Dimethylamine

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1982

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: acceptable well-documented publication, which meets basic scientific principles

Data source

Reference

Reference Type:

publication

Title:

Toxicity of nitrite and dimethylamine in rats

Author:

Darad, R., Kumar De, A., and Aiyar, A.S.

Year:

1983

Bibliographic source:

Toxicology Letters, 17 (1983) 125-130

Materials and methods

Principles of method if other than guideline:

Rats are fed nitrite and/or DMA, and the influence on microsomal lipoperoxidation, enzyme activities of acid phosphatase and cathepsin as lysosomal enzymes as well as the enzyme activity of superoxide dismutase (SOD) are evaluated.

GLP compliance:

no

Limit test:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Dimethylamine

EC Number:

204-697-4

EC Name:

Dimethylamine

Cas Number:

124-40-3

Molecular formula:

C2H7N

IUPAC Name:

N-methylmethanamine

Details on test material:

- Name of test material (as cited in study report): dimethylamine
- Substance type: amine
- Analytical purity: no data, beside that DMA gave only one peak in HPLC and was used without any further purification
- Impurities (identity and concentrations): no data
- Composition of test material, percentage of components: DMA in drinking water (0.2 %)

Test animals

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

weanling male Wistar strain rats maintained on a laboratory stock diet composed of: Bengal gram (Cicer arietinum) 20%) wheat 70%) fish meal 5 %, yeast powder 4%) shark liver oil 0.25 % and purified vegetable oil 0.75%.

Administration / exposure

Route of administration:

oral: drinking water

Vehicle:

water

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

9 month

Frequency of treatment:

ad libitum

Doses / concentrations

Dose / conc.:

0.2 other: %

Remarks:

nominal in water

No. of animals per sex per dose:

30 males per group, 6 groups
one group with sodium nitrite, one with DMA, one with sodium nitrite and DMA, one with 0.5 % BHT, one with 0.5 %v BHT, sodium nitrite and MDA, one control. (BHT significates: butylated hydroxtoluene)

Control animals:

yes, concurrent no treatment

Details on study design:

Administration through the drinking water: nitrite (0.2%) and dimethylamine (DMA) (0.2 %), either singly or in combination for 9 month.

Examinations

Observations and examinations performed and frequency:

no data

Sacrifice and pathology:

after 9 month killed by decapitation,
collection of the livers (cleaned and placed in suitable ice-cold media)

Other examinations:

For the study of in vitro microsomal lipoperoxidation, the livers were homogenised in 8 ~01s. of 50 mM Tris-maleate buffer (pH 6.5) containing 155 mM NaCl, and the microsomes isolated by differential centrifugation. Malondialdehyde formation was followed by the thiobarbituric acid method. Acid phosphatase and cathepsin in 10% liver homogenate were assayed in acetate buffers at pH 5.0 and 3.8, respectively. Bound activities of these enzymes were measured by including 0.1 ml of 0.25% Triton X-100 in the incubation media. For SOD activity, 10% liver homogenate was made in 0.25 M sucrose, and mitochondria and post-mitochondrial supernatant were separated at 20000 x g. The enzyme activity of both these fractions was estimated by the pyrogallol method.

Statistics:

no data

Results and discussion

Results of examinations

Clinical signs:

not specified

Mortality:

not specified

Body weight and weight changes:

not specified

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

increased lipoperoxidation, increased cytosolic superoxide dismutase, increased freee activity of acid phosphatase and cathepsin

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

not specified

Details on results:

Nitrite and DMA, individually, cause significantly higher hepatic microsomal peroxidation.
However, when fed together, the two chemicals do not elicit such a response and the lipoperoxidative values of these animals are similar to those of the control.
In the DMA-administered rats the free activities of acid phosphatase and cathepsin were both increased, the increase in cathepsin being more marked.
The administration of nitrite or DMA appears to decrease the total activity of both the lysosomal enzymes.
The results on SOD (superoxide dismutase) activities (Table III) of both the mitochondrial and the postmitochondrial fractions show that nitrite, both singly and in combination with DMA, significantly enhances the level of the enzyme in the supernatant. DMA alone, however, does not have any effect on SOD activity.
Rats administered nitrite and DMA are significantly protected against the increase in the enzyme activity, when their diet is supplemented with BHT (butylated hydroxtoIuene).

Effect levels

Basis for effect level:

other: The results indicate that nitrite and DMA may induce toxicity through some free radical reactions and that BHT can provide some protection.

Remarks on result:

not measured/tested

Remarks:

Effect level not specified

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

The increase in lipoperoxidation may result in membrane damage and is further indicated by the labilisation of lysosomal enzymes.

The increased levels of the cytosolic SOD (superoxide dismutase) due to the administration of nitrite or DMA may indicate a higher generation of the superoxide radicals.

Nitrite, as well as DMA, caused higher in vitro lipoperoxidation, free lysosomal enzyme activities and cytosolic superoxide dismutase activity in liver. Some of these increases viz., the enzyme activities in liver, were counteracted to a significant extent in the rats receiving a dietary supplement of BHT (butylated hydroxytoluene). The results indicate that nitrite and DMA may induce toxicity through some free radical reactions and that BHT can provide some protection.

Nitrite and DMA, individually, cause significantly higher peroxidation. However, when fed together, the two chemicals do not elicit such a response and the lipoperox idative values of these animals are similar to those of the control.

In the nitrite-administered animals, the free activities of acid phosphatase and cathepsin were both increased, the change in acid phosphatase being statistically significant. In the DMA-administered rats a similar trend in both the enzymes is seen, the increase in cathepsin being more marked

Applicant's summary and conclusion

Conclusions:

Many of the parameters examined in the present studies are indicative of a free radical-mediated damage to the cellular and subcellular membrane in rats administered nitrite and/or DMA.

Executive summary:

The administration of nitrite or DMA appears to decrease the total activity of both the lysosomal enzymes.

In animals fed both nitrite and dimethylamine, the proportion of the free activity of both the enzymes is increased, in spite of a significant reduction in total activity. In these animals, BHT feeding affords marked protection and the increase in the percentage of free activities is restored to control levels.

Nitrite, both singly and in combination with DMA, significantly enhances the level of the enzyme in the supernatant. DMA alone, however, does not have any effect on SOD (superoxide dismutase) activity.

Likewise, rats administered nitrite and DMA are significantly protected against the increase in the enzyme activity, when their diet is supplemented with BHT (butylated hydroxytoluene).

The increased levels of the cytosolic SOD due to the administration of nitrite or DMA may indicate a higher generation of the superoxide radicals. The oxidation of haemoglobin by nitrite has been reported to involve the superoxide radicals.