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Widjaja F, Zheng L, Wesseling S, Rietjens IMCM. Physiologically based kinetic modeling of senecionine N-oxide in rats as a new approach methodology to define the effects of dose and endpoint used on relative potency values of pyrrolizidine alkaloid N-oxides. Front Pharmacol 2023; 14:1125146. [PMID: 36937884 PMCID: PMC10017778 DOI: 10.3389/fphar.2023.1125146] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 02/14/2023] [Indexed: 03/06/2023] Open
Abstract
Over 1,000 pyrrolizidine alkaloids (PAs) and their N-oxides (PA-N-oxides) occur in 3% of all flowering plants. PA-N-oxides are toxic when reduced to their parent PAs, which are bioactivated into pyrrole intermediates that generate protein- and DNA-adducts resulting in liver toxicity and carcinogenicity. Literature data for senecionine N-oxide in rats indicate that the relative potency (REP) value of this PA-N-oxide compared to its parent PA senecionine varies with the endpoint used. The first endpoint was the ratio between the area under the concentration-time curve (AUC) for senecionine upon dosing senecionine N-oxide or an equimolar dose of senecionine, while the second endpoint was the ratio between the amount for pyrrole-protein adducts formed under these conditions. This study aimed to investigate the mode of action underlying this endpoint dependent REP value for senecionine N-oxide with physiologically based kinetic (PBK) modeling. Results obtained reveal that limitation of 7-GS-DHP adduct formation due to GSH depletion, resulting in increased pyrrole-protein adduct formation, occurs more likely upon high dose oral PA administration than upon an equimolar dose of PA-N-oxide. At high dose levels, this results in a lower REP value when based on pyrrole-protein adduct levels than when based on PA concentrations. At low dose levels, the difference no longer exists. Altogether, the results of the study show how the REP value for senecionine N-oxide depends on dose and endpoint used, and that PBK modeling provides a way to characterize REP values for PA-N-oxides at realistic low dietary exposure levels, thus reducing the need for animal experiments.
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He Y, Zhu L, Ma J, Lin G. Metabolism-mediated cytotoxicity and genotoxicity of pyrrolizidine alkaloids. Arch Toxicol 2021; 95:1917-1942. [PMID: 34003343 DOI: 10.1007/s00204-021-03060-w] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 04/21/2021] [Indexed: 02/06/2023]
Abstract
Pyrrolizidine alkaloids (PAs) and PA N-oxides are common phytotoxins produced by over 6000 plant species. Humans are frequently exposed to PAs via ingestion of PA-containing herbal products or PA-contaminated foods. PAs require metabolic activation to form pyrrole-protein adducts and pyrrole-DNA adducts which lead to cytotoxicity and genotoxicity. Individual PAs differ in their metabolic activation patterns, which may cause significant difference in toxic potency of different PAs. This review discusses the current knowledge and recent advances of metabolic pathways of different PAs, especially the metabolic activation and metabolism-mediated cytotoxicity and genotoxicity, and the risk evaluation methods of PA exposure. In addition, this review provides perspectives of precision toxicity assessment strategies and biomarker development for the risk control and translational investigations of human intoxication by PAs.
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Affiliation(s)
- Yisheng He
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, SAR, China
| | - Lin Zhu
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, SAR, China
| | - Jiang Ma
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, SAR, China
| | - Ge Lin
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, SAR, China.
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Schramm S, Köhler N, Rozhon W. Pyrrolizidine Alkaloids: Biosynthesis, Biological Activities and Occurrence in Crop Plants. Molecules 2019; 24:E498. [PMID: 30704105 PMCID: PMC6385001 DOI: 10.3390/molecules24030498] [Citation(s) in RCA: 77] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 01/28/2019] [Accepted: 01/29/2019] [Indexed: 12/13/2022] Open
Abstract
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.
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Affiliation(s)
- Sebastian Schramm
- Biotechnology of Horticultural Crops, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Liesel-Beckmann-Straße 1, 85354 Freising, Germany.
| | - Nikolai Köhler
- Biotechnology of Horticultural Crops, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Liesel-Beckmann-Straße 1, 85354 Freising, Germany.
| | - Wilfried Rozhon
- Biotechnology of Horticultural Crops, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Liesel-Beckmann-Straße 1, 85354 Freising, Germany.
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Muluneh F, Häkkinen MR, El-Dairi R, Pasanen M, Juvonen RO. New glutathione conjugate of pyrrolizidine alkaloids produced by human cytosolic enzyme-dependent reactions in vitro. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2018; 32:1344-1352. [PMID: 29788543 DOI: 10.1002/rcm.8173] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Revised: 05/06/2018] [Accepted: 05/11/2018] [Indexed: 06/08/2023]
Abstract
RATIONALE The toxic metabolites of pyrrolizidine alkaloids (PAs) are initially formed by cytochrome P450-mediated oxidation reactions and primarily eliminated as glutathione (GSH) conjugates. Although the reaction between the reactive metabolites and GSH can occur spontaneously, the role of the cytosolic enzymes in the process has not been studied. METHODS The toxic metabolites of selected PAs (retrorsine, monocrotaline, senecionine, lasiocarpine, heliotrine or senkirkine) were generated by incubating them in 100 mM phosphate buffer (pH 7.4) containing liver microsomes of human, pig, rat or sheep, NADPH and reduced GSH in the absence or presence of human, pig, rat or sheep liver cytosolic fraction. The supernatants were analyzed using liquid chromatography connected to Finnigan LTQ ion-trap, Agilent QTOF or Thermo Scientific Q Exactive Focus quadrupole-orbitrap mass spectrometers. RESULTS Retrorsine, senecionine and lasiocarpine yielded three GSH conjugates producing [M - H]- ions at m/z 439 (7-GSH-DHP (CHO)), m/z 441 (7-GSH-DHP (OH)) and m/z 730 (7,9-diGSH-DHP) in the presence of human liver cytosolic fraction. 7-GSH-DHP (CHO) was a novel metabolite. Monocrotaline, heliotrine and senkirkine did not produce this novel 7-GSH-DHP (CHO) conjugate. 7-GSH-DHP (CHO) disappeared when incubated with hydroxylamine, and a new oxime derivative was formed. This metabolite was formed only by the human liver cytosolic enzymes but not in the presence of rat or sheep liver cytosolic fractions under otherwise identical reaction conditions. CONCLUSIONS 7-GSH-DHP (CHO) has not been reported before, and thus it was considered as a novel metabolite of PAs. This may clarify the mechanisms involved in PA detoxification and widely observed but less understood species differences in response to PA exposure.
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Affiliation(s)
- Fashe Muluneh
- University of Eastern Finland, School of Pharmacy, Faculty of Health Sciences, Box 1627, 70211, Kuopio, Finland
- National Institute of Environmental Health Sciences, Reproductive & Developmental Biology Laboratory/Pharmacogenetics Group, NIH, Research Triangle Park, NC, 27709, USA
| | - Merja R Häkkinen
- University of Eastern Finland, School of Pharmacy, Faculty of Health Sciences, Box 1627, 70211, Kuopio, Finland
| | - Rami El-Dairi
- University of Eastern Finland, School of Pharmacy, Faculty of Health Sciences, Box 1627, 70211, Kuopio, Finland
| | - Markku Pasanen
- University of Eastern Finland, School of Pharmacy, Faculty of Health Sciences, Box 1627, 70211, Kuopio, Finland
| | - Risto O Juvonen
- University of Eastern Finland, School of Pharmacy, Faculty of Health Sciences, Box 1627, 70211, Kuopio, Finland
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Amin KA, Hashem KS, Al-muzafar HM, Taha EM. Oxidative hepatotoxicity effects of monocrotaline and its amelioration by lipoic acid, S-adenosyl methionine and vitamin E. JOURNAL OF COMPLEMENTARY & INTEGRATIVE MEDICINE 2014; 11:35-41. [PMID: 24413220 DOI: 10.1515/jcim-2013-0041] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2013] [Accepted: 12/07/2013] [Indexed: 01/06/2023]
Abstract
Liver is the major site for several xenobiotics metabolism, and formation of toxic metabolites that may be hepatotoxic, therefore the burden of metabolism and exposure to dangerous chemicals make liver vulnerable to a variety of disorders. Our work aimed to investigate the effects of some antioxidants such as lipoic acid (LA), S-adenosyl methionine (SAM) and vitamin E in a trail to investigate the possibility of using these substances to relieve and protect liver from exposure to monocrotaline (MCT). Twenty-five mature adult rats were classified into five groups (five rats in each group), control group, MCT-induced hepatic damage, LA+MCT, SAM+MCT and vitamin E+MCT group. Homogenates of liver samples were used for measuring the oxidative biomarkers and hepatic antioxidant status. The results showed that administration of vitamin E, SAM and LA caused a significant increase in liver glutathione contents, glutathione reductase, glutathione peroxidase and glutathione-S-transferase activities and a significant decrease in hepatic catalase and superoxide dismutase. We could conclude that administration of natural LA, SAM and vitamin E before and after MCT injection modulate the hepatic oxidative stresses induced by MCT in various extents.
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Barbehenn RV, Kochmanski J. Searching for synergism: effects of combinations of phenolic compounds and other toxins on oxidative stress in Lymantria dispar caterpillars. CHEMOECOLOGY 2013. [DOI: 10.1007/s00049-013-0136-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Chen Y, Ji L, Xiong A, Yang L, Wang Z. Involvement of intracellular glutathione in regulating isoline-induced cytotoxicity in human normal liver L-02 cells. Toxicol Ind Health 2012; 29:567-75. [PMID: 22474030 DOI: 10.1177/0748233712442707] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Pyrrolizidine alkaloid isoline is isolated from the traditional Chinese medicine Ligularia duciformis. Our previous reports have already demonstrated isoline-induced liver injury in mice. The present study is designed to observe the involvement of intracellular reduced glutathione (GSH) in isoline-induced cytotoxicity in human normal liver L-02 cells. The results showed that isoline decreased the cellular GSH and the ratio of GSH and oxidized glutathione in a time- and concentration-dependent manner in L-02 cells. l-Buthionine-S-R-sulfoximine (BSO) is reported to inhibit cellular GSH biosynthesis, and further results showed that isoline decreased the cell viability in L-02 cells after pretreated with 25 μM BSO for 24 h. Furthermore, adducts of isoline and GSH were identified in L-02 cells using liquid chromatography/electrospray ionization tandem mass spectrometry (ion trap) for the first time. In conclusion, our study provides the strongest evidence to support the important roles of GSH in regulating isoline-induced cytotoxicity in human normal liver L-02 cells.
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Affiliation(s)
- Ying Chen
- The MOE Key Laboratory for Standardization of Chinese Medicines and The SATCM Key Laboratory for New Resources and Quality Evaluation of Chinese Medicines, Institute of Chinese Materia Medica, Shanghai University of Traditional Chinese Medicine, Shanghai, China
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Amin KA, Hassan MS, Awad EST, Hashem KS. The protective effects of cerium oxide nanoparticles against hepatic oxidative damage induced by monocrotaline. Int J Nanomedicine 2011; 6:143-9. [PMID: 21289991 PMCID: PMC3026579 DOI: 10.2147/ijn.s15308] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Objective The objective of the present study was to determine the ability of cerium oxide (CeO2) nanoparticles to protect against monocrotaline (MCT)-induced hepatotoxicity in a rat model. Method Twenty male Sprague Dawley rats were arbitrarily assigned to four groups: control (received saline), CeO2 (given 0.0001 nmol/kg intraperitoneally [IP]), MCT (given 10 mg/kg body weight IP as a single dose), and MCT + CeO2 (received CeO2 both before and after MCT). Electron microscopic imaging of the rat livers was carried out, and hepatic total glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST), superoxide dismutase (SOD), and catalase (CAT) enzymatic activities were quantified. Results Results showed a significant MCT-induced decrease in total hepatic GSH, GPX, GR, and GST normalized to control values with concurrent CeO2 administration. In addition, MCT produced significant increases in hepatic CAT and SOD activities, which also ameliorated with CeO2. Conclusions These results indicate that CeO2 acts as a putative novel and effective hepatoprotective agent against MCT-induced hepatotoxicity.
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Affiliation(s)
- Kamal A Amin
- Department of Biochemistry, Faculty of Veterinary Medicine, Beni-Suef University, Beni-Suef, Egypt.
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Fu PP, Xia Q, Lin G, Chou MW. Pyrrolizidine Alkaloids—Genotoxicity, Metabolism Enzymes, Metabolic Activation, and Mechanisms. Drug Metab Rev 2004; 36:1-55. [PMID: 15072438 DOI: 10.1081/dmr-120028426] [Citation(s) in RCA: 364] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Pyrrolizidine alkaloid-containing plants are widely distributed in the world and are probably the most common poisonous plants affecting livestock, wildlife, and humans. Because of their abundance and potent toxicities, the mechanisms by which pyrrolizidine alkaloids induce genotoxicities, particularly carcinogenicity, were extensively studied for several decades but not exclusively elucidated until recently. To date, the pyrrolizidine alkaloid-induced genotoxicities were revealed to be elicited by the hepatic metabolism of these naturally occurring toxins. In this review, we present updated information on the metabolism, metabolizing enzymes, and the mechanisms by which pyrrolizidine alkaloids exert genotoxicity and tumorigenicity.
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Affiliation(s)
- Peter P Fu
- National Center for Toxicological Research, Jefferson, Arkansas 72079, USA.
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Schlenk D, Wolford L, Chelius M, Steevens J, Chan KM. Effect of arsenite, arsenate, and the herbicide monosodium methyl arsonate (MSMA) on hepatic metallothionein expression and lipid peroxidation in channel catfish. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART C, PHARMACOLOGY, TOXICOLOGY & ENDOCRINOLOGY 1997; 118:177-83. [PMID: 9440242 DOI: 10.1016/s0742-8413(97)00083-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Arsenic exerts its toxicity by the generation of reactive oxygen intermediates which caused lipid peroxidation and cellular damage. Metallothioneins (MTs) have been shown to be induced by oxidative stress and act as scavengers of reactive oxygen intermediates. Thus, hepatic MT was examined in channel catfish treated with the herbicide monosodium methyl arsonate (MSMA) and compared to equal doses of trivalent and pentavalent arsenic. Fish were exposed to 0.01, 0.1, and 1.0 mg/L of each compound for 1 week by static renewal. Hepatic MT was measured by the cadmium/hemoglobin (Cd/Hb) saturation assay, ELISA using antibodies raised against the first 10 amino acids of piscine MT, and Northern blot analysis using a cDNA encoding winter flounder hepatic MT. Cd/Hb and ELISA measurements of low molecular weight fractions from the hepatic cytosolic component of fish exposed to MSMA revealed a dose dependent increase in MT. MTs and MT mRNA of fish receiving the 1.0 mg/L dose were significantly induced vs control. Responses to arsenate exposure were more variable, but showed a trend toward a dose-dependent induction of MT and MT mRNA. MT mRNA and protein also showed a dose-dependent increase with arsenite exposure with no significant differences with untreated animals. Hepatic lipid peroxidation (as determined by TBARS) and glutathione was unaltered by any of the arsenical treatments. Thus, the lack of correlation between oxidative stress and MT expression suggest MT may not be a reliable indicator of oxidative stress. In addition, the induction of hepatic MT by various forms of As does not appear to be mediated through an oxidative stress mechanism in the liver.
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Affiliation(s)
- D Schlenk
- Department of Pharmacology, School of Pharmacy, University of Mississippi, MS 38677, USA.
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Yan CC, Huxtable RJ. Effects of monocrotaline, a pyrrolizidine alkaloid, on glutathione metabolism in the rat. Biochem Pharmacol 1996; 51:375-9. [PMID: 8573205 DOI: 10.1016/0006-2952(95)02189-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Monocrotaline (MONO), a pyrrolizidine alkaloid, causes veno-occlusive disease of the liver, pulmonary arterial hypertension, and right ventricular hypertrophy. Toxicity is due to the hepatic formation of a pyrolic metabolite that can be detoxified by conjugation with glutathione (GSH). We have shown that the GSH content of the liver affects the quantity of the pyrrolic metabolite that is released from the liver. We have now examined whether MONO, in turn, affects GSH metabolism. Twenty-four hours after administration of MONO to rats (65 mg/kg, i.p.), the highest concentration of bound pyrrolic metabolites was found in the liver, followed by the lung and kidney. Heart and brain contained lower concentrations of these metabolites. Significantly higher levels of GSH were found in liver and lungs of MONO-treated rats than in saline-injected control animals. In the liver, activities of the following enzymes were elevated: gamma-glutamylcysteine synthetase, GSH synthetase, gamma-glutamyl transpeptidase, dipeptidase, and microsomal GSH transferase. The same changes were seen in the lung. In the heart, gamma-glutamyl transpeptidase activity was decreased markedly, and cytosolic GSH transferase activity was elevated. In the kidney, the activities of GSH synthetase, gamma-glutamyl transpeptidase, and cytosolic GSH transferase were increased. Our results establish a mutual interaction of MONO and sulfur metabolism. It appears that an early metabolic action of MONO is to modify sulfur amino acid metabolism, diverting cysteine metabolism from oxidation to taurine towards synthesis of GSH.
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Affiliation(s)
- C C Yan
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson 85724, USA
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Yan CC, Huxtable RJ. Effect of the pyrrolizidine alkaloid monocrotaline on taurine and sulfur amino acid metabolism in the rat liver. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1996; 403:135-45. [PMID: 8915351 DOI: 10.1007/978-1-4899-0182-8_16] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- C C Yan
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson 85724, USA
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Yan CC, Huxtable RJ. Effect of taurine on toxicity of the pyrrolizidine alkaloid monocrotaline in rats. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1996; 403:315-25. [PMID: 8915367 DOI: 10.1007/978-1-4899-0182-8_33] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- C C Yan
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson 85724, USA
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Yan CC, Huxtable RJ. The effect of the pyrrolizidine alkaloids, monocrotaline and trichodesmine, on tissue pyrrole binding and glutathione metabolism in the rat. Toxicon 1995; 33:627-34. [PMID: 7660367 DOI: 10.1016/0041-0101(95)00004-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
One day after in vivo administration of equitoxic doses of the hepatotoxic and pneumotoxic pyrrolizidine alkaloid, monocrotaline (65 mg/kg, i. p.) or the related hepatotoxic and neurotoxic alkaloid trichodesmine (15 mg/kg, i. p.) hepatic GSH levels are increased by more than 50%. These doses of alkaloids represent 60% of the LD50 values. Accompanying these changes in GSH levels is an increase in the overall rate of GSH synthesis in supernatants of alkaloid-exposed livers. The ability of the rat to metabolize the two alkaloids was shown by the appearance of tissuebound pyrrolic metabolites of pyrrolizidines in various organs. The levels of these metabolites appear to correlate with organ toxicity. For the hepatic and pneumotoxic alkaloid, monocrotaline, higher levels are found in liver (17 nmoles/g tissue) and lung (10 nmoles/g) than for trichodesmine (7 nmoles/g and 8 nmoles/g, respectively). For the neurotoxic alkaloid, trichodesmine, higher levels are found in brain (3.8 nmoles/g tissue) than for monocrotaline (1.7 nmoles/g tissue).
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Affiliation(s)
- C C Yan
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson 85724, USA
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