A novel assay system for myeloperoxidase activity in whole saliva

Objectives The application of a novel assay system for the direct measurement of MPO (myeloperoxidase) activity in whole saliva. Design and methods The assay system employs a novel sensitive substrate from 3,3′-diaminobenzidine (DAB) and guaiacol in the presence of dapsone (4,4′-diaminodiphenylsulfone) to determine MPO activity in whole saliva using an original “sandwich” test-disk (DEAE-cellulose paper and cellulose chromatography paper). The saliva (0.1 mL) was directly applied to the sandwich test-disk, and then 0.1 mL of the substrate solution containing 1 mM dapsone in 0.3 M Tris–HCl buffer (pH 7.5) was added. After incubation for 30 min at room temperature, absorbance on the test-disk was measured at 460 nm with an optical analyzer. Results The assay system was shown to distinguish MPO from salivary peroxidase in whole mixed saliva and was sensitive, easy and cheap. The assays revealed that MPO activity in whole saliva from subjects with periodontal disease was significantly higher than in saliva from healthy subjects. There was also a significant positive correlation between MPO activity and the probing depth of subgingival pockets (r = 0.736, p < 0.001). Conclusions These results indicate that this novel assay system for measurement of MPO is a useful technique for predicting the progression of periodontal disease.