Mechanisms of neural cell death: implications for development of neuroprotective treatment strategies

Programmed cell death in Parkinson's disease

Parkinson's disease is a debilitating disorder characterized by a progressive loss of dopaminergic neurons caused by programmed cell death. The aim of this review is to provide an up-to-date summary of the major programmed cell death pathways as they relate to PD. For a long time, programmed cell death has been synonymous with apoptosis but there now is evidence that other types of programmed cell death exist, such as autophagic cell death or programmed necrosis, and that these types of cell death are relevant to PD. The pathways and signals covered here include namely the death receptors, BCL-2 family, caspases, calpains, cdk5, p53, PARP-1, autophagy, mitophagy, mitochondrial fragmentation, and parthanatos. The review will present evidence from postmortem PD studies, toxin-induced models (especially MPTP/MPP+, 6-hydroxydopamine and rotenone), and from α-synuclein, LRRK2, Parkin, DJ-1, and PINK1 genetic models of PD, both in vitro and in vivo.

Effect of PACAP in central and peripheral nerve injuries

Pituitary adenylate cyclase activating polypeptide (PACAP) is a bioactive peptide with diverse effects in the nervous system. In addition to its more classic role as a neuromodulator, PACAP functions as a neurotrophic factor. Several neurotrophic factors have been shown to play an important role in the endogenous response following both cerebral ischemia and traumatic brain injury and to be effective when given exogenously. A number of studies have shown the neuroprotective effect of PACAP in different models of ischemia, neurodegenerative diseases and retinal degeneration. The aim of this review is to summarize the findings on the neuroprotective potential of PACAP in models of different traumatic nerve injuries. Expression of endogenous PACAP and its specific PAC1 receptor is elevated in different parts of the central and peripheral nervous system after traumatic injuries. Some experiments demonstrate the protective effect of exogenous PACAP treatment in different traumatic brain injury models, in facial nerve and optic nerve trauma. The upregulation of endogenous PACAP and its receptors and the protective effect of exogenous PACAP after different central and peripheral nerve injuries show the important function of PACAP in neuronal regeneration indicating that PACAP may also be a promising therapeutic agent in injuries of the nervous system.

Site-specific and time-dependent activation of the endocannabinoid system after transection of long-range projections

Background

After focal neuronal injury the endocannabinioid system becomes activated and protects or harms neurons depending on cannabinoid derivates and receptor subtypes. Endocannabinoids (eCBs) play a central role in controlling local responses and influencing neural plasticity and survival. However, little is known about the functional relevance of eCBs in long-range projection damage as observed in stroke or spinal cord injury (SCI).

Methods

In rat organotypic entorhino-hippocampal slice cultures (OHSC) as a relevant and suitable model for investigating projection fibers in the CNS we performed perforant pathway transection (PPT) and subsequently analyzed the spatial and temporal dynamics of eCB levels. This approach allows proper distinction of responses in originating neurons (entorhinal cortex), areas of deafferentiation/anterograde axonal degeneration (dentate gyrus) and putative changes in more distant but synaptically connected subfields (cornu ammonis (CA) 1 region).

Results

Using LC-MS/MS, we measured a strong increase in arachidonoylethanolamide (AEA), oleoylethanolamide (OEA) and palmitoylethanolamide (PEA) levels in the denervation zone (dentate gyrus) 24 hours post lesion (hpl), whereas entorhinal cortex and CA1 region exhibited little if any changes. NAPE-PLD, responsible for biosynthesis of eCBs, was increased early, whereas FAAH, a catabolizing enzyme, was up-regulated 48hpl.

Conclusion

Neuronal damage as assessed by transection of long-range projections apparently provides a strong time-dependent and area-confined signal for de novo synthesis of eCB, presumably to restrict neuronal damage. The present data underlines the importance of activation of the eCB system in CNS pathologies and identifies a novel site-specific intrinsic regulation of eCBs after long-range projection damage.

Translating promising preclinical neuroprotective therapies to human stroke trials

Stroke is the third leading cause of mortality and carries the greatest socioeconomic burden of disease in North America. Despite several promising therapies discovered in the preclinical setting, there have been no positive results in human stroke clinical trials to date. In this article, we review the potential causes for failure and discuss strategies that have been proposed to overcome the barrier to translation of stroke therapies. To improve the chance of success in future human stroke trials, we propose that therapies be tested in stroke models that closely resemble the human condition with molecular, imaging and functional outcomes that relate to outcomes utilized in clinical trials. These strategies include higher-order, old-world, nonhuman primate models of stroke with clinically relevant outcome measures. Although stroke neuroprotection has been looked upon pessimistically given the many failures in clinical trials to date, we propose that neuroprotection in humans is feasible and will be realized with rigorous translational science.

Translati onal challenges of neuroprotection strategy in ischemic stroke

Neuroprotection is a therapeutic strategy that attempts to save neurons from irreversible injury by modifying the effects of the ischemic cascade or facilitating reperfusion. Although numerous agents have shown neuroprotective effect in preclinical trials, their translation to clinical trials failed to show any meaningful effect. The Stroke Therapy Academic Industry Roundtable (STAIR) guidelines were made for performing research on neuroprotective agents in pre-clinical and clinical trials. Although the STAIR guidelines have been available for more than ten years, we still do not have any adequate neuroprotective agents. Reasons for unsuccessful translation from preclinical to clinical research can be considered along stages of drug development: 1) preclinical, 2) transitional and 3) clinical. By extending the therapeutic window for application of intravenous thrombolysis in acute stroke patients to 4.5 hours, as well as increasing the use intra-arterial thrombolysis and development of mechanical devices for thrombectomy in 6 hour period we may be able to achieve some degree of neuroprotection in acute stroke. Future therapy is likely to add to the current thrombolytic therapy with potential neuroprotective drugs or procedures.

Metabolic reflow as a therapy for ischemic brain injury

Ischemic neuronal damage is a common feature of occlusive strokes, hemorrhagic strokes, and traumatic brain injury. In addition, ischemia can be an anticipated or unanticipated complication of a variety of surgical procedures. Most therapeutic strategies for managing ischemic injury seek to re-establish blood flow, suppress neural metabolism, and/or limit specific cellular injury cascades. An alternative therapeutic approach is to enhance the delivery of metabolic substrates to ischemic tissue. This strategy is typified by efforts to increase tissue oxygenation by elevating the levels of circulating oxygen. Our studies are examining a complementary approach in which the delivery of metabolic substrates is enhanced by facilitating the diffusion of oxygen and glucose from the vasculature into neural tissue during ischemia. This is achieved by increasing the diffusivity of small molecules in aqueous solutions, such as plasma and interstitial fluid. The carotenoid compound, trans-sodium crocetinate (TSC) is capable of increasing oxygen and glucose diffusivity, and our studies demonstrate that TSC increases cerebral tissue oxygenation in the penumbra of a focal ischemic event. In addition, TSC treatment reduces the volume of cerebral infarction in rodent models of both permanent and temporary focal ischemia. This strategy of "metabolic reflow" thus blunts the metabolic challenge in partially-perfused tissue and reduces ischemic neural injury.

Neuroprotective actions of neurosteroids

Neurosteroids were initially defined as steroid hormones locally synthesized within the nervous tissue. Subsequently, they were described as steroid hormone derivatives that devoid hormonal action but still affect neuronal excitability through modulation of ionotropic receptors. Neurosteroids are further subdivided into natural (produced in the brain) and synthetic. Some authors distinguish between hormonal and regular neurosteroids in the group of natural ones. The latter group, including hormone metabolites like allopregnanolone or tetrahydrodeoxycorticosterone, is devoid of hormonal activity. Both hormones and their derivatives share, however, most of the physiological functions. It is usually very difficult to distinguish the effects of hormones and their metabolites. All these substances may influence seizure phenomena and exhibit neuroprotective effects. Neuroprotection offered by steroid hormones may be realized in both genomic and non-genomic mechanisms and involve regulation of the pro- and anti-apoptotic factors expression, intracellular signaling pathways, neurotransmission, oxidative, and inflammatory processes. Since regular neurosteroids show no affinity for steroid receptors, they may act only in a non-genomic mode. Multiple studies have been conducted so far to show efficacy of neurosteroids in the treatment of the central and peripheral nervous system injury, ischemia, neurodegenerative diseases, or seizures. In this review we focused primarily on neurosteroid mechanisms of action and their role in the process of neurodegeneration. Most of the data refers to results obtained in experimental studies. However, it should be realized that knowledge about neuroactive steroids remains still incomplete and requires confirmation in clinical conditions.

Pathophysiological response to experimental diffuse brain trauma differs as a function of developmental age

The purpose of experimental models of traumatic brain injury (TBI) is to reproduce selected aspects of human head injury such as brain edema, contusion or concussion, and functional deficits, among others. As the immature brain may be particularly vulnerable to injury during critical periods of development, and pediatric TBI may cause neurobehavioral deficits, our aim was to develop and characterize as a function of developmental age a model of diffuse TBI (DTBI) with quantifiable functional deficits. We modified a DTBI rat model initially developed by us in adult animals to study the graded response to injury as a function of developmental age - 7-, 14- and 21-day-old rats compared to young adult (3-month-old) animals. Our model caused motor deficits that persisted even after the pups reached adulthood, as well as reduced cognitive performance 2 weeks after injury. Moreover, our model induced prominent edema often seen in pediatric TBI, particularly evident in 7- and 14-day-old animals, as measured by both the wet weight/dry weight method and diffusion-weighted MRI. Blood-brain barrier permeability, as measured by the Evans blue dye technique, peaked at 20 min after trauma in all age groups, with a second peak found only in adult animals at 24 h after injury. Phosphorus MR spectroscopy showed no significant changes in the brain energy metabolism of immature rats with moderate DTBI, in contrast to significant decreases previously identified in adult animals.

A pilot study on morphology and the mechanism involved in linearly patterned programmed cell necrosis in melanoma

Accumulating data provide evidence that autophagy contributes to programmed cell death (PCD) under certain circumstances. Immunohistochemistry and real-time PCR were performed to investigate the correlation the expression of autophagy-related proteins LC3 and Atg4B and linearly patterned programmed cell necrosis (LPPCN) in melanoma. LPPCN was recently reported to be a special PCD, which is similar to neither apoptosis nor conventional necrosis commonly observed in tumoral tissues. The mechanism involved in LPPCN remains unclear. Our data showed that the expression of LC3 and Atg4B in the LPPCN-positive group was significantly higher than that in the LPPCN-negative group regarding protein and mRNA levels (p<0.05). Based on morphological observation, immunohistochemistry and real-time PCR experiments in this study, it was concluded that autophagy may play a crucial role in the process of LPP+CN in melanoma. This study provides novel insights into the mechanism that regulates LPPCN in vivo during tumor development. We speculated that LPPCN may be an early stage event in tumoral neovascularization under hypoxic-microenvironmental conditions. Accordingly, LPPCN can be considered a novel target in the process of antiangiogenesis treatment, which can be expected to obtain a better clinical outcome in the future.

Devil inside: does plant programmed cell death involve the endomembrane system?

Eukaryotic cells have to constantly cope with environmental cues and integrate developmental signals. Cell survival or death is the only possible outcome. In the field of animal biology, tremendous efforts have been put into the understanding of mechanisms underlying cell fate decision. Distinct organelles have been proven to sense a broad range of stimuli and, if necessary, engage cell death signalling pathway(s). Over the years, forward and reverse genetic screens have uncovered numerous regulators of programmed cell death (PCD) in plants. However, to date, molecular networks are far from being deciphered and, apart from the autophagic compartment, no organelles have been assigned a clear role in the regulation of cellular suicide. The endomembrane system (ES) seems, nevertheless, to harbour a significant number of cell death mediators. In this review, the involvement of this system in the control of plant PCD is discussed in-depth, as well as compared and contrasted with what is known in animal and yeast systems.

The effect of Semax and its C-end peptide PGP on the morphology and proliferative activity of rat brain cells during experimental ischemia: a pilot study

The neuropeptide preparation Semax (Met-Glu-His-Phe-Pro-Gly-Pro) has been employed successfully in clinical practice for treating patients with severe brain blood circulation disorders. In spite of numerous studies, many aspects of the therapeutic effects of this preparation remain unknown. In this context, the effects of Semax and its C-end tripeptide PGP on the functional morphology of nervous tissue cells were studied in the normal rat brain and in a model of incomplete global rat brain ischemia. In control animals, both peptides activated the capillary network and caused similar morphological changes to neurons and the neuropil regions. We show here for the first time at the histological level that Semax and PGP increased proliferation of the neuroglia, blood vessel endothelium, and progenitor cells in the subventricular zone. In these experimental conditions, only Semax abated the manifestation of ischemic damage to the nervous tissue. This was probably attributable to a decrease in vascular stasis symptoms as well as the trophic effect of the peptide.

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.

Towards a dynamical network view of brain ischemia and reperfusion. Part III: therapeutic implications

The general failure of neuroprotectants in clinical trials of ischemic stroke points to the possibility of a fundamental blind spot in the current conception of ischemic brain injury, the "ischemic cascade". This is the third in a series of four papers whose purpose is to work towards a revision of the concept of brain ischemia by applying network concepts to develop a bistable model of brain ischemia. Here the bistable model of brain ischemia is compared to the ischemic cascade concept. The core weakness of the ischemic cascade concept is revealed to be its assumption of superposition, or that the elements of the ischemic cascade can be summed as linearly independent events. This assumption leads to a concept of neuroprotection as a subtraction of ostensibly independent damage events. The bistable model offers a different concept of neuroprotection where the role of individual molecular pathways decreases in relevance with respect to the efficacy of outcome. Network thinking provides a framework for critical assessment of widely-used preclinical experimental approaches. The importance of allometric scaling is also discussed. We illustrate that the bistable model provides a viable alternative to the ischemic cascade as an explanatory framework and as a guide for therapeutic development.

Update on protein biomarkers in traumatic brain injury with emphasis on clinical use in adults and pediatrics

PURPOSE

This review summarizes protein biomarkers in mild and severe traumatic brain injury in adults and children and presents a strategy for conducting rationally designed clinical studies on biomarkers in head trauma.

METHODS

We performed an electronic search of the National Library of Medicine's MEDLINE and Biomedical Library of University of Pennsylvania database in March 2008 using a search heading of traumatic head injury and protein biomarkers. The search was focused especially on protein degradation products (spectrin breakdown product, c-tau, amyloid-beta(1-42)) in the last 10 years, but recent data on "classical" markers (S-100B, neuron-specific enolase, etc.) were also examined.

RESULTS

We identified 85 articles focusing on clinical use of biomarkers; 58 articles were prospective cohort studies with injury and/or outcome assessment.

CONCLUSIONS

We conclude that only S-100B in severe traumatic brain injury has consistently demonstrated the ability to predict injury and outcome in adults. The number of studies with protein degradation products is insufficient especially in the pediatric care. Cohort studies with well-defined end points and further neuroproteomic search for biomarkers in mild injury should be triggered. After critically reviewing the study designs, we found that large homogenous patient populations, consistent injury, and outcome measures prospectively determined cutoff values, and a combined use of different predictors should be considered in future studies.

Endothelin B receptor antagonists block proliferation and induce apoptosis in glioma cells

The proliferative and antiapoptotic actions of endothelin (ET)-1 in cancer cells have been documented and ET receptor antagonists have been exploited as potential anticancer drugs. Glioblastoma cell lines express both ETA and ETB receptors and previous works have shown that ETB receptors are involved in the proliferation of different cancer cell types. In this study we have investigated the effects of two structurally unrelated ETB receptor antagonists, BQ788 and A192621, on cell survival, proliferation and apoptosis in 1321-N1, U87 and IPDDCA2 glioma cell lines. BQ788 and A192621 reduced glioma cells viability and proliferation assessed by BrdU incorporation and cell cycle analysis by flow cytometry, while in contrast the ETA receptor antagonist BQ123 had no effect on cell survival. TUNEL assay and immunocytochemical experiments showed that BQ788 and A192621 trigger apoptotic processes mainly via activation of the intrinsic mitochondrial pathway involving caspase-9 activation, AIF release and cytochrome c translocation. Furthermore, treatment with ETB antagonists downregulates ERK- and p38MAPK-dependent pathways but does not affect VEGF mRNA levels. Our findings support the hypothesis that ETB antagonists represent a new promising therapeutic strategy for the treatment of high grade gliomas.

The role of lysosomal rupture in neuronal death

Apoptosis research in the past two decades has provided an enormous insight into its role in regulating cell death. However, apoptosis is only part of the story, and inhibition of neuronal necrosis may have greater impact than apoptosis, on the treatment of stroke, traumatic brain injury, and neurodegenerative diseases. Since the "calpain-cathepsin hypothesis" was first formulated, the calpain- and cathepsin-mediated regulation of necrotic cascades observed in monkeys, has been demonstrated to be a common neuronal death mechanism occurring from simpler organisms to humans. However, the detailed mechanism inducing lysosomal destabilization still remains poorly understood. Heat-shock protein-70 (Hsp70) is known to stabilize lysosomal membrane and protect cells from oxidative stress and apoptotic stimuli in many cell death pathways. Recent proteomics approach comparing pre- and post-ischemic hippocampal CA1 neurons as well as normal and glaucoma-suffered retina of primates, suggested that the substrate protein upon which activated calpain acts at the lysosomal membrane of neurons might be Hsp70. Understanding the interaction between activated calpains and Hsp70 will help to unravel the mechanism that destabilizes the lysosomal membrane, and will provide new insights into clarifying the whole cascade of neuronal necrosis. Although available evidence is circumferential, it is hypothesized that activated calpain cleaves oxidative stress-induced carbonylated Hsp70.1 (a major human Hsp70) at the lysosomal membrane, which result in lysosomal rupture/permeabilization. This review aims at highlighting the possible mechanism of lysosomal rupture in neuronal death by a modified "calpain-cathepsin hypothesis". As the autophagy-lysosomal degradation pathway is a target of oxidative stress, the implication of autophagy is also discussed.

A review of published reports on neuroprotection in spinal cord injury

STUDY DESIGN

Literature review.

OBJECTIVES

To review the main published current neuroprotection research trends and results in spinal cord injury (SCI).

SETTING

This paper is the result of a collaboration between a group of European scientists.

METHODS

Recent studies, especially in genetic, immune, histochemical and bio (nano)-technological fields, have provided new insight into the cellular and molecular mechanisms occurring within the central nervous system (NS), including SCIs. As a consequence, a new spectrum of therapies aiming to antagonize the 'secondary injury' pathways (that is, to provide neuroprotection) and also to repair such classically irreparable structures is emerging. We reviewed the most significant published works related to such novel, but not yet entirely validated, clinical practice therapies.

RESULTS

There have been identified many molecules, primarily expressed by heterogenous glial and neural subpopulations of cells, which are directly or indirectly critical for tissue damaging/sparing/re-growth inhibiting, angiogenesis and neural plasticity, and also various substances/energy vectors with regenerative properties, such as MAG (myelin-associated glycoprotein), Omgp (oligodendrocyte myelin glycoprotein), KDI (synthetic: Lysine-Asparagine-Isoleucine 'gamma-1 of Laminin Kainat Domain'), Nogo (Neurite outgrowth inhibitor), NgR (Nogo protein Receptor), the Rho signaling pathway (superfamily of 'Rho-dopsin gene-including neurotransmitter-receptors'), EphA4 (Ephrine), GFAP (Glial Fibrillary Acidic Protein), different subtypes of serotonergic and glutamatergic receptors, antigens, antibodies, immune modulators, adhesion molecules, scavengers, neurotrophic factors, enzymes, hormones, collagen scar inhibitors, remyelinating agents and neurogenetic/plasticity inducers, all aiming to preserve/re-establish the morphology and functional connections across the lesion site. Accordingly, modern research and experimental SCI therapies focus on several intricate, rather overlapping, therapeutic objectives and means, such as neuroprotective, neurotrophic, neurorestorative, neuroreparative, neuroregenerative, neuro(re)constructive and neurogenetic interventions.

CONCLUSION

The first three of these therapeutical directions are generically assimilated as neuroprotective, and are synthetically presented and commented in this paper in an attempt to conceptually systematize them; thus, the aim of this article is, by emphasizing the state-of-the art in the domain, to optimize theoretical support in selecting the most effective pharmacological and physical interventions for preventing, as much as possible, paralysis, and for maximizing recovery chances after SCI.

Hypoxia influences linearly patterned programmed cell necrosis and tumor blood supply patterns formation in melanoma

To investigate the possibility that tumor cells undergoing linearly patterned programmed cell necrosis (LPPCN) establish a spatial foundation for vasculogenic mimicry (VM) and to reveal that hypoxia influences LPPCN formation as well as Endo G and DNase 1 expression, 78 C57 mice were divided evenly into two groups and engrafted with B16 melanoma. Starting 9 days after inoculation, subgroups of mice were killed every 2 days. LPPCN and the tumor blood supply vessel types were counted and Endo G and DNase 1 mRNA expression were measured. Additionally, 124 cases of human melanoma samples were collected to assess the clinical significance of LPPCN and VM. The data revealed that regions of LPPCN were positive for caspase-3, caspase-9 and Bax, and negative for TUNEL staining. Electron microscopy images indicated that these cells took on the morphologic changes of necrosis. There was more DNase I mRNA expression in the hypoxic group than in the control group (P<0.05) in vitro, and the expression of Endo G mRNA in the hypoxic groups was significantly higher than that in the control groups both in vitro and in vivo (P<0.05). VM and LPPCN cell numbers in the ischemic group were higher than those in the control group in the early stage of tumor growth. Finally, the survival time for patients whose samples showed LPPCN and VM was significantly shorter than that of patients with one or neither of those factors. We speculated that under hypoxic conditions, some melanoma cells might undergo LPPCN, thus providing a spatial foundation for VM channel formation.

Multifunctional drug treatment in neurotrauma

Although the concepts of secondary injury and neuroprotection after neurotrauma are experimentally well supported, clinical trials of neuroprotective agents in traumatic brain injury or spinal cord injury have been disappointing. Most strategies to date have used drugs directed toward a single pathophysiological mechanism that contributes to early necrotic cell death. Given these failures, recent research has increasingly focused on multifunctional (i.e., multipotential, pluripotential) agents that target multiple injury mechanisms, particularly those that occur later after the insult. Here we review two such approaches that show particular promise in experimental neurotrauma: cell cycle inhibitors and small cyclized peptides. Both show extended therapeutic windows for treatment and appear to share at least one important target.

Cell death in the injured brain: roles of metallothioneins

In traumatic brain injury (TBI), the primary, irreversible damage associated with the moment of impact consists of cells dying from necrosis. This contributes to fuelling a chronic central nervous system (CNS) inflammation with increased formation of proinflammatory cytokines, enzymes and reactive oxygen species (ROS). ROS promote oxidative stress, which leads to neurodegeneration and ultimately results in programmed cell death (secondary injury). Since this delayed, secondary tissue loss occurs days to months following the primary injury it provides a therapeutic window where potential neuroprotective treatment could alleviate ongoing neurodegeneration, cell death and neurological impairment following TBI. Various neuroprotective drug candidates have been described, tested and proven effective in pre-clinical studies, including glutamate receptor antagonists, calcium-channel blockers, and caspase inhibitors. However, most of the scientific efforts have failed in translating the experimental results into clinical trials. Despite intensive research, effective neuroprotective therapies are lacking in the clinic, and TBI continues to be a major cause of morbidity and mortality. This paper provides an overview of the TBI pathophysiology leading to cell death and neurological impairment. We also discuss endogenously expressed neuroprotectants and drug candidates, which at this stage may still hold the potential for treating brain injured patients.

Aging-related changes in astrocytes in the rat retina: imbalance between cell proliferation and cell death reduces astrocyte availability

The aim of this study was to investigate changes in astrocyte density, morphology, proliferation and apoptosis occurring in the central nervous system during physiological aging. Astrocytes in retinal whole-mount preparations from Wistar rats aged 3 (young adult) to 25 months (aged) were investigated qualitatively and quantitatively following immunofluorohistochemistry. Glial fibrillary acidic protein (GFAP), S100 and Pax2 were used to identify astrocytes, and blood vessels were localized using Griffonia simplicifolia isolectin B4. Cell proliferation was assessed by bromodeoxyuridine incorporation and cell death by TUNEL-labelling and immunolocalization of the apoptosis markers active caspase 3 and endonuclease G. The density and total number of parenchymal astrocytes in the retina increased between 3 and 9 months of age but decreased markedly between 9 and 12 months. Proliferation of astrocytes was detected at 3 months but virtually ceased beyond that age, whereas the proportion of astrocytes that were TUNEL positive and relative expression of active caspase 3 and endonuclease G increased progressively with aging. In addition, in aged retinas astrocytes exhibited gliosis-like morphology and loss of Pax2 reactivity. A small population of Pax2(+)/GFAP(-) cells was detected in both young adult and aged retinas. The reduction in the availability of astrocytes in aged retinas and other aging-related changes reported here may have a significant impact on the ability of astrocytes to maintain homeostasis and support neuronal function in old age.

Do ATP and NO interact in the CNS?

Enzymatically derived NO and extracellular ATP are receiving greater attention due to their role as messengers in the CNS during different physiological and pathological processes. Ionotropic (P2XR) and metabotropic (P2YR) purinergic receptors mediate ATP effects and are present throughout the body. Particularly P2XR are crucial for brain plasticity mechanisms, and are involved in the pathogenesis of different CNS illnesses. NO does not have a specific receptor and its actions are directly dependent on the production on demand by different nitric oxide synthase isoforms. NO synthesizing enzymes are present virtually in all tissues, and NO influences multifarious physiological and pathological functions. Interestingly, various are the tissue and organs modulated by both ATP and NO, such as the immune, brain and vascular systems. Moreover, direct interactions between purinergic and nitrergic mechanisms outside the CNS are well documented, with several studies also indicating that ATP and NO do participate to the same CNS functions. In the past few years, further experimental evidence supported the physiological and pathological relevance of ATP and NO direct interactions in the CNS. The aim of the present review is to provide an account of the available information on the interplay between purinergic and nitrergic systems, focussing on the CNS. The already established relevance of ATP and NO in different pathological processes would predict that the knowledge of ATP/NO cross-talk mechanisms would support pharmacological approaches toward the development of novel ATP/NO combined pharmacological agents.

Antiapoptotic therapies in the treatment of spinal cord injury

Mechanical trauma to the spinal cord triggers events resulting in the death of neurons and glia over several weeks following the initial injury. It has been suggested that the prevention of delayed apoptosis after spinal cord injury (SCI) is likely to have a beneficial effect by reducing the extent of neuronal and oligodendroglial death, which would translate into better functional outcomes. Drugs acting at different levels in the apoptotic cascade (i.e., caspase inhibitors and antiapoptotic Bcl-xL) have been shown to decrease apoptotic cell death, but benefits in functional outcomes result only when inflammation is also decreased. Furthermore, long-term antiapoptotic therapy can result in nonapoptotic death with necrotic features, which will further increase inflammation and worsen outcome. Even though neuroprotective therapies are one of the targets for the promotion of functional recovery after SCI, targeting only post-SCI apoptosis is unlikely to be as successful as more integrated interventions that also target inflammation.

Beta-amyloid toxicity in embryonic rat astrocytes

The senile plaques of Alzheimer's disease contain a high concentration of beta-amyloid (betaA) protein, which may affect the glial population in the septal nucleus, an area of increased risk in AD. BetaA toxicity was measured in septal glia, via a dose-response experiment, by quantifying the effects of three different doses (0.1, 1, and 10 microM) of betaA on cell survival. Astrocytes from embryonic day-16 rats were grown in serum-free media in a single layer culture. Cells were treated on day in vitro (DIV)1 and survival was determined on DIV3 to ascertain which concentration was most toxic. In a separate set of experiments, an attempt was made to protect glial cells from the degenerative effects of betaA, with treatments of growth factors and estrogen. BetaA (10 microM) treatment was administered on DIV1, on DIV2 the cells were treated with estrogen (EST, 10 nM), insulin-like growth factors (IGF1 and IGF2, each 10 ng/ml), basic fibroblast growth factor (bFGF, 5 ng/ml) or nerve growth factor (NGF, 100 ng/ml), and on DIV3 the cells were visualized and quantified by fluorescence microscopy with DAPI (4,6-diamidino-2-phenylindole). In addition to dose-response and glial protection, experiments were also conducted to determine whether toxic effects were due to apoptosis. Our results suggest that the survival of glial populations is significantly affected in all three concentrations (0.1, 1.0, and 10 microM) of betaA. Glial protection was evident in the presence of NGF, for it showed the significantly highest survival rate relative to the betaA treatment alone. Furthermore, toxic effects of betaA appear to be due primarily to apoptosis. Significant reversal of betaA-induced apoptosis was seen with bFGF and IGF1.

Detrimental effects of antiapoptotic treatments in spinal cord injury

Long-term functional impairments due to spinal cord injury (SCI) in the rat result from secondary apoptotic death regulated, in part, by SCI-induced decreases in protein levels of the antiapoptotic protein Bcl-xL. We have shown that exogenous administration of Bcl-xL spares neurons 24 h after SCI. However, long-term effects of chronic application of Bcl-xL have not been characterized. To counteract SCI-induced decreases in Bcl-xL and resulting apoptosis, we used the TAT protein transduction domain fused to the Bcl-xL protein (Tat-Bcl-xL), or its antiapoptotic domain BH4 (Tat-BH4). We used intrathecal delivery of Tat-Bcl-xL, or Tat-BH4, into injured spinal cords for 24 h or 7 days, and apoptosis, neuronal death and locomotor recovery were assessed up to 2 months after injury. Both, Tat-Bcl-xL and Tat-BH4, significantly decreased SCI-induced apoptosis in thoracic segments containing the site of injury (T10) at 24 h or 7 days after SCI. However, the 7-day delivery of Tat-Bcl-xL, or Tat-BH4, also induced a significant impairment of locomotor recovery that lasted beyond the drug delivery time. We found that the 7-day administration of Tat-Bcl-xL, or Tat-BH4, significantly increased non-apoptotic neuronal loss and robustly augmented microglia/macrophage activation. These results indicate that the antiapoptotic treatment targeting Bcl-xL shifts neuronal apoptosis to necrosis, increases the inflammatory response and impairs locomotor recovery. Our results suggest that a combinatorial treatment consisting of antiapoptotic and anti-inflammatory agents may be necessary to achieve tissue preservation and significant improvement in functional recovery after SCI.

Identification of novel neuroprotective agents using pharmacophore modeling

In addition to its endocrine function, for which it was named, thyrotropin-releasing hormone (TRH) has substantial neuroprotective actions as well as other physiological effects. We have developed a number of modified TRH analogues as well as cyclic dipeptides structurally related to a major metabolic product of TRH, which have enhanced neuroprotective activity but none of the other major physiological effects of TRH. The extensive structure-activity data developed with these compounds were used to develop a pharmacophore model. Subsequently, a web-based pharmacophore searching program was used to query several large three-dimensional databases. Of the 219 compounds identified whose structures met the pharmacophore model, 15 were chosen for study in a classical model of neuronal cell death in vitro; five of these, 2-6, showed neuroprotective activity. Thus, pharmacophore modeling developed from neuroprotective small peptides can be used to identify novel lead compounds as neuroprotective agents.

Cellular and subcellular change evoked by diffuse traumatic brain injury: a complex web of change extending far beyond focal damage

Until recently, our understanding of the cellular and subcellular changes evoked by diffuse traumatic brain injury has been framed in the context of primary focal injury. In this regard, the ensuing cell death cascades were linked to contusional-mediated changes associated with frank hemorrhage and ischemia, and these were assumed to contribute to the observed apoptotic and necrotic neuronal death. Little consideration was given to the potential that other non-contusional cell death cascades could have been triggered by the diffuse mechanical forces of injury. While the importance of these classical, contusion-related apoptotic and necrotic cell death cascades cannot be discounted with diffuse injury, more recent information suggests that the mechanical force of injury itself can diffusely porate the neuronal plasmalemma and its axolemmal membranes, evoking other forms of cellular response that can contribute to cell injury or death. In this regard, the duration of the membrane alteration appears to be a dependent factor, with enduring membrane change, potentially leading to irreversible damage, whereas more transient membrane perturbation can be followed by cell membrane resealing associated with recovery and/or adaptive change. With more enduring mechanical membrane perturbation, it appears that some of the traditional death cascades involving the activation of cysteine proteases are at work. Equally important, non-traditional pathways involving the lysosomal dependent release of hydrolytic enzymes may also be players in the ensuing neuronal death. These mechanically related factors that directly impact upon the neuronal somata may also be influenced by concomitant and/or secondary axotomy-mediated responses. This axonal injury, although once thought to involve a singular intraaxonal response to injury, is now known to be more complex, reflecting differential responses to injuries of varying severity. Moreover, it now appears that fiber size and type may also influence the axon's reaction to injury. In sum, this review explicates the complexity of the cellular and subcellular responses evoked by diffuse traumatic brain injury in both the neuronal somata and its axonal appendages. This review further illustrates that our once simplistic views framed by evidence based upon contusional and/or ischemic change do not fully explain the complex repertoire of change evoked by diffuse traumatic brain injury.

Effect of pinealectomy and melatonin replacement on morphological and biochemical recovery after traumatic brain injury

Numerous studies showed that melatonin, a free radical scavenger, is neuroprotective. In this study, we investigated the effect of pinealectomy and administration of exogenous melatonin on oxidative stress and morphological changes after experimental brain injury. The animals were divided into six groups, each having 12 rats. Group 1 underwent craniotomy alone. Group 2 underwent craniotomy followed by brain trauma and received no medication. Group 3 underwent craniotomy followed by brain trauma and received melatonin. Group 4 underwent pinealectomy and craniotomy alone. Group 5 underwent pinealectomy and craniotomy followed by brain injury and received no medication. Group 6 underwent pinealectomy and craniotomy followed by brain trauma and received melatonin. Melatonin (100 mg/kg) was given intraperitoneally immediately after trauma to the rats in Groups 3 and 6. Pinealectomy caused a significant increase in the malondialdehyde (MDA), nitric oxide (NO), glutathione (GSH), and xanthine oxidase (XO) levels, and a decrease in GSH levels as compared to the control group. Trauma to pinealectomized rats causes significantly higher oxidative stress. Exogeneous melatonin administration significantly reduced MDA, XO and NO levels, increased GSH levels, and attenuated tissue lesion area. These findings suggest that reduction in endogenous melatonin after pinealectomy makes the rats more vulnerable to trauma, and exogenous melatonin administration has an important neuroprotective effect.

Neuroprotection by resveratrol against traumatic brain injury in rats

Oxidative stress after traumatic brain injury may contribute to many of the pathophysiologic changes. Resveratrol, naturally present at high concentration in grape skin, seeds, and red wine, has significant antioxidant properties in a variety of in vitro and in vivo models. In this study, we investigate the effect of resveratrol on oxidative stress after traumatic brain injury in rat model.A total of 54 adult Wistar albino male rats weighing 250-300 g were used. The rats were allocated into three groups. The first group was control (sham-operated) group in which only a craniotomy was performed, the others were trauma and resveratrol groups. A 100 mg/kg single dose of resveratrol, freshly prepared by dissolving in 50% ethanol and diluted in physiological saline (2%), for resveratrol group, and 1 ml ethanol (2%) for trauma group, was administered intraperitoneally immediately after trauma. Weight-drop method was used for achieving head trauma. Then, all groups were separated into three subgroups for biochemical analysis, brain water content and histopathological assessment following trauma. Twenty-four hours after trauma brain water content and malondialdehyde (MDA), glutathione (GSH), nitric oxide (NO), xanthine oxidase (XO) levels of traumatic hemisphere were evaluated. Quantitative histopathological analysis was performed on 14th day postinjury. Trauma caused a significant increase in MDA, XO, NO levels and decrease in GSH level as compared to control group. Resveratrol administration significantly reduced MDA, XO and NO levels, increased GSH level, and also attenuated tissue lesion area. Our results indicate that treatment with resveratrol immediately after traumatic brain injury reduce oxidative stress and lesion volume. Future studies involving different doses and the dose-response relationship could promise better results.

Soman poisoning induces delayed astrogliotic scar and angiogenesis in damaged mouse brain areas

Gliotic scar formation and angiogenesis are two biological events involved in the tissue reparative process generally occurring in the brain after mechanically induced injury, ischemia or cerebral tumor development. For the first time, in this study, neo-vascularization and glial scar formation were investigated in the brain of soman-poisoned mice over a 3-month period after nerve agent exposure (1.2 LD50 of soman). Using anti-claudin-5 and anti-vascular endothelial growth factor (VEGF) immunostaining techniques on brain sections, blood vessels were quantified and VEGF expression was verified to appraise the level of neo-angiogenesis induced in damaged brain areas. Furthermore, glial scar formation and neuropathology were estimated over time in the same injured brain regions by anti-glial fibrillary acidic protein (GFAP) immunohistochemistry and hemalun-phloxin (H&P) dye staining, respectively. VEGF over-expression was noticed on post-soman day 3 in lesioned areas such as the hippocampal CA1 field and amygdala. This was followed by an increase in the quantity of mature blood vessels, 3 months after soman poisoning, in the same brain areas. On the other hand, massive astroglial cell activation was demonstrated on post-soman day 8. Reactive astroglial cells were located only in damaged cerebral regions where H&P-stained eosinophilic neurons were found. For longer experimental times, astroglial response slowly decreased overtime but remained detectable on post-soman day 90 in some discrete brain regions (i.e. CA1 field and amygdala) evidencing the formation of a glial scar. In this study, we discuss the key role of VEGF in the angiogenic process and in the glial or neuronal response induced by soman poisoning.

Caspase-3 immunoreactivity in different cortical areas of young and aging macaque (Macaca mulatta) monkeys

It has been shown that cytochrome-c-dependent caspase-3 activation is significantly elevated in the aging macaque brain. To assess the underlying age-related changes in the cellular distribution of caspase-3, we have examined the motor cortex, cerebellum and hippocampus of young (4-year-old, n = 4) and old (20-year-old, n = 4)rhesus monkeys by immunohistochemistry. Western blot analyses of brain homogenate showed that the antibody reacted only with inactive 32-kDa procaspase and its active 20- and 17-kDa subunits, formed after granzyme B exposure. In the motor cortex, pyramidal cells of layers III and V were moderately labeled; the underlying white matter contained weakly stained astrocytes. In the hippocampus, hilar neurons and pyramidal cells in CA3 showed the strongest immunoreaction, pyramidal cells in CA1 and granule cells of the dentate gyrus were also strongly labeled. In contrast, CA2 pyramidal cells were only weakly stained, and neurons of the molecular layer were unlabeled. Weak caspase-3 immunoreaction of CA2 neurons parallels known decreased susceptibility to apoptosis. In the cerebellar cortex, clusters of strongly labeled Purkinje cells were observed next to groups of weakly and unstained cells; granule cells were generally unstained. The brains of aging monkeys displayed a similar pattern of caspase-3 immunoreactivity. In neocortical layer V, however, scattered very strongly labeled pyramidal cells were regularly detected, which were not observed in younger animals. This clustering of caspase-3 indicates increased vulnerability of a subset of pyramidal cells in the aging brain.

Novel neuroprotective tripeptides and dipeptides

It has long been recognized that thyrotropin-releasing hormone (TRH) and certain TRH analogues are neuroprotective in a variety of animal models of CNS trauma. In addition to these neuroprotective actions, TRH and most TRH analogues have other physiological actions that may not be desirable for treatment of acute injury, such as analeptic, autonomic, and endocrine effects. We have developed a series of dual-substituted TRH analogues that have strong neuroprotective actions, but are largely devoid of these other physiological actions. In addition, we have developed a family of cyclized dipeptides (diketopiperazines), structurally somewhat related to a metabolic product of TRH, that appear even more effective as neuroprotective agents in vitro and in vivo, and may have nootropic properties. Here, we review these novel tripeptide and dipeptide compounds.

Acute Injury to the Immature Brain with Hypoxia with or Without Hypoperfusion

Hypoxia with or without hypoperfusion is a common mechanism of injury in the immature brain and can result in normal or minimally abnormal imaging studies in the first 12 hours. Often, injury progresses over time suggesting a central role for delayed cell death pathways. An awareness of the patterns of injury associated with different mechanisms of injury and the central role of delayed cell death pathways in injury evolution is important for the radiologist to understand the significance and potential outcome of these injuries.

Acute injury to the immature brain with hypoxia with or without hypoperfusion

This article reviews the imaging features and evolution of immature brain injury caused by hypoxia with or without hypoperfusion in the neonate and young child. Clinical presentations and available literature on mechanisms and clinical outcomes are discussed. In many of these cases, diffusion-weighted imaging does not show the full extent of the injury but detects a pattern of injury that is important in guiding clinical care. Awareness of the delayed cell death mechanisms is essential to understand diffusion-weighted imaging sensitivity and evolution and to provide the most accurate clinical interpretation, especially in cases of hypoxia with or without hypoperfusion.

Genetic alterations of the BRI2 gene: familial British and Danish dementias

Classic arguments sustaining the importance of amyloid in the pathogenesis of dementia are usually centered on amyloid beta (Abeta) and its role in neuronal loss characteristic of Alzheimer disease, the most common form of human cerebral amyloidosis. Two non-Abeta cerebral amyloidoses, familial British and Danish dementias, share many aspects of Alzheimer disease, including the presence of neurofibrillary tangles, parenchymal pre-amyloid and amyloid deposits, cerebral amyloid angiopathy, and a widespread inflammatory response. Both early-onset conditions are linked to specific mutations in the BRI2 gene, causing the generation of longer-than-normal protein products and the release of 2 de novo created peptides ABri and ADan, the main components of amyloid fibrils in these inherited dementias. Although the molecular mechanisms and signal transduction pathways elicited by the amyloid deposits and their relation to cognitive impairment remain to be clarified, new evidence indicates that, independent of the differences in their primary structures, Abeta, ABri, and ADan subunits are able to form morphologically compatible ion-channel-like structures and elicit single ion-channel currents in reconstituted lipid membranes. These findings reaffirm the notion that non-Abeta amyloidosis constitute suitable alternative models to study the role of amyloid deposition in the mechanism of neuronal cell death.

Challenges of Neuroprotection and Neurorestoration in Ischemic Stroke Treatment

Currently, the most important therapeutic approaches in the acute phase of ischemic stroke are focused on the restoration of regional cerebral blood flow, early admission to a stroke unit and the attempt to block, using neuroprotective drugs, the biochemical and metabolic changes involved in the 'ischemic cascade'. Treatment with rt-PA in the acute phase, although very effective, is still limited to a small number of patients and positive preclinical results of neuroprotective treatment have not, as yet, been endorsed in clinical trials. The remarkable lack of concordance between the positive results in experimental models and the negative results obtained in clinical trials has led to a change in attitude in the conduct of preclinical studies as well as to a modification of the design of clinical trials, with special attention being paid to patient selection criteria and clinical evaluation. Some neuroprotective drugs, such as citicoline, have shown some efficacy in subgroups of patients with cerebral infarction, even with a therapeutic window of up to 24 h, which would suggest a possible neurorestorative effect. Different degrees of functional recovery, weeks or months after the ischemic event, are currently observed in clinical practice and have been related to endogenous self-repair mechanisms. The growing understanding of the mechanisms involved in the phenomena of brain plasticity and their modulation, together with the possibility of restoring functional deficits by encouraging endogenous neurogenesis or by cell therapy, open up new directions in the treatment of stroke patients.

Calcium-mediated aponecrosis plays a central role in the pathogenesis of estrogenic chemical-induced neurotoxicity

Estrogen is traditionally associated with females but is also present in males, and influences aspects of brain chemistry and brain morphology in males, females and also during prenatal development. Humans as well as animals are additionally exposed to environmental products that mimic estrogen activity, also known as endocrine disrupters (EDCs). This hypothesis article investigates the role of estrogen (and also EDCs) in the brain and how it influences the Ca2+ pathway. Ca2+ and its movement in and out of the cell is an extremely important ion controlling normal cell physiology. Any dysfunction in the movement from outside to inside the cell or between organelles may have fundamentally negative effects and the disturbance may even lead to apoptosis and/or necrosis. Therefore we consider whether estrogen and EDCs may alter the Ca2+ physiology and whether these changes may be one of the main causes of interference in physiology that is seen when humans and animals are exposed to EDCs. We come to the conclusion that on a molecular level Ca2+ and Ca2+ fluxes ([Ca2+]i, endocrine disrupting chemicals, redox modulation, mitochondria and cytochrome c followed by apoptosis, necrosis or most likely aponecrosis may contribute to chemical-mediated developmental toxicity. Similarly, we hypothesize that calcium-mediated aponecrosis do not only play a central role in the pathophysiology of estrogenic chemical-induced neurotoxicity, but can contribute to chemical-mediated developmental toxicity in general, thereby affecting almost all cells and organs of the living organism.

The influence of age on apoptotic and other mechanisms of cell death after cerebral hypoxia-ischemia

Unilateral hypoxia-ischemia (HI) was induced in C57/BL6 male mice on postnatal day (P) 5, 9, 21 and 60, corresponding developmentally to premature, term, juvenile and adult human brains, respectively. HI duration was adjusted to obtain a similar extent of brain injury at all ages. Apoptotic mechanisms (nuclear translocation of apoptosis-inducing factor, cytochrome c release and caspase-3 activation) were several-fold more pronounced in immature than in juvenile and adult brains. Necrosis-related calpain activation was similar at all ages. The CA1 subfield shifted from apoptosis-related neuronal death at P5 and P9 to necrosis-related calpain activation at P21 and P60. Oxidative stress (nitrotyrosine formation) was also similar at all ages. Autophagy, as judged by the autophagosome-related marker LC-3 II, was more pronounced in adult brains. To our knowledge, this is the first report demonstrating developmental regulation of AIF-mediated cell death as well as involvement of autophagy in a model of brain injury.