Nitric oxide and cerebral ischemic preconditioning

Oxidative Metabolism in Brain Ischemia and Preconditioning: Two Sides of the Same Coin

Brain ischemia is one of the major causes of chronic disability and death worldwide. It is related to insufficient blood supply to cerebral tissue, which induces irreversible or reversible intracellular effects depending on the time and intensity of the ischemic event. Indeed, neuronal function may be restored in some conditions, such as transient ischemic attack (TIA), which may be responsible for protecting against a subsequent lethal ischemic insult. It is well known that the brain requires high levels of oxygen and glucose to ensure cellular metabolism and energy production and that damage caused by oxygen impairment is tightly related to the brain's low antioxidant capacity. Oxygen is a key player in mitochondrial oxidative phosphorylation (OXPHOS), during which reactive oxygen species (ROS) synthesis can occur as a physiological side-product of the process. Indeed, besides producing adenosine triphosphate (ATP) under normal physiological conditions, mitochondria are the primary source of ROS within the cell. This is because, in 0.2-2% of cases, the escape of electrons from complex I (NADPH-dehydrogenase) and III of the electron transport chain occurring in mitochondria during ATP synthesis leads to the production of the superoxide radical anion (O2•-), which exerts detrimental intracellular effects owing to its high molecular instability. Along with ROS, reactive nitrosative species (RNS) also contribute to the production of free radicals. When the accumulation of ROS and RNS occurs, it can cause membrane lipid peroxidation and DNA damage. Here, we describe the intracellular pathways activated in brain tissue after a lethal/sub lethal ischemic event like stroke or ischemic tolerance, respectively, highlighting the important role played by oxidative stress and mitochondrial dysfunction in the onset of the two different ischemic conditions.

Study of disorders in regulatory spatiotemporal neurodynamics of calcium and nitric oxide

Experimental studies have reported the dependence of nitric oxide (NO) on the regulation of neuronal calcium ([Ca2+]) dynamics in neurons. But, there is no model available to estimate the disorders caused by various parameters in their regulatory dynamics leading to various neuronal disorders. A mathematical model to analyze the impacts due to alterations in various parameters like buffer, ryanodine receptor, serca pump, source influx, etc. leading to regulation and dysregulation of the spatiotemporal calcium and NO dynamics in neuron cells is constructed using a system of reaction-diffusion equations. The numerical simulation is performed with the finite element approach. The disturbances in the different constitutive processes of [Ca2+] and nitric oxide including source influx, buffer mechanism, ryanodine receptor, serca pump, IP3 receptor, etc. can be responsible for the dysregulation in the [Ca2+] and NO dynamics in neurons. Also, the results reveal novel information about the magnitude and intensity of disorders in response to a range of alterations in various parameters of this neuronal dynamics, which can cause dysregulation leading to neuronal diseases like Parkinson's, cerebral ischemia, trauma, etc.

Regulatory mechanisms of tetramethylpyrazine on central nervous system diseases: A review

Central nervous system (CNS) diseases can lead to motor, sensory, speech, cognitive dysfunction, and sometimes even death. These diseases are recognized to cause a substantial socio-economic impact on a global scale. Tetramethylpyrazine (TMP) is one of the main active ingredients extracted from the Chinese herbal medicine Ligusticum striatum DC. (Chuan Xiong). Many in vivo and in vitro studies have demonstrated that TMP has a certain role in the treatment of CNS diseases through inhibiting calcium ion overload and glutamate excitotoxicity, anti-oxidative/nitrification stress, mitigating inflammatory response, anti-apoptosis, protecting the integrity of the blood-brain barrier (BBB) and facilitating synaptic plasticity. In this review, we summarize the roles and mechanisms of action of TMP on ischemic cerebrovascular disease, spinal cord injury, Parkinson’s disease, Alzheimer’s disease, cognitive impairments, migraine, and depression. Our review will provide new insights into the clinical applications of TMP and the development of novel therapeutics.

Typhae pollen polysaccharides protect hypoxia-induced PC12 cell injury via regulation of miR-34a/SIRT1

This current research was performed to investigate the role of typhae pollen polysaccharides (TPP) in hypoxia-treated PC12 cell which was an in vitro cell model of cerebral ischemia. Hypoxia-treated cells were treated with TPP for 12 h. Cell viability and apoptosis were detected by 3-(4,5-dimethylthiazol-2-yl)-2 5-diphenyl-2H-tetrazolium bromide (MTT) assay and flow cytometry, respectively. Cell apoptotic proteins and PI3K/AKT and Ras/Raf/MEK/ERK signal pathway–associated proteins were also examined by western blot. Furthermore, abnormal expression of miR-34a and silent information regulator 1 (SIRT1) was achieved by transfection. Besides, the expression of miR-34a and SIRT1 was examined by quantitative real-time polymerase chain reaction (qRT-PCR). The expression of SIRT1 was detected by qRT-PCR and western blot. The relationship between miR-34a and SIRT1 was verified by luciferase assay. We found that TPP enhanced cell viability and inhibited apoptosis in hypoxia-treated PC12 cells. Moreover, TPP increased the accumulated levels of Bcl-2 while decreased expression of Bax, cleaved Caspase-3, and cleaved PARP. TPP downregulated miR-34a expression while induced by hypoxia. Further results showed that miR-34a overexpression reversed the results led by TPP in cell viability, apoptosis, and its related proteins. In addition, SIRT1 was upregulated by TPP and was verified to be a target of miR-34a. Silence of SIRT1 led to the opposite results led by TPP. In the end, TPP activated PI3K/AKT and Ras/Raf/MEK/ERK signal pathways. In conclusion, TPP plays important roles in regulating cell viability and apoptosis in hypoxia-treated PC12 cells via modulating miR-34a/SIRT1, as well as activating PI3K/AKT and Ras/Raf/MEK/ERK signal pathways.

Inflammaging, hormesis and the rationale for anti-aging strategies

We propose in this review that hormesis, a concept profoundly and systematically addressed by Mark Mattson, has to be considered a sort of comprehensive "contact point" capable of unifying several conceptualizations of the aging process, including those focused on the stress response, oxidative stress and chronic inflammation/inflammaging. A major strength of hormesis and inflammaging is that they have a strong evolutionary basis. Moreover, both hormesis and inflammaging frame the aging process within a lifelong perspective of adaptation to different types of stresses. Such adaptation perspective also suggests that the aging process is malleable, and predicts that effective anti-aging strategies should mimic what evolution did in the course of million years and that we have to learn how to exploit the great potential inherent in the hormetic/inflammatory responses. To this regard, new topics such as the production of mitokines to cope with mitochondrial dysfunction are emerging as possible anti-aging target. This approach opens theoretically the door to the possibility of modulating the individual aging rate and trajectory by adopting the most effective scientifically-based lifestyle regarding fundamentally nutrition and physical activity. In this scenario Mark Mattson's lesson and personal example will permanently enlighten the aging field and the quest for a healthy aging and longevity.

Toxin-induced hormesis may restrain aging

Mild environmental stress might have beneficial effects in aging by activating maintenance and repair processes in cells and organs. These beneficial stress effects fit to the concept of hormesis. Prominent stressors acting in a hormetic way are physical exercises, fasting, cold and heat. This review will introduce some toxins, which have been found to induce hormetic responses in animal models of aging research. To highlight the molecular signature of these hormetic effects we will depict signaling pathways affected by low doses of toxins on cellular and organismic level. As prominent examples for signaling pathways involved in both aging processes as well as toxin responses, PI3K/Akt/mTOR- and AMPK-signal transduction will be described in more detail. Due to the striking overlap of signaling pathways mediating toxin induced responses and aging processes we propose considering the ability of low doses of toxins to slow down the rate of aging.

Aging and Parkinson's Disease: Inflammaging, neuroinflammation and biological remodeling as key factors in pathogenesis

In order to better understand the pathogenesis of Parkinson's Disease (PD) it is important to consider possible contributory factors inherent to the aging process, as age-related changes in a number of physiological systems (perhaps incurred within particular environments) appear to influence the onset and progression of neurodegenerative disorders. Accordingly, we posit that a principal mechanism underlying PD is inflammaging, i.e. the chronic inflammatory process characterized by an imbalance of pro- and anti-inflammatory mechanisms which has been recognized as operative in several age-related, and notably neurodegenerative diseases. Recent conceptualization suggests that inflammaging is part of the complex adaptive mechanisms ("re-modeling") that are ongoing through the lifespan, and which function to prevent or mitigate endogenous processes of tissue disruption and degenerative change(s). The absence of an adequate anti-inflammatory response can fuel inflammaging, which propagates on both local (i.e.- from cell to cell) and systemic levels (e.g.- via exosomes and other molecules present in the blood). In general, this scenario is compatible with the hypothesis that inflammaging represents a hormetic or hormetic-like effect, in which low levels of inflammatory stress may prompt induction of anti-inflammatory mediators and mechanisms, while sustained pro-inflammatory stress incurs higher and more durable levels of inflammatory substances, which, in turn prompt a local-to-systemic effect and more diverse inflammatory response(s). Given this perspective, new treatments of PD may be envisioned that strategically are aimed at exerting hormetic effects to sustain anti-inflammatory responses, inclusive perhaps, of modulating the inflammatory influence of the gut microbiota.

Hyperbaric oxygen therapy of spinal cord injury

Spinal cord injury (SCI) is a complex disease process that involves both primary and secondary mechanisms of injury and can leave patients with devastating functional impairment as well as psychological debilitation. While no curative treatment is available for spinal cord injury, current therapeutic approaches focus on reducing the secondary injury that follows SCI. Hyperbaric oxygen (HBO) therapy has shown promising neuroprotective effects in several experimental studies, but the limited number of clinical reports have shown mixed findings. This review will provide an overview of the potential mechanisms by which HBO therapy may exert neuroprotection, provide a summary of the clinical application of HBO therapy in patients with SCI, and discuss avenues for future studies.

Mediterranean diet and inflammaging within the hormesis paradigm

A coherent set of epidemiological data shows that the Mediterranean diet has beneficial effects capable of preventing a variety of age-related diseases in which low-grade, chronic inflammation/inflammaging plays a major role, but the underpinning mechanism(s) is/are still unclear. It is suggested here that the Mediterranean diet can be conceptualized as a form of chronic hormetic stress, similar to what has been proposed regarding calorie restriction, the most thoroughly studied nutritional intervention. Data on the presence in key Mediterranean foods of a variety of compounds capable of exerting hormetic effects are summarized, and the mechanistic role of the nuclear factor erythroid 2 pathway is highlighted. Within this conceptual framework, particular attention has been devoted to the neurohormetic and neuroprotective properties of the Mediterranean diet, as well as to its ability to maintain an optimal balance between pro- and anti-inflammaging. Finally, the European Commission-funded project NU-AGE is discussed because it addresses a number of variables not commonly taken into consideration, such as age, sex, and ethnicity/genetics, that can modulate the hormetic effect of the Mediterranean diet.

Pleiotropic effects of acarbose on atherosclerosis development in rabbits are mediated via upregulating AMPK signals

Acarbose, an α-glucosidase inhibitor, is reported to reduce the incidence of silent myocardial infarction and slow the progression of intima-media thickening in patients with glucose intolerance. Here we investigate other impacts of acarbose on atherosclerosis development and the underlying mechanisms of atherosclerosis initiation and progression in vivo and in vitro. Rabbits fed a high cholesterol diet (HCD) were treated with acarbose (2.5-5.0 mg kg^-1). Immunohistochemistry was used to assess the expression of inducible nitric oxide synthase (iNOS), Ras, proliferating cell nuclear antigen (PCNA), IL-6, β-galactosidase, and p-AMPK in atherosclerotic lesions. Treatment with acarbose in HCD-fed rabbits was found to significantly reduce the severity of aortic atheroma and neointimal expression of α-actin, PCNA, IL-6, TNF-α, Ras, and β-galactosidase; to significantly increase expression of iNOS and p-AMPK, but not to affect serum levels of glucose, total cholesterol, and LDL. Western blot analysis showed acarbose dose-dependently decreased β-galactosidase and Ras expression and increased p-AMPK expression in TNF-α-treated A7r5 cells. In addition, acarbose restored p-AMPK and iNOS levels in AMPK inhibitor- and iNOS inhibitor-treated A7r5 cells, respectively. In conclusion, acarbose can pleiotropically inhibit rabbit atherosclerosis by reducing inflammation, senescence, and VSMCs proliferation/migration via upregulating AMPK signals.

Anthraquinone derivative exerted hormetic effect on the apoptosis in oxygen-glucose deprivation-induced PC12 cells via ERK and Akt activated Nrf2/HO-1 signaling pathway

There were accumulated evidences that agents may attenuate neurological disorders through a hormetic effect. This study was designed to investigate hormetic effect of BME on the oxygen-glucose deprivation (OGD)-induced mitochondrial apoptosis in NGF-differentiated PC12 cells. The effect of BME on the intracellular reactive oxygen species (iROS) formation and pro-survival signals mediated by ERK and Akt as well as transcription factor nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) pathways was also determined. The present results showed that, at low concentrations, pretreatment with BME triggered stress response by causing ROS production, then, activated survival-promoting signals via ERK and Akt activated Nrf2/HO-1 signaling pathway, resulting in decrease in cytotoxicity induced by the OGD. It may be accepted that mild pretreatment with BME stimulated transient and moderate ROS production, but activated hormetic signals and induced stress responsive genes. In contrast, high concentrations of BME displayed toxic action due to massive ROS production. These results suggested that the effect of BME on the OGD-induced PC12 cells may be hormetic mechanism including induction of oxidative stress and subsequent activation of stress response gene expression.

Anesthesia specific differences in a cardio-pulmonary resuscitation rat model; halothane versus sevoflurane

OBJECTIVE

Our asphyxia cardiac arrest (ACA) rat model is well established. The original model was designed in the 1990th using halothane and nitrous oxide for pre-insult anesthesia. Because of its hepato-toxicity and its potential to induce severe liver failures, halothane is no longer used in clinical anesthesia for several years. In order to minimize the health risk for our laboratory staff as well as to keep the experimental settings of our model on a clinically oriented basis we decided to replace halothane by sevoflurane. In this study we intended to determine if the change of the narcotic gas regiment causes changes in the neurological damage and how far our model had to be adjusted.

METHODS

Adult rats were subjected to 5min of ACA followed by resuscitation. There were four treatment groups: ACA - halothane, ACA - sevoflurane and with halothane or sevoflurane sham operated animals. Vital and blood parameters were monitored during the 45min post-resuscitation intensive care phase. After a survival time of 7 days histological evaluation of the hippocampus was performed.

RESULTS

We observed that resuscitated rats anesthetized prior by sevoflurane (i) have had a lower heart rate and a higher MAP compared to halothane anesthetized animals; (ii) The neurological damaged were significantly reduced in the hippocampal CA1 region in sevoflurane treated rats.

CONCLUSION

Using sevoflurane instead of halothane for anesthesia requires some physiological and experimental changes. However the model keeps its validity. Sevoflurane caused less pronounced neurodegeneration in the CA1 region of the hippocampus. This had to be considered in further resuscitation-studies containing sevoflurane as anesthetic. Institutional protocol number for animal studies: 42502-2-2-947 Uni MD.

Novel Cellular Mechanisms for Neuroprotection in Ischemic Preconditioning: A View from Inside Organelles

Ischemic preconditioning represents an important adaptation mechanism of CNS, which results in its increased tolerance to the lethal cerebral ischemia. The molecular mechanisms responsible for the induction and maintenance of ischemic tolerance in the brain are complex and not yet completely clarified. In the last 10 years, great attention has been devoted to unravel the intracellular pathways activated by preconditioning and responsible for the establishing of the tolerant phenotype. Indeed, recent papers have been published supporting the hypothesis that mitochondria might act as master regulators of preconditioning-triggered endogenous neuroprotection due to their ability to control cytosolic calcium homeostasis. More interestingly, the demonstration that functional alterations in the ability of mitochondria and endoplasmic reticulum (ER) managing calcium homeostasis during ischemia, opened a new line of research focused to the role played by mitochondria and ER cross-talk in the pathogenesis of cerebral ischemia in order to identify new molecular mechanisms involved in the ischemic tolerance. In line with these findings and considering that the expression of the three isoforms of the sodium calcium exchanger (NCX), NCX1, NCX2, and NCX3, mainly responsible for the regulation of Ca²⁺ homeostasis, was reduced during cerebral ischemia, it was investigated whether these proteins might play a role in neuroprotection induced by ischemic tolerance. In this review, evidence supporting the involvement of ER and mitochondria interaction within the preconditioning paradigm will be provided. In particular, the key role played by NCXs in the regulation of Ca²⁺-homeostasis at the different subcellular compartments will be discussed as new molecular mechanism proposed for the establishing of ischemic tolerant phenotype.

Isoflurane provides neuroprotection in neonatal hypoxic ischemic brain injury

Isoflurane is a volatile anesthetic that is widely used clinically as an inhalational anesthetic. In recent years, several studies have indicated that isoflurane has neuroprotective properties. This has led to the beneficial effects of isoflurane being analyzed in both cell culture and animal models, including various models of brain injury. Neonatal hypoxia ischemia may be characterized as injury that occurs in the immature brain, resulting in delayed cell death via excitotoxicity and oxidative stress. These adverse events in the developing brain often lead to detrimental neurological defects in the future. Currently, there are no well-established effective therapies for neonatal hypoxia ischemia. In line with this, isoflurane, which displays neuroprotective properties in several paradigms and has been shown to improve neurological deficits caused by brain injuries, has the capability to be an extremely relevant clinical therapy for the resolution of deficits concomitant with neonatal hypoxic ischemic brain injuries. This review therefore seeks to explore and analyze the current information on isoflurane, looking at general isoflurane anesthetic properties, and the protection it confers in different animal models, focusing particularly on neuroprotection as shown in studies with neonatal hypoxic ischemic brain injury.

Qingkailing Suppresses the Activation of BV2 Microglial Cells by Inhibiting Hypoxia/Reoxygenation-Induced Inflammatory Responses

Qingkailing (QKL) is a well-known composite extract used in traditional Chinese medicine. This extract has been extensively administered to treat the acute phase of cerebrovascular disease. Our previous experiments confirmed that QKL exerts an inhibitory effect on cerebral ischemia-induced inflammatory responses. However, whether QKL suppresses the activation of microglia, the primary resident immune cells in the brain, has yet to be determined. In this study, BV2 microglial cells were used to validate the protective effects of QKL treatment following ischemia-reperfusion injury simulated via hypoxia/reoxygenation in vitro. Under these conditions, high expression levels of ROS, COX-2, iNOS, and p-p38 protein were detected. Following ischemia/reperfusion injury, QKL significantly increased the activity of BV2 cells to approximately the basal level by modulating microglial activation via inhibition of inflammatory factors, including TNF- α , COX-2, iNOS, and p-p38. However, QKL treatment also displayed dose-dependent differences in its inhibitory effects on p38 phosphorylation and inflammatory factor expression.

Endoplasmic reticulum refilling and mitochondrial calcium extrusion promoted in neurons by NCX1 and NCX3 in ischemic preconditioning are determinant for neuroprotection

Ischemic preconditioning (IPC), an important endogenous adaptive mechanism of the CNS, renders the brain more tolerant to lethal cerebral ischemia. The molecular mechanisms responsible for the induction and maintenance of ischemic tolerance in the brain are complex and still remain undefined. Considering the increased expression of the two sodium calcium exchanger (NCX) isoforms, NCX1 and NCX3, during cerebral ischemia and the relevance of nitric oxide (NO) in IPC modulation, we investigated whether the activation of the NO/PI3K/Akt pathway induced by IPC could regulate calcium homeostasis through changes in NCX1 and NCX3 expression and activity, thus contributing to ischemic tolerance. To this aim, we set up an in vitro model of IPC by exposing cortical neurons to a 30-min oxygen and glucose deprivation (OGD) followed by 3-h OGD plus reoxygenation. IPC was able to stimulate NCX activity, as revealed by Fura-2AM single-cell microfluorimetry. This effect was mediated by the NO/PI3K/Akt pathway since it was blocked by the following: (a) the NOS inhibitors L-NAME and 7-Nitroindazole, (b) the IP3K/Akt inhibitors LY294002, wortmannin and the Akt-negative dominant, (c) the NCX1 and NCX3 siRNA. Intriguingly, this IPC-mediated upregulation of NCX1 and NCX3 activity may control calcium level within endoplasimc reticulum (ER) and mitochondria, respectively. In fact, IPC-induced NCX1 upregulation produced an increase in ER calcium refilling since this increase was prevented by siNCX1. Moreover, by increasing NCX3 activity, IPC reduced mitochondrial calcium concentration. Accordingly, the inhibition of NCX by CGP37157 reverted this effect, thus suggesting that IPC-induced NCX3-increased activity may improve mitochondrial function during OGD/reoxygenation. Collectively, these results indicate that IPC-induced neuroprotection may occur through the modulation of calcium homeostasis in ER and mitochondria through NO/PI3K/Akt-mediated NCX1 and NCX3 upregulation.

Up-regulation of heme oxygenase-1 attenuates brain damage after cerebral ischemia via simultaneous inhibition of superoxide production and preservation of NO bioavailability

Cerebral ischemia exacerbates neuronal death and neurological dysfunction. Evidence supports the involvement of oxidative/nitrative stress in the pathophysiology of cerebral ischemia. Heme oxygenase-1 (HO-1) is a rate-limiting enzyme in heme catabolism, possessing potent anti-oxidant and anti-apoptosis effects. In transgenic mice, HO-1 overproduction is neuroprotective against cerebral ischemia injury, but by unclear mechanisms. The present study determined whether treatment with adenoviral vector overexpressing HO-1 (Ad-HO-1) attenuates post-ischemic brain damage via reduction of oxidative/nitrative stress. After focal cerebral ischemia, Ad-HO-1 reduced lipid peroxidation and protein nitration, decreased infarct volume, and attenuated neurologic deficits. Zinc protoporphyrin IX (ZnPP IX, a specific HO-1 inhibitor) blocked Ad-HO-1 mediated effects against ischemic brain damage. Although Ad-HO-1 slightly reduced ischemic brain NO concentrations, Ad-HO-1 treatment significantly inhibited cerebral expression of iNOS protein expression, without significant effect upon nNOS or eNOS expression compared to vehicle after focal cerebral ischemia. Ad-HO-1 preserved NO bioavailability by increasing eNOS phosphorylation during ischemia compared to vehicle. Together, our results suggest that Ad-HO-1 attenuates post-ischemic brain damage via simultaneous reduction of oxidative/nitrative stress and preservation of NO bioavailability.

Current therapeutic strategies to mitigate the eNOS dysfunction in ischaemic stroke

Impairment of endothelial nitric oxide synthase (eNOS) activity is implicated in the pathogenesis of endothelial dysfunction in many diseases including ischaemic stroke. The modulation of eNOS during and/or following ischaemic injury often represents a futile compensatory mechanism due to a significant decrease in nitric oxide (NO) bioavailability coupled with dramatic increases in the levels of reactive oxygen species that further neutralise NO. However, applications of a number of therapeutic agents alone or in combination have been shown to augment eNOS activity under a variety of pathological conditions by potentiating the expression and/or activity of Akt/eNOS/NO pathway components. The list of these therapeutic agents include NO donors, statins, angiotensin-converting enzyme inhibitors, calcium channel blockers, phosphodiesterase-3 inhibitors, aspirin, dipyridamole and ellagic acid. While most of these compounds exhibit anti-platelet properties and are able to up-regulate eNOS expression in endothelial cells and platelets, others suppress eNOS uncoupling and tetrahydrobiopterin (an eNOS stabiliser) oxidation. As the number of therapeutic molecules that modulate the expression and activity of eNOS increases, further detailed research is required to reveal their mode of action in preventing and/or reversing the endothelial dysfunction.

Low-dose-rate, low-dose irradiation delays neurodegeneration in a model of retinitis pigmentosa

The existence of radiation hormesis is controversial. Several stimulatory effects of low-dose (LD) radiation have been reported to date; however, the effects on neural tissue or neurodegeneration remain unknown. Here, we show that LD radiation has a neuroprotective effect in mouse models of retinitis pigmentosa, a hereditary, progressive neurodegenerative disease that leads to blindness. Various LD radiation doses were administered to the eyes in a retinal degeneration mouse model, and their pathological and physiological effects were analyzed. LD gamma radiation in a low-dose-rate (LDR) condition rescues photoreceptor cell apoptosis both morphologically and functionally. The greatest effect was observed in a condition using 650 mGy irradiation and a 26 mGy/minute dose rate. Multiple rounds of irradiation strengthened this neuroprotective effect. A characteristic up-regulation (563%) of antioxidative gene peroxiredoxin-2 (Prdx2) in the LDR-LD-irradiated retina was observed compared to the sham-treated control retina. Silencing the Prdx2 using small-interfering RNA administration reduced the LDR-LD rescue effect on the photoreceptors. Our results demonstrate for the first time that LDR-LD irradiation has a biological effect in neural cells of living animals. The results support that radiation exhibits hormesis, and this effect may be applied as a novel therapeutic concept for retinitis pigmentosa and for other progressive neurodegenerative diseases regardless of the mechanism of degeneration involved.

Long-lasting neuroprotective effect of sildenafil against 3,4-methylenedioxymethamphetamine- induced 5-hydroxytryptamine deficits in the rat brain

Sildenafil, given shortly before 3,4-methylenedioxymethamphetamine (MDMA), affords protection against 5-hydroxytryptamine (5-HT) depletions caused by this amphetamine derivative by an acute preconditioning-like mechanism. Because acute and delayed preconditionings do not share the same mechanisms, we investigated whether sildenafil would also protect the 5-HT system of the rat if given 24 hr before MDMA. For this, MDMA (3 × 5 mg/kg i.p., every 2 hr) was administered to rats previously treated with sildenafil (8 mg/kg p.o.). One week later, 5-HT content and 5-HT transporter density were measured in the striatum, frontal cortex, and hippocampus of the rats. Our findings indicate that sildenafil afforded significant protection against MDMA-induced 5-HT deficits without altering the acute hyperthermic response to MDMA or its metabolic disposition. Sildenafil promoted ERK1/2 activation an effect that was paralleled by an increase in MnSOD expression that persisted 24 hr later. In addition, superoxide and superoxide-derived oxidants, shown by ethidium fluorescence, increased after the last MDMA injection, an effect that was prevented by sildenafil pretreatment. Similarly, MDMA increased nitrotyrosine concentration in the hippocampus, an effect not shown by sildenafil-pretreated rats. In conclusion, our data demonstrate that sildenafil produces a significant, long-lasting neuroprotective effect against MDMA-induced 5-HT deficits. This effect is apparently mediated by an increased expression of MnSOD and a subsequent reduced susceptibility to the oxidative stress caused by MDMA.

Methylenedioxymethamphetamine (MDMA, 'Ecstasy'): Neurodegeneration versus Neuromodulation

The amphetamine analogue 3,4-methylenedioxymethamphetamine (MDMA, ‘ecstasy’) is widely abused as a recreational drug due to its unique psychological effects. Of interest, MDMA causes long-lasting deficits in neurochemical and histological markers of the serotonergic neurons in the brain of different animal species. Such deficits include the decline in the activity of tryptophan hydroxylase in parallel with the loss of 5-HT and its main metabolite 5-hydoxyindoleacetic acid (5-HIAA) along with a lower binding of specific ligands to the 5-HT transporters (SERT). Of concern, reduced 5-HIAA levels in the CSF and SERT density have also been reported in human ecstasy users, what has been interpreted to reflect the loss of serotonergic fibers and terminals. The neurotoxic potential of MDMA has been questioned in recent years based on studies that failed to show the loss of the SERT protein by western blot or the lack of reactive astrogliosis after MDMA exposure. In addition, MDMA produces a long-lasting down-regulation of SERT gene expression; which, on the whole, has been used to invoke neuromodulatory mechanisms as an explanation to MDMA-induced 5-HT deficits. While decreased protein levels do not necessarily reflect neurodegeneration, the opposite is also true, that is, neuroregulatory mechanisms do not preclude the existence of 5-HT terminal degeneration.

Up-regulation of erythropoietin receptor by nitric oxide mediates hypoxia preconditioning

Erythropoietin (Epo), known to stimulate erythroid progenitor cell survival, proliferation, and differentiation, has been shown to be neuroprotective against brain ischemia in animal models. Both Epo and Epo receptor (EpoR) are expressed in the brain and are up-regulated by hypoxia. Brain Epo signaling can stimulate neural cell survival and prevent neuron apoptosis. Neurons from EpoR null mice exhibit marked increased sensitivity to hypoxia. In endothelial cells, Epo has been shown to stimulate nitric oxide (NO) production, particularly at low pO(2). We found here that the EpoR expression on neural cells and Epo's neuroprotective effect were regulated by NO. Hypoxia increased NO production as well as EpoR expression, and inhibition of NOS activity reduced the proportion of EpoR-expressing neurons induced at low pO(2). Conversely, addition of NO donor to cultures grown under normoxia induced EpoR. Similarly, NO donor increased EpoR promoter activity in a reporter gene assay, suggesting that NO regulates EpoR at the transcription level. Preincubation of neurons with NO results in induction of EpoR, which gives rise to protection against hypoxia even in the absence of exogenous Epo, although at high concentration NO is toxic. These data provide evidence of a role for NO in Epo activity in brain and suggest links between NO production, EpoR expression, and Epo signaling in neuroprotection.

Regulation of endothelial nitric oxide synthase by agmatine after transient global cerebral ischemia in rat brain

Nitric oxide (NO) production by endothelial nitric oxide synthase (eNOS) plays a protective role in cerebral ischemia by maintaining vascular permeability, whereas NO derived from neuronal and inducible NOS is neurotoxic and can participate in neuronal damage occurring in ischemia. Matrix metalloproteinases (MMPs) are up-regulated by ischemic injury and degrade the basement membrane if brain vessels to promote cell death and tissue injury. We previously reported that agmatine, synthesized from L-arginine by arginine decarboxylase (ADC) which is expressed in endothelial cells, has shown a direct increased eNOS expression and decreased MMPs expression in bEnd3 cells. But, there are few reports about the regulation of eNOS by agmatine in ischemic animal model. In the present study, we examined the expression of eNOS and MMPs by agmatine treatment after transient global ischemia in vivo. Global ischemia was induced with four vessel occlusion (4-VO) and agmatine (100 mg/kg) was administered intraperitoneally at the onset of reperfusion. The animals were euthanized at 6 and 24 hours after global ischemia and prepared for other analysis. Global ischemia led severe neuronal damage in the rat hippocampus and cerebral cortex, but agmatine treatment protected neurons from ischemic injury. Moreover, the level and expression of eNOS was increased by agmatine treatment, whereas inducible NOS (iNOS) and MMP-9 protein expressions were decreased in the brain. These results suggest that agmatine protects microvessels in the brain by activation eNOS as well as reduces extracellular matrix degradation during the early phase of ischemic insult.

Regulation of endothelial nitric oxide synthase by agmatine after transient global cerebral ischemia in rat brain

Nitric oxide (NO) production by endothelial nitric oxide synthase (eNOS) plays a protective role in cerebral ischemia by maintaining vascular permeability, whereas NO derived from neuronal and inducible NOS is neurotoxic and can participate in neuronal damage occurring in ischemia. Matrix metalloproteinases (MMPs) are up-regulated by ischemic injury and degrade the basement membrane if brain vessels to promote cell death and tissue injury. We previously reported that agmatine, synthesized from L-arginine by arginine decarboxylase (ADC) which is expressed in endothelial cells, has shown a direct increased eNOS expression and decreased MMPs expression in bEnd3 cells. But, there are few reports about the regulation of eNOS by agmatine in ischemic animal model. In the present study, we examined the expression of eNOS and MMPs by agmatine treatment after transient global ischemia in vivo. Global ischemia was induced with four vessel occlusion (4-VO) and agmatine (100 mg/kg) was administered intraperitoneally at the onset of reperfusion. The animals were euthanized at 6 and 24 hours after global ischemia and prepared for other analysis. Global ischemia led severe neuronal damage in the rat hippocampus and cerebral cortex, but agmatine treatment protected neurons from ischemic injury. Moreover, the level and expression of eNOS was increased by agmatine treatment, whereas inducible NOS (iNOS) and MMP-9 protein expressions were decreased in the brain. These results suggest that agmatine protects microvessels in the brain by activation eNOS as well as reduces extracellular matrix degradation during the early phase of ischemic insult.

Protein modifications involved in neurotransmitter and gasotransmitter signaling

Covalent modifications of intracellular proteins, such as phosphorylation, are generally thought to occur as secondary or tertiary responses to neurotransmitters, following the intermediation of membrane receptors and second messengers such as cyclic AMP. By contrast, the gasotransmitter nitric oxide directly S-nitrosylates cysteine residues in diverse intracellular proteins. Recently, hydrogen sulfide has been acknowledged as a gasotransmitter, which analogously sulfhydrates cysteine residues in proteins. Cysteine residues are also modified by palmitoylation in response to neurotransmitter signaling, possibly in reciprocity with S-nitrosylation. Neurotransmission also elicits sumoylation and acetylation of lysine residues within diverse proteins. This review addresses how these recently appreciated protein modifications impact our thinking about ways in which neurotransmission regulates intracellular protein disposition.

NMDA-induced neuronal survival is mediated through nuclear factor I-A in mice

Identification of the signaling pathways that mediate neuronal survival signaling could lead to new therapeutic targets for neurologic disorders and stroke. Sublethal doses of NMDA can induce robust endogenous protective mechanisms in neurons. Through differential analysis of primary library expression and microarray analyses, here we have shown that nuclear factor I, subtype A (NFI-A), a member of the NFI/CAAT-box transcription factor family, is induced in mouse neurons by NMDA receptor activation in a NOS- and ERK-dependent manner. Knockdown of NFI-A induction using siRNA substantially reduced the neuroprotective effects of sublethal doses of NMDA. Further analysis indicated that NFI-A transcriptional activity was required for the neuroprotective effects of NMDA receptor activation. Additional evidence of the neuroprotective effects of NFI-A was provided by the observations that Nfia(-/-) neurons were highly sensitive to NMDA-induced excitotoxicity and were more susceptible to developmental cell death than wild-type neurons and that Nfia(+/-) mice were more sensitive to NMDA-induced intrastriatal lesions than were wild-type animals. These results identify NFI-A as what we believe to be a novel neuroprotective transcription factor with implications in neuroprotection and neuronal plasticity following NMDA receptor activation.

Methods for studying redox cycling of thioredoxin in mediating preconditioning-induced survival genes and proteins

Recent advances in molecular biology provide methods and tools for studying cell signaling pathways underlying hormetic mechanisms produced by radiation hormesis, ischemic, remote ischemic, and chemical preconditioning as well as withholding of nutrients and/or trophic factors. Most of the proposed key signaling pathways of hormetic mechanisms remain to be elucidated. For the investigation of possible role of thiol redox signaling systems in hormesis, a serum deprivation preconditioned human cell model, free radical assays, and molecular biological methods are employed for studying whether free radicals, the NO-cGMP-PKG cell signaling pathway, and the redox protein thioredoxin (Trx) play any roles in the hormetic mechanism against cytotoxicity caused by serum deprivation and also neurotoxin 1-methyl-4-phenyltetrahydropyridinium ion (MPP(+)). This NO-dependent cell signaling pathway of the redox protein Trx may play a key role in the cellular protective mechanism of several potential neuroprotective agents such as S-nitrosoglutathione (GSNO), 17beta-estradiol, selegiline as well as ebeselen, sildenafil, and rasagiline. Consistently, exogenously administrated Trx (<1 microM) provides a concentration-dependent protection for human neuroblasts against MPP(+)-induced oxidative injury. This newly discovered role of the redox protein of Trx in preconditioning-induced cell signaling and protection could lead to the development of new lead compounds for upregulation of Trx and related thiol redox proteins for cell survival, repair, proliferation, and neuronal plasticity.

The Akt-endothelial nitric oxide synthase pathway in lipopolysaccharide preconditioning-induced hypoxic-ischemic tolerance in the neonatal rat brain

BACKGROUND AND PURPOSE

Low-dose lipopolysaccharide (LPS) preconditioning provides neonatal rats long-term neuroprotection against hypoxic ischemia (HI). Upregulating endothelial nitric oxide synthase (eNOS) protects against cerebral ischemia; however, whether eNOS is required for LPS preconditioning-induced protection in neonatal rats is unknown. We hypothesized that Akt activation, which upregulates eNOS in neurons and endothelial cells, is required for LPS preconditioning-induced tolerance against HI in the neonatal brain.

METHODS

Six-day-old rat pups were intraperitoneally injected with LPS (0.05 mg/kg) or normal saline 24 hours before HI. Immunoblotting and immunohistochemistry were used to determine the phospho-Akt (pAkt Ser473), phospho-eNOS (peNOS Ser1177), and eNOS levels and immunofluorescence to determine the cellular distribution of eNOS and pAkt Ser473. Pharmacological and genetic approaches were used to regulate Akt and eNOS, and the weight loss of cerebral hemispheres on postnatal Day 21 was used to assess outcomes.

RESULTS

eNOS, peNOS (Ser1177), and pAkt (Ser473) levels were significantly higher in LPS- than in normal saline-treated rats 24 hours postinjection. LPS-induced eNOS was expressed primarily in neurons and vascular endothelial cells. N-omega(omega)-nitro-L-arginine and antisense oligodeoxynucleotide treatment significantly reduced eNOS expression in neurons and endothelial cells and inhibited LPS-induced protection against HI in rat pups. L-arginine and adenovirus eNOS transfection upregulated eNOS and protected the rat pups against HI. Wortmannin treatment before LPS preconditioning significantly reduced eNOS expression in neurons and endothelial cells, which inhibited LPS-induced protection against HI.

CONCLUSIONS

Akt-mediated eNOS upregulation in neurons and vascular endothelial cells is required for LPS-induced tolerance against HI in the neonatal rat brain.

Preconditioning-induced ischemic tolerance: a window into endogenous gearing for cerebroprotection

Ischemic tolerance defines transient resistance to lethal ischemia gained by a prior sublethal noxious stimulus (i.e., preconditioning). This adaptive response is thought to be an evolutionarily conserved defense mechanism, observed in a wide variety of species. Preconditioning confers ischemic tolerance if not in all, in most organ systems, including the heart, kidney, liver, and small intestine. Since the first landmark experimental demonstration of ischemic tolerance in the gerbil brain in early 1990's, basic scientific knowledge on the mechanisms of cerebral ischemic tolerance increased substantially. Various noxious stimuli can precondition the brain, presumably through a common mechanism, genomic reprogramming. Ischemic tolerance occurs in two temporally distinct windows. Early tolerance can be achieved within minutes, but wanes also rapidly, within hours. Delayed tolerance develops in hours and lasts for days. The main mechanism involved in early tolerance is adaptation of membrane receptors, whereas gene activation with subsequent de novo protein synthesis dominates delayed tolerance. Ischemic preconditioning is associated with robust cerebroprotection in animals. In humans, transient ischemic attacks may be the clinical correlate of preconditioning leading to ischemic tolerance. Mimicking the mechanisms of this unique endogenous protection process is therefore a potential strategy for stroke prevention. Perhaps new remedies for stroke are very close, right in our cells.

Hyperbaric oxygen preconditioning attenuates early apoptosis after spinal cord ischemia in rats

This study tested the hypothesis that spinal cord ischemic tolerance induced by hyperbaric oxygen preconditioning (HBO-PC) is mediated by inhibition of early apoptosis. Male Sprague-Dawley rats were preconditioned with consecutive 4 cycles of 1-h HBO exposures (2.5 atmospheres absolute [ATA], 100% O(2)) at a 12-h interval. At 24 h after the last HBO pretreatment, rats underwent 9 min of spinal cord ischemia induced by occlusion of the descending thoracic aorta in combination with systemic hypotension (40 mmHg). Spinal cord ischemia produced marked neuronal death and neurological dysfunction in animals. HBO-PC enhanced activities of Mn-superoxide dismutase (Mn-SOD) and catalase, as well as the expression of Bcl-2 in the mitochondria in the normal spinal cord at 24 h after the last pretreatment (before spinal cord ischemia), and retained higher levels throughout the early reperfusion in the ischemic spinal cord. In parallel, superoxide and hydrogen peroxide levels in mitochondria were decreased, cytochrome c release into the cytosol was reduced at 1 h after reperfusion, and activation of caspase-3 and -9 was subsequently attenuated. HBO-PC improved neurobehavioral scores and reduced neuronal apoptosis in the anterior, intermediate, and dorsal gray matter of lumbar segment at 24 h after spinal cord ischemia. HBO-PC increased nitric oxide (NO) production. L-nitroarginine-methyl-ester (L-NAME; 10 mg/kg), a nonselective NO synthase (NOS) inhibitor, applied before each HBO-PC protocol abolished these beneficial effects of HBO-PC. We conclude that HBO-PC reduced spinal cord ischemia-reperfusion injury by increasing Mn-SOD, catalase, and Bcl-2, and by suppressing mitochondrial apoptosis pathway. NO may be involved in this neuroprotection.

Neuroprotective effect of volatile anesthetic agents: molecular mechanisms

INTRODUCTION

Intra-operative cerebral ischemia can be catastrophic, and volatile anesthetic agents have been recognized for their potential neuroprotective properties since the 1960s. In this review, we examine the neuroprotective effects of five volatile anesthetic agents in current or recent clinical use: isoflurane, sevoflurane, desflurane, halothane and enflurane.

METHODS

A review of publications in the National Library of Medicine and National Institutes of Health database from 1970 to 2007 was conducted.

RESULTS

Volatile anesthetic agents have been shown to be neuroprotective in multiple animal works of ischemic brain injury. Short-term neuroprotection (<1 week post-ischemia) in experimental cerebral ischemia has been reported in multiple works, although long-term neuroprotection (> or = 1 week post-ischemia) remains controversial. Comparison works have not demonstrated superiority of one specific volatile agent over another in experimental models of brain injury. Relatively few human works have examined the protective effects of volatile anesthetic agents and conclusive evidence of a neuroprotective effect has yet to emerge from human works.

CONCLUSION

Proposed mechanisms related to the neuroprotective effect of volatile anesthetic agents include activation of ATP-dependent potassium channels, up-regulation of nitric oxide synthase, reduction of excitotoxic stressors and cerebral metabolic rate, augmentation of peri-ischemic cerebral blood flow and up-regulation of antiapoptotic factors including MAP kinases.

Inositol 1,4,5-triphosphate receptors and NAD(P)H mediate Ca2+ signaling required for hypoxic preconditioning of hippocampal neurons

Exposure of neurons to a non-lethal hypoxic stress greatly reduces cell death during subsequent severe ischemia (hypoxic preconditioning, HPC). In organotypic cultures of rat hippocampus, we demonstrate that HPC requires inositol triphosphate (IP3) receptor-dependent Ca2+ release from the endoplasmic reticulum (ER) triggered by increased cytosolic NAD(P)H. Ca2+ chelation with intracellular BAPTA, ER Ca2+ store depletion with thapsigargin, IP3 receptor block with xestospongin, and RNA interference against subtype 1 of the IP3 receptor all blunted the moderate increases in [Ca2+](i) (50-100 nM) required for tolerance induction. Increases in [Ca2+](i) during HPC and neuroprotection following HPC were not prevented with NMDA receptor block or by removing Ca2+ from the bathing medium. Increased NAD(P)H fluorescence in CA1 neurons during hypoxia and demonstration that NADH manipulation increases [Ca2+](i) in an IP3R-dependent manner revealed a primary role of cellular redox state in liberation of Ca2+ from the ER. Blockade of IP3Rs and intracellular Ca2+ chelation prevented phosphorylation of known HPC signaling targets, including MAPK p42/44 (ERK), protein kinase B (Akt) and CREB. We conclude that the endoplasmic reticulum, acting via redox/NADH-dependent intracellular Ca2+ store release, is an important mediator of the neuroprotective response to hypoxic stress.

Hormesis and disease resistance: activation of cellular stress response pathways

The survival of all organisms depends upon their ability to overcome stressful conditions, an ability that involves adaptive changes in cells and molecules. Findings from studies of animal models and human populations suggest that hormesis (beneficial effects of low levels of stress) is an effective means of protecting against many different diseases including diabetes, cardiovascular disease, cancers and neurodegenerative disorders. Such stress resistance mechanisms can be bolstered by diverse environmental factors including exercise, dietary restriction, cognitive stimulation and exposure to low levels of toxins. Some commonly used vitamins and dietary supplements may also induce beneficial stress responses. Several interrelated cellular signaling molecules are involved in the process of hormesis. Examples include the gases oxygen, carbon monoxide and nitric oxide, the neurotransmitter glutamate, the calcium ion and tumor necrosis factor. In each case low levels of these signaling molecules are beneficial and protect against disease, whereas high levels can cause the dysfunction and/or death of cells. The cellular and molecular mechanisms of hormesis are being revealed and include activation of growth factor signaling pathways, protein chaperones, cell survival genes and enzymes called sirtuins. Knowledge of hormesis mechanisms is leading to novel approaches for preventing and treating a range of human diseases.

Expression and activity of heme oxygenase-1 in artificially induced low-flow priapism in rat penile tissues

INTRODUCTION

The inducible isoform of heme oxygenase (HO)-1 regulates the vascular smooth muscle tone and responds to hypoxia.

AIM

To investigate the role of HO-1 in a low-flow priapism.

MATERIALS AND METHODS

Sixty male Sprague-Dawley rats were divided into five groups of six rats each. Each group of rats was sacrificed at 0 hour (group 1, control), 4 hours (group 2), 8 hours (group 3), 12 hours (group 4), and 24 hours (group 5) after inducing an artificial veno-occlusive priapism. The changes of the expression and activity of HO-1, and the expression of inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS), and levels of cyclic guanosine monophosphate in the penis were examined in a low-flow priapism. In addition, the HO-1 expression level in the aortas from each group was simultaneously measured to determine whether the changes in HO-1 were systemic.

MAIN OUTCOME MEASURES

The expression and activity of HO-1 was examined in artificially induced veno-occlusive priapism in rat penile tissues.

RESULTS

The expression of the HO-1 protein and the HO-1 enzyme activities in the penile tissues were gradually increased as time increased from 0 to 24 hours (P < 0.01). HO-1 immunoreactivities were localized in the endothelial layer of the cavernosal sinusoids. The expression of iNOS were also increased at 12 and 24 hours. The cyclic guanosine monophosphate level was also significantly increased at 24 hours (P < 0.05). However, the expression of the eNOS protein showed no statistically significant change with time, and the expression of the HO-1 protein in the aorta also showed no significant change with time.

CONCLUSIONS

A higher induction of HO-1 with time was observed in artificially induced veno-occlusive priapism, which might play a protective role against hypoxic injury. However, this may also play an important role in the vicious circle observed in a low-flow priapism.

Endogenous neuroprotection: mitochondria as gateways to cerebral preconditioning?

From single to multicellular organisms, protective mechanisms have evolved against endogenous and exogenous noxious stimuli. Preconditioning paradigms, in which stimulation below the threshold of injury results in subsequent protection of the brain, have played an important role in elucidating such endogenous protective mechanisms. Consequently, over the past decades numerous signaling pathways have been discovered by which the brain senses and reacts to such insults as neurotoxins, substrate deprivation, or inflammation. Research on preconditioning is aimed at understanding endogenous neuroprotection to boost it, or to supplement its effectors therapeutically once damage to the brain has occurred, such as after stroke or brain trauma. Another goal of establishing preconditioning protocols is to induce endogenous neuroprotection in anticipation of incipient brain damage. Currently several endogenous neuroprotectants are being investigated in controlled clinical trials. In the present review we will give a short overview on the signals, sensors, transducers, and effectors of endogenous neuroprotection. We will first focus on common mechanisms, on which pathways of endogenous neuroprotection converge, and in particular on mitochondria, which may be considered master integrators of endogenous neuroprotection. We will then discuss various applications of preconditioning, including pharmacological and anesthetic preconditioning, as well as postconditioning, and explore the prospects of endogenous neuroprotective therapeutic approaches.