Mechanism of the delay phenomenon: tissue protection is mediated by heme oxygenase-1

Abstract

Induction of the "delay phenomenon" by chronic ischemia is an established clinical procedure, but the mechanisms conferring tissue protection are still incompletely understood. To elucidate the role of heme oxygenase-1 [HO-1 or heat shock protein-32 (HSP-32)] in delay, we examined in the skin-flap model of the ear of the hairless mouse, 1) whether chronic ischemia (delay) is capable to induce expression of HO-1, and 2) whether delay-induced HO-1 affects skin-flap microcirculation and survival by either its carbon monoxide-associated vasodilatory action or its biliverdin-associated anti-oxidative mechanism. Chronic ischemia was induced by transsection of the central feeding vessel of the ear 7 days before flap creation. The flap was finally raised by an incision through four-fifths of the base of the ear. Microcirculatory dysfunction and tissue necrosis were studied with the use of laser Doppler fluxmetry and intravital fluorescence microscopy. HO-1 protein expression was determined with Western blot analysis. Seven days of chronic ischemia (delay) induced a marked expression of HO-1. This was paralleled by a significant improvement (P <0.05) of microvascular perfusion and a reduction (P <0.05) of flap necrosis when compared with nondelayed controls. Importantly, blockade of HO-1 activity by tin protoporhyrin-IX completely blunted the protection of microcirculation and the improvement of tissue survival. Additional administration of the vitamin E analog trolox after blockade of HO-1 to mimic exclusively the anti-oxidative action of the heat shock protein did not restore the HO-1-associated microcirculatory improvement and only transiently attenuated the manifestation of flap necrosis. Thus our data indicate that the delay-induced protection from tissue necrosis is mediated by HO-1, predominantly through its carbon monoxide-associated action of adequately maintaining nutritive capillary perfusion.

Local Preconditioning by Thermal Stress Accelerates Microvascular Thrombus Formation

“…Stress conditioning is known to advance viability of tissues subjected to ischemia and reperfusion (10,35,36). In line with previous reports, we could confirm the upregulation of HSP32 by heat shock and cooling preconditioning, respectively (10,11,24).…”

Ischemia-Induced Up-Regulation of Heme Oxygenase-1 Protects From Apoptotic Cell Death and Tissue Necrosis

“…Recently, we have shown that a 7-day preconditioning with mild hypoxia stimulates HO-1 expression, and that an initial HO-1 overexpression is capable of reducing tissue damage induced by severe ischemia. This represents the delay phenomenon [38], and has to be considered as a classical preconditioning procedure [39]. In the present study, we demonstrate that in nonpreconditioned musculocutaneous tissue, severe ischemia, which is not appropriate to induce preconditioning because it exerts, per se, a considerable amount of necrosis, also induces an up-regulation of endogenous HO-1.…”

Evolution of a “falx lunatica” in demarcation of critically ischemic myocutaneous tissue

“…Accordingly, microscopy early after flap elevation showed a temporary decrease of functional capillary density and capillary red blood cell velocity, whereas capillary dilation was detected only at day 3 and hyperemic capillary perfusion only at days 7 and 10. Thus the capillary hyperemic response within the red zone has to be considered a delayed and chronic rather than an acute process, indicating remodeling that also has been described as a response mechanism to chronic hypoxia in the brain (7) and in the delay phenomenon of the skin (19).…”