Peri-insular presence of collagenase during islet isolation procedures

Reportedly, higher islet yields are obtained by ductal collagenase administration and subsequent digestion of the pancreas than by the chopped tissue collagenase digestion technique. However, the exact mechanism of islet isolation is not known. This study aims to understand the underlying mechanism of a favorable effect of ductal collagenase administration. To this end, we investigated if the higher yields can be explained by a different distribution of the collagenase enzymes in the pancreatic tissue after ductal application as compared to during chopped tissue digestion. India ink was used to mimic and visualize the distribution of collagenase in histological sections of pancreases of several species. Ink particles were seen around and even within the islets both after ductal application and during chopped tissue collagenase digestion. Thus, collagenase enzymes are not restricted to the exocrine tissue compartment with either technique. In view of this observation, we compared the efficacy of both techniques in islet isolation procedures in paired experiments in rats. Both techniques gave similar islet yields to those reportedly obtained with the ductal collagenase method. However, with either technique, the islet yield was only approximately 50% of the endocrine volume of the pancreas, indicating that a substantial loss of islet tissue had occurred. We conclude that, irrespective of the route of collagenase administration, collagenase enzymes are present in the peri-insular space during islet isolation procedures. This is pertinent in view of the finding that both methods have similar islet yields in rats and that collagenase digestion, as such, is associated with loss of islet tissue.