Reperfusion injury
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Reperfusion injury refers to damage to tissue caused when blood supply returns to the tissue after a period of ischemia. The absence of oxygen and nutrients from blood creates a condition in which the restoration of circulation results in inflammation and oxidative damage through the induction of oxidative stress rather than restoration of normal function.
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[edit] Mechanisms of reperfusion injury
The damage of reperfusion injury is due in part to the inflammatory response of damaged tissues. White blood cells carried to the area by the newly returning blood release a host of inflammatory factors such as interleukins as well as free radicals in response to tissue damage [1].The restored blood flow reintroduces oxygen within cells that damages cellular proteins, DNA, and the plasma membrane. Damage to the cell's membrane may in turn cause the release of more free radicals. Such reactive species may also act indirectly in redox signaling to turn on apoptosis. Leukocytes may also build up in small capillaries, obstructing them and leading to more ischemia[1].
Reperfusion injury plays a part in the brain's ischemic cascade, which is involved in stroke and brain trauma. Repeated bouts of ischemia and reperfusion injury also are thought to be a factor leading to the formation and failure to heal of chronic wounds such as pressure sores and diabetic foot ulcers[2]. Continuous pressure limits blood supply and causes ischemia, and the inflammation occurs during reperfusion. As this process is repeated, it eventually damages tissue enough to cause a wound[2].
In prolonged ischemia (60 minutes or more), hypoxanthine is formed as breakdown product of ATP metabolism. The enzyme xanthine dehydrogenase is converted to xanthine oxidase as a result of the higher availability of oxygen. This oxidation results in molecular oxygen being converted into highly reactive superoxide and hydroxyl radicals. Excessive nitric oxide produced during reperfusion reacts with superoxide to produce the potent free radical peroxynitrite. These radicals attack cell membrane lipids, proteins, and glycosaminoglycans, causing further damage.
[edit] See also
[edit] References
- ^ a b Clark, Wayne M. (January 5, 2005). Reperfusion Injury in Stroke. eMedicine. WebMD. Retrieved on August 9, 2006.
- ^ a b Mustoe T. (2004). "Understanding chronic wounds: a unifying hypothesis on their pathogenesis and implications for therapy". AMERICAN JOURNAL OF SURGERY 187 (5A): 65S-70S. PMID 15147994.
