Impaired cerebral vasodilator responses to NO and PDE V inhibition after subarachnoid hemorrhage

2-PMAP Ameliorates Cerebral Vasospasm and Brain Injury after Subarachnoid Hemorrhage by Regulating Neuro-Inflammation in Rats

A subarachnoid hemorrhage (SAH), leading to severe disability and high fatality in survivors, is a devastating disease. Neuro-inflammation, a critical mechanism of cerebral vasospasm and brain injury from SAH, is tightly related to prognoses. Interestingly, studies indicate that 2-[(pyridine-2-ylmethyl)-amino]-phenol (2-PMAP) crosses the blood-brain barrier easily. Here, we investigated whether the vasodilatory and neuroprotective roles of 2-PMAP were observed in SAH rats. Rats were assigned to three groups: sham, SAH and SAH+2-PMAP. SAHs were induced by a cisterna magna injection. In the SAH+2-PMAP group, 5 mg/kg 2-PMAP was injected into the subarachnoid space before SAH induction. The administration of 2-PMAP markedly ameliorated cerebral vasospasm and decreased endothelial apoptosis 48 h after SAH. Meanwhile, 2-PMAP decreased the severity of neurological impairments and neuronal apoptosis after SAH. Furthermore, 2-PMAP decreased the activation of microglia and astrocytes, expressions of TLR-4 and p-NF-κB, inflammatory markers (TNF-α, IL-1β and IL-6) and reactive oxygen species. This study is the first to confirm that 2-PMAP has vasodilatory and neuroprotective effects in a rat model of SAH. Taken together, the experimental results indicate that 2-PMAP treatment attenuates neuro-inflammation, oxidative stress and cerebral vasospasm, in addition to ameliorating neurological deficits, and that these attenuating and ameliorating effects are conferred through the TLR-4/NF-κB pathway.

Phase dynamics of cerebral blood flow in subarachnoid haemorrhage in response to sodium nitrite infusion

Aneurysmal subarachnoid haemorrhage (SAH) is a devastating subset of stroke. One of the major determinates of morbidity is the development of delayed cerebral ischemia (DCI). Disruption of the nitric oxide (NO) pathway and consequently the control of cerebral blood flow (CBF), known as cerebral autoregulation, is believed to play a role in its pathophysiology. Through the pharmacological manipulation of in vivo NO levels using an exogenous NO donor we sought to explore this relationship. Phase synchronisation index (PSI), an expression of the interdependence between CBF and arterial blood pressure (ABP) and thus cerebral autoregulation, was calculated before and during sodium nitrite administration in 10 high-grade SAH patients acutely post-rupture. In patients that did not develop DCI, there was a significant increase in PSI around 0.1 Hz during the administration of sodium nitrite (33%; p-value 0.006). In patients that developed DCI, PSI did not change significantly. Synchronisation between ABP and CBF at 0.1 Hz has been proposed as a mechanism by which organ perfusion is maintained, during periods of physiological stress. These findings suggest that functional NO depletion plays a role in impaired cerebral autoregulation following SAH, but the development of DCI may have a distinct pathophysiological aetiology.

Cerebral artery myogenic reactivity: The next frontier in developing effective interventions for subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating cerebral event that kills or debilitates the majority of those afflicted. The blood that spills into the subarachnoid space stimulates profound cerebral artery vasoconstriction and consequently, cerebral ischemia. Thus, once the initial bleeding in SAH is appropriately managed, the clinical focus shifts to maintaining/improving cerebral perfusion. However, current therapeutic interventions largely fail to improve clinical outcome, because they do not effectively restore normal cerebral artery function. This review discusses emerging evidence that perturbed cerebrovascular "myogenic reactivity," a crucial microvascular process that potently dictates cerebral perfusion, is the critical element underlying cerebral ischemia in SAH. In fact, the myogenic mechanism could be the reason why many therapeutic interventions, including "Triple H" therapy, fail to deliver benefit to patients. Understanding the molecular basis for myogenic reactivity changes in SAH holds the key to develop more effective therapeutic interventions; indeed, promising recent advancements fuel optimism that vascular dysfunction in SAH can be corrected to improve outcome.

Microvascular insulin resistance in skeletal muscle and brain occurs early in the development of juvenile obesity in pigs

Impaired microvascular insulin signaling may develop before overt indices of microvascular endothelial dysfunction and represent an early pathological feature of adolescent obesity. Using a translational porcine model of juvenile obesity, we tested the hypotheses that in the early stages of obesity development, impaired insulin signaling manifests in skeletal muscle (triceps), brain (prefrontal cortex), and corresponding vasculatures, and that depressed insulin-induced vasodilation is reversible with acute inhibition of protein kinase Cβ (PKCβ). Juvenile Ossabaw miniature swine (3.5 mo of age) were divided into two groups: lean control ( n = 6) and obese ( n = 6). Obesity was induced by feeding the animals a high-fat/high-fructose corn syrup/high-cholesterol diet for 10 wk. Juvenile obesity was characterized by excess body mass, hyperglycemia, physical inactivity (accelerometer), and marked lipid accumulation in the skeletal muscle, with no evidence of overt atherosclerotic lesions in athero-prone regions, such as the abdominal aorta. Endothelium-dependent (bradykinin) and -independent (sodium nitroprusside) vasomotor responses in the brachial and carotid arteries (wire myography), as well as in the skeletal muscle resistance and 2A pial arterioles (pressure myography) were unaltered, but insulin-induced microvascular vasodilation was impaired in the obese group. Blunted insulin-stimulated vasodilation, which was reversed with acute PKCβ inhibition (LY333-531), occurred alongside decreased tissue perfusion, as well as reduced insulin-stimulated Akt signaling in the prefrontal cortex, but not the triceps. In the early stages of juvenile obesity development, the microvasculature and prefrontal cortex exhibit impaired insulin signaling. Such adaptations may underscore vascular and neurological derangements associated with juvenile obesity.

Intracranial aneurysm and sildenafil

Sildenafil is one of the most commonly used drugs for the treatment of erectile dysfunction. To date, we found five reported cases of intracerebral bleeding and two reported cases of subarachnoid hemorrhage related to sildenafil use. We report a 49-year-old hypertensive and diabetic patient who presented with acute pulmonary edema and loss of consciousness following ingestion of 100 mg of sildenafil prior to sexual intercourse. He was not previously aware of the presence of an aneurysm and had no family history of it. Computed tomography of his head revealed a subarachnoid hemorrhage due to rupture of a saccular aneurysm with subsequent repeat hemorrhage within a few hours of presentation. A sudden increase in blood pressure led to pulmonary edema. Studies have shown that sildenafil acts on phosphodiesterase-1, -2 and -5 receptors and leads to a secondary increase in intracerebral circulation and vasodilatory effects, leading to sympathetic overactivity which increases the risk for intracranial bleeding.

A Phase I proof-of-concept and safety trial of sildenafil to treat cerebral vasospasm following subarachnoid hemorrhage

OBJECTIVE

Studies show that phosphodiesterase-V (PDE-V) inhibition reduces cerebral vasospasm (CVS) and improves outcomes after experimental subarachnoid hemorrhage (SAH). This study was performed to investigate the safety and effect of sildenafil (an FDA-approved PDE-V inhibitor) on angiographic CVS in SAH patients.

METHODS

A2-phase, prospective, nonrandomized, human trial was implemented. Subarachnoid hemorrhage patients underwent angiography on Day 7 to assess for CVS. Those with CVS were given 10 mg of intravenous sildenafil in the first phase of the study and 30 mg in the second phase. In both, angiography was repeated 30 minutes after infusion. Safety was assessed by monitoring neurological examination findings and vital signs and for the development of adverse reactions. For angiographic assessment, in a blinded fashion, pre- and post-sildenafil images were graded as "improvement" or "no improvement" in CVS. Unblinded measurements were made between pre- and post-sildenafil angiograms.

RESULTS

Twelve patients received sildenafil; 5 patients received 10 mg and 7 received 30 mg. There were no adverse reactions. There was no adverse effect on heart rate or intracranial pressure. Sildenafil resulted in a transient decline in mean arterial pressure, an average of 17% with a return to baseline in an average of 18 minutes. Eight patients (67%) were found to have a positive angiographic response to sildenafil, 3 (60%) in the low-dose group and 5 (71%) in the high-dose group. The largest degree of vessel dilation was an average of 0.8 mm (range 0-2.1 mm). This corresponded to an average percentage increase in vessel diameter of 62% (range 0%-200%).

CONCLUSIONS

The results from this Phase I safety and proof-of-concept trial assessing the use of intravenous sildenafil in patients with CVS show that sildenafil is safe and well tolerated in the setting of SAH. Furthermore, the angiographic data suggest that sildenafil has a positive impact on human CVS.

Phosphodiesterase 5 inhibition attenuates cerebral vasospasm and improves functional recovery after experimental subarachnoid hemorrhage

BACKGROUND

Cerebral vasospasm is an independent predictor of poor outcome after subarachnoid hemorrhage (SAH). The nitric oxide-cyclic guanosine monophosphate (NO-cGMP) vasodilatory pathway is strongly implicated in its pathophysiology. Preliminary studies suggest that phosphodiesterase 5 (PDE5), an enzyme that degrades cGMP, may play a role because the PDE5 inhibitor sildenafil was found to reduce vasospasm after SAH. However, several questions that are critical when considering translational studies remain unanswered.

OBJECTIVE

To elucidate the mechanism of action of sildenafil against vasospasm and to assess whether sildenafil attenuates SAH-induced neuronal cell death, improves functional outcome after SAH, or causes significant physiological side effects when administered at therapeutically relevant doses.

METHODS

SAH was induced via endovascular perforation in male C57BL6 mice. Beginning 2 hours later, mice received sildenafil citrate (0.7, 2 or 5 mg/kg orally twice daily) or vehicle. Neurological outcome was assessed daily. Vasospasm was determined on post-SAH day 3. Brain PDE5 expression and activity, cGMP content, neuronal cell death, arterial blood pressure, and intracranial pressure were examined.

RESULTS

We found that PDE5 activity (but not expression) is increased after SAH, leading to decreased cGMP levels. Sildenafil attenuates this increase in PDE5 activity and restores cGMP levels after SAH. Post-SAH initiation of sildenafil was found to decrease vasospasm and neuronal cell death and markedly improve neurological outcome without causing significant physiological side effects.

CONCLUSION

Sildenafil, a US Food and Drug Administration-approved drug with a proven track record of safety in humans, is a promising new therapy for vasospasm and neurological deficits after SAH.

Safety and efficacy of sildenafil citrate in reversal of cerebral vasospasm: A feasibility study

Objective:

Cerebral vasospasm is the commonest cause for mortality and morbidity in patients following clipping of a ruptured aneurysm. Selective phosphodiesterase (PDE) inhibitor like sildenafil acts as a vasodilator. The objective of this study was to evaluate the safety and feasibility of oral sildenafil citrate in patients with symptomatic refractory vasospasm.

Methods:

A total of 832 patients with aneurysmal subarachnoid bleed were operated in 4 years. Two hundred and seventy-three patients had vasospasm. Of these, 72 patients had refractory cerebral vasospasm. Vasospasm was defined as refractory when institution of “HHH” failed to reverse the transcranial Doppler (TCD) values even after 24 hours. Computed tomography (CT) scan showed no infarct, hematoma, or hydrocephalus, and the serum electrolytes were within normal limits. They received 100–150 mg of sildenafil every 4 hours. Response was evaluated by 2-hourly TCD.

Results:

Eight patients had sustained (TCD values normal for >48 hours) and four had temporary relief in vasospasm, as suggested. Four patients developed complications significant enough to terminate the therapy.

Conclusions:

Sildenafil citrate may be effective in patients with refractory symptomatic vasospasm. It calls upon the pharmacologists and scientists to discover newer supraselective PDE inhibitors, specific to PDE receptors in brain vessels.

Metamorphosis of subarachnoid hemorrhage research: from delayed vasospasm to early brain injury

Delayed vasospasm that develops 3–7 days after aneurysmal subarachnoid hemorrhage (SAH) has traditionally been considered the most important determinant of delayed ischemic injury and poor outcome. Consequently, most therapies against delayed ischemic injury are directed towards reducing the incidence of vasospasm. The clinical trials based on this strategy, however, have so far claimed limited success; the incidence of vasospasm is reduced without reduction in delayed ischemic injury or improvement in the long-term outcome. This fact has shifted research interest to the early brain injury (first 72 h) evoked by SAH. In recent years, several pathological mechanisms that activate within minutes after the initial bleed and lead to early brain injury are identified. In addition, it is found that many of these mechanisms evolve with time and participate in the pathogenesis of delayed ischemic injury and poor outcome. Therefore, a therapy or therapies focused on these early mechanisms may not only prevent the early brain injury but may also help reduce the intensity of later developing neurological complications. This manuscript reviews the pathological mechanisms of early brain injury after SAH and summarizes the status of current therapies.

Comparative study of calcium ion dynamics and contractile response in rat middle cerebral and basilar arteries

The objective of this study was to compare intracellular calcium concentration ([Ca(2+)](i)) and contractile responses in isolated rat middle cerebral artery (MCA) with those in basilar artery (BA) employing real-time confocal laser microscopy. KCl elicited transient [Ca(2+)](i) elevation and sustained contraction in both arteries; moreover, nearly equal responses were evident in both arteries. Application of 5-hydroxytryptamine (5-HT), vasopressin (VP), and alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-me ATP) also induced elevation of [Ca(2+)](i) and contraction in both arteries. The maximum response of 5-HT and VP necessary to increase [Ca(2+)](i) and to constrict the MCA was less in comparison to the BA; however, a linear relationship emerged between the maximum response of [Ca(2+)](i) and that of contraction. Additionally, the slope of the correlation regression line of MCA was nearly identical to that of BA. On the other hand, cyclopiazonic acid (CPA)-induced Ca(2+) release from store sites following contraction of MCA was distinct from that of BA. In MCA, velocity of [Ca(2+)](i) elevation in smooth muscle cells and Ca(2+)-wave propagation along smooth muscle cells induced by 5-HT were slower than those in BA. These observations revealed that different regions of arteries along the same cerebral tissue may display distinct [Ca(2+)](i) response; moreover, this difference may be one reason for the distinct contractile response.

Angiogenesis and improved cerebral blood flow in the ischemic boundary area detected by MRI after administration of sildenafil to rats with embolic stroke

To dynamically investigate the long-term response of an ischemic lesion in rat brain to the administration of sildenafil, male Wistar rats subjected to embolic stroke were treated with sildenafil (n=11) or saline (n=10) at a dose of 10 mg/kg administered subcutaneously 24-h after stroke and daily for an additional 6 days. Magnetic resonance images were acquired and functional performance was measured in all animals at 1 day, 2 days and weekly for 6 weeks post-stroke. All rats were sacrificed 6 weeks after stroke and endothelial barrier antigen immunostaining was employed for morphological analysis and quantification of cerebral vessels. Map-ISODATA was computed from T(1), T(2) and T(1sat) maps. ISODATA derived tissue signatures characterize the degree of ischemic injury. Based on the map-ISODATA calculated at 6 weeks, the ischemic lesion for each animal was divided into two specific regions, the ischemic boundary and ischemic core. The temporal profiles of cerebral blood flow (CBF) and tissue signature were retrospectively tracked in these two regions and were compared with histological evaluation and functional outcome. After 1 week of sildenafil treatment, the ischemic lesion exhibited two significantly different regions, with higher CBF level and correspondingly, lower tissue signature value in the boundary region than in the core region. Sildenafil treatment did not significantly reduce the lesion size, but did enhance angiogenesis. Functional performance was significantly increased after sildenafil treatment compared with the control group. Administration of sildenafil to rats with embolic stroke enhances angiogenesis and selectively increases the CBF level in the ischemic boundary, and improves neurological functional recovery compared to saline-treated rats.

Increased phosphodiesterase-5 expression is involved in the decreased vasodilator response to nitric oxide in cirrhotic rat livers

BACKGROUND/AIMS

Cirrhotic livers have a deficient vasodilator response to nitric oxide (NO). The vasodilator effect of NO is normally limited by the degradation of its second messenger cyclic guanosine 3', 5' monophosphate by phosphodiesterases. We investigated (1) the phosphodiesterase-5 (PDE-5) expression in normal and cirrhotic rat livers, (2) the location of the deficient response to NO in cirrhotic livers, and (3) the effect of the PDE-5 inhibitor Sildenafil citrate on this deficient response.

METHODS

Normal and ascitic cirrhotic rats were subjected to liver perfusion with continuous measurement of both perfusion and sinusoidal (wedge hepatic) pressures. After incubation with N-monomethyl-l-arginine and pre-constriction with Methoxamine, concentration-response curves to the spontaneous NO donor S-nitroso-N-acetylpenicillamine were obtained in the absence or presence of Sildenafil (10(-8)M).

RESULTS

PDE-5 expression (Western blot) in cirrhotic livers was higher than in normal livers (P=0.042). Compared to normal livers, cirrhotic livers showed a decreased response to S-nitroso-N-acetylpenicillamine in the pre-sinusoidal area (P=0.003) but not in the sinusoidal/post-sinusoidal area (P=0.433). In the presence of Sildenafil, normal and cirrhotic livers showed similar pre-sinusoidal (P=0.419) and sinusoidal/post-sinusoidal (P=0.875) responses to S-nitroso-N-acetylpenicillamine.

CONCLUSIONS

Increased PDE-5 expression is involved in the decreased vascular response to NO in cirrhotic livers.

Reversal of delayed vasospasm by an inhibitor of the synthesis of 20-HETE

This study characterized the time course of changes in cerebral blood flow (CBF) and vascular diameter in a dual-hemorrhage model of subarachnoid hemorrhage (SAH) in rats and examined whether acute blockade of the synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE) with N-(3-chloro-4-morpholin-4-yl)phenyl-N'-hydroxyimido formamide (TS-011) can reverse delayed vasospasm in this model. Rats received an intracisternal injection of blood (0.4 ml) on day 0 and a second injection 2 days later. CBF was sequentially measured using laser-Doppler flowmetry, and the diameters of the cerebral arteries were determined after filling the cerebral vasculature with a casting compound. CBF fell to 67% of control after the first intracisternal injection of blood but returned to a value near control 24 h later. CBF again fell to 63% of control after a second intracisternal injection of blood and remained 30% below control for 5 days. The fall in CBF after the second intracisternal injection of blood was associated with a sustained 30% reduction in the diameters of the middle cerebral, posterior communicating, and basilar arteries. Acute blockade of the synthesis of 20-HETE with TS-011 (0.1 mg/kg i.v.), 5 days after the second SAH, increased the diameters of the cerebral arteries, and CBF returned to control. These results indicate that the rats develop delayed vasospasm after induction of the dual-hemorrhage model of SAH and that blockade of the synthesis of 20-HETE fully reverses cerebral vasospasm in this model. They also implicate 20-HETE in the development and maintenance of delayed cerebral vasospasm.

Activation of Rho-associated kinase during augmented contraction of the basilar artery to serotonin after subarachnoid hemorrhage

Delayed cerebral vasospasm after subarachnoid hemorrhage (SAH) may be due, in part, to altered regulation of arterial smooth muscle contraction. Contraction of cerebral arteries to serotonin is augmented after experimental SAH. We hypothesized that activation of Rho-associated kinase (Rho kinase) contributes to augmented contraction of cerebral arteries to serotonin after SAH. Autologous arterial blood (SAH) or artificial cerebrospinal fluid (control) was injected into the cisterna magna of anesthetized rabbits. At 2 days after injection, the basilar artery was excised and isometric contraction of arterial rings was recorded. Maximum contraction of the basilar artery to serotonin was augmented about fourfold in SAH compared with control rabbits ( P < 0.01). Contraction to histamine was similar in the two groups. Fasudil hydrochloride (3 μmol/l), an inhibitor of Rho kinase, markedly attenuated serotonin-induced contraction. Fasudil had little effect on contractions induced by histamine or phorbol 12,13-dibutyrate. In addition, phosphorylation of myosin phosphatase, a major target of Rho kinase in regulation of smooth muscle contraction, in the basilar artery was examined by Western blotting. In basilar arteries of SAH, but not control, rabbits, serotonin increased phosphorylation of myosin phosphatase about twofold at Thr853 of the myosin-targeting subunit. These results suggest that enhanced activation of Rho kinase contributes to augmented contraction of the basilar artery to serotonin after SAH.

Targeting cerebral arteries for gene therapy

After the steady progress towards application of gene therapy to cerebral arterial diseases, several applications, including modification of gene expression in cerebral arteries, are now feasible. There are several possible targets for cerebrovascular gene therapy, and numerous studies have tested gene therapy strategies in animal models of cerebrovascular disorders. However, some major obstacles, especially issues of safety, must be overcome before clinical use in humans. Gene therapy for cerebral arterial diseases is still in its infancy, and many basic and preclinical studies are yet to be done in order to develop effective and safe techniques.

Regulation of rat pial arteriolar smooth muscle relaxation in vivo through multidrug resistance protein 5-mediated cGMP efflux

Multidrug resistance protein 5 (MRP5) has been linked to cGMP cellular export in peripheral vascular smooth muscle cells (VSMCs) and is widely expressed in brain vascular tissue. In the present study, we examined whether knockdown of MRP5 in pial arterioles [via antisense oligodeoxynucleotide (ODN) applications] affected nitric oxide (NO)/cGMP-induced dilations. The antisense or (as a control) missense ODN was applied to the cortical surface approximately 24 h before study via closed cranial windows. The efficacy of the antisense vs. missense ODN in eliciting selective reductions in MRP5 expression was confirmed by analysis of MRP5 mRNA in pial tissue. Unexpectedly, in initial studies, a significantly lower maximal pial arteriolar diameter increase in the presence of the NO donor S-nitrosoacetylpenicillamine (SNAP) was seen in the antisense vs. missense ODN-treated rats (35 vs. 48% diameter increase, respectively). It was suspected that this related to a reduced vascular smooth muscle cell sensitivity to cGMP due to prolonged exposure to increased intracellular cGMP levels elevated by overnight restriction of cGMP efflux. That postulate was supported by a finding of a diminished vasodilating response to the cGMP-dependent protein kinase-activating cGMP analog 8-p-chlorophenylthio-cGMP in antisense vs. missense ODN-treated rats. To prevent desensitization, additional rats were studied in the presence of chronic NOS inhibition via Nomega-nitro-L-arginine. In the NO synthase (NOS)-inhibited rats, the maximal SNAP response was much higher in the antisense (62% increase) vs. the missense ODN (40% increase) group. A similar result was obtained when monitoring responses to the soluble guanylyl cyclase-activating drugs YC-1 and BAY 41-2272. Moreover, in the presence of NOS inhibition, the normal SNAP-induced rise in periarachnoid cerebrospinal fluid cGMP levels, which reflects cGMP efflux, was absent in the antisense ODN-treated rats, a finding consistent with loss of MRP5 function. In conclusion, if one minimizes the confounding effects of basal cGMP production, a clearer picture emerges, one that indicates an important role for MRP5-mediated cGMP efflux in the regulation of NO-induced cerebral arteriolar relaxation.

20-HETE contributes to the acute fall in cerebral blood flow after subarachnoid hemorrhage in the rat

This study examined the effects of blocking the formation of 20-hydroxyeicosatetraenoic acid (20-HETE) on the acute fall in cerebral blood flow after subarachnoid hemorrhage (SAH) in the rat. In vehicle-treated rats, regional cerebral blood flow (rCBF) measured with laser-Doppler flowmetry fell by 30% 10 min after the injection of 0.3 ml of arterial blood into the cisterna magna, and it remained at this level for 2 h. Pretreatment with inhibitors of the formation of 20-HETE, 17-octadecynoic acid (17-ODYA; 1.5 nmol intrathecally) and N-hydroxy-N'-(4-butyl-2-methylphenyl)formamidine (HET0016; 10 mg/kg iv), reduced the initial fall in rCBF by 40%, and rCBF fully recovered 1 h after induction of SAH. The concentration of 20-HETE in the cerebrospinal fluid rose from 12 +/- 2 to 199 +/- 17 ng/ml after SAH in vehicle-treated rats. 20-HETE levels averaged only 15 +/- 11 and 39 +/- 13 ng/ml in rats pretreated with 17-ODYA or HET0016, respectively. HET0016 selectively inhibited the formation of 20-HETE in rat renal microsomes with an IC(50) of <15 nM and human recombinant CYP4A11, CYP4F2, and CYP4F3 enzymes with an IC(50) of 42, 125, and 100 nM, respectively. These results indicate that 20-HETE contributes to the acute fall in rCBF after SAH in rats.