Alterações neuroinflamatórias e modulação da via colinérgica anti-inflamatória em um modelo experimental de asma

Abstract

INTRODUCTION: Asthma results from the continuous allergens inhalation, leading to airways inflammation. Immunoglobulin E (IgE) synthesis, eosinophilic recruitment, mucus overproduction and muscle cell hyperreactivity are typically driven by interleukins (IL) IL-4, IL-5, and IL-13, secreted by Th2 lymphocytes, resulting in airways obstruction. Asthma is often associated with anxiety. In fact, asthma not only induced lung inflammation but also results in neuroinflammation, characterized by the release of proinflammatory cytokines, such as IL-1β and tumor necrosis factor α (TNF-α) and an increase in mitochondrial size. To minimize these damages are required mechanisms that regulate the immune response. In this sense, Tracey and colleagues described the cholinergic anti- inflammatory pathway (CAP), that regulates the inflammation through of the vagus nerve and binding of acetylcholine (ACh) to α7 nicotinic acetylcholine receptor (α7nAChR). Diverse studies have demonstrated its therapeutic potential in diverse pathologies. OBJECTIVE: The scientific articles that compose this dissertation had as objective to identify the neuroinflammatory changes that can lead to anxiety in animals submitted to an experimental asthma model (article 1). To evaluate the modulation effects of cholinergic anti-inflammatory pathway with neostigmine over oxidative stress and airway inflammation in an experimental model of asthma (article 2). To evaluate the modulation effects of cholinergic anti- inflammatory pathway with neostigmine over oxidative stress in the cerebral cortex in an experimental model of asthma (article 3). METHODS: For experimental asthma model induction, the animals were sensitized by subcutaneous injections of ovalbumin (OVA), on days 0 and 7, followed by three intranasal challenges with OVA on days 14, 15, and 16 of the protocol. The animals of the control group received only DPBS in the sensitization and intranasal challenges. In articles 2 and 3 to evaluate the CAP effects, on days 14, 15, and 16 after 30 minutes of OVA challenge, mice received 80 μg/kg of neostigmine intraperitoneally. On 17º day mice were euthanized for sample obtain and development the described techniques, according to the objectives for each of the scientific articles. RESULTS: In the scientific article 1, we observed that the airways inflammation promoted important alterations in mice brain, we verified the oxidative stress formation and presence of mitochondrial energy dysfunction, resulting in activity alteration of the important enzymes, such as Na+,K+-ATPase and acetylcholinesterase (AChE). In addition, we also demonstrated increased proinflammatory cytokines (IL-9, IL-13, eotaxina, and IL-1β,). In response to these damages we demonstrate through microPET technique using 18F- fluorodeoxyglucose (18F-FDG) that increase glucose metabolism occurs in in structures of the hypothalamic-pituitary-adrenal (HPA) axis, leading to axis hyperactivity through the negative feedback deficiency, indicated by a decrease in glucocorticoid receptors. Finally, in response to these damages we also demonstrate that upregulation occurs at BDNF levels. In addition, we demonstrated that animals submitted to an experimental model of asthma present an increase in anxiety behavior. Thus, we propose, for the first time, that airway inflammation mediates critical neuroinflammatory changes within the brain, which lead to the anxiety phenotype in asthma. In the scientific article 2, we demonstrated that the CAP pharmacological activation with neostigmine significantly decreased the release of proinflammatory cytokines and attenuated oxidative stress and consequently decreased eosinophilic recruitment and mucus hypersecretion, leading to improved parameters of ventilatory mechanics. Finally, in article 3, it was observed that treatment with neostigmine was able to reduce eosinophilic recruitment in the airways and decreased the formation of oxidative stress in the cerebral cortex of animals submitted to an experimental model of asthma. CONCLUSION: The results found in this dissertation demonstrate that the inflammation in the airways in animals submitted to an experimental model of asthma promotes several neuroinflammatory changes that lead to the anxiety phenotype. One of these important alterations is the change in AChE activity, described as an important component of the cholinergic anti-inflammatory pathway that continuously regulates ACh levels. In this sense, using neostigmine, which inhibits the action of AChE in the neuromuscular junctions and does not have a direct effect on AChE in the CNS, since it does not exceed the blood brain barrier (BBB), we demonstrated that neostigmine treatment besides controlling the inflammatory response in the lung was also able to attenuate the oxidative stress in the cerebral cortex of animals submitted to an asthma model. We believe that these results can be explained by the reduction of inflammation in the airways, which decreases the subsequent signal from the vagus nerve to the CNS and thereby reduces neuroinflammation. Thus, we believe that our results may contribute to this huge gap between asthma and emotional disorders such as anxiety and we propose that asthma should be looked at not just as localized lung inflammation.