Chemical Composition, Anti-Quorum Sensing, Enzyme Inhibitory, and Antioxidant Properties of Phenolic Extracts of Clinopodium nepeta L. Kuntze

Abstract

Phenolic extracts of <i>Clinopodium nepeta</i> were prepared and their preliminary phenolic profiles determined using HPLC-DAD with 26 phenolic standards. Apigenin (21.75 ± 0.41 µg/g), myricetin (72.58 ± 0.57 µg/g), and rosmarinic acid (88.51 ± 0.55 µg/g) were the most abundant compounds in DCM (dichloromethane), AcOEt (ethyl acetate), and BuOH (butanol) extracts, respectively. The DCM and AcOEt extracts inhibited quorum-sensing mediated violacein production by <i>C. violaceum</i> CV12472. Anti-quorum-sensing zones on <i>C. violaceum</i> CV026 at MIC (minimal inhibitory concentration) were 10.3 ± 0.8 mm for DCM extract and 12.0 ± 0.5 mm for AcOEt extract. Extracts showed concentration-dependent inhibition of swarming motility on flagellated <i>P. aeruginosa</i> PA01 and at the highest test concentration of 100 μg/mL, AcOEt (35.42 ± 1.00%) extract displayed the best activity. FRAP assay indicated that the BuOH extract (A_0.50 = 17.42 ± 0.25 µg/mL) was more active than standard α-tocopherol (A_0.50 = 34.93 ± 2.38 µg/mL). BuOH extract was more active than other extracts except in the ABTS^●+, where the DCM extract was most active. This antioxidant activity could be attributed to the phenolic compounds detected. <i>C. nepeta</i> extracts showed moderate inhibition on acetylcholinesterase (AChE), butyrylcholinesterase (BChE), tyrosinase, and α-amylase. The results indicate that <i>C. nepeta</i> is a potent source of natural antioxidants that could be used in managing microbial resistance and Alzheimer's disease.