Inhibition of nitric oxide production by the carbazole compound LCY-2-CHO via blockade of activator protein-1 and CCAAT/enhancer-binding protein activation in microglia

Excessive nitric oxide (NO) production by activated microglia plays a critical role in neurodegenerative disorders. In this study, we found that 9-(2-chlorobenyl)-9H-carbazole-3-carbaldehyde (LCY-2-CHO) suppressed the NO production in lipopolysaccharide (LPS)/interferon-γ (IFNγ)-stimulated murine microglial N9 and BV-2 cells and in LPS-stimulated N9 cells and rat primary microglia. LCY-2-CHO had no cytotoxic effect on microglia. In activated N9 cells, LCY-2-CHO abolished the expression of inducible nitric oxide synthase (iNOS) protein and mRNA but failed to alter the stability of expressed iNOS mRNA and the enzymatic activity of expressed iNOS protein. LCY-2-CHO did not block DNA-binding activity of nuclear factor-κB (NF-κB) or cyclic AMP response element-binding protein (CREB), but abolished that of activator protein-1 (AP-1), CCAAT/enhancer-binding protein (C/EBP) and nuclear factor IL6 (NF-IL6). LCY-2-CHO attenuated the nuclear levels of c-Jun and C/EBPβ, but not those of p65, p50, C/EBPδ, signal transducer and activator of transcription-1 (STAT-1) or the nuclear expression of IFN regulatory factor-1 (IRF-1). LCY-2-CHO had no effect on the phosphorylation of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK), MAPK-activated protein kinase-2 (MAPKAPK-2), STAT-1, CREB or c-Jun in LPS/IFNγ-stimulated N9 cells, whereas it attenuated the phosphorylation of C/EBPβ at Ser105 and Thr235 residues, which occurred concomitantly with LCY-2-CHO inhibition of C/EBPβ expression and phosphorylation. Taken together, these results suggest that LCY-2-CHO inhibits NO production in microglia through the blockade of AP-1 and C/EBP activation.