XIAP Overexpression in Human Islets Prevents Early Posttransplant Apoptosis and Reduces the Islet Mass Needed to Treat Diabetes

Abstract

The Edmonton Protocol for treatment of type 1 diabetes requires islets from two or more donors to achieve euglycemia in a single recipient, primarily because soon after portal infusion, the majority of the transplanted cells undergo apoptosis due to hypoxia and hypoxia reperfusion injury. X-linked inhibitor of apoptosis protein (XIAP) is a potent endogenous inhibitor of apoptosis that is capable of blocking the activation of multiple downstream caspases, and XIAP overexpression has previously been shown to enhance engraftment of a murine ␤-cell line. In this study, human islets transduced with a XIAP-expressing recombinant adenovirus were resistant to apoptosis and functionally recovered following in vitro stresses of hypoxia and hypoxia with reoxygenation (models reperfusion injury). Furthermore Ad-XIAP transduction dramatically reduced the number of human islets required to reverse hyperglycemia in chemically diabetic immunodeficient mice. These results suggest that by transiently overexpressing XIAP in the immediate posttransplant period, human islets from a single donor might be used to effectively treat two diabetic recipients. Diabetes 54: [2541][2542][2543][2544][2545][2546][2547][2548] 2005 T he recent introduction of the Edmonton Protocol has demonstrated that islet transplantation is a viable route to achieve insulin independence in a population of patients with type 1 diabetes (1). Despite its promise, islet transplantation remains restricted to patients with severe hypoglycemia or glycemic lability and is currently unsuitable for the majority of patients with type 1 diabetes for several reasons. Most recipients require two or more islet transplant procedures (combined mass of Ͼ10,000 islet equivalents [IEQs]/kg body wt) in order to become insulin independent, which is a serious drawback given the prevalence of diabetes and the limited cadaveric organ donor pool (2,3). Also, the risks associated with islet transplantation appear to increase with the number of infusions and with the total packed cell volume of cumulative grafts (4).Expansion of clinical islet transplantation has been limited by the large requirement for donor tissue. The fact that most patients must receive Ͼ10,000 IEQs/kg to become insulin independent suggests that a large portion of the infused islets fail to engraft sufficiently. In fact, in murine models of islet transplantation, it has been determined that even under ideal circumstances, Ͼ60% of syngeneic islet graft mass is lost due to apoptosis (5). In clinical islet transplantation, it has been estimated that more than two-thirds of the implanted islets never become functional (2).This early profound loss in islet mass can be attributed to several factors. Within a healthy pancreas, islet function is maximized by the intimate proximity of the ␤-cells and circulating blood, and, as a result, ␤-cells require a microenvironment with highly oxygenated blood (pO 2 of 40 mmHg) and abundant nutrients (6). The current method of human islet isolation and purification destroys the cap...

Proapoptotic BH3-Only Protein Bid Is Essential For Death Receptor–Induced Apoptosis of Pancreatic β-Cells

“…Inhibition of extrinsic (i.e., dnFADD, cFLIP, or A20) or intrinsic (i.e., Bcl-2 or Bcl-X L ) signals of apoptosis has only limited impact on islet cell apoptosis and diabetes development. Overexpression of XIAP, which prevents activation of effector caspases late in apoptosis, has shown promising results (45,46). However, caspase inhibition is generally not sufficient for survival following mitochondrial outer membrane permeabilization (47,48).…”

XIAP inhibition of β-cell apoptosis reduces the number of islets required to restore euglycemia in a syngeneic islet transplantation model

“…11 Islets were transduced overnight with 0 or 5 plaque forming units (pfu; assuming 1,000 cells per islets) of recombinant adenovirus using the chicken b-actin promoter to drive Adenoviral XIAP expression has also been shown to reduce the mass of human islets required to reverse euglycemia in immunedeficient, diabetic mice, compared to control mice that received transplants of islets transduced with adenovirus expressing LacZ. 15 The present data are also in accordance with our previous report of the beneficial effects of XIAP overexpression in murine islet allografts. Islets are likely subject to a number of stresses during transplantation, including ischemic damage, sheer stress and exposure to pro-inflammatory cytokines.…”

“…15 XIAP is a potent inhibitor of cell death induced by a number of apoptotic triggers, presumably through its ability to inhibit caspases 3, 7 and 9. 16,17 The cytoprotective potential of XIAP has also been demonstrated in a number of animal models of cellular degeneration, including ischemia, 18,19 axotomy, 20,21 glaucoma, 22 MPTP-induced dopaminergic cell death 23,24 and muscular atrophy.…”

AEB071 (sotrastaurin) does not exhibit toxic effects on human islets in vitro nor after transplantation into immunodeficient mice

“…Using the method described by Emamaullee et al islets were stained for insulin and apoptotic cells concurrently to quantify the ratio of apoptotic to non-apoptotic β-cell. 29 Guinea pig antiinsulin antibody (Dako) at a dilution of 1:500 was used for insulin staining. Secondary TRITC-conjugated goat anti-guinea pig antibody (Jackson ImmunoResearch) was used for detection of the primary antibody.…”