Superoxide dismutase gene expression in the endotoxin-treated rat lung

Background: It is well known that oxygen free radicals (OFR) play a vital role in the various type of acute lung injury. Among various antioxidant defense mechanisms, the superoxide dismutases (SOD) are thought to be the first line of antioxidant defense by catalyzing the dismutation of two superoxide radicals to yield hydrogen peroxide and oxygen. Eukaryotic cells contain two types of intracellular SOD: cytosolic, dimeric copper/zinc-containing enzyme (CuZnSOD) and mitochondrial, tetrameric manganese-containing enzyme (MnSOD). The purpose of this study is to evaluate the time-dependent gene expression of MnSOD and CuZnSOD in the endotoxin-treated rats, and to compare with the manifestations of LPS-induced acute lung injury in rats. Methods: Total RNA from rat lung was isolated using single step phenol extraction 0, 1, 2, 4, 6, 12, 18, 24 hours after E. coli endotoxin injection (n = 3, respectively). RNA was separated by formaldehyde-containing 1.2% agarose gels eletrophoresis, transblotted, baked, prehybridized, and hybridized with ³²P-labeled cDNA probes for rat MnSOD and CuZnSOD, which were kindly donated by Dr. Ho (Duke Univeresity, Durham, NC, USA). The probes were labeled by nick translation. Blots were washed and autoradiography were quantitated using laser densitometry. Equivalent amounts of total RNA/gel were assessed by monitoring 28S and 18S rRNA. Results: Endotoxin caused a rise in steady-state MnSOD mRNA levels by 4 h with peak mRNA accumulation by 6 h. Continued MnSOD mRNA expression was observed at 12 h. CuZnSOD mRNA expression was observed from 1 h to 24 h with peak levels by 18 h. Conclusion: These results suggest that SOD plays an important defensive role in the endotoxin-induced acute lung injury in rats.