CYP-epoxygenases contribute to A2A receptor-mediated aortic relaxation via sarcolemmal KATP channels

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.

Cyp2j5-Gene Deletion Affects on Acetylcholine and Adenosine-Induced Relaxation in Mice: Role of Angiotensin-II and CYP-Epoxygenase Inhibitor

Previously, we showed vascular endothelial overexpression of human-CYP2J2 enhances coronary reactive hyperemia in Tie2-CYP2J2 Tr mice, and eNOS^−/− mice had overexpression of CYP2J-epoxygenase with adenosine A_2A receptor-induced enhance relaxation, but we did not see the response in CYP2J-epoxygenase knockout mice. Therefore, we hypothesized that Cyp2j5-gene deletion affects acetylcholine- and 5'-N-ethylcarboxamidoadenosine (NECA) (adenosine)-induced relaxation and their response is partially inhibited by angiotensin-II (Ang-II) in mice. Acetylcholine (Ach)-induced response was tested with N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide (MS-PPOH, CYP-epoxygenase inhibitor; 10⁻⁵M) and Ang-II (10⁻⁶M). In Cyp2j5^−/− mice, ACh-induced relaxation was different from C57Bl/6 mice, at 10⁻⁵ M (76.1 ± 3.3 vs. 58.3 ± 5.2, P < 0.05). However, ACh-induced relaxation was not blocked by MS-PPOH in Cyp2j5^−/−: 58.5 ± 5.0%, P > 0.05, but blocked in C57Bl/6: 52.3 ± 7.5%, P < 0.05, and Ang-II reduces ACh-induced relaxation in both Cyp2j5^−/− and C57Bl/6 mice (38.8 ± 3.9% and 45.9 ± 7.8, P <0.05). In addition, NECA-induced response was tested with Ang-II. In Cyp2j5^−/− mice, NECA-induced response was not different from C57Bl/6 mice at 10⁻⁵M (23.1 ± 2.1 vs. 21.1 ± 3.8, P > 0.05). However, NECA-induced response was reduced by Ang-II in both Cyp2j5^−/− and C57Bl/6 mice (−10.8 ± 2.3% and 3.2 ± 2.7, P < 0.05). Data suggest that ACh-induced relaxation in Cyp2j5^−/− mice depends on nitric oxide (NO) but not CYP-epoxygenases, and the NECA-induced different response in male vs. female Cyp2j5^−/− mice when Ang-II treated.

Ephx2-gene deletion affects acetylcholine-induced relaxation in angiotensin-II infused mice: role of nitric oxide and CYP-epoxygenases

Previously, we showed that adenosine A_2A receptor induces relaxation independent of NO in soluble epoxide hydrolase-null mice (Nayeem et al. in Am J Physiol Regul Integr Comp Physiol 304:R23-R32, 2013). Currently, we hypothesize that Ephx2-gene deletion affects acetylcholine (Ach)-induced relaxation which is independent of A_2AAR but dependent on NO and CYP-epoxygenases. Ephx2^-/- aortas showed a lack of sEH (97.1%, P < 0.05) but an increase in microsomal epoxide hydrolase (mEH, 37%, P < 0.05) proteins compared to C57Bl/6 mice, and no change in CYP2C29 and CYP2J protein (P > 0.05). Ach-induced response was tested with nitro-L-arginine methyl ester (L-NAME) NO-inhibitor; 10^-4 M), N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide (MS-PPOH) (CYP-epoxygenase inhibitor; 10^-5 M), 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, an epoxyeicosatrienoic acid-antagonist; 10^-5 M), SCH-58261 (A_2AAR-antagonist; 10^-6 M), and angiotensin-II (Ang-II, 10^-6 M). In Ephx2^-/- mice, Ach-induced relaxation was not different from C57Bl/6 mice except at 10^-5 M (92.75 ± 2.41 vs. 76.12 ± 3.34, P < 0.05). However, Ach-induced relaxation was inhibited with L-NAME (Ephx2^-/-: 23.74 ± 3.76% and C57Bl/6: 11.61 ± 2.82%), MS-PPOH (Ephx2^-/-: 48.16 ± 6.53% and C57Bl/6: 52.27 ± 7.47%), and 14,15-EEZE (Ephx2^-/-: 44.29 ± 8.33% and C57Bl/6: 39.27 ± 7.47%) vs. non-treated (P < 0.05). But, it did not block with SCH-58261 (Ephx2^-/-: 68.75 ± 11.41% and C57Bl/6: 66.26 ± 9.43%, P > 0.05) vs. non-treated (P > 0.05). Interestingly, Ang-II attenuates less relaxation in Ehx2^-/- vs. C57Bl/6 mice (58.80 ± 7.81% vs. 45.92 ± 7.76, P < 0.05). Our data suggest that Ach-induced relaxation in Ephx2^-/- mice depends on NO and CYP-epoxygenases but not on A_2A AR, and Ephx2-gene deletion attenuates less Ach-induced relaxation in Ang-II-infused mice.

Adenosine and the Cardiovascular System

Adenosine is an endogenous nucleoside with a short half-life that regulates many physiological functions involving the heart and cardiovascular system. Among the cardioprotective properties of adenosine are its ability to improve cholesterol homeostasis, impact platelet aggregation and inhibit the inflammatory response. Through modulation of forward and reverse cholesterol transport pathways, adenosine can improve cholesterol balance and thereby protect macrophages from lipid overload and foam cell transformation. The function of adenosine is controlled through four G-protein coupled receptors: A₁, A_2A, A_2B and A₃. Of these four, it is the A_2A receptor that is in a large part responsible for the anti-inflammatory effects of adenosine as well as defense against excess cholesterol accumulation. A_2A receptor agonists are the focus of efforts by the pharmaceutical industry to develop new cardiovascular therapies, and pharmacological actions of the atheroprotective and anti-inflammatory drug methotrexate are mediated via release of adenosine and activation of the A_2A receptor. Also relevant are anti-platelet agents that decrease platelet activation and adhesion and reduce thrombotic occlusion of atherosclerotic arteries by antagonizing adenosine diphosphate-mediated effects on the P2Y12 receptor. The purpose of this review is to discuss the effects of adenosine on cell types found in the arterial wall that are involved in atherosclerosis, to describe use of adenosine and its receptor ligands to limit excess cholesterol accumulation and to explore clinically applied anti-platelet effects. Its impact on electrophysiology and use as a clinical treatment for myocardial preservation during infarct will also be covered. Results of cell culture studies, animal experiments and human clinical trials are presented. Finally, we highlight future directions of research in the application of adenosine as an approach to improving outcomes in persons with cardiovascular disease.

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.

Role of oxylipins in cardiovascular diseases

Globally, cardiovascular diseases (CVDs) are the number one cause of mortality. Approximately 18 million people died from CVDs in 2015, representing more than 30% of all global deaths. New diagnostic tools and therapies are eagerly required to decrease the prevalence of CVDs related to mortality and/or risk factors leading to CVDs. Oxylipins are a group of metabolites, generated via oxygenation of polyunsaturated fatty acids that are involved in inflammation, immunity, and vascular functions, etc. Thus far, over 100 oxylipins have been identified, and have overlapping and interconnected roles. Important CVD pathologies such as hyperlipidemia, hypertension, thrombosis, hemostasis and diabetes have been linked to abnormal oxylipin signaling. Oxylipins represent a new era of risk markers and/or therapeutic targets in several diseases including CVDs. The role of many oxylipins in the progression or regression in CVD, however, is still not fully understood. An increased knowledge of the role of these oxygenated polyunsaturated fatty acids in cardiovascular dysfunctions or CVDs including hypertension could possibly lead to the development of biomarkers for the detection and their treatment in the future.

The Role of Adenosine A2A Receptor, CYP450s, and PPARs in the Regulation of Vascular Tone

Adenosine is an endogenous mediator involved in a myriad of physiologic functions, including vascular tone regulation. It is also implicated in some pathologic conditions. Four distinct receptor subtypes mediate the effects of adenosine, such as its role in the regulation of the vascular tone. Vascular tone regulation is a complex and continuous process which involves many mechanisms and mediators that are not fully disclosed. The vascular endothelium plays a pivotal role in regulating blood flow to and from all body organs. Also, the vascular endothelium is not merely a physical barrier; it is a complex tissue with numerous functions. Among adenosine receptors, A2A receptor subtype (A2AAR) stands out as the primary receptor responsible for the vasodilatory effects of adenosine. This review focuses on important effectors of the vascular endothelium, including adenosine, adenosine receptors, EETs (epoxyeicosatrienoic acids), HETEs (hydroxyeicosatetraenoic acids), PPARs (peroxisome proliferator-activated receptors), and KATP channels. Given the impact of vascular tone regulation in cardiovascular physiology and pathophysiology, better understanding of the mechanisms affecting it could have a significant potential for developing therapeutic agents for cardiovascular diseases.

Exploring Adenosine Receptor Ligands: Potential Role in the Treatment of Cardiovascular Diseases

Cardiovascular diseases remain the number one diseases affecting patients’ morbidity and mortality. The adenosine receptors are G-protein coupled receptors which have been of interest for drugs target for the treatment of multiple diseases ranging from cardiovascular to neurological. Adenosine receptors have been connected to several biological pathways affecting the physiology and pathology of the cardiovascular system. In this review, we will cover the different adenosine receptor ligands that have been identified to interact with adenosine receptors and affect the vascular system. These ligands will be evaluated from clinical as well as medicinal chemistry perspectives with more emphasis on how structural changes in structure translate into ligand potency and efficacy. Adenosine receptors represent a novel therapeutic target for development of treatment options treating a wide variety of diseases, including vascular disease and obesity.

Impaired Aortic Contractility to Uridine Adenosine Tetraphosphate in Angiotensin II-Induced Hypertensive Mice: Receptor Desensitization?

OBJECTIVE

We previously showed that uridine adenosine tetraphosphate (Up4A)-mediated aortic contraction is partly mediated through purinergic P2X1 receptors (P2X1R). It has been reported that the plasma level of Up4A is elevated in hypertensive patients, implying a potential role for Up4A-P2X1R signaling in hypertension. This study investigated the vasoactive effect of Up4A in aortas isolated from angiotensin (Ang) II-infused (21 days) hypertensive mice.

METHODS

Blood pressure was measured by tail cuff plethysmography. Aortas were isolated for isometric tension measurements, and protein expression was analyzed by western blot.

RESULTS

Mean and systolic arterial pressures were elevated by ~50% in Ang II-infused mice. Protein levels of both AT1R and P2X1R were upregulated in Ang II-infused aortas. Surprisingly, Up4A (10-9-10-5 M)-induced concentration-dependent contraction was significantly impaired in Ang II-infused mice. Studies in control mice revealed that both P2X1R (MRS2159) and AT1R (losartan) antagonists significantly attenuated Up4A-induced aortic contraction. In addition, desensitization of AT1R by prior Ang II (100 nM) exposure had no effect on Up4A-induced aortic contraction. However, subsequent serial exposure responses to Up4A-induced aortic contraction were markedly reduced, suggesting a desensitization of purinergic receptors. This desensitization was further confirmed in control mice by prior exposure of aortas to the P2X1R desensitizer α, β-methylene ATP (10 μM).

CONCLUSION

Despite upregulation of AT1R and P2X1R in hypertension, Up4A-mediated aortic contraction was impaired in Ang II-infused mice, likely through the desensitization of P2X1R but not AT1R. This implies that vascular P2X1R activity, rather than plasma Up4A level, may determine the role of Up4A in hypertension.

Drug Delivery and Nanoformulations for the Cardiovascular System

Therapeutic delivery to the cardiovascular system may play an important role in the successful treatment of a variety of disease state, including atherosclerosis, ischemic-reperfusion injury and other types of microvascular diseases including hypertension. In this review we evaluate the different options available for the development of suitable delivery systems that include the delivery of small organic compounds [adenosin A_2A receptor agonist (CGS 21680), CYP-epoxygenases inhibitor (N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide, trans-4-[4-(3-adamantan-1-ylureido)cyclohexyloxy] benzoic acid), soluble epoxide hydrolase inhibitor (N-methylsulfonyl-12,12-dibromododec-11-enamide), PPARγ agonist (rosiglitazone) and PPARγ antagonist (T0070907)], nanoparticles, peptides, and siRNA to the cardiovascular system. Effective formulations of nanoproducts have significant potential to overcome physiological barriers and improve therapeutic outcomes in patients. As per the literature covering targeted delivery to the cardiovascular system, we found that this area is still at infancy stage, as compare to the more mature fields of tumor cancer or brain delivery (e.g. blood-brain barrier permeability) with fewer publications focused on the targeted drug delivery technologies. Additionally, we show how pharmacology needs to be well understood when considering the cardiovascular system. Therefore, we discussed in this review various receptors agonists, antagonists, activators and inhibitors which will have effects on cardiovascular system.

Vascular endothelial over-expression of soluble epoxide hydrolase (Tie2-sEH) enhances adenosine A1 receptor-dependent contraction in mouse mesenteric arteries: role of ATP-sensitive K+ channels

Soluble epoxide hydrolase (sEH) converts epoxyeicosatrienoic acids that are endothelium-derived hyperpolarizing factors into less active dihydroxyeicosatrienoic acids. Previously, we reported a decrease in adenosine A₁ receptor (A₁AR) protein levels in sEH knockout (sEH^-/-) and an increase in sEH and A₁AR protein levels in A_2AAR^-/- mice. Additionally, K_ATP channels are involved in adenosine receptor (AR)-dependent vascular relaxation. Thus, we hypothesize that a potential relationship may exist among sEH over-expression, A₁AR upregulation, inactivation of K_ATP channels, and increased in vascular tone. We performed DMT myograph muscle tension measurements and western blot analysis in isolated mouse mesenteric arteries (MAs) from wild-type (WT) and endothelial over-expression of sEH (Tie2-sEH Tr) mice. Our data revealed that NECA (a non-selective adenosine receptors agonist)-induced relaxation was significantly reduced in Tie2-sEH Tr mice, and CCPA (A₁AR agonist)-induced contraction was increased in Tie2-sEH Tr mice. A₁AR-dependent contraction in Tie2-sEH Tr mice was significantly attenuated by pharmacological inhibition of CYP4A (HET0016, 10 µM), PKCα (GO6976, 1 µM), and ERK1/2 (PD58059, 1 µM). Our western blot analysis revealed significantly higher basal protein expression of CYP4A, A₁AR, and reduced p-ERK in MAs of Tie2-sEH Tr mice. Notably, pinacidil (K_ATP channel opener)-induced relaxation was also significantly reduced in MAs of Tie2-sEH Tr mice. Furthermore, K_ATP channel-dependent relaxation in MAs was enhanced by inhibition of PKCα and ERK1/2 in WT but not Tie2-sEH Tr mice. In conclusion, our data suggest that over-expression of sEH enhances A₁AR-dependent contraction and reduces K_ATP channel-dependent relaxation in MAs. These results suggest a possible interaction between sEH, A₁AR, and K_ATP channels in regulating vascular tone.

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.

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.

High salt diet modulates vascular response in A2AAR (+/+) and A 2AAR (-/-) mice: role of sEH, PPARγ, and K ATP channels

This study aims to investigate the signaling mechanism involved in HS-induced modulation of adenosine-mediated vascular tone in the presence or absence of adenosine A2A receptor (A2AAR). We hypothesized that HS-induced enhanced vascular relaxation through A2AAR and epoxyeicosatrienoic acid (EETs) is dependent on peroxisome proliferator-activated receptor gamma (PPARγ) and ATP-sensitive potassium channels (KATP channels) in A2AAR(+/+) mice, while HS-induced vascular contraction to adenosine is dependent on soluble epoxide hydrolase (sEH) that degrades EETs in A2AAR(-/-) mice. Organ bath and Western blot techniques were conducted in HS (4 % NaCl) and normal salt (NS, 0.45 % NaCl)-fed A2AAR(+/+) and A2AAR(-/-) mouse aorta. We found that enhanced vasodilation to A2AAR agonist, CGS 21680, in HS-fed A2AAR(+/+) mice was blocked by PPARγ antagonist (T0070907) and KATP channel blocker (Glibenclamide). Also, sEH inhibitor (AUDA)-dependent vascular relaxation was mitigated by PPARγ antagonist. PPARγ agonist (Rosiglitazone)-induced relaxation in HS-A2AAR(+/+) mice was attenuated by KATP channel blocker. Conversely, HS-induced contraction in A2AAR(-/-) mice was attenuated by sEH inhibitor. Overall, findings from this study that implicates the contribution of EETs, PPARγ and KATP channels downstream of A2AAR to mediate enhanced vascular relaxation in response to HS diet while, role of sEH in mediating vascular contraction in HS-fed A2AAR(-/-) mice.

Melanopsin mediates light-dependent relaxation in blood vessels

Melanopsin (opsin4; Opn4), a non-image-forming opsin, has been linked to a number of behavioral responses to light, including circadian photo-entrainment, light suppression of activity in nocturnal animals, and alertness in diurnal animals. We report a physiological role for Opn4 in regulating blood vessel function, particularly in the context of photorelaxation. Using PCR, we demonstrate that Opn4 (a classic G protein-coupled receptor) is expressed in blood vessels. Force-tension myography demonstrates that vessels from Opn4(-/-) mice fail to display photorelaxation, which is also inhibited by an Opn4-specific small-molecule inhibitor. The vasorelaxation is wavelength-specific, with a maximal response at ∼430-460 nm. Photorelaxation does not involve endothelial-, nitric oxide-, carbon monoxide-, or cytochrome p450-derived vasoactive prostanoid signaling but is associated with vascular hyperpolarization, as shown by intracellular membrane potential measurements. Signaling is both soluble guanylyl cyclase- and phosphodiesterase 6-dependent but protein kinase G-independent. β-Adrenergic receptor kinase 1 (βARK 1 or GRK2) mediates desensitization of photorelaxation, which is greatly reduced by GRK2 inhibitors. Blue light (455 nM) regulates tail artery vasoreactivity ex vivo and tail blood blood flow in vivo, supporting a potential physiological role for this signaling system. This endogenous opsin-mediated, light-activated molecular switch for vasorelaxation might be harnessed for therapy in diseases in which altered vasoreactivity is a significant pathophysiologic contributor.

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 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.