Choline hydroxide

Endpoint summary

Description of key information

Waiver, as the substance is a strong base (pH > 11.5)

 

Additionally, the following supporting information is presented:

Skin sensitisation:
- In vivo Guinea pig maximisation test on formulation of Choline chloride (CC) and Chlorocholine chloride (CCC) (320 g/L CC, 460 g/L CCC) in water, guinea pig (Dunkin Hartley), male, OECD Guideline 406, GLP, not sensitising
- In vivo Guinea pig Bühler test chlorocholine chloride in water, guinea pig (albino), m/f, OECD Guideline 406, GLP, not sensitising

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vitro

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance is a strong acid (pH ≤2.0) or base (pH =>11.5)

the study does not need to be conducted because the substance is classified as skin corrosion (Category 1, 1A, 1B or 1C)

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

First of all, Choline hydroxide is a strong base with a pH > 11.5 and therefore no skin sensitisation testing is required, and the endpoint can be waived.

 

Accordingly, there is no reliable information available for acute toxicity for Choline hydroxide. However, the following was also taken into account: since choline base would result in an immediate irritating effect due to the high pH (14.9 (45 % solution, Struyvelt E, 2012), resp. 13.1 - 14.2 (10 - 90 % (w/w) of 45 % solution in water, Intertek, 2013)) even if applied in diluted doses, the only possibility to assess the allergenic potential of choline hydroxide would be applying it in its neutralized form or by using very high dilutions, which are incapable to induce any reactions anyway. In case it is decided to neutralize the alkaline conditions in the test item, hydrochloric acid is the recommended acid. Hence, the neutralization of OH- by HCL would result in water and chloride ions (Cl-), which would create experimental conditions as if choline chloride had been used.

So, data on the source substance Choline chloride (CAS 67-48-1) and on a formulation of Choline chloride (CC) and Chlorocholine chloride (CCC) have been considered and the results obtained can be transferred to choline base and the available dose can be considered as sufficient and as high as possible.

 

There is a well-documented guideline study according to GLP available, which was conducted using a formulation of Choline chloride and Chlorocholine chloride aka chlormequat (supporting study, classified in this context as Klimisch 2). In addition to this, there is another well—documented guideline study (supportive information) on Chlormequat available, which is provided to allow correct interpretation of the results of the before mentioned study. Both studies are considered reliable to assess the possible skin sensitising properties of Choline hydroxide - due to immediate dissociation of both choline salts and the irrelevance of the inorganic anions. So no data gaps are identified for this endpoint out of the following reasons:

Both studies were performed according to OECD 406 and GLP, which is one of the reliable foreseen standard tests to cover this endpoint.

The study by Driscoll, 1998, was performed on an aqueous formulation with choline chloride (CC, 320 g/L) and chlorocholine chloride (CCC, 460 g/L), and contains therefore to relevant parts but not only the read-across substance choline chloride. It additionally contains CCC, which is a structural analogue for CC. In detail, the test item in the study by Driscoll, 1998, contains Choline chloride, i.e. 41 % of the solid ingredients and the solvent (water). The results of this study showed no skin reactions or differences in body weight gain compared to control.

Regarding the requirements set in OECD guideline 406 to choose the test doses based i.a. on skin irritating effects, the following needs to be added. The doses for the CCC-CC formulation were properly set but might be rather low regarding CC only as it is only contained to 41 % in the solid test item. However, as Choline chloride has been shown to be not irritating after application of undiluted compound on rabbits; so it is not possible to perform the induction in a sensitization study with the demanded concentration, i.e. which causes mild-to-moderate skin irritation. As such, the tested dose of Choline chloride in this study can be considered to be chosen high enough to detect a possible sensitizing effect, especially when taking into account the fact that the study by Driscoll was performed as a guinea pig maximization test.

Regarding the employed test method, the following remark is added. The guinea pig maximization test (GPMT) employed in the study Driscoll, 1998 is considered to be more sensitive than the alternative method by Buehler (employed in the supporting study), because it uses intradermal injections and Freund´s Complete Adjuvans, which is intended to stimulate unspecifically the immune system by the use of proteins as antigens. So, in general, the main problem when assessing the results obtained in a GPMT, is that the skin reactions may overestimate the situation in real life and lead to false positive results. However, since no skin reaction was seen in any of the test animals, this risk is not relevant anymore, and it can safely be concluded that the CC-CCC formulation does not exhibit skin-sensitizing properties.

The provided supporting study by Suresh, 1992, was conducted on the read-across substance for choline hydroxide, chlormequat (CCC), only. This information is provided to further support the results derived of the study Driscoll, 1998. The outcome of the study by Suresh on CCC only (very slight erythema in 2/8 animals after 72 hours) showed that also CCC is not a skin sensitiser. The observed and very slight results - only two of eight animals showed a very slight erythema only at one single timepoint (72h of challenge phase) and even no noted effects during the rechallenge phase – are expected to represent a worst-case (please also refer to arguments presented in the following paragraph).

 

Regarding possible mixture effects of the CC-CCC formulation, the following remarks are added: The CC-CCC formulation employed in the study Driscoll, 1998 did not induce any skin reactions in the Magnus-Kligmann test, CCC alone employed in the supporting study (Suresh, 1992) was also tested negative for skin sensitizing effects in the Buehler assay except a single very slight erythema 72h during the challenge phase in two out of eight animals. Although these results are definitively not sufficient to justify a classification as skin-sensitizing of chlormequat, it can be concluded that CCC is due to its chlorine moiety the more reactive component of the formulation and hence the possibly more immuno-modulating component. In case CCC could really enhance the formation of antigens and consequently the stimulation of the adaptive immune system, the immune system would be more reactive in general and could consequently easier detect possible antigens formed by CC, which can be assumed to be rather similar to the antigens formed by CCC and consequently be easily recognized. Since this possible stimulation would work according to the same principle as Freund´s complete adjuvans, it could to the max overestimate possible immunomodulating properties of CC, if there should any possible mixture effects.

The results derived in the two studies with occlusive dressing, especially the one from the GPMT, may only possibly overestimate the risk of skin sensitizing effects of Choline chloride in humans. First, CC is not intended to be injected into the human skin, and second, an occlusive dressing will not be applied on humans, which could enhance the skin penetration and reaction due to sweating, heat and softening of the skin.

So, since no skin sensitizing effects were seen and neither water nor CCC, was shown to be a dermal sensitizer, it can be concluded that every possible positive result obtained in the study Driscoll, 1998 from the formulation must be attributed to Choline chloride. Since no animal of the test group at no timepoint of observation showed any skin reaction during the challenge phase, and the dose of the test item was properly determined by preliminary sighing tests as the demanded highest non-irritating dose, it can safely be concluded that the test item (CC-CCC-formulation) did not exhibit any sensitizing properties, furthermore CCC alone was not a skin sensitizer as well. Consequently, Choline chloride is non-sensitizing, and therefore Choline hydroxide is expected to be non-sensitizing as well and does not need to be classified as a skin sensitiser according to Regulation 1272/2008/EC. 

 

Justification for selection of skin sensitisation endpoint:
According to REACH Annex VII column 2 the study 2 does not need to be conducted if i.a. the available information indicates that the substance should be classified for skin sensitisation or corrosivity or the substance is a strong acid (pH < 2.0) or base (pH > 11.5). According to company data, the test item (45 % Choline Base solution) has a pH = 14.9 (45 % solution, Struyvelt E, 2012), various dilutions have pH values of pH = 13.1 – 14.2 (10 - 90 % (w/w) of 45 % solution in water, Intertek, 2013), and hence, the test does not need to be conducted. However, sensitization data is available for the read-across substance choline chloride (CAS 67-48-1) and chlormequat, and will be mentioned within this chapter, because this information is still relevant to show that choline hydroxide does not need to be classified as a sensitizer.
The chosen study is one of two well-documented OECD guideline 406 studies according GLP. The study by Driscoll was performed on a formulation of Choline chloride with structural analogue (Chlorocholine chloride), whereas the study by Suresh was only performed on the read-across substance Chlorocholine chloride. Hence, the formulation is more similar to the registered substance choline hydroxide. Additionally, the study by Driscoll was performed as guinea pig maximisation test, which is more sensitive that the method of Bühler (Study by Suresh).

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Choline hydroxide does not need to be tested for skin sensitization potential, as it is a strong base (pH > 11.5).

However, there is data available on analogous substances. Both available in vivo sensitisation studies on guinea pigs revealed negative results for a formulation with Choline chloride (320 g/L) and Chlorocholine chloride (CCC, 460 g/L) and Chlorocholine chloride, a read-across substance, too, only. The results were assessed as reliable and transferrable to choline hydroxide.

In conclusion, choline hydroxide does not need to be classified as skin-sensitiser according to Regulation 1272/2008/EC.

Nevertheless, due to the corrosive properties of the test item, a classification as corrosive to the skin / eye is required according to Regulation 1272/2008/EC.