Alzheimer's

Fungal infection in brain highly associated with Alzheimer’s disease

Common example of fungi hyphae

Common example of fungi hyphae

Alzheimer’s disease is a brain disease in which slow and irreversible neuronal deterioration occurs. It is characterized by the accumulation and aggregation of proteins in the brain and central nervous system (CNS), although no one knows the cause of this protein aggregation, or if these amyloids are even responsible for the neurodegeneration that occurs, rather than just associated with it.  More recently, some scientists believe that Alzheimer’s is a disease caused by inflammation, because sufferers of the disease have high levels of many inflammatory signals in their brains.  Indeed, some infections that would drive inflammation have been found in Alzheimer’s patients, but nothing convincing as of yet.  This week though, scientists from Spain discovered that a fungal infection in the brain is highly associated with the disease.  They published their results in Nature Scientific Reports.

The scientists made histological sections from the brains of 10 patients with Alzheimer’s and 10 healthy controls, and stained them for the presence of fungi.  Remarkably, all 10 of the patients with Alzheimer’s showed signs of various fungi, whereas none of the healthy controls did.  The fungi were seen both intracellularly and extracellularly, meaning that in some cases the fungi actually entered the neurons in the brain.  The fungi included both yeasts, such as Sachromyces cerevisae, as well hyphae forming fungi such as Neosartorya hiratsukae. In addition, the scientists found traces of these fungi in the blood of the Alzheimer’s patients as well, suggesting that they may originate through common pathways, and spread into the brain.

While this study does not in any way prove these fungi are causing the disease, it certainly is compelling data that they are primary culprit for the disease.  As the authors state, if one were to assume that the etiology of the disease is caused by the fungi, all the symptoms of the disease can be explained.  For example, the slow progression and inflammatory nature of the disease.  Fortunately, If the fungi are responsible there could be many possible therapeutic approaches, including antifungals.

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The views expressed in the blog are solely those of the author of the blog and not necessarily the American Microbiome Institute or any of our scientists, sponsors, donors, or affiliates.

The Microbiome Podcast returns: Episode 10 with Dr. John Cryan on the gut-brain axis

The Microbiome Podcast has been on a hiatus since June so we wanted to make sure that our first episode back was a good one.  Our conversation with Dr. John Cryan from University College Cork in Ireland was very informative and for anyone interested in how the microbiome and the gut may impact the brain during development or in later stages of life, this is a great listen. 

Listen to the episode on our website. On iTunes. On Stitcher. 

On this week’s episode we discussed: 

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The views expressed in the blog are solely those of the author of the blog and not necessarily the American Microbiome Institute or any of our scientists, sponsors, donors, or affiliates.

A brief summary of a recent review of the gut-brain axis

Comparison of a normal aged brain (left) and the brain of a person with Alzheimer's (right). 

Comparison of a normal aged brain (left) and the brain of a person with Alzheimer's (right). 

The gut-brain axis refers to the interplay between the gut microbiome and our behavior.  There are a few mechanisms by which the gut microbiome can affect the brain, such as by directly communicating with it via the vagus nerve, by producing hormones or other metabolites that influence brain function, and by eliciting a systemic inflammatory response.  This past month researchers Timothy G. Dignan and John F. Cryan, both of the University College Cork, in Cork, Ireland, published a review of the recent advances in the gut-brain axis literature.  Many exciting scientific developments have occurred in the past few years, including new advances that connect the microbiome with depression, autism, Alzheimer’s disease, and schizophrenia.  Here, we discuss some of those studies and summarizing the review.

Depression: Studies have shown a possible association between the microbiome and feelings of depression.  It is not clear, however, if these changes are due to drugs that are being taken.  Other studies have shown that probiotics can reduce thoughts of depression, and a separate study showed that eating yogurt improved the moods of oil workers.

Autism:  Again, research has shown a correlation between the microbiome and autism, but not any sort of cause or relation with symptoms.  Multiple studies in mice have shown that a dysbiotic microbiome can lead to autism like symptoms, and that altering the microbiome can alleviate them.  Again, however, there are few mechanistic links between the microbiome and the disease.

Alzheimer’s disease:  Very few studies have linked Alzheimer’s and the microbiome.  Some studies have seen a broad decline in microbiome diversity amongst Alzheimer’s patients, but decreased diversity is known to be associated with many other phenotypes.  Smaller studies on mice have shown some symptoms of Alzheimer’s, such as memory loss, can be somewhat reversed using probiotics, but the results are hardly robust and do not necessarily imply a link with Alzheimer’s.

Schizophrenia:  Like Alzheimer’s, very few studies have linked the microbiome and schizophrenia.  Like all of the above, various associations have been made between the disease and the microbiome, but no strong correlations have been measured.  In mouse models of schizophrenia, antibiotics can alleviate symptoms of the disease.  In addition, there is evidence that antibiotics can also improve the mental state of humans. 

Taken collectively, there is a compelling reason to believe that the microbiome is important to each of these indications, and that it is critical to a healthy mind.  It is still early days though, and much more research is needed to prove mechanisms and pathways.  

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The views expressed in the blog are solely those of the author of the blog and not necessarily the American Microbiome Institute or any of our scientists, sponsors, donors, or affiliates.