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Carcinogenicity

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No increase in tumour incidence was observed in rats treated dermally or orally with TEA for 2 years, nor in mice exposed to TEA by oral administration for 2 years. In a dermal mouse carcinogenicity study there was an increased incidence of liver tumours in females at all doses tested. Mechanistic research specifically on TEA indicates that, to the extent TEA can potentially induce tumors in mice, it does so by a mechanism that is not relevant to humans. Therefore, based on the available data, TEA is not considered carcinogenic for humans.

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Additional information

In a dermal carcinogenicity study in rats performed to a similar method as OECD guideline 451 and under GLP, Fischer rats (60/sex/dose) were dermally exposed to 0, 32, 63, or 125 mg/kg bw/day (males) and 0, 63, 125, or 250 mg/kg bw/day (females) TEA in acetone, 5 days/week for 103 weeks (NTP, 1999). Ten male and ten female rats from each group were evaluated at 15 months for organ weights and histopathology.The survival rate of females in the 250 mg/kg bw group was slightly less than that of the vehicle controls. The mean body weight of females administered 250 mg/kg bw ranged from 9% to 12% less than that of the vehicle controls between weeks 73 and 93. Male and female rats receiving triethanolamine had irritated skin at the site of application; in dosed females, the site of application also had a crusty appearance. The number of animals in which these findings were observed increased with increasing dose. At the 15-month interim evaluation, the absolute left and right kidney weights and relative right kidney weight of females administered 250 mg/kg bw were significantly greater than those of the vehicle controls.

The incidence of acanthosis at the site of application in males administered 125 mg/kg bw and the incidences of acanthosis, inflammation, and ulceration in dosed females were greater than in the vehicle controls at the 15-month interim evaluation and at the end of the 2-year study. Males in the 125 mg/kg bw group also had greater incidences of inflammation and ulceration than the vehicle controls, and females receiving 125 or 250 mg/kg bw had greater incidences of epidermal erosion than the vehicle controls at 2 years. There were no skin neoplasms at or away from the site of application that were considered related to treatment with triethanolamine. At the end of the study, renal tubule adenomas were observed in seven dosed males and in one vehicle control female and one female in the 63 mg/kg group. One male in the 125 mg/kg bw group and one female in the 250 mg/kg bw group had renal tubule hyperplasia. Extended (step-section) evaluation of the kidneys of all male rats revealed additional renal tubule adenomas in one vehicle control male, one male in the 32 mg/kg bw group, two males in the 63 mg/kg bw group, and three males in the 125 mg/kg bw group (including one male from the 15-month interim evaluation). An oncocytoma was also identified in one male in the 32 mg/kg bw group. Hyperplasia was identified in eight additional vehicle control males and in 19 additional dosed males. The total incidences (combined standard and extended evaluations) of renal tubule adenoma in dosed male rats were slightly greater than the vehicle control incidence (vehicle control, 1/50; 32 mg/kg bw, 2/50; 63 mg/kg bw, 6/49; 125 mg/kg bw, 4/50). The total incidence of hyperplasia in dosed and vehicle control males was similar (9/50, 8/50, 7/49, 6/50). The severity of hyperplasia in males in the 32 and 125 mg/kg bw groups was greater than that in the vehicle controls.

Under the conditions of these dermal studies, there was equivocal evidence of carcinogenic activity of TEA in male rats based on a marginal increase in the incidences of renal tubule cell adenoma. There was no evidence of carcinogenic activity in female rats receiving 63, 125, or 250 mg/kg bw TEA. Based on these results, IARC (2000) concluded that there was no significant increase in the incidence of tumours at any site. Dosed rats had varying degrees of acanthosis and inflammation and ulceration, female rats had epidermal erosion at the site of skin application. 63 mg/kg bw/day was established to be the NOAEL for local effects in males, and the LOAEL in females, based on acanthosis and chronic active inflammation at theapplication site.

In a dermal carcinogenicity study in mice performed to a similar protocol as OECD guideline 451 and under GLP, B6C3F1 mice (50/sex/dose) were dermally exposed to 0, 200, 630, or 2000 mg/kg bw/day (males) and 0, 100, 300, or 1000 mg/kg bw/day (females) TEA in acetone, 5 days/week for 104 (males) or 105 (females) weeks (NTP, 2004). Survival of all dosed groups was similar to that of the vehicle control groups. Body weights of 2000 mg/kg bw males were less than those of the vehicle controls from weeks 17 to 37 and at the end of the study; body weights of dosed groups of females were similar to those of the vehicle controls throughout the study. Treatment-related clinical findings included skin irritation at the site of application, which increased with increasing dose and was more severe in males than in females. Gross lesions observed at necropsy included nodules and masses of the liver in dosed females. The incidences of hepatocellular adenoma and hepatocellular adenoma or carcinoma (combined) were significantly increased in all dosed groups of females. The incidence of hemangiosarcoma of the liver in 630 mg/kg bw males was marginally increased. The incidences of eosinophilic focus in all dosed groups of mice were greater than those in the vehicle controls. Gross lesions observed at necropsy included visible crusts at the site of application in all dosed groups of mice. Treatment-related epidermal hyperplasia, suppurative inflammation, ulceration, and dermal chronic inflammation occurred at the site of application in most dosed groups of mice, and the incidences and severities of these lesions generally increased with increasing dose.

Under the conditions of this 2-year dermal study, there was equivocal evidence of carcinogenic activity of TEA in male B6C3F1 mice based on the occurrence of liver hemangiosarcoma. There was some evidence of carcinogenic activity in female B6C3F1 mice based on increased incidences of hepatocellular adenoma. Exposure to TEA by dermal application resulted in increased incidences of eosinophilic focus of the liver in males and females. Dosed mice developed treatment-related nonneoplastic lesions at the site of application.

In an oral carcinogenicity study in rats, Fischer rats (50/sex/dose) were daily exposed to 0, 1, or 2% TEA via the drinking water (corresponding to a dose of approximately 667 and 1333 mg/kg bw/day) for 2 years (Maekawa et al, 1986). In week 69, dose levels in females were reduced to 0.5 and 1% (corresponding to ca. 333 and 667 mg/kg bw/day), because of associated nephrotoxicity. A variety of tumours developed in all groups, but no statistically significant differences were observed to control levels. A positive trend towards increased occurrence of hepatic tumours in males and of uterine endometrial sarcomas and renal-cell adenomas in females was judged as not related to the treatment. It was concluded that TEA is not carcinogenic under these conditions in the Fischer rat, but is toxic to the kidneys.

In another oral carcinogenicity study, B6C3F1 mice (50/sex/dose) were administered 0, 1, or 2% TEA in the drinking water (corresponding to a dose of ca. 1600 and 3200 mg/kg bw/day) for 82 weeks (Konishi et al, 1992). Neoplasms developed in all groups including the control group, but no dose-related increase in tumour incidence was observed. No adverse effects were noted on survival and organ weights. Thus, no evidence for carcinogenic potential of TEA upon oral administration was found in mice.

TEA was evaluated in a genetically modified mouse skin papilloma model (Spalding, 1999, 2000). Doses up to 30 mg of TEA were administered topically to groups of 15 to 20 female Tg.AC mice five times per week for 20 weeks. The experimental design also included positive and negative controls. In contrast to the positive controls, which developed multiple papillomas, there were no increases in the incidences of skin tumours in mice receiving TEA.

Thus, TEA has been reported to cause an increased incidence of liver tumours in female B6C3F1 mice, but not in males nor in Fischer 344 rats (NTP 1999, 2004). Effects on choline metabolism have been suggested to play a role in hepatic tumorigenesis in mice. Choline deficiency induces liver cancer in rodents, and TEA could compete with choline uptake into tissues. In a mechanistic study, the potential of TEA to cause choline deficiency in the liver of mice as a mode of tumorigenesis was investigated (Stott, 2004). Groups of female B6C3F1 mice were administered TEA at 0 or the maximum tolerated dose (MTD) of 1000 mg/kg bw/day (trail I), and 0, 10, 100, 300 or 1000 mg/kg bw/day (trial II) in acetone, 5 days/week for 3 weeks. Female CDF rats were also administered 0 or an MTD dose of 250 mg/kg bw/day TEA (trial II) in a similar manner. No clinical signs of toxicity were noted, and upon sacrifice, levels of hepatic choline, its primary storage form phosphocholine (PCho), and its primary oxidation product betaine, were determined. A statistically significant decrease in PCho and betaine was observed at the high dosage (26-42%) relative to controls and dose-related, albeit variable, decrease was noted in PCho levels. Choline levels were also decreased 13-35% at the high dose level in mice. No changes in levels of choline or metabolites were noted in treated rats. A subsequent evaluation of the potential of TEA to inhibit the uptake of 3H-choline by cultured Chinese hamster ovary cells revealed a dose-related effect upon uptake. It was concluded that TEA may cause liver tumours in mice via a choline-depletion mode of action and that this effects is likely caused by inhibition of choline uptake. A similar mechanism was identified for hepatic tumorigenesis in mice upon exposure to DEA. This nongenotoxic mechanism displays interspecies differences in sensitivity with humans being much more resistant. Therefore, based on the available data, TEA is not considered carcinogenic for humans.

Justification for classification or non-classification

Based on available data on carcinogenesis and the negative in vitro genotoxicity studies, TEA is considered to be non-carcinogenic; therefore classification according to Directive 67/548/EEC and EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008 is not warranted.