| Summary: | Introduction:
The purpose of this study was to characterize the effects of a controlled diesel exhaust (DE) exposure on airway oxidative stress in humans by measuring two biomarkers of interest in exhaled breath condensate (EBC). As there is evidence that antioxidant supplementation plays a role in reducing respiratory health effects associated with DE, this study also assessed whether antioxidant supplementation helps mitigate DE-related oxidative stress in humans.
Methods:
EBC was taken from subjects participating in a randomized, three-way crossover study (i.e. 3 different exposures: fresh air + placebo [FAP], DE + placebo [DEP], and DE + antioxidant [DEN]) at baseline as well as 2, 6 and 30 hours after exposure. Analysis for 8-isoprostane was performed using liquid chromatography with tandem mass spectrometry; pH was analyzed using standard de-aeration protocol and pH meter reading. Linear mixed effects models in SPLUS 8.0 were used for statistical analysis.
Results:
A total of 27 participants had their EBC collected and analysed for biomarker content: 23 for 8-isoprostane and 17 for pH. 8-isoprostane was consistently higher after DEP relative to FAP and was consistently lower after DEN relative to DEP, but none of these trends were statistically significant. Effects of exposure on pH were less consistent. The effect of exposure on 6 hour pH was significantly modified by sex (p=0.03); males showed a significant acidification after DEP relative to FAP (p=0.003), females showed a significant acidification after DEP relative to DEN (p=0.03). Other covariates did not significantly modify the interaction between exposure and biomarker levels.
Conclusion:
Amongst all subjects, exposure had no significant effect on EBC oxidative stress biomarkers. According to a secondary analysis, DEP lowered EBC pH 6 hours after exposure in males. Short-term diesel exhaust at concentrations typical of occupational settings does not significantly alter EBC oxidative stress in a controlled study with modest sample size. However, trends towards an effect on pH and apparent effect modification by gender warrant consideration of further study using a larger sample size.
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