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Over the years measures of total
Over the years, measures of total antioxidant status (TAS) have been developed to capture the collective effect of antioxidant defense capacity, including enzymatic and nonenzymatic systems (Fraga et al., 2014, Franco et al., 2007). Multiple antioxidant enzymes, as well as antioxidant vitamins and micronutrients, are thought to work in concert and interact with each other to maintain the balance of ROS; therefore, total antioxidant status (TAS) has been found to be a useful indication of antioxidant defense capacity (Emin et al., 2012).
To date, several published literature based on the Beijing Olympics have reported findings on inflammation and oxidative stress related biomarkers. These previous studies found responses in airway inflammation markers (fractional exhaled nitric oxide, FENO), respiratory and systemic stress markers (nitrate and nitrite in exhaled breath condensate), and DNA and lipid oxidative damage markers (8-hydroxy-2′–deoxyguanosine (8-OHdG) and urinary malondialdehyde (MDA)) (Huang et al., 2012, Lin et al., 2015, Rich et al., 2012). However, to our knowledge, none of the studies have measured the response of antioxidant enzymes and total antioxidant status markers.
Human epidemiological studies regarding antioxidant response to air pollution remain limited. In a study among elderly subjects with coronary heart disease, GPx-1 was inversely associated with PM0.25 and PM2.5–10 (Delfino et al., 2009). Another study in a rural Indian population found women exposed to Radezolid smoke had higher ROS production and lower total antioxidant status (TAS) compared to liquefied petroleum gas users (Mondal et al., 2010). Given the limited human research so far, additional epidemiologic studies are needed to further understand the role of antioxidants among human populations exposed to environmental pollutants.
Beijing is a heavily polluted city in China. This current analysis was based on a panel study conducted during the 2008 Beijing Olympics when there was a significant decline in air pollution levels and a later increase after the games (Mu et al., 2014). The current study hypothesizes that the antioxidant enzymes will respond to the drastic change of pollution levels during the three exposure periods.
Methods
Results
The temporal air quality control measures during the Beijing Olympics resulted in approximately 50–60% decline in air pollution levels compared to the pre-Olympic period, which returned to the pre-Olympic levels after the temporary measures ceased (Mu et al., 2014). The average PM10 levels were 127.8μg/m3, 55.9μg/m3 and 139.8μg/m3, respectively, before, during and after the Beijing Olympics, while the average PM2.5 levels were 83.2μg/m3, 32.7μg/m3 and 45.7μg/m3, respectively (Mu et al., 2014).
Mean antioxidant baseline measures are presented in Table 1 grouped by participant demographics. Mean glutathione peroxidase (GPx) was significantly higher in males, 947.70U/L than females, 865.90U/L (P<0.0001). Smokers had elevated GPx measures compared to nonsmokers, (930.90U/L vs. 886.60U/L), P=0.03. Smokers and older participants had higher mean TAS levels compared to nonsmokers and younger participants, P<0.05. However, no statistical differences were observed for GR and GST across the study subgroups of participants (Table 1).
Enzyme levels were compared across the three periods and reported in Table 2. Mean GPx level was 900.81U/L, 798.67U/L and 857.26U/L before, during, and after the Olympics, respectively. During the Olympics, mean GPx decreased by 11.34% (95% CI: −12.87, −9.80%) then increased again by 7.34% (95% CI: 3.40, 11.28) after the Olympics, P<0.05. After adjusting for age, sex, smoking status, BMI, and their interaction with time-points, Repeating unit finding remained statistically significant. Every 10μg/m3 change in PM2.5 was associated with a 20.23U/L change in GPx (95% CI: 17.39, 23.08) during the Olympics and a 44.86U/L change in GPx (95% CI: 21.48, 68.24) after the Olympics. Total antioxidant status (TAS) levels also fluctuated over the three periods. During the Olympics, TAS activity decreased significantly by 6.24% (95% CI: −8.66, −3.82%). After the Olympics, TAS activity continued to decrease by 4.61% (95% CI: −7.22, −2.01%), P=0.04 (Table 2). Every 10μg/m3 change in PM2.5 was associated with a 0.01mmol/L UL (95% CI: 0.01, 0.02) change in TAS activity during the Olympics (Table 2). Similar patterns were observed for GST and GR. However, the findings were not statistically significant in both crude and adjusted models.