Intrusion of inhaled exotic ultrafine particles into the knee joint in humans and animals: A risk to the joint and surrounding tissues

Mounting evidence recognizes a close connection between air pollution and arthropathy. Although the indirect effects of ultrafine particles (UFPs) on the joints, i.e., by inducing the inflammatory cytokines, has been documented, there are still significant knowledge gaps in understanding the direct threat of exotic particles to the joint. In the current study, we uncovered exotic UFPs in human knee joint effusions of osteoarthritis patients, and identified the ambient environmental exposure sources of these UFPs, including natural mineral and metal oxide particles (i.e., donpeacorite and hematite) through figuring out their chemical and structural fingerprints. Furthermore, animal experiments unveiled the translocation of in-haled UFPs into the joint. Histological examination recognized significant injuries to the synovium and cartilage in response to the intrusion of UFPs in the joint. With the aid of isotope-labelling, we substantiated the invasion of UFPs in the joints and obtained the according retention kinetics in mice. Collectively, our combined results provide direct evidence of the intrusion of exotic particles into the joint cavities, and define the translocation for inhaled UFPs from the inhalation system into the joints and impairment of the joint protection system. This work provides additional insights for the continued investigations into the adverse effects of air pollution on the joints, and has crucial implications in public health measures par-ticularly related to air pollution.(c) 2022 The Author(s). Published by Elsevier Ltd. CC_BY_NC_ND_4.0

Automated summary

Mounting evidence suggests a strong connection between air pollution and arthropathy. This study investigates the direct threat of exotic particles to joints and identifies the sources of these particles in knee joint effusions of osteoarthritis patients. Animal experiments demonstrate the translocation of inhaled particles into the joint, resulting in significant injuries to the synovium and cartilage. Isotope-labelling confirms the invasion of particles in the joints and provides the kinetics of retention. These findings provide direct evidence of the intrusion of exotic particles into joint cavities and highlight the adverse effects of air pollution on joint health.