bradykinin

Bradykinin
Identifiers
CAS number	58-82-2
PubChem	6026
MeSH	Bradykinin
Properties
Molecular formula	C50H73N15O11
Molar mass	1060.21
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Bradykinin is a peptide that causes blood vessels to enlarge (dilate), and therefore causes blood pressure to lower. 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 works on blood vessels through 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.

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. 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.

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 ^[1][2].

Physiological Role (Function)

Effects

Bradykinin is a potent endothelium-dependent vasodilator, causes contraction of non-vascular smooth muscle, increases vascular permeability and also is involved in the mechanism of pain. Bradykinin also causes natriuresis, contributing to a drop in blood pressure. In some aspects, it has similar actions to that of histamine, and like histamine is released from venules rather than arterioles.

Bradykinin raises internal calcium levels in neocortical astrocytes causing them to release glutamate.^[3]

Bradykinin is also thought to be the cause of the dry cough in some patients on angiotensin converting enzyme (ACE) inhibitor drugs. This refractory cough is a common cause for stopping ACE inhibitor therapy. In which case Angiotensin II Receptor Antagonists are the next line of treatment. But this is not as effective, and is meant more to reduce mild hypertension.

Overactivation of bradykinin is thought to play a role in a rare disease called Hereditary Angioedema, also known as Hereditary Angio-Neurotic Edema. ^[4]

Initial secretion of Bradykinin post-natally causes constriction and eventual atrophy of the ductus arteriosus, forming the ligamentum artertiosum between the pulmonary trunk and aortic arch.

Receptors

• The B₁ receptor (also called bradykinin receptor B1) is expressed only as a result of tissue injury, and is presumed to play a role in chronic pain. This receptor has been also described to play a role in inflammation. ^[5]. Most recently, it has been shown that the kinin B₁ receptor recruits neutrophil via the chemokine CXCL5 production. Moreover, endothelial cells have been described as a potential source for this B₁ receptor-CXCL5 pathway. ^[6]

• The B₂ receptor is constitutively expressed and participates in bradykinin's vasodilatory role.

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."

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. ^[7] Other substances that act as bradykinin inhibitors include aloe ^{[8] [9]} and polyphenols, substances found in red wine and green tea. ^[10]

References