Beta-cell replacement therapy: current outcomes and future landscape

Effects of sustained GABA releasing implants on pancreatic islets in mice

Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter that is strongly and selectively synthesized in and secreted from pancreatic beta cells. Exogenously delivered GABA has been proposed to induce beta cell regeneration in type 1 diabetes, but these results have been difficult to replicate and may depend on the specifics of the animal model and drug delivery method used. Here, we developed a GABA-releasing ethylene-vinyl acetate polymer implant for sustained GABA delivery to the intraperitoneal space as an alternative to injected or oral GABA. We explored the effect of the GABA-releasing polymer implants compared to implanted osmotic pumps loaded with GABA on islet size in non-diabetic, outbred mice. We also attempted to monitor in vivo GABA release using HPLC on blood samples, but these measurements were confounded by high variability within treatment groups and unexpectedly high serum GABA levels in mice receiving GABA-negative implants. The ethylene-vinyl acetate polymer implants became heavily fibrosed with abdominal adhesion tissue, while the osmotic pumps had no macroscopic fibrosis. Histological analysis showed no significant effect of the sustained GABA delivery polymer or osmotic pumps on islet size, alpha cell to beta cell ratio, or the number of Ki67-positive islet cells. The GABA treatment time course was limited to two weeks due to the drug-release window of the polymer, while others reported islet-trophic effects of GABA after 10 to 12 weeks of treatment. In summary, our study is consistent with the concept that exogenous GABA administration does not significantly alter islet cell mass in non-diabetic CD-1 mice in the short-term. However, more data are needed including higher GABA doses and more prolonged treatment regimens for a better comparison with contrasting reports.

Potential Benefits of Nrf2/Keap1 Targeting in Pancreatic Islet Cell Transplantation

Permanent pancreatic islet cell destruction occurs in type 1 diabetes mellitus (T1DM) through the infiltration of inflammatory cells and cytokines. Loss of β-cell integrity secondary to oxidation leads to an inability to appropriately synthesize and secrete insulin. Allogenic islet cell transplantation (ICT) has risen as a therapeutic option to mitigate problematic hypoglycemia. Nevertheless, during the process of transplantation, islet cells are exposed to oxidatively caustic conditions that severely decrease the islet cell yield. Islet cells are at a baseline disadvantage to sustain themselves during times of metabolic stress as they lack a robust anti-oxidant defense system, glycogen stores, and vascularity. The Nrf2/Keap1 system is a master regulator of antioxidant genes that has garnered attention as pharmacologic activators have shown a protective response and a low side effect profile. Herein, we present the most recently studied Nrf2/Keap1 activators in pancreas for application in ICT: Dh404, dimethyl fumarate (DMF), and epigallocatechin gallate (EGCG). Furthermore, we discuss that Nrf2/Keap1 is a potential target to ameliorate oxidative stress at every step of the Edmonton Protocol.

Novel Fusion Protein Targeting Mitochondrial DNA Improves Pancreatic Islet Functional Potency and Islet Transplantation Outcomes

Long-term graft survival is an ongoing challenge in the field of islet transplantation. With the growing demand for transplantable organs, therapies to improve organ quality and reduce the incidence of graft dysfunction are of paramount importance. We evaluated the protective role of a recombinant DNA repair protein targeted to mitochondria (Exscien I-III), as a therapeutic agent using a rodent model of pancreatic islet transplantation. We first investigated the effect of therapy on isolated rat islets cultured with pro-inflammatory cytokines (interleukin-1 β, interferon γ, and tumor necrosis factor α) for 48 h and documented a significant reduction in apoptosis by flow cytometry, improved viability by immunofluorescence, and conserved functional potency in vitro and in vivo in Exscien I-III-treated islets. We then tested the effect of therapy in systemic inflammation using a rat model of donor brain death (BD) sustained for a 6-h period. Donor rats were allocated to 4 groups: (non-BD + vehicle, non-BD + Exscien I-III, BD + vehicle, and BD + Exscien I-III) and treated with Exscien I-III (4 mg/kg) or vehicle 30 min after BD induction. Sham (non-BD)-operated animals receiving either Exscien I-III or vehicle served as controls. Islets purified from BD + Exscien I-III-treated donors showed a significant increase in glucose-stimulated insulin release in vitro when compared to islets from vehicle-treated counterparts. In addition, donor treatment with Exscien I-III attenuated the effects of BD and significantly improved the functional potency of transplanted islets in vivo. Our data indicate that mitochondrially targeted antioxidant therapy is a novel strategy to protect pancreas and islet quality from the deleterious effects of cytokines in culture and during the inflammatory response associated with donation after BD. The potential for rapid translation into clinical practice makes Exscien I-III an attractive therapeutic option for the management of brain-dead donors or as an additive to islets in culture after isolation setting.

Injectable Polyethylene Glycol Hydrogel for Islet Encapsulation: an in vitro and in vivo Characterization

An injection of hydrogel-encapsulated islets that controls blood glucose levels over long term would provide a much needed alternative treatment for type 1 diabetes mellitus (T1DM). To this end, we tested the feasibility of using an injectable polyethylene glycol (PEG) hydrogel as a scaffold for islet encapsulation. Encapsulated islets cultured in vitro for 6 days showed excellent cell viability and released insulin with higher basal and stimulated insulin secretion than control islets. Host responses to PEG hydrogels were studied by injecting PEG hydrogels (no treatment and vehicle controls used) into the peritoneal cavities of B6D2F1 mice and monitoring alterations in body weight, food and water intake, and blood glucose levels. After 2 weeks, peritoneal cavity cells were harvested, followed by hydrogel retrieval, and extraction of spleens. Body weights, food and water intake, and blood glucose levels were unaltered in mice injected with hydrogels compared to no treatment and vehicle-injected control mice. Frozen sections of a hydrogel showed the presence of tissues and small number of immune cells surrounding the hydrogel but no cell infiltration into the hydrogel bulk. Spleen sizes were not significantly different under the experimental conditions. Peritoneal cavity cells were slightly higher in mice injected with hydrogels compared to control mice but no statistical difference between vehicle- and hydrogel-injected mice was noted. As an in vivo feasibility study, streptozotocin-induced diabetic mice were injected with vehicle or hydrogels containing 50 islets each into two sites, the peritoneal cavity and a subcutaneous site on the back. Transient control of blood glucose levels were observed in mice injected with hydrogels containing islets. In summary, we developed an injectable PEG hydrogel that supported islet function and survival in vitro and in vivo and elicited only a mild host response. Our work illustrates the feasibility of using injectable PEG hydrogels for islet encapsulation.

Stepwise Approach to Problematic Hypoglycemia in Korea: Educational, Technological, and Transplant Interventions

Impaired awareness of hypoglycemia has been found to be prevalent in 20% to 40% of people with type 1 diabetes. If a similar prevalence exists in Koreans with type 1 diabetes, at a minimum, thousands of people with type 1 diabetes suffer at least one unpredicted episode of severe hypoglycemia per year in Korea. For patients with problematic hypoglycemia, an evidence-based stepwise approach was suggested in 2015. The first step is structured education regarding multiple daily injections of an insulin analog, and the second step is adding a technological intervention, such as continuous subcutaneous insulin infusion or real-time continuous glucose monitoring. The next step is a sensor-augmented pump, preferably with a low glucose suspension feature or very frequent contact, and the final step is islet or pancreas transplantation. In Korea, however, none of these treatments are reimbursed by the National Health Insurance, and thus have not been widely implemented. The low prevalence of type 1 diabetes means that Korean physicians are relatively unfamiliar with the new technologies in this field. Therefore, the roles of new technologies and pancreas or islet transplantation in the treatment of problematic hypoglycemia need to be defined in the current clinical setting of Korea.

Is islet transplantation a realistic approach to curing diabetes?

Since the report of type 1 diabetes reversal in seven consecutive patients by the Edmonton protocol in 2000, pancreatic islet transplantation has been reappraised based on accumulated clinical evidence. Although initially expected to therapeutically target long-term insulin independence, islet transplantation is now indicated for more specific clinical benefits. With the long-awaited report of the first phase 3 clinical trial in 2016, allogeneic islet transplantation is now transitioning from an experimental to a proven therapy for type 1 diabetes with problematic hypoglycemia. Islet autotransplantation has already been therapeutically proven in chronic pancreatitis with severe abdominal pain refractory to conventional treatments, and it holds promise for preventing diabetes after partial pancreatectomy due to benign pancreatic tumors. Based on current evidence, this review focuses on islet transplantation as a realistic approach to treating diabetes.

Induction, management, and complications of streptozotocin-induced diabetes mellitus in rhesus monkeys

BACKGROUND

Diabetes mellitus (DM) model using streptozotocin (STZ) which induces chemical ablation of β cell in the pancreas has been widely used for various research purposes in non-human primates. However, STZ has been known to have a variety of adverse effects such as nephrotoxicity, hepatotoxicity, and even mortality. The purpose of this study is to report DM induction by STZ, toxicity associated with STZ and procedure and complication of exogenous insulin treatment for DM management in rhesus monkeys (Macaca mulatta) that are expected to be transplanted with porcine islets within 2 months.

METHODS

Streptozotocin (immediately dissolved in normal saline, 110 mg/kg) was slowly infused via central catheter for 10 minutes in 22 rhesus monkeys. Clinical signs, complete blood count and blood chemistry were monitored to evaluate toxicity for 1 week after STZ injection. Monkey basal C-peptides were measured and intravenous glucose tolerance test was performed to confirm complete induction of DM. Exogenous insulin was subcutaneously injected to maintain blood glucose in diabetic rhesus monkeys and the complications were recorded while in insulin treatment.

RESULTS

Severe salivation and vomiting were observed within 1 hour after STZ injection in 22 rhesus monkeys. One monkey died at 6 hours after STZ injection and the reason for the death was unknown. Pancreatitis was noticed in one monkey after STZ injection, but the monkey recovered after 5 days by medical treatment. Serum total protein and albumin decreased whereas the parameters for the liver function such as aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase significantly increased (P<.05) after STZ injection, but they were resolved within 1 week. Azotemia was not observed. Monkey fasting C-peptide levels after STZ injection were <0.1 ng/mL in 18 rhesus monkeys, but 0.34, 0.22, 0.16 ng/mL in three monkeys, respectively. The value of daily insulin requirement was 0.92±0.26IU/kg/d (range=0.45-1.29) in the monkeys. Diabetic ketoacidosis was observed in one rhesus monkeys, but the monkey recovered after 24 hours by fluid and insulin treatment.

CONCLUSIONS

Streptozotocin was effective for inducing DM in rhesus monkeys, but various adverse effects such as pancreatitis, liver toxicity or death were observed. Therefore, careful and suitable medical managements should be implemented to eliminate the risks of mortality and severe adverse effects.