Mitochondrial permeability transition in CNS trauma: Cause or effect of neuronal cell death?

Low-molecular-mass peptides from the venom of the Amazonian viper Bothrops atrox protect against brain mitochondrial swelling in rat: potential for neuroprotection

The neurodegenerative diseases are important causes of morbidity and mortality in Western countries. Common mechanisms of toxicity involving mitochondrial damage have been suggested; however, a definitive treatment has not yet been found. Therefore, there has been great interest in the development of mitochondria-targeted protective compounds for the treatment of neuropathies. Animal toxins represent a promising source of new molecules with neuroprotective activity and potential to originate new drugs. We present here the effects of a low-molecular-mass peptides fraction (Ba-V) from Bothrops atrox snake venom, on rat brain mitochondrial function. Ba-V did not induce the mitochondrial swelling and moreover, was as effective as cyclosporin A (CsA) to inhibit the calcium/phosphate-induced swelling, which indicates its potential to prevent the mitochondrial permeability transition (MPT). The membrane electrochemical potential, the oxygen consumption during states-3 and -4 respirations as well as the respiratory control ratio (RCR) were not affected by Ba-V. Additionally, Ba-V did not induce reactive oxygen species (ROS) generation. Interestingly, Ba-V did not protect against the generation of ROS induced by t-BOH, which suggests a protection mechanism other than ROS scavenging. Given the important role of the mitochondrial damage and, more specifically, of MPT, in the development of neuropathies, Ba-V might be useful in the future strategies for the treatment of these diseases.

Traumatic brain injury: an overview of pathobiology with emphasis on military populations

This review considers the pathobiology of non-impact blast-induced neurotrauma (BINT). The pathobiology of traumatic brain injury (TBI) has been historically studied in experimental models mimicking features seen in the civilian population. These brain injuries are characterized by primary damage to both gray and white matter and subsequent evolution of secondary pathogenic events at the cellular, biochemical, and molecular levels, which collectively mediate widespread neurodegeneration. An emerging field of research addresses brain injuries related to the military, in particular blast-induced brain injuries. What is clear from the effort to date is that the pathobiology of military TBIs, particularly BINT, has characteristics not seen in other types of brain injury, despite similar secondary injury cascades. The pathobiology of primary BINT is extremely complex. It comprises systemic, local, and cerebral responses interacting and often occurring in parallel. Activation of the autonomous nervous system, sudden pressure-increase in vital organs such as lungs and liver, and activation of neuroendocrine-immune system are among the most important mechanisms significantly contributing to molecular changes and cascading injury mechanisms in the brain.

Brain metabolism is significantly impaired at blood glucose below 6 mM and brain glucose below 1 mM in patients with severe traumatic brain injury

INTRODUCTION

The optimal blood glucose target following severe traumatic brain injury (TBI) must be defined. Cerebral microdialysis was used to investigate the influence of arterial blood and brain glucose on cerebral glucose, lactate, pyruvate, glutamate, and calculated indices of downstream metabolism.

METHODS

In twenty TBI patients, microdialysis catheters inserted in the edematous frontal lobe were dialyzed at 1 microl/min, collecting samples at 60 minute intervals. Occult metabolic alterations were determined by calculating the lactate- pyruvate (L/P), lactate- glucose (L/Glc), and lactate- glutamate (L/Glu) ratios.

RESULTS

Brain glucose was influenced by arterial blood glucose. Elevated L/P and L/Glc were significantly reduced at brain glucose above 1 mM, reaching lowest values at blood and brain glucose levels between 6-9 mM (P < 0.001). Lowest cerebral glutamate was measured at brain glucose 3-5 mM with a significant increase at brain glucose below 3 mM and above 6 mM. While L/Glu was significantly increased at low brain glucose levels, it was significantly decreased at brain glucose above 5 mM (P < 0.001). Insulin administration increased brain glutamate at low brain glucose, but prevented increase in L/Glu.

CONCLUSIONS

Arterial blood glucose levels appear to be optimal at 6-9 mM. While low brain glucose levels below 1 mM are detrimental, elevated brain glucose are to be targeted despite increased brain glutamate at brain glucose >5 mM. Pathogenity of elevated glutamate appears to be relativized by L/Glu and suggests to exclude insulin- induced brain injury.

Mitochondria, oxidative stress, and temporal lobe epilepsy

Mitochondrial oxidative stress and dysfunction are contributing factors to various neurological disorders. Recently, there has been increasing evidence supporting the association between mitochondrial oxidative stress and epilepsy. Although certain inherited epilepsies are associated with mitochondrial dysfunction, little is known about its role in acquired epilepsies such as temporal lobe epilepsy (TLE). Mitochondrial oxidative stress and dysfunction are emerging as key factors that not only result from seizures, but may also contribute to epileptogenesis. The occurrence of epilepsy increases with age, and mitochondrial oxidative stress is a leading mechanism of aging and age-related degenerative disease, suggesting a further involvement of mitochondrial dysfunction in seizure generation. Mitochondria have critical cellular functions that influence neuronal excitability including production of adenosine triphosphate (ATP), fatty acid oxidation, control of apoptosis and necrosis, regulation of amino acid cycling, neurotransmitter biosynthesis, and regulation of cytosolic Ca(2+) homeostasis. Mitochondria are the primary site of reactive oxygen species (ROS) production making them uniquely vulnerable to oxidative stress and damage which can further affect cellular macromolecule function, the ability of the electron transport chain to produce ATP, antioxidant defenses, mitochondrial DNA stability, and synaptic glutamate homeostasis. Oxidative damage to one or more of these cellular targets may affect neuronal excitability and increase seizure susceptibility. The specific targeting of mitochondrial oxidative stress, dysfunction, and bioenergetics with pharmacological and non-pharmacological treatments may be a novel avenue for attenuating epileptogenesis.

Safety and tolerability of cyclosporin a in severe traumatic brain injury patients: results from a prospective randomized trial

Cyclosporin A (CsA) has recently been proposed for use in the early phase after traumatic brain injury (TBI), for its ability to preserve mitochondrial integrity in experimental brain injury models, and thereby provide improved behavioral outcomes as well as significant histological protection. The aim of this prospective, randomized, double-blind, dual-center, placebo-controlled trial was to evaluate the safety, tolerability, and pharmacokinetics of a single intravenous infusion of CsA in patients with severe TBI. Fifty adult severe TBI patients were enrolled over a 22-month period. Within 12 h of the injury patients received 5 mg/kg of CsA infused over 24 h, or placebo. Blood urea nitrogen (BUN), creatinine, hemoglobin, platelets, white blood cell count (WBC), and a hepatic panel were monitored on admission, and at 12, 24, 36, and 48 h, and on days 4 and 7. Potential adverse events (AEs) were also recorded. Neurological outcome was recorded at 3 and 6 months after injury. This study revealed only transient differences in BUN levels at 24 and 48 h and for WBC counts at 24 h between the CsA and placebo patients. These modest differences were not clinically significant in that they did not negatively impact on patient course. Both BUN and creatinine values, markers of renal function, remained within their normal limits over the entire monitoring period. There were no significant differences in other mean laboratory values, or in the incidence of AEs at any other measured time point. Also, no significant difference was demonstrated for neurological outcome. Based on these results, we report a good safety profile of CsA infusion when given at the chosen dose of 5 mg/kg, infused over 24 h, during the early phase after severe head injury in humans, with the aim of neuroprotection.

Expression profile of rat hippocampal neurons treated with the neuroprotective compound 2,4-dinitrophenol: up-regulation of cAMP signaling genes

2,4-Dinitrophenol (DNP) is classically known as a mitochondrial uncoupler and, at high concentrations, is toxic to a variety of cells. However, it has recently been shown that, at subtoxic concentrations, DNP protects neurons against a variety of insults and promotes neuronal differentiation and neuritogenesis. The molecular and cellular mechanisms underlying the beneficial neuroactive properties of DNP are still largely unknown. We have now used DNA microarray analysis to investigate changes in gene expression in rat hippocampal neurons in culture treated with low micromolar concentrations of DNP. Under conditions that did not affect neuronal viability, high-energy phosphate levels or mitochondrial oxygen consumption, DNP induced up-regulation of 275 genes and down-regulation of 231 genes. Significantly, several up-regulated genes were linked to intracellular cAMP signaling, known to be involved in neurite outgrowth, synaptic plasticity, and neuronal survival. Differential expression of specific genes was validated by quantitative RT-PCR using independent samples. Results shed light on molecular mechanisms underlying neuroprotection by DNP and point to possible targets for development of novel therapeutics for neurodegenerative disorders.

Role of cyclophilin D-dependent mitochondrial permeability transition in glutamate-induced calcium deregulation and excitotoxic neuronal death

In the present study we tested the hypothesis that the cyclophilin D-dependent (CyD) mitochondrial permeability transition (CyD-mPT) plays an important role in glutamate-triggered delayed calcium deregulation (DCD) and excitotoxic neuronal death. We used cultured cortical neurons from wild-type C57BL/6 and cyclophilin D-knockout mice (Ppif(-/-)). Induction of the mPT was identified by following the rapid secondary acidification of mitochondrial matrices monitored with mitochondrially targeted pH-sensitive yellow fluorescent protein. Suppression of the CyD-mPT due to genetic CyD ablation deferred DCD and mitochondrial depolarization, and increased the survival rate after exposure of neurons to 10 microM glutamate, but not to 100 microM glutamate. Ca(2+) influx into Ppif(-/-) neurons was not diminished in comparison with WT neurons judging by (45)Ca accumulation. In both types of neurons, 100 microM glutamate produced greater Ca(2+) influx than 10 microM glutamate. We hypothesize that greater Ca(2+) influx produced by higher glutamate rapidly triggered the CyD-independent mPT in both WT and Ppif(-/-) neurons equalizing their responses to supra-physiologic excitotoxic insults. In neurons exposed to moderate but pathophysiologically-relevant glutamate concentrations, an induction of the CyD-mPT appears to play an important role in mitochondrial injury contributing to DCD and cell death.

Methamphetamine- and trauma-induced brain injuries: comparative cellular and molecular neurobiological substrates

The use of methamphetamine (METH) is a growing public health problem, because its abuse is associated with long-term biochemical and structural effects on the human brain. Neurodegeneration is often observed in humans, because of mechanical injuries (e.g., traumatic brain injury [TBI]) and ischemic damage (strokes). In this review, we discuss recent findings documenting the fact that the psychostimulant drug METH can cause neuronal damage in several brain regions. The accumulated evidence from our laboratories and those of other investigators indicates that acute administration of METH leads to activation of calpain and caspase proteolytic systems. These systems are also involved in causing neuronal damage secondary to traumatic and ischemic brain injuries. Protease activation is accompanied by proteolysis of endogenous neuronal structural proteins (alphaII-spectrin protein and microtubule-associated protein-tau), evidenced by the appearance of their breakdown products after these injuries. When taken together, these observations suggest that METH exposure, like TBI, can cause substantial damage to the brain by causing both apoptotic and necrotic cell death in the brains of METH addicts who use large doses of the drug during their lifetimes. Finally, because METH abuse is accompanied by functional and structural changes in the brain similar to those in TBI, METH addicts might experience greater benefit if their treatment involved greater emphasis on rehabilitation in conjunction with potential neuroprotective pharmacological agents such as calpain and caspase inhibitors similar to those used in TBI.

Topical ophthalmic cyclosporine: pharmacology and clinical uses

Cyclosporine has been used successfully as a systemic immunomodulator for more than two decades, and numerous studies have investigated its mechanisms of action. In 2003 an ophthalmic formulation, cyclosporine 0.05% ophthalmic emulsion, was approved by the FDA to treat dry eye disease. Topical cyclosporine emulsion has also been investigated for treatment of other ocular surface disorders that may have an immune-based inflammatory component. In these trials, cyclosporine 0.05% ophthalmic emulsion has shown efficacy for management of posterior blepharitis, ocular rosacea, post-LASIK dry eye, contact lens intolerance, atopic keratoconjunctivitis, graft-versus-host disease, and herpetic stromal keratitis. As these disorders are often refractory to other available treatments, ophthalmic cyclosporine is a welcome nontoxic adjunct or replacement to potentially toxic topical or systemic immunosuppressive therapies.

Mitochondrial proteomics in experimental autoimmune uveitis oxidative stress

PURPOSE

Photoreceptor mitochondrial oxidative stress is the initial pathologic event in experimental autoimmune uveitis. In this study, the authors determined alterations in retinal mitochondrial protein levels in response to oxidative stress during the early phase of experimental autoimmune uveitis (EAU).

METHODS

Retinal mitochondrial fractions during early EAU were prepared and subjected to two-dimensional difference in gel electrophoresis (2D-DIGE). Protein spots showing differential expression were excised and subjected to matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) for peptide identification. Levels of these proteins were also confirmed by Western blot analysis. mRNA expression of these proteins was confirmed by real-time PCR. TUNEL staining was performed to detect apoptosis.

RESULTS

2D-DIGE analysis revealed differential expression of 13 proteins. Ten proteins were overexpressed, including manganese-SOD, alphaA crystallin, beta crystallin, and four proteins were downregulated, including adenosine triphosphate (ATP) synthase, malate dehydrogenase, and calretinin. Increased levels of alphaA crystallin, betaB2 crystallin, MnSOD, and aconitase and decreased levels of ATP synthase were confirmed by Western blot analysis. qPCR also confirmed the increased expression of alphaA crystallin, betaB2 crystallin, MnSOD, and Hsp70. Apoptosis was absent during this phase.

CONCLUSIONS

The presence of mitochondrial-specific oxidative stress-related proteins in the early EAU retina along with the downregulation of ATP synthase provides early evidence of stress-related retinal damage. The presence of high levels of alphaA and betaB2 crystallin in the mitochondria may prevent cell death during early EAU.

Effect of cyclosporin A on functional recovery in the spinal cord following contusion injury

Considerable evidence has shown that the immunosuppressant drug cyclosporin A (CsA) may have neuroprotective properties which can be exploited in the treatment of spinal cord injury. The aim of this study was to investigate the cellular environment within the spinal cord following injury and determine whether CsA has an effect on altering cellular interactions to promote a growth-permissive environment. CsA was administered to a group of rats 4 days after they endured a moderate contusion injury. Functional recovery was assessed using the Basso Beattie Bresnahan (BBB) locomotor rating scale at 3, 5 and 7 weeks post-injury. The rats were sacrificed 3 and 7 weeks post-injury and the spinal cords were sectioned, stained using histological and immunohistochemical methods and analysed. Using stereology, the lesion size and cellular environment in the CsA-treated and control groups was examined. Little difference in lesion volume was observed between the two groups. An improvement in functional recovery was observed within CsA-treated animals at 3 weeks. Although we did not see significant reduction in tissue damage, there were some notable differences in the proportion of individual cells contributing to the lesion. CsA administration may be used as a technique to control the cell population of the lesion, making it more permissive to neuronal regeneration once the ideal environment for regeneration and the effects of CsA administration at different time points post-injury have been identified.

Combination therapies for traumatic brain injury: prospective considerations

Traumatic brain injury (TBI) initiates a cascade of numerous pathophysiological events that evolve over time.Despite the complexity of TBI, research aimed at therapy development has almost exclusively focused on single therapies, all of which have failed in multicenter clinical trials. Therefore, in February 2008 the National Institute of Neurological Disorders and Stroke, with support from the National Institute of Child Health and Development, the National Heart, Lung, and Blood Institute, and the Department of Veterans Affairs, convened a workshop to discuss the opportunities and challenges of testing combination therapies for TBI. Workshop participants included clinicians and scientists from a variety of disciplines, institutions, and agencies. The objectives of the workshop were to: (1) identify the most promising combinations of therapies for TBI; (2) identify challenges of testing combination therapies in clinical and pre-clinical studies; and (3) propose research methodologies and study designs to overcome these challenges. Several promising combination therapies were discussed, but no one combination was identified as being the most promising. Rather, the general recommendation was to combine agents with complementary targets and effects (e.g., mechanisms and time-points), rather than focusing on a single target with multiple agents. In addition, it was recommended that clinical management guidelines be carefully considered when designing pre-clinical studies for therapeutic development.To overcome the challenges of testing combination therapies it was recommended that statisticians and the U.S. Food and Drug Administration be included in early discussions of experimental design. Furthermore, it was agreed that an efficient and validated screening platform for candidate therapeutics, sensitive and clinically relevant biomarkers and outcome measures, and standardization and data sharing across centers would greatly facilitate the development of successful combination therapies for TBI. Overall there was great enthusiasm for working collaboratively to act on these recommendations.

The optimal dosage and window of opportunity to maintain mitochondrial homeostasis following traumatic brain injury using the uncoupler FCCP

Experimental traumatic brain injury (TBI) leads to a rapid and extensive necrosis at the primary site of injury that appears to be driven in part by significant mitochondrial dysfunction. The present study is based on the hypothesis that TBI-induced, aberrant glutamate release increases mitochondrial Ca(2+) cycling/overload ultimately leading to mitochondrial damage. Previous work from our laboratory demonstrates that mitochondrial uncoupling during the acute phases of TBI-induced excitotoxicity can reduce mitochondrial Ca(2+) uptake (cycling), ROS production and mitochondrial damage resulting in neuroprotection and improved behavioral outcome. The current study was designed to determine the optimal dosage and therapeutic window of opportunity for the potent mitochondrial uncoupler FCCP following moderate TBI. For this study, we used young adult male Sprague-Dawley rats (300-350 g); either sham-operated or moderately (1.5 mm) injured using the controlled cortical impactor (CCI) model of TBI. In the first set of studies animals were injected with either vehicle (100% DMSO) or different concentrations of FCCP (0.5, 1, 2.5 and 5 mg/kg in 100% DMSO) intraperitoneally at 5 min post-injury; tested behaviorally at 10 days and cortical sparing assessed at 18 days post-injury. The results demonstrate that of all the dosages tested, 2.5 mg/kg rendered the maximum improvement in behavioral outcomes and tissue spared. Using this optimal dose (2.5 mg/kg) and time point for intervention (5 min post-injury), we assessed mitochondrial bioenergetics and mitochondrial structural integrity 24 h post-injury. Furthermore, using this dosage we assessed mitochondrial bioenergetics and Ca(2+) loading at 3 and 6 h post-injury to further verify our target mechanism and establish these assessments as a valid endpoint to use as a means to determine the therapeutic window of FCCP. To begin to address the window of opportunity for maintaining mitochondrial homeostasis, the optimal dose of FCCP was then administered at 5 min, 3, 6, or 24 h post-injury and several parameters of mitochondrial function were used as outcome measures. The results demonstrate that a prolonged window of opportunity exists for targeting mitochondrial dysfunction using uncouplers following TBI and give insight into the cellular pathology associated with TBI.

The role of mitochondrial transition pore, and its modulation, in traumatic brain injury and delayed neurodegeneration after TBI

Following severe traumatic brain injury (TBI), a complex interplay of pathomechanism, such as exitotoxicity, oxidative stress, inflammatory events, and mitochondrial dysfunction occurs. This leads to a cascade of neuronal and axonal pathologies, which ultimately lead to axonal failure, neuronal energy metabolic failure, and neuronal death, which in turn determine patient outcome. For mild and moderate TBI, the pathomechanism is similar but much less frequent and ischemic cell death is unusual, except with mass lesions. Involvement of mitochondria in acute post-traumatic neurodegeneration has been extensively studied during the last decade, and there are a number of investigations implicating the activation of the mitochondrial permeability transition pore (mPTP) as a "critical switch" which determines cell survival after TBI. Opening of the mPTP is modulated by several factors occurring after a severe brain injury. Modern neuroprotective strategies for prevention of the neuropathological squeal of traumatic brain injury have now begun to address the issue of mitochondrial dysfunction, and drugs that protect mitochondrial viability and prevent apoptotic cascade induced by mPTP opening are about to begin phase II and III clinical trials. Cyclosporin A, which has been reported to block the opening of mPTP, showed a significant decrease in mitochondrial damage and intra-axonal cytoskeletal destruction thereby protecting the axonal shaft and blunting axotomy. This review addresses an important issue of mPT activation after severe head injury, its role in acute post-traumatic neurodegeneration, and the rationale for targeting the mPTP in experimental and clinical TBI studies.

Mitochondrial mechanisms of cell death and neuroprotection in pediatric ischemic and traumatic brain injury

There are several forms of acute pediatric brain injury, including neonatal asphyxia, pediatric cardiac arrest with global ischemia, and head trauma, that result in devastating, lifelong neurologic impairment. The only clinical intervention that appears neuroprotective is hypothermia initiated soon after the initial injury. Evidence indicates that oxidative stress, mitochondrial dysfunction, and impaired cerebral energy metabolism contribute to the brain cell death that is responsible for much of the poor neurologic outcome from these events. Recent results obtained from both in vitro and animal models of neuronal death in the immature brain point toward several molecular mechanisms that are either induced or promoted by oxidative modification of macromolecules, including consumption of cytosolic and mitochondrial NAD(+) by poly-ADP ribose polymerase, opening of the mitochondrial inner membrane permeability transition pore, and inactivation of key, rate-limiting metabolic enzymes, e.g., the pyruvate dehydrogenase complex. In addition, the relative abundance of pro-apoptotic proteins in immature brains and neurons, and particularly within their mitochondria, predisposes these cells to the intrinsic, mitochondrial pathway of apoptosis, mediated by Bax- or Bak-triggered release of proteins into the cytosol through the mitochondrial outer membrane. Based on these pathways of cell dysfunction and death, several approaches toward neuroprotection are being investigated that show promise toward clinical translation. These strategies include minimizing oxidative stress by avoiding unnecessary hyperoxia, promoting aerobic energy metabolism by repletion of NAD(+) and by providing alternative oxidative fuels, e.g., ketone bodies, directly interfering with apoptotic pathways at the mitochondrial level, and pharmacologic induction of antioxidant and anti-inflammatory gene expression.

Adaptation to oxidative challenge induced by chronic physical exercise prevents Na+,K+-ATPase activity inhibition after traumatic brain injury

Physical exercise is likely to alter brain function and to afford neuroprotection in several neurological diseases. Although the favorable effects of physical exercise on traumatic brain injury (TBI) patients is well known, little information is available regarding the role of free radicals in the improvement induced by physical exercise in an experimental model of TBI induced by fluid percussion injury (FPI). Thus, we investigated whether 6 weeks of swimming training protects against oxidative damage (measured by protein carbonylation and thiobarbituric acid-reactive substances-TBARS) and neurochemical alterations represented by immunodetection of alpha subunit and activity of Na(+),K(+)-ATPase after FPI in cerebral cortex of rats. Statistical analysis revealed that physical training protected against FPI-induced TBARS and protein carbonylation increase. In addition, physical training was effective against Na(+),K(+)-ATPase enzyme activity inhibition and alpha(1) subunit level decrease after FPI. Pearson's correlation analysis revealed that the decrease in levels of catalytic alpha(1) subunit of Na(+),K(+)-ATPase induced FPI correlated with TBARS and protein carbonylation content increase. Furthermore, the effective protection exerted by physical training against FPI-induced free radical correlated with the immunocontent of the catalytic alpha(1) subunit maintenance. These data suggest that TBI-induced reactive oxygen species (ROS) generation decreases Na(+),K(+)-ATPase activity by decreasing the total number of enzyme molecules, and that physical exercise protects against this effect. Therefore, the effective protection of selected targets, such as Na(+),K(+)-ATPase induced by physical training, supports the idea that physical training may exert prophylactic effects on neuronal cell dysfunction and damage associated with TBI.

Differential effects of the mitochondrial uncoupling agent, 2,4-dinitrophenol, or the nitroxide antioxidant, Tempol, on synaptic or nonsynaptic mitochondria after spinal cord injury

We recently documented the progressive nature of mitochondrial dysfunction over 24 hr after contusion spinal cord injury (SCI), but the underlying mechanism has not been elucidated. We investigated the effects of targeting two distinct possible mechanisms of mitochondrial dysfunction by using the mitochondrial uncoupler 2,4-dinitrophenol (2,4-DNP) or the nitroxide antioxidant Tempol after contusion SCI in rats. A novel aspect of this study was that all assessments were made in both synaptosomal (neuronal)- and nonsynaptosomal (glial and neuronal soma)-derived mitochondria 24 hr after injury. Mitochondrial uncouplers target Ca(2+) cycling and subsequent reactive oxygen species production in mitochondria after injury. When 2,4-DNP was injected 15 and 30 min after injury, mitochondrial function was preserved in both populations compared with vehicle-treated rats, whereas 1 hr postinjury treatment was ineffective. Conversely, targeting peroxynitrite with Tempol failed to maintain normal bioenergetics in synaptic mitochondria, but was effective in nonsynaptic mitochondria when administered 15 min after injury. When administered at 15 and 30 min after injury, increased hydroxynonenal, 3-NT, and protein carbonyl levels were significantly reduced by 2,4-DNP, whereas Tempol only reduced 3-NT and protein carbonyls after SCI. Despite such antioxidant effects, only 2,4-DNP was effective in preventing mitochondrial dysfunction, indicating that mitochondrial Ca(2+) overload may be the key mechanism involved in acute mitochondrial damage after SCI. Collectively, our observations demonstrate the significant role that mitochondrial dysfunction plays in SCI neuropathology. Moreover, they indicate that combinatorial therapeutic approaches targeting different populations of mitochondria holds great potential in fostering neuroprotection after acute SCI.

The brain-specific protein, p42(IP4) (ADAP 1) is localized in mitochondria and involved in regulation of mitochondrial Ca2+

In brain, p42(IP4) (centaurin-alpha1; recently named ADAP 1, which signifies ADP ribosylation factor GTPase activating protein with dual PH domains 1, within the large family of Arf-GTPase activating proteins) is mainly expressed in neurons. p42(IP4) operates as a dual receptor recognising two second messengers, the soluble inositol(1,3,4,5)tetrakisphosphate and the lipid phosphatidylinositol(3,4,5)trisphosphate. We show here for the first time that p42(IP4) is localized in mitochondria, isolated from rat brain and from cells transfected with p42(IP4). In rat brain mitochondria we additionally found interaction of p42(IP4) with 2', 3'-cyclic nucleotide 3'-phosphodiesterase and alpha-tubulin by pull-down binding assay and by immunoprecipitation. In mitochondria from Chinese hamster ovary cells, p42(IP4) is predominantly associated with the intermembrane space and the inner membrane. This localization of p42(IP4) indicates that p42(IP4) might have a still unknown mitochondrial function. We studied whether p42(IP4) is involved in Ca(2+)-induced permeability transition pore opening, which is important in mitochondrial events leading to programmed cell death. We used mouse neuroblastoma cells as a model for the functional studies of p42(IP4) in mitochondria. In mitochondria isolated from p42(IP4)-transfected mouse neuroblastoma cells, over-expression of p42(IP4) significantly decreased Ca(2+) capacity and lag time for Ca(2+) retention. Thus, we suggest that p42(IP4) is involved in the regulation of Ca(2+) transport in mitochondria. We propose that p42(IP4) promotes Ca(2+)-induced permeability transition pore opening and thus destabilizes mitochondria.

Modified calcium accumulation after controlled cortical impact under cyclosporin A treatment: a 45Ca autoradiographic study

OBJECTIVE

As a neuroprotective drug, cyclosporin A (CsA) has been subject of multiple experimental works in traumatic brain injury (TBI) research. It is well known that CsA inhibits calcium (Ca2+) induced mitochondrial permeability transition (mPT). The aim of this study was to investigate the influence of CsA on the alteration of Ca2+ homeostasis after experimental brain injury.

METHODS

Sprague-Dawley male rats (n = 36) with a mean weight of 330 g (280-350 g) were general anesthetized with isofluran through gas mask. The anesthetized animals (n = 24) were subjected to a controlled cortical impact (CCI) over the left parietotemporal cortex using round-tip impounder with a 5 mm diameter at a velocity of approximately 3.7 m/s and a penetration depth of 2 mm. The sham group (n = 12) underwent anesthesia and craniotomy without CCI. In the CCI groups, CsA (n = 12) or vehicle (n = 12) was administered 15 minutes post-injury with a subsequent i.p. injection after 24 hours. Thirty-three hours after injury or sham craniotomy, 45calcium (45Ca) suspended in physiologic saline solution was injected in the left femoral vein. Five hours after isotope administration, animals were killed and the brain was quickly removed and placed in powdered dry ice. Coronal plane sections (20 microm thick) taken every 400 microm from the frontal cortex through the occipital cortex, were exposed to cyclotron films for 14 days at -18 degrees C. Relative optical density was utilized to provide a relative measure of 45Ca accumulation within seven different structures.

RESULTS

The difference of 45Ca accumulation (measured by relative optical density) in the CsA group was greater by 30-70% in the following structures compared to vehicle treated traumatized animals: temporal cortex, CA1, anteromedial and posteromedial thalamus (p < 0.05).

CONCLUSION

Post-traumatic 45Ca accumulation is modified under CsA. The crucial neuroprotective effect of CsA might be unrelated to a reduction of post-traumatic Ca2+ accumulation, especially with regard to the importance of Ca2+ as an intracellular messenger governing a large number of cellular functions.

Ethanol withdrawal provokes opening of the mitochondrial membrane permeability transition pore in an estrogen-preventable manner

We have reported that the major endogenous estrogen, 17beta-estradiol (E2), protects against oxidative injury during ethanol withdrawal (EW) in a cultured hippocampal cell line (HT22). Here, we investigated whether the pro-oxidant nature of EW mediates opening of the mitochondrial membrane permeability transition pore (PTP) in a manner protected by E2. Excess PTP opening provokes mitochondrial membrane swelling (MMS) and the collapse of membrane potential (DeltaPsim). HT22 cells were collected at the end of ethanol exposure (100 mM) for 24 h or at 4 h of EW to assess MMS by monitoring absorbance decline at 540 nm and to assess DeltaPsim using flow cytometry. Protective effects of E2 on PTP were compared with an antioxidant butylated hydroxytoluene (BHT) and an E2 analog, ZYC26 [(3-hydroxy-2-adamantyl(1)-4-methyl-estra-1,3,5(10)-17-one], with higher antioxidant potency than E2. To assess cellular consequences of PTP opening, effects of a PTP inhibitor (cyclosporin A) on EW-induced cell death were assessed using the calcein assay. Major findings were that: 1) EW resulted in rapid MMS and DeltaPsim collapse; 2) cyclosporin A attenuated EW-induced cell death; and 3) E2 treatment restricted to the EW phase protected against the PTP opening more prominently than BHT and to a similar degree to ZYC26. These findings suggest that EW provokes PTP opening partly but not entirely through the pro-oxidant nature and that E2 counteracts EW-associated factors to protect against the PTP opening.

KNS-760704 [(6R)-4,5,6,7-tetrahydro-N6-propyl-2, 6-benzothiazole-diamine dihydrochloride monohydrate] for the treatment of amyotrophic lateral sclerosis

Developing effective treatments for chronic neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS) has proven extremely difficult. ALS is universally fatal, characterized by progressive weakness due to the degeneration of upper and lower motor neurons, and leads eventually to respiratory failure which is the usual cause of death. Only a single treatment has been approved, the modestly effective nonspecific neuroprotectant Rilutek (riluzole; 2-amino-6-(trifluoromethoxy)benzothiazole). KNS-760704 [(6R)-4,5,6,7-tetrahydro-N6-propyl-2,6-benzothiazole-diamine dihydrochloride, RPPX], a synthetic amino-benzothiazole with demonstrated activity in maintaining mitochondrial function, is being developed as a treatment for ALS. It has proven to be effective in multiple in vitro and in vivo assays of neuroprotection, including the G93A-SOD1 mutant mouse model; however, its specific mechanism of action remains unknown. The potential of KNS-760604 as a treatment for ALS was first suggested by studies showing that its optical enantiomer, Mirapex[(6S)-4,5,6,7-tetrahydro-N6-propyl-2,6-benzothiazole-diamine; pramipexole dihydrochloride; PPX], a high-affinity agonist at dopamine D2, D3, and D4 receptors, exhibits important neuroprotective properties independent of its dopamine receptor agonism. In cell-based assays, both RPPX and PPX reduce the production of reactive oxygen species (ROS), attenuate the activation of apoptotic pathways, and increase cell survival in response to a variety of neurotoxins. However, PPX has limited utility as a clinical neuroprotective agent because the drug concentrations required for neuroprotection would likely produce unacceptable dopaminergic side effects. RPPX, on the other hand, while possessing the same neuroprotective potential as PPX, is a much lower-affinity dopamine receptor agonist and may therefore be more useful in the treatment of ALS. This review will examine the data supporting the hypothesis that the RPPX may have therapeutic potential for the treatment of neurodegenerative disorders including ALS. In addition, we will briefly review recent preclinical data in support of RPPX, and discuss the current status of its clinical development.

Brain metabolic and hemodynamic effects of cyclosporin A after human severe traumatic brain injury: a microdialysis study

BACKGROUND

Mitochondrial dysfunction is a major limiting factor in neuronal recovery following traumatic brain injury. Cyclosporin A (CsA) has been recently proposed for use in the early phase after severe head injury, for its ability to preserve mitochondrial bioenergetic state, potentially exerting a neuroprotective effect. The aim of this study was, therefore, to evaluate the effect of CsA on brain energy metabolism, as measured by cerebral microdialysis, and on cerebral hemodynamics, in a group of severely head injured patients.

METHODS

Fifty adult patients with a severe head injury were enrolled in this randomized, double-blind, placebo-controlled study. Patients received 5 mg/kg of CsA over 24 h, or placebo, within 12 h of the injury. A microdialysis probe was placed in all patients, who were managed according to standard protocols for the treatment of severe head injury.

FINDINGS

The most robust result of this study was that, over most of the monitoring period, brain dialysate glucose was significantly higher in the CsA treated patients than in placebo. Both lactate and pyruvate were also significantly higher in the CsA group. Glutamate concentration and lactate/pyruvate ratio were significantly higher in the placebo group than in CsA treated patients, respectively 1 to 2 days, and 2 to 3 days after the end of the 24-h drug infusion. The administration of CsA was also associated with a significant increase in mean arterial pressure (MAP) and cerebral perfusion pressure (CPP).

CONCLUSIONS

The administration of CsA in the early phase after head injury resulted in significantly higher extracellular fluid glucose and pyruvate, which may be evidence of a beneficial effect. The early administration of CsA was also associated with a significant increase in MAP and CPP and such a potentially beneficial hemodynamic effect might contribute to a neuroprotective effect.

Dosing and safety of cyclosporine in patients with severe brain injury

OBJECT

Cyclosporine neuroprotection has been reported in brain injury models but safety and dosing guidelines have not been determined in humans with severe traumatic brain injury (TBI). The purpose of this investigation was to establish the safety of cyclosporine using 4 clinically relevant dosing schemes.

METHODS

The authors performed a prospective, blinded, placebo-controlled, randomized, dose-escalation trial of cyclosporine administration initiated within 8 hours of TBI (Glasgow Coma Scale score range 4-8; motor score range 2-5). Four dosing cohorts (8 patients treated with cyclosporine and 2 receiving placebo treatment per cohort) received cyclosporine (1.25-5 mg/kg/day) or placebo in 2 divided doses (Cohorts I-III) or continuous infusion (Cohort IV) over 72 hours. Adverse events and outcome were monitored for 6 months.

RESULTS

Forty patients were enrolled over 3 years (cyclosporine cohorts, 24 male and 8 female patients; placebo group, 8 male patients). Systemic trough concentrations were below 250 ng/ml during intermittent doses. Higher blood concentrations were observed in Cohorts III and IV. There was no significant difference in immunological effects, adverse events, infection, renal dysfunction, or seizures. Mortality rate was not affected by cyclosporine administration, independent of dose, compared with placebo (6 of 32 patients receiving cyclosporine and 2 of 8 receiving placebo died, p>0.05). At 6 months, a dose-related improvement in favorable outcome was observed in cyclosporine-treated patients (p<0.05).

CONCLUSIONS

In patients with acute TBI who received cyclosporine at doses up to 5 mg/kg/day, administered intravenously, with treatment initiated within 8 hours of injury, the rate of mortality or other adverse events was not significantly different from that of the placebo group.

Pharmacology of traumatic brain injury: where is the "golden bullet"?

Traumatic brain injury (TBI) represents a major health care problem and a significant socioeconomic challenge worldwide. In the United States alone, approximately 1.5 million patients are affected each year, and the mortality of severe TBI remains as high as 35%-40%. These statistics underline the urgent need for efficient treatment modalities to improve posttraumatic morbidity and mortality. Despite advances in basic and clinical research as well as improved neurological intensive care in recent years, no specific pharmacological therapy for TBI is available that would improve the outcome of these patients. Understanding of the cellular and molecular mechanisms underlying the pathophysiological events after TBI has resulted in the identification of new potential therapeutic targets. Nevertheless, the extrapolation from basic research data to clinical application in TBI patients has invariably failed, and results from prospective clinical trials are disappointing. We review the published prospective clinical trials on pharmacological treatment modalities for TBI patients and outline future promising therapeutic avenues in the field.

Probing the molecular mechanisms of neuronal degeneration: importance of mitochondrial dysfunction and calcineurin activation

Cerebral injury is a critical aspect of the management of patients in intensive care. Pathological conditions induced by cerebral ischemia, hypoxia, head trauma, and seizure activity can result in marked residual impairment of cerebral function. We have investigated the potential mechanisms leading to neuronal cell death in pathological conditions, with the aim of discovering therapeutic targets and methods to minimize neuronal damage resulting from insults directed at the central nervous system (CNS). Over the years, deeper understanding of the mechanisms of neuronal cell death has indeed evolved, enabling clinical critical care management to salvage neurons that are at the brink of degeneration and to support recovery of brain function. However, no substantial breakthrough has been achieved in the quest to develop effective pharmacological neuroprotective therapy directed at tissues of the CNS. The current situation is unacceptable, and preservation of function and protection of the brain from terminal impairment will be a vital medical issue in the twenty-first century. To achieve this goal, it is critical to clarify the key mechanisms leading to neuronal cell death. Here, we discuss the importance of the calcineurin/immunophilin signal transduction pathway and mitochondrial involvement in the detrimental chain of events leading to neuronal degeneration.

Traumatic brain injury: can the consequences be stopped?

Traumatic brain injury is a leading cause of morbidity and death in both industrialized and developing countries. To date, there is no targeted pharmacological treatment that effectively limits the progression of secondary injury. The delayed progression of deterioration of grey and white matter gives hope that a meaningful intervention can be applied in a realistic timeframe following initial trauma. In this review we discuss new insights into the subcellular mechanisms of secondary injury that have highlighted numerous potential targets for intervention.

Duration of ATP reduction affects extent of CA1 cell death in rat models of fluid percussion injury combined with secondary ischemia

Secondary ischemia (SI) following traumatic brain injury (TBI) increases damage to the brain in both animals and humans. The current study determined if SI after TBI alters the extent or duration of reduced energy production within the first 24 h post-injury and hippocampal cell loss at one week post-injury. Adult male rats were subjected to sham injury, lateral (LFPI) or central fluid percussion injury (CFPI) only, or to combined LFPI or CFPI with SI. The SI was 8 min of bilateral forebrain ischemia combined with hemorrhagic hypotension, applied at 1 h following FPI. After LFPI alone adenosine triphosphate (ATP) levels within the ipsilateral CA1 were reduced at 2 h (p < 0.05) and subsequently recovered. After LFPI+SI the ATP reductions in CA1 ipsilateral to FPI persisted for 24 h (p < 0.01). ATP levels in the contralateral CA1 were not affected by LFPI alone or LFPI+SI. After CFPI alone CA1 ATP levels were depressed bilaterally only at 2 h (p < 0.05). Similar to the LFPI paradigm, CFPI+SI reduced ATP levels for 24 h (p < 0.01), with bilateral ATP reductions seen after CFPI+SI. Cell counts in the CA1 region at 7 days post-injury revealed no significant neuronal cell loss after LFPI or CFPI alone. Significant neuronal cell loss was present only within the ipsilateral (p < 0.001) CA1 after LFPI+SI, but cell loss was bilateral (p < 0.001) after CFPI+SI. Thus, SI prolongs ATP reductions induced by LFPI and CFPI within the CA1 region and this SI-induced energy reduction appears to adversely affect regional neuronal viability.

The injured nervous system: a Darwinian perspective

Much of the permanent damage that occurs in response to nervous system damage (trauma, infection, ischemia, etc.) is mediated by endogenous secondary processes that can contribute to cell death and tissue damage (excitotoxicity, oxidative damage and inflammation). For humans to evolve mechanisms to minimize secondary pathophysiological events following CNS injuries, selection must occur for individuals who survive such insults. Two major factors limit the selection for beneficial responses to CNS insults: for many CNS disease states the principal risk factor is advanced, post-reproductive age and virtually all severe CNS traumas are fatal in the absence of modern medical intervention. An alternative hypothesis for the persistence of apparently maladaptive responses to CNS damage is that the secondary exacerbation of damage is the result of unavoidable evolutionary constraints. That is, the nervous system could not function under normal conditions if the mechanisms that caused secondary damage (e.g., excitotoxicity) in response to injury were decreased or eliminated. However, some vertebrate species normally inhabit environments (e.g., hypoxia in underground burrows) that could potentially damage their nervous systems. Yet, neuroprotective mechanisms have evolved in these animals indicating that natural selection can occur for traits that protect animals from nervous system damage. Many of the secondary processes and regeneration-inhibitory factors that exacerbate injuries likely persist because they have been adaptive over evolutionary time in the healthy nervous system. Therefore, it remains important that researchers consider the role of the processes in the healthy or developing nervous system to understand how they become dysregulated following injury.

A connection between the mitochondrial permeability transition pore, autophagy, and cerebral amyloidogenesis

In a drug reprofiling attempt, we explored novel neuroprotective properties of 4-azasteroids by synthesizing chemical affinity tags capturing adenine nucleotide translocator-1, as a potential target. Dutasteride inhibits the mitochondrial transition pore and induces an increase of autophagosomal structures in human cell lines. In vivo, a surprising reduction of the beta-amyloid plaque load in a model for cerebral amyloidosis appears to connect release of neurotoxic peptides, mitochondrial apoptosis and autophagy.

Molecular mechanisms of Fas-mediated cell death in oligodendrocytes

Oligodendrocyte cell death is a significant component of the secondary damage following spinal cord injury (SCI) and other neurodegenerative disorders. However, the mechanisms underlying oligodendroglial apoptotic cell death and the potential relationship to Fas receptor (FasR) activation require further clarification. Here, using MO3.13, a human oligodendroglial cell line, we show clear evidence of apoptosis upon exposure to soluble Fas ligand (sFasL). Apoptosis was linked to caspase-8, -9, and -3 activity and resulted in DNA fragmentation detected by deoxynucleotide transferase dUTP nick end-labeling (TUNEL). Dissipation of mitochondrial membrane potential (DeltaPsim) was an early event and temporally coincided with mitochondrial outer membrane permeability (MOMP), demonstrated by the presence of cytochrome c and apoptosis inducing factor (AIF) in cytosolic fractions. Pretreatment with 100 microM of the caspase inhibitor zVAD-fmk prior to sFasL exposure reduced caspase activation, the dissipation of DeltaPsim, MOMP, and apoptotic cell death. These data provide clear evidence that Fas activation induces apoptosis in oligodendrocytes signaling through intrinsic and extrinsic events. Moreover, we provide evidence for the first time that AIF may play a role in caspase-independent apoptotic execution following Fas activation of oligodendrocytes. These data also add to an emerging body of evidence, which strongly implicates Fas-mediated apoptosis of oligodendrocytes as a potential mediator in the pathobiology of a variety of neurological disorders, including SCI.

Mechanisms of impaired mitochondrial energy metabolism in acute and chronic neurodegenerative disorders

Altered mitochondrial energy metabolism contributes to the pathophysiology of acute brain injury caused by ischemia, trauma, and neurotoxins and by chronic neurodegenerative disorders such as Parkinson's and Huntington's diseases. Although much evidence supports that the electron transport chain dysfunction in these metabolic abnormalities has both genetic and intracellular environmental causes, alternative mechanisms are being explored. These include direct, reversible inhibition of cytochrome oxidase by nitric oxide, release of mitochondrial cytochrome c, oxidative inhibition of mitochondrial matrix dehydrogenases and adenine nucleotide transport, the availability of NAD for dehydrogenase reactions, respiratory uncoupling by activities such as that of the permeability transition pore, and altered mitochondrial structure and intracellular trafficking. This review focuses on the catabolism of neuronal NAD and the release of neuronal mitochondrial NAD as important contributors to metabolic dysfunction. In addition, the relationship between apoptotic signaling cascades and disruption of mitochondrial energy metabolism is considered in light of the fine balance between apoptotic and necrotic neural cell death.

Ethanol withdrawal provokes mitochondrial injury in an estrogen preventable manner

We investigated whether ethanol withdrawal (EW) oxidizes mitochondrial proteins and provokes mitochondrial membrane swelling and whether estrogen deprivation contributes to this problem. Ovariectomized female rats with or without 17beta-estradiol (E2)-implantation received a control diet or a liquid ethanol diet (6.5%) for 5 weeks and were sacrificed during EW. Protein oxidation was assessed by measuring carbonyl contents and was visualized by immunochemistry. Mitochondrial membrane swelling as an indicator of mitochondrial membrane fragility was assessed by monitoring absorbance at 540 nm and was compared with that of male rats. Compared to the control diet group and ovariectomized rats with E2-implantation, ovariectomized rats without E2-implantation showed higher carbonylation of mitochondrial proteins and more rapid mitochondrial membrane swelling during EW. Such rapid mitochondrial membrane swelling was comparable to that of male rats undergoing EW. These findings demonstrate that EW provokes oxidative injury to mitochondrial membranes in a manner that is exacerbated by estrogen deprivation.

Spinal cord mitochondria display lower calcium retention capacity compared with brain mitochondria without inherent differences in sensitivity to cyclophilin D inhibition

The mitochondrial permeability transition (mPT) is a potential pathogenic mechanism in neurodegeneration. Varying sensitivity to calcium-induced mPT has been demonstrated for regions within the CNS possibly correlating with vulnerability following insults. The spinal cord is selectively vulnerable in e.g. amyotrophic lateral sclerosis and increased mPT sensitivity of mitochondria derived from the spinal cord has previously been demonstrated. In this study, we introduce whole-body hypothermia prior to removal of CNS tissue to minimize the effects of differential tissue extraction prior to isolation of spinal cord and cortical brain mitochondria. Spinal cord mitochondria were able to retain considerably less calcium when administered as continuous infusion, which was not related to a general increased sensitivity of the mPT to calcium, its desensitization to calcium by the cyclophilin D inhibitor cyclosporin-A, or to differences in respiratory parameters. Spinal cord mitochondria maintained a higher concentration of extramitochondrial calcium during infusion than brain mitochondria possibly related to an increased set-point concentration for calcium uptake. A hampered transport and retention capacity of calcium may translate into an increased susceptibility of the spinal cord to neurodegenerative processes involving calcium-mediated damage.

Attenuation of acute mitochondrial dysfunction after traumatic brain injury in mice by NIM811, a non-immunosuppressive cyclosporin A analog

Following traumatic brain injury (TBI), mitochondrial function becomes compromised. Mitochondrial dysfunction is characterized by intra-mitochondrial Ca(2+) accumulation, induction of oxidative damage, and mitochondrial permeability transition (mPT). Experimental studies show that cyclosporin A (CsA) inhibits mPT. However, CsA also inhibits calcineurin. In the present study, we conducted a dose-response analysis of NIM811, a non-calcineurin inhibitory CsA analog, on mitochondrial dysfunction following TBI in mice, and compared the effects of the optimal dose of NIM811 (10 mg/kg i.p.) against an optimized dose of CsA (20 mg/kg i.p.). Male CF-1 mice were subjected to severe TBI utilizing the controlled cortical impact model. Mitochondrial respiration was assessed from animals treated with either NIM811, CsA, or vehicle 15 min post-injury. The respiratory control ratio (RCR) of mitochondria from vehicle-treated animals was significantly (p<0.01) lower at 3 or 12 h post-TBI, relative to shams. Treatment of animals with either NIM811 or CsA significantly (p<0.03) attenuated this reduction. Consistent with this finding, both NIM811 and CsA significantly reduced lipid peroxidative and protein nitrative damage to mitochondria at 12 h post-TBI. These results showing the ability of NIM811 to fully duplicate the mitochondrial protective efficacy of CsA supports the conclusion that inhibition of the mPT may be sufficient to explain CsA's protective effects.

Temporal characterization of mitochondrial bioenergetics after spinal cord injury

Mitochondrial dysfunction following spinal cord injury (SCI) may be critical for the development of secondary pathophysiology and neuronal cell death. Previous studies have demonstrated a loss of mitochondrial bioenergetics at 24 h following SCI. To begin to understand the evolution and study the contribution of mitochondrial dysfunction in pathophysiology of SCI, we investigated mitochondrial bioenergetics in the mid-thoracic region at 6, 12, and 24 h following contusion SCI. It is widely accepted that increased free radical generation plays a critical role in neuronal damage after SCI. Hence, to ascertain the role of free radicals in SCI-induced mitochondrial dysfunction, markers for oxidative damage, including nitrotyrosine (3-NT), lipid peroxidation byproduct (4-hydroxynonenal [HNE]), and protein oxidation (protein carbonyls) were quantified in the same samples of isolated mitochondria during the 24-h time course. The results demonstrate that a significant decline in mitochondrial function begins to occur 12 h post-injury and persists for a least 24 h following SCI. Furthermore, there was a progressive increase in mitochondrial oxidative damage that preceded the loss of mitochondrial bioenergetics, suggesting that free radical damage may be a major mitochondrial secondary injury process. Based on the present results, the temporal profile of mitochondrial dysfunction indicates that interventions targeting mitochondrial oxidative damage and dysfunction may serve as a beneficial pharmacological treatment for acute SCI.

Effect of lactate therapy upon cognitive deficits after traumatic brain injury in the rat

BACKGROUND

In previous studies, it has been shown that intravenous lactate therapy can improve brain neurochemistry, adenosine triphosphate (ATP) generation and outcome after traumatic brain injury (TBI) in rats. In this study, we examined: (1) four L-lactate concentrations to determine the optimal therapeutic dose post TBI in terms of cognitive function; (2) ATP production after TBI for the L-lactate concentration found to be the optimal dose; (3) the possible production of lactic acidosis with the highest L-lactate concentration tested.

METHODS

Thirty minutes following a fluid percussion injury (FPI) over the left cerebral hemisphere, the animals received an intravenous infusion of 10, 28, 100, or 280 mM L-lactate (n = 10 for each group) for 3 h at a rate of 0.65 ml/h. Shams and control injured animals received a saline infusion. At 11-15 days post injury, cognitive deficits were examined using the Morris Water Maze (MWM) test. Three groups of rats were used for ATP analysis: shams, injured + saline infusion, and injury + the optimal lactate dose as determined by the MWM (n = 4/group). Additionally, a group receiving 280 mM L-lactate (n = 5) and one receiving a saline infusion (n = 3) were monitored for arterial blood variables and blood pressures.

FINDINGS

In the MWM test, only the 100 mM L-lactate-treated injured animals showed a significant reduction in cognitive deficits when compared to saline-treated injured animals (p <or= 0.05). In the ATP study, injured animals without treatment had a 53% reduction in ATP level in the ipsilateral cortex, while animals with 100 mM lactate treatment had a 28% reduction. (p <or= 0.05). No lactic acidosis was induced by the intravenous infusion of 280 mM L-lactate.

CONCLUSIONS

This study indicates that the intravenous infusion of 100 mM L-lactate provided the optimal concentration of the substrate to ameliorate cognitive impairment, probably via the regeneration of ATP following TBI in rats.

Post-Injury Administration of Mitochondrial Uncouplers Increases Tissue Sparing and Improves Behavioral Outcome following Traumatic Brain Injury in Rodents

Following experimental traumatic brain injury (TBI), a rapid and significant necrosis occurs at the site of injury which coincides with significant mitochondrial dysfunction. The present study is driven by the hypothesis that TBI-induced glutamate release increases mitochondrial Ca(2+)cycling/overload, ultimately leading to mitochondrial dysfunction. Based on this premise, mitochondrial uncoupling during the acute phases of TBI-induced excitotoxicity should reduce mitochondrial Ca(2+) uptake (cycling) and reactive oxygen species (ROS) production since both are mitochondrial membrane potential dependent. In the present study, we utilized a cortical impact model of TBI to assess the potential use of mitochondrial uncouplers (2,4-DNP, FCCP) as a neuroprotective therapy. Young adult male rats were intraperitoneally administered vehicle (DMSO), 2,4-DNP (5 mg/kg), or FCCP (2.5 mg/kg) at 5 min post-injury. All animals treated with the uncouplers demonstrated a significant reduction in the amount of cortical damage and behavioral improvement following TBI. In addition, mitochondria isolated from the injured cortex at 3 or 6 h post-injury demonstrated that treatment with the uncouplers significantly improved several parameters of mitochondrial bioenergetics. These results demonstrate that post-injury treatment with mitochondrial uncouplers significantly (p < 0.01) increases cortical tissue sparing ( approximately 12%) and significantly (p< 0.01) improves behavioral outcome following TBI. The mechanism of neuroprotection most likely involves the maintenance of mitochondrial homeostasis by reducing mitochondrial Ca(2+) loading and subsequent mitochondrial dysfunction. These results further implicate mitochondrial dysfunction as an early event in the pathophysiology of TBI and that targeting acute mitochondrial events can result in long-term neuroprotection and improve behavioral outcome following brain injury.

Proteomic identification of oxidized mitochondrial proteins following experimental traumatic brain injury

Experimental traumatic brain injury (TBI) results in a significant loss of cortical tissue at the site of injury, and in the ensuing hours and days a secondary injury exacerbates this primary injury, resulting in significant neurological dysfunction. The mechanism of the secondary injury is not well understood, but evidence implicates a critical role for mitochondria in this cascade. This mitochondrial dysfunction is believed to involve excitotoxicity, disruption of Ca(2+) homeostasis, production of reactive oxygen species (ROS), ATP depletion, oxidative damage of mitochondrial proteins, and an overall breakdown of mitochondrial bioenergetics. Although oxidative damage occurs following TBI, the identities of proteins undergoing oxidative modification after TBI have not been investigated. In the present study, we utilized the 3-h post-injury controlled cortical impact model of experimental TBI in 20 young adult male Sprague-Dawley rats, coupled with proteomics to identify specific mitochondrial fraction proteins from the cortex and hippocampus that were oxidatively modified after TBI. We identified, from the cortex, pyruvate dehydrogenase, voltage-dependent anion channel, fumarate hydratase 1, ATP synthase, and prohibitin. From the hippocampus, we identified cytochrome C oxidase Va, isovaleryl coenzyme A dehydrogenase, enolase-1, and glyceraldehyde-3-phosphate dehydrogenase as proteins that had undergone oxidative modification following TBI. In addition, we have also shown that, following TBI, there is a reduction in the activities of pyruvate dehydrogenase (PDH), complex I, and complex IV. These findings demonstrate that, following TBI, several proteins involved in mitochondrial bioenergetics are highly oxidatively modified, which may possibly underlie the massive breakdown of mitochondrial energetics and eventual cell death known to occur in this model. The identification of these proteins provides new insights into the mechanisms that take place following TBI and may provide avenues for possible therapeutic interventions after TBI.

High cyclophilin D content of synaptic mitochondria results in increased vulnerability to permeability transition

Mitochondria isolated from synaptosomes are more sensitive to Ca2+ overload and the resultant opening of the mitochondrial permeability transition pore (mPTP) than nonsynaptic mitochondria. To identify the mechanisms underlying these differences in Ca2+ dynamics, we examined relative levels of mPTP components in synaptic versus nonsynaptic mitochondria. Synaptic mitochondria had higher levels of cyclophilin D when compared with nonsynaptic mitochondria, whereas levels of the voltage-dependent anion channel and the adenine nucleotide translocase were similar in the two mitochondrial fractions. These differences in Ca2+ handling between synaptic and nonsynaptic mitochondria were greatly reduced in cyclophilin D null [Ppif-/- (peptidylprolyl isomerase F)] mice. Higher concentrations of cyclosporine A, which interacts with cyclophilin D to delay mPTP opening, were necessary to increase the Ca2+ uptake capacity of synaptic versus nonsynaptic mitochondria. To determine whether the differences in Ca2+ handling might reflect the relative abundance of neuronal and glial mitochondria in the two mitochondrial fractions, we compared cyclophilin D levels in primary cortical neurons and astrocytes. Primary rat cortical neurons possess higher cyclophilin D levels than do primary astrocytes. In the adult rat brain, cyclophilin D immunoreactivity was abundant in neurons but sparse in astrocytes. Together, these results demonstrate that the Ca2+ handling differences observed in synaptic versus nonsynaptic mitochondria are primarily the result of the high levels of cyclophilin D in synaptic mitochondria, reflecting the greater proportion of neuronal mitochondria in this fraction. The high levels of cyclophilin D in neuronal mitochondria result in their greater vulnerability to mPT and in higher levels of cyclosporine A being required to inhibit mPTP opening.

Acutely increased cyclophilin a expression after brain injury: A role in blood-brain barrier function and tissue preservation

Blood-brain barrier (BBB) compromise is a significant pathologic event that manifests early following traumatic brain injury (TBI). Because many signaling cascades are initiated immediately after the traumatic event, we were interested in examining acute differential protein expression that may be involved in BBB function. At acute time points postinjury, altered protein expression may result from altered translation efficiency or turnover rate rather than from a genomic response. The application of tandem 2-D gel electrophoresis and mass spectrometry analysis is a powerful approach for directly screening differential protein expression following TBI. Using comparative 2-D gel analysis, we selected candidate protein spots with apparent altered expression and identified them by mass spectrometry. Cyclophilin A was selected for further analysis because it has been implicated in endothelial cell activation and inflammation, and studies have suggested cyclosporine A, an inhibitor of all cyclophilin isoforms, might be beneficial after TBI. We examined if altered expression of cyclophilin A in the brain vasculature might play a role in BBB function. We found significantly increased cyclophilin A levels in isolated brain microvessels 30 min following injury. Postinjury administration of cyclosporine A significantly attenuated BBB permeability measured 24 hr postinjury, suggesting cyclophilin activity after TBI may be detrimental. However, direct injection of purified recombinant cyclophilin A attenuated both BBB permeability and tissue damage in a stab wound model of injury. These findings suggest that increased expression of cyclophilin A may play a protective role after TBI, whereas other cyclophilin isoforms may be detrimental.