Air Pollution as Risk Factor for Mental Disorders: In Search for a Possible Link with Alzheimer’s Disease and Schizophrenia

Abstract

As a global problem that has increasingly been causing worldwide concern, air pollution poses a significant and serious environmental risk to health. Risks of cardiovascular and respiratory diseases, as well as various types of cancer, have been consistently associated with the exposure to air pollutants. More recently, various studies have also shown that the central nervous system is also attacked by air pollution. Air pollution appears to be strongly associated with a higher risk of cognitive defects, neurodevelopmental (e.g., schizophrenia) and neurodegenerative (e.g., Alzheimer's disease) disorders. Subjects with schizophrenia, as well as subjects with Alzheimer's disease, experience a variety of neuropsychological deficits and cognitive impairments. This determines an adverse effect on social and professional functioning, and it contributes to the long-term disease burden. However, no final conclusions have been drawn on the matter of the direct relationship between schizophrenia and Alzheimer's disease. In recent years, the topic of urbanicity and mental health has become increasingly important. Urban exposure to environmental toxins and pollution is currently described as a reliable risk factor for schizophrenia and other psychoses, and it has been demonstrated more and more how exposure to air pollutants is associated with increased risk of dementia. Pathways by which air pollution can target and damage the brain, leading to an increased risk for developing schizophrenia and Alzheimer's disease, are multiple and complex. Results from epidemiological studies suggest potential associations, but are still insufficient to confirm causality. Further studies are needed in order to verify this hypothesis. And if confirmed, the clinical implications could be of substantial relevance for both public and mental health.

Neurodevelopmental toxicity induced by PM2.5 Exposure and its possible role in Neurodegenerative and mental disorders

“…Recent evidence indicates that exposure to air pollutants is associated with an increased risk for SZ. 134,135 PM2.5 play a key role in these epidemiological studies on SZ.…”

Six Decades of Dopamine Hypothesis: Is Aryl Hydrocarbon Receptor the New D2?

“…Translocation of Hafnei alvei, Pseudomonas aeruginosa, Morganella morganii, Pseudomonas putida, and Klebsiella pneumoniae [12][13][14] Comorbidity with IBD AhR/STAT3/IL-22-regulated intestinal permeability and microbiota translocation [11,15,16] Comorbidity with HIV AhR/STAT3/IL22-regulateted gut barrier permeability [12,17,18] Poor insight (anosognosia) IC activation by gut Prevotella and Bacteroides abundance [19][20][21][22][23][24][25] Higher prevalence in urban areas Pollutants are AhR ligands associated with SCZ and are more prevalent in industrialized countries and urban areas [26][27][28][29][30][31][32][33][34] Increasing prevalence with the distance from the equator Sunlight-driven vitamin D derivatives and tryptophan light metabolites are AhR ligands [35][36][37][38][39] Autoantibodies Gut microbes express molecules, including GABA and NMDA, which can elicit formation of antibodies upon translocation [40][41][42] Aryl hydrocarbon receptor (AhR), a cytosolic transcription factor, initially described as the dioxin receptor, responds to numerous exogenous and endogenous ligands, inducing both immune tolerance of gut microbes as well as their prompt elimination upon translocation into host tissues [43,44]. In the cytosol, AhR is bound by two heat shock protein 90 (HSP90) chaperones, molecules recently identified as both SCZ and Parkinson's disease (PD) targets [45][46]…”

The Gut Microbiome and Alzheimer’s Disease: Can the Gut be Used to Prevent or Treat Dementia?

“…Perhaps dysbiosis may similarly occur in humans with repetitive exposure to air pollutants. Importantly, air pollution is also thought to be associated with increased AD risk 84,85 . It is possible that dysbiosis triggered by air pollution may underlie this increased AD risk in humans with high exposure to air pollution, such as in urban environments.…”