Platelet activating factor (PAF) antagonists on cytokine induction of iNOS and sPLA2 in immortalized astrocytes (DITNC)

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) and its receptor are known to play important roles in modulating neuronal plasticity and inflammatory responses, particularly during neuronal injury. PAF receptors are widespread in different brain regions and are present on the cell surface as well as in intracellular membrane compartments. Astrocytes are immune active cells and are responsive to cytokines, which stimulate signaling cascades leading to transcriptional activation of genes and protein synthesis. Our recent studies indicate the ability of cytokines, e.g., tumor necrosis factor-alpha (TNF alpha), interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN gamma), to induce the inducible nitric oxide (iNOS) and secretory phospholipase A(2) (sPLA(2)) genes in immortalized astrocytes (DITNC) (Li et al., J. Interferon and Cytokine Res. 19: 121-127. 1999). The main objective for this study is to examine the effects of PAF antagonists on cytokine induction of iNOS and sPLA(2) in these cells. Results show that BN50730, a synthetic PAF antagonist, but not BN52021, a natural PAF antagonist (ginkolide B) can dose-dependently inhibit cytokine induction of NO production and sPLA(2) release. Inhibition of NO production by BN50730 corroborated well with the decrease in iNOS protein and mRNA levels as well as binding of NF-kappa B and STAT-1 to DNA, suggesting that BN50730 action is upstream of the transcriptional process. These results are in agreement with the role of intracellular PAF in regulating the cytokine signaling cascade in astrocytes and further suggest the possible use of BN50730 as a therapeutic agent for suppressing the inflammatory pathways elicited by cytokines.