Abstract:In this study, the in vitro bacterial growth inhibition, antioxidant activity and the content in bioactive components of Plectranthus barbatus, P. hadiensis var. tomentosus, P. madagascarensis, P. neochilus and P. verticillatus aqueous extracts were investigated and compared by three extraction methods (infusion, decoction and microwave extractions). The microwave extract of P. madagascariensis showed the higher antimicrobial activity against the Staphylococcus epidermidis strain with a minimum inhibitory concentration of 40 µg/mL. This extract also showed no toxicity in a general toxicity assay and no considerable cytotoxicity against a human keratinocyte cell line. The antioxidant activity of the extracts was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH method), and all showed antioxidant activity. The microwave extract of P. madagascariensis was the one with the highest antioxidant activity (IC 50 value of 41.66 µg/mL). To increase extract stability, the microwave P. madagascariensis extract was then successfully encapsulated into alginate beads with high efficiency. This effective and low-cost strategy seems to be easy to extrapolate to an industrial scale with a future application on the skin. OPEN ACCESSPolymers 2014, 6 480
Cytotoxicity screenings have identified Plectranthus plants as potential sources of antitumor lead compounds. In this work, several extracts from Plectranthus madagascariensis were prepared using different solvents (acetone, methanol, and supercritical CO 2 ) and extraction techniques (maceration, ultrasound-assisted, and supercritical fluid extraction), and their chemical composition was detailed using high-performance liquid chromatography with a diode array detector. The cytotoxic activity of the major compounds identified, namely, rosmarinic acid ( 1 ) and abietane diterpenes 7α,6β-dihydroxyroyleanone ( 2 ), 7α-formyloxy-6β-hydroxyroyleanone ( 3 ), 7α-acetoxy-6β-hydroxyroyleanone ( 4 ), and coleon U ( 5 ), was evaluated in a battery of human cancer cell lines, including breast (MDA-MB-231, MCF-7), colon (HCT116), and lung (NCI-H460, NCI-H460/R) cancer, and also in healthy lung (MCR-5) cells. Royleanone ( 3 ) was isolated for the first time from P. madagascariensis , and its full spectroscopic characterization (proton and carbon nuclear magnetic resonance) was accomplished. A high selectivity for lung cancer cells was observed for royleanones ( 2 , 4 ) with selectivity indexes of 4.3 and 3.2, respectively. The observed results combined with literature data allowed the establishment of important structure–activity relationships for substituted royleanone abietanes, such as the requirement for an electron-donating group at positions 6 and/or 7 in the abietane skeleton, and an improved cytotoxic effect for substituents with log P values between 2 and 5.
Medicinal plants of the Plectranthus genus (Lamiaceae) are known for their ethnopharmacological relevance, mainly against infectious, dermatologic and gastrointestinal pathologies. Three Plectranthus species originated from South Africa, namely P. madagascariensis, P. neochilus and the rare P. porcatus were hereby screened for their antimicrobial and cytotoxic activities related with their known and/or potential ethnomedicinal uses. Twenty-six extracts were prepared by the combination of extraction methods (infusion, decoction, microwave-assisted, ultrasound-assisted, maceration and supercritical fluid extraction) with different polarity solvents (water, methanol, acetone and supercritical CO2). The comparison study of these extracts was elucidated through the corresponding chemical characterization and cytotoxic activity data. Therefore, the acetone extract from P. madagascariensis prepared by ultrasound extraction method revealed potent antibacterial activity against Gram-positive bacteria (1.95 < minimum inhibitory concentration (MIC) < 7.81 μg/mL), including a methicillin-resistant Staphylococcus aureus (MRSA) strain. Additionally, acetone extracts from both P. madagascariensis and P. neochilus exhibited relevant antibacterial activity against Gram-negative Klebsiella pneumonia (0.48 < MIC < 3.91 μg/mL), validating the traditional uses of such plants as anti-infectious agents. All methanolic extracts showed potent antioxidant effects at 100 μg/mL measured as their radical scavenging activity (60.8–89.0%) in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The P. madagascariensis extract obtained by maceration in acetone showed moderate cytotoxic effects in the MDA-MB-231 cell line (triple negative human breast carcinoma). The extract concentration that caused a 50% inhibition in cell viability (IC50) was 64.52 μg/mL. All extracts in this comparative study were profiled by high-performance liquid chromatography-HPLC with a diode-array detector-DAD (HPLC-DAD) and the main known bioactive components were identified in each extract, which included polyphenols (caffeic 1, chlorogenic 2 and rosmarinic 3 acids), abietane diterpenes (7α-acetoxy-6β-hydroxyroyleanone 4 and coleon U 5) and flavone glycosides (rutin 6 and naringin 7).
127 Biomedical and Biopharmaceutical Research J o r n a l d e I n v e s t i g a ç ã o B i o m é d i c a e B i o f a r m a c ê u t i c a Antimicrobial screening of Plectranthus madagascariensis and P. neochilus extracts AbstractNatural products are widely used as traditional medicines and are a common source of bioactive molecules for the treatment of bacterial infections. In particular, some plants of the genus Plectranthus (Lamiaceae) have demonstrated several applications, including the treatment of various infections. In this work, aqueous, acetonic and methanolic extracts of P. madagascariensis and P. neochilus were prepared using several extraction methods (infusion, decoction, maceration, microwave-and ultrasoundassisted and supercritical fluids). All extracts were screened for their antimicrobial activity against Gram positive bacteria (Enterococcus faecalis, Staphylococcus aureus, Bacillus subtilis and Mycobacterium smegmatis) and Gram negative bacteria (Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli) and two yeast (Candida albicans and Saccharomyces cerevisiae) strains. The P. madagascariensis acetonic extracts obtained using ultrasound and maceration methods and P. neochilus acetonic extract obtained by ultrasound technique showed activity against the five tested Gram positive bacteria (5-24 mm of inhibition zone using the well diffusion test). The antimicrobial activity was further evaluated by the microdilution method (MIC values were between 250-0.49 μg/mL) and the bioautography assay against S. aureus. The P. madagascariensis ultrasound acetonic extract was the most active extract against all the tested Gram positive bacteria (MIC values ranged between 31.25 -0.49 μg/mL). It was also active against resistant MRSA and VRE strains (MIC values ranged between 31.25-0.98 μg/mL). The S. aureus bioautography assay showed that the more polar compounds were the responsible for the antimicrobial activity.Keywords: Antimicrobial activity; natural products; Plectranthus spp; extraction methods. ResumoOs produtos naturais são amplamente utilizados como remédios tradicionais e são uma fonte comum de moléculas bioativas para o tratamento de infeções bacterianas. Em particular, algumas plantas do género Plectranthus (Lamiaceae) demonstraram diversas aplicações, incluindo no tratamento de várias infeções. Neste trabalho, foram preparados extratos aquosos, acetónicos e metanólicos de P. madagascariensis e P. neochilus utilizando vários métodos de extração (infusão, decocção, maceração, extração assistida por micro-ondas e por ultrassom e com fluidos no estado supercrítico). Todos os extratos foram testados quanto à atividade antimicrobiana face a bactérias de Gram-positivo (Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis Bacillus subtilis e Mycobacterium smegmatis) e de Gram-negativo (Pseudomonas aeruginosa, Klebsiella pneumoniae e Escherichia coli) e duas estirpes de leveduras (Candida albicans e Saccharomyces cerevisiae). O extrato acetónico de P. madagascariensis obtid...
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