Dextromethorphan and neuromodulation: old drug coughs up new activities

Sigma-1 receptor and seizures

Over the last decade, sigma-1 receptor (Sig1R) has been recognized as a valid target for the treatment of seizure disorders and seizure-related comorbidities. Clinical trials with Sig1R ligands are underway testing therapies for the treatment of drug-resistant seizures, developmental and epileptic encephalopathies, and photosensitive epilepsy. However, the direct molecular mechanism by which Sig1R modulates seizures and the balance between excitatory and inhibitory pathways has not been fully elucidated. This review article aims to summarize existing knowledge of Sig1R and its involvement in seizures by focusing on the evidence obtained from Sig1R knockout animals and the anti-seizure effects of Sig1R ligands. In addition, this review article includes a discussion of the advantages and disadvantages of the use of existing compounds and describes the challenges and future perspectives on the use of Sig1R as a target for the treatment of seizure disorders.

Dextromethorphan Exhibits Anti-Inflammatory and Immunomodulatory Effects in a Murine Model: Therapeutic Implication in Psoriasis

Psoriasis is an immune-mediated skin disease with a worldwide prevalence of 2–4% that causes scaling erythematous skin lesions. It is a chronic relapsing and complex multifactorial disease that often necessitates long-term therapy. Despite various novel therapies, psoriasis remains a treatable but non-curable disease. Because the antitussive medication dextromethorphan (DXM) can inhibit murine bone marrow and human monocytes and slow the progression of arthritis in mice with type II collagen-induced arthritis, we explored whether the oral administration of DXM to mice with imiquimod (IMQ)-induced psoriasis can effectively alleviate psoriasis symptoms and improve immune regulation. Herein, we examined the therapeutic effects of DXM on psoriasis and its potential mechanisms of action in an IMQ-induced psoriasis mice model. We found that an oral dose of DXM (10 mg/kg) could more significantly reduce psoriasis symptoms compared with intraperitoneal injection. Seven days after the oral administration of DXM, the Psoriasis Area and Severity Index (PASI) score was significantly decreased compared with that in the vehicle group. Furthermore, DXM treatment also significantly ameliorated the psoriasis symptoms and the histopathological features of psoriasis, including stratum corneum thickening, desquamation, and immune cell infiltration. Additionally, DXM reduced the mRNA levels of the cytokines TNF-α, IL-6, IL-17A, and IL-22 in skin and the percentage of IL-17A and IL-22 producing T cell receptor γδ T cells (TCRγδT). Taken together, our research demonstrated that DXM could inhibit keratinocyte proliferation and alleviate psoriasis symptoms, which suggests the potential application of DXM in the treatment of chronic inflammation and autoimmune diseases.

The Association Between Dextromethorphan Use and the Risk of Dementia

Dementia is one of neurodegenerative disease without preventive medicine currently. Dextromethorphan (DXM) has been reported to reduce neuronal damage and neurodegeneration in animal and human models. The effect of DXM on the dementia has not been fully examined. We examined the medical records over 40 years old in Taiwan's National Health Insurance Research Database between 2000 and 2015 to establish matched cohorts. We used a Cox regression hazard model to identify risk factors of dementia during 16 years of follow-up, and the results indicate that a significantly lower percentage of subjects with DXM use (P < .001) developed dementia compared with those without DXM use (11.38%, 4541/39 895 vs 18.66%, 29 785/159 580). After adjustment for age and other variables [adjusted hazard ratio: .567 (95% confidence interval: .413-.678, P < .001)], this study also demonstrated that DXM use appeared to reduce the risk of developing dementia. DXM use may potentially provide a protective effect against dementia.

Using sigma-ligands as part of a multi-receptor approach to target diseases of the brain

INTRODUCTION

The sigma receptors are found abundantly in the central nervous system and are targets for the treatment of various diseases, including Alzheimer's (AD), Parkinson's (PD), Huntington's disease (HD), depression, amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). However, for many of these diseases, other receptors and targets have been the focus of the most, such as acetylcholine esterase inhibitors in Alzheimer's and dopamine replacement in Parkinson's. The currently available drugs for these diseases have limited success resulting in the requirement of an alternative approach to their treatment.

AREAS COVERED

In this review, we discuss the potential role of the sigma receptors and their ligands as part of a multi receptor approach in the treatment of the diseases mentioned above. The literature reviewed was obtained through searches in databases, including PubMed, Web of Science, Google Scholar, and Scopus.

EXPERT OPINION

Given sigma receptor agonists provide neuroprotection along with other benefits such as potentiating the effects of other receptors, further development of multi-receptor targeting ligands, and or the development of multi-drug combinations to target multiple receptors may prove beneficial in the future treatment of degenerative diseases of the CNS, especially when coupled with better diagnostic techniques.

Endocannabinoid control of glutamate NMDA receptors: the therapeutic potential and consequences of dysfunction

Glutamate is probably the most important excitatory neurotransmitter in the brain. The glutamate N-methyl-D-aspartate receptor (NMDAR) is a calcium-gated channel that coordinates with G protein-coupled receptors (GPCRs) to establish the efficiency of the synaptic transmission. Cross-regulation between these receptors requires the concerted activity of the histidine triad nucleotide-binding protein 1 (HINT1) and of the sigma receptor type 1 (σ1R). Essential brain functions like learning, memory formation and consolidation, mood and behavioral responses to exogenous stimuli depend on the activity of NMDARs. In this biological context, endocannabinoids are released to retain NMDAR activity within physiological limits. The efficacy of such control depends on HINT1/σ1R assisting in the physical coupling between cannabinoid type 1 receptors (CB1Rs) and NMDARs to dampen their activity. Subsequently, the calcium-regulated HINT1/σ1R protein tandem uncouples CB1Rs to prevent NMDAR hypofunction. Thus, early recruitment or a disproportionate cannabinoid induced response can bring about excess dampening of NMDAR activity, impeding its adequate integration with GPCR signaling. Alternatively, this control circuit can apparently be overridden in situations where bursts of NMDAR overactivity provoke convulsive syndromes. In this review we will discuss the possible relevance of the HINT1/σ1R tandem and its use by endocannabinoids to diminish NMDAR activity and their implications in psychosis/schizophrenia, as well as in NMDAR-mediated convulsive episodes.

Mechanisms of Nicotinic Modulation of Glutamatergic Neuroplasticity in Humans

The impact of nicotine (NIC) on plasticity is thought to be primarily determined via calcium channel properties of nicotinic receptor subtypes, and glutamatergic plasticity is likewise calcium-dependent. Therefore glutamatergic plasticity is likely modulated by the impact of nicotinic receptor-dependent neuronal calcium influx. We tested this hypothesis for transcranial direct current stimulation (tDCS)-induced long-term potentiation-like plasticity, which is abolished by NIC in nonsmokers. To reduce calcium influx under NIC, we blocked N-methyl-d-aspartate (NMDA) receptors. We applied anodal tDCS combined with 15 mg NIC patches and the NMDA-receptor antagonist dextromethorphan (DMO) in 3 different doses (50, 100, and 150 mg) or placebo medication. Corticospinal excitability was monitored by single-pulse transcranial magnetic stimulation-induced motor-evoked potential amplitudes after plasticity induction. NIC abolished anodal tDCS-induced motor cortex excitability enhancement, which was restituted under medium dosage of DMO. Low-dosage DMO did not affect the impact of NIC on tDCS-induced plasticity and high-dosage DMO abolished plasticity. For DMO alone, the low dosage had no effect, but medium and high dosages abolished tDCS-induced plasticity. These results enhance our knowledge about the proposed calcium-dependent impact of NIC on plasticity in humans and might be relevant for the development of novel nicotinic treatments for cognitive dysfunction.

Effects of dextromethorphan on MDMA-induced serotonergic aberration in the brains of non-human primates using [123I]-ADAM/SPECT

3,4-Methylenedioxymethamphetamine (MDMA), a common recreational drug, is known to cause serotonergic neurotoxicity in the brain. Dextromethorphan (DM) is a widely used antitussive reported to exert anti-inflammatory effect in vivo. In this study, we examined the long-term effect of MDMA on the primate serotonergic system and the protective property of DM against MDMA-induced serotonergic abnormality using single photon emission computed tomography (SPECT). Nine monkeys (Macaca cyclopis) were divided into three groups, namely control, MDMA and co-treatment (MDMA/DM). [¹²³I]-ADAM was used as the radioligand for serotonin transporters (SERT) in SPECT scans. SERT levels of the brain were evaluated and presented as the uptake ratios (URs) of [¹²³I]-ADAM in several regions of interest of the brain including midbrain, thalamus and striatum. We found that the URs of [¹²³I]-ADAM were significantly lower in the brains of MDMA than control group, indicating lower brain SERT levels in the MDMA-treated monkeys. This MDMA-induced decrease in brain SERT levels could persist for over four years. However, the loss of brain SERT levels was not observed in co-treatment group. These results suggest that DM may exert a protective effect against MDMA-induced serotonergic toxicity in the brains of the non-human primate.

Anticonvulsant effect of dextrometrophan on pentylenetetrazole-induced seizures in mice: Involvement of nitric oxide and N-methyl-d-aspartate receptors

Dextrometrophan (DM), widely used as an antitussive, has recently generated interest as an anticonvulsant drug. Some effects of dextrometrophan are associated with alterations in several pathways, such as inhibition of nitric oxide synthase (NOS) enzyme and N-methyl d-aspartate (NMDA) receptors. In this study, we aimed to investigate the anticonvulsant effect of acute administration of dextrometrophan on pentylenetetrazole (PTZ)-induced seizures and the probable involvement of the nitric oxide (NO) pathway and NMDA receptors in this effect. For this purpose, seizures were induced by intravenous PTZ infusion. All drugs were administrated by intraperitoneal (i.p.) route before PTZ injection. Our results demonstrate that acute DM treatment (10-100mg/kg) increased the seizure threshold. In addition, the nonselective NOS inhibitor L-NAME (10mg/kg) and the neural NOS inhibitor, 7-nitroindazole (40mg/kg), at doses that had no effect on seizure threshold, augmented the anticonvulsant effect of DM (3mg/kg), while the inducible NOS inhibitor, aminoguanidine (100mg/kg), did not affect the anticonvulsant effect of DM. Moreover, the NOS substrate l-arginine (60mg/kg) blunted the anticonvulsant effect of DM (100mg/kg). Also, NMDA antagonists, ketamine (0.5mg/kg) and MK-801 (0.05mg/kg), augmented the anticonvulsant effect of DM (3mg/kg). In conclusion, we demonstrated that the anticonvulsant effect of DM is mediated by a decline in neural nitric oxide activity and inhibition of NMDA receptors.

High-dose dextromethorphan produces myelinoid bodies in the hippocampus of rats

Dextromethorphan (DM) administered at supra-antitussive doses produce psychotoxic and neurotoxic effects in humans. We administered DM (80 mg/kg) to rats intraperitoneally to determine the ultrastructural change induced by DM, because intraperitoneal route is sensitive for the behavioral responses. Treatment with DM resulted in mitochondrial dysfunction and formation of myelinoid bodies in the hippocampus. MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate] attenuated DM-induced cytosolic oxidative burdens. However, neither MK-801 nor naloxone affected DM-induced mitochondrial dysfunction and formation of myelinoid bodies, indicating that the neurotoxic mechanism needs to be further elucidated. Therefore, the spectrum of toxicological effects associated with DM need to be reassessed.

Sublingual fast dissolving niosomal films for enhanced bioavailability and prolonged effect of metoprolol tartrate

The aim of the present work was to prepare and evaluate sublingual fast dissolving films containing metoprolol tartrate-loaded niosomes. Niosomes were utilized to allow for prolonged release of the drug, whereas the films were used to increase the drug's bioavailability via the sublingual route. Niosomes were prepared using span 60 and cholesterol at different drug to surfactant ratios. The niosomes were characterized for size, zeta-potential, and entrapment efficiency. The selected niosomal formulation was incorporated into polymeric films using hydroxypropyl methyl cellulose E15 and methyl cellulose as film-forming polymers and Avicel as superdisintegrant. The physical characteristics (appearance, texture, pH, uniformity of weight and thickness, disintegration time, and palatability) of the prepared films were studied, in addition to evaluating the in vitro drug release, stability, and in vivo pharmacokinetics in rabbits. The release of the drug from the medicated film was fast (99.9% of the drug was released within 30 minutes), while the drug loaded into the niosomes, either incorporated into the film or not, showed only 22.85% drug release within the same time. The selected sublingual film showed significantly higher rate of drug absorption and higher drug plasma levels compared with that of commercial oral tablet. The plasma levels remained detectable for 24 hours following sublingual administration, compared with only 12 hours after administration of the oral tablet. In addition, the absolute bioavailability of the drug (ie, relative to intravenous administration) following sublingual administration was found to be significantly higher (91.06%±13.28%), as compared with that after oral tablet administration (39.37%±11.4%). These results indicate that the fast dissolving niosomal film could be a promising delivery system to enhance the bioavailability and prolong the therapeutic effect of metoprolol tartrate.

Pharmacology of dextromethorphan: Relevance to dextromethorphan/quinidine (Nuedexta®) clinical use

Dextromethorphan (DM) has been used for more than 50years as an over-the-counter antitussive. Studies have revealed a complex pharmacology of DM with mechanisms beyond blockade of N-methyl-d-aspartate (NMDA) receptors and inhibition of glutamate excitotoxicity, likely contributing to its pharmacological activity and clinical potential. DM is rapidly metabolized to dextrorphan, which has hampered the exploration of DM therapy separate from its metabolites. Coadministration of DM with a low dose of quinidine inhibits DM metabolism, yields greater bioavailability and enables more specific testing of the therapeutic properties of DM apart from its metabolites. The development of the drug combination DM hydrobromide and quinidine sulfate (DM/Q), with subsequent approval by the US Food and Drug Administration for pseudobulbar affect, led to renewed interest in understanding DM pharmacology. This review summarizes the interactions of DM with brain receptors and transporters and also considers its metabolic and pharmacokinetic properties. To assess the potential clinical relevance of these interactions, we provide an analysis comparing DM activity from in vitro functional assays with the estimated free drug DM concentrations in the brain following oral DM/Q administration. The findings suggest that DM/Q likely inhibits serotonin and norepinephrine reuptake and also blocks NMDA receptors with rapid kinetics. Use of DM/Q may also antagonize nicotinic acetylcholine receptors, particularly those composed of α3β4 subunits, and cause agonist activity at sigma-1 receptors.

Combination With Low-dose Dextromethorphan Improves the Effect of Amlodipine Monotherapy in Clinical Hypertension: A First-in-human, Concept-proven, Prospective, Dose-escalation, Multicenter Study

The combination of low rather than high dose of dextromethorphan (DXM) with amlodipine (AM) could improve blood pressure (BP) reduction in hypertensive animals. The study aimed to evaluate the feasibility of different doses of DXM combined with standard AM treatment in clinical hypertension.This was a prospective, 14-week, dose-escalation, multicenter study. After 2-week run-in period with AM 5 mg/day, hypertensive patients who got the BP goal of 140/90 mmHg kept receiving AM monotherapy for another 12 weeks. The nonresponders, while kept on AM 5 mg/day, received additional DXM treatment for 3 sequential dose-titrated periods with initially 2.5 mg/day, followed by 7.5 mg/day, and finally 30 mg/day. Each period was for 4 weeks. The patients at BP goal after each treatment period were defined as the responders and kept on the same combination till the end of the study. The responder rate of each treatment period was recorded. The changes of BP and serum antioxidant/endothelial markers between week 14 and week 2 were evaluated.Of the 103 patients initially enrolled, 89 entered the treatment period. In the 78 patients completing the study, 31 (40%) at BP goal after 2-week AM run-in kept on AM monotherapy (DXM0). The addition of 2.5 (DXM2.5) and 7.5 mg/day (DXM7.5) of DXM enabled BP goal achievement in 22 (47%) nonresponders to AM monotherapy including 16 (29%) with DXM2.5 and 6 (18%) with DXM7.5. Only 4 patients (16%) reached BP goal with the combination of DXM 30 mg/day (DXM30). Overall, 73% of the 78 patients reached BP goal at the end of the 14-week study. Mean systolic BP was reduced by 7.9% ± 7.0% with DXM2.5 (P < 0.001) and by 5.4% ± 2.4% with DXM7.5 (P = 0.003) respectively at week 14 from that at week 2, which was unchanged in either DXM0 or DXM30 group. Besides, the effects of combination treatment were particularly significant in the patients with impaired endothelial function suggested by reduced serum NOx level at baseline.Accordingly, the combination with low dose of DXM was feasible to improve BP control in patients who failed to achieve the BP goal by standard AM monotherapy. The benefit effects might be significant especially in patients with impaired endothelial function.

Dextromethorphan: An update on its utility for neurological and neuropsychiatric disorders

Dextromethorphan (DM) is a commonly used antitussive and is currently the only FDA-approved pharmaceutical treatment for pseudobulbar affect. Its safety profile and diverse pharmacologic actions in the central nervous system have stimulated new interest for repurposing it. Numerous preclinical investigations and many open-label or blinded clinical studies have demonstrated its beneficial effects across a variety of neurological and psychiatric disorders. However, the optimal dose and safety of chronic dosing are not fully known. This review summarizes the preclinical and clinical effects of DM and its putative mechanisms of action, focusing on depression, stroke, traumatic brain injury, seizure, pain, methotrexate neurotoxicity, Parkinson's disease and autism. Moreover, we offer suggestions for future research with DM to advance the treatment for these and other neurological and psychiatric disorders.

Dual Therapeutic Effects of C-10068, a Dextromethorphan Derivative, Against Post-Traumatic Nonconvulsive Seizures and Neuroinflammation in a Rat Model of Penetrating Ballistic-Like Brain Injury

Post-traumatic seizures can exacerbate injurious outcomes of severe brain trauma, yet effective treatments are limited owing to the complexity of the pathology underlying the concomitant occurrence of both events. In this study, we tested C-10068, a novel deuterium-containing analog of (+)-N-methyl-3-ethoxymorphinan, in a rat model of penetrating ballistic-like brain injury (PBBI) and evaluated the effects of C-10068 on PBBI-induced nonconvulsive seizures (NCS), acute neuroinflammation, and neurofunctional outcomes. NCS were detected by electroencephalographic monitoring. Neuroinflammation was evaluated by immunohistochemical markers, for example, glial fibrillary acidic protein and major histocompatibility complex class I, for activation of astrocytes and microglia, respectively. Neurofunction was tested using rotarod and Morris water maze tasks. Three infusion doses of C-10068 (1.0, 2.5, and 5.0 mg/kg/h × 72 h) were tested in the antiseizure study. Neuroinflammation and neurofunction were evaluated in animals treated with 5.0 mg/kg/h × 72 h C-10068. Compared to vehicle treatment, C-10068 dose dependently reduced PBBI-induced NCS incidence (40-50%), frequency (20-70%), and duration (30-82%). The most effective antiseizure dose of C-10068 (5.0 mg/kg/h × 72 h) also significantly attenuated hippocampal astrocyte activation and perilesional microglial reactivity post-PBBI. Within C-10068-treated animals, a positive correlation was observed in reduction in NCS frequency and reduction in hippocampal astrocyte activation. Further, C-10068 treatment significantly attenuated astrocyte activation in seizure-free animals. However, C-10068 failed to improve PBBI-induced motor and cognitive functions with the dosing regimen used in this study. Overall, the results indicating that C-10068 exerts both potent antiseizure and antiinflammatory effects are promising and warrant further investigation.

A new look at auranofin, dextromethorphan and rosiglitazone for reduction of glia-mediated inflammation in neurodegenerative diseases

Neurodegenerative disorders including Alzheimer's disease are characterized by chronic inflammation in the central nervous system. The two main glial types involved in inflammatory reactions are microglia and astrocytes. While these cells normally protect neurons by providing nutrients and growth factors, disease specific stimuli can induce glial secretion of neurotoxins. It has been hypothesized that reducing glia-mediated inflammation could diminish neuronal loss. This hypothesis is supported by observations that chronic use of non-steroidal anti-inflammatory drugs (NSAIDs) is linked with lower incidences of neurodegenerative disease. It is possible that the NSAIDs are not potent enough to appreciably reduce chronic neuroinflammation after disease processes are fully established. Gold thiol compounds, including auranofin, comprise another class of medications effective at reducing peripheral inflammation. We have demonstrated that auranofin inhibits human microglia- and astrocyte-mediated neurotoxicity. Other drugs which are currently used to treat peripheral inflammatory conditions could be helpful in neurodegenerative disease. Three different classes of anti-inflammatory compounds, which have a potential to inhibit neuroinflammation are highlighted below.

Evaluating the safety and efficacy of dextromethorphan/quinidine in the treatment of pseudobulbar affect

Pseudobulbar affect (PBA) is a common manifestation of brain pathology associated with many neurological diseases, including amyotrophic lateral sclerosis, Alzheimer's disease, stroke, multiple sclerosis, Parkinson's disease, and traumatic brain injury. PBA is defined by involuntary and uncontrollable expressed emotion that is exaggerated and inappropriate, and also incongruent with the underlying emotional state. Dextromethorphan/quinidine (DM/Q) is a combination product indicated for the treatment of PBA. The quinidine component of DM/Q inhibits the cytochrome P450 2D6-mediated metabolic conversion of dextromethorphan to its active metabolite dextrorphan, thereby increasing dextromethorphan systemic bioavailability and driving the pharmacology toward that of the parent drug and away from adverse effects of the dextrorphan metabolite. Three published efficacy and safety studies support the use of DM/Q in the treatment of PBA; significant effects were seen on the primary end point, the Center for Neurologic Study-Lability Scale, as well as secondary efficacy end points and quality of life. While concentration-effect relationships appear relatively weak for efficacy parameters, concentrations of DM/Q may have an impact on safety. Some special safety concerns exist with DM/Q, primarily because of the drug interaction and QT prolongation potential of the quinidine component. However, because concentrations of dextrorphan (which is responsible for many of the parent drug's side effects) and quinidine are lower than those observed in clinical practice with these drugs administered alone, some of the perceived safety issues may not be as relevant with this low dose combination product. However, since patients with PBA have a variety of other medical problems and are on numerous other medications, they may not tolerate DM/Q adverse effects, or may be at risk for drug interactions. Some caution is warranted when initiating DM/Q treatment, particularly in patients with underlying risk factors for torsade de pointes and in those receiving medications that may interact with DM/Q.

Memantine may affect pseudobulbar affect in patients with Alzheimer's disease

OBJECTIVE

Behavioural symptoms are common in moderate to severe Alzheimer's disease (AD) and are improved by memantine with the most pronounced effect on agitation/aggression. Dextromethorphan in combination with quinidine is the only drug approved by US Food and Drug Administration for the treatment of pseudobulbar affect (PBA) on the basis of efficacy in patients with multiple sclerosis or amyotrophic lateral sclerosis. The aim of our study was to evaluate the efficacy of memantine on PBA in patients with AD.

METHODS

In a prospective, double-blind, case-control study to assess PBA with pathological laughter and crying scale patients were administered memantine (final dose of 20 mg daily) or citalopram (20 mg once daily), each for 10 weeks. The number of episodes of involuntary emotional expression, Neuropsychiatric Inventory (NPI) and Overt Aggression Scale-Modified (OAS-M) total scores were also recorded. Furthermore, the platelet serotonin (5-HT) concentration was measured.

RESULTS

Although memantine had beneficial effects on PBA, it also had a crucial impact on behavioural symptoms, especially aggression and agitation (to an average of 3.5 times higher end-point scores on OAS-M and increase of NPI total scores for an average of 114% of initial value). Therefore, the study was prematurely stopped. In addition, we had evidenced a drop of platelet 5-HT concentration (to an average of 73% of initial value).

CONCLUSION

Surprisingly, our research showed the opposite action of memantine on neuropsychiatric symptoms as expected. In a limited number of AD patients with PBA, memantine had a beneficial effect on involuntary emotional expression, but it potentiated agitation/aggression, irritability and caused a crucial drop of the platelet 5-HT concentration.

Dextromethorphan attenuates LPS-induced adhesion molecule expression in human endothelial cells

OBJECTIVE

This study examines the effect of Dextromethorphan (d-3-methoxy-17-methylmorphinan; DXM), a commonly used cough-suppressing drug, on the expression of VCAM-1 and ICAM-1 in human umbilical vein endothelial cells (HUVECs) stimulated with lipopolysaccharide (LPS).

METHODS

The effect of DXM on expression of cell adhesion molecules induced by LPS was evaluated by monocyte bindings in vitro and ex vivo and transmigration assays. The signaling pathways involved in the inflammation inhibitory effect of DXM were analyzed by Western blot and immunofluorescent stain.

RESULTS

Pretreatment of HUVECs with DXM inhibited LPS-induced adhesion of THP-1 cells in vitro and ex vivo, and reduced transendothelial migration of these cells. Furthermore, treatment of HUVECs with DXM can significantly decrease LPS-induced expression of ICAM-1 and VCAM-1. DXM abrogated LPS-induced phosphorylation of ERK and Akt. The translocation of early growth response gene-1 (Egr-1), a downstream transcription factor involved in the mitogen-activated kinase (MEK)-ERK signaling pathway, was suppressed by DXM treatment. Furthermore, DXM inhibited LPS-induced IκBα degradation and nuclear translocation of p65.

CONCLUSIONS

Dextromethorphan inhibits the adhesive capacity of HUVECs by reducing the LPS-induced ICAM-1 and VCAM-1 expression via the suppression of the ERK, Akt, and NF-κB signaling pathways. Thus, DXM is a potential anti-inflammatory therapeutic that may modulate atherogenesis.

Dextromethorphan inhibits osteoclast differentiation by suppressing RANKL-induced nuclear factor-κB activation

Dextromethorphan (DXM), a commonly used antitussive, is a dextrorotatory morphinan. Here, we report that DXM inhibits the receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclastogenesis and bone resorption by abrogating the activation of NF-κB signalling in vitro. Oral administration of DXM ameliorates ovariectomy (OVX)-induced osteoporosis in vivo.

INTRODUCTION

DXM was reported to possess anti-inflammatory properties through inhibition of the release of pro-inflammatory factors. However, the potential role and action mechanism of DXM on osteoclasts and osteoblasts remain unclear. In this study, in vitro and in vivo studies were performed to investigate the potential effects of DXM on osteoclastogenesis and OVX-induced bone loss.

METHODS

Osteoclastogenesis was examined by the TRAP staining, pit resorption, TNF-α release, and CCR2 and CALCR gene expression. Osteoblast differentiation was analyzed by calcium deposition. Osteogenic and adipogenic genes were measured by real-time PCR. Signaling pathways were explored using Western blot. ICR mice were used in an OVX-induced osteoporosis model. Tibiae were measured by µCT and serum markers were examined with ELISA kits.

RESULTS

DXM inhibited RANKL-induced osteoclastogenesis. DXM mainly inhibited osteoclastogenesis via abrogation of IKK-IκBα-NF-κB pathways. However, a higher dosage of DXM antagonized the differentiation of osteoblasts via the inhibition of osteogenic signals and increase of adipogenic signals. Oral administration of DXM (20 mg/kg/day) partially reduced trabecular bone loss in ovariectomized mice.

CONCLUSION

DXM inhibits osteoclast differentiation and activity by affecting NF-κB signaling. Therefore, DXM at suitable doses may have new therapeutic applications for the treatment of diseases associated with excessive osteoclastic activity.

Dextromethorphan-induced psychotoxic behaviors cause sexual dysfunction in male mice via stimulation of σ-1 receptors

Dextromethorphan (DM) is a well-known antitussive dextrorotatory morphinan. We and others have demonstrated that sigma (σ) receptors may be important for DM-mediated neuromodulation. Because an earlier report suggested that DM might affect sexual function and that σ receptor ligands affect signaling pathways in the periphery, we examined whether DM-induced psychotoxic burden affected male reproductive function. We observed that DM had a high affinity at σ-1 receptors in the brain and testis but relatively low affinity at σ-2 receptors. Prolonged treatment with DM resulted in conditioned place preference and hyperlocomotion, followed by an increase in Fos-related antigen expression in the nucleus accumbens in male mice. Simultaneously, DM induced significant reductions in gonadotropin-releasing-hormone immunoreactivity in the hypothalamus. Moreover, we observed that DM induced increased sperm abnormalities and decreased sperm viability and sexual behavior. These phenomena were significantly attenuated by combined treatment with BD1047, a σ-1 receptor antagonist, but not by SM-21, a σ-2 receptor antagonist. Thus, these results suggest that DM psychotoxicity might lead to reproductive stress in male mice by activating σ-1 receptors.

Efficacy of AR-R15896AR in the rat monofilament model of transient middle cerebral artery occlusion

The monofilament technique of transient middle cerebral artery occlusion (MCAO) was used in 3 separate studies to evaluate the efficacy of the low-affinity, use-dependent N-methyl-d-aspartate receptor antagonist, AR-R15896AR. First, a dose-response curve was attempted. Wister Kyoto rats received 2 hours of MCAO. Five minutes later, a 30-minute intravenous infusion of AR-R15896AR was given, followed by subcutaneous implantation of Alzet minipumps that were calibrated to maintain specified plasma levels (approximately 682, 1885, or 2682 ng/mL) of AR-R15896 (free base) for 1 week. The highest plasma level attained significantly decreased the percentage of damage to the subcortex, cortex, and total brain. Second, the high-dose, 1-week treatment regimen was repeated to determine if neuroprotection would extend to 8 weeks after MCAO. Indeed, in separate groups of animals, significant reduction in the percentage of damage, which was generally confined to the cortex and subcortex, was observed at 1, 2, 4, and 8 weeks. Third, verification was achieved in another laboratory. Lister Hooded rats received 60 minutes of transient MCAO. At 70 minutes, an acute dose of AR-R15896AR (20.3 mg/kg) was injected intraperitoneally and the rats were killed 23 hours later. This treatment group also exhibited significant reduction in the volume of infarction in the subcortex, cortex, and total brain. The outcome of these investigations supports the ongoing Phase II clinical trials in patients with acute stroke.

Low-dose dextromethorphan, a NADPH oxidase inhibitor, reduces blood pressure and enhances vascular protection in experimental hypertension

Background

Vascular oxidative stress may be increased with age and aggravate endothelial dysfunction and vascular injury in hypertension. This study aimed to investigate the effects of dextromethorphan (DM), a NADPH oxidase inhibitor, either alone or in combination treatment, on blood pressure (BP) and vascular protection in aged spontaneous hypertensive rats (SHRs).

Methodology/Principal Findings

Eighteen-week-old WKY rats and SHRs were housed for 2 weeks. SHRs were randomly assigned to one of the 12 groups: untreated; DM monotherapy with 1, 5 or 25 mg/kg/day; amlodipine (AM, a calcium channel blocker) monotherapy with 1 or 5 mg/kg/day; and combination therapy of DM 1, 5 or 25 mg/kg/day with AM 1 or 5 mg/kg/day individually for 4 weeks. The in vitro effects of DM were also examined. In SHRs, AM monotherapy dose-dependently reduced arterial systolic BP. DM in various doses significantly and similarly reduced arterial systolic BP. Combination of DM with AM gave additive effects on BP reduction. DM, either alone or in combination with AM, improved aortic endothelial function indicated by ex vivo acetylcholine-induced relaxation. The combination of low-dose DM with AM gave most significant inhibition on aortic wall thickness in SHRs. Plasma total antioxidant status was significantly increased by all the therapies except for the combination of high-dose DM with high-dose AM. Serum nitrite and nitrate level was significantly reduced by AM but not by DM or the combination of DM with AM. Furthermore, in vitro treatment with DM reduced angiotensin II-induced reactive oxygen species and NADPH oxidase activation in human aortic endothelial cells.

Conclusions/Significance

Treatment of DM reduced BP and enhanced vascular protection probably by inhibiting vascular NADPH oxidase in aged hypertensive animals with or without AM treatment. It provides the potential rationale to a novel combination treatment with low-dose DM and AM in clinical hypertension.

Interaction between dextromethorphan and norpethidine in rats

With increasing interest in the application of dextromethorphan in pain control, it is probable that patients will receive this drug in combination with analgesics such as opioids, giving rise to the potential for previously unobserved drug interactions. The interaction between dextromethorphan, and its pharmacologically active metabolite dextrorphan, and norpethidine, a toxic metabolite of pethidine, was examined in rats. Rats were assigned to receive dextromethorphan (0, 20 or 40 mg/kg) or dextrorphan (0, 15 or 30 mg/kg) combined with norpethidine (0, 28 or 42 mg/kg). The occurrence of seizures, myoclonic jerks and shivering was recorded for 60 min after drug administration. Norpethidine produced dose-related increases in the incidence of seizures, myoclonic jerks and shivering. Dextromethorphan, but not dextrorphan, increased the incidence of these behaviours. It is recommended that extreme caution be exercised if dextromethorphan and pethidine are to be used together.

Evaluation of the neuroprotective effect of dextromethorphan in the acute phase of ischaemic stroke

INTRODUCTION

Stroke is the second leading cause of death in the world. However, there is still no approved neuroprotective drug for acute ischaemic stroke. To clarify the neuroprotective efficacy and safety of dextromethorphan in stroke, the following study was carried out.

MATERIAL AND METHODS

Forty patients with acute stroke causing moderate deficit were randomized to be treated with either dextromethorphan 300 mg per day or placebo for 5 days. Plasma level of dextromethorphan and its active metabolite was not evaluated in this study. The NIHSS score was calculated on day 5 and the Barthel activities of daily living index and Rankin score were checked after 3 months by a blinded investigator. Collected data were analysed using the t-test and χ(2) test.

RESULTS

In the dextromethorphan-treated group, the mean NIHSS score was 16.8 ±3.9 at baseline, and was 14.2 ±4.8 for the placebo-treated group (p = 0.069). At day 5, there was also no significant difference regarding NIHSS score (p = 0.167). At the 3-month follow-up, there was no significant difference regarding Barthel scale and Rankin score between the dextromethorphan and placebo groups.

CONCLUSIONS

The results of our study suggest that although low-dose and short-term oral administration of dextromethorphan seems to be not neuroprotective, it does not worsen either patients' condition or NIHSS score. Moreover, patients treated with dextromethorphan showed a significant reduction in seizures (complication after stroke), but had increased chance of MI and renal failure by almost 5% when compared to the placebo-treated groups. More prolonged studies with a higher number of cases are recommended.

Dextromethorphan inhibits the glutamatergic synaptic transmission in the nucleus tractus solitarius of guinea pigs

Dextromethorphan (DEX) is a widely used non-opioid antitussive. However, the precise site of action and its mechanism were not fully understood. We examined the effects of DEX on AMPA receptor-mediated glutamatergic transmission in the nucleus tractus solitarius (NTS) of guinea pigs. Excitatory postsynaptic currents (evoked EPSCs: eEPSCs) were evoked in the second-order neurons by electrical stimulation of the tractus solitarius. DEX reversibly decreased the eEPSC amplitude in a concentration-dependent manner. The DEX-induced inhibition of eEPSC was accompanied by an increased paired-pulse ratio. Miniature EPSCs (mEPSCs) were also recorded in the presence of Cd(2+) or tetrodotoxin. DEX decreased the frequency of mEPSCs without affecting their amplitude. Topically applied AMPA provoked an inward current in the neurons, which was unchanged during the perfusion of DEX. BD1047, a σ-1-receptor antagonist, did not block the inhibitory effect of DEX on the eEPSCs, but antagonized the inhibition of eEPSCs induced by SKF-10047, a σ-1 agonist. Haloperidol, a σ-1 and -2 receptor ligand, had no influence on the inhibitory action of DEX. These results suggest that DEX inhibits glutamate release from the presynaptic terminals projecting to the second-order NTS neurons, but this effect of DEX is not mediated by the activation of σ receptors.

Neuropsychopharmacological understanding for therapeutic application of morphinans

Morphinans are a class of compounds containing the basic structure of morphine. It is well-known that morphinans possess diverse pharmacological effects on the central nervous system. This review will demonstrate novel neuroprotective effects of several morphinans such as, dextromethorphan, its analogs and naloxone on the models of multiple neurodegenerative disease by modulating glial activation associated with the production of a host of proinflammatory and neurotoxic factors, although dextromethorphan possesses neuropsychotoxic potentials. The neuroprotective effects and the therapeutic potential for the treatment of excitotoxic and inflammatory neurodegenerative diseases, and underlying mechanism of morphinans are discussed.

Post stroke depression: treatments and complications in a young adult

Post-stroke depression has been noted to be one of the most frequent complications of stroke with an estimated prevalence of as high as 80%. However, the incidence of stroke in the young is extremely low and evidence based therapy for this complication is quite limited. The case of a 28-year-old woman who experienced a basilar artery vasospasmic stroke resulting in anoxic brain injury to the midbrain and paramedian thalamus is presented, along with a literature review of psychiatric complications of this injury to include post-stroke depression (PSD). Therapeutic modalities such as TCAs, SSRIs, atypical antipsychotics and stimulant medications are also reviewed as these medications may aid in the treatment of such patients but may also contribute to psychiatric sequelae.

Effects of dextromethorphan/quinidine on auditory event-related potentials in multiple sclerosis patients with pseudobulbar affect

The purpose of this study was to characterize the brain activity and associated cortical structures involved in pseudobulbar affect (PBA), a condition characterized by uncontrollable episodes of laughing and/or crying in patients with multiple sclerosis before and after treatment with dextromethorphan/quinidine (DM/Q). Behavioral responses and event-related potentials (ERPs) in response to subjectively significant and neutral verbal stimuli were recorded from 2 groups: 6 multiple sclerosis patients with PBA before (PBA-preTx) and after (PBA-DM/Q) treatment with DM/Q and 6 healthy control (HC) subjects. Statistical nonparametric mapping comparisons of ERP source current density distributions between groups were conducted for subjectively significant and neutral stimuli separately before and after treatment with DM/Q. Treatment with DM/Q had a normalizing effect on the behavioral responses of PBA patients. Event-related potential waveform comparisons of PBA-preTx and PBA-DM/Q with HC, for both neutral and subjectively significant stimuli, revealed effects on early ERP components. Comparisons between PBA-preTx and HC, in response to subjectively significant stimuli, revealed both early and late effects. Source analysis comparisons between PBA-preTx and PBA-DM/Q indicated distinct activations in areas involved in emotional processing and high-level and associative visual processing in response to neutral stimuli and in areas involved in emotional, somatosensory, primary, and premotor processing in response to subjectively significant stimuli. In most cases, stimuli evoked higher current density in PBA-DM/Q compared with the other groups. In conclusion, differences in brain activity were observed before and after medication. Also, DM/Q administration resulted in normalization of behavioral and electrophysiological measures.

Neuroprotective profile of dextromethorphan in an experimental model of penetrating ballistic-like brain injury

Dextromethorphan (DM) has been well-characterized as a neuroprotective agent in experimental models of CNS injury. The goal of this study was to determine the neuroprotective profile of DM in a military-relevant model of penetrating ballistic-like brain injury (PBBI). In an acute (3 day) dose-response study, anesthetized male Sprague-Dawley rats were exposed to a unilateral frontal PBBI with DM (0.156-10 mg/kg) or vehicle delivered as an i.v. bolus from 30 min to 48 h post-injury. In a follow-up (7 day) experiment, the 10-mg/kg bolus injections of DM were administered in conjunction with a 6-h infusion (5 mg/kg/h). DM bolus injections alone produced a dose-dependent improvement in motor recovery on a balance beam task at 3 days post-injury. However, more rapid recovery (24 h) was observed on this task when the bolus injections were combined with the 6-h infusion. Moreover, the DM bolus/infusion treatment regimen resulted in a significant (76%) improvement in cognitive performance in a novel object recognition (NOR) task at 7 days post-injury. Although post-injury administration of DM (all doses) failed to reduce core lesion size, the maximum dose of DM (10 mg/kg) was effective in reducing silver-stained axonal fiber degeneration in the cortical regions adjacent to the injury.

Treatment with dextromethorphan improves endothelial function, inflammation and oxidative stress in male heavy smokers

BACKGROUND

Dextromethorphan (DM) is reported to reduce the inflammation-mediated degeneration of dopaminergic neurons.

OBJECTIVE

The goal of this study was to test if DM can improve the endothelial dysfunction and inflammatory markers in heavy smokers.

PATIENTS AND METHODS

Forty habitual smoking healthy male volunteers (mean age, 31.5 +/- 1.4 years) were randomly given either DM (120 mg day(-1)) or a placebo for 6 months. We determined endothelial function using the brachial artery diameter changes in flow-mediated dilatation (FMD) and measured their inflammatory and oxidative markers. A sex-and-age matched non-smoking group (n = 20) was compared as normal parameters.

RESULTS

Habitual smokers showed impaired baseline endothelial function in FMD (smoking vs. non-smoking: 6.3 +/- 1.8 vs. 10.2 +/- 2.3% respectively, P < 0.01). Without change in smoking behavior, lipid and metabolic parameters, a significant increase in FMD was found in the DM-treated group (32%), accompanied by a decrease in high-sensitivity C-reactive protein (hs-CRP), phospholipase A(2), matrix metalloproteinase-3, interleukin 6 (IL-6) and tumor necrosis factor-alpha receptor II (TNF-alpha RII) (all P < 0.05), but unchanged in von Willebrand factor (VWF)and plasminogen activator inhibitor-1 (PAI-1). An increase in plasma glutathione peroxidase and a decrease in spot urinary excretion of 8-epi-prostaglandin F(2a) were found in DM-treated smokers.

CONCLUSIONS

Our study suggests that a 6-month treatment with DM can improve endothelial function and attenuate vascular oxidative stress and inflammation markers in habitual smokers.

A comparison of the binding profiles of dextromethorphan, memantine, fluoxetine and amitriptyline: Treatment of involuntary emotional expression disorder

We compared the binding profiles of medications potentially useful in the treatment of involuntary emotional expression disorder at twenty-six binding sites in rat brain tissue membranes. Sites were chosen based on likelihood of being target sites for the mechanism of action of the agents in treating the disorder or their likelihood in producing side effects experienced by patients treated with psychoactive agents. We used radioligand binding assays employing the most selective labeled ligands available for sites of interest. Concentrations of labeled ligand were used at or below the K(i) value of the ligand for the target site. Compounds were initially screened at 1 muM. For compounds that competed for greater than 20-30% of specific binding at target sites of interest, full concentration curves were constructed. Dextromethorphan, amitriptyline and fluoxetine competed for binding to sigma(1) receptors and to serotonin transporters with high to moderate affinity. Of the target sites tested, these are the most likely to contribute to the therapeutic benefit of the various agents. In addition, all three drugs showed some activity at alpha(2) and 5-HT(1B/D) sites. Of the drugs tested, dextromethorphan bound to the fewest sites unlikely to be target sites. Although the mechanism of action of dextromethorphan or any drug that has been used in the treatment of involuntary emotional expression disorder is currently unknown, our data support that the affinity of the drug for sigma(1) receptors is consistent with its possible action through this receptor type in controlling symptoms of the disorder.

Current clinical trials in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is caused by selective degeneration of motor neurons in the brain and spinal cord. There are still no other effective therapies 10 years after the approval of riluzole for the treatment of amyotrophic lateral sclerosis, but advances in drug development and screening are substantially increasing the number of potential therapeutic agents. This review provides an overview of clinical trial methodology in amyotrophic lateral sclerosis followed by a systematic evaluation of drugs that are presently in Phase I, II and III clinical trials. There is an emphasis on the scientific evidence supporting the selection of each drug being tested, as well as on trial design.

Dextromethorphan as a Potential Neuroprotective Agent With Unique Mechanisms of Action

BACKGROUND

Dextromethorphan (DM) is a widely-used antitussive. DM's complex central nervous system (CNS) pharmacology became of interest when it was discovered to be neuroprotective due to its low-affinity, uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonism.

REVIEW SUMMARY

Mounting preclinical evidence has proven that DM has important neuroprotective properties in various CNS injury models, including focal and global ischemia, seizure, and traumatic brain injury paradigms. Many of these protective actions seem functionally related to its inhibitory effects on glutamate-induced neurotoxicity via NMDA receptor antagonist, sigma-1 receptor agonist, and voltage-gated calcium channel antagonist actions. DM's protection of dopamine neurons in parkinsonian models may be due to inhibition of neurodegenerative inflammatory responses. Clinical findings are limited, with preliminary evidence indicating that DM protects against neuronal damage. Negative findings seem to relate to attainment of inadequate DM brain concentrations. Small studies have shown some promise for treatment of perioperative brain injury, amyotrophic lateral sclerosis, and symptoms of methotrexate neurotoxicity. DM safety/tolerability trials in stroke, neurosurgery, and amyotrophic lateral sclerosis patients demonstrated a favorable safety profile. DM's limited clinical benefit is proposed to be associated with its rapid metabolism to dextrorphan, which restricts its central bioavailability and therapeutic utility. Systemic concentrations of DM can be increased via coadministration of low-dose quinidine (Q), which reversibly inhibits its first-pass elimination. Potential drug interactions with DM/Q are discussed.

CONCLUSIONS

Given the compelling preclinical evidence for neuroprotective properties of DM, initial clinical neuroprotective findings, and clinical demonstrations that the DM/Q combination is well tolerated, this strategy may hold promise for the treatment of various acute and degenerative neurologic disorders.

Therapeutic use of dextromethorphan: Key learnings from treatment of pseudobulbar affect

A variety of neurological conditions and disease states are accompanied by pseudobulbar affect (PBA), an emotional disorder characterized by uncontrollable outbursts of laughing and crying. The causes of PBA are unclear but may involve lesions in neural circuits regulating the motor output of emotional expression. Several agents used in treating other psychiatric disorders have been applied in the treatment of PBA with some success but data are limited and these agents are associated with unpleasant side effects due to nonspecific activity in diffuse neural networks. Dextromethorphan (DM), a widely used cough suppressant, acts at receptors in the brainstem and cerebellum, brain regions implicated in the regulation of emotional output. The combination of DM and quinidine (Q), an enzyme inhibitor that blocks DM metabolism, has recently been tested in phase III clinical trials in patients with multiple sclerosis and amyotrophic lateral sclerosis and was both safe and effective in palliating PBA symptoms. In addition, clinical studies pertaining to the safety and efficacy of DM/Q in a variety of neurological disease states are ongoing.

Involuntary emotional expression disorder: treating the untreated

Patients with involuntary emotional expression disorder (IEED) have impaired social and occupational functioning and there is currently no Food an Drug Administration-approved treatment. Treatment options include tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), dopaminergic agents, and a combination of dextromethorphan and quinidine. Studies of monaminergic agents have typically been small and executed in single-center settings. Assessment measures generally show significant symptomatic improvements, including a reduction in the number of laughing or crying episodes and improvements in patients' clinical condition. The tolerability profiles of these agents are well defined, and include dizziness, tachycardia and QTc prolongation (TCAs), and sleep and sexual disturbances (SSRIs). The combination of dextromethorphan and quinidine has also been assessed in two large multicenter studies in patients with amyotrophic lateral sclerosis and multiple sclerosis. Compared with placebo and either agent alone, there were significant improvements in symptoms, quality of life, and relationships. The most common side effects were dizziness and nausea, and potential drug interactions with quinidine should also be considered. Choice of treatment should be evidence-based, taking into account both efficacy and tolerability.

Pathophysiology of involuntary emotional expression disorder

Extensive clinical experience and research suggest that a cortico-limbic-subcortico-thalamic-ponto-cerebellar network plays a significant role in the expression of human emotions. This network includes specific cerebral, cerebellar, and brainstem areas and their multiple projections/pathways, with activity modulated through serotonergic, dopaminergic, glutamatergic, and possibly sigma receptor neurotransmitter systems. Disruptions of regulatory and inhibitory mechanisms in the structure and function of this network likely constitute a pathophysiological basis for the crying and laughing episodes characteristic of involuntary emotional expression disorder. Pharmacologic interventions targeting the neurochemical modulators of the emotional expression systems may afford opportunities for symptom control among persons affected by this disorder.

Beneficial effects of LK-4, an analog of dextromethorphan on lipopolysaccharide-induced sepsis in rats

Dextromethorphan (DM), an anti-tussive agent, has been claimed to have anti-inflammatory and immunomodulatory effects in vitro. In our preliminary screening test, LK-4, an analog of DM, can afford more protection against circulatory failure induced by LPS than that of DM. Thus, the aim of this study was to evaluate the effects of LK-4 on sepsis induced by intravenous (i.v.) administration of lipopolysaccharide (LPS; 10 mg/kg) in anesthetized Wistar rats and survival rate by intraperitoneal administration of LPS (70 mg/kg) in conscious ICR mice. Results demonstrated that posttreatment with LK-4 (3 and 5 mg/kg, i.v.) significantly attenuated the deleterious hemodynamic changes (e.g., hypotension and tachycardia) in rats treated with LPS. Meanwhile, LK-4 (3 mg/kg) significantly inhibited the elevation of plasma tumor necrosis factor-alpha, as well as values of GOT and GPT, and BUN and creatinine caused by LPS. The induction of inducible NO synthase and the overproduction of NO and superoxide anions by LPS were also reduced by LK-4. Moreover, infiltration of neutrophils into the lungs and liver of rats 8 h after treatment with LPS was also reduced by LK-4. Furthermore, LK-4 increased the survival rate of mice insulted by toxic dose of LPS. In conclusion, the beneficial effects of LK-4 on LPS-induced sepsis result from its anti-inflammatory and anti-oxidant effects. Thus, LK-4 can be potentially used as a therapeutic agent for sepsis in the future.

Pseudobulbar affect in multiple sclerosis: Toward the development of innovative therapeutic strategies

Pseudobulbar affect (PBA), a condition involving involuntary and uncontrollable episodes of crying and/or laughing, occurs frequently in patients with a variety of neurological disorders, including amyotrophic lateral sclerosis (ALS), stroke, traumatic brain injury, dementia including Alzheimer's disease, and multiple sclerosis (MS). Although PBA results in considerable distress for patients and caretakers, it is underrecognized and undertreated. Agents used to treat psychiatric disorders--particularly tricyclic antidepressants and selective serotonin reuptake inhibitors--are useful in alleviating PBA, but act on diffuse neural networks rather than targeting those involved in emotional motor expression. As a result of their nonspecific activity, these agents are associated with a range of unwanted effects that preclude many patients from using them. Dextromethorphan, a common cough suppressant, specifically targets sigma(1) receptors concentrated in the brainstem and cerebellum, thus providing the possibility of targeting regions implicated in emotional expression. When administered in a fixed combination with quinidine, dextromethorphan is effective in treating PBA in patients with ALS, and preliminary results suggest that this therapy also is effective in treating MS-related PBA.

Inhibition of the serotonin-induced inward current by dextromethorphan in rat nodose ganglion neurons

Dextromethorphan is one of the most widely used antitussives for the treatment of cough. In the present study, we investigated the effect of dextromethorphan on 5-hydroxytryptamine (5-HT)-induced currents in acutely dissociated rat nodose ganglion neurons using nystatin-perforated patch-clamp recording configuration. The 5-HT-induced current was inhibited by the 5-HT(3) receptor antagonist tropisetron, while the selective 5-HT(3) receptor agonist 1-(m-chlorophenyl)-biguanide hydrochloride (mCPBG) induced a similar current. Dextromethorphan reversibly and concentration-dependently inhibited the 5-HT-induced inward current. The inhibition did not appear to be voltage-dependent. Both the peak and steady-state 5-HT-induced currents were inhibited by dextromethorphan, although the peak current was more sensitive to dextromethorphan block. The IC(50) values for the inhibition of peak and steady currents evoked by 3 muM 5-HT were 16.4 and 34.4 muM, respectively. In the presence of 10 muM dextromethorphan, the concentration-response curve for 5-HT was shifted to the right without changing the maximum response, while high concentrations reduced the maximum current. The 5-HT EC(50) values in the presence of 0, 10, 30 and 60 muM dextromethorphan were 4.3, 6.8, 15.5 and 40.6 muM, respectively. The results indicate that dextromethorphan inhibits the 5-HT-induced current of rat nodose ganglion neurons, and further suggest that dextromethorphan at a low concentration acts as a competitive inhibitor of 5-HT(3) receptors.

Randomized, controlled trial of dextromethorphan/quinidine for pseudobulbar affect in multiple sclerosis

OBJECTIVE

To evaluate the efficacy and safety of DM/Q (capsules containing dextromethorphan [DM] and quinidine [Q]) compared with placebo, taken twice daily, for the treatment of pseudobulbar affect over a 12-week period in multiple sclerosis patients.

METHODS

A total of 150 patients were randomized in a double-blind, placebo-controlled study to assess pseudobulbar affect with the validated Center for Neurologic Study-Lability Scale. Each patient also recorded the number of episodes experienced between visits, estimated quality of life and quality of relationships on visual analog scales, and completed a pain rating scale.

RESULTS

Patients receiving DM/Q had greater reductions in Center for Neurologic Study-Lability Scale scores than those receiving placebo (p < 0.0001) at all clinic visits (days 15, 29, 57, and 85). All secondary end points also favored DM/Q, including the number of crying or laughing episodes (p <or= 0.0077), quality of life (p < 0.0001), quality of relationships (p = 0.0001), and pain intensity score (p = 0.0271). DM/Q was well tolerated; only dizziness occurred with greater frequency than with placebo.

INTERPRETATION

Results in multiple sclerosis patients were similar to those of a previous study in amyotrophic lateral sclerosis, demonstrating that DM/Q may be beneficial in treating potentially disabling pseudobulbar affect in a variety of neurological disorders.