Antibacterial activities of the methanol extracts and compounds from Erythrina sigmoidea against Gram-negative multi-drug resistant phenotypes

Pharmacology activity, toxicity, and clinical trials of Erythrina genus plants (Fabaceae): an evidence-based review

The concept of using plants to alleviate diseases is always challenging. In West Java, Indonesia, a local plant, named dadap serep has been traditionally used to reduce blood glucose, fever, and edema, by pounding the leaves and applying them on the inflamed skin, or boiled and consumed as herbal tea. This plant belongs to the Erythrina genus, which covers approximately 120 species. The scope of this review (1943-2023) is related to the Global Development Goals, in particular Goal 3: Good Health and Wellbeing, by focusing on the pharmacology activity, toxicity, and clinical trials of Erythrina genus plants and their metabolites, e.g., pterocarpans, alkaloids, and flavonoids. Articles were searched on PubMed and ScienceDirect databases, using "Erythrina" AND "pharmacology activity" keywords, and only original articles written in English and open access were included. In vitro and in vivo studies reveal promising results, particularly for antibacterial and anticancer activities. The toxicity and clinical studies of Erythrina genus plants are limitedly reported. Considering that extensive caution should be taken when prescribing botanical drugs for patients parallelly taking a narrow therapeutic window drug, it is confirmed that no interactions of the Erythrina genus were recorded, indicating the safety of the studied plants. We, therefore, concluded that Erythrina genus plants are promising to be further explored for their effects in various signaling pathways as future plant-based drug candidates.

In Silico and In Vitro Identification of P-Glycoprotein Inhibitors from a Library of 375 Phytochemicals

Cancer therapy with clinically established anticancer drugs is frequently hampered by the development of drug resistance of tumors and severe side effects in normal organs and tissues. The demand for powerful, but less toxic, drugs is high. Phytochemicals represent an important reservoir for drug development and frequently exert less toxicity than synthetic drugs. Bioinformatics can accelerate and simplify the highly complex, time-consuming, and expensive drug development process. Here, we analyzed 375 phytochemicals using virtual screenings, molecular docking, and in silico toxicity predictions. Based on these in silico studies, six candidate compounds were further investigated in vitro. Resazurin assays were performed to determine the growth-inhibitory effects towards wild-type CCRF-CEM leukemia cells and their multidrug-resistant, P-glycoprotein (P-gp)-overexpressing subline, CEM/ADR5000. Flow cytometry was used to measure the potential to measure P-gp-mediated doxorubicin transport. Bidwillon A, neobavaisoflavone, coptisine, and z-guggulsterone all showed growth-inhibitory effects and moderate P-gp inhibition, whereas miltirone and chamazulene strongly inhibited tumor cell growth and strongly increased intracellular doxorubicin uptake. Bidwillon A and miltirone were selected for molecular docking to wildtype and mutated P-gp forms in closed and open conformations. The P-gp homology models harbored clinically relevant mutations, i.e., six single missense mutations (F336Y, A718C, Q725A, F728A, M949C, Y953C), three double mutations (Y310A-F728A; F343C-V982C; Y953A-F978A), or one quadruple mutation (Y307C-F728A-Y953A-F978A). The mutants did not show major differences in binding energies compared to wildtypes. Closed P-gp forms generally showed higher binding affinities than open ones. Closed conformations might stabilize the binding, thereby leading to higher binding affinities, while open conformations may favor the release of compounds into the extracellular space. In conclusion, this study described the capability of selected phytochemicals to overcome multidrug resistance.

Review on Plant-Based Management in Combating Antimicrobial Resistance - Mechanistic Perspective

Antimicrobial resistance (AMR) occurs when microbes no longer respond to any pharmacological agents, rendering the conventional antimicrobial agents ineffective. AMR has been classified as one of the top 10 life-threatening global health problems needed multilevel attention and global cooperation to attain the Sustainable Development Goals (SDGs) according to the World Health Organization (WHO), making the discovery of a new and effective antimicrobial agent a priority. The recommended treatments for drug-resistant microbes are available but limited. Furthermore, the transformation of microbes over time increases the risk of developing drug resistance. Hence, plant metabolites such as terpenes, phenolic compounds and alkaloids are widely studied due to their antibacterial, antiviral, antifungal and antiparasitic effects. Plant-derived antimicrobials are preferred due to their desirable efficacy and safety profile. Plant metabolites work by targeting microbial cell membranes, interfering with the synthesis of microbial DNA/RNA/enzymes and disrupting quorum sensing and efflux pump expression. They also work synergistically with conventional antibiotics to enhance antimicrobial effects. Accordingly, this review aims to identify currently available pharmacological therapies against microbes and AMR, as well as to discuss the importance of plant and secondary metabolites as a possible solution for AMR together with their mechanisms of action. All the information was obtained from government databases, WHO websites, PubMed, Springer, Google Scholar and Science Direct. Based on the information obtained, AMR is regarded as a significant warning to global healthcare. Plant derivatives such as secondary metabolites may be considered as potential therapeutic targets to mitigate the non-ending AMR.

Neobavaisoflavone inhibits allergic inflammatory responses by suppressing mast cell activation

Neobavaisoflavone (NBIF), a monomolecular compound extracted from Psoralea corylifolia (Leguminosae), is commonly used in traditional Chinese medicine for multiple purposes. NBIF is known to exert anti-fungal and anti-tumor effects, and promote bone formation. Whether NBIF exhibits anti-allergic effects by regulating mast cell activation remains unclear. Therefore, we designed this study to investigate the anti-allergic effects of NBIF on IgE/Ag-induced mouse bone marrow-derived mast cells and ovalbumin-induced asthma, and the passive systemic anaphylaxis (PSA) reaction in mice. Our results showed that NBIF suppresses the production of leukotriene C4, prostaglandin D2 and inflammatory cytokines, and decreases the degranulation of BMMCs stimulated by IgE/Ag. A thorough investigation ascertained that NBIF suppresses the phosphorylation of mitogen-activated protein kinases, and represses the nuclear factor-κB-related signaling pathway. In addition, the oral administration of NBIF in mice inhibited the IgE-induced PSA reaction in a dose-dependent manner. Overall, we provide new insights into how NBIF regulates the IgE/Ag-mediated signaling pathways. Moreover, our investigation promotes the potential use of NBIF in treating allergy and asthma.

Bioactivity of Natural Polyphenols as Antiparasitic Agents and their Biochemical Targets

BACKGROUND

Leishmaniasis and trypanosomiasis are diseases that affect public health worldwide due to their high incidence, morbidity, and mortality. Available treatments are costly, prolonged, and toxic, not to mention the problem of parasite resistance. The development of alternative treatments is justified and polyphenols show promising activity.

OBJECTIVE

The main aim of this mini-review was to analyze the most promising phenolic compounds with reported antileishmanial and antitrypanosomal activity as well as their mechanisms of action.

RESULTS

We found that the mode of action of these natural compounds mainly lignans, neolignans, and flavonoids depends on the organism they act on and includes, macrophage activation, induction of morphological changes such as chromatin condensation, DNA fragmentation, accumulation of acidocalcisomes, and glycosomes, Golgi damage and mitochondrial dysfunction as well as negative regulation of mitochondrial enzymes and other essential enzymes for parasite survival such as arginase. This gives a wide scope for future research towards the rational development of anti-kinetoplastid drugs.

CONCLUSION

Although the specific molecular targets, bioavailability, route of administration, and dosages of some of these natural compounds need to be determined, polyphenols and their combinations represent a very promising and safe strategy to be considered for use against Leishmania spp and Trypanosoma spp. In addition, these compounds may provide a scaffold for developing new, more potent, and more selective antiprotozoal agents.

A Comprehensive Review on Current perspectives of Flavonoids as antimicrobial agent

Flavonoids are the secondary plant metabolites with diversities of pharmacological activities like antioxidant, anticancer, anti-inflammatory, hepatoprotective, free radical scavenging activity and antiviral activities. Flavonoids have also been proved as a major contributor to the antimicrobial phytochemicals. Being the major substituent of antibiotics today flavonoids has attained high attention as there is increase in persistence of untreatable microbial infections due to microbial resistance. This review demonstrates the screening, isolation of extracts and derivatisation of various flavonoids and their evaluation for antimicrobial potency. Recent advancements of various derivatives of flavonoids having antimicrobial activity has also been discussed in this review. This review helps researchers to get vast knowledge about flavonoids and also give an idea for current scenario of flavonoids and its applications as antimicrobial agent.

Reproducibility challenges in the search for antibacterial compounds from nature

BACKGROUND

Reproducibility of reported antibacterial activities of plant extracts has long remained questionable. Although plant-related factors should be well considered in serious pharmacognostic research, they are often not addressed in many research papers. Here we highlight the challenges in reproducing antibacterial activities of plant extracts.

METHODS

Plants with reported antibacterial activities of interest were obtained from a literature review. Antibacterial activities against Escherichia coli and Klebsiella pneumoniae were tested using extracts' solutions in 10% DMSO and acetone. Compositions of working solutions from both solvents were established using LC-MS analysis. Moreover, the availability of details likely to affect reproducibility was evaluated in articles which reported antibacterial activities of studied plants.

RESULTS

Inhibition of bacterial growth at MIC of 256-1024 μg/mL was observed in only 15.4% of identical plant species. These values were 4-16-fold higher than those reported earlier. Further, 18.2% of related plant species had MICs of 128-256 μg/mL. Besides, 29.2% and 95.8% of the extracts were soluble to sparingly soluble in 10% DMSO and acetone, respectively. Extracts' solutions in both solvents showed similar qualitative compositions, with differing quantities of corresponding phytochemicals. Details regarding seasons and growth state at collection were missing in 65% and 95% of evaluated articles, respectively. Likewise, solvents used to dissolve the extracts were lacking in 30% of the articles, whereas 40% of them used unidentified bacterial isolates.

CONCLUSION

Reproducibility of previously reported activities from plants' extracts is a multi-factorial aspect. Thus, collective approaches are necessary in addressing the highlighted challenges.

Ethnobotany and the Role of Plant Natural Products in Antibiotic Drug Discovery

The crisis of antibiotic resistance necessitates creative and innovative approaches, from chemical identification and analysis to the assessment of bioactivity. Plant natural products (NPs) represent a promising source of antibacterial lead compounds that could help fill the drug discovery pipeline in response to the growing antibiotic resistance crisis. The major strength of plant NPs lies in their rich and unique chemodiversity, their worldwide distribution and ease of access, their various antibacterial modes of action, and the proven clinical effectiveness of plant extracts from which they are isolated. While many studies have tried to summarize NPs with antibacterial activities, a comprehensive review with rigorous selection criteria has never been performed. In this work, the literature from 2012 to 2019 was systematically reviewed to highlight plant-derived compounds with antibacterial activity by focusing on their growth inhibitory activity. A total of 459 compounds are included in this Review, of which 50.8% are phenolic derivatives, 26.6% are terpenoids, 5.7% are alkaloids, and 17% are classified as other metabolites. A selection of 183 compounds is further discussed regarding their antibacterial activity, biosynthesis, structure-activity relationship, mechanism of action, and potential as antibiotics. Emerging trends in the field of antibacterial drug discovery from plants are also discussed. This Review brings to the forefront key findings on the antibacterial potential of plant NPs for consideration in future antibiotic discovery and development efforts.

Antibacterial activity of medicinal plants against ESKAPE: An update

Antibiotic resistance has emerged as a threat to global health, food security, and development today. Antibiotic resistance can occur naturally but mainly due to misuse or overuse of antibiotics, which results in recalcitrant infections and Antimicrobial Resistance (AMR) among bacterial pathogens.

These mainly include the MDR strains (multi-drug resistant) of ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). These bacterial pathogens have the potential to “escape” antibiotics and other traditional therapies. These bacterial pathogens are responsible for the major cases of Hospital-Acquired Infections (HAI) globally. ESKAPE Pathogens have been placed in the list of 12 bacteria by World Health Organisation (WHO), against which development of new antibiotics is vital. It not only results in prolonged hospital stays but also higher medical costs and higher mortality. Therefore, new antimicrobials need to be developed to battle the rapidly evolving pathogens. Plants are known to synthesize an array of secondary metabolites referred as phytochemicals that have disease prevention properties. Potential efficacy and minimum to no side effects are the key advantages of plant-derived products, making them suitable choices for medical treatments. Hence, this review attempts to highlight and discuss the application of plant-derived compounds and extracts against ESKAPE Pathogens.

Induction of promising antibacterial prenylated isoflavonoids from different subclasses by sequential elicitation of soybean

Elicited soybean (Glycine max (L.) Merrill, Leguminosae) seedlings can produce prenylated isoflavonoids from different subclasses, namely pterocarpans (glyceollins), isoflavones and coumestans. These prenylated isoflavonoids serve as defence compounds and can possess antimicrobial activity. Recently, we showed that priming with reactive oxygen species (ROS) specifically stimulated the production of glyceollins in Rhizopus spp.-elicited soybean seedlings (ROS + R). In this study, we achieved diversification of the inducible subclasses of prenylated isoflavonoids in soybean, by additional stimulation of two prenylated isoflavones and one prenylated coumestan. This was achieved by using a combination of the relatively long-lived ROS representative, H2O2, with AgNO3 prior to microbial elicitation. Microbial elicitation was performed with a live preparation of either a phytopathogenic fungus, Rhizopus spp. or a symbiotic bacterium, Bacillus subtilis. B. subtilis induced 30% more prenylated isoflavones than Rhizopus spp. in (H2O2 + AgNO3)-treated seedlings, without significantly compromising the total levels of glyceollins, compared to (ROS + R)-treated seedlings. The most abundant prenylated isoflavone induced was 6-prenyl daidzein, which constituted 60% of the total isoflavones. The prenylated coumestan, phaseol, was also induced in the (H2O2 + AgNO3)-treated and microbially elicited seedlings. Based on previously developed quantitative structure-activity relationship (QSAR) models, 6-prenyl daidzein and phaseol were predicted to be promising antibacterials. Overall, we show that treatment with H2O2 and AgNO3 prior to microbial elicitation leads to the production of promising antibacterial isoflavonoids from different subclasses. Extracts rich in prenylated isoflavonoids may potentially be applied as natural antimicrobial agents.

Defying Multidrug Resistance! Modulation of Related Transporters by Flavonoids and Flavonolignans

Multidrug resistance (MDR) is a major challenge for the 21th century in both cancer chemotherapy and antibiotic treatment of bacterial infections. Efflux pumps and transport proteins play an important role in MDR. Compounds displaying inhibitory activity toward these proteins are prospective for adjuvant treatment of such conditions. Natural low-cost and nontoxic flavonoids, thanks to their vast structural diversity, offer a great pool of lead structures with broad possibility of chemical derivatizations. Various flavonoids were found to reverse both antineoplastic and bacterial multidrug resistance by inhibiting Adenosine triphosphate Binding Cassette (ABC)-transporters (human P-glycoprotein, multidrug resistance-associated protein MRP-1, breast cancer resistance protein, and bacterial ABC transporters), as well as other bacterial drug efflux pumps: major facilitator superfamily (MFS), multidrug and toxic compound extrusion (MATE), small multidrug resistance (SMR) and resistance-nodulation-cell-division (RND) transporters, and glucose transporters. Flavonoids and particularly flavonolignans are therefore highly prospective compounds for defying multidrug resistance.

Multiple docking analysis and In silico absorption, distribution, metabolism, excretion, and toxicity screening of anti-leprosy phytochemicals and dapsone against dihydropteroate synthase of Mycobacterium leprae

Background

Leprosy is a neglected tropical disease affecting millions of people. The current treatment against leprosy includes various antibacterial drugs of which dapsone is known to bind to dihydropteroate synthase of Mycobacterium leprae. Dapsone is an expensive antibacterial drug with many side effects. A natural alternative for dapsone having less to no side effects and cheaper in production is needed. The three-dimensional protein structure of dihydropteroate synthase of M. leprae is not available.

Methods

Protein homology modeling of target protein was carried out, and protein structure validation and energy minimization were performed. Phytochemicals mentioned in literature having anti-leprosy properties were studied for absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties and that which passed ADMET filters were further carried for comparative in silico docking analysis along with dapsone. Preliminary docking analysis was carried using AutoDock Vina, and results obtained were validated using AutoDock 4.2.6 and SwissDock.

Results

Neobavaisoflavone was predicted to be ten times safer for administration than dapsone. On performing in silico docking, it was found that neobavaisoflavone has better binding affinity than dapsone and forms a stable protein-ligand complex. Residues GLY.50, THR.88, and VAL.107 play an important role as binding site residues.

Conclusion

Further, in vitro and in vivo experimental studies are required to confirm anti-leprosy properties of neobavaisoflavone over drug dapsone.

Antibacterial and antibiotic-modifying activities of fractions and compounds from Albizia adianthifolia against MDR Gram-negative enteric bacteria

Background

Albizia adianthifolia (Schum.) is medicinally used in Cameroon to manage bronchitis and skin diseases. Our previous study documented the antibacterial potential of its roots’ methanol extract. In this study, methanol roots extract was subjected to chromatography techniques and fractions (AARa and AARb), sub-fractions (AARa1–4, AARb1–2 and AARb11–14) together with isolated phytochemicals were assessed for their antimicrobial as well as their antibiotic-potentiating effects towards Gram-negative multidrug resistant (MDR) bacteria.

Methods

The antibacterial activities of the samples (determination of Minimal Inhibitory « MIC » and Minimal Bactericidal Concentration « MBC ») were determined by the modified rapid p-iodonitrotetrazolium chloride (INT) colorimetric assay, as well as those of antibiotics in association with the compounds. Column chromatography was applied to isolate phytochemicals from roots extract and their chemical structures were determined using spectroscopic techniques.

Results

The phytochemicals isolated were stearic acid (1), a mixture (1:1) of stigmasterol and β-sitosterol (2 +  3), β-sitosterol 3-O-β-_D-glucopyranoside (4), palmatin (5), homomangiferin (6) and mangiferin (7). Fraction AARa exhibited selective inhibitory effects whilst all tested bacteria were inhibited by AARb in MIC ranges of 8 to 1024 μg/mL. Sub-fractions AARb1–2 had MIC values between 8 μg/mL and 1024 μg/mL on all tested bacteria. Phytochemicals 4, 2 +  3 and 7 inhibited the growth of 54.54% (6/11), 45.45% (5/11) and 27.27% (3/11) tested bacterial strains, respectively. When tested with an efflux pumps inhibitor (Phenylalanine-Arginine-β-Naphthylamide or PAβN), the inhibitory effects of compounds 2 + 3 and 4 increased towards all the tested bacteria. In association with erythromycin (ERY), streptomycin (STR) and tetracycline (TET), compounds 2 + 3 and 4 had the most significant synergistic activity on the seven selected bacteria.

Conclusion

The present study provides information on the possible use of Albizia adianthifolia and its constituents in the control of Gram-negative infections including MDR phenotypes.

Electronic supplementary material

The online version of this article (10.1186/s12906-019-2537-1) contains supplementary material, which is available to authorized users.

Effect of Fractioning on Antibacterial Activity of Enantia chlorantha Oliver (Annonaceae) Methanol Extract and Mode of Action

Infectious diseases caused by bacteria constitute the main cause of morbidity and mortality throughout the world and mainly in developing countries. In this work, the influence of fractioning and the mode of action of stem barks methanol extract of Enantia chlorantha were investigated. The aim was to optimize the antibacterial activity of the methanol extract. The extract was prepared by maceration of barks powder in methanol. Fractioning was done using increasing solvents polarity. Standard phytochemical methods were used for phytochemical screening. Minimum Inhibitory Concentrations (MIC) and Minimum Bactericidal Concentration (MBC) of the methanol extract and fractions were determined using broth microdilution method. The studied mode of action of both methanol extract and n-butanol fraction included antibiofilm activity, H+-ATPase-mediated proton pumping assay, salt tolerance, and cells cycle. The methanol extract of E. chlorantha stem barks was found to be active on all the bacteria tested (32 ≤ MIC ≤ 512 μg/mL), its activity being significant (MIC < 100 μg/ml) out of 5 of the 28 clinical isolates used. Salmonella enterica serovar paratyphi A was the most sensitive (32 μg/mL). Compared to the extract and other fractions, the n-butanol fraction was found to be more active (32 ≤ MIC ≤ 256). Significant antibacterial activity of this fraction was observed out of 10 of the 28 bacterial isolates and 3 out of 7 bacterial strains. Lowest MIC values (32 μg/ml) of this fraction were obtained with Escherichia coli (136), Pseudomonas aeruginosa (CIP 76110), and Salmonella enterica serovar typhi 9. The methanol extract of E. chlorantha and its n-butanol fraction revealed several modes of action including the prolongation of the latency phase of the bacterial growth, the inhibition of the pump with protons H⁺ - ATPases bacterial, the loss of the salt tolerance of the Staphylococcus aureus, and inhibition of the formation of the bacterial biofilm. The present results showed that the n-butanol fraction of the methanol stem barks extract of E. chlorantha possess the essential antibacterial components and could best be used to fight against bacterial infections as compared to methanol extract.

Antibacterial activities of the methanol extract, fractions and compounds from Elaeophorbia drupifera (Thonn.) Stapf. (Euphorbiaceae)

Background

Elaeophorbia drupifera (Thonn.) Stapf. (Euphorbiaceae) is used in Cameroonian folk medicine to treat several ailments including bacterial-related diseases such as skin infections. In this study, the methanol extract from the leaves (EDL), fractions (EDLa-d), sub-fractions EDLc1-7 and EDLc31-35 as well as isolated compounds were tested for their antimicrobial activities against a panel of Gram-negative and Gram-positive bacteria including multidrug resistant (MDR) phenotypes.

Methods

The broth microdilution method was used to determine the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the above samples; column chromatography was used for the fractionation and purification of the leaves extract whilst the chemical structures of compounds were determined using spectroscopic techniques.

Results

Phytochemical investigation lead to the isolation of a mixture (1:3) of stigmasterol and β-sitosterol (1 + 2), euphol (3), sitosterol-O-β-_D-xylopyranoside (4), 3,3′,4′-tri-O-methylellagic acid (5), a mixture (1:1) of afzelin and quercetin-3-O-β-_D-xylopyranoside (6 + 7), 3,3′,4′-tri-O-methylellagic acid 4-O-β-_D-glucopyranoside (8), ellagic acid-4-O-β-xylopyranoside-3,3′,4′-trimethyl ether (9) from EDLc. Crude extract and fractions displayed selective activities with MIC values ranged from 32 to 1024 μg/mL for EDL against 84.9% of the 33 tested bacteria, 93.9% for EDLc, 69.7% for EDLb, 33.4% for EDLa and 0.03% for EDLd. MIC values ranged from 16 to 1024 μg/mL were obtained with EDLc3 and EDLc4 on all tested bacteria meanwhile other sub-fractions displayed selective activities. MIC value of 32 μg/mL was obtained with fractions EDLa against Escherichia coli AG100, EDLc against Enterobacer aerogenes ATCC13048 and EA298. For sub-fractions obtained from EDLc, the lowest MIC value of 16 μg/mL was recorded with EDLc3 against Staphylococcus aureus MRSA11. A corresponding value of 8 μg/mL against Providencia stuartii NAE16 was recorded with EDLc33 obtained from further fractionation of EDLc3. EDLc3 had MIC values below 100 μg/mL against all tested bacteria. Compound 5 as well as the mixture (1:1) of 6 and 7 inhibited the growth of all the tested bacteria with MICs ranged from 64 to 256 μg/mL.

Conclusion

Elaeophorbia drupifera is a potential source of phytomedicine to tackle MDR bacteria. Sub-fraction EDLc3 was more active than all isolated compounds and deserves further investigations to develop natural drug to combat Gram-negative, Gram-positive bacteria and otherwise MDR phenotypes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1509-y) contains supplementary material, which is available to authorized users.

Antibacterial and antibiotic-resistance modifying activity of the extracts and compounds from Nauclea pobeguinii against Gram-negative multi-drug resistant phenotypes

BACKGROUND

Multi-drug resistance of Gram-negative bacteria constitutes a major obstacle in the antibacterial fight worldwide. The discovery of new and effective antimicrobials and/or resistance modulators is necessary to combat the spread of resistance or to reverse the multi-drug resistance. In this study, we investigated the antibacterial and antibiotic-resistance modifying activities against 29 Gram-negative bacteria including multi-drug resistant (MDR) phenotypes of the methanol extracts from Nauclea pobeguiinii leaves (NPL), Nauclea pobeguiinii bark (NPB) and six compounds from the bark extract, identified as 3-acetoxy-11-oxo-urs-12-ene (1), p-coumaric acid (2), citric acid trimethyl ester (3), resveratrol (4), resveratrol β- D -glucopyranoside (5) and strictosamide (6).

METHODS

The broth microdilution method was used to determine the minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC) of crude extracts and compounds as well as the antibiotic-resistance modifying effects of MPB and 4.

RESULTS

MIC determinations indicate values ranging from 32-1024 μg/mL for NPB and NPL on 89.7 % and 69.0 % of the tested bacterial strains respectively. MIC values below 100 μg/mL were obtained with NPB against Escherichia coli ATCC10536, AG100 and Enterobacter aerogenes CM64 strains. The lowest MIC value for crude extracts of 32 μg/mL was obtained with NPB against E. coli ATCC10536. Compound 4 was active all tested bacteria, whilst 1, 3 and 6 displayed weak and selective inhibitory effects. The corresponding MIC value (16 μg/mL) was obtained with 4 against Klebsiella pneumoniae KP55 strain. Synergistic effects of the combination of NPB with chloramphenicol (CHL), kanamycin (KAN) as well as that of compound 4 with streptomycin (STR) and ciprofloxacin (CIP) were observed.

CONCLUSION

The present study provides information on the possible use of Nauclea pobeguinii and compound 4 in the control of Gram-negative bacterial infections including MDR phenotypes. It also indicates that NPB and 4 can be used as naturally occurring antibiotic-resistance modulators to tackle MDR bacteria.

Cytotoxicity of 15 Cameroonian medicinal plants against drug sensitive and multi-drug resistant cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE

Cameroonian medicinal plants are traditionally used to treat many ailments, including cancer and related diseases. Cancer is characterized as a condition with complex signs and symptoms. It has been recommended that ethnopharmacological usages such as immune and skin disorders, inflammatory, infectious, parasitic and viral diseases should be taken into account when selecting plants for anticancer screenings, since these reflect disease states bearing relevance to cancer or cancer-like symptoms.

AIM OF THE STUDY

The present study aims at investigating 20 methanol extracts from 15 Cameroonian medicinal plants on a panel of human cancer cell lines, including various drug-resistant phenotypes. Possible modes of action of the of the most active plant were analyzed.

MATERIALS AND METHODS

Methanol extracts from different plant parts (leaves, bark, roots, fruits or whole plant) were evaluated for their cytotoxicity using resazurin reduction assay on a panel of nine sensitive and multi-drug resistant (MDR) cancer cell lines. Cell cycle, apoptosis, mitochondrial membrane potential (MMP), and reactive oxygen species (ROS) were measured by flow cytometry.

RESULTS

Prescreening of extracts at 80µg/mL showed that 6 extracts out of 20 inhibited more than 50% proliferation of leukemia CCRF-CEM cells; these include extracts from Anthocleista schweinfurthii fruits (ASF; 48.28%), Morus mesozygia bark (MMB; 42.76%), Nauclea latifolia bark (NLB; 38.75%), Tridesmostemon omphalocarpoides bark (TOB; 38.53%), Nauclea latifolia leaves (NLL; 35.17%) and Erythrina sigmoidea bark (ESB; 33.77%). Subsequent investigations revealed IC50 values below or around 20µg/mL for extracts from MMB, NLB, NLL and ESB towards sensitive CCRF-CEM cells and its resistant P-glycoprotein over-expressing subline CEM/ADR5000. The best extract, ESB also displayed IC50 values below 20µg/mL colon carcinoma HCT116 (p53(+/+)) cells with an IC50 value of 19.63µg/mL and it resistant p53 knockout subline HCT116 (p53(-)(/-)) with an IC50 value of 16.22µg/mL.

CONCLUSION

Erythrina sigmoidea, Anthocleista schweinfurthii, Morus mesozygia, Nauclea latifolia, Tridesmostemon omphalocarpoides used in African traditional medicine are good cytotoxic plants that can be exploited to develop phytomedicine to fight cancers including MDR phenotypes.