Background
Chondroitin sulfate (CS) is a natural bioactive macromolecule belonging to the glycosaminoglycan (GAG) class. It is not only the main component of the extracellular matrix (ECM), but also usually connects with membrane proteins to form chondroitin sulfate proteoglycan (CSPG) distributed on the surface of almost all cells. It is a multifunctional signaling molecule and regulator that interacts with cytokines, growth factors and enzymes, and has a profound impact on many physiological processes such as inflammation, tumor progression and metastasis, vascular remodeling, and anti-oxidation.
The sugar chain of CS includes repeated β-1,3-linked N-acetylgalactosamine and β-1,4-linked D-glucuronic acid disaccharide units. According to the position and degree of sulfide, it is divided into five types: CSO, CSA, CSC, CSD, and CSE. In addition to the variability of the position of the sulfate group, different sulfate groups also have significantly different biological activities. For example, CS with 3-O-sulfo-glucuronic acid residues has been shown to stimulate neurite growth, and the sulfated fucose residues of fucosyl sulfate chondroitin have multiple activities such as anti-inflammatory and hematopoietic stimulation.
Figure 1. Application of chondroitin sulfate in biopharmaceuticals and tissue engineering. (Sharma R, et al.; 2022)
As a biopolysaccharide, CS has multivalency, controllable molecular weight and strong designability, and is favored by polymer science researchers. CS has good adhesion, biocompatibility, biodegradability and cell targeting, so it is widely used in the preparation of targeted delivery systems, which aims to embed drugs, cells or genes into composite biomaterials for targeted delivery and release under specific conditions, thereby reducing toxic side effects, prolonging the duration of drug action, improving pharmacodynamic functions, or overcoming the immunogenicity of inhibitory tissues to reduce the risk of rejection. In addition, CS is also widely used as a biological scaffold in the field of bone, cartilage, cornea, skin and nerve tissue engineering.
Biological Activity of CS
CS is one of the components of corneal stroma, with stable chemical properties, non-toxic and non-irritating, and is used to preserve cornea and composite viscoelastics for ophthalmic surgery. CS can stabilize the microenvironment of cell metabolism, provide a framework for cell migration, promote the migration of corneal epithelial cells, reduce inflammatory reactions, and thus promote the healing of corneal trauma. Therefore, CS compound eye drops are clinically used to treat corneal injuries and dry eyes. The repair process after corneal injury is jointly participated by resident cells such as ECM, cytokines and HCEC. Platelet lysate is a blood-derived substance rich in blood growth factors. Each repeated disaccharide unit of CS carries two negative charges, which can bind to the positively charged growth factors in platelet lysate through electrostatic action.
CS extracted from different biological tissues has different sulfation patterns and different molecular weight structures, and its role in immunoregulation is also different. In early studies, CS inhibited the nuclear translocation of NF-κB by reducing the phosphorylation of p38 mitogen-activated protein kinase and signal-regulated kinase 1/2 through cell surface receptors, and reduced the release of proinflammatory cytokines such as TNF-α, IL-6, and proinflammatory enzymes such as phospholipase A2, cyclooxygenase 2, matrix metalloproteinase-13, and nitric oxide synthase 2. The anti-inflammatory pathway has been demonstrated in chondrocytes. CS may also increase the expression of osteoprotegerin and inhibit the activation of osteoclasts through this pathway.
Osteoarthritis is a degenerative disease accompanied by the release of various proinflammatory factors. Currently, commonly used anti-inflammatory drugs and analgesics are still mainly used to relieve symptoms. Therefore, new treatment approaches focus on reducing bone and joint structural damage. The anti-inflammatory activity and cartilage protection activity of CS are beneficial to chondrocyte proliferation and ECM regeneration in osteoarthritis.
Natural CS is widely present on the cell surface and in the ECM, affecting cell behavior and the biomechanical and biochemical properties of the ECM. The latest research has found that changes in the sulfation pattern of CS may affect the binding ability of certain antibodies.
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Promote Biomineralization
Biomineralization is the process in which inorganic elements in the body's metabolic products selectively precipitate under the regulation of an organic environment and form highly ordered minerals, such as the formation of hydroxyapatite (HAP) in teeth and bones. Non-collagenous glycoproteins play an important regulatory role in HAP nucleation during new bone formation, because their abundant acidic groups have a strong affinity for calcium ions and accelerate the nucleation of hydroxyapatite crystals by increasing the local calcium concentration. CS, which is rich in sulfate and carboxylate groups, is considered to be an effective promoter of hydroxyapatite nucleation and growth, and can act as an intermediate in tissue mineralization, regulating the deposition and growth morphology of mineral crystals during osteogenesis. It has been pointed out that CS helps form highly ordered HAP by inhibiting the "supersaturation-driven interface structure mismatch" process in the mineralization process mediated by HAP crystals.
CS has a variety of antiviral biological activities. NS1 secreted by dengue virus attaches to the host cell surface through interactions with CSE and heparan sulfate, so exogenous CSE has antiviral activity targeting dengue virus envelope protein.
Application of CS in the field of biomaterials
Currently, CS adhesives suitable for cartilage tissue have been developed. Developers chemically functionalized CS with methacrylate and aldehyde groups to form two functional arms: one arm provides covalent binding sites to biomaterials and enhances material strength, and the other arm interacts with amine groups present on the tissue surface. CS adhesive serves as an adhesion layer between the implanted biomaterial and the natural cartilage tissue. It has strong adhesion and stable integration, and significantly promotes the fusion between the implant and the cartilage tissue.
Experiments have proven that the drug carrier constructed using CS has a suitable hydrodynamic diameter, controllable surface charge, optimal encapsulation rate, non-toxicity and resistance. Due to its extremely strong affinity with CD44, it is easy to utilize CD44 receptors. CS drug carriers designed through body-mediated endocytosis are a hot topic in tumor treatment research. At present, the hot spots of drug carriers constructed by CS mainly include hydrogels, nanoparticles and nanocapsules.
The key property of high-quality cell scaffolds is to provide suitable substrates for cell adhesion, proliferation, and differentiation. The interaction between cells and ECM plays a crucial role in the initial migration of cells to the wound area and the contraction of granulation tissue. Therefore, CS, gelatin (GEL), hyaluronic acid (HA) Adding ECM components to biological scaffolds is an effective method to influence cell activity to promote tissue regeneration. CS can provide abundant signal recognition sites and regulate cell growth and development by combining multiple growth factors. It is a biomaterial that cannot be ignored when designing cell scaffolds. The types of cell scaffolds developed with CS as materials mainly include: nanofiber scaffolds, hydrogel scaffolds, and porous scaffolds.
References
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Sharma R, et al.; Chondroitin Sulfate: Emerging biomaterial for biopharmaceutical purpose and tissue engineering. Carbohydr Polym. 2022, 286:119305.
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Schuurmans CCL, et al.; Hyaluronic acid and chondroitin sulfate (meth)acrylate-based hydrogels for tissue engineering: Synthesis, characteristics and pre-clinical evaluation. Biomaterials. 2021, 268:120602.
