Therapeutic effects of gefitinib-encapsulated thermosensitive injectable hydrogel in intervertebral disc degeneration

Progress in the Application of Hydrogels in Intervertebral Disc Repair: A Comprehensive Review

PURPOSE OF REVIEW

Intervertebral disc degeneration (IVDD) is a common orthopaedic disease and an important cause of lower back pain, which seriously affects the work and life of patients and causes a large economic burden to society. The traditional treatment of IVDD mainly involves early pain relief and late surgical intervention, but it cannot reverse the pathological course of IVDD. Current studies suggest that IVDD is related to the imbalance between the anabolic and catabolic functions of the extracellular matrix (ECM). Anti-inflammatory drugs, bioactive substances, and stem cells have all been shown to improve ECM, but traditional injection methods face short half-life and leakage problems.

RECENT FINDINGS

The good biocompatibility and slow-release function of polymer hydrogels are being noticed and explored to combine with drugs or bioactive substances to treat IVDD. This paper introduces the pathophysiological mechanism of IVDD, and discusses the advantages, disadvantages and development prospects of hydrogels for the treatment of IVDD, so as to provide guidance for future breakthroughs in the treatment of IVDD.

Injectable Hydrogels: A Paradigm Tailored with Design, Characterization, and Multifaceted Approaches

Biomaterials denoting self-healing and versatile structural integrity are highly curious in the biomedicine segment. The injectable and/or printable 3D printing technology is explored in a few decades back, which can alter their dimensions temporarily under shear stress, showing potential healing/recovery tendency with patient-specific intervention toward the development of personalized medicine. Thus, self-healing injectable hydrogels (IHs) are stunning toward developing a paradigm for tissue regeneration. This review comprises the designing of IHs, rheological characterization and stability, several benchmark consequences for self-healing IHs, their translation into tissue regeneration of specific types, applications of IHs in biomedical such as anticancer and immunomodulation, wound healing and tissue/bone regeneration, antimicrobial potentials, drugs, gene and vaccine delivery, ocular delivery, 3D printing, cosmeceuticals, and photothermal therapy as well as in other allied avenues like agriculture, aerospace, electronic/electrical industries, coating approaches, patents associated with therapeutic/nontherapeutic avenues, and numerous futuristic challenges and solutions.

Advancements in Regenerative Hydrogels in Skin Wound Treatment: A Comprehensive Review

This state-of-the-art review explores the emerging field of regenerative hydrogels and their profound impact on the treatment of skin wounds. Regenerative hydrogels, composed mainly of water-absorbing polymers, have garnered attention in wound healing, particularly for skin wounds. Their unique properties make them well suited for tissue regeneration. Notable benefits include excellent water retention, creating a crucially moist wound environment for optimal healing, and facilitating cell migration, and proliferation. Biocompatibility is a key feature, minimizing adverse reactions and promoting the natural healing process. Acting as a supportive scaffold for cell growth, hydrogels mimic the extracellular matrix, aiding the attachment and proliferation of cells like fibroblasts and keratinocytes. Engineered for controlled drug release, hydrogels enhance wound healing by promoting angiogenesis, reducing inflammation, and preventing infection. The demonstrated acceleration of the wound healing process, particularly beneficial for chronic or impaired healing wounds, adds to their appeal. Easy application and conformity to various wound shapes make hydrogels practical, including in irregular or challenging areas. Scar minimization through tissue regeneration is crucial, especially in cosmetic and functional regions. Hydrogels contribute to pain management by creating a protective barrier, reducing friction, and fostering a soothing environment. Some hydrogels, with inherent antimicrobial properties, aid in infection prevention, which is a crucial aspect of successful wound healing. Their flexibility and ability to conform to wound contours ensure optimal tissue contact, enhancing overall treatment effectiveness. In summary, regenerative hydrogels present a promising approach for improving skin wound healing outcomes across diverse clinical scenarios. This review provides a comprehensive analysis of the benefits, mechanisms, and challenges associated with the use of regenerative hydrogels in the treatment of skin wounds. In this review, the authors likely delve into the application of rational design principles to enhance the efficacy and performance of hydrogels in promoting wound healing. Through an exploration of various methodologies and approaches, this paper is poised to highlight how these principles have been instrumental in refining the design of hydrogels, potentially revolutionizing their therapeutic potential in addressing skin wounds. By synthesizing current knowledge and highlighting potential avenues for future research, this review aims to contribute to the advancement of regenerative medicine and ultimately improve clinical outcomes for patients with skin wounds.

Reviving Intervertebral Discs: Treating Degeneration Using Advanced Delivery Systems

Intervertebral disc degeneration (IVDD) is commonly associated with many spinal problems, such as low back pain, and significantly impacts a patient's quality of life. However, current treatments for IVDD, which include conservative and surgical methods, are limited in their ability to fully address degeneration. To combat IVDD, delivery-system-based therapy has received extensive attention from researchers. These delivery systems can effectively deliver therapeutic agents for IVDD, overcoming the limitations of these agents, reducing leakage and increasing local concentration to inhibit IVDD or promote intervertebral disc (IVD) regeneration. This review first briefly introduces the structure and function of the IVD, and the related pathophysiology of IVDD. Subsequently, the roles of drug-based and bioactive-substance-based delivery systems in IVDD are highlighted. The former includes natural source drugs, nonsteroidal anti-inflammatory drugs, steroid medications, and other small molecular drugs. The latter includes chemokines, growth factors, interleukin, and platelet-rich plasma. Additionally, gene-based and cell-based delivery systems are briefly involved. Finally, the limitations and future development of the combination of therapeutic agents and delivery systems in the treatment of IVDD are discussed, providing insights for future research.

From drugs to biomaterials: a review of emerging therapeutic strategies for intervertebral disc inflammation

Chronic low back pain (LBP) is an increasingly prevalent issue, especially among aging populations. A major underlying cause of LBP is intervertebral disc degeneration (IDD), often triggered by intervertebral disc (IVD) inflammation. Inflammation of the IVD is divided into Septic and Aseptic inflammation. Conservative therapy and surgical treatment often fail to address the root cause of IDD. Recent advances in the treatment of IVD infection and inflammation range from antibiotics and small-molecule drugs to cellular therapies, biological agents, and innovative biomaterials. This review sheds light on the complex mechanisms of IVD inflammation and physiological and biochemical processes of IDD. Furthermore, it provides an overview of recent research developments in this area, intending to identify novel therapeutic targets and guide future clinical strategies for effectively treating IVD-related conditions.

Application and development of hydrogel biomaterials for the treatment of intervertebral disc degeneration: a literature review

Low back pain caused by disc herniation and spinal stenosis imposes an enormous medical burden on society due to its high prevalence and refractory nature. This is mainly due to the long-term inflammation and degradation of the extracellular matrix in the process of intervertebral disc degeneration (IVDD), which manifests as loss of water in the nucleus pulposus (NP) and the formation of fibrous disc fissures. Biomaterial repair strategies involving hydrogels play an important role in the treatment of intervertebral disc degeneration. Excellent biocompatibility, tunable mechanical properties, easy modification, injectability, and the ability to encapsulate drugs, cells, genes, etc. make hydrogels good candidates as scaffolds and cell/drug carriers for treating NP degeneration and other aspects of IVDD. This review first briefly describes the anatomy, pathology, and current treatments of IVDD, and then introduces different types of hydrogels and addresses "smart hydrogels". Finally, we discuss the feasibility and prospects of using hydrogels to treat IVDD.

Pathogenesis and therapeutic implications of matrix metalloproteinases in intervertebral disc degeneration: A comprehensive review

Intervertebral disc (IVD) degeneration (IDD) is a common disorder that affects the spine and is a major cause of lower back pain (LBP). The extracellular matrix (ECM) is the structural foundation of the biomechanical properties of IVD, and its degradation is the main pathological characteristic of IDD. Matrix metalloproteinases (MMPs) are a group of endopeptidases that play an important role in the degradation and remodeling of the ECM. Several recent studies have shown that the expression and activity of many MMP subgroups are significantly upregulated in degenerated IVD tissue. This upregulation of MMPs results in an imbalance of ECM anabolism and catabolism, leading to the degradation of the ECM and the development of IDD. Therefore, the regulation of MMP expression is a potential therapeutic target for the treatment of IDD. Recent research has focused on identifying the mechanisms by which MMPs cause ECM degradation and promote IDD, as well as on developing therapies that target MMPs. In summary, MMP dysregulation is a crucial factor in the development of IDD, and a deeper understanding of the mechanisms involved is needed to develop effective biological therapies that target MMPs to treat IDD.

Multifunctional injectable hydrogels with controlled delivery of bioactive factors for efficient repair of intervertebral disc degeneration

Millions of people worldwide suffer from intervertebral disc degeneration (IVDD), which imposes a significant socioeconomic burden on society. There is an urgent clinical demand for more effective treatments for IVDD because conventional treatments can only alleviate the symptoms rather than preventing the progression of IVDD. Hydrogels, a class of elastic biomaterials with good biocompatibility, are promising candidates for intervertebral disc repair and regeneration. In recent years, various hydrogels have been investigated in vitro and in vivo for the repair of intervertebral discs, some of which are ready for clinical testing. This review summarizes the latest findings and developments in using bioactive factors-released bioactive injectable hydrogels for the repair and regeneration of intervertebral discs. It focuses on the analysis and summary of the use of multifunctional injectable hydrogels to delivery bioactive factors (cells, exosomes, growth factors, genes, drugs) for disc regeneration, providing guidance for future study. Finally, we discussed and analyzed the optimal timing for the application of controlled-release hydrogels in the treatment of IVDD to meet the high standards required for intervertebral disc regeneration and precision medicine.

Degenerated nucleus pulposus cells derived exosome carrying miR-27a-3p aggravates intervertebral disc degeneration by inducing M1 polarization of macrophages

BACKGROUND

Intervertebral disc degeneration (IVDD) is a major contributor to spinal disorders. Previous studies have indicated that the infiltration of immunocytes, specifically macrophages, plays a crucial role in the advancement of IVDD. Exosomes (exo) are believed to play a significant role in intercellular communication. This study aims to investigate the role of exosomes derived from degenerated nucleus pulposus (dNPc) in the process of macrophages M1 polarization.

METHODS

Nucleus pulposus (NP) tissue and nucleus pulposus cells (NPc) were collected from patients with intervertebral disc degeneration (IVDD) and idiopathic scoliosis. Immunohistochemistry analysis was performed to determine the number of M1 macrophages in NP tissue. Subsequently, exosomes derived from degenerated NP cells (dNPc-exo) and non-degenerated NP cells (nNPc-exo) were collected and co-cultured with M0 macrophages, which were induced from THP-1 cells. The M1 phenotype was assessed using western blot, flow cytometry, immunofluorescence staining, and qRT-PCR. RNA-sequencing analysis was conducted to examine the expression levels of microRNAs in the dNPc-exo and nNPc-exo groups, and qRT-PCR was performed to investigate the effect pf different microRNA to induce macrophage polarization. Furthermore, western blot and qRT-PCR were employed to demonstrate the regulatory effect of microRNAs carried by dNPc-exo on downstream target signaling pathways in macrophages. Finally, an animal model of IVDD was utilized to investigate the impact of dNPc-exo on inducing M1 polarization of macrophages and its role in the IVDD process.

RESULTS

In this study, we observed an increase in the number of M1 macrophages as the intervertebral disc (IVD) degraded. Additionally, we discovered that dNPc releases exosomes (dNPc-exo) could promote the polarization of macrophages towards the M1 phenotype. Notably, through RNA-sequencing analysis of dNPc-exo and nNPc-exo groups, we identified miR-27a-3p as a highly expressed miRNA in the dNPc-exo group, which significantly influences the induction of M1 polarization of macrophages. And then, we discovered that dNPc-exo has the ability to transport miR-27a-3p and target the PPARγ/NFκB/PI3K/AKT signaling pathway, thereby influencing the M1 polarization of macrophages. We conducted experiments using rat model of IVDD and observed that the exosomes carrying miR-27a-3p actually induced the M1 polarization of macrophages and exacerbated the degradation of IVD.

CONCLUSION

In conclusion, our findings highlight the significant role of dNPc-exo in IVDD process and provide a basis for further investigation into the mechanism of IVDD and the potential of exosome-based therapy.

Intervertebral disc degeneration-Current therapeutic options and challenges

Degeneration of the intervertebral disc (IVD) is a normal part of aging. Due to the spine's declining function and the development of pain, it may affect one's physical health, mental health, and socioeconomic status. Most of the intervertebral disc degeneration (IVDD) therapies today focus on the symptoms of low back pain rather than the underlying etiology or mechanical function of the disc. The deteriorated disc is typically not restored by conservative or surgical therapies that largely focus on correcting symptoms and structural abnormalities. To enhance the clinical outcome and the quality of life of a patient, several therapeutic modalities have been created. In this review, we discuss genetic and environmental causes of IVDD and describe promising modern endogenous and exogenous therapeutic approaches including their applicability and relevance to the degeneration process.

Spray-dried microparticles of encapsulated gefitinib for slow-release localized treatment of periodontal disease

Periodontal disease (PD) can be prevented by local or systemic application of epidermal growth factor receptor inhibitors (EGFRIs) that stabilize αvβ6 integrin levels in the periodontal tissue, leading to an increase in the expression of anti-inflammatory cytokines, such as transforming growth factor-β1. Systemic EGFRIs have side effects and, therefore, local treatment of PD applied into the periodontal pockets would be preferrable. Thus, we have developed slow-release three-layered microparticles of gefitinib, a commercially available EGFRI. A combination of different polymers [cellulose acetate butyrate (CAB), Poly (D, L-lactide-co-glycolide) (PLGA) and ethyl cellulose (EC)] and sugars [D-mannose, D-mannitol and D-(+)-trehalose dihydrate] were used for the encapsulation. The optimal formulation was composed of CAB, EC, PLGA, mannose and gefitinib (0.59, 0.24, 0.09, 1, and 0.005 mg/ml, respectively; labeled CEP-gef), and created microparticles of 5.7 ± 2.3 µm in diameter, encapsulation efficiency of 99.98%, and a release rate of more than 300 hours. A suspension of this microparticle formulation blocked EGFR phosphorylation and restored αvβ6 integrin levels in oral epithelial cells, while the respective control microparticles showed no effect.

An update on animal models of intervertebral disc degeneration and low back pain: Exploring the potential of artificial intelligence to improve research analysis and development of prospective therapeutics

Animal models have been invaluable in the identification of molecular events occurring in and contributing to intervertebral disc (IVD) degeneration and important therapeutic targets have been identified. Some outstanding animal models (murine, ovine, chondrodystrophoid canine) have been identified with their own strengths and weaknesses. The llama/alpaca, horse and kangaroo have emerged as new large species for IVD studies, and only time will tell if they will surpass the utility of existing models. The complexity of IVD degeneration poses difficulties in the selection of the most appropriate molecular target of many potential candidates, to focus on in the formulation of strategies to effect disc repair and regeneration. It may well be that many therapeutic objectives should be targeted simultaneously to effect a favorable outcome in human IVD degeneration. Use of animal models in isolation will not allow resolution of this complex issue and a paradigm shift and adoption of new methodologies is required to provide the next step forward in the determination of an effective repairative strategy for the IVD. AI has improved the accuracy and assessment of spinal imaging supporting clinical diagnostics and research efforts to better understand IVD degeneration and its treatment. Implementation of AI in the evaluation of histology data has improved the usefulness of a popular murine IVD model and could also be used in an ovine histopathological grading scheme that has been used to quantify degenerative IVD changes and stem cell mediated regeneration. These models are also attractive candidates for the evaluation of novel anti-oxidant compounds that counter inflammatory conditions in degenerate IVDs and promote IVD regeneration. Some of these compounds also have pain-relieving properties. AI has facilitated development of facial recognition pain assessment in animal IVD models offering the possibility of correlating the potential pain alleviating properties of some of these compounds with IVD regeneration.

Nanofiber reinforced alginate hydrogel for leak-proof delivery and higher stress loading in nucleus pulposus

Injectable hydrogels effectively remodel degenerative nucleus pulposus (NP) with a resemblance to the in vivo microenvironment. However, the pressure within the intervertebral disc requires load-bearing implants. The hydrogel must undergo a rapid phase transition upon injection to avoid leakage. In this study, an injectable sodium alginate hydrogel was reinforced with silk fibroin nanofibers with core-shell structures. The nanofiber-embedded hydrogel provided support to adjacent tissues and facilitated cell proliferation. Platelet-rich plasma (PRP) was incorporated into the core-shell nanofibers for sustained release and enhanced NP regeneration. The composite hydrogel exhibited excellent compressive strength and enabled leak-proof delivery of PRP. In rat intervertebral disc degeneration models, radiography and MRI signal intensities were significantly reduced after 8 weeks of injections with the nanofiber-reinforced hydrogel. The biomimetic fiber gel-like structure was constructed in situ, providing mechanical support for NP repair, promoting the reconstruction of the tissue microenvironment, and finally realizing the regeneration of NP.

An Injectable Hydrogel Scaffold Loaded with Dual-Drug/Sustained-Release PLGA Microspheres for the Regulation of Macrophage Polarization in the Treatment of Intervertebral Disc Degeneration

Due to the unique physical characteristics of intervertebral disc degeneration (IVDD) and the pathological microenvironment that it creates, including inflammation and oxidative stress, effective self-repair is impossible. During the process of intervertebral disc degeneration, there is an increase in the infiltration of M1 macrophages and the secretion of proinflammatory cytokines. Here, we designed a novel injectable composite hydrogel scaffold: an oligo [poly (ethylene glycol) fumarate]/sodium methacrylate (OPF/SMA) hydrogel scaffold loaded with dual-drug/sustained-release PLGA microspheres containing IL-4 (IL-4-PLGA) and kartogenin (KGN-PLGA). This scaffold exhibited good mechanical properties and low immunogenicity while also promoting the sustained release of drugs. By virtue of the PLGA microspheres loaded with IL-4 (IL-4-PLGA), the composite hydrogel scaffold induced macrophages to transition from the M1 phenotype into the M2 phenotype during the early induced phase and simultaneously exhibited a continuous anti-inflammatory effect through the PLGA microspheres loaded with kartogenin (KGN-PLGA). Furthermore, we investigated the mechanisms underlying the immunomodulatory and anti-inflammatory effects of the composite hydrogel scaffold. We found that the scaffold promoted cell proliferation and improved cell viability in vitro. While ensuring mechanical strength, this composite hydrogel scaffold regulated the local inflammatory microenvironment and continuously repaired tissue in the nucleus pulposus via the sequential release of drugs in vivo. When degenerative intervertebral discs in a rat model were injected with the scaffold, there was an increase in the proportion of M2 macrophages in the inflammatory environment and higher expression levels of type II collagen and aggrecan; this was accompanied by reduced levels of MMP13 expression, thus exhibiting long-term anti-inflammatory effects. Our research provides a new strategy for promoting intervertebral disc tissue regeneration and a range of other inflammatory diseases.

Precision medicine strategies for spinal degenerative diseases: Injectable biomaterials with in situ repair and regeneration

As the population ages, spinal degeneration seriously affects quality of life in middle-aged and elderly patients, and prevention and treatment remain challenging for clinical surgeons. In recent years, biomaterials-based injectable therapeutics have attracted much attention for spinal degeneration treatment due to their minimally invasive features and ability to perform precise repair of irregular defects. However, the precise design and functional control of bioactive injectable biomaterials for efficient spinal degeneration treatment remains a challenge. Although many injectable biomaterials have been reported for the treatment of spinal degeneration, there are few reviews on the advances and effects of injectable biomaterials for spinal degeneration treatment. This work reviews the current status of the design and fabrication of injectable biomaterials, including hydrogels, bone cements and scaffolds, microspheres and nanomaterials, and the current progress in applications for treating spinal degeneration. Additionally, registered clinical trials were also summarized and key challenges and clinical translational prospects for injectable materials for the treatment of spinal degenerative diseases are discussed.

Vasorin-containing small extracellular vesicles retard intervertebral disc degeneration utilizing an injectable thermoresponsive delivery system

Intervertebral disc degeneration (IDD) is the pathological reason of back pain and the therapeutic approaches are still unsatisfactory. Recently, mesenchymal stem cell-derived small extracellular vesicles (EVs) have emerged as the novel regenerative method for IDD. In this study, we intensively investigated the therapeutic mechanism of small EVs, and found that vasorin protein enriched in EVs promoted the proliferation and extracellular matrix anabolism of nucleus pulposus cells via the Notch1 signaling pathway. Then, we fabricated a thermoresponsive gel which composed of Pluronic F127 and decellularized extracellular matrix (FEC) for the delivery and sustained release of EVs. Besides, ex vivo and in vivo results showed that EVs embedded in FEC (EVs@FEC) ameliorate the disc degeneration efficiently and achieve better therapeutic effects than one-off EVs delivery. Collectively, these findings deepen the understanding of EVs mechanism in treating intervertebral disc degeneration, and also illustrate the promising capacity of sustained EVs release system for intervertebral disc regeneration.

Treatment outcomes of injectable thermosensitive hydrogel containing bevacizumab in intervertebral disc degeneration

Intervertebral disc (IVD) degeneration (IDD) is a common musculoskeletal disease and its treatment remains a clinical challenge. It is characterised by reduced cell numbers and degeneration of the extracellular matrix (ECM). Nucleus pulposus (NP) cells play a crucial role in this process. The purpose of this study is to explore the role of bevacizumab, a vascular endothelial growth factor (VEGF) inhibitor, in the treatment of IDD through local drug delivery. High expression of VEGF was observed in degenerating human and rat IVDs. We demonstrated that MMP3 expression was decreased and COL II synthesis was promoted, when VEGF expression was inhibited by bevacizumab, thereby improving the degree of disc degeneration. Thus, these findings provide strong evidence that inhibition of VEGF expression by local delivery of bevacizumab is safe and effective in ameliorating disc degeneration in rats. The injectable thermosensitive PLGA-PEG-PLGA hydrogels loaded with bevacizumab is a potential therapeutic option for disc degeneration.

Self-Healing Injectable Hydrogels for Tissue Regeneration

Biomaterials with the ability to self-heal and recover their structural integrity offer many advantages for applications in biomedicine. The past decade has witnessed the rapid emergence of a new class of self-healing biomaterials commonly termed injectable, or printable in the context of 3D printing. These self-healing injectable biomaterials, mostly hydrogels and other soft condensed matter based on reversible chemistry, are able to temporarily fluidize under shear stress and subsequently recover their original mechanical properties. Self-healing injectable hydrogels offer distinct advantages compared to traditional biomaterials. Most notably, they can be administered in a locally targeted and minimally invasive manner through a narrow syringe without the need for invasive surgery. Their moldability allows for a patient-specific intervention and shows great prospects for personalized medicine. Injected hydrogels can facilitate tissue regeneration in multiple ways owing to their viscoelastic and diffusive nature, ranging from simple mechanical support, spatiotemporally controlled delivery of cells or therapeutics, to local recruitment and modulation of host cells to promote tissue regeneration. Consequently, self-healing injectable hydrogels have been at the forefront of many cutting-edge tissue regeneration strategies. This study provides a critical review of the current state of self-healing injectable hydrogels for tissue regeneration. As key challenges toward further maturation of this exciting research field, we identify (i) the trade-off between the self-healing and injectability of hydrogels vs their physical stability, (ii) the lack of consensus on rheological characterization and quantitative benchmarks for self-healing injectable hydrogels, particularly regarding the capillary flow in syringes, and (iii) practical limitations regarding translation toward therapeutically effective formulations for regeneration of specific tissues. Hence, here we (i) review chemical and physical design strategies for self-healing injectable hydrogels, (ii) provide a practical guide for their rheological analysis, and (iii) showcase their applicability for regeneration of various tissues and 3D printing of complex tissues and organoids.

Biomaterials and Regenerative Medicine in Pain Management

Purpose of Review

Pain presents a unique challenge due to the complexity of the biological pathways involved in the pain perception, the growing concern regarding the use of opioid analgesics, and the limited availability of optimal treatment options. The use of biomaterials and regenerative medicine in pain management is being actively explored and showing exciting progress in improving the efficacy of conventional pharmacotherapy and as novel non-pharmacological therapy for chronic pain caused by degenerative diseases. In this paper we review current clinical applications, and promising research in the use of biomaterials and regenerative medicine in pain management.

Recent Findings

Regenerative therapies have been developed to repair damaged tissues in back, joint, and shoulder that lead to chronic and inflammatory pain. Novel regenerative biomaterials have been designed to incorporate biochemical and physical pro-regenerative cues that augment the efficacy of regenerative therapies. New biomaterials improve target localization with improved tunability for controlled drug delivery, and injectable scaffolds enhance the efficacy of regenerative therapies through improving cellular migration. Advanced biomaterial carrier systems have been developed for sustained and targeted delivery of analgesic agents to specific tissues and organs, showing improved treatment efficacy, extended duration of action, and reduced dosage. Targeting endosomal receptors by nanoparticles has shown promising anti-nociception effects. Biomaterial scavengers are designed to remove proinflammatory reactive oxygen species that trigger nociceptors and cause pain hypersensitivity, providing a proactive approach for pain management.

Summary

Pharmacotherapy remains the method of choice for pain management; however, conventional analgesic agents are associated with adverse effects. The relatively short duration of action when applied as free drug limited their efficacy in postoperative and chronic pain treatment. The application of biomaterials in pain management is a promising strategy to improve the efficacy of current pharmacotherapy through sustained and targeted delivery of analgesic agents. Regenerative medicine strategies target the damaged tissue and provide non-pharmacological alternatives to manage chronic and inflammatory pain. In the future, the successful development of regenerative therapies that completely repair damaged tissues will provide a more optimal alternative for the treatment of chronic pain caused. Future studies will leverage on the increasing understanding of the molecular mechanisms governing pain perception and transmission, injury response and tissue regeneration, and the development of new biomaterials and tissue regenerative methods.

Injectable hydrogels for articular cartilage and nucleus pulposus repair: Status quo and prospects

Osteoarthritis (OA) and chronic low back pain due to degenerative (intervertebral) disc disease (DDD) are two of the major causes of disabilities worldwide, affecting hundreds of millions of people and leading to a high socioeconomic burden. Although OA occurs in synovial joints and DDD occurs in cartilaginous joints, the similarities are striking, with both joints showing commonalities in the nature of the tissues and in the degenerative processes during disease. Consequently, repair strategies for articular cartilage (AC) and nucleus pulposus (NP), the core of the intervertebral disc, in the context of OA and DDD share common aspects. One of such tissue engineering approaches is the use of injectable hydrogels for AC and NP repair. In this review, the state-of-the-art and recent developments in injectable hydrogels for repairing, restoring, and regenerating AC tissue suffering from OA and NP tissue in DDD are summarized focusing on cell-free approaches. The various biomaterial strategies exploited for repair of both tissues are compared, and the synergies that could be gained by translating experiences from one tissue to the other are identified.

Hyaluronic acid-based interpenetrating network hydrogel as a cell carrier for nucleus pulposus repair

Hyaluronic acid (HA) is a key component of the intervertebral disc (IVD) that is widely investigated as an IVD biomaterial. One persisting challenge is introducing materials capable of supporting cell encapsulation and function, yet with sufficient mechanical stability. In this study, a hybrid interpenetrating polymer network (IPN) was produced as a non-covalent hydrogel, based on a covalently cross-linked HA (HA-BDDE) and HA-poly(N-isopropylacrylamide) (HA-pNIPAM). The hybrid IPN was investigated for its physicochemical properties, with histology and gene expression analysis to determine matrix deposition in vitro and in an ex vivo model. The IPN hydrogel displayed cohesiveness for at least one week and rheological properties resembling native nucleus pulposus (NP) tissue. When implanted in an ex vivo IVD organ culture model, the IPN supported cell viability, phenotype expression of encapsulated NP cells and IVD matrix production over four weeks under physiological loading. Overall, our results indicate the therapeutic potential of this HA-based IPN hydrogel for IVD regeneration.

Mesenchymal Stem Cell-Derived Exosomes as a Novel Strategy for the Treatment of Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) has been reported to be the most prevalent contributor to low back pain, posing a significant strain on the healthcare systems on a global scale. Currently, there are no approved therapies available for the prevention of the progressive degeneration of intervertebral disc (IVD); however, emerging regenerative strategies that aim to restore the normal structure of the disc have been fundamentally promising. In the last decade, mesenchymal stem cells (MSCs) have received a significant deal of interest for the treatment of IVDD due to their differentiation potential, immunoregulatory capabilities, and capability to be cultured and regulated in a favorable environment. Recent investigations show that the pleiotropic impacts of MSCs are regulated by the production of soluble paracrine factors. Exosomes play an important role in regulating such effects. In this review, we have summarized the current treatments for disc degenerative diseases and their limitations and highlighted the therapeutic role and its underlying mechanism of MSC-derived exosomes in IVDD, as well as the possible future developments for exosomes.

Network Pharmacological Dissection of the Mechanisms of Eucommiae Cortex-Achyranthis Radix Combination for Intervertebral Disc Herniation Treatment

Eucommiae cortex (EC) and Achyranthis radix (AR) are herbal medicines widely used in combination for the treatment of intervertebral disc herniation (IDH). The mechanisms of action of the herbal combination have not been understood from integrative and comprehensive points of view. By adopting network pharmacological methodology, we aimed to investigate the pharmacological properties of the EC-AR combination as a therapeutic agent for IDH at a systematic molecular level. Using the pharmacokinetic information for the chemical ingredients of the EC-AR combination obtained from the comprehensive herbal drug-associated databases, we determined its 31 bioactive ingredients and 68 IDH-related therapeutic targets. By analyzing their enrichment for biological functions, we observed that the targets of the EC-AR combination were associated with the regulation of angiogenesis; cytokine and chemokine activity; oxidative and inflammatory stress responses; extracellular matrix organization; immune response; and cellular processes such as proliferation, apoptosis, autophagy, differentiation, migration, and activation. Pathway enrichment investigation revealed that the EC-AR combination may target IDH-pathology-associated signaling pathways, such as those of cellular senescence and chemokine, neurotrophin, TNF, MAPK, toll-like receptor, and VEGF signaling, to exhibit its therapeutic effects. Collectively, these data provide mechanistic insights into the pharmacological activity of herbal medicines for the treatment of musculoskeletal diseases such as IDH.

Applications of Functionalized Hydrogels in the Regeneration of the Intervertebral Disc

Intervertebral disc degeneration (IDD) is caused by genetics, aging, and environmental factors and is one of the leading causes of low back pain. The treatment of IDD presents many challenges. Hydrogels are biomaterials that possess properties similar to those of the natural extracellular matrix and have significant potential in the field of regenerative medicine. Hydrogels with various functional qualities have recently been used to repair and regenerate diseased intervertebral discs. Here, we review the mechanisms of intervertebral disc homeostasis and degeneration and then discuss the applications of hydrogel-mediated repair and intervertebral disc regeneration. The classification of artificial hydrogels and natural hydrogels is then briefly introduced, followed by an update on the development of functional hydrogels, which include noncellular therapeutic hydrogels, cellular therapeutic hydrogel scaffolds, responsive hydrogels, and multifunctional hydrogels. The challenges faced and future developments of the hydrogels used in IDD are discussed as they further promote their clinical translation.

Development of a standardized histopathology scoring system for intervertebral disc degeneration in rat models: An initiative of the ORS spine section

BACKGROUND

Rats are a widely accepted preclinical model for evaluating intervertebral disc (IVD) degeneration and regeneration. IVD morphology is commonly assessed using histology, which forms the foundation for quantifying the state of IVD degeneration. IVD degeneration severity is evaluated using different grading systems that focus on distinct degenerative features. A standard grading system would facilitate more accurate comparison across laboratories and more robust comparisons of different models and interventions.

AIMS

This study aimed to develop a histology grading system to quantify IVD degeneration for different rat models.

MATERIALS & METHODS

This study involved a literature review, a survey of experts in the field, and a validation study using 25 slides that were scored by 15 graders from different international institutes to determine inter- and intra-rater reliability.

RESULTS

A new IVD degeneration grading system was established and it consists of eight significant degenerative features, including nucleus pulposus (NP) shape, NP area, NP cell number, NP cell morphology, annulus fibrosus (AF) lamellar organization, AF tears/fissures/disruptions, NP-AF border appearance, as well as endplate disruptions/microfractures and osteophyte/ossification. The validation study indicated this system was easily adopted, and able to discern different severities of degenerative changes from different rat IVD degeneration models with high reproducibility for both experienced and inexperienced graders. In addition, a widely-accepted protocol for histological preparation of rat IVD samples based on the survey findings include paraffin embedding, sagittal orientation, section thickness < 10 μm, and staining using H&E and/or SO/FG to facilitate comparison across laboratories.

CONCLUSION

The proposed histological preparation protocol and grading system provide a platform for more precise comparisons and more robust evaluation of rat IVD degeneration models and interventions across laboratories.

Metformin facilitates mesenchymal stem cell-derived extracellular nanovesicles release and optimizes therapeutic efficacy in intervertebral disc degeneration

Extracellular vesicles (EVs) are extracellular nanovesicles that deliver diverse cargoes to the cell and participate in cell communication. Mesenchymal stem cell (MSCs)-derived EVs are considered a therapeutic approach in musculoskeletal degenerative diseases, including intervertebral disc degeneration. However, limited production yield and unstable quality have impeded the clinical application of EVs. In the present study, it is indicated that metformin promotes EVs release and alters the protein profile of EVs. Metformin enhances EVs production via an autophagy-related pathway, concomitantly with the phosphorylation of synaptosome-associated protein 29. More than quantity, quality of MSCs-derived EVs is influenced by metformin treatment. Proteomics analysis reveals that metformin increases the protein content of EVs involved in cell growth. It is shown that EVs derived from metformin-treated MSCs ameliorate intervertebral disc cells senescence in vitro and in vivo. Collectively, these findings demonstrate the great promise of metformin in EVs-based intervertebral disc regeneration.

Small molecule-based treatment approaches for intervertebral disc degeneration: Current options and future directions

Low back pain (LBP) is a major reason for disability, and symptomatic intervertebral disc (IVD) degeneration (IDD) contributes to roughly 40% of all LBP cases. Current treatment modalities for IDD include conservative and surgical strategies. Unfortunately, there is a significant number of patients in which conventional therapies fail with the result that these patients remain suffering from chronic pain and disability. Furthermore, none of the current therapies successfully address the underlying biological problem - the symptomatic degenerated disc. Both spinal fusion as well as total disc replacement devices reduce spinal motion and are associated with adjacent segment disease. Thus, there is an unmet need for novel and stage-adjusted therapies to combat IDD. Several new treatment options aiming to regenerate the IVD are currently under investigation. The most common approaches include tissue engineering, growth factor therapy, gene therapy, and cell-based treatments according to the stage of degeneration. Recently, the regenerative activity of small molecules (low molecular weight organic compounds with less than 900 daltons) on IDD was demonstrated. However, small molecule-based therapy in IDD is still in its infancy due to limited knowledge about the mechanisms that control different cell signaling pathways of IVD homeostasis. Small molecules can act as anti-inflammatory, anti-apoptotic, anti-oxidative, and anabolic agents, which can prevent further degeneration of disc cells and enhance their regeneration. This review pursues to give a comprehensive overview of small molecules, focusing on low molecular weight organic compounds, and their potential utilization in patients with IDD based on recent in vitro, in vivo, and pre-clinical studies.

Therapeutic effect of the injectable thermosensitive hydrogel loaded with SHP099 on intervertebral disc degeneration

AIMS

Intervertebral disc (IVD) degeneration (IDD), a common musculoskeletal disease with limited self-healing ability, is challenging to treat. The development of innovative therapies to reverse IDD depends on the elucidation of its regulatory mechanisms. Therefore, the role of Src homology region 2-containing protein tyrosine phosphatase 2 (SHP2) in the pathogenesis of IDD and the therapeutic effect of its small-molecule inhibitor, SHP099, were investigated.

MATERIALS AND METHODS

The expression of SHP2 by nucleus pulposus (NP) cells in IVD was investigated in vitro and in vivo, and its molecular mechanism in IDD was explored using transfection technology. Injectable N-isopropylacrylamide-based thermosensitive hydrogels were synthesized for SHP099 delivery.

KEY FINDINGS

SHP2 was highly expressed in degenerated IVDs, where its overexpression in NP cells inhibited the expression of Sry-related HMG box-9 (Sox9), leading to the decreased expression of key proteins (collagen II and aggrecan) and consequently to IDD. SHP099 reversed the degeneration of NP cells in vitro. Moreover, its administration in rats via the injectable thermosensitive hydrogel had a therapeutic effect on IDD.

SIGNIFICANCE

Our results suggest that SHP2 is a key factor in IDD progression, and SHP099 inhibits both its expression and NP cell degeneration. Therefore, SHP099 delivery via injectable thermosensitive hydrogels is a potential treatment strategy for IDD.

Thermosensitive Polymer Dot Nanocomposites for Trimodal Computed Tomography/Photoacoustic/Fluorescence Imaging-Guided Synergistic Chemo-Photothermal Therapy

Precision delivery of theranostic agents to the tumor site is essential to improve their diagnostic and therapeutic efficacy and concurrently minimize adverse effects during treatment. In this study, a novel concept of near-infrared (NIR) light activation of conjugated polymer dots (Pdots) at thermosensitive hydrogel nanostructures is introduced for multimodal imaging-guided synergistic chemo-photothermal therapy. Interestingly, owing to the attractive photothermal conversion efficiency of Pdots, the Pdots@hydrogel as theranostic agents is able to undergo a controllable softening or melting state under the irradiation of NIR laser, resulting in light-triggered drug release in a controlled way and concurrently hydrogel degradation. Besides, the novel Pdots@hydrogel nanoplatform can serve as the theranostic agent for enhanced trimodal photoacoustic (PA)/computed tomography (CT)/fluorescence (FL) imaging-guided synergistic chemo-photothermal therapy of tumors. More importantly, the constructed intelligent nanocomposite Pdots@hydrogel exhibits excellent biodegradability, strong NIR absorption, bright PA/CT/FL signals, and superior tumor ablation effect. Therefore, the concept of a light-controlled multifunctional Pdots@hydrogel that integrates multiple diagnostic/therapeutic modalities into one nanoplatform can potentially be applied as a smart nanotheranostic agent to various perspectives of personalized nanomedicine.

Mesenchymal stem cells-derived exosomes ameliorate intervertebral disc degeneration through inhibiting pyroptosis

Mesenchymal stem cell (MSCs)‐based therapies have shown a promised result for intervertebral disc degeneration (IVDD) treatment. However, its molecular mechanisms remain unclear. Exosomes involve cell‐cell communication via transference of its contents among different cells, and the present potential effect on cell death regulation. This study aimed to investigate the role of MSCs‐derived exosomes on IVDD formation. Here, we first found the NLRP3‐mediated nucleus pulposus cell (NP cell) pyroptosis was activated in the IVDD mice model and lipopolysaccharide (LPS)‐induced model. However, MSCs treatment could inhibit NP cell pyroptosis in vitro. We then isolated MSCs‐derived exosomes by differential centrifugation and identified the characteristics. Secondly, we investigated the function of MSCs‐derived exosomes on LPS‐induced NP cell pyroptosis. Finally, we presented evidence that MSCs‐derived exosomal miR‐410 was a crucial regulator of pyroptosis. Results showed that MSCs‐derived exosomes play an anti‐pyroptosis role by suppressing the NLRP3 pathway. Moreover, it suggested that this effect was attributed to miR‐410, which was derived from MSCs‐exosomes and could directly bind to NLRP3mRNA. In conclusion, for the first time, we demonstrated that MSCs‐exosome treatment may inhibit pyroptosis and could be a promising therapeutic strategy for IVDD.

[Research progress of hydrogel used for regeneration of nucleus pulposus in intervertebral disc degeneration]

Objective

To summarize the research progress of hydrogels for the regeneration and repair of degenerative intervertebral disc and to investigate the potential of hydrogels in clinical application.

Methods

The related literature about the role of hydrogels in intervertebral disc degeneration especially for nucleus pulposus was reviewed and analyzed.

Results

Hydrogels share similar properties with nucleus pulposus, and it plays an important role in the regeneration and repair of degenerative intervertebral disc, which can be mainly applied in nucleus pulposus prosthesis, hydrogel-based cell therapy, non-cellular therapy, and tissue engineering repair.

Conclusion

Hydrogels are widely used in the regeneration and repair of intervertebral disc, which provides a potential treatment for intervertebral disc degeneration.

Reactive Oxygen Species-Scavenging Scaffold with Rapamycin for Treatment of Intervertebral Disk Degeneration

The chronic inflammatory microenvironment is characterized by the elevated level of reactive oxygen species (ROS). Here, it is hypothesized that developing an ROS-scavenging scaffold loaded with rapamycin (Rapa@Gel) may offer a new strategy for modulating the local inflammatory microenvironment to improve intervertebral disk tissue regeneration. The therapeutic scaffold consisting of ROS-degradable hydrogel can be injected into the injured degeneration site of intervertebral disk (IVD) and can release therapeutics in a programmed manner. The ROS scavenged by scaffold reduces the inflammatory responses. It is found that when rats are treated with Rapa@Gel, this results in an increase in the percentage of M2-like macrophages and a decrease in M1-like macrophages in the inflammatory environment, respectively. Regeneration of IVD is achieved by Rapa@Gel local treatment, due to the increased M2 macrophages and reduced inflammation. This strategy may be extended to the treatment of many other inflammatory diseases.

An oral drug delivery system with programmed drug release and imaging properties for orthotopic colon cancer therapy

Oral drug delivery systems (ODDSs) have attracted considerable attention in relation to orthotopic colon cancer therapy due to certain popular advantages. Unfortunately, their clinical applications are generally limited by the side-effects caused by systemic drug exposure and poor real-time monitoring capabilities. Inspired by the characteristics of pH changes of the gastrointestinal tract (GIT) and specific enzymes secreted by the colonic microflora, we anchored polyacrylic acid (PAA) and chitosan (CS) on Gd3+-doped mesoporous hydroxyapatite nanoparticles (Gd-MHAp NPs) to realize programmed drug release and magnetic resonance imaging (MRI) at the tumor sites. In particular, the grafted PAA, as a pH-responsive switch, could effect controlled drug release in the colon. Further, CS is functionalized as the enzyme-sensitive moiety, which could be degraded by β-glycosidase in the colon. Gadolinium is a paramagnetic lanthanide element used in chelates, working as a contrast medium agent for an MRI system. Interestingly, after oral administration, CS and PAA could protect the drug-loaded nanoparticles (NPs) against variable physiological conditions in the GIT, allowing the drug to reach the colon tumor sites, preventing premature drug release. Enhanced drug concentrations at the colon tumor sites were achieved via this programmed drug release, which subsequently ameliorated the therapeutic effect. In addition, encapsulating both chemotherapeutic (5-fluorouracil, 5-FU) and targeted therapy drug (gefitinib, Gef) within Gd-MHAp NPs produced a synergistic therapeutic effect. In summary, this study demonstrated that such a novel drug system (Gd-MHAp/5-FU/Gef/CS/PAA NPs) could protect, transport, and program drug release locally within the colonic environment; further, this system exhibited a worthwhile therapeutic effect, providing a promising novel treatment strategy for orthotopic colon cancer.

RIPK1 suppresses apoptosis mediated by TNF and caspase-3 in intervertebral discs

Background

Low back pain has become a serious social and economic burden and the leading cause of disability worldwide. Among a variety of pathophysiological triggers, intervertebral disc (IVD) degeneration plays a primary underlying role in causing such pain. Specifically, multiple independent endplate changes have been implicated in the initiation and progression of IVD degeneration.

Methods

In this study, we built a signaling network comprising both well-characterized IVD pathology-associated proteins as well as some potentially correlated proteins that have been associated with one or more of the currently known pathology-associated proteins. We then screened for the potential IVD degeneration-associated proteins using patients’ normal and degenerative endplate specimens. Short hairpin RNAs for receptor interacting serine/threonine kinase 1 (RIPK1) were constructed to examine the effects of RIPK1 knockdown in primary chondrocyte cells and in animal models of caudal vertebra intervertebral disc degeneration in vivo.

Results

RIPK1 was identified as a potential IVD degeneration-associated protein based on IVD pathology-associated signaling networks and the patients’ degenerated endplate specimens. Construction of the short hairpin RNAs was successful, with short-term RIPK1 knockdown triggering inflammation in the primary chondrocytes, while long-term knockdown triggered apoptosis through cleavage of the caspase 3 pathway, down-regulated NF-κB and mitogen-activating protein kinase (MAPK)s cascades, and decreased cell survival and inflammation. Animal models of caudal vertebra intervertebral disc degeneration further demonstrated that apoptosis was induced by up-regulation of tumor necrosis factor (TNF) accompanied by down-regulation of NF-κB and MAPKs cascades that are dependent on caspase and RIPK1.

Conclusions

These results provide proof-of-concept for developing novel therapies to combat IVD degeneration through interfering with RIPK1-mediated apoptosis signaling pathways especially in patients with RIPK1 abnormality.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1886-3) contains supplementary material, which is available to authorized users.

Therapeutic potential of growth differentiation factors in the treatment of degenerative disc diseases

Intervertebral disc (IVD) degeneration is a major contributing factor to chronic low back pain and disability, leading to imbalance between anabolic and catabolic processes, altered extracellular matrix composition, loss of tissue hydration, inflammation, and impaired mechanical functionality. Current treatments aim to manage symptoms rather than treat underlying pathology. Therefore, IVD degeneration is a target for regenerative medicine strategies. Research has focused on understanding the molecular process of degeneration and the identification of various factors that may have the ability to halt and even reverse the degenerative process. One such family of growth factors, the growth differentiation factor (GDF) family, have shown particular promise for disc regeneration in in vitro and in vivo models of IVD degeneration. This review outlines our current understanding of IVD degeneration, and in this context, aims to discuss recent advancements in the use of GDF family members as anabolic factors for disc regeneration. An increasing body of evidence indicates that GDF family members are central to IVD homeostatic processes and are able to upregulate healthy nucleus pulposus cell marker genes in degenerative cells, induce mesenchymal stem cells to differentiate into nucleus pulposus cells and even act as chemotactic signals mobilizing resident cell populations during disc injury repair. The understanding of GDF signaling and its interplay with inflammatory and catabolic processes may be critical for the future development of effective IVD regeneration therapies.