Inhibition of elastase by a synthetic cotton-bound serine protease inhibitor: in vitro kinetics and inhibitor release

A cotton-bound serine protease inhibitor of elastase (fiber-inhibitor) has been formulated for in vitro evaluation in chronic wound fluid. As a model to understand the properties of the inhibitor in wound dressings, the kinet ic profile and in vitro release of the fiber-inhibitor formulation have bee n examined. The elastase inhibitor N-Methoxysuccinyl-Ala-Ala-Pro-Val-chloro methylketone was modified onto cotton cellulose fibers and assayed as a col loidal system. Amino acid analysis and reversed phase high performance liqu id chromatography were compared as semiquantitative methods to assess elast ase inhibitor release from the cotton fibers. The kinetics of inhibition wa s assessed on treated fibers of synthetic dressings such that a colloidal s uspension of the fiber-inhibitor and elastase was employed as an assay. A d ose-response relationship was observed in the kinetics of substrate hydroly sis catalyzed by three elastases: porcine pancreatic elastase, which was em ployed to model this approach; human leukocyte elastase; and elastase in hu man chronic wound fluid. Both freely dissolved and fiber-bound inhibitors w ere studied. The initial rates of substrate hydrolysis were inversely linea r with freely dissolved inhibitor dose. The apparent first order rate const ants, k(obs), for the elastase-inhibitor complex were calculated from the k inetic profiles. The k(obs) for inhibitor bound enzyme varied as a function of inhibitor vs. enzyme concentration and based on the order of mixing of substrate, inhibitor and enzyme in the assay. Enzyme inhibition by the fibe r-inhibitor was measured as inhibitor concentration at 50% inhibition (I-50 ). I-50 values measured from the colloidal assay with fiber-released inhibi tor were within the same range to those for freely dissolved inhibitor. Inh ibition of elastase activity in chronic wound fluid was observed with 1-5 m g of fiber-inhibitor formulation. This approach constitutes an in vitro ass essment of synthetic serine protease inhibitors on fibers and may be employ ed to evaluate structure vs. function of elastase inhibition in the modifie d fibers of wound dressing composites.