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.
Beyond Sericin, components from the cocoon of the silkworm include:
Fibroin at 70% of cocoon by weight
Sericin at 25% of the cocoon by weight
'Non-Sericin' flavonoids and free amino acids, with potent biological effects.
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.
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.
Liver triglyerides and lipogenic enzymes (malate dehydrogenase, G6P dehydrogenase) were also reduced at this dose.
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.