Tuesday, 5 February 2013

Automobile exhausts and heart disease: Is the link an inflammatory molecule?

A recent study in America found evidence for increased levels of IL-1 beta,  a marker associated with inflammation in the blood of people who lived near the highways and had high exposures to vehicular exhausts.

As our consumption and usage of vehicles increases, our roads constantly brew  more particulate matter, black carbon, nitrogen dioxide, sulphur-di-oxide and carbon monoxide, all emitted from automobile exhausts. The danger about these emissions is that they don’t just stay there, but drift. Our busy highway and motorways, which have high traffic volume, are the worst offenders. Studies indicate that people living/working in such areas and spending significant time within approximately 200m of highways are exposed heavily to these pollutants compared to people who are based further away. Unsurprisingly, the exposures at highways are higher when compared to people living on busy urban streets.

A plethora of studies have linked vehicular emission exposure to heart disease. We had highlighted a couple of them in this blog. The closer people live or work near highways/motorways, the greater is their exposure to the  harmful effluents.  However, many of the studies in this field  of research are epidemiological in nature which are population based and  subject to the criticism that the observed correlation in the studies might not really signify causality. A recent study by researchers from Tufts School of Medicine, Boston, attempts to close the gulf and provides a molecular basis of the effects of vehicular emission exposure on human health and offers an explanation on how automobile exhausts could cause heart diseases. 

The study was conducted in the  Somerville area of  Massachusetts, USA.  The scientists compared blood samples from 20 people who lived less than 100m from the Interstate-93( a highway that connects Massachusetts to Vermont) and those residing a km away from the highway in urban backgrounds. To ensure that the  two groups were as  similar as possible,  the subjects in both groups were matched to age, gender and education. Though there were no significant differences between two groups in terms of body measurements (height, weight) and education, the group who lived in urban backgrounds were more likely to earn less, had higher exposure to vehicle exhausts that was occupationally related and high levels of bad cholesterols (LDL). The researchers factored the job related vehicle emission exposure in their calculations and found that the levels of IL-1 beta was increased significantly in those people who lived near the highway.

Inflammation plays a crucial role in the development and progression of a variety of heart diseases importantly atherosclerosis and congestive heart failure.  Inflammatory molecules linked to these processes includes interleukin-1 (IL-1), but this American study  is the first of its kind where such a link has been shown to occur  in humans with proximity to heavy traffic. The results are notable as it also recapitulates the trend shown by particulate matter  in increasing the  levels of   IL -1 family  in  animal models and cells in culture. In their paper, the researchers also point out that  IL-1 beta itself could have application as a biological marker of air pollution exposure. However, one thing to note is that  IL-1 family is also influenced by diet and this is a factor that has to be controlled for in further experiments. Cumulatively, the study by Professor Brugge and his colleagues  is a very interesting preliminary work which warrants larger carefully controlled follow up studies.

Fearon, W., & Fearon, D. (2008). Inflammation and Cardiovascular Disease: Role of the Interleukin-1 Receptor Antagonist Circulation, 117 (20), 2577-2579 DOI: 10.1161/CIRCULATIONAHA.108.772491 ResearchBlogging.org Brugge, D., Durant, J., & Rioux, C. (2007). Near-highway pollutants in motor vehicle exhaust: A review of epidemiologic evidence of cardiac and pulmonary health risks Environmental Health, 6 (1) DOI: 10.1186/1476-069X-6-23 Brugge, D., Lane, K., Stewart, A., Tai, A., & Woodin, M. (2013). Highway Proximity Associations with Blood Markers of Inflammation: Evidence for a Role for IL-1β Journal of Toxicology and Environmental Health, Part A, 76 (3), 201-205 DOI: 10.1080/15287394.2013.752325

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