Background: The failure of composite flaps despite anastomotic patency is thought to be mediated by the inflammatory response within the microvasculature, which results from unavoidable surgical trauma and transfer-related ischemia-reperfusion. Evidence suggests that stress conditioning may improve flap survival; however, the molecular mechanisms of protection are far from being clear. Therefore, we analyzed whether stress conditioning-induced heat-shock protein 32 is effective to prevent the inflammatory response in transferred osteomyocutaneous flaps.
Methods: In a rat model, leukocyte-endothelial cell interaction and endothelial integrity disruption as early indicators of the inflammatory response were quantitatively analyzed in muscle, subcuticular tissue, and periosteum of microvascularly transferred osteomyocutaneous flaps by using intravital fluorescence microscopy. Twenty-four hours before flap transfer, stress conditioning was induced by local heating of the left hindlimb up to 42.5 degrees C for 30 minutes. In additional animals, stress conditioning-induced activity of heat-shock protein 32 was inhibited by tin protoporphyrin-IX. Unconditioned flaps served as controls.
Results: In all tissues analyzed, control flaps showed significant leukocyte adherence in postcapillary venules, increased intercellular adhesion molecule-1 (ICAM-1) expression, and endothelial integrity disruption, but a lack of heat-shock protein 32. In contrast, stress conditioning induced marked heat-shock protein 32 expression, which was associated with a significant reduction (P <.05) of leukocyte adherence, ICAM-1 expression, and endothelial hyperpermeability. The inhibition of heat-shock protein 32 by tin protoporphyrin-IX completely abolished the stress conditioning-induced amelioration of the inflammatory response in all tissues analyzed.
Conclusions: Stress conditioning by local heat-shock priming reduces the inflammatory response in osteomyocutaneous flaps. The protective effect is predominantly mediated by the induction of heat-shock protein 32.