PROTECTIVE EFFECT OF TRANSFECTION WITH SECRETABLE SUPEROXIDE-DISMUTASE (SOD) (A SIGNAL SEQUENCE SOD FUSION PROTEIN-CODING CDNA) EXPRESSION VECTOR ON SUPEROXIDE ANION-INDUCED CYTOTOXICITY IN-VITRO

For ex vivo gene therapy, superoxide dismutase (SOD) must be secreted into the extracellular space and delivered to damaged cells, Recombina nt DNA technique can be used to produce a secretory protein that is fu sed to a non-secretory protein and a signal peptide of another secreto ry protein gene, We constructed a secretable SOD eukaryotic expression vector which expresses human SOD cDNA by fusing it to the signal pept ide DNA sequence of the human interleukin-2 (IL-2) gene, The ILSOD cDN A constructed by PCR-based gene expression was ligated into the multic loning site of the pRc/CMV plasmid (pRc/CMV-ILSOD). Rat lung epithelia l like cells (L2 cells) were transfected with pRc/CMV-ILSOD by lipofec tion, The extracellular son activity of ILSOD-L2 cells (transfected ce lls with pRc/CMV-ILSOD) was 3 times as high as that of host cells, We used the xanthin (X)/xanthin oxidase (XO) system to produce superoxide anions at the extracellular space, We initially investigated the dire ct cytotoxicity of superoxide anions upon cells, Host and ILSOD-L2 cel ls were killed by using X/XO, although the sensitivity of the ILSOD-L2 cells to X/XO induced cytotoxicity was significantly decreased compar ed,vith that of host cells, The production of lipid peroxidated substa nces in the host in the presence of X/XO increased to about twice the control (absence of X/XO) level, However, that of ILSOD-L2 cells did n ot change in the presence of X/XO, Therefore, ILSOD-L2 cells were resi stant to X/XO induced lipid peroxidation. These findings indicated tha t ILSOD gene transfection protected against direct oxidant stress by X /XO. We then investigated the effect of extracellular SOD secreted fro m ILSOD-L2 cells on extracellular superoxide anion induced cytotoxicit y in normal cells. The conditioned media of host cells had no signific ant effect upon X/XO induced cytotoxicity, However, the conditioned me dia of ILSOD-L2 cells protected against X/XO induced cytotoxicity, Fur thermore, the conditioned medium of ILSOD-L2 cells was more effective than that of host cells against the production of lipid peroxidated su bstances by normal cells under conditions of oxidative stress. These r esults indicated that non-secretable protein could be delivered to tar get cells by means of DNA engineering, This strategy could thus provid e an ex sire means of applying gene therapy using non-secretable prote ins.