It is now clear that reactive oxygen species (ROS) can act as signalling molecules in the cerebral circulation under both physiological and pathological conditions. Some major products of superoxide (O(2)(.)(-)) metabolism, such as hydrogen peroxide (H(2)O(2)) and hydroxyl radical (OH(.)), appear to be particularly good cerebral vasodilators and may, surprisingly, represent important molecules for increasing local cerebral blood flow. A major determinant of overall ROS levels in the cerebral circulation is the rate of generation of the parent molecule, O(2)(.)(-). Although the major enzymatic source of O(2)(.)(-) in cerebral arteries is yet to be conclusively established, the two most likely candidates are cyclo-oxygenase and nicotinamide adenine dinucleotide phosphate (reduced form) [NADPH] oxidase. The activity of endogenous superoxide dismutases (SODs) play a vital role in determining levels and effects of all individual ROS derived from metabolism of O(2)(.)(-). The term oxidative stress may be an over-simplification that hides the complexity and diversity of the ROS family in cerebrovascular health and disease. Although a generalised increase in ROS levels seems to occur during several vascular disease states, the consequences of this for cerebrovascular function are still unclear.Because enhanced breakdown of O(2)(.)(-) by SOD will increase the generation of the powerful cerebral vasodilator H(2)O(2), this latter molecule could conceivably act as a compensatory vasodilator mechanism in the cerebral circulation under conditions of elevated O(2)(.)(-) production. Some recent clinical data support the concept of a protective role for cerebrovascular NADPH oxidase activity. Although it is quite speculative at present, if NADPH oxidase were to emerge as a major source of beneficial vasodilator ROS in the cerebral circulation, this may represent a significant dilemma for treatment of ischaemic cerebrovascular ....
|Pages (from-to)||2143 - 2157|
|Number of pages||15|
|Publication status||Published - 2004|