Identification of metabolites of adonifoline, a hepatotoxic pyrrolizidine alkaloid, by liquid chromatography/tandem and high-resolution mass spectrometry

In Vitro Identification of Potential Metabolites of Plinabulin (NPI 2358) in Hepatic Preparations Using Liquid Chromatography-Ion Trap Mass Spectrometry

Plinabulin (1, NPI2358), a vascular disrupting agent (VDA) molecule, is a synthetic analogue of the natural product phenylahistin (2, NPI 2350), which is isolated from Aspergillus ustus. Evaluation of the in vitro metabolic profile of VDA plinabulin using human liver microsomes (HLMs) and HepaRG Cells Cryopreserved is described. HLMs and HepaRG Cells Cryopreserved were prepared in-house and incubated with plinabulin according to published methodologies. The incubated mixtures were analyzed by liquid chromatography-ion trap mass spectrometry to identify possible metabolic products. The incubated plinabulin (1) revealed the presence of several peaks representing 19 tentative metabolites in HLMs and HepaRG Cells Cryopreserved in the presence of NADPH (nicotinamide adenine dinucleotide phosphate) and in the absence of NADPH-generating system, respectively. However, in NADPH absence, no metabolites and microsomes were generated for 1 in incubated HLMs, indicating a likely involvement of CYP450 enzymes in the metabolism. The metabolite structures, obtained from HLMs and HepaRG Cells Cryopreserved incubations, were elucidated by LC-MS/MS fragmentation study. Seventeen phase-I metabolites were proposed to be the results of isomerization, hydroxylation, hydration, and oxygenation of 1 in HLMs and two isomeric phase-II sulfate conjugate metabolites of 1 in HepaRG Cells Cryopreserved incubation.

LC-MS/MS method for determination of seneciphylline and its metabolite, seneciphylline N-oxide in rat plasma, and its application to a rat pharmacokinetic study

A rapid and sensitive ultra-performance liquid chromatography-tandem electrospray ionization mass spectrometry (UPLC-ESI/MS) method was established and validated for simultaneous determination of seneciphylline and its main metabolite in rat plasma. The plasma sample was prepared by simple methanol-mediated precipitation. Chromatographic separation was achieved within 3 min by gradient elution using acetonitrile and water containing 0.1% formic acid as mobile phase on a Waters ACQUITY BEH C18 column (100 × 2.1 mm, i.d. 1.7  μm). Quantitation was conducted in a positive multiple reaction monitoring mode. The linearity of the method was over the range of 1-1,000 ng/mL, with the lower limit of quantification of 1 ng/mL. The intra- and inter-day precision and accuracy, extraction recovery, and matrix effect of analytes were within the acceptable limit. The analytes were stable during the process of sample collection, preparation, and analysis. The validated method was further applied to a pharmacokinetic study of seneciphylline in rats after oral and intravenous administration. The results revealed that seneciphylline was quickly absorbed into plasma (T_max , 0.23-0.32 h) and reached the maximum concentration of 0.82-1.75 μg/mL after oral administration. Both seneciphylline and seneciphylline N-oxide were eliminated from plasma quickly. The low system exposure (oral bioavailability, 5.43-10.31%) was related to the extensive metabolism in the liver and microflora.

Metabolic Pattern of Hepatotoxic Pyrrolizidine Alkaloids in Liver Cells

Contamination with 1,2-unsaturated pyrrolizidine alkaloids (PAs) is a serious problem for certain phytomedicines, foods, and animal feeds. Several of these PAs are genotoxic and carcinogenic, primarily in the liver, upon cytochrome P450 (CYP)-catalyzed activation into reactive (pyrrolic and pyrrole-like) metabolites. Here we investigated the metabolism of selected PAs (echimidine, europine, lasiocarpine, lycopsamine, retrorsine, and senecionine) in rat hepatocytes in primary culture and in human CYP3A4-transfected HepG2 cells. The open-chained diesters echimidine and lasiocarpine and the cyclic diester senecionine were extensively metabolized in rat hepatocytes into a broad spectrum of products released into the medium. A large portion of unidentified, possibly irreversibly bound, products remained in the cells while detectable amounts of reactive and other metabolites were found in the incubation media. In HepG2-CYP3A4 cells, lasiocarpine was more extensively metabolized than echimidine and senecionine which also gave rise to the release of pyrrolic metabolites. In human cells, no pyrrolic metabolites were detected in retrorsine or lycopsamine incubations, while no such metabolites were detected from europine in both cell types. Other types of metabolic changes comprised modifications such as side chain demethylation or oxygenation reactions like the formation of N-oxides. The latter, considered as a detoxification step, was a major pathway with cyclic diesters, was less distinctive for echimidine and lycopsamine and almost negligible for lasiocarpine and europine. Our data are in agreement with previously published cyto- and genotoxicity findings and suggests that the metabolic pattern may contribute substantially to the specific toxic potency of a certain congener. In addition, marked differences were found for certain congeners between rat hepatocytes and transfected human HepG2 cells, whereby a high level of bioactivation was found for lasiocarpine, whereas a very low level of bioactivation was observed for monoesters, in particular in human cells.

Qualitative and quantitative analysis of pyrrolizidine alkaloids for the entire process quality control from Senecio scandens to Senecio scandens-containing preparations by high performance liquid chromatography-tandem mass spectrometry

Senecio scandens as a commonly used traditional Chinese medicine that is used alone or in combination with other herbs in preparations such as QianBai BiYan tablets has attracted much attention because of its hepatotoxic pyrrolizidine alkaloids. Nowadays, most studies for pyrrolizidine alkaloids are only performed on herbs or a preparation, however, production of preparations is a dynamic process, control of toxic impurities for raw materials, or finished products cannot monitor the production process dynamically. Thus, in this study, qualitative and quantitative analysis of pyrrolizidine alkaloids for the entire process quality control from S. scandens to its preparations was carried out with HPLC-MS/MS for the first time, which was more comprehensive and dynamic than the previous single-layer analysis. First, the species of pyrrolizidine alkaloids in S. scandens were analyzed, and the characteristic fragmentation rules of pyrrolizidine alkaloids containing common parent nucleus were found, which can be used to identify these components rapidly in the future. Then, a quantitative method for S. scandens to QianBai BiYan tablets and other nine S. scandens-containing preparations was established, and after the medication safety speculation, all of them met the relevant safety requirements. After that, in order to ensure the stability and controllable of drug quality, the limit of pyrrolizidine alkaloids in preparations was determined according to the safe dosage that is stipulated to be the same as raw materials. Finally, the factors causing the content change of pyrrolizidine alkaloids in S. scandens from different source were studies, which can provide theoretical basis for selecting suitable raw materials for production.

Screening and identification of metabolites of two kinds of main active ingredients and hepatotoxic pyrrolizidine alkaloids in rat after lavage Farfarae Flos extract by UHPLC-Q-TOF-MS mass spectrometry

Farfarae Flos, the dried flower buds of Tussilago farfara L., is usually used to treat coughs, bronchitic and asthmatic conditions as an important traditional Chinese medicine. Tussilagone and methl butyric acid tussilagin ester are seen as representatives of two kinds of active substances. In addition, the pyrrolizidine alkaloids, mainly senkirkine and senecionine, present in the herb can be hepatoxic. In this study, a rapid and sensitive ultra-high-performance liquid chromatography coupled with hybrid triple quadrupole time-of-flight mass spectrometry method was successfully applied to identify the metabolites of tussilagone, methl butyric acid tussilagin ester, senkirkine and senecionine. A total of 35, 37, 18 and nine metabolites of tussilagone, methl butyric acid tussilagin ester, senkirkine and senecionine in rats were tentatively identified. Hydrolysis, oxidation, reduction and demethylation were the major metabolic reactions for tussilagone and methl butyric acid tussilagin ester. The main biotransformation routes of senkirkine and senecionine were identified as demethylation, N-methylation, oxidation and reduction. This study is the first reported analysis and characterization of the metabolites and the proposed metabolic pathways might provide further understanding of the metabolic fate of the chemical constituents after oral administration of Farfarae Flos extract in vivo.

Diversity of pyrrolizidine alkaloids in native and invasive Senecio pterophorus (Asteraceae): implications for toxicity

Changes in plant chemical defenses after invasion could have consequences on the invaded ecosystems by modifying the interactions between plants and herbivores and facilitating invasion success. However, no comprehensive biogeographical studies have yet determined the phenotypic levels of plant chemical defenses, as consumed by local herbivores, covering large distributional areas of a species. Senecio pterophorus is a perennial shrub native to Eastern South Africa, expanded into Western South Africa and introduced into Australia and Europe. As other Asteraceae, S. pterophorus contains pyrrolizidine alkaloids (PAs) toxic to vertebrate and invertebrate herbivores. Here we analyzed S. pterophorus PAs by LC-MS/MS on foliage sampled across its entire distributional range, including the native and all non-native areas. PA concentrations and diversity was very high: we found 57 compounds belonging to 6 distinct necine base-types, including the highly toxic 1,2-unsaturated PAs (retronecine and otonecines) and the less toxic 1,2-saturated PAs (platynecine and rosmarinecines). Plants from different origins diverged in their PA absolute and relative concentrations. Rosmarinine was the most abundant compound in Australia and South Africa, but it was nearly absent in Europe. We characterized three plant chemotypes: retrorsine-senkirkine chemotype in Eastern South Africa, rosmarinine chemotype in Australia and Western South Africa, and acetylseneciphylline chemotype in Europe. PA absolute concentrations were highest in Australia. The increased absolute and relative concentrations of retronecine PAs from Australia and Europe, respectively, indicate that S. pterophorus is potentially more toxic in the invasive range than in the native range.

Involvement of intracellular glutathione in regulating isoline-induced cytotoxicity in human normal liver L-02 cells

Pyrrolizidine alkaloid isoline is isolated from the traditional Chinese medicine Ligularia duciformis. Our previous reports have already demonstrated isoline-induced liver injury in mice. The present study is designed to observe the involvement of intracellular reduced glutathione (GSH) in isoline-induced cytotoxicity in human normal liver L-02 cells. The results showed that isoline decreased the cellular GSH and the ratio of GSH and oxidized glutathione in a time- and concentration-dependent manner in L-02 cells. l-Buthionine-S-R-sulfoximine (BSO) is reported to inhibit cellular GSH biosynthesis, and further results showed that isoline decreased the cell viability in L-02 cells after pretreated with 25 μM BSO for 24 h. Furthermore, adducts of isoline and GSH were identified in L-02 cells using liquid chromatography/electrospray ionization tandem mass spectrometry (ion trap) for the first time. In conclusion, our study provides the strongest evidence to support the important roles of GSH in regulating isoline-induced cytotoxicity in human normal liver L-02 cells.

Characteristic ion clusters as determinants for the identification of pyrrolizidine alkaloid N-oxides in pyrrolizidine alkaloid-containing natural products using HPLC-MS analysis

Pyrrolizidine alkaloid (PA)-containing plants are widely distributed in the world. PAs are hepatotoxic, affecting livestock and humans. PA N-oxides are often present together with PAs in plants and also exhibit hepatotoxicity but with less potency. HPLC-MS is generally used to analyze PA-containing herbs, although PA references are unavailable in most cases. However, to date, without reference standards, HPLC-MS methodology cannot distinguish PA N-oxides from PAs because they both produce the same characteristic ions in mass spectra. In the present study, the mass spectra of 10 PA N-oxides and the corresponding PAs were systemically investigated using HPLC-MS to define the characteristic mass fragment ions specific to PAs and PA N-oxides. Mass spectra of toxic retronecine-type PA N-oxides exhibited two characteristic ion clusters at m/z 118-120 and 136-138. These ion clusters were produced by three unique fragmentation pathways of PA N-oxides and were not found in their corresponding PAs. Similarly, the nontoxic platynecine-type PA N-oxides also fragmented via three similar pathways to form two characteristic ion clusters at m/z 120-122 and 138-140. Further application of using these characteristic ion clusters allowed successful and rapid identification of PAs and PA N-oxides in two PA-containing herbal plants. Our results demonstrated, for the first time, that these characteristic ion clusters are unique determinants to discriminate PA N-oxides from PAs even without the availability of reference samples. Our findings provide a novel and specific method to differentiate PA N-oxides from PAs in PA-containing natural products, which is crucial for the assessment of their intoxication.

Carry-over of pyrrolizidine alkaloids from feed to milk in dairy cows

Pyrrolizidine alkaloids are toxins present in many plants belonging to the families of Asteraceae, Boraginaceae and Fabaceae. Particularly notorious are pyrrolizidine alkaloids present in ragwort species (Senecio), which are held responsible for hepatic disease in horses and cows and may lead to the death of the affected animals. In addition, these compounds may be transferred to edible products of animal origin and as such be a threat for the health of consumers. To investigate the possible transfer of pyrrolizidine alkaloids from contaminated feed to milk, cows were put on a ration for 3 weeks with increasing amounts (50-200 g day(-1)) of dried ragwort. Milk was collected and sampled twice a day; faeces and urine twice a week. For milk, a dose-related appearance of pyrrolizidine alkaloids was found. Jacoline was the major component in milk despite being a minor component in the ragwort material. Practically no N-oxides were observed in milk, notwithstanding the fact that they constituted over 80% of the pyrrolizidine alkaloids in ragwort. The overall carry-over of the pyrrolizidine alkaloids was estimated to be only around 0.1%, but for jacoline 4%. Notwithstanding the low overall carry-over, this may be relevant for consumer health considering the genotoxic and carcinogenic properties demonstrated for some of these compounds. Analysis of the faeces and urine samples indicated that substantial metabolism of pyrrolizidine alkaloids is taking place. The toxicity and potential transfer of metabolites to milk is unknown and remains to be investigated.

Analysis of the volatile compounds in Senecio scandens Buch-Ham by gas chromatography-tandem mass spectrometry based on diversified scan technologies

Static headspace gas chromatography-tandem mass spectrometry was used to identify volatile compounds from Senecio scandens Buch-Ham. The elemental composition of compounds was confirmed by exploiting the tandem mass spectra of isotopic peaks from the precursor ion. Some isomers were well distinguished by the diversified scan technologies of tandem mass spectrometry (MS/MS). The MS/MS included a product ion scan, a precursor ion scan and a neutral loss scan. The results showed that 46 volatile compounds were completely identified, and the great of majority compounds were α-pinene (11.93%), n-caproaldehyde (9.02%) and dehydrosabinene (6.22%). This qualitative method is convenient and accurate and can be considered as a complementary identification method for the qualitative analysis of volatile compounds in complex samples.

Characterization of nuciferine metabolism by P450 enzymes and uridine diphosphate glucuronosyltransferases in liver microsomes from humans and animals

AIM

to characterize the metabolism of nuciferine by P450 enzymes and uridine diphosphate glucuronosyltransferase (UGT) in liver microsomes from humans and several other animals including rats, mice, dogs, rabbits and monkeys.

METHODS

nuciferine was incubated with both human and animal liver microsomal fractions containing P450 or UGT reaction components. Ultra performance liquid chromatography coupled with mass spectrometry was used to separate and identify nuciferine metabolites. Chemical inhibition was used to identify the involved isozymes. Species difference of nuciferine metabolism in human and various animals were investigated in the liver microsomal incubation system.

RESULTS

among the nuciferine metabolites detected and identified, seven were catalyzed by P450 and one by UGT. Ketoconazole inhibited the formation of M292, M294 and M312. Furafylline, 8-methoxypsoralen and quercetin inhibited the formation of M282. Hecogenin showed a significant inhibitory effect on nuciferine glucuronidation. While the P450-catalyzed metabolites showed no species differences, the glucuronidation product was only detected in microsomes from humans and rabbits.

CONCLUSION

the isozymes UGT 1A4, CYP 3A4, 1A2, 2A6 and 2C8 participated in the hepatic metabolism of nuciferine. Based on the observed species-specific hepatic metabolism of nuciferine, rats, mice, dogs and even monkeys are not suitable models for the pharmacokinetics of nuciferine in humans.