A review on antimicrobial potential of species of the genus Vernonia (Asteraceae)

Pyrroloquinolones B-F: Five unusual alkaloids from Vernonia glabra (Steetz) Vatke (Asteraceae)

Five unusual alkaloids featuring a pyrrolo[1,2-a]quinolone skeleton (pyrroloquinolones B-F, 1-5) were isolated from the ethanol extract of the whole plant of Vernonia glabra (Steetz) Vatke, along with sixteen known compounds. Their structures were established by means of spectroscopic (1D and 2D NMR, UV, IR, and ECD) and high resolution mass spectrometric techniques as well as by comparison of their spectroscopic data with those reported in the literature. The ethanol extract and some isolated compounds were assessed for their antibacterial activity against four bacterial strains. The extract was significantly active against Staphylococcus aureus ATCC1026 and S. epidermidis ATCC35984 (MIC = 64 μg/mL). All the tested compounds showed moderate activity against S. epidermidis (16 ≤ MIC ≤ 64 μg/mL). Furthermore, this is the first report on tricyclic pyrrolo[1,2-a]quinolone alkaloids from a plant source. A biosynthetic pathway for the formation of these compounds is also proposed.

Evaluation of the Antioxidant and Wound Healing Properties of 80% Methanol Extract and Solvent Fractions of the Leaves of Vernonia auriculifera Hiern. (Asteraceae)

Background

The leaves of Vernonia auriculifera (Asteraceae) have traditionally been used to treat wounds in several regions of Ethiopia. The purpose of this study was to assess the wound healing properties of the leaf extract and solvent fractions of V. auriculifera in mice. The leaf extract and solvent fractions of V. auriculifera have also been evaluated for their anti-oxidant properties because of their impact on the wound healing process.

Material and Methods

Air-dried leaves were extracted using 80% methanol. They were also successively fractionated with n-hexane, ethyl acetate, and methanol. The residue was then macerated in water for 72 hr. Simple ointment bases were formulated according to British Pharmacopoeia. Thereafter, two types of ointment formulations, 2.5% w/w and 5% w/w, were formulated. Wound healing and acute dermal toxicity studies were performed on mice. To assess free radical scavenging activity, a 2,2-diphenyl-2-picrylhydrazyl free radical (DPPH) assay was performed.

Results

In both models, wounds treated with 2.5% and 5% (w/w) of the ME, the aqueous fraction (AQF), methanol fraction (MEF), and ethyl acetate fraction (EAF) ointments demonstrated significant wound healing activity, as shown by enhanced wound contraction, a shortened epithelialization time, increased hydroxyproline content, and enhanced tissue breaking strength. The extract and solvent fractions displayed free radical scavenging activity with IC50 values of 1.2 mg/mL, 1.46 mg/mL, 1.5 mg/mL, and 2.83 mg/mL for ME, AQF, MEF, and EAF, respectively, as compared to 1.42 mg/mL for ascorbic acid.

Conclusion

The result of this study indicates that 80% of methanol extract and solvent fractions are endowed with wound healing activity. Additionally, this study has also revealed that ME, AQF, MEF, and EAF have the capacity to scavenge free radicals. The study indicated that the wound healing effect could be attributed to the anti-inflammatory and antioxidant activities.

Analgesic and Anti-Inflammatory Effects of 80% Methanol Extract and Solvent Fractions of the Leaves of Vernonia auriculifera Hiern. (Asteraceae)

Background

The leaves of V. auriculifera has been used traditionally for the treatment of inflammatory disorders, and pain in various parts of Ethiopia. However, to our knowledge, the analgesic and anti-inflammatory activity of the crude extract and solvent fractions has never been experimentally studied.

Objective

To assess the analgesic and anti-inflammatory activities of V. auriculifera leaf extract and solvent fractions in rodent models.

Material and methods

Air-dried leaves of V. auriculifera were grounded and macerated using 80% methanol. The air-dried, grounded leaves were also successively extracted with ethyl acetate, and methanol. The residue was then macerated in water for 72 hr. The extract's peripheral analgesic activity, as well as the solvent fractions, were determined using an acetic acid-induced writhing test. The hot plate model was used to assess the central analgesic effect. Carrageenan-induced hind paw edema and cotton pellet-induced granuloma models were used to assess the anti-inflammatory effect in rats.

Results

The 80% methanol leaf extract and solvent fractions have demonstrated significant (p < 0.05) peripheral and central analgesic activity. Both 80% methanol leaf extract and solvent fractions of V. auriculifera were found to have anti-inflammatory activity in a carrageenan-induced rat paw edema model. In the cotton pellet-induced granuloma model, all concentrations of 80% methanol leaf extract (ME), methanol fraction (MEF), and aqueous fractions (AQF) of V. auriculifera inhibited exudate and granuloma formation. Although all tested doses significantly inhibited granuloma mass formation, only the medium and highest ethyl acetate fraction (EAF) doses significantly inhibited the generation of inflammatory exudate.

Conclusion

This study's findings indicate that the solvent fractions and 80% methanol extract of V. auriculifera have analgesic and anti-inflammatory properties. This study's findings not only confirm the plants' traditional claim but also provide clues for further investigation of the active principles of this plant for the development of effective and safe analgesic and anti-inflammatory drugs.

Comparative studies on the hypoglycemic and antioxidant activities of Vernonia amygdalina delile and Baccharoides tenoreana olive in alloxan-induced hyperglycemic rats

Background

Vernonia amygdalina is a bitter culinary vegetable known to possess anti-diabetic principle. Baccharoides tenoreana belonging to the same species as V. amygdalina, is also used in cooking soup and it is comparatively non-bitter. However, its glycemic properties have not been studied. This study becomes imperative to find out if B. tenoreana possesses hypoglycemic and antioxidant properties and how it compares with V. amygdalina. Should B. tenoreana be better than V. amygdalina, it should be preferable since it is non-bitter and can comfortably be taken compared to V. amygdalina. This study investigated the comparative hypoglycemic and antioxidant potentials of V. amygdalina (VA) and B. tenoreana (BT).

Methods

Thirty male Albino wistar rats assigned into six groups of five rats per group were used for the study. Diabetes was induced in groups B-F rats by a single intraperitoneal injection of alloxan monohydrate at 160 mg/kg. Groups C-E rats were treated with VA (200 mg/kg), BT (200 mg/kg) and combination of VA & BT (100 mg/kg each) respectively. Group F rats were administered glibenclamide (2 mg/kg) whereas groups A and B rats were given distilled water. All treatments were through the oral administration, once daily for 21 consecutive days. Fasting blood glucose (FBG) levels were determined after 1 h, 3 h, 6 h, 24 h, 7 days, 14 days and 21 days while lipid profile, in vivo antioxidant and pancreatic histomorphology were assessed on day 21 post-treatment.

Results

The VA-treated rats recorded marginally reduced FBG, malondialdehyde and low-density lipoprotein levels when compared to the counterpart treated with BT. The high-density lipoprotein values were significantly higher in VA-treated rats than in BT-treated rats. The histomorphology of the pancreas of VA-treated rats expressed more islet cells compared to the counterpart treated with VT.

Conclusion

Both VA and BT exhibited hypoglycemic and antioxidant activities with varying potencies.

Evaluation of Wound Healing Activity of Methanolic Crude Extract and Solvent Fractions of the Leaves of Vernonia auriculifera Hiern (Asteraceae) in Mice

Background

Medicinal plants play an important role in treating various diseases. Vernonia auriculifera Hiern is one of the medicinal plants used traditionally for the management of wounds. However, there were no scientific reports documented so far on the wound healing activities to substantiate the claim. Thus, the present study provides a scientific evaluation for the wound healing potential of the crude extract as well as solvent fractions of the leaves of Vernonia auriculifera Hiern.

Methods

Extraction was carried out by maceration using 80% methanol and part of the crude extract fractionated with chloroform, ethyl acetate, and aqueous solvents. Simple ointment bases were prepared using hard paraffin, cetostearyl alcohol, white soft paraffin and wool fat according to British Pharmacopoeia. Then, two types of ointment formulations were prepared from the extract, ie, 5% w/w and 10% w/w. Mice and rats were employed for wound healing study and dermal toxicity test, respectively. Wound healing effects were evaluated by percent of wound contraction, period of epithelialization, tensile strength, and histological analysis as parameters in excision, incision, and burn wound models. Finally, the data were expressed as mean ± SEM, and the results were analyzed using one-way ANOVA followed by post hoc Tukey-test.

Results

In the excision wound model, the 10% w/w crude extract ointment showed significant wound contraction (P < 0.001) from day 4 to day 18 as compared to the negative control. Both the 5% w/w (P < 0.001) and 10% w/w (P < 0.05) crude extract ointments have showed statistically significant difference in epithelialization period as compared to the negative control. Groups treated with the ethyl acetate and aqueous fractions ointments in incision wound model showed a statistically significant (P < 0.001) increase in tensile. The 10% w/w and 5% w/w ointments of the crude extract showed a significant (P < 0.001) increase in breaking strength compared to simple ointment and the untreated control groups. In burn wound model, significant reduction in epithelialization period was observed in 5% w/w (P < 0.05) and 10% w/w (P < 0.001), and the percentage of wound contraction was significantly increased in most of post wounding days by 10% w/w (P < 0.001) and 5% w/w (P < 0.05) crude extract ointments and compared to the negative control.

Conclusion

The crude, aqueous, and ethyl acetate fraction of Vernonia auriculifera leaves possess wound healing activities. This finding justifies the use of the leaves of this plant for wound healing as claimed in the traditional medicine literature.

Antibacterial secondary metabolites from Vernonia auriculifera Hiern (Asteraceae) against MDR phenotypes

Purification of the aerial parts of Vernonia auriculifera Hiern afforded steroids (1-2), flavonoids (3-5), and polyalcohol (6). Their structures were determined using spectral evidences as well as by comparison with reported data. Iodonitrotetrazolium chloride (INT) colorimetric assay was used to assess the antibacterial activity of the extract and isolates against 13 pathogenic strains. The crude extract showed strong antibacterial activity (MIC < 100 µg/mL) against the tested bacterial strains. When combined with an efflux pump inhibitor phenylalanine beta naphthylamide (PAβN), the inhibition potency of the extract was substantially enhanced with the lowest MIC value at 4 µg/mL. Compounds 5 and 6 showed moderate activity (MIC < 100 µg/mL) against 12/13 (92.3%), and 8/13 (61.5%) bacterial strains, respectively. A minimal bactericidal concentration (MBC)/minimal inhibitory concentration (MIC) ratio ≤ 4 indicated their bactericidal effect against Escherichia coli, Enterbacter aerogenes, Klebsiella pneumoniae, Providencia stuartii, Pseudomonas aeruginosa, and Staphylococcus aureus.

Secondary metabolite contents and antimicrobial activity of leaf extracts reveal genetic variability of Vernonia amygdalina and Vernonia calvoana morphotypes

Vernonia species (Asteraceae) are indigenous medicinal and food leaf vegetables commonly consumed in some African countries like Cameroon where they constitute a staple dish called "ndolé." Previous studies have demonstrated the nutritional importance of Vernonia, but there is little knowledge of their agronomic value and genetic potentials. Wide genetic variability in the genus has been established earlier through the study of its pollen. However, to the best of our understanding, no such study has been undertaken on the genetic variability of Vernonia with respect to its secondary metabolites. This study was therefore aimed at evaluating the genetic variability of Vernonia amygdalina (VAA and VALF) and V. calvoana (VCAB, VCAV, VCSB, and VCSV) morphotypes in 2016 based on secondary metabolite content and antimicrobial properties. This involved phytochemical analysis by HPLC/MS for the detection of alkaloids, flavonoids, phenols, and tannins in leaves from each of the six genotypes. Results showed that all tested genotypes are rich in phenols (18 analyzed), flavonoids, and tannins with, VAA richer in phenols (206.1 ± 3.12 µg/g of dry extract), followed by VCAV (197.9 ± 18.03 µg/g). The lowest level of flavonoid was found in VCSV (81.6 ± 7.21 µg/g), while the highest was from VCAB (132.8 ± 31.5 µg/g). VCSV (56.3 ± 4.08 µg/g) had the lowest level of tannins, while VCAB (97.8 ± 23.8 µg/g) had the highest levels. Assessment of antimicrobial activity of leaf extracts from the six genotypes was done by culture on Mueller Hinton (MH) agar and MH broth agar for bacteria and in Sabouraud dextrose agar and Sabouraud dextrose broth media for fungi, respectively. All morphotypes exhibited inhibitory activity on bacteria except VAA, with isoquercetin characteristic of VCSV. Chemotaxonomic analyses of Vernonia morphotypes highlighted the genetic diversity within species and variability of antimicrobial properties of ethanolic leaf extracts among morphotypes. These results provide baseline data in the valuation of genetic resources and the establishment of improvement programs.

Isolation of a New Sesquiterpene Lactone From Vernonia Zeylanica (L) Less and its Anti-Proliferative Effects in Breast Cancer Cell Lines

Background/Objective:

Vernonia zeylanica (L) less is an endemic plant to Sri Lanka. The present study was designed to isolate potential cytotoxic compound/s from chloroform and ethyl acetate extracts of V. zeylanica by bio-activity guided isolation and to evaluate its anti-proliferative effects in three breast cancer phenotypes (MCF -7, MDA-MB-231, SKBR-3).

Methods:

Combined chloroform and ethyl acetate extracts were subjected to chromatographic separations to isolate a compound (1) and the structure of the isolated compound was elucidated using 1H, 13C and mass spectroscopic techniques. Cytotoxic effects of the compound were evaluated by the sulforhodamine B (SRB) and the MTT (3- (4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays. Effects of the compound on apoptosis were evaluated by fluorescent microscopy, caspase 3/7 activation, DNA fragmentation and real time PCR. Effects of the compound on the expression of heat shock protein complex were also evaluated by real time PCR and immunofluorescence.

Results:

Isolated compound was identified as a new sesquiterpene lactone (vernolactone). The compound mediated significant cytotoxic effects in SKBR-3 and MDA-MB-231 breast cancer cells, with little effect in MCF-7 and normal mammary epithelial MCF-10A cells. Morphological changes, DNA fragmentation, increased caspase 3/7 activities and up-regulation of p53, Bax and down regulation of Survivin confirmed the proapoptotic effects of the compound. Significant inhibition of HSP complex related genes were also observed in SKBR-3 and MDA-MB-231 breast cancer cells.

Conclusion:

Overall results indicate that vernolactone can mediate its cytotoxic effects via apoptosis and modulating the HSP complex.

Antibacterial and Antioxidant Compounds from the Flower Extracts of Vernonia amygdalina

Vernonia amygdalina is traditionally used in Ethiopia to treat various diseases. This prompted us to isolate bioactive compounds from the flowers of this plant. The CHCl₃ extract after silica gel column chromatography has led to the isolation of two compounds identified as tricosane (1) and vernolide (2), while the acetone extract furnished isorhamnetin (3) and luteolin (4). The acetone extract and isorhamnetin significantly scavenged the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical by 91.6 and 94%, respectively. It was also shown that the acetone extract and isorhamnetin inhibited lipid peroxidation by 74 and 80%, respectively. The extracts and isolated compounds were also evaluated for their antibacterial activity with the CHCl₃ extract and vernolide showing strong activity against S. aureus with an inhibition zone of 21 and 19 mm, respectively. On the other hand, the acetone extract and isorhamnetin were active against all bacterial pathogens tested. The work presented herein has demonstrated that vernolide and isorhamnetin had antibacterial activity. The antioxidant activity displayed by the flowers of V. amygdalina is accounted to the presence of isorhamnetin. Therefore, the biological activities displayed by the extracts and isolated compounds from this plant corroborate the traditional uses of this plant by the local people against various diseases.

Synthesis and anticancer studies of Michael adducts and Heck arylation products of sesquiterpene lactones, zaluzanin D and zaluzanin C from Vernonia arborea

Sesquiterpene lactones containing α-methylene-γ-lactones, zaluzanin D 1 and zaluzanin C 2 were isolated from the leaves of Vernonia arborea. Several diverse Michael adducts (3–22) and Heck arylation analogs (23–34) of 1 have been synthesized by reacting with various amines and aryl iodides, respectively and were assayed for their in vitro anticancer activities against human breast cancer cell lines MCF7 and MDA-MB-231. Among all the synthesized analogs, Michael adducts 9 and 10 showed better anticancer activities as compared to 1. However, among these compounds, only 10 has minimal cytotoxic effect on normal breast epithelial MCF10A cells. Our detailed mechanistic studies reveal that compounds 9 and 10 execute their antiproliferative activity through induction of apoptosis and thereby inhibit the cancer cells proliferation and compound 10 could be a lead compound for designing potential anti-cancer compound.

Sesquiterpene lactones containing α-methylene-γ-lactones, zaluzanin D 1 and zaluzanin C 2 were isolated from the leaves of Vernonia arborea.