Modulation of inducible nitric oxide synthase gene expression in RAW 264.7 murine macrophages by Pacific ciguatoxin

To investigate the possible involvement of the nitric oxide radical (NO) in ciguatera fish poisoning (CFP), the in vitro effects of the main Pacific ciguatoxin (P-CTX-1B) and bacterial lipopolysaccharide (LPS) were comparatively studied on neuroblastoma Neuro-2a and on macrophage RAW 264.7 cell lines. NO accumulation was quantified by measuring nitrite levels in cellular supernatant using Griess reagent while the up-regulation of inducible nitric oxide synthase (iNOS) at the mRNA level was quantified via Real-Time Reverse-Transcription Polymerase Chain Reaction (RT-PCR). P-CTX-1B caused a concentration- and time-dependent induction of iNOS in RAW 264.7 cells but not in Neuro-2a cells. NO production was evidenced by increased nitrite levels in the 10 μM range after 48 h of RAW 264.7 cells exposure to LPS and P-CTX-1B (0.05 μg/ml and 6 nM, respectively). The expression of iNOS mRNA peaked at 8 h for LPS then gradually decreased to low level at 48 h. In contrast, a sustained level was recorded with P-CTX-1B in the 8–48 h time interval. The addition of Nω-nitro-l-arginine methyl ester (l-NAME), a stereoselective NOS inhibitor, strongly diminished NO formation but had no effect on iNOS mRNA synthesis. The implication of NO in CFP paves the way for new therapies for both western and traditional medicines.