Adjustment of the ratio between collagenase class II and I improves islet isolation outcome

Background. Previous studies have clarified the distinct roles of collagenase class I (ccI) and class II (ccII) in enzymatic release of islets from pancreatic tissue. The present study sought to enhance the limited knowledge about the optimal ratio between collagenase classes. Methods. Rat islets were isolated utilizing 0.4 DMC-U of neutral protease and 20 PZ-U of fractionated NB-1 collagenase recombined to obtain a ccII/I ratio of 0.5, 1.0, and 1.5. Quality control included assessment of yield (islet equivalents), trypan-blue exclusion, insulin release during static glucose incubation, and transplant function in diabetic nude mice. Data are expressed as mean values SEM. Results. Digestion time was only minimally influenced by different ccII/I ratios. The highest islet yield (P < .05) was obtained using a ccII/I ratio of 1.0. Purity and glucose stimulation index were only marginally affected by different ccII/I ratios. A significant loss of islet viability after 24-hour culture (P < .05) was observed only in islets isolated by means of a ccII/I ratio of 0.5 and 1.5 but not 1.0. Transplantation into diabetic nude mice revealed sustained islet graft function in all experimental groups. Conclusions. The present study indicates that the ratio between ccII and ccI is of significant relevance for optimizing islet yield and viability.