Urinary prostaglandin D synthase as biomarker in lupus nephritis: a longitudinal study

Urinary prostaglandin D synthase (uPGDS) has been identified as a biomarker in lupus nephritis (LN) mice model as well as in humans. We studied the effect of therapy for LN on its levels in a longitudinal study and its ability to differentiate between active systemic lupus erythematosus (SLE) patients with and without nephritis.

Twenty-eight SLE patients with active LN, 6 patients with inactive disease, 12 patients with active non-renal disease and 19 healthy individuals were enrolled. Urine and serum samples were collected at baseline from all patients and at a 3-monthly follow-up from 25 patients in active nephritis group. uPGDS was measured by ELISA and normalised to urinary creatinine excretion.

In the cross-sectional study, median uPGDS was higher in patients with active nephritis (618.5 ng/mg) as compared to healthy controls (141.7ng/mg; p<0.001), active non-renal (130.1ng/mg; p=0.008) and inactive disease (56.2 ng/mg; p=0.002) patients and had modest correlation with urinary protein / creatinine ratio (r=0.39; p=0.014). In the longitudinal study, median uPDGS reduced from 618.5 ng/mg at baseline (n=28) to 91.9 at 6 months (n=25), 73.3 at 9 months (n=20) and 81.7 ng/mg at 12 months (n=13). uPGDS remained persistently elevated in a patient who developed CKD and showed an increase 2 months before the clinical relapse in another patient with relapse of LN.

Given that uPGDS levels fall after treatment of LN, uPGDS may be used to monitor the efficacy of therapy. It can also differentiate patients with active nephritis and active non renal lupus.