Self-assembling Peptide Reduces Glial Scarring, Attenuates Posttraumatic Inflammation, and Promotes Neurite Outgrowth of Spinal Motor Neurons

Self-Assembled Peptide Hydrogels in Regenerative Medicine

Regenerative medicine is a complex discipline that is becoming a hot research topic. Skin, bone, and nerve regeneration dominate current treatments in regenerative medicine. A new type of drug is urgently needed for their treatment due to their high vulnerability to damage and weak self-repairing ability. A self-assembled peptide hydrogel is a good scaffolding material in regenerative medicine because it is similar to the cytoplasmic matrix environment; it promotes cell adhesion, migration, proliferation, and division; and its degradation products are natural and harmless proteins. However, fewer studies have examined the specific mechanisms of self-assembled peptide hydrogels in promoting tissue regeneration. This review summarizes the applications and mechanisms of self-assembled short peptide and peptide hydrogels in skin, bone, and neural healing to improve their applications in tissue healing and regeneration.

The Application of Biomaterials in Spinal Cord Injury

The spinal cord and the brain form the central nervous system (CNS), which is the most important part of the body. However, spinal cord injury (SCI) caused by external forces is one of the most difficult types of neurological injury to treat, resulting in reduced or even absent motor, sensory and autonomic functions. It leads to the reduction or even disappearance of motor, sensory and self-organizing nerve functions. Currently, its incidence is increasing each year worldwide. Therefore, the development of treatments for SCI is urgently needed in the clinic. To date, surgery, drug therapy, stem cell transplantation, regenerative medicine, and rehabilitation therapy have been developed for the treatment of SCI. Among them, regenerative biomaterials that use tissue engineering and bioscaffolds to transport cells or drugs to the injured site are considered the most promising option. In this review, we briefly introduce SCI and its molecular mechanism and summarize the application of biomaterials in the repair and regeneration of tissue in various models of SCI. However, there is still limited evidence about the treatment of SCI with biomaterials in the clinic. Finally, this review will provide inspiration and direction for the future study and application of biomaterials in the treatment of SCI.

Hydrogels in Spinal Cord Injury Repair: A Review

Traffic accidents and falling objects are responsible for most spinal cord injuries (SCIs). SCI is characterized by high disability and tends to occur among the young, seriously affecting patients' lives and quality of life. The key aims of repairing SCI include preventing secondary nerve injury, inhibiting glial scarring and inflammatory response, and promoting nerve regeneration. Hydrogels have good biocompatibility and degradability, low immunogenicity, and easy-to-adjust mechanical properties. While providing structural scaffolds for tissues, hydrogels can also be used as slow-release carriers in neural tissue engineering to promote cell proliferation, migration, and differentiation, as well as accelerate the repair of damaged tissue. This review discusses the characteristics of hydrogels and their advantages as delivery vehicles, as well as expounds on the progress made in hydrogel therapy (alone or combined with cells and molecules) to repair SCI. In addition, we discuss the prospects of hydrogels in clinical research and provide new ideas for the treatment of SCI.

Self-assembling peptide hydrogel SPG-178 as a pancreatic fistula-preventing agent

PURPOSE

Pancreatic fistula (PF) is a common and challenging complication after pancreatic surgery. The aim of this study was to investigate the efficacy of a new method for preventing PF utilizing self-assembling peptide hydrogel SPG-178 as a preclinical study.

METHODS

The degradability of SPG-178 was confirmed by mixing it with protease. A PF rat model was then established to investigate the efficacy of SPG-178 at preventing PF. After transecting the pancreatic duct toward the spleen, SPG-178 was attached to both sides of the pancreatic stump. The levels of amylase and lipase in both the serum and ascites were measured and surgical specimens investigated pathologically.

RESULTS

The hardness of SPG-178 did not change when treated with protease over a short period. The ascitic amylase level was significantly lower in rats treated with SPG-178 than rats who were not 3 days after transection of the pancreatic duct toward the spleen. Pathological examination showed fewer inflammatory cells and presence of a structure body on the surface of the pancreatic stump in the SPG-178-treated group. SPG-178 remained on the surface and many cells that covered it formed fibrous tissue or mesothelium.

CONCLUSION

Self-assembling peptide hydrogel SPG-178 has potential as a tool for preventing PF.

Peptide-Protein Interactions: From Drug Design to Supramolecular Biomaterials

The self-recognition and self-assembly of biomolecules are spontaneous processes that occur in Nature and allow the formation of ordered structures, at the nanoscale or even at the macroscale, under thermodynamic and kinetic equilibrium as a consequence of specific and local interactions. In particular, peptides and peptidomimetics play an elected role, as they may allow a rational approach to elucidate biological mechanisms to develop new drugs, biomaterials, catalysts, or semiconductors. The forces that rule self-recognition and self-assembly processes are weak interactions, such as hydrogen bonding, electrostatic attractions, and van der Waals forces, and they underlie the formation of the secondary structure (e.g., α-helix, β-sheet, polyproline II helix), which plays a key role in all biological processes. Here, we present recent and significant examples whereby design was successfully applied to attain the desired structural motifs toward function. These studies are important to understand the main interactions ruling the biological processes and the onset of many pathologies. The types of secondary structure adopted by peptides during self-assembly have a fundamental importance not only on the type of nano- or macro-structure formed but also on the properties of biomaterials, such as the types of interaction, encapsulation, non-covalent interaction, or covalent interaction, which are ultimately useful for applications in drug delivery.

Assessment of a self-assembling peptide gel, SPG-178, in providing a clear operative field for trabeculectomy surgery for glaucoma in an animal model

The presence of blood during ophthalmic surgery is problematic, as it can obstruct a surgeon’s view of the operative field. This is particularly true when performing trabeculectomy surgery to enhance ocular fluid outflow and reduce intraocular pressure as a treatment for glaucoma, one of the most common vision loss conditions worldwide. In this study, we investigated the performance of a transparent, self-assembling peptide gel (SPG-178) and its ability to maintain visibility during trabeculectomy surgery. Unlike the hyaluronic acid gel commonly used in ophthalmic surgery, SPG-178 did not permit the ingress of blood into the gel itself. Rather, it forced blood to flow peripherally to the gel. Moreover, if bleeding occurred under the SPG-178 gel, perfusion with saline was able to effectively flush the blood away along the interface between the SPG-178 and the ocular tissue (in this case scleral) to clear the surgical field of view. In experimental trabeculectomy surgeries with mitomycin C used as an adjuvant, there were no differences in the postoperative recovery of intraocular pressure or bleb morphology with or without the use of SPG-178. SPG-178, therefore, when used in a gel formulation, represents a new material for use in intraocular surgery to ensure a clear operative field with likely beneficial treatment outcomes.

Decellularized brain matrix enhances macrophage polarization and functional improvements in rat spinal cord injury

Spinal cord injury (SCI) is a devastating lesion lacking effective treatment options currently available in clinics. The inflammatory process exacerbates the extent of the lesion through a secondary injury mechanism, where proinflammatory classically activated macrophages (M1) are prevalent at the lesion site. However, the polarized alternatively activated anti-inflammatory macrophages (M2) are known to play an important role in wound healing and regeneration following SCI. Herein, we introduce porcine brain decellularized extracellular matrix (dECM) to modulate the macrophages in the injured spinal cord. The hydrogels with collagen and dECM at various dECM concentrations (1, 5, and 8 mg/ml) were used to cultivate primary macrophages and neurons. The dECM hydrogels were shown to promote the polarization of macrophages toward M2 phase and the neurite outgrowth of cortical and hippocampal neurons. When the dECM hydrogels were applied to rat SCI models, the proportion of M1 and M2 macrophages in the injured spinal cord was substantially altered. When received dECM concetration of 5 mg/ml, the expression of molecules associated with M2 (CD206, arginase1, and IL-10) was significantly increased. Consistently, the population of total macrophages and cavity area were substantially reduced in the dECM-treated groups. As a result, the locomotor functions of injured spinal cord, as assessed by BBB and ladder scoring, were significantly improved. Collectively, the porcine brain dECM with optimal concentration promotes functional recovery in SCI models through the activation of M2 macrophages, suggesting the promising use of the engineered hydrogels in the treatment of acute SCI. STATEMENT OF SIGNIFICANCE: Spinal cord injury (SCI) is a devastating lesion, lacking effective treatment options currently available in clinics. Here we delineated that the treatment of injured spinal cord with porcine brain decellularized matrix-based hydrogels for the first time, and could modulate the macrophage polarization and the ultimate functional recovery. When appropriate formulations were applied to a contused spinal cord model in rats, the decellularized matrix hydrogels shifted the macrophages to polarize to pro-regenerative M2 phenotype, decreased the size of lesion cavity, and finally promoted the locomotor functions until 8 weeks following the injury. We consider this work can significantly augment the matrix(biomaterial)-based therapeutic options, as an alternative to drug or cell-free approaches, for the treatment of acute injury of spinal cord.

Combined effects of systemic parathyroid hormone (1-34) and locally delivered neutral self-assembling peptide hydrogel in the treatment of periodontal defects: An experimental in vivo investigation

AIM

To evaluate in vivo combination therapy of systemic parathyroid hormone (PTH) and locally delivered neutral self-assembling peptide (SAP) hydrogel for periodontal treatment.

MATERIALS AND METHODS

Viability/proliferation of rat periodontal ligament cells in a neutral SAP nanofibre hydrogel (SPG-178) was evaluated using WST-1 assay. Periodontal defects were created mesially to the maxillary first molars in 40 Wistar rats. Defects were filled with 1.5% SPG-178 or left unfilled. Animals received PTH (1-34) or saline injections every 2 days. Microcomputed tomography, histological, and immunohistochemical examinations were used to evaluate healing at 2 or 4 weeks postoperative.

RESULTS

At 72 hr, cells in 1.5% SPG-178 showed increased viability/proliferation compared to cells in 0.8% SPG-178 or untreated controls. In vivo, systemic PTH resulted in significantly greater bone volume in the Unfilled group at 2 weeks (p = .01) and 4 weeks (p < .0001) than in the saline control. At 4 weeks, a significantly greater bone volume was observed in the PTH/SPG-178 (p = .0003) and PTH/Unfilled (p = .004) groups than in Saline/SPG-178 group. Histologically, greater bone formation was observed in PTH/SPG-178 at 4 weeks than in other groups. In the PTH/SPG-178 group, increased proportions of PCNA-, VEGF-, and Osterix-positive cells were observed in the treated sites.

CONCLUSIONS

These findings suggest that intermittent systemic PTH and locally delivered neutral SAP hydrogel enhance periodontal healing.

Role and prospects of regenerative biomaterials in the repair of spinal cord injury

Axonal junction defects and an inhibitory environment after spinal cord injury seriously hinder the regeneration of damaged tissues and neuronal functions. At the site of spinal cord injury, regenerative biomaterials can fill cavities, deliver curative drugs, and provide adsorption sites for transplanted or host cells. Some regenerative biomaterials can also inhibit apoptosis, inflammation and glial scar formation, or further promote neurogenesis, axonal growth and angiogenesis. This review summarized a variety of biomaterial scaffolds made of natural, synthetic, and combined materials applied to spinal cord injury repair. Although these biomaterial scaffolds have shown a certain therapeutic effect in spinal cord injury repair, there are still many problems to be resolved, such as product standards and material safety and effectiveness.

Feasibility and effects of a self-assembling peptide as a scaffold in bone healing: An in vivo study in rabbit lumbar posterolateral fusion and tibial intramedullary models

Spinal fusion and bone defects after injuries, removal of bone tumors, and infections require repair by implantation. In this study, we show self-assembling peptide (SPG-178) hydrogel-induced bone healing in vivo. Posterolateral lumbar fusion and tibial intramedullary models of rabbits were prepared. In the tibia model, micro-CT analysis revealed a significantly higher degree of newly formed bone matrix in the SPG-178 group compared to the other groups. SEM/3D micrographs showed that the cavity filled with SPG-178 had collagen fibers attached to host bone. After 28 days, samples from the SPG-178 group showed significant repair of the defect. In the posterolateral lumbar fusion models, micro-CT showed a tendency for a higher degree of newly formed bone matrix in the SPG-178 group compared to the β-TCP and bone chips only groups. Von Kossa staining showed marked new bone formation attached to the lamina that was most prominent at the implanted SPG-178 composite margin. SPG-178 is a material that is likely to be used in clinical applications because it has several benefits. These include its favorable bone conduction properties, its ability to act as a support for various cells and growth factors, its lack of infection risk compared with materials of animal origin such as ECM, and the ease with which it can be used to fill defects with complex shapes and be combined with a wide range of other materials. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3285-3293, 2018.

Effects of a self-assembling peptide as a scaffold on bone formation in a defect

Spinal fusion and bone defect after injuries, removal of bone tumors, and infections need to be repaired by implantation. In an aging society, recovery from these procedures is often difficult. In this study, we found that injection of SPG-178 leads to expression of several bone marker genes and mineralization in vitro, and revealed a significantly higher degree of newly formed bone matrix with use of SPG-178 in vivo. MC3T3-E1 cells were used to evaluate osteoblast differentiation promoted by SPG-178. To analyze gene expression, total RNA was isolated from MC3T3-E1 cells cultured for 7 and 14 days with control medium or SPG-178 medium. Among the several bone marker genes examined, SPG-178 significantly increased the mRNA levels for ALP, BMP-2 and Osteocalcin, OPN, BSP and for the Osterix. Ten-week-old female Wistar rats were used for all transplantation procedures. A PEEK cage was implanted into a bony defect (5 mm) within the left femoral mid-shaft, and stability was maintained by an external fixator. The PEEK cages were filled with either a SPG-178 hydrogel plus allogeneic bone chips (n = 4) or only allogeneic bone chips (n = 4). The rats were then kept for 56 days. Newly formed bone matrix was revealed inside the PEEK cage and there was an increased bone volume per total volume with the cage filled with SPG-178, compared to the control group. SPG-178 has potential in clinical applications because it has several benefits. These include its favorable bone conduction properties its ability to act as a support for various different cells and growth factors, its lack of infection risk compared with materials of animal origin such as ECM, and the ease with which it can be used to fill defects with complex shapes and combined with a wide range of other materials.