Structural elucidation of rat biliary metabolites of corynoxeine and their quantification using LC-MSn

An enhanced strategy integrating offline two-dimensional separation with data independent acquisition mode and deconvolution: Characterization of metabolites of Uncaria rhynchophylla in rat plasma as a case

The importance to clarify the drug metabolites is beyond doubt in view of their potential efficacy and safety. However, due to the complex matrix interference, relatively low content and the co-eluting effect, it is of a great challenge to comprehensively and systematically characterize the metabolites in vivo, especially for the traditional Chinese medicines (TCMs) due to the numerous types of components. In the present study, a comprehensive off-line two-dimensional separation system combining with data independent acquisition (DIA) mode and multi-dimensional data deconvolution method was established for chromatographic separation, data acquisition and data procession of indole alkaloids in rat plasma after intragastrically administrated with the extract of Uncaria rhynchophylla at the dose of 1 g/kg. The orthogonality of the off-line 2D separation system consisting of HILIC for first-dimensional separation and the PRLC for second-dimensional separation was valuated with the "asterisk" equations, and the results showed that off-line 2D separation system had passable orthogonality (A₀ = 53.3%). Furthermore, the DIA mode was applied to capture MS/MS spectra in view of its advantage in acquiring MS data, and an effective multi-dimensional deconvolution method integrating the calculation of chemical formula, the extraction of diagnostic ion, the filter of ring double bond (RDB) and the judgement of neutral loss was established to parse the spectra for the complicated DIA data for comprehensive analysis of metabolites in rat plasma. Ultimately, a total of 127 indole alkaloids were tentatively characterized, and the main metabolic pathways were inferred as demethylation, dehydrogenation, hydroxylation and deglycosylation. The off-line two-dimensional separation system was applied for the comprehensive characterization of metabolites in vivo for the first time. This study suggested a new approach to enable the enrichment, separation and analysis of the low content components in vivo.

Properties, Pharmacology, and Pharmacokinetics of Active Indole and Oxindole Alkaloids in Uncaria Hook

Uncaria Hook (UH) is a dry stem with hook of Ucaria plant and is contained in Traditional Japanese and Chinese medicine such as yokukansan, yokukansankachimpihange, chotosan, Gouteng-Baitouweng, and Tianma-Gouteng Yin. UH contains active indole and oxindole alkaloids and has the therapeutic effects on ailments of the cardiovascular and central nervous systems. The recent advances of analytical technology led to reports of detailed pharmacokinetics of UH alkaloids. These observations of pharmacokinetics are extremely important for understanding the treatment’s pharmacological activity, efficacy, and safety. This review describes properties, pharmacology, and the recently accumulated pharmacokinetic findings of UH alkaloids, and discusses challenges and future prospects. UH contains major indole and oxindole alkaloids such as corynoxeine, isocorynoxeine, rhynchophylline, isorhynchophylline, hirsuteine, hirsutine, and geissoschizine methyl ether (GM). These alkaloids exert neuroprotective effects against Alzheimer’s disease, Parkinson’s disease, and depression, and the mechanisms of these effects include anti-oxidant, anti-inflammatory, and neuromodulatory activities. Among the UH alkaloids, GM exhibits comparatively potent pharmacological activity (e.g., agonist activity at 5-HT_1A receptors). UH alkaloids are absorbed into the blood circulation and rapidly eliminated when orally administered. UH alkaloids are predominantly metabolized by Cytochrome P450 (CYP) and converted into various metabolites, including oxidized and demethylated forms. Regarding GM metabolism by CYPs, a gender-dependent difference is observed in rats but not in humans. Several alkaloids are detected in the brain after passing through the blood–brain barrier in rats upon orally administered. GM is uniformly distributed in the brain and binds to various channels and receptors such as the 5-HT receptor. By reviewing the pharmacokinetics of UH alkaloids, challenges were found, such as differences in pharmacokinetics between pure drug and crude drug products administration, food-influenced absorption, metabolite excretion profile, and intestinal tissue metabolism of UH alkaloids. This review will provide readers with a better understanding of the pharmacokinetics of UH alkaloids and their future challenges, and will be helpful for further research on UH alkaloids and crude drug products containing UH.

Effective Separation and Simultaneous Determination of Corynoxeine and Its Metabolites in Rats by High-Performance Liquid Chromatography with Tandem Mass Spectrometry and Application to Pharmacokinetics and In Vivo Distribution in Main Organs

An effective separation and simultaneous determination of corynoxeine and its metabolites using high-performance liquid chromatography with tandem mass spectrometry was developed and validated. The method was applied to pharmacokinetics and in vivo distribution investigations in rats after oral (0.105 mmol kg(-1)) and intravenous (0.0105 mmol kg(-1)) doses of corynoxeine. Its brain uptake index was of 3.08 × 10(-11) mol g(-1) at 3 h and 3.75 × 10(-11) mol g(-1) at 74 min after oral and intravenous doses, respectively.

Stereoselective in vitro metabolism of rhynchophylline and isorhynchophylline epimers of Uncaria rhynchophylla in rat liver microsomes

1. The objective was to investigate the underlying mechanism of the stereoselectivity in the metabolism of rhynchophylline (RIN) and isorhynchophylline (IRN) epimers in rat liver microsomes (RLM). 2. After incubation, eight metabolites of RIN (M1-5) and IRN (M6-8) reacted at A- and C-ring were identified using LC-Q-TOF/MS. Metabolic pathways included oxidation, hydroxylation, N-oxidation and dehydrogenation. In addition, hydroxylation at A-ring was the major metabolic pathway for RIN whereas the oxidation at C-ring was the major one for IRN. 3. Enzyme kinetics showed that the intrinsic clearance (CL_int) for IRN elimination was 1.9-fold higher than RIN and the degradation half-life (T_1/2) of RIN was 4.7-fold higher than that of IRN, indicating IRN was more favorable to be metabolized than RIN in RLM. 4. Data from chemical inhibition study demonstrated CYP3A was the predominant isoform involved in the metabolic elimination of both epimers, as well as the formation of M1-8. 5. In conclusion, data revealed that due to the spatial configurations at C-7 position, RIN and IRN epimers possessed different hepatic metabolic pathways and elimination rates which were mainly mediated by CYP3A.

Metabolic Profile of Isocorynoxeine in Rats Obtained by Ultra-High Performance Liquid Chromatography/Quadrupole Time-of-Flight Mass Spectrometry

BACKGROUND AND OBJECTIVE

Isocorynoxeine (IC), a major alkaloid found in Uncaria rhynchophylla, exhibits wide beneficial effects on the cardiovascular and cardiocerebral vascular systems. Its metabolic pathway, however, has not been well studied yet. In this study, an ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (U-HPLC/Q-TOFMS) method was developed to investigate IC metabolism in plasma, urine and bile in rats given IC orally at 40 mg/kg.

METHODS

Nine male Wistar rats were given IC 40 mg/kg orally. Blood, urine and bile samples were collected at pre-specified times to measure the concentration of IC.

RESULTS

A total of 35 metabolites were tentatively identified by the co-chromatography of biosamples and comparison of the retention time, characteristic molecular ions and fragment ions with those of the authentic standards or tentatively identified by MS/MS determination along with MassFragment software. Among them, 18, 33 and 18 metabolites were found in plasma, urine and bile samples, respectively. The relative percentage area of each metabolite was also determined to better understand the major metabolic pathways of IC in rats.

CONCLUSIONS

The result indicates that IC undergoes extensive metabolism in vivo, mainly including hydrolysis, oxidation, isomerization, demethylation, epoxidation, reduction, glucuronidation, hydroxylation and N-oxidation, which is helpful for the further pharmacokinetic study of IC in vivo.

Pharmacokinetic study of isocorynoxeine metabolites mediated by cytochrome P450 enzymes in rat and human liver microsomes

Isocorynoxeine (ICN) is one of the major bioactive tetracyclic oxindole alkaloids found in Uncaria rhynchophylla (Miq.) Jacks. that is widely used for the treatment of hypertension, vascular dementia, and stroke. The present study was undertaken to assess the plasma pharmacokinetic characteristics of major ICN metabolites, and the role of simulated gastric and intestinal fluid (SGF and SIF), human and rat liver microsomes (HLMs and RLMs), and seven recombinant human CYP enzymes in the major metabolic pathway of ICN. A rapid, sensitive and accurate UHPLC/Q-TOF MS method was validated for the simultaneous determination of ICN and its seven metabolites in rat plasma after oral administration of ICN at 40mg/kg. It was found that 18.19-dehydrocorynoxinic acid (DCA) and 5-oxoisocorynoxeinic acid (5-O-ICA) were both key and predominant metabolites, rather than ICN itself, due to the rapid and extensive metabolism of ICN in vivo. The further study indicated that ICN was mainly metabolized in human or rat liver, and CYPs 2C19, 3A4 and 2D6 were the major enzymes responsible for the biotransformation of ICN to DCA and 5-O-ICA in human. These findings are of significance in understanding of the pharmacokinetic nature of tetracyclic oxindole alkaloids, and provide helpful information for the clinical co-administration of the herbal preparations containing U. rhynchophylla with antihypertensive drugs that are mainly metabolized by CYP3A4 and CYP2C19.

Multiple stage MS in analysis of plasma, serum, urine and in vitro samples relevant to clinical and forensic toxicology

This paper reviews MS approaches applied to metabolism studies, structure elucidation and qualitative or quantitative screening of drugs (of abuse) and/or their metabolites. Applications in clinical and forensic toxicology were included using blood plasma or serum, urine, in vitro samples, liquids, solids or plant material. Techniques covered are liquid chromatography coupled to low-resolution and high-resolution multiple stage mass analyzers. Only PubMed listed studies published in English between January 2008 and January 2015 were considered. Approaches are discussed focusing on sample preparation and mass spectral settings. Comments on advantages and limitations of these techniques complete the review.

Medicinal uses, phytochemistry and pharmacology of the genus Uncaria

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Uncaria belongs to the family Rubiaceae, which mainly distributed in tropical regions, such as Southeast Asia, Africa and Southeast America. Their leaves and hooks have long been thought to have healing powers and are already being tested as a treatment for asthma, cancer, cirrhosis, diabetes, hypertension, stroke and rheumatism. The present review aims to provide systematically reorganized information on the ethnopharmacology, phytochemistry and pharmacology of the genus Uncaria to support for further therapeutic potential of this genus. To better understanding this genus, information on the stereo-chemistry and structure-activity relationships in indole alkaloids is also represented.

MATERIAL AND METHODS

The literature study of this review is based on various databases search (SCIFinder, Science Direct, CNKI, Wiley online library, Spring Link, Web of Science, PubMed, Wanfang Data, Medalink, Google scholar, ACS, Tropicos, Council of Heads of Australasian Herbaria, The New York Botanical Garden, African Plants Database at Genera Botanical Garden, The Plant List and SEINet) and library search for Biological Abstract and some local books on ethnopharmacology.

RESULTS

19 species of the genus Uncaria are found to be important folk medicines in China, Malaysia, Phillippines, Africa and Southeast America, etc, and have been served for the treatment of asthma, rheumatism, hyperpyrexia, hypertension and headaches, etc. More than 200 compounds have been isolated from Uncaria, including indole alkaloids, triterpenes, flavonoids, phenols, phenylpropanoids, etc. As characteristic constituents, indole alkaloids have been considered as main efficacy component for hypertension, epilepsy, depressant, Parkinson's disease and Alzheimer's disease. In addition, pharmacokinetic and metabolism investigation reveal that the indole alkaloids are likely to be absorbed, metabolized and excreted at early time points. Moreover, the specific inhibition of CYP isozymes can regulate their hydroxylation metabolites at C-10 and C-11.

CONCLUSION

Preliminary investigations on pharmacological properties of the Uncaria species have enlightened their efficacious remedy for hypertension, asthma, cancer, diabetes, rheumatism and neurodegenerative diseases. To ensure the safety and effectiveness in clinical application, research on bioactive compounds, pharmacological mechanisms and toxicity of the genus Uncaria as well as the stereo-chemistry and structure-activity relationships of indole alkaloids seem very important.

Metabolites of isocorynoxeine in rats after its oral administration

This work presents the metabolites of isocorynoxeine (ICOR), which is one of four bioactive tetracyclic oxindole alkaloids isolated from Uncaria hooks used commonly in the traditional Chinese medicines and Kampo medicines. After oral administration of 40 mg kg(-1) ICOR to rats, bile was drained and analyzed by LC-MS. Two phase I metabolites, namely 11-hydroxyisocorynoxeine (M1) and 10-hydroxyisocorynoxeine (M2), and two phase II metabolites, namely 11-hydroxyisocorynoxeine 11-O-β-D-glucuronide (M3) and 10-hydroxyisocorynoxeine 10-O-β-D-glucuronide (M4), were isolated from rat excreta and bile, respectively, whose structures were elucidated on the basis of CD, NMR, and MS.