Addition of AT1 blocker fails to overcome resistance to ACE inhibition in adriamycin nephrosis

Background. Angiotensin-converting enzyme (ACE) inhibitors provide renoprotection, but there is considerable interindividual variability in therapeutic efficacy, with residual proteinuria and progressive renal function loss in many individuals. This requires additional strategies to optimize therapy response, particularly for individuals with a poor response to ACE inhibition. We studied whether co-treatment with an angiotensin II subtype 1 (AT(l)) receptor antagonist (AII-A) improves the individual antiproteinuric response of maximal ACE inhibition in established adriamycin nephrosis. Methods. Rats were instituted on lisinopril (75 mg/L) six weeks after disease induction. After two weeks rats were restratified for residual proteinuria to continue this regimen, to a higher dose of lisinopril (150 mg/L) or to co-treatment with the AII-A L 158,809 for another four weeks. Groups on monotherapy AII-A and vehicle served as controls (all groups N = 15). Results. Lisinopril lowered proteinuria by 63% from 741 to 246 g/day (range of percentage change -90 to +2%). Neither increasing the dose of the ACE inhibitor nor addition of AII-A to ACE inhibition improved the antiproteinuric efficacy on a group or individual level: non-responders remained non-responders. All drug categories reduced hard end-points of focal glomerulosclerosis to a similar degree. Conclusions. ACE inhibition has variable renal protective efficacy in the adriamycin model. Neither increasing the dose of the ACE inhibitor beyond the optimal level nor co-treatment with AII-A overcome the individual therapy resistance. Thus, in established adriamycin nephrosis, blockade of the renin-angiotensin system at two different levels offers no additional benefit over ACE inhibition alone, either on the group or individual level.