Role of Adenosine Receptor(s) in the Control of Vascular Tone in the Mouse Pudendal Artery

Adenosine relaxes vagina smooth muscle through the cyclic guanosine monophosphate- and cyclic guanosine monophosphate-dependent pathways

BACKGROUND

In males, adenosine (ADO) is known to relax penile smooth muscles, although its role in the vagina is not yet fully elucidated.

AIM

This study investigated the effect of ADO on vagina smooth muscle activity, using a validated female Sprague-Dawley rat model.

METHODS

Contractility studies, using noradrenaline-precontracted vaginal strips, tested the effects of ADORA1/3 antagonists and ADORA2A/2B antagonists and agonists. Increasing doses of ADO were tested after in vivo or in vitro treatment with Nω-nitro-L-arginine-methyl-ester hydrochloride (L-NAME) or with guanylate or adenylate cyclase inhibitors. Immunopositivity for ADORA2A and ADORA2B was assessed, and messenger RNA (mRNA) analysis was performed. Cyclic ADO monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were quantified both in rat vagina smooth muscle cells (rvSMCs) and in vaginal tissues with increasing doses of ADO.

OUTCOMES

Demonstrating ADO's role in the relaxing/contractile mechanism in distal vagina smooth muscle.

RESULTS

All ADO receptors mRNAs were expressed in vaginal tissue, with a prevalent content of ADORA2B. A high expression of genes regulating ADO catabolism (ADK) and de novo synthesis (NT5E) was found. In vaginal strips, ADO induced relaxation with IC50 = 144.7 μM and a flat pseudo-Hill coefficient value = -0.42, indicating an activity on heterogeneous receptors. Blocking ADORA1/3 shifted ADO response to the left and with a steeper slope. ADORA2A/2B agonists showed a higher potency than ADO in inducing relaxation. Immunolocalization confirmed the presence of ADORA2A/2B in vaginal musculature, in the blood vessels endothelium, and in the epithelium. ADO stimulation of vagina tissues induced a significant increase in cAMP and cGMP contents. Experiments on rvSMCs confirmed that ADO time- and dose-dependently stimulated cAMP production in these cells. However, ADORA2A/2B antagonists, although reducing the ADO-induced relaxation, did not completely block it. A similar inhibition was obtained by blocking adenylate cyclase. Overall, these findings suggest that ADO relaxation involves other pathways, eg, nitric oxide (NO)/cGMP. Accordingly, blocking NO formation through L-NAME substantially blunted ADO responsiveness, as it does the block of cGMP formation through 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one. Simultaneous incubation with cGMP and cAMP blockers completely inhibited ADO responsiveness.

CLINICAL TRANSLATION

The study highlights ADO's role in regulating vaginal smooth muscle activity, suggesting its potential effect on the vagina.

STRENGTHS AND LIMITATIONS

This is the first study on ADO in the vagina, although the results are preliminary and limited to the rat model.

CONCLUSION

These results show that ADO acts as a vaginal relaxing modulator through selective activation of receptors involving not only cAMP but also cGMP.

Adenosine signaling: a potential therapeutic target for psychogenic erectile dysfunction

Therapeutic modalities for psychogenic erectile dysfunction (PED) are poorly targeted because of the lack of specific pathological features. The common symptoms of PED include psychological stress-related negative emotions and erectile dysfunction. Exploring their common therapeutic targets is helpful in the development of effective PED treatment strategies. Adenosine locally acts as a vasodilator or neuromodulator in the penis and promotes erection. Recent studies have demonstrated that adenosine (ADO) signaling is also involved in psychological stress. Herein, we review the pathogenesis of PED and the interaction between ADO and the erection regulator nitric oxide (NO) in brain and penile tissues. In addition, we summarize the regulatory role of ADO signal transduction in penile erection, psychological stress and negative emotions. Through our study, we found that ADO is involved in psychological stress and erectile events by combining adenosine A1 receptors (A1R) and adenosine A2A receptors (A2AR). The application of A1R selective agonists may promote erection and improve psychological state.

Short Sleep Duration and Erectile Dysfunction: A Review of the Literature

The meaning of sleep has puzzled people for millennia. In modern society, short sleep duration is becoming a global problem. It has been established that short sleep duration can increase the risk of several diseases, such as cardiovascular and metabolic diseases. Currently, a growing body of research has revealed a possible link between sleep disorders and erectile dysfunction (ED). However, the mechanisms linking short sleep duration and ED are largely unknown. Thus, we provide a review of clinical trials and animal studies. In this review, we propose putative pathways connecting short sleep duration and ED, including neuroendocrine pathways and molecular mechanisms, aiming to pave the way for future research. Meanwhile, the assessment and improvement of sleep quality should be recommended in the diagnosis and treatment of ED patients.

Rapid discovery of potentially vasodilative compounds from Uncaria by UHPLC/Q-Orbitrap-MS based metabolomics and correlation analysis

The genus Uncaria belongs to the family of Rubiaceae, which contains approximately 34 species. It has been widely used as a traditional Chinese medicine (TCM) in China to treat hypertension, fevers, headaches, gastrointestinal illness, epilepsy, wounds, and ulcers. Uncaria rhynchophylla. (Miq.) Miq. ex Hvail.(URM) and Uncaria hirsuta Havil.(UHH) are mainly used as remedies for hypertension, which both belong to the resource of "Gou-teng" in the Chinese Pharmacopoeia. However, the authentic antihypertensive components of Uncaria still have not been fully elucidated until now. In this work, we firstly explored and compared the vasorelaxation effect of URM and UHH on the isolated rat mesenteric artery ring. Then, the variations of metabolite profiles between URM and UHH samples were investigated by UHPLC/Q-Orbitrap-MS, and 16 different metabolites have been found through multivariate statistical analysis. Further, the potential vasodilative compounds which include corynoxeine, isocorynoxeine, isorhynchophylline, rhynchophylline, hirsuteine and hirsutine were screened through the correlation analysis between metabolites and anti-hypertension activities. And the relaxation effects of the six compounds on the mesenteric artery have verified. The results indicated that metabolomics combined with correlation analysis could be effective strategies to rapid explore the active compounds from TCM.

Low androgen status inhibits erectile function by up-regulating the expression of P2X receptors in rat corpus cavernosum

The aim of our study was to investigate whether low androgen level inhibits the erectile function of rats by regulating the expression of P2X receptors. Thirty-six 8-week-old male SD rats were randomly divided into six groups: sham-operated groups (4w-sham, 8w-sham), castration groups (4w-cast, 8w-cast) and androgen replacement after castration groups (4w-cast + T, 8w-cast + T). The maximum intracavernous pressure/mean arterial pressure (ICPmax/MAP), the levels of serum testosterone (T) and nitric oxide (NO), and the expression of P2X1, P2X2, P2X3, eNOS, p-eNOS, ROCK1 and ROCK2 in the cavernous tissue of rats were determined. The serum T, ICPmax/MAP and NO levels in penile corpus cavernosum in the castration groups were significantly lower than those in other groups (p < .01). The protein expression of P2X1, P2X2, P2X3, ROCK1 and ROCK2 in the castration groups was significantly higher than those in other groups (p < .01). P-eNOS/eNOS of the castration groups were significantly lower than those of other groups (p < .01). The serum T level was negatively correlated with the expression of P2X1, P2X2 and P2X3 in the corpus cavernosum. Low androgen level inhibits erectile function by up-regulating the expression of P2X1, P2X2, P2X3 and RhoA/Rho-kinase resulting in reducing the ratio of p-eNOS/eNOS and the level of NO in corpus cavernosum of rats.

Mechanisms underlying priapism in sickle cell disease: targeting and key innovations on the preclinical landscape

Introduction: Priapism is prolonged penile erection in the absence of sexual arousal or desire and is a devastating condition affecting millions of patients with sickle cell disease (SCD) globally. Available drug treatments for SCD-related priapism remain limited and have been primarily reactive rather than preventive. Hence, there is an unmet need for new drug targets and pharmacologic therapies.Areas covered: We examine the molecular mechanisms underlying SCD-associated priapism evaluated mostly in animal models. In mouse models of SCD, molecular defects of priapism operating at the cavernous tissue level include reduced tonic NO/cGMP signaling, elevated oxidative/nitrosative stress, vascular adhesion molecule derangements, excessive adenosine and opiorphin signaling, dysregulated vasoconstrictive RhoA/ROCK signaling, and testosterone deficiency. We discuss the consequences of downregulated cGMP-dependent phosphodiesterase type 5 (PDE5) activity in response to these molecular signaling derangements, as the main effector mechanism causing unrestrained cavernous tissue relaxation that results in priapism.Expert opinion: Basic science studies are crucial for understanding the underlying pathophysiology of SCD-associated priapism. Understanding the molecular mechanisms could unearth new therapeutic targets for this condition based on these mechanisms. Treatment options should aim to improve deranged erection physiology regulatory signaling to prevent priapism and potentially restore or preserve erectile function.

Dysregulation of adenosine kinase isoforms in breast cancer

Dysregulated adenosine signaling pathway has been evidenced in the pathogenesis of breast cancer. However, the role of adenosine kinase (ADK) in tumorigenesis remains unclear while it crucially regulates the removal and availability of adenosine. ADK has two isoforms that localize to discrete subcellular spaces: i.e., nuclear, long-isoform (ADK-L) and cytosolic, short-isoform (ADK-S). We hypothesized that these two ADK isoforms would be differentially expressed in breast cancer and may contribute to divergent cellular actions in cancer. In this study, we examined the expression profiles of ADK isoforms in breast cancer tissues from 46 patient and followed up with an in vitro investigation by knocking down the expression of ADK-L or ADK-S using CRISPR gene editing to evaluate the role of ADK isoform in cancer progression and metastasis of cultured triple-negative breast cancer cell line MDA-MB-231. We demonstrated that (i) ADK-L expression level was significantly increased in breast cancer tissues versus paired normal tissues adjacent to tumor, whereas the ADK-S expression levels were not significantly different between cancerous and normal tissues; (ii) CRISPR/Cas9-mediated downregulation of ADK isoforms, led to suppressed cellular proliferation, division, and migration of cultured breast cancer cells; (iii) ADK-L knockdown significantly upregulated gene expression of matrix metalloproteinase (ADAM23, 9.93-fold; MMP9, 24.58-fold) and downregulated expression of cyclin D2 (CCND2, -30.76-fold), adhesive glycoprotein THBS1 (-8.28-fold), and cystatin E/M (CST6, -16.32-fold). Our findings suggest a potential role of ADK-L in mitogenesis, tumorigenesis, and tumor-associated tissue remodeling and invasion; and the manipulation of ADK-L holds promise as a therapeutic strategy for aggressive breast cancer.

Role of CSE-Produced H2S on Cerebrovascular Relaxation via RhoA-ROCK Inhibition and Cerebral Ischemia-Reperfusion Injury in Mice

The role of CSE-produced H₂S on cerebrovascular relaxation and cerebral ischemia-reperfusion (I/R) injury was investigated using CSE knockout (CSE^-/-) and wild-type (CSE^+/+) mice. The relaxation of the cerebral basilar artery (BA) to CSE-produced H₂S and its mechanism were detected. The results revealed that both NaHS, a donor of exogenous H₂S, and ROCK inhibitor Y27632 could induce significant relaxation of the BA, but the relaxation of the BA to NaHS was significantly attenuated by Y27632. In addition, removal of endothelium could reduce the relaxation of the BA to Y27632; CSE knockout also significantly attenuated Y27632-induced BA relaxation with endothelium rather than without endothelium. By contrast, the contraction of the BA from CSE^-/- mice to RhoA agonist LPA or U₄₆₆₁₉ was stronger than that from CSE^+/+ mice. Furthermore, RhoA activity and ROCK protein expression remarkably increased in the BA vascular smooth muscle cells (VSMCs) from CSE^-/- mouse, which were inhibited by NaHS pretreatment. These findings revealed that the CSE-produced H₂S induced cerebrovascular relaxation is generated from endothelial cells and the mechanism of vascular relaxation may relate to inhibition of RhoA-ROCK pathway. We next sought to confirm the protective effect of CSE-produced H₂S on cerebral I/R injury produced by middle cerebral artery occlusion and bilateral common carotid artery occlusion in mice. We investigated the changes of neurological deficit, cerebral infarct, brain water content, LDH decrease, MDA increase as well as impairment of learning and memory function. The results showed that the cerebral injury became more grievous in CSE^-/-mice than that in CSE^+/+mice, which could be remarkably alleviated by NaHS pretreatment.

Enhanced Electrical Field Stimulated Nitrergic and Purinergic Vasoreactivity in Distal vs Proximal Internal Pudendal Arteries

BACKGROUND

The internal pudendal arteries (IPAs) supply blood to the penis and are highly susceptible to vascular remodeling in rodent models of diabetes, hypertension, aging, and chronic kidney disease, thus contributing to erectile dysfunction. Interestingly, vascular remodeling primarily occurs in the distal and not in the proximal IPA, suggesting distinct local physiologic signaling differences within the IPA.

AIM

To examine the role of purinergic signaling and neurotransmitter release by electrical field stimulation (EFS) in the regulation of proximal and distal IPA vascular tone.

METHODS

Proximal and distal IPAs were mounted in wire myographs and vascular responses to phenylephrine, acetylcholine, and 2-(N,N-diethylamino)-diazenolate-2-oxide, diethyl-ammonium salt (DEA NONOate) were measured. EFS-mediated contraction and non-adrenergic non-cholinergic (NANC) relaxation were evaluated in the absence and presence of a nitric oxide synthase antagonist. Purinergic agonist and NANC relaxation responses were assessed in the presence and absence of P2X1 and P2Y1 antagonists. Protein expression of P2X1 and P2Y1 receptors was measured by western blot.

MAIN OUTCOME MEASURES

Proximal and distal IPA contraction and relaxation were measured during increasing agonist administration and EFS in the presence and absence of antagonists.

RESULTS

Proximal and distal IPA concentration response curves to phenylephrine, acetylcholine, and DEA NONOate did no differ. Interestingly, distal IPA exhibited greater EFS-mediated contraction and NANC relaxation compared with proximal IPA. Nitric oxide synthase inhibition completely inhibited distal IPA NANC relaxation but did not affect proximal IPA relaxation. P2X1 or P2Y1 receptor antagonism during NANC relaxation increased distal IPA relaxation but decreased proximal IPA relaxation. Combined P2X1 and P2Y1 receptor antagonism had no effect on proximal IPA relaxation but significantly increased distal IPA NANC relaxation.

CLINICAL TRANSLATION

Understanding neurovascular regulation of IPA vascular tone through nitrergic and purinergic mechanisms could yield new therapeutic targets to improve IPA blood flow and treat vasculogenic erectile dysfunction.

STRENGTHS AND LIMITATIONS

This study is the first to illustrate the differences in mechanisms responsible for regulating vascular tone in the proximal and distal IPAs. All presented findings are currently limited to ex vivo vascular function.

CONCLUSION

The regulation of vascular tone differs regionally in the IPA. The distal IPA is controlled through neurotransmitter-mediated NO-dependent mechanisms and increased sensitivity to purinergic P2X1 and P2Y1 receptor inhibition. Odom MR, Pak ES, Brown DA, Hannan JL. Enhanced Electrical Field Stimulated Nitrergic and Purinergic Vasoreactivity in Distal vs Proximal Internal Pudendal Arteries. J Sex Med 2017;14:1285-1296.

Functional changes in vascular reactivity to adenosine receptor activation in type I diabetic mice

Activation of adenosine receptors has been implicated in several biological functions, including cardiovascular and renal function. Diabetes causes morphological and functional changes in the vasculature, resulting in abnormal responses to various stimuli. Recent studies have suggested that adenosine receptor expression and signaling are altered in disease states such as hypertension, diabetes. Using a streptozotocin (STZ) mouse model of type I diabetes (T1D), we investigated the functional changes in aorta and resistance mesenteric arteries to adenosine receptor agonist activation in T1D. Organ baths and DMT wire myographs were used for muscle tension measurements in isolated vascular rings, and western blotting was used for protein analysis. Concentration response curves to selective adenosine receptor agonists, including CCPA (A₁ receptor agonist), Cl-IBMECA (A₃ receptor agonist), CGS-21680 (A_2A receptor agonist), and BAY 60-6583 (A_2B receptor agonist), were performed. We found that diabetes did not affect adenosine receptor agonist-mediated relaxation or contraction in mesenteric arteries. However, aortas from diabetic mice exhibited a significant decrease (P < 0.05) in A₁ receptor-mediated vasoconstriction. In addition, the aortas from STZ-treated mice exhibited an increase in phenylephrine-mediated contraction (EC₅₀ 7.40 ± 0.08 in STZ vs 6.89 ± 0.14 in vehicle; P < 0.05), while relaxation to A_2A receptor agonists (CGS-21680) tended to decrease in aortas from the STZ-treated group (not statistically significant). Our data suggest that changes in adenosine receptor(s) vascular reactivity in T1D is tissue specific, and the decrease in A₁ receptor-mediated aortic contraction could be a compensatory mechanism to counterbalance the increased adrenergic vascular contractility observed in aortas from diabetic mice.

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.