Kinetic characterizations of diallyl sulfide analogs for their novel role as CYP2E1 enzyme inhibitors

Hepatic, Extrahepatic and Extracellular Vesicle Cytochrome P450 2E1 in Alcohol and Acetaminophen-Mediated Adverse Interactions and Potential Treatment Options

Alcohol and several therapeutic drugs, including acetaminophen, are metabolized by cytochrome P450 2E1 (CYP2E1) into toxic compounds. At low levels, these compounds are not detrimental, but higher sustained levels of these compounds can lead to life-long problems such as cytotoxicity, organ damage, and cancer. Furthermore, CYP2E1 can facilitate or enhance the effects of alcohol-drug and drug-drug interactions. In this review, we discuss the role of CYP2E1 in the metabolism of alcohol and drugs (with emphasis on acetaminophen), mediating injury/toxicities, and drug-drug/alcohol-drug interactions. Next, we discuss various compounds and various nutraceuticals that can reduce or prevent alcohol/drug-induced toxicity. Additionally, we highlight experimental outcomes of alcohol/drug-induced toxicity and potential treatment strategies. Finally, we cover the role and implications of extracellular vesicles (EVs) containing CYP2E1 in hepatic and extrahepatic cells and provide perspectives on the clinical relevance of EVs containing CYP2E1 in intracellular and intercellular communications leading to drug-drug and alcohol-drug interactions. Furthermore, we provide our perspectives on CYP2E1 as a druggable target using nutraceuticals and the use of EVs for targeted drug delivery in extrahepatic and hepatic cells, especially to treat cellular toxicity.

A comprehensive review of cytochrome P450 2E1 for xenobiotic metabolism

Cytochrome P450 2E1 (CYP2E1) plays a vital role in drug-induced hepatotoxicity and cancers (e.g. lung and bladder cancer), since it is responsible for metabolizing a number of medications and environmental toxins to reactive intermediate metabolites. CYP2E1 was recently found to be the highest expressed CYP enzyme in human livers using a proteomics approach, and CYP2E1-related toxicity is strongly associated with its protein level that shows significant inter-individual variability related to ethnicity, age, and sex. Furthermore, the expression of CYP2E1 demonstrates regulation by extensive genetic polymorphism, endogenous hormones, cytokines, xenobiotics, and varying pathological states. Over the past decade, the knowledge of pharmacology, toxicology, and biology about CYP2E1 has grown remarkably, but the research progress has yet to be summarized. This study presents a timely systematic review on CYP2E1's xenobiotic metabolism, genetic polymorphism, and inhibitors, with the focus on their clinical relevance for the efficacy and toxicity of various CYP2E1 substrates. Moreover, several knowledge gaps have been identified towards fully understanding the potential interactions among different CYP2E1 substrates in clinical settings. Through in-depth analyses of these knowns and unknowns, we expect this review will aid in future drug development and improve management of CYP2E1 related clinical toxicity.

Plasma exosomes exacerbate alcohol- and acetaminophen-induced toxicity via CYP2E1 pathway

Cellular CYP2E1 is well-known to mediate alcohol- (ALC) and acetaminophen- (APAP) induced toxicity in hepatic and extra-hepatic cells. Although exosomes have been gaining importance in understanding mechanism of intra- and inter-cellular communication, the functional role of drug metabolizing cytochrome P450 (CYP) enzymes in human plasma exosomes are yet to be explored. In our previous study, we reported that human plasma-derived exosomes contain substantial level of functional CYP2E1. In the current project, we investigated the potential role of plasma exosomal CYP2E1 in mediating ALC- and APAP-induced toxicity. We treated hepatic and extra-hepatic (monocytic) cells with exosomes ± ALC/APAP. We observed that the plasma exosomes containing CYP2E1 cargo further exacerbate ALC- and APAP-induced toxicity in both hepatic and monocytic cells. Further, both exosomes- and ALC/APAP-induced toxicity was reduced/abolished by a selective inhibitor of CYP2E1 enzyme activity (diallyl ether). However, only ALC-, but not exosome-induced toxicity was reduced/abolished by CYP2E1 siRNA. These findings suggest that ALC/APAP-induced toxicity in the presence of exosomes are mediated, at least in part, by CYP2E1 enzyme. To validate these in vitro findings, we characterized plasma exosomal contents in a binge-drinking animal model and their effect on ALC/APAP-induced toxicity in monocytic cells. Our results showed that ALC exposure caused a significant induction of the plasma exosomal CYP2E1 level in a binge drinking murine model. These exosomes containing increased levels of CYP2E1 caused significant toxicity in monocytic cells compared to exosomes derived from control mice. Overall, our results showed an important role of exosomal CYP2E1 in exacerbating ALC- and APAP-induced toxicity. The study is significant in terms of understanding the role of exosomal CYP2E1 in cell-cell interactions, and their effects on drug-induced toxicity.

The role of cytochrome P450 2E1 on ethanol-mediated oxidative stress and HIV replication in human monocyte-derived macrophages

Background

Alcohol consumption is considered to be a major health problem among people living with HIV/AIDS. Our previous reports have shown that ethanol reduced intracellular concentrations of antiretroviral drugs elvitegravir and darunavir in the HIV-1-infected U1 cell line. Ethanol also increased HIV-1 replication despite the presence of elvitegravir. Our previous finding has also shown that the levels of cytochrome P450 enzyme 2E1 (CYP2E1) and oxidative stress in blood monocytes were induced, while the concentration of alcohol in the plasma was reduced in HIV-1-infected alcohol users compared to uninfected alcohol users. However, the role of CYP2E1 in ethanol-enhanced oxidative stress and HIV-1 replication is still unclear.

Methods

This study examined the chronic effects (14 days) of ethanol on HIV viral load, oxidative DNA damage, expression of CYP2E1, expression of antioxidant enzymes (AOEs), expression of reactive oxygen species (ROS) in human monocyte-derived macrophages (MDM). Further, to evaluate the role of CYP2E1 in mediating ethanol-induced viral replication, CYP2E1 siRNA and CYP2E1 selective inhibitor were used in the HIV-1-infected U1 cell line following ethanol treatment.

Results

Chronic ethanol exposure demonstrated an increase in oxidative DNA damage and CYP2E1 expression in both non-infected and HIV-1-infected MDM. Our results showed that ethanol chronic exposure increased HIV-1 replication by ~3-fold in HIV-1-infected MDM. This ethanol-enhanced HIV-1 replication was associated with an increased oxidative DNA damage, an increased expression of CYP2E1, and a decreased expression of antioxidant enzyme PRDX6. In HIV-1-infected U1 cell line, we observed a decreased viral replication (~30%) and a decreased DNA damage (~100%) after repression of CYP2E1 by siRNA, upon ethanol exposure. We also observed a decreased viral replication (~25%) after inhibition of CYP2E1 by using selective CYP2E1 inhibitor.

Conclusions

The data suggest that chronic ethanol exposure increases HIV-1 replication in MDM, at least in part, through CYP2E1-mediated oxidative stress. These results are clinically relevant to potentially find effective treatment strategies for HIV-1-infected alcohol users.

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Chronic EtOH exposure increased HIV-1 replication and oxidative DNA damage in MDM.

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Chronic EtOH exposure increased CYP2E1 expression in MDM.

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EtOH-enhanced HIV replication and DNA damage were prevented by CYP2E1 siRNA.

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Selective CYP2E1 inhibitor decreased HIV-1 replication upon ethanol exposure.

Kinetic characterizations of diallyl sulfide analogs for their novel role as CYP2E1 enzyme inhibitors

Diallyl sulfide (DAS), a selective inhibitor of CYP2E1, has shown protective effects against alcohol‐ and acetaminophen‐induced hepatotoxicity in many studies. However, DAS is also a CYP2E1 substrate that on metabolism produces toxic metabolites and causes cytotoxicity. The objective of this study was to find a potent DAS analog as a CYP2E1 inhibitor and has the characteristic of producing less toxic metabolites. We selected seven commercially available compounds that are similar to DAS (DAS analogs). First, we performed ligand‐CYP2E1 docking study to determine the binding mode and binding energy. The analysis suggested a relative potential for these DAS analogs as CYP2E1 inhibitor. We then performed a comprehensive inhibition kinetics of DAS analogs and determined the relative IC₅₀, K_i, and types of inhibition compared to that of DAS. The results showed that compared to DAS, diallyl ether and allyl methyl sulfide have lower K_i values (3.1 and 4.4 μmol/L, respectively, vs. 6.3 μmol/L for DAS) and IC₅₀ values (6.3 and 11.4 μmol/L, respectively, vs. 17.3 μmol/L for DAS). However, allyl methyl sulfide and thiophene showed similar inhibitory capacities to that of DAS, and four other DAS analogs showed lower potency than DAS. In conclusion, we have found relatively more potent inhibitors of CYP2E1, which have lower toxicity than DAS. These compounds can replace DAS not only as a tool for in vitro and in vivo studies that involve CYP2E1 inhibition, but also can lead the way for their use in preventing CYP2E1‐mediated hepatic toxicity of alcohol and acetaminophen.

In vitro evaluation of structural analogs of diallyl sulfide as novel CYP2E1 inhibitors for their protective effect against xenobiotic-induced toxicity and HIV replication

Diallyl sulfide (DAS) has been shown to prevent xenobiotic (e.g. ethanol, acetaminophen) induced toxicity and disease (e.g. HIV-1) pathogenesis. DAS imparts its beneficial effect by inhibiting CYP2E1-mediated metabolism of xenobiotics, especially at high concentration. However, DAS also causes toxicity at relatively high dosages and with long exposure times. Therefore, the goal of the current study was to investigate the structural analogs of DAS for their improved toxicity profiles and their effectiveness in reducing xenobiotic-induced toxicity and HIV-1 replication. Previously, we identified commercially available analogs that possessed CYP2E1 inhibitory capacity greater than or equal to that of DAS. In this study, we evaluated the toxicity and efficacy of these analogs using hepatocytes, monocytes, and astrocytes where CYP2E1 plays an important role in xenobiotic-mediated toxicity. Our results showed that thiophene, allyl methyl sulfide, diallyl ether, and 2-prop-2-enoxyacetamide are significantly less cytotoxic than DAS in these cells. Moreover, these analogs reduced ethanol- and acetaminophen-induced toxicity in hepatocytes and HIV-1 replication in monocytes more effectively than DAS. Overall, our findings are significant in terms of using these DAS analogs as a tool in vitro and in vivo, especially to examine chronic xenobiotic-induced toxicity and disease pathogenesis that occurs through the CYP2E1 pathway.