Detection of glutathione conjugates derived from 4-ipomeanol metabolism in bile of rats by liquid chromatography-tandem mass spectrometry.
Earlier studies postulated that bioactivation of 4-ipomeanol by cytochrome P450 enzymes may occur through oxidation of its furan ring, following a mechanism similar to the bioactivation of other furan-containing compounds. This would lead to the formation of furan epoxides and alpha,beta-unsaturated di-aldehyde-reactive metabolites that can conjugate with glutathione. These metabolites are thought to be responsible for the cytotoxic and anticancer properties of 4-ipomeanol. We hypothesized that if 4-ipomeanol is metabolized following this pathway, its glutathione conjugates would be isobaric (molecular ion mass = 492 Da) and would be excreted in bile. To investigate this hypothesis, we analyzed by liquid chromatography-tandem mass spectrometry the bile of rats administered d0/d6 4-ipomeanol (1:1 ratio) intravenously. Hexadeuterated 4-ipomeanol had all deuterium atoms incorporated on its aliphatic chain. Multiple reaction monitoring scans of bile for the mass transition: MH+/(MH - 129)+, which is characteristic of glutathione conjugates, detected four glutathione conjugates. The observation of the isotope cluster (M + 1)+ (d0)/(MH + 6)+ (d6) in a 1:1 molar ratio confirmed that these conjugates were derived from 4-ipomeanol. Retention of the six deuterium atoms in the glutathione conjugates detected, (MH + 6)+, indicates that the bioactivation of 4-ipomeanol took place on the furan ring moiety. Rat hepatic microsomal incubations provided additional evidence. From this study, the mass of the reactive metabolites of 4-ipomeanol can be inferred. The inferred mass (186 Da) matches the mass postulated. A pathway of 4-ipomeanol bioactivation is proposed here. This work represents one step forward to understanding the mechanism of bioactivation of 4-ipomeanol.
Department of Pharmaceutical Sciences, School of Pharmacy, Bouvé College of Health Sciences, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, USA.
Teresa M
TM
Alvarez-Diez
Jiang
J
Zheng
D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics*; D001646:Bile / Q000378:metabolism*; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003903:Deuterium; D005978:Glutathione / Q000378:metabolism*; D066298:In Vitro Techniques; D007553:Isotope Labeling; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013729:Terpenes / Q000493:pharmacokinetics*
D000970:Antineoplastic Agents; D013729:Terpenes; D003577:Cytochrome P-450 Enzyme System; D003903:Deuterium; D005978:Glutathione; C001470:4-ipomeanol