title: A gamma-glutamyl peptide isolated from onion (Allium cepa L.) by bioassay-guided fractionation inhibits resorption activity of osteoclasts.
abstract: One gram of onion added to the food of rats inhibits significantly (p < 0.05) bone resorption as assessed by the urinary excretion of tritium released from bone of 9-week-old rats prelabeled with tritiated tetracycline from weeks 1 to 6. To isolate and identify the bone resorption inhibiting compound from onion, onion powder was extracted and the extract fractionated by column chromatography and medium-pressure liquid chromatography. A single active peak was finally obtained by semipreparative high-performance liquid chromatography. The biological activity of the various fractions was tested in vitro on the activity of osteoclasts to form resorption pits on a mineralized substrate. Medium, containing the various fractions or the pure compound, was added to osteoclasts of new-born rats settled on ivory slices. After 24 h of incubation, the tartrate-resistant acid phosphatase positive multinucleated cells, that is, osteoclasts, were counted. Subsequently, the number of resorption pits was determined. Activity was calculated as the ratio of resorption pits/osteoclasts and was compared to a negative control, that is, medium containing 10% fetal bovine serum only and to calcitonin (10(-12) M) as a positive control. Finally, a single peak inhibited osteoclast activity significantly (p < 0.05). The structure of this compound was elucidated with high-performance liquid chromatography-electrospray ionization-mass spectrometry, time-of-flight electrospray ionization mass spectrometry, and nuclear magnetic resonance spectroscopy. The single peak was identified as gamma-L-glutamyl-trans-S-1-propenyl-L-cysteine sulfoxide (GPCS). It has a molecular mass of 306 Da and inhibits dose-dependently the resorption activity of osteoclasts, the minimal effective dose being approximately 2 mM. As no other peak displayed inhibitory activity, it likely is responsible for the effect of onion on bone resorption.
authors.affiliation: Laboratory for Phytopharmacology, Department of Clinical Research, University of Bern, Murtenstrasse 35, CH-3010 Bern, Switzerland.
authors.forename: Herbert A
authors.initials: HA
authors.lastname: Wetli
authors.forename: Rudolf
authors.initials: R
authors.lastname: Brenneisen
authors.forename: Ingrid
authors.initials: I
authors.lastname: Tschudi
authors.forename: Manuela
authors.initials: M
authors.lastname: Langos
authors.forename: Peter
authors.initials: P
authors.lastname: Bigler
authors.forename: Thomas
authors.initials: T
authors.lastname: Sprang
authors.forename: Stefan
authors.initials: S
authors.lastname: Schürch
authors.forename: Roman C
authors.initials: RC
authors.lastname: Mühlbauer
mesh_terms: D000818:Animals; D001681:Biological Assay; D001862:Bone Resorption / Q000517:prevention & control*; D005591:Chemical Fractionation; D002851:Chromatography, High Pressure Liquid; D004151:Dipeptides / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D019697:Onions / Q000737:chemistry*; D010010:Osteoclasts / Q000187:drug effects*; D051381:Rats; D021241:Spectrometry, Mass, Electrospray Ionization; D013454:Sulfoxides
chemical_list: D004151:Dipeptides; D013454:Sulfoxides; C501487:gamma-L-glutamyl-trans-S-1-propenyl-L-cysteine sulfoxide