Insulin-dependent diabetes mellitus induced by the antitussive agent dextromethorphan

Pancreatic islet protection at the expense of secretory function involves serine-linked mitochondrial one-carbon metabolism

Type 2 diabetes is characterized by insulin hypersecretion followed by reduced glucose-stimulated insulin secretion (GSIS). Here we show that acute stimulation of pancreatic islets with the insulin secretagogue dextrorphan (DXO) or glibenclamide enhances GSIS, whereas chronic treatment with high concentrations of these drugs reduce GSIS but protect islets from cell death. Bulk RNA sequencing of islets shows increased expression of genes for serine-linked mitochondrial one-carbon metabolism (OCM) after chronic, but not acute, stimulation. In chronically stimulated islets, more glucose is metabolized to serine than to citrate, and the mitochondrial ATP/ADP ratio decreases, whereas the NADPH/NADP+ ratio increases. Activating transcription factor-4 (Atf4) is required and sufficient to activate serine-linked mitochondrial OCM genes in islets, with gain- and loss-of-function experiments showing that Atf4 reduces GSIS and is required, but not sufficient, for full DXO-mediated islet protection. In sum, we identify a reversible metabolic pathway that provides islet protection at the expense of secretory function.

Acute D-Serine Co-Agonism of β-Cell NMDA Receptors Potentiates Glucose-Stimulated Insulin Secretion and Excitatory β-Cell Membrane Activity

Insulin-secreting pancreatic β-cells express proteins characteristic of D-serine regulated synapses, but the acute effect of D-serine co-agonism on its presumptive β-cell target, N-methyl D-aspartate receptors (NMDARs), is unclear. We used multiple models to evaluate glucose homeostasis and insulin secretion in mice with a systemic increase in D-serine (intraperitoneal injection or DAAO mutants without D-serine catabolism) or tissue-specific loss of Grin1-encoded GluN1, the D-serine binding NMDAR subunit. We also investigated the effects of D-serine ± NMDA on glucose-stimulated insulin secretion (GSIS) and β-cell depolarizing membrane oscillations, using perforated patch electrophysiology, in β-cell-containing primary isolated mouse islets. In vivo models of elevated D-serine correlated to improved blood glucose and insulin levels. In vitro, D-serine potentiated GSIS and β-cell membrane excitation, dependent on NMDAR activating conditions including GluN1 expression (co-agonist target), simultaneous NMDA (agonist), and elevated glucose (depolarization). Pancreatic GluN1-loss females were glucose intolerant and GSIS was depressed in islets from younger, but not older, βGrin1 KO mice. Thus, D-serine is capable of acute antidiabetic effects in mice and potentiates insulin secretion through excitatory β-cell NMDAR co-agonism but strain-dependent shifts in potency and age/sex-specific Grin1-loss phenotypes suggest that context is critical to the interpretation of data on the role of D-serine and NMDARs in β-cell function.

Dextromethorphan and Dextrorphan Influence Insulin Secretion by Interacting with KATP and L-type Ca2+ Channels in Pancreatic β-Cells

The NMDA receptor antagonist dextromethorphan (DXM) and its metabolite dextrorphan (DXO) have been recommended for treatment of type 2 diabetes mellitus because of their beneficial effects on insulin secretion. This study investigates how different key points of the stimulus-secretion coupling in mouse islets and β-cells are influenced by DXM or DXO. Both compounds elevated insulin secretion, electrical activity, and [Ca²⁺]_c in islets at a concentration of 100 µM along with a stimulating glucose concentration. DXO and DXM increased insulin secretion approximately 30-fold at a substimulatory glucose concentration (3 mM). Patch-clamp experiments revealed that 100 µM DXM directly inhibited K_ATP channels by about 70%. Of note, DXM decreased the current through L-type Ca²⁺ channels about 25%, leading to a transient reduction in Ca²⁺ action potentials. This interaction might explain why elevating DXM to 500 µM drastically decreased insulin release. DXO inhibited K_ATP channels almost equally. In islets of K_ATP channel-deficient sulfonylurea receptor 1 knockout mice, the elevating effects of 100 µM DXM on [Ca²⁺]_c and insulin release were completely lost. By contrast, 100 µM DXO still increased glucose-stimulated insulin release around 60%. In summary, DXM-induced alterations in stimulus-secretion coupling of wild-type islets result from a direct block of K_ATP channels and are partly counteracted by inhibition of L-type Ca²⁺ channels. The stimulatory effect of DXO seems to be based on a combined antagonism on K_ATP channels and NMDA receptors and already occurs under resting conditions. Consequently, both compounds seem not to be suitable candidates for treatment of type 2 diabetes mellitus. SIGNIFICANCE STATEMENT: This study shows that the use of dextromethorphan as an antidiabetic drug can cause unpredictable alterations in insulin secretion by direct interaction with K_ATP and L-type Ca²⁺ channels besides its actual target, the NMDA receptor.

Glutamate as intracellular and extracellular signals in pancreatic islet functions

l-Glutamate is one of the most abundant amino acids in the body and is a constituent of proteins and a substrate in metabolism. It is well known that glutamate serves as a primary excitatory neurotransmitter and a critical neuromodulator in the brain. Recent studies have shown that in addition to its pivotal role in neural functions, glutamate plays many important roles in a variety of cellular functions, including those as intracellular and extracellular signals. In pancreatic islets, glutamate is now known to be required for the normal regulation of insulin secretion, such as incretin-induced insulin secretion. In this review, we primarily discuss the physiological and pathophysiological roles of glutamate as intracellular and extracellular signals in the functions of pancreatic islets.

Evaluation of the role of N-methyl-D-aspartate (NMDA) receptors in insulin secreting beta-cells

The possibility that antagonism of N-methyl-D-aspartate (NMDA) receptors represent a novel drug target for diabetes prompted the current studies probing NMDA receptor function in the detrimental actions of homocysteine on pancreatic beta-cell function. Cellular insulin content and release, changes in membrane potential and intracellular Ca(2+) and gene expression were assessed following acute (20min) and long-term (18h) exposure of pancreatic clonal BRIN-BD11 beta-cells to known NMDA receptor modulators in the absence and presence of cytotoxic concentrations of homocysteine. As expected, acute or long-term exposure to homocysteine significantly suppressed basal and secretagogue-induced insulin release. In addition, NMDA reduced glucose-stimulated insulin secretion (GSIS). Interestingly, the selective NMDA receptor antagonist, MK-801, had no negative effects on GSIS. The effects of the NMDA receptor modulators were largely independent of effects on membrane depolarisation and increases of intracellular Ca(2+). However, combined culture of the NMDA antagonist, MK-801, with homocysteine did enhance intracellular Ca(2+) levels. Actions of NMDA agonists/antagonists and homocysteine on signal transduction pathways were independent of changes in cellular insulin content, cell viability, DNA damage or expression of key beta-cell genes. Taken together, the data support a role for NMDA receptors in controlling pancreatic beta-cell function. However, modulation of NMDA receptor function was unable to prevent the detrimental beta-cell effects of homocysteine.

Characterization of pancreatic NMDA receptors as possible drug targets for diabetes treatment

In the nervous system, NMDA receptors (NMDARs) participate in neurotransmission and modulate the viability of neurons. In contrast, little is known about the role of NMDARs in pancreatic islets and the insulin-secreting beta cells whose functional impairment contributes to diabetes mellitus. Here we found that inhibition of NMDARs in mouse and human islets enhanced their glucose-stimulated insulin secretion (GSIS) and survival of islet cells. Further, NMDAR inhibition prolonged the amount of time that glucose-stimulated beta cells spent in a depolarized state with high cytosolic Ca(2+) concentrations. We also noticed that, in vivo, the NMDAR antagonist dextromethorphan (DXM) enhanced glucose tolerance in mice, and that in vitro dextrorphan, the main metabolite of DXM, amplified the stimulatory effect of exendin-4 on GSIS. In a mouse model of type 2 diabetes mellitus (T2DM), long-term treatment with DXM improved islet insulin content, islet cell mass and blood glucose control. Further, in a small clinical trial we found that individuals with T2DM treated with DXM showed enhanced serum insulin concentrations and glucose tolerance. Our data highlight the possibility that antagonists of NMDARs may provide a useful adjunct treatment for diabetes.

Recommendations for the proper use of nonprescription cough suppressants and expectorants in solid-organ transplant recipients

OBJECTIVE

To describe the pharmacology and safety of oral over-the-counter cough suppressants and expectorants and to present recommendations for the use of these agents in solid-organ transplant recipients based on the potential for adverse drug reactions or drug-disease interactions.

DATA SOURCES AND EXTRACTION

Data from journal articles and other sources describing the pharmacology and safety of over-the-counter cough suppressants and expectorants, drug-drug interactions with immunosuppressive agents, and drug-disease state interactions are reviewed.

DATA SYNTHESIS

Potential and documented drug-drug interactions between immunosuppressive agents and over-the-counter cough medications guaifenesin, dextromethorphan, diphenhydramine, and codeine were evaluated on the basis of pharmacokinetic and pharmacodynamic principles. Interactions between these cough medications and the physiological changes in the body following transplantation also were examined.

CONCLUSION

Diphenhydramine requires additional monitoring when used to treat cough in transplant recipients owing to its anticholinergic properties and the potential for interactions with cyclosporine. Dextromethorphan can be used in most transplant recipients, although greater caution should be exercised if the patient has undergone liver transplant or has liver impairment. Guaifenesin can be used in transplant recipients but should be used with caution in patients receiving kidney or lung transplants and in patients with renal impairment. Codeine combined with guaifenesin is another option for cough and can be used in most transplant patients although those with reduced renal function should be monitored carefully for adverse events.

Recommendations for the Proper Use of Nonprescription Cough Suppressants and Expectorants in Solid-Organ Transplant Recipients

Objective

To describe the pharmacology and safety of oral over-the-counter cough suppressants and expectorants and to present recommendations for the use of these agents in solid-organ transplant recipients based on the potential for adverse drug reactions or drug-disease interactions.

Data Sources and Extraction

Data from journal articles and other sources describing the pharmacology and safety of over-the-counter cough suppressants and expectorants, drug-drug interactions with immunosuppressive agents, and drug-disease state interactions are reviewed.

Data Synthesis

Potential and documented drug-drug interactions between immunosuppressive agents and over-the-counter cough medications guaifenesin, dextromethorphan, diphenhydramine, and codeine were evaluated on the basis of pharmacokinetic and pharmacodynamic principles. Interactions between these cough medications and the physiological changes in the body following transplantation also were examined.

Conclusion

Diphenhydramine requires additional monitoring when used to treat cough in transplant recipients owing to its anticholinergic properties and the potential for interactions with cyclosporine. Dextromethorphan can be used in most transplant recipients, although greater caution should be exercised if the patient has undergone liver transplant or has liver impairment. Guaifenesin can be used in transplant recipients but should be used with caution in patients receiving kidney or lung transplants and in patients with renal impairment. Codeine combined with guaifenesin is another option for cough and can be used in most transplant patients although those with reduced renal function should be monitored carefully for adverse events.

A comparison of the effect of honey, dextromethorphan, and diphenhydramine on nightly cough and sleep quality in children and their parents

OBJECTIVES

Coughing is a prevalent symptom of upper respiratory infections (URIs) that cause disturbance in the sleep of children and their parents. There is as yet no reliable treatment to control URIs and their related cough; however, drugs such as dextromethorphan (DM) and diphenhydramine (DPH) are now mainly used in the world. The aim of this study is to compare the effect of honey, DM, and DPH on the nightly cough and sleep quality of children and their parents.

DESIGN

This was a clinical trial study in which 139 children aged 24-60 months suffering from coughing due to URIs were selected and assigned randomly to 4 groups. The first group received honey (HG), the second one DM (DMG), the third DPH (DPHG), but the fourth group or control group (CG) was assigned to a supportive treatment.

OUTCOME MEASURES

After approximately a 24-hour intervention, the 4 groups were reexamined and their cough frequency, cough severity, and sleep quality in children and their parents were recorded by using the questionnaire with Likert-type questions.

RESULTS

The mean of cough frequency score HG is 4.09 +/- 0.72 and 1.93 +/- 0.65 before and after the intervention, respectively, while these figures for the CG are 4.11 +/- 0.78 and 3.11 +/- 0.57, respectively. After the intervention, the difference of the mean score of the variables in all groups became statistically significant. The mean score of all variables in HG has stood significantly higher than those in other groups. There is also a significant relationship between the DMG and CG groups, even though there is no statistically difference between DMG and DPHG groups.

CONCLUSIONS

The result of the study demonstrated that receiving a 2.5-mL dose of honey before sleep has a more alleviating effect on URIs-induced cough compared with DM and DPH doses.

Dextromethorphan: a review of N-methyl-d-aspartate receptor antagonist in the management of pain

Dextromethorphan (DM) is a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist, which is widely used as an antitussive agent. DM also prevents neuronal damage and modulates pain sensation via noncompetitive antagonism of excitatory amino acids (EAAs). DM has been found to be useful in the treatment of pain in cancer patients and in the treatment of methotrexate-induced neurotoxicity. Clinical studies with DM in cancer patients are reviewed in this article.

Effect of dextromethorphan, diphenhydramine, and placebo on nocturnal cough and sleep quality for coughing children and their parents

OBJECTIVES

To determine whether the commonly used over-the-counter medications dextromethorphan and diphenhydramine are superior to placebo for the treatment of nocturnal cough and sleep difficulty associated with upper respiratory infections and to determine whether parents have improved sleep quality when their children receive the medications when compared with placebo.

METHODS

Parents of 100 children with upper respiratory infections were questioned to assess the frequency, severity, and bothersome nature of the nocturnal cough. Their answers were recorded on 2 consecutive days, initially on the day of presentation, when no medication had been given the previous evening, and then again on the subsequent day, when either medication or placebo was given before bedtime. Sleep quality for both the child and the parent were also assessed for both nights.

RESULTS

For the entire cohort, all outcomes were significantly improved on the second night of the study when either medication or placebo was given. However, neither diphenhydramine nor dextromethorphan produced a superior benefit when compared with placebo for any of the outcomes studied. Insomnia was reported more frequently in those who were given dextromethorphan, and drowsiness was reported more commonly in those who were given diphenhydramine.

CONCLUSIONS

Diphenhydramine and dextromethorphan are not superior to placebo in providing nocturnal symptom relief for children with cough and sleep difficulty as a result of an upper respiratory infection. Furthermore, the medications given to children do not result in improved quality of sleep for their parents when compared with placebo. Each clinician should consider these findings, the potential for adverse effects, and the individual and cumulative costs of the drugs before recommending them to families.