Abstract
Genus Salsola (family Amaranthaceae) is one of the most prevailing genera in Saudi Arabia. Although several species were reported for their traditional uses, the majority of Salsola species still need to be phytochemically and biologically explored. The current study presents the GC-MS profiling as well as an in vitro investigation of the bioactivities of the n-hexane extracts from the five Salsola species: Salsola arabica, S. cyclophylla, S. imbricata, S. incanescens and S. villosa. Additionally, the compounds identified in the most active extracts were screened for their interaction with the active sites of cyclooxygenase enzyme isoforms (COX-1 and COX-2). GC-MS analysis of the n-hexane extracts from the five species resulted in the identification of 67 constituents. Oleic acid (75.57%), 1-octadecene (14.46%), cinnamaldehyde alpha-hexyl (57.15%), octacosyl heptafluorobutyrate (25.36%) and hexadecanoic acid methyl ester (26.15%) represent the major constituents in S. arabica, S. cyclophylla, S. imbricata, S. inscanescence and S. villosa, respectively. Results of bioactivity testing highlighted S. villosa as having the highest anti-oxidant activity (IC50 0.99 +/- 0.05 mg/mL), which was closely followed by S. cyclophylla (IC50 1.36 +/- 0.06 mg/mL) compared to the IC50 of 0.16 +/- 0.01 mg/mL recorded by ascorbic acid. S. villosa was further noted for having the strongest COX-2 inhibitory activity (IC50 4.6 +/- 0.13 mu g/mL) among the tested extracts followed by S. arabica (IC50 13.1 +/- 0.37 mu g/mL) and S. cyclophylla (IC50 20.1 +/- 0.57 mu g/mL). On the other hand, S. imbricata extract displayed the most characteristic inhibition activity against COX-1 (IC50 10.2 +/- 0.52 mu g/mL), which was non-significant from the standard drug celecoxib. Based upon bioactivity results, the phytoconstituents identified in S. villosa and S. imbricata extracts were investigated for their capability to interact with the active sites of both cyclooxygenase enzyme isoforms adopting molecular docking. Results indicated the possibility to incorporate the compounds to active sites of the enzymes where some of them bind with their polar end into the cavity beyond Arg120 and their aliphatic chain oriented to the catalytically important Tyr385 similar to the natural substrate arachidonic acid, indicating that they could be promising candidates for the future development of selective COX inhibitors.