Interactions between A(2A) adenosine receptors, hydrogen peroxide, and KATP channels in coronary reactive hyperemia

A2AR-mediated lymphangiogenesis via VEGFR2 signaling prevents salt-sensitive hypertension

AIMS

Excess dietary sodium intake and retention lead to hypertension. Impaired dermal lymphangiogenesis and lymphatic dysfunction-mediated sodium and fluid imbalance are pathological mechanisms. The adenosine A2A receptor (A2AR) is expressed in lymphatic endothelial cells (LECs), while the roles and mechanisms of LEC-A2AR in skin lymphangiogenesis during salt-induced hypertension are not clear.

METHODS AND RESULTS

The expression of LEC-A2AR correlated with lymphatic vessel density in both high-salt diet (HSD)-induced hypertensive mice and hypertensive patients. Lymphatic endothelial cell-specific A2AR knockout mice fed HSD exhibited 17 ± 2% increase in blood pressure and 17 ± 3% increase in Na+ content associated with decreased lymphatic density (-19 ± 2%) compared with HSD-WT mice. A2AR activation by agonist CGS21680 increased lymphatic capillary density and decreased blood pressure in HSD-WT mice. Furthermore, this A2AR agonist activated MSK1 directly to promote VEGFR2 activation and endocytosis independently of VEGF as assessed by phosphoprotein profiling and immunoprecipitation assays in LECs. VEGFR2 kinase activity inhibitor fruquintinib or VEGFR2 knockout in LECs but not VEGF-neutralizing antibody bevacizumab suppressed A2AR activation-mediated decrease in blood pressure. Immunostaining revealed phosphorylated VEGFR2 and MSK1 expression in the LECs were positively correlated with skin lymphatic vessel density and A2AR level in hypertensive patients.

CONCLUSION

The study highlights a novel A2AR-mediated VEGF-independent activation of VEGFR2 signaling in dermal lymphangiogenesis and sodium balance, which might be a potential therapeutic target in salt-sensitive hypertension.

Basal NAD(H) redox state permits hydrogen peroxide-induced mesenteric artery dilatation

Smooth muscle voltage-gated K+ (Kv) channels in resistance arteries control vascular tone and contribute to the coupling of blood flow with local metabolic activity. Members of the Kv1 family are expressed in vascular smooth muscle and are modulated upon physiological elevation of local metabolites, including the glycolytic end-product l-lactate and superoxide-derived hydrogen peroxide (H2 O2 ). Here, we show that l-lactate elicits vasodilatation of small-diameter mesenteric arteries in a mechanism that requires lactate dehydrogenase (LDH). Using the inside-out configuration of the patch clamp technique, we show that increases in NADH that reflect LDH-mediated conversion of l-lactate to pyruvate directly stimulate the activity of single Kv1 channels and significantly enhance the sensitivity of Kv1 activity to H2 O2 . Consistent with these findings, H2 O2 -evoked vasodilatation was significantly greater in the presence of 10 mM l-lactate relative to lactate-free conditions, yet was abolished in the presence of 10 mM pyruvate, which shifts the LDH reaction towards the generation of NAD+ . Moreover, the enhancement of H2 O2 -induced vasodilatation was abolished in arteries from double transgenic mice with selective overexpression of the intracellular Kvβ1.1 subunit in smooth muscle cells. Together, our results indicate that the Kvβ complex of native vascular Kv1 channels serves as a nodal effector for multiple redox signals to precisely control channel activity and vascular tone in the face of dynamic tissue-derived metabolic cues. KEY POINTS: Vasodilatation of mesenteric arteries by elevated external l-lactate requires its conversion by lactate dehydrogenase. Application of either NADH or H2 O2 potentiates single Kv channel currents in excised membrane patches from mesenteric artery smooth muscle cells. The binding of NADH enhances the stimulatory effects of H2 O2 on single Kv channel activity. The vasodilatory response to H2 O2 is differentially modified upon elevation of external l-lactate or pyruvate. The presence of l-lactate enhances the vasodilatory response to H2 O2 via the Kvβ subunit complex in smooth muscle.

Crosstalk between adenosine receptors and CYP450-derived oxylipins in the modulation of cardiovascular, including coronary reactive hyperemic response

Adenosine is a ubiquitous endogenous nucleoside or autacoid that affects the cardiovascular system through the activation of four G-protein coupled receptors: adenosine A₁ receptor (A₁AR), adenosine A_2A receptor (A_2AAR), adenosine A_2B receptor (A_2BAR), and adenosine A₃ receptor (A₃AR). With the rapid generation of this nucleoside from cellular metabolism and the widespread distribution of its four G-protein coupled receptors in almost all organs and tissues of the body, this autacoid induces multiple physiological as well as pathological effects, not only regulating the cardiovascular system but also the central nervous system, peripheral vascular system, and immune system. Mounting evidence shows the role of CYP450-enzymes in cardiovascular physiology and pathology, and the genetic polymorphisms in CYP450s can increase susceptibility to cardiovascular diseases (CVDs). One of the most important physiological roles of CYP450-epoxygenases (CYP450-2C & CYP2J2) is the metabolism of arachidonic acid (AA) and linoleic acid (LA) into epoxyeicosatrienoic acids (EETs) and epoxyoctadecaenoic acid (EpOMEs) which generally involve in vasodilation. Like an increase in coronary reactive hyperemia (CRH), an increase in anti-inflammation, and cardioprotective effects. Moreover, the genetic polymorphisms in CYP450-epoxygenases will change the beneficial cardiovascular effects of metabolites or oxylipins into detrimental effects. The soluble epoxide hydrolase (sEH) is another crucial enzyme ubiquitously expressed in all living organisms and almost all organs and tissues. However, in contrast to CYP450-epoxygenases, sEH converts EETs into dihydroxyeicosatrienoic acid (DHETs), EpOMEs into dihydroxyoctadecaenoic acid (DiHOMEs), and others and reverses the beneficial effects of epoxy-fatty acids leading to vasoconstriction, reducing CRH, increase in pro-inflammation, increase in pro-thrombotic and become less cardioprotective. Therefore, polymorphisms in the sEH gene (Ephx2) cause the enzyme to become overactive, making it more vulnerable to CVDs, including hypertension. Besides the sEH, ω-hydroxylases (CYP450-4A11 & CYP450-4F2) derived metabolites from AA, ω terminal-hydroxyeicosatetraenoic acids (19-, 20-HETE), lipoxygenase-derived mid-chain hydroxyeicosatetraenoic acids (5-, 11-, 12-, 15-HETEs), and the cyclooxygenase-derived prostanoids (prostaglandins: PGD₂, PGF_2α; thromboxane: Txs, oxylipins) are involved in vasoconstriction, hypertension, reduction in CRH, pro-inflammation and cardiac toxicity. Interestingly, the interactions of adenosine receptors (A_2AAR, A₁AR) with CYP450-epoxygenases, ω-hydroxylases, sEH, and their derived metabolites or oxygenated polyunsaturated fatty acids (PUFAs or oxylipins) is shown in the regulation of the cardiovascular functions. In addition, much evidence demonstrates polymorphisms in CYP450-epoxygenases, ω-hydroxylases, and sEH genes (Ephx2) and adenosine receptor genes (ADORA1 & ADORA2) in the human population with the susceptibility to CVDs, including hypertension. CVDs are the number one cause of death globally, coronary artery disease (CAD) was the leading cause of death in the US in 2019, and hypertension is one of the most potent causes of CVDs. This review summarizes the articles related to the crosstalk between adenosine receptors and CYP450-derived oxylipins in vascular, including the CRH response in regular salt-diet fed and high salt-diet fed mice with the correlation of heart perfusate/plasma oxylipins. By using A_2AAR^-/-, A₁AR^-/-, eNOS^-/-, sEH^-/- or Ephx2^-/-, vascular sEH-overexpressed (Tie2-sEH Tr), vascular CYP2J2-overexpressed (Tie2-CYP2J2 Tr), and wild-type (WT) mice. This review article also summarizes the role of pro-and anti-inflammatory oxylipins in cardiovascular function/dysfunction in mice and humans. Therefore, more studies are needed better to understand the crosstalk between the adenosine receptors and eicosanoids to develop diagnostic and therapeutic tools by using plasma oxylipins profiles in CVDs, including hypertensive cases in the future.

Inhibition of Endoplasmic Reticulum Stress Improves Acetylcholine-Mediated Relaxation in the Aorta of Type-2 Diabetic Rats

Endoplasmic reticulum (ER) stress contributes to insulin resistance and macro- and microvascular complications associated with diabetes. This study aimed to evaluate the effect of ER stress inhibition on endothelial function in the aorta of type-2 diabetic rats. Type-2 diabetes was developed in male Sprague-Dawley rats using a high-fat diet and low-dose streptozotocin. Rat aortic tissues were harvested to study endothelial-dependent relaxation. The mechanisms for acetylcholine-mediated relaxation were investigated using pharmacological blockers, Western blotting, oxidative stress, and inflammatory markers. Acetylcholine-mediated relaxation was diminished in the aorta of diabetic rats compared to control rats; supplementation with TUDCA improved relaxation. In the aortas of control and diabetic rats receiving TUDCA, the relaxation was mediated via eNOS/PI3K/Akt, NAD(P)H, and the KATP channel. In diabetic rats, acetylcholine-mediated relaxation involved eNOS/PI3K/Akt and NAD(P)H, but not the KATP channel. The expression of ER stress markers was upregulated in the aorta of diabetic rats and reduced with TUDCA supplementation. The expression of eNOS and Akt were lower in diabetic rats but were upregulated after supplementation with TUDCA. The levels of MDA, IL-6, and SOD activity were higher in the aorta of the diabetic rats compared to control rats. This study demonstrated that endothelial function was impaired in diabetes, however, supplementation with TUDCA improved the function via eNOS/Akt/PI3K, NAD(P)H, and the KATP channel. The improvement of endothelial function was associated with increased expressions of eNOS and Akt. Thus, ER stress plays a crucial role in the impairment of endothelial-dependent relaxation. Mitigating ER stress could be a potential strategy for improving endothelial dysfunction in type-2 diabetes.

Adenosine and adenosine receptor-mediated action in coronary microcirculation

Adenosine is an ubiquitous extracellular signaling molecule and plays a fundamental role in the regulation of coronary microcirculation through activation of adenosine receptors (ARs). Adenosine is regulated by various enzymes and nucleoside transporters for its balance between intra- and extracellular compartments. Adenosine-mediated coronary microvascular tone and reactive hyperemia are through receptors mainly involving A_2AR activation on both endothelial and smooth muscle cells, but also involving interaction among other ARs. Activation of ARs further stimulates downstream targets of H₂O₂, K_ATP, K_V and K_Ca2+ channels leading to coronary vasodilation. An altered adenosine-ARs signaling in coronary microcirculation has been observed in several cardiovascular diseases including hypertension, diabetes, atherosclerosis and ischemic heart disease. Adenosine as a metabolite and its receptors have been studied for its both therapeutic and diagnostic abilities. The present review summarizes important aspects of adenosine metabolism and AR-mediated actions in the coronary microcirculation.

Alteration of purinergic signaling in diabetes: Focus on vascular function

Diabetes is an important risk factor for the development of cardiovascular disease including atherosclerosis and ischemic heart disease. Vascular complications including macro- and micro-vascular dysfunction are the leading causes of morbidity and mortality in diabetes. Disease mechanisms at present are unclear and no ideal therapies are available, which urgently calls for the identification of novel therapeutic targets/agents. An altered nucleotide- and nucleoside-mediated purinergic signaling has been implicated to cause diabetes-associated vascular dysfunction in major organs. Alteration of both purinergic P1 and P2 receptor sensitivity rather than the changes in receptor expression accounts for vascular dysfunction in diabetes. Activation of P2X₇ receptors plays a crucial role in diabetes-induced retinal microvascular dysfunction. Recent findings have revealed that both ecto-nucleotidase CD39, a key enzyme hydrolyzing ATP, and CD73, an enzyme regulating adenosine turnover, are involved in the renal vascular injury in diabetes. Interestingly, erythrocyte dysfunction in diabetes by decreasing ATP release in response to physiological stimuli may serve as an important trigger to induce vascular dysfunction. Nucleot(s)ide-mediated purinergic activation also exerts long-term actions including inflammatory and atherogenic effects in hyperglycemic and diabetic conditions. This review highlights the current knowledge regarding the altered nucleot(s)ide-mediated purinergic signaling as an important disease mechanism for the diabetes-associated vascular complications. Better understanding the role of key receptor-mediated signaling in diabetes will provide more insights into their potential as targets for the treatment.

Activation of adenosine A2A but not A2B receptors is involved in uridine adenosine tetraphosphate-induced porcine coronary smooth muscle relaxation

Activation of both adenosine A_2A and A_2B receptors (A_2BR) contributes to coronary vasodilation. We previously demonstrated that uridine adenosine tetraphosphate (Up₄A) is a novel vasodilator in the porcine coronary microcirculation, acting mainly on A_2AR in smooth muscle cells (SMC). We further investigated whether activation of A_2BR is involved in Up₄A-mediated coronary SMC relaxation. Both A_2AR and A_2BR may stimulate H₂O₂ production leading to activation of K_ATP channels in SMCs, we also studied the involvement of H₂O₂ and K_ATP channels in Up₄A-mediated effect. Coronary small arteries dissected from the apex of porcine hearts were mounted on wire myograph for Up₄A concentration responses. Up₄A-induced coronary SMC relaxation was attenuated by A_2AR but not A_2BR antagonism or non-selective P2R antagonism, despite greater endogenous A_2BR expression vs. A_2AR in both coronary small arteries and primary cultured coronary SMCs. Moreover, Up₄A-induced coronary SMC relaxation was blunted by H₂O₂ catabolism. This effect was not altered by K_ATP channel blockade. Combination of H₂O₂ catabolism and A_2AR antagonism attenuated Up₄A-induced coronary SMC relaxation to the similar extent as A_2AR antagonism alone. Collectively, Up₄A-induced porcine coronary SMC relaxation is mediated by activation of A_2AR-H₂O₂ pathway. This process does not involve A_2BR, P2R or K_ATP channels.

Enhanced A1 adenosine receptor-induced vascular contractions in mesenteric artery and aorta of in L-NAME mouse model of hypertension

L-NAME-induced hypertension is commonly used to study endothelial dysfunction and related vascular effects. It has been reported that genetic deletion of A₁ adenosine receptor (AR) reduces blood pressure (BP) increases in mice and thus, suggesting the involvement of A₁AR. Thus, we sought to determine whether A₁AR-induced vascular responses were altered in this mouse model of hypertension. L-NAME (1 mg/ml) was given in the drinking water for 28 days to mice. The BP was monitored using non-invasive tail-cuff system. Muscle tension studies were performed using DMT for mesenteric arteries (MAs) and organ bath for aorta. Protein expression was analyzed by western blot. Significantly, higher systolic and mean arterial blood pressure was noted in L-NAME mice. In MAs, higher 2-Chloro-N⁶-cyclopentyladenosine (CCPA, selective A₁AR agonist) induced contractions in hypertensive mice were observed. This enhanced contraction was inhibited by HET0016 (Cytochrome 450 4A inhibitor, 10 µM, 15 min). Contrary, 5'-(N-Ethylcarboxamido) adenosine (NECA, non-selective AR agonist) induced vascular responses were comparable in both groups. Pinacidil (K_ATP channel opener) induced relaxation was significantly increased in hypertensive mice. In aorta, CCPA-induced contractions were enhanced and inhibited by HET0016 in hypertensive mice. Notably, NECA-induced contractions in aorta were enhanced in hypertensive mice. Higher expressions of A₁AR and Cyp4A were noted in MAs of hypertensive mice. In addition, in aorta, higher A₁AR and comparable Cyp4A levels were observed in hypertensive mice. A₁AR-induced vascular contractions were enhanced in hypertensive mice aorta and MAs. Cyp4A plays a role in altered vascular responses in MAs.

Kv1.3 channels facilitate the connection between metabolism and blood flow in the heart

The connection between metabolism and flow in the heart, metabolic dilation, is essential for cardiac function. We recently found redox-sensitive Kv1.5 channels play a role in coronary metabolic dilation; however, more than one ion channel likely plays a role in this process as animals null for these channels still showed limited coronary metabolic dilation. Accordingly, we examined the role of another Kv1 family channel, the energetically linked Kv1.3 channel, in coronary metabolic dilation. We measured myocardial blood flow (contrast echocardiography) during norepinephrine-induced increases in cardiac work (heart rate x mean arterial pressure) in WT, WT mice given correolide (preferential Kv1.3 antagonist), and Kv1.3-null mice (Kv1.3-/- ). We also measured relaxation of isolated small arteries mounted in a myograph. During increased cardiac work, myocardial blood flow was attenuated in Kv1.3-/- and in correolide-treated mice. In isolated vessels from Kv1.3-/- mice, relaxation to H2 O2 was impaired (vs WT), but responses to adenosine and acetylcholine were equivalent to WT. Correolide reduced dilation to adenosine and acetylcholine in WT and Kv1.3-/- , but had no effect on H2 O2 -dependent dilation in vessels from Kv1.3-/- mice. We conclude that Kv1.3 channels participate in the connection between myocardial blood flow and cardiac metabolism.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Inosine attenuates spontaneous activity in the rat neurogenic bladder through an A2B pathway

Neurogenic detrusor overactivity (NDO) is among the most challenging complications of spinal cord injury (SCI). A recent report by us demonstrated an improvement in NDO in SCI rats following chronic systemic treatment with the purine nucleoside inosine. The objective of this study was to investigate the mechanism of action of inosine underlying improvement of NDO. Male Sprague-Dawley rats underwent complete spinal cord transection at T8. Inosine (1 mM) delivered intravesically to SCI rats during conscious cystometry significantly decreased the frequency of spontaneous non-voiding contractions. In isolated tissue assays, inosine (1 mM) significantly decreased the amplitude of spontaneous activity (SA) in SCI bladder muscle strips. This effect was prevented by a pan-adenosine receptor antagonist CGS15943, but not by A₁ or A₃ receptor antagonists. The A_2A antagonist ZM241385 and A_2B antagonist PSB603 prevented the effect of inosine. The effect of inosine was mimicked by the adenosine receptor agonist NECA and the A_2B receptor agonist BAY60-6583. The inhibition of SA by inosine was not observed in the presence of the BK antagonist, iberiotoxin, but persisted in the presence of K_ATP and SK antagonists. These findings demonstrate that inosine acts via an A_2B receptor-mediated pathway that impinges on specific potassium channel effectors.

Effect of Soluble Epoxide Hydrolase on the Modulation of Coronary Reactive Hyperemia: Role of Oxylipins and PPARγ

Coronary reactive hyperemia (CRH) is a physiological response to ischemic insult that prevents the potential harm associated with an interruption of blood supply. The relationship between the pharmacologic inhibition of soluble epoxide hydrolase (sEH) and CRH response to a brief ischemia is not known. sEH is involved in the main catabolic pathway of epoxyeicosatrienoic acids (EETs), which are converted into dihydroxyeicosatrienoic acids (DHETs). EETs protect against ischemia/reperfusion injury and have numerous beneficial physiological effects. We hypothesized that inhibition of sEH by t-AUCB enhances CRH in isolated mouse hearts through changing the oxylipin profiles, including an increase in EETs/DHETs ratio. Compared to controls, t-AUCB-treated mice had increased CRH, including repayment volume (RV), repayment duration, and repayment/debt ratio (p < 0.05). Treatment with t-AUCB significantly changed oxylipin profiles, including an increase in EET/DHET ratio, increase in EpOME/DiHOME ratio, increase in the levels of HODEs, decrease in the levels of mid-chain HETEs, and decrease in prostanoids (p < 0.05). Treatment with MS-PPOH (CYP epoxygenase inhibitor) reduced CRH, including RV (p < 0.05). Involvement of PPARγ in the modulation of CRH was demonstrated using a PPARγ-antagonist (T0070907) and a PPARγ-agonist (rosiglitazone). T0070907 reduced CRH (p < 0.05), whereas rosiglitazone enhanced CRH (p < 0.05) in isolated mouse hearts compared to the non-treated. These data demonstrate that sEH inhibition enhances, whereas CYP epoxygenases-inhibition attenuates CRH, PPARγ mediate CRH downstream of the CYP epoxygenases-EET pathway, and the changes in oxylipin profiles associated with sEH-inhibition collectively contributed to the enhanced CRH.

Potassium Channels in Regulation of Vascular Smooth Muscle Contraction and Growth

Potassium channels importantly contribute to the regulation of vascular smooth muscle (VSM) contraction and growth. They are the dominant ion conductance of the VSM cell membrane and importantly determine and regulate membrane potential. Membrane potential, in turn, regulates the open-state probability of voltage-gated Ca²⁺ channels (VGCC), Ca²⁺ influx through VGCC, intracellular Ca²⁺, and VSM contraction. Membrane potential also affects release of Ca²⁺ from internal stores and the Ca²⁺ sensitivity of the contractile machinery such that K⁺ channels participate in all aspects of regulation of VSM contraction. Potassium channels also regulate proliferation of VSM cells through membrane potential-dependent and membrane potential-independent mechanisms. VSM cells express multiple isoforms of at least five classes of K⁺ channels that contribute to the regulation of contraction and cell proliferation (growth). This review will examine the structure, expression, and function of large conductance, Ca²⁺-activated K⁺ (BK_Ca) channels, intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channels, multiple isoforms of voltage-gated K⁺ (K_V) channels, ATP-sensitive K⁺ (K_ATP) channels, and inward-rectifier K⁺ (K_IR) channels in both contractile and proliferating VSM cells.

Deletion of soluble epoxide hydrolase enhances coronary reactive hyperemia in isolated mouse heart: role of oxylipins and PPARγ

The relationship between soluble epoxide hydrolase (sEH) and coronary reactive hyperemia (CRH) response to a brief ischemic insult is not known. Epoxyeicosatrienoic acids (EETs) exert cardioprotective effects in ischemia/reperfusion injury. sEH converts EETs into dihydroxyeicosatrienoic-acids (DHETs). Therefore, we hypothesized that knocking out sEH enhances CRH through modulation of oxylipin profiles, including an increase in EET/DHET ratio. Compared with sEH^+/+, sEH^-/- mice showed enhanced CRH, including greater repayment volume (RV; 28% higher, P < 0.001) and repayment/debt ratio (32% higher, P < 0.001). Oxylipins from the heart perfusates were analyzed by LC-MS/MS. The 14,15-EET/14,15-DHET ratio was 3.7-fold higher at baseline (P < 0.001) and 5.6-fold higher post-ischemia (P < 0.001) in sEH^-/- compared with sEH^+/+ mice. Likewise, the baseline 9,10- and 12,13-EpOME/DiHOME ratios were 3.2-fold (P < 0.01) and 3.7-fold (P < 0.001) higher, respectively in sEH^-/- compared with sEH^+/+ mice. 13-HODE was also significantly increased at baseline by 71% (P < 0.01) in sEH^-/- vs. sEH^+/+ mice. Levels of 5-, 11-, 12-, and 15-hydroxyeicosatetraenoic acids were not significantly different between the two strains (P > 0.05), but were decreased postischemia in both groups (P = 0.02, P = 0.04, P = 0.05, P = 0.03, respectively). Modulation of CRH by peroxisome proliferator-activated receptor gamma (PPARγ) was demonstrated using a PPARγ-antagonist (T0070907), which reduced repayment volume by 25% in sEH^+/+ (P < 0.001) and 33% in sEH^-/- mice (P < 0.01), and a PPARγ-agonist (rosiglitazone), which increased repayment volume by 37% in both sEH^+/+ (P = 0.04) and sEH^-/- mice (P = 0.04). l-NAME attenuated CRH in both sEH^-/- and sEH^+/+ These data demonstrate that genetic deletion of sEH resulted in an altered oxylipin profile, which may have led to an enhanced CRH response.

Sex Difference in Coronary Endothelial Dysfunction in Apolipoprotein E Knockout Mouse: Role of NO and A2A Adenosine Receptor

OBJECTIVE

Sex plays an important role in the pathophysiology of cardiovascular diseases. This study aims to investigate how sex impacts on the coronary flow regulation during atherosclerosis.

METHODS

ApoE KO mouse fed with western diet were used for atherosclerosis model. Coronary RH and flow response were measured using Langendorff-perfused isolated hearts.

RESULTS

Coronary RH and A23187-induced NO-dependent flow increases were significantly reduced in female (by ~28% and 48%, respectively), but not in male atherosclerotic mice. However, SNP-induced coronary vasodilation remains intact in both sexes of ApoE KO mice. L-NAME (NOS inhibitor) reduced baseline flow and RH to a lesser extent in ApoE KO (by ~19% and 31%) vs. WT (~30% and 59%, respectively), and abolished the sex difference in RH. In contrast, SCH58261 (a selective A2A AR antagonist) reduced the baseline flow and RH to a greater extent in atherosclerotic mice, but did not affect the sex difference. Immunofluorescent staining of coronary arteries showed a similar A2A AR upregulation in both sexes of ApoE KO mice.

CONCLUSIONS

Our results suggest that during atherosclerosis, female mice are more susceptible to NO-dependent endothelial dysfunction and the upregulation of A2A AR may serve as a compensatory mechanism to counteract the compromised endothelial function.

Adenosine relaxation in isolated rat aortic rings and possible roles of smooth muscle Kv channels, KATP channels and A2a receptors

BACKGROUND

An area of ongoing controversy is the role adenosine to regulate vascular tone in conduit vessels that regulate compliance, and the role of nitric oxide (NO), potassium channels and receptor subtypes involved. The aim of our study was to investigate adenosine relaxation in rat thoracic aortic rings, and the effect of inhibitors of NO, prostanoids, Kv, KATP channels, and A2a and A2b receptors.

METHODS

Aortic rings were freshly harvested from adult male Sprague Dawley rats and equilibrated in an organ bath containing oxygenated, modified Krebs-Henseleit solution, 11 mM glucose, pH 7.4, 37 °C. Isolated rings were pre-contracted sub-maximally with 0.3 μM norepinephrine (NE), and the effect of increasing concentrations of adenosine (1 to 1000 μM) were examined. The drugs L-NAME, indomethacin, 4-aminopyridine (4-AP), glibenclamide, 5-hydroxydecanoate, ouabain, 8-(3-chlorostyryl) caffeine and PSB-0788 were examined in intact and denuded rings. Rings were tested for viability after each experiment.

RESULTS

Adenosine induced a dose-dependent, triphasic relaxation response, and the mechanical removal of the endothelium significantly deceased adenosine relaxation above 10 μM. Interestingly, endothelial removal significantly decreased the responsiveness (defined as % relaxation per μM adenosine) by two-thirds between 10 and 100 μM, but not in the lower (1-10 μM) or higher (>100 μM) ranges. In intact rings, L-NAME significantly reduced relaxation, but not indomethacin. Antagonists of voltage-dependent Kv (4-AP), sarcolemma KATP (glibenclamide) and mitochondrial KATP channels (5-HD) led to significant reductions in relaxation in both intact and denuded rings, with ouabain having little or no effect. Adenosine-induced relaxation appeared to involve the A2a receptor, but not the A2b subtype.

CONCLUSIONS

It was concluded that adenosine relaxation in NE-precontracted rat aortic rings was triphasic and endothelium-dependent above 10 μM, and relaxation involved endothelial nitric oxide (not prostanoids) and a complex interplay between smooth muscle A2a subtype and voltage-dependent Kv, SarcKATP and MitoKATP channels. The possible in vivo significance of the regulation of arterial compliance to left ventricular function coupling is discussed.

Enhanced A2A adenosine receptor-mediated increase in coronary flow in type I diabetic mice

Adenosine A2A receptor (A2AAR) activation plays a major role in the regulation of coronary flow (CF). Recent studies from our laboratory and others have suggested that A2AAR expression and/or signaling is altered in disease conditions. However, the coronary response to AR activation, in particular A2AAR, in diabetes is not fully understood. In this study, we use an STZ mouse model of type 1 diabetes (T1D) to look at CF responses to the nonspecific AR agonist NECA and the A2AAR specific agonist CGS 21680 in-vivo and ex-vivo. Using immunofluorescence, we also explored the effect of diabetes on A2AAR expression in coronary arteries. NECA mediated increase in CF was significantly increased in hearts isolated from STZ-induced diabetic mice. In addition, both in in-vivo and ex-vivo responses to A2AAR activation using CGS 21680 were significantly higher in diabetic mice when compared to their controls. Immunohistochemistry showed an upregulation of A2AAR in both coronary smooth muscle and endothelial cells (~160% and ~140%, respectively). Our data suggest that diabetes resulted in an increased A2AAR expression in coronary arteries which resulted in enhanced A2AAR-mediated increase in CF observed in diabetic hearts. This is the first report implying that A2AAR has a role in the regulation of CF in diabetes, supporting recent studies suggesting that the use of adenosine and its A2A selective agonist (regadenoson, Lexiscan®) may not be appropriate for the detection of coronary artery diseases in T1D and the estimation of coronary reserve.

Angiotensin II stimulation alters vasomotor response to adenosine in mouse mesenteric artery: role for A1 and A2B adenosine receptors

BACKGROUND AND PURPOSE

Stimulation of the A1 adenosine receptor and angiotensin II receptor type-1 (AT1 receptor) causes vasoconstriction through activation of cytochrome P450 4A (CYP4A) and ERK1/2. Thus, we hypothesized that acute angiotensin II activation alters the vasomotor response induced by the non-selective adenosine receptor agonist, NECA, in mouse mesenteric arteries (MAs).

EXPERIMENTAL APPROACH

We used a Danish Myo Technology wire myograph to measure muscle tension in isolated MAs from wild type (WT), A1 receptor and A2B receptor knockout (KO) mice. Western blots were performed to determine the expression of AT1 receptors and CYP4A.

KEY RESULTS

Acute exposure (15 min) to angiotensin II attenuated the NECA-dependent vasodilatation and enhanced vasoconstriction. This vasoconstrictor effect of angiotensin II in NECA-treated MAs was abolished in A1 receptor KO mice and in WT mice treated with the A1 receptor antagonist DPCPX, CYP4A inhibitor HET0016 and ERK1/2 inhibitor PD98059. In MAs from A2B receptor KO mice, the vasoconstrictor effect of angiotensin II on the NECA-induced response was shown to be dependent on A1 receptors. Furthermore, in A2B receptor KO mice, the expression of AT1 receptors and CYP4A was increased and the angiotensin II-induced vasoconstriction enhanced. In addition, inhibition of KATP channels with glibenclamide significantly reduced NECA-induced vasodilatation in WT mice.

CONCLUSIONS AND IMPLICATIONS

Acute angiotensin II stimulation enhanced A1 receptor-dependent vasoconstriction and inhibited A2B receptor-dependent vasodilatation, leading to a net vasoconstriction and altered vasomotor response to NECA in MAs. This interaction may be important in the regulation of BP.

Metabolic hyperemia requires ATP-sensitive K+ channels and H2O2 but not adenosine in isolated mouse hearts

We have previously demonstrated that adenosine-mediated H2O2 production and opening of ATP-sensitive K(+) (KATP) channels contributes to coronary reactive hyperemia. The present study aimed to investigate the roles of adenosine, H2O2, and KATP channels in coronary metabolic hyperemia (MH). Experiments were conducted on isolated Langendorff-perfused mouse hearts using combined pharmacological approaches with adenosine receptor (AR) knockout mice. MH was induced by electrical pacing at graded frequencies. Coronary flow increased linearly from 14.4 ± 1.2 to 20.6 ± 1.2 ml·min(-1)·g(-1) with an increase in heart rate from 400 to 650 beats/min in wild-type mice. Neither non-selective blockade of ARs by 8-(p-sulfophenyl)theophylline (8-SPT; 50 μM) nor selective A2AAR blockade by SCH-58261 (1 μM) or deletion affected MH, although resting flow and left ventricular developed pressure were reduced. Combined A2AAR and A2BAR blockade or deletion showed similar effects as 8-SPT. Inhibition of nitric oxide synthesis by N-nitro-l-arginine methyl ester (100 μM) or combined 8-SPT administration failed to reduce MH, although resting flows were reduced (by ∼20%). However, glibenclamide (KATP channel blocker, 5 μM) decreased not only resting flow (by ∼45%) and left ventricular developed pressure (by ∼36%) but also markedly reduced MH by ∼94%, resulting in cardiac contractile dysfunction. Scavenging of H2O2 by catalase (2,500 U/min) also decreased resting flow (by ∼16%) and MH (by ∼24%) but to a lesser extent than glibenclamide. Our results suggest that while adenosine modulates coronary flow under both resting and ischemic conditions, it is not required for MH. However, H2O2 and KATP channels are important local control mechanisms responsible for both coronary ischemic and metabolic vasodilation.

Adenosine-induced coronary vasospasm following drug-eluting stent implantation

We present the case of coronary vasospasm during adenosine stress in a patient with a prior drug-eluting stent implantation. The patient had a stent implantation in the left anterior descending coronary artery 3 years ago. Recently, he developed a chest pain and underwent adenosine stress myocardial perfusion single photon emission CT (SPECT). During the adenosine stress, he felt severe chest pain and ST elevation on electrocardiogram. An invasive coronary angiography showed no in-stent restenosis. This phenomenon deemed to be adenosine-induced coronary vasospasm after stent implantation.

A1 adenosine receptor negatively modulates coronary reactive hyperemia via counteracting A2A-mediated H2O2 production and KATP opening in isolated mouse hearts

We previously demonstrated that A2A, but not A2B, adenosine receptors (ARs) mediate coronary reactive hyperemia (RH), possibly by producing H2O2 and, subsequently, opening ATP-dependent K(+) (KATP) channels in coronary smooth muscle cells. In this study, A1 AR knockout (KO), A3 AR KO, and A1 and A3 AR double-KO (A1/A3 DKO) mice were used to investigate the roles and mechanisms of A1 and A3 ARs in modulation of coronary RH. Coronary flow of isolated hearts was measured using the Langendorff system. A1 KO and A1/A3 DKO, but not A3 KO, mice showed a higher flow debt repayment [~30% more than wild-type (WT) mice, P < 0.05] following a 15-s occlusion. SCH-58261 (a selective A2A AR antagonist, 1 μM) eliminated the augmented RH, suggesting the involvement of enhanced A2A AR-mediated signaling in A1 KO mice. In isolated coronary arteries, immunohistochemistry showed an upregulation of A2A AR (1.6 ± 0.2 times that of WT mice, P < 0.05) and a higher magnitude of adenosine-induced H2O2 production in A1 KO mice (1.8 ± 0.3 times that of WT mice, P < 0.05), which was blocked by SCH-58261. Catalase (2,500 U/ml) and glibenclamide (a KATP channel blocker, 5 μM), but not N(G)-nitro-l-arginine methyl ester, also abolished the enhanced RH in A1 KO mice. Our data suggest that A1, but not A3, AR counteracts the A2A AR-mediated CF increase and that deletion of A1 AR results in upregulation of A2A AR and/or removal of the negative modulatory effect of A1 AR, thus leading to an enhanced A2A AR-mediated H2O2 production, KATP channel opening, and coronary vasodilation during RH. This is the first report implying that A1 AR has a role in coronary RH.

Evidence for the involvement of NADPH oxidase in adenosine receptors-mediated control of coronary flow using A1 and A3 knockout mice

The NADPH oxidase (Nox) subunits 1, 2 (gp91 phox) and 4 are the major sources for reactive oxygen species (ROS) in cardiovascular system. In conditions such as ischemia-reperfusion injury and hypoxia, both ROS and adenosine are released suggesting a possible interaction. We hypothesized that ROS generated through Nox is involved in adenosine-induced coronary flow (CF) responses. Adenosine (10^-8-10^-5.5 M) increased CF in isolated hearts from wild type (WT; C57/BL6), A₁ adenosine receptor (AR) knockout (A₁KO), A₃AR KO (A₃KO) and A₁ and A₃AR double KO (A₁/A₃DKO) mice. The Nox inhibitors apocynin (10^-5 M) and gp91 ds-tat (10^-6 M) or the SOD and catalase-mimicking agent EUK134 (50 μM) decreased the adenosine-enhanced CF in the WT and all the KOs. Additionally, adenosine increased phosphorylation of p47-phox subunit and ERK 1/2 without changing protein expression of Nox isoforms in WT. Moreover, intracellular superoxide production was increased by adenosine and CGS-21680 (a selective A_2A agonist), but not BAY 60-6583 (a selective A_2B agonist), in mouse coronary artery smooth muscle cells (CASMCs) and endothelial cells (CAECs). This superoxide increase was inhibited by the gp91 ds-tat and ERK 1/2 inhibitor (PD98059). In conclusion, adenosine-induced increase in CF in isolated heart involves Nox2-generated superoxide, possibly through ERK 1/2 phosphorylation with subsequent p47-phox subunit phosphorylation. This adenosine/Nox/ROS interaction occurs in both CASMCs and CAECs, and involves neither A₁ nor A₃ ARs, but possibly A_2A ARs in mouse.

Adenosine A1 receptor signaling inhibits BK channels through a PKCα-dependent mechanism in mouse aortic smooth muscle

Adenosine receptors (AR; A₁, A_2A, A_2B, and A₃) contract and relax smooth muscle through different signaling mechanisms. Deciphering these complex responses remains difficult because relationships between AR subtypes and various end-effectors (e.g., enzymes and ion channels) remain to be identified. A₁AR stimulation is associated with the production of 20–hydroxyeicosatetraenoic acid (20–HETE) and activation of protein kinase C (PKC). 20–HETE and PKC can inhibit large conductance Ca²⁺/voltage-sensitive K⁺ (BK) channels that regulate smooth muscle contraction. We tested the hypothesis that activation of A₁AR inhibits BK channels via a PKC-dependent mechanism. Patch clamp recordings and Western blots were performed using aortae of wild type (WT) and A₁AR knockout (A₁KO) mice. There were no differences in whole-cell K⁺ current or α and β1 subunits expression between WT and A₁KO. 20–HETE (100 nmol/L) inhibited BK current similarly in WT and A₁KO mice. NECA (5′–N–ethylcarboxamidoadenosine; 10 μmol/L), a nonselective AR agonist, increased BK current in myocytes from both WT and A₁KO mice, but the increase was greater in A₁KO (52 ± 15 vs. 17 ± 3%; P < 0.05). This suggests that A₁AR signaling negatively regulates BK channel activity. Accordingly, CCPA (2–chloro–N(6)-cyclopentyladenosine; 100 nmol/L), an A₁AR-selective agonist, inhibited BK current in myocytes from WT but not A₁KO mice (81 ± 4 vs. 100 ± 7% of control; P < 0.05). Gö6976 (100 nmol/L), a PKCα inhibitor, abolished the effect of CCPA to inhibit BK current (99 ± 3% of control). These data lead us to conclude that, in aortic smooth muscle, A₁AR inhibits BK channel activity and that this occurs via a mechanism involving PKCα.