Gene transfer of extracellular superoxide dismutase increases superoxide dismutase activity in cerebrospinal fluid

Abstract

Background and Purpose - Copper-zinc superoxide dismutase (CuZnSOD) is expressed intracellularly, while extracellular SOD (EC-SOD) is released from cells. The purpose of this study was to determine whether gene transfer of CuZnSOD increases SOD activity predominantly in tissues, and gene transfer of EC-SOD increases SOD activity in cerebrospinal fluid (CSF). We also determined whether heparin or dextran sulfate releases EC-SOD into CSF. Methods - We injected recombinant adenoviruses expressing EC-SOD (AdEC-SOD), CuZnSOD (AdCuZnSOD), or β-galactosidase (Adβ-gal) into the cisterna magna of rabbits. Results - Total SOD activity in CSF was 39±11 U/mL (mean±SE) before virus injection. Three days later, total SOD activity in CSF increased to 148±22 U/mL after AdEC-SOD and 92±10 U/mL after AdCuZnSOD (P<0.05 versus AdEC-SOD), with no change after Adβ-gal (49±5 U/mL). EC-SOD protein was detected in CSF after AdEC-SOD but not AdCuZnSOD or Adβ-gal. Injection of heparin or dextran sulfate into the cisterna magna increased total SOD activity 27-fold and 32-fold over basal values, respectively, in CSF of rabbits that received AdEC-SOD. In contrast to effects in CSF, total SOD activity in basilar artery and meninges was significantly higher after AdCuZnSOD and tended to be higher after AdEC-SOD than after Adβ-gal. Conclusions - We have developed a method for intracranial gene transfer of CuZnSOD and EC-SOD. After gene transfer, CuZnSOD was expressed mainly in tissues, and EC-SOD was released into the CSF, especially after injection of heparin or dextran sulfate. Gene transfer of different isoforms of SOD may be useful in studies of cerebral vascular physiology and pathophysiology.