Antimicrobial mechanism of epsilon-poly-L-lysine
Polyepsilon-lysine (hereinafter referred to as "PL") is highly antibacterial and is mainly used as a natural food preservative (GRAS) produced by the fermentation of microorganisms, and is a hydrophilic homo-poly-amino acid with 25 to 35 L-lysines connected in a straight line. PL has been used as a food preservative in Japan since the 1980s, which is biodegradable and is known not to cause toxicity in the human body. However, if a large amount is added to food, it can taste bitter. PL is synthesized by linking 25 to 35 L-lysine branches by polymerization of microbial membrane bound ε-PL synthetase. It is known that the antibacterial activity of PL is also affected by the number of L-lysine branches. Although the exact antibacterial mechanism has not yet been identified, it is known that PL with a positive charge interferes with the action of LPS on the surface of the cell membrane of Gram-negative bacteria with a negative charge (1, 2). The detailed mechanism is shown in (Figure 1). (3) In step (B) of Figure 1, the LPS layer is removed due to electrostatic bonding between the phosphate groups of PL (red) and LPS (blue), which enter the periplasmatic space. After that, it binds to the peptidoglycan layer in step (C) or enters the inner membrane. At this time, the higher the concentration of PL, the greater the amount of PL entering the inner membrane, which forms a negative curve by binding to the phospholipid of the inner membrane in step (D). After that, it forms a micelle-like shape in the (E) step, and finally, the phospholipid of the inner membrane is removed in the (F) step, and the bacterial cells are damaged by forming a hole. Through the above mechanism, after treating PL in E. coli and reacting it at 25°C for 4 hours, as a result of observing through CLSM, it can be confirmed that LPS protrudes as indicated by the arrow (3) (Figure 2).
Outer membrane (OM), peptidoglycan layer (PG), inner membrane (IM).
Antimicrobial activity of caprylyl glyceryl ether
The antibacterial mechanism of caprylyl glyceryl ether has not been identified, but it is thought to be similar to that of ethylhexylglycerin (EHG) or 1,2-dodecanediol, which have similar structures. The structures of EHG, 1,2-dodecanediol, and caprylyl glyceryl ether are compared in Figure 3 (Figure 3).
According to a reference literature that confirmed the antibacterial activity against Staphylococcus aureus and Staphylococcus epidermidis of 1,2-dodecanediol (C12), the number of carbon of 1,2-alkanediol increased (C12 : 1,2-dodecanediol) and the minimum inhibition concentration (MIC) was lowered, resulting in high antibacterial properties (4) (Figure 4 (A)). It has also been confirmed that as the number of carbon increases, Log P increases and solubility decreases, which reduces the solubility of water but increases the effect of inhibiting the growth of microorganisms (Figure 4 (B)). However, the solubility in water was so low that the bactericidal effect of 1,2-dodecanediol (C12) was not confirmed.
On the other hand, a paper on EHG’s antibacterial activity on E. coli has shown that EHG has a mechanism that inhibits growth by ultimately inhibiting the synthesis of ATP through a series of processes such as inducing proton leakage by penetrating the cell membrane and reducing its ATP-level (5). However, until now, most of EHG is produced through chemical synthesis, so it is limited to be used as a natural antiseptic substitute.
Taken together, the high antibacterial activity and mechanism of action of caprylyl glyceryl ether can be inferred through the antibacterial activity of 1,2-dodecanediol and the antibacterial action mechanism of EHG. Caprylyl glyceryl ether is an ether group with one less carbon than 1,2-dodecanediol. It has improved solubility compared to 1,2-dodecanediol, and it is an excellent cosmetic preservative material with antibacterial activity similar to that of EHG or 1,2-dodecanediol. Unlike EHG and 1,2-dodecanediol, it is considered to be a natural raw material that has excellent safety and can be applied in various fields as a nature-friendly raw material.
Antiseptic Effect of Activonol Green-PASS
Activonol Green-PASS is a mixture of Caprylyl glyceryl ether, Polyepsilon-lysine, Propanediol, and water as its natural antiseptic substitute, and each raw material is composed of the optimal composition ratio that produces antibacterial synergistic effects.
MIC (Minimum Inhibitory Concentration)
The results of MIC (Minimum Inhibitory Concentration) for the three types of Activonol Green-PASS (one gram-positive and two gram-negative bacteria), one yeast, and one fungus are as follows (Table 1). It showed a low MIC result of less than 0.4% in all strains except Pseudomonas aeruginosa. It also shows the same MIC results in various pH (pH 5~9), various temperatures (room temperature ~ 80°C), and various storage conditions (25 ~ 50°C, 1 month), which is considered to be highly antibacterial in the formulation of various cosmetics and various storage conditions (Figure 5).
MIC (A) for various pH, MIC (B) for various temperatures, and MIC (C) for various storage conditions.
Challenge test
Among the raw materials that make up Activonol Green-PASS, Caprylyl glyceryl ether and Polyepsilon-lysine were applied to Cream (O/W type), respectively, and preservative tests for Bacteria, yeast, and fungi were performed (PCPC 2018 Guideline). As a result, when each of the two raw materials was used, the bacteria and yeast showed high antiseptic effects, but for fungi, the log reduction values on the 7th day were 0.7 and 0.1, respectively, showing a low antiseptic effect (Figure 6 (A), (B)). On the other hand, an antiseptic test conducted by applying Active Green-PASS to the same formulation showed that bacteria and yeast killed 100% on the 7th day, and for fungi, the two materials worked together at 3.2 of the reduction value of Log on the 7th day, resulting in a high preservative synergy effect (Fig. 6 (C)).
Caprylyl glyceryl ether (A), polyepsilon-lysine (B), Activonol Green-PASS (C).
2.5~3% of Activonol Green-PASS was prescribed for four different formulations (mask pack solution, cream (O/W type), essence solution, and shampoo solution) to check the preservative power in various cosmetic formulations. Afterwards, antiseptic testing was performed on bacteria, yeast, and fungi (PCPC 2018 Guideline). As a result, bacteria and yeast in four different formulations were 100% killed on the 7th day, and more than 90% of fungi was killed on the 7th day as well. Since then, it continued to decline on the 14th, 21st, and 28th days, making it suitable for the PCPC Guideline (2018) (Figure 7).
Bacteria (A), yeast (B), and fungi (C).
Stability of Activonol Green-PASS
After prescribing 3% Activonol Green-PASS in four different formulations (mask pack solution, cream (O/W type), essence solution, and shampoo solution) to check the stability in various cosmetic formulations, the appearance and pH were confirmed for 30 days in an environment of -20 ~ 50℃. As a result, it was found that the appearance and pH of all temperature conditions in various formulations prescribed with Activonol Green-PASS were stably maintained. Therefore, Activonol Green-PASS can be used as an excellent cosmetic ingredient that does not affect the formulation of skin care products or hair care products.
Activonol Green-PASS, a 100% Natural Alternative Preservative
Active Green-PASS has a similar structure to polyepsilon-lysine, a substitute for food produced using microorganisms, and a synthetic defense system with high antibacterial effects, and is a natural preservative mixed with naturally derived substances of caprylyl glyceryl ether and propanediol. It consists of an optimal construction ratio to create synergy between polyepsilon-lysine, which destroys the cell membrane with a static bond with LPS, and caprylyl glyceryl ether, an action mechanism that inhibits ATP synthesis. It shows a high antiseptic effect when applied to skincare products and hair care products at a concentration of 2-3%, which is a natural antiseptic substitute that can be applied to the formulation of all cosmetics.
Product Name : Activonol Green-PASS
Label Name (Cosmetics) : Polyepsilon-lysine, caprylyl glyceryl ether, propanediol, purified water
INCI Name : POLYEPSIOLN-LYSINE, CAPRYLYL GLYCERYL ETHER, PROPANEDIOL, WATER
Recommended Concentration : 2.5~3%
Activonol Green-PASS is a naturally derived alternative preservative certified by COSMOS. (In progress)
Domestic patent application number: KR20-143891
PCT application number: (In progress)
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References
1. Yoshida T, Nagasawa T, et al. “ε-poly-L-lysine: Microbial production, biodegradation and application potential.” Applied Microbiology and Biotechnology 62 (2003):21-26
2. Yamanaka K, Maruyama C, Takagi H, Hamano Y, et al. “ε-poly-L-lysine dispersity is controlled by a highly unusual nonribosomal peptide synthetase.” Nature Chemical Biology 4 (2008):766-772
3. Hyldgaard, Morten, et al. "The antimicrobial mechanism of action of epsilon-poly-l-lysine." Applied and environmental microbiology 80.24 (2014): 7758-7770.
4. Okukawa, Minako, et al. “Antibacterial activity of 1,2-alkanediol against Staphylococcus aureus and Staphylococcus epidermidis.” Journal of oleo science (2019): ess19074
5. Langsrud, Solveig, et al. “Ethylhexylglycerin impairs membrane integrity and enhances the lethal effect of phenoxyethanol.” PloSone 11.10 (2016): e0165228