Taking antibiotics long-term may reduce Alzheimer’s symptoms and the plaques thought to underlie the disease, a new study in mice suggests.

But it only works in males. 

In recent years, scientists have amassed a growing body of research suggesting a link between gut bacteria and Alzheimer’s disease.  

Antibiotics alter the gut microbiome – sometimes for the worse – so the team at the University of Chicago experimented with treating bred to have Alzheimer’s with the disease.  

They found that treating male mice with a cocktail of several antibiotics slowed the build up of Alzheimer’s-associated amyloid beta plaques in their brains, but females treated the same way reaped no benefits. 

A long-term cocktail of antibiotics did nothing to treat Alzheimer's disease in female mice (left) but it altered males' gut bacteria to shrink amyloid plaques related to the disease (right)

A long-term cocktail of antibiotics did nothing to treat Alzheimer's disease in female mice (left) but it altered males' gut bacteria to shrink amyloid plaques related to the disease (right)

A long-term cocktail of antibiotics did nothing to treat Alzheimer’s disease in female mice (left) but it altered males’ gut bacteria to shrink amyloid plaques related to the disease (right)

Alzheimer’s is a fearful disease for many reasons, not least of all because it remains mysterious, incurably, and only barely treatable.  

For decades, the amyloid beta theory has prevailed as best explanation science had to offer for the debilitating and ultimately deadly memory loss of Alzheimer’s. 

But autopsies have also shown similar tangles and plaques in people who had had perfectly good memories before their deaths. 

DNA partially determines Alzheimer’s risks – most notably, the APOE-e4 gene – but what separates those whose beta amyloid plaques cause Alzheimer’s and whose don’t has been something of a scientific black box. 

Now, researchers think that the key to the brain disease may lie bacteria. 

Both P gingivalis – the bacteria involved in gum disease, an Alzheimer’s risk factor – and certain gut bacteria have been linked to Alzheimer’s, which often comes with digestive problems. 

And studies in mice have shown that altering these bacteria can actually increase or decrease inflammation and the build up of amyloid plaques. 

Gut bacteria, we now know, can produce amyloid, so an overabundance of the kind of microbes that do so may encourage the development of plaques. 

What’s more, the gut and the immune system are closely linked and previous research has shown that gut flora play a regulatory role for the brain’s microglia, brain cells that can help remove amyloid beta. 

However, over-activation of these cells can also cause inflammation, which worsens Alzheimer’s disease and its progression. 

So some researchers have suggested that if we could find a way to make adjustments to the gut bacteria, they might be able to interfere with the development of amyloid plaques, too.  

The University of Chicago team tried doing so with a cocktail of antibiotics. 

Antibiotics are administered to treat bacterial infections, but broad spectrum antibiotics don’t discriminate much in which bacteria they attack and go after the microbes in the gut, too. 

This discovery explains why many wind up with an upset stomach while on a course of antibiotics. 

But, perhaps, that could be harnessed to alter the gut in ways that would be protective against Alzheimer’s disease, the University of Chicago researchers posited. 

So, they treated the Alzheimer’s-bred mice with a cocktail of the drugs. 

Remarkably, the buildup of amyloid beta plaques was significantly reduced in the brains of male mice on the antibiotic regimen. 

And, it switch their microglia back to an Alzheimer’s-fighting state, rather than the inflamed one that worsens the disease. 

Oddly, the antibiotic treatment did nothing to help the Alzheimer’s stricken female mice. 

Alzheimer’s is far more common in women, who account for 60 percent of all cases, making it vital to understand how the disease develops and can be treated in women. 

Male and female guts are also known to respond differently to the same diet, according to recent research. 

So it may be that the same antibiotics have different effects on them too, and, in turn, on Alzheimer’s plaques.   

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