The anti-parkinsonian drug amantadine inhibits the N-methyl-D-aspartic acid-evoked release of acetylcholine from rat neostriatum in a non-competitive way

A review on natural products with cage-like structure

Natural products with diverse structures and significant biological activities are essential sources of drug lead compounds, and play an important role in the research and development of innovative drugs. Cage-like compounds have various structures and are widely distributed in nature, especially caged xanthones isolated from Garcinia genus, paeoniflorin and its derivatives isolated from Paeonia lactiflora Pall, tetrodotoxin (TTX) and its derivatives, and so on. In recent years, the development and utilization of cage-like compounds have been a research hotspot in chemistry, biology and other fields due to their special structures and remarkable biological activities. In this review, we mainly summarized the cage-like compounds with various structures found and isolated from natural drugs since 1956, summarized its broad biological activities, and introduced the progress in the biosynthesis of some compounds, so as to provide a reference for the discovery of more novel compounds, and the development and application of innovative drugs.

Amantadine: reappraisal of the timeless diamond-target updates and novel therapeutic potentials

The aim of the current review was to provide a new, in-depth insight into possible pharmacological targets of amantadine to pave the way to extending its therapeutic use to further indications beyond Parkinson's disease symptoms and viral infections. Considering amantadine's affinities in vitro and the expected concentration at targets at therapeutic doses in humans, the following primary targets seem to be most plausible: aromatic amino acids decarboxylase, glial-cell derived neurotrophic factor, sigma-1 receptors, phosphodiesterases, and nicotinic receptors. Further three targets could play a role to a lesser extent: NMDA receptors, 5-HT3 receptors, and potassium channels. Based on published clinical studies, traumatic brain injury, fatigue [e.g., in multiple sclerosis (MS)], and chorea in Huntington's disease should be regarded potential, encouraging indications. Preclinical investigations suggest amantadine's therapeutic potential in several further indications such as: depression, recovery after spinal cord injury, neuroprotection in MS, and cutaneous pain. Query in the database http://www.clinicaltrials.gov reveals research interest in several further indications: cancer, autism, cocaine abuse, MS, diabetes, attention deficit-hyperactivity disorder, obesity, and schizophrenia.

Recent Advances in the Pharmacology of Tardive Dyskinesia

Tardive dyskinesia (TD) is a syndrome of abnormal involuntary movements that follows treatment with dopamine D2-receptor antagonists. Recent approval of vesicular monoamine transporter-2 (VMAT2) inhibitors offers hope for reducing the impact of TD. Although these drugs represent a significant advance in patient care and a practical step forward in providing relief for patients with TD, understanding of the pharmacology of TD that could inform future research to prevent and reverse TD remains incomplete. This review surveys evidence for the effectiveness of VMAT2 inhibitors and other agents in the context of theories of pathogenesis of TD. In patients for whom VMAT2 inhibitors are ineffective or intolerable, as well as for extending therapeutic options and insights regarding underlying mechanisms, a review of clinical trial results examined as experimental tests of etiologic hypotheses is worthwhile. There are still compelling reasons for further investigations of the pharmacology of TD, which could generate alternative preventive and potentially curative treatments. Finally, benefits from novel drugs are best realized within an overall treatment strategy addressing the condition and needs of individual patients.

Amantadine Extended-Release (GOCOVRI™): A Review in Levodopa-Induced Dyskinesia in Parkinson's Disease

Amantadine extended-release (ER) capsules (GOCOVRI^™) are approved in the USA for the treatment of dyskinesia in patients with Parkinson's disease (PD) receiving levodopa-based therapy, with or without concomitant dopaminergic medications. With a recommended dosage of 274 mg once daily at bedtime, this new formulation of amantadine allows a more gradual time to peak plasma amantadine concentration and higher drug concentrations in the morning and throughout the day, the time period when levodopa-induced dyskinesia (LID) is the most problematic. In 13-week (EASE LID 3) and 25-week (EASE LID), randomized, double-blind phase III trials, once-daily amantadine ER 274 mg capsules significantly improved levodopa-induced dyskinesia (LID), while also increasing ON time without troublesome dyskinesia and reducing OFF time and ON time with troublesome dyskinesia from the morning and throughout the day, compared with placebo. In the ongoing, longer-term EASE LID 2 study (with interim results reported for up to 64 weeks), patients previously treated with amantadine ER maintained improvements in LID, as per patient-reported Unified Dyskinesia Rating Scale (UDysRS) scoring and ON/OFF times. Amantadine ER was generally well tolerated, with most adverse events (AEs) being transient and mild or moderate in severity. The most common (incidence > 15%) treatment-related AEs in the placebo-controlled trials were hallucinations, dizziness, dry mouth and peripheral oedema. While long-term data are needed to establish durability of response and safety, including the completion of the ≈ 2-year EASE LID 2 study, current evidence indicates that amantadine ER is an effective treatment option to consider in the management of LID in PD patients.

Efficacy and safety of amantadine for the treatment of L-DOPA-induced dyskinesia

L-DOPA induced dyskinesias (LIDs) may affect up to 40% of Parkinson's disease (PD) and impact negatively health-related quality of life. Amantadine has demonstrated significant antidyskinetic effects in animal PD models and in randomized double-blind placebo-controlled trials (RCTs) in patients with PD. These effects are thought to be related to the blockade of NMDA receptors modulating cortico-striatal glutamatergic-dopaminergic interactions involved in the genesis of LIDs. There are three pharmaceutical forms of amantadine currently available in the market: an oral immediate-release (IR) formulation, which is widely available; an extended-release (ER) formulation (ADS-5102) which has been recently developed and approved by the FDA; and an intravenous infusion (IV) solution, which is not commonly used in clinical practice. RCTs with amantadine IR or ER, involving more than 650 patients have shown consistent and long-lasting reductions in LIDs. Interestingly, ADS-5102 not only reduced LIDs, but also reduced significantly at the same time the duration of daily OFF-time, a unique finding compared with other antiparkinsonian medications that usually reduce time spent OFF at the cost of worsening of LIDs. Amantadine IR might also have possible effects on other PD symptoms such as apathy or fatigue. The most common adverse reactions with amantadine are constipation, cardiovascular dysfunction including QT prolongation, orthostatic hypotension and edema, neuropsychiatric symptoms such as hallucinations, confusion and delirium, nausea and livedo reticularis. Corneal degeneration is rare but critical. In summary, amantadine immediate and extended-release are effective and safe for the treatment of LIDs.

Cell Cycle-independent Role of Cyclin D3 in Host Restriction of Influenza Virus Infection

To identify new host factors that modulate the replication of influenza A virus, we performed a yeast two-hybrid screen using the cytoplasmic tail of matrix protein 2 from the highly pathogenic H5N1 strain. The screen revealed a high-score interaction with cyclin D3, a key regulator of cell cycle early G₁ phase. M2-cyclin D3 interaction was validated through GST pull-down and recapitulated in influenza A/WSN/33-infected cells. Knockdown of Ccnd3 by small interfering RNA significantly enhanced virus progeny titers in cell culture supernatants. Interestingly, the increase in virus production was due to cyclin D3 deficiency per se and not merely a consequence of cell cycle deregulation. A combined knockdown of Ccnd3 and Rb1, which rescued cell cycle progression into S phase, failed to normalize virus production. Infection by influenza A virus triggered redistribution of cyclin D3 from the nucleus to the cytoplasm, followed by its proteasomal degradation. When overexpressed in HEK 293T cells, cyclin D3 impaired binding of M2 with M1, which is essential for proper assembly of progeny virions, lending further support to its role as a putative restriction factor. Our study describes the identification and characterization of cyclin D3 as a novel interactor of influenza A virus M2 protein. We hypothesize that competitive inhibition of M1-M2 interaction by cyclin D3 impairs infectious virion formation and results in attenuated virus production. In addition, we provide mechanistic insights into the dynamic interplay of influenza virus with the host cell cycle machinery during infection.

Amantadine-induced patulous eustachian tubes in Parkinson's disease

Patulous Eustachian tube (PET) is a common condition that produces symptoms of aural fullness and autophony. We describe a Parkinson's disease (PD) patient that experienced a reversible bilateral patulous (hyperpatent) Eustachian tube syndrome induced by treatment with amantadine hydrochloride. The clinical features, relevant anatomy and physiology, and associated risk factors for PET are reviewed.

Classifying risk factors for dyskinesia in Parkinson's disease

BACKGROUND

Currently there is no classification of risk factors applicable to an individual patient with Parkinson's disease for the development of dyskinesia.

METHODS

We conducted literature search to identify and classifying risk factors into groups - (a) intrinsic vs extrinsic and (b) modifiable vs non-modifiable.

RESULTS

Younger age, young age of onset and severity of PD are major intrinsic non-modifiable risk factors for dyskinesia, female gender is another factor but not independent of other factors. Genetic expression and plasticity may determine pre-disposition to age of onset of PD and dyskinesia, these are currently non-modifiable factors arising due to an interaction of intrinsic and extrinsic factors. Lower initial body weight and weight loss during the course of the disease increase the risk of dyskinesia. Levodopa dose per kilogram body weight is a more significant risk factor than absolute levodopa dose. Early use of longer acting non-levodopa (i.e. dopamine agonists) medications delays the onset of dyskinesia. Interaction between body weight, levodopa dose and mode and duration of drug delivery is a significant modifiable factor.

CONCLUSION

Dyskinesia in PD arises as a consequence of the interaction of intrinsic versus extrinsic and modifiable versus non-modifiable factors. Identification and manipulation of modifiable factors for an individual patient may reduce the risk and burden of dyskinesia. Adjustment of levodopa dose according to body weight during the course of the disease seems to be a significant modifiable risk factor for dyskinesia.

Cocaine-induced neuroadaptations in glutamate transmission: potential therapeutic targets for craving and addiction

A growing body of evidence indicates that repeated exposure to cocaine leads to profound changes in glutamate transmission in limbic nuclei, particularly the nucleus accumbens. This review focuses on preclinical studies of cocaine-induced behavioral plasticity, including behavioral sensitization, self-administration, and the reinstatement of cocaine seeking. Behavioral, pharmacological, neurochemical, electrophysiological, biochemical, and molecular biological changes associated with cocaine-induced plasticity in glutamate systems are reviewed. The ultimate goal of these lines of research is to identify novel targets for the development of therapies for cocaine craving and addiction. Therefore, we also outline the progress and prospects of glutamate modulators for the treatment of cocaine addiction.

Modulation of human motor cortex excitability by single doses of amantadine

Amantadine-sulfate has been used for several decades to treat acute influenza A, Parkinson's disease (PD), and acute or chronic drug-induced dyskinesia. Several mechanisms of actions detected in vivo/in vitro including N-methyl-D-aspartate (NMDA)-receptor antagonism, blockage of potassium channels, dopamine receptor agonism, enhancement of noradrenergic release, and anticholinergic effects have been described. We used transcranial magnetic stimulation (TMS) to evaluate the effect of single doses of amantadine on human motor cortex excitability in normal subjects. Using a double-blind, placebo-controlled, crossover study design, motor thresholds, recruitment curves, cortical stimulation-induced silent period (CSP), short intracortical inhibition (ICI), intracortical facilitation (ICF), and late inhibition (L-ICI) in 14 healthy subjects were investigated after oral doses of 50 and 100 mg amantadine with single and paired pulse TMS paradigms. Spinal cord excitability was investigated by distal latencies and M-amplitudes of the abductor digiti minimi muscle. After intake of amantadine, a significant dose-dependent decrease of ICF was noticed as well as a significant increase of L-ICI as compared to placebo. The effect on ICF and L-ICI significantly correlated with amantadine serum levels. ICI was slightly increased after amantadine intake, but the effect failed to be significant. Furthermore, amantadine had no significant effects on motor thresholds, MEP recruitment curves, CSP, or peripheral excitability. In conclusion, a low dose of amantadine is sufficient in modulating human motor cortex excitability. The decrease of ICF and increase of L-ICI may reflect glutamatergic modulation or a polysynaptic interaction of glutamatergic and GABA-ergic circuits. Although amantadine has several mechanisms of action, the NMDA-receptor antagonism seems to be the most relevant effect on cortical excitability. As L-ICI can be influenced by this type of drug, it may be an interesting parameter for studies of motor learning and use-dependent plasticity.

Inhibition of influenza-virus-induced cytopathy by sialylglycoconjugates

The anti-viral activity of gangliosides such as SPG (sialylparagloboside), GD1a, GM3, and GM4 was assessed by inhibition of the cytopathy of MDCK cells due to infection with the influenza virus A/PR/8/34. The inhibitory effect was in the following sequence: SPG>GD1a>GM3>GM4. The IC50 of SPG and GD1a was 7 and 70 microM, respectively, indicating that they are more effective than the representative inhibitor amantadine. Although 3'-sialyllactose (3'-SL) and 3'-sialyllactosamine (3'-SLN), which are identical to the terminal trisaccharides of GM3 and SPG, respectively, did not show any inhibitory effect, introduction of an amino group to the reducing end of 3'-SL following amidation with lauroyl chloride gave the inhibitory potency, which was comparable to that of GM3. These results suggest that the viral hemagglutinin recognizes exogenous sialyloligosaccharides rather than inherent sialyloligosaccharides expressed on MDCK cells, since introduction of the hydrophobic moiety to oligosaccharides might cause micelle formation.

Emerging pharmacological strategies in the fight against cocaine addiction

Cocaine addiction continues to be an important public health problem worldwide. At present, there are no proven pharmacotherapies for cocaine addiction. The studies reviewed here revealed a number of emerging targets for cocaine pharmacotherapy. First, disulfiram, a medication with dopaminergic effects, reduced cocaine use in a number of clinical trials. Second, GABA medications, tiagabine and topiramate, were found promising in clinical trials. Third, a beta-adrenergic blocker, propranolol, may be effective especially among cocaine-addicted individuals with high withdrawal severity. Fourth, treatment with a stimulant medication, modafinil, has reduced cocaine use. Last, a cocaine vaccine that slows entry of cocaine into the brain holds promise. These promising findings need to be further tested in controlled clinical trials.

Effects of pre-treatment with amantadine on morphine induced antinociception during second phase formalin responses in rats

The clinically available NMDA-receptor antagonist drug, amantadine, has been shown to result in morphine sparing effects in humans after surgery. However, no data are available to describe the exact form of interaction. The present study aims to profile the possible effects of amantadine (0, 12.5, 25 or 50 mgkg(-1) i.p.) pre-treatment on morphine (0, 0.63, 1.25, 2.5 or 5 mgkg(-1) s.c.) induced antinociception in rats. The (automated) formalin test (5% formalin, 50 microl) was used to assess if amantadine enhances the antinociceptive activity of morphine. Possible motor impairment was assessed with a rotarod test. Morphine was measured in serum of amantadine or vehicle treated rats to search for possible pharmacokinetic interactions between amantadine and morphine. Isobolographic analysis provided evidence for a synergistic interaction between amantadine and morphine in the second phase of the formalin test. No evidence was found to indicate that amantadine induced motor impairment at the doses potentiating morphine during the second phase of the formalin test. There was no evidence for a pharmacokinetic interaction between amantadine and morphine. Since, the second phase of the formalin test is dependent on activation of the NMDA receptor system it is concluded that an antagonistic activity of amantadine at the NMDA receptor most likely contributes to the synergistic interaction observed between amantadine and morphine in rats.

Effect of amantadine on motor memory consolidation in humans

Motor skills, once learned, need to be consolidated over time in order to become resistant to disruption or interference. In some instances, the consolidation phase can also include spontaneous gains in performance even in the absence of further rehearsal on a motor task. Clinical and behavioral evidence suggest that N-methyl-D-aspartate (NMDA)-receptor activity is required for motor learning acquisition and behavioral synaptic plasticity. However, the involvement of NMDA receptors in motor consolidation, leading to stabilization of the recently formed motor memory, has not yet been assessed in humans. To address this issue, we used post-training administration of amantadine, a low-affinity NMDA-receptor channel blocker. In a double-blind design, 200 mg of amantadine or a matching placebo was given orally to two different groups of 11 healthy young volunteers each. The subjects were tested twice 24 h apart, using a motor adaptation paradigm consisting of an eight-target-pointing task. Comparison of the mean performance levels on this task revealed that subjects in both groups improved their performance levels significantly on Day 2 compared to Day 1, regardless of the treatment administered. Our data indicate that amantadine failed to block motor learning consolidation in subjects that had already learned the motor adaptation task. Thus, although required in some stages (e.g. acquisition) of motor memory processes, the present results suggest that NMDA-receptor activation may not be essential for consolidation of motor adaptation in humans.

Pharmacologic management of relapse prevention in addictive disorders

Substance use disorders are an important public health problem associated with significant mortality and morbidity. Effective maintenance pharmacotherapies are available for tobacco, alcohol, and opioid use disorders. For optimum treatment response, these medications should be used in conjunction with behavioral interventions. For other drugs of abuse, especially for cocaine, medication development is an active area of research. Further research is needed to develop new pharmacotherapies for substance use disorders and establish clinical guidelines on how to use these medications most effectively.

Open label study of the effect of amantadine on weight gain induced by olanzapine

The purpose of the present paper was to investigate the effects of the dopamine agonist amantadine in those patients with weight gain induced by olanzapine. An open trial was conducted in those patients who gained >3 kg in weight induced by olanzapine use. All subjects were evaluated by weight, body mass index (BMI), the Brief Psychiatric Rating Scale (BPRS), and the Extrapyramidal Symptom Rating Scale (ESRS) before and after the use of amantadine in addition to olanzapine. Twenty-five of 30 enrolled patients completed the present study. Mean bodyweight and BMI was increased by 6.44 +/- 4.42 kg and 5.04 +/- 3.47 kg/m2 significantly with olanzapine alone (P < 0.001). When amantadine and olanzapine were used together, the average weight and BMI decreased by 1.07 +/- 3.19 kg and 0.84 +/- 2.5 kg/m2, but did not have statistical significance. The average values of BPRS showed a significant decrease (P < 0.001). No significant changes were present in ESRS. Amantadine did not have an effect on weight gain induced by olanzapine. Randomized placebo-controlled prospective studies are needed.

Motor-learning impairment by amantadine in healthy volunteers

NMDA receptor antagonists impair learning and memory in animal models, presumably by inhibiting long-term potentiation in the motor cortex. Human studies are limited and restricted by the paucity of safe NMDA antagonists. Here, we investigated the contribution of glutamatergic neurotransmission to the capacity of acquiring motor-adaptation learning in humans. In a double-blind design, 200 mg of amantadine (a low-affinity NMDA receptor channel blocker) or a matching placebo were given orally to groups of 14 and 13 human healthy young volunteers, respectively. Blood samples were collected 3 h after treatment to assay plasma concentrations, and the subjects were then tested using a motor-adaptation paradigm consisting of an eight-target-pointing task. To rule out drug-related generalized impairments such sedation, tests measuring motor dexterity and attention were also administered pre- and post-treatment. Comparison of the mean performance levels on the motor-adaptation task revealed that subjects in the amantadine group performed at a lower level than those in the placebo group, but this difference did not reach significance. Interestingly, however, despite plasma amantadine concentrations being relatively low, ranging from 2.09 to 4.74 microM (mean=3.3 microM), they nevertheless correlated negatively with motor learning. Furthermore, when the amantadine group was divided into low-performance and high-performance subgroups, subjects in the former subgroup displayed mean amantadine concentrations 36% higher than the latter subgroup, and performed significantly worser than the placebo group. No change in performance was found on the motor-dexterity and attention tests. Altogether, our results lend support to the hypothesis that normal NMDA receptor function is necessary for the acquisition of motor adaptation.

Amantadine increases L-DOPA-derived extracellular dopamine in the striatum of 6-hydroxydopamine-lesioned rats

We investigated the effect of amantadine on L-DOPA-derived extracellular dopamine (DA) levels and aromatic L-amino acid decarboxylase (AADC) activity in the striatum of rats with nigrostriatal dopaminergic denervation by 6-hydroxydopamine (6-OHDA). Pretreatment with 30 mg/kg amantadine increased the cumulative amount of extracellular DA in the striatum of 6-OHDA-lesioned rats treated with 10 mg/kg benserazide and 50 mg/kg L-DOPA to 250% of that without amantadine (P<0.01). Under pretreatment with 10 mg/kg benserazide, AADC activity after 30 mg/kg amantadine administration was reduced to 43% of controls (P<0.01). Amantadine-induced increase in L-DOPA-derived extracellular DA provides the basis for the clinical usefulness of amantadine in combination with L-DOPA. However, the effect of amantadine on L-DOPA-derived extracellular DA may not be caused by changes in AADC activity.

Clinical pharmacokinetic and pharmacodynamic properties of drugs used in the treatment of Parkinson's disease

Current research in Parkinson's disease (PD) focuses on symptomatic therapy and neuroprotective interventions. Drugs that have been used for symptomatic therapy are levodopa, usually combined with a peripheral decarboxylase inhibitor, synthetic dopamine receptor agonists, centrally-acting antimuscarinic drugs, amantadine, monoamine oxidase-B (MAO-B) inhibitors and catechol-O-methyltransferase (COMT) inhibitors. Drugs for which there is at least some evidence for neuroprotective effect are certain dopamine agonists, amantadine and MAO-B inhibitors (selegiline). Levodopa remains the most effective drug for the treatment of PD. Several factors contribute to the complex clinical pharmacokinetics of levodopa: erratic absorption, short half-life, peripheral O-methylation and facilitated transport across the blood-brain barrier. In patients with response fluctuations to levodopa, the concentration-effect curve becomes steeper and shifts to the right compared with patients with stable response. Pharmacokinetic-pharmacodynamic modelling can affect decisions regarding therapeutic strategies. The dopamine agonists include ergot derivatives (bromocriptine, pergolide, lisuride and cabergoline), non-ergoline derivatives (pramipexole, ropinirole and piribedil) and apomorphine. Most dopamine agonists have their specific pharmacological profile. They are used in monotherapy and as an adjunct to levodopa in early and advanced PD. Few pharmacokinetic and pharmacodynamic data are available regarding centrally acting antimuscarinic drugs. They are characterised by rapid absorption after oral intake, large volume of distribution and low clearance relative to hepatic blood flow, with extensive metabolism. The mechanism of action of amantadine remains elusive. It is well absorbed and widely distributed. Since elimination is primarily by renal clearance, accumulation of the drug can occur in patients with renal dysfunction and dosage reduction must be envisaged. The COMT inhibitors entacapone and tolcapone dose-dependently inhibit the formation of the major metabolite of levodopa, 3-O-methyldopa, and improve the bioavailability and reduce the clearance of levodopa without significantly affecting its absorption. They are useful adjuncts to levodopa in patients with end-of-dose fluctuations. The MAO-B inhibitor selegiline may have a dual effect: reducing the catabolism of dopamine and limiting the formation of neurotoxic free radicals. The pharmacokinetics of selegiline are highly variable; it has low bioavailability and large volume of distribution. The oral clearance is many-fold higher than the hepatic blood flow and the drug is extensively metabolised into several metabolites, some of them being active. Despite the introduction of several new drugs to the antiparkinsonian armamentarium, no single best treatment exists for an individual patient with PD. Particularly in the advanced stage of the disease, treatment should be individually tailored.

A screening trial of amantadine as a medication for cocaine dependence

This screening trial evaluated whether amantadine hydrochloride (100 mg bid) demonstrated sufficient clinical efficacy compared to placebo to recommend development as a pharmacotherapy for cocaine dependence. Participants were randomized to amantadine (n=34) or placebo (n=35) conditions in a 16-week, placebo-controlled, double blind trial with three times per week group counseling. Amantadine-treated participants were retained significantly longer than placebo. Based on results of a joint probability index for urine drug testing results (i.e. the proportion of cocaine-metabolite free urine samples divided by the number of participants assigned to the condition), participants assigned to amantadine were found to be significantly more likely to be cocaine abstinent on the last day of 8-weeks of treatment than participants assigned to placebo. Results at the end of 16 weeks of treatment were similar. Standard measures of urine drug testing consistently favored the amantadine condition over placebo, although not at levels of statistical significance. There was no statistical significance infrequency or severity of reported adverse events by treatment condition. Participants assigned to amantadine exhibited greater reductions in global staff ratings of cocaine dependence severity from baseline to termination compared with placebo. There were no significant differences in frequency or severity of reported adverse events by treatment condition. These results provide moderate support for further study of amantadine for the treatment of cocaine dependence.

An O-glycoside of sialic acid derivative that inhibits both hemagglutinin and sialidase activities of influenza viruses

The compound Neu5Ac3alphaF-DSPE (4), in which the C-3 position was modified with an axial fluorine atom, inhibited the catalytic hydrolysis of influenza virus sialidase and the binding activity of hemagglutinin. The inhibitory activities to sialidases were independent of virus isolates examined. With the positive results obtained for inhibition of hemagglutination and hemolysis induced by A/Aichi/2/68 virus, the inhibitory effect of Neu5Ac3alphaF-DSPE (4) against MDCK cells was examined, and it was found that 4 inhibits the viral infection with IC50 value of 5.6 microM based on the cytopathic effects. The experimental results indicate that compound 4 not only inhibits the attachment of virus to the cell surface receptor but also disturbs the release of the progeny viruses from infected cells by inhibiting both hemagglutinin and sialidase of the influenza viruses. The study suggested that the compound is a new class of bifunctional drug candidates for the future chemotherapy of influenza.

Beneficial effects of amantadine on L-dopa-induced dyskinesias in Parkinson's disease

L-Dopa-induced dyskinesias constitute a challenge to the management of advanced Parkinson's disease. According to recent reports, treatment with the NMDA receptor antagonist amantadine may significantly diminish L-dopa-induced dyskinesias. In the present study, the effect of amantadine on L-dopa-induced dykinesias was assessed in a 5-week, double-blind crossover trial. Dyskinesia severity as assessed following oral L-dopa challenges and by self-scoring dyskinesia diaries were reduced approximately 50% after amantadine treatment compared with baseline or placebo phases. Similarly, dyskinesia assessments on the Unified Parkinson's Disease Rating Scale, part IV (items 32 and 33) also revealed significant improvement after treatment with amantadine. The magnitude of the L-dopa motor response to oral challenges was not different after amantadine or placebo treatment, and there was no significant reduction of daily off-time when patients received active treatment. These results confirm previous observations concerning the antidyskinetic potential of amantadine.

Stimulation of dopa decarboxylase activity in striatum of healthy human brain secondary to NMDA receptor antagonism with a low dose of amantadine

The efficacy of amantadine in alleviating motor symptoms of Parkinson's disease may be mediated in part by stimulation of cerebral dopa decarboxylase (DDC) activity, secondary to antagonism of N-methyl-D-aspartate (NMDA) type glutamate receptors. We tested the specific hypothesis that amantadine increases the decarboxylation rate of 6-[(18)F]fluoro-L-DOPA (FDOPA), an exogenous substrate for DDC, in healthy human brain. Radioactivity concentrations in brain tissue of neurologically normal volunteers (n = 5) injected intravenously with FDOPA ( approximately 4.5 mCi) were recorded by positron emission tomography (PET) for 120 min, first in a baseline condition, and again following three consecutive days of treatment with amantadine (100 mg/day, p.o.). Data from four telencephalic regions of interest containing appreciable DDC activity were analyzed with the tissue slope-intercept plot, using cerebellar cortex as the reference tissue, to estimate a coefficient of in situ FDOPA decarboxylation (k(3)(r), min(-1)). Mean estimates of k(3)(r) were increased following amantadine treatment in caudate nucleus (+12%), putamen (+28%), ventral striatum (+27%), and frontal cortex (+9%). For an initial confidence level of 95%, paired one-sided Student's t-tests with Bonferroni correction for multiple comparisons revealed a statistically significant drug effect in ventral striatum. Present results are consistent with stimulation of DDC activity in striatum of healthy human brain secondary to NMDA receptor antagonism with a low dose of amantadine, and suggest that this response is an important mechanism underlying the anti-parkinsonian properties of amantadine. Nonetheless, PET studies in parkinsonian patients using higher, clinically effective doses of amantadine may reveal more pronounced enhancements of cerebral DDC activity.

Involvement of the corticostriatal glutamatergic pathway in ethanol-induced ascorbic acid release in rat striatum

The mechanism of ethanol-induced ascorbic acid (AA) release in striatum is not well understood. In the present work, the possible involvement of NMDA receptors in the corticostriatal pathway was studied by microdialysis coupled to high performance liquid chromatography with electrochemical detection. Ethanol (3.0 g/kg i.p.) stimulated significant striatal AA release to more than 200% above the baseline. This effect of ethanol could be partially antagonized by amantadine, a non-selective NMDA receptor antagonist and dopamine releaser, at a dose of 200 mg/kg i.p. and significantly antagonized by MK-801, a non-competitive NMDA receptor antagonist, at the doses of 0.5 and 1.0 mg/kg i.p. Furthermore, deafferentation of the glutamatergic projection from cortex to striatum by undercutting the prefrontal cortex completely eliminated ethanol-induced AA release in rat striatum. The basal level of AA in striatum could only be reduced by high doses of MK-801, but not by low doses of MK-801, amantadine or decortication. The results further confirm that NMDA receptors are involved in ethanol-induced AA release and provide the first evidence for the necessity of the activation of corticostriatal glutamatergic pathway in ethanol-induced AA release in rat striatum.

Memantine is a clinically well tolerated N-methyl-D-aspartate (NMDA) receptor antagonist--a review of preclinical data

N-methyl-D-aspartate (NMDA) receptor antagonists have therapeutic potential in numerous CNS disorders ranging from acute neurodegeneration (e.g. stroke and trauma), chronic neurodegeneration (e.g. Parkinson's disease, Alzheimer's disease, Huntington's disease, ALS) to symptomatic treatment (e.g. epilepsy, Parkinson's disease, drug dependence, depression, anxiety and chronic pain). However, many NMDA receptor antagonists also produce highly undesirable side effects at doses within their putative therapeutic range. This has unfortunately led to the conclusion that NMDA receptor antagonism is not a valid therapeutic approach. However, memantine is clearly an uncompetitive NMDA receptor antagonist at therapeutic concentrations achieved in the treatment of dementia and is essentially devoid of such side effects at doses within the therapeutic range. This has been attributed to memantine's moderate potency and associated rapid, strongly voltage-dependent blocking kinetics. The aim of this review is to summarise preclinical data on memantine supporting its mechanism of action and promising profile in animal models of chronic neurodegenerative diseases. The ultimate purpose is to provide evidence that it is indeed possible to develop clinically well tolerated NMDA receptor antagonists, a fact reflected in the recent interest of several pharmaceutical companies in developing compounds with similar properties to memantine.

Direct inhibition of the N-methyl-D-aspartate receptor channel by dopamine and (+)-SKF38393

1. Dopamine is known to modulate glutamatergic synaptic transmission in the retina and in several brain regions by activating specific G-protein-coupled receptors. We have examined the possibility of a different type of mechanism for this modulation, one involving direct interaction of dopamine with ionotropic glutamate receptors. 2. Ionic currents induced by fast application of N-methyl-D-aspartate (NMDA) were recorded under whole-cell patch-clamp in cultured striatal, thalamic and hippocampal neurons of the rat and in retinal neurons of the chick. Dopamine at concentrations above 100 microM inhibited the NMDA response in all four neuron types, exhibiting an IC50 of 1.2 mM in hippocampal neurons. The time course of this inhibition was fast, developing in less than 100 ms. 3. The D1 receptor agonist (+)-SKF38393 mimicked the effect of dopamine, with an IC50 of 58.9 microM on the NMDA response, while the enantiomer (-)-SKF38393 was ineffective at 50 microM. However, the D1 antagonist R(+)-SCH23390 did not prevent the inhibitory effect of (+)-SKF38393. 4. The degree of inhibition by dopamine and (+)-SKF38393 depended on transmembrane voltage, increasing 2.7 times with a hyperpolarization of about 80 mV. The voltage-dependent block by dopamine was also observed in the presence of MgCl2 1 mM. 5. Single-channel recordings showed that the open times of NMDA-gated channels were shortened by (+)-SKF38393. 6. These data suggested that the site to which the drugs bound to produce the inhibitory effect was distinct from the classical D1-type dopamine receptor sites, possibly being located inside the NMDA channel pore. It is concluded that dopamine and (+)-SKF38393 are NMDA channel ligands.

Parkinson's Disease: Motor Fluctuations

Motor fluctuations represent important late complications of Parkinson's disease treated with levodopa. Although treatment of these problems has improved with the emergence of numerous pharmacologic and surgical therapies, the various options can make it confusing. Pharmacologic treatment is the first step. Polytherapy is often the rule in this case with a variety of agents available as adjunctive therapy with levodopa. These adjuncts include dopamine agonists (bromocriptine, pergolide, pramipexole, ropinirole), catechol-O-methyltransferase (COMT) inhibitors (tolcapone), controlled-release formulations of levodopa, monoamine oxidase (MAO) B inhibitors (selegiline), and amantadine. The treatment can consist of any of a number of combinations of these agents. No single algorithm can be used in all patients; therapy should be individualized. Physicians treating these patients need to be well versed in late complication patterns as well as the medications chosen. In addition, optimal doses vary, and often patients are considered treatment failures and taken off medications before reaching that level. In the more complicated cases, patients should be evaluated by specialists in movement disorders. With this in mind, some guidelines are offered for the pharmacologic approach to patients with fluctuating responses to medications. For simple wearing off, controlled-release levodopa (Sinemet CR, Dupont Pharmaceuticals, Wilmington, DE), COMT inhibitors, MAO inhibitors, and dopamine agonists are reasonable options. For more complicated fluctuations, dopamine agonists with limits on levodopa are the first choice, especially when dyskinesia is present; when dyskinesia is not a factor, COMT inhibitors may be used. For dyskinesia specifically, dopamine agonists or addition of amantadine can be helpful. Surgery should be a treatment of last resort for patients in whom medical therapy fails. Patients who are candidates for medial pallidotomy should be fluctuators with severe dyskinesia and "off" periods that have not improved with pharmacologic therapy. Thalamic deep brain stimulation (DBS) should be used only in patients with tremor-predominant disease and severe intractable tremor that is unresponsive to medication and occurs not only at rest but with posture and action as well. Surgical therapy should be performed only in centers with surgeons experienced in stereotactic techniques and movement disorder specialists to ensure that the appropriate patients come to surgery and that complications are kept to a minimum. Dietary adjustment has a limited role in treating advanced Parkinson's disease.

Motor fluctuations in Parkinson's disease: pathophysiology and treatment

At the initial stages of Parkinson's disease (PD), levodopa (LD) is able to reduce most motor symptoms and to significantly improve the patient's quality of life. However, in the vast majority of patients with prolonged LD usage, some decline in efficacy occurs and motor complications eventually begin to appear. These complications consist not only of daily fluctuations in the voluntary motor performance often accompanied by involuntary movements, but also of fluctuations in cognitive, autonomic, and sensory functions. Several recent studies on LD complications in PD have led to a better understanding of their pathophysiology and of the possible therapeutic interventions, and a summary of these findings is presented in this review. Different observations now suggest that postsynaptic pharmacodynamic factors play a major role in determining fluctuations in PD. Two explanations are given: chronic intermittent dopaminergic therapy may lead to postsynaptic receptor downregulation in PD; or, receptor changes in the striatum may occur independently of treatment as a result of structural adaptation of the postsynaptic dopaminergic system to the progressive decline of the nigrostriatal pathway. The hypothesis of reversible postsynaptic changes as the main mechanism underlying a fluctuating response to LD lends itself to a possible pharmacological manipulation of the dopaminergic response to reverse, or even avoid, motor fluctuations (initial monotherapy with dopamine agonists and early combination LD/dopamine agonists). The role of peripheral pharmacokinetics factors is also critical and the use of controlled release LD formulations, of monoamine oxidase (MAO)-B and of catechol-O-methyltransferase (COMT) inhibitors may all, to a different degree, improve such phenomena. In the last decade, there has been a resurgence in surgical therapies in advanced PD, due to higher levels of accuracy and safety provided by the new surgical devices, and to a more precise localization of the target areas allowed by the neurophysiological mapping techniques. The surgical procedures currently used in advanced PD are stereotactic brain lesions (internal globus pallidus and subthalamic nucleus), chronic brain stimulation (of the same nuclei) and striatal grafting of dopamine-producing cells. All these procedures have already shown their efficacy in the management of severe fluctuations in PD, but their indications, and relative advantages and disadvantages, are still the subject of considerable debate and controversy.

Budipine is a low affinity, N-methyl-D-aspartate receptor antagonist: patch clamp studies in cultured striatal, hippocampal, cortical and superior colliculus neurones

The NMDA receptor antagonistic effects of budipine were assessed using concentration- and patch-clamp techniques on cultured striatal, hippocampal, cortical and superior colliculus neurones. Inward current responses of striatal neurones to NMDA (200 microM) at -70 mV were antagonized by budipine in a concentration-dependent manner (50% inhibitory concentration (IC50) 59.4 +/- 10.7 microM, n = 17) with 24 times lower potency than memantine but similar potency to amantadine. In striatal neurones, budipine blocked outward currents at +70 mV with an IC50 of 827 microM, suggesting that the binding site is less deep in the channel (delta = 0.45) than for memantine. However, more detailed analysis of the fractional block by budipine 300 microM in hippocampal neurones gave a delta-value of 0.90, but revealed that 28% block is mediated at a voltage-independent site. This voltage-insensitive site was accessible in the absence of agonist. Budipine exhibited concentration-dependent open channel blocking kinetics (kappa(on) = 0.71 x 10(4) M(-1) s(-1)) whereas the fast offset rate was concentration-independent (kappa(off) = 0.63 s(-1)). Calculation of the ratio kappa(off)/kappa(on) revealed an apparent Kd value of 88.7 microM. Budipine, memantine and amantadine had similar effects against NMDA-induced currents in cultured hippocampal, cortical and superior colliculus neurones, although amantadine was somewhat more potent in cultured striatal neurones. The relevance of NMDA receptor antagonism to the anti-Parkinsonian effects of budipine remains to be established.

Aminoadamantanes as NMDA receptor antagonists and antiparkinsonian agents--preclinical studies

Aminoadamantanes such as 1-aminoadamantane (amantadine) and 1-amino-3,5-dimethyladamantane (memantine) are N-methyl-D-aspartate (NMDA) receptor antagonists which show antiparkinsonian-like activity in animal models and in Parkinson's patients. The issue of whether NMDA antagonism plays a role in the symptomatological antiparkinsonian activity of amantadine and memantine is addressed by comparing: behaviourally effective doses, serum/brain levels, and their potency as NMDA receptor antagonists. In the case of memantine, blockade of NMDA receptors is probably the only mechanism responsible for antiparkinsonian activity, whereas for amantadine the situation is clearly far more complex. There are a number of differences between memantine and amantadine both in vitro and in vivo, and although NMDA receptor antagonism certainly participates in the antiparkinsonian activity of amantadine, other effects, some of which are elusive, also play a role. Moreover, it has been suggested that the pathomechanism of Parkinson's disease involves excitotoxic processes and that treatment with NMDA receptor antagonists might also slow the progression of neurodegeneration. If this claim is true, such an effect could be achieved with amantadine and memantine which show neuroprotective activity in animals at therapeutically relevant doses.

Amantadine in the early treatment of cocaine dependence: a double-blind, placebo-controlled trial

A 4-week, double-blind, placebo-controlled trial of amantadine was conducted in 61 cocaine dependent outpatients. Subjects received 100 mg of amantadine 3 times daily. A follow-up visit was conducted at week 8. There were no significant differences between groups in treatment retention, or in the number of benzoylecgonine positive urine samples. Self-reported drug and alcohol use declined in both groups. At week 8 follow-up, self-reported drug use was significantly lower in the placebo group. Amantadine was not effective, and discontinuation of it may have been associated with an increase in cocaine use.

Comparative patch-clamp studies with freshly dissociated rat hippocampal and striatal neurons on the NMDA receptor antagonistic effects of amantadine and memantine

Patch- and concentration-clamp techniques were used to compare the effects of the uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists (+)-MK-801 (dizocilpine, (+)-5-methyl-10, 11-dihydro-5H-dibenzocyclohepten-5, 10-imine maleate), ketamine, memantine (1-amino-3,5-dimethyladamantane) and amantadine (1-amino-adamantane) on agonist-induced inward currents in freshly dissociated rat hippocampal and striatal neurons. In hippocampal neurons, ketamine (5 microM), menantine (10 microM) and amantadine (100 microM) selectively antagonized inward current responses to NMDA (500 microM plus glycine 5 microM) in a voltage-dependent manner without affecting responses to (s)-alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (100 microM) or gamma-aminobutyric acid (10 microM). The NMDA receptor antagonistic effect of all four agents was typical of open channel blockade. The kinetics of blockade/unblockade was inversely related to antagonist affinity. In hippocampal neurons amantadine was the least potent NMDA receptor antagonist (IC50 18.6 +/- 0.9 microM) and showed the fastest blocking kinetics, whereas (+)-MK-801 was the most potent (IC50 0.12 +/- 0.01 microM) and showed the slowest blocking kinetics. Memantine (IC50 1.04 +/- 0.26 microM) and ketamine (IC50 0.43 +/- 0.10 microM) were almost equipotent and had similar, intermediate blocking kinetics. In striatal neurons recorded under identical conditions (+)-MK-801, ketamine and memantine were 3- to 4-fold less potent whereas amantadine was somewhat more potent than on hippocampal neurons. This could offer an explanation for the better clinical profile of amantadine in Parkinson's disease, as therapeutically relevant concentrations of amantadine are likely to be more active in the striatum whereas memantine is likely to be more active in other structures.

Orphenadrine is an uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist: binding and patch clamp studies

Orphenadrine has been used as an antiparkinsonian, antispastic and analgesic drug for many years. Here we show that orphenadrine inhibits [3H]MK-801 binding to the phencyclidine (PCP) binding site of the N-methyl-D-aspartate (NMDA)-receptor in homogenates of postmortem human frontal cortex with a Ki-value of 6.0 +/- 0.7 microM. The NMDA receptor antagonistic effects of orphenadrine were assessed using concentration- and patch-clamp techniques on cultured superior colliculus neurones. Orphenadrine blocked open NMDA receptor channels with fast kinetics and in a strongly voltage-dependent manner. The IC50-value against steady state currents at -70 mV was 16.2 +/- 1.6 microM (n = 6). Orphenadrine exhibited relatively fast, concentration-dependent open channel blocking kinetics (Kon 0.013 +/- 0.002 10(6) M-1S-1) whereas the offset rate was concentration-independent (Koff 0.230 +/- 0.004 S-1). Calculation of the ratio Koff/Kon revealed an apparent Kd-value of 17.2 microM which is nearly identical to the IC50 calculated at equilibrium.

Synthesis and bioactivity studies of 1-adamantanamine derivatives of peptides

Small enkephalin-related peptides containing a 1-adamantanamine moiety coupled through an amide linkage at the C-terminus were synthesized. Several of the compounds showed high mu opioid activity and mu receptor selectivity. The new adamantanamine derivatives were also examined for antiviral activity against HIV-1 in a cell culture system. Some of them inhibited syncytia formation even when the antigen assay gave evidence for viral replication.