Presence of free radicals in pigment gallstone in vivo

OBJECTIVE: To clarify whether free radical, which may play a role in pigment gallstone formation, is present in pigment gallstones in vivo. MATERIALS AND METHODS: Free radical signal of gallstones from 18 patients was detected by electron paramagnetic resonance spectroscopy at 77K under anaerobic condition and in air (control). As soon as the anaerobic determination was finished, the fresh anaerobic sample was exposed to air and stored in a freezer at -20 degrees C. RESULTS: Free radical signal (g = 2.0038) was detected in fresh anaerobic samples containing more than 2% bilirubin compound, and the signal intensity correlated linearly with the content of calcium bilirubinate (r = +0.95, P < 0.0005). During the storage at -20 degrees C and exposure to air, the signal intensity of each anaerobic sample and its control increased gradually, eventually reaching the same stable level. Fe(III) signal intensity was enhanced synchronously and related linearly with free radical signal (r = +0.99, P < 0.0005). CONCLUSIONS: Free radical exists originally in pigment gallstones in vivo, and it may play an important role in pigment gallstone formation. The free radical signal carried by gallstones may be strengthened by the action of oxygen in air on bilirubin. The transition metal ions probably take part in the formation of bilirubin free radical.