In Alzheimer's brains on autopsy, markers of mTOR activation have been found to be as much as 100 times higher than age-matched brains of those dying from other causes.

That makes sense, since nerve cells rarely divide once they reach maturity, which would

otherwise dilute damaged cell debris, autophagy is particularly important in the brain. Given the

striking improvement in cognitive function in old mice from the mTOR blocker rapamycin,

and studies showing the prevention and possible restoration

in some cases of memory defects in transgenic mouse models of Alzheimer's disease,

there have been calls for clinical trials of rapamycin for Alzheimer's patients.

After all, mTOR regulates Alzheimer's biggest risk factor aging itself.

The risk of developing this dementia approximately doubles every five years after the age of 65,

with the risk of death from Alzheimer's skyrocketing approximately 700-fold from age 55 to 85.

Unfortunately, no such clinical trial has been attempted. It doesn't even look

like the dementia rates of organ transplant patients given rapamycin have ever been tracked.

When kidney transplant patients are initially switched to mTOR inhibitors, they do seem to

experience a significant improvement in executive function, memory, and mood,

but that may be in part because they were switching from drugs like cyclosporin, which

can on their own cause adverse neuropsychiatric effects.

Rapamycin has been off-patent for more than a decade, so drug companies can no longer charge

whatever they want. Without such price protection, there isn't a strong profit motive to study the drug,

so we shouldn't expect any large clinical trials anytime soon.

Another reason for clinical trial hesitancy may be the frequent and sometimes life-threatening side effects,

like immunosuppression.

In one cancer trial of an mTOR inhibitor, for example,

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