Reduced Mechanical Stretch Induces Enhanced Endothelin B Receptor-Mediated Contractility via Activation of Focal Adhesion Kinase and Extracellular Regulated Kinase 1/2 in Cerebral Arteries from Rat

Protein kinase C-inhibition reduces critical weight loss and improves functional outcome after experimental subarachnoid haemorrhage

OBJECTIVES

Subarachnoid haemorrhage (SAH) carries a high burden of morbidity and mortality. One in three patients develop vasospasm, which is associated with Delayed Cerebral Ischemia. The pathophysiology includes vasoconstrictor receptor upregulation in cerebral arteries. The protein kinase C - inhibitor RO-31-7549 reduces the expression of several vasoconstrictor receptors and normalizes cerebral blood flow in experimental SAH but functional and behavioural effects are unknown. This study was undertaken to analyse functional outcomes up to 14 days after experimental SAH.

MATERIALS AND METHODS

54 male rats were randomised to experimental SAH or sham, using the pre-chiasmatic, single injection model, and subsequent treatment or vehicle. 42 remained for final analysis. The animals were euthanized on day 14 or when reaching a humane endpoint. The primary endpoint was overall survival, defined as either spontaneous mortality or when reaching a predefined humane endpoint. The secondary outcomes were differences in the rotating pole test, weight, open field test, novel object recognition and qPCR of selected inflammatory markers.

RESULTS

In the vehicle group 6/15 rats reached the humane endpoint of >20 % weight loss compared to 1/14 in the treatment group. This resulted in a significant reduced risk of early euthanasia due to >20 % weight loss of HR 0.15 (0.03-0.66, p = 0.04). Furthermore, the treatment group did significantly better on the rotating pole test, RR 0.64 (0.47-0.91, p = 0.02).

CONCLUSION

RO-31-7549 improved outcomes in terms >20 % weight loss and rotating pole performance after experimental SAH and could be investigated.

Switching Off Vascular MAPK Signaling: A Novel Strategy to Prevent Delayed Cerebral Ischemia Following Subarachnoid Hemorrhage

Patients who initially survive the rupture and repair of a brain aneurysm often take a devastating turn for the worse some days later and die or suffer permanent neurologic deficits. This catastrophic sequela is attributed to a delayed phase of global cerebral ischemia (DCI) following aneurysmal subarachnoid hemorrhage (aSAH), but we lack effective treatment. Here we present our view, based on 20 years of research, that the initial drop in blood flow at the time of rupture triggers genomic responses throughout the brain vasculature that manifest days later as increased vasoconstriction and decreased cerebral blood flow. We propose a novel treatment strategy to prevent DCI by early inhibition of the vascular mitogen-activated protein kinase (MAPK) pathway that triggers expression of vasoconstrictor and inflammatory mediators. We summarize evidence from experimental SAH models showing early treatment with MAPK inhibitors "switches off" these detrimental responses, maintains flow, and improves neurological outcome. This promising therapy is currently being evaluated in clinical trials.

Indoxyl sulfate enhances endothelin-1-induced contraction via impairment of NO/cGMP signaling in rat aorta

The microbiome-derived tryptophan metabolite, indoxyl sulfate, is considered a harmful vascular toxin. Here, we examined the effects of indoxyl sulfate on endothelin-1 (ET-1)-induced contraction in rat thoracic aortas. Indoxyl sulfate (10-3 M, 60 min) increased ET-1-induced contraction but did not affect isotonic high-K+-induced contraction. The ET-1-induced contraction was enhanced by endothelial denudation in both control and indoxyl sulfate-treated groups. BQ123 (10-6 M), an ETA receptor antagonist, reduced the ET-1-induced contraction in both control and indoxyl sulfate groups. BQ788 (10-6 M), an ETB receptor antagonist, increased the contraction in the control group but had no effect on the indoxyl sulfate group. Conversely, indoxyl sulfate inhibited relaxation induced by IRL1620, an ETB receptor agonist. L-NNA, an NO synthase (NOS) inhibitor, increased the ET-1-induced contractions in both the control and indoxyl sulfate groups, whereas L-NPA (10-6 M), a specific neuronal NOS inhibitor, did not affect the ET-1-induced contraction in both groups. However, ODQ, an inhibitor of soluble guanylyl cyclase, increased the ET-1-induced contraction in both groups. Organic anion transporter (OAT) inhibitor probenecid (10-3 M) and antioxidant N-acetyl-L-cysteine (NAC; 5 × 10-3 M) inhibited the effects of indoxyl sulfate. A cell-permeant superoxide scavenger reduced the ET-1-induced contraction in the indoxyl sulfate group. The aortic activity of SOD was reduced by indoxyl sulfate. The present study revealed that indoxyl sulfate augments ET-1-induced contraction in rat aortae. This enhancement may be due to the impairment of NO/cGMP signaling and may be attributed to impairment of the antioxidant systems via cellular uptake through OATs.

Synergistic effects of a cremophor EL drug delivery system and its U0126 cargo in an ex vivo model

Neuroprotection has proven clinically unsuccessful in subarachnoid hemorrhage. We believe that this is because the major component in the early damage pathway, the vascular wall, has not been given the necessary focus. U0126 is a potent inhibitor of vascular phenotypical changes, exemplified by functional endothelin B (ET_B) receptor upregulation. The current study aimed to determine the optimal dose of U0126 ex vivo and test the toxicology of this dose in vivo. To find the optimal dose and test a suitable in vivo delivery system, we applied an ex vivo model of blood flow cessation and investigated functional ET_B receptor upregulation (using a specific agonist) as the primary endpoint. The secondary endpoint was depolarization-induced contractility assessed by 60 mM K⁺ stimuli. Furthermore, an in vivo toxicology study was performed on the optimal selected doses. U0126 (10 µM) had a strong effect on the prevention of functional ET_B receptor contractility, combined with minimal effect on the depolarization-induced contractility. When cremophor EL was chosen for drug delivery, it had an inhibitory and additive effect (combined with U0126) on the ET_B receptor contractility. Hence, 10 µM U0126 in 0.5% cremophor EL seems to be a dose that will be close to the maximal inhibition observed ex vivo on basilar arteries, without exhibiting side effects in the toxicology studies. U0126 and cremophor EL are well tolerated at doses that have effect on ET_B receptor upregulation. Cremophor EL has an additional positive effect, preventing functional ET_B receptor upregulation, making it suitable as a drug delivery system.

Blixt F, Edvinsson L, Ansar S. Acute mitogen-activated protein kinase 1/2 inhibition improves functional recovery and vascular changes after ischaemic stroke in rat-monitored by 9.4 T magnetic resonance imaging

AIM

The aim was to evaluate the beneficial effect of early mitogen-activated protein kinase (MEK)1/2 inhibition administered at a clinical relevant time-point using the transient middle cerebral artery occlusion model and a dedicated rodent magnetic resonance imaging system (9.4T) to monitor cerebrovascular changes non-invasively for 2 weeks.

METHOD

Transient middle cerebral artery occlusion was induced in male rats for two hours followed by reperfusion. The specific MEK1/2 inhibitor U0126 was administered ip at 6 and 24 hours post-reperfusion. Neurological functions were evaluated by 6- and 28-point tests. 9.4 T magnetic resonance imaging was used to monitor morphological infarct changes at day 2, 8 and 14 after stroke and to evaluate cerebral perfusion at day 14. Immunohistochemistry evaluation of Ki67 was performed 14 days post-stroke.

RESULTS

U0126 improved long-term behavioural outcome and significantly reduced infarct size. In addition, cerebral perfusion in U0126-treated animals was improved compared to the vehicle group. Immunohistochemistry showed a significant increase in Ki67⁺ cells in U0126-treated animals compared to the vehicle group.

CONCLUSION

Early MEK1/2 inhibition improves long-term functional outcome, promotes recovery processes after stroke and most importantly provides a realistic time window for therapy.