Systemic protection through remote ischemic preconditioning is spread by platelet-dependent signaling in mice

Abstract

Remote ischemic preconditioning (RIPC), the repetitive transient mechanical obstruction of vessels at a limb remote to the operative site, is a novel strategy to mitigate distant organ injury associated with surgery. In the clinic, RIPC has demonstrated efficacy in protecting various organs against ischemia reperfusion (IR), but a common mechanism underlying the systemic protection has not been identified. Here, we reasoned that protection may rely on adaptive physiological reponses toward local stress, as is incurred through RIPC. Standardized mouse models of partial hepatic IR and of RIPC to the femoral vascular bundle were applied. The roles of platelets, peripheral serotonin, and circulating vascular endothelial growth factor (Vegf) were studied in thrombocytopenic mice, Tph1−/− mice, and through neutralizing antibodies, respectively. Models of interleukin‐10 (Il10) and matrix metalloproteinase 8 (Mmp8) deficiency were used to assess downstream effectors of organ protection. The protection against hepatic IR through RIPC was dependent on platelet‐derived serotonin. Downstream of serotonin, systemic protection was spread through up‐regulation of circulating Vegf. Both RIPC and serotonin‐Vegf induced differential gene expression in target organs, with Il10 and Mmp8 displaying consistent up‐regulation across all organs investigated. Concerted inhibition of both molecules abolished the protective effects of RIPC. RIPC was able to mitigate pancreatitis, indicating that it can protect beyond ischemic insults. Conclusions: We have identified a platelet‐serotonin‐Vegf‐Il10/Mmp8 axis that mediates the protective effects of RIPC. The systemic action, the conservation of RIPC effects among mice and humans, and the protection beyond ischemic insults suggest that the platelet‐dependent axis has evolved as a preemptive response to local stress, priming the body against impending harm. (Hepatology 2014;60:1409–1417)

Omega-3 Fatty Acids Protect Fatty and Lean Mouse Livers After Major Hepatectomy

“…For ischemia/ reperfusion (I/R) experiments, 68% hepatic ischemia was induced as described. 22 Animals were sacrificed 6 hours after reperfusion, a time point that well reflects injury levels at later reperfusion times. 22 Hepatectomies (68% for normal liver regeneration, 86% for inducing liver failure) were performed as reported.…”

“…22 Animals were sacrificed 6 hours after reperfusion, a time point that well reflects injury levels at later reperfusion times. 22 Hepatectomies (68% for normal liver regeneration, 86% for inducing liver failure) were performed as reported. 23 Omegaven (parenteral fish oil emulsion; Fresenius Kabi AG, Oberdorf, Switzerland), was intravenously (i.v.)…”

“…Six hours after reperfusion, 22 liver injury was assessed via multiple parameters. Necrosis on histology was visibly reduced in the HFD-V3FA versus the HFD group (Figure 2A), as was sinusoidal plugging indicated by stuck erythrocytes.…”

Remote Ischemic Preconditioning

“…Brief episodes of ischemia with intermittent reperfusion are introduced at, for example, a limb, leading to systemic protection against subsequent insults as evinced on kidney, heart, liver, and other tissues. 17 We have recently identified a general mechanism that underlies the systemic protection conferred through RIPC 18 ; remote blood occlusion leads to serotonin release from platelets, which stimulates endothelial Vegf secretion to upregulate in target organs Il10 and Mmp8, acting in concert for protection. Interrupting this serotonin-Vegf-Il10/Mmp8 axis at any point renders RIPC inefficient in protecting against hepatic IR.…”

“…Interrupting this serotonin-Vegf-Il10/Mmp8 axis at any point renders RIPC inefficient in protecting against hepatic IR. 18 Whether RIPC can likewise protect old liver is unclear. However, we have shown that Vegf administration is able to restore the diminished regenerative capacity of old liver to levels seen in young animals.…”