L-leucine

Endpoint summary

Additional information

L-leucine was negative in a number of Ames tests, and in an in-vitro chromosome aberration test that was conducted with Leucine according to OECD guidelines.

No reliable test results for L-leucine are available for gene mutation in mammalian cells and in the available key Ames test for L-leucine only 3 bacterial strains were tested. Therefore, information available on structural analogue L-valine was used to further substantiate the assessment of the genetic toxicity of L-leucine.

Read-across to the test results available for structural analogue L-valine is deemed justified based on a comparison of the main factors driving genetic toxicity: the (bio-)chemical reactivity of the substance and its bioavailability, which in itself is determined by the substance's molecular weight, pKa, log Kow and water solubility.

- both are essential amino acids that are in the zwitterion state at physiological pH

- the chemical structure differs only in that L-leucine has one extra methylene group in the aliphatic side chain

- the pKa values of the α-COOH group is very similar: 2.36 for LEU, 2.32 for VAL

- the pKa values of the α-NH2 group is very similar: 9.60 for LEU, 9.62 for VAL

- both amino acids are quite small molecules with a low MW (LEU: 131 g/mol, VAL: 117 g/mol)

- both amino acids have log Kow values below -1 (LEU: -1.52, VAL: -2.26)

- the water solubility of leucine and valine is high (LEU: 23 g/L, VAL: 58 g/L)

As the chemical reactivity and the parameters driving the bioavailability of L-leucine and L-valine are in good agreement, it can be concluded that read-across of genotoxic information between those 2 substances is acceptable.

The Ames and gene mutation tests available for L-valine are carried out according to OECD guidelines and reveal no effects. L-valine was concluded to not be genotoxic.

In conclusion, based on the above information with regard to available tests for L-leucine and its structural analogue L-valine, L-leucine was concluded to not be genotoxic.

These results were foreseeable as L-leucine is a naturally occurring essential amino acid. L-leucine is a normal constituent in living cells occurring as a free amino acid, bound to RNA and incorporated in proteins and peptides. It is ingested daily in significant amounts. Therefore human exposure through food is orders of magnitude higher than the anticipated levels of exposure from the uses covered by this dossier.

 

L-leucine is present in significant amounts in human body fluids – e. g. human blood plasma (Cynober 2002) - as well as in human cells. It is a basic metabolite and building block of all living organisms and therefore a genotoxic/mutagenic potential could be excluded.

 

Cynober L (2002): Plasma Amino Acid Levels With a Note on Membrane Transport: Characteristics,Regulation, and Metabolic Significance. Nutrition 18 (9), 761 -766

Short description of key information:
L-leucine was negative in a number of Ames tests and in an in-vitro chromosome aberration test. No reliable test is available that assesses the gene mutation potential of L-leucine in mammalian cells. However, based on test results available for read-across substance L-valine it can be concluded that no gene mutation effects are to be expected upon exposure to L-leucine.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

As all in-vitro tests are negative, classification of L-leucine for this endpoint is not required.