Minocycline inhibits contusion-triggered mitochondrial cytochrome c release and mitigates functional deficits after spinal cord injury

Minocycline alleviates death of oligodendrocytes by inhibiting pro-nerve growth factor production in microglia after spinal cord injury

Spinal cord injury (SCI) causes a permanent neurological disability, and no satisfactory treatment is currently available. After SCI, pro-nerve growth factor (proNGF) is known to play a pivotal role in apoptosis of oligodendrocytes, but the cell types producing proNGF and the signaling pathways involved in proNGF production are primarily unknown. Here, we show that minocycline improves functional recovery after SCI in part by reducing apoptosis of oligodendrocytes via inhibition of proNGF production in microglia. After SCI, the stress-responsive p38 mitogen-activated protein kinase (p38MAPK) was activated only in microglia, and proNGF was produced by microglia via the p38MAPK-mediated pathway. Minocycline treatment significantly reduced proNGF production in microglia in vitro and in vivo by inhibition of the phosphorylation of p38MAPK. Furthermore, minocycline treatment inhibited p75 neurotrophin receptor expression and RhoA activation after injury. Finally, minocycline treatment inhibited oligodendrocyte death and improved functional recovery after SCI. These results suggest that minocycline may represent a potential therapeutic agent for acute SCI in humans.

Inflammation and its role in neuroprotection, axonal regeneration and functional recovery after spinal cord injury

Trauma to the central nervous system (CNS) triggers intraparenchymal inflammation and activation of systemic immunity with the capacity to exacerbate neuropathology and stimulate mechanisms of tissue repair. Despite our incomplete understanding of the mechanisms that control these divergent functions, immune-based therapies are becoming a therapeutic focus. This review will address the complexities and controversies of post-traumatic neuroinflammation, particularly in spinal cord. In addition, current therapies designed to target neuroinflammatory cascades will be discussed.

p38alpha MAP kinase mediates hypoxia-induced motor neuron cell death: a potential target of minocycline's neuroprotective action

Hypoxia-ischemia (HI) may play a significant role in motor neuron death associated with the pathology of spinal cord injury and, perhaps, amyotrophic lateral sclerosis. The present study employs an in vitro model of HI to investigate the role of a stress kinase pathway, i.e., p38 MAP kinase, in cell death signaling in a motor neuron cell line, i.e., NSC34, subjected to oxygen-glucose deprivation (OGD). Although the neurons were essentially tolerant to either hypoxia (0.2% O(2)) or low glucose (1 mM) alone, more than 60% of them died in response to combined low oxygen and low-glucose exposure. Minocycline, a semi-synthetic tetracycline known for its neuroprotective effects in models of neurodegeneration, afforded substantial (approximately 50%) protection against hypoxic cell death, assessed by lactate dehydrogenase release and flow cytometry, while suppressing OGD-induced p38 MAP kinase activation. An inhibitor of p38 kinase, SB203580, as well as siRNA-mediated down-regulation of p38 kinase elicited an almost complete blockade of OGD-induced cell death. The use of p38 isoform-specific siRNAs further revealed preferential involvement of the alpha over the beta isoform of p38 MAP kinase in hypoxic neuronal cell death in our model.

Olfactory ensheathing cell apoptosis induced by hypoxia and serum deprivation

Olfactory ensheathing cell (OEC) transplantation is one promising technology for the treatment of spinal cord injury. Many studies have been focusing on the functional improvement after OEC implantation in spinal cord injury of animals. However, little is known about the mechanisms about how OECs respond to the proapoptotic microenvironment after transplantation. We use the hypoxia and serum deprivation (HSD) paradigm in OECs to evaluate the effects of the ischemic damage. OECs underwent caspase-dependent apoptosis during HSD and a pan-caspase inhibitor specifically blocked the cell death. In addition, HSD resulted in a time-dependent decrease of mitochondrial membrane potential DeltaPsi(m), triggering a transient increase in p53 content and activated p53 in a time-dependent manner. In summary, our data suggest that HSD trigger apoptotic OECs death, which may be related to mitochondria dysfunction and the dependence of p53.

Cytoplasmic extracts from adipose tissue stromal cells alleviates secondary damage by modulating apoptosis and promotes functional recovery following spinal cord injury

Spinal cord injury (SCI) typically results from sustained trauma to the spinal cord, resulting in loss of neurologic function at the level of the injury. However, activation of various physiological mechanisms secondary to the initial trauma including edema, inflammation, excito-toxicity, excessive cytokine release and apoptosis may exacerbate the injury and/or retard natural repair mechanisms. Herein, we demonstrate that cytoplasmic extracts prepared from adipose tissue stromal cells (ATSCs) inhibits H(2)O(2)-mediated apoptosis of cultured spinal cord-derived neural progenitor cells (NPCs) resulting in increased cell survival. The ATSC extracts mediated this effect by decreasing caspase-3 and c-Jun-NH2-terminal kinase (SAPK/JNK) activity, inhibiting cytochrome c release from mitochondria and reducing Bax expression levels in cells. Direct injection of ATSC extracts mixed with Matrigel into the spinal cord immediately after SCI also resulted in reduced apoptotic cell death, astrogliosis and hypo-myelination but did not reduce the extent of microglia infiltration. Moreover, animals injected with the ATSC extract showed significant functional improvement of hind limbs as measured by the BBB (Basso, Beattie and Bresnahan) scale. Collectively, these studies show a prominent therapeutic effect of ATSC cytoplasmic extracts on SCI principally caused by an inhibition of apoptosis-mediated cell death, which spares white matter, oligodendrocytes and neurons at the site of injury. The ability of ATSC extracts to prevent secondary pathological events and improve neurologic function after SCI suggests that extracts prepared from autologous cells harvested from SCI patients may have clinical utility.

Contusion, dislocation, and distraction: primary hemorrhage and membrane permeability in distinct mechanisms of spinal cord injury

Object

In experimental models of spinal cord injury (SCI) researchers have typically focused on contusion and transection injuries. Clinically, however, other injury mechanisms such as fracture–dislocation and distraction also frequently occur. The objective of the present study was to compare the primary damage in three clinically relevant animal models of SCI.

Methods

Contusion, fracture–dislocation, and flexion–distraction animal models of SCI were developed. To visualize traumatic increases in cellular membrane permeability, fluorescein–dextran was infused into the cerebrospi-nal fluid prior to injury. High-speed injuries (approaching 100 cm/second) were produced in the cervical spine of deeply anesthetized Sprague–Dawley rats (28 SCI and eight sham treated) with a novel multimechanism SCI test system. The animals were killed immediately thereafter so that the authors could characterize the primary injury in the gray and white matter.

Sections stained with H & E showed that contusion and dislocation injuries resulted in similar central damage to the gray matter vasculature whereas no overt hemorrhage was detected following distraction. Contusion resulted in membrane disruption of neuronal somata and axons localized within 1 mm of the lesion epicenter. In contrast, membrane compromise in the dislocation and distraction models was observed to extend rostrally up to 5 mm, particularly in the ventral and lateral white matter tracts.

Conclusions

Given the pivotal nature of hemorrhagic necrosis and plasma membrane compromise in the initiation of downstream SCI pathomechanisms, the aforementioned differences suggest the presence of mechanism-specific injury regions, which may alter future clinical treatment paradigms.

The PPAR gamma agonist Pioglitazone improves anatomical and locomotor recovery after rodent spinal cord injury

Traumatic spinal cord injury (SCI) is accompanied by a dramatic inflammatory response, which escalates over the first week post-injury and is thought to contribute to secondary pathology after SCI. Peroxisome proliferator-activated receptors (PPAR) are widely expressed nuclear receptors whose activation has led to diminished pro-inflammatory cascades in several CNS disorders. Therefore, we examined the efficacy of the PPARgamma agonist Pioglitazone in a rodent SCI model. Rats received a moderate mid-thoracic contusion and were randomly placed into groups receiving vehicle, low dose or high dose Pioglitazone. Drug or vehicle was injected i.p. at 15 min post-injury and then every 12 h for the first 7 days post-injury. Locomotor function was followed for 5 weeks using the BBB scale. BBB scores were greater in treated animals at 7 days post-injury and significant improvements in BBB subscores were noted, including better toe clearance, earlier stepping and more parallel paw position. Stereological measurements throughout the lesion revealed a significant increase in rostral spared white matter in both Pioglitazone treatment groups. Spinal cords from the high dose group also had significantly more gray matter sparing and motor neurons rostral and caudal to epicenter. Thus, our results reveal that clinical treatment with Pioglitazone, an FDA-approved drug used currently for diabetes, may be a feasible and promising strategy for promoting anatomical and functional repair after SCI.

Mitochondrial membrane permeabilization in cell death

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Proinflammatory cytokine synthesis in the injured mouse spinal cord: multiphasic expression pattern and identification of the cell types involved

We have studied the spatial and temporal distribution of six proinflammatory cytokines and identified their cellular source in a clinically relevant model of spinal cord injury (SCI). Our findings show that interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF) are rapidly (<5 and 15 minutes, respectively) and transiently expressed in mice following contusion. At 30-45 minutes post SCI, IL-1beta and TNF-positive cells could already be seen over the entire spinal cord segment analyzed. Multilabeling analyses revealed that microglia and astrocytes were the two major sources of IL-1beta and TNF at these times, suggesting a role for these cytokines in gliosis. Results obtained from SCI mice previously transplanted with green fluorescent protein (GFP)-expressing hematopoietic stem cells confirmed that neural cells were responsible for the production of IL-1beta and TNF for time points preceding 3 hours. From 3 hours up to 24 hours, IL-1beta, TNF, IL-6, and leukemia inhibitory factor (LIF) were strongly upregulated within and immediately around the contused area. Colocalization studies revealed that all populations of central nervous system resident cells, including neurons, synthesized cytokines between 3 and 24 hours post SCI. However, work done with SCI-GFP chimeric mice revealed that at least some infiltrating leukocytes were responsible for cytokine production from 12 hours on. By 2 days post-SCI, mRNA signal for all the above cytokines had nearly disappeared. Notably, we also observed another wave of expression for IL-1beta and TNF at 14 days. Overall, these results indicate that following SCI, all classes of neural cells initially contribute to the organization of inflammation, whereas recruited immune cells mostly contribute to its maintenance at later time points.

Re-evaluation of mitochondrial permeability transition as a primary neuroprotective target of minocycline

Minocycline has been shown to be neuroprotective in ischemic and neurodegenerative disease models and could potentially be relevant for clinical use. We revisited the hypothesis that minocycline acts through direct inhibition of calcium-induced mitochondrial permeability transition (mPT) resulting in reduced release of cytochrome c (cyt c). Minocycline, at high dosage, was found to prevent calcium-induced mitochondrial swelling under energized conditions similarly to the mPT inhibitor cyclosporin A (CsA) in rodent mitochondria derived from the CNS. In contrast to CsA, minocycline dose-dependently reduced mitochondrial calcium retention capacity (CRC) and respiratory control ratios and was ineffective in the de-energized mPT assay. Further, minocycline did not inhibit calcium- or tBid-induced cyt c release. We conclude that the neuroprotective mechanism of minocycline is likely not related to direct inhibition of mPT and propose that the mitochondrial effects of minocycline may contribute to toxicity rather than tissue protection at high dosing in animals and humans.

Update on the treatment of spinal cord injury

Acute spinal cord injury (SCI) is a devastating neurological disorder that can affect any individual at a given instance. Current treatment options for SCI include the use of high dose methylprednisolone sodium succinate, a corticosteroid, surgical interventions to stabilize and decompress the spinal cord, intensive multisystem medical management, and rehabilitative care. While utility of these therapeutic options provides modest benefits, there is a critical need to identify novel approaches to treat or repair the injured spinal cord in hope to, at the very least, improve upon the patient's quality of life. Thankfully, several discoveries at the preclinical level are now transitioning into the clinical arena. These include the Surgical Treatment for Acute Spinal Cord Injury Study (STASCIS) Trial to evaluate the role and timing of surgical decompression for acute SCI, neuroprotection with the semisynthetic second generation tetracycline derivative, minocycline; aiding axonal conduction with the potassium channel blockers, neuroregenerative/neuroprotective approaches with the Rho antagonist, Cethrin; the use of anti-NOGO monoclonal antibodies to augment plasticity and regeneration; as well as cell-mediated repair with stem cells, bone marrow stromal cells, and olfactory ensheathing cells. This review overviews the pathobiology of SCI and current treatment choices before focusing the rest of the discussion on the variety of promising neuroprotective and cell-based approaches that have recently moved, or are very close, to clinical testing.

Minocycline blocks acute bilirubin-induced neurological dysfunction in jaundiced Gunn rats

BACKGROUND

Extreme hyperbilirubinemia is treated with double volume exchange transfusion, which may take hours to commence. A neuroprotective agent that could be administered immediately might be clinically useful. Minocycline, an anti-inflammatory and anti-apoptotic semisynthetic tetracycline, prevents hyperbilirubinemia-induced cerebellar hypoplasia in Gunn rats. Acute brainstem auditory evoked potential (BAEP) abnormalities occur after giving sulfadimethoxine to 16-day-old jaundiced Gunn rats to displace bilirubin into tissue including brain.

OBJECTIVE

To assess whether minocycline is neuroprotective in this model of acute bilirubin encephalopathy.

METHODS

We recorded BAEPs at baseline and 6 h after injecting sulfadimethoxine. Minocycline 0.5 mg/kg (n = 4), 5 mg/kg (n = 9), 50 mg/kg (n = 9) or 500 mg/kg (n = 3, all died) was administered 15 min before sulfadimethoxine (0 h). Controls received saline followed by either sulfadimethoxine (n = 13) or saline (n = 7).

RESULTS

At 6 h total plasma bilirubin decreased from 10.84 +/- 0.88 mg/dl (mean +/- SD) to 0.70 +/- 0.35 mg/dl (p <10(-9)) in all sulfadimethoxine-injected groups. At 6 h, there was complete protection against decreased amplitudes of BAEP waves II and III and increased I-II and I-III interwave intervals (brainstem conduction times corresponding to I-III and I-V in humans) with 50 mg/kg minocycline, and partial protection with lower doses.

CONCLUSIONS

Minocycline 50 mg/kg 15 min prior to an intervention that normally produces acute bilirubin neurotoxicity is neuroprotective in jaundiced Gunn rat pups. Further studies are needed to investigate the temporal course and mechanism of neuroprotection. Minocycline, administered immediately, may be clinically useful in treating extreme neonatal hyperbilirubinemia and preventing kernicterus. We believe our model provides an efficient in vivo model to screen and evaluate new agents that are neuroprotective against bilirubin toxicity and kernicterus.

Transient neuroprotection by minocycline following traumatic brain injury is associated with attenuated microglial activation but no changes in cell apoptosis or neutrophil infiltration

Cerebral inflammation and apoptotic cell death are two processes implicated in the progressive tissue damage that occurs following traumatic brain injury (TBI), and strategies to inhibit one or both of these pathways are being investigated as potential therapies for TBI patients. The tetracycline derivative minocycline was therapeutically effective in various models of central nervous system injury and disease, via mechanisms involving suppression of inflammation and apoptosis. We therefore investigated the effect of minocycline in TBI using a closed head injury model. Following TBI, mice were treated with minocycline or vehicle, and the effect on neurological outcome, lesion volume, inflammation and apoptosis was evaluated for up to 7 days. Our results show that while minocycline decreases lesion volume and improves neurological outcome at 1 day post-trauma, this response is not maintained at 4 days. The early beneficial effect is likely not due to anti-apoptotic mechanisms, as the density of apoptotic cells is not affected at either time-point. However, protection by minocycline is associated with a selective anti-inflammatory response, in that microglial activation and interleukin-1beta expression are reduced, while neutrophil infiltration and expression of multiple cytokines are not affected. These findings demonstrate that further studies on minocycline in TBI are necessary in order to consider it as a novel therapy for brain-injured patients.

Inflammation and Spinal Cord Injury: Infiltrating Leukocytes as Determinants of Injury and Repair Processes

The immune response that accompanies spinal cord injury contributes to both injury and reparative processes. It is this duality that is the focus of this review. Here we consider the complex cellular and molecular immune responses that lead to the infiltration of leukocytes and glial activation, promote oxidative stress and tissue damage, influence wound healing, and subsequently modulate locomotor recovery. Immunomodulatory strategies to improve outcomes are gaining momentum as ongoing research carefully dissects those pathways, which likely mediate cell injury from those, which favor recovery processes. Current therapeutic strategies address divergent approaches including early immunoblockade and vaccination with immune cells to prevent early tissue damage and support a wound-healing environment that favors plasticity. Despite these advances, there remain basic questions regarding how inflammatory cells interact in the injured spinal cord. Such questions likely arise as a result of our limited understanding of immune cell/neural interactions in a dynamic environment that culminates in progressive cell injury, demyelination, and regenerative failure.

Physical activity-mediated functional recovery after spinal cord injury: potential roles of neural stem cells

As data elucidating the complexity of spinal cord injury pathophysiology emerge, it is increasingly being recognized that successful repair will probably require a multifaceted approach that combines tactics from various biomedical disciplines, including pharmacology, cell transplantation, gene therapy and material sciences. Recently, new evidence highlighting the benefit of physical activity and rehabilitation interventions during the post-injury phase has provided novel possibilities in realizing effective repair after spinal cord injury. However, before a comprehensive therapeutic strategy that optimally utilizes the benefits of each of these disciplines can be designed, the basic mechanisms by which these various interventions act must be thoroughly explored and important synergistic and antagonistic interactions identified. In examining the mechanisms by which physical activity-based functional recovery after spinal cord injury is effected, endogenous neural stem cells, in our opinion, engender a potentially key role. Multipotent neural stem cells possess many faculties that abet recovery, including the ability to assess the local microenvironment and deliver biofactors that promote neuroplasticity and regeneration, as well as the potential to replenish damaged or eradicated cellular elements. Encouragingly, the functional recovery owing to physical activity-based therapies appears relatively robust, even when therapy is initiated in the chronic stage of spinal cord injury. In this article, we review experimental outcomes related to our hypothesis that endogenous neural stem cells mediate the functional recovery noted in spinal cord injury following physical activity-based treatments. Overall, the data advocates the incorporation of increased physical activity as a component of the multidimensional treatment of spinal cord injury and underscores the critical need to employ research-based mechanistic approaches for developing future advances in the rehabilitation of neurological injury and disorders.

Therapeutic interventions after spinal cord injury

Spinal cord injury (SCI) can lead to paraplegia or quadriplegia. Although there are no fully restorative treatments for SCI, various rehabilitative, cellular and molecular therapies have been tested in animal models. Many of these have reached, or are approaching, clinical trials. Here, we review these potential therapies, with an emphasis on the need for reproducible evidence of safety and efficacy. Individual therapies are unlikely to provide a panacea. Rather, we predict that combinations of strategies will lead to improvements in outcome after SCI. Basic scientific research should provide a rational basis for tailoring specific combinations of clinical therapies to different types of SCI.

Single muscle fiber size and contractility after spinal cord injury in rats

Spinal cord injury (SCI) results in muscle weakness but the degree of impairment at the level of single fibers is not known. The purpose of this study was to examine the effects of T9-level SCI on single muscle fibers from the tibialis anterior of rats. Significant decreases in cross-sectional area (CSA), maximal force (Po), and specific force (SF = Po/CSA) were noted at 2 weeks. Atrophy and force-generating capacity were reversed at 4 weeks, but SF remained impaired. Maximum shortening velocity (Vo) did not change after injury. SCI thus appears to affect various contractile properties of single muscle fibers differently. Normal cage activity may partially restore function but new interventions are needed to restore muscle fiber quality.

6-Shogaol, a natural product, reduces cell death and restores motor function in rat spinal cord injury

Spinal cord injury (SCI) results in progressive waves of secondary injuries, which via the activation of a barrage of noxious pathological mechanisms exacerbate the injury to the spinal cord. Secondary injuries are associated with edema, inflammation, excitotoxicity, excessive cytokine release, caspase activation and cell apoptosis. This study was aimed at investigating the possible neuroprotective effects of 6-shogaol purified from Zingiber officinale by comparing an experimental SCI rat group with SCI control rats. Shogaol attenuated apoptotic cell death, including poly(ADP-ribose) polymerase activity, and reduced astrogliosis and hypomyelination which occurs in areas of active cell death in the spinal cords of SCI rats. The foremost protective effect of shogaol in SCI would therefore be manifested in the suppression of the acute secondary apoptotic cell death. However, it does not attenuate active microglia and macrophage infiltration. This finding is supported by a lack of histopathological changes in the areas of the lesion in the shogaol-treated SCI rats. Moreover, shogaol-mediated neuroprotection has been linked with shogaol's attenuation of p38 mitogen-activated protein kinase, p-SAPK/JNK and signal transducer, and with transcription-3 activation. Our results demonstrate that shogaol administrated immediately after SCI significantly diminishes functional deficits. The shogaol-treated group recovered hindlimb reflexes more rapidly and a higher percentage of these rats regained responses compared with the untreated injured rats. The overall hindlimb functional improvement of hindlimbs, as measured by the Basso, Beattie and Bresnahan scale, was significantly enhanced in the shogaol-treated group relative to the SCI control rats. Our data show that the therapeutic outcome of shogaol probably results from its comprehensive effects of blocking apoptotic cell death, resulting in the protection of white matter, oligodendrocytes and neurons, and inhibiting astrogliosis. Our finding that the administration of shogaol prevents secondary pathological events in traumatic SCIs and promotes recovery of motor functions in an animal model raises the issue of whether shogaol could be used therapeutically in humans after SCI.

Molecular insights of the injured lesions of rat spinal cords: Inflammation, apoptosis, and cell survival

Spinal cord injury (SCI) is a devastating neurologic injury with functional deficits. In the acute phase, which starts at the moment of the injury and extends over the first few days, numerous pathological processes begin. In this study, we made several additional advances to broaden our understanding of SCI-induced gene expression changes. We examined changes at multiple time points: 0, 6, 24, 48, and 72 h after injury, with the latter time period being added. Also, we utilized multiple analysis methods such as real-time RT-PCR, Western blot, and immunohistochemistry to increase confidence in our candidate gene and molecular processes. From the pool of information, we generated profiles of expression changes and molecular mechanisms of several injury processing. Early stages after the injury are characterized by the strong upregulation of genes involved in transcription, inflammation, and signaling proteins, and a general downregulation of neural function-related genes. In addition, edema of the spinal cord develops, and metabolic disturbances involving intra-neuronal Ca2+ accumulation occur. This translates into a general failure of normal neural functions and a stage of signal shock that lasts for a few days in experimental rat models. Traumatic injury to the spinal cord also leads to a strong inflammatory response with the recruitment of peripherally derived immature cells, such as ED1-positive macrophages. After the trauma, apoptotic cell death continues, and scarring and demyelination accompany Wallerian degeneration. Strong expression of transcription factors of the Janus-activated kinase (JAK) and signal transducer and activator of transcription (STAT) family represents an early attempt of spinal cord repair and regeneration. Our study allowed us to conclude that combined therapeutic strategies for enhanced recovery should be performed until the chronic phase of the injury in areas distal to the lesion epicenter of spinal cords.

Effects of second generation tetracyclines on penicillin-epilepsy-induced hippocampal neuronal loss and motor incoordination in rats

Epileptic seizures cause pathological changes such as sclerosis and pyramidal neuronal loss in the hippocampus. Experimentally, epilepsy can be induced by application of various chemicals directly to the cerebral cortex. In this study, epilepsy was induced in rats by intracortical application of 500 IU penicillin G, and the effect of minocycline and doxycycline on the resulting motor incoordination (rotarod) and hippocampal neuronal loss in CA1, CA2 and CA3 fields (optical fractionator method) were investigated. The rotarod performance was reduced in the epilepsy group to 285.1+/-6.9 s (P<0.05 vs. sham-300 s). Minocycline and doxycycline increased this performance to 297.4+/-1.0 s and 296.9+/-1.2 s respectively. No significant difference was detected between minocycline and doxycycline. The present results also showed that the number of neurons (x10(3)) in the sham group was 150+/-9. In the penicillin-epileptic rats, the number was decreased to 105+/-7 (P<0.01). Minocycline, but not doxycycline (125+/-8), significantly increased the number to 131+/-3 (P<0.05). In conclusion, the second generation tetracycline minocycline decreased the loss of hippocampal neurons and motor incoordination in penicillin-epileptic rats. Minocycline could protect against a variety of neurological insults including epilepsy.

Strategies of medical intervention in the management of acute spinal cord injury

STUDY DESIGN

: Literature review.

OBJECTIVE

: The purpose of this paper is to review clinical treatment strategies and future developments in the treatment of acute spinal cord injury.

SUMMARY OF BACKGROUND DATA

: The treatment of acute spinal cord injury continues to be supportive. The search for specialized pharmacologic agents to prevent secondary injury and promote repair or regeneration remains heated.

METHODS

: Medline search from 1996 to present limited to clinical research and basic science review articles in the English Language.

RESULTS

: Steroids continue to be administered in the clinical setting of acute spinal cord injury primarily out of peer pressure and fear of litigation. Basic science experiments suggest that modulation of post-traumatic inflammation may provide the best opportunity to arrest the secondary injury cascade. Protein kinase and metalloproteinase inhibition are promising treatment strategies. Regeneration techniques are concentrating on cell transplantation and manipulating glial receptors and protein production. Clinical investigations are limited to Phase III trials on a very select few of these drugs.

CONCLUSIONS

: While many advances in the basic science of spinal cord injury provide optimism for future treatments, clinical science lags. At present, there are no pharmacologic strategies of proven benefit. Although steroids continue to be given to patients with spinal cord injury in many institutions, evidence of deleterious effects continues to accumulate. Current standard of care management includes support of arterial oxygenation and spinal cord perfusion pressure.

Activated microglia contribute to the maintenance of chronic pain after spinal cord injury

Traumatic spinal cord injury (SCI) results not only in motor impairment but also in chronic central pain, which can be refractory to conventional treatment approaches. It has been shown recently that in models of peripheral nerve injury, spinal cord microglia can become activated and contribute to development of pain. Considering their role in pain after peripheral injury, and because microglia are known to become activated after SCI, we tested the hypothesis that activated microglia contribute to chronic pain after SCI. In this study, adult male Sprague Dawley rats underwent T9 spinal cord contusion injury. Four weeks after injury, when lumbar dorsal horn multireceptive neurons became hyperresponsive and when behavioral nociceptive thresholds were decreased to both mechanical and thermal stimuli, intrathecal infusions of the microglial inhibitor minocycline were initiated. Electrophysiological experiments showed that minocycline rapidly attenuated hyperresponsiveness of lumbar dorsal horn neurons. Behavioral data showed that minocycline restored nociceptive thresholds, at which time spinal microglial cells assumed a quiescent morphological phenotype. Levels of phosphorylated-p38 were decreased in SCI animals receiving minocycline. Cessation of delivery of minocycline resulted in an immediate return of pain-related phenomena. These results suggest an important role for activated microglia in the maintenance of chronic central below-level pain after SCI and support the newly emerging role of non-neuronal immune cells as a contributing factor in post-SCI pain.

Delayed minocycline treatment reduces long-term functional deficits and histological injury in a rodent model of focal ischemia

The absence of effective treatments for stroke presents a critical need for novel strategies that can reduce ischemic injury. Neuroinflammation following focal ischemia induces secondary injury in the region surrounding the insult, thus anti-inflammatory agents are potential neuroprotectants. Minocycline is one such agent possessing neuroprotective properties, however many studies examining minocycline after ischemia have used minimal delays between ischemia and treatment, short survival periods, and lack measures of functional outcome. Such studies do not distinguish whether minocycline provides sustained protection or merely delays cell death. This study was designed to address some of these concerns. Male Sprague-Dawley rats were treated with multiple doses of minocycline (45 mg/kg i.p.) or vehicle beginning 2.5 h after endothelin-1-induced focal ischemia. Measures of forelimb asymmetry and skilled reaching (staircase test) were used to determine functional outcome 7, 15 and 28 days after ischemia. Long-term functional assessment indicates that minocycline provides limited benefit in the staircase test, but confers long-term benefit in the forelimb asymmetry test. Subcortical and whole hemisphere infarct volumes were reduced by 41 and 39% respectively in minocycline-treated animals. Further analysis revealed that minocycline attenuated long-term white matter damage adjacent to the striatal injury core, which correlated with sustained functional benefits. This study indicates that delayed minocycline treatment improves long-term functional outcome which is linked to protection of both white and gray matter.

Minocycline treatment prevents cavitation in rats after a cortical devascularizing lesion

Minocycline, a second-generation tetracycline, has been shown to possess neuroprotective effects in animal models of stroke. Pial vessel disruption in adult Wistar rats leads to a cone-shaped cortical lesion and turns into a fluid-filled cavity surrounded by a GFAP+ glia limitans 21 days after injury. This mimics the clinical situation in lacunar infarcts. Minocycline was given intraperitoneally at a dose of 45 mg/kg 1 and 12 h after lesioning, followed by 22.5 mg/kg twice daily until 6 days after lesioning. Control rats received intraperitoneal injections of equivalent volumes of saline. Cavitation was prevented in five out of six minocycline-treated animals and the glia limitans did not appear as the space was filled with GFAP+ reactive astrocytes. However, the number of activated microglia showed no difference between minocycline-treated and -untreated groups. Minocycline did not reduce the number of infiltrating leukocytes, predominately polymorphonuclear neutrophils (PMNs) determined by myeloperoxidase immunoreactivity, or infiltration of CD3+ lymphocytes. The pial vessel occlusion induced a significant upregulation of IL-1beta expression; however, minocycline treatment did not significantly alter this upregulation of IL-1beta. In this study, we found minocycline facilitated the repopulation of the lesion by reactive astrocytes and therefore prevented cavitation; however, we could not identify the molecular signal.

Neuroprotection in brain and spinal cord trauma

PURPOSE OF REVIEW

Traumatic brain and spinal cord injuries continue to be a public health problem. These types of injuries often occur in early adulthood and have a major impact for society. This review discusses strategies and therapeutic agents for perioperative neuroprotection in the management of brain and spinal cord trauma.

RECENT FINDINGS

There are no definitive drugs or strategies that can be utilized to provide perioperative neuroprotection in brain and spinal cord trauma patients. Phase III trials of several pharmacologic agents, including inhibitors of oxidative and excitotoxic injury, have been unable to demonstrate clinical efficacy. Although experimental animal data for hypothermia have been promising over the years, clinical application of therapeutic hypothermia cannot be recommended for routine use in neurotrauma patients. Administration of methylprednisolone, which has become common practice in acute spinal cord injury, has come under close scrutiny. Various experimental animal investigations suggest that potential therapeutic agents include estrogen, progesterone, minocycline, erythropoietin, and magnesium.

SUMMARY

The main priority in the initial treatment of brain and spinal cord trauma is to maintain oxygenation and perfusion in order to avoid aggravating secondary injury. Future progress will depend on the translation of neuroprotective strategies into well designed clinical trials with promising outcomes.

Minocycline neuroprotects, reduces microgliosis, and inhibits caspase protease expression early after spinal cord injury

Minocycline, a clinically used tetracycline for over 40 years, crosses the blood-brain barrier and prevents caspase up-regulation. It reduces apoptosis in mouse models of Huntington's disease and familial amyotrophic lateral sclerosis (ALS) and is in clinical trial for sporadic ALS. Because apoptosis also occurs after brain and spinal cord (SCI) injury, its prevention may be useful in improving recovery. We analyzed minocycline's neuroprotective effects over 28 days following contusion SCI and found significant functional recovery compared to tetracycline. Histology, immunocytochemistry, and image analysis indicated statistically significant tissue sparing, reduced apoptosis and microgliosis, and less activated caspase-3 and substrate cleavage. Since our original report in abstract form, others have published both positive and negative effects of minocycline in various rodent models of SCI and with various routes of administration. We have since found decreased tumor necrosis factor-alpha, as well as caspase-3 mRNA expression, as possible mechanisms of action for minocycline's ameliorative action. These results support reports that modulating apoptosis, caspases, and microglia provide promising therapeutic targets for prevention and/or limiting the degree of functional loss after CNS trauma. Minocycline, and more potent chemically synthesized tetracyclines, may find a place in the therapeutic arsenal to promote recovery early after SCI in humans.

Update on antimicrobial agents: new indications of older agents

The discovery of newly recognised pathogens and the emergence of antimicrobial resistance have led to the development of new antimicrobial agents or to new indications for older agents. The indications have continued to increase because of new discoveries on the older agents' antimicrobial and non-antimicrobial activities. Macrolides and tetracyclines have received attention for their non-antimicrobial properties and potential use in chronic inflammatory disorders. Doxycycline, minocycline and trimethoprim-sulfamethoxazole regained interest for their activity against methicillin-resistant Staphylococcus aureus, whereas colistin has regained interest for its activity against multiple drug-resistant, Gram-negative pathogens (i.e., Pseudomonas aeruginosa). Despite the recent development of new antimicrobial agents, older and less costly agents maintain an important role today in the treatment of infectious diseases.

Expression of two temporally distinct microglia-related gene clusters after spinal cord injury

The dual role of microglia in cytotoxicity and neuroprotection is believed to depend on the specific, temporal expression of microglial-related genes. To better clarify this issue, we used high-density oligonucleotide microarrays to examine microglial gene expression after spinal cord injury (SCI) in rats. We compared expression changes at the lesion site, as well as in rostral and caudal regions after mild, moderate, or severe SCI. Using microglial-associated anchor genes, we identified two clusters with different temporal profiles. The first, induced by 4 h postinjury to peak between 4 and 24 h, included interleukin-1beta, interleukin-6, osteopontin, and calgranulin, among others. The second was induced 24 h after SCI, and peaked between 72 h and 7 days; it included C1qB, Galectin-3, and p22(phox). These two clusters showed similar expression profiles regardless of injury severity, albeit with slight decreases in expression in mild or severe injury vs. moderate injury. Expression was also decreased rostral and caudal to the lesion site. We validated the expression of selected cluster members at the mRNA and protein levels. In addition, we demonstrated that stimulation of purified microglia in culture induces expression of C1qB, Galectin-3, and p22(phox). Finally, inhibition of p22(phox) activity within microglial cultures significantly suppressed proliferation in response to stimulation, confirming that this gene is involved in microglial activation. Because microglial-related factors have been implicated both in secondary injury and recovery, identification of temporally distinct clusters of genes related to microglial activation may suggest distinct roles for these groups of factors.

Minocycline protects PC12 cells against NMDA-induced injury via inhibiting 5-lipoxygenase activation

Recently, we have reported that minocycline, a semi-synthetic tetracycline with neuroprotective effects, inhibits the in vitro ischemic-like injury and 5-lipoxygenase (5-LOX) activation in PC12 cells. In the present study, we further determined whether minocycline protects PC12 cells from excitotoxicity via inhibiting 5-LOX activation. We used N-methyl-d-aspartate (NMDA, 200 microM) to induce early (exposure for 6 h) and delayed (exposure for 6 h followed by 24 h recovery) injuries. We found that NMDA receptor antagonist ketamine, 5-LOX inhibitor caffeic acid and minocycline concentration dependently attenuated NMDA-induced early and delayed cell injuries (viability reduction and cell death). However, only ketamine (1 microM) inhibited NMDA-evoked elevation of intracellular calcium. In addition, immunohistochemical analysis showed that NMDA induced 5-LOX translocation to the nuclear membrane after 1- to 6-h exposure which was confirmed by Western blotting, indicating that 5-LOX was activated. Ketamine, caffeic acid and minocycline (each at 1 microM) inhibited 5-LOX translocation after early injury. After delayed injury, PC12 cells were shrunk, and 5-LOX was translocated to the nuclei and nuclear membrane; ketamine, caffeic acid and minocycline inhibited both cell shrinking and 5-LOX translocation. As a control, 12-LOX inhibitor baicalein showed a weak effect on cell viability and death, but no effect on 5-LOX translocation. Therefore, we conclude that the protective effect of minocycline on NMDA-induced injury is partly mediated by inhibiting 5-LOX activation.

Minocycline for short-term neuroprotection

Minocycline is a widely used tetracycline antibiotic. For decades, it has been used to treat various gram-positive and gram-negative infections. Minocycline was recently shown to have neuroprotective properties in animal models of acute neurologic injury. As a neuroprotective agent, the drug appears more effective than other treatment options. In addition to its high penetration of the blood-brain barrier, minocycline is a safe compound commonly used to treat chronic infections. Its several mechanisms of action in neuroprotection -- antiinflammatory and antiapoptotic effects, and protease inhibition -- make it a desirable candidate as therapy for acute neurologic injury, such as ischemic stroke. Minocycline is ready for clinical trials of acute neurologic injury.

Respiratory abnormalities resulting from midcervical spinal cord injury and their reversal by serotonin 1A agonists in conscious rats

Respiratory dysfunction after cervical spinal cord injury (SCI) has not been examined experimentally using conscious animals, although clinical SCI most frequently occurs in midcervical segments. Here, we report a C5 hemicontusion SCI model in rats with abnormalities that emulate human post-SCI pathophysiology, including spontaneous recovery processes. Post-C5 SCI rats demonstrated deficits in minute ventilation (Ve) responses to a 7% CO2 challenge that correlated significantly with lesion severities (no injury or 12.5, 25, or 50 mm x 10 g weight drop; New York University impactor; p < 0.001) and ipsilateral motor neuron loss (p = 0.016). Importantly, C5 SCI resulted in at least 4 weeks of respiratory abnormalities that ultimately recovered afterward. Because serotonin is involved in respiration-related neuroplasticity, we investigated the impact of activating 5-HT1A receptors on post-C5 SCI respiratory dysfunction. Treatment with the 5-HT1A agonist 8-hydroxy-2-(di-n-propylmino)tetralin (8-OH DPAT) (250 microg/kg, i.p.) restored hypercapnic Ve at 2 and 4 weeks after injury (i.e., approximately 39.2% increase vs post-SCI baseline; p < or = 0.033). Improvements in hypercapnic Ve response after single administration of 8-OH DPAT were dose dependent and lasted for approximately 4 h(p < or = 0.038 and p < or = 0.024, respectively). Treatment with another 5-HT1A receptor agonist, buspirone (1.5 mg/kg, i.p.), replicated the results, whereas pretreatment with a 5-HT1A-specific antagonist, 4-iodo-N-[2-[4(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide (3 mg/kg, i.p.) given 20 min before 8-OH DPAT negated the effect of 8-OH DPAT. These results imply a potential clinical use of 5-HT1A agonists for post-SCI respiratory disorders.

Combination therapy using minocycline and coenzyme Q10 in R6/2 transgenic Huntington's disease mice

Huntington's disease (HD) is a fatal neurodegenerative disorder of genetic origin with no known therapeutic intervention that can slow or halt disease progression. Transgenic murine models of HD have significantly improved the ability to assess potential therapeutic strategies. The R6/2 murine model of HD, which recapitulates many aspects of human HD, has been used extensively in pre-clinical HD therapeutic treatment trials. Of several potential therapeutic candidates, both minocycline and coenzyme Q10 (CoQ10) have been demonstrated to provide significant improvement in the R6/2 mouse. Given the specific cellular targets of each compound, and the broad array of abnormalities thought to underlie HD, we sought to assess the effects of combined minocycline and CoQ10 treatment in the R6/2 mouse. Combined minocycline and CoQ10 therapy provided an enhanced beneficial effect, ameliorating behavioral and neuropathological alterations in the R6/2 mouse. Minocycline and CoQ10 treatment significantly extended survival and improved rotarod performance to a greater degree than either minocycline or CoQ10 alone. In addition, combined minocycline and CoQ10 treatment attenuated gross brain atrophy, striatal neuron atrophy, and huntingtin aggregation in the R6/2 mice relative to individual treatment. These data suggest that combined minocycline and CoQ10 treatment may offer therapeutic benefit to patients suffering from HD.

Experimental strategies to promote spinal cord regeneration--an integrative perspective

Detailed pathophysiological findings of secondary damage phenomena after spinal cord injury (SCI) as well as the identification of inhibitory and neurotrophic proteins have yielded a plethora of experimental therapeutic approaches. Main targets are (i) to minimize secondary damage progression (neuroprotection), (ii) to foster axon conduction (neurorestoration) and (iii) to supply a permissive environment to promote axonal sprouting (neuroregenerative therapies). Pre-clinical studies have raised hope in functional recovery through the antagonism of growth inhibitors, application of growth factors, cell transplantation, and vaccination strategies. To date, even though based on successful pre-clinical animal studies, results of clinical trials are characterized by dampened effects attributable to difficulties in the study design (patient heterogeneity) and species differences. A combination of complementary therapeutic strategies might be considered pre-requisite for future synergistic approaches. Here, we line out pre-clinical interventions resulting in improved functional neurological outcome after spinal cord injury and track them on their intended way to bedside.

Intravenous polyethylene glycol inhibits the loss of cerebral cells after brain injury

We have tested the effectiveness of polyethylene glycol (PEG) to restore the integrity of neuronal membranes after mechanical damage secondary to severe traumatic brain injury (TBI) produced by a standardized head injury model in rats. We provide additional detail on the standardization of this model, particularly the use and storage of foam bedding that serves to both support the animal during the impact procedure-and as a dampener to the acceleration of the brass weight. Further, we employed a dye exclusion technique using ethidium bromide (EB; quantitative evaluation) and horseradish peroxidase (HRP; qualitative evaluation). Both have been successfully used previously to evaluate neural injury in the spinal cord since they enter cells when their plasma membranes are damaged. We quantified EB labeling (90 microM in 110 microL of sterile saline) after injection into the left lateral ventricle of the rat brain 2 h after injury. At six h after injection and 8 h after injury, the animals were sacrificed and the brains were analyzed. In the injured rat brain, EB entered cells lining and medial to the ventricles, particularly the axons of the corpus callosum. There was minimal EB labeling in uninjured control brains, limited to cells lining the luminal surfaces of the ventricles. Intravenous injections of PEG (1 cc of saline, 30% by volume, 2000 MW) immediately after severe TBI resulted in significantly decreased EB uptake compared with injured control animals. A similar result was achieved using the larger marker, HRP. PEG-treated brains closely resembled those of uninjured animals.

Minocycline and intracerebral hemorrhage: influence of injury severity and delay to treatment

Intracerebral hemorrhage (ICH) is a devastating condition currently lacking a defined line of treatment. The inflammatory response that ensues following its onset is thought to contribute to secondary injury following ICH, making inflammation a potential therapeutic target. Minocycline (MC), a commonly used antibiotic that also has anti-inflammatory and anti-apoptotic properties, provides histological protection in several animal stroke models when given soon after injury. However, its ability to provide protection with more clinically relevant delays is unknown. The objective of this study was to examine the effects of MC on histopathological changes and long-term functional outcomes in a collagenase-induced ICH model in rats when drug administration was delayed 3 h following the onset of ICH. In accordance with other studies, MC suppressed microglial/macrophage activation in the peri-infarct region at 5 days based on B4 isolectin histochemistry. However, no reduction in infarct volume was detected at 5 or 28 days post-ICH. Minocycline given for either 5 or 14 days also provided no functional benefit as assessed with a battery of sensory-motor tests (i.e., staircase, cylinder, ladder tests). These findings raise questions about the ability of MC to provide protection in ICH when delay to treatment is increased.

Minocycline up-regulates BCL-2 levels in mitochondria and attenuates male germ cell apoptosis

In this study, we determined the efficacy of minocycline, a second generation tetracycline, in preventing male germ cell apoptosis after withdrawal of gonadotropins and intratesticular testosterone (T). Groups of 5 male rats received one of the following treatments daily for 5 days: (i) daily sc injection of GnRH-A (1.6 mg/kg BW), (ii) oral administration of 30% gum acacia as a vehicle control, and (iii) GnRH-A + oral administration of 50 or 100 mg/kg BW of minocycline. Minocycline at both 50 and 100 mg dose levels significantly (P < 0.05) prevented GnRH-A -induced germ cell apoptosis by 59.4% and 62.2%, respectively, and fully prevented PARP cleavage. Minocycline-mediated protection occurred at the mitochondria, involving the restoration of the BCL-2 levels and, in turn, suppression of cytochrome c and DIABLO release. Minocycline was also effective in preventing human male germ cell apoptosis induced by hormone free culture condition.

Intrathecal minocycline attenuates peripheral inflammation-induced hyperalgesia by inhibiting p38 MAPK in spinal microglia

Activation of p38 mitogen-activated protein kinase (p38) in spinal microglia is implicated in spinal nociceptive processing. Minocycline, a tetracycline derivative, displays selective inhibition of microglial activation, a function that is distinct from its antibiotic activity. In the present study we examined antinociceptive effects of intrathecal (IT) administration of minocycline in experimental models of inflammation-evoked hyperalgesia in addition to the effect of minocycline on stimulation-induced activation of p38 in spinal microglia. Intrathecal minocycline produced a dose-dependent reduction of formalin-evoked second-phase flinching behaviour in rats, and prevented thermal hyperalgesia induced by carrageenan injection into the paw. In contrast, systemic delivery (intraperitoneally) of minocycline inhibited the first but not the second phase of formalin-induced flinching, and it had no effect on carrageenan-induced hyperalgesia. Centrally mediated hyperalgesia induced by IT delivery of N-methyl-d-aspartate was completely blocked by IT minocycline. An increase in phosphorylation (activation) of p38 (P-p38) was observed in the dorsal spinal cord after carrageenan paw injection, assessed by both Western blotting and immunohistochemistry. The increased P-p38 immunoreactivity was seen primarily in microglia but also in a small population of neurons. Minocycline, at the IT dose that blocked carrageenan-induced hyperalgesia, also attenuated the increased P-p38 in microglia. In addition, minocycline suppressed lipopolysaccharide-evoked P-p38 in cultured spinal microglial cells. Taken together, these findings show that minocycline given IT produces a potent and consistent antinociception in models of tissue injury and inflammation-evoked pain, and they provide strong support for the idea that this effect is mediated by direct inhibition of spinal microglia and subsequent activation of p38 in these cells.

Protecting Neurons

Brain injury evolves over time, often taking days or even weeks to fully develop. It is a dynamic process that involves immediate oxidative stress and excitotoxicity followed by inflammation and preprogrammed cell death. This article presents a brief overview of mechanisms of neuroprotection in the developing brain. Although the focus is on ischemic injury, the conclusions drawn apply to any type of brain insult-epileptic seizures, trauma, or ischemia. Strategies of neuroprotection include salvaging neurons through the use of targeted pharmacotherapies, protecting neurons through preconditioning, and repairing neurons by enhancing neurogenesis. Drug therapies that dampen the impact of immediate and downstream postinjury events are only modestly effective in protecting the brain from ischemic injury. In experimental models, complete or true protection can be achieved only through preconditioning, a process during which an animal develops tolerance to an otherwise lethal stressor. Although of no clinical use, preconditioning models have provided valuable insight into how repair systems work in the brain. Cumulative evidence indicates that the same genes that are upregulated during preconditioning, those mediating true protection, are also upregulated during injury and repair. Specifically, hypoxic preconditioning and hypoxic-ischemic insult have been shown to induce hypoxia inducible factor-1 (HIF-1) and its target survival genes, vascular endothelial growth factor (VEGF), and erythropoietin (Epo) in rodents. Of particular interest is the upregulation of Epo, a growth factor that may have therapeutic potential in the treatment of ischemic stroke. At this time, however, the postinjury enhancement of neurogenesis appears to offer the best hope for long-lasting functional recovery following brain injury.

Antioxidant properties of minocycline: neuroprotection in an oxidative stress assay and direct radical-scavenging activity

Minocycline is neuroprotective in animal models of a number of acute CNS injuries and neurodegenerative diseases. While anti-inflammatory and anti-apoptotic effects of minocycline have been characterized, the molecular basis for the neuroprotective effects of minocycline remains unclear. We report here that minocycline and a number of antioxidant compounds protect mixed neuronal cultures in an oxidative stress assay. To evaluate the role of minocycline's direct antioxidant properties in neuroprotection, we determined potencies for minocycline, other tetracycline antibiotics, and reference antioxidant compounds using a panel of in vitro radical scavenging assays. Data from in vitro rat brain homogenate lipid peroxidation and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays show that minocycline, in contrast to tetracycline, is an effective antioxidant with radical scavenging potency similar to vitamin E. Our findings suggest that the direct antioxidant activity of minocycline may contribute to its neuroprotective effects in some cell-based assays and animal models of neuronal injury.

Strategies to promote neural repair and regeneration after spinal cord injury

STUDY DESIGN

Retrospective review of current literature regarding neuroprotection and axonal regeneration therapies for acute spinal cord injury.

OBJECTIVES

To provide an update for spine clinicians of the emerging therapeutic strategies for promoting neural repair and regeneration after spinal cord injury.

SUMMARY OF BACKGROUND DATA

The neuroscientific community has generated a number of novel potential treatments for spinal injuries, some of which have entered clinical trials. Clinicians who manage spinal cord trauma are likely to encounter patients and their families who have questions or wish to be involved in these emerging treatments.

METHODS

Literature review, with particular focus on currently used medications that may have neuroprotective potential in spinal cord injury, and axonal regeneration strategies that are emerging in preliminary human clinical trials.

RESULTS

A number of medications such as erythropoietin and minocycline have demonstrated neuroprotective properties in animal models of spinal cord injury, and their long-established safety in humans make them appealing candidates for clinical trials. Human experience with novel neuroprotective and axonal regeneration strategies is growing around the world, and the peer-reviewed reporting of this is anxiously awaited.

CONCLUSIONS

The initiation of human clinical trials for spinal cord-injured patients heralds great hope that effective therapies will be forthcoming, although a great deal remains to be learned. Clinicians must provide leadership in the epidemiologic design and rigor of these initial forays into human evaluation.

Minocycline confers early but transient protection in the immature brain following focal cerebral ischemia-reperfusion

The incidence of neonatal stroke is high and currently there are no strategies to protect the neonatal brain from stroke or reduce the sequelae. Agents capable of modifying inflammatory processes hold promise. We set out to determine whether delayed administration of one such agent, minocycline, protects the immature brain in a model of transient middle cerebral artery (MCA) occlusion in 7-day-old rat pups. Injury volume in minocycline (45 mg/kg/dose, beginning at 2 h after MCA occlusion) and vehicle-treated pups was determined 24 h and 7 days after onset of reperfusion. Accumulation of activated microglia/macrophages, phosphorylation of mitogen-activated protein kinase (MAPK) p38 in the brain, and concentrations of inflammatory mediators in plasma and brain were determined at 24 h. Minocycline significantly reduced the volume of injury at 24 h but not 7 days after transient MCA occlusion. The beneficial effect of minocycline acutely after reperfusion was not associated with changed ED1 phenotype, nor was the pattern of MAPK p38 phosphorylation altered. Minocycline reduced accumulation of IL-1beta and CINC-1 in the systemic circulation but failed to affect the increased levels of IL-1beta, IL-18, MCP-1 or CINC-1 in the injured brain tissue. Therefore, minocycline provides early but transient protection, which is largely independent of microglial activation or activation of the MAPK p38 pathway.

Cytochrome C release from CNS mitochondria and potential for clinical intervention in apoptosis-mediated CNS diseases

Apoptosis is critical for normal development and tissue homeostasis. However, its abnormal occurrence has been implicated in a number of disorders, including neurodegenerative diseases and stroke. Translocation of cytochrome c (Cyt c) from mitochondria to the cytoplasm is a key step in the initiation and/or amplification of apoptosis. Here we discuss Cyt c release in apoptosis with its impact on the CNS and review our studies of Cyt c release from isolated rat brain mitochondria in response to several insults. Calcium-induced Cyt c release, as occurs in neurons during stroke and ischemia, involves rupture of the mitochondrial outer membrane (MOM) and can be blocked by inhibitors of the mitochondrial permeability transition (mPT). Thus, inhibitors of the mPT have shown efficacy in animal models of ischemia. In contrast, proapoptotic proteins, such as BID, BAX, and BAK, induce Cyt c release independently of the mPT without lysing the MOM. Several inhibitors of BAX-induced Cyt c release have shown promise in models of CNS apoptosis. Because of their distinct mechanisms for Cyt c release, both the mPT and proapoptotic proteins should be targeted for effective clinical intervention in CNS disorders involving apoptosis.

Molecular targets in spinal cord injury

The spinal cord can be compared to a highway connecting the brain with the different body levels lying underneath, with the axons being the ultimate carriers of the electrical impulse. After spinal cord injury (SCI), many cells are lost because of the injury. To reconstitute function, damaged axons from surviving neurons have to grow through the lesion site to their initial targets. However, the territory they have to traverse has changed: the highway is full of inhibitory signals (myelin and scar components); the pavement itself has become bumpy (demyelination); and specialized cells are recruited to clear the way (inflammatory cells). Thus, actual strategies to treat spinal injuries aim at providing a permissive environment for regenerating axons and boosting the endogenous potential of axons to regenerate while limiting progression of secondary damage. Here we review some of the strategies currently under consideration to treat spinal injuries.

Neuroprotective effects of minocycline against in vitro and in vivo retinal ganglion cell damage

The purpose of this study was to determine whether minocycline, a semi-synthetic tetracycline derivative, reduces (a) the in vitro neuronal damage occurring after serum deprivation in cultured retinal ganglion cells (RGC-5, a rat ganglion cell line transformed using E1A virus) and/or (b) the in vivo retinal damage induced by N-methyl-D-aspartate (NMDA) intravitreal injection in mice. In addition, we examined minocycline's putative mechanisms of action against oxidative stress and endoplasmic reticulum (ER) stress. In vitro, retinal damage was induced by 24-h serum deprivation, and cell viability was measured by Hoechst 33342 staining or resazurin reduction assay. In cultures of RGC-5 cells maintained in serum-free medium for up to 24 h, the number of cells undergoing cell death was reduced by minocycline (0.2-20 microM). Serum deprivation resulted in increased oxidative stress, as revealed by an increase in the fluorescence intensity for 5-(and-6)-chloromethyl-2', 7'-dichlorodihydrofluorescein diacetate (CM-H2DCFDA), a reactive oxygen species (ROS) indicator. Minocycline at 2 and 20 microM inhibited this ROS production. However, even at 20 microM minocycline did not inhibit the retinal damage induced by tunicamycin (an ER stress inducer). Furthermore, in mice in vivo minocycline at 90 mg/kg intraperitoneally administered 60 min before an NMDA intravitreal injection reduced the NMDA-induced retinal damage. These findings indicate that minocycline has neuroprotective effects against in vitro and in vivo retinal damage, and that an inhibitory effect on ROS production may contribute to the underlying mechanisms.

Chemotherapy for the brain: the antitumor antibiotic mithramycin prolongs survival in a mouse model of Huntington's disease

Huntington's disease (HD) is a fully penetrant autosomal-dominant inherited neurological disorder caused by expanded CAG repeats in the Huntingtin gene. Transcriptional dysfunction, excitotoxicity, and oxidative stress have all been proposed to play important roles in the pathogenesis of HD. This study was designed to explore the therapeutic potential of mithramycin, a clinically approved guanosine-cytosine-rich DNA binding antitumor antibiotic. Pharmacological treatment of a transgenic mouse model of HD (R6/2) with mithramycin extended survival by 29.1%, greater than any single agent reported to date. Increased survival was accompanied by improved motor performance and markedly delayed neuropathological sequelae. To identify the functional mechanism for the salubrious effects of mithramycin, we examined transcriptional dysfunction in R6/2 mice. Consistent with transcriptional repression playing a role in the pathogenesis of HD, we found increased methylation of lysine 9 in histone H3, a well established mechanism of gene silencing. Mithramycin treatment prevented the increase in H3 methylation observed in R6/2 mice, suggesting that the enhanced survival and neuroprotection might be attributable to the alleviation of repressed gene expression vital to neuronal function and survival. Because it is Food and Drug Administration-approved, mithramycin is a promising drug for the treatment of HD.

Minocycline reduces proinflammatory cytokine expression, microglial activation, and caspase-3 activation in a rodent model of diabetic retinopathy

Diabetes leads to vascular leakage, glial dysfunction, and neuronal apoptosis within the retina. The goal of the studies reported here was to determine the role that retinal microglial cells play in diabetic retinopathy and assess whether minocycline can decrease microglial activation and alleviate retinal complications. Immunohistochemical analyses showed that retinal microglia are activated early in diabetes. Furthermore, mRNAs for interleukin-1beta and tumor necrosis factor-alpha, proinflammatory mediators known to be released from microglia, are also increased in the retina early in the course of diabetes. Using an in vitro bioassay, we demonstrated that cytokine-activated microglia release cytotoxins that kill retinal neurons. Furthermore, we showed that neuronal apoptosis is increased in the diabetic retina, as measured by caspase-3 activity. Minocycline represses diabetes-induced inflammatory cytokine production, reduces the release of cytotoxins from activated microglia, and significantly reduces measurable caspase-3 activity within the retina. These results indicate that inhibiting microglial activity may be an important strategy in the treatment of diabetic retinopathy and that drugs such as minocycline hold promise in delaying or preventing the loss of vision associated with this disease.

Minocycline inhibits oxidative stress and decreases in vitro and in vivo ischemic neuronal damage

The neuroprotective effects of minocycline-which is broadly protective in neurologic-disease models featuring cell death and is being evaluated in clinical trials-were investigated both in vitro and in vivo. For the in vivo study, focal cerebral ischemia was induced by permanent middle cerebral artery occlusion in mice. Minocycline at 90 mg/kg intraperitoneally administered 60 min before or 30 min after (but not 4 h after) the occlusion reduced infarction, brain swelling, and neurologic deficits at 24 h after the occlusion. For the in vitro studies, we used cortical-neuron cultures from rat fetuses in which neurotoxicity was induced by 24-h exposure to 500 microM glutamate. Furthermore, the effects of minocycline on oxidative stress [such as lipid peroxidation in mouse forebrain homogenates and free radical-scavenging activity against diphenyl-p-picrylhydrazyl (DPPH)] were evaluated to clarify the underlying mechanism. Minocycline significantly inhibited glutamate-induced cell death at 2 microM and lipid peroxidation and free radical scavenging at 0.2 and 2 microM, respectively. These findings indicate that minocycline has neuroprotective effects in vivo against permanent focal cerebral ischemia and in vitro against glutamate-induced cell death and that an inhibition of oxidative stress by minocycline may be partly responsible for these effects.

Functional Role of Caspases in Heat-Induced Testicular Germ Cell Apoptosis1

In the present study, we determined whether a pan caspase inhibitor could prevent or attenuate heat-induced germ cell apoptosis. Groups of five adult (8 wk old) C57BL/6 mice pretreated with vehicle (DMSO) or Quinoline-Val-Asp (Ome)-CH2-O-Ph (Q-VD-OPH), a new generation broad-spectrum caspase inhibitor, were exposed once to local testicular heating (43 degrees C for 15 min) and killed 6 h later. The inhibitor (40 mg/kg body weight) or vehicle was administered intraperitoneally (i.p.) 1 h before local testicular heating. Germ cell apoptosis was detected by TUNEL assay and quantitated as number of apoptotic germ cells per 100 Sertoli cells at stages XI-XII. Compared with controls (16.8 +/- 3.1), mild testicular hyperthermia within 6 h resulted in a marked activation (277.3 +/- 21.6) of germ cell apoptosis, as previously reported by us. Q-VD-OPH at this dose markedly inhibited caspase 3 activation and significantly prevented (by 67.0%) heat-induced germ cell apoptosis. Q-VD-OPH-mediated rescue of germ cells was independent of cytosolic translocation of mitochondrial cytochrome c and DIABLO. Electron microscopy further revealed normal appearance of these rescued cells. Similar protection from heat-induced germ cell apoptosis was also noted after pretreatment with minocycline, a second-generation tetracycline that effectively inhibits cytochrome c release and, in turn, caspase activation. Collectively, the present study emphasizes the role of caspases in heat-induced germ cell apoptosis.

Neuroprotection by tetracyclines

The neuroprotective properties of tetracyclines have been clearly established in rodent models of acute and chronic neurodegeneration during the past few years. Recent findings have provided novel insights into the molecular and cellular mechanisms of protection of neurons and oligodendrocytes by tetracyclines. These advances have prompted several clinical trials with minocycline, the most effective tetracycline, which are still in their early phases. Thus, tetracyclines hold great promise as therapeutic agents for the treatment of human neurodegenerative diseases.

Setting the stage for functional repair of spinal cord injuries: a cast of thousands

Here we review mechanisms and molecules that necessitate protection and oppose axonal growth in the injured spinal cord, representing not only a cast of villains but also a company of therapeutic targets, many of which have yet to be fully exploited. We next discuss recent progress in the fields of bridging, overcoming conduction block and rehabilitation after spinal cord injury (SCI), where several treatments in each category have entered the spotlight, and some are being tested clinically. Finally, studies that combine treatments targeting different aspects of SCI are reviewed. Although experiments applying some treatments in combination have been completed, auditions for each part in the much-sought combination therapy are ongoing, and performers must demonstrate robust anatomical regeneration and/or significant return of function in animal models before being considered for a lead role.