Toxicity of inhaled particulate matter on the central nervous system: neuroinflammation, neuropsychological effects and neurodegenerative disease.

Particulate matter (PM) combined with meteorological factors cause the haze, which brings inconvenience to people's daily life and deeply endanger people's health. Accumulating literature, to date, reported that PM are closely related to cardiopulmonary disease. Outpatient visits and admissions as a result of asthma and heart attacks gradually increase with an elevated concentration of PM. Owing to its special physicochemical property, the brain could be a potential target beyond the cardiopulmonary system. Possible routes of PM to the brain via a direct route or stimulation of pro-inflammatory cytokines have been reported in several documents concerning toxicity of engineered nanoparticles in rodents. Recent studies have demonstrated that PM have implications in oxidative stress, inflammation, dysfunction of cellular organelles, as well as the disturbance of protein homeostasis, promoting neuron loss and exaggerating the burden of central nervous system (CNS). Moreover, the smallest particles (nano-sized particles), which were involved in inflammation, reactive oxygen species (ROS), microglial activation and neuron loss, may accelerate the process of the neurodevelopmental disorder and neurodegenerative disease. Potential or other undiscovered mechanisms are not mutually exclusive but complementary aspects of each other. Epidemiology studies have shown that exposure to PM could bring about neurotoxicity and play a significant role in the etiology of CNS disease, which has been gradually corroborated by in vivo and in vitro studies. This review highlights research advances on the health effects of PM with an emphasis on neurotoxicity. With the hope of enhancing awareness in the public and calling for prevention and protective measures, it is a critical topic that requires proceeding exploration.