Plants Causing Toxic Myopathies.

Boxelder and sycamore maple contain hypoglycin A (HGA), the toxic metabolite of which, MCPA-CoA, inhibits fatty acid ß-oxidation, causing seasonal pasture myopathy (SPM) or atypical myopathy (AM), respectively. White snakeroot and rayless goldenrod contain multiple benzofuran ketones (BFKs). The identity/toxicity of BFKs appear variable, possibly involving interactions between toxins/toxic metabolites, but ultimately inhibit cellular energy metabolism. Unthrifty horses grazing sparse pastures during the fall appear predisposed to these plant-associated, frequently fatal, toxic myopathies. Toxidromes are characterized by varying degrees of rhabdomyolysis and cardiac myonecrosis, with plant toxins remaining toxic in hay and being excreted in milk.

Rayless goldenrod (Isocoma pluriflora) poisoning in chicks (Gallus gallusdomesticus).

Rayless goldenrod (Isocoma spp.) and white snakeroot (Ageratina altissima) poison livestock, wildlife and humans. The suggested toxin for both plants is tremetone, a mixture of benzofuran ketones. However, plant tremetone concentrations often do not correlate with poisoning, and they have not been identified in contaminated milk that poisons nursing neonates. This suggests there may be unidentified metabolites or toxins. Previous studies using various cell culture and large animal models have been inconsistent with varying animal response that often require large doses. The objective of this work is to document the toxicity of rayless goldenrod in California white leghorn chicks, a susceptible small animal model, that would require relatively small amounts of plant material or purified toxins. Four groups of 15 chicks were gavaged with finely ground I. pluriflora at rates of 0, 1%, 2% or 3% of their bodyweight per day for 7 days. After 7 exposure days the chicks were euthanized, necropsied and tissues were collected, fixed and examined microscopically. Myocyte damage was evaluated using clinical signs, weight gain, serum biochemical changes, and histologic lesions and scores. The 3% group had focally extensive myocyte degeneration and necrosis most severely affecting leg muscles (semitendinosus, iliotibialis, peroneus longus and gastrocnemius). This was supported by serum biochemical changes and reduced weight gains. These findings indicate young chicks are a sensitive model of toxicity that may be useful to better identify the rayless goldenrod and white snakeroot toxins, including those unidentified toxins of transmammary poisoning.

Competitive Interactions between Two Non-Native Species (Alliaria petiolata [M. Bieb.] Cavara & Grande and Hesperis matronalis L.) and a Native Species (Ageratina altissima [L.] R.M. King & H. Rob.).

Alliaria petiolata and Hesperis matronalis are wide-ranging non-native species in North America. Ageratina altissima is native to North America but has become a concern as an invasive species in Asia. A replacement series experiment was established to quantify the competitive interactions between these three species and to rank their relative competitiveness with each other. We assessed leaf count, chlorophyll content, and aboveground biomass with comparisons between replacement series mixtures and competition species. Overall leaf count and aboveground biomass were greatest in A. altissima and chlorophyll content was lowest in A. petiolata. Chlorophyll content and aboveground biomass were lower for A. altissima in competition with A. petiolata compared to H. matronalis. Leaf count for A. petiolata was lower in competition with A. altissima compared to H. matronalis. Aboveground biomass for H. matronalis was lower in competition regardless of the species compared to monoculture. There were also negative trends in biomass for A. petiolata in competition with increasing neighbors. However, for A. altissima, the negative trend in biomass was with A. petiolata, H. matronalis did not negatively affect A. altissima biomass. Our rank order of competitiveness was A. altissima > A. petiolata >> H. matronalis.

Microsomal activation, and SH-SY5Y cell toxicity studies of tremetone and 6-hydroxytremetone isolated from rayless goldenrod (Isocoma pluriflora) and white snakeroot (Agertina altissima), respectively.

This research compared the cytotoxic actions of the benzofuran ketone, tremetone in B16 murine melanoma cells to SH-SY5Y human neuroblastoma cells with an MTT assay. Tremetone was not cytotoxic in B16 cells. In SH-SY5Y cells, concentration-dependent tremetone cytotoxicity occurred without microsomal activation. No cytotoxicity was observed with 6-hydroxytremetone. This suggests that SH-SY5Y cells are a better model for the cytotoxic actions of tremetone and that tremetone is toxic without microsomal activation.

Effect of grinding and long-term storage on the toxicity of white snakeroot (Ageratina altissima) in goats.

White snakeroot (Ageratina altissima) contains the putative toxin tremetone and can produce a disease called "trembles" or "milk sickness". However the toxicity of tremetone has not been demonstrated in vivo. It has been reported that the plant is less toxic after drying and grinding. The objectives of these studies were to determine: 1) the toxic effect of grinding white snakeroot 4 months prior to dosing and, 2) the toxic effect of storing white snakeroot at ambient temperature for 5 years. Dried white snakeroot, ground 1 day, 1 month, and 4 months prior to dosing, was orally gavaged to goats at 2% of their body weight for up to 28 days or until they were minimally poisoned (minimal muscular weakness and increased serum creatine kinase (CK) activities). All four goats dosed with white snakeroot that had been ground 4 months previously and stored at room temperature were poisoned, became exercise intolerant, and had increased serum CK activities (>5600 U/ L). White snakeroot stored for 5 years was toxic as 3 of 5 dosed goats developed clinical disease within only 6 days of dosing even though approximately 80% of the tremetone in the plant had disappeared during the 5-year storage period. The results from this study demonstrate that previous grinding and extended storage did not significantly alter white snakeroot toxicity. The results also indicate that tremetone concentration is not the singular indicator of toxicity and that other white snakeroot toxins or toxic tremetone degradation products remain in dried, stored white snakeroot.

White snakeroot poisoning in goats: Variations in toxicity with different plant chemotypes.

Tremetone and possibly other benzofuran ketones are believed to be the toxic compounds in white snakeroot. However, disease has not been reproduced with purified toxins and the concentrations of the benzofuran ketones in white snakeroot populations that cause toxicosis have not been documented. The objectives of this study were to compare the toxicity of seven plant populations, better characterize the clinical and pathologic changes of poisoning, and correlate intoxication with benzofuran ketone content. Four of the seven white snakeroot collections were toxic at the dose and duration used in the study. Affected goats became exercise intolerant, had significant serum enzyme changes and histological lesions in the large appendicular muscles. The incidence and severity of poisoning was not correlated with total doses of tremetone or total benzofuran ketone concentrations suggesting they may not be closely involved in producing toxicity and the possible involvement of an unidentified toxin. The results also demonstrate that white snakeroot populations vary chemically and toxicologically.

Toxicity of white snakeroot (Ageratina altissima) and chemical extracts of white snakeroot in goats.

White snakeroot (Ageratina altissima) is a sporadically toxic plant that causes trembles in livestock and milk sickness in humans that drink tainted milk. The putative toxin in white snakeroot is tremetone and possibly other benzofuran ketones, even though it has not been demonstrated in vivo. Toxic white snakeroot was dosed to goats, and they developed clinical signs of poisoning, exercise intolerance, significant increases in serum enzyme activities, and histological changes. Tremetone and the other benzofuran ketones were extracted with hexane; the extracts and residues were analyzed for tremetone and dosed to goats at tremetone and benzofuran ketone concentrations similar to the original plant material. However, none of the dosed goats developed the disease. The results demonstrate for the first time that white snakeroot is a potent myotoxin in goats and that other compound(s), which may be lost or modified during the extraction process, could be involved in causing trembles and milk sickness.