This occurs due to a severe loss of white substance from the brain with a reduction in basal forebrain cholinergic neurons that can be observed in the postmortem cerebral cortex of Alzheimer’s patients. Another theory is the cholinergic hypothesis, which is based on the significant loss of cholinergic signaling. According to this hypothesis, the accumulation of amyloid-beta (amyloid plaques) triggers a cascade of events that lead to synaptic dysfunction, memory loss, and structural damage in the brain in the advanced stages of the disease. The first hypothesis is the amyloid cascade. The most important theories are described below. The cause of AD occurrence is unknown however, several hypotheses try to explain the development of this pathology. In most cases, the patients who have been diagnosed with this disease are over 65 years old.
The duration of AD is approximately from 8 to 10 years. This causes widespread damage to nerve cells throughout the brain cortex, accompanied by early loss of cholinergic neurons from the basal region of the forebrain. The mutations in these genes lead to the formation of senile plaques in the extracellular region by amyloid-β protein (Aβ) and the hyperphosphorylation of tau protein that forms the neurofibrillary tangles intracellularly.
The origin of the disease is associated with the mutations in three major genes encoding amyloid precursor protein (APP) on chromosome 21, presenilin-1 (PS1) on chromosome 14, and presenilin-2 (PS2).
Īlzheimer’s is characterized by the presence of amyloid-beta plaques and neurofibrillary tangles that are formed in the patient’s brain, and its pathogenesis is multifactorial. Currently, there are approximately 50 million people who suffer from dementia worldwide, and this number is expected to increase to 66 million by 2030 and to 115 million by 2050. Consequently, motor, sensory, emotional, and cognitive alterations emerge. This is characterized by a progressive loss of neurons, which results in brain atrophy mainly in the memory and learning areas of the brain. The term dementia is defined as a chronic progressive mental disorder that affects memory, thinking, understanding, and other essential brain functions. Alois Alzheimer in 1906 and is the most common cause of dementia in the elderly. One of the most common NDs is Alzheimer’s disease (AD), which was first diagnosed and described by the German neurologist Dr. NDs represent the seventh leading cause of mortality worldwide, and their prevalence increases exponentially with age. Aging stands as a common factor to a diverse group of syndromes, and still few therapeutic advances towards finding a cure have been achieved. One of the dominant factors for the escalation of these pathologies is the increase in the average life expectancy. Neurodegenerative diseases (NDs) are the XXI century paradigm, since they result from progressive loss of structure and/or function of neurons, sometimes leading to cell death. The present article attempts to describe the processes of extraction and isolation of bioactive compounds derived from sponges, algae, marine bacteria, invertebrates, crustaceans, and tunicates as drug candidates against AD, with a focus on the success of pharmacological activity in the process of finding new and effective drug compounds. Marine natural products have been shown to be promising candidates, and some have been proven to exert a high neuroprotection effect, constituting a large reservoir of potential drugs and nutraceutical agents. Currently, the scientific community is gathering efforts to disclose new natural compounds effective against Alzheimer’s disease and other neurodegenerative pathologies. The most used prophylaxis relies on anticholinesterase drugs and NMDA receptor antagonists, whose main action is to relieve symptoms and not to treat or prevent the disease. Though the etiology of this pathology is still unknown, it is usually associated with the appearance of senile plaques and neurofibrillary tangles. This pathology is characterized by brain impairment linked to a neurodegenerative process culminating in cognitive decline and behavioral disorders. Neurodegenerative diseases are sociosanitary challenges of today, as a result of increased average life expectancy, with Alzheimer’s disease being one of the most prevalent.
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