Ptaeroxylon obliquum leaf extracts, fractions and isolated compounds as potential inhibitors of 15-lipoxygenase and lipopolysaccharide-induced nitric oxide production in RAW 264.7 macrophage cells

Abstract

Ptaeroxylon obliquum is used traditionally to treat inflammatory diseases and related symptoms such as arthritis, rheumatism, fever and headache. The aim of the study was to determine the anti-inflammatory activities of the crude extracts, fractions and isolated compounds from P. obliquum leaves. Nitric oxide (NO) production in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages and soybean 15-lipoxygenase (15-LOX) inhibitory assays were used to evaluate the anti-inflammatory activity. The acetone crude extracts and fractions had weak 15-LOX inhibitory activity and also had some toxicity against the RAW 264.7 macrophage cells. The three isolated compounds, obliquumol, lupeol and β-amyrin mixture, and eranthin had good 15-LOX inhibitory activity with IC50 values ranging from 7.4 to 13.9 µg/mL which was in the same order as the positive control quercetin (2.1 µg/mL). The high percentage inhibition of NO production by the crude extracts, fractions and isolated compounds appeared to be due to the toxicity to the macrophage cells. Eranthin had the most promising activity with 71.1% inhibition and 89.1% cell viability at a 0.5 µg/mL concentration. The 15-LOX inhibitory activity of obliquumol, lupeol and β-amyrin mixture and eranthin may explain the traditional uses of P. obliquum to treat various inflammatory diseases even though the possibility that the anti-inflammatory activity might still be exerted through other inflammatory mechanisms.