Pretreatment of fetal porcine pancreas in culture with nicotinamide accelerates reversal of diabetes after transplantation to nude mice.

Successful transplantation of fetal pancreatic beta-cells to recipients with diabetes requires that differentiation of the immature beta-cells is induced. In this study isletlike cell clusters (ICC) were produced from fetal porcine pancreas in tissue culture, in medium RPMI-1640 supplemented with 10% human serum and in the presence or absence of 10 mmol/L nicotinamide. Light microscopy of immunostained ICC on day 4 of culture showed that nicotinamide caused a more than doubling in the frequency of insulin-positive cells, whereas no stimulatory effect by nicotinamide on DNA replication was found. Transplantation of ICC into nude mice with alloxan diabetes revealed that ICC formed in nicotinamide normalized the hyperglycemia faster than did control ICC (3 to 4 weeks compared with 6 to 8 weeks). The DNA content of the transplanted ICC increased two to three times over an 8-week period, whereas the insulin content increased 100-fold. The total insulin, total DNA content, and the insulin concentration of the grafts were significantly higher in the nicotinamide grafts in comparison with control grafts. In fact, the insulin concentration in the nicotinamide grafts was almost identical to that normally observed in fully differentiated mouse islets. Furthermore, perfusion in vitro of the graft-bearing kidneys 18 weeks after transplantation showed that the total amount of insulin released from the nicotinamide grafts on stimulation with glucose was more than five times higher than the amount from the control grafts. The perfusion of grafts from the nicotinamide group revealed a marked biphasic insulin response to glucose, which was less obvious in the control grafts. We conclude that nicotinamide induces beta-cell differentiation in porcine ICC and that this effect is beneficial when such explants are used for transplantation to recipients with diabetes.