Formation of DHP-derived DNA adducts in vivo from dietary supplements and Chinese herbal plant extracts containing carcinogenic pyrrolizidine alkaloids

Biochemical biomarkers for the toxicity induced by Traditional Chinese Medicine: A review update

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine (TCM) is widely used in China for disease treatment and has become a valuable resource for drug development due to its high efficacy and low risk of side-effects. However, growing toxicity reports has garnered significant global attention. A major challenge in addressing TCM-induced toxicity is lack of specific and sensitive biomarkers for diagnosing and predicting its toxicity. Identifying toxicological biomarkers reflecting TCM-induced toxicity is crucial for timely detection and intervention, and provides significant clues for elucidating the underlying toxic mechanism and key target.

AIM OF THE STUDY

This article aims to summarize and classify some potential toxicological biomarkers for side-effects induced by TCM and its contained phytochemical ingredients.

METHODS

The keywords "biomarkers", "traditional Chinese medicine", "Chinese herb", "phytochemical ingredient", "natural product", "toxicity", "hepatotoxicity", "nephrotoxicity", "cardiotoxicity" were used to collect relevant information from literature databases (including PubMed, Web of Science) up to October 2024.

RESULTS

Research has indicated that more sensitive and specific biomarkers are needed for reflecting TCM's side-effects. PA-protein adducts and AA-DNA adducts could be served as diagnostic biomarkers for hepatotoxicity and nephrotoxicity induced by TCM containing PA and AA, respectively. Multiple miRNAs like miRNA-122-3p, miRNA-5099, and miRNA-21-3p, as well as some endogenous metabolites such as hypoxanthine, choline, and L-valine could be potential biomarkers associated with TCM-induced hepatotoxicity, nephrotoxicity, and cardiotoxicity.

CONCLUSION

In this review, different research demonstrates that DNA/protein-adducts, noncoding RNAs, endogenous metabolites and so on show the potential to be new early-warning biomarkers for TCM-induced toxicity with high specificity and sensitivity.

Association between pyrrolizidine alkaloids exposure and risk of abnormal serum indices-Insights from a descriptive cross-sectional study in Yunnan Province

The hazard of pyrrolizidine alkaloids (PAs) has been widely reported in animal studies but rarely in population-based research, especially reports about daily exposure. A single-centre descriptive cross-sectional study was conducted on 552 Lahu Autonomous County residents recruited in 2021. Blood PAs exposure biomarker (pyrrole- protein adduct, PPA) and serum biochemical indices were measured. The prevalence of abnormal serum indices and PAs exposure in this region were elucidated using descriptive analyses. 75 % of Lahu Autonomous County participants were exposed to PAs. PAs exposure risk in males was lower than in females (OR=0.357, 95 % CI: 0.222-0.574), and varied with the ethnicity of Lahu Autonomous County. PPA concentration was positively correlated with serum alanine transaminase (ALT) activity (r=0.6263, P < 0.01) and triglyceride level (r=0.2327, P < 0.01); PAs exposure was positively associated with anbormal serum ALT activity (x2=99.629, P < 0.001; OR=1.428, 95 % CI: 1.293-2.319) and hypertriglyceridemia (x2=15.376, P < 0.001; OR=1.629, 95 % CI: 1.229-2.251). These results suggest that PAs exposure might be a risk factor for serum ALT abnormality and hypertriglyceridemia in the local population. This study conducted the first epidemiological study on PAs exposure in China and established the etiological hypotheses for health issues in Lahu Autonomous County.

Formation of DHP-DNA Adducts from Rat Liver Microsomal Metabolism of 1,2-Unsaturated Pyrrolizidine Alkaloid-Containing Plant Extracts and Dietary Supplements

1,2-Unsaturated pyrrolizidine alkaloids (PAs) are carcinogenic phytochemicals. We previously determined that carcinogenic PAs and PA N-oxides commonly form a set of four (±)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-DNA adducts, namely, DHP-dG-3, DHP-dG-4, DHP-dA-3, and DHP-dA-4. This set of DHP-DNA adducts has been implicated as a potential biomarker of PA-induced liver tumor initiation from metabolism of individual carcinogenic PAs. To date, it is not known whether this generality occurs from metabolism of PA-containing plant extracts. In this study, we investigate the rat liver microsomal metabolism of nine PA-containing plant extracts and two PA-containing dietary supplements in the presence of calf thymus DNA. The presence of carcinogenic PAs and PA N-oxides in plant extracts was first confirmed by LC-MS/MS analysis with selected reaction monitoring mode. Upon rat liver microsomal metabolism of these PA-containing plant extracts and dietary supplements, the formation of this set of DHP-DNA adducts was confirmed. Thus, these results indicate that metabolism of PA-containing plant extracts and dietary supplements can generate DHP-dG-3, DHP-dG-4, DHP-dA-3, and DHP-dA-4 adducts, thereby potentially initiating liver tumor formation.

The chemical structure impairs the intensity of genotoxic effects promoted by 1,2-unsaturated pyrrolizidine alkaloids in vitro

1,2-unsaturated pyrrolizidine alkaloids (PAs) represent a large group of secondary plant metabolites exhibiting hepatotoxic, genotoxic, and carcinogenic properties upon bioactivation. To examine how the degree of esterification affects the genotoxic profile of PA we investigated cytotoxicity, histone H2AX phosphorylation, DNA strand break induction, cell cycle perturbation, micronuclei formation, and aneugenic effects in different cell models. Analysis of cytotoxicity and phosphorylation of histone H2AX was structure- and concentration-dependent: diester-type PAs (except monocrotaline) showed more pronounced effects than monoester-type PAs. Cell cycle analysis identified that diester-type PAs induced a S-phase arrest and a decrease in the occurrence of cells in the G1-phase. The same structure-dependency was observed by flow-cytometric analysis of PA-induced micronuclei in CYP3A4-overexpressing V79 cells. Analysis of centromeres induced by lasiocarpine in the micronuclei by fluorescence in situ hybridization indicated an aneugenic effect in V79_h3A4 cells. Comet assays revealed no significant induction of DNA strand breaks for all investigated PAs. Overall, diester-type PAs induced more pronounced effects than monoester-type PAs. Furthermore, our results indicate aneugenic effects upon exposure towards lasiocarpine in vitro. These data improve our understanding how structural features of PA influence the genotoxic profile. Especially, the monoester-type PAs seem to induce less severe effects than other PAs.

Diurnal hepatic CYP3A11 contributes to chronotoxicity of the pyrrolizidine alkaloid retrorsine in mice

1. Retrorsine (RTS) is a pyrrolizidine alkaloid (distributed in many medicinal plants) that has significant hepatotoxicity. Here, we aimed to determine the daily variations in RTS hepatotoxicity (chronotoxicity) in mice, and to investigate the role of metabolism in generating RTS chronotoxicity.2. Acute toxicity and pharmacokinetic studies were performed with mice after RTS administration at different times of the day. Hepatotoxicity was assessed by measuring plasma ALT (alanine aminotransferase) and AST (aspartate aminotransferase) levels. mRNA and proteins were determined by qPCR and Western blotting, respectively. Time-dependent in vitro metabolism of RTS was assessed by using mouse liver microsomes.3. We found that RTS toxicity was more severe in the dark phase (zeitgeber time 14 or ZT14 and ZT18) than in the light phase (ZT2 and ZT6). This chronotoxicity was associated with a dosing time difference in the systemic exposures of RTS and a pyrrolic ester metabolite (a cause of hepatotoxicity, measured by the levels of pyrrole-GSH conjugate and pyrrole-protein adducts due to a high chemical reactivity). Moreover, the CYP3A11 (a major enzyme for RTS bioactivation) inhibitor ketoconazole decreased the production of pyrrole-GSH conjugate and abrogated diurnal rhythm in RTS metabolism. In addition, E4bp4 (a circadian regulator of Cyp3a11) ablation abolished the rhythm of CYP3A11 expression and abrogated the dosing time-dependency of RTS toxicity.4. In conclusion, RTS chronotoxicity in mice was attributed to time-varying hepatic metabolism regulated by the circadian clock. Our findings have implications for reducing pyrrolizidine alkaloid-induced toxicity via a chronotherapeutic approach.

Symphytum Species: A Comprehensive Review on Chemical Composition, Food Applications and Phytopharmacology

Symphytum species belongs to the Boraginaceae family and have been used for centuries for bone breakages, sprains and rheumatism, liver problems, gastritis, ulcers, skin problems, joint pain and contusions, wounds, gout, hematomas and thrombophlebitis. Considering the innumerable potentialities of the Symphytum species and their widespread use in the world, it is extremely important to provide data compiling the available literature to identify the areas of intense research and the main gaps in order to design future studies. The present review aims at summarizing the main data on the therapeutic indications of the Symphytum species based on the current evidence, also emphasizing data on both the efficacy and adverse effects. The present review was carried out by consulting PubMed (Medline), Web of Science, Embase, Scopus, Cochrane Database, Science Direct and Google Scholar (as a search engine) databases to retrieve the most updated articles on this topic. All articles were carefully analyzed by the authors to assess their strengths and weaknesses, and to select the most useful ones for the purpose of review, prioritizing articles published from 1956 to 2018. The pharmacological effects of the Symphytum species are attributed to several chemical compounds, among them allantoin, phenolic compounds, glycopeptides, polysaccharides and some toxic pyrrolizidine alkaloids. Not less important to highlight are the risks associated with its use. In fact, there is increasing consumption of over-the-counter drugs, which when associated with conventional drugs can cause serious and even fatal adverse events. Although clinical trials sustain the folk topical application of Symphytum species in musculoskeletal and blunt injuries, with minor adverse effects, its antimicrobial potency was still poorly investigated. Further studies are needed to assess the antimicrobial spectrum of Symphytum species and to characterize the active molecules both in vitro and in vivo.

Symphytum Species: A Comprehensive Review on Chemical Composition, Food Applications and Phytopharmacology

Symphytum species belongs to the Boraginaceae family and have been used for centuries for bone breakages, sprains and rheumatism, liver problems, gastritis, ulcers, skin problems, joint pain and contusions, wounds, gout, hematomas and thrombophlebitis. Considering the innumerable potentialities of the Symphytum species and their widespread use in the world, it is extremely important to provide data compiling the available literature to identify the areas of intense research and the main gaps in order to design future studies. The present review aims at summarizing the main data on the therapeutic indications of the Symphytum species based on the current evidence, also emphasizing data on both the efficacy and adverse effects. The present review was carried out by consulting PubMed (Medline), Web of Science, Embase, Scopus, Cochrane Database, Science Direct and Google Scholar (as a search engine) databases to retrieve the most updated articles on this topic. All articles were carefully analyzed by the authors to assess their strengths and weaknesses, and to select the most useful ones for the purpose of review, prioritizing articles published from 1956 to 2018. The pharmacological effects of the Symphytum species are attributed to several chemical compounds, among them allantoin, phenolic compounds, glycopeptides, polysaccharides and some toxic pyrrolizidine alkaloids. Not less important to highlight are the risks associated with its use. In fact, there is increasing consumption of over-the-counter drugs, which when associated with conventional drugs can cause serious and even fatal adverse events. Although clinical trials sustain the folk topical application of Symphytum species in musculoskeletal and blunt injuries, with minor adverse effects, its antimicrobial potency was still poorly investigated. Further studies are needed to assess the antimicrobial spectrum of Symphytum species and to characterize the active molecules both in vitro and in vivo.

Hepatobiliary Events in Migraine Therapy with Herbs-The Case of Petadolex, A Petasites Hybridus Extract

Petadolex^®, a defined butterbur extract has clinically proven efficacy against migraine attacks. However, spontaneous reports indicate cases of herbal induced liver injury (HILI). While most HILI patients presented mild serum biochemistry changes (<3 ULN, dose range 50 to 225 mg/day; treatment duration 4–730 days) nine developed severe HILI (average time-to-onset 103 days, ALT-range 3–153; AST 2–104-fold ULN). HILI cases resolved after medication withdrawal though two patients required liver transplantation. Liver biopsies revealed an inconsistent injury pattern, i.e. necrosis, macrovesicular steatosis, inflammation, cholestasis, and bile duct proliferation. Causality assessment rated 3 cases likely, 13 possible, 8 unlikely and 24 as unclassifiable/unclassified. Note, 22 patients reported hepatotoxic co-medications especially during periods of pain. A no-observable-adverse-effect-level at 15-fold of the maximal clinical dose (3 mg/kg/day MCD) was established for rats. At >45 and 90-fold MCD bile duct hyperplasia was observed but could not be confirmed in an explorative minipig study at 218-fold MCD. Human hepatocyte studies at 49-fold C_max serum petasins (=active ingredient) and therapeutic Ibuprofen, Paracetamol and Naratriptan concentrations evidenced liver transaminase and CYP-monooxygenase changes. Collectively, Petadolex^® HILI cases are rare, idiosyncratic and frequently confounded by co-medications. A physician-supervised self-medication plan with herbs and pain relief medication is needed to minimize risk for HILI.

Naturally complex: Perspectives and challenges associated with Botanical Dietary Supplement Safety assessment

Due to the extensive use of botanical dietary supplements by consumers in the United States, there is a need for appropriate research and data to support safety assessments. Complexity and variability, both natural and introduced, of botanical dietary supplements make research on these products difficult. Botanical dietary supplements are regulated by the Food and Drug Administration (FDA) under the Federal Food, Drug, and Cosmetic Act (FD&C Act), as amended by the 1994 Dietary Supplement Health and Education Act (DSHEA). They are regulated as a category of food, which differs from the regulation of pharmaceutical products. Both manufacturers and the FDA are faced with the challenge of determining the best approaches for evaluating and monitoring the safety of botanical products. High quality botanicals research requires accurate identification and characterization of the material being studied. Inconsistent results in efficacy studies of botanical dietary supplements have led to efforts to improve the rigor and reproducibility of research in the field. Addressing the challenges associated with botanical dietary supplement safety is a global effort requiring coordination between numerous stakeholders, including researchers, suppliers, manufacturers, and regulators, all of whom play a role in ensuring that high quality products are available on the market.

Toxicity of plant extracts containing pyrrolizidine alkaloids using alternative invertebrate models

Pyrrolizidine alkaloids (PAs) are a widespread class of hepatotoxic heterocyclic organic compounds found in approximately 3% of world flora. Some PAs have been shown to have genotoxic and carcinogenic effects. The present study focuses on the toxicity effects of four dry extracts obtained from medicinal plants (Senecio vernalis, Symphytum officinale, Petasites hybridus and Tussilago farfara), on two aquatic organisms, Artemia salina and Daphnia magna, and the correlation with their PAs content. A new GC‑MS method, using a retention time (TR)‑5MS type capillary column was developed. PAs Kovats retention indices, for this type of column were computed for the first time. The lethal dose 50% (LC50) values for the two invertebrate models were correlated (Pearson 's coefficient, >0.9) and the toxicity was PA concentration-dependent, for three of the four extracts. All tested extracts were found to be toxic in both aquatic organism models. The results can be used to develop a GC‑MS validated method for the assay of PAs in medicinal plants with a further potential application in the risk assessment study of PAs toxicity in humans.

Mitochondrial dysfunction as a mechanism of drug-induced hepatotoxicity: current understanding and future perspectives

Mitochondria are critical cellular organelles for energy generation and are now also recognized as playing important roles in cellular signaling. Their central role in energy metabolism, as well as their high abundance in hepatocytes, make them important targets for drug-induced hepatotoxicity. This review summarizes the current mechanistic understanding of the role of mitochondria in drug-induced hepatotoxicity caused by acetaminophen, diclofenac, anti-tuberculosis drugs such as rifampin and isoniazid, anti-epileptic drugs such as valproic acid and constituents of herbal supplements such as pyrrolizidine alkaloids. The utilization of circulating mitochondrial-specific biomarkers in understanding mechanisms of toxicity in humans will also be examined. In summary, it is well-established that mitochondria are central to acetaminophen-induced cell death. However, the most promising areas for clinically useful therapeutic interventions after acetaminophen toxicity may involve the promotion of adaptive responses and repair processes including mitophagy and mitochondrial biogenesis, In contrast, the limited understanding of the role of mitochondria in various aspects of hepatotoxicity by most other drugs and herbs requires more detailed mechanistic investigations in both animals and humans. Development of clinically relevant animal models and more translational studies using mechanistic biomarkers are critical for progress in this area.

Relevance for patients:This review focuses on the role of mitochondrial dysfunction in liver injury mechanisms of clinically important drugs like acetaminophen, diclofenac, rifampicin, isoniazid, amiodarone and others. A better understanding ofthe mechanisms in animal models and their translation to patients will be critical for the identification of new therapeutic targets.

7-Glutathione-pyrrole and 7-cysteine-pyrrole are potential carcinogenic metabolites of pyrrolizidine alkaloids

Many pyrrolizidine alkaloids (PAs) are hepatotoxic, genotoxic, and carcinogenic phytochemicals. Metabolism of PAs in vivo generates four (±)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-DNA adducts that have been proposed to be responsible for PA-induced liver tumor formation in rats. In this present study, we determined that the same set of DHP-DNA adducts was formed upon the incubation of 7-glutathione-DHP and 7-cysteine-DHP with cultured human hepatocarcinoma HepG2 cells. These results suggest that 7-glutathione-DHP and 7-cysteine-DHP are reactive metabolites of PAs that can bind to cellular DNA to form DHP-DNA adducts in HepG2 cells, and can potentially initiate liver tumor formation.

7-N-Acetylcysteine-pyrrole conjugate-A potent DNA reactive metabolite of pyrrolizidine alkaloids

Plants containing pyrrolizidine alkaloids (PAs) are widespread throughout the world and are the most common poisonous plants affecting livestock, wildlife, and humans. PAs require metabolic activation to form reactive dehydropyrrolizidine alkaloids (dehydro-PAs) that are capable of alkylating cellular DNA and proteins, form (±)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-DNA and DHP-protein adducts, and lead to cytotoxicity, genotoxicity, and tumorigenicity. In this study, we determined that the metabolism of riddelliine and monocrotaline by human and rat liver microsomes in the presence of N-acetylcysteine both produced 7-N-acetylcysteine-DHP (7-NAC-DHP) and DHP. Reactions of 7-NAC-DHP with 2'-deoxyguanosine (dG), 2'-deoxyadenosine (dA), and calf thymus DNA in aqueous solution followed by enzymatic hydrolysis yielded DHP-dG and/or DHP-dA adducts. These results indicate that 7-NAC-DHP is a reactive metabolite that can lead to DNA adduct formation.

Identification of Toxic Pyrrolizidine Alkaloids and Their Common Hepatotoxicity Mechanism

Pyrrolizidine Alkaloids (PAs) are currently one of the most important botanical hepatotoxic ingredients. Glutathion (GSH) metabolism is the most reported pathway involved in hepatotoxicity mechanism of PAs. We speculate that, for different PAs, there should be a common mechanism underlying their hepatotoxicity in GSH metabolism. Computational methods were adopted to test our hypothesis in consideration of the limitations of current experimental approaches. Firstly, the potential targets of 22 PAs (from three major PA types) in GSH metabolism were identified by reverse docking; Secondly, glutathione S-transferase A1 (GSTA1) and glutathione peroxidase 1 (GPX1) targets pattern was found to be a special characteristic of toxic PAs with stepwise multiple linear regressions; Furthermore, the molecular mechanism underlying the interactions within toxic PAs and these two targets was demonstrated with the ligand-protein interaction analysis; Finally, GSTA1 and GPX1 were proved to be significant nodes in GSH metabolism. Overall, toxic PAs could be identified by GSTA1 and GPX1 targets pattern, which suggests their common hepatotoxicity mechanism: the interfering of detoxication in GSH metabolism. In addition, all the strategies developed here could be extended to studies on toxicity mechanism of other toxins.

7-cysteine-pyrrole conjugate: A new potential DNA reactive metabolite of pyrrolizidine alkaloids

Pyrrolizidine alkaloids (PAs) require metabolic activation to exert cytotoxicity, genotoxicity, and tumorigenicity. We previously reported that (±)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived DNA adducts are responsible for PA-induced liver tumor formation in rats. In this study, we determined that metabolism of riddelliine and monocrotaline by human or rat liver microsomes produced 7-cysteine-DHP and DHP. The metabolism of 7-glutathionyl-DHP by human and rat liver microsomes also generated 7-cysteine-DHP. Further, reaction of 7-cysteine-DHP with calf thymus DNA in aqueous solution yielded the described DHP-derived DNA adducts. This study represents the first report that 7-cysteine-DHP is a new PA metabolite that can lead to DNA adduct formation.

Safety concerns of herbal products and traditional Chinese herbal medicines: dehydropyrrolizidine alkaloids and aristolochic acid

In many countries, including the United States, herbal supplements, tisanes and vegetable products, including traditional Chinese medicines, are largely unregulated and their content is not registered, monitored or verified. Consequently, potent plant toxins including dehydropyrrolizidine alkaloids and other potential carcinogens can contaminate these products. As herbal and food supplement producers are left to their own means to determine the safety and purity of their products prior to marketing, disturbingly often good marketing practices currently in place are ignored and content is largely undocumented. Historical examples of poisoning and health issues relating to plant material containing dehydopyrrolizidine alkaloids and aristolochic acids were used as examples to demonstrate the risk and potential toxicity of herbal products, food supplements, or traditional medicines. More work is needed to educate consumers of the potential risk and require the industry to be more responsible to verify the content and insure the safety of their products.

Detection of pyrrolizidine alkaloids in German licensed herbal medicinal teas

BACKGROUND

Because of the hepatotoxic, mutagenic, and cancerogenic effects of pyrrolizidine alkaloids (PAs) the German Federal Institute for Risk Assessment (BfR) recommends not to exceed a daily PA intake of 0.007 µg/kg body weight (0.42 µg/60 kg adult). In a recent study conducted by the BfR, up to 5647 µg PA/kg dried herbal material were detected in tea products marketed as food.

PURPOSE

The present study aimed at elucidating whether medicinal teas licensed or registered as medicinal products contain PAs as well.

STUDY DESIGN

One hundred sixty-nine different commercially available medicinal teas, i.e. 19 nettle (Urtica dioica L.), 12 fennel (Foeniculum vulgare Mill.), 14 chamomile (Matricaria recutita L.), 11 melissa (Melissa officinalis L.) and 4 peppermint (Mentha piperita L.) teas as well as 109 tea mixtures were analyzed for the presence of 23 commercially available PAs.

METHOD

LC/MS was used for the determination of the PAs

RESULTS

In general, the total PA contents ranging 0-5668 µg/kg. Thirty percent of the tested single-ingredient tea products and 56.9% of the tested medicinal tea mixtures were found to contain PA concentrations above the limit of quantification (LOQ) of 10 µg/kg. In 11 medicinal teas PA contents >300 µg/kg dry herb were determined thus exceeding the recommended limit for PA intake by BfR. In addition three products of the investigated tea mixtures revealed extremely high PA contents of 4227, 5137, and 5668 µg/kg. Generally, single-ingredient tea products contained much less or even no detectable amounts of PAs when compared to the tea mixtures. PAs in the range between 13 and 1080 µg/kg were also detected in five analyzed aqueous herbal infusions of the medicinal tea mixture products with the highest PA content. Two out of the five investigated herbal infusions exceeded the recommended BfR limit for PA intake.

CONCLUSION

This study demonstrates clearly that also medicinal teas licensed as medicinal products may partly contain high amounts of PAs exceeding current recommendations. For that reason manufacturers are advised to carry out more rigorous quality control tests devoted to the detection of PAs. This is very important to minimize PAs in medicinal teas accounting for possible additional exposure of the consumer to PAs from other food sources (e.g. honey).

Pyrrolizidine Alkaloids: Potential Role in the Etiology of Cancers, Pulmonary Hypertension, Congenital Anomalies, and Liver Disease

Large outbreaks of acute food-related poisoning, characterized by hepatic sinusoidal obstruction syndrome, hemorrhagic necrosis, and rapid liver failure, occur on a regular basis in some countries. They are caused by 1,2-dehydropyrrolizidine alkaloids contaminating locally grown grain. Similar acute poisoning can also result from deliberate or accidental consumption of 1,2-dehydropyrrolizidine alkaloid-containing herbal medicines, teas, and spices. In recent years, it has been confirmed that there is also significant, low-level dietary exposure to 1,2-dehydropyrrolizidine alkaloids in many countries due to consumption of common foods such as honey, milk, eggs, salads, and meat. The level of 1,2-dehydropyrrolizidine alkaloids in these foods is generally too low and too intermittent to cause acute toxicity. However, these alkaloids are genotoxic and can cause slowly developing chronic diseases such as pulmonary arterial hypertension, cancers, cirrhosis, and congenital anomalies, conditions unlikely to be easily linked with dietary exposure to 1,2-dehydropyrrolizidine alkaloids, especially if clinicians are unaware that such dietary exposure is occurring. This Perspective provides a comprehensive review of the acute and chronic toxicity of 1,2-dehydropyrrolizidine alkaloids and their potential to initiate certain chronic diseases, and suggests some associative considerations or indicators to assist in recognizing specific cases of diseases that may have resulted from dietary exposure to these hazardous natural substances. If it can be established that low-level dietary exposure to 1,2-dehydropyrrolizidine alkaloids is a significant cause of some of these costly and debilitating diseases, then this should lead to initiatives to reduce the level of these alkaloids in the food chain.

Involvement of organic cation transporter 1 and CYP3A4 in retrorsine-induced toxicity

Retrorsine (RTS) is a hepatotoxic pyrrolizidine alkaloid present in plants of the Senecio genus. The present study is aimed at clarifying the role of organic cation transporters (OCTs) in the liver disposition of RTS, and the coupling of OCT1 and cytochrome P450 (CYP) 3A4 in the hepatotoxicity of RTS. MDCK or LLC-PK1 cells stably expressing liver uptake or efflux transporters were used to investigate the interaction of RTS with these transporters. Primary cultured rat hepatocytes (PCRH) and double-transfected MDCK-hOCT1-CYP3A4 cells were used to determine the contribution of OCT1 and CYP3A4 to the toxicity of RTS. The results showed that RTS inhibited the OCT1-mediated 1-methyl-4-phenylpyridinium (MPP(+)) uptake in MDCK-hOCT1 cells with the IC50 of 2.25±0.30μM. The uptake of RTS in MDCK-hOCT1 cells and PCRH was significantly inhibited by OCT1 inhibitors, while hOCT3, human multidrug and toxin extrusion (hMATE) transporter 1, multidrug resistance 1 (MDR1), and breast cancer resistance protein (BCRP) showed weak or no obvious interaction with RTS. The toxic effect of RTS on the PCRH was attenuated by OCT1 inhibitors, quinidine and (+)-tetrahydropalmatine ((+)-THP). Compared to mock cells, MDCK-CYP3A4 cells showed a decrease in viability after being treated with RTS. Furthermore, RTS showed a more severe toxicity in the OCT1/CYP3A4 double-transfected cells compared to all other cells. Our data suggests that OCT1 mediates the liver-specific uptake of RTS, and plays an important role in RTS-induced hepatotoxicity together with CYP3A4. Consequently, the OCT1 inhibitors could be applied to protect the liver from the toxicity of RTS.

Metabolic activation of pyrrolizidine alkaloids leading to phototoxicity and photogenotoxicity in human HaCaT keratinocytes

Pyrrolizidine alkaloids, produced by a large number of poisonous plants with wide global distribution, are associated with genotoxicity, tumorigenicity, and hepatotoxicity in animals and humans. Mammalian metabolism converts pyrrolizidine alkaloids to reactive pyrrolic metabolites (dehydropyrrolizidine alkaloids) that form covalent protein and DNA adducts. Although a mechanistic understanding is currently unclear, pyrrolizidine alkaloids can cause secondary (hepatogenous) photosensitization and induce skin cancer. In this study, the phototoxicity of monocrotaline, riddelliine, dehydromonocrotaline, dehydroriddelliine, and dehydroretronecine (DHR) in human HaCaT keratinocytes under ultraviolet A (UVA) irradiation was determined. UVA irradiation of HaCaT cells treated with dehydromonocrotaline, dehydroriddelline, and DHR resulted in increased release of lactate dehydrogenase and enhanced photocytotoxicity proportional to the UVA doses. UVA-induced photochemical DNA damage also increased proportionally with dehydromonocrotaline and dehydroriddelline. UVA treatment potentiated the formation of 8-hydroxy-2'-deoxyguanosine DNA adducts induced by dehydromonocrotaline in HaCaT skin keratinocytes. Using electron spin resistance trapping, we found that UVA irradiation of dehydromonocrotaline and dehydroriddelliine generates reactive oxygen species (ROS), including hydroxyl radical, singlet oxygen, and superoxide, and electron transfer reactions, indicating that cytotoxicity and genotoxicity of these compounds could be mediated by ROS. Our results suggest that dehydropyrrolizidine alkaloids formed or delivered to the skin cause pyrrolizidine alkaloid-induced secondary photosensitization and possible skin cancer.

Evidence-based toxicity evaluation and scheduling of Chinese herbal medicines

ETHNOPHARMACOLOGICAL RELEVANCE

While there is an increasing number of toxicity report cases and toxicological studies on Chinese herbal medicines, the guidelines for toxicity evaluation and scheduling of Chinese herbal medicines are lacking.

AIM

The aim of this study was to review the current literature on potentially toxic Chinese herbal medicines, and to develop a scheduling platform which will inform an evidence-based regulatory framework for these medicines in the community.

MATERIALS AND METHODS

The Australian and Chinese regulations were used as a starting point to compile a list of potentially toxic herbs. Systematic literature searches of botanical and pharmaceutical Latin name, English and Chinese names and suspected toxic chemicals were conducted on Medline, PubMed and Chinese CNKI databases.

RESULTS

Seventy-four Chinese herbal medicines were identified and five of them were selected for detailed study. Preclinical and clinical data were summarised at six levels. Based on the evaluation criteria, which included risk-benefit analysis, severity of toxic effects and clinical and preclinical data, four regulatory classes were proposed: Prohibited for medicinal usage, which are those with high toxicity and can lead to injury or death, e.g., aristolochia; Restricted for medicinal usage, e.g., aconite, asarum, and ephedra; Required warning label, e.g., coltsfoot; and Over-the-counter herbs for those herbs with a safe toxicity profile.

CONCLUSION

Chinese herbal medicines should be scheduled based on a set of evaluation criteria, to ensure their safe use and to satisfy the need for access to the herbs. The current Chinese and Australian regulation of Chinese herbal medicines should be updated to restrict the access of some potentially toxic herbs to Chinese medicine practitioners who are qualified through registration.

MicroRNAs and their predicted target messenger RNAs are deregulated by exposure to a carcinogenic dose of comfrey in rat liver

MicroRNAs (MiRNAs) are small noncoding RNAs that function as regulators of gene expression to control cell growth and differentiation. In this study, we analyzed miRNA and mRNA expression in the livers of rats treated with a carcinogenic dose of comfrey (Symphytum officinale) for 12 weeks. Groups of six rats were fed a normal diet or a diet containing 8% comfrey root. The animals were sacrificed 1 day after the last treatment and the livers were isolated for miRNA expression analysis using LC Sciences miRNA microarrays and for mRNA expression analysis using Affymetrix rat genome microarrays. MiRNA expression levels were significantly changed by comfrey treatment. The treated samples were separated clearly from the control samples in both principal component analysis (PCA) and hierarchical clustering analysis (HCA). Quantitative measurements of seven miRNAs using TaqMan real-time PCR were consistent with the microarray results in terms of fold-change and the direction of the change in expression. Forty-five miRNAs (P < 0.01) and 1,921 mRNAs (q = 0) were significantly changed by comfrey treatment. Using a target prediction algorithm, 434 differentially expressed genes (DEGs) were predicted to be targeted by the differentially expressed miRNAs (DEMs). The DEM-targeted DEGs were more likely to be involved in carcinogenesis than the DEGs that were not targeted by the DEMs. The nontargeted DEGs were enriched in noncancer-related biological processes. Our data suggest that comfrey may exert its carcinogenic effects by disturbing miRNA expression resulting in altered mRNA levels of the DEM-targeted genes that are functionally associated with carcinogenesis.

Photoirradiation of dehydropyrrolizidine alkaloids--formation of reactive oxygen species and induction of lipid peroxidation

Pyrrolizidine alkaloid (PA)-containing plants are widespread in the world and are probably the most common poisonous plants affecting livestock, wildlife, and human. PAs require metabolic activation to generate pyrrolic metabolites (dehydro-PAs) that bind cellular protein and DNA, leading to hepatotoxicity and genotoxicity, including tumorigenicity. In this study we report that UVA photoirradiation of a series of dehydro-PAs, e.g., dehydromonocrotaline, dehydroriddelliine, dehydroretrorsine, dehydrosenecionine, dehydroseneciphylline, dehydrolasiocarpine, dehydroheliotrine, and dehydroretronecine (DHR) at 0-70 J/cm2 in the presence of a lipid, methyl linoleate, resulted in lipid peroxidation in a light dose-responsive manner. When irradiated in the presence of sodium azide, the level of lipid peroxidation decreased; lipid peroxidation was enhanced when methanol was replaced by deuterated methanol. These results suggest that singlet oxygen is a photo-induced product. When irradiated in the presence of superoxide dismutase, the level of lipid peroxidation decreased, indicating that lipid peroxidation is also mediated by superoxide. Electron spin resonance (ESR) spin trapping studies confirmed that both singlet oxygen and superoxide anion radical were formed during photoirradiation. These results indicate that UVA photoirradiation of dehydro-PAs generates reactive oxygen species (ROS) that mediated the initiation of lipid peroxidation. UVA irradiation of the parent PAs and other PA metabolites, including PA N-oxides, under similar experimental conditions did not produce lipid peroxidation. It is known that PAs induce skin cancer and are secondary (hepatogenous) photosensitization agents. Our results suggest that dehydro-PAs are the active metabolites responsible for skin cancer formation and PA-induced secondary photosensitization.

Metabolism, genotoxicity, and carcinogenicity of comfrey

Comfrey has been consumed by humans as a vegetable and a tea and used as an herbal medicine for more than 2000 years. Comfrey, however, produces hepatotoxicity in livestock and humans and carcinogenicity in experimental animals. Comfrey contains as many as 14 pyrrolizidine alkaloids (PA), including 7-acetylintermedine, 7-acetyllycopsamine, echimidine, intermedine, lasiocarpine, lycopsamine, myoscorpine, symlandine, symphytine, and symviridine. The mechanisms underlying comfrey-induced genotoxicity and carcinogenicity are still not fully understood. The available evidence suggests that the active metabolites of PA in comfrey interact with DNA in liver endothelial cells and hepatocytes, resulting in DNA damage, mutation induction, and cancer development. Genotoxicities attributed to comfrey and riddelliine (a representative genotoxic PA and a proven rodent mutagen and carcinogen) are discussed in this review. Both of these compounds induced similar profiles of 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived DNA adducts and similar mutation spectra. Further, the two agents share common mechanisms of drug metabolism and carcinogenesis. Overall, comfrey is mutagenic in liver, and PA contained in comfrey appear to be responsible for comfrey-induced toxicity and tumor induction.

Genotoxicity of pyrrolizidine alkaloids

Pyrrolizidine alkaloids (PAs) are common constituents of many plant species around the world. PA-containing plants are probably the most common poisonous plants affecting livestock and wildlife. They can inflict harm to humans through contaminated food sources, herbal medicines and dietary supplements. Half of the identified PAs are genotoxic and many of them are tumorigenic. The mutagenicity of PAs has been extensively studied in different biological systems. Upon metabolic activation, PAs produce DNA adducts, DNA cross-linking, DNA breaks, sister chromatid exchange, micronuclei, chromosomal aberrations, gene mutations and chromosome mutations in vivo and in vitro. PAs induced mutations in the cII gene of rat liver and in the p53 and K-ras genes of mouse liver tumors. It has been suggested that all PAs produce a set of (+/-)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine-derived DNA adducts and similar types of gene mutations. The signature types of mutations are G : C --> T : A transversion and tandem base substitutions. Overall, PAs are mutagenic in vivo and in vitro and their mutagenicity appears to be responsible for the carcinogenesis of PAs.

Comfrey (Symphytum Officinale. l.) and Experimental Hepatic Carcinogenesis: A Short-term Carcinogenesis Model Study

Comfrey or Symphytum officinale (L.) (Boraginaceae) is a very popular plant used for therapeutic purposes. Since the 1980s, its effects have been studied in long-term carcinogenesis studies, in which Comfrey extract is administered at high doses during several months and the neoplastic hepatic lesions are evaluated. However, the literature on this topic is very poor considering the studies performed under short-term carcinogenesis protocols, such as the 'resistant hepatocyte model' (RHM). In these studies, it is possible to observe easily the phenomena related to the early phases of tumor development, since pre-neoplastic lesions (PNLs) rise in about 1-2 months of chemical induction. Herein, the effects of chronic oral treatment of rats with 10% Comfrey ethanolic extract were evaluated in a RHM. Wistar rats were sequentially treated with N-nitrosodiethylamine (ip) and 2-acetilaminofluorene (po), and submitted to hepatectomy to induce carcinogenesis promotion. Macroscopic/microscopic quantitative analysis of PNL was performed. Non-parametric statistical tests (Mann-Whitney and χ(2)) were used, and the level of significance was set at P ≤ 0.05. Comfrey treatment reduced the number of pre-neoplastic macroscopic lesions up to 1 mm (P ≤ 0.05), the percentage of oval cells (P = 0.0001) and mitotic figures (P = 0.007), as well as the number of Proliferating Cell Nuclear Antigen (PCNA) positive cells (P = 0.0001) and acidophilic pre-neoplastic nodules (P = 0.05). On the other hand, the percentage of cells presenting megalocytosis (P = 0.0001) and vacuolar degeneration (P = 0.0001) was increased. Scores of fibrosis, glycogen stores and the number of nucleolus organizing regions were not altered. The study indicated that oral treatment of rats with 10% Comfrey alcoholic extract reduced cell proliferation in this model.

Retrorsine, but not monocrotaline, is a mechanism-based inactivator of P450 3A4

Retrorsine (RTS) and monocrotaline (MCT) cause severe toxicities via P450-mediated metabolic activation. The screening of mechanism-based inhibitors showed RTS inactivated 3A4 in the presence of NADPH. Unlike RTS, MCT failed to inhibit P450 3A4 and other enzymes tested. Further studies showed the loss of P450 3A4 activity occurred in a time- and concentration-dependent way, which was not recovered after dialysis. Dextromethorphan, a P450 3A4 substrate, protected the enzyme from the inactivation. Exogenous nucleophile glutathione (GSH) and reactive oxygen species scavengers catalase and superoxide dismutase did not protect P450 3A4 from the inactivation. GSH trapping experiments showed both P450 3A4 and 2C19 converted RTS and MCT to the corresponding electrophilic metabolites which could be trapped by GSH to form 7-GSH-DHP conjugate. We conclude that RTS and MCT are metabolically activated by P450 3A4 and 2C19, and that RTS, but not MCT, is a mechanism-based inactivator of P450 3A4.

Gene expression profiling as an initial approach for mechanistic studies of toxicity and tumorigenicity of herbal plants and herbal dietary supplements

Dietary supplements are consumed by more than 300 million people worldwide, and herbal dietary supplements represent the most rapidly growing portion of this industry. Even though adverse health effects of many herbal dietary supplements have been reported, safety assurances are not being addressed adequately. Toxicological data on the identification of genotoxic and tumorigenic ingredients in many raw herbs are also lacking. Currently, more than 30 herbal dietary supplements and active ingredients have been selected by the National Toxicology Program (NTP) for toxicity and tumorigenicity studies. Due to the complexity of the chemical components present in plant extracts, there are no established methodologies for determining the mechanisms of toxicity (particularly tumorigenicity) induced by herbs, such as Gingko biloba leaf extract (GBE) and other herbal plant extracts. Consequently, the understanding of toxicity of herbal dietary supplements remains limited. We have proposed that application of DNA microarrays could be a highly practical initial approach for revealing biological pathways and networks associated with toxicity induced by herbal dietary supplements and the generation of hypotheses to address likely mechanisms. The changes in expression of subsets of genes of interest, such as the modulation of drug metabolizing genes, can be analyzed after treatment with an herbal dietary supplement. Although levels of gene expression do not represent fully the levels of protein activities, we propose that subsequent biochemical and genomic experiments based on these initial observations will enable elucidation of the mechanisms leading to toxicity, including tumorigenicity. This review summarizes the current practices of microarray analysis of gene expressions in animals treated with herbal dietary supplements and discusses perspectives for the proposed strategy.

Quality assurance and safety of herbal dietary supplements

Since the U.S. Congress passed the Dietary Supplement Health and Education Act (DSHEA) in 1994, use of herbal products has been growing rapidly worldwide. To ensure consumer health protection, the quality and safety of herbal plants, particularly those used for dietary supplement preparations, must be determined. To date, toxicological data on the identification of genotoxic and tumorigenic ingredients in many raw herbs and their mechanisms of action are lacking. Thus, identification of carcinogenic components in herbal plants is timely and important. In this review, the issues of quality control and safety evaluation of raw herbs and herbal dietary supplements are discussed. Two examples of tumorigenicity and mechanism of tumor induction are discussed: aristolochic acid and riddelliine, both of which have been detected in Chinese herbal plants. It is proposed that an organized effort with international participation on cancer risk assessment should be actively pursued so that the safety of commercial herbal plants and herbal dietary supplements can be ensured.

Analysis of gene expression changes of drug metabolizing enzymes in the livers of F344 rats following oral treatment with kava extract

The association of kava product use with liver-related risks has prompted regulatory action in many countries. We studied the changes in gene expression of drug metabolizing enzymes in the livers of Fischer 344 male rats administered kava extract by gavage for 14 weeks. Analysis of 22,226 genes revealed that there were 14, 41, 110, 386, and 916 genes significantly changed in the 0.125, 0.25, 0.5, 1.0, and 2.0 g/kg treatment groups, respectively. There were 16 drug metabolizing genes altered in all three high-dose treatment groups, among which seven genes belong to cytochrome P450 isozymes. While gene expression of Cyp1a1, 1a2, 2c6, 3a1, and 3a3 increased; Cyp 2c23 and 2c40 decreased, all in a dose-dependent manner. Real-time PCR analyses of several genes verified these results. Our results indicate that kava extract can significantly modulate drug metabolizing enzymes, particularly the CYP isozymes, which could cause herb-drug interactions and may potentially lead to hepatotoxicity.

Chemical markers for the quality control of herbal medicines: an overview

Selection of chemical markers is crucial for the quality control of herbal medicines, including authentication of genuine species, harvesting the best quality raw materials, evaluation of post-harvesting handling, assessment of intermediates and finished products, and detection of harmful or toxic ingredients. Ideal chemical markers should be the therapeutic components of herbal medicines. However, for most herbal medicines, the therapeutic components have not been fully elucidated or easily monitored. Bioactive, characteristic, main, synergistic, correlative, toxic and general components may be selected. This article reviews the effective use of chemical markers in the quality control of herbal medicines including the selection criteria considering the roles and physicochemical factors which may affect the effective use of chemical markers.

Formation of DHP-derived DNA adducts from metabolic activation of the prototype heliotridine-type pyrrolizidine alkaloid, heliotrine

Pyrrolizidine alkaloid-containing plants are widespread in the world and may be the most common poisonous plants affecting livestock, wildlife, and humans. Pyrrolizidine alkaloids require metabolism to exert their genotoxicity and tumorigenicity. Our mechanistic studies have determined that metabolism of the retronecine-type (riddelliine, retrorsine, and monocrotaline), heliotridine-type (lasiocarpine), and otonecine-type (clivorine) tumorigenic pyrrolizidine alkaloids in vivo and/or in vitro all generates a common set of 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived DNA adducts responsible for tumor induction. All the pyrrolizidine alkaloids studied previously are diesters with an ester linkage at the C7 and C9 positions of the necine base. In this study, we report that F344 rat liver microsomal metabolism of heliotrine, a tumorigenic monoester bearing a hydroxyl group at the C7 of the necine base, resulted in the formation of the dehydroheliotridine (DHH) metabolite. When incubations of heliotrine were carried out in the presence of calf thymus DNA, the same set of DHP-derived DNA adducts was formed. These results support that DHP-derived DNA adducts are potential common biomarkers of pyrrolizidine alkaloid exposure and tumorigenicity. For comparison, the dehydroretronecine (DHR)-derived DNA adducts formed from metabolism of riddleiine, retrorsine, monocrotaline, riddelleiine N-oxide, and retrorsine N-oxide were measured in parallel; the levels of DHP-derived DNA adduct formation were in the order: riddelliine approximately retrorsine>monocrotaline>retrorsine N-oxide>or=riddelliine N-oxide>heliotrine.