Search for antibacterial agents from Malaysian rainforest and tropical plants

Alternanthera sessilis: Uncovering the nutritional and medicinal values of an edible weed

ETHNOPHARMACOLOGICAL RELEVANCE

Weeds are often considered undesirable as they interfere with the habitat of native plants, and therefore they are underestimated and underutilised. In fact, some edible weeds have beneficial nutritional and medicinal values. Alternanthera sessilis (L.) R. Br. ex DC., an edible medicinal weed is a species of the Amaranthaceae family that consists of two cultivars: green and red. Local communities in different regions have traditionally consumed the plants as food and medicine, with the green cultivar being applied to relieve pain, treat wound healing, dysentery, asthma and hypertension, while the red cultivar is applied to prevent cardiovascular and liver diseases in general.

AIM OF THE STUDY

The present review intends to provide an in-depth discussion and scientific basis of A. sessilis green and red's health-promoting properties in relation to their ethnobotanical use, nutritional components and bioactive compounds.

MATERIALS AND METHODS

The literature search was conducted using relevant keywords on scientific search engines such as the Web of Science, Google Scholar, Medline and Scopus.

RESULTS

A. sessilis shows potent antioxidant activity as a result of its diverse phytochemical constituents, such as polyphenols, terpenes, alkaloid and carotenoids in addition to its nutritional components: vitamin C, E and unsaturated fatty acids, which contribute to its various bioactive properties: anti-microbial and anthelmintic, anti-diabetic, lipid lowering, anti-inflammatory and analgesic activities, anti-cancer and other biological activities. Toxicity evaluation revealed the absence of adverse effect of A. sesslis extracts.

CONCLUSION

A. sessilis has a great potential to be used as complementary medicine and ingredients for pharmaceuticals, nutraceuticals and functional foods, instead of being regarded as a pest. Prospects for enhancing the development and commercialisation of this edible medicinal weed as a high value health-promoting product are suggested.

Chemical composition and anticholinesterase inhibitory activity of the essential oil of Pseuduvaria macrophylla (Oliv.) Merr. from Malaysia

This study was designed to examine the chemical composition and anticholinesterase inhibitory activity of the essential oil of Pseuduvaria macrophylla (Oliv.) Merr. (Annonaceae) from Malaysia. The essential oil was obtained by hydrodistillation and fully analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The analysis led to the identification of thirty-four chemical components that represented 87.7 ± 0.5% of the total oil. The essential oil was found to be rich in germacrene D (21.1 ± 0.4%), bicyclogermacrene (10.5 ± 0.5%), δ-cadinene (5.6 ± 0.2%), α-copaene (5.1 ± 0.3%), and α-cadinol (5.0 ± 0.3%). Anticholinesterase activity was evaluated using Ellman method. The essential oil showed weak inhibitory activity against acetylcholinesterase (I%: 32.5%) and butyrylcholinesterase (I%: 35.4%) assays. Our findings demonstrate that the essential oil could be very useful for the characterization, pharmaceutical and therapeutic applications of the essential oil from Pseuduvaria macrophylla.

Antiviral and virucidal activities of Duabanga grandiflora leaf extract against Pseudorabies virus in vitro

BACKGROUND

Duabanga grandiflora or known in Malaysia as Berembang Bukit, Megawasih, or Pedada Bukit, is a native plant of the Southeast Asian countries. In this study, the anti-viral properties of D. grandiflora were investigated.

METHODS

The D. grandiflora leaf extracts were obtained with ethyl acetate, hexane, and ethanol as solvents and labelled 37 leaf ethyl acetate (37 L EA), 37 leaf hexane (37 L H), 37 leaf ethanol (37 L ET), respectively. The cytotoxicity of the extracts on Vero cells were determined by the 3-(4,5-Diamethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay.

RESULTS

Among extracts, 37 L EA was most cytotoxic to Vero cells, followed by 37 L H and 37 L ET, with CC50 of 218, 833, and >1000 μg/mL, respectively. The cytopathic effect (CPE) and plaque reduction, inhibition, and virucidal assays and the selective index (SI) were employed to determine the effect of the extracts on infectivity and replication of pseudorabies virus (PrV) in Vero cells. The D. grandiflora leaf extracts showed dose-dependent antiviral activities, with higher activities at high doses. The 37 L ET and 37 L EA showed anti-viral effects through plaque formation and viral replication inhibitions, and virucidal property. The SI of the 37 L ET and 37 L EA by the viral replication inhibition assay was 8.3 and 1.9, respectively, and by the CPE reduction assay, 6.7 and 2.9, respectively.

CONCLUSION

Ethanol is the best solvent for the preparation of D. grandiflora leaf extract as an antiviral agent.

Inhibition of penicillin-binding protein 2a (PBP2a) in methicillin resistant Staphylococcus aureus (MRSA) by combination of ampicillin and a bioactive fraction from Duabanga grandiflora

Background

The inhibition of penicillin-binding protein 2a (PBP2a) is a promising solution in overcoming resistance of methicillin resistance Staphylococcus aureus (MRSA). A potential approach in achieving this is by combining natural product with currently available antibiotics to restore the activity as well as to amplify the therapeutic ability of the drugs. We studied inhibition effects of a bioactive fraction, F-10 (isolated from the leaves of Duabanga grandiflora) alone and in combination with a beta-lactam drug, ampicillin on MRSA growth and expression of PBP2a. Additionally, phytochemical analysis was conducted on F-10 to identify the classes of phytochemicals present.

Methods

Fractionation of the ethyl acetate leaf extract was achieved by successive column chromatography which eventually led to isolation of an active fraction, F-10. Both extract and F-10 were analyzed for the presence of major classes of phytochemicals in addition to obtaining a high performance liquid chromatography (HPLC) profile to reveal the complexity of the fraction F-10. Broth microdilution method was employed to determine minimum inhibitory concentration (MIC) of the extract and fractions against MRSA. Evaluation of synergistic activity of the active fraction with ampicillin was determined using checkerboard methodand kinetic growth experiments. Effect of combination treatments on expression of PBP2a, a protein that confers resistance to beta-lactam antibiotics, was elucidated with the Western blot assay.

Results

MIC of F-10 against MRSA was 750 mg/L which showed an improved activity by 4-fold compared to its crude extract (MIC = 3000 mg/L). Phytochemical analysis revealed occurrence of tannins, saponin, flavonoids, sterols, and glycosides in F10 fraction. In FIC index interpretation, the most synergistic activity was achieved for combinations of 1/64 × MIC ampicillin + 1/4 × MIC F-10. The combination also evidently inhibited MRSA growth in kinetic growth curve assay. As a result of this synergistic interaction, MIC of ampicillin against MRSA was reduced to 0.78 mg/L (64-fold) from initial value of 50 mg/L. Western blot analysis suggested inhibition of PBP2a in MRSA cultures grown in synergistic combination treatment in which no PBP2a band was expressed.

Conclusions

The results demonstrated synergism between fraction F-10 of D. grandiflora with ampicillin in suppressing MRSA growth via PBP2a inhibition.

(6E,10E) Isopolycerasoidol and (6E,10E) Isopolycerasoidol Methyl Ester, Prenylated Benzopyran Derivatives from Pseuduvaria monticola Induce Mitochondrial-Mediated Apoptosis in Human Breast Adenocarcinoma Cells

Phytochemicals from Pseuduvaria species have been reported to display a wide range of biological activities. In the present study, a known benzopyran derivative, (6E,10E) isopolycerasoidol (1), and a new benzopyran derivative, (6E,10E) isopolycerasoidol methyl ester (2), were isolated from a methanol extract of Pseuduvaria monticola leaves. The structures of the isolated compounds were elucidated by spectroscopic methods including 1D and 2D NMR, IR, UV, and LCMS-QTOF, and by comparison with previously published data. The anti-proliferative and cytotoxic effects of these compounds on human breast cancer cell-lines (MCF-7 and MDA-MB-231) and a human normal breast epithelial cell line (MCF-10A) were investigated. MTT results revealed both (1) and (2) were efficient in reducing cell viability of breast cancer cells. Flow cytometry analysis demonstrated that (1) and (2) induced cell death via apoptosis, as demonstrated by an increase in phosphotidylserine exposure. Both compounds elevated ROS production, leading to reduced mitochondrial membrane potential and increased plasma membrane permeability in breast cancer cells. These effects occurred concomitantly with a dose-dependent activation of caspase 3/7 and 9, a down-regulation of the anti-apoptotic gene BCL2 and the accumulation of p38 MAPK in the nucleus. Taken together, our data demonstrate that (1) and (2) induce intrinsic mitochondrial-mediated apoptosis in human breast cancer cells, which provides the first pharmacological evidence for their future development as anticancer agents.

Inhibitory effect of Duabanga grandiflora on MRSA biofilm formation via prevention of cell-surface attachment and PBP2a production

Formation of biofilms is a major factor for nosocomial infections associated with methicillin-resistance Staphylococcus aureus (MRSA). This study was carried out to determine the ability of a fraction, F-10, derived from the plant Duabanga grandiflora to inhibit MRSA biofilm formation. Inhibition of biofilm production and microtiter attachment assays were employed to study the anti-biofilm activity of F-10, while latex agglutination test was performed to study the influence of F-10 on penicillin-binding protein 2a (PBP2a) level in MRSA biofilm. PBP2a is a protein that confers resistance to beta-lactam antibiotics. The results showed that, F-10 at minimum inhibitory concentration (MIC, 0.75 mg/mL) inhibited biofilm production by 66.10%; inhibited cell-surface attachment by more than 95%; and a reduced PBP2a level in the MRSA biofilm was observed. Although ampicilin was more effective in inhibiting biofilm production (MIC of 0.05 mg/mL, 84.49%) compared to F-10, the antibiotic was less effective in preventing cell-surface attachment. A higher level of PBP2a was detected in ampicillin-treated MRSA showing the development of further resistance in these colonies. This study has shown that F-10 possesses anti-biofilm activity, which can be attributed to its ability to reduce cell-surface attachment and attenuate the level of PBP2a that we postulated to play a crucial role in mediating biofilm formation.

Reversal of ampicillin resistance in MRSA via inhibition of penicillin-binding protein 2a by Acalypha wilkesiana

The inhibitory activity of a semipure fraction from the plant, Acalypha wilkesiana assigned as 9EA-FC-B, alone and in combination with ampicillin, was studied against methicillin-resistant Staphylococcus aureus (MRSA). In addition, effects of the combination treatment on PBP2a expression were investigated. Microdilution assay was used to determine the minimal inhibitory concentrations (MIC). Synergistic effects of 9EA-FC-B with ampicillin were determined using the fractional inhibitory concentration (FIC) index and kinetic growth curve assay. Western blot experiments were carried out to study the PBP2a expression in treated MRSA cultures. The results showed a synergistic effect between ampicillin and 9EA-FC-B treatment with the lowest FIC index of 0.19 (synergism ≤ 0.5). The presence of 9EA-FC-B reduced the MIC of ampicillin from 50 to 1.56 μg mL⁻¹. When ampicillin and 9EA-FC-B were combined at subinhibitory level, the kinetic growth curves were suppressed. The antibacterial effect of 9EA-FC-B and ampicillin was shown to be synergistic. The synergism is due the ability of 9EA-FC-B to suppress the activity of PBP2a, thus restoring the susceptibility of MRSA to ampicillin. Corilagin was postulated to be the constituent responsible for the synergistic activity showed by 9EA-FC-B.

Acalypha wilkesiana extracts induce apoptosis by causing single strand and double strand DNA breaks

ETHNOPHARMACOLOGICAL RELEVANCE

The seeds of Acalypha wilkesiana have been used empirically by traditional healers in Southwest Nigeria together with other plants as a powder mixture to treat patients with breast tumours and inflammation.

AIM OF THE STUDY

There is an increasing interest among researchers in searching for new anticancer drugs from natural resources, particularly plants. This study aimed to investigate the anticancer properties of Acalypha wilkesiana extracts and the characteristics of DNA damage against brain and lung cancer cells.

MATERIALS AND METHODS

The antiproliferative activity of Acalypha wilkesiana extracts (ethyl acetate, hexane, and ethanol) was examined on human glioma (U87MG), human lung carcinoma (A549), and human lung fibroblast (MRC5) cells.

RESULTS

Cell viability MTT assay revealed that ethyl acetate extract of the plant possessed significant antiproliferative effects against both U87MG (GI(50)=28.03 ± 6.44 μg/ml) and A549 (GI(50)=89.63 ± 2.12 μg/ml) cells (p value<0.0001). The hexane extract was found to exhibit crucial antiproliferative effects on U87MG (GI(50)=166.30 ± 30.50 μg/ml) (p value<0.0001) but not on A549 cells. Neither plant extract possessed noticeable antiproliferative effects on the non-cancerous MRC5 cells (GI(50)>300 μg/ml). The ethanol extract showed no antiproliferative effects on any cell line examined. Haematoxylin & Eosin (H & E) staining and single cell gel electrophoresis (SCGE) comet assay confirmed that plant extract-treated cells underwent apoptosis and not necrosis. SCGE comet assays confirmed that plant extracts caused both single strand (SSB) and double strand (DSB) DNA breaks that led to the execution of apoptosis.

CONCLUSION

The extracts (especially ethyl acetate and hexane) of Acalypha wilkesiana possess valuable cytotoxic effects that trigger apoptosis in U87MG and A549 cancer cells through induction of DNA SSBs and DSBs.