Impact of ischemia on tissue oxygenation and wound healing: intravital microscopic studies on the hairless mouse ear model

Various effects of 11,12 EET rescue wound healing in a combined model of diabetes and ischemia

Chronic non healing wounds in diabetic patients still impose a major problem in modern medicine. Especially additional peripheral vascular disease complicates treatment success in these patients. Thus, we analyzed the effects of 11,12 epoxyeicosatrienoic acid (EET) in a combined model of hyperglycemia and ischemia in mice. Hyperglycemia was induced by Streptozotozin 2 weeks prior to wounding. 3 days before wound creation 2 of the 3 suppling vessels of the moue ear were cautherized for ischemia. Either 11,12 EET or solvent for control was applied. Wound closure as well as TNF-α, TGF-β, SDF-1α, VEGF, CD31, and Ki67 were measured. The wounds closed on day 14.4 ± 0.4 standard deviation (SD). 11,12 EET treatment enhanced healing to 9.8 ± 0.6 SD. TNF-α level was augmented on day 9 compared to control and receded on day 18. TGF-β seemed to be elevated all days observed after 11,12 EET treatment. SDF-1α was enhanced on day 6 and 9 by 11,12 EET, and VEGF on day 6 and 18 as well as CD13 on day 3, 6, and 18. 11,12 EET did not alter Ki67. 11,12 EET are able to rescue deteriorated wound healing in a combined model of hyperglycamia and ischemia by resolution of inflammation, augmentation of neovascularization and increasing expression of TGF-β as well as SDF-1α.

Animal experimental models of ischemic wounds - A review of literature

Critical limb ischemia is a serious form of peripheral arterial disease (PAD). The consequences of lower limb ischemia are pain, claudication and chronic non-healing wounds. Patients with diabetes are especially at a high risk for developing non-healing ulcers. The most serious complication is major amputation. For this reason, there is a significant medical requirement to develop new therapies in order to prevent the progression of PAD. For research purposes, it is crucial to find an appropriate model of chronic ischemia to explore the processes of wound healing. According to recently acquired information, rodents are currently the most commonly used animals in these types of studies. The main advantage of using small animals is the low financial cost due to the relatively small demand for food, water and living space. The disadvantage is their anatomy, which is different from that of humans. Larger animals have a more human-like anatomy and physiology, but they require more expense and space for housing. A bipedicle skin flap and its modifications are popular models for ischemic wounds. In order to secure healing through re-epithelisation, as opposed to contraction in rodents, there is a need to remove the panniculus carnosus muscle. Wounds in other experimental animals heal primarily through re-epithelisation. The application of a silicone mesh underneath the flap prevents vascular regrowth in ischemic tissue. There is an ongoing effort to create in vivo diabetic models for chronic ulcer research. This work presents an overview of existing animal models of ischemic wounds.

Photobiomodulation therapy was more effective than photobiomodulation plus arginine on accelerating wound healing in an animal model of delayed healing wound

The combined and individual influences of photobiomodulation therapy (PBMT) and arginine on wound strength, stereological parameters, and gene expressions of some related growth factors in ischemic and delayed healing wounds in rats were analyzed. We divided 108 rats into six groups: control, lower energy density (LOW)-PBMT, 2% arginine ointment (Arg 2%), LOW-PBMT + Arg 2%, high energy density (HIGH)-PBMT, and HIGH-PBMT + Arg 2%. First, we generated an ischemic and delayed healing wound model in each rat. We examined wound strength, stereological parameters, and gene expressions of basic fibroblast growth factor (bFGF), vascular endothelial growth factor A (VEGF-A), and stromal cell-derived factor 1 (SDF-1) by quantitative real-time polymerase chain reaction (qRT-PCR). PBMT alone and PBMT + Arg 2% considerably increased wound strength compared to the control and Arg 2% groups during the inflammatory and proliferative steps of wound healing (p < 0.05). In these steps, PBMT alone significantly induced an anti-inflammatory effect and increased fibroblast counts; Arg 2% alone induced an inflammatory response (p < 0.05). Concurrently, PBMT and PBMT + Arg 2% significantly increased keratinocyte counts and volume of the new dermis (p < 0.05). At the remodeling step, the Arg 2% groups had significantly better wound strength than the other groups (p < 0.05). In this step, PBMT and PBMT + Arg 2% significantly decreased inflammation, and increased fibroblast counts, vascular length, and the volume of new epidermis and dermis compared to the control and Arg 2% groups (p < 0.05). In all cases of gene analysis, there were statistically better results in the PBMT and PBMT + Arg 2% groups compared with the Arg 2% and control groups (p < 0.05). The anti-inflammatory and repairing effects of PBMT on an ischemic and delayed healing wound model in rats were shown by significant improvements in wound strength, stereological parameters, and gene expressions of bFGF, VEGF-A, and SDF-1α.

11,12 and 14,15 epoxyeicosatrienoic acid rescue deteriorated wound healing in ischemia

Introduction

Epoxyeicosatrienoic acids (EETs) are able to enhance angiogenesis and regulate inflammation that is especially important in wound healing under ischemic conditions. Thus, we evaluated the effect of local EET application on ischemic wounds in mice.

Methods

Ischemia was induced by cautherization of two of the three supplying vessels to the mouse ear. Wounding was performed on the ear three days later. Wounds were treated either with 11,12 or 14,15 EET and compared to untreated control and normal wounds. Epithelialization was measured every second day. VEGF, TNF-α, TGF-β, matrix metalloproteinases (MMP), tissue inhibitors of metalloproteinases (TIMP), Ki67, and SDF-1α were evaluated immunohistochemically in wounds on day 3, 6, and 9.

Results

Ischemia delayed wound closure (12.8 days ± 1.9 standard deviation (SD) for ischemia and 8.0 days ± 0.94 SD for control). 11,12 and14,15 EET application ameliorated deteriorated wound healing on ischemic ears (7.6 ± 1.3 SD for 11,12 EET and 9.2 ± 1.4 SD for 14,15 EET). Ischemia did not change VEGF, TNF-α, TGF-β, SDF-1α, TIMP, MMP7 or MMP9 level significantly compared to control. Local application of 11,12 as well as 14,15 EET induced a significant elevation of VEGF, TGF-β, and SDF-1α expression as well as proliferation during the whole phase of wound healing compared to control and ischemia alone.

Conclusion

In summary, EET improve impaired wound healing caused by ischemia as they enhance neovascularization and alter inflammatory response in wounds. Thus elevating lipid mediator level as 11,12 and 14,15 EET in wounds might be a successful strategy for amelioration of deranged wound healing under ischemia.

Development and Characterisation of a Human Chronic Skin Wound Cell Line-Towards an Alternative for Animal Experimentation

Background: Chronic skin wounds are a growing financial burden for healthcare providers, causing discomfort/immobility to patients. Whilst animal chronic wound models have been developed to allow for mechanistic studies and to develop/test potential therapies, such systems are not good representations of the human chronic wound state. As an alternative, human chronic wound fibroblasts (CWFs) have permitted an insight into the dysfunctional cellular mechanisms that are associated with these wounds. However, such cells strains have a limited replicative lifespan and therefore a limited reproducibility/usefulness. Objectives: To develop/characterise immortalised cell lines of CWF and patient-matched normal fibroblasts (NFs). Methods and Results: Immortalisation with human telomerase resulted in both CWF and NF proliferating well beyond their replicative senescence end-point (respective cell strains senesced as normal). Gene expression analysis demonstrated that, whilst proliferation-associated genes were up-regulated in the cell lines (as would be expected), the immortalisation process did not significantly affect the disease-specific genotype. Immortalised CWF (as compared to NF) also retained a distinct impairment in their wound repopulation potential (in line with CWF cell strains). Conclusions: These novel CWF cell lines are a credible animal alternative and could be a valuable research tool for understanding both the aetiology of chronic skin wounds and for therapeutic pre-screening.

Alternatives for animal wound model systems

In this chapter a review of animal model systems already being utilized to study normal and pathologic wound healing is provided. We also go into details on alternatives for animal wound model systems. The case is made for limitations in the various approaches. We also discuss the benefits/limitations of in vitro/ex vivo systems bringing everything up to date with our current work on developing a cell-based reporter system for diabetic wound healing.

C-type natriuretic peptide slows down wound healing but promotes angiogenesis in SKH1-hr hairless mice

C-type natriuretic peptide (CNP) is known to increase growth rate of endothelial cells in vitro. In addition, gene transfer of CNP into ischaemic muscle was shown to induce angiogenesis. So far, no study has addressed the effect of CNP on dermal wound healing. The ear wound model in mice was used in this study. The first group was treated with dsRed-CNP plasmid, whereas the second group was transfected with the empty dsRed-sine plasmid, lacking sequence coding for CNP. The third group was sham operated and treated with saline to serve as second control. Wound size was measured on days 0, 1, 3, 5, 7, 9, 11 and 14. On days 7 and 14 capillary density was analysed. Wound closure rate was significantly reduced in mice treated with CNP [dsRed-CNP 73·3 ± 3·2% versus dsRed-sine 94·5 ± 2·4% versus saline 92·1 ± 2·4%, n = 8 per group, analysis of variance (ANOVA) P < 0·001] at day 7 postop. Capillary density was found to be significantly higher in CNP-treated mice (dsRed-CNP 18·7 ± 3·9 versus dsRed-sine 12·3 ± 2·7 versus control 10·1 ± 4·7, CD31(+) capillaries per microscope field, ANOVA P = 0·018) at day 14 postoperative. CNP significantly reduces wound closure rate in hairless mice but promotes the development of new blood vessels. A possible explanation is the dual effect of CNP, inhibiting growth of fibromyoblasts but stimulating growth of endothelial cells. Thus, CNP may serve as a therapeutic approach to diseases caused by hyperfibrosis.

Effects of buflomedil and pentoxifylline on hamster skin-flap microcirculation: prediction of flap viability using orthogonal polarization spectral imaging

OBJECTIVE

This study investigated the effects of buflomedil and pentoxifylline, both of which are used in reconstructive surgery of hamster skin flap microcirculation, and evaluated the skin flap survival rate by orthogonal polarization spectral imaging.

METHOD

Twenty-four adult male Syrian golden hamsters were divided into three groups: a control (C, 0.1 ml 0.9% saline), buflomedil (B, 3 mg/kg/day), and pentoxifylline group (P, 14.5 mg/kg/day). Treatments administered intraperitoneally were initiated 1 hour before skin flap preparation and continued for 7 days post-operatively at 12-hour intervals. Preparations (skin flaps) were divided into 12 fields, which were organized into six bands. Functional capillary density (FCD, in mm/mm(2)), distance from the skin flap base to blood flow cessation (Dist(with flow), in cm), percentage of viable skin (VA, in%), and qualitative analysis of blood flow by orthogonal polarization spectral imaging were performed at 1 and 24 hours and on the seventh post-operative day.

RESULT

Bands IV, V, and VI presented no flow independent of time. The functional capillary density group B was higher than that of groups C and P, primarily after 24 hours. All groups showed an increase in D with time but reached similar final distances (C = 2.73, B = 2.78 and P = 2.70 cm). Moreover, the percentage of viable areas remained at approximately 50%. The orthogonal polarization spectral imaging was useful to assess viability by counting fields with and without blood flow.

CONCLUSIONS

Functional capillary density values were higher in the buflomedil group compared to the control and pentoxifylline groups in this model. Functional capillary density did not influence D or the percentage of VA, and the technique showed favorable potential to assess/predict the viability of skin flaps within 1 h after surgery.

Orthogonal polarization spectral imaging versus intravital fluorescent microscopy for microvascular studies in wounds

The aim of this study was to validate orthogonal polarization spectral (OPS) imaging against intravital fluorescence microscopy (IFM) for microvascular measurements in normal skin and during wound healing. Experiments were performed on the ears of hairless mice (N = 8). The diameter of arterioles and venules, red blood cell velocity in venules, and the functional capillary density were assessed under normal conditions using OPS imaging and IFM. After creation of a circular wound, these observations were repeated at the identical microvascular regions on days 4, 7, 10, and 15. Images were videotaped, and CapImage was used for off-line computer-assisted analysis. Using OPS imaging, the microcirculation of wounded skin in hairless mice could be observed successfully. The regression analyses against standard IFM revealed a significant (p < 0.001) correlation for measurements of all microcirculatory parameters investigated (venular diameter: r(2) = 0.98, N = 345; red blood cell velocity: r(2) = 0.51, N = 326; functional capillary density: r(2) = 0.44, N = 156). However, for diameter as well as for functional capillary density measurements, OPS imaging yielded lower absolute values compared with IFM. The authors were able to validate OPS imaging against IFM for the measurement of microvascular parameters in an animal model of skin wound healing. Such a device should now help to study the role of microcirculation in physiology and pathophysiology during wound healing in patients. First clinical investigations are promising.

Approaches to study of ischemia in bone

Ischemic osteonecrosis is a complication of certain traumatic and a number of idiopathic conditions. The course of the disease may result in collapse of the convex member of a joint and osteoarthritis, often requiring arthroplasty. Increasing incidence in young adults poses a challenge for development of long-term joint prostheses. Current status of research into the disease is discussed and three new models using intravital microscopy described. The first, an arterial occlusion (AO) model, creates ischemia by occluding the common iliac artery exclusively, avoiding direct trauma on other tissues in the limb. The second, a total occlusion (TO) model utilizes classical tourniquet occlusion of the thigh vessels. The third, a venous occlusion (VO) model, is also a tourniquet procedure but it blocks occlusion of the femoral artery with a protective sheath. Preliminary results from AO and TO studies are reported which show that reperfusion injury is detectible after ischemia doses as short as 4 h. This complication was confirmed by observation of leukocyte adherence, secondary ischemia, and abnormal vessel leakage. Also, a new quantitation of osteonecrosis is introduced whereby fluorescently-tagged dead osteocytes and computer-based image processing provide values for an "osteonecrosis index." Viewing of all vascular events is made possible by intravital microscopy through a bone chamber window implanted in rabbit tibias. It is proposed that such chronic visual techniques allow quantitation of events leading to osteonecrosis as well as the revascularization, resorption and bone apposition of creeping substitution which characterizes postischemia recovery.

Ischemia increases the angiogenic potency of basic fibroblast growth factor (FGF-2)

The aim of this study was to investigate the angiogenic response to exogenously administered basic fibroblast growth factor (FGF-2) in normal and ischemic skin, using the hairless mouse ear microcirculatory model. The hairless mouse ear is a well-established model for in vivo studies of skin microcirculation. Using this model, angiogenesis- and angiogenesis-associated changes in the microcirculation can be directly and continuously viewed and quantified in a variety of different experimental settings. To create ischemia in the mouse ear, all but one of the three to four feeding vessels nourishing the ear were ligated 3 days prior to a local subdermal injection of FGF-2 (9.3 + 1-0.5 mm/mm2) or saline into the dorsum of the ears. Angiogenesis was quantified by direct observation, at high magnification, of the injection site where increases in total vessel length (TVL) were measured repeatedly over 18 days following injection. We found a significant (P < 0.01) increase in TVL in normal and ischemic ears injected with FGF-2. Saline injection also induced a significant increase in TVL in ischemic ears. However, the angiogenic response to FGF-2 in ischemic ears was significantly stronger than saline alone in ischemic ears or saline or FGF-2 in normal ears. This response could be used clinically to accelerate angiogenesis and thus increase perfusion in ischemic tissue.

Sutured wound in myxomatous mitral valve one month after repair surgery: report of two cases

There have been no reports concerning wound healing at the site of the suture line in myxomatous leaflets. We microscopically studied the sutured wounds in two myxomatous posterior mitral leaflets which underwent quadrangular resection of the frail middle segment followed by primary suture. The sutured wounds had a thick scar which was abundant in collagen fibers about 1 month after the repair surgery. This suggests that severe myxomatous degeneration itself would not be a cause of wound dehiscence, and that a sutured wound could be a cause of rigidity and deformity of leaflets.

Microcirculation research, angiogenesis, and microsurgery

Angiogenesis, the formation of new blood vessels, is essential to a variety of normal and pathologic processes such as wound healing and tumor growth. In microsurgery the development of new vessels between the transferred tissue and the recipient bed is critical to the final outcome of the reconstruction. Several experimental models have been previously developed to study angiogenesis and the effect that new substances have on regulating this process, but they lack the ability to make quantitative measurements. Therefore, we have developed an animal model using the homozygous (hr/hr) hairless mouse ear; by using intravital microscopy and computer-assisted analysis, angiogenesis can be quantitatively measured. Using this model we showed that basic fibroblast growth factor and transforming growth factor beta significantly increased total vessel length by 32% and 63%, respectively, during 20 days following subcutaneous injection. In this paper the importance of angiogenesis research to reconstructive microsurgery is presented and discussed.

Scope and perspectives of intravital microscopy--bridge over from in vitro to in vivo

As observations in vitro become more sophisticated, it is increasingly important to be able to assess their relevance to the intact animal. Intravital microscopy provides an advanced set of tools for the dissection of the in vivo situation.

Basic fibroblast growth factor accelerates wound healing in chronically ischaemic tissue

The influence of subcutaneously injected recombinant human basic fibroblast growth factor (bFGF) on wound healing in normal (n = 20) and ischaemic (n = 28) skin tissue was investigated. Standardized wounds (5 mm2) were created on the ears of hairless mice and treated for the first 3 days after wound creation with total doses of 720 ng (n = 24) and 4050 ng (n = 24) bFGF. The bFGF had no effect on wound healing in non-ischaemic tissue. In ischaemic skin, mean(s.d.) wound surface area after treatment with 720 ng bFGF was 1.6(0.9), 0.5(0.6) and 0.1(0.3) mm2 compared with 2.8(1.0), 1.4(1.0) and 0.8(0.7) mm2 for control wounds on days 7 (P < 0.04), 10 (P < 0.03) and 13 (P < 0.04) respectively. High-dose bFGF (4050 ng) reduced the mean(s.d.) wound surface area to 2.4(0.7) and 0.8(0.7) mm2 compared with 3.9(0.6) and 2.1(0.8) mm2 for control wounds on days 7 (P < 0.006) and 10 (P < 0.02) respectively. These results suggest that bFGF may be of use for the treatment of wounds in ischaemic tissue.