Protective effects of organoselenium compounds against methylmercury-induced oxidative stress in mouse brain mitochondrial-enriched fractions

We evaluated the potential neuroprotective effect of 1-100 µM of four organoselenium compounds: diphenyl diselenide, 3’3-ditri-fluoromethyldiphenyl diselenide, p-methoxy-diphenyl diselenide, and p-chloro-diphenyl diselenide, against methylmercury-induced mitochondrial dysfunction and oxidative stress in mitochondrial-enriched fractions from adult Swiss mouse brain. Methylmercury (10-100 µM) significantly decreased mitochondrial activity, assessed by MTT reduction assay, in a dose-dependent manner, which occurred in parallel with increased glutathione oxidation, hydroperoxide formation (xylenol orange assay) and lipid peroxidation end-products (thiobarbituric acid reactive substances, TBARS). The co-incubation with diphenyl diselenide (100 µM) completely prevented the disruption of mitochondrial activity as well as the increase in TBARS levels caused by methylmercury. The compound 3’3-ditrifluoromethyldiphenyl diselenide provided a partial but significant protection against methylmercury-induced mitochondrial dysfunction (45.4 ± 5.8% inhibition of the methylmercury effect). Diphenyl diselenide showed a higher thiol peroxidase activity compared to the other three compounds. Catalase blocked methylmercury-induced TBARS, pointing to hydrogen peroxide as a vector during methylmercury toxicity in this model. This result also suggests that thiol peroxidase activity of organoselenium compounds accounts for their protective actions against methylmercury-induced oxidative stress. Our results show that diphenyl diselenide and potentially other organoselenium compounds may represent important molecules in the search for an improved therapy against the deleterious effects of methylmercury as well as other mercury compounds.

Methylmercury intoxication activates nitric oxide synthase in chick retinal cell culture

The visual system is a potential target for methylmercury (MeHg) intoxication. Nevertheless, there are few studies about the cellular mechanisms of toxicity induced by MeHg in retinal cells. Various reports have indicated a critical role for nitric oxide synthase (NOS) activation in modulating MeHg neurotoxicity in cerebellar and cortical regions. The aim of the present study is to describe the effects of MeHg on cell viability and NOS activation in chick retinal cell cultures. For this purpose, primary cultures were prepared from 7-day-old chick embryos: retinas were aseptically dissected and dissociated and cells were grown at 37ºC for 7-8 days. Cultures were exposed to MeHg (10 µM, 100 µM, and 1 mM) for 2, 4, and 6 h. Cell viability was measured by MTT method and NOS activity by monitoring the conversion of L-[H³]-arginine to L-[H³]-citrulline. The incubation of cultured retina cells with 10 and 100 µM MeHg promoted an increase of NOS activity compared to control (P < 0.05). Maximum values (P < 0.05) were reached after 4 h of MeHg incubation: increases of 81.6 ± 5.3 and 91.3 ± 3.7%, respectively (data are reported as mean ± SEM for 4 replicates). MeHg also promoted a concentration- and time-dependent decrease in cell viability, with the highest toxicity (a reduction of about 80% in cell viability) being observed at the concentration of 1 mM and after 4-6 h of incubation. The present study demonstrates for the first time the modulation of MeHg neurotoxicity in retinal cells by the nitrergic system.

Heavy metal toxicity in rice and soybean plants cultivated in contaminated soil

Heavy metals can accumulate in soil and cause phytotoxicity in plants with some specific symptoms. The present study evaluated the specific symptoms on rice and soybeans plants caused by excess of heavy metals in soil. Rice and soybean were grown in pots containing soil with different levels of heavy metals. A completely randomized design was used, with four replications, using two crop species and seven sample soils with different contamination levels. Rice and soybean exhibited different responses to the high concentrations of heavy metals in the soil. Rice plants accumulated higher Cu, Mn, Pb and Zn concentrations and were more sensitive to high concentrations of these elements in the soil, absorbing them more easily compared to the soybean plants. However, high available Zn concentrations in the soil caused phytotoxicity symptoms in rice and soybean, mainly chlorosis and inhibited plant growth. Further, high Zn concentrations in the soil reduced the Fe concentration in the shoots of soybean and rice plants to levels considered deficient.

Modulatory activity of antioxidants against the toxicity of Rifampicin in vivo

The World Health Organization (WHO) has shown concern about the burden of tuberculosis in the developing countries. Even though rifampicin is an effective drug in the management of tuberculosis, it has been documented to have some toxic effects in humans. Therefore, this study intends to investigate the modulatory effect of vitamins C and E on the hepatotoxicity, sperm quality and brain toxicity of Rifampicin. Forty Wistar albino rats were used, 10 animals per group. Group 1 animals received 0.3 mL of distilled water, the Group 2 animals received the therapeutic dose of rifampicin, Group 3 animals received therapeutic doses of rifampicin plus vitamin E, while Group 4 received therapeutic doses of rifampicin and vitamin C. The administration was performed orally during three months; the animals were sacrificed by cervical dislocation at the end of that period. Blood samples were collected and liver function and lipid profile was analyzed using fully automated clinical chemistry device. The liver, brain and reproductive organs underwent histopathological examination. Sperm samples were collected from the epididymis to achieve count and motility and morphological analysis. Results showed rifampicin alone to raise (p < 0.05) liver function enzymes (Aspartate amino transferase [AST], Serum alanine amino transferase [ALT] and Total Bilirubin) when compared with controls. While the vitamin E treated group showed remarkable protection, the vitamin C treated group showed questionable protection against the rifampicin induced liver damage. Sperm count results showed an important (p < 0.05) increase in the sperm quality in vitamin E and C treated groups. However, the vitamin E plus Rifampicin treated group showed increased lipid peroxidation. The histopathological findings revealed structural damages by rifampicin in liver, brain and epididymis while some remarkable architectural integrity was observed in the antioxidant-treated groups. It can be concluded that vitamin E or C improved sperm quality and protected against the brain damage caused by rifampicin. Moreover, vitamin E demonstrated remarkable hepatoprotection against rifampicin induced damage while vitamin C shows a questionable hepatoprotection.

Toxicity of saponin isolated from Gymnema sylvestre R. Br. (Asclepiadaceae) against Culex tritaeniorhynchus Giles (Diptera: Culicidae) Japanese encephalitis vector mosquito in India

To determine the larvicidal activity of various extracts of Gymnema sylvestre against the Japanese Encephalitis vector, Culex tritaeniorynchus in Tamilnadu, India. To identify the active principle present in the promising fraction obtained in Chlorofom:Methanol extract of Fraction 2. The G. sylvestre leaf extracts were tested, employing WHO procedure against fourth instar larvae of C. tritaeniorhynchus and the larval mortalities were recorded at various concentrations (6.25, 12.5, 25.0, 50 and 100 µg/mL); the 24h LC50 values of the G. Sylvestre leaf extracts were determined following Probit analysis. It was noteworthy that treatment level 100 µg/mL exhibited highest mortality rates for the three different crude extracts and was significantly different from the mean mortalities recorded for the other concentrations. The LC50 values of 34.756 µg/mL (24.475-51.41), 31.351 µg/mL (20.634-47.043) and 28.577 µg/mL (25.159-32.308) were calculated for acetone, chloroform and methanol extract with the chi-square values of 10.301, 31.351 and 4.093 respectively. The present investigation proved that G. Sylvestre could be possibly utilized as an important component in the Vector Control Program.

Chemical composition, toxicity and larvicidal and antifungal activities of Persea americana (avocado) seed extracts

The present study had the aim of testing the hexane and methanol extracts of avocado seeds, in order to determine their toxicity towards Artemia salina, evaluate their larvicidal activity towards Aedes aegypti and investigate their in vitro antifungal potential against strains of Candida spp, Cryptococcus neoformans and Malassezia pachydermatis through the microdilution technique. In toxicity tests on Artemia salina, the hexane and methanol extracts from avocado seeds showed LC50 values of 2.37 and 24.13mg mL-1 respectively. Against Aedes aegypti larvae, the LC50 results obtained were 16.7mg mL-1 for hexane extract and 8.87mg mL-1 for methanol extract from avocado seeds. The extracts tested were also active against all the yeast strains tested in vitro, with differing results such that the minimum inhibitory concentration of the hexane extract ranged from 0.625 to 1.25mg L-¹, from 0.312 to 0.625mg mL-1 and from 0.031 to 0.625mg mL-1, for the strains of Candida spp, Cryptococcus neoformans and Malassezia pachydermatis, respectively. The minimal inhibitory concentration for the methanol extract ranged from 0.125 to 0.625mg mL-1, from 0.08 to 0.156mg mL-1 and from 0.312 to 0.625mg mL-1, for the strains of Candida spp., Cryptococcus neoformans and Malassezia pachydermatis, respectively.

Evaluation of larvicidal activity and brine shrimp toxicity of rhizome extracts of Zingiber zerumbet (L.) Smith

Introduction In this study, we used dichloromethane (DCM) and methanol (MeOH) extracts of the Zingiber zerumbet rhizome to evaluate brine shrimp lethality and larvicidal activity on Aedes aegypti and Anopheles nuneztovari mosquitoes. Methods Bioassays were performed by exposing third-instar larvae of each mosquito species to the DCM or MeOH extracts. Results Probit analysis with DCM and MeOH extracts demonstrated efficient larvicidal activity against A. aegypti and A. nuneztovari larvae. Conclusions The DCM and MeOH extracts showed higher activity against A. nuneztovari larvae than against A. aegypti larvae, suggesting that the extracts have species-specific activity.

Effects of piperonyl butoxide on the toxicity of the organophosphate temephos and the role of esterases in the insecticide resistance of Aedes aegypti

IntroductionThe effects of piperonyl butoxide (PBO) on the toxicity of the organophosphate temephos (TE) and the role of esterases in the resistance of Aedes aegypti to this insecticide were evaluated.MethodsA. aegypti L4 larvae susceptible and resistant to TE were pre-treated with PBO solutions in acetone at concentrations of 0.125, 0.25, 0.5, 1, and 2% for 24h and subsequently exposed to a diagnostic concentration of 0.02mg/L aqueous TE solution. The esterase activity of the larvae extracts pre-treated with varying PBO concentrations and exposed to TE for three time periods was determined.ResultsAt concentrations of 0.25, 0.5, 1, and 2%, PBO showed a significant synergistic effect with TE toxicity. High levels of esterase activity were associated with the survival of A. aegypti L4 larvae exposed to TE only.ConclusionsThe results of the biochemical assays suggest that PBO has a significant inhibitory effect on the total esterase activity in A. aegypti larvae.

Analysis of toxicity on Bacillus sphaericus from amazonian soils to Anopheles darlingi and Culex quinquefasciatus larvae

Bioassays under laboratory conditions aiming to determine the larvicidal activity of Bacillus sphaericus were carried out on Anopheles darlingi and Culex quinquefasciatus. In order to estimate the toxicity through median lethal concentration (LC50) and the relative potency of the strains to B. sphaericus standard strain 2362, probit analysis was performed utilizing the POLO-PC program. The findings of LC50 pointed out high effectiveness on strains IB15 (0.040 ppm), IB19 and S1116 (0.048 ppm), IB16 (0.052 ppm) and S265 (0.057 ppm). Strain IB15 presented nearly 50% more potency than strain 2362 in bioassays conducted on A. darlingi. It was observed that IB16 and S1116 strains were the most powerful against C. quinquefasciatus, showing to be about 300-400% stronger than 2362 strain. The results show that laboratory conditioned evaluation can be an important way to select promising bacteria with entomopathogenic action on biolarvicides production for use on mosquitoes breeding sites.

Mercury and methylmercury concentration assessment in children's hair from Manaus, Amazonas state, Brazil

The present study evaluated Hg and MeHg content in hair samples of 201 children 2 to 7 years old, living in six neighborhoods of the city of Manaus, Amazonas State, Brazil. In general, the total Hg and MeHg median ranges in hair were similar (0.91 to 1.71 mg kg-1) except for the São Jose neighborhood, which was lower (0.16 mg kg-1). De spite the fact that the Manaus population consumes fish as part of the normal dietary intake, the Hg hair levels were below the level for an adult population not exposed to mercury (2.0 mg kg-1). These data were compared to demographic, socioeconomic information and eating habits of the families that took part in the study. The results were also compared to other published data from the Amazon region, other regions of Brazil and other countries. Future studies to set Hg and MeHg levels in hair of children in Brazil should take into account and assess the diversity of the country, mainly in terms of eating habits, socio-economic and cultural aspects.

Toxicity and repellency of essential oils to Zabrotes subfasciatus (Boheman) (Coleoptera, Chrysomelidae, Bruchinae) in Phaseolus vulgaris L

The effects of tangerine (Phaseolus vulgaris Blanco), lemon (Citrus medica limonum Lush), pear orange (Citrus sinensis L. Osbeck), red copaiba (Copaifera langsdorffii Desf.), rosemary (Baccharis dracunculifolia De Candole), Eucalyptus (Eucalyptus globulus Labillardière and E. citriodora Hook), lemongrass (Cymbopogon citratus Stapf.) and citronella (Cimbopogon nardus Linnaeus) oils at several concentrations on Zabrotes subfasciatus (Boheman) were studied. In toxicity tests, grains of Phaseolus vulgaris L. cv. Rajadinho were impregnated with oils and infested with adults of Z. subfasciatus up to 24 hours old. All tested oils were effective in reducing the viable egg-laying and adult emergence of this pest, in function of the concentrations used, highlighting E. citriodora and E. globulus oils which caused 100% effectiveness from 0.5 mL Kg-1 concentration. In repellency tests, two arenas consisting of plastic containers, connected symmetrically to a central box by two plastic tubes were used. In one of the boxes, untreated beans were placed and on the other ones beans treated with each oil concentration were used. In the central box, five couples of Z. subfasciatus were released. Grains of P. vulgaris treated with oils of E. citriodora, C. citratus and C. oleifera reduced the attraction percentage of Z. subfasciatus adults, while the E. globulus increased this percentage. The percentages of reduced viable eggs ranged from 17.9% (C. medica limonum) to 93.3% (C. nardus), while the reduction on the number of emerged insects was 23.9% and 95.9%, respectively for these same oils.

Copper toxicity for Scinax ruber and Rhinella granulosa (Amphibia: Anura) of the Amazon: Potential of Biotic Ligand Model to predict toxicity in urban streams

In the last years many populations of anurans have declined and extinctions have been recorded. They were related to environmental pollution, changes of land use and emerging diseases. The main objective of this study was to determine copper sensitivity of the anuran of the Amazon Rhinella granulosa and Scinax ruber tadpoles at stage 25 and Scinax ruber eggs exposed for 96 h to copper concentrations ranging from 15 µg Cu L-1 to 94 µg Cu L-1. LC50 at 96 h of Rhinella granulosa Gosner 25, Scinax ruber Gosner 25 and Scinax ruber eggs in black water of the Amazon were 23.48, 36.37 and 50.02 µg Cu L-1, respectively. The Biotic Ligand Model was used to predict the LC50 values for these species and it can be considered a promising tool for these tropical species and water conditions. Copper toxicity depends on water physical-chemical composition and on the larval stage of the tadpoles. The Gosner stage 19-21 (related to the appearance of external gills) is the most vulnerable and the egg stage is the most resistant. In case of contamination by copper, the natural streams must have special attention, since copper is more bioavailable.

Cloning, Expression and Toxicity of a Mosquitocidal Toxin Gene of Bacillus thuringiensis subsp. medellin

Bacillus thuringiensis (Bt) subsp. medellin (Btmed) produces parasporal crystalline inclusions which are toxic to mosquito larvae. It has been shown that the inclusions of this bacterium contain mainly proteins of 94, 68 and 28-30 kDa. EcoRI partially digested total DNA of Btmed was cloned by using the Lambda Zap II cloning kit. Recombinant plaques were screened with a mouse policlonal antibody raised against the 94 kDa crystal protein of Btmed. One of the positive plaques was selected, and by in vivo excision, a recombinant pBluescript SK(-) was obtained. The gene encoding the 94 kDa toxin of Btmed DNA was cloned in a 4.4 kb DNA fragment. Btmed DNA was then subcloned as a EcoRI/EcoRI fragment into the shuttle vector pBU4 producing the recombinant plasmid pBTM3 and used to transform by electroporation Bt subsp. israelensis (Bti) crystal negative strain 4Q2-81. Toxicity to mosquito larvae was estimated by using first instar laboratory reared Aedes aegypti, and Culex quinquefasciatus larvae challenged with whole crystals. Toxicity results indicate that the purified inclusions from the recombinant Bti strain were toxic to all mosquito species tested, although the toxicity was not as high as the one produced by the crystal of the Btmed wild type strain. Poliacrylamide gel electrophoresis indicate that the inclusions produced by the recombinant strain Bti (pBTM3) were mainly composed of the 94 kDa protein of Btmed, as it was determined by Western blot

Toxicity of pyrethroids and repellency of diethyltoluamide in two deltamethrin-resistant colonies of Triatoma infestans Klug, 1834 (Hemiptera: Reduviidae)

The aim of the currrent investigation was to evaluate (a) the toxicity of three pyrethroids (deltamethrin, lambda-cyhalothrin, and tetramethrin); (b) the effect of these insecticides on the locomotor activity; and (c) the repellent effect of N,N-diethyl-m-toluamide (DEET) on two deltamethrin-resistant strains of Triatoma infestans from Argentina (El Chorro and La Toma), and one susceptible strain. The resistance ratios (RRs) obtained for the La Toma strain were: > 10,769, 50.7, and > 5.2 for deltamethrin, lambda-cyhalothrin, and tetramethrin respectively. The RRs for the El Chorro strain were: > 10,769, 85.8, and > 5.2 for deltamethrin, lambda-cyhalothrin, and tetramethrin respectively. The hyperactivity usually caused by the three pyrethroids was in both the deltamethrin-resistant strains compared to the susceptible reference strain. No differences were observed in the repellent effect of DEET between the three groups. These results indicate that the deltamethrin-resistant insects have a cross resistance to lambda-cyhalothrin and tetramethrin, and are also resistant to the first symptom of pyrethroid poisoning (hyperactivity). However, the sensorial process related to DEET repellency does not appear to be altered.

Latex constituents from Calotropis procera (R. Br.) display toxicity upon egg hatching and larvae of Aedes aegypti (Linn.)

Calotropis procera R. Br. (Asclepiadaceae) is a well-known medicinal plant with leaves, roots, and bark being exploited by popular medicine to fight many human and animal diseases. This work deals with the fractionation of the crude latex produced by the green parts of the plant and aims to evaluate its toxic effects upon egg hatching and larval development of Aedes aegypti. The whole latex was shown to cause 100% mortality of 3rd instars within 5 min. It was fractionated into water-soluble dialyzable (DF) and non-dialyzable (NDF) rubber-free materials. Both fractions were partially effective to prevent egg hatching and most of individuals growing under experimental conditions died before reaching 2nd instars or stayed in 1st instars. Besides, the fractions were very toxic to 3rd instars causing 100% mortality within 24 h. When both fractions were submitted to heat-treatment the toxic effects were diminished considerably suggesting low thermostability of the toxic compounds. Polyacrylamide gel electrophoresis of both fractions and their newly fractionated peaks obtained through ion exchange chromatography or desalting attested the presence of proteins in both materials. When submitted to protease digestion prior to larvicidal assays NDF lost most of its toxicity but DF was still strongly active. It may be possible that the highly toxic effects of the whole latex from C. procera upon egg hatching and larvae development should be at least in part due to its protein content found in NDF. However the toxicity seems also to involve non protein molecules present in DF.