Bruce A. Mast

Interactions of cytokines, growth factors, and proteases in acute and chronic wounds.

A healing wound represents a complex series of interactions between cells, soluble mediators, and extracellular matrix. Within this multifaceted environment, there are multiple regulatory points which control the ordered series of events that lead to normal tissue repair. An alteration in this physiologic network can lead to the development of a chronic wound. This article presents an update on the numerous mediators that exist within the wound environment in both acute normal healing and chronic nonhealing wounds. We also present a hypothesis which may provide a conceptual pathophysiologic mechanism with which to understand all chronic wounds.

In vivo degradation of fetal wound hyaluronic acid results in increased fibroplasia, collagen deposition, and neovascularization.

Fetal tissue repair occurs without acute inflammation, prominent fibroplasia, or marked neovascularization. The fetal wound extracellular matrix is rich in hyaluronic acid (HA), while collagen is deposited in an organized normal dermal pattern. In various biologic systems, including regeneration and development, the controlled accumulation and subsequent degradation of hyaluronic acid is associated with distinct cellular and matrix events. Therefore, it is hypothesized that the abundance of hyaluronic acid in fetal wounds may influence cellular and/or matrix events such that tissue repair is highly organized and adult-like scarring does not occur. To test this hypothesis, the hyaluronic acid content of fetal rabbit wounds was reduced by specific degradation with Streptomyces hyaluronidase. Control wounds were treated with either enzyme buffer (n = 12) or denatured enzyme solution (n = 8) and exhibited a normal fetal healing response with scattered peripheral fibroblasts, a matrix of hyaluronic acid, and no infiltrating collagen. In marked contrast, the hyaluronidase-treated wounds (n = 14) demonstrated increased fibroblast infiltration, collagen deposition, and capillary formation. A significant reduction in the hyaluronic acid content of the hyaluronidase-treated wounds was confirmed biochemically. Since the degradation of hyaluronic acid resulted in an altered healing response, this study demonstrates that hyaluronic acid affects the cellular and matrix events in fetal healing and may be partially responsible for the unique qualities of this regenerative repair process.

Molecular and mechanistic validation of delayed healing rat wounds as a model for human chronic wounds.

The purpose of this study was to provide molecular and mechanistic evaluation of an ischemic wound model in rats to determine if it is a valid model for human chronic wounds. Compared to acute wounds, human chronic wounds contain markedly elevated levels of proinflammatory cytokines and matrix metalloproteinases, while matrix metalloproteinase inhibitors and growth factor activity are diminished. Accordingly, tissue from ischemic and normal rat wounds were analyzed for cytokine, proteases and growth factor levels. Dorsal full thickness punch wounds were created in rats using a reproducible template. The ischemic wound group (n = 10) had six uniformly placed wounds within a bipedicled dorsal flap. The control group (n = 10) had the same wounds created without elevation of a flap. On postwound days 3, 6 and 13 wounds were excised and analyzed. Protein levels for tumor necrosis factor‐α were determined with a rat‐specific enzyme‐linked immunosorbent assay, while mRNA was determined by RNase protection assay. Matrix metalloproteinases and serine protease detection was done using gelatin and casein zymography, respectively. Significant delay in healing was achieved in the ischemic group: 50% healing for control wounds was at 7 days and 11 days for ischemic wounds (p < 0.001). No significant differences between wound groups were found for interleukin‐1β, and mRNA for tumor necrosis factor‐α and interleukin‐1β. However, at day 13 ischemic wounds contained significantly more tumor necrosis factor‐α than controls and normal skin (586 ± 106 pg/biopsy vs. 79 ± 7 pg/biopsy vs. 52 ± 2 pg/biopsy; p < 0.001). Zymography showed substantially greater quantities of matrix metalloproteinase‐2, matrix metalloproteinase‐9, and serine proteases in ischemic wounds. This model of delayed healing in rats shares many of the key biochemical, molecular and mechanistic characteristics found in human chronic wounds, namely elevated tumor necrosis factor‐α and protease levels. As such, this model will likely prove to be useful in chronic wound research, particularly in developing novel therapeutics.

HEALING IN OTHER TISSUES

Wound healing in many tissue types is essentially the same as that which occurs in skin. The repair processes that occur in bone, tendon, the alimentary tract, skin grafts, and bone grafts are substantially different from cutaneous wound repair. Because surgeons frequently encounter these tissues, it is essential to understand how they heal.

Comparison of magnetic resonance angiography and digital subtraction angiography for visualization of lower extremity arteries.

Objective vascular assessment is frequently required before microvascular reconstruction involving the lower extremities. The purpose of this study was to evaluate the reliability of magnetic resonance angiography (MRA) for preoperative assessment before free flap surgery. Five patients underwent preoperative MRA: one before fibula harvest for oromandibular reconstruction, and four before muscle free flap reconstruction of the lower extremity. In all patients, the tibioperoneal trunk, anterior tibial, posterior tibial, and peroneal arteries were well visualized to the ankle, including pathological occlusions. The radiographic findings were demonstrated at surgery and were confirmed to be accurate. These findings facilitated and guided the surgical procedure. This study strongly suggests the accuracy and surgical relevance of MRA before free flap surgery. MRA is desirable over angiography because of its noninvasive nature. It may also be better than ultrasonography because the latter is highly dependent on the technician (particularly in identifying the peroneal artery). MRA may likely replace angiography as the objective procedure of choice before microvascular surgery.

Subtotal maxillectomy for melanotic neuroectodermal tumor of infancy

Melanotic neuroectodermal tumor of infancy is a rare pigmented neoplasm occurring in infants before 1 year of age. It is a rapidly growing tumor that most frequently affects the craniofacial skeleton. Although melanotic neuroectodermal tumor of infancy is benign in the vast majority of cases, inadequate excision, occasional multicentricity, and a small malignant potential result in a fairly high recurrence rate. On the basis of data obtained from the literature and our clinical experience, we advocate an aggressive surgical approach consisting of complete surgical excision when vital structures are not involved. Histopathologic confirmation of complete excision is mandatory to minimize the risk of recurrence and provide the patient with curative treatment and minimal morbidity.

Tissue repair in the fetal intestinal tract occurs with adhesions, fibrosis, and neovascularization.

Cutaneous wound healing in the fetus can occur in a nonfibrotic, regenerative manner. However, other fetal tissues such as bone and stomach heal with scar formation. In light of potential ramifications for adult hollow visceral scarring (biliary and intestinal strictures), this study was undertaken to determine if tubular visceral tissue repair in the fetus is regenerative or fibrotic. Fetal rabbits underwent laparotomy on day 24 of gestation, during which a controlled intestinal enterotomy was created and suture repaired immediately using microsurgical techniques. Maternal rabbits and adult male rabbits also underwent enterotomy and repair. After 5 days all animals were sacrificed and the wounds analyzed histologically by a pathologist in a blinded fashion. All animals demonstrated a similar degree of peri-intestinal adhesion formation. Fetal and maternal wounds contained fibroblastic and smooth muscle cell proliferation, mild inflammatory infiltration, and new blood vessel formation. The male adult wounds demonstrated a more pronounced fibrovascular healing response. Immunohistochemical staining for CD31 (endothelial cell marker) was quantitated on a scale of 0 to 4+, indicating degree of neovascularization. The mean scores for the fetal and maternal groups were similar (1.70 ± 0.68 and 1.23 ± 1.07 respectively), but were significantly greater for male adults (2.93 ± 0.12; p = 0.001 by analysis of variance). The results of this study indicate that hollow visceral tissue repair in the fetal rabbit intestine occurs in a similar fibrotic manner as adult healing. This provides further evidence that regenerative healing in the fetus is not ubiquitous. Differences in the degrees of fibrosis and neovascularization between adult male and pregnant female wounds deserve further investigation.

Hyaluronic acid degradation products induce neovascularization and fibroplasia in fetal rabbit wounds

Scarless fetal wound healing occurs with mild fibroplasia and neovascularization, while the wound is persistently enriched with hyaluronic acid. Conversely, adult wounds are characterized by prominent fibroplasia, neovascularization, and scar formation, and hyaluronic acid is a transient component of the early adult wound matrix. Our group has reported that enzymatic degradation of fetal rabbit wound hyaluronic acid results in marked increases in fibroplasia, collagen deposition, and neovascularization. This altered, adultlike healing response is hypothesized to have resulted from the generation of biologically active hyaluronic acid degradation products. Therefore, this study analyzes the fibrovascular inductive activity of hyaluronic acid degradation products. Fetal rabbit wounds were treated with hyaluronic acid degradation products generated by methods known to produce oligosaccharides with significant angiogenic activity. Implants from wounds treated with either of the control solutions (n = 4 for each control) had identical histologic features characterized by a mild mononuclear cell infiltrate but neither infiltrating fibroblasts nor collagen. In marked contrast, implants from wounds treated with hyaluronic acid degradation products contained infiltrating fibroblasts and collagen intermixed with numerous blood vessels. Quantitation of capillary ingrowth showed a sixfold increase in the neovascular response in wounds treated with hyaluronic acid degradation products compared with either controls (p < 0.05). This study shows that hyaluronic acid degradation products stimulate neovascularization and fibroplasia in fetal wounds. These observations suggest that a balance between hyaluronic acid accumulation and degradation has significant regulatory influence in fetal tissue repair.

Painful pectoralis major myospasm as a result of sternal wound reconstruction: complete resolution with bilateral pectoral neurectomies.

We report a patient with a highly unusual and previously unreported complication with the use of the pectoralis major muscle to treat the infected median sternotomy. The diagnosis of painful myospasm was made by a combination of physical findings and exclusion of other conditions such as recurrent infection. Treatment by pectoral denervation was relatively simple and highly successful. Patients with chest-wall pain after sternal wound reconstruction should have myospasm entertained as a possible cause.

The nasolabial flap revisited as an adjunct to floor-of-mouth reconstruction.

Composite free tissue reconstruction for floor-of-mouth defects are thought of as single-stage procedures. However, postoperative wound complications often require additional soft-tissue coverage to salvage the initial reconstruction. Nasolabial flaps interpolated into the oral cavity offer an expedient solution to soft-tissue deficits encountered during complicated floor-of-mouth reconstructions. The records of 39 patients undergoing free tissue reconstruction, from July 1995 to December 1999 at Shands Hospital and the Gainesville VA Medical Center, for floor-of-mouth defects were reviewed. Six patients developed postoperative wound complications that compromised the initial reconstruction. In all patients, inferiorly based nasolabial flaps were used to provide additional soft-tissue coverage and wound closure. Radiation therapy and facial artery ligation did not affect the outcome. Complete wound healing and salvage of the initial reconstruction was achieved in all 6 patients.