Development of antidotes for sodium monofluoroacetate (1080)

Baits containing sodium monofluoroacetate (1080) are commonly used in New Zealand during feral pest control operations. However, each year, a number of domestic dogs are unintentionally killed during these control operations, and a suitable antidote to 1080 intoxication is required. The primary toxic mechanism of 1080 is well known. However, as with other pathologies where energy deprivation is the main effect of intoxication, the cascade of effects that arises from this primary mechanism is complex. At present, putative antidotes for 1080 are generally unable to address the primary mechanism of intoxication but such agents may be able to control the cascade of secondary effects, which can result during intoxication. Part of the reason for this is that targeting the cascade can provide a longer window of time for antidote success. We have undertaken studies that identified some of the central nervous system (CNS) and systemic pathophysiological cascades caused by 1080 intoxication. Using this information we designed antidotes, on the basis of preventing different steps in this cascade. In the chicken model targeting systemic changes, in particular reducing effects of nitric oxide derivatives generated in cardiac muscle, proved successful in reducing fatality associated with 1080. In rats and sheep, targeting the CNS with a number of compounds including: glutamate; calcium and dopamine antagonists; gamma amino butyric acid agonists, and astressin-like compounds reduced fatalaties. However, to be successful in the rat and sheep model a given antidote needed to move quickly from systemic circulation across the blood brain barrier and into the CNS. The work also suggests ways in which specific biomarkers of 1080 exposure may be developed with respect to different species.     

A preliminary report on a bacteriological assay for compound 1080 (sodium monofluoroacetate)

A new, inexpensive, simple and rapid bioassay for sodium monofluoroacetate (compound 1080) was developed using bacteria. Two 1080-sensitive isolates ( Bacillus sp. DHW and Acinetobacter sp. DHW) from local aquatic environments were tested on different agar media using the disc diffusion technique. Both bacteria exhibited zones of growth inhibition surrounding the 1080 discs that were linearly proportional to the concentrations (log₁₀) of 1080. Preliminary studies indicate that this technique can be used for assaying 1080 in environmental and biological samples.     

Controlling small mammal predators using sodium monofluoroacetate (1080) in bait stations along forestry roads in a New Zealand beech forest

A single five night pulse of sodium monofluroacetate (0.15% 1080) applied in bait stations at two different spacing intervals, 100 and 200 m, along forestry roads in New Zealand beech forest, killed all four of the resident radio-tagged stoats (Mustela erminea) and all three of the resident radio- tagged wild house cats (Felis catus) by secondary poisoning. Gut contents of predators indicated that house mice (Mus musculus), ship rats (Rattus rattus) and bushtail possums (Trichosurus vulpecula) were important sources of the toxin. High kills of predators, possums and rats at both 100 and 200 m spacing regimes suggest that greater efficacy of controlling these pests would be achieved with the latter method. Evidence suggests that routine management of possums and rats using 1080 and brodifacoum has resulted in widespread control of small mammalian carnivores by secondary poisoning in New Zealand forests. However, aerial application of poison can kill large numbers of tomtits (Petroica macrocephala) and robins (Petroica australis) and few other native bird species have been adequately monitored through such operations. Reducing risks to native wildlife is responsible ecological management. Use of bait stations along forestry roads or tracks may be fundamental in mounting cost-effective :Large-scale ground-based protection of native wildlife through safer predator controls.     

Fate of sodium monofluroacetate (1080) following disposal of pest bait to a landfill

The results of a programme to monitor the containment and natural breakdown of approximately 12 000 kg of toxic vertebrate pest bait, containing compound 1080 (sodium monofluroacetate), in a landfill site are reported. The baits were buried in a purpose-dug pit in a managed solid waste disposal site at Winton in central Southland, New Zealand, in August 1996. Compound 1080 is used extensively in a bait form to control a range of introduced vertebrate pests, (e.g., European rabbit, Australian brush tailed possum), which cause considerable economic and environmental damage in New Zealand. Two shallow monitor bores, sited 5 and 13 m from the disposal pit, were sampled weekly for five weeks and thereafter monthly for 13 months. Analyses detected 1080 in 5 of the 28 groundwater/leachate samples. The 1080 concentrations in those samples, except for one result, were low. These were either below or close to the Ministry of Health provisional maximum acceptable value standards (PMAV) for drinking water, currently 0.005 mu g ml(-1). The concentrations of 1080 in groundwater in the more distant bore (13 m) were markedly lower than those in the nearer bore (5 m). 1080 was first detected in the near bore after 5 weeks and the more distant bore after 16 weeks. The level and frequency of incidence of 1080 in both holes decreased over the sampling period until none was detected after 10 months. In situ sampling of the residual waste material indicated the 1080 concentration in the disposal pit decreased to less than 10% of its original level in 12 months. The active anaerobic bacterial processes operating in the organic refuse pile appear to provide an ideal environment for the rapid natural breakdown of 1080. The findings will assist with the setting of conditions for resource consents concerning the disposal of materials containing 1080 in landfill sites.     

The toxicity of thallium(I) to cardiac and skeletal muscle

The effects of (a) partial or complete replacement of K⁺ by Tl⁺ in saline perfusing isolated rat heart and diaphragm preparations and (b) pulse injections of high concentrations of Tl⁺ or K⁺, have been studied. The immediate effect of Tl⁺ resembles that of higher concentrations of K⁺ and may reflect its more rapid penetration into the tissue. Tl⁺ appears to replace K⁺ on a 1 : 1 basis to an extent dependent upon the relative abundance of the two cations in the perfusion solution. However, analysis of diaphragm preparations after perfusion with salines containing increasing Tl⁺ but constant [K⁺ + Tl⁺] showed a related and progressive increase in total cation content. This effect, which was not seen in the presence of constant high (normal) K⁺ concentrations, may reflect an increase of the intracellular space brought about by the thallium.Functional effects of Tl⁺ were (a) preferential block of the phrenic nerve or neuromuscular junction over the muscle fibre and (b) transient but marked acceleration of cardiac frequency following pulse injections, which may be of value in analysing the pacemaker mechanism of the heart. In both tissues Tl⁺ is eventually toxic and probably irreversibly so.     

Sodium Monofluoroacetate (1080) Water-Residue Analysis after Large-Scale Possum Control

Successful possum control operations were conducted in 1990, using aerially-sown sodium monofluoroacetate (1080) possum baits, at Waipoua (85% kill) and on Rangitoto Island (93% kill). In Waipoua Forest Sanctuary, streams and rivers were monitored for 4 months after 100 tonnes of 1080 possum baits were sown over 17 000 ha of forest. At Rangitoto Island, adjacent to Auckland, surface and ground water samples were analysed for 6 months after 20 tonnes of 1080 possum baits were sown over the 2300 ha island. No 1080 was detected in the streams and rivers of the Waipoua forest or in the surface or ground water of Rangitoto Island.     

The use of metabolism to evaluate the toxicity of dodecil benzen sodium sulfonate (LAS-C12) on the Mugil platanus (mullet) according to the temperature and salinity

The effects of watering exposition to different concentrations of LAS-C12 (1, 2.5 and 5 mg l⁻¹) about the Mugil platanus routine metabolism were evaluated. The metabolic rates were estimated through experiments accomplished in each of the twelve possible combinations of three temperatures (25, 20 and 15 °C) and three salinities (35, 20 and 5). The results show that the oxygen consumption increases according to the LAS-C12 concentration in all temperatures and salinities studied. At the highest concentration employed (5 mg l⁻¹), and the salinity 5 in the temperatures 25 and 20 °C, oxygen consumption increases 80% in relation to the control. In general, the pollutant effects on oxygen consumption were more pronounced at the highest temperatures and salinities 5 and 35.     

Mechlorethamine-induced DNA-protein cross-linking in human fibrosarcoma (HT1080) cells

Antitumor nitrogen mustards, such as bis(2-chloroethyl)methylamine (mechlorethamine), are useful chemotherapeutic agents with a long history of clinical application. The antitumor effects of nitrogen mustards are attributed to their ability to induce DNA-DNA and DNA-protein cross-links (DPCs) that block DNA replication. In the present work, a mass spectrometry-based methodology was employed to characterize in vivo DNA-protein cross-linking following treatment of human fibrosarcoma (HT1080) cells with cytotoxic concentrations of mechlorethamine. A combination of mass spectrometry-based proteomics and immunological detection was used to identify 38 nuclear proteins that were covalently cross-linked to chromosomal DNA following treatment with mechlorethamine. Isotope dilution HPLC-ESI(+)-MS/MS analysis of total proteolytic digests revealed a concentration-dependent formation of N-[2-(S-cysteinyl)ethyl]-N-[2-(guan-7-yl)ethyl]methylamine (Cys-N7G-EMA) conjugates, indicating that mechlorethamine cross-links cysteine thiols within proteins to N-7 positions of guanine in DNA.     

Prevention by sodium 4,5-dihydroxybenzene1,3-disulfonate (tiron) of vanadium-induced behavioral toxicity in rats

Recent studies have shown that oral vanadate (V⁵⁺) administration results in behavioral toxicity in rats. The chelating agent Tiron (sodium 4,5-dihydroxybenzene-l,3-disulfonate) is an effective antidote in the removal of vanadium from vanadium-loaded rats. In this study, the protective activity of Tiron on vanadate-induced behavioral toxicity was evaluated in adult rats. Intraperitoneal treatment with Tiron at 235 or 470 mg/kg was initiated after 6 wk of oral sodium metavanadate administration (16 mg/kg/d) and continued for 2 wk. Although vanadate exposure did not result in a significant reduction in the general activity of the animals in an open field, a lower active avoidance acquisition could be observed. However, the vanadate-induced behavioral deficit was reverted by Tiron administration at 470 mg/kg. The present results suggest that Tiron may protect, at least in part, against metavanadate-induced behavioral toxicity.     

Mechanisms of mutagenicity and toxicity of sodium selenite (Na2SeO3) in Salmonella typhimurium

The mechanisms of selenite toxicity and mutagenicity in S. typhimurium have been characterized. In contrast to previous reports, selenite toxicity was shown not to involve nonspecific incorporation into protein via the sulfur metabolic pathways. Selenite toxicity was, however, shown to involve its ability to act as an oxidizing agent, primarily through reactions with sulfhydryls. Strains which lack glutathione (GSH) are more sensitive to killing by sulfhydryl reagents. The selenite sensitivity of such a mutant was a biphasic phenomenon. The mutant was much more sensitive than a strain which contained GSH at lower selenite concentrations whereas, at higher concentrations, the mutant was much more resistant to selenite. The mechanism of selenite toxicity at lower concentrations in this mutant thus appeared to involve damage to intracellular sulfhydryls. The sensitization to higher doses of selenite by GSH could be explained by the generation of toxic oxygen species. The in vitro reactions of selenite with both cysteine and GSH readily produced H2O2 and O2-. A S. typhimurium strain which overproduces superoxide dismutase (SOD) and catalase was more resistant to high concentrations of selenite, but not killing by the lower doses. Pretreatment of cells with a nonlethal dose of selenite induced the synthesis of proteins which protected the cells from killing by H2O2 or high doses of selenite. Selenite was also a mutagen in the tester strain TA104, in which a number of other oxidizing agents have also been found to be mutagens. These results were consistent with a model in which the reactions of selenite and intracellular thiols with concomitant production of active oxygen species are the primary causal agents of selenite mutagenicity and toxicity in S. typhimurium.     

Nitric oxide (as sodium nitroprusside) supplementation ameliorates Cd toxicity in hydroponically grown wheat roots

Cadmium (Cd) is a non-redox toxic heavy metal present in the environment and induces oxidative stress in plants. We investigated whether exogenous nitric oxide (NO) supplementation as sodium nitroprusside (SNP) has any ameliorating action against Cd-induced oxidative damage in plant roots and thus protective role against Cd toxicity. Cd treatment (50 or 250 μM) alone or in combination with 200 μM SNP was given to hydroponically grown wheat roots for a short time period of 24 h and then these were shifted to distilled water to observe changes in levels of oxidative markers (lipid peroxidation, H₂O₂ content and electrolyte leakage). Supplementation of Cd with SNP significantly reduced the Cd-induced lipid peroxidation, H₂O₂ content and electrolyte leakage in wheat roots. It indicated a reactive oxygen species (ROS) scavenging activity of NO. However, even upon removal of Cd-treatment solution, the levels of oxidative markers increased during 24 h recovery stage and later at 48 h these decreased. Cd treatment resulted in an upregulation of activities of antioxidant enzymes—superoxide dismutase (SOD, 1.15.1.1), guaiacol peroxidase (GPX, 1.11.1.7), catalase (CAT, 1.11.1.6), and glutathione reductase (GR, 1.6.4.2). SNP supply resulted in a reduction in Cd-induced increased activities of scavenging enzymes. The protective role of exogenous NO in decreasing Cd-induced oxidative damage was also evident from the histochemical localization of lipid peroxidation, plasma membrane integrity and superoxides. The study concludes that an exogenous supply of NO protects wheat roots from Cd-induced toxicity.     

The synthesis and defluorination of monofluoroacetate in some Dichapetalum species

Leaves from Dichapetalum toxicarium (G. Don) Baill. (Dichapetalaceae) removed from the plant and aqueous extracts prepared from the leaves of D. heudelotii (Planch. ex Oliv.) Baill. were able to synthesize monofluoroacetate from NaF. D. pallidum (Oliv.) Engl. leaves were not able to synthesize monofluoroacetate from NaF. Aqueous extracts from both D. toxicarium and D. heudelotii containing monofluoroacetate and possibly other organo-fluorine compounds were defluorinated by a micro-organism from the air. This organism was able to defluorinate fluorocitrate but not difluoroacetate or trifluoroacetate. In D. toxicarium monofluoroacetate is present in a form which is easily leached from the leaves, and which is defluorinated if the leaves are kept under herbarium conditions. The monofluoroacetate in this species is not defluorinated if the leaves are dried at 100° and stored in sealed polythene bags.