Intravascular Endothelin-1 does not trigger or increase susceptibility to Spreading Depolarizations

DOI: https://doi.org/10.1186/s10194- 020- 01194- 3

Abstract-Summary We tested whether intracarotid ET-1 infusion triggers SD and whether systemic ET-1 infusion increases the susceptibility to SD.

Intracarotid ET-1 (1.25 nmol/mL) was infused at various rates (2–16 μL/min) with or without heparin in the catheter and compared with vehicle infusion (PBS with 0.01% acetic acid) or sham-operated mice (n = 5).

Systemic infusions ET-1 (1 nmol/kg, n = 7) or vehicle (n = 7) infusions were per-

formed in rats (Sprague-Dawley, male) via the tail vein.

Electrical SD threshold and KCl-induced SD frequency were measured after the

infusion.

Intracarotid infusion of saline (n = 19), vehicle (n = 7) or ET-1 (n = 12) all trig-

gered SDs at various proportions (21%, 14% and 50%, respectively).

Heparinizing the infusion catheter completely prevented SD occurrence during the infusions (n = 8), implicating microembolization from carotid thrombi as the trigger.

Systemic infusion of ET-1 did not affect the electrical SD threshold or KCl-

induced SD frequency.

Intravascular ET-1 does not trigger or increase susceptibility to SD. Microembolization was the likely trigger for migraine auras in patients during

carotid puncture.

Extended: We tested the hypothesis that endovascular exposure to ET-1 in the

cerebral circulation can trigger or predispose to migraine aura.

Our study highlights the importance that future studies using intracarotid infu-

sions must control for embolization and inadvertent triggering of SD.

Background Spreading depolarization (SD), and associated spreading depression, is a slowly propagating wave of pandepolarization involving all cell types in cerebral gray mat- ter, and likely underlies migraine aura [274].

Direct carotid puncture can trigger aura in migraine patients [239, 275]. Genome-wide association studies found a link between migraine and a gene vari- ant that results in higher expression of the ET-1 and increased binding of ET-1 to ETA receptors on vascular smooth muscle cells [276].

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2 Mechanisms

There has been good reason to hypothesize that ET-1 could be a pathophysiologi- cal link between vascular injury (e.g. carotid puncture, dissections) and migraine aura attacks.

We tested the hypothesis that endovascular exposure to ET-1 in the cerebral cir-

culation can trigger or predispose to migraine aura.

We examined whether intracarotid ET-1 infusions trigger cortical SD as the physiological surrogate of aura, and whether systemic intravenous ET-1 infusions alter the overall susceptibility to SD.

Methods After saline infusion at baseline (1.5 μl/min), vehicle (phosphate-buffered saline with 0.01% acetic acid; n = 7) or ET-1 (1.25 nmol/ml; n = 12) was infused through the carotid catheter.

In a separate cohort, we filled the carotid catheter with heparinized saline prior

to ET-1 infusion (n = 8).

We also studied sham-operated mice without infusion (n = 5); four of these mice had arterial manipulation but no cannulation and one had an external carotid artery catheter placed without infusion.

The electrical SD threshold and KCl-induced SD frequency were determined in

this order in the right hemisphere 5 min after ET-1 infusion.

ET-1 infusion was then repeated, and SD susceptibility assessed in the left hemi-

sphere 5 min later as above.

SD threshold and frequency were analyzed using mixed-effects 2-way repeated measures ANOVA (independent variables: infusion and hemisphere) followed by Sidak’s multiple comparisons test.

Results The occurrence of SDs even during saline or vehicle infusions, and hypoperfusion preceding SDs, implicated carotid emboli as the SD trigger.

In support of an embolic mechanism, all animals that developed an SD showed severe hypoperfusion (CBF ~ 20% of baseline) preceding the SD, regardless of the infusion solution.

The sequence of events was suggestive of a sudden and massive clot emboliza- tion into the carotid system, including the anterior cerebral artery, which forms a confluence perfusing the parasagittal cortex in both hemispheres, to explain the con- tralateral ischemia and SD.

We did not observe any spontaneous SD after intravenous vehicle or ET-1 (1

nmol/kg) infusions.

Discussion Our data show that intravascular ET-1 does not trigger or increase susceptibil- ity to SD.

We did not observe a dose-rate-dependent decrease in CBF during ET-1 infusions. Although SD itself can lead to blood brain barrier disruption after a few hours [277] careful monitoring for accidental SDs during cranial preparation ensured that the blood brain barrier was not disrupted prior to ET-1 infusions in our experiments.

2.2 Biology

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Although SD was not more common in ET-1 group compared with saline when normalized for the volume of infusion, there was a trend for higher proportion of animals exposed to ET-1 to develop severe hypoperfusion followed by SD.

It is still possible that even the lowest infusion rate of ET-1 might have activated

platelets and promoted clotting at the catheter tip.

We did not induce ET-1 release but rather directly administered it intravascularly, and we did not infuse heparin into cerebral vasculature along with ET-1 but rather pre-treated the catheters with heparin to prevent local clotting.

Conclusions We show that intravascular ET-1 does not trigger or increase susceptibility to SD.

Microembolization was the likely trigger for SDs in our study and migraine

auras in patients during carotid puncture.

With recent clinical data, it is unlikely that intravascular ET-1 plays a major

causative role as a migraine trigger.

Acknowledgement A machine generated summary based on the work of Sugimoto, Kazutaka; Morais, Andreia; Sadeghian, Homa; Qin, Tao; Chung, David Y.; Ashina, Messoud; Hougaard, Anders; Ayata, Cenk. 2020 in The Journal of Headache and Pain.

Auditory brainstem function in women with vestibular migraine: a controlled study