Blood ceramides as novel markers for renal impairment in systemic lupus erythematosus.

Background: Lupus nephritis (LN) is the most common organ manifestation in systemic lupus erythematosus (SLE) and associated with a poor prognosis. Still, a noninvasive but reliable method to diagnose LN has not been established. Thus, we evaluated whether blood sphingolipids could serve as valid biomarkers for renal injury.

Methods: In this cross-sectional study, 82 participants were divided into three groups: 36 healthy controls and 17 SLE patients without renal injury (both: estimated glomerular filtration rate (eGFR) ≥ 80 ml/min/1.73 m and albumin/creatinine ≤ 30 mg/g) and 29  LN patients. LN patients were identified by renal biopsies and impaired renal function (eGFR < 80 ml/min/1.73 m and albumin/creatinine ratio > 30 mg/g). Venous blood was collected from all participants and sphingolipid levels in plasma and serum were measured by LC-MS/MS.

Results: Most interesting, concentrations of some specific ceramides, C16ceramide (Cer), C18Cer, C20Cer and C24:1Cer, were elevated in both, plasma and serum samples of patients suffering from biopsy-proven LN and impaired renal function, compared to healthy controls as well as SLE patients without renal injury. C24:1dhCer levels were elevated in plasma and serum samples from LN patients compared to SLE patients. Sphingosine levels were higher in plasma and serum of LN patients compared to healthy controls, but not compared to SLE patients. Sphinganine concentrations were significantly elevated in serum samples from LN patients compared to healthy controls and SLE. S1P and SA1P levels were higher in plasma samples of SLE and LN patients compared to healthy controls. Subsequent ROC analyses of plasma and serum data of the most altered ceramide species (C16Cer, C18Cer, C20Cer, C24:1Cer) between LN patients and SLE patients display a high diagnostic differentiation with significant AUCs especially for C24:1Cer serum levels. Further, C24:1Cer serum levels were not affected by glucocorticoid treatment and did not correlate with other renal markers, such as serum creatinine, eGFR and albumin/creatinine ratio.

Conclusion: Our data reveal that chain-length specific ceramides in blood, most likely C24:1Cer levels in serum, could act as potent biomarkers for renal impairment in patients suffering from SLE.