ADK and diabetic retinopathy: The modulation observed in the expression and protein levels of the receptors A1AR, A2AAR and A3AR and enzymes AK and ADA, as well as the impact on ADA activity and extracellular adenosine levels, may reveal a possible mechanism for the mitigation of the inflammatory and excitotoxic conditions observed in diabetic retinas, and thus a potential tool for the prevention of the neuronal cell death that occurs in the early stages of diabetic retinopathy.