Characterization of in vitro and in vivo metabolites of carnosic acid, a natural antioxidant, by high performance liquid chromatography coupled with tandem mass spectrometry.

Carnosic acid (CA) is a widely employed antioxidant and the main active component in rosemary and sage, but its metabolism remains largely unknown. The present study investigated the metabolism of CA in vitro and in vivo for the first time, using high performance liquid chromatography coupled with hybrid triple quadrupole-linear ion trap mass spectrometry (HPLC-Q-trap-MS). A couple of scan modes were adopted in mass spectrometer domain, including Q1 full scan, neutral loss scan-information dependent acquisition-enhanced product ion (NL-IDA-EPI) and precursor ion scan-information dependent acquisition-enhanced product ion (PI-IDA-EPI). In particular, a prediction was carried out on the basis of in vitro metabolism results, and gave birth to a multiple ion monitoring-information dependent acquisition-enhanced product ion (MIM-IDA-EPI) mode aiming to detect the trace metabolites in CA-treated biological samples. A total of ten metabolites (M4-13), along with three degradative products (M1-3), were identified for CA from in vitro metabolism models, including liver microsomes of human and rats (HLMs and RLMs), human intestinal microsomes (HIMs) and two species of Cunninghamella elegans. Twelve (U1-12) and six (F1-6) metabolites were detected from CA-treated urine and feces, respectively. In addition, five metabolites (SM2-6) in vivo were purified and definitely identified using NMR spectroscopy. The results of both in vitro and in vivo metabolism studies indicated poor metabolic stability for CA, and the glucuronidation and oxidation metabolisms extensively occurred for CA in vitro, while oxidation, glucuronidation and methylation were the main metabolic pathways observed in vivo.