Jorge D. Coussio

Insecticidal activity against Aedes aegypti larvae of some medicinal South American plants.

The insecticidal activity of 11 extracts from nine South American medicinal plants has been studied using the Aedes aegypti larvicidal assay. Eight of the 11 plant extracts studied showed toxicity against the A. aegypti larvae (LC(50)<500 microg/ml). The dichloromethane extracts of Abuta grandifolia and Minthostachys setosa demonstrated high larvicidal activity, the most active being the dichloromethane extract of A. grandifolia, with an LC(50)=2.6 microg/ml (LC(100)= 8.1 microg/ml), indicating an activity 2-fold higher than beta-asarone, a natural botanical insecticide used as a positive control (LC(100)=16 microg/ml). On the other hand, the dichloromethane extract of M. setosa was quite potent against A. aegypti larvae showing an LC(50)=9.2 microg/ml (LC(100)=25.2 microg/ml). The results obtained suggest that the extracts of A. grandifolia and M. setosa are promising as larvicides against A. aegypti larvae and could be useful in the search for new larvicidal natural compounds.

Argentine plants as potential source of insecticidal compounds

CH2Cl2 and MeOH extracts of 15 Argentine plants used locally as insecticides, were evaluated for their insecticidal activity. Chenopodium multifidum L. (Chenopodiaceae); Flaveria bidentis (L.) O.K. (Compositae); Aristolochia argentina Gris. (Aristolochiaceae) and Tagetes erecta L. (Compositae) showed a significant activity against Sitophilus oryzae.

Antioxidant and free radical scavenging effects in extracts of the medicinal herb Achyrocline satureioides (Lam.) DC. ("marcela")

Achyrocline satureioides (Lam.) DC. (Compositae) is a medicinal herb used in Argentina, Uruguay, Brazil and Paraguay for its choleretic, antispasmodic and hepatoprotective properties. The presence of the flavonoid quercetin and its derivatives, and of different phenolic acids such as caffeic, chlorogenic and isochlorogenic acids in the aerial parts of this plant has led us to study the antioxidant activity of its extracts using different bioassays. The inhibition of luminol-enhanced chemiluminescence by the aqueous and methanolic extracts was used to show that their total reactive antioxidant potential index (TRAP; in microM Trolox equivalents) was 91.0 +/- 15.4 and 128.1 +/- 20.1 microM, respectively, while the total antioxidant reactivity index (TAR) was calculated to be 1537 +/- 148 and 1910 +/- 171 microM. Only the methanolic extract was capable of reducing iron (II)-dependent DNA damage. Lipid peroxidation was assessed by two different methods. The aqueous extract reduced hydroperoxide-initiated chemiluminescence in rat liver homogenates at all concentrations in a dose-dependent manner, with a calculated IC50 = 225 micrograms/ml, while the methanolic extract was only effective at higher concentrations (100 and 1000 micrograms/ml). Both aqueous and methanolic extracts were capable of reducing the production of thiobarbituric acid reactive substances (TBARS) in rat liver homogenates, with an IC50 > 1000 micrograms/ml. The results obtained suggest that the extracts of A. satureioides possess significant free radical scavenging and antioxidant activity in vitro, a fact that should encourage future in vivo studies.

Survey of Argentine Medicinal Plants -Folklore and Phytochemical - Screening. II

Argentina has around 500 native medicinal plants, according to the folklore use, plus nearly 200 toxic species. So there are 700 indigenous species suitable to be used in pharmacognostical-pharmacological studies with a high probability of getting active compounds from them. As the Instituto Nacional de Farmacologia y Bromatologia was interested in the medicinal flora to be studied we considered that a catalog of Argentine species with their uses and chemical composition would help in promoting research on them. Nevertheless, as there have been few species exhaustively investigated we screened them for different constituents ( 1,2) (Table I) while surveying the literature for chemical composition and folklore data for medicinal use up to 1972 (Table II)2.

First cyclotide from Hybanthus (Violaceae)

Hypa A, a novel macrocyclic polypeptide containing 30 amino acid residues, has been isolated from the n-butanol extract of the Argentine plant Hybanthus parviflorus. The sequence, cyclo-(SCVYIPCTITALLGCSCKNKVCYNGIPCAE), was determined by automated Edman degradation, quantitative amino acid analysis and nanospray MS/MS(2). Three intramolecular disulfide bridges stabilize the cyclic peptide backbone of hypa A. Using these structural features to classify the peptide as a cyclotide, we extended the distribution of that substance class to a new genus, and now propose a uniform nomenclature for cyclotides.

Cytotoxic and DNA interaction activities of extracts from medicinal plants used in Argentina

Eight crude extracts from seven Argentine plants with cancer-related ethnobotanical uses have been subjected to a bioscreening study to detect cytotoxic activity. The plants studied were: Aristolochia triangularis, Baccharis grisebachii, Bolax gummifera, Eupatorium hecatanthum, Erythrina crista-galli, Pterocaulon polystachium and Salpichroa origanifolia. Crown gall tumour inhibition, DNA interaction and cytotoxicity towards KB cells were assayed using the potato disc, the DNA-methyl green (DNA-MG) and the KB cells cytotoxicity bioassays respectively. The results obtained indicate that A. triangularis (ED50=47 microg/ml), B. gummifera (ED50=32 microg/ml) and E. hecatanthum (ED50=35 microg/ml) contained cytotoxic compounds against KB cells. All of the plants studied inhibited the growth of crown gall tumours, showing correlation between the experimental data and the uses reported for these plants. Moreover, the results obtained for the extracts of E. hecatanthum and P. polystachium indicate the presence of compounds that interact with DNA (48 and 22% of absorbance decrease, respectively). The results obtained suggest that cytotoxicity could play an important role in the activities claimed for the plants under study.

Evaluation of the in vitro antioxidant activity in extracts of Uncaria tomentosa (Willd.) DC.

Different extracts of U. tomentosa were tested in vitro for their antioxidant activity utilizing tert ‐butyl‐hydroperoxide‐initiated chemiluminescence in rat liver homogenates. Methanol fractions of both stem‐bark and roots were capable of exerting antioxidant activity by this technique. The presence of different concentrations of bark and root methanol extracts also prevented TBARS production and free radical‐mediated DNA‐sugar damage.

Mate substitutes or adulterants: study of xanthine content

The xanthine (caffeine, theobromine and theophylline) content of decoctions of seven Ilex spp. was studied by HPLC using UV and a photodiode‐array detector. Ilex paraguariensis (‘Mate’ or ‘Yerba Mate’) is widely used in South America as a tealike beverage and the other six species are used as substitutes or adulterants of it. The results showed that I. paraguariensis has the highest amounts of caffeine and theobromine. Traces of caffeine were detected in I. theezans, I. dumosa, I. microdonta and I. pseudobuxus. Traces of theobromine were detected in I. argentina and I. microdonta. From the seven Ilex species investigated, theophylline was detected in I. theezans, I. dumosa and I. pseudobuxus, but only I. pseudobuxus has quantifiable amounts: 0.6 mg% (6 ppm).

Caffeoylquinic acids from Pterocaulon virgatum and Pluchea sagittalis

Pterocaulon virgatum (L.) DC. and Pluchea sagittalis (Lam.) Cabrera (common name ‘lucera’) are two Compositae widely distributed in the northeastern region of Argentina [l]. They are used in folk medicine due to their tonic, sour and digestive properties ([2, 31; Bowes, N., personal communication). Infusions of P. sugittalis have been described as colagogue and choleretic when given to patients with liver and gall-bladder problems [4]. In a previous paper we have reported the isolation of a flavone from P. sagittalis [S]. The present paper reports the isolation of 3,klicafieoylquinic acid (yield 1%) from P. uirgattun and isochlorogenic acid (yield 0.2 %) (a mixture of 3,4-; 4,5and 3,5&ATeoylquinic acid) from P. sagittalis. This is the first report of 3,4-dicaffeoylquinic acid as a single product; it always occurs in other sources with its isomers. Caffeic acid and its esters have proved to increase bile flow in rats [6, 71. The medicinal properties of these plants are presumably related to the high content of caffeic acid esters found in them.

Polyphenols from Achyrocline satureioides

Abstract Galangin, galangin 3-methyl ether, querectin, querectin 3-methyl ether, caffeic acid and two esters of calleryanin (3,4-dihydroxybenzylalcohol 4-glucoside), with caffeic acid and protocatechuic acid, have been isolated from aerial parts of Achyrocline satureioides .