Stimulation of soluble guanylyl cyclase in erythrocytes induces export of cGMP and cardioprotection in type 2 diabetes

Abstract Background Red blood cells (RBCs) are known to export cardioprotective nitric oxide (NO) bioactivity. Although, RBCs contain a functional soluble guanylyl cyclase (sGC), the signalling behind the export of NO bioactivity remains unclear. Impairment of NO signalling in RBCs has been suggested to contribute to augmented cardiac ischemia-reperfusion injury in type 2 diabetes (T2D). We hypothesized that increased NO signaling by stimulation of sGC in RBCs protects from myocardial ischemia-reperfusion injury by release of a cardioprotective signal. Purpose To investigate whether stimulation of sGC, the intracellular NO receptor, in RBCs from T2D patients induces export of a cardioprotective factor and to determine its nature. Methods RBCs were collected from patients with T2D and from gender- and age-matched healthy subjects and incubated with different pharmacological compounds affecting the NO-signalling pathway. The RBCs or their supernatant were then administered to isolated Langendorff-perfused rat hearts subjected to 25 min global ischemia and 60 min reperfusion. Left ventricular developed pressure and infarct size were measured. ELISA and immunofluorescence were used to determine levels of cyclic guanosine monophosphate (cGMP) and substrate of protein kinase G activation. All animal experiments and procedures were performed according to the guidelines by the U.S National Institutes of Health (NIH publication no 85-23, revised 1996). The present study was performed following The Code of Ethics of the World Medical Association outlined in the Declaration of Helsinki of 1975 and revised in 1983 for experiments that involve human subjects. Results RBCs from T2D patients impaired post-ischemic cardiac function and increased infarct size compared to RBCs from healthy subjects, and these effects were prevented by pre-incubation of the RBCs with the sGC stimulator CYR715. Administration of the supernatant from RBCs incubated with the sGC stimulator resulted in similar cardioprotection, indicating release of a cardioprotective factor from the RBCs (Figure 1A and B). The cardioprotection was abolished by inhibition of transport of cGMP with MK571, an inhibitor of cyclic nucleotide transport. Extracellular cGMP levels in the supernatant from RBCs were increased following sGC stimulation, and administration of exogenous cGMP induced cardioprotection (Figure 1C and D). Expression of protein kinase G-dependent phosphorylated vasodilator-specific phosphoprotein in cardiomyocytes was increased following administration of supernatant from RBCs incubated with the sGC stimulator (Figure 1E). Conclusions This study shows that stimulation of sGC in RBCs leads to release of a cardioprotective mediator, identified as cGMP, that activates cardiac protein kinase G and protects from ischemia-reperfusion injury. It further identifies RBC sGC as a novel therapeutic target to prevent cardiovascular injury in T2D.Figure 1