Neil R. Crouch

Antidiabetic screening and scoring of 11 plants traditionally used in South Africa

AIM To investigate the traditional antidiabetic uses of indigenous or naturalised South African plants using an optimised screening and scoring method. MATERIALS AND METHODS Eleven plant species were screened against Chang liver, 3T3-L1 adipose and C2C12 muscle cells measuring glucose utilisation in all three cell lines and toxicity in the hepatocytes and adipocytes only. A scoring system was devised to aid interpretation of results. RESULTS Catharanthus roseus results correlated with previously reported in vivo results, with best stimulation of glucose utilisation in hepatocytes. Momordica foetida and Momordica balsamina extracts were active in myocytes but only the latter stimulated glucose utilisation in hepatocytes. Brachylaena discolor gave the best overall results, with all plant parts giving high activity scores and negligible toxicity. In vitro toxicity results for Catharanthus roseus, Vinca major, Momordica balsamina and some Sclerocarya birrea extracts raise concern for chronic use. CONCLUSION This screening system increases the likelihood of identifying drug candidates using in vitro antidiabetic screening of crude plant extracts, whilst the scoring system aids data interpretation. ETHNOPHARMACOLOGICAL RELEVANCE The multitude of metabolic steps affected by Type II diabetes offer many drug targets but they complicate in vitro screening to validate traditional uses or find new drug leads from plants.

Homoisoflavanones from three South African Scilla species

Abstract The bulbs of three South African Scilla species have been investigated. Scilla kraussii yielded 5,7-dihydroxy-3-(4-hydroxy-4-methoxybenzyl)chroman-4-one, Scilla dracomontana yielded the novel 5,7-dihydroxy-6-methoxy-3-(3-methoxybenzyl)chroman-4-one and also eucomol and 5,7-dihydroxy-6-methoxy-3-(4-hydroxybenzyl)chroman-4-one. Scilla natalensis again yielded 5,7-dihydroxy-6-methoxy-3-(4-hydroxybenzyl)chroman-4-one and 5,7-dihydroxy-3-(3-hydroxy-4-methoxybenzyl)chroman-4-one.

Hitting the right target: taxonomic challenges for, and of, plant invasions.

Taxonomic resources are essential for the effective management of invasive plants because biosecurity strategies, legislation dealing with invasive species, quarantine, weed surveillance and monitoring all depend on accurate and rapid identification of non-native taxa, and incorrect identifications can impede ecological studies. On the other hand, biological invasions have provided important tests of basic theories about species concepts. Modern taxonomy therefore needs to integrate both classical and new concepts and approaches to improve the accuracy of species identification and further refine taxonomic classification at the level of populations and genotypes in the field and laboratory.

Homoisoflavanones and stilbenoids from Scilla nervosa

Abstract The bulbs of Scilla nervosa have yielded three novel compounds, 5,7-dimethoxy-3-(4-methoxybenzyl)chroman-4-one, 5-hydroxy-7-methoxy-3-(3-hydroxy-4-methoxybenzyl)-chroman-4-one, 5,7-dimethoxy-3-(4-hydroxybenzyl)chroman-4-one and the known compounds 5-hydroxy-7-methoxy-3-(4-methoxybenzyl)chroman-4-one, ( E )-5,7-dihydroxy-3-(4-hydroxybenzylidene)chroman-4-one, ( E )-resveratrol and ( E )-3,3′,5-trihydroxy-4′-methoxystilbene (rhapontigenin).

In vitro anti-plasmodial activity of Dicoma anomala subsp. gerrardii (Asteraceae): identification of its main active constituent, structure-activity relationship studies and gene expression profiling.

BackgroundAnti-malarial drug resistance threatens to undermine efforts to eliminate this deadly disease. The resulting omnipresent requirement for drugs with novel modes of action prompted a national consortium initiative to discover new anti-plasmodial agents from South African medicinal plants. One of the plants selected for investigation was Dicoma anomala subsp. gerrardii, based on its ethnomedicinal profile.MethodsStandard phytochemical analysis techniques, including solvent-solvent extraction, thin-layer- and column chromatography, were used to isolate the main active constituent of Dicoma anomala subsp. gerrardii. The crystallized pure compound was identified using nuclear magnetic resonance spectroscopy, mass spectrometry and X-ray crystallography. The compound was tested in vitro on Plasmodium falciparum cultures using the parasite lactate dehydrogenase (pLDH) assay and was found to have anti-malarial activity. To determine the functional groups responsible for the activity, a small collection of synthetic analogues was generated - the aim being to vary features proposed as likely to be related to the anti-malarial activity and to quantify the effect of the modifications in vitro using the pLDH assay. The effects of the pure compound on the P. falciparum transcriptome were subsequently investigated by treating ring-stage parasites (alongside untreated controls), followed by oligonucleotide microarray- and data analysis.ResultsThe main active constituent was identified as dehydrobrachylaenolide, a eudesmanolide-type sesquiterpene lactone. The compound demonstrated an in vitro IC50 of 1.865 μM against a chloroquine-sensitive strain (D10) of P. falciparum. Synthetic analogues of the compound confirmed an absolute requirement that the α-methylene lactone be present in the eudesmanolide before significant anti-malarial activity was observed. This feature is absent in the artemisinins and suggests a different mode of action. Microarray data analysis identified 572 unique genes that were differentially expressed as a result of the treatment and gene ontology analysis identified various biological processes and molecular functions that were significantly affected. Comparison of the dehydrobrachylaenolide treatment transcriptional dataset with a published artesunate (also a sesquiterpene lactone) dataset revealed little overlap. These results strengthen the notion that the isolated compound and the artemisinins have differentiated modes of action.ConclusionsThe novel mode of action of dehydrobrachylaenolide, detected during these studies, will play an ongoing role in advancing anti-plasmodial drug discovery efforts.

Cembranolides from the stem bark of the southern African medicinal plant, Croton gratissimus (Euphorbiaceae)

The stem bark of Croton gratissimus (Euphorbiaceae) yielded four cembranolides, including the first reported example of a 2,12-cyclocembranolide, (+)-[1R*,2S*,7S*,8S*,12R*]-7,8-epoxy-2,12-cyclocembra-3E,10Z-dien-20,10-olide, whose structure was confirmed by means of single crystal X-ray analysis. This compound showed moderate activity against the PEO1 and PEO1TaxR ovarian cancer cell lines.

Toddaculin, a natural coumarin from Toddalia asiatica, induces differentiation and apoptosis in U-937 leukemic cells

Chemotherapeutics represent the main approach for the treatment of leukemia. However, the occurrence of adverse side effects and the complete lack of effectiveness in some cases make it necessary to develop new drugs. As part of our screening program to evaluate the potential chemotherapeutic effect of natural coumarins, we investigated the anti-leukemic activities of a series of six prenylated coumarins isolated from the stem bark of Toddalia asiatica (Rutaceae). Among these, 6-(3-methyl-2-butenyl)-5,7-dimethoxycoumarin (toddaculin) displayed the most potent cytotoxic and anti-proliferative effects in U-937 cells. To determine whether these effects resulted from induction of cell death or differentiation, we further evaluated the expression of several apoptosis and maturation markers. Interestingly, while toddaculin at 250 μM was able to induce apoptosis in U-937 cells, involving decreased phosphorylation levels of ERK and Akt, 50 μM toddaculin exerted differentiating effects, inducing both the capacity of U-937 cells to reduce NBT and the expression of differentiation markers CD88 and CD11b, but no change in p-Akt or p-ERK levels. Taken together, these findings indicate that toddaculin displays a dual effect as a cell differentiating agent and apoptosis inducer in U-937 cells, suggesting it may serve as a pharmacological prototype for the development of novel anti-leukemic agents.

Alkaloids and triterpenoids from Ammocharis coranica (Amaryllidaceae).

The bulbs of Ammocharis coranica yielded eight alkaloids: lycorine, acetylcaranine and crinamine, which have been reported previously from A. coranica, 1-O-acetyllycorine, hippadine, 6 alpha-hydroxypowelline and hamayne, which have been reported from other members of the Amaryllidaceae, 1-O-acetyl-9-O-demethylpuviine, which has not been described previously, and the known cycloartane compounds: 24-methylenecycloartan-3 beta-ol, cycloeucalenol, cycloeucalenone and also 24-methylenepollinastanone, which has not been described previously.

Cardamonin Is a Bifunctional Vasodilator that Inhibits Cav1.2 Current and Stimulates KCa1.1 Current in Rat Tail Artery Myocytes

An in-depth analysis of the effects of cardamonin, 2′,4′-dihydroxy-6′-methoxychalcone, on rat tail artery preparations was performed by means of whole-cell patch-clamp recordings of Cav1.2 Ca2+ [ICa(L)] or Ba2+ [IBa(L)] current as well as KCa1.1 currents in single myocytes and by measuring contractile responses in endothelium-denuded isolated rings. At a holding potential (Vh) of −80 mV, cardamonin decreased both IBa(L) and ICa(L) in a concentration-dependent manner with similar pIC50 values. The maximum of the IBa(L)-voltage relationship was shifted by 10 mV in the hyperpolarizing direction, but threshold remained unaffected. Cardamonin modified both the activation and the inactivation kinetics of IBa(L) and shifted the voltage dependence of both inactivation and activation curves to more negative potentials by 19 and 7 mV, respectively, thus markedly decreasing the Ba2+ window current. Block of IBa(L) was frequency-dependent, and rate of recovery from inactivation was slowed. Cardamonin increased KCa1.1 currents in a concentration-dependent manner; this stimulation was iberiotoxin- and BAPTA [1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid]-sensitive. On the contrary, iberiotoxin did not modify cardamonin-induced relaxation of rings precontracted either with phenylephrine or with (S)-(−)-methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridine-5-carboxylate [(S)-(−)-Bay K 8644]. The overall effects of cardamonin were incompletely reversed by washout. In conclusion, cardamonin is a naturally occurring, bifunctional vasodilator that, by simultaneously inhibiting ICa(L) and stimulating KCa1.1 current, may represent a scaffold for the design of novel drugs of potential interest for treatment of systemic hypertension.

Cembranolides from the Leaves of Croton gratissimus.

Ten new cembranolides, (-)-(1R*,4R*,10R*)-4-methoxycembra-2E,7E,11Z-trien-20,10-olide (1), (-)-(1S*,4R*,10R*)-1-hydroxy-4-methoxycembra-2E,7E,11Z-trien-20,10-olide (2), (-)-(1S*,4S*,10R*)-1,4-dihydroxycembra-2E,7E,11Z-trien-20,10-olide (3), (-)-(1S*,4S*,10R*)-1,4-dihydroxycembra-2E,7E,11Z-trien-20,10-olide (4), (+)-(10R*)-cembra-1E,3E,7E,11Z,16-pentaen-20,10-olide (5), (+)-(10R*)-cembra-1Z,3Z,7E,11Z,15-pentaen-20,10-olide (6), (+)-(5R*,10R*)-5-methoxycembra-1E,3E,7E,11Z,15-pentaen-20,10-olide (7), (+)-(1S*,4S*,7R*,10R*)-1,4,7-trihydroxycembra-2E,8(19),11Z-trien-20,10-olide (8), (-)-(1S*,4S*,7S*,10R*)-1,4,7-trihydroxycembra-2E,8(19),11Z-trien-20,10-olide (9), and (+)-(1S*,4R*,8S*,10R*)-1,4,8-trihydroxycembra-2E,6E,11Z-trien-20,10-olide (10), together with six known compounds, lupeol, 4(15)-eudesmene-1β,6α-diol, α-glutinol, 24-ethylcholesta-4,22-dien-3-one, (+)-(1R*,10R*)-cembra-2E,4E,7E,11Z-tetraen-20,10-olide, and (+)-(1R*,4S*,10R*)-4-hydroxycembra-2E,7E,11Z-trien-20,10-olide (4a), have been isolated from the leaves of Croton gratissimus. The acetyl derivatives of 8 and 4a were evaluated against a chloroquine-sensitive strain of Plasmodium falciparum (D10).