Until fairly recently our various microbes were thought of as freeloaders without any meaningful benefit to our functioning as healthy human beings.
The microbial daily routine
As scientists investigate the links between our internal daily patterns, electric light and health, new information about the rhythmicity of our microbiome might hold clues about how this all works together.
The crucial question is whether the microbes simply respond to their host human’s circadian rhythm or whether they can actually alter our rhythm somehow. And does this really matter anyway?
Microbiota calling the shots
Amino acids, lipids and vitamins that the microbes release circulate in the host mouse’s blood. As the levels of these molecules in the blood changed throughout the day, they altered the expression of genes in the mouse’s liver that code for many metabolic enzymes.
This is the first clear demonstration of the gut microbiota changing the circadian activity of an essential organ — in this case, the liver, which is the engine of our physiology and crucial to our health.
The authors showed this link by administering an antibiotic to mice that kills much of the gut microbiota. Afterward they found significant changes in liver physiology. They could produce the same effect just by changing the feeding times of the mice; mice forced to eat only during the day showed different patterns of microbiota metabolites circulating in the blood than those allowed to eat at night, their natural active period.
In addition, the authors showed the liver changes how it responds to an overdose of acetaminophen over the span of the day in response to signals from the microbiota in the gut. They used acetaminophen as an example of a drug that could damage the liver depending on how it’s broken down. Interestingly, an overdose was less toxic at the beginning of the day, dawn, and most toxic at the end of the day, dusk.
They concluded that the microbiota regulates how effectively the liver can detoxify over the course of the day. The authors argue that this finding can be extrapolated to apply to metabolism of drugs in general, including chemotherapeutic agents we use to treat disease. If so, then the time of day that a medication is administered could have a big impact on its effectiveness, and on the severity of its adverse side effects.
This work has exciting implications. Understanding how time of day matters might allow for better treatment of disease, and for prevention of maladies like obesity, metabolic syndrome and perhaps other serious conditions.
Technology drives the science
The findings described by the Weizmann group were made possible by advances in the technology of DNA research. As so often happens, scientific insights follow on technological development.
Each of these has advanced to an extent that now studies like the one from the Weizmann Institute are achievable.
In other words, it doesn’t appear possible to separate out only one bacterial species from the group, and understand how it functions in isolation. The community works as a whole.
For example, some of its members are bacteria that cannot absorb iron, which is necessary for growth. They require iron-binding molecules made by other members of the community to survive. So you can’t grow this guy in a Petri dish by itself.
Gut and rhythm
The findings of the new study from Israel, which extends previous exciting work in this area, are relevant to humans for many reasons.
For example, people who must take antibiotics for extended periods, or shift workers who eat at the “wrong” time of day, may be at risk via these microbiome pathways.
A root cause of these human health issues we see on the macro scale may be our gut microbiota and whether or not it is happy.
Richard G. “Bugs” Stevens is a professor in the School of Medicine at the University of Connecticut.