Pioglitazone, a PPAR-y agonist, as one of the new therapeutic candidates for C3 glomerulopathy

BACKGROUND

C3-glomerulopathy (C3G) is a rare pediatric kidney disease characterised by dysregulation of the alternative complement pathway, with glomerular deposition of C3. C3G may often present as a steroid-resistant nephrotic syndrome (SRNS), and there is no established effective therapy: the usual treatment involves corticosteroids and immunosuppressive drugs. Pioglitazone, a PPAR-γ agonist with a protective action on podocytes, was reported in a few cases as helpful in reducing proteinuria when combined with steroids.

CASE-DIAGNOSIS/TREATMENT

We report the case of a 13-year-old girl with silent past medical history who presented with SRNS. A kidney biopsy showed findings indicative of C3G. A low sodium diet and angiotensin-converting enzyme inhibitor were started; immunosuppressive treatment with mycophenolate mofetil (MMF) was administered due to the cortico-resistance. Because of poor response to the immunosuppressant, a trial with eculizumab was attempted without significant response and persistence of proteinuria in the nephrotic range. A further therapeutic trial was performed with tacrolimus with no disease remission. Due to a severe deterioration in her condition, the girl was hospitalized and treated with high-dose steroid bolus. A daily dose of oral prednisone and MMF were re-started without benefit with persistent levels of nephrotic range proteinuria. The administration of pioglitazone consistently lowered proteinuria levels for the first time since the onset of the disease, with a maintenance of the effect and normalization (< 0.15 g/24 h) at the 10-month follow-up.

CONCLUSIONS

In this patient affected by C3G, pioglitazone proved effective in reducing proteinuria levels.

[Comparative characteristics of the complement system in patients with C3-glomerulopathy and atypical hemolytic uremic syndrome of chronic course who suffered an acute episode of thrombotic microangiopathy]

AIM

To compare changes in the complement system in C3-glomerulopathy (C3-GP) and atypical hemolytic uremic syndrome (aHUS) after the relief of an acute episode of thrombotic microangiopathy.

MATERIALS AND METHODS

The study included 8 patients diagnosed with C3-GP and 8 with aHUS in remission. The blood levels of the complement system components were determined: C3, C4, C3a, C5a, factor H (CFH), factor B (CFB), membrane-attacking complex (MAC), antibodies to C3b (anti-C3b-AT), the level of hemolytic activity (CH50), the content of factor D (CFD) in the urine.

RESULTS

C3 and CH50 levels were within the reference range in both groups, however, in the C3-GP group they were at the lower limit, and C3 level was significantly lower than in the aHUS group: 0.56 [0.44; 0.96] vs 1.37 [1.16; 2.52] (p=0.003). CFB increased level was detected in both groups, but in the C3-GP group it was significantly lower than in the aHUS group - 275.1 [222.1; 356.6] vs 438.7 [323.3; 449.3] (p=0.010). C3a, C5a and MAC levels were increased in both groups, but the maximum was in the C3-GP group, and the MAC level in the C3-GP group was 2 times higher than that in aHUS, and these differences reached statistical significance - 123 555±6686 vs 5603±1294 (p=0.036). CFH and CFD levels was increased in both groups, but their highest values was in the aHUS group.

CONCLUSION

Alternative complement pathway activation signs were present in both groups of patients with complement-mediated nephropathies, regardless the stage of the disease. In C3-GP, alternative complement pathway activation was more pronounced than in aHUS after the relief of an acute episode of thrombotic microangiopathy.

Validation of distinct pathogenic patterns in a cohort of membranoproliferative glomerulonephritis patients by cluster analysis

Background

A novel data-driven cluster analysis identified distinct pathogenic patterns in C3-glomerulopathies and immune complex-mediated membranoproliferative glomerulonephritis. Our aim was to replicate these observations in an independent cohort and elucidate disease pathophysiology with detailed analysis of functional complement markers.

Methods

A total of 92 patients with clinical, histological, complement and genetic data were involved in the study, and hierarchical cluster analysis was done by Ward method, where four clusters were generated.

Results

High levels of sC5b-9 (soluble membrane attack complex), low serum C3 levels and young age at onset (13 years) were characteristic for Cluster 1 with a high prevalence of likely pathogenic variations (LPVs) and C3 nephritic factor, whereas for Cluster 2—which is not reliable because of the small number of cases—strong immunoglobulin G staining, low C3 levels and high prevalence of nephritic syndrome at disease onset were observed. Low plasma sC5b-9 levels, decreased C3 levels and high prevalence of LPV and sclerotic glomeruli were present in Cluster 3, and patients with late onset of the disease (median: 39.5 years) and near-normal C3 levels in Cluster 4. A significant difference was observed in the incidence of end-stage renal disease during follow-up between the different clusters. Patients in Clusters 3–4 had worse renal survival than patients in Clusters 1–2.

Conclusions

Our results confirm the main findings of the original cluster analysis and indicate that the observed, distinct pathogenic patterns are replicated in our cohort. Further investigations are necessary to analyse the distinct biological and pathogenic processes in these patient groups.