Insulin treatment of mice recipients preserves beta-cell function in porcine islet transplantation

AN69 Hollow Fiber Membrane will Reduce but Not Abolish the Risk of Transmission of Porcine Endogenous Retroviruses

As the risk of porcine endogenous retrovirus (PERV) infection is a major obstacle to the xenotransplantation of porcine tissue, we investigated whether an AN69 hollow fibre membrane, used for islets of Langerhans transplantation, could prevent the transfer of PERVs and thus reduce the risk of PERV infection. PK15 cells were used as a PERV source. A specific and highly sensitive RCR was used for detection of a PERV provirus DNA (gag region) and a porcine mtDNA. Human U293 cells were incubated in vitro with encapsulated PK15 cells, concentrated encapsulated PK15 supernatant, or concentrated PK15 supernatant as a control. CD1 mice were implanted in vivo with encapsulated PK15 cells or injected with PK15 supernatant. We found no infection in human cells incubated with either encapsulated PK15 supernatant or in 10 out of 11 samples after coincubation with encapsulated PK15 cells. Infection of human cells was, however, detected in 1 out of 11 samples after coincubation with encapsulated PK15 cells. The presence of PERV provirus DNA and porcine mtDNA was detected in all the investigated tissues of the mice injected with PK15 supernatant and in various tissues of the mice implanted with encapsulated PK15 cells. Four weeks after the last injection of PK15 supernatant or a fiber explantation, no mouse showed any presence of PERV provirus DNA or porcine mtDNA. Our results demonstrate that AN69 hollow fiber membrane will reduce but not abolish the risk of PERV infection. Because the real risk of PERV infection still remains unknown, it is necessary to investigate further the real protection that could be provided by hollow fibers to ensure the safety of clinical xenotransplantation.

A novel resting strategy for improving islet engraftment in the liver

BACKGROUND

Several studies have revealed that posttransplant insulin treatment is beneficial to rest the islet grafts. However, insulin infusion per se is not enough to completely suppress the heavy workload arising caused by postprandial hyperglycemia. Therefore, the present study examined whether short-term fasting combined with insulin treatment could effectively prevent graft exhaustion after intraportal islet transplantation.

METHODS

A marginal dose of syngeneic rat islet grafts were transplanted intraportally into the control, insulin-treated, and insulin+rest groups of streptozotocin-induced diabetic rats. The control group fed freely without insulin treatment, and the other groups were continuously treated with an optimal amount of insulin to maintain normoglycemia. In addition, the insulin+rest group fasted and received total parenteral nutrition during the 2 weeks after transplantation.

RESULTS

The curative rate was significantly higher in both the insulin and insulin+rest groups than the control group (P<0.0001). The glucose tolerance, residual graft mass, and graft function were significantly ameliorated in the insulin+rest group, but not in the insulin group, compared to the control group (P<0.01, P=0.03, P=0.001).

CONCLUSIONS

These data suggest that short-term fasting combined with insulin treatment, especially during the avascular period of the grafts, could therefore be a promising regimen for improving pancreatic islet engraftment in the liver.

Increased β-cell replication and β-cell mass regeneration in syngeneically transplanted rat islets overexpressing insulin-like growth factor II

Insulin-like growth factor II (IGF2) is a growth-promoting peptide that increases β-cell proliferation and survival. The aim of the study was to determine the effect of IGF2 overexpression on β-cell mass in transplanted islets. Islets infected with adenovirus encoding for IGF2 (Ad-IGF2 group), for luciferase (Ad-Luc control group), or with uninfected islets (control group) were syngeneically transplanted to streptozotocin-diabetic Lewis rats. Eight hundred islets, a minimal mass model to restore normoglycemia, or 500 islets, a clearly insufficient mass, were transplanted. Rats transplanted with 800 Ad-IGF2 islets showed a better metabolic evolution than control groups. As expected, rats transplanted with 500 Ad-IGF2 or control islets maintained similar hyperglycemia throughout the study, ensuring comparable metabolic conditions among both groups. β-Cell replication was higher in Ad-IGF2 group than in control group on days 3 [1.45% (IQR: 0.26) vs. 0.58% (IQR: 0.18), p = 0.006], 10 [1.58% (IQR: 1.40) vs. 0.90% (IQR: 0.61), p = 0.035], and 28 [1.35% (IQR: 0.35) vs. 0.64% (IQR: 0.28), p = 0.004] after transplantation. β-Cell mass was similarly reduced on day 3 after transplantation in Ad-IGF2 and control group [0.36 mg (IQR: 0.26) vs. 0.38 mg (IQR: 0.19)], it increased on day 10, and on day 28 it was higher in Ad-IGF2 than in control group [0.63 mg (IQR: 0.38) vs. 0.42 mg (IQR: 0.31), p = 0.008]. Apoptosis was similarly increased in Ad-IGF2 and control islets after transplantation. No differences in insulin secretion were found between Ad-IGF2 and uninfected control islets. In summary, IGF2 overexpression in transplanted islets increased β-cell replication, induced the regeneration of the transplanted β-cell mass, and had a beneficial effect on the metabolic outcome reducing the β-cell mass needed to achieve normoglycemia.

Islet graft response to transplantation injury includes upregulation of protective as well as apoptotic genes

Pancreatic islets are particularly vulnerable in the initial days after transplantation when multiple factors converge to damage the islet graft. The aim of this study was to investigate the expression profile of genes involved in damage and protection of beta-cells in the initial days after syngeneic islet transplantation. We studied the expression of a set of selected genes involved in apoptosis (Bcl2, Bclx(L), Bax, Bad, Bid, and CHOP), cytokine defense, (SOCS-1 and SOCS-3), or free radical protection (Hmox1, Cu/Zn-SOD, Mn-SOD, and Hsp70). Because hyperglycemia has deleterious effects on islet transplantation outcome, we studied its effect on the expression of these genes. Five hundred islets were syngeneically transplanted under the kidney capsule of normoglycemic or streptozotocin-induced diabetic Lewis rats. Gene expression was analyzed by quantitative real-time RT-PCR in grafts 1, 3, and 7 days after transplantation, and in freshly isolated islets. The expression of proapoptotic genes Bid and CHOP, as well as protective genes Bclx(L), Socs1, Socs3, Hmox1, and MnSod, was maximally increased 1 day after transplantation, and in most cases it remained increased 7 days later, indicating the presence of a protective response against cell damage. In contrast, the expression of Bcl2, Bax, Bad, Cu/ZnSod, and Hsp70 genes did not change. Hyperglycemia did not modify the expression of most studied genes. However, MnSod and Ins2 expression was increased and reduced, respectively, on day 7 after transplantation to diabetic recipients, suggesting that hyperglycemia increased oxidative stress and deteriorated beta-cell function in transplanted islets.

Encapsulation of porcine islets permits extended culture time and insulin independence in spontaneously diabetic BB rats

The ability to culture porcine islets for extended times allows for both their functional assessment and the assurance of their microbiological safety prior to transplantation. We have previously shown that agarose-encapsulated porcine islets can be cultured for at least 24 weeks. In the current study, porcine islet agarose macrobeads cultured for up to 67 weeks were assessed for their ability to restore normoglycemia, respond to an intraperitoneal glucose challenge, maintain spontaneously diabetic BB rats free of insulin therapy for more than 6 months, and for their biocompatibility. Porcine islets were encapsulated in agarose macrobeads and subjected to weekly static perifusion assays for the assessment of insulin production. After in vitro culture for either 9, 40, or 67 weeks, 56-60 macrobeads were transplanted to each spontaneously diabetic BB rat. Transplanted rats were monitored daily for blood glucose levels. Glucose tolerance tests and assessments for porcine C-peptide were conducted at various intervals throughout the study. Normoglycemia (100-200 mg/dl) was initially restored in all islet transplanted rats. Moderate hyperglycemia (200-400 mg/dl) developed at around 30 days posttransplantation and continued throughout the study period of 201-202 days. Importantly, all rats that received encapsulated porcine islets continued to gain weight and were free of exogenous insulin therapy for the entire study. Porcine C-peptide (0.2-0.9 ng/ml) was detected in the serum of islet recipients throughout the study period. No differences were detected between recipient animals receiving islet macrobeads of various ages. These results demonstrate that the encapsulation of porcine islets in agarose macrobeads allows for extended culture periods and is an appropriate strategy for functional and microbiological assessment prior to clinical use.

Delayed functional maturation of neonatal porcine islets in recipients under strict glycemic control

BACKGROUND

The aim of this study was to compare the functional maturation of neonatal porcine islet (NPI) grafts exposed to long-term hyperglycemia with those implanted under euglycemic conditions.

METHODS

mice Neonatal porcine islets were transplanted under the left renal capsule of diabetic SCID mice (group H), or in diabetic SCID mice who were also implanted with 500 BALB/c islets under the right renal capsule (group N). On day 42, the right kidneys were removed in both groups.

RESULTS

No animals in group H achieved euglycemia within 3 weeks after transplantation. Thus, these mice were exposed to long-term hyperglycemia. Mice in group N became euglycemic immediately after transplantation, however after removal of BALB/c grafts on day 42 they exhibited significantly higher blood glucose levels than in group H and showed glucose intolerance after glucose administration. Cellular insulin content of NPI grafts harvested on day 58 or 72 was significantly lower in group N mice compared to group H.

CONCLUSIONS

These results suggest that tight control of glycemia reduces the functional maturation of NPI grafts.