The effects of ACE inhibition on serum angiotensin II concentration following cardiac transplantation

Aims. ANGII mediates vascular neointimal formation through smooth muscle cell stimulation and enhanced production of growth factors leading to increased arterial medial layer thickness, which is a characteristic of transplant arteriosclerosis. ACE inhibition is known to be of benefit to patients with cardiovascular risk factors. We aimed to determine the effect of ACE inhibitor therapy on ACE enzymatic activity and serum ANGII levels following cardiac transplantation. Methods. A total of 43 serum samples from eight transplant recipients were used for analysis. Samples were taken monthly from the date of transplant for the initial 6 months. ANGII was measured using sandwich ELISA. ACE enzymatic activity was measured using spectrophotometric kinetic analysis. Results. There was a significant reduction in ACE enzymatic activity among individuals treated with ACE inhibitor therapy (18.0 ± 16.6 vs 31.8 ± 23.4, P = .008). We found significantly higher ANGII serum levels in patients receiving ACE inhibitor therapy compared to those not (2.4 ± 2.1 vs 8.0 ± 7.4, P = .002). There was also a significant positive correlation between ACE enzymatic activity and ANGII serum level (coefficient 0.332, P = .03). Conclusions. Our results suggest an effective ACE independent pathway for ANGII conversion. Chymase can convert ANGI with higher affinity than ACE. Also, chymase is stored in mast cells, which infiltrate the myocardium following transplantation. This data indicate that pharmacological chymase inhibition may be a possible therapeutic strategy following transplantation. © 2005 by Elsevier Inc. All rights reserved.