Pharmacotherapeutic approaches to the treatment of Alzheimer's disease

Nonmedical Influences on the Use of Cholinesterase Inhibitors in Dementia Care

We examined primary care physicians' (PCPs) attitudes toward cholinesterase inhibitors (ChEI) to better understand nonmedical factors influencing prescribing decisions in dementia care. In a cross-sectional, qualitative study, 40 PCPs were interviewed concerning their general approach to managing patients with dementia, and their care for a particular dementia case. Three readers independently identified and categorized themes associated with prescribing ChEI. Physicians' attitudes toward ChEI were also coded. Physicians were predominantly ambivalent (51%) or negative (31%) about prescribing ChEI for their patients with dementia. Nonmedical factors affecting prescribing included lack of knowledge, dependence on specialists, influence of family wishes and involvement, and physicians' values. PCPs reported that lack of knowledge and experience made prescribing decisions for ChEI challenging. Physicians reported feeling pressured by families to prescribe ChEI. Under these ambiguous conditions, some physicians prescribed medications simply to be able to offer "something" to patients.

New natural cholinesterase inhibiting and calcium channel blocking quinoline alkaloids

During this study, one new coumarin; 7-O-beta-D-glucopyranoside-2H-1-benzopyran-2-one (1) and three quinoline alkaloids; 3-hydroxy, 2, 2, 6-trimethyl-3, 4, 5, 6-tetrahydro-2H-pyrano[3,2-c] quinoline 5-one (2), ribalinine (3) and methyl isoplatydesmine (4) were isolated from the aerial parts of Skimmia laureola and their structures established by spectroscopic studies. Compounds 2-4 were found to be linear mixed type inhibitors of acetylcholinesterase (K(i) = 110.0, 30.0 and 30.0 microM, respectively). Compounds 2 and 3 were also found to be linear mixed type inhibitors of butyrylcholinesterase, while compound 4 was a noncompetitive inhibitor of the enzyme (K(i) = 90.0, 70.0 and 19.0 microM, respectively). The inhibition of acetyl- and butyryl-cholinesterase enzymes persists as the most promising therapeutic strategy for activating the impaired cholinergic functions in Alzheimer's disease and related dementias. Compound 4 also showed dose-dependent spasmolytic activity in the isolated rabbit jejunum intestinal preparation by relaxing the spontaneous (EC50 = 0.1 mg/mL) and K(+)-induced contractions (EC50 = 0.4 mg/mL), suggesting that the spasmolytic effect of compound 4 is mediated through the blockade of voltage-dependent Ca2+ channels.

Added therapeutic value of memantine in the treatment of moderate to severe Alzheimer's disease

When evaluating the added therapeutic value of a drug, evidence of greater overall benefit or at least an add-on benefit is increasingly being required. Therefore, cost-effectiveness in addition to clinical efficacy is an important consideration. The efficacy of a drug must be examined on the basis of clinical trials by measuring specific parameters that are affected by the drug (for example blood pressure with antihypertensive treatment). Today not only efficacy but also patient-relevant changes (patient benefits) must be demonstrated for a drug, often by measuring quality of life. In order to evaluate the benefit of monotherapy with the N-methyl-D-aspartate antagonist memantine in the management of moderate to severe Alzheimer's disease, a systematic literature review was conducted. The results showed a benefit for memantine in comparison with placebo in terms of a decrease in nursing care, a delay in care dependency and a delay in admission to nursing homes. In addition, an increase in quality of life has been observed.

Donepezil is a strong antagonist of voltage-gated calcium and potassium channels in molluscan neurons

Donepezil is an acetylcholinesterase inhibitor used in Alzheimer's disease therapy. The neuroprotective effect of donepezil has been demonstrated in a number of different models of neurodegeneration including beta-amyloid toxicity. Since the mechanisms of neurodegeneration involve the activation of both Ca(2+)- and K(+)-channels, the study of donepezil action on voltage-gated ionic currents looked advisable. In the present study, the action of donepezil on voltage-gated Ca(2+)- and K(+)-channels was investigated on isolated neurons of the edible snail (Helix pomatia) using the two-microelectrodes voltage-clamp technique. Donepezil rapidly and reversibly inhibited voltage activated Ca(2+)-current (I(Ca)) (IC(50)=7.9 microM) and three types of high threshold K(+)-current: Ca(2+)-dependent K(+)-current (I(C)) (IC(50)=6.4 microM), delayed rectifier K(+)-current (I(DR)) (IC(50)=8.0 microM) and fast transient K(+)-current (I(Adepol)) (IC(50)=9.1 microM). The drug caused a dual effect on low-threshold fast transient K(+)-current (I(A)), potentiating it at low (5 microM) concentration, but inhibiting at higher (7 microM and above) concentration. Donepezil also caused a significant hyperpolarizing shift of the voltage-current relationship of I(Ca) (but not of any type of K(+)-current). Results suggest the possible contribution of the blocking effect of donepezil on the voltage-gated Ca(2+)- and K(+)-channels to the neuroprotective effect of the drug.

Dementia care: mental health effects, intervention strategies, and clinical implications

Caring for elderly people with dementia is associated with well-documented increases in burden, distress, and decrements in mental health and wellbeing. More severe behavioural, cognitive, and functional impairments in a patient are associated with higher levels of burden and distress. Distress increases with care hours per week, number of tasks, and declining coping and support resources. Demographic factors also affect levels of burden and distress. Promising, evidence-based interventions exist, but substantial economic and policy barriers preclude their widespread dissemination. Health-care policy makers should consider addressing these barriers; clinicians and families must campaign for reimbursement; and clinical researchers must develop more potent preventive interventions. In this article we review how dementia care affects the mental health of the carer and identify interventions that might be useful in mitigating carer burden and distress.

In vitro galantamine-memantine co-application: mechanism of beneficial action

Several drugs are in clinical use for symptomatic treatment of Alzheimer's disease patients. Since Alzheimer's disease is known to be associated with down-regulation of the cholinergic and N-methyl-D-aspartate (NMDA) systems, most of these drugs inhibit acetylcholinesterase, potentiate the activity of nicotinic acetylcholine receptors (nAChRs), or modulate NMDA receptors. Galantamine is an anticholinesterase and allosterically potentiates the activity of the nicotinic receptors. We have recently found that galantamine potentiates the activity of NMDA receptors as well. Memantine is unique in that it inhibits the NMDA receptors. We have developed a hypothesis that combining galantamine and memantine will be more effective for improving the patient's conditions than monotherapy with either drug. Patch clamp and intracellular Ca(2+) imaging experiments using rat cortical and hippocampal neurons clearly provided the in vitro bases for our hypothesis. Memantine blocked the extrasynaptic NMDA receptor 100 times more potently than the synaptic NMDA receptor at negative membrane potentials and the block of both types of NMDA receptors was attenuated with depolarization. However, galantamine potentiation of the NMDA receptors was not voltage dependent. Thus, co-application of memantine with galantamine prevented the galantamine potentiation and the activation of extrasynaptic NMDA receptors, but membrane depolarization revealed the galantamine potentiation. Therefore, cell death is expected to be prevented by memantine near the resting potential while the NMDA-mediated synaptic transmission, which is down-regulated in the patients, is maintained and potentiated by galantamine. These results provide in vitro bases for the beneficial actions of galantamine and memantine combinations.

Current Status and Future Promise of Pharmacotherapeutic Strategies for Alzheimer’s Disease

BACKGROUND AND OBJECTIVE

The pharmacotherapy of Alzheimer's disease (AD) is evolving rapidly. Unless new discoveries continue to emerge to facilitate prevention and effective treatment of the disease, the anticipated burden of this disease on caregivers and society at large will overwhelm resources. The objective of this paper is to review the state of development of approaches likely to yield effective interventional measures with regard to AD in the future.

DESIGN

A comprehensive systematic search of MEDLINE using focused search criteria, a search of reference lists from these studies and reviews, a review of the Cochrane Database of Systematic Reviews, and a hand search of relevant journals was conducted. Selection of articles was based on the clinical focus. Additional inclusion criteria preferentially selected key articles that contained higher-level evidence in accordance with explicit, validated criteria.

RESULTS

Pharmaceutical interventions are being developed and tested that confer neuroprotective benefits by targeting causative mechanisms.

CONCLUSION

The paradigm that AD is pharmacologically unresponsive is shifting. Our understanding of the molecular mechanisms of neurodegeneration will soon allow us to more specifically target and interrupt the processes that contribute to this dementia.

Comparison of Galantamine and Donepezil for Effects on Nerve Growth Factor, Cholinergic Markers, and Memory Performance in Aged Rats

This study was designed to determine 1) whether repeated exposures to the acetylcholinesterase inhibitors (AChEIs) galantamine (GAL) or donepezil (DON) resulted in positive effects on nerve growth factor (NGF) and its receptors, cholinergic proteins, and cognitive function in the aged rat, and 2) whether GAL had any advantages over DON given its allosteric potentiating ligand (APL) activity at nicotinic acetylcholine receptors. Behavioral tests (i.e., water maze and light/dark box) were conducted in aged Fisher 344 rats during 15 days of repeated (subcutaneous) exposure to either GAL (3.0 or 6.0 mg/kg/day) or DON (0.375 or 0.75 mg/kg/day). Forty-eight hours after the last drug injection, cholinergic receptors were measured by [(125)I]-(+/-)-exo-2-(2-iodo-5-pyridyl)-7-azabicyclo[2.2.1]heptane ([(125)I]IPH; epibatidine analog), (125)I-alpha-bungarotoxin ((125)I-BTX), [(3)H]pirenzepine ([(3)H]PRZ), and [(3)H]-5,11-dihydro-11-[((2-(2-((dipropylamino)methyl)-1-piperidinyl)ethyl)amino)carbonyl]-6H-pyrido(2,3-b)(1,4)-benzodiazepin-6-one methanesulfonate ([(3)H]AFDX-384, or [(3)H]AFX) autoradiography. Immunochemical methods were used to measure NGF, high (TrkA and phospho-TrkA)- and low (p75 neurotrophin receptor)-affinity NGF receptors, choline acetyltransferase (ChAT), and the vesicular acetylcholine transporter (VAChT) in memory-related brain regions. Depending on dose, both GAL and DON enhanced spatial learning (without affecting anxiety levels) and increased [(125)I]IPH, [(3)H]PRZ, and [(3)H]AFX (but decreased (125)I-BTX) binding in some cortical and hippocampal brain regions. Neither AChEI was associated with marked changes in NGF, NGF receptors, or VAChT, although DON did moderately increase ChAT in the basal forebrain and hippocampus. The results suggest that repeated exposures to either GAL or DON results in positive (and sustained) behavioral and cholinergic effects in the aged mammalian brain but that the APL activity of GAL may not afford any advantage over acetylcholinesterase inhibition alone.

Peripheral electrical stimulation in Alzheimer's disease

In a number of studies, peripheral electrical nerve stimulation has been applied to Alzheimer's disease (AD) patients who lived in a nursing home. Improvements were observed in memory, verbal fluency, affective behavior, activities of daily living and on the rest-activity rhythm and pupillary light reflex. The aim of the present, randomized, placebo-controlled, parallel-group clinical trial was to examine the effects of electrical stimulation on cognition and behavior in AD patients who still live at home. Repeated measures analyses of variance revealed no effects of the intervention in the verum group (n = 32) compared with the placebo group (n = 30) on any of the cognitive and behavioral outcome measures. However, the majority of the patients and the caregivers evaluated the treatment procedure positively, and applying the daily treatment at home caused minimal burden. The lack of treatment effects calls for reconsideration of electrical stimulation as a symptomatic treatment in AD.

Responsiveness to cholinesterase inhibitors in Alzheimer's disease: A possible role for the 192 Q/R polymorphism of the PON-1 gene

Cholinesterase inhibitors (ChEIs) are the most established treatment strategy in Alzheimer's disease (AD). However, the responsiveness to these drugs is widely heterogeneous and the majority of AD subjects do not respond to treatment. Paraoxonase-1 (PON-1) is a potent endogenous ChEI and has been widely studied for its ability to hydrolyze environmental neurotoxins. Serum levels and biological activity of PON-1 display wide inter-individual variability and are strongly influenced by a common polymorphism at position 192 of the PON-1 gene. Here, we evaluated whether this gene variation is associated with differences in the ability of AD subjects to respond to therapy with ChEIs. We found that individuals that respond to ChEIs had a significantly higher frequency of the R allele, compared to non-responders (P<0.05). This study indicates that the 192 Q/R polymorphism of the PON-1 gene might influence responsiveness to ChEIs, with potentially important implications for the treatment of AD. Mutations of genes encoding for endogenous modulators of the cholinergic system should merit further investigation as prognostic indicators of individual response to treatment in AD subjects.

Current Status and Future Promise of Pharmacotherapeutic Strategies for Alzheimer’s Disease

BACKGROUND AND OBJECTIVE

The pharmacotherapy of Alzheimer's disease (AD) is evolving rapidly. Unless new discoveries continue to emerge to facilitate prevention and effective treatment of the disease, the anticipated burden of this disease on caregivers and society at large will overwhelm resources. The objective of this paper is to review the state of development of approaches likely to yield effective interventional measures with regard to AD in the future.

DESIGN

A comprehensive systematic search of MEDLINE using focused search criteria, a search of reference lists from these studies and reviews, a review of the Cochrane Database of Systematic Reviews, and a hand search of relevant journals was conducted. Selection of articles was based on the clinical focus. Additional inclusion criteria preferentially selected key articles that contained higher-level evidence in accordance with explicit, validated criteria.

RESULTS

Pharmaceutical interventions are being developed and tested that confer neuroprotective benefits by targeting causative mechanisms.

CONCLUSION

The paradigm that AD is pharmacologically unresponsive is shifting. Our understanding of the molecular mechanisms of neurodegeneration will soon allow us to more specifically target and interrupt the processes that contribute to this dementia.

Novel dimeric acetylcholinesterase inhibitor bis7-tacrine, but not donepezil, prevents glutamate-induced neuronal apoptosis by blocking N-methyl-D-aspartate receptors

The neuroprotective properties of bis(7)-tacrine, a novel dimeric acetylcholinesterase (AChE) inhibitor, on glutamate-induced excitotoxicity were investigated in primary cultured cerebellar granule neurons (CGNs). Exposure of CGNs to 75 mum glutamate resulted in neuronal apoptosis as demonstrated by Hoechst staining, TUNEL, and DNA fragmentation assays. The bis(7)-tacrine treatment (0.01-1 mum) on CGNs markedly reduced glutamate-induced apoptosis in dose- and time-dependent manners. However, donepezil and other AChE inhibitors, even at concentrations of inhibiting AChE to the similar extents as 1 mum bis(7)-tacrine, failed to prevent glutamate-induced excitotoxicity in CGNs; moreover, both atropine and dihydro-beta-erythroidine, the cholinoreceptor antagonists, did not affect the anti-apoptotic properties of bis(7)-tacrine, suggesting that the neuroprotection of bis(7)-tacrine appears to be independent of inhibiting AChE and cholinergic transmission. In addition, ERK1/2 and p38 pathways, downstream signals of N-methyl-d-aspartate (NMDA) receptors, were rapidly activated after the exposure of glutamate to CGNs. Bis(7)-tacrine inhibited the apoptosis and the activation of these two signals with the same efficacy as the coapplication of PD98059 and SB203580. Furthermore, using fluorescence Ca(2+) imaging, patch clamp, and receptor-ligand binding techniques, bis(7)-tacrine was found effectively to buffer the intracellular Ca(2+) increase triggered by glutamate, to reduce NMDA-activated currents and to compete with [(3)H]MK-801 with an IC(50) value of 0.763 mum in rat cerebellar cortex membranes. These findings strongly suggest that bis(7)-tacrine prevents glutamate-induced neuronal apoptosis through directly blocking NMDA receptors at the MK-801-binding site, which offers a new and clinically significant modality as to how the agent exerts neuroprotective effects.