Comparative study of fourteen alkaloids from Uncaria rhynchophylla hooks and leaves using HPLC-diode array detection-atmospheric pressure chemical ionization/MS method

Validated Quantitative 1H NMR Method for Simultaneous Quantification of Indole Alkaloids in Uncaria rhynchophylla

Uncariae Ramulus Cum Uncis, known as "Gou-Teng" in Chinese, is derived mainly from the dried hook-bearing stems of Uncaria rhynchophylla. Quantitative determination of monoterpenoid indole alkaloids is critical for controlling its quality. In the present study, a rapid, accurate, and precise method was developed for the simultaneous quantitation of four characteristic components, namely, rhynchophylline (1), isorhynchophylline (2), corynoxeine (3), and isocorynoxeine (4), through 1H NMR spectrometry techniques. This method was performed on a 600 MHz NMR spectrometer with optimized acquisition parameters for performing quantitative experiments within 14 min. The highly deshielded signal of NH was at δH 10-11 in the aprotic solvent DMSO-d 6, which enables satisfactory separation of the signals to be integrated. Validation of the quantitative method was also performed in terms of specificity, linearity, sensitivity, accuracy, and precision. The method is linear in the concentration range of 25-400 μg/mL. The lower limit of quantification is 25 μg/mL. The intra- and interday relative standard deviation across three validation runs over the entire concentration range is less than 2.51%. The accuracy determined at three concentrations was within ±4.4% in terms of relative error. The proposed qNMR method was demonstrated to be a powerful tool for quantifying the alkaloids in traditional Chinese medicines (TCMs) due to its unique advantages of high precision, rapid analysis, and nonrequirement of standard compounds for calibration curve preparation. Moreover, qNMR represents a feasible alternative to high-performance liquid chromatography-based methods for the quality control of TCMs.

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.

Recent Advances in the Anti-Inflammatory Activity of Plant-Derived Alkaloid Rhynchophylline in Neurological and Cardiovascular Diseases

Rhynchophylline (Rhy) is a plant-derived indole alkaloid isolated from Uncaria species. Both the plant and the alkaloid possess numerous protective properties such as anti-inflammatory, neuroprotective, anti-hypertensive, anti-rhythmic, and sedative effects. Several studies support the significance of the anti-inflammatory activity of the plant as an underlying mechanism for most of the pharmacological activities of the alkaloid. Rhy is effective in protecting both the central nervous system and cardiovascular system. Cerebro-cardiovascular disease primarily occurs due to changes in lifestyle habits. Many previous studies have highlighted the significance of Rhy in modulating calcium channels and potassium channels, thereby protecting the brain from neurodegenerative diseases and related effects. Rhy also has anticoagulation and anti-platelet aggregation activity. Although Rhy has displayed its role in protecting the cardiovascular system, very little is explored about its intervention in early atherosclerosis. Extensive studies are required to understand the cardioprotective effects of Rhye. This review summarized and discussed the various pharmacological effects of Rhy in neuro- and cardioprotection and in particular the relevance of Rhy in preventing early atherosclerosis using Rhy-loaded nanoparticles.

Simultaneous Determination of Six Uncaria Alkaloids in Mouse Blood by UPLC-MS/MS and Its Application in Pharmacokinetics and Bioavailability

A specific ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method has been developed for the simultaneous determination of six Uncaria alkaloids in mouse blood with midazolam as the internal standard (IS). Only 20 μL blood was needed for sample preparation, and the protein was precipitated with acetonitrile. The UPLC BEH C18 column (2.1 mm × 100 mm, 1.7 μm) was used for chromatographic separation. The mobile phase consisted of 0.1% formic acid and acetonitrile with gradient elution within 5.5 min. Multiple reaction monitoring (MRM) and the positive electrospray ionization model were used for quantitative analysis. The accuracy of the UPLC-MS/MS method ranged from 86.5% to 110.4%. The precision for intraday and interday was ≤15% each. The mean recovery and the matrix effects were found to be 64.4-86.8% and 94.1-109.4%, respectively. The calibration curves in blood were linear in the range of 1-1000 ng/mL with a favorable correlation coefficient (r²) of 0.995. The pharmacokinetic results showed that six Uncaria alkaloids metabolized rapidly in mice with a half-life between 0.6 h and 4.4 h. The bioavailability of corynoxeine, isocorynoxeine, rhynchophylline, isorhynchophylline, hirsutine, and hirsuteine was 27.3%, 32.7%, 49.4%, 29.5%, 68.9%, and 51.0%, respectively, which showed satisfactory oral absorption of each alkaloid.

Safety and biological activity evaluation of Uncaria rhynchophylla ethanolic extract

Uncaria rhynchophylla (UR) belongs to the Rubiaceae family, and its dried hooks are usually used in traditional medicine. It is effective in treating diseases related to the central nervous system. This study aimed to evaluate the safety of UR extract, investigate its antimutagenic and antioxidative activities, and elucidate its active components. Extraction and fractionation of the UR extract resulted in yields of 6.71%, 0.037%, 0.042%, 0.152%, 0.332%, and 5.132%, for hexane, ether, DCM, EtOAC, and aqueous fractions, respectively. The four indole alkaloids, total phenolic content (TPC), and total flavonoid content (TFC) of UR extract and its subfractions were measured. Alkaloid content was highest in the UR extract. TPC was the highest in the EtOAC fraction (373.7 ± 20.9 mg gallic acid equivalent (GAE)/g), whereas TFC was the highest in the UR extract (33.5 ± 2.4 mg quercetin equivalent (QE)/g). To assess the safety of UR extract mutagenicity, cytotoxicity, and oxidative stress inducibility assays were performed. The UR extract (2000 µg/plate) showed excellent antimutagenic activity (above 90%) against BaP in both TA98 and TA100 strains. The UR extract exhibited efficient DPPH (RC₅₀ 239.2 ± 16.5 µg/mL) and ABTS scavenging activity (RC₅₀ 458.7 ± 25.0 µg/mL). The UR extract (150 µg/mL) showed cytoprotective activity (65.6% ± 9.2%) against t-BHP. Among the subfractions, the EtOAC fraction possessed the strongest activities, overall. UR generally showed excellent biological activity at nontoxic concentrations (determined in vitro in current work), although the chemical composition of UR requires further investigation prior to its potential future use.

UFLC-PDA-MS/MS Profiling of Seven Uncaria Species Integrated with Melatonin/5-Hydroxytryptamine Receptors Agonistic Assay

Uncariae Ramulus Cum Uncis (Gou-Teng), the dried hook-bearing stems of several Uncaria plants (Rubiaceae), is a well-known herbal medicine in China. The clinical application of Gou-Teng is bewildered for the morphological and chemical similarity between different species. In order to discern their chemical and biological difference, an ultra-fast liquid chromatography equipped with ion trap time-of-flight mass spectrometry (UFLC-IT/TOF-MS) combining with melatonin (MT1 and MT2) and 5-hydroxytryptamine (5-HT1A and 5-HT2C) receptors agonistic assay in vitro was conducted on seven Uncaria species. As a result, 57 compounds including 35 indole alkaloids, ten flavonoids, five triterpenoids, five chlorogenic analogues, and two other compounds were characterized based on their MS/MS patterns and UV absorptions. Specifically, cadambine-type and corynanthein-type alkaloids were exclusively present in U.rhynchophylla and U.scandens, whereas corynoxine-type alkaloids were commonly detected in all the seven Uncaria plants. Three Uncaria species, U. rhynchophylla, U. macrophylla, and U. yunnanensis showed obviously agnostic activity on four neurotransmitter receptors (MT1, MT2, 5-HT1A, and 5-HT2C). This first-time UFLCMS-IT-TOF analyses integrated with biological assay on seven Uncaria plants will provide scientific viewpoints for the clinical application of Gou-Teng.

Rhynchophylline attenuates allergic bronchial asthma by inhibiting transforming growth factor-β1-mediated Smad and mitogen-activated protein kinase signaling transductions in vivo and in vitro

Rhynchophylline (Rhy) is a major active component of Uncaria rhynchophylla and exhibits the potential to inhibit the proliferation of airway smooth muscle cells (ASMCs). In the current study, it was hypothesized that Rhy serves a key role in the anti-asthma effect of Uncaria rhynchophylla by inhibiting transforming growth factor-β1 (TGF-β1)-mediated activation of Smad and mitogen-activated protein kinase (MAPK) signaling. Allergic asthma was induced in mice using ovalbumin (OVA), and the effect of Rhy treatment on inflammatory and allergic responses in the bronchoalveolar lavage fluid (BALF) and serum of mice was determined. Subsequently, the changes in TGF-β1-induced Smad and MAPK signaling following Rhy administration were detected to determine the mechanism associated with this treatment. In addition, TGF-β1 was employed to induce hyperplasia of ASMCs, and the effect of Rhy on proliferation of ASMCs, and Smad and MAPK signaling in vitro was also assessed. The administration of Rhy attenuated the recruitment of eosinophils in BALF induced by OVA, which was associated with the suppressed production of immunoglobulin E, interleukin (IL)-13, IL-4 and IL-5. At the molecular level, the administration of Rhy suppressed the expression levels of TGF-β1, Smad4, p-Smad2 and p-Smad3, while it induced the expression of Smad7, indicating the inhibitory effect of Rhy on TGF-β1-mediated Smad and MAPK signaling. Furthermore, Rhy inhibited the proliferation of ASMCs and, similar to the results of the in vivo assay, it blocked the pro-hyperplasia signaling transduction in vitro. In conclusion, the current study demonstrated the anti-asthma effect of Rhy, which depended on the inhibition of TGF-β1-mediated Smad and MAPK signaling.

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.

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.

Molecular identification of Uncaria (Gouteng) through DNA barcoding

Background

While DNA barcoding is an important technology for the authentication of the botanical origins of Chinese medicines, the suitable markers for DNA barcoding of the genus Uncaria have not been reported yet. This study aims to determine suitable markers for DNA barcoding of the genus Uncaria (Gouteng).

Methods

Genomic DNA was extracted from the freshly dried leaves of Uncaria plants by a Bioteke’s Plant Genomic DNA Extraction Kit. Five candidate DNA barcode sites (ITS2, rbcL, psbA–trnH, ITS, and matK) were amplified by PCR with established primers. The purified PCR products were bidirectionally sequenced with appropriate amplification primers in an ABI-PRISM3730 instrument. The candidate DNA barcodes of 257 accessions of Uncaria in GenBank were aligned by ClustalW. Sequence assembly and consensus sequence generation were performed with CodonCode Aligner 3.7.1. The identification efficiency of the candidate DNA barcodes was evaluated with BLAST and nearest distance methods. The interspecific divergence and intraspecific variation were assessed by the Kimura 2-Parameter model. Genetic distances were computed with Molecular Evolutionary Genetics Analysis 6.0.

Results

The accessions of the five candidate DNA barcodes from 11 of 12 species of Uncaria in China and four species from other countries were included in the analysis, while 54 of total accessions were submitted to GenBank. In a comparison of the interspecific genetic distances of the five candidate barcodes, psbA–trnH exhibited the highest interspecific divergence based on interspecific distance, theta prime, and minimum interspecific distance, followed by ITS2. The distribution of the interspecific distance of ITS2 and psbA–trnH was higher than the corresponding intraspecific distance. Additionally, psbA–trnH showed 95.9 % identification efficiency by both the BLAST and nearest distance methods regardless of species or genus level. ITS2 exhibited 92.2 % identification efficiency by the nearest distance method, but 87 % by the BLAST method.

Conclusion

While psbA–trnH and ITS2 (used alone) were applicable barcodes for species authentication of Uncaria, psbA–trnH was a more suitable barcode for authentication of Uncaria macrophylla.

Electronic supplementary material

The online version of this article (doi:10.1186/s13020-015-0072-7) contains supplementary material, which is available to authorized users.

Qualitative and quantitative analyses of alkaloids in Uncaria species by UPLC-ESI-Q-TOF/MS

An ultra performance liquid chromatography (UPLC) coupled with quadrupole time-of-flight mass spectrometry (Q-TOF/MS) method has been optimized and established for the rapid analysis of the alkaloids in 22 samples originating from five Uncaria (U.) species. The accurate mass measurement of all the protonated molecules and subsequent fragment ions offers higher quality structural information for the interpretation of fragmentation pathways of the various groups of alkaloids. A total of 19 oxindole alkaloids, 16 indole alkaloids and 1 flavone were identified by co-chromatography of the sample extract with authentic standards, comparison of the retention time, characteristic molecular ions and fragment ions, or were tentatively identified by MS/MS determination. Moreover, the method was validated for the simultaneous quantification of the 24 components within 10.5 min. The potential chemical markers were identified for classification of the U. species samples by principal component analysis (PCA) and orthogonal partial least squared discriminant analysis (OPLS-DA). The results demonstrate the similarity and differences in alkaloids among the five U. species, which is helpful for the standardization and quality control of the medical materials of the U. Ramulus Cum Unics (URCU). Furthermore, with multivariate statistical analysis, the determined markers are more definite and useful for chemotaxonomy of the U. genus.

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.

Chemical profiling with HPLC-FTMS of exogenous and endogenous chemicals susceptible to the administration of chotosan in an animal model of type 2 diabetes-induced dementia

In our previous study, the daily administration of chotosan (CTS), a Kampo formula consisting of Uncaria and other 10 different crude drugs, ameliorated cognitive deficits in several animal models of dementia including type 2 diabetic db/db mice in a similar manner to tacrine, an acetylcholinesterase inhibitor. The present study investigated the metabonomics of CTS in db/db mice, a type 2 diabetes model, and m/m mice, a non-diabetes control strain, to identify the exogenous and endogenous chemicals susceptible to the administration of CTS using high performance liquid chromatography equipped with an orbitrap hybrid Fourier transform mass spectrometer. The results obtained revealed that the systemic administration of CTS for 20 days led to the distribution of Uncalia plant-derived alkaloids such as rhynchophylline, hirsuteine, and corynoxeine in the plasma and brains of db/db and m/m mice and induced alterations in four major metabolic pathways; i.e., (1) purine, (2) tryptophan, (3) cysteine and methionine, (4) glycerophospholipids in db/db mice. Moreover, glycerophosphocholine (GPC) levels in the plasma and brain were significantly higher in CTS-treated db/db mice than in vehicle-treated control animals. The results of the in vitro experiment using organotypic hippocampal slice cultures demonstrated that GPC (10-30 μM), as well as tacrine, protected hippocampal cells from N-methyl-d-aspartate-induced excitotoxicity in a manner that was reversible with the muscarinic receptor antagonist scopolamine, whereas GPC had no effect on the activity of acetylcholinesterase in vitro. Our results demonstrated that some CTS constituents with neuropharmacological activity were distributed in the plasma and brain tissue following the systemic administration of CTS and may subsequently have affected some metabolic pathways including glycerophospholipid metabolism and cognitive function in db/db mice. Moreover, the present metabonomic analysis suggested that GPC is a putative endogenous chemical that may be involved in the tacrine-like actions of CTS in the present diabetic animal model.

Urinary metabolites of isorhynchophylline in rats and their neuroprotective activities in the HT22 cell assay

Isorhynchophylline is one of the major alkaloids from the Uncaria hook possessing the effects of lowered blood pressure, vasodilatation and protection against ischemia-induced neuronal damage. However, the metabolic pathway of isorhynchophylline has not been fully reported yet. In this paper, the metabolism of isorhynchophylline was investigated in rats. Five metabolites were isolated by using solvent extraction and repeated chromatographic methods, and identified by spectroscopic methods including UV, MS, NMR and CD experiments. Three new compounds were identified as 5-oxoisorhynchophyllic acid-22-O-β-D-glucuronide (M1), 17-O-demethyl-16,17-dihydro isorhynchophylline (M2) and 5-oxoisorhynchophyllic acid (M4) together with two known compounds isorhynchophylline (M0) and rhynchophylline (M3). Possible metabolic pathways of isorhynchophylline are proposed. Furthermore, the activity assay for all the metabolites showed that isorhynchophylline (M0) exhibited potent neuroprotective effects against glutamate-induced HT22 cell death. However, little or weak neuroprotective activities were observed for M1-M4. Our present study is important to further understand its metabolic fate and disposition in humans.