Abstract
In this study, we investigated the chemical composition and potential biological properties of essential oils extracted from the rhizomes of two Homalomena species, H. pendula (Blume) Bakh.f. and H. cochinchinensis Engl. Using GC–MS analysis, we found that H. pendula essential oil contains 59 components while H. cochinchinensis essential oil contains 58. Both essential oils were rich in oxygenated monoterpenes, with linalool and terpinen-4-ol being the most prevalent compounds. Additionally, H. cochinchinensis essential oil exhibited moderate anti-inflammatory activity with an IC50 value of 170.81 ± 11.44 µg/mL, whereas H. pendula essential oil showed moderate activity against acetylcholinesterase (AChE) with an IC50 value of 130.65 ± 1.27 µg/mL. This study is the first to report the chemical composition and biological effects of H. pendula essential oil, as well as the anti-inflammatory effects of H. cochinchinensis essential oil.
Introduction
Homalomena, a diverse and extensive genus of tropical plants in the Araceae family, contains over 150 species, the greatest diversity of which is located in the perhumid climate of Southeast Asia. 1 These plants are known for their ornamental value, attractive foliage, and medicinal properties. They are important not only for their cultural and ecological value but also for their potential use in traditional medicine. For centuries, Homalomena species have been used in traditional medicine for ailments such as stomach disorders, fever, pain, inflammation, and infections. 2 H. occulta is used to treat rheumatism and stomach pain, as well as to stimulate digestion, whereas H. pendula can suppress cough and reduce pain. In addition, in China, H. pendula rhizomes are used to treat high fevers, cough, influenza, and joint pain. 3 Essential oils have also received considerable attention for their potential therapeutic effects; several Homalomena species have been investigated in this context, including H. aromatica, H. cochinchinensis, H. occulta, H. pierreana, H. pineodora, H. sagittifolia, 4 and H. josefii. 5 These studies have revealed that Homalomena essential oils contain abundant terpenoids, phenolic compounds, and fatty acids, compounds known for health benefits such as antibacterial,5-7 antifungal, 8 and antioxidant 5 properties.
Despite the promising therapeutic potential of Homalomena essential oils, little is known about the essential oils of H. pendula and H. cochinchinensis, which are rare species in Vietnam. Recently, Van et al. reported the chemical composition and antibacterial activities of H. cochinchinensis essential oil. 7 However, the chemical composition and bioactivities of H. pendula essential oil have not been published. Investigating the phytochemical composition and biological activity of these essential oils is crucial for validating their traditional uses and exploring their potential therapeutic applications.
In the current study, we report the phytochemical compositions of the essential oils of H. pendula and H. cochinchinensis rhizomes. In addition, their anti-inflammatory and anti-cholinesterase activities are described. By exploring the potential therapeutic applications of these Homalomena species, this study may contribute to the development of natural and effective remedies for various ailments. Understanding the chemical constituents and biological activities of Homalomena essential oils may also lead to the discovery of novel therapeutic agents for treating human diseases.
Results and Discussion
Extraction and Profiling
The proportion of essential oil extracted from H. pendula and H. cochinchinensis rhizomes was 0.15% (v/w) and 0.20% (v/w), respectively, calculated on a fresh weight basis. Table 1 displays the chemical compositions of these essential oils as determined by GC–MS analysis.
Components of Essential Oil from Rhizomes of H. pendula and H. cochinchinensis.
Elution order on Equity-5 column.
Retention indices taken from Ref. 9
Retention indices on Equity-5 column.
Retention indices taken from Ref. 10
–, not identified.
This analysis (Supplementary Figures S1 and S2) revealed that the essential oils extracted from H. pendula and H. cochinchinensis rhizomes are dominated by oxygenated monoterpenes (45.3% and 71.9%, respectively). Notably, H. pendula essential oil contains substantial amounts of hydrocarbon monoterpenes (23.3%) and hydrocarbon sesquiterpenes (11.5%), whereas these types of compounds occur in low concentrations in H. cochinchinensis essential oil. The two major components found in both essential oils are linalool (31.6% and 56.3% in H. pendula and H. cochinchinensis, respectively) and terpinen-4-ol (4.0% and 5.2% in H. pendula and H. cochinchinensis, respectively). Interestingly, these compounds have also been reported as major constituents of other Homalomena essential oils. In particular, the essential oil extracted from H. aromatica rhizomes was composed of 62.5% linalool and 7.08% terpinen-4-ol, 8 whereas the oil extracted from its roots contained 58.3% linalool and 16.7% terpinen-4-ol. 11 Linalool was also the most abundant compound in the essential oils extracted from H. occulta (36.9%) 12 and H. sagittifolia (61.9%) rhizomes. 13 Thus, it is reasonable to consider linalool a “marker” of Homalomena essential oils.
The chemical composition of H. cochinchinensis rhizome essential oil reported herein is generally consistent with that reported in the literature 7 in terms of primary components and major classes of volatile compounds. In particular, two independent studies of H. cochinchinensis rhizome essential oil detected a large proportion of oxygenated monoterpenes (71.9% and 76.5%, respectively), linalool (56.3% and 57.4%, respectively), and terpinen-4-ol (5.2% and 10.6%, respectively). Interestingly, the H. cochinchinensis rhizome essential oil used in the present study was obtained from Dong Nai province; its hydrocarbon monoterpene and oxygenated sesquiterpene contents were very different from those of essential oil from Binh Phuoc province (5.4% vs 13.1% and 13.3% vs 6.3%, respectively). 7 These differences may be due to differences in species distributions, sample collection times, and analytical and identification methods.
Furthermore, we compared the chemical composition of H. cochinchinensis rhizome essential oil with that of essential oil from the aerial parts of the plant.
7
This comparison revealed substantial differences in the prevalence of the primary components. Specifically, Van et al.
7
reported that myrcene (41.1%), sabinene (8.2%), and
Finally, we note that this report is the first to characterize the chemical composition of H. pendula rhizome essential oil. In addition to its primary components, linalool and terpinen-4-ol, this essential oil also contained a number of highly prevalent compounds including sabinene (6.2%), valerianol (5.6%), δ-3-carene (5.1%), 1,8-cineole (4.5%), δ-cadinene (3.9%), and cubenol (3.5%).
Anti-Inflammatory Activity and Anti-Acetylcholinesterase Activity
The anti-inflammatory and acetylcholinesterase (AChE) activities of H. cochinchinensis and H. pendula rhizome essential oils are presented in Table 2.
In Vitro Anti-Inflammatory and Anti-Acetylcholinesterase Activity of Essential Oil from Rhizomes of H. pendula and H. cochinchinensis.
NA: not available.
The H. cochinchinensis essential oil showed moderate nitric oxide inhibitory capacity with an IC50 value of 170.81 ± 11.44 µg/mL. In addition, an MTT assay revealed that cell viability was 93.14% when treated with a concentration of 200 µg/mL. This finding implies that this essential oil did not elicit any significant cytotoxicity.
The AChE-inhibitory activities of the two essential oils were determined using a microplate assay. H. pendula essential oil elicited moderate AChE-inhibitory activity (IC50 = 130.65 ± 1.27 µg/mL). Our study is the first to show that H. pendula essential oil exhibits anti-AChE activity. This anti-cholinesterase activity may result from the high monoterpene content (α-pinene, δ-3-carene, and 1,8-cineole) observed in this study.17,18 Monoterpenoids can be either competitive or non-competitive cholinesterase inhibitors; given their lipophilicity, migration into and throughout membranous structures such as the blood–brain barrier may promote their AChE-inhibitory activities on its hydrophobic sites. 19 The AChE-inhibitory activity of H. pendula essential oil extract may also be explained by its high hydrocarbon sesquiterpene (11.5%) and oxygenated sesquiterpene (12.8%) content. Sesquiterpenes are lipophilic terpenes with a wide range of pharmacological properties, including AChE-inhibitory activity. In the literature, multiple sesquiterpenes have been shown to play crucial roles in improving cholinergic transmission by inhibiting AChE. 20 However, whether or not the three major sesquiterpene constituents of H. pendula oil—valerianol, δ-cadinene, and cubenol—can inhibit AChE activity is unknown. However, other studies contend that essential oils in which these components predominate have anti-AChE effects. 21 Hence, our findings indicate that these compounds in their purified forms should be investigated for their inhibitory effects.
Conclusion
This study is the first to report the biological activities and chemical composition of volatile compounds in H. pendula rhizome essential oil. Oxygenated monoterpenes predominated in rhizome essential oils from both H. pendula and H. cochinchinensis. Linalool, followed by terpinen-4-ol, were additional major compounds in both essential oils. Furthermore, we observed for the first time that H. cochinchinensis essential oil exhibits moderate anti-inflammatory activity and that H. pendula essential oil possesses anti-AChE activity. These bioactivity data indicate that these species should be examined further in future studies.
Materials and Methods
Plant Materials
The rhizomes of H. pendula were collected from Lam Dong Province, Vietnam (geographical coordinates: 11°25′25.3″N; 108°03′28.9″E) in January 2021 (Supplementary Figure S3). The plant was authenticated by Dr Chinh Tien Vu (Vietnam National Museum of Nature, VAST, Vietnam). The rhizomes of H. cochinchinensis were collected from Dong Nai Province, Vietnam (geographical coordinates: 11°22′51.1″N; 107°03′46.3″E) in May 2022 (Supplementary Figure S4). The plant was authenticated by Dr Anh Tuan Le (Mientrung Institute for Scientific Research, Vietnam National Museum of Nature, VAST, Vietnam). Voucher specimens (TNK-LD-01, TNK-DN-02) have been deposited at the Faculty of Pharmacy, Hue University of Medicine and Pharmacy, Hue University, Vietnam.
Distillation of the Essential Oils
The essential oils from H. pendula and H. cochinchinensis rhizomes were obtained by hydro-distillation. From 1 kg of each Homalomena rhizome, we obtained 1.5 mL of H. pendula essential oil and 2.0 mL of H. cochinchinensis essential oil. The essential oils were dried over anhydrous sodium sulfate to remove the remaining water and then the essential oils were kept under refrigeration until further experiments. The obtained essential oil was used to analyze chemical composition and evaluate biological activities. The essential oil yields were determined: H = VEO/m × 100%, where VEO is the volume of the extracted essential oil (mL) and m is the initial rhizomes biomass (g).
Gas Chromatography–Mass Spectrometry (GC–MS) Analysis
The chemical composition of the volatile compounds was identified using gas chromatography coupled with mass spectrometry (GC–MS). The GC–MS analyses were performed using a Shimadzu GCMS-QP2010 Plus system (Kyoto, Japan) with an Equity-5 capillary column (30 m × 0.25 mm, 0.25 m film thickness), and a mass spectrometer (MSD QP2010 Plus). The essential oil (1 mg) was diluted in a 1:100 ratio with dichloromethane, and 1 µL was used for analysis. The oven temperature was set at 60°C (2 minutes hold) and then programmed from 240°C at a rate 3°C/min (10 min hold) and increasing to 280°C at a rate of 5°C/min (40 minutes hold). The carrier gas was helium at a flow rate of 1.5 mL/min. Mass detector conditions were set up as follows: interface temperature 280°C and mass acquisition range 40–500. Splitless injection mode was used to inject the samples. The constituents were identified by matching their mass spectra to Wiley 7 and National Institute of Standards and Technology (NIST 11) library. In addition, a standard solution of C8–C38 alkanes was used to obtain the retention index of compounds and comparing them with literature values. 9 The relative amounts of individual components were calculated based on the peak area in GC–MS chromatogram without correction.
Anti-Inflammatory Assay
The inhibitory activity of essential oils against the production of nitrogen monoxide (NO) induced by lipopolysaccharide in RAW 264.7 cells was assessed. Nitrite concentration, a marker for the presence of NO in the culture medium, was measured using the Griess reaction. The detailed protocols for the evaluation were previously described in our reports.22,23
Acetylcholinesterase Inhibition Assay
The evaluation of essential oils for their AChE inhibitory activity was conducted using 96-well microtiter plates. The assay method was based on Ellman's method 24 with slight modification. The detailed protocols are presented in our previous publication. 25
Supplemental Material
sj-docx-1-npx-10.1177_1934578X231175263 - Supplemental material for Phytochemical Composition and Bioactivities of Essential Oils from Rhizomes of Homalomena pendula and Homalomena cochinchinensis
Supplemental material, sj-docx-1-npx-10.1177_1934578X231175263 for Phytochemical Composition and Bioactivities of Essential Oils from Rhizomes of Homalomena pendula and Homalomena cochinchinensis by Linh Thuy Khanh Nguyen, Tuan Quoc Doan and Phu Quynh Dinh Nguyen, Chau Bao Hoai Nguyen, Linh Thuy Thi Tran, Thi Van Anh Tran, Hoai Thi Nguyen, Duc Viet Ho in Natural Product Communications
Footnotes
Acknowledgements
This research was supported by Hue University (ID No. DHH2022-04-165), Vingroup Innovation Foundation (Nguyen Khanh Thuy Linh was funded by the Master, PhD Scholarship Programme of Vingroup Innovation Foundation (VINIF), code VINIF.2022.TS163). The authors also acknowledge the partial support of Hue University under the Core Research Program, Grant No. NCM.DHH.2023.02.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Ethical Approval
Not applicable, because this article does not contain any studies with human or animal subjects.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by Hue University (ID No. DHH2022-04-165), Vingroup Innovation Foundation (Nguyen Khanh Thuy Linh was funded by the Master, PhD Scholarship Programme of Vingroup Innovation Foundation (VINIF), code VINIF.2022.TS163). The authors also acknowledge the partial support of Hue University under the Core Research Program, Grant No. NCM.DHH.2023.02.
Informed Consent
Not applicable, because this article does not contain any studies with human or animal subjects.
Trial Registration
Not applicable, because this article does not contain any clinical trials.
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References
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