Skip to main content
  • Submit
  • About
    • Editorial Board
    • PNAS Staff
    • FAQ
    • Accessibility Statement
    • Rights and Permissions
    • Site Map
  • Contact
  • Journal Club
  • Subscribe
    • Subscription Rates
    • Subscriptions FAQ
    • Open Access
    • Recommend PNAS to Your Librarian
  • Log in
  • My Cart

Main menu

  • Home
  • Articles
    • Current
    • Special Feature Articles - Most Recent
    • Special Features
    • Colloquia
    • Collected Articles
    • PNAS Classics
    • List of Issues
  • Front Matter
  • News
    • For the Press
    • This Week In PNAS
    • PNAS in the News
  • Podcasts
  • Authors
    • Information for Authors
    • Editorial and Journal Policies
    • Submission Procedures
    • Fees and Licenses
  • Submit
  • About
    • Editorial Board
    • PNAS Staff
    • FAQ
    • Accessibility Statement
    • Rights and Permissions
    • Site Map
  • Contact
  • Journal Club
  • Subscribe
    • Subscription Rates
    • Subscriptions FAQ
    • Open Access
    • Recommend PNAS to Your Librarian

User menu

  • Log in
  • My Cart

Search

  • Advanced search
Home
Home

Advanced Search

  • Home
  • Articles
    • Current
    • Special Feature Articles - Most Recent
    • Special Features
    • Colloquia
    • Collected Articles
    • PNAS Classics
    • List of Issues
  • Front Matter
  • News
    • For the Press
    • This Week In PNAS
    • PNAS in the News
  • Podcasts
  • Authors
    • Information for Authors
    • Editorial and Journal Policies
    • Submission Procedures
    • Fees and Licenses

New Research In

Physical Sciences

Featured Portals

  • Physics
  • Chemistry
  • Sustainability Science

Articles by Topic

  • Applied Mathematics
  • Applied Physical Sciences
  • Astronomy
  • Computer Sciences
  • Earth, Atmospheric, and Planetary Sciences
  • Engineering
  • Environmental Sciences
  • Mathematics
  • Statistics

Social Sciences

Featured Portals

  • Anthropology
  • Sustainability Science

Articles by Topic

  • Economic Sciences
  • Environmental Sciences
  • Political Sciences
  • Psychological and Cognitive Sciences
  • Social Sciences

Biological Sciences

Featured Portals

  • Sustainability Science

Articles by Topic

  • Agricultural Sciences
  • Anthropology
  • Applied Biological Sciences
  • Biochemistry
  • Biophysics and Computational Biology
  • Cell Biology
  • Developmental Biology
  • Ecology
  • Environmental Sciences
  • Evolution
  • Genetics
  • Immunology and Inflammation
  • Medical Sciences
  • Microbiology
  • Neuroscience
  • Pharmacology
  • Physiology
  • Plant Biology
  • Population Biology
  • Psychological and Cognitive Sciences
  • Sustainability Science
  • Systems Biology
Research Article

Magnetite pollution nanoparticles in the human brain

Barbara A. Maher, View ORCID ProfileImad A. M. Ahmed, Vassil Karloukovski, Donald A. MacLaren, Penelope G. Foulds, David Allsop, David M. A. Mann, Ricardo Torres-Jardón, and Lilian Calderon-Garciduenas
PNAS first published September 6, 2016; https://doi.org/10.1073/pnas.1605941113
Barbara A. Maher
aCentre for Environmental Magnetism and Palaeomagnetism, Lancaster Environment Centre, University of Lancaster, Lancaster LA1 4YQ, United Kingdom;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: b.maher@lancaster.ac.uk
Imad A. M. Ahmed
bDepartment of Earth Sciences, University of Oxford, Oxford OX1 3AN, United Kingdom;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • ORCID record for Imad A. M. Ahmed
Vassil Karloukovski
aCentre for Environmental Magnetism and Palaeomagnetism, Lancaster Environment Centre, University of Lancaster, Lancaster LA1 4YQ, United Kingdom;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Donald A. MacLaren
cScottish Universities Physics Alliance, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Penelope G. Foulds
dDivision of Biomedical and Life Sciences, Faculty of Health and Medicine, University of Lancaster, Lancaster LA1 4YQ, United Kingdom;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
David Allsop
dDivision of Biomedical and Life Sciences, Faculty of Health and Medicine, University of Lancaster, Lancaster LA1 4YQ, United Kingdom;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
David M. A. Mann
eDivision of Neuroscience & Experimental Pyschology, School of Biological Sciences, University of Manchester, Manchester M6 8HD, United Kingdom;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Ricardo Torres-Jardón
fCentro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Mexico City 04310, Mexico;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Lilian Calderon-Garciduenas
gNeurotoxicology Laboratory, The University of Montana, Missoula, MT 59812;
hUniversidad del Valle de México, Mexico City, 04850, Mexico
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  1. Edited by Yinon Rudich, Weizmann Institute of Science, Rehovot, Israel, and accepted by Editorial Board Member A. R. Ravishankara July 25, 2016 (received for review April 13, 2016)

See related content:

  • Magnetite in the human body
    - Oct 11, 2016
  • Article
  • Figures & SI
  • Info & Metrics
  • PDF
Loading

Significance

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.

Abstract

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.

  • brain magnetite
  • magnetite pollution particles
  • Alzheimer's disease
  • combustion-derived nanoparticles
  • airborne particulate matter

Magnetic analyses of human brain samples have identified the presence of nanoparticles of magnetite, a strongly magnetic (ferrimagnetic) mixed Fe2+/Fe3+ iron oxide (1⇓–3). Based on their nanoscale dimensions and euhedral (cubo-octahedral or prismatic) crystal shapes, these magnetite nanoparticles are thought to have formed by biological processes (1, 4), via in situ crystallization, possibly within the 8-nm-diameter cores of the iron storage protein, ferritin (e.g., ref. 5).

The specific presence of magnetite in the brain is important because it has been causally linked with potential cellular responses to external magnetic fields (e.g., in magnetic resonance imaging studies) (1), aging (6), and with neurodegenerative disease (e.g., refs. 2, 3, and 7). Previous work has shown a correlation between the amount of brain magnetite and the incidence of Alzheimer’s disease (AD) (2, 3). Neuropathological changes associated with AD include the formation of senile plaques, containing β-amyloid fibrils (e.g., refs. 8, and 9). When associated with redox-active transition metal ions, such as Fe2+ ions, β-amyloid can generate damaging reactive oxygen species, directly contributing to oxidative brain damage, a key early feature of AD (e.g., refs. 8⇓–10). Magnetite nanoparticles have been found directly associated with AD plaques and tangles (e.g., refs. 11⇓–13). In vitro experimental data show that magnetite acts synergistically to enhance the toxicity of β-amyloid (7).

We used magnetometry, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and energy dispersive X-ray (EDX) analysis to examine the mineralogy, morphology, and composition of magnetic nanoparticles in and from the frontal cortex of 37 human brain samples, obtained from subjects who lived in Mexico City (14) (29 cases; ages 3 to 85 y; two females) and in Manchester, UK (8 cases; ages 62 to 92 y; five females; Tables S1 and S2). These brain magnetites display compelling similarity with the magnetite nanospheres formed by combustion, which are ubiquitous and prolific in urban, airborne particulate matter (PM) (15⇓⇓⇓–19). We report here identification of the presence in human brain tissue of magnetite nanoparticles with an external, rather than an endogenous, source.

View this table:
  • View inline
  • View popup
Table S1.

Summary of Mexico City cases studied

View this table:
  • View inline
  • View popup
Table S2.

Summary of Manchester cases studied

Results

To quantify brain magnetic content, a cryogenic magnetometer was used to measure, at room and low temperature (77 K), the saturation magnetic remanence (SIRM) of frontal tissue samples, initially fresh-frozen and subsequently freeze-dried. The SIRM 77 K captures the magnetic contribution of ferrimagnetic grains that are so small (<∼20 nm) as to be magnetically unstable (superparamagnetic) at room temperature. The magnetic brain particles were then examined directly, by HRTEM and EDX analyses both of ultrathin tissue sections and of magnetically extracted particles, after tissue digestion with the proteolytic enzyme, papain. Every analytical step was designed and monitored to preclude any possible magnetic contamination.

The brain magnetic analyses identify the presence in all of the samples of strongly magnetic, easily magnetized nanoparticles, with concentrations ranging from 0.2 to 12 µg/g dry tissue (Fig. S1). The sample magnetic properties are dominated by behavior characteristic of interacting clusters of ferrimagnetic magnetite or maghemite (Fig. S2). Although highest brain magnetite concentrations (>10 µg/g dry tissue) are seen in many of the oldest cases, several of the much younger Mexico City cases, some exposed to high ambient concentrations of fine-grained (<2.5 µm aerodynamic diameter) airborne PM, also display high ferrimagnetic concentrations. Indeed, the highest brain magnetite content is found in a 32-y-old Mexico City resident (Fig. S1).

Fig. S1.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S1.

SIRM 77 K (10−6 A m2/kg) and estimated magnetite concentration (micrograms per gram) for frontal cortex samples versus age at death, Mexico City and Manchester cases. The annual mean airborne PM2.5 concentration (micrograms per cubic meter) is given for the residence area of the Mexican cases (inside each data symbol); SIRM values for gray (g) and white (w) matter are given for the Manchester cases, together with their clinical diagnosis upon death (CAA, cerebral amyloid angiopathy; CVD, cerebrovascular disease; DLB, dementia with Lewy bodies; see Tables S1 and S2).

Fig. S2.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S2.

Magnetic analyses of brain tissue samples (freeze-dried): (A) acquisition of isothermal (RT) remanent magnetization in applied DC fields from 5 mT to 1 T. All samples acquire most of their magnetization at fields < 100 mT, indicating the dominant presence of ferrimagnetic minerals (e.g., magnetite and/or maghemite). The magnetically softest sample (the Mexico City case to the left of all remaining samples) has the highest SIRM value (case 282). (B) Measurement of LT remanence (77 K, DC field 1 T) upon warming to RT, showing the thermal unblocking of the superparamagnetic particles. (C) Comparison between the brain samples and sized, synthetic magnetites of known grain size and degree of dispersion (37), as measured by the RT ARM, normalized by the SIRM, plotted against the median destructive field of the ARM (MDFARM, in milliteslas). All of the measurable brain samples fall within the region of the least-dispersed synthetic, submicrometer magnetites, indicating magnetic interactions, and hence agglomeration/clustering of some of the brain magnetite particles.

HRTEM and EELS analyses of the tissue sections identify the presence within frontal cells of magnetite, occurring as two distinct types of nanoparticle (Fig. 1 and Figs. S3 and S4). The majority of particles display rounded, even spherical morphologies (Fig. 1A, with higher magnification in Fig. 1B, and Fig. 1F), with diameters between 10 and 150 nm (Fig. S5). The additional presence in the brain cells of other transition metal nanoparticles, containing Pt, Ni, and Co (and possibly Cu), is identified by EELS (Fig. S6) and EDX (Figs. S7 and S8). These rounded magnetites contrast strongly with the angular, cubo-octahedral magnetite crystals also observed (relatively very rarely) within the brain tissue samples (Fig. 1C, and with higher magnification in Fig. 1D).

Fig. 1.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. 1.

Transmission electron micrographs of brain thin sections, identifying two distinct types of magnetite morphologies within frontal cells: (A and F) rounded particles (A shown at higher magnification in B); and (C) angular, euhedral particles, which we attribute to endogenous formation (particles from C shown at higher magnification in D). (E) EELS spectra (in blue) for the rounded particle shown in F and for standard iron oxide species. The position of the Fe−L3 edge absorption peak, the broad feature of the Fe−L2 (compared with the sharp edges, arrowed, of the fully oxidized Fe3+ phases), and the integrated areas of the L3/L2 (5.5) and the Fe/O (0.56) are all consistent with magnetite (also see Figs. S3 and S4).

Fig. S3.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S3.

(A) High-angle annular diffraction and (B) dark-field TEM micrographs showing spherical magnetic nanoparticles in brain tissues. (C) Fe−L2,3 EELS spectra of nanoparticles identified in the selected areas (boxes 1 through 4) showing the absence of any preedges (see hematite, goethite, and ferrihydrite preedge at ∼708.8 eV), Fe−L3 edges centered at 708 eV, and broad Fe−L2 features characteristic of magnetite, compared with the Fe−L2,3 EELS spectra (D) of standard magnetite, siderite, hematite, goethite, and two-line ferrihydrite.

Fig. S4.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S4.

Fe−L2,3-edge spectra of magnetic particles found in brain samples. The Fe−L3 and Fe−L2 edges in all three samples are at 708.7 to 709.8 eV and 72 to 723 eV, in excellent agreement with the chemical shift in EELS spectra for the magnetite structure (also see Fig. S3).

Fig. S5.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S5.

Particle size distribution of magnetic particles in brain magnetic extracts. Particle size measurements were carried out on all of the HRTEM micrographs collected from six brain magnetic extracts from different subjects. The ImageJ software package was used to describe the imaged particles (spherical and nonspherical) in terms of the longest and shortest diameters, perimeter projected area, or equivalent spherical diameter.

Fig. S6.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S6.

(A) Co−L2,3 EELS spectra of cobalt (II, III) oxide nanoparticles associated with magnetite particles in brain tissues. Co−L3 and Co−L2 edges from different areas of a brain tissue sample (B) are centered at ∼780 and ∼796 eV, respectively, in a good match with an EELS spectrum of a standard cobalt (II,III) oxide.

Fig. S7.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S7.

EDX analysis of metal-bearing NPs in brain tissue samples, showing presence of Fe, Ni, and Co (and possibly Cu, with the caveat that the samples were mounted on holey carbon films on Cu grids).

Fig. S8.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S8.

EDX analysis of metal-bearing NPs in brain tissue samples, showing the presence of Fe, Ni, Pt, Co, and, possibly, Cu.

Crystallographic analysis of the particles within the tissue sections is difficult (due to rapid carbon buildup under the microscope electron beam). We therefore examined magnetically extracted (20) brain particles, to more fully characterize their mineralogy, surface textures, and particle size distribution. In accord with the observations on the untreated tissue samples, many of the extracted particles display rounded to spherical morphologies (Fig. 2 and Figs. S7–S10). In particular, some have fused surface crystallites (Fig. 2H) that would be very difficult to reconcile with low-temperature growth or dissolution formation processes. Indexing of the lattice fringes of the HRTEM of these particles is consistent with the magnetite crystal structure (Fig. 2 C, E, and G). Some surface oxidation toward its oxidized counterpart, maghemite, is evident (Fig. 2I). The particle size distribution of the rounded brain magnetite particles is notably broad, with a median (longest) diameter of 18 nm and maximum diameter of ∼150 nm (Fig. S5). Such dimensions greatly exceed those of nanoparticles formed within the 8-nm diameter of ferritin cores (5).

Fig. 2.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. 2.

Transmission electron micrographs of rounded particles magnetically extracted from human brain samples: (A, D, F, and H) Mexico City cases; (B) Manchester case. (H) A large (∼150-nm diameter) spherical particle with fused, interlocking magnetite/maghemite surface crystallites. (C, E, and G) Indexing of the lattice fringes of the brain particles is consistent with the (400) reflection of magnetite and (I) mixed magnetite and maghemite of selected areas 1–5 in H.

Fig. S9.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S9.

(A–I) A collection of HRTEM micrographs of magnetite particles, extracted from brain tissues, showing dominant rounded morphologies. (C) Micrograph shows fused magnetite particles, and (D and E) micrographs show aggregated magnetite particles.

Fig. S10.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S10.

(A) HRTEM micrograph of magnetically extracted magnetite particles from brain tissues. (B−D) FFT patterns of selected areas (1, 2, and 3, respectively) featuring a single crystal (B) and magnetite particles superimposed at ∼90° (C and D).

Discussion

The geometric, angular particles resemble the in situ, biogenic magnetite previously reported (1, 4); we thus ascribe these euhedral magnetite particles to endogenous formation. The rounded magnetite nanoparticles (up to ∼150-nm diameter, with distinctive surface textures, and cooccurring with other PM-associated metals, including Pt) have not been identified previously in brain tissue sections. Apparently similar spherical structures, with diameters of 8 to 50 nm, have been found recently within amyloid plaque cores isolated from human brain (13) but were attributed to a biological rather than an external pollution-derived source. However, the surface textures, size, and size distribution of the spherical magnetites identified in our study, and the cooccurrence of PM-associated transition metal nanoparticles, are all inconsistent with the characteristics of biogenically formed magnetite (1, 4, 12). They bear compelling resemblance, instead, to the rounded/spherical magnetite nanoparticles (nanospheres) that are both ubiquitous and prolific within airborne, high-temperature (combustion-derived) PM (15⇓⇓⇓–19, 21). The rounded shapes of these airborne, PM-derived magnetites (Fig. 3 and Fig. S11), and fusing of interlocking, surface crystallites (Fig. 3 C and D), reflect their high-temperature sources, and their subsequent crystallization, upon rapid cooling and/or oxidation, as Fe-rich nanospheres. Depending on PM source(s) (vehicular, subway, industrial, indoor), other transition metals are often coassociated with magnetite and other pollution nanoparticles (15⇓–17, 19). Pt release, for instance, is associated with increasing vehicular use of catalytic converters (e.g., ref. 22). Frictional heating, e.g., of brake pads, can also produce high-temperature magnetite nanoparticles (21). Magnetite can arise from combustion of many types of organic matter, depending on heating temperature and atmosphere, and source Fe content (23⇓–25).

Fig. 3.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. 3.

TEM/scanning EM micrographs of anthropogenic (combustion-derived), magnetically extracted airborne particles. (A, shown at higher magnification in B) Magnetite nanoparticles from airborne PM (<10 µm), from Cable Street, Lancaster, United Kingdom (March 2009), sampled with a cascade impactor. Many particles display rounded profiles; some are fused together. (C and D) Spherical magnetite particles, Didcot power station, comprising fused magnetite particles (note the variable lattice orientations in C and the fused surface crystallites in D).

Fig. S11.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. S11.

TEM image of magnetite nanoparticles captured from the exhaust plume of a diesel engine. Adapted from ref. 19.

Although PM mass has conventionally been used for setting of legislative airborne PM concentration limits, it is possible that ultrafine particle size and number are of greater significance in terms of mortality (26) and health impacts (e.g., ref. 27). Our magnetic measurements of roadside airborne PM [in Lancaster, United Kingdom (28)] indicate magnetite particle numbers equivalent to ∼2.01 × 108 m−3 of roadside air, for ∼50-nm-sized magnetite particles, for an ambient PM10 concentration of ∼40 µg⋅m−3 (compared, for example, with the annual mean PM10 for Mexico City of between ∼30 and 70 µg⋅m−3).

The abundant combustion-derived magnetite particles found in airborne PM can range widely in size, from less than 5 nm to more than 1 µm (15⇓–17, 19). Those particles of nanoscale dimensions, requiring analysis by transmission rather than scanning electron microscopy, have, until recently, received less attention than the larger, often more heterogenous spherules. Magnetite nanospheres up to ≾ 200 nm can have a direct entry route to the brain through the axons of the olfactory nerve, as suggested by experimental studies on carbon (29) and TiO2 nanoparticles (30), and the reported presence of NPs in the olfactory bulb of some Mexico City cases (14, 31⇓–33).

Although many of the highly magnetic brain samples come from the older Manchester cases (>65 y at death), especially those with severe to moderate AD, equivalent or higher magnetite concentrations are also displayed by young (<40 y at death) Mexico City residents, especially those exposed to high PM2.5 levels (annual mean ≳25 µg⋅m−3). Increased metals content and AD neuropathological hallmarks have been found in young human brains exposed to high airborne PM2.5 concentrations in Mexico City (14, 33). However, it was not previously known if the presence of metals in AD brains was due to transport to the brain of nanoparticles themselves or of their solubilized compounds. Our HRTEM results provide compelling evidence for the presence of externally sourced magnetite, and other metal-bearing nanoparticles in the frontal cortex of both the Mexico City and Manchester cases. It is notable that less than 5% of AD cases are directly inherited, indicating that nongenetic (environmental) factors, and/or gene/environment interactions, are likely playing a major role in initiating and/or promoting the disease. Jung et al. (34) found a 138% risk of increase of AD per increase of 4.34 μg⋅m−3 in PM2.5 over a 9-y follow-up period in 95,690 individuals in Taiwan. It is not yet understood which PM properties (e.g., size, number, mineralogy, and associated chemical species) contribute most to toxic effects (e.g., ref. 35). Our preliminary magnetic results regarding both PM exposure and AD are thus both intriguing and warrant more intensive study. Because of their combination of ultrafine size, specific brain toxicity, and ubiquity within airborne PM, pollution-derived magnetite nanoparticles might require consideration as a possible AD risk factor. In addition to occupational settings [including, for example, exposure to printer toner powders (36)], higher concentrations of magnetite pollution nanoparticles are likely to arise in the indoor environment from open fires (25) or poorly sealed stoves used for cooking and/or heating, and in the outdoor environment from vehicle (especially diesel) and/or industrial PM sources.

Materials and Methods

Brain Samples.

Fresh, frozen brain tissues were obtained from 38 individuals (Tables S1 and S2), 9 from the Manchester Brain Bank (ethical review and approval by the Manchester Brain Bank Management Committee and the Newcastle and North Tyneside I Regional Ethics Committee) and 29 from Mexico City, from forensic cases (fatal accidents) with no identifiable personal data, not meeting the regulatory definition of human subject research (University of Montana Institutional Review Board). A block (∼25 g) of tissue was cut from the frontal lobes; subsamples were cut using nonmagnetic [polytetrafluoroethylene (PTFE)] instruments. The Manchester samples were dissected into gray (nine samples) and white (eight samples) matter.

To preclude any contamination, or operator bias, samples were handled with nonmagnetic instruments in a laminar flow clean bench environment and measured blind to diagnostics, and sample holder remanences were removed. The tissue samples were freeze-dried and placed in polystyrene sample holders (10 cc) for magnetic measurements.

Magnetic Analyses.

Magnetic measurements were made at the Centre for Environmental Magnetism and Paleomagnetism, Lancaster University, using superconducting quantum interference device magnetometry. Room-temperature isothermal remanent magnetizations (IRMs) (Fig. S2A) were measured with a GM400 Cryogenic Magnetometer (mean background noise level 5.9 ×10−11 A2; Cryogenic Consultants Ltd.); Low-temperature IRMs were measured (Fig. S2B) at temperatures between 293 and 77 K (±0.5 K) on a single-axis magnetic property measurement system XL magnetometer (Quantum Design). To identify magnetic grain sizes and/or magnetic interactions (37), anhysteretic remanence (ARM) was induced in a decaying (100 mT, peak) alternating magnetic field (af), with a small superimposed direct current (DC) field (0.08 mT), and subsequently af-demagnetized (Fig. S2C). Stepwise remanence acquisition was measured with incremental application of DC fields of 10, 20, 30, 50, 75, 100, and 300 mT and 1 T. The samples were cooled to 77 K and subjected to an applied DC field, 1 T, and their remanence was measured as they warmed to room temperature.

Tissue Sections.

Magnetically extracted particles.

A subset of samples (six tissue samples, and one blank without any tissue) was subjected to a magnetic extraction procedure, designed to maximize removal of submicrometer ferrimagnets (20). All reagents were prepared from ultrapurity Milli-Q water and prefiltered (<0.1 µm PTFE membrane filter) to preclude any particulate contamination; all instruments and sample holders were nonmagnetic (PTFE and polystyrene, respectively).

Papain from papaya latex (twice-crystallized; Sigma) was solubilized in 50 mM sodium acetate (prefiltered and magnetically measured multiple times to demonstrably preclude magnetic contamination). The tissue samples were digested overnight in papain at 65 °C and at fixed pH 7.0 ± 0.02, in a strictly oxygen-free environment inside a particulate-clean laboratory. The resultant suspension was circulated continuously (2 to 3 d, with a peristaltic pump) past a magnetized probe, producing a high field gradient at its tip (maximum field ∼40 mT). The magnetically extracted particles were mounted on holey carbon films on carbon-coated copper grids for transmission electron microscopy (TEM).

HRTEM, EELS, and EDX.

Electron microscopy was conducted on two instruments, a JEOL ARM200cF and an FEI Tecnai F20, operated at 200 kV. A Gatan Quantum spectrometer was used for EELS in scanning TEM (STEM) mode. Due to rapid carbon buildup under the electron beam, only point acquisition spectra were collected; each spectrum typically summed from several spectra from each nanoparticle and from multiple nanoparticles. This procedure also minimized the electron dose experienced by individual nanoparticles and ensured that their chemical reduction was avoided. Time-dependent observations did not reveal any obvious structural or spectroscopic changes to the nanoparticles within the acquisition time (but were observed under prolonged exposure), and we conclude that the EELS data presented are representative of the nanoparticles' as-formed chemistry. EELS data were processed in Python using Hyperspy package. To determine dominant lattice spacings, fast Fourier transforms (FFTs) of high-resolution micrographs were compared with a simulated diffraction pattern of face-centered cubic magnetite (space group Fd3¯m, no. 227, a = 8.3941 Å), and maghemite (space group P4332, no. 212, a = 8.3457 Å). Sample sensitivity under STEM imaging precluded elemental mapping by EDX.

Acknowledgments

We appreciate the reviewers’ comments, which improved our manuscript. We thank Dr. Zabeada Aslam for her technical help, Dr. Mark Taylor (University of Lancaster) and Angelica Gonzalez-Maciel (Instituto Nacional de Pediatria, Mexico City) for assistance with tissue subsampling, and the University of Leeds Engineering and Physical Sciences Research Council-funded Nanoscience and Nanotechnology Facility for access to the HRTEM. We acknowledge the support of the Manchester Brain Bank by Alzheimer’s Research UK and Alzheimer’s Society through their funding of Brains for Dementia Research initiative, and service support costs from Medical Research Council.

Footnotes

  • ↵1To whom correspondence should be addressed. Email: b.maher{at}lancaster.ac.uk.
  • Author contributions: B.A.M. designed research; B.A.M., I.A.M.A., V.K., and D.A.M. performed research; P.G.F. and D.A. contributed new reagents/analytic tools; B.A.M., I.A.M.A., V.K., D.A.M., D.M.A.M., R.T.-J., and L.C.-G. analyzed data; B.A.M. wrote the paper; D.M.A.M. provided brain tissue samples and medical diagnosis data; R.T.-J. provided airborne PM data; and L.C.-G. provided brain tissue samples.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission. Y.R. is a Guest Editor invited by the Editorial Board.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1605941113/-/DCSupplemental.

View Abstract

References

  1. ↵
    1. Kirschvink JL,
    2. Kobayashi-Kirschvink A,
    3. Woodford BJ
    (1992) Magnetite biomineralization in the human brain. Proc Natl Acad Sci USA 89(16):7683–7687.
    .
    OpenUrlAbstract/FREE Full Text
  2. ↵
    1. Pankhurst Q,
    2. Hautot D,
    3. Khan N,
    4. Dobson J
    (2008) Increased levels of magnetic iron compounds in Alzheimer’s disease. J Alzheimers Dis 13(1):49–52.
    .
    OpenUrlPubMed
  3. ↵
    1. Hautot D,
    2. Pankhurst QA,
    3. Khan N,
    4. Dobson J
    (2003) Preliminary evaluation of nanoscale biogenic magnetite in Alzheimer’s disease brain tissue. Proc Biol Sci 270(Suppl 1):S62–S64.
    .
    OpenUrlAbstract/FREE Full Text
  4. ↵
    1. Schultheiss-Grassi PP,
    2. Wessiken R,
    3. Dobson J
    (1999) TEM investigations of biogenic magnetite extracted from the human hippocampus. Biochim Biophys Acta 1426(1):212–216.
    .
    OpenUrlPubMed
  5. ↵
    1. Quintana C,
    2. Cowley JM,
    3. Marhic C
    (2004) Electron nanodiffraction and high-resolution electron microscopy studies of the structure and composition of physiological and pathological ferritin. J Struct Biol 147(2):166–178.
    .
    OpenUrlCrossRefPubMed
  6. ↵
    1. Dobson J
    (2002) Investigation of age-related variations in biogenic magnetite levels in the human hippocampus. Exp Brain Res 144(1):122–126.
    .
    OpenUrlCrossRefPubMed
  7. ↵
    1. Teller S,
    2. Tahirbegi IB,
    3. Mir M,
    4. Samitier J,
    5. Soriano J
    (2015) Magnetite-Amyloid-β deteriorates activity and functional organization in an in vitro model for Alzheimer's disease. Sci Rep 5:17261.
    .
    OpenUrlCrossRefPubMed
  8. ↵
    1. Allsop D,
    2. Mayes J,
    3. Moore S,
    4. Masad A,
    5. Tabner BJ
    (2008) Metal-dependent generation of reactive oxygen species from amyloid proteins implicated in neurodegenerative disease. Biochem Soc Trans 36(Pt 6):1293–1298.
    .
    OpenUrlAbstract/FREE Full Text
  9. ↵
    1. Tabner BJ,
    2. Mayes J,
    3. Allsop D
    (2010) Hypothesis: Soluble Aβ oligomers in association with redox-active metal ions are the optimal generators of reactive oxygen species in Alzheimer’s disease. Int J Alzheimers Dis 2011:546380.
    .
    OpenUrlPubMed
  10. ↵
    1. Castellani RJ, et al.
    (2007) Iron: The redox-active center of oxidative stress in Alzheimer disease. Neurochem Res 32(10):1640–1645.
    .
    OpenUrlCrossRefPubMed
  11. ↵
    1. Collingwood J,
    2. Dobson J
    (2006) Mapping and characterization of iron compounds in Alzheimer's tissue. J Alzheimer's Dis 10(2-3):215–222.
    .
    OpenUrlPubMed
  12. ↵
    1. Quintana C, et al.
    (2006) Study of the localization of iron, ferritin, and hemosiderin in Alzheimer’s disease hippocampus by analytical microscopy at the subcellular level. J Struct Biol 153(1):42–54.
    .
    OpenUrlCrossRefPubMed
  13. ↵
    1. Plascencia-Villa G, et al.
    (2016) High-resolution analytical imaging and electron holography of magnetite particles in amyloid cores of Alzheimer’s disease. Sci Rep 6:24873.
    .
    OpenUrlCrossRefPubMed
  14. ↵
    1. Calderón-Garcidueñas L, et al.
    (2016) Prefrontal white matter pathology in air pollution exposed Mexico City young urbanites and their potential impact on neurovascular unit dysfunction and the development of Alzheimer’s disease. Environ Res 146:404–417.
    .
    OpenUrl
  15. ↵
    1. Mitchell R,
    2. Maher BA
    (2009) Evaluation and application of biomagnetic monitoring of traffic-derived particulate pollution. Atmos Environ 43(13):2095–2103.
    .
    OpenUrlCrossRef
  16. ↵
    1. Moreno T, et al.
    (2015) A new look at inhalable metalliferous airborne particles on rail subway platforms. Sci Total Environ 505:367–375.
    .
    OpenUrlCrossRefPubMed
  17. ↵
    1. Chen Y,
    2. Shah N,
    3. Huggins FE,
    4. Huffman GP
    (2006) Microanalysis of ambient particles from Lexington, KY, by electron microscopy. Atmos Environ 40(4):651–663.
    .
    OpenUrlCrossRef
  18. ↵
    1. Puffer JH,
    2. Russell EWB,
    3. Rampino MR
    (1980) Distribution and origin of magnetite spherules in air, waters, and sediments of the greater New York City Area and the North Atlantic Ocean. J Sediment Petrol 50(1):247–256.
    .
    OpenUrlAbstract/FREE Full Text
  19. ↵
    1. Liati A,
    2. Pandurangi SS,
    3. Boulouchos K,
    4. Schreiber D,
    5. Dasilva YAR
    (2015) Metal nanoparticles in diesel exhaust derived by in-cylinder melting of detached engine fragments. Atmos Environ 101:34–40.
    .
    OpenUrlCrossRef
  20. ↵
    1. Hounslow MW,
    2. Maher BA
    (1996) Quantitative extraction and analysis of carriers of magnetization in sediments. Geophys J Int 124(1):57–74.
    .
    OpenUrlAbstract/FREE Full Text
  21. ↵
    1. Kukutschová J, et al.
    (2011) On airborne nano/micro-sized wear particles released from low-metallic automotive brakes. Environ Pollut 159(4):998–1006.
    .
    OpenUrlCrossRefPubMed
  22. ↵
    1. Gómez B,
    2. Gómez M,
    3. Sanchez JL,
    4. Fernández R,
    5. Palacios MA
    (2001) Platinum and rhodium distribution in airborne particulate matter and road dust. Sci Total Environ 269(1-3):131–144.
    .
    OpenUrlCrossRefPubMed
  23. ↵
    1. Abdul-Razzaq W,
    2. Gautam M
    (2001) Discovery of magnetite in the exhausted material from a diesel engine. Appl Phys Lett 78(14):2018–2019.
    .
    OpenUrlCrossRef
  24. ↵
    1. Jordanova N, et al.
    (2006) Magnetism of cigarette ashes. J Magn Magn Mater 301(1):50–66.
    .
    OpenUrlCrossRef
  25. ↵
    1. Mcclean RG,
    2. Kean WF
    (1993) Contributions of wood ash magnetism to archaeomagnetic properties of fire pits and hearths. Earth Planet Sci Lett 119(3):387–394.
    .
    OpenUrlCrossRef
  26. ↵
    1. Brunekreef B,
    2. Forsberg B
    (2005) Epidemiological evidence of effects of coarse airborne particles on health. Eur Respir J 26(2):309–318.
    .
    OpenUrlAbstract/FREE Full Text
  27. ↵
    1. Pieters N, et al.
    (2015) Blood pressure and same-day exposure to air pollution at school: Associations with nano-sized to coarse PM in children. Environ Health Perspect 123(7):737–742.
    .
    OpenUrlPubMed
  28. ↵
    1. Halsall CJ,
    2. Maher BA,
    3. Karloukovski VV,
    4. Shah P,
    5. Watkins SJ
    (2008) A novel approach to investigating indoor/outdoor pollution links: Combined magnetic and PAH measurements. Atmos Environ 42(39):8902–8909.
    .
    OpenUrlCrossRef
  29. ↵
    1. Oberdörster G, et al.
    (2004) Translocation of inhaled ultrafine particles to the brain. Inhal Toxicol 16(6-7):437–445.
    .
    OpenUrlCrossRefPubMed
  30. ↵
    1. Wang J, et al.
    (2008) Time-dependent translocation and potential impairment on central nervous system by intranasally instilled TiO2 nanoparticles. Toxicology 254(1-2):82–90.
    .
    OpenUrlCrossRefPubMed
  31. ↵
    1. Calderón-Garcidueñas L, et al.
    (2003) DNA damage in nasal and brain tissues of canines exposed to air pollutants is associated with evidence of chronic brain inflammation and neurodegeneration. Toxicol Pathol 31(5):524–538.
    .
    OpenUrlAbstract/FREE Full Text
  32. ↵
    1. Block ML,
    2. Calderón-Garcidueñas L
    (2009) Air pollution: Mechanisms of neuroinflammation and CNS disease. Trends Neurosci 32(9):506–516.
    .
    OpenUrlCrossRefPubMed
  33. ↵
    1. Calderón-Garcidueñas L, et al.
    (2013) The impact of environmental metals in young urbanites’ brains. Exp Toxicol Pathol 65(5):503–511.
    .
    OpenUrlCrossRefPubMed
  34. ↵
    1. Jung C-R,
    2. Lin Y-T,
    3. Hwang B-F
    (2015) Ozone, particulate matter, and newly diagnosed Alzheimer’s disease: A population-based cohort study in Taiwan. J Alzheimers Dis 44(2):573–584.
    .
    OpenUrlPubMed
  35. ↵
    1. Könczöl M, et al.
    (2011) Cytotoxicity and genotoxicity of size-fractionated iron oxide (magnetite) in A549 human lung epithelial cells: Role of ROS, JNK, and NF-κB. Chem Res Toxicol 24(9):1460–1475.
    .
    OpenUrlCrossRefPubMed
  36. ↵
    1. Gminski R, et al.
    (2011) Genotoxic effects of three selected black toner powders and their dimethyl sulfoxide extracts in cultured human epithelial A549 lung cells in vitro. Environ Mol Mutagen 52(4):296–309.
    .
    OpenUrlCrossRefPubMed
  37. ↵
    1. Maher BA
    (1988) Magnetic properties of some synthetic sub-micron magnetites. Geophys J Int 94(1):83–96.
    .
    OpenUrlAbstract/FREE Full Text
Next
Back to top
Article Alerts
Email Article

Thank you for your interest in spreading the word on PNAS.

NOTE: We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail. We do not capture any email address.

Enter multiple addresses on separate lines or separate them with commas.
Magnetite pollution nanoparticles in the human brain
(Your Name) has sent you a message from PNAS
(Your Name) thought you would like to see the PNAS web site.
CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
Citation Tools
Magnetite pollution particles 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, Lilian Calderon-Garciduenas
Proceedings of the National Academy of Sciences Sep 2016, 201605941; DOI: 10.1073/pnas.1605941113

Citation Manager Formats

  • BibTeX
  • Bookends
  • EasyBib
  • EndNote (tagged)
  • EndNote 8 (xml)
  • Medlars
  • Mendeley
  • Papers
  • RefWorks Tagged
  • Ref Manager
  • RIS
  • Zotero
Request Permissions
Share
Magnetite pollution particles 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, Lilian Calderon-Garciduenas
Proceedings of the National Academy of Sciences Sep 2016, 201605941; DOI: 10.1073/pnas.1605941113
Digg logo Reddit logo Twitter logo Facebook logo Google logo Mendeley logo
  • Tweet Widget
  • Facebook Like
  • Mendeley logo Mendeley
Proceedings of the National Academy of Sciences: 118 (4)
Current Issue

Submit

Sign up for Article Alerts

Jump to section

  • Article
    • Abstract
    • Results
    • Discussion
    • Materials and Methods
    • Acknowledgments
    • Footnotes
    • References
  • Figures & SI
  • Info & Metrics
  • PDF

You May Also be Interested in

Abstract depiction of a guitar and musical note
Science & Culture: At the nexus of music and medicine, some see disease treatments
Although the evidence is still limited, a growing body of research suggests music may have beneficial effects for diseases such as Parkinson’s.
Image credit: Shutterstock/agsandrew.
Large piece of gold
News Feature: Tracing gold's cosmic origins
Astronomers thought they’d finally figured out where gold and other heavy elements in the universe came from. In light of recent results, they’re not so sure.
Image credit: Science Source/Tom McHugh.
Dancers in red dresses
Journal Club: Friends appear to share patterns of brain activity
Researchers are still trying to understand what causes this strong correlation between neural and social networks.
Image credit: Shutterstock/Yeongsik Im.
Yellow emoticons
Learning the language of facial expressions
Aleix Martinez explains why facial expressions often are not accurate indicators of emotion.
Listen
Past PodcastsSubscribe
Goats standing in a pin
Transplantation of sperm-producing stem cells
CRISPR-Cas9 gene editing can improve the effectiveness of spermatogonial stem cell transplantation in mice and livestock, a study finds.
Image credit: Jon M. Oatley.

Similar Articles

Site Logo
Powered by HighWire
  • Submit Manuscript
  • Twitter
  • Facebook
  • RSS Feeds
  • Email Alerts

Articles

  • Current Issue
  • Special Feature Articles – Most Recent
  • List of Issues

PNAS Portals

  • Anthropology
  • Chemistry
  • Classics
  • Front Matter
  • Physics
  • Sustainability Science
  • Teaching Resources

Information

  • Authors
  • Editorial Board
  • Reviewers
  • Librarians
  • Press
  • Site Map
  • PNAS Updates

Feedback    Privacy/Legal

Copyright © 2021 National Academy of Sciences. Online ISSN 1091-6490