Escherichia coli lipopolysaccharide potentiation and inhibition of rat neonatal microglia superoxide anion generation: Correlation with prior lactic dehydrogenase, nitric oxide, tumor necrosis factor-alpha, thromboxane B-2, and metalloprotease release

The effects of lipopolysaccharide (LPS) on the central nervous system, one of the first organs to be affected by sepsis, are still incompletely unders tood. Rat microglia (BM phi) constitute the main leukocyte-dependent source of reactive oxygen species in the central nervous system. The in vitro eff ect of LPS on agonist-stimulated superoxide (O-2(-)) generation from BM phi appears controversial. Our purpose was to determine the time- and concentr ation-dependent effect of Escherichia coli LPS on phorbol-12 myristate 13-a cetate-stimulated O-2(-) generation from BM phi. Our results demonstrate th at BM phi O-2(-) generation in vitro peaked 17 h after stimulation of with .3 ng/mL LPS. Furthermore, stimulation of BM phi with LPS for 17 h resulted in the following concentration-dependent responses: .1-1 ng/mL LPS induced no prior mediator generation but potently enhanced subsequent phorbol-12 m yristate 13-acetate-stimulated O-2(-) generation; 3-10 ng/mL LPS caused nit ric oxide, tumor necrosis factor-alpha (TNF-alpha), thromboxane B-2 and mat rix metalloproteinase-9 release although partially inhibiting ensuing phorb ol-12 myristate 13-acetate-stimulated O-2(-) generation; 30-100 ng/mL LPS, maximized nitric oxide, TNF-alpha, thromboxane B-2, matrix metalloproteinas e-9 generation with concomitant lactic dehydrogenase release although stron gly deactivating successive phorbol-12 myristate 13-acetate-stimulated O-2( -) production. Our in vitro studies suggest that enhanced release of these four mediators (nitric oxide, TNF-alpha, thromboxane B-2, and matrix metall oproteinase-9) during stimulation of BM phi with LPS might play a critical role in the subsequent ability of BM phi to generate O-2(-) in vivo. Potent ial clinical implications of our findings are suggested by the fact that LP S levels similar to the ones used in this study have been observed in cereb rospinal fluid both in Gramnegative meningitis and sepsis.