Ectonucleotidases in Inflammation, Immunity, and Cancer.

Nucleoside triphosphate diphosphohydrolases (NTPDases) are a family of enzymes that hydrolyze nucleotides such as ATP, UTP, ADP, and UDP to monophosphates derivates such as AMP and UMP. The NTPDase family consists of eight enzymes, of which NTPDases 1, 2, 3, and 8 are expressed on cell membranes thereby hydrolyzing extracellular nucleotides. Cell membrane NTPDases are expressed in all tissues, in which they regulate essential physiological tissue functions such as development, blood flow, hormone secretion, and neurotransmitter release. They do so by modulating nucleotide-mediated purinergic signaling through P2 purinergic receptors. NTPDases 1, 2, 3, and 8 also play a key role during infection, inflammation, injury, and cancer. Under these conditions, NTPDases can contribute and control the pathophysiology of infectious, inflammatory diseases and cancer. In this review, we discuss the role of NTPDases, focusing on the less understood NTPDases 2-8, in regulating inflammation and immunity during infectious, inflammatory diseases, and cancer.

Insulin activates microglia and increases COX-2/IL-1ß expression in young but not in aged hippocampus.

Brain insulin resistance and neuroinflammation are known to increase with age. Insulin exerts metabolic roles on neurons and astrocytes, but its effects on microglia is unclear. In this study we investigated whether insulin affected microglia in the hippocampus of young and aged rats. We injected intracerebroventricular (i.c.v.) insulin (20 mU) or vehicle for five days and evaluated microglial inflammatory markers in the hippocampus of young (3 months) Wistar rats. Increased microglial activation (Iba-1+CD68+cells) and COX-2/IL-1ß levels in the hippocampus were found. Since the aged brain is an experimental model for brain insulin resistance and chronic neuroinflammation we submitted aged rats (22 months) to i.c.v. insulin/vehicle administration and found no significant increase in Iba-1+CD68+ microglia or COX-2/IL-1ß levels. To further investigate whether insulin triggered transient or persistent proinflammatory responses, young rats were evaluated eight-days after the last insulin injection. Microglia were persistently activated, and COX-2 levels remained elevated in the hippocampus, which paralleled increased spatial memory performance in the Morris Water Maze behavioral task. To determine if microglia were directly responsive to insulin, primary microglia were challenged with insulin and increased Akt Ser473 phosphorylation, a protein activated by the insulin receptor, was detected. These data suggest that microglia in the hippocampus integrate insulin signaling and neuroinflammatory responses and that this signal is disrupted during chronic inflammation. In our concept, the disruption between microglia activation by insulin signaling is a new pathological mechanism behind insulin resistance in the aging brain.

Memantine mediates astrocytic activity in response to excitotoxicity induced by PP2A inhibition.

Reduced activity of protein phosphatase 2 A (PP2A) is a common feature in Alzheimer's disease (AD) and non-AD tauopathies. The administration of okadaic acid (OKA), a potent PP2A and PP1 inhibitor, is a common research tool for inducing AD-like alterations such as tau hyperphosphorylation and cognitive decline. Recently, we showed that OKA increases cerebrospinal fluid (CSF) glutamate levels, which was strongly correlated with cognitive decline. Also, we demonstrated that memantine (MN), a glutamatergic NMDAR channel blocker, was capable of preventing the increase in CSF glutamate levels and cognitive decline. Here, we aimed to analyze whether the protective effects of MN involve intrinsic astrocytic properties, particularly related to glutamate uptake and astrocytic reactivity - indexed by the expression of S100B and glial fibrillary acidic protein (GFAP). Rats received intraperitoneal injections of MN or saline over 3 consecutive days before receiving intrahippocampal infusion of OKA or saline. Afterward, they were submitted to behavioral tasks and then, euthanatized for neurochemical analysis. Here, we showed that the neuroprotective effects of MN in response to OKA neurotoxicity involve astrocytic activation. MN decreased glutamate uptake in the hippocampus and increased the release of S100B protein in the CSF in response to OKA neurotoxicity, which indicates a possible neurons-astrocyte coupling protective mechanism. These findings shed light on astrocytes as potential targets for treating neurological disorders associated with decreased PP2A activity.

Peripheral Oxidative Stress Biomarkers in Spinocerebellar Ataxia Type 3/Machado-Joseph Disease.

OBJECTIVES: Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is a polyglutamine disorder with no current disease-modifying treatment. Conformational changes in mutant ataxin-3 trigger different pathogenic cascades, including reactive oxygen species (ROS) generation; however, the clinical relevance of oxidative stress elements as peripheral biomarkers of SCA3/MJD remains unknown. We aimed to evaluate ROS production and antioxidant defense capacity in symptomatic and presymptomatic SCA3/MJD individuals and correlate these markers with clinical and molecular data with the goal of assessing their properties as disease biomarkers. METHODS: Molecularly confirmed SCA3/MJD carriers and controls were included in an exploratory case-control study. Serum ROS, measured by 2',7'-dichlorofluorescein diacetate (DCFH-DA) as well as superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) antioxidant enzyme activities, levels were assessed. RESULTS: Fifty-eight early/moderate stage symptomatic SCA3/MJD, 12 presymptomatic SCA3/MJD, and 47 control individuals were assessed. The DCFH-DA levels in the symptomatic group were 152.82 nmol/mg of protein [95% confidence interval (CI), 82.57-223.08, p < 0.001] higher than in the control and 243.80 nmol/mg of protein (95% CI, 130.64-356.96, p < 0.001) higher than in the presymptomatic group. The SOD activity in the symptomatic group was 3 U/mg of protein (95% CI, 0.015-6.00, p = 0.048) lower than in the presymptomatic group. The GSH-Px activity in the symptomatic group was 13.96 U/mg of protein (95% CI, 5.90-22.03, p < 0.001) lower than in the control group and 20.52 U/mg of protein (95% CI, 6.79-34.24, p < 0.001) lower than in the presymptomatic group and was inversely correlated with the neurological examination score for spinocerebellar ataxias (R = -0.309, p = 0.049). CONCLUSION: Early/moderate stage SCA3/MJD patients presented a decreased antioxidant capacity and increased ROS generation. GSH-Px activity was the most promising oxidative stress disease biomarker in SCA3/MJD. Further longitudinal studies are necessary to identify both the roles of redox parameters in SCA3/MJD pathophysiology and as surrogate outcomes for clinical trials.

Cytokines in Machado Joseph Disease/Spinocerebellar Ataxia 3.

The aim of the present study is to describe the serum concentrations of a broad spectrum of cytokines in symptomatic and asymptomatic carriers of Machado Joseph disease (SCA3/MJD) CAG expansions. Molecularly confirmed carriers and controls were studied. Age at onset, disease duration, and clinical scales Scale for the Assessment and Rating of Ataxia (SARA), Neurological Examination Score for Spinocerebellar Ataxias (NESSCA), SCA Functional Index (SCAFI), and Composite Cerebellar Functional Score (CCFS) were obtained from the symptomatic carriers. Serum was obtained from all individuals and a cytokine panel "consisted of" eotaxin, granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon (IFN)-α, IFN-γ, interleukin (IL)-1ß, IL-1RA, IL-2, IL-2R, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, IL-15, IL-17, interferon gamma-induced protein (IP)-10, monocyte chemoattractant protein (MCP)-1, monokine induced by gamma interferon (MIG), macrophage inflammatory protein (MIP)-a, MIP-b, regulated on activation, normal T cell expressed and secreted (RANTES) and tumor necrosis factor (TNF)-α was analyzed. In a subgroup of symptomatic carriers, the cytokine panel was repeated after 360 days. Cytokine distribution among groups was studied by discriminant analysis; changes in serum levels after 360 days were studied by generalized estimation equation. Sixty-six symptomatic carriers, 13 asymptomatic carriers, and 43 controls were studied. No differences in cytokine patterns were found between controls and carriers of the CAG expansions or between controls and symptomatic carriers only. In contrast, eotaxin concentrations were significantly higher in asymptomatic than in symptomatic carriers or in controls (p = 0.001, ANCOVA). Eotaxin did not correlate with age, disease duration, CAG expansion, NESSCA score, and SARA score. Among symptomatic carriers, eotaxin dropped after 360 days (p = 0.039, GEE). SCA3/MJD patients presented a benign pattern of serum cytokines. In contrast, levels of eotaxin, a peptide secreted by astrocytes, were elevated in the asymptomatic carriers, suggesting that a specific response of these cells can be related to symptom progression, in SCA3/MJD.

Intracerebroventricular metformin decreases body weight but has pro-oxidant effects and decreases survival.

Metformin (Met), which is an insulin-sensitizer, decreases insulin resistance and fasting insulin levels. The precise molecular target of Met is unknown; however, several reports have shown an inhibitory effect on mitochondrial complex I of the electron transport chain (ETC), which is a related site for reactive oxygen species production. In addition to peripheral effects, Met is capable of crossing the blood-brain barrier, thus regulating the central mechanism involved in appetite control. The present study explores the effects of intracerebroventricular (i.c.v.) infusion of Met on ROS production on brain, insulin sensitivity and metabolic and oxidative stress outcomes in CF1 mice. Metformin (Met 50 and 100 µg) was injected i.c.v. in mice daily for 7 days; the brain mitochondrial H2O2 production, food intake, body weight and fat pads were evaluated. The basal production of H2O2 of isolated mitochondria from the hippocampus and hypothalamus was significantly increased by Met (100 µg). There was increased peripheral sensitivity to insulin (Met 100 µg) and glucose tolerance tests (Met 50 and 100 µg). Moreover, Met decreased food intake, body weight, body temperature, fat pads and survival rates. Additionally, Met (1, 4 or 10 mM) decreased mitochondrial viability and increased the production of H2O2 in neuronal cell cultures. In summary, our data indicate that a high dose of Met injected directly into the brain has remarkable neurotoxic effects, as evidenced by hypothermia, hypoglycemia, disrupted mitochondrial ETC flux and decreased survival rate.

Nandrolone-induced aggressive behavior is associated with alterations in extracellular glutamate homeostasis in mice.

Nandrolone decanoate (ND), an anabolic androgenic steroid (AAS), induces an aggressive phenotype by mechanisms involving glutamate-induced N-methyl-d-aspartate receptor (NMDAr) hyperexcitability. The astrocytic glutamate transporters remove excessive glutamate surrounding the synapse. However, the impact of supraphysiological doses of ND on glutamate transporters activity remains elusive. We investigated whether ND-induced aggressive behavior is interconnected with GLT-1 activity, glutamate levels and abnormal NMDAr responses. Two-month-old untreated male mice (CF1, n=20) were tested for baseline aggressive behavior in the resident-intruder test. Another group of mice (n=188) was injected with ND (15mg/kg) or vehicle for 4, 11 and 19days (short-, mid- and long-term endpoints, respectively) and was evaluated in the resident-intruder test. Each endpoint was assessed for GLT-1 expression and glutamate uptake activity in the frontoparietal cortex and hippocampal tissues. Only the long-term ND endpoint significantly decreased the latency to first attack and increased the number of attacks, which was associated with decreased GLT-1 expression and glutamate uptake activity in both brain areas. These alterations may affect extracellular glutamate levels and receptor excitability. Resident males were assessed for hippocampal glutamate levels via microdialysis both prior to, and following, the introduction of intruders. Long-term ND mice displayed significant increases in the microdialysate glutamate levels only after exposure to intruders. A single intraperitoneal dose of the NMDAr antagonists, memantine or MK-801, shortly before the intruder test decreased aggressive behavior. In summary, long-term ND-induced aggressive behavior is associated with decreased extracellular glutamate clearance and NMDAr hyperexcitability, emphasizing the role of this receptor in mediating aggression mechanisms.

Insulin prevents mitochondrial generation of H2O2 in rat brain.

The mitochondrial electron transport system (ETS) is a main source of cellular ROS, including hydrogen peroxide (H2O2). The production of H2O2 also involves the mitochondrial membrane potential (ΔΨm) and oxygen consumption. Impaired insulin signaling causes oxidative neuronal damage and places the brain at risk of neurodegeneration. We evaluated whether insulin signaling cross-talks with ETS components (complexes I and F0F1ATP synthase) and ΔΨm to regulate mitochondrial H2O2 production, in tissue preparations from rat brain. Insulin (50 to 100 ng/mL) decreased H2O2 production in synaptosomal preparations in high Na(+) buffer (polarized state), stimulated by glucose and pyruvate, without affecting the oxygen consumption. In addition, insulin (10 to 100 ng/mL) decreased H2O2 production induced by succinate in synaptosomes in high K(+) (depolarized state), whereas wortmannin and LY290042, inhibitors of the PI3K pathway, reversed this effect; heated insulin had no effect. Insulin decreased H2O2 production when complexes I and F0F1ATP synthase were inhibited by rotenone and oligomycin respectively suggesting a target effect on complex III. Also, insulin prevented the generation of maximum level of ∆Ψm induced by succinate. The PI3K inhibitors and heated insulin maintained the maximum level of ∆Ψm induced by succinate in synaptosomes in a depolarized state. Similarly, insulin decreased ROS production in neuronal cultures. In mitochondrial preparations, insulin neither modulated H2O2 production or oxygen consumption. In conclusion, the normal downstream insulin receptor signaling is necessary to regulate complex III of ETS avoiding the generation of maximal ∆Ψm and increased mitochondrial H2O2 production.

Pretreatment with memantine prevents Alzheimer-like alterations induced by intrahippocampal okadaic acid administration in rats.

Cerebral okadaic acid (OA) administration induces Alzheimer's disease (AD)-like phenotype in rats. Alterations in glutamate levels associated with hyperactivation of cyclin dependent kinase 5 (Cdk5) signaling pathway downstream Tau phosphorylation may participate in the genesis of this pathological phenotype. Here, we examined the efficacy of memantine (MN) pretreatment on reducing OA-induced AD-like phenotypes in rats. Wistar rats were given daily intraperitoneal injections of MN for 3 days and then given an intrahippocampal infusion of OA. Animals were divided into four groups: control (CO), MN, OA and MN/OA. Spontaneous locomotion and spatial memory performance were assessed by open field and Morris water maze respectively. Additionally, we measured glutamate levels in the cerebrospinal fluid (CSF) and the immunocontent of Cdk5, p35, p25 and phosphorylated Tau (pTauSer199/202) in the hippocampus. Spontaneous locomotion did not differ between groups. The OA group showed a significant decrease in spatial memory performance compared to all groups. The OA infusion also increased CSF glutamate levels and the immunocontents of Cdk5, p25 and pTauSer199/202 in the hippocampus. Conversely, pretreatment with MN prevented OA-induced spatial memory deficits and the increment of CSF glutamate level; which paralleled with normal immunocontents of Cdk5, p25 and pTau- Ser199/202 proteins. There were positive correlations between spatial memory performance and the neurochemical parameters. In summary, pretreatment with MN prevents spatial memory deficits induced by intrahippocampal OA administration in rats. The prevention of increase CSF glutamate levels, along with the reduced hippocampal phosphorylation of TauSer199/202 by Cdk5/p25 signaling pathway, are the mechanisms proposed to participate in the prophylactic effects of MN in this AD-like model.