Remote Ischemic Preconditioning Stimulus Decreases the Expression of Kinin Receptors in Human Neutrophils

Background Remote ischemic preconditioning (RIPC) has been shown to reduce ischemic-reperfusion injury and is induced by brief forearm ischemia. Kinins are known to be involved in RIPC and act via the G protein coupled B1 and B2 receptors. Interaction of the kinins with their respective receptors causes receptor internalization, thereby reducing the potential for further activation. This may be critical for the protective effect of RIPC and if so, we hypothesized, would significantly decrease the expression of kinin receptors on the surface of neutrophils. Methods The study was performed on five healthy human volunteers. The left forearm was rendered ischemic for three 5-min periods, each separated by 5min of reperfusion. Three venous blood samples were taken from the right arm, one before and two after RIPC. Neutrophil isolation, immunofluorescence labeling, and confocal microscopy were performed. Mean pixel intensity data were generated using a fixed circular area of interest (AOI, 40 × 40 μm). For every image, the AOI was placed over a cell and the mean pixel intensity was recorded. The mean intensity was expressed as pixel × 102 /μm2 and presented as mean ± SEM. Immunofluorescence at the different time points was compared by one way analysis of variance with Bonferroni's post-hoc test. A P value < 0.05 was considered significant. Results The mean pixel intensity for kinin B1 receptors was decreased at 24h after RIPC compared with both baseline and 15min after RIPC ( P < 0.001). Similarly, the intensity for B2 receptor labeling on neutrophils was significantly decreased 24h after RIPC compared with the baseline value ( P < 0.001). Conclusions RIPC decreases expression of kinin receptors on circulating human neutrophils. Reduction in kinin surface receptors suggests internalization of receptors and is consistent with the concepts of kinin receptor activation and their role in RIPC.