UV-filter benzophenones suppress human, pig, rat, and mouse 11β-hydroxysteroid dehydrogenase 1: Structure-activity relationship and in silico docking analysis

Benzophenone chemicals (BPs) have been developed to prevent the adverse effects of UV radiation and they are widely contaminated. 11β-Hydroxysteroid dehydrogenase 1 (11β-HSD1) catalyze the conversion of inactive glucocorticoid to active glucocorticoid, playing critical role in many physiological function. However, the direct effect of BPs on human, pig, rat, and mouse 11β-HSD1 remains unclear. In this study, we screened the inhibitory strength of 12 BPs on 4 species, and performed the structure-activity relationship (SAR) and in silico docking analysis. The inhibitory potency of BPs was: for human 11β-HSD1, BP6 (IC50 = 18.76 μM) > BP8 (40.84 μM) > BP (88.89 μM) > other BPs; for pig 11β-HSD1, BP8 (45.57 μM) > BP6 (59.44 μM) > BP2 (65.12 μM) > BP (135.56 μM) > other BPs; for rat 11β-HSD1, BP7 (67.17 μM) > BP (68.83 μM) > BP8 (133.04 μM) > other BPs; and for mouse 11β-HSD1, BP8 (41.41 μM) > BP (50.61 μM) > other BPs. These BP chemicals were mixed/competitive inhibitors of these 11β-HSD1 enzymes. The 2,2'-dihydroxy substitutions in two benzene rings play a key role in enhancing the effectiveness of inhibiting 11β-HSD1, possibly via increasing hydrogen bond interactions. Docking analysis shows that these BPs bind to NADPH/glucocorticoid binding sites and forms hydrogen bonds with catalytic residues Ser and/or Tyr. In conclusion, this study demonstrates that BP chemicals can inhibit 11β-HSD1 from 4 species, and there are subtle species-dependent difference in the inhibitory strength and structural variations of BPs.

Metabolic activation of 2,4,6-trinitrotoluene; a case for ROS-induced cell damage

The explosive compound 2,4,6-trinitrotoluene (TNT) is well known as a major component of munitions. In addition to its potential carcinogenicity and mutagenicity in humans, recent reports have highlighted TNT toxicities in diverse organisms due to its occurrence in the environment. These toxic effects have been linked to the intracellular metabolism of TNT, which is generally characterised by redox cycling and the generation of noxious reactive molecules. The reactive intermediates formed, such as nitroso and hydroxylamine compounds, also interact with oxygen molecules and cellular components to cause macromolecular damage and oxidative stress. The current review aims to highlight the crucial role of TNT metabolism in mediating TNT toxicity, via increased generation of reactive oxygen species. Cellular proliferation of reactive species results in depletion of cellular antioxidant enzymes, DNA and protein adduct formation, and oxidative stress. While TNT toxicity is well known, its ability to induce oxidative stress, resulting from its reductive activation, suggests that some of its toxic effects may be caused by its reactive metabolites. Hence, further research on TNT metabolism is imperative to elucidate TNT-induced toxicities.

Computational study on the endocrine-disrupting metabolic activation of Benzophenone-3 catalyzed by cytochrome P450 1A1: A QM/MM approach

Predicting the metabolic activation mechanism and potential hazardous metabolites of environmental endocrine-disruptors is a challenging and significant task in risk assessment. Here the metabolic activation mechanism of benzophenone-3 catalyzed by P450 1A1 was investigated by using Molecular Dynamics, Quantum Mechanics/Molecular Mechanics and Density Functional Theory approaches. Two elementary reactions involved in the metabolic activation of BP-3 with P450 1A1: electrophilic addition and hydrogen abstraction reactions were both discussed. Further conversion reactions of epoxidation products, ketone products and the formaldehyde formation reaction were investigated in the non-enzymatic environment based on previous experimental reports. Binding affinities analysis of benzophenone-3 and its metabolites to sex hormone binding globulin indirectly demonstrates that they all exhibit endocrine-disrupting property. Toxic analysis shows that the eco-toxicity and bioaccumulation values of the benzophenone-3 metabolites are much lower than those of benzophenone-3. However, the metabolites are found to have skin-sensitization effects. The present study provides a deep insight into the biotransformation process of benzophenone-3 catalyzed by P450 1A1 and alerts us to pay attention to the adverse effects of benzophenone-3 and its metabolites in human livers.

Mechanism of cytochrome P450s mediated interference with glutathione and amino acid metabolisms from halogenated PAHs exposure

Epidemiological evidence indicates that exposure to halogenated polycyclic aromatic hydrocarbons (HPAHs) is associated with many adverse effects. However, the mechanisms of metabolic disorder of HPAHs remains limited. Herein, effects of pyrene (Pyr), and its halogenated derivatives (1-chloropyrene (1-Cl-Pyr), 1-bromopyrene (1-Br-Pyr)) on endogenous metabolic pathways were investigated, in human hepatoma (HepG2) and HepG2-derived cell lines expressing various human cytochrome P450s (CYPs). Non-targeted metabolomics results suggested that 1-Br-Pyr and Pyr exposure (625 nM) induced disruption in glutathione and riboflavin metabolism which associated with redox imbalance, through abnormal accumulation of oxidized glutathione, mediated by bioactivation of CYP2E1. Conversely, CYP2C9-mediated 1-Cl-Pyr significantly interfered with glutathione metabolism intermediates, including glycine, L-glutamic acid and pyroglutamic acid. Notably, CYP1A1-mediated Pyr-induced perturbation of amino acid metabolism which associated with nutrition and glycolipid metabolism, resulting in significant upregulation of most amino acids, whereas halogenated derivatives mediated by CYP1A2 substantially downregulated amino acids. In conclusion, this study suggested that Pyr and its halogenated derivatives exert potent effects on endogenous metabolism disruption under the action of various exogenous metabolic enzymes (CYPs). Thus, new evidence was provided to toxicological mechanisms of HPAHs, and reveals potential health risks of HPAHs in inducing diseases caused by redox and amino acid imbalances.

Metabolism-dependent mutagenicity of two structurally similar tobacco-specific nitrosamines (N-nitrosonornicotine and N-nitrosoanabasine) in human cells, partially different CYPs being activating enzymes

N-nitrosonornicotine (NNN) and N-nitrosoanabasine (NAB) are both tobacco-specific nitrosamines bearing two heterocyclic amino groups, NAB bearing an extra -CH2- group (conferring a hexa- rather than penta-membered cycle) but with significantly decreased carcinogenicity. However, their activating enzymes and related mutagenicity remain unclear. In this study, the chemical-CYP interaction was analyzed by molecular docking, thus the binding energies and conformations of NNN for human CYP2A6, 2A13, 2B6, 2E1 and 3A4 appeared appropriate as a substrate, so did NAB for human CYP1B1, 2A6, 2A13 and 2E1. The micronucleus test in human hepatoma (HepG2) cells with each compound (62.5-1000 μM) exposing for 48 h (two-cell cycle) was negative, however, pretreatment with bisphenol AF (0.1-100 nM, CYPs inducer) and ethanol (0.2% v:v, CYP2E1 inducer) potentiated micronucleus formation by both compounds, while CITCO (1 μM, CYP2B6 inducer) selectively potentiated that by NNN. In C3A cells (endogenous CYPs enhanced over HepG2) both compounds induced micronucleus, which was abolished by 1-aminobenzotriazole (60 μM, CYPs inhibitor) while unaffected by 8-methoxypsoralen (1 μM, CYP2A inhibitor). Consistently, NNN and NAB induced micronucleus in V79-derived recombinant cell lines expressing human CYP2B6/2E1 and CYP1B1/2E1, respectively, while negative in those expressing other CYPs. By immunofluorescent assay both compounds selectively induced centromere-free micronucleus in C3A cells. In PIG-A assays in HepG2 cells NNN and NAB were weakly positive and simply negative, respectively; however, in C3A cells both compounds significantly induced gene mutations, NNN being slight more potent. Conclusively, both NNN and NAB are mutagenic and clastogenic, depending on metabolic activation by partially different CYP enzymes.

The metabolic activation of pentachlorophenol to chloranil as a potent inhibitor of human and rat placental 3β-hydroxysteroid dehydrogenases

Pentachlorophenol (PCP) is a widely used pesticide. However, whether PCP and its metabolite chloranil have endocrine-disrupting effects by inhibiting placental 3β-hydroxysteroid dehydrogenase 1 (3β-HSD1) remains unclear. The study used in vitro assays with human and rat placental microsomes to measure 3β-HSD activity as well as human JAr cells to evaluate progesterone production. The results showed that PCP exhibited moderate inhibition of human 3β-HSD1, with an IC50 value of 29.83 μM and displayed mixed inhibition in terms of mode of action. Conversely, chloranil proved to be a potent inhibitor, demonstrating an IC50 value of 147 nM, and displaying a mixed mode of action. PCP significantly decreased progesterone production by JAr cells at 50 μM, while chloranil markedly reduced progesterone production at ≥1 μM. Interestingly, PCP and chloranil moderately inhibited rat placental homolog 3β-HSD4, with IC50 values of 27.94 and 23.42 μM, respectively. Dithiothreitol (DTT) alone significantly increased human 3β-HSD1 activity. Chloranil not PCP mediated inhibition of human 3β-HSD1 activity was completely reversed by DTT and that of rat 3β-HSD4 was partially reversed by DTT. Docking analysis revealed that both PCP and chloranil can bind to the catalytic domain of 3β-HSDs. The difference in the amino acid residue Cys83 in human 3β-HSD1 may explain why chloranil is a potent inhibitor through its interaction with the cysteine residue of human 3β-HSD1. In conclusion, PCP is metabolically activated to chloranil as a potent inhibitor of human 3β-HSD1.

Metabolic activation and cytochrome P450 inhibition of piperlonguminine mediated by CYP3A4

Piperlonguminine (PLG) is a major alkaloid found in Piper longum fruits. It has been shown to possess a variety of biological activities, including anti-tumor, anti-hyperlipidemic, anti-renal fibrosis and anti-inflammatory properties. Previous studies have reported that PLG inhibits various CYP450 enzymes. The main objective of this study was to identify reactive metabolites of PLG in vitro and assess its ability to inhibit CYP450. In rat and human liver microsomal incubation systems exposed to PLG, two oxidized metabolites (M1 and M2) were detected. Additionally, in microsomes where N-acetylcysteine was used as a trapping agent, N-acetylcysteine conjugates (M3, M4, M5 and M6) of four isomeric O-quinone-derived reactive metabolites were found. The formation of metabolites was dependent on NADPH. Inhibition and recombinant CYP450 enzyme incubation experiments showed that CYP3A4 was the primary enzyme responsible for the metabolic activation of PLG. This study characterized the O-dealkylated metabolite (M1) through chemical synthesis. The IC50 shift assay showed time-dependent inhibition of CYP3A4, 2C9, 2E1, 2C8 and 2D6 by PLG. This research contributes to the understanding of PLG-induced enzyme inhibition and bioactivation.

Human CYP1A1-activated aneugenicity of aflatoxin B1 in mammalian cells and its combined effect with benzo(a)pyrene

Aflatoxin B1 (AFB1) is the most toxic mycotoxin and a proven human carcinogen that requires metabolic activation, known by cytochrome P450 (CYP) 1A2 and 3A4. Previous evidence showed that AFB1 is activated by human recombinant CYP1A1 expressed in budding yeast. Yet, the toxicity, in particular the genotoxicity of the reactive metabolites formed from AFB1 remains unclear. Humans could be exposed to both AFB1 and benzo(a)pyrene (BaP) simultaneously, thus we were interested in their combined genotoxic effects subsequent to metabolic activation by CYP1A1. In this study, molecular docking of AFB1 to human CYP1A1 indicated that AFB1 is valid as a substrate. In the incubations with AFB1 in human CYP1A1-expressed microsomes, AFM1 as a marking metabolite of AFB1 was detected. Moreover, AFB1 induced micronucleus formation in a Chinese hamster V79-derived cell line and in a human lung epithelial BEAS-2B cell line, both expressing recombinant human CYP1A1, V79-hCYP1A1 and 2B-hCYP1A1 cells, respectively. Immunofluorescence of centromere protein B stained micronuclei was dominant in AFB1-treated BEAS-2B cells exposed to AFB1, suggesting an aneugenic effect. Moreover, AFB1 elevated the levels of ROS, 8-OHdG, AFB1-DNA adduct, and DNA breaks in 2B-hCYP1A1 cells, compared with those in the parental BEAS-2B cells. Meanwhile, AFB1 increased CYP1A1, RAD51, and γ-H2AX protein levels in 2B-hCYP1A1 cells, which were attenuated by the CYP1A1 inhibitor bergamottin. Co-exposure of AFB1 with BaP increased 8-OHdG, RAD51, and γ-H2AX levels (indicating DNA damage). In conclusion, AFB1 could be activated by human CYP1A1 for potent aneugenicity, which may be further enhanced by co-exposure to BaP.

In vitro and in vivo metabolic activation and hepatotoxicity of chlorzoxazone mediated by CYP3A

Chlorzoxazone (CZX), a benzoxazolone derivative, has been approved for the treatment of musculoskeletal disorders to relieve localized muscle spasm. However, its idiosyncratic toxicity reported in patients brought attention, particularly for hepatotoxicity. The present study for the first time aimed at the relationship between CZX-induced hepatotoxicity and identification of oxirane intermediate resulting from metabolic activation of CZX. Two N-acetylcysteine (NAC) conjugates (namely M1 and M2) and two glutathione (GSH) conjugates (namely M3 and M4) were detected in rat & human microsomal incubations with CZX (200 μM) fortified with NAC or GSH, respectively. The formation of M1-M4 was NADPH-dependent and these metabolites were also observed in urine or bile of SD rats given CZX intragastrically at 10 mg/kg or 25 mg/kg. NAC was found to attach at C-6' of the benzo group of M1 by sufficient NMR data. CYPs3A4 and 3A5 dominated the metabolic activation of CZX. The two GSH conjugates were also observed in cultured rat primary hepatocytes after exposure to CZX. Inhibition of CYP3A attenuated the susceptibility of hepatocytes to the cytotoxicity of CZX (10-400 μM). The in vitro and in vivo studies provided solid evidence for the formation of oxirane intermediate of CZX. This would facilitate the understanding of the underlying mechanisms of toxic action of CZX.

Role of covalent modification by hepatic aldehydes in dictamnine-induced liver injury

Dictamnine is a representative furan-containing hepatotoxic compound. Administration of dictamnine caused acute liver injury in mice and the metabolic activation of furan to reactive epoxy intermediate was responsible for the hepatotoxicity. This study aimed to characterize the protein adduction by endogenous hepatic aldehydes and investigate its role in dictamnine-induced hepatotoxicity. In the liver sample of dictamnine-treated mice, the protein adduction by five aldehydes was characterized as lysine residue-aldehyde adducts using high-resolution UPLC-Q/Orbitrap MS after exhaustive proteolytic digestion. The levels of protein adduct were increased at 2-3 h after the treatment with dictamnine. The formation of protein adduction increased with increasing doses of dictamnine. Inhibition of the bioactivation by CYP3A inhibitor ketoconazole prevented the protein adduction. Treatment with 2,3-dihydro-dictamnine, an analog of dictamnine that was unable to form the epoxy intermediate, did not lead to an increase in protein adduction. Application of aldehyde dehydrogenase-2 activator ALDA-1 or nucleophilic trapping reagent N-acetyl-L-lysine significantly reduced the protein adduction and attenuated dictamnine-induced liver injury without affecting the bioactivation. In conclusion, the metabolic activation of the furan ring of dictamnine resulted in the protein adduction by multiple hepatic aldehydes and the protein modification played a crucial role in dictamnine-induced liver injury.

The inhibitory effect of licorice on the hepatotoxicity induced by the metabolic activation of Euodiae Fructus

ETHNOPHARMACOLOGICAL RELEVANCE

Euodiae Fructus (EF), the dried, unripe, scented fruit of Tetradium ruticarpum (A. Juss, T.G.Hartley), is a traditional food and herb with mild toxicity. In Asia, it is processed with licorice (EFP), which has been used for centuries to alleviate pain and suppress cough. Pharmacological studies have reported that this herb could cause liver injury by activating the P450 3A enzyme, thus carrying the risk of clinical application. Processing with licorice is an effective method to reduce EF toxicity. It is urgent to explore the toxic components of EF and the attenuation mechanism of licorice.

AIM OF THE STUDY

This study aimed to indicate the specific pathway of EF-induced damage and identify the mechanism of action of licorice in reducing P450 activation and resulting in reduced liver damage.

MATERIALS AND METHODS

Male C57BL-6 mice were used to investigate the toxicity of EF to the liver and determine the attenuation effect on P450 from licorice ingestion. Glutathione (GSH) was used to capture the metabolic activation intermediates of EF. The key component reducing the EF toxicity of licorice was investigated by comparing the differences in chemical components and inhibition on the EF metabolism of licorice from different habitats.

RESULTS

The intermediate product of evodiamine (EVO) in EF was found to be activated by the P450 enzyme during metabolism, causing liver injury and inflammation. Isoliquiritigenin and liquiritigenin in licorice produced by intestinal bacterial metabolism and glycyrrhizin inhibited the metabolic activation of EF. Glycosides in licorice are metabolized into aglycones by intestinal bacteria, inhibiting the metabolic activation of EF and alleviating hepatotoxicity.

CONCLUSIONS

By combining with GSH, the electrophilic intermediates produced by the P450 enzyme's metabolic activation of the indole ring of EVO might cause hepatotoxicity. Glycyrrhizin from licorice and the liquiritigenin and isoliquiritigenin generated by intestinal bacterial metabolism play an attenuated function by inhibiting the P450 enzyme and preventing the metabolic activation of EF.

Synthesis and evaluation of indomethacin prodrugs with a diester structure that are metabolically activated by human carboxylesterases

1. Carboxylesterase (CES) has been studied extensively, mostly with substrates in the monoester structures. We investigated the relationship between indomethacin diester prodrugs and metabolic activation by microsomes and recombinant human CES.2. Eight indomethacin diester prodrugs were synthesised in two steps. They were used as substrates and hydrolysis rates were calculated.3. As a result, the major hydrolysis enzyme was CES. The hydrolysis rate of recombinant CES2A1 was comparable to that of recombinant CES1A1.4. In this study, by changing the structure of the prodrug to a diester structure, it was found that CES2 activity was equivalent to CES1 activity.5. It should be noted that the use of diester prodrugs in prodrug discovery, where organ-specific hydrolysis reactions are expected, may not yield the expected results.

Research progress on bioleaching recovery technology of spent lithium-ion batteries

Bioleaching of lithium-ion batteries is a microbially catalyzed process. Under the action of redox, acid leaching and complexation in the presence of microorganisms, the valuable metals in the cathode material enter the liquid phase as ions and are subsequently recovered from the succeeding process. This technique has the advantages of being inexpensive, environmentally friendly and having simple needs. However, it is still in development and has not yet commercialized. In this paper, the technology is fully discussed based on numerous excellent studies. The contents include commonly utilized microorganisms, bioleaching mechanism, microbial stress response and metabolic activation, enhancement strategies, leaching characteristics and interfacial phenomena, process evaluation, and a critical discussion of recent research breakthroughs. They give readers with comprehensive and in-depth understanding on the bioleaching of lithium-ion batteries and help to improve the technology's industrialization. Researchers can make new explorations from the potential research directions and methods presented in this work to make biotechnology better serve resource recovery and social development.

Glutathione conjugation and protein modification resulting from metabolic activation of pesticide metalaxyl in vitro and in vivo

Metalaxyl (MTL), a germicidal agent, is widely used in agriculture. Due to the biological amplification effect, MTL entering the ecological environment would result in a threat to human health through the food chain. MTL is reportedly accumulated in liver. The objectives of the study included investigating the metabolic activation of MTL in liver and defining the mechanisms participating in the hepatotoxicity of MTL. The corresponding glutathione (GSH), N-acetylcysteine (NAC) conjugate, and cysteine conjugates were observed in liver microsomes, prepared from liver tissues of mice, containing MTL and GSH, NAC or cysteine. These conjugates were also detected in urine and bile of rats receiving MTL. Apparently, MTL was biotransformed to a quinone imine intermediate dose-dependently attacking the thiols and cysteine residues of protein. The bioactivation of MTL required cytochrome P450 enzymes, and CYP3A dominated the bio-activation of MTL.

New in vitro screening system to detect drug-induced liver injury using a culture plate with low drug sorption and high oxygen permeability

Drug-induced liver injury (DILI) is a major factor underlying drug withdrawal from the market. Therefore, it is important to predict DILI during the early phase of drug discovery. Metabolic activation and mitochondrial toxicity are good indicators of the potential for DILI. However, hepatocyte function, including drug-metabolizing enzyme activity and mitochondrial function, reportedly decreases under conventional culture conditions; therefore, these conditions fail to precisely detect metabolic activation and mitochondrial toxicity-induced cell death. To resolve this issue, we employed a newly developed cell culture plate with high oxygen permeability and low drug sorption (4-polymethyl-1-pentene [PMP] plate). Under PMP plate conditions, cytochrome P450 (CYP) activity and mitochondrial function were increased in primary rat hepatocytes. Following l-buthionine-sulfoximine-induced glutathione depletion, acetaminophen-induced cell death significantly increased under PMP plate conditions. Additionally, 1-aminobenzotriazole reduced cell death. Moreover, mitochondrial toxicity due to mitochondrial complex inhibitors (ketoconazole, metformin, and phenformin) increased under PMP plate conditions. In summary, PMP plate conditions could improve CYP activity and mitochondrial function in primary rat hepatocytes and potentially detect metabolic activation and mitochondrial toxicity.

Metabolic activation and cytotoxicity of metaxalone mediated by cytochrome P450 enzymes and sulfotransferases

Metaxalone (MTX) is a central nervous system (CNS) depressant used for the treatment of acute skeletal muscle pain. Several cases of fatal overdose deaths in the clinical use of MTX, along with the presence of ischemic hepatitis in deceased patients, have been documented. The present study aimed to investigate the metabolic activation of MTX and to define the possible correlation between the metabolic activation and cytotoxicity of MTX. An oxidative metabolite (M1) and a GSH conjugate (M2) were observed in S9 fraction incubations as well as in rat primary hepatocyte culture after exposure to MTX. M1 and M2 were also observed in bile of MTX-treated rats. CYP2A6 was found to dominate the oxidation of MTX. Both methoxsalen (MTS, a CYP2A6 inhibitor) and 2,6-dichloro-4-nitrophenol (DCNP, a sulfotransferase inhibitor) dramatically decreased the formation of M2. Pre-treatment of primary hepatocytes with DCNP or MTS significantly decreased the susceptibility to the cytotoxicity of MTX.

Elucidation of the relationship between evodiamine-induced liver injury and CYP3A4-mediated metabolic activation by UPLC-MS/MS analysis

Evodiamine (EVD), which has been reported to cause liver damage, is the main constituent of Evodia rutaecarpa (Juss.) Benth and may be bioactivated into reactive metabolites mediated by cytochrome P450. However, the relationships between bioactivation and EVD-induced hepatotoxicity remain unknown. In this study, comprehensive hepatotoxicity evaluation was explored, which demonstrated that EVD caused hepatotoxicity in both time- and dose-dependent manners in mice. By application of UPLC-Q/TOF-MS/MS, two GSH conjugates (GM1 and GM2) derived from reactive metabolites of EVD were identified, in microsomal incubation systems exposed to EVD with glutathione (GSH) as trapping agents. CYP3A4 was proved to be the main metabolic enzyme. Correspondingly, the N-acetyl-L-cysteine conjugate derived from the degradation of GM2 was detected in the urine of mice after exposure to EVD. For the first time, the iminoquinone intermediate was found in EVD-pretreated rat bile by the high-resolution MS platform. Pretreatment with ketoconazole protected the animals from hepatotoxicity, decreased the protein expression of cleaved caspase-1 and -3, but increased the area under the serum-concentration-time curve of EVD in blood determined by UPLC-QQQ-MS/MS. Depletion of GSH by buthionine sulfoximine exacerbated EVD-induced hepatotoxicity. These results implicated that the CYP3A4-mediated metabolic activation was responsible for the observed hepatotoxicity induced by EVD.

Identification of intestinal metabolic activation of loganin generated dialdehyde reactive intermediates improves intestinal bile salt hydrolase activities

Loganin is an iridoid with potent pharmacological effects. Loganin contains a hemiacetal structure and can convert to dialdehyde intermediates after deglycosylation. We hypothesized that the metabolites of loganin with hemiacetal can generate reactive dialdehyde intermediates. This study aims to characterize the metabolic profiling of loganin and especially for the unstable dialdehyde intermediates by using ultra-performance liquid chromatograph-quadrupole orbitrap mass spectrometry. In this study, a total of 26 stable metabolites were identified in loganin-treated rats. Loganin underwent different metabolism in the intestine and liver, which was confirmed mainly by the metabolites in the hepatic portal vein. In the intestine, the major metabolic pathways were ester hydrolysis and deglycosylation, followed by methylation and dehydrogenation. The hepatic metabolism pathways were hydrogenation, hydroxylation, glucuronidation, and sulfonation. The circulating metabolites with high abundance were mainly derived from intestinal metabolism. Importantly, 11 unstable dialdehyde intermediates of loganin were identified and described for the first time. The dialdehyde intermediates were identified by their dihydropyridine conjugates with amino acids. The dialdehyde intermediates were mainly produced in the intestine. The dialdehyde intermediates enable covalent modification of intestinal proteins. Loganin can up-regulate the activity of intestinal bile salt hydrolase (BSH), catalyzing bile acid metabolism. The level of protein adducts was positively associated with BSH activity, indicating dialdehyde intermediates played a key role in the up-regulation of BSH activities. In conclusion, this study not only demonstrates the characteristic metabolic fate of loganin but also facilitates the understanding of the pharmacologic effects of dialdehyde intermediates.

Difference in hepatotoxicity of furan-containing components in cortex dictamni correlates the efficiency of their metabolic activation

BACKGROUND

Cortex Dictamni (CD) has been associated with an increased risk of liver injury, which may be attributable to the metabolic activation of its furan-containing components (FCC). However, the hepatotoxic potencies of these FCCs and the mechanisms behind the differences in their toxicity intensity remain unknown.

METHODS

The constituents of CD extract were determined by LC-MS/MS. Potentially toxic FCCs were screened by a previously published method. Hepatotoxicity of potentially toxic FCCs was evaluated in cultured mouse primary hepatocytes and mice. The ability to deplete hepatic glutathione (GSH), along with the formation of the corresponding GSH conjugates, resulting from the metabolic activation was determined ex vivo in mice. Intrinsic clearance rates (CL_int,V_max/K_m) were assessed by a microsome-bases assay.

RESULTS

A total of 18 FCCs were detected in CD extract. Among them, four FCCs, including rutaevin (RUT), limonin (LIM), obacunone (OBA) and fraxinellone (FRA) were found to be bioactivated in microsomal incubations. Only FRA displayed significant hepatotoxicity in vitro and in vivo. Similarly, FRA caused GSH depletion and GSH conjugation the most in vivo. The order of CL_int for the four FCCs was FRA>>OBA>LIM>RUT.

CONCLUSION

FRA is the major toxic FCC component of hepatotoxic CD extract. The hepatotoxicity of FCCs is closely related to the efficiency of their metabolic activation.

Metabolic activation and cytotoxicity of 4-Methylquinoline mediated by CYP3A4 and sulfotransferases in rats

4-Methylquinoline (4-MQ) is a quinoline derivative widely present in groundwater and soil and has been reported to be genotoxic. The mechanisms of the toxic action remain unknown. This study aimed to elucidate the metabolic activation of 4-MQ and to determine the possible role of reactive metabolites in 4-MQ-induced liver injury in rats. In the present study, a hydroxylation metabolite (M1), a GSH conjugate (M2) and an NAC conjugate (M3) derived from 4-MQ were detected in vitro and in vivo. The structures of the two conjugates were verified by chemical synthesis, mass spectrometry, and nuclear magnetic resonance. CYP3A4 was found to dominate the hydroxylation of 4-MQ. Sulfotransferases also participated in the metabolic activation of 4-MQ. Pretreatment of primary hepatocytes with ketoconazole (KTC) or 2,6-dichloro-4-nitrophenol (DCNP) not only reduced the production of GSH conjugate M2 but also decreased the susceptibility of hepatocytes to the cytotoxicity of 4-MQ. Urinary NAC conjugate M3 was found in rats given 4-MQ, and M3 may be a potential biomarker for 4-MQ exposure.

The attenuation effect of licorice on the hepatotoxicity of Euodiae Fructus by inhibiting the formation of protein conjugates and GSH depletion

ETHNOPHARMACOLOGICAL RELEVANCE

As a traditional Chinese medicine and food, Euodiae Fructus (EF) is widely used in clinics to relieve pain and prevent vomiting and for making tea for more than a thousand years. In recent years, hepatotoxic reactions to EF have been reported. The intermediates produced by evodiamine and rutaecarpine metabolism in vitro were captured by glutathione (GSH), suggesting that the toxicity of EF may be related to metabolic activation. Whether licorice can inhibit the metabolic activation of EF has not been reported, which needed an effective strategy to clarify the correlation between protein conjugates and hepatotoxicity and the attenuation mechanism of licorice processing.

AIM OF THE STUDY

This study aimed to explore the toxic components and mechanisms of EF based on metabolic activation and the detoxification of licorice.

MATERIALS AND METHODS

The content and toxicity index of protein conjugates in the liver were determined by orally administering mice and rats with EF. The attenuation mechanism of licorice was examined in cell and enzymology experiments.

RESULTS

The change in evodiamine-cysteinylglycine (EVO-Cys-Gly) and evodiamine-cysteine (EVO-Cys) levels was consistent with the change in hepatotoxicity. Licorice inhibited the formation of the protein conjugates of EF and increased the content of GSH in L02 cells.

CONCLUSION

EF mediated by P450 enzymes produced toxic intermediates, which combined with cysteine residues in animal liver and inactivate them, leading to hepatotoxicity. Interestingly, licorice can alleviate the GSH depletion caused by EF and inhibit the production of protein conjugates by inhibiting P450 enzymes.

Formation of RNA adducts resulting from metabolic activation of spice ingredient safrole mediated by P450 enzymes and sulfotransferases

Safrole (SFL) is an IARC class 2B carcinogen. To better understand the mechanism involved in SFL toxicity, we explored the potential interactions between SFL metabolites and RNA. Three guanosine adducts (G1-G3), two adenosine adducts (A1-A2), and two cytosine adducts (C1-C2) were detected by LC-MS/MS in mouse liver S9 incubations, cultured mouse primary hepatocytes, and liver tissues of mice after exposure to SFL. These adducts were chemically synthesized, and one of the guanosine adducts was structurally characterized by ¹H-NMR. Studies in vitro and in vivo showed that SFL was oxidized by cytochrome P450 enzymes to the corresponding 1'-hydroxyl metabolite which was further metabolized by sulfotransferases to form allylic sulfate esters. The formed reactive intermediate(s) subsequently reacted with bases of RNA, leading to RNA adduction, which could play a partial role in the toxicities of SFL through the alteration of RNA biochemical properties and interruption of RNA functions.

DNA damage and up-regulation of PARP-1 induced by columbin in vitro and in vivo

Columbin (CLB) is the most abundant (>1.0%) furan-containing diterpenoid lactone in herbal medicine Tinospora sagittate (Oliv.) Gagnep. The furano-terpenoid was found to be hepatotoxic, but the exact mechanisms remain unknown. The present study demonstrated that administration of CLB at 50 mg/kg induced hepatotoxicity, DNA damage and up-regulation of PARP-1 in vivo. Exposure to CLB (10 μM) induced GSH depletion, over-production of ROS, DNA damage, up-regulation of PARP-1 and cell death in cultured mouse primary hepatocytes in vitro. Co-treatment of mouse primary hepatocytes with ketoconazole (10 μM) or glutathione ethyl ester (200 μM) attenuated the GSH depletion, over-production of ROS, DNA damage, up-regulation of PARP-1, and cell death induced by CLB, while co-exposure to L-buthionine sulfoximine (BSO, 1000 μM) intensified such adverse effects resulting from CLB exposure. These results suggest that the metabolic activation of CLB by CYP3A resulted in the depletion of GSH and increase of ROS formation. The resultant over-production of ROS subsequently disrupted the DNA integrity and up-regulated the expression of PARP-1 in response to DNA damage, and ROS-induced DNA damage was involved in the hepatotoxicity of CLB.

Triphenyl phosphate induces clastogenic effects potently in mammalian cells, human CYP1A2 and 2E1 being major activating enzymes

As a new-type flame retardant and toxic substance, triphenyl phosphate (TPP) is a ubiquitous pollutant present even in human blood. TPP is transformed by human CYP enzymes to oxidized/dealkylated metabolites. The impact of TPP metabolism on its toxicity, however, remains unclear. In this study, the genotoxicity of TPP in several mammalian cell lines and its relevance to CYP/sulfortransferase (SULT) activities were investigated. The results indicated that TPP induced micronucleus formation at ≥1 μM concentrations in a human hepatoma (C3A, endogenous CYPs being substantial) cell line, which was abolished by 1-aminobenzotriazole (CYPs inhibitor). In cell line HepG2 (parental to C3A with lower CYP expression) TPP was inactive up to 10 μM, while pretreatment with ethanol (CYP2E1 inducer), PCB 126 (CYP1A inducer), or rifampicin (CYP3A inducer) led to micronucleus formation by TPP. In V79-Mz and V79-derived cells expressing human CYP1A1 TPP was inactive (up to 32 μM), and in cells expressing human CYP1B1, 2B6 and 3A4 it induced micronucleus weakly (positive only at 32 μM). However, TPP induced micronucleus potently in V79-derived cells expressing human CYP1A2, while this effect was drastically reduced by human SULT1A1 co-expression; likewise, TPP was inactive in cells expressing both human CYP2E1 and SULT1A1, but became positive with pentachlorophenol (inhibitor of SULT1) co-exposure. Moreover, in C3A cells TPP selectively induced centromere-free micronucleus (immunofluorescent assay), and TPP increased γ-H2AX (by Western blot, indicating double-strand DNA breaks). In conclusion, this study suggests that TPP is potently clastogenic, human CYP1A2 and 2E1 being major activating enzymes while SULT1A1 involved in detoxification.

Origin of metabolites diversity and selectivity of P450 catalyzed benzo[a]pyrene metabolic activation

Polycyclic Aromatic Hydrocarbon (PAHs) presents one of the most abundant class of environmental pollutants. Recent study shows a lab-synthesized PAHs derivative, helicenium, can selectively kill cancer cells rather than normal cells, calling for the in-depth understanding of the metabolic process. However, the origin of metabolites diversity and selectivity of P450 catalyzed PAHs metabolic activation is still unclear to a great extent. Here we systematically investigated P450 enzymes catalyzed activation mechanism of a representative PAHs, benzo[a]pyrene (BaP), and found the corresponding activation process mainly involves two elementary steps: electrophilic addition and epoxidation. Electrophilic addition step is evidenced to be rate determining step. Two representative binding modes of BaP with P450 were found, which enables the electrophilic addition of Heme (FeO) to almost all the carbons of BaP. This electrophilic addition was proposed to be accelerated by the P450 enzyme environment when compared with the gas phase and water solvent. To dig deeper on the origin of metabolites diversity, we built several linear regression models to explore the structural-energy relationships. The selectivity was eventually attributed to the integrated effects of structural (e.g. O-C distance and O-C-Fe angle) and electrostatic parameters (e.g. charge of C and O) from both BaP and P450.

Bisphenol-A reduces DNA methylation after metabolic activation

Bisphenol-A (BPA) is an important environmental contaminant with adverse health effects suspected to be mediated through epigenetic mechanisms. We had reported that the FLO1-dependent flocculation of transgenic yeast expressing human DNA methyltransferase (DNMT yeast) is a useful tool in epigenotoxicology studies. In this report, we have investigated the effects of BPA in the presence of metabolic activation (S-9 mix) on the transcription level of the FLO1 gene in the DNMT yeast. In the presence of metabolic activation, BPA inhibited the intensity of green fluorescence reporter protein (GFP) driven by the FLO1 promoter. A metabolite of BPA, 4-methyl-2,4-bis(p-hydroxyphenyl) pent-1-ene (MBP), also exhibited similar inhibitory effect. Furthermore, BPA in the presence of S-9 mix had only a weak while MBP had no inhibitory effects on the expression of modified GFP reporter gene under the control of FLO1 promoter with reduced CpG motifs. Aforementioned behavior was confirmed by the inhibition of flocculation as well as FLO1 gene mRNA expression. In addition, the global DNA methylation level in the human HEK293 cells was also reduced by MBP. These results indicate that BPA metabolites have inhibitory effect on DNA methylation. Our approach offers a novel in vitro method for screening for chemicals that can alter the epigenome by a mechanism dependent on their metabolic activation.

Diosbulbin B: An important component responsible for hepatotoxicity and protein covalent binding induced by Dioscorea bulbifera L

BACKGROUND

Dioscorea bulbifera L. (DBL) is an herbal medicine used for the treatment of thyroid diseases and tumors in China. However, the hepatotoxicity of DBL limits its wide safe use. Diosbulbin B (DSB) is the most abundant diterpene lactone occurring in DBL. Numbers of studies showed that this furanoterpenoid plays an important role in DBL-induced liver injury and that DSB is metabolized to a cis-enedial intermediate which reacts with protein to form protein covalent binding and induces hepatotoxicity.

PURPOSE

The present study aimed to define the association of DSB content in DBL with the severity of DBL hepatotoxicity to ensure the safe use of the herbal medicine in clinical practice and to determine the role of DSB in DBL-induced liver injury.

METHODS

Chemical chromatographic fingerprints of DBL were established by UPLC-MS/MS. Their hepatotoxicity potencies were evaluated in vitro and in vivo. Metabolic activation of DSB was evaluated by liver microsomal incubation. Protein modification was assessed by mass spectrometry and immunostaining.

RESULTS

The contents of DSB in DBL herbs collected from 11 locations in China varied dramatically with as much as 47-fold difference. The hepatotoxicity potencies of DBL herbs were found to be proportional to the contents of DSB. Intensified protein adduction derived from the reactive metabolite of DSB was observed in mice administered DBL with high contents of DSB.

CONCLUSION

The findings not only demonstrated that contents of DSB can be quite different depending on harvest location and special attention needs to pay for quality control of DBL but also suggest DSB is a key contributor for DBL-induced hepatotoxicity.

Anastrozole and Related Glucuronic Acid Conjugate are Electrophilic Species

Anastrozole (ANA), is an inhibitor of non-steroidal aromatase, widely employed for the treatment of breast cancer. However, ANA-associated liver injury cases have been documented in the application of the drug.The major purposes of the present study were to identify the structure of reactive metabolites derived from ANA and to study related metabolic pathways of ANA.We found ANA itself is an electrophilic species reactive to GSH. ANA can be metabolized to ANA-N⁺-glucuronide (1) catalyzed by UGT1A4. An ANA GSH conjugate (2) was detected in bile and livers of rats treated with ANA. UGT1A4 participated in the phase II metabolic pathway.This work allowed us to better understand the mechanisms of the hepatotoxicity of ANA and provided new avenue to define the possible role of metabolic activation in hepatotoxicity.

Estrogenic and growth inhibitory responses to organophosphorus flame retardant metabolites in zebrafish embryos

Recent evidence has revealed that organophosphorus flame retardants (OPFRs) elicit a variety of toxic effects, including endocrine disruption. The present study examined estrogenic and growth inhibitory responses to OPFR metabolites in comparison to their parent compounds using zebrafish eleutheroembryos.¹ Exposure to 4-hydroxylphenyl diphenyl phosphate (HO-p-TPHP) but not its parent compound triphenyl phosphate (TPHP) elicited upregulation of a marker gene of estrogenic responses, cytochrome P450 19A1b (CYP19A1b), and this upregulation was reversed by co-exposure to an estrogen receptor antagonist. Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), as well as 3-hydroxylphenyl diphenyl phosphate (HO-m-TPHP) and diphenyl phosphate (DPHP), did not elicit significant changes in the CYP19A1b expression. Reduction in body length was induced by TPHP and to a lesser extent by its hydroxylated metabolites. Altered expression of genes involved in the synthesis and action of thyroid hormones, including iodothyronine deiodinases 1 and 2, thyroid hormone receptor alpha, and transthyretin, were commonly observed for TPHP and its hydroxylated metabolites. Reduction in the body length was also seen in embryos exposed to TDCIPP but not BDCIPP. The transcriptional effect of TDCIPP was largely different from that of TPHP, with decreased expression of growth hormone and prolactin observed only in TDCIPP-exposed embryos. Considering the concentration-response relationships for the growth retardation and gene expression changes, together with existing evidence from other researchers, it is likely that prolactin is in part involved in the growth inhibition caused by TDCIPP. The present study showed similarities and differences in the endocrine disruptive effects of OPFRs and their metabolites.

The protein adduction derived from reactive metabolites of multiple furanoids in cortex Dictamni-treated mice

The association of herb medicine Cortex Dictamni (CD) with severe even fatal hepatotoxicity has been widely reported. Recently, we demonstrated that the metabolic activation of at least ten furanoids in CD was responsible for the liver injury caused by the ethanol extract of CD (ECD) in mice. Protein adduction by reactive metabolites is considered to initiate the process of liver injury. Unlike single chemicals, the mode of and the details of protein modification by multiple components in an herb is unclear. This study aimed to characterize protein adductions derived from the reactive metabolite of furanoids in ECD-treated mice and define the association of protein adduction with liver injury. The hepatic cysteine- and lysine-based protein adducts derived from epoxide or cis-enedione of at least six furanoids were identified in mice. The furanoids with an earlier serum content T_max were mainly to bind with hepatic glutathione and no protein adducts were formed except for dictamnine. The hepatic proteins were modified by the later absorbed furanoids. The levels of hepatic protein adduct were correlated with the degree of liver injury. In addition, the reactive metabolites of different furanoids can simultaneously bind to the model peptide by the identical reactive moiety, indicating the additive effects of the individual furanoids in the modification of hepatic proteins. In conclusion, hepatic protein adduction by multiple furanoids may play a role in ECD-induced liver injury. The earlier absorbed furanoids were mainly to bind with glutathione whereas the hepatic proteins were modified by the later furanoids.

Fasting augments pyrrolizidine alkaloid-induced hepatotoxicity

Pyrrolizidine alkaloids (PAs) are phytotoxins widely present in various natural products and foodstuffs. The present study aims to investigate the effects of fasting on PA-induced hepatotoxicity and the underlying biochemical mechanisms. The results of hepatotoxic study showed that 15-h overnight fasting significantly exacerbated the hepatotoxicity of retrorsine (RTS, a representative toxic PA) in fasted rats compared to fed rats, as indicated by remarkably elevated plasma ALT and bilirubin levels and obvious liver histological changes. Further toxicokinetic studies revealed that fasting significantly enhanced cytochromes P450 enzymes (CYPs)-mediated metabolic activation of RTS leading to increased formation of pyrrole-protein adducts and thus decreased the in vivo exposure and excretion of both parent RTS and its N-oxide metabolite. Metabolic studies demonstrated that fasting induced enzyme activities of CYP1A2, CYP2B6 and CYP2E1 that participated in catalyzing RTS to its reactive pyrrolic metabolites. Moreover, fasting also dramatically decreased hepatic glutathione (GSH) content, which restricted the detoxification of GSH by neutralizing the reactive pyrrolic metabolite of RTS, further contributing to the enhanced hepatotoxicity. The present findings may have an impact on future PA toxicity tests with different dietary styles and/or risk assessment of metabolite-mediated toxins by considering the profound effects of fasting.

Human CYP enzyme-activated clastogenicity of 2-ethylhexyl diphenyl phosphate (a flame retardant) in mammalian cells

2-Ethylhexyl diphenyl phosphate (EHDPP) is a common flame retardant and environmental pollutant, exposing humans with endocrinal disrupting potentials. Its mutagenicity, especially following metabolism, remains unclear. In this study, molecular docking analysis indicated that EHDPP was a potential substrate for several human CYP enzymes except for CYP1A1. Among V79-derived cell lines genetically engineered for the expression of each CYP, EHDPP (6 h exposure/18 h recovery) did not induce micronuclei in the V79 or V79-derived cells expressing human CYP1A1, however, it was positive in V79-derived cell lines expressing human CYP2E1, 3A4, and 2B6. In a human hepatoma (HepG2) cell line, EHDPP (48 h exposure) moderately induced micronuclei, which was blocked by 1-aminobenzotriazole (ABT, 60 μM, inhibitor of CYPs); pretreating HepG2 cells with bisphenol AF, another organic pollutant as inducer of CYPs (0.1 μM for 16 h), significantly potentiated micronuclei formation by EHDPP, threshold being decreased from 10 to 1.25 μM. This effect was blocked by ABT, drastically reduced by ketoconazole (inhibiting CYP3A expression/activity), and moderately inhibited by trans-1,2-dichloroethylene (selective CYP2E1 inhibitor). Immunofluorescent centromere protein B staining indicated that EHDPP-induced micronuclei in V79-derived cell lines expressing human CYP2E1 and 3A4 were predominantly centromere-negative, and that in HepG2 cells pretreated with bisphenol AF (for inducing multiple CYPs) were purely centromere-negative. In bisphenol AF-pretreated HepG2 cells EHDPP potently induced DNA breaks, as indicated by the comet assay and Western blot analysis of γ-H2AX. In conclusion, our study suggests that EHDPP is potently clastogenic, following activation by several human CYP enzymes, CYP3A4 being a major one.

Case Study 11: Considerations for Enzyme Mapping Experiments-Interaction Between the Aldehyde Oxidase Inhibitor Hydralazine and Glutathione

Often it may be convenient and efficient to address multiple research questions with a single experiment. In many instances, however, the best approach is to design the experiment to address one question at a time. The design of enzyme mapping experiments is discussed in this chapter, focusing on considerations pertinent to the study of aldehyde oxidase (AO) vs. cytochrome P450 metabolism. Specifically, a case is presented in which reduced glutathione (GSH) was included in an experiment with human liver S9 fraction to trap reactive metabolites generated from cytochrome P450-mediated metabolism of lapatinib and its O-dealkylated metabolite, M1 (question 1). The AO inhibitor hydralazine was included in this experiment to investigate the involvement of AO-mediated metabolism of M1 (question 2). The presence of GSH was found to interfere with the inhibitory activity of hydralazine. Consideration of the time-dependent nature of hydralazine inhibitory activity toward AO when designing this experiment could have predicted the potential for GSH to interfere with hydralazine. This case underscores the importance of clearly identifying the research question, tailoring the experimental protocol to answer that question, and then meticulously considering how the experimental conditions could influence the results, particularly if attempting to address multiple questions with a single experiment.

Metabolism-mediated cytotoxicity and genotoxicity of pyrrolizidine alkaloids

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.

Metabolic Activation of Aegeline Mediated by CYP2C19

1. Aegeline (AGL) is a natural alkaloidal amide mainly isolated from the leaves and fruits of tropical plant Aegle marmelos, with multiple pharmacological activities.2. As one component of several dietary supplements, AGL caused a series of acute and chronic liver injuries. Nevertheless, the mechanisms of AGL-induced hepatotoxicity remain unclear. This study was conducted to identify reactive metabolite(s), to determine related metabolic pathways, and define the possible association of the bioactivation with AGL cytotoxicity.3. A demethylation metabolite (M1) and a GSH conjugate (M2) were detected in rat liver microsomal incubations containing AGL and GSH. The two metabolites were both found in bile of rats and rat primary hepatocytes after AGL administration.4. Recombinant P450 enzyme incubations showed that CYP2C19 was the principal enzyme catalyzing this metabolic activation.5. Ticlopidine, a selective inhibitor of CYP2C19, decreased the formation of M1 and M2 in hepatocytes and attenuated the susceptibility of hepatocytes to the cytotoxicity of AGL. The results suggest that AGL was metabolized to a p-quinone methide intermediate which could in part participate in AGL-induced cytotoxicity.

1-Methylpyrene induces chromosome loss and mitotic apparatus damage in a Chinese hamster V79-derived cell line expressing both human CYP1A2 and sulfotransferase 1A1

1-Methylpyrene (1-MP) is a ubiquitous environmental pollutant and rodent carcinogen. Its mutagenic activity depends on sequential activation by various CYP and sulfotransferase (SULT) enzymes. Previously we have observed induction of micronuclei and mitotic arrest by 1-MP in a Chinese hamster (V79)-derived cell line expressing both human CYP1A2 and SULT1A1 (V79-hCYP1A2-hSULT1A1), however, the mode of chromosome damage and the involvement of mitotic tubulin structures have not been clarified. In this study, we used immunofluorescent staining of centromere protein B (CENP-B) with the formed micronuclei, and that of β- and γ-tubulin reflecting the structures of mitotic spindle and centrioles, respectively, in V79-hCYP1A2-hSULT1A1 cells. The results indicated that 1-MP induced micronuclei in V79-hCYP1A2-hSULT1A1 cells from 0.125 to 2 μM under a 24 h/0 h (exposure/recovery) regime, while in the parental V79-Mz cells micronuclei were induced by 1-MP only at concentrations ≥ 8 μM; in both cases, the micronuclei induced by 1-MP were predominantly CENP-B positive. Following 54 h of exposure, 1-MP induced mitotic spindle non-congression and centrosome amplification (multipolar mitosis) in V79-hCYP1A2-hSULT1A1 cells, and anaphase/telophase retardation, at concentrations ≥ 0.125 μM with concentration-dependence; while in V79-Mz cells it was inactive up to 8 μM. This study suggests that in mammalian cells proficient in activating enzymes 1-MP may induce chromosome loss and mitotic disturbance, probably by interfering with the mitotic spindle and centrioles.

Refinement of the zebrafish embryo developmental toxicity assay

Several pharmaceutical and chemical companies are using the zebrafish embryo as an alternative to animal testing for early detection of developmental toxicants. Unfortunately, the protocol of this zebrafish embryo assay varies between labs, resulting in discordant data for identical compounds. The assay also has some limitations, such as low biotransformation capacity and fewer morphological endpoints in comparison with the in vivo mammalian developmental toxicity studies. Consequently, there is a need to standardize and further optimize the assay for developmental toxicity testing. We developed a Zebrafish Embryo Developmental Toxicity Assay (ZEDTA) that can be extended with a metabolic activation system and/or skeletal staining to increase its sensitivity. As such, the ZEDTA can be used as a modular system depending on the compound of interest.•

Our protocol is customized with a metabolic activation system for test compounds, using human liver microsomes. This system ensures exposure of zebrafish embryos to metabolites that are relevant for human risk and safety assessment. As human liver microsomes are toxic for the zebrafish embryo, we developed a preincubation system with an ultracentrifugation and subsequent dilution step.

•

Additionally, we developed a skeletal staining protocol that can be added to the ZEDTA modular system. Our live Alizarin Red staining method detects several bone structures in 5-day old zebrafish larvae in a consistent manner.

Protein cross-linking in primary cultured mouse hepatocytes by dehydropyrrolizidine alkaloids: Structure-toxicity relationship

Pyrrolizidine alkaloids (PAs) are natural toxins found in about 3%-5% of flowering plants. Dehydropyrrolizidine alkaloids contain a double bond in 1, 2-position of the necine bases, including retronecine type PAs (RET-PAs) and their N-oxides (RET N-oxide-PAs), and otonecine type PAs (OTO-PAs), and are known for their significant hepatotoxicity. Most dehydropyrrolizidine alkaloids are metabolically activated by cytochrome P450 (CYP450) enzymes to generate active pyrroles, which further bind to proteins to form pyrrole-protein adducts (PPAs). Methods for predicting PA-induced liver injury are generally performed on in vitro models with extremely low activities of CYP450 enzymes, which is different from the situation in vivo. In this regard, primary cultured mouse hepatocytes, which showed comparable CYP450 activity with the in vivo models, were applied to illustrate the structure-toxicity relationship of 13 dehydropyrrolizidine alkaloids, namely, eight RET-PAs, three RET N-oxide-PAs, and two OTO-PAs. PA-induced cytotoxicity and PA-generated PPAs were analyzed in primary mouse hepatocytes treated with different PAs. Results showed that PA-induced toxicity was correlated with the amount of PA-generated PPAs. RET-PAs and OTO-PAs were generally more toxic than RET N-oxide-PAs and generated higher amount of PPAs. PPAs were utilized to evaluate the efficiency of metabolic activation and predict the toxic potencies of dehydropyrrolizidine alkaloids. The proposed model could be a new approach for toxicity evaluation and risk control of exposure to PAs.

Cortex dictamni-induced liver injury in mice: The role of P450-mediated metabolic activation of furanoids

Many furan containing compounds have been reported to be toxic resulted from the metabolic activation of the furan ring to reactive metabolite (RM). Cortex Dictamni (CD), a widely used herbal medicine, has been reported to cause severe even fatal hepatotoxicity. The injurious components and mechanism of CD-induced liver injury remain unclear. Our preliminary study showed that dictamnine, one major furanoid in CD, caused mouse liver injury via its reactive epoxide metabolite. Besides dictamnine, the major components of CD are series of bioactivation-alerting furanoids. Thus, we hypothesize that series of furanoids in CD may undergo metabolic activation and play a key role in CD-induced liver injury. Here, a single oral dose of 60 g/kg ethanol extract of CD (ECD) caused severe hepatocellular necrosis in mice at 24 h post-dose. ECD-induced liver injury showed a dose- and time-dependent manner. The hepatotoxic effects could be completely abolished by P450 nonselective inhibitor 1-aminobenzotriazole (ABT) and strongly modulated by other P450 modulators. The furanoids-concentrated fraction of ECD was responsible for the hepatotoxicity. At least ten furanoids with high abundance in ECD, such as obakunone, dictamnine, fraxinellone, limonin, were found to be metabolized to reactive epoxide or cis-enedione. The RM levels were consistent with the liver injury degree. Multiple furanoids, rather than single one, cooperatively contributed to the hepatotoxicity. ECD-induced liver injury could be reproduced by a mixture of pure furanoids. In summary, this study provides toxic component profiles of CD and demonstrates that P450-mediated bioactivation of multiple furanoids is responsible for CD-induced liver injury.

Algal toxicity induced by effluents from textile-dyeing wastewater treatment plants

This research aimed to evaluate the alga Scenedesmus obliquus toxicity induced by textile-dyeing effluents (TDE). The toxicity indicator of TDE in alga at the physiological (algal growth), biochemical (chlorophyll-a (Chl-a) synthesis and superoxide dismutase (SOD) activity) and structural (cell membrane integrity) level were investigated. Then we further study the relationship among toxicity indicators at physiological and biochemical level, and supplemented by research on algal biomacromolecules. According to the analysis of various endpoints of the alga, the general sensitivity sequence of toxicity endpoints of Scenedesmus obliquus was: SOD activity > Chl-a synthesis > algal growth. The stimulation rate of SOD activity increased from day 3 (57.25%~83.02%) to day 6 (57.25%~103.81%), and then decreased on day 15 (-4.23%~-32.96%), which indicated that the antioxidant balance system of the algal cells was destroyed. The rate of Chl-a synthesis inhibition increased gradually, reaching 19.70%~79.39% on day 15, while the rate of growth inhibition increased from day 3 (-12.90%~10.16%) to day 15 (-21.27%~72.46%). Moreover, the algal growth inhibition rate was positively correlated with the inhibition rate of SOD activity or Chl-a synthesis, with the correlation coefficients were 0.6713 and 0.5217, respectively. Algal cells would be stimulating to produce excessive reactive oxygen species, which would cause peroxidation in the cells, thereby destroying chloroplasts, inhibiting chlorophyll synthesis and reducing photosynthesis. With increasing exposure time, irreversible damage to algae can lead to death. This study is expected to enhance our understanding of the ecological risks through algal tests caused by TDE.

Synthesis and evaluation of nevirapine analogs to study the metabolic activation of nevirapine

Nevirapine (NVP) is widely used as a non-nucleoside reverse transcriptase inhibitor of HIV-1, however, it is associated with severe skin and liver injury. The mechanisms of these adverse reactions are not yet clear, but the metabolic activation of NVP is thought to be related to the injury process. Until now, several metabolic activation pathways of NVP have been reported. In this study, in order to identify the reactive metabolite of NVP mainly responsible for CYP inhibition and liver injury, we synthesized five NVP analogs designed to avoid the proposed bioactivation pathway and evaluated their metabolic stabilities, CYP3A4 time-dependent inhibitory activities, and cytotoxicity. As a result, only a pyrimidine analog of NVP, which could avoid the formation of a reactive epoxide intermediate, did not inhibit CYP3A4. Outside of this compound, the other synthesized compounds, which could avoid the generation of a reactive quinone-methide intermediate, inhibited CYP3A4 equal to or stronger than NVP. The pyrimidine analog of NVP did not induce cytotoxicity in HepG2 and transchromosomic HepG2 cells, expressing major four CYP enzymes and CYP oxidoreductase. These results indicated that the epoxide intermediate of NVP might play an important role in NVP-induced liver injury.

Toxicity of fine and quasi-ultrafine particles: Focus on the effects of organic extractable and non-extractable matter fractions

To date no study has been able to clearly attribute the observed toxicological effects of atmospheric particles (PM) to a specific class of components. The toxicity of both the organic extractable matter (OEM_2.5-0.3) and non-extractable matter (NEM_2.5-0.3) of fine particles (PM_2.5-0.3) was compared to that of PM_2.5-0.3 in its entirety on normal human epithelial bronchial BEAS-2B cells in culture. The specific effect of the quasi-ultrafine fraction (PM_0.3) was assessed, by comparing the responses of cells exposed to the PM_2.5-0.3 and PM_0.3 organic extractable matter, OEM_2.5-0.3 and OEM_0.3 respectively. Chemically, PAH, O-PAH, and N-PAH were respectively 43, 17, and 4 times more concentrated in PM_0.3 than in PM_2.5-0.3, suggesting thereby a predominant influence of anthropogenic activities and combustion sources. BEAS-2B cells exposed to PM_2.5-0.3, NEM_2.5-0.3, EOM_2.5-0.3 and OEM_0.3 lead to different profiles of expression of selected genes and proteins involved in the metabolic activation of PAH, O-PAH, and N-PAH, and in the genotoxicity pathways. Specifically, OEM_0.3 was the most inducer for phase I and phase II enzymes implicated in the metabolic activation of PAH (AHR, AHRR, ARNT, CYP1A1, CYP1B1, EPHX-1, GSTA-4) thereby producing the highest DNA damage, felt by ATR and, thereafter, a cascade of protein phosphorylation (CHK1/CHK2/MDM2) closely related to the cell cycle arrest (P21 and P53 induction). This study underlined the crucial role played by the organic chemicals present in PM_0.3. These results should be considered in any future study looking for the main chemical determinants responsible for the toxicity of ambient fine PM.

Dietary phytochemicals as the potential protectors against carcinogenesis and their role in cancer chemoprevention

Health-threatening consequences of carcinogen exposure are mediated via occurrence of electrophiles or reactive oxygen species. As a result, the accumulation of biomolecular damage leads to the cancer initiation, promotion or progression. Accordingly, there is an association between lifestyle factors including inappropriate diet or carcinogen formation during food processing, mainstream, second or third-hand tobacco smoke and other environmental or occupational carcinogens and malignant transformation. Nevertheless, increasing evidence supports the protective effects of naturally occurring phytochemicals against carcinogen exposure as well as carcinogenesis in general. Isolated phytochemicals or their mixtures present in the whole plant food demonstrate efficacy against malignancy induced by carcinogens widely spread in our environment. Phytochemicals also minimize the generation of carcinogenic substances during the processing of meat and meat products. Based on numerous data, selected phytochemicals or plant foods should be highly recommended to become a stable and regular part of the diet as the protectors against carcinogenesis.

The molecular mechanism of the antagonistic activity of hydroxylated polybrominated biphenyl (OH-BB80) toward thyroid receptor β

Polybrominated biphenyls (PBBs) were widely used as additive brominated flame retardants. Their hydroxylated products (OH-PBBs) have been detected frequently in various marine mammals, causing an increased health risk. Till now, there lacks information on the potential disruption of OH-PBBs toward thyroid hormone receptor (TR) and the molecular characteristics of their interactions remain largely unknown. We herein in vitro and in silico evaluated the disrupting effect of 3,3',5,5'-tetrabromobiphenyl (BB80) and its metabolite 2,2'-dihydroxy- 3,3',5,5'-tetrabromobiphenyl (OH-BB80) toward human TR. The recombinant human TRβ two-hybrid yeast assay reveals the moderate antagonistic activity of OH-BB80 with IC₂₀ at 2 μmol/L, while BB80 shows no agonistic or antagonistic activity. OH-BB80 binds at the binding cavity of TRβ ligand binding domain (LBD) and forms one hydrogen bond with Phe272. Electrostatic interactions and hydrophobic interactions contribute much to their interactions. The binding of OH-BB80 quenches the intrinsic fluorescence of TRβ LBD at static quenching mode. Our study extends knowledge on the endocrine disrupting effect of OH-PBBs and suggests the full consideration of the biotransformation for further health risk assessment of PBBs and related structurally similar emerging contaminants.

Metabolic activation of TM5441 in vitro and in vivo: Formation of reactive metabolites and human enzymes involved

TM5441, a furan-containing drug, is an inhibitor of plasminogen activator inhibitor-1 (PAI-1), which can induce intrinsic apoptosis of human cancer cell lines. The aim of this study was to identify the reactive metabolites of TM5441 and to reveal the bioactivation pathways that are associated with its hepatotoxicity. The reactive metabolites were trapped by using glutathione (GSH) or N-acetyl-lysine (NAL) in rat, dog, and human liver microsomal incubation system after exposure to TM5441. Two metabolic activation pathways were disclosed. The first bioactivation pathway was dominated by Cytochrome P450 enzymes (CYP450s); TM5441 was metabolized into cis-2-butene-1,4-dial derivative dependent on NADPH, which can be trapped in the liver microsomal incubations fortified with GSH or NAL as trapping agents. Five metabolites (M1, M2, M9, M12 and M13) associated with GSH and three metabolites (M4, M7 and M14) associated with NAL were identified by liquid chromatography-high resolution mass spectrometry. The second bioactivation pathway was catalyzed by UDP-glucuronosyltransferases (UGTs); TM5441 was conjugated with glucuronide to form acyl-glucuronide (M10), which further reacted with GSH, resulting in the identification of a TM5441-S-acyl-GSH adduct (M11) in liver microsomal incubations fortified with uridine-5'-diphosphoglucuronidc acid (UDPGA) and GSH. M9, M10, M11, M12 and M13 were also detected in bile samples of rats given TM5441. Compared with rat, dog would display closer bioactivation profiles to human. The CYP450 enzyme responsible for the bioactivation of TM5441 was mainly identified as CYP3A4, using human recombinant CYP450 enzymes and specific inhibitory studies. The UGT enzymes responsible for the bioactivation of TM5441 mainly involved UGT2B7, 1A1 and 1A4. These results facilitate the understanding of the bioactivation of TM5441 and potential toxicological implications.

Exploring the effective materials of flavonoids-enriched extract from Scutellaria baicalensis roots based on the metabolic activation in influenza A virus induced acute lung injury

Flavonoids-enriched extract from Scutellaria baicalensis roots (FESR) ameliorated influenza A virus (IAV) induced acute lung injury (ALI) in mice by inhibiting the excessive activation of complement system in vivo. However, FESR had no anti-complementary activity in vitro. In order to reveal the effective materials of FESR for the treatment of IAV-induced ALI, the present research explored the metabolic process of FESR both in nomal and IAV infected mice by the method of UHPLC-ESI-LTQ/MS, as well as the metabolic activating mechanism. The results showed that the inactive flavonoid glycosides of FESR were partly metabolized into anti-complementary aglycones in vivo, mainly including 5,7,4'-trihydroxy-8-methoxy-flavone, norwogonin, baicalein, wogonin, oroxylin A and chrysin. Moreover, compared with the normal mice, IAV-induced ALI mice exhibited more efficient on producing and absorbing these active metabolites, with AUC_0-t and C_max in plasma and concentrations in lungs and intestines markedly elevated in the IAV treated groups (P <  0.05). Interestingly, the intestinal bacteria from IAV-induced ALI mice showed stronger β-glucuronidase activity and also had higher efficiency on transforming FESR to the flavonoid aglycones. These findings suggested that the anti-complementary aglycones produced by metabolic activation in vivo should be the potential effective materials of FESR against IAV infections, and intestinal bacteria might play an important role on the higher bioavailability of FESR in IAV infected mice. Additionally, the animals under the pathological state are more suitable for the metabolic study of traditional Chinese medicine.

In vitro and in vivo studies of the metabolic activation of chelidonine

Chelidonium majus L. is a herbal medicine widely employed in Europe and Western Asia. Chelidonine (CHE) is a major constituent of the herb and has been reported to be an inhibitor of the cytochrome P450 enzymes (CYP). The major objective of the present study was to study the metabolic pathways of CHE in order to identify potential reactive metabolites responsible for the enzyme inhibition. Three oxidative metabolites (M1-M3) were detected in human liver microsomal incubations after exposure to CHE. M1 and M2 were two isomers of catechol derivatives, and M3 was a dicatechol compound. The M1-M3 metabolites were also observed in bile of rats given CHE. A total of five glutathione (GSH) conjugates (M4-M8) were detected in microsomes containing CHE, GSH, and NADPH. Moreover, M4 and M6 originated from M1, M5 and M7 resulted from M2, and M8 was a M3-derived GSH conjugate. Three biliary CHE-derived GSH conjugates (M4, M5 and M8) were found in CHE-treated rats. This indicates that CHE was bioactivated to ortho-quinone derivatives both in vitro and in vivo. Recombinant P450 enzyme incubations demonstrated that the CYPs3A4, 1A2, 2C19 and 2D6 were mainly involved in metabolic activation of CHE. This study generated data that may be useful in understanding possible mechanisms of CHE-induced P450 inhibition.

Immunometabolism: A target for the comprehension of immune response toward transplantation

Organ transplantation is a life-saving procedure, however predicting graft survival is still challenging. Understanding immune-cell pathobiology is critical to the development of effective therapies to prevent rejection. Over the recent years it has become progressively evident that the complex nature of immune cell behavioral dynamics is strongly dependent on cellular metabolism, which in turn, relies on competition for nutrients, oxygen and metabolites with other immune cells and microbiota. Furthermore, the influence of the inflammatory state can lead to substantial changes in conditions within the tissue micro-environment. Considering the context of immunity, alterations in metabolic pathways (glycolysis, the tricarboxylic acid cycle, the pentose phosphate pathway, the fatty acid oxidation and synthesis, and the amino acid metabolic pathways) will influence the production of different sets of cytokines and affect transplantation outcome. It is now known that naïve, resting and effector cells acquire different metabolic profiles and studies have shown that specifically targeting some of these metabolic routes can prevent differentiation of effector T cells in favor of Tregs. Ultimately, to develop effective therapies that will prevent graft loss and understanding how cell metabolism impacts the fate and function of immune cells is now a critical point of discussion. The distinct metabolic features and requirements observed in effector and suppressive cell subsets offer promising opportunities for selective regulation of the immune responses in transplantation and will be discussed in this review.

Development of novel and safer anti-breast cancer agents, SS1020 and SS5020, based on a fundamental carcinogenic research

Tamoxifen (TAM) has been prescribed worldwide to patients with and women at high-risk of breast cancer. However, long-term use of TAM increases the incidence of endometrial cancer. The carcinogenic mechanisms of TAM have been extensively investigated. TAM is hydroxylated and sulfonated at α-carbon to form α-hydroxytamoxifen-O-sulfonate. This metabolite readily reacts with genomic DNA, particularly with 2′-deoxyguanosine, leading to DNA replication error. TAM also exerts estrogenic activity at endometrial tissue to induce endometrial hyperplasia. Therefore, our efforts focused on the development of novel and safer anti-estrogens to diminish carcinogenic potential of TAM based on chemical modifications. In this review, we describe a crucial idea of our drug design and introduce our compounds SS1020 and SS5020, possessing high effectiveness, and no genotoxic and estrogenic activities.

Sex difference in monocrotaline-induced developmental toxicity and fetal hepatotoxicity in rats

Pyrrolizidine alkaloids (PAs) are a class of hepatic toxins widely existing in plants. Cytochromes P450 (CYP) mediates PA bioactivation and toxicities in mammals. It has been reported that PAs can induce developmental toxicity, but systematic research is lacking. In this study, we investigated developmental toxicity of monocrotaline (MCT) in rats. Pregnant rats were administered with MCT (20 mg/kg) intragastrically from gestation day 9 to 20, followed by determination of changes in fetal growth, hepatic morphology, serum biochemical indices, and indicators of hepatocytes apoptosis. MCT was found to induce developmental toxicity and fetal hepatotoxicity, particularly in female fetuses. Metabolic activation was also studied by examination of bioactivation efficiency of MCT in fetal liver microsomes, serum MCT, pyrrole-protein adduction derived from MCT, and hepatic CYP3 A expression of fetuses in vivo. Male fetuses showed greater basal MCT bioactivation than that of female fetuses, but continuous exposure to MCT caused a selective CYP3 A induction in female fetuses, which may contribute to the sex difference in MCT-induced developmental toxicity.