Use of urinary bilirubin oxidative metabolites as a psychological stress-marker.

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Some authors have suggested that psychological stress induces the production of reactive oxygen species(ROS). Some studies have supported that bilirubin exerts anti-oxidative effects in vivo. However, it is not known whether ROS induced by psychological stress provoke bilirubin oxidation in vivo. We investigated if the concentration of biopyrrin, a bilirubin oxidative metabolite, increased in urine from subjects exposed to psychological stress. Sixty healthy male volunteers working in a pharmaceutical company were divided into a Group I which did not attend a conference, a Group II which attended a conference but did not deliver a speech, and a Group III which attended a conference and delivered speeches in the presence of the company executives. Subjective stress was scored (self-rating score) after subjects in Group III delivered their speeches at the conference. Urine was collected on the next day. The biopyrrin concentrations, as measured by enzyme-linked immunosorbent assay, were normalized to the urinary concentration of creatinine. The concentration of biopyrrin in Group III was significantly higher compared to that in Groups I and II (p<0.01 and p<0.05, respectively). Furthermore, in Group III, the concentration of biopyrrin correlated with the self-rating stress score (r=0.53, p<0.01). These findings suggest that emotional stimuli are associated with an increase in the oxidative metabolites of bilirubin in human urine, and that biopyrrins could be useful markers of psychological stress. Based on these reports on the possible relationship among psychological stress, oxidative stress and bilirubin as the antioxidant, we examined the possibility that psychological stress contributed to the oxidative conditions, and the subsequent increase of the urinary concentration of biopyrrins produced by the reaction of bilirubin with ROS.