Research published in the journal Nature Communications shows that microbes in the human gut play an important role in protecting against arsenic toxicity, a problem that affects an estimated 200 million people who are exposed to arsenic through contaminated drinking water.
With arsenic topping the federal Agency for Toxic Substances and Disease Registry's list of the most toxic chemicals for the past 20 years, the research is particularly important because even chronic low levels can lead to cancer or cardiovascular disease later in life.
Past studies have shown that microbes in the environment can biochemically transform naturally occurring arsenic in soil or rocks -- either into less toxic or more toxic. What researchers don't know as much about is what microbes in the human gut do with arsenic before it is absorbed into the body, said the senior author of the paper.
"There are many factors that influence disease -- a person's environment, diet, genetics -- but we can only evaluate some of those things in human studies by observing different genotypes of people who have different diets or drink water from different sources," the senior author said.
The authors found that antibiotics disrupted the gut microbiome, allowing more arsenic to accumulate in the tissues, rather than being excreted. "That was an interesting finding because it showed that even though there was some microbial activity in the gut, the mice were not as good at getting rid of the arsenic and were probably taking more of it into their system and building up more in their tissues," the lead author said.
Mice raised without any microorganisms were similarly affected, the author said. But when organisms from the human microbiome were introduced, they had a protective effect.
"That was a big advance," the senior author said, "because we were able to look at the germ-free mice and put back the microbiomes we wanted to examine from different people. We found that depending on which microbiome the mice got, they were protected to varying degrees."
Those results suggest that the microbiome of some people may be more protective than others, the senior author said, and may answer the question of why some people who drink from a shared water source tainted with arsenic develop disease later in life while others don't.
"That idea really hasn't been incorporated into any epidemiological study or model," the senior author said. "Folks are moving into this field, but what our data shows pretty definitively is that both the microbiome and its composition matter.
"So, in order to predict how likely certain individuals are to develop disease, we need to account for the microbiome and just how protective it is," the senior author said. "These results help us establish that foundation."
A better understanding of how the microbiome protects against toxins like arsenic could benefit communities or villages with contaminated water sources through probiotic or other microbiome therapies, especially since it is not always practical or possible to replace a water source, the senior author said.
Gut microbiome protects against acute arsenic toxicity
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