Bioassay-guided fractionation, phospholipase A-inhibitory activity and structure elucidation of compounds from leaves of .

Context: Harms (Rubiaceae) is used traditionally in Nigeria for the treatment of snake bites. Snake venom contains phospholipase A (PLA) which plays a key role in causing inflammation and pain.

Objective: To assess the anti-inflammatory effect of the methanol extract of (MESM) leaves through the inhibition of PLA and investigate the compounds responsible for the effect.

Materials And Methods: PLA-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 -hexane, dichloromethane, ethyl acetate and aqueous-methanol (90:10 v/v), after which PLA-inhibitory activity of the partitions was determined. The best partition was subjected to chromatographic techniques and the fractions obtained were assessed for PLA 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 activity at 0.8 mg/mL (44.253%) compared to prednisolone (35.207%). -Hexane partition (SMP1) proved more active with inhibition of 55.870% observed at 0.1 mg/mL. Fraction 1 (SMF1) showed the highest PLA-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-inhibitory activity of MESM suggests that its compounds may be explored further in monitoring anti-inflammatory genes affected by the venoms.