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

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.

Expanding the boundaries of silk sericin biomaterials in biomedical applications

Silk sericin (SS) has a long history as a by-product of the textile industry. SS has emerged as a sustainable material for biomedical engineering due to its material properties including water solubility, diverse impact on biological activities including antibacterial and antioxidant properties, and ability to promote cell adhesion and proliferation. This review addresses the origin, structure, properties, extraction, and underlying functions of this protein. An overview of the growing research studies and market evolution is presented, along with highlights of the most common fabrication matrices (hydrogels, bioinks, porous and fibrous scaffolds) and tissue engineering applications. Finally, the future trends with this protein as a multifaceted toolbox for bioengineering are explored, along with the challenges with SS. Overall, the present review can serve as a foundation for the creation of innovative biomaterials utilizing SS as a fundamental building block that hold market potential.

Development and Investigation of an Innovative 3D Biohybrid Based on Collagen and Silk Sericin Enriched with Flavonoids for Potential Wound Healing Applications

Skin tissue injuries necessitate particular care due to associated complex healing mechanisms. Current investigations in the domain of tissue engineering and regenerative medicine are focused on obtaining novel scaffolds adapted as potential delivery systems to restore lost tissue functions and properties. In this study, we describe the fabrication and evaluation of a novel 3D scaffold structure based on collagen and silk sericin (CollSS) enriched with microcapsules containing natural compounds, curcumin (C), and/or quercetin (Q). These 3D composites were characterized by FT-IR spectroscopy, water uptake, in vitro collagenase degradation, and SEM microscopy. Furthermore, they were biologically evaluated in terms of biocompatibility, cell adhesion, anti-inflammatory, and antioxidant properties. All tested materials indicated an overall suitable biocompatibility, with the best results obtained for the one containing both flavonoids. This study suggests the cumulative beneficial effect of C and Q, encapsulated in the same composite, as a potential non-invasive therapeutic strategy for skin tissue regeneration in patients suffering from chronic wounds.

Anti-inflammatory effects of sericin and swimming exercise in treating experimental Achilles tendinopathy in rat

The aim of this study was to assess the effectiveness of combining sericin with swimming exercise as a treatment for type-I collagenase-induced Achilles tendinopathy (AT) in rats, with a focus on inflammatory cytokines. An experimental AT model was established using type-I collagenase in male Sprague-Dawley rats, categorized into five groups: Group 1 (Control + Saline), Group 2 (AT), Group 3 (AT + exercise), Group 4 (AT + sericin), and Group 5 (AT + sericin + exercise). Intratendinous sericin administration (0.8 g/kg/mL) took place from days 3 to 6, coupled with 30 min daily swimming exercise sessions (5 days/week, 4 weeks). Serum samples were analyzed using ELISA for tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), interleukin-10 (IL-10), and total antioxidant-oxidant status (TAS-TOS), alongside histopathological and immunohistochemical assessments of Achilles tendon samples. Elevated TNF-α and IL-1β and decreased IL-10 levels were evident in Group 2; Of these, TNF-α and IL-1β were effectively reduced and IL-10 increased across all treatment groups, particularly groups 4 and 5. Serum TAS was notably lower in Group 2 and significantly increased in Group 5 compared to Group 2. Histopathologically, Group 2 displayed severe degeneration, irregular fibers, and round cell nuclei, while Group 5 exhibited decreased degeneration and spindle-shaped fibers. The Bonar score increased in Group 2 and decreased in groups 4 and 5. Collagen type-I alpha-1 (Col1A1) expression was notably lower in Group 2 (P = 0.001) and significantly increased in groups 4 and 5 compared to Group 2 (P = 0.011 and 0.028, respectively). This study underscores the potential of sericin and swimming exercises in mitigating inflammation and oxidative stress linked to AT pathogenesis, presenting a promising combined therapeutic strategy.

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.

Advances of regenerated and functionalized silk biomaterials and application in skin wound healing

The cocoon silk of silkworms (Bombyx mori) has multiple potential applications in biomedicine due to its good biocompatibility, mechanical properties, degradability, and plasticity. Numerous studies have confirmed that silk material dressings are more effective than traditional ones in the skin wound healing process. Silk material research has recently moved toward functionalized biomaterials and achieved remarkable results. Herein, we summarize the recent advances in functionalized silk materials and their efficacy in skin wound healing. In particular, transgenic technology has realized the specific expression of human growth factors in the silk glands of the silkworms, which lays the foundation for fabricating novel and low-cost functionalized materials. Without a green and safe preparation process, the best raw silk materials cannot be made into medically safe products. Therefore, we provide an overview of green and gentle approaches for silk degumming and silk sericin (SS) extraction. Moreover, we summarize and discuss the processing methods of silk fibroin (SF) and SS materials and their potential applications, such as burns, diabetic wounds, and other wounds. This review aims to enhance our understanding of new advances and directions in silk materials and guide future biomedical research.

A Sterile, Injectable, and Robust Sericin Hydrogel Prepared by Degraded Sericin

The application of sericin hydrogels is limited mainly due to their poor mechanical strength, tendency to be brittle and inconvenient sterilization. To address these challenges, a sericin hydrogel exhibiting outstanding physical and chemical properties along with cytocompatibility was prepared through crosslinking genipin with degraded sericin extracted from fibroin deficient silkworm cocoons by the high temperature and pressure method. Our reported sericin hydrogels possess good elasticity, injectability, and robust behaviors. The 8% sericin hydrogel can smoothly pass through a 16 G needle. While the 12% sericin hydrogel remains intact until its compression ratio reaches 70%, accompanied by a compression strength of 674 kPa. 12% sericin hydrogel produce a maximum stretch of 740%, with breaking strength and tensile modulus of 375 kPa and 477 kPa respectively. Besides that, the hydrogel system demonstrated remarkable cell-adhesive capabilities, effectively promoting cell attachment and, proliferation. Moreover, the swelling and degradation behaviors of the hydrogels are pH responsiveness. Sericin hydrogel releases drugs in a sustained manner. Furthermore, this study addresses the challenge of sterilizing sericin hydrogels (sterilization will inevitably lead to the destruction of their structures). In addition, it challenges the prior notion that sericin extracted under high temperature and pressure is difficult to directly cross-linked into a stable hydrogel. This developed hydrogel system in this study holds promise to be a new multifunctional platform expanding the application area scope of sericin.

Could an Anterior Cruciate Ligament Be Tissue-Engineered from Silk?

Silk has a long history as an exclusive textile, but also as a suture thread in medicine; nowadays, diverse cell carriers are manufactured from silk. Its advantages are manifold, including high biocompatibility, biomechanical strength and processability (approved for nearly all manufacturing techniques). Silk's limitations, such as scarcity and batch to batch variations, are overcome by gene technology, which allows for the upscaled production of recombinant "designed" silk proteins. For processing thin fibroin filaments, the sericin component is generally removed (degumming). In contrast to many synthetic biomaterials, fibroin allows for superior cell adherence and growth. In addition, silk grafts demonstrate superior mechanical performance and long-term stability, making them attractive for anterior cruciate ligament (ACL) tissue engineering. Looking at these promising properties, this review focusses on the responses of cell types to silk variants, as well as their biomechanical properties, which are relevant for ACL tissue engineering. Meanwhile, sericin has also attracted increasing interest and has been proposed as a bioactive biomaterial with antimicrobial properties. But so far, fibroin was exclusively used for experimental ACL tissue engineering approaches, and fibroin from spider silk also seems not to have been applied. To improve the bone integration of ACL grafts, silk scaffolds with osteogenic functionalization, silk-based tunnel fillers and interference screws have been developed. Nevertheless, signaling pathways stimulated by silk components remain barely elucidated, but need to be considered during the development of optimized silk cell carriers for ACL tissue engineering.