Amelioration of the Progression of an Atopic Dermatitis-Like Skin Lesion by Silk Peptide and Identification of Functional Peptides

Molecular mechanism analysis of apoptosis induced by silk fibroin peptides

Silk fibroin derived from silkworm cocoons exhibits excellent mechanical properties, good biocompatibility, and low immunogenicity. Previous studies showed that silk fibroin had an inhibitory effect on cells, suppressing proliferation and inducing apoptosis. However, the source of the toxicity and the mechanism of apoptosis induction are still unclear. In this study, we hypothesized that the toxicity of silk fibroin might originate from the crystalline region of the heavy chain of silk fibroin. We then verified the hypothesis and the specific induction mechanism. A target peptide segment was obtained from α-chymotrypsin. The potentially toxic mixture of silk fibroin peptides (SFPs) was separated by ion exchange, and the toxicity was tested by an MTT assay. The results showed that SFPs obtained after 4 h of enzymatic hydrolysis had significant cytotoxicity, and SFPs with isoelectric points of 4.0-6.8 (SFPα II) had a significant inhibitory effect on cell growth. LC-MS/MS analysis showed that SFPα II contained a large number of glycine-rich and alanine-rich repetitive sequence polypeptides from the heavy-chain crystallization region. A series of experiments showed that SFPα II mediated cell death through the apoptotic pathway by decreasing the expression of Bcl-2 protein and increasing the expression of Bax protein. SFPα II mainly affected the p53 pathway and the AMPK signaling pathway in HepG2 cells. SFPα II may indirectly increase the expression of Cers2 by inhibiting the phosphorylation of EGFR, which activated apoptotic signaling in the cellular mitochondrial pathway and inhibited the Akt/NF-κB pathway by increasing the expression of PPP2R2A.

Low dose administration of mature silkworm powder induces gastric mucosal defense factors in ethanol-induced gastric injury rat model

Gastric mucosa is important to protect the gastric damage against external factors. We previously reported the gastro-protective effects of steamed and freeze-dried mature silkworm larval powder (SMSP) in ethanol-treated rats. However, the factors that promote mucosal formation still remain unclarified. In this study, we evaluated the effect of SMSP on the restoration and maintenance of gastric mucosal layer as well as anti-inflammatory response in ethanol-induced stomach injury in rats. A significant decrease of ulcer indexes, histopathological scores and pro-inflammatory cytokine levels was observed in SMSP-treated group. In addition, SMSP protected the mucosal layer from ethanol-induced gastric damage by increasing the expression of nitric oxide synthases and heat shock proteins, along with promoting genes related gastric mucosal protection and biosynthesis including mucin 5AC and trefoil factors. These results demonstrate that SMSP attenuates the pro-inflammatory responses and strengthens the gastric mucosal layer, thus exhibiting gastro-protective effect against ethanol-induced gastric injury in rats.

Dietary administration of silk microparticles improves the epidermal and dermal regeneration after a skin wounding in gilthead seabream (Sparus aurata L.)

The impact of dietary supplementation with silk fibroin (SF) microparticles on the wound healing process in gilthead seabream (Sparus aurata) skin was studied. A control diet was enriched with different SF levels: 0 (control), 50 (SF50 diet), and 100 (SF100 diet) mg Kg^-1 to form three experimental diets and was fed to seabream for 30 days. Experimental wounds were performed and after 7 days post-wounding (dpw) skin mucus immunity, macroscopic wound closure, and skin regeneration were studied at a microscopic and genetic level. Results indicated that fish fed SF100 did not suffer the decreases in protease and IgM levels observed in the skin mucus of wounded fish fed with the control diet. Macroscopic findings illustrated that dietary SF100 significantly improved the wound closure ratio compared to those reared in the control group. At a microscopic level, changes in the shape of keratocyte cells were evident in the wounded fish. In addition, the intercellular spaces present between epidermal cells and their proliferation in the epidermis, as well as the presence of blood vessels in the dermis were significantly statistically higher in the skin of fish fed the SF100 diet and sampled at 7 dpw compared to those observed in the skin of fish fed the control or SF50 diets. Moreover, regarding the RNA: DNA ratio, statistically significant increases and decreases were observed in fish fed the control and SF100 diet, respectively, in non-wounded and wounded fish. Interestingly, dietary SF100 supplementation improved skin cell proliferation, enhanced the inflammatory phase, and increased the expression of important genes involved in tissue repair and extracellular matrix formation. In conclusion, the SF100 diet can be considered as an appropriate feed additive to improve wound healing in gilthead seabream.

Immune Response to Silk Sericin-Fibroin Composites: Potential Immunogenic Elements and Alternatives for Immunomodulation

The unique properties of silk proteins (SPs), particularly silk sericin (SS) and silk fibroin (SF), have attracted attention in the design of scaffolds for tissue engineering over the past decades. Since SF has good mechanical properties, while SS displays bioactivity, scaffolds combining both proteins should exhibit complementary properties enhancing the potential of these materials. Unfortunately, SS-SF composites can generate chronic immune responses and their immunogenic element is not completely clear. The potential of SS-SF composites in tissue engineering, elements which may contribute to their immunogenicity, and alternatives for their preparation and design, to modulate the immune response and take advantage of their useful properties, are discussed in this review. It is known that SS can enhance β-sheet formation in SF, which may act as hydrophobic regions with a strong affinity for adsorption proteins inducing the chronic recruitment of inflammatory cells. Therefore, tailoring the exposure of hydrophobic regions at the scaffold surface should represent a viable strategy to modulate the immune response. This can be achieved by coating SS-SF composites with SS or other hydrophilic polymers, to take advantage of their antibiofouling properties. Research is still needed to realize the full potential of these composites for tissue engineering.

Silk peptide production from whole silkworm cocoon using ultrasound and enzymatic treatment and its suppression of solar ultraviolet-induced skin inflammation

Silk fibroin, which is derived from sericin through degumming, is mainly used as a biomaterial. However, interest in functional verification and industrial applications of sericin has been growing for several years. We used ultrasonication to simplify the extraction process of the silk peptide under low salt conditions at 20 °C, instead of using the conventional conditions of high salt and temperature. The concentration of the silk peptide was measured to determine the optimized extraction time and solvent, which were 4 h and 0.1 N NaOH, respectively. The molecular weight of the enzyme-treated silk peptide was measured using SDS-PAGE and GPC. Silk peptide treated with papain after ultrasound had a molecular weight of less than 5 kDa, and the papain treated-silk peptide reduced solar ultraviolet-induced COX-2 expression through inhibition of ERK phosphorylation. This is the first study investigating simultaneous extraction of fibroin and sericin, which can be used for mass production of food materials.

Silk peptide treatment potentiates natural killer cell activity in vitro and induces natural killer cell maturation and activation in mouse splenocytes

Context: Silk peptide from cocoons of silkworm (Bombyx mori L., Bombycidae) has been employed as a biomedical material and exhibits various bioactivities, including immune-modulating activity. Objective: We analyzed whether silk peptide exerts direct modulating effects on NK cells using an NK cell line in vitro and ex vivo splenocytes. We also attempted to delineate the mechanism underlying the modulation. Material and methods: In vitro activity of silk peptide on NK cells was determined by measurement of cytolytic activity against K562 cells at an effector-to-target ratio of 5:1 after incubation of NK-92MI cells with silk peptide (0-2000 μg/mL) for 48 and 72 h. Ex vivo activity of silk peptide on mouse splenic NK cells was determined similarly by using YAC-1 cells. Results: Treatment of NK-92MI NK cells with silk peptide (500-2000 μg/mL) significantly increased cytolytic activity on target cells by 2- to 4-fold. The same concentrations (500-2000 μg/mL) of silk peptide treatment also significantly enhanced the cytolytic activity of splenic NK cells against YAC-1 cells. Silk peptide treatment of IL-2-stimulated splenocytes induced enhanced expression of Th1, 2 and 17 cytokines including TNF-α, IFN-γ, IL-6, IL-4 and IL-17. Finally, ex vivo treatment with silk peptide on mouse splenocytes significantly enhanced the degree of NK cell maturation in a dose-dependent manner from 3.49 to 23.79%. Discussion and conclusions: These findings suggest that silk peptide stimulates NK cells, thereby influencing systemic immune functions and improving natural immunity. Thus, silk peptide could be useful as a complementary therapy in cancer patients.

Oral Administration of Silk Peptide Enhances the Maturation and Cytolytic Activity of Natural Killer Cells

Silk peptide, the hydrolysate of silk protein derived from cocoons, has been employed as a biomedical material and is believed to be safe for human use. Silk peptide display various bioactivities, including anti-inflammatory, immune-regulatory, anti-tumor, anti-viral, and anti-bacterial. Although earlier investigations demonstrated that silk peptide stimulates macrophages and the production of pro-inflammatory cytokines, its effect on natural killer (NK) cell function has not yet been explored. In this study, we initially confirmed that silk peptide enhances NK cell activity in vitro and ex vivo. To assess the modulatory activity of silk peptide on NK cells, mice were fed various amounts of a silk peptide-supplemented diet for 2 months and the effects on immune stimulation, including NK cell activation, were evaluated. Oral administration of silk peptide significantly enhanced the proliferation of mitogen- or IL-2-stimulated splenocytes. In addition, oral silk peptide treatment enhanced the frequency and degree of maturation of NK cells in splenocytes. The same treatment also significantly enhanced the target cell cytolytic activity of NK cells, which was determined by cell surface CD107a expression and intracellular interferon-γ expression. Finally, oral administration of silk peptide stimulated T helper 1-type cytokine expression from splenic lymphocytes. Collectively, our results suggest that silk peptide potentiates NK cell activity in vivo and could be used as a compound for immune-modulating anti-tumor treatment.