Memantine and Cholinesterase Inhibitors: Complementary Mechanisms in the Treatment of Alzheimer’s Disease

This review describes the preclinical mechanisms that may underlie the increased therapeutic benefit of combination therapy—with the N-methyl-d-aspartate receptor antagonist, memantine, and an acetylcholinesterase inhibitor (AChEI)—for the treatment of Alzheimer’s disease (AD). Memantine, and the AChEIs target two different aspects of AD pathology. Both drug types have shown significant efficacy as monotherapies for the treatment of AD. Furthermore, clinical observations indicate that their complementary mechanisms offer superior benefit as combination therapy. Based on the available literature, the authors have considered the preclinical mechanisms that could underlie such a combined approach. Memantine addresses dysfunction in glutamatergic transmission, while the AChEIs serve to increase pathologically lowered levels of the neurotransmitter acetylcholine. In addition, preclinical studies have shown that memantine has neuroprotective effects, acting to prevent glutamatergic over-stimulation and the resulting neurotoxicity. Interrelations between the glutamatergic and cholinergic pathways in regions of the brain that control learning and memory mean that combination treatment has the potential for a complex influence on disease pathology. Moreover, studies in animal models have shown that the combined use of memantine and the AChEIs can produce greater improvements in measures of memory than either treatment alone. As an effective approach in the clinical setting, combination therapy with memantine and an AChEI has been a welcome advance for the treatment of patients with AD. Preclinical data have shown how these drugs act via two different, but interconnected, pathological pathways, and that their complementary activity may produce greater effects than either drug individually

Further pharmacological characterization of eltoprazine: focus on its anxiolytic, anorexic, and adverse‑effect potential

Eltoprazine, a drug that had previously been developed for aggression, has recently been investigated for L‑DOPA‑induced dyskinesia in animal models of Parkinson´s disease (PD) and in dyskinetic PD patients. Much less is known about effects of eltoprazine in other therapeutic indications. Indeed, the pharmacological profile of eltoprazine might suggest its effects on anxiety and food intake, but also adverse effect potential, which is the focus of the present study. Given for 2 weeks either as infusion or as twice‑daily treatment, eltoprazine produced a decrease in food intake and body weight at doses leading to 200–500 nM plasma concentrations. In the elevated plus maze eltoprazine increased anxiety‑like behavior. On the other hand, it induced a clear‑cut anxiolytic effect in context fear conditioning test starting at ca. 0.3 mg/kg, and failed to produce any significant effect in fear potentiated startle test. Regarding adverse effects, eltoprazine was found to produce hypothermia starting from 1 mg/kg. At similar doses it also increased locomotion in the open field. However, eltoprazine failed to affect acquisition in context fear conditioning paradigm, which may indicate lack of its detrimental effect on learning at the doses tested (i.e., up to 5 mg/kg). In summary, effects of eltoprazine in different anxiety tests were equivocal while its effect on body weight seems robust and requires further investigation. It is to be determined whether these effects can be expected at the doses free of adverse effects

Modulation of l-DOPA-induced abnormal involuntary movements by clinically tested compounds: Further validation of the rat dyskinesia model.

l-DOPA-induced dyskinesia (LID) is a major complication of the pharmacotherapy of Parkinson's Disease. A model of LID has recently been described in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions. In the present study, the model was used in order to compare the efficacies of some clinically available compounds that have shown antidyskinetic effects in nonhuman primate models of LID and/or in patients, namely, amantadine (20 and 40 mg/kg), buspirone (1, 2 and 4 mg/kg), clonidine (0.01, 0.1 and 1 mg/kg), clozapine (4 and 8 mg/kg), fluoxetine (2.5 and 5 mg/kg), propranolol (5, 10 and 20 mg/kg), riluzole (2 and 4 mg/kg), and yohimbine (2 and 10 mg/kg). Rats were treated for 3 weeks with l-DOPA for an induction and monitoring of abnormal involuntary movements (AIMs) prior to the drug screening experiments. The antidyskinetic drugs or their vehicles were administered together with l-DOPA, and their effects were evaluated according to a randomized cross-over design both on the AIM rating scale and on the rotarod test. Most of the compounds under investigation attenuated the l-DOPA-induced axial, limb and orolingual AIM scores. However, the highest doses of many of these substances (but for amantadine and riluzole) had also detrimental motor effects, producing a reduction in rotarod performance and locomotor scores. Since the present results correspond well to existing clinical and experimental data, this study indicates that axial, limb and orolingual AIMs possess predictive validity for the preclinical screening of novel antidyskinetic treatments. Combining tests of general motor performance with AIMs ratings in the same experiment allows for selecting drugs that specifically reduce dyskinesia without diminishing the anti-akinetic effect of l-DOPA

Investigation on tolerance development to subchronic blockade of mGluR5 in models of learning, anxiety, and levodopa-induced dyskinesia in rats

In the present study, we evaluated the effects of subchronic blockade of mGluR5 by 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) on learning, anxiety and levodopa-induced dyskinesia in rats. In addition, we excluded the possibility that subchronic treatment produced pharmacokinetic changes using brain microdialysis. MTEP (5 mg/kg) impaired spatial learning in a radial maze task and contextual fear conditioning (CFC) when administered acutely, and the same effect was observed following a 4-day pre-treatment regime. Similarly, MTEP (5 mg/kg) exerted anxiolytic-like effects in CFC when given before the test whether administered after acute or sub-chronic treatment. Similarly, in levodopa-induced dyskinesia, sub-chronic (7 subsequent days) treatment with MTEP (5 mg/kg) resulted in a significant reduction in abnormal involuntary movements (AIMs), comparable to single acute administration. The data indicate that tolerance does not develop to the anxiolytic and antidyskinetic effects of mGluR5 antagonist MTEP at least at the used treatment mode and tested doses. However, at least at the doses tested, also no tolerance to the memory impairing effect of MTEP was observed. Depending on the indication and model, the amnesic effects of MTEP should be taken into account as a potential limitation, also after repetitive treatment

Pharmacological modulation of glutamate transmission in a rat model of L-DOPA-induced dyskinesia: effects on motor behavior and striatal nuclear signalling.

L-DOPA-induced dyskinesia (LID) in Parkinson's disease has been linked to altered dopamine and glutamate transmission within the basal ganglia. In the present study, we compared compounds targeting specific subtypes of glutamate receptors or calcium channels for their ability to attenuate LID and the associated activation of striatal nuclear signalling and gene expression in the rat. Rats with 6-hydroxydopamine lesions were treated acutely or chronically with L-DOPA in combination with the following selective compounds: antagonists of group I metabotropic glutamate receptors (MTEP for mGluR5, and EMQMCM for mGluR1), agonist of group II mGluR (LY379268), NR2B-selective NMDA receptor antagonists (Ro631908 and Ro256981), and antagonist of L-type calcium channels (isradipine). Dyskinesia and rotarod performance were monitored during chronic drug treatment. The striatal expression of phospho-ERK1/2 and MSK-1, or prodynorphin mRNA were examined following acute or chronic treatment, respectively. In the acute treatment studies, only MTEP and EMQMCM significantly attenuated L-DOPA-induced phospho-ERK 1/2 and/or phospho-MSK-1 expression, MTEP being the most effective (70-80% reduction). In the chronic experiment, only MTEP significantly attenuated dyskinesia without adverse motor effects, whereas EMQMCM and LY379268 inhibited the L-DOPA-induced improvement in rotarod performance. The NR2B antagonist had positive anti-akinetic effects but did not reduce dyskinesia. Only MTEP blocked the upregulation of prodynorphin mRNA induced by L-DOPA. Among the pharmacological treatments here examined, MTEP was most effective in inhibiting LID and the associated molecular alterations. Antagonism of mGluR5 seems to be a promising strategy to reduce dyskinesia in Parkinson's disease

Antagonism of metabotropic glutamate receptor type 5 attenuates l-DOPA-induced dyskinesia and its molecular and neurochemical correlates in a rat model of Parkinson's disease.

Metabotropic glutamate receptor type 5 (mGluR5) modulates dopamine and glutamate neurotransmission at central synapses. In this study, we addressed the role of mGluR5 in L-DOPA-induced dyskinesia, a movement disorder that is due to abnormal activation of both dopamine and glutamate receptors in the basal ganglia. A selective and potent mGluR5 antagonist, 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl] pyridine, was tested for its ability to modulate molecular, behavioural and neurochemical correlates of dyskinesia in 6-hydroxydopamine-lesioned rats treated with L-DOPA. The compound significantly attenuated the induction of abnormal involuntary movements (AIMs) by chronic L-DOPA treatment at doses that did not interfere with the rat physiological motor activities. These effects were paralleled by an attenuation of molecular changes that are strongly associated with the dyskinesiogenic action of L-DOPA (i.e. up-regulation of prodynorphin mRNA in striatal neurons). Using in vivo microdialysis, we found a temporal correlation between the expression of L-DOPA-induced AIMs and an increased GABA outflow within the substantia nigra pars reticulata. When co-administered with L-DOPA, 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl] pyridine greatly attenuated both the increase in nigral GABA levels and the expression of AIMs. These data demonstrate that mGluR5 antagonism produces strong anti-dyskinetic effects in an animal model of Parkinson's disease through central inhibition of the molecular and neurochemical underpinnings of L-DOPA-induced dyskinesia

Duration and onset of effect of incobotulinumtoxinA for the treatment of blepharospasm in botulinum toxin-naive subjects

PLAIN LANGUAGE SUMMARY Blepharospasm is a condition in which involuntary contractions of the eyelid muscles cause the eye to close. The condition can be treated with botulinum neurotoxin type A (BoNT-A) injections. This study assessed the duration of effect and time to onset of effect for the BoNT-A formulation incobotulinumtoxinA (Xeomin, Merz Pharmaceuticals GmbH) in adults with blepharospasm. Subjects received a single injection of one of two doses of incobotulinumtoxinA (total dose 25 or 50 U) or placebo and received a second injection of incobotulinumtoxinA only (total dose <= 70 U; the second injection was not compared with placebo) if needed 6-20 weeks after the first injection. After the first injection, the median (mid-point of values from all subjects) duration of treatment effect was longer with the higher incobotulinumtoxinA dose (20 weeks) than with the lower dose (11 weeks) and was longer with both incobotulinumtoxinA doses than with placebo (6 weeks). After the second incobotulinumtoxinA injection, the median duration of treatment effect was 20 weeks. The time to onset of effect was quicker with both incobotulinumtoxinA doses (5 and 7 days for the higher and lower doses, respectively) than with placebo (14 days) and the difference was statistically significant for the higher incobotulinumtoxinA dose compared with placebo. The time to waning of treatment effect was similar for the two incobotulinumtoxinA doses and placebo. This study shows that incobotulinumtoxinA is an effective treatment for blepharospasm, with a fast onset of action. In addition, the effects of one injection can last for up to 20 weeks. Objective Blepharospasm is a focal dystonia whereby excessive eyelid muscle contractions cause involuntary eye closure. Botulinum neurotoxin type A (BoNT-A) injections are an approved treatment. This randomized placebo-controlled trial (NCT01896895; EudraCT number 2012-004821-26) assessed the efficacy, safety, and treatment effect duration of incobotulinumtoxinA (Xeomin, Merz Pharmaceuticals GmbH), a BoNT-A formulation without complexing proteins, in BoNT-A-naive adults with blepharospasm. Methods Subjects received incobotulinumtoxinA 50 U, 25 U (total dose) or placebo during a main study period (MP; 6-20 weeks). Patients needing a second injection received incobotulinumtoxinA <= 70 U in an open-label extension period (EP; 6-20 weeks). Treatment effect durations were time from first injection to EP injection or final MP visit and from EP injection to end-of-study visit. Times to effect onset and to waning of effect (MP) were time from injection to first subject-assessed onset effect and time from injection to subject-reported waning of effect, respectively. Results Of 61 subjects, 39 entered the EP. During the MP, median duration of treatment effect was longer with incobotulinumtoxinA 50 U (20 weeks) versus incobotulinumtoxinA 25 U (11 weeks) or placebo (6 weeks). Median duration of treatment effect was 20 weeks during the EP. Median time to effect onset was 5, 7, and 14 days with 50 U, 25 U, and placebo, respectively (p = .022 for 50 U versus placebo). Median time to waning of treatment effect was comparable between groups. Conclusion Subjects reported an effect onset from 5 days after injection lasting up to 20 weeks (maximum observation period). Data indicate that incobotulinumtoxinA re-treatment of blepharospasm may not be required at fixed 12-week intervals and provide evidence for a patient-tailored approach

Proteomic analysis of striatal proteins in the rat model of l-DOPA-induced dyskinesia.

L-DOPA-induced dyskinesia (LID) is among the motor complications that arise in Parkinson's disease (PD) patients after a prolonged treatment with L-DOPA. To this day, transcriptome analysis has been performed in a rat model of LID [Neurobiol. Dis., 17 (2004), 219] but information regarding the proteome is still lacking. In the present study, we investigated the changes occurring at the protein level in striatal samples obtained from the unilaterally 6-hydroxydopamine-lesion rat model of PD treated with saline, L-DOPA or bromocriptine using two-dimensional difference gel electrophoresis and mass spectrometry (MS). Rats treated with L-DOPA were allocated to two groups based on the presence or absence of LID. Among the 2000 spots compared for statistical difference, 67 spots were significantly changed in abundance and identified using matrix-assisted laser desorption/ionization time-of-flight MS, atmospheric pressure matrix-assisted laser desorption/ionization and HPLC coupled tandem MS (LC/MS/ MS). Out of these 67 proteins, LID significantly changed the expression level of five proteins: alpha beta-crystalin, gamma-enolase, guanicloacetate methyltransferase, vinculin, and proteasome alpha-2 subunit. Complementary techniques such as western immunoblotting and immunohistochernistry were performed to investigate the validity of the data obtained using the proteomic approach. In conclusion, this study provides new insights into the protein changes occurring in LID