Evaluating the effect of serine proteases on collagenase activity during human islet isolation

Inconsistencies in human islet yields after collagenase digestion have been attributed to the activation of endogenous enzymes of the donor pancreas. It has been suggested that pancreatic serine proteases contribute to the proteolysis of collagenase. This study defined the effects of endogenous enzymes within the pancreas on pancreas dissociation during collagenase digestion. Levels of collagenase activity from samples taken throughout several steps in islet isolation procedures, both with and without the addition of the serine protease inhibitor Pefabloc, were determined by a spectrophotometric assay using N-[3-(2-furyl)acryloyl]-Leu-Gly-Pro-Ala as the substrate. Results clearly demonstrated that the level of collagenase activity remains stable throughout the isolation procedure despite differences in the donor factors from several cadaveric donor pancreases. This was further demonstrated by observing no difference in activity levels after incubating commercial collagenase preparations with serine proteases and analyzing by means of collagenase activity and SDS-PAGE. These data show that the presence of serine proteases does not affect the level of collagenase activity; however, they likely damage the islet cells upon prolonged digestion of the pancreatic tissue. Further efforts at examining exogenous and endogenous enzyme levels may result in the development of an enzyme cocktail that is both stable and effective for digesting the human pancreas while preserving islet function and viability.