1,3,5-triazine-2,4,6-triamine phosphate

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Metabolism, disposition and excretion of 14C-Melamine in male Fischer 344 rats

Author:

Mast R.W. et al.

Year:

1985

Bibliographic source:

Food Chem. Toxicol., 21, 807-810, (1983)

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

1982

Report date:

1982

Materials and methods

Objective of study:

other: metabolism, excretion and disposition

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

only one dose level tested

Principles of method if other than guideline:

The metabolism, excretion and disposition of melamine were determined after administration of a single oral dose.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Melamine

EC Number:

203-615-4

EC Name:

Melamine

Cas Number:

108-78-1

Molecular formula:

C3H6N6

IUPAC Name:

1,3,5-triazine-2,4,6-triamine

Specific details on test material used for the study:

RADIOLABELLING INFORMATION
- Radiochemical purity: 98.4 %
- Specific activity: 8.1 mCi/mmol
- Locations of the label: uniformly labelled in the triazine ring

Radiolabelling:

yes

Remarks:

14 C (uniformly labelled in the triazine ring)

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Kingston, N)
- Weight at study initiation: 250 to 400g
- Fasting period before study: food was withheld for 12 hr before and 4 hr after dosing
12-hr light/dark cycle .
- Housing: singly in glass metabolism chambers for collection of urine, faeces and breath
- Individual metabolism cages: yes
- Diet: ad libitum
- Water: ad libitum

ENVIRONMENTAL CONDITIONS
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

Study design 1 (excretion routes): Intubation with 1 mL of the solution
Study design 2 (tissue distribution and residues): no data (presumably equivalent to study design 1)

Duration and frequency of treatment / exposure:

Study design 1 (excretion routes): single administration
Study design 2 (tissue distribution and residues): single administration, rats were killed 0.5, 1 .0, 4 .0, 8 .0 . 24, 48 or 96 hr later .

Doses / concentrations

Dose / conc.:

1.3 mg/kg bw (total dose)

Remarks:

Study design 1 (excretion routes): 0.025 mCi/rat
Study design 2 (tissue distribution and residues): 0.025 mCi/rat

No. of animals per sex per dose / concentration:

Study design 1 (excretion routes): 4
Study design 2 (tissue distribution and residues): 3-4/group

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
Study design 1 (excretion routes):
- Tissues and body fluids sampled: urine, faeces, and expired air
- Time and frequency of sampling: four consecutive 24hr periods; in one study, expired air was not collected, faeces were collected at 96 hr
and urine at 2, 4, 8, 12, 24, 48, 72 and 96 hr after dosing . The urine from each rat was assayed separately.

Study design 2 (tissue distribution and residues):
- Tissues and body fluids sampled: At autopsy, samples of liver, kidneys, ureters . rinsed bladder and blood were taken and plasma was obtained by centrifugation. The half-life of melamine in the plasma was determined.

MELAMINE DETERMINATIONS
The [14C] in aliquots of plasma, urine and breath-trapping solutions was measured directly by liquid scintillation. [14C] Melamine was measured in urine and in boiling-water extracts of blood, plasma and faeces

Results and discussion

Main ADME results

Main ADME results 1

Type:

absorption

Results:

Tmax= 30 min (blood)

Main ADME results 2

Type:

distribution

Results:

high level in bladder after 24 h

Main ADME results 3

Type:

metabolism

Results:

no metabolites detected

Main ADME results 4

Type:

excretion

Results:

urine major route of elimination (elimination t1/2= 3h)

Toxicokinetic / pharmacokinetic studies

Details on distribution in tissues:

Results obtained from study design 2:
Plasma and liver:
The plasma [14C] melamine level 30 min after treatment was 1.1 ppm, but 30 min later, this level had dropped by 53% to 0.52 ppm .
Over the next 3 hr, the plasma [14 C] melamine level dropped by another 52% .
The terminal phase half-life of melamine in plasma was 2.7 hr. Whole-blood and liver levels of [14C] melamine were indistinguishable from plasma levels over this period. At 24 hr or after, no [14C] was detected in the blood or plasma. Melamine levels in liver were 1-2 ppb or less over these periods
Kidney and bladder:
Melamine levels in the kidney were 2-3 times greater than in the plasma. These elevated kidney levels were probably due to renal concentration of the melamine prior to its urinary excretion . At 24 hr or after melamine levels in kidney were 1-2 ppb or less. Bladder radioactivity levels were very high. While bladder levels were similar to the plasma levels 30 min after treatment, they increased to a peak of 6 .6 ppm at 4 hr (26.4 times the plasma level) and showed considerable variability (1 .4, 4 .5 and 14 ppm. At 8 hr the level was still elevated and continued to show marked variability (4.0, 11 and 1 .8 ppm).
This elevated bladder content of [14C] was probably caused by back diffusion or contamination of the tissue by urine. The cause of the high variability between bladders is unknown. At 24 hr or after Melamine levels in the bladder and ureter were higher than those of the other tissues showing the residual effects of the high initial urinary [14C] levels (see also Table 1).

Details on excretion:

Results obtained from study design 1:
Urine:
Virtually all the radioactivity was excreted within the first 24 hr and was present in the urine. By 96 hr, 93 ± 4% of the administered radioactivity had been excreted in the urine.
Faeces and breath:
Only 0.20 and 0.64% of the administered radioactivity appeared in breath and faeces, respectively, during the total 96-hr period . The radioactivity in the faeces was most probably the result of urinary contamination. (An additional 4% of the administered radioactivity was recovered in the cage washings . From the urinary data, it seems likely that this 4% was excreted in the first 24 hr . The total recovery of 14C was 99%.
Elimination half-life and renal clearance:
Kinetic analysis of the radioactivity data from urine yielded an elimination half-life of 3.0 hr (95% CI 2 .6-3 .5) and a renal clearance of 2 .5 ± 0 .1 mL/min (mean ± SEM).

Metabolite characterisation studies

Metabolites identified:

no

Details on metabolites:

While analyzing the samples by HPLC analysis no metabolites could be detected. This is an indication that melamine was not metabolized. Between 97 and 100% of the [14C] in blood and plasma was also present as melamine at all sampling times. Although the percentage of [14C] present as melamine was lower in the faeces, the total non-melamine [14C] in faeces accounted for less than 0.14% of the administered radioactivity (see also Table 2).

Any other information on results incl. tables

Table I . Concentrations of [14C]melamine in the tissues of male Fischer 344 rats treated orally with a single dose of 0.025 mCi

		Melamine concentration (ppb) in:
Time after treatment (hr)	No of rats	Blood*	Plasma	Bladder	Liver	Kidney	Ureter
0.5		Similar to plasma levels	1.1	Similar to plasma levels	Similar to plasma levels	No data
1.0		“	0.52	No data	“
4.0		“	0.25	6.6 (high variability)	“
8.0	No data
24.0	3	0	ND	31 +/- 15	1.8 +/- 0.1	1.3 +/- 0.7	12 +/- 4
48.0	3	0	0	4 +/- 2	2.6 +/- 1.2	0.7 +/- 0.9	9 +/- 5
96.0	4	0	0	8 +/- 2	0.4 +/- 0.2	0.1	12 +/- 5

* Limit of detection 1ppb

Data are expressed as means +/- SEM for the numbers of rats indicated

Table 2: Percentage of radioactivity present as melamine in the urine, blood, plasma and faeces

	14C as 14C-melamine* (% of total) in:
Time after treatment (hr)	Urine	Blood	Plasma	Faeces
0.5		98.9+/- 6.2	98.5+/- 0.4
1.0		99.3+/- 0.1	99.4+/- 0.1
4.0		99.5+/- 0.1	99.1+/- 0.1
8.0		97.4+/- 1.9	98.3+/- 0.8
24.0	98.5+/- 0.1			78.4 +/- 2.9
48.0	98.1+/- 0.2			64.2 +/- 2.8
72.0	94.9+/- 2.2
96.0	96.5+/- 0.8

* *Radiochemical purity of [14C]melamine in dosing solution was 98 %.

Values are means ± SEM for groups of three or four rats .