Activation Of Adenosine A1 Receptors Research Articles

“Adenosine an old player with new possibilities in kidney diseases”: Preclinical evidences and clinical perspectives

Renal injury might originate from multiple factors like ischemia reperfusion (I/R), drug toxicity, cystic fibrosis, radio contrast agent etc. The four adenosine receptor subtypes have been identified and found to show diverse physiological and pathological roles in kidney diseases. The activation of A1 adenosine receptor (A1) protects against acute kidney injury by improving renal hemodynamic alterations, decreasing tubular necrosis and its inhibition might facilitate removal of toxin or drug metabolite in chronic kidney disease models. Furthermore, recent findings revealed that A2A receptor subtype activation regulates macrophage phenotype in experimental models of nephritis. Interestingly the emerging role of adenosine kinase inhibitors in kidney diseases has been discussed which act by increasing adenosine availability at target sites and thereby promote A2A receptor stimulation. In addition, the least explored adenosine receptor subtype A3 inhibition was observed to exert anti- oxidant, immunosuppressive and anti-fibrotic effects, but more studies are required to confirm its benefits in other renal injury models. The clinical studies targeting A1 receptor in patients with pre-existing kidney disease have yielded disappointing results, perhaps owing to the origin of unexpected neurological complications during the course of trial. Importantly, conducting well designed clinical trials and testing adenosine modulators with lesser brain penetrability could clear the way for clinical approval of these agents for patients with renal functional impairments.

Adenosine A3 receptor as a novel therapeutic target to reduce secondary events and improve neurocognitive functions following traumatic brain injury

BackgroundTraumatic brain injury (TBI) is a common pathological condition that presently lacks a specific pharmacological treatment. Adenosine levels rise following TBI, which is thought to be neuroprotective against secondary brain injury. Evidence from stroke and inflammatory disease models suggests that adenosine signaling through the G protein-coupled A3 adenosine receptor (A3AR) can provide antiinflammatory and neuroprotective effects. However, the role of A3AR in TBI has not been investigated.MethodsUsing the selective A3AR agonist, MRS5980, we evaluated the effects of A3AR activation on the pathological outcomes and cognitive function in CD1 male mouse models of TBI.ResultsWhen measured 24 h after controlled cortical impact (CCI) TBI, male mice treated with intraperitoneal injections of MRS5980 (1 mg/kg) had reduced secondary tissue injury and brain infarction than vehicle-treated mice with TBI. These effects were associated with attenuated neuroinflammation marked by reduced activation of nuclear factor of kappa light polypeptide gene enhancer in B cells (NFκB) and MAPK (p38 and extracellular signal-regulated kinase (ERK)) pathways and downstream NOD-like receptor pyrin domain-containing 3 inflammasome activation. MRS5980 also attenuated TBI-induced CD4+ and CD8+ T cell influx. Moreover, when measured 4–5 weeks after closed head weight-drop TBI, male mice treated with MRS5980 (1 mg/kg) performed significantly better in novel object-placement retention tests (NOPRT) and T maze trials than untreated mice with TBI without altered locomotor activity or increased anxiety.ConclusionOur results provide support for the beneficial effects of small molecule A3AR agonists to mitigate secondary tissue injury and cognitive impairment following TBI.

Activation of Adenosine A3 Receptor Inhibits Microglia Reactivity Elicited by Elevated Pressure.

Glaucoma is a progressive chronic retinal degenerative disease and a leading cause of global irreversible blindness, characterized by optic nerve damage and retinal ganglion cell (RGC) death. Elevated intraocular pressure (IOP) is a main risk factor of glaucoma. Neuroinflammation plays an important role in glaucoma. We have been demonstrating that elevated pressure triggers microglia reactivity that contribute to the loss of RGCs. Adenosine, acting on adenosine receptors, is a crucial modulator of microglia phenotype. Microglia express all adenosine receptors. Previously, we demonstrated that the activation of adenosine A3 receptor (A3R) affords protection to the retina, including RGCs, unveiling the possibility for a new strategy for glaucoma treatment. Since microglial cells express A3R, we now studied the ability of a selective A3R agonist (2-Cl-IB-MECA) in controlling microglia reactivity induced by elevated hydrostatic pressure (EHP), used to mimic elevated IOP. The activation of A3R reduced EHP-induced inducible nitric oxide synthase (iNOS) expression, microglia migration and phagocytosis in BV-2 cells. In retinal microglia, proliferation and phagocytosis elicited by EHP were also decreased by A3R activation. This work demonstrates that 2-Cl-IB-MECA, the selective agonist of A3R, is able to hinder microglia reactivity, suggesting that A3R agonists could afford protection against glaucomatous degeneration through the control of neuroinflammation.

Adenosine Receptor Modulation of Hypoxic-ischemic Injury in Striatum of Newborn Piglets

Hypoxic-ischemic encephalopathy (HIE) is a major cause of pediatric and adult mortality and morbidity. Unfortunately, to date, no effective treatment has been identified. In the striatum, neuronal injury is analogous to the cellular mechanism of necrosis observed during NMethyl- D-Aspartate (NMDA) excitotoxicity. Adenosine acts as a neuromodulator in the central nervous system, the role of which relies mostly on controlling excitatory glutamatergic synapses. To examine the effect of pretreatment of SCH58261, an adenosine 2A (A2A) receptor antagonist and modulator of NMDA receptor function, following hypoxic-ischemia (HI) on sodium- potassium ATPase (Na+, K+-ATPase) activity and oxidative stress. Piglets (4-7 days old) were subjected to 30 min hypoxia and 7 min of airway occlusion producing asphyxic cardiac arrest. Groups were divided into four categories: HI samples were divided into HI-vehicle group (n = 5) and HI-A2A group (n = 5). Sham controls were divided into Sham vehicle (n = 5) and Sham A2A (n = 5) groups. Vehicle groups were pretreated with 0.9% saline, whereas A2A animals were pretreated with SCH58261 10 min prior to intervention. Striatum samples were collected 3 h post-arrest. Sodium-potassium ATPase (Na+, K+-ATPase) activity, malondialdehyde (MDA) + 4-hydroxyalkenals (4-HDA) and glutathione (GSH) levels were compared. Pretreatment with SCH58261 significantly attenuated the decrease in Na+, K+-ATPase, decreased MDA+4-HDA levels and increased GSH in the HI-A2A group when compared to HIvehicle. A2A receptor activation may contribute to neuronal injury in newborn striatum after HI in association with decreased Na+, K+-ATPase activity and increased oxidative stress.

Intracellular adenosine released from THP-1 differentiated human macrophages is involved in an autocrine control of Leishmania parasitic burden, mediated by adenosine A2A and A2B receptors

Leishmania infected macrophages have conditions to produce adenosine. Despite its known immunosuppressive effects, no studies have yet established whether adenosine alter Leishmania parasitic burden upon macrophage infection. This work aimed at investigating whether endogenous adenosine exerts an autocrine modulation of macrophage response towards Leishmania infection, identifying its origin and potential pharmacological targets for visceral leishmaniasis (VL), using THP-1 differentiated macrophages. Adenosine deaminase treatment of infected THP-1 cells reduced the parasitic burden (29.1 ± 2.2%, P < 0.05). Adenosine A2A and A2B receptor subtypes expression was confirmed by RT-qPCR and by immunocytochemistry and their blockade with selective adenosine A2A and A2B antagonists reduced the parasitic burden [14.5 ± 3.1% (P < 0.05) and 12.3 ± 3.1% (P < 0.05), respectively; and 24.9 ± 2.8% (P < 0.05), by the combination of the two antagonists)], suggesting that adenosine A2 receptors are tonically activated in infected THP-1 differentiated macrophages. The tonic activation of adenosine A2 receptors was dependent on the release of intracellular adenosine through equilibrative nucleoside transporters (ENT1/ENT2): NBTI or dipyridamole reduced (~25%) whereas, when ENTs were blocked, adenosine A2 receptor antagonists failed to reduce and A2 agonists increase parasitic burden. Effects of adenosine A2 receptors antagonists and ENT1/2 inhibitor were prevented by L-NAME, indicating that nitric oxide production inhibition prevents adenosine from increasing parasitic burden. Results suggest that intracellular adenosine, released through ENTs, elicits an autocrine increase in parasitic burden in THP-1 macrophages, through adenosine A2 receptors activation. These observations open the possibility to use well-established ENT inhibitors or adenosine A2 receptor antagonists as new therapeutic approaches in VL.

Sensory satellite glial Gq-GPCR activation alleviates inflammatory pain via peripheral adenosine 1 receptor activation

Glial fibrillary acidic protein expressing (GFAP+) glia modulate nociceptive neuronal activity in both the peripheral nervous system (PNS) and the central nervous system (CNS). Resident GFAP+ glia in dorsal root ganglia (DRG) known as satellite glial cells (SGCs) potentiate neuronal activity by releasing pro-inflammatory cytokines and neuroactive compounds. In this study, we tested the hypothesis that SGC Gq-coupled receptor (Gq-GPCR) signaling modulates pain sensitivity in vivo using Gfap-hM3Dq mice. Complete Freund’s adjuvant (CFA) was used to induce inflammatory pain, and mechanical sensitivity and thermal sensitivity were used to assess the neuromodulatory effect of glial Gq-GPCR activation in awake mice. Pharmacogenetic activation of Gq-GPCR signaling in sensory SGCs decreased heat-induced nociceptive responses and reversed inflammation-induced mechanical allodynia via peripheral adenosine A1 receptor activation. These data reveal a previously unexplored role of sensory SGCs in decreasing afferent excitability. The identified molecular mechanism underlying the analgesic role of SGCs offers new approaches for reversing peripheral nociceptive sensitization.

Alkaline Phosphatase Activity Is a Key Determinant of Vascular Responsiveness to Norepinephrine.

Here, we tested the hypothesis that TNAP (tissue nonspecific alkaline phosphatase) modulates vascular responsiveness to norepinephrine. In the isolated, Tyrode's-perfused rat mesentery, 50 µmol/L of L-p-bromotetramisole (L-p-BT; selective TNAP inhibitor, Ki=56 µmol/L) significantly reduced TNAP activity and caused a significant 9.0-fold rightward-shift in the norepinephrine concentration versus vasoconstriction relationship. At 100 µmol/L, L-p-BT further reduced mesenteric TNAP activity and caused an additional significant right-shift of the norepinephrine concentration versus vasoconstriction relationship. A higher concentration (200 µmol/L) of L-p-BT had no further effect on either mesenteric TNAP activity or norepinephrine-induced vasoconstriction. L-p-BT did not alter vascular responses to vasopressin, thus ruling-out nonspecific suppression of vascular reactivity. Since in the rat mesenteric vasculature α1-adrenoceptors mediate norepinephrine-induced vasoconstriction, these finding indicate that TNAP inhibition selectively interferes with α1-adrenoceptor signaling. Additional experiments showed that the effects of TNAP inhibition on norepinephrine-induced vasoconstriction were not mediated by accumulation of pyrophosphate or ATP (TNAP substrates) nor by reduced adenosine levels (TNAP product). TNAP inhibition significantly reduced the Hillslope of the norepinephrine concentration versus vasoconstriction relationship from 1.8±0.2 (consistent with positive cooperativity of α1-adrenoceptor signaling) to 1.0±0.1 (no cooperativity). Selective activation of A1-adenosine receptors, which are known to participate in coincident signaling with α1-adrenoceptors, reversed the suppressive effects of L-p-BT on norepinephrine-induced vasoconstriction. In vivo, L-p-BT administration achieved plasma levels of ≈60 µmol/L and inhibited mesenteric vascular responses to exogenous norepinephrine and sympathetic nerve stimulation. TNAP modulates vascular responses to norepinephrine likely by affecting positive cooperativity of α1-adrenoceptor signaling via a mechanism involving A1 receptor signaling.

Analgesic action of adenosine A1 receptor involves the dephosphorylation of glycine receptor α1ins subunit in spinal dorsal horn of mice

Glycine receptor α1ins subunit is located at inhibitory synapses in the superficial dorsal horn of adult spinal cord and is engaged in the glycinergic inhibition of nociceptive neuronal excitability and transmission. The α1ins phosphorylation at Ser380 by extracellular signal-regulated kinase (ERK) has been shown to decrease glycinergic synaptic currents and contribute to spinal disinhibition. Here we found that peripheral inflammation induced by Complete Freund's Adjuvant increased Ser380 phosphorylation in spinal cord dorsal horn of mice, which was repressed by specific activation of adenosine A1 receptor (A1R). Protein phosphatase-1 (PP1), a ubiquitously-distributed serine/threonine phosphatase, was required for A1R to reduce Ser380 phosphorylation. Our data showed that Gβγ dimer, when released after activation of Gi protein-coupled A1R, interacted with PP1 and directed this phosphatase to α1ins, allowing for the full dephosphorylation of Ser380 residue. Sequestration of Gβγ dimer by viral expression of the C-terminal tail of β-adrenergic receptor kinase (βARKct) dissociated PP1 from α1ins complex, leading to robust Ser380 phosphorylation. Meanwhile, Gβγ inhibition compromised the ability of A1R to alleviate inflammatory pain. The inhibitory effect of A1R on Ser380 phosphorylation was also attributed to the inactivation of ERK in CFA mice. Our data thus identified glycine receptor α1ins subunit as an important target for adenosinergic suppression of inflammatory pain.

Astrocyte Signaling Gates Long-Term Depression at Corticostriatal Synapses of the Direct Pathway.

Despite extensive research into understanding synaptic mechanisms of striatal plasticity, the functional role played by astrocytes in this region remains to be fully elucidated. It was recently demonstrated that high-frequency stimulation (HFS) of cortical inputs induced long-term depression (LTD) mediated by adenosine A1 receptor (A1R) activation at corticostriatal synapses of the direct pathway [cortico-striatal projection neuron (dSPN)] in the dorsolateral striatum (DLS). Because astrocyte-derived adenosine has been shown to regulate synaptic transmission in several brain areas, we investigated whether this form of neuron-astrocyte signaling contributes to synaptic plasticity in the DLS of male and female mice. We found that cortical HFS increases calcium (Ca2+) levels in striatal astrocytes through activation of metabotropic glutamate receptor type 5 (mGluR5) signaling and that this astrocyte-mediated response is necessary for A1R-mediated LTD. Consistent with this, astrocyte activation with Gq designer receptors exclusively activated by designer drugs (DREADDs) induced A1R-mediated synaptic depression at cortico-dSPN synapses. Together, these results indicate that astrocytes are integral elements of striatal A1R-mediated LTD.SIGNIFICANCE STATEMENT Abnormal striatal circuit function is implicated in several disorders such as Parkinson's disease and Huntington's disease. Thus, there is a need to better understand the mechanisms supporting proper striatal activity. While extensive work has revealed the many important contributions from neurons in striatal function, far less is known about the role of astrocytes in this brain area. We show that long-term depression (LTD) at corticostriatal synapses of the direct pathway is not strictly a neuronal phenomenon; astrocytes respond to corticostriatal stimulation and this astrocyte response is necessary for LTD. This research adds to the accumulating evidence that astrocytes are active and integral players in synaptic communication, and that neuron-astrocyte interactions are key cellular processes involved in brain function.

Paeoniflorin exerts neuroprotective effects in a transgenic mouse model of Alzheimer’s disease via activation of adenosine A1 receptor

Alzheimer’s disease (AD) is the most common cause of dementia, characterised by advanced cognitive and memory deterioration with no effective treatments available. Previous in vitro and in vivo studies suggest that paeoniflorin (PF), a major bioactive constituent of Radix Paeoniae, might possess anti-dementia properties; however, the underlying mechanism remains unclear. The aim of the current study was to determine the therapeutic effects of PF in a transgenic mouse model of AD and to identify its mechanism. Transgenic mice with five familial AD mutations (5XFAD) were used in this study. We showed that 28 days of PF (5 mg/kg, ip) treatment significantly decreased the escape latency and path length in the Morris water maze test and increased the alternation rate in the T-maze test, compared to the vehicle treatment group. In addition, PF treatment significantly alleviated amyloid β plaque burden, inhibited astrocyte activation, and decreased IL-1β and TNF-α expression in the brain of 5XFAD mice. However, the anti-cognitive deficits, anti-amyloidogenic, and anti-inflammatory effects of PF were abolished by 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 0.3 mg/kg), an adenosine A1 receptor (A1R) antagonist. In conclusion, our results suggest that PF might act as a potential therapeutic agent for AD via activation of adenosine A1R.

Activation of adenosine A3 receptor protects retinal ganglion cells from degeneration induced by ocular hypertension

Glaucoma is a progressive chronic retinal degenerative disease and a leading cause of global irreversible blindness. This disease is characterized by optic nerve damage and retinal ganglion cell (RGC) death. The current treatments available target the lowering of intraocular pressure (IOP), the main risk factor for disease onset and development. However, in some patients, vision loss progresses despite successful IOP control, indicating that new and effective treatments are needed, such as those targeting the neuroprotection of RGCs. Adenosine A3 receptor (A3R) activation confers protection to RGCs following an excitotoxic stimulus. In this work, we investigated whether the activation of A3R could also afford protection to RGCs in the laser-induced ocular hypertension (OHT) model, a well-characterized animal model of glaucoma. The intravitreal injection of 2-Cl-IB-MECA, a selective A3R agonist, abolished the alterations induced by OHT in the negative and positive components of scotopic threshold response (STR) without changing a- and b-wave amplitudes both in scotopic and photopic conditions. Moreover, the treatment of OHT eyes with the A3R agonist promoted the survival of RGCs, attenuated the impairment in retrograde axonal transport, and improved the structure of the optic nerve. Taking into consideration the beneficial effects afforded by 2-Cl-IB-MECA, we can envisage that A3R activation can be considered a good therapeutic strategy to protect RGCs from glaucomatous damage.

Imbalance Between α1‐Antitrypsin and Neutrophil Elastase in Simple Steatosis Promotes Inflammation and Fibrosis Through Regulation of Adenosine a3 Receptor Signaling in Non‐alcoholic Steatohepatitis

Study objectivesNon‐alcoholic fatty liver disease (NAFLD) has been considered leading cause of developing liver failure. However, the underlying mechanisms for transition from benign steatosis to clinically significant non‐alcoholic steatohepatitis (NASH) and non‐alcoholic steatofibrosis (NASF) have not been fully understood.MethodIn mouse model, NAFLD was induced by fast food diet (FFD) with a high glucose‐fructose solution for 24 weeks. For secretome proteomics, we used primary hepatocytes (HPs) isolated from normal chow diet (NCD) or FFD‐fed liver. The biased agonist of A3 adenosine receptor (A3AR), FM101 was utilized for the study of A3AR signaling.ResultsIn secretome proteomics, we found α1‐antitrypsin (A1AT) was decreased 0.2‐fold in FFD hepatocytes compared with NCD hepatocytes. Consistently, serum levels of A1AT from mice and human patients with NAFLD were significantly decreased compared to normal group. Conversely, the mRNA and protein level of Neutrophil Elastase (NE) were increased in FFD‐fed liver compared to NCD‐fed liver. We next confirmed inflammatory role of NE in Kupffer cells (KCs) as various cytokines (CCL2, TNF‐α, IL‐1β, iNOS and IL‐6) were increased in KCs with treatment of NE. Of note, NE has been reported to exert proteolytic activity that can prevent activation of G‐protein‐coupled receptors (GPCRs). We observed similar proteolysis that A3AR, a member of the adenosine receptor group of GPCRs, was cleaved in hepatic stellate cells (HSCs) after treatment of NE, indicating that A1AT‐NE system may regulate the A3AR signaling. Interestingly, A3AR was predominantly expressed in KCs and HSCs, but not in HPs. In vitro activation of A3AR signaling with FM101 significantly inhibited activation of KCs and HSCs as demonstrated by inflammatory cytokines (TNF‐α, IL‐6 and IL‐1β), and profibrogenic genes (Col1a1, Timp1 Acta2) expression, respectively. Moreover, in vivo activation of A3AR with FM101, lowered liver weight, liver to body ratio, and serum level of ALT and cholesterol induced by FFD. Furthermore, FM101 effectively improved steatofibrosis as assessed by quantification of collagen deposition. Mechanistically, FM101 treatment strongly blocked mitochondrial oxidative phosphorylation. Using pMito‐Timer and Mt‐Keima system, we observed FM101‐induced mitochondria vulnerability as demonstrated by increased accumulation of damaged mitochondria and subsequence mitophagic degradation. Consequently, CCCP‐induced cell death in macrophage was further enhanced by FM101 treatment.ConclusionsThe imbalance between A1AT and NE in simple steatosis mediates the progression of NASH and NASF through proteolytic inactivation of A3AR in KCs and HSCs. Thus, A3AR agonism with FM101 may have therapeutic potentials for treatment of NAFLD.Support or Funding InformationNational Research Foundation of Korea (NRF) ‐ 2019R1A2C1090178FM101 ameliorates FFD‐induced steatohepatitis and stetofibrosisFigure 1Adenosine A3 receptor signaling contributes to mitochondria vulnerabilityFigure 2

Influence of RGS6 on Inhibitory G Protein Signaling in Mouse Sinoatrial Nodal Cells

IntroductionM2 muscarinic (M2R) activation of G protein‐gated inwardly rectifying K+ (GIRK) channels in sinoatrial nodal (SAN) cells is a key mediator of vagal/parasympathetic slowing of heart rate. The strength of M2R‐GIRK signaling is negatively regulated by Regulator of G protein Signaling 6 (RGS6). Adenosine, used clinically to diagnose and treat certain arrhythmias, exerts these actions through A1 adenosine receptor (A1R) activation of GIRK channels. The extent to which RGS6 regulates A1R‐GIRK signaling, however, is unclear. Here, we investigated the impact of RGS6 on A1R‐GIRK and M2R‐GIRK signaling in mouse SAN cells.Methods and ResultsWe measured the efficacy and potency of M2R‐ and A1R‐GIRK signaling in adult SAN cells from wild‐type and RGS6−/− mice using whole‐cell patch‐clamp electrophysiology. As previously reported, SAN cells from RGS6−/− mice displayed prolonged channel deactivation kinetics and increased channel sensitivity to the non‐selective cholinergic agonist carbachol (CCh), relative to wild‐type counterparts. In contrast, we observed a striking increase in the amplitude of the GIRK response evoked by adenosine (Ado) in RGS6−/− SAN cells compared to wild‐type controls, with no impact on channel deactivation kinetics or sensitivity. Further recordings in wild‐type SAN cells revealed that M2R activation completely occludes the Ado‐induced response, whereas Ado application activates only a smaller fraction of GIRK channels. Both CCh‐ and Ado‐ induced currents were abolished in SAN cells treated by pertussis toxin (PTX), indicating these responses are mediated by Gi/o G proteins. Utilizing a bioluminescence resonance energy transfer (BRET) assay in transfected HEK cells, we found that RGS6 prefers Gαo as a substrate for over Gαi. Additionally, we found that while A1R does not discriminate between Gαo and Gαi, M2R displays a clear preference for Gαo. We next employed a Cre/flox strategy to remove Gαo from atrial tissue, including SAN cells. Loss of Gαo yielded significantly blunted CCh‐induced responses, which also displayed prolonged activation and deactivation kinetics. While Ado‐induced responses had prolonged deactivation kinetics, activation kinetics and response amplitude were unaffected.ConclusionsThese results suggest that RGS6 negatively regulates A1R‐GIRK signaling distinct from its influence on M2R‐GIRK signaling in mouse SAN cells likely due to differing utilization of Gao by M2R and A1R.Support or Funding InformationThis work was supported by NIH grants R01 HL105550 and F31 HL139090.

Differential spinal tissue oxygen profile during moderate and severe acute intermittent hypoxia

Plasticity is a hallmark of the neural system controlling breathing. A frequently studied model of respiratory motor plasticity is phrenic long‐term facilitation (pLTF), a persistent increase in phrenic burst amplitude induced by acute intermittent hypoxia (AIH). Two independent mechanisms underlie pLTF, depending on details of the AIH protocol. For example, moderate AIH (3, 5 min hypoxic episodes of moderate arterial PO2 with 5 min intervals) elicits a form of pLTF that requires intact carotid bodies, raphe neuron spinal serotonin release, and phrenic motor neuron serotonin type 2 receptor activation; this mechanism is known as the Q pathway to phrenic motor facilitation. The same protocol with more severe hypoxic episodes elicits a distinct cellular mechanism known as the S pathway; severe AIH leads to spinal adenosine accumulation and phrenic motor neuron adenosine 2A receptor activation, initiating the S pathway to pLTF. Since these pathways interact via mutual cross‐talk inhibition, intermediate AIH protocols fail to elicit pLTF since the Q and S pathways cancel one another. Thus, the balance of raphe serotonergic neuron activation (fast) versus spinal tissue hypoxia (slower) is a key determinant in regulating pLTF expression. Since the specific levels of spinal tissue hypoxia tipping this balance are not known, we compared spinal tissue oxygen profiles between moderate (PaO2 40 – 50 mmHg) vs severe AIH (PaO2 25 – 30 mmHg). Ventral cervical spinal tissue oxygen pressure (PtO2) and phrenic nerve activity were recorded in anesthetized, paralyzed and ventilated rats (IFO2 = 60%). As reported before, severe AIH elicited greater short‐term hypoxic phrenic responses and pLTF vs moderate AIH. Severe AIH elicited greater decreases in PtO2, reaching a nadir below ~5 mmHg. Following each episode, a transient overshoot in PtO2 was observed, reaching 90 mmHg above baseline conditions. Following the third hypoxic episode, PtO2 remained above baseline for at least 15 minutes post AIH (~ 10 mmHg). With moderate AIH, tissue hypoxia was less severe (PtO2 nadir ~ 16 mmHg), and post‐hypoxia overshoots far less prominent. In summary, spinal tissue oxygen dynamics are complex during AIH protocols; differences in PtO2 profiles likely underlie mechanistic differences in pLTF observed with moderate vs severe AIH. Understanding these dynamics (including the post‐AIH PtO2 “memory”) may help understand how to optimize AIH protocols to maximize plasticity and, potentially, functional benefits when harnessing AIH to restore breathing deficits with neural injury and/or disease.Support or Funding InformationNIH HL147554 and HL148030

β3 Adrenoceptor-induced cholinergic inhibition in human and rat urinary bladders involves the exchange protein directly activated by cyclic AMP 1 favoring adenosine release.

The mechanism by which β3 receptor agonists (e.g. mirabegron) control bladder overactivity may involve adenosine release from human and rat detrusor smooth muscle. Retrograde activation of adenosine A1 receptors reduces ACh release from cholinergic bladder nerves. β3 -Adrenoceptors usually couple to adenylyl cyclase. Here we investigated, which of the cAMP targets, protein kinase A or the exchange protein directly activated by cAMP (EPAC) could be involved in this cholinergic inhibition of the bladder. [3 H]ACh and adenosine release from urothelium-denuded detrusor strips of cadaveric human organ donors and rats were measured by liquid scintillation spectrometry and HPLC, respectively. In vivo cystometry was also performed in urethane-anaesthetized rats. The exchange protein directly activated by cAMP (EPAC) inhibitor, ESI-09, prevented mirabegron- and isoprenaline-induced adenosine release from human and rat detrusor strips respectively. ESI-09, but not the PKA inhibitor, H-89, attenuated inhibition of [3 H]ACh release from stimulated (10 Hz) detrusor strips caused by activating β3 -adrenoceptors, AC (forskolin) and EPAC1 (8-CTP-2Me-cAMP). Isoprenaline-induced inhibition of [3 H]ACh release was also prevented by inhibitors of PKC (chelerythrine and Go6976) and of the equilibrative nucleoside transporter 1 (ENT1; dipyridamole and NBTI), but not by PLC inhibition with U73122. Pretreatment with ESI-09, but not with H-89, prevented the reduction of the voiding frequency caused by isoprenaline and forskolin in vivo. Data suggest that β3 -adrenoceptor-induced inhibition of cholinergic neurotransmission in human and rat urinary bladders involves activation of an EPAC1/PKC pathway downstream cAMP production resulting in adenosine outflow via ENT1.

Neuroprotection by trans-resveratrol against collagenase-induced neurological and neurobehavioural deficits in rats involves adenosine A1 receptors

ABSTRACTObjective: Trans-resveratrol has been shown to have neuroprotective effects and could be a promising therapeutic agent in the treatment of intracerebral haemorrhage (ICH). This study aimed to investigate the involvement of the adenosine A1 receptor (A1R) in trans-resveratrol-induced neuroprotection in rats with collagenase-induced ICH.Methods: Sixty male Sprague–Dawley rats weighing 330–380 g were randomly divided into five groups (n = 12): (i) control, (ii) sham-operated rats, (iii) ICH rats pretreated with vehicle (0.1% DMSO saline, i.c.v.), (iv) ICH rats pretreated with trans-resveratrol (0.9 µg, i.c.v.) and (v) ICH rats pretreated with trans-resveratrol (0.9 µg) and the A1R antagonist, DPCPX (2.5 µg, i.c.v.). Thirty minutes after pretreatment, ICH was induced by intrastriatal injection of collagenase (0.04 U). Forty-eight hours after ICH, the rats were assessed using a variety of neurobehavioural tests. Subsequently, rats were sacrificed and brains were subjected to gross morphological examination of the haematoma area and histological examination of the damaged area.Results: Severe neurobehavioural deficits and haematoma with diffuse oedema were observed after intrastriatal collagenase injection. Pretreatment with trans-resveratrol partially restored general locomotor activity, muscle strength and coordination, which was accompanied with reduction of haematoma volume by 73.22% (P < 0.05) and damaged area by 60.77% (P < 0.05) in comparison to the vehicle-pretreated ICH group. The trans-resveratrol-induced improvement in neurobehavioural outcomes and morphological features of brain tissues was inhibited by DPCPX pretreatment.Conclusion: This study demonstrates that the A1R activation is possibly the mechanism underlying the trans-resveratrol-induced neurological and neurobehavioural protection in rats with ICH.

Activation of adenosine A3 receptor inhibits inflammatory cytokine production in colonic mucosa of patients with ulcerative colitis by down-regulating the nuclear factor-kappa B signaling.

The activation of the adenosine A3 receptor (A3AR) can regulate inflammation, but the way that this regulates colonic mucosal inflammation in ulcerative colitis (UC) remains unclear. This study aimed at examining A3AR expression and investigating the effect of A3AR activation on ex vivo cytokine expression and nuclear factor-kappa B (NF-κB) signaling in colonic mucosa. Colonic mucosal biopsied tissue from 18 patients with UC and 11 healthy controls was tested for A3AR expression by immunofluorescence, quantitative real-time polymerase chain reaction and Western blot. Following treatment for 24 hours with or without 2-Cl-IB-MECA, an A3AR agonist, TNF-α and IL-1β secreted by the cultured colonic mucosal tissue were quantified by ELISA. The colonic mucosal epithelia were dissected and treated with, or without 2-Cl-IB-MECA for 24 hours. The NF-κB p65 protein and its distribution in the cultured colonic epithelia were examined by immunofluorescence and Western blot. Compared with the controls, down-regulated A3AR expression and up-regulated TNF-α and IL-1β production and NF-κB p65 protein were observed in the UC colonic mucosa. The activation of A3AR by 2-Cl-IB-MECA significantly decreased TNF-α and IL-1β production and attenuated the NF-κB p65 activation in colonic tissues from patients with UC. A3AR activation inhibited inflammation by mitigating pro-inflammatory cytokine production and the NF-κB signal activation in colonic mucosa of patients with UC. A3AR activation may play a role in the pathogenesis of UC.

Adenosine 2A Receptor Activation Contributes to Ang II-Induced Aortic Remodeling by Promoting Macrophage Retention.

The A2AR (adenosine 2A receptor) plays a crucial role in the pathophysiological process of cardiovascular diseases, yet its effect on aortic remodeling remains unclear. We observed elevated adenosine and A2AR levels following infusion of mice with Ang II (angiotensin II), suggesting a potential role for the adenosine-A2AR system in macrophage accumulation and subsequent aortic remodeling. The effects and mechanisms of A2AR on macrophage dynamics during aortic remodeling were further investigated using mice with macrophage knockout of A2AR and by transplantation of A2AR-/- bone marrow. We demonstrated that macrophage knockout of A2AR inhibited macrophage accumulation and subsequent aortic remodeling by inhibiting macrophage retention. This was shown to occur via promotion of macrophage emigration to the draining lymph node. These effects correlated with restoration of the expression and surface content of CCR7 (CC chemokine receptor 7). Consistently, A2AR-/- bone marrow transplantation relieved Ang II-induced aortic remodeling, macrophage retention, and CCR7 downregulation and internalization, all of which were rescued by A2AR+/+ bone marrow transplantation. In addition, CCR7 antibody treatment blocked all the protective effects observed in A2AR-cKO mice, including attenuation of aortic remodeling and decreased macrophage retention. In in vitro studies, A2AR activation induced by Ang II suppressed macrophage migration to CCL19 (CC-chemokine ligand) 19 through downregulation and internalization of CCR7. In summary, A2AR activation contributes to Ang II-induced macrophage retention and subsequent aortic remodeling by inhibiting migration of macrophages to the draining lymph node through regulating CCR7 expression and internalization.

Abstract 13: Adenosine Receptor Activation During Extracorporeal Cardiopulmonary Resuscitation Improves Survival After Cardiac Arrest in Swine

Introduction: Despite advances in resuscitation protocols, including the addition of Extracorporeal Cardiopulmonary Resuscitation (ECPR), survival after cardiac arrest remains less than 40% and novel methods are needed to attenuate global injury and improve outcomes. ATL1223, an adenosine 2A receptor (A2AR) agonist has been shown to attenuate organ specific reperfusion injury by modulating the interaction of inflammatory cells. Hypothesis: A2AR activation during ECPR will improve survival and decrease the burden of injury in a large animal model of cardiac arrest. Methods: Adult swine underwent 20 minutes of circulatory arrest followed by defibrillation and 6 hours of ECPR. Animals were randomized to receive saline control (n=5) or the A2AR agonist Regadenoson (0.144 and 14.4mcg/kg/hr, n=5/group). Animals were subsequently weaned from ECPR and monitored for 24 hours. Clinical and biochemical endpoints were compared between groups. Results: The administration of Regadenoson increased survival after cardiac arrest compared to saline controls (10/10, 100% vs 2/5, 40%, p=0.02, Figure 1). Anesthetic administration (p=0.41), fluid resuscitation (p=0.54), and epinephrine required to maintain target arterial pressure (p=0.08) were similar for all subjects. Biochemical markers of organ damage, including creatinine (p=0.87), aspartate aminotransferase (p=0.89), and troponin I (p=0.38), were similar among groups (Figure 2). Conclusions: In a clinically relevant model of cardiac arrest treated with ECPR, selective A2AR agonism increased survival from 40% to 100% at 24 hours. These results suggest A2AR activation is a promising therapeutic target after cardiac arrest.

Mild hypothermia protects synaptic transmission from experimental ischemia through reduction in the function of nucleoside transporters in the mouse hippocampus

Ischemia, a severe metabolic stress, increases adenosine levels and causes the suppression of synaptic transmission through adenosine A1 receptors. Although temperature also regulates extracellular adenosine levels, the effect of temperature on ischemia-induced activation of adenosine receptors is not yet fully understood. Here we examined the role of adenosine A1 receptors in mild hypothermia-mediated neuroprotection during the acute phase of ischemia. Severe ischemia-induced neurosynaptic impairment was reproduced by oxygen-glucose deprivation at normothermia (36 °C) and assessed with extracellular recordings or whole-cell patch clamp recordings in acute hippocampal slices in mice. Mild hypothermia (32 °C) induced the protection of synaptic transmission by activating adenosine A1 receptors. Stricter hypothermia (28 °C) caused additional neuroprotective effects by extending the onset time to anoxic depolarization; however, this effect was not associated with adenosine A1 receptors. The response of exogenous adenosine-induced inhibition of hippocampal synaptic transmission was increased by lowering the temperature to 32 °C or 28 °C. Hypothermia also reduced the function of dipryidamole-sensitive nucleoside transporters. These findings suggest that an increased response of adenosine A1 receptors, caused by a reduction in the function of nucleoside transporters, is one mechanism by which therapeutic hypothermia (usually used within the mild range) mediates neurosynaptic protection in the acute phase of stroke.