3. Discussion
It is important to point that literature searches were conducted in the Google Scholar, SciELO, ScienceDirect, Pubmed, Wiley Online Libraries, and Springer Link databases, as well as in university repositories in Mexico (IPN, UNAM, and the UMSNH Digital Library) in the 2021–2024 period. The keywords used were “Hedeoma piperita”, “quiensabe”, “phytochemistry”, “volatile compounds”, “traditional use”, and “biological activity”. Only two articles were found, one describing the morphotype and genetic divergence of
H. piperita [
6], as well as its cultural importance, and one on its management and conservation in an indigenous community of Michoacán [
4]. In addition, four theses were found, two of which describe the phenology and ecological aspects of the plant in regard to its reproduction and use [
3,
7]; one describes the antidepressant activity of hydroalcoholic extracts of
H. piperita leaves evaluated in mice [
8]; and only one describes, in a general way, the effect of drying and storage time of leaves on the antioxidant and anti-inflammatory activities and the phenolic compounds and terpenes contents in
H. piperita infusions [
5]. The above supports the relevance of carrying out this research.
TPC (42.5 GAE/g DW) and TFC (23.2 QE/g DW) have been reported in infusions of the aerial parts of dehydrated
H. piperita, at values that were, respectively, 1.7 and 2.7 times lower than those obtained in this work. TTC (18.75 mg PE/g PS) was 1.4 times higher than that found in infusions [
5]. The differences observed could be due to the processing or conditioning of the sample. Raya-Ramírez [
5] performed room temperature drying treatments and dark storage for 30, 60, and 90 days, observing significantly lower values of TPC and TFC during storage time of
H. piperita. The negative impact of plant dehydration through natural convection on its nutraceutical characteristics (e.g., antioxidant activities) has been reported; therefore, freeze-drying is preferred as the drying process for medicinal plants.
The content of phytochemicals extracted can vary between different species of the genus Hedeoma. TPC in polyphenolic extracts of oregano (
H. patens) has been reported (99.58 ± 0.42 GAE/g) [
9] at levels around 0.7 times higher than those found in
H. piperita in this work; the authors attributed the elevated TPC of
H. patens to the growth conditions, collection, and storage of samples. Likewise, a five-fold lower TPC has been reported in methanolic extract of aerial parts of
H. drummondii or “pennyroyal tea” (32.36 ± 0.86 mg GAE/g) compared to that found in the purple leaf extracts of
H. piperita in this work [
10].
Phenolics compounds, flavonoids, and anthocyanins function as response molecules during stress by activating specific enzymes [
11]. For example, an increase in anthocyanins production in the aerial part of
Arabidopsis thaliana has been connected to the activation of the dihydroflavonol 4-reductase enzyme in plants subjected to stress due to N scarcity [
12].
The presence of anthocyanins in stems and leaves has been reported in several species of the Lamiaceae family. Compared to the methanolic extracts of
Artemisia annua, the TAC in ethanolic extracts of
H. piperita was 1.7 times higher in stems (0.26 mg C3GE/g) and 2.7 times lower in purple leaves (3.59 mg C3GE/g), respectively [
13]. In European lemon balm (
Melissa officinalis), it has been hypothesized that reactive oxygen species (ROS) induced the biosynthesis of anthocyanins and terpenes to mitigate the production of reducing agents derived from a decrease in CO
2 absorption through the Calvin cycle [
14]. It has also been shown that anthocyanins accumulate in stems, leaves, and other organs, which can play direct and indirect roles as modulators of signaling cascades caused by ROS and are involved in plant growth, development, and stress responses [
15].
The presence of hydroxycinnamic acids such as rosmarinic, chlorogenic, and caffeic acids have been reported in plants of the Lamiaceae family and has been related to their potential biological activity [
16]. Rosmarinic acid has been reported as the most abundant phenolic acid in 20 species of Lamiaceae [
17], such as in in
Salvia officinalis (up to 230 μg/mL) and
Mentha pulegium (up to 400 μg/mL), followed by chlorogenic and caffeic acids, hyperoside, rutin, and gallic acid. For the genus
Hedeoma, predominant presence of RA and CGA has been reported [
18], and both are the main phenolic acids identified in the methanolic extracts of
H. drummondi [
18], which is consistent with what was found in the infusions and ethanolic extracts of
H. piperita. RA has been found in the ethanolic extract of the aerial parts of
H. mandoniana (0.02 mg/g extract), which is eight times lower than that found in
H. piperita [
18]. In addition, RA has been found in infusions of
M. spicata,
M. longifolia,
M. piperita, and
M. suaveolens (32.34 to 43.9 mg/g) [
19], where its content was 0.7 times higher than that found in infusions of purple leaves of
H. piperita.
CGA eliminates free radicals, and it is often detected in its dimeric form (RA) [
18]. RA has been detected in high concentrations in Lamiaceae plants, such as
Satureja montana,
Origanum marjoram, and
Thymus vulgaris, whose aqueous extracts showed concentrations of 1.57, 0.82, and 0.471 mg/mL, respectively [
20], which were up to three times lower than those obtained in the infusions of the green and purple leaves of
H. piperita, which indicated that the traditionally consumed infusion is an excellent source of RA and CGA.
LT is a recurrent flavonoid in Lamiaceae plants such as
Thymus vulgaris,
Origanum marjoram, and
Salvia microphylla, whose biological antioxidant, anti-inflammatory, anticancer, and antidiabetic activities have been evidenced [
19,
21].
Even though there is limited information on the presence of LT or its derivatives in the genus
Hedeoma, the presence of LT glycosides (LT-7-O-glucuronide-3′-O-glucoside and LT-7-O-glucoronide) in chloroformic extract of Mexican oregano (
H. patens) has been observed [
22]. Similarly, LT-glucoside-glucoronide (339.58 μg/mg dry extract) has been reported in the methanolic extract of
H. patens [
23].
The SPME/GC-MS is a highly sensitive technique that allows the separation of molecules, their subsequent ionization and an accurate identification by the molecular structure elucidation [
24]. For this reason, it was chosen to generate knowledge about the phytochemical profile of
H. piperita. Additionally, this technique allows us to obtain quantitative data by providing the relative proportion of the area under the curve of each detected compound in the samples, based on the established concentrations of known standards [
25,
26].
Menthone content has been reported in
Mentha spicata [
27] (2.18 mg/g of fresh weight) at up to 42.7 times lower than that reported in the purple leaves of
H. piperita. Menthol has been reported in the stems (4.23 mg/g) and leaves (39.06 mg/mL) of
Mentha aruensis [
28], at 5.47 and 2.37 times lower, respectively, than that found in purple stems and leaves of
H. piperita. In addition, it was observed that pulegone content in the green and purple leaves of
H. piperita was up to 2.7 times higher than that reported in the leaves of
Satureja macrostema (34.05 mg/g of fresh weight) [
29].
Terpenes such as pulegone, menthol, and menthone have been reported in infusions of fresh
H. piperita leaves [
5], which agreed with the results of this work. In the genus
Hedeoma, pulegone has been reported as the main monoterpene in the essential oil of
H. pulegioides (860 mg/mL) [
30] and
H. multiflorum (39%) [
31], whose content was equal to that detected in the green leaves of
H. piperita. In addition, the presence of menthone (23%) and piperitenone (0.1%) was detected in
H. multiflorum, the contents of which were 1.6 and 0.4 times lower than those found in purple leaves of
H. piperita.
The volatile profile of
H. piperita was consistent with that reported by Muñoz et al. [
18] in the essential oil of
H. mandoniana, a Bolivian species used as an infusion to treat digestive problems and respiratory diseases. The presence of pinene, sabinene, phellandrene, myrcene, terpinene, limonene, pulegone and its derivatives, menthone and its derivatives, germacrene D, and piperitone, in different proportions, was detected, with a 68.4% similarity to the levels observed in
H. piperita.
Pulegone (C
10H
16O, molecular weight 152.23 g/mol) is an oxygenated monoterpene with a strong and refreshing odor that has been reported as having antioxidant, antimicrobial, carminative, and insect repellent properties in most species of
Mentha, specifically
M. pulegium from which it was first isolated [
32]. Pulegone is derived from terpinolene conjugation through piperitenone and is a menthone [
33]. Isopulegol is derived from pulegone by reducing a ketone group to hydroxyl, resulting in a milder menthol-smelling alcohol than menthol [
34]; both terpenes have been reported as antimicrobials, anti-inflammatories, antinociceptives, and analgesics [
33,
34].
Menthol is a monocyclic monoterpene alcohol (C
10H
20O, molecular weight 156.27 g/mol). It has a strong and refreshing smell and is widely used in the food industry as a flavoring agent and in the pharmaceutical industry due to its biological activity as an antimicrobial, anti-inflammatory, analgesic, antitussive, and antiviral [
35]. It has eight different stereoisomers, namely (−)-menthol, (−)-neomenthol, (−)-isomenthol, and (−)-neoisomentol, and their four respective enantiomers [
36]; (−)-menthol and (−)-neomenthol have been reported as components of the essential oil of
Mentha (
M. suaveolens,
M. pulegium,
M. piperita and
M. longifolium) in proportions of 16–46% menthol and 2–9% neomenthol [
37,
38], which was consistent with the findings in
H. piperita stems and green leaves.
Menthone (C
10H
18O, molecular weight 154.25 g/mol) is a ketone analog of menthol with a less intense minty smell [
36]. It has been identified as the main constituent of essential oil of
M. suaveolens leaves (39.4%) and has also shown immunomodulatory, antiparasitic, antibacterial, and anti-inflammatory activities [
38,
39,
40].
Pinene is a bicyclic monoterpene present in plants, with the α and β enantiomers known for having antifungal, antibacterial, and anticancer activities [
41]. Both have been reported in the essential oil of
M. longifolia and
M. pulegium (1.7–9%) in amounts up to three times higher than those found in
H. piperita tissues [
42]. Camphene, campholenal, and camphor are derivatives of the mevalonic acid pathway and exhibit antimicrobial, antitussive, antidiabetic, antiparasitic, and anticancer activities [
43]. These have been reported in the essential oils of Lamiaceae family plants, for example,
M. spicata (>3%, in leaves) [
42],
Dracocephalum kotschyi (0.3–6%) [
44], and
Lavandula pedunculata (1–7%, in trichomes) [
45]; in all cases, its content was higher than that found in the different organs of
H. piperita (<1%).
α-phellandrene, myrcene, limonene, terpinolene, p-menthadienol, and terpineol, as well as their derivatives, are olefinic P-menthanes found in stems, young leaves, and flowers, and act in the chemical defense of plants against pathogens and insects. These compounds have exhibited biological activities such as anti-inflammatory, antioxidant, soothing, and anticancer activities [
46,
47,
48]. They also have been reported in the essential oils of
M. piperita (<3%),
Calamintha nepeta (<1%), and
R. officinalis (<1%) [
33,
49,
50].
Sylvestrene and sabinene are simple, fresh-smelling, and spicy bicyclic monoterpenes with antioxidant, anti-inflammatory, and antimicrobial activities, reported in
Salvia stenophylla (Lamiaceae) essential oil in small proportions (0.1–0.2%), that matched those found in
H. piperita [
51]. Verbenol and verbenone are bicyclic monoterpenes distinguished by their functional groups (alcohol and ketone, respectively), whose precursor is α-pinene [
52]. These have been reported among the essential oil constituents of
Rosmarinus officinalis leaves and
Otostegia persica (less than 1%) [
50,
53], which have powerful acaricides, antimicrobials, antioxidants, and anti-ischemic activities [
52].
Endoborneol, fenchol, and 5-caranol are monoterpene alcohols derived from geranyl pyrophosphate that have potential as antimicrobials and antioxidants; their essential oil contents in the leaves of
Ocimum forskolei and
Teucrium yemense (Lamiaceae) [
54] and the ethanolic extract of
R. officinalis leaves [
55] vary between 1 and 31%, up to 20 times greater than that found in the stems and purple leaves of
H. piperita.
Dihydrocarvone is a monoterpene ketone obtained from the reduction in carvone and is present in
M. longifolia and
M. spicata in proportions less than 2% [
42]. Piperitone and its isomer piperitenone are also common monoterpene ketones in the essential oils of
M. cervina and
M. piperita, although piperitone is only present in smaller amounts (0.6–6.4%) than piperitenone (3–30%) [
37]; both have been reported to have antimicrobial and antifungal activities against pathogenic plant microorganisms [
56].
Copaene, bourbonene, germacrene D, cadinene, and cadinol are sesquiterpenes that originate from the mevalonate and methylerythritol phosphate pathways [
57]; copaene has been reported in low amounts (<1%) in the essential oils of
M. suaveolens and
M. spicata [
56], bourbonene has been found in
C. nepeta (>3%) [
33], and germacrene D and cadinene have been identified in
M. cardiaca and
M. spicata (1–4.46%) [
42], while cadinol, along with the other sesquiterpenes mentioned above, has been detected in the essential oil of
Marrubium vulgare and
Thymus algeriensis [
58].
The observed differences in the phytochemical compositions of stems, green leaves, and purple leaves of
H. piperita can be explained by the theory of optimal defense (ODT), which states that the distribution of chemical defense in different organs of the plant depends on the importance of these in basic functions such as growth. ODT predicts that young leaves are more important for the plant, so the greatest accumulation of phytochemical compounds involved in chemical defense must be found in them, while in more mature tissues, the accumulation of metabolites decreases due to the decrease in photosynthetic rate and nitrogen concentrations [
59,
60]. This behavior was reflected in the significant differences found in TPC, TFC, TAC, TTC, CGA, RA, LT, and the majority terpenes menthone, menthol, and pulegone between the stems, green leaves, and purple leaves of
H. piperita.
The antioxidant activity of infusions of the aerial section of
H. piperita was reported by Raya-Ramírez [
5], measured by DPPH· (40%) and ABTS+ inhibition (80%), which was two times lower than that found in this research. The antioxidant activity for other Lamiaceae species such as
Stachys sylvatica and
Stachys officinalis has been reported, which was higher than that obtained here in infusions evaluated with DPPH· and ABTS (1.7 and 2.4 times, respectively) [
61]. The results agreed with those reported by Franco-Aguirre et al. [
62] in the ethanolic extracts of
M. piperita leaves, in which higher inhibition percentages of DPPH· (70.6%) and ABTS+ (97.6%) were obtained. The differences between the two techniques could be explained by the different interactions (e.g., ionic bonds, hydrophobic interactions, and van der Waals forces) between DPPH· or ABTS+ with the components of plant extracts [
62].
RA presence in infusions and acidified methanolic extracts of Lamiaceae such as mint (
M. piperita), lemon balm (
Melissa officinalis), and lavender (
Lavandula angustifolia) has been reported and connected to the antioxidant capacity determined by ABTS+ cation inhibition [
63]. In this sense, Truong et al. [
64] stated that the antioxidant potential shown by RA in its aqueous phase involved the formal hydrogen transfer (FHT) pathway and the single electron transfer (SET) pathway, which broadens its spectrum to eliminate radicals such as superoxide and hydroperoxides, as is the case for other phenolic compounds such as anthocyanins [
65]. This confirmed the results obtained in this research, since the infusions of different tissues of
H. piperita showed greater antioxidant activity than those observed in ethanolic extracts.
The presence of terpenes has also been correlated with the antioxidant activity presented by
H. piperita extracts. Sarikurkcu et al. [
66], analyzed the antioxidant capacity of
M. pulegium essential oil, the main components of which were pulegone (71.47%) and menthone (7.67%), and reported a lower antioxidant activity (5.96% inhibition of DPPH) in the essential oil (1 mg/mL) compared to the 94.77% inhibition shown by the methanolic mint extract, which was rich in phenolic compounds and flavonoids. Pulegone and menthone, present in other Lamiaceae such as
Satureja macrostema, are oxygenated monoterpenes with a ketone group that give them low reactivity, which explains the low correlation between their content and antioxidant activity [
67].
ACE is a fundamental enzyme of the renin–angiotensin–aldosterone system (RAAS), which is involved in the regulation of blood pressure and fluid balance in the body. ACE is responsible for converting angiotensin I into angiotensin II, a vasoconstrictor that increases blood pressure. In addition, it stimulates the secretion of aldosterone in adrenal glands, increasing the reabsorption of sodium and water in kidneys, thus raising blood pressure. ACE inhibitors substances work by blocking the conversion of angiotensin I to angiotensin II and lowering blood pressure [
68].
ACE inhibitory activity shown by
H. piperita agreed with that reported for different Lamiaceae plants. Cam et al. [
69] showed that ACE activity was inhibited in 94% by methanolic extracts of
M. piperita, a percentage that was found in the inhibition range shown by the ethanolic extracts of green and purple leaves of
H. piperita. However, the IC
50 was seven times lower in
M. piperita (600 μg/mL) than in the ethanolic extract of green leaves of
H. piperita (4.25 mg/mL, the most prominent IC
50). In addition, ACE has been effectively inhibited by the hydroalcoholic extracts of
Lavandula pedunculata, with an IC
50 of 0.98 to 1.17 mg extract/mL [
70]. The authors mentioned that enzyme inhibition was influenced by the high concentrations of RA in the extracts (up to 58 mg RA/g DW), which resulted in blood systolic pressure reduction, emulating commercial inhibitors such as captopril. The authors concluded that other compounds such as chlorogenic and caffeic acids, luteolin, and apigenin, could act synergistically with RA.
CGA and caffeic acid have been reported as potential ACE inhibitory agents and other key enzymes linked to hypertension, with an inhibition percentage of less than 50% for both phenolic acids, compared to 80% for the positive control (captopril) [
71]. This inhibitory activity was attributed to interaction between the phenolic hydroxyl groups and the peptides of enzyme’s active site through hydrogen bonds, which can restrict substrate entry and the catalysis rate.
The relationship between the structures of various flavonoids, such as LT, apigenin, rutin, quercetin, and kaempferol, and ACE inhibitory activity has been examined [
72]. A total of 23 μM IC
50 was reported for LT, followed by quercetin, rutin, kaempferol, and apigenin (43, 64, 178, and 183 μM, respectively), attributing the effects shown to influence of different structural groups that constitute the molecular skeleton of each flavonoid, including hydroxyl groups and the groups of glycosides attached to them. LT features two hydroxyls that allow it to interact with active ACE sites, like the effect of carboxylic acid from other commercial inhibitors of the enzyme, such as lisinopril.
Terpenes present in extracts may also contribute to ACE inhibition. The major volatile compounds detected in
H. piperita organs, such as pulegone, menthol, and menthone have been reported as potential blood pressure reducers. The hypotensive effect in hypertensive rats, in which ACE expression was reduced by treatments with pulegone, at doses up to 40 mg/kg [
73], has been reported. Menthol has been reported as a potential hypotensive agent as well; thus, Demirci et al. [
74] evaluated the inhibitory effect of essential oils from three different mint species (
M. arvensis,
M. citrate, and
M. spicata) as well as the direct effect of menthol on ACE activity. Inhibition percentages of 33, 22, and 73% were reported for each mint species, respectively, while menthol reached an enzyme inhibition of 99.8%, results comparable to those obtained in the present research. The hypotensive effect was attributed to the presence of menthol and other terpenes found in peppermint essential oils.
The antibacterial activity of
H. piperita agreed with that reported against enteropathogenic bacteria in several species of the Lamiaceae family. MIC reported against
E. coli using the methanolic extract of
M. piperita (Mahmoudi et al. [
75]), which was two times higher (MIC = 50 μg DW/mL) than that found in purple leaf ethanolic extracts of
H. piperita, while MBC recorded for extract of
M. piperita equaled that obtained in the same ethanolic extract of purple leaves in this study (>100 μg/mL). The antimicrobial activity of
Satureja bachtiarica essential oil against
S. flexneri has been reported (MIC = 6.25 μg/mL) [
76], being two times lower than that obtained in the ethanolic extract of the purple leaves of
H. piperita. The observed antibacterial potential was attributed to the presence of monoterpenes such as carvacrol, which interacts with the bacterial cell membrane, facilitating its entry into the cell. In addition, a synergistic effect with other compounds, such as α-pinene, camphene, myrcene, α-terpinene, and p-cymene, present in lower concentrations, was suggested [
77]. In this work, the observed antibacterial activity was inversely correlated with the phytochemical content of
H. piperita, including its majority monoterpene composition. In this sense, pulegone has been reported as the main monoterpene associated with the antibacterial potential of the
M. pulegium essential oil against enteropathogens such as
E. coli (MIC 1.4 μL/mL, MBC 2.8 μL/mL) and
S. aureus (MIC 2.8 μL/mL, MBC 5.6 μL/mL); a synergistic effect with other monoterpenes such as menthone and piperitone was also suggested [
77]. These compounds were also found in the purple leaves of
H. piperita, an organ that showed the highest antimicrobial activity against three bacteria evaluated.
Since the highest inhibitory activity of enteropathogenic bacteria evaluated was observed in the ethanolic extracts and infusions of the purple leaf of
H. piperita, the presence of phenolic compounds, flavonoids, and anthocyanins in the extracts could be related to their antimicrobial activity. In Lamiaceae plants, the antibacterial activity of the infusions of
Teucrium arduini leaves and flowers, against pathogens such as
Staphylococcus aureus,
Bacillus subtilis,
E. coli, and
Pseudomonas aeruginosa, has been reported. Inhibitory activity against
S. aureus from flower infusions (MIC 16.66 mg/mL) and leaves (MIC 1.56–4.16 mg/mL), and against
B. subtilis from leaf infusions (MIC 25–50 mg/mL), has been positively correlated with TPC and TFC [
78].
In other plants, it is more common to detect the antibacterial activity associated with the presence of anthocyanins. For example, the antibacterial activity of hydroalcoholic flower extracts, as well as the anthocyanin-rich fraction of
Clitoria ternatea (Fabaceae) against pathogens such as
S. flexneri,
S. typhimurium,
E. coli,
P. aeruginosa,
Enterococcus faecalis, and
methicillin-resistant S. aureus (MRSA), has been determined; showing 40 mg/mL MIC against all bacteria evaluated, with the exception of
E. coli, which had greater sensitivity to the anthocyanin fraction (MIC 10 mg/mL) [
79]. The antimicrobial activity was attributed to the presence of ternatins (acylated anthocyanins derived from delphinidin), and their synergistic action to inactivate enzymes crucial for cell division and alter the Krebs cycle was identified, which could lead to weakened cellular respiration and inadequate energy supply, with eventual bacterial death.
XOD is a crucial enzyme for nucleic acid metabolism within the body and is found in organs such as the lungs, heart, and liver; it participates in the catalyzation of purines, degrading them by oxidation into hypoxanthines and xanthines, which are then converted into uric acid, superoxide anions (O
2−), and hydrogen peroxide (H
2O
2). When XOD production is inadequate, or there is a high consumption of foods rich in purines (e.g., red meat, fish, and seafood), uric acid accumulates, which can cause pathophysiological processes such as inflammatory disease, hyperuricemia, ischemic damage, and gout. In addition, elevated uric acid levels can lead to chronic cardiovascular diseases, such as hypertension or acute ischemic stroke in severe cases [
80].
The anti-inflammatory activity determined by XOD inhibition has already been reported in different species of the Lamiaceae family. Hudaib et al. [
81] analyzed the XOD inhibitory capacity of methanolic extracts of medicinal plants from Jordan, including some species of Lamiaceae family such as
Salvia spinosa,
Rosmarinus officinalis,
M. spicata, and
Lavandula angustifolia, at concentrations of 200 μg/mL. The percentage of XOD inhibition (22.5 to 71.5%) was similar to that found in
H. piperita organs. Nguyen et al. [
82] analyzed the anti-inflammatory activity of methanolic extracts of aerial parts of
Artemisia vulgaris and
A. apiacea and reported 89.3% and 57.4% XOD inhibition at a concentration of 100 μg/mL. The inhibitory activity was attributed to the presence of major flavonoids such as LT, apigenin, kaempferol, and eriodictyol, in addition to the presence of monoterpenes such as E-piperitol and β-pinene.
XOD inhibition by specific phenolic compounds and flavonoids has already been reported. Hydroxycinnamic acids such as rosmarinic, chlorogenic, and coumaric acid, as well as the flavonoids luteolin, apigenin, kaempferol, and quercetin have been reported as effective XOD inhibitors, with IC
50 in the range of 1.5–2.38 μM [
83]; thus, infusions and ethanolic extracts of
H. piperita could be considered potential XOD inhibitors.
Bioactive compounds inhibiting XOD have been isolated and identified in infusions of
Perilla frutescens (Lamiaceae) leaves, resulting in RA, caffeic acid, methyl rosmarinate, vinyl caffeate, and apigenin as the main XOD inhibitor compounds, with an IC
50 in a range of 0.44 to 121.22 μM, pointing to a competitive inhibition [
84]. The inhibitory effect of phenolic compounds on XOD can be explained by their interaction as proton and/or electron donors; this, in addition to involving a potential antioxidant effect, comprises processes such as the vinylation or methylation of the original phenolic compounds, which seems to promote XOD inhibitory activity [
84].
α-glycosidase is a key enzyme in the digestion of complex carbohydrates, which acts by breaking them down into glucose molecules that are then absorbed in the intestine and passed into the bloodstream, thus raising blood glucose levels, which regulates the rate of glucose absorption. When the process is uncontrolled, it can contribute to the development of type 2 diabetes mellitus, one of the most common diseases today [
85]. The inhibition of α-glucosidase is therefore an effective strategy to control glucose in patients with diabetes, as it helps to avoid sudden glucose spikes that complicate the management of the disease. Inhibitors such as acarbose act competitively on the enzyme’s active site, blocking its function by preventing interaction with substrates [
86].
The effective inhibition of α-glucosidase by the ethanolic and aqueous extracts of 18 Lamiaceae, including
M. piperita (50–92%),
Origanum vulgare (50–78%), and
Satureja montana (39–89%), has been reported [
87]. The highest inhibitory activity shown by aqueous extracts agreed with that observed in
H. piperita infusions, with inhibition percentages up to 0.93 times higher than those found in ethanolic extracts. Common phenolic compounds and flavonoids in Lamiaceae such as caffeic acid, chlorogenic acid, kaempferol, rosmarinic acid, and quercitrin may be linked to this enzyme inhibition by a competitive mechanism of action.
The acetic extracts of leaves of
Perilla frutescens (Lamiaceae), as well as its isolated fraction, which corresponds to RA, presented IC
50 of 0.42 and 0.23 mg/mL, respectively; these values are up to 5.9 times lower than the IC
50 found in this work. Likewise, the inhibition of α-glucosidase by phenolic compounds and flavonoids has been reported, and IC
50 values of RA (0.8 mg/mL), LT (0.07 mg/mL), quercetin (0.45 mg/mL), and rutin (0.27 mg/mL) were determined, as well as their mechanisms of action as competitive inhibitors [
88]. These IC
50 values were 8.8 times higher than those shown by ethanolic extracts and infusions of
H. piperita, which suggests that compounds diversity may promote a synergistic effect in terms of enzyme inhibition.
Terpenes present in aromatic Lamiaceae plants can exert inhibitory activity on α-glucosidase; for example, the essential oil of
M. spicata leaves, whose described aromatic profile includes menthol, carvone, pulegone, menthone, pinene, caryophyllene, and p-menthone, showed a 54.93% inhibition (1.5 times lower than the percentage found in the purple leaf infusion of
H. piperita) and an 0.68 mg/mL IC
50 [
89], which is 9.7 times greater than that of
H. piperita. Likewise, a higher inhibitory activity has been connected to a high content of pulegone and menthol in the essential oil of
Thymus pubescens [
90], which could indicate the relationship between the majority presence of both terpenes in
H. piperita organs and α-glucosidase inhibitory effects.