Abstract
Background
Glibenclamide (GLB) reduces brain edema and improves neurological outcome in animal experiments and preliminary clinical studies. Recent studies also suggested a strong anti-inflammatory effect of GLB, via inhibiting Nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome activation. However, it remains unknown whether the anti-inflammatory effect of GLB is independent of its role in preventing brain edema, and how GLB inhibits the NLRP3 inflammasome is not fully understood.
Methods
Sprague-Dawley male rats underwent 10-min asphyxial cardiac arrest and cardiopulmonary resuscitation or sham-operation. Wild type and Trpm4−/− C57BL/6 male mice underwent radiation-induced brain injury or sham-operation. The Trpm4 siRNA and GLB were injected to block sulfonylurea receptor 1-transient receptor potential M4 (SUR1-TRPM4) channel in rats and mice. Western blotting, quantitative real-time polymerase chain reaction, behavioral analysis, histological examination, and MRI Scanning were used to evaluate the role of GLB in preventing NLRP3-mediated neuroinflammation through inhibiting SUR1-TRPM4, and corresponding neuroprotective effect. To further explore the underlying mechanism, BV2 cells were subjected to lipopolysaccharides, oxygen-glucose deprivation/reperfusion, or radiation.
Results
Here, in mice model of radiation-induced brain injury with minimal brain edema, GLB significantly alleviated neurocognitive deficit and neuropathological damage, via the inhibition of radiation-induced microglial NLRP3 inflammasome activation by blocking SUR1-TRPM4. Likewise, above neuroprotective effects were also confirmed in rat model of cardiac arrest with brain edema combined with neuroinflammation, through preventing SUR1-TRPM4-mediated NLRP3 activation. Of note, the above effects of GLB could be achieved by gene silencing or knockdown of Trpm4. In vitro, SUR1-TRPM4 and NLRP3 inflammasome were also activated in BV2 cells subjected to lipopolysaccharides, oxygen-glucose deprivation/reperfusion, or radiation, which could be blocked by GLB or 9-phenanthrol, a TRPM4 inhibitor. Importantly, activation of SUR1-TRPM4 in BV2 cells required the P2X7 receptor-mediated Ca2+ influx, which in turn magnified the K+ efflux via the Na+ influx-driven opening of K+ channels, leading to the NLRP3 inflammasome activation.
Conclusions
These findings suggest that GLB has a direct anti-inflammatory neuroprotective effect independent of its role in preventing brain edema, through inhibition of SUR1-TRPM4 which amplifies K+ efflux and promotes NLRP3 inflammasome activation.
Knocking down TRPM2 expression reduces cell injury and NLRP3 inflammasome activation in PC12 cells subjected to oxygen-glucose deprivation
