Identification of Low-Abundance Urinary Biomarkers in Lupus Nephritis Using Electrochemiluminescence Immunoassays.

OBJECTIVE: To investigate the utility of a sensitive platform using electrochemiluminescence (ECL) for the identification of low-abundance urinary protein biomarkers in lupus nephritis (LN). METHODS: Forty-eight urine samples were obtained from subjects in 2 independent cohorts, each consisting of 3 groups (matched for age, sex, and race) of 8 patients with active LN (renal Systemic Lupus Erythematosus Disease Activity Index [SLEDAI] >0), 8 patients with inactive SLE (renal SLEDAI 0), and 8 healthy controls. Samples were tested using a preexisting 40-plex ECL panel. A custom 5-plex ECL panel was then developed for further validation studies and used to test 140 urine samples (from 44 patients with active LN, 41 patients with inactive SLE, 28 healthy controls, and 27 patients with other kidney diseases). RESULTS: Levels of 17 urinary proteins were elevated (P < 0.05 by 2-tailed Mann-Whitney U test) in samples from patients with active LN compared to samples from patients with inactive SLE and healthy controls in cohort 1, while 9 were similarly elevated in cohort 2. Of these, interleukin-7 (IL-7), IL-12p40, IL-15, interferon-γ-inducible protein 10 (IP-10), and thymus and activation-regulated chemokine (TARC) were chosen for further validation. These 5 proteins were undetectable by enzyme-linked immunosorbent assay (ELISA). Hence, a custom 5-plex ECL panel was developed and used to validate the results from the initial 40-plex screening panel. Urinary IL-7, IL-12p40, IL-15, IP-10, and TARC levels were again significantly elevated in patients with active LN compared to those with inactive SLE and healthy controls, and correlated well with the renal SLEDAI and physician's global assessment of disease activity (R > 0.67, P < 0.05). All 5 urinary proteins were more frequently elevated in LN compared to controls with other chronic kidney diseases, although overall group differences attained significance only for urinary IL-7 and IL-15. CONCLUSION: Urinary levels of IL-7, IL-12p40, IL-15, IP-10, and TARC are potentially useful diagnostic tools in LN. The use of ECL assays may allow detection of urinary biomarkers that are below ELISA detection limits.

Correlation of urine and plasma cytokine levels among reproductive-aged women.

BACKGROUND: Inflammation is implicated in many adverse health conditions, and recent interest has focused on the effects of chronic low-grade inflammation in generally healthy populations. Cytokines measured in plasma or serum are commonly used as biomarkers of systemic levels of inflammation. Measurement of cytokines in urine may offer a simpler and less invasive alternative, although the degree to which levels of cytokines correlate in plasma and urine among healthy individuals is unknown. MATERIALS AND METHODS: We assessed the correlation of blood and urine levels of 13 cytokines, including interleukin (IL)-1b, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12(p70) and IL-13, granulocyte macrophage colony-stimulating factor, interferon gamma and tumour necrosis factor alpha in 61 healthy women aged 18-30. Cytokine concentrations were considered with and without correction for creatinine. RESULTS: Plasma and urine levels of the 13 cytokines were not significantly correlated using measured urinary cytokine concentrations and after adjustment for creatinine. Correlation coefficients for log-transformed cytokine concentrations in paired plasma and urine specimens ranged from -0.28 to 0.087. CONCLUSIONS: These results suggest that urine has limited utility as a proxy for plasma for the measurement of inflammatory factors in a healthy population with low levels of inflammation.