Induction of cyclooxygenase-2 following anoxic stress in piglet cerebral arteries

Sequential expression of cyclooxygenase-2, glutamate receptor-2, and platelet activating factor receptor in rat hippocampal neurons after fluid percussion injury

Traumatic brain injury causes gene expression changes in different brain regions. Occurrence and development of traumatic brain injury are closely related, involving expression of three factors, namely cyclooxygenase-2, glutamate receptor-2, and platelet activating factor receptor. However, little is known about the correlation of these three factors and brain neuronal injury. In this study, primary cultured rat hippocampal neurons were subjected to fluid percussion injury according to Scott's method, with some modifications. RT-PCR and semi-quantitative immunocytochemical staining was used to measure the expression levels of cyclooxygenase-2, glutamate receptor-2, and platelet activating factor receptor. Our results found that cyclooxygenase-2 expression were firstly increased post-injury, and then decreased. Both mRNA and protein expression levels reached peaks at 8 and 12 hours post-injury, respectively. Similar sequential changes in glutamate receptor 2 were observed, with highest levels mRNA and protein expression at 8 and 12 hours post-injury respectively. On the contrary, the expressions of platelet activating factor receptor were firstly decreased post-injury, and then increased. Both mRNA and protein expression levels reached the lowest levels at 8 and 12 hours post-injury, respectively. Totally, our findings suggest that these three factors are involved in occurrence and development of hippocampal neuronal injury.

Neuronal and nonneuronal COX-2 expression confers neurotoxic and neuroprotective phenotypes in response to excitotoxin challenge

Treating acute brain injuries with COX-2 inhibitors can produce both neuroprotective and neurotoxic effects. This study investigated the role of COX-2 in modulating acute brain injury induced by excitotoxic neural damage. Intrastriatal injection of excitotoxin (RS)-(tetrazole-5yl) glycine elicited COX-2 expression in two distinct groups of cells. cortical neurons surrounding the lesion and vascular cells in the lesion core. The vascular COX-2 was expressed in two cell types, endothelial cells and monocytes. Selective deletion of COX-2 in vascular cells in Tie2Cre Cox-2(flox/flox) mice did not affect the induction of COX-2 in neurons after the excitotoxin injection but resulted in increased lesion volume, indicating a neuroprotective role for the COX-2 expressed in the vascular cells. Selective deletion of monocyte COX-2 in LysMCre Cox-2(flox/flox) mice did not reduce COX-2-dependent neuroprotection, suggesting that endothelial COX-2 is sufficient to confer neuroprotection. Pharmacological inhibition of COX-2 activity in Tie2Cre Cox-2(flox/flox) mice reduced lesion volume, indicating a neurotoxic role for the COX-2 expressed in neurons. Furthermore, COX-2-dependent neurotoxicity was mediated, at least in part, via the activation of the EP1 receptor. These results show that Cox-2 expression induced in different cell types can confer opposite effects.

Nicotine enhances skin necrosis and expression of inflammatory mediators in a rat pressure ulcer model

BACKGROUND

Many bedridden patients develop pressure ulcers, not only in hospital but also at home. Clinical studies have indicated cigarette smoking to be a risk factor for pressure ulcers. However, the contribution of nicotine to pressure ulcer formation has not been identified.

OBJECTIVES

We aimed to clarify the effect of nicotine on pressure ulcer formation, and its mechanism.

METHODS

Ischaemia-reperfusion (I/R) was performed in rat dorsal skin to induce pressure ulcers. The extent of the resulting necrotic area was determined. To clarify the mechanism of the effect of nicotine, mRNA levels of cyclooxygenase-2 (COX-2), interleukin (IL)-1beta, IL-6 and inducible nitric oxide synthase (iNOS) and protein expression of COX-2 and iNOS in the necrotic area were investigated by real-time reverse transcription-polymerase chain reaction and Western blotting, respectively. Furthermore, the effects of the COX-2 inhibitor NS-398 and the iNOS inhibitor aminoguanidine on necrosis were examined.

RESULTS

Skin necrosis in the I/R-treated area was significantly increased by intraperitoneal administration of nicotine (0.175 mg kg(-1) daily). Repeated nicotine administration had little effect on systolic and diastolic blood pressure. I/R treatment increased mRNA levels of COX-2, IL-1beta, IL-6 and iNOS, which were further augmented by nicotine in a dose-dependent manner. Correspondingly, nicotine (0.35 mg kg(-1) daily) markedly enhanced the protein expression of COX-2 and iNOS. Moreover, NS-398 and aminoguanidine showed a tendency to abrogate the increase of I/R-induced skin necrosis caused by nicotine.

CONCLUSIONS

These results suggest that the increased risk of pressure ulcers due to cigarette smoking is mediated, in part, by nicotine. They also indicated that the effect of nicotine is not mediated by a change in blood pressure, but is elicited via an increase of inflammatory mediators in the I/R-treated skin.

Pituitary adenylate cyclase-activating polypeptide induces pial arteriolar vasodilation through cyclooxygenase-dependent and independent mechanisms in newborn pigs

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a cerebrovascular dilator and was found neuroprotective in numerous in vitro and in vivo models of cerebral ischemia. However, the mechanism of its cerebrovascular action is poorly known, especially in newborns. Therefore, we tested pial arteriolar responses to the two naturally occurring forms PACAP27 and 38 as well as to shorter sequences (PACAP6-27, 6-38, 1-15, 6-15, 20-31). We also investigated the involvement of nitric oxide synthase (NOS), cyclooxygenase-1 and -2 (COX-1 and -2) activity in PACAP-induced pial arteriolar responses using the NOS inhibitor N-omega-nitro-l-arginine methyl ester (L-NAME 15 mg/kg iv), the non-selective COX inhibitor indomethacin (5 mg/kg iv), and the selective COX-1 and COX-2 inhibitors SC-560 (1 mg/kg iv) and NS-398 (1 mg/kg iv), respectively. Anesthetized, ventilated piglets (n=127) were equipped with closed cranial windows, and pial arteriolar diameters were determined via intravital microscopy. Topical application of both natural PACAPs, but none of the PACAP segments, resulted in prominent, repeatable, dose-dependent vasodilation. Percentage changes ranged 5+/-1-29+/-6 (n=7) and 4+/-1-36+/-7 (n=9) to 10(-)(8) to 10(-)(6) M PACAP27 and 38 (mean+/-SEM), respectively. Vasodilation to both natural PACAPs was significantly reduced by co-application with PACAP6-27 or 6-38, but not by L-NAME. Indomethacin abolished PACAP38 but not PACAP27-induced vasodilation. Arteriolar responses to PACAP38 were also sensitive to SC-560 but not to NS-398 suggesting the unique involvement of COX-1 activity in this response. In summary, PACAP27 and 38 are potent vasodilators in the neonatal cerebral circulation with at least two distinct mechanisms of action: a COX-dependent and a COX-independent pathway.

Contributions of cyclooxygenase-2 to neuroplasticity and neuropathology of the central nervous system

Cyclooxygenase (COX) enzymes, or prostaglandin-endoperoxide synthases (PTGS), are heme-containing bis-oxygenases that catalyze the first committed reaction in metabolism of arachidonic acid (AA) to the potent lipid mediators, prostanoids and thromboxanes. Two isozymes of COX enzymes (COX-1 and COX-2) have been identified to date. This review will focus specifically on the neurobiological and neuropathological consequences of AA metabolism via the COX-2 pathway and discuss the potential therapeutic benefit of COX-2 inhibition in the setting of neurological disease. However, given the controversy surrounding the use of COX-2 selective inhibitors with respect to cardiovascular health, it will be important to move beyond COX to identify which down-stream effectors are responsible for the deleterious and/or potentially protective effects of COX-2 activation in the setting of neurological disease. Important advances toward this goal are highlighted herein. Identification of unique effectors in AA metabolism could direct the development of new therapeutics holding significant promise for the prevention and treatment of neurological disorders.

Regulation of cerebral microvascular endothelial cell cyclooxygenase-2 message and activity by blood derived vasoactive agents

We have investigated the effects of prolonged treatment of cerebral microvascular endothelial cells with vasoconstrictor products of blood clot hemolysis on prostanoid production and cyclooxygenase (COX)/prostacyclin synthase activity and message. Confluent primary cultures of endothelial cells derived from piglet cerebral microvessels were incubated with endothelin-1 (ET-1; 10 nM) or thromboxane A(2) analog U-46619 (1 microM), alone or combined, and COX/prostacyclin synthase activity determined following exposure of treated cells to arachidonic acid (10 microM) for 30 min. 6-KetoPGF(1)alpha and PGE(2) levels in the medium were determined using radioimmunoassay. Effect of treatments on COX-2 message was determined by RNAse Protection Assay. Combined treatment with ET-1 (10 nM) and U-46619 (1 microM) for 24h significantly reduced 6-ketoPGF(1)alpha and PGE(2) levels in the media by 57% and 33%. Treatment of cells with U-46619 alone increased both 6-ketoPGF(1)alpha and PGE(2) level in the media by 170% and 42%. Incubation of control cells with arachidonic acid (10 microM) for 30 min increased 6-ketoPGF(1)alpha and PGE(2) production by 163% and 567%. Pretreatment with ET-1 or U-46619 alone for 24h had no significant effect on 6-ketoPGF(1)alpha produced from exogenous arachidonic acid. However, PGE(2) production from exogenous arachidonic acid by cells pretreated with ET-1 but not with U-46619 was attenuated by 35%. Combined treatment with ET-1 and U-46619 reduced both PGE(2) and 6-ketoPGF(1)alpha production from arachidonic acid by 14% and 40%, respectively. Acute incubation of cells with ET-1 or U-46619 did not have any significant effects on COX-2 mRNA. In conclusion, combined ET-1 and U-46619 reduced prostanoid production. The reduction cannot be fully explained by changes in COX/prostacyclin synthase activity and/or message, but the changes could be due to reduced availability of free arachidonic acid potentially resulting from inhibition of endothelial phospholipase A(2).

Cyclooxygenase-2-specific inhibitor improves functional outcomes, provides neuroprotection, and reduces inflammation in a rat model of traumatic brain injury

OBJECTIVE

Increases in brain cyclooxygenase-2 (COX2) are associated with the central inflammatory response and with delayed neuronal death, events that cause secondary insults after traumatic brain injury. A growing literature supports the benefit of COX2-specific inhibitors in treating brain injuries.

METHODS

DFU [5,5-dimethyl-3(3-fluorophenyl)-4(4-methylsulfonyl)phenyl-2(5)H)-furanone] is a third-generation, highly specific COX2 enzyme inhibitor. DFU treatments (1 or 10 mg/kg intraperitoneally, twice daily for 3 d) were initiated either before or after traumatic brain injury in a lateral cortical contusion rat model.

RESULTS

DFU treatments initiated 10 minutes before injury or up to 6 hours after injury enhanced functional recovery at 3 days compared with vehicle-treated controls. Significant improvements in neurological reflexes and memory were observed. DFU initiated 10 minutes before injury improved histopathology and altered eicosanoid profiles in the brain. DFU 1 mg/kg reduced the rise in prostaglandin E2 in the brain at 24 hours after injury. DFU 10 mg/kg attenuated injury-induced COX2 immunoreactivity in the cortex (24 and 72 h) and hippocampus (6 and 72 h). This treatment also decreased the total number of activated caspase-3-immunoreactive cells in the injured cortex and hippocampus, significantly reducing the number of activated caspase-3-immunoreactive neurons at 72 hours after injury. DFU 1 mg/kg amplified potentially anti-inflammatory epoxyeicosatrienoic acid levels by more than fourfold in the injured brain. DFU 10 mg/kg protected the levels of 2-arachidonoyl glycerol, a neuroprotective endocannabinoid, in the injured brain.

CONCLUSION

These improvements, particularly when treatment began up to 6 hours after injury, suggest exciting neuroprotective potential for COX2 inhibitors in the treatment of traumatic brain injury and support the consideration of Phase I/II clinical trials.

Interactions between Alzheimer's disease and cerebral ischemia--focus on inflammation

Progressive memory impairment, beta-amyloid (Abeta) plaques associated with local inflammation, neurofibrillary tangles, and loss of neurons in selective brain areas are hallmarks of Alzheimer's disease (AD). Although beta-amyloid precursor protein (APP) and Abeta have a central role in the etiology of AD, it is not clear which forms of APP or Abeta are responsible for the neuronal vulnerability in AD brain. Brain ischemia, another cause of dementia in the elderly, has recently been recognized to contribute to the pathogenesis of AD and individuals with severe cognitive decline and possibly underlying AD are at increased risk for ischemic events in the brain. Moreover, the epsilon4 allele of apolipoprotein E (ApoE) is a risk factor for both AD and poor outcome following brain ischemia and hemorrhage. Several factors and molecular mechanisms that lower the threshold of neuronal death in models of AD have recently been described. Among these neuroinflammation seems to play an important role. The development and maturation of both AD neuropathology and ischemic lesions in the central nervous system are characterized by activation of glial cells and upregulation of inflammatory mediators. Indeed, anti-inflammatory approaches have proven to be beneficial in the prevention and treatment of AD-like neuropathology and ischemic injuries in vivo. This review summarizes some of the findings suggesting that neuronal overexpression of human APP renders the brain more vulnerable to ischemic injury and describes the factors that are involved in increased neuronal susceptibility to ischemic stroke.

Metabolic changes of arachidonic acid after cerebral ischemia–reperfusion in diabetic rats

The purpose of this study is to discuss an important component-arachidonic acid (AA) cascade of inflammatory reaction in diabetic rats with cerebral ischemia. Using the model of middle cerebral artery occlusion (MCAO), we have compared the expression of cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX), and measured the levels of their products prostaglandin E2 (PGE(2)) and cysteine-containing leukotrienes (cys-LTs) after different reperfusion periods in diabetic and normal rats. Cerebral ischemia-reperfusion was accompanied by increased expression of COX-2 and release of PGE(2), peaking at 12 h after reperfusion. The expression of COX-2 was maintained at a high level until 24 h after reperfusion, while the levels of PGE(2) were declined rapidly to baseline. The expression of 5-LOX and levels of cys-LTs reached a peak at 6 and 12 h after reperfusion, respectively, and was returned to baseline at 24 h after reperfusion. Compared with normal rats, the expression of COX-2 and 5-LOX as well as release of PGE(2) and cys-LTs was elevated in the brains of diabetic rats, revealing a possible mechanism for hyperglycemia-mediated aggravation of cerebral ischemic injury. A reduction of arachidonic acid metabolites mediated by inhibitors of its metabolites could be helpful in preventing ischemic brain injury in diabetic rats.

The therapeutic potential of NO-NSAIDs

NSAIDs, including those that are selective for cyclooxygenase-2, are among the most widely used drugs. However, these drugs produce significant side effects in the gastrointestinal and cardiorenal systems, which greatly limit their utility. In recent years, a new type of anti-inflammatory agent has been developed that appears to offer significant advantages over conventional and Cox-2-selective NSAIDs. No-NSAIDs are derivatives of conventional NSAIDs, which are able to release nitric oxide over prolonged periods of time. The combination of balanced inhibition of the two main isoforms of COX with controlled release of nitric oxide yields a series of drugs that exert anti-inflammatory and analgesic activities in a wide range of settings, and have markedly reduced gastrointestinal and cardiorenal toxicity. Recent clinical trials of NO-NSAIDs have provided a 'proof of concept' that is completely consistent with pre-clinical characterization of these compounds.

Developmental changes in cyclo-oxygenase mRNA induction by hypoxia in rat kidney

BACKGROUND

Prostaglandins, synthesized by cyclo-oxygenase (COX), regulate renal hemodynamics and also epithelial water and solute transport. Developmental changes occur in COX-2 mRNA expression and its response to lipopolysaccharide stimulation in rats. We examined age-related changes in COX mRNA expression induced by hypoxia in the renal cortex and medulla of developing rats.

METHODS

Total RNA was extracted from 1- and 4-week-old male Wistar rats exposed to one or 4 h of hypoxia (8% O2). Cyclo-oxygenase mRNA was quantitatively analyzed using a real-time polymerase chain reaction with dual-labeled fluorogenic probes.

RESULTS

Expression of COX-1 mRNA did not change in response to hypoxia in the cortex or medulla in either infantile or adult rats. In infantile rats, COX-2 mRNA expression was not induced by one or 4 h of hypoxia. In adults, 1- and 4-h exposures to hypoxia induced COX-2 mRNA in the renal cortex, and 1-h of exposure induced COX-2 mRNA in the medulla.

CONCLUSIONS

Response of expression of COX-2 mRNA in rats exposed to acute hypoxia show age-related variability treated by acute hypoxia. Cyclo-oxygenase-2 might not play a major role in the hypoxic infantile rat kidney.

Inhibition of cyclo-oxygenase-2 exacerbates ischaemia-induced acute myocardial dysfunction in the rabbit

1. The effects of treatment with a number of cyclo-oxygenase inhibitors, (celecoxib, meloxicam, DuP-697 and aspirin) on ischaemia-reperfusion-induced myocardial dysfunction were examined using an in vitro perfused rabbit heart model. 2. Ischaemia resulted in myocardial dysfunction, as indicated by a significant increase in left ventricular end diastolic pressure and marked changes in coronary perfusion pressure and left ventricular developed pressure. In the post-ischaemic state, coronary perfusion pressure increased dramatically, left ventricular developed pressure recovered to a small degree and there were significant increases in creatinine kinase release (indicative of myocardial damage) and prostacyclin release. 3. Pretreatment with aspirin, or with drugs that selectively inhibit cyclo-oxygenase-2 (celecoxib, meloxicam and DuP-697), resulted in a concentration-dependent exacerbation of the myocardial dysfunction and damage. Exacerbation of myocardial dysfunction and damage was evident with 10 microM concentrations of the cyclo-oxygenase-2 inhibitors, which inhibited prostacyclin release but did not affect cyclo-oxygenase-1 activity (as measured by whole blood thromboxane synthesis). 4. NCX-4016, a nitric oxide-releasing aspirin derivative, significantly reduced the myocardial dysfunction and damage caused by ischaemia and reperfusion. Beneficial effects were observed even at a concentration (100 microM) that significantly inhibited prostacyclin synthesis by the heart. 5. The results suggest that prostacyclin released by cardiac tissue in response to ischaemia and reperfusion is derived, at least in part, from cyclo-oxygenase-2. Cyclo-oxygenase-2 plays an important protective role in a setting of ischaemia-reperfusion of the heart.

Cerebrovascular inflammation following subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage frequently results in complications including intracranial hypertension, rebleeding and vasospasm. The extravasated blood is responsible for a cascade of reactions involving release of various vasoactive and pro-inflammatory factors (several of which are purported to induce vasospasm) from blood and vascular components in the subarachnoid space. The authors review the available evidence linking these factors to the development of inflammatory lesions of the cerebral vasculature, emphasizing: 1) neurogenic inflammation due to massive release of sensory nerve neuropeptides; 2) hemoglobin from lysed erythrocytes, which creates functional lesions of endothelial and smooth muscle cells; 3) activity, expression and metabolites of lipoxygenases cyclooxygenases and nitric oxide synthases; 4) the possible role of endothelin-1 as a pro-inflammatory agent; 5) serotonin, histamine and bradykinin which are especially involved in blood-brain barrier disruption; 6) the prothrombotic and pro-inflammatory action of complement and thrombin towards endothelium; 7) the multiple actions of activated platelets, including platelet-derived growth factor production; 8) the presence of perivascular and intramural macrophages and granulocytes and their interaction with adhesion molecules; 9) the evolution, origins, and effects of pro-inflammatory cytokines, especially IL-1, TNF-alpha and IL-6. Human and animal studies on the use of anti-inflammatory agents in subarachnoid hemorrhage include superoxide and other radical scavengers, lipid peroxidation inhibitors, iron chelators, NSAIDs, glucocorticoids, and serine protease inhibitors. Many animal studies claim reduced vasospasm, but these effects are not always confirmed in human trials, where symptomatic vasospasm and outcome are the major endpoints. Despite recent work on penetrating vessel constriction, there is a paucity of studies on inflammatory markers in the microcirculation.

Selective cyclooxygenase-2 inhibitors: after the smoke has cleared

An enormous amount of fanfare and marketing preceded the introduction of selective inhibitors of cyclooxygenase-2 to the marketplace. These drugs were purported to offer equivalent anti-inflammatory and analgesic effects to conventional non-steroidal anti-inflammatory drugs without causing gastrointestinal injury. Now that there is considerable clinical experience with four drugs of this class having been available for at least two years, it is worthwhile re-visiting some of the original claims to determine whether selective cyclooxygenase-2 inhibitors have thus far lived up to their promise. In short, selective cyclooxygenase-2 inhibitors have proven to be somewhat safer in terms of gastrointestinal toxicity, than some (but not all) conventional non-steroidal antiinflammatory drugs. However their efficacy of the selective cyclooxygenase inhibitors has not always matched that of the conventional nonsteroidal anti-inflammatory drugs and there are significant safety concerns with some of the new drugs that deserve very careful consideration.

Prostaglandin H synthase and vascular function

Prostaglandin H synthase (PGHS) is a rate-limiting enzyme in the production of prostaglandins and thromboxane, which are important regulators of vascular function. Under normal physiological conditions, PGHS-dependent vasodilators (such as prostacyclin) modulate vascular tone. However, PGHS-dependent vasoconstriction (mediated by thromboxane and/or its immediate precursor, PGH(2)) predominates in some vascular pathologies (eg, systemic hypertension, diabetes, cerebral ischemia, and aging). This review will discuss the role of PGHS-dependent modulation of vascular function in a number of vascular beds (systemic, pulmonary, cerebral, and uterine) with an emphasis on vascular pathophysiology. Moreover, the specific contributions of the different isoforms (PGHS-1 and PGHS-2) are discussed. Understanding the role of PGHS in vascular function is of particular importance because they are the targets of the commonly used nonsteroidal antiinflammatory drugs (NSAIDs), which include aspirin and ibuprofen. Importantly, with the advent of specific PGHS-2 inhibitors for treatment of conditions such as chronic inflammatory disease, it is an opportune time to review the data regarding PGHS-dependent modulation of vascular function.

Overexpression of cyclooxygenase-2 in rabbit basilar artery endothelial cells after subarachnoid hemorrhage

OBJECTIVE

We investigated the expression in rabbit basilar arteries of cyclooxygenase (COX)-2, which is the inducible isoform of the enzyme of prostaglandin (PG) production, and the concentrations of the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) and representative PGs in the cerebrospinal fluid (CSF) after experimental subarachnoid hemorrhage (SAH).

METHODS

Seven sets of basilar arteries were removed from control rabbits and from rabbits killed 1 and 3 days after induced SAH. The arteries were subjected to identical simultaneous immunolabeling for examination with a confocal microscope. One-half of each artery was stained for the constitutive form COX-1 and the other half for COX-2. CSF was sampled in control animals and at 6 hours, 1 day, and 3 days for assays of TNFalpha, PGE2, and 6-keto-PGF1 (metabolite of PGI2).

RESULTS

COX-1 immunoreactivity in the endothelial layer was similar in the three groups. Weak endothelial COX-2 immunoreactivity was found in arteries of control animals. COX-2 staining was higher in the group killed at 3 days compared with the control group (P < 0.05). The levels of PGE2 and 6-keto-PGF1alpha in the CSF peaked significantly at 6 hours, then decreased at 3 days to the basal level (PGE2) or significantly lower (6-keto-PGF1). TNFalpha was undetectable in control CSF, significantly higher (P < 0.001) at 6 hours, and undetectable at 3 days.

CONCLUSION

After SAH, endothelial COX-1 immunoreactivity does not change, whereas overexpression of COX-2 occurs at 3 days. This induction does not seem linked to TNFalpha production, nor is it responsible for early raised levels of PGE2 and PGI2 in the CSF. We suggest that the role of induced COX-2 may be to modify gene expression and hence alter the properties of the vessel wall after SAH.

Sp1 increases expression of cyclooxygenase-2 in hypoxic vascular endothelium. Implications for the mechanisms of aortic aneurysm and heart failure

Cyclooxygenase-2 (COX-2) catalyzes prostaglandin synthesis from arachidonic acid and is expressed locally in aortic aneurysm and heart failure. Cellular hypoxia is also found in these conditions. We have previously shown that cox-2 is transcriptionally regulated by hypoxia in human umbilical vein endothelial cells (HUVEC) in culture via the transactivation factor NF-kappaB p65, leading to increased production of prostaglandin E(2), an inhibitor of vascular smooth muscle cell proliferation. Sp1 is a transactivation factor known to be important in the regulation of cytokine expression in association with NF-kappaB. We hypothesized that Sp1 is involved in the induction of cox-2 in hypoxic HUVEC. Electrophoretic mobility shift assays with hypoxic HUVEC nuclear protein showed that both Sp1 and the related protein Sp3 specifically bound to the cox-2 promoter. Immunoblotting demonstrated that hypoxia increased the nuclear localization of Sp1 but did not change the Sp3 content in HUVEC. Overexpression of Sp1 through transfection of HUVEC enhanced cox-2 promoter activity as measured by reporter gene expression and by the production of COX-2. The specificity of the results was confirmed by mutation of the Sp1-binding site in the cox-2 promoter construct and by reproducibility in an Sp-deficient Drosophila SL2 cell line. The regulatory role of Sp1 discovered in this work supports the concept that a mechanistic link exists between vascular cellular hypoxia and mediators of inflammation associated with aortic aneurysm and heart failure.

Prolonged cyclooxygenase-2 induction in neurons and glia following traumatic brain injury in the rat

Cyclooxygenase-2 (COX2) is a primary inflammatory mediator that converts arachidonic acid into precursors of vasoactive prostaglandins, producing reactive oxygen species in the process. Under normal conditions COX2 is not detectable, except at low abundance in the brain. This study demonstrates a distinctive pattern of COX2 increases in the brain over time following traumatic brain injury (TBI). Quantitative lysate ribonuclease protection assays indicate acute and sustained increases in COX2 mRNA in two rat models of TBI. In the lateral fluid percussion model, COX2 mRNA is significantly elevated (>twofold, p < 0.05, Dunnett) at 1 day postinjury in the injured cortex and bilaterally in the hippocampus, compared to sham-injured controls. In the lateral cortical impact model (LCI), COX2 mRNA peaks around 6 h postinjury in the ipsilateral cerebral cortex (fivefold induction, p < 0.05, Dunnett) and in the ipsilateral and contralateral hippocampus (two- and six-fold induction, respectively, p < 0.05, Dunnett). Increases are sustained out to 3 days postinjury in the injured cortex in both models. Further analyses use the LCI model to evaluate COX2 induction. Immunoblot analyses confirm increased levels of COX2 protein in the cortex and hippocampus. Profound increases in COX2 protein are observed in the cortex at 1-3 days, that return to sham levels by 7 days postinjury (p < 0.05, Dunnett). The cellular pattern of COX2 induction following TBI has been characterized using immunohistochemistry. COX2-immunoreactivity (-ir) rises acutely (cell numbers and intensity) and remains elevated for several days following TBI. Increases in COX2-ir colocalize with neurons (MAP2-ir) and glia (GFAP-ir). Increases in COX2-ir are observed in cerebral cortex and hippocampus, ipsilateral and contralateral to injury as early as 2 h postinjury. Neurons in the ipsilateral parietal, perirhinal and piriform cortex become intensely COX2-ir from 2 h to at least 3 days postinjury. In agreement with the mRNA and immunoblot results, COX2-ir appears greatest in the contralateral hippocampus. Hippocampal COX2-ir progresses from the pyramidal cell layer of the CA1 and CA2 region at 2 h, to the CA3 pyramidal cells and dentate polymorphic and granule cell layers by 24 h postinjury. These increases are distinct from those observed following inflammatory challenge, and correspond to brain areas previously identified with the neurological and cognitive deficits associated with TBI. While COX2 induction following TBI may result in selective beneficial responses, chronic COX2 production may contribute to free radical mediated cellular damage, vascular dysfunction, and alterations in cellular metabolism. These may cause secondary injuries to the brain that promote neuropathology and worsen behavioral outcome.

Cycloheximide rapidly inhibits cortical COX activity and COX-dependent pial arteriolar dilation in piglets

We have previously shown that cycloheximide (CHX) preserved neuronal function after global cerebral ischemia in piglets, in a manner similar to indomethacin. To elucidate the mechanism of this protection, we tested the hypothesis that CHX would inhibit cyclooxygenase (COX) activity in the piglet cerebral cortex and vasculature. Pial arteriolar responses to hypercapnia, arterial hypotension, and sodium nitroprusside (SNP) were determined before and 20 min after treatment with CHX (0.3-1 mg/kg iv) using a closed cranial window and intravital microscopy. We also determined baseline and arachidonic acid (AA)-stimulated cortical PGF(2alpha) and 6-keto-PGF(1alpha) production before and 20-60 min after CHX (1 mg/kg iv) treatment, using ELISA kits. CHX did not affect baseline diameters (approximately 100 microm) but significantly decreased arteriolar dilation to COX-dependent stimuli, such as hypercapnia and hypotension, but not to COX-independent SNP. In the 1 mg/kg CHX-treated group, increases in vascular diameters were reduced from 22 +/- 2 to 10 +/- 2%, from 49 +/- 5 to 31 +/- 3% (means +/- SE, 5 and 10% CO2, respectively, n = 8), from 12 +/- 3 to 3 +/- 1%, and from 26 +/- 5 to 6 +/- 2% ( approximately 25 and 40% decreases in blood pressure, respectively, n = 6). CHX also inhibited conversion of exogenous AA to both PGF(2alpha) and 6-keto-PGF(1alpha); for example, 20 min after CHX treatment 10 microg/ml AA-stimulated PGF(2alpha) concentrations in the artificial cerebrospinal fluid decreased from 14.28 +/- 3.04 to 5.90 +/- 1.26 ng/ml (n = 9). Thus CHX rapidly decreases COX activity in the piglet cerebral cortex. This result may explain in part the preservation of neuronal function of CHX in cerebral ischemia.

Ischemia-reperfusion rapidly increases COX-2 expression in piglet cerebral arteries

In the newborn, cyclooxygenase (COX)-derived products play an important role in the cerebrovascular dysfunction after ischemia-reperfusion (I/R). We examined effects of I/R on expression of COX-1 and COX-2 isoforms in large cerebral arteries of anesthetized piglets. The circle of Willis, the basilar, and the middle cerebral arteries were collected from piglets at 0.5-12 h after global ischemia (2.5-10 min, n = 50), hypoxia (n = 3), or hypercapnia (n = 2) and from time-control (n = 19) or untreated animals (n = 7). Tissues were analyzed for COX-1 and COX-2 mRNA and protein using RNase protection assay and immunoblot analysis, respectively. Ischemia increased COX-2 mRNA by 30 min, and maximal levels were reached at 2 h. Hypoxia or hypercapnia had minimal effects on COX-2 mRNA. COX-2 protein levels were also consistently elevated by 8 h after I/R. Increases in COX-2 mRNA or protein were not influenced by pretreatment with either indomethacin (5 mg/kg iv, n = 5) or nitro-L-arginine methyl ester (15 mg/kg iv, n = 7). COX-1 mRNA levels were low in time controls, and ischemic stress had no significant effect on COX-1 expression. Thus ischemic stress leads to relatively rapid, selective induction of COX-2 in cerebral arteries.

Expression and vascular effects of cyclooxygenase-2 in brain

BACKGROUND AND PURPOSE

Cyclooxygenase-2 (COX-2) is an inducible isoform of cyclooxygenase. Several types of brain cells in culture can express COX-2 when treated with lipopolysaccharide (LPS) or some cytokines. LPS produces dilatation of cerebral arterioles in vivo through a mechanism that is partially inhibited by indomethacin. In the present study we examined the hypothesis that LPS causes increased expression of COX-2 in brain as well as COX-2-dependent dilatation of cerebral arterioles.

METHODS

Cranial windows were implanted in anesthetized rats and used to measure diameter of cerebral arterioles under control conditions and during topical application of various agonists and antagonists. Windows were flushed every 30 minutes for 4 hours with vehicle (artificial cerebrospinal fluid; n=5), LPS (100 ng/mL; n=8), LPS and NS-398 (100 micromol/L; n=8), a selective inhibitor of COX-2, or LPS and dexamethasone (1 micromol/L; n=5), which attenuates expression of COX-2. To examine expression of COX-2 protein in vivo, other animals were injected intracisternally with artificial cerebrospinal fluid (n=3) or LPS (40 ng; n=4). Four hours after injection, the leptomeninges were harvested and analyzed by Western blot for expression of COX-2 protein. In a third group of experiments, COX-2 expression and prostaglandin E2 (PGE2) production were determined in leptomeningeal tissue treated for 4 hours ex vivo with vehicle (n=4), LPS (100 ng/mL; n=4), LPS and NS-398 (100 micromol/L; n=4), or LPS and dexamethasone (1 micromol/L; n=4).

RESULTS

LPS caused marked, progressive dilatation of cerebral arterioles, with a maximum increase in diameter of 55+/-9% (mean+/-SEM) at 4 hours. Coapplication of either NS-398 or dexamethasone with LPS reduced dilatation of cerebral arterioles at hours 2 through 4 (P<0.05). In contrast, NS-398 did not inhibit dilatation of cerebral arterioles in response to bradykinin or ADP. In animals injected intracisternally with vehicle, COX-2 protein was expressed at a very low level in leptomeningeal tissue. Intracisternal injection of LPS increased COX-2 protein expression by approximately 20-fold (P<0.05). In leptomeningeal tissue treated ex vivo with LPS, there was also expression of COX-2. Both dexamethasone and NS-398 markedly reduced COX-2 protein expression in ex vivo LPS-treated tissue. PGE2 production was detectable under control conditions in leptomeningeal tissue incubated in vehicle ex vivo for 4 hours (6.5+/-1.1 pmol/mg protein). LPS treatment significantly increased PGE2 production to 12.8+/-1.1 pmol/mg protein (P<0.05). Both dexamethasone and NS-398 significantly attenuated LPS-induced PGE2 production (P<0.05).

CONCLUSIONS

LPS increased expression of COX-2 protein in leptomeningeal tissue and caused COX-2-dependent dilatation of cerebral arterioles in vivo. Ex vivo, both NS-398 and dexamethasone suppressed LPS-induced PGE2 production and COX-2 expression in leptomeningeal tissue. Inhibition of LPS-induced dilatation of cerebral arterioles in vivo by NS-398 and dexamethasone suggests that the dilatation was dependent on expression and activity of COX-2. These findings support the concept that exposure of brain to LPS causes cerebral vasodilatation that is dependent in part on expression and activity of COX-2.

Regulation of prostaglandin H synthase-2 expression in cerebromicrovascular smooth muscle by serum and epidermal growth factor

Growth factors may play a role in the formation of prostaglandins (PG) by cerebral blood vessels during development or reaction to injury. In smooth muscle cultures isolated from murine cerebral microvessels PG production was induced with either serum or epidermal growth factor (EGF). Prostaglandin H synthase (PGHS) activity peaked at 6 h after the addition of 10% serum or 50 ng/ml EGF. Increases in expression of PGHS-1 mRNA were small (7- to 10-fold) compared with PGHS-2 (30- to 120-fold), and the induction patterns were different for serum and EGF. An increase in PGHS-2 message was detected by 0.5 h of adding either agent, but peak induction occurred earlier for EGF than for serum, 1 h vs. 3 h, respectively. The response to either stimulus had returned to prestimulation levels by 12 h. The induction of PGHS-2 protein was also transient, but followed a more delayed time course (peak levels at 6 h). Induction of activity, message, and protein by either agent was blocked by 1 microM dexamethasone and attenuated by genistein (100 microM), a nonspecific tyrosine kinase inhibitor. Tyrphostin 47, a more selective EGF receptor tyrosine kinase inhibitor, dose-dependently inhibited EGF-stimulated PGHS activity, completely abolishing PG production at 100 microM. However, this inhibitor had no effect on serum-stimulated PG production. Curiously, 100 microM tyrphostin 47 enhanced EGF-induced PGHS-2 mRNA and protein expression. These data suggest that EGF induces the expression of PGHS-2 in cerebromicrovascular smooth muscle by a mechanism that requires tyrosine kinase activity and that is distinct from serum.

Inducible cyclooxygenase expression in canine basilar artery after experimental subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Inducible cyclooxygenase (COX-2) has been found to play a pathological role in cerebral insult. We investigated the expression of COX-2 in the basilar artery after experimental subarachnoid hemorrhage (SAH).

METHODS

In a canine "two-hemorrhage" model of SAH, the basilar arteries were obtained on day 2 after a cisternal injection of autologous blood or on days 4, 6, 7, or 9 after the second injection. Basilar arteries also were obtained 12 hours after intracisternal injection a cytokine: interleukin (IL)-1 beta (0.03 microgram), IL-6 (3 micrograms), or IL-8 (10 micrograms). Western blotting with a polyclonal anti-COX-2 antibody was performed in these arteries.

RESULTS

COX-2 protein was not demonstrated in the basilar artery in control animals without SAH. However, it was expressed in the basilar artery on days 2, 4, 6, and 7 after blood injection but not on day 9. Intracisternal injection of IL-1 beta, IL-6, or IL-8 also induced COX-2 in the basilar artery.

CONCLUSIONS

COX-2 expression was detected in basilar arterial tissue in both acute and chronic stages after SAH. Elevation of inflammatory cytokines after SAH may be involved in the induction of COX-2, which may produce sufficient quantities of eicosanoids to affect hemodynamics after SAH.

Effects of ischemia on prostaglandin H synthase-2 expression in piglet choroid plexus

We examined effects of ischemia on expression of prostaglandin H synthase-1 (PGHS-1) and prostaglandin H synthase-2 (PGHS-2) in piglet choroid plexus. Ten minutes of ischemia was induced by increasing intracranial pressure. Whole choroid plexus was removed and fixed and/or frozen after 1, 2, 4, and 8 h of recovery from anoxic stress. In addition, tissues were obtained from untreated animals or from time control animals. Tissues were analyzed for mRNA, using RNase protection assays, and for proteins, using immunohistochemical approaches. Limited, but detectable PGHS-2 immunoreactivity was present in choroid plexus under normal conditions, and there was no difference between time-control and non-treated animals. Further, PGHS-2 mRNA increased by 2-4 h after ischemia, and enhanced immunoreactivity for PGHS-2 was present at 8 h after ischemia. Enhanced immunoreactivity for PGHS-2 was present in vascular endothelial cells as well as cuboidal epithelial cells and macrophages. In contrast, PGHS-1 mRNA did not increase following ischemia. We conclude that PGHS-2 is present in piglet choroid plexus under normal conditions and that ischemia increases levels of PGHS-2 in choroid plexus.

Effects of anoxic stress on prostaglandin H synthase isoforms in piglet brain

We examined effects of ischemia and asphyxia on levels of prostaglandin H synthase-1 (PGHS-1) and prostaglandin H synthase-2 (PGHS-2) in piglet brain. Ischemia was induced by increasing intracranial pressure and asphyxia was induced by turning off the respirator. Duration of anoxic stress was 10 min. In some animals, indomethacin (5 mg/kg, i.v.) or 7-nitroindazole (7-NI) was administered prior to ischemia to block PGHS or brain nitric oxide synthase (bNOS), respectively. Tissues from cerebral cortex and hippocampus were removed and fixed and/or frozen after 1, 2, 4 and 8 h of recovery from anoxic stress. In addition, tissues were obtained from untreated animals or from time control animals. Levels of mRNA and proteins were determined using RNase protection assay and immunohistochemical approaches, respectively. In the tissues studied, only a few neurons were immunopositive for PGHS-1, and neither ischemia or asphyxia affected PGHS-1 immunostaining at 8 h after recovery. Likewise, PGHS-1 mRNA did not increase following anoxic stress. In contrast, substantial PGHS-2 immunoreactivity was present in neurons and glial cells in the cerebral cortex and hippocampus and there was no difference between time control and non treated animals. PGHS-2 mRNA increased by 2-4 h after ischemia, and heightened immunoreactivity for PGHS-2 was present at 8 h after ischemia in cerebral cortex and hippocampus. However, asphyxia did not increase PGHS-2 mRNA or immunostaining. Indomethacin pretreatment inhibited increases in mRNA and protein for PGHS-2 after ischemia, while 7-NI had little effect on increases in PGHS-2 immunoreactivity. We conclude that: (1) PGHS-2 is the predominant isoform present in piglet cerebral cortex and hippocampus; (2) Ischemia but not asphyxia increases levels of PGHS-2; (3) Ischemia does not increase levels of PGHS-1; and (4) Indomethacin but not 7-NI attenuates ischemia-induced increases in PGHS-2.

Regional distribution of prostaglandin H synthase-2 and neuronal nitric oxide synthase in piglet brain

Immunohistochemical techniques were used to examine the distribution of prostaglandin H synthase (PGHS)-2 and neuronal nitric oxide synthase (nNOS) in piglet brain. Samples from parietal cortex, hippocampus, and cerebellum were immersion fixed in 10% formalin, sectioned at 50 microm, and immunostained using specific antibodies against PGHS-2 and nNOS. Immunoreactivity for PGHS-2 was extensive throughout the areas examined. For example, PGHS-2 immunoreactive cells were present in all layers of the cortex, but were particularly dense among neurons in layers II/II, V, and VI. In addition, glial cells associated with microvessels in white matter showed PGHS-2 immunoreactivity. In contrast, nNOS immunoreactive neurons were limited in number and widely dispersed across all layers of the cortex and thus did not form a definable pattern. In the hippocampus, heavy PGHS-2 immunoreactivity was present in neurons and glial cells in the subgranular region, stratum radiatum, adjacent to the hippocampal sulcus, and in CA1 and CA3 pyramidal cells. Immunostaining for nNOS displayed a different pattern from PGHS-2 in the hippocampus, and was mainly localized to the granule cell layer of the dentate gyrus and the mossy fiber layer. In the cerebellum, PGHS-2 immunoreactivity was heavily represented in the Bergmann glia and to a lesser extent in cells of the granular layer, whereas nNOS was detected only in Basket cells. There are four conclusions from this study. First, PGHS-2 immunoreactivity is widely represented in the cerebral cortex, hippocampus, and cerebellum of neonatal pigs. Second, glia cells as well as neurons can show immunoreactivity for PGHS-2. And third, the distribution of nNOS is different from PGHS-2 immunoreactivity in the cerebral cortex, hippocampus, and cerebellum.