INVOLVEMENT OF IL-1beta IN THE MITOCHONDRIAL OXIDATIVE STRESS AND NEURONAL IMPAIRMENT IN HYPOTHALAMIC NUCLEI OF ANIMALS WITH EXPERIMENTAL POLYMICROBIAL SEPSIS

Abstract

Sepsis induces excessive production and release of inflammatory mediators such as cytokines and nitric oxide (NO), which may directly or indirectly activate the central nervous system and affect autonomic and neuroendocrine functions. In sepsis, an important neuroendocrine change is the biphasic response in the secretion of vasopressin (AVP). The AVP is a nonapeptide synthesized in the magnocellular neurons of supraoptic (SON) and paraventricular (PVN) of hypothalamus. This nonapeptide is initially synthesized as an inactive pre-pro-hormone with high molecular weight. The correct structural formation of the AVP precursor and the efficient proteolytic maturation of the hormone seems to be related to the C-terminal glycopeptide nominated as copeptin and that is secreted stoichiometrically with AVP in the circulation. In the initial phase of sepsis there is an increase in the plasma AVP concentration, but in the late phase the hormone release is basal, despite persistent hypotension. This change has intrigued many researchers. In recent experiments, using quantitative PCR (real time PCR), we observed that after sepsis by cecal ligation and puncture (CLP) the NO centrally produced mainly by inducible NO synthase (iNOS) decreases the expression of AVP in the SON and PVN. The reduction or blockage of neuronal activation in different brain regions related to neuroendocrine and autonomic functions have also been observed after CLP, suggesting possible neuronal impairment in the late phase of sepsis. The increase of cytokines, especially IL-1beta seems to activate the expression of messenger RNA for iNOS in the hypothalamus. After induction, the iNOS produces high concentrations of NO, which can plays a dual role in mitochondrial bioenergetics: affecting oxygen consumption and favoring the generation of superoxide anions by decreasing electron flux through the cytochrome C oxidase. These changes may result in a "metabolic hypoxia" situation and formation of hydrogen peroxide. The latter one may further stimulate the iNOS expression and the NO increase. The hypoxia induces the expression and stabilization of the hypoxia-induced factor 1 alpha subunit (HIF1alpha). The dimerization of HIF1alpha with HIF1beta form the HIF1, which regulates the expression of several genes related to energy metabolism and apoptosis. The HIF1 can be activated by the increase of cytokines such as TNFalpha and IL-1beta. Thus, our hypothesis is that decreased expression of AVP after sepsis is due to apoptosis induced by HIF1 formation after oxidative stress and increased IL-1beta. The bioenergetics changes could also alter the formation of the AVP precursor and may result in inefficient proteolytic maturation of the active hormone. Considering the role of AVP in the vasopressor response, the elucidation of the mechanisms of the deficient hormone synthesis may contribute to therapy during sepsis. The objectives of this study are: 1) investigate the involvement of IL-1beta in the central production of nitric oxide, mitochondrial oxidative stress and neuronal impairment in hypothalamic nuclei of animals with experimental polymicrobial sepsis, 2) develop an immunoassay for rat copeptin determination.