Metabolic-induced cytotoxicity of diosbulbin B in CYP3A4-expressing cells

Mechanistic study of cytochrome P450 enzyme-mediated cytotoxicity of psoralen and isopsoralen

Psoralen and isopsoralen are the major components responsible for Psoraleae Fructus-induced hepatotoxicity. This study explored the role of metabolic activation by cytochrome P450 (CYP) enzymes in psoralen- and isopsoralen-induced cytotoxicity and its potential mechanisms. Inhibitors of CYP1A2, 2C9, 2C19, 2D6, 2E1, and 3A4 were used to screen specific CYP enzymes responsible for the metabolic activation of psoralen and isopsoralen in mouse primary hepatocytes, which was verified using the corresponding transfected cell lines. Network toxicology and transcriptome analyses were performed to explore the mechanisms underlying toxicity. Psoralen and isopsoralen decreased the viability of mouse primary hepatocytes, whereas the inhibition of CYP2C9, 2C19, 2D6, and 2E1 significantly increased their viability. Psoralen-induced cytotoxicity was significantly enhanced by the overexpression of CYP2C19 in Chinese hamster ovary cells, whereas the overexpression of the above CYP enzymes did not affect the cytotoxicity of isopsoralen. Psoralen- and isopsoralen-induced cytotoxic effects were associated with putative core targets (i.e., Fn1, Thbs1, and Tlr2) and multiple signaling pathways (e.g., PI3K-Akt, MAPK, and TNF pathways). Our results demonstrate that the metabolic activation of psoralen and isopsoralen is mediated by CYP enzymes, thereby regulating multiple core targets and signaling pathways and resulting in cytotoxicity.

Metabolism and toxicity of usnic acid and barbatic acid based on microsomes, S9 fraction, and 3T3 fibroblasts in vitro combined with a UPLC-Q-TOF-MS method

Introduction: Usnic acid (UA) and barbatic acid (BA), two typical dibenzofurans and depsides in lichen, have a wide range of pharmacological activities and hepatotoxicity concerns. This study aimed to clarify the metabolic pathway of UA and BA and illuminate the relationship between metabolism and toxicity. Methods: An UPLC-Q-TOF-MS method was developed for metabolite identification of UA and BA in human liver microsomes (HLMs), rat liver microsomes (RLMs), and S9 fraction (RS9). The key metabolic enzymes responsible for UA and BA were identified by enzyme inhibitors combined with recombinant human cytochrome P450 (CYP450) enzymes. The cytotoxicity and metabolic toxicity mechanism of UA and BA were determined by the combination model of human primary hepatocytes and mouse 3T3 fibroblasts. Results: The hydroxylation, methylation, and glucuronidation reactions were involved in the metabolic profiles of UA and BA in RLMs, HLMs, and RS9. CYP2C9, CYP3A4, CYP2C8, and UGT1A1 are key metabolic enzymes responsible for metabolites of UA and CYP2C8, CYP2C9, CYP2C19, CYP1A1, UGT1A1, UGT1A3, UGT1A7, UGT1A8, UGT1A9, and UGT1A10 for metabolites of BA. UA and BA did not display evident cytotoxicity in human primary hepatocytes at concentrations of 0.01-25 and 0.01-100 µM, respectively, but showed potential cytotoxicity to mouse 3T3 fibroblasts with 50% inhibitory concentration values of 7.40 and 60.2 µM. Discussion: In conclusion, the attenuated cytotoxicity of BA is associated with metabolism, and UGTs may be the key metabolic detoxification enzymes. The cytotoxicity of UA may be associated with chronic toxicity. The present results provide important insights into the understanding of the biotransformation behavior and metabolic detoxification of UA and BA.

Ferulic acid prevents Diosbulbin B-induced liver injury by inhibiting covalent modifications on proteins

Diosbulbin B (DIOB) has been reported to cause serious liver injury. However, in traditional medicine, DIOB-containing herbs are highly safe in combination with ferulic acid (FA)-containing herbs, suggesting potential neutralizing effect of FA on the toxicity of DIOB. DIOB can be metabolized to generate reactive metabolites (RMs), which can covalently bind to proteins and lead to hepatoxicity. In the present study, the quantitative method was firstly established for investigating the correlation between DIOB RM-protein adducts (DRPAs) and hepatotoxicity. Then, we estimated the detoxication effect of FA in combination with DIOB and revealed the underlying mechanism. Our data indicated that the content of DRPAs positively correlate with the severity of hepatotoxicity. Meanwhile, FA is able to reduce the metabolic rate of DIOB in vitro. Moreover, FA suppressed the production of DRPAs and decreased the serum alanine/aspartate aminotransferase (ALT/AST) levels elevated by DIOB in vivo. Thus, FA can ameliorate DIOB-induced liver injury through reducing the production of DRPAs.

Characterization of the chemical constituents and in vivo metabolic profile of Scutellaria barbata D. Don by ultra-high performance liquid chromatography-high resolution mass spectrometry

Scutellaria barbata D. Don (S. barbata) is one of the most frequently used anticancer herb medicine in China. Mechanistic understanding of the biological activities of S. barbata is hindered by limited knowledge regarding its components and metabolic profile. In this study, ultra-high-performance liquid chromatography coupled with high resolution mass spectrometry (quadrupole time-of-flight mass spectrometry,) was used to identify the chemical constituents in S. barbata and their metabolic profiles in rats. By applying cleavage rules and comparison with reference substances, 89 components were identified, which included 45 flavonoids, 28 diterpenoids, 10 phenolics, and 6 others. A total of 110 compounds, including 32 prototype compounds and 78 metabolites, were identified or tentatively characterized in vivo. Methylation, sulfonation, and glucuronidation were the main metabolic pathways, which could be attributed to the fact that several of the compounds in S. barbata have phenolic hydroxyl groups. This is the first systematic study on the chemical constituents and in vivo metabolic profile of S. barbata. The analytical method features a quick and comprehensive dissection of the chemical composition and metabolic profile of S. barbata and provides a basis for exploring its various biological activates. This article is protected by copyright. All rights reserved.

Metabolic Activation of the Toxic Natural Products From Herbal and Dietary Supplements Leading to Toxicities

Currently, herbal and dietary supplements have been widely applied to prevent and treat various diseases. However, the potential toxicities and adverse reactions of herbal and dietary supplements have been increasingly reported, and have gradually attracted widespread attention from clinical pharmacists and physicians. Metabolic activation of specific natural products from herbal and dietary supplements is mediated by hepatic cytochrome P450 or intestinal bacteria, and generates chemical reactive/toxic metabolites that bind to cellular reduced glutathione or macromolecules, and form reactive metabolites-glutathione/protein/DNA adducts, and these protein/DNA adducts can result in toxicities. The present review focuses on the relation between metabolic activation and toxicities of natural products, and provides updated, comprehensive and critical comment on the toxic mechanisms of reactive metabolites. The key inductive role of metabolic activation in toxicity is highlighted, and frequently toxic functional groups of toxic natural products were summarized. The biotransformation of drug cytochrome P450 or intestinal bacteria involved in metabolic activation were clarified, the reactive metabolites-protein adducts were selected as biomarkers for predicting toxicity. And finally, further perspectives between metabolic activation and toxicities of natural products from herbal and dietary supplements are discussed, to provide a reference for the reasonable and safe usage of herbal and dietary supplements.

Angelica sinensis polysaccharide (ASP) attenuates diosbulbin-B (DB)-induced hepatotoxicity through activating the MEK/ERK pathway

Diosbulbin-B (DB) is a promising therapeutic drug for cancer treatment; however, DB-induced hepatotoxicity seriously limits its clinical utilization. Based on this, the present study investigated whether the Angelica sinensis extract, angelica sinensis polysaccharide (ASP), was effective to attenuate DB-induced cytotoxicity in hepatocytes. The primary hepatocytes were isolated from rats and cultured in vitro, which were subsequently treated with high-dose DB (100 μM) and ASP (12 μg/ml) to establish the DB-induced hepatotoxicity models. MTT assay and flow cytometry (FCM) were performed to evaluate cell viability, and the results showed that high-dose DB-induced cell apoptosis and inhibition of proliferation were reversed by co-treating cells with ASP, which were supported by our Western Blot assay data that ASP upregulated Cyclin D1 and CDK2 to abrogate high-dose DB-induced cell cycle arrest. In addition, ASP exerted its regulating effects on cell autophagy, and we found that ASP increased LC3B-II/I ratio and Atg5, but decreased p62 to activate the autophagy flux. Of note, the MEK/ERK pathway could be activated by ASP in the DB-treated hepatocytes, and the protective effects of ASP on high-dose DB-induced hepatocyte death were abolished by co-treating cells with the autophagy inhibitor (3-methyladenine, 3-MA) and MEK/ERK selective inhibitor (SCH772984). Moreover, blockage of the MEK/ERK pathway suppressed cell autophagy in the hepatocytes co-treated with ASP and high-dose DB. Taken together, this in vitro study illustrated that ASP activated the MEK/ERK pathway mediated autophagy to suppress high-dose DB-induced hepatotoxicity.

Metabonomic approaches investigate diosbulbin B-induced pulmonary toxicity and elucidate its underling mechanism in male mice

Air Potato Yam is widely used in the treatment of many conditions such as cancer, inflammation, and goiter. Diosbulbin B (DIOB) is the primary active component of Air Potato Yam, and it exhibits anti-tumor and anti-inflammatory properties. The main purpose of this study was to determine the mechanism by which DIOB induces lung toxicity, using metabonomics and molecular biology techniques. The results showed that the lung toxicity induced by DIOB may occur because of a DIOB-induced increase in the plasma levels of long-chain free fatty acids and endogenous metabolites related to inflammation. In addition, treatment with DIOB increases the expression of the cyp3a13 enzyme, which leads to enhanced toxicity in a dose-dependent manner. The molecular mechanism underlying toxicity in mouse lung cells is the DIOB-mediated inhibition of fatty acid β-oxidation, partial glycolysis, and the TCA cycle, but DIOB treatment can also compensate for the low Adenosine triphosphate (ATP) supply levels by improving the efficiency of the last step of the glycolysis reaction and by increasing the rate of anaerobic glycolysis. Using metabonomics and other methods, we identified the toxic effects of DIOB on the lung and clarified the underlying molecular mechanism.

The marine compound and elongation factor 1A1 inhibitor, didemnin B, provides benefit in western diet-induced non-alcoholic fatty liver disease

Inhibition of eukaryotic elongation factor 1A1 (EEF1A1) with the marine compound didemnin B decreases lipotoxic HepG2 cell death in vitro and improves early stage non-alcoholic fatty liver disease (NAFLD) in young genetically obese mice. However, the effects of didemnin B on NAFLD in a model of long-term diet-induced obesity are not known. We investigated the effects of didemnin B on NAFLD severity and metabolic parameters in western diet-induced obese mice, and on the cell types that contribute to liver inflammation and fibrosis in vitro. Male 129S6 mice were fed either standard chow or western diet for 26 weeks, followed by intervention with didemnin B (50 μg/kg) or vehicle by intraperitoneal (i.p.) injection once every 3 days for 14 days. Didemnin B decreased liver and plasma triglycerides, improved oral glucose tolerance, and decreased NAFLD severity. Moreover, didemnin B moderately increased hepatic expression of genes involved in ER stress response (Perk, Chop), and fatty acid oxidation (Fgf21, Cpt1a). In vitro, didemnin B decreased THP-1 monocyte proliferation, disrupted THP-1 monocyte-macrophage differentiation, decreased THP-1 macrophage IL-1β secretion, and decreased hepatic stellate cell (HSteC) proliferation and collagen secretion under both basal and lipotoxic (high fatty acid) conditions. Thus, didemnin B improves hepatic steatosis, glucose tolerance, and blood lipids in obesity, in association with moderate, possibly hormetic, upregulation of pathways involved in cell stress response and energy balance in the liver. Furthermore, it decreases the activity of the cell types implicated in liver inflammation and fibrosis in vitro. These findings highlight the therapeutic potential of partial protein synthesis inhibition in the treatment of NAFLD.

The crucial role of metabolic regulation in differential hepatotoxicity induced by furanoids in Dioscorea bulbifera

Diterpenoid lactones (DLs), a group of furan-containing compounds found in Dioscorea bulbifera L. (DB), have been reported to be associated with hepatotoxicity. Different hepatotoxicities of these DLs have been observed in vitro, but reasonable explanations for the differential hepatotoxicity have not been provided. Herein, the present study aimed to confirm the potential factors that contribute to varied hepatotoxicity of four representative DLs (diosbulbins A, B, C, F). In vitro toxic effects were evaluated in various cell models and the interactions between DLs and CYP3A4 at the atomic level were simulated by molecular docking. Results showed that DLs exhibited varied cytotoxicities, and that CYP3A4 played a modulatory role in this process. Moreover, structural variation may cause different affinities between DLs and CYP3A4, which was positively correlated with the observation of cytotoxicity. In addition, analysis of the glutathione (GSH) conjugates indicated that reactive intermediates were formed by metabolic oxidation that occurred on the furan moiety of DLs, whereas, GSH consumption analysis reflected the consistency between the reactive metabolites and the hepatotoxicity. Collectively, our findings illustrated that the metabolic regulation played a crucial role in generating the varied hepatotoxicity of DLs.

Evidence for Polyamine, Biogenic Amine, and Amino Acid Adduction Resulting from Metabolic Activation of Diosbulbin B

Dioscorea bulbifera L. (DBL), a traditional Chinese medicine, is a well-known herb with hepatotoxicity, and the biochemical mechanisms of the toxic action remain unknown. Diosbulbin B (DSB), a major component of DBL, can induce severer liver injury which requires cytochrome P450-catalyzed oxidation of the furan ring. It is reported that a cis-enedial reactive intermediate resulting from metabolic activation of DSB can react with thiols and amines to form pyrrole or pyrroline derivatives. In this study, we investigated the interaction of the reactive intermediate with polyamines, biogenic amines, and amino acids involved in the polyamine metabolic pathway, including putrescine, spermidine, spermine, histamine, arginine, ornithine, lysine, glutamine, and asparagine. Seven DSB-derived amine adducts were detected in microsomal incubations supplemented with DSB and individual amines. Six adducts were observed in cultured rat primary hepatocytes after exposure to DSB. DSB was found to induce apoptosis and cell death in time- and concentration-dependent manners. Apparently, the observed apoptosis was associated with the detected amine adduction. The findings facilitate the understanding of the mechanisms of toxic action of DSB.

Systems Toxicology Approaches Reveal the Mechanisms of Hepatotoxicity Induced by Diosbulbin B in Male Mice

Diosbulbin B (DIOB) is an effective component of air potato yam with antitumor and anti-inflammatory activities, and it is the main toxic component leading to hepatotoxicity. However, the mechanism of its hepatotoxicity remains unclear. In this study, we aimed to systematically elucidate the molecular action of DIOB on liver metabolic function through systems toxicology approaches. C57BL/6 mice were orally treated with DIOB (10, 30, 60 mg/kg) for 28 days, and the liver metabonomics and histopathology, molecular docking, mRNA expression levels, and activities of enzymes were analyzed. The results illustrated that DIOB could affect fatty acid and glucose metabolism, block the TCA cycle, and DIOB also could disorder bile acid synthesis and transport and promote the occurrence of hyperbilirubinemia. In addition, DIOB increased Cyp3a11 expression in a dose-dependent manner. Thus, these results provide new insights into the mechanism of hepatotoxicity caused by DIOB.

Classification, hepatotoxic mechanisms, and targets of the risk ingredients in traditional Chinese medicine-induced liver injury

Traditional Chinese medicine (TCM) has become a crucial cause of drug-induced liver injury (DILI). Differ from chemical medicines, TCM feature more complex and mostly indefinite components. This review aimed to clarify the classification, underlying mechanisms and targets of the risk components in TCM-induced liver injury to further guide the secure application of TCM. Relevant studies or articles published on the PubMed database from January 2008 to December 2019 were searched. Based on the different chemical structures of the risk ingredients in TCM, they are divided into alkaloids, glycosides, toxic proteins, terpenoids and lactones, anthraquinones, and heavy metals. According to whether drug metabolism is activated or hepatocytes are directly attacked during TCM-induced liver injury, the high-risk substances can be classified into metabolic activation, non-metabolic activation, and mixed types. Mechanisms of the hepatotoxic ingredients in TCM-induced hepatotoxicity, including cytochrome P450 (CYP450) induction, mitochondrial dysfunction, oxidative damage, apoptosis, and idiosyncratic reaction, were also summarized. The targets involved in the risk ingredient-induced hepatocellular injury mainly include metabolic enzymes, nuclear receptors, transporters, and signaling pathways. Our periodic review and summary on the risk signals of TCM-induced liver injury must be beneficial to the integrated analysis on the multi-component, multi-target, and multi-effect characteristics of TCM-induced hepatotoxicity.

The Modulatory Role of CYP3A4 in Dictamnine-Induced Hepatotoxicity

Dictamni Cortex (DC) has been reported to be associated with acute hepatitis in clinic and may lead to a selective sub-chronic hepatotoxicity in rats. Nevertheless, the potent toxic ingredient and the underlying mechanism remain unknown. Dictamnine (DTN), the main alkaloid from DC, possesses a furan ring which was suspected of being responsible for hepatotoxicity via metabolic activation primarily by CYP3A4. Herein, the present study aimed to evaluate the role of CYP3A4 in DTN-induced liver injury. The in vitro results showed that the EC₅₀ values in primary human hepatocytes (PHH), L02, HepG2 and NIH3T3 cells were correlated with the CYP3A4 expression levels in corresponding cells. Furthermore, the toxicity was increased in CYP3A4-induced PHH by rifampicin, and CYP3A4 over-expressed (OE) HepG2 and L02 cells. Contrarily, the cytotoxicity was decreased in CYP3A4-inhibited PHH and CYP3A4 OE HepG2 and L02 cells inhibited by ketoconazole (KTZ). In addition, the hepatotoxicity of DTN in enzyme induction/inhibition mice was further investigated in the aspects of biochemistry, histopathology, and pharmacokinetics. Administration of DTN in combination with KTZ resulted in attenuated liver injury, including lower alanine transaminase and aspartate transaminase activities and greater AUC and C_max of serum DTN, whereas, pretreatment with dexamethasone aggravated the injury. Collectively, our findings illustrated that DTN-induced hepatotoxicity correlated well with the expression of CYP3A4, namely inhibition of CYP3A4 alleviated the toxicity both in vitro and in vivo, and induction aggravated the toxicity effects.

Tangeretin inhibits the proliferation of human breast cancer cells via CYP1A1/CYP1B1 enzyme induction and CYP1A1/CYP1B1-mediated metabolism to the product 4' hydroxy tangeretin

Tangeretin is a polymethoxylated flavone with multifaceted anticancer activity. In the present study, the metabolism of tangeretin was evaluated in the CYP1 expressing human breast cancer cell lines MCF7 and MDA-MB-468 and in the normal breast cell line MCF10A. Tangeretin was converted to 4' OH tangeretin by recombinant CYP1 enzymes and by CYP1 enzymes expressed in MCF7 and MDA-MB-468 cells. This metabolite was absent in MCF10A cells that did not express CYP1 enzymes. Tangeretin exhibited submicromolar IC50 (0.25 ± 0.15 μM) in MDA-MB-468 cells, whereas it was less active in MCF7 cells (39.3 ± 1.5 μM) and completely inactive in MCF10A cells (>100 μM). In MDA-MB-468 cells that were coincubated with the CYP1 inhibitor acacetin, an approximately 70-fold increase was noted in the IC50 (18 ± 1.6 μM) of tangeretin. In the presence of the CYP1 inhibitor acacetin, the conversion of tangeretin to 4' OH tangeretin was significantly reduced in MDA-MB-468 cells (2.55 ± 0.19 μM vs. 6.33 ± 0.12 μM). The mechanism of antiproliferative action involved cell cycle arrest at the G1 phase for MCF7 and MDA-MB-468 cells. Tangeretin was further shown to induce CYP1 enzyme activity and CYP1A1/CYP1B1 protein expression in MCF7 and MDA-MB-468 cells. These results suggest that tangeretin inhibits the proliferation of breast cancer cells via CYP1A1/CYP1B1-mediated metabolism to the product 4' hydroxy tangeretin.

Discovery of Hepatotoxic Equivalent Combinatorial Markers from Dioscorea bulbifera tuber by Fingerprint-Toxicity Relationship Modeling

Due to extremely chemical complexity, identification of potential toxicity-related constituents from an herbal medicine (HM) still remains challenging. Traditional toxicity-guided separation procedure suffers from time- and labor-consumption and neglects the additive effect of multi-components. In this study, we proposed a screening strategy called “hepatotoxic equivalent combinatorial markers (HECMs)” for a hepatotoxic HM, Dioscorea bulbifera tuber (DBT). Firstly, the chemical constituents in DBT extract were globally characterized. Secondly, the fingerprints of DBT extracts were established and their in vivo hepatotoxicities were tested. Thirdly, three chemometric tools including partial least squares regression (PLSR), back propagation-artificial neural network (BP-ANN) and cluster analysis were applied to model the fingerprint-hepatotoxicity relationship and to screen hepatotoxicity-related markers. Finally, the chemical combination of markers was subjected to hepatotoxic equivalence evaluation. A total of 40 compounds were detected or tentatively characterized. Two diterpenoid lactones, 8-epidiosbulbin E acetate (EEA) and diosbulbin B (DIOB), were discovered as the most hepatotoxicity-related markers. The chemical combination of EEA and DIOB, reflecting the whole hepatotoxicity of original DBT extract with considerable confidential interval, was verified as HECMs for DBT. The present study is expected not only to efficiently discover hepatotoxicity-related markers of HMs, but also to rationally evaluate/predict the hepatotoxicity of HMs.