The Impact of Chain Length and Flexibility in the Interaction between Sulfated Alginates and HGF and FGF-2

Marine polysaccharides: Biological activities and applications in drug delivery systems

The ocean is the common home of a large number of marine organisms, including plants, animals, and microorganisms. Researchers can extract thousands of important bioactive components from the oceans and use them extensively to treat and prevent diseases. In contrast, marine polysaccharide macromolecules such as alginate, carrageenan, Laminarin, fucoidan, chitosan, and hyaluronic acid have excellent physicochemical properties, good biocompatibility, and high bioactivity, which ensures their wide applications and strong therapeutic potentials in drug delivery. Drug delivery systems (DDS) based on marine polysaccharides and modified marine polysaccharide molecules have emerged as an innovative technology for controlling drug distribution on temporal, spatial, and dosage scales. They can detect and respond to external stimuli such as pH, temperature, and electric fields. These properties have led to their wide application in the design of novel drug delivery systems such as hydrogels, polymeric micelles, liposomes, microneedles, microspheres, etc. In addition, marine polysaccharide-based DDS not only have smart response properties but also can combine with the unique biological properties of the marine polysaccharide base to exert synergistic therapeutic effects. The biological activities of marine polysaccharides and the design of marine polysaccharide-based DDS are reviewed. Marine polysaccharide-based responsive DDS are expected to provide new strategies and solutions for disease treatment.

A pH/enzyme dual responsive PMB spatiotemporal release hydrogel promoting chronic wound repair

Suppressing persistent multidrug-resistant (MDR) bacterial infections and excessive inflammation is the key for treating chronic wounds. Therefore, developing a microenvironment-responsive material with good biodegradability, drug-loading, anti-infection, and anti-inflammatory properties is desired to boost the chronic wounds healing process; however, using ordinary assembly remains a defect. Herein, we propose a pH/enzyme dual-responsive polymyxin B (PMB) spatiotemporal-release hydrogel (GelMA/OSSA/PMB), namely, the amount of OSSA and PMB released from GelMA/OSSA/PMB was closely related the wound pH and the enzyme concentration changing. The GelMA/OSSA/PMB showed better biosafety than equivalent free PMB, owing to the controlled release of PMB, which helped kill planktonic bacteria and inhibit biofilm activity in vitro. In addition, the GelMA/OSSA/PMB exhibited excellent antibacterial and anti-inflammatory properties. A MDR Pseudomonas aeruginosa caused infection was effectively resolved by the GelMA/OSSA/PMB hydrogel in vivo, thereby significantly boosting wound closure during the inflammatory phase. Furthermore, GelMA/OSSA/PMB accelerated the sequential phases of wound repair.

Structural Characterization and Anti-Nonalcoholic Fatty Liver Effect of High-Sulfated Ulva pertusa Polysaccharide

The high-sulfated derivative of Ulva pertusa polysaccharide (HU), with unclear structure, has better anti-hyperlipidmia activity than U pertusa polysaccharide ulvan (U). In this study, we explore the main structure of HU and its therapeutic effect against nonalcoholic fatty liver disease (NAFLD). The main structure of HU was elucidated using FT-IR and NMR (13C, 1H, COSY, HSQC, HMBC). The anti-NAFLD activity of HU was explored using the high-fat diet mouse model to detect indicators of blood lipid and liver function and observe the pathologic changes in epididymal fat and the liver. Results showed that HU had these main structural fragments: →4)-β-D-Glcp(1→4)-α-L-Rhap2,3S(1→; →4)-α-L-Rhap3S(1→4)-β-D-Xylp2,3S(1→; →4)-α-L-Rhap3S(1→4)-β-D-Xylp(1→; →4)-α-L-IdopA3S(1→4)-α-L-Rhap3S(1→; →4)-β-D-GlcpA(1→3)-α-L-Rhap(1→; →4)-α-L-IdopA3S(1→4)-β-D-Glcp3Me(1→; →4)-β-D-Xylp2,3S(1→4)-α-L-IdopA3S(1→; and →4)-β-D-Xylp(1→4)-α-L-IdopA3S(1→. Treatment results indicated that HU markedly decreased levels of TC, LDL-C, TG, and AST. Furthermore, lipid droplets in the liver were reduced, and the abnormal enlargement of epididymal fat cells was suppressed. Thus, HU appears to have a protective effect on the development of NAFLD.

Phenol-Grafted Alginate Sulfate Hydrogel as an Injectable FGF-2 Carrier

In the field of tissue engineering, fibroblast growth factor-2 (FGF-2) effectively regenerates damaged tissue and restores its biological function. However, FGF-2 readily diffuses and degrades under physiological conditions. Therefore, methods for the sustained and localized delivery of FGF-2 are needed. Drug delivery systems using hydrogels as carriers have attracted significant interest. Injectable hydrogels with an affinity for FGF-2 are candidates for FGF-2 delivery systems. In this study, we fabricated a hydrogel from phenol-grafted alginate sulfate (AlgS-Ph) and investigated its application to the delivery of FGF-2. The hydrogel was prepared under mild conditions via horseradish peroxidase (HRP)-mediated cross-linking. Surface plasmon resonance (SPR) measurements show that the AlgS-Ph hydrogel has an affinity for FGF-2 in accordance with its degree of sulfation. Conditions for the preparation of the AlgS-Ph hydrogel, including HRP and H₂O₂ concentrations, are optimized so that the hydrogel can be used as an injectable drug carrier. The hydrogel shows no cytotoxicity when using 10T1/2 cells as a model cell line. The angiogenesis assay shows that FGF-2 released from the AlgS-Ph hydrogel promotes the formation of blood vessels. These results indicate that the AlgS-Ph hydrogel is a suitable candidate for the FGF-2 carrier.

Alginate oligosaccharides: The structure-function relationships and the directional preparation for application

Alginate oligosaccharides (AOS) are degradation products of alginate extracted from brown algae. With low molecular weight, high water solubility, and good biological activity, AOS present anti-inflammatory, antimicrobial, antioxidant, and antitumor properties. They also exert growth-promoting effects in animals and plants. Three types of AOS, mannuronate oligosaccharides (MAOS), guluronate oligosaccharides (GAOS), and heterozygous mannuronate and guluronate oligosaccharides (HAOS), can be produced from alginate by enzymatic hydrolysis. Thus far, most studies on the applications and biological activities of AOS have been based mainly on a hybrid form of HAOS. To improve the directional production of AOS for practical applications, systematic studies on the structures and related biological activities of AOS are needed. This review provides a summary of current understanding of structure-function relationships and advances in the production of AOS. The current challenges and opportunities in the application of AOS is suggested to guide the precise application of AOS in practice.

Pericapsular fibrotic overgrowth mitigated in immunocompetent mice through microbead formulations based on sulfated or intermediate G alginates

Cell encapsulation in alginate microbeads is a promising approach to provide immune isolation in cell therapy without immunosuppression. However, the efficacy is hampered by pericapsular fibrotic overgrowth (PFO), causing encapsulated cells to lose function. Stability of the microbeads is important to maintain immune isolation in the long-term. Here, we report alginate microbeads with minimal PFO in immunocompetent C57BL/6JRj mice. Microbead formulations included either alginate with an intermediate (47 %) guluronate (G) content (IntG) or sulfated alginate (SA), gelled in Ca²⁺/Ba²⁺ or Sr²⁺. A screening panel of eleven microbead formulations were evaluated for PFO, yielding multiple promising microbeads. Two candidate formulations were evaluated for 112 days in vivo, exhibiting maintained stability and minimal PFO. Microbeads investigated in a human whole blood assay revealed low cytokine and complement responses, while SA microbeads activated coagulation. Protein deposition on microbeads explanted from mice investigated by confocal laser scanning microscopy (CLSM) showed minimal deposition of complement C3. Fibrinogen was positively associated with PFO, with a high deposition on microbeads of high G (68 %) alginate compared to IntG and SA microbeads. Overall, stable microbeads containing IntG or SA may serve in long-term therapeutic applications of cell encapsulation. STATEMENT OF SIGNIFICANCE: Alginate-based hydrogels in the format of micrometer size beads is a promising approach for the immunoisolation of cells in cell therapy. Clinical trials in type 1 diabetes have so far had limited success due to fibrotic responses that hinder the diffusion of nutrients and oxygen to the encapsulated cells, resulting in graft failure. In this study, minimal fibrotic response towards micrometer size alginate beads was achieved by chemical modification of alginate with sulfate groups. Also, the use of alginate with intermediate guluronic acid content resulted in minimally fibrotic microbeads. Fibrinogen deposition was revealed to be a good indicator of fibrosis. This study points to both new microsphere developments and novel insight in the mechanisms behind the fibrotic responses.

Potential applications of alginate oligosaccharides for biomedicine - A mini review

Extensive research on marine algae, especially on their health-promoting properties, has been conducted. Various ingredients with potential biomedical applications have been discovered and extracted from marine algae. Alginate oligosaccharides are low molecular weight alginate polysaccharides present in cell walls of brown algae. They exhibit various health benefits such as anti-inflammatory, anti-microbial, anti-oxidant, anti-tumor and immunomodulation. Their low-toxicity, non-immunogenicity, and biodegradability make them an excellent material in biomedicine. Alginate oligosaccharides can be chemically or biochemically modified to enhance their biological activity and potential in pharmaceutical applications. This paper provides a brief overview on alginate oligosaccharides characteristics, modification patterns and highlights their vital health promoting properties.

Multi-Dimensional Printing for Bone Tissue Engineering

The development of 3D printing has significantly advanced the field of bone tissue engineering by enabling the fabrication of scaffolds that faithfully recapitulate desired mechanical properties and architectures. In addition, computer-based manufacturing relying on patient-derived medical images permits the fabrication of customized modules in a patient-specific manner. In addition to conventional 3D fabrication, progress in materials engineering has led to the development of 4D printing, allowing time-sensitive interventions such as programed therapeutics delivery and modulable mechanical features. Therapeutic interventions established via multi-dimensional engineering are expected to enhance the development of personalized treatment in various fields, including bone tissue regeneration. Here, recent studies utilizing 3D printed systems for bone tissue regeneration are summarized and advances in 4D printed systems are highlighted. Challenges and perspectives for the future development of multi-dimensional printed systems toward personalized bone regeneration are also discussed.

Sulfated alginate based complex for sustained calcitonin delivery and enhanced osteogenesis

Direct medications of salmon calcitonin (sCT) through subcutaneous or intramuscular injection are limited for its low effeciency. Drug delivery systems with sustained delivery property and high bioactivity are imminently needed. In consideration of the clinic application, a cost-effective and effective carrier is demanded, which is still a challenge until now. In this study, a simple alginate/ alginate sulfate-sCT (Alg/AlgS-sCT) complex was succesfully constructed for sustained release of sCT. The negtively charged sulphate groups facilitate the bonding with sCT, which avoids the burst release of sCT and extends the release time up to 15 days (only 2 days for pure sCT). More importantly, the bioactivity of the released sCT is not affected during such long release time, suggesting a conformation similar to native sCT. In vitro analysis implies the biocompatibility of the complex. Moreover, the combination of AlgS and sCT synergistically impoved the osteogenic ability of MC3T3 cells, showing higher ALP level, intracellular and extracellular calcium ions concentrations. Note that the concentration of intracellular calcium ions displays 5.26 fold increments of control group after 10 days of incubation. We envision this simple yet effective system has potential applications in clinical trails and give inspiration for the design of other protein delivery system.

Anti-Tumor Effects of Biomimetic Sulfated Glycosaminoglycans on Lung Adenocarcinoma Cells in 2D and 3D In Vitro Models

Lung cancer development relies on cell proliferation and migration, which in turn requires interaction with extracellular matrix (ECM) components such as glycosaminoglycans (GAGs). The mechanisms through which GAGs regulate cancer cell functions are not fully understood but they are, in part, mediated by controlled interactions with cytokines and growth factors (GFs). In order to mechanistically understand the effect of the degree of sulfation (DS) of GAGs on lung adenocarcinoma (LUAD) cells, we synthesized sulfated alginate (AlgSulf) as sulfated GAG mimics with DS = 0.0, 0.8, 2.0, and 2.7. Human (H1792) and mouse (MDA-F471) LUAD cell lines were treated with AlgSulf of various DSs at two concentrations 10 and 100 µg/mL and their anti-tumor properties were assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), trypan blue exclusion, and wound healing assays for 2D models and sphere formation assay for the 3D model. The proliferation and number of live MDA-F471 cells at the concentration of 100 µg/mL decreased significantly with the increase in the DS of biomimetic GAGs. In addition, the increase in the DS of biomimetic GAGs decreased cell migration (p < 0.001 for DS = 2.0 and 2.7 compared to control) and decreased the diameter and number of spheres formed (p < 0.001). The increased DS of biomimetic GAGs attenuated the expression of cancer stem cell (CSC)/progenitor markers in the 3D cultures. In conclusion, GAG-mimetic AlgSulf with increased DS exhibit enhanced anti-proliferative and migratory properties while also reducing growth of KRAS-mutant LUAD spheres in vitro. We suggest that these anti-tumor effects by GAG-mimetic AlgSulf are possibly due to differential binding to GFs and consequential decreased cell stemness. AlgSulf may be suitable for applications in cancer therapy after further in vivo validation.

Effects of Sulfated Fucans from Laminaria hyperborea Regarding VEGF Secretion, Cell Viability, and Oxidative Stress and Correlation with Molecular Weight

BACKGROUND

Sulfated fucans show interesting effects in the treatment of ocular diseases (e.g., age-related macular degeneration), depending on their chemical structure. Here, we compared three purified sulfated fucans from Laminaria hyperborea (LH) regarding cell viability, oxidative stress protection, and vascular endothelial growth factor (VEGF) secretion in ocular cells.

METHODS

High-molecular-weight sulfated fucan (Mw = 1548.6 kDa, Fuc1) was extracted with warm water and purified through ultrafiltration. Lower-molecular-weight samples (Mw = 499 kDa, Fuc2; 26.9 kDa, Fuc3) were obtained by mild acid hydrolysis of ultrapurified sulfated fucan and analyzed (SEC-MALS (Size-exclusion chromatography-Multi-Angle Light Scattering), ICP-MS, and GC). Concentrations between 1 and 100 µg/mL were tested. Cell viability was measured after 24 h (uveal melanoma cell line (OMM-1), retinal pigment epithelium (RPE) cell line ARPE-19, primary RPE cells) via MTT/MTS (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide/3-(4,5-Dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay. Oxidative stress protection was determined after 24 h (OMM-1, ARPE-19). VEGF secretion was analyzed via ELISA after three days (ARPE-19, RPE).

RESULTS

Fuc2 and Fuc3 were antiproliferative for OMM-1, but not for ARPE. Fuc1 protected OMM-1. VEGF secretion was lowered with all fucans except Fuc3 in ARPE-19 and RPE. The results suggest a correlation between molecular weight and biological activity, with efficiency increasing with size.

CONCLUSION

The LH sulfated fucan Fuc1 showed promising results regarding VEGF inhibition and protection, encouraging further medical research.

3D Bone Biomimetic Scaffolds for Basic and Translational Studies with Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are recognized as an attractive tool owing to their self-renewal and differentiation capacity, and their ability to secrete bioactive molecules and to regulate the behavior of neighboring cells within different tissues. Accumulating evidence demonstrates that cells prefer three-dimensional (3D) to 2D culture conditions, at least because the former are closer to their natural environment. Thus, for in vitro studies and in vivo utilization, great effort is being dedicated to the optimization of MSC 3D culture systems in view of achieving the intended performance. This implies understanding cell–biomaterial interactions and manipulating the physicochemical characteristics of biomimetic scaffolds to elicit a specific cell behavior. In the bone field, biomimetic scaffolds can be used as 3D structures, where MSCs can be seeded, expanded, and then implanted in vivo for bone repair or bioactive molecules release. Actually, the union of MSCs and biomaterial has been greatly improving the field of tissue regeneration. Here, we will provide some examples of recent advances in basic as well as translational research about MSC-seeded scaffold systems. Overall, the proliferation of tools for a range of applications witnesses a fruitful collaboration among different branches of the scientific community.

Three dimensional cell printing with sulfated alginate for improved bone morphogenetic protein-2 delivery and osteogenesis in bone tissue engineering

Three-dimensional (3D) cell printing is a unique technique that enables free-form fabrication of cell-laden hydrogel scaffolds with controllable features and interconnected pores for tissue engineering applications. To this end, bioink materials able to offer good printability and favorable cellular interaction are highly required. Herein, we synthesized alginate sulfate, which is a structural mimic of heparin that can strongly bind with growth factors to prolong their activities, and studied its feasibility for cell printing applications. Several bio-inks composed of alginate and alginate-sulfate were studied to characterize their material properties and their utilities in 3D printing. The inclusion of alginate-sulfate in bio-inks (alginate/alginate-sulfate) did not significantly influence their rheological properties and allowed for a good 3D printing processibility with distinct pores and features. Moreover, alginate/alginate-sulfate bio-inks exhibited an improved retention of bone morphogenetic protein 2 in 3D-printed scaffolds. Osteoblastic proliferation and differentiation in vitro were promoted by alginate/alginate-sulfate 3D-printed constructs with an optimal composition of 3% alginate and 2% alginate-sulfate. We envision that bio-inks displaying prolonged interactions with growth factors will be useful for tissue engineering applications including bone regeneration.

OligoG CF-5/20 normalizes cystic fibrosis mucus by chelating calcium

The goal of this study was to determine whether the guluronate (G) rich alginate OligoG CF-5/20 (OligoG) could detach cystic fibrosis (CF) mucus by calcium chelation, which is also required for normal mucin unfolding. Since bicarbonate secretion is impaired in CF, leading to insufficient mucin unfolding and thereby attached mucus, and since bicarbonate has the ability to bind calcium, we hypothesized that the calcium chelating property of OligoG would lead to detachment of CF mucus. Indeed, OligoG could compete with the N-terminus of the MUC2 mucin for calcium binding as shown by microscale thermophoresis. Further, effects on mucus thickness and attachment induced by OligoG and other alginate fractions of different length and composition were evaluated in explants of CF mouse ileum mounted in horizontal Ussing-type chambers. OligoG at 1.5% caused effective detachment of CF mucus and the most potent alginate fraction tested, the poly-G fraction of about 12 residues, had similar potency compared to OligoG whereas mannuronate-rich (M) polymers had minimal effect. In conclusion, OligoG binds calcium with appropriate affinity without any overt harmful effect on the tissue and can be exploited for treating mucus stagnation.

Encapsulated Islet Transplantation: Where Do We Stand?

Transplantation of pancreatic islets encapsulated within immuno-protective microcapsules is a strategy that has the potential to overcome graft rejection without the need for toxic immunosuppressive medication. However, despite promising preclinical studies, clinical trials using encapsulated islets have lacked long-term efficacy, and although generally considered clinically safe, have not been encouraging overall. One of the major factors limiting the long-term function of encapsulated islets is the host's immunological reaction to the transplanted graft which is often manifested as pericapsular fibrotic overgrowth (PFO). PFO forms a barrier on the capsule surface that prevents the ingress of oxygen and nutrients leading to islet cell starvation, hypoxia and death. The mechanism of PFO formation is still not elucidated fully and studies using a pig model have tried to understand the host immune response to empty alginate microcapsules. In this review, the varied strategies to overcome or reduce PFO are discussed, including alginate purification, altering microcapsule geometry, modifying alginate chemical composition, co-encapsulation with immunomodulatory cells, administration of pharmacological agents, and alternative transplantation sites. Nanoencapsulation technologies, such as conformal and layer-by-layer coating technologies, as well as nanofiber, thin-film nanoporous devices, and silicone based NanoGland devices are also addressed. Finally, this review outlines recent progress in imaging technologies to track encapsulated cells, as well as promising perspectives concerning the production of insulin-producing cells from stem cells for encapsulation.

Sulfated Alginates as Heparin Analogues: A Review of Chemical and Functional Properties

Heparin is widely recognized for its potent anticoagulating effects, but has an additional wide range of biological properties due to its high negative charge and heterogeneous molecular structure. This heterogeneity has been one of the factors in motivating the exploration of functional analogues with a more predictable modification pattern and monosaccharide sequence, that can aid in elucidating structure-function relationships and further be structurally customized to fine-tune physical and biological properties toward novel therapeutic applications and biomaterials. Alginates have been of great interest in biomedicine due to their inherent biocompatibility, gentle gelling conditions, and structural versatility from chemo-enzymatic engineering, but display limited interactions with cells and biomolecules that are characteristic of heparin and the other glycosaminoglycans (GAGs) of the extracellular environment. Here, we review the chemistry and physical and biological properties of sulfated alginates as structural and functional heparin analogues, and discuss how they may be utilized in applications where the use of heparin and other sulfated GAGs is challenging and limited.

Current and Future Perspectives on Alginate Encapsulated Pancreatic Islet

Transplantation of pancreatic islets in immune protective capsules holds the promise as a functional cure for type 1 diabetes, also about 40 years after the first proof of principal study. The concept is simple in using semipermeable capsules that allow the ingress of oxygen and nutrients, but limit the access of the immune system. Encapsulated human islets have been evaluated in four small clinical trials where the procedure has been evaluated as safe, but lacking long-term efficacy. Host reactions toward the biomaterials used in the capsules may be one parameter limiting the long-term function of the graft in humans. The present article briefly discusses important capsule properties such as stability, permeability and biocompatibility, as well as possible strategies to overcome current challenges. Also, recent progress in capsule development as well as the production of insulin-producing cells from human stem cells that gives promising perspectives for the transplantation of encapsulated insulin-producing tissue is briefly discussed. Stem Cells Translational Medicine 2017;6:1053-1058.

Anti-oxidant and immune-modulatory properties of sulfated alginate derivatives on human chondrocytes and macrophages

A sulfated biopolymer was found to have anti-oxidant and immunemodulatory properties. This class of materials has promise for treatment of joint disease.

Sulfated alginate microspheres associate with factor H and dampen the inflammatory cytokine response

Alginate microspheres show promise for cell-encapsulation therapy but encounter challenges related to biocompatibility. In the present work we designed novel microbeads and microcapsules based on sulfated polyalternating MG alginate (SMG) and explored their inflammatory properties using a human whole blood model. SMG was either incorporated within the alginate microbeads or used as a secondary coat on poly-l-lysine (PLL)-containing microcapsules, resulting in reduction of the inflammatory cytokines (IL-1β, TNF, IL-6, IL-8, MIP-1α). The sulfated alginate microbeads exhibited a complement inert nature with no induction of terminal complement complex (TCC) above the values in freshly drawn blood and low surface accumulation of C3/C3b/iC3b. Conversely, SMG as a coating material lead to substantial TCC amounts and surface C3/C3b/iC3b. A common thread was an increased association of the complement inhibitor factor H to the alginate microbeads and microcapsules containing sulfated alginates. Factor H was also found to associate to non-sulfated alginate microbeads in lower amounts, indicating factor H binding as an inherent property of alginate. We conclude that the dampening effect on the cytokine response and increased factor H association points to sulfated alginate as a promising strategy for improving the biocompatibility of alginate microspheres.

STATEMENT OF SIGNIFICANCE

Alginate microspheres are candidate devices for cell encapsulation therapy. The concept is challenged by the inflammatory host response, and modification strategies for improved biocompatibility are urgently needed. One potential strategy is using sulfated alginates, acting as versatile heparin analogues with similar anti-inflammatory properties. We designed novel alginate microspheres using sulfated alginate with an alternating sequence mimicking glycosominoglycans. Evaluation in a physiologically relevant human whole blood model revealed a reduction of inflammatory cytokines by a sulfated alginate coating, and sulfated alginate microbeads were complement inert. These effects were correlated with a strong factor H association, which may represent the mechanistic explanation. This novel approach could improve the biocompatibility of alginate microspheres in vivo and present a new strategy toward clinical use.