The biology and toxicology of molluscicides, Bayluscide

Toxicity of lapachol and isolapachol and their potassium salts against Biomphalaria glabrata, Schistosoma mansoni cercariae, Artemia salina and Tilapia nilotica

The toxicity of soluble derivatives (potassium salt) of lapachol and isolapachol in different stages of the life cycle of Schistosoma mansoni is evaluated. The potassium salts of isolapachol and lapachol showed significant molluscicidal activity against the adult snail (LC90<7 ppm) and snail egg masses (LC90<3 ppm). Cercaricidal assays revealed strong activities for both compounds. Lethality assays against brine shrimp eggs (Artemia salina Leach) indicated very high toxicity for the potassium salt of isolapachol (LC90=1.54 ppm), differently from the potassium salt of lapachol that can be considered non toxic (LC90=176.3 ppm). The same tendency is observed with piscicidal activity, for which the isolapachol salt has showed higher toxicity. The obtained selectivity ratios concerning LC50 and LC90 for lapachol, in relation to Tilapia nilotica lethality assay are 2.33 and 1.26, respectively. Despite the piscicidal toxicity, the use of the salt of lapachol can be recommended for field tests in Schistosomiasis, with caution.

Antischistosomal bioactivity of isoflavonoids from Millettia thonningii (Leguminosae)

Extracts of the seeds of the leguminous tree Millettia thonningii are molluscicidal and schistosomicidal and contain a mixture of isoflavonoids and 3-phenylcoumarins. Robustic acid and a pure mixture of alpinumisoflavone and dimethylalpinumisoflavone, as characterized by nuclear magnetic resonance, were isolated from a dichloromethane extract. The bioactivity of these compounds against Schistosoma mansoni miracidia, cercariae, and adult worms was tested in vitro. Both robustic acid and the alpinumisoflavone mixture killed cercariae and adult schistosomes in vitro. At sublethal concentrations of the isoflavonoids, reductions in miracidial motility were measured using a video-imaging technique. The inhibition of mitochondrial electron transport at site I by the isolated isoflavonoids was also investigated. The results suggest that robustic acid and at least 1 alpinumisoflavone compound from the dichloromethane extract of the seeds of M. thonniogii are responsible for some of the observed bioactivity of this extract against schistosomes.

The control of the schistosome-transmitting snail Biomphalaria glabrata by the plant Molluscicide Euphorbia splendens var. hislopii (syn milli Des. Moul): a longitudinal field study in an endemic area in Brazil

Under laboratory conditions, latex from Euphorbia splendens has shown promise as a plant molluscicide for control of Biomphalaria species, intermediate hosts for Schistosoma mansoni. The purpose of this study was to evaluate its efficiency under field conditions. Application of filtered latex at 12 ppm to one stream in an endemic rural area in Minas Gerais state, Brazil, in September 1995, did result in a reduction in snail density as compared to an untreated stream but the snail population recovered quickly. However, two applications with a two-week interval of unfiltered E. splendens latex at 5 ppm in November 1996 in the same stream resulted in complete disappearance of B. glabrata and snails did not reappear until the 14th month after the applications. In the control stream, without treatment, the snails were found during all months. Laboratory studies confirmed that unfiltered latex is a more potent molluscicide than filtered latex. Considering the advantages of the latex such as its low toxicity to other aquatic animals and its photobiodegradability, as well as the simple method of application, this natural product is promising as an effective molluscicide.

Synthesis, electrochemistry, and molluscicidal activity of nitroaromatic compounds: effects of substituents and the role of redox potential

Abstract-Molluscicidal bioassays and electrochemical studies (measurement of first wave reduction potential, Epcl) were performed on several synthetic nitroaromatics, in relation to possible correlation between biological activity, redox potential and structural effects. Five of them presented a significant molluscicidal activity on Biomphalaria glabrata (LD50 < 20 ppm). The Epc1 values ranged from -0.532 to -0.857 V versus Ag/AgCl (0.1 M) (-0.260 to -0.585 V versus NHE), all of them, in the favorable range for reduction in vivo. Data comparison between Epc1 and molluscicidal activity indicates that the presence of the electroactive nitro group is important for the biological activity. Correlation with redox potential, however, was not evident. Structural effects seem to be the most important parameter. Higher activity is noticeable for phenols, including the para-nitro azo or hydrazo-containing compounds. No activity was observed for compounds having the benzylic substituent in meta position to the nitro group. These results suggest that activity undoubtedly involves more than reduction characteristics and that the possible formation of electrophilic species, after nitro reduction, can play an important role in molluscicidal activity against B. glabrata.

Molluscicidal activity of 2-hydroxy-3-alkyl-1,4-naphthoquinones and derivatives

In the search for new molluscicidal agents we tested the activity of lapachol and other 2-hydroxy-3-alkylnaphthoquinones possessing nitrogenated alkyl chains, against the snail Biomphalaria glabrata. Lapachol, isolapachol and nor-lapachol showed strong molluscicidal activity against the adult snail (LD(90)<10 ppm) and significant toxicity against snail egg masses (LD(90)<0.2 ppm). As lapachol is easily extracted, and the derivatives can be synthesised without any difficulty, large-scale synthesis and field tests can be conducted, with a view to large-scale molluscicidal programs.

Toxicity of Euphorbia milii latex and niclosamide to snails and nontarget aquatic species

The toxicity of Euphorbia milii molluscicidal latex and niclosamide (NCL) to target snails (Biomphalaria glabrata and Biomphalaria tenagophila) and nontarget aquatic organisms is evaluated. Planorbidae snails were killed by very low concentrations of lyophilized latex (48-h LC(50), mg/L: B. glabrata, 0.12; B. tenagophila, 0.09; Helisoma duryi, 0.10). Latex was less toxic (48-h LC(50) or EC(50), mg/L) to oligochaeta (Tubifex tubifex, 0.31), planktonic crustacea (Daphnia similis, 0.38; C. dubia, 1.07; Artemia sp., 0.93), and fishes (Danio rerio, 0.96; Poecilia reticulata, 1. 39), and considerably less toxic to Ampullariidae snails (Pomacea sp. , 10.55) and frog tadpoles (Rana catesbeiana, 7.50). Latex (up to 100 mg/L) was not toxic to bacteria (P. putida and V. fischeri), algae (Selenastrum capricornutum and Chlorella vulgaris), and mosquito larvae (Anopheles albitarsis, Aedes aegypti, Aedes fluviatilis). NCL was very toxic (48-h LC(50) or EC(50), mg/L) to Planorbidae snails (B. glabrata, 0.15, B. tenagophila, 0.13; H. duryi, 0.10), T. tubifex (0.11), crustacea (D. similis, 0.19; Ceriodaphnia dubia, 0.47; Artemia sp. 0.18), fishes (D. rerio, 0.25; P. reticulata, 0.29), R. catesbeiana (0.16), and Pomacea sp. (0.76). NCL was toxic to bacteria, algae (96-h IC(50), mg/L: S. capricornutum, 0.34; C. vulgaris, 1.23) and slightly toxic to mosquito larvae. In conclusion, E. milii latex, as compared with the reference molluscicide niclosamide, presents a higher degree of selectivity toward snails which are intermediate hosts of Schistosoma trematodes.

Toxic activities of the plant Jatropha curcas against intermediate snail hosts and larvae of schistosomes

The aim of studies on plant molluscicides is to complement methods for controlling snails acting as intermediate hosts of schistosomes. We report on the toxic activity of extracts from Jatropha curcas L. (Euphorbiaceae) against snails transmitting Schistosoma mansoni and S. haematobium. We studied different extracts' effects on infectious larvae, cercariae and miracidia of S. mansoni. Compared to aqueous extract, methanol extract showed the highest toxicity against all tested organisms with LC100-values of 25 p.p.m. for cercariae and the snail Biomphalaria glabrata and 1 p.p.m. for the snails Bulinus truncatus and B. natalensis. Attenuation of cercariae leading to reduced infectivity in mice could be achieved in concentrations below those exerting acute toxicity. In view of our results and the ongoing exploitation of J. curcas for other purposes, this plant could become an affordable and effective component of an integrated approach to schistosomiasis control.

Evaluation of three methods to control Bulinus truncatus, the intermediate host of Schistosoma haematobium in an irrigation scheme, Tessaout-Amont, Morocco

In Morocco, the implementation of new irrigation schemes resulted in the introduction of schistosomiasis haematobium to new areas. Canal structures (especially syphon boxes) were found to be favourable habitats for Bulinus truncatus and they constitute important transmission sites. Three methods for snail control in these syphon boxes were assessed in the Tessaout-Amont irrigation scheme. Molluscicide (niclosamide) application resulted in a pronounced reduction in the snail population density, but snails started to recolonise the sites a few months later. Regular brushing of the inner sides of the syphon boxes and covering the syphon boxes, so as to exclude light, resulted in significant reductions in snail numbers. However, the latter methods were not as efficient as the molluscicide.

Mammal toxicity assessment of the plant molluscicide, Apodytes dimidiata (Icacinaceae), in South Africa

Apodytes dimidiata has recently come to the fore as a potential plant molluscicide for schistosomiasis control in rural communities in South Africa. Prior to field applications of its leaves and extract to waterbodies, selected acute and sub-acute mammal toxicity tests were conducted in accordance with the Organisation of Economic Cooperation and Development (OECD) Guidelines to identify any potential hazards that might arise form the plant's use. Acute and sub-acute mammal toxicity test results classified A. dimidiata as non-toxic and non-irritating. Based on this toxicity evaluation, the dried leaf material and aqueous extracts of this plant are considered safe for use in preliminary field trials.

Acute toxicity evaluation of the plant molluscicide, Apodytes dimidiata (Icacinaceae), to Eisenia fetida (Oligochaeta) and Oreochromis mossambicus (Cichlidae) in South Africa

The crude aqueous leaf extract of a South African tree, Apodytes dimidiata, has been identified as a potential molluscicide for snail control in anti-schistosomiasis programmes in rural communities. Before preliminary field trials could be implemented its acute toxic effects on two non-target organisms were examined in accordance with the OECD guidelines to identify any potential hazards that might arise from the plant's use. Laboratory results showed that working molluscicidal concentrations of the plant extract were non-toxic to earthworms suggesting that it is non-hazardous to soil-dwelling fauna. The plant extract proved toxic to fish and was assigned the risk phrase 'harmful to the aquatic environment' according to the EEC classification scheme. Based on these toxicity evaluations, aqueous extracts of A. dimidiata are considered safe for use in preliminary field trials.

Novel anthelmintic compounds and molluscicides from medicinal plants

This review assesses the role that can be played by allelochemicals (bioactive secondary compounds) from medicinal and other plants in the control of human helminthic diseases. In the search for new anthelmintics among plant allelochemicals, 3 practical issues have considerable significance. They are the range and capacity of anthelmintic bioassays utilised in preclinical studies in vitro on plant extracts, the phenomenon of coexistent allelochemicals with overlapping activity spectra within single plants, and the problem of non-specific cytotoxins among plant allelochemicals. These topics are discussed in the context of the present absence of any clinically useful plant anthelmintics. In the search for new plant molluscicides for schistosomiasis control, the characteristics of a range of molluscicidal plants are measured against those of the synthetic molluscicide of choice, niclosamide, and against the postulated attributes of practically useful plant molluscicides.

Currently available molluscicides

Views about the importance of the role of molluscicides in the integrated control of human schistosomiasis have passed through cyclical changes over the past 15 years. For a time, it was hoped that chemotherapy alone would achieve significant morbidity control; it has since become clear that molluscicides cannot be easily excluded from the anti-schistosome armoury. In this review, Sheena Perrett and Phil Whitfield summarize the evidence for this conclusion and provide an overview of currently available synthetic molluscicides and those natural product molluscicides currently under active investigation.

Hirudinicidal activities of some natural molluscicides used in schistosomiasis control

Experiments were conducted with (molluscicides) aridanin isolated from Tetrapleura tetraptera, aridan, an extract from T. tetraptera, endod, an extract from Phytolacca dodecandra and niclosamide on non-target aquatic organisms such as leech, hydra, tadpoles, anopheline mosquito larvae and brine shrimps and compared with their toxicity to the target snail. Biomphalaria glabrata. Aridanin, aridan, endod, and niclosamide produced rapid knockdown effects on B. glabrata at 0.04, 1.00, 30.00, and 40.00 ppm, respectively. All the molluscicides killed the leech, a pest of animals and man at molluscicidal concentrations. The hydra and tadpoles tested were sensitive to the molluscicides except aridanin but the shrimps and anopheline mosquito larvae were resistant to all the molluscicides.

Dermal absorption of niclosamide in rats and minipigs

The dermal absorption of niclosamide, a drug shown to prevent Schistosomiasis by blocking the dermal penetration of cercariae, has been examined in Sinclair minipigs and rats. Radioactivity in the urine and feces collected daily for 7 days after application of 14C-niclosamide accounted for less than 2 per cent and 10 per cent of the labelled compound applied to pig and rat skin, respectively. Approximately 20 per cent of the radioactivity from the dose solution was recovered on the skin excised from the area of application in both minipigs and rats. No radioactivity was detected in organs removed from the pig 7 days after application of radiolabelled drug while less than 6 per cent of the dose could be accounted for in the rat organs/carcass. Radioactivity in swine blood, removed 0.5, 1, 2, 4 and at 24 h intervals after dosing, was at or below three times background in all of the samples. Total recovery of the applied radioactivity was 78 per cent in pigs and 57 per cent in rats. These studies indicate that niclosamide is very poorly absorbed after dermal application. The results are consistent with earlier comparative studies showing that dermal penetration of xenobiotics in rats is generally higher than in swine.

Laboratory evaluation of B-2 as a molluscicide in the control of the snail intermediate hosts of schistosomiasis in South Africa

There is a continuous need for the development and evaluation of new, inexpensive but highly effective molluscides for the control of freshwater snails acting as intermediate hosts of schistomiasis. For this reason B-2 (Hokko Chemical Industry Co. Ltd, Japan), also called Phebrol (sodium 2,5-dichloro-4-bromophenol), was evaluated in our laboratory as a candidate molluscicide for the control of freshwater snails in South Africa. Bulinus africanus and Biomphalaria pfeifferi, intermediate hosts of Schistosoma haematobium and Schistosoma mansoni respectively, were exposed to different B-2 concentrations for 24 and 48 hours. An indigenous fish species, Oreochromis mossambicus, which is common in local schistosomiasis endemic areas, was also exposed to the molluscicide. The calculated values obtained from a probit analysis (LC50, 24 hours: B. africanus = 2.6 mg 1(-1) and B. pfeifferi = 2.9 mg 1(-1), indicated that these species from southern Africa are less sensitive to B-2 than are B. truncatus and B. pfeifferi from northern Africa, which in turn are less sensitive than the Oncomelania spp. from Japan, China and the Philippines. It is expected that molluscicidal levels of B-2 would be harmful to O. mossambicus populations. Although B-2 has a marked potential for snail control in South Africa, niclosamide (Bayluscide) remains the molluscicide of choice.

Schistosoma mansoni: salicylanilides as topical prophylactic against cercarial penetration of mice

Salicylanilide and 37 of its analogs were applied topically to mice as candidate chemoprophylactic agents against Schistosoma mansoni cercarial penetration. The compounds were solubilized in absolute methanol, dimethyl sulfoxide, or isopropanol at concentrations not exceeding 1.25% W/V. The tails of the mice of each experimental group were treated by immersion for 5 min in the test compound solution or in the vehicle. The treated tails of 5 mice from each group were washed for 30 min in flowing tap water 3-4 hr after compound application. Tails of all mice were then exposed to approximately 100 cercariae by tail immersion for 1 hr, 24 hr after treatment. The portal veins were perfused 49 days after exposure and worm burdens were determined. The protective capacity of each compound was calculated by comparing the reduction of the mean worm burdens of the compound treated mice to the worm burdens of those treated with only the vehicle and expressing the resulting value as percentage protection. Of the 38 compounds tested, 20 provided 98% or better protection if the treated tails were not washed before exposure to cercariae. Of these 20 active compounds, 16 provided 98% or better protection from infection by S. mansoni cercariae even after the mouse tails were subjected to the 30 min wash.

On the use of plants and plant-derived compounds for the control of schistosomiasis

The rising costs of chemotherapy and synthetic molluscides have led to an increasing interest in plants which are lethal to the intermediate host of schistosomiasis (bilharzia). Over one thousand species have been tested but only a few have been phytochemically examined. Approximately fifty molluscicidal compounds have so far been isolated from plants, including saponins, terpenoids, flavonoids, naphthoquinones and tannins. The saponins from Phytolacca dodecandra are the most active and have been successfully employed in field tests. The latest results in this area and the problems involved in the use of plants and natural products for the control of schistosomiasis are discussed here.

[Histopathologic studies on epithelial proliferation in the peripheral region of the lung with special consideration of tumorlets]

Niclosamide is an oral antihelminthic drug used to treat parasitic infections in millions of people worldwide. However recent studies have indicated that niclosamide may have broad clinical applications for the treatment of diseases other than those caused by parasites. These diseases and symptoms may include cancer, bacterial and viral infection, metabolic diseases such as Type II diabetes, NASH and NAFLD, artery constriction, endometriosis, neuropathic pain, rheumatoid arthritis, sclerodermatous graft-versus-host disease, and systemic sclerosis. Among the underlying mechanisms associated with the drug actions of niclosamide are uncoupling of oxidative phosphorylation, and modulation of Wnt/β-catenin, mTORC1, STAT3, NF-κB and Notch signaling pathways. Here we provide a brief overview of the biological activities of niclosamide, its potential clinical applications, and its challenges for use as a new therapy for systemic diseases.

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Niclosamide is an oral antihelminthic drug used to treat parasitic infections.

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Niclosamide is a multifunctional drug inhibiting multiple signaling pathways and biological processes.

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Niclosamide has biological activities potentially against systemic diseases.