E-cigarette Aerosol Exposure Induces Neurotoxic Accumulation of Metals in Mouse Brains
The past decade has seen a sharp rise in the use of e-cigarettes, especially among young people where they are seen as healthier alternatives to tobacco products. But just how healthy are e-cigarettes really? Recent research has shown that e-cigarette aerosol (vape clouds) contains metals that are neurotoxic and that could, depending on their levels, damage the central nervous system or CNS. Some of these metals are well-known carcinogens and are categorized as xenobiotic, meaning that they are not typically expected to be present in the body. Other metals, like iron and manganese, are usually beneficial to the body, but can become neurotoxic if their concentrations dip or rise beyond a normal range. However, it is largely unknown whether these metals accumulate at dangerous levels in the brain from direct inhalation or inadvertent exposure to e-cigarette aerosol.
To identify if metals from e-cigarette aerosol accumulate at neurotoxic levels in the CNS, Diane B. Re, Markus Hilpert, Brianna Saglimbeni, et al. utilized a mouse model to simulate firsthand use and secondhand exposure to e-cigarette aerosol. Two experimental groups and one control group of mice were used. The mice in the experimental groups were exposed to low and high doses of e-cigarette aerosol. The low dose group received fewer hours of exposure per twice daily session compared to the high dose group, while the control group was not exposed to any e-cigarette aerosol. After two months of routine exposure, the mice were euthanized and CNS regions were dissected to measure the accumulation of ten metals/metalloids. Accumulation of metals was measured at the NIEHS Center of Northern Manhattan Trace Metal Core using a technique called inductively coupled plasma mass spectrometry, which allows measuring elements at trace levels in biological specimens.
Results show both some significant accumulation and depletion of metals in the CNS of mice from both the low and high-dose experimental groups. Chromium, Copper, Iron, Manganese, and Lead were all found in the CNS at accumulated levels that would have neurotoxic effects on cognition and motor control. The accumulation of some of these metals in a brain region called the striatum is especially concerning given that damage or dysregulation to this region has been demonstrated in a variety of neurodegenerative diseases like Parkinson’s, Huntington’s, certain dementias, and neurological disorders like addiction, bipolar disorder, depression, obsessive-compulsive disorders, and autism spectrum disorders. Depletion of essential metals was observed in various CNS regions, though none were profound enough to be considered neurotoxic. These results indicate that exposure to e-cigarette aerosol not only causes accumulation of metals in brain regions, but may also affect how the brain manages its levels of essential metals that play important roles in normal brain functioning.
These findings confirm the need for additional studies looking at the potential health hazards posed by e-cigarette aerosol. The knowledge that these accumulations happened in both the low and high-dose groups hint at neurotoxic risks for both consumers and those who are exposed through secondhand inhalation. To build on these findings, future experimental studies must include larger sample sizes both in human populations and animal models to assess behavioral and pathological changes from chronic exposure over longer periods of time and ideally should be paralleled with human studies to identify biomarkers of neurotoxicity.
Re DB, Hilpert M, Saglimbeni B, Strait M, Ilievski V, Coady M, Talayero M, Wilmsen K, Chesnais H, Balac O, Glabonjat RA, Slavkovich V, Yan B, Graziano J, Navas-Acien A, Kleiman NJ. Exposure to e-cigarette aerosol over two months induces accumulation of neurotoxic metals and alteration of essential metals in mouse brain. Environ Res. 2021 Jul 8;202:111557. doi: 10.1016/j.envres.2021.111557. Epub ahead of print. PMID: 34245728.