Summary of Silk Amino Acids
Primary Information, Benefits, Effects, and Important Facts
Silk Amino Acids are a mixture of amino acids obtained from the cocoon of the Silk Worm Bombix Mori. The mixture of amino acids is very high in the amino acids serine and aspartate, and some versions are rich in tyrosine as well.
The protein can be found in a hydrolyzed (pre-digested) form known as Sericin-S, or as a undigestible form known as Sericin-L. The undigestible form appears to exert protective effects on the colon and intestinal tract, whereas the hydrolyzed form can beneficially affect systemic (post-intestinal) metabolic functions.
Sericin also appears to beneficially affect the skin, in both a protective sense (anti-oxidation, anti-UV radiation) as well as increasing moisture content. These effects may be seen with both topical application or ingestion.
It looks to be a promising compound, but no human studies on health have been conducted.
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Things To Know & Note
Silk Amino Acids are proteins, and thus should have a caloric value of 4kcal per gram. If they are Sericin-L or resistant proteins, they may not be absorbed though
How to Take Silk Amino Acids
Recommended dosage, active amounts, other details
There is insufficient evidence to recommend an optimal dosage of silk amino acids for human supplementation, although it is known that for any purpose where silk amino acids need to be absorbed a hydrolyzed form of the supplement is required. Hydrolyzed silk amino acids are not required if the target are the intestines or colon.
Scientific Research on Silk Amino Acids
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Silk Amino Acids are a selection of dietary amino acids from silk. They are arranged in such an order that they form the bioactive peptide 'Sericin'. There are multiple 'Sericin' components, such as Sericin Small (Sericin-S) (5-100kDa in size) which is hydrolyzed and prepared from basic Sericin and Sericin Large (Sericin-L) (50-200kDa) which is non-hydrolyzed. The general idea is that they possess a specific amino acid sequence, which are rich in serine amino acids, at around 30-33% Serine by weight.
Sericin prepared in culture as per this study recorded the sequence of SSTGS SSNTD SNSNS AGSST TYGYS SNSRD GSV. These researchers denoted 'SerD' as a dimer of the above sequence and 'SerT' as a trimer.
They are extracted from the Bombix Mori cocoon of the silkworm, which is named as it feeds exclusively on the leaves of the Morus Alba plant; seems silkworm neonates are attracted to the aroma of these plants.
Sericin has been implicated as having mitogenic properties in vitro on mammalian cells.
It is being explored as being a tool for cell cultures as a replacement for Bovine Serum Albumin. In regards to its ability to feed cell division, the hydrolyzed fragment (Sericin-S) appears to be almost twice as potent (as assessed by viable cells after incubation) as Sericin-L.
In a study on human HepG2 cells, the pathway appears to be through activation of the Erb-b2 receptor and eventual signalling on ERK1/2 via Src and Ras.
These effects on accelerating cell culture growth appear to be dose dependent (as evidenced by doses of 0.01% and 0.1% culture) but showed harm to the medium at higher dosages (0.1%).
Appears to induce cell proliferation and growth when used as a protein medium in vitro, but no evidence suggests this occurs after oral consumption
One study in mice, with oral dosages of 50,160, and 500mg/kg bodyweight daily, increased performance in the forced swim test in a dose dependent manner over 44 days of treatment. The SAA used in this study was freeze-dried and higher in Alanine (34.36%) with a Serine content of 9.58%. This enhancement of performance was also found in a past study, albeit confounded with supplemental tyrosine.
Only high dose SAA showed benefit in two weeks time, whereas both 160mg and 500mg showed benefits at the end of the study (albeit with a dose-dependent benefit). The numbers were a 35.9% time to exhaustion from 500mg/kg daily at 14 days, and 58.8%/121.4% increased time to exhaustion at day 44 with 160mg and 500mg/kg bodyweight respectively.
The former study also found that the weight gain (from diet) was attenuated with exercise and further attenuated with SAA. Muscle glycogen depletion from exercise was also attenuated in a dose dependent manner with SAA.
Decent preliminary results, but needs replication
Silk Amino Acid supplementation was able to prevent the decline in testosterone associated with excessive exercise in rats subject to a weighted swim test.
In rats fed with 3% of their diet as sericin, intestinal absorption of minerals (Zn, Fe, Mg, Ca) increased by 41%, 41%, 21% and 17% respectively. However, this study did not note elevated serum levels. Final body weight was also unaffected by the supplementation.
The 'apparent increase in absorption' was noted due to decreased fecal mineral levels, which was thought to be due to enhanced solubilization of the elements in the GI tract through serine and aspartate's hydroxyl and carboxyl groups (respectively); a mechanism of action only currently known to be attributed to casein phosphopeptides.
In the digestive tract, it has been noted to be resistant to 'several proteases' as noted by these authors in their previous, but unpublished, work. Specific proteases were not mentioned.
One study in rats showed that sericin had the potential to increase fecal immunogluboulin A, mucins, and cecal acids in vivo at a high dose; suggesting that it can interact with the intestinal barrier and immune status and possibly fermantation. A similar dose has also been found to reduce serum triglycerides and glucose during high-fat feeding (the former of which the previous study also found).
Although it is noted to be a 'resistant protein' and thus exert some biological effects in the intestine pre-absorption, at least one study noted that systemic effects were attenuated after injection of glucose (suggesting sericin can affect systemic metabolism).
In regards to its effects as a resistant protein (undigestible), it can protect against colonic tumor growth when it reaches the colon, and shows benefit in rats at 3% of feed (which replaced casein) due to its anti-oxidative properties. This appears to be attributable to Sericin-L, as the preparation method used by Zhaoirgetu et al. was without hydrolysis.
Colonic anti-oxidative effects may be mediated through chelation of copper ions in the intestines, which are normally pro-oxidative.
Sericin appears to possess anti-lipid peroxidation properties and thus is an anti-oxidant in vitro. It has been used with success as a moisterizer in human volunteers and in rats orally through 1% of the diet.
Sericin also appears to be UV resistant although this has not been studied in relation to skin damage.
- Terada S, et al. Preparation of silk protein sericin as mitogenic factor for better mammalian cell culture. J Biosci Bioeng. (2005)
- Kato N, et al. Silk protein, sericin, inhibits lipid peroxidation and tyrosinase activity. Biosci Biotechnol Biochem. (1998)
- Terada S, et al. Sericin, a protein derived from silkworms, accelerates the proliferation of several mammalian cell lines including a hybridoma. Cytotechnology. (2002)
- Tsujimoto K, et al. Cryoprotective effect of the serine-rich repetitive sequence in silk protein sericin. J Biochem. (2001)
- Dugo P, et al. Characterization of the polyphenolic fraction of Morus alba leaves extracts by HPLC coupled to a hybrid IT-TOF MS system. J Sep Sci. (2009)
- Mooney AC, Robertson HM, Wanner KW. Neonate silkworm (Bombyx mori) larvae are attracted to mulberry (Morus alba) leaves with conspecific feeding damage. J Chem Ecol. (2009)
- Wang HY, et al. Isolation and bioactivities of a non-sericin component from cocoon shell silk sericin of the silkworm Bombyx mori. Food Funct. (2012)
- Sato W, et al. Mitogenic effect of sericin on mammalian cells. BMC Proc. (2011)
- Even MS, Sandusky CB, Barnard ND. Serum-free hybridoma culture: ethical, scientific and safety considerations. Trends Biotechnol. (2006)
- Yanagihara K, et al. Effect of the silk protein sericin on the production of adenovirus-based gene-therapy vectors. Biotechnol Appl Biochem. (2006)
- Shin S, et al. Silk amino acids improve physical stamina and male reproductive function of mice. Biol Pharm Bull. (2010)
- Tyrosine-fortified silk amino acids improve physical function of Parkinson’s disease rats.
- Okazaki Y, et al. Consumption of sericin reduces serum lipids, ameliorates glucose tolerance and elevates serum adiponectin in rats fed a high-fat diet. Biosci Biotechnol Biochem. (2010)
- Consumption of silk protein, sericin elevates intestinal absorption of zinc, iron, magnesium and calcium in rats.
- Okazaki Y, et al. Consumption of a resistant protein, sericin, elevates fecal immunoglobulin A, mucins, and cecal organic acids in rats fed a high-fat diet. J Nutr. (2011)
- Zhang YQ. Applications of natural silk protein sericin in biomaterials. Biotechnol Adv. (2002)
- Zhaorigetu S, Sasaki M, Kato N. Consumption of sericin suppresses colon oxidative stress and aberrant crypt foci in 1,2-dimethylhydrazine-treated rats by colon undigested sericin. J Nutr Sci Vitaminol (Tokyo). (2007)
- Padamwar MN, et al. Silk sericin as a moisturizer: an in vivo study. J Cosmet Dermatol. (2005)
- Kim H, et al. Dietary silk protein, sericin, improves epidermal hydration with increased levels of filaggrins and free amino acids in NC/Nga mice. Br J Nutr. (2012)