Reappraising neurotransmitter-based strategies

Nantenine as an acetylcholinesterase inhibitor: SAR, enzyme kinetics and molecular modeling investigations

Nantenine, as well as a number of flexible analogs, were evaluated for acetylcholinesterase (AChE) inhibitory activity in microplate spectrophotometric assays based on Ellman's method. It was found that the rigid aporphine core of nantenine is an important structural requirement for its anticholinesterase activity. Nantenine showed mixed inhibition kinetics in enzyme assays. Molecular docking experiments suggest that nantenine binds preferentially to the catalytic site of AChE but is also capable of interacting with the peripheral anionic site (PAS) of the enzyme, thus accounting for its mixed inhibition profile. The aporphine core of nantenine may thus be a useful template for the design of novel PAS or dual-site AChE inhibitors. Inhibiting the PAS is desirable for prevention of aggregation of the amyloid peptide Aβ, a major causative factor in the progression of Alzheimer's disease (AD).

Symptomatic effect of donepezil, rivastigmine, galantamine and memantine on cognitive deficits in the APP23 model

RATIONALE

APP23 mice are a promising model of Alzheimer's disease, expressing several histopathological, cognitive and behavioural hallmarks of the human condition. A valid animal model should respond to therapeutic interventions in an equivalent manner as human patients.

OBJECTIVES

To further validate the APP23 model, we examined whether cognitive deficits could be antagonised by donepezil, rivastigmine, galantamine or memantine, which are approved drugs for symptomatic treatment of dementia.

METHODS

Animals were tested at an age at which untreated APP23 mice display severe deficits in visual-spatial learning. Four-month-old APP23 mice and control littermates were administered donepezil (0.3 or 0.6 mg kg(-1)), rivastigmine (0.5 or 1.0 mg kg(-1)), galantamine (1.25 or 2.5 mg kg(-1)), memantine (2 or 10 mg kg(-1)) or saline through daily i.p. injections. After 1 week of treatment, acquisition phase commenced, with daily treatment continuing during cognitive testing.

RESULTS

All cholinesterase inhibitors reduced cognitive deficits with the following optimal daily doses: galantamine 1.25 mg kg(-1), rivastigmine 0.5 mg kg(-1) and donepezil 0.3 mg kg(-1). Higher dosages often did not exert beneficial effects in accordance with inverted U-shaped dose-response curves described for cholinomimetics. Symptomatic efficacy of memantine on cognition was mild, with significant amelioration manifesting during probe trial.

CONCLUSIONS

This is the first study to simultaneously evaluate the efficacy of therapeutically relevant doses of these four compounds in one particular learning and memory paradigm, being the Morris water maze. The fact that symptomatic intervention was able to diminish cognitive impairment, substantially adds to the validity of the APP23 model as a valuable tool to evaluate future therapeutic approaches.

Strategies for disease modification in Alzheimer's disease

Treating Alzheimer's disease (AD) is the biggest unmet medical need in neurology. Current drugs improve symptoms, but do not have profound disease-modifying effects. Three main classes of disease-modification approaches can be defined: one that is broadly neurotrophic or neuroprotective, one that targets specific aspects of AD pathology, and one that is based on epidemiological observation. This review discusses all three approaches, with particular emphasis on anti-amyloid strategies - currently the most active area of investigation. The approaches that are reviewed include secretase inhibition, amyloid-beta aggregation inhibition, immunotherapy and strategies that might indirectly affect the amyloid pathway.

Alzheimer's disease: molecular understanding predicts amyloid-based therapeutics

Degenerative diseases of the brain were long considered among the most obscure and intractable of human maladies. However, recent advances in understanding their mechanisms have brought us to the verge of potential disease-modifying agents. This progress is perhaps best exemplified by the case of Alzheimer's disease. The application of molecular pathology and genetics has led to the recognition that the four genes implicated to date in familial Alzheimer's disease all chronically elevate cerebral levels of the amyloid beta-protein (Abeta). Accordingly, small molecule inhibitors of the beta- and gamma-secretases, the proteases that generate Abeta from its precursor, are under active development, and some have shown in vivo efficacy in mouse models. An alternative approach, active or passive immunization against Abeta, has received extensive pre-clinical validation in mice, but an effective preparation free of significant side effects in humans is still awaited. Several other potential therapies are also reviewed here. If one or more of these varied approaches is ultimately proven to slow or prevent dementia, Alzheimer's disease will become a salient example of the successful application of reductionist biology to the most complex of organs, the human cerebral cortex.

Pathogenic theories and intrathecal analysis of the sporadic form of Alzheimer's disease

Alzheimer's disease (AD) is an age-dependent dementia characterized by progressive loss of cognitive functions and by characteristic pathological changes in the brain: the formation of aggregates extracellularly by beta-amyloid (Abeta) peptide and intracellularly by tau proteins. The disease presents several major diagnostic difficulties: (1) AD develops slowly; (2) analysis of damaged brain tissues is difficult, requiring a biopsy which poses ethical problems; (3) no biochemical markers are available for the diagnosis and monitoring of the disease progression. Since the cerebrospinal fluid (CSF) is in contact with the extracellular space of the brain, many studies have tried to correlate the levels of the intrathecal peptides and amino acids and the development of dementia. The present review analyzes the main results of intrathecal content analyses in light of pathogenic theories proposed to explain the damage associated with AD and observed in the brain of patients by postmortem examination.

Treatment of Alzheimer's disease: rationale and strategies

This article reviews the rationale and provides a progress update regarding the major treatment strategies being developed for the prevention and treatment of Alzheimer's disease. Various therapeutic areas are discussed, including acetylcholinesterase inhibitors and other cholinergic agents, antioxidants, anti-inflammatory drugs, hormone replacement therapy, antiamyloid treatment, and neurotrophic agents.

A 5-month, randomized, placebo-controlled trial of galantamine in AD. The Galantamine USA-10 Study Group

OBJECTIVE

To investigate the efficacy and tolerability of galantamine, using a slow dose escalation schedule of up to 8 weeks, in 978 patients with mild to moderate AD.

METHODS

A 5-month multicenter, placebo-controlled, double-blind trial. Following a 4-week placebo run-in, patients were randomized to one of four treatment arms: placebo or galantamine escalated to final maintenance doses of 8, 16, or 24 mg/day. Outcome measures included the cognitive subscale of the AD Assessment Scale (ADAS-cog), the Clinician's Interview-Based Impression of Change plus Caregiver Input (CIBIC-plus), the AD Cooperative Study Activities of Daily Living inventory, and the Neuropsychiatric Inventory. Standard safety evaluations and adverse event monitoring were carried out.

RESULTS

After 5 months, the galantamine-placebo differences on ADAS-cog were 3.3 points for the 16 mg/day group and 3.6 points for the 24 mg/day group (p < 0.001 versus placebo, both doses). Compared with placebo, the galantamine 16- and 24-mg/day groups also had a significantly better outcome on CIBIC-plus, activities of daily living, and behavioral symptoms. Treatment discontinuations due to adverse events were low in all galantamine groups (6 to 10%) and comparable with the discontinuation rate in the placebo group (7%). The incidence of adverse events in the galantamine groups, notably gastrointestinal symptoms, was low and most adverse events were mild.

CONCLUSIONS

Galantamine 16 and 24 mg/day significantly benefits the cognitive, functional, and behavioral symptoms of AD as compared with placebo. Slow dose escalation appears to enhance the tolerability of galantamine, minimizing the incidence and severity of adverse events.