The effect of the thromboxane synthetase inhibitor Dazmegrel (UK-38,485) on wound healing, dermal ink perfusion and skin blood flow measurements in deep partial thickness burns

Cooling of burns: Mechanisms and models

The role of cooling in the acute management of burns is widely accepted in clinical practice, and is a cornerstone of basic first aid in burns. This has been underlined in a number of animal models. The mechanism by which it delivers its benefit is poorly understood, but there is a reduction in burns progression over the first 48 h, reduced healing time, and some subjective improvements in scarring when cooling is administered after burning. Intradermal temperature normalises within a matter of seconds to a few minutes, yet the benefits of even delayed cooling persist, implying it is not simply the removal of thermal energy from the damaged tissues. Animal models have used oedema formation, preservation of dermal perfusion, healing time and hair retention as indicators of burns severity, and have shown cooling to improve these indices, but pharmacological or immunological blockade of humoural and cellular mediators of inflammation did not reproduce the benefit of cooling. More recently, some studies of tissue from human and animal burns have shown consistent, reproducible, temporal changes in gene expression in burned tissues. Here, we review the experimental evidence of the role and mechanism of cooling in burns management, and suggest future research directions that may eventually lead to improved treatment outcomes.

Failure of Ibuprofen to prevent progressive dermal ischemia after burning in guinea pigs

OBJECTIVE

It is controversial whether the use of prostaglandin inhibitors could prevent progressive dermal ischemia in the postburn stasis zone. This study evaluated the effect of Ibuprofen on preventing postburn dermal ischemia using an animal model of India ink perfusion and skin transparent preparation techniques.

METHODS

The closely clipped backs of the guinea pigs were bathed in 75 degrees C water for 10s. Ibuprofen-treated groups were fed intragastrically with Ibuprofen (12.5mg/kg) every 6h. All animals were perfused with 70% India ink via a cervical artery cannula at 16 kPa constant pressure at 0, 8, 16, 24h postburn. Skin transparent preparations were made, and 6-keto-PGF(1 alpha) and T x B(2) levels in skin tissue were assessed.

RESULTS

India ink filling rates in skin capillary plexuses decreased gradually with postburn time elapsing (P<0.01). 6-keto-PGF(1 alpha) and T x B(2) levels in two groups increased. The increase of T x B(2) was dominant, which was related to postburn dermal ischemia (r=0.742, P<0.01). Though levels of 6-keto-PGF(1 alpha) and T x B(2) decreased in Ibuprofen-treated groups, India ink filling rates showed no significant difference between controls and experimental groups (P>0.05). The results were also confirmed by observation of skin transparent preparations.

CONCLUSION

This study suggests that Ibuprofen has no preventive effect on progressive dermal ischemia after burning.

Frostbite: pathogenesis and treatment

Frostbite, once almost exclusively a military problem, is becoming more prevalent among the general population and should now be considered to be within the scope of the civilian physician's practice. Studies into the epidemiology of civilian frostbite have identified several risk factors that may aid the clinician in the diagnosis and management of cold injuries. Research into the pathophysiology has revealed marked similarities in inflammatory processes to those seen in thermal burns and ischemia/reperfusion injury. Evidence of the role of thromboxanes and prostaglandins has resulted in more active approaches to the medical treatment of frostbite wounds. Although the surgical management of frostbite involves delayed debridement 1 to 3 months after demarcation, recent improvements in radiologic assessment of tissue viability have led to the possibility of earlier surgical intervention. In addition, several adjunctive therapies, including vasodilators, thrombolysis, hyperbaric oxygen, and sympathectomy, are discussed.

A standardized model of partial thickness scald burns in mice

BACKGROUND

Large mammal partial thickness wound models were developed primarily for their anatomical similarity to human wounds, yet lack the economy, ease of handling, and statistical power afforded with rodent models. Previous small mammal models of partial thickness burn injury have failed to demonstrate complete reepithelialization in less than 3 weeks. We present a murine partial thickness scald model with a reepithelialization rate comparable to that of porcine wound models.

METHODS

Thirty-eight adult male mice were secured in a burn template allowing exposure of a 2 x 3-cm area of the shaved dorsum to 60 degreesC water for 45 s, followed by 4 degreesC water for 45 s. Four wounds were harvested daily on Postburn Days 1-7, 10, and 14 for histologic evaluation.

RESULTS

Histologic evidence of partial thickness dermal injury with sparing of dermal appendage epithelial cells was seen in all wounds. Of 134 wound sections evaluated 26 contained some areas of full thickness dermal injury, with only 8 of these 26 sections showing full thickness injury in 50% or more of the cross-sectional area of the wounds. Complete wound reepithelialization was seen between Postburn Days 10 and 14. The viable dermal thickness in all burn cross sections was at least 40-80 micrometers, and up to 1400 micrometers in reepithelialized wounds.

CONCLUSIONS

This murine model of partial thickness scald injury provides a standardized thermal wound with consistent depth of injury, low mortality, and a reepithelialization rate between 10 and 14 days. A simple protocol allows easy production of 30-50 wounds daily with one technician.

Pathophysiology of the burn wound and pharmacological treatment. The Rudi Hermans Lecture, 1995

The body's reaction to thermal injury is much more than an initial, local inflammatory response. The burn wound is a continuous, severe threat against the rest of the body due to invasion of infectious agents, antigen challenge and repeated additional trauma caused by wound cleaning and excision. The inflammatory mediators which control blood supply and microvascular permeability in the wound have been extensively studied and are largely understood. Attempts to suppress the inflammatory reaction by different drugs, have, however, been less successful. Extensive thermal injury and sepsis also results in immunosuppression. The defects causing immunosuppression are still very much under consideration. An understanding of these defects is essential for the development of therapies. The increasing interest in the control of the inflammatory reactions by cytokines may, in the near future, be of great importance.

Principles of wound healing

Wound healing can be divided into immediate (zero to 1 hour), early (1 to 24 hours), intermediate (1 to 7 days), and late (greater than 7 days) stages. Many physical and physiologic events occur simultaneously and sequentially during these stages to produce the final wound scar. The processes of skin retraction, scab formation, would debridement, wound contraction, epithelial migration and proliferation, fibroplasia, and collagen maturation all must occur for healing to be successful. Many factors affect the size and shape of the resulting scar, including anatomic location and skin tension forces, systemic condition of the patient, blood supply to the wound, nutritional factors, environmental temperature, the presence of systemic drugs, wound infection, motion, wound oxygen gradient, wound moisture, and bandaging. Ideally, each of the factors would occur at a level compatible with optimal healing, but, in many clinical cases, one or more factors compromise normal, rapid healing. When we intervene with therapy, we probably adversely affect another factor in healing, while trying to correct the factor that is out of balance. In these decisions, the effects of our treatment on wound healing should be considered. The trade-off should be weighed and the treatment pursued only as long as necessary to allow healing to progress; then it should be discontinued or changed. With these considerations, it is hoped that we can attain healing at the most rapid physiologic rate.

Is postburn dermal ischaemia enhanced by oxygen free radicals?

The accumulated data suggest that oxygen free radicals are actively involved in the pathophysiology of the wound healing process. Since OH. and O2- directly correlate with the release of arachidonic acid and catalyse some of the enzymes participating in its cascade, their involvement in the enhancement of dermal ischaemia in the stasis zone is postulated. Experimental data using topically applied scavengers of superoxide have shown their beneficial effects on the burn wound healing process.

Evidence that 1 per cent Meshushit ointment prevents progressive dermal ischaemia of experimental deep partial skin thickness burns: a preliminary, quantitative controlled study

This study quantitatively assessed the topical effects of Meshushit, a new herbal compound, on the healing process of experimental deep partial skin thickness burns over 27 days. To symmetrical circular burns were inflicted on the back of 15 animals by aluminium templates. The Meshushit and its control vehicle containing 0.1 per cent gentamycin or the control vehicle plus antibiotic alone, were applied topically to randomly selected burns at equal time intervals. Epithelialization and contraction were assessed on postburn days 6, 10, 15, 18, 22 and 27 using a computerized planimeter. The newly formed granulation tissue was assessed histologically on postburn day 27, while the hair follicles were counted in the same sections. Student's t test was used to differentiate the rates of contraction and epithelialization; hair follicle counts and the thickness of the newly formed granulation tissue. None of the animals died during the experiment. The epithelialization and contraction rates did not differ significantly between the test groups. The Meshushit-treated wounds showed a significantly thicker granulation tissue layer as compared to its control (828.72 +/- 46.39 microns vs. 540.78 +/- 37.81 microns, P less than 0.01). The count of hair follicles was significantly higher in the Meshushit-treated burns (23.38 +/- 1.84 vs. 3.76 +/- 0.35, P less than 0.001). It is concluded that the herbal Meshushit ointment enhanced the newly formed granulation tissue and preserved better the hair follicles in the present burn wound model. It is suggested that these findings are due to the preservation of the dermal microcirculation.

Effect of Dazmegrel (UK-38,485) on immune function in a burned guinea-pig model

We investigated the effects of Dazmegrel, a highly effective and selective thromboxane synthetase inhibitor, on the immune system in a bilateral 5 per cent total body surface area (TBSA) deep partial thickness scald in a guinea-pig model. The animals were randomized into two groups: one received Dazmegrel at 3.4 mg kg-1 day-1 by i.m. injection; the other received the same volume of saline. Cell-mediated immunity was evaluated by the response to the hapten dinitrofluorobenzene (DNFB), as measured by ear swelling in response to cutaneous application. The ear swelling of the Dazmegrel-treated group was 52.8 +/- 3.8 per cent, compared to 41.4 +/- 2.4 per cent for the control group (P less than 0.02). Neutrophil bactericidal function was determined on post-burn day (PBD) 7 and opsonic function on both post-burns days 7 and 22. The serum opsonic indices were nearly identical at both times, but the Dazmegrel-treated animals had a significantly improved neutrophil bactericidal index (1.15 +/- 0.05 v. 1.68 +/- 0.17, P less than 0.01). Dazmegrel exerted a stimulating effect on the immune system in this burn model, improving neutrophil antibacterial function and cell-mediated immunity.