Neuroprotective effect of ebselen against intracerebroventricular streptozotocin-induced neuronal apoptosis and oxidative stress in rats

NOX2 in Alzheimer's and Parkinson's disease

Alzheimer's Disease (AD), and related dementias, represent a growing concern for the worldwide population given the increased numbers of people of advanced age. Marked by significant degradation of neurological tissues and critical processes, in addition to more specific factors such as the presence of amyloid plaques and neurofibrillary tangles in AD, robust discussion is ongoing regarding the precise mechanisms by which these diseases arise. One of the major interests in recent years has been the contribution of reactive oxygen species (ROS) and, particularly, the contribution of the ROS-generating NADPH Oxidase proteins. NADPH Oxidase 2 (NOX2), the prototypical member of the family, represents a particularly interesting target for study given its close association with vascular and inflammatory processes in all tissues, including the brain, and the association of these processes with AD development and progression. In this review, we discuss the most relevant and recent work regarding the contribution of NOX2 to AD progression in neuronal, microglial, and cerebrovascular signaling. Furthermore, we will discuss the most promising NOX2-targeted therapeutics for potential AD management and treatment.

Evaluation of the Neuroprotective Effect of Organic Selenium Compounds: An in Vitro Model of Alzheimer's Disease

Selenium (Se) is an essential trace element for human health and plays an important role in the development and maintenance of central nervous system functions. Se deficiency has been associated with cognitive decline and increased oxidative stress. The increase in oxidative stress is one of the hypotheses for the emergence and worsening of neurodegenerative diseases, such as Alzheimer's disease (AD). To investigate the neuroprotective effects of organic Se compounds in human neuroblastoma cells (SH-SY5Y) differentiated into cholinergic neurons-like. The SH-SY5Y cells were differentiated into cholinergic neuron-like with retinoic acid (RA) and brain-derived neurotrophic factor (BDNF). AD was mimicked exposing the cells to okadaic acid (OA) and beta-amyloid protein (Aβ). The neuroprotective effect of organic Se compounds, selenomethionine (SeMet) and Ebselen, was evaluated through cell viability tests, acetylcholinesterase and antioxidant enzyme activities, and detection of reactive oxygen species (ROS). None of the SeMet concentrations tested protected against the toxic effect of OA + Aβ. On the other hand, previous exposure to 0.1 and 1 µM Ebselen protected cells from the toxic effect of OA + Aβ. Cell differentiation induced by RA and BDNF exposure was effective, showing characteristics of neuronal cells, and pointing to a promising model of AD. Ebselen showed a protective effect, but more studies are needed to identify the mechanism of action.

New cyclophilin D inhibitor rescues mitochondrial and cognitive function in Alzheimer's disease

Mitochondrial dysfunction is an early pathological feature of Alzheimer disease and plays a crucial role in the development and progression of Alzheimer's disease. Strategies to rescue mitochondrial function and cognition remain to be explored. Cyclophilin D (CypD), the peptidylprolyl isomerase F (PPIase), is a key component in opening the mitochondrial membrane permeability transition pore, leading to mitochondrial dysfunction and cell death. Blocking membrane permeability transition pore opening by inhibiting CypD activity is a promising therapeutic approach for Alzheimer's disease. However, there is currently no effective CypD inhibitor for Alzheimer's disease, with previous candidates demonstrating high toxicity, poor ability to cross the blood-brain barrier, compromised biocompatibility and low selectivity. Here, we report a new class of non-toxic and biocompatible CypD inhibitor, ebselen, using a conventional PPIase assay to screen a library of ∼2000 FDA-approved drugs with crystallographic analysis of the CypD-ebselen crystal structure (PDB code: 8EJX). More importantly, we assessed the effects of genetic and pharmacological blockade of CypD on Alzheimer's disease mitochondrial and glycolytic bioenergetics in Alzheimer's disease-derived mitochondrial cybrid cells, an ex vivo human sporadic Alzheimer's disease mitochondrial model, and on synaptic function, inflammatory response and learning and memory in Alzheimer's disease mouse models. Inhibition of CypD by ebselen protects against sporadic Alzheimer's disease- and amyloid-β-induced mitochondrial and glycolytic perturbation, synaptic and cognitive dysfunction, together with suppressing neuroinflammation in the brain of Alzheimer's disease mouse models, which is linked to CypD-related membrane permeability transition pore formation. Thus, CypD inhibitors have the potential to slow the progression of neurodegenerative diseases, including Alzheimer's disease, by boosting mitochondrial bioenergetics and improving synaptic and cognitive function.

Neuroprotective role of vitamin B12 in streptozotocin-induced type 1 diabetic rats

Chronic hyperglycemia-induced neuropathological changes include neuronal apoptosis, astrogliosis, decrease in neurotrophic support, impaired synaptic plasticity, and impaired protein quality control (PQC) system. Vitamin B12 is indispensable for neuronal development and brain function. Several studies reported the neuroprotective effect of B12 supplementation in diabetic patients. However, the underlying molecular basis for the neuroprotective effect of B12 supplementation in diabetes needs to be thoroughly investigated. Two-month-old Sprague-Dawley rats were randomly assigned into three groups: Control (CN), diabetes (D; induced with streptozotocin; STZ), and diabetic rats supplemented with vitamin B12 (DBS; vitamin B12; 50 μg/kg) for four months. At the end of 4 months of experimentation, the brain was dissected to collect the cerebral cortex (CC). The morphology of CC was investigated with H&E and Nissl body staining. Neuronal apoptosis was determined with TUNEL assay. The components of neurotrophic support, astrogliosis, synaptic plasticity, and PQC processes were investigated by immunoblotting and immunostaining methods. H& E, Nissl body, and TUNEL staining revealed that diabetes-induced neuronal apoptosis and degeneration. However, B12 supplementation ameliorated the diabetes-induced neuronal apoptosis. Further, B12 supplementation restored the markers of neurotrophic support (BDNF, NGF, and GDNF), and synaptic plasticity (SYP, and PSD-95) in diabetic rats. Interestingly, B12 supplementation also attenuated astrogliosis, ER stress, and ameliorated autophagy-related proteins in diabetic rats. Overall, these findings suggest that B12 acts as a neuroprotective agent by inhibiting the neuropathological changes in STZ-induced type 1 diabetes. Thus, B12 supplementation could produce beneficial outcomes including neuroprotective effects in diabetic patients.

Morus Alba Fruit Extract and its Fractions Ameliorate Streptozotocin Induced Cognitive Deficit in Mice via Modulating Oxidative and Cholinergic Systems

Increased oxidative stress and acetylcholinesterase (AChE) activity are key pathological characters contributing to the memory disorders. Thus, drugs targeting both oxidative stress and AChE are being explored for the management of cognitive dysfunction. Morus alba fruits (commonly consumed for its high nutritious value) are known to have antioxidant and AChE inhibitory effects. However, the role of Morus alba fruits in the management of memory disorders has not reported yet. This investigation was conducted to assess the antioxidant and AChE inhibitory potential of Morus alba fruit extracts in-vitro and to identify the components responsible for such effects. Further, the obtained bioactive component was studied for possible memory improvement effects against streptozotocin (STZ) induced dementia. To isolate the bioactive component in-vitro DPPH and AChE assays guided fractionation was performed. Memory functions in mice were determined using Morris Water Maze test while brain biochemical parameters were measured to understand the mechanism of action. In-vitro assays revealed strong AChE and DPPH inhibitory potential of methanol extract (ME), therefore, it was further fractionated. Among various fractions obtained, ethyl-acetate fraction (EAF) was found to possess marked AChE and DPPH inhibitory activities. On subsequent fractionation of EAF, bioactivity of obtained sub-fractions was found to be inferior to EAF. Further, both ME and EAF improved STZ (intracerebroventricular) induced cognitive dysfunction in animals by restoring endogenous antioxidant status (superoxide dismutase and reduced glutathione) and reducing thiobarbituric acid reactive species and nitric oxide levels along with brain AChE and myeloperoxidase activity. TLC densitometric studies showed appreciable levels of phenolic acids and quercetin in both EAF and ME. It can be concluded that Morus alba fruit extract has the ability to modulate cholinergic and oxidative system due to presence of phenolic and flavonoid compounds and hence, could aid in the management of memory disorders.

Selenium-Derivative Compounds: A Review of New Perspectives in the Treatment of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is one of the most prevalent types of dementia, affecting millions of older people worldwide. AD is stimulating efforts to develop novel molecules targeting its main features associated with a decrease in acetylcholine levels, an increase in oxidative stress and depositions of amyloid-β (Aβ) and tau protein. In this regard, selenium-containing compounds have been demonstrated as potential multi-targeted compounds in the treatment of AD. These compounds are known for their antioxidant and anticholinesterase properties, causing a decrease in Aβ aggregation.

OBJECTIVE

In this review, we approach structure-activity relationships of each compound, associating the decrease of ROS activity, an increase of tau-like activity and inhibition of AChE with a decrease in the self-aggregation of Aβ.

METHODS

We also verify that the molecular descriptors apol, nHBAcc and MlogP may be related to optimized pharmacokinetic properties for anti-AD drugs.

RESULTS

In our analysis, few selenium-derived compounds presented similar molecular features to FDA-approved drugs.

CONCLUSION

We suggest that unknown selenium-derived molecules with apol, nHBAcc and MlogP like FDA-approved drugs may be better successes with optimized pharmacokinetic properties in future studies in AD.

Novel therapeutic mechanism of action of metformin and its nanoformulation in Alzheimer's disease and role of AKT/ERK/GSK pathway

INTRODUCTION

Brain Insulin-resistance plays a critical role in pathogenesis of Alzheimer's disease (AD). Current study explored the therapeutic mechanism of metformin (insulin sensitizer) and its solid-lipid nanoformulation (SLN) in rat-model of AD. In our study, SLN was prepared using microemulsion method. AD was induced with ICV-Aβ whereas the control-group (sham) received ICV-NS. Treatment arms included, disease-control (no treatment), Metformin (50 mg/kg, 100 mg/kg and 150 mg/kg), SLN-metformin 50 mg/kg and memantine 1.8 mg/kg (positive-control). Animals were tested for cognitive performance (EPM, MWM) after 21 days of therapy and sacrificed. Aβ (1-42), hyperphosphorylated tau, pAKTser473, GSK-3β, p-ERK (ELISA), metformin level(HPLC), neuronal injury score(H&E), Bcl2 and Bax(IHC) was evaluated in isolated brain. In our study, metformin-SLN were of spherical shape (size<200 nm) with 94.08% entrapment efficiency. Metformin was detectable in brain. Compared to sham, the disease-control group showed significantly higher (p ≤ 0.05) memory impairment(MWM and EPM), hyperphosphorylated tau, Aβ(1-42), neuronal-injury, Bax and lower Bcl-2 expression. Treatment with metformin and nanoformulation significantly reverse these parameters. AKT-ERK-GSK3β-Hyperphosphorylated tau pathway was found to be involved in the protective efficacy of metformin. To conclude, both metformin and its SLN were found to be effective as therapeutic agents in AD which act through the AKT-ERK-GSK3β-Hyperphosphorylated tau pathway. We need population based studies to confirm the same.

NADPH oxidase family proteins: signaling dynamics to disease management

Reactive oxygen species (ROS) are pervasive signaling molecules in biological systems. In humans, a lack of ROS causes chronic and extreme bacterial infections, while uncontrolled release of these factors causes pathologies due to excessive inflammation. Professional phagocytes such as neutrophils (PMNs), eosinophils, monocytes, and macrophages use superoxide-generating NADPH oxidase (NOX) as part of their arsenal of antimicrobial mechanisms to produce high levels of ROS. NOX is a multisubunit enzyme complex composed of five essential subunits, two of which are localized in the membrane, while three are localized in the cytosol. In resting phagocytes, the oxidase complex is unassembled and inactive; however, it becomes activated after cytosolic components translocate to the membrane and are assembled into a functional oxidase. The NOX isoforms play a variety of roles in cellular differentiation, development, proliferation, apoptosis, cytoskeletal control, migration, and contraction. Recent studies have identified NOX as a major contributor to disease pathologies, resulting in a shift in focus on inhibiting the formation of potentially harmful free radicals. Therefore, a better understanding of the molecular mechanisms and the transduction pathways involved in NOX-mediated signaling is essential for the development of new therapeutic agents that minimize the hyperproduction of ROS. The current review provides a thorough overview of the various NOX enzymes and their roles in disease pathophysiology, highlights pharmacological strategies, and discusses the importance of computational modeling for future NOX-related studies.

Mangostanaxanthone IV Ameliorates Streptozotocin-Induced Neuro-Inflammation, Amyloid Deposition, and Tau Hyperphosphorylation via Modulating PI3K/Akt/GSK-3β Pathway

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is characterized by amyloid deposition and neurofibrillary tangles formation owing to tau protein hyperphosphorylation. Intra-cerebroventricular (ICV) administration of streptozotocin (STZ) has been widely used as a model of sporadic AD as it mimics many neuro-pathological changes witnessed in this form of AD. In the present study, mangostanaxanthone IV (MX-IV)-induced neuro-protective effects in the ICV-STZ mouse model were investigated. STZ (3 mg/kg, ICV) was injected once, followed by either MX-IV (30 mg/kg/day, oral) or donepezil (2.5 mg/kg/day, oral) for 21 days. Treatment with MX-IV diminished ICV-STZ-induced oxidative stress, neuro-inflammation, and apoptosis which was reflected by a significant reduction in malondialdehyde (MDA), hydrogen peroxide (H₂O₂), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) brain contents contrary to increased glutathione (GSH) content. Moreover, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase content and cleaved caspase-3 activity were reduced together with a marked decrement in amyloid plaques number and phosphorylated tau expression via PI3K/Akt/GSK-3β pathway modulation, leading to obvious enhancement in neuronal survival and cognition. Therefore, MX-IV is deemed as a prosperous nominee for AD management with obvious neuro-protective effects that were comparable to the standard drug donepezil.

Toxicology and pharmacology of synthetic organoselenium compounds: an update

Here, we addressed the pharmacology and toxicology of synthetic organoselenium compounds and some naturally occurring organoselenium amino acids. The use of selenium as a tool in organic synthesis and as a pharmacological agent goes back to the middle of the nineteenth and the beginning of the twentieth centuries. The rediscovery of ebselen and its investigation in clinical trials have motivated the search for new organoselenium molecules with pharmacological properties. Although ebselen and diselenides have some overlapping pharmacological properties, their molecular targets are not identical. However, they have similar anti-inflammatory and antioxidant activities, possibly, via activation of transcription factors, regulating the expression of antioxidant genes. In short, our knowledge about the pharmacological properties of simple organoselenium compounds is still elusive. However, contrary to our early expectations that they could imitate selenoproteins, organoselenium compounds seem to have non-specific modulatory activation of antioxidant pathways and specific inhibitory effects in some thiol-containing proteins. The thiol-oxidizing properties of organoselenium compounds are considered the molecular basis of their chronic toxicity; however, the acute use of organoselenium compounds as inhibitors of specific thiol-containing enzymes can be of therapeutic significance. In summary, the outcomes of the clinical trials of ebselen as a mimetic of lithium or as an inhibitor of SARS-CoV-2 proteases will be important to the field of organoselenium synthesis. The development of computational techniques that could predict rational modifications in the structure of organoselenium compounds to increase their specificity is required to construct a library of thiol-modifying agents with selectivity toward specific target proteins.

Role of reactive oxygen species in the progression of Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) involves neurodegeneration following the deposition of β-amyloid (Aβ) plaques and neurofibrillary tangles in vulnerable brain regions. The vulnerability of the brain to reactive oxygen species (ROS) is now emerging as a key detrimental factor driving AD pathogenesis. Oxidative stress (OS) irreversibly damages cellular biomolecules and perturbs neuronal functions. Scientific evidence is emerging that supports the therapeutic effects of antioxidants in preventing the onset and delaying the progression of AD pathology. In this review, we highlight the role of the OS in AD and the importance of antioxidants in its treatment.

Regulation of Diabetes: a Therapeutic Strategy for Alzheimer's Disease?

Accumulated evidence suggests that sporadic cases of Alzheimer's disease (AD) make up more than 95% of total AD patients, and diabetes has been implicated as a strong risk factor for the development of AD. Diabetes shares pathological features of AD, such as impaired insulin signaling, increased oxidative stress, increased amyloid-beta (Aβ) production, tauopathy and cerebrovascular complication. Due to shared pathologies between the two diseases, anti-diabetic drugs may be a suitable therapeutic option for AD treatment. In this article, we will discuss the well-known pathologies of AD, including Aβ plaques and tau tangles, as well as other mechanisms shared in AD and diabetes including reactive glia and the breakdown of blood brain barrier in order to evaluate the presence of any potential, indirect or direct links of pre-diabetic conditions to AD pathology. In addition, clinical evidence of high incidence of diabetic patients to the development of AD are described together with application of anti-diabetic medications to AD patients.

The role of NOX inhibitors in neurodegenerative diseases

Oxidative stress is a key player in both chronic and acute brain disease due to the higher metabolic demand of the brain. Among the producers of free radicals, NADPH-oxidase (NOX) is a major contributor to oxidative stress in neurological disorders. In the brain, the superoxide produced by NOX is mainly found in leukocytes. However, recent studies have reported that it can be found in several other cell types. NOX has been reported to regulate neuronal signaling, memory processing, and central cardiovascular homeostasis. However, overproduction of NOX can contribute to neurotoxicity, CNS degeneration, and cardiovascular disorders. Regarding the above functions, NOX has been shown to play a crucial role in chronic CNS diseases like Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS), and in acute CNS disorders such as stroke, spinal cord injury, traumatic brain injury (TBI), and related cerebrovascular diseases. NOX is a multi-subunit complex consisting of two membrane-associated and four cytosolic subunits. Thus, in recent years, inhibition of NOX activity has drawn a great deal of attention from researchers in the field of treating chronic and acute CNS disorders and preventing secondary complications. Mounting evidence has shown that NOX inhibition is neuroprotective and that inhibiting NOX in circulating immune cells can improve neurological disease conditions. This review summarizes recent studies on the therapeutic effects and pharmacological strategies regarding NOX inhibitors in chronic and acute brain diseases and focuses on the hurdles that should be overcome before their clinical implementation.

Protective Effects of 5-HT1A Receptor Inhibition and 5-HT2A Receptor Stimulation Against Streptozotocin-Induced Apoptosis in the Hippocampus

INTRODUCTION

Intracerebroventricular administration of streptozotocin (icv-STZ) induced apoptosis changes in neurons similar to Alzheimer's disease. The serotonergic system via its receptor involved in survival of neurons. The present study examined the ability of selective 5-HT1A receptor antagonist (NAD-299) and 5-HT2A receptor agonist (TCB-2) to attenuate the apoptosis caused by the icv-STZ in the rat.

METHODS

The icv-STZ (3 mg/kg, 10 μL, twice) induced neuronal loss in the hippocampus of adult male rats. Animals were divided into naive control, sham-operated, STZ+saline (1 μL, icv), STZ+NAD-299 (5 μg/μL, icv), STZ+TCB-2 (5 μg/μL, icv), and STZ+NAD-299+TCB-2 (5 μg/μL of any agent, icv) groups. Following the 35 days' treatment period, neuronal apoptosis was detected using the Tunnel. Cells with morphological features of apoptotic cell were contended by microscopy.

RESULTS

TCB-2 and NAD-299 administration decreased number of apoptotic neurons in the treatment group compared with the STZ group. Combined treatment of STZ rat with NAD+TCB more decreased number of apoptotic cells in compare to TCB-2 or NAD-299 treated STZ groups.

CONCLUSION

Treatment with 5-HT1A receptor antagonist or 5-HT2A receptor agonist diminished apoptosis. The beneficial effect of 5HT1A receptor inhibition was potentiated with activation of 5-HT2A receptor in prevention of apoptosis in hippocampus.

A multifunctional compound ebselen reverses memory impairment, apoptosis and oxidative stress in a mouse model of sporadic Alzheimer's disease

Alzheimer 's disease (AD) is characterized by progressive cognitive decline including memory impairment, cortical dysfunction, and neuropsychiatric disturbances. The drug discovery to treat AD consists to develop compounds able to act in multiple molecular targets involved in the pathogenesis of the disease and the repositioning of old drugs for new application. This way, the intracerebroventricular (icv) injection of streptozotocin (STZ) has been used as a metabolic model of sporadic AD. The aim of the present study was to investigate whether ebselen (1-10 mg/kg), a multifunctional selenoorganic compound, ameliorates memory impairment, hippocampal oxidative stress, apoptosis and cell proliferation in a mouse model of sporadic AD induced by icv STZ (3 mg/kg, 1 μl/min). The administration of ebselen (10 mg/kg, i.p.) reversed memory impairment and hippocampal oxidative stress, by increasing the activities of antioxidant enzymes and the level of a non-enzymatic antioxidant defense, in Swiss mice administered with icv STZ. The anti-apoptotic property of ebselen was demonstrated by its effectiveness against the increase in the ratios of Bax/Bcl-2, cleaved PARP/PARP and the cleaved caspase-3 levels in the hippocampus of icv STZ mice. Although ebselen reversed memory impairment, it was ineffective against the reduction in the number of BrdU positive cells induced by icv STZ. In conclusion, the multifunctional selenoorganic compound ebselen was effective to reverse memory impairment, hippocampal oxidative stress and apoptosis in a mouse model of sporadic AD induced by icv STZ.

Streptozotocin Impairs Proliferation and Differentiation of Adult Hippocampal Neural Stem Cells in Vitro-Correlation With Alterations in the Expression of Proteins Associated With the Insulin System

Rats intracerebroventricularily (icv) treated with streptozotocin (STZ), shown to generate an insulin resistant brain state, were used as an animal model for the sporadic form of Alzheimer’s disease (sAD). Previously, we showed in an in vivo study that 3 months after STZ icv treatment hippocampal adult neurogenesis (AN) is impaired. In the present study, we examined the effects of STZ on isolated adult hippocampal neural stem cells (NSCs) using an in vitro approach. We revealed that 2.5 mM STZ inhibits the proliferation of NSCs as indicated by reduced number and size of neurospheres as well as by less BrdU-immunoreactive NSCs. Double immunofluorescence stainings of NSCs already being triggered to start with their differentiation showed that STZ primarily impairs the generation of new neurons, but not of astrocytes. For revealing mechanisms possibly involved in mediating STZ effects we analyzed expression levels of insulin/glucose system-related molecules such as the glucose transporter (GLUT) 1 and 3, the insulin receptor (IR) and the insulin-like growth factor (IGF) 1 receptor. Applying quantitative Real time-PCR (qRT-PCR) and immunofluorescence stainings we showed that STZ exerts its strongest effects on GLUT3 expression, as GLUT3 mRNA levels were found to be reduced in NSCs, and less GLUT3-immunoreactive NSCs as well as differentiating cells were detected after STZ treatment. These findings suggest that cultured NSCs are a good model for developing new strategies to treat nerve cell loss in AD and other degenerative disorders.

Angiotensin II Type 2 Receptor Activation With Compound 21 Augments Islet Function and Regeneration in Streptozotocin-Induced Neonatal Rats and Human Pancreatic Progenitor Cells

OBJECTIVES

We investigated the effects of compound 21 (C21), a nonpeptide angiotensin II type 2 receptor agonist, on islet cell function and survival in streptozotocin (STZ)-treated neonatal rats and human pancreatic progenitor cells.

METHODS

Neonatal rats were randomized into 5 groups, including a control, an STZ (100 mg/kg, intraperitoneally), and 3 STZ + C21 (0.25, 0.5, and 1 mg/kg per day for 7 days, intraperitoneally) groups. Body weight and blood glucose were monitored daily. On the last experimental day, serum insulin levels and glucose tolerance were assessed, and the rat pups' pancreata were extracted for examination of islet cell function/mass and involvement of signaling pathways.

RESULTS

The C21-treated STZ rats, particularly in the 0.5- and 1 mg/kg-dosage groups, had significantly decreased blood glucose, increased serum insulin concentrations, higher glucose-stimulated insulin secretion activity, and greater islet-cell mass and up-regulated expression of insulin and Ngn3 in the pancreas than did the control groups; these rats also demonstrated increased β-cell proliferation, lower superoxide levels and enhanced SOD1 expression, and up-regulated phospho-AKT expression; consistently, similar results were also observed in human pancreatic progenitor cells.

CONCLUSIONS

These data suggest that C21 has a beneficial effect on islet cell function and regeneration, probably via proliferative and antioxidative pathways.

Selenium in the Therapy of Neurological Diseases. Where is it Going?

Selenium (₃₄Se), an antioxidant trace element, is an important regulator of brain function. These beneficial properties that Se possesses are attributed to its ability to be incorporated into selenoproteins as an amino acid. Several selenoproteins are expressed in the brain, in which some of them, e.g. glutathione peroxidases (GPxs), thioredoxin reductases (TrxRs) or selenoprotein P (SelP), are strongly involved in antioxidant defence and in maintaining intercellular reducing conditions. Since increased oxidative stress has been implicated in neurological disorders, including Parkinson’s disease, Alzheimer’s disease, stroke, epilepsy and others, a growing body of evidence suggests that Se depletion followed by decreased activity of Se-dependent enzymes may be important factors connected with those pathologies. Undoubtedly, the remarkable progress that has been made in understanding the biological function of Se in the brain has opened up new potential possibilities for the treatment of neurological diseases by using Se as a potential drug. However, further research in the search for optimal Se donors is necessary in order to achieve an effective and safe therapeutic income.

Different dose-dependent effects of ebselen in sciatic nerve ischemia-reperfusion injury in rats

Ebselen is an organoselenium compound which has strong antioxidant and anti-inflammatory effects. We investigated the neuroprotective role of ebselen pretreatment in rats with experimental sciatic nerve ischemia-reperfusion (I/R) injury. Adult male Sprague Dawley rats were divided into four groups (N = 7 in each group). Before sciatic nerve I/R was induced, ebselen was injected intraperitoneally at doses of 15 and 30 mg/kg. After a 2 h ischemia and a 3 h reperfusion period, sciatic nerve tissues were excised. Tissue levels of malondialdehyde (MDA) and nitric oxide (NO), and activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) were measured. Sciatic nerve tissues were also examined histopathologically. The 15 mg/kg dose of ebselen reduced sciatic nerve damage and apoptosis (p<0.01), levels of MDA, NO, and inducible nitric oxide synthase (iNOS) positive cells (p<0.01, p<0.05, respectively), and increased SOD, GPx, and CAT activities (p<0.001, p<0.01, p<0.05, respectively) compared with the I/R group that did not receive ebselen. Conversely, the 30 mg/kg dose of ebselen increased sciatic nerve damage, apoptosis, iNOS positive cells (p<0.01, p<0.05, p<0.001) and MDA and NO levels (p<0.05, p<0.01) and decreased SOD, GPx, and CAT activities (p<0.05) compared with the sham group. The results of this study suggest that ebselen may cause different effects depending on the dose employed. Ebselen may be protective against sciatic nerve I/R injury via antioxidant and antiapoptotic activities at a 15 mg/kg dose, conversely higher doses may cause detrimental effects.

Streptozotocin Intracerebroventricular-Induced Neurotoxicity and Brain Insulin Resistance: a Therapeutic Intervention for Treatment of Sporadic Alzheimer's Disease (sAD)-Like Pathology

Alzheimer's disease (AD) is a neurodegenerative disorder that is remarkably characterized by pathological hallmarks which include amyloid plaques, neurofibrillary tangles, neuronal loss, and progressive cognitive loss. Several well-known genetic mutations which are being used for the development of a transgenic model of AD lead to an early onset familial AD (fAD)-like condition. However, these settings are only reasons for a small percentage of the total AD cases. The large majorities of AD cases are considered as a sporadic in origin and are less influenced by a single mutation of a gene. The etiology of sporadic Alzheimer's disease (sAD) remains unclear, but numerous risk factors have been identified that increase the chance of developing AD. Among these risk factors are insulin desensitization/resistance state, oxidative stress, neuroinflammation, synapse dysfunction, tau hyperphosphorylation, and deposition of Aβ in the brain. Subsequently, these risk factors lead to development of sAD. However, the underlying molecular mechanism is not so clear. Streptozotocin (STZ) produces similar characteristic pathology of sAD such as altered glucose metabolism, insulin signaling, synaptic dysfunction, protein kinases such as protein kinase B/C, glycogen synthase-3β (GSK-3β) activation, tau hyperphosphorylation, Aβ deposition, and neuronal apoptosis. Further, STZ also leads to inhibition of Akt/PKB, insulin receptor (IR) signaling molecule, and insulin resistance in brain. These alterations mediated by STZ can be used to explore the underlying molecular and pathophysiological mechanism of AD (especially sAD) and their therapeutic intervention for drug development against AD pathology.

Ebselen protects against behavioral and biochemical toxicities induced by 3-nitropropionic acid in rats: correlations between motor coordination, reactive species levels, and succinate dehydrogenase activity

The protective effect of ebselen was investigated against 3-nitropropionic acid (3-NP)-induced behavioral and biochemical toxicities in rats. Ebselen (10 or 25 mg/kg, intragastrically) was administered to rats 30 min before 3-NP (20 mg/kg, intraperitoneally) once a day for a period of 4 days. Locomotor activity, motor coordination, and body weight gain were determined. The striatal content of reactive oxygen species (ROS), reduced glutathione (GSH), ascorbic acid (AA), and protein carbonyl as well as catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione-S-transferase (GST) activities was determined 24 h after the last dose of 3-NP. Na(+)/ K(+)-ATPase, succinate dehydrogenase (SDH), and δ-aminolevulinic dehydratase (δ-ALA-D) activities were also determined. The results demonstrated that ebselen at a dose of 25 mg/kg, but not at 10 mg/kg, protected against (1) a decrease in locomotor activity, motor coordination impairment, and body weight loss; (2) striatal oxidative damage, which was characterized by an increase in ROS levels, protein carbonyl content, and GR activity, an inhibition of CAT and GPx activities, and a decrease in GSH levels; and (3) an inhibition of SDH and Na(+)/K(+)-ATPase activities, induced by 3-NP. GST activity and AA levels were not modified by ebselen or 3-NP. Ebselen was not effective against the inhibition of δ-ALA-D activity induced by 3-NP. The results revealed a significant correlation between SDH activity and ROS levels, and SDH activity and latency to fall (rotarod test). The present study highlighted the protective effect of ebselen against 3-NP-induced toxicity in rats.