Repression of proinflammatory gene expression by lipid extract of Nostoc commune var sphaeroides Kützing, a blue-green alga, via inhibition of nuclear factor-κB in RAW 264.7 macrophages

We investigated whether lipid extract from a blue-green alga, N commune, modulates proinflammatory gene expression in RAW 264.7 macrophages. The cells were incubated with N commune lipid extract (0-100 μg/mL) and subsequently activated by LPS (100 ng/mL). Quantitative real-time PCR analysis showed that mRNA abundance of proinflammatory mediators, including TNF-α, COX-2, IL-1β, IL-6, and iNOS, was significantly reduced by N commune lipid extract in a dose-dependent manner. Secretion of TNF-α and IL-1β into cell culture medium was also significantly decreased by N commune lipid extract. Thin-layer chromatography–densitometry analysis showed that N commune lipid extract contained approximately 15% of fatty acids. To determine whether the inhibition of proinflammatory mediator production by N commune lipid extract is primarily conferred by fatty acids in the lipid extract, macrophages were incubated with 100 μg/mL of N commune lipid extract or 15 μg/mL of a fatty acid mixture, which was formulated to reflect the fatty acid composition of N commune lipid extract. The fatty acid mixture significantly reduced RNA abundance of TNF-α and COX-2, but to a lesser extent than did the N commune lipid extract, suggesting the presence of additional bioactive compounds with an antiinflammatory property in the lipid extract. As NF-κB is a major regulator for the proinflammatory gene expression, we measured its DNA-binding activity. DNA-binding activity of NF-κB was significantly reduced by N commune lipid extract. In conclusion, our study suggests that N commune lipid extract represses the expression of proinflammatory genes in RAW 264.7 macrophages, at least in part, by inhibiting the activation of NF-κB pathway.