Angiotensin-converting enzyme insertion/deletion polymorphism modulates the human in vivo metabolism of bradykinin

Background - Bradykinin is a cardioprotective peptide metabolized by the angiotensin-converting enzyme (ACE). An insertion/deletion (I/D) polymorphism in the ACE gene determines plasma ACE levels. The D allele is associated with cardiovascular disease, which may relate to enhanced angiotensin II production or to increased bradykinin degradation to the inactive metabolite bradykinin 1-5 (BK1-5). Therefore, we determined the effect of the ACE I/D polymorphism on human bradykinin metabolism in vivo. Methods and Results - Bradykinin (400 ng/min) was infused into the brachial artery of volunteers with ACE I/I, I/D, or D/D genotypes (n=9 each). The bradykinin and BK1-5 levels in forearm venous return were quantified by liquid chromatography-mass spectroscopy. Plasma ACE activity was highest in those with the D/D genotype (36.8±6.2 U/mL), intermediate in those with the I/D genotype (25.3±3.3 U/mL), and lowest in those with the I/I genotype (20.3±2.3 U/mL; P=0.017 for effect of number of D alleles). Bradykinin concentrations were 726±242, 469±50, and 545±104 fmol/mL in I/I, I/D, and D/D subjects, respectively (P>0.10). Significant correlations existed between the number of D alleles and BK1-5 concentrations (1113±290, 1520±318, and 1887±388 fmol/mL in the I/I, I/D, and D/D groups, respectively; P=0.027) and the ratio of BK1-5 to bradykinin (1.87±0.35, 3.09±0.40, and 4.31±0.97 in the I/I, I/D, and D/D volunteers, respectively; P=0.010). The venous blood BK1-5:bradykinin ratio correlated with plasma ACE activity (r²=0.16, P=0.039), and total kinin concentration correlated with net tissue plasminogen activator release across the forearm (r²=0.20, P=0.027). Conclusions - The ACE D allele has a significant effect on the in vivo degradation of bradykinin in humans. The ratio of BK1-5:bradykinin may serve as a marker for tissue ACE activity.