Validation of some pathophysiological mechanisms of the CKD progression theory and outcome prediction in IgA nephropathy

Claudio Bazzi, Virginia Rizza, Daniela Casellato, Gilda Stivali, Gregorio Rachele, Pietro Napodano, Giulia Olivieri, Maurizio Gallieni, Giuseppe D'Amico
Journal of Nephrology 2012, 25 (5): 810-8

BACKGROUND: The "remnant kidney" chronic kidney disease (CKD) progression theory based on hemodynamic, proteinuric and inflammatory mechanisms consequent to nephron loss has not been confirmed in a human disease. The aim of this study was to evaluate whether some of these mechanisms are present in IgA nephropathy (IgAN) and predict functional outcome.

METHODS: In 132 IgAN patients (68 untreated, 64 angiotensin-converting enzyme inhibitor [ACEi]-treated) fractional excretion of IgG (FEIgG) and α1-microglobulin, proteinuria/day and β-NAG excretion were divided by percentage of nonglobally sclerotic glomeruli ("surviving glomeruli" [SG]) to assess the effective glomerular loss and tubular load of proteins in surviving nephrons. Proteinuric markers were compared between 4 SG groups: group 1: ≤50%; group 2: >50% and <80%; group 3: ≥80% and <100%; and group 4: 100%. The outcome prediction (estimated glomerular filtration rate [eGFR] improvement and stability, progression) was assessed comparing low- and high-risk groups for each marker.

RESULTS: Proteinuric markers showed increasing values in parallel with reduction of percentages of SG (p<0.0001). FEIgG/SG, 40-fold higher in patients with SG ≤50% vs. SG=100% (0.00040 ± 0.00039 vs. 0.00001 ± 0.00002, p<0.0001), was the most powerful outcome predictor: in ACEi-untreated patients, FEIgG/SG less or greater than 0.00010 predicted eGFR improvement and stability (88% vs. 12%, p<0.0001) and end-stage renal disease (ESRD) + eGFR reduction ≥50% (2% vs. 87.5%, p<0.0001); ACEi treatment reduced ESRD+eGFR reduction ≥50%: 36% vs. 87.5% (p=0.002). In patients with FEIgG/SG <0.00010 the eGFR increase is significantly higher in ACEi-treated for ≥70 months versus ACEi-untreated with follow up ≥70 months (+35% ± 23% vs. +13% ± 8%, p=0.004).

CONCLUSIONS: In IgAN, progressive nephron loss is associated with an increase of proteinuric markers of glomerular and tubular damage. FEIgG/SG is the best outcome predictor. These data represent the first validation in a human disease of some pathophysiological mechanisms of CKD progression theory.

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