Pyrrolizidine alkaloids (PAs) are naturally occurring phytotoxins widely distributed in about 3% of flowering plants. The formation of PA-derived pyrrole-protein adducts is considered as a primary trigger initiating PA-induced hepatotoxicity. The present study aims to (i) further validate our previous established derivatization method using acidified ethanolic AgNO3 for the analysis of pyrrole-protein adducts and (ii) apply this method to characterize the binding tendency, dose-response, and elimination kinetics of pyrrole-protein adducts in blood samples. Two pyrrole amino acid conjugates, (+/-)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-cysteine (7-cysteine-DHP) and 9-histidine-DHP, were synthesized and used to demonstrate that acidified ethanolic AgNO3 derivatization can cleave both S-linkage and N-linkage of pyrrole-protein adducts. Subsequently, using precolumn AgNO3 derivatization followed by ultra-high-pressure liquid chromatography/mass spectrometry analysis, we quantified pyrrole-protein adducts in monocrotaline-treated rat blood protein fractions, including hemoglobin (Hb), plasma, albumin, and plasma residual protein fractions, and found that the amount of pyrrole-Hb adducts was significantly higher than that in all plasma fractions. Moreover, elimination half-life of pyrrole-Hb adducts was also significantly longer than pyrrole-protein adducts in plasma fractions (12.08 vs 2.54-2.93 days). In addition, we also tested blood samples obtained from five PA-induced liver injury patients and found that the amount of pyrrole-protein adducts in blood cells was also remarkably higher than that in plasma. In conclusion, our findings for the first time confirmed that the AgNO3 derivatization method could be used to measure both S- and N-linked pyrrole-protein adducts and also suggested that pyrrole Hb adducts with remarkably higher level and longer life span could be a better biomarker of PA exposure.
[1]Chinese Univ Hong Kong, Sch Biomed Sci, Fac Med, Hong Kong, Peoples R China;
[2]Chinese Univ Hong Kong, Joint Res Lab Promoting Globalizat Tradit Chinese, Shanghai 201203, Peoples R China;
[3]Chinese Acad Sci, Shanghai Inst Mat Med, Shanghai 201203, Peoples R China;
[4]Fudan Univ, Div Gastroenterol, ZhongShan Hosp, Shanghai 200000, Peoples R China;
[5]Chinese Acad Sci, State Key Lab Drug Res, Shanghai Inst Mat Med, Shanghai 201203, Peoples R China;
[6]US FDA, Natl Ctr Toxicol Res, Jefferson, AR 72079 USA
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