Comparison of different collagenases in isolation of adult pig islets

Insulin secretory characteristics of monkey pancreatic islets: a simple method of islet isolation and the effect of various density gradients on separation

We describe a simple stationary digestion method of islet isolation and separation by various density gradients from monkey pancreas (Macaca radiata radiata). Effective method, different types and concentrations of collagenase were standardized. Sigma type XI collagenase yielded >1000 islets/gram pancreas at the concentration of 4 mg/ml and 3 ml Hank's/gram pancreas. Slow digestion with less concentration of collagenase was suitable for monkey islet isolation. Discontinuous density gradients of bovine serum albumin (BSA) and dextran were compared with standard Ficoll for separation of islets. Islet yield (1038 +/- 81), insulin secretory response (stimulation index, S.I.11) and histological examination revealed dextran gradients were more appropriate for monkey islets when compared to BSA and Ficoll. Insulin secretory characteristics of monkey islets were studied by exposing them to low and high concentrations glucose (S.I.11.5), arginine (S.I.4.2), leucine (S.I.2.3) and tolbutamide (S.I.1.7). The results indicated that the magnitude of glucose induced insulin secretion of monkey islet is about half as that of rat and mouse islets. However, it is higher than that of porcine and bovine islets. In conclusion, the knowledge of insulin secretory ability of Indian bonnet monkey islets together with the techniques of isolation and separation are useful tool for diabetic research especially islet transplantation.

A newly developed three-layer agarose microcapsule for a promising biohybrid artificial pancreas: rat to mouse xenotransplantation

We examined the effectiveness of an improved version of a three-layer agarose microcapsule in islet xenotransplantation. The microcapsule is composed of a mixture of 5% agarose and 5% polystyrene sulfonic acid. The other two outer layers are polybrene and carboxymethyl cellulose. The agarose/polystyrene sulfonic acid membrane is for the purpose of immunoisolation, suppression of complement activity and reinforcement of the microcapsule. The polybrene layer suppresses the polystyrene sulfonic acid leakage by forming a polyionic complex at the surface of the agarose/polystyrene sulfonic acid membrane. The outermost layer, a carboxymethyl cellulose coating, improves the biocompatibility of the microcapsule. In vitro static incubation study showed that the insulin secretion from rat islets in microcapsules in response to 16.7 mM glucose stimulation was more than four times higher than that on 3.3 mM glucose stimulation (n = 8). In an in vivo study, 500 rat islets in microcapsules were xenogenically implanted in the abdominal cavity of mice with streptozotocin-induced diabetes. The graft survival times ranged from 2 to 5 mo, the average being 75 days (n = 5). Our results demonstrate that the improved version of the three-layer agarose microcapsule can effectively prolong the xenograft survival time without employing immunosuppressants, suggesting that this microcapsule could provide a promising biohybrid artificial pancreas for future clinical applications.