Metabolism of diosgenin-derived saponins: implications for hepatogenous photosensitization diseases in ruminants

Disposition of sapogenins in the gastrointestinal tract of a lamb was deter mined after daily dosing of a diosgenin-derived saponin extract during late spring. The saponin (26.1 g) was obtained by ethanolic extraction of powde red Costus speciosus rhizomes followed by butanol-water partitioning. Upon completion of dosing, samples of gut contents and internal organs were subj ected to chemical analysis and histological examination. No clinical sympto ms, changes in serum chemistry, or microscopic changes were observed. Dosin g of a saponin extract revealed that ruminal metabolism resulted in convers ion of diosgenin to epismilagenin, smilagenone, smilagenin and tigogenin. E lectrospray mass spectrometry of selected ethanolic ruminal extracts showed the absence of diosgenin-derived saponins 1h after dosing, indicating that rapid hydrolysis of saponins by ruminal micro-flora occurred. Epismilageni n was the dominant conjugated sapogenin detected in the bile sample, no fre e sapogenins were identified. Three distinct zones of metabolic activity we re identified in the gastrointestinal tract of the dosed lamb. The rumen ap peared to be a region where the ingested diosgenin-derived saponins underwe nt hydrolysis and reduction and were converted to tigogenin, smilagenin, sm ilagenone and epismilagenin. The duodenum, jejunum and ileum formed an abso rption and secretion zone where there appeared to be variation in both the concentrations of free and conjugated sapogenins. Sapogenins appeared to un dergo continued epimerization in the caecum and colon. The plant saponins a dministered in this study were readily metabolized, but did not appear to i nduce crystal-associated hepatogenous photosensitization in the dosed lamb. (C) 2001 Elsevier Science B.V. All rights reserved.