On the Path to Preventing Alzheimer’s Diseaseby Cristiano Batista, PhD | March 23, 2013
Nearly 30 million people worldwide are affected by the Alzheimer’s disease (AD) and the most recent estimates indicate that this number will quadruple within the next 40 years. The concern increases as AD is the leading cause of dementia, and, so far, there is no effective treatment to slow the progression or delay the onset of this malady.
It is known that AD is a disease of protein aggregation mainly involving accumulation of beta-amyloid (Abeta) in the brain, a peptide of 36-43 amino acids, mostly in the form of tau fibrils and amyloid plaques.
Currently, 10 genes have been identified as influencers of the AD’s risk. The autosomal dominant mutations in the precursor protein (APP) and presenilin (PSEN) genes encoding amyloid precursor protein and the presenilin proteins are accepted as the causes of the hereditary forms of AD.
Most of these mutations increase total Abeta or Abeta42 production, leading to an increased amyloid plaque formation — a pathological hallmark of AD. Thus, Abeta lowering has become a vital therapeutic goal, with various paths within antibodies against Abeta (anti-Abeta) being tested. Over the past few years, the research has been mostly developed after the detection of disease, pursuing a means of lowering the production of the Abeta by inhibiting the enzymes responsible for the generation of this peptide, preventing the formation of Abeta aggregates, and increasing the rate of Abeta clearance from the brain. Presently, several different anti-Abeta therapies are in clinical trials worldwide. Although some modest reductions in plaque burden have been achieved, no obvious clinical benefit or arrest in the progression of cognitive decline was further confirmed.
Given this lack of success, the Alzheimer’s research community has moved toward a consensus that diagnosing and treating the disease before overt symptoms may be more advantageous to slow the disease’s pathogenic process. Among this novel approach, has been particularly suggested that pre-symptomatic individuals with deterministic mutations in APP, PSEN1, or PSEN2 could undergo treatment with an anti-Abeta agent before the expected age of onset of frank symptoms. Individuals with brain amyloid deposits (detected by positron emission tomography) exceeding normal thresholds, as well as low cerebrospinal fluid Abeta 42 levels, may respond to an anti-Abeta treatment.
The Dominantly Inherited Alzheimer Network (DIAN) investigators showed that the changes in cerebrospinal fluid levels of Abeta42 that accompany Abeta deposition are possible to be detected nearly 25 years before the symptom’s onset. This suggests that, in persons with mutations for dominantly inherited AD, the primary prevention with anti-Abeta agents might need to begin, at least, 25 years before the earliest signs.
Following this lead, a prevention trial with an anti-Abeta in around 300 presymptomatic individuals with presenilin mutations has been approved to be carried out by an academic consortium sponsored in part by the United States National Institutes of Health (NIH) and a biotechnology company. Still in the domain of the autosomal dominant AD, another secondary prevention trial has been proposed to the NIH by the Dominantly Inherited Alzheimer Network, the Alzheimer’s Association and some pharmaceutical companies.
Nevertheless, beyond these prevention trials in presymptomatic participants with rare, dominantly inherited AD, there is an intention to initiate similar studies in presymptomatic persons with common, late-onset (so-called sporadic) AD. Hereupon, another secondary prevention trial of an anti-Abeta in sporadic AD subjects (the A4 trial) will be carried out by a consortium led by the Alzheimer’s Disease Cooperative Study group funded by NIH. They recently announced the selection of Eli Lilly’s monoclonal antibody solanezumab as the first therapeutic drug to be evaluated.
Will this novel approach help overcoming this terrible disease? We shall see.
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