Hypericum triquetrifolium—Derived Factors Downregulate the Production Levels of LPS‐Induced Nitric Oxide and Tumor Necrosis Factor‐α in THP‐1 Cells

Based on knowledge from traditional Arab herbal medicine, this in vitro study aims to examine the anti-inflammatory mechanism of Hypericum triquetrifolium by measuring the expression and release of pro-inflammatory cytokines, tumor necrosis factor- α (TNF- α ) and interleukine-6 (IL-6), and inducible nitric oxide synthase (iNOS) in human monocytic cells, THP-1. The effects were assessed by measuring the levels of secretory proteins and mRNA of TNF- α and IL-6, the levels of nitric oxide (NO) secretion and the expression of iNOS in THP-1 cells. Cells were treated with 5  μ g lipopolysaccharide/ml (LPS) in the presence and absence of increasing concentrations of extracts from the aerial parts of H. triquetrifolium . During the entire experimental period, we used extract concentrations (up to 250  μ g mL −1 ) that had no cytotoxic effects, as measured with MTT and LDH assays. Hypericum triquetrifolium extracts remarkably suppressed the LPS-induced NO release, significantly attenuated the LPS-induced transcription of iNOS and inhibited in a dose-dependent manner the expression and release of TNF- α . No significant effects were observed on the release of IL-6. Taken together, these results suggest that H. triquetrifolium probably exerts anti-inflammatory effects through the suppression of TNF- α and iNOS expressions.