N-Methyl-D-Aspartate (NMDA) Antagonists—S(+)-ketamine, Dextrorphan, and Dextromethorphan—Act as Calcium Antagonists on Bovine Cerebral Arteries

Dextromethorphan Reduces Oxidative Stress and Inhibits Uremic Artery Calcification

Medial vascular calcification has emerged as a key factor contributing to cardiovascular mortality in patients with chronic kidney disease (CKD). Vascular smooth muscle cells (VSMCs) with osteogenic transdifferentiation play a role in vascular calcification. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors reduce reactive oxygen species (ROS) production and calcified-medium-induced calcification of VSMCs. This study investigates the effects of dextromethorphan (DXM), an NADPH oxidase inhibitor, on vascular calcification. We used in vitro and in vivo studies to evaluate the effect of DXM on artery changes in the presence of hyperphosphatemia. The anti-vascular calcification effect of DXM was tested in adenine-fed Wistar rats. High-phosphate medium induced ROS production and calcification of VSMCs. DXM significantly attenuated the increase in ROS production, the decrease in ATP, and mitochondria membrane potential during the calcified-medium-induced VSMC calcification process (p < 0.05). The protective effect of DXM in calcified-medium-induced VSMC calcification was not further increased by NADPH oxidase inhibitors, indicating that NADPH oxidase mediates the effect of DXM. Furthermore, DXM decreased aortic calcification in Wistar rats with CKD. Our results suggest that treatment with DXM can attenuate vascular oxidative stress and ameliorate vascular calcification.

AVP-786 as a promising treatment option for Alzheimer's Disease including agitation

INTRODUCTION

To date, there is no FDA-approved treatment for agitation in Alzheimer's disease (AD). Medications currently used off-label have modest clinical efficacy and serious side effects.

AREAS COVERED

The authors review the pharmacology, mechanism of action, pharmacokinetics, efficacy, safety and tolerability data of AVP-786, for the treatment of agitation in AD.

EXPERT OPINION

AVP-786, the deuterated form of dextromethorphan/quinidine (AVP-923) which is an approved treatment for Pseudo-Bulbar Affect, emerges as a promising and safe treatment for agitation in AD. Deuteration is an innovative technology that accelerates drug development by conducting faster and less costly clinical trials. No phase II trial was conducted with AVP-786 for the treatment of agitation in AD; the decision to expedite the development of this drug was based on a successful phase II study with AVP-923. Phase III trials with AVP-786 (TRIAD-1 and TRIAD-2) showed mixed findings probably due to the difference in study design. Future phase III studies should use innovative study designs such as the Sequential Parallel Comparison Design to mitigate high placebo response, and the Cohen-Mansfield Agitation Inventory for agitation assessment. They should also include positron emission tomography studies to assess occupancy of various receptors in the brain after AVP-786 is administered.

Regulation of cytochrome P450 gene expression by ketamine: a review

INTRODUCTION

Although used as an anesthetic drug for decades, ketamine appears to have garnered renewed interest due to its potential therapeutic uses in pain therapy, neurology, and psychiatry. Ketamine undergoes extensive oxidative metabolism by cytochrome P450 (CYP) enzymes. Considerable efforts have been expended to elucidate the ketamine-induced regulation of CYP gene expression. The safety profile of chronic ketamine administration is still unclear. Understanding how ketamine regulates CYP gene expression is clinically meaningful. Areas covered: In this article, the authors provide a brief review of clinical applications of ketamine and its metabolism by CYP enzymes. We discuss the effects of ketamine on the regulation of CYP gene expression, exploring aspects of cytoskeletal remodeling, mitochondrial functions, and calcium homeostasis. Expert opinion: Ketamine may inhibit CYP gene expression through inhibiting calcium signaling, decreasing ATP levels, producing excessive reactive oxygen species, and subsequently perturbing cytoskeletal dynamics. Further research is still needed to avoid possible ketamine-drug interactions during long-term use in the clinic.

Multiple Actions of Phencyclidine and (+)MK-801 on Isolated Bovine Cerebral Arteries

This study examines the direct effects of 3 noncompetitive N-methyl-D-aspartate receptor antagonists, phencyclidine (PCP), (+)MK-801, and (-)MK-801, on bovine middle cerebral arteries (BMCA). Rings of BMCA were mounted in isolated tissue chambers equipped with isometric tension transducers to obtain pharmacologic dose-response curves. In the absence of endogenous vasoconstrictors, the 3 N-methyl-D-aspartate antagonists each produced direct constriction of BMCA. The thromboxane A2 receptor antagonist SQ-29,548, the TxA2 synthase inhibitor furegrelate, the calcium antagonist nimodipine, and calcium-deficient media all inhibited maximal phencyclidine or (+)MK-801-induced constriction. Direct constriction by PCP or (+)MK-801 was independent of the presence of endothelium. When BMCA were preconstricted with potassium-depolarizing solution, PCP, (+)MK-801, and (-)MK-801 each produced only concentration-dependent relaxation. When BMCA were preconstricted with the stable TxA2 analog U-46,619 and exposed to increasing concentrations of PCP, (+)MK-801, or (-)MK-801, tension increased. Thromboxane A2 may contract BMCA by acting as a potassium channel blocker; iberiotoxin and tetraethylammonium both constrict BMCA. In Ca-deficient media containing either potassium or U-46,619, phencyclidine and (+)MK-801 each produced competitive inhibition of subsequent Ca-induced constriction. In additional experiments, arterial strips were mounted in isolated tissue chambers to directly measure calcium uptake, using Calcium as a radioactive tracer. Both phencyclidine and (+)MK-801 blocked potassium-stimulated or U-46,619-stimulated Ca uptake into arterial strips. These results suggest that phencyclidine and (+)MK-801 have 2 separate actions on BMCA. They may constrict arterial rings by releasing TxA2 from cerebrovascular smooth muscle, and relax arterial rings by acting as calcium antagonists.

Modulation of N-methyl-d-aspartate receptors in isolated rat heart

Considering the limited data on the role of NMDA-Rs in the cardiovascular system, the aim of the present study was to examine the effects of NMDA and DL-Hcy TLHC, alone and in combination with glycine, memantine, and ifenprodil, in the isolated rat heart. The hearts of Wistar albino rats were retrogradely perfused according to the Langendorff technique at a constant perfusion pressure. The experimental protocol for all experimental groups included the stabilization period, application of estimated substance for 5 min, followed by a washout period of 10 min. Using a sensor placed in the left ventricle, we registered the following parameters of myocardial function: dp/dt_max, dp/dt_min, SLVP, DVLP, HR; CF was measured using flowmetry). We estimated the following oxidative stress biomarkers in the coronary venous effluent using spectrophotometry: TBARS, NO₂^-, O₂^-, and H₂O₂. NMDA alone did not induce any change in any of the observed parameters, while DL-Hcy TLHC alone, as well as a combined application of NMDA and DL-Hcy TLHC with glycine, induced a reduction of most cardiodynamic parameters. Memantine and ifenprodil induced a reduction of cardiodynamic parameters and CF, as well as some oxidative stress biomarkers.

Ketamine modulation of the haemodynamic response to spreading depolarization in the gyrencephalic swine brain

Spreading depolarization (SD) generates significant alterations in cerebral haemodynamics, which can have detrimental consequences on brain function and integrity. Ketamine has shown an important capacity to modulate SD; however, its impact on SD haemodynamic response is incompletely understood. We investigated the effect of two therapeutic ketamine dosages, a low-dose of 2 mg/kg/h and a high-dose of 4 mg/kg/h, on the haemodynamic response to SD in the gyrencephalic swine brain. Cerebral blood volume, pial arterial diameter and cerebral blood flow were assessed through intrinsic optical signal imaging and laser-Doppler flowmetry. Our findings indicate that frequent SDs caused a persistent increase in the baseline pial arterial diameter, which can lead to a diminished capacity to further dilate. Ketamine infused at a low-dose reduced the hyperemic/vasodilative response to SD; however, it did not alter the subsequent oligemic/vasoconstrictive response. This low-dose did not prevent the baseline diameter increase and the diminished dilative capacity. Only infusion of ketamine at a high-dose suppressed SD and the coupled haemodynamic response. Therefore, the haemodynamic response to SD can be modulated by continuous infusion of ketamine. However, its use in pathological models needs to be explored to corroborate its possible clinical benefit.

Sedation of Patients with Acute Aneurysmal Subarachnoid Hemorrhage with Ketamine Is Safe and Might Influence the Occurrence of Cerebral Infarctions Associated with Delayed Cerebral Ischemia

BACKGROUND

Ketamine has neuroprotective characteristics as well as beneficial cardiocirculatory properties and may thus reduce vasopressor consumption. In contrast, sedation with ketamine (like any other sedative drug) has side effects. This study assesses the influence of ketamine on intracranial pressure (ICP), on the consumption of vasopressors in induced hypertension therapy, and on the occurrence of delayed cerebral ischemia (DCI)-associated cerebral infarctions, with particular focus on the complications of sedation in patients with aneurysmal subarachnoid hemorrhage (SAH).

METHODS

This is a retrospective, observational study. Sixty-five patients with SAH who underwent a period of sedation were included. The clinical course variables (Richmond Agitation and Sedation scale score, ICP values, consumption of vasopressors, complications of sedation, outcome, and other clinical parameters) were analyzed. Cranial computed tomography results were analyzed.

RESULTS

Forty-one patients underwent sedation including ketamine (63.1%). Ketamine decreased the ICP in 92.7% of the cases. Vasopressors was reduced in 53.6%. DCI-associated cerebral infarctions occurred significantly less often in the patient cohort being treated with sedation including ketamine (7.3% vs. 25% in the nonketamine group; P = 0.04). The rate of major complications was not higher in the ketamine group. Outcome was not different regarding the groups if they were sedated with or without ketamine.

CONCLUSIONS

Ketamine decreases the ICP and is not associated with a higher rate of complications. The rate of DCI-associated cerebral infarctions was lower in the ketamine group. Ketamine administration led to a reduction of vasopressors used for induced hypertension.

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.

Intravenous dextromethorphan/quinidine inhibits activity of dura-sensitive spinal trigeminal neurons in rats

BACKGROUND

Migraine is a chronic neurological disorder characterized by episodes of throbbing headaches. Practically all medications currently used in migraine prophylaxis have a number of substantial disadvantages and use limitations. Therefore, the further search for principally new prophylactic antimigraine agents remains an important task. The objective of our study was to evaluate the effects of a fixed combination of dextromethorphan hydrobromide and quinidine sulphate (DM/Q) on activity of the spinal trigeminal neurons in an electrophysiological model of trigemino-durovascular nociception.

METHODS

The study was performed in 15 male Wistar rats, which were anaesthetized with urethane/α-chloralose and paralysed using pipecuronium bromide. The effects of cumulative intravenous infusions of DM/Q (three steps performed 30 min apart, 15/7.5 mg/kg of DM/Q in 0.5 mL of isotonic saline per step) on ongoing and dural electrical stimulation-induced neuronal activities were tested in a group of eight rats over 90 min. Other seven animals received cumulative infusion of equal volumes of saline and served as control.

RESULTS

Cumulative administration of DM/Q produced steady suppression of both the ongoing activity of the spinal trigeminal neurons and their responses to electrical stimulation of the dura mater.

CONCLUSIONS

It is evident that the observed DM/Q-induced suppression of trigeminal neuron excitability can lead to a reduction in nociceptive transmission from meninges to higher centres of the brain. Since the same mechanism is believed to underlie the pharmacodynamics of many well-known antimigraine drugs, results of the present study enable us to anticipate the potential efficacy of DM/Q in migraine.

An extension of hypotheses regarding rapid-acting, treatment-refractory, and conventional antidepressant activity of dextromethorphan and dextrorphan

It was previously hypothesized that dextromethorphan (DM) and dextrorphan (DX) may possess antidepressant properties, including rapid and conventional onsets of action and utility in treatment-refractory depression, based on pharmacodynamic similarities to ketamine. These similarities included sigma-1 (σ(1)) agonist and NMDA antagonist properties, calcium channel blockade, muscarinic binding, serotonin transporter (5HTT) inhibition, and μ receptor potentiation. Here, six specific hypotheses are developed in light of additional mechanisms and evidence. Comparable potencies to ketamine for DM and DX are detailed for σ(1) (DX>DM>ketamine), NMDA PCP site (DX>ketamine>DM), and muscarinic (DX>ketamine>>>>DM) receptors, 5HTT (DM>DX≫ketamine), and NMDA antagonist potentiation of μ receptor stimulation (DM>ketamine). Rapid acting antidepressant properties of DM include NMDA high-affinity site, NMDR-2A, and functional NMDR-2B receptor antagonism, σ(1) stimulation, putative mTOR activation (by σ(1) stimulation, μ potentiation, and 5HTT inhibition), putative AMPA receptor trafficking (by mTOR activation, PCP antagonism, σ(1) stimulation, μ potentiation, and 5HTT inhibition), and dendritogenesis, spinogenesis, synaptogenesis, and neuronal survival by NMDA antagonism and σ(1) and mTOR signaling. Those for dextrorphan include NMDA high-affinity site and NMDR-2A antagonism, σ(1) stimulation, putative mTOR activation (by σ(1) stimulation and ß adrenoreceptor stimulation), putative AMPA receptor trafficking (by mTOR activation, PCP antagonism, σ(1) stimulation, ß stimulation, and μ antagonism), and dendritogenesis, spinogenesis, synaptogenesis, and neuronal survival by NMDA antagonism and σ(1) and mTOR signaling. Conventional antidepressant properties for dextromethorphan and dextrorphan include 5HTT and norepinephrine transporter inhibition, σ(1) stimulation, NMDA and PCP antagonism, and possible serotonin 5HT1b/d receptor stimulation. Additional properties for dextromethorphan include possible presynaptic α(2) adrenoreceptor antagonism or postsynaptic α(2) stimulation and, for dextrorphan, ß stimulation and possible muscarinic and μ antagonism. Treatment-refractory depression properties include increased serotonin and norepinephrine availability, PCP, NMDR-2B, presynaptic alpha-2 antagonism, and the multiplicity of other antidepressant receptor mechanisms. Suggestions for clinical trials are provided for oral high-dose dextromethorphan and Nuedexta (dextromethorphan combined with quinidine to block metabolism to dextrorphan, thereby increasing dextromethorphan plasma concentrations). Suggestions include exclusionary criteria, oral dosing, observation periods, dose-response approaches, and safety and tolerability are considered. Although oral dextromethorphan may be somewhat more likely to show efficacy through complementary antidepressant mechanisms of dextrorphan, a clinical trial will be more logistically complex than one of Nuedexta due to high doses and plasma level variability. Clinical trials may increase our therapeutic armamentarium and our pharmacological understanding of treatment-refractory depression and antidepressant onset of action.

Dextromethorphan as a potential rapid-acting antidepressant

Dextromethorphan shares pharmacological properties in common with antidepressants and, in particular, ketamine, a drug with demonstrated rapid-acting antidepressant activity. Pharmacodynamic similarities include actions on NMDA, μ opiate, sigma-1, calcium channel, serotonin transporter, and muscarinic sites. Additional unique properties potentially contributory to an antidepressant effect include actions at ß, alpha-2, and serotonin 1b/d receptors. It is therefore, hypothesized that dextromethorphan may have antidepressant efficacy in bipolar, unipolar, major depression, psychotic, and treatment-resistant depressive disorders, and may display rapid-onset of antidepressant response. An antidepressant response may be associated with a positive family history of alcoholism, prediction of ketamine response, increased AMPA-to-NMDA receptor activity ratio, antidepressant properties in animal models of depression, reward system activation, enhanced erythrocyte magnesium concentration, and correlation with frontal μ receptor binding potential. Clinical trials of dextromethorphan in depressive disorders, especially treatment-resistant depression, now seem warranted.