Pyrrolizidine alkaloids in food: a spectrum of potential health consequences

Regulatory role of oxidative stress in retrorsine - Induced apoptosis and autophagy in primary rat hepatocytes

Pyrrolizidine alkaloids (PAs) are a group of naturally occurring alkaloids widely present in plants. PAs are highly hepatotoxic and have been documented to cause many incidents of human and animal poisoning. Retrorsine (RTS) is a pyrrolizidine alkaloid (PA) derived from the Compositae Senecio, which has been shown to cause hepatotoxicity. Human liver poisoning occurs through the consumption of RTS-contaminated food, and animals can also be poisoned by ingesting RTS-containing toxic plants. The mechanism of RTS-induced liver toxicity is not fully understood. In this study, we demonstrated that RTS-induced oxidative stress plays a pivotal role in RTS-induced liver toxicity involving apoptosis and autophagy. The results showed that RTS treatment in the cultured Primary rat hepatocytes caused cytotoxicity and release of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in a time- and dose-dependent manner. Our study showed that treatment of RTS induced ROS and MDA (malondialdehyde, a lipid peroxidation marker) in the hepatocytes, and reduced antioxidant capacity (GSH content, SOD activity), suggesting RTS treatment caused oxidative stress response in the hepatocytes. Furthermore, we found that RTS induced apoptosis and autophagy in the hepatocytes, and RTS-induced apoptosis and autophagy could be alleviated by ROS scavenger N-acetylcysteine (NAC) and the MAPK pathway inhibitors suggesting ROS/MAPK signaling pathway plays a role in RTS induced apoptosis and autophagy. Collectively, this study reveals the regulatory mechanism of oxidative stress in RTS-induced apoptosis and autophagy in the hepatocytes, providing important insights of molecular mechanisms of hepatotoxicity induced by RTS and related pyrrolizidine alkaloids in liver. This mechanism provides a basis for the prevention and treatment of PA poisoning in humans and animals.

Effects of dietary exposure to plant toxins on bioaccumulation, survival, and growth of black soldier fly (Hermetia illucens) larvae and lesser mealworm (Alphitobius diaperinus)

In their natural habitat, insects may bioaccumulate toxins from plants for defence against predators. When insects are accidently raised on feed that is contaminated with toxins from co-harvested herbs, this may pose a health risk when used for human or animal consumption. Plant toxins of particular relevance are the pyrrolizidine alkaloids (PAs), which are genotoxic carcinogens produced by a wide variety of plant species and the tropane alkaloids (TAs) which are produced by a number of Solanaceae species. This study aimed to investigate the transfer of these plant toxins from substrates to black soldier fly larvae (BSFL) and lesser mealworm (LMW). PAs and the TAs atropine and scopolamine were added to insect substrate simulating the presence of different PA- or TA-containing herbs, and BSFL and LMW were grown on these substrates. Bioaccumulation from substrate to insects varied widely among the different plant toxins. Highest bioaccumulation was observed for the PAs europine, rinderine and echinatine. For most PAs and for atropine and scopolamine, bioaccumulation was very low. In the substrate, PA N-oxides were quickly converted to the corresponding tertiary amines. More research is needed to verify the findings of this study at larger scale, and to determine the potential role of the insect and/or substrate microbiome in metabolizing these toxins.

Diagnosis, toxicological mechanism, and detoxification for hepatotoxicity induced by pyrrolizidine alkaloids from herbal medicines or other plants

Pyrrolizidine alkaloids (PAs) are one type of phytotoxins distributed in various plants, including many medicinal herbs. Many organs might suffer injuries from the intake of PAs, and the liver is the most susceptible one. The diagnosis, toxicological mechanism, and detoxification of PAs-induced hepatotoxicity have been studied for several decades, which is of great significance for its prevention, diagnosis, and therapy. When the liver was exposed to PAs, liver sinusoidal endothelial cells (LSECs) loss, hemorrhage, liver parenchymal cells death, nodular regeneration, Kupffer cells activation, and fibrogenesis occurred. These pathological changes classified the PAs-induced liver injury as acute, sub-acute, and chronic type. PAs metabolic activation, mitochondria injury, glutathione (GSH) depletion, inflammation, and LSECs damage-induced activation of the coagulation system were well recognized to play critical roles in the pathological process of PAs-induced hepatotoxicity. A lot of natural compounds like glycyrrhizic acid, (-)-epicatechin, quercetin, baicalein, chlorogenic acid, and so on were demonstrated to be effective in alleviating PAs-induced liver injury, which rendered them huge potential to be developed into therapeutic drugs for PAs poisoning in clinics. This review presents updated information about the diagnosis, toxicological mechanism, and detoxification studies on PAs-induced hepatotoxicity.

Bitter yet beneficial: The dual role of dietary alkaloids in managing diabetes and enhancing cognitive function

With the rising prevalence of diabetes and its association with cognitive impairment, interest in the use of dietary alkaloids and other natural products has grown significantly. Understanding how these compounds manage diabetic cognitive dysfunction (DCD) is crucial. This comprehensive review explores the etiology of DCD and the effects of alkaloids in foods and dietary supplements that have been investigated as DCD therapies. Data on how dietary alkaloids like berberine, trigonelline, caffeine, capsaicin, 1-deoxynojirimycin, nuciferine, neferine, aegeline, tetramethylpyrazine, piperine, and others regulate cognition in diabetic disorders were collected from PubMed, Research Gate, Web of Science, Science Direct, and other relevant databases. Dietary alkaloids could improve memory in behavioral models and modulate the mechanisms underlying the cognitive benefits of these compounds, including their effects on glucose metabolism, gut microbiota, vasculopathy, neuroinflammation, and oxidative stress. Evidence suggests that dietary alkaloids hold promise for improving cognition in diabetic patients and could open exciting avenues for future research in diabetes management.

Pyrrolizidine Alkaloids in Food on the Italian Market

Pyrrolizidine alkaloids (PAs) are secondary metabolites produced by over 6000 plant species worldwide. PAs enter the food chain through accidental co-harvesting of PA-containing weeds and through soil transfer from the living plant to surrounding acceptor plants. In animal studies, 1,2-unsaturated PAs have proven to be genotoxic carcinogens. According to the scientific opinion expressed by the 2017 EFSA, the foods with the highest levels of PA contamination were honey, tea, herbal infusions, and food supplements. Following the EFSA's recommendations, data on the presence of PAs in relevant food were monitored and collected. On 1 July 2022, the Commission Regulation (EU) 2020/2040 came into force, repealed by Commission Regulation (EU) 2023/915, setting maximum levels for the sum of pyrrolizidine alkaloids in certain food. A total of 602 food samples were collected from the Italian market between 2019 and 2022 and were classified as honey, pollen, dried tea, dried herbal infusions, dried herbs, and fresh borage leaves. The food samples were analyzed for their PA content via an in-house LC-MS/MS method that can detect PAs according to Regulation 2023/915. Overall, 42% of the analyzed samples were PA-contaminated, 14% exceeded the EU limits, and the items most frequently contaminated included dried herbs and tea. In conclusion, the number of food items containing considerable amounts of PAs may cause concern because they may contribute to human exposure, especially considering vulnerable populations-most importantly, children and pregnant women.

Pyrrolizidine Alkaloids from Monofloral and Multifloral Italian Honey

Pyrrolizidine alkaloids (PAs) are secondary metabolites produced by plants as a self-defense against insects. After bioactivation in the liver, some PAs can cause acute or chronic toxicity in humans. The aim of this study was to determine the presence of PAs in 121 samples of monofloral and multifloral honey from three different Italian regions (Friuli-Venezia Giulia, Marche and Calabria) to meet the European Food Safety Authority (EFSA) suggestion. An in-house liquid chromatography with tandem mass spectrometry (LC-MS/MS) method was validated according to European Union Reference Laboratory (EURL) performance criteria. This method allowed the detection and quantification of 35 PAs. Of the 121 honey samples, 38 (31%), mostly from Calabria, contained PAs. The total content of the PAs ranged from 0.9 µg/kg to 33.1 µg/kg. In particular, echimidine was the most prevalent PA. A rapid human exposure assessment to PAs in honey and a risk characterization was performed using the EFSA RACE tool. The assessment highlighted a potential health concern only for toddlers who frequently consume elevated quantities of honey. This study showed a low presence of PAs in Italian honey; however, the importance of continuously monitoring these compounds is stressed, along with the suggestion that the relevant authorities establish maximum limits to guarantee support for producers and consumer safety.

Monocrotaline induces acutely cerebrovascular lesions, astrogliosis and neuronal degeneration associated with behavior changes in rats: A model of vascular damage in perspective

Pyrrolizidine alkaloids (PAs) are secondary plant metabolites playing an important role as phytotoxins in the plant defense mechanisms and can be present as contaminant in the food of humans and animals. The PA monocrotaline (MCT), one of the major plant derived toxin that affect humans and animals, is present in a high concentration in Crotalaria spp. (Leguminosae) seeds and can induce toxicity after consumption, characterized mainly by hepatotoxicity and pneumotoxicity. However, the effects of the ingestion of MCT in the central nervous system (CNS) are still poorly elucidated. Here we investigated the effects of MCT oral acute administration on the behavior and CNS toxicity in rats. Male adult Wistar were treated with MCT (109 mg/Kg, oral gavage) and three days later the Elevated Pluz Maze test demonstrated that MCT induced an anxiolytic-like effect, without changes in novelty habituation and in operational and spatial memory profiles. Histopathology revealed that the brain of MCT-intoxicated animals presented hyperemic vascular structures in the hippocampus, parahippocampal cortex and neocortex, mild perivascular edema in the neocortex, hemorrhagic focal area in the brain stem, hemorrhage and edema in the thalamus. MCT also induced neurotoxicity in the cortex and hippocampus, as revealed by Fluoro Jade-B and Cresyl Violet staining, as well astrocyte reactivity, revealed by immunocytochemistry for glial fibrillary acidic protein. Additionally, it was demonstrated by RT-qPCR that MCT induced up-regulation on mRNA expression of neuroinflammatory mediator, especially IL1β and CCL2 in the hippocampus and cortex, and down-regulation on mRNA expression of neurotrophins HGDF and BDNF in the cortex. Together, these results demonstrate that the ingestion of MCT induces cerebrovascular lesions and toxicity to neurons that are associated to astroglial cell response and neuroinflammation in the cortex and hippocampus of rats, highlighting CNS damages after acute intoxication, also putting in perspective it uses as a model for cerebrovascular damage.

Combined Hepatotoxicity and Toxicity Mechanism of Intermedine and Lycopsamine

Pyrrolizidine alkaloids (PAs) are common constituents of plants and have serious hepatotoxicity. Intermedine (Im) and lycopsamine (La) are two monoesters of PAs that frequently coexist in the PA-containing plants (e.g., comfrey and tea). The present study aimed to explore the combined hepatotoxicity and toxicity mechanism of the Im and La mixture. In vitro, the combined cytotoxicity of the Im and La mixture on human hepatocytes (HepD) was examined by CCK-8, colony formation, wound healing, and Annexin V/PI staining assays. The combination of Im and La inhibited the ability of HepD cells to proliferate, colonize, and migrate and induced hepatocytes apoptosis in a dose-dependent manner. In addition to significantly causing a burst of intracellular reactive oxygen species (ROS), mitochondrial apoptosis, and endoplasmic reticulum (ER) stress, the Im and La mixture can also cause an increase in intracellular Ca2+, triggering the PERK/eIF2α/ATF4/CHOP apoptosis pathway. This study provided the first direct evidence that the combined PAs induced hepatotoxicity through ER-mediated apoptosis. These results supplemented the basic toxicity data for the combined PAs and provided a new perspective for the risk assessment of combined PA toxicity.

Ortholog genes from cactophilic Drosophila provide insight into human adaptation to hallucinogenic cacti

Cultural transformations of lifestyles and dietary practices have been key drivers of human evolution. However, while most of the evidence of genomic adaptations is related to the hunter-gatherer transition to agricultural societies, little is known on the influence of other major cultural manifestations. Shamanism is considered the oldest religion that predominated throughout most of human prehistory and still prevails in many indigenous populations. Several lines of evidence from ethno-archeological studies have demonstrated the continuity and importance of psychoactive plants in South American cultures. However, despite the well-known importance of secondary metabolites in human health, little is known about its role in the evolution of ethnic differences. Herein, we identified candidate genes of adaptation to hallucinogenic cactus in Native Andean populations with a long history of shamanic practices. We used genome-wide expression data from the cactophilic fly Drosophila buzzatii exposed to a hallucinogenic columnar cactus, also consumed by humans, to identify ortholog genes exhibiting adaptive footprints of alkaloid tolerance. Genomic analyses in human populations revealed a suite of ortholog genes evolving under recent positive selection in indigenous populations of the Central Andes. Our results provide evidence of selection in genetic variants related to alkaloids toxicity, xenobiotic metabolism, and neuronal plasticity in Aymara and Quechua populations, suggesting a possible process of gene-culture coevolution driven by religious practices.

Sorting out the plants responsible for a contamination with pyrrolizidine alkaloids in spice seeds by means of LC-MS/MS and DNA barcoding: Proof of principle with cumin and anise spice seeds

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Identification of contaminating plants in seed spice with DNA barcoding.

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The obtained data concurs the previously obtained results with DNA metabarcoding.

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Heliotropium sp. is the predominant source of phytotoxic PA/PANOs in those samples.

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The presence of only 2 Heliotropium seeds/jar can render a sample non-compliant.

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The benefit combining chemical and molecular approach to check for phytotoxins.

High value commodities such as spices suffer from occasional contaminations of both chemical and biological origin. Consequently, quality control and safety monitoring has become a pressing issue for the spice industry. Two recent independent studies showed that at least one third of the analyzed cumin and green anise spice seeds samples surpassed the by the European Union recently established threshold value for toxic pyrrolizidine alkaloids (PAs) and their corresponding N-oxides (PANOs). These heterocyclic secondary plant metabolites are produced by a large number of different plant families. In those spice seeds, it was found by means of DNA metabarcoding, that predominant contamination was due to the presence of herbal material from the Heliotropium genus (Boraginaceae). Unfortunately, the use of this specific type of DNA-based identification remains controversial for the majority of the official instances and preference is still given to the use of more tangible classical approaches, including microscopy and chemical analysis. However, these methodologies often suffer from inherent drawbacks. Here we demonstrate that at least for spice seeds, a combinatory approach of microscopy, chemical analysis and classical DNA barcoding of the isolated contaminants using the matK and trnH-psbA loci, provides qualitative and quantitative information on the amount of plant material responsible for the contaminations and the extent of the contamination. The generated data also demonstrates that the presence of a very limited number of Heliotropium sp. seeds in a standard commercially available canister is sufficient to surpass the allowed threshold value, illustrating once more the importance of weed control.

Detection, dietary exposure assessment and risk evaluation of quinolones and pyrrolizidine alkaloids in commercial honey from Brazil

Pyrrolizidine alkaloids are secondary plant metabolites that have already been designated as a potential health risk due to their toxicity. Quinolones are antimicrobials related to bacterial resistance, one of the world's largest contemporary public health problems. This study searched for 22 pyrrolizidine alkaloids and 7 quinolones in honey available for sale in the state of Rio de Janeiro - Brazil - employing an analytical method based on LC-Q-TOF-HRMS. No quinolones were identified, while pyrrolizidine alkaloids were found in 39 out of 80 samples, mainly erucifoline (detected in 17% of the samples) and intermedine/lycopsamine (quantified in 27% of the samples). Considering the highest value found, 141.8 µg kg^-1 for senecionine and a consumption of 20 g of honey per person per day, the dietary exposure reached 47.3 ng kg^-1, resulting in a MOE value of 5.010, that might lead to a risk for human health.

High abundance of pyrrolizidine alkaloids in bee pollen collected in July 2019 from Southern Germany

Pyrrolizidine alkaloids (PA) are secondary plant defense compounds and known pre-toxins when containing a 1,2-double bond. They are commonly produced by various plants and may thus be present in bee pollen which may be consumed by humans as food supplements. In this study, PA were determined in bee pollen samples from 57 locations in Southern Germany sampled by means of pollen traps in July 2019. Samples were analyzed by using palynological methodology and solid-phase extraction (SPE) followed by LC-MS/MS. In total, 52 pollen samples featured total pyrrolizidine alkaloids (ΣPA) with concentrations up to 48,000 ng/g bee pollen, while the N-oxides (NO) echinatine-NO and rinderine-NO clearly dominated. In contrast, the palynological analysis only detected 33 samples with pollen from PA-producing plants. Accordingly, the results showed that palynological analysis is not sufficient to determine PA in pollen. In addition, a risk assessment was followed to estimate the risk of the detected PA concentrations to humans.

1,2-Dehydropyrrolizidine Alkaloids: Their Potential as a Dietary Cause of Sporadic Motor Neuron Diseases

Sporadic motor neuron diseases (MNDs), such as amyotrophic lateral sclerosis (ALS), can be caused by spontaneous genetic mutations. However, many sporadic cases of ALS and other debilitating neurodegenerative diseases (NDDs) are believed to be caused by environmental factors, subject to considerable debate and requiring intensive research. A common pathology associated with MND development involves progressive mitochondrial dysfunction and oxidative stress in motor neurons and glial cells of the central nervous system (CNS), leading to apoptosis. Consequent degeneration of skeletal and respiratory muscle cells can lead to death from respiratory failure. A significant number of MND cases present with cancers and liver and lung pathology. This Perspective explores the possibility that MNDs could be caused by intermittent, low-level dietary exposure to 1,2-dehydropyrrolizidine alkaloids (1,2-dehydroPAs) that are increasingly recognized as contaminants of many foods consumed throughout the world. Nontoxic, per se, 1,2-dehydroPAs are metabolized, by particular cytochrome P450 (CYP450) isoforms, to 6,7-dihydropyrrolizines that react with nucleophilic groups (-NH, -SH, -OH) on DNA, proteins, and other vital biochemicals, such as glutathione. Many factors, including aging, gender, smoking, and alcohol consumption, influence CYP450 isoform activity in a range of tissues, including glial cells and neurons of the CNS. Activation of 1,2-dehydroPAs in CNS cells can be expected to cause gene mutations and oxidative stress, potentially leading to the development of MNDs and other NDDs. While relatively high dietary exposure to 1,2-dehydroPAs causes hepatic sinusoidal obstruction syndrome, pulmonary venoocclusive disease, neurotoxicity, and diverse cancers, this Perspective suggests that, at current intermittent, low levels of dietary exposure, neurotoxicity could become the primary pathology that develops over time in susceptible individuals, along with a tendency for some of them to also display liver and lung pathology and diverse cancers co-occurring with some MND/NDD cases. Targeted research is recommended to investigate this proposal.

Natural plant toxins in honey: An ignored threat to human health

Consumers often believe that "natural food" is harmless, however naturally occurring toxins in food represent a health risk to humans. Honey as a natural, nutritious sweetener, is one of the most commonly consumed foods throughout the world. However, food safety concerns for honey arise when honeybees collect nectar from poisonous plants such as Rhododendron sp., Coriaria arborea, and Tripterygium wilfordii Hook F. Such honey contains natural plant toxins. Humans may develop intoxication symptoms after consuming toxic honey; in some cases, it can be fatal. As a result, toxic honey poses an often-ignored threat to public health. Typical plant toxins such as grayanotoxins, triptolides, tutin and pyrrolizidine alkaloids, have been identified in toxic honey. Although different toxic honeys elicit similar symptoms, such as vomiting, nausea, and dizziness, the mechanism of toxicity may be different. Thus, it is necessary to determine the exact toxicity mechanism of different toxins to further develop effective antidotes and cures. Another important challenge is preventing toxic honey from entering the food chain. Liquid chromatography-mass spectrometry has a wide range of applications in the detection of different toxins due to its accuracy and simplicity. More methods, however, are urgently needed to detect multiple plant-derived toxins in honey and its derivatives. Developing uniform international standards for toxin detection during quarantine using advanced techniques is critical for preventing human consumption of toxic honey.

Regulatory Perspectives of Pyrrolizidine Alkaloid Contamination in Herbal Medicinal Products

The toxicity of plants containing certain pyrrolizidine alkaloids has long been recognized in grazing animals and humans. Genotoxicity and carcinogenicity data from in vitro and in vivo (animal) studies were published over the last few decades for some of the 1,2-unsaturated pyrrolizidine alkaloids, leading to regulatory action on herbal medicinal products with pyrrolizidine alkaloid-containing plants more than 30 years ago. In recent years, it has become evident that in addition to herbal medicinal products containing pyrrolizidine alkaloid-containing plants, these products may also contain pyrrolizidine alkaloids without actually including pyrrolizidine alkaloid-containing plants. This is explained by contamination by accessory herbs (weeds). The national competent authorities of the European member states and the European Medicines Agency, in this case, the Committee on Herbal Medicinal Products, reacted to these findings by setting limits for all herbal medicinal products. This review article will briefly discuss the data leading to the establishment of thresholds and the regulatory developments and consequences, as well as the current discussions and research in this area.

Characterization and Lifetime Dietary Risk Assessment of Eighteen Pyrrolizidine Alkaloids and Pyrrolizidine Alkaloid N-Oxides in New Zealand Honey

Pyrrolizidine alkaloids (PAs) are a large group of botanical toxins of concern, as they are considered genotoxic carcinogens, with long-term dietary exposure presenting an elevated risk of liver cancer. PAs can contaminate honey through honeybees visiting the flowers of PA-containing plant species. A program of monitoring New Zealand honey has been undertaken over several years to build a comprehensive dataset on the concentration, regional and seasonal distribution, and botanical origin of 18 PAs and PA N-oxides. A bespoke probabilistic exposure model has then been used to assess the averaged lifetime dietary risk to honey consumers, with exposures at each percentile of the model characterized for risk using a margin of exposure from the Joint World Health Organization and United Nations Food and Agriculture Organization Expert Committee on Food Additives (JECFA) Benchmark Dose. Survey findings identify the typical PA types for New Zealand honey as lycopsamine, echimidine, retrorsine and senecionine. Regional and seasonal variation is evident in the types and levels of total PAs, linked to the ranges and flowering times of certain plants. Over a lifetime basis, the average exposure an individual will receive through honey consumption is considered within tolerable levels, although there are uncertainties over high and brand-loyal consumers, and other dietary contributors. An average lifetime risk to the general population from PAs in honey is not expected. However, given the uncertainties in the assessment, risk management approaches to limit or reduce exposures through honey are still of value.

Characterization of liver injury induced by a pyrrolizidine alkaloid in rats

BACKGROUND

Pyrrolizidine alkaloids (PAs) are common phytotoxins. PA intoxication is reported to cause severe acute liver damage, typically known as hepatic sinusoidal obstruction syndrome (HSOS), but it remains obscure whether the acute liver damage may progress into chronic liver disease characterized by hepatic fibrosis.

PURPOSE

This study aims to characterize the biochemical markers of liver injury and histological features of regressive and progressive liver fibrosis, and to examine changes in hepatic gene expression that may underpin mechanisms of fibrogenesis in rats induced by retrorsine (RTS), a representative toxic PA.

STUDY DESIGN/METHODS

Rats were gavaged with RTS via two dosing regimens, i.e. a single dose of 40 mg/kg (Group 1) and two doses of 40 mg/kg and 20 mg/kg on day 0 and day 7 (Group 2), respectively. Rats receiving one (Group 3) or two (Group 4) doses of vehicle served as negative controls. The animals were followed for up to 16 weeks by serum biochemical analyses and histological examination, and gene expression assays of liver tissues.

RESULTS

Acute liver injury on day 2 manifested as HSOS, characterized by sinusoidal dilation, endothelial cell damage, and elevated serum alanine aminotransferase activity and bilirubin levels. In Group 1, mild liver fibrosis developed at sinusoids and perisinusoidal space surrounding the central veins at week 1 and 2, and thereafter, all liver injury resolved gradually. In Group 2, liver fibrosis progressed within the 16-week observation period. No apparent liver injury was observed in Groups 3 and 4. Compared with negative control groups, RTS induced myofibroblastic activation, TGF-β1 signaling, and changes in expression of matrix metalloproteinase 9 (MMP-9) and tissue inhibitor of metalloproteinase 1 (TIMP-1). These dynamic changes differed in Groups 1 and 2, corresponding with the regression and progression of liver fibrosis, respectively, in these groups.

CONCLUSION

This study has provided in-vivo proof of concept that "one hit" and "two hits" of RTS lead to acute resolving liver injury and chronic progressive liver fibrosis, respectively. These animal models may serve as powerful tools for studying RTS toxicology and related preventive and therapeutic strategies and as positive controls for studying other PA- and non-PA-induced liver injury.

Hepatic sinusoidal obstruction syndrome caused by the ingestion of Gynura segetum in a patient with alcoholic cirrhosis: a case report

Hepatic sinusoidal obstruction syndrome (HSOS) is a rare hepatic vascular disorder characterized by intrahepatic congestion, liver injury, and post-sinusoidal portal hypertension, and it is frequently associated with hematopoietic stem cell transplantation. In this study, we observed a case of HSOS associated with the ingestion of Gynura segetum, a pyrrolizidine alkaloid (PA)-containing Chinese herb, in a patient with alcoholic cirrhosis. The patient was a 43-year-old man with chief complaints of physical asthenia and a loss of appetite for more than a month. The diagnosis of HSOS combined with alcoholic cirrhosis was confirmed via the histopathological examination of liver tissues. With proper supportive and symptomatic care and anticoagulation therapy using low-molecular-weight heparin, the patient’s condition was stabilized. Because of its nonspecific symptoms in the early stage and a lack of information about PA consumption, PA-induced HSOS (PA-HSOS) has been long neglected, especially in patients with underlying liver diseases. Early identification and intervention are critical for optimizing outcomes. Further efforts are needed to supervise the use of PA-containing herbal medicines and identify accurate biomarkers for PA-HSOS.

Use of Herbarium Voucher Specimens To Investigate Phytochemical Composition in Poisonous Plant Research

Poisonous plants cause large losses to the livestock industry through death, reduced production efficiency, reproductive dysfunction, and compromised harvesting of rangeland and pasture forages. Research investigating poisonous plants is complex because there are hundreds of genera of toxic plants representing thousands of species. To investigate the effects of poisonous plants on livestock, a clear understanding of the taxonomic identity of the plant and the ability to collect the plant in sufficient quantities for scientific studies is required. Subsequently, the active principles must be defined and investigated in the taxa of interest to better predict risk and make recommendations to reduce losses. Herbaria are collections of preserved plant specimens and are an important resource in poisonous plant research. Voucher specimens have often been used in the identification of the plant for the experimental reproduction of suspected livestock poisoning associated with a spontaneous case. More recently, herbarium specimens have been used to investigate the chemical composition of toxic plants as well as the distribution of different chemotypes over the landscape. The primary purpose of this review is to highlight the chemical analysis of herbarium specimens in poisonous plant research.

Current Knowledge and Perspectives of Pyrrolizidine Alkaloids in Pharmacological Applications: A Mini-Review

Pyrrolizidine alkaloids (PAs) are a widespread group of secondary metabolites in plants. PAs are notorious for their acute hepatotoxicity, genotoxicity and neurological damage to humans and animals. In recent decades, the application of PAs for beneficial biological activities to cure disease has drawn greater attention. Here, we review the current knowledge regarding the pharmacological properties of PAs and discuss PAs as promising prototypes for the development of new drugs.

Targeted LC-MS/MS combined with multilocus DNA metabarcoding as a combinatory approach to determine the amount and the source of pyrrolizidine alkaloids contamination in popular cooking herbs, seeds, spices and leafy vegetables

Pyrrolizidine alkaloids (PAs) and their corresponding N-oxides (PANOs) are natural protoxins biosynthesised by many plant species and are responsible for occasional fatal intoxication outbreaks due to the consumption of contaminated food. However, only in rare cases has the origin of the contamination been determined. Although their presence has been studied in many matrices, occurrence data on popular widely used cooking herbs, seeds, spices and leafy vegetables is very scarce. Therefore, a systematic study on the occurrence of PA/PANOs contaminations in these popular herbal items, available on the Belgian market, was performed, by means of a validatedtargeted LC-MS/MS analysis, followed by multilocus DNA metabarcoding to track back the origin of the contamination for seven highly to moderately contaminated samples. Our results clearly indicate that 21% of the seed spices and 25% seed-based aromatic mixes contain an amount higher than 400 μg of the 30 summed targeted PAs and PANOs per kg, the value which is currently under discussion by the European member states to be set as a maximum threshold. For both the herbs and the herb-based mixes only 7% of analysed samples exceeded these levels. As a proof of concept, multilocus DNA metabarcoding was performed on six highly contaminated samples, belonging to each subtype matrix, containing high levels of heliotrine type of PA/PANOs. Each time the analysis demonstrated the presence of DNA from a plant species belonging to the plant genus Heliotropium. Moreover, a contaminated leafy vegetable sample, containing solely senecionine type PA/PANOs, contained DNA from Senecio vulgaris. Taken together, it can be stated that the proposed combinatory chemical and molecular techniques could be used to verify if a PA/PANO(s) contamination occurred in these popular cooking items and to pinpoint the origin the contamination, which is pivotal in the case of a detrimental intoxication or intoxication outbreak.

Lung injury induced by pyrrolizidine alkaloids depends on metabolism by hepatic cytochrome P450s and blood transport of reactive metabolites

Pyrrolizidine alkaloids (PAs) are common phytotoxins with both hepatotoxicity and pneumotoxicity. Hepatic cytochrome P450 enzymes are known to bioactivate PAs into reactive metabolites, which can interact with proteins to form pyrrole-protein adducts and cause intrahepatic cytotoxicity. However, the metabolic and initiation biochemical mechanisms underlying PA-induced pneumotoxicity remain unclear. To investigate the in vivo metabolism basis for PA-induced lung injury, this study used mice with conditional deletion of the cytochrome P450 reductase (Cpr) gene and resultant tissue-selective ablation of microsomal P450 enzyme activities. After oral exposure to monocrotaline (MCT), a pneumotoxic PA widely used to establish animal lung injury models, liver-specific Cpr-null (LCN) mice, but not extrahepatic Cpr-low (xh-CL) mice, had significantly lower level of pyrrole-protein adducts in the serum, liver and lungs compared with wild-type (WT) mice. While MCT-exposed LCN mice had significantly higher blood concentration of intact MCT, compared to MCT-exposed WT or xh-CL mice. Consistent with the MCT in vivo bioactivation data, MCT-induced lung injury, represented by vasculature damage, in WT and xh-CL mice but not LCN mice. Furthermore, reactive metabolites of MCT were confirmed to exist in the blood efflux from the hepatic veins of MCT-exposed rats. Our results provide the first mode-of-action evidence that hepatic P450s are essential for the bioactivation of MCT, and blood circulating reactive metabolites of MCT to the lung causes pneumotoxicity. Collectively, this study presents the scientific basis for the application of MCT in animal lung injury models, and more importantly, warrants public awareness and further investigations of lung diseases associated with exposure to not only MCT but also different PAs.

Clinical application of pyrrole-hemoglobin adducts as a biomarker of pyrrolizidine alkaloid exposure in humans

Pyrrolizidine alkaloids (PAs) are naturally occurring hepatotoxins widely present in hundreds of plant species and also known to contaminate many foodstuffs, such as grain, honey, and tea. The formation of pyrrole-protein adducts via metabolic activation of PAs has been suggested as a primary trigger initiating hepatotoxicity. The present study for the first time tested the suitability of pyrrole-hemoglobin adducts as a novel and specific biomarker of PA exposure in humans. The level and elimination kinetics of pyrrole-hemoglobin adducts were systematically investigated in the blood samples of 43 PA-induced liver injury (PA-ILI) patients. The results revealed significantly higher concentrations (84.50 ± 78.38 nM) and longer persistence (~ 4 months) of pyrrole-hemoglobin adducts than that (concentration: 9.53 ± 10.72 nM; persistence: ~ 2 months) of pyrrole-plasma protein adducts, our previously developed PA exposure biomarker. Our findings confirmed that pyrrole-hemoglobin adducts with higher level and longer persistence should serve as a more applicable PA exposure biomarker for future clinical diagnosis of PA-ILI in drug/herb-induced liver injury patients.

The invasive butterbur contaminates stream and seepage water in groundwater wells with toxic pyrrolizidine alkaloids

Pyrrolizidine alkaloids (PAs) are persistent mutagenic and carcinogenic compounds produced by many common plant species. Health authorities recommend minimising human exposure via food and medicinal products to ensure consumer health and safety. However, there is little awareness that PAs can contaminate water resources. Therefore, no regulations exist to limit PAs in drinking water. This study measured a PA base concentration of ~ 70 ng/L in stream water adjacent to an invasive PA-producing plant Petasites hybridus (Asteraceae). After intense rain the PA concentration increased tenfold. In addition, PAs measured up to 230 ng/L in seepage water from groundwater wells. The dominant PAs in both water types corresponded to the most abundant PAs in the plants (senkirkine, senecionine, senecionine N-oxide). The study presents the first discovery of persistent plant toxins in well water and their associated risks. In addition, it for the first time reports monocrotaline and monocrotaline N-oxide in Petasites sp.

Screening of food supplements for toxic pyrrolizidine alkaloids

Pyrrolizidine alkaloids (PA) and PA-N-oxides (PANO) are a group of more than 660 secondary plant metabolites with hepatotoxic, carcinogenic and mutagenic effects in animals and humans. The phytotoxins can enter the food chain by transfer of PA/PANO between plants via the soil, unintended co-harvesting of PA/PANO-producing weeds, as well as by honeybees collecting pollen and nectar of these plants. Thus, bee- and plant-based products, e.g. (herbal) teas, spices and culinary herbs were identified to be a main source of consumers’ exposure to PA/PANO. Consequently, food supplements based on those ingredients may as well be contaminated with PA/PANO, but so far there are only very few studies available on this topic. Therefore, the current study investigated 50 herbal and bee product-based food supplements available in German retail pharmacies, drugstores, and online on the occurrence of 44 PA/PANO. In total, 19 samples contained PA/PANO with sum contents ranging from 0.1 to 105.1 ng/g in solid samples and from 0.03 to 2.20 ng/mL in liquid preparations. Considering the recommended daily consumption, the sum contents were of no or little concern for the health risk of adults, whereas in case of children the contents of singular samples could significantly contribute to the overall PA/PANO exposure.

Establishment of a novel CYP3A4-transduced human hepatic sinusoidal endothelial cell model and its application in screening hepatotoxicity of pyrrolizidine alkaloids

Pyrrolizidine alkaloids (PAs) are extensively distributed in plants and are known to damage hepatic sinusoidal endothelial cells (HSECs) via metabolic activation mediated by hepatic cytochrome P450 enzymes (CYPs), particularly the CYP3A4 isozyme. Different PAs have distinct toxic potencies and their toxic effects on HSECs are difficult to be determined in cultured cells, because HSECs lack the key CYP3A4 isozyme for metabolic activation. This study aims to establish a novel, convenient and reliable CYP3A4-expressing HSEC model using human HSECs transduced with lentivirus carrying CYP3A4-ires-eGFP, for evaluating the hepatotoxicity of different PAs on their target HSECs. The developed CYP3A4-expressing HSEC (HSEC-CYP3A4) model was verified by the expression of GFP and CYP3A4 and by the ability to metabolize nifedipine, a classic CYP3A4 substrate. Treated with retrorsine, a representative toxic PA, HSEC-CYP3A4 cells showed significantly reduced cell viability, depletion of GSH, and increased formation of pyrrole-protein adducts. Furthermore, this newly developed cell model successfully discriminated the cytotoxic potency of different PAs evidenced by their IC₄₀ values. In conclusion, the established HSEC-CYP3A4 cell model can be used as a rapid screening platform for assessing the relative potencies of individual PAs on their target HSECs and for investigating the mechanisms underlying PA-induced hepatic sinusoidal damage.

Echium plantagineum L. honey: Search of pyrrolizidine alkaloids and polyphenols, anti-inflammatory potential and cytotoxicity

For a long time, honey has been recognized for its health-promoting properties and, consequently, has been used in traditional medicine worldwide. Apart from the beneficial bioactive compounds found in this food (e.g. polyphenols), molecules with potentially harmful effects may also be present, such as pyrrolizidine alkaloids. Aiming the quality assessment of honeys produced from Echium plantagineum L., a species known for its content in pyrrolizidine alkaloids, this work was focused in the search of these alkaloids and of polyphenols in one monofloral and two multifloral honeys, using chromatographic techniques. Additionally, their cytotoxicity and anti-inflammatory potential were assessed in cellular models. Several polyphenols were determined, but no pyrrolizidine alkaloid was detected in the analysed honey samples. Honey extracts exhibited capacity to decrease NO levels in lipopolysaccharide-stimulated murine macrophage-like cells (RAW 264.7) up to 40% at concentrations of 0.25 mg/mL. Therefore, this work highlights the health benefits of these honey samples.

Genetic and chemical diversity of the toxic herb Jacobaea vulgaris Gaertn. (syn. Senecio jacobaea L.) in Northern Germany

Tansy ragwort, Jacobaea vulgaris Gaertn. (syn. Senecio jacobaea L.), is a common Asteraceae in Europe and Asia and known to be an invasive pest in several regions in the world. Recently it is also spreading immensely in native regions like Northern Germany. Pyrrolizidine alkaloids (PAs), which are found in high amounts in Jacobaea vulgaris, are toxic for humans and potentially lethal for grazing animals. In this study we investigated 27 populations of tansy ragwort in Northern Germany for their PA concentration and composition using liquid chromatography coupled to high resolution mass spectrometry. Furthermore, we investigated the genetic structure of selected populations using amplified length polymorphism markers. We detected 98 different PAs in the samples and considerable differences of PA composition between populations. In contrast, PA content of populations did not differ significantly. Genetic (4%) differentiation among populations was low while average genetic diversity was high (0.35). There was no correlation between genetic and geographic distance. Neither genetic markers nor chemical composition revealed any connection to the geographic pattern. As we could not detect any pattern in genetic or chemical diversity, we suggest that the existence of this diversity is a result of a broad interaction with the environment rather than that of evolutionary constraints in the current selection process driving PA composition in J. vulgaris in certain chemotypes.

Occurrence and Risk Assessment of Pyrrolizidine Alkaloids in Spices and Culinary Herbs from Various Geographical Origins

Pyrrolizidine alkaloids (PA) and their N‑oxides (PANO) are a group of toxic secondary plant metabolites occurring predominantly as contaminants in (herbal) teas, honeys and food supplements, as well as in spices and culinary herbs. Depending on the botanical origin of the contaminating plant, the pattern of PA/PANO can strongly vary within a sample. The current study aimed to broaden the existing data on the occurrence of PA/PANO in spices and culinary herbs. For this, 305 authentic samples covering 15 different matrices mainly harvested in 2016 or 2017 and originating from 36 countries were investigated for the presence of 44 PA/PANO. Fifty-eight percent of the samples contained at least one PA/PANO. The average sum content over all samples was 323 µg/kg (median of 0.9 µg/kg, 95% percentile of 665 µg/kg). The highest amount of 24.6 mg/kg was detected in an oregano sample. Additionally, conspicuous analyte patterns were discovered in samples from similar cultivation regions, indicating related botanical sources of PA/PANO contaminations. Particularly, oregano and cumin from Turkey often contained high amounts of PA/PANO. The results were used to assess the acute and chronic health risks related to PA/PANO intake via spices and culinary herbs, indicating a potential health risk in particular for adults and children with high consumption or when considering worst‑case contamination scenarios of a sum content of 5500 µg/kg.

Pyrrolizidine alkaloids in bee pollen identified by LC-MS/MS analysis and colour parameters using multivariate class modeling

Toxic pyrrolizidine alkaloids (PAs) and their N-oxides (PANOs) can be present in bee pollen depending on the plants visited by bees. A liquid chromatography-mass spectrometry (LC-MS/MS) method was developed and validated to monitor 17 PAs/PANOs in 44 bee pollens. The CIE-L∗a∗b∗ colour coordinates with the specular component either included or excluded were recorded in pellets and ground aliquots. Lightness (L∗) and yellowness (b∗) of ground bee pollen were significantly correlated to PAs/PANOs content. The L∗ and b∗ cut-offs sorted by a receiver operating characteristic analysis to predict PAs/PANOs presence showed a significant increase in the relative risk to detect amounts higher than 84 μg kg-1. Two supervised canonical discriminant analyses confirmed that pollen without PAs could be distinguished from those containing PAs/PANOs. The data suggest that instrumental colour coupled with supervised models could be used as a screening test for PAs/PANOs in bee pollen, before the confirmatory LC-MS/MS analysis.

Detection of pyrrolizidine alkaloids in jamu available on the Indonesian market and accompanying safety assessment for human consumption

The occurrence and accompanying risks of pyrrolizidine alkaloids (PAs) in Indonesian jamu were evaluated. PAs were detected in 34 out of 35 jamu containing PA-producing botanicals, in the range of 12.3-235,376 μg/kg. A total PA level of 5.9-3,421 μg/kg was found in 17 out of 23 jamu made of non-PA-producing botanicals pointing to contamination with PA-producing plants. Short-time consumption of jamu is unlikely to result in acute toxic effects, although one sample would exceed an intake of 10 μg PA/kg bw/day which may cause hepatic veno-occlusive disease (HVOD) in humans. The risk assessment for the genotoxic and carcinogenic potential of PAs revealed Margin of Exposure (MOE) values below 10,000 for 27 out of all samples analysed (46.6%), indicating a priority for risk management when assuming daily lifelong consumption. Assuming consumption for two weeks every year during a lifetime, and using Haber's rule, 13 out of 35 jamu samples containing PA-producing botanicals (37%) still pose a priority, while the jamu consisting of non-PA-producing botanicals would be of low priority (MOE>10,000). This study provides data that can support risk management actions in Indonesia to minimize the potential health risk for jamu consumers due to the occurrence of toxic PAs in these products.

A systematic review and quality assessment of case reports of adverse events for borage (Borago officinalis), coltsfoot (Tussilago farfara) and comfrey (Symphytum officinale)

Symphytum officinale (comfrey), Tussilago farfara (coltsfoot) and Borago officinalis (borage) have long histories of therapeutic use, but their safety has been questioned due to the presence of unsaturated pyrrolizidine alkaloids (PAs). The evidence base underlying these concerns relies in part on case reports. This systematic review assesses these case reports for their reliability to inform this debate.

METHOD

Study selection was restricted to case reports describing possible pyrrolizidine alkaloid related harm and ingestion of comfrey, coltsfoot or borage. An extensive search of academic databases was conducted. Papers meeting the criteria were critically appraised.

RESULTS

The search resulted in 11 appropriate case reports, none of which involved borage. Nine reports were assessed for causality and indicated some degree of association between the material ingested and the adverse event. Lack of unequivocal identification of the species ingested compromised attribution and was a significant source of uncertainty. Three levels of identity confusions were found; misidentification or substitution at the level of the whole herb; omission of appropriate botanical identification and attribution of a specific PA to either comfrey or coltsfoot when it is a constituent found in other plants of established toxicity.

CONCLUSION

These cases are an unreliable body of evidence on which to draw conclusions about the safety of the oral consumption of Symphytum officinale and Tussilago farfara. Toxicological studies based on oral ingestion of phytochemically-complex preparations of these herbs may be the most accurate methodology for assessing clinical risk.

Application of the sum parameter method for the determination of pyrrolizidine alkaloids in teas

Tea samples from the Polish market were analysed for the determination of pyrrolizidine alkaloids (PAs). The method applied in the study is based on the GC-MS technique and uses the sum parameter approach for quantification. The analytical protocol was subjected to validation in terms of linearity, repeatability, reproducibility, the limit of quantification and determination, matrix effect, selectivity, and uncertainty, and all evaluated parameters fulfilled the requirements of Commission Decision 2002/657. A total of 78% of the analysed samples contained 1,2-unsaturated PAs, and the concentrations were determined to fall in the range of 2-6498 µg kg^-1. The highly contaminated samples were additionally subjected to LC-MS analysis. Much higher PA concentrations were determined with the sum parameter method, proving its superior quantification capability. The high contamination found prompted an assessment of the dietary exposure from the consumption of infusions prepared from the analysed teas. Two approaches were adopted: one assuming 100% transfer of PAs to the infusions and the second assuming only partial transfer. Regardless of the adopted approach, consumption of several infusions was shown to greatly exceed the maximum acceptable daily intake of PAs.

Analysis of Pyrrolizidine Alkaloids in Queensland Honey: Using Low Temperature Chromatography to Resolve Stereoisomers and Identify Botanical Sources by UHPLC-MS/MS

Pyrrolizidine alkaloids (PAs) are a diverse group of plant secondary metabolites with known varied toxicity. Consumption of 1,2-unsaturated PAs has been linked to acute and chronic liver damage, carcinogenicity and death, in livestock and humans, making their presence in food of concern to food regulators in Australia and internationally. In this survey, honey samples sourced from markets and shops in Queensland (Australia), were analysed by high-resolution Orbitrap UHPLC-MS/MS for 30 common PAs. Relationships between the occurrence of pyrrolizidine alkaloids and the botanical origin of the honey are essential as pyrrolizidine alkaloid contamination at up to 3300 ng/g were detected. In this study, the predominant alkaloids detected were isomeric PAs, lycopsamine, indicine and intermedine, exhibiting identical MS/MS spectra, along with lesser amounts of each of their N-oxides. Crucially, chromatographic UHPLC conditions were optimised by operation at low temperature (5 °C) to resolve these key isomeric PAs. Such separation of these isomers by UHPLC, enabled the relative proportions of these PAs present in honey to be compared to alkaloid levels in suspect source plants. Overall plant pyrrolizidine alkaloid profiles were compared to those found in honey samples to help identify the most important plants responsible for honey contamination. The native Australian vines of Parsonsia spp. are proposed as a likely contributor to high levels of lycopsamine in many of the honeys surveyed. Botanical origin information such as this, gained via low temperature chromatographic resolution of isomeric PAs, will be very valuable in identifying region of origin for honey samples.

Development of a sensitive analytical method for determining 44 pyrrolizidine alkaloids in teas and herbal teas via LC-ESI-MS/MS

Pyrrolizidine alkaloids (PA) and PA-N-oxides (PANO) are a large group of secondary plant metabolites comprising more than 660 compounds. Exhibiting geno- and hepatotoxic properties, they are responsible for multiple cases of food and feed poisoning over the last 100 years. For food and feed safety reasons, relevant PA/PANO should be monitored extensively in the main sources of PA/PANO intake. In this study, a sensitive analytical method was developed for detecting a broad range of 44 commercially available PA/PANO compounds, and in-house validation procedures were performed for several (herbal) teas. Various extraction solvents and procedures, as well as solid phase extraction materials for sample clean-up and analyte concentration, were tested to establish the methods' efficiency and effectiveness. Chromatographic conditions were optimised to obtain the best possible separation of isomers for the 44 PA/PANO analytes. The final method was proven very sensitive and accurate, with detection limits ranging from 0.1 to 7.0 μg/kg and precisions between 0.7 and 16.1%. For 40 of the analytes, the recovery rates ranged from 60.7 to 128.8%. The applicability and trueness of the method were examined by analysing tea samples from a local supermarket and comparing them to a reference material. At least one PA/PANO analyte was detected in 17 of the 18 samples under investigation, and the sum contents of the samples ranged from 0.1 to 47.9 μg/kg. Knowledge of the PA/PANO composition in a sample can be used to indicate the botanical origin of the impurity and, thus, the geographical region of cultivation.

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.

Pyrrole-Hemoglobin Adducts, a More Feasible Potential Biomarker of Pyrrolizidine Alkaloid Exposure

Pyrrolizidine alkaloids (PAs) are naturally occurring phytotoxins widely distributed in about 3% of flowering plants. The formation of PA-derived pyrrole-protein adducts is considered as a primary trigger initiating PA-induced hepatotoxicity. The present study aims to (i) further validate our previous established derivatization method using acidified ethanolic AgNO₃ for the analysis of pyrrole-protein adducts and (ii) apply this method to characterize the binding tendency, dose-response, and elimination kinetics of pyrrole-protein adducts in blood samples. Two pyrrole-amino acid conjugates, (±)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5 H-pyrrolizine (DHP)-cysteine (7-cysteine-DHP) and 9-histidine-DHP, were synthesized and used to demonstrate that acidified ethanolic AgNO₃ derivatization can cleave both S-linkage and N-linkage of pyrrole-protein adducts. Subsequently, using precolumn AgNO₃ derivatization followed by ultra-high-pressure liquid chromatography/mass spectrometry analysis, we quantified pyrrole-protein adducts in monocrotaline-treated rat blood protein fractions, including hemoglobin (Hb), plasma, albumin, and plasma residual protein fractions, and found that the amount of pyrrole-Hb adducts was significantly higher than that in all plasma fractions. Moreover, elimination half-life of pyrrole-Hb adducts was also significantly longer than pyrrole-protein adducts in plasma fractions (12.08 vs 2.54-2.93 days). In addition, we also tested blood samples obtained from five PA-induced liver injury patients and found that the amount of pyrrole-protein adducts in blood cells was also remarkably higher than that in plasma. In conclusion, our findings for the first time confirmed that the AgNO₃ derivatization method could be used to measure both S- and N-linked pyrrole-protein adducts and also suggested that pyrrole-Hb adducts with remarkably higher level and longer life span could be a better biomarker of PA exposure.

Occurrence of Nine Pyrrolizidine Alkaloids in Senecio vulgaris L. Depending on Developmental Stage and Season

The contamination of phytopharmaceuticals and herbal teas with toxic plants is an increasing problem. Senecio vulgaris L. is a particularly noxious weed in agricultural and horticultural crops due to its content of toxic pyrrolizidine alkaloids (PAs). Since some of these compounds are carcinogenic, the distribution of this plant should be monitored. The amount of PAs in S. vulgaris is affected by various factors. Therefore, we investigated the occurrence of PAs depending on the developmental stage and season. A systematic study using field-plot experiments (four seasons, five developmental stages of the plants: S1 to S5) was performed and the PA concentration was determined via LC-MS/MS analysis. The total amount of PAs in the plant increased with the plant development, however, the total PA concentrations in µg/g dry matter remained nearly unchanged, whilst trends for specific PAs were observed. The concentrations of PA-N-oxides (PANOs) were much higher than that of tertiary PAs. Maximal amounts of the PA total were 54.16 ± 4.38 mg/plant (spring, S5). The total amount of PAs increased strongly until later developmental stages. Therefore, even small numbers of S. vulgaris may become sufficient for relevant contaminations set out by the maximal permitted daily intake levels recommended by the European Food Safety Authority (EFSA).

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.

Potentially toxic pyrrolizidine alkaloids in Eupatorium perfoliatum and three related species. Implications for herbal use as boneset

INTRODUCTION

Pro-toxic dehydropyrrolizidine alkaloids are associated with liver disease in humans. The potential for long-term, low-level or intermittent exposures to cause or contribute to chronically-developing diseases is of international concern. Eupatorium perfoliatum is a medicinal herb referred to as boneset. While the presence of dehydropyrrolizidine alkaloids in some Eupatorium species is well-established, reports on Eupatorium perfoliatum are scant and contradictory.

OBJECTIVE

To investigate the presence of dehydropyrrolizidine alkaloids in a survey of boneset samples and related alcoholic tinctures, and hot water infusions and decoctions.

METHODS

Methanol, hot water or aqueous ethanol extracts of Eupatorium perfoliatum and three closely-related species were subjected to HPLC-ESI(+)MS and MS/MS analysis using three complementary column methods. Dehydropyrrolizidine alkaloids were identified from their MS data and comparison with standards.

RESULTS

Forty-nine samples of Eupatorium perfoliatum were shown to contain dehydropyrrolizidine alkaloids (0.0002-0.07% w/w), the majority dominated by lycopsamine and intermedine, their N-oxides and acetylated derivatives. Alcoholic tinctures and hot water infusions and decoctions had high concentrations of the alkaloids. Different chemotypes, hybridisation or contamination of some Eupatorium perfoliatum samples with related species were suggested by the co-presence of retronecine- and heliotridine-based alkaloids.

CONCLUSIONS

Sampling issues, low and high alkaloid chemotypes of Eupatorium perfoliatum or interspecies hybridization could cause the wide variation in dehydropyrrolizidine alkaloid concentrations or the different profiles observed. Concerns associated with dehydropyrrolizidine alkaloids provide a compelling reason for preclusive caution until further research can better define the toxicity and carcinogenicity of the dehydropyrrolizidine alkaloid content of Eupatorium perfoliatum. [Correction added on 12 July 2018, after first online publication: The 'Conclusions' section in the abstract has been added.].

The role of formation of pyrrole-ATP synthase subunit beta adduct in pyrrolizidine alkaloid-induced hepatotoxicity

Pyrrolizidine alkaloids (PAs) are one of the most significant groups of hepatotoxic phytotoxins. It is well-studied that metabolic activation of PAs generates reactive pyrrolic metabolites that rapidly bind to cellular proteins to form pyrrole-protein adducts leading to hepatotoxicity. Pyrrole-protein adducts all contain an identical core pyrrole moiety regardless of structures of the different PAs; however, the proteins forming pyrrole-protein adducts are largely unknown. The present study revealed that ATP synthase subunit beta (ATP5B), a critical subunit of mitochondrial ATP synthase, was a protein bound to the reactive pyrrolic metabolites forming pyrrole-ATP5B adduct. Using both anti-ATP5B antibody and our prepared anti-pyrrole-protein antibody, pyrrole-ATP5B adduct was identified in the liver of rats, hepatic sinusoidal endothelial cells, and HepaRG hepatocytes treated with retrorsine, a well-studied representative hepatotoxic PA. HepaRG cells were then used to further explore the consequence of pyrrole-ATP5B adduct formation. After treatment with retrorsine, significant amounts of pyrrole-ATP5B adduct were formed in HepaRG cells, resulting in remarkably reduced ATP synthase activity and intracellular ATP level. Subsequently, mitochondrial membrane potential and respiration were reduced, leading to mitochondria-mediated apoptotic cell death. Moreover, pre-treatment of HepaRG cells with a mitochondrial membrane permeability transition pore inhibitor significantly reduced retrorsine-induced toxicity, further revealing that mitochondrial dysfunction caused by pyrrole-ATP5B adduct formation significantly contributed to PA intoxication. Our findings for the first time identified ATP5B as a protein covalently bound to the reactive pyrrolic metabolites of PAs to form pyrrole-ATP5B adduct, which impairs mitochondrial function and significantly contributes to PA-induced hepatotoxicity.

Pyrrole-protein adducts - A biomarker of pyrrolizidine alkaloid-induced hepatotoxicity

Pyrrolizidine alkaloids (PAs) are phytotoxins identified in over 6000 plant species worldwide. Approximately 600 toxic PAs and PA N-oxides have been identified in about 3% flowering plants. PAs can cause toxicities in different organs particularly in the liver. The metabolic activation of PAs is catalyzed by hepatic cytochrome P450 and generates reactive pyrrolic metabolites that bind to cellular proteins to form pyrrole-protein adducts leading to PA-induced hepatotoxicity. The mechanisms that pyrrole-protein adducts induce toxicities have not been fully characterized. Methods for qualitative and quantitative detection of pyrrole-protein adducts have been developed and applied for the clinical diagnosis of PA exposure and PA-induced liver injury. This mini-review addresses the mechanisms of PA-induced hepatotoxicity mediated by pyrrole-protein adducts, the analytical methods for the detection of pyrrole-protein adducts, and the development of pyrrole-protein adducts as the mechanism-based biomarker of PA exposure and PA-induced hepatotoxicity.

Analytical strategies for the determination of pyrrolizidine alkaloids in plant based food and examination of the transfer rate during the infusion process

Two sample preparation methods were developed (graphitised carbon and C18 solid phase extraction clean-up) and validated in house using liquid chromatography and tandem mass spectrometry (MS/MS) for the determination of 30 pyrrolizidine alkaloids (PAs) in salads, herbs, tea, herbals teas as well as tea infusion and ice-tea beverages. Total PAs concentration of samples purchased on the Belgian market varied greatly with matrix type ranging from <LOD to 187151 ng/g for dry samples, while for infusions and ice-tea beverages the highest PAs concentration was 2106 ng/mL. Surprisingly high PAs concentrations were detected in herbs and spices mixes. The infusion study indicated a transfer rate between 16 and 28% (except for monocrotaline) which highlights the overestimation of PAs concentrations in infusions when derived from a dilution factor (transfer rate of 100%) to the measured concentrations of the dry tea sample.