Urea, reaction products with formaldehyde, glyoxal and methanol

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

From OCT 1984 to OCT 1985

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well-documented study report which meets basic scientific principles

Reason / purpose for cross-reference:

reference to same study

Objective of study:

absorption

distribution

excretion

metabolism

Principles of method if other than guideline:

Toxicokinetic behaviour of the test substance was investigated in vivo via the oral and dermal route, as well as after intravenous application.

GLP compliance:

not specified

Radiolabelling:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeders, Kongston, NY, USA
- Age at study initiation: adult
- Weight at study initiation: 232 - 308 g
- Individual metabolism cages: yes
- Diet: certified Purina rat chow, ad libitum
- Water: ad libitum
- Acclimation period: at least one week

Route of administration:

other: Experiment 1: i.v.; Experiment 2: oral; Experiment 3: dermal

Vehicle:

not specified

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: was done freshly before each experiment

HOMOGENEITY AND STABILITY OF TEST MATERIAL: the reaction mixture was stirred at room temperature

Experiment 3:
TEST SITE
- Area of exposure: either 2 cm² circular area or 10 cm² rectangular area
- % coverage: non-occlusive or partially occlusive
- Time intervals for shavings or clipplings: only once, approx. 24 h before dosing

USE OF RESTRAINERS FOR PREVENTING INGESTION: yes

Duration and frequency of treatment / exposure:

- single treatment
- Duration:
Experiment 1 (i.v.): 0.5, 2 or 72 h
Experiment 2 (oral): 72 h
Experiment 3 (dermal): 144 h

Remarks:

Doses / Concentrations:
Experiment 1 (i.v.): approx. 0.5 mL of radiolabelled reaction solution (approx. 50 mg/kg bw)
Experiment 2 (oral): 502, 979 and 1979 mg/ kg bw (1.1 to 1.5 mL of radiolabelled reaction solution)
Experiment 3 (dermal):
in case of application to 2 cm² circular area: 2, 22 and 105 mg/kg bw (i.e. 0.294, 3.5 and 13.3 mg/cm²)
in case of application to 10 cm² rectangular area: 133 +/- 22 mg/kg bw (i.e. 4.2+/-0.3 mg/cm²)

No. of animals per sex per dose / concentration:

Experiment 1 (i.v.): 0.5 and 2 h: 3 animals each; 72 h: 4 animals
Experiment 2 (oral): 4 animals
Experiment 3 (dermal):
in case of application to 2 cm² circular area: dose levels of 2 and 22 mg/kg bw: 2 animals each; dose level 105 mg/kg bw: 4 animals
in case of application to 10 cm² rectangular area: 3 animals

Control animals:

no

Details on dosing and sampling:

KINETIC STUDY (Absorption, distribution, metabolism,excretion)
- Tissues and body fluids sampled: urine, faeces, breath and other tissues (adipose, adrenal gland, bladder, blood, brain, cecum, esophagus, eye, heart, intestines, kidney, liver, lung, muscle, plasma, prostate, seminal vesicle, skin, spleen, stomach, testis, trachea, contents of bladder, stomach, cecum and samll and large intestines); tissue blood ratios (TBR) were calculated
- Time and frequency of sampling: in intervalls of about 6 to 24 h
- Method type(s) for identification: HPLC-MS

Disposition after Intravenous Administration

After administration of 48 mg/kg of [14C]DMDHEU, excretion of 14C was rapid and almost entirely via urine. The 0 - 6 h urine collection contained 85% of the administered [14C] . Urinary excretion of 14C increased to 95% of the dose by 24 h and 96% in 72 h. Minor amounts of 14C were excreted in feces, accounting for 2.2% of the dose in 24 h and 2.7% in 72 h . Fecal excretion was not contaminated with urine since the animals were fitted with tail cups. Less than 0.2% of the dose was excreted as [14C]O2 in 48 h. Almost no metabolism or degradation of the DMDHEU was observed. HPLC analysis of the 0-6 and 12-24 h urine collections gave radiochromatograms virtually identical to that of the dose preparation of radiolabelled DMDHEU. In a typical radio chromatogram the major DMDHEU peak accounted for 86 -93% of the 0 - 6 h urinary [14C], the MMDHEU peak for 5-11% (i.e. 1-methylol-4,5-dihydroxy-2-imidazolidinone, which is an inpurity), and the tail of the major MDMHEU peak for 0-3% . In the 12-24 h urine, the major DMDHEU peak still accounted for ca 90% of the urinary [14C] while the amount in the MMDHEU peak decreased to about 2% and that in the tail increased to about 6%. One-half hour after an intravenous dose of 51 mg/kg of radiolabelled DMDHEU, an average of 26% of the dose was recovered from the bladder contents. Tissues containing significant fractions of the dose were skin (13%), muscle (12%), blood (6%), liver (6%) and kidney (5%) . Two hours after dose administration the percent dose in these tissues had decreased by factors of 4 -12 . Two tissues had tissue-blood ratios significantly greater than 1 at this time point - prostate (TBR=11) and seminal vesicle (TBR=5). By 72 h after dosing, less than 0.5% of the dose remained in the tissues. Most of this (0.3%) was found in muscle. Approximately 6 times as much [14C] was present in blood at 72 h as was in plasma alone. A number of other tissues showed tissue-blood ratios greater than 1. This suggests that a very small portion of the DMDHEU may be metabolized to a relatively long lasting metabolite which may be covalently linked to biomolecules.

Absorption and Disposition after Oral Administration

Orally administered DMDHEU was excreted both in urine and in feces. More than 90% of the [14C] that was excreted in urine was excreted within 24 h after dosing. Oral absorption of DMDHEU, based on urinary excretion, increased with increasing dosed amounts. An average of 17% of the 502 mg/kg dose was absorbed, 28% of the 979 mg/kg dose and 38% of the 1970 mg/kg dose. The reason for this increase in oral absorption with increasing dose level is not clear.

Concentrations of radiolabelled compounds in tissues, in general, reflect the increased systemic load of [14C]DMHEU as the dose increased from 502 mg/kg (85 mg/kg absorbed) to 979 mg/kg (274 mg/kg absorbed) to 1970 mg/kg (749 mg/kg absorbed). Distribution of the [14C] in tissues following oral dosing was similar to that found after intravenous dosing .

Disposition after dermal Administration

After dermal administration, [14C]-labelled compounds were excreted in both urine and feces. Since intravenous administration of [14C]DMDHEU resulted in excretion of [14C] almost entirely via urine, any radiolabelled DMDHEU that enters the general circulation should be excreted via this route. On the other hand, orally administered [14C]DMDHEU is excreted via feces and urine due to the partial oral absorption of the [14C]DMDHEU. Thus the excretion of [14C] in feces following dermal administration of [14C]DMDHEU can be indicative of one of at least two different occurances:

(1) [14C]DMDHEU on the skin is first metabolised to another compound which is absorbed and excreted via the feces or

(2) somehow oral absorption of DMDHEU is occurring.

Although the dose site was protected in all of the studies, a complete sealing-off of the entire dose site was difficult to maintain for the entire 6 day (144 h) period of the study. Those animals who had removed their protective devices and had obviously ingested a portion of the dose were removed from the study. Animals for which the protective covering had become partially detached were noted. There were no obvious signs that ingestion of any of the dose had occurred for these animals. Analysis of tissues following dermal exposure to [14C]DMDHEU showed that only small amounts of [14C]-labelled material were found in the tissues. The distribution of [14C] in the tissues is somewhat different than that observed following intravenous and oral dosing, with larger amounts of [14C] being found in adipose and smaller amounts in muscle than following the other routes of administration.

Conclusions:

In general, the test item does not undergo major metabolism nor degradation and there is no evidence of bioaccumulation.

Reference 2

Endpoint:

dermal absorption in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

From OCT 1984 to OCT 1985

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well-documented study report, which meets basic scientific principles

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

toxicokinetic testing of the test substance with rats inlcuding investigation of dermal absorption

GLP compliance:

not specified

Radiolabelling:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeders, Kongston, NY, USA
- Age at study initiation: adult
- Weight at study initiation: 246 - 347 g
- Individual metabolism cages: yes
- Diet: certified Purina rat chow, ad libitum
- Water: ad libitum
- Acclimation period: at least one week

Type of coverage:

open

Vehicle:

not specified

Duration of exposure:

144 h (i.e. 6 d)

Doses:

in case of application to 2 cm² circular area: 2, 22 and 105 mg/kg bw (i.e. 0.294, 3.5 and 13.3 mg/cm²)
in case of application to 10 cm² rectangular area: 133 +/- 22 mg/kg bw (i.e. 4.2+/-0.3 mg/cm²)

No. of animals per group:

dose levels of 2 and 22 mg/kg bw: 2 animals each
dose level 105 mg/kg bw: 4 animals
dose level 133 mg/kg bw: 3 animals

Control animals:

no

Details on study design:

PREPARATION OF DOSING SOLUTIONS: was done freshly before each experiment

HOMOGENEITY AND STABILITY OF TEST MATERIAL: the reaction mixture was stirred at room temperature

APPLICATION OF DOSE: The dose was spread evenly over the dose site with the side of a curved,blunted 22 gauge needle fitted on a 100 microlitre gas tight syringe.

TEST SITE
- Area of exposure: either 2 cm² circular area or 10 cm² rectangular area
- % coverage: non-occlusive or partially occlusive
- Time intervals for shavings or clipplings: only once, approx. 24 h before dosing

USE OF RESTRAINERS FOR PREVENTING INGESTION: yes

Signs and symptoms of toxicity:

not specified

Dermal irritation:

not specified

Dose:

2 mg/kg bw

Parameter:

percentage

Absorption:

1 %

Remarks on result:

other: 144 h

Remarks:

non-occluded dose site

Dose:

22 mg/kg bw

Parameter:

percentage

Absorption:

ca. 5 %

Remarks on result:

other: 144 h

Remarks:

non-occluded dose site

Dose:

105 mg/kg bw

Parameter:

percentage

Absorption:

5 %

Remarks on result:

other: 144 h

Remarks:

non-occluded dose site

Dose:

133 mg/kg bw

Parameter:

percentage

Absorption:

17 %

Remarks on result:

other: 144 h

Remarks:

partially occluded dose site

Conclusions:

Dermal absorption in rats of the test substance from a non-occluded dose site is rather low (i.e. over a 144 h exposure period: absorption of ca. 5% of the applied dose for doses of 13 and 3.5 mg/cm² (i.e. 105 and 22 mg/kg bw) and ca. 1% of the applied dose for a dose of 0.3 mg/cm² (i.e. 2 mg/kg bw). Partial occlusion of the dose site resulted in a higher dermal absorption, probably due to increased hydration of the skin.

Additional information

There is one available study including several experiments describing the toxicokinetic behaviour of 1,3-DIMETHYLOL-4,5-DIHYDROXY-2-IMIDAZOLIDINONE (DMDHEU), a surrogate substance for the submission substance (NIEHS, 1985).

Intravenous administration of about 50 mg/kg bw of [14C]DMDHEU to male F-344 rats, resulted in rapid excretion of 14C, almost entirely via the urine. About 85% of radioactivity was recovered in urine within 6 h, increasing up to 95% after 24 h and 96% after 72 h, and only minor amounts were found in the faeces (about 2.2 % in 24 h), and less than 0.2 % was exhaled as 14CO2 in 48 h.

Distribution in tissue occurred within 0.5 h with an average of 26 % of the dose in the urinary bladder contents. Moreover significant fractions of the dose after this period were found in the skin (13 %), muscles (12 %), blood (6 %), liver (6 %), and kidneys (5 %).

By 2 h p.a. these levels were reduced by a factor of 4 to 12 and less than 0.5% of the dose remained in the tissues at 72 h p.a. (mostly in muscle (0.3%)).

 

HPLC chromatographic urinary analysis only showed minor changes in the profile of the excreted components compared to the applied test material, indicating to negligible or no metabolism or degradation. Moreover tested in vitro the test compound was stable in blood for at least 18.5 h incubated at 0 or 37 °C.

 

After oral application of 14C-DMDHEU (by gavage) to rats, the absorbed fraction increased over the dose range of 500 to 2000 mg/kg bw (based on urinary excretion; at 500 mg/kg bw: 17%, at 1000 mg/kg bw: 28%, and at 2000 mg/kg bw: 38%). This increase in relation to the dose occurred for unexplained reasons.

The distribution pattern in the body was similar to that found after i.v. injection. Within 24 h more than 90 % of the excreted radioactivity was recovered in the urine.

There were still residual quantities of radioactivity (<10 microgram DMDHEU equivalents/g tissue, except higher amounts in intestine and cecum) left in the tissues after 72 h.

Elimination took place in a somewhat delayed fashion.

 

Dermal absorption of[14C]DMDHEU from a non-occluded dose site over a 144 h exposure period was approx. 5% of the applied dose for doses of 13.3 and 3.5 mg/cm² and approx.1% of the applied dose for a dose of 0.3 mg/cm². Partial occlusion of the dose site resulted in a higher dermal absorption, probably due to increased hydration of the skin.

Distribution of [14C] in tissues following a 144 h dermal exposure to DMDHEU was somewhat different than that observed following oral or intravenous doses of this xenobiotic. Increased amounts of [14C] were found in adipose following the dermal exposure and lesser percentages in muscle. This may be due to the exact nature of the compounds being absorbed following the dermal exposure.

The conclusion of these studies is that the test item is absorbed well after oral administration, but has a rather low percutaneous absorption rate (i.e. only 5% of the high dose within 144 h). Moreover the test substance does not undergo major metabolism or degradation and there is no evidence of bioaccumulation. Highest concentrations were found in excretory and reproductive organs. After i.v. and oral administration muscle and skin were loaded with [14C], after dermal application the adipose was concerned more than e.g. the muscles.