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Silk amino acid

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Silk amino acids (SAAs) also known as Sericin is a natural water-soluble glyco-protein extracted from raw silk. It is a non-animal protein source used as an additive in skin and hair care products due to it's high levels of serine which has excellent moisture preservation characteristics.[1][2] As a water-based additive it is used to provide a protective barrier and silky feel to lotions, soaps, personal lubricants, hair and skincare products.[3] Silk amino acids are produced by hydrolyzing (or breaking apart) silk proteins into smaller peptide chains, typically 18 to 19 amino acids in length. Silk amino acids have a lower molecular weight than silk protein powders and are moisturizing to skin and hair.[4] Although silk proteins have been used in traditional medicine in both China and Korea for centuries [citation needed], silk amino acids may comprise a new source of orally ingested amino acids as they have been shown to provide a variety of biological effects in animals, ranging from enhancing exercise performance to lowering blood cholesterol and blood glucose levels to possessing antioxidant and antiviral activities.[citation needed]

Silk amino acids are used in formulating shampoos, conditioner, hair treatments, bodywash, body lotions, cleansers, toners and facial moisturizers, mascara, lipstick and color cosmetics.[5][6]


Background

Silk is made up of two primary proteins; a fibrous protein known as fibroin, and a sticky protein known as sericin, with the two comprising 70-80% and 20-30% of silk, respectively. Both of these proteins provide the unique functionality of silk that makes silk clothes so unique and so popular, with the production of silk material dating back to as early as 3500 BC.[citation needed] What is not so well known though is that silk has been used in traditional medicine in both China and Korea for centuries.[original research?] The source of these silk amino acids is typically the domesticated moth, silkworm (Latin name: Bombyx mori).

Sericin has a high hydroxy amino acid content which is important for the water-binding capacity which regulates the skin's moisture content. It also has a unique carbohydrate moiety and a unique repetitive amino acid sequence which give it a high affinity for proteins resulting in a tightening, anti-wrinkle effect. In addition, because of it's high molecular weight, it leaves a substantive semi-occlusive film that persists even after washing, and can increase the skins permeability.[7]

Composition

Predominant composition of silk amino acids (by weight*):[8]

  • L-Alanine (34.36%)
  • Glycine (27.23%)
  • L-Serine (9.58%)
  • L-Valine (3.49%)
  • L-Threonine (2.00%)
  • [*SAAs contains other amino acids but only those representing >2.00% are listed due to their greater relevance]

Applications

Due its proteinous nature sericin is susceptible to the action of proteolytic enzymes, making it digestible; and because of properties like it's gelling ability, moisture retention capacity and skin adhesion, it has numerous medical pharmaceutical and cosmetic applications.

Biological effects on mice and rats

Blood Lipids

Feeding of silk protein hydrolysates to animals resulted in the lowering of both blood cholesterol and triglycerides.[9] Feeding diabetic mice hydrolyzed silk protein for 4 weeks resulted in significantly lower total cholesterol, low-density lipoprotein (LDL) cholesterol and atherogenic scores of 11%, 27% and 26%, respectively, when given 200 milligrams per kilogram of bodyweight per day (abbreviated 200 mg/kg bw/d), but not with the lower dose of 100 mg/kg bw/d.[10] No significant effect on lowering triglycerides was found.

In contrast, the addition of silkworm powder (200 mg/kg bw/day and 400 mg/kg bw/day) for 6 weeks in rats significantly lowered triglyceride levels 10% and 25%, respectively, yet had no effect on total cholesterol, LDL or high-density lipoprotein (HDL) levels.[11]

One potential explanation why similar studies have found different results may be the form of the silk provided, whether it be a silk powder or a silk protein hydrolysate.

Diabetes

One of the more well-researched biological effects of silk proteins is their anti-diabetic, or blood glucose lowering, effect. Feeding diabetic mice hydrolyzed silk protein for 4 weeks resulted in significantly lowering of elevated blood glucose by 15% and 25% with 100 and 200 mg/kg bw/d doses, respectively.[12] Interestingly, the mechanism by which the hydrolyzed silk protein produced its blood glucose lowering effect was through enhancing the insulin releasing effects of the beta-cells in the pancreas. This mechanism of action (MOA) would classify silk protein hydrolysate as an insulin secretagogue, which is one of the three categories used to describe oral antidiabetic agents; the other two being, insulin sensitizers, or alpha-glucosidase inhibitors. Silk fibroin has also been shown to increase insulin transport into adipocytes (fat cells) in vitro.[13]

Others have also found similar anti-diabetic effects with the addition of silk protein hydrolysates to diabetic mice or rats.[14][15][16]

The blood glucose lowering effect was also seen in type 2 diabetics when given silk protein hydrolysate, in addition to seeing enhanced insulin releasing activity.[17]

Antioxidant

Silkworm powder has been shown to have a significant effect on reducing oxidation (eg, ~10% reduction in lipid peroxides and oxidized proteins) as well as increasing the activity of endogenous antioxidant enzymes (eg, SOD, CAT, GSHPx) dose dependently.[18] More specifically, superoxide dismutase (SOD) and catalase (CAT) activities were increased 10% and 40% in rats fed 200 mg/kg bw/d, respectively, while increasing 25% and 50% when an even larger dose was given (400 mg/kg bw/d). The larger dose also increased glutathione peroxidase (GSHPx) activity 10%.

In addition, sericin, the minor protein in silk has been shown to possess antioxidant effects by itself.[19]

Lastly, silkworm powder has also been shown to have a synergistic effect in enhancing antioxidant enzyme activity in diabetic rats when combined with equal amounts of mulberry fruit and leaves.[20]

Exercise

A recent animal study,[21] found that when exercising mice were given three different doses of silk amino acids for 44 days, the mice experienced:

  • SAA fed mice exercised more than twice as long as mice not fed SAAs (28 minutes vs 13 minutes)
  • In terms of absolute improvement in exercise performance, SAAs produced improvements that were six times greater than that seen with just exercise (18 minute increase compared to 3 minute increase)
  • Eliminated the increase in blood lactate levels (which were significantly increased with just exercise)
  • Eliminated the increase in muscle oxidation (which was also significantly increased with just exercise)
  • Maintained blood glucose levels (vs being significantly lowered in exercising mice)
  • Increased muscle glycogen and liver glycogen (compared to exercise alone)
  • Increased testosterone levels (64% increase vs 36% reduction in exercise group; in absolute terms, blood testosterone levels that were 2.6 times higher in SAAs group compared to exercise group)
  • Reduced cortisol (140% increase in cortisol in exercising group while no significant increase was seen when SAAs were given)
  • Increased anabolic ratio (4-fold higher anabolic ratio; ie, the testosterone to cortisol ratio compared to mice not receiving any)
  • Increased muscle size (16% increase with high-dose)

Although the results from the animal trial described above are very interesting, human data is still needed, including how silk amino acids compare to other sources of amino acids, whether they be free-form amino acids, other sources of protein hydrolysates or proteins themselves.

Other effects of silk amino acids (SAAs) or silk protein hydrolysates include regulating the immune system,[22] lowering muscle and liver damage,[23] as well as having anti-tumor,[24] and anti-viral effects.[25]

References

  1. ^ [1]
  2. ^ [2]
  3. ^ Journal of Scientific & Industrial Research Vol. 63, April 2004, pp323-329
  4. ^ [3]
  5. ^ Silk amino acids add a velvety touch to cosmetics and also helps to prevent dehydration of the skin.
  6. ^ Hair care: a growing market: hair care marketers get to the root of their customers' needs.
  7. ^ http://www.gerovital.co.ro/sericin.pdf
  8. ^ Shin S, Park D, Yeon S et al. Stamina-enhancing effects of silk preparations in mice. Lab Anim Res 2009;25:127-34.
  9. ^ Hwang E, Kang B, Kim B, Lee HJ. Protein quality evaluation and effect of plasma contents of acid hydrolysates of cocoon in rats fed high cholesterol, high triglyceride and high sucrose diet. J Korea Soc Food Sci Nutr 2001;30:1004-9.
  10. ^ Jung EY, Lee HS, Lee HJ et al. Feeding silk protein hydrolysates to C57BL/KsJ-db/db mice improves blood glucose and lipid profiles. Nutr Res 2010;30:783-90.
  11. ^ Choi JH, Kim DI, Park SH et al. Effects of silkworm powder on oxygen radicals and their scavenger enzymes in serum of rats. Korean J Seric Sci 1999;41:141-6.
  12. ^ Jung EY, Lee HS, Lee HJ et al. Feeding silk protein hydrolysates to C57BL/KsJ-db/db mice improves blood glucose and lipid profiles. Nutr Res 2010;30:783-90.
  13. ^ Hyun CK, Kim IY, Frost SC. Soluble fibroin enhances insulin sensitivity and glucose metabolism in 3T3-L1 adipocytes. J Nutr 2004;134:3257-63.
  14. ^ Shin M, Park M, Youn M et al. Effects of silk protein hydrolysates on blood glucose and serum lipid in db/db diabetic mice. J Korean Soc Food Sci Nutr 2006;35:1343-8.
  15. ^ Park KJ, Hong SE, Do MS, Hyun CK. Stimulation of insulin secretion by silk fibroin hydrolysate in streptozotocin-induced diabetic rat and db/db mice. Korea J Pharmacogn 2002;33:21-8.
  16. ^ Lee Y, Park M, Choi J et al. Effect of silk protein hydrolysates on blood glucose level, serum insulin and leptin secretion on OLEFT rats. J Korean Soc Food Sci Nutr 2007;36:703-7.
  17. ^ Cho MR, Choue R, Chung SH, Ryu JW. Effects of silkworm powder on blood glucose and lipid levels in NIDDM (type 2) patients. Korean J Nutr 1998;31:1139-50.
  18. ^ Choi JH, Kim DI, Park SH et al. Effects of silkworm powder on oxygen radicals and their scavenger enzymes in serum of rats. Korean J Seric Sci 1999;41:141-6.
  19. ^ Kato N, Sato S, Yamanaka A et al. Silk protein, sericin, inhibits lipid peroxidation and tyrosinase activity. Biosci Biotechnol Biochem 1998;62:145-7.
  20. ^ Kwon EH, Jung MA, Rhee SJ et al. Antioxidant effects and improvement of lipid metabolism of mulberry fruit, mulberry leaves and silkworm powder with different mixing ratios in streptozotocin-induced diabetic rats. Korean J Nutr 2006;39:91-9.
  21. ^ Shin S, Yeon S, Park D et al. Silk amino acids improve physical stamina and male reproductive function in mice. Biol Pharm Bull 2010;33:273-8.
  22. ^ Ryu JM, Kim TM, Seo IK et al. Effect of repeated administration of silk peptide on the immune system of rats. Lab Anim Res 2008;24:361-9.
  23. ^ Kim TM, Ryu JM, Seo IK et al. Four-week repeated-dose toxicity of silk amino acids in rats. Lab Anim Res 2008;24:565-73.
  24. ^ Zhaorigetu S, Yanaka N, Sasaki M et al. Silk protein, sericin, suppresses DMBA-TPA-induced mouse skin tumorigenesis by reducing oxidative stress, inflammatory responses and endogenous tumor promoter TNF-alpha. Oncol Rep 2003;10:537-4.
  25. ^ Gotoh K, Izumi H, Kanamoto T et al. Sulfate fibroin, a novel sulfated peptide derived from silk, inhibits immunodeficiency virus replication in vitro. Biosci Biotechnol Biochem 2000;64:1664-70.
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