L-serine

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

L-Serine is used in parenteral nutrition, as a dietary supplement, in biochemical research, in cell culture media, as feed additive, and is a common component found in moisturizers and skin cosmetics.

Based on the available information, there is no human or animal data that indicates L-serine to be a skin sensitiser. Considering the extensive, widespread dermal exposure to L-serine in preparations repeatedly applied to the skin, the absence of case reports of humans showing skin reactions is consistent with L-serine having a very low skin sensitisation potential.

Skin sensitization is the process following the epicutaneous application of a substance to the skin which results in an immunological response specific for this substance. Skin sensitisation is also called "delayed contact hypersensitivity", "contact hypersensitivity", "contact allergy" or "allergic contact dermatitis".To behave as a contact allergen, a substance must penetrate into the skin and react with proteins. L-serine is a normal constituent in living cells occurring as a free amino acid, bound to RNA and incorporated in proteins and peptides. Therefore, it is highly improbable that L-serine acts as a skin sensitizing agent.

Further, an in vivo OECD 406 GLP-guideline study is available for L-threonine. L-Serine and L-threonine belong to the group of polar amino acids as their side chains are polar but not charged. Their chemical structure is very similar with both having the same set of functional groups. The only difference between the two molecules is that L-threonine contains one additional methyl group in the amino acid side chain. Both substances have a low molecular weight, nearly identical logKow values (~-3) and also very similar pKa values. In addition to the similar physico-chemical properties also the toxicological and ecotoxicological/fate data indicate a very low toxicity (if any) of both substances for the environment (toxicity for aquatic organisms) as well as a very low toxicity for human health (toxicity to experimental animals). The absence of significant toxicity is not surprising as both substances are ubiquitous occurring substances (also in body fluids of animals and humans) which serve as building blocks for protein synthesis in all animals (including humans).Due to the very similar chemical structure resulting in very similar physico-chemical properties and chemical reactivity and a very low (eco)toxicity profile of both substances it is justified to fulfil the data requirements with regard to skin sensitization for L-serine by a read-across approach from available data for L-threonine.

In the available study L-threonine has no skin sensitising properties.

 

This finally leads to the conclusion that L-serine is not a skin sensitiser.