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Endothelin-1 (ET-1) and adrenomedullin (ADM) are circulating vasoactive peptides involved in vascular homeostasis and endothelial function. Elevated levels of plasma ET-1 and ADM, and their biologically stable surrogates, C-terminal-pro-endothelin-1 (CT-pro-ET-1) and midregional proadrenomedullin (MR-pro-ADM), are predictors of cardiac death and heart failure. We studied the association of common genetic variation with MR-pro-ADM and CT-pro-ET-1 by genome-wide association analyses in 3444 participants of European ancestry. We performed follow-up genotyping of single nucleotide polymorphisms (SNPs) that showed suggestive or significant association in the discovery stage in additional 3230 participants. The minor variants in KLKB1 (rs4253238) and F12 (rs2731672), both part of the kallikrein-kinin system, were associated with higher MR-pro-ADM (P=4.46E-52 and P=5.90E-24, respectively) and higher CT-pro-ET-1 levels (P=1.23E-122 and P=1.26E-67, respectively). Epistasis analyses showed a significant interaction between the sentinel SNP of F12 and KLKB1 for both traits. In addition, a variant near the ADM gene (rs2957692) was associated with MR-pro-ADM (P=1.05E-12) and a variant in EDN-1 (rs5370) was associated with CT-pro-ET-1 (P=1.49E-27). The total phenotypic variation explained by the genetic variants was 7.2% for MR-pro-ADM and 14.6% for CT-pro-ET-1. KLKB1 encodes plasma kallikrein, a proteolytic enzyme known to cleave high-molecular-weight kininogen to bradykinin and prorenin to renin. We cloned the precursors of ADM and ET-1 and demonstrated that purified plasma kallikrein can cleave these recombinant proteins into multiple smaller peptides. The discovery of genetic variants in the kallikrein-kinin system and in the genes encoding pre-pro-ET-1 and pre-pro-ADM provides novel insights into the (co-)regulation of these vasoactive peptides in the vascular system.

Objective: Experimental studies have shown that adrenomedullin (ADM) has an important role in circulatory homeostasis. Mid-regional pro-ADM (MR-proADM) is a stable form of ADM. Observational studies found an important association with age, body mass index and kidney function. The aim of this study was to evaluate the prognostic performance of MR-proADM in the general population, controlling for these potential confounders., Methods: 7903 subjects (mean age 49 ± 13 years, 49% male) from the Prevention of REnal and Vascular ENd-stage Disease (PREVEND) cohort with a median follow-up of 10.5 years were enrolled in a prospective cohort study., Results: Mean baseline MR-proADM was 0.39 ± 0.14 nmol/l. In cross-sectional analyses, age, blood pressure, C reactive protein, cystatin-C, N-terminal pro-brain type natriuretic peptide and urinary albumin excretion remained as independent determinants of MR-proADM. In prospective analyses, MR-proADM was associated with the primary endpoint (combined cardiovascular mortality and cardiovascular morbidity), with event rates ranging from 8% in the lowest quintile to 45% in the highest quintile (p for trend <0.001) independent of age, sex, components of the Framingham risk score and other cardiovascular markers. Overall Net Reclassification Improvement against the Framingham risk score was 2.2%, which was non-significant. However, significant modification of the effect of MR-proADM on outcome by age was observed. In subjects aged ≤70 years (N=7475), 8.8% were correctly reclassified in a higher risk category (p=0.017) and 3.4% in a lower risk category (p<0.001). In subjects aged >70 years (N=428) there was no improvement of reclassification (p=0.32)., Conclusion: This study gives a detailed overview of the distribution of ADM in a general population and provides evidence that it is a potent and interesting biomarker in predicting cardiovascular events. These results seem especially applicable to younger subjects.