Proteolytic activity in human burn wounds

Wound healing is the result of a dynamic balance between synthetic and degradative processes. After a burn, proteolytic activity increases at the wound site. Excised burn wounds and donor skin were examined from 20 pediatric burn patients, to determine which of two classes of neutral proteinases, serine or metalloproteinases, accounts for the majority of this proteolytic activity in these tissues; to examine messenger RNA expression of three of the principal enzymes and inhibitors of this class; and to measure enzymatic activity of two of these metalloproteinases. The majority of the increased proteolysis was due to metalloproteinases. By polymerase chain reaction assays, messenger RNAs for matrix metalloproteinase-1, -3, and -9 were strongly expressed in burn tissue and absent or weakly expressed in unburned skin. Messenger RNA for tissue inhibitor of metalloproteinase-1 and -2 was consistently present in burned and unburned skin. By zymography, there was a significant increase in matrix metalloproteinase-2 (twofold to threefold) and matrix metalloproteinase-9 (20- to 30-fold) activity in burned versus unburned skin. We suggest that postburn there is an upregulation of some matrix metalloproteinases that exceeds the level of inhibitors with the net result of an increase in proteolysis in burned tissue. This increased proteolysis may play a role in wound repair and scar formation.