N,N'-diphenylguanidine monohydrochloride

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics, other

Remarks:

Expert Statement

Type of information:

other: Expert Statement

Adequacy of study:

key study

Study period:

2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Expert Statement, no study available

Data source

Reference

Reference Type:

other: Expert Statement

Title:

Unnamed

Year:

2018

Report date:

2018

Materials and methods

Objective of study:

absorption

distribution

excretion

metabolism

Test guideline

Qualifier:

according to guideline

Guideline:

other: ECHA Guidance on Information Requirements and Chemical Safety Assessment Chapter R.7c: Endpoint specific guidance

Version / remarks:

2017

Deviations:

no

Test material

Test material information

Constituent 1

Reference substance name:

N,N'-diphenylguanidine monohydrochloride

EC Number:

246-107-8

EC Name:

N,N'-diphenylguanidine monohydrochloride

Cas Number:

24245-27-0

Molecular formula:

C13H13N3.ClH

IUPAC Name:

N,N'-diphenylguanidine hydrochloride

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Bioavailability via oral route is strongly linked to physico-chemical properties of the substance. Generally, oral absorption is favoured for molecular weights below 500 g/mol. Furthermore, a high water solubility of more than 100 mg/L enables the substance to readily dissolve in the gastrointestinal fluids, allowing direct uptake into the systemic circulation through aqueous pores or via carriage of the molecules across membranes with the bulk passage of water. The test item has a molecular weight of 247.72 g/mol and is well soluble in water (solubility of 16.71 g/L). Therefore, it is expected to be well absorbed in GIT. Further, the substance being the salt of 1,3-diphenylguanidine and mono-hydrochloride is expected to readily dissociate in aqueous environments such as the intestinal fluids. The small ionised molecules are expected to be well absorbed by bulk passage of water. Taken together, the physiochemical properties indicate that the test item becomes bioavailable via the oral route. This assumption is confirmed by the results of an acute oral toxicity study (OECD 423) with the test item itself and an 28 days repeated dose toxicity study (OECD 407) with a read-across substance, i. e. the uncharged base 1,3-diphenylguanidine. Clear substance related effects were observed in both studies indicating their bioavailability via the oral route.

The volatility indicates whether a substance may be available for inhalation as a vapour. Highly volatile substances are those with a vapour pressure greater than 25 KPa and substances with low volatility have a vapour pressure of less than 0.5 KPa. Due to the very low vapour pressure of the test item (3.244E-6 Pa), and also taking into account the high melting point, it is unlikely that the substance will be available as a vapour. However, if it was the case, absorption via inhalation route is expected to occur due to the relatively low molecular weight and good water solubility.

Dermal uptake is favoured for substances with a molecular weight < 100 g/mol. The molecular weight of the test item is 247.72 g/mol. The substances must be sufficiently soluble in water to partition from the stratum corneum into the epidermis. Absorption is anticipated to be moderate to high if water solubility is between 100 and 10000 mg/L. However, if water solubility is above 10000 mg/L and the logPow is below 0 the substance may be too hydrophilic to cross the lipid rich environment of the stratum corneum, limiting dermal uptake (ECHA guidance on chemical safety assessment and information requirements, Chapter R.7c, 2017). The test item’s water solubility is > 10 g/L and its logPow is -1.77. Thus, a low dermal absorption is expected. No mortality or clinical signs related to the test substance in the acute dermal toxicity study (OECD 402), indicating that the substances did not become systemically available via the dermal route since it would be of considerable toxicity as observed in the acute oral toxicity study.

Details on distribution in tissues:

In general, the smaller molecules are the wider their distribution in the organism is expected. The test item has a relatively low molecular weight of 247.72 g/mol. In addition, it is well soluble in water. Therefore, it is expected to be rapidly and widely distributed. This assumption is further supported by the results of the acute and repeated oral toxicity studies with the test item and structural analogue substance indicated by the systemic toxicity observed (OECD 423, 407 and 421). Based on its low logPow the test item is not expected to bioaccumulate in the organism.

Details on excretion:

The test item and/or its metabolites are most likely excreted via the urine due to its relatively low molecular weight and its good water solubility.

Metabolite characterisation studies

Details on metabolites:

Based on the chemical structure of diphenylguanidine it may be metabolized by Phase I enzymes while undergoing functionalization reactions increasing its hydrophilicity. Furthermore, Phase II conjugation reactions may covalently link an endogenous substrate to the parent compound or the Phase I metabolite in order to ultimately facilitate excretion.

Metabolism to more toxic metabolites could be expected based on the results obtained in the in vitro bacterial reverse mutation test (Ames test). This assay revealed positive results in two strains only in the presence of S9. In contrast, in the chromosome aberration test with mammalian cells the presence or absence of metabolic activation did not alter the effect outcome. The above considerations could be supported by QSAR predictions (QSAR toolbox). Diphenylguanidine was evaluated and possible metabolites (rat liver metabolism) were predicted.

Aromatic rings of Diphenylguanidine are predicted to become oxidized and/or hydroxylised, probably by Phase I CYP 450 enzymes increasing the hydrophilicity of the molecule. Further, N-substitution as well as cleavage of the urea structure is predicted. Among others, Aniline and 2-aminophenol are predicted structures that may be formed among metabolism. Terminal amino-group may be further oxidized and/or hydroxylised. QSAR Toolbox only provides prediction for Phase I metabolism. Thus, these anticipated metabolites likely undergo further conjugation reactions faciliated by Phase II enzymes.
The free base (read-across substances) was experimentally demonstrated to be metabolised to three main metabolites. These however, were not further identified.

Applicant's summary and conclusion

Conclusions:

Based on physicochemical characteristics (low molecular weight, good water solubility) well absorption by the oral and inhalative but less absorption via the dermal route is anticipated. Further, rapid and wide distribution of the test substance in the organism is expected. This assumption is further supported by the results of the oral and dermal acute toxicity studies as well as by the results of the repeated dose toxicity studies, revealing systemic substance related effects. Enzymatic activation (toxification) may be expected to occur based on QSAR prediction. Renal excretion of the test item or its metabolites is expected and was confirmed by experimental results of a structural analogue substance. The test item is not considered to bioaccumulate in the organism.

Executive summary:

The test item is a mono-constituent substance appearing as colorless powder at ambient conditions with a molecular weight of 247.72 g/mol. It is well soluble in water with an n-octanol/water partition coefficient of -1.77. Freezing or melting point of the substance was determined to be 144 - 150 °C whereas decomposition was observed at temperatures of 267 and above. Vapour pressure was determined to be 3.2E-6 Pa.

 

The test item being the salt of 1,3-diphenylguanidine and mono-hydrochloride is expected to readily dissociate in aqueous environments such as the intestinal fluids or mucosal membranes. Chloride ions are ubiquitously present in every-day nutrition and are part of a variety of physiological processes. Therefore, this constituent will not be further assessed for its toxicokinetic behaviour since it is expected to be well regulated by endogenous mechanism of the organism.

 

Absorption

 

Bioavailability via oral route is strongly linked to physico-chemical properties of the substance. Generally, oral absorption is favoured for molecular weights below 500 g/mol. Furthermore, a high water solubility of more than 100 mg/L enables the substance to readily dissolve in the gastrointestinal fluids, allowing direct uptake into the systemic circulation through aqueous pores or via carriage of the molecules across membranes with the bulk passage of water. The test item has a molecular weight of 247.72 g/mol and is well soluble in water (solubility of 16.71 g/L). Therefore, it is expected to be well absorbed in GIT. Further, the substance being the salt of 1,3-diphenylguanidine and mono-hydrochloride is expected to readily dissociate in aqueous environments such as the intestinal fluids. The small ionised molecules are expected to be well absorbed by bulk passage of water. Taken together, the physiochemical properties indicate thatthetest item becomes bioavailable via the oral route. This assumption isconfirmed by the results of an acute oral toxicity study (OECD 423) with the test item itself and an 28 daysrepeated dose toxicity study (OECD 407) with a read-across substance, i. e. the uncharged base1,3-diphenylguanidine. Clear substance related effects were observed in both studies indicating their bioavailability via the oral route.

The volatility indicates whether a substance may be available for inhalation as a vapour. Highly volatile substances are those with a vapour pressure greater than 25 KPa and substances with low volatility have a vapour pressure of less than 0.5 KPa. Due to the very low estimated vapour pressure of the test item (3.2E-6 Pa), and also taking into account the high melting point, it is unlikely that the substance will be available as a vapour. However, if it was the case, absorption via inhalation route is expected to occur due to the relatively low molecular weight and good water solubility.

Dermal uptake is favoured for substances with a molecular weight < 100 g/mol. The molecular weight of the test item is 247.72 g/mol. The substances must be sufficiently soluble in water to partition from the stratum corneum into the epidermis. Absorption is anticipated to be moderate to high if water solubility is between 100 ‑ 10000 mg/L. However, if water solubility is above 10000 mg/L and the logPow is below 0 the substance may be too hydrophilic to cross the lipid rich environment of the stratum corneum, limiting dermal uptake (ECHA guidance on chemical safety assessment and information requirements, Chapter R.7c, 2017). The test item’s water solubility is > 10 g/L and its logPow is -1.77. Thus, a low dermal absorption is expected.

No mortality or clinical signs related to the test substanceinthe acute dermal toxicity study (OECD 402), indicating that the substances did not become systemically available via the dermal route since it would be of considerable toxicity as observed in the acute oral toxicity study.

Distribution

 

In general, the smaller molecules are the wider their distribution in the organism is expected. The test item has a relatively low molecular weight of 247.72 g/mol. In addition, it is well soluble in water. Therefore, it is expected to be rapidly and widely distributed. This assumption is further supported by the results of the acute and repeated oral toxicity studies with the test item and structural analogue substance indicated by the systemic toxicity observed (OECD 423, 407 and 421). Based on its low logPow the test item is not expected to bioaccumulate in the organism.

Metabolism

 

Based on the chemical structure of diphenylguanidine it may be metabolized by Phase I enzymes while undergoing functionalization reactions increasingits hydrophilicity. Furthermore, Phase II conjugation reactions maycovalently link an endogenous substrate to the parent compound or the Phase I metabolite in order to ultimately facilitate excretion.

 

Metabolism to more toxic metabolites could be expected based on the results obtained in the in vitro bacterial reverse mutation test (Ames test). This assay revealed positive results in two strains only in the presence of S9. In contrast, in the chromosome aberration test with mammalian cells the presence or absence of metabolic activation did not alter the effect outcome. The above considerations could be supported by QSAR predictions (QSAR toolbox). Diphenylguanidinewas evaluated and possible metabolites (rat liver metabolism) were predicted.

Aromatic rings of Diphenylguanidineare predicted to become oxidized and/or hydroxylised, probably by Phase I CYP 450 enzymes increasing the hydrophilicity of the molecule. Further, N-substitution as well as cleavage of the urea structure is predicted. Among others, Aniline and 2-aminophenol are predicted structures that may be formed among metabolism. Terminal amino-group may be further oxidized and/or hydroxylised. QSAR Toolbox only provides prediction for Phase I metabolism. Thus, these anticipated metabolites likely undergo further conjugation reactions faciliated by Phase II enzymes.

The free base (read-across substances) was experimentally demonstrated to be metabolised to three main metabolites. These however, were not further identified.

Excretion

 

The test item and/or its metabolites are most likely excreted via the urine due to its relatively low molecular weight and its good water solubility.