Insulin-induced normoglycemia reduces islet number needed to achieve normoglycemia after allogeneic islet transplantation in diabetic mice

Early Metabolic Measures Predict Long-term Insulin Independence in Recipients of Total Pancreatectomy and Islet Autotransplantation

Background

Although diabetes after total pancreatectomy and islet autotransplantation (TP-IAT) is one of the biggest concerns for TP-IAT recipients and physicians, reliable prediction of post-TP-IAT glycemic control remains unestablished. This study was conducted to identify early predictors of insulin independence and goal glycemic control by hemoglobin A1c (HbA1c) ≤ 6.5% after TP-IAT.

Methods

In this single-center, retrospective study, patients who underwent TP-IAT (n = 227) were reviewed for simple metabolic markers or surrogate indices of β-cell function obtained 3 mo after TP-IAT as part of standard clinical testing. Long-term metabolic success was defined as (1) insulin independence and (2) HbA1c ≤ 6.5% 1, 3, and 5 y after TP-IAT. Single- and multivariate modeling used 3-mo markers to predict successful outcomes.

Results

Of the 227 recipients, median age 31 y, 30% male, 1 y after TP-IAT insulin independence, and HbA1c ≤ 6.5% were present in 39.6% and 72.5%, respectively. In single-predictor analyses, most of the metabolic markers successfully discriminated between those attaining and not attaining metabolic goals. Using the best model selected by random forests analysis, we accurately predicted 1-y insulin independence and goal HbA1c control in 77.3% and 86.4% of the patients, respectively. A simpler "clinically feasible" model using only transplanted islet dose and BETA-2 score allowed easier prediction at a small accuracy loss (74.1% and 82.9%, respectively).

Conclusions

Metabolic testing measures performed 3 mo after TP-IAT were highly associated with later diabetes outcomes and provided a reliable prediction model, giving valuable prognostic insight early after TP-IAT and help to identify recipients who require early intervention.

Implanting 1.1B4 human β-cell pseudoislets improves glycaemic control in diabetic severe combined immune deficient mice

AIM

To investigate the potential of implanting pseudoislets formed from human insulin-releasing β-cell lines as an alternative to islet transplantation.

METHODS

In this study, the anti-diabetic potential of novel human insulin releasing 1.1B4 β-cells was evaluated by implanting the cells, either as free cell suspensions, or as three-dimensional pseudoislets, into the subscapular region of severe combined immune deficient mice rendered diabetic by single high-dose administration of streptozotocin. Metabolic parameters including food and fluid intake, bodyweight and blood glucose were monitored throughout the study. At the end of the study animals were given an intraperitoneal glucose tolerance test. Animals were then culled and blood and tissues were collected for analysis. Insulin and glucagon contents of plasma and tissues were measured by insulin radioimmunoassay and chemiluminescent enzyme-linked immunosorbance assay respectively. Histological analyses of pancreatic islets were carried out by quantitative fluorescence immunohistochemistry staining.

RESULTS

Both pseudoislet and cell suspension implants yielded well vascularised β-cell masses of similar insulin content. This was associated with progressive amelioration of hyperphagia (P < 0.05), polydipsia (P < 0.05), body weight loss (P < 0.05), hypoinsulinaemia (P < 0.05), hyperglycaemia (P < 0.05 - P < 0.001) and glucose tolerance (P < 0.01). Islet morphology was also significantly improved in both groups of transplanted mice, with increased β-cell (P < 0.05 - P < 0.001) and decreased alpha cell (P < 0.05 - P < 0.001) areas. Whereas mice receiving 1.1B4 cell suspensions eventually exhibited hypoglycaemic complications, pseudoislet recipients displayed a more gradual amelioration of diabetes, and achieved stable blood glucose control similar to non-diabetic mice at the end of the study.

CONCLUSION

Although further work is needed to address safety issues, these results provide proof of concept for possible therapeutic applicability of human β-cell line pseudoislets in diabetes.

Successful Application of Closed-Loop Artificial Pancreas Therapy After Islet Autotransplantation

Total pancreatectomy with islet autotransplantation (TPIAT) may relieve the pain of chronic pancreatitis while avoiding postsurgical diabetes. Minimizing hyperglycemia after TPIAT limits beta cell apoptosis during islet engraftment. Closed-loop (CL) therapy combining an insulin pump with a continuous glucose monitor (CGM) has not been investigated previously in islet transplant recipients. Our objective was to determine the feasibility and efficacy of CL therapy to maintain glucose profiles close to normoglycemia following TPIAT. Fourteen adult subjects (36% male; aged 35.9 ± 11.4 years) were randomized to subcutaneous insulin via CL pump (n = 7) or multiple daily injections with blinded CGM (n = 7) for 72 h at transition from intravenous to subcutaneous insulin. Mean serum glucose values were significantly lower in the CL pump group than in the control group (111 ± 4 vs. 130 ± 13 mg/dL; p = 0.003) without increased risk of hypoglycemia (percentage of time <70 mg/dL: CL pump 1.9%, control 4.8%; p = 0.46). Results from this pilot study suggest that CL therapy is superior to conventional therapy in maintaining euglycemia without increased hypoglycemia. This technology shows significant promise to safely maintain euglycemic targets during the period of islet engraftment following islet transplantation.

Near-euglycemia can be achieved safely in pediatric total pancreatectomy islet autotransplant recipients using an adapted intravenous insulin infusion protocol

BACKGROUND

Children with severe chronic pancreatitis may undergo total pancreatectomy with islet autotransplantation (TPIAT) to relieve pain while minimizing the risk of postsurgical diabetes. Because overstimulation of transplanted islets by hyperglycemia can result in β-cell loss, we developed a specialized intravenous insulin infusion protocol (IIP) for pediatric TPIAT recipients to maintain euglycemia or near-euglycemia posttransplant.

SUBJECTS AND METHODS

Our objective was to review glucose control using an IIP specific for TPIAT recipients at a single institution. We reviewed postoperative blood glucose (BG) levels for 32 children 4-18 years old with chronic pancreatitis who underwent TPIAT between July 2011 and June 2013. We analyzed the proportion of BG values in the range of 70-140 mg/dL, mean glucose, glucose variability, and occurrence of hypoglycemia during the IIP; we also evaluated the transition to subcutaneous therapy (first 72 h with multiple daily injections [MDI]).

RESULTS

During IIP, the mean patient BG level was 116±27 mg/dL, with 83.1% of all values in the range of 70-140 mg/dL. Hypoglycemia was rare, with only 2.5% of values <70 mg/dL. The more recent era (n=16) had a lower mean BG and less variability than the early era (first 16 patients) (P≤0.004). Mean glucose level (116 vs. 128 mg/dL) and glucose variability were significantly lower during the IIP compared with MDI therapy (P<0.0001).

CONCLUSIONS

Tight glycemic control without excessive severe hypoglycemia was achieved in children undergoing TPIAT using an IIP specifically designed for this population; the ability to maintain BG in target range improved with experience with the protocol.

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.

Leptin administration enhances islet transplant performance in diabetic mice

Islet transplantation is an effective method to obtain long-term glycemic control for patients with type 1 diabetes, yet its widespread use is limited by an inadequate supply of donor islets. The hormone leptin has profound glucose-lowering and insulin-sensitizing action in type 1 diabetic rodent models. We hypothesized that leptin administration could reduce the dose of transplanted islets required to achieve metabolic control in a mouse model of type 1 diabetes. We first performed a leptin dose-response study in C57Bl/6 mice with streptozotocin (STZ)-induced diabetes to determine a leptin dose insufficient to reverse hyperglycemia. Subsequently, we compared the ability of suboptimal islet transplants of 50 or 125 syngeneic islets to achieve glycemic control in STZ-induced diabetic C57Bl/6 mice treated with or without this dose of leptin. The dose-response study revealed that leptin reverses STZ-induced diabetes in a dose-dependent manner. Supraphysiological leptin levels were necessary to restore euglycemia but simultaneously increased risk of hypoglycemia, and also lost efficacy after 12 days of administration. In contrast, 1 µg/day leptin only modestly reduced blood glucose but maintained efficacy throughout the study duration. We then administered 1 µg/day leptin to diabetic mice that underwent transplantation of 50 or 125 islets. Although these islet doses were insufficient to ameliorate hyperglycemia alone, coadministration of leptin with islet transplantation robustly improved control of glucose and lipid metabolism, without increasing circulating insulin levels. This study reveals that low-dose leptin administration can reduce the number of transplanted islets required to achieve metabolic control in STZ-induced diabetic mice.

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.

Expectations and Strategies Regarding Islet Transplantation: Metabolic Data From the GRAGIL 2 Trial

BACKGROUND

Whether islet transplantation should be aimed at restoring insulin independence or providing adequate metabolic control is still debated. The GRAGIL2 trial was designed as a phase 1-2 study where primary outcome was the rate of insulin independence, and secondary outcome was the success rate defined by a composite score based upon basal C-peptide, HbA1c, hypoglycemic events, and exogenous insulin needs.

METHODS

C-peptide negative type 1 brittle diabetic patients experiencing severe hypoglycemia were eligible to receive a maximum of two islet preparations totalizing 10,000 IE/kg or more, with a threshold of 5,000 IE/kg for the first infusion, according to the Edmonton protocol, within the Swiss-French GRAGIL multicentric network. A sequential analysis with a triangular test was performed in every five patients after 6- and 12-month follow-up. Maximal inefficiency was set at 40% and minimal efficiency at 66%.

RESULTS

From September 2003 to October 2005, 10 patients were included. Median waiting time was 6.7 months (first injection) and 9 weeks (second injection). All but one patient received 11,089+/-505 IE/kg: one received a single graft of 5398 IE/kg. At 6 months, insulin independence and composite success rates were 6 of 10 and 6 of 10, respectively. At 12 months, insulin independence was observed in 3 of 10 patients and success in 5 of 10 patients.

CONCLUSION

Based upon our sequential analysis settings, islet transplantation failed to achieve the primary goal, insulin independence, but tended to succeed in reaching the secondary goal, successful metabolic control. Currently it appears to be a successful biological closed-loop glucose control method for brittle diabetes.

Mitochondrial Targeting with Antioxidant Peptide SS-31 Prevents Mitochondrial Depolarization, Reduces Islet Cell Apoptosis, Increases Islet Cell Yield, and Improves Posttransplantation Function

Apoptotic cell death is a defined pathway for islet cell demise, and mitochondrial dysfunction contributes to islet cell apoptosis. The hypothesis that the novel peptide D-Arg-2', 6'-dimethyltyrosine-Lys-Phe-NH2 (SS-31), previously shown to target inner mitochondrial membrane and prevent oxidative damage of neuronal cells and other cell types, optimizes pancreatic islet isolation and improves posttransplantation function in recipients with diabetes was investigated. Herein is demonstrated that SS-31 readily penetrates intact mouse islets, preserves mitochondrial polarization, reduces islet cell apoptosis, and increases islet cell yield. Optimization of islet isolation is demonstrable after SS-31 pretreatment of islet (pancreas) donor mice and with the addition of SS-31 to reagents that are used in the isolation of mouse islets. The supplementation of in vitro culture medium with SS-31 reduced islet cell apoptosis and increased the viability of human islets, as ascertained by dual-parameter flow cytometry analysis. In a stringent marginal islet cell mass transplantation model (200 mouse islets transplanted under the renal capsule of syngeneic diabetic mice) and using islets that were derived from old mice (>24 wk), SS-31 treatment was associated with prompt and sustained normoglycemia, whereas the untreated islet graft recipients remained diabetic. Our data suggest a novel strategy to optimize islet isolation and reduce the need for multiple pancreata to achieve insulin independence in the recipient with type 1 diabetes. Because SS-31 was effective with "extended" islet donors, it is hypothesized that the antioxidant SS-31 may serve to increase the pool of eligible organ donors.

Individual differences in glucose homeostasis: do our early life interactions with bacteria matter?

Exposure to endotoxin during the neonatal period in the rat has been shown to alter the development of the hypothalamic-pituitary-adrenal axis, inducing hyper-responsivity and increased glucocorticoid production in later-life. Glucocorticoids are known to have major metabolic effects, therefore, early life endotoxin exposure may have potentially serious consequences for metabolic homeostasis in the exposed animal. The aims of this study were therefore to assess the effect of neonatal bacterial endotoxin exposure on subsequent glucose homeostasis, insulin action and corticosterone production from puberty through to senescence. Male Fischer-344 rat pups were treated with bacterial endotoxin (0.05 mg/kg Salmonella enteritidis i.p.) or vehicle (sterile pyrogen free saline) on days 3 and 5 postnatally. Insulin and glucose levels were assessed before and during and intraperitoneal glucose tolerance test (IPGTT) together with body mass on postnatal days 40, 80, and 400. In addition, circulating levels of corticosterone were measured at 0, 30, and 90 min following a 30-min restraint challenge at these ages. Neonatal endotoxin challenge did not alter fasting plasma glucose or insulin, but impaired glucose tolerance at puberty (p<.05), improved glucose tolerance in adulthood (p<.05) and had no effect at senescence. During the IPGTT insulin was reduced at all ages (p<.05) following neonatal endotoxin challenge, but insulin sensitivity was unaltered, except for an increase in adulthood (p<.05), which is consistent with the observed improvement in glucose tolerance at this age. Neonatal endotoxin challenge reduced body mass during puberty and senescence (p<.05) but did not alter basal or stressed plasma corticosterone levels at any of the three developmental time points examined. These findings suggest that variations in an individual's early life bacterial environment may contribute to differences in glucose homeostasis, insulin action and disease susceptibility later in life.

Islet transplantation outcomes in mice are better with fresh islets and exendin-4 treatment

AIMS/HYPOTHESIS

Although islet transplantation in diabetes holds great promise, two or three donor pancreases are usually required to achieve normoglycaemia in human or rodent recipients. We investigated whether there were differences between fresh and cultured islets in terms of transplantation outcome. We also investigated the effects of normoglycaemia during engraftment and the effects of exendin-4, a glucagon-like peptide-1 receptor agonist, on islet transplantation.

MATERIALS AND METHODS

Seventy-five fresh islets were transplanted to the right kidney of diabetic mice and 425 fresh islets were transplanted to the left kidney. The mice were treated with exendin-4 or vehicle for 14 days, after which the large graft was removed by left nephrectomy. In a separate set of experiments, islets cultured in the presence or absence of exendin-4 for 72 h, or fresh islets, were transplanted to diabetic mice. In both sets of experiments, blood glucose levels were monitored.

RESULTS

Compared with cultured islets, fresh islets were more effective at reversing hyperglycaemia in mice. The treatment of the recipient mice with exendin-4 did not have beneficial effects on glucose homeostasis. However, when islets are cultured, exendin-4 treatment increases the rate of reversal of hyperglycaemia, but not to the degree of fresh islets.

CONCLUSIONS/INTERPRETATION

Fresh islets are more effective than cultured islets at reversing hyperglycaemia. Exendin-4 has beneficial effects on islet transplantation.

Syngeneic islet transplantation into seminal vesicles of diabetic rats

Pancreatic islet transplantation has been proposed as an attractive option for the treatment of type I diabetes. Transplantation into different sites has been investigated, among them those that are immuno-logically privileged (e.g., thymus, uterus, brain, anterior eye chamber, and testicle). Because of their characteristics, seminal vesicles could be considered as immunologically privileged organs, but there is no worldwide experience that can confirm it. The purpose of the present study is to assess the viability and functionality of islet transplantation into seminal vesicles of diabetic rats. One hundred ninety inbred adult male syngeneic Lewis rats were used as donors (n = 72), receptors (n = 36), and controls(n = 11). Diabetes was chemically induced through a single intraperitoneal injection of streptozotocin. Groups of 1200 purified islets were introduced in the right seminal vesicle of diabetic rats. Diabetic control rats were sham transplanted. Body weight and glycemia were monitored every 2 d. Of transplanted rats, 16.7% achieved a good function due to islet engraftment, while 30.6% achieved a partially good response, and 52.7% were considered as nonresponding. This is the first report about islet transplantation into seminal vesicles of diabetic animals. Our results indicate that islet transplantation into rat seminal vesicles is technically possible, and that islets can function normally after engraftment into the wall of the seminal vesicle.

Factors Influencing Quantification of in Vivo Bioluminescence Imaging: Application to Assessment of Pancreatic Islet Transplants

The aim of this study is to determine and characterize factors influencing in vivo bioluminescence imaging (BLI) and apply them to the specific application of imaging transplanted pancreatic islets. Noninvasive quantitative assessment of transplanted pancreatic islets poses a formidable challenge. Murine pancreatic islets expressing firefly luciferase were transplanted under the renal capsule or into the portal vein of nonobese diabetic-severe combined immunodeficiency mice and the bioluminescence was quantified with a cooled charge coupled device camera and digital photon image analysis. The important, but often neglected, effects of wound healing, mouse positioning, and transplantation site on bioluminescence measurements were investigated by imaging a constant emission, isotropic light-emitting bead (lambda = 600) implanted at the renal or hepatic site. The renal beads emitted nearly four times more light than hepatic beads with a smaller spot size, indicating that light absorption and scatter are greatly influenced by the transplant site and must be accounted for in BLI measurements. Detected luminescence decreased with increasing angle between the mouse surface normal and optical axis. By defining imaging parameters such as postsurgical effects, animal positioning, and light attenuation as a function of transplant site, this study develops BLI as a useful imaging modality for quantitative assessment of islets post-transplantation.