CXC chemokine expression and synthesis in skeletal muscle during ischemia/reperfusion

Background. The chemokines keratinocyte-Derived Cytokine (KC) and macrophage inflammatory protein (MIP)-2, murine equivalents of human interleukin 8, have been implicated in remote injury after acute hind limb ischemia/ reperfusion (I/R). These studies were designed to determine whether the cytokines responsible for remote tissue injury are also synthesized and accumulate in the ischemic or reperfused hind limb. Methods. B6, 129SF2/J mice were subjected to either 3 hours of unilateral hind limb ischemia alone (IA) or 3 hours of ischemia followed by 4 or 24 hours of reperfusion (I/R). After IA or I/R, experimental and control (nonischemic) contralateral hind limbs were harvested for analysis of protein content, messenger RNA (mRNA), tissue edema, and viability. Results. IA did not increase KC or MIP-2 mRNA or protein levels. In contrast, I/R resulted in a 15- and 10-fold increase in KC mRNA after 4 and 24 hours of reperfusion, respectively. KC protein levels were increased 10-fold after 4 hours of reperfusion and 30-fold after 24 hours (vs IA or sham; P <.001). MIP-2 mRNA transiently increased 42-fold after 4 hours of reperfusion but decreased to basal levels after 24 hours of reperfusion. Despite the relative increase in MIP-2 mRNA by 4 hours of reperfusion, significantly increased (8- to 10 fold) MIP-2 protein levels were not detected until 24 hours of reperfusion only in the reperfused limbs. Tissue edema was increased significantly (P <.01) compared with sham after just 4 hours of reperfusion and remained increased at 24 hours. Tissue viability decreased 52% after 4 hours of reperfusion and did not change significantly by 24 hours. Conclusions. Skeletal muscle is a site of significant ongoing chemokine synthesis during reperfusion. The persistent increase in muscle chemokine levels at 24 hours of reperfusion was not associated with increased edema or injury. The role of these chemokines during reperfusion may be further investigated by local or oral administration of chemokines or chemokine receptor antagonists.