Marise M. O. Cabral

Effects of some lignans and neolignans on the development and excretion of Rhodnius prolixus.

The effects of six lignans and neolignans as inhibitors of ecdysis and on the water balance in fourth-instar larvae of Rhodnius prolixus were studied by oral, topical and continuous contact treatments. The main results may be summarised as follows: (i) burchellin, pinoresinol, sesamin, licarin A and nordihydroguaiaretic acid (NDGA) did not cause feeding inhibition at doses of 100 micrograms/ml blood; podophyllotoxin had no antifeedant effect but caused a high moulting inhibition and significant toxicity when applied either orally or topically; (ii) the highest ecdysis inhibitory effects were observed with pinoresinol and NDGA when applied orally at a dose of 100 micrograms/ml (58% and 50% of moulting inhibition, respectively); burchellin inhibited 30% of the moulting at this concentration; (iii) by topical treatment none of the compounds presented any influence on the moulting cycle; and (iv) podophyllotoxin and burchellin significantly reduced the excretion of the insect in 24 h; the other compounds had no effect on excretion. The implications of these findings in relation to the pertinent biological events in R. prolixus are discussed.

Larvicidal Activity of Grandisin Against Aedes aegypti

Abstract Dengue is a tropical disease caused by an arbovirus transmitted by the mosquito Aedes aegypti. Because no effective vaccine is available for the disease, the strategy for its prevention has focused on vector control by the use of natural insecticides. The aim of this study was to evaluate the larvicidal activity of the lignan grandisin, a leaf extract from Piper solmsianum, against Ae. aegypti.

Effects of the lignan, pinoresinol on the moulting cycle of the bloodsucking bug Rhodnius prolixus and of the milkweed bug Oncopeltus fasciatus

Abstract The furano-lignan pinoresinol was toxic to fourth-instar larvae of the milkweed bug Oncopeltus fasciatus and of the haematophagous insect Rhodnius prolixus , a vector of Chagas disease. At lower doses, it also exerted antifeedant activity and dose-dependent antimoulting activity on both insects.

Neolignans from plants in northeastern Brazil (Lauraceae) with activity against Trypanosoma cruzi

Trypanosoma cruzi is the ethiological agent for Chagas disease in Latin America. This study aimed to test the trypanocidal effect of licarin A and burchellin isolated from plants in northeastern Brazil. These neolignans were tested on T. cruzi and on peritoneal macrophages, to evaluate drug toxicity. Epimastigote growth was inhibited in 45% with licarin A and 20% with burchellin with an IC(50)/96 h of 462.7 microM and 756 microM, respectively. Epimastigotes treated with licarin A presented swollen mitochondria and disorganized mitochondrial cristae, kDNA and Golgi complex. When treated with burchellin, they presented enormous autophagosomes and chromatin disorganization. Licarin A and burchellin were able to induce trypomastigote death with IC(50)/24 h of 960 microM and 520 microM, respectively. Although licarin A presented an IC(50) for trypomastigotes higher than for epimastigotes, both substances acted as therapeutic trypanocidal agents, because they were able to kill parasites without affecting macrophages. Due to our results, burchellin and licarin A need to be further analysed to observe if they may be used as alternative blood additive prophylaxis against Chagas disease, since it has been established that blood transfusion is an important mechanism in the transmission process.

Effects of lignoids on a hematophagous bug, Rhodnius prolixus: feeding, ecdysis and diuresis

The effects of lignoids on feeding, ecdysis and diuresis in fourth-instar larvae of Rhodnius prolixus (Hemiptera) were investigated. Up to 100 microg/ml burchellin, podophyllotoxin, pinoresinol, sesamin, licarin A, or nordihydroguaiaretic acid (NDGA) in the diet did not induce antifeedant effects. Pinoresinol and NDGA significantly inhibited ecdysis. In experiments in vivo, burchellin and podophyllotoxin reduced the production of urine after feeding. 5-Hydroxytryptamine (5-HT), a diuretic hormone, partially counteracted this effect of burchellin. In experiments in vitro, using isolated Malpighian tubules, (i) burchellin reduced diuretic hormone levels in the hemolymph but not the amount of diuretic hormone stored in the thoracic ganglionic masses (including axons), (ii) burchellin decreased the volume of urine secreted by isolated Malpighian tubules, and (iii) 5-HT could not overcome the effect of burchellin upon the Malpighian tubules. We conclude that burchellin interfered with the release, but not with the production of diuretic hormone by the thoracic ganglionic mass or induced an antidiuretic hormone and directly affected the Malpighian tubules.

Lignanes from the Brazilian Melia azedarach, and their activity in Rhodnius prolixus (Hemiptera, Reduviidae)

A study of the phagoinhibitor and anti-moulting activities of the Brazilian Melia azedarach, collected in the State of Rio de Janeiro, Brazil, allowed the isolation of four lignanes identified as pinoresinol (1), bis-epi-pinoresinol (2), the hemicetal (3) and the diacid (4). These substances are devoid of anti-moulting activity.

Neolignans inhibit Trypanosoma cruzi infection of its triatomine insect vector, Rhodnius prolixus

Abstract Two neolignans, burchellin and nordihydroguaiaretic acid (NDGA), were toxic only to Trypanosoma cruzi clone Dm28c maintained in brain heart infusion (BHI) medium at a concentration of 100 μg/ml, not 10 μg/ml. When Rhodnius prolixus was fed with epimastigotes of T. cruzi and treated simultaneously with a single dose of burchellin or NDGA at 10 μg/ml of blood meal the number of parasites in the gut decreased. Whereas burchellin was only partially active, NDGA drastically reduced the number of epimastigotes and metacyclic trypomastigotes of T. cruzi in the excreta (urine plus feces). When the insect larvae were pretreated with burchellin or NDGA at 20 days before the infection with T. cruzi a significant reduction in the number of parasites in the gut occurred. However, when both compounds were applied at 20 days after the establishment of T. cruzi infection, although burchellin significantly reduced the gut infection, neither compound could abolish the infection entirely within the subsequent 15 days.

Grandisin caused morphological changes larval and toxicity on Aedes aegypti

Dengue is a tropical disease caused by an arbovirus transmitted by Aedes aegypti. Since no effective vaccine is available for treating dengue, the present study focused on population vector control through investigating the use of the lignan grandisin, isolated from Piper solmsianum C. DC., Piperaceae, against the larvae of A. aegypti. Grandisin caused larval (L3) mortality at LC50 150 µg/mL. Histological analysis on A. aegypti larvae treated with grandisin (LC50 50 µg/mL) showed changes in the anterior-middle midgut, with intense tissue destruction and cell disorganization.

Biological Activity of Yangambin on the Postembryonic Development of Chrysomya megacephala (Diptera: Calliphoridae)

Abstract Phytochemicals endowed with hormonal, antihormonal, or toxic activity are potential agents for insect control. Thus, we became interested in testing Brazilian plant metabolites on Chrysomya megacephala (F.) (Diptera: Calliphoridae), a public health menace that is one of the most prevalent flies in Brazilian urban areas. We tested the lignan yangambin, from the leaves of Ocotea duckei Vattimo (Lauraceae). Topical treatment of eggs and first instars with yangambin as well as feeding larvae a yangambin-treated diet resulted in inhibition of postembryonic development, morphological alteration, and oviposition reduction.

Anti-moulting activity in Brazilian Melia azedarach.

Departamento de Bioquimica e Biologia Molecular, Instituto Oswaldo Cruz, Av. Brasil 4365, 21045-900Rio de Janeiro, RJ, Brasil *Max-Planck Institut fur Biochemie, Martinsried bei Munchen, D-8033,Deutchland **Instituto de Biologia, Universidade Federal Fluminense, Caixa Postal 100.436,24001-970 Niteroi, RJ, BrasilKey words : Melia azedarach L. - seeds - anti-moulting activity