Transplantation for the treatment of type 1 diabetes. World J Gastroenterol. 2007;13:6347-6355. [PMID: 18081223 DOI: 10.3748/wjg.13.6347]

Hypoglycemia in patients with type 1 diabetes: epidemiology, pathogenesis, and prevention

Hypoglycemia is uncommon in the general, nondiabetic population but occurs frequently in persons with diabetes treated with insulin or insulin secretagogues. Thus, iatrogenic hypoglycemia explains the majority of cases among persons with type 1 diabetes (T1DM). Since T1DM is characterized by absolute insulin dependence, the current imperfections in insulin replacement therapies often lead to a mismatch between caloric supply and circulating insulin levels, thus increasing the risk for glycemic fluctuations. Hypoglycemia is the limiting factor to excellent glycemic control in insulin-treated subjects. Intensification of glycemic control was associated with a 300 % increase in the rate of hypoglycemia in the Diabetes Control and Complications Trial. Recent measurements using continuous glucose monitoring reveal an alarming rate of daytime and nocturnal episodes of hypoglycemia in patients with T1DM. Etiological factors underlying hypoglycemia in T1DM include predictable triggers (skipped meals, exercise, insulin over dosage) as well as defective counterregulation, a component of hypoglycemia-associated autonomic failure.

Revascularization of transplanted pancreatic islets and role of the transplantation site

Since the initial reporting of the successful reversal of hyperglycemia through the transplantation of pancreatic islets, significant research efforts have been conducted in elucidating the process of revascularization and the influence of engraftment site on graft function and survival. During the isolation process the intrinsic islet vascular networks are destroyed, leading to impaired revascularization after transplant. As a result, in some cases a significant quantity of the beta cell mass transplanted dies acutely following the infusion into the portal vein, the most clinically used site of engraftment. Subsequently, despite the majority of patients achieving insulin independence after transplant, a proportion of them recommence small, supplemental exogenous insulin over time. Herein, this review considers the process of islet revascularization after transplant, its limiting factors, and potential strategies to improve this critical step. Furthermore, we provide a characterization of alternative transplant sites, analyzing the historical evolution and their role towards advancing transplant outcomes in both the experimental and clinical settings.

Intra-epidermal nerve fibers density and nociception in EPO-treated type 1 diabetic rats with peripheral neuropathy

Small-diameter nerve fibers, which subserve nociception, can be affected early in peripheral neuropathies, although their injury may not be detectable by routine neurophysiologic tests. On the other hand, skin biopsy has proved to be a reliable tool to examine nonmyelinated nerve fibers, as assessed by the quantification of intra-epidermal nerve fiber (IENF) density not only along with the degenerative process but, noteworthy, IENF density could be very helpful in evaluating drug efficacy such as erythropoietin (EPO) treatment.

Ultrathin polymeric coatings based on hydrogen-bonded polyphenol for protection of pancreatic islet cells

Though transplantation of pancreatic islet cells has emerged as a promising treatment for Type 1 diabetes its clinical application remains limited due to a number of limitations including both pathogenic innate and adaptive immune responses. We report here on a novel type of multifunctional cytoprotective material applied to coat living pancreatic islets. The coating utilizes hydrogen-bonded interactions of a natural polyphenol (tannic acid) with poly(N-vinylpyrrolidone) deposited on the islet surface via non-ionic layer-by-layer assembly. We demonstrate that the coating is conformal over the surface of mammalian islets including those derived from rat, non-human primate (NHP), and human. In contrast to unmodified controls, the coated islets maintain their viability and β-cell functionality for at least 96 hours in vitro. We also determine that the coating demonstrates immunomodulatory cytoprotective properties suppressing pro-inflammatory cytokine synthesis in stimulated bone marrow-derived macrophages and diabetogenic BDC-2.5 T cells. The coating material combines high chemical stability under physiologically relevant conditions with capability of suppressing cytokine synthesis, crucial parameters for prolonged islet integrity, viability, and function in vivo. Our study offers new opportunities in the area of advanced multifunctional materials to be used for a cell-based transplantation therapy.

Poly(ethylene glycol) cross-linked hemoglobin with antioxidant enzymes protects pancreatic islets from hypoxic and free radical stress and extends islet functionality

The objective of this study was to investigate the efficiency of multifunctional poly(ethylene glycol)-based hemoglobin conjugates crosslinked with antioxidant enzymes for their ability to protect an oxygen carrier (hemoglobin) and insulin secreting islets from the combination of hypoxic and free radical stress under simulated transplantation conditions. In this study, RINm5F cells and isolated pancreatic islets were challenged with oxidants (H(2)O(2) or xanthine and xanthine oxidase) and incubated with conjugates (hemoglobin-hemoglobin or superoxide dismutase-catalase-hemoglobin) in normoxia (21% oxygen) or hypoxia (6% or 1% oxygen). Hemoglobin protection, intracellular free radical activity and cell viability in RINm5F cells measured by methemoglobin, dichlorofluorescein-diacetate, and (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay, respectively, showed that cells were better protected by conjugates containing antioxidant enzymes. Insulin secretion from islets and qualitative confocal evaluation of viability showed beta cells were protected by conjugates containing antioxidant enzymes when exposed to induced stress. Our study suggested that antioxidant enzymes play a significant role in hemoglobin protection and thus extended cell protection.

Current status of immunomodulatory and cellular therapies in preclinical and clinical islet transplantation

Clinical islet transplantation is a β-cell replacement strategy that represents a possible definitive intervention for patients with type 1 diabetes, offering substantial benefits in terms of lowering daily insulin requirements and reducing incidences of debilitating hypoglycemic episodes and unawareness. Despite impressive advances in this field, a limiting supply of islets, inadequate means for preventing islet rejection, and the deleterious diabetogenic and nephrotoxic side effects associated with chronic immunosuppressive therapy preclude its wide-spread applicability. Islet transplantation however allows a window of opportunity for attempting various therapeutic manipulations of islets prior to transplantation aimed at achieving superior transplant outcomes. In this paper, we will focus on the current status of various immunosuppressive and cellular therapies that promote graft function and survival in preclinical and clinical islet transplantation with special emphasis on the tolerance-inducing capacity of regulatory T cells as well as the β-cells regenerative capacity of stem cells.

Reversible immortalization of rat pancreatic β cells with a novel immortalizing and tamoxifen-mediated self-recombination tricistronic vector

Although the strategy of "Cre/LoxP-based reversible immortalization" holds great promise to overcome the cellular senescence of primary cell cultures for their further use, a secondary gene transfer for Cre expression is usually utilized to trigger the excision of the immortalizing genes in a large number of cells, thus presenting a formidable hurdle for large-scale application. We modified the strategy by utilizing a tricistronic retroviral vector pLCRSTP, in which Cre-ER, simian virus 40 large T antigen (SV40LTAg) oncogene, and a reporter gene were flanked by the same pair of LoxA sites. Five immortalized rat pancreatic β cell clones transduced with pLCRSTP, and six immortalized rat pancreatic β cell clones co-transduced with pLCRSTP and another vector encoding the human telomerase reverse transcriptase (hTERT) gene, were obtained, respectively. The Cre-ER protein could be induced to translocate from the cytoplasm to the nucleus by 4-hydroxytamoxifen to make SV40LTAg, hTERT and the Cre-ER gene itself excise without a secondary gene transfer. Our studies suggest that this system is useful to expand rat β cells and may allow for large-scale production due to its simpler manipulation.

Effect of adenosine A2 receptor agonist on oxygen free radicals and apoptosis during ischemia reperfusion injury in rat pancreas

AIM: To investigate the role of adenosine A2 receptor agonist in protection from production of oxygeon free radicals and induction of apoptosis during ischemia and reperfusion injury in rat pancreas.

METHODS: The rats were divided randomly into sham, control and experimental groups. After 30 min clamping of subsplenic artery, normal saline (2 mL/kg body weight) or A2 receptor agonist CGS21680 (300 µg/kg body weight) was injected via dorsal penis vein, and at 15 min, 30 min and 60 min reperfusion, the changes of lipoperoxides (LPO), apoptosis and morphology in pancreas tissues were examined.

RESULTS: After 15, 30 and 60 min reperfusion, LPO increased significantly in control group compared with the sham operation group (8.25 ± 1.15 vs 1.63 ± 0.46, 10.67 ± 2.04 vs 1.85 ± 0.62, 15.31 ± 3.02 vs 2.02 ± 0.86, all P < 0.05) and experimental group (8.25 ± 1.15 vs 6.51 ± 1.38, 10.67 ± 2.04 vs 6.84 ± 1.74, 15.31 ± 3.02 vs 10.22 ± 2.91 µmol/L, all P < 0.05). Apoptosis increased significantly in control group compared with the sham operation group (0.55 ± 0.08 vs 0.18 ± 0.04, 1.21 ± 0.15 vs 0.20 ± 0.06, 2.63 ± 0.52 vs 0.23 ± 0.06, P < 0.05 or 0.01) and experimental group (0.55 ± 0.08 vs 0.32 ± 0.16 P < 0.05; 1.21 ± 0.15 vs 0.44 ± 0.20, 2.63 ± 0.52 vs 0.50 ± 0.43, all P < 0.05 or 0.01). In the control group, compared with 15 min reperfusion, LPO and apoptosis increased significantly at 30 min or 60 min reperfusion (P < 0.05 or 0.01). In sham operation group and experimental group, no remarked damage of pancreas was detected, but in control group, the pancreas damage became more serious with the prolonging of reperfusion.

CONCLUSION: Adenosine A2 receptor agonist attenuates postischemic production of oxygen free radicals and induction of apoptosis in pancreas tissues, thereby minimizes the ischemia reperfusion injury.