Long-term pre- and postconditioning with low doses of erythropoietin protects critically perfused musculocutaneous tissue from necrosis

Abstract

It has been shown that pre- and postconditioning of ischemically challenged tissue with erythropoietin (EPO) is able to reduce necrosis in a dose-dependent manner. The aim of this study was to determine the tissue-protective effects of different EPO dosages and administration regimes. Three groups of six C57Bl/6-mice each were analyzed: (1) pre- and postconditioning with initial high doses of EPO (starting at 2500 I.U./kg bw i.p.) followed by low doses of EPO (125 I.U./kg bw i.p.) (EPO-high-dose); (2) pre- and postconditioning with low doses of EPO (125 I.U./kg bw i.p.) (EPO-low-dose); and (3) untreated control group. Randomly perfused musculocutaneous flaps were mounted on dorsal skinfold chambers undergoing acute persistent ischemia and developing ∼50% necrosis without treatment. Intravital epifluorescence microscopy was performed at days 1, 3, 5, 7, and 10 after surgery, assessing flap necrosis, microcirculation, and angiogenesis. The hematocrit was measured at days 0, 3, 7, and 10. Only the EPO-low-dose regimen was associated with a significant reduction of necrosis when compared to untreated controls. EPO-low-dose showed a higher increase in both arteriolar diameter and velocity, thereby resulting in a significantly increased arteriolar blood flow and a hence higher functional capillary density (FCD) of the critically perfused zone. EPO-induced angiogenesis was significantly increased in EPO-low-dose at days 7 and 10. Only EPO-high-dose reached a significant hematocrit increase by day 10. Tissue pre- and postconditioning with low doses of EPO protects the critically perfused musculocutaneous tissue by maintaining capillary perfusion because of increased arteriolar blood flow mediated by nitric oxide (NO) expression.