Neuroprotection by peptide growth factors against anoxia and nitric oxide toxicity requires modulation of protein kinase C

Regeneration in the nervous system with erythropoietin

Globally, greater than 30 million individuals are afflicted with disorders of the nervous system accompanied by tens of thousands of new cases annually with limited, if any, treatment options. Erythropoietin (EPO) offers an exciting and novel therapeutic strategy to address both acute and chronic neurodegenerative disorders. EPO governs a number of critical protective and regenerative mechanisms that can impact apoptotic and autophagic programmed cell death pathways through protein kinase B (Akt), sirtuins, mammalian forkhead transcription factors, and wingless signaling. Translation of the cytoprotective pathways of EPO into clinically effective treatments for some neurodegenerative disorders has been promising, but additional work is necessary. In particular, development of new treatments with erythropoiesis-stimulating agents such as EPO brings several important challenges that involve detrimental vascular outcomes and tumorigenesis. Future work that can effectively and safely harness the complexity of the signaling pathways of EPO will be vital for the fruitful treatment of disorders of the nervous system.

Targeting molecules to medicine with mTOR, autophagy and neurodegenerative disorders

Neurodegenerative disorders are significantly increasing in incidence as the age of the global population continues to climb with improved life expectancy. At present, more than 30 million individuals throughout the world are impacted by acute and chronic neurodegenerative disorders with limited treatment strategies. The mechanistic target of rapamycin (mTOR), also known as the mammalian target of rapamycin, is a 289 kDa serine/threonine protein kinase that offers exciting possibilities for novel treatment strategies for a host of neurodegenerative diseases that include Alzheimer's disease, Parkinson's disease, Huntington's disease, epilepsy, stroke and trauma. mTOR governs the programmed cell death pathways of apoptosis and autophagy that can determine neuronal stem cell development, precursor cell differentiation, cell senescence, cell survival and ultimate cell fate. Coupled to the cellular biology of mTOR are a number of considerations for the development of novel treatments involving the fine control of mTOR signalling, tumourigenesis, complexity of the apoptosis and autophagy relationship, functional outcome in the nervous system, and the intimately linked pathways of growth factors, phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), AMP activated protein kinase (AMPK), silent mating type information regulation two homologue one (Saccharomyces cerevisiae) (SIRT1) and others. Effective clinical translation of the cellular signalling mechanisms of mTOR offers provocative avenues for new drug development in the nervous system tempered only by the need to elucidate further the intricacies of the mTOR pathway.

Stem cell guidance through the mechanistic target of rapamycin

Stem cells offer great promise for the treatment of multiple disorders throughout the body. Critical to this premise is the ability to govern stem cell pluripotency, proliferation, and differentiation. The mechanistic target of rapamycin (mTOR), 289-kDa serine/threonine protein kinase, that is a vital component of mTOR Complex 1 and mTOR Complex 2 represents a critical pathway for the oversight of stem cell maintenance. mTOR can control the programmed cell death pathways of autophagy and apoptosis that can yield variable outcomes in stem cell survival and be reliant upon proliferative pathways that include Wnt signaling, Wnt1 inducible signaling pathway protein 1 (WISP1), silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), and trophic factors. mTOR also is a necessary component for the early development and establishment of stem cells as well as having a significant impact in the regulation of the maturation of specific cell phenotypes. Yet, as a proliferative agent, mTOR can not only foster cancer stem cell development and tumorigenesis, but also mediate cell senescence under certain conditions to limit invasive cancer growth. mTOR offers an exciting target for the oversight of stem cell therapies but requires careful consideration of the diverse clinical outcomes that can be fueled by mTOR signaling pathways.

Platelet-rich growth factor in oral and maxillofacial surgery

Platelet-rich growth factor is an innovative regenerative therapy used to promote hard and soft tissue healing. It involves the application of autologous platelet-leukocyte-rich plasma containing growth factors and thrombin directly to the site of treatment. It is the intrinsic growth factors released by activated platelets which are concentrated in a topical gel formula. Clinically, it is an affordable treatment with potentially broad spectrum of applications in maxillofacial surgery especially in the treatment of complex or refractory wounds. The present article reviews its various applications not only in the specialization of oral and maxillofacial surgery but also in regenerative medicine.

Perspectives and challenges in regenerative medicine using plasma rich in growth factors

Plasma rich in growth factors (PRGF-Endoret) is an endogenous therapeutic technology that is gaining interest in regenerative medicine due to its potential to stimulate and accelerate tissue healing and bone regeneration. This autologous biotechnology is designed for the in situ delivery of multiple cellular modulators and the formation of a fibrin scaffold, thereby providing different formulations that can be widely used in numerous medical and scientific fields including dentistry, oral implantology, orthopedics, ulcer treatment and tissue engineering among others. Here we discuss the important progress that has been accomplished in this field. Furthermore, a comprehensive outlook of the intriguing therapeutic applications of this technology is presented.

Novel avenues of drug discovery and biomarkers for diabetes mellitus

Globally, developed nations spend a significant amount of their resources on health care initiatives that poorly translate into increased population life expectancy. As an example, the United States devotes 16% of its gross domestic product to health care, the highest level in the world, but falls behind other nations that enjoy greater individual life expectancy. These observations point to the need for pioneering avenues of drug discovery to increase life span with controlled costs. In particular, innovative drug development for metabolic disorders such as diabetes mellitus becomes increasingly critical given that the number of diabetic people will increase exponentially over the next 20 years. This article discusses the elucidation and targeting of novel cellular pathways that are intimately tied to oxidative stress in diabetes mellitus for new treatment strategies. Pathways that involve wingless, β-nicotinamide adenine dinucleotide (NAD(+)) precursors, and cytokines govern complex biological pathways that determine both cell survival and longevity during diabetes mellitus and its complications. Furthermore, the role of these entities as biomarkers for disease can further enhance their utility irrespective of their treatment potential. Greater understanding of the intricacies of these unique cellular mechanisms will shape future drug discovery for diabetes mellitus to provide focused clinical care with limited or absent long-term complications.

Therapeutic promise and principles: metabotropic glutamate receptors

For a number of disease entities, oxidative stress becomes a significant factor in the etiology and progression of cell dysfunction and injury. Therapeutic strategies that can identify novel signal transduction pathways to ameliorate the toxic effects of oxidative stress may lead to new avenues of treatment for a spectrum of disorders that include diabetes, Alzheimer's disease, Parkinson's disease and immune system dysfunction. In this respect, metabotropic glutamate receptors (mGluRs) may offer exciting prospects for several disorders since these receptors can limit or prevent apoptotic cell injury as well as impact upon cellular development and function. Yet the role of mGluRs is complex in nature and may require specific mGluR modulation for a particular disease entity to maximize clinical efficacy and limit potential disability. Here we discuss the potential clinical translation of mGluRs and highlight the role of novel signal transduction pathways in the metabotropic glutamate system that may be vital for the clinical utility of mGluRs.

Mammalian target of rapamycin: hitting the bull's-eye for neurological disorders

The mammalian target of rapamycin (mTOR) and its associated cell signaling pathways have garnered significant attention for their roles in cell biology and oncology. Interestingly,the explosion of information in this field has linked mTOR to neurological diseases with promising initial studies. mTOR, a 289 kDa serine/threonine protein kinase, plays an important role in cell growth and proliferation and is activated through phosphorylation in response to growth factors, mitogens and hormones. Growth factors, amino acids, cellular nutrients and oxygen deficiency can downregulate mTOR activity. The function of mTOR signaling is mediated primarily through two mTOR complexes: mTORC1 and mTORC2. mTORC1 initiates cap-dependent protein translation, a rate-limiting step of protein synthesis, through the phosphorylation of the targets eukaryotic initiation factor 4E-binding protein 1 (4EBP1) and p70 ribosomal S6 kinase (p70S6K). In contrast, mTORC2 regulates development of the cytoskeleton and also controls cell survival. Although closely tied to tumorigenesis, mTOR and the downstream signaling pathways are significantly involved in the central nervous system (CNS) with synaptic plasticity, memory retention, neuroendocrine regulation associated with food intake and puberty and modulation of neuronal repair following injury. The signaling pathways of mTOR also are believed to be a significant component in a number of neurological diseases, such as Alzheimer disease, Parkinson disease and Huntington disease, tuberous sclerosis, neurofibromatosis, fragile X syndrome, epilepsy, traumatic brain injury and ischemic stroke. Here we describe the role of mTOR in the CNS and illustrate the potential for new strategies directed against neurological disorders.

Diabetes mellitus: channeling care through cellular discovery

Diabetes mellitus (DM) impacts a significant portion of the world's population and care for this disorder places an economic burden on the gross domestic product for any particular country. Furthermore, both Type 1 and Type 2 DM are becoming increasingly prevalent and there is increased incidence of impaired glucose tolerance in the young. The complications of DM are protean and can involve multiple systems throughout the body that are susceptible to the detrimental effects of oxidative stress and apoptotic cell injury. For these reasons, innovative strategies are necessary for the implementation of new treatments for DM that are generated through the further understanding of cellular pathways that govern the pathological consequences of DM. In particular, both the precursor for the coenzyme beta-nicotinamide adenine dinucleotide (NAD(+)), nicotinamide, and the growth factor erythropoietin offer novel platforms for drug discovery that involve cellular metabolic homeostasis and inflammatory cell control. Interestingly, these agents and their tightly associated pathways that consist of cell cycle regulation, protein kinase B, forkhead transcription factors, and Wnt signaling also function in a broader sense as biomarkers for disease onset and progression.

Oxidative stress: Biomarkers and novel therapeutic pathways

Oxidative stress significantly impacts multiple cellular pathways that can lead to the initiation and progression of varied disorders throughout the body. It therefore becomes imperative to elucidate the components and function of novel therapeutic strategies against oxidative stress to further clinical diagnosis and care. In particular, both the growth factor and cytokine erythropoietin (EPO) and members of the mammalian forkhead transcription factors of the O class (FoxOs) may offer the greatest promise for new treatment regimens since these agents and the cellular pathways they oversee cover a range of critical functions that directly influence progenitor cell development, cell survival and degeneration, metabolism, immune function, and cancer cell invasion. Furthermore, both EPO and FoxOs function not only as therapeutic targets, but also as biomarkers of disease onset and progression, since their cellular pathways are closely linked and overlap with several unique signal transduction pathways. However, biological outcome with EPO and FoxOs may sometimes be both unexpected and undesirable that can raise caution for these agents and warrant further investigations. Here we present the exciting as well as complicated role EPO and FoxOs possess to uncover the benefits as well as the risks of these agents for cell biology and clinical care in processes that range from stem cell development to uncontrolled cellular proliferation.

New strategies for Alzheimer's disease and cognitive impairment

Approximately five million people suffer with Alzheimer's disease (AD) and more than twenty-four million people are diagnosed with AD, pre-senile dementia, and other disorders of cognitive loss worldwide. Furthermore, the annual cost per patient with AD can approach $200,000 with an annual population aggregate cost of $100 billion. Yet, complete therapeutic prevention or reversal of neurovascular injury during AD and cognitive loss is not achievable despite the current understanding of the cellular pathways that modulate nervous system injury during these disorders. As a result, identification of novel therapeutic targets for the treatment of neurovascular injury would be extremely beneficial to reduce or eliminate disability from diseases that lead to cognitive loss or impairment. Here we describe the capacity of intrinsic cellular mechanisms for the novel pathways of erythropoietin and forkhead transcription factors that may offer not only new strategies for disorders such as AD and cognitive loss, but also function as biomarkers for disease onset and progression.

Erythropoietin, forkhead proteins, and oxidative injury: biomarkers and biology

Oxidative stress significantly impacts multiple cellular pathways that can lead to the initiation and progression of varied disorders throughout the body. It therefore becomes imperative to elucidate the components and function of novel therapeutic strategies against oxidative stress to further clinical diagnosis and care. In particular, both the growth factor and cytokine erythropoietin (EPO), and members of the mammalian forkhead transcription factors of the O class (FoxOs), may offer the greatest promise for new treatment regimens, since these agents and the cellular pathways they oversee cover a range of critical functions that directly influence progenitor cell development, cell survival and degeneration, metabolism, immune function, and cancer cell invasion. Furthermore, both EPO and FoxOs function not only as therapeutic targets, but also as biomarkers of disease onset and progression, since their cellular pathways are closely linked and overlap with several unique signal transduction pathways. Yet, EPO and FoxOs may sometimes have unexpected and undesirable effects that can raise caution for these agents and warrant further investigations. Here we present the exciting as well as the complex role that EPO and FoxOs possess to uncover the benefits as well as the risks of these agents for cell biology and clinical care in processes that range from stem cell development to uncontrolled cellular proliferation.

The application of platelet-rich plasma may be a novel treatment for central nervous system diseases

As a potential biological product, platelet-rich plasma (PRP) has been widely utilized in the areas of oral and maxillofacial reconstruction, bone and soft tissue restoration and wound healing. A recent study reported that the application of PRP on interrupted sciatic nerve could promote remyelinization of peripheral nerve. This renovated a notion that the application of PRP might extend to the nervous system. Most central nervous system (CNS) diseases have a series of common pathological changes in the later period of diseases which induce neurons and glia apoptosis and aggravate neurological dysfunction. It has been demonstrated that the potent restorative function of PRP is mainly based on neurotrophic capacity of preparation rich in growth factors (PRGFs) and scaffolding effect of platelet-rich gel (PRG), all of which could be certified to ameliorate the pathological process of CNS diseases. In view of this, we propose a hypothesis that the application of PRP and its derivatives might provide a novel therapeutic approach for CNS diseases, especially for traumatic brain or spinal cord injury, autoimmune diseases and neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis.

The vitamin nicotinamide: translating nutrition into clinical care

Nicotinamide, the amide form of vitamin B(3) (niacin), is changed to its mononucleotide compound with the enzyme nicotinic acide/nicotinamide adenylyltransferase, and participates in the cellular energy metabolism that directly impacts normal physiology. However, nicotinamide also influences oxidative stress and modulates multiple pathways tied to both cellular survival and death. During disorders that include immune system dysfunction, diabetes, and aging-related diseases, nicotinamide is a robust cytoprotectant that blocks cellular inflammatory cell activation, early apoptotic phosphatidylserine exposure, and late nuclear DNA degradation. Nicotinamide relies upon unique cellular pathways that involve forkhead transcription factors, sirtuins, protein kinase B (Akt), Bad, caspases, and poly (ADP-ribose) polymerase that may offer a fine line with determining cellular longevity, cell survival, and unwanted cancer progression. If one is cognizant of the these considerations, it becomes evident that nicotinamide holds great potential for multiple disease entities, but the development of new therapeutic strategies rests heavily upon the elucidation of the novel cellular pathways that nicotinamide closely governs.

A "FOXO" in sight: targeting Foxo proteins from conception to cancer

The successful treatment for multiple disease entities can rest heavily upon the ability to elucidate the intricate relationships that govern cellular proliferation, metabolism, survival, and inflammation. Here we discuss the therapeutic potential of the mammalian forkhead transcription factors predominantly in the O class, FoxO1, FoxO3, FoxO4, and FoxO6, which play a significant role during normal cellular function as well as during progressive disease. These transcription factors are integrated with several signal transduction pathways, such as Wnt proteins, that can regulate a broad array of cellular process that include stem cell proliferation, aging, and malignancy. FoxO transcription factors are attractive considerations for strategies directed against human cancer in light of their pro-apoptotic effects and ability to lead to cell cycle arrest. Yet, FoxO proteins can be associated with infertility, cellular degeneration, and unchecked cellular proliferation. As our knowledge continues to develop for this novel family of proteins, potential clinical applications for the FoxO family should heighten our ability to limit disease progression without clinical compromise.

Proteomic analysis of protein S-nitrosylation

Nitric oxide (NO) produces covalent PTMs of specific cysteine residues, a process known as S-nitrosylation. This route is dynamically regulated and is one of the major NO signalling pathways known to have strong and dynamic interactions with redox signalling. In agreement with this scenario, binding of NO to key cysteine groups can be linked to a broad range of physiological and pathological cellular events, such as smooth muscle relaxation, neurotransmission and neurodegeneration. The characterization of S-nitrosylated residues and the functional relevance of this protein modification are both essential information needed to understand the action of NO in living organisms. In this review, we focus on recent advances in this field and on state-of-the-art proteomic approaches which are aimed at characterizing the S-nitrosylome in different biological backgrounds.

Erythropoietin: elucidating new cellular targets that broaden therapeutic strategies

Given that erythropoietin (EPO) is no longer believed to have exclusive biological activity in the hematopoietic system, EPO is now considered to have applicability in a variety of nervous system disorders that can overlap with vascular disease, metabolic impairments, and immune system function. As a result, EPO may offer efficacy for a broad number of disorders that involve Alzheimer's disease, cardiac insufficiency, stroke, trauma, and diabetic complications. During a number of clinical conditions, EPO is robust and can prevent metabolic compromise, neuronal and vascular degeneration, and inflammatory cell activation. Yet, use of EPO is not without its considerations especially in light of frequent concerns that may compromise clinical care. Recent work has elucidated a number of novel cellular pathways governed by EPO that can open new avenues to avert deleterious effects of this agent and offer previously unrecognized perspectives for therapeutic strategies. Obtaining greater insight into the role of EPO in the nervous system and elucidating its unique cellular pathways may provide greater cellular viability not only in the nervous system but also throughout the body.

Erythropoietin and oxidative stress

Unmitigated oxidative stress can lead to diminished cellular longevity, accelerated aging, and accumulated toxic effects for an organism. Current investigations further suggest the significant disadvantages that can occur with cellular oxidative stress that can lead to clinical disability in a number of disorders, such as myocardial infarction, dementia, stroke, and diabetes. New therapeutic strategies are therefore sought that can be directed toward ameliorating the toxic effects of oxidative stress. Here we discuss the exciting potential of the growth factor and cytokine erythropoietin for the treatment of diseases such as cardiac ischemia, vascular injury, neurodegeneration, and diabetes through the modulation of cellular oxidative stress. Erythropoietin controls a variety of signal transduction pathways during oxidative stress that can involve Janus-tyrosine kinase 2, protein kinase B, signal transducer and activator of transcription pathways, Wnt proteins, mammalian forkhead transcription factors, caspases, and nuclear factor kappaB. Yet, the biological effects of erythropoietin may not always be beneficial and may be poor tolerated in a number of clinical scenarios, necessitating further basic and clinical investigations that emphasize the elucidation of the signal transduction pathways controlled by erythropoietin to direct both successful and safe clinical care.

Triple play: promoting neurovascular longevity with nicotinamide, WNT, and erythropoietin in diabetes mellitus

Oxidative stress is a principal pathway for the dysfunction and ultimate destruction of cells in the neuronal and vascular systems for several disease entities, not promoting the ravages of oxidative stress to any less of a degree than diabetes mellitus. Diabetes mellitus is increasing in incidence as a result of changes in human behavior that relate to diet and daily exercise and is predicted to affect almost 400 million individuals worldwide in another two decades. Furthermore, both type 1 and type 2 diabetes mellitus can lead to significant disability in the nervous and cardiovascular systems, such as cognitive loss and cardiac insufficiency. As a result, innovative strategies that directly target oxidative stress to preserve neuronal and vascular longevity could offer viable therapeutic options to diabetic patients in addition to more conventional treatments that are designed to control serum glucose levels. Here we discuss the novel application of nicotinamide, Wnt signaling, and erythropoietin that modulate cellular oxidative stress and offer significant promise for the prevention of diabetic complications in the nervous and vascular systems. Essential to this process is the precise focus upon diverse as well as common cellular pathways governed by nicotinamide, Wnt signaling, and erythropoietin to outline not only the potential benefits, but also the challenges and possible detriments of these therapies. In this way, new avenues of investigation can hopefully bypass toxic complications, or at the very least, avoid contraindications that may limit care and offer both safe and robust clinical treatment for patients.

The Wnt signaling pathway: aging gracefully as a protectionist?

No longer considered to be exclusive to cellular developmental pathways, the Wnt family of secreted cysteine-rich glycosylated proteins has emerged as versatile targets for a variety of conditions that involve cardiovascular disease, aging, cancer, diabetes, neurodegeneration, and inflammation. In particular, modulation of Wnt signaling may fill a critical void for the treatment of disorders that impact upon both cellular survival and cellular longevity. Yet, in some scenarios, Wnt signaling can become the catalyst for disease development or promote cell senescence that can compromise clinical utility. This double edge sword in regards to the role of Wnt and its signaling pathways highlights the critical need to further elucidate the cellular mechanisms governed by Wnt in conjunction with the development of robust pharmacological ligands that may open new avenues for disease treatment. Here we discuss the influence of the Wnt pathway during cell survival, metabolism, and aging in order for one to gain a greater insight for the novel role of Wnt signaling as well as exemplify its unique cellular pathways that influence both normal physiology and disease.

Presenilin 1 regulates epidermal growth factor receptor turnover and signaling in the endosomal-lysosomal pathway

Mutations in the gene encoding presenilin 1 (PS1) cause the most aggressive form of early-onset familial Alzheimer disease. In addition to its well established role in Abeta production and Notch proteolysis, PS1 has been shown to mediate other physiological activities, such as regulation of the Wnt/beta-catenin signaling pathway, modulation of phosphatidylinositol 3-kinase/Akt and MEK/ERK signaling, and trafficking of select membrane proteins and/or intracellular vesicles. In this study, we present evidence that PS1 is a critical regulator of a key signaling receptor tyrosine kinase, epidermal growth factor receptor (EGFR). Specifically, EGFR levels were robustly increased in fibroblasts deficient in both PS1 and PS2 (PS(-/-)) due to delayed turnover of EGFR protein. Stable transfection of wild-type PS1 but not PS2 corrected EGFR to levels comparable to PS(+/+) cells, while FAD PS1 mutations showed partial loss of activity. The C-terminal fragment of PS1 was sufficient to fully reduce EGFR levels. In addition, the rapid ligand-induced degradation of EGFR was markedly delayed in PS(-/-) cells, resulting in prolonged signal activation. Despite the defective turnover of EGFR, ligand-induced autophosphorylation, ubiquitination, and endocytosis of EGFR were not affected by the lack of PS1. Instead, the trafficking of EGFR from early endosomes to lysosomes was severely delayed by PS1 deficiency. Elevation of EGFR was also seen in brains of adult mice conditionally ablated in PS1 and in skin tumors associated with the loss of PS1. These findings demonstrate a critical role of PS1 in the trafficking and turnover of EGFR and suggest potential pathogenic effects of elevated EGFR as well as perturbed endosomal-lysosomal trafficking in cell cycle control and Alzheimer disease.

Genistein inhibits glutamate-induced apoptotic processes in primary neuronal cell cultures: an involvement of aryl hydrocarbon receptor and estrogen receptor/glycogen synthase kinase-3beta intracellular signaling pathway

Phytoestrogens prevent neuronal damage, however, mechanism of their neuroprotective action has not been fully elucidated. This study aimed to evaluate the effects of genistein on glutamate-induced apoptosis in mouse primary neuronal cell cultures. Glutamate (1 mM) enhanced caspase-3 activity and lactate dehydrogenase (LDH) release in the hippocampal, neocortical and cerebellar neurons in time-dependent manner, and these data were confirmed at the cellular level with Hoechst 33342 and calcein AM staining. Genistein (10-10,000 nM) significantly inhibited glutamate-induced apoptosis, and the effect of this isoflavone was most prominent in the hippocampal cells. Next, we studied an involvement of estrogen and aryl hydrocarbon receptors in anti-apoptotic effects of genistein. A high-affinity estrogen receptor antagonist, ICI 182, 780 (1 microM), reversed, whereas less specific antagonist/partial agonist, tamoxifen (1 microM), either intensified or partially inhibited genistein effects. Aryl hydrocarbon receptor antagonist, alpha-naphthoflavone (1 microM), exhibited a biphasic action: it enhanced genistein action toward a short-term exposure (3 h) to glutamate, but antagonized genistein action toward prolonged exposure (24 h) to that insult. SB 216763 (1 microM), which preferentially inhibits glycogen synthase kinase-3beta (GSK-3beta), potentiated genistein effects. These data point to strong effects of genistein at low micromolar concentrations in various brain tissues against glutamate-evoked apoptosis. Moreover, this study provided evidence for involvement of aryl hydrocarbon receptor and estrogen receptor/GSK-3beta intracellular signaling pathway in anti-apoptotic action of genistein.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

The physiology and pathophysiology of nitric oxide in the brain

Nitric oxide (NO) is a molecule with pleiotropic effects in different tissues. NO is synthesized by NO synthases (NOS), a family with four major types: endothelial, neuronal, inducible and mitochondrial. They can be found in almost all the tissues and they can even co-exist in the same tissue. NO is a well-known vasorelaxant agent, but it works as a neurotransmitter when produced by neurons and is also involved in defense functions when it is produced by immune and glial cells. NO is thermodynamically unstable and tends to react with other molecules, resulting in the oxidation, nitrosylation or nitration of proteins, with the concomitant effects on many cellular mechanisms. NO intracellular signaling involves the activation of guanylate cyclase but it also interacts with MAPKs, apoptosis-related proteins, and mitochondrial respiratory chain or anti-proliferative molecules. It also plays a role in post-translational modification of proteins and protein degradation by the proteasome. However, under pathophysiological conditions NO has damaging effects. In disorders involving oxidative stress, such as Alzheimer's disease, stroke and Parkinson's disease, NO increases cell damage through the formation of highly reactive peroxynitrite. The paradox of beneficial and damaging effects of NO will be discussed in this review.

Effect of NMDA on staurosporine-induced activation of caspase-3 and LDH release in mouse neocortical and hippocampal cells

To achieve a better understanding of developmentally regulated NMDA- and staurosporine-induced apoptotic processes, we investigated the concerted action of these agents on caspase-3 activity and LDH release in neocortical and hippocampal cell cultures at different stages in vitro (DIV). Hoechst 33342 and MAP-2 stainings were additionally employed to visualize apoptotic changes and cell damage. The vulnerability of neocortical cells to NMDA was more prominent at later culture stages, whereas hippocampal neurons were more susceptible to NMDA treatment at earlier stages. A persistent activation of caspase-3 by staurosporine was found at all experimental stages. Despite of certain differences in susceptibility to NMDA and staurosporine, both tissues responded to regulatory action of NMDA towards staurosporine-activated caspase-3 in a similar way. Combined treatment with NMDA and staurosporine resulted in a substantial increase in caspase-3 activity in neocortical and hippocampal neurons on 2 DIV. Additive effects were also observed in neocortical cultures on 12 DIV. In contrast, NMDA substantially inhibited staurosporine-induced caspase-3 activity on 7 DIV in neocortical and hippocampal cultures. Additionally, pro-apoptotic effects of 17beta-estradiol were attenuated by NMDA on 7 DIV. Changes in vulnerability to NMDA- and staurosporine-mediated activation of caspase-3 were not strictly related to LDH release. Our data revealed that NMDA can both enhance and inhibit the staurosporine-induced neuronal cell apoptosis. The pro-apoptotic effect of NMDA was exhibited at early and late culture stages, whereas the anti-apoptotic effect was transient occurring on 7 DIV only.

Suppression of protein kinase Cepsilon mediates 17beta-estradiol-induced neuroprotection in an immortalized hippocampal cell line

Although estrogens are neuroprotective in a variety of neuroprotection models, the precise underlying mechanisms are currently not well understood. Here, we examined the role of protein kinase C (PKC) in mediating estrogen-induced neuroprotection in the HT-22 immortalized hippocampal cell line. The neuroprotection model utilized calcein fluorescence to quantitate cell viability following glutamate insults. 17beta-Estradiol (betaE2) protected HT-22 cells when treatment was initiated before or after the glutamate insult. The inhibition of PKC by bis-indolylmaleimide mimicked and enhanced betaE2-induced neuroprotection. In contrast, the inhibition of specific PKC isozymes (alpha and beta) by Go6976, inhibition of 1-phosphatidylinositol 3 kinase by wortmannin, or inhibition of protein kinase A by H-89, did not alter cell viability, suggesting a specific involvement of PKC in an isozyme-dependent manner. We further examined whether estrogen interacts with PKC in a PKC isozyme-specific manner. Protein levels and activity of PKC isozymes (alpha, delta, epsilon, and zeta) were assessed by western blot analysis and radiolabeled phosphorylation assays respectively. Among the isozymes tested, betaE2 altered only PKCepsilon; it reduced the activity and membrane translocation of PKCepsilon in a manner that correlated with its protection against glutamate toxicity. Furthermore, betaE2 reversed the increased activity of membrane PKCepsilon induced by glutamate. These data suggest that the neuroprotective effects of estrogens are mediated in part by inhibition of PKCepsilon activity and membrane translocation.

Oxidative stress in the brain: novel cellular targets that govern survival during neurodegenerative disease

Despite our present knowledge of some of the cellular pathways that modulate central nervous system injury, complete therapeutic prevention or reversal of acute or chronic neuronal injury has not been achieved. The cellular mechanisms that precipitate these diseases are more involved than initially believed. As a result, identification of novel therapeutic targets for the treatment of cellular injury would be extremely beneficial to reduce or eliminate disability from nervous system disorders. Current studies have begun to focus on pathways of oxidative stress that involve a variety of cellular pathways. Here we discuss novel pathways that involve the generation of reactive oxygen species and oxidative stress, apoptotic injury that leads to nuclear degradation in both neuronal and vascular populations, and the early loss of cellular membrane asymmetry that mitigates inflammation and vascular occlusion. Current work has identified exciting pathways, such as the Wnt pathway and the serine-threonine kinase Akt, as central modulators that oversee cellular apoptosis and their downstream substrates that include Forkhead transcription factors, glycogen synthase kinase-3beta, mitochondrial dysfunction, Bad, and Bcl-x(L). Other closely integrated pathways control microglial activation, release of inflammatory cytokines, and caspase and calpain activation. New therapeutic avenues that are just open to exploration, such as with brain temperature regulation, nicotinamide adenine dinucleotide modulation, metabotropic glutamate system modulation, and erythropoietin targeted expression, may provide both attractive and viable alternatives to treat a variety of disorders that include stroke, Alzheimer's disease, and traumatic brain injury.

Neurotrophic factor effects on oxidative stress-induced neuronal death

Neurotrophic factors have been shown to potentiate necrotic neuronal death in cortical cultures. In this study we characterized the death induced by various oxidative insults and tested the effects of neurotrophic factors on that death. Treatment with fibroblast growth factor-2, neurotrophin-4, or insulin-like growth factor-1 potentiated neuronal cell death induced by iron-citrate (Fe) or buthionine sulfoximine (BSO), but not ethacrynic acid (EA). Neuronal death induced by each insult was blocked by the free radical scavenger, trolox. An analysis of the death indicated that Fe and BSO induced necrotic cell death, while EA induced apoptotic cell death. BSO and EA caused decreased cellular glutathione levels, whereas Fe had no effect on glutathione levels. Neurotrophic factors had no effect on the changes in glutathione. The results indicate that oxidative insults can induce either apoptotic or necrotic death and that the effects of neurotrophic factors are dependent on the type of cell death.

Nicotinamide: A Nutritional Supplement that Provides Protection Against Neuronal and Vascular Injury

In addition to functioning as an essential nutrient for cellular growth and maintenance, nicotinamide also may be an attractive therapeutic agent with efficacy demonstrated against free radical ischemic programmed cell death (PCD). Yet, the cellular mechanisms that mediate cellular PCD, as well as protection by nicotinamide, are considered to require further definition. In primary rat hippocampal neurons and rat cerebrovascular endothelial cells (ECs), cellular injury was determined through trypan blue dye exclusion, externalization of membrane phosphatidylserine (PS) residues, and activation of the mitogen-activated protein kinase p38 through Western blot analysis. Nicotinamide was without cellular toxicity at concentrations lower than 50 mM in both neuronal and EC populations. Exposure to either anoxia or the nitric oxide (NO) donors sodium nitroprusside and NOC-9 significantly decreased neuronal and EC survival from approximately 85% to 38% and increased membrane PS exposure from approximately 10% to 80% over a 24-hour period. Pretreatment with nicotinamide (12.5 mM) prevented anoxic and NO cytodegeneration by significantly increasing survival and decreasing membrane PS expression. Protection by nicotinamide in both neurons and ECs appeared to be independent and downstream from p38 activation. Further investigations that define the cellular and molecular mechanisms employed by the nutrient nicotinamide may provide greater insight into the potential therapeutic targets that determine neuronal and vascular injury.

A critical assessment of the neurodestructive and neuroprotective effects of nitric oxide

Whether nitric oxide is cytodestructive or cytoprotective is of obvious clinical importance. The debate on this subject in the past decade has generated much "heat and light". This paper focuses on the actions of NO on the nervous system and reexamines the controversial issue and the contribution of the authors and their colleagues in the light of recent findings. We also report new findings, critically assesses previous experimental data, and share perspectives on this important subject.

Group I metabotropic glutamate receptors prevent endothelial programmed cell death independent from MAP kinase p38 activation in rat

Activation of Group I metabotropic glutamate receptors (mGluRs) prevents neuronal programmed cell death (PCD), but the role of these receptors in the vascular endothelial cell (EC) system has not been defined. Since ECs are principal targets for ischemic free radical injury, we examined whether the mGluR system could modulate vascular PCD. Activation of the Group I mGluR system, but not antagonism, addressed two distinct pathways of PCD by preventing the destruction of genomic DNA and maintaining EC membrane asymmetry. The induction of nitric oxide (NO)-induced PCD in ECs paralleled the specific activation of the MAP kinase p38 pathway, but the vascular protection conferred by the Group I mGluR system appears to rely on more downstream cellular pathways. We provide initial evidence for Group I mGluRs to prevent NO-induced vascular injury and offer new directions for vascular disease treatment.

The metabotropic glutamate system promotes neuronal survival through distinct pathways of programmed cell death

Activation of the metabotropic glutamate receptor (mGluR) system can prevent free radical, nitric oxide (NO)-induced programmed cell death (PCD). To investigate the mechanisms utilized by the mGluR system to regulate the induction of PCD, we examined the course of PCD in real time in individual, living, primary hippocampal neurons. We assessed both phosphatidylserine (PS) externalization, an early event in PCD, and DNA fragmentation during NO toxicity and mGluR modulation to determine the individual contributions of PS externalization and genomic DNA fragmentation during neuronal PCD. Exposure to the NO donors (300 microM SNP or 300 microM NOC-9) induced PCD in approximately 75% of neurons over a 24-h period. The externalization of PS in neurons increased to 21 +/- 2% as early as 3 h following NO exposure and then increased to 80 +/- 2% over a 24-h period. The externalization of PS was independent of the loss of membrane integrity. Agonists for individual mGluR subgroups were equally able to prevent NO-induced neuronal death and DNA degradation, yet they possessed differential abilities to regulate PS externalization. The group I agonist DHPG (750 microM) and the group III agonist L-AP4 (750 microM) both prevented and reversed NO-induced PS externalization. In contrast, activation of group II subtypes using L-CCG-I (750 microM) did not prevent PS externalization. Employing an experimental model that independently led to the externalization of PS residues, we demonstrated that PS externalization does not immediately impact on neuronal survival. Yet, subsequent neuronal survival may ultimately depend upon preventing PS externalization to avoid neuronal tagging for phagocytosis. Since group I and III mGluR subtypes possess the unique ability to maintain genomic integrity and membrane PS asymmetry, these agents may provide superior overall protection against NO-induced neuronal injury.

Group I and group III metabotropic glutamate receptor subtypes provide enhanced neuroprotection

Neuroprotection by the metabotropic glutamate receptor (mGluR) system has been linked to the modulation of both the free radical nitric oxide (NO) and programmed cell death (PCD). Because the cellular mechanisms that ultimately determine neuronal PCD rely upon the independent pathways of genomic DNA degradation, externalization of membrane phosphatidylserine (PS) residues, and the activation of associated cysteine proteases, we investigated the ability of the individual mGluR subtypes to modulate the distinct pathways of NO-induced PCD in primary rat hippocampal neurons. Membrane PS residue externalization occurred within the initial 3 hr after exposure to the NO donors (300 microM SNP or 300 microM NOC-9), preceded genomic DNA fragmentation, and was present in 80 +/- 2% of the neurons within a 24-hr period. NO exposure also led to the rapid induction of both caspase 1-like and caspase 3-like activities that were determined to be necessary, at least in part, for the generation of NO-induced genomic DNA degradation, but distinct from the detrimental effects of intracellular acidification. Yet, only caspase 1-like activity was necessary for the modulation of PS residue externalization. Activation of group I mGluR subtypes utilized an effective, "upstream" mechanism for the inhibition of cysteine protease activity that offered an enhanced level of neuroprotection through both the preservation of genomic DNA integrity and the maintenance of PS membrane asymmetry. Group II and Group III mGluR subtypes maintained DNA integrity and group III mGluR subtypes additionally prevented PS residue externalization through mechanisms that were targeted below the level of caspase activation. Our work elucidates the independent nature of the mGluR subtypes to not only provide discrete levels of protection against neuronal PCD, but also offer robust therapeutic strategies for neurodegenerative disease.

Prevention of nitric oxide-induced neuronal injury through the modulation of independent pathways of programmed cell death

Neuronal injury may be dependent upon the generation of the free radical nitric oxide (NO) and the subsequent induction of programmed cell death (PCD). Although the nature of this injury may be both preventable and reversible, the underlying mechanisms that mediate PCD are not well understood. Using the agent nicotinamide as an investigative tool in primary rat hippocampal neurons, the authors examined the ability to modulate two independent components of PCD, namely the degradation of genomic DNA and the early exposure of membrane phosphatidylserine (PS) residues. Neuronal injury was determined through trypan blue dye exclusion, DNA fragmentation, externalization of membrane PS residues, cysteine protease activation, and the measurement of intracellular pH (pHi). Exposure to the NO donors SIN-1 and NOC-9 (300 micromol/L) alone rapidly increased genomic DNA fragmentation from 20 +/- 4% to 71 +/- 5% and membrane PS exposure from 14 +/- 3% to 76 +/- 9% over a 24-hour period. Administration of a neuroprotective concentration of nicotinamide (12.5 mmol/L) consistently maintained DNA integrity and prevented the progression of membrane PS exposure. Posttreatment paradigms with nicotinamide at 2, 4, and 6 hours after NO exposure further demonstrated the ability of this agent to prevent and reverse neuronal PCD. Although not dependent upon pHi, neuroprotection by nicotinamide was linked to the modulation of two independent components of neuronal PCD through the regulation of caspase 1 and caspase 3-like activities and the DNA repair enzyme poly(ADP-ribose) polymerase. The current work lays the foundation for the development of therapeutic strategies that may not only prevent the course of PCD, but may also offer the ability for the repair of neurons that have been identified through the loss of membrane asymmetry for subsequent destruction.

Epidermal growth factor induces oxidative neuronal injury in cortical culture

Recently, we have demonstrated that certain neurotrophic factors can induce oxidative neuronal necrosis by acting at the cognate tyrosine kinase-linked receptors. Epidermal growth factor (EGF) has neurotrophic effects via the tyrosine kinase-linked EGF receptor (EGFR), but its neurotoxic potential has not been studied. Here, we examined this possibility in mouse cortical culture. Exposure of cortical cultures to 1-100 ng/ml EGF induced gradually developing neuronal death, which was complete in 48-72 h; no injury to astrocytes was noted. Electron microscopic findings of EGF-induced neuronal death were consistent with necrosis; severe mitochondrial swelling and disruption of cytoplasmic membrane occurred, whereas nuclei appeared relatively intact. The EGF-induced neuronal death was accompanied by increased free radical generation and blocked by the anti-oxidant Trolox. Suggesting mediation by the EGFR, an EGFR tyrosine kinase-specific inhibitor, C56, attenuated EGF-induced neuronal death. In addition, inhibitors of extracellular signal-regulated protein kinase 1/2 (Erk-1/2) (PD98056), protein kinase A (H89), and protein kinase C (GF109203X) blocked EGF-induced neuronal death. A p38 mitogen-activated protein kinase inhibitor (SB203580) or glutamate antagonists (MK-801 and 6-cyano-7-nitroquinoxaline-2,3-dione) showed no protective effect. The present results suggest that prolonged activation of the EGFR may trigger oxidative neuronal injury in central neurons.

Critical temporal modulation of neuronal programmed cell injury

1. As a free radical, nitric oxide (NO) may be toxic to neurons through mechanisms that directly involve DNA damage. Lubeluzole, a novel benzothiazole compound, has recently been demonstrated to be neuroprotective through the signal transduction pathways of NO. We therefore examined whether neuroprotection by lubeluzole was dependent upon the molecular pathways of programmed cell death (PCD). 2. In primary hippocampal neurons, evidence of PCD was determined by hematoxylin and eosin (H&E) stain, transmission electron microscopy, and annexin-V binding. NO administration with the NO generators sodium nitroprusside (300 microM) or SIN-1 (300 microM) directly induced PCD. 3. Neurons positive for PCD increased from 22+/-3% (untreated) to 72+/-3% (NO) over a 24-hr period. Coadministration of NO and lubeluzole (750 nM), a neuroprotective concentration, actively decreased PCD expression on H&E stain from 72+/-3% (NO only) to 25+/-3% (NO and lubeluzole). Significant reduction in DNA fragmentation by lubeluzole also was evident on electron microscopy. Application of lubeluzole in concentrations that were not neuroprotective or administration of the biologically inactive R-isomer did not significantly alter NO-induced PCD, suggesting that neuroprotection by lubeluzole was intimately linked to the modulation of PCD. Lubeluzole also was able to prevent the initial stages of cellular membrane inversion labeled with annexin-V binding, an early and sensitive indicator of PCD. Interestingly, the critical period for lubeluzole to reverse PCD induction appeared to be within the first 4 hr following NO exposure. 4. Further investigation into the neuroprotective pathways that alter PCD may provide greater insight into the molecular mechanisms that ultimately determine neuronal injury.

Membrane asymmetry and DNA degradation: functionally distinct determinants of neuronal programmed cell death

The ability to elucidate the molecular mechanisms that modulate programmed cell death (PCD) may provide the crucial clues to unravel the cellular basis of neurodegenerative disorders. Employing both a novel assay to follow serially PCD in individual living neurons and the neuroprotective agent lubeluzole as an investigative tool, we examined the development of nitric oxide (NO)-induced PCD over time through the reversible annexin V labelling of membrane phosphatidylserine (PS) exposure and the electron microscopy of genomic DNA in primary rat hippocampal neurons. Exposure to the NO generators SNP (300 microM) or NOC-9 (300 microM) alone increased annexin V-positive neurons in the population from 7% +/- 4% in untreated cultures to 13% +/- 4% at 1 hr and to 61% +/- 5% at 24 hr. Administration of a neuroprotective concentration of lubeluzole (750 nM) at the time of NO exposure initially prevented the exposure of PS residues, but consistently maintained DNA integrity over a 24 hr period. During posttreatment paradigms of lubeluzole (750 nM) at 2, 4, and 6 hr following NO exposure, progression of membrane PS inversion was reversed and subsequently suppressed over a 24 hr course. Our work illustrates that neuronal PCD is composed of at least two physiologically distinct and separate pathways that consist of the externalization of membrane PS residues and the independent maintenance of genomic DNA integrity. In addition, neuronal injury is fluid and reversible in nature, suggesting a "window of opportunity" for the repair and reversal of neurons yet to be committed to PCD.

Neuronal intracellular pH directly mediates nitric oxide-induced programmed cell death

Neuronal injury is intricately linked to the activation of three distinct neuronal endonucleases. Since these endonucleases are exquisitely pH dependent, we investigated in primary rat hippocampal neurons the role of intracellular pH (pH(i)) regulation during nitric oxide (NO)-induced toxicity. Neuronal injury was assessed by both a 0.4% Trypan blue dye exclusion survival assay and programmed cell death (PCD) with terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) 24 h following treatment with the NO generators sodium nitroprusside (300 microM), 3-morpholinosydnonimine (300 microM), or 6-(2-hyrdroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-hex anamine (300 microM). The pH(i) was measured using the fluorescent probe BCECF. NO exposure yielded a rapid intracellular acidification during the initial 30 min from pH(i) 7.36 +/- 0.01 to approximately 7.00 (p <.0001). Within 45 min, a biphasic alkaline response was evident, with pH(i) reaching 7.40 +/- 0.02, that was persistent for a 6-h period. To mimic the effect of NO-induced acidification, neurons were acid-loaded with ammonium ions to yield a pH(i) of 7.09 +/- 0.02 for 30 min. Similar to NO toxicity, neuronal survival decreased to 45 +/- 2% (24 h) and DNA fragmentation increased to 58 +/- 8% (24 h) (p <.0001). Although neuronal caspases did not play a dominant role, neuronal injury and the induction of PCD during intracellular acidification were dependent upon enhanced endonuclease activity. Furthermore, maintenance of an alkaline pH(i) of 7.60 +/- 0.02 during the initial 30 min of NO exposure prevented neuronal injury, suggesting the necessity for the rapid but transient induction of intracellular acidification during NO toxicity. Through the identification of the critical role of both NO-induced intracellular acidification and the induction of the neuronal endonuclease activity, our work suggests a potential regulatory trigger for the prevention of neuronal degeneration.

Direct temporal analysis of apoptosis induction in living adherent neurons

Destruction of neurons through the genetically directed process of programmed cell death (PCD) is an area of intense interest because this is the underlying mechanism in a variety of developmental and neurodegenerative diseases. The ability to identify and track viable neurons subjected to PCD could be invaluable in development of strategies to prevent or reverse the downstream mechanisms of neuronal PCD. We have developed a novel assay for PCD in viable, adherent cells using annexin V labeling. Annexin V binds to the highly negatively charged plasma membrane phosphatidylserine residues that undergo membrane translocation during PCD. Current annexin V techniques are almost exclusively restricted to flow cytometric analysis. Our unique technique permits repeated examination of individual viable neurons without altering their survival. Correlation with electron microscopy and dye exclusion assays demonstrate both sensitivity and specificity for our method to detect PCD. To our knowledge, this is the first account of a technique that positively identifies PCD in viable, adherent cells.

Nitric oxide induction of neuronal endonuclease activity in programmed cell death

Neuronal survival is intricately linked to the maintenance of intact DNA. In contrast, neuronal degeneration following nitric oxide (NO) exposure is dependent, in part, on the degradation of DNA through programmed cell death (PCD). We therefore investigated in primary rat hippocampal neurons the role of endogenous deoxyribonucleases, enzymes responsible for metabolically derived DNA cleavage, during NO-induced neurodegeneration. Twenty-four hours following exposure to the NO generators sodium nitroprusside (300 microM) and SIN-1 (300 microM), neuronal survival was reduced from approximately 88 to 23%. Treatment with aurintricarboxylic acid (1-100 microM), an endonuclease inhibitor, during NO exposure increased neuronal survival from 23 to 80% and decreased DNA fragmentation from 70 to 30% over a 24-h period. Enhancement of endonuclease activity alone with zinc chelation actively decreased neuronal survival from approximately 80% to approximately 34%. DNA digestion assays identified not only two constitutively active endonucleases, an acidic endonuclease (pH 4.0-7.0) and a calcium/magnesium-dependent endonuclease (pH 7.2-8.0), but also a NO-inducible magnesium-dependent endonuclease (pH 8.0). In the absence of endonuclease activity, DNA degradation did not occur during NO application, suggesting that endonuclease activity was a requisite pathway for NO-induced PCD. In addition, NO independently altered intracellular pH in ranges that were physiologically relevant for the activity of the endonucleases responsible for DNA degradation. Our identification and characterization of specific neuronal endonucleases suggest that the constitutive endonucleases may play a role in the initial stages of NO-induced PCD, but the subsequent "downstream" degradation of DNA may ultimately be dependent upon the NO-inducible endonuclease.

Metabotropic glutamate receptors prevent programmed cell death through the modulation of neuronal endonuclease activity and intracellular pH

Metabotropic glutamate receptor (mGluR) activation prevents neurodegeneration against nitric oxide (NO)-induced programmed cell death (PCD). We therefore investigated whether specific neuronal endogenous deoxyribonucleases, enzymes recently identified to be responsible for the maintenance of DNA integrity, mediated mGluR protection against NO. In rat primary hippocampal neurons, injury was assessed by using a 0.4% trypan blue dye exclusion method and TUNEL assay 24 h following treatment with the NO generators sodium nitroprusside (300 microM) or SIN-1 (300 microM). DNA digestion studies using neuronal cell extracts were employed to assess specific endonuclease activity. Individual application of aurintricarboxylic acid (ATA) (10 microM), an endonuclease inhibitor, or the mGluR agonists 1S,3R-ACPD (750 microM), DHPG (750 microM), L-CCG-I (750 microM), or L-AP4 (750 microM) prior to NO exposure significantly increased neuronal survival. Yet, combination therapy with ATA (10 microM) and the mGluR agonists did not synergistically improve neuronal survival, suggesting a common pathway of protection for ATA and the mGluRs that is dependent upon the modulation of neuronal endonuclease activity. In further support of this premise, protection by the mGluR agonists 1S,3R-ACPD, DHPG, L-CCG-I, and L-AP4 was significantly decreased during enhancement of endonuclease activity with the zinc chelator, N,N,N',N',-tetrakis (2-pyridylmethyl) ethylenediamine. Antagonism of the mGluR system was ineffective against endonuclease induced DNA destruction. Further assessment with DNA digestion assays identified two distinct mechanisms to maintain DNA integrity, a Ca2+/Mg2+-dependent endonuclease inhibited by L-AP4 and a magnesium dependent endonuclease inhibited by 1S,3R-ACPD. These neuroprotective mechanisms during activation of the mGluR system were also intricately linked to the active reversal of the biphasic intracellular pH changes induced by NO. Further investigation into the molecular pathways modulated by mGluRs may identify specific mechanisms that can maintain DNA integrity during adverse cellular environments.

Determination of the dose proportionality of single intravenous doses (5, 10, and 15 mg) of lubeluzole in healthy volunteers

The dose proportionality of lubeluzole, a drug in clinical development for the treatment of acute ischemic stroke, was evaluated in a Phase I, single-center, open-label, randomized-dosing-sequence, three-way crossover clinical trial in 12 healthy adults. An equal number of male and female volunteers were enrolled in the trial, with a mean weight (+/- SD) of 73.2 +/- 11.9 kg, mean height (+/- SD) of 66.8 +/- 4.6 inches, and a mean age of 36.1 +/- 5.2 years. Subjects received intravenous infusions of 5 (A), 10 (B), and 15 mg (C) of lubeluzole over 1 hour on three separate occasions, with a minimum washout period of 2 weeks. The treatment sequences were A-B-C; A-C-B; B-A-C; B-C-A; C-A-B; and C-B-A. One male and one female were assigned to each sequence. After the 5-, 10-, and 15-mg doses, maximum concentration (Cmax) was 58.1, 113, and 138 microg/L, respectively, and the area under the curve from 0 to (AUC(0-infinity)) was 771, 1384, and 2025 microg x h/L. There were no statistically significant differences among the groups in mean terminal half-life, steady-state volume of distribution, total plasma clearance, or dose-normalized AUC(0-infinity). Dose-normalized values of Cmax differed significantly between the groups. No serious adverse events were reported, and no changes were observed in cardiac function, as judged by the QT(c) interval. The pharmacokinetics of lubeluzole appear to be linear at intravenous infusion doses of 5, 10, and 15 mg, and these doses are well tolerated by healthy adults.

Culture medium components modulate retina cell damage induced by glutamate, kainate or "chemical ischemia"

The aim of this study was to determine whether culture-conditioned medium (CCM) can prevent neuronal damage caused by excitotoxicity or by "chemical ischemia" in cultured chick retina cells. Excitotoxic conditions were obtained by incubating retina cells with glutamate or kainate and "chemical ischemia" was induced by metabolic inhibition. In this case, cultures were briefly exposed to sodium cyanide, to block oxidative phosphorylation and iodoacetic acid, to block glycolysis. The assessment of neuronal injury was made spectrophotometrically by quantification of cellularly reduced MTT. Stimulation of retina cells with glutamate or kainate in serum deprived culture medium (BME-FCS), lead to a decrease in the MTT metabolism that was dependent on the time of exposure to the toxic agents. CCM prevented cell damage, either when present during the stimulation period or during the recovery period. This protection was more prominent in the case of kainate-induced neuronal death. "Chemical ischemia" also lead to a decrease of the MTT metabolism in a time-dependent manner and CCM protected retina cells from "ischemia"-induced lesions when present during the stimulation period and during the recovery period. The protective effect of CCM was partially decreased by the tyrosine kinase inhibitor, genistein, when the cells were stimulated with kainate, but not with glutamate, or when the cells were subjected to "chemical ischemia". CCM protected retina cells against both the acute and the delayed toxicity induced by either glutamate or kainate, or by "chemical ischemia", when present during both the insult and the recovery period. The presence of survival factors in the media may effectively inhibit the cell death signals generated by glutamate receptor activation or by "chemical ischemia".

Hemodynamic effects of nitric oxide synthase inhibition before and after cardiac arrest in infant piglets

Using infant piglets, we studied the effects of nonspecific inhibition of nitric oxide (NO) synthase by NG-nitro-L-arginine methyl ester (L-NAME; 3 mg/kg) on vascular pressures, regional blood flow, and cerebral metabolism before 8 min of cardiac arrest, during 6 min of cardiopulmonary resuscitation (CPR), and at 10 and 60 min of reperfusion. We tested the hypotheses that nonspecific NO synthase inhibition 1) will attenuate early postreperfusion hyperemia while still allowing for successful resuscitation after cardiac arrest, 2) will allow for normalization of blood flow to the kidneys and intestines after cardiac arrest, and 3) will maintain cerebral metabolism in the face of altered cerebral blood flow after reperfusion. Before cardiac arrest, L-NAME increased vascular pressures and cardiac output and decreased blood flow to brain (by 18%), heart (by 36%), kidney (by 46%), and intestine (by 52%) compared with placebo. During CPR, myocardial flow was maintained in all groups to successfully resuscitate 24 of 28 animals [P value not significant (NS)]. Significantly, L-NAME attenuated postresuscitation hyperemia in cerebellum, diencephalon, anterior cerebral, and anterior-middle watershed cortical brain regions and to the heart. Likewise, cerebral metabolic rates of glucose (CMRGluc) and of lactate production (CMRLac) were not elevated at 10 min of reperfusion. These cerebral blood flow and metabolic effects were reversed by L-arginine. Flows returned to baseline levels by 60 min of reperfusion. Kidney and intestinal flow, however, remained depressed throughout reperfusion in all three groups. Thus nonspecific inhibition of NO synthase did not adversely affect the rate of resuscitation from cardiac arrest while attenuating cerebral and myocardial hyperemia. Even though CMRGluc and CMRLac early after resuscitation were decreased, they were maintained at baseline levels. This may be clinically advantageous in protecting the brain and heart from the damaging effects of hyperemia, such as blood-brain barrier disruption.

Metabotropic glutamate receptors prevent nitric oxide-induced programmed cell death

Activation of metabotropic glutamate receptor (mGluR) subtypes can prevent neuronal injury through the signal transduction pathways of nitric oxide (NO). It is this link to NO free radical injury and subsequent DNA damage that is the most intriguing. We therefore examined whether neuronal protection through mGluR activation was dependent on the molecular mechanisms of programmed cell death (PCD). The NO generators sodium nitroprusside and 3-morpholino-sydnonimine were administered to induce NO toxicity in primary hippocampal neurons. PCD was documented by hematoxylin and eosin nuclear staining, DNA gel electrophoresis, transmission electron microscopy, and protein synthesis assays. Following NO exposure, PCD induction was rapid and robust in approximately 70% of the neuronal population. Activation of specific mGluR subtypes with 1S,3R-ACPD and L-AP4, agents that are neuroprotective against NO, significantly limited the progression of PCD. In contrast, antagonism of mGluRs with L-AP3 did not prevent the development of PCD. Induction of new protein synthesis, a common requisite for PCD, was evident following NO exposure, but did not appear to represent a principal pathway of modulation by the mGluR agonists. Our studies suggest that mGluR modulation of NO-induced PCD represents a primary molecular pathway responsible for neuronal survival. Further elucidation of the molecular mGluR signaling pathways may yield new insight into specific genetic regulatory mechanisms responsible for neuronal injury.

Basic fibroblast growth factor is highly neuroprotective against seizure-induced long-term behavioural deficits

Basic fibroblast growth factor has been reported to protect neurons of various structures from excitotoxic damage. To study the effects of basic fibroblast growth factor on seizure-induced brain damage we infused the growth factor into the lateral ventricles of 35-day-old rats receiving convulsant dosages of kainic acid. Artificial cerebrospinal fluid or basic fibroblast growth factor at dosages of 0.5 ng/h or 2.5 ng/h was infused into the lateral ventricle continuously for seven days starting two days before and continuing for five days after the animals had kainic acid-induced status epilepticus. At age 80 days the animals underwent behavioural testing using the water maze, open field, and handling tests and at age 95 days were tested for seizure threshold using flurothyl inhalation. Neither artificial cerebrospinal fluid or basic fibroblast growth factor modified the latency or duration of the acute seizures following kainic acid. However, rats infused with 2.5 ng/h, but not 0.5 ng/h of basic fibroblast growth factor, had fewer spontaneous recurrent seizures, a higher seizure threshold, better performance in the handling, open field and water maze test, and less cell loss in the hippocampus when compared to rats receiving artificial cerebrospinal fluid or 0.5 ng/h of basic fibroblast growth factor. These results show that basic fibroblast growth factor has a dose-related neuroprotective effect against seizure-induced long-term behavioural deficits when administered by osmotic pump prior to seizure onset. This neuroprotective effect is not related to an anticonvulsant effect.

NMDA Receptor-dependent increase of cerebral glucose utilization after hypoxia-ischemia in the immature rat

Post-treatment with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 reduces hypoxic-ischemic brain injury in immature animals. To elucidate possible mechanisms, cerebral glucose utilization (CMRglc) and cerebral blood flow (CBF) were measured 1-5 h after hypoxia-ischemia and administration of MK-801 in 7-day-old rats. After 100 min of unilateral hypoxia-ischemia, half of the pups were injected with MK-801. CMRglc was assessed by the [14C]deoxyglucose (2-DG) method. The brains were analyzed either by autoradiography or for energy metabolites and chromatographic separation of 2-DG-6-phosphate and 2-DG. CBF was measured by the autoradiographic [14C]iodoantipyrine method. Mean CMRglc in the cerebral cortex was increased ipsilaterally after hypoxia-ischemia to 15 +/- 3.3 mumol 100 g-1 min-1 (p < 0.01) and areas with CMRglc > 20 mumol 100 g-1 min-1 amounted to 8.0 +/- 7.7 mm2 in the ipsilateral hemisphere compared with 1.2 +/- 1.6 mm2 contralaterally (p < 0.001). Treatment with MK-801 decreased CMRglc bilaterally (p < 0.05) and reduced ipsilateral areas with increased CMRglc by 64% (p < 0.01). CBF was unaltered after hypoxia-ischemia and by MK-801 treatment. In conclusion, regional glucose hyperutilization in the parietal cortex after hypoxia-ischemia was attenuated by MK-801; this may have relevance to the neuroprotective effect of NMDA-receptor antagonists in this model.

Apoptosis induced in neuronal cultures by either the phosphatase inhibitor okadaic acid or the kinase inhibitor staurosporine is attenuated by isoquinolinesulfonamides H-7, H-8, and H-9

Protein phosphorylation is kept in balance by an orchestrated action of kinases and phosphatases; when this balance is lost, neuronal apoptosis may occur. Okadaic acid (OKA), a marine toxin that inhibits specifically protein phosphatases 1 and 2A (EC 3.1.3.16), and staurosporine, an inhibitor of protein kinase C (PKC; EC 2.7.1.37), induced apoptosis in primary cultures of rat cerebellar granule neurons. We assayed apoptosis by the DNA gel electrophoresis, by the in situ TUNEL assay, and by morphological appearance following propidium iodide staining. Cell viability was assessed by the Trypan blue assay. Both OKA- and staurosporine-induced neuronal apoptosis were prevented by a macromolecular synthesis inhibitor actinomycin D and by a group of isoquinolinesulfonamide kinase inhibitors (H-7, 1-[5-isoquinolinesulfonyl]-2-methylpiperazine; H-8, N-¿2-[methylamino]ethyl¿-5-isoquinolinesulfonamide; H-9, N-(2-aminoethyl)-5-isoquinolinesulfonamide, but not by inhibitors of PKC, cyclic-GMP- and cyclic-AMP-dependent kinases, calcium/calmodulin-dependent kinases, tyrosine kinases, or by antioxidants. We postulate that a common mechanism, possibly an increased protein phosphorylation, is responsible for apoptosis triggered by an inhibition of phosphatases 1 and 2A and PKC. Elucidating the isoquinolinesulfonamide-sensitive mechanism may help us find new therapies for neurodegenerative diseases that involve apoptosis.