Seasonal pasture myopathy/atypical myopathy in North America associated with ingestion of hypoglycin A within seeds of the box elder tree

Abstract

SummaryReasons for performing study : We hypothesised that seasonal pasture myopathy (SPM), which closely resembles atypical myopathy (AM), was caused by ingestion of a seed-bearing plant abundant in autumn pastures. Objectives: To identify a common seed-bearing plant among autumn pastures of horses with SPM, and to determine whether the toxic amino acid hypoglycin A was present in the seeds and whether hypoglycin metabolites were present in SPM horse serum or urine. Methods: Twelve SPM cases, 11 SPM pastures and 23 control farms were visited to identify a plant common to all SPM farms in autumn. A common seed was analysed for amino acid composition (n = 7/7) by GC-MS and its toxic metabolite (n = 4/4) identified in conjugated form in serum [tandem mass spectrometry (MS/MS)] and urine [gas chromatography (GC) MS]. Serum acylcarnitines and urine organic acid profiles (n = 7) were determined for SPM horses. Results: Seeds from box elder trees (Acer negundo) were present on all SPM and 61% of control pastures. Hypoglycin A, known to cause acquired multiple acyl-CoA dehydrogenase deficiency (MADD), was found in box elder seeds. Serum acylcarnitines and urine organic acid profiles in SPM horses were typical for MADD. The hypoglycin A metabolite methylenecyclopropylacetic acid (MCPA), known to be toxic in other species, was found in conjugated form in SPM horse serum and urine. Horses with SPM had longer turn-out, more overgrazed pastures, and less supplemental feeding than control horses. Potential relevance: For the first time, SPM has been linked to a toxin in seeds abundant on autumn pastures whose identified metabolite, MCPA, is known to cause acquired MADD, the pathological mechanism behind SPM and AM. Further research is required to determine the lethal dose of hypoglycin A in horses, as well as factors that affect annual seed burden and hypoglycin A content in Acer species in North America and Europe.

Rapid diagnosis of hypoglycin A intoxication in atypical myopathy of horses

“…10 Concentrations of 3-160 µg/seed were found. 10 Freeze-dried seeds of Acer pseudoplatanus (sycamore maple tree) have been found to contain up to 9,120 µg/g/seed. 9 Solid-phase extraction plus dansyl chloride derivatization has been described as a useful tool in the quantification of HGA.…”

“…Such cases are now ascribed to intoxication by hypoglycin A (2-amino-3-(2-methylidenecyclopropyl)propanoic acid, HGA). 10 This nonproteogenic amino acid has been detected in the seeds of Acer negundo (box elder tree) 10 and was quantified by gas chromatography-mass spectrometry (GC-MS) after methyl chloroformate derivatization. 10 Concentrations of 3-160 µg/seed were found.…”

“…10 This nonproteogenic amino acid has been detected in the seeds of Acer negundo (box elder tree) 10 and was quantified by gas chromatography-mass spectrometry (GC-MS) after methyl chloroformate derivatization. 10 Concentrations of 3-160 µg/seed were found. 10 Freeze-dried seeds of Acer pseudoplatanus (sycamore maple tree) have been found to contain up to 9,120 µg/g/seed.…”

“…The often lethal disease that results is also described as acquired multiple acyl-CoA dehydrogenase deficiency (MADD). Previous studies 10,14 successfully used ultra-high-performance liquid chromatography (UPLC)-tandem mass spectrometry (MS/MS) to determine the carnitine ester of MCPA in serum or plasma and urine after converting it into a butyl ester.…”

“…10,14 In vivo MCPA is transformed to a coenzyme A (CoA) ester and, in this form, it binds to multiple acyl-CoA dehydrogenases, 4,[6][7][8] without further metabolization. Enzymes loaded with MCPA-CoA are blocked and no longer available for degradation of fatty acids in the mitochondrial ß-oxidation pathway.…”