Exploring Echinops polyceras Boiss. from Jordan: Essential Oil Composition, COX, Protein Denaturation Inhibitory Power and Antimicrobial Activity of the Alcoholic Extract

In this article, we present the first detailed analysis of the hydro-distilled essential oil (HDEO) of the inflorescence heads of Echinops polyceras Boiss. (Asteraceae) from the flora of Jordan, offering observations at different growth (pre-flowering, full-flowering and post-flowering) stages. Additionally, we investigated the methanolic extract obtained from the aerial parts of the plant material at the full flowering stage in order to determine its inhibitory activity in terms of COX and protein denaturation and evaluate its antimicrobial effects against S. aureus (Gram-positive) and E. coli (Gram-negative) bacteria. Performing GC/MS analysis of HDEO, obtained from the fresh inflorescence heads at the different growth stages, resulted in the identification of 192 constituents. The main class of compounds detected in these three stages comprised aliphatic hydrocarbons and their derivatives, which amounted to 50.04% (pre-flower), 40.28% (full-flower) and 41.34% (post-flower) of the total composition. The oils also contained appreciable amounts of oxygenated terpenoids, primarily sesquiterpenoids and diterpenoids. The pre-flowering stage was dominated by (2E)-hexenal (8.03%) in addition to the oxygenated diterpene (6E,10E)-pseudo phytol (7.54%). The full-flowering stage primarily contained (6E,10E)-pseudo phytol (7.84%), β-bisabolene (7.53%, SH) and the diterpene hydrocarbon dolabradiene (5.50%). The major constituents detected in the HDEO obtained at the post-flowering stage included the oxygenated sesquiterpenoid intermedeol (5.53%), the sesquiterpene hydrocarbon (E)-caryophyllene (5.01%) and (6E,10E)-pseudo phytol (4.47%). The methanolic extract obtained from air-dried aerial parts of E. polyceras displayed more COX-2 inhibition than COX-1 inhibition at a concentration level of 200 µg/mL. The extract exhibited a capacity to inhibit protein denaturation that was comparable with respect to the activity of diclofenac sodium and displayed moderate levels of antimicrobial activity against both bacterial species. The current results demonstrate the need to perform further detailed phytochemical investigations to isolate and characterize active constituents.


Introduction
The Asteraceae family, commonly known as Compositae, is among the largest families in the plant kingdom, with almost 1620 genera and 23,600 species distributed in almost all habitats worldwide, except underwater. Plants belonging to this family are commonly described as herbs, shrubs and trees. Echinops, one of the genera belonging to this family, is known to comprise approximately 120-130 distinct species [1][2][3]. Echinops plants, described as perennials, annuals and biennials, are known to grow wild in Eastern and Southern

COX-1, COX-2 and Protein Denaturation Inhibitory Activity
The methanolic extract obtained from the air-dried aerial parts of E. polyceras (EPM) was investigated for its capacity to inhibitory effects against COX-1, COX-2 and protein denaturation. Results are shown in Table 2.

Antimicrobial Activity
The EPM extract was assayed for its antimicrobial activity against S. aureus and E. coli. Results are shown in Table 3 and Figure 2.

Discussion
GC/MS analysis of the HDEO obtained from the inflorescence parts of E. polyceras collected at the different growth stages resulted in the identification of a total of 192 compounds (Table 1). Figure 2 reveals the different classes of compounds detected at the different growth stages. The results of this analysis revealed simple nonterpenic aliphatic hydrocarbons and their derivatives (AH&D) to be the main class that dominated the composition in all growth stages.
During the pre-F stage, HDEO contained good amounts of oxygenated diterpenes Control (5% DMSO) is marked "C".

Discussion
GC/MS analysis of the HDEO obtained from the inflorescence parts of E. polyceras collected at the different growth stages resulted in the identification of a total of 192 compounds (Table 1). Figure 2 reveals the different classes of compounds detected at the different growth stages. The results of this analysis revealed simple nonterpenic aliphatic hydrocarbons and their derivatives (AH&D) to be the main class that dominated the composition in all growth stages.
Via a thorough investigation of the literature, it was revealed that the essential oil composition of the flowering heads of E. polyceras had never previously been investigated before. Previous studies concentrated on evaluating the constituents of the essential oils extracted from the roots of most Echinops species, including E. polyceras [18]. Recently, the study of Belabbes et al. [18] identified 5-(but-1-yn-3-enyl)-2,2'bithiophene and α-terthienyle (54.4 and 26.3%, respectively) as the primary constituents of the essential oil extracted from the roots of E. spinousus from Algeria. These two compounds were also detected in the essential oil obtained from the roots of E. spinousus of Tunisian origin (21.334%, 18.024%., respectively) [19]. These studies confirm that the essential oils extracted from different plant organs can have quite different compositions. Other factors can also affect the essential oil composition, including harvesting time, extraction method, soil type and many other environmental factors.
The chemical compositions of the essential oils of other Echinops species were investigated [20][21][22][23][24][25]. In these studies, the essential oils were extracted from a variety of different organs including the roots and aerial organs (stems, leaves, flowers, tubers). Table 4 summarizes the results of these studies and compares them to our current investigation [20][21][22][23][24][25]. These data shown in Table 4 reveal great qualitative and quantitative differences between the constituents of the EOs among the different Echinops species. It was noticed that some chemical constituents were common to all species, including 1,8-cineole, E-caryophyllene, caryophellene oxide and hexadecanoic acid.
In the current study, the methanolic extract (EPM) obtained from the air-dried aerial parts of E. polyceras was investigated for its COX-1, COX-2 and protein denaturation inhibitory effects in addition to its antimicrobial potential against the Gram-positive and Gram-negative bacteria. The preliminary screening results indicated that the extract displayed more COX-2 inhibition than COX-1 inhibition. The percentage inhibition of COX-2 was 96.4% and 99.0% at 200 µg/mL and 400 µg/mL EPM concentration levels, respectively. The standard drug used, celecoxib, produced an 88.6% inhibition under the same experimental conditions. It has been widely reported that the COX-1 enzyme is responsible for the synthesis of the constitutional prostaglandins that are responsible for maintaining the integrity of the stomach lining and kidney functions. The inhibition of COX-1 produced certain side effects such as bleeding and ulceration. In this study, it was observed that EPM extracted at a concentration level of 200 µg/mL inhibited only 65.0% of COX-1 enzyme, while the standard reference compound SC-560 (5 ng/mL) inhibited 50.2% COX-1. These findings suggest that fractionation of the extract is required to explore the selective COX-2 activity of the isolated compounds.     Moreover, the EPM extract displayed moderate antibacterial activity against Grampositive S. aureus. The extract showed weak antibacterial activity against the Gram-negative E. coli (Figure 1), with lower levels of activity than those observed for the extract obtained from the E. polyceras from Saudi Arabia [26].

Plant Material
The plant material was collected from the area surrounding Al-Balqa Applied University, (

Hydro-Distillation and Extraction of Essential Oils
Essential oils (EOs) were extracted from fresh inflorescence heads of E. polyceras at different growth stages and according to the procedure described in the literature [27,28]. Briefly, a 300 g sample of fresh inflorescence heads collected at each flowering stage was coarsely powdered and then subjected to hydro-distillation for 3 h in a Clevenger-type apparatus. The obtained essential oil (HDEO) from each growth stage was extracted (twice) with GC-grade n-hexane, dried using anhydrous MgSO 4 , and then stored in amber glass vials at 4 • C until analysis was performed.

GC-MS Analysis
GC/MS analysis was done according to the procedure previously described in the literature [29,30]. The analysis was performed on a Shimadzu QP2020 GC-MS equipped with GC-2010 Plus (Shimadzu Corporation, Kyoto, Japan) with a split-splitless injector, utilizing a DB5-MS fused silica column (5% phenyl, 95% polydimethylsiloxane, 30 m × 0.25 mm, 25 µm film thickness). Briefly, a linear temperature program was used to separate the different components. The oven temperature was set to 50 • C for 1 min, after which temperature programming was applied at 7 • C/min. The heating rate started from 50 • C (initial temperature) to 280 • C (final temperature); this was then held at 280 • C for 10 min, and the total run time was 44 min. The injector temperature was 260 • C with a split ratio of 20:1; an injection volume of 1 µL; a carrier gas: helium (flow rate 1.50 mL/min); and a flow control mode: pressure, 88.3 kPa. MS source temperature/detector temperature: 240 • C; interface temperature: 250 • C; ionization energy (EI): 70 eV; scan range 35-500 amu; scan speed 1666. The solvent cut was 3 min, while these data were acquired in 4.5 min. These data were collected using Windowsbased Lab-Solution GC-MS version 4.45SP1 Software. The mass spectra of isolated components were compared to those reported in ADAMS-2007 and NIST 2017 mass spectrometry libraries. To confirm the identified compound, a comparison was performed between reported values and relative retention indices (RRI) with reference to n-alkanes (C 8 -C 30 ) in addition to these data published in the literature [31].

Preparation of the Alcoholic Extract
The alcoholic extract was prepared according to the procedure described in the literature with slight modifications [27,32]. Air-dried aerial parts of E. polyceras (20 g) were ground down to fine powder and then soaked in methanol (400 mL) at room temperature (3 × 24 h). The solvent was then evaporated under reduced pressure at 55 • C. The obtained methanol extract (EPM, 2.2479 g; yield: 11.24%) was then used for bioactivity screening.

COX-1 and COX-2 Inhibitory Activity
To evaluate the COX activity and to judge the NSAID activity of the methanolic extract (EPM), a COX-1 inhibitory screening assay kit containing SC-560 as standard (Fluorometric, ab204698, Abcam, Tokyo, Japan) and COX-2 inhibitor screening kit (Fluorometric, ab283401, Abcam, Tokyo, Japan) containing celecoxib as standard were used as per the instruction provided with the kit without any modification [33][34][35]. Two different concentrations of the EPM extract were prepared for initial screening in the supplied buffer. The buffer solution was used as a control.

Inhibition of Protein Denaturation
The procedure described in [35,36], was used to estimate the inhibition of protein denaturation with slight modifications. Different solutions were prepared for the assay, including the test solution (EPM extract), test control, product control and standard solution. All solutions were prepared using a buffer with pH 6.3. These prepared samples were kept at 37 • C for 20 min; then, they were incubated at 50 • C for another 20 min. The absorbance was measured at 416 nm using a synergy HTC multimode reader (Viotek, Winooski, VT, USA). Absorbance measurements were performed after all samples had cooled down. The percent inhibition of protein denaturation was calculated using the given formula:

Antimicrobial Activity
Gram-positive (S. aureus ATCC 6538) and Gram-negative (E. coli ATCC 8739) bacteria were used to assess the antibacterial activity of the EPM extract and moxifloxacin (standard drug) according to the procedure described in the literature [34]. Nutrient agar was added to a sterile Petri disc (9 cm, diameter). The plates were inoculated with bacterial culture using sterilized cotton swaps. Subsequently, 6 mm wells were created with sterilized 6 mm surgical punches. The wells were filled with 60 µL of extract solution (5000, 2500 or 1250 µg/mL) and moxifloxacin standard solution (40 µg/mL). A 5% DMSO solution was used as a control. The plates were incubated at 37 • C for 24 h. Duplicate runs of each experiment were produced.

Statistical Analysis
The results obtained in the present study are expressed as mean ± standard deviation (SD). For the statistical analysis of the experimental data, Graph-Pad Prism 5 (Graph-Pad Software, San Diego, CA, USA) was used.

Conclusions
This is the first study to report on the chemical composition of hydro-distilled essential oil obtained from the inflorescence heads of Jordanian E. polyceras at different growth stages. When comparing our current results with those reported in the literature, it can be concluded that the essential oil obtained from flowering heads of E. polyceras had a quite different composition than that obtained from the roots. The EO was rich in chemical constituents such as (6E,10E)-Pseudo phytol, dolabradiene, isoamyl dodecanoate, intermedeol, β-bisabolene, linalool, (E)-caryophyllene, caryophyllene oxide, nerol, β-elemene, hexaxecanoic acid and iso-longifolol. The methanolic extract obtained from the aerial parts of E. polyceras showed significant COX-1, COX-2 and protein denaturation inhibitory activities, but moderate antimicrobial activity, against S. aureus and E. coli. The current results of this study encourage researchers to undertake further detailed phytochemical investigations of the alcoholic extract in order to isolate and characterize its active constituents.

Supplementary Materials:
The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/molecules28104238/s1. Figure S1: GC-MS analysis of GC-MS analysis of essential oil during pre-flowering stage of E. polyceras inflorescence; Figure S2: GC-MS analysis of essential oil during full-flowering stage of E. polyceras inflorescence; Figure  Data Availability Statement: Data will be provided upon request.