Oxalonitrile

Neurotoxicity

Description of key information

The central nervous system is the primary target of acute cyanide toxicity. Inhalation of hydrogen cyanide causes first short-time stimulation followed by depression, convulsions, unconsciousness and suppression of primary reflexes, dilatation of pupils, paralysis and even death.

Neurologic lesions attributed to subchronic cyanide poisoning in humans are similar to those described for experimental animals.

Neurological disorders (tremor, ataxia, cerebral cells injury) are observed in medium-term studies on laboratory animals with HCN concentration of 50 mg/m3 HCN and higher for several hours per day.

Delayed polyneuropathy studies:

The ethanedinitrile is not related to compounds causing polyneuropathy.A study of cassava food effect on polyneuropathy, shows no direct correlation to cyanide exposure and polyneuropathy. The study of Oluwole at al. (2002) shows that the occurrence of ataxic polyneuropathy is low in a community where exposure to cyanide is high. This suggests that exposure to cyanide is not a direct cause of ataxic polyneuropathy.

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Link to relevant study records

Reference

Endpoint:

neurotoxicity, other

Remarks:

Neurotoxicity of cyanides

Type of information:

not specified

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Neurotoxicity studies

Test	Tested organism	Concentration Dose	Result	Report References
180-day inhalation of ethanedinitrile	rhesus monkeys	11 or 25 ppm ethanedinitrile 6h/d, 5 d/w	No relevant changes in behaviour for 4.7 mg CN /kg bw (top dose)	Lewis et al. 1984
Oral exposure of KCN, 24 weeks, dosed daily	Miniature pigs	0 – 1.2 mg/kg bw	LOAEL 1.2 mg/kg bw, decrease of high energy demanding behaviour	Jackson 1988 as cited in WHO 2004
NaCN in capsules, 13-15 months	Dogs	0 – 4 mg/kg bw	Degenerative changes in ganglia, caused by acute hypoxia	Hertting et al. 1960 as cited in WHO 2004

Conclusions:

Cyanides
The central nervous system is the primary target of acute cyanide toxicity. Inhalation of hydrogen cyanide causes first short-time stimulation followed by depression, convulsions, unconsciousness and suppression of primary reflexes, dilatation of pupils, paralysis and even death.
Neurologic lesions attributed to repeated exposures to cyanides in humans are similar to those described for experimental animals. Clinical signs of acute neurotoxicity and corresponding histopathological findings in white matter of CNS were reported in repeated dose studies on animals administered cyanides by gavage, at daily dose of 1 mg/kg bw given in two portions. Studies that managed to avoid high peaks of blood cyanide level report much higher threshold doses. Neurological disorders (tremor, ataxia, cerebral cells injury) were observed in medium-term studies on laboratory animals with HCN concentration above 50 mg/m3for several hours per day, corresponding to daily doses of >12 mg/kg bw whereas even higher daily doses result in no effect if it is distributed over longer time interval.
Neurotoxicity findings in acute exposure to cyanides in laboratory animals are discussed in the acute toxicity section.
 
The central nervous system is an important target for cyanide toxicity in humans and animals following exposure by all three routes.
Experimental studies in animals exposed to hydrogen cyanide or cyanide compounds by the inhalation (Purser et al. 1984; Valade 1952), oral (Philbrick et al. 1979), or dermal routes (Ballantyne 1983b), have found neurological effects similar to those seen in humans. Behavioral changes were reported in pigs after oral exposure to potassium cyanide (Jackson 1988).
 
The effects of cyanide on behaviour were studied in fasted 25-week-old miniature pigs (12 litter mates: 5 females and 7 castrated males) randomized in four groups. The animals were dosed daily for 24 weeks with a single bolus of cyanide as aqueous potassium cyanide just prior to the daily feeding. The doses were 0, 0.4, 0.7, or 1.2 mg cyanide/kg body weight, chosen to be equivalent to those consumed by West Africans in their diet. Every 6 weeks, thyroid function (T3 and T4) and fasting blood glucose were measured, but not thyroid-stimulating hormone (TSH). Daily observations were made of clinical signs and various behavioural measurements, including social, antagonistic, exploratory, learning, feeding, and excretory behaviour. In all treatment groups, dose-related decreases were evident from week 6 in blood levels of T3 and T4, and an increase in fasting blood glucose was noted, particularly in top-dose animals. Statistical analysis was not provided for each dose group versus control, but changes in top-dose animals appeared significant by week 18; by week 24, decreases of 35% for T3 and 15% for T4 and an increase of 60% in fasting blood glucose were observed. Behavioural observations revealed a picture of decreased high energy-demanding behaviour, such as exploration and aggression, slower eating, more frequent drinking, and shivering consistent with the decreased thyroid activity. A LOAEL of 1.2 mg/kg body weight per day could be suggested from this study (Jackson 1988).
 
Dogs administered sodium cyanide in capsules at levels of 0, 0.5, 2, or 4 mg/kg body weight (one dog at each dose level) daily for 13–15 months showed severe signs of acute cyanide poisoning right after the daily dosing (the dog at the lowest dose died). In the autopsy, the only significant findings were degenerative changes in ganglia cells of the central nervous system, interpreted to be caused by multiple episodes of acute cerebral hypoxia (Hertting et al. 1960).
 
Potentiation to noise-induced hearing loss by exposure of rats to low concentrations of hydrogen cyanide was reported by Fechter et al. (2002). It was suggested that hydrogen cyanide (34 mg/m3for 3.5 h) plus noise produced impaired auditory function by producing significant oxidative stress in the cochlea. Hydrogen cyanide alone did not cause significant hearing loss or hair cell loss.
 
A single intraperitoneal dose and 25 repeated intraperitoneal doses of sodium cyanide (2 mg/kg body weight [1 mg cyanide/kg body weight]), stated to represent 25 % of the LD50, administered to Wistar strain albino rats resulted in similar reductions of memory (Tmaze test), along with reductions in the levels of dopamine and 5-hydroxytryptamine and increases in norepinephrine and epinephrine levels in the hippocampus, measured after a month of treatment (Mathangi and Namasivayam 2000).
 
In experiments with rats (Philbrick et al. 1979, Lessell 1971, Lessell 1974) cats, and monkeys (Ferraro, Hurst), selective destruction of white matter in the brain was a striking and consistent feature of poisoning from prolonged exposure to cyanide. In most of these experiments, animals were injected with increasing doses of sodium or potassium cyanide for up to 132days, and the doses used were high enough to cause significant death rates from acute toxicity. However, in the study (Philbrick et al. 1979), weanling rats exposed to low concentrations of potassium cyanide in feed had a marked decrease in weight gain, but no deaths or clinical signs of toxicity. Early necrosis of gray and white matter was a common occurrence in rats and monkeys, but repeated exposure appeared to selectively favor destruction of white matter. The histopathologic lesions observed in all species consisted of demyelination, especially of the optic nerve tracts and the corpus callosum. Swelling of astrocytes and myelin damage were apparent within 2 days in rats injected with sodium cyanide at doses sufficient to keep the rats comatose for 225 to 260 minutes (Lessell 1974). Axonal damage, with vacuolation and loss of microtubules, also occurred. Blindness was common in cyanide-treated animals and was considered to be a result of persistent anoxia in the brain.
 
Conclusion
The central nervous system is the primary target of acute cyanide toxicity. Inhalation of hydrogen cyanide causes first short-time stimulation followed by depression, convulsions, unconsciousness and suppression of primary reflexes, dilatation of pupils, paralysis and even death.
Neurologic lesions attributed to subchronic cyanide poisoning in humans are similar to those described for experimental animals.
Neurological disorders (tremor, ataxia, cerebral cells injury) are observed in medium-term studies on laboratory animals with HCN concentration of 50 mg/m3 HCN and higher for several hours per day.
 
Delayed polyneuropathy studies
The ethanedinitrile is not related to compounds causing polyneuropathy.A study of cassava food effect on polyneuropathy, shows no direct correlation to cyanide exposure and polyneuropathy. The study of Oluwole at al. (2002) shows that the occurrence of ataxic polyneuropathy is low in a community where exposure to cyanide is high. This suggests that exposure to cyanide is not a direct cause of ataxic polyneuropathy

Executive summary:

 

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Effect on neurotoxicity: via inhalation route

Link to relevant study records

Reference

Reference 1

Endpoint:

neurotoxicity: chronic inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

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

GLP compliance:

no

Specific details on test material used for the study:

ethanedinitrile 99%

Species:

other: Rhesus monkey, albino rats

Strain:

other: Macacca mulatta, Sprague-Dawley

Sex:

male

Route of administration:

inhalation: gas

Vehicle:

air

Details on analytical verification of doses or concentrations:

A 6-month (6 hr/day, 5 days/week) inhalation exposure was conducted with ethanedinitrile gas using male rhesus monkeys (Macacca mulatta) and male rats (SD). Fifteen monkeys and 90 rats were divided into three groups of 5 monkeys and 30 rats. One group, the Controls, was exposed to the air; the other two groups were exposed to ethanedinitrile concentrations of 11 or 25 ppm.

Duration of treatment / exposure:

180 days

Frequency of treatment:

6h/d, 5d/w

Dose / conc.:

0 ppm

Dose / conc.:

11 ppm

Remarks:

analytical 11.2 ±1.5 ppm

Dose / conc.:

25 ppm

Remarks:

analytical 25.3 ±3.3 ppm

No. of animals per sex per dose:

5 monkeys per treatment group
30 rats per treatment group

Control animals:

yes

Observations and clinical examinations performed and frequency:

Organ weights
lungs

Specific biochemical examinations:

Haematology
Parameters: hematocrit, haemoglobin concentration
number of animals: each monkey, 6 rats per exposure level
time points: monkey – 0 day, 30 days, 90 days, 180 days of exposure rats -2 days, 5 days, 30days, 90 days, 180 days of exposure

Clinical Chemistry
Parameters: T3 and T4
number of animals: each monkey, 6 rats per exposure level
time points: monkey – 0 day, 30 days, 90 days, 180 days of exposure rats -2 days, 5 days, 30days, 90 days, 180 days of exposure

Neurobehavioural examinations performed and frequency:

Behavioural testing
1 day per week for 12 monkeys, and 5 days per week for 3 monkeys (one in each of the groups)

Sacrifice and (histo)pathology:

Gross and histopathology
all dose groups (2 days of exposure and again 5 days, 1 months, 3 months, 180 days – rats; 11 monkeys were similarly sacrificed immediately after the termination of exposures, 3 monkeys – 4 weeks later)
organs: thyroid, liver, kidneys, spleen, heart, lungs, bone marrow, cerebellum, cerebrum

Other examinations:

ECG in monkeys before exposures and after the last exposure

Statistics:

ANOVA, non-parametric tests

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One (control) monkey died near the start of the exposures from causes unrelated to the experiment. 3 rats (control) died, 1 (11 ppm), 4 (25 ppm) – was not significantly different from change.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Mean body weights of rats exposed to ethanedinitrile at 25 ppm was significantly depressed compared to control.

Food efficiency:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

Haematology
No consistent effects

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

Clinical chemistry
No effects on T3 uptake and T4 concentration

Urinalysis findings:

not examined

Behaviour (functional findings):

effects observed, treatment-related

Description (incidence and severity):

Behavioural testing
There was an increase in response rate in all three groups during the exposure period compared to the baseline period. The mean increase was 20%, 14%, 145% in T-CO, T-11 and T-25 subjects, respectively. The rate changes for each group were evaluated statistically by mean of a randomization test for matched pair. The increase in response rate in the T-25 group was marginally significant. The probability that the rate increases in the T-CO and T-11 groups could have occurred by chance was greater than 0.10

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Description (incidence and severity):

No effects in rats; lungs from control monkeys contained more moisture than lungs from monkeys exposed to ethanedinitrile gas.

Neuropathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Conclusions:

Transient behavioural changes in monkeys but not in rats exposed for 6 months to 54 mg ethanedinitrile/m3 have been reported. The 6 months (6 h/day, 5 days/week) inhalation toxicity study was conducted with ethanedinitrile gas using male rhesus monkeys (Macacca mulatta) and male rats (SD) as experimental animals. Fifteen monkeys and 90 rats were divided into three groups of 5 monkeys and 30 rats. One group, the Controls, was not exposed to the test material; the other two groups were exposed to either 11 ppm (corresponding to 27 mg cyanide/m3) or 25 ppm ethanedinitrile (corresponding to 54 mg cyanide/m3). At the outset of exposures, there was a doubling of the rate of responding on a variable interval 2.9 min schedule of reinforcement in monkeys exposed to 25 ppm ethanedinitrile, and increases were also seen in the monkeys receiving 11 ppm exposures; the increases were transitory as the rate returned to control levels before exposures were terminated. At the end of the 6 months exposure, there were no effects in hematologic or clinical chemistry parameters attributable to the inhalation exposure to ethanedinitrile. The electrocardiograms and gross pathologic and histopathologic examinations of test animals were normal when compared with the Control animals. Total lung moisture content was significantly lower in monkeys exposed to either 11 ppm or 25 ppm ethanedinitrile than in Control animals. Body weights were significantly lower in rats exposed to 25 ppm than in Controls. The results suggest that subchronic 25 ppm ethanedinitrile exposures are marginally toxic, but the evidence on 11 ppm does not support a similar conclusion (Lewis et al. 1984).

Executive summary:

Transient behavioural changes in monkeys but not in rats exposed for 6 months to 54 mg ethanedinitrile/m3 have been reported. The 6 months (6 h/day, 5 days/week) inhalation toxicity study was conducted with ethanedinitrile gas using male rhesus monkeys (Macacca mulatta) and male rats (SD) as experimental animals. Fifteen monkeys and 90 rats were divided into three groups of 5 monkeys and 30 rats. One group, the Controls, was not exposed to the test material; the other two groups were exposed to either 11 ppm (corresponding to 27 mg cyanide/m3) or 25 ppm ethanedinitrile (corresponding to 54 mg cyanide/m3). At the outset of exposures, there was a doubling of the rate of responding on a variable interval 2.9 min schedule of reinforcement in monkeys exposed to 25 ppm ethanedinitrile, and increases were also seen in the monkeys receiving 11 ppm exposures; the increases were transitory as the rate returned to control levels before exposures were terminated. At the end of the 6 months exposure, there were no effects in hematologic or clinical chemistry parameters attributable to the inhalation exposure to ethanedinitrile. The electrocardiograms and gross pathologic and histopathologic examinations of test animals were normal when compared with the Control animals. Total lung moisture content was significantly lower in monkeys exposed to either 11 ppm or 25 ppm ethanedinitrile than in Control animals. Body weights were significantly lower in rats exposed to 25 ppm than in Controls. The results suggest that subchronic 25 ppm ethanedinitrile exposures are marginally toxic, but the evidence on 11 ppm does not support a similar conclusion.

Reference 2

Endpoint:

neurotoxicity, other

Remarks:

Neurotoxicity of cyanides

Type of information:

not specified

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Neurotoxicity studies

Test	Tested organism	Concentration Dose	Result	Report References
180-day inhalation of ethanedinitrile	rhesus monkeys	11 or 25 ppm ethanedinitrile 6h/d, 5 d/w	No relevant changes in behaviour for 4.7 mg CN /kg bw (top dose)	Lewis et al. 1984
Oral exposure of KCN, 24 weeks, dosed daily	Miniature pigs	0 – 1.2 mg/kg bw	LOAEL 1.2 mg/kg bw, decrease of high energy demanding behaviour	Jackson 1988 as cited in WHO 2004
NaCN in capsules, 13-15 months	Dogs	0 – 4 mg/kg bw	Degenerative changes in ganglia, caused by acute hypoxia	Hertting et al. 1960 as cited in WHO 2004

Conclusions:

Cyanides
The central nervous system is the primary target of acute cyanide toxicity. Inhalation of hydrogen cyanide causes first short-time stimulation followed by depression, convulsions, unconsciousness and suppression of primary reflexes, dilatation of pupils, paralysis and even death.
Neurologic lesions attributed to repeated exposures to cyanides in humans are similar to those described for experimental animals. Clinical signs of acute neurotoxicity and corresponding histopathological findings in white matter of CNS were reported in repeated dose studies on animals administered cyanides by gavage, at daily dose of 1 mg/kg bw given in two portions. Studies that managed to avoid high peaks of blood cyanide level report much higher threshold doses. Neurological disorders (tremor, ataxia, cerebral cells injury) were observed in medium-term studies on laboratory animals with HCN concentration above 50 mg/m3for several hours per day, corresponding to daily doses of >12 mg/kg bw whereas even higher daily doses result in no effect if it is distributed over longer time interval.
Neurotoxicity findings in acute exposure to cyanides in laboratory animals are discussed in the acute toxicity section.
 
The central nervous system is an important target for cyanide toxicity in humans and animals following exposure by all three routes.
Experimental studies in animals exposed to hydrogen cyanide or cyanide compounds by the inhalation (Purser et al. 1984; Valade 1952), oral (Philbrick et al. 1979), or dermal routes (Ballantyne 1983b), have found neurological effects similar to those seen in humans. Behavioral changes were reported in pigs after oral exposure to potassium cyanide (Jackson 1988).
 
The effects of cyanide on behaviour were studied in fasted 25-week-old miniature pigs (12 litter mates: 5 females and 7 castrated males) randomized in four groups. The animals were dosed daily for 24 weeks with a single bolus of cyanide as aqueous potassium cyanide just prior to the daily feeding. The doses were 0, 0.4, 0.7, or 1.2 mg cyanide/kg body weight, chosen to be equivalent to those consumed by West Africans in their diet. Every 6 weeks, thyroid function (T3 and T4) and fasting blood glucose were measured, but not thyroid-stimulating hormone (TSH). Daily observations were made of clinical signs and various behavioural measurements, including social, antagonistic, exploratory, learning, feeding, and excretory behaviour. In all treatment groups, dose-related decreases were evident from week 6 in blood levels of T3 and T4, and an increase in fasting blood glucose was noted, particularly in top-dose animals. Statistical analysis was not provided for each dose group versus control, but changes in top-dose animals appeared significant by week 18; by week 24, decreases of 35% for T3 and 15% for T4 and an increase of 60% in fasting blood glucose were observed. Behavioural observations revealed a picture of decreased high energy-demanding behaviour, such as exploration and aggression, slower eating, more frequent drinking, and shivering consistent with the decreased thyroid activity. A LOAEL of 1.2 mg/kg body weight per day could be suggested from this study (Jackson 1988).
 
Dogs administered sodium cyanide in capsules at levels of 0, 0.5, 2, or 4 mg/kg body weight (one dog at each dose level) daily for 13–15 months showed severe signs of acute cyanide poisoning right after the daily dosing (the dog at the lowest dose died). In the autopsy, the only significant findings were degenerative changes in ganglia cells of the central nervous system, interpreted to be caused by multiple episodes of acute cerebral hypoxia (Hertting et al. 1960).
 
Potentiation to noise-induced hearing loss by exposure of rats to low concentrations of hydrogen cyanide was reported by Fechter et al. (2002). It was suggested that hydrogen cyanide (34 mg/m3for 3.5 h) plus noise produced impaired auditory function by producing significant oxidative stress in the cochlea. Hydrogen cyanide alone did not cause significant hearing loss or hair cell loss.
 
A single intraperitoneal dose and 25 repeated intraperitoneal doses of sodium cyanide (2 mg/kg body weight [1 mg cyanide/kg body weight]), stated to represent 25 % of the LD50, administered to Wistar strain albino rats resulted in similar reductions of memory (Tmaze test), along with reductions in the levels of dopamine and 5-hydroxytryptamine and increases in norepinephrine and epinephrine levels in the hippocampus, measured after a month of treatment (Mathangi and Namasivayam 2000).
 
In experiments with rats (Philbrick et al. 1979, Lessell 1971, Lessell 1974) cats, and monkeys (Ferraro, Hurst), selective destruction of white matter in the brain was a striking and consistent feature of poisoning from prolonged exposure to cyanide. In most of these experiments, animals were injected with increasing doses of sodium or potassium cyanide for up to 132days, and the doses used were high enough to cause significant death rates from acute toxicity. However, in the study (Philbrick et al. 1979), weanling rats exposed to low concentrations of potassium cyanide in feed had a marked decrease in weight gain, but no deaths or clinical signs of toxicity. Early necrosis of gray and white matter was a common occurrence in rats and monkeys, but repeated exposure appeared to selectively favor destruction of white matter. The histopathologic lesions observed in all species consisted of demyelination, especially of the optic nerve tracts and the corpus callosum. Swelling of astrocytes and myelin damage were apparent within 2 days in rats injected with sodium cyanide at doses sufficient to keep the rats comatose for 225 to 260 minutes (Lessell 1974). Axonal damage, with vacuolation and loss of microtubules, also occurred. Blindness was common in cyanide-treated animals and was considered to be a result of persistent anoxia in the brain.
 
Conclusion
The central nervous system is the primary target of acute cyanide toxicity. Inhalation of hydrogen cyanide causes first short-time stimulation followed by depression, convulsions, unconsciousness and suppression of primary reflexes, dilatation of pupils, paralysis and even death.
Neurologic lesions attributed to subchronic cyanide poisoning in humans are similar to those described for experimental animals.
Neurological disorders (tremor, ataxia, cerebral cells injury) are observed in medium-term studies on laboratory animals with HCN concentration of 50 mg/m3 HCN and higher for several hours per day.
 
Delayed polyneuropathy studies
The ethanedinitrile is not related to compounds causing polyneuropathy.A study of cassava food effect on polyneuropathy, shows no direct correlation to cyanide exposure and polyneuropathy. The study of Oluwole at al. (2002) shows that the occurrence of ataxic polyneuropathy is low in a community where exposure to cyanide is high. This suggests that exposure to cyanide is not a direct cause of ataxic polyneuropathy

Executive summary:

 

Additional information

Neurotoxicity studies:

Test	Tested organism	Concentration Dose	Result	Report References
180-day inhalation of ethanedinitrile	rhesus monkeys	11 or 25 ppm ethanedinitrile 6h/d, 5 d/w	No relevant changes in behaviour for 4.7 mg CN /kg bw (top dose)	Lewis et al. 1984
Oral exposure of KCN, 24 weeks, dosed daily	Miniature pigs	0 – 1.2 mg/kg bw	LOAEL 1.2 mg/kg bw, decrease of high energy demanding behaviour	Jackson 1988 as cited in WHO 2004
NaCN in capsules, 13-15 months	Dogs	0 – 4 mg/kg bw	Degenerative changes in ganglia, caused by acute hypoxia	Hertting et al. 1960 as cited in WHO 2004

Justification for classification or non-classification

CLP criteria not met