Abstract
Objective: Ischemic tolerance (IT) is known to improve resistance to ischemia/reperfusion (I/R)-induced injury; however, the mechanisms remain unknown. The authors hypothesized that induction of heme oxygenase (HO), a heat shock protein, would provide anti-inflammatory benefits during IT, thereby preventing leukocyte-derived I/R injury.
Methods: Male Wistar rats were randomly assigned to sham (n = 4), I/R (n = 9), preconditioning (PC)+I/R (n = 7), chromium mesoporphyrrin, to inhibit HO (CrMP; n = 4), or PC+I/R+CrMP (n = 6) groups. PC consisted of 5 cycles of I/R, each lasting 10 min, induced by tightening a tourniquet placed above the greater trochantor of the hindlimb. Twenty-four hours later, the hindlimb underwent 2 h of no-flow ischemia followed by intravital microscopy during 90 min reperfusion to assess capillary perfusion (#/mm), tissue injury (ratio of ethidium bromide to bisbenzimide labeled cells/100 μ m2), leukocyte rolling (Lr, #/1000 μ m2), and adhesion (La, #/1000 μ m2) in postcapillary venules of the extensor digitorum longus (EDL) muscle. Results: In the I/R group, Lr was significantly increased (7.1 ± 0.4) compared to sham (3.1 ± 0.4). PC+I/R increased Lr (10.8 ± 0.72), which was further exacerbated by the removal of HO (14.2 ± 1.3). La (7.8 ± 2.0) was significantly increased compared to sham (2.4 ± 0.9), while PC returned La back to sham levels (1.9 ± 0.7). Removal of HO activity, via CrMP, had no significant effect on La (3.9 ± 0.7). However, CrMP removed the protection to microvascular perfusion (I/R = 9.4 ± 1.1, PC = 16.6 ± 1.8, sham = 20.5 ± 2.8, PC+CrMP+I/R = 12.3 ± 2.3) and prevented protection from ischemia-induced tissue injury.
Conclusion: The data suggest that HO is an important protective mechanism during IT in skeletal muscle, but such protection was by mechanisms other than altered leukocyte–endothelial cell interaction.
This work was supported by a grant from Canadian Institutes of Health Research.