Genotoxic and tumorigenic pyrrolizidine alkaloids in Chinese herbal plants

Pyrrolizidine alkaloids are a class of hepatotoxic and tumorigenic compounds detected in Chinese herbal plants, contaminated foods, and dietary supplements. In this review, the sources, toxicity, genotoxicity, tumorigenicity, and the metabolic pathways, particular the activation pathways leading to hepatotoxicity and tumorigenicity, of pyrrolizidine alkaloids are briefly discussed, with a focus on the most recent important findings concerning the genotoxic mechanism by which riddelliine liver tumors. This mechanism involves the formation of 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived DNA adducts and may be general to most carcinogenic pyrrolizidine alkaloids.

Recent advances on the synthesis of natural pyrrolizidine alkaloids: alexine, and its stereoisomers

Natural products have attracted the interest of the scientific community due to their importance and application.Alexine is a naturally polyhydroxylated pyrrolizidine alkaloid that is broadly found in plant sources and isolated from Alexa leiopetala.The biological properties such as glycosidase inhibitors,anti-virus,and anti-HIV activities,makes it interesting target for synthetical studies.This review reports different approaches and methodologies to the synthesis of alexine,and its stereoisomers as the target compounds in numerous studies.

Validation of the Nanjing Criteria for Diagnosing Pyrrolizidine Alkaloids-induced Hepatic Sinusoidal Obstruction Syndrome

Background and Aims:Hepatic sinusoidal obstruction syndrome(HSOS)is caused by toxic injury to sinusoidal endothelial cells in the liver.The intake of pyrrolizidine alkaloids(PAs)in some Chinese herbal remedies/plants remains the major etiology for HSOS in China.Recently,new diagnostic criteria for PA-induced HSOS(i.e.PA-HSOS)have been developed;however,the efficacy has not been clinically validated.This study aimed to assess the performance of the Nanjing criteria for PA-HSOS.Methods:Data obtained from consecutive patients in multiple hospitals,which included 86 PA-HSOS patients and 327 patients with other liver diseases,were retrospectively analyzed.Then,the diagnostic performance of the Nanjing criteria and simplified Nanjing criteria were evaluated and validated.The study is registered in www.chictr.org.cn(ID:ChiCTR1900020784).Results:The Nanjing criteria have a sensitivity and specificity of 95.35%and 100%,respectively,while the simplified Nanjing criteria have a sensitivity and specificity of 96.51%and 96.33%,respectively,for the diagnosis of PA-HSOS.Notably,a proportion of patients with Budd-Chiari syndrome(11/49)was misdiagnosed as PA-HSOS on the basis of the simplified Nanjing criteria,and this was mainly due to the overlapping features in the enhanced computed tomography/magnetic resonance imaging examinations.Furthermore,most of these patients(10/11)had occlusion or thrombosis of the hepatic vein,and communicating vessels in the liver were found in 8/11 patients,which were absent in PA-HSOS patients.Conclusions:The Nanjing criteria and simplified Nanjing criteria exhibit excellent performance in diagnosing PA-HSOS.Thus,both could be valuable diagnostic tools in clinical practice.

Three new pyrrolizidine alkaloids derivatives from Liparis nervosa

Three new pyrrolizidine alkaloids, nervosineⅦ（1）, nervosine Ⅷ（2） and nervosine IX （3） were isolated from the whole plant extract of Liparis nervosa. Their structures were elucidated by extensive spectroscopic analyses （including 1 D, 2D NMR, and HR-ESI-MS） and chemical methods. Compounds 1-3 were evaluated for their cytotoxic activity against A549, MCF-7and H460 human cancer cell lines.

Pyrrolizidine alkaloids:An update on their metabolism and hepatotoxicity mechanism

Pyrrolizidine alkaloids(PAs)are among the most hepatotoxic natural compounds that are widely distributed throughout the world.Most PAs are metabolically activated to trigger toxicity.Exposure to herbal medicine containing PAs and food supplements contaminated by PAs is considered to be one of the two main causes of hepatic sinusoidal obstruction syndrome(HSOS),which is a rare hepatic vascular disease with a high mortality rate.PAs-induced HSOS cases have been reported worldwide.However,there is no clinically effective therapy for PAs-induced HSOS,which is partially because the toxic mechanism is not fully understood.This review focuses on updating the information on the metabolism and the molecular mechanisms of PAs hepatotoxicity,including oxidative stress,apoptosis,and dysfunction of bile acid metabolism,and their interactions.

Chemical Diversity Investigation of Hepatotoxic Pyrrolizidine Alkaloids in Qianliguang(Senecio scandens)and Related Species by UHPLC-QTOF-MS

Objective: Qianliguang(Senecio scandens) is a common Chinese medicinal herb. Qianliguang-containing herbal proprietary products are registered as over-the-counter remedies in China and exported to Western countries. The presence of hepatotoxic pyrrolizidine alkaloids(PAs)has raised concerns about the safety of using Qianliguang and its products. The present study aims at investigation of different types of PAs present in Qianliguang collected from representative locations in China.Methods: In this study, a simple but specific UHPLC-QTOF-MS method for the determination of toxic PAs was developed, based on the characteristic fragment ions specific to different types of PAs. It was successfully applied for the identification and distinguishing of PAs present in Qianliguang and related Senecio species growing in different locations of China.Results: Significant diversity of the PA types and quantities were revealed among the samples tested. The estimated total amounts of toxic PAs in three of the samples exceed the toxic limits of PA intake restricted by WHO, demonstrating the timely and highly demand for regulating both types and quantities of PAs present in Qianliguang.Conclusions: This study provides the methodology for simultaneous identification and quantification of PAs present in herbs without requiring corresponding standards, which could be further used for more systematic investigations of the PA distribution in Qianliguang and other PA-containing herbs.

Transjugular intrahepatic portosystemic shunt for pyrrolizidine alkaloid-related hepatic sinusoidal obstruction syndrome

BACKGROUND Treatments for hepatic sinusoidal obstruction syndrome(HSOS)are limited.AIM To evaluate transjugular intrahepatic portosystemic shunting(TIPS)as a treatment for pyrrolidine alkaloid-related HSOS(PA-HSOS).METHODS This retrospective analysis included patients with PA-HSOS admitted to the First Affiliated Hospital of the University of Science and Technology of China(June 2015 to January 2019).Baseline clinical characteristics and follow-up data were extracted from the medical records.All patients included in this study experienced failure of initial therapy.Patients were divided into the TIPS and conservative treatment groups according to the therapy they received.Liver function,maximal ascites depth,imaging characteristics,pathology findings,and survival were compared between groups.RESULTS The TIPS group included 37 patients(28 males),and the conservative treatment group included 17 patients(11 males).Baseline characteristics were similar between groups.There were two deaths in the TIPS group and seven deaths in the conservative treatment group during follow-up(3-48 mo).The 3-,6-,12-and 24-mo survival rates were 94.6%,94.6%,94.6%and 94.6%,respectively,in the TIPS group and 70.6%,57.8%,57.8%and 57.8%,respectively,in the conservative treatment group.Kaplan-Meier analysis revealed significantly longer survival for the TIPS group than for the conservative treatment group(P=0.001).Compared with the pre-treatment value,maximal ascites depth was significantly lower at 1 wk,2 wk,1 mo,and 3 mo for the TIPS group(all P<0.05)but not in the conservative treatment group.Contrast-enhanced computed tomography demonstrated the disappearance of patchy liver enhancement after TIPS.Pathology showed that liver congestion and hepatocyte swelling improved with time after TIPS placement.CONCLUSION TIPS may achieve better outcomes than conventional symptomatic treatment in patients with PA-HSOS.

Two New Lactones Metabolized from Isoline by Rat Liver Microsomes

Two new metabolites, namely bisline lactone and isolinecic acid lactone, were isolated from the resultant incubates after a scale-up incubation of isoline with rat liver microsomes. Their structures were determined by spectroscopic data, especially those from 1D and 2D NMR experiments.

The key role of gut-liver axis in pyrrolizidine alkaloid-induced hepatotoxicity and enterotoxicity

Pyrrolizidine alkaloids(PAs) are the most common phytotoxins with documented human hepatotoxicity.PAs require metabolic activation by cytochromes P450 to generate toxic intermediates which bind to proteins and form protein adducts,thereby causing cytotoxicity.This study investigated the role of the gut-liver axis in PA intoxication and the underlying mechanisms.We exposed mice to retrorsine(RTS),a representative PA,and for the first time found RTS-induced intestinal epithelium damage and disruption to intestinal barrier function.Using mice with tissue-selective ablation of P450 activity,we found that hepatic P450 s,but not intestinal P450 s,were essential for PA bioactivation.Besides,in RTS-exposed,bile duct-cannulated rats,we found the liver-derived reactive PA metabolites were transported by bile into the intestine to exert enterotoxicity.The impact of gut-derived pathogenic factors in RTS-induced hepatotoxicity was further studied in mice with dextran sulfate sodium(DSS)-induced chronic colitis.DSS treatment increased the hepatic endotoxin level and depleted hepatic reduced glutathione,thereby suppressing the PA detoxification pathway.Compared to RTS-exposed normal mice,the colitic mice displayed more severe RTS-induced hepatic vasculature damage,fibrosis,and steatosis.Overall,our findings provide the first mode-of-action evidence of PA-induced enterotoxicity and highlight the importance of gut barrier function in PA-induced liver injury.

Bear bile powder attenuates senecionine-induced hepatic sinusoidal obstruction syndrome in mice

Hepatic sinusoidal obstruction syndrome(HSOS)via exposure to pyrrolizidine alkaloids(PAs)is with high mortality and there is no effective treatment in clinics.Bear bile powder(BBP)is a famous traditional animal drug for curing a variety of hepatobiliary diseases such as cholestasis,inflammation,and fibrosis.Here,we aim to evaluate the protective effect of BBP against HSOS induced by senecionine,a highly hepatotoxic PA compound.Our results showed that BBP treatment protected mice from senecionine-induced HSOS dose-dependently,which was evident by improved liver histology including reduced infiltration of inflammatory cells and collagen positive cells,alleviated intrahepatic hemorrhage and hepatic sinusoidal endothelial cells,as well as decreased conventional serum liver function indicators.In addition,BBP treatment lowered matrix metalloproteinase 9 and pyrrole-protein adducts,two well-known markers positively associated with the severity of PA-induced HSOS.Further investigation showed that BBP treatment prevents the development of liver fibrosis by decreasing transforming growth factor beta and downstream fibrotic molecules.BBP treatment also alleviated senecionine-induced liver inflammation and lowered the pro-inflammatory cytokines,in which taurours-odeoxycholic acid played an important role.What’s more,BBP treatment also decreased the accumulation of hydrophobic bile acids,such as cholic acid,taurocholic acid,glycocholic acid,as well.We concluded that BBP attenuates senecionine-induced HSOS in mice by repairing the bile acids homeostasis,preventing liver fibrosis,and alleviating liver inflammation.Our present study helps to pave the way to therapeutic approaches of the treatment of PA-induced liver injury in clinics.

Retrorsine Cooperates with Gut Microbiota to Promote Hepatic Sinusoidal Obstruction Syndrome by Disrupting the Gut Barrier

Background and Aims:Hepatic sinusoidal obstruction syndrome(HSOS)is a life-threatening syndrome,and a cause is exposure to pyrrolizidine alkaloid(PA)-containing products.It is well-established that retrorsine(RTS),a rep-resentative Pas,insults hepatic sinusoidal endothelial cells and ensues congestion of hepatic sinusoids.However,little known about the impact of Pas on gut microbiota and intesti-nal barrier and inflammation in HSOS.Methods:Mice were gavaged with or without nonabsorbable antibiotics(ABX),followed by a single dose of RTS.The gut microbiota was examined by 16S rDNA sequencing.Results:ABX pretreat-ment significantly reversed RTS-induced liver damage.RTS altered gut microbiota composition,increasing Gram-nega-tive bacteria and resulting in a sharp elevation of circulating lipopolysaccharides(LPS)in HSOS mice.Gut decontamina-tion with ABX alleviated RTS-induced intestine inflamma-tion,protected against disruption of the intestinal epithelial barrier and gut vascular barrier(GVB),and suppressed he-patic LPS-NF-κB pathway activation in RTS-induced HSOS.Importantly,the LPS level was positively correlated with MELD score in patients with HSOS.Elevated LPS in patients with HSOS confirmed that Gram-negative bacteria were in-volved in the pathogenesis of HSOS.Conclusions:RTS,a PA,cooperated with gut dysbiosis to cause intestinal inflam-mation and gut barrier compromise that increased transport of gut-derived LPS into the liver through the portal vein,which contributed to the pathology of HSOS.Modulating the gut microbiota,protecting the intestinal barrier,and sup-pressing intestinal inflammation with prebiotics or antibiot-ics might be a useful pharmacologic intervention in HSOS.

Genomic scanning enabling discovery of a new antibacterial bicyclic carbamate-containing alkaloid

Non-ribosomal peptides are a group of structurally diverse natural products with various important therapeutic and agrochemical applications.Bacterial pyrrolizidine alkaloids(PAs),containing a scaffold of two fused five-membered ring system with a nitrogen atom at the bridgehead,have been found to originate from a multidomain non-ribosomal peptide synthetase to generate indolizidine intermediates,followed by multistep oxidation,catalysed by single Bayer-Villiger(BV)enzymes,to yield PA scaffolds.Although bacterial PAs are rare in natural product inventory,bioinformatics analysis suggested that the biosynthetic gene clusters(BGCs)that are likely to be responsible for the production of PA-like metabolites are widely distributed in bacterial genomes.However,most of the strains containing PA-like BGCs are not deposited in the public domain,therefore preventing further assessment of the chemical spaces of this group of bioactive metabolites.Here,we report a genomic scanning strategy to assess the potential of PA metabolites production in our culture collection without prior knowledge of genome information.Among the strains tested,we found fifteen contain the key BV enzymes that are likely to be involved in the last step of PA ring formation.Subsequently one-strain-many-compound(OSMAC)method,supported by a combination of HR-MS,NMR,SMART 2.0 technology,and GNPS analysis,allowed identification and characterization of a new[5+7]heterobicyclic carbamate,legoncarbamate,together with five known PAs,bohemamine derivatives,from Streptomyces sp.CT37,a Ghanaian soil isolate.The absolute stereochemistry of legoncarbamate was determined by comparison of measured and calculated ECD spectra.Legoncarbamate displays antibacterial activity against E.coli ATCC 25922 with an MIC value of 3.1μg/mL.Finally,a biosynthetic model of legoncarbamate and other bohemamines was proposed based on the knowledge we have gained so far.

Discovery of New Bohemamines and Synthesis of Methylene-Bridged Chimeric Derivatives through Natural Product Chimera Strategy

Five new pyrrolizidine alkaloids,bohemamines J—N(1-5),were isolated from Streptomyces sp.CPCC 200497.Their structures were assigned based on detailed spectroscopic analysis and semisynthesis.Bohemamine J(1)possesses a new chimeric skeleton derived from bohemamine A(6)and phenylacetaldehyde.Inspired by the nonenzymatic formation mechanism of the methylene-bridged dimers isolated from this strain,we synthesized a series of chimeric derivatives(8,9,and 12-23)through natural product chimera strategy.Compounds 13,15,19,and 21 showed significant antioxidant activity.

Plant-herbivore assemblages under natural conditions are driven by plant size,not chemical defenses

Aims Plant secondary metabolites have been traditionally recognized as key traits regulating plant-herbivore assemblages.However,the ecological relevance of secondary metabolites as resistance mecha-nisms in comparison to other plant attributes,including physical,morphological or ecological traits,has been recently questioned.We aim to evaluate the role of chemical defenses,plant size and the presence of insect competitors on driving the differences in her-bivory damage under natural conditions.Methods We performed a replicated field study on the herbivore commu-nity associated with four Senecio species(S.lividus,S.vulgaris,S.inaequidens and S.pterophorus)during a full-reproductive season in Montseny Natural Park(catalonia,NE Spain).Pyrrolizidine alka-loids(PAs),the most characteristic chemical defenses of Senecio due to their toxic effects on herbivores,were analyzed by gas chro-matography.Individual plant size was estimated by the number of flower heads produced over the entire reproductive season.We used linear mixed models to explore the relationships between total PA concentrations,plant size and herbivory levels.Important Findings PA concentrations were not related to the natural guild of herbivores within any plant species or insect type.Moreover,no significant interactions were found between insect species sharing the same host plants.In contrast,herbivore abundance was positively related to plant size in S.vulgaris,S.lividus and S.inaequidens.We found no evidence that PAs confer an increased plant resistance against herbivores in Senecio.Our study supports the hypothesis that plant chemical defenses have a secondary role in determining plant-her-bivore assemblages in comparison to other plant traits under the complexity of natural conditions.