Glenn Greenleaf

Composite grafts of human keratinocytes grown on a polyglactin mesh-cultured fibroblast dermal substitute function as a bilayer skin replacement in full-thickness wounds on athymic mice.

We have developed and tested in athymic mice a new, cultured, dermal-epidermal graft composed of two human cell types coupled with a biodegradable dermal scaffold. Cultured, proliferating human keratinocytes (HK) were applied to the surface of a living dermal tissue replacement that is composed of human fibroblasts cultured on a polyglactin mesh. After 4 to 6 days of coculture, proliferating HKs achieved confluency on the surface of the living dermal tissue replacement. Grafts were then transferred to full-thickness wounds on the dorsum of athymic mice. Sixteen animals were grafted, and the mean percentage of graft take (original wound area covered) on day 20 after grafting was 51.25%. Staining with antibody specific for human involucrin confirmed the presence of HKs on closed wounds, and staining with antibody specific for human laminin revealed a continuous layer of laminin at the dermal-epidermal junction on day 20. Animals closed with living dermal tissue replacement alone markedly contracted, whereas application of living dermal tissue replacement-HK grafts appeared to retard contraction. Because polyglactin mesh fibers are absorbed by hydrolysis rather than by enzymatic degradation, this living composite graft may be more resistant to destruction when placed on excised human wounds than are composite grafts, which are composed of a collagen matrix. The inclusion of the living dermal substitute may ultimately provide better skin quality than is achieved from the use of cultured keratinocytes alone. Fragility of the epidermal layer is probably due to the short-term culture of HKs on the living dermal tissue replacement, and further efforts to develop a thicker epithelial layer may improve graft durability.

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.

Current Trends in the Use of Allograft Skin for Patients With Burns and Reflections on the Future of Skin Banking in the United States

Cadaveric allograft skin can play a critical role in the care of patients with massive burns. It is difficult, however, to estimate current use and levels of enthusiasm for allograft skin in the United States. We report on a survey of 40 skin banks and 140 United States burn center medical directors as listed in the American Burn Associations Directory of Burn Care Resources for North America 1991-1992. Response rate was 45% for skin banks and 38% for burn directors. Overall, 12% of admitted patients were treated with allograft skin at the responding burn centers. Sixty-nine percent of burn center directors preferred to use fresh skin, although only 47% of skin banks were able to supply fresh cadaver skin. Tabulated survey results and a review and discussion of future directions in skin banking and replacement research are discussed in this paper and were presented to the Tissue Bank Special Interest group at the 1993 American Burn Association annual meeting.

Reduction of bacterial translocation and intestinal structural alterations by heparin in a murine burn injury model.

Burn injury produces acute gastrointestinal (GI) derangements that may predispose the burn victim to bacterial translocation (BT). We studied the effects of heparin on gastrointestinal (GI) anatomic alterations and BT after 25% and 32% total body surface area (TBSA), full-thickness murine burn injuries. Heparin (100 U/kg) was administered with 1 mL of normal saline (NS) resuscitation solution immediately postburn and 4 hours and 18 hours postburn in volumes of 0.5 mL NS. Mice with 25% TBSA burns treated with heparin maintained small intestine weight, measured 24 hours postburn, and ileal mucosal height was preserved, whereas burned, untreated mice lost organ weight and mucosal height. Bacterial translocation was decreased in mice with 25% TBSA burn injuries treated with heparin (35.0% vs. 10.7%, p < 0.025). After 32% TBSA burn injuries, BT was also decreased in heparin-treated animals (64.3% vs. 31.6%; p < 0.025). Analysis of mixed venous blood gases showed that heparin did not affect the severe metabolic acidosis that follows burn injury in this animal model, indicating that general tissue perfusion was not improved. Heparin administered in the acute postburn period ameliorates GI structural and functional damage in this murine burn model and decreases BT.

Effects of small-volume bolus treatment with intravenous normal saline and 7.5 per cent saline in combination with 6 per cent dextran-40 on metabolic acidosis and survival in burned mice

Standard murine burn models include the administration of intraperitoneal (i.p.) saline solutions which are intended to resuscitate the animals during subsequent burn shock. Prehospital administration of small volumes of concentrated salt solutions has been recommended for the early treatment of haemorrhagic shock, and have also been utilized for burn shock. We studied the effects of bolus intravenous (i.v.) hypertonic saline (HS) or hypertonic saline/dextran-40 (HS + DEX) on animal survival and acid-base balance following 25 per cent total body surface area, full-thickness burn injury in mice. I.v. injections were administered via a tail vein immediately prior to burn injury. Some mice received 1 ml i.p. normal saline (NS) immediately after burn injury. Acid-base balance of vena caval blood was measured during the period of maximal metabolic acidosis following burn injury (12 h postburn). Preburn i.v. administration of 5 ml/kg of HS or HS+DEX, followed by 1 ml i.p. NS, only slightly decreased the degree of metabolic acidosis compared to animals receiving i.p. fluid alone, the standard resuscitation regimen for burned mice. Preburn i.v. administration of 0.2 ml volumes of HS or HS + DEX, without i.p. fluid administration, resulted in extremely high mortality. Immediate preburn i.v. administration of HS or HS + DEX did not eliminate metabolic acidosis in this murine burn model, and markedly increased the mortality when subsequent i.p. fluids were not administered. The degree of metabolic acidosis in the murine experimental burn model has not previously been clearly described. Furthermore, adequate fluid resuscitation of these animals may be difficult to achieve without indwelling vascular catheters which could deliver continuous i.v. fluids following burn injury.

Effects of High-Dose Vitamin C Administration on Bacterial Translocation and Lung Neutrophil Sequestration in Burned Mice

Severe burn injury produces shock and induces acute gastrointestinal derangements that may disrupt mucosal integrity and facilitate bacterial translocation (BT) to mesenteric lymph nodes, accompanied by endotoxemia. Antioxidant treatments may be beneficial after shock by acting as scavenger agents for highly reactive oxygen intermediates. We studied the effects of high dosages of vitamin C, a water-soluble antioxidant, on the incidence of BT and on levels of lung myeloperoxidase in burned mice. Myeloperoxidase is primarily found in neutrophils, and levels of myeloperoxidase in tissues reflect neutrophil sequestration. The doses of vitamin C used were equivalent on a weight basis to 1 gm/hr administered to humans over a 24-hour period, doses that have shown efficacy in improvement of resuscitation in other experimental burn models and currently are being used in clinical trials in patients with burns. Mice were anesthetized and received 32% total body surface area, full-thickness burn injury to the dorsum, followed by injection of 1 ml of Ringers lactate (RL) for resuscitation. Mice were divided into three groups: (1) unburned, received anesthesia and RL injections; (2) burned, received vitamin C (14 mg/kg/hr) in 1 ml RL by intraperitoneal injection immediately after burn and via subcutaneous injection (0.5 ml) at 6 and 12 hours after burn; (3) burned, received identical injections of RL alone (control animals). Mesenteric lymph nodes were removed by use of sterile technique at 24 hours after burn and cultured; any growth was considered evidence of BT. The incidence of BT in burned mice was not altered by administration of vitamin C (normal, 10% BT; burn, 41.37% BT; burn+vitamin C, 45.83% BT). Similarly, burned animals that received vitamin C or RL alone did not differ in the levels of myeloperoxidase in the lungs (normal, 0.015 +/- 0.003 U/gm; burn, 0.2231 +/- 0.029 U/gm; burn+vitamin C, 0.281 +/- 0.041 U/gm).(ABSTRACT TRUNCATED AT 250 WORDS)

Burn injury results in decreased gastric acid production in the acute shock period

Gastrointestinal complications including acute stress ulcerations occur after burn injury. The causes of acute gastric derangements are multiple, and tissue ischemia in the acute period of burn shock may promote breakdown of the gastric mucosal protective barrier. We compared gastric pH in mice after 25% total body surface area, full-thickness murine burn injury with that in unburned control animals. Animals were anesthetized with methoxyflurane and were resuscitated with 1 ml normal saline solution immediately after burn. Animals were killed at intervals up to 24 hours after burn injury, stomachs were removed and opened, and gastric mucosal pH was measured by use of a surface pH probe. In other animals mixed venous blood was obtained via direct inferior vena cava puncture, and blood gas analysis was performed at intervals up to 24 hours after burn injury. Unexpectedly, gastric mucosal pH increased in burned mice compared with that in controls. The peak difference, greater than one log pH unit, occurred at 3 hours after burn injury (pH 4.45 burn vs pH 3.34 control, p < 0.00001), and this difference was maintained through 12 hours (pH 4.88 burn vs pH 3.20 control, p < 0.005). In this model, shock was observed to begin as early as 1 hour after burn injury and reached its maximal period (base deficit, -27.8 mEq/L) at 12 hours after burn injury. In view of the higher gastric pH in burned mice with concomitant profound shock, gastric acid production appears to be impaired during this time, which suggests acute postburn gastrointestinal ulcerations may be primarily due to ischemia. Prevention of organ ischemia may play a key role in the prevention of acute gastric ulcerations after burn injury.

Effects of fluid resuscitation, burn eschar excision, and blockade of afferent pain responses on bacterial translocation and acid-base balance after murine burn injury

We tested effects of fluid resuscitation, early burn excision/grafting, and blockade of afferent stimuli from the burn wound on bacterial translocation and acid-base balance after murine burn injury. Burn excisions were performed with patients either 15 minutes or 2 hours after burn injury under anesthesia, and excised wounds were immediately closed with murine allograft skin. Twenty-four hours after 25% total body surface area (TBSA) burn injury and 48 hours after 32% TBSA injury, mesenteric lymph nodes were cultured. Incidences of bacterial translocation in 25% and 32% TBSA burns were 31.6% and 68.4% of animals, respectively. Burned animals were in severe shock, and metabolic acidosis reached a nadir 12 hours after burn injury, with base deficit -27.8 +/- 0.6 mEq/L; 5% to 10% of animals died acutely after burn injury. After excision/grafting of burned mice at 2 hours after burn injury, the incidence of bacterial translocation was unchanged (35.7% with 25% TBSA burn, 73.3% with 32% TBSA burn), and mortality did not change. When 32% TBSA excisions were performed exactly 10 minutes after burn injury, four of the 13 mice died within several hours, and five (55.5%) of the nine survivors translocated. Rates of bacterial translocation in mice receiving anesthesia or excision/grafting without burn injury were 15.0% and 20%, respectively (p = NS compared with normal mice). Subcutaneous implantation of normal or burned skin into normal animals neither elicited shock nor increased the incidence of bacterial translocation. Increasing amounts of fluid resuscitation in the 25% TBSA burn model provided only delayed improvement of acid-base balance; increased amounts of fluid did not decrease bacterial translocation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of corticotropin releasing factor on acid-base alterations and bacterial translocation in a murine model of thermal injury

Corticotropin-releasing factor (CRF) is a 41 amino acid polypeptide produced by the hypothalamus which has been shown to decrease inflammation and tissue oedema when administered following burns, cold and acid injuries in some animal models, and to increase mesenteric blood flow. We determined whether systemic administration of CRF to burned mice would decrease metabolic acidosis and protect the gastrointestinal (GI) tract from ischaemic injury leading to bacterial translocation (BT). Synthetic CRF was administered by intraperitoneal injection in doses of 20 and 200 micrograms/kg to mice immediately following 25 and 32 per cent TBSA burn injuries; the doses were repeated at 8 and 16 h postburn. Severe metabolic acidosis, measured 12 h after burn injury, was not improved in mice which received CRF treatment. Bacterial translocation, measured by quantifying bacteria in mesenteric lymph nodes harvested from animals 48 h postburn, was also not decreased with CRF treatment. CRF does not improve general tissue perfusion nor decrease GI derangements leading to bacterial translocation in this animal model of burn injury.