Fractional urinary excretion of IgG is the most powerful predictor of renoprotection by ACE inhibitors in IgA nephropathy.

BACKGROUND: Several aspects of renoprotection by angiotensin-converting enzyme inhibitors (ACEi) in IgA nephropathy (IgAN) are poorly defined: factors affecting responsiveness, role of proteinuria components and histological lesions, and criteria to identify patients who may benefit from ACEi.
METHODS: In an observational study of 140 IgAN patients (follow up 62 +/- 36 months), 73 untreated and 67 ACEitreated for 53 +/- 28 months, 9 baseline risk factors (RFs) (blood pressure, serum creatinine, proteinuria/day, fractional excretion of IgG [FEIgG] and alpha1-microglobulin, global and segmental [SS] glomerular sclerosis, tubulointerstitial damage and arteriolar hyalinosis [AH] score), each divided into 2 subgroups according to a cutoff with the highest sensitivity and specificity for progression, were evaluated for ability to predict renoprotection. Primary end point: end-stage renal disease (ESRD) and doubling of serum creatinine (sCr); secondary end point: increase >or=25% of sCr with last sCr >or=1.58 mg/dL; total progression: sum of end points.
RESULTS: Patients with RFs below cutoffs did not benefit from ACEi. All clinical and proteinuric and 2 histological RFs (SS, AH score) with values above cutoffs showed significant reduction of progression in ACEitreated vs. untreated patients; FEIgG showed the highest prediction of renoprotection: ESRD/sCrx2: 20% vs. 62% (p=0.0004); total progression: 40% vs. 85% (p=0.0003). By multivariate analysis, independent predictors of progression were FEIgG, sCr and no ACEi treatment. Proteinuria reduction from -100% to -30%, spontaneous or after ACEi treatment, did not affect progression in treated vs. untreated patients (19% vs. 13%, p=0.85). Patients with proteinuria increased or reduced <30% showed a reduction of total progression if ACEi-treated (15% vs. 77%, p=0.0002). Presence of 1 clinical or proteinuric RF above the cutoff may be a criterion to identify patients who may benefit from ACEi.
CONCLUSIONS: Renoprotection by ACEi is a multifactorial phenomenon: the best predictor of renoprotection is FEIgG, a marker of disruption of glomerular barrier to proteins; renoprotection depends not only on ability to reduce proteinuria, but probably also on antiinflammatory and antifibrotic activity.