Combination stroke therapy: easy as APC?

Blocking a vicious cycle nNOS/peroxynitrite/AMPK by S-nitrosoglutathione: implication for stroke therapy

BACKGROUND

Stroke immediately sets into motion sustained excitotoxicity and calcium dysregulation, causing aberrant activity in neuronal nitric oxide synthase (nNOS) and an imbalance in the levels of nitric oxide (NO). Drugs targeting nNOS-originated toxicity may therefore reduce stroke-induced damage. Recently, we observed that a redox-modulating agent of the NO metabolome, S-nitrosoglutathione (GSNO), confers neurovascular protection by reducing the levels of peroxynitrite, a product of aberrant NOS activity. We therefore investigated whether GSNO-mediated neuroprotection and improved neurological functions depend on blocking nNOS/peroxynitrite-associated injurious mechanisms using a rat model of cerebral ischemia reperfusion (IR).

RESULTS

IR increased the activity of nNOS, the levels of neuronal peroxynitrite and phosphorylation at Ser(1412) of nNOS. GSNO treatment of IR animals decreased IR-activated nNOS activity and neuronal peroxynitrite levels by reducing nNOS phosphorylation at Ser(1412). The Ser(1412) phosphorylation is associated with increased nNOS activity. Supporting the notion that nNOS activity and peroxynitrite are deleterious following IR, inhibition of nNOS by its inhibitor 7-nitroindazole or reducing peroxynitrite by its scavenger FeTPPS decreased IR injury. GSNO also decreased the activation of AMP Kinase (AMPK) and its upstream kinase LKB1, both of which were activated in IR brain. AMPK has been implicated in nNOS activation via Ser(1412) phosphorylation. To determine whether AMPK activation is deleterious in the acute phase of IR, we treated animals after IR with AICAR (an AMPK activator) and compound c (an AMPK inhibitor). While AICAR potentiated, compound c reduced the IR injury.

CONCLUSIONS

Taken together, these results indicate an injurious nNOS/peroxynitrite/AMPK cycle following stroke, and GSNO treatment of IR inhibits this vicious cycle, resulting in neuroprotection and improved neurological function. GSNO is a natural component of the human body, and its exogenous administration to humans is not associated with any known side effects. Currently, the FDA-approved thrombolytic therapy suffers from a lack of neuronal protective activity. Because GSNO provides neuroprotection by ameliorating stroke's initial and causative injuries, it is a candidate of translational value for stroke therapy.

Nitric oxide donors as neuroprotective agents after an ischemic stroke-related inflammatory reaction

Cerebral ischemia initiates a cascade of detrimental events including glutamate-associated excitotoxicity, intracellular calcium accumulation, formation of Reactive oxygen species (ROS), membrane lipid degradation, and DNA damage, which lead to the disruption of cellular homeostasis and structural damage of ischemic brain tissue. Cerebral ischemia also triggers acute inflammation, which exacerbates primary brain damage. Therefore, reducing oxidative stress (OS) and downregulating the inflammatory response are options that merit consideration as potential therapeutic targets for ischemic stroke. Consequently, agents capable of modulating both elements will constitute promising therapeutic solutions because clinically effective neuroprotectants have not yet been discovered and no specific therapy for stroke is available to date. Because of their ability to modulate both oxidative stress and the inflammatory response, much attention has been focused on the role of nitric oxide donors (NOD) as neuroprotective agents in the pathophysiology of cerebral ischemia-reperfusion injury. Given their short therapeutic window, NOD appears to be appropriate for use during neurosurgical procedures involving transient arterial occlusions, or in very early treatment of acute ischemic stroke, and also possibly as complementary treatment for neurodegenerative diseases such as Parkinson or Alzheimer, where oxidative stress is an important promoter of damage. In the present paper, we focus on the role of NOD as possible neuroprotective therapeutic agents for ischemia/reperfusion treatment.

Roles of inflammation and the activated protein C pathway in the brain edema associated with cerebral venous sinus thrombosis

BACKGROUND AND PURPOSE

Increased blood-brain barrier (BBB) permeability, brain edema, and hemorrhage are important consequences of cerebral venous sinus thrombosis (CVST). The objective of this study was to define the role of the protein C pathway in the BBB permeability and edema elicited by experimental CVST. The role of neutrophil recruitment was also evaluated.

METHODS

Edema, BBB permeability, leukocyte-endothelial cell adhesion (LECA) and inflammatory cytokine levels were monitored in a murine model of CVST. The role of activated protein C (APC) was assessed in wild type mice (WT) receiving APC neutralizing antibody and in endothelial protein C receptor overexpressing mice (EPCR-tg). Neutrophil involvement was evaluated using an anti-CD18 antibody (Ab) and antineutrophil serum.

RESULTS

Brain edema and increases in BBB permeability and LECA were noted 48 hours after CVST. APC immunoblockade exacerbated these responses, while EPCR-tg exhibited blunted responses, as did WT treated with either antineutrophil serum or the CD18 Ab.

CONCLUSIONS

The protein C pathway protects the brain against the deleterious microvascular responses to CVST, a response that appears to be linked to the recruitment of inflammatory cells.

Caffeic acid phenethyl ester reduces neurovascular inflammation and protects rat brain following transient focal cerebral ischemia

Ischemic stroke is a neurovascular disease treatable by thrombolytic therapy, but the therapy has to be initiated within 3 h of the incident. This therapeutic limitation stems from the secondary injury which results mainly from oxidative stress and inflammation. A potent antioxidant/anti-inflammatory agent, caffeic acid phenethyl ester (CAPE) has potential to mitigate stroke's secondary injury, and thereby widening the therapeutic window. We observed that CAPE protected the brain in a dose-dependent manner (1-10 mg/kg body weight) and showed a wide therapeutic window (about 18 h) in a rat model of transient focal cerebral ischemia and reperfusion. The treatment also increased nitric oxide and glutathione levels, decreased lipid peroxidation and nitrotyrosine levels, and enhanced cerebral blood flow. CAPE down-regulated inflammation by blocking nuclear factor kappa B activity. The affected mediators included adhesion molecules (intercellular adhesion molecule-1 and E-selectin), cytokines (tumor necrosis factor-alpha and interleukin-1beta) and inducible nitric oxide synthase. Anti-inflammatory action of CAPE was further documented through reduction of ED1 (marker of activated macrophage/microglia) expression. The treatment inhibited apoptotic cell death by down-regulating caspase 3 and up-regulating anti-apoptotic protein Bcl-xL. Conclusively, CAPE is a promising drug candidate for ischemic stroke treatment due to its inhibition of oxidative stress and inflammation, and its clinically relevant wide therapeutic window.

Memantine reduces hematoma expansion in experimental intracerebral hemorrhage, resulting in functional improvement

Glutamate is accumulated in abundance during the early period of experimental hematoma, and the activation of N-methyl-D-aspartate (NMDA) receptors by glutamate can result in an influx of calcium and neuronal death in cases of intracerebral hemorrhage (ICH). Memantine, which is known to be a moderate-affinity, uncompetitive, NMDA receptor antagonist, was investigated with regard to its ability to block the glutamate overstimulation and tissue plasminogen activator (tPA)/urokinase plasminogen activator (uPA)/matrix metalloproteinase (MMP)-9 modulation in experimental ICH. Intracerebral hemorrhage was induced via the infusion of collagenase into the left basal ganglia of adult rats. Either memantine (20 mg/kg/day) or PBS was intraperitoneally administered 30 min after the induction of ICH, and, at daily intervals afterwards, for either 3 or 14 days. Hemorrhage volume decreased by 47% in the memantine group, as compared with the ICH-only group. In the memantine group, the numbers of TUNEL+, myeloperoxidase (MPO)+, and OX42+ cells decreased in the periphery of the hematoma. Memantine resulted in an upregulation of bcl-2 expression and an inhibition of caspase-3 activation. Memantine also exerted a profound inhibitory effect on the upregulation of tPA/uPA mRNA, and finally decreased the MMP-9 level in the hemorrhagic brain. In modified limb-placing test, the memantine-treated rats exhibited lower scores initially, and recovered more quickly and thoroughly throughout the 35 days of the study. Here, we show that memantine causes a reduction of hematoma expansion, coupled with an inhibitory effect on the tPA/uPA and MMP-9 level. Subsequently, memantine was found to reduce inflammatory infiltration and apoptosis, and was also determined to induce functional recovery after ICH.

Cerebrovascular protection by various nitric oxide donors in rats after experimental stroke

The efficacy of nitric oxide (NO) treatment in ischemic stroke, though well recognized, is yet to be tested in clinic. NO donors used to treat ischemic injury are structurally diverse compounds. We have shown that treatment of S-nitrosoglutathione (GSNO) protects the brain against injury and inflammation in rats after experimental stroke [M. Khan, B. Sekhon, S. Giri, M. Jatana, A. G. Gilg, K. Ayasolla, C. Elango, A. K. Singh, I. Singh, S-Nitrosoglutathione reduces inflammation and protects brain against focal cerebral ischemia in a rat model of experimental stroke, J. Cereb. Blood Flow Metab. 25 (2005) 177-192.]. In this study, we tested structurally different NO donors including GSNO, S-nitroso-N-acetyl-penicillamine (SNAP), sodium nitroprusside (SNP), methylamine hexamethylene methylamine NONOate (MAHMA), propylamine propylamine NONOate (PAPA), 3-morpholinosydnonimine (SIN-1) and compared their neuroprotective efficacy and antioxidant property in rats after ischemia/reperfusion (I/R). GSNO, in addition to neuroprotection, decreased nitrotyrosine formation and lipid peroxidation in blood and increased the ratio of reduced versus oxidized glutathione (GSH/GSSG) in brain as compared to untreated animals. GSNO also prevented the I/R-induced increase in mRNA expression of ICAM-1 and E-Selectin. SNAP and SNP extended limited neuroprotection, reduced nitrotyrosine formation in blood and blocked increase in mRNA expression of ICAM-1 and E-Selectin in brain tissue. PAPA, MAHMA, and SIN-1 neither protected the brain nor reduced oxidative stress. We conclude that neuroprotective action of NO donors in experimental stroke depends on their ability to reduce oxidative stress both in brain and blood.