Current Immunology Reviews, 2012, 8, 39-49 39 Modulation of Apoptosis in Acute Ischemic Stroke as Treatment Challenges Joaquin Jordan1, Laura Moreno-Parrado1,2, David Anton-Martinez1,3, Kurt A. Jellinger4 and Maria F. Galindo*,5 1Grupo de Neurofarmacología, Dpto Ciencias Médicas, Fac de Medicina, Universidad de Castilla La Mancha, Avenida Almansa, 14, Albacete 02006, Spain 2Sección de Microbiologia, Complejo Hospitalario Universitario de Albacete, Albacete, Spain 3Sección de Bioquímica, Complejo Hospitalario Universitario de Albacete, Albacete, Spain 4Institute of Clinical Neurobiology, Kenyongasse 18; A-1070 Vienna, Austria 5Unidad de Neuropsicofarmacología Translacional, Complejo Hospitalario Universitario de Albacete, Albacete, Spain Abstract: Stroke is a major cause of death and disability throughout the world. Its pathophysiology is complex and includes excitotoxity, inflammatory pathways, oxidative damage, ionic imbalances, apoptosis and other cell death mechanisms, angiogenesis, and neuroprotection. The ultimate result of the complex ischemic cascade is neuronal death with irreversible loss of neuronal functions. New developments in stroke pathophysiology have induced significant advances in acute stroke management. Among the extracellular signals, inflammation, microglia and cytokines as major consequences of hypoxia may be targets for future therapies. Among the intracellular signals, calcium-induced cell death and oxidative stress as most important factors of ischemic cell death and for dysfunctions of the blood-brain barrier are important goals for neuroprotective agents. Third messengers, like p53, peroxisome proliferator-activated receptors and nuclear factor kappa-B (NF-kB) also play important roles in the pathogenesis of ischemic cell death, and may be further important targets of modern neuroprotective agents. The final stage of ischemic cell death via apopotosis and other cell death cascades, mainly influenced by energy deficiency and mitochondrial dysfunction may be influenced by antiapoptotic and other strategies as potential new targets for designing newer and more successful therapeutic modalities of acute ischemic stroke. Keywords: Apoptosis, extracellular signals, inflammation, intracellular signals, ROS, stroke. INTRODUCTION Here we review the currently available knowledge about the inflammatory and death pathways activated in acute The need for better stroke therapies has inspired research stroke and their implications for neuronal cell death via into the cellular and molecular mechanisms of ischemic apoptosis. brain damage, with major focus on the neuronal response under ischemic conditions. The neuronal response is poorly EXTRACELLULAR SIGNALS characterised in stroke patients and details about the molecular mechanisms of neuronal death are mainly based Inflammation on studies in animal models of ischemic injury (global, focal, hypoxia/ischemia). This depends on the nature and duration Although less well understood, inflammation is a of the ischemic insult, the location of the cells relative to the consequence of hypoxia and has been considered as a infarcted area and the neuronal subtype being affected. Acute therapeutic target in acute ischemic stroke [4-6]. The central neurological conditions such as cerebrovascular diseases are nervous system (CNS) has for long been regarded as an associated with irreversible loss of neurons and glial cells. immune privileged organ, with the blood–brain barrier Severe or prolonged injury results in uncontrollable cell (BBB) tightly regulating the influx of immune cells and death within the core of lesions. In addition, ischemic cell mediators from the vascular compartment to the brain death is also characterized by a long delay between the insult parenchyma [7]. There are many evidences that and manifestation of major cell damage. This delay varies inflammation and immune response play an important role in greatly, depending on the nature of the insult and the brain the outcome of ischemic stroke patients, and they have been region being affected. In some cases it is as long as several associated with larger brain damage. Brain inflammation is days or even weeks [1, 2] whereas in others it is a few hours characterized by activation of microglia and astrocytes, or less [3]. expression of key inflammatory mediators, but limited invasion of circulating immune cells. Inflammation induces rapid expression of key inflammatory mediators -cytokines, *Address correspondence to this author at the Unidad de chemokines and prostaglandins- which in turn up-regulate Neuropsicofarmacología, Complejo Hospitalario Universitario de Albacete, adhesion molecules, increase permeability of the BBB, c/ Hermanos Falcó 37, 02003 Albacete, Spain; Tel: +34 967 597477; Fax: facilitating invasion of peripheral immune cells, induce +34 967 597173; E-mail: [email protected] release of potentially toxic molecules and compromise brain 1875-631X/12 $58.00+.00 © 2012 Bentham Science Publishers 40 Current Immunology Reviews, 2012, Vol. 8, No. 1 Jordan et al. cells. Because the BBB is disrupted after stroke, the immune cytokines, chemokines, play an important role in recruiting system comes into contact with CNS antigens, in both the cells into areas of active inflammation [13]. brain and periphery [5, 8]. The production of arachidonic acid potentially Microglia are primarily involved in immune surveillance exacerbates the injury process by increasing extracellular [8, 9], but when activated have macrophage-like capabilities levels of aspartate and glutamate by inhibiting sodium- including phagocytosis, inflammatory cytokine production, dependent uptake and by stimulating exocytosis of glutamate and antigen presentation [10]. Normally these in synergy with PKC activation. Activation of the amino acid neuroinflammatory changes are transient with microglia cascade also leads to the synthesis of eicosanoids which returning to a resting state as the immune stimulus is regulate neuronal ion channels and the formation of - resolved. Activated microglia secrete a wide range of factors, superoxide free radicals (O2 ). Therefore, cytokines have the some of which can actively trigger apoptosis in neuronal cell capacity to create downstream modulation of cell signaling cultures [11, 12]. At the same time, microglia are also events and at the extreme cell death. reported to increase neuronal survival through the release of Recently it has been shown that patients with acute stroke trophic and anti-inflammatory factors (Table 1). Cytokines had significantly better outcome with minocycline treatment can be classified into four major groups: growth factors, compared with placebo [14], by involving minocycline anti- interleukins, interferons, and tumor necrosis factor. Cytokine inflammatory properties, especially its ability to suppress receptors, based on their three-dimensional structures, have activation of microglia, that may contribute to cytoprotection been classified into: receptors of the hematopoetin receptor in the CNS [15, 16]. Minocycline neuroprotection has also family, interferon receptors, transforming growth factors been reported in experimental ischemic stroke [17, 18] and (TGF), tumor necrosis factors (TNF) receptors, receptors for excitotoxic conditions [19]. the immunoglobulin (Ig) superfamily, and chemokine receptors. Inflammation after stroke involves leukocytes infiltration in brain parenchyma, specially neutrophils, that contribute to The concept that cytokine expression may be beneficial cerebral damage after ischemia [20] through reperfusion or and/or deleterious is illustrated by the potential dichotomous secondary injury mechanisms. Therefore, adhesion role of the immune response in stroke. The chemotactic molecules in leukocytes and endothelial cells are key Table 1. Adhesion Molecules Model Approach Effects Ref. Selectins Knockout mice Blockade with a P-selectin MCAO ischemia monoclonal antibody Decrease infarct volumes [90] sCRsLex Improvement in neurological outcome and reduction Focal cerebral ischemia Blockage or deficiency cerebral infarcts volumes Global cerebral ischemia Antibodies Reduction survival periods [91] E-selectin Cerebral ischemia Intranasal administration Induction immune tolerance and reduction injury [92] L-selectin Cerebral ischemia Antibodies against L-selectin Ineffective in stroke [93] Immunoglobulin Superfamily Less cerebral damage [94] ICAM-1 Cerebral ischemia Anti-ICAM-1 Reduction in neutrophil accumulation, apoptosis and [95] neurological deficits Clinical trials Anti-ICAM-1 Side effects and no improvement in outcome at 90 days. Improvement in neurological deficits and reduction in VCAM-1 Focal cerebral ischemia Leukotriene receptor antagonist neuron death by inhibition the ischemia-induced [96] upregulation of VCAM-1 Treatment with VCAM-1 Cerebral ischemia Ineffective in stroke antibodies Integrins Protection to injury by reduction of the upregulation of In vitro studies Aprotinin [97] neutrophil CD11b expression Anti-CD11b or Anti-CD18 Reduction in infarct volumes, apoptosis and decreased [98] MCAO in rats monoclonal antibodies. accumulation of neutrophils [99] anti-integrin [100] Clinical studies Negative results in acute stroke anti-CD11b or anti-CD18 [101] Modulation of Apoptosis in Acute Ischemic Stroke as Treatment Challenges Current Immunology Reviews, 2012, Vol. 8, No. 1 41 molecules that contribute to cerebral damage. In Table 1 we chemokines after cerebral ischemia is thought to be resume their effects and function as well as their