Endothelial cell hypertrophy is associated with microvascular occlusion in horse wounds.

Wound repair in horse limbs is often complicated by excessive fibroplasia and scarring. Occlusion of the microvessels populating the granulation tissue appears to be involved in the excessive accumulation of extracellular matrix during the repair of limb wounds. This study aimed to determine whether endothelial cell hypertrophy or hyperplasia, or both, contribute to microvascular occlusion and whether the pericyte is involved in this anomaly. We created 5 wounds, each 2.5 x 2.5 cm, on both forelimbs and on the body of 6 horses. One limb was bandaged to stimulate excessive wound fibroplasia. Weekly biopsy specimens were evaluated by transmission electron microscopy to measure microvessel luminal diameters and the surface area of endothelial cells and to count endothelial cells and pericytes. Microvessels were occluded significantly more often in limb wounds than in body wounds. The surface area of endothelial cells lining occluded microvessels (mean +/- standard error, 28.4013 +/- 1.5154 microm2) was significantly greater (P = 0.05) than that of cells lining patent microvessels (26.2220 +/- 1.5268 microm2). Conversely, neither the number of endothelial cells nor the number of pericytes differed between patent and occluded microvessels or between limb and body wounds. Furthermore, the wound location and the status of the microvessels (patent or occluded) did not alter the ratio of endothelial cells to pericytes. These data suggest that endothelial cell hypertrophy might play a role in the microvascular occlusion present in granulation tissue of limb wounds in horses, but the contribution of the pericyte remains obscure.

Comparative study on microvascular occlusion and apoptosis in body and limb wounds in the horse.

Wound repair in horse limbs is often complicated by exuberant granulation tissue, a condition characterized by excessive fibroplasia and scarring and that resembles hypertrophic scars and keloids in man. The aim of this study was to compare microvascular occlusion and apoptosis in wounds of the limb with those of the body, which heal normally. Five 6.25 cm(2) wounds were created on both forelimbs and on the body of six horses. One limb was bandaged to stimulate excessive fibroplasia. Weekly biopsies were evaluated histologically and immunohistochemically for mutant p53 protein by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling to localize and quantify apoptosis, and by electron microscopy to measure microvessel luminal diameters. Histologic examination revealed protracted inflammation as well as slowed epithelialization and deficient fibroblast orientation in limb wounds, particularly those with excessive fibroplasia. Microvessels were occluded significantly more often in limb wounds, and the balance of apoptotic signals was altered against apoptosis in the former, although this could not be confirmed quantitatively. Data suggest that microvascular occlusion and a dysregulated apoptotic process may be involved in the excessive accumulation of extracellular matrix within limb wounds. This might provide a basis for the development of targeted therapies to prevent and treat excessive fibroplasia and extensive scarring in horses.

Effect of a silicone-containing dressing on exuberant granulation tissue formation and wound repair in horses.

OBJECTIVE: To determine the effect of a silicone dressing on the rate and quality of repair of limb wounds and compare microvascular occlusion and apoptosis in wounds treated with the silicone dressing and those treated with a conventional dressing in horses. ANIMALS: 5 horses. PROCEDURE: Horses received two 6.25-cm2 wounds on each metacarpus. Ten wounds were treated with a silicone dressing; the other 10 were treated with a control dressing. Quality of repair and wound size were evaluated at each bandage change. Time to healing and the number of excisions of exuberant granulation tissue were recorded. Biopsy specimens taken from healed wounds were evaluated semiquantitatively via histologic examination, p53 immunohistochemical analysis, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) to quantify apoptosis, and electron microscopic examination to measure microvessel luminal diameters. RESULTS: The silicone dressing surpassed the conventional dressing in preventing formation of exuberant granulation tissue and improving tissue quality. Microvessels were occluded significantly more often in wounds dressed with the silicone gel, which also diminished the expression of mutant p53, an indirect inhibitor of apoptosis, although greater apoptosis was not confirmed quantitatively by use of TUNEL. CONCLUSIONS AND CLINICAL RELEVANCE: Because the silicone dressing inhibited the formation of exuberant granulation tissue, it may be integrated in a management strategy designed to improve the repair of limb wounds in horses.