(2Z)-2-phenylhex-2-enenitrile

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics, other

Remarks:

An assessment of toxicokinetics, based on available data, in accordance with Annex VIII, Section 8.8.1 of Regulation (EC) No 1907/2006

Type of information:

other: Desk-based assessment

Adequacy of study:

key study

Study period:

Not applicable

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Objective of study:

toxicokinetics

Principles of method if other than guideline:

An assessment of toxicokinetics, based on available data, in accordance with Annex VIII, Section 8.8.1 of Regulation (EC) No 1907/2006

GLP compliance:

no

Details on species / strain selection:

No animals were used in this desk-based assessment.

Details on test animals or test system and environmental conditions:

Not applicable

Details on exposure:

Desk-based assessment.

Duration and frequency of treatment / exposure:

Desk-based assessment.

No. of animals per sex per dose / concentration:

No animals were used in this desk-based assessment.

Positive control reference chemical:

Desk-based assessment.

Details on study design:

Not applicable

Details on dosing and sampling:

Not applicable

Statistics:

Not applicable

Preliminary studies:

Desk-based assessment.

Details on absorption:

The physicochemical properties of the substance i.e. molecular weight of 171.238 g/mol, n-octanol/water partition coefficient of log Pow 3.93, and water solubility 19 mg/L and vapour pressure of 0.59 Pa at 25°C are suggestive of favourable absorption via the oral route with limited absorption via dermal and inhalation routes. Clear evidence of systemic effects was detected in acute and repeated dose oral toxicity studies indicating substance adsorption from the gastro-intestinal tract. The substance has a low water solubility which may suggest poor diffusion across membranes (paracellular absorption) and hence absorption, however, the low molecular weight and n-octanol/water partition coefficient will aid intracellular absorption. This results in substance delivery into the liver via portal and systemic circulation. This is supported by the systemic effects on liver and kidney weights as well as the effects liver enzyme activities observed in a repeated dose toxicity study. Although the substance is not considered to be very volatile based on low vapour pressure and high boiling point, the low molecular weight, moderate log Pow values (between -1 and 4) and water solubility, the substance is expected to be absorbed directly across the respiratory tract epithelium by passive diffusion. The low water solubility of the substance does not favour dissolution of the substance in the mucus lining of the respiratory tract. However, the low molecular weight and n-octanol/water partition coefficient enhance absorption through the aqueous pores (alveolar and capillary membranes). Since first pass metabolism is limited via this route, systemic half-life of the substance is expected to be higher compared to oral absorption because the substance enters general circulation before reaching metabolic organs. This is supported by the macroscopic abnormalities observed in the thymus, jejunum, ileum, caecum and colon, liver and/or spleen. Although these properties make uptake from the dermal route possible, the surface tension of 59.6 mN/m at 20 ± 0.5 °C may restrict transfer between the stratum corneum and the epidermis and therefore overall uptake via this route may be limited. Available acute dermal toxicity, in vivo and dermal irritation and sensitisation studies showed no systemic effects, therefore there is limited evidence of absorption through the skin.

Details on distribution in tissues:

Distribution of the test item via oral absorption is limited, based on the substance physicochemical properties (mainly: molecular weight, water solubility and n-octanol/water partition coefficient) meaning upon oral exposure, the substance passes through aqueous pores via the hepatic portal vein to the liver where it get metabolised before reaching systemic circulation. Furthermore, the nitrogen group is ionisable, particularly under the acidic conditions prevalent in the stomach. Potential for absorption would be greatest from the intestine as demonstrated by haemorrhage of the gastric mucosa, non-glandular region of the stomach, small and large intestines. As a result, systemic distribution of the parent compound via this route of absorption will be limited and therefore resulting in a reduced half-life of the parent compound in blood plasma. This is supported by the high liver weight associating centrilobular hypertrophy in the liver, increased hematopoiesis in the spleen and tubular hypertrophy in the kidneys. A wide distribution is expected following inhalation exposure. The low molecular weight and n-octanol/water partition coefficient enhance absorption through the aqueous pores (alveolar and capillary membranes) and into the systemic circulation, preferentially. Therefore, resulting in distribution into the heart, lungs and general circulatory system. A high plasma half-life is expected.as demonstrated by the systemic effects which included; hunched posture, lethargy, ataxia, tiptoe gait, pilo-erection, decreased respiratory rate, laboured respiration and abnormally red lungs observed in the acute oral study and lethargy, hunched posture, slow breathing, piloerection and ptosis observed in the acute inhalation study. Systemic distribution via dermal absorption is limited as demonstrated by the lack of systemic toxicity observed during the in vivo acute dermal toxicity, skin irritation and sensitisation. The substance is a mild contact sensitiser and may therefore be capable of binding to proteins.

Details on excretion:

Based on the absorption, distribution and potential metabolic pathways highlighted, coupled with available systemic data, after uptake via inhalation or orally: the substance will most likely be excreted via feces and urine. This is supported by elevated relative kidney weights in both sexes at 200 and 600 mg/kg/day and females at 60 mg/kg/day and tubular hypertrophy in the kidneys in the mid and high dose groups. Unabsorbed parent substance is expected to be excreted via feces. While absorbed portion will most likely be excreted in urine as metabolites as well as the unchanged parent substance. Bioaccumulation is unlikely for a substance with a low log Pow of 3.93 and low molecular weight.

Metabolites identified:

not measured

Details on metabolites:

The nitrile group is quite robust in most cases and is not readily metabolised. However, there is indirect evidence to indicate hepatic metabolism occurs due to the increased liver weight, centrilobular hepatocyte hypertrophy, increase liver enzymes such as alanine aminotransferase (ALAT) and increased hematopoiesis in the spleen identified in the repeated dose oral toxicity study. This could be associated with microsomal enzyme induction in the liver. In cases where metabolism occurs, hydrolysis, oxidation and conjugation with sulphate, glucuronides and glutathione is likely. The biotransformation of the parent compound is likely aided by the NADPH-dependent cytochrome P-450 monooxygenase system to cyanohydrin, which then spontaneously decomposes to hydrogen cyanide and its aldehyde derivative. The aldehyde derivative undergoes further hydrolysis and conjugation with sulphate, glucuronides and glutathione which is excreted in urine. The hydrogen cyanide/cyanide released is detoxified by conversion into thiocyanate by rhodanase. Evidence of released cyanide is demonstrated by the reduced mean corpuscular haemoglobin concentration (MCHC) and decreased haemoglobin distribution width (HDW), an indication of cyanide binding to haemoglobin in the blood. As a result, adaptive responses such as increasing hematopoiesis, elevated relative and absolute reticulocytes along with elevated H-reticulocytes are triggered to account for the reduction in blood haemoglobin. The effect is dose dependant, i.e. the higher the dose of the substance the higher the concentration of cyanide and reduction in blood haemoglobin.

Conclusions:

The substance possesses physicochemical properties which are favourable for ADME. Exposure by the oral and inhalation routes is more favourable with more limited bioavailability via dermal route exposure. This is supported by the acute oral adverse effects such as hunched posture, lethargy, ataxia, tiptoe gait, pilo-erection, decreased respiratory rate and laboured respiration during acute and sub-acute exposure. Hypothermia was noted prior to termination, abnormally red lungs and haemorrhage of the gastric mucosa, non-glandular region of the stomach and small and large intestines were noted in treated individuals in the acute oral toxicity test. Furthermore, lethargy, hunched posture, slow breathing, piloerection and ptosis. Macroscopic abnormalities were noted of the thymus (dark red/black-brown foci and/or pale/black-brown discoloration), jejunum, ileum, caecum and colon (contents black-brown discoloration), liver (pale discoloration) and/or spleen (reduced in size) in the acute inhalation toxicity test. No adverse systemic effects were observed in the following exposure via the dermal route. The low water solubility of 19 mg/L ensures slow absorption from the gut and respiratory tract. However, the n-octanol/water partition coefficient log Pow 3.93, molecular weight of 171.238 g/mol and nitrogen group being potentially ionisable under the acidic conditions prevalent in the stomach, would lead to the highest potential for absorption from the gastrointestinal (GI) tract resulting in rapid metabolism and elimination. Furthermore, the low molecular weight and n-octanol/water partition coefficient enhance absorption through the aqueous pores of pulmonary membranes (alveolar and capillary membranes). Systemic half-life of the substance is expected to be higher following absorption through pulmonary membranes. The substance is expected to undergo transformation to more polar metabolites with elimination via faeces and urine. Biotransformation and elimination are expected to be more rapid following oral exposure compared to inhalation route due to first past metabolism. At a high acute oral or inhalation dose, the substance is not well tolerated. This could be due to the potential binding of the substance to proteins in the GI and pulmonary tracts with potential release of cyanide which is associated with respiratory effects due to binding to the haemoglobin resulting in reduction of oxygen to tissues. Sub-acute exposure up to 600 mg/kg bw/day showed non-adverse effects, mainly associated with adaptive responses to xenobiotics. The effects were reversible in all recovery groups and there was no site-specific accumulation of the substance noted, no clinical signs related to the treatment and no effects of toxicological importance to humans. It was considered that this indicates no bioaccumulation potential of the substance. It can be concluded that the toxicokinetics of the substance do not pose significant toxicological concern through the evaluation of the available data.

Executive summary:

A desk-based assessment of the basic toxicokinetics of the substance, in accordance with Regulation (EC) 1907/2006: Annex VIII - Section 8.8.1. The substance possesses physicochemical properties which are favourable for ADME. Exposure by the oral and inhalation routes is more favourable with more limited bioavailability via dermal route exposure. This is supported by the acute oral adverse effects such as hunched posture, lethargy, ataxia, tiptoe gait, pilo-erection, decreased respiratory rate and laboured respiration during acute and sub-acute exposure. Hypothermia was noted prior to termination, abnormally red lungs and haemorrhage of the gastric mucosa, non-glandular region of the stomach and small and large intestines were noted in treated individuals in the acute oral toxicity test, OECD 420. Furthermore, lethargy, hunched posture, slow breathing, piloerection and ptosis. Macroscopic abnormalities were noted of the thymus (dark red/black-brown foci and/or pale/black-brown discoloration), jejunum, ileum, caecum and colon (contents black-brown discoloration), liver (pale discoloration) and/or spleen (reduced in size) in the acute inhalation toxicity test, OECD 403. No adverse systemic effects were observed in the following exposure via the dermal route as demonstrated in the OECD 404 and OECD 429. The low water solubility of 19 mg/L ensures slow absorption from the gut and respiratory tract. However, the n-octanol/water partition coefficient log Pow 3.93, molecular weight of 171.238 g/mol and nitrogen group being potentially ionisable under the acidic conditions prevalent in the stomach, would lead to the highest potential for absorption from the gastrointestinal (GI) tract resulting in rapid metabolism and elimination. Furthermore, the low molecular weight and n-octanol/water partition coefficient enhance absorption through the aqueous pores of pulmonary membranes (alveolar and capillary membranes). Systemic half-life of the substance is expected to be higher following absorption through pulmonary membranes. Based on the properties of the substance no significant bioaccumulation is expected. The substance is expected to undergo transformation to more polar metabolites with elimination via faeces and urine. Biotransformation and elimination are expected to be more rapid following oral exposure compared to inhalation route due to first past metabolism. At a high acute oral or inhalation dose, the substance is not well tolerated as demonstrated by mortalities in OECD 420 and OECD 403 at 2000 mg/kg bw and 5 mg/L, respectively. Clinical signs such as hunched posture, lethargy, ataxia, tiptoe gait, pilo-erection, decreased respiratory rate and laboured respiration with macroscopic abnormally noted in the lung and haemorrhage of the gastric mucosa within the gastrointestinal tract. This could be due to the potential binding of the substance to proteins in the GI and pulmonary tracts with potential release of cyanide which is associated with respiratory effects due to binding to the haemoglobin resulting in reduction of oxygen to tissues.Sub-acute exposure up to 600 mg/kg bw/day showed non-adverse effects, mainly associated with adaptive responses to xenobiotics. The effects were reversible in all recovery groups and there was no site-specific accumulation of the substance noted, no clinical signs related to the treatment and no effects of toxicological importance to humans. There were additionally no effects seen on sensory reactivity, grip strength or motor activity. Bodyweight and food consumption were also unaffected and there were no treatment-related ophthalmic lesions reported. Based on available data the substance can be considered to be acutely toxic via the oral route. The substance is expected to have the potential to cause skin sensitisation. Subacute exposure demonstrated non-adverse effects without target organ toxicity and all individuals demonstrated full recovery two weeks post exposure. This indicates no bioaccumulation potential of the substance. It can be concluded that the toxicokinetics of the substance do not pose significant toxicological concern through the evaluation of the available data.

Description of key information

Toxicokinetics Assessment: no bioaccumulation potential; desk-based assessment in accordance with Regulation (EC) 1907/2006: Annex VIII, Section 8.8.1, 2020

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

100

Absorption rate - inhalation (%):

100

Additional information

Basictoxicokinetics: expert assessment, 2020 : The substance possesses physicochemical properties which are favourable for ADME. Exposure by the oral and inhalation routes is more favourable with more limited bioavailability via dermal route exposure. This is supported by the acute oral adverse effects such as hunched posture, lethargy, ataxia, tiptoe gait, pilo-erection, decreased respiratory rate and laboured respiration during acute and sub-acute exposure. Hypothermia was noted prior to termination, abnormally red lungs and haemorrhage of the gastric mucosa, non-glandular region of the stomach and small and large intestines were noted in treated individuals in the acute oral toxicity test, OECD 420. Furthermore, lethargy, hunched posture, slow breathing, piloerection and ptosis. Macroscopic abnormalities were noted of the thymus (dark red/black-brown foci and/or pale/black-brown discoloration), jejunum, ileum, caecum and colon (contents black-brown discoloration), liver (pale discoloration) and/or spleen (reduced in size) in the acute inhalation toxicity test, OECD 403. No adverse systemic effects were observed in the following exposure via the dermal route as demonstrated in the OECD 404 and OECD 429. The low water solubility of 19 mg/L ensures slow absorption from the gut and respiratory tract. However, the n-octanol/water partition coefficient log Pow 3.93, molecular weight of 171.238 g/mol and nitrogen group being potentially ionisable under the acidic conditions prevalent in the stomach, would lead to the highest potential for absorption from the gastrointestinal (GI) tract resulting in rapid metabolism and elimination. Furthermore, the low molecular weight and n-octanol/water partition coefficient enhance absorption through the aqueous pores of pulmonary membranes (alveolar and capillary membranes). Systemic half-life of the substance is expected to be higher following absorption through pulmonary membranes. Based on the properties of the substance no significant bioaccumulation is expected. The substance is expected to undergo transformation to more polar metabolites with elimination via faeces and urine. Biotransformation and elimination are expected to be more rapid following oral exposure compared to inhalation route due to first past metabolism. At a high acute oral or inhalation dose, the substance is not well tolerated as demonstrated by mortalities in OECD 420 and OECD 403 at 2000 mg/kg bw and 5 mg/L, respectively. Clinical signs such as hunched posture, lethargy, ataxia, tiptoe gait, pilo-erection, decreased respiratory rate and laboured respiration with macroscopic abnormally noted in the lung and haemorrhage of the gastric mucosa within the gastrointestinal tract. This could be due to the potential binding of the substance to proteins in the GI and pulmonary tracts with potential release of cyanide which is associated with respiratory effects due to binding to the haemoglobin resulting in reduction of oxygen to tissues.Sub-acute exposure up to 600 mg/kg bw/day showed non-adverse effects, mainly associated with adaptive responses to xenobiotics. The effects were reversible in all recovery groups and there was no site-specific accumulation of the substance noted, no clinical signs related to the treatment and no effects of toxicological importance to humans. There were additionally no effects seen on sensory reactivity, grip strength or motor activity. Bodyweight and food consumption were also unaffected and there were no treatment-related ophthalmic lesions reported. Based on available data the substance can be considered to be acutely toxic via the oral route. The substance is expected to have the potential to cause skin sensitisation. Subacute exposure demonstrated non-adverse effects without target organ toxicity and all individuals demonstrated full recovery two weeks post exposure. This indicates no bioaccumulation potential of the substance. It can be concluded that the toxicokinetics of the substance do not pose significant toxicological concern through the evaluation of the available data.

 

References:

1. ECHA Guidance on Information Requirements and Chemical Safety Assessment (Chapter R.7c: Endpoint Specific Guidance, June 2017)