ABT-702, an adenosine kinase inhibitor, attenuates inflammation in diabetic retinopathy

Aims This study was undertaken to determine the effect of an adenosine kinase inhibitor (AKI) in diabetic retinopathy (DR). We have shown previously that adenosine signaling via A_2A receptors (A_2AAR) is involved in retinal protection from diabetes-induced inflammation. Here we demonstrate that AKI-enhanced adenosine signaling provides protection from DR in mice. Main methods We targeted AK, the key enzyme in adenosine metabolism, using a treatment regime with the selective AKI, ABT-702 (1.5 mg/kg intraperitoneally twice a week) commencing at the beginning of streptozotocin-induced diabetes at the age of eight weeks. This treatment, previously demonstrated to increase free adenosine levels in vivo, was maintained until the age of 16 weeks. Retinal inflammation was evaluated using Western blot, Real-Time PCR and immuno-staining analyses. Role of A _2AAR signaling in the anti-inflammation effect of ABT-702 was analyzed in Amadori-glycated-albumin (AGA)-treated microglial cells. Key findings At 16 weeks, when diabetic mice exhibit significant signs of retinal inflammation including up-regulation of oxidative/nitrosative stress, A _2AAR, ENT1, Iba1, TNF-α, ICAM1, retinal cell death, and down-regulation of AK, the ABT-702 treated group showed lower signs of inflammation compared to control animals receiving the vehicle. The involvement of adenosine signaling in the anti-inflammation effect of ABT-702 was supported by the TNF-α release blocking effect of A_2AAR antagonist in AGA-treated microglial cells. Significance These results suggest a role for AK in regulating adenosine receptor signaling in the retina. Inhibition of AK potentially amplifies the therapeutic effects of site- and event-specific accumulation of extracellular adenosine, which is of highly translational impact.