Prevention of Early Loss of Transplanted Islets in the Liver of Mice by Adenosine

Diabetes and the fabkin complex: A dual-edged sword

The Fabkin complex, composed of FABP4, ADK, and NDPKs, emerges as a novel regulator of insulin-producing beta cells, offering promising prospects for diabetes treatment. Our approach, which combines literature review and database analysis, sets the stage for future research. These findings hold significant implications for both diabetes treatment and research, as they present potential therapeutic targets for personalized treatment, leading to enhanced patient outcomes and a deeper comprehension of the disease. The multifaceted role of the Fabkin complex in glucose metabolism, insulin resistance, anti-inflammation, beta cell proliferation, and vascular function underscores its therapeutic potential, reshaping diabetes management and propelling advancements in the field.

Recrystallization of Adenosine for Localized Drug Delivery

Adenosine (ADO) is an endogenous metabolite with immense potential to be repurposed as an immunomodulatory therapeutic, as preclinical studies have demonstrated in models of epilepsy, acute respiratory distress syndrome, and traumatic brain injury, among others. The currently licensed products Adenocard and Adenoscan are formulated at 3 mg/mL of ADO for rapid bolus intravenous injection, but the systemic administration of the saline formulations for anti-inflammatory purposes is limited by the nucleoside's profound hemodynamic effects. Moreover, concentrations that can be attained in the airway or the brain through direct instillation or injection are limited by the volumes that can be accommodated in the anatomical space (<5 mL in humans) and the rapid elimination by enzymatic and transport mechanisms in the interstitium (half-life <5 s). As such, highly concentrated formulations of ADO are needed to attain pharmacologically relevant concentrations at sites of tissue injury. Herein, we report a previously uncharacterized crystalline form of ADO (rcADO) in which 6.7 mg/mL of the nucleoside is suspended in water. Importantly, the crystallinity is not diminished in a protein-rich environment, as evidenced by resuspending the crystals in albumin (15% w/v). To the best of our knowledge, this is the first report of crystalline ADO generated using a facile and organic solvent-free method aimed at localized drug delivery. The crystalline suspension may be suitable for developing ADO into injectable formulations for attaining high concentrations of the endogenous nucleoside in inflammatory locales.

A2a adenosine receptor agonist improves endoplasmic reticulum stress in MIN6 cell line through protein kinase A/ protein kinase B/ Cyclic adenosine monophosphate response element-binding protein/ and Growth Arrest And DNA-Damage-Inducible 34/ eukaryotic Initiation Factor 2α pathways

Endoplasmic reticulum (ER) stress is one of the main molecular events underlying pancreatic beta cell (PBC) failure, apoptosis, and a decrease in insulin secretion. Recent studies have highlighted the fundamental role of A2a adenosine receptor (A2aR) in potentiation of insulin secretion and proliferation of PBCs. However, possible protective effects of A2aR signaling against ER stress have not been elucidated yet. Thus, in the present study, we aimed to investigate the effects of A2aR activation in MIN6 beta cells undergoing tunicamycin (TM)-mediated ER stress. A2aR expression and activity were evaluated using real-time polymerase chain reaction and measurement of the cyclic adenosine monophosphate (cAMP), protein kinase A (PKA), phospho-protein kinase B or Akt (p-Akt)/Akt, and phospho-Cyclic adenosine monophosphate response element-binding protein/CREB levels in response to a specific agonist (CGS 21680). Survival and proliferation in TM and CGS 21680 cotreated cells were evaluated using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), annexin V-fluorescein isothiocyanate (FITC)/propidium iodide staining, colony formation, and 5-bromo-2'-deoxyuridine (Brdu) assays. In addition, the effects of A2aR stimulation on insulin secretion were evaluated using the enzyme-linked immunosorbent assay. B-cell lymphoma 2 (Bcl-2), phospho-eukaryotic Initiation Factor 2α (p-eIF2α)/eIF2α, growth arrest and DNA-damage-inducible 34 (GADD34), X-box binding protein 1 (XBP-1), spliced X-box binding protein 1 (XBP-1s), immunoglobulin heavy-chain-binding protein (BIP), and CCAAT-enhancer-binding protein homologous protein (CHOP) levels were evaluated using western blotting. Our results showed a decrease in A2aR expression and p-Akt/Akt and p-CREB/CREB levels in TM-pretreated cells. We also mentioned that CGS 21680 effectively increased cell survival, proliferation, and insulin secretion in TM-treated cells. The antiapoptotic effects were possibly mediated through Bcl-2 upregulation. Our western blotting results indicated that A2aR effectively downregulated p-eIF2α/eIF2α, XBP-1, XBP-1s, BIP, and CHOP levels, whereas GADD34 was upregulated. Altogether, the present study revealed that A2aR signaling through PKA/Akt/CREB mediators alleviated TM cytotoxicity effects in MIN6 beta cells. Thus, the stimulation of this receptor was seen as a new approach to control ER stress in the PBC cells.

Unlocking the Potential of Purinergic Signaling in Transplantation

Purinergic signaling has been recognized as playing an important role in inflammation, angiogenesis, malignancy, diabetes and neural transmission. Activation of signaling pathways downstream from purinergic receptors may also be implicated in transplantation and related vascular injury. Following transplantation, the proinflammatory "danger signal" adenosine triphosphate (ATP) is released from damaged cells and promotes proliferation and activation of a variety of immune cells. Targeting purinergic signaling pathways may promote immunosuppression and ameliorate inflammation. Under pathophysiological conditions, nucleotide-scavenging ectonucleotidases CD39 and CD73 hydrolyze ATP, ultimately, to the anti-inflammatory mediator adenosine. Adenosine suppresses proinflammatory cytokine production and is associated with improved graft survival and decreased severity of graft-versus-host disease. Furthermore, purinergic signaling is involved both directly and indirectly in the mechanism of action of several existing immunosuppressive drugs, such as calcineurin inhibitors and mammalian target of rapamycin inhibitors. Targeting of purinergic receptor pathways, particularly in the setting of combination therapies, could become a valuable immunosuppressive strategy in transplantation. This review focuses on the role of the purinergic signaling pathway in transplantation and immunosuppression and explores possible future applications in clinical practice.

Advances in Local Drug Release and Scaffolding Design to Enhance Cell Therapy for Diabetes

Islet transplant is a curative treatment for insulin-dependent diabetes. However, challenges, including poor tissue survival and a lack of efficient engraftment, must be overcome. An encapsulating or scaffolding material can act as a vehicle for agents carefully chosen for the islet transplant application. From open porous scaffolds to spherical capsules and conformal coatings, greater immune protection is often accompanied by greater distances to microvasculature. Generating a local oxygen supply from the implant material or encouraging vessel growth through the release of local factors can create an oxygenated engraftment site. Intricately related to the vascularization response, inflammatory interaction with the cell supporting implant is a long-standing hurdle to material-based islet transplant. Modulation of the immune responses to the islets as well as the material itself must be considered. To match the post-transplant complexity, the release rate can be tuned to orchestrate temporal responses. Material degradation properties can be utilized in passive approaches or external stimuli and biological cues in active approaches. A combination of multiple carefully chosen factors delivered in an agent-specialized manner is considered by this review to improve the long-term function of islets transplanted in scaffolding and encapsulating materials.

HMGB1-Mediated Early Loss of Transplanted Islets Is Prevented by Anti-IL-6R Antibody in Mice

OBJECTIVES

The limited success in achieving insulin independence of patients with type 1 diabetes mellitus after islet transplantation from a single donor, mainly due to early loss of transplanted islets, hampers clinical application of islet transplantation. Previously, we have shown in mice that the early loss of transplanted islets in the liver, the site of islet transplantation, is caused by innate immune rejection triggered by high-mobility group box 1 (HMGB1) protein released from transplanted islets. We herein determined whether the HMGB1-mediated early loss of transplanted mouse islets is prevented by anti-interleukin-6 receptor (IL-6R) antibody.

METHODS

The effect of anti-IL-6R antibody on amelioration of hyperglycemia in streptozocin-induced diabetic mice receiving 200 islets into the liver from a single donor was evaluated in association with HMGB1-stimulated interferon-γ production of hepatic mononuclear cells.

RESULTS

Hyperglycemia of diabetic mice receiving 200 syngeneic islets was ameliorated with down-regulation of interferon-γ production of hepatic natural killer T cells and neutrophils when anti-IL-6R was administered at the time of transplantation. This beneficial effect was also seen in allografts when alloimmune rejection was prevented by anti-CD4 antibody.

CONCLUSIONS

These findings demonstrate that anti-IL-6R antibody prevented the early loss of intrahepatic islet grafts with inhibiting HMGB1-induced immune activation after islet transplantation.

Role of adenosine signalling and metabolism in β-cell regeneration

Glucose homeostasis, which is controlled by the endocrine cells of the pancreas, is disrupted in both type I and type II diabetes. Deficiency in the number of insulin-producing β cells - a primary cause of type I diabetes and a secondary contributor of type II diabetes - leads to hyperglycemia and hence an increase in the need for insulin. Although diabetes can be controlled with insulin injections, a curative approach is needed. A potential approach to curing diabetes involves regenerating the β-cell mass, e.g. by increasing β-cell proliferation, survival, neogenesis or transdifferentiation. The nucleoside adenosine and its cognate nucleotide ATP have long been known to affect insulin secretion, but have more recently been shown to increase β-cell proliferation during homeostatic control and regeneration of the β-cell mass. Adenosine is also known to have anti-inflammatory properties, and agonism of adenosine receptors can promote the survival of β-cells in an inflammatory microenvironment. In this review, both intracellular and extracellular mechanisms of adenosine and ATP are discussed in terms of their established and putative effects on β-cell regeneration.

The protective effects of CD39 overexpression in multiple low-dose streptozotocin-induced diabetes in mice

Islet allograft survival limits the long-term success of islet transplantation as a potential curative therapy for type 1 diabetes. A number of factors compromise islet survival, including recurrent diabetes. We investigated whether CD39, an ectonucleotidase that promotes the generation of extracellular adenosine, would mitigate diabetes in the T cell-mediated multiple low-dose streptozotocin (MLDS) model. Mice null for CD39 (CD39KO), wild-type mice (WT), and mice overexpressing CD39 (CD39TG) were subjected to MLDS. Adoptive transfer experiments were performed to delineate the efficacy of tissue-restricted overexpression of CD39. The role of adenosine signaling was examined using mutant mice and pharmacological inhibition. The susceptibility to MLDS-induced diabetes was influenced by the level of expression of CD39. CD39KO mice developed diabetes more rapidly and with higher frequency than WT mice. In contrast, CD39TG mice were protected. CD39 overexpression conferred protection through the activation of adenosine 2A receptor and adenosine 2B receptor. Adoptive transfer experiments indicated that tissue-restricted overexpression of CD39 conferred robust protection, suggesting that this may be a useful strategy to protect islet grafts from T cell-mediated injury.

Long-term remission of diabetes in NOD mice is induced by nondepleting anti-CD4 and anti-CD8 antibodies

Residual β-cells found at the time of clinical onset of type 1 diabetes are sufficient to control hyperglycemia if rescued from ongoing autoimmune destruction. The challenge, however, is to develop an immunotherapy that not only selectively suppresses the diabetogenic response and efficiently reverses diabetes, but also establishes long-term β-cell-specific tolerance to maintain remission. In the current study, we show that a short course of nondepleting antibodies (Abs) specific for the CD4 and CD8 coreceptors rapidly reversed clinical disease in recent-onset diabetic NOD mice. Once established, remission was maintained indefinitely and immunity to foreign antigens unimpaired. Induction of remission involved selective T-cell purging of the pancreas and draining pancreatic lymph nodes and upregulation of transforming growth factor (TGF)-β1 by pancreas-resident antigen-presenting cells. Neutralization of TGF-β blocked the induction of remission. In contrast, maintenance of remission was associated with tissue-specific immunoregulatory T cells. These findings demonstrate that the use of nondepleting Ab specific for CD4 and CD8 is a robust approach to establish long-term β-cell-specific T-cell tolerance at the onset of clinical diabetes.

IFN-γ receptor deficiency prevents diabetes induction by diabetogenic CD4+, but not CD8+, T cells

IFN-γ is generally believed to be important in the autoimmune pathogenesis of type 1 diabetes (T1D). However, the development of spontaneous β-cell autoimmunity is unaffected in NOD mice lacking expression of IFN-γ or the IFN-γ receptor (IFNγR), bringing into question the role IFN-γ has in T1D. In the current study, an adoptive transfer model was employed to define the contribution of IFN-γ in CD4(+) versus CD8(+) T cell-mediated β-cell autoimmunity. NOD.scid mice lacking expression of the IFNγR β chain (NOD.scid.IFNγRB(null)) developed diabetes following transfer of β cell-specific CD8(+) T cells alone. In contrast, β cell-specific CD4(+) T cells alone failed to induce diabetes despite significant infiltration of the islets in NOD.scid.IFNγRB(null) recipients. The lack of pathogenicity of CD4(+) T-cell effectors was due to the resistance of IFNγR-deficient β cells to inflammatory cytokine-induced cell death. On the other hand, CD4(+) T cells indirectly promoted β-cell destruction by providing help to CD8(+) T cells in NOD.scid.IFNγRB(null) recipients. These results demonstrate that IFN-γR may play a key role in CD4(+) T cell-mediated β-cell destruction.

IFN-γ receptor deficiency prevents diabetes induction by diabetogenic CD4+, but not CD8+, T cells

IFN-γ is generally believed to be important in the autoimmune pathogenesis of type 1 diabetes (T1D). However, the development of spontaneous β-cell autoimmunity is unaffected in NOD mice lacking expression of IFN-γ or the IFN-γ receptor (IFNγR), bringing into question the role IFN-γ has in T1D. In the current study, an adoptive transfer model was employed to define the contribution of IFN-γ in CD4(+) versus CD8(+) T cell-mediated β-cell autoimmunity. NOD.scid mice lacking expression of the IFNγR β chain (NOD.scid.IFNγRB(null)) developed diabetes following transfer of β cell-specific CD8(+) T cells alone. In contrast, β cell-specific CD4(+) T cells alone failed to induce diabetes despite significant infiltration of the islets in NOD.scid.IFNγRB(null) recipients. The lack of pathogenicity of CD4(+) T-cell effectors was due to the resistance of IFNγR-deficient β cells to inflammatory cytokine-induced cell death. On the other hand, CD4(+) T cells indirectly promoted β-cell destruction by providing help to CD8(+) T cells in NOD.scid.IFNγRB(null) recipients. These results demonstrate that IFN-γR may play a key role in CD4(+) T cell-mediated β-cell destruction.

Adenosine signaling promotes regeneration of pancreatic β cells in vivo

Diabetes can be controlled with insulin injections, but a curative approach that restores the number of insulin-producing β cells is still needed. Using a zebrafish model of diabetes, we screened ~7,000 small molecules to identify enhancers of β cell regeneration. The compounds we identified converge on the adenosine signaling pathway and include exogenous agonists and compounds that inhibit degradation of endogenously produced adenosine. The most potent enhancer of β cell regeneration was the adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA), which, acting through the adenosine receptor A2aa, increased β cell proliferation and accelerated restoration of normoglycemia in zebrafish. Despite markedly stimulating β cell proliferation during regeneration, NECA had only a modest effect during development. The proliferative and glucose-lowering effect of NECA was confirmed in diabetic mice, suggesting an evolutionarily conserved role for adenosine in β cell regeneration. With this whole-organism screen, we identified components of the adenosine pathway that could be therapeutically targeted for the treatment of diabetes.

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.

Evolution of β-Cell Replacement Therapy in Diabetes Mellitus: Islet Cell Transplantation

Diabetes mellitus remains one of the leading causes of morbidity and mortality worldwide. According to the Centers for Disease Control and Prevention, approximately 23.6 million people in the United States are affected. Of these individuals, 5 to 10% have been diagnosed with Type 1 diabetes mellitus (T1DM), an autoimmune disease. Although it often appears in childhood, T1DM may manifest at any age, leading to significant morbidity and decreased quality of life. Since the 1960s, the surgical treatment for diabetes mellitus has evolved to become a viable alternative to insulin administration, beginning with pancreatic transplantation. While islet cell transplantation has emerged as another potential alternative, its role in the treatment of T1DM remains to be solidified as research continues to establish it as a truly viable alternative for achieving insulin independence. In this paper, the historical evolution, procurement, current status, benefits, risks, and ongoing research of islet cell transplantation are explored.

Effect of globus pallidus internus stimulation on neuronal activity in the pedunculopontine tegmental nucleus in the primate model of Parkinson's disease

The pedunculopontine tegmental nucleus (PPN) is being explored as a site for deep brain stimulation (DBS) for the treatment of patients with medically refractory gait and postural abnormalities (MRGPA) associated with Parkinson's disease (PD). The PPN is involved in initiation and modulation of gait and other stereotyped motor behaviors and is inter-connected with the pallido-thalamo-cortical circuit. Internal segment of the globus pallidus (GPi) DBS is effective at treating the motor signs associated with PD, however its impact on MRGPA is limited and its effect on PPN neuronal activity is unknown. The current work characterizes the effect of therapeutically-effective GPi DBS on PPN neuronal activity in a single rhesus monkey made parkinsonian using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). A scaled-down, quadripolar DBS lead was implanted into sensorimotor GPi under electrophysiological and stereotactic guidance. Single-neuron activity was recorded from PPN before, during and after DBS. GPi DBS reduced the mean discharge rate of PPN neurons from 16.8 Hz to 12.8 Hz, with 30 (66.7%) neurons showing a decreased mean rate, 3 (6.7%) increased and 12 (26.7%) unchanged. Consistent with known GABAergic projections from GPi to PPN, and with previous observations that stimulation increases output from the stimulated structure, GPi DBS suppressed activity in the PPN. The present observations, together with previous reports of improvement in MRGPA during low frequency stimulation in PPN, suggest that activation of PPN output may be required to improve MRGPA and may account for the lack of improvement in MRGPA typically observed with GPi or subthalamic nucleus (STN) DBS.

Adenosine A(2A) agonist administration improves islet transplant outcome: Evidence for the role of innate immunity in islet graft rejection

Activation of adenosine A(2A) receptors inhibits inflammation in ischemia/reperfusion injury, and protects against cell damage at the injury site. Following transplantation 50% of islets die due to inflammation and apoptosis. This study investigated the effects of adenosine A(2A) receptor agonists (ATL146e and ATL313) on glucose-stimulated insulin secretion (GSIS) in vitro and transplanted murine syngeneic islet function in vivo. Compared to vehicle controls, ATL146e (100 nM) decreased insulin stimulation index [SI, (insulin)(high glucose)/(insulin)(low glucose)] (2.36 +/- 0.22 vs. 3.75 +/- 0.45; n = 9; p < 0.05). Coculture of islets with syngeneic leukocytes reduced SI (1.41 +/- 0.17; p < 0.05), and this was restored by ATL treatment (2.57 +/- 0.18; NS). Addition of a selective A(2A)AR antagonist abrogated ATL's protective effect, reducing SI (1.11 +/- 0.42). ATL treatment of A(2A)AR(+/+) islet/A(2A)AR(-/-) leukocyte cocultures failed to protect islet function (SI), implicating leukocytes as likely targets of A(2A)AR agonists. Diabetic recipient C57BL/6 mice (streptozotocin; 250 mg/kg, IP) received islet transplants to either the renal subcapsular or hepatic-intraportal site. Recipient mice receiving ATL therapy (ATL 146e or ATL313, 60 ng/kg/min, IP) achieved normoglycemia more rapidly than untreated recipients. Histological examination of grafts suggested reduced cellular necrosis, fibrosis, and lymphocyte infiltration in agonist-treated animals. Administration of adenosine A(2A) receptor agonists (ATL146e or ATL313) improves in vitro GSIS by an effect on leukocytes, and improves survival and functional engraftment of transplanted islets by inhibiting inflammatory islet damage in the peritransplant period, suggesting a potentially significant new strategy for reducing inflammatory islet loss in clinical transplantation.