Abstract
Atypical myopathy (AM) in horses is caused by ingestion of seeds of the Acer species (Sapindaceae family). Methylenecyclopropylacetyl-CoA (MCPA-CoA), derived from hypoglycin A (HGA), is currently the only active toxin in Acer pseudoplatanus or Acer negundo seeds related to AM outbreaks. However, seeds or arils of various Sapindaceae (e.g., ackee, lychee, mamoncillo, longan fruit) also contain methylenecyclopropylglycine (MCPG), which is a structural analogue of HGA that can cause hypoglycaemic encephalopathy in humans. The active poison formed from MCPG is methylenecyclopropylformyl-CoA (MCPF-CoA). MCPF-CoA and MCPA-CoA strongly inhibit enzymes that participate in β-oxidation and energy production from fat. The aim of our study was to investigate if MCPG is involved in Acer seed poisoning in horses. MCPG, as well as glycine and carnitine conjugates (MCPF-glycine, MCPF-carnitine), were quantified using high-performance liquid chromatography-tandem mass spectrometry of serum and urine from horses that had ingested Acer pseudoplatanus seeds and developed typical AM symptoms. The results were compared to those of healthy control horses. For comparison, HGA and its glycine and carnitine derivatives were also measured. Additionally, to assess the degree of enzyme inhibition of β-oxidation, several acyl glycines and acyl carnitines were included in the analysis. In addition to HGA and the specific toxic metabolites (MCPA-carnitine and MCPA-glycine), MCPG, MCPF-glycine and MCPF-carnitine were detected in the serum and urine of affected horses. Strong inhibition of β-oxidation was demonstrated by elevated concentrations of all acyl glycines and carnitines, but the highest correlations were observed between MCPF-carnitine and isobutyryl-carnitine (r = 0.93) as well as between MCPA- (and MCPF-) glycine and valeryl-glycine with r = 0.96 (and r = 0.87). As shown here, for biochemical analysis of atypical myopathy of horses, it is necessary to take MCPG and the corresponding metabolites into consideration.
Highlights
Atypical myopathy (AM) of horses is a frequently fatal disease characterized by acute rhabdomyolysis in pastured horses that consume seeds of Acer spp. (e.g., Acer pseudoplatanus, Acer negundo) [1,2,3,4,5] that belong to the Sapindaceae family of plants
Due to the lack of original compound values obtained for MCPF-carnitine and MCPA-carnitine, the values do not represent an absolute quantification but rather a relative quantification of their concentration in the samples
It has been demonstrated that in addition to hypoglycin A (HGA), MCPG is involved in Acer seed poisoning of horses
Summary
Atypical myopathy (AM) of horses is a frequently fatal disease characterized by acute rhabdomyolysis in pastured horses that consume seeds of Acer spp. (e.g., Acer pseudoplatanus, Acer negundo) [1,2,3,4,5] that belong to the Sapindaceae family of plants. And on-going studies of the chemical components of these plants have shown that seeds and arils of Sapindaceae (ackee, lychee, longan, mamoncillo fruits) may contain the toxins hypoglycin A (HGA) and the lower homologue of HGA, methylenecyclopropylglycine (MCPG) [7, 10,11,12,13,14,15,16]. The ingestion of ackee and lychee fruits led to the detection of the metabolic products of exposure to HGA and MCPG [16]. These specific urinary metabolites of HGA and MCPG are methylenecyclopropylacetyl-glycine (MCPA-glycine) and methylenecyclopropylformyl-glycine (MCPFglycine), respectively
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