Mast cells, heparin and bradykinin: The effects of mast cells on the kinin-kallikrein system
The kinin-kallikrein system is a hormonal system with effects on inflammation, blood pressure, coagulation and pain perception. This system is known to have a significant role on the cardiovascular system, including cardiac failure, ischemia and left ventricular hypertrophy. Despite significant research, it is not entirely understood.
Kininogens are proteins that have extra pieces on them. Kininogenases cut off those extra pieces. Active kinins that can act on the body are the result of this action. So kininogenases change kininogens to form kinins.
There are two types of kininogens: low molecular weight (smaller) and high molecular weight (larger.) We are going to focus on HMW, which circulates in the blood.
Also circulating in the blood are two other components called prekallikrein (sometimes called Fletcher factor) and Hageman factor (Factor XII.) When Hageman factor lands on a negatively charged surface, it changes shape and becomes Factor XIIa. Factor XIIa changes the prekallikrein to kallikrein. Kallikrein is a kininogenase.
When kallikrein finds a kininogen, it cuts off the extra piece to release bradykinin. Bradykinin is a kinin and is ready to act on the body.
Bradykinin has several functions in the body. It contributes to contractility of duodenum, ileum and cecum. In the lungs, it can cause chloride secretion and bronchoconstriction. It can cause smooth muscle contraction in the uterus, bladder and vas deferens. It contributes to rheumatoid arthritis, inflammation, pain sensation and hyperalgesia. It also induces cell proliferation, collagen synthesis, and release of nitric oxide, prostacyclin, TNF-a and interleukins. It can also cause release of glutamate by nerve cells. Glutamate has a variety of actions in the body and excessive release can cause epileptic seizures, ALS, lathyrism, autism and stroke.
Bradykinin acts on the endothelium, the cells that line the inner surface of blood and lymphatic vessels, to cause the blood vessels to dilate. This decreases blood pressure. It also regulates sodium excretion from the kidneys, which can further decrease blood pressure. Kininogen levels are reduced in hypertensive patients. Kinins, including bradykinin, oppose the action of angiotensin II, a hypertensive agent.
So how are mast cells related to this system? A couple of ways. The first way is that they release kininogenases and bradykinin. Tryptase can actually behave as a kininogenase. The second way is by being the exclusive producers of heparin.
As I mentioned above, Factor XII needs to change to Factor XIIa to initiate the formation of bradykinin. It does this when it contacts a negatively charged surface. In the lab, you can use a surface like glass for this. But in the body, it often happens on the surfaces of large, negatively charged proteins like heparin. (Side note: Factor XII is part of the clotting cascade. It can be activated by medical devices like PICC lines and that is why they carry a risk of clot formation.) So by releasing heparin, mast cells cause the formation of bradykinin. When the mast cells release heparin in inappropriate amounts, too much bradykinin is formed.
Overproduction of bradykinin is one of the principal causes of angioedema. In hereditary angioedema, the body is deficient in a component that regulates bradykinin. One of the reasons that physical trauma can cause mast cell degranulation is because it causes formation of bradykinin. Bradykinin in turn causes mast cell degranulation with release of histamine and serotonin, among other contents.
Bradykinin antagonists are being researched as possible therapies for hereditary angioedema. Icatibant is one such medication. Bromelain, found in the stems and leaves of pineapples, are known to suppress swelling caused by bradykinin. Aloe and polyphenols, like those in green tea, are also known to suppress bradykinin activity.
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Oschatz C, et al. Mast cells increase vascular permeability by heparin-initiated bradykinin formation in vivo. Immunity. 2011 Feb 25; 34(2):258-68.
Brunnée T, et al. Mast cell derived heparin activates the contact system: a link to kinin generation in allergic reactions. Clin Exp Allergy. 1997 Jun;27(6):653-63.