Silk sericin has significantly hypoglycaemic effect in type 2 diabetic mice via anti-oxidation and anti-inflammation

Sericin coats of silk fibres, a degumming waste or future material?

Silk is a fibrous biopolymer with a recorded history in the textile industries for centuries. This fibre is constituted of two different proteins: fibroin and sericin, of which the latter accounting for approximately 20-30 % of the silk mass. Silk sericin (SSER) was previously considered as a waste by-product in silk fibroin extraction. SSER has recently garnered significant scientific interest due to its extensive biological and pharmacological properties. These include antioxidant effects, biocompatibility, low immunogenicity, controlled biodegradability, and the ability to induce cell proliferation. This review covers studies about various aspects of this emerging material, namely, its general morphology, specific structure, molecular weight, features of different layers, and gene sequences. The impact of different extraction methods and the application of extracted SSER based on molecular weight are discussed. Additionally, the characteristic functional groups in the amino acids of sericin facilitate its applications in regenerative medicine, wound healing, drug delivery, textile, environment, and energy, in various forms like hydrogels, films, scaffolds, and conduits. SSER-based materials offer great potentials for multi-functional applications in the upcoming decades, showcasing adaptability for various functional uses and promising future technological advancements.

Fabrication of sustainable functional cotton fabric with silk sericin and chitosan for protective textiles

The use of bio-based sources for producing multifunctional cotton fabric with UV-protective and antibacterial properties is essential. Hence, the primary aim of this work was to develop sustainable functional cotton fabric (antibacterial and UV-protective) by applying silk sericin and chitosan using a simple and environmentally benign pad-dry curing method. The modification as well as functional properties of the treated fabric were evaluated in terms of antimicrobial efficacy, moisture management, UV protection, scavenging activity, surface morphology, thermal stability and mechanical strength. The results indicated that the concentration of chitosan around 10 mg/mL demonstrated remarkable antibacterial efficacy against gram-positive S. aureus bacteria. The quantitative analysis revealed an 87 %, reduction of bacteria, which surpassed the reduction rates in cotton fabric treated with sericin at concentrations of 10 mg/mL and 20 mg/mL. The chitosan/sericin treated fabric showed antioxidant i.e. radical scavenging activity (RSA) of 47.44 % while the fabric treated with chitosan and sericin individually had RSAs of 42.35 % and 53.04 %. Compared to cloth treated with chitosan and sericin separately, the fabric treated with chitosan/sericin showed significantly better resistance to ultraviolet (UV) light (UFP 16.80). Based on the study, it is possible to create sustainable, multipurpose cotton fabrics with potential uses in protective textiles by combining silk sericin with chitosan.

Sericin Protein: Structure, Properties, and Applications

Silk sericin, the glue protein binding fibroin fibers together, is present in the Bombyx mori silkworms' cocoons. In recent years, sericin has gained attention for its wide range of properties and possible opportunities for various applications, as evidenced by the meta-analysis conducted in this review. Sericin extraction methods have evolved over the years to become more efficient and environmentally friendly, preserving its structure. Due to its biocompatibility, biodegradability, anti-inflammatory, antibacterial, antioxidant, UV-protective, anti-tyrosinase, anti-aging, and anti-cancer properties, sericin is increasingly used in biomedical fields like drug delivery, tissue engineering, and serum-free cell culture media. Beyond healthcare, sericin shows promise in industries such as textiles, cosmetics, and food packaging. This review aims to highlight recent advancements in sericin extraction, research, and applications, while also summarizing key findings from earlier studies.

Oral sericin ameliorates type 2 diabetes through passive intestinal and bypass transport into the systemic circulation

ETHNOPHARMACOLOGICAL RELEVANCE

Boiled silkworm cocoons have been used to treat 'Xiaoke disease' (diabetes mellitus) recorded in Chinese medicine for over 800 years. In recent years, it has been found that the active substance silk sericin (SS) has therapeutic benefits in treating type 2 diabetes mellitus (T2DM). SS promotes pancreatic islet signalling, the proliferation of pancreatic islet cells, and insulin secretion. It is inferred that SS enters the bloodstream after oral administration and plays a role in the body's circulation. As a natural protein, SS needs to resist digestion by proteases in the gastrointestinal tract and cross the gastrointestinal barrier after oral administration. It is currently unclear how SS crosses the gastrointestinal barrier and whether it exerts therapeutic effects on T2DM by entering the circulation.

AIM OF THE STUDY

To study how SS crosses the gastrointestinal barrier and whether it enters the body circulation to exert a therapeutic effect on T2DM.

MATERIALS AND METHODS

SS was extracted from silkworm cocoons using an alkaline method with sodium carbonate. The antidigestive capacity of SS was detected using SDS-PAGE gel electrophoresis experiments. The mode of uptake and translocation of orally consumed SS in vivo was analysed using the AP-side to BL-side and BL-side-AP-side translocations, apparent Permeability coefficient (Papp), and Exocytosis rates (ER). The study compared the differences between the adSS group and the adSS + EDTA group by using Ethylenediaminetetraacetic acid (EDTA) to separate the tight junctions between Caco-2 cells. The aim was to analyze whether the transport mode of oral filaggrin proteins in vivo could be absorbed by bypass transport. By administering SS through oral and intraperitoneal injection to type 2 diabetic mice, we measured its concentration in the blood, as well as blood glucose and insulin levels, to determine its effectiveness in treating diabetes and its ability to enter the body's circulation for treatment.

RESULTS

The molecular weight of SS decreased from 10k∼25 kDa to 10k∼15 kDa after in vitro simulated gastrointestinal fluid digestion, indicating its good antidigestive properties. The apparent Papp was greater than 1 × 10-6 cm·s-1, and the ER was between 0.5 and 1.5, indicating that adSS was well-absorbed and mainly passively transported. The Caco-2 cell model showed that the addition of EDTA promoted the transport of adSS, resulting in significantly larger Papp and ER values, indicating that adSS was absorbed by bypass transport. After oral administration of SS, the concentration of SS in the blood was lower than after intraperitoneal injection, which is 60% of intraperitoneal administration. Mice with a T2DM model who were administered SS for 5 weeks showed significant improvement in insulin resistance and glucose tolerance. Additionally, the pancreatic tissue appeared more regular. In the treatment of T2DM, injections of SS have been shown to be more effective than oral administration. Both oral and intraperitoneal injections have been partially involved in the circulation.

CONCLUSIONS

SS is enzymatically cleaved by proteolytic enzymes in the gastrointestinal tract. The smaller molecules are partially absorbed into the body's circulation through passive and paracrine transport, exerting a therapeutic effect on T2DM.

Advancements in silk fibroin and silk sericin-based biomaterial applications for cancer therapy and wound dressing formulation: A comprehensive review

Silks are a class of proteins generated naturally by different arthropods, including silkworms, spiders, scorpions, mites, wasps, and bees. This review discusses the silk fibroin and silk sericin fabricated by Bombyx mori silkworm as versatile fibers. This silk fiber is predominantly composed of hydrophobic silk fibroin and hydrophilic silk sericin. Fibroin is defined as a structural protein that bestows silk with strength, while sericin is characterized as a gum-like protein, tying the two fibrous proteins together and endowing silk proteins with elasticity. Due to their versatile structures, biocompatibility, and biodegradability, they could be tailored into intricate structures to warrant particular demands. The intrinsic functional groups of both proteins enable their functionalization and cross-linking with various biomaterials to endow the matrix with favorable antioxidant and antibacterial properties. Depending on the target applications, they can be integrated with other materials to formulate nanofibrous, hydrogels, films, and micro-nanoparticles. Given the outstanding biological and controllable physicochemical features of fibroin and sericin, they could be exploited in pharmaceutical applications involving tissue engineering, wound repair, drug delivery, and cancer therapy. This review comprehensively discusses the advancements in the implementation of different formulations of silk fibroin and sericin in wound healing and drug delivery systems, particularly for cancer treatment.

Eco-Friendly Production of Polyvinyl Alcohol/Carboxymethyl Cellulose Wound Healing Dressing Containing Sericin

Wound dressing production represents an important segment in the biomedical healthcare field, but finding a simple and eco-friendly method that combines a natural compound and a biocompatible dressing production for biomedical application is still a challenge. Therefore, the aim of this study is to develop wound healing dressings that are environmentally friendly, low cost, and easily produced, using natural agents and a physical crosslinking technique. Hydrogel wound healing dressings were prepared from polyvinyl alcohol/carboxymethyl cellulose and sericin using the freeze-thawing method as a crosslinking method. The morphological characterization was carried out by scanning electron microscopy (SEM), whereas the mechanical analysis was carried out by dynamic mechanical analysis (DMA) to test the tensile strength and compression properties. Then, the healing property of the wound dressing material was tested by in vitro and ex vivo tests. The results show a three-dimensional microporous structure with no cytotoxicity, excellent stretchability with compressive properties similar to those of human skin, and excellent healing properties. The proposed hydrogel dressing was tested in vitro with HaCaT keratinocytes and ex vivo with epidermal tissues, demonstrating an effective advantage on wound healing acceleration. Accordingly, this study was successful in developing wound healing dressings using natural agents and a simple and green crosslinking method.

Ad libitum feeding of silkworm larvae powder-containing diets specifically influences metabolism-related and short-chain fatty acid-producing gut bacteria in mice

Silkworm (Bombyx mori) larvae are expected to be useful as an ingredient in entomophagy. They are full of nutrients, including indigestible proteins; however, there have been few studies on the effects of the consumption of the entire body of silkworms on the intestinal microflora. We prepared a customized diet containing silkworm larval powder (SLP), and investigated the effects of ad libitum feeding of the SLP diet on the intestinal microbiota and the amount of short-chain fatty acids (SCFAs) in mice. We found that the diversity of the cecal and fecal microbiota increased in the mice fed the SLP diet (SLP group), and that the composition of their intestinal microbiota differed from that of the control mice. Furthermore, a genus-level microbiota analysis showed that in the SLP group, the proportions of Alistipes, Lachnospiraceae A2, and RF39, which are associated with the prevention of obesity, were significantly increased, while the proportions of Helicobacter and Anaerotruncus, which are associated with obesity, were significantly decreased. Additionally, the level of butyrate was increased in the SLP group, and Clostridia UCG 014 and Lachnospiraceae FCS020 were found to be associated with the level of butyrate, one of the major SCFAs. These findings indicated that silkworm powder may be useful as an insect food that might also improve obesity.

Development and Application of an Advanced Biomedical Material-Silk Sericin

Sericin, a protein derived from silkworm cocoons, is considered a waste product derived from the silk industry for thousands of years due to a lack of understanding of its properties. However, in recent decades, a range of exciting properties of sericin are studied and uncovered, including cytocompatibility, low-immunogenicity, photo-luminescence, antioxidant properties, as well as cell-function regulating activities. These properties make sericin-based biomaterials promising candidates for biomedical applications. This review summarizes the properties and bioactivities of silk sericin and highlights the latest developments in sericin in tissue engineering and regenerative medicine. Furthermore, the extended application of sericin in developing flexible electronic devices and 3D bioprinting is also discussed. It is believed that sericin-based biomaterials have great potential of being developed into novel tissue engineering products and smart implantable devices for various medical applications toward improving clinical outcomes.

Transparent injectable sericin-honey hydrogel with antioxidant and antibacterial activities combined with feeding sericin accelerates diabetic wound healing

Wound healing in diabetics is often impaired or delayed due to the presence of high reactive oxygen species and low antioxidant levels. Here, a sericin-honey semi-interpenetrating network hydrogel with excellent antioxidant activity was prepared. Besides, the sericin-honey hydrogel is transparent, injectable, sticky, highly porous, and has good swelling properties, antibacterial activity, and cell compatibility. Based on its good performancein vitro, sericin-honey hydrogel achieved effectivein vivotreatment on a mouse diabetic wound model, significantly accelerating the wound healing process. Furthermore, the combined effect of feeding sericin solution played a positive role in strengthening the effect of diabetic wound repair.

Sericin and melatonin mitigate diethylnitrosamine-instigated testicular impairment in mice: Implications of oxidative stress, spermatogenesis, steroidogenesis, and modulation of Nrf2/WT1/SF-1 signaling pathways

AIMS

This study aimed to investigate the therapeutic influence of combination therapy with sericin and melatonin on attenuating diethylnitrosamine (DEN)-instigated testicular dysfunction in mice and defining the molecular mechanisms involved in orchestrating redox signaling pathways and restoring spermatogenesis and steroidogenesis.

MATERIALS AND METHODS

Different groups of male Swiss albino mice were established and injected with respective drugs intraperitoneally. Semen analysis, hormonal assays, and oxidative stress biomarkers were evaluated. Additionally, melatonin and its receptors, WT1, SF-1, vimentin, Nrf2, and ANXA1 expressions were assessed. Histopathological and ultrastructural features of the testes were investigated by semithin, SEM, and TEM analyses.

KEY FINDINGS

Exposure to DEN exhibited pathophysiological consequences, including a remarkable increase in lipid peroxidation associated with substantial diminutions in SOD, CAT, GPx, GSH, GSH:GSSG, and GST. Furthermore, it disrupted spermatozoa integrity, testosterone, FSH, LH, melatonin, and its receptors (MT1 and MT2) levels, implying spermatogenesis dysfunction. By contrast, treatment with sericin and melatonin significantly restored these disturbances. Interestingly, the combination therapy of sericin and melatonin noticeably augmented the Nrf2, WT1, and SF-1 expressions compared to DEN-treated mice, deciphering the amelioration perceived in antioxidant defense and spermatogenesis inside cells. Furthermore, immunohistochemical detection of ANXA1 alongside histopathological and ultrastructural analyses revealed evident maintenance of testicular structures without discernible inflammation or anomalies in mice administered with sericin and melatonin compared to the DEN-treated group.

SIGNIFICANCE

Our findings highlighted that treatment with sericin and melatonin alleviated the testicular tissues in mice from oxidative stress and dysregulated spermatogenesis and steroidogenesis engendered by DEN.

Sericin enhances ammonia detoxification by promotes urea cycle enzyme genes and activates hepatic autophagy in relation to CARD-9/MAPK pathway

Urea cycle is an important metabolic process that initiates in liver mitochondria and converts ammonia to urea. The impairment of ammonia detoxification, both primary and secondary causes, lead to hyperammonemia, a life-threatening condition affecting to the brain. Current treatments are not enough effective. In addition, our recent proteomics study in hypercholesterolemic rat model demonstrated that sericin enhances hepatic nitrogenous waste removal through carbamoyl-phosphate synthase 1 (CPS-1), aldehyde dehydrogenase-2 (ALDH-2), and uricase proteins. However, the underlining mechanisms regard to this property is not clarified yet. Therefore, the present study aims to examine the effect of sericin on urea cycle enzyme genes (CPS-1 and ornithine transcarbamylase; OTC) and proteins (mitogen-activated protein kinase; MAPK, caspase recruitment domain-containing protein 9; CARD-9, Microtubule-associated protein light chain 3; LC-3), which relate to urea production and liver homeostasis in hepatic cell line (HepG2) and hypercholesterolemic rat treated with or without sericin. qRT-PCR, immunohistochemistry, and electron microscopy techniques were performed. In vitro study determined that high dose of sericin at 1 mg/ml increased liver detoxification enzyme (Cytochrome P450 1A2; CYP1A2 and ALDH-2) and urea cycle enzyme (CPS-1 and OTC) genes. Both in HepG2 cell and rat liver mitochondria, sericin significantly downregulated CARD-9 (apoptotic protein) expression while upregulated MAPK (hepatic homeostasis protein) and LC-3 (autophagic protein) expressions. Hence, it might be concluded that sericin promotes ammonia detoxification by both increases urea cycle enzyme genes and enhances hepatic autophagy in associated with CARD-9/MAPK pathway (as shown by their own negative relationship). This study presents another beneficial property of sericin to develop an upcoming candidate for ammonia toxicity alleviation and liver function improvement.

Phycocyanin as a nature-inspired antidiabetic agent: A systematic review

BACKGROUND

Nutraceuticals have been important for more than two decades for their safety, efficacy, and outstanding effects. Diabetes is a major metabolic syndrome, which may be improved using nutritional pharmaceuticals. Some microalgae species, such as spirulina, stand out by providing biomass with exceptional nutritional properties. Spirulina has a wide range of pharmacological effects, mostly related to phycocyanin. Phycocyanin is a protein compound with antidiabetic properties, known as a nutraceutical.

OBJECTIVE

This review delves into phycocyanin applications in diabetes and its complications and ascertains the mechanisms involved.

METHODS

Scopus, PubMed, Cochrane Library, Web of Science, and ProQuest databases were systematically reviewed (up to April 30, 2023), in which only animal and cellular studies were found.

RESULTS

According to animal studies, the administration of phycocyanin affected biochemical parameters (primary outcome) related to diabetes. These results showed an increase in fasting insulin serum and a decrease in fasting blood glucose, glycosylated serum protein, and glycosylated hemoglobin. In cellular studies, though, phycocyanin prevented methylglyoxal and human islet amyloid polypeptide-induced dysfunction in β-cells and induced apoptosis through different molecular pathways (secondary outcome), including activation of Nrf2, PI3K/Akt, and suppression of JNK and p38. Also, phycocyanin exerted its antidiabetic effect by affecting the pathways regulating hepatic glucose metabolism.

CONCLUSIONS

Thus, based on the available information and literature, targeting these pathways by phycocyanin may unleash an array of benefits, including positive outcomes of the antidiabetic effects of phycocyanin as a nutraceutical.

OTHER

This systematic review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) at the National Institute of Health. The registration number is CRD42022307522.

Protein and Peptide-Based Nanotechnology for Enhancing Stability, Bioactivity, and Delivery of Anthocyanins

Anthocyanin, a unique natural polyphenol, is abundant in plants and widely utilized in biomedicine, cosmetics, and the food industry due to its excellent antioxidant, anticancer, antiaging, antimicrobial, and anti-inflammatory properties. However, the degradation of anthocyanin in an extreme environment, such as alkali pH, high temperatures, and metal ions, limits its physiochemical stabilities and bioavailabilities. Encapsulation and combining anthocyanin with biomaterials could efficiently stabilize anthocyanin for protection. Promisingly, natural or artificially designed proteins and peptides with favorable stabilities, excellent biocapacity, and wide sources are potential candidates to stabilize anthocyanin. This review focuses on recent progress, strategies, and perspectives on protein and peptide for anthocyanin functionalization and delivery, i.e., formulation technologies, physicochemical stability enhancement, cellular uptake, bioavailabilities, and biological activities development. Interestingly, due to the simplicity and diversity of peptide structure, the interaction mechanisms between peptide and anthocyanin could be illustrated. This work sheds light on the mechanism of protein/peptide-anthocyanin nanoparticle construction and expands on potential applications of anthocyanin in nutrition and biomedicine.

Simulation of Cortical and Cancellous Bone to Accelerate Tissue Regeneration

Different tissues have complex anisotropic structures to support biological functions. Mimicking these complex structures in vitro remains a challenge in biomaterials designs in support of tissue regeneration. Here, inspired by different types of silk nanofibers, a composite materials strategy was pursued towards this challenge. A combination of fabrication methods was utilized to achieve separate control of amorphous and beta-sheet rich silk nanofibers in the same solution. Aqueous solutions containing these two structural types of silk nanofibers were then simultaneously treated with an electric field and with ethylene glycol diglycidyl ether (EGDE). Under these conditions, the beta-sheet rich silk nanofibers in the mixture responded to the electric field while the amorphous nanofibers were active in the crosslinking process with the EGDE. As a result, cryogels with anisotropic structures were prepared, including mimics for cortical- and cancellous-like bone biomaterials as a complex osteoinductive niche. In vitro studies revealed that mechanical cues of the cryogels induced osteodifferentiation of stem cells while the anisotropy inside the cryogels influenced immune reactions of macrophages. These bioactive cryogels also stimulated improved bone regeneration in vivo through modulation of inflammation, angiogenesis and osteogenesis responses, suggesting an effective strategy to develop bioactive matrices with complex anisotropic structures beneficial to tissue regeneration.

Sericin from Fibroin-Deficient Silkworms Served as a Promising Resource for Biomedicine

Sericin, a fascinating natural biomaterial derived from silkworms, has received increasing interest in recent years for its unique bioactivity and high compatibility. Silkworms can be divided into wild-type or silk fibroin-deficient mutants according to whether they synthesize and secrete silk fibroin. Silk fibroin-deficient mutant silkworms and their cocoons are convenient for us to obtain diverse and high-quality sericin, which has been applicated in various fields such as cell culture, tissue engineering, drug delivery, and cosmetics. Here, we present an overview of our silkworm varieties resources, especially silk fibroin-deficient mutant silkworms. We optimized various extraction methods of sericin and summarized the characteristics and advantages of sericin. Finally, we developed and discussed a series of sericin-based biomaterials for promising applications for a diverse set of needs.

Vinyl chloride enhances high-fat diet-induced proteome alterations in the mouse pancreas related to metabolic dysfunction

Alterations in physiological processes in pancreas have been associated with various metabolic dysfunctions and can result from environmental exposures, such as chemicals and diet. It was reported that environmental vinyl chloride (VC) exposure, a common industrial organochlorine and environmental pollutant, significantly exacerbated metabolic-related phenotypes in mice fed concurrently with high-fat diet (HFD) but not low-fat diet (LFD). However, little is known about the role of the pancreas in this interplay, especially at a proteomic level. The present study was undertaken to examine the protein responses to VC exposure in pancreas tissues of C57BL/6J mice fed LFD or HFD, with focus on the investigation of protein expression and/or phosphorylation levels of key protein biomarkers of carbohydrate, lipid, and energy metabolism, oxidative stress and detoxification, insulin secretion and regulation, cell growth, development, and communication, immunological responses and inflammation, and biomarkers of pancreatic diseases and cancers. We found that the protein alterations may indicate diet-mediated susceptibility in mouse pancreas induced by HFD to concurrent exposure of low levels of inhaled VC. These proteome biomarkers may lead to a better understanding of pancreas-mediated adaptive or adverse response and susceptibility to metabolic disease.

Effects of sericin on oxidative stress and PI3K/AKT/mTOR signal pathway in cryopreserved mice ovarian tissue

Ovarian tissue cryopreservation is an effective fertility protective strategy for preadolescent female cancer patients, whose tumor treatment cannot be delayed. In the present study, the effects of sericin, as an antioxidant, on mice ovarian tissue freezing and thawing were investigated. Mice ovarian tissues were cryopreserved and thawed in medium containing 0.5% or 1%sericin (w/v), and 0.1 mM melatonin. Then, the follicular morphology was observed. The levels of antioxidant enzymes were determined, including glutathione (GSH), glutathione peroxidase (GSH-Px), total superoxide dismutase (T-SOD), total antioxidant capacity (T-AOC) and catalase (CAT). Moreover, the levels of nitric oxide (NO), malondialdehyde (MDA) and lactate dehydrogenase (LDH) were also tested. Besides, apoptosis-related proteins Bcl-2 and Bax were determined. Our results showed that 1% sericin maintained follicular morphology, inhibited apoptosis, decreased MDA and NO levels, and boosted endogenous antioxidant enzyme levels, while had no significant effect on LDH levels. Furthermore, these effects may be related with the activation of the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of Rapamycin (mTOR) signaling pathway, as demonstrated by increased PI3K, p-AKT and mTOR levels. These findings demonstrate that 1% sericin may reduce oxidative stress and protect ovarian tissues during freezing and thawing via PI3K/AKT/mTOR signaling pathway.

Analysis of the antimicrobial potential of sericin-coated silver nanoparticles against human pathogens

The antibacterial activity of synthetic antimicrobial agents is well known, but most of them have several side effects and are effective against selective microbes. Recently, major concern for the microbiologists is to investigate for some stable, non-toxic, cheap, and eco-friendly antimicrobial agents with a wide range of bactericidal potential. A cost-effective and environmentally friendly alternate has been proposed in the form of green synthesized nanoparticles. The Present study was designed to fabricate sericin-coated silver nanoparticles (S-AgNPs) using sericin as stabilizer and reductant of silver ions and their antibacterial potential was evaluated at various concentrations and temperatures (8, 40, and 50°C). Antimicrobial activities were assessed by the agar well diffusion method. Antibacterial activity of S-AgNPs was measured at different concentrations (1-6 mg/ml) whereas; antifungal activity was tested at 5-20 mg/ml of S-AgNPs. Nanoparticles were characterized by UV-visible spectrophotometer, Fourier transform infrared spectroscopy, and scanning electron microscopy. These nanoparticles significantly subdued the growth of Clostridium difficile (18.7 ± 0.9 mm), Proteus mirabilis (12.3 ± 0.3 mm) and Bacillus licheniformis (10.7 ± 0.9 mm) and Aspergillus flavus (18.7 ± 2.0 mm), Mucor mycetes (13 .0 ± 1.5 mm), Candida albicans (15.3 ± 0.3 mm) and Aspergillus niger (10.0 ± 0.6 mm). S-AgNPs were stable at all temperatures and the maximum growth inhibition was found at 8°C for all pathogenic strains. We concluded that the S-AgNPs could be a potential candidate to inhibit the growth of bacterial and fungal pathogens at a wide range of environmental conditions like temperature. In various biomedical applications including antimicrobial and wound dressings, S-AgNPs can be used in the future to treat various bacterial and fungal infections.

Regulatory effect of sericin protein in inflammatory pathways; A comprehensive review

Sericin protein is a type of protein derived from silk cocoons. Sericin hydrogen bonds cause adhesion to the silk cocoon. This substance contains a large amount of serine amino acids in its structure. At first, the medicinal properties of this substance were unknown, but today many properties have been discovered for this substance. The unique properties of this substance have made it widely used in the pharmaceutical and cosmetic industries. The applications of Sericin in pharmacy are as follows. Sericin is used to repair wounds by producing collagen. Other uses for the drug include anti-diabetic, anti-cholesterol, metabolic modulator, anti-tumor, heart protection, antioxidant, antibacterial, wound healing, cell proliferation, UV protection, freezing, and skin moisturizing. The physicochemical properties of Sericin have attracted the attention of pharmacists and their widespread use in the production of drugs and treatment of diseases. One of the critical and unique properties of Sericin is its anti-inflammatory property. In this article, this property of Sericin is discussed in detail, and according to the experiments performed by pharmacists, this substance has shown a significant effect in eliminating inflammation. This study aimed to evaluate the impact of Sericin protein in relieving inflammation.

Effects of sericin and egg white on the inflammation of damaged skin in mice

Sericin and egg white (EW) have shown the ability to promote wound healing. However, there have been insufficient studies regarding the effects of sericin and EW mixtures on wound healing. This study aimed to investigate the effects of a hybrid sericin and EW solution on wound repair and inflammation-related indicators in mouse skin. In this work, sericin with a low molecular weight was first mixed with homogeneous EW to prepare a hybrid wound dressing. Histology evaluation, the expression of C-reactive protein (CRP) and inflammatory cytokines in mice were tested to determine the effects of this dressing on skin injuries in mice. The results showed that sericin and the hybrid solution of sericin and EW effectively promoted wound healing in mouse skin. The wound recovery rates of mice 12 days after treatment with a medium dose of sericin (0.2 g ml^-1) and the same dosage of sericin with added EW were 1.32 and 1.65 times that of mice treated with phosphate buffer saline as a control, respectively. In addition, the mixture solution was more effective in wound healing than sericin alone. Sericin with EW significantly reduced the expression of CRP and inflammatory cytokines in mice during wound healing. A sericin and EW hybrid solution can effectively shorten the time needed for wound healing and reduce inflammation-related indicators in mice, making it a promising candidate for wound dressing.

Dietary administration with hydrolyzed silk sericin improves the intestinal health of diabetic rats

Type II diabetes (T2D) is a global epidemic disease with an increased incidence and prevalence. Gut microbiota plays an important role in controlling T2D development. Dietary administration of prebiotics, probiotics, and drugs, including metformin, showed the regulatory impact on the change of gut microbiota, which is associated with the improvement of glucose tolerance. In this study, silk sericin was manufactured into hydrolyzed sericin peptide (HSP) powders as a dietary additive to investigate the effect on the gut microbiota of T2D model rats. The results indicated that the HSP-augmented dietary administration lowers the fast glucose level of diabetic rats, and HSP augmentation induces a change in the gut microbiota composition of T2D model rats toward the normal rats. Some key taxa, including Lactobacillus gasseri, were suggested to be involved in controlling T2D development. This finding provides new insight into developing sericin as functional food or therapeutic prebiotics against T2D in clinical practice.

Silk sericin as building blocks of bioactive materials for advanced therapeutics

Silk sericin is a class of protein biopolymers produced by silkworms. Increasing attention has been paid to silk sericin for biomedical applications in the last decade, not only because of its excellent biocompatibility and biodegradability but also due to the pharmacological activities stemming from its unique amino acid compositions. In this review, the biological properties of silk sericin, including curing specific diseases and promoting tissue regeneration, as well as underlying mechanisms are summarized. We consider the antioxidant activity of silk sericin as a fundamental property, which could account for partial biological activities, despite the exact mechanisms of silk sericin's effect remaining unknown. Based on the reactive groups on silk sericin, approaches of bottom-up fabrication of silk sericin-based biomaterials are highlighted, including non-covalent interactions and chemical reactions (reduction, crosslinking, bioconjugation, and polymerization). We then briefly present the cutting-edge advances of silk sericin-based biomaterials applied in tissue engineering and drug delivery. The challenges of silk sericin-based biomaterials are proposed. With more bioactivities and underlying mechanisms of silk sericin uncovered, it is going to boost the therapeutic potential of silk sericin-based biomaterials.

Multi-Omics Integration to Reveal the Mechanism of Sericin Inhibiting LPS-Induced Inflammation

Sericin is a natural protein with high application potential, but the research on its efficacy is very limited. In this study, the anti-inflammatory mechanism of sericin protein was investigated. Firstly, the protein composition of sericin extracts was determined by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). This was then combined with Enzyme-linked Immunosorbent Assay (ELISA) and Quantitative Real-time PCR (qRT-PCR), and it was confirmed that the anti-inflammation ability of sericin was positively correlated with the purity of sericin 1 protein. Finally, RNA-seq was performed to quantify the inhibitory capacity of sericin sample SS2 in LPS-stimulated macrophages. The gene functional annotation showed that SS2 suppressed almost all PRRs signaling pathways activated by lipopolysaccharides (LPS), such as the Toll-like receptors (TLRs) and NOD-like receptors (NLRs) signaling pathways. The expression level of adaptor gene MyD88 and receptor gene NOD1 was significantly down-regulated after SS2 treatment. SS2 also reduced the phosphorylation levels of NF-κB P65, P38, and JNK, thereby reducing the expressions of IL-1β, IL-6, INOS, and other inflammatory cytokines. It was confirmed that sericin inhibited LPS-induced inflammation through MyD88/NF-κB pathway. This finding provides necessary theoretical support for sericin development and application.

Silk Sericin: A Promising Sustainable Biomaterial for Biomedical and Pharmaceutical Applications

Silk is a natural composite fiber composed mainly of hydrophobic fibroin and hydrophilic sericin, produced by the silkworm Bombyx mori. In the textile industry, the cocoons of B. mori are processed into silk fabric, where the sericin is substantially removed and usually discarded in wastewater. This wastewater pollutes the environment and water sources. However, sericin has been recognized as a potential biomaterial due to its biocompatibility, immunocompatibility, biodegradability, anti-inflammatory, antibacterial, antioxidant and photoprotective properties. Moreover, sericin can produce hydrogels, films, sponges, foams, dressings, particles, fibers, etc., for various biomedical and pharmaceutical applications (e.g., tissue engineering, wound healing, drug delivery, cosmetics). Given the severe environmental pollution caused by the disposal of sericin and its beneficial properties, there has been growing interest in upcycling this biomaterial, which could have a strong and positive economic, social and environmental impact.

Toxicological evaluation of water-extract sericin from silkworm (Bombyx mori) in pregnant rats and their fetus during pregnancy

Sericin is a natural protein produced by the silkworm Bombyx mori, which has a wide range of biological activities and has a broad application prospect in multiple areas. However, systemic toxicity and safety assessment of sericin is still rare. This study was aimed to evaluate the toxic effects of water-extract sericin from cocoons of Bombyx mori in pregnant rats and their fetuses during pregnancy. Eighty pregnant rats were randomly divided into three treatment groups, one negative and one positive control group. The treatment groups were administered water-extract sericin solutions at doses of 1,000, 500, and 250 mg/kg, while the negative and positive control groups were administered pure water and 300 mg/kg aspirin, respectively. Rats were exposed daily by oral gavage from the seventh day of gestation for 10 consecutive days and sacrificed on the 20th day of gestation. The results showed that water-extract sericin did not induce any treatment-related changes on pregnant rats (clinical signs, body weights, food consumption, ovarian and uterine weights) and fetuses (body weights, body lengths, tail lengths, visceral, and skeletal development). The no-observed-adverse-effect-level (NOAEL) of sericin was determined to be 1,000 mg/kg body weight in rats. These results indicated that water-extract sericin is of low teratogenic potential under the experimental conditions of this study.

Bombyx mori cocoon as a promising pharmacological agent: A review of ethnopharmacology, chemistry, and biological activities

Silk cocoon, naturally produced by silkworms scientifically named Bombyx mori L. (Lepidoptera, Bombycidae), is one of the well-known medicinal agents with several therapeutic activities. The present study aims to review the various aspects of the silk cocoon, including chemical composition, traditional uses, biological and biotechnological activities, and toxicological issues, to provide a scientific source for scholars. For this purpose, Electronic databases including PubMed, Scopus, Google Scholar, Web of Science, and traditional literature, were searched up to December 2021. According to the historical data, silk farming is acknowledged as one of the most ancient agricultural findings. The silk is generally composed of 75–83% fibroin, 17–25% sericin, and 1–5% non-sericin components, including secondary metabolites, wax, pigments, carbohydrates, and other impurities. Flavonoids, especially quercetin and kaempferol, alkaloids, coumarin derivatives, and phenolic acids, are among the secondary metabolites isolated from the silk cocoon. In recent years the biological properties of the silk cocoon, especially its major proteins, namely fibroin and sericin, have drawn special attention. Scientific literature has investigated several pharmacological effects of the silk cocoon and its ingredients, including cardioprotective, antioxidant, anticancer, antidiabetic, antihyperlipidemia, gastroprotective, as well as ameliorated skin health activities. In addition, it has been extensively taken into consideration in drug delivery and tissue engineering study fields. Furthermore, its toxicity is in acceptable range.

Silk sericin-based materials for biomedical applications

Silk sericin, a natural protein extracted from silkworm cocoons, has been extensively studied and utilized in the biomedical field because of its superior biological activities and controllable chemical-physical properties. Sericin is biocompatible and naturally cell adhesive, enabling cell attachment, proliferation, and differentiation in sericin-based materials. Moreover, its abundant functional groups from variable amino acids composition allow sericin to be chemically modified and cross-linked to form versatile constructs serving as alternative matrixes for biomedical applications. Recently, sericin has been constructed into various types of biomaterials for tissue engineering and regenerative medicine, including various bulk constructions (films, hydrogels, scaffolds, conduits, and devices) and micro-nano formulations. In this review, we systemically summarize the properties of silk sericin, introduce its different forms, and demonstrate their newly-developed as well as potential biomedical applications.

Bibliometric Analysis of Trends in Mulberry and Silkworm Research on the Production of Silk and Its By-Products

Simple Summary

Over the past two decades scientific research on sericulture, the agricultural activity of silk production, generated a great number of outputs in the form of articles reported and classified by one of the most well-known and used database dealing with scientific literature. This occurrence demonstrates an increasing interest in this sector especially starting from 2000s; results presented in relevant papers showed their applicability even in fields apparently not related to silk production as commonly meant, like medicine, cosmetics, and engineering. To understand how sericulture has been transcending its usual boundaries, which are its current “hotspots”, and links with other fields of study, the authors propose a text-mining based analysis of the outputs of scientific research on sericulture and silk; the final goal is to establish “quantitative” indicators for researchers, entrepreneurs, and scholars.

Abstract

Traditionally, sericulture is meant as the agricultural activity of silk production, from mulberry (Morus sp.pl.) cultivation to silkworm (Bombyx mori L.) rearing. The aim of the present work is to analyze the trends and outputs of scientific research on sericulture-related topics during the last two decades, from 2000 to 2020. In this work the authors propose a text-mining analysis of the titles, abstracts and keywords of scientific articles focused on sericulture and available in the SCOPUS database considering the above-mentioned period of time; from this article collection, the 100 most recurrent terms were extracted and studied in detail. The number of publications per year in sericulture-related topics increased from 87 in 2000 to 363 in 2020 (+317%). The 100 most recurrent terms were then aggregated in clusters. The analysis shows how in the last period scientific research, besides the traditional themes of sericulture, also focused on alternative products obtainable from the sericultural practice, as fruits of mulberry trees (increment of +134% of the occurrences in the last five years) and chemical compounds as antioxidants (+233% of occurrences), phenolics (+330% of occurrences) and flavonoids (+274% of occurrences). From these considerations, the authors can state how sericulture is an active and multidisciplinary research field.

Genetically engineered pH-responsive silk sericin nanospheres with efficient therapeutic effect on ulcerative colitis

Ulcerative colitis (UC) is one type of inflammatory bowel disease (IBD) and lactoferrin (LF) is a promising protein drug to treat UC. However, targeted LF delivery to optimize bioavailability, targeting and effectiveness remains a challenge. Here, we report an effective strategy to fabricate silk sericin nanospheres systems for the delivery of recombinant human lactoferrin (SS-NS-rhLF). The system is based on the use of optimized transgenic silkworms to generate genetically engineered silk fibers (rhLF-silks). The rhLF silks were used for fabricating SS-NS-rhLF by ethanol precipitation. The SS-NS-rhLF were stable with a spherical morphology with an average diameter of 123 nm. The negatively charged sericins in a pH ≥ 5.5 environment achieved specific targeting of the SS-NS-rhLF to positively charged colonic sites. The SS-NS-rhLF achieved efficient uptake by cells in the inflamed colon of mice when compared to free lactoferrin in solution (SOL-rhLF). Furthermore, oral administration of the SS-NS-rhLF with low dose of rhLF significantly relived symptoms of UC in mice and achieved comparable therapeutic effect to the high dose of SOL-rhLF by supporting the reformation of cell structure and length of colon tissue, reducing the release of inflammatory factors, inhibiting the activation of the NF-κB inflammatory pathway, and maintaining a stable intestinal microbial population in mice. These results showed that the SS-NS-rhLF is a promising system for colitis treatment. STATEMENT OF SIGNIFICANCE: Targeting and effective delivery of multiple biological functional protein human lactoferrin (rhLF) is a promising strategy to treat ulcerative colitis in the clinic. Here, rhLF-transgenic silk cocoons were used to fabricate a rhLF-sericin nanosphere delivery system (SS-NS-rhLF). The fabricated SS-NS-rhLF showed identical spherical morphology, stable structure, sustainable rhLF release, efficient cell uptake and negative charge in an environment of pH above 5.5, thus realized the specific targeting to the positively charged colonic sites to treat UC mice through oral administration. The therapeutic effect of SS-NS-rhLF with a low rhLF dose in the UC mice was comparable to the high dose of free rhLF treatment in solution form, suggesting that the SS-NS-rhLF is a promising system for colitis treatment.

The Protective Effect of Sericin on AML12 Cells Exposed to Oxidative Stress Damage in a High-Glucose Environment

Two types of sericin peptides with high molecular weight (HS) and low molecular weight (LS) were obtained by the green water boiling ultrasonic method and the Ca(OH)2 ultrasonic method, respectively. In this experiment, a high-glucose medium was used to simulate a high-glucose environment in the body, and appropriate concentrations of normal alpha mouse liver 12 (AML12) hepatocytes were exposed to a series of concentrations of HS and LS. The effects of the two sericin peptides on AML12 cells in a high-glucose environment were investigated in detail in terms of oxidative stress and inflammatory factor expression in cells. HS and LS-groups reduced the levels of oxidative stress, inflammation, and tumor necrosis factor (TNF), and the latter significantly reduced the levels of TNF-α, interleukin (IL)-6, and nuclear factor (NF)-κB in AML12 cells. Additionally, it significantly reduced the oxidative stress damage caused by the high-glucose environment compared with normal AML12 cells. These results indicate that sericin may be an antioxidant recovered from industrial waste, and has potential and for use in the reduction of environmental pollution and the development of functional foods with antioxidation and antihyperglycemic effect.

Targeting the PI3K/Akt signaling pathway in pancreatic β-cells to enhance their survival and function: An emerging therapeutic strategy for type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease caused by the destruction of the insulin-producing β-cells within the pancreas. Islet transplantation represents one cure; however, during islet preparation and post transplantation significant amounts of β-cell death occur. Therefore, prevention and cure of T1D is dependent upon the preservation of β-cell function and the prevention of β-cell death. Phosphoinositide 3-kinase (PI3K)/Akt signaling represents a promising therapeutic target for T1D due to its pronounced effects on cellular survival, proliferation, and metabolism. A growing amount of evidence indicates that PI3K/Akt signaling is a critical determinant of β-cell mass and function. Modulation of the PI3K/Akt pathway, directly (via the use of highly specific protein and peptide-based biologics, excretory/secretory products of parasitic worms, and complex constituents of plant extracts) or indirectly (through microRNA interactions) can regulate the β-cell processes to ultimately determine the fate of β-cell mass. An important consideration is the identification of the specific PI3K/Akt pathway modulators that enhance β-cell function and prevent β-cell death without inducing excessive β-cell proliferation, which may carry carcinogenic side effects. Among potential PI3K/Akt pathway agonists, we have identified a novel parasite-derived protein, termed FhHDM-1 (Fasciola hepatica helminth defense molecule 1), which efficiently stimulates the PI3K/Akt pathway in β-cells to enhance function and prevent death without concomitantly inducing proliferation unlike several other identified stimulators of PI3K/Akt signaling . As such, FhHDM-1 will inform the design of biologics aimed at targeting the PI3K/Akt pathway to prevent/ameliorate not only T1D but also T2D, which is now widely recognized as an inflammatory disease characterized by β-cell dysfunction and death. This review will explore the modulation of the PI3K/Akt signaling pathway as a novel strategy to enhance β-cell function and survival.

Investigation of the Repairing Effect and Mechanism of Oral Degraded Sericin on Liver Injury in Type II Diabetic Rats

In the sericulture and silk production industry, sericin is discharged in the degumming wastewater, resulting in a large amount of wasted natural protein and environmental pollution. This study investigated the effect of degraded sericin recovered by the Ca(OH)₂–ultrasound degumming method (a green process) on liver injury in T2D rats. After 4 weeks of dietary sericin supplementation, the liver masses and organ coefficients of the T2D rats improved compared with those of the model rats that were not fed sericin. Oral sericin activated the damaged PI3K/AKT/AMPK pathway to enhance glycogen synthesis, accelerate glycolysis, and inhibit gluconeogenesis. The protein expression levels of the inflammatory factors NF-κB, IL-6, and TNF-α in the T2D model group were up to two times higher than in the normal group. However, all three T2D groups that received oral sericin showed significant decreases in these factors to the level found in the normal group, indicating that inflammation in the body was significantly reduced. These results show that the sericin protein might improve glycogen synthesis, accelerate glycolysis, and inhibit gluconeogenesis by enhancing the anti-oxidation capability and reducing inflammatory reactions. Therefore, sericin recovered by Ca(OH)₂ degradation has potential use in the development of functional health foods that can lower blood sugar.

Enhancing the In Vitro Biological Activity of Degraded Silk Sericin and Its Analog Metabolites

Two sericins of high and low molecular weight (HS and LS) were prepared from commercial silkworm cocoon silk with a boiling water and Ca(OH)₂ solution with ultrasonic treatments, respectively. This study first investigated the release concentration of the two abovementioned sericins in simulated saliva, gastric juice, and intestinal juice (pH 6.8, 2.0, and 7.4, respectively) within 10 h. The results showed that the order of sericin release rate and its amount in the simulated environment was gastric juice > saliva > intestinal juice. Second, the molecular weights of both sericin metabolites formed by in vitro enzymatic degradation were lower than 15 kDa. The α-glucosidase inhibitory activities of both sericins and their analog metabolites were positively correlated with their concentrations. The IC₅₀ values of the HS- and LS-derived metabolites were 1.02 ± 0.12 mg/mL and 0.91 ± 0.15 mg/mL, respectively, which were five to seven times lower than those of both original sericins. The total antioxidant capacities and hydroxyl radical scavenging capacities of both metabolites were enhanced by one- to three-fold compared with HS and LS. These results indicate that both sericins, regardless of molecular size, have significantly enhanced antioxidant, superoxide free radical scavenging, and glycosidase inhibitory activities after simulated metabolism, and that LS is better than HS regardless of simulated digestion. These results confirm that sericin is important in the sustainable development and utilization of silk resources, especially the reduction in environmental pollution, and provides new ideas for the development of adjuvant treatments for diabetes and the development of foods with anti-hyperglycemic functions.

Silk Protein Composite Bioinks and Their 3D Scaffolds and In Vitro Characterization

This paper describes the use of silk protein, including fibroin and sericin, from an alkaline solution of Ca(OH)2 for the clean degumming of silk, which is neutralized by sulfuric acid to create calcium salt precipitation. The whole sericin (WS) can not only be recycled, but completely degummed silk fibroin (SF) is also obtained in this process. The inner layers of sericin (ILS) were also prepared from the degummed silk in boiling water by 120 °C water treatment. When the three silk proteins (SPs) were individually grafted with glycidyl methacrylate (GMA), three grafted silk proteins (G-SF, G-WS, G-ILS) were obtained. After adding I2959 (a photoinitiator), the SP bioinks were prepared with phosphate buffer (PBS) and subsequently bioprinted into various SP scaffolds with a 3D network structure. The compressive strength of the SF/ILS (20%) scaffold added to G-ILS was 45% higher than that of the SF scaffold alone. The thermal decomposition temperatures of the SF/WS (10%) and SF/ILS (20%) scaffolds, mainly composed of a β-sheet structures, were 3 °C and 2 °C higher than that of the SF scaffold alone, respectively. The swelling properties and resistance to protease hydrolysis of the SP scaffolds containing sericin were improved. The bovine insulin release rates reached 61% and 56% after 5 days. The L929 cells adhered, stretched, and proliferated well on the SP composite scaffold. Thus, the SP bioinks obtained could be used to print different types of SP composite scaffolds adapted to a variety of applications, including cells, drugs, tissues, etc. The techniques described here provide potential new applications for the recycling and utilization of sericin, which is a waste product of silk processing.

Sericin cocoon bio-compatibilizer for reactive blending of thermoplastic cassava starch

Cassava starch was blended with glycerol to prepare thermoplastic starch (TPS). Thermoplastic starch was premixed with sericin (TPSS) by solution mixing and then melt-blended with polyethylene grafted maleic anhydride (PEMAH). The effect of sericin on the mechanical properties, morphology, thermal properties, rheology, and reaction mechanism was investigated. The tensile strength and elongation at break of the TPSS10/PEMAH blend were improved to 12.2 MPa and 100.4%, respectively. The TPS/PEMAH morphology presented polyethylene grafted maleic anhydride particles (2 μm) dispersed in the thermoplastic starch matrix, which decreased in size to approximately 200 nm when 5% sericin was used. The melting temperature of polyethylene grafted maleic anhydride (121 °C) decreased to 111 °C because of the small crystal size of the polyethylene grafted maleic anhydride phase. The viscosity of TPS/PEMAH increased with increasing sericin content because of the chain extension. Fourier-transform infrared spectroscopy confirmed the reaction between the amino groups of sericin and the maleic anhydride groups of polyethylene grafted maleic anhydride. This reaction reduced the interfacial tension between thermoplastic starch and polyethylene grafted maleic anhydride, which improved the compatibility, mechanical properties, and morphology of the blend.

Comparison of Sericins from Different Sources as Natural Therapeutics against Ulcerative Colitis

Sericin has become a promising natural anti-inflammatory protein. However, the biological functions of sericins largely depend on their origins; no study has yet been carried out to comparatively investigate the therapeutic effects of sericins from different sources against inflammatory diseases. Herein, we extracted and purified three kinds of sericins, namely silkworm sericin (SS), tussah sericin (TS), and castor silk sericin (CSS). These sericins showed negligible cytotoxicities against colitis-associated cells (colon epitheliums and activated macrophages). Further investigations displayed that these sericins could remarkably downregulate the secreted amounts of TNF-α, promote the recovery of the damaged colonic epithelial barrier, and eliminate endogenous reactive oxygen species in Raw 264.7 macrophages and Caenorhabditis elegans. In vivo experiments demonstrated that chitosan/alginate hydrogel-encapsulating SS could achieve efficient accumulation of SS in the colitis tissues and thereby play a more effective role in relieving ulcerative colitis (UC) than TS and CSS. Our findings collectively demonstrate that SS can be extracted, formulated, and used as a robust therapeutic agent for the oral treatment of UC.

Degraded Sericin Significantly Regulates Blood Glucose Levels and Improves Impaired Liver Function in T2D Rats by Reducing Oxidative Stress

Sericin could be degraded well into low-molecular-weight sericin (SS) through a novel and environmentally friendly recycling process using an ultrasonically degumming method in Ca(OH)₂ aqueous solution. The oral administration of the SS has an evidently hypoglycemic effect on STZ-induced T2D rats. At oral doses of 2.5 and 5% SS for four weeks, the fasting blood glucose decreased by over 60% compared with that in the untreated model group. Oral glucose tolerance and insulin tolerance were ameliorated by the peptide treatment. The serum insulin level was reduced by approximately 35%, the insulin resistance index was reduced by more than 66%. The 8-hydroxy-2 deoxyguanosine level showed a large reduction of 20%, and the total antioxidant activities significantly increased. Hematoxylin-eosin staining and fluorescent immunostaining sections showed that liver and pancreas damage was partly recovered in T2D rats. In summary, oral SS demonstrated evidently hypoglycemic effects mainly related to reducing oxidative stress in the damaged liver and pancreas of T2D rats. Therefore, these results have suggested that the degraded sericin has a potential use in SS-based healthy functional food or hypoglycemic drugs as a waste recovered from sericulture resources.

Bioinspired Design of Sericin/Chitosan/Ag@MOF/GO Hydrogels for Efficiently Combating Resistant Bacteria, Rapid Hemostasis, and Wound Healing

Due to the spread of drug-resistant bacteria in hospitals, the development of antibacterial dressings has become a strategy to control wound infections caused by bacteria. Here, we reported a green strategy for in situ biomimetic syntheses of silver nanoparticles@organic frameworks/graphene oxide (Ag@MOF-GO) in sericin/chitosan/polyvinyl alcohol hydrogel. Ag@MOF-GO was synthesized in situ from the redox properties of tyrosine residues in silk sericin without additional chemicals, similar to a biomineralization process. The sericin/chitosan/Ag@MOF-GO dressing possessed a high porosity, good water retention, and a swelling ratio. The hemolysis rate of the composite was 3.9% and the cell viability rate was 131.2%, which indicated the hydrogel possessed good biocompatibility. The composite also showed excellent lasting antibacterial properties against drug-sensitive and drug-resistant pathogenic bacteria. The composite possessed excellent hemostatic activity. The coagulation effect of the composite may be related to its effect on the red blood cells and platelets, but it has nothing to do with the activation of coagulation factors. An in vitro cell migration assay confirmed and an in vivo evaluation of mice indicated that the composite could accelerate wound healing and re-epithelialization. In summary, the composite material is an ideal dressing for accelerating hemostasis, preventing bacterial infection, and promoting wound healing.

Thermoplastic mung bean starch/natural rubber/sericin blends for improved oil resistance

Oil resistant thermoplastic elastomers (TPE) were prepared using mung bean thermoplastic starch (MTPS) blending with rubbers and sericin. Sericin was incorporated into MTPS as a compatibilizer. MTPS with sericin (MTPSS) was blended with natural rubber (NR) and epoxidized NR (ENR). Sericin at 5% improved the tensile strength (10 MPa), elastic recovery (52%) and morphology of the MTPSS/ENR blend. The mechanical properties, elastic recovery and morphology of the MTPSS5/NR blend were improved by the addition of ENR. The MTPSS/ENR showed palm (28%) and motor oils (8%) swelling resistance because of the hydrophilicity of MTPS and high polarity of ENR. The MTPSS/ENR/NR showed gasoline swelling resistance (104%) because of the hydrophilicity of MTPS and low polarity of NR. FTIR confirmed a reaction between the -NH groups of sericin and the epoxy groups of ENR. This reaction improved the compatibility, mechanical properties, elastic recovery, morphology and oils swelling resistance of the blends.

Effects of trypsin-induced limited hydrolysis on the structural, functional, and bioactive properties of sericin

The effects of trypsin-induced hydrolysis on the structural, functional, and antioxidant properties of sericin were studied. The structural properties of sericin and its hydrolysates were characterized by using SDS-PAGE, SEC-HPLC, surface hydrophobicity, and circular dichroism. Antioxidative properties were evaluated based on quenching capacity against hydroxyl, DPPH, and ABTS, and metal (Fe²⁺, Cu²⁺) chelating activity. The enzymatic hydrolysis raised the flexibility, changed emulsifying and foaming properties, and improved the solubility and antioxidant activity of sericin. Meanwhile, the hydrolysis led to a decline in gelation capacity, oil holding capacity, and water holding capacity. Sericin and its hydrolysates exhibited excellent function with regard to oil holding, emulsifying, and foaming. Sericin and its hydrolysates had clear effects on the growth of both Enterococcus faecalis and Lactobacillus bulgaricus strains.

Sericin was hydrolyzed to a limited extent using trypsin, then the physicochemical, prebiotic, and antioxidative properties of the obtained hydrolysates were investigated.

Sericin protects against acute sleep deprivation-induced memory impairment via enhancement of hippocampal synaptic protein levels and inhibition of oxidative stress and neuroinflammation in mice

Sleep deprivation (SD) induces learning and memory deficits via inflammatory responses and oxidative stress. On the other hand, sericin (Ser) possesses potent antioxidant and neuroprotective effects. We investigated the effect of different doses of Ser on the SD-induced cognitive impairment. Ser (100, 200, and 300 mg/kg) was administered to animals via oral gavage for 8 days, 5 days before to SD, and during SD. SD was induced in mice using a modified multiple platform model, starting on the 6th day for 72 h. Spatial learning and memory were assessed using the Lashley III maze. Serum corticosterone level, and hippocampal malondialdehyde (MDA), total antioxidant capacity (TAC), and the activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx) enzymes were evaluated. The expression of growth-associated protein 43 (GAP-43), post-synaptic density-95 (PSD-95), synapsin 1 (SYN-1), and synaptophysin (SYP), and inflammation markers were detected by western blotting. SD caused cognitive impairment, while Ser pretreatment prevented such an effect. Serum corticosterone also increased with SD, but its levels were suppressed in SD mice receiving Ser. Furthermore, Ser normalized SD-induced reduction in the hippocampus activity of SOD and GPx, increased TAC, and decreased MDA levels. Besides, Ser pretreatment increased GAP-34, SYP, SYN-I, and PSD-95 and reduced IL1-β and TNF-α in the hippocampus. SD induced memory impairment and pretreatment with Ser improved memory via its antioxidant, anti-inflammation, and up-regulation of synaptic proteins in the hippocampus.

Identification and location of sericin in silkworm with anti-sericin antibodies

Sericin, as the main component of silkworm cocoon silk, surrounds and protects the silk fibroin. Sericin is a natural macromolecular protein complex encoded by the genes Ser1, Ser2, and Ser3. At present, there are no available antibodies against sericin that may be used to identify and locate it at the protein level, hindering the study of its secretion mechanism and materials application. Therefore, the development of effective antibodies against sericin is an urgent necessity. To address this problem, we prepared polyclonal antibodies against the Ser1, Ser2 and Ser3 proteins using synthesized peptides for the first time. The specificity of the antibodies was confirmed using dot blot, immunoblotting and mass spectrometry on the hybrid bands of the middle silk gland. The immunoblotting results of anti-sericin antibodies showed that sericin has different molecular weights in different regions of the middle silk gland and strains in the 5th instar. Through immunohistochemistry, anti-sericin antibodies revealed that sericin presented different distributions in the anterior part of the middle silk gland of 872 strain at the 7th day of 5th instar. In addition, the prepared antibodies not only detected intact sericin molecules, but also detected degraded sericin that was dissolved in five different solvents. In summary, this work prepared effective sericin antibodies for silk protein synthesis and secretion research and provides a possible molecular detection method for biological products containing silkworm sericin.

Long-term silk peptide intake promotes skeletal muscle mass, reduces inflammation, and modulates gut microbiota in middle-aged female rats

Aging alters body composition to induce sarcopenia, particularly in women, but the mechanism remains unclear. We hypothesized that silk peptide(SP) intake could prevent an age-related decrease in muscle mass and strength in middle-aged female rats and explored the action mechanism. After the acute intake of SP and defatted soybean peptides, serum concentrations of amino acids were measured in ten middle-aged rats in each group. Forty 12-month-old female Sprague-Dawley rats were fed a high-fat and high-carbohydrate diet for 12 weeks including 0.5 g casein/kg body weight(BW)/day(Aged), 0.15 g SP plus 0.35 g casein/kg BW/day(Low-SP), 0.5 g SP/kg BW/day(High-SP), or 40 mg metformin plus 0.5 g casein/kg BW/day(Metformin). Ten rats aged 7-week old(Young) had the same treatment as the Aged-group. The body composition, grip strength, glucose metabolism, intestinal tissue morphology, and gut microbiota were also determined. After an acute consumption, total amino acids were more quickly absorbed and maintained at higher levels in SP than soybean peptides. Lean body mass(LBM) and grip strength were lower in the Aged-group than the Young and Low-SP groups, and the High-SP regimen increased these parameters as much as the Young-group. Serum concentrations and mRNA expression of TNF-α in the gastrocnemius and quadriceps muscles were higher in the Aged-group than the Young-group, whereas SP intake reduced their serum levels and skeletal muscles. Glucose and insulin tolerance indicated that insulin resistance was elevated in the Aged-group compared to the Young-group, while Low-SP and High-SP alleviated them as much as the Young-group. High-SP increased serum propionate and butyrate concentrations compared to the Aged-group. SP intake increased the relative abundance of Bacteroides and Prevotella and decreased Blautia and Clostridium in the feces. In conclusion, SP intake protects against a decrease in lean body mass and grip strength in middle-aged female rats. The protection was partly related to maintaining higher serum concentrations of total amino acids after SP consumption and decreasing inflammation and insulin resistance through gut microbiota modulation.

Sericin modulates learning and memory behaviors by tuning of antioxidant, inflammatory, and apoptotic markers in the hippocampus of aged mice

Sericin is a protein derived from silkworm cocoons and identified as an anti-aging agent. This study aimed to examine the effects of sericin administration on episodic and avoidance memories, social interaction behavior, and molecular mechanisms including oxidative stress, inflammation, and apoptosis in the hippocampus of aged mice. Sericin was administered at 250 mg/kg/day (oral gavage) to 2-year-old BALB/c mice for a duration of 21 consecutive days. Lashley III Maze and Shuttle-Box tests were performed to assess episodic and avoidance memories, respectively. Subjects also underwent social interaction test to reveal any changes in their social behavior. Besides, markers of oxidative stress (TAC, SOD, GPx, and MDA) and neuroinflammation mediators (TNF-α, IL-1β, and IL-10) were measured in the hippocampus. The extent of apoptosis in the hippocampal tissue was further determined by TUNEL assay and histological assessment. The obtained results suggest that sericin promotes episodic and avoidance memories and social behaviors in aged mice. As of the molecular assay outcomes, it was noted that sericin regulates hippocampal inflammation by inhibiting the pro-inflammatory cytokines, TNF-α and IL-1β, and by increasing the anti-inflammatory factor IL-10. Moreover, sericin suppressed oxidative stress by enhancing antioxidant markers (TAC, SOD, and GPx) and inhibiting MDA. It was also identified that sericin can substantially suppress the apoptosis in the hippocampal tissue. Overall, sericin modulates memory and sociability behavior by tuning hippocampal antioxidant, inflammatory, and apoptotic markers in the aged mice.

Safety Assessment of Water-Extract Sericin from Silkworm (Bombyx mori) Cocoons Using Different Model Approaches

Sericin is a natural protein component of silks of silkworm and has potential utility in multiple areas such as pharmacological, cosmetics, and biotechnological industries. However, the understanding of its toxicological safety is still limited. This study evaluated the safety of water-extract sericin from silkworm (Bombyx mori) cocoons using different model approaches, including three genotoxicity studies (the bacterial reverse mutation test, the mammalian erythrocyte micronucleus test, and the mouse spermatogonia chromosomal aberration test) and a 90-day subchronic toxicity study in Sprague-Dawley (SD) rats. The results of this study showed that water-extract sericin was nonmutagenic and nongenotoxic both in vitro and in vivo. Sericin did not induce significant changes in the body and organ weight, food intake, blood hematology and serum biochemistry, urine index, and histopathology in rats. The NOAEL of sericin was determined to be 1 g/kg/day for male and female rats. These results indicated that water-extract sericin was of low toxicity in the experimental conditions of the current study and had the potential for application in food-related products.

Biosynthetic sericin 1-like protein skews dendritic cells to tolerogenic-like phenotype

Silkworm sericin has been widely exploited in biomaterials due to its favorable biological activities. However, the extraction processes of sericin from silkworm cocoons can alter the biological and biophysical properties, including a structural diversity of natural sericin. In addition, extracted natural sericin is often contaminated with fibroin that may be harmful to human cells. Induction of tolerogenic dendritic cell (DC) has become a strategy in biomaterial fields because this cell type plays a key role in immune modulation and wound healing. To overcome undesired effects of extracted natural sericin and to improve its biological properties, we biosynthesized sericin 1-like protein that contained only functional motifs and tested its biological activity and immunomodulatory properties in fibroblasts and DCs, respectively. In comparison to natural sericin, biosynthetic sericin 1 promoted collagen production in fibroblasts at a late time point. Furthermore, DCs treated with biosynthetic sericin 1 exhibited a tolerogenic-like phenotype with semimaturation and low production of proinflammatory cytokines, but high production of anti-inflammatory cytokine, IL-10. Biosynthetic sericin 1 might be developed as immunomodulator or immunosuppressant.