Activation of σ1 and σ2 receptors by afobazole increases glial cell survival and prevents glial cell activation and nitrosative stress after ischemic stroke

Abstract

Activation of sigma receptors at delayed time points has been shown to decrease injury following ischemic stroke. The mixed σ1/σ2 receptor agonist, 5-ethoxy-2-[2-(morpholino)-ethylthio]benzimidazole (afobazole), provides superior long-term outcomes compared to other σ ligands in the rat middle cerebral artery occlusion (MCAO) stroke model. Experiments using the MCAO model were carried out to determine the molecular mechanism involved in the beneficial effects of afobazole. Administration of afobazole (3 mg/kg) at delayed time points post-stroke significantly increased the number of microglia and astrocytes detected in the ipsilateral hemisphere at 96 h post-surgery. Morphological analysis of the microglia indicated that a greater number of these cells were found in the ramified resting state in MCAO animals treated with afobazole relative to MCAO vehicle controls. Similarly, fewer reactive astrocytes were detected in the injured hemisphere of afobazole-treated animals. Both the enhanced survival and reduced activation of glial cells were abolished by co-application of either a σ1 (BD-1063) or a σ2 (SM-21) receptor antagonist with afobazole. To gain further insight into the mechanisms by which afobazole lessens stroke injury, we probed the brain sections for markers of neuroinflammation (tumor necrosis factor α) and nitrosative stress (S-nitrosocysteine). Data show that afobazole significantly reduces S-nitrosocysteine levels, but does not alter tumor necrosis factor α expression 96 h after an ischemic stroke. Taken together our data indicate that afobazole acting via both σ1 and σ2 receptors decreases stroke injury by enhancing glial cell survival, blocking ischemia-induced glial cell activation, and decreasing nitrosative stress.

Activation of Sigma Receptors With Afobazole Modulates Microglial, but Not Neuronal, Apoptotic Gene Expression in Response to Long-Term Ischemia Exposure

“…Experiments in our laboratory have shown that σ receptor activation with afobazole can reduce activation of microglia and lessen microglial cell death in vitro and in vivo (Cuevas et al, 2011b; Katnik et al, 2016). Previous studies have shown that following an ischemic stroke there is an increase in ATP release, which leads to activation and migration of microglial cells (Davalos et al, 2005).…”

“…Ischemic stroke has been shown to be a multicellular disease, and any attempts to treat this disease must target several cell types (Hall et al, 2009b; Leonardo et al, 2010; Cuevas et al, 2011a,b). Neurons have previously been the primary target in the treatment of stroke, but microglia and astrocytes play a dynamic role in the pathophysiology of stroke (Hu et al, 2012; Katnik et al, 2016; Xu et al, 2017). In response to stroke or other types of CNS injury, microglia become activated and migrate to the site of injury (Kierdorf and Prinz, 2013).…”

“…Largely distributed throughout the mammalian body, σ receptors perform a number of other functions such as regulating membrane ion channels (Tchedre et al, 2008; Hayashi et al, 2000), altering expression of anti-apoptotic and pro-apoptotic transcription factors (Yang et al, 2007; Tchedre and Yorio, 2008; Meunier and Hayashi, 2010) and modulating activation and migration of microglial cells (Hall et al, 2009a). Additionally, these receptors have been shown to provide protection to both neurons and glial cells following in vitro ischemia and in vivo middle cerebral artery occlusion (MCAO) stroke models (Ajmo et al, 2006; Katnik et al, 2006, 2016). However, the cellular mechanisms responsible for the reduced cell death remain poorly understood and it is unknown if activation of σ receptors provides cytoprotection in neurons and microglial cells via identical pathways.…”

Deferred Administration of Afobazole Induces Sigma1R-Dependent Restoration of Striatal Dopamine Content in a Mouse Model of Parkinson’s Disease

“…Afobazole decreased the microglial cells migration induced by nucleoside triphosphates and amyloid Aβ 25–35 in vitro [ 80 , 81 ]. In an in vivo model of ischemic stroke, afobazole prevents glial activation and death, while selective Sigma1R antagonists blocked the effect of the drug [ 77 ]. These stimuli of afobazole correspond to Sigma1R activation [ 58 ] and the neuroprotective effect of PRE-084 in the model of 6-OHDA-induced PD accompanied by the inhibition of microglia migration in SNc [ 20 ].…”

“…Afobazole has an affinity to chaperone Sigma1R (Ki = 5.9 µM) and regulatory sites of ribosyldihydronicotinamide dehydrogenase [quinone] (NQO2, Ki = 0.97 µM) and monoamine oxidase A (MAO-A, Ki = 3.6 µM) [ 74 , 75 ]. In vitro and in vivo experiments suggest a role of Sigma1R in the mechanisms of previously described cytoprotective [ 76 ] and neuroprotective [ 77 , 78 , 79 , 80 , 81 , 82 ] properties of afobazole. Afobazole restored DA content in the striatum of mice with unilateral intrastriatal 6-OHDA lesions [ 83 ].…”