Complement Activation in Patients with Focal Segmental Glomerulosclerosis

Abstract

Background: Recent pre-clinical studies have shown that complement activation contributes to glomerular and tubular injury in experimental FSGS. Although complement proteins are detected in the glomeruli of some patients with FSGS, it is not known whether this is due to complement activation or whether the proteins are simply trapped in sclerotic glomeruli. We measured complement activation fragments in the plasma and urine of patients with primary FSGS to determine whether complement activation is part of the disease process.

Study design: Plasma and urine samples from patients with biopsy-proven FSGS who participated in the FSGS Clinical Trial were analyzed.

Setting and participants: We identified 19 patients for whom samples were available from weeks 0, 26, 52 and 78. The results for these FSGS patients were compared to results in samples from 10 healthy controls, 10 patients with chronic kidney disease (CKD), 20 patients with vasculitis, and 23 patients with lupus nephritis.

Outcomes: Longitudinal control of proteinuria and estimated glomerular filtration rate (eGFR).

Measurements: Levels of the complement fragments Ba, Bb, C4a, and sC5b-9 in plasma and urine.

Results: Plasma and urine Ba, C4a, sC5b-9 were significantly higher in FSGS patients at the time of diagnosis than in the control groups. Plasma Ba levels inversely correlated with the eGFR at the time of diagnosis and at the end of the study. Plasma and urine Ba levels at the end of the study positively correlated with the level of proteinuria, the primary outcome of the study.

Limitations: Limited number of patients with samples from all time-points.

Conclusions: The complement system is activated in patients with primary FSGS, and elevated levels of plasma Ba correlate with more severe disease. Measurement of complement fragments may identify a subset of patients in whom the complement system is activated. Further investigations are needed to confirm our findings and to determine the prognostic significance of complement activation in patients with FSGS.

Fig 1. Complement activation fragments are elevated in the plasma and urine of patients with FSGS.

Ba, Bb, C4a, and sC5b-9 fragments were measured in the (A) plasma and (B) urine of FSGS patients collected at the time of diagnosis. These fragments were also measured in samples from control subjects. Levels of all four complement activation fragments were increased in the plasma of FSGS patients. C4a and sC5b-9 were elevated in the urine of FSGS patients. The □ symbol indicates those FSGS patients with the full nephrotic syndrome (UPC > 3.5 g/g and serum albumin <3.0 g/dL). The groups were compared by ANOVA, and the statistical results shown are for FSGS versus the other indicated control groups. *P < 0.05, ***P < 0.001.

Fig 2. Levels of plasma Ba correlate with proteinuria and a reduced glomerular filtration rate.

The levels of Ba, Bb, C4a, and sC5b-9 for individual patients were correlated with the degree of proteinuria (urine protein/creatinine ratio; Up/c) and the estimated glomerular filtration rate (eGFR). (A) None of the fragments measured in plasma were significantly correlated with the Up/c. (B) Plasma Ba was inversely correlated with the eGFR. (C) Urine Ba was significantly correlated with the Up/c. (D) None of the fragments measured in the urine were significantly correlated with the eGFR.

Fig 3. sC5b-9 patients decrease in patients treated with mycophenolate mofetil.

The levels of (A) Ba and (B) Bb did not change over the course of the study (n = 19 for all time-points). (C) The levels of sC5b-9 decreased over time (P < 0.001 by linear regression; n = 19 for all time-points). When analyzed separately based upon treatment, the decrease in sC5b-9 levels was due to a decrease in patients treated with mycophenolate mofetil (P < 0.001 by linear regression; n = 12 for all time-points). The sC5b-9 levels did not decrease in patients treated with cyclosporine (n = 7 for all time-points).

Fig 4. Plasma and urine Ba levels at the end of the study were correlated with clinical outcomes.

Ba, Bb, and sC5b-9 levels were measured in samples obtained at the end of the FSGS CT (week 78). The plasma Ba level was significantly correlated with the (A) primary outcome and (B) eGFR at the end of the study. (C) The urine Ba level was significantly correlated with primary outcome for the study. No significant correlations between Bb levels or sC5b-9 levels and clinical outcomes were seen.