Ischemia-induced up-regulation of heme oxygenase-1 protects from apoptotic cell death and tissue necrosis.
BACKGROUND
Tissues are endowed with protective mechanisms to counteract chronic ischemia. Previous studies have demonstrated that endogenous heme oxygenase (HO)-1 may protect parenchymal tissue from inflammation- and reoxygenation-induced injury. Nothing is known, however, on whether endogenous HO-1 also plays a role in chronic ischemia to protect from development of tissue necrosis. The aim of this study is, therefore, to evaluate in vivo whether endogenous HO-1 exerts protection on chronically ischemic musculocutaneous tissue, and whether this protection is mediated by an attenuation of the microcirculatory dysfunction.


METHODS
In C57BL/6-mice, a chronically ischemic flap was elevated and fixed into a dorsal skinfold chamber. In a second group, tin-protoporphyrin-IX was administrated to competitively block the action of HO-1. Animals without flap elevation served as controls. With the use of intravital fluorescence microscopy, microcirculation, apoptotic cell death, and tissue necrosis were analyzed over a 10-day observation period. The time course of HO-1 expression was determined by Western blotting.


RESULTS
Chronic ischemia induced an increase of HO-1 expression, particularly at day 1 and 3. This was associated with arteriolar dilation and hyperperfusion, which was capable of maintaining an adequate capillary perfusion density in the critically perfused central part of the flap, demarcating the distal necrosis. Inhibition of endogenous HO-1 by tin-protoporphyrin-IX completely abrogated arteriolar dilation (44.6 +/- 6.2 microm versus untreated flaps: 71.3 +/- 7.3 microm; P < 0.05) and hyperperfusion (3.13 +/- 1.29 nL/s versus 8.55 +/- 3.56 nL/s; P < 0.05). This resulted in a dramatic decrease of functional capillary density (16 +/- 16 cm/cm(2)versus 84 +/- 31 cm/cm(2); P < 0.05) and a significant increase of apoptotic cell death (585 +/- 51 cells/mm(2)versus 365 +/- 53 cells/mm(2); P < 0.05), and tissue necrosis (73% +/- 5% versus 51% +/- 5%; P < 0.001).


CONCLUSIONS
Thus, our results suggest that chronic ischemia-induced endogenous HO-1 protects ischemically endangered tissue, probably by the vasodilatory action of the HO-1-associated carbon monoxide.
Harder
Yves
Y
Institute for Clinical and Experimental Surgery, University of Saarland, Homburg/Saar, Germany. yves.harder@hcuge.ch
Amon
Michaela
M
Schramm
René
R
Rücker
Martin
M
Scheuer
Claudia
C
Pittet
Brigitte
B
Erni
Dominique
D
Menger
Michael D
MD
D000818:Animals; D017209:Apoptosis; D001160:Arterioles / Q000503:physiopathology; D002196:Capillaries / Q000503:physiopathology; D051547:Heme Oxygenase-1 / Q000378:metabolism*; D007511:Ischemia / Q000201:enzymology* / Q000503:physiopathology; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008833:Microcirculation; D009336:Necrosis / Q000201:enzymology*; D013524:Surgical Flaps / Q000502:physiology*; D015854:Up-Regulation; D014666:Vasomotor System / Q000503:physiopathology
D008565:Membrane Proteins; D051547:Heme Oxygenase-1; C496542:Hmox1 protein, mouse