In vitro organ culture of the bovine intervertebral disc: effects of vertebral endplate and potential for mechanobiology studies

STUDY DESIGN

Whole bovine coccygeal discs were cultured under static load, with or without vertebral endplates (VEPs), and assessed for cell viability, biochemical stability, biosynthetic activity, and biosynthetic responsiveness to changes in mechanical load.

OBJECTIVES

To assess the effects of VEPs on biochemical and cellular stability of disc cells during in vitro culture of large disc explants. To determine whether cultured discs could respond to mechanical perturbation.

SUMMARY OF BACKGROUND DATA

Previous methods for culturing the intervertebral disc have focused on rabbit and rat discs, but the small size of these discs limits the relevance of these culture systems to the human condition. Bovine coccygeal discs have similar dimensions to the human lumbar disc (i.e., similar size and nominal stresses), but long-term culture of these discs has not been reported.

METHODS

Bovine coccygeal discs were harvested with or without VEPs, cultured under static load (5 kg, approximately 0.25 MPa, in situ swelling pressure) for up to 1 week, and evaluated for changes in hydration, glycosaminoglycan content, cell viability, and biosynthetic activity. Additionally, the biochemical and biosynthetic response of discs cultured without VEP to increasing the load to a 20-kg (approximately 1 MPa, the estimated stress in human lumbar disc during heavy lifting) static load for 6 hours was assessed.

RESULTS

During the first 24 hours, culturing discs with endplates was moderately better with regards to maintaining in situ anulus hydration and nucleus glycosaminoglycan levels. The endplates, however, obstructed media flow to the disc, resulting in a marked decrease in cell viability after 1 week of culture. Nucleus pulposus cell viability was maintained in discs cultured without endplates, but there was a significant drop in biosynthetic activity within 2 days of culture. Despite this drop, the disc cells in the discs without VEP remained biosynthetically responsive to changes in mechanical loading.

CONCLUSIONS

It is possible to maintain cell viability and the biosynthetic responsiveness of large discs for up to 1 week in vitro when the discs are cultured under static load and without VEP.

Possible pathogenesis of painful intervertebral disc degeneration

STUDY DESIGN

We collected the specimens of lumbar intervertebral disc (i.e., the symptomatic degenerative disc) from patients with discogenic low back pain to study the histopathologic features and growth factor expressions.

OBJECTIVES

To study the pathogenesis of disc degeneration, meanwhile discriminating between common disc degeneration (aging disc) (i.e., black asymptomatic disc, not clinically relevant) and painful disc degeneration (i.e., symptomatic disc, clinically relevant).

SUMMARY OF BACKGROUND DATA

The pathogenesis of intervertebral disc degeneration is poorly understood, mainly because of the difficulty to establish the experimental model with good reproducibility. Recently, the popularity of spinal fusion leads to more opportunities to obtain disc specimens, which could be applied to explore the pathogenesis of disc degeneration with modern biologic techniques.

METHODS

There were 21 specimens of lumbar intervertebral discs from 15 patients with discogenic low back pain during posterior lumbar interbody fusion, 16 aging discs from patients without low back pain, and 10 normal discs as control collected for the study of their histopathologic features, as well as the expressions of basic fibroblast growth factor (bFGF) and its receptor (Flg), transforming growth factor-beta1 (TGF-beta1) and its receptor (TGF-betaRI) by immunohistochemistry. The distribution of macrophages and mast cells was also noted. Proliferating cell nuclear antigen was assessed to evaluate proliferating activities of disc cells.

RESULTS

The distinct histologic characteristic of the disc from the patient with discogenic low back pain was the ingrowth of vascularized granulation tissue along torn fissures, extending from the external layer of the anulus fibrosus into the nucleus pulposus. The immunohistochemical staining showed that there were strong expressions of bFGF and TGF-beta1 and their receptors, as well as a strong expression of proliferating cell nuclear antigen in the zones of granulation tissue in the painful discs. However, there were only weak expressions in the nongranulation tissue zones in the painful discs and aging discs, and no expression in the control discs. In addition, abundant macrophages and mast cells were found in the granulation tissue zones of painful discs but absent in the nongranulation tissue zones of painful discs or aging discs and the normal control discs.

CONCLUSIONS

The findings indicated that degeneration of the painful disc might originate from the injury and subsequent repair of anulus fibrosus. Growth factors, such as bFGF and TGF-beta1, macrophages and mast cells might play a key role in the repair of the injured anulus fibrosus and subsequent disc degeneration.

Nucleus pulposus-induced apoptosis in dorsal root ganglion following experimental disc herniation in rats

STUDY DESIGN

The mechanisms behind the formation of a characteristic tissue reaction at the surface of the dorsal root ganglion (DRG) exposed to nucleus pulposus was studied with special reference to apoptosis using electron microscopy and immunohistochemistry in rats.

OBJECTIVES

To study the mechanism of the characteristic tissue reaction at the surface of the DRG exposed to nucleus pulposus.

SUMMARY OF BACKGROUND DATA

Recently, it was observed that local application of nucleus pulposus may induce a characteristic tissue reaction at the surface of the DRG. This change occurred as early as 1 day after the application of nucleus pulposus. METHODS.: Herniation of nucleus pulposus was created in the L4-L5 disc in rats. The L4 DRG were resected 3 and 24 hours after surgery. The sections of the specimens were observed using light and electron microscopy. The sections were processed for immunohistochemistry using antibodies to single-stranded DNA (ssDNA), caspase 3, and tumor necrosis factor alpha (TNF).

RESULTS

There were typical changes of the cell nuclei observed by light and electron microscopy, especially those of the small-sized cells, in the DRG 24 hours after application of nucleus pulposus, indicating the presence of apoptosis. The presence of ssDNA, caspase 3, and TNF further enhanced the impression that there was apoptosis in the DRG. Nucleus pulposus induced apoptosis in the DRG at the site of application within as little as 24 hours.

CONCLUSIONS

Nucleus pulposus herniated from the disc induced apoptosis in at the surface of the DRG exposed to nucleus pulpous as early as 24 hours after exposure.

Up-regulation of niacinamide in intervertebral disc aggrecanin vitro

The regulatory effects of niacinamide (Nia) on intervertebral disc (IVD) aggrecan in vitro was investigated. Chiba's 10 ng/mL interleukin-1 (IL-1)-induced rabbit IVD degeneration model in vitro was established. 0.5, 0.25 and 0.05 mg/mL Nia was added to normal and degenerated IVDs for intervention. On the first and second week after intervention, safranin O-fast green staining intensity and glycosaminoglycan (GS) content were measured. The expression of aggrecan core protein was detected by RT-PCR. The results showed: (1) After treatment with 0.5 mg/mL Nia for one week, the GS content in nucleus pulposus (NP) was increased by 44.8% as compared with control group (P < 0 01); The GS content in IL-1 induction groups was increased with the increase of Nia concentrations: After treatment with 0.5 mg/mL for one week, the GS content in NP was increased by 68.3% as compared with control group (P < 0.01). After two weeks, GS content in NP and fibrous rings was still higher than in control group at the same period (P < 0.01) and untreated group (P < 0.01). (2) Safranin O-fast green staining revealed that with the increase of Nia concentrations, staining density in NP and fibrous rings was increased and histological structure damage to IVDs by IL-1beta was alleviated. (3) RT-PCR showed that the expression of core protein gene in IL-1beta-induced degenerated IVDS was increased with the increase of Nia concentrations. It was concluded that under conditions in vitro, Nia could up-regulate the expression of aggrecan in IVDs and protect IVDs from IL-1beta-induced degeneration at least partially, which offers a potential choice for IVD degeneration clinical therapy.

Coordinate expression of BMP-2, BMP receptors and Noggin in normal mouse spine

The purpose of this study was to determine the localization of bone morphogenetic protein-2 (BMP-2), BMP receptors (BMPRs) and Noggin in mouse spinal tissues. The coordinate expression of these positive and negative regulators of BMP signaling may elucidate regulatory mechanisms for bone induction in the spine. Whole spines from 3-week-old mice were used and the spatial expression profiles of BMP-2, BMPR-1a, -1b, -2 and Noggin were examined using in situ hybridization. BMP-2, BMPR-1b and -2 were observed in bone marrow cells in the vertebrae, chondrocytes, hyaline cartilage cells and fibrous cells in the intervertebral discs and neurons of the spinal cord in the entire spine. BMPR-1a was also observed in these cells, but only in the cervical spine. Noggin was expressed in bone marrow cells in the vertebrae, chondrocytes and hyaline cartilage cells and fibrous cells in the intervertebral discs in the entire spine and in neurons in the spinal cord in the cervical and thoracic regions. Noggin was also expressed in the anterior longitudinal, posterior longitudinal and yellow ligaments in the cervical spine, and in the fibrous cells in the anterior longitudinal and yellow ligaments of the lumbar spine.

Effects of cyclic mechanical stress on the production of inflammatory agents by nucleus pulposus and anulus fibrosus derived cells in vitro

STUDY DESIGN

Cyclic mechanical stress (CMS) was applied to cultured nucleus pulposus and anulus fibrosus cells, and the production of inflammatory agents by these cells was evaluated.

OBJECTIVE

To investigate the involvement of CMS in the production of inflammatory agents by disc cells.

SUMMARY OF BACKGROUND DATA

It has been reported that CMS affects degeneration of the disc. However, little is known about the effect of CMS on the production of inflammatory agents by both cell types in vitro.

METHODS

Cells derived from nucleus pulposus and anulus fibrosus of Sprague-Dawley rat tails were cultured with or without CMS applied by the Flexercell Strain Unit (Flexcell International Corp., Hillsborough, NC) in the presence or absence of inflammatory stimulus. Doses of prostaglandin-E2 (PGE2) were measured in the culture supernatants. Semiquantitative evaluations of the expressions of cyclooxygenase (COX)-2 and phospholipase-A2 IIA messenger ribonucleic acids (mRNAs) were also examined.

RESULTS

Sole application of CMS on nucleus pulposus and anulus fibrosus cells increased PGE2 synthesis. Coincidence of CMS and inflammatory stimulus synergistically enhanced PGE2 synthesis of both cell types. Anulus fibrosus cells showed a stronger reactivity to these stimuli than nucleus pulposus cells. The expression of COX-2 mRNA of anulus fibrosus cells tended to correlate to the amount of PGE2, whereas COX-2 mRNA was constitutively expressed in nucleus pulposus cells, suggesting that the roles of COX-2 might be different between nucleus pulposus and anulus fibrosus. Phospholipase-A2 IIA mRNA was constitutively expressed in both cell types.

CONCLUSIONS

The results of this study suggested that CMS might be involved in the pathomechanism of pain induction of lumbar disc diseases.

Alterations in biochemical components of extracellular matrix in intervertebral disc herniation: role of MMP-2 and TIMP-2 in type II collagen loss

Alterations in the composition of intervertebral disc extracellular matrix, mainly collagen and proteoglycans, may cause changes in mechanical properties of the disc, leading to dysfunction, nerve root compression, and herniation with severe clinical manifestations. Matrix metalloproteinases may be involved in degradation by hydrolysing extracellular matrix components. Inhibitors of matrix metalloproteinases, in contrast, function in the maintenance of degradation control. In this study, we investigated: (i) whether the level of matrix degradation correlated with the duration of the symptomatic disease, (ii) roles of matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) in intervertebral disc degeneration. Nucleus pulposus of intervertebral discs were obtained from 22 patients and analysed for collagen and proteoglycan contents, and pro-MMP-2, TIMP-2 levels. Collagen content was determined as hydroxyproline and proteoglycan content was measured as glycosaminoglycans. The loss in matrix components did not correlate with the duration of the degenerative disc disease. Pro-MMP-2 levels were higher at early stages of the degenerative disc disease (r = -0.495, P < 0.05). TIMP-2 levels were similar in all samples. Pro-MMP-2 and TIMP-2 levels negatively correlated in herniated discs samples (r = -0.855, P < 0.01). Pro- MMP-2 levels negatively correlated with the collagen content in herniated disc material. Our findings may suggest a silent period of active disease prior to symptomatic outcome during which irreversible matrix loss occurs. Involvement of other proteolytic enzymes at different stages of the disease should also be investigated to help to control the degradation cascade at relatively early stages of disc degeneration before the clinical onset of disease.

Nucleus pulposus cells express HIF-1α under normoxic culture conditions: A metabolic adaptation to the intervertebral disc microenvironment

Nucleus pulposus (NP) cells of the intervertebral disc reside in an environment that has a limited vascular supply and generate energy through anaerobic glycolysis. The goal of the present study was to examine the expression and regulation of HIF-1alpha, a transcription factor that regulates oxidative metabolism in nucleus pulposus cells. Nucleus pulposus cells were isolated from rat, human, and sheep disc and maintained at either 21% or 2% oxygen for various time periods. Cells were also treated with desferrioxamine (Dfx), a compound that mimics the effects of hypoxia (Hx). Expression and function of HIF-1alpha were assessed by immunofluorescence microscopy, Western blot analysis, gel shift assays, and luciferase reporter assays. In normoxia (Nx), rat, sheep, and human nucleus pulposus cells consistently expressed the HIF-1alpha subunit. Unlike other skeletal cells, when maintained under low oxygen tension, the nucleus pulposus cells exhibited a minimal induction in HIF-1alpha protein levels. Electromobility shift assays confirmed the functional binding of normoxic HIF-1alpha protein to its putative DNA binding motif. A dual luciferase reporter assay showed increased HIF-1alpha transcriptional activity under hypoxia compared to normoxic level, although this induction was small when compared to HeLa and other cell types. These results indicate that normoxic stabilization of HIF-1alpha is a metabolic adaptation of nucleus pulposus cells to a unique oxygen-limited microenvironment. The study confirmed that HIF-1alpha can be used as a phenotypic marker of nucleus pulposus cells.

Morphologic comparison of cervical, thoracic, lumbar intervertebral discs of cynomolgus monkey (Macaca fascicularis)

The aim was to analyze the morphological differences of the intervertebral disc and endplates at different levels. Forty-five vertebral motion segments were obtained from the spine of nine 3 to 4-year-old cynomolgus monkeys (Macaca fascicularis). From every spine, five discs were sectioned (C5-C6, T3-T4, T9-T10, L2-L3, L4-L5). In all the groups, tissue samples were collected and sections were stained with Masson's trichrome, Safranine-O and van Gieson's connective tissue stain to analyze the intervertebral discs. Immunohistochemistry was performed, using specific antibodies to detect collagens I and II. The intervertebral disc height, the maximum nucleus pulposus height, the superior and inferior endplate heights were histomorphometrically measured and different indexes were calculated to compare the differences between specimens of the same animal and between discs of the same level, and finally the differences between groups of discs of different levels. There were no differences existing in annular fibers anchoring on the endplate between discs of different levels. A positive immune reaction for type I collagen was observed in the longitudinal ligaments and in the annular region adjacent to them. Collagen II immune reactivity was found in the annulus close to the nucleus pulposus, in the endplates and in the nucleus. There were no differences between discs of different levels in the collagen I and II localization. The height of the discs varied along the spine. The smallest value was measured in T3-T4, with a larger increase caudally than cranially. The highest value was measured in L2-L3. A cervical disc was 55% the height of a lumbar one. The endplate height increased along the length of the spine. The inferior EP was always higher than the superior. The study provides a detailed structural characterization of the intervertebral disc and may be useful for further investigations on the disc degeneration process.

An immunohistochemical evaluation of extracellular matrix components in the spinal posterior longitudinal ligament and intervertebral disc of the tiptoe walking mouse

Ossification of the posterior longitudinal ligament (OPLL) in the spine is caused by systemic and/or regional factors affecting the regulation of osteocartilaginous formation and maintenance. The aims of this study were to elucidate the relationship between the degeneration of the intervertebral discs and changes in the posterior longitudinal ligament (PLL) in the tiptoe walking (ttw) mouse, an animal model of OPLL, and to analyze the sequential changes of the cells producing extracellular matrix components using immunohistochemical methods. At 6 weeks of age, the discs degenerated and the chondrocytes in the nucleus pulposus were positive for chondroitin-6-sulfate in the ttw mice. The fibroblasts in the PLL at the disc level were positively stained with type II and XI collagens. At 14 weeks, the discs herniated into the thickened PLL, and chondrocyte-like cells appeared in the PLL at vertebral endplate level. At 18 and 22 weeks, the number of chondrocyte-like cells increased in the PLL and expressed type I collagen. A potent regional factor causing OPLL in the ttw mice appears to be the initial degeneration and subsequent herniation of the nucleus pulposus. These sequential changes in the ttw mice were accelerated by administration of etidronate. It was suggested that etidronate stimulated the cartilaginous hyperplasia in the PLL of the ttw mice. It appeared as if the PLL transformed itself into cartilaginous tissue to repair the degeneration of the intervertebral disc.

Evaluation of the relationship between inducible nitric oxide synthase (iNOS) activity and effects of melatonin in experimental osteoporosis in the rat

Inducible nitric oxide synthase (iNOS) plays a critical role in the pathogenesis of osteoporosis. iNOS generates nitric oxide (NO), a free radical contributing to the imbalance between bone formation and resorption caused by estrogen depletion. Melatonin is the major product of the pineal gland which is known to diminish iNOS expression and NO production significantly. The aim of this study was to determine the distribution of iNOS and the amount of apoptotic cells after melatonin treatment in ovariectomized rats. Since previous studies have shown that constitution of bone formation is primarily sustained in nucleus pulposus and epiphyseal cartilage, experiments were carried out on nucleus pulposus and epiphyseal cartilage; additional quantitation of osteoblasts and osteoclasts were evaluated on vertebral area as well. Vertebral sections of ovariectomized rats were obtained from formalin-fixed and parafin-embedded blocks. iNOS expression and quantitation of apoptotic cells in nucleus pulposus and epiphyseal cartilage were evaluated using indirect immunoperoxidase and TUNEL techniques, respectively. The number of osteoclasts and osteoblasts in trabecular bone was determined using histomorphometry. Ovariectomy increased iNOS expression and the number of apoptotic cells in nucleus pulposus and epiphyseal cartilage, whereas a 4-week treatment with melatonin (10 mg/kg/day) resulted in the reduction of both effects. These data indicate that there is strong influence of melatonin application on expression of iNOS, apoptosis, osteoclast and osteoblast numbers after ovariectomy. In conclusion, melatonin besides its usual use as an antiaging hormone, may also be an effective hormone in treatment of bone changes in estrogen deficiency states.

Expression of receptors for putative anabolic growth factors in human intervertebral disc: implications for repair and regeneration of the disc

Low back pain (LBP) is a common, debilitating and economically important disorder. Current evidence implicates loss of intervertebral disc (IVD) matrix consequent upon 'degeneration' as a major cause of LBP. Degeneration of the IVD involves increases in degradative enzymes and decreases in the extracellular matrix (ECM) component in a process that is controlled by a range of cytokines and growth factors. Studies have suggested using anabolic growth factors to regenerate the normal matrix of the IVD, hence restoring disc height and reversing degenerative disc disease. However, for such therapies to be successful it is vital that the target cells (i.e. the disc cells) express the appropriate receptors. This immunohistochemical study has for the first time investigated the expression and localization of four potentially beneficial growth factor receptors (i.e. TGFbetaRII, BMPRII, FGFR3 and IGFRI) in non-degenerate and degenerate human IVDs. Receptor expression was quantified across regions of the normal and degenerate disc and showed that cells of the nucleus pulposus (NP) and inner annulus fibrosus (IAF) expressed significantly higher levels of the four growth factor receptors investigated. There were no significant differences between the four growth factor expression in non-degenerate and degenerate biopsies. However, expression of TGFbetaRII, FGFR3 and IGFRI, but not BMP RII, were observed in the ingrowing blood vessels that characterize part of the disease aetiology. In conclusion, this study has demonstrated the expression of the four growth factor receptors at similar levels in the chondrocyte-like cells of the NP and IAF in both non-degenerate and degenerate discs, implicating a role in normal disc homeostasis and suggesting that the application of these growth factors to the degenerate human IVD would stimulate matrix production. However, the expression of some of the growth factor receptors on ingrowing blood vessels might be problematic in a therapeutic approach.

CD24 is expressed specifically in the nucleus pulposus of intervertebral discs

Intervertebral disc (IVD) consists of a soft gelatinous material in its center, the nucleus pulposus (NP), bounded peripherally by fibrocartilage, annulus fibrosus (AF). Despite the number of patients with IVD degeneration, gene expression analysis has not been undertaken in NP and therefore little is known about the molecular markers expressed in NP. Here, we undertook a microarray screen in NP with the other nine tissues to identify the specific cell surface markers for NP. Five membrane associating molecules out of 10,490 genes were identified as highly expressing genes in NP compared with the other tissues. Among them, we identified CD24, a glycosylphosphatidylinositol (GPI) anchor protein as a cell surface marker for NP. CD24 expression was also detected in the herniated NP and chordoma, a malignant primary tumor derived from notochordal cells, while it was absent in chondrosarcoma. Therefore, CD24 is a molecular marker for NP as well as the diseases of IVD.

Correlation of HR-MAS spectroscopy derived metabolite concentrations with collagen and proteoglycan levels and Thompson grade in the degenerative disc

STUDY DESIGN

A quantitative high-resolution magic angle spinning (HR-MAS) NMR study of human lumbar discs was conducted to determine biomarkers of disc degeneration.

OBJECTIVES

To correlate HR-MAS quantification of compounds relevant to human lumbar disc degeneration to conventional methods of disc grading such as Thompson grading and biochemical analysis.

SUMMARY OF BACKGROUND DATA

It has been shown that there is poor correlation between MRI and CT morphologic findings, spinal biomechanics, and patient symptoms in degenerative disc disease and low back pain. There is a need for an objective, quantitative measurement of biochemical status, morphology, and function.

METHODS

A total of 17 cadaveric human lumbar intervertebral discs were harvested from patients ranging from 20 to 85 years of age. Quantitative HR-MAS data were acquired, and proteoglycan and collagen biochemical analyses were conducted on 3-mm biopsy punches taken from the anulus fibrosus and nucleus pulposus of each sample. HR-MAS data were fitted and analyzed for hydroxyproline (3.42 ppm), glycine (3.56 ppm), and the N-acetyl peak (2.04 ppm) associated with proteoglycans in comparison with an internal standard. These concentrations were then compared directly to biochemical analyses and Thompson grade.

RESULTS

HR-MAS data correlated well with Thompson grade (P < 0.001). An increase was seen in the levels of unbound hydroxyproline and glycine in annular tissue, which is directly associated to collagen breakdown. This trend also correlates with the changes of total collagen measured by a collagen biochemical assay. HR-MAS also detected a decrease in concentration of nucleus pulposus proteoglycans with degeneration. This proteoglycan decrease was verified by a standard proteoglycan biochemical assay.

CONCLUSIONS

Changes in disc chemical composition can be accurately quantified using quantitative HR-MAS NMR spectroscopy ex vivo. This noninvasive method of qualitatively and quantitatively assessing disc degeneration supports the utility of these biomarkers and underlines the need for developing in vivo magnetic resonance spectroscopic imaging (MRSI) for characterizing intervertebral disc degeneration.

[Effects of yiqi huayu recipe and its decomposed formulas on apoptosis-related factors of anulus fibrosus cells in rats]

OBJECTIVE

To study the effects of Yiqi Huayu Recipe and its decomposed formulas-medicated sera on expressions of bcl-2, Bax and caspase-8 of apoptotic anulus fibrosus cells in rats.

METHODS

Immunohistochemical and integral optical density analytic methods were used to observe the effects of Yiqi Huayu Recipe-, Yiqi Recipe-, Huayu Recipe-medicated sera and insulin-like growth factor 1 (IGF-1) on the expressions of bcl-2, Bax and caspase-8 of apoptotic anulus fibrosus cells in rats induced by anti-Fas antibody.

RESULTS

As compared with apoptosis group, bcl-2 expression was higher, Bax and caspase-8 expressions were lower in Yiqi Huayu-treated, Yiqi-treated, Huayu-treated and IGF-1 groups (P<0.01). As compared with Yiqi-treated group and Huayu-treated group, Bax expression was lower in Yiqi Huayu-treated group (P<0.05).

CONCLUSION

Yiqi Huayu Recipe and its decomposed formulas can delay degeneration of the cervical intervertebral disc, which may be due to its action in regulating the expressions of bcl-2, Bax and caspase-8.

Exposure to pulsed low intensity ultrasound stimulates extracellular matrix metabolism of bovine intervertebral disc cells cultured in alginate beads

STUDY DESIGN

In vitro study on the effects of pulsed low intensity ultrasound on the cellular metabolism of bovine intervertebral disc cells.

OBJECTIVE

To determine whether pulsed low intensity ultrasound has effects on cell proliferation and extracellular matrix metabolism by bovine intervertebral disc cells.

SUMMARY OF BACKGROUND DATA

The application of pulsed low intensity ultrasound is known to be effective in stimulating fracture and cartilage repair. However, the effects of pulsed low intensity ultrasound on intervertebral disc cells are not known.

METHODS

Cells of the nucleus pulposus and inner and outer anulus fibrosus were enzymatically isolated from bovine coccygeal tissue and precultured in alginate beads for 14 days. In the ultrasound group, pulsed low intensity ultrasound was administered to the culture for 20 minutes daily for an additional 20 days. The control group was cultured in the same way but without administration of ultrasound. Cell viability, DNA content, proteoglycan and collagen synthesis, and proteoglycan content at days 10 and 20 after the initiation of treatment were evaluated. Characterization of newly synthesized collagen and proteoglycan was performed.

RESULTS

No significant differences in cell viability and DNA content were observed between the two groups. On day 20, proteoglycan synthesis was increased by the application of pulsed low intensity ultrasound in nucleus pulposus and inner and outer anulus fibrosus cells (24%-26% increase, P < 0.001). The application of pulsed low intensity ultrasound increased proteoglycan content in alginate beads containing inner and outer anulus fibrosus cells (P < 0.05). Collagen synthesis by cells isolated from all three zones of the intervertebral disc was increased by the application of pulsed low intensity ultrasound (16%-19% increase, P < 0.05-0.0001).

CONCLUSIONS

The application of pulsed low intensity ultrasound stimulated extracellular matrix metabolism in intervertebral disc cells. Pulsed low intensity ultrasound may prove useful for the physical stimulation of cell metabolism for tissue engineering of intervertebral disc tissue.

Intrinsically radiopaque hydrogels for nucleus pulposus replacement

Degeneration of the intervertebral disc is the most common cause of back pain. In case of early stage degenerative disc disease or traumatic herniations, a suitable treatment may be to replace the nucleus pulposus, preserving the annulus fibrosus. Eight new hydrogel biomaterials were prepared and studied for their potential as a nucleus replacement. The hydrogels were designed according to the following criteria: (i), they should exhibit adequate radiopacity; (ii), they should be non-cytotoxic; (iii), implantation in the dry state and subsequent swelling in situ to fill the entire nucleus cavity; (iv), after swelling they should match the physical-mechanical properties of the native nucleus. The approach was to use copolymers consisting of 2-(4'-iodobenzoyl)-oxo-ethyl methacrylate (4IEMA) and a hydrophilic building block (either N-vinyl-2-pyrrolidinone (NVP) or 2-hydroxyethyl methacrylate (HEMA)); 4 copolymers of NVP/4IEMA and 4 copolymers of HEMA/4IEMA in different compositions (5, 10, 15 and 20 mol% 4IEMA). The study comprised 1H-NMR analysis of the copolymerization reaction NVP+4IEMA. Furthermore, the copolymers were studied with respect to their swelling behavior, mechanical properties, cytotoxicity in vitro and X-ray contrast. Hydrogels with 5 mol% 4IEMA appear to meet all criteria: they are non-cytotoxic, have adequate physical-mechanical properties and feature sufficient radiopacity in a realistic model. The potential implications of these new results with respect to treatment of degenerative disc disease are discussed briefly.

Effects of lumbar sympathectomy on pain behavioral changes caused by nucleus pulposus-induced spinal nerve damage in rats

It has been suggested that lumbar sympathectomy can reduce pain behavior, including mechanical allodynia and thermal hyperalgesia, caused by ligation of the spinal nerve. One well-characterized model, which involves application of nucleus pulposus to the spinal nerve and displacement of the adjacent nerve, shows behavioral changes in rats. However, there have been no previous reports regarding sympathectomy performed in this model. Disk incision and adjacent spinal nerve displacement were performed with (n=6) or without (n=6) sympathectomy. Sham surgery was also performed with (n=6) or without (n=6) sympathectomy. The animals were tested for 3 days before surgery and on days 1, 3, 7, 14, and 21 after surgery. Non-noxious mechanical thresholds were tested by determining the hind paw withdrawal response to von Frey hair stimulation of the plantar surface of the footpad using a touch stimulator. Thermal nociceptive thresholds were tested using a sensitive thermal-testing device. While rats in the disk incision with displacement surgery group showed allodynia and hyperalgesia after surgery on the experimental side, sympathectomized animals did not. No allodynia was observed in the sham groups. Sympathectomy seemed to prevent the pain behavioral changes caused by the combination of disk incision and nerve displacement.

Flow-related mechanics of the intervertebral disc: the validity of an in vitro model

STUDY DESIGN

An in vitro mechanical study on porcine motion segments.

OBJECTIVES

To test the validity of in vitro studies of the flow-related mechanics of the intervertebral disc and, in particular, to investigate whether fluid flows back into the disc during unloading after a loading cycle.

SUMMARY OF BACKGROUND DATA

In vivo studies show both the inflow and outflow of fluid in the intervertebral disc. The resistance to flow out of the disc is higher than to inflow. The fluid flow is regulated via unbalance between the external load and the osmotic pressure of the nucleus pulposus.

MATERIALS

There were 8 porcine lumbar motion segments (without posterior elements) and 8 isolated discs tested in a physiologic saline bath (39 degrees C). The specimens were preloaded at 0.025 MPa for 15 minutes. Three 15-minute loading periods at 2.0 MPa were applied, each followed by an unloading period of 30 minutes. Loads, axial displacements, and nucleus pressure were recorded online.

RESULTS

Over the 3 loading and unloading periods, all specimens showed a net loss of height and mass. The time series of specimen height during the 3 unloading periods showed virtually identical responses. The pressure in the nucleus decreased in the subsequent loading periods and showed no increase during unloading.

CONCLUSION

The data show the limitations of an in vitro model for studying fluid flow-related intervertebral disc mechanics. During loading, outflow of fluid occurred, but inflow appears to be virtually absent during unloading. Poro-elastic behavior cannot be reproduced in an in vitro model.

Effects of Ge Gen Decoction on PGE2 content and COX activity in the degenarated cervical intervertebral discs of rats

After the rat model of cervical spondylosis was developed for 6 months, the PGE2 content and COX activity in the cervical intervertebral discs were determined respectively by radioimmunoassay and catalytic activity assay. The results indicated that the PGE2 content and COX activity in the model rat increased significantly, and that Ge Gen Decoction could down-regulate the PGE2 content and inhibit COX activity. This is possibly one of the mechanisms of Ge Gen Decoction for treating cervical spondylosis.

Tumor necrosis factor-alpha modulates matrix production and catabolism in nucleus pulposus tissue

STUDY DESIGN

This study examines changes in the production of extracellular matrix molecules as well as the induction of tissue degradation in in vitro formed nucleus pulposus (NP) tissues following incubation with tumor necrosis factor (TNF)alpha.

OBJECTIVE

To characterize the response of NP cells to TNF-alpha, a proinflammatory cytokine present in herniated NP tissues.

SUMMARY OF BACKGROUND DATA

TNF-alpha is a proinflammatory cytokine expressed by NP cells of degenerate intervertebral discs. It is implicated in the pain associated with disc herniation, although its role in intervertebral disc degeneration remains poorly understood.

METHODS

In vitro formed NP tissues were treated with TNF-alpha (up to 50 ng/mL) over 48 hours. Tissues were assessed for histologic appearance, proteoglycan and collagen contents, as well as proteoglycan and collagen synthesis. Reverse transcriptase polymerase chain reaction was used to determine the effect of TNF-alpha on NP cell gene expression. Proteoglycan degradation was assessed by immunoblot analysis.

RESULTS

At doses of 1-5 ng/mL, TNF-alpha induced multiple cellular responses, including: decreased expression of both aggrecan and type II collagen genes; decreases in the accumulation and overall synthesis of aggrecan and collagen; increased expression of MMP-1, MMP-3, MMP-13, ADAM-TS4, and ADAM-TS5; and induction of ADAM-TS dependent proteoglycan degradation. Within 48 hours, these cellular responses resulted in NP tissue with only 25% of its original proteoglycan content.

CONCLUSIONS

Because low levels of TNF-alpha, comparable to those present physiologically, induced NP tissue degradation, this suggests that TNF-alpha may contribute to the degenerative changes that occur in disc disease.

Osteogenic protein-1 (osteogenic protein-1/bone morphogenetic protein-7) inhibits degeneration and pain-related behavior induced by chronically compressed nucleus pulposus in the rat

STUDY DESIGN

To study the therapeutic efficacy of intradiscal injection of osteogenic protein-1 (OP-1) to reduce degeneration and associated discogenic pain.

OBJECTIVE

To evaluate if intradiscal injection of OP-1 can reverse disc degeneration and reduce hyperalgesia, a pain-related behavior.

SUMMARY OF BACKGROUND DATA

We showed that induction of hyperalgesia was higher in rats exposed to compressed nucleus pulposus (NP). It has been reported that intradiscal injection of OP-1 stimulates synthesis of proteoglycans and collagen in normal intervertebral discs.

METHODS

Rats were divided into several groups. In the sham group, the rings of an Ilizarov-type apparatus were only applied to the tail without compression. In the compressed NP group, the apparatus was used to apply chronically compression to the tail. Four weeks after surgery, the NP group was subdivided into 3 groups: saline-treated and OP-1-treated, which was divided into 2 groups (i.e., the continuous compression OP-1 [COP-1] group, in which compression was continuously applied to the tail for 4 weeks after OP-1 treatment and the release compression OP-1 [ROP-1] group, in which compression was released at treatment. Either physiologic saline or OP-1 was injected into the instrumented NP. The treated NP was harvested and applied to the left lumbar nerve roots 4 weeks after injection. Hyperalgesia was measured up to 3 weeks after surgery. The degree of disc degeneration and the appearance of the extracellular matrix in the intervertebral discs were evaluated by histology.

RESULTS

Mechanical hyperalgesia was observed in the sham and saline groups, but not in the OP-1 treated group. In the saline group, NP cells became spindle-shaped. In the OP-1 group, the NP cells became swollen with vacuolated cytoplasm, and the content of the extracellular matrix was markedly increased.

CONCLUSION

OP-1 injection into degenerative intervertebral disc resulted in the enhancement of the extracellular matrix and the inhibition of pain-related behavior.

Advanced glycation end products in intervertebral discs and hip joint capsules: correlation with senile amyloid?

Advanced glycation end-products (AGEs) may be involved in either amyloidogenesis or complications related to amyloid. The incidence of AGE increases with age as does the prevalence of amyloid affecting the hip joint capsule and intervertebral discs. We hypothesized that AGEs may be involved in the pathology of these amyloidoses and investigated the spatial and temporal relationship between AGEs and amyloid of intervertebral discs and hip joint capsules. Using immunohistochemistry, AGEs were found in all 71 intervertebral discs and all 87 hip joint capsules. Amyloid was present in 59 (83%) intervertebral discs and 65 (75%) hip joint capsules. AGEs were found in the immediate vicinity of amyloid deposits in 104 of 253 (41%) investigated amyloid deposits of the intervertebral discs and 159 of 311 (51%) investigated amyloid deposits of the hip joint capsules. However, only rarely were AGEs demonstrated within amyloid deposits. No linear correlation was found between the amount of AGEs and the amount of amyloid deposited. As AGEs are more common than amyloid in intervertebral discs and hip joint capsules, it is conceivable to suggest that AGEs might be involved in the pathogenesis of amyloid at these anatomical sites. However, the amyloid proteins appear not to be modified and AGE modification is not a general characteristic of senile amyloidoses.