A vasoconstrictor role for cyclooxygenase-1-mediated prostacyclin synthesis in mouse renal arteries

Prostacyclin Promotes Degenerative Pathology in a Model of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is the most common form of dementia in aged populations. A substantial amount of data demonstrates that chronic neuroinflammation can accelerate neurodegenerative pathologies. In AD, chronic neuroinflammation results in the upregulation of cyclooxygenase and increased production of prostaglandin H2, a precursor for many vasoactive prostanoids. While it is well-established that many prostaglandins can modulate the progression of neurodegenerative disorders, the role of prostacyclin (PGI2) in the brain is poorly understood. We have conducted studies to assess the effect of elevated prostacyclin biosynthesis in a mouse model of AD. Upregulated prostacyclin expression significantly worsened multiple measures associated with amyloid-β (Aβ) disease pathologies. Mice overexpressing both Aβ and PGI2 exhibited impaired learning and memory and increased anxiety-like behavior compared with non-transgenic and PGI2 control mice. PGI2 overexpression accelerated the development of Aβ accumulation in the brain and selectively increased the production of soluble Aβ42. PGI2 damaged the microvasculature through alterations in vascular length and branching; Aβ expression exacerbated these effects. Our findings demonstrate that chronic prostacyclin expression plays a novel and unexpected role that hastens the development of the AD phenotype.

Sex differences in rat renal arterial responses following exercise training

During aerobic exercise, hemodynamic alterations occure; while blood flow in skeletal muscle arteries increases, it decreases in visceral vessels due to mesenterial vasoconstriction. However, maintaining renal blood flow during intensive sport is also a priority. Our aim was to investigate the changes of vascular reactivity and histology of isolated renal artery of male and female rats in response to swim-training. Wistar rats were distributed into four groups: male sedentary (MSed), male trained (MTr), female sedentary (FSed), and female trained (FTr). Trained animals underwent a 12-week-long intensive swimming program. Vascular function of isolated renal artery segments was examined by wire myography. Phenylephrine-induced contraction was lower in FSed compared to MSed animals, and it was decreased by training in male but not in female animals. Inhibition of cyclooxygenases by indomethacin reduced contraction in both sedentary groups, and in MTr but not in FTr animals. Inhibition of nitric oxide production increased contraction in both trained groups. Acetylcholine induced relaxation was similar in all experimental groups showing predominant NO-dependency. Elastin and smooth muscle cell actin density was reduced in female rats after aerobic training. This study shows that, as a result of 12-weeks-long training, there are sex differences in renal arterial responses following exercise training. Swimming moderates renal artery vasoconstriction in male animals, while it depresses elastic fiber and smooth muscle actin density in females.

Endothelium-dependent contraction: The non-classical action of endothelial prostacyclin, its underlying mechanisms, and implications

Although commonly thought to produce prostacyclin (prostaglandin I₂ ; PGI₂ ) that evokes vasodilatation and protects vessels from the development of diseases, the endothelial cyclooxygenase (COX)-mediated metabolism has also been found to release substance(s) called endothelium-derived contracting factor(s) (EDCF) that causes endothelium-dependent contraction and implicates in endothelial dysfunction of disease conditions. Various mechanisms have been proposed for the process; however, the major endothelial COX metabolite PGI₂ , which has been classically considered to activate the I prostanoid receptor (IP) that mediates vasodilatation and opposes the effects of thromboxane (Tx) A₂ produced by COX in platelets, emerges as a major EDCF in health and disease conditions. Our recent studies from genetically altered mice further suggest that vasomotor reactions to PGI₂ are collectively modulated by IP, the vasoconstrictor Tx-prostanoid receptor (TP; the prototype receptor of TxA₂ ) and E prostanoid receptor-3 (EP3; a vasoconstrictor receptor of PGE₂ ) although with differences in potency and efficacy; a contraction to PGI₂ reflects activities of TP and/or EP3 outweighing that of the concurrently activated IP. Here, we discuss the history of endothelium-dependent contraction, evidences that support the above hypothesis, proposed mechanisms for the varied reactions to endothelial PGI₂ synthesis as well as the relation of its dilator activity to the effect of another NO-independent vasodilator mechanism, the endothelium-derived hyperpolarizing factor. Also, we address the possible pathological and therapeutic implications as well as questions remaining to be resolved or limitations of our above findings obtained from genetically altered mouse models.

Endothelial cyclooxygenase-1 paradoxically drives local vasoconstriction and atherogenesis despite underpinning prostacyclin generation

Endothelial cyclooxygenase-1-derived prostanoids, including prostacyclin, have clear cardioprotective roles associated with their anti-thrombotic potential but have also been suggested to have paradoxical pathological activities within arteries. To date it has not been possible to test the importance of this because no models have been available that separate vascular cyclooxygenase-1 products from those generated elsewhere. Here, we have used unique endothelial-specific cyclooxygenase-1 knockout mice to show that endothelial cyclooxygenase-1 produces both protective and pathological products. Functionally, however, the overall effect of these was to drive pathological responses in the context of both vasoconstriction in vitro and the development of atherosclerosis and vascular inflammation in vivo. These data provide the first demonstration of a pathological role for the vascular cyclooxygenase-1 pathway, highlighting its potential as a therapeutic target. They also emphasize that, across biology, the role of prostanoids is not always predictable due to unique balances of context, products, and receptors.

Differential properties of E prostanoid receptor-3 and thromboxane prostanoid receptor in activation by prostacyclin to evoke vasoconstrictor response in the mouse renal vasculature

Vasomotor reactions of prostacyclin (prostaglandin I₂ ; PGI₂ ) can be collectively modulated by thromboxane prostanoid receptor (TP), E-prostanoid receptor-3 (EP3), and the vasodilator I prostanoid receptor (IP). This study aimed to determine the direct effect of PGI₂ on renal arteries and/or the whole renal vasculature and how each of these receptors is involved. Experiments were performed on vessels or perfused kidneys of wild-type mice and/or mice with deficiency in TP (TP^-/- ) and/or EP3. Here we show that PGI₂ did not evoke relaxation, but instead resulted in contraction of main renal arteries (from ~0.001-0.01 µM) or reduction of flow in perfused kidneys (from ~1 µM); either of them was reversed into a dilator response in TP^-/- /EP3^-/- counterparts. Also, we found that in renal arteries although it has a lesser effect than TP^-/- on the maximal contraction to PGI₂ (10 µM), EP3^-/- but not TP^-/- resulted in relaxation to the prostanoid at 0.01-1 µM. Meanwhile, TP^-/- only significantly reduced the contractile activity evoked by PGI₂ at ≥0.1 µM. These results demonstrate that PGI₂ may evoke an overall vasoconstrictor response in the mouse renal vasculature, reflecting activities of TP and EP3 outweighing that of the vasodilator IP. Also, our results suggest that EP3, on which PGI₂ can have a potency similar to that on IP, plays a major role in the vasoconstrictor effect of the prostanoid of low concentrations (≤1 µM), while TP, on which PGI₂ has a lower potency but higher efficacy, accounts for a larger part of its maximal contractile activity.

Prostaglandin E2 sequentially activates E-prostanoid receptor-3 and thromboxane prostanoid receptor to evoke contraction and increase in resistance of the mouse renal vasculature

Although recognized to have an in vivo vasodepressor effect blunted by the vasoconstrictor effect of E-prostanoid receptor-3 (EP3), prostaglandin E₂ (PGE₂ ) evokes contractions of many vascular beds that are sensitive to antagonizing the thromboxane prostanoid receptor (TP). This study aimed to determine the direct effect of PGE₂ on renal arteries and/or the whole renal vasculature and how each of these two receptors is involved in the responses. Experiments were performed on isolated vessels and perfused kidneys of wild-type mice and/or mice with deficiency in TP (TP^-/- ), EP3 (EP3^-/- ), or both TP and EP3 (TP^-/- /EP3^-/- ). Here we show that PGE₂ (0.001-30 μM) evoked not only contraction of main renal arteries, but also a decrease of flow in perfused kidneys. EP3^-/- diminished the response to 0.001-0.3 μM PGE₂ , while TP^-/- reduced that to the prostanoid of higher concentrations. In TP^-/- /EP3^-/- vessels and perfused kidneys, PGE₂ did not evoke contraction but instead resulted in vasodilator responses. These results demonstrate that PGE₂ functions as an overall direct vasoconstrictor of the mouse renal vasculature with an effect reflecting the vasoconstrictor activities outweighing that of dilation. Also, our results suggest that EP3 dominates the vasoconstrictor effect of PGE₂ of low concentrations (≤0.001-0.3 μM), but its effect is further added by that of TP, which has a higher efficacy, although activated by higher concentrations (from 0.01 μM) of the same prostanoid PGE₂ .

EP3 Blockade Adds to the Effect of TP Deficiency in Alleviating Endothelial Dysfunction in Atherosclerotic Mouse Aortas

Endothelial dysfunction, which leads to ischemic events under atherosclerotic conditions, can be attenuated by antagonizing the thromboxane-prostanoid receptor (TP) that mediates the vasoconstrictor effect of prostanoids including prostacyclin (PGI₂). This study aimed to determine whether antagonizing the E prostanoid receptor-3 (EP3; which can also be activated by PGI₂) adds to the above effect of TP deficiency (TP^-/-) under atherosclerotic conditions and if so, the underlying mechanism(s). Atherosclerosis was induced in ApoE^-/- mice and those with ApoE^-/- and TP^-/-. Here, we show that in phenylephrine pre-contracted abdominal aortic rings with atherosclerotic lesions of ApoE^-/-/TP^-/- mice, although an increase of force (which was larger than that of non-atherosclerotic controls) evoked by the endothelial muscarinic agonist acetylcholine to blunt the concurrently activated relaxation in ApoE^-/- counterparts was largely removed, the relaxation evoked by the agonist was still smaller than that of non-atherosclerotic TP^-/- mice. EP3 antagonism not only increased the above relaxation, but also reversed the contractile response evoked by acetylcholine in NO synthase-inhibited atherosclerotic ApoE^-/-/TP^-/- rings into a relaxation sensitive to I prostanoid receptor antagonism. In ApoE^-/- atherosclerotic vessels the expression of endothelial NO synthase was decreased, yet the production of PGI₂ (which evokes contraction via both TP and EP3) evoked by acetylcholine was unaltered compared to non-atherosclerotic conditions. These results demonstrate that EP3 blockade adds to the effect of TP^-/- in uncovering the dilator action of natively produced PGI₂ to alleviate endothelial dysfunction in atherosclerotic conditions.

Endothelial prostacyclin protects the kidney from ischemia-reperfusion injury

Prostacyclin, or PGI₂, is a product of PGI synthase (PGIS), down-stream of cyclooxygenase pathway. PGI₂ has been demonstrated to play an important role in maintaining renal blood flow. Non-steroidal anti-inflammatory drugs (NSAIDs) that inhibit cyclooxygenase are reported to increase the susceptibility of patients to acute kidney injury (AKI). This study explores the role of endothelium-derived prostacyclin in ischemia-reperfusion injury (I/RI). The renal PGIS expression and PGI₂ production markedly increased following I/RI. Loss of one allele of PGIS gene or selective endothelial PGIS deletion (TEK-CRE PGIS^fl/fl mice) caused more severe renal damage following I/RI than control mice. Iloprost, a PGI₂ analog, administered 30 min before the I/R surgery, markedly attenuated the renal damage in both control mice and TEK-CRE PGIS^fl/fl mice. Renal p-PKA expression significantly increased after I/RI in wild-type mice but not in the PGIS deletion mice, consistent with IP receptor mediating the protective effect. Further studies showed that PGIS deficiency was associated with reduced fluorescence microsphere accumulation in the kidney following I/R. Folic acid also induced marked kidney injury; however, endothelial PGIS deletion did not worsen kidney injury compared with wild-type mice. These studies indicate that PGIS-derived PGI₂ can protect the kidney from acute injury caused by ischemia and reperfusion and PGIS/PGI₂ is a potential intervention target for AKI.

Lymphatic endothelial cells attenuate inflammation via suppression of dendritic cell maturation

Vascular endothelial growth factor-C (VEGF-C)-induced lymphangiogenesis and increased tissue drainage have been reported to inhibit acute and chronic inflammation, and an activated lymphatic endothelium might mediate peripheral tolerance. Using transgenic mice overexpressing VEGF-C in the skin, we found that under inflammatory conditions, VEGF-C-mediated expansion of the cutaneous lymphatic network establishes an immune-inhibitory microenvironment characterised by increased regulatory T (Treg) cells, immature CD11c+CD11b+ dendritic cells (DCs) and CD8+ cells exhibiting decreased effector function. Strikingly, lymphatic endothelial cell (LEC)-conditioned media (CM) potently suppress DC maturation with reduced expression of MHCII, CD40, and IL-6, and increased IL-10 and CCL2 expression. We identify an imbalance in prostaglandin synthase expression after LEC activation, favoring anti-inflammatory prostacyclin synthesis. Importantly, blockade of LEC prostaglandin synthesis partially restores DC maturity. LECs also produce TGF-ß1, contributing to the immune-inhibitory microenvironment. This study identifies novel mechanisms by which the lymphatic endothelium modulates cellular immune responses to limit inflammation.

Increased role of E prostanoid receptor-3 in prostacyclin-evoked contractile activity of spontaneously hypertensive rat mesenteric resistance arteries

This study aimed to determine whether E prostanoid receptor-3 (EP3) is involved in prostacyclin (PGI₂)-evoked vasoconstrictor activity of resistance arteries and if so, how it changes under hypertensive conditions. Mesenteric resistance arteries from Wistar-Kyoto rats (WKYs) and spontaneously hypertensive rats (SHRs) were isolated for functional and biochemical studies. Here we show that in vessels from WKYs, PGI₂ or the endothelial muscarinic agonist ACh (which stimulates in vitro PGI₂ synthesis) evoked vasoconstrictor activity, which increased in SHRs. The thromboxane-prostanoid receptor (TP) antagonist SQ29548 partially removed the vasoconstrictor activity, and an increased contractile activity of PGI₂ resistant to SQ29548 was observed in SHRs. Interestingly, L798106, an antagonist of EP3 (whose expression was higher in SHRs than in WKYs), not only added to the effect of SQ29548 but also caused relaxation to PGI₂ more than that obtained with SQ29548. In accordance, EP3 deletion, which reduced PGI₂-evoked contraction, together with SQ29548 resulted in relaxation evoked by the agonist in mouse aortas. These results thus demonstrate an explicit involvement of EP3 in PGI₂-evoked vasoconstrictor activity in rat mesenteric resistance arteries and suggest that up-regulation of the receptor contributes significantly to the increased contractile activity evoked by PGI₂ under hypertensive conditions.

Atherosclerosis and Cancer; A Resemblance with Far-reaching Implications

Atherosclerosis and cancer are chronic diseases considered two of the main causes of death all over the world. Taking into account that both diseases are multifactorial, they share not only several important molecular pathways but also many ethiological and mechanistical processes from the very early stages of development up to the advanced forms in both pathologies. Factors involved in their progression comprise genetic alterations, inflammatory processes, uncontrolled cell proliferation and oxidative stress, as the most important ones. The fact that external effectors such as an infective process or a chemical insult have been proposed to initiate the transformation of cells in the artery wall and the process of atherogenesis, emphasizes many similarities with the progression of the neoplastic process in cancer. Deregulation of cell proliferation and therefore cell cycle progression, changes in the synthesis of important transcription factors as well as adhesion molecules, an alteration in the control of angiogenesis and the molecular similarities that follow chronic inflammation, are just a few of the processes that become part of the phenomena that closely correlates atherosclerosis and cancer. The aim of the present study is therefore, to provide new evidence as well as to discuss new approaches that might promote the identification of closer molecular ties between these two pathologies that would permit the recognition of atherosclerosis as a pathological process with a very close resemblance to the way a neoplastic process develops, that might eventually lead to novel ways of treatment.

Role of E-type prostaglandin receptor EP3 in the vasoconstrictor activity evoked by prostacyclin in thromboxane-prostanoid receptor deficient mice

Prostacyclin, also termed as prostaglandin I₂ (PGI₂), evokes contraction in vessels with limited expression of the prostacyclin receptor. Although the thromboxane-prostanoid receptor (TP) is proposed to mediate such a response of PGI₂, other unknown receptor(s) might also be involved. TP knockout (TP^-/-) mice were thus designed and used to test the hypothesis. Vessels, which normally show contraction to PGI₂, were isolated for functional and biochemical analyses. Here, we showed that the contractile response evoked by PGI₂ was indeed only partially abolished in the abdominal aorta of TP^-/- mice. Interestingly, further antagonizing the E-type prostaglandin receptor EP3 removed the remaining contractile activity, resulting in relaxation evoked by PGI₂ in such vessels of TP^-/- mice. These results suggest that EP3 along with TP contributes to vasoconstrictor responses evoked by PGI₂, and hence imply a novel mechanism for endothelial cyclooxygenase metabolites (which consist mainly of PGI₂) in regulating vascular functions.

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.

A vasoconstrictor response to COX-1-mediated prostacyclin synthesis in young rat renal arteries that increases in prehypertensive conditions

This study aimed to determine whether prostacyclin (PGI2) functions as an endothelium-derived contracting factor (EDCF) in young rat renal arteries, and, if so, we wanted to examine the underlying mechanism(s) and how it changes in prehypertensive conditions. Vessels from Wistar-Kyoto (WKY) and prehypertensive spontaneously hypertensive rats (SHRs) of 25-28 days of age were isolated for functional and biochemical analyses. Result showed that following NO synthase (NOS) inhibition PGI2 and the thromboxane-prostanoid (TP) receptor agonist U-46619 evoked contractions in young WKY renal arteries that were similar to those in prehypertensive SHRs. Meanwhile, the endothelial muscarinic receptor agonist ACh evoked an endothelium-dependent contraction under NOS-inhibited conditions and a production of the PGI2 metabolite 6-keto-PGF1α; both were sensitive to cyclooxygenase (COX) and/or COX-1 inhibition but higher in prehypertensive SHRs than in young WKYs. Interestingly, in WKY renal arteries PGI2 did not evoke relaxation even after TP receptor antagonism that diminished the contraction evoked by the agonist. Indeed, PGI2 (IP) receptors were not detected in the vessel with Western blot. Moreover, we noted that treatment with the nonselective COX inhibitor indomethacin, which was started at the prehypertensive stage, blunted the elevation of systolic blood pressure and reduced the heart-to-body ratio in SHR within 2 mo of treatment. These results demonstrate that due to scarcity of IP receptors, PGI2, which is derived mainly from COX-1-mediated metabolism, acts as an EDCF in young WKY renal arteries, and it increases in prehypertensive conditions. Also, our data revealed that COX inhibition starting from the prehypertensive stage has an antihypertensive effect in young SHRs.

COX-2 is involved in vascular oxidative stress and endothelial dysfunction of renal interlobar arteries from obese Zucker rats

Obesity is related to vascular dysfunction through inflammation and oxidative stress and it has been identified as a risk factor for chronic renal disease. In the present study, we assessed the specific relationships among reactive oxygen species (ROS), cyclooxygenase 2 (COX-2), and endothelial dysfunction in renal interlobar arteries from a genetic model of obesity/insulin resistance, the obese Zucker rats (OZR). Relaxations to acetylcholine (ACh) were significantly reduced in renal arteries from OZR compared to their counterpart, the lean Zucker rat (LZR), suggesting endothelial dysfunction. Blockade of COX with indomethacin and with the selective blocker of COX-2 restored the relaxations to ACh in obese rats. Selective blockade of the TXA2/PGH2 (TP) receptor enhanced ACh relaxations only in OZR, while inhibition of the prostacyclin (PGI2) receptor (IP) enhanced basal tone and inhibited ACh vasodilator responses only in LZR. Basal production of superoxide was increased in arteries of OZR and involved NADPH and xanthine oxidase activation and NOS uncoupling. Under conditions of NOS blockade, ACh induced vasoconstriction and increased ROS generation that were augmented in arteries from OZR and blunted by COX-2 inhibition and by the ROS scavenger tempol. Hydrogen peroxide (H2O2) evoked both endothelium- and vascular smooth muscle (VSM)-dependent contractions, as well as ROS generation that was reduced by COX-2 inhibition. In addition, COX-2 expression was enhanced in both VSM and endothelium of renal arteries from OZR. These results suggest that increased COX-2-dependent vasoconstriction contributes to renal endothelial dysfunction through enhanced (ROS) generation in obesity. COX-2 activity is in turn upregulated by ROS.

Prostaglandin I2 IP Receptor Agonist, Beraprost, Prevents Transient Global Cerebral Ischemia Induced Hippocampal CA1 Injury in Aging Mice

Beraprost sodium is a new stable, orally active Prostaglandin I2 analogue. The aim of this study was to determine the effect of beraprost on cognitive dysfunction and locomotor impairment induced by bilateral common carotid artery occlusion in mice. We investigated the ameliorating effect of beraprost through PGI2 IP receptor by studying neurologic deficit assessment and T-maze testing in young and old male C57Bl/6 wild-type (WT) and IP receptor knockout (IP KO) mice following a 12 min bilateral common carotid artery occlusion (BCCAo) and 7 days of reperfusion. Beraprost reversed BCCAo induced cognitive impairment and neurological deficit in a dose dependent manner. Immunohistochemical studies showed attenuation of neuronal cell death, astrogliosis, microglial invasion, and myeloperoxidase (MPO) activity in both young and old WT mice after post treatment with beraprost. Moreover, after BCCAo, phosphorylated cAMP response element binding protein positive cell numbers were increased with beraprost treatment over vehicle treated controls. These results show that beraprost treatment attenuated cognitive dysfunction and neurological deficits induced by BCCAo, and suggest that this effect may be mediated by the neuroprotective effects of treatment.

Vasomotor Reaction to Cyclooxygenase-1-Mediated Prostacyclin Synthesis in Carotid Arteries from Two-Kidney-One-Clip Hypertensive Mice

This study tested the hypothesis that in hypertensive arteries cyclooxygenase-1 (COX-1) remains as a major form, mediating prostacyclin (prostaglandin I2; PGI2) synthesis that may evoke a vasoconstrictor response in the presence of functional vasodilator PGI2 (IP) receptors. Two-kidney-one-clip (2K1C) hypertension was induced in wild-type (WT) mice and/or those with COX-1 deficiency (COX-1-/-). Carotid arteries were isolated for analyses 4 weeks after. Results showed that as in normotensive mice, the muscarinic receptor agonist ACh evoked a production of the PGI2 metabolite 6-keto-PGF1α and an endothelium-dependent vasoconstrictor response; both of them were abolished by COX-1 inhibition. At the same time, PGI2, which evokes contraction of hypertensive vessels, caused relaxation after thromboxane-prostanoid (TP) receptor antagonism that abolished the contraction evoked by ACh. Antagonizing IP receptors enhanced the contraction to the COX substrate arachidonic acid (AA). Also, COX-1-/- mice was noted to develop hypertension; however, their increase of blood pressure and/or heart mass was not to a level achieved with WT mice. In addition, we found that either the contraction in response to ACh or that evoked by AA was abolished in COX-1-/- hypertensive mice. These results demonstrate that as in normotensive conditions, COX-1 is a major contributor of PGI2 synthesis in 2K1C hypertensive carotid arteries, which leads to a vasoconstrictor response resulting from opposing dilator and vasoconstrictor activities of IP and TP receptors, respectively. Also, our data suggest that COX-1-/- attenuates the development of 2K1C hypertension in mice, reflecting a net adverse role yielded from all COX-1-mediated activities under the pathological condition.

Cannabidiol improves vasorelaxation in Zucker diabetic fatty rats through cyclooxygenase activation

Cannabidiol (CBD) decreases insulitis, inflammation, neuropathic pain, and myocardial dysfunction in preclinical models of diabetes. We recently showed that CBD also improves vasorelaxation in the Zucker diabetic fatty (ZDF) rat, and the objective of the present study was to establish the mechanisms underlying this effect. Femoral arteries from ZDF rats and ZDF lean controls were isolated, mounted on a myograph, and incubated with CBD (10 μM) or vehicle for 2 hours. Subsequent vasorelaxant responses were measured in combination with various interventions. Prostaglandin metabolites were detected using enzyme immunoassay. Direct effects of CBD on cyclooxygenase (COX) enzyme activity were measured by oxygraph assay. CBD enhanced the maximum vasorelaxation to acetylcholine (ACh) in femoral arteries from ZDF lean rats (P < 0.01) and especially ZDF rats (P < 0.0001). In ZDF arteries, this enhancement persisted after cannabinoid receptor (CB) type 1, endothelial CB, or peroxisome proliferator-activated receptor-γ antagonism but was inhibited by CB2 receptor antagonism. CBD also uncovered a vasorelaxant response to a CB2 agonist not previously observed. The CBD-enhanced ACh response was endothelium-, nitric oxide-, and hydrogen peroxide-independent. It was, however, COX-1/2- and superoxide dismutase-dependent, and CBD enhanced the activity of both purified COX-1 and COX-2. The CBD-enhanced ACh response in the arteries was inhibited by a prostanoid EP4 receptor antagonist. Prostaglandin E2 metabolite levels were below the limits of detection, but 6-keto prostaglandin F1 α was decreased after CBD incubation. These data show that CBD exposure enhances the ability of arteries to relax via enhanced production of vasodilator COX-1/2-derived products acting at EP4 receptors.

Vasoconstrictor role of cyclooxygenase-1-mediated prostacyclin synthesis in non-insulin-dependent diabetic mice induced by high-fat diet and streptozotocin

This study tested the hypothesis that in diabetic arteries, cyclooxygenase (COX)-1 mediates endothelial prostacyclin (PGI2) synthesis, which evokes vasoconstrictor activity under the pathological condition. Non-insulin-dependent diabetes was induced to C57BL/6 mice and those with COX-1 deficiency (COX-1−/− mice) using a high-fat diet in combination with streptozotocin injection. In vitro analyses were performed 3 mo after. Results showed that in diabetic aortas, the endothelial muscarinic receptor agonist ACh evoked an endothelium-dependent production of the PGI2 metabolite 6-keto-PGF1α, which was abolished in COX-1−/− mice. Meanwhile, COX-1 deficiency or COX-1 inhibition prevented vasoconstrictor activity in diabetic abdominal aortas, resulting in enhanced relaxation evoked by ACh. In a similar manner, COX-1 deficiency increased the relaxation evoked by ACh in nitric oxide synthase-inhibited diabetic renal arteries. Also, in diabetic abdominal aortas and/or renal arteries, both PGI2 and the COX substrate arachidonic acid evoked contractions similar to those of nondiabetic mice. However, the contraction to arachidonic acid, but not that to PGI2, was abolished in vessels from COX-1−/− mice. Moreover, we found that 3 mo after streptozotocin injection, systemic blood pressure increased in diabetic C57BL/6 mice but not in diabetic COX-1−/− mice. These results explicitly demonstrate that in the given arteries from non-insulin-dependent diabetic mice, COX-1 remains a major contributor to the endothelial PGI2 synthesis that evokes vasoconstrictor activity under the pathological condition. Also, our data suggest that COX-1 deficiency prevents or attenuates diabetic hypertension in mice, although this could be related to the loss of COX-1-mediated activities derived from both vascular and nonvascular tissues.

COX-2 protects against atherosclerosis independently of local vascular prostacyclin: identification of COX-2 associated pathways implicate Rgl1 and lymphocyte networks

Cyxlo-oxygenase (COX)-2 inhibitors, including traditional nonsteroidal anti-inflammatory drugs (NSAIDs) are associated with increased cardiovascular side effects, including myocardial infarction. We and others have shown that COX-1 and not COX-2 drives vascular prostacyclin in the healthy cardiovascular system, re-opening the question of how COX-2 might regulate cardiovascular health. In diseased, atherosclerotic vessels, the relative contribution of COX-2 to prostacyclin formation is not clear. Here we have used apoE(-/-)/COX-2(-/-) mice to show that, whilst COX-2 profoundly limits atherosclerosis, this protection is independent of local prostacyclin release. These data further illustrate the need to look for new explanations, targets and pathways to define the COX/NSAID/cardiovascular risk axis. Gene expression profiles in tissues from apoE(-/-)/COX-2(-/-) mice showed increased lymphocyte pathways that were validated by showing increased T-lymphocytes in plaques and elevated plasma Th1-type cytokines. In addition, we identified a novel target gene, rgl1, whose expression was strongly reduced by COX-2 deletion across all examined tissues. This study is the first to demonstrate that COX-2 protects vessels against atherosclerotic lesions independently of local vascular prostacyclin and uses systems biology approaches to identify new mechanisms relevant to development of next generation NSAIDs.

Therapeutic implications of the prostaglandin pathway in Alzheimer's disease

An important pathologic hallmark of Alzheimer's disease (AD) is neuroinflammation, a process characterized in AD by disproportionate activation of cells (microglia and astrocytes, primarily) of the non-specific innate immune system within the CNS. While inflammation itself is not intrinsically detrimental, a delicate balance of pro- and anti-inflammatory signals must be maintained to ensure that long-term exaggerated responses do not damage the brain over time. Non-steroidal anti-inflammatory drugs (NSAIDs) represent a broad class of powerful therapeutics that temper inflammation by inhibiting cyclooxygenase-mediated signaling pathways including prostaglandins, which are the principal mediators of CNS neuroinflammation. While historically used to treat discrete or systemic inflammatory conditions, epidemiologic evidence suggests that protracted NSAID use may delay AD onset, as well as decrease disease severity and rate of progression. Unfortunately, clinical trials with NSAIDs have thus far yielded disappointing results, including premature discontinuation of a large-scale prevention trial due to unexpected cardiovascular side effects. Here we review the literature and make the argument that more targeted exploitation of downstream prostaglandin signaling pathways may offer significant therapeutic benefits for AD while minimizing adverse side effects. Directed strategies such as these may ultimately help to delay the deleterious consequences of brain aging and might someday lead to new therapies for AD and other chronic neurodegenerative diseases.