Nitric oxide synthase/K+ channel cascade triggers the adenosine A(2B) receptor-sensitive renal vasodilation in female rats

Neutrophil Adhesion and the Release of the Free Amino Acid Hydroxylysine

During infection or certain metabolic disorders, neutrophils can escape from blood vessels, invade and attach to other tissues. The invasion and adhesion of neutrophils is accompanied and maintained by their own secretion. We have previously found that adhesion of neutrophils to fibronectin dramatically and selectively stimulates the release of the free amino acid hydroxylysine. The role of hydroxylysine and lysyl hydroxylase in neutrophil adhesion has not been studied, nor have the processes that control them. Using amino acid analysis, mass spectrometry and electron microscopy, we found that the lysyl hydroxylase inhibitor minoxidil, the matrix metalloproteinase inhibitor doxycycline, the PI3K/Akt pathway inhibitors wortmannin and the Akt1/2 inhibitor and drugs that affect the actin cytoskeleton significantly and selectively block the release of hydroxylysine and partially or completely suppress spreading of neutrophils. The actin cytoskeleton effectors and the Akt 1/2 inhibitor also increase the phenylalanine release. We hypothesize that hydroxylysine release upon adhesion is the result of the activation of lysyl hydroxylase in interaction with matrix metalloproteinase, the PI3K/Akt pathway and intact actin cytoskeleton, which play important roles in the recruitment of neutrophils into tissue through extracellular matrix remodeling.

Does ischemic preconditioning increase flap survival by ADORA2B receptor activation?

BACKGROUND

Ischemic preconditioning (IPC) is defined as raising tolerance to subsequent ischemic stress by exposing tissues to sub-lethal ischemia. Although many candidates have been suggested, recent studies have clearly demonstrated that adenosine-mediated ADORA2B receptor (ADORA2BR) activation is the main mechanism involved in IPC. While the tissue-protective role of this mechanism has been demonstrated in different ischemia/reperfusion (I/R) models, its role in flap surgery-derived I/R damage has not to date been investigated.

OBJECTIVE

To investigate the role of adenosine and ADORA2BR activation in IPC-mediated tissue protection in an epigastric flap model.

METHODS

Animals were divided into five main groups, all of which were then divided into two subgroups depending on whether or not they were exposed to IPC before the I/R procedure, which consisted of 6 hours of ischemia and 6 days of reperfusion. No drugs were administered in Group 1 (the control group). Animals in Group 2 were pretreated with CD73-inhibitor before IPC application or the ischemic period. Animals in Group 3 were pretreated with adenosine. Animals in Group 4 were pretreated with an ADORA2BR antagonist, and those in Group 5 with an ADORA2BR agonist. After 6 days of reperfusion, tissue survival was evaluated via histological and macroscopic analysis.

RESULTS

IPC application significantly enhanced CD73 expressions and adenosine concentrations (p < 0.01). Flap survivals were increased by IPC in Group 1 (p < 0.05). However, CD73 inhibition blocked this increase (Group 2). In Group 3, adenosine improved flap survival even in the absence of IPC (p < 0.01). While an ADORA2BR antagonist attenuated the tissue-protective effect of IPC (p < 0.01), the ADORA2BR agonist improved flap survival by mimicking IPC in groups 4 and 5.

CONCLUSION

These results provide pharmacological evidence for a contribution of CD73 enzyme-dependent adenosine generation and signaling through ADORA2BR to IPC-mediated tissue protection. They also suggest for the first time that ADORA2BR agonists may be used as a potential preventive therapy against I/R injury in flap surgeries.

Cardiac Na+/Ca2+ exchange stimulators among cardioprotective drugs

We previously reviewed our study of the pharmacological properties of cardiac Na+/Ca2+ exchange (NCX1) inhibitors among cardioprotective drugs, such as amiodarone, bepridil, dronedarone, cibenzoline, azimilide, aprindine, and benzyl-oxyphenyl derivatives (Watanabe et al. in J Pharmacol Sci 102:7-16, 2006). Since then we have continued our studies further and found that some cardioprotective drugs are NCX1 stimulators. Cardiac Na+/Ca2+ exchange current (INCX1) was stimulated by nicorandil (a hybrid ATP-sensitive K+ channel opener), pinacidil (a non-selective ATP-sensitive K+ channel opener), flecainide (an antiarrhythmic drug), and sodium nitroprusside (SNP) (an NO donor). Sildenafil (a phosphodiesterase-5 inhibitor) further increased the pinacidil-induced augmentation of INCX1. In paper, here I review the NCX stimulants that enhance NCX function among the cardioprotective agents we examined such as nicorandil, pinacidil, SNP, sildenafil and flecainide, in addition to atrial natriuretic (ANP) and dofetilide, which were reported by other investigators.

Effect of Interaction between Adenosine and Nitric Oxide on Central Nervous System Oxygen Toxicity

The metabolism of adenosine (ADO) and nitric oxide (NO) in brain tissues is closely associated with the change of oxygen content. They have contrary effects in the onset of hyperbaric oxygen (HBO)-induced central nervous system oxygen toxicity (CNS OT): ADO can suppress the onset, while NO promotes it. We adopted the ADO-augmenting measure and NO-inhibiting measure in this study and found the combined use had a far superior preventive and therapeutic effect in protecting against CNS OT compared with the use of either measure alone. So we hypothesized that there is an interaction between ADO and NO which has an important impact on the onset of CNS OT. On this basis, we administered ADO-augmenting or ADO-inhibiting drugs to rats. After exposure to HBO, the onset of CNS OT was evaluated, followed by the measurement of NO content in brain tissues. In another experiment, rats were administered NO-augmenting or NO-inhibiting drugs. After exposure to HBO, the onset of CNS OT was evaluated, followed by measurement of the activities of ADO metabolism-related enzymes in brain tissues. The results showed that, following ADO augmentation, the content of NO and its metabolite was significantly reduced, and the onset of CNS OT significantly improved. After ADO inhibition, just the opposite was observed. NO promotion resulted in a decrease in the activity of ADO-producing enzyme, an increase in the activity of ADO-decomposing enzyme, and an aggravation in CNS OT. The above results were all reversed after an inhibition in NO content. Studies have shown that exposure to HBO has a significant impact on the content of ADO and NO in brain tissues as well as their biological effects, and ADO and NO might have an intense interaction, which might generate an important effect on the onset of CNS OT. The prophylaxis and treatment effects of CNS OT can be greatly enhanced by augmenting ADO and inhibiting NO.

Vascular Occlusion Restores Endothelium-Dependent Effects of Adenosine Previously Diminished by Diabetes: The Preliminary Report

The aim of this study was to investigate the effect of adenosine in non-occluded or occluded femoral arteries (FA) that were isolated from healthy or diabetic Wistar rats. Determining the role of endothelium, and a transmembrane flow of potassium ions in adenosine actions were also of interest. Diabetes was experimentally induced by alloxan, while the vascular occlusion was performed for 45 min on randomly selected FA. Vascular tone changes were continuously recorded. Selected markers of endothelial dysfunction were measured in animal serum. Thus, adenosine produced a concentration-dependent relaxation of rat FA, which was endothelium-dependent, too, except in a group of diabetic animals. Moreover, serum asymmetric dimethylarginine (ADMA) levels were higher in diabetic animals, thus reflecting endothelial dysfunction (ED). Still, an occlusion of FA enhanced the relaxation effect of adenosine in endothelium-intact rings from diabetic animals. Oppositely, in the presence of high potassium concentration in the buffer, adenosine-induced relaxation was significantly reduced in all of the investigated groups/subgroups. These results suggest that in diabetic animals, an occlusion of FA most probably reversed adenosine-induced relaxation from endothelium-independent into an endothelium-dependent relaxation, thus indicating the possible protective mechanism against ischemic episodes of FA in the presence of diabetes.

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.

Adenosine contribution to normal renal physiology and chronic kidney disease

Adenosine is a nucleoside that is particularly interesting to many scientific and clinical communities as it has important physiological and pathophysiological roles in the kidney. The distribution of adenosine receptors has only recently been elucidated; therefore it is likely that more biological roles of this nucleoside will be unveiled in the near future. Since the discovery of the involvement of adenosine in renal vasoconstriction and regulation of local renin production, further evidence has shown that adenosine signaling is also involved in the tubuloglomerular feedback mechanism, sodium reabsorption and the adaptive response to acute insults, such as ischemia. However, the most interesting finding was the increased adenosine levels in chronic kidney diseases such as diabetic nephropathy and also in non-diabetic animal models of renal fibrosis. When adenosine is chronically increased its signaling via the adenosine receptors may change, switching to a state that induces renal damage and produces phenotypic changes in resident cells. This review discusses the physiological and pathophysiological roles of adenosine and pays special attention to the mechanisms associated with switching homeostatic nucleoside levels to increased adenosine production in kidneys affected by CKD.

Overview of Antagonists Used for Determining the Mechanisms of Action Employed by Potential Vasodilators with Their Suggested Signaling Pathways

This paper is a review on the types of antagonists and the signaling mechanism pathways that have been used to determine the mechanisms of action employed for vasodilation by test compounds. Thus, we exhaustively reviewed and analyzed reports related to this topic published in PubMed between the years of 2010 till 2015. The aim of this paperis to suggest the most appropriate type of antagonists that correspond to receptors that would be involved during the mechanistic studies, as well as the latest signaling pathways trends that are being studied in order to determine the route(s) that atest compound employs for inducing vasodilation. The methods to perform the mechanism studies were included. Fundamentally, the affinity, specificity and selectivity of the antagonists to their receptors or enzymes were clearly elaborated as well as the solubility and reversibility. All the signaling pathways on the mechanisms of action involved in the vascular tone regulation have been well described in previous review articles. However, the most appropriate antagonists that should be utilized have never been suggested and elaborated before, hence the reason for this review.

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

Activation of adenosine receptors (ARs) has been implicated in the modulation of renal and cardiovascular systems, as well as erectile functions. Recent studies suggest that adenosine-mediated regulation of erectile function is mainly mediated through A2BAR activation. However, no studies have been conducted to determine the contribution of AR subtype in the regulation of the vascular tone of the pudendal artery (PA), the major artery supplying and controlling blood flow to the penis. Our aim was to characterize the contribution of AR subtypes and identify signaling mechanisms involved in adenosine-mediated vascular tone regulation in the PA. We used a DMT wire myograph for muscle tension measurements in isolated PAs from wild-type, A2AAR knockout, A2BAR knockout, and A2A/A2BAR double-knockout mice. Real-time reverse transcription-polymerase chain reaction was used to determine the expression of the AR subtypes. Data from our pharmacologic and genetic approaches suggest that AR activation-mediated vasodilation in the PA is mediated by both the A2AAR and A2BAR, whereas neither the A1AR nor A3AR play a role in vascular tone regulation of the PA. In addition, we showed that A2AAR- and A2BAR-mediated vasorelaxation requires activation of nitric oxide and potassium channels; however, only the A2AAR-mediated response requires protein kinase A activation. Our data are complemented by mRNA expression showing the expression of all AR subtypes with the exception of the A3AR. AR signaling in the PA may play an important role in mediating erection and represent a promising therapeutic option for the treatment of erectile dysfunction.

The effects of A2B receptor modulators on vascular endothelial growth factor and nitric oxide axis in chronic cyclosporine nephropathy

Introduction:

To investigate the actions of adenosine A_2B receptor modulators on VEGF and NO levels in CsA nephropathy.

Materials and Methods:

Nephropathy was induced by administrating 25 mg/kg (s.c) of CsA for 5 weeks. The VEGF and NO levels were measured in kidney tissue. Serum creatinine, creatinine clearance, urinary albumin excretion, blood urea nitrogen, kidney pathology score were measured to assess renal function. The analysis of mRNA expression of A_2B receptor and VEGF was performed.

Results:

Administration of CsA for 5 weeks induced adverse renal function. The mRNA expression of VEGF was reduced in renal tissue after 5 weeks of CsA treatment. The renal VEGF and NO levels were also reduced in these animals. In vivo administration of A_2B adenosine receptor agonist increased renal VEGF which was inhibited by a selective A_2B AR antagonist (MRS1754) in CsA-treated animals. The increase in VEGF was associated with reversal of adverse renal functions. The effects of A_2B AR modulators were prominent in CsA-treated animals compared with control animals suggesting CsA treatment may upregulate A_2B ARs. The mRNA expression of A_2B AR was increased after 5 weeks of CsA.

Conclusions:

A_2B AR modulators may provide new therapeutic options to retard CsA nephropathy by mediating renal VEGF and NO.

Adenosine A2B receptor stimulates angiogenesis by inducing VEGF and eNOS in human microvascular endothelial cells

Angiogenesis is critical to wound repair due to its role in providing oxygen and nutrients that are required to support the growth and function of reparative cells in damaged tissues. Adenosine receptors are claimed to be of paramount importance in driving wound angiogenesis by inducing VEGF. However, the underlying mechanisms for the regulation of adenosine receptors in VEGF as well as eNOS remain poorly understood. In the present study, we found that adenosine and the non-selective adenosine receptor agonists (NECA) induced tube formation in HMEC-1 in a dose-dependent manner. Adenosine or NECA (10 µmol/L) significantly augmented the number and length of the segments in comparison with the control. Simultaneously, VEGF and eNOS were significantly upregulated following the administration of 10 µmol/L NECA, while they were suppressed after A2B AR genetic silencing and pharmacological inhibition by MRS1754. In addition, VEGF expression and eNOS bioavailability elimination significantly reduced the formation of capillary-like structures. Furthermore, the activation of A2B AR by NECA significantly increased the intracellular cAMP levels and concomitant CREB phosphorylation, eventually leading to the production of VEGF in HMEC-1. However, the activated PKA-CREB pathway seemed to be invalidated in the induction of eNOS. Moreover, we found that the elicited PI3K/AKT signaling in response to the induction of NECA assisted in regulating eNOS but failed to impact on VEGF generation. In conclusion, the A2B AR activation-driven angiogenesis via cAMP-PKA-CREB mediated VEGF production and PI3K/AKT-dependent upregulation of eNOS in HMEC-1.