Lithium amide

Repeated dose toxicity: oral

Administrative data

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

HYPOTHESIS FOR THE ANALOGUE APPROACH
Lithium amide completely highly reacts with water and dissociates forming lithium hydroxide and ammonium. Thus, lithium salts with different anion moieties and ammonium compounds were found to be suitable candidates for read-across. (Eco)toxicological properties were extrapolated to different endpoints by using the lowest effect concentration.
For further information, please refer to the read-across justification in IUCLID, section 13.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Expert statement

Qualifier:

no guideline followed

Principles of method if other than guideline:

Expert statement on chronic exposure.

GLP compliance:

no

Key result

Dose descriptor:

NOAEL

Effect level:

1.2 mg/kg bw/day (nominal)

Based on:

other: NOAEL Lithium

Sex:

male/female

Basis for effect level:

other: NOAEL refers to lithium in human

Key result

Critical effects observed:

no

Conclusions:

Based on human data obtained from routine long-term treatment of bipolar disorder with lithium (administered as lithium carbonate), a NOAEL for long-term oral toxicity of 1.2 mg lithium/kg bw/ day was calculated. Based on these data, a NOAEL value of 4 mg/kg bw/day was calculated for lithium amide.

Executive summary:

No NOAEL/ DNEL/ ADI value was available for lithium amide due to the high reactivity of the substance when moistured. Nevertheless, NOAEL/ DNEL/ ADI values from human data are available for lithium (see below). Furthermore NOAEL values derived from animal data for ammonium sulfate are available. Thereof, NOAEL values based on animal and human data could be derived and calculated for lithium amide (see below).

Determination of Li NOAEL oral 

In humans, lithium has been used for decades in psychiatric therapy for the treatment of bipolar disorder. In case of long-term treatment, the recommended dose is 450 to 900 mg/day lithium carbonate, equivalent to 84 to 169 mg lithium / day, and corresponding to a desired sustained therapeutic serum concentration of 0.5 to 1.0 mmol lithium/L. Based on experience with long-term application e.g. lithium carbonate for therapy in humans, there is no evidence that lithium is of concern with respect to repeated oral toxicity at medical doses as the ones indicated above.

The effect level (NOAEL) determined for lithium for repeated dose toxicity by the oral route is based on human data and can be calculated in two ways that complete one another:

One option is based on the therapeutic serum concentrations of 0.5 to 1.0 mmol lithium/L and the extracellular fluid (ECF) volume. Lithium has a large volume of distribution of 0.6-0.9 L/kg (42 L – 63 L for a 70 kg adult). It is distributed throughout the body water both extra and intracellularly. Lithium shifts into the intracellular compartments of cells because of its large volume of distribution. Although in long-term use, the intracellular concentration increases, the intracellular concentration is not reflected by the plasma level which measures only the extracellular fluid concentration. Therefore, a desired concentration of 1 mmol/L of lithium is expected to be sustained and reflected in the extracellular fluid (ECF) only and not in the intracellular fluid. Thus, the volume considered is of the ECF only which comprises of plasma, interstitial fluid (spaces between cells) and transcellular fluid (lymph, cerebrospinal fluid, synovial fluid, serous fluid, gastrointestinal secretions) and is typically 15 L (reported in different references to be between 14 – 19 L (for 70 kg adult)). Based on this data the derived NOAEL (considering a lithium concentration of 1mmol/L and an ECF volume of 15 L) is 1.5 mg/kg bw/day. This NOAEL value can be considered as a conservative value as it is based on a bioavailable dose in humans after absorption and on a smaller volume than its actual distribution volume.

Another way to calculate NOAEL oral for lithium is based as well on data taken from the routine long-term treatment of bipolar disorder. Instead of calculating the NOAEL from the therapeutic serum concentration of lithium, the lithium NOAEL oral can be calculated from the administered oral dose for long-term treatment of bipolar disorder as detailed above: 84 to 169 mg lithium / day (corresponding to the desired sustained concentrations of 0.5 - 1 mmol lithium/L in blood/serum). When dividing the oral doses (84 to 169 mg lithium / day) to 70 kg, the following values are obtained respectively: 1.2 to 2.4 mg/kg bw/day or when dividing to 60 kg the following values are obtained respectively: 1.4 to 2.8 mg/kg bw/day, representing the optional NOAEL values for lithium for the oral route.

In both ways of calculation, the values obtained are in same order of magnitude and similar to one another. As a worst–case value, a NOAEL repeated dose toxicity oral of 1.2 mg lithium/kg bw was chosen. Further, this value could be used as a starting value for route-to-route extrapolation in calculation of the repeated dose toxicity for the dermal and inhalation routes.

Derived NOAEL value for lithium amide

As detailed above, for calculation of the NOAEL long-term oral of lithium amide the following (human) data was available: the NOAEL/DNEL of lithium (1.2 mg lithium/kg bw/day). Additionally, the molecular weights of lithium and lithium amide were considered.

A NOAEL oral of lithium amide of 4 mg/kg bw/day has been calculated based on the NOAEL of lithium.

Cross-reference 2

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

no data

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

no

Principles of method if other than guideline:

In this study, the chronic toxicity (52-week oral feeding) and carcinogenicity (104-week oral feeding) was investigated.

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Yoneyama Kagaku Kogyo (Osaka Japan)
- Age at study initiation: 5 weeks
- Housing: groupwise (three or four rats per cage)
- Diet: ad libitum
- Water: Tap water ad libitum
- Acclimation period: 1 week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 24 ± 1
- Humidity (%): 55 ± 5
- Air changes (per hr): 18
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Recapture rates for ammonium sulfate from the admixed diet at each concentration level were confirmed to be 95.4 - 98.7 %.

Duration of treatment / exposure:

52 and 104 weeks

Frequency of treatment:

continuously in the diet

Dose / conc.:

42 mg/kg bw/day (actual dose received)

Remarks:

males (0.1% in diet)

Dose / conc.:

256 mg/kg bw/day (actual dose received)

Remarks:

males (0.6 % in diet)

Dose / conc.:

1 527 mg/kg bw/day (actual dose received)

Remarks:

males (3% in diet)

Dose / conc.:

48 mg/kg bw/day (actual dose received)

Remarks:

females (0.1% in diet)

Dose / conc.:

284 mg/kg bw/day (actual dose received)

Remarks:

females (0.6% in diet)

Dose / conc.:

1 490 mg/kg bw/day (actual dose received)

Remarks:

females (3% in diet)

Dose / conc.:

564.1 mg/kg bw/day (actual dose received)

Remarks:

males (1.5% in diet)

Dose / conc.:

1 288.2 mg/kg bw/day (actual dose received)

Remarks:

males (3% in diet)

Dose / conc.:

649.9 mg/kg bw/day (actual dose received)

Remarks:

females (1.5% in diet)

Dose / conc.:

1 371.4 mg/kg bw/day (actual dose received)

Remarks:

females (3% in diet)

No. of animals per sex per dose:

Chronic toxicity study: 10/sex
Carcinogenicity study: 50/sex

Control animals:

yes, plain diet

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: every 2 weeks until week 10 and every 5 weeks thereafter.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

OPHTHALMOSCOPIC EXAMINATION: No data

HAEMATOLOGY: Yes
- Time schedule for collection of blood: 52 weeks
- Anaesthetic used for blood collection: Yes: ether
- Animals fasted: Yes: overnight
- How many animals: 10
- Parameters checked: red blood cell count (RBC), hemoglobin concentration (Hb), hematocrit (Ht), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), platelet count (Plt) and white blood cell count (WBC). Differential leukocyte counts and the reticulocyte count (Ebl).

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: 52 weeks
- Animals fasted: Yes: overnight
- How many animals: 10
- Parameters checked: total protein (TP), albumin (Alb), albumin/globulin ratio (AIG), total bilirubin (T-bil), total cholesterol (T-Cho), triglyceride (TG), blood urea nitrogen (BUN), creatinine (Cre), calcium (Ca), inorganic phosphorus (IP), sodium (Na), potassium (K), chloride Cl), aspartate transaminase (AsT), alanine transaminase (AlT), alkaline phosphatase (ALP) and gamma-glutamyl transpeptidase (gamma-GTP)

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes
Brain, lungs, heart, spleen, liver, adrenals, kidneys and testes were weighed. As for adrenals, kidneys and testes, weights of each side were separately recorded and the total of both sides was used for calculation of group mean and SD values.
In addition to these organs, the nasal cavity, trachea, aorta, pituitary, thyroids, parathyroids, salivary glands, tongue, esophagus, stomach, duodenum, jejunum, ileum, caecum, colon, rectum, pancreas, urinary bladder, epididymides, prostate, seminal vesicles, ovaries, uterus, vagina, mammary glands, skin, mesenteric and submandibular lymph nodes, thymus, sternum, femur including bone marrow, sciatic nerve, trigeminal nerve, spinal cord (cervical, thoracic and lumber cords), eye, Harderian gland and thigh muscle. All organs and tissues in the control and 3.0% group animals were histopathologically examined. Additionally, macroscopically abnormal sites in the 0.1% and 0.6% group animals in the chronic study and all organs and tissues of the 1.5% animals in the carcinogenicity study were also histopathologically examined.

Statistics:

Variance in data for body weights, hematology, serum biochemistry and organ weights were checked for homogeneity by Bartlett test. When the data were homogeneous, one-way analysis of variance (ANOVA) was used. In the heterogeneous cases, the Kruskal-Wallis test was applied. When statistically significant differences were indicated, Dunnett's multiple test was employed for comparison between control and treated groups. Final survival rates and the incidences of tumor and non-neoplastic lesions were compared with the Fisher's exact probability test or the Mann-Whitney's U-test.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

effects observed, non-treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY
In the chronic toxicity study, no mortality was found in any groups throughout the treatment period.
In the carcinogenicity study, the survival rate of control, 1.5% and 3.0% groups were 88%, 78% and 76%, respectively, for males, and 76%, 80% and 80%, respectively, for females, and no significant differences were observed among the groups.

BODY WEIGHT AND WEIGHT GAIN
No test substance-related change in the body weights was found.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study)
A tendency for increase of food intake in the male 3.0% group in the chronic toxicity study was noted.

HAEMATOLOGY
No significant variation was found.

CLINICAL CHEMISTRY
No dose related alteration was found.

ORGAN WEIGHTS
Absolute and relative kidney weights were increased or showed a tendency for increase at 3.0% in both sexes in the chronic toxicity study. Absolute spleen weights were decreased and relative liver weights were increased in the 3.0% male dose group. No dose-related changes were found in the other organs.

GROSS PATHOLOGY
There were no obvious macroscopic findings in any group in either the chronic toxicity or carcinogenicity studies, except for massive, nodular or focal lesions suggesting neoplastic change in the carcinogenicity study.

HISTOPATHOLOGY:
In the carcinogenicity study, non-neoplastic and neoplastic lesions were noted in the control and treatment groups, with no significant inter-group difference in their incidences or severity.

Key result

Dose descriptor:

NOAEL

Effect level:

256 mg/kg bw/day (actual dose received)

Sex:

male

Basis for effect level:

other: 0.6% in the diet

Key result

Dose descriptor:

NOAEL

Effect level:

284 mg/kg bw/day (actual dose received)

Sex:

female

Basis for effect level:

other: 0.6% in the diet

Key result

Critical effects observed:

no

Organ weight of male rats fed diet containing ammonium sulfate for 52 weeks (Chronic toxicity study).

	control	0.1%	0.6%	3.0%
Body weight (g)	410.9 ± 12.3	428.6 ± 17.6	416.7 ± 23.7	400.5 ± 15.1
Brain (g)	2.04 ± 0.05	2.03 ± 0.07	2.05 ± 0.05	2.04 ± 0.05
Lungs (g)	1.20 ± 0.09	1.23 ± 0.21	1.16 ± 0.07	1.13 ± 0.06
Heart (g)	1.09 ± 0.08	1.10 ± 0.07	1.08 ± 0.05	1.08 ± 0.07
Spleen (g)	0.73 ± 0.05	0.72 ± 0.04	0.83 ± 0.36	0.68 ± 0.04 *
Liver (g)	9.62 ± 0.58	9.92 ± 0.73	10.26 ± 0.63	10.0 ± 0.85
Adrenals (g)	0.03 ± 0.01	0.04 ± 0.01	0.04 ± 0.00	0.04 ± 0.00
Kidneys (g)	2.35 ± 0.25	2.32 ± 0.11	2.42 ± 0.11	2.51 ± 0.11 *
Testes (g)	3.38 ± 0.17	3.27 ± 0.11	3.25 ± 0.25	3.29 ± 0.14

Organ weight of female rats fed diet containing ammonium sulfate for 52 weeks (Chronic toxicity study).

	control	0.1%	0.6%	3.0%
Body weight (g)	207.4 ± 13.49	220.3 ± 8.68	219.2 ± 13.62	212.7 ± 24.39
Brain (g)	1.86 ± 0.04	1.83 ± 0.04	1.83 ± 0.05	1.82 ± 0.05
Lungs (g)	0.82 ± 0.06	0.79 ± 0.10	0.83 ± 0.12	0.79 ± 0.05
Heart (g)	0.65 ± 0.05	0.67 ± 0.05	0.70 ± 0.03	0.67 ± 0.05
Spleen (g)	0.44 ± 0.04	0.44 ± 0.02	0.45 ± 0.03	0.45 ± 0.07
Liver (g)	4.44 ± 0.26	4.66 ± 0.35	4.69 ± 0.40	4.89 ± 0.42
Adrenals (g)	0.04 ± 0.00	0.04 ± 0.01	0.04 ± 0.01	0.04 ± 0.01
Kidneys (g)	1.25 ± 0.07	1.35 ± 0.08 *	1.35 ± 0.09	1.39 ± 0.08 **

* Significantly different from the control at p<0.05. **Significantly different from the control at p<0.01.

Conclusions:

Based on the observed organ weight changes in kidney and liver, the NOAEL was estimated to be 0.6 %, which equals 256 and 284 mg/kg bw/d for male and female animals, respectively.

Executive summary:

A chronic oral toxicity and carcinogenicity study was conducted in rats, similar to the requirements of OECD TG 453. In the subchronic part of the study, groups of 10 rats/sex were fed a diet containing the test substance (purity not given) at concentrations of 0, 0.1, 0.6, or 3 % for 1 year. These concentrations corresponded to average daily intakes of 0, 42, 256, and 1527 mg/kg bw/d for males and 0, 48, 248, and 1490 mg/kg bw/d for females, respectively. For investigation of the carcinogenic potential, groups of 50 rats/sex were fed a diet containing the test substance (purity not given) at concentrations of 0, 1.5, or 3 % for 2 years. These concentrations corresponded to average daily intakes of 0, 465.1, and 1288.2 mg/kg bw/d for males and 0, 649.9, and 1371.4 mg/kg bw/d for females respectively.

Absolute and relative kidney weights were increased at the high dose level for both sexes. Absolute spleen weights were decreased and relative liver weights were increased in high dose males. No macroscopic changes were recorded by gross pathology, except for massive nodular or focal lesions suggesting neoplastic changes. At histopathological examination, non-neoplastic and neoplastic lesions were noted in the control and treatment groups, with no significant inter-group difference in their incidences or severity.

The authors concluded that the no observed adverse effect level of ammonium sulfate was the 0.6 % diet, which is equivalent to 256 and 284 mg/kg bw/d in males and females, respectively, and the compound is noncarcinogenic under the conditions of the study. There was no evidence of a long-term carcinogenic activity of the test substance. (Ota et al., 2006)

Materials and methods

Test material

Test material information

Constituent 1

Reference substance name:

Lithium amide

EC Number:

231-968-4

EC Name:

Lithium amide

Cas Number:

7782-89-0

Molecular formula:

H2LiN

IUPAC Name:

lithium amide

Test material form:

solid

Results and discussion

Effect levels

1

Key result

Dose descriptor:

NOAEL

Effect level:

4 mg/kg bw/day (nominal)

Based on:

other: recalculated for lithium amide

Sex:

male/female

Remarks on result:

other: Based on lithium (human data)

2

Key result

Dose descriptor:

NOAEL

Effect level:

104 mg/kg bw/day (nominal)

Based on:

other: recalculated for lithium amide

Sex:

male

Basis for effect level:

organ weights and organ / body weight ratios

Remarks on result:

other: Based on (NH4)2SO4 (Ota et al., 2006)

3

Key result

Dose descriptor:

NOAEL

Effect level:

111 mg/kg bw/day (nominal)

Based on:

other: recalculated for lithium amide

Sex:

female

Basis for effect level:

organ weights and organ / body weight ratios

Remarks on result:

other: Based on (NH4)2SO4 (Ota et al. 2006)

Target system / organ toxicity

Key result

Critical effects observed:

no