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Why hasn't natural selection eliminated Alzheimer's?

Tradeoffs.

The Alzheimer's Disease-Associated Amyloid beta-Protein Is an Antimicrobial Peptide
[See comment below for an earlier paper making this suggestion.]

Life-long protection against brain infections, in exchange for increased risk of dementia at an age few of our ancestors reached? Sounds like a reasonable tradeoff to me. Except that now we may have better options:

"it raises the possibility of preventing amyloidosis from initiating by pre-emptive targeting of pathogens/insults that stimulate the brain's innate immune system."

All we need is a good noninvasive way to detect brain infections early, so we can treat them with nonAlzheimer's-inducing antibiotics before amyloid beta-protein gets into the act.

Comments

My 2006 publication (excerpt below) explicitly described Aβ as an antimicrobial peptide based on its multiple similarities to melittin.

In addition, the described antimicrobial action was explicitly cited as a basis for Aβ to be considered a component of the innate immune system, likely as a rapid response to infections by enveloped viruses such as HSV.

Excerpt from Kammerman et al., 2006:

"Numerous groups have reported that Aβ42 can disrupt lipid membranes by creating pore-like holes (ion channels) within the membranes. This property of Aβ42 appears to be related to an antimicrobial function; nature is replete with examples of peptide antimicrobials that effect their function through membrane disruption. In fact, some of these peptides show strong activity against HSV-1. For example, melittin, which has an α-helical amphipathic structure similar to Aβ42, has anti-HSV activity. We assert that β amyloid, by virtue of its similar molecular shape and size, is a peptide antimicrobial component of the innate immune system which can neutralize enveloped viruses such as HSV-1. We contend accordingly that ion-channel pore formation in the HSV-1 envelope generated by Aβ42 is virucidal."

References:
Kammerman EM, Neumann DM, Ball MJ, Lukiw W, Hill JM. Senile plaques in Alzheimer's diseased brains: possible association of beta-amyloid with herpes simplex virus type 1 (HSV-1) L-particles. Med Hypotheses. 2006;66(2):294-9.

I had a similar experience once; someone published a paper whose key idea I had already published, without citing my paper. I'm pretty sure it was an honest mistake. Since then, I always try to put the key idea in the title of my paper. That might have helped in your case also, although there are so many journals that it's easy to miss relevant papers.

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