An adenosine A2A agonist, ATL-146e, reduces paralysis and apoptosis during rabbit spinal cord reperfusion

Comparative effects of methylprednisolone and tetracosactide (ACTH1-24) on ischemia/reperfusion injury of the rabbit spinal cord

INTRODUCTION

Tetracosactide is an engineered peptide that applies the same biological impacts as the endogenous adrenocorticotropic hormone. Previous studies indicated that tetracosactide has anti-inflammatory, antioxidant and neurotrophic activity. In this study, we hypothesized that tetracosactide may have protective effects in spinal cord ischemia-reperfusion injury.

MATERIAL AND METHODS

Rabbits were randomized into the accompanying four groups of eight animals each: group 1 (control), group 2 (ischemia), group 3 (methylprednisolone) and group 4 (tetracosactide). In the control group, just a laparotomy was performed. In the various groups, the spinal cord ischemia model was made by the impediment of the aorta only caudal to the renal vein. Neurological assessment was conducted with the Tarlov scoring system. Levels of myeloperoxidase, malondialdehyde and catalase were analyzed, similar to the activities of xanthine oxidase and caspase-3. Histopathological and ultrastructural assessments were additionally performed.

RESULTS

After ischemia-reperfusion injury, increments were found in the tissue myeloperoxidase levels (p < 0.001), malondialdehyde levels (p < 0.001), xanthine oxidase action (p < 0.001) and caspase-3 movement (p < 0.001). Conversely, both serum and tissue catalase levels were diminished (p < 0.001 for both). After the administration of tetracosactide, declines were seen in the tissue myeloperoxidase levels (p < 0.001), malondialdehyde levels (p = 0.003), xanthine oxidase action (p < 0.001) and caspase-3 movement (p < 0.001). Conversely, both the serum and tissue catalase levels were expanded (p < 0.001). Besides, tetracosactide treatment indicated enhanced results related to the histopathological scores (p < 0.001), the ultra-structural score (p = 0.008) and the Tarlov scores (p < 0.001).

CONCLUSIONS

The findings showed for the first time that tetracosactide shows significant neuroprotective activity against ischemia-reperfusion injury of the spinal cord.

Adenosine: An endogenous mediator in the pathogenesis of gynecological cancer

Extracellular concentration of adenosine increases in the hypoxic tumor microenvironment. Adenosine signaling regulates apoptosis, angiogenesis, metastasis, and immune suppression in cancer cells. Adenosine-induced cell responses depend upon different subtypes of adenosine receptors activation and type of cancer. Suppression of adenosine signaling via inhibition of adenosine receptors or adenosine generating enzymes including CD39 and CD73 on ovarian or cervical cancer cells is a potentially novel therapeutic approach for gynecological cancer patients. This review summarizes the role of adenosine in the pathogenesis of gynecological cancer for a better understanding and hence a better management of this disease.

An introduction to the roles of purinergic signalling in neurodegeneration, neuroprotection and neuroregeneration

Purinergic signalling appears to play important roles in neurodegeneration, neuroprotection and neuroregeneration. Initially there is a brief summary of the background of purinergic signalling, including release of purines and pyrimidines from neural and non-neural cells and their ectoenzymatic degradation, and the current characterisation of P1 (adenosine), and P2X (ion channel) and P2Y (G protein-coupled) nucleotide receptor subtypes. There is also coverage of the localization and roles of purinoceptors in the healthy central nervous system. The focus is then on the roles of purinergic signalling in trauma, ischaemia, stroke and in neurodegenerative diseases, including Alzheimer's, Parkinson's and Huntington's diseases, as well as multiple sclerosis and amyotrophic lateral sclerosis. Neuroprotective mechanisms involving purinergic signalling are considered and its involvement in neuroregeneration, including the role of adult neural stem/progenitor cells. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Ionotropic receptors and ion channels in ischemic neuronal death and dysfunction

Loss of energy supply to neurons during stroke induces a rapid loss of membrane potential that is called the anoxic depolarization. Anoxic depolarizations result in tremendous physiological stress on the neurons because of the dysregulation of ionic fluxes and the loss of ATP to drive ion pumps that maintain electrochemical gradients. In this review, we present an overview of some of the ionotropic receptors and ion channels that are thought to contribute to the anoxic depolarization of neurons and subsequently, to cell death. The ionotropic receptors for glutamate and ATP that function as ligand-gated cation channels are critical in the death and dysfunction of neurons. Interestingly, two of these receptors (P2X7 and NMDAR) have been shown to couple to the pannexin-1 (Panx1) ion channel. We also discuss the important roles of transient receptor potential (TRP) channels and acid-sensing ion channels (ASICs) in responses to ischemia. The central challenge that emerges from our current understanding of the anoxic depolarization is the need to elucidate the mechanistic and temporal interrelations of these ion channels to fully appreciate their impact on neurons during stroke.

Purinergic signalling: from normal behaviour to pathological brain function

Purinergic neurotransmission, involving release of ATP as an efferent neurotransmitter was first proposed in 1972. Later, ATP was recognised as a cotransmitter in peripheral nerves and more recently as a cotransmitter with glutamate, noradrenaline, GABA, acetylcholine and dopamine in the CNS. Both ATP, together with some of its enzymatic breakdown products (ADP and adenosine) and uracil nucleotides are now recognised to act via P2X ion channels and P1 and P2Y G protein-coupled receptors, which are widely expressed in the brain. They mediate both fast signalling in neurotransmission and neuromodulation and long-term (trophic) signalling in cell proliferation, differentiation and death. Purinergic signalling is prominent in neurone-glial cell interactions. In this review we discuss first the evidence implicating purinergic signalling in normal behaviour, including learning and memory, sleep and arousal, locomotor activity and exploration, feeding behaviour and mood and motivation. Then we turn to the involvement of P1 and P2 receptors in pathological brain function; firstly in trauma, ischemia and stroke, then in neurodegenerative diseases, including Alzheimer's, Parkinson's and Huntington's, as well as multiple sclerosis and amyotrophic lateral sclerosis. Finally, the role of purinergic signalling in neuropsychiatric diseases (including schizophrenia), epilepsy, migraine, cognitive impairment and neuropathic pain will be considered.

Adenosine A2A receptor is a unique angiogenic target of HIF-2alpha in pulmonary endothelial cells

Hypoxia, through the hypoxia-inducible transcription factors HIF-1alpha and HIF-2alpha (HIFs), induces angiogenesis by up-regulating a common set of angiogenic cytokines. Unlike HIF-1alpha, which regulates a unique set of genes, most genes regulated by HIF-2alpha overlap with those induced by HIF-1alpha. Thus, the unique contribution of HIF-2alpha remains largely obscure. By using adenoviral mutant HIF-1alpha and adenoviral mutant HIF-2alpha constructs, where the HIFs are transcriptionally active under normoxic conditions, we show that HIF-2alpha but not HIF-1alpha regulates adenosine A(2A) receptor in primary cultures of human lung endothelial cells. Further, siRNA knockdown of HIF-2alpha completely inhibits hypoxic induction of A(2A) receptor. Promoter studies show a 2.5-fold induction of luciferase activity with HIF-2alpha cotransfection. Analysis of the A(2A) receptor gene promoter revealed a hypoxia-responsive element in the region between -704 and -595 upstream of the transcription start site. By using a ChIP assay, we demonstrate that HIF-2alpha binding to this region is specific. In addition, we demonstrate that A(2A) receptor has angiogenic potential, as assessed by increases in cell proliferation, cell migration, and tube formation. Additional data show increased expression of A(2A) receptor in human lung tumor cancer samples relative to adjacent normal lung tissue. These data also demonstrate that A(2A) receptor is regulated by hypoxia and HIF-2alpha in human lung endothelial cells but not in mouse-derived endothelial cells.

Adenosine receptors and neurological disease: neuroprotection and neurodegeneration

Adenosine receptors modulate neuronal and synaptic function in a range of ways that may make them relevant to the occurrence, development and treatment of brain ischemic damage and degenerative disorders. A(1) adenosine receptors tend to suppress neural activity by a predominantly presynaptic action, while A(2A) adenosine receptors are more likely to promote transmitter release and postsynaptic depolarization. A variety of interactions have also been described in which adenosine A(1) or A(2) adenosine receptors can modify cellular responses to conventional neurotransmitters or receptor agonists such as glutamate, NMDA, nitric oxide and P2 purine receptors. Part of the role of adenosine receptors seems to be in the regulation of inflammatory processes that often occur in the aftermath of a major insult or disease process. All of the adenosine receptors can modulate the release of cytokines such as interleukins and tumor necrosis factor-alpha from immune-competent leukocytes and glia. When examined directly as modifiers of brain damage, A(1) adenosine receptor (AR) agonists, A(2A)AR agonists and antagonists, as well as A(3)AR antagonists, can protect against a range of insults, both in vitro and in vivo. Intriguingly, acute and chronic treatments with these ligands can often produce diametrically opposite effects on damage outcome, probably resulting from adaptational changes in receptor number or properties. In some cases molecular approaches have identified the involvement of ERK and GSK-3beta pathways in the protection from damage. Much evidence argues for a role of adenosine receptors in neurological disease. Receptor densities are altered in patients with Alzheimer's disease, while many studies have demonstrated effects of adenosine and its antagonists on synaptic plasticity in vitro, or on learning adequacy in vivo. The combined effects of adenosine on neuronal viability and inflammatory processes have also led to considerations of their roles in Lesch-Nyhan syndrome, Creutzfeldt-Jakob disease, Huntington's disease and multiple sclerosis, as well as the brain damage associated with stroke. In addition to the potential pathological relevance of adenosine receptors, there are earnest attempts in progress to generate ligands that will target adenosine receptors as therapeutic agents to treat some of these disorders.

Timing of adenosine 2A receptor stimulation relative to reperfusion has differential effects on infarct size and cardiac function as assessed in mice by MRI

The activation of adenosine 2A receptors before reperfusion following coronary artery occlusion reduces infarct size and improves ejection fraction (EF). In this study, we examined the effects of delaying treatment with the adenosine 2A receptor agonist ATL146e (ATL) until 1 h postreperfusion. The infarct size and EF were serially assessed by gadolinium-diethylenetriaminepentaacetic acid-enhanced MRI in C57BL/6 mice at 1 and 24 h postreperfusion. The infarct size was also assessed by 2,3,5-triphenyltetrazolium chloride staining at 24 h. Mice were treated with ATL (10 microg/kg ip) either 2 min before reperfusion (early ATL) or 1 h postreperfusion (late ATL) following the 45-min coronary occlusion. The two methods used to assess infarct size at 24 h postreperfusion (MRI and 2,3,5-triphenyltetrazolium chloride) showed an excellent correlation (R=0.96). The risk region, determined at 24 h postreperfusion, was comparable between the control and ATL-treated groups. The infarct size by MRI at 1 versus 24 h postreperfusion was 25+/-1 vs. 26+/-1% of left ventricular mass (means+/-SE) in control mice, 16+/-2 versus 17+/-2% in early-ATL mice, and 24+/-2 versus 25+/-2% in late-ATL mice (intragroup, P=not significant; and intergroup, early ATL vs. control or late ATL, P<0.05). EF was reduced in control mice but was largely preserved between 1 and 24 h in both early-ATL and late-ATL mice (P<0.05). In conclusion, after coronary occlusion in mice, the extent of myocellular death due to ischemia-reperfusion injury is 95% complete within 1 h of reperfusion. The infarct size was significantly reduced by ATL when given just before reperfusion, but not 1 h postreperfusion. Either treatment window helped preserve the EF between 1 and 24 h postreperfusion.

Early adenosine receptor activation ameliorates spinal cord reperfusion injury

OBJECTIVES

Adenosine receptor activation at reperfusion has been shown to ameliorate ischemia-reperfusion injury of the spinal cord, but the effects of therapy given in response to ischemic injury are unknown. We hypothesized that adenosine receptor activation with ATL-146e would produce similar protection from ischemic spinal cord injury, whether given at reperfusion or in a delayed fashion.

METHODS

Twenty-two New Zealand white rabbits were divided into three groups. All three groups, including the ischemia-reperfusion group (IR, n = 8), underwent 45 min of infrarenal aortic occlusion. The early treatment group (early, n = 8) received 0.06 mug/kg/min of ATL-146e for 3 h beginning 10 min prior to reperfusion. The delayed treatment group (delayed, n = 6) received ATL-146e starting 1 h after reperfusion. After 48 h, hind limb function was graded using the Tarlov score. Finally, lumbar spinal cord neuronal cytoarchitecture was evaluated.

RESULTS

Hemodynamic parameters were similar among the groups. Hind limb function at 48 h was significantly better in the early group (3.5 +/- 1.0) compared to the IR group (0.625 +/- 0.5, P < or = 0.01). There was a trend towards better hind limb function in the early group compared to the delayed group (2.4 +/- 1.1, P = 0.08). Hind limb function was similar between delayed and IR groups. Hematoxylin-eosin spinal cord sections demonstrated preservation of viable motor neurons in the early group compared to the delayed and IR groups.

CONCLUSIONS

Early therapy with ATL-146e provided better protection in this study; therefore, therapy should not be delayed until there is evidence of ischemic neurological deficit. This study suggests that adenosine receptor activation is most effective as a preventive strategy at reperfusion for optimal protection in spinal cord ischemia-reperfusion injury.

Adenosine protects against suicidal erythrocyte death

Suicidal death of erythrocytes or eryptosis is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine exposure at the erythrocyte surface. The cell membrane scrambling is triggered by an increase in cytosolic Ca(2+) activity and activation of protein kinase C (PKC). Phosphatidylserine exposure fosters adherence of affected erythrocytes to the vascular wall. Thus, microcirculation in ischemic tissues may be impaired by the appearance of eryptotic erythrocytes. Ischemia leads to release of adenosine, which in most tissues leads to vasodilation and protects against cell injury. The present experiments explored whether adenosine influences mechanisms underlying eryptosis. Erythrocyte phosphatidylserine exposure was estimated from annexin V binding, cell volume from forward scatter and cytosolic Ca(2+) activity from Fluo3 fluorescence. Glucose depletion (for 24 or 48 h) significantly increased annexin binding and decreased forward scatter, effects partially reversed by adenosine. The protective effect of adenosine reached statistical significance (s.d.) at > =30 microM. Low Cl(-) solution (Cl(-) exchanged by gluconate for 24 h) similarly increased annexin binding and decreased forward scatter, effects again reversed by adenosine (s.d. at > or =10 and 30 microM, respectively). Similarly, phosphatase inhibitor okadaic acid (OA, 1 microM) and PKC activator phorbol 12-myristate-13-acetate (PMA, 3 microM) significantly enhanced annexin binding and decreased forward scatter. Adenosine significantly blunted the effects of OA and PMA on annexin V binding (s.d. at > or =30 and 10 microM, respectively) and the effect of OA on forward scatter (s.d. at > or =10 microM). In conclusion, adenosine inhibits eryptosis by a mechanism presumably effective downstream of PKC. The effect may participate in the maintenance of microcirculation in ischemic tissue.

Functional and cytoarchitectural spinal cord protection by ATL-146e after ischemia/reperfusion is mediated by adenosine receptor agonism

BACKGROUND

ATL-146e protects the spinal cord from ischemia/reperfusion injury, presumably via adenosine A(2A) receptor activation, but this relationship remains unproven. We hypothesized that spinal cord functional and cytoarchitectural preservation from ATL-146e would be lost with simultaneous administration of the specific adenosine A(2A) antagonist ZM241385 (ZM), thus proving that adenosine A(2A) receptor activation is responsible for the protective effects of this compound.

METHODS

New Zealand White rabbits underwent 45 minutes of infrarenal aortic cross-clamping. Groups (n = 10) included sham, ischemia, ischemia plus ATL-146e (ATL-146E), ischemia plus ZM, or ischemia with both compounds (agonist-antagonist). Tarlov scores were recorded every 12 hours. After 48 hours, the spinal cord was fixed for histology and microtubule-associated protein 2 immunohistochemistry.

RESULTS

Tarlov scores at 48 hours were significantly better in the sham and ATL-146E groups (5.0 and 3.9, respectively) compared with the other three groups (all < or =1.3; P < .001). On hematoxylin and eosin, neuronal viability was higher in the sham, ATL-146E, and agonist-antagonist groups compared with the control and ZM groups (P < .05). Microtubule-associated protein 2 expression was preserved in the sham and ATL-146E groups but was lost in the ATL + ZM, ZM241385, and control groups.

CONCLUSIONS

ATL-146e preserves the spinal cord in terms of both cytoarchitecture and function after reperfusion of the ischemic spinal cord, but this preservation is not completely blocked by competitive adenosine A(2A) receptor antagonism. Although ATL-146e does seem to partially function through activation of the adenosine A(2A) receptor, the neuroprotective mechanism may not be limited to this particular receptor.

Comparison of systemic and retrograde delivery of adenosine A2A agonist for attenuation of spinal cord injury after thoracic aortic cross-clamping

BACKGROUND

Paraplegia remains a devastating complication of thoracic aortic surgery, which has been attenuated by retrograde adenosine and systemic adenosine A2A receptor activation. We hypothesized that despite retrograde spinal perfusion of an adenosine A2A agonist (ATL-146e), systemic therapy produces superior spinal cord protection with reduced inflammation.

METHODS

Forty pigs underwent 30-minute thoracic aortic cross-clamping. Pigs received: no therapy (control); retrograde saline (retrograde control); retrograde ATL-146e; systemic ATL-146e; systemic ATL-146e with retrograde saline; or systemic and retrograde ATL-146e. Retrograde therapies were given during ischemia. Systemic ATL-146e (0.06 microg.kg(-1).min(-1)) was given intravenously for 3 hours at reperfusion. At 24 hours, motor function was assessed using the Tarlov scale. Tissue was analyzed for neuronal viability, microtubule-associated protein-2 expression, and neutrophil sequestration (myeloperoxidase activity).

RESULTS

Four pigs received retrograde barium showing both radiographic and histologic spinal cord perfusion. Tarlov scores at 24 hours were significantly improved versus both control groups in all ATL groups except the combined ATL-146e group (all p < 0.05). Neuronal viability by hematoxylin and eosin stain was significantly preserved in systemic ATL groups compared with both control groups (all p < 0.05). Microtubule-associated protein-2 expression was significantly preserved compared with both control groups in all systemic ATL groups. Systemic ATL significantly lowered myeloperoxidase activity versus both control groups (p < 0.01).

CONCLUSIONS

Both retrograde and systemic ATL-146e therapies attenuate ischemic spinal cord injury, but combining the two routes was less effective. Given comparable results between the two routes and the simplicity of systemic delivery, peripheral venous ATL-146e at reperfusion should be preferred for spinal cord protection in thoracic aortic surgery.

Optimization of a mouse locomotor rating system to evaluate compression-induced spinal cord injury: correlation of locomotor and morphological injury indices

Object

Due to the usefulness of mouse genetics, there is a need to improve procedures for producing and assessing spinal cord injury (SCI) in mice. The authors describe an improved locomotor scoring system for evaluating SCI. The modified Basso-Beattie-Bresnahan (mBBB) scoring system for mice is compared with existing procedures as well as histological SCI criteria.

Methods

Mice were subjected to SCI by placing a weight on the cord at T-12 for 5 to 15 minutes after laminectomy to produce spinal cord ischemia. Injury was assessed using mBBB scoring that incorporates elements of the rat BBB and the mouse motor function scoring systems that are best suited for precisely assessing mouse SCI. The mBBB score was found to be more discriminating than the inclined plane test, and in the authors’ laboratory it had a significantly lower coefficient of variation than the Basso mouse scale score. The mBBB score is well correlated with sparing of white matter as assessed by eriochrome cyanine staining of myelin.

Conclusions

Weight placement at T-12 in the mouse causes reproducible SCI. A new mBBB scoring system is useful for accurately assessing locomotor dysfunction following SCI in mice and is well correlated with histological assessment of spinal cord white matter.

Neuroprotection by adenosine in the brain: From A(1) receptor activation to A (2A) receptor blockade

Adenosine is a neuromodulator that operates via the most abundant inhibitory adenosine A(1) receptors (A(1)Rs) and the less abundant, but widespread, facilitatory A(2A)Rs. It is commonly assumed that A(1)Rs play a key role in neuroprotection since they decrease glutamate release and hyperpolarize neurons. In fact, A(1)R activation at the onset of neuronal injury attenuates brain damage, whereas its blockade exacerbates damage in adult animals. However, there is a down-regulation of central A(1)Rs in chronic noxious situations. In contrast, A(2A)Rs are up-regulated in noxious brain conditions and their blockade confers robust brain neuroprotection in adult animals. The brain neuroprotective effect of A(2A)R antagonists is maintained in chronic noxious brain conditions without observable peripheral effects, thus justifying the interest of A(2A)R antagonists as novel protective agents in neurodegenerative diseases such as Parkinson's and Alzheimer's disease, ischemic brain damage and epilepsy. The greater interest of A(2A)R blockade compared to A(1)R activation does not mean that A(1)R activation is irrelevant for a neuroprotective strategy. In fact, it is proposed that coupling A(2A)R antagonists with strategies aimed at bursting the levels of extracellular adenosine (by inhibiting adenosine kinase) to activate A(1)Rs might constitute the more robust brain neuroprotective strategy based on the adenosine neuromodulatory system. This strategy should be useful in adult animals and especially in the elderly (where brain pathologies are prevalent) but is not valid for fetus or newborns where the impact of adenosine receptors on brain damage is different.

Adenosine A2A Receptor Agonist Improves Cardiac Dysfunction From Pulmonary Ischemia-Reperfusion Injury

BACKGROUND

Ischemia-reperfusion (IR) injury negatively impacts patient outcome in lung transplantation. Clinically, we observed that lung transplant patients with ischemia-reperfusion injury tend to have cardiac dysfunction. Previous studies have shown that ATL-146e (4-{3-[6-amino-9-(5-ethylcarbamoyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-9H-purin-2-yl]-prop-2-ynyl}-cyclohexanecarboxylic acid methyl ester), a selective adenosine A2A receptor agonist, reduces lung inflammation after ischemia-reperfusion. We hypothesized that pulmonary ischemia-reperfusion causes secondary heart dysfunction and ATL-146e will improve this dysfunction.

METHODS

We utilized an in vivo rabbit lung ischemia-reperfusion model. The Sham group underwent 120 minutes single lung ventilation. The IR and ATL groups underwent 90 minutes right lung ischemia with 30 minutes right lung reperfusion. The ATL-146e was given intravenously to the ATL group during reperfusion. Cardiac output and arterial blood gases were monitored, and neutrophil sequestration was measured by myeloperoxidase activity.

RESULTS

Upon reperfusion, cardiac output (mL/min) significantly dropped in the IR and ATL groups. By 15 minutes reperfusion, cardiac output in the ATL group improved significantly over the IR group and remained significant thereafter. Lung myeloperoxidase activity was significantly reduced by ATL-146e. Although never hypoxemic, arterial oxygenation was lower in the IR and ATL groups while central venous pressures and mean arterial pressures were similar among groups. A separate experiment demonstrated that reperfusion with the antioxidant N-(2-mercaptopropionyl)glycine prevented cardiac dysfunction.

CONCLUSIONS

Pulmonary ischemia-reperfusion causes cardiac dysfunction independent of preload, afterload, and oxygenation. The ATL-146e improves this dysfunction presumably by the antiinflammatory effects of adenosine A2A receptor activation on neutrophils. One likely mechanism involves the release of oxidants from the ischemic lung upon reperfusion, which has immediate negative effects on the heart.

Therapeutic potential of adenosine A2A receptor antagonists in Parkinson's disease

In the pursuit of improved treatments for Parkinson's disease (PD), the adenosine A(2A) receptor has emerged as an attractive nondopaminergic target. Based on the compelling behavioral pharmacology and selective basal ganglia expression of this G-protein-coupled receptor, its antagonists are now crossing the threshold of clinical development as adjunctive symptomatic treatment for relatively advanced PD. The antiparkinsonian potential of A(2A) antagonism has been boosted further by recent preclinical evidence that A(2A) antagonists might favorably alter the course as well as the symptoms of the disease. Convergent epidemiological and laboratory data have suggested that A(2A) blockade may confer neuroprotection against the underlying dopaminergic neuron degeneration. In addition, rodent and nonhuman primate studies have raised the possibility that A(2A) receptor activation contributes to the pathophysiology of dyskinesias-problematic motor complications of standard PD therapy--and that A(2A) antagonism might help prevent them. Realistically, despite being targeted to basal ganglia pathophysiology, A(2A) antagonists may be expected to have other beneficial and adverse effects elsewhere in the central nervous system (e.g., on mood and sleep) and in the periphery (e.g., on immune and inflammatory processes). The thoughtful design of new clinical trials of A(2A) antagonists should take into consideration these counterbalancing hopes and concerns and may do well to shift toward a broader set of disease-modifying as well as symptomatic indications in early PD.

Control of programmed cell death by neurotransmitters and neuropeptides in the developing mammalian retina

It has long been known that a barrage of signals from neighboring and connecting cells, as well as components of the extracellular matrix, control cell survival. Given the extensive repertoire of retinal neurotransmitters, neuromodulators and neurotrophic factors, and the exhuberant interconnectivity of retinal interneurons, it is likely that various classes of released neuroactive substances may be involved in the control of sensitivity to retinal cell death. The aim of this article is to review evidence that neurotransmitters and neuropeptides control the sensitivity to programmed cell death in the developing retina. Whereas the best understood mechanism of execution of cell death is that of caspase-mediated apoptosis, current evidence shows that not only there are many parallel pathways to apoptotic cell death, but non-apoptotic programs of execution of cell death are also available, and may be triggered either in isolation or combined with apoptosis. The experimental data show that many upstream signaling pathways can modulate cell death, including those dependent on the second messengers cAMP-PKA, calcium and nitric oxide. Evidence for anterograde neurotrophic control is provided by a variety of models of the central nervous system, and the data reviewed here indicate that an early function of certain neurotransmitters, such as glutamate and dopamine, as well as neuropeptides such as pituitary adenylyl cyclase-activating polypeptide and vasoactive intestinal peptide is the trophic support of cell populations in the developing retina. This may have implications both regarding the mechanisms of retinal organogenesis, as well as pathological conditions leading to retinal dystrophies and to dysfunctional cellular behavior.

The evolution of ischemic spinal cord injury in function, cytoarchitecture, and inflammation and the effects of adenosine A2A receptor activation

OBJECTIVE

Spinal cord ischemia/reperfusion injury involves multiple factors that may be modulated by adenosine A 2A receptor activation. This study defines injury progression in terms of function, cytoarchitecture, and inflammation and assesses whether adenosine A 2A receptor activation by ATL-146e limits injury progression.

METHODS

Mature swine were divided into 3 groups: sham thoracotomy, IR (30 minutes of ischemia followed by reperfusion), and ATL (ischemia/reperfusion with ATL-146e administration for the first 3 hours of reperfusion). Subgroups were killed at 0, 3, 6, 12, 24, and 48 hours after reperfusion. Function was followed up with Tarlov scores. Spinal cord tissue was evaluated for neuronal viability, microtubule-associated protein-2 immunohistochemistry, and neutrophil sequestration (myeloperoxidase assay). Spinal cord tissue, cerebrospinal fluid, and serum were evaluated for tumor necrosis factor-alpha by enzyme-linked immunosorbent assay.

RESULTS

Function was significantly impaired at 24, 36, and 48 hours in the IR group compared with the sham and ATL groups ( P < .05). Neuronal viability and microtubule-associated protein-2 staining were significantly preserved in the sham and ATL groups compared with the IR group at 24 and 48 hours ( P < .05). Spinal cord myeloperoxidase levels were significantly higher in the IR group than in the sham and ATL groups at 24 and 48 hours. Although negligible in serum and cerebrospinal fluid, tumor necrosis factor-alpha levels in the spinal cord peaked significantly higher in the IR group compared with the sham and ATL groups at 6 and 24 hours ( P < .05).

CONCLUSIONS

Spinal cord ischemia/reperfusion induced changes in neutrophil sequestration, microtubule-associated protein-2 expression, and neuronal viability within 24 hours of reperfusion. Spinal cord tumor necrosis factor-alpha increased significantly by 6 to 12 hours after reperfusion. Adenosine A 2A receptor activation attenuates spinal cord inflammation, which may be critical for the preservation of neuronal function and cytoarchitecture after ischemia/reperfusion.

Building a Better Fluid for Emergency Resuscitation of Traumatic Brain Injury

Hextend (HEX) is a colloid solution that is FDA-approved for volume expansion during surgery. ATL-146e is a novel adenosine A2A receptor agonist that has anti-inflammatory, neuroprotective, and coronary vasodilator properties. Three series of experiments were designed to evaluate the therapeutic potential of HEX+/-ATL-146e for emergency resuscitation from traumatic brain injury (TBI) + hemorrhagic hypotension.

METHODS

In the first two studies in vivo, anesthetized, ventilated pigs (30-45 kg) received a fluid percussion TBI, 45% arterial hemorrhage, and 30 minutes shock period. In Series 1, resuscitation consisted of unlimited crystalloid (n = 8) or HEX (n = 8) to correct systolic arterial pressure >100 mm Hg and heart rate <100 bpm for the first 60 minutes ("emergency phase"), and then maintain cerebral perfusion pressure (CPP) > 70 mm Hg for 60-240 minutes. In Series 2 (n = 31), resuscitation consisted of a 1 L bolus of HEX + ATL-146e (10 ng/kg/min, n = 10) or HEX +placebo (n = 10) followed by crystalloid to the same endpoints. In Series 3 in vivo, the hemodynamic response evoked by 0, 10, 50, or 100 ng/kg/min ATL-146e was measured before or 60 minutes after HEX resuscitation from 45% hemorrhage.

RESULTS

Following TBI+hemorrhage, there were 4/22 deaths in series 1 and 11/31 deaths in series 2. In those alive at 30 minutes, mean arterial pressure, cardiac index, mixed venous O2 saturation, and cerebral venous O2 saturation were all reduced by 40-60%, while heart rate and lactate were increased 2-5 fold. With no resuscitation (n = 2), there was minimal hemodynamic compensation and progressive acidosis. Upon resuscitation, these values corrected but intracranial pressure progressively rose from <5 mm Hg to 15-20 mm Hg. Series 1: With HEX (n = 8) versus crystalloid (n = 8), CPP was less labile, acid/base was maintained, and the fluid requirement was reduced by 60% (all p < 0.05) Series 2: With ATL-146e (n = 10) versus placebo (n = 10), stroke volume and cardiac output were improved by 40-60%, and the fluid requirement was reduced by 30% (all p < 0.05). Series 3: ATL-146e caused a dose-related increase (p < 0.05) in stroke volume after, but not before, hemorrhage. The effects on pre-load, afterload, and heart rate were similar before and after hemorrhage.

CONCLUSIONS

HEX alone is a safe and efficacious low volume alternative to initial crystalloid resuscitation after TBI. An adenosine A2A agonist combined with 1 L of HEX safely and effectively counteracted a decrease in cardiac performance noted after TBI+hemorrhage without causing hypotension or bradycardia.

Resveratrol, a red wine polyphenol, protects spinal cord from ischemia-reperfusion injury

OBJECTIVE

The cardioprotective effect of red wine has been attributed to resveratrol. The resveratrol-induced protection against ischemia-reperfusion (I/R) injury has been documented in heart, kidney, and brain. Resveratrol scavenges free O(2) radicals and upregulates nitric oxide (NO). However, the presence of resveratrol-induced spinal cord protection against I/R injury has not been reported in the literature. The objective of this study was to evaluate the effects of resveratrol on neurologic functions, histopathologic changes, and NO metabolism following temporary spinal cord ischemia (SCI) in rabbits. Material and methods SCI was induced with occlusion of the infrarenal aorta in rabbits. In addition to the sham group (group S, n = 7), group C (n = 7) received vehicle 30 minutes before ischemia. Group R1 (n = 7) and R10 (n = 7) received 1 mg/kg and 10 mg/kg resveratrol instead of vehicle, respectively. Blood samples were taken to obtain nitrite/nitrate levels during the surgical procedure. After neurologic evaluation at the 48th hour of reperfusion, lumbar spinal cords were removed for histopathologic examination and malondialdehyde measurement as a marker of oxidative stress.

RESULTS

Five animals in group C had paraplegia while 5 in group R10 had normal neurologic functions. The average Tarlov score of group R10 was significantly higher than that the score of group C (4.1 +/- 1.2, vs 1.2 +/- 2.2; P =.014). Histopathologic examination revealed higher neuronal viability index in group R10 compared with that of group C (0.82 +/- 0.24 vs. 0.46 +/- 0.34; P =.018). Nitrite/nitrate levels decreased in group C (from 357 +/- 20.15 micromol/L to 281 +/- 47.9 micromol/L; P <.01) whereas they increased both in group R1 and group R10 (from 287+/-28 micromol/L to 310 +/- 33.9 micromol/L and from 296 +/- 106 micromol/L to 339 +/- 87 micromol/L, respectively) during SCI. Malondialdehyde levels of group R10 was lower than those of group C (55 +/- 12.9 nmol/mg protein vs 83.9 +/- 15.1 nmol/mg protein; P =.001, respectively).

CONCLUSIONS

In this model of SCI, resveratrol decreased oxidative stress, increased NO release, and protected spinal cord from I/R injury. Resveratrol-induced neuroprotection is probably mediated by its antioxidant and NO promoting properties. Before considering the clinical use of this natural antioxidant, further research is warranted about its mechanism of effects, timing, and optimum dose.

CLINICAL RELEVANCE

Paraplegia that results from spinal cord ischemia is a catastrophic complication of thoracic and thoracoabdominal aorta surgical procedures. Despite several surgical modifications and pharmacologic approaches, paraplegia has not been totally eliminated. On clinical grounds, the efficiency of currently used pharmacologic agents to prevent spinal cord injury during thoracic and thoracoabdominal aorta surgery is very limited and their benefit is controversial. Preischemic infusion of resveratrol protects the spinal cord from ischemia reperfusion injury in rabbits. Following clarification of the underlying protective mechanism, optimal dose, and timing, resveratrol may used in humans as an adjunct to eliminate this catastrophic complication.

A glance at adenosine receptors: novel target for antitumor therapy

Adenosine can be released from a variety of cells throughout the body, as the result of increased metabolic rates, in concentrations that can have a profound impact on the vasculature, immunoescaping, and growth of tumor masses. It is recognized that the concentrations of this nucleoside are increased in cancer tissues. Therefore, it is not surprising that adenosine has been shown to be a crucial factor in determining the cell progression pathway, either during apoptosis or during cytostatic state. From the perspective of cancer, the most important question then may be "Can activation and/or blockade of the pathways downstream of the adenosine receptor contribute to tumor development?" Rigorous examinations of the role of adenosine in in vivo and in vitro systems need to be investigated. The present review therefore proposes multiple adenosine-sustained ways that could prime tumor development together with the critical combinatorial role played by adenosine receptors in taking a choice between proliferation and death. This review proposes that adenosine acts as a potent regulator of normal and tumor cell growth. It is hypothesized that this effect is dependent on extracellular adenosine concentrations, cell surface expression of different adenosine receptor subtypes, and signal transduction mechanisms activated following the binding of specific agonists. We venture to suggest that the clarification of the role of adenosine and its receptors in cancer development may hold great promise for the treatment of chemotherapy in patients affected by malignancies.

The role of pharmacology in spinal cord protection during thoracic aortic reconstruction

Surgery of the thoracic aorta continues to have a significant risk of neurologic complication. Several strategies to minimize this risk are emerging. Pharmacologic protection from these complications continues to be researched, but at this point few medications are being used clinically. This article reviews the pathophysiology of ischemic spinal cord injury and summarizes the investigational pharmacology that may prevent these serious complications.

A dual role of adenosine A2A receptors in 3-nitropropionic acid-induced striatal lesions: implications for the neuroprotective potential of A2A antagonists

Reduction of A2A receptor expression is one of the earliest events occurring in both Huntington's disease (HD) patients and mice overexpressing the N-terminal part of mutated huntingtin. Interestingly, increased activity of A2A receptors has been found in striatal cells prone to degenerate in experimental models of this neurodegenerative disease. However, the role of A2A receptors in the pathogenesis of HD remains obscure. In the present study, using A2A-/- mice and pharmacological compounds in rat, we demonstrate that striatal neurodegeneration induced by the mitochondrial toxin 3-nitropropionic acid (3NP) is regulated by A2A receptors. Our results show that the striatal outcome induced by 3NP depends on a balance between the deleterious activity of presynaptic A2A receptors and the protective activity of postsynaptic A2A receptors. Moreover, microdialysis data demonstrate that this balance is anatomically determined, because the A2A presynaptic control on striatal glutamate release is absent within the posterior striatum. Therefore, because blockade of A2A receptors has differential effects on striatal cell death in vivo depending on its ability to modulate presynaptic over postsynaptic receptor activity, therapeutic use of A2A antagonists in Huntington's as well as in other neurodegenerative diseases could exhibit undesirable biphasic neuroprotective-neurotoxic effects.

Novel resuscitation strategy for pulmonary contusion after severe chest trauma

BACKGROUND

Adenosine A2a receptor stimulation can increase coronary perfusion and also reduce leukocyte-mediated inflammatory responses in some conditions. Hextend is a novel colloid solution that may have antioxidant properties. All these actions might be beneficial after severe chest trauma, but have never been investigated. To fill these gaps, this study evaluated the therapeutic potential of a novel adenosine A2a agonist during fluid resuscitation from severe chest trauma with either standard-of-care crystalloid or Hextend.

METHODS

Anesthetized, ventilated swine received unilateral, blunt trauma to the right chest via captive bolt gun, followed by a 10- to 12-mL/kg arterial hemorrhage. After 25 minutes of shock, ATL-146e was started (10 ng/kg/min intravenously for 180 minutes). After an additional 5 minutes, the minimum amount of either colloid (Hextend, 5% hetastarch in lactate-buffered, balanced electrolyte solution) or crystalloid (lactated Ringer's [LR] solution) was administered to maintain mean arterial pressure > 70 mm Hg and heart rate < 100 beats/min and to correct lactate for 180 minutes postinjury. Cardiopulmonary function was monitored and serial bronchoalveolar lavage samples were analyzed for protein, leukocyte infiltration, and expression of cyclooxygenase (COX)-1 and COX-2 isozymes as markers of the inflammatory cascade.

RESULTS

Fluid requirements were reduced by half with Hextend compared with LR (p < 0.05). ATL-146e in either Hextend or LR transiently increased cardiac output, cardiac contractility, and systemic oxygen delivery (all p < 0.05). Pao(2)/Fio(2) ratio was 50 to 100 higher and bronchoalveolar lavage leukocytes were reduced by half with Hextend versus LR (both p < 0.05), but there was no added effect of ATL-146e. COX-1 expression was induced in macrophages (Mphis), whereas COX-2 was induced in neutrophils. Neither Hextend nor ATL-146e reduced COX expression.

CONCLUSION

Hextend reduced the volume for initial resuscitation, which may offer logistical advantages in prehospital field conditions or whenever there is limited medical resources or prolonged transport times; ATL-146e improved early cardiac performance without causing hypotension or bradycardia; when administered 25 to 30 minutes after injury, neither Hextend nor ATL-146e altered inflammatory changes in pulmonary Mphis or infiltrating PMNs; and further studies are needed to determine whether these short-term benefits correlate with long-term outcome.

Rapid modification of the glycocalyx caused by ischemia-reperfusion is inhibited by adenosine A2A receptor activation

Ischemia-reperfusion (I/R) has been shown to cause microvascular dysfunction and to alter the appearance of the glycocalyx in electron micrographs. We hypothesized that I/R injury might alter the structure and/or permeability of the glycocalyx. Prior work had shown a role for adenosine in protection from I/R injury, and, therefore, we also explored the idea that activation of the adenosine A(2A) receptor would attenuate I/R glycocalyx injury. Here, we report that I/R causes a rapid and dramatic decrease in the ability of the glycocalyx to exclude FITC-Dextran 70 (Dex70). Over a reperfusion period of 45 min, the glycocalyx dye exclusion zone for Dex70 decreased by one-half in capillaries and postcapillary venules, whereas the red blood cell exclusion zone was very slightly reduced in capillaries only. Pretreatment with the A(2A) agonist ATL-146e significantly inhibited the changes in both vessel types. The modifications of the glycocalyx appear to be an early step in the inflammatory cascade typically associated with reperfusion injury, and adenosine A(2A) receptor activation may play a role in protection from this injury.

Adenosine in the spinal cord and periphery: release and regulation of pain

In the central nervous system (CNS), adenosine is an important neuromodulator and regulates neuronal and non-neuronal cellular function (e.g. microglia) by actions on extracellular adenosine A(1), A(2A), A(2B) and A(3) receptors. Extracellular levels of adenosine are regulated by synthesis, metabolism, release and uptake of adenosine. Adenosine also regulates pain transmission in the spinal cord and in the periphery, and a number of agents can alter the extracellular availability of adenosine and subsequently modulate pain transmission, particularly by activation of adenosine A(1) receptors. The use of capsaicin (which activates receptors selectively expressed on C-fibre afferent neurons and produces neurotoxic actions in certain paradigms) allows for an interpretation of C-fibre involvement in such processes. In the spinal cord, adenosine availability/release is enhanced by depolarization (K(+), capsaicin, substance P, N-methyl-D-aspartate (NMDA)), by inhibition of metabolism or uptake (inhibitors of adenosine kinase (AK), adenosine deaminase (AD), equilibrative transporters), and by receptor-operated mechanisms (opioids, 5-hydroxytryptamine (5-HT), noradrenaline (NA)). Some of these agents release adenosine via an equilibrative transporter indicating production of adenosine inside the cell (K(+), morphine), while others release nucleotide which is converted extracellularly to adenosine by ecto-5'-nucleotidase (capsaicin, 5-HT). Release can be capsaicin-sensitive, Ca(2+)-dependent and involve G-proteins, and this suggests that within C-fibres, Ca(2+)-dependent intracellular processes regulate production and release of adenosine. In the periphery, adenosine is released from both neuronal and non-neuronal sources. Neuronal release from capsaicin-sensitive afferents is induced by glutamate and by neurogenic inflammation (capsaicin, low concentration of formalin), while that from sympathetic postganglionic neurons (probably as adenosine 5'-triphosphate (ATP) with NA) occurs following more generalized inflammation. Such release is modified differentially by inhibitors of AK and AD. Following nerve injury, there is an alteration in capsaicin-sensitive adenosine release, as spinal release now is less responsive to opioids, while peripheral release is less responsive to inhibitors of metabolism. Following inflammation, adenosine is released from a variety of cell types in addition to neurons (e.g. endothelial cells, neutrophils, mast cells, fibroblasts). ATP is released both spinally and peripherally following inflammation or injury, and may be converted to adenosine by ecto-5'-nucleotidase contributing an additional source of adenosine. Release of adenosine from both spinal and peripheral compartments has inhibitory effects on pain transmission, as methylxanthine adenosine receptor antagonists reduce analgesia produced by agents which augment extracellular levels of adenosine spinally (morphine, 5-HT, substance P, AK inhibitors) and peripherally (AK inhibitors, AD inhibitors). Increases in extracellular adenosine availability also may contribute to antiinflammatory effects of certain agents (methotrexate, sulfasalazine, salicylates, AK inhibitors), and this could have secondary effects on pain signalling in chronic inflammation. The purpose of the present review is to consider: (a). the factors that regulate the extracellular availability of adenosine in the spinal cord and at peripheral sites; and (b). the extent to which this adenosine affects pain signalling in these two distinct compartments.

DNA damage and repair system in spinal cord ischemia

BACKGROUND AND PURPOSE

Spinal cord ischemia-reperfusion injury may be initiated by a number of mediators, including reactive oxygen species. Recent studies have shown that human MutY homologue (hMYH), human 8-oxo-7,8-dihydrodeoxyguanine (8-oxoG) glycosylase (hOGG1), and human MutS homologue 2 (hMSH2) are important DNA mismatch repair genes. We hypothesized that ischemia-reperfusion injury in spinal cord causes DNA damage manifested by 8-oxoG production and activates the DNA repair system involving hMYH, hOGG1, and hMSH2.

METHODS

Spinal cords of rabbits were removed at 1, 3, 6, 24, and 48 hours after 30 minutes of infrarenal aortic occlusion. DNA damage was determined with 8-oxoG staining. The expression and localization of DNA repair enzymes, such as hMYH, hOGG1, and hMSH2, were studied with Western blot analysis and immunohistochemical staining. The level of apoptosis was determined with TUNEL study. Activation of caspase-3, an enzyme induced by cellular injury that leads to apoptosis by degrading cellular structural proteins, was also studied.

RESULTS

DNA damage monitored with 8-oxoG level was significantly present from 1 hour to 6 hours after reperfusion in gray matter neurons of ischemic spinal cord. The levels of hMYH, hOGG1, and hMSH2 were markedly increased in gray matter neurons at 6 hours after reperfusion. Caspase-3 was also induced at 6 hours to 24 hours after reperfusion in ischemic spinal cord. However, the peak level of TUNEL reactivity was found at 48 hours after reperfusion in spinal cord neurons.

CONCLUSION

This study has shown, for the first time, the rapid expression of DNA damage-repair processes associated with spinal cord ischemia and subsequent reperfusion.

Adenosine A2A agonist reduces paralysis after spinal cord ischemia: correlation with A2A receptor expression on motor neurons

BACKGROUND

The adenosine A2A agonist ATL-146e ameliorates reperfusion inflammation, reducing subsequent paralysis and neuronal apoptosis after spinal cord ischemia. We hypothesized that neuroprotection with ATL-146e involves inducible neuronal adenosine A2A receptors (A2A-R) that are upregulated after ischemia.

METHODS

Eighteen rabbits underwent laparotomy, and 14 sustained spinal cord ischemia from cross-clamping the infrarenal aorta for 45 minutes. One group (ischemia-reperfusion [I/R] + ATL) received ATL-146e intravenously for 3 hours during spinal cord reperfusion. A second group (I/R) received equivolume intravenous saline solution for 3 hours and served as an ischemic control, and a third group (Sham) underwent sham laparotomy. At 48 hours, all subjects were assessed for motor impairment using the Tarlov scoring system (0 to 5). Lumbar spinal cord sections were immunolabeled for A2A-R and graded in a blinded fashion using light microscopy.

RESULTS

There was a significant improvement in Tarlov scores in I/R + ATL animals compared with the I/R group. Sham-operated animals demonstrated no A2A-R immunoreactivity. There was a dramatic increase in A2A-R immunoreactivity in neurons of lumbar spinal cord sections from I/R compared with I/R + ATL and sham-operated animals.

CONCLUSIONS

Reduction in paralysis in animals receiving ATL-146e correlates with the new finding of A2A-R expression on lumbar spinal cord motor neurons after ischemia. Adenosine A2A agonists may exert neuroprotective effects by binding to inducible neuronal A2A-R that are upregulated during spinal cord reperfusion, and reduced in response to administration of an A2A-R-specific agonist.

Adenosine A2A analogue improves neurologic outcome after spinal cord trauma in the rabbit

BACKGROUND

ATL-146e, an adenosine A2A agonist, reduces paralysis after spinal cord ischemia-reperfusion. We hypothesized that systemic ATL-146e could improve neurologic outcome after blunt spinal cord trauma.

METHODS

Twenty rabbits survived a thoracic spinal cord impact of 30 g-cm. One group received 0.06 microg/kg/min ATL-146e for the first 3 hours after impact (A2A group), whereas a second group received saline carrier (T/C group). Neurologic outcome was measured using the Tarlov scale (0-5). Histologic sections from the A2A and T/C groups were compared for neuronal viability.

RESULTS

There was significant improvement in Tarlov scores of A2A animals compared with T/C animals at 12 hours (p = 0.007), with a trend toward improvement at 36 (p = 0.08) and 48 (p = 0.09) hours after injury. There was decreased neuronal attrition in A2A animals (p = 0.06).

CONCLUSION

Systemic ATL-146e given after spinal cord trauma results in improved neurologic outcome. Adenosine A2A agonists may hold promise as a rapidly acting alternative to steroids in the early treatment of the spinal cord injured patient.