Improved in vitro function of islets using small intestinal submucosa

Transplantation of human pancreatic islets has been demonstrated to be a viable alternative to exogenous insulin therapy for diabetes mellitus. However, optimum results require transplantation of islets from two to three pancreas donors after a minimum number of days in culture. This implies that a substantial part of the transplanted islet mass may be nonfunctional. This study investigates the ability of an optimized technique to retain islet function using porcine-derived small intestinal submucosa (SIS) during in vitro culture. Groups of purified human islets were cultured for 3 weeks in modified standard islet culture conditions of CMRL = 1066 tissue culture medium supplemented with 25 mmol/L HEPES, penicillin/streptomycin, and a commercial insulin-transferin-selenium (ITS) supplement. Islets (50 to 200 IE/condition; n = 5 preparations) were cultured in plates containing noncoated Biopore membrane inserts alone, or on inserts that had been covered with SIS. Function was assessed by static incubation with low (4 mmol/L), or high (20 mmol/L) glucose at the end of each week. Glucose-stimulated release of human insulin was measured by radioimmunoassay (Linco, St. Charles, Missouri). Remaining islets were stained and evaluated visually. Neither culture condition resulted in significantly different basal secretion until week 3 (P =.05). However, by the end of week 2 and for the duration of the experiment thereafter, SIS-treated islets exhibited a higher SI (P <.05). At the end of the experiment, islets cultured on the SIS exhibited excellent morphology, with greater than 90% staining positive with Dithizone. Islets cultured on the inserts alone lost their initial morphology, becoming "loose" in appearance. The results of this study indicate that SIS enables enhanced function of islets in vitro as compared to non-SIS supported culture conditions.