Reactive oxygen species: production and role in the kidney.

Reactive oxygen species (ROS) are formed by incomplete reduction of molecular oxygen. They include superoxide anion (O2-.), hydrogen peroxide (H2O2), hydroxyl radical (OH.), and singlet oxygen (1O2). ROS may induce different types of cell injury, particularly lipid peroxidation and membrane damage. ROS have been shown to play an essential role in the mechanisms of experimental models of several renal diseases: ischemic acute renal failure, renal graft rejection, acute glomerulonephritis, and toxic renal diseases. They are produced by the renal cells and also by the inflammatory bone marrow-derived cells invading the renal tissue. ROS, regardless of their origin, may degrade the glomerular basement membrane and alter the glomerular and tubular cell functions. Particularly, they produce an increase in cyclic AMP synthesis and prostaglandin production in the glomeruli. Recent studies have shown that the glomerular mesangial cells themselves generated ROS on stimulation by phagocytosis of foreign particles or exposure to the complement membrane attack complex or platelet-activating factor. Production of ROS is in narrow relationship with the metabolism of arachidonic acid. Conversion of this fatty acid via the lipoxygenase pathway is associated with an increase of ROS, whereas its transformation into prostaglandins via the cyclooxygenase pathway results in the opposite effect. Production of ROS in activated mesangial cells can be inhibited by glucocorticoids via a receptor-mediated mechanism. The fact that some of these characteristics are different in leukocytes suggests the possibility in the future of the more specific pharmacological control of the inflammatory process in the glomerular mesangium.