Further Investigation Into an Environmental Source for Aminorex

In 2009, levamisole was identified as a source for several aminorex positives reported in postrace equine samples in Canada. Since then, unexplained detections of aminorex continue to be identified in equine samples where there is no evidence to link these detections to a levamisole administration. Previous studies identified a compound named barbarin in some species of plants from the Brassicaceae family and suggested that barbarin may be a possible precursor for aminorex. The objectives of this study were to (1) investigate the link between barbarin and aminorex and (2) identify other biomarkers of plant origin. Methods were developed and validated for the detection of aminorex, barbarin, glucobarbarin, and other associated compounds. Aminorex was administered to one horse, and barbarin was not detected in any plasma and urine samples. Barbarea stricta and Barbarea orthoceras were administered to two horses, and aminorex was detected in all plasma and urine samples collected. Barbarin was detected in some plasma but not in urine samples. Resedine was observed in retrospective examination of chromatograms of the plant material and from all plants postadministration plasma and urine samples from the two horses. Resedine was administered to one horse and was detected in plasma and urine samples, but aminorex was only detected in urine samples. These results provide evidence that resedine is an intermediary compound between barbarin and aminorex in horses and that resedine can be used as a biomarker to eliminate the reporting of aminorex positives originating from the ingestion of plants from the Brassicaceae family.