Léon Azefack Tapondjou

Effect of essential oils from leaves of Ageratum conyzoides, Lantana camara and Chromolaena odorata on the mortality of Sitophilus zeamais (Coleoptera, Curculionidae).

Ageratum conyzoides, Chromolaena odorata, and Lantana camara, are common weed species in Cameroon. Essential oil extracts from their leaves were tested for efficacy on the morality of the maize grain weevil, Sitophilus zeamais (Coleoptera, Curculionidae). Concentrations of the essential oils relative to the maize grains of 0.013, 0.025, 0.05 and 0.1% (v/w) were used for A. conyzoides and 0.063, 0.125, 0.25 and 0.50% (v/w) for C. odorata and L. camara. Twenty 7-day old adult weevils were fed on maize grains treated with the above concentrations of the essential oils in Petri dishes. Control dishes contained insects and maize grains without essential oils. The experiment was repeated three times. Dishes were incubated in the laboratory for 7 days at 26 degrees C and 75-85% relative humidity. Insect mortality was recorded every 24 h. Graphs of percentage mortality versus the duration of exposure were constructed and the LD(50) was computed for each oil. Significant insect mortality was obtained with all the essential oils used. The mortality of S. zeamais increased with the concentration of the essential oils of the three plants and the duration of exposure of the weevils on the treated substrates. The essential oil extract of Ageratum conyzoides was the most effective insecticide (LD(50)=0.09% in 24 h), followed by that of L. camara (LD(50)=0.16%) and C. odorata (LD(50)=6.78%). These results show that the essential oils of the leaves of some of these weed species may be exploited for insect control in stored products.

Dimeric antioxidant and cytotoxic triterpenoid saponins from Terminalia ivorensis A. Chev.

Three saponins, including two dimeric triterpenoid glucosides possessing an unusual skeleton, ivorenosides A and B, and a monomeric triterpenoid saponin (ivorenoside C), together with the known sericoside, were isolated from the bark of Terminalia ivorensis. Their structures were established on the basis of 1D and 2D NMR data, chemical methods and tandem MS-MS spectrometry as a dimer of β-D-glucopyranosyl-18,19-seco-2α,3β,19,19,24-pentahydroxyolean-12-en-28-oate and β-D-glucopyranosyl-2α,3β,19α,24-tetrahydroxyolean-12-en-28-oate (ivorenoside A, 1), a dimer of β-D-glucopyranosyl-18,19-seco-24-carboxyl-2α,3β,19,19-tetrahydroxyolean-12-en-28-oate and β-D-glucopyranosyl-2α,3β,19α,24-tetrahydroxyolean-12-en-28-oate (ivorenoside B, 2) and β-D-glucopyranosyl-2α,3β,19β,24-tetrahydroxyolean-11-oxo-olean-12-en-28-oate (ivorenoside C, 3). Ivorenosides A and B are the first examples in nature of dimeric triterpenoid saponins with a 18,19-seco E ring of one of the two units. These isolated compounds were evaluated for their antioxidant properties and further for their cytotoxic activity against four human cancer cell lines. Ivorenoside B and C exhibited scavenging activity against DPPH and ABTS(+) radicals with IC(50) values comparable with that of the standard drug Trolox and ivorenoside A showed antiproliferative activity against MDA-MB-231 and HCT116 human cancer cell lines with IC(50) values of 3.96 and 3.43 μM, respectively.

Rheediinosides A and B, two antiproliferative and antioxidant triterpene saponins from Entada rheedii

Two triterpenoid saponins have been isolated from the seed kernels of Entada rheedii. Their structures have been established using 1D- and 2D-NMR and mass spectrometry as 3-O-beta-D-xylopyranosyl-(1-->3)-O-alpha-l-arabinopyranosyl-(1-->6)-2-acetylamino-2-deoxy-beta-D-glucopyranosylentagenic acid 28-O-beta-apiofuranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->2)-beta-D-glucopyranoside (Rheediinoside A, 1) and 3-O-beta-D-glucopyranosyl-(1-->3)-O-[beta-D-xylopyranosyl-(1-->3)-alpha-l-arabinopyranosyl-(1-->6)]-2-acetylamino-2-deoxy-beta-D-glucopyranosylentagenic acid 28-O-beta-apiofuranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->2)-beta-D-glucopyranoside (Rheediinoside B, 2). Compounds 1 and 2 were tested for their antiproliferative activity against T98G, A431, PC3 and B16-F1 cell lines, and further for their antioxidant properties. Moderate cytotoxic potency and antioxidant properties were found for these compounds whereas Rheediinoside B was in all assays more active than Rheediinoside A.

In vivo anti-nociceptive and anti-inflammatory effect of the two triterpenes, ursolic acid and 23-hydroxyursolic acid, from Cussonia bancoensis.

Triterpenoids, ursolic acid (1) and 23-hydroxyursolic acid (2) were obtained from the hydrolysis of BuOH fraction ofCussonia bancoensis extract to test antinociceptive and anti-inflammatory effect ofC. bancoensis (Araliaceae). Compound1 and2 exhibited anti-nociceptive effects, which were determined by acetic acid-induced writhing test and hot plate test. The effect of2 was much more potent in acetic acid-induced writhing test than in hot plate test. Compound1 and2 significantly inhibited 1%-carrageenan-induced edema in the rat. These results suggest that the two triterpenes, ursolic acid and 23-hydroxyursolic acid, are responsible for the antinociceptive and anti-inflammatory effect ofC. bancoesnsis.

Antinociceptive activities of the methanol extract of the bulbs of Dioscorea bulbifera L. var sativa in mice is dependent of NO-cGMP-ATP-sensitive-K+ channel activation.

ETHNOPHARMACOLOGICAL RELEVANCE Dioscorea bulbifera var sativa is a medicinal plant commonly used in Cameroonian traditional medicine to treat pain and inflammation. AIM The present work evaluated the effects of the methanol extract of the bulbs of Dioscorea bulbifera in inflammatory and neuropathic models of pain and further investigated its possible mechanism of action. MATERIALS AND METHODS The effects of Dioscorea bulbifera administered orally at the doses of 250 and 500mg/kg were tested in mechanical hypernociception induced by intraplantar (i.pl.) injection of complete Freunds adjuvant (CFA), lipopolysaccharides (LPS) or prostaglandin-E(2) (PGE(2)), as well as in partial ligation sciatic nerve (PLSN), nociception induced by capsaicin and thermal hyperalgesia induced by i.pl. injection of CFA. The therapeutic effects of Dioscorea bulbifera on PGE(2)-induced hyperalgesia were evaluated in the absence and in the presence of l-NAME, an inhibitor of nitric oxide synthase (NOS) and glibenclamide, an inhibitor of ATP-sensitive potassium channels. RESULTS The extract showed significant antinociceptive effects in persistent pain induced by CFA and on neuropathic pain induced by PLSN. The effects of Dioscorea bulbifera persisted for 5 days after two administrations in CFA-induced hypernociception. Dioscorea bulbifera significantly inhibited acute LPS-induced pain but failed to reduce thermal hypernociception and capsaicin-induced spontaneous nociception. The antinociceptive effects of this plant extract in PGE(2) model was antagonized by either l-NAME or glibenclamide. CONCLUSION Present demonstrate the antinociceptive activities of Dioscorea bulbifera both in inflammatory and neuropathic models of pain and these effects may result, at least partially, from its ability to activate the NO-cGMP-ATP-sensitive potassium channels pathway.

Insecticidal activities of essential oil of Callistemon viminalis applied as fumigant and powder against two bruchids

The fumigant and contact toxicity of essential oil (EO) extracted from the leaves of Callistemon viminalis and its aromatized clay powder (ACP) was evaluated against adults of Acanthoscelides obtectus and Callosobruchus maculatus (Coleoptera: Bruchidae). The results obtained for fumigation assays showed that C. maculatus seems to be more susceptible (LC50 = 0.019 μl/cm3) to the vapours of the essential oil than A. obtectus (LC50 = 0.011 μl/cm3) after 12 h exposure. On the other hand, A. obtectus seems to be more susceptible (LD50 = 0.133 μl/g) to the essential oil applied by contact on grains than C. maculatus (LD50 = 0.170 μl/g) after 2 days exposure. The ACP was also very toxic towards the adults of A. obtectus (LD50 = 0.100 μl/g) and C. maculatus (LD50 = 0.098 μl/g) by contact on grains. At the doses of 0.133 μl/g and 0.266 μl/g, mortalities caused by ACP on grains were higher than those caused by the same dose of EO against the two bruchids. It is also established that both the EO and the ACP caused higher inhibition of F1 progeny production of A. obtectus than that of C. maculatus. The loss of insecticidal activity of the two materials in the course of time has been observed; however, the toxicity of the ACP was more persistent than that of the oil in the course of time when applied on grains. These results suggest that EO from the leaves of C. viminalis can be used as fumigant agent against A. obtectus and C. maculatus. In addition, it could be advisable to use an adsorbent mineral material as carrier of this EO for the prolongation of its insecticidal activity in the course of time.

A dimeric triterpenoid glycoside and flavonoid glycosides with free radical-scavenging activity isolated from Rubus rigidus var. camerunensis.

The aerial part of Rubus rigidus var. camerunensis (Rosaceae) is used to treat respiratory and cardiovascular disorders in the Cameroonian traditional medicine. The ethanol extract exhibited more potent antioxidant activity (Emaxs of 119% and 229% activity on DPPH and β-carotene test) than aqueous extract. Bioactivity-guided fractionation of the ethanol extract based on free radical-scavenging assay (DPPH assay) afforded five flavonoid glycosides (four flavonol glycosides and an anthocyanin) and three glucosides of 19α-hydroxyursane-type triterpenoid (two monomeric and one dimeric triterpenoids). The flavonoids were identified as kaempferol 3-O-(2″-O-E-p-coumaroyl)-β-D-glucopyranoside (1), kaempferol-3-O-β-D-glucopyranoside (astragalin, 2), kaempferol-3-O-α-L-arabinofuranoside (juglanin, 3), quercetin-3-O-β-D-glucopyranoside (isoquercitrin, 4), pelargonidin-3-O-β-D-glucopyranoside (callistephin, 5). The three triterpenoids were 2α, 3β, 19α, 23-tetrahydroxyurs-12-ene-28-O-β-D-glucopyranosyl ester (nigaichigoside F1, 6), 2α, 3β, 19α-trihydroxyurs-12-ene-23-carboxyl-28-O-β-D-glucopyranosyl ester (suavissimoside R1, 7) as monomeric triterpenoids and coreanoside F1 (8) as a dimeric triterpenoid. The flavonoids exhibited potent antioxidant activities (66 to 93.56% against DPPH radical) and they were also active on β-carotene test. Coreanoside F1 exhibited a 63% antioxidant activity, meanwhile the other two triterpenoids showed a weak activity. Three important facts on structure-activity relationship were observed: Compound 8, a dimeric triterpenoid glycoside, strongly enhanced antioxidant activity of its monomers, compound 3 with 3-O-α-L-arabinofuranyl has much more potent activity than compound 2 with 3-O-β-D-glucopyranosyl, and antocyanin (5) is more potent than its corresponding flavonol glycosides.

In vivo anti-inflammatory effect of a new steroidal saponin, mannioside A, and its derivatives isolated from Dracaena mannii

A new steroidal saponin, mannioside A (1), was isolated from the stem bark of Dracaena mannii, together with the known pennogenin (2), pennogenin-3-O-β-D-glucopyranoside (3) and pennogenin-3-O-α-L-rhamnopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→3)]-β-D-glucopyranoside (4). Their structures were determined using 1D-and 2D-NMR spectroscopy and mass spectrometry. Compounds 1 and 3 significantly inhibited carrageenan-induced paw edema in the rat; compound 4 was moderately active whereas 2 showed very weak activity.

Volatile oil from striped African pepper (Xylopia parviflora, Annonaceae) possesses notable chemopreventive, anti-inflammatory and antimicrobial potential

Fruits of Xylopia parviflora, well known as striped African pepper, are sold in the Cameroonian markets as a flavouring ingredient to make traditional soups. The essential oil hydrodistilled from fruits was analysed for in vitro biological activities, namely cytotoxic, anti-inflammatory, antimicrobial and antioxidant, by MTT, nitric oxide inhibitory assay, agar disc diffusion method, and DPPH and ABTS assays. The essential oil composition, analysed by GC and GC-MS, was dominated by monoterpene hydrocarbons (50.0%) responsible for the pepper odour, such as β-pinene (34.0%) and α-pinene (10.3%). The oil induced a strong inhibitory effect on tumour cells MDA-MB 231 and HCT116, with inhibition values close to those of cisplatin. A dose-dependent decrease in NO production was noted in RAW 264.7 macrophages treated with the oil, revealing a promising anti-inflammatory potential. The essential oil showed a measurable antimicrobial activity against all the species tested, while the radical scavenging activity was low.

Antibacterial activities of the extracts, fractions and compounds from Dioscorea bulbifera

BackgroundDioscorea bulbifera is an African medicinal plant used to treat microbial infections. In the present study, the methanol extract, fractions (DBB1 and DBB2) and six compounds isolated from the bulbils of D. bulbifera, namely bafoudiosbulbins A (1), B (2), C (3), F (4), G (5) and 2,7-dihydroxy-4-methoxyphenanthrene (6), were tested for their antimicrobial activities against Mycobacteria and Gram-negative bacteria involving multidrug resistant (MDR) phenotypes expressing active efflux pumps.MethodsThe microplate alamar blue assay (MABA) and the broth microdilution methods were used to determine the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the above samples.ResultsThe results of the MIC determinations indicated that when tested alone, the crude extract, fractions DBB1 and DBB2 as well as compounds 2 to 5 were able to prevent the growth of all the fifteen studied microorganisms, within the concentration range of 8 to 256 μg/mL. The lowest MIC value for the methanol extract and fractions (16 μg/mL) was obtained with DBB1 and DBB2 on E, coli AG100A and DBB2 on Mycobacterium tuberculosis MTCS2. The lowest value for individual compounds (8 μg/mL) was recorded with compound 3 on M. smegmatis and M. tuberculosis ATCC and MTCS2 strains respectively. The activity of the samples on many MDR bacteria such as Enterobacter aerogenes EA289, CM64, Klebsiella pneumoniae KP63 and Pseudomonas aeruginosa PA124 was better than that of chloramphenicol. When tested in the presence of the efflux pump inhibitor against MDR Gram-negative bacteria, the activity of most of the samples increased. MBC values not greater than 512 μg/mL were recorded on all studied microorganisms with fraction DBB2 and compounds 2 to 5.ConclusionsThe overall results of the present investigation provided evidence that the crude extract D. bulbifera as well as some of the compounds and mostly compounds 3 could be considered as potential antimicrobial drugs to fight against MDR bacteria.