Seasonal and Species Variation of the Hepatotoxin Indospicine in Australian Indigofera Legumes As Measured by UPLC-MS/MS

Abstract

Livestock industries have maintained a keen interest in pasture legumes because of the high protein content and nutritive value. Leguminous Indigofera plant species have been considered as having high feeding values to be utilized as pasture, but the occurrence of the toxic constituent indospicine in some species has restricted this utility. Indospicine has caused both primary and secondary hepatotoxicosis and also reproductive losses, but has only previously been determined in a small number of Indigofera species. This paper validates a high-throughput ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method to determine the indospicine content of various Indigofera species found in Australian pasture. Twelve species of Indigofera together with Indigastrum parviflorum plants were collected and analyzed. Of the 84 samples analyzed, *I. spicata (the asterisk indicates a naturalized species) contained the highest indospicine level (1003 ± 328 mg/kg DM, n = 4) followed by I. linnaei (755 ± 490 mg/kg DM, n = 51). Indospicine was not detected in 9 of the remaining 11 species and at only low levels (<10 mg/kg DM) in 2 of 8 I. colutea specimens and in 1 of 5 I. linifolia specimens. Indospicine concentrations were below quantitation levels for other Indigofera spp. (I. adesmiifolia, I. georgei, I. hirsuta, I. leucotricha, *I. oblongifolia, I. australis, and I. trita) and Indigastrum parviflorum. One of the more significant findings to emerge from this study is that the indospicine content of I. linnaei is highly variable (from 159 to 2128 mg/kg DM, n = 51) and differs across both regions and seasons. Its first regrowth after spring rain has a higher (p < 0.01) indospicine content than growth following more substantial summer rain. The species collected include the predominant Indigofera in Australia pasture, and of these, only *I. spicata and I. linnaei contain high enough levels of indospicine to pose a potential toxic threat to grazing herbivores.

Release of Indospicine from Contaminated Camel Meat following Cooking and Simulated Gastrointestinal Digestion: Implications for Human Consumption

“…The hepatotoxic amino acid indospicine is found only in plant species of the Indigofera genus [ 1 ] and has been linked with poisoning of grazing livestock [ 2 ], and the deaths of dogs consuming contaminated meat from livestock that had grazed on these plants [ 5 , 17 ]. These canine deaths in Australia following the consumption of indospicine-contaminated camel [ 17 ] and horse meat [ 5 ] have raised both industry and consumer concern with regard to the potential contamination of meat for human consumption.…”

“…The non-proteinogenic amino acid indospicine ( l -6-amidino-2-amino-hexanoic acid) is a hepatotoxic arginine analog ( Figure 1 ) found widely in plants of the Indigofera genus [ 1 ]. This genus contains over 700 species distributed across tropical Africa, Asia, Australia, and North and South America, and includes species such as I. spicata , I. hendecaphylla , I. linnaei , I. lespedezioides , I. vicioides and I. volkensii that have all been reported to contain in excess of 500 mg indospicine/kg dry matter of foliage.…”

Assessing the risk of residues of the toxin indospicine in bovine muscle and liver from north-west Australia

“…It occurs across diverse landscapes, including the most arid regions of Australia, and with a thick taproot typically dies off in dry winter months, and is then one of the first plants to reshoot after the first spring/summer rain (Gracie et al, 2010). The indospicine content of this species was found to be highly variable, differing across both regions and seasons (Tan et al, 2016b). Most notably, new growth following spring rain was found to have significantly higher indospicine content than later growth following more substantial summer rain.…”

“…There are approximately native and 10 naturalized exotic species of Indigofera distributed across Australia, but of these only the native I. linnaei and the naturalized I. spicata are reported to contain appreciable levels of indospicine (Tan et al, 2016b). Both species are considered perennial plants and are highly palatable to grazing livestock.…”

“…The Kimberley Region experiences a high rainfall, tropical climate, in which 94% of the average annual 950 mm rainfall falls between November and April (CSIRO, 2009), a period during which properties in this region become largely inaccessible. I. linnaei has a known seasonal prevalence as one of the first plants to regrow at the start of the wet season (Gracie et al, 2010), with associated new growth reported to contain higher indospicine levels (Tan et al, 2016b). This seasonal plant variation, when combined with the known persistence of indospicine residues in cattle for several months after Indigofera intake (Fletcher et al, 2018), was considered likely to impact on seasonal prevalence of bovine tissue residues at time of slaughter.…”