Lysine hydrochloride

Endpoint summary

Description of key information

For risk assessment purposes the following absorption factors were derived:

oral absorption factor: 100%

dermal absorption factor: 10%

inhalation absorption factor: 100%

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

L-lysine is an essential amino acid that is required for normal functioning of humans. In other words, the human body cannot synthesize lysine, and it must be obtained from the diet. A sufficient supply of this amino acid is particularly important during pregnancy and breastfeeding, as it promotes bone growth and cell division. Lysine is abundant in foods from animal origin, like meat (specifically red meat, lamb, pork, and poultry), milk and dairy products like cheese (particularly Parmesan), eggs, and fish (such as cod and sardines). It is also abundant in foods from vegetal origin like soy, beans and peas.
High levels of lysine are in Parmesan cheese which contains 3170 mg/100 g cheese for example. This shows that high levels of lysine (more than 3 g) can be ingested per meal.
The L-isomer of lysine is the only form that is involved in protein synthesis, and one of the 20 standard amino acids common in animal proteins and required for normal functioning in humans. It has noted roles in building muscle protein, tissue repair and growth, and the body's production of hormones, enzymes, and antibodies (Longe 2005). Lysine is metabolised in mammals to give acetyl-CoA, via an initial transamination with α-ketoglutarate.

Amino acids are absorbed in the small intestines by carrier-mediated transport, and for most L-amino acids, transport has been shown to be active (Matthews, 1972). The active transport mechanisms appear to be situated in the plasma membrane of the mucosal poles of the absorptive cells, since amino acids are concentrated in the cells while transport is going on. Lysine transport is not completely sodium-dependent. It is metabolised and/or incorporated into proteins of tissues. Any excess is excreted through the kidneys as urea/uric acid and carbon dioxide. The renal uptake of amino acids from arterial blood takes place via plasma. (Tizianello et al., 1980, J. Clin. Invest 65: 1162-1173)
In human blood a median plasma concentration of 242 µmol/L (corresponds to 35,4 mg/L plasma and 160-212 mg/adult) was measured in a cohort study 2016 (Schmidt et al., 2016, European Journal of Clinical Nutrition 70: 306–312) and correlates to former analysis (Stein and Moore, 1954, J. Biol. Chem. 211: 915-926).
The nutritional requirements of lysine of humans varies from ~60 mg/kg bw/d in infancy to ~30 mg/kg bw/d in adults. Lysine intake in the western human diet is in the range 40–180 mg/kg bw/d. This corresponds to a maximum of 2.8- 12.6 g Lysine /day for an adult weighing 70 kg. The well-balanced and protein-adequatic North American diet with about 5-8 g of lysine daily is in this range.

This substance is an essential nutrient and, as such, human exposure through food has at least the same order of magnitude or even higher as the doses used in the OECD guideline studies.

For risk assessment purposes oral absorption of L-Lysine Monohydrochloride is set at 100%.

Due to the low vapour pressure (< 1.33´10-8Pa) and large particle size of the substance it is not to be expected that L-lysine will reach the nasopharyngeal region or subsequently the tracheobronchial or pulmonary region. As a very hydrophilic substance with a molecular weight below 200,any L-lysine reaching the lungs might be absorbed through aqueous pores. For risk assessment purposes, although it is unlikely that L-Lysine Monohydrochloride will be available to a high extent after inhalation via the lungs due to the low vapour pressure and large particle size, the inhalation absorption of L-Lysine Monohydrochloride is set at 100%.

L-lysine with water solubility above 10 g/l and the log P value below 0 may be too hydrophilic to cross the lipid rich environment of the stratum corneum. Therefore, 10% dermal absorption of L-Lysine Monohydrochloride is proposed for risk assessment purposes.

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