Polyphenol Proﬁle and Antimicrobial and Cytotoxic Activities of Natural Mentha × piperita and Mentha longifolia Populations in Northern Saudi Arabia

: New sources of polyphenols with anticancer, antioxidant, and antimicrobial properties in arid environments are critical for the development of alternative medicines and natural remedies. This study explored the polyphenol proﬁles and biological activities of methanolic leaf extracts from natural Mentha × piperita and Mentha longifolia populations in northern Saudi Arabia. Chromatographic analyses identiﬁed several polyphenols in M. × piperita including phenolic acids: rosmarinic acid (1547.6 mg / 100 g DW (dry weight)), cryptochlorogenic acid (91.7 mg / 100 g DW), and chlorogenic acid (69.4 mg / 100 g DW), as well as ﬂavonoids: naringin (328.8 mg / 100 g DW) and cynaroside (162.8 mg / 100 g DW). The major polyphenols in M. longifolia were: rosmarinic acid (781.6 mg / 100 g DW), cryptochlorogenic acid (191.1 mg / 100 g DW), p-coumaric acid (113.0 mg / 100 g DW), m-coumaric acid (112.2 mg / 100 g DW), and chlorogenic acid (63.8 mg / 100 g DW). M. × piperita and M. longifolia leaf extracts had high antioxidant activities due to the major polyphenols (cynaroside, rosmarinic and cryptochlorogenic acids). M. × piperita had higher activities against di ﬀ erent cancer cells than M. longifolia . Naringin, cryptochlorogenic acid, and rosmarinic acid had the highest activities against cancer cells. The leaf extracts had antibacterial e ﬀ ects against most bacteria species ( Pseudomonas aeruginosa was most sensitive), which was attributed to the polyphenols. Antifungal activities were similarly broad ( Aspergillus ﬂavus was most sensitive) and attributed to naringin, cryptochlorogenic acid, and ca ﬀ eic acid. Populations of M. × piperita and M. longifolia in Northern Riyadh may be a valuable source of natural biologically active compounds. compositions and biological activities of their leaves methanolic extracts. The polyphenol proﬁles were qualitatively and quantitatively evaluated by high-performance liquid chromatography with diode-array detection (HPLC–DAD). The results presented here represent the ﬁrst examination of the antioxidant, antiproliferative, cytotoxic e ﬀ ects, and the antibacterial and antifungal potential of these plants.


Introduction
Polyphenols may be the most important secondary metabolite in the plant kingdom due to their pharmacological and medicinal properties. The medical applications of polyphenols include cancer control [1][2][3][4], bacterial and fungal infections [5,6], age elongation as antioxidants [7], and the treatment of diseases related to obesity [8], neurology [9], diabetes [10], and cardiovascular inflammation [11,12]. Polyphenols are also used in food processing and as functional foods [13].
The biochemical effects of polyphenols as antioxidants is based on their ability to scavenge free radicals and control metal chelation reactions [1,[14][15][16][17][18][19]. In humans, healthy metabolic functioning is maintained by specific polyphenols that remove reactive oxygen species (ROS) such as hydrogen peroxide and singlet oxygen from the cells [7]. The anticancer properties of polyphenols are also partially related to antioxidant mechanisms, including the detoxification of enzymes and the reduction of free radicals [1,[14][15][16][17][18][19]. The antiproliferative and apoptotic activities of polyphenols on cancer cells may be the backbone of the anticancer effects of dozens of polyphenols, via their arrestment of the cell cycle and molecular regulation of specific gene expression [1,[14][15][16][17][18].
Bacterial and fungal infections cause serious human diseases such as pneumonia, soft tissue infection, sepsis, listeriosis, candidiasis, and peritonitis [20][21][22][23][24]. However, antibiotic resistance is an increasingly prevalent issue in the medical and scientific communities [25], and thus the discovery of new polyphenol sources to control these diseases is important. Medicinal plants are a key source of polyphenols-they have essential oils in the leaves and the leaf extracts contain phenolic acids, flavonoids, and catechins [26][27][28][29][30]. The Mentha genus in the Lamiaceae family contains several medicinal plants such as basil and sage, and Mentha piperita L. (syn. Mentha balsamea Wild.) is one of the most widely used herbal medicines [31].
Mentha piperita folium and Mentha piperita aetheroleum are listed in official phytotherapy documents, e.g., the World Health Organization (WHO) monographs on selected medicinal plants [32] in the European Pharmacopoeia [33]. Peppermint tea, brewed from the plant leaves, and peppermint essential oil are used as traditional medicines. Mentha longifolia L. (syn. M. spicata var. longifolia L., M. sylvestris L., M. tomentosa D'Urv, M. incana Willd.) is native to continental Europe, western and central Asia, and northern and southern (but not tropical) Africa. It is a variable herbaceous perennial with numerous morphological and phytochemical similarities to M. × piperita [34,35]. The Mentha genus is highly diverse, with more than 19 species, 13 hybrids, and new cultivars, all of which possess variable molecular, morphological, biochemical, and geographical properties [30,[36][37][38][39]. The chemical composition of Mentha plants is influenced by many factors (e.g., geography, region, climate, or plant growth conditions), but the phytochemical composition is less variable among species [40]. Most research has focused on M. × piperita, revealing dozens of terpenes in the essential oil that is commonly used as a cough treatment or as an ointment [40]. The biological activity of Mentha has been attributed to the volatile oil constitutes, but the phenolic compounds may also play an important role [41]. The phenolic acid content is estimated to be 2.7-5.5%, consisting mainly of rosmarinic acid, caffeic acid, and protocatechuic acid. The flavonoid content is estimated to be 3.0-6.3% [42], containing mainly luteolin-7-O-rutinoside, eriocitrin, narirutin, and hesperidin [40,41].
In this study, natural M. × piperita and M. longifolia populations from northern Saudi Arabia were investigated for the chemical compositions and biological activities of their leaves methanolic extracts. The polyphenol profiles were qualitatively and quantitatively evaluated by high-performance liquid chromatography with diode-array detection (HPLC-DAD). The results presented here represent the first examination of the antioxidant, antiproliferative, cytotoxic effects, and the antibacterial and antifungal potential of these plants.

Plant Material and Preparation
Leaf extracts were obtained from natural M. × piperita and M. longifolia populations growing in the Riyadh region of northern Saudi Arabia. Plant samples were identified and vouchered at the College of Food and Agricultural Sciences, King Saud University (Hosam0002164-100). The leaves were dried in a lyophilizer, powdered, and then extracted with methanol (0.2 g DW (dry weight) in 10 mL) by sonication (Sonic-2, Polsonic) twice for 30 min at 30 • C. The extracts were purified with Whatman paper, and the residues were left to dry at room temperature (i.e., allowing methanol evaporation). The residues were stored at −80 • C. For liquid chromatography, the residues were dissolved in methanol (1 mL, Merck, Darmstadt, Germany), and for the bioassays, a rotary evaporator was used to remove methanol from the samples [2,43]. All of the experimental procedures were approved by the animal committee of the University of Johannesburg in collaboration with the Egyptian partners of Damietta (2018-2019-75364). The microorganisms and cancer cell lines (ATCC collection) were obtained from the Faculty of Agriculture, Alexandria, Egypt.

Antiproliferative and Cytotoxic Activities
The antiproliferative and cytotoxic activities of the leaf extracts were examined in T-cell lymphoblast-like (Jurkat), breast adenocarcinoma (MCF-7), colon adenocarcinoma (HT-29), HEK-293 (normal human cells), and cervical adenocarcinoma (HeLa) cell lines [1,2,46]. To measure the changes in cells viability, the MTT assay was used. Leaf extracts were solubilized in DMSO (1%). Cancer cells were grown in standard media (MEM) using (10% fetal bovine serum (FBS), 0.1 mM nonessential amino acids, 17.8 mM sodium bicarbonate (NaHCO 3 ), and 1 mM sodium pyruvate in 75 cm 2 flasks. The cells were seeded on microtiter plates at 4 × 10 −4 cells per µL in 270 µL medium for 48 h (37 • C, 5% CO 2 ). After 48 h, the extracts were added to final concentrations of 50, 100, 200, 300, and 400 µg/mL. The plates were washed with phosphate-buffered saline (PBS), and then 12 mM of MTT (dissolved in PBS) was added to the medium. Next, isopropanol (0.04 N hydrochloric acid, HCl) was added to each well, and the plates were left undisturbed for 40 min. Negative (untreated) and positive controls (vinblastine sulfate and taxol) were used, and the inhibition activity percentage (IAA) was calculated from the absorbance at 570 nm as: where (AB 570nm ) C and (AB 570nm ) s are the absorbances (AB) at 570 nm for the control and test samples.
To determine the IC 50, the percentage of viable cells was plotted against extract concentration in µg/mL. The IC 50 was used in the flow cytometry assay to study the cytotoxic activities of leaf extracts and apoptotic cell populations (FAC Scan, USA) [1,46,47]. Cultured cancer cells in 6-well plates were subjected the IC 50 of leaf extracts as well as naringin, cryptochlorogenic acid and rosmarinic acid.

Antioxidant Activity
The leaf extracts were examined by β-carotene bleaching, ferric reducing antioxidant power (FRAP), and DPPH (2,2-Diphenyl-1-picrylhydrazyl) assays [2,[48][49][50][51][52]. The amount of leaf extract required to scavenge 50% of both solutions from the β-carotene bleaching and DPPH assays was named the IC 50 (µg/mL). The IC 50 value was determined by plotting the inhibition percent against extract concentration. The absorbance was measured at 470 nm for β-carotene bleaching, at 517 nm for DPPH, and at 593 nm for FRAP. The FRAP reagent was prepared as in previous work [43]. Aliquots (100 µL) of the leaf extracts/Trolox (Sigma-Aldrich, Berlin, Germany) were added to the reagent (3 mL), mixed, and incubated for 30 min at 37 • C. The FRAP calibration procedure involved serial dilutions of Trolox (0-0.5 Mmol/L) as the standard. Butylated hydroxytoluene (BHT) was used as the standard for β-carotene bleaching and DPPH. All of the assays were conducted in triplicate and repeated twice.

Antibacterial Effect
We assayed bacterial isolates of Listeria monocytogenes (clinical isolate), Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 35210) ria, Bacillus cereus (ATCC 14579), Pseudomonas aeruginosa (ATCC 27853), and Micrococcus flavus (ATCC 10240). A microtiter plates-based protocol (micro-dilution) [4,23,29,53] was followed by mixing serial concentrations of the leaf extracts with bacterial inoculum (1.0 × 10 4 CFU) and 100 µL of tryptic soy broth in each well. The plates were incubated for one day at 37 • C on a rotary shaker. The minimum inhibitory concentration (MIC) was defined as the lowest concentration that caused no visible growth. The minimum bacterial concentration (MBC) was determined by serial subculturing of the extracts (2 µL) and defined as the minimal concentration that caused 99.5% elimination of the inoculum. The optical density (OD) was measured at 655 nm, and a positive control (streptomycin; 0.01-10 mg/mL) was used alongside a negative control (DMSO, 1%).

Statistical Analyses
Differences among the groups were tested as the least significant differences (LSD) in SPSS software. The mean and standard deviation (SD) were calculated from the three replicates (of each assay).

Antioxidant Effects
M. × piperita and M. longifolia leaf extracts and the individual compounds showed significant antioxidant activities, as presented in Table 2. M. longifolia showed higher antioxidant activities than M. × piperita using β-carotene bleaching assay. However, DPPH and FRAP assays did not show these differences at p ≤ 0.05. The phenolic compounds, rosmarinic acid, cynaroside, and cryptochlorogenic acid, had high antioxidant activities that were comparable to the BHT and Trolox standards. Naringin showed relatively low antioxidant activities compared to the other compounds and the leaf extracts.

Antiproliferative and Cytotoxic Effects
Antiproliferative activities were measured against the Jurkat, MCF-7, HT-29, HEK-293, and HeLa cell lines. The leaf extracts of M. × piperita and M. longifolia showed antiproliferative activities against a diversity of cancer cells as shown in Table 3, and M. × piperita had higher activities than M. longifolia. Naringin, cryptochlorogenic acid, and rosmarinic acid had the highest activities among the identified compounds. The apoptotic assay using flow cytometry of M. × piperita and M. longifolia is shown in Figure 2. Necrotic cell accumulation was observed in the early and late apoptotic periods. Necrotic and apoptotic cell accumulation was observed in the upper left (necrotic) and upper right and lower quadrants (apoptotic).

Antibacterial Activities
The leaf extracts of M. × piperita and M. longifolia showed variable antibacterial activities against the screened bacterial strains, as shown in Table 4. Most of the bacteria, including Pseudomonas aeruginosa, Micrococcus flavus, Bacillus cereus, Staphylococcus aureus, and Escherichia coli, were sensitive to both leaf extracts. Listeria monocytogenes was relatively sensitive to the leaf extracts, and M. × piperita showed higher antibacterial activity than M. longifolia. Among the individual compounds, caffeic and cryptochlorogenic acids had higher activities compared to rosmarinic acid and naringin.

Antibacterial Activities
The leaf extracts of M. × piperita and M. longifolia showed variable antibacterial activities against the screened bacterial strains, as shown in Table 4. Most of the bacteria, including Pseudomonas aeruginosa, Micrococcus flavus, Bacillus cereus, Staphylococcus aureus, and Escherichia coli, were sensitive to both leaf extracts. Listeria monocytogenes was relatively sensitive to the leaf extracts, and M. × piperita showed higher antibacterial activity than M. longifolia. Among the individual compounds, caffeic and cryptochlorogenic acids had higher activities compared to rosmarinic acid and naringin.

Antifungal Effects
The leaf extracts of M. × piperita and M. longifolia showed antifungal effects against all of the screened bacteria including P. ochrochloron, P. funiculosum, A. ochraceus, A. niger, and A. flavus, as shown in Table 5. M. × piperita had higher activity than M. longifolia, and caffeic acid and naringin had the highest activities among the polyphenols. Cryptochlorogenic acid showed moderate effects against the fungi, while rosmarinic acid had the weakest antifungal activity. A. niger, A. ochraceus, and C. albicans were most resistant to the leaf extracts.
In this study, an HPLC-DAD phenolic profile analyses revealed the qualitative and quantitative differences of M. × piperita and M. longifolia methanolic leaf extracts, as shown in Table 1 and Figure 1. In M. × piperita extracts, six phenolic acids were detected, while in M. longifolia, nine were identified. Four depsides (cryptochlorogenic acid, chlorogenic acid, isochlorogenic acid, and rosmarinic acid) and two simple phenolic acids (caffeic acid and protocatechuic acid) were observed among the M. × piperita polyphenols. Among the M. longifolia polyphenols, there were five depsides (caftaric acid, chlorogenic acid, cryptochlorogenic acid, neochlorogenic acid, and rosmarinic acid) and four simple phenolic acids (caffeic acid, p-, m-, and o-coumaric acids). In both Mentha leaf extracts, rosmarinic acid was the major compound; at 1547.6 mg/100 g DW, it was almost two times higher in M. × piperita than in M. longifolia (781.6 mg/100 g DW). Earlier studies also reported rosmarinic acid as the main phenolic acid in Mentha species [60,61]. For M. × piperita specifically, caffeic acid and protocatechuic acid were also reported [40]. We confirmed the presence of these simple phenolic acids in the leaf extracts of M. × piperita, observing 17.4 and 24.9 mg/100 g DW, respectively. We also, for the first time, confirmed the presence of other biologically active depsides: cryptochlorogenic acid (91.7 mg/100 g DW) and isochlorogenic acid (10.3 mg/100 g DW). Among depsides, only chlorogenic acid was confirmed before in M. × piperita leaf extracts by Kapp et al. [62], but without quantification. In the current study we calculated the amount of this compound as 69.4 mg/100 g DW. Zgórka and Głowniak [63] performed the quantitative analyses of extracts from different plants belonging to the Lamiaceae family by HPLC with UV-Vis detection. They found rosmarinic acid (ca. 70 mg/100 g DW), caffeic acid (ca. 20 mg/100 g DW), and also protocatechuic acid (2.5 mg/100 g DW) in M. × piperita leaf extracts of Polish origin, as the dominant compounds. The amounts of rosmarinic acid and protocatechuic acid were respectively 22 and 10 times lower in comparison to our Saudi-origin samples. The amounts of caffeic acid were similar. The quantitative estimations of phenolic acid content in Serbian origin M. × piperita leaf extracts were performed by Mišan et al. [64], and they detected a 10 times higher amount of caffeic acid (186 mg/100 g DW), the similar amount of chlorogenic acid (73 mg/100 g DW) and an extremely lower-130 times-amount of rosmarinic acid (12 mg/100 g DW), in comparison to our study.
Cynaroside (luteolin-7-glucoside) was confirmed in M. × piperita leaf extracts of Polish origin by Fecka et al. [67] in the amount of ca. 37 mg/100 g DW, using planar chromatography. That amount was 4.4 times lower in comparison to our samples of Saudi-origin plants. The naringin was detected by Figueroa Pérez et al. [68] in Mexican-origin M. × piperita leaf extracts at 56 mg/100 g DW, which was almost six times lower than detected under our study. Additionally, derivatives of naringin in M. × piperita were detected before by Mišan et al. [64] using the HPLC-DAD method. They confirmed naringenin in amount of 146 mg/100 g DW in the Serbian M. × piperita leaf extracts.
Phytochemically, M. longifolia is the less-known and less-studied species. Gulluce et al. [69] studied the essential oil and methanol extracts of M. longifolia ssp. longifolia. This resulted in the identification of 45 essential oil compounds; the main components were cis-piperitone epoxide, pulegone, piperitenone oxide, and menthone. The phenolic compound analyses were limited to spectrophotometric total phenolic constituent estimations using the Folin-Ciocalteu reagent, but the assay revealed total phenolic contents of 4.5 g/100 g of gallic acid equivalent. Akroum et al. [70] studied the flavonoid composition of M. longifolia extracts and identified five flavonoids (luteolin-7-O-glycoside, luteolin-7,3'-O-diglycoside, apigenin, quercetin-3-O-glycoside, and kaempferol-3-O-glycoside). We did not detect any flavonoids in M. longifolia, but we screened for only 16 flavonoids and used simple HPLC-DAD methods (see Materials and Methods). It is still possible that flavonoids are present in M. longifolia of Saudi origin, but in small amounts. In this study, we identified nine phenolic acids, including five depsides: rosmarinic acid (781.6 mg/100 g DW), cryptochlorogenic acid (191.1 mg/100 g DW), neochlorogenic acid (56.8 mg/100 g DW), chlorogenic acid (63.8 mg/100 g DW), and caftaric acid (47.6 mg/100 g DW), and four simple phenolic acids: caffeic acid (19.6 mg/100 g DW), p-coumaric acid (113.0 mg/100 g DW), m-coumaric acid (112.2 mg/100 g DW), and o-coumaric acid (39.8 mg/100 g DW). Adham [71], reported rosmarinic acid in an amount 3.75 times lower than in our samples (208 mg/100 g DW) in M. longifolia. The high amount of rosmarinic acid was also reported by Bahadori et al. in the M. longifolia var. calliantha [72] leaf extracts of plants growing in West Azerbaijan province of Iran. The amount of this depside was equal to 2225 µg/g in the ethanol extract. They confirmed also the presence of o-coumaric acid (134 µg/g), p-coumaric acid (113 µg/g), caffeic acid (86 µg/g) and chlorogenic acid (27 µg/g). Shekarchi et al. [73] with the HPLC-UV-Vis technique detected the rosmarinic acid in the leaf extracts of M. longifolia of Iranian origin in an amount of 2260 mg/100 g DW; that was 3.4 times more than in our Saudi plants. Dudai et al. [74] studied 40 genetic variants from 25 populations of M. longifolia native to Israel. They stated that rosmarinic and caffeic acids were the most abundant. The accumulation of rosmarinic acid, varied from 2000 to 8000 mg/100 g DW, caffeic acid from 60 to 1800 mg/100 g DW, and p-coumaric acid from 2.5 to 25 mg/100 g DW. These compounds were detected also in our study. The amounts of rosmarinic and caffeic acids were lower, but the amount of p-coumaric acid in the Saudi origin samples was higher.
We confirmed the availability of some polyphenols such as m-coumaric acid, neochlorogenic acid and caftaric acid in M. longifolia and cryptochlorogenic acid and isochlorogenic acid in M. × piperita in the Saudi origin plants for the first time (see Table S1 in the Supplementary Material). However, other phenols were reported in previous studies. Indeed, further investigations may reveal other compounds not confirmed here which could be considered as limitation of this study.
The DPPH, β-carotene bleaching, and FRAP assays showed higher antioxidant activities in M. longifolia than in M. × piperita. The phenolic compounds (rosmarinic acid, cynaroside, and cryptochlorogenic acid) also showed high antioxidant activities, while naringin showed relatively low activities compared to other compounds and leaf extracts. Our results for the antioxidant activity of rosmarinic acid via DPPH is consistent with prior work on Melissa officinalis [75]. Citrus junos extracts rich in naringin showed moderate antioxidant activities [76], but a different study documented weaker activities [77]. Cynaroside obtained from Elsholtzia bodinieri had strong antioxidant activities (via the DPPH assay) [78], and cryptochlorogenic and chlorogenic acids from Hibiscus sabdariffa showed strong antioxidant activities [79]. These results agree with the observations of our study.
M. × piperita showed higher activities against different cancer cells than M. longifolia, and the highest activities of the phenolic compounds were found in naringin, cryptochlorogenic acid, and rosmarinic acid. Previous work documented antiproliferative effects of rosemary leaf extracts against HT-29 cancer cells by inhibiting cell proliferation, increasing cell cycle arrest, and increasing apoptosis [80]. The major component of this extract was rosmarinic acid [81]. Rosmarinic acid has strong anticancer activities against MCF-7 [82] and HT-29 [83]. Naringin is a bioflavonoid that inhibits the growth of different cancer cells (e.g., MCF-7 [84]) and may induce apoptosis by reducing the NF-κB/COX-2-caspase-1 pathway in HeLa cells [85]. This explains the strong antiproliferative and cytotoxic activities reported here.
M. × piperita showed higher antibacterial activity than M. longifolia. Caffeic and cryptochlorogenic acids showed higher activities against bacteria compared to rosmarinic acid and naringin. M. × piperita also showed higher antifungal activity than M. longifolia, and caffeic acid and naringin had the highest antifungal activities among the polyphenols. Cryptochlorogenic acid was moderately effective against fungi, but rosmarinic acid was the weakest. Previous studies reported moderate-to-low antimicrobial activities for rosmarinic acid [86,87] and naringin [88], and high antibacterial activities have been reported for chlorogenic acid (cryptochlorogenic acid derivatives) from Mammillaria extracts [4,89]. Chlorogenic acid displayed fungicidal activities against other pathogenic fungi such as Fusarium solani, Sclerotinia sclerotiorum, and Botrytis cinerea [90], and caffeic acid showed strong antibacterial and antifungal activities against several bacterial strains [2].

Conclusions
This is the first investigation of the phenol profiles of natural Mentha populations from the Riyadh region in northern Saudi Arabia. HPLC identified several polyphenols including rosmarinic acid, naringin, cryptochlorogenic acid, and cymaroside. The main component of the polyphenols in M. × piperita and M. longifolia was rosmarinic acid. M. × piperita contained flavonoids (naringin and cymaroside), and other polyphenols were present in M. longifolia, including cryptochlorogenic, m-coumaric acid, and p-coumaric acid. Most of the phenols showed antioxidant activities and were associated with the antioxidant activities of the leaf extracts. The M. × piperita and M. longifolia leaf extracts displayed antiproliferative and cytotoxic effects against most of the cancer cell lines, which was attributed to the accumulation of necrotic cells in the early and late apoptotic periods. Antibacterial effects were detected in both of the leaf extracts and in the polyphenols and were effective against most of the bacteria. Furthermore, M. × piperita showed higher antibacterial activity than M. longifolia. This activity was attributed to the specific polyphenol profile of the plant (i.e., cryptochlorogenic and caffeic acids and twice the amount of rosmarinic acid). Antifungal activities were also detected for both species and were attributed to the polyphenols caffeic acid, cryptochlorogenic acid, and naringin. This is the first study confirming the availability of some polyphenols such as m-coumaric acid, neochlorogenic acid, caftaric acid in M. Longifolia and cryptochlorogenic acid and isochlorogenic acid in M. x Piperita. Together, these results indicate that both mint species may represent new natural sources of biologically active polyphenols.