Targeting the host inflammatory response in traumatic spinal cord injury

Increased Expression of Cyclo-Oxygenase 2 and Vascular Endothelial Growth Factor in Lesioned Spinal Cord by Transplanted Olfactory Ensheathing Cells

Olfactory ensheathing cells (OECs) were transplanted in adult rats after photochemical injury of the spinal cord. Rats received either 180,000 OECs suspended in DMEM or DMEM alone. Locomotor ability scored by the BBB-scale, pain sensibility, and motor and somatosensory evoked potentials were evaluated during the first 14 days post-surgery. At 3, 7, and 14 days, 5 rats per day of both groups were perfused and transverse sections from proximal, lesioned and distal spinal cord blocks were stained for COX-2, VEGF, GFAP and lectin. The BBB-score and the amplitude of motor and somatosensory evoked potentials were significantly higher in OEC- than in DMEM-injected animals throughout follow-up, whereas the withdrawal latency to heat noxious stimulus was lower in OEC- than in DMEM-injected rats. The area of preserved spinal cord and the levels of COX-2 and VEGF staining were significantly higher in OEC- than in DMEM-injected rats. GFAP- but no LEC-positive cells expressed COX-2 staining in OEC-transplanted rats. The density of blood vessels was also significantly increased in OEC- with respect to DMEM-injected rats. Our results show that OECs promote functional and morphological preservation of the spinal cord after photochemical injury, increasing neoangiogenesis and up-regulation of COX-2 and VEGF expression in astrocytes.

Accumulation of Ym1/2 protein in the mouse olfactory epithelium during regeneration and aging

A unique feature of the olfactory system is its efficiency to produce new neurons in the adult. Thus, destruction of the olfactory receptor neurons (ORNs) using chemical (intranasal perfusion with ZnSO4) or surgical (axotomy or bulbectomy) methods, leads to an enhanced rate of proliferation of their progenitors and to complete ORNs regeneration. The aim of our study was to identify new factors implied in this regenerative process. Using an electrophoretic method, we observed the accumulation of a 42 kDa protein after axotomy in the olfactory mucosa, but not in the olfactory bulb. Its expression started after a few days following injury and increased massively during the phase of ORN regeneration. The purification and the sequence characterization revealed that this protein was Ym1/2, recently identified in activated macrophages present in various tissues during inflammation. Western blotting analysis of Ym1/2 confirmed the accumulation of this protein in the regenerating olfactory mucosa consecutively to olfactory axotomy or bulbectomy but also after ZnSO4 irrigation of the nasal cavity. In the olfactory mucosa of control mice, Ym1/2 was hardly detectable in young animals and became more and more abundant with increasing age. In injured and aged mice, Ym1/2 mainly accumulates in the cytoplasm of supporting cells as well as in other cells located throughout the olfactory epithelium. Our results suggest that Ym1/2 is involved in olfactory epithelium remodeling following several kinds of lesions of the adult olfactory mucosa and support the view of a critical role of inflammatory cues in neurodegeneration and aging.

Interactions between the cells of the immune and nervous system: neurotrophins as neuroprotection mediators in CNS injury

Inflammatory processes in the central nervous system (CNS) are considered neurotoxic, although recent studies suggest that they also can be beneficial and confer neuroprotection (neuroprotective autoimmunity). Cells from the immune system have been detected in CNS injury and found to produce and secrete a variety of neurotrophins such as NGF, BDNF, NT-3 and NT-4/5, and to express (similarly to neuronal cells), members of the tyrosine kinase (Trk) receptor family such as TrkA, TrkB and TrkC. Indeed, autocrine and paracrine interactions are observed at the site of CNS injury, resulting in a variety of homologic-heterologic modulations of immune and neuronal cell function. The end result of the inflammatory process, neurotoxicity and/or neuroprotection, is a function of the fine balance between the two cellular systems, i.e., of the complex signaling relationships between anti-inflammatory neuroprotective factors (neurotrophins and other chemical mediators) and proinflammatory neurotoxic factors (TNF, free radicals, certain cytokines, etc.). Autoimmune neuroprotection is a novel therapeutic approach aimed at shifting the balance between the immune and neuronal cells towards survival pathways in a variety of CNS injuries. This review focuses on data supporting this concept and its future therapeutical implications for optic nerve injury and multiple sclerosis.

Pathophysiology of cerebral ischemia and brain trauma: similarities and differences

Current knowledge regarding the pathophysiology of cerebral ischemia and brain trauma indicates that similar mechanisms contribute to loss of cellular integrity and tissue destruction. Mechanisms of cell damage include excitotoxicity, oxidative stress, free radical production, apoptosis and inflammation. Genetic and gender factors have also been shown to be important mediators of pathomechanisms present in both injury settings. However, the fact that these injuries arise from different types of primary insults leads to diverse cellular vulnerability patterns as well as a spectrum of injury processes. Blunt head trauma produces shear forces that result in primary membrane damage to neuronal cell bodies, white matter structures and vascular beds as well as secondary injury mechanisms. Severe cerebral ischemic insults lead to metabolic stress, ionic perturbations, and a complex cascade of biochemical and molecular events ultimately causing neuronal death. Similarities in the pathogenesis of these cerebral injuries may indicate that therapeutic strategies protective following ischemia may also be beneficial after trauma. This review summarizes and contrasts injury mechanisms after ischemia and trauma and discusses neuroprotective strategies that target both types of injuries.

VEGF165 therapy exacerbates secondary damage following spinal cord injury

Vascular endothelial growth factor (VEGF) demonstrates potent and well-characterized effects on endothelial cytoprotection and angiogenesis. In an attempt to preserve spinal microvasculature and prolong the endogenous neovascular response observed transiently following experimental spinal cord injury (SCI), exogenous recombinant human VEGF (rhVEGF165) was injected into the injured rat spinal cord. Adult female Fischer 344 rats were subjected to moderate SCI (12.5 g-cm) using the NYU impactor. At 72 h after injury, animals were randomly assigned to three experimental groups receiving no microinjection or injection of saline or saline containing 2 microg of rhVEGF165. Acutely, VEGF injection resulted in significant microvascular permeability and infiltration of leukocytes into spinal cord parenchyma. 6 weeks postinjection, no significant differences were observed in most measures of microvascular architecture following VEGF treatment, but analysis of histopathology in spinal cord tissue revealed profound exacerbation of lesion volume. These results support the idea that intraparenchymal application of the proangiogenic factor VEGF may exacerbate SCI, likely through its effect on vessel permeability.

Inflammation, degeneration and regeneration in the injured spinal cord: insights from DNA microarrays

GeneChip microarrays have recently been introduced to the field of neurobiology to identify and monitor the expression levels of thousands of genes simultaneously. This powerful technique is now used for studying the pathophysiology of CNS injuries including spinal cord lesions. Early stages after injury are characterized by the strong upregulation of genes involved in transcription and inflammation and a general downregulation of structural proteins and proteins involved in neurotransmission. Later, an increase in the expression of growth factors, axonal guidance factors, extracellular matrix molecules and angiogenic factors reflects the attempts for repair, while upregulation of stress genes and proteases and downregulation of cytoskeletal and synaptic mRNA reflect the struggle of the tissue to survive. DNA microarrays have the potential to aid discovery of new targets for neuroprotective or restorative therapeutic approaches

Nicotine Attenuates Arachidonic Acid-Induced Apoptosis of Spinal Cord Neurons by Preventing Depletion of Neurotrophic Factors

Increased levels of free fatty acids and, in particular, arachidonic acid can lead to induction of apoptosis of spinal cord neurons. Because of the importance of neurotrophic factors in cell survival and death, mRNA and protein levels of brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (FGF-2) were studied in cultured spinal cord neurons treated with arachidonic acid. In addition, the present study focused on the effects of nicotine and neuronal nicotinic acetylcholine receptors (nAChRs) on these processes. A 2-h exposure to arachidonic acid markedly diminished expression of BDNF and FGF-2. These effects were fully prevented by pretreatment with 10 microM nicotine. Mecamylamine (a non-specific antagonist of nAChRs) and alpha-bungarotoxin (a specific antagonist of the nAChRalpha7) completely inhibited nicotine-mediated protection against arachidonic acid-induced alterations of BDNF and FGF-2. In addition, nicotine, BDNF and FGF-2 fully protected against arachidonic acid-induced apoptosis of spinal cord neurons. BDNF and FGF-2 were effective in prevention of apoptotic cell death even when applied 2 h after the beginning of arachidonic acid treatment. These results suggest that arachidonic acid can induce apoptosis of spinal cord neurons by depletion of neurotrophic factors and that nicotine can protect against these effects through the nAChRalpha7-mediated pathway.

Reducing inflammation decreases secondary degeneration and functional deficit after spinal cord injury

Injury to the spinal cord is followed by degeneration, which leads to progressive tissue loss and usually cystic cavitation. Cellular and humoral immune responses have been implicated as mediators of secondary degeneration, and the expression of leukocyte chemoattractants has been shown to precede immune cell influx. However, the relationship between the increased expression of chemoattractants, the invasion of lymphocytes, and overall lesion evolution is poorly understood. Here, we show that the T-lymphocyte chemoattractant CXCL10 is upregulated after dorsal hemisection injury to the adult mammalian spinal cord of C57/BL6 mice, and that antibody neutralization of CXCL10 beginning 1 day prior to injury dramatically reduces the T-lymphocyte invasion that normally occurs after trauma. Notably, this treatment resulted in a significant reduction of secondary tissue loss and functional deficit. We conclude that CXCL10 plays a critical role in recruitment of T lymphocytes to sites of spinal cord injury, and that a reduction of T-lymphocyte recruitment significantly enhances tissue preservation and functional outcome.

Cortical changes in cholecystokinin mRNA are related to spontaneous pain behaviors following excitotoxic spinal cord injury in the rat

Cholecystokinin (CCK) in the CNS antagonizes the opioid system and has been implicated post-spinal cord injury (SCI) pain. The current study found that excitotoxic SCI alters levels of CCK mRNA levels in the cortex, diencepahlon, and mesencephalon of rats. Animals that developed pain post-SCI had significantly higher levels than animals that did not develop pain. Upregulation of CCK mRNA in the cortex may be related to post-SCI pain in rats.

Features of skin-coincubated macrophages that promote recovery from spinal cord injury

Uncontrolled inflammation is considered to exacerbate the neuronal loss that follows spinal cord trauma. However, controlled inflammation response appears to be beneficial. Skin-coincubated macrophages injected into contused spinal cord of rats resulted in improved motor recovery and reduced spinal cyst formation. The macrophages express elevated levels of cell-surface molecules CD80, CD86, CD54 and MHC-II, markers characteristic of antigen presenting cells (APCs). Additionally, skin-coincubation elevates secretion of interleukin-1 beta (IL-1 beta) and Brain-Derived Neurotrophic Factor (BDNF), and reduces secretion of tumor necrosis factor alpha (TNF-alpha). We propose that macrophages activated by skin-coincubation bolster neuroprotective immune activity in the spinal cord, making the environment less cytotoxic and less hostile to axonal regeneration.

Significance of fixation of the vertebral column for spinal cord injury experiments

STUDY DESIGN

Thoracic spinal cord transections were performed in adult rats. The animals were divided into two groups, with or without internal fixation of the involved vertebral column. Histologic and immunohistochemical studies were performed to compare the effect of internal fixation of the vertebral column.

OBJECTIVES

To find out the aspects and extent of beneficial effects of vertebral column fixation for spinal cord repair.

SUMMARY OF BACKGROUND DATA

Vertebral column fixation is a routine procedure in clinical spinal cord surgery. Paradoxically, most, if not all, animal spinal cord experiments seem to have ignored the importance of vertebral column fixation. During trunk movements, the vertebral column flexes to different directions, accompanied by bending of the spinal cord. Following spinal cord lesions, with frequent bending of the cord there will be repeated bleeding, inflammation, and other pathologic processes at the lesion site. Thus, the healing process will be hampered. The severity of the damages that will be brought about by bending of the cord is, to a certain degree, unpredictable. There will be rather big individual variations in injury and repair among the same type of experiments, rendering quantification and conclusion difficult.

METHODS

Adult Sprague-Dawley rats were used. The thoracic spinal cord was transected. Strong stainless steel wires were used for internal fixation of the vertebral column. The histology of the horizontal sections of the spinal cord segment, which included the lesion site, was examined at the 14th postoperative day. The volumes of the secondary degeneration and meningeal scar, the gap between the borders of the proximal and distal stumps of the transected spinal cord, the thickness of the meningeal scar, the astrocytic reaction, and the abundance of regenerating nerve fibers at the lesion site were compared between the vertebral column fixed and nonfixed groups. Whenever possible, the results were evaluated quantitatively.

RESULTS

In all these aspects, the internally fixed group was consistently far better than the unfixed group. The quantitative analyses were as follows (fixed/unfixed): 1)volume of secondary degeneration: 1.07 +/- 0.20/1.81 +/- 0.43 mm3 (P < 0.01); 2) volume of meningeal scar: 2.38 +/- 0.55/4.34 +/- 1.40 mm3 (P < 0.05); 3) distance between cord stumps: 1.38 +/- 0.34/2.35 +/- 0.79 mm (P < 0.05); 4) the mean thinnest dimension of the meningeal scar: 0.90 +/- 0.43/1.98 +/- 0.85 mm (P < 0.05).

CONCLUSION

Vertebral column fixation is a crucial procedure for spinal cord animal experiments.

To die or not to die for neurons in ischemia, traumatic brain injury and epilepsy: a review on the stress-activated signaling pathways and apoptotic pathways

After a severe episode of ischemia, traumatic brain injury (TBI) or epilepsy, it is typical to find necrotic cell death within the injury core. In addition, a substantial number of neurons in regions surrounding the injury core have been observed to die via the programmed cell death (PCD) pathways due to secondary effects derived from the various types of insults. Apart from the cell loss in the injury core, cell death in regions surrounding the injury core may also contribute to significant losses in neurological functions. In fact, it is the injured neurons in these regions around the injury core that treatments are targeting to preserve. In this review, we present our cumulated understanding of stress-activated signaling pathways and apoptotic pathways in the research areas of ischemic injury, TBI and epilepsy and that gathered from concerted research efforts in oncology and other diseases. However, it is obvious that our understanding of these pathways in the context of acute brain injury is at its infancy stage and merits further investigation. Hopefully, this added research effort will provide a more detailed knowledge from which better therapeutic strategies can be developed to treat these acute brain injuries.

Inflammatory mechanisms after ischemia and stroke

Inflammation has been implicated as a secondary injury mechanism following ischemia and stroke. A variety of experimental models, including thromboembolic stroke, focal and global ischemia, have been used to evaluate the importance of inflammation. The vasculature endothelium promotes inflammation through the upregulation of adhesion molecules such as ICAM, E-selectin, and P-selectin that bind to circulating leukocytes and facilitate their migration into the CNS. Once in the CNS, the production of cytotoxic molecules may facilitate cell death. The macrophage and microglial response to injury may either be beneficial by scavenging necrotic debris or detrimental by facilitating cell death in neurons that would otherwise recover. While many studies have tested these hypotheses, the importance of inflammation in these models is inconclusive. This review summarizes data regarding the role of the vasculature, leukocytes, blood-brain barrier, macrophages, and microglia after experimental and clinical stroke.

Sexual dimorphism in the spontaneous recovery from spinal cord injury: a gender gap in beneficial autoimmunity?

Immune cells have been shown to contribute to spontaneous recovery from central nervous system (CNS) injury. Here we show that adult female rats and mice recover significantly better than their male littermates from incomplete spinal cord injury (ISCI). This sexual dimorphism is wiped out and recovery is worse in adult mice deprived of mature T cells. After spinal cord contusion in adult rats, functional recovery (measured by locomotor scores in an open field) was significantly worse in females treated with dihydrotestosterone prior to the injury than in placebo-treated controls, and significantly better in castrated males than in their noncastrated male littermates. Post-traumatic administration of the testosterone receptor antagonist flutamide promoted the functional recovery in adult male rats. These results, in line with the known inhibitory effect of testosterone on cell-mediated immunity, suggest that androgen-mediated immunosuppression plays a role in ISCI-related immune dysfunction and can therefore partly explain the worse outcome of ISCI in males than in female. We suggest that females, which are more prone to develop autoimmune response than males, benefit from this response in cases of CNS insults.