Metabolites of traffic-related volatile organic compounds in age-related macular degeneration

Volatile organic compounds (VOCs), commonly emitted from vehicle exhaust and industrial activities, are prevalent air pollutants in urban environments. These compounds have been reported to cause various health effects through mechanisms such as oxidative stress and neurotoxicity. Recently, air pollution has attracted attention as a potential risk factor for age-related macular degeneration (AMD); however, the association between VOC exposure and AMD remains unclear.

This study aimed to assess VOC exposure levels among urban-dwelling AMD patients by quantifying urinary metabolites and investigating the association between VOCs and AMD.

This cross-sectional study included 40 untreated AMD patients (AMD group), 10 cataract patients (Cataract group), and 10 healthy controls (Healthy group). Representative urinary metabolites of VOCs-2-methylhippuric acid, 3-methylhippuric acid, mandelic acid, phenylglyoxylic acid, and trans,trans-muconic acid-were measured using gas chromatography-mass spectrometry (GC/MS), with concentrations corrected for urinary creatinine. Group comparisons were performed based on creatinine-adjusted metabolite levels.

The AMD group exhibited elevated urinary VOC metabolite levels compared to both control groups. The ratios of mean concentrations in the AMD group versus the Healthy and Cataract groups, respectively, were: 2-methylhippuric acid (201% and 181%), 3-methylhippuric acid (190% and 139%), mandelic acid (304% and 198%), phenylglyoxylic acid (118% and 90%), and trans,trans-muconic acid (214% and 92%). Among these, 2-methylhippuric acid and mandelic acid were significantly higher in the AMD group than in both controls (p < 0.001 and p = 0.042; p < 0.001, respectively). Trans,trans-muconic acid also showed a significant increase compared to the Healthy group (p < 0.001). Correlation analysis within the AMD group revealed moderate but significant associations for 2-methylhippuric acid (r = 0.29, p = 0.011), mandelic acid (r = 0.47, p < 0.001), and trans,trans-muconic acid (r = 0.27, p = 0.020). Multivariate logistic regression identified mandelic acid as an independent factor significantly associated with AMD (odds ratio = 17.20, p < 0.001). Subgroup analysis categorized the AMD group into drusenoid AMD, typical AMD (t-AMD), polypoidal choroidal vasculopathy (PCV), and retinal angiomatous proliferation (RAP). No significant differences in urinary VOC metabolite levels were observed among the four subtypes after multiple comparison adjustment.

These findings indicate that AMD patients are exposed to higher levels of traffic-related VOCs. While mandelic acid-a styrene metabolite-was independently associated with AMD, its role should be interpreted as a potential exposure marker rather than a definitive disease biomarker. Further longitudinal studies are warranted to clarify causal relationships between VOC exposure and AMD development.