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We are all exposed to a vast and dynamic cloud of microbes, chemicals and particles that, if visible, could make us look like Pig-Pen from Peanuts.
Using a redesigned air monitoring device, scientists at Stanford University School of Medicine examined this plume and discovered a multitude of biological and chemical details that swirl around us.
Their discoveries show, in unprecedented detail, the variety of bacteria, viruses, chemicals, plant particles, fungi and even tiny microscopic animals that enter our personal space – a bombardment called "human exposome".
"Human health is influenced by two things: your DNA and the environment," said Michael Snyder, professor and chair of genetics at Stanford. "People have measured things like large-scale air pollution, but no one has really measured biological and chemical exposures on a personal level. Nobody really knows how much the human exponent is vast or what are the things that are found there.
According to Snyder, this curiosity – to see, for the first time, what an individual's exposure looks like and how much it varies from one individual to another – motivated this study.
But the study of the exposome also offers an opportunity to clarify factors of environmental influence of human health that are otherwise obscure, he said. For example, rather than simply blaming pollen, people with seasonal allergies would be able to identify exactly what they are allergic to by monitoring their exposure data and symptoms throughout the year.
The results of the study also reveal information on chemical and household peaks and weather trends, and also show the wide range of chemical and biological particles that can be found between individuals, even in a relatively small geographic area like San Francisco Bay Area.
The study was published in Cell.
About 70 billion reads
For two years, scientists collected data from 15 participants who went through more than 50 different locations. Some people were monitored for a month, some for a week and one (Snyder) for two full years.
To capture fragments of each individual's exposome, a small apparatus attached to the participant's arm "breathes" small bursts of air – about one-fifteenth of the volume of average human breathing.
The device, the size and shape of a large box of matches, accompanies participants everywhere and is equipped with a sub-micron filter that traps particles in the body. ;apparatus. The data, including bacteria, viruses, chemicals, fungi and other objects aspirated by the device are brought back to the Snyder laboratory and extracted for DNA and RNA sequencing, as well as chemical profiling to identify all the organisms and chemicals collected. exposed to.
This idea of siphoning parts of an individual's exposome and systematically classifying what it contains is pretty new, Snyder said. Jiang had to assemble an entirely new database.
"Scientists have collected separate databases on bacteria, viruses or fungi, but to completely decode our environmental exposures, we have created a pan-domain database covering over 40,000 species," Jiang said.
It includes information about bacteria, viruses, fungi, animals, plants and others all organized in a single searchable database.
"We have sequenced these samples in incredible detail," Snyder said. "Nobody has ever done a study as thorough before. We finished with about 70 billion reads.
Particle analysis
Between the participants, Snyder and Jiang found that the exposures could be very different, even in a relatively small geographic area – in this case, San Francisco Bay.
Snyder cited a particularly well-controlled part of the study, in which four participants, including Snyder, were closely monitored for a month, for example.
Each person lived in a separate area of the San Francisco Bay Area: Palo Alto, Sunnyvale, Redwood City and San Francisco (although the person who lived in Redwood City crossed the bay for his work).
"It turns out that, even at very close distances, we have very different exposure profiles or signatures," Snyder said.
These personal signatures are essentially traces of specific fungi, plants, chemicals and bacteria, visible regularly on or around a single person, but which vary from person to person. Many environmental aspects contribute to this microscopic amalgam: domestic animals, household chemicals, flowers in bloom and even rain.
"The bottom line is that we all have our own microbiome cloud that we are reducing," Snyder said.
Specific and unique signatures were captured for each individual (although Snyder added that DEET, an insect repellent, as well as several carcinogens were found in just about every chemical sample). For example, the San Francisco resident has shown high levels of "slime bacteria" or bacteria that are commonly found in sewage and sewer treatments. Snyder constantly had fungal exposures at home because of what he suspected was the use of "green" paint.
"The guy who painted my house was a green and green person. And he avoided using paints containing a substance called pyridine, "Snyder said.
Pyridine, which was a popular additive for indoor paints, has an inverse relationship with fungi, that is, less pyridine, plus there are fungi.
Snyder's profile was the most diverse, as he took the camera everywhere he went, nationally and internationally, for two years, trading his filters for each new location.
Apart from exhibits of his pet (Snyder has a cat, a dog and a guinea pig), his signature also showed signs of eucalyptus in early spring, providing nuanced information about what could cause his allergies d & # 39; in April.
Connect to human health
In addition to the four highly controlled participants, a dozen participants were added at different times of the year, helping Snyder to grasp the exposures brought by weather, seasons and location.
"There are many results that have not been described before – all kinds of seasonal patterns of fungi, bacteria and plants," Snyder said.
The device can even capture viral / bacterial signatures and carcinogenic particles in the air. Although the devices have detected potentially pathogenic viral and bacterial sequences, it can be difficult to distinguish a threatening pathogen from one of its near innocuous relatives.
Carcinogens are also more complicated than simply detecting them in the device.
"We measure individual exposures, not absolute levels," he said. "So, at this point, the data is not generalizable enough to make general statements."
But that does not mean that one day it will not be the case.
Snyder said the study only scratches the surface of human exposure data and its link to health, and that his team's future goals are to better understand exposure to human health.
"We want to measure more people in more diverse environments," said Snyder. "We also want to simplify the technology, ideally to the point that everyone can measure their personal exposures, perhaps a bit like an exposure-sensing smartwatch.
The work is an example of Stanford Medicine's focus on precision health, where the goal is to anticipate and prevent disease in healthy people and accurately diagnose and treat disease in patients.
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