Newly
published research in rodents and ongoing research in humans examines the
effects of psychiatric drugs, including antidepressants, on the composition of
gut bacteria.
More and
more studies are supporting the role of the gut microbiota in psychiatric
conditions.
Anxiety and depression are only
some of the mental health conditions
that researchers have linked to changes in the composition of the gut
microbiota.
For
example, a recent study that Medical News Today has reported on listed a
range of bacteria that contribute to creating neuroactive compounds in the gut
— that is, substances that interact with the nervous system, influencing the
likelihood of developing depression.
Other research in
mice has shown that rodents bred to be germ-free develop symptoms of anxiety
and depression and become socially withdrawn.
So given
this intimate link between mental health and the composition of gut bacteria,
do psychiatric drugs that affect mood also impact the population of bacteria in
the gut?
Researchers
led by Sofia Cussotto, from University College Cork, in Ireland, set out to
investigate this in rodents. First, the team "investigated the
antimicrobial activity of psychotropics against two bacterial strain residents
in the human gut, Lactobacillus
rhamnosus and Escherichia
coli."
The
psychotropics that the researchers focused on included: fluoxetine,
escitalopram, venlafaxine, lithium, valproate, and aripiprazole.
Then,
the scientists tested "the impact of chronic treatment with these
drugs" on the rats' microbiota.
Cussotto
and her team published the first part of their results last year in the
journal Psychopharmacology.
They have now presented their full findings at the European College of Neuropsychopharmacology Congress,
in Copenhagen, Denmark.
The results of the first study of its kind
The
scientists gave the rodents psychiatric drugs for a period of 4 weeks, at the
end of which they analyzed the compositions of the rodents' gut microbiota.
They
found that lithium and valproate — which are both mood stabilizers that can
treat conditions such as bipolar disorder —
raised the numbers of certain types of bacteria, such as Clostridium, Peptoclostridium, Intestinibacter, and Christenellaceae.
By
contrast, selective serotonin reuptake
inhibitors (SSRIs), such as the antidepressants fluoxetine
and escitalopram, stopped the growth of bacterial strains such as Escherichia coli.
"We found that certain drugs,
including the mood stabilizer lithium and the antidepressant fluoxetine,
influenced the composition and richness of the gut microbiota," says
Cussotto.
"Although some psychotropic drugs have been
previously investigated in in vitro settings, this is the first evidence in an
animal model."
Sofia Cussotto
Implications of the new research
Commenting
independently, Dr. Serguei Fetissov, a professor of physiology at Rouen
University, in France, who did not participate in the research, offers his
opinion on the findings.
He says,
"These early data are intriguing and worthy of further investigation. At
the moment, it would be premature to ascribe a direct role of gut bacteria in
the action of antidepressant drugs until this work can be reproduced in humans,
which is what the authors now hope to do."
Indeed,
Cussotto and colleagues are currently trying to unravel the effects that
psychiatric drugs may have on individuals, and to this purpose, they are
conducting a large scale observational study in humans.
"The
composition of gut microbiota is very sensitive to the metabolic processes of
the body and can change naturally, through drug-induced metabolic shifts in the
brain and other organs," explains Dr. Fetissov.
"Some of the changes reported
here, for example increased Christensenella, can indeed be beneficial,
but overall significance of drug-induced changes of bacterial composition on
[...] metabolic and mental health needs further research."
The
study's lead researcher also inventories the significance of the findings.
"There are several implications of this work," she says.
"First
of all, some studies have shown that depressed or schizophrenic patients can
have altered microbiota composition, therefore psychotropic drugs might work on
intestinal microbes as part of their mechanisms of action. Of course, this has
to be proved."
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