Common Salivary Protein 1 in Serum of Diabetes Patients

Background: Recently, the human common salivary protein 1 (CSP1) was identified as an ortholog of the Demilune cell and parotid protein of mouse. However, its function remains to be determined. Here, we show that the serum CSP1 concentration of diabetes mellitus (DM) patients is much higher than that of healthy controls. Methods: Recombinant human CSP1 was expressed as a Glutathione-S-transferase (GST)-tagged protein, and the purified fusion protein was used as an immunogen to generate monoclonal antibody (mAb) to CSP1. The produced mAb was tested as a probe in Western blotting of human saliva and in immunohistochemistry of various human tissues. The serum CSP1 levels of 31 DM patients and 38 normal adults were quantified by a house-fabricated CSP1 sandwich enzyme-linked immunosorbent assay (ELISA) system. Results: Immunoblot analysis by mAb-hCSP1#4 showed that CSP1 in human saliva exists in a 27 kDa glycosylated form. Among the various human tissues tested, the salivary gland was the only tissue stained with mAb-hCSP1#4 by immunohistochemistry. Quantification of serum CSP1 concentration by CSP1 ELISA showed that the median values (25th–75th percentile) of DM patients and healthy adults were 22.2 (15.8–28.2) and 3.2 (0–11.4), respectively. Student's t-test results indicated that there was a statistically significant difference between the two groups (P < 0.01). Conclusion: The significant difference between the CSP1 levels of the two groups indicated that CSP1 would be a potential biomarker for detection or screening of DM patients.