COMPLEMENTARY ACTION OF ANTIOXIDANT ENZYMES IN THE PROTECTION OF BIOENGINEERED INSULIN-PRODUCING RINM5F CELLS AGAINST THE TOXICITY OF REACTIVE OXYGEN SPECIES

To determine the importance of different antioxidative enzymes for the defense status of insulin-producing cells, the effects of stable over expression of glutathione peroxidase (Gpx), catalase (Cat), or Cu/Zn s uperoxide dismutase (SOD) in insulin-producing RINm5F cells on the cyt otoxicity of hydrogen peroxide (H2O2), hypoxanthine/xanthine oxidase ( H/XO), and menadione have been investigated. Single overexpression of Cat or Gpx provided less protection than the combined expression of Ca t plus SOD or Cat plus Gpx, while single overexpression of SOD either had no effect on the toxicity of the test compounds or increased it. R INm5F cells were also susceptible to butylalloxan, a Lipophilic alloxa n derivative that is selectively toxic to pancreatic p-cells. Overexpr ession of enzymes, both alone and in combination, did not protect agai nst butylalloxan-induced toxicity while SOD overexpression increased i t, as evident from a half maximally effective concentration (EC,,) val ue. The addition of Cat to the culture medium completely prevented the toxic effects of H2O2 and H/XO but had no significant effect on the t oxicity of menadione or butylalloxan. Extracellular SOD had no effect on the toxicity of any of the test compounds. The results of this stud y show the importance of a combination of antioxidant enzymes in prote cting against the toxicity of reactive oxygen species. Thus, overexpre ssion of Cat and Gpx, alone or in combination with SOD, by use of mole cular biology techniques can protect insulin-producing cells against o xidative damage. This may represent a strategy to protect pancreatic p -cells against destruction during the development of autoimmune diabet es and emphasizes the importance of optimal antioxidative enzyme equip ment for protection against free radical-mediated diseases.