Metabolism of calycosin, an isoflavone from Astragali Radix, in zebrafish larvae.

Although zebrafish has become a popular animal model for drug discovery and screening, drug metabolism in zebrafish remains largely unknown. In this study, we probed the metabolic capability of zebrafish larvae with calycosin, one of the major isoflavone constituents of Radix Astragali that was previously demonstrated to be angiogenic in the zebrafish model. The metabolism of calycosin and accumulation of its metabolites in zebrafish larvae were determined using an LC-MS/MS method. Calycosin showed a slow but steady decrease from the culture medium as well as a steady accumulation in zebrafish larvae. Calycosin underwent major conjugation and minor oxidation in zebrafish larvae. A total of ten calycosin metabolites formed from glucuronidation, glucosylation, sulfation, oxidation or a combination of two of these metabolisms were identified, most of which were reported for the first time. Most metabolites increased steadily in the larvae over 24-h experimental period. The dominant phase II conjugation of calycosin in zebrafish larvae matched well with existing knowledge of isoflavone metabolism in mammalians. The findings shed a light in certain degree of similarity of phase II drug metabolism between zebrafish larvae and mammals and warrant further investigation on feasibility of adopting the zebrafish larvae as a whole-organism model for examining drug metabolism.

Combined in vivo imaging and omics approaches reveal metabolism of icaritin and its glycosides in zebrafish larvae.

Flavonoids isolated from Herba Epimedii such as icaritin, icariin and epimedin C have been suggested as potential bone anabolic compounds. However, the "specific localized effects" of these flavonoids in bone, in vivo, and the metabolism of these flavonoids in zebrafish larvae have never been demonstrated. In this study, we used multiple methods including in vivo imaging, drug metabolites profiling, transcriptomic and proteomic approaches to determine the mechanisms involved in the distribution and metabolism of the flavonoids in zebrafish larvae by measuring the fluorescence emission, in vivo, of icaritin and its glycoside derivatives. The fluorescence emission mechanism of icaritin in vitro was identified by spectrophotometric analysis, and the fluorescent property of icaritin was used as a probe to visualize the metabolism and distribution of icaritin and its glycoside derivatives in zebrafish larvae. Phase I and phase II metabolism of icaritin and its derivatives were identified in zebrafish by mass spectrometry. The combined transcriptomics and proteomics demonstrate a high degree of conservation of phase I and phase II drug metabolic enzymes between zebrafish larvae and mammals. Icaritin and its glycoside derivatives were demonstrated using combined approaches of in vivo imaging, drug metabolites identification, and transcriptomic and proteomic profiling to illustrate phase I and phase II metabolism of the flavonoids and their distribution in bone of zebrafish larvae. This study provides a new methodological model for use of the zebrafish larvae to examine drug metabolism.

Senkyunolides reduce hydrogen peroxide-induced oxidative damage in human liver HepG2 cells via induction of heme oxygenase-1.

Rhizoma Chuanxiong is widely used as folk medicine to treat the diseases caused by oxidative stress and inflammation. To delineate the underlying molecular mechanisms, we recently found that Rhizoma Chuanxiong extract significantly induced heme oxygenase-1 (HO-1), an enzyme that degrades intracellular heme into three bioactive products: biliverdin, carbon monoxide and free iron. The anti-inflammatory, antiapoptotic and antiproliferative actions of these products highlight HO-1 as a key endogenous antioxidant and cytoprotective gene. This study was designed to further characterize HO-1 induction of Rhizoma Chuanxiong through bioactivity-guided fractionation. All isolated fractions were assayed for HO-1 induction in human HepG2 cell line at mRNA and protein levels. Based on chromatographic profiling, nuclear magnetic resonance (NMR) and mass spectrometric analysis, the active compounds were identified as senkyunolide-H and its stereoisomer senkyunolide-I. Both senkyunolide isomers inhibited the formation of reactive oxygen species and lipid peroxidation and enhanced the cellular resistance to hydrogen peroxide-induced oxidative damage. Notably, heme oxygenase inhibitor tin protoporphyrin IX (SnPP) significantly suppressed the antioxidant activity of senkyunolide stereoisomers. Thus, this study demonstrated that senkyunolide-H and -I attenuated oxidative damage via activation of HO-1 pathway.

Are the radical centers in peptide radical cations mobile? The generation, tautomerism, and dissociation of isomeric alpha-carbon-centered triglycine radical cations in the gas phase.

The mobility of the radical center in three isomeric triglycine radical cations[G(*)GG](+), [GG(*)G](+), and [GGG(*)](+) has been investigated theoretically via density functional theory (DFT) and experimentally via tandem mass spectrometry. These radical cations were generated by collision-induced dissociations (CIDs) of Cu(II)-containing ternary complexes that contain the tripeptides YGG, GYG, and GGY, respectively (G and Y are the glycine and tyrosine residues, respectively). Dissociative electron transfer within the complexes led to observation of [Y(*)GG](+), [GY(*)G](+), and [GGY(*)](+); CID resulted in cleavage of the tyrosine side chain as p-quinomethide, yielding [G(*)GG](+), [GG(*)G](+), and [GGG(*)](+), respectively. Interconversions between these isomeric triglycine radical cations have relatively high barriers (> or = 44.7 kcal/mol), in support of the thesis that isomerically pure [G(*)GG](+), [GG(*)G](+), and [GGG(*)](+) can be experimentally produced. This is to be contrasted with barriers < 17 kcal/mol that were encountered in the tautomerism of protonated triglycine [Rodriquez C. F. et al. J. Am. Chem. Soc. 2001, 123, 3006-3012]. The CID spectra of [G(*)GG](+), [GG(*)G](+), and [GGG(*)](+) were substantially different, providing experimental proof that initially these ions have distinct structures. DFT calculations showed that direct dissociations are competitive with interconversions followed by dissociation.