Remote ischemic preconditioning in patients undergoing cardiac surgery with six ischemic cycles

Abstract

Background We have previously shown that remote ischemic preconditioning (RIP), which utilizes in part the extracellular RNA (eRNA)/RNase1 pathway, can induce ischemic tolerance in humans. Because RIP has thus far been tested only with four cycles of extremity ischemia/reperfusion, we investigated the influence of six cycles of ischemia on the eRNA/RNase1 pathway in cardiac patients. Methods Six cycles of RIP were carried out in 14 patients undergoing cardiac surgery. Blood samples were taken at 13 timepoints during surgery and at three timepoints after surgery for determining serum levels of RNase1, eRNA, and TNF-α. Trans-cardiac gradients between the myocardial blood inflow and outflow were calculated. Results Between the fourth and the sixth RIP cycles, a noticeable increase in the levels of eRNA (fourth: 151.6 (SD: 44.2) ng/ml vs sixth: 181.8 (SD: 87.5) ng/ml, p = .071), and a significant increase in RNase1 (fourth: 151.1 (SD: 42.6) U/ml vs sixth: 175.3 (SD: 41.2) U/ml, p = .001), were noted. The trans-cardiac gradients of RNase1 and eRNA before and after ischemia were not significantly different ( p = .158 and p = .221; p = .397 and p = .683, respectively). Likewise, the trans-cardiac gradient of TNF-α was similar before and after ischemia. During the first 48 h after the surgery, RNase1 activity rose significantly and exceeded baseline values (135.7 (SD: 40.6) U/ml before and 279.2 (SD: 85.6) U/ml after surgery, p = .001) as did eRNA levels (148,6 (SD: 35.4) ng/ml before and 396.5 (SD: 154.5) ng/ml after surgery, p = .005), whereas TNF-α levels decreased significantly (91.7 (SD: 47.7) pg/ml before and 35.7 (SD: 36.9) pg/ml after surgery, p = .001). Conclusion Six RIP cycles increased the RNase1 levels significantly above those observed with four cycles. More clinical data are required to show whether this translates into a benefit for patients.

Broadening Horizons: Exploring mtDAMPs as a Mechanism and Potential Intervention Target in Cardiovascular Diseases

“…A clinical study on patients with cardiac bypass surgery found that the levels of cardioprotective RNase1 were enhanced, whereas the levels of exRNA and TNF-α were decreased upon remote ischemic preconditioning by cycles of blood pressure cuff inflation around the left arm prior to the surgery. The direct effect on cardiac function and the causality between the increase in RNAse1 and a reduction in exRNA and TNF-α were not reported in this study [128]. Consequently, the exact mechanism of RNase1-induced cardioprotection remains to be elucidated.…”