Abstract
Pyrrolizidine alkaloids (PAs) are considered as the major constituents that cause hepatoxicity in Senecio plants. PAs can be found in about 3%–5% of the world's flowering plants. Nowadays, the identification method of PAs by separation and preparation was too slow and lacked effective power. A rapid method to identify PAs in plants must be developed. Based on the fragmentation regularity, the hepatoxic PAs and nonhepatoxic PAs were characterized by liquid chromatography-mass spectrometry (LC-MS). The detailed structures of PAs in five Senecio plants were identified based on tandem mass spectrometry (MS/MS) spectrum and chemical research information. In the present study, some new fragmentation regularities of PAs have been found, such as product ions at m/z 122, m/z 140 and m/z 124, m/z 142, which have been discovered as the characteristic fragments of lactone and mono-esterase type of saturated PAs, respectively. Moreover, two product ions at m/z 120 and m/z 138 have been reported as the characteristic fragments of unsaturated PAs. Some of them were found in Senecio species for the first time, and some of them may be new nature product or even new compound. Finally, we classified these plants into five categories based on PAs which were identified in the present study; the result corresponded with the classification by morphology. In addition, we have found some constituents that have odd molecular weight number only in Senecio species but not in Ligularia species; the detailed structures of these non-PAs constituents need penetrating study. LC-MS was rapid and sensitive method for detecting and identifying PAs in plants. Pyrrolizidine alkaloids were the toxiferous constituent of Senecio plants. In this study, we found that PAs can be used as the characteristic constituent of Senecio species.
Highlights
In Traditional Chinese Medicine, Senecio plants were applied for thousands of years
Methods for analyzing PAs have been developed in this field for many years including thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and LC-MS
We have identified the detailed structure of PAs in five Senecio plants that belong to Compositae by LC-MS technology combined with the chemical research information of these five plants, which can be differentiated from each other based on the PAs constituents in the present study
Summary
In Traditional Chinese Medicine, Senecio plants were applied for thousands of years. In the world, about 3%–5% of all flowering plants contain PAs, which are one of the most toxic constituents in plants and cause hepatotoxicity mainly with the major clinical symptom of veno-occlusive disease (VOD) and other toxicities such as neurotoxicity, genotoxicity, et al [1]. The mechanism of the toxicity of PAs is considered as metabolic activation; first, PAs was metabolized by P450 enzymes to generate dehydropyrrolizidine (DHP), DHP with strong electrophilicity attacks proteins or DNA molecules to generate adducts, and various signs of toxicity are induced [2]. This kind of compounds come from the esterification of carboxylic acid named necic acid and double pyrrole ring named necine and have been classified into two types named retronecine and otonecine, and 1,2-double bond is the key structure that causes toxicity (Figure 1).
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