The pharmacological suppression of spreading depolarization in ischemic neuroprotection

Background: Spontaneous, recurrent spreading depolarizations (SD) are increasingly more appreciated as a pathomechanism behind ischemic brain injuries. Hence, the pharmacological inhibition of SDs is the subject of growing interest. Here, we set out to explore the SD suppressive potential of three distinct pharmacological agents. First we evaluated the action of LA1011, a novel of dihydropyridine derivative, which acts as a co inducer of heat shock proteins, but is devoid of calcium channel antagonistic and vasodilator effects. Next, we applied AL-8810, a selective FP receptor antagonist to test the hypothesis that FP receptor blockade may achieve neuroprotection by the inhibition of SD, and possibly improve cerebral blood flow (CBF) in the ischemic rat cortex. Lastly, the endogenous hallucinogen and non-selective sigma 1 receptor (Sig-1R) agonist dimethyltryptamine (DMT) was used. DMT exerts tissue protective effects against hypoxia, but it was to be explored whether DMT was effective to reduce cerebral ischemic injury. Methods: Rats were treated with LA1011 either by chronic, systemic, or acute, local administration. In the latter treatment group, global forebrain ischemia was induced in half of the animals by bilateral common carotid artery occlusion under isoflurane anaesthesia. Functional hyperemia in the somatosensory cortex was created by mechanical stimulation of the contralateral whisker pad under α‐chloralose anaesthesia. SD events were elicited subsequently by 1 M KCl. Local field potential and CBF in the parietal somatosensory cortex were monitored by electrophysiology and laser Doppler flowmetry. AL-8810 or its vehicle were intravenously administered to anesthetized rats with acute cerebral ischemia/reperfusion exacerbated with recurrent SD induction. In this set of experiments, CBF was monitored with laser speckle contrast imaging. Finally, in a similar experimental model of ischemia/hypoxia/reperfusion, DMT, or the selective Sig 1R agonist PRE 084, or the Sig 1R antagonist NE 100, or the wide range serotonin receptor antagonist asenapine were administered alone or in combination intravenously. Results: LA1011 did not alter CBF, but intensified SD, presumably indicating the co‐induction of heat shock proteins, and, perhaps an anti inflammatory effect. The antagonism of FP receptors suppressed SD in the ischemic rat cerebral cortex and reduced the duration of recurrent SDs by facilitating repolarization. In parallel, FP receptor antagonism improved perfusion in the ischemic cerebral cortex, and attenuated hypoemic CBF responses associated with SD. Further, FP receptor antagonism appeared to restrain apoptotic cell death related to SD recurrence. Both DMT and PRE 084 reduced SD amplitude, the rate of depolarization, and the cumulative duration of SDs, which were suppressed by the addition of NE-100. Further, DMT attenuated SD when co-administered with asenapine, compared to asenapine alone. DMT administration reduced the number of apoptotic and ferroptotic cells and supported astrocyte survival, but had no effect on microglia. Sig-1Rs were associated with the perinuclear cytoplasm of neurons, astrocytes and microglia, and with glial processes. Conclusions: LA1011 seemed not to have any discernible cerebrovascular effects as was expected. Although, LA1011 had been proven neuroprotective in another experimental model of neurodegerative diseases, the treatment with LA1011 was inefficient in experimetal ischemic injury. Further investigation is needed to understand the mechanism of action of LA1011. Conversely, the antagonism of FP receptors (located at the neuro-vascular unit, neurons, astrocytes and microglia) has emerged as a promising approach to inhibit the evolution of SDs in cerebral ischemia. At last, the administration of DMT, alone or in combination with a Sig 1R antagonist suggested that DMT attenuated SD, at least in part, through Sig-1R activation, and achieved neuroprotection in the acute phase of cerebral ischemia. These data suggest that DMT may applicable as an adjuvant pharmacological therapy in the management of acute cerebral ischemic injury.