Characterization of chondroitinase-induced lumbar intervertebral disc degeneration in a sheep model intended for assessing biomaterials

A bovine nucleus pulposus explant culture model

Low back pain is a global health problem that is frequently caused by intervertebral disc degeneration (IVDD). Sulfated glycosaminoglycans (sGAGs) give the healthy nucleus pulposus (NP) a high fixed charge density (FCD), which creates an osmotic pressure that enables the disc to withstand high compressive forces. However, during IVDD sGAG reduction in the NP compromises biomechanical function. The aim of this study was to develop an ex vivo NP explant model with reduced sGAG content and subsequently investigate biomechanical restoration via injection of proteoglycan-containing notochordal cell-derived matrix (NCM). Bovine coccygeal NP explants were cultured in a bioreactor chamber and sGAG loss was induced by chondroitinase ABC (chABC) and cultured for up to 14 days. Afterwards, diurnal loading was studied, and explant restoration was investigated via injection of NCM. Explants were analyzed via histology, biochemistry, and biomechanical testing via stress relaxation tests and height measurements. ChABC injection induced dose-dependent sGAG reduction on Day 3, however, no dosing effects were detected after 7 and 14 days. Diurnal loading reduced sGAG loss after injection of chABC. NCM did not show an instant biomechanical (equilibrium pressure) or biochemical (FCD) restoration, as the injected fixed charges leached into the medium, however, NCM stimulated proliferation and increased Alcian blue staining intensity and matrix organization. NCM has biological repair potential and biomaterial/NCM combinations, which could better entrap NCM within the NP tissue, should be investigated in future studies. Concluding, chABC induced progressive, time-, dose- and loading-dependent sGAG reduction that led to a loss of biomechanical function. Keywords biomechanics | intervertebral disc | matrix degradation | low back pain | proteoglycans.

Comparisons between needle puncture and chondroitinase ABC to induce intervertebral disc degeneration in rabbits

PURPOSE

This study aimed to compare the effect of needle puncture and chondroitinase ABC (ChABC) injection on inducing intervertebral disc (IVD) degeneration (IVDD) in rabbits.

METHODS

Sixteen New Zealand white rabbits were used in this study. Briefly, the rabbits were divided into four groups. In the annulus fibrosis (AF) needle puncture group, a 16-G needle was used to puncture the L5-6 and L6-7 IVDs, while in the sham group, these IVDs were not punctured. In the ChABC group, 30 μL 0.5 Unit/mL ChABC was injected into L5-6 and L6-7 IVDs using a 26-G needle, while in the vehicle group, these IVDs were injected with 30 μL phosphate-buffered saline (PBS). X-ray and MRI scans were performed at the 4th, 12th and 16th weeks postoperatively. Histological, immunohistochemical and biochemical analyses were performed at the 16th week postoperatively.

RESULTS

Both needle puncture and ChABC successfully established IVDD in rabbits at 4th, 12th and 16th weeks, confirmed by X-ray and MRI scan. The progression of IVDD went in a time-dependent manner. The IVDD in the ChABC group was less severe than in the needle puncture group throughout the study. Aggrecan and type II collagen significantly decreased, while tumor necrosis factor-α and superoxide dismutase 2 increased in the needle puncture and ChABC groups, compared with the sham and PBS groups.

CONCLUSIONS

Both AF needle puncture and ChABC injection can successfully induce IVDD in rabbits. Compared with ChABC injection, AF needle puncture can induce more severe IVDD.

In Vitro Studies for Investigating Creep of Intervertebral Discs under Axial Compression: A Review of Testing Environment and Results

Creep responses of intervertebral discs (IVDs) are essential for spinal biomechanics clarification. Yet, there still lacks a well-recognized investigation protocol for this phenomenon. Current work aims at providing researchers with an overview of the in vitro creep tests reported by previous studies, specifically specimen species, testing environment, loading regimes and major results, based on which a preliminary consensus that may guide future creep studies is proposed. Specimens used in creep studies can be simplified as a “bone–disc–bone” structure where three mathematical models can be adopted for describing IVDs’ responses. The preload of 10–50 N for 30 min or three cycles followed by 4 h-creep under constant compression is recommended for ex vivo simulation of physiological condition of long-time sitting or lying. It is worth noticing that species of specimens, environment temperature and humidity all have influences on biomechanical behaviors, and thus are summarized and compared through the literature review. All factors should be carefully set according to a guideline before tests are conducted to urge comparable results across studies. To this end, this review also provides a guideline, as mentioned before, and specific steps that might facilitate the community of biomechanics to obtain more repeatable and comparable results from both natural specimens and novel biomaterials.

Intervertebral Disc Degeneration Models for Pathophysiology and Regenerative Therapy -Benefits and Limitations

Aim:This review summarized the recent intervertebral disc degeneration (IDD) models and described their advantages and potential disadvantages, aiming to provide an overview for the current condition of IDD model establishment and new ideas for new strategies development of the treatment and prevention of IDD.Methods:The database of PubMed was searched up to May 2021 with the following search terms: nucleus pulposus, annulus fibrosus, cartilage endplate, intervertebral disc(IVD), intervertebral disc degeneration, animal model, organ culture, bioreactor, inflammatory reaction, mechanical stress, pathophysiology, epidemiology. Any IDD model-related articles were collected and summarized.Results:The best IDD model should have the features of repeatability, measurability and controllability. There are a lot of aspects to be considered in the selection of animals. Mice, rats and rabbits are low-cost and easy to access. However, their IVD size and shape are more different from human anatomy than pigs, cattle, sheep and goats. Organ culture models and animal models are two options in model establishment for IDD. The IVD organ culture model can put the studying variables into the controllable system for transitional research. Unlike the animal model, the organ culture model can only be used to evaluate the short-term effects and it is not applicable in simulating the complex process of IDD. Similarly, the animal models induced by different methods also have their advantages and disadvantages. For studying the mechanism of IDD and the corresponding treatment and prevention strategies, the selection of model should be individualized based on the purpose of each study.Conclusions:Various models have different characteristics and scope of application due to their different rationales and methods of construction. Currently, there is no experimental model that can perfectly mimic the degenerative process of human IVD. Personalized selection of appropriate model based on study purpose and experimental designing can enhance the possibility to obtain reliable and real results.

A comprehensive tool box for large animal studies of intervertebral disc degeneration

Preclinical studies involving large animal models aim to recapitulate the clinical situation as much as possible and bridge the gap from benchtop to bedside. To date, studies investigating intervertebral disc (IVD) degeneration and regeneration in large animal models have utilized a wide spectrum of methodologies for outcome evaluation. This paper aims to consolidate available knowledge, expertise, and experience in large animal preclinical models of IVD degeneration to create a comprehensive tool box of anatomical and functional outcomes. Herein, we present a Large Animal IVD Scoring Algorithm based on three scales: macroscopic (gross morphology, imaging, and biomechanics), microscopic (histological, biochemical, and biomolecular analyses), and clinical (neurologic state, mobility, and pain). The proposed algorithm encompasses a stepwise evaluation on all three scales, including spinal pain assessment, and relevant structural and functional components of IVD health and disease. This comprehensive tool box was designed for four commonly used preclinical large animal models (dog, pig, goat, and sheep) in order to facilitate standardization and applicability. Furthermore, it is intended to facilitate comparison across studies while discerning relevant differences between species within the context of outcomes with the goal to enhance veterinary clinical relevance as well. Current major challenges in pre-clinical large animal models for IVD regeneration are highlighted and insights into future directions that may improve the understanding of the underlying pathologies are discussed. As such, the IVD research community can deepen its exploration of the molecular, cellular, structural, and biomechanical changes that occur with IVD degeneration and regeneration, paving the path for clinically relevant therapeutic strategies.

Open-source image analysis software yields reproducible MRI measures of lumbar intervertebral disc degeneration in sheep models

Sheep are established models for intervertebral disc degeneration (IVDD) translational research. Objectives of this retrospective, secondary analysis, observational study were to evaluate reproducibility of two magnetic resonance imaging (MRI) measures of IVDD in sheep using open-source image analysis software. Sagittal planar, T2-weighted, lumbar MRI scans from a previous, prospective study were evaluated (4 sheep @ 3 treatment periods/sheep @ 7 lumbar discs /treatment period = 84 discs). A standardized protocol was developed for measuring MRI index (nucleus pulposus signal intensity × nucleus pulposus sagittal area), and nucleus pulposus signal intensity standard deviation (NPSISD). Scans were randomized and four observers with varying experience levels applied the protocol to independently perform triplicate measures. Mean coefficient of variation values for both the MRI index and NPSISD were within an acceptable range (< 10). Mean values for the three readers with at least 2 months of image analysis experience did not differ (P > .05).