Myeloperoxidase and Progression of Aortic Valve Stenosis in Patients Undergoing Hemodialysis

Background and aim of the study: Currently, there is an increased incidence of aortic valve stenosis (AS) in patients undergoing hemodialysis (HD), though the exact mechanisms are not fully understood. Myeloperoxidase (MPO) is a leukocyte-derived enzyme that catalyzes the formation of reactive oxygen species and is an index of oxidative stress. The study aim was to examine, immunohistochemically, the expression of MPO, using surgically resected aortic valve specimens from AS patients undergoing HD. Methods: The study population consisted of 15 HD patients and 19 non-HD patients with severe AS undergoing aortic valve replacement. Frozen aortic valve samples obtained surgically from AS patients were stained immunohistochemically with antibodies against smooth muscle cells, neutrophils, macrophages, T lymphocytes, CD31, MPO and 4-hydroxy-2-nonenal (4-HNE). Results: Quantitative analyses showed that the macrophage-positive area, and numbers of T lymphocytes, neutrophils, CD31-positive microvessels and MPO-positive cells in HD patients were significantly higher than in non-HD patients (macrophages, p <0.0001; T lymphocytes, p <0.0001; neutrophils, p <0.0001; CD31, p <0.0001; MPO, p <0.0001). Moreover, the number of MPO-positive cells was positively correlated with CD31-positive microvessels and the 4-HNE-positive macrophage score (CD31, R = 0.73, p <0.0001; 4-HNE, R = 0.49; p <0.005). Conclusion: These findings suggest that MPO is highly expressed in the aortic valves of AS patients undergoing HD. Furthermore, MPO is positively associated with neovascularization and oxidative stress, which contribute to a rapid progression of AS in HD patients.