Cyclo-oxygenase-2 contributes to constitutive prostanoid production in rat kidney and brain

Inhibition of rat locus coeruleus neurons by prostaglandin E2 EP3 receptors: pharmacological characterization ex vivo

Prostaglandin E2 (PGE2) is an inflammatory mediator synthesized by the brain constitutive cyclooxygenase enzyme. PGE2 binds to G protein-coupled EP1-4 receptors (EP1 to Gq, EP2,4 to Gs, and EP3 to Gi/o). EP2, EP3 and EP4 receptors are expressed in the locus coeruleus (LC), the main noradrenergic nucleus in the brain. EP3 receptors have been explored in the central nervous system, although its role regulating the locus coeruleus neuron activity has not been pharmacologically defined. Our aim was to characterize the function of EP3 receptors in neurons of the LC. Thus, we studied the effect of EP3 receptor agonists on the firing activity of LC cells in rat brain slices by single-unit extracellular electrophysiological techniques. The EP3 receptor agonist sulprostone (0.15 nM-1.28 µM), PGE2 (0.31 nM-10.2 µM) and the PGE1 analogue misoprostol (0.31 nM-2.56 µM) inhibited the firing rate of LC neurons in a concentration-dependent manner (EC50 = 15 nM, 110 nM, and 51 nM, respectively). The EP3 receptor antagonist L-798,106 (3-10 µM), but not the EP2 (PF-04418948, 3-10 µM) or EP4 (L-161,982, 3-10 µM) receptor antagonists, caused rightward shifts in the concentration-effect curves for the EP3 receptor agonists. Sulprostone-induced effect was attenuated by the Gi/o protein blocker pertussis toxin (pertussis toxin, 500 ng ml-1) and the inhibitors of inwardly rectifying potassium channels (GIRK) BaCl2 (300 µM) and SCH-23390 (15 µM). In conclusion, LC neuron firing activity is regulated by EP3 receptors, presumably by an inhibitory Gi/o protein- and GIRK-mediated mechanism.

Pre- and Neonatal Exposure to Lead (Pb) Induces Neuroinflammation in the Forebrain Cortex, Hippocampus and Cerebellum of Rat Pups

Lead (Pb) is a heavy metal with a proven neurotoxic effect. Exposure is particularly dangerous to the developing brain in the pre- and neonatal periods. One postulated mechanism of its neurotoxicity is induction of inflammation. This study analyzed the effect of exposure of rat pups to Pb during periods of brain development on the concentrations of selected cytokines and prostanoids in the forebrain cortex, hippocampus and cerebellum. Methods: Administration of 0.1% lead acetate (PbAc) in drinking water ad libitum, from the first day of gestation to postnatal day 21, resulted in blood Pb in rat pups reaching levels below the threshold considered safe for humans by the Centers for Disease Control and Prevention (10 µg/dL). Enzyme-linked immunosorbent assay (ELISA) method was used to determine the levels of interleukins IL-1β, IL-6, transforming growth factor-β (TGF-β), prostaglandin E2 (PGE2) and thromboxane B2 (TXB2). Western blot and quantitative real-time PCR were used to determine the expression levels of cyclooxygenases COX-1 and COX-2. Finally, Western blot was used to determine the level of nuclear factor kappa B (NF-κB). Results: In all studied brain structures (forebrain cortex, hippocampus and cerebellum), the administration of Pb caused a significant increase in all studied cytokines and prostanoids (IL-1β, IL-6, TGF-β, PGE2 and TXB2). The protein and mRNA expression of COX-1 and COX-2 increased in all studied brain structures, as did NF-κB expression. Conclusions: Chronic pre- and neonatal exposure to Pb induces neuroinflammation in the forebrain cortex, hippocampus and cerebellum of rat pups.

Development of multitarget agents possessing soluble epoxide hydrolase inhibitory activity

Over the last two decades polypharmacology has emerged as a new paradigm in drug discovery, even though developing drugs with high potency and selectivity toward a single biological target is still a major strategy. Often, targeting only a single enzyme or receptor shows lack of efficacy. High levels of inhibitor of a single target also can lead to adverse side effects. A second target may offer additive or synergistic effects to affecting the first target thereby reducing on- and off-target side effects. Therefore, drugs that inhibit multiple targets may offer a great potential for increased efficacy and reduced the adverse effects. In this review we summarize recent findings of rationally designed multitarget compounds that are aimed to improve efficacy and safety profiles compared to those that target a single enzyme or receptor. We focus on dual inhibitors/modulators that target the soluble epoxide hydrolase (sEH) as a common part of their design to take advantage of the beneficial effects of sEH inhibition.

The endothelial cyclooxygenase pathway: Insights from mouse arteries

To date, cyclooxygenase-2 (COX-2) is commonly believed to be the major mediator of endothelial prostacyclin (prostaglandin I2; PGI2) synthesis that balances the effect of thromboxane (Tx) A2 synthesis mediated by the other COX isoform, COX-1 in platelets. Accordingly, selective inhibition of COX-2 is considered to cause vasoconstriction, platelet aggregation, and hence increase the incidence of cardiovascular events. This idea has been claimed to be substantiated by experiments on mouse models, some of which are deficient in one of the two COX isoforms. However, results from our studies and those of others using similar mouse models suggest that COX-1 is the major functional isoform in vascular endothelium. Also, although PGI2 is recognized as a potent vasodilator, in some arteries endothelial COX activation causes vasoconstrictor response. This has again been recognized by studies, especially those performed on mouse arteries, to result largely from endothelial PGI2 synthesis. Therefore, evidence that supports a role for COX-1 as the major mediator of PGI2 synthesis in mouse vascular endothelium, reasons for the inconsistency, and results that elucidate underlying mechanisms for divergent vasomotor reactions to endothelial COX activation will be discussed in this review. In addition, we address the possible pathological implications and limitations of findings obtained from studies performed on mouse arteries.

Celecoxib offsets the negative renal influences of cyclosporine via modulation of the TGF-β1/IL-2/COX-2/endothelin ET(B) receptor cascade

Endothelin (ET) signaling provokes nephrotoxicity induced by the immunosuppressant drug cyclosporine A (CSA). We tested the hypotheses that (i): celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, counterbalances renal derangements caused by CSA in rats and (ii) the COX-2/endothelin ET(B) receptor signaling mediates the CSA-celecoxib interaction. Ten-day treatment with CSA (20 mg/kg/day) significantly increased biochemical indices of renal function (serum urea, creatinine), inflammation (interleukin-2, IL-2) and fibrosis (transforming growth factor-β₁, TGF-β₁). Histologically, CSA caused renal tubular atrophy along with interstitial fibrosis. These detrimental renal effects of CSA were largely reduced in rats treated concurrently with celecoxib (10 mg/kg/day). We also report that cortical glomerular and medullary tubular protein expressions of COX-2 and ET(B) receptors were reduced by CSA and restored to near-control values in rats treated simultaneously with celecoxib. The importance of ET(B) receptors in renal control and in the CSA-celecoxib interaction was further verified by the findings (i) most of the adverse biochemical, inflammatory, and histopathological profiles of CSA were replicated in rats treated with the endothelin ETB receptor antagonist BQ788 (0.1 mg/kg/day, 10 days), and (ii) the BQ788 effects, like those of CSA, were alleviated in rats treated concurrently with celecoxib. Together, the data suggest that the facilitation of the interplay between the TGF-β1/IL-2/COX-2 pathway and the endothelin ET(B) receptors constitutes the cellular mechanism by which celecoxib ameliorates the nephrotoxic manifestations of CSA in rats.

Effects of nitric oxide on magnocellular neurons of the supraoptic nucleus involve multiple mechanisms

Physiological evidence indicates that the supraoptic nucleus (SON) is an important region for integrating information related to homeostasis of body fluids. Located bilaterally to the optic chiasm, this nucleus is composed of magnocellular neurosecretory cells (MNCs) responsible for the synthesis and release of vasopressin and oxytocin to the neurohypophysis. At the cellular level, the control of vasopressin and oxytocin release is directly linked to the firing frequency of MNCs. In general, we can say that the excitability of these cells can be controlled via two distinct mechanisms: 1) the intrinsic membrane properties of the MNCs themselves and 2) synaptic input from circumventricular organs that contain osmosensitive neurons. It has also been demonstrated that MNCs are sensitive to osmotic stimuli in the physiological range. Therefore, the study of their intrinsic membrane properties became imperative to explain the osmosensitivity of MNCs. In addition to this, the discovery that several neurotransmitters and neuropeptides can modulate their electrical activity greatly increased our knowledge about the role played by the MNCs in fluid homeostasis. In particular, nitric oxide (NO) may be an important player in fluid balance homeostasis, because it has been demonstrated that the enzyme responsible for its production has an increased activity following a hypertonic stimulation of the system. At the cellular level, NO has been shown to change the electrical excitability of MNCs. Therefore, in this review, we focus on some important points concerning nitrergic modulation of the neuroendocrine system, particularly the effects of NO on the SON.

Centrally administered bombesin activates COX-containing spinally projecting neurons of the PVN in anesthetized rats

The paraventricular nucleus (PVN) of the hypothalamus has a heterogenous structure containing different types of output neurons that project to the median eminence, posterior pituitary, brain stem autonomic centers and sympathetic preganglionic neurons in the spinal cord. Presympathetic neurons in the PVN send mono- and poly-synaptic projections to the spinal cord. In the present study using urethane-anesthetized rats, we examined the effects of centrally administered bombesin (a homologue of the mammalian gastrin-releasing peptide) on the mono-synaptic spinally projecting PVN neurons pre-labeled with a retrograde tracer Fluoro-Gold (FG) injected into T8 level of the spinal cord, with regard to the immunoreactivity for cyclooxygenase (COX) isozymes (COX-1/COX-2) and Fos (a marker of neuronal activation). FG-labeled spinally projecting neurons were abundantly observed in the dorsal cap, ventral part and posterior part of the PVN. The immunoreactivity of each COX-1 and COX-2 was detected in FG-labeled spinally projecting PVN neurons in the vehicle (10 μl of saline/animal, i.c.v.)-treated group, while bombesin (1 nmol/animal, i.c.v.) had no effect on the number of these immunoreactive neurons for each COX isozyme with labeling of FG. On the other hand, the peptide significantly increased the number of double-immunoreactive neurons for Fos and COX-1/COX-2 with FG-labeling in the PVN (except triple-labeled neurons for FG, COX-2 and Fos in the dorsal cap of the PVN), as compared to those of vehicle-treated group. These results suggest that centrally administered bombesin activates spinally projecting PVN neurons containing COX-1 and COX-2 in rats.

Role of cyclooxygenase-1-mediated prostacyclin synthesis in endothelium-dependent vasoconstrictor activity of porcine interlobular renal arteries

This study aimed to determine whether PGI2 would be evoked by the endogenous endothelial B2 receptor agonist bradykinin (BK) in the porcine interlobular renal artery and, if so, to determine how it would influence the vasomotor reaction, and the specific cyclooxygenase (COX) isoform(s) involved in its synthesis. The production of the PGI2 metabolite 6-keto-PGF1α was analyzed with HPLC-mass spectroscopy, while vasomotor reaction to PGI2 or BK was determined with isometric force measurement. Results showed that BK evoked an increase in the production of 6-keto-PGF1α, which was abolished by endothelial denudation that removed COX-1 expression, or was reduced by COX-1 inhibition. Interestingly, PGI2 evoked a potent contraction, which was prevented by antagonizing thromboxane-prostanoid (TP) receptors and was not enhanced by antagonizing the vasodilator PGI2 (IP) receptors. The IP receptor agonists MRE-269 and iloprost did not induce any relaxation. Moreover, iloprost, which is also a PGI2 analog, caused a contraction, which was sensitive to TP receptor antagonism, but was to a significantly lesser extent than that of PGI2. Indeed, IP receptors were not detected by RT-PCR or Western blotting in the vessel. Following nitric oxide synthase (NOS) inhibition, BK also evoked an endothelium-dependent contraction, which was blocked by TP receptor antagonism. In addition, inhibition of COX-1 (but not COX-2) impeded the vasoconstrictor activity of BK and expedited the relaxation induced by the agonist in NOS-intact vessels. These results demonstrate that in the porcine interlobular renal artery BK evokes endothelial COX-1-mediated PGI2 synthesis, which mainly leads to the activation of TP receptors and a vasoconstrictor response, possibly due to a scarcity of vasodilator activity mediated by IP receptors. Also, our data suggested that the effect of a PGI2 analog on TP receptors could be reduced compared with that of PGI2 due to modified structure as with iloprost.

Concomitant activation of functionally opposing prostacyclin and thromboxane prostanoid receptors by cyclo-oxygenase-1-mediated prostacyclin synthesis in mouse arteries

This study aimed to determine whether cyclo-oxygenase-1 (COX-1) mediates dilatation of mouse arteries via synthesis of prostacyclin (PGI(2)) and, if so, how PGI(2) (IP) receptors contribute and whether thromboxane prostanoid (TP) receptors are implicated in the process. Mesenteric arteries were isolated from wild-type mice or mice with COX-1 deficiency (COX-1(-/-)). The vasomotor reaction to the COX substrate arachidonic acid (AA) was determined with isometric force measurement, while the in vitro production or the plasma level of the PGI(2) metabolite 6-keto-PGF(1α) was analysed with high-performance liquid chromatography-mass spectroscopy or enzyme immunoassay, respectively. Results showed that AA, which evoked endothelium-dependent 6-keto-PGF(1α) production, elicited relaxation that was inhibited or enhanced by antagonizing IP or TP receptors, respectively. Also, IP receptor blockade resulted in contraction in response to AA (following NO synthase inhibition), which was prevented by a concomitant TP receptor antagonism. Meanwhile, COX-1(-/-) or COX-1 inhibition abolished the in vitro 6-keto-PGF(1α) production and reduced the relaxation or contraction observed with AA. Real-time PCR showed that whereas TP receptor mRNAs were detected at similar levels, IP receptor mRNAs were present at higher levels in the branches than in the main stem of the mesenteric artery. In addition, antagonizing the IP receptors enhanced the contraction evoked by PGI(2) in the carotid artery. Also, we noted that COX-1(-/-) mice had a reduced basal plasma 6-keto-PGF(1α) level. These results demonstrate an explicit vasodilator role for COX-1-mediated endothelial PGI(2) synthesis and suggest that the functionally opposing IP and TP receptors concomitantly mediate the vasomotor reaction to PGI(2), with the dilator activity of IP receptors being compromised by the vasoconstrictor effect of TP receptors and vice versa.

Possible involvement of S-nitrosylation of brain cyclooxygenase-1 in bombesin-induced central activation of adrenomedullary outflow in rats

We previously reported that both nitric oxide (NO) generated from NO synthase by bombesin and NO generated from SIN-1 (NO donor) activate the brain cyclooxygenase (COX) (COX-1 for bombesin), thereby eliciting the secretion of both catecholamines (CA) from the adrenal medulla by brain thromboxane A(2)-mediated mechanisms in rats. NO exerts its effects via not only soluble guanylate cyclase, but also protein S-nitrosylation, covalent modification of a protein cysteine thiol. In this study, we clarified the central mechanisms involved in the bombesin-induced elevation of plasma CA with regard to the relationship between NO and COX-1 using anesthetized rats. Bombesin (1 nmol/animal, i.c.v.)-induced elevation of plasma CA was attenuated by carboxy-PTIO (NO scavenger) (0.5 and 2.5 μmol/animal, i.c.v.), but was not influenced by ODQ (soluble guanylate cyclase inhibitor) (100 and 300 nmol/animal, i.c.v.). The bombesin-induced response was effectively reduced by dithiothreitol (thiol-reducing reagent) (0.4 and 1.9 μmol/kg/animal, i.c.v.) and by N-ethylmaleimide (thiol-alkylating reagent) (0.5 and 2.4 μmol/kg/animal, i.c.v.). The doses of dithiothreitol also reduced the SIN-1 (1.2 μmol/animal, i.c.v.)-induced elevation of plasma CA, but had no effect on the U-46619 (thromboxane A(2) analog) (100 nmol/animal, i.c.v.)-induced elevation of plasma CA even at higher doses (1.9 and 9.7 μmol/kg/animal, i.c.v.). Immunohistochemical studies demonstrated that the bombesin increased S-nitroso-cysteine-positive cells co-localized with COX-1 in the spinally projecting neurons of the hypothalamic paraventricular nucleus (PVN). Taken together, endogenous NO seems to mediate centrally administered bombesin-induced activation of adrenomedullary outflow at least in part by S-nitrosylation of COX-1 in the spinally projecting PVN neurons in rats.

Eicosanoids in inflammation and cancer: the role of COX-2

Eicosanoids, a family of oxygenated metabolites of eicosapolyenoic fatty acids, such as arachidonic acid, formed via the lipoxygenase, cyclooxygenase (COX) and epoxygenase pathways, play an important role in the regulation of various pathophysiological processes, including inflammation and cancer. COX-2, the inducible isoform of COX, has emerged as the key enzyme regulating inflammation, and promises to play a considerable role in cancer. Although NSAIDs have been in use for centuries, the COX-2 selective inhibitors - coxibs - have emerged as potent anti-inflammatory drugs with fewer gastric side effects. As COX-2 plays a major role in neoplastic transformation and cancer growth, by downregulating apoptosis and promoting angiogenesis, invasion and metastasis, coxibs have a potential role in the prevention and treatment of cancer. Recent studies indicate their possible application in overcoming drug resistance by downregulating the expression of MDR-1. However, the cardiac side effects of some of the coxibs have limited their application in treating various inflammatory disorders and warrant the development of COX-2 inhibitors without side effects. This review will focus on the role of COX-2 in inflammation and cancer, with an emphasis on novel approaches to the development of COX-2 inhibitors without side effects.

Urinary tract obstruction induces transient accumulation of COX-2-derived prostanoids in kidney tissue

Inhibitors of cyclooxygenase (COX)-2 prevent suppression of aquaporin-2 and reduce polyuria in the acute phase after release of bilateral ureteral obstruction (BUO). We hypothesized that BUO leads to COX-2-mediated local accumulation of prostanoids in inner medulla (IM) tissue. To test this, rats were subjected to BUO and treated with selective COX-1 or COX-2 inhibitors. Tissue was examined at 2, 6, 12, and 24 h after BUO. COX-2 protein abundance increased in IM 12 and 24 h after onset of BUO but did not change in cortex. COX-1 did not change at any time points in any region. A full profile of all five primary prostanoids was obtained by mass spectrometric determination of PGE(2), PGF(2alpha), 6-keto-PGF(1alpha), PGD(2), and thromboxane (Tx) B(2) concentrations in kidney cortex/outer medulla and IM fractions. IM concentration of PGE(2), 6-keto-PGF(1alpha), and PGF(2alpha) was increased at 6 h BUO, and PGE(2) and PGF(2alpha) increased further at 12 h BUO. TxB(2) increased after 12 h BUO. 6-keto-PGF(1alpha) remained significantly increased after 24 h BUO. The COX-2 inhibitor parecoxib lowered IM PGE(2,) TxB(2), 6-keto-PGF(1alpha), and PGF(2alpha) below vehicle-treated BUO and sham rats at 6, 12 and, 24 h BUO. The COX-1 inhibitor SC-560 lowered PGE(2), PGF(2alpha), and PGD(2) in IM compared with untreated 12 h BUO, but levels remained significantly above sham. In cortex tissue, PGE(2) and 6-keto-PGF(1alpha) concentrations were elevated at 6 h only. In conclusion, COX-2 activity contributes to the transient increase in prostacyclin metabolite 6-keto-PGF(1alpha) and TxB(2) concentration in the kidney IM, and COX-2 is the predominant isoform that is responsible for accumulation of PGE(2) and PGF(2alpha) with minor, but significant, contributions from COX-1. PGD(2) synthesis is mediated exclusively by COX-1. In BUO, therapeutic interventions aimed at the COX-prostanoid pathway should target primarily COX-2.

In vitro cyclooxygenase activity assay in tissue homogenates

The use of in vitro cyclooxygenase (COX) activity assays has been particularly useful for comparing the effect of different drugs on COX activity in different tissues. In addition, this assay is relatively quick, cheap, and a large number of samples can be tested at the same time. However, one limitation of this assay is the fact that it does not discriminate between the activities of different COX isoforms.

Prostanoid extraction and measurement

Prostanoids are involved in numerous physiological and pathophysiological processes in all body organs. Therefore, measurement of the concentration of the prostanoids has always been of importance for research and drug development purposes as a measure of cyclooxygenase (COX) activities. Techniques used for the measurement of prostanoids have been described decades ago. These techniques have come a long way and improvements have been reported, especially with the specificity in competition immunoassays that rely on the use of specific antibodies against a given prostanoid. These assays are relatively fast and do not involve the use of radioactive isotopes as radioimmunoassay. However, prior extraction is required in order to concentrate the prostanoids and remove interfering substances such as proteins. In this chapter, we describe two protocols for the extraction and measurement of prostanoids using C18 columns and commercial enzyme immunoassays, which do not require specialized equipments and can be performed in any laboratory with standard equipments.

Possible involvement of microglia containing cyclooxygenase-1 in the accumulation of gonadotrophin-releasing hormone in the preoptic area in female rats

Prostaglandins (PGs), especially PGE(2), are involved in the hypothalamic control of gonadotrophin-releasing hormone (GnRH) release, acting at least in part on the terminal of GnRH axons in the median eminence. The present study aimed: (i) to clarify the role of PG(s) in regulating GnRH cell function at the level of the perikarya in the preoptic area; (ii) to determine the cyclooxygenase (COX) isozyme responsible for producing PG(s) that regulates GnRH perikarya; and (iii) to identify cell types that contain the responsible COX isozyme in female rats. A surge of luteinising hormone (LH) secretion was induced by oestrogen and progesterone in ovariectomised rats. Treatment of the rat before the LH surge with indomethacin, a nonselective COX inhibitor, or NS-398, a selective COX-2 inhibitor, did not interfere with the surge. However, treatment with indomethacin or flurbiprofen, a selective COX-1 inhibitor, significantly reduced the number of GnRH-immunoreactive cells in the preoptic area at the time of peak LH secretion during the surge. NS-398 did not affect the GnRH immunoreactivity. Double-labelled immunofluorescent histochemistry revealed COX-1 immunoreactivity in the vicinity of, but not within, GnRH containing neurones in the preoptic area. COX-2 immunoreactivity was not found in the same area. The COX-1 immunoreactivity was almost entirely localised in microglia in the preoptic area, but not in neurones or astrocytes. These results suggest that microglia in the preoptic area containing COX-1 are responsible for producing PG(s), which, in turn, facilitates the accumulation of GnRH during the gonadotrophin surge in female rats.

Heritability of thromboxane A2 and prostaglandin E2 biosynthetic machinery in a Spanish population

OBJECTIVE

Prostanoids play a critical role in clinical areas such as inflammation, thrombosis, immune response, and cancer. Although some studies suggest that there are genes that determine variability of some prostanoid-related phenotypes, the genetic influence on these traits has not been evaluated.

METHODS AND RESULTS

The relative contributions of genetic and environmental influences to the prostanoid biosynthetic pathway-related phenotypes, cyclooxygenase isoenzymes, microsomal-PGE-synthase-1 and TxA-synthase expression, and thromboxane-A(2) and prostaglandin-E(2) production by stimulated whole blood, were assessed in a sample of 308 individuals in 15 extended families. The effects of measured covariates (such as sex, age, and smoking), genes, and environmental variables shared by members of a household were quantified. Heritabilities ranging from 0.406 to 0.634 for enzyme expression and from 0.283 to 0. 751 for prostanoid production were found.

CONCLUSIONS

These results demonstrate clearly the importance of genetic factors in determining variation in phenotypes that are components of the prostanoid biosynthetic pathways. The presence of such strong genetic effects suggest that it will be possible to localize previously unknown genes that influence quantitative variation in these phenotypes, some of which affect multiple aspects of cell biology, with important clinical implications.

Lipocalin-prostaglandin D synthase is a critical beneficial factor in transient and permanent focal cerebral ischemia

Prostaglandin D(2) (PGD(2)) is the most abundant prostaglandin produced in the brain. It is a metabolite of arachidonic acid and synthesized by prostaglandin D(2) synthases (PGDS) via the cyclooxygenase pathway. Two distinct types of PGDS have been identified: hematopoietic prostaglandin D synthase (H-PGDS) and lipocalin-type prostaglandin D synthase (L-PGDS). Because relatively little is known about the role of L-PGDS in the CNS, here we examined the outcomes in L-PGDS knockout and wild-type (WT) mice after two different cerebral ischemia models, transient middle cerebral artery (MCA) occlusion (tMCAO) and permanent distal middle cerebral artery occlusion (pMCAO). In the tMCAO model, the MCA was occluded with a monofilament for 90 min and then reperfused for 4 days. In the pMCAO model, the distal part of the MCA was permanently occluded and the mice were sacrificed after 7 days. Percent corrected infarct volume and neurological score were determined after 4 and 7 days, respectively. L-PGDS knockout mice had significantly greater infarct volume and brain edema than did WT mice after tMCAO (P<0.01). Similarly, L-PGDS knockout mice showed greater infarct volume and neurological deficits as compared to their WT counterparts after pMCAO (P<0.01). Using the two models enabled us to study the role of L-PGDS in both early (tMCAO) and delayed (pMCAO) ischemic processes. Our findings suggest that L-PGDS is beneficial for protecting the brain against transient and permanent cerebral ischemia. These results provide a better understanding of the role played by the enzymes that control eicosanoid synthesis and how they can be utilized as potential targets to prevent damage following either acute or potentially chronic neurological disorders.

Inhibition of arachidonic acid metabolism and its implication on cell proliferation and tumour-angiogenesis

Arachidonic acid (AA) and its metabolites have recently generated a heightened interest due to growing evidence of their significant role in cancer biology. Thus, inhibitors of the AA cascade, first and foremost COX inhibitors, which have originally been of interest in the treatment of inflammatory conditions and certain types of cardiovascular disease, are now attracting attention as an arsenal against cancer. An increasing number of investigations support their role in cancer chemoprevention, although the precise molecular mechanisms that link levels of AA, and its metabolites, with cancer progression have still to be elucidated. This article provides an overview of the AA cascade and focuses on the roles of its inhibitors and their implication in cancer treatment. In particular, emphasis is placed on the inhibition of cell proliferation and neo-angiogenesis through inhibition of the enzymes COX-2, 5-LOX and CYP450. Downstream effects of inhibition of AA metabolites are analysed and the molecular mechanisms of action of a selected number of inhibitors of catalytic pathways reviewed. Lastly, the benefits of dietary omega-3 fatty acids and their mechanisms of action leading to reduced cancer risk and impeded cancer cell growth are mentioned. Finally, a proposal is put forward, suggesting a novel and integrated approach in viewing the molecular mechanisms and complex interactions responsible for the involvement of AA metabolites in carcinogenesis and the protective effects of omega-3 fatty acids in inflammation and tumour prevention.

Perioperative use of beta-blockers and COX-2 inhibitors may improve immune competence and reduce the risk of tumor metastasis

BACKGROUND

COX inhibitors and beta-blockers were recently suggested to reduce cancer progression through inhibition of tumor proliferation and growth factor secretion, induction of tumor apoptosis, and prevention of cellular immune suppression during the critical perioperative period. Here we evaluated the perioperative impact of clinically applicable drugs from these categories in the context of surgery, studying natural killer (NK) cell activity and resistance to experimental metastases.

METHODS

F344 rats were treated with COX-1 inhibitors (SC560), COX-2 inhibitors (indomethacin, etodolac, or celecoxib), a beta-blocker (propranolol), or a combination of a COX-2 inhibitor and a beta-blocker (etodolac and propranolol). Rats underwent laparotomy, and were inoculated intravenously with syngeneic MADB106 tumor cells for the assessment of lung tumor retention (LTR). Additionally, the impact of these drug regimens on postoperative levels of NK cytotoxicity was studied in peripheral blood and marginating-pulmonary leukocytes.

RESULTS

Surgery increased MADB106 LTR. COX-2 inhibition, but not COX-1 inhibition, reduced postoperative LTR. Etodolac and propranolol both attenuated the deleterious impact of surgery, and their combined use abolished it. Surgery decreased NK cytotoxicity per NK cell in both immune compartments, and only the combination of etodolac and propranolol significantly attenuated these effects. Lastly, the initiation of drug treatment three days prior to surgery yielded the same beneficial effects as a single pre-operative administration, but, as discussed, prolonged treatment may be more advantageous clinically.

CONCLUSIONS

Excess prostaglandin and catecholamine release contributes to postoperative immune-suppression. Treatment combining perioperative COX-2 inhibition and beta-blockade is practical in operated cancer patients, and our study suggests potential immunological and clinical benefits.

Prostaglandins in the kidney: developments since Y2K

There are five major PGs (prostaglandins/prostanoids) produced from arachidonic acid via the COX (cyclo-oxygenase) pathway: PGE(2), PGI(2) (prostacyclin), PGD(2), PGF(2alpha) and TXA(2) (thromboxane A(2)). They exert many biological effects through specific G-protein-coupled membrane receptors, namely EP (PGE(2) receptor), IP (PGI(2) receptor), DP (PGD(2) receptor), FP (PGF(2alpha) receptor) and TP (TXA(2) receptor) respectively. PGs are implicated in physiological and pathological processes in all major organ systems, including cardiovascular function, gastrointestinal responses, reproductive processes, renal effects etc. This review highlights recent insights into the role of each prostanoid in regulating various aspects of renal function, including haemodynamics, renin secretion, growth responses, tubular transport processes and cell fate. A thorough review of the literature since Y2K (year 2000) is provided, with a general overview of PGs and their synthesis enzymes, and then specific considerations of each PG/prostanoid receptor system in the kidney.

Are there attacking points in the eicosanoid cascade for chemotherapeutic options in benign meningiomas?

Object

The current treatment for recurrent or malignant meningiomas with adjuvant therapies has not been satisfactory, and there is an intense interest in evaluating new molecular markers to act as therapeutic targets. Enzymes of the arachidonic acid (AA) cascade such as cyclooxygenase (COX)–2 or 5-lipoxygenase (5-LO) are upregulated in a number of epithelial tumors, but to date there are hardly any data about the expression of these markers in meningiomas. To find possible targets for chemotherapeutic intervention, the authors evaluated the expression of AA derivatives at different molecular levels in meningiomas.

Methods

One hundred and twenty-four meningioma surgical specimens and normal human cortical tissue samples were immunohistochemically and cytochemically stained for COX-2, COX-1, 5-LO, and prostaglandin E receptor 4 (PTGER4). In addition, Western blot and polymerase chain reaction (PCR) analyses were performed to detect the presence of eicosanoids in vivo and in vitro.

Results

Sixty (63%) of 95 benign meningiomas, 21 (88%) of 24 atypical meningiomas, all five malignant meningiomas, and all normal human cortex samples displayed high COX-2 immunoreactivity. All cultured specimens and IOMM-Lee cells stained positive for COX-2, COX-1, 5-LO, and PTGER4. The PCR analysis demonstrated no changes in eicosanoid expression among meningiomas of different World Health Organization grades and in normal human cortical and dura mater tissue.

Conclusions

Eicosanoid derivatives COX-1, COX-2, 5-LO, and PTGER4 enzymes show a high universal expression in meningiomas but are not upregulated in normal human cortex and dura tissue. This finding of the ubiquitous presence of these enzymes in meningiomas offers an excellent baseline for testing upcoming chemotherapeutic treatments.

MF-tricyclic inhibits growth of experimental abdominal aortic aneurysms

BACKGROUND

Experimental abdominal aortic aneurysm (AAA) development can be pharmacologically suppressed by inhibiting matrix metalloproteinase-9 (MMP-9). Cyclooxygenase-2 (COX-2) inhibitors are potent anti-inflammatory agents that have been demonstrated to inhibit experimental aneurysm development. We hypothesized that treatment with MF-tricyclic, a selective COX-2 inhibitor, incorporated into rodent chow would inhibit aneurysm development in a rat AAA model.

METHODS

Twelve male Sprague Dawley rats underwent induction of experimental AAA using intra-aortic porcine elastase infusion. Six rats received control feed, and six received MF-tricyclic rodent chow for a period of 14 days. Aortic diameters were measured pre- and postinfusion as well as at harvest. Aortic tissue samples were evaluated by real-time polymerase chain reaction (RT-PCR) for MMP-9, by immunohistochemistry for elastin.

RESULTS

Elastase infusion produced AAA in all untreated rats. At 14 days MF-tricyclic-treated rats had significantly reduced aortic diameter (1.9 +/- 0.1 mm versus 2.4 +/- 0.0 mm, P = 0.00001). Percent increase in aortic diameter was also significantly less in animals receiving MF-tricyclic (65.7 +/- 8.5% versus 132.3 +/- 7.3%, P = 0.0001). RT-PCR demonstrated a decrease in the mean expression of MMP-9 in the treated animals (0.414 ng of RNA versus 1.114 ng of RNA) (P = 0.07). Sections stained for elastin demonstrated preserved elastin integrity in MF-tricyclic treated aortas.

CONCLUSIONS

COX-2 inhibition helps to retard the growth of experimental AAAs possibly through inhibition of MMP-9. Experimentally treated animals demonstrated smaller aortic diameters and lower levels of tissue MMP-9 when compared to untreated animals. Selective COX-2 inhibition may offer an additional method to pharmacologically inhibit AAAs.

Selective COX-2 inhibition markedly slows disease progression and attenuates altered prostanoid production in Han:SPRD-cy rats with inherited kidney disease

Selective cyclooxygenase-2 (COX-2) inhibitors appear to have beneficial renoprotective effects in most, but not all, renal disease conditions. The objective of our study was to examine the effects of COX-2 inhibition in a rat model of polycystic kidney disease. Four-week-old Han:SPRD-cy rats were given a standard rodent diet containing NS-398 (3 mg.kg body wt(-1).day(-1)) or a control diet without NS-398 for 7 wk. In diseased rats, selective COX-2 inhibition resulted in 18% and 67% reduction in cystic expansion and interstitial fibrosis, respectively, but no change in renal function. NS-398 also ameliorated disease-associated pathologies, such as renal inflammation, cell proliferation, and oxidant injury (by 33, 38, and 59%, respectively). Kidney disease was associated with elevated renal COX-1 and COX-2 enzyme activities, and NS-398 blunted the increase in COX-2 enzyme activity (as indicated by 21 and 28% lower renal thromboxane B2 and PGE2 levels, respectively). NS-398 reduced urinary excretion of prostanoid metabolites in diseased rats. In summary, COX-2 inhibition attenuated renal injury, reduced the elevated renal COX-2 activity, and ameliorated disease-related alterations in prostanoid production in this rat model of chronic renal disease.

Up-regulation of cyclooxygenase-2 in different grades of acute human renal allograft rejection

BACKGROUND

Cyclooxygenase-2 (COX-2) is up-regulated by a variety of stimuli that are associated with tissue injury and inflammation.

METHODS

The purpose of this study was to analyze COX-2 detection during different grades of acute human renal allograft rejection. COX-2 expressions were analyzed by immunohistochemistry in 74 samples obtained from biopsies with acute rejection of different grades (n= 48), tubular changes (n=13) and from kidney allografts with stable function (n=13).

RESULTS

In interstitial area, there was a significant correlation of COX-2 induction in acute rejection in comparison to tubular changes (1.67 vs. 0.76, p=0.02) and stable function (vs. 0.07, p<0.001), as well as in vessels in the group with acute rejection in relation to stable function (1.1 vs. 0, p=0.04). When the group with acute rejection was analyzed in subgroups, there was a clear increase of COX-2 expression from acute rejection grade IB to III in vessels, in inflammatory infiltrating cells in interstitial area and in glomeruli, while borderline and IA grades were intermediate.

CONCLUSION

COX-2 is up-regulated during acute human renal allograft rejection according to the severity of acute rejection and could be used as a marker of inflammation in kidney transplantation.

Pharmacological characterization of a selective COX-2 inhibitor MF-tricyclic, [3-(3,4-difluorophenyl)-4-(4-(methylsulfonyl)phenyl)-2-(5H)-furanone], in multiple preclinical species

Selective type 2 cyclooxygenase (COX-2) inhibitors are often used in preclinical studies without potency and selectivity data in the experimental species. To address this issue, we assessed a selective COX-2 inhibitor MF-tricyclic in four commonly used species, namely mice, rats, guinea pigs and rabbits, in the present study. In both the guinea pig and rabbit whole blood assay, the compound inhibited lipopolysaccharide (LPS)-induced PGE(2) production with an IC(50) (COX-2) of 0.6 and 2.8 microM, respectively. By comparison, the compound displayed a much weaker activity on clot-induced formation of thromboxane with an IC(50) (COX-1) of >10 microM (guinea pigs) and 23 microM (rabbits). In keeping with the in vitro potency data, the compound significantly inhibited interleukin-1 beta (IL-1beta) -induced PGE(2) formation in the rabbit synovium at plasma concentrations near the whole blood assay IC(50) for COX-2 but much lower than that for COX-1. MF-tricyclic was also potent and selective toward COX-2 in mice, inhibiting carrageenan-induced PGE(2) accumulation in the air pouch dose-dependently (ED(50)=0.5 mg/kg) without affecting stomach PGE(2) levels. In rats, MF-tricyclic was found to be effective in three standard in vivo assays utilized for assessing COX-2 inhibitors, namely, LPS-induced pyresis, carrageenan-induced paw edema and adjuvant-induced arthritis at the doses that did not inhibit stomach PGE(2) levels. Similar to that in rats, the compound displayed pharmacological efficacy in mice, guinea pigs and rabbits when tested in the LPS pyresis model. Our data reveal that MF-tricyclic has the desired biochemical and pharmacological properties for selective COX-2 inhibition in all four test species.

Double-label expression studies of prostacyclin synthase, thromboxane synthase and COX isoforms in normal aortic endothelium

We have performed double-label immunofluorescence microscopy studies to evaluate the extent of co-localization of prostacyclin synthase (PGIS) and thromboxane synthase (TXS) with cyclooxygenase (COX)-1 and COX-2 in normal aortic endothelium. In dogs, COX-2 expression was found to be restricted to small foci of endothelial cells while COX-1, PGIS and TXS were widely distributed throughout the endothelium. Quantification of the total cross-sectioned aortic endothelium revealed a 6- to 7-fold greater expression of COX-1 relative to COX-2 (55 vs. 8%) and greater co-distribution of PGIS with COX-1 compared to COX-2 (19 vs. 3%). These results are in contrast to the extensive co-localization of PGIS and COX-2 in bronchiolar epithelium. In rat and human aortas, immunofluorescence studies also showed significant COX-1 and PGIS co-localization in the endothelium. Only minor focal COX-2 expression was detected in rat endothelium, similar to the dog, while COX-2 was not detected in human specimens. Inhibition studies in rats showed that selective COX-1 inhibition caused a marked reduction of 6-keto-PGF(1alpha) and TXB(2) aortic tissue levels, while COX-2 inhibition had no significant effect, providing further evidence for a functionally larger contribution of COX-1 to the synthesis of prostacyclin and thromboxane in aortic tissue. The data suggest a major role for COX-1 in the production of both prostacyclin and thromboxane in normal aortic tissue. The extensive co-localization of PGIS and COX-2 in the lung also indicates significant tissue differences in the co-expression patterns of these two enzymes.

Cyclooxygenase-2 inhibition normalizes arterial blood pressure in CYP1A1-REN2 transgenic rats with inducible ANG II-dependent malignant hypertension

The present study was performed to determine the effects of cyclooxygenase (COX)-1 and COX-2 inhibition on blood pressure and renal hemodynamics in transgenic rats with inducible malignant hypertension [strain name: TGR(Cyp1a1Ren2)]. Male Cyp1a1-Ren2 rats ( n = 7) were fed a normal diet containing the aryl hydrocarbon, indole-3-carbinol (I3C; 0.3%), for 6–9 days to induce malignant hypertension. Mean arterial pressure (MAP) and renal hemodynamics were measured in pentobarbital sodium-anesthetized Cyp1a1-Ren2 rats during control conditions, following administration of the COX-2 inhibitor nimesulide (3 mg/kg iv), and following administration of the nonspecific COX inhibitor meclofenamate (5 mg/kg iv). Rats induced with I3C had higher MAP than noninduced rats ( n = 7; 188 ± 6 vs. 136 ± 4 mmHg, P < 0.01). There was no difference in renal plasma flow (RPF) or glomerular filtration rate (GFR) between induced and noninduced rats. Nimesulide elicited a larger decrease in MAP in hypertensive rats (188 ± 6 to 140 ± 8 mmHg, P < 0.01) than in normotensive rats (136 ± 4 to 113 ± 8 mmHg, P < 0.01). Additionally, nimesulide decreased GFR (0.9 ± 0.13 to 0.44 ± 0.05 ml·min−1·g−1, P < 0.05) and RPF (2.79 ± 0.27 to 1.35 ± 0.14 ml·min−1·g−1, P < 0.05) in hypertensive rats but did not alter GFR or RPF in normotensive rats. Meclofenamate further decreased MAP in hypertensive rats (to 115 ± 10 mmHg, P < 0.05) but did not decrease MAP in normotensive rats. Meclofenamate did not alter GFR or RPF in either group. These findings demonstrate that COX-1- and COX-2-derived prostanoids contribute importantly to the development of malignant hypertension in Cyp1a1-Ren2 transgenic rats. The data also indicate that COX-2-derived vasodilatory metabolites play an important role in the maintenance of RPF and GFR following induction of malignant hypertension in Cyp1a1-Ren2 transgenic rats.

Centrally administered histamine evokes the adrenal secretion of noradrenaline and adrenaline by brain cyclooxygenase-1- and thromboxane A2-mediated mechanisms in rats

Plasma adrenaline is originated from adrenal medulla, while plasma noradrenaline reflects the release from sympathetic nerves in addition to the secretion from adrenal medulla. The present study was designed to characterize the source of plasma catecholamines induced by centrally administered histamine, with regard to the brain prostanoids. Intracerebroventricularly (i.c.v.) administered histamine (1, 5 and 10 microg/animal) elevated plasma noradrenaline and adrenaline (noradrenaline<adrenaline) in a dose-dependent manner. Ketoprofen (a selective inhibitor of cyclooxygenase-1) (100, 250 and 500 microg/animal, i.c.v.) dose-dependently reduced the histamine (5 microg/animal, i.c.v.)-induced elevation of both catecholamines, while NS-398 (a selective inhibitor of cyclooxygenase-2) (250 and 500 microg/animal, i.c.v.) had no effect. The histamine-induced response was dose-dependently attenuated by furegurelate (an inhibitor of thromboxane A(2) synthase) (250 and 500 microg/animal, i.c.v.), and abolished by acute bilateral adrenalectomy. These results suggest that centrally administered histamine evokes plasma noradrenaline and adrenaline from adrenal medulla by brain cyclooxygenase-1- and thromboxane A(2)-mediated mechanisms in rats.

Interaction between prostaglandin E2 and l-cis-diltiazem, a specific blocker of cyclic nucleotide gated channels in bovine aortic endothelial cells

Prostaglandins are known to transduce their signals via 7 transmembrane prostanoid receptors, which typically signal through coupling to G proteins and downstream second messenger molecules and protein kinase activation. Recently we have shown that cyclic nucleotides affect prostaglandins binding to bovine aortic endothelial cells independent of protein kinases. Here we show that incubation of bovine aortic endothelial cells with permeable analogs of cAMP or cGMP leads to a rapid and reversible reduction in PGE(2) binding to the cells. Since cyclic nucleotides are known modulators of cyclic nucleotide gated channels, we examined the effect of a specific cyclic nucleotide gated channel blocker l-cis-diltiazem on prostaglandin E(2) (PGE(2)) binding to bovine aortic endothelial cells. L-cis-diltiazem is shown to displace PGE(2) binding to bovine aortic endothelial cells in a dose dependent manner. In addition the effect of PGE(2) and l-cis-diltiazem on thapsigargin induced calcium elevation in the cells was compared. Both agents reduced in bovine aortic endothelial cells the thapsigargin induced calcium elevation by about half. PGE(2) also retarded the time course of the response to thapsigargin. Simultaneous treatment of the cells with both PGE(2) and l-cis-diltiazem did not yield an inhibitory effect beyond that observed with l-cis-diltiazem alone. Together our data point at the cyclic nucleotide gated channels as a feasible candidate for association with the PGE(2) binding site in bovine aortic endothelial cells.