Quantification of the Pyrrolizidine Alkaloid Jacobine in Crassocephalum crepidioides by Cation Exchange High-Performance Liquid Chromatography

Chromatographic Methods for Detection and Quantification of Pyrrolizidine Alkaloids in Flora, Herbal Medicines, and Food: An Overview

Pyrrolizidine alkaloids (PAs) are natural toxins produced by some plants that gained special interest due to their potential hazardous effects in humans and animals. These substances have been found in wild flora, herbal medicines and food products raising health concerns. Recently, maximum concentration levels of PAs were established for some food products; however, maximum daily intake frequently surpasses the upper limit set by the competent authorities posing a health risk. Given the scarcity or absence of occurrence data on PAs in many products, there is an urgent need to measure their levels and establish safety intake levels. Analytical methods have been reported to detect and quantify PAs in different matrices. The commonly used chromatographic methodologies provides accurate and reliable results. Analytical methods include diverse steps as extraction and sample preparation procedures that are critical for sensitivity and selectivity of the analytical method. Great efforts have been directed toward optimization of extraction procedures, clean up and chromatographic conditions to improve recovery, reduce matrix effects, and achieve low limits of detection and quantification. Therefore, this paper aims to give a general overview about the occurrence of PAs in flora, herbal medicines, and foodstuff; and discuss the different chromatographic methodologies used for PAs analysis, namely extraction and sample preparation procedures and chromatographic conditions.

Species-Specific Variation in Abscisic Acid Homeostasis and Responses Impacts Important Traits in Crassocephalum Orphan Crops

Crassocephalum rubens and Crassocephalum crepidioides are plant species native to Africa, but grow in most tropical and subtropical regions of the world. They are rich in vitamins, minerals, and essential oils and are traditional leafy vegetables and medicinal plants in Sub-Saharan Africa. The plants are still mainly collected from the wild but shall be taken into cultivation and an important aim in the domestication of these species is to improve traits that are relevant for crop production. Here, seed formation and germination capacities in C. crepidioides and C. rubens were investigated, and it was found that C. crepidioides exhibits a higher level of seed dormancy, which could be broken with light, and was correlated with higher amounts of abscisic acid (ABA), a plant hormone that promotes seed dormancy. ABA is also very well-known for its role in abiotic stress tolerance, and it is shown that tetraploid C. crepidioides exhibits a higher level of resistance against drought and heat stress than diploid C. rubens, traits that will benefit the cultivation of these plants, particularly in rain-fed cropping systems. The potential of Crassocephalum to improve nutrition and increase the resilience of marginal cropping systems in Africa is discussed.

The Orphan Crop Crassocephalum crepidioides Accumulates the Pyrrolizidine Alkaloid Jacobine in Response to Nitrogen Starvation

Crassocephalum crepidioides is an African orphan crop that is used as a leafy vegetable and medicinal plant. Although it is of high regional importance in Sub-Saharan Africa, the plant is still mainly collected from the wild and therefore efforts are made to promote its domestication. However, in addition to beneficial properties, there was first evidence that C. crepidioides can accumulate the highly toxic pyrrolizidine alkaloid (PA) jacobine and here it was investigated, how jacobine production is controlled. Using ecotypes from Africa and Asia that were characterized in terms of their PA profiles, it is shown that the tetraploid C. crepidioides forms jacobine, an ability that its diploid close relative Crassocephalum rubens appears to lack. Evidence is provided that nitrogen (N) deficiency strongly increases jacobine in the leaves of C. crepidioides, that this capacity depends more strongly on the shoot than the root system, and that homospermidine synthase (HSS) activity is not rate-limiting for this reaction. A characterization of HSS gene representation and transcription showed that C. crepidioides and C. rubens possess two functional versions, one of which is conserved, that the HSS transcript is mainly present in roots and that its abundance is not controlled by N deficiency. In summary, this work improves our understanding of how environmental cues impact PA biosynthesis in plants and provides a basis for the development of PA-free C. crepidioides cultivars, which will aid its domestication and safe use.

Phytobiological-facilitated Production of Silver Nanoparticles From Selected Non-cultivated Vegetables in Nigeria and Their Biological Potential

Objectives

Plant-mediated synthesis [silver (Ag) to form Ag nanoparticles (AgNPs)] is becoming progressively well accepted in many scientific and pharmaceutical fields. The aim of this study was to synthesize AgNPs using air-dried leaves of four neglected vegetables, i.e. Ceratotheca sesamoides, Ceiba pentandra, Crassocephalum crepidioides, and Launaea taraxacifolia.

Materials and Methods

Ultraviolet-visible (UV-Vis) spectroscopy, fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) were used for characterization. Cell stabilization membrane and lipoxidase assays were used to determine used to assess the antiinflammatory activities while 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS+) assays were used to assess the antioxidant activities of AgNPs [L. taraxacifolia-AgNPs, C. sesamoides Ag nanoparticles (CS-AgNPs), C. pentandra Ag nanoparticles (CP-AgNPs), and C. crepidioides AgNPs (CC-AgNPs)].

Results

The UV-Vis spectra of the synthesized NPs displayed absorption bands at around 360-440 nm, which is a characteristic band for AgNPs. The SEM image showed that the AgNPs formed were spherical in morphology. CC-AgNPs exhibited the most significant inhibitory activity against human red blood cell membrane stabilizasyonu [median inhibitory concentration (IC₅₀): 32.2 μg/mL] while CS-AgNPs displayed the most significant inhibitory activity against lipoxygenases (IC₅₀: 32.8 μg/mL). CP-AgNPs exhibited the most significant antioxidant effect against both ABTS and DPPH (IC₅₀: 5.5 and 6.4 μg/mL) when compared to ascorbic acid (IC₅₀: 4.7 μg/mL).

Conclusion

The synthesized AgNPs were found to be stable and the FTIR evidence suggested that the phytochemicals in the vegetables might have played an important role in the reduction and stabilization of AgNPs. This work showed that the synthesized AgNPs from non-cultivated vegetables can find relevance and application in health, drugs, food and environmental science. The evidences herein further confirmed their ethnopharmacological applications.

Liquid chromatographic separation of alkaloids in herbal medicines: Current status and perspectives

Alkaloids are a widespread group of basic compounds in herbal medicines and have attracted great interest due to various pharmaceutical activities and desirable druggability. Their distinctive structures make chromatographic separation fairly difficult. Peak tailing, poor resolution, and inferior column-to-column reproducibility are common obstacles to overcome. In order to provide a valuable reference, the methodologies and/or strategies on liquid chromatographic separation of alkaloids in herbal medicines proposed from 2012 to 2019 are thoroughly summarized.

Medicinal and edible plants used by the Lhoba people in Medog County, Tibet, China

ETHNOPHARMACOLOGICAL RELEVANCE

The Lhoba people are a small, ancient, tribal ethnic group from the Himalayas and are located in the Tibet Autonomous Region of China. Medog County is rich in biocultural diversity. For a long time, Medog has been almost isolated from the outside world. The Lhoba people, who live in Medog, have maintained a relatively unique lifestyle and have accumulated rich traditional knowledge (TK), especially about medicinal and edible plants. Currently, there is very little documentation of the plants traditionally used by the local Lhoba communities.

AIM OF THE STUDY

Our investigation aimed to (i) document the species of medicinal and food plants used by the Lhoba people in Medog County, Tibet, China; (ii) screen the most important plant taxa for specific medicines, and identify the aliments treated to further contribute to drug and food supplement research; and (iii) examine whether the ethnobotanical knowledge of the Lhoba is similar among different tribes and discuss traditional uses in the health practices and livelihoods of the local communities.

METHODS

Ethnobotanical data were recorded through semi-structured interviews, guided field trips, and quantitative analysis. The informant consensus factor (FIC) was used as a quantitative index.

RESULTS

Ninety-one informants (61 men and 30 women) were interviewed. A total of 75 species, including 37 medicinal plants for 14 categories of diseases and 57 edible plants from six types of food, were recorded. Among the usage types of medicinal plants, the highest FIC values were recorded for antidotes (FIC = 0.98), anthelmintics (FIC = 0.98), and treatments of gastrointestinal problems (FIC = 0.93). The FIC values for different types of edible plants were very similar. The most frequently used medicinal and food plants in the studied communities are Zanthoxylum motuoense, Crassocephalum crepidioides, and Swertia nervosa. According to the comparative study, few differences in the use of wild plants were found. There appeared to be more overlapping species between two Lhoba tribes in Medog, named Mixingba and Miguba, with 46 (61%) common species, compared with the Bo'gaer tribe in Milin, which had only two (2.7%) overlapping species. This might be due to the different geographical environments, vegetation types, and different influences of other ethnic cultures.

CONCLUSIONS

The Lhoba people in Medog County, Tibet, China, have rich TK about the uses of wild plants. However, the TK is seriously threatened due to environmental degradation and acculturation, and it showed signs of being forgotten and abandoned by the younger generation. Therefore, measures are urgently needed to document and protect the TK of the uses of the wild plant resources; and (i) the most frequently used medicinal and/or edible plants; (ii) the plants used to treat the most commonly mentioned diseases; and (iii) the endemic species that are widely used in Medog, which should be assessed for their potential future as food supplements and therapeutic products.

Determination of Selected Pyrrolizidine Alkaloids in Honey by Dispersive Liquid-Liquid Microextraction and Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry

The contamination of honey with hepatotoxic pyrrolizidine alkaloids (PAs) is an actual concern for food safety. This study reports the first application of dispersive liquid-liquid microextraction (DLLME) in the determination of five relevant PAs, and the relative N-oxide derivatives (PANOs), in honey. The effects of different experimental parameters (pH, ionic strength, type and volume of DLLME solvents) affecting the extraction efficiency were carefully investigated and optimized. PAs were extracted from honey (diluted solution 10% w/v at pH 9.5) by injecting a mixture of chloroform and isopropyl alcohol. A reduction step (zinc powder in acidic aqueous solution) before DLLME was performed to convert PANOs in PAs and to obtain the total PA levels. Both sample preparation protocols (DLLME and Zn-DLLME) showed negligible matrix effects on PA signal intensity in honeys of different botanical origins. The overall recoveries of DLLME and Zn-DLLME ranged from 71 to 102% and from 63 to 103%, respectively, with a good precision (standard deviations in the range from 1 to 12%). The attained method quantification limits stayed between 0.03 and 0.06 μg kg^-1, and the linear response range extended to 25 μg kg^-1. Additionally, the proposed method provides results comparable to those of the SPE protocol in the analysis of real samples. An analysis of retail honeys revealed PA residues in all analyzed samples, with a maximum level of 17.5 μg kg^-1 (total PAs). Globally, the proposed method provides a sensitive and accurate determination of analytes and offers numerous advantages, such as simplicity, low cost, and a high sample throughput, which make it suitable for screening and quality control programs in food chain and occurrence studies.

Determination of the [15N]-Nitrate/[14N]-Nitrate Ratio in Plant Feeding Studies by GC⁻MS

Feeding experiments with stable isotopes are helpful tools for investigation of metabolic fluxes and biochemical pathways. For assessing nitrogen metabolism, the heavier nitrogen isotope, [¹⁵N], has been frequently used. In plants, it is usually applied in form of [¹⁵N]-nitrate, which is assimilated mainly in leaves. Thus, methods for quantification of the [¹⁵N]-nitrate/[¹⁴N]-nitrate ratio in leaves are useful for the planning and evaluation of feeding and pulse–chase experiments. Here we describe a simple and sensitive method for determining the [¹⁵N]-nitrate to [¹⁴N]-nitrate ratio in leaves. Leaf discs (8 mm diameter, approximately 10 mg fresh weight) were sufficient for analysis, allowing a single leaf to be sampled multiple times. Nitrate was extracted with hot water and derivatized with mesitylene in the presence of sulfuric acid to nitromesitylene. The derivatization product was analyzed by gas chromatography–mass spectrometry with electron ionization. Separation of the derivatized samples required only 6 min. The method shows excellent repeatability with intraday and interday standard deviations of less than 0.9 mol%. Using the method, we show that [¹⁵N]-nitrate declines in leaves of hydroponically grown Crassocephalum crepidioides, an African orphan crop, with a biological half-life of 4.5 days after transfer to medium containing [¹⁴N]-nitrate as the sole nitrogen source.

Pyrrolizidine Alkaloids: Biosynthesis, Biological Activities and Occurrence in Crop Plants

Pyrrolizidine alkaloids (PAs) are heterocyclic secondary metabolites with a typical pyrrolizidine motif predominantly produced by plants as defense chemicals against herbivores. They display a wide structural diversity and occur in a vast number of species with novel structures and occurrences continuously being discovered. These alkaloids exhibit strong hepatotoxic, genotoxic, cytotoxic, tumorigenic, and neurotoxic activities, and thereby pose a serious threat to the health of humans since they are known contaminants of foods including grain, milk, honey, and eggs, as well as plant derived pharmaceuticals and food supplements. Livestock and fodder can be affected due to PA-containing plants on pastures and fields. Despite their importance as toxic contaminants of agricultural products, there is limited knowledge about their biosynthesis. While the intermediates were well defined by feeding experiments, only one enzyme involved in PA biosynthesis has been characterized so far, the homospermidine synthase catalyzing the first committed step in PA biosynthesis. This review gives an overview about structural diversity of PAs, biosynthetic pathways of necine base, and necic acid formation and how PA accumulation is regulated. Furthermore, we discuss their role in plant ecology and their modes of toxicity towards humans and animals. Finally, several examples of PA-producing crop plants are discussed.

Pyrrolizidine alkaloids quantified in soil and water using UPLC-MS/MS

Pyrrolizidine alkaloids (PAs) are produced in plants as defence compounds against insects. PAs present a serious health risk to humans and livestock; therefore it is necessary to have a validated analytical method to monitor PAs in the environment. The objective of this work is to present an UPLC-MS/MS method for quantification of PAs in environmental samples of both soil and water. A fast, reliable, and sensitive approach is developed to identify and quantify PAs in soil and water. Sample preparation was performed by clean-up and pre-concentration of the samples using MCX solid phase extraction cartridges with full optimization, and then PAs were determined by UPLC coupled with TQ-MS. In the liquid chromatography, most of the parameters were optimized and tested including gradient time, solvents, additives, and pH of the mobile phases and flow rate. In addition, the MS parameters of cone voltage, desolvation temperature, cone flows, and collision energy were optimized. The instrument limit of detection (2–7 μg L⁻¹) and limit of quantification (5–9 μg L⁻¹) were determined experimentally, and the method was linearity validated up to 1000 μg L⁻¹. The method was applied to analyse soil and surface water samples collected in April and May 2018 in Vejle, Borup, and Holte, Denmark. In total, 15 PAs were quantified and reported for the first time in environmental samples, in a range of 3–1349 μg kg⁻¹ in soil and 4–270 μg L⁻¹ in surface water.

Pyrrolizidine alkaloids quantified in soil and water.