Chemical composition and antibacterial activity of the essential oil the leaf of Nepeta persica
Department of Chemistry, Islamic Azad University, Ardabil Branch, Ardabil, Iran
E-mails: chem.salehzadeh@yahoo.com; soraya.akhshi@yahoo.com; ali.shafaghat@gmail.com
* Corresponding author, Phone: +98 9144524649; Fax: +98 4512239088
Abstract
The essential oil from the leaf of Nepeta persica Boiss, analyzed by gas chromatography (GC) and gas chromatography (GC)/mass spectrometry (MS), were shown to contain 4aα, 7α, 7aβ-nepetalactone (49.46%) and 4aα, 7α, 7aα-nepetalactone (14.18%). The other main constituents were n-octane (13.10%), n-decane (3.67%) and germacrene-D (2.04%). Antibacterial activities of the leaf oil were evaluated using the micro-dilution broth method. Inhibitory effects on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella typhi and Enterococcus faecalis were recorded. The leaf oil has difference activities against the test microorganisms. The antibacterial property of the essential oil might be ascribed to their high content of nepetalactone isomers.
Keywords
Nepeta Persica; Lamiaceae; Essential oil composition; Nepetalactone; antibacterial activity
Introduction
Several Nepeta species (Lamiaceae/Labiatae) are reported to contain nepetalactone in their essential oils. The genus Nepeta, with almost 280 species, is widespread in Europe, Asia and a few parts of Africa; 67 species of this genus are found in Iran [1], one of which, N. persica Boiss, is endemic [2]. Nepeta species are used in folk medicine [3,4] for the treatment of various disorders, such as nervous, respiratory and gastrointestinal diseases [5].
Nepeta species are also used in the traditional medicine of many countries as a diuretic, diaphoretic, antitussive, anti-asthmatic, vulnerary, antispasmodic, febrifuge, tonic, emmenagogue, and sedative agent [6].The bacteriostatic, fungistatic [7] and antiviral activities have been attributed to nepetalactones [8]. Antibacterial and cytotoxic activity of N. cataria and N. cataria var. Citriodora essential oils [9], essential oil composition of two subspecies of N. glomerulosa [10] and antimicrobial activity of N. isolates has been reported. The main component of the essential oil of N. cephalotes from Iran was 4aα, 7α, 7aα-nepetalactone [11], whereas 1, 8-cineol was the major component of N. denudata, N. ispahanica and N. binaludensis [12], terpinen-4-ol of N. asterotrichus, and spathulenol of N. depauperata [13]. The hydrodistilled oils of N. sintenesii from Iran were reported to have, as their major components, 4aβ, 7α, 7aβ-nepetalactone (60.3%), germacrene-D (12.7%) and 1, 8-cineol (8.2%) in the flower oil, 4aβ, 7α, 7aβ-nepetalactone (34.6%), germacrene D (14.1%), 1, 8-cineol (7.9%), α-cadinol (6.8%) and δ-cadinene (5.8%) in the leaf oil, 4aβ, 7α, 7aβ-nepetalactone (64.2%), α-cadinol (8.9%) and α-pinene (6.7%) in the stem oil, and 4aβ, 7α, 7aβ-nepetalactone (61.2%), germacrene-D (12.0%), 4aα, 7α, 7aβ-nepetalactone (8.5%), and 1, 8-cineol (5.7%) in the root oil [14]. The major compound found in the essential oils of N. racemosa collected from different localities in Turkey was 4aα, 7α, 7aβ-nepetalactone (31.5-91.5%) [15]. Relatively high concentrations of nepetalactones in many Nepeta species have been reported [16].
Material and method
Plant material
The plant material was collected on June 29, 2013 in the Khalkhal (Ardabil province) area in northwest Iran at an altitude of 1955 m. A voucher specimen (N-324) is kept at the Herbarium of Agriculture Research in Ardabil Center, Iran.
Distillation
Plant material was air-dried in the shade prior to isolation of their oil. Leaf (120 g) was subjected to 3 h of hydro distillation in a Clevenger-type apparatus. The resulting oil (yield: 1.1%, v/w) was dried over anhydrous sodium sulfate and immediately placed into a dark glass tube and sealed. The sample was stored at 2°C until chemical analysis.
GC and GC/MS analysis
GC analysis was performed on a Shimadzu 15A Gas Chromatograph equipped with a split/split less injector (250°C) and a flame ionization detector (250°C). N2 was used as carrier gas (1 mL/min) and the capillary column used was a DB-5 (50 m × 0.2 mm, film thickness 0.32 μm). The column temperature was kept at 60°C for 3 min and then raised to 220°C at a 5°C/min rate and kept constant at 220°C for 5 min. Alkanes (C8—C22) were used as reference points in the calculation of relative retention indices (RRI). The relative percentages of the characterized components are given in Table 1. GC/MS analysis was performed using a Hewlett Packard 5973 with an HP-5MS column (30 m × 0.25 mm, film thickness 0.25 μm). The column temperature was kept at 60°C for 3 min and programmed to 220°C at a rate of 5°C/min and kept constant at 220°C for 5 min. The flow rate of helium as carrier gas was 1 mL/min. MS were taken at 70 eV. Identification of the constituents of the oils was made by comparison of their MS and RIs with those given in the literature and with those of authentic samples [17]. Relative percentage amounts were calculated from peak area using a Shimadzu C-R4A chromatopac, without the use of correction factors.
Antibacterial screening
Screening of the essential oil for activity by the agar diffusion disc impregnated method was adopted. The oil was prepared as 50% v/w solution. A Whatman paper disc, 4mm in diameter, was impregnated and oven dried at 37°C for 1 h to remove the presence of solvent. 1×106 CFU/mL of the test bacteria was prepared and seeded into the solid agar medium. The impregnated paper discs were placed at intervals and incubated for 24 h at 37°C. After 24 h the plate reading was taken and the zone of inhibition was measured and recorded (Table 2). The microorganisms used were: Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella typhi and Enterococcus faecalis.
Results and discussion
The compositions of the leaf oil of N. persica are listed in Table 1. In dried plant oil, 19 components, which represented about 93.46% of the total composition, were identified. In addition, as can be seen in Table 1, the leaf oil consisted of five sesquiterpenes (4.82%), eight monoterpene hydrocarbons (8.79%), two oxygenated nonoterpenes (63.64%) and four other components (16.21%). 4aα, 7α, 7aβ-nepetalactone (49.46%) and 4aα, 7α, 7aα-nepetalactone (14.18%), n-octane(13.10%) and n-decane (3.67%) were the major components of this oil. Oxygenated monoterpenes (total nepetalactones, 63.64%) constituted the major fraction of the oil, while monoterpene, sesquiterpene and the other hydrocarbons accounted for only 29.82%.
Table 1. Chemical composition (%) of the oil of Nepeta persica leaf
|
Compound |
RI |
Percentage |
|
Octene(1-) |
792 |
1.56 |
|
Octane(n-) |
800 |
13.10 |
|
Citronellene |
937 |
0.30 |
|
Decane(n-) |
1000 |
3.67 |
|
1, 8-Cineole(Eucalyptol) |
1031 |
0.68 |
|
Cis-β-ocimene |
1037 |
1.06 |
|
Trans-β-ocimene |
1050 |
1.05 |
|
γ-Terpinene |
1060 |
0.39 |
|
α-Terpinolene |
1088 |
0.48 |
|
Dodecane(n-) |
1200 |
1.16 |
|
4aα, 7α, 7aα-nepetalactone |
1360 |
14.18 |
|
4aα, 7α, 7aβ-nepetalactone |
1387 |
49.46 |
|
β-Caryophyllene |
1419 |
0.81 |
|
Trans-β-farnesene |
1457 |
1.01 |
|
Germacrene-D |
1485 |
2.04 |
|
Spathulenol |
1578 |
0.50 |
|
α-Cedrene epoxide |
1575 |
0.46 |
|
Methyl hexadecanoate |
1922 |
0.34 |
|
Methyl linoleate |
2095 |
1.21 |
|
% Identification |
---- |
93.46 |
|
|
||
In a previous study, the essential oil of N. persica was investigated by GLC and GC-MS. Forty-one components, representing 86.4% of the oil, were characterized, the major ones being 1, 4-hexadiene-2, 3, 4, 5-tetramethyl and 4aβ, 7α, 7aα-nepetalactone [18]. The oil of the aerial parts of N. sintenisii contained 4aβ, 7α, 7aβ-nepetalactone (23.4%), elemol (16.1%), (E)-β-famesene (9.5%) and 1, 8-cineole (8.2%) as the major constituents among the forty characterized, comprising (96.5%) of the total components detected [19].
In the N. sintenisii Bornm. 4aβ, 7α, 7aβ-nepetalactone was characterized in the flower, leaf, stem and root oils (60.3%, 34.6%, 64.2% and 61.2%, respectively) as the main constituent [11].
Essential oils from the aerial parts of N. crispa Willd, N. mahanensis Jamzad & Simmonds, N. ispahanica Boiss and N. eremophila Hausskn. & Bornm. were analyzed. 1, 8-Cineole (62.8%), 4aα, 7α, 7aα-nepetalactone (10.3%) and 4aβ, 7α, 7aβ-nepetalactone (9.2%) were reported as the main constituents of N. crispa oil. Eighteen compounds were identified in the oil of N. mahanensis with nepetalactone (37.6%), 1, 8-cineole (27.2%) and germacrene-D (6.5%) as the main components. Twenty-seven compounds were characterized in the oil of N. ispahanica with 1, 8-cineole (71.7%) as the main constituent. Twenty-six compounds were recorded for the oil of N. eremophila with 4aβ, 7α, 7aβ-nepetalactone (73.3%) and 1, 8-cineole (13.1%) as the main constituents. The results of this study showed that, although the nepetalactone isomers are the main components of the essential oils of N. sintenisii, N. mahanensis and N. eremophila, the oil of N. crispa consists of about 20% nepetalactone and the oils of other species have different compositions [20].
Nepetalactone isomers also present in the leaf oil (63.64%) were constituted. Our survey showed that Nepeta species can be divided into two groups of nepetalactone-containing and nepetalactone-free species. The essential oils of N. racemosa collected from different localities in Turkey had as their major compound 4aα, 7α, 7aβ-nepetalactone (31.5-91.5%) [21]. In the Iranian N. raceme, 4aα, 7α, 7aα-nepetalactone (25.6%) and 4aβ, 7α, 7aβ-nepetalactone (33.6%) were reported [22]. Also, nepetalactone isomers have been recorded for N. cratssifolia [23], N. nuda ssp. albiflora [24], N. italica [25], N. cadmea [26] and N. persica [18]. However, in the oils of N. depauperata [27], N. cilicia [28], N. nuda ssp. nuda [29], N. glomerulosa ssp. carmanica [30] and N. macrostphone [31], no nepetalactor es were found. Spathulenol (31.8%), β-caryophyllene (12.9%) and caryophyllene oxide (10.3%) were the major components of the oil of N. depauperata Benth [27].
Results obtained in the antibacterial study of the essential oil from leaf of N. persica are shown in Table 2. With the agar disc diffusion assay the oil of leaf was found to be active against all the test microorganisms. Comparison of the composition of N. persica leaf oil revealed some differences, especially in the major components. It is conceivable that the antibacterial property of the essential oil might be ascribed to the high content of nepetalactone isomers in the oil.
Table 2. Antibacterial activity of the essential oil from leaf of Nepeta persica
|
Tested bacteria |
Zone of inhibition (mm) |
|
|
|
|
Escherichia colt |
11 |
|
Pseudomonas aeruginosa |
9 |
|
Staphylococcus aureus |
12 |
|
Salmonella typhi |
10 |
|
Entemcoccus faecalis |
12 |
|
|
|
The most sensitive microorganisms were Staphylococcus aureus and Entemcoccus faecalis, with inhibition zones of 12 mm.
Conclusion
The finding of the present study and previously published one suggest that two chemotypes of oil: neptalactone and n-octane may be present in Nepeta persica.
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