Proteinuria predicting outcome in renal disease: nondiabetic nephropathies (REIN)

About two thirds of patients on renal replacement therapy irreversibly lose their kidney function because of progressive nephropathies, such as diabetic nephropathy and nondiabetic chronic renal disease. Halting the progression of these patients to end-stage renal disease (ESRD) is instrumental to substantially decrease the need and cost for renal replacement therapy. A large number of experimental studies have demonstrated that chronic nephropathies share common pathogenic mechanisms that contribute to renal disease progression, even independently of the original etiology. Actually, a variety of insults may result in a common pathway of systemic hypertension, increased glomerular pressure and protein ultrafiltration, glomerular and tubular protein overload, chronic inflammation and, ultimately, scarring. Experimental and clinical data converge to indicate that in chronic renal disease increased protein traffic is nephrotoxic, proteinuria predicts disease progression, and proteinuria reduction is renoprotective. Initial clinical trials, mostly in patients with no or mild proteinuria, failed to demonstrate that ACE inhibition therapy is renoprotective in nondiabetic chronic nephropathies. Consistently, meta-analyses based on data generated by these trials failed to detect a specific, blood pressure-independent, renoprotective effect of ACE inhibition therapy. The Ramipril Efficacy In Nephropathy (REIN) study found that ACE inhibitors, by reducing urinary proteins, may contribute to improve the outcome of nondiabetic renal disease, and reduce the risk of progression to ESRD by about 50%. Cumulative meta-analyses, including the REIN study results, confirmed and extended these findings. Thus, well-designed trials in properly selected and carefully monitored study populations continue to be the best approach to test the efficacy of novel treatments. The meta-analyses may help confirming the consistency of these findings and their generalizability to larger cohorts of patients.