Currently, no oral medications are available for type 1 diabetes (T1D). While our recent randomized placebo-controlled T1D trial revealed that oral verapamil had short-term beneficial effects, their duration and underlying mechanisms remained elusive. Now, our global T1D serum proteomics analysis identified chromogranin A (CHGA), a T1D-autoantigen, as the top protein altered by verapamil and as a potential therapeutic marker and revealed that verapamil normalizes serum CHGA levels and reverses T1D-induced elevations in circulating proinflammatory T-follicular-helper cell markers. RNA-sequencing further confirmed that verapamil regulates the thioredoxin system and promotes an anti-oxidative, anti-apoptotic and immunomodulatory gene expression profile in human islets. Moreover, continuous use of oral verapamil delayed T1D progression, promoted endogenous beta-cell function and lowered insulin requirements and serum CHGA levels for at least 2 years and these benefits were lost upon discontinuation. Thus, the current studies provide crucial mechanistic and clinical insight into the beneficial effects of verapamil in T1D.

Diabetes is characterized by hyperglycemia, loss of functional islet beta cell mass, deficiency of glucose-lowering insulin, and persistent alpha cell secretion of gluconeogenic glucagon. Still, no therapies that target these underlying processes are available. We therefore performed high-throughput screening of 300,000 compounds and extensive medicinal chemistry optimization and here report the discovery of SRI-37330, an orally bioavailable, non-toxic small molecule, which effectively rescued mice from streptozotocin- and obesity-induced (db/db) diabetes. Interestingly, in rat cells and in mouse and human islets, SRI-37330 inhibited expression and signaling of thioredoxin-interacting protein, which we have previously found to be elevated in diabetes and to have detrimental effects on islet function. In addition, SRI-37330 treatment inhibited glucagon secretion and function, reduced hepatic glucose production, and reversed hepatic steatosis. Thus, these studies describe a newly designed chemical compound that, compared to currently available therapies, may provide a distinct and effective approach to treating diabetes.

Pancreatic beta-cell death is a major factor in the pathogenesis of type 1 diabetes (T1D), but straightforward methods to measure beta-cell loss in humans are lacking, underlining the need for novel biomarkers. Using studies in INS-1 cells, human islets, diabetic mice, and serum samples of subjects with T1D at different stages, we have identified serum miR-204 as an early biomarker of T1D-associated beta-cell loss in humans. MiR-204 is a highly enriched microRNA in human beta-cells, and we found that it is released from dying beta-cells and detectable in human serum. We further discovered that serum miR-204 was elevated in children and adults with T1D and in autoantibody-positive at-risk subjects but not in type 2 diabetes or other autoimmune diseases and was inversely correlated with remaining beta-cell function in recent-onset T1D. Thus, serum miR-204 may provide a much needed novel approach to assess early T1D-associated human beta-cell loss even before onset of overt disease.

Loss of functional beta cell mass represents a major factor in the pathogenesis of diabetes. Currently, there are no therapies that halt this process; however, thioredoxin-interacting protein (TXNIP) has recently emerged as a promising therapeutic target. TXNIP was found to be the top glucose-induced gene in a human pancreatic islet microarray, is increased in diabetes, and TXNIP overexpression results in beta cell apoptosis. TXNIP reduction has shown favorable effects in vivo, where whole body TXNIP-deficient and beta cell-specific TXNIP knockout mice have decreased beta cell apoptosis, increased beta cell mass, elevated insulin levels, and are protected from diabetes. We have also shown that pharmacologic TXNIP inhibition, via the anti-hypertensive medication verapamil, was able to mimic the protective effects of genetic TXNIP deletion and reversed overt diabetes in mice. In addition, it has been established that TXNIP downregulation is beneficial in multiple tissues, making it unnecessary and even undesirable to have a beta cell-specific TXNIP inhibitor and suggesting that detrimental off target effects are unlikely. We have since undertaken a high-throughput screen of 300,000 small molecules that has yielded a novel compound, TI-37330, which is more effective than verapamil in inhibiting TXNIP expression. Moreover, TI-37330 protected primary human islets and INS-1 beta cells against glucose- and cytokine-induced TXNIP and beta cell apoptosis. TI-37330 has also shown in vivo potential as it was found to have good pharmacokinetic properties and was well tolerated in healthy mice. In the context of streptozotocin-induced diabetes, oral administration of TI-37330 promoted beta cell survival, prevented diabetes, and even significantly improved overt diabetes. Collectively, these data establish small molecule TXNIP inhibitors, especially TI-37330, as robust candidates for further development. Disclosure L. Thielen: None. J. Chen: None. G. Xu: None. G. Jing: None. T. Grayson: None. S. Jo: None. A. Shalev: None.

Pancreatic beta cell loss is a key factor in the pathogenesis of type 1 diabetes (T1D), but therapies to halt this process are lacking. We previously reported that the approved antihypertensive calcium-channel blocker verapamil, by decreasing the expression of thioredoxin-interacting protein, promotes the survival of insulin-producing beta cells and reverses diabetes in mouse models1. To translate these findings into humans, we conducted a randomized double-blind placebo-controlled phase 2 clinical trial ( NCT02372253 ) to assess the efficacy and safety of oral verapamil added for 12 months to a standard insulin regimen in adult subjects with recent-onset T1D. Verapamil treatment, compared with placebo was well tolerated and associated with an improved mixed-meal-stimulated C-peptide area under the curve, a measure of endogenous beta cell function, at 3 and 12 months (prespecified primary endpoint), as well as with a lower increase in insulin requirements, fewer hypoglycemic events and on-target glycemic control (secondary endpoints). Thus, addition of once-daily oral verapamil may be a safe and effective novel approach to promote endogenous beta cell function and reduce insulin requirements and hypoglycemic episodes in adult individuals with recent-onset T1D.

Glucagon-like peptide 1 receptor (GLP1R) agonists are widely used to treat diabetes. However, their function is dependent on adequate GLP1R expression, which is downregulated in diabetes. GLP1R is highly expressed on pancreatic β-cells, and activation by endogenous incretin or GLP1R agonists increases cAMP generation, which stimulates glucose-induced β-cell insulin secretion and helps maintain glucose homeostasis. We now have discovered that the highly β-cell–enriched microRNA, miR-204, directly targets the 3′ UTR of GLP1R and thereby downregulates its expression in the β-cell–derived rat INS-1 cell line and primary mouse and human islets. Furthermore, in vivo deletion of miR-204 promoted islet GLP1R expression and enhanced responsiveness to GLP1R agonists, resulting in improved glucose tolerance, cAMP production, and insulin secretion as well as protection against diabetes. Since we recently identified thioredoxin-interacting protein (TXNIP) as an upstream regulator of miR-204, we also assessed whether in vivo deletion of TXNIP could mimic that of miR-204. Indeed, it also enhanced islet GLP1R expression and GLP1R agonist–induced insulin secretion and glucose tolerance. Thus, the present studies show for the first time that GLP1R is under the control of a microRNA, miR-204, and uncover a previously unappreciated link between TXNIP and incretin action.

Type 1 diabetes (T1D) is characterized by T-cell and cytokine-mediated pancreatic beta cell loss, but some of the mechanisms involved are still unknown. Growth differentiation factor 15 (GDF15), which is a distant member of the transforming growth factor β (TGFβ) family, has been shown to be increased in various diseases including cancer, heart failure and type 2 diabetes and to promote cancer cell apoptosis. Although we found that GDF15 is highly expressed in adult human beta cells, its role in beta cells and T1D has not been studied. In the present study, we found that GDF15 is significantly elevated in the islets of diabetic female NOD mice compared to nondiabetic female NOR and male NOD mice. In addition, by using human islets, Akita beta cells and INS-1 beta cells, we found that the expression and content of GDF15 are significantly increased by T1D-associated cytokines and thapsigargin/ER stress. Furthermore, we demonstrated that GDF15 knockdown significantly blunts cytokines-induced beta cell apoptosis, while GDF15 overexpression exacerbates T1D-associated cytokines-induced beta cell apoptosis. Taken together, these findings suggest that GDF15 is induced by cytokine-induced ER-stress in beta cells and might contribute to the beta cell loss in T1D. Targeting beta cell GDF15 may therefore represent a novel strategy to inhibit beta cell loss in T1D. Disclosure G. Xu: None. L. Thielen: None. J. Chen: None. S. Jo: None. A. Shalev: None.

Purpose of review Thioredoxin-interacting protein has emerged as a major factor regulating pancreatic β-cell dysfunction and death, key processes in the pathogenesis of type 1 and type 2 diabetes. Accumulating evidence based on basic, preclinical, and retrospective epidemiological research suggests that TXNIP represents a promising therapeutic target for diabetes. The present review is aimed at providing an update regarding these developments. Recent findings TXNIP has been shown to be induced by glucose and increased in diabetes and to promote β-cell apoptosis, whereas TXNIP deletion protected against diabetes. More recently, TXNIP inhibition has also been found to promote insulin production and glucagon-like peptide 1 signaling via regulation of a microRNA. β-Cell TXNIP expression itself was found to be regulated by hypoglycemic agents, carbohydrate-response-element-binding protein, and cytosolic calcium or the calcium channel blocker, verapamil. Retrospective studies now further suggest that verapamil use might be associated with a lower incidence of type 2 diabetes in humans. Summary TXNIP has emerged as a key factor in the regulation of functional β-cell mass and TXNIP inhibition has shown beneficial effects in a variety of studies. Thus, the inhibition of TXNIP may provide a novel approach to the treatment of diabetes.

Glucagon-like peptide 1 receptor (GLP-1R) is a G protein-coupled receptor that is highly expressed on pancreatic beta-cells and activated by endogenous incretins or antidiabetic GLP-1R agonist drugs. GLP-1R function is important in maintaining glucose homeostasis and involves stimulation of glucose-induced beta-cell insulin secretion via cAMP generation. While GLP-1R expression has been shown to be downregulated in diabetes, the molecular mechanisms have not been fully elucidated. In this study, we have discovered that miR-204, a highly beta-cell-enriched microRNA that is upregulated in diabetes, directly targets the 3’ UTR of GLP-1R and decreases its expression in INS-1 cells as well as primary mouse and human islets. Moreover, genetic knockout of miR-204 in vivo increased islet GLP-1R expression and enhanced GLP-1R agonist-induced cAMP production and insulin secretion, resulting in improved glucose tolerance as well as protection against diabetes. In addition, miR-204 antagomir administration was able to mimic the effects of genetic miR-204 deletion and resulted again in GLP-1R agonist-induced insulin secretion as well as improved glucose tolerance. Thus, these results indicate for the first time that GLP-1R is under the control of a micro RNA and suggest that antagomir-mediated inhibition of miR-204 represents a potential novel therapeutic approach to promote the actions of GLP-1R agonist drugs in a beta-cell-specific manner and thereby help treat diabetes. Disclosure S. Jo: None. J. Chen: None. G. Xu: None. T. Grayson: None. L. Thielen: None. A. Shalev: None.