Common Household Chemicals Tied to Brain Cell Damage
Two classes of chemicals present in common household products may impair the development of oligodendrocytes, the myelinating cells of the central nervous system (CNS), which are critical to brain development and function. However, the researchers as well as outside experts agree more research is needed before any firm conclusions can be drawn.
Quaternary ammonium compounds, ubiquitous in disinfecting agents and personal care products, and organophosphate flame retardants, which are commonly found in household items such as furniture and electronics had “surprising effects specifically on the non-nerve cells in the brain,” lead researcher Paul Tesar, PhD, professor and director of the Institute for Glial Sciences, Case Western Reserve University School of Medicine, Cleveland, Ohio, told Medscape Medical News.
“Other studies have shown that our exposures to the chemicals in disinfecting agents nearly doubled during the pandemic,” Tesar noted. The finding that quaternary ammonium chemicals in disinfecting agents are harmful to specific brain cells suggests “we need to think about our increased utilization and exposure,” he added.
The results were published online on March 25 in Nature Neuroscience.
Motor Dysfunction
Exposure to various chemicals in the environment has been shown to impair brain development. However, most of this research has focused on neurons. Less is known about effects on oligodendrocytes, which form the electrical insulation around the axons of CNS cells. Oligodendrocyte development continues from before birth into adulthood, thus these cells may be particularly vulnerable to damage from toxic chemicals.
The researchers analyzed the effects of 1823 chemicals on mouse oligodendrocyte development in cell cultures. They identified 292 chemicals that cause oligodendrocytes to die and 47 that inhibit oligodendrocyte generation. These chemicals belonged to two different classes.
They found that quaternary compounds were potently and selectively cytotoxic to developing oligodendrocytes and that organophosphate flame retardants prematurely arrested oligodendrocyte maturation. These effects were confirmed in mice and cultured human oligodendrocytes.
In addition, an analysis of epidemiologic data from the National Health and Nutrition Examination Survey (2013-2018) showed that one flame retardant metabolite, bis(1,3-dichloro-2-propy) phosphate (BDCIPP), was present in nearly all urine samples of children aged 3-11 years who were examined (1753 out of 1763 children).
After adjusting for multiple confounding factors, results showed that compared with children with urinary BDCIPP concentration in the lowest quartile, those with concentrations in the highest quartile were twice as likely to require special education (adjusted odds ratio [aOR], 2.0; 95% CI, 1.0-3.8) and were six times as likely to have gross motor dysfunction (aOR, 6.0; 95% CI, 1.7-21.9).
Children with urinary BDCIPP concentration within the third quartile also had significantly increased odds of motor dysfunction (aOR, 4.2; 95% CI, 1.1-16.2).
“These results suggest that the identified chemicals are potentially hazardous to human health. However, we want to be clear that more studies are needed to make definitive connections between chemical exposure and human disease,” said Tesar.
“Future studies will need to deepen our understanding of the duration and timing of exposure required to initiate or exacerbate disease. This information is needed before specific recommendations, such as behavioral interventions, can be made to reduce exposure. Some of these chemicals have useful roles in our homes, but we need to consider how they’re being used and what level of exposure might be considered safe,” Tesar said.
In his view, the results “provide a starting point to understand what exposure levels to these chemicals might be putting ourselves or kids at risk for toxicity.”
Too Soon to Tell
Commenting for Medscape Medical News, Shaheen Lakhan, MD, a neurologist and researcher based in Miami, Florida, who was not involved in the study, echoed the need for more research.
“The biological mechanisms uncovered provide plausible pathways by which these chemicals could potentially impact human brain development related to oligodendrocytes and myelination. Oligodendrocytes play a critical role in plastic neurological processes throughout life, not just early neurodevelopment. So, disrupting their maturation and function theoretically could contribute to neurodevelopmental disorders as well as adult conditions like multiple sclerosis,” Lakhan said.
“This study alone shouldn’t sound neurotoxicant alarms yet. We’ve seen many past chemical scares like saccharin and phthalates fizzle despite alarming lab results when real-world human brain impacts failed to materialize,” Lakhan cautioned.
“Far more rigorous research directly linking household chemical exposures to cognitive deficits in people is still needed before drawing firm conclusions or prompting overreactions from the general public. Policymakers will eventually need to weigh potential risks vs benefits, but no definitive human health threat has currently been established,” Lakhan said.
Sarah Evans, PhD, MPH, assistant professor in the Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai in New York, also emphasized the need for further study.
“Given that most of the experiments in this study were conducted in isolated cells and a mouse model, further research is needed to determine whether exposure to these chemicals at levels experienced by the general population during critical windows of development impairs myelination and leads to adverse health outcomes like learning and behavior problems in humans,” Evans, who was involved in the study, told Medscape Medical News.
“The authors’ finding of an association between higher urinary levels of the organophosphate flame-retardant metabolite BDCIPP and gross motor problems or need for special education in children aged 3-11 years in the CDC National Health and Nutrition Examination Survey strengthen their laboratory findings and warrant further investigation,” Evans added.
The research was supported by grants from the National Institutes of Health, National Multiple Sclerosis Society, Howard Hughes Medical Institute and New York Stem Cell Foundation, and philanthropic support by sTF5 Care and the Long, Walter, Peterson, Goodman, and Geller families. Tesar, Lakhan, and Evans report no relevant disclosures.
