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Reference
Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
11 July 1994 - 6 May 1997
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Objective of study:
toxicokinetics
Qualifier:
according to guideline
Guideline:
EPA OPP 85-1 (Metabolism and Pharmacokinetics)
Version / remarks:
November 1984
GLP compliance:
yes
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material (radiolabelled): 443-11
- Source and lot/batch No.of test material (non-labelled): NHL/11/93

RADIOLABELLING INFORMATION
- Radiochemical purity: 99.5%
- Specific activity: 4.43 µCi/g (164 kBq/g)
- Locations of the label: 14C

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material (radiolabelled): ca. -20°C
- Storage condition of test material (non-labelled): 4°C in the dark



Radiolabelling:
yes
Remarks:
14C
Species:
rat
Strain:
Wistar
Remarks:
Crl: (WI)BR
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River (UK9 Ltd., Margate, Kent, UK
- Age at study initiation: 7 to 11 weeks
- Weight at study initiation: 190-350 g
- Housing: in groups of up to 5 per cage in wire floor polypropylene cages suspended over polypropylene dirt trays containing soft white wood sawdust
- Diet: ad libitum, pellet diet, SQC Rat and mouse Maintenance Diet No.1, Expanded
- Water: ad libitum
- Acclimation period: 7 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19-23
- Humidity (%): 40-70
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): 12 hours/12 hours

Route of administration:
oral: gavage
Vehicle:
CMC (carboxymethyl cellulose)
Remarks:
1%
Duration and frequency of treatment / exposure:
single administration
Dose / conc.:
5 other: mg/kg
Remarks:
corresounding to a nominal dose of 15 µCi/animal (0.555 MBq)
No. of animals per sex per dose / concentration:
pharmacokinetic study: 5 males
excretion balance: 5 males
Control animals:
no
Details on study design:
Study duration 168 h
Details on dosing and sampling:
TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, serum, expired air, adrenals, residual carcass, brain, fat (abdominal), spleen, stomach (minus contents), kidney, liver, gross lesions, muscle (quadriceps), bone (femur), skin (dorso-lumbar), stomach contents, gonads, heart, thyroids, lungs
- Time and frequency of sampling:
Blood: 0 (pre dose), 0.5, 1.5, 3, 6, 9,12, 24, 48, 72, 120, and 168 h
Urine: 6,12, 24, 48, 72, 96, 120,144 and 168 h post-dose
Faeces: 24, 48, 72, 96, 120, 144 and 168 h post-dose
Expired air: 12, 24, and 48 h post dose

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine, faeces
- Time and frequency of sampling: 0 to 6, 6 to 12, 12 to 24, and 24 to 48 h (urine); 0to24, and 24 to 48 h (faeces)
- From how many animals: samples pooled
- Method type for identification: HPLC-MS, TLC

OTHER
- An additional experiment was carried out using LC-MS (MRM) to confirm the presence and concentration of carboxy-Mecoprop-P in urine. Carboxy-Mecoprop-P is a known plant metabolite.
Type:
absorption
Results:
Rapid absorption after oral exposure.
Type:
distribution
Results:
Distribution throughout the body water.
Type:
metabolism
Results:
Predominantly hydrolysis of the ester to the corresponding acid. No evidence of the presence of the unchanged ester.
Type:
excretion
Results:
Predominantly and fast via urine.
Details on absorption:
Following oral administration of [14C]-MCCP-P 2-EHE, radioactivity was rapidly absorbed.
Details on distribution in tissues:
Distribution throughout the body water.
Details on excretion:
Excretion predominately in urine. No radioactivity was detected in expired air and there was no accumulation of radioactivity in any of the tissues excised after the 168 h study period or in the carcass from either dose group.
Metabolites identified:
yes
Details on metabolites:
LC-MS analysis of urine and faeces samples showed that the radiolabelled ester was excreted predominantly as its corresponding acid. In addition, there were at least five minor components which together accounted for less than 5% of the urinary radioactivity. There was no evidence of the presence of the unchanged MCPP-P 2 EHE. The presence of Carboxy-mecoprop-P could not be confirmed.

Pharmacokinetic studies (Dose groups A and B) - mean data, n=5

The following pharmacokinetic parameters were determined for plasma after a single oral dose of [14C]-MCPP-P 2-EHE and [14C]-MCPP-P DMA at nominal dose level of 5 mg/kg body weight:

 Plasma

 [14C]-MCPP-P 2-EHE

(Group A)

 [14C]-MCPP-P DMA

(Group B)

 Cmax (μg equiv./g)  19.98  26.85
 Tmax (h)  3.6  2.0
 T 1/2 elim (h)  8.36  6.61
 AUC(0-t) (μg equiv.h/g)  187.6  276.2
  AUC(0 -∞ ) (μg equiv.h/g)  188.5  277.0

Excretion balance studies (Dose groups C and D) –mean data, n=5

The excretion and tissue retention of radioactivity was determined after a single oral dose of [14C]-MCPP-P 2-EHE and [14C]-MCPP-P-DMA at a nominal dose level of 5 mg/kg body weight. The results are summarised below expressed as percentage of administered radioactivity in each sample type:

   [14C]-MCPP-P 2-EHE  (Group C)   [14C]-MCPP-P DMA  (Group D) 
     Normalized to 100%    Normalized to 100%
 Urine  71.09  81.99  86.43  84.90
 Faeces  3.29  3.79  4.68  4.60
 Cage wash  12.17  14.04  10.68  10.49
 CO2 trap 1  ND  ND  ND  ND
  CO2 trap 2  ND  ND  ND  ND
 Cage debris  0.15  0.17  0.06  0.06
 Final cage  0.01  0.01  < 0.01  < 0.01
 Total  86.71  100  101.80 100 

ND = None detected

Following a single oral dose of [14C]-MCPP-P 2-EHE, 86.7 % of the administered radioactivity was recovered. This recovery is lower than would normally be expected, however, there was no evidence of accumulation in any of the tissue samples excised after the 168 h period or in the carcass. The ester is insoluble in water and these consistently low recoveries were probably due to a lack of homogeneity in the suspended test article. This observation appears to be a general feature of ester forms of this class of compound.

Radioactivity was rapidly absorbed and excreted predominately in urine. For dose groups C and D where the distribution and excretion balance was investigated, 95.5 % and 96.3 % of the total urinary radioactivity respectively was recovered within 24 h.

No radioactivity was detected in expired air and there was no accumulation of radioactivity in any of the tissues excised after the 168 h study period or in the carcass from either dose group.

Characterization of metabolites

LC-MS analysis of urine and faeces samples (Group C) showed that [14C]-MCPP-P 2-EHE was excreted predominately as MCPP-P acid (53.9 % of the administered dose) and a hydroxylated metabolite (almost certainly the 2-hydroxymethyl derivative) (17.30 % of the administered dose). There were at least five additional minor components but together these metabolites accounted for less than 5 % of the urinary radioactivity. There was no evidence for the presence of the unchanged ester.

Dose group D samples were not analysed as the DMA salt is chromatographically identical to MCPP-P acid.

The presence of carboxy-Mecoprop-P was not confirmed in urine. However, in a MCPP-P acid ADME study (HE study no. 1149/3), using a semi-quantitative LC-MS (NRM) method, the presence of this metabolite was confirmed, levels of radioactivity accounting for up to 0.07 % of the administered dose.

Conclusions:
MCPP-P 2-EHE was rapidly absorbed and distributed throughout the body water and no bioaccumulation was observed. Hydrolysis to MCPP-P acid occurred rapidly and excretion of this metabolite was predominantly via urine.
Executive summary:

An OCED TG 417 study was performed to assess the toxicokinetics of MCPP-P 2-EHE in male rats. Following oral administration of 5 mg/kg bw [14C]-labeled test item, radioactivity is rapidly absorbed and excreted predominantly in urine. There was no accumulation of radioactivity in any tissue or organ after 168 hours. LC-MS analysis of urine and faeces samples showed that MCPP-p 2 EHE was excreted predominantly as MCPP-P acid (53.9% of the administered dose) and a hydroxylated metabolite (17.3 % of the administered dose). At least 5 minor components accounted together for less than 5% of the urinary radioactivity. There was no evidence of the presence of the unchanged ester. The data clearly show that MCPP-P 2-EHE is metabolised through MCPP-P acid, which is then metabolized by the scheme described for MCPP-P acid.

Description of key information

Adsoprtion: rapid

Distribution: throughout the body water

Metabolism: predominantly to MCPP-P acid and a hydroxylated metabolite

Excretion: predominantly via urine

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

An OCED TG 417 study was performed to assess the toxicokinetics of MCPP-P 2 EHE in male rats. Following oral administration of 5 mg/kg bw [14C]-labeled test item, radioactivity is rapidly absorbed and excreted predominantly in urine. There was no accumulation of radioactivity in any tissue or organ after 168 hours. LC-MS analysis of urine and faeces samples showed that MCPP-P 2EHE was excreted predominantly as MCCP-P acid (53.9% of the administered dose) and a hydroxylated metabolite (17.3 % of the administered dose). At least 5 minor components accounted together for less than 5% of the urinary radioactivity. There was no evidence of the presence of the unchanged ester. The data clearly show that MCPP-P 2-EHE is metabolised through Mecoprop-P-acid, which is then metabolized by the scheme described for MCPP-P acid (MCPP-p Task Force 1149/14 -1007; 1997). For details see read across justification in section 13.

In a non-guideline study, the in vitro metabolism of [14C] MCPP-p 2 Ethylhexylester in plasma, stomach contents, gastro-intestinal tract (GIT) and liver post-mitochondrial fraction (S9) isolated from the rat was investigated over a 30 min incubation period at ca. 37°C. Radioactivity was measured using liquid scintillation counting after incubation of radioactive labeled test substance with each single matrix. Hydrolysis is slow in the lumen of the GIT (< 2% after 30 min) but rapid and substantially complete in the plasma and liver preparation systems (> 90% after 30 min). In the liver S9 fraction, conversion is only due in part to enzymatic reactions requiring the presence of NADPH. Hydrolysis to MCPP-P acid did not occur in blank incubations and was dependent on the presence of each tissue examined. In vivo, compounds absorbed through the wall of the intestine enter the blood vascular system without passing all the way through to the peritoneal cavity. It should therefore be noted that the in vitro determination of absorption by the jejunum is probably an underestimate, as there was no vascular supply to the preparation (MCPP-p Task Force 1149/1; 1994).

In another study, the metabolic fate of radioactive labeled MCCP-P acid (CAS 7085-19-0), the hydrolysis product of MCPP-P 2-EHE, was studied in the rat following both single and repeated (20 and 40 days) oral administration. In the single dose study, a dose of 107 mg/kg bw was administered to male and female rats. In the repeated dose studies, a dosage of 1 mg/kg bw/day was administered by gavage. A rapid absorption of the test item was observed. Highest plasma and tissue concentrations were reached after 3-6 h, but declined substantially in all tissues, except fat, during 192 h period. Low levels are found in the nervous system (brain and spinal chord). After repeated dosing, the highest concentration of test item was reached after 11days in all tissues, with greatest in fat, kidneys and plasma. The majority of radioactivity was excreted in urine, while fecal excretion was of minor relevance. Bile cannulation demonstrated extensive biliary excretion of radioactivity (Phenoxyacid Herbicide Consortium 1333R3 -277/1; 1978).