Role of superoxide anion in host cell injury induced by mycoplasma pneumoniae infection. A study in normal and trisomy 21 cells.

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Abstract
The role of Mycoplasma pneumoniae-generated superoxide and hydrogen peroxide in inducing host cell injury was studied in normal and trisomy 21 human cells. As a result of M. pneumoniae infection, catalase activity in infected normal skin fibroblasts and ciliated epithelial cells decreased by 74-77% as compared with uninfected controls. Addition of superoxide dismutase to the infected cultured cells totally prevented the inhibition whereas addition of catalase or catalytically inactivated superoxide dismutase had no protective effect. Trisomy 21 erythrocytes and cultured skin fibroblasts in which CuZn-superoxide dismutase content is 50% greater than in normal cells were infected by M. pneumoniae. The inhibition of catalase activity in these cells was 7-33% and 0-20.5%, respectively, as compared with 65-72% and 48-68% inhibition in normal infected controls. Following M. pneumoniae infection, the levels of malonyldialdehyde, an indicator for membrane lipid peroxidation were raised in trisomy 21 cultured fibroblasts by 10-32% while in normal cells malonyldialdehyde increased by 140-870%. Externally added superoxide dismutase, but not catalase, reduced the extent of lipid peroxidation in normal infected cells. Lactate dehydrogenase release from normal infected cells was time correlated with the increase in their malonyldialdehyde formation. It is suggested that superoxide generated during M. pneumoniae infection is involved in the inhibition of host cell catalase activity. The inactivation of this cellular antioxidative defense mechanism results in progressive oxidative damage to the M. pneumoniae-infected cells.