- Email: [email protected]
Air Pollution, Multiple Sclerosis and its Relevance to Mexico City
Archives of Medical Research 50 (2019) 111e112
OPINION
Air Pollution, Multiple Sclerosis and its Relevance to Mexico City Teresa Corona-Vazquez, Jose De Jesus Flores Rivera, Mayela RodrıguezViolante, and Amin Cervantes-Arriaga Instituto Nacional de Neurologıa y Neurocirugıa, Unidad Clınica de Investigacion en Enfermedades Neurodegenerativas, Ciudad de Mexico, Mexico Received for publication April 25, 2019; accepted July 15, 2019 (ARCMED_2019_350).
Long-term exposure to air pollution has been linked with the development of neurodegenerative diseases. The proposed mechanisms include neuroinflammation and brain oxidative stress. Multiple sclerosis (MS) is a neurodegenerative disease with an auto-immune physiopathology and some studies have associated it with long-term exposure to airborne particulate matter. In this opinion we discuss the current body of knowledge regarding air pollution and the risk of MS as well as MS relapses. Also, its relevance in the case of Mexico City is discussed. Ó 2019 IMSS. Published by Elsevier Inc. Key Words: Pollution, Particulate matter, Multiple sclerosis, Relapses, Mexico.
Long-term exposure to airborne particulate matter (PM) has been linked with the development of a broad spectrum of health conditions with neurodegenerative diseases not being an exception. PM is commonly classified based on aerodynamic diameter into PM10 (diameter #10 mm) and PM2.5 (diameter #2.5 mm). Ultrafine particulate (UFPM, diameter #100 hm), appear to be the more relevant to health issues. Suggested mechanisms are still not well established, but it has been demonstrated that inhalation by the respiratory tract may lead to deposition along the airway; while particles are in contact with olfactory epithelium, translocation along the olfactory bulb is plausible providing direct access to the central nervous system. After gaining access to the central nervous system, PM2.5 and UFPM can lead to neuroinflammation and brain oxidative stress. Multiple sclerosis (MS) is an auto-immune disease hallmarked by inflammatory demyelination. Little is known about the effect of air pollution on the prevalence of MS. A study in Turkey found a two-fold prevalence of MS in a high-polluted city in comparison to a coastal city (1). Conversely, two large cohort studies failed to find any significant association (2).
Address reprint requests to: Amin Cervantes-Arriaga, Clınica de trastornos del movimiento, Instituto Nacional de Neurologıa y Neurocirugıa, Insurgentes Sur #3877 Col. La Fama, 14269 Mexico City, Mexico; Phone: (þ52) 55 56063822x5018; FAX: (þ52) 55 51716456; E-mail: [email protected]
Regarding air pollution and disease course, a study assessed air quality index (AQI) and the severity of disease of patients with MS. Higher AQI level were associated with higher disability, but after adjusting for several confounders the effect was no longer present (3). Another study did not find any association between PM and the risk of MS admissions (4). On the other hand, a study in France found that MS relapse increase was associated with PM10 during the cold season (5). A previous study in the same city found an association between relapse and PM10 levels 1e3 d before only during the cold season (6). A study in Italy found a 42% increase in MS hospital admissions on the days preceded by one week with PM10 levels in the highest quartile (7). These finding were also replicated by a study in Serbia. High air pollution index during the so-called ‘‘low vitamin D season’’ (January-April) were correlated with an increase in the number of relapses (8). In summary, air pollution appears to be associated with relapses, but this should be interpreted cautiously since it is also related to the cold season, where several other risk factors such as less sunlight exposure and viral infections. Also, it is well known that pollution levels increase as temperature lowers. Nevertheless, seasonal pollution levels depend on the specific pollutant. Particulate matter may be higher in the winter; while ozone is higher in the summer. The increase frequency of MS in large cities can also be partially explained by other factors. It has been suggested that higher frequencies of MS in industrialized countries may be due to heavy metal exposure.
0188-4409/$ - see front matter. Copyright Ó 2019 IMSS. Published by Elsevier Inc. https://doi.org/10.1016/j.arcmed.2019.07.003
112
Corona-Vazquez et al./ Archives of Medical Research 50 (2019) 111e112
The case of Mexico City is relevant for several reasons. The city has drastically reduced air pollutants since the early nineties. In fact, comparison of data between 2006 and 2013 indicates a decrease in PM2.5 in the Metropolitan area of Mexico City (9). As consequence Mexico City epidemiological data can offer some insight not only the impact of air pollution on neurodegenerative diseases such as Alzheimer, Parkinson’s disease and MS, but also on the effect of reducing air pollution regarding such diseases. In this matter, it is important to consider that different sources (i.e. traffic versus industrial activities) may have a distinct impact on pollution and individual analysis would be desirable. In addition, geographical reasons such as altitude preventing proper burning of fuels, being located at a tropical latitude within a valley surrounded by mountains makes the city more prone to air pollution. In the case of Mexico City data is available from 1990 to date, but most interestingly PM10 and PM2.5 levels have been steadily dropping in the last decade bringing a great opportunity to assess its impact on the prevalence and incidence of MS. A cohort study according to exposure status assessing incidence, or a cohort of MS patients assessing the relationship between relapses and pollution would be needed. The general hypothesis would be that as pollution decreases, incidence of MS (or relapses) would also decrease. Currently, the Epidemiological Surveillance Automated System of the General Direction of Epidemiology only includes data for two neurodegenerative diseases, Parkinson’s disease and Alzheimer. For the case of
MS, data is only available through local registries so a collaborative effort will be required. References
€ Bilgic¸ AB, K€oseoglu Toksoy C, et al. Prevalence of multiple 1. B€or€u UT, sclerosis in a Turkish City bordering an iron and steel factory. J Clin Neurol 2018;14:234e241. 2. Palacios N, Munger KL, Fitzgerald KC, et al. Exposure to particulate matter air pollution and risk of multiple sclerosis in two large cohorts of US nurses. Environ Int 2017;109:64e72. 3. Ashtari F, Esmaeil N, Mansourian M, et al. An 8-year study of people with multiple sclerosis in Isfahan, Iran: association between environmental air pollutants and severity of disease. J Neuroimmunol 2018; 319:106e111. 4. Carmona R, Linares C, Recio A, et al. Emergency multiple sclerosis hospital admissions attributable to chemical and acoustic pollution: Madrid (Spain), 2001e2009. Sci Total Environ 2018;612:111e118. 5. Jeanjean M, Bind MA, Roux J, et al. Ozone, NO2 and PM10 are associated with the occurrence of multiple sclerosis relapses. Evidence from seasonal multi-pollutant analyses. Environ Res 2018; 163:43e52. 6. Roux J, Bard D, Le Pabic E, et al. Air pollution by particulate matter PM10 may trigger multiple sclerosis relapses. Environ Res 2017;156: 404e410. 7. Angelici L, Piola M, Cavalleri T, et al. Effects of particulate matter exposure on multiple sclerosis hospital admission in Lombardy region, Italy. Environ Res 2016;145:68e73. 8. Vojinovic S, Savic D, Lukic S, et al. Disease relapses in multiple sclerosis can be influenced by air pollution and climate seasonal conditions. Vojnosanit Pregl 2015;72:44e49. 9. Morton-Bermea O, Garza-Galindo R, Hernandez-Alvarez E, et al. Atmospheric PM2.5 mercury in the metropolitan area of Mexico City. Bull Environ Contam Toxicol 2018;100:588e592.
OPINION
Air Pollution, Multiple Sclerosis and its Relevance to Mexico City Teresa Corona-Vazquez, Jose De Jesus Flores Rivera, Mayela RodrıguezViolante, and Amin Cervantes-Arriaga Instituto Nacional de Neurologıa y Neurocirugıa, Unidad Clınica de Investigacion en Enfermedades Neurodegenerativas, Ciudad de Mexico, Mexico Received for publication April 25, 2019; accepted July 15, 2019 (ARCMED_2019_350).
Long-term exposure to air pollution has been linked with the development of neurodegenerative diseases. The proposed mechanisms include neuroinflammation and brain oxidative stress. Multiple sclerosis (MS) is a neurodegenerative disease with an auto-immune physiopathology and some studies have associated it with long-term exposure to airborne particulate matter. In this opinion we discuss the current body of knowledge regarding air pollution and the risk of MS as well as MS relapses. Also, its relevance in the case of Mexico City is discussed. Ó 2019 IMSS. Published by Elsevier Inc. Key Words: Pollution, Particulate matter, Multiple sclerosis, Relapses, Mexico.
Long-term exposure to airborne particulate matter (PM) has been linked with the development of a broad spectrum of health conditions with neurodegenerative diseases not being an exception. PM is commonly classified based on aerodynamic diameter into PM10 (diameter #10 mm) and PM2.5 (diameter #2.5 mm). Ultrafine particulate (UFPM, diameter #100 hm), appear to be the more relevant to health issues. Suggested mechanisms are still not well established, but it has been demonstrated that inhalation by the respiratory tract may lead to deposition along the airway; while particles are in contact with olfactory epithelium, translocation along the olfactory bulb is plausible providing direct access to the central nervous system. After gaining access to the central nervous system, PM2.5 and UFPM can lead to neuroinflammation and brain oxidative stress. Multiple sclerosis (MS) is an auto-immune disease hallmarked by inflammatory demyelination. Little is known about the effect of air pollution on the prevalence of MS. A study in Turkey found a two-fold prevalence of MS in a high-polluted city in comparison to a coastal city (1). Conversely, two large cohort studies failed to find any significant association (2).
Address reprint requests to: Amin Cervantes-Arriaga, Clınica de trastornos del movimiento, Instituto Nacional de Neurologıa y Neurocirugıa, Insurgentes Sur #3877 Col. La Fama, 14269 Mexico City, Mexico; Phone: (þ52) 55 56063822x5018; FAX: (þ52) 55 51716456; E-mail: [email protected]
Regarding air pollution and disease course, a study assessed air quality index (AQI) and the severity of disease of patients with MS. Higher AQI level were associated with higher disability, but after adjusting for several confounders the effect was no longer present (3). Another study did not find any association between PM and the risk of MS admissions (4). On the other hand, a study in France found that MS relapse increase was associated with PM10 during the cold season (5). A previous study in the same city found an association between relapse and PM10 levels 1e3 d before only during the cold season (6). A study in Italy found a 42% increase in MS hospital admissions on the days preceded by one week with PM10 levels in the highest quartile (7). These finding were also replicated by a study in Serbia. High air pollution index during the so-called ‘‘low vitamin D season’’ (January-April) were correlated with an increase in the number of relapses (8). In summary, air pollution appears to be associated with relapses, but this should be interpreted cautiously since it is also related to the cold season, where several other risk factors such as less sunlight exposure and viral infections. Also, it is well known that pollution levels increase as temperature lowers. Nevertheless, seasonal pollution levels depend on the specific pollutant. Particulate matter may be higher in the winter; while ozone is higher in the summer. The increase frequency of MS in large cities can also be partially explained by other factors. It has been suggested that higher frequencies of MS in industrialized countries may be due to heavy metal exposure.
0188-4409/$ - see front matter. Copyright Ó 2019 IMSS. Published by Elsevier Inc. https://doi.org/10.1016/j.arcmed.2019.07.003
112
Corona-Vazquez et al./ Archives of Medical Research 50 (2019) 111e112
The case of Mexico City is relevant for several reasons. The city has drastically reduced air pollutants since the early nineties. In fact, comparison of data between 2006 and 2013 indicates a decrease in PM2.5 in the Metropolitan area of Mexico City (9). As consequence Mexico City epidemiological data can offer some insight not only the impact of air pollution on neurodegenerative diseases such as Alzheimer, Parkinson’s disease and MS, but also on the effect of reducing air pollution regarding such diseases. In this matter, it is important to consider that different sources (i.e. traffic versus industrial activities) may have a distinct impact on pollution and individual analysis would be desirable. In addition, geographical reasons such as altitude preventing proper burning of fuels, being located at a tropical latitude within a valley surrounded by mountains makes the city more prone to air pollution. In the case of Mexico City data is available from 1990 to date, but most interestingly PM10 and PM2.5 levels have been steadily dropping in the last decade bringing a great opportunity to assess its impact on the prevalence and incidence of MS. A cohort study according to exposure status assessing incidence, or a cohort of MS patients assessing the relationship between relapses and pollution would be needed. The general hypothesis would be that as pollution decreases, incidence of MS (or relapses) would also decrease. Currently, the Epidemiological Surveillance Automated System of the General Direction of Epidemiology only includes data for two neurodegenerative diseases, Parkinson’s disease and Alzheimer. For the case of
MS, data is only available through local registries so a collaborative effort will be required. References
€ Bilgic¸ AB, K€oseoglu Toksoy C, et al. Prevalence of multiple 1. B€or€u UT, sclerosis in a Turkish City bordering an iron and steel factory. J Clin Neurol 2018;14:234e241. 2. Palacios N, Munger KL, Fitzgerald KC, et al. Exposure to particulate matter air pollution and risk of multiple sclerosis in two large cohorts of US nurses. Environ Int 2017;109:64e72. 3. Ashtari F, Esmaeil N, Mansourian M, et al. An 8-year study of people with multiple sclerosis in Isfahan, Iran: association between environmental air pollutants and severity of disease. J Neuroimmunol 2018; 319:106e111. 4. Carmona R, Linares C, Recio A, et al. Emergency multiple sclerosis hospital admissions attributable to chemical and acoustic pollution: Madrid (Spain), 2001e2009. Sci Total Environ 2018;612:111e118. 5. Jeanjean M, Bind MA, Roux J, et al. Ozone, NO2 and PM10 are associated with the occurrence of multiple sclerosis relapses. Evidence from seasonal multi-pollutant analyses. Environ Res 2018; 163:43e52. 6. Roux J, Bard D, Le Pabic E, et al. Air pollution by particulate matter PM10 may trigger multiple sclerosis relapses. Environ Res 2017;156: 404e410. 7. Angelici L, Piola M, Cavalleri T, et al. Effects of particulate matter exposure on multiple sclerosis hospital admission in Lombardy region, Italy. Environ Res 2016;145:68e73. 8. Vojinovic S, Savic D, Lukic S, et al. Disease relapses in multiple sclerosis can be influenced by air pollution and climate seasonal conditions. Vojnosanit Pregl 2015;72:44e49. 9. Morton-Bermea O, Garza-Galindo R, Hernandez-Alvarez E, et al. Atmospheric PM2.5 mercury in the metropolitan area of Mexico City. Bull Environ Contam Toxicol 2018;100:588e592.