Myeloperoxidase-positive inflammatory cells participate in bile duct damage in primary biliary cirrhosis through nitric oxide-mediated reactions

Previous studies have suggested that increased nitric oxide (NO)-mediated products are found in the livers of subjects with primary biliary cirrhosis (PBC), but the mechanisms involved remain enigmatic. We took advantage of immunohistochemistry and several unique monoclonal antibodies to study inflammatory cells responsible for the generation of NO, the enzymes responsible for NO production, the expression of 3-nitrotyrosine, and the presence of CD68(+) and/or myeloperoxidase (MPO)(+) cells. We examined a total of 113 liver specimens, including 64 with PBC, 19 with primary sclerosing cholangitis (PSC), 6 with non-A, non-B hepatitis, 6 with alcoholic liver disease, 4 with cryptogenic cirrhosis, 4 with biliary atresia, and 10 normal subjects. Twenty-two percent of PBC had elevated expression of 3-nitrotyrosine in their bile duct epithelial cells (BECs) (P =.0316). Furthermore, the BECs in PBC also demonstrated apoptotic changes. MPO-positive inflammatory cells were also noted adjacent to the basement membrane. In contrast, the liver of normal subjects showed few apoptotic changes in the bile ducts, with no evidence of MPO staining in the portal area. Furthermore, sections from livers of subjects with stage I or stage II PBC demonstrated significantly increased inflammatory cell infiltration (P =.0064) and elevated 3-nitrotyrosine expression in BECs (P =.0246) compared with stage III and IV. The presence of 3-nitrotyrosine was closely associated with infiltrating CD68- and/or MPO-positive cells. There was also a stage-associated difference in the presence of bile duct infiltrating cells and 3-nitrotyrosine in PBC with an increase dominant in early stage disease. In conclusion, NO and reactive oxygen species, collectively determined as 3-nitrotyrosine, are associated with bile duct destruction in PBC and are particularly prevalent in early stage disease.