The pathogenic effects of particulate matter on neurodegeneration: a review

Abstract

The increasing amount of particulate matter (PM) in the ambient air is a pressing public health issue globally. Epidemiological studies involving data from millions of patients or volunteers have associated PM with increased risk of dementia and Alzheimer's disease in the elderly and cognitive dysfunction and neurodegenerative pathology across all age groups, suggesting that PM may be a risk factor for neurodegenerative diseases. Neurodegenerative diseases affect an increasing population in this aging society, putting a heavy burden on economics and family. Therefore, understanding the mechanism by which PM contributes to neurodegeneration is essential to develop effective interventions. Evidence in human and animal studies suggested that PM induced neurodenegerative-like pathology including neurotoxicity, neuroinflammation, oxidative stress, and damage in blood-brain barrier and neurovascular units, which may contribute to the increased risk of neurodegeneration. Interestingly, antagonizing oxidative stress alleviated the neurotoxicity of PM, which may underlie the essential role of oxidative stress in PM's potential effect in neurodegeneration. This review summarized up-to-date epidemiological and experimental studies on the pathogenic role of PM in neurodegenerative diseases and discussed the possible underlying mechanisms.

Keywords: Alzheimer’s disease; Cognitive dysfunctions; Neurodegeneration; Neuroinflammation; Oxidative stress; Particulate matter.

Fig. 1

Schematic summary: Airborne PM may enter the brain, inducing neurotoxic effects in the brain and is associated with increased risk of neurodegeneration. This review summarized the studies that linked PM exposure to increased risk of neurodegeneration. Firstly, the airborne PM can enter the brain via either the olfactory route which involves the olfactory system or the trigeminal nerve, or the passing through BBB after enter the circulation. Then the deposited PM can induce neurotoxicity, oxidative stress, neuroinflammation, and BBB and NVU damage. These adverse effects in the brain may result in neurodegenerative pathology, such as brain structural abnormality and pathological hallmarks for neurodegenerative diseases. Epidemiological studies has associated PM exposure with cognitive impairment and increased risk of developing neurodegenerative diseases such as AD. AD Alzheimer’s disease, BBB blood–brain barrier, NVU neurovascular units, PM Particulate matter