Insulin Degradation by Acinar Cell Proteases Creates a Dysfunctional Environment for Human Islets Before/After Transplantation: Benefits of α-1 Antitrypsin Treatment

Abstract

Background Pancreatic acinar cells are commonly co-transplanted along with islets during auto-and allo-transplantations. The aims of this study were to identify how acinar cell proteases cause human islet cell loss before and after transplantation of impure islet preparations and to prevent islet loss and function with supplementation of alpha-1 antitrypsin (A1AT). Methods Acinar cell protease activity, insulin levels, and percent islet loss were measured after culture of pure and impure clinical islet preparations. The effect of proteases on ultra-structure of islets and beta cell insulin granules were examined by transmission electron microscopy (TEM). The number of insulin granules and insulin-labeled immune-gold particles were counted. The in vivo effect of proteases on islet function was studied by transplanting acinar cells adjacent to islet grafts in diabetic mice. The effects of A1AT culture supplementation on protease activity, insulin levels, and islet function were assessed in pure and impure islets. Results Islet loss after culture was significantly higher in impure relative to pure preparations (30 vs. 14%, p<0.04). Lower islet purity was associated with increased protease activity and decreased insulin levels in culture supernatants. Reduced beta cell insulin granules and insulin degradation by proteases were confirmed by TEM. Transplantation results showed delayed islet graft function when acinar cells were transplanted adjacent to the islets under the kidney capsule. Supplementation of A1AT to impure islet cultures maintained islet mass, restored insulin levels, and preserved islet functional integrity. Conclusions Culture of impure islets in the presence of A1AT prevents insulin degradation and improves islet recovery.

Continuous Quadrupole Magnetic Separation of Islets during Digestion Improves Purified Porcine Islet Viability

“…Islets, making up only about 2% of the total pancreatic mass, are purified after digestion to decrease the volume of tissue being transplanted and to eliminate unnecessary and potentially harmful exocrine tissue. The exocrine tissue itself releases endogenous enzymes that may contribute to islet damage and loss in culture [21]. Coculture of islets with contaminating exocrine tissue has been shown to decrease the overall viability of the preparation, which may have lasting effects decreasing the success of the graft after transplant.…”

Beta-cell replacement therapy

“…However, to reduce islet loss through purification, no or minimal processing with density centrifugation is performed, and so islets are transplanted with varying amounts of exocrine tissue. This exocrine tissue may impact local inflammation and cell loss [23,24]. Alternatively, data suggest a potential benefit of cotransplantation of pancreatic duct cells which are a source of pancreatic ductal progenitor cells which may support islet neogenesis, as well as angiogenic proteins [25][26][27][28]29 in-vivo experience with observation of unexpected insulin independence in children receiving lowdose autologous islet transplants [30,31 && ].…”

Alpha-1-antitrypsin in cell and organ transplantation

“…A complete discussion of AAT in diabetes is beyond the scope of this review, but data on β‐cell survival in NOD mice suggest that AAT exerts similar beneficial activities during islet recovery and transplantation. Indeed, inclusion of AAT during islet culture increases β‐cell viability, insulin content, and insulin secretion in response to glucose and other secretagogues 29, 30. When a marginal mass of islets was infused into the livers of syngeneic diabetic mice, AAT improved graft acceptance and reduced infiltration of neutrophils and macrophages into the graft, concomitant with reduced TNF‐α expression and decreased islet apoptosis 33.…”