Post-stroke Intranasal (+)-Naloxone Delivery Reduces Microglial Activation and Improves Behavioral Recovery from Ischemic Injury

Abstract

Ischemic stroke is the leading cause of disability, and effective therapeutic strategies are needed to promote complete recovery. Neuroinflammation plays a significant role in stroke pathophysiology, and there is limited understanding of how it affects recovery. The aim of this study was to characterize the spatiotemporal expression profile of microglial activation and whether dampening microglial/macrophage activation post-stroke facilitates the recovery. For dampening microglial/macrophage activation, we chose intranasal administration of naloxone, a drug that is already in clinical use for opioid overdose and is known to decrease microglia/macrophage activation. We characterized the temporal progression of microglia/macrophage activation following cortical ischemic injury in rat and found the peak activation in cortex 7 d post-stroke. Unexpectedly, there was a chronic expression of phagocytic cells in the thalamus associated with neuronal loss. (+)-Naloxone, an enantiomer that reduces microglial activation without antagonizing opioid receptors, was administered intranasally starting 1 d post-stroke and continuing for 7 d. (+)-Naloxone treatment decreased microglia/macrophage activation in the striatum and thalamus, promoted behavioral recovery during the 14-d monitoring period, and reduced neuronal death in the lesioned cortex and ipsilateral thalamus. Our results are the first to show that post-stroke intranasal (+)-naloxone administration promotes short-term functional recovery and reduces microglia/macrophage activation. Therefore, (+)-naloxone is a promising drug for the treatment of ischemic stroke, and further studies should be conducted.

Inflammatory Responses in the Secondary Thalamic Injury After Cortical Ischemic Stroke

“…Microglia/macrophage activation in the ipsilesional thalamus occurs at a delayed time point compared to the activation in the primary cortical injury site. In a time course study of cortical stroke, microglia/macrophage activation markers (CD68 and Iba1) increase at Day 7, peak at Day 14 and 28, and persist up to Day 112 in the ipsilesional thalamus (77). We also observed microglia with dynamic morphologies and gene expression changes as the secondary thalamic injury develops (78).…”

β-Funaltrexamine Displayed Anti-Inflammatory and Neuroprotective Effects in Cells and Rat Model of Stroke

“…Contrary to the actions of the µ opioid receptor agonists, the agonists of δ and κ opioid receptors suppress inflammatory responses [20][21][22][23]. The opioid-immune crosstalk is further complicated by the findings that the nonselective opioid receptor antagonist (−)-naloxone and its inactive stereoisomer (+)-naloxone share both anti-inflammatory and neuroprotective effects under certain situations [3,11,13,18,[24][25][26]. Currently, the opioid receptor-dependent and -independent anti-inflammatory mechanisms in the relevant studies have been described as being associated with the involvement of TLRs, P2XRs, Histone Deacetylase 6 (HDAC6), Protein Kinase C, Mitogen-Activated Protein Kinase (MAPKs), NF-κB, LPS binding, superoxide anion, and macrophages/microglia polarization.…”

“…Clinically, cancer patients undergoing intensive morphine treatment have an increased risk of stroke incidence [34]. Accordingly, a growing body of evidence has revealed the neuroprotective effects of the nonselective opioid receptor antagonist naloxone, δ opioid receptor agonists, and κ opioid receptor agonists in rodent models experiencing neurodegeneration [3,7,[9][10][11][24][25][26][35][36][37]. Being a CNS-penetrating compound, the selective µ opioid receptor antagonist β-funaltrexamine is capable of inhibiting LPS-induced neuroinflammation in mice after receiving an intraperitoneal injection [29,30].…”

“…Beyond its effect on the nociceptive/analgesic systems, the opioidergic system also displays effects on physiological and behavioral functions, including respiration, ion channel activity, and immune responses [1,2]. Additionally, alteration in the opioidergic system has been reported in the disease initiation and progression of several acute and chronic diseases, including neurodegenerative diseases [3][4][5][6][7][8][9]. These phenomena highlight the potential pathogenic roles that the opioidergic system may have and candidate targets for intervention with an aim to prevent and/or treat diseases.…”

“…The anti-inflammatory and neuroprotective effects of (−)-naloxone, a nonselective opioid receptor antagonist, have been described [11,[24][25][26]. However, the anti-inflammatory effects of its inactive stereoisomer (+)-naloxone occur through an opioid receptor in an independent manner [3,18]. β-funaltrexamine is a selective µ opioid receptor antagonist.…”