Bradykinin

Bradykinin (BK-9) — Endogenous Vasoactive Kinin

Evidence & Status

  • Moderate Evidence
  • Established

At a Glance

An endogenous nonapeptide in the kallikrein-kinin system that helps explain vascular regulation, vascular permeability, pain and inflammatory signaling, hereditary angioedema, and ACE-inhibitor pharmacology. Human evidence supports B2-receptor involvement in bradykinin-induced vasodilation.

Plain English

Bradykinin is a short-lived messenger that can widen blood vessels and increase the leakiness of blood-vessel walls. It matters because elevated bradykinin signaling is associated with hereditary angioedema and because ACE normally helps break bradykinin down. Icatibant blocks the B2 receptor that mediates many acute bradykinin effects. Human evidence supports this pathway, but not every proposed cardiovascular or COVID-19 claim.

Overview

Bradykinin (BK) is an endogenous nine-amino-acid nonapeptide in the kallikrein-kinin system. It acts primarily through bradykinin B2 receptors for many acute physiological effects. In controlled human forearm experiments, bradykinin produced vasodilation and icatibant suppressed that response, supporting B2-receptor involvement. Bradykinin signaling is relevant to vascular responses, increased vascular permeability, and pain and inflammatory signaling. Human measurements found elevated bradykinin during acute angioedema attacks associated with C1-inhibitor deficiency. ACE participates in bradykinin degradation, providing mechanistic context for ACE-inhibitor-associated cough and angioedema; impaired degradation is an important contributing mechanism rather than a reason to treat every case as identical. Bradykinin itself is not an approved therapeutic product, and icatibant is a separate B2-receptor antagonist used to study or block this pathway.

Research Summary

Bradykinin is rapidly degraded in human serum: in 116 healthy individuals, exogenous bradykinin had a half-life of 27 ± 10 seconds under the studied conditions, and ACE inhibition potentiated measured bradykinin exposure 9-fold. In human angioedema observations, bradykinin was very high during acute attacks associated with C1-inhibitor deficiency; the same publication also observed elevated bradykinin in some ACE-inhibitor-related angioedema cases. In controlled human forearm experiments, bradykinin increased blood flow and icatibant dose-dependently inhibited this B2-mediated vasodilation. Experimental and preclinical literature has implicated bradykinin signaling in ischemic preconditioning, but a controlled human study did not support a major B2-receptor-mediated role in its studied remote-ischemic-preconditioning model. During the COVID-19 pandemic, a RAS-mediated 'bradykinin storm' was proposed as a mechanistic model; it is historical hypothesis-level material, not an established clinical mechanism or proven therapeutic framework.

Research Areas

  • Blood pressure regulation
  • Pain and inflammation
  • Vascular permeability
  • Hereditary angioedema
  • ACE inhibitor pharmacology
  • B2-receptor pharmacology
  • Ischemic preconditioning (human evidence remains uncertain)
  • SARS-CoV-2 / COVID-19 (historical bradykinin-storm hypothesis)

Safety & Risks

Serious Risks

  • Pathological bradykinin elevation is associated with hereditary C1-inhibitor-deficiency angioedema attacks.
  • Bradykinin accumulation is associated with ACE-inhibitor-related angioedema.

Reported Side Effects

  • Experimental bradykinin infusion: vasodilation
United States
Not FDA-approved for therapeutic use; endogenous research subject
United Kingdom
Research only
Australia
Research only
Canada
Research only

Citations & Sources