The Air We Breathe: Air Pollution as a Prevalent Proinflammatory Stimulus Contributing to Neurodegeneration

Abstract

Air pollution is regarded as an important risk factor for many diseases that affect a large proportion of the human population. To date, accumulating reports have noted that particulate matter (PM) is closely associated with the course of cardiopulmonary disorders. As the incidence of Alzheimer’s disease (AD), Parkinson’s disease (PD), and autoimmune disorders have risen and as the world’s population is aging, there is an increasing interest in environmental health hazards, mainly air pollution, which has been slightly overlooked as one of many plausible detrimental stimuli contributing to neurodegenerative disease onset and progression. Epidemiological studies have indicated a noticeable association between exposure to PM and neurotoxicity, which has been gradually confirmed by in vivo and in vitro studies. After entering the body directly through the olfactory epithelium or indirectly by passing through the respiratory system into the circulatory system, air pollutants are subsequently able to reach the brain. Among the potential mechanisms underlying particle-induced detrimental effects in the periphery and the central nervous system (CNS), increased oxidative stress, inflammation, mitochondrial dysfunction, microglial activation, disturbance of protein homeostasis, and ultimately, neuronal death are often postulated and concomitantly coincide with the main pathomechanisms of neurodegenerative processes. Other complementary mechanisms by which PM could mediate neurotoxicity and contribute to neurodegeneration remain unconfirmed. Furthermore, the question of how strong and proven air pollutants are as substantial adverse factors for neurodegenerative disease etiologies remains unsolved. This review highlights research advances regarding the issue of PM with an emphasis on neurodegeneration markers, symptoms, and mechanisms by which air pollutants could mediate damage in the CNS. Poor air quality and insufficient knowledge regarding its toxicity justify conducting scientific investigations to understand the biological impact of PM in the context of various types of neurodegeneration.

Long-term exposure to particulate matter was associated with increased dementia risk using both traditional approaches and novel machine learning methods

“…Human and toxicological studies have provided evidence that air pollution induces brain toxicity [68][69][70] . Increased oxidative stress, inflammation, mitochondrial dysfunction, microglial activation, disturbance of protein homeostasis, and ultimately neuronal death often postulate and concomitantly coincide with the main mechanisms of air pollution-related neurodegenerative processes 71 . Further investigations are needed to understand the biological impact of air pollution on various types of neurodegeneration.…”

Effect of Short- to Long-Term Exposure to Ambient Particulate Matter on Cognitive Function in a Cohort of Middle-Aged and Older Adults: KoGES

“…In another recent study, PM 2.5 exposure induced pathological injury (i.e., changes in the values of inflammatory cytokines and oxidative stress factors) and deoxyribonucleic acid (DNA) damage related to micro-ribonucleic acids (microRNAs) and DNA methylation in rats, suggesting the epigenetic modification capacity of PM exposure [ 66 ]. The specific mechanisms require further elucidation; however, the key underlying path of PM-induced effects may include inflammation, oxidative stress, mitochondrial dysfunction, microglial activation, disturbed protein homeostasis, epigenetic modification, genotoxicity, and neuronal death, which leads to neurodegeneration [ 72 ]. Future studies are warranted to determine the extent of the association between various types of PMs, including nanoparticles, and to clarify the causal mechanisms between PM exposure and cognitive function.…”

Gene Expression Changes Induced by Exposure of RAW 264.7 Macrophages to Particulate Matter of Air Pollution: The Role of Endotoxins

“…Numerous data from the literature indicate that exposure to PM induces local inflammatory processes in the respiratory system that lead to systemic changes, and thus can affect distant organs [ 19 ]. It is noteworthy to mention its negative effect on the central nervous system and neurodegenerative processes (reviewed by Jankowska-Kieltyka et al [ 88 ]). As a result of PM exposure, in addition to the pro-inflammatory changes in the respiratory system mentioned above, disturbances in the composition of the intestinal flora [ 89 ] and an increase in gut permeability occur [ 90 ].…”