Popular disinfectants caused brain cell death
Modern man lives among many thousands of chemicals that are created by civilization and are not found in nature. Their health effects are most often poorly understood. The authors of the new article used a new platform of high-performance screening and evaluated the effect of 1823 chemicals on oligodendrocytes - cells that ensure the work of brain neurons. Among them, commonly used quaternary ammonium derivatives (components of cosmetics and disinfectants) and some organophosphates (non-flammable additives) had toxic effects on oligodendrocytes or impaired their development.
In its short century, mankind has invented, synthesized and released into the environment many xenobiotics - chemical substances, mostly organic, that do not exist in nature. Sometimes they decompose very slowly and have poorly predictable effects on living organisms, including humans. To describe it, it is necessary to consider many substances and their groups individually and remember that many different cells coexist in the human body. They differ in the set of receptors on the surface and the activity of genes, which determines and different sensitivity to foreign chemicals.
The authors of a new paper in Nature Neuroscience have taken on a specific part of this big task. They found out which of the common chemicals affect the growth of oligodendrocytes - glia cells that serve the work of neurons in the brain. More specifically, they serve as an insulating "wrapper" for axons, facilitating rapid transmission of nerve impulses. The construction is very similar to a roll, in which the neuron serves as a "filling" wrapped in multiple layers of glial cells instead of dough.
Oligodendrocytes are absolutely essential for normal brain function - their loss causes a number of diseases, including multiple sclerosis. However, they, unlike nerve cells, are usually given less attention when studying the effects of xenobiotics on the brain.
The authors of the new study used their own original high-throughput chemical screening platform - that is, a method for assessing the effects of chemicals on cells. It involves computer modeling as well as culturing cells and organoids - three-dimensional structures that mimic a real human organ - they were exposed to the drugs in an experiment.
The scientists looked at 1,823 compounds that are actively used in household and industry and therefore regularly enter the human body. Among them, the vast majority (1539) did not affect oligodendrocytes. However, 71 substances markedly changed cell development, and 22 accelerated it - these are compounds acting on thyroid hormone receptors, which are produced in the thyroid gland. Scientists knew about their role in the differentiation of oligodendrocytes from precursors before.
At the same time, 49 drugs disrupted the growth of such cells. Thus, substances from the group of quaternary ammonium compounds were toxic to oligodendrocytes - the cells died due to a nonspecific reaction to stress by the mechanism of programmed cell death (apoptosis). The result is alarming because quaternary ammonium derivatives are actively added to cosmetics (including hair conditioners) and used for disinfection. Many such disinfectants (e.g., benzalkonium chloride) were recommended to protect against coronavirus during the Covid-19 pandemic.
Other organic substances - organophosphates, which are used as flame retardants to prevent additives from igniting - did not kill oligodendrocytes but inhibited their development. The authors emphasize that the compounds described are able to penetrate the brain across the blood-brain barrier (BBB) and affect the child's brain development both in utero and after birth.
For one of the organophosphate diesters, bis(1,3-dichloro-2-propiono)phosphate (BDCIPP), scientists have also conducted epidemiologic studies. The substance was found in the urine of almost all of the children studied (99 percent), and exposure to BDCIPP was correlated with signs of brain developmental pathology: gross motor impairment, the need for special educational conditions and psychiatric observation.