Calcium channel blockers and dementia

Abstract

Degenerative dementia is mainly caused by Alzheimer's disease and/or cerebrovascular abnormalities. Disturbance of the intracellular calcium homeostasis is central to the pathophysiology of neurodegeneration. In Alzheimer's disease, enhanced calcium load may be brought about by extracellular accumulation of amyloid-β. Recent studies suggest that soluble forms facilitate influx through calcium-conducting ion channels in the plasma membrane, leading to excitotoxic neurodegeneration. Calcium channel blockade attenuates amyloid-β-induced neuronal decline in vitro and is neuroprotective in animal models. Vascular dementia, on the other hand, is caused by cerebral hypoperfusion and may benefit from calcium channel blockade due to relaxation of the cerebral vasculature. Several calcium channel blockers have been tested in clinical trials of dementia and the outcome is heterogeneous. Nimodipine as well as nilvadipine prevent cognitive decline in some trials, whereas other calcium channel blockers failed. In trials with a positive outcome, BP reduction did not seem to play a role in preventing dementia, indicating a direct protecting effect on neurons. An optimization of calcium channel blockers for the treatment of dementia may involve an increase of selectivity for presynaptic calcium channels and an improvement of the affinity to the inactivated state. Novel low molecular weight compounds suitable for proof-of-concept studies are now available. AbbreviationsAβ, amyloid-β; AD, Alzheimer's disease; APP, amyloid precursor protein; LTP, long-term potentiation; VaD, vascular dementia; VGCC, voltage-gated calcium channel IntroductionDementia affects 7% of the population over the age of 65, and then progressively increases with age Rocca et al., 1991). Alzheimer's disease (AD) is the leading cause of dementia, followed by vascular dementia (VaD). AD is characterized by three neuropathological hallmarks: extracellular aggregates of amyloid-β (Aβ) peptide (amyloid plaques), neurofibrillary tangles and synaptic loss (Bell and Cuello, 2006). According to the amyloid cascade hypothesis, overproduction of the hydrophobic peptide Aβ 1-42 is the basis for AD pathology (Hardy and Higgins, 1992).Aggregation of Aβ 1-42 is thought to occur in several steps via fibrils, which are finally deposited as amyloid plaques. It was suggested that an alternative pathway leads to the generation of stable oligomeric aggregates, Aβ oligomers (Gellermann et al., 2008;Yu et al., 2009b), which are considered to mediate the toxic Aβ effects (Hardy and Selkoe, 2002). Different forms of Aβ oligomers can be generated synthetically (e.g. Stine et al., 2003; Barghorn et al., 2005) or are harvested from cell lines (Walsh et al., 2002). These preparations were tested in vitro and in animal models, and the results lead to the generally accepted view that Aβ oligomers specifically disturb synaptic function . Constant impairment of neurotransmission leads to a retraction of synapses, which is then evident in the autopsy of AD brains (for a review, see Nimmrich a...

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