Thrombolysis for acute stroke

Microsomal prostaglandin E synthase-1 is a critical factor of stroke-reperfusion injury

Although augmented prostaglandin E(2) (PGE(2)) synthesis and accumulation have been demonstrated in the lesion sites of rodent transient focal ischemia models, the role of PGE(2) in neuronal survival has been controversial, showing both protective and toxic effects. Here we demonstrate the induction of microsomal PGE synthase 1 (mPGES-1), an inducible terminal enzyme for PGE(2) synthesis, in neurons, microglia, and endothelial cells in the cerebral cortex after transient focal ischemia. In mPGES-1 knockout (KO) mice, in which the postischemic PGE(2) production in the cortex was completely absent, the infarction, edema, apoptotic cell death, and caspase-3 activation in the cortex after ischemia were all reduced compared with those in wild-type (WT) mice. Furthermore, the behavioral neurological dysfunctions observed after ischemia in WT mice were significantly ameliorated in KO mice. The ameliorated symptoms observed in KO mice after ischemia were reversed to almost the same severity as WT mice by intracerebroventricular injection of PGE(2) into KO mice. Our observations suggest that mPGES-1 may be a critical determinant of postischemic neurological dysfunctions and a valuable therapeutic target for treatment of human stroke.

Drug therapy of neurovascular disease

Recent advances in the prevention and pharmacotherapy of cerebrovascular disease have provided more favorable clinical outcomes. For the treatment of an acute ischemic stroke, the early use of thrombolytic agents can reduce the degree of brain damage while improving functional outcomes. However, trials evaluating various classes of other neuroprotective agents have not shown benefit to date. For the prevention of second stroke, the use of antiplatelet drugs, HMG-CoA reductase inhibitors, and angiotensin-converting enzyme inhibitors with a diuretic have shown benefit in reducing new events. In patients with underlying heart disease or atrial fibrillation, warfarin appears to be the drug of choice in preventing stroke. Early treatment of hemorrhagic stroke with calcium channel blockers can improve the functional outcome. Innovative therapies are now available for the treatment of migraine and vascular dementia. Primary prevention of stroke remains the optimal therapeutic strategy and includes treatment of systemic hypertension and hypercholesterolemia.

Thrombolytic effect of lonomin V in a rabbit jugular vein thrombosis model

Thrombolytic efficacy of lonomin V (LV), a protein isolated from Lonomia achelous caterpillars haemolymph, administered either as a single intravenous bolus or as a continuous infusion, was evaluated in a rabbit jugular vein thrombosis model, and compared with those of single-chain tissue-type plasminogen activator (sct-PA) and two-chain urokinase-type plasminogen activator (tcu-PA). As a bolus LV, at doses of 100 000 IU/kg body weight (bw) produced an activator-induced thrombolysis (AIL) of 50.94% +/- 12.4 compared with 14.4% +/- 10.8 for tcu-PA at the same dose. As a continuous infusion at doses of 200 000 IU/kg bw LV produced an AIL of 45.8%, whereas sct-PA and tcu-PA produced an AIL of 69.9 and 33.7%, respectively. Fibrinogen, plasminogen and alpha-2-antiplasmin levels decreased significantly with the higher doses of LV, sct-PA, and tcu-PA. Factor XIII levels were significantly reduced in a dose-dependent manner only with LV. In conclusion, LV produces a dose-dependent thrombolysis in combination with a decrease in factor XIII activity.

Reduced susceptibility to ischemic brain injury and N-methyl-D-aspartate-mediated neurotoxicity in cyclooxygenase-2-deficient mice

Cyclooxygenase-2 (COX-2), a prostanoid-synthesizing enzyme that contributes to the toxicity associated with inflammation, has recently emerged as a promising therapeutic target for several illnesses, ranging from osteoarthritis to Alzheimer's disease. Although COX-2 has also been linked to ischemic stroke, its role in the mechanisms of ischemic brain injury remains controversial. We demonstrate that COX-2-deficient mice have a significant reduction in the brain injury produced by occlusion of the middle cerebral artery. The protection can be attributed to attenuation of glutamate neurotoxicity, a critical factor in the initiation of ischemic brain injury, and to abrogation of the deleterious effects of postischemic inflammation, a process contributing to the secondary progression of the damage. Thus, COX-2 is involved in pathogenic events occurring in both the early and late stages of cerebral ischemia and may be a valuable therapeutic target for treatment of human stroke.

Metalloproteinase inhibition reduces thrombolytic (tissue plasminogen activator)-induced hemorrhage after thromboembolic stroke

BACKGROUND AND PURPOSE

A potentially dangerous side effect associated with tissue plasminogen activator (tPA) use is cerebral hemorrhage. We have focused on developing drugs that could be administered with tPA to reduce the rate of hemorrhage. Since recent studies suggest that various matrix metalloproteinases (MMPs) are important in tumor necrosis factor-alpha production and membrane and vessel remodeling after ischemia, we investigated whether MMP inhibition affected the rate of hemorrhage and infarct production in the absence or presence of tPA treatment.

METHODS

We occluded the middle cerebral artery of New Zealand White rabbits with radiolabeled blood clots. Five minutes after embolization, we administered either the MMP inhibitor BB-94 (30 mg/kg SC) or its vehicle. Additional groups received BB-94 or vehicle in combination with tPA, administered 60 minutes after embolization (3.3 mg/kg tPA). After 48 hours, the rabbits were killed and brains were removed, immersion fixed for 1 week in 4% paraformaldehyde, and then cut into 5-mm coronal sections that were examined for the presence of hemorrhage, infarcts, and recanalization.

RESULTS

Hemorrhage after embolic stroke was detected in 24% of the control group. tPA induced macroscopically visible hemorrhage in 77% of the tPA-treated group. The rabbits treated with BB-94 had an 18% incidence of hemorrhage (P:>0.05 compared with control). However, when the combination of BB-94 and tPA was administered to rabbits, there was only a 41% incidence of hemorrhage (compared with 77% in the tPA group; P:<0. 05). Both tPA and BB-94/tPA were similarly effective at lysing clots, at 49% and 35% (P:<0.05), respectively, compared with the 5% rate of lysis in the control group. There was a trend for a reduction in the number of infarcts, but it did not reach statistical significance.

CONCLUSIONS

Our data suggest that MMP inhibition attenuates mechanisms involved in tPA-induced hemorrhage. This novel form of combination therapy may show promise as a treatment strategy for acute stroke.