Treatment of acute focal cerebral ischemia with prostacyclin

Synthetic approaches to isocarbacyclin and analogues as potential neuroprotective agents against ischemic stroke

Isocarbacyclin is a valuable synthetic analogue of prostacyclin with potential neuroprotective effects for the treatment of ischemic stroke. Herein, we describe the synthesis of isocarbacyclin and bicyclic analogues in only 7-10 steps, with the ω-side chain diversified at a late stage. A combination of new reaction design, function-oriented synthesis, and late-stage diversification led to a series of compounds that were tested for their neuroprotective activities. Efforts toward the synthesis of tricyclic analogues of isocarbacyclin, using the same combination of metal-catalyzed reactions, is also described.

Prostacyclin receptor deletion aggravates hippocampal neuronal loss after bilateral common carotid artery occlusion in mouse

Transient global cerebral ischemia causes delayed neuronal death in the hippocampal CA1 region. It also induces an increase in cyclooxygenase 2 (COX-2), which generates several metabolites of arachidonic acid, known as prostanoids, including prostacyclin (PGI(2)). To determine the role of the PGI(2) receptor (IP) in post-ischemic delayed cell death, wild-type and IP knockout (IP(-/-)) C57Bl/6 mice were subjected to 12-min bilateral common carotid artery occlusion or sham surgery, followed by 7 days of reperfusion. In the sham-operated mice, no statistical difference in CA1 hippocampal neuronal density was observed between the wild-type (2836+/-18/mm(2)) and IP(-/-) (2793+/-43/mm(2)) mice. Interestingly, in animals subjected to ischemia, surviving neuronal density in wild-type mice decreased to 50.5+/-7.9% and that of IP(-/-) mice decreased to 23.0+/-4.5% of their respective sham-operated controls (P<0.05). The results establish a role for the IP receptor in protecting pyramidal hippocampal neurons after this global ischemic model and suggest that IP receptor agonists could be developed to prevent delayed pyramidal neuronal cell death.

Effect of TTC-909 on cerebral infarction following permanent occlusion of the middle cerebral artery in stroke prone spontaneously hypertensive rats

We investigated the effect of TTC-909, a drug preparation of the stable prostaglandin I(2) analogue clinprost (isocarbacyclin methylester; methyl 5-[(1S,5S,6R,7R)-7-hydroxy-6-[(E)-(S)-3-hydroxy-1-octenyl] bicyclo[3.3.0]oct-2-en-3-yl] pentanoate) incorporated into lipid microspheres, on cerebral infarction 7 days after permanent occlusion of the middle cerebral artery (MCA) in stroke prone spontaneously hypertensive rats (SHRSP). Under the anesthesia, the MCA was permanently occluded above the rhinal fissure. In schedule 1, vehicle or TTC-909 was injected i.v. once daily over 7 days starting immediately after MCA occlusion. In schedule 2, vehicle or TTC-909 was infused for 3 h starting immediately after MCA occlusion. In schedule 3, vehicle or TTC-909 was infused for 3 h starting immediately after MCA occlusion followed by bolus injection once daily over 6 days. Seven days later, the infarct volume was estimated following hematoxylin and eosin staining. Cerebral infarction produced by permanent occlusion of MCA was limited to the cerebral cortex. While this volume was reduced significantly in case of schedule 3, the infarct volume was not reduced significantly in schedules 1 and 2. Ozagrel, a thromboxane A(2) synthetase inhibitor, had no effect on the infarct volume in schedule 3. These results suggest that cerebral infarction can be developed progressively not only during the first few hours but also after a permanent occlusion of MCA in SHRSP. TTC-909 inhibited cerebral infarction, maybe by improving cerebral blood flow and by protecting against neuronal damage.

Effect of TTC-909 in a middle cerebral artery thrombosis model in stroke-prone spontaneously hypertensive rats

We investigated the effect of TTC-909, a preparation of the stable prostaglandin I(2) analogue clinprost (isocarbacyclin methylester; methyl 5-[(1S,5S,6R,7R)-7-hydroxy-6-[(E)-(S)-3-hydroxy-1-octenyl] bicyclo[3.3.0]oct-2-en-3-yl] pentanoate) incorporated into lipid microspheres, on infarct volume 24 h after photochemically induced thrombotic occlusion of the middle cerebral artery in stroke-prone spontaneously hypertensive rats (SHR). Under anesthesia, the photosensitizing dye rose bengal (20 mg/kg) was administered intravenously and photoirradiation with green light (wavelength 540 nm) on the middle cerebral artery above the rhinal fissure was achieved using a xenon lamp for 10 min. Infarct volume 24 h after the photochemically induced thrombotic occlusion of the middle cerebral artery was significantly larger in stroke-prone SHR than in Wistar rats. When TTC-909 in doses of 100, 300 and 900 ng/kg/h was intravenously infused for 3 h, starting immediately after the end of the 10-min photoirradiation, the infarct volume was dose-dependently reduced and was statistically significant at a dose of 900 ng/kg/h (p < 0.05). Ozagrel, a thromboxane A(2) synthetase inhibitor, significantly reduced the infarct volume. The model of photochemically induced thrombotic occlusion of the middle cerebral artery in stroke-prone SHR is very useful, because the cerebral infarction is large enough and reproducible. TTC-909 may be effective for the treatment of acute ischemic stroke.

Cyclooxygenase inhibition as a strategy to ameliorate brain injury

Cyclooxygenase (COX) is the obligate, rate-limiting enzyme for the conversion of arachidonic acid into prostaglandins. Two COX enzymes have been identified: a constitutively expressed COX-1 and an inducible, highly regulated COX-2. Widely used to treat chronic inflammatory disorders, COX inhibitors have shown promise in attenuating inflammation associated with brain injury. However, the use of COX inhibition in the treatment of brain injury has met with mixed success. This review summarizes our current understanding of COX expression in the central nervous system and the effects of COX inhibitors on brain injury. Three major targets for COX inhibition in the treatment brain injury have been identified. These are the cerebrovasculature, COX-2 expression by vulnerable neurons, and the neuroinflammatory response. Evidence suggests that given the right treatment paradigm, COX inhibition can influence each of these three targets. Drug interactions and general considerations for administrative paradigms are also discussed. Although therapies targeted to specific prostaglandin species, such as PGE2, might prove more ameliorative for brain injury, at the present time non-specific COX inhibitors and COX-2 specific inhibitors are readily available to researchers and clinicians. We believe that COX inhibition will be a useful, ameliorative adjunct in the treatment of most forms of brain injury.

Infusion of prostacyclin following experimental brain injury in the rat reduces cortical lesion volume

Endothelial-derived prostacyclin is an important regulator of microvascular function, and its main actions are inhibition of platelet/leukocyte aggregation and adhesion, and vasodilation. Disturbances in endothelial integrity following traumatic brain injury (TBI) may result in insufficient prostacyclin production and participate in the pathophysiological sequelae of brain injury. The objective of this study was to evaluate the potential therapeutic effects of a low-dose prostacyclin infusion on cortical lesion volume, CA3 neuron survival and functional outcome following TBI in the rat. Anesthetized animals (sodium pentobarbital, 60 mg/kg, i.p.) were subjected to a lateral fluid percussion brain injury (2.5 atm) or sham injury. Following TBI, animals were randomized to receive a constant infusion of either prostacyclin (1 ng/kg x min(-1) i.v.) or vehicle over 48 h. All sham animals received vehicle (n = 6). Evaluation of neuromotor function, lesion volume, and CA3 neuronal loss was performed blindly. By 7 days postinjury, cortical lesion volume was significantly reduced by 43% in the prostacyclin-treated group as compared to the vehicle treated group (p < 0.01; n = 12 prostacyclin, n = 12 vehicle). No differences were observed in neuromotor function (48 h and 7 days following TBI), or in hippocampal cell loss (7 days following TBI) between the prostacyclin- and vehicle-treated groups. We conclude that prostacyclin in a low dose reduces loss of neocortical neurons following TBI and may be a potential clinical therapeutic agent to reduce neuronal cell death associated with brain trauma.

Protective effect of a prostaglandin I2 analog, TEI-7165, on ischemic neuronal damage in gerbils

TTC-909 (Clinprost), a chemically stable PGI2 analog, isocarbacyclin methyl ester (TEI-9090 or Clinprost) incorporated in lipid microspheres, when administered intravenously after brain ischemia, prevents ischemic neuronal damage possibly by modulating cerebral blood flow and platelet aggregation. However, the possibility exists that TEI-7165, which is the free acid form and a central metabolite of TEI-9090, has direct neurotrophic action in vivo, since TEI-7165 has been shown to block neuronal voltage-dependent Ca2+ channels in vitro, and a novel prostacyclin receptor showing high affinity with TEI-7165 has been detected in a variety of brain regions including the hippocampus. In the present study, we infused TEI-7165 for 7 days into the lateral ventricle of gerbils starting 2 h before or just after 3-min forebrain ischemia. TEI-7165 infusion prevented significantly the ischemia-induced shortening of response latency time as revealed by a step-down passive avoidance task. Subsequent light and electron microscopic examinations showed that pyramidal neurons in the hippocampal CA1 region, as well as synapses within the strata moleculare, radiatum and oriens of the region, were significantly more numerous in gerbils infused with TEI-7165 than in those receiving vehicle infusion. TEI-7165 infusion did not affect hippocampal blood flow or temperature. These findings, together with the previously depicted accumulation of centrally administered [3H]TEI-7165 around hippocampal neurons, suggest that TEI-7165 has a direct neuroprotective action in brain ischemia.

Effect of the prostacyclin analogue, iloprost, on infarct size after permanent focal cerebral ischemia

This investigation was undertaken to study the effect of iloprost, a stable analogue of prostacyclin, on infarct size after permanent focal cerebral ischemia in the rabbit. Forty-two adult rabbits were subjected to left middle cerebral artery occlusion via the transorbital route. Fourteen rabbits received an intravenous (i.v.) infusion of 30 micrograms/kg iloprost, 7 rabbits received an i.v. infusion of 10 micrograms/ kg, and 9 rabbits received an i.v. infusion of 20 micrograms/kg iloprost. Twelve rabbits received an intravenous infusion of saline. Treatment with iloprost started immediately after middle cerebral artery occlusion and continued for 1 h. After killing the animals, brains were removed and five coronal slices were incubated in a 2,3,5-triphenyltetrazolium chloride solution to determine the infarct size. Treatment with 30 micrograms/kg iloprost significantly reduced the infarct size compared with treatment with saline (3.49 +/- 2.79% vs. 9.03 +/- 4.26%, P < 0.001), but the lower doses of iloprost did not have a beneficial effect on the size of the infarct. These results suggest that intravenous iloprost treatment after occlusion has a highly protective effect without any side effects such as hypotension.

N-methyl-D-aspartate-evoked release of cyclo-oxygenase products in rabbit hippocampus: an in vivo microdialysis study

In vivo microdialysis of the rabbit hippocampus was used to study the effects of N-methyl-D-aspartate (NMDA) receptor stimulation on dialysate concentrations of thromboxane B2 (Tx B2)- and 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha)-immunoreactive materials that are stable metabolites of biologically active thromboxane A2 and prostacyclin. All pharmacological substances were applied in the dialysis medium. The application of 1 mM NMDA for 20 min resulted in five- and eightfold increases in Tx B2 and 6-keto PGF1 alpha concentrations, respectively. An increase in NMDA concentration to 2.5 mM did not potentiate a peak eicosanoid release, but significantly prolonged this effect. Either 10 microM MK-801 or the extrusion of Ca2+ from the dialysis medium inhibited the release by about 50%. Quinacrine, a phospholipase A2 inhibitor (250 microM), decreased the NMDA-evoked eicosanoid release by 30%, whereas 10 microM indomethacin, a cyclo-oxygenase inhibitor, completely suppressed the release. One hundred micromolar furegrelate, an inhibitor of thromboxane synthase, reduced by 75% Tx B2 release with concomitant 100% increase in 6-keto PGF1 alpha formation. Thus, stimulation of NMDA receptors induces calcium-dependent formation of thromboxane A2 and prostacyclin in the hippocampus, which may have pathophysiological implications. The neuronal site of their formation seems probable, although a transcellular mechanism of their synthesis should be also considered.

Stable prostacyclin improves postischaemic microcirculatory changes in hypertensive rats

The prostacyclin analogue TTC-909 is incorporated in lipid microspheres and is chemically very stable. We examined the efficacy of TTC-909 on cerebral microcirculation following focal cerebral ischaemia. Focal cerebral ischaemia was produced by the occlusion of the distal middle cerebral artery in stroke-prone spontaneously hypertensive rats. Intravenous administration of TTC-909 (100 ng/kg/day) or vehicle was started 30 minutes after the occlusion and repeated for 7 days. On day 7, cerebral blood flow and blood-brain barrier permeability were measured autoradiographically. Brain oedema was estimated by the gravimetric method. The size of the infarction was calculated from area measurements on serial histologic sections. Treatment with TTC-909 resulted in significant improvement in regional blood flow in the ischaemic rim (p < 0.01) and the surrounding area (p < 0.05). With TTC-909 treatment, the increased permeability was significantly reduced in the ischaemic centre (p < 0.01) and rim (p < 0.05). A decrease in specific gravity in the ischaemic region and the remote non-ischaemic regions was prevented by the treatment (p < 0.01). We assumed that the efficacy of TTC-909 maintains the blood supply in the ischaemic area, improves disruption of the blood-brain barrier and prevents development of ischaemic oedema.

Why do all drugs work in animals but none in stroke patients? 1. Drugs promoting cerebral blood flow

Medical treatments which presumably alter cerebral blood flow (CBF) have been quite unimpressive in their effect on stroke outcome. In considering experimental and clinical data from the use of haemodilution and of the antiplatelet agent prostacyclin in focal cerebral ischaemia, and the current work with fibrinolytic agents in acute stroke, several lessons are apparent. Often agents hypothesized to affect CBF receive an underserved reputation based on sparse experimental evidence. Significant even unsuspected differences between species limit application to the clinical setting. Limitations of CBF measurements in experimental models and in humans raise questions about apparent responses to those agents. The failure to confirm a relationship between CBF enhancement and reduction in infarct development experimentally has plagued these approaches. The need for early application of agents which may modulate CBF during cerebral ischaemia is critical. Attention to these general issues and careful application of appropriate models are necessary so that a potentially useful therapeutic intervention is not overlooked.

Effect of beraprost sodium (BPS) on the postischemic neuropathological changes and stroke index after left carotid artery occlusion in gerbils

We investigated the effect of beraprost sodium (BPS), a new prostacyclin analog, on behavioral and neuropathological changes induced by a 10-min occlusion of the left carotid artery in gerbils. Gerbils were treated orally with BPS (1-100 micrograms/kg) 30 min before occlusion. Pathological evaluation of neural damage in the CA1 region of the hippocampus was performed 7 d after the ischemic insults. In the symptomatic group, in which the stroke index score was > 10, symptomatic behaviors, such as head cocked, splayed out hind limb, circling, and various similar behaviors, were observed. Pathologically, almost all CA1 neurons were destroyed 7 d after ischemia in the symptomatic group. BPS improved the stroke index during ischemia and neuropathological changes 7 d later, with statistical significant improvement occurring at a dose of 100 micrograms/kg.

Effect of beraprost sodium (BPS), a prostacyclin analog, and dizocilpine (MK-801) on repeated ischemia-induced chronic cortical atrophy in gerbils

We investigated the effect of beraprost sodium (BPS), a new prostacyclin analog, and dizocilpine (MK-801) on repeated ischemia-induced cerebral atrophy and chronic cortical neuronal loss in gerbils. The left common carotid artery of gerbils was repeatedly occluded (for 10, 7, 7, and 7 min) at intervals of 24 h. The thickness of the cerebral cortex of the ischemic hemisphere diminished with increasing time of reperfusion after an ischemic insult. The animals were given BPS (1-100 micrograms/kg, po) or MK-801 (3-300 micrograms/kg, sc) after the first ischemic insult, and then twice daily for 4 wk. Increases in the amount of neuronal loss and acidophilic neurons, and progressive atrophy were observed with increasing time of reperfusion in the cerebral cortex of the ischemic hemisphere. Cortical sections revealed no astrocytes positive for glial fibrillary acidic protein (GFAP), whereas the hippocampal CA1 area showed neuronal loss accompanied by GFAP-positive astrocytes. In control animals at 4 wk survival, the area ratio (area of ischemic cortex/area of opposite cortex) and the cortical neurons ratio (number of neurons in ischemic cortex/number of neurons in opposite cortex) were 89.8 +/- 3.0% and 74.6 +/- 3.4%, respectively. BPS was found to inhibit atrophy and chronic cortical neuronal loss in the ischemic hemisphere in a dose-dependent manner, whereas MK-801 showed no inhibitory effects at any dose tested. These results may suggest that the nature of neuronal degeneration differs between the cortical and hippocampal areas, that cortical neuronal degeneration might not involve glutamate pathways with NMDA receptors in this model, and that prostacyclin could play an essential role in prevention of ischemia-induced progressive neuronal loss.

Prostacyclin attenuates in the rabbit hippocampus early consequences of transient complete cerebral ischemia

The effects of prostacyclin (PGI2) on ischemic changes of extracellular calcium concentration (CaE+2) and the blood-brain barrier (BBB) permeability were studied by microdialysis of the rabbit hippocampus. This was combined with morphological and neurophysiological observations. Complete cerebral ischemia lasting 15 min was produced by ligation of the brachiocephalic trunk, the left subclavian and both internal thoracic arteries. PGI2 was infused continuously i.v. in the last 3 min of ischemia and for 40 min after it, at a rate of 2 micrograms/kg/min. Control rabbits were submitted to untreated 15-min complete cerebral ischemia. The animals treated with PGI2 were found to have recovered bioelectric activity of the cortex and hippocampus in half the time that it took the untreated group. Application of PGI2 reduced by 60% the depth of ischemia-evoked drop of CaE+2 without acceleration of recovery during recirculation. The postischemic increase of BBB permeability to fluorescein was diminished. The number of morphologically changed neurons in the hippocampus of PGI2-treated animals was significantly lower than in the untreated group.

Effects of nicardipine on the ex vivo release of eicosanoids after experimental subarachnoid hemorrhage

The activation of lipid peroxidation and the enhancement of arachidonic acid metabolism have been demonstrated as indicators of brain damage after subarachnoid hemorrhage (SAH). Meanwhile, the final common pathway of neuronal damage seems to be related to the impaired homeostasis of Ca++. The present study evaluated the effect of the calcium-antagonist nicardipine on arachidonate metabolism after experimental induction of SAH. The ex vivo release of four eicosanoids (prostaglandin (PG)D2, PGE2, 6-keto-PGF1 alpha, and leukotriene (LT)C4) was measured at different intervals after SAH induction. Rats were separated into the following three groups: a sham-operated group, an SAH group (rats were injected with 0.3 ml autologous arterial blood), and an SAH-treated group (after SAH induction, rats were treated with nicardipine 1.2 mg/kg intraperitoneally). Nicardipine significantly decreased the ex vivo release of PGD2 at 48 hours after SAH (p less than 0.01). The release of PGE2 was significantly enhanced at 6 hours after SAH, while in the nicardipine-treated group PGE2 release is significantly reduced. Nicardipine also affects the lipoxygenase pathway, reducing the release of LTC4 at 1, 6, and 48 hours after SAH induction. The results of the present study show that nicardipine treatment exerts an inhibitory effect on both biochemical pathways of arachidonic acid metabolism; aside from vascular effects, nicardipine could exert a protective role against the release of arachidonate metabolites, which could play a significant role in the pathogenesis of brain damage after SAH.

Cerebral ischemia in gerbils: improvement of survival after postischemic treatment with oligo-prostaglandin B

Gerbils were subjected to bilateral carotid artery occlusion for either 15 or 20 min. After ischemia the animals were injected i.p. with oligo-prostaglandin B (oligo-PGB; trimer of 16,16'-dimethyl-15-dehydro-prostaglandin B1) dissolved in 4% sodium-bicarbonate, or with the vehicle. The dosing regimen of oligo-PGB was 0.5, 1, 2, 5, 10 mg/kg injected 5 min postischemia, or 1 mg/kg injected 30, 60, 90, 120 min after ischemia, or 10 mg/kg injected 5 min and 24 h postischemia. Behaviour of the animals and their mortality were studied for 14 days after ischemia. Administration of the drug did not affect recovery of the electrical activity in the brain and did not reduce the number of postischemic seizures. Following 15 min ischemia, administration of oligo-PGB resulted in statistically valid improvement of survival (P less than 0.04 or better) in all treatment groups. After 20 min ischemia only the double injection (10 mg/kg at 5 min and 24 h postischemia) resulted in a substantial survival improvement (64%, P less than 0.005). The mechanism of the drug action is unknown but, based on the available data, the authors believe it to be related to the modification of arachidonic acid metabolism in the late postischemic period.

Effect of a prostacyclin analog OP-2507 on acute ischemic cerebral edema in cats

We evaluated the inhibitory activity of a novel prostacyclin analog, OP-2507 (15-cis-(4-n-propylcyclohexyl)-16,17,18,19,20-pentanor-9-deo xy-6,9 alpha- nitriloprostaglandin F1 methyl ester) on the brain edema induced by occlusion of the middle cerebral artery in cats. Middle cerebral artery occlusion for 4h caused a decrease of regional cerebral blood flow. The specific gravity of the cerebral cortex measured 4h after the middle cerebral artery occlusion as an index of cerebral edema showed a significant reduction. Intravenous infusion of OP-2507 at infusion rates of 10 and 50 ng/kg per min was started 30 min before the middle cerebral artery occlusion and was continued for 4.5 h. While OP-2507 did not affect the blood pressure, heart rate and regional cerebral blood flow before and after the middle cerebral artery occlusion, the reduction of the specific gravity of cerebral cortex was significantly prevented by OP-2507 treatment at both doses. Prostacyclin prevented the reduction of the specific gravity only at the higher dose of 50 ng/kg per min. The present results indicate the potential usefulness of OP-2507 in acute ischemic cerebral disorders.

Cerebral resuscitation: pathophysiology and therapy

The interest in the possibility of cerebral resuscitation has been growing exponentially during the last decade. It became clear that pharmacotherapeutic interaction can possibly alter the outcome of cerebral hypoxia/ischemia. The present review is an attempt to provide an organizational framework for a systematic integration of studies specifically dealing with pharmacological treatment post-insult.

Focal cerebral ischemia: pathophysiologic mechanisms and rationale for future avenues of treatment

Although approximately 500,000 patients suffer from a stroke each year in the United States, treatment of these patients to date has consisted primarily of prevention, supportive measures, and rehabilitation. The modification of experimental cerebral infarction by new pharmacologic agents, along with encouraging results from the restoration of blood flow to areas of focal ischemia in both laboratory and clinical trials, suggests that a more aggressive approach might be considered in selected patients with acute stroke.

Cerebral acidosis in focal ischemia: II. Nimodipine and verapamil normalize cerebral pH following middle cerebral artery occlusion in the rat

The effects of prostacyclin, nimodipine, and verapamil on local cerebral pH (LCpH) and CBF (LCBF) in middle cerebral artery (MCA)-occluded rats were compared with those in controls and others receiving nimodipine carrier. LCpH and LCBF were determined simultaneously by a double-label autoradiographic technique. The infusions were intravenous, started 15 min following the occlusion, and ended at decapitation 4 h postocclusion. The dosages were 0.5 micrograms/kg/min for nimodipine, 40 micrograms/kg/min for verapamil, and 5 ng/kg/min for prostacyclin. Cortical LCpH in the MCA territory of control and carrier-infused rats varied between 6.72 +/- 0.05 and 6.76 +/- 0.05 (means +/- SEM). These values were significantly lower than the LCpH in the same structures in the contralateral hemisphere (7.09 +/- 0.06; p less than 0.05). LCBF on the side of occlusion varied between 54 +/- 5 ml/100 g/min for the parietal and 57 +/- 7 ml/100 g/min for the sensorimotor cortex, while on the contralateral side, LCBF in these same structures was 190 +/- 18 and 191 +/- 4 ml/100 g/min, respectively. LCpH was not modified by prostacyclin treatment following MCA occlusion, but the pH in the structures that were acidotic in the controls became indistinguishable from contralateral values in nimodipine- and verapamil-treated animals. In contrast, LCBF was statistically higher than controls in many structures only in rats treated with prostacyclin. This suggested that the correction of LCpH produced by calcium blockers was not related to an effect they had on blood flow. Animals receiving calcium blockers tended to have smaller areas of infarction. These results may have therapeutic implications in cerebral ischemia.