Friday, 15 May 2015
It is well known that environmental factors play a significant role in respiratory disease. The association is all the more problematic in developing countries undergoing accelerated programmes of industrialisation.
What is not so clear is how these factors relate to exacerbation of symptoms in specific conditions such chronic obstructive pulmonary disease (COPD), nor how environmental influences might interact with known triggers of COPD exacerbations like viruses or bacteria.
A prospective observational study conducted in Guangzhou, China from 2010-2012 sought to address these issues. A cohort of 203 COPD patients and 51 age–matched controls was drawn from Guangzhou, one of the largest cities in China and one with significant air pollution.
Individual COPD patients were studied over a two-year period, while researchers monitored the occurrence and frequency of exacerbations. Samples were taken from study participants to test for the presence of viruses or bacteria and to measure a broad range of inflammatory biomarkers.
The researchers also monitored local pollution levels, humidity and temperature daily to explore any link between these factors and COPD exacerbations. The aim was to study the relationship between environmental factors and exacerbations, and to find out whether they interact in some way with the viruses and bacteria commonly associated with COPD exacerbations. This was the first time the disease had been studied in a Chinese population from so many different perspectives.
One intriguing finding was that, while COPD exacerbations were distributed quite evenly throughout the study, in two of the three calendar years the frequency of exacerbations peaked during the month of March. By contrast, COPD exacerbations due to viral infection tend to occur during the winter months.
March was also a month in which high levels of particulate matter (PM10) were recorded in Guangzhou, peaking in 2012. The researchers found that high pollution levels in one week seemed to anticipate a higher frequency of COPD exacerbations the following week. Further analysis identified PM10 levels as a strong discriminator of COPD exacerbations versus scheduled visits to the clinic during stable disease.
The proportion of COPD exacerbations associated with viral infections in Guangzhou – around 50% – was relatively high compared to that observed in similar studies worldwide.
This demonstrates that, while pollution is likely to be an important trigger of COPD exacerbations, viral infections remain a major cause of exacerbations in China. There may, however, be some form of interaction between viruses and pollution in triggering COPD exacerbations – a possibility the study team would like to investigate further
Another finding was that 15-16% of the patients monitored were women who had never been smokers. Smoking is thought to be the major cause of COPD. Nonetheless, it is recognised that a large proportion of women in China develop the disease due to exposure to biomass fuels through cooking over open fires.
Using the comprehensive dataset available from the study, the research team is keen to identify biomarkers, as well as molecular and cellular mechanisms that can distinguish this form of COPD from smoking-associated COPD. That work is ongoing. The resulting data may ultimately lead to the development of targeted therapies for this important and growing patient segment in China and other countries with similar issues.
With further analysis, the Guangzhou study may provide insights into multiple factors influencing COPD exacerbations. The next step is identifying new predictive biomarkers, patient segments and disease phenotypes to facilitate the development of more targeted COPD therapies.
The study was recently published in the Journal of Thoractic Disease