The structure and composition of chronic wound eschar.

Wounds with a covering of eschar require debridement before optimal wound healing can proceed. There are several different methods available but these have been derived empirically with no direct evidence of the structure or composition of the tissue they are designed to remove, or of the potential autolytic mechanisms which are the targets for some of these treatments. The aim of this study therefore was to determine the composition of chronic wound eschar and hence identify potential targets for the induction of autolytic debridement. Chronic wound eschar was removed by surgical debridement and analysed using immunohistochemistry, polyacrylamide gel electrophoresis (PAGE) and gelatin zymography. Immunohistochemistry using antibodies specific for extracellular matrix (ECM) proteins revealed a definite tissue structure, consisting of many fibrous regions and fine fibrillar elements separated by areas of tissue which were of a more irregular and amorphous nature. An antibody specific for all leucocytes revealed the presence of leucocytes in the region of tissue closest to the wound bed. The presence of this leucocyte population correlated to elevated levels of gelatinase activity as identified by gelatin zymography. PAGE analysis identified various protein species in the range 3.5-60 kDa molecular weight. These data indicate that wound debridement is likely to require multiple enzyme specificities to degrade the eschar and that these enzymes may be supplied by inflammatory leucocytes infiltrating the eschar from the wound bed. The various protein species demonstrated by PAGE may represent ECM proteins, those with lower molecular weight possibly representing the degradation products of autolytic debridement.