Free radical-mediated oxidative stress has been implicated in the genesis of gallstone in vitro. This study was designed to examine the oxidative stress changes during pigment gallstone formation and to investigate whether melatonin (MLT) could act as a chemopreventive agent for cholelithiasis in a guinea pig model. The common bile duct of guinea pigs was ligated with or without MLT pretreatment. Animals were studied on day 7, 9, 12, and 14 after surgery. Stone and/or sludge developed in ligated guinea pigs without MLT. Fourier transform infrared spectra of the sludge showed the presence of calcium bilirubinate, whose peak height per milligram of sludge gradually increased with time after ligation. Total antioxidant activity (TAA) in bile of guinea pigs at day 14 after ligation reduced to one third of the level in sham-operated controls (P < .001). In addition, the bile of ligated guinea pigs had increased pH (P < .001), bile salts (P < .01), and malondialdehyde (MDA) (P < .05), compared to sham controls. Pretreatment of guinea pigs with MLT at a dose of 1,000 μg/kg significantly decreased the incidence of pigment gallstone formation at day 14 after ligation, as compared to no pretreatment (0/7 vs. 8/10). MLT also reverted the ligation-induced changes in biliary bile salts, pH, MDA, and TAA to control levels. These in vivo findings support a causative role of oxidative stress in the bile duct ligation-induced pigment gallstone formation. Antioxidants may prove useful in preventing pigment gallstone formation in humans.
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