Synthesis of Superoxide Dismutase Derivative That Specifically Accumulates in Renal Proximal Tubule Cells

Abstract

Protection of tissues from oxygen toxicity is one of the major prerequisites to aerobic life. Since a wide variety of xenobiotics with prooxidant activity is excreted by the kidney, renal tubule cells should be protected from hazardous oxygen species. Because intravenously injected Cu/Zn-type superoxide dismutase (SOD) is rapidly excreted in the urine in its intact form, effective dismutation of superoxide radicals cannot be achieved in vivo by intravenously administered SOD. To scavenge superoxide radicals and inhibit their toxic effects in and around renal tubule cells, a hexamethylene–diamine (AH)-conjugated SOD (AH–SOD) was synthesized. When injected intravenously into the rat, 125I-labeled AH–SOD disappeared from the circulation with a half-life of 3 min and accumulated in the kidney. After 30 min of administration, more than 80% of the radioactivity derived from AH–SOD was found to localize in the kidney without being excreted in the urine. Immunohistochemical examination revealed that, 60 min after administration, the major part of AH–SOD localized in renal proximal tubule cells. Kinetic analysis using right-side-out-oriented renal brush border vesicles revealed that AH–SOD bound to their membrane surface by some mechanism which was inhibited by AH but not by heparin and albumin. These results indicated that AH–SOD rapidly underwent renal glomerular filtration, bound to apical plasma membranes of proximal tubule cells, and localized in these cells for a fairly long time without being excreted in the urine. Thus, AH–SOD might permit studies on the role of superoxide radicals in and around renal proximal tubule cells.