Abstract

Angioedema (AE) is a rare but potentially life-threatening side effect of therapy with inhibitors of angiotensin-converting enzyme (ACE), the main bradykinin (BK)- inactivating metallopeptidase in humans. The pathogenesis of ACE inhibitor (ACEi)- associated AE (AE+) is presently unknown, although there is increasing evidence of a kinin role. We analyzed the metabolism of endogenous BK (B₂ receptor agonist) and its active metabolite, des-Arg⁹-BK (B₁ receptor agonist), in the presence of an ACEi during in vitro contact activation of plasma from hypertensive patients (n = 39) who presented AE+. Kinetic parameters were compared with those measured in a control group (AE−) of hypertensive patients (n = 39) who never manifested any acute or chronic side effects while treated with an ACEi. The different kinetic parameters were analyzed using a mathematical model (y = k t^αe^{−β t}) previously applied to a normal, healthy population. The slope of BK degradation, but not its formation from high-molecular-weight kininogen, was lower in AE+ patients when compared with the AE− controls. des-Arg⁹-BK accumulation during the kinetic measurements was significantly higher in AE+ plasma. This accumulation of the B₁ agonist in AE+ patients paralleled its half-life of degradation. In conclusion, our results show, for the first time, that an abnormality of endogenous des-Arg⁹-BK degradation exists in the plasma of patients with ACEi-associated AE, suggesting that its pathogenetic mechanism lies in the catabolic site of kinin metabolism.