Indospicine, a Hepatotoxic Amino Acid from Indigofera Spicat A: Isolation, Structure, and Biological Studies

Abstract

SummaryIndospicine (L-2-amino-6-amidinohexanoic acid) has been newly characterized as a component of a higher plant, being isolated from the leaves and seeds of Indigofera 8picata. Indospicine was hydrolysed in distilled water at 120°C to 2-aminopimelamic acid and ammonia (1 mole). Mild acid hydrolysis of the latter compound yielded optically pure L-oc-aminopimelic acid. The infrared, nuclear magnetic resonance, and mass spectra of indospicine and of its degradation products supported the proposed structure.When injected subcutaneously into mice (1 mg/g body weight) indospicine produced fat accumulation and cytologioal ohanges in the liver. The fat aocumulation was inhibited by simultaneous injeotion of arginine but not by oanavanine. A substantial part of the hepatotoxioity of extracts of 1. 8picata seed was accounted for in terms of indospicine. The ooncentration of indospicine in the seeds exoeeded that in the leaves and stems of the plant.

The Occurrence and Toxicity of Indospicine to Grazing Animals

“…Likewise Miller and Smith [17] Wide variations in indospicine content have been reported within individual Indigofera species with some suggestion that levels are influenced by the locale in which the taxa is growing, and particularly wide ranges of concentration (more than 10 fold variations between individual samples) have been reported for plant samples of I. linnaei [13] and I. lespedezioides [14]. Growth stage also effects indospicine levels [4], with highest levels of indospicine found in harvested seed of I. spicata [4] and I. linnaei [12] and lesser concentrations found in other parts of the plant including tips, leaves and the stem.…”

“…This toxin was isolated as the first naturally occurring hepatotoxic amino acid in 1970 by Hegarty and Pound from Indigofera spicata hence the name indospicine [4]. Plant classification within this species has been confused over the years and the I. spicata complex now comprises both I. spicata (Forsk.)…”

“…Aylward reported the "universality" of indospicine in I. spicata [7], whereas Charlwood [15] reported the absence of indospicine in 75% of seed samples of this species, and most remarkably detected only trace indospicine levels in the same seed accession [CPI 16110] that had contained 1240 mg/kg fresh weight when analysed by Hegarty and Pound [4]. The seed analysed by Hegarty and Pound in 1970 was green seed from fresh field-grown plants [4], while that analysed by Charlwood in 1984 was from a seed collection "collected from sites throughout Australia" and of unreported age [15]. This difference in seed source may well be a major contributor to the difference in reported results.…”

“…Species in which high levels of indospicine have been determined in foliage (in excess of 500 mg/kg DM) include I. hendecaphylla [4,11], I. linnaei [12,13], I. lespedezioides [7,14,15], I. spicata [4,11,[13][14][15][16], I. vicioides [9] and I. volkensii [7]. Indeed levels up to an exceptional 1.2% (DM basis) have been reported in I. spicata [7].…”

“…Indospicine has been shown experimentally to cause both liver degeneration and also teratogenic and embryo-lethal effects [3,4], but the mechanism of this toxicity has never been fully elucidated. …”