Lysine (L-lysine) is an essential amino acid for humans widely used as a food supplement, for the composition of pharmaceutical products and as a raw material for cosmetics and synthetic materials. It is primarily produced by microbial fermentation (e.g. Corynebacterium glutamicum, Escherichia, Streptomyces). It is also used in animal feed.

It is an α-amino acid.

Amino acids play a key metabolic function in the human body and are constituents of proteins. 

As food additives they perform different functions: preservatives, flavour enhancers, food supplements and more.

Amino acids together with their salts are used in cosmetics as conditioning agents for both hair and skin (e.g. as moisturisers and other similar functions). Moisturisers are different in nature: the best are the natural ones that exploit the mechanism of integration between the ingredient and the skin by moisturising the horny hydrolipid film, i.e. the thin protective layer that covers the epidermis protecting it from harmful external microbes, keeping the skin moisturised and supple and its pH or acidity value between 4 and 6.  Then there are the occlusive moisturisers, usually derived from petroleum (Paraffinum, Paraffinum liquidum and others), but also triglycerides, lanolin oil, natural or synthetic waxes, fatty acid esters and others that create an artificial occlusive layer on the stratum corneum of the skin with the advantage of accelerating the protective process but with the disadvantage of preventing the skin's natural transpiration.

α-amino acids that have similar physical structures undergo similar changes with regard to solubility in water/ethanol mixtures, and technologies to separate α-amino acids from industrial residues, which may not even be innocuous, are constantly being improved. However, many data on the solubility in water-ethanol and ethanol of some α-amino acids are contradictory or even lacking, and the effects of ethanol on the solubility of amino acids may be different. Overall, the scientific literature considers that α-amino acids do not pose significant problems for human health when taken orally, except in people with certain genetic diseases.

Food safety: amino acid α generally considered safe.

Cosmetic safety: amino acid α generally considered safe when formulated to be non-irritant.

What it is used for and where

Medical

It promotes proper tissue function, growth and healing and improves the immune system, stimulates calcium absorption. It also appears to be active in the fight against herpes simplex.

A neuroprotective activity of L-lysine has been observed that confers neuroprotection after intracerebral haemorrhage injury by improving M2 microglial polarization and reducing inflammatory response in mice (1).

L-lysine plays a protective role in the toxicity of high glucose levels by counteracting hyperglycemia which is a characteristic element of diabetes, normally associated with protein glycation (2).

The intake of L-Lysine, given its recent spread as a dietary supplement, has revealed some subjective contraindications to its use. Most of these contraindications concerned the gastrointestinal tract with disorders such as nausea, stomach pain, diarrhea. The provisional level of absence of observed adverse effects obtained on the basis of these gastrointestinal symptoms was estimated at 6000 mg/person per day (3).

The increasing frequency of infections in implantable devices has encouraged the search for biocompatible antimicrobial surfaces. poly-l-lysine has been shown to inhibit adhesion and bacterial proliferation on biomaterials (4).

The antibacterial activity of L-Lysine on the growth of bacterial contaminants in platelets stored at room temperature is also confirmed (5).

Cosmetics

It has a protective action on the skin and contributes to the optimal oligomerisation of cell membranes.

The most relevant studies on this ingredient have been selected with a summary of their contents:

L-lysine, studies

• Molecular Formula: C₆H₁₄N₂O₂
• Linear Formula :  H₂N(CH₂)₄CH(NH₂)CO₂H
• Molecular Weight: 146.19 g/mol
• CAS: 56-87-1
• EC Number: 200-294-2
• DSSTox Substance ID: DTXSID6023232
• MDL number MFCD00064433
• FEMA 3487
• Beilstein/REAXYS Number 1722531
• PubChem Substance ID 329752387

Synonyms: 

• lysine
• h-Lys-oh
• (2S)-2,6-diaminohexanoic acid
• lysine acid
• Aminutrin
• L-Norleucine, 6-amino-
• Hexanoic acid, 2,6-diamino-, (S)-

References__________________________________________

(1) l-lysine confers neuroprotection by suppressing inflammatory response via microRNA-575/PTEN signaling after mouse intracerebral hemorrhage injury.  Cheng J, Tang JC, Pan MX, Chen SF, Zhao D, Zhang Y, Liao HB, Zhuang Y, Lei RX, Wang S, Liu AC, Chen J, Zhang ZH, Li HT, Wan Q, Chen QX.  Exp Neurol. 2020 Jan 24;327:113214. doi: 10.1016/j.expneurol.2020.113214.

(2) L-lysine protects C2C12 myotubes and 3T3-L1 adipocytes against high glucose damages and stresses.  Ebrahimi SM, Bathaie SZ, Faridi N, Taghikhani M, Nakhjavani M, Faghihzadeh S.  PLoS One. 2019 Dec 19;14(12):e0225912. doi: 10.1371/journal.pone.0225912

(3) Safety assessment of L-lysine oral intake: a systematic review.  Hayamizu K, Oshima I, Fukuda Z, Kuramochi Y, Nagai Y, Izumo N, Nakano M.  Amino Acids. 2019 Apr;51(4):647-659. doi: 10.1007/s00726-019-02697-3.

(4) Highly Stabilized Nanoparticles on Poly-l-Lysine-Coated Oxidized Metals: A Versatile Platform with Enhanced Antimicrobial Activity.  Ghilini F, Rodríguez González MC, Miñán AG, Pissinis D, Creus AH, Salvarezza RC, Schilardi PL.  ACS Appl Mater Interfaces. 2018 Jul 18;10(28):23657-23666. doi: 10.1021/acsami.8b07529.

(5) Efficacy of ε-Poly-L-lysine as an Antibacterial Additive for Platelets Stored at Room Temperature.  Naghadeh HT, Sharifi Z, Soleimani S, Jamaat ZPM, Ferdowsi S.  Iran J Med Sci. 2017 Sep;42(5):509-511.