A rat model for chronic spinal nerve root compression

Quercetin relieves compression-induced cell death and lumbar disc degeneration by stabilizing HIF1A protein

Background

Lumbar disc degeneration (LDD) is a prevalent condition characterized by the decreased viability and functional impairment of nucleus pulposus mesenchymal stem cells (NPMSCs). Shaoyao-Gancao decoction (SGD), a traditional Chinese medicine formula, has been used to treat LDD, but its active components and mechanisms are unclear.

Methods

An integrative network pharmacology and transcriptome analysis were conducted to identify bioactive compounds in SGD that could target LDD. NPMSCs were cultured under mechanical compression as a cellular model of LDD. A rat model of annulus fibrosus needle-puncture was established to induce intervertebral disc degeneration. The effects of quercetin, a predicted active component, on alleviating compression-induced NPMSC death and LDD were evaluated in vitro and in vivo.

Results

The analysis identified hypoxia-inducible factor 1-alpha (HIF1A) as a potential target of quercetin in LDD. HIF1A was upregulated in degenerated human disc samples and compression-treated NPMSCs. Quercetin treatment alleviated compression-induced oxidative stress, apoptosis, and loss of viability in NPMSCs by stabilizing HIF1A. The protective effects of quercetin were abrogated by HIF1A inhibition. In the rat model, quercetin ameliorated intervertebral disc degeneration.

Conclusion

Our study identified HIF1A as a protective factor against compression-induced cell death in NPMSCs. Quercetin, a bioactive compound found in the traditional Chinese medicine formula SGD, improved the survival of NPMSCs and alleviated LDD progression by stabilizing HIF1A. Targeting the HIF1A pathway through natural compounds like quercetin could represent a promising strategy for the clinical management of LDD and potentially other degenerative disc diseases.

A closed-body preclinical model to investigate blast-induced spinal cord injury

Blast-induced spinal cord injuries (bSCI) are common and account for 75% of all combat-related spinal trauma. It remains unclear how the rapid change in pressure contributes to pathological outcomes resulting from these complex injuries. Further research is necessary to aid in specialized treatments for those affected. The purpose of this study was to develop a preclinical injury model to investigate the behavior and pathophysiology of blast exposure to the spine, which will bring further insight into outcomes and treatment decisions for complex spinal cord injuries (SCI). An Advanced Blast Simulator was used to study how blast exposure affects the spinal cord in a non-invasive manner. A custom fixture was designed to support the animal in a position that protects the vital organs while exposing the thoracolumbar region of the spine to the blast wave. The Tarlov Scale and Open Field Test (OFT) were used to detect changes in locomotion or anxiety, respectively, 72 h following bSCI. Spinal cords were then harvested and histological staining was performed to investigate markers of traumatic axonal injury (β-APP, NF-L) and neuroinflammation (GFAP, Iba1, S100β). Analysis of the blast dynamics demonstrated that this closed-body model for bSCI was found to be highly repeatable, administering consistent pressure pulses following a Friedlander waveform. There were no significant changes in acute behavior; however, expression of β-APP, Iba1, and GFAP significantly increased in the spinal cord following blast exposure (p < 0.05). Additional measures of cell count and area of positive signal provided evidence of increased inflammation and gliosis in the spinal cord at 72 h after blast injury. These findings indicated that pathophysiological responses from the blast alone are detectable, likely contributing to the combined effects. This novel injury model also demonstrated applications as a closed-body SCI model for neuroinflammation enhancing relevance of the preclinical model. Further investigation is necessary to assess the longitudinal pathological outcomes, combined effects from complex injuries, and minimally invasive treatment approaches.

Glutamatergic systems in neuropathic pain and emerging non-opioid therapies

Neuropathic pain, a disease of the somatosensory nervous system, afflicts many individuals and adequate management with current pharmacotherapies remains elusive. The glutamatergic system of neurons, receptors and transporters are intimately involved in pain but, to date, there have been few drugs developed that therapeutically modulate this system. Glutamate transporters, or excitatory amino acid transporters (EAATs), remove excess glutamate around pain transmitting neurons to decrease nociception suggesting that the modulation of glutamate transporters may represent a novel approach to the treatment of pain. This review highlights and summarizes (1) the physiology of the glutamatergic system in neuropathic pain, (2) the preclinical evidence for dysregulation of glutamate transport in animal pain models, and (3) emerging novel therapies that modulate glutamate transporters. Successful drug discovery requires continuous focus on basic and translational methods to fully elucidate the etiologies of this disease to enable the development of targeted therapies. Increasing the efficacy of astrocytic EAATs may serve as a new way to successfully treat those suffering from this devastating disease.

A double-network hydrogel for the dynamic compression of the lumbar nerve root

Current animal models of nerve root compression due to lumbar disc herniation only assess the mechanical compression of nerve roots and the inflammatory response. Moreover, the pressure applied in these models is static, meaning that the nerve root cannot be dynamically compressed. This is very different from the pathogenesis of lumbar disc herniation. In this study, a chitosan/polyacrylamide double-network hydrogel was prepared by a simple two-step method. The swelling ratio of the double-network hydrogel increased with prolonged time, reaching 140. The compressive strength and compressive modulus of the hydrogel reached 53.6 and 0.34 MPa, respectively. Scanning electron microscopy revealed the hydrogel’s crosslinked structure with many interconnecting pores. An MTT assay demonstrated that the number of viable cells in contact with the hydrogel extracts did not significantly change relative to the control surface. Thus, the hydrogel had good biocompatibility. Finally, the double-network hydrogel was used to compress the L4 nerve root of male sand rats to simulate lumbar disc herniation nerve root compression. The hydrogel remained in its original position after compression, and swelled with increasing time. Edema appeared around the nerve root and disappeared 3 weeks after operation. This chitosan/polyacrylamide double-network hydrogel has potential as a new implant material for animal models of lumbar nerve root compression. All animal experiments were approved by the Animal Ethics Committee of Neurosurgical Institute of Beijing, Capital Medical University, China (approval No. 201601006) on July 29, 2016.

Neurological function following early versus delayed decompression surgery for drop foot caused by lumbar degenerative diseases

The purpose of this study was to investigate the effectiveness of early (<72 h) versus late (≥72 h) decompression surgery after the onset of drop foot caused by root disorder in lumbar degenerative diseases (LDDs). Data were included from 60 patients who underwent decompression surgery for drop foot caused by LDDs, including lumbar disk herniation or lumbar spinal stenosis. The primary outcome was ordinal change in the manual muscle test (MMT) at 2 years follow-up. Secondary outcomes included changes in the Japanese Orthopedic Association's (JOA) score. The early- and late-stage surgery groups included 20 and 40 patients with mean durations from the onset of drop foot to operation of 0.8 days (range, 0-3 days) and 117.1 days (range, 10-891 days), respectively. There was no significant difference (p = 0.33) between the early- and late-stage surgery groups in the improvement of MMT scores to >4 (90% versus 80%, respectively). However, more patients in the early-stage group achieved an MMT score >5 compared with those in the late-stage surgery group (80% versus 45%; p = 0.03). Furthermore, the recovery rate of JOA scores was significantly higher in the early-stage (89.1%) compared with the late-stage surgery group (68.6%; p < 0.001). Early decompression surgery produced better neurological recovery; however, an improvement of >4 in the MMT score was achieved in 80% of cases with late decompression.

Novel compression rat model for developmental spinal stenosis

Developmental spinal stenosis (DSS) is characterized by pre-existing circumferential narrowing of the bony spinal canal which predisposes neural tissue to compression. This study aims to create a reproducible animal model mimicking DSS for investigation of its pathoanatomy. Developmental spinal canal constriction was simulated using circumferential compression. Eighteen female Sprague-Dawley rats (13.0-14.5 weeks-old) underwent circumferential compression at L4-L5 using silicone sheets; or dorsal compression using overlapping silicone sheets; or as controls. A series of outcome scores were used for locomotor function assessment, together with electrophysiological and histological assessment. Assessment time-points were at preoperative, postoperative 1-week, 2-weeks, 3-weeks, 1-month, and pre-sacrifice. Statistical analyses were performed. At all postoperative time-points, circumferential group had the worst mean Basso, Beattie and Bresnahan locomotor scores with significant difference from the control group (p < 0.05), as well as the lowest mean Louisville Swim Scale scores, as compared to the dorsal (p < 0.05) and to the control (p < 0.01) groups. Circumferential group had worse mean foot fault score for both hindlimbs (p < 0.01 to p < 0.05) and highest error rate in foot placement accuracy, especially higher than dorsal (p < 0.05) and control (p < 0.05) groups at pre-sacrifice. Electrophysiological assessment revealed postoperative increase in P1 latency was higher in circumferential than dorsal compression. Highest postoperative mean P1 latency was observed for both paws at all postoperative time-points for circumferential group (except at postoperative 1-week). Circumferential group had lower myelin-to-axonal area ratio and higher g-ratio than both the dorsal and control groups (p < 0.001). For each study group, hindlimb P1 latency and P1-N1 amplitude were each correlated with g-ratio (p < 0.05); and mean myelin-to-axonal area ratio correlated with P1 latency of both hindlimbs (p < 0.05). Based on these more severe axonal demyelination and neurological deficits, a valid DSS rat model is created with somatosensory evoked potential neuro-monitoring technique. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Bone mesenchymal stem cells attenuate radicular pain by inhibiting microglial activation in a rat noncompressive disk herniation model

Spinal disk herniation can induce radicular pain through chemical irritation caused by proinflammatory and immune responses. Bone marrow mesenchymal stem cells (BMSCs) are a unique type of adult stem cell with the functions of suppressing inflammation and modulating immune responses. This study was undertaken to observe the effect of intrathecal BMSCs on the treatment of mechanical allodynia and the suppression of microglial activation in a rat noncompressive disk herniation model. The model was induced by the application of nucleus pulposus (NP) to the L5 dorsal root ganglion (DRG). The study found that the use of NP in the DRG can induce abnormal mechanical pain, increase the contents of the proinflammatory factors TNF-α and IL-1β, decrease the content of the anti-inflammatory cytokine TGF-β1 and activate microglia in the spinal dorsal horns (L5) (P < 0.05). BMSC administration could increase the mechanical withdrawal thresholds dramatically, decrease the contents of IL-1β and TNF-α, increase the content of TGF-β1 significantly (P < 0.05) and inhibit microglial activation in the bilateral spinal dorsal horn. Our results indicate that BMSC administration can reduce mechanical allodynia and downregulate the expression of proinflammatory cytokines by inhibiting microglial activation in the spinal dorsal horn in a rat noncompressive disk herniation model.

Quantitative Evaluation of Compressed L4-5 and S1 Nerve Roots of Lumbar Disc Herniation Patients by Diffusion Tensor Imaging and Fiber Tractography

OBJECTIVE

To delineate fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of compressed nerve roots in patients with lumbar disc herniation by diffusion tensor imaging and fiber bundle tracing and investigate the relationship between FA and ADC values and Swiss Spinal Stenosis Questionnaire and visual analog scale scores.

METHODS

Twenty patients with lumbar disc herniation and 20 age- and sex-matched healthy volunteers were assessed using the Swiss Spinal Stenosis Questionnaire and visual analog scale. All subjects underwent conventional sagittal T1-weighted and T2-weighted magnetic resonance imaging, axial T2-weighted imaging, and diffusion tensor imaging and fiber tractography.

RESULTS

In 20 patients with lumbar disc herniation, there were 31 nerve roots involved (9/31 L4, 15/31 L5, and 7/31 S1). Mean Swiss Spinal Stenosis Questionnaire scores of patients were 53.55% ± 11.91%, and mean visual analog scale scores were 5.96 ± 1.64. FA values of lumbar nerve roots were 0.332 ± 0.014 in healthy volunteers. FA values of compressed lumbar nerve roots were 0.251 ± 0.022, significantly lower than FA values of contralateral noncompressed nerve roots and lumbar nerve roots of healthy volunteers. ADC values of lumbar nerve roots were 1.763 ± 0.075 in healthy volunteers. ADC values of compressed lumbar nerve roots were 2.090 ± 0.078, significantly higher than ADC values of contralateral noncompressed nerve roots and lumbar nerve roots of healthy volunteers.

CONCLUSIONS

Fiber tractography is capable of delineating microstructural changes of lumbosacral nerve roots, and radiculopathy in lumbar disc herniation is associated with significant changes in FA and ADC values.

Correlation of lumbar lateral recess stenosis in magnetic resonance imaging and clinical symptoms

AIM

To assess the correlation of lateral recess stenosis (LRS) of lumbar segments L4/5 and L5/S1 and the Oswestry Disability Index (ODI).

METHODS

Nine hundred and twenty-seven patients with history of low back pain were included in this uncontrolled study. On magnetic resonance images (MRI) the lateral recesses (LR) at lumbar levels L4/5 and L5/S1 were evaluated and each nerve root was classified into a 4-point grading scale (Grade 0-3) as normal, not deviated, deviated or compressed. Patient symptoms and disability were assessed using ODI. The Spearman’s rank correlation coefficient was used for statistical analysis (P < 0.05).

RESULTS

Approximately half of the LR revealed stenosis (grade 1-3; 52% at level L4/5 and 42% at level L5/S1) with 2.2% and 1.9% respectively reveal a nerve root compression. The ODI score ranged from 0%-91.11% with an arithmetic mean of 34.06% ± 16.89%. We observed a very weak statistically significant positive correlation between ODI and LRS at lumbar levels L4/5 and L5/S1, each bilaterally (L4/5 left: rho < 0.105, P < 0.01; L4/5 right: rho < 0.111, P < 0.01; L5/S1 left: rho 0.128, P < 0.01; L5/S1 right: rho < 0.157, P < 0.001).

CONCLUSION

Although MRI is the standard imaging tool for diagnosing lumbar spinal stenosis, this study showed only a weak correlation of LRS on MRI and clinical findings. This can be attributed to a number of reasons outlined in this study, underlining that imaging findings alone are not sufficient to establish a reliable diagnosis for patients with LRS.

A New Animal Model of Brachial Plexus Neuralgia Produced by Injection of Cobra Venom into the Lower Trunk in the Rat

BACKGROUND

To establish a new animal model for the study of neuropathic pain developed by administration of cobra venom to the brachial plexus (BP) lower trunk.

METHODS

Fifty-eight adult male Sprague-Dawley rats were randomly divided into 5 groups. Under pentobarbital sodium anesthesia, cobra venom was injected into the lower trunk or sham operation was performed in the animals. On postoperative day 1 and day 12, pregabalin was administered intragastricly at 30 mg/kg in two groups. Mechanical withdrawal thresholds (MWT) were tested with von Frey filaments. Video recordings were used to analyze the spontaneous behaviors. Meanwhile, our model was confirmed by observing ultrastructural alterations of the BP and cervical cord (C8-T1) via electron microscope examination.

RESULTS

In comparison to the blank and sham-operated group, cobra venom-treated rats showed a profound decrease in the MWT, exploratory and increase in grooming behaviors (P<0.05). The changes were long-lasting (up to 60 days), in both ipsilateral and contralateral paws. Furthermore, it was observed under microscopic examination that the myelin sheath was demyelinated in the BP and cervical cord (C8-T1) after injection of cobra venom to the lower trunk. Pregabalin group rats showed changes in MWT and spontaneous behaviors after pregabalin treatment at postoperative day 1 (P>0.05), compared with the control and sham-operated groups. In pregabalin test POD12 group, the decreased MWT and the increased grooming behavior were improved at 20 days after operation. However, pregabalin had no effect on exploratory activity. Results indicate that pregabalin effectively attenuates mechanical hyperalgesia in acute period.

CONCLUSIONS

The cobra venom model can be used as a model to induce neuropathic pain and to enable study of the mechanism and treatment.