Inosine Reduces Pain-Related Behavior in Mice: Involvement of Adenosine A<sub>1</sub> and A<sub>2A</sub> Receptor Subtypes and Protein Kinase C Pathways

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Inosine is the first metabolite of adenosine. It exerts an antinociceptive effect by activating the adenosine A 1 and A 2A receptors. We have previously demonstrated that inosine exhibits antinociceptive properties in acute and chronic mice models of nociception. The aim of this study was to investigate the involvement of pertussis toxinsensitive G-protein-coupled receptors, as well as K + and Ca 2+ channels, in the antinociception promoted by inosine in the formalin test. Mice were pretreated with pertussis toxin (2.5 μg/site, i.t., an inactivator of G i/0 protein); after 7 days, they received inosine (10 mg/kg, i.p.) or morphine (2.5 mg/kg, s.c., used as positive control) immediately before the formalin test. Another group of animals received tetraethylammonium (TEA) or 4-aminopyridine (4-AP) (1 μg/site, i.t., a non-specific voltage-gated K + channel blockers), apamin (50 ng/site, i.t., a small conductance Ca 2+ -activated K + channel blocker), charybdotoxin (250 pg/site, i.t., a largeconductance Ca 2+ -activated K + channel blocker), glibenclamide (100 μg/site, i.t., an ATP-sensitive K + channel blocker) or CaCl 2 (200 nmol/site, i.t.). Afterwards, the mice received inosine (10 mg/kg, i.p.), diclofenac (10 mg/kg, i.p., a positive control), or morphine (2.5 mg/kg, s.c., a positive control) immediately before the formalin test. The antinociceptive effect of inosine was reversed by the pre-administration of pertussis toxin (2.5 μg/site, i.t.), TEA, 4-aminopyridine, charybdotoxin, glibenclamide, and CaCl 2 , but not apamin. Further, all K + channel blockers and CaCl 2 reversed the antinociception induced by diclofenac and morphine, respectively. Taken together, these data suggest that the antinociceptive effect of inosine is mediated, in part, by pertussis toxinsensitive G-protein coupled receptors and the subsequent activation of voltage gated K + channel, large conductance Ca 2+ -activated and ATP-sensitive K + channels or inactivation of voltage-gated Ca 2+ channels. Finally, small conductance Ca 2+ -activated K + channels are not involved in the antinociceptive effect of inosine.

Section: Discussionsupporting

confidence: 76%

Section: Drug Administration Pertussis Toxin Ksupporting

confidence: 47%

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Role of pertussis toxin-sensitive G-protein, K+ channels, and voltage-gated Ca2+ channels in the antinociceptive effect of inosine

Macedo-Júnior

Nascimento

Luiz-Cerutti

et al. 2012

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“…The same selective antagonists were given in absence of inosine to evaluate the per se effects. The doses of antagonists used here were based on previous in vivo studies [23,26].…”

Section: Drug Treatmentsmentioning

confidence: 99%

Anti-inflammatory effects of inosine in allergic lung inflammation in mice: evidence for the participation of adenosine A2A and A3 receptors

Lapa

Oliveira

Accetturi

et al. 2013

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Inosine, a naturally occurring purine formed from the breakdown of adenosine, is associated with immunoregulatory effects. Evidence shows that inosine modulates lung inflammation and regulates cytokine generation. However, its role in controlling allergen-induced lung inflammation has yet to be identified. In this study, we aimed to investigate the role of inosine and adenosine receptors in a murine model of lung allergy induced by ovalbumin (OVA). Intraperitoneal administration of inosine (0.001-10 mg/kg, 30 min before OVA challenge) significantly reduced the number of leukocytes, macrophages, lymphocytes and eosinophils recovered in the bronchoalveolar lavage fluid of sensitized mice compared with controls. Interestingly, our results showed that pre-treatment with the selective A 2A receptor antagonist (ZM241385), but not with the selective A 2B receptor antagonist (alloxazine), reduced the inhibitory effects of inosine against macrophage count, suggesting that A 2A receptors mediate monocyte recruitment into the lungs. In addition, the pre-treatment of mice with selective A 3 antagonist (MRS3777) also prevented inosine effects against macrophages, lymphocytes and eosinophils. Histological analysis confirmed the effects of inosine and A 2A adenosine receptors on cell recruitment and demonstrated that the treatment with ZM241385 and alloxazine reverted inosine effects against mast cell migration into the lungs. Florianópolis 88040-900, Santa Catarina, Brazil Purinergic Signalling (2013) 9:325-336 DOI 10.1007 Accordingly, the treatment with inosine reduced lung elastance, an effect related to A 2 receptors. Moreover, inosine reduced the levels of Th 2 -cytokines, interleukin-4 and interleukin-5, an effect that was not reversed by A 2A or A 2B selective antagonists. Our data show that inosine acting on A 2A or A 3 adenosine receptors can regulate OVA-induced allergic lung inflammation and also implicate inosine as an endogenous modulator of inflammatory processes observed in the lungs of asthmatic patients.

“…It has been suggested that inosine elicits neuroprotective effects in neurons and astrocytes subjected to hypoxia, glucose-oxygen deprivation, and oxidative damage [18,19]; stimulates neurite outgrowth in vitro [20]; and induces axonal outgrowth in vivo and in vitro studies [21][22][23][24][25]. Moreover, systemic administration of inosine causes antinociceptive, antiallodynic, and antihyperalgesic effects in mice [26,27]. Evidence from clinical studies has suggested antioxidant and protective properties of inosine in multiple sclerosis and Parkinson's disease patients [28][29][30].…”

Section: Introductionmentioning

confidence: 99%

Signaling pathways underlying the antidepressant-like effect of inosine in mice

Gonçalves

Neis

Rieger

et al. 2016

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Inosine is a purine nucleoside formed by the breakdown of adenosine that elicits an antidepressant-like effect in mice through activation of adenosine A 1 and A 2A receptors. However, the signaling pathways underlying this effect are largely unknown. To address this issue, the present study investigated the influence of extracellular-regulated protein kinase (ERK)1/2, Ca 2+ /calmoduline-dependent protein kinase (CaMKII), protein kinase A (PKA), phosphoinositide 3-kinase (PI3K)/Akt, and glycogen synthase kinase 3beta (GSK-3β) modulation in the antiimmobility effect of inosine in the tail suspension test (TST) in mice. In addition, we attempted to verify if inosine treatment was capable of altering the immunocontent and phosphorylation of the transcription factor cyclic adenosine monophosphatate (cAMP) responsebinding element protein (CREB) in mouse prefrontal cortex and hippocampus. Intracerebroventricular administration of U0126 (5 μg/mouse, MEK1/2 inhibitor), KN-62 (1 μg/ mouse, CaMKII inhibitor), H-89 (1 μg/mouse, PKA inhibitor), and wortmannin (0.1 μg/mouse, PI3K inhibitor) prevented the antiimmobility effect of inosine (10 mg/kg, intraperitoneal (i.p.)) in the TST. Also, administration of a subeffective dose of inosine (0.1 mg/kg, i.p.) in combination with a sub-effective dose of AR-A014418 (0.001 μg/mouse, GSK-3β inhibitor) induced a synergic antidepressant-like effect. None of the treatments altered locomotor activity of mice. Moreover, 24 h after a single administration of inosine (10 mg/kg, i.p.), CREB phosphorylation was increased in the hippocampus. Our findings provided new evidence that the antidepressant-like effect of inosine in the TST involves the activation of PKA, PI3K/Akt, ERK1/2, and CaMKII and the inhibition of GSK-3β. These results contribute to the comprehension of the mechanisms underlying the purinergic system modulation and indicate the intracellular signaling pathways involved in the antidepressant-like effect of inosine in a preclinical test of depression.