Variations of the proteoglycans of the canine intervertebral disc with ageing

CT-Scan Based Evaluation of Dorsal-to-Ventral Ratios of Paraspinal Musculature in Chondrodystrophic and Non-chondrodystrophic Dogs

Objective: To assess and objectively quantify, with CT-scan exams, differences in cervical paraspinal musculature and vertebrae angulation that might influence the different predisposed sites for intervertebral disk disease observed in chondrodystrophic and non-chondrodystrophic breeds.

Sample: Retrospective evaluation and analysis of cervical spine CT-scans performed on 30 dogs presented for clinical reasons unrelated to a cervical disk problem. 15 chondrodystrophic (Dachshunds) and 15 non-chondrodystrophic dogs (Labrador Retrievers) were included.

Procedures: Height measurements of dorsal and ventral paraspinal musculature were performed on sagittal CT-scan reconstructions to generate dorsal-to-ventral height ratios. Additionally, disk angulation to the floor of the vertebral canal was determined for each cervical disk. On transverse plane images the areas of the dorsal and the ventral paraspinal musculature were measured and ratios calculated. Furthermore, estimations of moments exerted on the disk were evaluated through calculation of a dorsal-to-ventral ratio of moments applied at the level of each disk.

Results: Dachshunds showed a relatively more prominent dorsal paraspinal musculature than Labrador Retrievers with statistically significant higher dorsal-to-ventral height ratios at C3/C4, C4/C5, C7/T1 (p = 0.034^*, p = 0,004^**, p = 0.004^**) and a dorsal-to-ventral area ratio at C3/C4 (p < 0.001^**). Regarding the disk angle to the spinal canal floor along the cervical spine, Labrador Retrievers had a less steep conformation compared to Dachshunds with a significant difference at C2/C3 (p < 0.001^**). Relation of moments calculations revealed statistically significant differences at C2/C3 (p = 0.021^*).

Conclusion and Clinical Relevance: Significant differences have been found in the cervical spine of chondrodystrophic and non-chondrodystrophic dogs, regarding paraspinal musculature height and area ratios along with ratio of moments and vertebrae angulation. These differences may affect the anatomical and biomechanical dorsal-to-ventral paraspinal muscle relationship and potentially influence the load on intervertebral disks, especially in the upper cervical spine. Our findings could play a role in understanding the development of intervertebral disk disease.

Molecular mechanisms of biological aging in intervertebral discs

Advanced age is the greatest risk factor for the majority of human ailments, including spine-related chronic disability and back pain, which stem from age-associated intervertebral disc degeneration (IDD). Given the rapid global rise in the aging population, understanding the biology of intervertebral disc aging in order to develop effective therapeutic interventions to combat the adverse effects of aging on disc health is now imperative. Fortunately, recent advances in aging research have begun to shed light on the basic biological process of aging. Here we review some of these insights and organize the complex process of disc aging into three different phases to guide research efforts to understand the biology of disc aging. The objective of this review is to provide an overview of the current knowledge and the recent progress made to elucidate specific molecular mechanisms underlying disc aging. In particular, studies over the last few years have uncovered cellular senescence and genomic instability as important drivers of disc aging. Supporting evidence comes from DNA repair-deficient animal models that show increased disc cellular senescence and accelerated disc aging. Additionally, stress-induced senescent cells have now been well documented to secrete catabolic factors, which can negatively impact the physiology of neighboring cells and ECM. These along with other molecular drivers of aging are reviewed in depth to shed crucial insights into the underlying mechanisms of age-related disc degeneration. We also highlight molecular targets for novel therapies and emerging candidate therapeutics that may mitigate age-associated IDD. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1289-1306, 2016.

Longitudinal Comparison of Enzyme- and Laser-Treated Intervertebral Disc by MRI, X-Ray, and Histological Analyses Reveals Discrepancies in the Progression of Disc Degeneration: A Rabbit Study

Regenerative medicine is considered an attractive prospect for the treatment of intervertebral disc (IVD) degeneration. To assess the efficacy of the regenerative approach, animal models of IVD degeneration are needed. Among these animal models, chemonucleolysis based on the enzymatic degradation of the Nucleus Pulposus (NP) is often used, but this technique remains far from the natural physiopathological process of IVD degeneration. Recently, we developed an innovative animal model of IVD degeneration based on the use of a laser beam. In the present study, this laser model was compared with the chemonucleolysis model in a longitudinal study in rabbits. The effects of the treatments were studied by MRI (T2-weighted signal intensity (T2wsi)), radiography (IVD height index), and histology (NP area and Boos' scoring). The results showed that both treatments induced a degeneration of the IVD with a decrease in IVD height and T2wsi as well as NP area and an increase in Boos' scoring. The enzyme treatment leads to a rapid and acute process of IVD degeneration. Conversely, laser radiation induced more progressive and less pronounced degeneration. It can be concluded that laser treatment provides an instrumental in vivo model of slowly evolving IVD degenerative disease that can be of preclinical relevance for assessing new prophylactic biological treatments of disc degeneration.

Mechanical properties of the extra-fibrillar matrix of human annulus fibrosus are location and age dependent

The mechanical behavior of the annulus fibrosus (AF) of the intervertebral disc can be modeled as a mixture of fibers, extra-fibrillar matrix (EFM), ions, and fluid. However, the properties of the EFM have not been measured directly. We measured mechanical properties of the human EFM at several locations, determined the effect of age and degeneration, and evaluated whether changes in EFM properties correspond to AF compositional changes. EFM mechanical properties were measured using a method that combines osmotic loading and confined compression. AF samples were dissected from several locations, and mechanical properties were correlated with age, degeneration, and composition. EFM modulus was found to range between 10 and 50 kPa, increasing nonlinearly with compression magnitude and being highest in the AF outer-anterior region. EFM properties were not correlated with composition or degeneration. However, the EFM modulus, its relative contribution to tissue modulus, and model parameters were correlated with age. These measurements will result in more accurate predictions of deformations in the intervertebral disc. Additionally, parameters such as permeability and diffusivity used for biotransport analysis of glucose and other solutes depend on EFM deformation. Consequently, the accuracy of biotransport simulations will be greatly improved.

Intervertebral disc degeneration in the dog. Part 1: Anatomy and physiology of the intervertebral disc and characteristics of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is common in dogs and can give rise to a number of diseases, such as IVD herniation, cervical spondylomyelopathy, and degenerative lumbosacral stenosis. Although there have been many reports and reviews on the clinical aspects of canine IVD disease, few reports have discussed and reviewed the process of IVD degeneration. In this first part of a two-part review, the anatomy, physiology, histopathology, and biochemical and biomechanical characteristics of the healthy and degenerated IVD are described. In Part 2, the aspects of IVD degeneration in chondrodystrophic and non-chondrodystrophic dog breeds are discussed in depth.

Emerging technologies for molecular therapy for intervertebral disk degeneration

Intervertebral disks are biologically regulated by the maintenance of a balance between the anabolic and catabolic activities of disk cells. Therapeutic agents, initially evaluated using in vitro studies on disk cells and explants, have been used as intradiscal injections in preclinical settings to test in vivo efficacy. These include anabolic growth factors, other biostimulatory agents, and antagonistic agents against matrix-degrading enzymes and cytokines. Additional work is needed to identify patient populations, using methods such as MRI, and to better understand the mechanism of healing. Clinical trials are underway for a few of these agents and other promising candidates are on the horizon.

Abundance of calpain and aggrecan-cleavage products of calpain in degenerated human intervertebral discs

OBJECTIVE

To assess the expression of calpains and calpain-induced aggrecan fragmentation in early and advanced stages of degeneration of human intervertebral discs (IVDs).

DESIGN

Disc tissue samples of 55 patients (mean age, 51.2 ± 22.3 years) who underwent intervertebral fusion were divided into groups with early and advanced degeneration based on the Thompson magnetic resonance imaging (MRI) scale. In advanced degeneration group, five patients (mean age, 35.5 ± 11.4 years) of lumbar disc herniation (LDH) were included. Protein levels of m- and μ-calpains and their inhibitor calpastatin were assayed, and immunohistochemical techniques were used to localize and quantify the production of the enzymes. To investigate calpain activity, we assayed purified aggrecan fragmentation in disc tissue by Western blotting and immunohistochemistry with VPGVA antibody, which recognizes the m-calpain generated neo-epitope GVA.

RESULTS

Discs at early stages of degeneration expressed low levels of m- and μ-calpains and calpastatin, and few cells expressed degenerative enzymes. At more advanced stages of degeneration, the expression and number of cells immunopositive for m-calpain, μ-calpain and calpastatin were significantly higher. Further finding showed that anti-GVA-reactive aggrecan fragments were significantly higher in discs at advanced compared with early stages of degeneration. Herniated disc samples showed stronger expression and more cells immunopositive for calpains, calpastatin and GVA in the nucleus pulposus than in the annulus fibrous.

CONCLUSIONS

The expression of calpains, together with m-calpain-induced degradation products of extracellular matrix, was correlated with the degree of disc degeneration in human IVD tissue. These findings suggest that calpains may be involved in IVD degeneration via proteoglycan (PG) cleavage.

Cellular mechanobiology of the intervertebral disc: new directions and approaches

The more we learn about the intervertebral disc (IVD), the more we come to appreciate the intricacies involved in transmission of forces through the ECM to the cell, and in the biological determinants of its response to mechanical stress. This review highlights recent developments in our knowledge of IVD physiology and examines their impact on cellular mechanobiology. Discussion centers around the continually evolving cellular and microstructural anatomy of the nucleus pulposus (NP) and the annulus fibrosus (AF) in response to complex stresses generated in support of axial load and spinal motion. Particular attention has been given to cells from the immature NP and the interlamellar AF, and assessment of their potential mechanobiologic contributions to the health and function of the IVD. In addition, several innovative approaches that have been brought to bear on studying the interplay between disc cells and their micromechanical environment are discussed. Techniques for "engineering" cellular function and technologies for fabricating more structurally defined biomaterial scaffolds have recently been employed in disc research. Such tools can be used to elucidate the biological and physical mechanisms by which different IVD cell populations are regulated by mechanical stress, and contribute to advancement of preventative and therapeutic measures.

Expression of proteinase-activated receptor-2 in the intervertebral disc

STUDY DESIGN

Immunohistochemical and biochemical analyses of proteinase-activated receptor-2 (PAR-2) in rat and human intervertebral discs (IVDs).

OBJECTIVES

To examine the expression and function of PAR-2 in rat IVD cells, and to determine if PAR-2 is expressed in human IVDs.

SUMMARY OF BACKGROUND DATA

PAR-2 is a G protein-coupled receptor that contributes to the regulation of inflammatory reactions and the pathophysiology of inflammatory diseases, including arthritis. The expression of PAR-2 in the IVD has not been determined.

METHODS

PAR-2 expression by rat IVD cells and tissues was examined using immunohistochemistry and western blot. Rat anulus fibrosus cells in monolayer culture were used to examine the biologic role of PAR-2 in vitro. The effect of PAR-2-activating peptide (PAR-2AP) on the catabolic cascade was assessed by western blot and real-time PCR. The expression of PAR-2 by human IVD tissues at different stages of degeneration was determined by immunohistochemical analyses.

RESULTS

PAR-2 was expressed by rat IVD cells and in both anulus fibrosus and nucleus pulposus tissues, PAR-2 expression was up-regulated by interleukin-1beta (IL-1beta). PAR-2AP significantly increased the release of IL-1beta into the medium. Although PAR-2AP had no direct effect on matrix metalloproteinase-3 (MMP-3) and MMP-13 mRNA levels, treatment with PAR-2AP significantly up-regulated the mRNA levels of a disintegrin and metalloproteinase with thrombospondin motif-4. The simultaneous administration of PAR-2AP and IL-1beta synergistically up-regulated the mRNA levels of a disintegrin and metalloproteinase with thrombospondin motif-4, MMP-3, and MMP-13. The expression of PAR-2 was identified in human IVD tissues. The number of PAR-2-expressing cells was significantly elevated in advanced stages of IVD degeneration compared with those in early stages of degeneration.

CONCLUSION

Our results demonstrate for the first time that IVD cells express PAR-2. The expression of PAR-2 is regulated by IL-1beta stimulation. PAR-2 activation accelerates the expression of matrix-degrading enzymes. PAR-2 may play an important role in the cytokine-mediated catabolic cascade and consequently may be involved in IVD degeneration.

Aggrecanases and aggrecanase-generated fragments in the human intervertebral disc at early and advanced stages of disc degeneration

STUDY DESIGN

A comparative study of aggrecanases and aggrecan fragmentation profile in the human intervertebral disc at early and advanced stages of disc degeneration.

OBJECTIVE

To determine differences in the content of the aggrecanases and the profile of aggrecan fragmentation in early and advanced stages of disc degeneration using cadaveric human intervertebral discs.

SUMMARY OF BACKGROUND DATA

Aggrecanases and aggrecanase-generated aggrecan fragments have been found in human degenerated discs. However, the association between the grade of disc degeneration and the content of the aggrecanases and the profile of aggrecan fragments has not been well studied.

METHODS

A total of 108 cadaveric donor spines were assessed by MRI T2 imaging and graded based on the Thompson scale. Twelve donor spines (average age, 63 years), each specifically exhibiting 2 different stages (Grade 2 and Grade 4) of disc degeneration at different disc levels, were included in this study. After harvesting the preselected discs, tissue samples were obtained from the center of the nucleus pulposus (NP) and the middle zone of the anulus fibrosus (AF). The amount of the aggrecanases, specifically ADAMTS-4 and ADAMTS-5, and the pattern of aggrecan fragmentation in the isolated tissues were assessed by western blot using specific antibodies.

RESULTS

In both NP and the AF tissues, the amount of ADAMTS-4 detected was higher in disc tissues with a higher level of degeneration (Grade 4) than in Grade 2 disc tissues with a lower level of degeneration. However, the amount of ADAMTS-5 detected did not differ between the 2 disc tissue grades. The aggrecan fragmentation analysis of these samples demonstrated the presence of aggrecanase-mediated fragmentation in both groups; however, there was no apparent difference in the aggrecan fragmentation profile between discs at early and advanced stages of disc degeneration.

CONCLUSION

Aggrecanases are involved in aggrecanolysis at both the early and advanced stages of disc degeneration. The aggrecan fragmentation profile analysis demonstrates the involvement of aggrecanases, as well as that of matrix metalloproteinases and/or cathepsins, during disc degeneration.

Are animal models useful for studying human disc disorders/degeneration?

Intervertebral disc (IVD) degeneration is an often investigated pathophysiological condition because of its implication in causing low back pain. As human material for such studies is difficult to obtain because of ethical and government regulatory restriction, animal tissue, organs and in vivo models have often been used for this purpose. However, there are many differences in cell population, tissue composition, disc and spine anatomy, development, physiology and mechanical properties, between animal species and human. Both naturally occurring and induced degenerative changes may differ significantly from those seen in humans. This paper reviews the many animal models developed for the study of IVD degeneration aetiopathogenesis and treatments thereof. In particular, the limitations and relevance of these models to the human condition are examined, and some general consensus guidelines are presented. Although animal models are invaluable to increase our understanding of disc biology, because of the differences between species, care must be taken when used to study human disc degeneration and much more effort is needed to facilitate research on human disc material.

Notochord cells regulate intervertebral disc chondrocyte proteoglycan production and cell proliferation

STUDY DESIGN

Non-chondrodystrophic dog notochord cell conditioned medium was used to evaluate chondrocyte proteoglycan production and cell proliferation.

OBJECTIVES

To evaluate the responsiveness of bovine disc-derived chondrocytes to notochord-cell conditioned medium with respect to proteoglycan and cell proliferation. In addition, to examine phenotypic changes of notochord cells cultured in monolayered as compared to 3-dimensional culture.

SUMMARY OF BACKGROUND DATA

Non-chondrodystrophic dogs maintain their intervertebral disc notochord cells into adulthood and are protected from having degenerative disc disease develop. The chondrodystrophic breeds such as beagles do not preserve these cells and have disc disease develop much earlier in life. The role of the notochord cell within the disc nucleus is poorly understood.

METHODS

Canine notochord cells were cultured within alginate beads in serum-deficient conditions using Dulbecco modified Eagle medium to produce notochord cell conditioned medium (NCCM). NCCM was used to stimulate bovine disc chondrocytes from which we evaluated proteoglycan production and cell proliferation as compared to chondrocytes grown in DMEM alone. In addition, parallel cultures of notochord cells were seeded within alginate beads as well as in monolayer and cultured in order to examine for differences in phenotype between the 2 culture conditions.

RESULTS

The morphologic aspects of the intervertebral disc between the species differed markedly. A dose- dependent relationship was seen between proteoglycan production and NCCM concentration across various concentrations of NCCM in repeated experiments. Although there was a 4-fold increase in cell proliferation under all NCCM concentrations, this increase in cell proliferation was not dose dependent in the concentrations tested. Unlike chondrocytes, notochord cells do not adhere to tissue culture plate (monolayer) until at least day 4-6, do not markedly alter their phenotype, and rapidly assume masses of cells while floating within tissue culture medium.

CONCLUSIONS

The biology of the disc-derived chondrocyte is profoundly affected by NCCM in that various concentrations of NCCM activate proteoglycan production in a dose-dependent fashion. However, in the doses tested in our study, cell proliferation was increased but in a nondose-dependent fashion. Notochord cells retain their phenotype even in monolayer and through the development of floating intimately associated masses of cells suggest the development and maintenance of cell-cell interaction. These masses of cells are retained even after 6 days in culture when they do attach to the tissue plate surface. The persistence of notochord cells in non-chondrodystrophic dog species suggests that these in vitro studies may mirror the milieu of the disc in vivo, in which the notochord cell may play a key role in disc homeostasis.

Osteogenic protein-1 injection into a degenerated disc induces the restoration of disc height and structural changes in the rabbit anular puncture model

STUDY DESIGN

In vivo study of the effect of injection of osteogenic protein-1 (OP-1) on a rabbit anular needle puncture model of intervertebral disc (IVD) degeneration.

OBJECTIVE

To study radiographic, magnetic resonance imaging (MRI), biochemical, and histologic changes in the rabbit IVD after injection of OP-1 into the nucleus pulposus in a needle puncture disc degeneration model.

SUMMARY OF THE BACKGROUND DATA

Growth factors, such as OP-1, have the ability to stimulate synthesis of proteoglycans and collagen in vitro. The in vivo injection of OP-1 into the normal rabbit IVD has increased disc height and proteoglycan content in the anulus fibrosus and nucleus pulposus. However, to our knowledge, no attempts have yet been made to determine the effects of these growth factors in an in vivo model of disc degeneration.

METHODS

New Zealand adolescent white rabbits (n = 90, 8 for baseline evaluation, 82 at 8 times) received an anular puncture in 2 noncontiguous discs with an 18-gauge needle to induce disc degeneration. Four weeks later, either 5% lactose (10 microL) or OP-1 (100 microg in 10 microL 5% lactose) was injected into the center of the nucleus pulposus. The disc height was followed radiographically for up to 24 weeks after the injections. At the 2, 4, 8, 12, and 24-week times after the injection, rabbits were euthanized, and MRI of the harvested spinal columns was obtained to grade the degeneration. The discs injected with OP-1 or lactose and noninjected discs were subjected to biochemical and histologic analysis. The specimens at the 24-week time were limited to histologic evaluation.

RESULTS

The anular puncture with a needle induced a consistent disc narrowing within 4 weeks. The injection of OP-1 induced a restoration of disc height at 6 weeks, which was sustained for the entire experimental period, up to 24 weeks after the injection. The injection of lactose alone did not change the course of disc narrowing over the same time. MRI grading score showed significant differences between the OP-1 and lactose groups at the 8, 12, and 24-week times, suggesting an increase in water content in the nucleus pulposus of the OP-1 group. The proteoglycan content of the nucleus pulposus and anulus fibrosus was significantly higher in the OP-1 group than in the control group. The degeneration grades of the punctured discs in the OP-1 group were significantly lower than those in the lactose group.

CONCLUSION

The results of this study show the feasibility of restoring degenerative rabbit discs by a single injection of OP-1 into the nucleus pulposus. Importantly, the effects of the OP-1 injection on disc height were sustained for up to 24 weeks. The metabolic changes in the cells, following a single injection, might be sustained and, thus, induce long-term changes in disc structure. An efficacy study in large animals is required to show further that the intradiscal injection of OP-1, or bone morphogenetic proteins or growth factors with similar properties would be useful for the structural restoration of the IVD in humans.

Relevance of in vitro and in vivo models for intervertebral disc degeneration

Models available for the study of intervertebral disc degeneration are designed to answer many important questions. In vitro biologic models employ a variety of cell, tissue, or organ culture techniques with culture conditions that partially mimic the cellular environment of the degenerated human intervertebral disc. In vitro biomechanical models include intervertebral disc or motion-segment loading experiments as well as finite element modeling techniques. The literature describes numerous in vivo animal models for use in the study of intervertebral disc degeneration, each of which has its own advantages and disadvantages. Human-subject studies have included the use of magnetic resonance imaging and other techniques to assess diffusion into the intervertebral disc, to measure intradiscal pressure, to conduct kinematic or stiffness studies of lumbar motion segments, and to evaluate muscular forces on the spine. Although all of these studies are helpful in answering specific questions, their relevance in assessing disc degeneration in patients with symptoms of discogenic pain must be carefully considered.

Animal models for human disc degeneration

Despite the significant impairment associated with degenerative disc disease, a clear understanding of its pathogenesis is still lacking. Currently, no particular model parallels the complex nature of human disc degeneration. Naturally occurring animal models have the drawback that the basis for the high rate of disc degeneration is not known. Although the interventions in artificial animal models that create disc degeneration are known, the relationship of those to the events leading to disc degeneration in humans is not. With the recent progress in biomechanics, cell biology and molecular biology, an easily reproducible and valid animal model may help unlock the complex cascade of events surrounding human disc degeneration.

Low-dose interleukin-1 partially counteracts osteogenic protein-1-induced proteoglycan synthesis by adult bovine intervertebral disk cells

OBJECTIVE

Low back pain associated with degenerative disk disease is a common clinical problem that has enormous socioeconomic impact in today's aging population. As an alternative to the surgical removal of the diseased intervertebral disk, the direct application of a purified growth factor into the intervertebral disk may provide physiatrists a valuable tool to halt or slow down disk degeneration. Our goal here is to determine if low levels of interleukin-1 (IL-1), a proinflammatory cytokine present in the degenerating disk, could interfere with the potentially beneficial effects of growth factors on proteoglycan synthesis. New knowledge gained from this study will prove useful in the development of new treatment modalities that take advantage of the stimulatory effects of growth factors such as osteogenic protein-1 (OP-1).

DESIGN

This was an in vitro study of proteoglycan accumulation and synthesis by cells from the nucleus pulposus, inner annulus fibrosus, and outer annulus fibrosus in the bovine intervertebral disk.

RESULTS

In cells cultured with serum and no additional exogenous growth factor, treatment with low-dose IL-1 does not result in a significant decrease in proteoglycan synthesis. However, in the case of cells stimulated with OP-1, treatment with IL-1 resulted in a statistically significant decrease in sulfur-35-proteoglycan synthesis by cells derived from all three zones of the bovine intervertebral disk (nucleus pulposus, 60.3% [P < 0.0001]; inner annulus fibrosus, 18.4% [P = 0.0330]; outer annulus fibrosus, 12.3% [P = 0.0255]). Proteoglycan accumulation over the 12-day culture period also decreased significantly (nucleus pulposus, 26.8% [P < 0.0001]; inner annulus fibrosus, 15.8% [P = 0.0276]; outer annulus fibrosus, 16.8% [P = 0.0102]). It is worth noting that cells cultured in the presence of both OP-1 and IL-1 synthesized proteoglycan at a faster rate than cells cultured in the presence of IL-1 alone (nucleus pulposus, 58.5% [P < 0.0001]; inner annulus fibrosus, 39.7% [P = 0.0055]; outer annulus fibrosus, 45.1% [P = 0.0164]). Likewise, cells treated with OP-1 and IL-1 accumulated more proteoglycan in their newly formed matrix than cells cultured in the presence of IL-1 alone (nucleus pulposus, 65.3% [P < 0.0001]; inner annulus fibrosus, 60.5% [P = 0.0034]; outer annulus fibrosus, 19.4% (P = 0.0840]).

CONCLUSIONS

Intervertebral disk cells that are stimulated by the growth factor OP-1, to increase the rate at which they produce a proteoglycan-rich matrix become more susceptible to the inhibitory effects of the proinflammatory cytokine IL-1 on the rate of proteoglycan synthesis and accumulation in the matrix over time. This notwithstanding, IL-1 at the low dose used did not totally obliterate the stimulatory effects of OP-1 on matrix formation. Consequently, this growth factor may remain partially effective in stimulating disk repair in vivo even when proinflammatory cytokines such as IL-1 are present.

Osteogenic protein-1 is most effective in stimulating nucleus pulposus and annulus fibrosus cells to repair their matrix after chondroitinase ABC-induced in vitro chemonucleolysis

BACKGROUND CONTEXT

Chondroitinase ABC (C-ABC) is used in chemonucleolysis to degrade, with great specificity, the chondroitin sulfate and dermatan sulfate chains of proteoglycans (PGs). A recent study showed that osteogenic protein-1 (OP-1) is very effective in stimulating the production and formation of the extracellular matrix by rabbit intervertebral disc cells.

PURPOSE

To test the hypothesis that the repair of the extracellular matrix of the intervertebral disc after chemonucleolysis by C-ABC can be stimulated by exposure to a low dose of a growth factor, OP-1.

STUDY DESIGN

An alginate bead cell culture system was used to monitor the effects of OP-1 on the repair of damaged matrices after in vitro chemonucleolysis with C-ABC.

METHODS

Rabbit nucleus pulposus (NP) or annulus fibrosus (AF) cells cultured for 2 weeks in alginate gel were briefly exposed to low concentrations of C-ABC and then cultured in the presence or absence of OP-1. The control group was cultured without enzyme treatment for the same period in the absence of OP-1. At each time point, the contents of DNA and proteoglycan accumulation and proteoglycan synthesis were measured.

RESULTS

NP or AF cells cultured in alginate beads, which were digested with C-ABC and then treated with OP-1, recover PG content more rapidly than those cultured in the absence of OP-1. The major contributor to the superior matrix repair in the cells treated with OP-1 was an up-regulation of proteoglycan synthesis.

CONCLUSIONS

OP-1 was effective in stimulating matrix repair by NP and AF cells after their matrices were nearly totally depleted of sulfated glycosaminoglycans. The use of OP-1 after chemonucleolysis might help the disc to regain biomechanical strength, weakened by enzyme digestion, by stimulating matrix metabolism.

Intradiscal administration of osteogenic protein-1 increases intervertebral disc height and proteoglycan content in the nucleus pulposus in normal adolescent rabbits

STUDY DESIGN

A study of the disc height and biochemical changes in the rabbit intervertebral disc after injection of osteogenic protein-1 into the nucleus pulposus.

OBJECTIVES

To evaluate the in vivo effects of osteogenic protein-1 administered intradiscally to the intervertebral disc of rabbits.

SUMMARY OF BACKGROUND DATA

Growth factors, such as osteogenic protein-1 and transforming growth factor-beta, have the ability to stimulate synthesis of proteoglycan and collagen in vitro. No attempts have yet been made to determine the effects of these growth factors in an in vivo model.

METHODS

Twenty-four New Zealand adolescent white rabbits were divided evenly into two subject groups. In one group, three consecutive intervertebral discs were injected with saline; whereas in the other group, they were injected with osteogenic protein-1 in saline. At 2, 4, and 8 weeks after the injection, the intervertebral disc heights of the injected specimens were measured by lateral plain radiographs and compared with preinjection measurements. The change in disc height was expressed as the percent disc height index compared with the preinjection value. After the radiographic measurements were obtained, the intervertebral discs were removed and analyzed for DNA, proteoglycan, and collagen contents.

RESULTS

At 2 weeks after the injections, the mean disc height index of the osteogenic protein-1-injected discs was 15% greater than that of the saline group. The increase in disc height with osteogenic protein-1 injection was still statistically significant at the 4- and 8-week time points. The proteoglycan content of the nucleus pulposus in discs injected with osteogenic protein-1 was higher than that in the saline group at the 2-week time point. The osteogenic protein-1-induced effect on the proteoglycan content was also present at the 4- and 8- week time intervals; however, these increases were not statistically significant. There were no significant differences in the DNA content, normalized to noninjected control, of the nucleus pulposus between the saline and osteogenic protein-1 groups. However, a significant increase in the DNA content of the anulus fibrosus in the osteogenic protein-1 group, compared with that of the anulus fibrosus in the saline group, was observed after 4 weeks.

CONCLUSION

To date, no study has demonstrated the potential in vivo effects of growth factors on the intervertebral disc. The present study reports that the intradiscal administration of osteogenic protein-1 in vivo results in an increased disc height present at 2, 4, and 8 weeks and an increase in PG content of the nucleus pulposus at the 2-week time point. Therefore, osteogenic protein-1 may act to stimulate metabolic activity in the nucleus pulposus. Continued research is needed to evaluate the potential of growth factor-induced reversal of age-related disc degeneration in an appropriate animal model. In addition, studies in a nonhuman primate animal model will be essential before considering intradiscal injection of growth factors in humans.

Value and limitations of using the bovine tail as a model for the human lumbar spine

STUDY DESIGN

The contents of DNA, proteoglycan, type II collagen, and denatured type II collagen in the bovine coccygeal intervertebral discs were examined in situ in relation to disc level, age, and tissue region.

OBJECTIVE

To determine whether bovine coccygeal discs are a suitable model to study human lumbar discs.

SUMMARY OF BACKGROUND DATA

Bovine coccygeal discs have been suggested as a suitable alternative model because they are readily available, in contrast to human discs, and represent a common source of tissue in the disc field. However, it is not known whether the changes in matrix contents in bovine coccygeal discs are similar to those found in the human lumbar spine.

METHODS

Intervertebral discs from bovine tails were dissected into the nucleus pulposus (NP) and anulus fibrosus (AF). Tissues were weighed and analyzed for matrix contents using specific assays.

RESULTS

Similar to water content, the proteoglycan content was higher in the NP than in the AF. Water content of the bovine NP did not change with age, unlike the proteoglycan content, which decreased. type II collagen content was higher in the NP than in the AF, and both did not change overall significantly with age. The percent of denatured type II collagen decreased with age only in the NP. The DNA content did not vary with age in the AF and in the NP.

CONCLUSION

Differences in matrix contents exist between the bovine coccygeal discs and the human lumbar spine. Thus, caution must be exercised when using the bovine tail as a model for the human lumbar spine in biochemical studies.

Growth factors and treatment of intervertebral disc degeneration

STUDY DESIGN

Literature review.

OBJECTIVE

To review the most recent findings of the effects of growth factors on the intervertebral disc and, further, to discuss trends in the biologic repair of the degenerated intervertebral disc.

SUMMARY OF BACKGROUND DATA

Since early in 1990, advancements in molecular biology and cell culture technology have enabled researchers to accumulate knowledge about the in vitro actions of growth factors on intervertebral disc cells. More recently, the use of growth factors for the biologic regeneration of the intervertebral disc is of increasing interest to the orthopedic field, and indeed, some preliminary in vivo studies have proven their efficacy.

METHODS

Based on a literature search conducted using available databases, such as the National Library of Medicine, as well as data presented at scientific conferences held in the past 2 years, primarily in the United States, the current status of biologic therapy for disc degeneration using growth factors was summarized.

RESULTS

With increasing evidence to support the feasibility of biologically regenerating intervertebral disc tissues, the clinical application of growth factors has become more plausible. The effects of growth factors on the metabolism of intervertebral disc cells or tissues have been extensively studied using in vitro approaches. More recently, the efficacy of an injection of growth factor protein to reverse disc regeneration has been shown in vivo using a small animal disc degeneration model. The confirmation of those effects and a detailed dose-response study, as well as a long-term safety study, in a large animal model is highly anticipated. Hopefully, the expansion of the clinical use of improved imaging techniques for the early detection of disc degeneration and promising results about the effects of growth factors on intervertebral disc regeneration will benefit the human population in the near future.

CONCLUSIONS

The results from these in vitro and in vivo studies reviewed here clearly suggest the potential usefulness of growth factor injections as a new approach to restore intervertebral disc degeneration at an early stage.

Anabolic and catabolic mRNA levels of the intervertebral disc vary with the magnitude and frequency of in vivo dynamic compression

The goal of this study was to characterize the anabolic and catabolic mRNA response of the disc to dynamic loading to determine if variations in the magnitude and/or frequency of loading could elicit different cellular responses. Sixty-eight Wistar rats were instrumented with an Ilizarov-type device spanning caudal disc 8-9. Seventy-two hours after surgery, animals were anesthetized and loaded at either 1 or 0.2 MPa at a frequency of 1, 0.2 or 0.01 Hz for 2 h (6 groups). The surgical control (Sham) animals underwent anesthesia with no loading. Loaded (c8-9) and internal-control discs (c6-7 and c10-11) were dissected and annulus and nucleus tissue were separately analyzed by real-time RT-PCR for levels of anabolic (collagen-1A1, collagen-2A1, aggrecan) and catabolic (MMP-3, MMP-13, ADAMTs-4) mRNA. In the nucleus, a frequency-dependent response was seen at 1 MPa with anabolic genes stimulated at 0.01 Hz and catabolic genes at 1 Hz. In the annulus all frequencies resulted in significant up-regulation of catabolic mRNA at 1 MPa loading. In general loading at 0.2 MPa or 0.2 Hz had little effect on gene expression. The results suggest that gene expression of the annulus appears to be more dependent on the magnitude of applied stress, while the nucleus is both magnitude- and frequency-dependent.

Growth Factor Osteogenic Protein-1

OBJECTIVE

The objective of this study was to determine if cells isolated from three distinct zones in the bovine intervertebral disc (IVD) differ in their response to growth factor osteogenic protein-1 (OP-1) because of inherent biological differences. The new knowledge gained will help determine if treatment of degenerative disc disease with purified growth factors is effective and will provide guidance in terms of the injection technique and frequency of treatments required.

DESIGN

This was an in vitro study measuring the effects of OP-1 on proteoglycan accumulation and synthesis by cells from the nucleus pulposus, inner-annulus fibrosus (inner-AF), and outer-annulus fibrosus (outer-AF) in the bovine IVD.

RESULTS

Growth factor OP-1, at 100 ng/ml, stimulated proteoglycan accumulation and resulted in a statistically significant increase in the proteoglycan content of cells derived from three zones of the bovine IVD: 97% in the nucleus pulposus, 40% in the inner-AF, and 75% in the outer-AF. To elucidate the mechanism of enhanced proteoglycan accumulation in response to OP-1, we studied the rate of proteoglycan synthesis and cell proliferation. OP-1 stimulation resulted in a statistically significant increase in the DNA content in cultures containing cells from all three zones of the IVDs: 79% in the nucleus pulposus, 100% in the inner-AF, and 73% in the outer-AF. After dividing by DNA content, OP-1 resulted in a statistically significant increase in the rate of proteoglycan synthesis in the nucleus pulposus (78%) and outer-AF (17%) cells, but the increase in inner-AF cells (23%) did not achieve statistical significance.

CONCLUSIONS

OP-1 stimulates proteoglycan accumulation by bovine IVD cells isolated from all three zones of the bovine IVDs. Cells from all three zones proliferated significantly. Individual cells derived from nucleus pulposus and outer-AF, but not those from the inner-AF, synthesized proteoglycans at a significantly faster rate with OP-1 stimulation.

Recombinant osteogenic protein-1 upregulates extracellular matrix metabolism by rabbit annulus fibrosus and nucleus pulposus cells cultured in alginate beads

This study was performed to determine if recombinant human osteogenic protein-1 (rhOP-1) is effective in promoting matrix synthesis and matrix formation by rabbit nucleus pulposus (NP) and annulus fibrosus (AF) cells cultured in alginate beads. The effects of culturing the cells in the presence of various concentrations of rhOP-1 were assessed by measuring changes in cell proliferation, proteoglycan (PG) and collagen synthesis and mRNA expression, and in the matrix contents of PG and collagen, as indicators of matrix accumulation. At high concentrations, rhOP-1 had a moderate mitogenic effect on both NP and AF cells. It also stimulated the synthesis of PG and collagen in a dose-dependent manner: this was associated with a corresponding increase in the expression of mRNA for aggrecan core protein and collagen type II. The stimulatory effect of rhOP-1 on PG synthesis was more pronounced than that on collagen synthesis. Continuous treatment with rhOP-1 led to an increase in the total DNA, PG and collagen contents in both NP and AF cultures. The results presented here provide evidence of the ability of rhOP-1 to stimulate the metabolism of both rabbit AF and NP cells cultured in alginate beads.

Glucosamine and chondroitin sulfate supplementation to treat symptomatic disc degeneration: biochemical rationale and case report

BACKGROUND

Glucosamine and chondroitin sulfate preparations are widely used as food supplements against osteoarthritis, but critics are skeptical about their efficacy, because of the lack of convincing clinical trials and a reasonable scientific rationale for the use of these nutraceuticals. Most trials were on osteoarthritis of the knee, while virtually no documentation exists on spinal disc degeneration. The purpose of this article is to highlight the potential of these food additives against cartilage degeneration in general, and against symptomatic spinal disc degeneration in particular, as is illustrated by a case report. The water content of the intervertebral disc is a reliable measure of its degeneration/ regeneration status, and can be objectively determined by Magnetic Resonance Imaging (MRI) signals.

CASE PRESENTATION

Oral intake of glucosamine and chondroitin sulfate for two years associated with disk recovery (brightening of MRI signal) in a case of symptomatic spinal disc degeneration. We provide a biochemical explanation for the possible efficacy of these nutraceuticals. They are bioavailable to cartilage chondrocytes, may stimulate the biosynthesis and inhibit the breakdown of their extracellular matrix proteoglycans.

CONCLUSION

The case suggests that long-term glucosamine and chondroitin sulfate intake may counteract symptomatic spinal disc degeneration, particularly at an early stage. However, definite proof requires well-conducted clinical trials with these food supplements, in which disc de-/regeneration can be objectively determined by MRI. A number of biochemical reasons (that mechanistically need to be further resolved) explain why these agents may have cartilage structure- and symptom-modifying effects, suggesting their therapeutic efficacy against osteoarthritis in general.

Effects of immobilization and dynamic compression on intervertebral disc cell gene expression in vivo

STUDY DESIGN

An in vivo analysis of the intervertebral disc's cellular response to dynamic compression and immobilization was performed using a rat-tail model.

OBJECTIVE

To assess the effects of immobilization and short-term dynamic compression on intervertebral disc cell expression of anabolic and catabolic genes.

SUMMARY OF BACKGROUND DATA

Static compressive loads applied in vivo alter the composition of the disc matrix and cell viability in a dose-dependent manner. The effects of in vivo dynamic compression, which is a more physiologic load, and reported risk factor for low back pain have not been investigated.

METHODS

An Ilizarov-type device was implanted on the rat tail and used to determine the effects from 72 hours of immobilization (n = 6), 2 hours of dynamic compression (1 MPa/0.2 Hz) (n = 8), and the coupled effect of immobilization followed by compression (n = 8). Real-time reverse transcription-polymerase chain reaction was used to measure changes in anabolic and catabolic gene levels relative to both internal control subjects and a sham-operated group (n = 7).

RESULTS

Immobilization and dynamic compression affect anabolic and catabolic genes, with an overall downregulation of types 1 and 2 collagen and upregulation of aggrecanase, collagenase, and stromelysin in the anulus. The effects of immobilization and compression appear to be additive for collagen types 1 and 2 in the anulus, but not in the nucleus, and not for catabolic genes.

CONCLUSIONS

Short-duration dynamic compression and immobilization alter gene expression in the rat disc. In studying the response of the disc to loading, it is necessary to look at both anabolic and catabolic pathways, and to consider strain history.

Potential sources of neck and back pain in clinical conditions of dogs and cats: a review

Pathological neck and back pain occurs in many medical conditions of dogs and cats. Pain may arise from a variety of structures including the intervertebral discs, facet joint capsules, dorsal root ganglia, vertebral ligaments, the vertebral periosteum, and the meninges. The source of this pain is dependent upon the type of disease process and its location within or surrounding the spinal column. Diseases can directly or indirectly stimulate pain sensors (nociceptors). Inflammatory diseases may hypersensitize these receptors or nociceptive pathways with inflammatory mediating substances such as serotonin, histamine and potassium. Diseases resulting in mechanical compression of nociceptors or nociceptive pathways may also result in neck or back pain. A thorough understanding of spinal pain occurring in dogs and cats will lead to more accurate diagnoses and treatments and may provide information regarding prognoses for various diseases. Evidence pointing to sources of spinal pain taken from scientific and clinical studies of a variety of species including humans is provided. Suspected or known sources of neck and back pain occurring in several clinical conditions of dogs and cats are discussed.

Proteoglycans synthesized by canine intervertebral disc cells grown in a type I collagen-glycosaminoglycan matrix

The objective of this study was to determine the characteristics of proteoglycans synthesized by canine annulus fibrosus cells expanded in number in monolayer culture through passage 4 and subsequently grown in a type I collagen-glycosaminoglycan matrix to be employed for tissue engineering. Newly synthesized [35S]sulfate-labeled proteoglycans were analyzed by gel chromatography, including sequential digestion with enzymes and nitrous acid. After 1 week in culture, the percentage of cell-associated, aggregated proteoglycans synthesized in type I collagen-glycosaminoglycan matrices was 52% compared with 38% by the cells in monolayer. The percentage of aggregated proteoglycan in each group increased only slightly with the addition of exogenous hyaluronic acid, but remained significantly different from each other. There were at least three different hydrodynamic sizes of proteoglycans both in the collagen-glycosaminoglycan matrix and in monolayer; the average size was larger in the collagen matrices and the glycosaminoglycan chains were longer. The proteoglycans contained chondroitin sulfate, dermatan sulfate, heparan sulfate, and keratan sulfate. The results provide a foundation for future investigations of collagen-glycosaminoglycan matrices for intervertebral disc tissue engineering.

Osteogenic protein-1 enhances matrix replenishment by intervertebral disc cells previously exposed to interleukin-1

STUDY DESIGN

A study of the mechanisms involved in matrix repair by intervertebral disc cells cultured in alginate gel was performed.

OBJECTIVES

To determine the effects of osteogenic protein-1 on the extracellular matrix of intervertebral disc cells previously exposed to interleukin-1, which is an in vitro model for degraded extracellular matrix.

SUMMARY OF BACKGROUND DATA

Disc degeneration is accompanied by a decrease in the content of negatively charged proteoglycans in the matrix. No previous attempt has been made to repair the degraded matrix of the disc.

METHODS

Nucleus pulposus and anulus fibrosus cells were isolated from the lumbar discs of New Zealand white rabbits and were separately encapsulated in alginate beads. The alginate beads were cultured with or without osteogenic protein-1 after previous exposure to interleukin-1alpha in the presence of 10% fetal bovine serum. The total contents of proteoglycan, collagen, and DNA in the alginate beads were measured. The rate of proteoglycan synthesis by the encapsulated cells was also determined.

RESULTS

Treatment with interleukin-1alpha resulted in a significant decrease in proteoglycan and collagen contents in the matrix formed by both the nucleus pulposus and anulus fibrosus. However, subsequent treatment with osteogenic protein-1 led in both cases to rapid recovery of proteoglycans and collagens, whose contents returned to the levels seen in cells not previously exposed to interleukin-1alpha. By the end of the culture period (day 21), those values reached levels higher than those found in beads containing cells never exposed to interleukin-1alpha. Further, the rate of proteoglycan synthesis by both cell types in beads treated with osteogenic protein-1 after previous exposure to interleukin-1alpha was significantly higher than in beads whose cells were not treated with osteogenic protein-1 after previous exposure to interleukin-1alpha.

CONCLUSION

Disc cells that have been previously exposed to interleukin-1alpha have lost none of their potential to upregulate proteoglycan synthesis in response to stimulation with osteogenic protein-1. On stimulation with osteogenic protein-1, these disc cells not only replenished the matrix with proteoglycans that had been lost during interleukin-1alpha treatment but proceeded to reform a matrix that was richer in these resilient molecules than that formed by disc cells never exposed to interleukin-1alpha.

Proliferation of canine intervertebral disk chondrocytes in three-dimensional alginate microsphere culture

Proliferation of chondrocytes from nucleus pulposus (NP) and anulus fibrosus (AF) was confirmed in three-dimensional culture using alginate microspheres. Cells isolated from NP and AF were incorporated in microspheres and cultured for 14 days. Round mononuclear cells of 20-25 microm in diameter proliferated and formed aggregates. At day 14, alcian blue positive matrix surrounded the proliferating cells. The cells had cytoplasmic vacuoles stained positively by toluidine blue. On electron microscopy, the cells contained proteoglycan vacuoles and lipid droplets in the cytoplasm and synthesized collagen fibrils and electron dense granules surrounding the cell. These features of the cells were characteristic for chondrocytes. This culture system should be useful to further investigate metabolic activities of intervertebral disk chondrocytes.

Spinal biomechanics and aging are major determinants of the proteoglycan metabolism of intervertebral disc cells

STUDY DESIGN

The proteoglycan metabolism of ovine disc nucleus pulposus and anulus fibrosus cells was investigated in relation to age, spinal level, and intrinsic spinal biomechanical properties.

OBJECTIVE

To evaluate the hypothesis that with aging loss of proteoglycans from the lumbosacral disc exceeds that from upper lumbar discs because of its proximity to a rigid segment, the sacrum.

SUMMARY OF BACKGROUND DATA

The proteoglycan and associated water of the disc decreases with aging.

METHODS

Proteoglycans were extracted directly from the disc tissues using 4 M GuHCl and examined by composite agarose polyacrylamide gel electrophoresis. Disc cells were cultured in alginate beads, and their metabolic activity was assessed by 3H-thymidine incorporation into DNA and by bioreduction of a cell proliferation dye. Newly synthesized proteoglycans were radiolabeled with 35S, and their molecular weight distributions and ability to aggregate with hyaluronan were determined by Sephacryl S1000 gel chromatography. Resident proteoglycans extracted from disc tissues with 4 M GuHCl were similarly evaluated. A group of adult animals also were studied biomechanically to evaluate the range of spinal motion (L4/L5 to L7/S1).

RESULTS

In contrast to the neonatal proteoglycan samples, the biosynthesis of proteoglycans by nucleus pulposus cells of adult discs increased progressively toward the sacrum. This correlated with increased metabolic activity. Analysis of the resident proteoglycans by composite agarose polyacrylamide gel electrophoresis indicated that although the aggrecan-1 population was present almost exclusively in the neonatal group, it was the aggrecan-2 population that predominated in the adult discs, and it became progressively more heterogeneous with aging and proximity of the disc to the sacrum.

CONCLUSIONS

The proteoglycans of the lumbosacral disc of adult animals turned over faster than proteoglycans of adjacent lumbar discs. The reduced proteoglycan content and ability to aggregate, particularly in the nucleus pulposus of lumbosacral discs, indicated that proteoglycan catabolism exceeded the rate of biosynthesis. These events in the lumbosacral disc are thought to be determined mechanically by its proximity to the sacrum.

Mechanical factors affecting the occurrence of intervertebral disc calcification in the dachshund--a population study

In a population sample comprising 48 standard wirehaired dachshunds, the occurrence of intervertebral disc calcification was determined by plain spinal radiography. Body dimensions of the dogs were measured and information obtained from owners about exercise patterns, including stair climbing, and the relation of these variables to the number of calcified discs was analysed by logistic regression. In the Danish population of wirehaired dachshunds, the prevalence of disc calcification was estimated at 77%. The spinal distribution of calcified discs is similar amongst different populations, while the prevalence varies significantly. Most types of exercise included in the variable 'duration of exercise' as well as moderate stair climbing seemed to reduce the rate of occurrence of disc calcification. The effects of moderate stair climbing (OR = 0.34) and duration of exercise (OR = 0.52) were statistically significant and the effects appear to be additive. Running next to a bicycle was the only type of exercise with a positive association with the number of calcified discs. This was, however, not significant. Effects of body conformation, including absolute and relative body measurements, were not found.

The effect of compressive force applied to the intervertebral disc in vivo. A study of proteoglycans and collagen

STUDY DESIGN

Coil springs were stretched and attached to produce a compressive force across the lumbar intervertebral discs of dogs for up to 27 weeks.

OBJECTIVE

To test the hypothesis that a high compressive force applied over a period of time affects the production of proteoglycans and collagen by the intervertebral disc cells.

SUMMARY OF BACKGROUND DATA

It is a commonly held belief that high forces applied to the intervertebral disc, and to joints in general, play a role in causing degeneration.

METHODS

Pairs of stainless steel coil springs were stretched and attached to produce a compressive force across the lumbar intervertebral discs (L1-L2 and L3-L4) of 16 dogs. Dogs were killed between 13 and 27 weeks after the springs were attached. The discs (L1-L2 and L3-L4) were excised and assessed using immunohistochemical analyses and enzyme-linked immunosorbent assay; T13-L1 and L4-L5 were used as controls.

RESULTS

The main result relates to a group effect in the six dogs, assessed using enzyme-linked immunosorbent assay, that were generally at the highest values of force for the greatest number of weeks. For the nucleus, but not the anulus, Spearman rank correlations revealed a strong correlation between increases in force and force-weeks (force multiplied by number of weeks) and increases in collagen type I accompanied by decreases in proteoglycans, chondroitin sulfate, and collagen type II for both experimental discs (L1-L2 and L3-L4), as compared with corresponding values in the controls (T13-L1 and L4-L5). In other words, as either the force or the force-weeks increased, the effect on the nucleus became greater.

CONCLUSION

A high compressive force applied to the disc over a period of time initiates changes in proteoglycans and collagen.

Changes in proteoglycans of intervertebral disc in diabetic patients. A possible cause of increased back pain

STUDY DESIGN

Characterization of the analytic profile of proteoglycans in the intervertebral discs at L4-L5 of nondiabetic (n = 5) and diabetic (n = 5) age-matched subjects. The discs used were discarded material from operations.

OBJECTIVES

To clarify the reason for the higher risk of disc prolapse in diabetic patients.

SUMMARY OF BACKGROUND DATA

The pathogenesis of diabetes results from a combination of neurologic dysfunctions and a yet undefined metabolic failure, which leads to an abnormal proteoglycan profile.

METHODS

The following methods were used to determine the proteoglycan profile: the measurement of 35S-sulfate uptake per gram wet tissue into sulfated glycosaminoglycan using fresh tissue explants; extraction of proteoglycans by 4 M guanidinium chloride containing protease inhibitors, with further purification by ultracentrifugation on cesium chloride buoyant density gradient under dissociative conditions; total uronic acid and protein contents in the various gradient fractions; assessing the length of sugar side chains of isolated 35Sulfate-glycosaminoglycan molecules by separation of the glycosaminoglycan molecules on a Sepharose 6B-CL column; and paper chromatography of the final digest products of glycosaminoglycan molecules obtained by chondroitinase ABC, a glycosaminoglycan-degrading enzyme.

RESULTS

The findings show that discs from normal nondiabetic subjects have 15 times the rate of 35Sulfate incorporation into glycosaminoglycan molecules than do discs of diabetic patients. The proteoglycans of diabetic patients are banded at a lower buoyant density, indicating a lowered glycosylation rate and a lower number of sugar side chains per core protein. In discs of diabetic patients, there is a slight increase in the chain length of chondroitin sulfate. Further analysis of the glycosaminoglycan chains showed a decreased amount of keratan sulfate, compared with that in nondiabetic subjects. However, the total uronic acid content of the disc tissues and the ratio of uronic acid to protein of each fraction were unchanged in diabetic patients versus that in control subjects.

CONCLUSIONS

Discs in patients with diabetes have proteoglycans with lower buoyant density and substantially undersulfated glycosaminoglycan, which with the specific neurologic damage in these patients, might lead to increased susceptibility to disc prolapse.

The serine proteinase inhibitory proteins of the chondrodystrophoid (beagle) and non-chondrodystrophoid (greyhound) canine intervertebral disc

Trypsin inhibitory proteins of low buoyant density (p < or = 1.35 g/mL) fractions were prepared by CsCl density gradient ultracentrifugation of 4 M guanidinium hydrochloride extracts of lumbar beagle and greyhound annulus fibrosus and nucleus pulposus from animals aged 1 to 6 years. Affinity blotting with biotinylated trypsin was used to identify active trypsin inhibitory protein species; these species were also identified immunologically by Western blotting using antibodies against bovine pancreatic trypsin inhibitor (BPTI), and human inter-alpha-trypsin inhibitor (ITI). None of the trypsin inhibitory species evident in Western blots were reactive with anti-human alpha1-proteinase inhibitor (alpha-1-PI), alpha2-macroglobulin or secretory leucocyte proteinase inhibitor. The greyhound intervertebral disc samples generally had higher levels of active trypsin inhibitor species per unit weight of tissue extracted, and a more extensive range of inhibitor species. Inhibitor species of 30, 32, 34 kDa were identified in both beagle and greyhound intervertebral disc samples; these species were generally most prominent in the annulus fibrosus samples. In contrast, the nucleus pulposus samples contained relatively large trypsin inhibitor species; the anti-BPTI detected an inhibitor species of approximately 85-90 kDa; anti-ITI detected species of 120-250 kDa; biotinylated trypsin detected species of 60-110 kDa. A small molecular mass trypsin inhibitor species of 6 kDa, which was of similar mobility to BPTI, was also detected in annulus fibrosus samples; however, this species did not react with anti-BPTI.

The human lumbar intervertebral disc: evidence for changes in the biosynthesis and denaturation of the extracellular matrix with growth, maturation, ageing, and degeneration

Very little is known about the turnover of extracellular matrix in the human intervertebral disc. We measured concentrations of specific molecules reflecting matrix synthesis and degradation in predetermined regions of 121 human lumbar intervertebral discs and correlated them with ageing and Thompson grade of degeneration. Synthesis in intervertebral discs, measured by immunoassay of the content of a putative aggrecan biosynthesis marker (846) and the content of types I and II procollagen markers, is highest in the neonatal and 2-5-yr age groups. The contents of these epitopes/molecules progressively diminished with increasing age. However, in the oldest age group (60-80 yr) and in highly degenerated discs, the type I procollagen epitope level increased significantly. The percentage of denatured type II collagen, assessed by the presence of an epitope that is exposed with cleavage of type II collagen, increased twofold from the neonatal discs to the young 2-5-yr age group. Thereafter, the percentage progressively decreased with increasing age; however, it increased significantly in the oldest group and in highly degenerate discs. We identified three matrix turnover phases. Phase I (growth) is characterized by active synthesis of matrix molecules and active denaturation of type II collagen. Phase II (maturation and ageing) is distinguished by a progressive drop in synthetic activity and a progressive reduction in denaturation of type 11 collagen. Phase III (degeneration and fibrotic) is illustrated by evidence for a lack of increased synthesis of aggrecan and type II procollagen, but also by an increase in collagen type II denaturation and type I procollagen synthesis, both dependent on age and grade of tissue degeneration.

Difference of mineral contents in human intervertebral disks and its age-related change

To establish a difference of the relative contents (RCs) of elements among the cervical, thoracic, and lumbar intervertebral disks and its age-related change, the intervertebral disks between the axis and the sacrum, which were resected from the nine cadavers who died at 53 to 99 yr old, were analyzed by inductively coupled atomic plasma emission spectrometry. It was found that both the RCs of calcium and phosphorus were high in the cervical disks, especially the highest in the disk between the 6th and 7th cervical vertebrae, and lower in the order of the cervical, thoracic, and lumbar intervertebral disks. In regard to the RCs of sulfur and magnesium, there were no significant differences among the cervical, thoracic, and lumbar intervertebral disks. In addition, it was found that both the RCs of calcium and phosphorus in the cervical intervertebral disks started to increase in the sixth decade of life, became the highest in the eighth decade of life, and then decreased.

Intervertebral disc reconstitution after chemonucleolysis with chymopapain is dependent on dosage

STUDY DESIGN

The current report describes a study in beagles in which the effects of intradiscal injection of three doses of chymopapain were evaluated with respect to the reduction of disc width and reconstitution of the nucleus pulposus.

OBJECTIVES

To establish an intradiscal dose of chymopapain that would achieve optimal reduction in disc height followed by maximum reconstitution of the nucleus pulposus.

SUMMARY OF BACKGROUND DATA

Earlier reports of the efficacy of high and low doses of chymopapain for chemonucleolysis have provided conflicting data, and a scientific basis for an appropriate dose is lacking.

METHODS

Four mature, female beagles were subjected to chemonucleolysis using three doses of chymopapain as Chymodiactin (31, 63 and 125 picokatals/disc) injected into the L2-L3, L1-L2, and L3-L4 discs. Disc widths were monitored radiographically over 32 weeks. Proteoglycans were radiolabeled by intravenous injection with Na2 35SO4 (1 mCi/kg) 24 hours before sacrifice, and their specific activities (disintegrations per minute/mg proteoglycan), hydrodynamic size, and ability to aggregate determined.

RESULTS

Sixty-three picokatals of Chymodiactin produced optimal disc reconstitution after chemonucleolysis. A reduction in disc height of approximately 35% was evident within 1 month and this slowly returned to approximately 90% of the preinjection value after 32 weeks. The nucleus pulposus contained approximately 75% of the proteoglycan content of control tissues, and most of these formed aggregates with hyaluronan. Disc collagen levels remained relatively unaffected by treatment.

CONCLUSIONS

This study demonstrates that an effective reduction in disc width compatible with later reconstitution of the nucleus pulposus can be achieved experimentally with an appropriate dose of chymopapain. These data clearly indicate that an optimal dose of chymopapain for chemonucleolysis in humans needs to be established.

Evaluation of digestive proteinases from the Antarctic krill Euphasia superba as potential chemonucleolytic agents. In vitro and in vivo studies

Chemonucleolysis is a therapeutic procedure whereby a degradative enzyme is injected intradiscally to reduce disc height/width by depolymerisation of extracellular matrix components. This process is considered to diminish disc pressure on inflamed nerve roots, resulting in the alleviation of sciatic pain. In the present study two krill (Euphasia superba) enzyme preparations, a proteinase and an esterase preparation, were evaluated for their potential as chemonucleolytic agents. Initially, their ability to degrade several protein (azocoll, casein, proteoglycans, PGs) and peptide (CBZ-arg-4-nitroanilide, CBZ-lys-thiobenzyl ester) substrates was assessed in vitro. The krill proteinase preparation rapidly converted azocoll, casein and PGs to small peptides. Furthermore, when this degradative enzyme preparation was evaluated in vivo, a relatively low intradiscal dose (0.54 mg/disc) was found to reduce intervertebral disc widths in beagles to 48% +/- 10.5% (mean +/- SEM) of their pre-injection values within 2 weeks of administration. Moreover, the discs injected with this proteinase had reconstituted up to 80% +/- 9% (mean +/- SEM) of their pre-injection widths at the termination of the experiment (32 weeks). These data suggest that the krill protease preparation has potential as a chemonucleolytic agent which would allow disc matrix reconstitution. Conversely, the krill esterase preparation also degraded PGs, but into relatively large fragments. This limited digestion of PGs indicates that the krill esterase would be a less effective chemonucleolytic agent than the corresponding proteinase.

Proteoglycan heterogeneity in the normal adult ovine intervertebral disc

Proteoglycans (PGs) were isolated from 4 M GuHCl extracts of young adult ovine Intervertebral disc (IVD) tissues using sequential CsCl density gradient centrifugation, and a combination of gel-permeation and hydrophobic chromatography. A total of six PG sub-populations were identified in both the Annulus fibrosus (AF) and Nucleus pulposus (NP), i.e. two high buoyant density aggregatable PGs, two high buoyant density non-aggregatable PGs and two small, low-intermediate buoyant density, non-aggregatable, DS-rich PG species. These latter PGs were identified as biglycan and decorin on the basis of analyses of their core protein native size, and glycosaminoglycan composition. Additional low-intermediate buoyant density PG species were also evident in the non-aggregatable PG pool, particularly in extracts of NP tissues. These PGs did not bind to the octyl affinity matrix under the experimental conditions employed and thus were readily separated from the DS-PGs by hydrophobic chromatography, their constituent glycosaminoglycans (CS and KS) also differed and were of a smaller size to the CS and KS chains isolated from the large high buoyant density PGs, the small PGs which did not bind to octyl-sepharose may therefore represent distinct PG species in their own right. Differences were evident in the absolute size, and in the distribution of individual PG species in the respective IVD tissues but the NP always contained a larger proportion of high buoyant density non-aggregatable PGs of somewhat smaller size than those isolated from the AF. Decorin and biglycan, however, were generally more abundant in AF tissues.

Proteoglycan synthesis in canine intervertebral discs after long-distance running training

The alterations and distribution of proteoglycan (PG) synthesis in the intervertebral discs of young dogs exercised with long-distance running (40 km/day) were studied with a method based on image analysis of tissue sections. Ten dogs were run on a treadmill daily for 55 weeks, and 10 dogs from the same litters served as controls. The daily running distance gradually was increased to 40 km and was maintained at that level for the final 15 weeks. Midsagittal disc segments C7-T1, T8-9, and L1-2 were labeled with 35SO4, and histological sections of the segments were apposed against autoradiographic film to determine the synthesis of PGs. Next, the same sections were stained with safranin O to estimate possible alterations in PG concentration. The radiographs and stained sections were digitized with a flatbed scanner and measured by image analysis. The lumbar discs of runners displayed a significantly lower rate of 35SO4 incorporation, while a tendency toward enhanced incorporation was seen in the cervical and thoracic discs. Safranin O staining showed a pattern just opposite to 35SO4 incorporation: decreased staining in the cervical and thoracic discs and increased staining in the lumbar discs of the runners. The results demonstrate qualitatively different influences of long-term running training on PG metabolism at the cervical, thoracic, and lumbar levels in young dogs.

A longitudinal study of the matrix changes induced in the intervertebral disc by surgical damage to the annulus fibrosus

A 5 x 5-mm anterolateral incision was made in the annulus fibrosus (AF) of lumbar discs of 16 sheep; four animals of similar age not operated on were used as controls. The experimental animals were sacrificed 2, 4, 6, 8, 12, and 18 months postoperatively (PO), and the incised and adjacent lumbar discs were collected. Discs were dissected into four zones: AF (zones 1 and 2) and nucleus pulposus (NP) (zones 3 and 4) corresponding to the half of the AF in which the cut was made and its opposite half, and the complementary halves of the NP. Each zone was analyzed for moisture, proteoglycan (PG), collagen, and noncollagenous protein (NCP) content. The PG extractability, aggregation, and hydrodynamic size were also examined. The NP of injured discs showed a significant loss of PGs and collagen 8 months PO, but NCP levels increased. In the incised discs, PG aggregation initially declined but recovered to within control values 6-8 months PO. The NP of discs adjacent to the incised disc also showed time-dependent changes in matrix components that included loss of collagen and PG; however, the AF matrix remained essentially uneffected. Double immunodiffusion studies indicated that a sizeable proportion of the NCPs present in the injured discs (but not the adjacent lumbar discs) were derived from serum.

Chemonucleolysis with collagenase. A radiographic and pathologic study in dogs

Collagenase, a proteolytic enzyme, was injected intradiscally in nine clinically normal, middle-aged beagles. Calcium chloride diluent solution (control), 100 ABC units of collagenase, and 250 ABC units of collagenase, were injected in randomly selected intervertebral discs (T13-L1 to L5-L6). On day 11, the discs injected with collagenase were narrowed radiographically, but there was no significant change in myelograms. Grossly and histologically, there was dissolution of the intervertebral discs, mainly nucleus pulposus, and protrusion of nucleus material in the vertebral body through bony end-plates in discs injected with collagenase. Collagenase chemonucleolysis may be an alternative to spinal surgery for intervertebral disc protrusion in dogs.

A comparison of the high buoyant density proteoglycans isolated from the intervertebral discs of chondrodystrophoid and non-chondrodystrophoid dogs

Groups of purebred beagles and greyhounds of similar ages (1.5-2.5 years) were used for the study. Intervertebral disc proteoglycans (PGs) were radiolabelled in vivo (with [35SO4(2-)], 24 hours and 60 days prior to euthanasia, when lumbar discs were dissected into nucleus pulposus (NP) and annulus fibrosus (AF). Aliquots of each disc region were separately analysed for total PG content as hexuronate. The remaining tissue was subjected to extraction with 4.0 M GuHCl. High buoyant density PGs were isolated from these extracts by CsCl density gradient ultracentrifugation. The hydrodynamic size and aggregatability of the 24-hour, 60-day-old, and resident PG populations were determined by Sepharose CL2B chromatography in the presence or absence of excess hyaluronic acid. While the hydrodynamic sizes of the newly synthesized (24-hour) disc PG preparations appeared to be similar, the 60-day-old greyhound disc PGs were found to be larger than the corresponding beagle disc PG populations. However, the keratan sulphate-core protein complexes prepared by chondroitinase ABC digestion of the newly synthesized (24 hour) disc PGs showed that the greyhound disc preparations were also larger than those from beagle discs. Approximately 80% of the newly synthesized PGs from beagle and greyhound discs were capable of aggregating with hyaluronic acid, however, this was reduced to 55% for the 60 day-old PGs in NP and AF and even less for the resident PG populations (as determined by hexuronate analysis). Significantly, PG aggregation was lower in the greyhound NP and AF preparations than in the corresponding PGs isolated from the beagle disc.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of tiaprofenic acid (Surgam) on cartilage proteoglycans in the rabbit joint immobilisation model

A well established model of arthritis induced in rabbit knee joints by immobilisation in full extension for 30 days was used to evaluate the in vivo effects of 2.5, 5.0, and 10.0 mg/kg body weight of tiaprofenic acid on articular cartilage proteoglycans. The drug was given subcutaneously every 24 hours during the entire immobilisation period. Immobilised animals not treated with drugs and normal animals were used as controls. In the non-drug treated immobilised animals articular cartilage showed evidence of surface damage accompanied by synovial hypertrophy and effusion. Proteoglycan concentrations were reduced in cartilages of these joints and the incorporation of 35SO2-4 into macromolecular proteoglycans was higher than in cartilages of non-immobilised controls. Gel filtration chromatographic studies of both resident and 35S labelled proteoglycans isolated from immobilised joint cartilage showed reduced aggregation and the presence of degraded proteoglycan subunit species. Whereas the administration of 10.0 mg/kg tiaprofenic acid every 24 hours to immobilised animals exacerbated the degradation and loss of proteoglycans from joint cartilages, 5.0 mg/kg tiaprofenic acid provided some protection of these macromolecules, as shown by the concentrations and extractability of proteoglycans from cartilages, which were comparable with those from non-immobilised controls. A high incorporation of 35S into proteoglycans was demonstrated, together with reduced catabolism of proteoglycans, indicating preservation of chondrocyte anabolic activity. At a tiaprofenic acid dose of 2.5 mg/kg, however, no beneficial effects on cartilage proteoglycans could be shown.

The effects of long term monolayer culture on the proteoglycan phenotype of a clonal population of mature human malignant chondrocytes

Articular cartilage chondrocytes maintain biosynthetic heterogeneity in cell culture, but undergo irreversible dedifferentiation of their proteoglycan phenotype, as defined by keratan sulfate content. A recently described cell line of malignant human chondrocytes, 105KC, was the first to maintain a differentiated keratan sulfate-proteoglycan phenotype in long-term culture. A clone of 105KC, labeled KC2H3, is currently described and represents a distinct and metabolically more homogeneous population of mature chondrocytes than 105KC. KC2H3 cells universally express keratan sulfate biosynthesis, as defined by indirect immunofluorescence. In addition, KC2H3 expresses a more mature proteoglycan phenotype than 105KC, as demonstrated by the keratan sulfate content: 24% of glycosaminoglycan content of the aggregating proteoglycans of KC2H3 versus 13% for 105KC. Further reported are the effects of long term monolayer culture on the proteoglycan phenotype expressed by KC2H3. After more than 16 months in continuous monolayer, KC2H3 cells remained morphologically indistinguishable from those maintained in suspension alternating with monolayer. In addition, the proteoglycan phenotype remained mature, without a tendency towards dedifferentiation. The flattened morphology adopted by chondrocytes while in monolayer has been considered a stimulus of dedifferentiation; the present study is the first to examine the direct effects of physical state on a homogeneous and stable population of chondrocytes.

Double-blind multicenter trial on a new medium molecular weight glycosaminoglycan. Current therapeutic effects and perspectives for clinical use

The ability of glycosaminoglycans to bind to a wide number of biologically active macromolecules has already been investigated. Recent clinical trials on the possible therapeutic benefits of glycosaminoglycans must be placed in perspective, even if they appear to be particularly encouraging, especially as regards the glycosaminoglycan effects on certain coagulation factors. A multicenter, medium-term, double-blind, crossover trial was performed by several Italian Lipid Clinics to determine whether administration of a medium molecular weight glycosaminoglycan (Sulodexide) has a significant clinical effect. Patients affected by peripheral vascular disease and/or hyperlipidemia (type IIa, IIb and IV) were submitted to a 4-week wash-out period, followed by parenteral Sulodexide (S) or placebo (P) administration for 2 weeks, another 2 week wash-out period, parenteral crossover drug or P administration for 2 weeks and, finally, oral S administration for 6 months. Sulodexide lowered plasma viscosity and plasma fibrinogen in all patients. There was also a drop in triglycerides together with a rise in apo A-I and HDL-C in type IV hyperlipoproteinemics, whereas there was no significant effect on total or LDL-plasma cholesterol in type IIa and IIb patients. Moreover, there was a percent increase in peak flow and rest flow in the lower limbs of peripheral vascular disease patients. No side effects or intolerance phenomena were detected. The results indicate that Sulodexide administration may be useful in long-term treatment of patients with peripheral vascular disease and a concomitant increase in plasma triglycerides and/or fibrinogen and/or viscosity.

Age-related changes in the beagle spine

Age-related changes were evaluated in the spines of beagle dogs by radiology, histology, and mechanical testing. Thirty healthy beagle dogs were divided into five groups having mean ages of 2-14 years. Radiographs were taken of intact spines at the time of death and of defleshed spines at necropsy. Cervical, thoracic, and lumbar segments were tested in compression to calculate peak stress, peak strain, and elastic modulus. Adjacent spine segments were graded grossly for osteophyte development, and sections of the intervertebral discs were evaluated histologically. Histologic evidence of disc degeneration and changes in the mechanical properties of the intervertebral disc joint preceded radiographic changes. Changes in the mechanical properties of the disc space were probably a result of the disc degeneration rather than the spondylitic lesions.

Proteoglycans of the human intervertebral disc. Electrophoretic heterogeneity of the aggregating proteoglycans of the nucleus pulposus

Nuclei pulposi were dissected from lumbar discs of radiologically normal human spines of cadavers aged 17, 20 and 21 years. Proteoglycans were extracted with 4 M guanidine hydrochloride (dissociative conditions) with proteinase inhibitors and isolated as A1 fractions by associative density-gradient centrifugation. Aggregating and non-aggregating proteoglycans were separated by Sepharose 2B chromatography. Both aggregating and non-aggregating proteoglycans contained a keratan sulphate-rich region as isolated by chondroitinase/trypsin/chymotrypsin digestion and Sepharose CL-6B chromatography. Agarose/acrylamide-gel electrophoresis of individual fractions of a Bio-Gel A-50m dissociative-column separation of the aggregating proteoglycans revealed two, well-separated bands: S and F, the slower and faster migrating bands respectively. The non-aggregating proteoglycan fractions were eluted under associative conditions (0.5 M-sodium acetate, pH 6.8) and migrated as a single band in the electrophoretic system. The gel-electrophoretic heterogeneity of the aggregating proteoglycans was still evident after hydroxylamine fragmentation and removal of the hyaluronate-binding portion of the molecule. Dissociative density-gradient centrifugation of the aggregating proteoglycans partially separated the Band-S proteoglycans from the Band-F population. Subsequent dissociative chromatography of the high-buoyant-density Band F proteoglycans permitted discrimination of this band into two gel-electrophoresis-distinguishable populations (Bands F-1 and F-2). Enzyme-linked immunosorbent assays with a monoclonal antibody that recognized keratan sulphate demonstrated that the D1 fraction containing the Band F-1 proteoglycans was enriched in keratan sulphate compared with the total aggregating or non-aggregating pool of proteoglycans. The proteoglycans of young adult nucleus pulposus could then be ascribed to one of four structurally and/or electrophoretically distinct populations: (1) the non-aggregating population, which comprised about 70% of the total extractable proteoglycans; (2) the aggregating pool, comprising: (a) Band F-1 proteoglycans, which had a relatively large hydrodynamic size, uronate/protein weight ratio, were enriched in keratan sulphate and had a high buoyant density; (b) Band S proteoglycans, which migrated slower in agarose/acrylamide gels, had a smaller hydrodynamic size, lower buoyant density and a lower uronate/protein ratio than the Band F-1 population; (c) Band F-2 proteoglycans, which were lower in buoyant density, smaller in hydrodynamic size and slightly faster in electrophoretic mobility than the Band F-1 proteoglycans.