Acute Opioid Receptor Blockade Restores Vascular Endothelial Growth Factor and Astrocyte Response in db/db Mouse Brain Following Hypoxia-Ischemic Injury

Abstract

Diabetes plays an important role in the pathogenesis of ischemic stroke and brain recovery. We have reported the neuroprotective effect of low dose naltrexone (LDN) in type 2 diabetic (db/db) mice post-hypoxia-ischemia (HI) injury. In this study, we explored LDN mediated mechanisms of neuroprotection in diabetic mice. Adult male db/db and non-diabetic (db/+) mice underwent right common carotid artery occlusion followed by hypoxia (8% O₂) for 20 min. LDN (1 mg/kg) was administered at 4, 24, and 48 h post-HI, and mice were euthanized at 72 h. Blood and brain tissue were analyzed for cytokines and growth factors by multiplex array, immunofluorescence and western blotting. LDN treatment resulted in an increased number of reactive astrocytes in the motor cortex and caudate and hippocampus of diabetic mice, which was decreased in db/+ mice, except in the CA3 hippocampal region. LDN did not show any significant change in the cytokine response between db/+ and db/db mice. However, the vascular endothelial growth factor (VEGF) levels in the plasma and brain tissue of LDN-treated db/db mice that were significantly reduced in the vehicle-treated db/db group were restored to the level of the db/+ treated group. When infarct size was categorized, LDN increased VEGF+ neurons in the motor cortex and caudate in small infarcts, and in the motor cortex of large infarcts, in db/db mice. The study suggests that acute LDN increased the number of VEGF+ neurons and prevented astrocytic cell death in db/db mice, thus enhancing neuroprotection following brain HI injury.