Salivary Biomarkers in SLE
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Background: Lupus Nephritis (LN) affects close to half of all SLE patients and is currently diagnosed through kidney biopsy. In search for a more noninvasive diagnostic method, four serum biomarkers of SLE (IGFBP2, sTNFRII, Axl, VCAM1) were valued for their diagnostic potential in the saliva of SLE patients. This study was aimed at detecting whether these four biomarkers were significantly elevated in the serum and saliva of active nonrenal and active renal SLE patients. Methods: IGFBP2, STNFRII, Axl, VCAM1 were validated by ELISA in the serum 50 SLE patients (16 inactive, 10 active nonrenal, 10 active renal) and 14 healthy controls. The same four molecules were validated by ELISA and normalized to total protein concentration in the saliva of 43 of the same SLE patients (13 inactive, 9 active nonrenal, 10 active renal) and 20 matched healthy controls. Group wise analysis was completed by the Mann Whitney test and fold change (FC) while correlation analysis between serum and saliva was done using Spearman correlation. Results: IGFBP2 showed elevation in the serum of SLE patients compared to controls (FC=3.2 P=0.0002) while sTNFRII and VCAM1 showed elevation in active compared to inactive SLE (FC=2.2 P=0.002 and FC=2.8 P<0.0001 respectively). In the saliva, IGFBP2 and sTNFRII showed elevation in SLE patients compared to controls (FC=2.4 P=0.01, FC=2.8 P=0.04 respectively). No significant differences were found in the four proteins when comparing active to inactive SLE patients and active renal to active nonrenal patients. Saliva and serum biomarker concentration did not correlate in this sample cohort. Conclusion: Although all four biomarkers (IGFBP2, sTNFRII, Axl, VCAM1) have shown diagnostic potential in human serum, only IGFBP2 and sTNFRII showed elevation in the saliva of SLE patients. As IGFBP2 and sTNFRII seem to have potential in use of saliva for diagnosing SLE, further exploration into other biomarkers through an unbiased aptamer based protein screening platform is planned as a future direction.