Antimicrobial, antioxidant, anti-inflammatory activities and phytoconstituents of extracts from the roots of Dissotis thollonii Cogn. (Melastomataceae)

Background: Dissotis thollonii Cogn. belonging to the Malastomataceae family is used in the West Region of Cameroon for the treatment of inflammation, kidney diseases, pregnancy control and sinusitis. Despite the traditional use of this plant, no scientific report or informationwas found in the literature regarding neither its biological activity nor its chemical constituents. Aim of the study: The present work was designed to determine the antimicrobial, antioxidant and antiinflammatory activities of different extracts of the roots of D. thollonii Cogn. as well as the isolation and identification of the chemical constituents of this plant. Materials and methods: The tests for antimicrobial, antioxidant and anti-inflammatory activities were performed over the MeOH, EtOAc, n-BuOH and aqueous extracts. Compounds were isolated from EtOAc and n-BuOH extracts of the roots of D. thollonii Cogn. through column chromatography and their structures were determined by means of NMR and MS analysis, and published data. Results: According to the antimicrobial and antioxidant assays, the EtOAc and n-BuOH extracts were submitted to further separation and purification. This led to the isolation of twelve compounds identified as 3,3′-di-Omethylellagic acid 4′-O-β-D-xylopyranoside 1, 3-O-methylellagic acid 4′-O-β-D-arabinopyranoside 2, casuarinin 3, betulinic acid 4, β-sitosterol-3-O-D-glucopyranosyl-6′-mirystate 5, cellobiosylsterol 6, β-sitosterol 7, β- sitosterol-3-O-β-D-glucopyranoside 8, arjunolic acid 9, 3,3′-di-O-methylellagic acid 10, ellagic acid 11, and 3,3′-di-O-methylellagic acid 4′-O-β-D-glucopyranoside 12. The EtOAc extract was the only antimicrobial active sample [diameter of the zone of inhibition (DZI) of 10 mm against Staphyloccocus aureus] among all the tested extracts. The analysis of fractions of this extract revealed the presence of bioactive compounds with a described antimicrobial activity such as β-sitosterol, β-sitosterol-3-O-β-D-glucopyranoside and arjunolic acid. By using Trolox as the standard drug, all extracts showed antioxidant activity against DPPH in the following order of scavenging ability: Trolox N nBuOHN EtOAc N MeOH NWE(water extract). The ABTS•+ scavenging abilitywas similar to that found for the DPPH assay, being Trolox N n-BuOH N MeOH N EtOAc N WE. Alongwith the DPPH and ABTS assays, the FRAP assay showed the scale n-BuOH N MeOH N WE N EtOAc. The phytochemical study of the EtOAc and n-BuOH extracts revealed the presence of important known antioxidant compounds such as ellagic acid derivatives, arjunolic acid, betulinic acid and β-sitosterol. The anti-inflammatory properties of D. thollonii extracts were investigated using RAW264.7murine macrophage cells. TheMeOH extract reduced the stimulatedNOproduction in a concentration-dependent manner. 86% reduction was observed at the highest tested concentration of 100 μg/ml (IC50=5.9 μg/ml). The n-BuOH extract showed higher dose dependent reduction of NO formation (IC50=6.5 μg/ml) than the EtOAc extract (IC50=18.1 μg/ml), whereas the water extract had no significant influence on the NO production. All the extracts did not have any influence on the macrophage viability. The phytochemical investigation of the EtOAc and n-BuOH extracts revealed that the main compounds identified do have potent anti-inflammatory properties.