Rodrigo Medeiros

Connecting TNF-α Signaling Pathways to iNOS Expression in a Mouse Model of Alzheimer's Disease: Relevance for the Behavioral and Synaptic Deficits Induced by Amyloid β Protein

Increased brain deposition of amyloid β protein (Aβ) and cognitive deficits are classical signals of Alzheimers disease (AD) that have been highly associated with inflammatory alterations. The present work was designed to determine the correlation between tumor necrosis factor-α (TNF-α)-related signaling pathways and inducible nitric oxide synthase (iNOS) expression in a mouse model of AD, by means of both in vivo and in vitro approaches. The intracerebroventricular injection of Aβ1–40 in mice resulted in marked deficits of learning and memory, according to assessment in the water maze paradigm. This cognition impairment seems to be related to synapse dysfunction and glial cell activation. The pharmacological blockage of either TNF-α or iNOS reduced the cognitive deficit evoked by Aβ1–40 in mice. Similar results were obtained in TNF-α receptor 1 and iNOS knock-out mice. Aβ1–40 administration induced an increase in TNF-α expression and oxidative alterations in prefrontal cortex and hippocampus. Likewise, Aβ1–40 led to activation of both JNK (c-Jun-NH2-terminal kinase)/c-Jun and nuclear factor-κB, resulting in iNOS upregulation in both brain structures. The anti-TNF-α antibody reduced all of the molecular and biochemical alterations promoted by Aβ1–40. These results provide new insights in mouse models of AD, revealing TNF-α and iNOS as central mediators of Aβ action. These pathways might be targeted for AD drug development.

Kinin B1 receptors: key G-protein-coupled receptors and their role in inflammatory and painful processes

Kinins are a family of peptides implicated in several pathophysiological events. Most of their effects are likely mediated by the activation of two G‐protein‐coupled receptors: B1 and B2. Whereas B2 receptors are constitutive entities, B1 receptors behave as key inducible molecules that may be upregulated under some special circumstances. In this context, several recent reports have investigated the importance of B1 receptor activation in certain disease models. Furthermore, research on B1 receptors in the last years has been mainly focused in determining the mechanisms and pathways involved in the process of induction. This was essentially favoured by the advances obtained in molecular biology studies, as well as in the design of selective and stable peptide and nonpeptide kinin B1 receptor antagonists. Likewise, development of kinin B1 receptor knockout mice greatly helped to extend the evidence about the relevance of B1 receptors during pathological states. In the present review, we attempted to remark the main advances achieved in the last 5 years about the participation of kinin B1 receptors in painful and inflammatory disorders. We have also aimed to point out some groups of chronic diseases, such as diabetes, arthritis, cancer or neuropathic pain, in which the strategic development of nonpeptidic oral‐available and selective B1 receptor antagonists could have a potential relevant therapeutic interest.

Effect of two active compounds obtained from the essential oil of Cordia verbenacea on the acute inflammatory responses elicited by LPS in the rat paw

α‐Humulene and trans‐caryophyllene are sesquiterpene compounds identified in the essential oil of Cordia verbenacea which display topical and systemic anti‐inflammatory effects in different experimental models. However, the molecular mechanisms through which they exert their anti‐inflammatory activity still remain unclear. Here, we evaluate the effects of α‐humulene and trans‐caryophyllene on the acute inflammatory responses elicited by LPS.

Mechanisms involved in the nociception produced by peripheral protein kinase c activation in mice.

&NA; Protein kinase C (PKC) is able to phosphorylate several cellular components that serve as key regulatory components in signal transduction pathways of nociceptor excitation and sensitisation. Therefore, the present study attempted to assess some of the mechanisms involved in the overt nociception elicited by peripheral administration of the PKC activator, phorbol 12‐myristate 13‐acetate (PMA), in mice. The intraplantar (i.pl.) injection of PMA (16–1600 pmol/paw), but not its inactive analogue α‐PMA, produced a long‐lasting overt nociception (up to 45 min), as well as the activation of PKCα and PKCε isoforms in treated paws. Indeed, the local administration of the PKC inhibitor GF109203X completely blocked PMA‐induced nociception. The blockade of NK1, CGRP, NMDA, β1‐adrenergic, B2 or TRPV1 receptors with selective antagonists partially decreased PMA‐induced nociception. Similarly, COX‐1, COX‐2, MEK or p38 MAP kinase inhibitors reduced the nociceptive effect produced by PMA. Notably, the nociceptive effect promoted by PMA was diminished in animals treated with an antagonist of IL‐1β receptor or with antibodies against TNFα, NGF or BDNF, but not against GDNF. Finally, mast cells as well as capsaicin‐sensitive and sympathetic fibres, but not neutrophil influx, mediated the nociceptive effect produced by PMA. Collectively, the results of the present study have shown that PMA injection into the mouse paw results in PKC activation as well as a relatively delayed, but long‐lasting, overt nociceptive behaviour in mice. Moreover, these results demonstrate that PKC activation exerts a critical role in modulating the excitability of sensory neurons.

Astrocytes: conductors of the Alzheimer disease neuroinflammatory symphony.

Alzheimer disease (AD) is the most prevalent cause of dementia in humans, and the symptoms are commonly manifested after the seventh decade of life. Numerous pathological changes have been described in the postmortem brains of AD patients, including senile plaques, neurofibrillary tangles, neuroinflammation, synapse loss, and neuronal death. Reactive astrocytes surrounding senile plaques seem to be responsible for the ongoing inflammatory process in the disease through the release of cytokines and other toxic products. However, little is known about the regulation of these cells in the AD brain. Here we discuss the potential translational impact of the recent findings of Carrero and colleagues, published in Experimental Neurology, that shows the underlying molecular mechanism of astrocyte activation in response to β-amyloid (Aβ). Likewise, the relevance of pro-inflammatory mediators tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), cyclooxygenase-2 (COX-2) and nuclear factor-κB (NF-κB), as integral players in disease progression will be discussed.

The risk is in the air: Intranasal administration of MPTP to rats reproducing clinical features of Parkinson's disease

Many studies have shown that deficits in olfactory and cognitive functions precede the classical motor symptoms seen in Parkinsons disease (PD) and that olfactory testing may contribute to the early diagnosis of this disorder. Although the primary cause of PD is still unknown, epidemiological studies have revealed that its incidence is increased in consequence of exposure to certain environmental toxins. In the present study, we demonstrated that rats treated with intranasal infusion of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at low concentrations (0.1 mg/nostril) suffered progressive impairments in olfactory, cognitive and motor functions that were assessed with the olfactory discrimination, Morris water maze and open field tests, respectively. Moreover, intranasal administration of MPTP reduced the expression of the enzyme tyrosine hydroxylase in the olfactory bulb and substantia nigra of rats, resulting in a significant reduction of dopamine concentration in the olfactory bulb, prefrontal cortex and striatum, but not in the hippocampus. These results reinforce the notion that the olfactory system represents a particularly sensitive route for the transport of neurotoxins into the central nervous system that may be related to the etiology of PD. In addition, the time course of the olfactory, cognitive and motor impairments verified in rats treated intranasally with MPTP, which appears to be correlated with different stages of the human PD, suggest that the MPTP intranasal model in rats may provide new insights into the underlying mechanisms of PD pathogenesis.

Inflammation Induced by Infection Potentiates Tau Pathological Features in Transgenic Mice

Comorbidities that promote the progression of Alzheimers disease (AD) remain to be uncovered and evaluated in animal models. Because elderly individuals are vulnerable to viral and bacterial infections, these microbial agents may be considered important comorbidities that could potentiate an already existing and tenuous inflammatory condition in the brain, accelerating cognitive decline, particularly if the cellular and molecular mechanisms can be defined. Researchers have recently demonstrated that triggering inflammation in the brain exacerbates tau pathological characteristics in animal models. Herein, we explore whether inflammation induced via viral infection, compared with inflammation induced via bacterial lipopolysaccharide, modulates AD-like pathological features in the 3xTg-AD mouse model and provide evidence to support the hypothesis that infectious agents may act as a comorbidity for AD. Our study shows that infection-induced acute or chronic inflammation significantly exacerbates tau pathological characteristics, with chronic inflammation leading to impairments in spatial memory. Tau phosphorylation was increased via a glycogen synthase kinase-3β-dependent mechanism, and there was a prominent shift of tau from the detergent-soluble to the detergent-insoluble fraction. During chronic inflammation, we found that inhibiting glycogen synthase kinase-3β activity with lithium reduced tau phosphorylation and the accumulation of insoluble tau and reversed memory impairments. Taken together, infectious agents that trigger central nervous system inflammation may serve as a comorbidity for AD, leading to cognitive impairments by a mechanism that involves exacerbation of tau pathological characteristics.

Differential susceptibility following β-amyloid peptide-(1–40) administration in C57BL/6 and Swiss albino mice: Evidence for a dissociation between cognitive deficits and the glutathione system response

Considerable evidence supports the role of oxidative stress in the pathogenesis of Alzheimers disease (AD). Previous studies suggest that the central nervous system (CNS) administration of beta-amyloid peptide, the major constituent of senile plaque in AD, induces oxidative stress in rodents which may contribute to the learning and memory deficits verified in the beta-amyloid model of AD. In the present study, we compared the effects of a single intracerebroventricular (i.c.v.) injection of aggregated beta-amyloid peptide-(1-40) (Abeta(1-40)) (400pmol/mouse) on spatial learning and memory performance, synaptic density and the glutathione (GSH)-dependent antioxidant status in adult male C57BL/6 and Swiss albino mice. Seven days after Abeta(1-40) administration, C57BL/6 and Swiss mice presented similar spatial learning and memory impairments, as evaluated in the water maze task, although these impairments were not found in Abeta(40-1)-treated mice. Moreover, a similar decline of synaptophysin levels was observed in the hippocampus (HC) and prefrontal cortex (PFC) of both Swiss and C57BL/6 mice treated with Abeta(1-40), which suggests synaptic loss. C57BL/6 mice presented lower levels of glutathione-related antioxidant defences (total glutathione (GSH-t) levels, glutathione peroxidase (GPx) and glutathione reductase (GR) activity) in the HC and PFC in comparison to Swiss mice. Despite the reduced basal GSH-dependent antioxidant defences observed in C57BL/6 mice, Abeta(1-40) administration induced significant alterations in the brain antioxidant parameters only in Swiss mice, decreasing GSH-t levels and increasing GPx and GR activity in the HC and PFC 24h after treatment. These results indicate strain differences in the susceptibility to Abeta(1-40)-induced changes in the GSH-dependent antioxidant defences in mice, which should be taken into account in further studies using the Abeta model of AD in mice. In addition, the present findings suggest that the spatial learning and memory deficits induced by beta-amyloid peptides in rodents may not be entirely related to glutathione-dependent antioxidant response.

Aspirin-Triggered Lipoxin A4 Stimulates Alternative Activation of Microglia and Reduces Alzheimer Disease–Like Pathology in Mice

Microglia play an essential role in innate immunity, homeostasis, and neurotropic support in the central nervous system. In Alzheimer disease (AD), these cells may affect disease progression by modulating the buildup of β-amyloid (Aβ) or releasing proinflammatory cytokines and neurotoxic substances. Discovering agents capable of increasing Aβ uptake by phagocytic cells is of potential therapeutic interest for AD. Lipoxin A4 (LXA4) is an endogenous lipid mediator with potent anti-inflammatory properties directly involved in inflammatory resolution, an active process essential for appropriate host responses, tissue protection, and the return to homeostasis. Herein, we demonstrate that aspirin-triggered LXA4 (15 μg/kg) s.c., twice a day, reduced NF-κB activation and levels of proinflammatory cytokines and chemokines, as well as increased levels of anti-inflammatory IL-10 and transforming growth factor-β. Such changes in the cerebral milieu resulted in recruitment of microglia in an alternative phenotype, as characterized by the up-regulation of YM1 and arginase-1 and the down-regulation of inducible nitric oxide synthase expression. Microglia in an alternative phenotype-positive cells demonstrated improved phagocytic function, promoting clearance of Aβ deposits and ultimately leading to reduction in synaptotoxicity and improvement in cognition. Our data indicate that activating LXA4 signaling may represent a novel therapeutic approach for AD.

The role of TNF-α signaling pathway on COX-2 upregulation and cognitive decline induced by β-amyloid peptide

Alzheimers disease (AD), a chronic degenerative and inflammatory brain disorder characterized by neuronal dysfunction and loss, is linked to accumulation of beta-amyloid (Abeta) peptide. Tumor necrosis factor-alpha (TNF-alpha) and cyclooxygenase-2 (COX-2) are proteins that have key roles in immune cell activation, inflammation and cognitive function in the brain. Here, we evaluated the link between TNF-alpha and COX-2 on the acute responses elicited by Abeta. Behavioral and molecular analyses were performed in mice after an intracerebroventricular (i.c.v.) injection of Abeta(1-40). Genetic and/or pharmacological approaches were used to inhibit TNF-alpha and COX-2. I.c.v. Abeta(1-40) injection in mice activates TNF-alpha signaling pathway resulting in COX-2 upregulation, synaptic loss and cognitive decline. Pharmacological studies revealed that COX-2 is involved in the cognitive impairment mediated by TNF-alpha. However, COX-2 inhibition failed in reducing the synaptophysin loss induced by Abeta(1-40). The COX-2 upregulation induced by Abeta(1-40) was attributed to activation of different protein kinases and transcriptional factors that are greatly regulated by TNF-alpha. Together, these results indicate that Abeta(1-40) induces the activation of several TNF-alpha-dependent intracellular signaling pathways that play a key role in the control of COX-2 upregulation and activation, synaptic loss and cognitive decline in mice. Therefore, selective TNF-alpha inhibitors may be potentially interesting tools for AD drug development.