2,2'-iminodiethanol

Carcinogenicity

Description of key information

DEA formulated in ethanol showed no oncogenic potential in the rat after unoccluded daily dermal exposure for 2 years. In the dermal mouse carcinogenicity study there was an increased incidence of liver neoplasms in males and females at all doses tested and increased incidences of renal tubule adenomas in males at the high dose level only. Mechanistic research specifically on DEA indicates that, to the extent DEA can potentially induce tumours in mice, it does so by a mechanism that is not relevant to humans. Therefore, based on the available data, DEA is not considered carcinogenic for humans.

Justification for classification or non-classification

Based on the available data, DEA does not need to be classified for carcinogenicity according to Annex I of Directive 67/548/EEC and according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.

Additional information

In rats, ethanolic DEA solutions were dermally applied to 50 male and 50 female F344 rats at dose levels of 0, 16, 32, 64 mg/kg bw/day in males or 0, 8, 16, 32 mg/kg bw/day in females for 5 days per week during a period of 103 weeks. The survival of dosed male and female rats was not affected. Mean body weights of the high dose males (64 mg/kg bw/day) were less than those of the vehicle controls during weeks 8 – 89, while the top dose females (32 mg/kg bw/day) revealed body weight reductions after week 97. DEA led to skin irritation (acanthosis, hyperkeratosis, exudation) predominantly at doses of 32 mg/kg bw/day and above at the site of application. In the kidney the incidences and severities of nephropathy in dosed female groups were significantly greater than those in the vehicle controls, DEA was not carcinogenic in this study and the NOAEL for local irritation was 16 mg/kg bw/day and 32 mg/kg bw/day for systemic toxicity in males. In females the LOAEL was 8 mg/kg bw/day for local irritation and systemic toxicity (National Toxicology Program, 1999).

 

In the mouse oncogenicity study (B6C3F1), the test conditions were similar. Fifty animals per dose group and gender received topically ethanolic DEA solutions of 0, 40, 80 and 160 mg/kg bw/day, 5 times/week for 103 weeks. Survival of dosed female mice was reduced (44/50, 33/50, 33/50; 23/50 for the control, low-, mid- and high-dose groups, respectively). This was attributed to liver neoplasms observed, while there was no effect on survival in males. The mean body weights of the mid/high-dose males were lower at ≥ weeks 88/77, respectively. The mean body weights of the low- and mid-dose females were reduced from week 73 onwards, those of the high-dose females at ≥ week 53. In male mice, the incidences of hepatocellular adenoma and of hepatocellular adenoma and carcinoma (combined) were significantly increased in all dosed groups, while the incidences of hepatoblastoma showed an increase in the mid- and high-dose groups. In the female mice, the incidences of hepatocellular neoplasms were significantly higher in all treated groups compared to the control. Non-neoplastic lesions were seen only in the liver of all dosed male and female mice and consisted of cytoplasmic alteration, characterized by mild to moderate enlargement of centrilobular hepatocytes, and syncytial alteration, characterized by scattered hepatocytes with three or more small nuclei. The incidences of renal tubule adenoma in males occurred with a positive trend; but the incidences of carcinoma and hyperplasia did not follow this pattern. An extended evaluation of kidney step sections revealed additional adenomas and hyperplasias in all dosed groups. The combined analysis of single and step sections indicated a dose-related increase in the incidences of renal tubule hyperplasia and renal tubule adenoma or carcinoma (combined), and an increase in the incidences of renal tubule adenoma in male mice. Incidences of thyroid gland follicular cell hyperplasia were increased in dosed male and female mice compared to vehicle controls. Hyperkeratosis, acanthosis, and exudate were treatment-related changes in the skin at the site of application and the LOAEL for local and systemic effects was 40 mg/kg bw/day (National Toxicology Program, 1999).

 

The liver tumours in mice in the NTP study (1999) were considered to be directly related to the observed increase in the cellular proliferation rate, which is due to the observed enzyme induction, weak peroxisome proliferation and choline depletion with subsequent disturbance of its metabolism. While nitrosamine formation has been highlighted as a matter of concern for DEA, and for this reason it has been banned for use in cosmetics in the EU, nitrosamine formation was ruled out under the conditions of this study. Benign kidney tumours (adenomas) were only observed in male mice at the high dose level at a low incidence, when using serial sections. Based on the increased S-phase synthesis observed in this organ, it is conceivable that a similar non-genotoxic mode of action involving choline deficiency is responsible for the renal tubular adenomas.

 

In short term tests on carcinogenicity, DEA was not carcinogenic, when tested in the Tg.AC transgenic mouse model up to topical dose levels exceeding the MTD (Spalding et al, 2000).

 

Various mechanistic in vitro and in vivo studies identified that DEA induced choline depletion is the key event in the toxic mode of action. The major results are summarised briefly in this section, the studies are described in detail in section 7.9.3.

DEA decreased gap junctional intracellular communication in primary cultured mouse and rat hepatocytes, but all these events were prevented with choline supplementation. DNA hypomethylation was observed in mouse hepatocytes as a further epigenetic mechanism involved in liver tumourigenesis.

DEA decreased phosphatidylcholine synthesis by blocking the cellular uptake of choline in vitro, but these events did not occur in the presence of excess choline.

DEA increased S-phase DNA synthesis in mouse hepatocytes but had no effect on apoptosis. No such effects were noted in human hepatocytesin vitro. Apparent differences in the susceptibility of two different mice strains (B6C3F1 > C57BL) were noted. B6C3F1 mice are extremely sensitive to non-genotoxic effects and are known to possess a relatively high incidence of spontaneous liver tumours. Moreover, chronic stimulation and compensatory adaptive changes of hepatocyte hypertrophy and proliferation are able to enhance the incidence of common spontaneous liver tumours in the mouse by mechanisms not relevant to humans.

Analysis of gene expressions in animal studies showed an increase in genes associated with cell proliferation, while a decrease in genetic processes relevant for apoptotic mechanisms was observed.

In conclusion, mechanistic research specifically on DEA indicates that, to the extent DEA can potentially induce tumours in mice, it does so by a mechanism that is not relevant to humans. Therefore, based on the available data, DEA is not considered carcinogenic for humans.