The induction of ICAM-1 and Mn SOD in response to ischemia-reperfusion of skeletal muscle in humans

Introduction: Ischemia-reperfusion results in the release of cytokine mediators of inflammation due to tissue damage. Different cytokines, e.g. TNFα, IL-1β, and chemokines induce expression of intercellular adhesion molecule-1 (ICAM-1) which in turn binds to the integrins (LFA-1, Mac-1) of leukocytes. Reperfusion injury is also caused by superoxides generated by activated neutrophils. In order to attenuate superoxide-induced tissue damage, the mitochondrial superoxide scavanging enzyme, manganese-superoxide dismutase (MnSOD), is produced during oxidative stress of reperfusion. In this study, we examined the levels of induction of ICAM-1, several cytokines and MnSOD activity to evaluate reperfusion injury in humans subjected to tourniquet induced lower extremity ischemia. Methods: Muscle biopsies from four patients were collected 5 minutes prior to tourniquet application and 5 minutes after reperfusion. Venous- and arterial blood samples were also collected 5 minutes prior to and 5-, 60-, and 240-minutes after tourniquet release. Differences in the pool level of ICAM-1, TNFα, IL-1β, TGFβ, and MnSOD mRNAs were determined by Northern analysis both in pre- and post-reperfused muscle and blood cells (granulocytes and mononuclear cells). The levels of soluble ICAM-1 in circulatory plasma were also determined. Results: A 2-7 fold increase in ICAM-1 mRNA levels was detected in muscle biopsies 5 minutes after reperfusion, i.e., either in endothelial cells and/or muscle cells at the sites of injury. No changes in the constitutive level of ICAM-1 mRNA levels were observed in blood cells or in sICAM-1 in plasma from the same patient. TNFα and IL-1β were not detected by Northern analysis of the muscle samples. Although the constitutive levels of MnSOD mRNA did not change in either muscle or blood sampled at 5 minutes after reperfusion, a dramatic increase of mRNA level occurred in blood (granulocytes) collected at 60- and 240-minutes after reperfusion. Conclusions: In conclusion, we propose that the induction of ICAM-1 and MnSOD are tissue-specific responses, i.e., skeletal muscle and granulocytes, to ischemia-reperfusion. The high levels of ICAM-1 mRNA in muscle tissues at 5 minutes is an early response and increased MnSOD produced by granulocytes is a late response to attenuate superoxide induced injury following reperfusion.