Silk amino acid (SAA)

Last Updated: August 17 2022

SAAs are amino acids derived from the Silkworm cocoon, containing the peptide compounds Sericin-S and Sericin-L (small and large). Hydrolyzed SAAs are needed to be digested, and SAAs appear to be very nice compounds for skin, hair, and nail health when orally ingested.

Silk amino acid (SAA) is most often used for


1.

Sources and Composition

1.1

Sources

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[1] and prepared from basic Sericin[2] and Sericin Large (Sericin-L) (50-200kDa) which is non-hydrolyzed.[3] The general idea is that they possess a specific amino acid sequence, which are rich in serine amino acids,[4] at around 30-33% Serine by weight.[2]

Sericin prepared in culture as per this study[1] 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.[1]

They are extracted from the Bombix Mori cocoon of the silkworm,[4] which is named as it feeds exclusively on the leaves of the Morus Alba plant;[5] seems silkworm neonates are attracted to the aroma of these plants.[6]

1.2

Other compounds in Silk Amino Acids

Beyond Sericin, components from the cocoon of the silkworm include:

  • Fibroin at 70% of cocoon by weight[7]

  • Sericin at 25% of the cocoon by weight[7]

  • 'Non-Sericin' flavonoids and free amino acids, with potent biological effects.[7]

2.

Interactions with Cell proliferation

Sericin has been implicated as having mitogenic properties in vitro on mammalian cells.[8]

It is being explored as being a tool for cell cultures as a replacement for Bovine Serum Albumin.[9][10] 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.[1]

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.[8]

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%).[8]

Appears to induce cell proliferation and growth when used as a protein medium in vitro, but no evidence suggests this occurs after oral consumption

3.

Effects on Performance

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.[11] 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.[12]

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).[11] 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.[11]

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.[11]

Decent preliminary results, but needs replication

4.

Interactions with Hormones

Silk Amino Acid supplementation was able to prevent the decline in testosterone associated with excessive exercise in rats subject to a weighted swim test.[11]

5.

Interactions with Fat and Glucose Metabolism

After high dose feeding in rats, Sericin (4% of diet by weight) appears to reduce serum levels of free fatty acids and LDL/vLDL lipoproteins.[13]

Liver triglyerides and lipogenic enzymes (malate dehydrogenase, G6P dehydrogenase) were also reduced at this dose.[13]

6.

Intestinal Interactions

6.1

Minerals

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.[14] 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[14] in their previous, but unpublished, work. Specific proteases were not mentioned.

6.2

Other effects

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.[15] 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).[13]

Although it is noted to be a 'resistant protein'[16] 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).[13]

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.[17] This appears to be attributable to Sericin-L, as the preparation method[2] used by Zhaoirgetu et al. was without hydrolysis.[17]

Colonic anti-oxidative effects may be mediated through chelation of copper ions in the intestines, which are normally pro-oxidative.[2]

7.

Cosmetic Usages

Sericin appears to possess anti-lipid peroxidation properties and thus is an anti-oxidant in vitro.[2] It has been used with success as a moisterizer in human volunteers[18] and in rats orally through 1% of the diet.[19]

Sericin also appears to be UV resistant[16] although this has not been studied in relation to skin damage.

References
1.^Terada S, Sasaki M, Yanagihara K, Yamada HPreparation of silk protein sericin as mitogenic factor for better mammalian cell cultureJ Biosci Bioeng.(2005 Dec)
2.^Kato N, Sato S, Yamanaka A, Yamada H, Fuwa N, Nomura MSilk protein, sericin, inhibits lipid peroxidation and tyrosinase activityBiosci Biotechnol Biochem.(1998 Jan)
4.^Tsujimoto K, Takagi H, Takahashi M, Yamada H, Nakamori SCryoprotective effect of the serine-rich repetitive sequence in silk protein sericinJ Biochem.(2001 Jun)
5.^Dugo P, Donato P, Cacciola F, Germanò MP, Rapisarda A, Mondello LCharacterization of the polyphenolic fraction of Morus alba leaves extracts by HPLC coupled to a hybrid IT-TOF MS systemJ Sep Sci.(2009 Nov)
8.^Sato W, Fukumoto K, Yanagihara K, Sasaki M, Kunitomi Y, Terada SMitogenic effect of sericin on mammalian cellsBMC Proc.(2011 Nov 22)
9.^Even MS, Sandusky CB, Barnard NDSerum-free hybridoma culture: ethical, scientific and safety considerationsTrends Biotechnol.(2006 Mar)
10.^Yanagihara K, Terada S, Miki M, Sasaki M, Yamada HEffect of the silk protein sericin on the production of adenovirus-based gene-therapy vectorsBiotechnol Appl Biochem.(2006 Sep)
11.^Shin S, Yeon S, Park D, Oh J, Kang H, Kim S, Joo SS, Lim WT, Lee JY, Choi KC, Kim KY, Kim SU, Kim JC, Kim YBSilk amino acids improve physical stamina and male reproductive function of miceBiol Pharm Bull.(2010 Feb)
13.^Okazaki Y, Kakehi S, Xu Y, Tsujimoto K, Sasaki M, Ogawa H, Kato NConsumption of sericin reduces serum lipids, ameliorates glucose tolerance and elevates serum adiponectin in rats fed a high-fat dietBiosci Biotechnol Biochem.(2010)
18.^Padamwar MN, Pawar AP, Daithankar AV, Mahadik KRSilk sericin as a moisturizer: an in vivo studyJ Cosmet Dermatol.(2005 Dec)