From the Journals

Air pollution seen acting on stress hormones

Publish date: August 14, 2017

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How pollution exposure may lead to disease

Although the past decade has seen much advancement in our knowledge of how air pollutants promote cardiovascular diseases, important questions remain.

There is a need to better understand the precise nature and systemic pathways whereby ambient air pollution elicits a multitude of adverse responses in the heart and vasculature anatomically remote from the site of inhalation. Also, what can (and should) an individual do to protect oneself against the hazards of air pollution, given that substantial improvements in air quality throughout many parts of the world are likely decades away?

Li and colleagues have provided some significant insights into both of these issues. Responses to short-term exposure to high levels of pollution include increased blood pressure and insulin resistance, along with alterations in a battery of circulating markers indicative of systemic inflammation, oxidative stress, and platelet activation.

A distinguishing feature of their work is the detailed exploration of health responses using state-of-the-art metabolomic profiling. Although similar outcomes after brief exposure to ozone have been shown, this was the first usage of an untargeted metabolomic approach to evaluate the impact of ambient air pollution. The results confirm and extend the growing body of evidence that air pollution elicits systemic perturbations favoring the development of the metabolic syndrome. The findings also add to the growing body of evidence that simple interventions such as air purifier systems with high-efficiency filters can help protect against adverse health impacts of air pollution. The reduction in estimated exposure afforded by filtration favorably influenced most of the health outcomes (blood pressure, insulin resistance, oxidative stress, inflammation), curtailed pollution-induced activation of the sympathetic nervous system and hypothalamic-pituitary-adrenal axis, and helped mitigate the ensuing metabolomic perturbations.

Robert D Brook, MD, of the University of Michigan in Ann Arbor, and Sanjay Rajagopalan, MD, of Cleveland Hospitals, made these comments in an editorial (Circulation. 2017 Aug 14;136:628-31). Dr. Brook receives research support from RB, Inc. Dr. Rajagopalan had no disclosures.

FROM CIRCULATION

Increases in stress hormone levels and other adverse metabolic changes accompany higher exposure to air pollution, Chinese researchers have found, while cutting indoor pollution levels appears to mitigate these effects.

Air pollution has been linked in epidemiological studies to increased risk of cardiovascular and metabolic diseases, but the mechanisms remain poorly understood. The new findings, published online Aug. 14 in Circulation, offer compelling evidence that air pollution may impact the central nervous system, and the hypothalamus-pituitary-adrenal axis especially (Circulation 2017 Aug 14;136:618-27).

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For their research, Huichu Li, MS, and Jing Cai, PhD, and their colleagues at Fudan University in Shanghai, China, recruited 55 college students (27 female) living in nonsmoking dormitories into a randomized controlled trial in which air purifiers were placed in half the cohort’s dormitories for 9 days, with sham purifiers used in the other half. Students’ serum and urine metabolites were analyzed after 9 days using gas and liquid chromatography–mass spectrometry. After a washout period of 12 days, the study arms were switched for another 9 days, and the tests repeated.

The study design required that students spend as much time in their dorms as possible with the windows closed, though they could venture out for classes and exams. Fine particle concentration in the dorms treated by purifiers was 8.6 mcg per cubic meter during the study period, compared with a mean 101.4 outdoors. The researchers determined that the time-weighted average student exposure to fine particle pollutants was reduced by more than half when the dorm air was being purified, though average student exposure was estimated at 24 mcg per cubic meter at best. The World Health Organization considers levels below 10 mcg to be safe.

Students in untreated dorms had significant increases in cortisol, cortisone, epinephrine, norepinephrine, and biomarkers of oxidative stress at 9 days compared to those in treated ones. Glucose, insulin, measures of insulin resistance, amino acids, fatty acids, and lipids differed significantly between treatment assignments, and the untreated dorm groups also saw 2.61% higher systolic blood pressure (95% confidence interval [CI], 0.39-4.79).

Glucocorticoids are known to affect blood pressure, the investigators noted. Serum cortisol and cortisone levels were 1.3 and 1.2 times higher for the students in the sham-treated dorms, with each 10-mcg increase in pollutant exposure associated with a 7.8% increase in cortisol (95% CI, 4.75-10.91) and a nearly 3.8% increase in cortisone (95% CI, 1.84-5.71). Similar exposure-dependent increases were seen for norepinephrine, melatonin, phenylalanine, tyrosine, L-tryptophan and other compounds.

“To the best of our knowledge, this is the first study that used the untargeted metabolomics approach to investigate human global metabolic changes in relation to changes in ambient [air pollution] exposures,” the investigators wrote in their analysis, adding that the findings “provide insights into the potential mechanisms of the adverse health effects that have been found to be associated with [pollution] exposure.”

Mr. Li and Dr. Cai recommended the use of indoor air purification technology as a practical way to reduce harmful exposure, noting that the benefits of long-term use, particularly relating to cardiovascular and metabolic health, remain to be established.

The study was funded with grants from national and regional government agencies in China, and none of its authors declared conflicts of interest.

Air pollution seen acting on stress hormones

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