Bioactive interleukin-8 is expressed in wounds and enhances wound healing.

BACKGROUND: Wound healing is a sequential biological process that involves the integration of chemotaxis of neutrophils, mitosis and migration of keratinocytes, and remodeling of the scar, all of which are regulated by specific soluble mediators. To modulate wound healing specific mediators have to be identified and functionally characterized. Therefore we addressed this study on the polymorphonuclear leukocyte (PMN) attractant interleukin-8 (IL-8) and its function in epidermal wound healing. MATERIALS AND METHODS: Peptide purification, bioassays for PMN chemotaxis, and sequential IL-8 measurements were performed on human wound fluid from burn blisters and skin graft donor sites. Histology for IL-8 immunoreactivity was included. In vitro human keratinocytes were assayed for proliferation, migration, and integrin expression after IL-8 treatment. Wounding experiments with topical IL-8 were performed in a chimeric mouse model. RESULTS: IL-8 was found to be the major bioactive chemoattractant for PMNs in human blister and skin graft donor site wound fluids (mean levels ranging from 173 ng/ml Postoperative Day (POD) 1 to 2130 ng/ml (POD 5)). Released intracellular epidermal IL-8 immunoreactivity at the wound edge was considered as an immediate source of IL-8 while NH(2)-terminal analysis revealed the 77-amino-acid residue form as a second source of IL-8 possibly PMN derived. In vitro experiments on the effect of recombinant human (rh) IL-8 on keratinocyte proliferation revealed a rise in cell number (4.8-fold, ED(50) = 0.6 ng/ml), which was accompanied by an increase in cells in S phase and overexpression of the integrin subunit alpha6. In vivo topically applied IL-8 (1 microg/ml) on human skin grafts in a chimeric mouse model enhanced reepithelialization in IL-8 treated animals over controls due to elevated numbers of mitotic keratinocytes. Wound contraction was significantly diminished by topical IL-8. CONCLUSIONS: These results indicate the sequential function of endogenous IL-8 in all phases of human wound healing. Topical IL-8 may be useful in impaired wound healing.

Expression of pig endogenous retrovirus by primary porcine endothelial cells and infection of human cells.

BACKGROUND: The risk of interspecies transmission of retroviruses during xenotransplantation is suggested by reports of pig endogenous retrovirus (PERV) released from porcine cell lines productively infecting human cell lines in vitro and of infectious PERV being released from pig peripheral blood mononuclear cells after mitogenic stimulation. Endothelial cells are the main interface between a xenograft and the recipient's leucocytes and tissues. METHODS: We have analysed pig primary aortic endothelial cells (PAEC) together with other transplantation-relevant porcine cells and tissues for expression of PERV mRNA. Release of virus particles by PAEC was monitored by reverse transcriptase (RT) activity in the medium of cultured PAEC. Infectivity for human cells was tested by co-cultivation of irradiated PAEC with the human embryonal kidney cell line HEK293 and looking for virus release from the human cells. FINDINGS: PAECs, hepatocytes, lung, and skin from a variety of pig strains and breeds expressed PERV mRNA. PAEC released infectious particles. Co-cultivation of PAEC and HEK293 led to productive infection of the human cells and expression of PERV types A and B. INTERPRETATION: Release of infectious virus from PAEC occurred without mitogenic stimulation, suggesting a serious risk of retrovirus transfer after xenotransplantation.

Porcine endogenous retrovirus (PERV) was not transmitted from transplanted porcine endothelial cells to baboons in vivo.

The discussion about the clinical risk of zoonoses in xenotransplantation has recently culminated in the demand for a moratorium on clinical organ transplantation using pig donors. The basis for this discussion was a recent report showing a possible trans-species transmission of pig endogenous retrovirus (PERV) by in vitro transfer to human cell lines. At present, it remains unclear if this could also happen in vivo or in the setting of xenotransplantation. Potential in vivo transfer of PERV after xenotransplantation was investigated in an experimental pig-to-baboon cell transplantation model. Baboons were immunosuppressed with high-dose cyclophosphamide (total 45-150 mg/kg) and transplanted with primary porcine aortic endothelial cells (PAEC). Tissue samples (skin, lymph nodes, lung) and peripheral blood leukocytes of 15 baboons, taken about 12-24 months after transplantation of PAEC, were then analyzed by PCR and showed no PERV infection. PERV expression in PAEC was also analyzed: PERV mRNA and reverse transcriptase in the culture supernatant could be detected. In spite of the release of retroviral particles from cultured PAEC, transplantation of these cells into baboon recipients did not result in virus transmission, not even under heavy immunosuppression.

Acellular human dermis promotes cultured keratinocyte engraftment.

In full-thickness skin injury, loss of dermis may result in compromised wound repair, including contracture, hypertrophic scarring, and wound breakdown. This report examines the effect of an acellular dermal matrix on in vivo skin repair. Human keratinocytes cultured onto a synthetic hydrophilic dressing were applied with (N = 9) and without (N = 11) an acellular dermal matrix to full-thickness skin defects on athymic mice. Host cells progressively repopulated the acellular dermal component of the grafts. All animals with dermal matrix revealed fully differentiated epidermis by postoperative day 21. Human keratinocytes persisted in all animals grafted with dermal matrix, compared to only 63.6% of those animals without a dermal component. Planimetric analysis revealed significantly reduced wound contraction (p = 0.016) in animals receiving the dermal matrix. Histologic, immunohistochemical, and electron microscopic analyses also were performed. These studies suggest that an acellular dermal matrix can effectively direct regeneration of normal skin morphology.

Role of melanoma growth stimulatory activity (MGSA/gro) on keratinocyte function in wound healing.

Melanoma growth stimulatory activity/gro alpha (MGSA), a member of the alpha-chemokine family, is produced by a variety of dermal and epidermal cells and can act in a paracrine and autocrine fashion. However, little is known about the importance of MGSA in wound healing. In this study, we quantified the levels of MGSA protein in burn blister and donor site wound fluids. We studied the effects of MGSA on proliferation and migration of primary human keratinocytes and modulation of their integrin expression. Blister fluids contained 0.79 ng/ml (range 0.018 to 4.86 ng/ml) MGSA. Substantial increasing amounts of MGSA were found in donor site fluids from day 1 through day 5 with mean levels ranging from 1.77 to 103 ng/ml at postoperative day 5, which correlated with increasing amounts of tumor necrosis factor alpha (r = 0.86), a known stimulus for MGSA production. In vitro proliferation experiments revealed a maximum stimulation (2.6-fold) with 10 ng/ ml MGSA for 7 days over unstimulated keratinocyte controls; the ED50 was 0.2 ng/ml. DNA content analysis revealed an increase in S phase with 10 ng/ml MGSA stimulation. In cultured keratinocytes, MGSA enhanced the mean fluorescence intensity for alpha 6, while no significant change was seen for beta 1, alpha 2 and alpha 5. We also studied the effect of topically applied MGSA (50 ng/cm2) on the healing of meshed split-thickness human skin grafts on athymic mice. In these wounds, MGSA stimulated the rate of epithelialization (P < 0.05) at day 7, and an increased proportion of mitotic keratinocytes was observed. Wound contraction was significantly (P < 0.05) reduced on days 7 and 14 in the MGSA-treated group. These results suggest that MGSA participates in wound healing by stimulating keratinocyte proliferation.

Effects of recombinant bactericidal, permeability-increasing protein on bacterial translocation and pulmonary neutrophil sequestration in burned mice.

Burn injury induces bacterial translocation (BT) from the gut in multiple animal models. Etiologic factors contributing to BT may be an ischemia-reperfusion injury to the gut, the release of inflammatory cytokines, oxygen metabolites and other mediators, and cytotoxic effects mediated by endotoxin (lipopolysaccharide). Bactericidal, permeability-increasing protein is a neutrophil granule protein with potent bactericidal and lipopolysaccharide-neutralizing activities. The use of this protein has not been previously reported in a burn-injury model. The purpose of this study was to determine whether recombinant bactericidal, permeability-increasing protein (rBPI23) affects the incidence of BT and myeloperoxidase content in lung tissue (a measure of leukocyte sequestration) in a burn-injury model. Mice received a 32% total body surface area, full-thickness, scald burn, and 10 mg/kg body weight rBPI23 in saline solution was given by intraperitoneal injection at 0, 3, and 6 hours after the burn. Control animals received intraperitoneal saline solution only. All animals received a total of 1 ml saline solution intraperitoneally immediately after burn injury for fluid resuscitation. At 24 hours after burn injury, mesenteric lymph nodes (MLN) were harvested, homogenized, and plated. Lung tissue was harvested and assayed for myeloperoxidase. Burned mice treated with rBPI23 had significantly (p = 0.005, Fisher's Exact Test, two-tailed) decreased incidence of BT, compared to burned mouse controls. Leukosequestration into lung tissues was not affected by rBPI23. Postburn administration of rBPI23 reduces but does not abolish the incidence of BT after burn injury in mice, perhaps by reducing intestinal injury during burn shock and the ischemia-reperfusion period by inhibiting the effects of lipopolysaccharide. An alternate explanation may be that rBPI23 could increase clearance and killing of bacteria by host defenses.

Growth peptide release from biologic dressings: a comparison.

Biologic dressings are believed to stimulate wound healing in a variety of wound types. Cryopreserved allograft skin (CAS) is used as a biologic dressing for excised wounds, partial-thickness wounds, and meshed split-thickness skin grafts, and the use of allogenic or autologous cultured epithelial sheets (CES) has been reported to enhance healing of skin ulcers and deep partial-thickness wounds. However, limitations of allograft skin include bacteriologic and viral safety, limited availability, cost, and ease of handling. Previously we have reported the successful use of human keratinocytes cultured to single-layer confluence on Hydroderm polyurethane membranes (HD/HK) for grafting of full-thickness wounds. In this study we evaluated the release of five different growth peptides (transforming growth factors alpha and beta (TGF-alpha, TGF-beta), interleukin-6, interleukin-8, and melanoma growth stimulatory activity from CAS, CES, and HD/HK grafts. Highest levels of TGF-alpha were found for HD/HK (728 +/- 115 pg/10 cm2 of membrane) followed by CES (491 +/- 137 pg/10 cm2; NS). No TGF-alpha was detectable for CAS, and 3.7-fold, and 25-fold higher levels of interleukin-6 were found for CES (257 +/- 12.7 U/10 cm2) compared with HD/HK and CAS, respectively. Interleukin-8 had similar levels for CES (0.65 +/- 0.7 ng/10 cm2) and HD/HK (0.88 +/- 0.12 ng/10 cm2), whereas melanoma growth stimulatory activity was elevated in CES (2314 +/- 97 pg/10 cm2) compared with HD/HK (1071 +/- 55 pg/10 cm2). TGF-beta was barely detectable for CES and HD/HK. Cryopreserved allograft showed high levels of TGF-beta (5.2 +/- 1.6 ng/10 cm2). Overall mitogenic activity of the supernatants on keratinocyte cultures was assessed. Highest proliferation was seen for CES supernatants followed by HD/HK (NS). Supernatants from CAS had an antiproliferative effect on keratinocytes. We conclude that a single layer of keratinocytes cultured on a polyurethane membrane facilitates keratinocyte proliferation similar to CES, whereas cryopreserved allograft has no mitogenic effect on keratinocytes.

Effects of E-selectin and P-selectin blockade on neutrophil sequestration in tissues and neutrophil oxidative burst in burned rats.

OBJECTIVE: Neutrophil deposition in tissues (leukosequestration) after shock may produce local tissue injury from proteases and high-energy oxygen species released from sequestered neutrophils. The initial step in the binding of neutrophils to capillary endothelium is the interaction of adhesion molecule (selectin) receptors between neutrophils and endothelial cells. We quantified leukosequestration in the tissues of burned rats using two methods of analysis: a) measurement of lung myeloperoxidase; and b) measurement of radiolabeled neutrophils and erythrocytes deposited in multiple tissues. We then determined the ability of a selectin receptor blocking agent to affect neutrophil deposition in tissues after burn injury. DESIGN: Prospective, controlled, laboratory study. SETTING: University research laboratory. SUBJECTS: Male Wistar rats (200 to 300 g). INTERVENTIONS: After tracheostomy and venous cannulation, rats received 17% total body surface area full-thickness contact burns and were resuscitated with saline (20 mL i.p.). Experimental animals received 2 mg/kg body weight i.v. administration of a P- and E-selectin blocking monoclonal antibody, CY-1747, immediately after burn. Lung tissue neutrophils were estimated by measuring myeloperoxidase in lung tissue. Neutrophil retention in lung, liver, spleen, gut, skin, muscle, kidney, and brain tissues was determined by removing (preburn) and differentially radiolabeling neutrophils (111In) and erythrocytes (51Cr), reinfusing cells 4.5 hrs after burn, and measuring tissue radioactivity 30 mins later. Edema was estimated by measuring extravasated 125 I-labeled albumin in the various tissues. Peripheral blood neutrophils were analyzed for intracellular hydrogen peroxide content, utilizing a fluorescent dye that reacts with hydrogen peroxide, coupled with analysis of cell fluorescence by flow cytometry. MEASUREMENTS AND MAIN RESULTS: Myeloperoxidase concentration was increased in lungs 5 hrs after burn (p < .05), indicating neutrophil deposition. Radioisotope studies demonstrated significant (p < .05) leukosequestration into the lung, gut, kidney, skin, and brain tissues at 5 hrs after burn. Flow cytometry showed increased intracellular hydrogen peroxide content in peripheral blood neutrophils 5 hrs after burn. Tissue edema, manifested by radiolabeled albumin retention, was not seen in any tissues. Postburn neutrophil deposition in lungs and liver was blocked (p < .05) by administration of CY-1747 after burn, but maximal neutrophil hydrogen peroxide content was unaffected. CONCLUSION: Burn injury in rats results in accumulation of neutrophils in multiple tissues. Neutrophil deposition in the lungs and liver is blocked by administration of the E/P-selectin blocking antibody, CY-1747. Since sequestration of metabolically active neutrophils may induce tissue injury, therapies that block postburn leukosequestration may improve clinical outcomes by limiting remote tissue injury.

Wound closure with human keratinocytes cultured on a polyurethane dressing overlaid on a cultured human dermal replacement.

BACKGROUND: Burn excision followed by immediate wound coverage has become the clinical standard for managing extensive burn injuries in much of the world. When sufficient autograft skin to achieve permanent wound closure is unavailable, cell culture technology has made the use of cultured human keratinocyte (HK) sheets clinically feasible. Whereas previous techniques have focused on development of multilayered, differentiated HK sheets, our attention has been drawn to using HK in a highly proliferative, less differentiated state. Time requirements for preparation of multistratified cultured HK are high, and preparatory steps may destroy important integrin adhesion molecules. METHODS: We describe the use of HK cultured to single layer confluence on a polyurethane membrane(HD), with serum-free medium. HK-HD grafts were transplanted to full-thickness wounds on athymic mice (n = 31). A second group of mice (DG-HK-HD), n = 28) received a living human dermal replacement containing cultured fibroblasts before placement of HK-HD. Control mice received HD alone (n = 4). Basement membrane proteins on healed wounds and surface integrins on cultured HK were identified by means of immunostaining and direct microscopic visualization. RESULTS: HK cultured just to the confluent state on polyurethane membrane were positive for integrins alpha(5) and alpha(6), major integrins on proliferating HK. Histologic analysis showed epithelialized wounds in all groups after 21 days. Using an anti-human involucrin antibody we demonstrated the presence of HK in 64.5% of the HK-HD group, 61% of the DG-HK-HD group, and 0% in the HD group. Mice that received the living human dermal replacement containing cultured fibroblasts in combination with HK-HD grafts developed a thick, well-vascularized neodermis. Strong laminin and collagen IV staining was observed in wound areas covered with HK. CONCLUSIONS: These data show that full-thickness wounds can be closed by application of a single layer of proliferating HK cultured on a biocompatible polyurethane membrane. This technique is an alternative to the use of multilayered, differentiated HK sheets. Preparation times for HK-HD grafts should be significantly shorter than required for multilayered HK sheets, technical efforts should be less, and more extensive wound areas could be covered.

Effects of recombinant bactericidal/permeability-increasing protein (rBPI23) on neutrophil activity in burned rats.

Bactericidal/permeability-increasing protein (BPI) is a neutrophil granule protein with potent bactericidal and lipopolysaccharide (LPS)-neutralizing activities. The purpose of this study was to determine if a human recombinant BPI product, rBPI23, would influence neutrophil (PMN) sequestration into various tissues in a rat burn injury model. Leukosequestration may produce local tissue injury from proteases and high-energy oxygen species released from PMNs. Rats received tracheostomy and venous cannulation, then received 17 to 20% total body surface area full-thickness contact burns and resuscitation with 20 ml, of intraperitoneal saline. Ten mg/kg body weight rBPI23 in saline was given by intravenous injection immediately after burn injury, followed by intravenous doses of 2 mg/kg at 2 and 4 hours. Control animals received intravenous saline only. PMN retention in lung, liver, spleen, gut, skin, muscle, kidney, and brain tissues was determined by removing (before burn injury) and differentially radiolabeling PMNs (111In) and erythrocytes (51Cr), reinfusing cells 4.5 hours after burn injury, and measuring tissue radioactivity 30 minutes later. Edema was estimated by measuring extravasated 125I-labeled albumin in the various tissues, 30 minutes after injection. Peripheral blood PMNS were analyzed for intracellular H2O2 content by flow cytometry using a fluorescent dye that reacts with H2O2. Radioisotope studies demonstrated significant (p < 0.05) leukosequestration into lung, liver, gut, kidney, and skin tissues at 5 hours after burn injury. Tissue edema, manifested by radiolabeled albumin retention, was not observed in any tissues. Postburn PMN deposition in lungs and skin was decreased (p < 0.05) by the immediate administration of rBPI23 after burn injury. Flow cytometry showed increased intracellular H2O2 content in peripheral blood PMNs 5 hours after burn injury (p < 0.05), which was unaffected by administration of rBPI23. Since sequestration of metabolically active PMNs may induce tissue injury, therapies that block leukosequestration after burn injury may improve clinical outcomes by limiting remote tissue injury.

Integrin and matrix molecule expression in cultured skin replacements.

Current tissue culture techniques enable human keratinocytes (HK) from a small section of skin to be grown into sheets of epithelium for treating extensive wounds. The additional use of dermal replacements coupled with cultured skin substitutes may improve handling properties and effect ultimate healing results. Adhesion of cultured HK grafts to wounds, and final success rates of HK grafting, are variable and frequently unsatisfactory. To evaluate adhesion molecule (integrin) expression by cultured grafts, as well as matrix molecule distribution, we performed immunohistologic analysis of integrin expression on HK cultured on plastic and a polyurethane membrane, as well as on two dermal substitutes. Multilayered HK sheet grafts were prepared by culturing cells in plastic tissue culture dishes, and HK were cultured to single-layer confluence on polyurethane membranes (Hydroderm; Wilshire Medical Inc., Dallas, Texas). Composite grafts were prepared by seeding proliferating HK on Dermagraft, composed of human neonatal fibroblasts cultured in polyglactin mesh (Advanced Tissue Sciences, La Jolla, Calif.) and on AlloDerm, an acellular human dermis (LifeCell Inc., The Woodlands, Texas). Immunohistologic staining was performed for the integrin subunits alpha 5, alpha 6, and alpha v. Staining for matrix molecules included fibronectin, laminin-1, and laminin-5. HK in cultured epithelial sheets showed integrin alpha 6 expression on basal cells, and only faint alpha 5 and alpha v staining. HK cultured to confluence on Hydroderm reacted with monoclonal antibodies specific for alpha 5, alpha 6, and alpha v. Through HK adhered well to Dermagraft, there was reduced adhesion of HK on AlloDerm that was not accelerated by addition of fibronectin. HK in composite grafts showed distinct reactivity according to the time in culture. HK on Dermagraft lost alpha 5 reactivity by day 17 and only weak alpha v reactivity was seen. Basal keratinocytes on AlloDerm, however, remained alpha 5 and alpha v positive. In both composite grafts, integrin alpha 6 expression was limited to basal keratinocytes.

Current concepts in the development of cultured skin replacements.

Current tissue-culture techniques permit the rapid expansion of keratinocyte populations, such that an area of cultured epithelium equivalent to that of the surface of an adult can be obtained from an initial small skin biopsy. Unfortunately, technical obstacles have delayed the widespread clinical use of multilayered sheets of epithelium. These factors include difficulties in preparing and transferring fragile cultured epithelial sheets, as well as frequent unsatisfactory "take" of cultured grafts on the wound bed. As greater understanding of the complex interactions of cells and matrix evolves, so have new techniques in the field of cultured keratinocytes for grafting. We have utilized an animal model that allows us to examine some of these new methods and the factors which influence graft take. It has become clear that adhesion properties of keratinocytes, early delivery of proliferative keratinocytes to the wound, the development of dermal replacements, and improved delivery systems for keratinocytes are important factors which must be considered for the optimal provision of skin replacements.

Neutrophil activation and tissue neutrophil sequestration in a rat model of thermal injury.

Neutrophil (PMN) deposition in tissues (leukosequestration) after shock may produce local tissue injury from proteases and oxygen intermediaries which are released from sequestered PMNs. We quantified leukosequestration in tissues in burned rats using two methods of analysis: 1), measurement of lung myeloperoxidase (MPO); 2), measurement of radiolabeled PMNs and erythrocytes deposited in multiple tissues. After tracheostomy and venous cannulation, rats received 17% TBSA full-thickness contact burns and were resuscitated with 20 cc intraperitoneal saline. Lung PMNs were estimated by measuring MPO in lung tissue. PMN influx into lung, liver, spleen, gut, skin, muscle, kidney, and brain was determined by removing (preburn) and differentially radiolabeling PMNs (111In) and erythrocytes (51Cr), reinfusing cells 4.5 hr postburn, and measuring tissue radioactivity 5 hr postburn. Tissue edema was measured by determining extravasation of 125I-labeled albumin in tissues. Peripheral blood PMNs were analyzed for intracellular H2O2 content utilizing a fluorescent dye which reacts with H2O2 coupled with analysis of cell fluorescence by flow cytometry. MPO was elevated in lungs 8 hr postburn (P < 0.05). PMN influx into lung tissues was confirmed by histologic examination. Radioisotope studies demonstrated significant (P < 0.05) leukosequestration into lung, gut, kidney, skin, and brain tissues at 5 hr postburn. Respiratory burst activity of peripheral blood PMNs was increased 5 hr postburn (P < 0.05). Flow cytometric analysis indicated that peripheral blood PMNs were capable of producing markedly increased H2O2 levels 5 hr postburn. Tissue edema, manifested by radiolabeled albumin influx, was not seen in any tissues. Since others have shown that sequestration of metabolically active PMNs may induce remote tissue injury, therapies which block postburn leukosequestration may be able to improve clinical outcomes by limiting remote tissue injury.

Effects of early and delayed wound excision on pulmonary leukosequestration and neutrophil respiratory burst activity in burned mice.

BACKGROUND: Tissue myeloperoxidase (MPO) is a marker of neutrophil (PMN) accumulation in tissues (leukosequestration). We measured MPO in the livers, guts, and lungs of mice after burn injury and studied the additive effect of burn excision on lung MPO. Lung histologic characteristics were also examined. PMN respiratory activity was assessed by measuring intracellular H2O2 content. METHODS: Mice received 32% total body surface area (TBSA) burns; some underwent burn excision followed by wound closure with allograft skin, either immediately or 48 hours after burn. Tissue MPO was measured by a colormetric assay, and intracellular H2O2 was quantified by flow cytometry. RESULTS: MPO was elevated in lungs 8 to 24 hours after burn (p < 0.05) but not in the liver or ileum. Other burned mice received either immediate or 48-hour-delayed wound excision and allografting. In controls a similar-size area was excised and grafted with normal or burned skin. Burned animals had increased lung MPO compared with nonburned animals (p < 0.05). Highest lung MPO levels were seen after burn/immediate excision (p < 0.001). Lung MPO levels were not different comparing unburned mice undergoing skin excision and grafting with either nonburned or burned skin. When burn excision was delayed 48 hours, lung MPO was increased moderately (p < 0.05) but remained far below levels in mice that were excised immediately after burn. PMN influx into lung tissues was confirmed by histologic examination. PMN H2O2 production was increased in burned mice and was additionally increased after immediate wound excision. CONCLUSIONS: Although burn injury produces pulmonary leukosequestration, the phenomenon is unrelated to local effects of burned skin. In this experimental model immediate postburn wound excision increased pulmonary leukosequestration to higher levels than after burn injury alone, and intracellular H2O2 content also increased. Pulmonary leukosequestration may predispose to lung injury, possibly limiting the benefits of wound excision performed extremely early postburn.