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

Heme oxygenase‑1 improves the survival of ischemic skin flaps (Review)

Heat shock protein 32 (Hsp32), also known as heme oxygenase‑1 (HO‑1), is an enzyme that exists in microsomes. HO‑1 can be induced by a variety of stimuli, including heavy metals, heat shock, inflammatory stimuli, heme and its derivatives, stress, hypoxia, and biological hormones. HO‑1 is the rate‑limiting enzyme of heme catabolism, which splits heme into biliverdin, carbon monoxide (CO) and iron. The metabolites of HO‑1 have anti‑inflammatory and anti‑oxidant effects, and provide protection to the cardiovascular system and transplanted organs. This review summarizes the biological characteristics of HO‑1 and the functional significance of its products, and specifically elaborates on its protective effect on skin flaps. HO‑1 improves the survival rate of ischemic skin flaps through anti‑inflammatory, anti‑oxidant and vasodilatory effects of enzymatic reaction products. In particular, this review focuses on the role of carbon monoxide (CO), one of the primary metabolites of HO‑1, in flap survival and discusses the feasibility and existing challenges of HO‑1 in flap surgery.

The Delay Phenomenon: Is One Surgical Delay Technique Superior?

Background:

Surgical delay remains a common method for improving flap survival. However, the optimal surgical technique has not been determined. In this article, we compare flap perfusion, viable surface area, and flap contraction of 2 surgical delay techniques.

Methods:

Male Sprague-Dawley rats were divided into 3 groups. In the incisional surgical delay group (n = 9), a 9 × 3 cm dorsal flap was incised on 3 sides without undermining, leaving a cranial pedicle. In the bipedicle surgical delay group (BSD, n = 9), a 9 × 3 cm dorsal flap was incised laterally and undermined, leaving cranial and caudal pedicles. Control group (n = 16) animals did not undergo a delay procedure. Ten days following surgical delay, all flaps for all groups were raised, leaving a cranial pedicle. A silicone sheet separated the flap and the wound bed. On postoperative day (POD) 7, viable surface area was determined clinically. Contraction compared to POD 0 was measured with ImageJ software. Perfusion was measured with Laser Doppler Imaging. The Kruskal-Wallis with Dunn’s multiple comparisons test was performed for group comparisons.

Results:

BSD preserved significantly more viable surface area on POD 7 (13.7 ± 4.5 cm²) than Control (8.7 ± 1.8 cm²; P = 0.01). BSD also showed significantly less contraction (21.0% ± 13.5%) than Control (45.9% ± 19.7%; P = 0.0045). BSD and incisional surgical delay showed significantly increased perfusion compared with Control on POD 0 (P = 0.02 and 0.049, respectively), which persisted on POD 3. This trend resolved by POD 7.

Conclusion:

BSD showed improved early perfusion, increased viable surface area, and reduced contraction compared to control, suggesting that BSD is the superior flap design for preclinical modeling.

Silk Ligation Delay for the Random Pattern Flap

OBJECTIVE

The purpose of this study is to explore a silk ligation delay for the expanded and unexpanded random flaps to improve the vascularization and survival length of the flap.

METHODS

Marked incision points 2 to 3 cm at every interval along the design line with methylene blue, each incision was about 3 mm long. A subepidermal tunnel was formed on the superfacial layer of dermis between every adjacent incision; another gap was done on the surface of the expander. One end of a No 7 silk thread was inserted into the incision and traversed the surface of the expander until the adjacent incision point, then returned back to the original site through subepidermal tunnel. The both ends of the thread were ligated together to a single knot. All the designed points were performed as above. Then, the ligation procedure was performed along the long axis of the flap from proximal to distal. Both ends of each silk thread were tightly ligated together to a square knot to clamp the soft tissues including the vessels entering the flap. The progress of ligation should depend on blood supply changes of the flap. Remainders would finish under local anesthesia with 0.5% lidocaine or surface anesthetic cream in dressing room at 5 to 7 days after operation as schedule. After that the authors tested the blood supply of the flap and decided the opportunity of final transfer.

RESULTS

There were no complications such as infection, wound dehiscence, expander exposure, significant effusion, and necrosis of the flap in all patients. All the flaps survived completely. Only 1 expander rupture happened during delay operation.

CONCLUSIONS

The technique is a safe and reliable method, it is simple and easy for application, it may provide another choice for the surgical delay.

Umbilical cord-derived mesenchymal stem cells retain immunomodulatory and anti-oxidative activities after neural induction

The immunomodulatory and anti-oxidative activities of differentiated mesenchymal stem cells contribute to their therapeutic efficacy in cell-replacement therapy. Mesenchymal stem cells were isolated from human umbilical cord and induced to differentiate with basic fibroblast growth factor, nerve growth factor, epidermal growth factor, brain-derived neurotrophic factor and forskolin. The mesenchymal stem cells became rounded with long processes and expressed the neural markers, Tuj1, neurofilament 200, microtubule-associated protein-2 and neuron-specific enolase. Nestin expression was significantly reduced after neural induction. The expression of immunoregulatory and anti-oxidative genes was largely unchanged prior to and after neural induction in mesenchymal stem cells. There was no significant difference in the effects of control and induced mesenchymal stem cells on lymphocyte proliferation in co-culture experiments. However, the expression of human leukocyte antigen-G decreased significantly in induced neuron-like cells. These results suggest that growth factor-based methods enable the differentiation of mesenchymal stem cell toward immature neuronal-like cells, which retain their immunomodulatory and anti-oxidative activities.

Paradoxical effects of heme arginate on survival of myocutaneous flaps

Ischemia reperfusion injury (IRI) contributes to partial flap and solid organ transplant failure. Heme-oxygenase 1 (HO-1) is an inducible, cytoprotective enzyme which protects against IRI in solid organ transplant models. Heme arginate (HA), a HO-1 inducer, is a promising, translatable, preconditioning agent. This study investigated the effects of preconditioning with HA on the clinical outcome of a myocutaneous IRI model. Forty male Lewis rats were randomized to intravenously receive 1) Control-NaCl, 2) HA, 3) HA and tin mesoporphyrin (SnMP), a HO-1 inhibitor; and 4) SnMP alone. Twenty-four hours later, an in situ transverse rectus abdominis myocutaneous flap was performed under isoflurane anesthesia. Viability of flaps was measured clinically and by laser-Doppler perfusion scanning. In vitro work on human epidermal keratinocytes (HEKa) assessed the effects of HA, SnMP, and the iron chelator desferrioxamine on 1) cytotoxicity, 2) intracellular reactive oxygen species (ROS) concentration, and 3) ROS-mediated DNA damage. In contrast to our hypothesis, HA preconditioning produced over 30% more flap necrosis at 48 h compared with controls (P = 0.02). HA-containing treatments produced significantly worse flap perfusion at all postoperative time points. In vitro work showed that HA is cytotoxic to keratinocytes. This cytotoxicity was independent of HO-1 and was mediated by the generation of ROS by free heme. In contrast to solid organ data, pharmacological preconditioning with HA significantly worsened clinical outcome, thus indicating that this is not a viable approach in free flap research.

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.

MATERIALS AND 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).

CONCLUSION

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.

Aging is associated with an increased susceptibility to ischaemic necrosis due to microvascular perfusion failure but not a reduction in ischaemic tolerance

In the present study in a murine model of chronic ischaemia, we analysed: (i) whether aging was associated with an increased susceptibility to ischaemic necrosis, and (ii) whether this was based on microvascular dysfunction or reduced ischaemic tolerance. An ischaemic pedicled skin flap was created in the ear of homozygous hairless mice. The animals were assigned to three age groups, including adolescent (2±1 months), adult (10±2 months) and senescent (19±3 months). Microvascular perfusion of the ischaemic flap was assessed over 5 days by intravital microscopy, evaluating FCD (functional capillary density), capillary dilation response and the area of tissue necrosis. Expression of the stress-protein HO (haem oxygenase)-1 was determined by immunohistochemistry and Western blotting. Induction of chronic ischaemia stimulated a significant expression of HO-1 without a significant difference between the three age groups. This was associated with capillary dilation, which, however, was more pronounced in adolescent (10.5±2.8 μm compared with 3.95±0.79 μm at baseline) and adult (12.1±3.1 μm compared with 3.36±0.45 μm at baseline) animals compared with senescent animals (8.5±1.7 μm compared with 3.28±0.69 μm at baseline; P value not significant). In senescent animals, flap creation further resulted in complete cessation of capillary flow in the distal area of the flap (FCD, 0±0 cm/cm2), whereas adult (11.9±13.5 cm/cm2) and, in particular, adolescent animals (58.4±33.6 cm/cm2; P<0.05) were capable of maintaining residual capillary perfusion. The age-associated microcirculatory dysfunction resulted in a significantly increased flap necrosis of 49±8% (P<0.05) and 42±8% (P<0.05) in senescent and adult animals respectively, compared with 31±6% in adolescent mice. Of interest, functional inhibition of HO-1 by SnPP-IX (tin protoporphyrin-IX) in adolescent mice abrogated capillary dilation, decreased functional capillary density and aggravated tissue necrosis comparably with that observed in senescent mice. Thus aging is associated with an increased susceptibility to tissue necrosis, which is due to a loss of vascular reactivity to endogenous HO-1 expression, rather than a reduction in ischaemic tolerance.

Oral administration of nicorandil enhances the survival of ischemic skin flaps in rats

Nicorandil has an anti-apoptotic effect on ischemic myocardium through the activation of ATP-sensitive potassium (K(ATP)) channel. We tested the hypothesis that oral administration of nicorandil had a protective effect on ischemic skin flaps. A cranially based skin flap measuring 3x7 cm in full thickness was made on the back of rats. The rats were divided into a control group and 8 nicorandil groups (group 1-8) according to different doses and timings of administration. On day 7 at 5 cm, groups 1 to 6 (10 or 30 mg/kg twice per day for 3 days starting at 24 h before, 0.5 h before or 0.5 h after the operation) showed significantly higher blood perfusion change rate (73.3+/-2.9%-79.1+/-4.1% vs. 25.9+/-8.6%, P<0.01), and significantly higher survival rate (68.8+/-4.8-75.2+/-8.2% vs. 47.0+/-2.8%, P<0.05) than the control group. Many more surviving blood vessels were also observed in these groups. In contrast, no significant effects were found either in group 7 (30 mg/kg twice per day for 3 days starting 24 h after the operation) or group 8 (30 mg/kg once at 0.5 h after the operation). We did not find an angiogenic effect of nicorandil in vitro. Therefore, our results confirmed that the oral administration of nicorandil could protect tissues from necrosis in ischemic skin flaps. In addition, its protective effect depends on the time of first administration and the duration.

The heat shock proteins and plastic surgery

Heat shock proteins are diverse and essential components of cell physiology. Their expression is elevated in the cell undergoing stress, where they protect the cell from death by necrosis or apoptosis and accelerate recovery. Significant advances have been made in studies relevant to plastic surgery regarding these proteins and their manipulation. This review introduces the heat shock proteins and appraises these studies in skin, ultraviolet light exposure, neoplasia, wound healing, ageing, burns, and reconstructive surgery.

Experimental cooling-induced preconditioning attenuates skin flap failure

BACKGROUND

Microvascular perfusion failure is a leading cause of tissue necrosis in reconstructive surgery. In the present experimental study the effect of local hypothermia was investigated as a possible preconditioning procedure that could induce stress proteins such as heat-shock protein (HSP) 70 and HSP-32 (haem oxygenase (HO) 1). The effect on flap microcirculation and survival was also studied.

METHODS

Ears of hairless mice were subjected to local hypothermia (30 min, 4 degrees C) 24 h before flap creation. A pedicled flap was elevated by incision of four-fifths of the base of the ear. Microcirculatory dysfunction and tissue necrosis were analysed quantitatively over 5 days by means of intravital fluorescence microscopy. HO-1 and HSP-70 protein expression were determined by western blot analysis. HO-1 distribution within the flap tissue was also analysed by immunohistochemistry. Animals with unconditioned flaps served as controls.

RESULTS

Cooling induced a marked expression of HO-1 without induction of HSP-70 protein. This was paralleled by a significant improvement in microvascular perfusion (P < 0.050) that was predominantly regulated by the dilatation of nutritive capillaries. The cooling-mediated improvement in microcirculation resulted in a significant reduction in final flap necrosis (P < 0.050).

CONCLUSION

In this experimental study preoperative cooling was associated with the expression of HO-1 and was an effective conditioning procedure.

Influence of heme-based solutions on stress protein expression and organ failure after hemorrhagic shock

OBJECTIVE

Hemoglobin-based oxygen carriers (e.g., diaspirin-cross-linked hemoglobin [DCLHb] and hemoglobin glutamer-200 [HbG]) may have potential in the treatment of hemorrhagic shock. The nitric oxide scavenging and direct vasoconstrictive side effects of free hemoglobin of currently available preparations may increase organ injury after shock in contrast to non-oxygen-carrying heme solutions (e.g., hemin arginate [HAR]). However, both classes of substances might induce the protective enzyme heme oxygenase (HO)-1, particularly in the liver. The aim of the study was to assess the role of pretreatment with DCLHb, HbG, or HAR on HO-1 expression and organ injury after hemorrhagic shock.

DESIGN

Prospective controlled laboratory study.

SETTING

Animal research laboratory at a university hospital.

SUBJECTS

Male Sprague-Dawley rats (200-300 g body weight, n = 5-12/group).

INTERVENTIONS

Twenty-four hours after different doses of DCLHb, HbG (each 1, 2, or 3 g/kg of body weight), or HAR (5, 25, or 75 mg/kg of body weight), the protein expression of HO-1 and heat shock protein-70 in liver, kidney, heart, lungs, and aorta was determined. Twenty-four hours after pretreatment with DCLHb, HbG, or HAR, rats were subjected to hemorrhage (mean arterial blood pressure, 35-40 mm Hg for 1 or 2 hrs)/resuscitation (5 or 4 hrs, respectively). Animals treated with Ringer's solution (30 mL/kg of body weight) served as controls. In additional experiments, HO activity was blocked with tin mesoporphyrin-IX.

MEASUREMENTS AND MAIN RESULTS

DCLHb, HbG, and HAR dose-dependently induced HO-1 protein but not heat shock protein-70. Pretreatment with DCLHb or HbG shortened the onset of decompensation in shock (DCLHb, 40 +/- 11 mins; HbG, 36 +/- 4 mins) compared with vehicle (68 +/- 4 mins, p < .05) and HAR pretreatment (81 +/- 7 mins, p < .05). High doses of DCLHb pretreatment increased mortality (2 hrs of shock, 80%; p < .05 vs. vehicle or HAR). Pretreatment with HAR led to higher shed blood volumes (p < .05) and higher hepatocellular ATP levels (2 hrs of shock, p < .05 vs. DCLHb and HbG). Blockade of HO activity by tin mesoporphyrin-IX abolished the protection mediated by HAR.

CONCLUSIONS

Although DCLHb, HbG, and HAR induce HO-1 in the absence of an unspecific stress response, only HAR pretreatment protects against shock-induced organ failure. Although the underlying mechanisms of positive HAR priming are not completely understood, the induction of HO-1 expression and the lack of nitric oxide scavenging through HAR may play an important role.

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

Using intravital microscopy in a chronic in vivo mouse model, we studied the demarcation of myocutaneous flaps and evaluated microvascular determinants for tissue survival and necrosis. Chronic ischemia resulted in a transition zone, characterized by a red fringe and a distally adjacent white falx, which defined the demarcation by dividing the proximally normal from the distally necrotic tissue. Tissue survival in the red zone was determined by hyperemia, as indicated by recovery of the transiently reduced functional capillary density, and capillary remodeling, including dilation, hyperperfusion, and increased tortuosity. Angiogenesis and neovascularization were not observed over the 10-day observation period. The white rim distal to the red zone, appearing as “falx lunatica,” showed a progressive decrease of functional capillary density similar to that of the necrotic distal area but without desiccation, and thus transparency, of the tissue. Development of the distinct zones of the critically ischemic tissue could be predicted by partial tissue oxygen tension (Pt[Formula: see text]) analysis by the time of flap elevation. The falx lunatica evolved at a Pt[Formula: see text] between 6.2 ± 1.3 and 3.8 ± 0.7 mmHg, whereas tissue necrosis developed at <3.8 ± 0.7 mmHg. Histological analysis within the falx lunatica revealed interstitial edema formation and muscle fiber nuclear rarefaction but an absence of necrosis. We have thus demonstrated that ischemia-induced necrosis does not demarcate sharply from normal tissue but develops beside a fringe of tissue with capillary remodeling an adjacent falx lunatica that survives despite nutritive capillary perfusion failure, probably by direct oxygen diffusion.