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Basic toxicokinetics

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Endpoint:
basic toxicokinetics
Type of information:
other: experimental result and PBPK model
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Cross-reference
Reason / purpose for cross-reference:
reference to same study
Reference
Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Qualifier:
no guideline available
Principles of method if other than guideline:
A physiologically based pharmacokinetic model has been formulated to predict the pharmacokinetics and systemic disposition of alkylmethacrylate esters in rats and humans.
GLP compliance:
not specified
Species:
other: rat and human
Strain:
other: Wistar/Fischer F344/ not applicable
Sex:
male
Details on test animals or test system and environmental conditions:
Epidermal membrane absorption studies
Skin was used from male rats of the Wistar-derived strain (supplied by Charles River UK Ltd, Margate, Kent, UK.) aged 28 days ± 2 days

Whole skin absorption studies
Skin was taken from male Fisher F344 (supplied by Harlan Olac) rats weighing between 200 and 250 g.

Human epidermal membrane absorption studies
Extraneous tissue was removed from human abdominal whole skin samples obtained post mortem in accordance with local ethical guidelines
Type of coverage:
occlusive
Vehicle:
unchanged (no vehicle)
Duration of exposure:
up to 48 h
Doses:
100 µL/cm2
No. of animals per group:
3 (human: 2)
Time point:
8 h
Dose:
100 µL/cm2
Parameter:
percentage
Absorption:
ca. 45 %
Remarks on result:
other: rat epidermis
Remarks:
linear absorption during this time period
Time point:
16 h
Dose:
100 µL/cm2
Parameter:
percentage
Absorption:
ca. 55 %
Remarks on result:
other: rat epidermis
Time point:
8 h
Dose:
100 µl/cm2
Parameter:
rate
Absorption:
5 888 mg cm-2 h-1
Remarks on result:
other: rat epidermis
Time point:
24 h
Dose:
100 µL/m2
Parameter:
percentage
Absorption:
ca. 10 %
Remarks on result:
other: human epidermis
Remarks:
linear absorption for >= 24 h
Time point:
24 h
Dose:
100 µL/cm2
Parameter:
rate
Absorption:
453 mg cm-2 h-1
Remarks on result:
other: human epidermis
Time point:
24 h
Dose:
100 µL/cm2
Parameter:
rate
Absorption:
360 mg cm-2 h-1
Remarks on result:
other: rat skin

Rat epidermis

The fastest rate of absorption of MMA through rat epidermal membrane was recorded as being 5688 μg*cm-2*hr-1 and this occurred between 2 and 8 hrs following application of the chemical. The rate slowed considerably after 8 hours, falling to virtually zero by 16 hours. Nearly half (45.5%) of the donor reservoir had been depleted by 8 hours with 55% of the chemical appearing in the receptor chamber by 16 hours. The rate plateaus after eight hours, which is indicative of the donor reservoir being depleted.

 

Human epidermis

Methyl methacrylate absorbed at a peak rate of 453 μg*cm-2*hr-1, between 4 and 24 hrs, with 10.2% of the applied dose having been absorbed during this time. There appears to be a lag time with the rate of absorption between 0-4 hrs calculated to be 259 μg cm-2 hr-1. The rates of absorption through human epidermis are considerably slower than those measured for MMA through rat epidermis.

 

Whole rat skin

Of the alkyl-methacrylate esters whose rate of absorption through whole rat skin was investigated, methyl methacrylate is the most rapidly absorbed chemical. Carboxylesterases present in the viable tissue mediate the hydrolysis of these esters, producing the acid metabolite, together with the structurally corresponding alcohol. In contrast to the larger esters, MMA is not completely hydrolysed during the absorption process; this is substantiated by the appearance of both the parent ester and the metabolite MAA in the receptor fluid. Appearance of both chemicals in the receptor fluid can be explained by MMA possessing a rate of absorption that is higher than the rate with which it is hydrolysed.

The peak rate of appearance of MMA, which occurred between 2.5-24 hrs was calculated to be 360 μg*cm-2*hr-1. This compares to a peak rate of appearance for the metabolite MAA, which occurred between 4-24 hrs and was calculated as 108 μg cm-2 hr-1. Of the original dose applied to the whole skin, 8.7% appeared as MMA in the receptor chamber, while 2.6% appeared as MAA. Therefore in total, 11.3% of the ester was depleted from the donor reservoir.

---

The results of the whole-skin penetration studies and the model predictions for 

other methacrylate esters are  presented in the table.



Summary of the peak rates of absorption of MAA & alkyl-methacrylate esters through whole rat and human skin

Substance

Molecular volume

Rat whole rat

Human whole skin

Peak rate of appearance (µg*cm-2*h-1)+- SEM

Period of

peak

absorption

rate (hours)

% age of

applied

dose

absorbed

over x hours

Rate of

absorption of

ester/MAA

(μg*cm-2 *hr-1)

Ester

MAA

MAA

78.96

 

4584+-344

5-8

70%/24

327

MMA

93.1978

360+-20.9

108+-4.59

2.5-24

11.3%/24

33.4**

EMA

107.436

 

190**

 

 

13.6**

iBMA

135.646

 

56**

 

 

4**

nBMA

135.856

 

40+-9.4

2-10

0.4%/10

2.9**

6HMA

164.277

 

20**

 

 

1.4**

2EHMA

191.66

 

9**

 

 

0.6**

OMA

192.696

 

10.3+-0.65

8-24

0.24%/24

0.7**

12LMA

249.536

 

11.8+-2.11

8-24

0.26%/24

0.8**

The values in normal type were obtained experimentally, whilst those in italics are predicted values.

** Values are predicted rates of appearance of total chemical including parent ester and metabolite


Conclusions:
The in vivo and in vitro investigations as well as the PBPK models developed from the data showed that alkyl-methacrylate esters are rapidly absorbed and are hydrolyzed at exceptionally high rates to methacrylic acid by high capacity, ubiquitous carboxylesterases. Further, the removal of the hydrolysis product, methacrylic acid, also is very rapid (minutes).
Executive summary:

The in vivo and in vitro investigations as well as the PBPK models developed from the data showed that alkyl-methacrylate esters are rapidly absorbed and are hydrolyzed at exceptionally high rates to methacrylic acid by high capacity, ubiquitous carboxylesterases. Further, the removal of the hydrolysis product, methacrylic acid, also is very rapid (minutes).

The fastest rate of absorption of MMA through rat epidermal membrane was recorded as being 5688 μg /cm²/hr and this occurred between 2 and 8 hrs following application of the chemical. Absorption through human epidermal membrane was slower with a peak rate of 453 μg/cm²/hr, between 4 and 24 hrs, with 10.2% of the applied dose having been absorbed during this time. There appears to be a lag time with the rate of absorption between 0-4 hrs calculated to be 259 μg /cm²/hr.

Penetration of alkyl methacrylate through whole rat skin was slower than through separated epidermal membrane. MMA was the most rapidly absorbed chemical of the alkyl methacrylates studied. Carboxylesterases present in the viable tissue mediate the hydrolysis of these esters, producing the acid metabolite, together with the structurally corresponding alcohol. In contrast to the larger esters, MMA is not completely hydrolysed during the absorption process; this is substantiated by the appearance of both the parent ester and the metabolite MAA in the receptor fluid. Appearance of both chemicals in the receptor fluid can be explained by MMA possessing a rate of absorption that is higher than the rate with which it is hydrolysed.

The peak rate of appearance of MMA, which occurred between 2.5-24 hrs was calculated to be 360 μg /cm²/hr. This compares to a peak rate of appearance for the metabolite MAA, which occurred between 4-24 hrs and was calculated as 108 μg /cm²/hr. Of the original dose applied to the whole skin, 8.7% appeared as MMA in the receptor chamber, while 2.6% appeared as MAA. Therefore in total, 11.3% of the ester was depleted from the donor reservoir.

Data source

Reference
Reference Type:
other: Thesis
Title:
Unnamed
Year:
2002

Materials and methods

Objective of study:
absorption
metabolism
Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
A physiologically based pharmacokinetic model has been formulated to predict the pharmacokinetics and systemic disposition of alkylmethacrylate esters in rats and humans.
GLP compliance:
not specified

Test material

Constituent 1
Chemical structure
Reference substance name:
Methyl methacrylate
EC Number:
201-297-1
EC Name:
Methyl methacrylate
Cas Number:
80-62-6
Molecular formula:
C5H8O2
IUPAC Name:
methyl methacrylate
Test material form:
liquid

Test animals

Species:
other: rat and human
Strain:
other: Wistar/Fischer F344/ not applicable
Sex:
male
Details on test animals or test system and environmental conditions:
Epidermal membrane absorption studies
Skin was used from male rats of the Wistar-derived strain (supplied by Charles River UK Ltd, Margate, Kent, UK.) aged 28 days ± 2 days

Whole skin absorption studies
Skin was taken from male Fischer F344 (supplied by Harlan Olac) rats weighing between 200 and 250 g.

Human epidermal membrane absorption studies
Extraneous tissue was removed from human abdominal whole skin samples obtained post mortem in accordance with local ethical guidelines.

Administration / exposure

Route of administration:
intravenous
Details on study design:
A series of in vitro and in vivo studies with a series of methacrylates were used to develop PBPK models that accurately predict the metabolism and fate of these monomers. The studies confirmed that alkyl-methacrylate esters are rapidly hydrolyzed by ubiquitous carboxylesterases. First pass (local) hydrolysis of the parent ester has been shown to be significant for all routes of exposure. In vivo measurements of rat liver indicated this organ has the greatest esterase activity. Similar measurements for skin microsomes indicated approximately 20-fold lower activity than for liver. However, this activity was substantial and capable of almost complete first-pass metabolism of the alkyl-methacrylates. For example, no parent ester penetrated whole rat skin in vitro for n-butyl methacrylate, octyl methacrylate or lauryl methacrylate tested experimentally with only methacrylic acid identified in the receiving fluid. In addition, model predictions indicate that esters of ethyl methacrylate or larger would be completely hydrolyzed before entering the circulation via skin absorption. This pattern is consistent with a lower rate of absorption for these esters such that the rate is within the metabolic capacity of the skin. Parent ester also was hydrolyzed by S9 fractions from nasal epithelium and was predicted to be effectively hydrolyzed following inhalation exposure.

Results and discussion

Main ADME results
Type:
metabolism
Results:
Half-life of MMA after i.V. injection: 4.4 min (PBPK estimate)

Toxicokinetic / pharmacokinetic studies

Toxicokinetic parametersopen allclose all
Test no.:
#1
Toxicokinetic parameters:
half-life 1st: 4.4 min
Remarks:
i.v./ rat liver microsomes
Test no.:
#1
Toxicokinetic parameters:
other: 98.8% removed from liver blood flow i.e. by first pass liver clearance
Remarks:
clearance/ i.v./ rat liver microsomes
Test no.:
#1
Toxicokinetic parameters:
Cmax: 14.7  (mg/L) of MAA in blood
Remarks:
i.v./ rat liver microsomes
Test no.:
#1
Toxicokinetic parameters:
Tmax: 1.7 min to peak MAA concentration in blood from model predictions
Remarks:
i.v./rat liver microsomes

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
Methacrylic acid

Any other information on results incl. tables

These studies showed that any systemically absorbed parent ester will be effectively removed during the first pass through the liver (CL as % LBF, 

see table). In addition, removal of methacrylic acid from the blood also

occurs rapidly (T50%; see table).  

Table 1:
Rate constants for ester hydrolysis by rat-liver microsomes and predicted 

systemic fate kinetics for methacrylates following i.v. administration:

 Ester    Vmax       Km        CL    T50%    Cmax    Tmax
----------------------------------------------------------
MAA        -         -       51.6%    -       -       -
MMA       445.8     164.3    98.8%    4.4    14.7     1.7
EMA       699.2     106.2    99.5%    4.5    12.0     1.8
i-BMA     832.9     127.4    99.5%   11.6     7.4     1.6
n-BMA     875.7      77.3    99.7%    7.8     7.9     1.8
HMA       376.4      34.4    99.7%   18.5     5.9     1.2
2EHMA     393.0      17.7    99.9%   23.8     5.0     1.2
OMA       224.8      11.0    99.9%   27.2     5.0     1.2
----------------------------------------------------------

Vmax (nM/min/mg) and Km (µM) from rat-liver microsome (100 µg/ml)

determinations;  
CL = clearance as % removed from liver blood flow, T50% = Body  elimination time  (min) for 50% parent ester, Cmax = maximum concentration  (mg/L) of MAA in 

blood, Tmax = time (min) to peak MAA concentration in  blood from model 

predictions.

---

Table 2:
Rate constants for ester hydrolysis by human-liver microsome samples:

 Ester    Vmax (nM/min*mg) Km (mM) CL (µL/min*mg)    
-----------------------------------------------
MMA       1721      4103     419   
EMA        936      1601     584  
i-BMA       80       441     181
n-BMA      211       158    1332
HMA        229 66 3465
2EHMA      53        48    1109
OMA        243 38 6403 ----------------------------------------------------------

CL is calculated from the mean Vmax and Km

Applicant's summary and conclusion

Conclusions:
The in vivo and in vitro investigations as well as the PBPK models developed from the data showed that MMA, like other alkyl-methacrylate esters, is rapidly absorbed and hydrolyzed at exceptionally high rates to methacrylic acid by high capacity, ubiquitous carboxylesterases. Further, the removal of the hydrolysis product, methacrylic acid, also is very rapid (within minutes). The half-time after i.v. application in rat liver is 4.4 min for MMA.
Executive summary:

The in vivo and in vitro investigations as well as the PBPK models developed from the data showed that MMA, like other alkyl-methacrylate esters, is rapidly absorbed and hydrolyzed at exceptionally high rates to methacrylic acid by high capacity, ubiquitous carboxylesterases. Further, the removal of the hydrolysis product, methacrylic acid, also is very rapid (within minutes). The half-time after i.v. application in rat liver is 4.4 min for MMA.