Formula C50H73N15O11 | Molar mass 1,060.21 g/mol | |
 | ||
Bradykinin is an inflammatory mediator. It is a peptide that causes blood vessels to dilate (enlarge), and therefore causes blood pressure to fall. A class of drugs called ACE inhibitors, which are used to lower blood pressure, increase bradykinin (by inhibiting its degradation) further lowering blood pressure. Bradykinin dilates blood vessels via the release of prostacyclin, nitric oxide, and Endothelium-Derived Hyperpolarizing Factor.
Contents
Bradykinin is a physiologically and pharmacologically active peptide of the kinin group of proteins, consisting of nine amino acids.
Structure
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.
Synthesis
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.
Metabolism
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.
Effects
Bradykinin is a potent endothelium-dependent vasodilator, leading to a drop in 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. Bradykinin also causes natriuresis, contributing to the drop in blood pressure.
Bradykinin raises internal calcium levels in neocortical astrocytes causing them to release glutamate.
Bradykinin is also thought to be the cause of the dry cough in some patients on 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, which causes a dry cough via bronchoconstriction. This refractory cough is a common cause for stopping ACE inhibitor therapy, in which case angiotensin II receptor antagonists (ARBs) are the next line of treatment.
Overactivation of bradykinin is thought to play a role in a rare disease called hereditary angioedema, formerly known as hereditary angio-neurotic edema.
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.
Receptors
The kinin B1 and B2 receptors belong to G protein coupled receptor (GPCR) family.
History
Bradykinin was discovered in 1948 by three Brazilian physiologists and pharmacologists working at the Instituto Biológico, in São Paulo, Brazil, led by Dr. Maurício Rocha e Silva. Together with colleagues Wilson Teixeira Beraldo and Gastão Rosenfeld, they discovered the powerful hypotensive effects of bradykinin in animal preparations. Bradykinin was detected in the blood plasma of animals after the addition of venom extracted from the Bothrops jararaca (Brazilian lancehead snake), brought by Rosenfeld from the Butantan Institute. The discovery was part of a continuing study on circulatory shock and proteolytic enzymes related to the toxicology of snake bites, started by Rocha e Silva as early as 1939. Bradykinin was to prove a new autopharmacological principle, i.e., a substance that is released in the body by a metabolic modification from precursors, which are pharmacologically active. According to B.J. Hagwood, Rocha e Silva's biographer, "The discovery of bradykinin has led to a new understanding of many physiological and pathological phenomena including circulatory shock induced by venoms and toxins." Etymology: brady [Gk] slow, kinin [Gk ] kīn(eîn) to move, set in motion, ? from the effect of snake venom on intestinal smooth muscle, which was noted to slowly contract.
Therapeutic implications
The practical importance of the discovery of bradykinin became apparent when one of his collaborators at the Medical School of Ribeirão Preto at the University of São Paulo, Dr. Sérgio Henrique Ferreira, discovered a bradykinin-potentiating factor (BPF) in the bothropic venom, which increases powerfully both the duration and magnitude of its effects on vasodilation and the consequent fall in blood pressure. On the basis of this finding, Squibb scientists developed the first of a new generation of highly-effective anti-hypertensive drugs, the so-called ACE inhibitors, such as captopril (trademarked Capoten).
Currently, bradykinin inhibitors (antagonists) are being developed as potential therapies for hereditary angioedema. Icatibant is one such inhibitor. Additional bradykinin inhibitors exist. It has long been known in animal studies that bromelain, a substance obtained from the stems and leaves of the pineapple plant, suppresses trauma-induced swelling caused by the release of bradykinin into the bloodstream and tissues. Other substances that act as bradykinin inhibitors include aloe and polyphenols, substances found in red wine and green tea.
Bradykinin is also released by carcinoid tumors, and results in asthma-like symptoms.