Enzyme-linked immunosorbent assay for human manganese-containing superoxide dismutase and its content in lung cancer

A manganese-containing superoxide dismutase (Mn-SOD) was purified from human liver. Polyclonal antibody for the Mn-SOD was prepared in goat, and a simple and specific enzyme-linked immunosorbent assay (ELISA) for the Mn-SOD was developed. This assay was found to be sensitive to nanogram amounts of the enzyme. With respect to Mn-SOD levels of normal lung tissues, a positive correlation (r = 0.92, P less than .001) was observed between the results of enzymatic assay and those of immunochemical assay by ELISA. In lung carcinoma tissue the enzyme activity was in the same order of magnitude as in uninvolved tissues. However, the enzyme content determined by ELISA was significantly higher in adenocarcinoma than in the uninvolved lung tissue, whereas no significant difference from the control was observed in other histologic types. The discrepancy between the enzyme activity and immunoreactive content suggested that in the adenocarcinoma of the lung an immunoreactive but enzymatically inactive Mn-SOD protein existed and that a high content of this enzyme was characteristic of lung adenocarcinoma.