17 March 2006

Beta Amyloid and Alzheimer's: What it Does, How to Stop it

Beta Amyloid protein, Abeta, is involved in neuron damage in several diseases, including Alzheimer's. A recent report from Johns Hopkins has solidly established the association between Beta Amyloid and memory loss in a mouse model of Alzheimer's.

A research team that included members from The Johns Hopkins University and the University of Minnesota Medical School has for the first time identified a substance in the brain that is proven to cause memory loss. This identification gives drug developers a target for creating drugs to treat memory loss in patients with dementia.

....The researchers hypothesized that there was a substance in the brain that causes memory decline that is present even before nerve cells begin to die. To test that hypothesis, the team used mice whose genetic makeup was manipulated to develop memory loss much in a way people develop subtle memory problems before the earliest stages of Alzheimer's disease. Using mice that showed early signs of memory loss and had no plaques or nerve cell loss in the brain, they discovered a form of the amyloid-beta protein that is distinct from plaques. They extracted and purified this newly found protein complex and injected it into healthy rats. The rats suffered cognitive impairment, confirming that this protein has a detrimental effect on memory.

Read the full report here.

We learn even more about beta amyloid, and how it kills brain cells in alzheimer's, from this research report from Children's Hospital and Recearch Center, Oakland.

In a study published in the February 28th issue of the Proceedings of the National Academy of Sciences, lead scientist Hani Atamna, Ph.D., found that alterations in the production of heme (a molecule that contains iron) may be the key to understanding why excessive amyloid-beta is toxic to brain cells. Dr. Atamna had previously discovered that Alzheimer's patients have abnormal amounts of heme in their brains. In new research results, Atamna's team showed that amyloid-beta readily binds with heme to form a compound that can be flushed from cells. When there is insufficient heme or too much amyloid-beta, however, the amyloid-beta forms large toxic "clumps" that the cell cannot dissolve and eliminate.

Though heme binding with amyloid-beta can be beneficial, if too much heme is bound up with amyloid-beta, there may be insufficient heme available for the cell to properly function. When this happens, the cell's mitochondria, which are the tiny structures inside brain cells that produce the energy the cells need to function, begin to decay. Dr. Atamna refers to this phenomenon as a "functional heme deficiency" because the cells are still forming heme, but it is trapped within an amyloid-beta/heme compound.

When they examined the heme/ amyloid-beta compound researchers in the Atamna laboratory were surprised to discover it was a peroxidase--a type of enzyme that reacts harmfully with biological materials essential for proper brain function such as serotonin and L-DOPA. Dr. Atamna believes that the combination of functional heme deficiency, which harms mitochondria needed to produce energy, together with the increase in oxidative damage caused by the peroxidase, is what eventually kills the cell.

So we can see that beta amyloid first causes confusion and memory loss, then it binds heme and triggers oxidative damage to neurons, and mitochondrial dysfunction leading to apoptosis of the neuron. Now we need to look at ways to prevent and arrest those processes before the damage is irrevocable.

In this research report, we learn how researchers used Herpes Simplex Virus (HSV) as a vector for gene therapy, to inhibit amyloid beta production and accumulation.

We generated replication-defective herpes simplex virus (HSV) vectors that inhibit Abeta accumulation, both in vitro and in vivo. In cell culture, HSV vectors expressing either (i) short hairpin RNA directed to the APP transcript (HSV-APP/shRNA), or (ii) neprilysin, an endopeptidase that degrades Abeta (HSV-neprilysin), substantially inhibited accumulation of Abeta. To determine whether these vectors showed similar activity in vivo, we developed a novel mouse model, in which overexpression of a mutant form of APP in the hippocampus, using a lentiviral vector (LV-APP(Sw)), resulted in rapid Abeta accumulation. Co-inoculation of LV-APP(Sw) with each of the HSV vectors showed that either HSV-APP/shRNA or HSV-neprilysin inhibited Abeta accumulation in this model, whereas an HSV control vector did not. These studies demonstrate the utility of HSV vectors for reducing Abeta accumulation in the brain, thus providing useful tools to clarify the role of Abeta in AD that may facilitate the development of novel therapies for this important disease.Gene Therapy advance online publication, 16 March 2006

Read more here.

There is a great deal more involved with Alzheimer's than what is discussed in these three articles. You may be wondering where the beta amyloid protein came from in the first place. This useful review article will help to answer that question, and discusses several present and future treatments for Alzheimer's as well. It may take an hour or two to read and digest, but while doing so, be thankful you have that capacity.

There are many, many unanswered questions remaining. But since Alzheimer's is considered a priority by most western governments, well designed research that addresses those questions is very likely to be funded.


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Blogger Avendale said...


Good to see someone else posting on Alzheimer’s. It has been a remarkable couple of weeks in the publication of significant research on Alzheimer’s.

Some excellent stuff on early assessment techniques particular the finding of inverse levels of beta-amyloid in the spine compared to the brain. A clear indication they are not being removed from the brain as.


Also a small sample with some very significant results measuring changes in hippocampal densities and volumes.


Interesting stuff on treatment with a drug AF267B significantly lowering amyloid proteins around the hippocampus in mice but sadly not other parts of the brain. Only in mice at this stage.


That aside concerning to see 11 people dying in a new anti-cholinesterase trial but nobody on placebo.

Chris Allan

Friday, 17 March, 2006  
Blogger al fin said...

Thanks for the information, Chris. I have placed a link to your blog in the Singularity section of my sidebar.

I agree that the deaths in the donepezil group have to be explained. According to the company the mortality rate in the 648 subjects receiving donepezil was not unusual, given age and health. Not having seen the data, I cannot comment.

Memantine appears to be the best available drug for Alzheimer's at this time. AF267B has potential, but the purported mechanism of action does not explain the results. We just have to keep tabs on the research.

Saturday, 18 March, 2006  
Blogger Avendale said...

You are right about AF267B not necessarily explaining the result but these is true of vast numbers of drug affecting cognitive and affective processes, the SSRI’s in depression are a classic example. We know they affect serotonin reuptake but that hardly explains their reducing depressive symptoms. At this stage we also seem to be learning new things each day about the bimolecular process of the development of dementia

I meant to add another paper in my comment the other day and that is a recent review of the stem cell research and aging. Brazel and Rao’s paper is very balanced review of both the upside and downsides of both using brain stem cells and embryonic stem cells to treat various aged related illness and decline. Sadly our neural stem cells age like every other cell in the body and are prone to all their defects as well.


Chris Allan
BTW is there a way to hide links when posting comments in Blogger

Saturday, 18 March, 2006  
Blogger al fin said...

BTW is there a way to hide links when posting comments in Blogger [?]

I am not certain I understand your question. Which links did you wish to hide? If you want to post a clickable link inside a comment, you can use the [a href=""][/a] html tag which will work inside blogger comments. Use the angle bracket instead of the plain bracket above, and insert the address inside the quotation marks.

Please clarify if you had a different question.

Tuesday, 21 March, 2006  

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