Beneficial Effects of Desferrioxamine on Encapsulated Human Islets—In Vitro and In Vivo Study

Abstract

As many as 2000 IEQs (islet equivalent) of encapsulated human islets are required to normalize glucose levels in diabetic mice. To reduce this number, encapsulated islets were exposed to 100 lM desferrioxamine (DFO) prior to transplantation. Cell viability, glucoseinduced insulin secretion, VEGF (Vascular endothelial growth factor), HIF-1a (Hypoxia inducible factor-1 alpha), caspase-3 and caspase-8 levels were assessed after exposure to DFO for 12, 24 or 72 h. Subsequently, 1000, 750 or 500 encapsulated IEQs were infused into peritoneal cavity of diabetic mice after 24 h exposure to DFO. Neither viability nor function in vitro was affected by DFO, and levels of caspase-3 and caspase-8 were unchanged. DFO significantly enhanced VEGF secretion by 1.6-and 2.5-fold at 24 and 72 h, respectively, with a concomitant increase in HIF-1a levels. Euglycemia was achieved in 100% mice receiving 1000 preconditioned IEQs, as compared to only 36% receiving unconditioned IEQs (p < 0.001). Similarly, with 750 IEQ, euglycemia was achieved in 50% mice receiving preconditioned islets as compared to 10% receiving unconditioned islets (p = 0.049). Mice receiving preconditioned islets had lower glucose levels than those receiving unconditioned islets. In summary, DFO treatment enhances HIF-1a and VEGF expression in encapsulated human islets and improves their ability to function when transplanted.

Preconditioning with Associated Blocking of Ca2+ Inflow Alleviates Hypoxia-Induced Damage to Pancreatic β-Cells

“…It seems possible that an accelerated rise in HIF-1 alpha during hypoxia could lessen damage afflicted by hypoxia. Such notion is in line with the observation that forced over-expression of HIF-1 alpha improved the results of beta cell transplantation [31], [32]. As to effects on AMPK this parameter which is sensitive to changes in metabolism was enhanced by diazoxide in response to hypoxia, i.e.…”

Alginate Microencapsulation of Human Islets Does Not Increase Susceptibility to Acute Hypoxia

“…Based on the hypoxia-induced rise in basal insulin release that we observe for nonencapsulated islets, one possible explanation could be that islets within the microcapsule are subjected to mild hypoxia, which subsequently gives rise to the basal secretion. Data from Vaithilingam et al could support such notion since pretreatment with the hypoxia-mimicking desferrioxamine agent induces slightly elevated basal insulin secretion [25]. …”

“…At first glance this finding in nonencapsulated islets is paradoxical, since treatment of human islets with the hypoxia-mimicking agent desferrioxamine increased the expression of VEGF [25]. However, a study with islets indicated that a 48 h culture in normoxia increased VEGF mRNA and protein to an extent that further increase was not observed after hypoxia [41].…”

Effect of prolonged gelling time on the intrinsic properties of barium alginate microcapsules and its biocompatibility

“…Alginates microcapsules cross-linked with Ca 2þ or Ba 2þ are used successfully in both allograft and xenograft settings without the need for anti-rejection drugs, at least in rodents, with recipients becoming normoglycaemic (Silva et al, 2006). Previously, we have demonstrated successful encapsulation of human and foetal pig islets into simple barium alginate microcapsules and established their function in vivo (Foster et al, 2007;Vaithilingam et al, 2010). Recently, a phase 1 clinical trial by the Sydney group using barium alginate microcapsules showed that allografting of microencapsulated human islets is safe although only a minor clinical benefit was observed.…”