Exposure to household chemicals harms myelin-making cells

Two types of chemicals in household disinfectants and furniture can disrupt the development of oligodendrocytes, the brain cells chiefly responsible for making myelin, a new study shows.

The finding suggests that exposure to these chemicals may be a risk factor for disorders related to myelin such as multiple sclerosis (MS), where the immune system launches an inflammatory attack that damages myelin, and oligodendrocytes have limited ability to repair the damage.

“Loss of oligodendrocytes underlies multiple sclerosis and other neurological diseases. We now show that specific chemicals in consumer products can directly harm oligodendrocytes, representing a previously unrecognized risk factor for neurological disease,” Paul Tesar, PhD, co-author of the study at Case Western Reserve University School of Medicine in Ohio, said in a news release.

The results of the study, “Pervasive environmental chemicals impair oligodendrocyte development,” which was published in Nature Neuroscience, might “help explain a missing link in how some neurological diseases arise,” said Erin Cohn, a graduate student at Case Western and lead author.

People are exposed as part of modern life to thousands of different chemicals, most of which have safety profiles that aren’t fully understood. The increased exposure to these chemical may be associated with the rising prevalence of certain brain diseases, which cannot be explained solely by genetic and other environmental factors.

Very few commonly used chemicals have been tested for their impact on oligodendrocytes, which are highly vulnerable to environmental chemical exposure, leading researchers here to screen these myelin-making cells by exposing them to more than 1,800 chemicals to see if any of them interfered with oligodendrocyte growth.

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This type of screening “is a powerful tool to prioritize chemicals of concern and identify environmental triggers of [disease] on the basis of their toxic effects to relevant neural cell types,” the researchers wrote.

Most of the chemicals had no effect on oligodendrocytes and 22 stimulated the growth of these cells, but more than 300 chemicals were identified as either being toxic to the cells or inhibiting their growth.

The toxic effects of the most potent chemicals were validated in further experiments and two classes of common chemicals seemed to most affect oligodendrocytes in mice and human cell models: quaternary ammonium compounds, which are present in many disinfectants and personal care products, and organophosphate flame retardants, which are used in furniture and electronics. The chemicals weren’t particularly toxic to any other type of cell tested, however.

“We found that oligodendrocytes, but not other brain cells, are surprisingly vulnerable to quaternary ammonium compounds and organophosphate flame retardants,” Cohn said.

Previous studies have shown that organophosphate flame retardants are often detectable in the blood and other bodily fluids in children. In fact, in data on more than 1,700 children ages 3-11 collected by the U.S. Centers for Disease Control and Prevention (CDC), more than 99% of children had a chemical called BDCIPP in their urine, which is a marker of exposure to the TDCIPP organophosphate flame retardant.

Analyses of this study showed children with higher urine BDCIPP were significantly more likely to show signs of neurological issues such as needing special education assistance in school.

These data indicate “strong evidence of a positive association between organophosphate flame retardant exposure and abnormal neurodevelopment,” the researchers wrote.

Quaternary compounds, meanwhile, have become much more present since the onset of the COVID-19 pandemic. These chemicals are present in more than half of the disinfectants registered for killing the virus that causes COVID-19.

The compounds showed toxic effects to oligodendrocytes even at very low levels, similar to expected levels in the blood of children exposed to these disinfectants.

Further experiments in mice showed these quaternary compounds can cross from the blood into the brain, which the researchers said “raises significant health concerns for neurodevelopmental toxicity.”

The scientists called for more research into the possible consequences of exposure to the chemicals, noting that solid data about the risks are vital to inform risk-reduction policies.

“Our findings suggest that more comprehensive scrutiny of the impacts of these common household chemicals on brain health is necessary,” Tesar said. “We hope our work will contribute to informed decisions regarding regulatory measures or behavioral interventions to minimize chemical exposure and protect human health.”