Activation of phosphatidylinositol 3-kinase/protein kinase B pathway by a vanadyl compound mediates its neuroprotective effect in mouse brain ischemia

The promotive effect of activation of the Akt/mTOR/p70S6K signaling pathway in oligodendrocytes on nerve myelin regeneration in rats with spinal cord injury

PURPOSE

Akt/mTOR/p70S6K signaling pathway promotes motor function recovery after spinal cord injury (SCI) in both neurons and astrocytes. But the role and mechanism of this pathway in oligodendrocytes during nerve repair following SCI has not been researched. This study aimed to investigate the effect and mechanism of this signaling pathway in oligodendrocytes on nerve myelin regeneration and motor function recovery in rats with SCI.

METHODS

After inhibiting or activating this signaling pathway, Western blotting and double immunofluorescence labeling were used to determine the levels of the signaling molecules in this pathway and myelin formation-related proteins in the plane of the thoracic segment of the injured spinal cord. The level of motor function recovery was evaluated and the oligodendrocytes involved in nerve myelin regeneration were studied. Primary oligodendrocytes were isolated and cultured in vitro, then MBP, PLP, and MOG were measured with reverse transcription-quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Akt/mTOR/p70S6K signaling pathway was activated after SCI compared with the sham-operated rats, prominently elevated levels of the pathway components were observed in the SC79-treated group. The activation of the signaling pathway significantly increased the expression levels of myelin formation-related proteins, including MBP, PLP, and MOG, and improved the Basso, Beattie, and Bresnahan (BBB) scores in the injured spinal cord. Conversely, rapamycin suppressed the expression of these signaling molecules and reduced the levels of myelin formation-related proteins.

CONCLUSION

Akt/mTOR/p70S6K signaling pathway activation can contribute to nerve myelin regeneration and has the potential to improve the regenerative environment and motor function, as well as the potential to promote repair of SCI.

Ultrastructural alterations due to sodium metavanadate treatment in the blood stages of Plasmodium yoelii yoelii

Malaria is a potentially mortal disease caused by parasites of the genus Plasmodium spp. It has a wide distribution in the world and unfortunately there are several factors that make its control difficult; among which the development of pharmacological resistance to the different drugs used to treat this disease stands out, which makes it necessary to design new compounds that have an antimalarial effect. Previous studies have shown that vanadium has a broad antiparasitic spectrum and is also safe for the host, so the objective of this research was to evaluate the antimalarial potential of sodium metavanadate (SM) and to analyze the ultrastructural changes in parasites exposed. The method consisted of inoculating CD-1 male mice with Plasmodium yoelii yoelii and administering a 10 mg/kg/day dose of SM orally for 4 days. On the fifth day, whole blood samples were obtained, processed for ultrastructural analysis, and the changes in the different parasite stages were compared against the control. Our results showed that SM decreased parasitemia compared to the group that did not receive treatment and modified the ultrastructure in all parasitic stages because it damaged the membranes, causing alterations mainly in the nucleus and in the mitochondria as well as the loss of cellular organization, which could affect the integrity of these parasites and decrease its viability.

The role of autophagy and apoptosis in early brain injury after subarachnoid hemorrhage: an updated review

Subarachnoid hemorrhage (SAH) is a worldwide devastating type of stroke with high mortality and morbidity. Accumulating evidence show early brain injury (EBI) as the leading cause of mortality after SAH. The pathological processes involved in EBI include decreased cerebral blood flow, increased intracranial pressure, vasospasm, and disruption of the blood-brain barrier. In addition, neuroinflammation, oxidative stress, apoptosis, and autophagy have also been proposed to contribute to EBI. Among the various processes involved in EBI, neuronal apoptosis has been proven to be a key factor contributing to the poor prognosis of SAH patients. Meanwhile, as another important catabolic process maintaining the cellular and tissue homeostasis, autophagy has been shown to be neuroprotective after SAH. Studies have shown that enhancing autophagy reduced apoptosis, whereas inhibiting autophagy aggravate neuronal apoptosis after SAH. The physiological substrates and mechanisms of neuronal autophagy and apoptosis by which defects in neuronal function are largely unknown. In this review, we summarize and discuss the role of autophagy and apoptosis after SAH and contribute to further study for investigation of the means to control the balance between them.

Dysregulation of mTOR Signaling after Brain Ischemia

In this review, we provide recent data on the role of mTOR kinase in the brain under physiological conditions and after damage, with a particular focus on cerebral ischemia. We cover the upstream and downstream pathways that regulate the activation state of mTOR complexes. Furthermore, we summarize recent advances in our understanding of mTORC1 and mTORC2 status in ischemia–hypoxia at tissue and cellular levels and analyze the existing evidence related to two types of neural cells, namely glia and neurons. Finally, we discuss the potential use of mTORC1 and mTORC2 as therapeutic targets after stroke.

The impact of concomitant administration of vanadium and insulin on endothelial dysfunction markers (PAI-1 and ET-1) in type 1 diabetic rats

Endothelial dysfunction in type 1 diabetes mellitus (T1DM) is an important factor in the pathogenesis of micro- and macrovascular complications. The present study was to investigate the impact of combined vanadium and insulin for proper control and protection against endothelial dysfunction in T1DM rats. Sixty male Sprague-Dawley rats were randomly divided into six groups; control non-treated; control vanadium treated; T1DM; T1DM + insulin; T1DM + vanadium; T1DM + insulin + vanadium treated groups. At the end of the experiment (6 weeks), serum C-reactive protein, tumour necrosis factor-alpha, IL-6, endothelin-1, plasminogen activator inhibitor-1, fasting glucose serum lipogram, liver homogenate SOD activity and MDA levels were determined. Concomitant insulin and vanadium treatment improved the diabetic metabolic disturbances in addition to endothelial dysfunction and inflammatory markers. We can conclude that concomitant administration of both vanadium and insulin in T1DM decreased the risk for the development of endothelial dysfunction, micro- and macrovascular complications.

Effects of Akt/mTOR/p70S6K Signaling Pathway Regulation on Neuron Remodeling Caused by Translocation Repair

Peripheral nerve injury repair has been considered a difficult problem in the field of trauma for a long time. Conventional surgical methods are not applicable in some special types of nerve injury, prompting scholars to seek to develop more effective nerve translocation repair technologies. The purpose of this study was to explore the functional state of neurons in injured lower limbs after translocation repair, with a view to preliminarily clarify the molecular mechanisms underlying this process. Eighteen Sprague–Dawley rats were divided into the normal, tibial nerve in situ repair, and common peroneal nerve transposition repair tibial nerve groups. Nerve function assessment and immunohistochemical staining of neurofilament 200 (NF-200), protein kinase B (Akt), mammalian target of rapamycin (mTOR), and ribosomal protein S6 kinase (p70S6K) in the dorsal root ganglia were performed at 12 weeks after surgery. Tibial nerve function and neuroelectrophysiological analysis, osmic acid staining, muscle strength testing, and muscle fiber staining showed that the nerve translocation repair could restore the function of the recipient nerve to a certain extent; however, the repair was not as efficient as the in situ repair. Immunohistochemical staining showed that the translocation repair resulted in changes in the microstructure of neuronal cell bodies, and the expressions of Akt, mTOR, and p70S6K in the three dorsal root ganglia groups were significantly different (p < 0.05). This study demonstrates that the nerve translocation repair technology sets up a new reflex loop, with the corresponding neuroskeletal adjustments, in which, donor neurons dominate the recipient nerves. This indicates that nerve translocation repair technology can lead to neuronal remodeling and is important as a supplementary treatment for a peripheral nerve injury. Furthermore, the Akt/mTOR/p70S6K signaling pathway may be involved in the formation of the new neural reflex loop created as a result of the translocation repair.

Vanadium: Risks and possible benefits in the light of a comprehensive overview of its pharmacotoxicological mechanisms and multi-applications with a summary of further research trends

BACKGROUND

Vanadium (V) is an element with a wide range of effects on the mammalian organism. The ability of this metal to form organometallic compounds has contributed to the increase in the number of studies on the multidirectional biological activity of its various organic complexes in view of their application in medicine.

OBJECTIVE

This review aims at summarizing the current state of knowledge of the pharmacological potential of V and the mechanisms underlying its anti-viral, anti-bacterial, anti-parasitic, anti-fungal, anti-cancer, anti-diabetic, anti-hypercholesterolemic, cardioprotective, and neuroprotective activity as well as the mechanisms of appetite regulation related to the possibility of using this element in the treatment of obesity. The toxicological potential of V and the mechanisms of its toxic action, which have not been sufficiently recognized yet, as well as key information about the essentiality of this metal, its physiological role, and metabolism with certain aspects on the timeline is collected as well. The report also aims to review the use of V in the implantology and industrial sectors emphasizing the human health hazard as well as collect data on the directions of further research on V and its interactions with Mg along with their character.

RESULTS AND CONCLUSIONS

Multidirectional studies on V have shown that further analyses are still required for this element to be used as a metallodrug in the fight against certain life-threatening diseases. Studies on interactions of V with Mg, which showed that both elements are able to modulate the response in an interactive manner are needed as well, as the results of such investigations may help not only in recognizing new markers of V toxicity and clarify the underlying interactive mechanism between them, thus improving the medical application of the metals against modern-age diseases, but also they may help in development of principles of effective protection of humans against environmental/occupational V exposure.

Bis(ethylmaltolato)oxidovanadium(iv) inhibited the pathogenesis of Alzheimer's disease in triple transgenic model mice

Vanadium compounds have been reported to mimic the anti-diabetes effects of insulin on rodent models, but their effects on Alzheimer's disease (AD) have rarely been explored. In this paper, 9-month-old triple transgenic AD model mice (3×Tg-AD) received bis(ethylmaltolato)oxidovanadium(iv) (BEOV) at doses of 0.2 mmol L^-1 (68.4 μg mL^-1) and 1.0 mmol L^-1 (342 μg mL^-1) for 3 months. BEOV at both doses was found to improve contextual memory and spatial learning in AD mice. It also improved glucose metabolism and protected neuronal synapses in the AD brain, as evidenced respectively by ¹⁸F-labeled fluoro-deoxyglucose positron emission tomography (¹⁸F-FDG-PET) scanning and by transmission electron microscopy. Inhibitory effects of BEOV on β-amyloid (Aβ) plaques and neuronal impairment in the cortex and hippocampus of fluorescent AD mice were visualized three-dimensionally by applying optical clearing technology to brain slices before confocal laser scanning microscopy. Western blot analysis semi-quantitatively revealed the altered levels of Aβ₄₂ in the brains of wildtype, AD, and AD treated with 0.2 and 1.0 mmol L^-1 BEOV mice (70.3%, 100%, 83.2% and 56.8% in the hippocampus; 82.4%, 100%, 66.9% and 42% in the cortex, respectively). The mechanism study showed that BEOV increased the expression of peroxisome proliferator-activated receptor γ (PPARγ) (140%, 100%, 142% and 160% in the hippocampus; 167%, 100%, 124% and 133% in the cortex) to inactivate the JAK2/STAT3/SOCS-1 pathway and to block the amyloidogenesis cascade, thus attenuating Aβ-induced insulin resistance in AD models. BEOV also reduced protein tyrosine phosphatase 1B (PTP1B) expression (74.8%, 100%, 76.5% and 53.8% in the hippocampus; 71.8%, 100%, 94.2% and 81.8% in cortex) to promote insulin sensitivity and to stimulate the PI3K/Akt/GSK3β pathway, subsequently reducing tau hyperphosphorylation (phosphorylated tau396 levels were 51.1%, 100%, 56.1% and 50.2% in the hippocampus; 22.2%, 100%, 36.1%, and 24% in the cortex). Our results suggested that BEOV reduced the pathological hallmarks of AD by targeting the pathways of PPARγ and PTP1B in 3×Tg AD mice.

Physicochemical-property guided design of a highly sensitive probe to image nitrosative stress in the pathology of stroke

In vivo real-time imaging of nitrosative stress in the pathology of stroke has long been a formidable challenge due to both the presence of the blood–brain barrier (BBB) and the elusive nature of reactive nitrogen species, while this task is also informative to gain a molecular level understanding of neurovascular injury caused by nitrosative stress during the stroke episode. Herein, using a physicochemical property-guided probe design strategy in combination with the reaction-based probe design rationale, we have developed an ultrasensitive probe for imaging nitrosative stress evolved in the pathology of stroke. This probe demonstrates an almost zero background fluorescence signal but a maximum 1000-fold fluorescence enhancement in response to peroxynitrite, the nitrosative stress marker. Due to its good physicochemical properties, the probe readily penetrates the BBB after intravenous administration, and quickly accumulates in mice brain to sense local vascular injuries. After accomplishing its imaging mission, the probe is easily metabolized and therefore won't cause safety concerns. These desirable features make the probe competent for the straightforward visualization of nitrosative stress progression in stroke pathology.

A brain–blood barrier permeable probe was developed for fluorogenically sensing nitrosative stress caused by brain vascular injury.

Copaiba Oil Attenuates Right Ventricular Remodeling by Decreasing Myocardial Apoptotic Signaling in Monocrotaline-Induced Rats

There is an increase in oxidative stress and apoptosis signaling during the transition from hypertrophy to right ventricular (RV) failure caused by pulmonary arterial hypertension (PAH) induced by monocrotaline (MCT). In this study, it was evaluated the action of copaiba oil on the modulation of proteins involved in RV apoptosis signaling in rats with PAH. Male Wistar rats (±170 g, n = 7/group) were divided into 4 groups: control, MCT, copaiba oil, and MCT + copaiba oil. PAH was induced by MCT (60 mg/kg intraperitoneally) and, 7 days later, treatment with copaiba oil (400 mg/kg by gavage) was given for 14 days. Echocardiographic and hemodynamic measurements were performed, and the RV was collected for morphometric evaluations, oxidative stress, apoptosis, and cell survival signaling, and eNOS protein expression. Copaiba oil reduced RV hypertrophy (24%), improved RV systolic function, and reduced RV end-diastolic pressure, increased total sulfhydryl levels and eNOS protein expression, reduced lipid and protein oxidation, and the expression of proteins involved in apoptosis signaling in the RV of MCT + copaiba oil as compared to MCT group. In conclusion, copaiba oil reduced oxidative stress, and apoptosis signaling in RV of rats with PAH, which may be associated with an improvement in cardiac function caused by this compound.

Neuroprotective effects of a protein tyrosine phosphatase inhibitor against hippocampal excitotoxic injury

Neuronal excitotoxicity is the neuronal cell death arising from prolonged exposure to glutamate and the associated excessive influx of ions into the cell. Sodium orthovanadate (Na₃VO₄,) competitively inhibits the protein tyrosine phosphatases that affect intracellular protein phosphorylation. No study has examined the role of protein tyrosine phosphatases in kainic acid (KA)-induced excitotoxic injury using sodium orthovanadate. Thus, the present study was conducted to determine the neuroprotective effects of sodium orthovanadate on KA-induced neuronal death in organotypic hippocampal slice culture. We also performed an in vivo electrophysiology study in Sprague-Dawley rats to observe the function of surviving cells after sodium orthovanadate treatment in KA-induced excitotoxicity. Rats were anaesthetized with sodium pentobarbital and KA was injected unilaterally in CA3 of the hippocampus by microinjection-cannula. Neuronal cell death, as assessed by propidium iodide uptake, was reduced by 10 and 25 μM sodium orthovanadate treatment (24 and 48 h) compared with the KA-only group. Sodium orthovanadate enhanced survival signals by increasing levels of phospho-Akt and superoxide dismutase. In addition, sodium orthovanadate treatment reduced calcineurin level for neuronal protection, which regulates activation of cellular calcium caused by KA-induced injury. In vivo results showed that sodium orthovanadate treatment elicited resistance to KA-induced behavior seizures and significantly reduced the duration of epileptiform discharges. In addition, sodium orthovanadate treatment (25 mM) significantly prevented the increase in power spectra induced by KA injection. These results suggest that sodium orthovanadate decreases the acute effects of KA, thereby inducing neuroprotective effects with reduced reactive oxygen species and cellular Ca²⁺. Thus, sodium orthovanadate may protect hippocampal neurons against excitotoxicity, and surviving neurons may function to reduce seizures.

FoxO3 transcription factor promotes autophagy after transient cerebral ischemia/reperfusion

Aim: Autophagy was activated after cerebral ischemia reperfusion (I/R) injury. However, the molecular mechanisms underlying regulation of autophagy in cerebral I/R injury were not completely understood. Studies reported that Forked-box class O (FoxO) transcription factors involved in autophagy and might be the regulator of autophagy in multiple cells. In this study, we investigated the effects of FoxO3 on regulating autophagy after cerebral I/R injury. Materials and methods: Rats were subjected to MCAO for 2 h and reperfusion for different times, western blot was used to examine the expression of p-FoxO3, FoxO3 and the autophagic marker LC3 and Beclin-1 in penumbral region. Then rats were injected with WT-FoxO3 or TM-FoxO3 adenovirus by lateral cerebral ventricle to increase the function of FoxO3, western blot was used to examine the expression of LC3 and Beclin-1 in penumbral region. TTC and HE staining were used to evaluate the effects of increased FoxO3 activation on I/R induced brain damage. Results: Our studies showed that I/R injury resulted in induction of autophagy in penumbral brain tissue with concomitant dephosphorylation of FoxO3, consistent with increased activity of nuclear FoxO3 transcription factor. Increased FoxO3 activation led to autophagy significantly increased and had a protective effects on I/R injury. Conclusion: These data revealed an important role of FoxO3 in regulating autophagy in brain, and provided a new approach for further prevention and treatment of cerebral ischemia.

DFT study on the redox behavior of two dioxovanadium(v) complexes with N2O donor Schiff base ligands and their use in catalytic oxidation ofortho-aminophenol

Solution phase redox behavior of two vanadium(v) Schiff base complexes was checked. The results agree well with DFT calculations. Both complexes exhibited good catalytic efficiency for the conversion ofo-aminophenol to 2-aminophenoxazine-3-one.

Neuroprotective effects of protein tyrosine phosphatase 1B inhibitor on cerebral ischemia/reperfusion in mice

Akt (Protein kinase B, PKB), a serine/threonine kinase, plays a critical role in cell development, growth, and survival. Akt phosphorylation mediates a neuroprotective effect against ischemic injury. Recently, a protein-tyrosine phosphatase-1B (PTP1B) inhibitor (KY-226) was developed to elicit anti-diabetic and anti-obesity effects via enhancement of insulin signaling. Previously, we reported that the nonselective PTP1B inhibitor, sodium orthovanadate, rescued neurons from delayed neuronal death during brain ischemia. In this study, we confirmed the ameliorative effects of KY-226 on ischemia/reperfusion (I/R) injury using a murine model of middle cerebral artery occlusion (MCAO). ICR mice were subjected to MCAO for 2 h followed by reperfusion. Although KY-226 permeability was poor through the blood-brain barrier (BBB) of normal mice, it could penetrate through the BBB of mice after I/R insult. Intraperitoneal KY-226 administration elicited dose-dependent reductions in infarcted brain areas and improved neurological deficits. The neuroprotective effects of KY-266 were obtained when administered within 0.5 h after reperfusion. KY-226 (10 mg/kg) also restored reduced Akt phosphorylation and eNOS phosphorylation (Ser-1177) levels following I/R insult. Moreover, 10 mg/kg of KY-226 improved I/R-induced decreased extracellular signal-regulated kinase (ERK) phosphorylation. Furthermore, KY-226 attenuated the generation of reactive oxygen species (ROS) in mouse cortex. These results suggest that KY-226 may act as a novel therapeutic candidate for ischemic stroke. Activation of Akt and ERK possibly underlie the neuroprotective mechanism of KY-226.

CoQ10 Augments Rosuvastatin Neuroprotective Effect in a Model of Global Ischemia via Inhibition of NF-κB/JNK3/Bax and Activation of Akt/FOXO3A/Bim Cues

Statins were reported to lower the Coenzyme Q10 (CoQ10) content upon their inhibition of HMG-CoA reductase enzyme and both are known to possess neuroprotective potentials; therefore, the aim is to assess the possible use of CoQ10 as an adds-on therapy to rosuvastatin to improve its effect using global I/R model. Rats were allocated into sham, I/R, rosuvastatin (10 mg/kg), CoQ10 (10 mg/kg) and their combination. Drugs were administered orally for 7 days before I/R. Pretreatment with rosuvastatin and/or CoQ10 inhibited the hippocampal content of malondialdehyde, nitric oxide, and boosted glutathione and superoxide dismutase. They also opposed the upregulation of gp91^phox, and p47^phox subunits of NADPH oxidase. Meanwhile, both agents reduced content/expression of TNF-α, iNOS, NF-κBp65, ICAM-1, and MPO. Besides, all regimens abated cytochrome c, caspase-3 and Bax, but increased Bcl-2 in favor of cell survival. On the molecular level, they increased p-Akt and its downstream target p-FOXO3A, with the inhibition of the nuclear content of FOXO3A to downregulate the expression of Bim, a pro-apoptotic gene. Additionally, both treatments downregulate the JNK3/c-Jun signaling pathway. The effect of the combination regimen overrides that of either treatment alone. These effects were reflected on the alleviation of the hippocampal damage in CA1 region inflicted by I/R. Together, these findings accentuate the neuroprotective potentials of both treatments against global I/R by virtue of their rigorous multi-pronged actions, including suppression of hippocampal oxidative stress, inflammation, and apoptosis with the involvement of the Akt/FOXO3A/Bim and JNK3/c-Jun/Bax signaling pathways. The study also nominates CoQ10 as an adds-on therapy with statins.

Selenium, Vanadium, and Chromium as Micronutrients to Improve Metabolic Syndrome

Trace metals play an important role in the proper functioning of carbohydrate and lipid metabolism. Some of the trace metals are thus essential for maintaining homeostasis, while deficiency of these trace metals can cause disorders with metabolic and physiological imbalances. This article concentrates on three trace metals (selenium, vanadium, and chromium) that may play crucial roles in controlling blood glucose concentrations possibly through their insulin-mimetic effects. For these trace metals, the level of evidence available for their health effects as supplements is weak. Thus, their potential is not fully exploited for the target of metabolic syndrome, a constellation that increases the risk for cardiovascular disease and type 2 diabetes. Given that the prevalence of metabolic syndrome is increasing throughout the world, a simpler option of interventions with food supplemented with well-studied trace metals could serve as an answer to this problem. The oxidation state and coordination chemistry play crucial roles in defining the responses to these trace metals, so further research is warranted to understand fully their metabolic and cardiovascular effects in human metabolic syndrome.

Neuronal functions of FOXO/DAF-16

The FOXO family of transcription factors plays a conserved role in longevity and tissue homeostasis across species. In the mammalian nervous system, emerging evidence has implicated FOXOs in cognitive performance, stem cell maintenance, regeneration, and protection against stress. Much of what we know about neuronal functions of FOXO emerged from recent studies in C. elegans. Similar to mammalian FOXO, the worm FOXO ortholog, called DAF-16, regulates learning and memory, regeneration, and stress resistance in neurons. Here, we discuss the current state of our knowledge of FOXO’s functions in neurons in mammals and invertebrates, and highlight areas where our understanding is limited. Defining the function of FOXO factors in the healthy, aged, and diseased brain may have important implications for improving healthspan and treating neurodegenerative disease.

Glycyrrhetinic acid protects H9c2 cells from oxygen glucose deprivation-induced injury through the PI3K/AKt signaling pathway

Glycyrrhetinic acid (GA) is an ingredient of triterpene saponins found in Gancao (Radix Glycyrrhizae). Here, we investigated the protective effects of GA in H9c2 cells, and explored its possible mechanism of action. Different concentrations of GA were used to treat H9c2 cells under oxygen glucose deprivation. We analyzed cell necrosis and apoptosis using optical microscopy, Hoechst 33342 staining, FITC-annexin V/PI double-staining and lactate dehydrogenase (LDH), creatine kinase-MB (CK-MB) and interleukin (IL)-1β assays. Changes in related pro-apoptosis and anti-apoptosis proteins were detected by Western blot. Optical microscopy showed that GA improved cell morphology, including cell shrinkage, cauliflower-like membrane blebbing, and even some cell debris. Meanwhile, GA also ameliorated cell nuclei characteristics such as nucleus size, chromatin condensation and bright staining from Hoechst 33342 staining. GA also lowered the apoptotic rate and the levels of LDH, CK-MB and IL-1β in a dose-dependent manner. Furthermore, GA treatment increased Bcl-2 protein expression and decreased caspase-8 and Bax protein expression, while elevating the Bcl-2/Bax ratio. GA preconditioning increased p-AKt protein expression; however, after adding LY 294002, the p-AKt expression decreased obviously. Our results demonstrated that GA could protect H9c2 cells from apoptosis in a dose-dependent manner, and the potential mechanism might be related to the PI3K/AKt signaling pathway.

Recombinant osteopontin attenuates experimental cerebral vasospasm following subarachnoid hemorrhage in rats through an anti-apoptotic mechanism

Cerebral vasospasm (CVS) is an important pathological process following subarachnoid hemorrhage (SAH). Osteopontin (OPN), a pleiotropic extracellular glycoprotein, has been reported to be able to induce MKP-1 in the spastic cerebral arteries and prevent vasospasm after SAH. The purpose of this study was to investigate the protective effects of recombinant OPN (r-OPN) on CVS following SAH and the underlying mechanisms associated with its anti-apoptotic effect. Eighty male Sprague Dawley rats (weighing 300-375g) were randomly assigned to four groups: (1) sham+vehicle (n=20), (2) SAH+vehicle (n=20), (3) SAH+OPN0.03 (0.03μg) (n=20), (4) SAH+OPN0.1 (0.1μg) (n=20). The double injection model of cisterna magna was performed on day 0 and 48h after the first induction. r-OPN was administered intraventricularly nearly 30min after the first SAH. After neurological score assessment, rats were sacrificed 72h after the first SAH. The cross-sectional area and thickness of basilar arteries (BA) were measured under Hematoxylin-eosin (H&E) staining. Endothelial cell apoptosis was identified by terminal deoxynucleotidyl transferase mediated nick end labeling (TUNEL) staining. Immunohistochemistry was used to assess the expression of p-Akt and cleaved caspase-3 in BA. Western blot analysis was applied to evaluate the expression of p-Akt, cleaved caspase-3, Bax and Bcl-2 in BA. r-OPN improved neurological scores and attenuated vasospasm. r-OPN significantly reduced expression of cleaved caspase-3 and Bax in BA following SAH, and increased the level of p-Akt and Bcl-2, coupled with reduced apoptosis of endothelial cell in BA. These results demonstrate that r-OPN can attenuate vasospasm after SAH through a suppressed apoptotic response, which may provide a novel therapeutic target for cerebral vasospasm.

The cardioprotection of the insulin-mediated PI3K/Akt/mTOR signaling pathway

Apoptosis occurs frequently in myocardial infarction, oxidative stress injury, and ischemia/reperfusion injury, and plays a pivotal role in the development of heart diseases. Inhibition of apoptosis alone does not necessarily lead to meaningful rescue in terms of either cardiomyocyte survival or function. Activation of the PI3K/Akt signaling pathway induced by insulin not only inhibits cardiomyocyte apoptosis but also substantially preserves and even improves regional and overall cardiac function. Insulin can protect cardiomyocytes from apoptosis by regulating a number of signaling molecules, such as eNOS, FOXOs, Bad, GSK-3β, mTOR, NDRG2, and Nrf2, through activating PI3K and Akt. This review focuses on the protective mechanisms and targets of insulin identified in the prevention and treatment of myocardial injury.

Bis maltolato oxovanadium (BMOV) and ischemia/reperfusion-induced acute kidney injury in rats

Background

The aim of the present study was to test the potential protective effects of the organic vanadium salt bis (maltolato) oxovanadium (BMOV; 15 mg/kg) in the context of renal ischemia/reperfusion (30 min of ischemia) and its effects on renal oxygenation and renal function in the acute phase of reperfusion (up to 90 min post-ischemia).

Methods

Ischemia was established in anesthetized and mechanically ventilated male Wistar rats by renal artery clamping. Renal microvascular and venous oxygenation were measured using phosphorimetry. Creatinine clearance rate, sodium reabsorption, and renal oxygen handling efficiency were considered markers for renal function.

Results

The main findings were that BMOV did not affect the systemic and renal hemodynamic and oxygenation variables and partially protected renal sodium reabsorption.

Conclusions

Pretreatment with the organic vanadium compound BMOV did not protect the kidney from I/R injury.

Akt regulates β-catenin in a rat model of focal cerebral ischemia-reperfusion injury

The present study aimed to investigate the effects of the phosphoinositide 3‑kinase (PI3K)/Akt signaling pathway on the Wnt/β‑catenin signaling pathway in rats with focal cerebral ischemia‑reperfusion injury. A total of 96 rat focal cerebral ischemia‑reperfusion models, established according to a modified version of Longa's method, were randomly divided into four groups: Sham‑operated (S), cerebral ischemia‑reperfusion injury (I), cerebral ischemia‑reperfusion + basic fibroblast growth factor (bFGF) post‑processing and, finally, cerebral ischemia‑reperfusion + bFGF post‑processing + PI3K inhibitor LY294002 (LY). Each group consisted of 24 rats and each group was divided into four subgroups according to the indicated reperfusion times of 12, 24, 48 and 72 h. The morphological changes of the cortical tissue and the cellular apoptosis were determined using hematoxylin and eosin staining and the terminal deoxynucleotidyl transferase dUTP nick end labeling method, respectively. The expression levels of phosphorylated (p‑)Akt, glycogen synthase kinase‑3β (GSK‑3β) mRNA and β‑catenin in the cortical tissue were detected at different time‑points. The number of apoptotic cells and the expression levels of p‑Akt, GSK‑3β mRNA and β‑catenin in the I and LY groups were significantly higher compared with those in the S group (P<0.05). In the bFGF group, the number of apoptotic cells and the mRNA expression levels of GSK‑3β were significantly decreased, whereas the expression levels of p‑Akt and β‑catenin were significantly increased compared with those in the I and LY groups (P<0.05). In cerebral ischemia‑reperfusion injury, the PI3K/Akt signaling pathway regulated β‑catenin, the main member of the Wnt signaling pathway, via GSK‑3β, providing information to assist in further investigation of the mechanism of β‑catenin in ischemia‑reperfusion injury.

In vivo two-photon fluorescence microscopy reveals disturbed cerebral capillary blood flow and increased susceptibility to ischemic insults in diabetic mice

AIMS

Diabetes mellitus increases the risk of stroke, but the mechanisms are unclear. The present study tested the hypothesis that diabetes mellitus disturbs the brain microcirculation and increases the susceptibility to cerebral damage in a middle cerebral artery occlusion (MCAO) model of ischemia.

METHODS

Diabetes was induced by streptozocin in mice expressing green fluorescent protein in endothelial cells (Tie2-GFP mice). Four weeks later, they were subjected to transient (20 min) MCAO. In vivo blood flow was measured by two-photon laser-scanning microscopy (TPLSM) in cerebral arteries, veins, and capillaries.

RESULTS

There was a significant decrease in red blood cell (RBC) velocity in capillaries in diabetic mice as assessed by TPLSM, yet the regional cerebral blood flow, as assessed by laser Doppler flowmetry, was maintained. Brain capillary flow developed turbulence after MCAO only in diabetic mice. These mice sustained increased neurological deficits after MCAO which were accompanied by an exaggerated degradation of tight junction proteins and blunted CaMKII phosphorylation in cerebral tissues indicating disruption of the blood-brain barrier and disturbed cognitive potential.

CONCLUSION

Diabetic mice are more susceptible to disturbances of cerebral capillary blood flow which may predispose them to neurovascular defects following ischemia.

Akt and mTOR mediate programmed necrosis in neurons

Necroptosis is a newly described form of regulated necrosis that contributes to neuronal death in experimental models of stroke and brain trauma. Although much work has been done elucidating initiating mechanisms, signaling events governing necroptosis remain largely unexplored. Akt is known to inhibit apoptotic neuronal cell death. Mechanistic target of rapamycin (mTOR) is a downstream effector of Akt that controls protein synthesis. We previously reported that dual inhibition of Akt and mTOR reduced acute cell death and improved long term cognitive deficits after controlled-cortical impact in mice. These findings raised the possibility that Akt/mTOR might regulate necroptosis. To test this hypothesis, we induced necroptosis in the hippocampal neuronal cell line HT22 using concomitant treatment with tumor necrosis factor α (TNFα) and the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. TNFα/zVAD treatment induced cell death within 4 h. Cell death was preceded by RIPK1–RIPK3–pAkt assembly, and phosphorylation of Thr-308 and Thr473 of AKT and its direct substrate glycogen synthase kinase-3β, as well as mTOR and its direct substrate S6 ribosomal protein (S6), suggesting activation of Akt/mTOR pathways. Pretreatment with Akt inhibitor viii and rapamycin inhibited Akt and S6 phosphorylation events, mitochondrial reactive oxygen species production, and necroptosis by over 50% without affecting RIPK1–RIPK3 complex assembly. These data were confirmed using small inhibitory ribonucleic acid-mediated knockdown of AKT1/2 and mTOR. All of the aforementioned biochemical events were inhibited by necrostatin-1, including Akt and mTOR phosphorylation, generation of oxidative stress, and RIPK1–RIPK3–pAkt complex assembly. The data suggest a novel, heretofore unexpected role for Akt and mTOR downstream of RIPK1 activation in neuronal cell death.

Effects of sodium metavanadate on in vitro neuroblastoma and red blood cells

Toxicity of vanadium on cells is one of the less studied effects. This prompted us to study the structural effects induced on neuroblastoma and erythrocytes by vanadium (V) sodium metavanadate. This salt was incubated with mice cholinergic neuroblastoma cells and intact human erythrocytes. To learn whether metavanadate interacts with membrane lipid bilayers it was incubated with bilayers built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE). These are phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. Exposure of neuroblastoma cells to metavanadate showed significant decreases in cell viability as well as in cell number correlating with inhibition of aconitase activity. In scanning electron microscopy (SEM) and defocusing microscopy (DM) it was observed that induced on erythrocytes the formation of echinocytes. However, no effects were obtained when metavanadate was made to interact with DMPC and DMPE multibilayers and liposomes, assays performed by X-ray diffraction and differential scanning calorimetry (DSC), respectively. These results imply that the effects of metavanadate on erythrocytes are through interactions with proteins located in the membrane outer moiety, and could still involve other minor lipid components as well. Also, partly unsaturated lipids could interact differently the fully saturated chains in the model systems.

Interference of apoptosis in the pathophysiology of subarachnoid hemorrhage

Programmed cell death is crucial for the correct development of the organism and the clearance of harmful cells like tumor cells or autoreactive immune cells. Apoptosis is initiated by the activation of cell death receptors and in most cases it is associated with the activation of the cysteine proteases, which lead to apoptotic cell death. Cells shrink, chromatin clumps and forms a large, sharply demarcated, crescent-shaped or round mass; the nucleus condenses, apoptotic bodies are formed and eventually dead cells are engulfed by a neighboring cell or cleared by phagocytosis. The authors have summarized the most important data concerning apoptosis in subarachnoid hemorrhage that have been issued in the medical literature in the last 20 years.

Human erythrocytes and neuroblastoma cells are in vitro affected by sodium orthovanadate

Research on biological influence of vanadium has gained major importance because it exerts potent toxic, mutagenic, and genotoxic effects on a wide variety of biological systems. However, hematological toxicity is one of the less studied effects. The lack of information on this issue prompted us to study the structural effects induced on the human erythrocyte membrane by vanadium (V). Sodium orthovanadate was incubated with intact erythrocytes, isolated unsealed human erythrocyte membranes (IUM) and molecular models of the erythrocyte membrane. The latter consisted of bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. This report presents evidence in order that orthovanadate interacted with red cell membranes as follows: a) in scanning electron microscopy (SEM) studies it was observed that morphological changes on human erythrocytes were induced; b) fluorescence spectroscopy experiments in isolated unsealed human erythrocyte membranes (IUM) showed that an increase in the molecular dynamics and/or water content at the shallow depth of the lipids glycerol backbone at concentrations as low as 50μM was produced; c) X-ray diffraction studies showed that orthovanadate 0.25-1mM range induced increasing structural perturbation to DMPE; d) somewhat similar effects were observed by differential scanning calorimetry (DSC) with the exception of the fact that DMPC pretransition was shown to be affected; and e) fluorescence spectroscopy experiments performed in DMPC large unilamellar vesicles (LUV) showed that at very low concentrations induced changes in DPH fluorescence anisotropy at 18°C. Additional experiments were performed in mice cholinergic neuroblastoma SN56 cells; a statistically significant decrease of cell viability was observed on orthovanadate in low or moderate concentrations.

Ras family small GTPase-mediated neuroprotective signaling in stroke

Selective neuronal cell death is one of the major causes of neuronal damage following stroke, and cerebral cells naturally mobilize diverse survival signaling pathways to protect against ischemia. Importantly, therapeutic strategies designed to improve endogenous anti-apoptotic signaling appear to hold great promise in stroke treatment. While a variety of complex mechanisms have been implicated in the pathogenesis of stroke, the overall mechanisms governing the balance between cell survival and death are not well-defined. Ras family small GTPases are activated following ischemic insults, and in turn, serve as intrinsic switches to regulate neuronal survival and regeneration. Their ability to integrate diverse intracellular signal transduction pathways makes them critical regulators and potential therapeutic targets for neuronal recovery after stroke. This article highlights the contribution of Ras family GTPases to neuroprotective signaling cascades, including mitogen-activated protein kinase (MAPK) family protein kinase- and AKT/PKB-dependent signaling pathways as well as the regulation of cAMP response element binding (CREB), Forkhead box O (FoxO) and hypoxiainducible factor 1(HIF1) transcription factors, in stroke.

Cortical neurons develop insulin resistance and blunted Akt signaling: a potential mechanism contributing to enhanced ischemic injury in diabetes

Patients with diabetes are at higher risk of stroke and experience increased morbidity and mortality after stroke. We hypothesized that cortical neurons develop insulin resistance, which decreases neuroprotection via circulating insulin and insulin-like growth factor-I (IGF-I). Acute insulin treatment of primary embryonic cortical neurons activated insulin signaling including phosphorylation of the insulin receptor, extracellular signal-regulated kinase (ERK), Akt, p70S6K, and glycogen synthase kinase-3β (GSK-3β). To mimic insulin resistance, cortical neurons were chronically treated with 25 mM glucose, 0.2 mM palmitic acid (PA), or 20 nM insulin before acute exposure to 20 nM insulin. Cortical neurons pretreated with insulin, but not glucose or PA, exhibited blunted phosphorylation of Akt, p70S6K, and GSK-3β with no change detected in ERK. Inhibition of the phosphatidylinositol 3-kinase (PI3-K) pathway during insulin pretreatment restored acute insulin-mediated Akt phosphorylation. Cortical neurons in adult BKS-db/db mice exhibited higher basal Akt phosphorylation than BKS-db(+) mice and did not respond to insulin. Our results indicate that prolonged hyperinsulinemia leads to insulin resistance in cortical neurons. Decreased sensitivity to neuroprotective ligands may explain the increased neuronal damage reported in both experimental models of diabetes and diabetic patients after ischemia-reperfusion injury.

Protein S blocks the extrinsic apoptotic cascade in tissue plasminogen activator/N-methyl D-aspartate-treated neurons via Tyro3-Akt-FKHRL1 signaling pathway

Background

Thrombolytic therapy with tissue plasminogen activator (tPA) benefits patients with acute ischemic stroke. However, tPA increases the risk for intracerebral bleeding and enhances post-ischemic neuronal injury if administered 3-4 hours after stroke. Therefore, combination therapies with tPA and neuroprotective agents have been considered to increase tPA's therapeutic window and reduce toxicity. The anticoagulant factor protein S (PS) protects neurons from hypoxic/ischemic injury. PS also inhibits N-methyl-D-aspartate (NMDA) excitotoxicity by phosphorylating Bad and Mdm2 which blocks the downstream steps in the intrinsic apoptotic cascade. To test whether PS can protect neurons from tPA toxicity we studied its effects on tPA/NMDA combined injury which in contrast to NMDA alone kills neurons by activating the extrinsic apoptotic pathway. Neither Bad nor Mdm2 which are PS's targets and control the intrinsic apoptotic pathway can influence the extrinsic cascade. Thus, based on published data one cannot predict whether PS can protect neurons from tPA/NMDA injury by blocking the extrinsic pathway. Neurons express all three TAM (Tyro3, Axl, Mer) receptors that can potentially interact with PS. Therefore, we studied whether PS can activate TAM receptors during a tPA/NMDA insult.

Results

We show that PS protects neurons from tPA/NMDA-induced apoptosis by suppressing Fas-ligand (FasL) production and FasL-dependent caspase-8 activation within the extrinsic apoptotic pathway. By transducing neurons with adenoviral vectors expressing the kinase-deficient Akt mutant Akt^K179A and a triple FKHRL1 Akt phosphorylation site mutant (FKHRL1-TM), we show that Akt activation and Akt-mediated phosphorylation of FKHRL1, a member of the Forkhead family of transcription factors, are critical for FasL down-regulation and caspase-8 inhibition. Using cultured neurons from Tyro3, Axl and Mer mutants, we show that Tyro3, but not Axl and Mer, mediates phosphorylation of FHKRL1 that is required for PS-mediated neuronal protection after tPA/NMDA-induced injury.

Conclusions

PS blocks the extrinsic apoptotic cascade through a novel mechanism mediated by Tyro3-dependent FKHRL1 phosphorylation which inhibits FasL-dependent caspase-8 activation and can control tPA-induced neurotoxicity associated with pathologic activation of NMDA receptors. The present findings should encourage future studies in animal stroke models to determine whether PS can increase the therapeutic window of tPA by reducing its post-ischemic neuronal toxicity.

Apoptotic mechanisms for neuronal cells in early brain injury after subarachnoid hemorrhage

OBJECTS

The major causes of death and disability in subarachnoid hemorrhage (SAH) may be early brain injury (EBI) and cerebral vasospasm. Although cerebral vasospasm has been studied and treated by a lot of drugs, the outcome is not improved even if vasospasm is reversed. Based on these data, EBI is considered a primary target for future research, and apoptosis may be involved in EBI after experimental SAH.

METHODS

We reviewed the published literature about the relationship between SAH induced EBI and apoptosis in PubMed.

RESULT

Most available information can be obtained from the endovascular filament perforation animal model. After onset of SAH, intracranial pressure is increased and then cerebral blood flow is reduced. Many factors are involved in the mechanism of apoptotic cell death in EBI after SAH. In the neuronal cells, both intrinsic and extrinsic pathways of apoptosis can occur. Some antiapoptotic drugs were studied and demonstrated a protective effect against EBI after SAH. However, apoptosis in EBI after SAH has been little studied and further studies will provide us more beneficial findings.

CONCLUSIONS

The study of apoptosis in EBI after experimental SAH may give us new therapies for SAH.

Activated cell survival cascade protects cardiomyocytes from cell death in Tako-Tsubo cardiomyopathy

AIMS

Tako-Tsubo cardiomyopathy (TTC) is characterized by rapid regeneration of contractile dysfunction. From recent studies it is known that excessive catecholamine levels due to emotional or physical stress might play a central role. After sympathetic activation, the PIK3/AKT pathway is a key regulator of many cellular responses, including cytoprotective effects. Thus, the purpose of this study was to investigate whether the PIK3/AKT pathway plays a pivotal role in TTC.

METHODS AND RESULTS

A total of 16 consecutive patients diagnosed with TTC were studied. Left ventricular biopsies were taken during the acute phase and after functional recovery. Specimens were examined by quantitative RT-PCR and western blotting. Representative genes of the PI3K/AKT pathway (PIK3-R1, PTEN, GSK3beta, mTOR, PP2A, eIF4E) were compared with left ventricular controls from non-transplanted healthy hearts. PI3K expression was increased during the acute phase and after functional recovery. AKT protein levels were unaltered, but phosphorylation significantly increased during the acute phase. Both PTEN (PI3K antagonist) and PP2 (unspecific phosphatase) were down-regulated. Phosphorylation of the PI3K/AKT downstream target mTOR was increased, while expression of both GSK3 isoforms was decreased. The Bax/Bcl2 ratio was increased in the acute and recovery phases.

CONCLUSION

PI3K/AKT signalling is activated in TTC. This activated cell survival cascade might protect cardiomyocytes from cell death and also contribute to rapid regeneration in TTC.

Restoration of Akt activity by the bisperoxovanadium compound bpV(pic) attenuates hippocampal apoptosis in experimental neonatal pneumococcal meningitis

Pneumococcal meningitis causes apoptosis of developing neurons in the dentate gyrus of the hippocampus. The death of these cells is accompanied with long-term learning and memory deficits in meningitis survivors. Here, we studied the role of the PI3K/Akt (protein kinase B) survival pathway in hippocampal apoptosis in a well-characterized infant rat model of pneumococcal meningitis. Meningitis was accompanied by a significant decrease of the PI3K product phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) and of phosphorylated (i.e., activated) Akt in the hippocampus. At the cellular level, phosphorylated Akt was decreased in both the granular layer and the subgranular zone of the dentate gyrus, the region where the developing neurons undergo apoptosis. Protein levels and activity of PTEN, the major antagonist of PI3K, were unaltered by infection, suggesting that the observed decrease in PIP(3) and Akt phosphorylation is a result of decreased PI3K signaling. Treatment with the PTEN inhibitor bpV(pic) restored Akt activity and significantly attenuated hippocampal apoptosis. Co-treatment with the specific PI3K inhibitor LY294002 reversed the restoration of Akt activity and attenuation of hippocampal apoptosis, while it had no significant effect on these parameters on its own. These results indicate that the inhibitory effect of bpV(pic) on apoptosis was mediated by PI3K-dependent activation of Akt, strongly suggesting that bpV(pic) acted on PTEN. Treatment with bpV(pic) also partially inhibited the concentration of bacteria and cytokines in the CSF, but this effect was not reversed by LY294002, indicating that the effect of bpV(pic) on apoptosis was independent of its effect on CSF bacterial burden and cytokine levels. These results indicate that the PI3K/Akt pathway plays an important role in the death and survival of developing hippocampal neurons during the acute phase of pneumococcal meningitis.

Role of serum- and glucocorticoid-inducible kinase-1 in regulating torsion-induced apoptosis in rats

Serum- and glucocorticoid-inducible kinase-1 (SGK1) is a serine/threonine protein kinase that responds to various stimuli and mediates cell survival. Although it is known that testicular torsion leads to testicular damage and male infertility, the role of SGK1 in torsion remains unclear. This study investigated whether torsion-induced apoptosis is associated with changes in phosphoinositide-dependent protein kinase-1 (PDK1), SGK1 and forkhead transcription factor FOXO3a expression and/or phosphorylation in rats. Sprague-Dawley rats were divided into four groups: sham (control), 1, 2 and 4 h of unilateral torsion. Bilateral testes, testicular interstitial fluid (TIF) and blood samples were collected immediately after torsion. Our results revealed that SGK1 protein and mRNA were abundantly present in testes and were induced by 2 h of torsion, but that phosphorylation of SGK1, PDK1 and FOXO3a decreased simultaneously. After 2 h of torsion, the testosterone secretion capacity of the primary Leydig cells and testicular interstitial cells (TICs) was impaired and apoptotic spermatogonia and TICs were observed; in addition, the mean seminiferous tubular diameter was decreased. Torsion increased plasma corticosterone levels, but decreased plasma luteinizing hormone and testosterone levels. However, the testosterone levels of the TIF in the ipsilateral testes were significantly enhanced after 2 h of torsion, but suppressed in the contralateral testes. This animal study suggests that PDK1, SGK1 and FOXO3a are involved in torsion-induced apoptosis and that medical therapy should be performed as early as 2 h after the occurrence of torsion to prevent further damage.

Neuroprotective effects of PDGF against oxidative stress and the signaling pathway involved

The neuroprotective effects of platelet-derived growth factor (PDGF) and the major signaling pathways involved in these were examined using primary cultured mouse cortical neurons subjected to H(2)O(2)-induced oxidative stress. The specific function of the PDGF beta-receptor (PDGFR-beta) was examined by the selective deletion of the corresponding gene using the Cre-loxP system in vitro. In wild-type neurons, PDGF-BB enhanced the survival of these neurons and suppressed H(2)O(2)-induced caspase-3 activation. The prosurvival effect of PDGF-AA was less than that of PDGF-BB. PDGF-BB highly activated Akt, extracellular signal-regulated kinase (ERK), c-jun amino-terminal kinase (JNK) and p38. PDGF-AA activated these molecules at lesser extent than PDGF-BB. In particular, PDGF-AA induced activation of Akt was at very low level. The neuroprotective effects of PDGF-BB were antagonized by inhibitors of phosphatidylinositol 3-kinase (PI3-K), mitogen-activated protein kinase kinase (MEK), JNK and p38. The PDGFR-beta-depleted neurons showed increased vulnerability to oxidative stress, and less responsiveness to PDGF-BB-induced cytoprotection and signal activation, in which Akt activation was most strongly suppressed. After all, these results demonstrated the neuroprotective effects of PDGF and the signaling pathways involved against oxidative stress. The effects of PDGF-BB were more potent than those of PDGF-AA. This might be due to the activation and additive effects of two PDGFRs after PDGF-BB stimulation. Furthermore, the PI3-K/Akt pathway that was deduced to be preferentially activated by PDGFR-beta may explain the potent effects of PDGF-BB.

ATP-mediated protein kinase B Akt/mammalian target of rapamycin mTOR/p70 ribosomal S6 protein p70S6 kinase signaling pathway activation promotes improvement of locomotor function after spinal cord injury in rats

The protein kinase B (Akt)/mammalian target of rapamycin (mTOR)/p70 ribosomal S6 protein kinase (p70S6K) signaling pathway, as a central controller of cell growth, proliferation, survival, and differentiation in response to extracellular signals, growth factors, nutrient availability, energy status of the cell, and stress, has recently gained attention in neuroscience. The effects of this signaling pathway on repair of spinal cord injury (SCI), however, have not been well elucidated. ATP is increasingly recognized as an important regulator of signal transduction pathways, and plays important roles in functional recovery after nervous system injury. In the present study, we examined the ATP-induced changes of the Akt/mTOR/p70S6K signaling pathway in injured spinal cord of adult rats and potential therapeutic effects of this pathway on SCI-induced locomotor dysfunction. SCI was produced by extradural weight-drop using modified Allen's stall with damage energy of 50 g-cm force. The rats were divided into four groups: SCI plus ATP, SCI plus saline, SCI plus ATP and rapamycin, and sham-operated. Using immunostaining studies, Western blot analyses and real-time qualitative RT-PCR analyses, we demonstrated that the Akt/mTOR/p70S6K signaling pathway is present in the injured spinal cord and the expression of its components at the protein and mRNA levels is significantly elevated by exogenous administration of ATP following SCI. We observed the effectiveness of the activated Akt/mTOR/p70S6K signaling pathway in improving locomotor recovery, significantly increasing the expression of nestin, neuronal nuclei (NeuN), neuron specific enolase (NSE), and neurofilament 200 (NF200), and relatively inhibiting excessive reactive astrogliosis after SCI in a rapamycin-sensitive manner. We concluded that ATP injection produced a significant activation of the Akt/mTOR/p70S6K signaling pathway in the injured spinal cord and that enhancement of rapamycin-sensitive signaling produces beneficial effects on SCI-induced motor function defects and repair potential. We suggest that modulation of this protein kinase signaling pathway activity should be considered as a potential therapeutic strategy for SCI.

Activation of Akt/FoxO signaling pathway contributes to induction of neuroprotection against transient global cerebral ischemia by hypoxic pre-conditioning in adult rats

It is well established that pre-conditioning protects neuronal injury against ischemia. However, the molecular mechanisms underlying ischemic tolerance are not completely understood. The purpose of the present study was to investigate the role of Akt/forkhead transcription factor, class O (FoxO) pathway in hypoxic pre-conditioning (HPC) using a newly developed HPC to transient global cerebral ischemia (tGCI) model in adult rats. HPC for 30-120 min significantly reduced cell death in the CA1 subregion after 10 min of tGCI. HPC was effective only when applied 1-4 days before ischemia. The maximum protection was observed with 30 min of hypoxia and 1 day interval between hypoxia and ischemia. The phosphorylated Akt and FoxOs measured by western blot and immunohistochemistry were significantly increased after hypoxia-ischemia except for a transient decrease in the HPC group. Lateral ventricular infusion of LY294002 before HPC blocked the increase in phosphorylated Akt and FoxOs and increased neuronal damage in HPC animals. These results suggest that pre-exposure to hypoxia induces protection against tGCI in adult rats. Activation of Akt results in the inactivation of FoxOs which may mediate ischemic tolerance after HPC.

Cardioprotection by vanadium compounds targeting Akt-mediated signaling

Treatment with inorganic and organic compounds of vanadium has been shown to exert a wide range of cardioprotective effects in myocardial ischemia/reperfusion-induced injury, myocardial hypertrophy, hypertension, and vascular diseases. Furthermore, administration of vanadium compounds improves cardiac performance and smooth muscle cell contractility and modulates blood pressure in various models of hypertension. Like other vanadium compounds, we documented bis(1-oxy-2-pyridinethiolato) oxovanadium (IV) [VO(OPT)] as a potent cardioprotective agent to elicit cardiac functional recovery in myocardial infarction and pressure overload-induced hypertrophy. Vanadium compounds activate Akt signaling through inhibition of protein tyrosine phosphatases, thereby eliciting cardioprotection in myocardial ischemia/reperfusion-induced injury and myocardial hypertrophy. Vanadium compounds also promote cardiac functional recovery by stimulation of glucose transport in diabetic heart. We here discuss the current understanding of mechanisms underlying vanadium compound-induced cardioprotection and propose a novel therapeutic strategy targeting for Akt signaling to rescue cardiomyocytes from heart failure.

Simvastatin attenuation of cerebral vasospasm after subarachnoid hemorrhage in rats via increased phosphorylation of Akt and endothelial nitric oxide synthase

The mechanisms involved in simvastatin-mediated attenuation of cerebral vasospasm after subarachnoid hemorrhage (SAH) are unclear. We investigated the role of the phosphatidylinositol 3-kinase/Akt (PI3K/Akt) pathway and endothelial nitric oxide synthase (eNOS) in the cerebral vasculature in statin-mediated attenuation of cerebral vasospasm using wortmannin, an irreversible pharmacological PI3K inhibitor, and a rat SAH endovascular perforation model. Simvastatin was administered intraperitoneally in two dosages (1 mg/kg and 20 mg/kg) at 0.5, 24, and 48 hr after SAH and histological parameters of ipsilateral intracranial carotid artery (ICA) were assessed at 24 and 72 hr. SAH significantly decreased ICA diameter and perimeter while increasing wall thickness at both 24 and 72 hr. High-dosage simvastatin prevented the reduction of ICA diameter and perimeter following SAH, whereas both high and low dosages reduced wall thickness significantly at 24 and 72 hr. The effects of simvastatin were significantly reversed by wortmannin. High-dosage simvastatin increased pAkt and peNOS (phosphorylated forms) levels without increasing Akt and eNOS expression compared with the SAH group and also improved neurological deficits at 24 and 72 hr. Simvastatin did not affect protein levels by itself compared with untreated sham group. The present study elucidates the critical role of the PI3K activation leading to phosphorylation of Akt and eNOS in simvastatin-mediated attenuation of cerebral vasospasm after SAH.

Effects of transient focal cerebral ischemia in mice deficient in puma

Bcl-2 homology domain 3 (BH3)-only pro-apoptotic proteins may play an important role in upstream cell death signaling pathways underlying ischemic brain injury. Puma is a potent BH3-only protein that can be induced via p53, FoxO3a and endoplasmic reticulum stress pathways and is upregulated by global cerebral ischemia. To more completely define the contribution of Puma to ischemic brain injury we measured the expressional response of Puma to transient focal cerebral ischemia in mice and also compared infarct volumes in puma-deficient versus puma-expressing mice. Real-time quantitative PCR determined puma mRNA levels were significantly increased 8h after 90min middle cerebral artery (MCA) occlusion in the ipsilateral cortex, while expression remained unchanged contralaterally. Puma protein levels were also increased in the ischemic cortex over the same period. However, cortical and striatal infarct volumes were not significantly different between puma-deficient and puma-expressing mice at 24h, and no differences between genotypes were found for post-ischemic neurological deficit scores. These data demonstrate that focal cerebral ischemia is associated with puma induction but suggest that Puma does not contribute significantly to lesion development in the present model.

Prevention of Glutamate Accumulation and Upregulation of Phospho-Akt may Account for Neuroprotection Afforded by Bergamot Essential Oil against Brain Injury Induced by Focal Cerebral Ischemia in Rat

The effects of bergamot essential oil (BEO; Citrus bergamia, Risso) on brain damage caused by permanent focal cerebral ischemia in rat were investigated. Administration of BEO (0.1-0.5 ml/kg but not 1 ml/kg, given intraperitoneally 1 h before occlusion of the middle cerebral artery, MCAo) significantly reduced infarct size after 24 h permanent MCAo. The most effective dose (0.5 ml/kg) resulted in a significant reduction of infarct extension throughout the brain, especially in the medial striatum and the motor cortex as revealed by TTC staining of tissue slices. Microdialysis experiments show that BEO (0.5 ml/kg) did not affect basal amino acid levels, whereas it significantly reduced excitatory amino acid, namely aspartate and glutamate, efflux in the frontoparietal cortex typically observed following MCAo. Western blotting experiments demonstrated that these early effects were associated, 24 h after permanent MCAo, to a significant increase in the phosphorylation and activity of the prosurvival kinase, Akt. Indeed, BEO significantly enhanced the phosphorylation of the deleterious downstream kinase, GSK-3beta, whose activity is negatively regulated via phosphorylation by Akt.

Activation of Endothelial Nitric Oxide Synthase by a Vanadium Compound Ameliorates Pressure Overload-Induced Cardiac Injury in Ovariectomized Rats

We here investigated the effect of bis(1-oxy-2-pyridinethiolato) oxovanadium (IV), [VO(OPT)], against myocardial hypertrophy and cardiac functional recovery in pressure overload–induced hypertrophy in ovariectomized female rats and defined mechanisms underlying its cardioprotective action. Wistar rats subjected to bilateral ovariectomy were further treated with abdominal aortic stenosis. VO(OPT) (containing 1.25 and 2.50 mg of vanadium per kg) was administered orally once a day for 14 days starting from 2 weeks after aortic banding. Treatment with VO(OPT) significantly inhibited pressure overload–induced increase both in the heart weight:body weight ratio and the lung weight:body weight ratio. VO(OPT) also attenuated hypertrophy-induced impaired left ventricular end-diastolic pressure, left ventricular developed pressure, and left ventricular contractility (±dp/dt max ). VO(OPT) treatment significantly restored pressure overload–induced impaired endothelial NO synthase activity with concomitant increased phosphorylation of endothelial NO synthase (Ser1179). Moreover, VO(OPT) treatment significantly restored pressure overload–induced reduced Akt activity, as indicated by increased phosphorylation at Ser473 and at Thr308. Treatment with VO(OPT) also secondarily inhibited calpastatin and dystrophin breakdown and decreased myosin light chain phosphorylation. Finally, VO(OPT) treatment significantly attenuated mortality after repeated isoproterenol administration in pressure overloaded–ovariectomized rats. Taken together, VO(OPT) attenuates cardiac myocytes hypertrophy in vivo in pressure overload–induced hypertrophy in ovariectomized rats and prevents the process from hypertrophy to heart failure. These effects are mediated by inhibition of calpastatin and dystrophin breakdown in addition to increased Akt and endothelial NO synthase activities.

Pathophysiological relevance of forkhead transcription factors in brain ischemia

Forkhead box transcription factor, class 0 (FOXO) is a mammalian homologue of DAF-16, which is known to regulate the lifespan of Caenorhabditis elegans and includes subfamiies of forkhead transcription factors such as FOXO1 (FKHR). FOXO3 (FKHRL1), FOXO4 (AFX) and FOXO6. All these FOXO members are expressed in the brain with different spatial patterns. FOXO1 is phosphorylated on three sites (Thr-24, Ser-256 and Ser-319) in phosphatidylinositol 3-kinase (PI3-K)/Akt-dependenr manner, thereby inhibiting apoptosis signals. We here documented dephosphorylation of FOXO1, FOXO3 and FOXO4 following transient forebrain ischemia with its concomitant translocation into the nucleus in neurons in the gerbil and mouse brains. The dephosphorylarion of FOXO1 following brain ischemia is in part mediated by constirutively active calcineurin in the mouse hippocampus. The activation of FOXOs preceded delayed neuronal death in the vulnerable hippocampal regions following ischemic brain injury. The FOXOl activation is accompanied by an increase in DNA binding activity for FOXO1-responsive element on the Fas ligand promoter. Thus, downstream targets induced by FOXOl include Fas ligand and Bcl-2-interacting mediator of cell death (Bim) in the brain ischemia. Accumulating evidence documented how FOXO activation is involved in the mechanisms of ischemic cell death. In this chapter, we document the activation mechanism of FOXO factors following brain ischemia and deline their downstream targets underlying neuronal death. The pathophysiological relevance of crosstalk between FOXOs and calcineurmn pathways is also discussed. Finally, we propose therapeutic perspectives to rescue neurons from delayed neuronal death by promoting the Akt signaling. Vanadium compounds, protein tyrosine phosphatase inhibitor, up-regulates Akt activity in the brain and thereby rescues neurons from delayed neuronal death by inhibiting FOXO-dependent and -independent death signals in neurons.