Bradykinin

Bradykinin (Greek brady-, slow; -kinin, kīn(eîn) to move) is an inflammatory mediator. It is a peptide that causes blood vessels to dilate (enlarge) via the release of prostacyclin, nitric oxide, and Endothelium-Derived Hyperpolarizing Factor. Bradykinin is a physiologically and pharmacologically active peptide of the kinin group of proteins, consisting of nine amino acids. Bradykinin (Greek brady-, slow; -kinin, kīn(eîn) to move) is an inflammatory mediator. It is a peptide that causes blood vessels to dilate (enlarge) via the release of prostacyclin, nitric oxide, and Endothelium-Derived Hyperpolarizing Factor. Bradykinin is a physiologically and pharmacologically active peptide of the kinin group of proteins, consisting of nine amino acids. A class of drugs called angiotensin converting enzyme (ACE) inhibitors increase bradykinin levels by inhibiting its degradation, thereby increasing its blood pressure lowering effect. ACE inhibitors are FDA approved for the treatment of hypertension and heart failure. Bradykinin is a 9-amino acid peptide chain. The amino acid sequence of bradykinin is: Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg (RPPGFSPFR). Its empirical formula is therefore C50H73N15O11. The kinin-kallikrein system makes bradykinin by proteolytic cleavage of its kininogen precursor, high-molecular-weight kininogen (HMWK or HK), by the enzyme kallikrein. Moreover, there is compelling evidence that plasmin, a fibrinolytic enzyme, is able to generate bradykinin after HMWK cleavage. In humans, bradykinin is broken down by three kininases: angiotensin-converting enzyme (ACE), aminopeptidase P (APP), and carboxypeptidase N (CPN), which cleave the 7-8, 1-2, and 8-9 positions, respectively. Bradykinin is a potent endothelium-dependent vasodilator and mild diuretic, which may cause a lowering of the blood pressure. It also causes contraction of non-vascular smooth muscle in the bronchus and gut, increases vascular permeability and is also involved in the mechanism of pain. Initial secretion of bradykinin post-natally causes constriction and eventual atrophy of the ductus arteriosus, forming the ligamentum arteriosum between the pulmonary trunk and aortic arch. It also plays a role in the constriction and eventual occlusion of a number of other fetal vessels, including the umbilical arteries and vein. The differential vasoconstriction of these fetal vessels compared to the vasodilator response of other vessels suggest that the walls of these fetal vessels are different than other vessels. The kinin B1 and B2 receptors belong to G protein coupled receptor (GPCR) family. Bradykinin is also thought to be the cause of the dry cough in some patients on widely prescribed angiotensin-converting enzyme (ACE) inhibitor drugs. It is thought that bradykinin is converted to inactive metabolites by ACE, therefore inhibition of this enzyme leads to increased levels of bradykinin; increased bradykinin sensitizes somatosensory fibers and thus causes hyperalgesia. Bradykinin may mediate this via pro-inflammatory peptides (e.g. substance P, neuropeptide Y) and a local release of histamine.