Using plasma circRNA_002453 as a novel biomarker in the diagnosis of lupus nephritis

This study aimed to determine the expression of circRNAs in plasma from lupus nephritis (LN) patients to identify novel biomarkers for LN screening. We initially performed microarray screening of circRNA changes in plasma from 5 L N patients, 5 systemic lupus erythematosus (SLE) patients without LN, and 5 healthy controls. We then confirmed the selected circRNA changes in plasma from 59 SLE patients (30 with LN and 29 without LN), 26 rheumatoid arthritis (RA) patients, and 27 age- and sex-matched controls using real-time quantitative reverse transcription-polymerase chain reaction. Spearman's correlation test was performed to assess the correlation of circRNAs and clinical variables. The receiver operating characteristic (ROC) curve was created to evaluate the diagnostic value. We confirmed that plasma circRNA_002453 was significantly elevated in LN patients when compared with SLE patients without LN, RA patients, and healthy controls. Plasma circRNA_002453 was also found to be upregulated in SLE patients when compared with RA patients and healthy controls. Among these LN patients, we detected no significant correlation between plasma circRNA_002453 and disease activity, including complement 3 (C3), complement 4 (C4), and SLE disease activity index 2000 (SLEDAI-2 K) score. However, its expression level was significantly and positively correlated with 24-hour proteinuria (r = 0.571, p = 0.001) and renal SLEDAI score (r = 0.640, p < 0.001). ROC analysis showed that plasma circRNA_002453 had an area under the curve of 0.906 (95% CI 0.838-0.974, p < 0.001) to discriminate LN patients from controls (SLE patients without LN, RA patients, and healthy controls) with sensitivity of 0.900 and specificity of 0.841. The highest Youden index was 0.741 and the corresponding optimal cut-off value was 0.001. This study suggests that upregulated plasma circRNA_002453 level in LN patients is associated with the severity of renal involvement and may also serve as a potential biomarker for LN patient diagnosis.