Chemometric Analysis Based on GC-MS Chemical Profiles of Three Stachys Species from Uzbekistan and Their Biological Activity

The chemical composition of the essential oils (EOs) of Stachys byzantina, S. hissarica and S. betoniciflora growing in Uzbekistan were determined, and their antioxidant and enzyme inhibitory activity were assessed. A gas chromatography-mass spectrometry (GC-MS) analysis revealed the presence of 143 metabolites accounting for 70.34, 76.78 and 88.63% of the total identified components of S. byzantina, S. hissarica and S. betoniciflora, respectively. Octadecanal (9.37%) was the most predominant in S. betoniciflora. However, n-butyl octadecenoate (4.92%) was the major volatile in S. byzantina. Benzaldehyde (5.01%) was present at a higher percentage in S. hissarica. A chemometric analysis revealed the ability of volatile profiling to discriminate between the studied Stachys species. The principal component analysis plot displayed a clear diversity of Stachys species where the octadecanal and benzaldehyde were the main discriminating markers. The antioxidant activity was evaluated in vitro using 2,2-diphenyl-1-picryl-hydrazyl (DPPH), 2,2-azino bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), cupric reducing antioxidant capacity (CUPRAC), ferric reducing power (FRAP), chelating and phosphomolybdenum (PBD). Moreover, the ability of the essential oils to inhibit both acetyl/butyrylcholinesterases (AChE and BChE), α-amylase, α-glucosidase and tyrosinase was assessed. The volatiles from S. hissarica exhibited the highest activity in both the ABTS (226.48 ± 1.75 mg Trolox equivalent (TE)/g oil) and FRAP (109.55 ± 3.24 mg TE/g oil) assays. However, S. betoniciflora displayed the strongest activity in the other assays (174.94 ± 0.20 mg TE/g oil for CUPRAC, 60.11 ± 0.36 mg EDTA equivalent (EDTAE)/g oil for chelating and 28.24 ± 1.00 (mmol TE/g oil) for PBD. Regarding the enzyme inhibitory activity, S. byzantina demonstrated the strongest AChE (5.64 ± 0.04 mg galantamine equivalent (GALAE)/g oil) and tyrosinase inhibitory (101.07 ± 0.60 mg kojic acid equivalent (KAE)/g) activity. The highest activity for BChE (11.18 ± 0.19 mg GALAE/g oil), amylase inhibition (0.76 ± 0.02 mmol acarbose equivalent (ACAE)/g oil) and glucosidase inhibition (24.11 ± 0.06 mmol ACAE/g oil) was observed in S. betoniciflora. These results showed that EOs of Stachys species could be used as antioxidant, hypoglycemic and skincare agents.


Introduction
The genus Stachys L. is one of the largest genera in the family Lamiaceae (Labiatae) that includes about 300 species of herbaceous annuals and perennial plants in the subtropical and tropical regions of the world [1]. The species name comes from Greek and means "an ear of grain", referring to the shape of the inflorescence spike that is present in many members [2].
Stachys plants (known as mountain tea) have traditionally been consumed in various countries as decoction or infusion teas. These extracts were used to treat various ailments, such as vaginal tumors, sclerosis of the spleen, asthma, cough, ulcers, abdominal pains, fever, diarrhea, sore mouth and throat, internal bleeding, and weaknesses of the liver and heart in addition to inflammatory and rheumatic disorders [3][4][5][6].
Many Stachys species are known as alimentary plants that are consumed for preparing foods such as yoghourt or jelly to improve the taste and flavor [7]. In Poland, various organs of S. palustris are used as soup and vodka additives [3]. The tubers can also be dried and crushed into a powder for making bread [8] due to their nutritional value as a rich source of carbohydrates, even for diabetic people, not only for humans but also for wild pigs [9][10][11].
The wide range of applications of various Stachys species, either as food or medicinal remedies, is mainly attributed to the major volatile components. Many studies reported the principal active metabolites present in the ethereal oil of different Stachys species worldwide [4]. Essential oils of the aerial parts of many Stachys species collected from Iran were determined, where the main identified components were linalool, α-terpineol, germacrene D, α/β-pinene and α/β-phellandrene [16,[20][21][22][23]. Similar results were obtained for those species growing in Turkey [7,24]. In Greece, the major identified components were caryophyllene, caryophyllene oxide and α-calacorene, [25][26][27]. Comparable results were obtained by analyzing the Stachys essential oils in Serbia and Montenegro [28,29].
Regarding S. byzantina K. Koch., (syn. Stachys lanata) commonly known as "lamb's ear" or "lamb's tongue", growing in the north and north-west of Iran, Turkey, Caucasia and Afghanistan [30]. Leaf infusions have traditionally been used as anti-inflammatories in Brazil [31]. However, leaf decoctions have been applied to infected wounds and cuts in Iran [32,33].
The genus Stachys is well-distributed in Uzbekistan [34]. Stachys betoniciflora Rupr and Stachys hissarica Rgl. are widely used as traditional remedies in Uzbekistan. S. betoniciflora has been used in traditional medicine for the treatment of diarrhea, genital tumors, hemorrhage, inflammation, heart disease, cough, ulcers, menstrual irregularities, bleeding, hysteria, hypertension, epilepsy, fainting, gout, jaundice and rheumatism [34]. A tea made from the herb is used to treat gastrointestinal pain, hemoptysis, respiratory disease, inflammation of the kidneys and bladder, and is also used as a sedative. An infusion of the roots is used as a laxative [35]. However, the folklore uses have never been scientifically evaluated, and other medicinal benefits of these plants are unknown.
The aim of this study was to investigate the essential oils of different Stachys species growing in Uzbekistan via GC-MS. S. byzantina, S. hissarica and betoniciflora were investigated, and this was the first such investigation for the two later species. In addition, the principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied to discriminate various Stachys species based on their chemical profiles rather than their growing location, which could be used as a tool for the proper use of the plants and prevent adulteration. Furthermore, the volatile oils obtained from different Stachys species were investigated for their antioxidant and enzyme inhibitory activities for the first time for these species.

Chemometric Analysis Based on GC-MS Analysis
Due to the complexity of the GC-MS-based data comprising the qualitative and quantitative discrepancies of various Stachys species, the multivariate analysis was applied using a principal component analysis (PCA) and a hierarchal cluster analysis (HCA) to discriminate between closely related Stachys species as well as to detect any significant relationship between these species. A matrix of all samples and their replicates (9 samples) multiplied by 143 variables (GC/MS peak area %) was constructed in MS Excel ® , then subjected to a multivariate analysis (PCA and HCA). Owing to the large number of variables, PCA was applied to reduce the dimensionality of the multiple data sets in addition to removing the redundancy in the variables, where the 1st PC accounts for a maximal amount of total variable variance in the observed data, and the 2nd PC accounts for a maximal amount of variance in the data set that was not accounted for by the first component. No transformation was performed, and the model was constructed utilizing raw data (peak area % for each compound as in Table 1). Figure 1a,b represent the PCA score and loading plots based on the GC-MS chemical profiles of the volatile components in the three Stachys species, respectively. maximal amount of variance in the data set that was not accounted for by the first component. No transformation was performed, and the model was constructed utilizing raw data (peak area % for each compound as in Table 1). Figure 1a,b represent the PCA score and loading plots based on the GC-MS chemical profiles of the volatile components in the three Stachys species, respectively. The result of this study indicated that there is a significant variance among the different Stachys species. The first two principal components explained about 97% of the variation in the dataset, with PC1 accounting for 63% and PC2 accounting for 34% of the variance. The three Stachys samples were clearly dispersed along the PCs in the PCA plot. S. byzantina and S. hissarica, in particular, exhibited negative PC1 scores and were positioned on the left side of the figure, while S. betoniciflora was plotted on the other side with a positive PC1 score.
Within the most discriminating compounds on positive PC1, octadecanal and eucalyptol were identified in S. betoniciflora. However, n-butyl octadecenoate and n-triacontane were the main differentiating markers in S. byzantina. Nevertheless, benzaldehyde (5.01%), n-hexadecanoic acid (4.68%) and pulegone were the major distinctive bioactive compounds discriminating S. hissarica. The result of this study indicated that there is a significant variance among the different Stachys species. The first two principal components explained about 97% of the variation in the dataset, with PC1 accounting for 63% and PC2 accounting for 34% of the variance. The three Stachys samples were clearly dispersed along the PCs in the PCA plot. S. byzantina and S. hissarica, in particular, exhibited negative PC1 scores and were positioned on the left side of the figure, while S. betoniciflora was plotted on the other side with a positive PC1 score.
An HCA clustering was performed to have a better insight into species classification. Figure 2 shows the HCA dendrogram based on the GC-MS aromatic profiles. The HCA dendrogram clustered the Stachys species into three main clusters. Clusters I, II and III displayed S. betoniciflora, S. byzantina and S. hissarica, respectively. The dendrogram confirmed the results obtained from the PCA, revealing the closeness of S. byzantina and S. hissarica. An HCA clustering was performed to have a better insight into species classification. Figure 2 shows the HCA dendrogram based on the GC-MS aromatic profiles. The HCA dendrogram clustered the Stachys species into three main clusters. Clusters I, II and III displayed S. betoniciflora, S. byzantina and S. hissarica, respectively. The dendrogram confirmed the results obtained from the PCA, revealing the closeness of S. byzantina and S. hissarica.  Table 1. S. hissarica (Sh), S. betoniciflora (Se) and S. byzantina (Sz).
The results displayed in Table 2 revealed that the studied samples showed moderate antioxidant potential in the assays. Most of the species showed antioxidant potential in the performed assays, except for the DPPH assay where only S. hissarica exhibited activity (13.04 ± 0.97 mg TE/g oil). Concerning the ABTS and FRAP assays, S. hissarica displayed the best activity (226.48 ± 1.75 and 109.55 ± 3.24 mg TE/g oil), followed by S. betoniciflora (128.54 ± 1.32 mg and 56.94 ± 0.75 mg TE/g oil), respectively. On the contrary, S. betoniciflora displayed the strongest activity in the other assays (174.94 ± 0.20 mg TE/g oil for CU-PRAC, 60.11 ± 0.36 mg EDTAE/g oil for chelating and 28.24 ± 1.00 mmol TE/g oil for PBD), followed by S. hissarica (162.62 ± 1.15 mg TE/g oil for CUPRAC, 24.30 ± 1.50 mg EDTAE/g oil for chelating and 5.69 ± 0.21 mmol TE/g oil for PBD. It was observed that S. byzantina exhibited the lowest antioxidant activity in all applied experiments. The obtained results could be explained by the chemical components of the tested essential oils. For example, the antioxidant properties of S. hissarica essential oil could be attributed to the presence of pulegone. Consistent with our observation, Torres-Martínez et al. [41] reported the significant antioxidant properties of pulegone. In addition, the presence of eucalyptol, linalool and p-cymene was linked to the antioxidant properties of S. betoniciflora. In previous stud-  Table 1. S. hissarica (Sh), S. betoniciflora (Se) and S. byzantina (Sz).
The results displayed in Table 2 revealed that the studied samples showed moderate antioxidant potential in the assays. Most of the species showed antioxidant potential in the performed assays, except for the DPPH assay where only S. hissarica exhibited activity (13.04 ± 0.97 mg TE/g oil). Concerning the ABTS and FRAP assays, S. hissarica displayed the best activity (226.48 ± 1.75 and 109.55 ± 3.24 mg TE/g oil), followed by S. betoniciflora (128.54 ± 1.32 mg and 56.94 ± 0.75 mg TE/g oil), respectively. On the contrary, S. betoniciflora displayed the strongest activity in the other assays (174.94 ± 0.20 mg TE/g oil for CUPRAC, 60.11 ± 0.36 mg EDTAE/g oil for chelating and 28.24 ± 1.00 mmol TE/g oil for PBD), followed by S. hissarica (162.62 ± 1.15 mg TE/g oil for CUPRAC, 24.30 ± 1.50 mg EDTAE/g oil for chelating and 5.69 ± 0.21 mmol TE/g oil for PBD. It was observed that S. byzantina exhibited the lowest antioxidant activity in all applied experiments. The obtained results could be explained by the chemical components of the tested essential oils. For example, the antioxidant properties of S. hissarica essential oil could be attributed to the presence of pulegone. Consistent with our observation, Torres-Martínez et al. [41] reported the significant antioxidant properties of pulegone. In addition, the presence of eucalyptol, linalool and p-cymene was linked to the antioxidant properties of S. betoniciflora. In previous studies [42][43][44], these compounds were described as remarkable radical scavengers and reductive agents. However, because higher levels of hydrocarbons (such as n-butyl octadecenoate and n-triacontane) were present in S. byzantina essential oil, it exhibited the weakest antioxidant properties. Table 2. Antioxidant activities of the volatile oils of Stachys species according to the 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH), 2,2-azino bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), cupric reducing antioxidant capacity (CUPRAC), ferric reducing power (FRAP), chelating and phosphomolybdenum (PBD) assays. Concerning S. byzantina, few studies reported the oxidation inhibition properties of its essential oil by various assays. S. byzantina exhibited a slight DPPH scavenging potential, with the value of 1.03 mg TEs/g EO. For the phosphomolybdenum test, it displayed 1.96 mmol TEs/g EO. Concerning the CUPRAC and FRAP assays, S. byzantina showed a high reducing power potential (81.79 and 44.77 mg TEs/g EO, respectively). In the chelating experiment, it revealed 15.65 mg EDTAEs/g EO [20].

Enzyme Inhibitory Activity of Stachys Species
The enzyme inhibitory potentials of the Stachys essential oils were assessed against various enzymes, including acetylcholinesterase (AChE), butyrylcholinesterase (BChE), tyrosinase, amylase and glucosidase. The enzymes were chosen to assess the potential of the tested essential oils in global health problems, the prevalence of which is increasing by the day. For example, cholinesterases are the main target in the treatment of Alzheimer's disease. In addition, amylase and glucosidase are the major players in controlling blood sugar levels in diabetics. The results (Table 3) are presented in the form of galantamine equivalent (GALAE), kojic acid equivalent (KAE) and acarbose equivalent (ACAE). In this study, Stachys EOs exerted a valuable cholinesterase inhibitory potential. The best AChE inhibitory potential was found in S. byzantina with 5.64 mg GALAE/g oil, followed by S. hissarica (5.05 mg GALAE/g oil) and S. betoniciflora (4.09 mg GALAE/g oil). However, the order for BChE was S. betoniciflora (13.81 mg GALAE/g oil) > S. hissarica (11.82 mg GALAE/g oil) > S. byzantina (11.18 mg GALAE/g oil). Nevertheless, our results were in accordance with those reported for S. byzantina, where the enzyme inhibition potential of S. byzantina essential oil was investigated to be 5.06 and 6.62 mg GALAEs/g EO against BChE and AChE, respectively [20]. Concerning tyrosinase inhibition, S. byzantina exhibited the strongest activity (101. 07 mg KAE/g oil), followed by S. hissarica (92.26 mg KAE/g oil) and S. betoniciflora (75.77 mg KAE/g oil). Concerning tyrosinase, S. byzantina EOs exhibited lower potency compared to our results, with 25.26 mg KAEs/g EO [20]. With regards to α-amylase activity, the highest and lowest activity were associated with S. betoniciflora and S. byzantina with values 0.76 and 0.59 mmol ACAE/g oil, respectively. Meanwhile, S. hissarica displayed an intermediate value (0.68 mmol ACAE/g oil). On the other side, the measurement of the α-glucosidase inhibition activity of the tested oils revealed that the strongest effect was presented by S. betoniciflora (24.89 mmol ACAE/g oil) compared to other Stachys species. With reference to α-amylase activity, S. byzantina displayed an approximately similar value with 0.74 mmol ACEs/g EO. On the other hand, the measurement of the α-glucosidase inhibition activity of the EOs showed S. byzantina with 4.56 mmol ACEs/g EO [20]. Similar to the antioxidant properties, the enzyme inhibitory properties can be linked to the chemical components of the tested essential oils. For example, Aazza et al. [45] reported that the cholinesterase inhibition abilities of several volatile compounds, including eucalyptol, which is found in S. betoniciflora. In addition, Basak and Ferda [46] reported the amylase and glucosidase inhibitory properties of eucalyptol. In a study performed by Matailo et al. [47], the BChE inhibitory effect of pulegone was described. However, we must take into account the presence of other compounds, even at low concentrations, because the essential oils are complex mixtures, and their constituents may exhibit different synergetic or antagonistic interactions.

Essential Oil Isolation
The plant samples were air-dried at a temperature not exceeding 30 • C and then powdered before use. The preparation of the volatile samples of the powdered Stachys (100 g of powder in 1 L of distilled water) was performed by hydrodistillation for 2 h using a Clevenger-type apparatus. The oil samples were dried by passing over anhydrous sodium sulphate to remove the moisture and were maintained at 30 • C in dark brown and air-tight closed vials until their analyses.

GC-MS Analysis
The GC-MS characterization of volatile components was performed on an Agilent 7890 B gas chromatograph (Agilent Technologies, Rotterdam, The Netherlands) equipped with a VF-Wax CP 9205 fused silica column (100% polyethylene glycol, 30 m × 0.25 mm, 0.25 µm). It was coupled with a 5977A mass selective detector (Agilent Technologies). The interface temperature: 280 • C; MS source temperature: 230 • C; ionization energy: 70 eV; scan range: 45-950 atomic mass units. The sample (0.5 µL) was automatically injected into the chromatograph using a GC auto sampler. The oven temperature was kept at 50 • C for 5 min, then rising from 50 • C to 280 • C at 5 • C/min, and was finally held isothermally at 280 • C for 15 min; injector temperature 250 • C; detector temperature 270 • C; carrier gas helium (0.9 mL/min); with split mode (split ratio, 1:20). C7-C40 standard saturated alkanes were purchased from Sigma-Aldrich (Merck, Germany). Enhanced ChemStation software, version MSD F.01.01.2317 (Agilent Technologies) was used for recording and integrating the chromatograms. The compounds were identified by comparison of their mass-spectral data and retention indices (RIs) with those of the Wiley Registry of Mass Spectral Data (9th Ed.), NIST Mass Spectral Library (2011), references [48,49] and our own laboratory database [50].

Antioxidant and Enzyme Inhibitory Assays
Different procedures were applied to investigate the antioxidant activities of the tested Stachys oils. These procedures included free radical scavenging (DPPH and ABTS), reducing power (CUPRAC and FRAP), metal chelating and phosphomolybdenum. The experimental details were as previously described [51,52]. A similar method was applied for the inhibitory effects of the Stachys oils that were tested against different enzymes (tyrosinase, amylase, glucosidase and cholinesterase) [52,53]. Both the antioxidant and enzyme inhibition assays were described by standard equivalents (Trolox and EDTA for antioxidant, galantamine for cholinesterase, kojic acid for tyrosinase, and acarbose for amylase and glucosidase activity). All samples were analyzed in triplicate in three independent experiments.

Statistical Analysis
Unless otherwise specified in the technique, all tests were repeated three times. Continuous variables were expressed as means ± SD. A one-way analysis of variance (ANOVA) was used to determine statistical significance, followed by a multiple comparison test (Tukey's post hoc test) with a significance level of p < 0.05.

Multivariate Analysis
The data obtained from the GC-MS were subjected to a chemometric analysis. A principal component analysis (PCA) was applied as an initiative phase in the data investigation to afford an overview of all sample groupings and to identify the markers responsible for this grouping. A hierarchal cluster analysis (HCA) was used to allow the clustering of samples. Hierarchical clustering techniques are based on the creation of branched structures, called dendrograms, which are qualitative in nature and permit the visualization of clusters and correlations amongst samples [54]. The clustering patterns were built by applying the complete linkage method. This exhibition is more effective when the distance between the samples (points) is computed by the squared Euclidean method. PCA and HCA were accomplished using CAMO's Unscrambler ® X 10.4 software (Computer-Aided Modeling, AS, Norway).

Conclusions
Stachys species are used as pleasant and fragrant medicinal herbal teas due to their volatiles and bioactive principles. In the present study, a comparative investigation of the EOs obtained from three popular Stachys species, namely, S. byzantina, S. hissarica and S. betoniciflora, indicated that they showed modest natural antioxidant agents. Their major bioactive components were identified as octadecanal, eucalyptol, linalool, n-butyl octadecenoate, n-triacontane, benzaldehyde, n-hexadecanoic acid and pulegone. In addition, the EOs exhibited moderate enzyme inhibitory activities, demonstrating the health benefits of various Stachys species, such as neuroprotective, hypoglycemic and fat adsorption preventive effects. Accordingly, these EOs could be considered as promising candidates that could be used for many therapeutic conditions. However, more clinical trials are needed to validate their potential uses. This is the first report comparing S. hissarica and S. betoniciflora to S. byzantina growing in Uzbekistan utilizing a multivariate analysis based on GC-MS chemical profiles in addition to reporting their antioxidant and enzyme inhibitory activities.