Spontaneous Hypoglycemia After Islet Transplantation: The Case For Using Non-Hepatic Sites.

This Perspective provides a brief history of intrahepatic alloislet and autoislet transplantation in humans and an update of the recent success rates. It also examines the important role that hypoglycemia plays in clinical outcomes. On the one hand, recurrent serious hypoglycemic episodes related to insulin therapy are a major criterion for alloislet transplantation. On the other hand, spontaneous clinical hypoglycemia, perhaps related to the accompanying Roux-en-Y procedure for total pancreatectomy, is a complication of autoislet transplantation. Complex alterations in glucagon secretion compromise counter-regulation of hypoglycemia in both situations. The glucagon response to hypoglycemia is intrinsically defective in type 1 diabetes before transplant because of the absence of physiological regulation of α-cell secretion by neighboring β-cells. Glucagon secretion from intrahepatic islets during systemic hypoglycemia is also defective, although β-cells in the graft are normally regulated by glucose and arginine. My personal perspective is that the latter is caused by intrahepatic glycogenolysis stimulated by systemic hypoglycemia with consequent increases in intrahepatic glucose flux, which incorrectly signals intrahepatic α-cells to be quiescent. This defect is liver-specific, which strongly suggests modifying the current approach to islet transplantation by placing a portion of allo- and autoislets in nonhepatic sites in addition to hepatic sites to ensure physiological glucagon secretion as a strategy to ameliorate post-transplant hypoglycemia.