Introduction

 Plants have been used by Traditional healers for centuries as a source of curative agent, and it has been spread-out globally and is gaining fame [1]. In Ethiopia, about 80% of the people, especially those who are living outside the cities are still dependent on traditional medicines [2,3]. Among different Ethiopia plants, Acokanthera schimperia (A. DC.), which belongs to family Apocynaceae, is a well-known African arrow poison plant and dispersed in Eritrea, Ethiopia, Tanzania, West Uganda, Rwanda and Eastern DR Congo. Outside Africa, It is also found in southern Yemen [4]. In Ethiopia, it is a tree of dry woodland, thickets, and grasslands in Dry and Moist agro-climatic zones in nearly all regions [5].

 A. schimperia is a plant locally called “መረንዝ”, which means “Toxic” used for the preparation of arrow poison in East Africa. It is either used on its own or mixed with other plants or animal parts. The bark, wood, and roots are the usual ingredients for arrow poison, and they are also used for suicide and homicide. The poison from this plant is also used for hunting wild animals and stray dogs from fields and homes [6]. The leaves and bark are used to treat different disease and shows antiviral activity in the cases of skin disorders caused by viruses, and antimalarial activity [7]. In addition, Ethiopian traditional healers used this indigenous plant for the treatment of epilepsy, amnesia, eye disease, syphilis, rheumatic pain, elephantiasis, scabies, leprosy, wound, eczema and warts [8].

 Essential oils are combinations of volatile constituents that present at little amount in the plant, and used as flavor and fragrances agent in food, pharmaceutical and perfumery industries [9]. In this paper, we will focus on the essential oil from the leaves of A. schimperia, including its chemical constituents and bioactivities.

 Materials and Methods

 Plant material

In September 2015, the leaves of A. schimperia were collected from a well-known monastery called Debre Libanos which is 90km far from Addis Ababa, the capital city of Ethiopia and the species of the plant was identified by Amare Seifu Assefa, a botanist from the Ethiopian Biodiversity Institute.

 Extraction of essential oil

200 g coarsely grinded leaves of A. schimperia were socked in 350 mL tap water for 12 hrs and transferred to 3L volume Clevengers apparatus (flask). Then 1.5 L distilled water was added to maintain the level of water above the sample. After that the sample was subjected to steam distillation process for eight hrs. The distillates were saturated with NaCl and extracted by diethyl ether. The organic phase was dried by anhydrous Na₂SO₄ as water absorbent agent. Diethyl ether was removed from the oil by putting it at open air until the essential oil remains. Finally, the essential oil was stored at 4 °C in refrigerator for further use.

 Analysis of essential oil

The investigation of the essential oil were done by an Agilent 6890 gas chromatograph interfaced with an Agilent 5973N mass spectrometer engaged with an HP-5MS capillary column (30 m × 0.25 mm, 0.25 μm film thickness). The condition for Gas Chromatography (GC): the temperature programmed at 70 °C for the first 2 minutes, increased sequentially with a rate of 5 °C/minute until it reaches 300 °C. After that, the temperature was set to remain constant for the next 2 minutes; The injector temperature and volume were set at 250 °C and 1μL respectively; the carrier gas was Helium with flow rate 1 mL/min under split ratio of 1:20; Mass Spectrometry (MS) condition: EI ionization mode, 70eV, scan range 30-500 Amu, ion spring temperature was 230°C. Each constituents mass spectra were compared with the spectrometer database (NIST 11). For quantification purposes, relative area percentages were used without the use of correction factors.

 Antimicrobial activities

Escherichia coli (ATCC 25922) and Bacillus subtilis (ATCC 6633) were used for evaluation of antibacterial activities and Candida albicans (ATCC 60193) was used for antifungal evaluation. The bioassays tests were made in 96-well decontaminated micro-plates using a micro-dilution method [10, 11]. E. coli and B. subtilis were cultured for 18-hrs and added to Lysogeny Broth (LB) medium (1 L water, 10 g tryptone, 5 g yeast, and 10 g NaCl) to attain 1 × 105 CFU/ml, and C. albicans was grown for 4-days and added to Potato Dextrose Broth (PDB) medium (potato 20%, glucose 2%) to get 1 × 103 spores/mL. The test samples were dissolved by Dimethyl Sulfoxide (DMSO) to attain from 0.5 to 512 μg/mL concentration range, which were made by 2-fold sequential dilution method. The wells holding test strains and diluted samples were incubated for 24 hrs in isothermal condition (37 °C) for antibacterial bioassay. With the same condition for antifungal bioassay, the sample was incubated for 4 days at 28 °C. The wells which contain a culture suspension and DMSO were set as negative controls. Kanamycin and Nystatin were set as positive controls for bacteria and fungi respectively. All tests were performed twice. The Minimal Inhibitory Concentration (MIC) was well-thought-out as the lowest antibiotic concentration that indicates a total production inhibition for the tested microorganisms.

 Results and Discussion

The essential oil extracted from the leaves of A. schimperia gave pale yellow oil (yield 0.007 % w/w). The constituents of the essential oils with their retention time and relative percentages were given in Figure 1 and Table 1.

To View Figure 1, click below
Figure 1: GC-MS profile of essential oil from A. schimperia.

To View Table 1, click below
Table 1: Chemical components (%) of the essential oil from A. schimperia.

A total of twenty-one compounds were identified representing 75.52 % of the total essential oil of A. schimpera, and damascenone (14.83 %), dihydroactinidiolide (10.87 %), kaur-16-ene (5.74 %) and (E)-2-tridecenal(5.51 %) were the main components. Sesquiterpenoids, including six compounds, were found as major in the oil and represented 32.98 % of the total identified components. The essential oil extracted from the leaves of A. schimperia was tested for its antibacterial activity against E. coli (Gram-negative) and B. subtilis (Gram-positive), and its antifungal activities against C. albicans (fungi). The results as shown in Table 2 indicated that the essential oil from A. schimperia did not show any antimicrobial activities.

Table 2: Antimicrobial activities of the essential oil (MIC: μg/ml).

Conclusion

This report shows that the essential oil of A. schimperia is rich in terpenoids. However, the oil was not found to show any significant antimicrobial activities against E. coli, B. subtilis and C. albicans. Nevertheless, this is the first report on the essential oil of A. schimperia. According to literatures, A. schimperia can be found an attractive medicinal plant.  Although, several research works have been done on some plants of this genus till to date, but a large number of this plant is still chemically or pharmacologically unknown. Consequently, a broad future research remains possible in which the isolation of new active principles from A. schimperia would be a great scientific worth.

 References

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4.        Leeuwenberg AJM. Apocynaceae. In: Flora of Ethiopia and Eritrea (ed) Hedberg I, Edwards S and Nemomissa S (2003) The National Herbarium, Addis Ababa University, Addis Ababa, Ethiopia and Uppsala, Sweden, Europe 87-88.

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8.        Mohammed T, Erko B and Giday M. Evaluation of antimalarial activity of leaves of Acokanthera schimperi and Croton macrostachyus against Plasmodium berghei in Swiss albino mice (2014) BMC Complem Altern Med 14: 314. https://doi.org/10.1186/1472-6882-14-314

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 Corresponding author:

Xie G, University of Electronic Science and Technology of China, Chengdu, China, Tel: +86-28-83208238, E-mail: gbxie@uestc.edu.cn

Citation:

Matebie AW, Zhang W, Zhang S and Guangbo Xie. Essential oil and its antimicrobial activity from ethiopian Acokanthera schimperia (2019) Edelweiss Appli Sci Tech 3: 1-3

Keywords

Acokanthera schimperia, Essential oil, GC-MS, Antimicrobial activity.