The N-Methyl-D-Aspartate Receptor Antagonist Dextromethorphan Improves Glucose Homeostasis and Preserves Pancreatic Islets in NOD Mice.

For treatment of type 1 diabetes mellitus, a combination of immune-based interventions and medication to promote beta-cell survival and proliferation has been proposed. Dextromethorphan (DXM) is an N-methyl-D-aspartate receptor antagonist with a good safety profile, and to date, preclinical and clinical evidence for blood glucose-lowering and islet-cell-protective effects of DXM have only been provided for animals and individuals with type 2 diabetes mellitus. Here, we assessed the potential anti-diabetic effects of DXM in the non-obese diabetic mouse model of type 1 diabetes. More specifically, we showed that DXM treatment led to five-fold higher numbers of pancreatic islets and more than two-fold larger alpha- and beta-cell areas compared to untreated mice. Further, DXM treatment improved glucose homeostasis and reduced diabetes incidence by 50%. Our data highlight DXM as a novel candidate for adjunct treatment of preclinical or recent-onset type 1 diabetes.

Congenital Hyperinsulinism in Humans and Insulin Secretory Dysfunction in Mice Caused by Biallelic DNAJC3 Variants.

The BiP co-chaperone DNAJC3 protects cells during ER stress. In mice, the deficiency of DNAJC3 leads to beta-cell apoptosis and the gradual onset of hyperglycemia. In humans, biallelic DNAJC3 variants cause a multisystem disease, including early-onset diabetes mellitus. Recently, hyperinsulinemic hypoglycemia (HH) has been recognized as part of this syndrome. This report presents a case study of an individual with HH caused by DNAJC3 variants and provides an overview of the metabolic phenotype of individuals with HH and DNAJC3 variants. The study demonstrates that HH may be a primary symptom of DNAJC3 deficiency and can persist until adolescence. Additionally, glycemia and insulin release were analyzed in young DNACJ3 knockout (K.O.) mice, which are equivalent to human infants. In the youngest experimentally accessible age group of 4-week-old mice, the in vivo glycemic phenotype was already dominated by a reduced total insulin secretion capacity. However, on a cellular level, the degree of insulin release of DNAJC3 K.O. islets was higher during periods of increased synthetic activity (high-glucose stimulation). We propose that calcium leakage from the ER into the cytosol, due to disrupted DNAJC3-controlled gating of the Sec61 channel, is the most likely mechanism for HH. This is the first genetic mechanism explaining HH solely by the disruption of intracellular calcium homeostasis. Clinicians should screen for HH in DNAJC3 deficiency and consider DNAJC3 variants in the differential diagnosis of congenital hyperinsulinism.

Selective Inhibition of N-Methyl-d-aspartate Receptors with GluN2B Subunit Protects ß Cells against Stress-Induced Apoptotic Cell Death.

Participation of N-methyl-d-aspartate (NMDA) receptors (NMDARs) in the failure of pancreatic ß cells during development of type 2 diabetes mellitus is discussed. Our study investigates whether ß cell mass and function can be preserved by selectively addressing the GluN2B subunit of the NMDAR. NMDAR activation by NMDA and its coagonist glycine moderately influenced electrical activity and Ca2+ handling in islet cells at a threshold glucose concentration (4-5 mM) without affecting glucose-mediated insulin secretion. Exposure of islet cells to NMDA/glycine or a glucolipotoxic milieu increased apoptosis by 5% and 8%, respectively. The GluN2B-specific NMDAR antagonist WMS-1410 (0.1 and 1 µM) partly protected against this. In addition, WMS-1410 completely prevented the decrease in insulin secretion of about 32% provoked by a 24-hour-treatment with NMDA/glycine. WMS-1410 eliminated NMDA-induced changes in the oxidation status of the islet cells and elevated the sensitivity of intracellular calcium to 15 mM glucose. By contrast, WMS-1410 did not prevent the decline in glucose-stimulated insulin secretion occurring after glucolipotoxic culture. This lack of effect was due to a decrease in insulin content to 18% that obviously could not be compensated by the preservation of cell mass or the higher percentage of insulin release in relation to insulin content. In conclusion, the negative effects of permanent NMDAR activation were effectively counteracted by WMS-1410 as well as the apoptotic cell death induced by high glucose and lipid concentrations. Modulation of NMDARs containing the GluN2B subunit is suggested to preserve ß cell mass during development of type 2 diabetes mellitus. SIGNIFICANCE STATEMENT: Addressing NMDA receptors containing the GluN2B subunit in pancreatic islet cells has the potential to protect the ß cell mass that progressively declines during the development of type 2 diabetes. Furthermore, this study shows that harmful effects of permanent NMDAR activation can be effectively counteracted by the compound WMS-1410, a selective modulator for NMDARs containing the GluN2B subunit.

Peripherally active dextromethorphan derivatives lower blood glucose levels by targeting pancreatic islets.

Dextromethorphan (DXM) acts as cough suppressant via its central action. Cell-protective effects of this drug have been reported in peripheral tissues, making DXM potentially useful for treatment of several common human diseases, such as type 2 diabetes mellitus (T2DM). Pancreatic islets are among the peripheral tissues that positively respond to DXM, and anti-diabetic effects of DXM were observed in two placebo-controlled, randomized clinical trials in humans with T2DM. Since these effects were associated with central side effects, we here developed chemical derivatives of DXM that pass the blood-brain barrier to a significantly lower extent than the original drug. We show that basic nitrogen-containing residues block central adverse events of DXM without reducing its anti-diabetic effects, including the protection of human pancreatic islets from cell death. These results show how to chemically modify DXM, and possibly other morphinans, as to exclude central side effects, while targeting peripheral tissues, such as pancreatic islets.

NMDAR antagonists for the treatment of diabetes mellitus-Current status and future directions.

Diabetes mellitus is characterized by chronically elevated blood glucose levels accelerated by a progressive decline of insulin-producing ß-cells in the pancreatic islets. Although medications are available to transiently adjust blood glucose to normal levels, the effects of current drugs are limited when it comes to preservation of a critical mass of functional ß-cells to sustainably maintain normoglycemia. In this review, we recapitulate recent evidence on the role of pancreatic N-methyl-D-aspartate receptors (NMDARs) in ß-cell physiology, and summarize effects of morphinan-based NMDAR antagonists that are beneficial for insulin secretion, glucose tolerance and islet cell survival. We further discuss NMDAR-mediated molecular pathways relevant for neuronal cell survival, which may also be important for the preservation of ß-cell function and mass. Finally, we summarize the literature for evidence on the role of NMDARs in the development of diabetic long-term complications, and highlight beneficial pharmacologic aspects of NMDAR antagonists in diabetic nephropathy, retinopathy as well as neuropathy.