New horizons in spine research: Intervertebral disc repair and regeneration

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.

Recent Progress in Electrospun Nanofiber-Based Degenerated Intervertebral Disc Repair

Annulus fibrosus fissure and fibrosis of nucleus pulposus are severe morphological characteristics of intervertebral disc degeneration. Currently, surgery or drugs are used to relieve pain in such cases. Tissue engineering is a new multidisciplinary strategy with great potential for use in joint replacement and organ regeneration. Based on the natural anatomy of intervertebral discs, intervertebral disc scaffolds are fabricated by exploiting the special arrangement of extracellular matrix fibers. Electrospun nanofibers possess clear advantages in repairing degenerated intervertebral discs. This article reviews and summarizes recently developed methods for improving and fabricating electrospun nanofiber annulus fibrosus scaffolds in terms of nanofiber alignment, material selection, loading additives, and the progress made in combining other advanced technologies with electrospun nanofibers. In addition, the improvement in mechanical properties and biocompatibility of nucleus pulposus scaffolds by electrospun nanofiber-reinforced hydrogels is discussed. Finally, complete intervertebral disc scaffolds can be fabricated using the disc-like angle-ply structure and other emerging fabrication methods. Taken together, electrospun nanofiber intervertebral disc scaffolds are promising for clinical applications.

The Dual Effect of Abnormal Serum Uric Acid on Intervertebral Disc Degeneration

An abnormal serum uric acid (SUA) level is associated with many diseases. To our knowledge, there is no research on the association between SUA and intervertebral disc degeneration (IDD). The purpose of this study was to determine the relationship between SUA and IDD. From June 2011 to July 2020, 691 patients undergoing surgery for lumbar disc herniation (LDH) were included in the LDH group, and 684 patients who underwent endoscopic surgery for knee trauma were included in the non-LDH group. We examined the baseline characteristics of all these patients and divided the SUA level into 10 groups according to the percentiles in males, females, and the total population. Subsequently, the relationship between the SUA level and IDD was further analyzed. There was no statistically significant difference in the baseline characteristics of the two groups (p > 0.05). Among the 10 groups, the LDH rate was higher at both lower and higher SUA levels. In multiple logistic regression analysis, after adjustment for age, sex, body mass index, smoking, and drinking, when the SUA level was <20% or >80%, compared with 60-80%, the odds ratio (OR) and 95% confidence interval (CI) of LDH of the total population were 1.821 (1.125-2.946) and 1.701 (1.186-2.438), respectively, and in the males, they were 1.922 (1.169-3.161) and 2.800 (1.766, 4.439), respectively. In females, when the SUA was <20%, there was a higher LDH rate (OR = 1.951, 95% CI 1.091-3.486). The present study suggests that there is a U-shaped relationship between SUA and IDD, being particularly prominent among male. Lower and higher SUA level may be risk factors for IDD.

Cell-based strategies for IVD repair: clinical progress and translational obstacles

Intervertebral disc (IVD) degeneration is a major cause of low back pain, a prevalent and chronic condition that has a striking effect on quality of life. Currently, no approved pharmacological interventions or therapies are available that prevent the progressive destruction of the IVD; however, regenerative strategies are emerging that aim to modify the disease. Progress has been made in defining promising new treatments for disc disease, but considerable challenges remain along the entire translational spectrum, from understanding disease mechanism to useful interpretation of clinical trials, which make it difficult to achieve a unified understanding. These challenges include: an incomplete appreciation of the mechanisms of disc degeneration; a lack of standardized approaches in preclinical testing; in the context of cell therapy, a distinct lack of cohesion regarding the cell types being tested, the tissue source, expansion conditions and dose; the absence of guidelines regarding disease classification and patient stratification for clinical trial inclusion; and an incomplete understanding of the mechanisms underpinning therapeutic responses to cell delivery. This Review discusses current approaches to disc regeneration, with a particular focus on cell-based therapeutic strategies, including ongoing challenges, and attempts to provide a framework to interpret current data and guide future investigational studies.

Site-Directed Differentiation of Human Adipose-Derived Mesenchymal Stem Cells to Nucleus Pulposus Cells Using an Injectable Hydroxyl-Functional Diblock Copolymer Worm Gel

Adipose-derived mesenchymal stem cells (ASCs) have been identified for their promising therapeutic potential to regenerate and repopulate the degenerate intervertebral disk (IVD), which is a major cause of lower back pain. The optimal cell delivery system remains elusive but encapsulation of cells within scaffolds is likely to offer a decisive advantage over the delivery of cells in solution by ensuring successful retention within the tissue. Herein, we evaluate the use of a fully synthetic, thermoresponsive poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer worm gel that mimics the structure of hydrophilic glycosaminoglycans. The objective was to use this gel to direct differentiation of human ASCs toward a nucleus pulposus (NP) phenotype, with or without the addition of discogenic growth factors TGFβ or GDF6. Accordingly, human ASCs were incorporated into a cold, free-flowing aqueous dispersion of the diblock copolymer, gelation induced by warming to 37 °C and cell culture was conducted for 14 days with or without such growth factors to assess the expression of characteristic NP markers compared to those produced when using collagen gels. In principle, the shear-thinning nature of the biocompatible worm gel enables encapsulated human ASCs to be injected into the IVD using a 21G needle. Moreover, we find significantly higher gene expression levels of ACAN, SOX-9, KRT8, and KR18 for ASCs encapsulated within worm gels compared to collagen scaffolds, regardless of the growth factors employed. In summary, such wholly synthetic worm gels offer considerable potential as an injectable cell delivery scaffold for the treatment of degenerate disk disease by promoting the transition of ASCs toward an NP-phenotype.

Prognostic factors in the progression of intervertebral disc degeneration: Which patient should be targeted with regenerative therapies?

OBJECTIVE

Possible regenerative treatments for lumbar intervertebral disc degeneration (DD) are rapidly emerging. There is consensus that the patient that would benefit most has early-stage DD, with a predicted deterioration in the near future. To identify this patient, the aim of this study was to identify prognostic factors for progression of DD.

STUDY DESIGN

Systematic review.

METHODS

A systematic search was performed on studies evaluating one or more prognostic factor(s) in the progression of DD. The criteria for inclusion were (a) patients diagnosed with DD on MRI, (b) progression of DD at follow-up, and (c) reporting of one or more prognostic factor(s) in progression of DD. Two authors independently assessed the methodological quality of the included studies. Due to heterogeneity in DD determinants and outcomes, only a best-evidence synthesis could be conducted.

RESULTS

The search generated 3165 references, of which 16 studies met our inclusion criteria, involving 2.423 patients. Within these, a total of 23 clinical and environmental and 12 imaging factors were identified. There was strong evidence that disc herniation at baseline is associated with progression of DD at follow-up. There is limited evidence that IL6 rs1800795 genotype G/C male was associated with no progression of DD. Some clinical or environmental factors such as BMI, occupation and smoking were not associated with progression.

CONCLUSIONS

Disc herniation is strongly associated with the progression of DD. Surprisingly, there was strong evidence that smoking, occupation, and several other factors were not associated with the progression of DD. Only one genetic variant may have a protective effect on progression, otherwise there was conflicting or only limited evidence for most prognostic factors. Future research into these prognostic factors with conflicting and limited evidence is not only needed to determine which patients should be targeted by regenerative therapies, but will also contribute to spinal phenotyping.

Intervertebral Disc Nucleus Repair: Hype or Hope?

Chronic back pain is a common disability, which is often accredited to intervertebral disc degeneration. Gold standard interventions such as spinal fusion, which are mainly designed to mechanically seal the defect, frequently fail to restore the native biomechanics. Moreover, artificial implants have limited success as a repair strategy, as they do not alter the underlying disease and fail to promote tissue integration and subsequent native biomechanics. The reported high rates of spinal fusion and artificial disc implant failure have pushed intervertebral disc degeneration research in recent years towards repair strategies. Intervertebral disc repair utilizing principles of tissue engineering should theoretically be successful, overcoming the inadequacies of artificial implants. For instance, advances in the development of scaffolds aided with cells and growth factors have opened up new possibilities for repair strategies. However, none has reached the stage of clinical trials in humans. In this review, we describe the hitches encountered in the musculoskeletal field and summarize recent advances in designing tissue-engineered constructs for promoting nucleus pulposus repair. Additionally, the review focuses on the effect of biomaterial aided with cells and growth factors on achieving effective functional reparative potency, highlighting the ways to enhance the efficacy of these treatments.

Axial loading during MRI reveals deviant characteristics within posterior IVD regions between low back pain patients and controls

PURPOSE

To investigate differences in functional intervertebral disk (IVD) characteristics between low back pain (LBP) patients and controls using T2-mapping with axial loading during MRI (alMRI).

METHODS

In total, 120 IVDs in 24 LBP patients (mean age 39 years, range 25-69) were examined with T2-mapping without loading of the spine (uMRI) and with alMRI (DynaWell^® loading device) and compared with 60 IVDs in 12 controls (mean age 38 years, range 25-63). The IVD T2-value was acquired after 20-min loading in five regions of interests (ROI), ROI1-5 from anterior to posterior. T2-values were compared between loading states and cohorts with adjustment for Pfirrmann grade.

RESULTS

In LBP patients, mean T2-value of the entire IVD was 64 ms for uMRI and 66 ms for alMRI (p = 0.03) and, in controls, 65 ms and 65 ms (p = 0.5). Load-induced T2-differences (alMRI-uMRI) were seen in all ROIs in both patients (0.001 > p < 0.005) and controls (0.0001 > p < 0.03). In patients, alMRI induced an increase in T2-value for ROI1-3 (23%, 18% and 5%) and a decrease for ROI4 (3%) and ROI5 (24%). More pronounced load-induced decrease was detected in ROI4 in controls (9%/p = 0.03), while a higher absolute T2-value was found for ROI5 during alMRI in patients (38 ms) compared to controls (33 ms) (p = 0.04).

CONCLUSION

The alMRI-induced differences in T2-value in ROI4 and ROI5 between patients and controls most probably indicate biomechanical impairment in the posterior IVD regions. Hence, alMRI combined with T2-mapping offers an objective and clinical feasible tool for biomechanical IVD characterization that may deepen the knowledge regarding how LBP is related to altered IVD matrix composition. These slides can be retrieved under Electronic Supplementary Material.