Chemical Composition and Biological Properties of Essential Oil From Aerial Parts of Veronicastrum stenostachyum

Published in Khimiya Prirodnykh Soedinenii, No. 1, January–February, 2023, pp. 150–152.

Veronicastrum stenostachyum (Hemsl.) T. Yamaz. (V. stenostachyum) is a perennial herb of the family Plantaginaceae, with horizontal and short rhizomes, erect or arching stem, alternate leaves, and axillary inflorescence [[1]]. This plant is primarily distributed in Southern China. V. stenostachyum is usually used as a folk medicine for the remedy of intestinal conditions and cirrhotic ascites [[2]]. To the best of our knowledge, no previous study has been done on the composition and biological activity of V. stenostachyum essential oil. The present study describes for the first time the composition of the essential oil from the aerial parts of V. stenostachyum and some of its biological activities. In particular, we evaluated the possible antibacterial effects of the essential oil against different bacteria strains, as well as its cytotoxic activities on HepG2 and MCF-7 cancer cells.

Aerial parts of the wild-growing Veronicastrum stenostachyum (Hemsl.) T. Yamaz. were gathered in June 2020 from Lishui City in Zhejiang Province of China. The experimental plant material was identified by the botanist Dr. Hong Zhao, and the voucher specimen (No. 020011) was deposited in the Laboratory of Botany of Marine College, Shandong University, China. The fresh plant materials were crushed and then hydrodistilled conventionally for 4 h using a Clevenger-type apparatus. The essential oil was separated from water using ethyl ether and dried over anhydrous sodium sulfate and stored in tightly closed dark vials at 4°C until analysis. The average yield of the essential oil from V. stenostachyum aerial parts was 0.11% (on a dry mass basis).

Constitutes present in the essential oil were characterized by gas chromatography with flame ionization detector (GC/FID) and gas chromatography/mass spectrometry (GC/MS). GC/FID analysis was conducted on an Agilent Technologies 6890 gas chromatograph equipped with a flame ionization detector and a capillary column of HP-5MS (30 m × 0.25 mm i.d.; 0.25 μm film thicknesses). GC/MS analysis was carried out using an Agilent 6890 gas chromatograph coupled to an Agilent 5975C mass selective detector, following the protocol as previously described [[3]]. Retention indices (RI) were calculated by the retention time of C7–C30n-alkanes series on the HP-5MS column under identical experimental conditions. The components were recognized by computer matching against NIST 14 mass spectral libraries and by comparison with data already available in the literature [[4]].

As shown in Table 1, a total of 39 compounds, accounting for 96.1% of the total oil, were identified. Longifolene (9.5%) was the predominant component of the essential oil, followed by lavender lactone (7.6%), globulol (5.8%), nootkatene (5.3%), β-ionone (4.8%), (Z)-linalool oxide (4.8%), dihydroedulan (4.7%), and (E)-tetradec-2-enal (4.4%).

Table 1. Chemical Composition of the Essential Oil Isolated from the Aerial Parts of V. stenostachyum

aRetention index determined with respect to a homologous series of n-alkanes (C7–C30) on an HP-5MS column.

The micro-broth dilution method was used to assess the antibacterial activity of the essential oil against four bacteria strains and the results were expressed in terms of the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values [[6]]. From Table 2, the V. stenostachyum essential oil showed the best antibacterial activity against Staphylococcus aureus, with a MIC value of 0.16 mg/mL equal to its MBC value, followed by Bacillus subtilis (MIC: 0.16 mg/mL, MBC: 0.32 mg/mL). Gram-negative bacteria, on the other hand, were less sensitive to the V. stenostachyum essential oil than Gram-positive bacteria, which was likely due to considerable differences in their outer layers.

Table 2. Antibacterial Activity of Essential Oil of the Aerial Parts of V. stenostachyum

*Positive control.

The cytotoxic effects of the essential oil of the aerial parts of V. stenostachyum on human hepatocellular carcinoma HepG2 and human breast adenocarcinoma MCF-7 cells were tested by the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric test [[6]]. Doxorubicin was tested as a reference. The essential oil of V. stenostachyum was toxic against both cell lines with IC50 values of 14.28 ± 2.69 and 14.72 ± 2.38 μg/mL on HepG2 and MCF-7, respectively. These results indicate that the essential oil of V. stenostachyum exhibits a significant cytotoxic effect in vitro (Table 3).

Table 3. Cytotoxic Activity of the Essential Oil of the Aerial Parts of V. stenostachyum on HepG2 and MCF-7 Cells (IC50, μg/mL)

The biological properties of plant essential oils are intimately related to their chemical compositions [[7]]. The major constituent of the V. stenostachyum essential oil, longifolene, has been reported to possess minor activity against Gram-positive bacteria, but did not inhibit the growth of the Gram-negative bacteria [[8]]. The antimicrobial effects of globulol and β-ionone have also been demonstrated against a variety of fungal and bacterial species [[10]]. Furthermore, numerous researchers have confirmed that β-ionone exerts antiproliferative capabilities and induces apoptosis in different cancer cells both in vitro and in vivo [[11]–[17]]. Therefore, the antibacterial and cytotoxic activities of the essential oil of V. stenostachyum could be mainly due to the longifolene, globulol, and β-ionone. However, owing to the complexity of the essential oil ingredients, their biological activities are rather determined by the interactions of the individual constituents.