The researchers hypothesize that magnetite particles from the air are inhaled and enter the brain via the olfactory bulb, a neuronal gateway to the brain that does not have the same blood-brain barrier protection that other brain regions do, Maher said.
Magnetite pollution nanoparticles in the human brain
Barbara A. Maher, Imad A. M. Ahmed, Vassil Karloukovski, Donald A. MacLaren, Penelope G. Foulds, David Allsop, David M. A. Mann, Ricardo Torres-Jardón, and Lilian Calderon-Garciduenas
From the Cover: Magnetite pollution nanoparticles in the human brain
PNAS 2016 113 (39) 10797-10801; published ahead of print September 6, 2016,
Proceedings of the National Academy of Sciences of the United States of America (PNAS)
We identify the abundant presence in the human brain of magnetite nanoparticles that match precisely the high-temperature magnetite nanospheres, formed by combustion and/or friction-derived heating, which are prolific in urban, airborne particulate matter (PM). Because many of the airborne magnetite pollution particles are <200 nm in diameter, they can enter the brain directly through the olfactory nerve and by crossing the damaged olfactory unit. This discovery is important because nanoscale magnetite can respond to external magnetic fields, and is toxic to the brain, being implicated in production of damaging reactive oxygen species (ROS). Because enhanced ROS production is causally linked to neurodegenerative diseases such as Alzheimer’s disease, exposure to such airborne PM-derived magnetite nanoparticles might need to be examined as a possible hazard to human health.
Biologically formed nanoparticles of the strongly magnetic mineral, magnetite, were first detected in the human brain over 20 y ago [Kirschvink JL, Kobayashi-Kirschvink A, Woodford BJ (1992) Proc Natl Acad Sci USA 89(16):7683–7687]. Magnetite can have potentially large impacts on the brain due to its unique combination of redox activity, surface charge, and strongly magnetic behavior. We used magnetic analyses and electron microscopy to identify the abundant presence in the brain of magnetite nanoparticles that are consistent with high-temperature formation, suggesting, therefore, an external, not internal, source. Comprising a separate nanoparticle population from the euhedral particles ascribed to endogenous sources, these brain magnetites are often found with other transition metal nanoparticles, and they display rounded crystal morphologies and fused surface textures, reflecting crystallization upon cooling from an initially heated, iron-bearing source material. Such high-temperature magnetite nanospheres are ubiquitous and abundant in airborne particulate matter pollution. They arise as combustion-derived, iron-rich particles, often associated with other transition metal particles, which condense and/or oxidize upon airborne release. Those magnetite pollutant particles which are <～200 nm in diameter can enter the brain directly via the olfactory bulb. Their presence proves that externally sourced iron-bearing nanoparticles, rather than their soluble compounds, can be transported directly into the brain, where they may pose hazard to human health.
首先在20年前在人脑中检测到生物形成的强磁性矿物磁铁矿的纳米颗粒[Kirschvink JL，Kobayashi-Kirschvink A，Woodford BJ（1992）Proc Natl Acad Sci USA 89（16）：7683-7687] 。由于氧化还原活性，表面电荷和强磁性行为的独特组合，磁铁矿可能对大脑产生潜在的巨大影响。我们使用磁分析和电子显微镜来鉴定在磁铁矿纳米颗粒中与高温形成一致的大量存在，因此表明外部而不是内部来源。包括来自归因于内源来源的自形粒子的单独的纳米粒子群，这些脑磁铁矿经常与其他过渡金属纳米粒子一起发现，并且它们显示圆形的晶体形态和熔融的表面纹理，在从初始加热的含铁源冷却时反映结晶材料。这种高温磁铁矿纳米球是普遍存在和丰富的空气中颗粒物污染。它们作为燃烧产生的富铁颗粒而出现，通常与其他过渡金属颗粒结合，其在空气释放时冷凝和/或氧化。那些直径<〜200nm的磁铁矿污染物颗粒可以通过嗅球直接进入大脑。他们的存在证明，外部来源的含铁纳米粒子，而不是其可溶性化合物，可以直接运输到大脑，在那里他们可能对人类健康构成危害。
Environmental Magnetite in the Human Brain
Mineral nanoparticles similar to those that have been associated with Alzheimer’s disease may enter the brain through the inhalation of polluted air.
By Ashley P. Taylor | September 6, 2016
In addition to angular, endogenous magnetite nanoparticles (left), researchers found spherical magnetite particles in postmortem human brains (middle) resembling those found in polluted air (right).
In more than three dozen postmortem human brains, scientists have detected nanoparticles of magnetite that they suspect came from the environment. The brain produces magnetite particles that are associated with Alzheimer’s disease, but these endogenous particles are angular in shape, whereas the newly discovered compounds are spherical. Their shape and other properties suggest that the nanoparticles were generated during high-temperature processes like combustion.
The results, published yesterday (September 6) in PNAS, suggests that inhaled magnetite, which is known to be a ubiquitous air pollutant, can make its way to the brain. Barbara Maher, an environmental scientist at the University of Lancaster, and her coauthors now speculate that this environmental magnetite could pose a health risk.
“This is the first report of iron oxide particles in brain tissue that may have come from an industrial source. As such, this opens up questions about potential neurotoxic effects from industrial pollutants that had not been previously considered,” University of Florida’s Jon Dobson, who researches the potential neurodegenerative role of biologically produced magnetic compounds and was not involved in the study, told The Scientist in an email.
In 1992, researchers discovered angular particles of magnetite in the human brain. Sixteen years later, a comparison of healthy and Alzheimer’s brains revealed that higher levels of magnetite correlated with the incidence of disease. Most recently, scientists studying rat neuronal cell cultures found that magnetite and amyloid-β peptides seemed to stabilize each other; the two particles together were more harmful to neurons in culture than amyloid-β peptides alone.
Maher had been studying the airborne particulate matter, including magnetite, along roadsides, and decided to examine whether that magnetite might enter the brain, where it could potentially have similar toxic effects. She and her colleagues examined the quantity and structure of the magnetite within frontal cortex samples of 37 human brains, which came from the Manchester Brain Bank in the U.K. and from people who had died in fatal accidents in Mexico City between 2004 and 2008.
Using high-resolution transmission electron microscopy, the researchers searched the brain slices. They identified endogenous, angular magnetite particles, which ranged in diameter from 50 to 150 nanometers, as well as spherical particles that ranged from less than 5 nanometers to more than 100 nanometers. The researchers believed these spherical compounds came from particulate matter in the air, Maher said.
Both in shape and in texture, these round magnetite particles resembled magnetite particles from roadside particulate matter, “and some of the particles have some very distinctive surface textures,” Maher said. Moreover, the magnetite particles “co-occur with other rather exotic metals, [which] are not metals that you would expect normally to find in the human brain,” she added. The researchers hypothesize that magnetite particles from the air are inhaled and enter the brain via the olfactory bulb, a neuronal gateway to the brain that does not have the same blood-brain barrier protection that other brain regions do, Maher said.
Dobson noted that a causal link between magnetite particles of any type and neurodegeneration has not been established. However “mechanisms proposed for a potential role in neurodegeneration would be the pretty much the same for both types of particles,” he added.
Although researchers do not know if environmentally derived magnetite has the same effects as endogenous magnetite on neuron health, “it would be foolish to ignore the possibility that it could be creating an additional health hazard for humans,” Maher said.
The study “gives an explanation for the high abundance of magnetite in the brain and, in turn, points towards its connection with Alzheimer’s,” Jordi Soriano, a University of Barcelona biophysicist who has studied magnetite’s effects on neurons in cell culture and was not involved the present study, told The Scientist in an email.
He noted, however, that the researchers did not sample any brains from people who had lived in nonurban areas, which would be necessary “to prove the connection between pollution and magnetic nanoparticles accumulation and structure.” This type of epidemiological study correlating likely magnetite exposure and neurodegenerative disease is one area for future research, Maher said.
B. Maher et al., “Magnetite pollution nanoparticles in the human brain,” PNAS, doi:10.1073/pnas.1605941113, 2016.
