Alzheimer's disease research is perhaps the largest single theme in the aging research community, with the majority of National Institute on Aging funding going towards Alzheimer's programs. The most advanced of efforts in Alzheimer's research are those that seek to clear the accumulation of amyloid-β in the brain through the use of immunotherapies, enlisting the immune system to break down and remove the unwanted amyloid. To date, however, this has proven to be a road of great expense characterized by disappointment and slow progress, to the point at which it was possible to question whether amyloid was the right target. Other theories and lines of research have begun to prosper due to the lack of tangible human results for anti-amyloid immunotherapies, in particular that neurofibrillary tangles of misfolded tau protein are just as much a target for clearance as is amyloid-β, and that perhaps it is time to focus on the decline of known clearance mechanisms rather than the amyloid itself.
Still, over the past couple of years, one of the latest entries to the class of anti-amyloid immunotherapies has lived up to some of the promise first seen in animal studies of amyloid clearance. It may well be that the light at the end of the tunnel is in sight. In a human trial that has now lasted a year, this new immunotherapy cleared near all detectable amyloid-β from patients, and the patients showed improvement in the sense that their decline appeared to slow significantly. The caveat here is that a year is not long enough to declare a slowing of the condition in certainty given the number of people treated in the trial, 165 individuals. Certainty will arrive given time and more patients. Regardless, simply through the demonstrated clearance of amyloid in human patients this is a big step forward for the field. If this holds up over the next few years of larger trials it should become very clear as to the degree to which amyloid-β is or is not in fact the primary cause of pathology in Alzheimer's disease.
I have long said that the best way to answer these questions of cause and contribution is to remove the mechanism in question and see what happens. As an approach that is much, much faster - and thus more cost-effective - than trying to infer the answer by analyzing the enormously complex workings of cellular biochemistry. It is an important point when arguing for more funding for SENS rejuvenation therapies: fix the damage, and see whether it works, because that is cheap and fast in comparison to all of the other options. This principle is well demonstrated here in the matter of amyloid, I think, given the past decade of theorizing on the degree to which the harm of Alzheimer's is due to amyloid, tau, or other causes, and the lack of progress on that front from theorizing alone. As soon as a treatment can reliably and safely remove the amyloid from a sizable number of Alzheimer's patients, we will have the answer.
Although the causes of Alzheimer's disease are still unknown, it is clear that the disease commences with progressive amyloid deposition in the brains of affected persons between ten and fifteen years before the emergence of initial clinical symptoms such as memory loss. Researchers have now been able to show that Aducanumab, a human monoclonal antibody, selectively binds brain amyloid plaques, thus enabling microglial cells to remove the plaques. A one-year treatment with the antibody, as part of a phase Ib study, resulted in almost complete clearance of the brain amyloid plaques in the study group patients. "The results of this clinical study make us optimistic that we can potentially make a great step forward in treating Alzheimer's disease. The effect of the antibody is very impressive. And the outcome is dependent on the dosage and length of treatment."
The antibody was developed with the help of a technology platform from Neurimmune. Using blood collected from elderly persons aged up to one hundred and demonstrating no cognitive impairment, the researchers isolated precisely those immune cells whose antibodies are able to identify toxic beta-amyloid plaques but not the amyloid precursor protein that is present throughout the human body and that presumably plays an important role in the growth of nerve cells. The good safety profile of Aducanumab in patients may well be attributed to the antibody's specific capacity to bond with the abnormally folded beta-amyloid protein fragment as well as the fact that the antibody is of human origin.
165 patients with early-stage Alzheimer's disease were treated in the phase 1b clinical trial. Although not initially planned as a primary study objective, the good results encouraged researchers to additionally investigate how the treatment affected the symptoms of disease. This was evaluated via standardized questionnaires to assess the cognitive abilities and everyday activities of the patients. "Aducanumab also showed positive effects on clinical symptoms. While patients in the placebo group exhibited significant cognitive decline, cognitive ability remained distinctly more stable in patients receiving the antibody."
The trial mainly tested the safety of the drug in people, and so the final word on whether aducanumab works to ameliorate the memory and cognitive losses associated with Alzheimer's will have to wait until the completion of two larger phase III trials. They are now in progress, and planned to run until at least 2020. Patients in the groups that got the drug were given one of four different doses of aducanumab. Individuals who received the highest doses also saw the highest reductions in plaques. And a group of 91 patients treated for 54 weeks saw slower cognitive declines than did those who received placebo infusions. Scientists have debated for years whether the build-up of amyloid-β causes the memory loss and other symptoms of Alzheimer's. This trial is a point in favour of the "amyloid hypothesis", which suggests that elimination of the protein itself might alleviate the disease's symptoms. Still, the trial is too small to prove that the drug actually works. Numerous other Alzheimer's drugs have looked promising in early-stage trials, yet ended in failure.
Alzheimer's disease (AD) is characterized by deposition of amyloid-β (Aβ) plaques and neurofibrillary tangles in the brain, accompanied by synaptic dysfunction and neurodegeneration. Antibody-based immunotherapy against Aβ to trigger its clearance or mitigate its neurotoxicity has so far been unsuccessful. Here we report the generation of aducanumab, a human monoclonal antibody that selectively targets aggregated Aβ. In a transgenic mouse model of AD, aducanumab is shown to enter the brain, bind parenchymal Aβ, and reduce soluble and insoluble Aβ in a dose-dependent manner. In patients with prodromal or mild AD, one year of monthly intravenous infusions of aducanumab reduces brain Aβ in a dose- and time-dependent manner. This is accompanied by a slowing of clinical decline measured by Clinical Dementia Rating-Sum of Boxes and Mini Mental State Examination scores. These results justify further development of aducanumab for the treatment of AD. Should the slowing of clinical decline be confirmed in ongoing phase 3 clinical trials, it would provide compelling support for the amyloid hypothesis.