Molecular Mechanisms of Disease Progression and Renoprotective Pharmacotherapy in Children With Chronic Renal Failure

Chronic kidney diseases affecting the nephron mass are characterized by a progressive decline of glomerular filtration rate (GFR) occurring irrespectively of the cause of the renal damage once a critical number of nephrons has been lost. Current clinical research efforts focus on preventive strategies to slow down or arrest disease progression. Systemic hypertension and glomerular hyperfiltration with resulting proteinuria and activation of vasoactive, profibrotic and proinflammatory systems have been identified as major causes of further nephron damage. Angiotensin converting enzyme (ACE) inhibitors are not only potent antihypertensive agents but also reduce proteinuria, glomerulosclerosis and tubulointerstitial fibrosis via reduction of the local angiotensin tone in the kidney, and have been demonstrated to slow down renal failure progression in adult patients. Childhood-onset ESRD is a rare but particularly devastating disease with poor life expectancy and quality of life. Chronic renal failure in children is caused by a different spectrum of nephropathies than in adults, with a preponderance of congenital or inherited abnormalities. Since hypertension, proteinuria and tubulointerstitial fibrosis are also common in pediatric chronic renal failure, there is a rationale for pharmacological renoprotection by ACE inhibition in children. The prospective, randomized European clinical trial launched by our consortium will provide the critical mass to assess several aspects of renoprotective therapy in children. Specifically, the trial is designed to address the following scientific objectives:

Objective 1 is to evaluate whether ACE inhibition is equally effective in slowing down the progression rate of chronic renal failure in children with different congenital and acquired renal disorders. 400 pediatric patients will be stratified according to their underlying diseases, and the rate of loss in glomerular filtration rate will be assessed from 6 months before to 5 years after start of treatment with the ACE inhibitor ramipril.

Objective 2 of the trial is to evaluate whether renal failure progression in patients treated with a fixed dose of ramipril can be further slowed down by additional antihypertensive treatment, achieving a blood pressure below the 50th percentile. To this end, patients will be randomized upon initiation of ramipril to either intensified (aiming below 50th percentile of 24-hour mean arterial pressure) or conventional antihypertensive treatment.

Several gene polymorphisms have been described that may affect the rate of renal failure progression and/or the individual susceptibility to ACE inhibition. These polymorphisms include genes encoding for key proteins of the renin-angiotensin system and extracellular matrix turnover. In addition, we will screen for novel polymorphisms in genes determining structural proteins of the glomerular filter, and search for gene mutations causing renal hypo-/dysplasia. Objective 3 is to evaluate whether any of these mutations predict spontaneous disease progression and the therapeutic response to ACE inhibition and intensified blood pressure control.

Glomerular endothelin (ET1) synthesis is upregulated in chronic renal failure, and urinary ET1 excretion is correlated with disease progression. ET1 antagonists partially preserve renal function and decrease proteinuria independent of the angiotensin tone. Objective 4 of the trial is to assess ET1 turnover before and after start of ACE inhibition, and to evaluate a possible predictive role of ET1 and/or ET1 degrading peptidase excretion for the persistence of proteinuria and disease progression during ACE inhibition and intensified antihypertensive therapy.