Structure-function relationships of inhibition of human cytochromes P450 1A1, 1A2, 1B1, 2C9, and 3A4 by 33 flavonoid derivatives

CYP1A inhibitors: Recent progress, current challenges, and future perspectives

Mammalian cytochrome P450 1A (CYP1A) are key phase I xenobiotic-metabolizing enzymes that play a distinctive role in metabolic activation or metabolic clearance of a variety of procarcinogens, drugs, and endogenous substances. Human CYP1A subfamily contains two members (hCYP1A1 and hCYP1A2), which are known to catalyze the oxidative activation of some environmental procarcinogens into carcinogenic species. Increasing evidence has demonstrated that CYP1A inhibitor therapies are promising strategies for cancer chemoprevention or overcoming CYP1A-associated drug toxicity and resistance. Herein, we reviewed recent advances in the discovery and characterization of hCYP1A inhibitors, from the discovery approaches to structural features and biomedical applications of hCYP1A inhibitors. The inhibition potentials, inhibition modes, and inhibition constants of all reported hCYP1A inhibitors are comprehensively summarized. Meanwhile, the structural features and structure-activity relationships of different classes of hCYP1A1 and hCYP1A2 inhibitors are analyzed and discussed in depth. Furthermore, the major challenges and future directions for this field are presented and highlighted. Collectively, the information and knowledge presented here will strongly facilitate the researchers to discover and develop more efficacious CYP1A inhibitors for specific purposes, such as chemo-preventive agents or as tool molecules in hCYP1A-related fundamental studies.

Wogonin alleviates BaP-induced DNA damage and oxidative stress in human airway epithelial cells by dual inhibiting CYP1A1 activity and expression

Benzo[a]pyrene (BaP) is a common air pollutant that has been reported to cause oxidative stress and carcinogenesis. Wogonin, a flavonoid compound extracted from the roots of Scutellaria baicalensis, has been found to possess a variety of pharmacological activities, including anti-inflammatory and anti-cancer effects. The purpose of this study was to examine the ability of wogonin to alleviate the cytotoxicity induced by BaP in human airway epithelial cells and explore the corresponding mechanism. Our study found that wogonin treatment inhibited DNA damage and reactive oxygen species overproduction induced by BaP in human airway epithelial cells. In vitro enzyme assays showed that wogonin significantly inhibited the enzymatic activity of CYP1A1. In addition, wogonin decreased the basal level of CYP1A1 and inhibited the CYP1A1 overexpression induced by BaP, whereas overexpression of CYP1A1 partially reversed the effect of wogonin on BaP-induced DNA damage. Meanwhile, a CYP1A1 inhibitor and CYP1A1 knockdown also showed these same effects. Further studies showed that wogonin regulates CYP1A1 expression by inhibiting CDK7 and CDK9 activity. The use of CDK7 or CDK9 inhibitors decreased BaP-induced cytotoxicity and CYP1A1 expression. Finally, we found that the methoxy group of wogonin was crucial for its inhibitory activity. In conclusion, our data indicated that wogonin could effectively relieve BaP induced cytotoxicity, and its mechanism was related to the dual inhibition of CYP1A1 activity and expression.

In Vitro and In Silico Activities of E. radiata and E. cinerea as an Enhancer of Antibacterial, Antioxidant, and Anti-Inflammatory Agents

Eucalyptus, a therapeutic plant mentioned in the ancient Algerian pharmacopeia, specifically two species belonging to the Myrtaceae family, E. radiata and E. cinerea, were investigated in this study for their antibacterial, antioxidant, and anti-inflammatory properties. The study used aqueous extracts (AE) obtained from these plants, and the extraction yields were found to be different. The in vitro antibacterial activity was evaluated using a disc diffusion assay against three typical bacterial strains. The results showed that the two extracts were effective against all three strains. Both extracts displayed significant antioxidant activity compared to BHT. The anti-inflammatory impact was evaluated using a protein (BSA) inhibition denaturation test. The E. radiata extract was found to inhibit inflammation by 85% at a concentration of 250 µg/mL, significantly higher than the Aspirin. All phytoconstituents present good pharmacokinetic characteristics without toxicity except very slight toxicity of terpineol and cineol and a maximum binding energy of -7.53 kcal/mol for its anti-TyrRS activity in silico. The study suggests that the extracts and their primary phytochemicals could enhance the efficacy of antibiotics, antioxidants, and non-steroidal anti-inflammatory drugs (NSAIDs). As pharmaceutical engineering experts, we believe this research contributes to developing natural-based drugs with potential therapeutic benefits.

Inhibition of Cancer Development by Natural Plant Polyphenols: Molecular Mechanisms

Malignant tumors remain one of the main sources of morbidity and mortality around the world. A chemotherapeutic approach to cancer treatment poses a multitude of challenges, primarily due to the low selectivity and genotoxicity of the majority of chemotherapeutic drugs currently used in the clinical practice, often leading to treatment-induced tumors formation. Highly selective antitumor drugs can largely resolve this issue, but their high selectivity leads to significant drawbacks due to the intrinsic tumor heterogeneity. In contrast, plant polyphenols can simultaneously affect many processes that are involved in the acquiring and maintaining of hallmark properties of malignant cells, and their toxic dose is typically much higher than the therapeutic one. In the present work we describe the mechanisms of the action of polyphenols on cancer cells, including their effects on genetic and epigenetic instability, tumor-promoting inflammation, and altered microbiota.

Comparative Inhibitory Effects of Natural Biflavones from Ginkgo against Human CYP1B1 in Recombinant Enzymes and MCF-7 Cells

Human cytochrome P450 1B1 (CYP1B1) is an extrahepatic enzyme overexpressed in many tumors and associated with angiogenesis. Ginkgetin, isoginkgetin, sciadopitysin, and amentoflavone, the primary biflavones found in Ginkgo biloba, have excellent anti-inflammatory and anti-tumor effects. However, the effect of biflavones on CYP1B1 activities remains unknown. In this study, 7-ethoxyresorufin O-deethylation (EROD) was used to characterize the activities of CYP1 families. The impacts of four ginkgo biflavones on CYP1B1 activity and the cellular protein expression of CYP1B1 were systematically investigated. The results showed that amentoflavone with six hydroxyl substituents exhibited the most potent selective inhibitory effect on CYP1B1 activity with IC₅₀ of 0.054 µM in four biflavones. Sciadopitysin, with three hydroxyl and three methoxy substituents, had the weakest inhibitory activity against CYP1B1. Ginkgetin and isoginkgetin, both with four hydroxyl and two methoxy substituents, showed similar inhibitory intensity towards CYP1B1 with IC₅₀ values of 0.289 and 0.211 µM, respectively. Kinetic analysis showed that ginkgetin and amentoflavone inhibited CYP1B1 in a non-competitive mode, whereas sciadopitysin and isoginkgetin induced competitive or mixed types of inhibition. Notably, four ginkgo biflavones were also confirmed to suppress the protein expressions of CYP1B1 and AhR in MCF-7. Furthermore, molecular docking studies indicated more hydrogen bonds formed between amentoflavone and CYP1B1, which might explain the strongest inhibitory action towards CYP1B1. In summary, these findings suggested that biflavones remarkably inhibited both the activity and protein expression of CYP1B1 and the inhibitory activities enhanced with the increasing hydroxyl substitution, providing new insights into the anti-tumor potentials of biflavones.

Primary and ultimate degradation of benzophenone-type UV filters under different environmental conditions and the underlying structure-biodegradability relationships

Ten common benzophenone-based UV filters (BPs), sharing the same basic structure and differing only in their substituents, were investigated with respect to their primary and ultimate biodegradability. This study was carried out in order to gain deeper insights into the relationship between structure and biodegradability. The primary biodegradation of the selected BPs was studied in river water at environmentally relevant concentrations (1 µg/L) while varying specific, crucial environmental conditions (aerobic, suboxic, supplementation of nutrients). For this purpose, both batch and column degradation tests were performed, which allowed a systematic study of the effects. Subsequently, the ultimate biodegradation, i.e. the potential to achieve full mineralization of BPs, was examined according to OECD guideline 301 F. The results indicate that mineralization is limited to derivatives in which both aromatic rings contain substituents. This hypothesis was supported by docking simulations showing systematic differences in the orientation of BPs within the active site of the cytochrome P450 enzyme. These differences in orientation correspond to the substitution pattern of the BPs. This study provides valuable insights for assessing the environmental hazards of this class of trace organic compounds.

Effects of xenobiotics on CYP1 enzyme-mediated biotransformation and bioactivation of estradiol

Endogenous estradiol (E2) exerts diverse physiological and pharmacological activities, commonly used for hormone replacement therapy. However, prolonged and excessive exposure to E2 potentially increases estrogenic cancer risk. Reportedly, CYP1 enzyme-mediated biotransformation of E2 is largely concerned with its balance between detoxification and carcinogenic pathways. Among the three key CYP1 enzymes (CYP1A1, CYP1A2, and CYP1B1), CYP1A1 and CYP1A2 mainly catalyze the formation of nontoxic 2-hydroxyestradiol (2-OH-E2), while CYP1B1 specifically catalyzes the formation of genotoxic 4-hydroxyestradiol (4-OH-E2). 4-OH-E2 can be further metabolized to electrophilic quinone intermediates accompanied by the generation of reactive oxygen species (ROS), triggering DNA damage. Since abnormal alterations in CYP1 activities can greatly affect the bioactivation process of E2, regulatory effects of xenobiotics on CYP1s are essential for E2-associated cancer development. To date, thousands of natural and synthetic compounds have been found to show potential inhibition and/or induction actions on the three CYP1 members. Generally, these chemicals share similar planar polycyclic skeletons, the structural motifs and substituent groups of which are important for their inhibitory/inductive efficiency and selectivity toward CYP1 enzymes. This review comprehensively summarizes these known inhibitors and/or inductors of E2-metabolizing CYP1s based on chemical categories and discusses their structure-activity relationships, which would contribute to better understanding of the correlation between xenobiotic-regulated CYP1 activities and estrogenic cancer susceptibility.

Herbacetin Broadly Blocks the Activities of CYP450s by Different Inhibitory Mechanisms

Herbacetin is a bioactive flavanol compound that has various pharmacological effects. However, the pharmacokinetic characteristics have not been thoroughly investigated. Previously, we screened a natural compound library and identified herbacetin as a potent CYP blocker. Herein, we aimed to mechanistically determine the inhibitory effects of herbacetin on CYP450 and its potential application. A human liver microsome incubation system was developed based on a UPLC-MS/MS method. Moreover, an in silico docking assay and a human CYP recombinase reaction system were developed and used to investigate binding affinity and inhibitory efficacy. Subsequently, the effects of the combination of herbacetin and sorafenib on HepG2 cells were assessed by MTT and immunoblotting assays. The concentration of sorafenib and its main metabolite were measured by UPLC-MS/MS after incubation with or without herbacetin. As a result, we found herbacetin almost completely inhibited the functions of major CYPs at 100 µM. Moreover, through analysis of the structure-activity relationship, we found 4-, 6-, and 8-hydroxyl were essential groups for the inhibitory effects. Herbacetin inhibited CYP3A4, CYP2B6, CYP2C9, and CYP2E1 in a mixed manner, but non-competitively blocked CYP2D6. These results are in good agreement with the recombinase reaction in vitro results, with an IC₅₀ < 10 µM for each tested isoenzyme. Interestingly, the stimulatory effects of sorafenib on HepG2 cell apoptosis were significantly enhanced by combining with herbacetin, which was associated with increased sorafenib exposure. In summary, herbacetin is a potent inhibitor of a wide spectrum of CYP450s, which may enhance the exposure of drugs in vivo.

Oxidation of 3'-methoxyflavone, 4'-methoxyflavone, and 3',4'-dimethoxyflavone and their derivatives having 5,7-dihydroxyl moieties by human cytochromes P450 1B1 and 2A13

Oxidation of 3'-methoxyflavone, 4'-methoxyflavone, and 3',4'-dimethoxyflavone and their derivatives containing 5,7-dihydroxyl groups by human cytochrome P450 (P450 or CYP) 1B1 and 2A13 was determined using LC-MS/MS systems.3'-Methoxyflavone and 4'-methoxyflavone were mainly O-demethylated to form 3'-hydroxyflavone and 4'-hydroxyflavone, respectively, and then 3',4'-dihydroxyflavone at higher rates with CYP1B1 than with CYP2A13. 4'-Methoxy-5,7-dihydroxyflavone (acacetin) was found to be demethylated by CYP1B1 and 2A13 to form 4',5,7-trihydroxyflavone (apigenin) at rates of 0.098^-1 and 0.42 min^-1, respectively. 3'-Methoxy-5,7-dihydroxyflavone was also demethylated by both P450s, with CYP2A13 being more active.3',4'-Dimethoxyflavone was a good substrate for CYP1B1 but not for CYP2A13 and was found to be mainly O-demethylated to form 3',4'-dihydroxyflavone (at a rate of 4.2 min^-1) and also several ring-oxygenated products having m/z 299 fragments. Molecular docking analysis supported the proper orientation for formation of these products by CYP1B1.Our present results showed that 3'- and 4'-methoxyflavone can be oxidised to their O-demethylated products and, to a lesser extent, to ring oxidation products by both P450s 1B1 and 2A13 and that 3',4'-dimethoxyflavone is a good substrate for CYP1B1 in forming both O-demethylated and ring-oxidation products. Introduction of a 57diOHF moiety into these methoxylated flavonoids caused decreased in oxidation by CYP1B1 and 2A13.

Risk assessment of the inhibition of hydroxygenkwanin on human and rat cytochrome P450 by cocktail method

Hydroxygenkwanin (HGK), a natural flavonoid extracted from the buds of Daphne genkwa Sieb.et Zucc. (Thymelaeaceae), possesses a wide range of pharmacological activities, including anti-inflammatory, antibacterial and anticancer. However, the inhibitory effect of HGK on cytochrome P450 (CYP) remains unclear. This study investigated the potential inhibitory effects of HGK on CYP1A2, 2B1/6, 2C9/11, 2D1/6, 2E1 and 3A2/4 enzymes in human and rat liver microsomes (HLMs and RLMs) by the cocktail approach. HGK exhibited no time-dependent inhibition of CYP activities in HLMs and RLMs. Enzyme inhibition kinetics indicated that HGK was not only a competitive inhibitor of human CYP1A2 and 2C9, but also competitively inhibited rat CYP1A2 and 2C11 activities, with K_i value at 0.84 ± 0.03, 8.09 ± 0.44, 2.68 ± 0.32 and 8.35 ± 0.31 μM, respectively. Further studies showed that the inhibitory effect of HGK on CYP enzymes was weaker than that of diosmetin, which may be related to the substitution of hydroxyl and methoxy in the A and B rings of the flavone skeleton. Therefore, the low K_i values of HGK for CYP1A2 and 2C may lead to potential drug-drug interactions and toxicity.

Contribution of Biotransformations Carried Out by the Microbiota, Drug-Metabolizing Enzymes, and Transport Proteins to the Biological Activities of Phytochemicals Found in the Diet

The consumption of dietary phytochemicals has been associated with several health benefits and relevant biological activities. It is postulated that biotransformations of these compounds regulated by the microbiota, Phase I/II reactions, transport proteins, and deconjugating enzymes contribute not only to their metabolic clearance but also, in some cases, to their bioactivation. A number of factors (age, genetics, sex, physiopathological conditions, and the interplay with other dietary phytochemicals) modulating metabolic activities are important sources and contributors to the interindividual variability observed in clinical studies evaluating the biological activities of phytochemicals. In this review, we discuss all the processes that can affect the bioaccessibility and beneficial effects of these bioactive compounds. Herein, we argue that the role of these factors must be further studied to correctly understand and predict the effects observed following the intake of phytochemicals. This is, in particular, with regard to in vitro investigations, which have shown great inconsistency with preclinical and clinical studies. The complexity of in vivo metabolic activity and biotransformation should therefore be considered in the interpretation of results in vitro and their translation to human physiopathology.

Evaluation system for cell-permeable CYP3A4 inhibitory activity using 1α,25-dihydroxy-vitamin D3-induced intestinal cell lines

We developed an assay system to evaluate the cytochrome P450 (CYP) 3A4-inhibitory activity of compounds, taking account of their cellular permeability, using intestine-derived cell lines pre-treated with the CYP3A4 inducer 1α,25-dihydroxy-vitamin D₃ (250 nM).Ketoconazole (KTZ), saquinavir (SQV), naringin, naringenin (NGE), bergamottin (BG), 6',7'-dihydroxybergamottin (DHBG), epigallocatechin gallate (EGCG), and resveratrol (RES) were evaluated as known CYP3A4 inhibitors. The apparent IC₅₀ (IC_50,app) values of known inhibitors were determined in Caco-2 cells with 10 µM midazolam as a CYP3A4 substrate, and compared with the IC₅₀ values in a human liver microsome assay.SQV and BG with high lipophilicity and good membrane permeability show similar concentrations inside and outside the cells, and consequently IC_50,app and IC₅₀ are similar.KTZ, EGCG, DHBG, NGE, and RES showed a difference between IC₅₀ and IC_50,app. This is considered to result from a difference between the intracellular and extracellular concentrations of the compound, which is likely due to the involvement of efflux and/or influx transporters.This method to evaluate CYP inhibition taking account of membrane permeation should be helpful to assess the potential clinical relevance of drug-drug or drug-food interactions in the gastrointestinal tract.

New Perspectives of CYP1B1 Inhibitors in the Light of Molecular Studies

Human cytochrome P450 1B1 (CYP1B1) is an extrahepatic heme-containing monooxygenase. CYP1B1 contributes to the oxidative metabolism of xenobiotics, drugs, and endogenous substrates like melatonin, fatty acids, steroid hormones, and retinoids, which are involved in diverse critical cellular functions. CYP1B1 plays an important role in the pathogenesis of cardiovascular diseases, hormone-related cancers and is responsible for anti-cancer drug resistance. Inhibition of CYP1B1 activity is considered as an approach in cancer chemoprevention and cancer chemotherapy. CYP1B1 can activate anti-cancer prodrugs in tumor cells which display overexpression of CYP1B1 in comparison to normal cells. CYP1B1 involvement in carcinogenesis and cancer progression encourages investigation of CYP1B1 interactions with its ligands: substrates and inhibitors. Computational methods, with a simulation of molecular dynamics (MD), allow the observation of molecular interactions at the binding site of CYP1B1, which are essential in relation to the enzyme’s functions.

CYP1B1 as a therapeutic target in cardio-oncology

Cardiovascular complications have been frequently reported in cancer patients and survivors, mainly because of various cardiotoxic cancer treatments. Despite the known cardiovascular toxic effects of these treatments, they are still clinically used because of their effectiveness as anti-cancer agents. In this review, we discuss the growing body of evidence suggesting that inhibition of the cytochrome P450 1B1 enzyme (CYP1B1) can be a promising therapeutic strategy that has the potential to prevent cancer treatment-induced cardiovascular complications without reducing their anti-cancer effects. CYP1B1 is an extrahepatic enzyme that is expressed in cardiovascular tissues and overexpressed in different types of cancers. A growing body of evidence is demonstrating a detrimental role of CYP1B1 in both cardiovascular diseases and cancer, via perturbed metabolism of endogenous compounds, production of carcinogenic metabolites, DNA adduct formation, and generation of reactive oxygen species (ROS). Several chemotherapeutic agents have been shown to induce CYP1B1 in cardiovascular and cancer cells, possibly via activating the Aryl hydrocarbon Receptor (AhR), ROS generation, and inflammatory cytokines. Induction of CYP1B1 is detrimental in many ways. First, it can induce or exacerbate cancer treatment-induced cardiovascular complications. Second, it may lead to significant chemo/radio-resistance, undermining both the safety and effectiveness of cancer treatments. Therefore, numerous preclinical studies demonstrate that inhibition of CYP1B1 protects against chemotherapy-induced cardiotoxicity and prevents chemo- and radio-resistance. Most of these studies have utilized phytochemicals to inhibit CYP1B1. Since phytochemicals have multiple targets, future studies are needed to discern the specific contribution of CYP1B1 to the cardioprotective and chemo/radio-sensitizing effects of these phytochemicals.

Therapy-related acute myeloid leukemia and its prevention

BACKGROUND

Secondary tumors, including therapy-related acute myeloid leukemia (t-AML), represent one of the most undesirable side effects of chemotherapy, which arise several years after primary cancer treatment. This review aims to analyze the current data on molecular pathogenesis of t-AML revealing potential criteria for predicting predisposition to the disease. Another objective is to analyze the information on promising approaches for t-AML prevention.

METHODS

We analyzed studies regarding t-AML and possible approaches for cancer prevention of drug-induced tumors. Publications in the databases, such as SciVerse Scopus (948), PubMed (1837) and Web of Science (935) were used. Among 92 the most important publications cited in the review, 79 were published during the last decade.

RESULTS

The review provides the information concerning t-AML pathogenesis, molecular markers of primary cancer patients with high risk of t-AML. The role of the bone marrow niche in clonal hematopoiesis and t-AML pathogenesis is discussed. Current approaches for t-AML prevention both at the stage of therapy and at the latent period are described. Inhibition effects of polyphenols on cell proliferation and on the appearance of hemopoetic clones of indeterminate potential are proposed for t-AML prevention.

CONCLUSION

The problem of the t-AML, a cancer induced by genotoxic chemotherapeutic drugs, is considered from the point of view of the fundamental mechanisms of chemical carcinogenesis, highlighting initiation and promotion stages. It enables to reveal the possible markers for the group of patients with high risk for t-AML and to demonstrate perspectives for the use of plant polyphenols for t-AML prevention.

Liquid chromatography-tandem mass spectrometry analysis of oxidation of 2'-, 3'-, 4'- and 6-hydroxyflavanones by human cytochrome P450 enzymes

2'-Hydroxyflavanone (2'OHFva), 3'OHFva, 4'OHFva, and 6OHFva, the major oxidative products of flavanone by human cytochrome P450 (P450, CYP) enzymes, were studied in regard to further oxidation by human CYP1A1, 1A2, 1B1.1, 1B1.3, and 2A6. The products formed were analyzed with LC-MS/MS and characterized by their positive ion fragmentations on mass spectrometry. Several di-hydroxylated flavanone (diOHFva) and di-hydroxylated flavone (diOHFvo) products, detected by analyzing parent ions at m/z 257 and 255, respectively, were found following incubation of these four hydroxylated flavanones with P450s. The m/z 257 products were produced at higher levels than the latter with four substrates examined. The structures of the m/z 257 products were characterized by LC-MS/MS product ion spectra, and the results suggest that 3'OHFva and 4'OHFva are further oxidized mainly at B-ring by P450s while 6OHFva oxidation was at A-ring. Different diOHFvo products (m/z 255) were also characterized by LC-MS/MS, and the results suggested that most of these diOHFvo products were formed through oxidation or desaturation of the diOHFva products (m/z 257) by P450s. Only when 4'OHFva (m/z 241) was used as a substrate, formation of 4'OHFvo (m/z 239) was detected, indicating that diOHFvo might also be formed through oxidation of 4'OHFvo by P450s. Finally, our results indicated that CYP1 family enzymes were more active than CYP2A6 in catalyzing the oxidation of these four hydroxylated flavanones, and these findings were supported by molecular docking studies of these chemicals with active sites of P450 enzymes.

Evaluation of acacetin inhibition potential against cytochrome P450 in vitro and in vivo

Acacetin is a natural flavonoid that is widely distributed in plants and possesses numerous pharmacological activities. The aim of the present study was to investigate the effects of acacetin on the activities of the cytochrome P450 family members CYP1A2, CYP2B1, CYP2C11, CYP2D1, CYP2E1, and CYP3A2 in rat liver microsomes in vitro and rats in vivo to evaluate potential herb-drug interactions by using a cocktail approach. Phenacetin, bupropion, tolbutamide, dextromethorphan, chlorzoxazone, and midazolam were chosen as the probe substrates. An ultra-performance liquid chromatography-tandem mass spectrometry method was developed for the simultaneous detection of the probe substrates and their metabolites. In vitro, the mode of acacetin inhibition of CYP2B1, CYP2C11, and CYP2E1 was competitive, while mixed inhibition was observed for CYP1A2 and CYP3A2. The Ki values in this study were less than 8.32 μM. In vivo, the mixed probe substrates were administered by gavage after daily intraperitoneal injection with 50 mg/kg acacetin or saline for 2 weeks. The main pharmacokinetic parameters, area under the plasma concentration-time curve (AUC), plasma clearance (CL), and maximum plasma concentration (C_max) of the probe substrates were significantly different in the experimental group than in the control group. Overall, the in vitro and in vivo results indicated that acacetin would be at high risk to cause toxicity and drug interactions via cytochrome P450 inhibition.

Inhibitory effects of polyphenols and their colonic metabolites on CYP2D6 enzyme using two different substrates

Polyphenolic compounds (including flavonoids, chalcones, phenolic acids, and furanocoumarins) represent a common part of our diet, but are also the active ingredients of several dietary supplements and/or medications. These compounds undergo extensive metabolism by human biotransformation enzymes and the microbial flora of the colon. CYP2D6 enzyme metabolizes approximately 25% of the drugs, some of which has narrow therapeutic window. Therefore, its inhibition can lead to the development of pharmacokinetic interactions and the disruption of drug therapy. In this study, the inhibitory effects of 17 plant-derived compounds and 19 colonic flavonoid metabolites on CYP2D6 were examined, employing two assays with different test substrates. The O-demethylation of dextromethorphan was tested employing CypExpress 2D6 kit coupled to HPLC analysis; while the O-demethylation of another CYP2D6 specific substrate (AMMC) was investigated in a plate reader assay with BioVision Fluorometric CYP2D6 kit. Interestingly, some compounds (e.g., bergamottin) inhibited both dextromethorphan and AMMC demethylation; however, certain substances proved to be inhibitors only in one of the assays applied. Our results demonstrate that some polyphenols and colonic metabolites are inhibitors of CYP2D6-catalyzed reactions. Nevertheless, the inhibitory effects showed strong substrate dependence.

How the AHR Became Important in Intestinal Homeostasis-A Diurnal FICZ/AHR/CYP1A1 Feedback Controls Both Immunity and Immunopathology

Ever since the 1970s, when profound immunosuppression caused by exogenous dioxin-like compounds was first observed, the involvement of the aryl hydrocarbon receptor (AHR) in immunomodulation has been the focus of considerable research interest. Today it is established that activation of this receptor by its high-affinity endogenous ligand, 6-formylindolo[3,2-b]carbazole (FICZ), plays important physiological roles in maintaining epithelial barriers. In the gut lumen, the small amounts of FICZ that are produced from L-tryptophan by microbes are normally degraded rapidly by the inducible cytochrome P4501A1 (CYP1A1) enzyme. This review describes how when the metabolic clearance of FICZ is attenuated by inhibition of CYP1A1, this compound passes through the intestinal epithelium to immune cells in the lamina propria. FICZ, the level of which is thus modulated by this autoregulatory loop involving FICZ itself, the AHR and CYP1A1, plays a central role in maintaining gut homeostasis by potently up-regulating the expression of interleukin 22 (IL-22) by group 3 innate lymphoid cells (ILC3s). IL-22 stimulates various epithelial cells to produce antimicrobial peptides and mucus, thereby both strengthening the epithelial barrier against pathogenic microbes and promoting colonization by beneficial bacteria. Dietary phytochemicals stimulate this process by inhibiting CYP1A1 and causing changes in the composition of the intestinal microbiota. The activity of CYP1A1 can be increased by other microbial products, including the short-chain fatty acids, thereby accelerating clearance of FICZ. In particular, butyrate enhances both the level of the AHR and CYP1A1 activity by stimulating histone acetylation, a process involved in the daily cycle of the FICZ/AHR/CYP1A1 feedback loop. It is now of key interest to examine the potential involvement of FICZ, a major physiological activator of the AHR, in inflammatory disorders and autoimmunity.

Effects of Chrysin and Its Major Conjugated Metabolites Chrysin-7-Sulfate and Chrysin-7-Glucuronide on Cytochrome P450 Enzymes and on OATP, P-gp, BCRP, and MRP2 Transporters

Chrysin is an abundant flavonoid in nature, and it is also contained by several dietary supplements. Chrysin is highly biotransformed in the body, during which conjugated metabolites chrysin-7-sulfate and chrysin-7-glucuronide are formed. These conjugates appear at considerably higher concentrations in the circulation than the parent compound. Based on previous studies, chrysin can interact with biotransformation enzymes and transporters; however, the interactions of its metabolites have been barely examined. In this in vitro study, the effects of chrysin, chrysin-7-sulfate, and chrysin-7-glucuronide on cytochrome P450 enzymes (2C9, 2C19, 3A4, and 2D6) as well as on organic anion-transporting polypeptides (OATPs; 1A2, 1B1, 1B3, and 2B1) and ATP binding cassette [P-glycoprotein, multidrug resistance-associated protein 2, and breast cancer resistance protein (BCRP)] transporters were investigated. Our observations revealed that chrysin conjugates are strong inhibitors of certain biotransformation enzymes (e.g., CYP2C9) and transporters (e.g., OATP1B1, OATP1B3, OATP2B1, and BCRP) examined. Therefore, the simultaneous administration of chrysin-containing dietary supplements with medications needs to be carefully considered due to the possible development of pharmacokinetic interactions. SIGNIFICANCE STATEMENT: Chrysin-7-sulfate and chrysin-7-glucuronide are the major metabolites of flavonoid chrysin. In this study, we examined the effects of chrysin and its conjugates on cytochrome P450 enzymes and on organic anion-transporting polypeptides and ATP binding cassette transporters (P-glycoprotein, breast cancer resistance protein, and multidrug resistance-associated protein 2). Our results demonstrate that chrysin and/or its conjugates can significantly inhibit some of these proteins. Since chrysin is also contained by dietary supplements, high intake of chrysin may interrupt the transport and/or the biotransformation of drugs.

Multistep Binding of the Non-Steroidal Inhibitors Orteronel and Seviteronel to Human Cytochrome P450 17A1 and Relevance to Inhibition of Enzyme Activity

Orteronel (TAK-700) is a substituted imidazole that was developed for the treatment of castration-resistant prostate cancer but was dropped in phase III clinical trials. Both enantiomers of this inhibitor of cytochrome P450 (P450) 17A1 show some selectivity in differentially blocking the 17α-hydroxylation and lyase activities of the enzyme. Although both enantiomers of this compound have sub-micromolar IC₅₀ values and bind to the enzyme with a type II spectral change (indicative of nitrogen-iron bonding) and reported K_d values of 56 and 40 nM (R and S, respectively), the rates of binding to P450 17A1 were relatively slow. We considered the possibility that the drug is a slow, tight-binding inhibitor. Analysis of the kinetics of binding revealed rapid formation of an initial complex, presumably in the substrate binding site, followed by a slower change to the spectrum of a final iron complex. Similar kinetics were observed in the interaction of another inhibitor, the triazole (S)-seviteronel (VT-464), with P450 17A1. Kinetic tests and modeling indicate that the further change to the iron-complexed form of the orteronel- or seviteronel-P450 complex is not a prerequisite for enzyme inhibition. Accordingly, the inclusion of heme-binding heterocyclic nitrogen moieties in P450 17A1 inhibitors may not be necessary to achieve inhibition but may nevertheless augment the process.

Preference for O-demethylation reactions in the oxidation of 2'-, 3'-, and 4'-methoxyflavones by human cytochrome P450 enzymes

2'-, 3'-, and 4'-Methoxyflavones (MeFs) were incubated with nine forms of recombinant human cytochrome P450 (P450 or CYP) enzymes in the presence of an NADPH-generating system and the products formed were analyzed with LC-MS/MS methods.CYP1B1.1 and 1B1.3 were highly active in demethylating 4'MeF to form 4'-hydroxyflavone (rate of 5.0 nmol/min/nmol P450) and further to 3',4'-dihydroxyflavone (rates of 2.1 and 0.66 nmol/min/nmol P450, respectively). 3'MeF was found to be oxidized by P450s to m/z 239 (M-14) products (presumably 3'-hydroxyflavone) and then to 3',4'-dihydroxyflavone. P450s also catalyzed oxidation of 2'MeF to m/z 239 (M-14) and m/z 255 (M-14, M-14 + 16) products, presumably mono- and di-hydroxylated products, respectively.At least two types of ring oxidation products having m/z 269 fragments were formed, although at slower rates than the formation of mono- and di-hydroxylated products, on incubation of these MeFs with P450s; one type was products oxidized at the C-ring, having m/z 121 fragments, and the other one was the products oxidized at the A-ring (having m/z 137 fragments).Molecular docking analysis indicated the preference of interaction of O-methoxy moiety of methoxyflavones in the active site of CYP1A2.These results suggest that 2'-, 3'-, and 4'-methoxyflavones are principally demethylated by human P450s to form mono- and di-hydroxyflavones and that direct oxidation occurs in these MeFs to form mono-hydroxylated products, oxidized at the A- or B-ring of MeF.

Testing the Pharmacokinetic Interactions of 24 Colonic Flavonoid Metabolites with Human Serum Albumin and Cytochrome P450 Enzymes

Flavonoids are abundant polyphenols in nature. They are extensively biotransformed in enterocytes and hepatocytes, where conjugated (methyl, sulfate, and glucuronide) metabolites are formed. However, bacterial microflora in the human intestines also metabolize flavonoids, resulting in the production of smaller phenolic fragments (e.g., hydroxybenzoic, hydroxyacetic and hydroxycinnamic acids, and hydroxybenzenes). Despite the fact that several colonic metabolites appear in the circulation at high concentrations, we have only limited information regarding their pharmacodynamic effects and pharmacokinetic interactions. Therefore, in this in vitro study, we investigated the interactions of 24 microbial flavonoid metabolites with human serum albumin and cytochrome P450 (CYP2C9, 2C19, and 3A4) enzymes. Our results demonstrated that some metabolites (e.g., 2,4-dihydroxyacetophenone, pyrogallol, O-desmethylangolensin, and 2-hydroxy-4-methoxybenzoic acid) form stable complexes with albumin. However, the compounds tested did not considerably displace Site I and II marker drugs from albumin. All CYP isoforms examined were significantly inhibited by O-desmethylangolensin; nevertheless, only its effect on CYP2C9 seems to be relevant. Furthermore, resorcinol and phloroglucinol showed strong inhibitory effects on CYP3A4. Our results demonstrate that, besides flavonoid aglycones and their conjugated derivatives, some colonic metabolites are also able to interact with proteins involved in the pharmacokinetics of drugs.

Phytochemical Investigation on Volatile Compositions and Methoxylated Flavonoids of Agrostis gigantea Roth

In this study, methoxylated flavonoids and volatile constitutions of Agrostis gigantea Roth (Poaceae) were investigated for the first time. The flavonoids were identified by spectroscopic methods (1H-NMR, 13C-NMR, COSY, NOSEY, TCOSY, and HMBC). The volatile constitutions of aerial parts and seeds were analyzed by gas chromatography-mass spectrometry (GC-MS). Two methoxylated flavonoids, luteolin 5-methyl ether (1), and cirsilineol (2) were isolated from the aerial parts of this plant. According to the GC-MS data the main constitutions of these volatile oils belong to the simple phenolic category which include coniferyl alcohol (18.80%) and eugenol (12.19%) in aerial parts and seeds, respectively. By using the computer- aided molecular modeling approaches, the binding affinity of these compounds was predicted in the catalytic domains of aryl hydrocarbon receptor (AhR). These two isolated flavonoids were investigated in-vitro for their inhibitory activity on 4T1 breast carcinoma cells. It was predicted that these compounds could be well-matched in aryl hydrocarbon receptor (3H82) active site, but based on the in-vitro assay, the IC50 values on cytotoxicity were 428.24 ±3.21 and 412.7±3.02 μg/mL for luteolin 5-methyl ether and cirsilineol, respectively. Thus, it can be concluded that these flavonoids exhibit low cytotoxicity against 4T1 breast carcinoma cell line.

CYPs-mediated drug-drug interactions on psoralidin, isobavachalcone, neobavaisoflavone and daidzein in rats liver microsomes

The incubation system of CYP2E1 and CYP3A4 enzymes in rat liver microsomes was established to investigate the effects of psoralidin, isobavachalcone, neobavaisoflavone and daidzein from Fructus Psoraleae in vitro. The relevant metabolites were measured by the method of high performance liquid chromatography (HPLC), after probe substrates of 4-nitrophenol, testosterone and the drugs at different concentrations were added to the incubation systems. In addition, real-time RT-PCR was performed to determine the effect of psoralidin, neobavaisoflavone and daidzein on the mRNA expression of CYP3A4 in rat liver. The results suggested that psoralidin, isobavachalcone and neobavaisoflavone were Medium-intensity inhibitors of CYP2E1 with K_i values of 2.58, 1.28 and 19.07 μM, respectively, which could inhibit the increase of CYP2E1 and reduce diseases caused by lipid peroxidation. Isobavachalcone (K_i = 37.52 μM) showed a weak competitive inhibition on CYP3A4. Psoralidin and neobavaisoflavone showed obvious induction effects on CYP3A4 in the expression level of mRNA, which could accelerate the effects of drug metabolism and lead to the risk of inducing DDIs and serious adverse reactions. The results could be used for guideline of Fructus Psoraleae in clinic, which aimed to calculate the drug toxicity by studying the drug-drug interactions caused by the induction and inhibition of CYP450.

Interactions of 7,8-Dihydroxyflavone with Serum Albumin as well as with CYP2C9, CYP2C19, CYP3A4, and Xanthine Oxidase Biotransformation Enzymes

7,8-dihydroxyflavone (DHF) is a flavone aglycone which has beneficial effects in several central nervous system diseases. Most of the pharmacokinetic properties of DHF have been characterized, while only limited information is available regarding its interactions with serum albumin and biotransformation enzymes. In this study, the interactions of DHF with albumin was examined employing fluorescence spectroscopy and ultrafiltration. Furthermore, the inhibitory effects of DHF on cytochrome P450 (CYP2C9, CYP2C19, and CYP3A4) and xanthine oxidase (XO) enzymes were also tested using in vitro models. Our results demonstrate that DHF forms a stable complex with albumin (K = 4.9 × 10⁵ L/mol) and that it is able to displace both Site I and Site II ligands. Moreover, DHF proved to be a potent inhibitor of each enzyme tested, showing similar or slightly weaker effects than the positive controls used. Considering the above-listed observations, the coadministration of DHF with drugs may interfere with the drug therapy due to the development of pharmacokinetic interactions.

Human CYP1A1 inhibition by flavonoids

Cytochrome P4501A1 (CYP1A1) is involved in the metabolism of several genotoxic/carcinogenic environmental xenobiotics including polycyclic aromatic hydrocarbons (PAHs) like benzo[a]pyrene. Several authors had proposed CYP1A inhibition as a plausible strategy for cancer chemoprevention. Using ethoxyresorufin O-deethylase activity (EROD), we tested the inhibitory properties of nine flavonoids: quercetin, miricetin, luteolin, fisetin, morin, kaempferol, 5-hydroxyflavone (5-HF), 3-hydroxyflavone (3-HF), and flavone (F) against human recombinant CYP1A1. The last three compounds exerted the highest inhibitory effect with IC₅₀ values of 0.07, 0.10 and 0.08 μM respectively; the more hydroxyl-groups were present, the lower the potency of inhibition was. Biochemical characterization leads to the conclusion that flavone and its hydroxy derivatives are mixed-type inhibitors. In silico studies have shown that, Phe224 and other aromatic residues in the human CYP1A1 active site play an important role in flavonoid-CYP interaction, through a π/π stacking between the aminoacid and the flavonoid C-ring. Outside the active site, the three flavonoids bind preferentially between A and K helices of the enzyme. Results from the Ames test using human S9 fraction revealed that none of the three compounds was mutagenic. We can consider 5-HF, 3-HF, and F as potential chemopreventive agents against genotoxic damage caused by metabolites resulting from CYP1A1 activity.

Structure-activity relationship and in vitro inhibition of human cytochrome CYP2A6 and CYP2A13 by flavonoids

Cigarette smoking is one of the major risk factors of various diseases including respiratory diseases and lung cancer. While the liver-specific CYP2A6 is associated with the nicotine clearance and smoking addiction, the metabolic activation of the tobacco-specific nitrosamine by lung-specific CYP2A13 can lead to lung tumorigenesis.It has been reported that inhibition of CYP2A6 and CYP2A13 enzymes by flavonoids constituents could be an aids in smoking cessation. This study demonstrates the inhibition activity of kaempferol and myricetin and the structure-function relationship of these two flavonoids and previously isolated flavonoids from Vernonia cinerea and Pluchea indica against both enzymes.Kaempferol could inhibit CYP2A6 with K_ic value of 1.77 ± 0.47 µM while inhibit CYP2A13 with K_ic value of 0.12 ± 0.01 µM. Myricetin could inhibit CYP2A6 with K_ic value of 4.06 ± 0.52 µM while inhibit CYP2A13 with K_ic value of 1.88 ± 0.03 µM.Molecular docking indicated that CYP2A13 enzyme has strong hydrophobic interaction with ring B of flavonoids compared to CYP2A6 enzyme. The presence of the hydroxyl group at C3 position of ring C and the hydroxyl group at C5' of ring B affected inhibitory activity on both enzymes.

Natural-Product-Inspired Compounds as Countermeasures against the Liver Carcinogen Aflatoxin B1

Aflatoxin B₁ (AfB₁) ranks among the most potent liver carcinogens known, and the accidental or intentional exposure of humans and livestock to this toxin remains a serious global threat. One protective measure that had been proposed is employing small-molecule therapeutics capable of mitigating the toxicity of AfB₁; however, to date, these efforts have had little clinical success. To identify molecular scaffolds that reduce the toxicity of AfB₁, we developed a cell-based high-throughput high-content imaging assay that enabled our team to test natural products (pure compounds, fractions, and extracts) for protection of monolayers and spheroids composed of HepG2 liver cells against AfB₁. The spheroid assay showed notable potential for further development, as it afforded greater sensitivity of HepG2 cells to AfB1, which is believed to better mimic the in vivo response of hepatocytes to the toxin. One of the most bioactive compounds to arise from this investigation was alternariol-9-methyl ether (1, purified from an Alternaria sp. isolate), which inspired the synthesis and testing of several structurally related molecules. Based on these findings, it is proposed that several types of natural and synthetic polyarene molecules that have undergone oxidative functionalization (e.g., compounds containing 3-methoxyphenol moieties) are promising starting points for the development of new agents that protect against AfB₁ toxicity.

Phe-125 and Phe-226 of pig cytochrome P450 1A2 stabilize the binding of aflatoxin B1 and 7-ethoxyresorufin through the key CH/π interactions

Cytochrome P450 1A2 (CYP1A2) plays important roles in the metabolism of many planar and aromatic drugs and also contributes to the bioactivation of aflatoxin B₁ (AFB₁) in vivo. To date, the structural basis for CYP1A2's preference to the planar substrates remains unclear. Herein, we investigated the structure-activity relationships for pig CYP1A2 catalyzing AFB₁ and 7-ethoxyresorufin (7-ER). A molecular docking study was performed based on a constructed model of pig CYP1A2, which predicted the contributions of Thr-118, Thr-124, Phe-125, Phe-226, Leu-260, and Asp-313 to the substrate catalysis. Site-directed mutagenesis and kinetic analyses exhibited the common grounds: Phe-125, Phe-226 and Asp-313 were vital to AFB₁ oxidation (including exo-epoxidation and 9A-hydroxylation) and ethoxyresorufin O-deethylation. Meanwhile, Phe-125 and Phe-226 formed CH/π interactions with AFB₁/7-ER, and Asp-313 formed hydrogen bonds with them. Based on other published reports, this study further emphasizes the critical roles of Phe-125 and Phe-226 in recognizing the planar substrates. Our findings highlight the structural basis of pig CYP1A2 specifically catalyzing AFB₁ and 7-ER, and may help to elucidate the underlying mechanism of CYP1A2's metabolic preference to the planar and aromatic substrates.

Coumarins and P450s, Studies Reported to-Date

Cytochrome P450 enzymes (CYPs) are important phase I enzymes involved in the metabolism of endogenous and xenobiotic compounds mainly through mono-oxygenation reactions into more polar and easier to excrete species. In addition to their role in detoxification, they play important roles in the biosynthesis of endogenous compounds and the bioactivation of xenobiotics. Coumarins, phytochemicals abundant in food and commonly used in fragrances and cosmetics, have been shown to interact with P450 enzymes as substrates and/or inhibitors. In this review, these interactions and their significance in pharmacology and toxicology are discussed in detail.

Multiple CH/π Interactions Maintain the Binding of Aflatoxin B₁ in the Active Cavity of Human Cytochrome P450 1A2

Human cytochrome P450 1A2 (CYP1A2) is one of the key CYPs that activate aflatoxin B₁ (AFB₁), a notorious mycotoxin, into carcinogenic exo-8,9-epoxides (AFBO) in the liver. Although the structure of CYP1A2 is available, the mechanism of CYP1A2-specific binding to AFB₁ has not been fully clarified. In this study, we used calculation biology to predict a model of CYP1A2 with AFB₁, where Thr-124, Phe-125, Phe-226, and Phe-260 possibly participate in the specific binding. Site-directed mutagenesis was performed to construct mutants T124A, F125A, F226A, and F260A. Escherichia coli-expressed recombinant proteins T124A, F226A, and F260A had active structures, while F125A did not. This was evidenced by Fe²⁺∙Carbon monoxide (CO)-reduced difference spectra and circular dichroism spectroscopy. Mutant F125A was expressed in HEK293T cells. Steady kinetic assays showed that T124A had enhanced activity towards AFB₁, while F125A, F226A, and F260A were significantly reduced in their ability to activate AFB₁, implying that hydrogen bonds between Thr-124 and AFB₁ were not important for substrate-specific binding, whereas Phe-125, Phe-226, and Phe-260 were essential for the process. The computation simulation and experimental results showed that the three key CH/π interactions between Phe-125, Phe-226, or Phe-260 and AFB₁ collectively maintained the stable binding of AFB₁ in the active cavity of CYP1A2.

Effect of an anxiolytic botanical containing Souroubea sympetala and Platanus occidentalis on in-vitro diazepam human cytochrome P450-mediated metabolism

OBJECTIVES

A novel anxiolytic natural health product (NHP) containing Souroubea sympetala and Platanus occidentalis is available for the companion animal market and is currently being developed for clinical evaluation. Addressing the risk of potential NHP-drug interactions, this study investigated S. sympetala and P. occidentalis plant extracts, and their identified bioactive compounds, for effects on the activity of cytochrome P450 (CYP) isozymes and the metabolism of the conventional anti-anxiety medication diazepam.

METHODS

Souroubea sympetala and P. occidentalis extracts, a 1 : 1 blend of the two extracts, and five triterpenes were tested for inhibitory effects on human recombinant CYP3A4, CYP2D6, CYP2C9 and CYP2C19 activity using a fluorometric plate assay. Direct effects on the metabolism of diazepam were evaluated using human liver microsomes with drug and metabolite quantification by ultra-high-pressure liquid chromatography and mass spectroscopy.

KEY FINDINGS

The active substances betulinic acid (BA) and ursolic acid (UA) strongly inhibited CYP3A4 activity while UA and lupeol moderately inhibited CYP2C19. All extracts exhibited strong activity against the tested isozymes at 50-100 μg/ml. BA and all plant extracts blocked the formation of major diazepam metabolites.

CONCLUSIONS

Betulinic acid, UA and both the extracts and blended product are expected to affect the metabolism of diazepam when given in high dose.

Adaptable Small Ligand of CYP1 Enzymes for Use in Understanding the Structural Features Determining Isoform Selectivity

Although several families of compounds have been identified as scaffolds for inhibitors of the CYP1 family, the isoform selectivity determining structural features has not been fully clarified at the molecular interaction level. We studied the CYP1 isoform selectivity for stilbenoid inhibitors using integrated induced fit docking and molecular dynamics simulations. The hydrophobic interactions with the specific phenylalanine residues in the F helix are correlated with inhibitory potency in the CYP1 family. Through this study, we found that the adaptable, small, and semirigid ligand is a promising starting point for the development of isoform-selective inhibitors and investigation of selectivity-determining features.

Site-specific oxidation of flavanone and flavone by cytochrome P450 2A6 in human liver microsomes

The roles of human cytochrome P450 (P450 or CYP) 2A6 in the oxidation of flavanone [(2R)- and (2S)-enantiomers] and flavone were studied in human liver microsomes and recombinant human P450 enzymes. CYP2A6 was highly active in oxidizing flavanone to form flavone, 2'-hydroxy-, 4'-, and 6-hydroxyflavanones and in oxidizing flavone to form mono- and di-hydroxylated products, such as mono-hydroxy flavones M6, M7, and M11 and di-hydroxy flavones M3, M4, and M5. Liver microsomes prepared from human sample HH2, defective in coumarin 7-hydroxylation activity, were very inefficient in forming 2'-hydroxyflavanone from flavanone and a mono-hydroxylated product, M6, from flavone. Coumarin and anti-CYP2A6 antibodies strongly inhibited the formation of these metabolites in microsomes prepared from liver samples HH47 and 54, which were active in coumarin oxidation activities. Molecular docking analysis showed that the C2'-position of (2R)-flavanone (3.8 Å) was closer to the iron center of CYP2A6 than the C6-position (10 Å), while distances from C2' and C6 of (2S)-flavanone to the CYP2A6 were 6.91 Å and 5.42 Å, respectively. These results suggest that CYP2A6 catalyzes site-specific oxidation of (racemic) flavanone and also flavone in human liver microsomes. CYP1A2 and CYP2B6 were also found to play significant roles in some of the oxidations of these flavonoids by human liver microsomes.

Structure-Based Drug Design for Cytochrome P450 Family 1 Inhibitors

Cytochromes P450 are a class of metalloproteins which are responsible for electron transfer in a wide spectrum of reactions including metabolic biotransformation of endogenous and exogenous substrates. The superfamily of cytochromes P450 consists of families and subfamilies which are characterized by a specific structure and substrate specificity. Cytochromes P450 family 1 (CYP1s) play a distinctive role in the metabolism of drugs and chemical procarcinogens. In recent decades, these hemoproteins have been intensively studied with the use of computational methods which have been recently developed remarkably to be used in the process of drug design by the virtual screening of compounds in order to find agents with desired properties. Moreover, the molecular modeling of proteins and ligand docking to their active sites provide an insight into the mechanism of enzyme action and enable us to predict the sites of drug metabolism. The review presents the current status of knowledge about the use of the computational approach in studies of ligand-enzyme interactions for CYP1s. Research on the metabolism of substrates and inhibitors of CYP1s and on the selectivity of their action is particularly valuable from the viewpoint of cancer chemoprevention, chemotherapy, and drug-drug interactions.

Cytochrome P4501-inhibiting chemicals amplify aryl hydrocarbon receptor activation and IL-22 production in T helper 17 cells

The aryl hydrocarbon receptor (AHR) controls interleukin 22 production by T helper 17 cells (Th17). IL-22 contributes to intestinal homeostasis but has also been implicated in chronic inflammatory disorders and colorectal cancer, highlighting the need for appropriate regulation of IL-22 production. Upon activation, the AHR induces expression of cytochrome P4501 (CYP1) enzymes which in turn play an important feedback role that curtails the duration of AHR signaling by metabolizing AHR ligands. Recently we described how agents that inhibit CYP1 function potentiate AHR signaling by disrupting metabolic clearance of the endogenous ligand 6-formylindolo[3,2-b]carbazole (FICZ). In the present study, we investigated the immune-modulating effects of environmental pollutants such as polycyclic aromatic hydrocarbons on Th17 differentiation and IL-22 production. Using Th17 cells deficient in CYP1 enzymes (Cyp1a1/1a2/1b1-/-) we show that these chemicals potentiate AHR activation through inhibition of CYP1 enzymes which leads to increases in intracellular AHR agonists. Our findings demonstrate that IL-22 production by Th17 cells is profoundly enhanced by impaired CYP1-function and strongly suggest that chemicals able to modify CYP1 function or expression may disrupt AHR-mediated immune regulation by altering the levels of endogenous AHR agonist(s).

Genistein Exposure Interferes with Pharmacokinetics of Celecoxib in SD Male Rats by UPLC-MS/MS

Objective

To discuss the effects of genistein on the metabolism of celecoxib in vitro and in vivo.

Method

In vitro, the effects of genistein on the metabolism of celecoxib were studied using rat and human liver microsomes. In vivo, pharmacokinetics of celecoxib was evaluated in rats with or without genistein. Fifteen Sprague-Dawley (SD) rats were randomized into three groups: celecoxib (A group), celecoxib and 50 mg/kg genistein (B group), and celecoxib and 100 mg/kg genistein (C group). Single dose of 33.3 mg/kg celecoxib was orally administered 30 min after genistein ig. At 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 h after celecoxib administration, 300–400 µl blood samples were collected and the concentration of celecoxib was analyzed by ultrahigh-performance liquid chromatography-tandem mass spectrometry system.

Result

Genistein showed notable inhibitory effects on three microsomes. It affected pharmacokinetics of celecoxib in vivo experiments. Genistein had dramatically ability to suppress CYP2C9∗1 and ∗3. After pretreatment with genistein, AUC and C_max of the C group were higher than B group. CL_z/F of C group was lower than the B group.

Conclusion

Genistein inhibits the conversion of celecoxib in vitro and in vivo. So, the dosage of celecoxib should be adjusted if it was used associated with genistein.

Cytochrome P450 2A6 and other human P450 enzymes in the oxidation of flavone and flavanone

1. We previously reported that flavone and flavanone interact spectrally with cytochrome P450 (P450 or CYP) 2A6 and 2A13 and other human P450s and inhibit catalytic activities of these P450 enzymes. In this study, we studied abilities of CYP1A1, 1A2, 1B1, 2A6, 2A13, 2C9 and 3A4 to oxidize flavone and flavanone. 2. Human P450s oxidized flavone to 6- and 5-hydroxylated flavones, seven uncharacterized mono-hydroxylated flavones, and five di-hydroxylated flavones. CYP2A6 was most active in forming 6-hydroxy- and 5-hydroxyflavones and several mono- and di-hydroxylated products. 3. CYP2A6 was also very active in catalyzing flavanone to form 2'- and 6-hydroxyflavanones, the major products, at turnover rates of 4.8 min^-1 and 1.3 min^-1, respectively. Other flavanone metabolites were 4'-, 3'- and 7-hydroxyflavanone, three uncharacterized mono-hydroxylated flavanones and five mono-hydroxylated flavones, including 6-hydroxyflavone. CYP2A6 catalyzed flavanone to produce flavone at a turnover rate of 0.72 min^-1 that was ∼3-fold higher than that catalyzed by CYP2A13 (0.29 min^-1). 4. These results indicate that CYP2A6 and other human P450s have important roles in metabolizing flavone and flavanone, two unsubstituted flavonoids, present in dietary foods. Chemical mechanisms of P450-catalyzed desaturation of flavanone to form flavone are discussed.

Cancer chemoprevention revisited: Cytochrome P450 family 1B1 as a target in the tumor and the microenvironment

Cancer chemoprevention is the use of synthetic, natural or biological agents to prevent or delay the development or progression of malignancies. Intriguingly, many phytochemicals with anti-inflammatory and anti-angiogenic effects, recently proposed as chemoprevention strategies, are inhibitors of Cytochrome P450 family 1B1 (CYP1B1), an enzyme overexpressed in a wide variety of tumors and associated with angiogenesis. In turn, pro-inflammatory cytokines were reported to boost CYP1B1 expression, suggesting a key role of CYP1B1 in a positive loop of inflammatory angiogenesis. Other well-known pro-tumorigenic activities of CYP1B1 rely on metabolic bioactivation of xenobiotics and steroid hormones into their carcinogenic derivatives. In contrast to initial in vitro observations, in vivo studies demonstrated a protecting role against cancer for the other CYP1 family members (CYP1A1 and CYP1A2), suggesting that the specificity of CYP1 family inhibitors should be carefully taken into account for developing potential chemoprevention strategies. Recent studies also proposed a role of CYP1B1 in multiple cell types found within the tumor microenvironment, including fibroblasts, endothelial and immune cells. Overall, our review of the current literature suggests a positive loop between inflammatory cytokines and CYP1B1, which in turn may play a key role in cancer angiogenesis, acting on both cancer cells and the tumor microenvironment. Strategies aiming at specific CYP1B1 inhibition in multiple cell types may translate into clinical chemoprevention and angioprevention approaches.

Effects of Vernonia cinerea Compounds on Drug-metabolizing Cytochrome P450s in Human Liver Microsomes

Vernonia cinerea has been widely used in traditional medicines for various diseases and shown to aid in smoking abstinence and has anticancer properties. V. cinerea bioactive compounds, including flavonoids and hirsutinolide-type sesquiterpene lactones, have shown an inhibition effect on the nicotine-metabolizing cytochrome P450 2A6 (CYP2A6) enzyme and hirsutinolides reported suppressing cancer growth. In this study, V. cinerea ethanol extract and its bioactive compounds, including four flavonoids and four hirsutinolides, were investigated for an inhibitory effect on human liver microsomal CYPs 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 using cocktail inhibition assays combined with LC-MS/MS analysis. Among tested flavonoids, chrysoeriol was more potent in inhibition on CYP2A6 and CYP1A2 than other liver CYPs, with better binding efficiency toward CYP2A6 than CYP1A2 (K_i values in competitive mode of 1.93 ± 0.05 versus 3.39 ± 0.21 μM, respectively). Hirsutinolides were prominent inhibitors of CYP2A6 and CYP2D6, with IC₅₀ values of 12-23 and 15-41 μM, respectively. These hirsutinolides demonstrated time-dependent inhibition, an indication of mechanism-based inactivation, toward CYP2A6. Quantitative prediction of microsomal metabolism of these flavonoids and hirsutinolides, including half-lives and hepatic clearance rate, was examined. These findings may have implications for further in vivo studies of V. cinerea. Copyright © 2017 John Wiley & Sons, Ltd.

Modulation of estrogen synthesis and metabolism by phytoestrogens in vitro and the implications for women's health

Phytoestrogens are increasingly used as dietary supplements due to their suggested health promoting properties, but also by women for breast enhancement and relief of menopausal symptoms. Generally, phytoestrogens are considered to exert estrogenic activity via estrogen receptors (ERs), but they may also affect estrogen synthesis and metabolism locally in breast, endometrial and ovarian tissues. Considering that accurate regulation of local hormone levels is crucial for normal physiology, it is not surprising that interference with hormonal synthesis and metabolism is associated with a wide variety of women's health problems, varying from altered menstrual cycle to hormone-dependent cancers. Yet, studies on phytoestrogens have mainly focused on ER-mediated effects of soy-derived phytoestrogens, with less attention paid to steroid synthesis and metabolism or other phytoestrogens. This review aims to evaluate the potential of phytoestrogens to modulate local estrogen levels and the implications for women's health. For that, an overview is provided of the effects of commonly used phytoestrogens, i.e. 8-prenylnaringenin, biochanin A, daidzein, genistein, naringenin, resveratrol and quercetin, on estrogen synthesizing and metabolizing enzymes in vitro. The potential implications for women's health are assessed by comparing the in vitro effect concentrations with blood concentrations that can be found after intake of these phytoestrogens. Based on this evaluation, it can be concluded that high-dose supplements with phytoestrogens might affect breast and endometrial health or fertility in women via the modulation of steroid hormone levels. However, more data regarding the tissue levels of phytoestrogens and effect data from dedicated, tissue-specific assays are needed for a better understanding of potential risks. At least until more certainty regarding the safety has been established, especially young women would better avoid using supplements containing high doses of phytoestrogens.

Oxidation of 1-chloropyrene by human CYP1 family and CYP2A subfamily cytochrome P450 enzymes: catalytic roles of two CYP1B1 and five CYP2A13 allelic variants

1. 1-Chloropyrene, one of the major chlorinated polycyclic aromatic hydrocarbon contaminants, was incubated with human cytochrome P450 (P450 or CYP) enzymes including CYP1A1, 1A2, 1B1, 2A6, 2A13, 2B6, 2C9, 2D6, 2E1, 3A4 and 3A5. Catalytic differences in 1-chloropyrene oxidation by polymorphic two CYP1B1 and five CYP2A13 allelic variants were also examined. 2. CYP1A1 oxidized 1-chloropyrene at the 6- and 8-positions more actively than at the 3-position, while both CYP1B1.1 and 1B1.3 preferentially catalyzed 6-hydroxylation. 3. Five CYP2A13 allelic variants oxidized 8-hydroxylation much more than 6- and 3-hydroxylation, and the variant CYP2A13.3 was found to slowly catalyze these reactions with a lower k_cat value than other CYP2A13.1 variants. 4. CYP2A6 catalyzed 1-chloropyrene 6-hydroxylation at a higher rate than the CYP2A13 enzymes, but the rate was lower than the CYP1A1 and 1B1 variants. Other human P450 enzymes had low activities towards 1-chloropyrene. 5. Molecular docking analysis suggested differences in the interaction of 1-chloropyrene with active sites of CYP1 and 2 A enzymes. In addition, a naturally occurring Thr134 insertion in CYP2A13.3 was found to affect the orientation of Asn297 in the I-helix in interacting with 1-chloropyrene (and also 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK) and caused changes in the active site of CYP2A13.3 as compared with CYP2A13.1.

Review of Ligand Specificity Factors for CYP1A Subfamily Enzymes from Molecular Modeling Studies Reported to-Date

The cytochrome P450 (CYP) family 1A enzymes, CYP1A1 and CYP1A2, are two of the most important enzymes implicated in the metabolism of endogenous and exogenous compounds through oxidation. These enzymes are also known to metabolize environmental procarcinogens into carcinogenic species, leading to the advent of several types of cancer. The development of selective inhibitors for these P450 enzymes, mitigating procarcinogenic oxidative effects, has been the focus of many studies in recent years. CYP1A1 is mainly found in extrahepatic tissues while CYP1A2 is the major CYP enzyme in human liver. Many molecules have been found to be metabolized by both of these enzymes, with varying rates and/or positions of oxidation. A complete understanding of the factors that govern the specificity and potency for the two CYP 1A enzymes is critical to the development of effective inhibitors. Computational molecular modeling tools have been used by several research groups to decipher the specificity and potency factors of the CYP1A1 and CYP1A2 substrates. In this review, we perform a thorough analysis of the computational studies that are ligand-based and protein-ligand complex-based to catalog the various factors that govern the specificity/potency toward these two enzymes.