Solamargine, a bioactive steroidal alkaloid isolated from Solanum aculeastrum induces non-selective cytotoxicity and P-glycoprotein inhibition.

BACKGROUND: Solanum aculeastrum fruits are used by some cancer sufferers as a form of alternative treatment. Scientific literature is scarce concerning its anticancer activity, and thus the aim of the study was to assess the in vitro anticancer and P-glycoprotein inhibitory potential of extracts of S. aculeastrum fruits. Furthermore, assessment of the combinational effect with doxorubicin was also done. METHODS: The crude extract was prepared by ultrasonic maceration. Liquid-liquid extraction yielded one aqueous and two organic fractions. Bioactive constituents were isolated from the aqueous fraction by means of column chromatography, solid phase extraction and preparative thin-layer chromatography. Confirmation of bioactive constituent identity was done by nuclear magnetic resonance and ultra-performance liquid chromatography mass spectrometry. The crude extract and fractions were assessed for cytotoxicity and P-glycoprotein inhibition in both cancerous and non-cancerous cell lines using the sulforhodamine B and rhodamine-123 assays, respectively. RESULTS: Both the crude extract and aqueous fraction was cytotoxic to all cell lines, with the SH-SY5Y neuroblastoma cell line being most susceptible to exposure (IC50 = 10.72 µg/mL [crude], 17.21 µg/mL [aqueous]). Dose-dependent P-glycoprotein inhibition was observed for the crude extract (5.9 to 18.9-fold at 100 µg/mL) and aqueous fraction (2.9 to 21.2 at 100 µg/mL). The steroidal alkaloids solamargine and solanine were identified. While solanine was not bioactive, solamargine displayed an IC50 of 15.62 µg/mL, and 9.1-fold P-glycoprotein inhibition at 100 µg/mL against the SH-SY5Y cell line. Additive effects were noted for combinations of doxorubicin against the SH-SY5Y cell line. CONCLUSIONS: The crude extract and aqueous fraction displayed potent non-selective cytotoxicity and noteworthy P-glycoprotein inhibition. These effects were attributed to solamargine. P-glycoprotein inhibitory activity was only present at concentrations higher than those inducing cytotoxicity, and thus does not appear to be the likely mechanism for the enhancement of doxorubicin's cytotoxicity. Preliminary results suggest that non-selective cytotoxicity may hinder drug development, however, further assessment of the mode of cell death is necessary to determine the route forward.

Antitrypanosomal isoflavan quinones from Abrus precatorius.

Human African trypanosomiasis is a neglected tropical disease in sub Saharan Africa that is fatal if left untreated. In a search for new natural products with antitrypanosomal activity, we recently identified abruquinones B and I from Abrus precatorius as potent in vitro trypanocidal compounds with high selectivity indices. To obtain sufficient compound for in vivo efficacy tests in mice, a second batch of plant material was re-collected and extracted. However, the chemical profiles of the two batches differed, and additional abruquinones were isolated and identified by HR-ESI-MS, and 1D and 2D NMR ((1)H, (13)C, COSY, HMBC, HSQC, and NOESY) spectroscopy. Abruquinones J (1), K (2), and L (3) were new, while abruquinones A (4) and D (5) were known from the first batch of plant material. The absolute configuration of compounds 1 to 3 was determined by comparison of electronic circular dichroism (ECD) spectra with calculated ECD data. Compounds 2 to 5 showed high in vitro activity against T. b. rhodesiense (IC50 of 0.01, 0.02, 0.02 and 0.01 µM, respectively), and remarkable SIs of 508, 374, 1379, and 668, respectively.

Antiprotozoal screening of 60 South African plants, and the identification of the antitrypanosomal germacranolides schkuhrin I and II.

Two hundred and seven extracts were prepared from sixty plants from South Africa and screened for in vitro activity against Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani, and Plasmodium falciparum. For the 21 extracts which inhibited the growth of one or more parasites with more than 95 % at 10 µg/mL, the IC50 values against all four protozoal parasites and cytotoxic IC50 values against L6 myoblasts were determined. Amongst the most notable results are the activities of Psoralea pinnata (IC50 of 0.15 µg/mL), Schkuhria pinnata (2.04 µg/mL), and Vernonia mespilifolia (1.01 µg/mL) against Trypansoma brucei rhodesiense. HPLC-based activity profiling was used to identify the active constituents in the extracts, and the germacranolide sesquiterpene lactones schkuhrin I and II from S. pinnata, and cynaropicrin from V. mespilifolia were identified, with IC50 values of 0.9, 1.5, and 0.23 µM, respectively.

Antimicrobial activity and cytotoxicity of triterpenes isolated from leaves of Maytenus undata (Celastraceae).

BACKGROUND: Plants of the genus Maytenus belong to the family Celastraceae and are widely used in folk medicine as anti-tumour, anti-asthmatic, analgesic, anti-inflammatory, antimicrobial and anti-ulcer agents, and as a treatment for stomach problems. The aim of this study was to isolate and identify active compounds with antifungal activity from Maytenus undata after a preliminary study highlighted promising activity in crude extracts. METHODS: Sequential extracts of M. undata leaves prepared using hexane, dichloromethane (DCM), acetone and methanol (MeOH) were tested for activity against Cryptococcus neoformans, a fungal organism implicated in opportunistic infections. Bioassay-guided fractionation of the hexane extract using C. neoformans as test organism was carried out to isolate antifungal compounds. The cytotoxicity of compounds isolated in sufficient quantities was evaluated using a tetrazolium-based colorimetric cellular assay (MTT) and a haemagglutination assay (HA). RESULTS: The hexane extract was most active with an MIC of 20 µg/ml against C. neoformans. The triterpene compounds friedelin (1), epifriedelanol (2), taraxerol (3), 3-oxo-11α-methoxyolean-12-ene-30-oic acid (4), 3-oxo-11α-hydroxyolean-12-ene-30-oic acid (5) and 3,11-dihydroxyolean-12-ene-30-oic acid (6) were isolated. Compound 6 was isolated for the first time from a plant species. The antimicrobial activity of compounds 1, 3, 5 and 6 was determined against a range of bacteria and fungi implicated in opportunistic and nosocomial infections. Compounds 5 and 6 were the most active against all the tested microorganisms with MIC values ranging between 24 and 63 µg/ml, except against Staphylococcus aureus which was relatively resistant. Compounds 1 and 3 had a low toxicity with an LC50 > 200 µg/ml towards Vero cells in the MTT assay. Compounds 5 and 6 were toxic with LC50 values of 6.03±0.02 and 2.98±0.01 µg/ml, respectively. Compounds 1 and 3 similarly were not toxic to the red blood cells (RBCs) but compounds 5 and 6 were toxic, showing HA titer values of 1.33 and 0.67 respectively. CONCLUSIONS: Compounds 5 and 6 were the most active but were also relatively cytotoxic to monkey kidney cells and red blood cells, while the other isolated compounds were less active and less cytotoxic.

Antiprotozoal isoflavan quinones from Abrus precatorius ssp. africanus.

A library of 206 extracts from selected South African plants was screened in vitro against a panel of protozoan parasites, Plasmodium falciparum, Trypanosoma brucei rhodesiense, and Leishmania donovani. A CH2Cl2/MeOH (1 : 1) extract of Abrus precatorius L. ssp. africanus strongly inhibited P. falciparum (98 %), T. b. rhodesiense (100 %), and L. donovani (76 %) when tested at a concentration of 10.0 µg/mL. The active constituents were tracked by HPLC-based activity profiling and isolated by preparative and semipreparative RP-HPLC chromatography. Structures were established by HR-ESIMS, and 1D and 2D NMR (1H, 13C, COSY, HMBC, HSQC, and NOE difference spectroscopy). Five compounds were obtained and identified as two isoflavan hydroquinones, abruquinone H (1) and abruquinone G (2), and three isoflavan quinones, abruquinone I (3), abruquinone B (4), and 7,8,3''5'-tetramethoxyisoflavan-1',4'-quinone (5). Compounds 1 and 3 were new natural products. The absolute configuration of compounds was determined by comparison of electronic circular dichroism spectra with calculated ECD data. Compounds 3 and 4 showed strong activity against T. b. rhodesiense (IC50 values of 0.30 and 0.16 µM, respectively) and good selectivity (selectivity indices of 73.7 and 50.5, respectively).

In vitro screening of traditional South African malaria remedies against Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani, and Plasmodium falciparum.

Three hundred extracts were prepared from plants traditionally used in South Africa to treat malaria and screened in vitro for activity against Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani, and Plasmodium falciparum. For the 43 extracts which inhibited the growth of one or more parasites to more than 95 % at 9.7 µg/mL, the IC50 values against all four protozoal parasites and cytotoxic IC50s against rat myoblast L6 cells were determined. Amongst the most notable results are the activities of AGATHOSMA APICULATA (IC50 of 0.3 µg/mL) against Plasmodium falciparum, as well as Salvia repens and Maytenus undata against Leishmania donovani with IC50s of 5.4 µg/mL and 5.6 µg/mL, respectively. This screening is the starting point for a HPLC-based activity profiling project in antiprotozoal lead discovery.