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Background and Purpose Experimental Approach Key results Conclusion and Implications Adenosine receptor activation induces delayed, sustained cardioprotection against ischaemia–reperfusion (IR) injury (24–72 h), but the mechanisms underlying extended cardioprotection duration remain unresolved. We hypothesized that a positive feedback loop involving adenosine receptor‐induced proteasomal degradation of adenosine kinase (ADK) and decreased myocardial adenosine metabolism extends the duration of cardioprotection.Mice were administered an ADK inhibitor, ABT‐702, to induce endogenous adenosine signalling. Cardiac ADK protein and mRNA levels were analysed 24–120 h later. Theophylline or bortezomib was administered 24 h after ABT‐702 to examine the late roles of adenosine receptors or proteasomal activity, respectively, in ADK expression and cardioprotection at 72 h. Coronary flow and IR tolerance were analysed by Langendorff technique. The potential for continuous adenosinergic cardioprotection was examined using heterozygous, cardiac‐specific ADK KO (cADK+/−) mice. Cardiac ADK expression was also examined after A1 or A3 receptor agonist, phenylephrine, lipopolysaccharide or sildenafil administration.ABT‐702 treatment decreased ADK protein content and provided cardioprotection from 24 to 72 h. ADK mRNA upregulation restored ADK protein after 96–120 h. Adenosine receptor or proteasome inhibition at 24 h reversed ABT‐702‐induced ADK protein deficit and cardioprotection at 72 h. cADK+/− hearts exhibited continuous cardioprotection. Diverse preconditioning agents also diminished cardiac ADK protein expression.A positive feedback loop driven by adenosine receptor‐induced ADK degradation and renewed adenosine signalling extends the duration of cardioprotection by ABT‐702 and possibly other preconditioning agents. The therapeutic potential of continuous adenosinergic cardioprotection is demonstrated in cADK+/− hearts. [ABSTRACT FROM AUTHOR]

Pharmacological inhibition of adenosine kinase (ADK), the major route of myocardial adenosine metabolism, can elicit acute cardioprotection against ischemia-reperfusion (IR) by increasing adenosine signaling. Here, we identified a novel, extended effect of the ADK inhibitor, ABT-702, on cardiac ADK protein longevity and investigated its impact on sustained adenosinergic cardioprotection. We found that ABT-702 treatment significantly reduced cardiac ADK protein content in mice 24–72 h after administration (IP or oral). ABT-702 did not alter ADK mRNA levels, but strongly diminished (ADK-L) isoform protein content through a proteasome-dependent mechanism. Langendorff perfusion experiments revealed that hearts from ABT-702-treated mice maintain higher adenosine release long after ABT-702 tissue elimination, accompanied by increased basal coronary flow (CF) and robust tolerance to IR. Sustained cardioprotection by ABT-702 did not involve increased nitric oxide synthase expression, but was completely dependent upon increased adenosine release in the delayed phase (24 h), as indicated by the loss of cardioprotection and CF increase upon perfusion of adenosine deaminase or adenosine receptor antagonist, 8-phenyltheophylline. Importantly, blocking adenosine receptor activity with theophylline during ABT-702 administration prevented ADK degradation, preserved late cardiac ADK activity, diminished CF increase and abolished delayed cardioprotection, indicating that early adenosine receptor signaling induces late ADK degradation to elicit sustained adenosine release. Together, these results indicate that ABT-702 induces a distinct form of delayed cardioprotection mediated by adenosine receptor-dependent, proteasomal degradation of cardiac ADK and enhanced adenosine signaling in the late phase. These findings suggest ADK protein stability may be pharmacologically targeted to achieve sustained adenosinergic cardioprotection. [ABSTRACT FROM AUTHOR]

Dysfunction of vascular nitric oxide (NO)/cGMP signaling is believed to contribute essentially to various cardiovascular disorders. Besides synthesis and/or bioavailability of endothelial NO, impaired function of soluble guanylate cyclase (sGC) may play a key role in vascular dysfunction. Based on the proposal that desensitization of sGC through S-nitrosation contributes to vascular NO resistance ( Proc Natl Acad Sci U S A 104: 12312-12317, 2007 ), we exposed purified sGC to dinitrosyl iron complexes (DNICs), known as potent nitrosating agents. In the presence of 2 mM GSH, DNICs stimulated cGMP formation with EC(50) values of 0.1 to 0.5 microM and with an efficacy of 70 to 80% of maximal activity measured with 10 microM 2,2-diethyl-1-nitroso-oxyhydrazine (DEA/NO). In the absence of GSH, the efficacy of DNICs was markedly reduced, and sGC stimulation was counteracted by the inhibition of both basal and DEA/NO-stimulated cGMP formation at higher DNIC concentrations. Inactivation of sGC was slowly reversed in the presence of 2 mM GSH and associated with stoichiometric S-nitrosation of the protein (2.05 +/- 0.18 mol S-nitrosothiol per mol of 143-kDa heterodimer). S-Nitrosoglutathione and sodium nitroprusside caused partial inhibition of DEA/NO-stimulated sGC that was prevented by GSH, whereas nitroglycerin (0.3 mM) had no effect. Our findings indicate that nitrosation of two cysteine residues in sGC heterodimers results in enzyme inactivation. Protection by physiologically relevant concentrations of GSH (10 microM to 3 mM) suggests that S-nitrosation of sGC may contribute to vascular dysfunction in inflammatory disorders associated with nitrosative and oxidative stress and GSH depletion.