Abstract 15607: Mitochondrial and Biochemical Effects of Repetitive Cycles of Remote Ischemic Conditioning (RIC) in Human Upper and Lower Extremities

Abstract

Introduction: RIC is protective against heart and brain ischemia. The mechanisms are still debated as are dose effects of repetitive cycles using the upper or lower extremity. Increases in reactive hyperemia (RH), plasma nitrite and reactive oxygen species (ROS) may underlie protective signaling. Hypothesis: Repetitive cycles of RIC will be more effective in thigh than forearm increasing plasma nitrite and inhibiting mitochondrial function with small increases in ROS. Methods: Ten healthy individuals were subjected to 4 cycles of 5 min of limb ischemia, delivered by blood pressure cuff occlusion, and 5 min reperfusion (RIC). Subjects were randomized to right forearm or right thigh RIC first, then crossed over to the other extremity 2 weeks later. Blood flow and perfusion were monitored using laser speckle contrast imaging and by tissue oximetry on the ipsilateral and contralateral foot or hand. Blood was obtained at baseline and after each cycle and 24 h later for determination of platelet nitrite levels (chemiluminescence), mitochondrial function (Seahorse) and superoxide (ROS) generation (mitoSOX flow cytometry) and plasma nitrite. Results: RH, nitrite levels, mitochondrial oximetry and ROS were similar in arm (presented below) and thigh(p>0.2). RH (178% increased blood flow, 17% increased oximetry; p<0.0001) occurred after each RIC cycle with no difference between cycles 1-4. Plasma nitrite significantly increased (23%; p=0.033) after four cycles RIC and returned to baseline 24h later. The platelet rich plasma (PRP) nitrite was highest after cycle 1 (76% increase; p=0.002) with steady reduction after each cycle (15% over baseline by cycle 4; p=0.001). With each cycle platelet mitochondrial respiration declined (24% max by cycle 4) whereas superoxide generation increased (27% max by cycle 4; p<0.05). Conclusions: RIC using arm or leg produce similar physiologic and biochemical effects. RH of similar degree occurs with each cycle whereas nitrite production peaks after the first cycle and is consumed with subsequent cycles coincident with gradual mitochondrial inhibition and superoxide generation. These biochemical responses have been suggested in pre-clinical work to underlie protective signaling and differ little based on extremity used.