There is strong evidence that intracellular
calcium dysregulation plays an important pathological role in
Alzheimer's disease, and specifically that
beta amyloid may induce increases in intracellular
calcium and lead to neuronal cell dysfunction and death. Here we investigated the feasibility of modifying Alzheimer's pathology with the L-type voltage-gated
calcium channel blockers verapamil,
diltiazem,
isradipine and
nimodipine. All four compounds protected MC65
neuroblastoma cells from
amyloid beta protein precursor C-terminal fragment (APP CTF)-induced neurotoxicity.
Isradipine was the most potent blocker, preventing APP CTF neurotoxicity at nanomolar concentrations. Intracellular
beta amyloid expression was associated with increased expression of Cav 1.2
calcium channels and increased intracellular
calcium influx from the extracellular space. Despite the cytoprotection afforded by
calcium channel blockers,
amyloid beta oligomer formation was not suppressed. The mechanism of cell death in MC65 cells is appeared to be
caspase-3 independent. With the goal of determining if there is sufficient experimental support to move forward with animal trials of
isradipine, we determined its bioavailability in the triple transgenic mouse model of AD. Subcutaneous implantation of carrier-bound
isradipine (3 μg/g/day) for 60 days resulted in nanomolar concentrations in both the plasma and brain. Taken together, our in vitro results support the theory that
calcium blockers exert protective effects downstream of the effects of
beta amyloid.
Isradipine's
neuroprotective effect at concentrations that are clinically relevant and achievable in vitro and in vivo suggests that this particular
calcium blocking agent may have therapeutic value in the treatment of
Alzheimer's disease.