Tunisian Native Mentha pulegium L. Extracts: Phytochemical Composition and Biological Activities

Abstract

Mint species (Lamiaceae family) have been used as traditional remedies for the treatment of several diseases. In this work, we aimed to characterize the biological activities of the total phenolic and flavonoid contents of Mentha pulegium L. extracts collected from two different regions of Tunisia. The highest amounts of total phenols (74.45 ± 0.01 mg GAE/g DW), flavonoids (28.87 ± 0.02 mg RE/g DW), and condensed tannins (4.35 ± 0.02 mg CE/g DW) were found in the Bizerte locality. Methanolic leaf extracts were subjected to HPLC-UV analysis in order to identify and quantify the phenolic composition. This technique allowed us to identify seven phenolic compounds: two phenolic acids and five flavonoid compounds, such as eriocitrin, hesperidin, narirutin, luteolin, and isorhoifolin, which were found in both extracts with significant differences between samples collected from the different regions (p < 0.05). Furthermore, our results showed that the methanolic extract from leaves collected from Bizerte had the highest antioxidant activities (DPPH IC₅₀ value of 16.31 μg/mL and 570.08 μmol Fe²⁺/g, respectively). Both extracts showed high radical-scavenging activity as well as significant antimicrobial activity against eight tested bacteria. The highest antimicrobial activities were observed against Gram-positive bacteria with inhibition zone diameters and MIC values ranging between 19 and 32 mm and 40 and 160 µg/mL, respectively. Interestingly, at 10 μg/mL, the extract had a significant effect on cell proliferation of U87 human glioblastoma cells. These findings open perspectives for the use of Mentha pulegium L. extract in green pharmacy, alternative/complementary medicine, and natural preventive therapies for the development of effective antioxidant, antibacterial, and/or antitumoral drugs.

Keywords: antioxidant; antiproliferative and antibacterial activities; medicinal plant; polyphenols.

Figure 1

HPLC chromatograms of Mentha pulegium L. methanolic extracts (Bizerte (A) and Kef (B)). Peaks: 1, caffeic acid; 2, eriocitrin; 3, isorhoifolin; 4, luteolin; 5, narirutin; 6, hesperidin; and 7, rosmarinic acid detected at 280 nm.

Figure 2

Effect of methanolic extract of Mentha pulegium L. from the Bizerte locality on U87 cells: (A) Cells were treated with the extract at the indicated concentrations for 24 h, and cell viability was assessed by MTT assay. The cell viability of the vehicle control cells was assumed as 100%. (B) The methanolic extract from the Bizerte locality inhibited U87 cell proliferation. U87 cells were cultured in MEM containing 10% FCS for the indicated periods of time in the absence (control) or in the presence of 10 µg/mL of extract. At daily intervals, U87 cells were fixed with 3.7% formaldehyde, stained with a solution of 0.1% crystal violet/MetOH 20%, and lysed with 1% SDS. Absorbance was then measured at 590 nm. All data represent the mean ± SEM of three separate experiments performed in triplicate (p < 0.05).