Lessons from the physiological role of guanosine in neurodegeneration and cancer: Toward a multimodal mechanism of action?

Neurodegenerative diseases and brain tumours represent important health challenges due to their severe nature and debilitating consequences that require substantial medical care. Interestingly, these conditions share common physiological characteristics, namely increased glutamate, and adenosine transmission, which are often associated with cellular dysregulation and damage. Guanosine, an endogenous nucleoside, is safe and exerts neuroprotective effects in preclinical models of excitotoxicity, along with cytotoxic effects on tumour cells. However, the lack of well-defined mechanisms of action for guanosine hinders a comprehensive understanding of its physiological effects. In fact, the absence of specific receptors for guanosine impedes the development of structure-activity research programs to develop guanosine derivatives for therapeutic purposes. Alternatively, given its apparent interaction with the adenosinergic system, it is plausible that guanosine exerts its neuroprotective and anti-tumorigenic effects by modulating adenosine transmission through undisclosed mechanisms involving adenosine receptors, transporters, and purinergic metabolism. Here, several potential molecular mechanisms behind the protective actions of guanosine will be discussed. First, we explore its potential interaction with adenosine receptors (A1R and A2AR), including the A1R-A2AR heteromer. In addition, we consider the impact of guanosine on extracellular adenosine levels and the role of guanine-based purine-converting enzymes. Collectively, the diverse cellular functions of guanosine as neuroprotective and antiproliferative agent suggest a multimodal and complementary mechanism of action.

Guanosine Prevents Spatial Memory Impairment and Hippocampal Damage Following Amyloid-ß1-42 Administration in Mice.

Alzheimer's disease (AD) is a progressive neurodegenerative illness responsible for cognitive impairment and dementia. Accumulation of amyloid-beta (Aß) peptides in neurons and synapses causes cell metabolism to unbalance, and the production of reactive oxygen species (ROS), leading to neuronal death and cognitive damage. Guanosine is an endogenous nucleoside recognized as a neuroprotective agent since it prevents glutamate-induced neurotoxicity by a mechanism not yet completely elucidated. In this study, we evaluated behavioral and biochemical effects in the hippocampus caused by the intracerebroventricular (i.c.v.) infusion of Aß1-42 peptide (400 pmol/site) in mice, and the neuroprotective effect of guanosine (8 mg/kg, i.p.). An initial evaluation on the eighth day after Aß1-42 infusion showed no changes in the tail suspension test, although ex vivo analyses in hippocampal slices showed increased ROS production. In the second protocol, on the tenth day following Aß1-42 infusion, no effect was observed in the sucrose splash test, but a reduction in the recognition index in the object location test showed impaired spatial memory. Analysis of hippocampal slices showed no ROS production and mitochondrial membrane potential alteration, but a tendency to increase glutamate release and a significant lactate release, pointing to a metabolic alteration. Those effects were accompanied by decreased cell viability and increased membrane damage. Guanosine treatment prevented behavioral and biochemical alterations evoked by Aß1-42, suggesting a potential role against behavioral and biochemical damage evoked by Aß in the hippocampus.

Neonatal Isoflurane Exposure in Rats Impairs Short-Term Memory, Cell Viability, and Glutamate Uptake in Slices of the Frontal Cerebral Cortex, But Not the Hippocampus, in Adulthood.

Neonatal exposure to general anesthetics has been associated with neurotoxicity and morphologic changes in the developing brain. Isoflurane is a volatile anesthetic widely used in pediatric patients to induce general anesthesia, analgesia, and perioperative sedation. In the present study, we investigated the effects of a single neonatal isoflurane (3% in oxygen, 2 h) exposure in rats at postnatal day (PND) 7, in short-term (24 h - PND8) and long-term (adulthood) protocols. In PND8, ex vivo analysis of hippocampal and frontal cortex slices evaluated cell viability and susceptibility to in vitro glutamate challenge. In adult rats, behavioral parameters related to anxiety-like behavior, short-term memory, and locomotor activity (PND60-62) and ex vivo analysis of cell viability, membrane permeability, glutamate uptake, and susceptibility to in vitro glutamate challenge in hippocampal and cortical slices from PND65. A single isoflurane (3%, 2 h) exposure at PND7 did not acutely alter cell viability in cortical and hippocampal slices of infant rats (PND8) per se and did not alter slice susceptibility to in vitro glutamate challenge. In rat's adulthood, behavioral analysis revealed that the neonatal isoflurane exposure did not alter anxiety-like behavior and locomotor activity (open field and rotarod tests). However, isoflurane exposure impaired short-term memory evaluated in the novel object recognition task. Ex vivo analysis of brain slices showed isoflurane neonatal exposure selectively decreased cell viability and glutamate uptake in cortical slices, but it did not alter hippocampal slice viability or glutamate uptake (PND65). Isoflurane exposure did not alter in vitro glutamate-induced neurotoxicity to slices, and isoflurane exposure caused no significant long-term damage to cell membranes in hippocampal or cortical slices. These findings indicate that a single neonatal isoflurane exposure did not promote acute damage; however, it reduced cortical, but not hippocampal, slice viability and glutamate uptake in the adulthood. Additionally, behavioral analysis showed neonatal isoflurane exposure induces short-term recognition memory impairment, consolidating that neonatal exposure to volatile anesthetics may lead to behavioral impairment in the adulthood, although it may damage brain regions differentially.

Anti-cancer Effects of Fucoxanthin on Human Glioblastoma Cell Line.

BACKGROUND/AIM: Glioblastomas (GBMs) are the most malignant primary brain tumor. New treatment strategies against the disease are urgently needed, as therapies are not completely efficient. In this study, we evaluated the antitumorigenic activity of the carotenoid fucoxanthin (Fx) on human GBM cells in vitro. MATERIALS AND METHODS: GBM1 cell viability and proliferation was assessed by MTT reduction, Ki67 and single cell cloning assays. GBM1 migration and invasion were analyzed by wound healing and Transwell assays. Apoptosis and necrosis were analyzed by flow cytometry, and the mitochondrial membrane potential (ΔΨm) by the selective fluorescent dye tetramethylrhodamine ethyl ester. Cell morphology was analyzed through scanning electron microscopy and transmission electron microscopy. Fx anti-angiogenic effect was assessed by the CAM ex ovo assay. RESULTS: Fx decreased cell viability in a concentration-dependent manner (40-100 µ M) in GBM1, A172 and C6 cell lines and was not cytotoxic to murine astrocytes. In addition, Fx inhibited the proliferation and clonogenic potential, and decreased migration and invasion of GBM1 cells. Furthermore, Fx induced apoptosis, loss of ΔΨm and ultrastructural alterations in GBM1. Fx-treated GBM1 cells-conditioned medium reduced the quail yolk membrane vascularity. CONCLUSION: Fx induces cytotoxicity, anti-proliferative, anti-invasive and anti-angiogenic effects on GBM1 cells.

Role of Prefrontal Cortex on Recognition Memory Deficits in Rats following 6-OHDA-Induced Locus Coeruleus Lesion.

Degeneration of the locus coeruleus (LC), the main source of cerebral noradrenaline (NA), has been reported in diverse neurodegenerative diseases, including Parkinson's diseases (PD). There is increasing evidence indicating the role of NA deficiency in the prefrontal cortex (PFC) and the development of early cognitive impairments in PD. Here, we evaluated whether a selective noradrenergic lesion of LC caused by 6-hydroxydopamine (6-OHDA) may induce memory deficits and neurochemical alterations in the PFC. Adult male Wistar rats received stereotaxic bilateral injections of 6-OHDA (5 µg/2 µl) into the LC, and two stainless-steel guide cannulas were implanted in the PFC. The SHAM group received just vehicle. To induce a selective noradrenergic lesion, animals received nomifensine (10 mg/kg), a dopamine transporter blocker, one hour before surgery. 6-OHDA-lesioned rats displayed impairments of the short- and long-term object recognition memory associated to reduced content of tyrosine hydroxylase in the LC. Neurochemical analysis revealed an altered mitochondrial membrane potential in LC. Regarding the PFC, an increased ROS production, cell membrane damage, and mitochondrial membrane potential disruption were observed. Remarkably, bilateral NA (1 µg/0.2 µl) infusion into the PFC restored the recognition memory deficits in LC-lesioned rats. These findings indicate that a selective noradrenergic LC lesion induced by 6-OHDA deregulates a noradrenergic network in the PFC, which could be involved in the early memory impairments observed in nondemented PD patients.

Guanosine Neuroprotective Action in Hippocampal Slices Subjected to Oxygen and Glucose Deprivation Restores ATP Levels, Lactate Release and Glutamate Uptake Impairment: Involvement of Nitric Oxide.

Stroke is a major cause of disability and death worldwide. Oxygen and glucose deprivation (OGD) in brain tissue preparations can reproduce several pathological features induced by stroke providing a valuable ex vivo protocol for studying the mechanism of action of neuroprotective agents. Guanosine, an endogenous guanine nucleoside, promotes neuroprotection in vivo and in vitro models of neurotoxicity. We previously showed that guanosine protective effect was mimicked by inhibition of nitric oxide synthases (NOS) activity. This study was designed to investigate the involvement of nitric oxide (NO) in the mechanisms related to the protective role of guanosine in rat hippocampal slices subjected to OGD followed by reoxygenation (OGD/R). Guanosine (100 µM) and the pan-NOS inhibitor, L-NAME (1 mM) afforded protection to hippocampal slices subjected to OGD/R. The presence of NO donors, DETA-NO (800 µM) or SNP (5 µM) increased reactive species production, and abolished the protective effect of guanosine or L-NAME against OGD/R. Guanosine or L-NAME treatment prevented the impaired ATP production, lactate release, and glutamate uptake following OGD/R. The presence of a NO donor also abolished the beneficial effects of guanosine or L-NAME on bioenergetics and glutamate uptake. These results showed, for the first time, that guanosine may regulate cellular bioenergetics in hippocampal slices subjected to OGD/R injury by a mechanism that involves the modulation of NO levels.

Guanosine Promotes Proliferation in Neural Stem Cells from Hippocampus and Neurogenesis in Adult Mice.

Neural stem cells can generate new neurons in the mouse adult brain in a complex multistep process called neurogenesis. Several factors regulate this process, including neurotransmitters, hormones, neurotrophic factors, pharmacological agents, and environmental factors. Purinergic signaling, mainly the adenosinergic system, takes part in neurogenesis, being involved in cell proliferation, migration, and differentiation. However, the role of the purine nucleoside guanosine in neurogenesis remains unclear. Here, we examined the effect of guanosine by using the neurosphere assay derived from neural stem cells of adult mice. We found that continuous treatment with guanosine increased the number of neurospheres, neural stem cell proliferation, and neuronal differentiation. The effect of guanosine to increase the number of neurospheres was reduced by removing adenosine from the culture medium. We next traced the neurogenic effect of guanosine in vivo. The intraperitoneal treatment of adult C57BL/6 mice with guanosine (8 mg/kg) for 26 days increased the number of dividing bromodeoxyuridine (BrdU)-positive cells and also increased neurogenesis, as identified by measuring doublecortin (DCX)-positive cells in the dentate gyrus (DG) of the hippocampus. Antidepressant-like behavior in adult mice accompanied the guanosine-induced neurogenesis in the DG. These results provide new evidence of a pro-neurogenic effect of guanosine on neural stem/progenitor cells, and it was associated in vivo with antidepressant-like effects.

Guanosine prevents depressive-like behaviors in rats following bilateral dorsolateral striatum lesion induced by 6-hydroxydopamine.

The dorsolateral striatum (DLS) processes motor and non-motor functions and undergoes extensive dopaminergic degeneration in Parkinson's disease (PD). Beyond the nigrostriatal pathway, dopaminergic degeneration also affects other brain areas including the pre-frontal cortex (PFC) and hippocampus, which have been associated with the appearance of anhedonia and depression at pre-motor phases of PD. Herein, using behavioral and biochemical approaches, we investigated the protective effects of guanosine (GUO) (7.5 mg/kg, i.p.) against emotional impairments and cellular events in cortical, striatal and hippocampal slices of rats submitted to a bilateral infusion of 6-OHDA (10 µg/hemisphere) into the DLS. 6-OHDA-lesioned rats displayed anhedonic- and depressive-like behaviors addressed in the splash and forced swimming tests (at 8 and 21 days after lesion, respectively). In addition, no alterations in motor performance in the open field test and social interaction were observed. Biochemical analyses were performed 22 days after 6-OHDA lesions. 6-OHDA lesion induced hippocampal mitochondrial membrane potential disruption. However, intra-striatal 6-OHDA administration did not alter the ROS levels measured in cortical, striatal and hippocampal slices. GUO treatment attenuated anhedonic- and depressive-like behaviors in 6-OHDA-lesioned rats and protected hippocampal slices against the mitochondrial membrane potential disruption. These results indicate antidepressant-like effects of GUO in a rat model of PD, indicating the potential of GUO for the treatment of depression associated with PD.

New ionic targets of 3,3',5'-triiodothyronine at the plasma membrane of rat Sertoli cells.

The functions of Sertoli cells, which structurally and functionally support ongoing spermatogenesis, are effectively modulated by thyroid hormones, amongst other molecules. We investigated the mechanism of action of rT3 on calcium (45Ca2+) uptake in Sertoli cells by means of in vitro acute incubation. In addition, we performed electrophysiological recordings of potassium efflux in order to understand the cell repolarization, coupled to the calcium uptake triggered by rT3. Our results indicate that rT3 induces nongenomic responses, as a rapid activation of whole-cell potassium currents in response to rT3 occurred in <5 min in Sertoli cells. In addition, the rT3 metabolite, T2, also exerted a rapid effect on calcium uptake in immature rat testis and in Sertoli cells. rT3 also modulated calcium uptake, which occurred within seconds via the action of selective ionic channels and the Na+/K+ ATPase pump. The rapid response of rT3 is essentially triggered by calcium uptake and cell repolarization, which appear to mediate the secretory functions of Sertoli cells.

Guanosine Protects Striatal Slices Against 6-OHDA-Induced Oxidative Damage, Mitochondrial Dysfunction, and ATP Depletion.

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by loss of dopaminergic neurons in substantia nigra pars compacta which induces severe motor symptoms. 6-OHDA is a neurotoxin widely used in PD animal models due to its high affinity by dopamine transporter, its rapid non-enzymatic auto-oxidation which generates reactive oxygen species (ROS), oxidative stress, and for induced mitochondrial dysfunction. We previously reported an in vitro protocol of 6-OHDA-induced toxicity in brain regions slices, as a simple and sensitive assay to screen for protective compounds related to PD. Guanosine (GUO), a guanine-based purine nucleoside, is a neuroprotective molecule that is showing promising effects as an antiparkinsonian agent. To investigate the mechanisms involved on GUO-induced neuroprotection, slices of cortex, striatum, and hippocampus were incubated with GUO in the presence of 6-OHDA (100 µM). 6-OHDA promoted a decrease in cellular viability and increased ROS generation in all brain regions. Disruption of mitochondrial potential, depletion in intracellular ATP levels, and increase in cell membrane permeabilization were evidenced in striatal slices. GUO prevented the increase in ROS generation, disruption in mitochondrial potential, and depletion of intracellular ATP induced by 6-OHDA in striatal slices. In conclusion, GUO was effective to prevent oxidative events before cell damage, such as mitochondrial disruption, intracellular ATP levels depletion, and ROS generation in striatal slices subjected to in vitro 6-OHDA-induced toxicity.

Long-Term Neurobehavioral Consequences of a Single Ketamine Neonatal Exposure in Rats: Effects on Cellular Viability and Glutamate Transport in Frontal Cortex and Hippocampus.

The neonatal exposure to general anesthetics has been associated with neuronal apoptosis and dendritic spines morphologic changes in the developing brain. Ketamine, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, is widely used in pediatric patients to induce general anesthesia, analgesia, and perioperative sedation. In the present study, we investigated short- and long-term effects of a single ketamine (20 mg/kg, s.c.) neonatal exposure at postnatal day 7 in rats on the hippocampal and frontal cortical cellular viability. Additionally, putative neurochemical alterations and neurobehavioral impairments were evaluated in the adulthood. Ketamine neonatal administration selectively decreased cellular viability in the hippocampus, but not in the frontal cortex, 24 h after the treatment. Interestingly, a single ketamine neonatal exposure prevented the vulnerability to glutamate-induced neurotoxicity in the frontal cortex of adult rats. No short- or long-term damage to cellular membranes, as an indicative of cell death, was observed in hippocampal or cortical slices. However, ketamine induced a long-term increase in hippocampal glutamate uptake. Regarding behavioral analysis, neonatal ketamine exposure did not alter locomotor activity and anxiety-related parameters evaluated in the open-field test. However, ketamine administration disrupted the hippocampal-dependent object recognition ability of adult rats, while improved the motor coordination addressed on the rotarod. These findings indicate that a single neonatal ketamine exposure induces a short-term reduction in the hippocampal, but not in cortical, cellular viability, and long-term alterations in hippocampal glutamate transport, improvement on motor performance, and short-term recognition memory impairment.

Folic Acid Protects Against Glutamate-Induced Excitotoxicity in Hippocampal Slices Through a Mechanism that Implicates Inhibition of GSK-3ß and iNOS.

Folic acid (folate) is a vitamin of the B-complex group crucial for neurological function. Considering that excitotoxicity and cell death induced by glutamate are involved in many disorders, the potential protective effect of folic acid on glutamate-induced cell damage in rat hippocampal slices and the possible intracellular signaling pathway involved in such effect were investigated. The treatment of hippocampal slices with folic acid (100 µM) significantly abrogated glutamate (1 mM)-induced reduction of cell viability measured by MTT reduction assay and inhibited glutamate-induced D-[3H]-aspartate release. To investigate the putative intracellular signaling pathways implicated in the protective effect of folic acid, we used a PI3K inhibitor, LY294002, which abolished the protective effects of folic acid against glutamate-induced cell damage and D-[3H] aspartate release. Moreover, hippocampal slices incubated with folic acid alone for 30 min presented increased phosphorylation of GSK-3ß at Ser9, indicating an inhibition of the activity of this enzyme. Furthermore, folic acid in the presence of glutamate insult in hippocampal slices maintained for an additional period of 6 h in fresh culture medium without glutamate and/or folic acid induced phosphorylation of GSK-3ß and ß-catenin expression. In addition, glutamate-treated hippocampal slices showed increased iNOS expression that was reversed by folic acid. In conclusion, the results of this study show that the protective effect of folic acid against glutamate-induced excitotoxicity may involve the modulation of PI3K/GSK-3ß/ß-catenin pathway and iNOS inhibition.

Inhibition of reductase systems by 2-AAPA modulates peroxiredoxin oxidation and mitochondrial function in A172 glioblastoma cells.

Thiol homeostasis has a critical role in the maintenance of proper cellular functions and survival, being coordinated by the action of several reductive enzymes, including glutathione (GSH)/glutathione reductase (GR) and thioredoxin (Trx)/thioredoxin reductase (TrxR) systems. Here, we investigated the effects of the GR inhibitor 2-acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanylthiocarbonylamino)phenylthiocarbamoylsulfanyl]propionic acid (2-AAPA) on the activity of thiol reductases (GR and TrxR), redox balance and mitochondrial function of A172 glioblastoma cells. 2-AAPA inhibited cell GR (IC50=6.7µM) and TrxR (IC50=8.7µM). A significant decrease in the cellular ability to decompose cumene hydroperoxide was observed and associated to a greater susceptibility to this peroxide. The redox state of peroxiredoxins (Prx1, Prx2 and Prx3) was markedly shifted to dimer 30min after treatment with 100µM 2-AAPA, an event preceding 2-AAPA-induced decrease in cell viability. Furthermore, mitochondrial function was also severely impaired, leading to a decrease in the respiratory control ratio, reserve capacity, and ATP synthesis-coupled respiration, as well as an increase in mitochondrial membrane potential. Our results indicate that inhibition of GR and TrxR activities, disruption of the ability to detoxify peroxides, increased oxidation of Prxs, as well as compromised mitochondrial function represent early events mediating 2-AAPA toxicity to A172 glioblastoma cells.

Guanosine promotes cytotoxicity via adenosine receptors and induces apoptosis in temozolomide-treated A172 glioma cells.

Gliomas are a malignant tumor group whose patients have survival rates around 12 months. Among the treatments are the alkylating agents as temozolomide (TMZ), although gliomas have shown multiple resistance mechanisms for chemotherapy. Guanosine (GUO) is an endogenous nucleoside involved in extracellular signaling that presents neuroprotective effects and also shows the effect of inducing differentiation in cancer cells. The chemotherapy allied to adjuvant drugs are being suggested as a novel approach in gliomas treatment. In this way, this study evaluated whether GUO presented cytotoxic effects on human glioma cells as well as GUO effects in association with a classical chemotherapeutic compound, TMZ. Classical parameters of tumor aggressiveness, as alterations on cell viability, type of cell death, migration, and parameters of glutamatergic transmission, were evaluated. GUO (500 and 1000 µM) decreases the A172 glioma cell viability after 24, 48, or 72 h of treatment. TMZ alone or GUO plus TMZ also reduced glioma cell viability similarly. GUO combined with TMZ showed a potentiation effect of increasing apoptosis in A172 glioma cells, and a similar pattern was observed in reducing mitochondrial membrane potential. GUO per se did not elevate the acidic vesicular organelles occurrence, but TMZ or GUO plus TMZ increased this autophagy hallmark. GUO did not alter glutamate transport per se, but it prevented TMZ-induced glutamate release. GUO or TMZ did not alter glutamine synthetase activity. Pharmacological blockade of glutamate receptors did not change GUO effect on glioma viability. GUO cytotoxicity was partially prevented by adenosine receptor (A1R and A2AR) ligands. These results point to a cytotoxic effect of GUO on A172 glioma cells and suggest an anticancer effect of GUO as a putative adjuvant treatment, whose mechanism needs to be unraveled.

Involvement of PI3K/Akt/GSK-3ß and mTOR in the antidepressant-like effect of atorvastatin in mice.

Atorvastatin is a cholesterol-lowering statin that has been shown to exert several pleiotropic effects in the nervous system as a neuroprotective and antidepressant-like agent. Antidepressant-like effect of atorvastatin in mice is mediated by glutamatergic and serotoninergic receptors, although the precise intracellular signaling pathways involved are unknown. PI3K/Akt/GSK-3ß/mTOR signaling pathway has been associated to neurobiology of depression and seems to be modulated by some pharmacological antidepressant strategies. The present study investigated the participation of the PI3K/Akt/GSK-3ß/mTOR signaling pathway in the antidepressant-like effect of an acute atorvastatin treatment in mice. Atorvastatin sub-effective (0.01 mg/kg) or effective (0.1 mg/kg) doses in the tail suspension test (TST) was administered orally alone or in combination with PI3K, GSK-3ß or mTOR inhibitors. The administration of PI3K inhibitor, LY294002 (10 nmol/site, i.c.v) completely prevented the antidepressant-like effect of atorvastatin (0.1 mg/kg, p.o.). The participation of GSK-3ß in the antidepressant-like effect of atorvastatin was demonstrated by co-administration of a sub-effective dose of atorvastatin (0.01 mg/kg, p.o.) with AR-A014418 (0.01 µg/site, i.c.v., a selective GSK-3ß inhibitor) or with lithium chloride (10 mg/kg, p.o., a non-selective GSK-3ß inhibitor). The mTOR inhibitor, rapamycin (0.2 nmol/site, i.c.v.) was also able to prevent atorvastatin (0.1 mg/kg, p.o.) antidepressant-like effect. These behavioral findings were supported by neurochemical observations, as atorvastatin treatment increased the immunocontent of the phosphorylated isoforms of Akt, GSK-3ß and mTOR in the hippocampus of mice. Taken together, our results suggest an involvement of the PI3K/Akt/GSK-3ß/mTOR signaling pathway in the antidepressant-like effect of atorvastatin in mice.

Novel synthetic chalcones induces apoptosis in human glioblastoma cells.

Glioblastoma multiforme is the main and most frequent tumor in adults' central nervous system. With a survival average of 5% two years after diagnosis, this type of cancer is a main health problem. Substances like the chalcones have been tested in order to develop new treatments. Here, we studied the effects of three synthetic chalcones (A23, C31 and J11) on A172 and surgery obtained-glioma cells. All chalcones showed a decrease in cell viability, mainly C31. An increase in apoptosis levels with no further increase of necrosis was observed. This augmentation may be linked to the high oxidative effect found, caused by the increased presence of reactive oxygen species and nitric oxide production. Cell cycle distribution showed an arrest at G0/G1 and S phases, suggesting that C31 interferes in cell cycle control. Our results shall aid in directing future research with this substance and its antitumor effect.

Battling Alzheimer's Disease: Targeting SUMOylation-Mediated Pathways.

SUMO (small ubiquitin-like modifier) conjugation is a critically important control process in all eukaryotic cells, because it acts as a biochemical switch and regulates the function of hundreds of proteins in many different pathways. Although the diverse functional consequences and molecular targets of SUMOylation remain largely unknown, SUMOylation is becoming increasingly implicated in the pathophysiology of Alzheimer's disease (AD). Apart from the central SUMO-modified disease-associated proteins, such as amyloid precursor protein, amyloid ß, and tau, SUMOylation also regulates several other processes underlying AD. These are involved in inflammation, mitochondrial dynamics, synaptic transmission and plasticity, as well as in protective responses to cell stress. Herein, we review current reports on the involvement of SUMOylation in AD, and present an overview of potential SUMO targets and pathways underlying AD pathogenesis.

Influence of environmental enrichment vs. time-of-day on behavioral repertoire of male albino Swiss mice.

Environmental enrichment (EE) is a non-pharmacological manipulation that promotes diverse forms of benefits in the central nervous system of captive animals. It is thought that EE influences animal behavior in a specie-(strain)-specific manner. Since rodents in general present different behaviors during distinct periods of the day, in this study we aimed to investigate the influence of time-of-day on behavioral repertoire of Swiss mice that reared in EE. Forty male Swiss mice (21days old) were housed in standard (SC) or enriched conditions (EC) for 60days. Behavioral assessments were conducted during the light phase (in presence of light) or dark phase (in absence of light) in the following tasks: open field, object recognition and elevated plus maze. First, we observed that the locomotor and exploratory activities are distinct between SC and EC groups only during the light phase. Second, we observed that "self-protective behaviors" were increased in EC group only when mice were tested during the light phase. However, "less defensive behaviors" were not affected by both housing conditions and time-of-day. Third, we showed that the performance of EE animals in object recognition task was improved in both light and dark conditions. Our findings highlight that EE-induced alterations in exploratory and emotional behaviors are just evident during light conditions. However, EE-induced cognitive benefits are remarkable even during dark conditions, when exploratory and emotional behaviors were similar between groups.

Cerebral cortex, hippocampus, striatum and cerebellum show differential susceptibility to quinolinic acid-induced oxidative stress.

Quinolinic acid (QA) is a NMDA receptor agonist implicated in pathological conditions, such as neurodegenerative diseases and epilepsy. Time-course responses of different brain regions after QA i.c.v. infusion are not known. We aimed to investigate the time-course effects of QA infusion on oxidative stress-related parameters on different brain regions. In cerebral cortex, QA infusion promoted an early (1 h) decrease of NPSH levels and GR activity followed by a later increase in ROS production (8 h) and TBARS detection (24-72 h). In the hippocampus, QA promoted an increase in ROS production that lasted 8 h. Striatal tissue presented a later increase in ROS generation (8-72 h) after QA infusion. In the cerebellum, an increase in the GPx activity after 8 h was the only effect observed. These results show that oxidative stress induced by QA i.c.v. infusion is region and time dependent.

Statins enhance cognitive performance in object location test in albino Swiss mice: involvement of beta-adrenoceptors.

Statins are inhibitors of the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, thereby inhibiting cell synthesis of cholesterol and isoprenoids. Moreover, several studies have been evaluating pleiotropic effects of statins, mainly because they present neuroprotective effects in various pathological conditions. However, knowledge about behavioral effects of statins per se is relatively scarce. Considering these facts, we aimed to analyze behavioral responses of atorvastatin or simvastatin-treated mice in the open field test, elevated plus maze and object location test. Atorvastatin treatment for 7 consecutive days at 1 mg/kg or 10 mg/kg (v.o.) or simvastatin 10 mg/kg or 20 mg/kg enhanced cognitive performance in object location test when compared to control group (saline-treated mice). Simvastatin effects on mice performance in the object location test was abolished by post-training infusion of the beta-adrenoceptor antagonist propranolol. Atorvastatin and simvastatin did not change the behavioral response in open field and elevated plus-maze (EPM) tests in any of the used doses. These data demonstrate the positive effects of both statins in cognitive processes in mice, without any alteration in locomotor parameters in the open field test or anxiolytic-like behavior in EPM. In conclusion, we demonstrate that atorvastatin and simvastatin per se improve the cognitive performance in a rodent model of spatial memory and this effect is related to beta-adrenergic receptors modulation.