New Antibody Drug Clears Brain of Amyloid Plaques and Delays Onset of Alzheimer’s Disease Symptoms in Small Clinical Trial


An experimental drug called aducanumab seem to be able to remove the toxic proteins that build up and cause the onset of Alzheimer’s disease in the brain, according to findings from a small clinical trial. Because of the small size of this trial, I must stress that these results, though potentially exciting, should also elicit some caution.

The results of this small clinical trial were reported in the journal Nature on August, 31, 2016. In this trial, aducanumab dissolved amyloid-β proteins in patients suffering from early-stage Alzheimer’s disease. This was a Phase I clinical trial, and therefore, was designed mainly to test the safety of aducanumab in human patients. Thus, the final word on whether aducanumab works to mitigate the memory losses and cognitive decline associated with Alzheimer’s disease must be subjected to clinical trials specifically designed to test such things. Two larger phase III trials are presently in progress, and are planned to be completed approximately in 2020 (note: this is an estimate).

The latest study enrolled 165 subjects who were split into different groups; subjects in one group received aducanumab and subjects in the other group were administered a placebo. In the group that received aducanumab infusions, 103 patients were given the drug once a month for up to 54 weeks. These patients experienced a reduction in the amount of tangled amyloid-β in their brains. These clinical recapitulated the results of pre-clinical experiments in laboratory mice that were actually reported in the same paper. Aducanumab seems to clear amyloid-β plaques from the brains of laboratory mice and human patients.

“This drug had a more profound effect in reversing amyloid-plaque burden than we have seen to date,” says psychiatrist Eric Reiman, who serves as executive director of the Banner Alzheimer’s Institute in Phoenix, Arizona. Reiman and his colleagues are in the process of testing other approaches for Alzheimer’s prevention and treatment. “That is a very striking and encouraging finding and a major advance.” Reiman wrote a commentary accompanying the article.

“This is the best news we’ve had in my 25 years of doing Alzheimer’s research, and it brings hope to patients and families affected by the disease,” says neurologist Stephen Salloway of Butler Hospital in Providence, Rhode Island, who is a member of the clinical team that ran the trial.

Patients in those groups that received aducanumab were divided into different subgroups that were given one of four different doses. Those patients who received the highest doses also had the highest reductions in plaques, and a group of 91 patients who had been treated for 54 weeks saw slower cognitive declines than did those who received placebo infusions.

Neuroscientists have had a long-standing and often spirited debate over the significance of the accumulation of amyloid-β in the pathology of Alzheimer’s disease. The memory loss and other symptoms of Alzheimer’s disease almost certainly result from the die-off of neurons in the brain, but do the amyloid-β plaques form as a consequence of this massive neuronal die-off or are they the cause of it? This clinical trial seems to provide good evidence for the “amyloid hypothesis,” since the elimination of amyloid-β protein seems to ameliorate the symptoms of Alzheimer’s disease.

Reiman however, cautions, wisely I think, that this trial is too small to definitively demonstrate that aducanumab actually works. Several other drugs for Alzheimer’s disease have shown promising results in the early-stage of clinical trials only to end in failure, and even in the deaths of patients.

Aducanumab led to abnormalities on brain-imaging scans in less than one-third of the patients. Researchers must closely monitor these anomalies in Alzheimer’s trials, because some participants in previous Alzheimer’s antibody trials have died as a result of brain inflammation. Fortunately, all of the reported imaging abnormalities eventually disappeared in about 4 to 12 weeks, and none of the patients who showed such abnormalities were hospitalized. Curiously, some of the patients who showed imaging anomalies continued to take the drug despite these side effects. Patients who received higher doses of the drug, or who had genetic risk factors for Alzheimer’s, were more likely to develop the brain anomalies.

Biogen, the company that makes aducanumab, has adjusted the drug’s dosage and the monitoring schedule for patients who have an increased genetic risk for Alzheimer’s in its phase 3 trials. According to Reiman, drug makers, like Biogen, must determine if a particular dosage that hits a “sweet spot” that is strong enough to work without causing potentially lethal brain inflammation.

Aducanumab is a bright spot in the field of Alzheimer’s therapeutics after years of failed antibodies and other types of drug trials. The antibody drug solanezumab failed to slow cognitive decline in two large 2013 clinical trials.  However solanezumab may have a second life and is being tested in multiple other trials, one of which includes individuals with mild Alzheimer’s disease. Results from this trial might be reported as early as the end of 2016.

Other therapeutic strategies undergoing clinical trials include strategies that target enzymes called β-secretase 1 that processes amyloid proteins, antibodies that attack the so-called the microtubule-binding tau protein, which is found in high concentrations in the neurofibrillary tangles found in the brains of many Alzheimer’s disease patients.

“The fact that we now have an antibody that gets into the brain sufficiently enough to engage its target and remove plaques is an important development, and we look forward to seeing results from this and other phase 3 trials,” Reiman says.

Genetically Modified As a Potential Treatment of Alzheimer’s Disease


A neurobiology team from UC Irvine (full disclosure, my alma mater) has used genetically engineered neural stem cells to treat mice with a form of Alzheimer’s disease (AD). Such implanted neural stem cells ameliorated some of the symptoms and pathological consequences of this disease in affected mice.

Patients with AD show accumulation of the protein amyloid-beta in their brains. These amyloid-beta clusters form clear plaques in the brain that are also quite toxic to nearby neurons.

Amyloid beta plaques can be cleared with the protein in them is degraded. Fortunately, the enzyme neprilysin can degrade these plaques, but the brains of AD patients show low levels of this enzyme. Neprilysin levels decrease with age and this is probably one of the reasons AD tends to be a disease of the aged.

The UC Irvine group, under the direction of Mathew Blurton-Jones, tried to deliver neprilysin to the brains of afflicted mice and used neural stem cells to do it. The goal of this work was to determine if increased degradation of the amyloid plaques abated the pathological effects of AD.

In this work, two different AD model systems were used. Thy1-APP and 3xTg-AD mice both exhibit many of the pathological effects of AD, and both were used in this study. Neural stem cells were transfected in express 25 times more neprilysin that normal. Then these genetically modified neural stem cells were transplanted into two areas of the brain known to be affected by AD: the hippocampus and the subiculum, which lies just below the hippocampus. Other AD mice were transplanted with neural stem cells that had not been transformed with neprilysin.

Post-mortem examination of both groups of mice even up to three months after transfection of the neural stem cells showed that those mice that received injections of neprilysin-expressing neural stem cells had significant reductions in amyloid-beta plaques within their brains compared to control mice. The neprilysin-expressing cells even seemed to promote the growth of neurons and the establishment of connections between them.

A truly remarkable finding of this work was that numbers of amyloid-beta plaques were also reduced in area of the brain that were some distance from the areas where the stem cells were injected. This suggests that the injected stem cells migrates across the brain, reducing plaque formation as they went.

Future experiments will seek to see if the reduction in amyloid-beta plaques also leads to improvements in cognition. Also, before this protocol can make its transition from animal models of human trials, the UC Irvine group will need to determine if the neprilysin also degrades soluble forms of amyloid-beta.

Every AD mouse model varies as to the types of pathologies observed in the brains of the affected mice. For this reason, this group tested their treatment strategy in two distinct AD mouse models, and in both cases, the neprilysin-expressing neural stem cells reduced the incidence of amyloid beta plaques. This strengthens the conclusion and neprilysin-expressing neural stem cells can indeed degrade amyloid-beta plaques.

More work needs to be done before this work can be used to support a human trial, but this is certainly an encouraging start to something great.

Brain Cell Regeneration Might Improve Alzheimer’s Disease Symptoms


Adi Shruster and Daniel Offen from Tel Aviv University in Israel have shown in a rodent model of Alzheimer’s disease (AD) that stimulating brain cell regeneration can alleviate some of the symptoms of AD.

A particular mouse strain called 3xTgAD serves as a model system for the study of AD. These mice have several genetic modifications that cause the formation of senile plaques in the brain that also lead to behavioral abnormalities and cognitive decline. In short, the Presenilin gene, which plays a definitive role in the onset of AD, has a mutation engineered in it. This particular mutation (M146V) shows a very strong causative link to inherited forms of AD (MA Riudavets, et al., Brain Pathology 2013 23(5): 595–600).

APP+PS1+Notch

 

Additionally, 3xTgAD mice have a synthetic gene inserted in them that overproduces two proteins that also contribute to the onset of AD: amyloid precursor protein (APP) and another protein called tau. The combination of these three genes causes the formation of amyloid plaques and neurofibrillary tangles that are so characteristic of AD, although these plaques are not exactly the same as those observed in human AD patients (see Matthew J. Winton, et al., Journal of Neuroscience 31(21):7691–7699).

Beta_amyloid

Shruster and Offen used these 3XTgAD mice to determine if inducing new brain cells in the brain could improve their condition. Offen overexpressed a gene called Wnt3a in a part of the brain known to play a role in regulating behavior. Wnt3a is known to drive cell proliferation in this part of the brain. After driving Wnt3a expression in the brains of 3XTgAD mice, Offen subjected them to behavioral tests.

Normal mice tend to pause and assess their surroundings when they enter unfamiliar places. However, 3xTgAD mice tend to charge straight in when entering new surroundings. This lack of proper danger assessment in 3xTgAD mice disappeared when Wnt3a was expressed in their brains. Upon post-mortem examination, these mice showed the formation of new nerve cells in their brains. When new brain cell formation was abrogated with X-rays, the behavioral defect was maintained.

Offen commented: “Until 15 years ago, the common belief was that you were born with a finite number of neurons. You would lose them as you age or as a result of injury or disease.”

Human AD patients can lose their sense of space and reality and do very inappropriate things at particular times. Therefore, these mice do recapitulate particular features of the human disease.

Offen and his colleagues think that establishing the growth of new brain cells in human AD patients might alleviate some of the behavioral abnormalities. Furthermore, stem cell treatments might also have a positive role to play in the treatment of AD, although Offen will readily admit that more work must be done.