Biochemical signaling by remote ischemic conditioning of the arm versus thigh: Is one raise of the cuff enough?

Remote Ischemic Conditioning (RIC), induced by brief cycles of ischemia and reperfusion, protects vital organs from a prolonged ischemic insult. While several biochemical mediators have been implicated in RIC's mechanism of action, it remains unclear whether the localization or "dose" of RIC affects the extent of protective signaling. In this randomized crossover study of healthy individuals, we tested whether the number of cycles of RIC and its localization (arm versus thigh) determines biochemical signaling and cytoprotection. Subjects received either arm or thigh RIC and then were crossed over to receive RIC in the other extremity. Blood flow, tissue perfusion, concentrations of the circulating protective mediator nitrite, and platelet mitochondrial function were measured after each RIC cycle. We found that plasma nitrite concentration peaked after the first RIC cycle and remained elevated throughout RIC. This plasma nitrite conferred cytoprotection in an in vitro myocyte model of hypoxia/reoxygenation. Notably, though plasma nitrite returned to baseline at 24h, RIC conditioned plasma still mediated protection. Additionally, no difference in endpoints between RIC in thigh versus arm was found. These data demonstrate that localization and "dose" of RIC does not affect cytoprotection and further elucidate the mechanisms by which nitrite contributes to RIC-dependent protection.