Bioassay-guided fractionation, phospholipase A(2)-inhibitory activity and structure elucidation of compounds from leaves of Schumanniophyton magnificum

CONTEXT: Schumanniophyton magnificum Harms (Rubiaceae) is used traditionally in Nigeria for the treatment of snake bites. Snake venom contains phospholipase A(2) (PLA(2)) which plays a key role in causing inflammation and pain. OBJECTIVE: To assess the anti-inflammatory effect of the methanol extract of Schumanniophyton magnificum (MESM) leaves through the inhibition of PLA(2) and investigate the compounds responsible for the effect. MATERIALS AND METHODS: PLA(2)-inhibitory activity of MESM was assessed at concentrations of 0.1–0.8 mg/mL using human red blood cells as substrate. Prednisolone was used as the standard control. MESM was subsequently partitioned using n-hexane, dichloromethane, ethyl acetate and aqueous-methanol (90:10 v/v), after which PLA(2)-inhibitory activity of the partitions was determined. The best partition was subjected to chromatographic techniques and the fractions obtained were assessed for PLA(2) inhibition at 0.4 mg/mL. Compounds in the most active fraction were determined using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). RESULTS: MESM significantly inhibited PLA(2) activity at 0.8 mg/mL (44.253%) compared to prednisolone (35.207%). n-Hexane partition (SMP1) proved more active with inhibition of 55.870% observed at 0.1 mg/mL. Fraction 1 (SMF1) showed the highest PLA(2)-inhibitory activity of 58.117%. FTIR studies revealed the presence of some functional groups in SMF1, and GC-MS confirmed the presence of 9 compounds which are first reported in this plant. Hexadecanoic acid, ethyl ester was identified as the major compound (24.906%). DISCUSSION AND CONCLUSIONS: The PLA(2)-inhibitory activity of MESM suggests that its compounds may be explored further in monitoring anti-inflammatory genes affected by the venoms.