The apparent Km for AA metabolism in mitochondria and liver homogenates was about 0.1 mM, but this value was abaut 5 -fold higher in rat hepatocytes. The apparent Vmax was highest in mitochondria and was about 35 and 95% lower in isolated hepatocytes and liver homogenates, respectively.

HPLC analysis of [1-14C]AA metabolites following mitochondrial metabolism revealed the presence of a metabolite that coeluted with a synthetic standard of 3 -hydroxypropionic acid.

The presented results are consistent with the incorporation of AA into a secondary pathway for propionic acid metabolism in which 3 -hydroxypropionate is an intermediate. In this pathway, AA is first converted to acrylyl-CoA which is subsequently oxidized to 3 -hydroxypropionate. 3 -Hydroxypropionate is, in turn, metabolized to acetate and CO2 via malonic semialdehyde. The resultant acetate is then incorporated into intermediary metabolism. This pathway has been reported to be a major pathway for the metabolism of propionic acid in various insect and plant species, but is a secondary pathway in mammals. Identification of 3 -hydroxypropionate as a metabolite of AA in conjunction with the observed inhibition of the mitochondrial metabolism of AA by propionic acid indicates that AA is incorporated into this secondary pathway.

Endpoint:
basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Objective of study:
toxicokinetics
Principles of method if other than guideline:
A hybrid computational fluid dynamics (CFD) and physiologically-based pharmacokinetic (PBPK) dosimetry inhalation model was constructed to estimate the regional tissue dose of acrylic acid in the rat and human nasal cavity, respectively.
GLP compliance:
not specified
Specific details on test material used for the study:
- Name of test material (as cited in study report): Glacial acrylic acid
- Analytical purity: 99.9 ± 0.1% (GC)
- Impurities (identity and concentrations): 200 ppm MEHQ (flocculent grade)
- Supplier: Rohm & Haas Co., Deer Park, TX
Radiolabelling:
no
Species:
rat
Strain:
other: F344/N
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River laboratories, Wilmington, MA
- Age at study initiation: approx. 60-75 days old
- Weight at study initiation: 160-175 g
- Individual metabolism cages: yes
- Diet (ad libitum)
- Water (ad libitum): tap water


Route of administration:
inhalation: vapour
Details on exposure:
TYPE OF INHALATION EXPOSURE: whole body


GENERATION OF TEST ATMOSPHERE / CHAMPER DESCRIPTION
- Exposure apparatus: 240-liter exposure chamber
- Source and rate of air: The exposure atmosphere was generated by passing compressed air over the surface of acrylic acid liquid maintained at approximately 40°C in a 250-mL glass jar. The vapor was diluted with conditioned laboratory air to the appropriate concentration (monitored by a Foxboro MIRAN lA infrared gas analyzer that had been calibrated by gas chromatography of impinger samples) and entered the top of the exposure
chamber.


Duration and frequency of treatment / exposure:
3 and 6 hrs
Dose / conc.:
75 ppm
Remarks:
75 ppm corresponding to approx. 0.22 mg/L
(weight to volume/ppm conversion: concentration (mg/m3) = concentration (ppm) x MW/24.5;
where MW = molecular weight (72.06 g/mol) and 24.5 = universal gas constant at 25 °C and 760 mmHg; according to Derelanko MJ (2008). The Toxicologist's Pocket Handbook, 2nd ed.)
Control animals:
yes, sham-exposed
Metabolites identified:
no

1. Acute inhalation exposure of rats:

The olfactory epithelium of the nasal cavity was identified as the primary target tissue in rats inhaling 75 ppm acrylic acid vapour for either 3 or 6 hrs. Control animals exhibited no detectable lesions in the nasal cavity, nor were lesions present in the squamous epithelium of rats exposed to acrylic acid. Lesions were confined to the dorsal aspects of the nasal cavity, in particular the dorsal meatus, the dorsomedial aspects of the nasoturbinate, and ethmoturbinate 3. The lesions were small and most of the olfactory and respiratory epithelium in the treated animals was normal histologically. However, the extent of the lesions increased as the exposure time was increased from 3 to 6 hrs. Olfactory epithelial cell degeneration was accompanied by sustentacular cell necrosis. These lesions were observed in all four sections of the nasal cavity at both 3 and 6 hrs of exposure, although the area of mucosa affected and the incidence of affected animals was greater in the anterior three sections. Limited regions of respiratory epithelial degeneration and desquamation were present in Section I in animals exposed for 6 hrs. Lesions of the respiratory epithelium were not observed in Sections II and III. Section IV did not contain respiratory epithelium.

2. In vitro incubation of nasal explants:

Short-term organ culture of nasal explants with media containing acrylic acid resulted in histopathological lesions very similar to those observed in vivo. No cytotoxicity was observed in the respiratory epithelium, suggesting that the acrylic acid concentration required to induce cytotoxicity in respiratory epithelium in this assay was in excess of 6 mM.

3. Partition coefficients:

The partitioning of acrylic acid between air and liquid phases was evaluated with unbuffered, neutral, and acidic liquid phases. The data indicate a strong preference for acrylic acid partitioning into the aqueous phase, regardless of blood pH (i.e., acid dissociation contributes to the preference for the liquid phase, but it is not the determining factor), which is consistent with the highly polar structure of this small organic acid.

4. Evaluation of regional nasal air flow and gas phase ass transport coeficients from CFD simulations:

The data from the CFD simulations indicated that a relatively small fraction of the inspired air ventilates the human olfactory epithelium relative to the rat olfactory epithelium. This difference is greater in the posterior olfactory region of the human nasal cavity (olfactory air flow decreases to only approximately 3% of total nasal air flow as the dorsal medial air stream moves ventrally into the medial region) relative to the posterior olfactory region of rats (olfactory air flow increases to approximately 20% of total flow as medial air flow contributes to the dorsal medial stream in the posterior region). Generally, where data can be compared, the regional compartmental gas phase mass transport coefficients for the rat nasal cavity are one to two orders of magnitude higher than those of the human nasal cavity. This indicates that the rat nasal cavity is much more efficient than the human nasal cavity in "scrubbing" an organic vapor from inhaled air (i.e., equilibrating vapor with the nasal mucus layer as opposed to allowing it to reach the downstream tracheobronchial region).

5. Regional tissue dose estimates from physiologically based inhalation modeling:

A hybrid CFD-PBPK inhalation model was constructed with the aim to evaluate the relationship between inhaled acrylic acid vapour concentration and the tissue concentration in various regions of the nasal cavity of rats and humans, respectively. An explicit effort was made to derive the parameters for rat and human used in the model either from experimental data or from physicochemical principles without "fitting" model parameters (gas phase diffusivity: 0.l cm2/sec; air minute volumes: 250 mL/min (rat), 7500 mL/min (human); blood flow to nasal cavity (human) estimated). Deposition of vapours in the rat nasal cavity is relatively insensitive to significant variation in the gas phase mass transport coefficients, but the human CFD-PBPK model was sensitive to variation in air phase and liquid phase parameters (liquid diffusivity, mucus:air partition coefficient). The diffusivity of acrylic acid (ionized and non-ionized) in mucus and epithelium was defined as 0.01 cm2/h as an adjustable parameter. The mucus:air partition coefficient was defined as 1780 (saline, pH 2.0; the liquid:air partition coefficient value for saline, pH 7.4, is 3210).

Unidirectional simulations were conducted with the model at a flow rate of 500 mL/min (rat) to estimate the steady-state tissue concentration in the anterior olfactory epithelium lining the dorsal meatus of the rat nasal cavity over a wide range of acrylic acid vapour concentrations (0 to 25 ppm for one hour). A dose-response of acrylic acid exposures was simulated for an adult resting male rat and an adult resting male human using the appropriate inspiratory flow rate (based on the minute volumes of each species), nasal anatomy, and nasal air flow patterns from CFD simulations. The cyclic flow simulation was conducted for a reference resting rat and human exposed to 2 ppm acrylic acid for 3 min (minute volume 250 mL/min (rat), 7500 mL/min (human)). The CFD-PBPK model simulations predict that olfactory epithelium of the human nasal cavity is exposed to 2-3 fold lower tissue concentrations of acrylic acid than the olfactory epithelium of the rodent nasal cavity under either unidirectional flow exposure conditions or cyclic flow conditions. The authors are of the opinion that the model predicts olfactory tissue concentrations for acrylic acid that correlate with acute histopathological lesions observed in vivo (rats, exposed with 75 ppm acrylic acid for 3 or 6 h in a chamber) and with those observed in vitro (rats nasal septa incubated for two hours at 37°C with concentrations from 0.0 to 6.0 mM acrylic acid).

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Objective of study:
metabolism
Principles of method if other than guideline:
The reaction of acrylic acid with glutathione and nonprotein sulfhydryls of rat blood in vitro were measured by the methods of Nachtomi (1970) and Beutler et al. (1963), respectively.

Nachtomi (1970). Biochem. Pharmacol. 19: 2853-3860
Beutler et al. (1963). J. Lab. Clin. Med. 61 (5): 882-888
GLP compliance:
no
Specific details on test material used for the study:
- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 99 %
- Supplier: Celanese Chemical Company, Houston, Texas
Radiolabelling:
no
Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., Wilmington, Mass.
- Age at study initiation: 8 weeks for biotransformation studies and 4-8 months for non-protein sulfhydryl studies.
- Housing: 2/ cage in stainless steel cages with wire bottoms
- Diet: Purina Lab Chow, ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks
Metabolites identified:
not measured

Reaction of acrylic acid with reduced glutathione in vitro:

Only a 6 % depletion of GSH occurred in 30 min after adding 4 mM acrylic acid to 2 mM GSH in phosphate buffer, indicating that there is only a minimal spontaneous reaction between acrylic acid and GSH. Addition of an aliquot of a soluble enzyme preparation (100000 x g fraction) did not increase the reaction between acrylic acid and GSH. In contrast, the addition of 2 mM and 4 mM ethylacrylate caused a 40 and 74 % depletion of GSH within 30 min, respectively.

Effects of acrylic acid on nonprotein sulfhydryls of rat blood in vitro:

8 mM acrylic acid had only a minimal effect on blood NPSH. By comparison, a pronounced depletion of NPSH occurred when ethyl acrylate was added to rat blood in vitro at final concentrations ranging from 1 to 8 mM.

Description of key information

Extensive in-vitro and in-vivo data on toxicokinetic properties are available. These data consistenly show the absence of potential for bioaccumulation.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

Following oral administration of [14C]-Acrylic acid in rats and mice, a high percentage of the radiolabel (60 – 80 %) was rapidly absorbed and eliminated as 14CO2 within 24 hours by both species. Excretion in urine and faeces accounted for 1-4 %, respectively. In rats, about 19-25 % of the acrylic acid-derived radioactivity remained in the tissues examined after 72 hr, mostly in adipose tissue and muscle. High-performance liquid chromatography (HPLC) analysis of rat urine and rat and mouse tissues indicated that absorbed acrylic acid (AA) was rapidly metabolized by the ß-oxidation pathway of propionate catabolism. No unchanged acrylic acid was detected; however, several metabolites that were more polar than acrylic acid were measured, including 3-hydroxypropionate.

The presented results are consistent with the incorporation of AA into a secondary pathway for propionic acid metabolism in which 3 -hydroxypropionate is an intermediate. In this pathway, AA is first converted to acrylyl-CoA which is subsequently oxidized to 3 -hydroxypropionate. 3 -Hydroxypropionate is, in turn, metabolized to acetate and CO2 via malonic semialdehyde. The resultant acetate is then incorporated into intermediary metabolism. This pathway has been reported to be a major pathway for the metabolism of propionic acid in various insect and plant species, but is a secondary pathway in mammals.

On the other hand, reaction with reduced glutathion does not play a major role in the detoxification and metabolism of acrylic acid.

A hybrid CFD-PBPK inhalation model was constructed with the aim to evaluate the relationship between inhaled acrylic acid vapour concentration and the tissue concentration in various regions of the nasal cavity of rats and humans, respectively. The CFD-PBPK model simulations indicated that the olfactory epithelium of the human nasal cavity is exposed to two- to threefold lower tissue concentrations of a representative inhaled organic acid vapour, acrylic acid, than the olfactory epithelium of the rodent nasal cavity when the exposure conditions are the same. The magnitude of this difference varies somewhat with the specific exposure scenario that is simulated. The increased olfactory tissue dose in rats relative to humans may be attributed to the large rodent olfactory surface area (greater than 50% of the nasal cavity) and its highly susceptible location (particularly, a projection of olfactory epithelium extending anteriorly in the dorsal meatus region). In contrast, human olfactory epithelium occupies a much smaller surface area (less than 5% of the nasal cavity), and it is in a much less accessible dorsal posterior location. In addition, CFD simulations indicated that human olfactory epithelium is poorly ventilated relative to rodent olfactory epithelium. These studies suggest that the human olfactory epithelium is protected from irritating acidic vapours significantly better than rat olfactory epithelium due to substantive differences in nasal anatomy and nasal air flow.

Discussion on bioaccumulation potential result:

In Vivo Studies:

C3H mice and Fischer 344 rats, respectively, were treated by gavage (40 or 150 mg/kg bw) with [1-14C]-acrylic acid. Mice rapidly absorbed and metabolised orally administered acrylic acid, with about 80% of the dose exhaled as 14CO2 within 24 h. Excretion in urine and faeces accounted for approximately 3% and 1% of the dose, respectively. Elimination of the 14C radiolabel from plasma, liver and kidney was rapid but it was slower from fat. The disposition of orally administered acrylic acid in rats was similar to the results obtained from mice. High-performance liquid chromatography (HPLC) analysis of rat urine and rat and mouse tissues indicated that absorbed AA was rapidly metabolized by the ß-oxidation pathway of propionate catabolism. No unchanged AA was detected 1 h after oral administration; however, several metabolites that were more polar than AA were measured, including 3-hydroxypropionate. Neither AA nor its metabolites were detected at later times after oral administration (Black et al., 1995).

Sprague-Dawley rats received single oral doses of [2,3-14C]-acrylic acid (4, 40 or 400 mg/kg bw in a 0.5 % aqueous methylcellulose solution). Within 8 hours, 35-60% of the dose was eliminated from the animal, mostly as expired CO2. After 72 hours, 44-65% of the radioactivity had been eliminated via expired air, while 2.9-4.3% remained in urine, 2.4-3.6% in faeces and 18.9-24.6% in tissues examined (adipose tissue 9-15%, liver 1.7-2.2%, muscle 6.5-7.5% and blood 0.8-1.1%) (De Bethizy et al., 1987).

The HPLC profile of metabolites observed in the urine of rats indicated two major metabolites. One of the major metabolites co-eluted with 3-hydroxypropionic acid. Radioactivity could not be detected at the retention times corresponding to that of 2,3-epoxypropionic acid or N-acetyl-S-(2-carboxy-2-hydroxyethyl)cysteine leading to the conclusion that AA is not epoxidized to 2,3-epoxypropionic acid in vivo. This result was supported by an in vitro study. Hepatic microsomes were prepared using conventional methods from rats and incubations were started by the addition of 10 µL of [2,3-14C]-acrylic acid. No epoxidized metabolites could be detected and the parent compound was recovered from the incubation mixture unchanged (DeBethizy et al., 1987).

In addition, Glutathione Depletion Studies were conducted in rats that were administered doses of 4, 40, 400 or 1000 mg/kg bw AA by gavage. One hour following oral administration of acrylic acid in rats a significant depletion of NPSH in the glandular stomach was reported at doses above 4 mg/kg bw. In the forestomach NPSH depletion occurred at a dose of 1000 mg/kg bw. No significant effect of acrylic acid on NPSH in the blood or liver was observed (DeBethizy et al., 1987).

In Vitro Studies:

Dow Chemical (1979) have studied the metabolism of acrylic acid in rat tissue homogenates. Acrylic acid did not react with reduced glutathione either in the presence or absence of the soluble enzyme fraction. Non-protein sulfhydryl concentrations were not appreciably lower in blood after addition of acrylic acid in vitro (Dow Chemical, 1979; Miller et al., 1981).

The rate of 14CO2 formation from [14C]-acrylic acid was measured in vitro with preparations from rat liver hepatocytes. Rapid oxidation of acrylic acid to CO2 was observed. Mitochondria isolated from the liver homogenates were incubated with acrylic acid under the same conditions and yielded higher rates of acrylic acid-oxidation than homogenates. HPLC analysis of the mitochondrial incubation mixtures indicated 3-hydroxypropionic acid as a major metabolite of AA (Finch & Frederick, 1992).

Black et al. (1993) determined the rate of the in vitro oxidation of acrylic acid in 13 tissues of mice. The maximal rate of acrylic acid oxidation in kidney, liver and skin was 2890, 616 and 48 nmol/h/g, respectively. In remaining organs acrylic acid was oxidized at rates less than 40% of the rate in liver. 3-Hydroxypropionic acid was the only metabolite detected by HPLC analysis.

Acrylic acid oxidation rates and blood tissue partition coefficients were studied in slices of rat tissue using [1-14C]-acrylic acid. Acrylic acid oxidation in rat kidney and liver slices was described by saturable kinetics with maximal rates of about 4 and 2 μmol/h/g, respectively. Acrylic acid oxidation rates in 11 additional tissues were 40% or less than that in liver (Black & Finch, 1995).

Computational Modeling Data:

A hybrid computational fluid dynamics (CFD) and physiologically-based pharmacokinetic (PBPK) dosimetry inhalation model was constructed to estimate the regional tissue dose of acrylic acid in the rat and human nasal cavity, respectively (Frederick et al., 1998). This study provides a scientific basis for interspecies extrapolation of nasal olfactory irritants from rodents to humans. By using a series of short-term in vivo studies, in vitro studies with nasal explants, and computer modeling, regional nasal tissue dose estimates were made and comparisons of tissue doses between species were conducted. To make these comparisons, this study assumes that human and rodent olfactory epithelium have similar susceptibility to the cytotoxic effects of organic acids based on similar histological structure and common mode of action considerations. Interspecies differences in susceptibility to the toxic effects of acidic vapours are therefore assumed to be driven primarily by differences in nasal tissue concentrations that result from regional differences in nasal air flow patterns relative to the species-specific distribution of olfactory epithelium in the nasal cavity.

The rodent model uses two olfactory compartments to incorporate both the olfactory epithelium in the projection extending along the dorsal meatus and the ethmoid olfactory region. This model was based on a compartmental rat nasal model of Bush et al. (1998). The human model uses one olfactory compartment since the human nasal cavity lacks a counterpart for the rodent ethmoid olfactory region (Subramaniam et al., 1998). The liquid phase of the model of Bush et al. was modified to include the effect of buffering capacity on the ionization of the acid in the mucus, diffusion of both the ionized form of the acid and the non-ionized species, liquid:air partition coefficients, tissue:blood partition coefficients (Black and Finch, 1995), and metabolism of acrylic acid (Black and Finch, 1995).

A hybrid CFD-PBPK inhalation model was constructed with the aim to evaluate the relationship between inhaled acrylic acid vapour concentration and the tissue concentration in various regions of the nasal cavity of rats and humans, respectively. An explicit effort was made to derive the parameters for rat and human used in the model either from experimental data or from physicochemical principles without "fitting" model parameters (gas phase diffusivity: 0.1 cm2/sec; air minute volumes: 250 mL/min (rat), 7500 mL/min (human); blood flow to nasal cavity (human) estimated). Deposition of vapours in the rat nasal cavity is relatively insensitive to significant variation in the gas phase mass transport coefficients, but the human CFD-PBPK model was sensitive to variation in air phase and liquid phase parameters (liquid diffusivity, mucus:air partition coefficient).

Unidirectional simulations were conducted with the model at a flow rate of 500 mL/min (rat) to estimate the steady-state tissue concentration in the anterior olfactory epithelium lining the dorsal meatus of the rat nasal cavity over a wide range of acrylic acid vapour concentrations (0 to 25 ppm for one hour). A dose-response of acrylic acid exposures was simulated for an adult resting male rat and an adult resting male human using the appropriate inspiratory flow rate (based on the minute volumes of each species), nasal anatomy, and nasal air flow patterns from CFD simulations. The cyclic flow simulation was conducted for a reference resting rat and human exposed to 2 ppm acrylic acid for 3 min (minute volume 250 mL/min (rat), 7500 mL/min (human)).

The acute inhalation, and in vitro studies have demonstrated that the nasal olfactory epithelium is the most sensitive tissue to the effects of inhalation exposure to organic acids and that the sustentacular cells are the most sensitive cell type of this epithelium. The CFD-PBPK model simulations indicated that the olfactory epithelium of the human nasal cavity is exposed to two- to threefold lower tissue concentrations of a representative inhaled organic acid vapour, acrylic acid, than the olfactory epithelium of the rodent nasal cavity when the exposure conditions are the same. The magnitude of this difference varies somewhat with the specific exposure scenario that is simulated. The increased olfactory tissue dose in rats relative to humans may be attributed to the large rodent olfactory surface area (greater than 50% of the nasal cavity) and its highly susceptible location (particularly, a projection of olfactory epithelium extending anteriorly in the dorsal meatus region). In contrast, human olfactory epithelium occupies a much smaller surface area (less than 5% of the nasal cavity), and it is in a much less accessible dorsal posterior location. In addition, CFD simulations indicated that human olfactory epithelium is poorly ventilated relative to rodent olfactory epithelium. These studies suggest that the human olfactory epithelium is protected from irritating acidic vapours significantly better than rat olfactory epithelium due to substantive differences in nasal anatomy and nasal air flow.

Discussion on absorption rate:

The absorption of [14C]-acrylic acid from acetone, water, and phosphate buffer was measured through human and mouse skin in vitro. Membranes were mounted in glass diffusion cells and acrylic acid was applied in each solvent at 0.01 %, 0.1 %, 1 %, and 4 %, respectively (100 µL/cm2) under occlusive conditions. Samples were taken from the receptor solutions at recorded times, between 0 and 32 hr, and assayed for 14C content which was regarded as equivalent to acrylic acid. Steady state absorption rates were calculated to be between 0.007 µg/cm2/hr (human, 0.01 % AA in phosphate buffer) and 201 µg/cm2/hr (mouse, 4 % AA in acetone). Thus, absorption rates were influenced by the vehicle (acetone > water > phosphate buffer) and were proportional to the applied concentration in each vehicle. Mouse skin was 3 times more permeable than human skin under the conditions of this in vitro study (BAMM 1988).

C3H mice and Fischer 344 rats, respectively, were treated dermally (10 or 40 mg/kg bw in acetone) with [1-14C]-acrylic acid. After cutaneous application to mice, about 12% of the dose was absorbed, while the remainder was apparently evaporated. Approximately 80% of the absorbed fraction of the dose was metabolised to 14CO2within 24 h. Excretion in urine and faeces 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 (0.5% of the higher dose) than at 8 h (0.1% of the higher dose). After cutaneous administration to rats, 19-26% of the dose was absorbed. Disposition of the absorbed fraction of the dose was similar to results found in mice. Results from an in vitro experiment with rat skin (Frantz cell) 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 ß-oxidation pathway of propionate catabolism (Black et al., 1995).