Adrenomedullin (ADM) is a 52-amino acid vasoactive peptide originally isolated in 1993 by Kitamura et al. from human pheochromocytoma tissue based on its ability to elevate cyclic AMP in rat platelets. Despite its name suggesting adrenal specificity, adrenomedullin is expressed ubiquitously across virtually all tissues, with particularly high levels in the adrenal medulla, lung, kidney, heart, and vascular endothelium.

Overview

Adrenomedullin belongs to the calcitonin gene-related peptide (CGRP) superfamily, which includes calcitonin, CGRP, amylin, and intermedin/adrenomedullin 2. ADM is synthesized as a 185-amino acid preproadrenomedullin, which is processed to proadrenomedullin (proADM), and then cleaved to yield the mature 52-amino acid ADM peptide (with a C-terminal amidation essential for biological activity) and the 20-amino acid proadrenomedullin N-terminal peptide (PAMP), which also has independent vasodilatory properties.

ADM signals primarily through the calcitonin receptor-like receptor (CRLR, also called CLR) complexed with receptor activity-modifying protein 2 (RAMP2). The CRLR/RAMP2 complex forms the AM1 receptor, while CRLR/RAMP3 forms the AM2 receptor, which also binds ADM. CRLR/RAMP1 forms the CGRP receptor. Receptor activation stimulates adenylyl cyclase (cAMP), phospholipase C, and nitric oxide synthase pathways, producing vasodilation, increased cardiac output, natriuresis, and anti-inflammatory effects.

The clinical utility of ADM measurement is limited by its short half-life (~22 minutes) and binding to complement factor H in plasma. MR-proADM (mid-regional proadrenomedullin, amino acids 45-92 of proADM) is a stable stoichiometric surrogate that reflects ADM production and has been validated as a prognostic biomarker in sepsis, pneumonia, heart failure, and critical illness.

Mechanism of Action

Adrenomedullin activates multiple signaling pathways through its receptor complexes:

CRLR/RAMP2 (AM1 Receptor) — cAMP/PKA Pathway: The primary ADM receptor activates Gs-coupled adenylyl cyclase, increasing intracellular cAMP and activating protein kinase A (PKA). In vascular smooth muscle, PKA phosphorylates myosin light chain kinase (MLCK), reducing calcium sensitivity and producing vasodilation. In the heart, cAMP/PKA increases calcium cycling, producing positive inotropy and lusitropy.

Nitric Oxide Signaling: ADM stimulates endothelial nitric oxide synthase (eNOS) through PI3K/Akt-mediated phosphorylation, increasing NO production. NO activates soluble guanylyl cyclase (sGC) in adjacent vascular smooth muscle, increasing cGMP and producing additional vasodilation. This endothelium-dependent vasodilation complements the direct smooth muscle relaxation via cAMP.

Endothelial Barrier Protection: ADM stabilizes endothelial barrier function through Rac1/cortactin-mediated cytoskeletal reorganization and enhancement of VE-cadherin-based adherens junctions. This anti-permeability effect is particularly relevant in sepsis, where endothelial barrier breakdown leads to capillary leak, tissue edema, and organ dysfunction.

Anti-inflammatory Effects: ADM suppresses NF-kappaB activation, reduces pro-inflammatory cytokine production (TNF-alpha, IL-6, IL-1beta), and inhibits macrophage activation. ADM also promotes M2 macrophage polarization and reduces endothelial adhesion molecule expression (ICAM-1, VCAM-1, E-selectin), decreasing leukocyte recruitment.

Renal Protection: In the kidney, ADM increases renal blood flow, glomerular filtration rate, and sodium excretion through direct vasodilation of renal vasculature and inhibition of aldosterone secretion. ADM also has direct tubular effects that promote natriuresis and diuresis.

Cardioprotection: ADM reduces cardiomyocyte apoptosis through PI3K/Akt and ERK1/2 survival signaling pathways, decreases oxidative stress, and inhibits cardiac fibroblast proliferation and collagen synthesis. These effects provide protection against ischemia-reperfusion injury and pathological cardiac remodeling.

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Research

Safety Profile

Endogenous adrenomedullin has no intrinsic safety concerns and serves as a protective cardiovascular peptide. For exogenous ADM infusion (investigational), the primary adverse effect is dose-dependent systemic hypotension, reflecting its potent vasodilatory action. At doses producing hemodynamically significant effects (15-50 ng/kg/min IV), mean arterial pressure typically decreases by 10-25%, which can be clinically significant in patients with borderline hemodynamics. Reflex tachycardia may occur due to baroreceptor activation. Facial flushing, headache, and mild nausea have been reported during ADM infusion studies. No significant end-organ toxicity, arrhythmias, or immunogenicity have been observed in clinical studies of short-term ADM infusion. Adrecizumab (anti-ADM antibody) had an acceptable safety profile in the AdrenOSS-2 trial, with no significant differences in serious adverse events between treatment and placebo groups. The non-neutralizing mechanism of adrecizumab theoretically minimizes the risk of blocking ADM's beneficial effects.

Clinical Research Protocols

• ADM infusion (investigational — cardiovascular): 15-50 ng/kg/min continuous IV infusion. Studies in heart failure and PAH have used infusion durations of 30 minutes to 14 days. Blood pressure monitoring every 5 minutes during initiation.
• Inhaled ADM (investigational — PAH): 15-150 ng/kg nebulized, targeting pulmonary vasculature with minimal systemic effects.
• Adrecizumab (AdrenOSS-2 protocol): Single IV dose of 4 mg/kg administered over 1 hour in septic shock patients with bio-ADM >70 pg/mL, within 12 hours of vasopressor initiation.
• MR-proADM biomarker cutpoints: Community-acquired pneumonia mortality risk: low <0.75 nmol/L, intermediate 0.75-1.5 nmol/L, high >1.5 nmol/L. Sepsis 28-day mortality: elevated >1.5-2.0 nmol/L (assay-dependent).
• Key trials: AdrenOSS-1 (observational, sepsis biomarker), AdrenOSS-2 (phase 2, adrecizumab in septic shock), ProHOSP (MR-proADM in pneumonia).

Subpopulation Research

• Sepsis and septic shock: Bio-ADM >70 pg/mL identifies patients with endothelial dysfunction, higher organ failure scores, and increased mortality. Adrecizumab targets this high bio-ADM subpopulation (PMID: 30075790).
• Community-acquired pneumonia: MR-proADM outperforms CRP, procalcitonin, and CURB-65 for predicting 30-day mortality and adverse outcomes (PMID: 23497568).
• Heart failure: ADM levels are elevated in HFrEF and HFpEF, correlating with NYHA class and predicting mortality independently of BNP/NT-proBNP.
• Acute myocardial infarction: Elevated ADM in STEMI predicts larger infarct size, reduced LVEF, and higher mortality. ADM may serve as a compensatory vasodilator in the peri-infarct zone.
• Pulmonary arterial hypertension: ADM levels correlate with pulmonary artery pressure and predict survival. Exogenous ADM reduces PVR in PAH (PMID: 15234434).
• Critical COVID-19: Bio-ADM at ICU admission predicted mechanical ventilation, AKI, and mortality in severe COVID-19 (PMID: 34070269).
• Preeclampsia: ADM levels are altered in preeclampsia, and ADM may play a role in placental vascular development and maternal hemodynamic adaptation.

Pharmacokinetic Profile

Ongoing & Future Research

• AdrenOSS-3 and beyond: Phase 3 trials of adrecizumab in septic shock are anticipated, with enrichment strategies based on bio-ADM levels to identify patients most likely to benefit.
• ADM in cardio-renal syndrome: Investigation of ADM's renal protective effects in cardiorenal syndrome, potentially as adjunctive therapy to standard heart failure treatment.
• Inhaled ADM for pulmonary hypertension: Development of inhaled ADM formulations (nebulized or dry powder) to achieve pulmonary selectivity without systemic hypotension.
• ADM-based peptide analogs: Design of ADM analogs with longer half-lives, enhanced receptor selectivity, and improved pharmacokinetic profiles for subcutaneous administration.
• Dual biomarker-therapeutic paradigm: Using bio-ADM to both identify patients and guide adrecizumab therapy represents a precision medicine approach in critical care — a biomarker-enriched therapeutic strategy.
• ADM in organ transplantation: Preclinical evidence of ADM's protective effects against ischemia-reperfusion injury in transplanted organs, with potential for machine perfusion-based delivery.