Air pollution is a risk factor for cardiovascular and Alzheimer's disease (AD). Iron-rich, strongly magnetic, combustion- and friction-derived nanoparticles (CFDNPs) are abundant in particulate air pollution. Metropolitan Mexico City (MMC) young residents have abundant brain CFDNPs associated with AD pathology. We aimed to identify if magnetic CFDNPs are present in urbanites' hearts and associated with cell damage. We used magnetic analysis and transmission electron microscopy (TEM) to identify heart CFDNPs and measured oxidative stress (cellular prion protein, PrPC), and endoplasmic reticulum (ER) stress (glucose regulated protein, GRP78) in 72 subjects age 23.8 ± 9.4y: 63 MMC residents, with Alzheimer Continuum vs 9 controls. Magnetite/maghemite nanoparticles displaying the typical rounded crystal morphologies and fused surface textures of CFDNPs were more abundant in MMC residents' hearts. NPs, ∼2–10 × more abundant in exposed vs controls, were present inside mitochondria in ventricular cardiomyocytes, in ER, at mitochondria-ER contact sites (MERCs), intercalated disks, endothelial and mast cells. Erythrocytes were identified transferring ‘hitchhiking’ NPs to activated endothelium. Magnetic CFDNP concentrations and particle numbers ranged from 0.2 to 1.7 μg/g and ∼2 to 22 × 109/g, respectively. Co-occurring with cardiomyocyte NPs were abnormal mitochondria and MERCs, dilated ER, and lipofuscin. MMC residents had strong left ventricular PrPC and bi-ventricular GRP78 up-regulation.

The health impact of up to ∼22 billion magnetic NPs/g of ventricular tissue are likely reflecting the combination of surface charge, ferrimagnetism, and redox activity, and includes their potential for disruption of the heart's electrical impulse pathways, hyperthermia and alignment and/or rotation in response to magnetic fields. Exposure to solid NPs appears to be directly associated with early and significant cardiac damage. Identification of strongly magnetic CFDNPs in the hearts of children and young adults provides an important novel layer of information for understanding CVD pathogenesis emphasizing the urgent need for prioritization of particulate air pollution control.