Pharmacotherapies for Alzheimer's disease: Beyond cholinesterase inhibitors

Alzheimer's disease (AD) is the most common cause of memory impairment and dementia in the elderly. AD is pathologically characterized by extracellular deposits of beta-amyloid (Aβ) peptide, neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau, neuronal loss, and neurotransmitter dysfunction. Clinically, AD is characterized by progressive cognitive decline that usually starts with memory impairment and progresses to cause a more generalized cognitive dysfunction, behavioral dysregulation, and neuropsychiatric symptoms. These symptoms collectively lead to a progressive and relentless decline in the ability to perform functions of daily living, eventually leading to total incapacitation. The incidence and prevalence of AD are expected to exponentially increase with the aging of the population. Currently approved treatments, including the acetylcholinesterase inhibitors (AChEIs) donepezil, galantamine and rivastigmine, and the N-methyl-D-aspartate (NMDA) antagonist memantine, do not halt the progression of the disease, and have provided marginal therapeutic benefits. Accordingly, there is an urgent need to develop novel and effective medications for AD that go beyond AChEIs and NMDA antagonists. Modern research has focused on discovering effective disease-modifying therapies, which specifically target the pathophysiologic cascade, hoping to delay the onset of the disease and slow its progression. In this review, different pharmacological drugs and therapeutic approaches will be discussed, with an emphasis on novel therapies that are currently being investigated in clinical trials.