Potential chemoprevention of LPS-stimulated nitric oxide and prostaglandin E2 production by α-l-rhamnopyranosyl-(1→6)-β-d-glucopyranosyl-3-indolecarbonate in BV2 microglial cells through suppression of the ROS/PI3K/Akt/NF-κB pathway

• RG3I was isolated from C. mandshurica and characterized.
• RG3I inhibits NF-κB activity, along with suppression of iNOS and Cox-2.
• PI3K/Akt and ROS are the main regulators of NF-κB activity in RG3I-induced anti-inflammatory response.

α-l-Rhamnopyranosyl-(1→6)-β-d-glucopyranosyl-3-indolecarbonate (RG3I) is a chemical constituent isolated from the commonly used Asian traditional medicinal plant, Clematis mandshurica; however, no studies have been reported on its anti-inflammatory properties. In the present study, we found that RG3I attenuates the lipopolysaccharide (LPS)-induced DNA-binding activity of nuclear factor-κB (NF-κB) via the dephosphorylation of PI3K/Akt in BV2 microglial cells, leading to a suppression of nitric oxide (NO) and prostaglandin E2 (PGE2) production, along with that of their regulatory genes, inducible NO synthase (iNOS) and cyclooxygenase-2 (Cox-2). Further, the PI3K/Akt inhibitor, LY294002 diminished the expression of LPS-stimulated iNOS and COX-2 genes by suppressing NF-κB activity. Moreover, RG3I significantly inhibited LPS-induced reactive oxygen species (ROS) generation similar to the ROS inhibitors, N-acetylcysteine (NAC) and glutathione (GSH). Notably, NAC and GSH abolished the LPS-induced expression of iNOS and Cox-2 in BV2 microglial cells by inhibiting NF-κB activity. Taken together, our data indicate that RG3I suppresses the production of proinflammatory mediators such as NO and PGE2 as well as their regulatory genes in LPS-stimulated BV2 microglial cells by inhibiting the PI3K/Akt- and ROS-dependent NF-κB signaling pathway, suggesting that RG3I may be a good candidate to regulate LPS-induced inflammatory response.