Synthesis of Ursolic Acid-based Hybrids: In Vitro Antibacterial, Cytotoxicity Studies, In Silico Physicochemical and Pharmacokinetic Properties

BACKGROUND

There is a critical need for the discovery of novel and effective antibacterial or anticancer molecules.

OBJECTIVES

Amine-linked ursolic acid-based hybrid compounds were prepared in good yields in the range of 60-68%.

METHODS

Their molecular structures were successfully confirmed using different spectroscopic methods including 1H/13C NMR, UHPLC-HRMS and FTIR spectroscopy. The in vitro cytotoxicity of some of these hybrid molecules against three human tumour cells, such as MDA-MB23, MCF7, and HeLa was evaluated using the MTT colorimetric method.

RESULT

Their antibacterial efficacy was evaluated against eleven bacterial pathogens using a serial dilution assay. Majority of the bacterial strains were inhibited significantly by compounds 17 and 24, with the lowest MIC values in the range of 15.3-31.25 μg/mL. Compound 16 exhibited higher cytotoxicity against HeLa cells than ursolic acid, with an IC50 value of 43.64 g/mL.

CONCLUSION

The in vitro antibacterial activity and cytotoxicity of these hybrid compounds demonstrated that ursolic acid-based hybrid molecules are promising compounds. Further research into ursolic acid-based hybrid compounds is required.

Dissolvable sodium alginate-based antibacterial wound dressing patches: Design, characterization, and in vitro biological studies

The treatment of infected wounds in patients with highly sensitive skin is challenging. Some of the available wound dressings cause further skin tear and bleeding upon removal thereby hindering the healing process. In this study, dissolvable antibacterial wound dressing patches loaded with cephalexin monohydrate were prepared from different amounts of sodium alginate (SA) and carboxymethyl cellulose (CMC) by the solvent casting evaporation technique. The patches displayed good tensile strength (3.83-13.83 MPa), appropriate thickness (0.09 to 0.31 mm) and good flexibility (74-98 %) suitable for the skin. The patches displayed good biodegradability and low moisture uptake suitable to prevent microbial invasion on the wound dressings upon storage. The release profile of the drug from the patches was sustained in the range of 47-80 % for 48 h, revealing their capability to inhibit bacterial infection. The biological assay showed that the patches did not induce cytotoxic effects on HaCaT cells, revealing good biocompatibility. The antimicrobial effect of the patches on the different strains of bacteria used in the study was significant. The cell migration (66.7-74.3 %) to the scratched gap was promising revealing the patches' capability to promote wound closure. The results obtained show that the wound dressings are potential materials for the treatment of infected wounds.

Synthesis, antibacterial, and cytotoxicity evaluation of oleanolic acid-4-aminoquinoline based hybrid compounds

AIM

To prepare a class of oleanolic-based compounds.

BACKGROUND

Conventional drugs used to treat infectious diseases suffer from limitations such as drug toxicity and drug resistance. The resistance of microbes to antimicrobial agents is a significant challenge in treating microbial infections. Combining two or more drugs with different modes of action to treat microbial infections results in a delay in developing drug resistance by the microbes. However, it is challenging to select the appropriate choice of drugs for combination therapy due to the differences in stability and pharmacokinetic profile of the drugs.Therefore, developing hybrid compounds using the existing drugs is a promising approach to design effective antimicrobial agents.

OBJECTIVES

To prepare oleanolic-based hybrid compounds followed by characterization, in vitro antibacterial, and cytotoxicity evaluation.

METHODS

Oleanolic acid-4-aminoquinoline-based hybrid compounds weresynthesized via esterification and amidation. The compounds werecharacterized using FTIR, NMR, and UHPLC-HRMS. Oleanolic acid was isolated from the flower buds of Syszygium aromaticum (L.) Merr. & L.M.Perry, a specie from Kingdom Plantae, order Mytales in Myrtaceae family. Their antibacterial and cytotoxicity activity was determined against selected strains of bacteria assessed using the microdilution assay and sulforhodamine B assay against selected cancer cell lines.

RESULTS

The synthesized hybrid compounds exhibited significant antibacterial activity against the Gram-positive bacteria Enterococcus faecalis (ATCC13047), Bacillus subtilis (ATCC19659), Staphylococcus aureus as well as Gram-negative bacteria,Klebsiella oxytoca (ATCC8724), Escherischia coli (ATCC25922), and Proteus vulgaris (ATCC6380)with minimum inhibitory concentrations of 1.25 mg/mLcompared to oleanolic acid (2.5 mg/mL). Compounds 13 and 14 displayed significant cytotoxic effectsin vitro against the cancer cell lines (MCF-7 and DU 145) compared to the oleanolic acid (IC50 ˃ 200 µM).

CONCLUSION

The present study revealed that the modification of C28 of OA enhanced its biological properties.

Alginate-gum acacia based sponges as potential wound dressings for exuding and bleeding wounds

The improper management of wound exudates can expose the wound to bacterial invasion, skin maceration etc. thereby resulting in prolonged wound healing. Biopolymers are characterized by hydrophilic functional groups which when employed for the development of wound dressings promote the wound dressings capability to absorb a high amount of wound exudates. Alginate-gum acacia sponges were prepared from a combination of biopolymers such as sodium alginate and gum acacia in varying amounts with carbopol via crosslinking with 1 and 2% CaCl₂. The prepared sponges were loaded with a combination of ampicillin and norfloxacin. In vitro antibacterial analysis revealed that the antibacterial activity of the loaded antibiotics was retained and the sponges were effective against gram-positive and gram-negative bacteria. The sponges displayed rapid and high absorption capability in the range of 1022-2419% at pH 5.5 simulating wound exudates, and 2268-5042% at pH 7.4 simulating blood within a period of 1-3 h. Furthermore, the whole blood clotting studies further revealed low absorbance values when compared to the control revealing the good clotting capability of the sponges. The unique features of the sponges revealed their potential application for the management of infected, high exuding and bleeding wounds.

Secondary metabolites from Tetracera potatoria stem bark with anti-mycobacterial activity

ETHNOPHARMACOLOGICAL RELEVANCE

Tetracera potatoria Afzel. Exg. Don (Dilleniaceae) is a medicinal plant used traditionally in Africa for the treatment of tuberculosis related ailments and respiratory infections. The antibacterial activity of the medium polar extracts of T. potatoria leaves and stem bark was recently reported against Mycobacterium smegmatis (MIC 25µg/mL) and M. aurum (65µg/mL), two fast-growing Mycobacterium strains used as model micro-organisms for the more pathogenic strain Mycobacterium tuberculosis (Fomogne-Fodjo et al., 2014). The aim of this study was consequently to isolate the compounds possibly contributing to this activity, and which may therefore be promising precursors to be used for the development of novel anti-TB drugs.

MATERIALS AND METHODS

T. potatoria medium polar extract [MeOH/DCM (1:1, v/v)] was fractionated sequentially with petroleum ether to which EtOAC and MeOH were gradually added to increase the polarity. The examination of T. potatoria extract and its fractions was guided by bioassays for anti-mycobacterial activity against M. smegmatis (ATCC 23246) and M. aurum (NCTC 10437) using the minimum inhibitory concentration (MIC) method. All the isolated compounds were structurally elucidated using spectroscopic techniques and evaluated for their anti-mycobacterial activity.

RESULTS

Two novel secondary metabolites (1, 2) named tetraceranoate and N-hydroxy imidate-tetracerane, together with five known compounds [β-stigmasterol (3), stigmast-5-en-3β-yl acetate (4), betulinic acid (5), betulin (6) and lupeol (7)] were isolated and identified. Tetraceranoate exhibited the best activity against M. smegmatis with a minimum inhibitory concentration (MIC) of 7.8µg/mL, while β-stigmasterol, betulinic acid and betulin showed appreciable anti-mycobacterial activity against both strains (MIC 15µg/mL).

CONCLUSION

Seven compounds were isolated from the medium polar extract [MeOH/DCM (1:1, v/v)] of T. potatoria stem bark. Only tetraceranoate one of the isolated compounds showed antibacterial activity against M. smegmatis having efficacy as high as rifampicin (one of a three drug regimen recommended in the initial phase short-course anti-tuberculosis therapy). Thus, tetraceranoate might be an interesting target for systematic testing of anti-TB treatment and management. This research supports the use of T. potatoria in African traditional medicine for the treatment of tuberculosis related symptoms.

Antibacterial effects of Alchornea cordifolia (Schumach. and Thonn.) Müll. Arg extracts and compounds on gastrointestinal, skin, respiratory and urinary tract pathogens

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves, stems and roots of Alchornea cordifolia (Schumach. and Thonn.) Müll. Arg. are used as traditional medicine in many African countries for the management of gastrointestinal, respiratory and urinary tract infections as well as for the treatment of wounds.

AIM OF THE STUDY

To determine the in vitro antibacterial activity of the crude extracts of leaves and stems of A. cordifolia on gastrointestinal, skin, respiratory and urinary tract pathogens and to identify the compounds in the extracts that may be responsible for this activity.

MATERIALS AND METHODS

The antibacterial activities of crude extracts [hexane, chloroform (CHCl3), ethyl acetate (EtOAc), ethanol (EtOH), methanol (MeOH) and water (H2O)] as well as pure compounds isolated from these extracts were evaluated by means of the micro-dilution assay against four Gram-positive bacteria, i.e. Bacillus cereus ATCC 11778, Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 25923 and S. saprophyticus ATCC 15305, as well as four Gram-negative bacterial strains, i.e. Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 13883, Moraxella catarrhalis ATCC 23246 and Proteus mirabilis ATCC 43071. The isolation of the active constituents was undertaken by bio-autographic assays in conjunction with chromatographic techniques. The identification and characterisation of the isolated compounds were done using mass spectrometry (MS) and Fourier transformed infrared spectrometry (FTIR) as well as 1D- and 2D- nuclear magnetic resonance (NMR) analyses.

RESULTS

The leaves and stems of A. cordifolia exhibited varied antibacterial activity against all eight pathogens. Most of the MIC values ranged between 63 and 2000µg/ml. The highest activities for the crude extracts (63µg/ml) were observed against S. saprophyticus [stem (EtOAc, CHCl3 and hexane), leaves (MeOH, EtOH, EtOAc and CHCl3)], E. coli [stem (MeOH and EtOH), leaves (MeOH, EtOH, EtOAc and CHCl3)], M. catarrhalis [leaves (EtOAc and CHCl3)], K. pneumoniae [stem (CHCl3), leaves (CHCl3)] and S. aureus [leaves (CHCl3)]. Seven constituents [stigmasterol (1), stigmasta-4,22-dien-3-one (2), friedelin (3), friedelane-3-one-28-al (4), 3-O-acetyl-aleuritolic acid (5), 3-O-acetyl-erythrodiol (6) and methyl-3,4,5-trihydroxybenzoate (methyl gallate) (7)] were isolated from the stem MeOH extract. All these compounds displayed some antibacterial activity against the eight pathogens with highest activity against S. saprophyticus (2µg/ml). Furthermore, this is the first report of compounds 1, 2, 3, 4, 6 and 7 isolated from A. cordifolia and where a complete set of 2D-NMR data for fridelane-3-one-28-al (4) is presented.

CONCLUSION

The study demonstrated that the antibacterial activities of A. cordifolia extracts may be due to the presence of the seven isolated compounds, where compounds 3-6 showed the best activity. The observed activity against gastrointestinal, skin, respiratory and urinary tract pathogens supports the traditional use for the treatment of such ailments.

Antibacterial activities of plants from Central Africa used traditionally by the Bakola pygmies for treating respiratory and tuberculosis-related symptoms

ETHNOPHARMACOLOGICAL RELEVANCE

The antibacterial activities of 18 plants from 10 different families were investigated for their antimicrobial efficacy, based on the traditional uses of these species by Bakola pygmies living in Central Africa, especially along the Ngoyang area in Cameroon for the treatment of respiratory and tuberculosis-related symptoms. The aim of the study is to test the antimicrobial efficacy of these plants against some pathogens associated with respiratory disease and to determine if there is any validation for the traditional use against Mycobacterium species.

MATERIALS AND METHODS

Medium polar extracts were prepared in MeOH/DCM (1:1, v/v) from the plant parts of each species used traditionally and were assayed against pathogens associated with respiratory tract ailments [Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 13883) and Morexella cattarhalis (ATCC 14468)] using the minimum inhibitory concentration (MIC) method. Two additional faster growing Mycobacterium strains [Mycobacterium smegmatis (ATCC 23246) and Mycobacterium aurum (NCTC 10437)] were included in the assay as predictive test organisms for the more pathogenic strain Mycobacterium tuberculosis.

RESULTS

Some plant species, such as Alchornea floribunda, Musanga cecropioides (both leaves and stem bark), Tetracera potatoria and Xylopia aethiopica (stem bark), were effective in inhibiting Morexella cattarhalis, having MIC values between 65 and 250 μg/mL. Some noteworthy antimycobacterial inhibition (MIC≤200 μg/mL and as low as MIC 6.5 µg/mL) for 54% of the extracts were observed.

CONCLUSION

While moderate activity was shown for pathogens causing respiratory tract infections, these plant species seems to be selectively targeting Mycobacteria spp. suggesting that the traditional use for treating tuberculosis related symptoms may be indeed be accurate.

Antibacterial activity of the roots, stems and leaves of Alchornea floribunda

ETHNOPHARMACOLOGICAL RELEVANCE

Alchornea floribunda Müll. Arg. is used in traditional medicine across Africa for the treatment of bacterial, fungal, parasitic and inflammatory disorders.

AIM OF THE STUDY

To evaluate the antibacterial activity of the crude extracts of different plant parts in order to provide a scientific rationale for the proposed broad efficacy of Alchornea floribunda in the treatment of bacterial infections.

MATERIALS AND METHODS

Extracts of roots, stems and leaves were prepared using solvents of various polarities in order to extract a wide range of phytochemicals. The antibacterial activity of these crude extracts was evaluated by micro-dilution assay, against Gram-positive (i.e. Bacillus cereus, Enterococcus faecalis, Staphylococcus aureus and Staphylococcus saprophyticus) as well as Gram-negative (i.e. Escherichia coli, Klebsiella pneumoniae, Moraxella catarrhalis and Proteus mirabilis) bacteria.

RESULTS

Generally, the ethanol (EtOH), methanol (MeOH), ethyl acetate (EtOAc) and chloroform (CHCl3) extracts demonstrated the best activities, with the leaves exhibiting the highest average activity for six of the eight pathogens. Of these, the ethanolic leaf extract was the most active against Staphylococcus aureus with an MIC value of 50µg/mL. Some other notable activity was observed for the ethyl acetate and chloroform root extracts against Staphylococcus aureus (50µg/mL), and for selected stem extracts against Staphylococcus aureus (50µg/mL), Klebsiella pneumoniae (63µg/mL) and Staphylococcus saprophyticus (63µg/mL).

CONCLUSION

This study demonstrates the promising antibacterial activity of Alchornea floribunda against both Gram-positive and Gram-negative bacteria responsible for gastrointestinal, skin, respiratory and urinary ailments, and validates its use in the ethnopharmacology of the region.