Inhibition of CYP2E1 with natural agents may be a feasible strategy for minimizing the hepatotoxicity of ethanol

Acetaminophen-induced liver injury: Molecular mechanism and treatments from natural products

Acetaminophen (APAP) is a widely used analgesic and antipyretic over-the-counter medicine worldwide. Hepatotoxicity caused by APAP overdose is one of the leading causes of acute liver failure (ALF) in the US and in some parts of Europe, limiting its clinical application. Excessive APAP metabolism depletes glutathione and increases N-acetyl-p-benzoquinoneimide (NAPQI) levels, leading to oxidative stress, DNA damage, and cell necrosis in the liver, which in turn leads to liver damage. Studies have shown that natural products such as polyphenols, terpenes, anthraquinones, and sulforaphane can activate the hepatocyte antioxidant defense system with Nrf2 as the core player, reduce oxidative stress damage, and protect the liver. As the key enzyme metabolizing APAP into NAPQI, cytochrome P450 enzymes are also considered to be intriguing target for the treatment of APAP-induced liver injury. Here, we systematically review the hepatoprotective activity and molecular mechanisms of the natural products that are found to counteract the hepatotoxicity caused by APAP, providing reference information for future preclinical and clinical trials of such natural products.

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.

Alcoholic Liver Disease: Alcohol Metabolism, Cascade of Molecular Mechanisms, Cellular Targets, and Clinical Aspects

Alcoholic liver disease is the result of cascade events, which clinically first lead to alcoholic fatty liver, and then mostly via alcoholic steatohepatitis or alcoholic hepatitis potentially to cirrhosis and hepatocellular carcinoma. Pathogenetic events are linked to the metabolism of ethanol and acetaldehyde as its first oxidation product generated via hepatic alcohol dehydrogenase (ADH) and the microsomal ethanol-oxidizing system (MEOS), which depends on cytochrome P450 2E1 (CYP 2E1), and is inducible by chronic alcohol use. MEOS induction accelerates the metabolism of ethanol to acetaldehyde that facilitates organ injury including the liver, and it produces via CYP 2E1 many reactive oxygen species (ROS) such as ethoxy radical, hydroxyethyl radical, acetyl radical, singlet radical, superoxide radical, hydrogen peroxide, hydroxyl radical, alkoxyl radical, and peroxyl radical. These attack hepatocytes, Kupffer cells, stellate cells, and liver sinusoidal endothelial cells, and their signaling mediators such as interleukins, interferons, and growth factors, help to initiate liver injury including fibrosis and cirrhosis in susceptible individuals with specific risk factors. Through CYP 2E1-dependent ROS, more evidence is emerging that alcohol generates lipid peroxides and modifies the intestinal microbiome, thereby stimulating actions of endotoxins produced by intestinal bacteria; lipid peroxides and endotoxins are potential causes that are involved in alcoholic liver injury. Alcohol modifies SIRT1 (Sirtuin-1; derived from Silent mating type Information Regulation) and SIRT2, and most importantly, the innate and adapted immune systems, which may explain the individual differences of injury susceptibility. Metabolic pathways are also influenced by circadian rhythms, specific conditions known from living organisms including plants. Open for discussion is a 5-hit working hypothesis, attempting to define key elements involved in injury progression. In essence, although abundant biochemical mechanisms are proposed for the initiation and perpetuation of liver injury, patients with an alcohol problem benefit from permanent alcohol abstinence alone.

Porcine cytochrome 2A19 and 2E1

Cytochrome P450 (CYP) is a major group of enzymes, which conduct Phase I metabolism. Among commonly used animal models, the pig has been suggested as the most suitable model for investigating drug metabolism in human beings. Moreover, porcine CYP2A19 and CYP2E1 are responsible for the biotransformation of both endogenous and exogenous compounds such as 3‐methylindole (skatole), sex hormones and food compounds. However, little is known about the regulation of porcine CYP2A19 and CYP2E1. In this MiniReview, we summarise the current knowledge about the regulation of porcine CYP2A19 and CYP2E1 by environmental, biological and dietary factors. Finally, we reflect on the need for further research, to clarify the interaction between active feed components and the porcine CYP system.

The effect of quercetin on the pharmacokinetics of chlorzoxazone, a CYP2E1 substrate, in healthy subjects

PURPOSE

Previous in vitro studies have demonstrated that quercetin inhibits CYP2E1 enzyme, but there are no available data to indicate that quercetin inhibits CYP2E1 enzyme in humans. The purpose of the present study was to assess the effect of quercetin on CYP2E1 enzyme activity in healthy subjects using chlorzoxazone (CHZ) as a CYP2E1 substrate.

METHODS

An open-label, two-period, sequential study was conducted in 12 healthy subjects. A single dose of CHZ 250 mg was given to subjects during control phase and after treatment phases. Quercetin at a dose of 500 mg was given to subjects twice daily for a period of 10 days. The blood samples were collected at predetermined time intervals after CHZ dosing and analyzed to determine the concentrations of CHZ and 6-hydroxychlorzoxazone (6-OHCHZ).

RESULTS

Treatment with quercetin significantly enhanced the maximum plasma concentration (C _max), area under the curve (AUC), and half-life (t _1/2) by 47.8, 69.3, and 36.4%, respectively, while significantly decreased the elimination rate constant (k _el) and apparent oral clearance (CL/F) of CHZ by 25.1 and 41.6%, respectively, in comparison with the control. On the other hand, C _max and AUC of 6-OHCHZ were decreased by 30.1 and 32.6%, respectively, after quercetin treatment when compared to control. In addition, geometric mean ratios and 90% confidence intervals for C _max and AUC of CHZ and 6-OHCHZ were both out of the no-effect boundaries of 0.80-1.25, which indicates a significant pharmacokinetic interaction present between CHZ and quercetin. Furthermore, treatment with quercetin significantly decreased the metabolic ratios of C _max and AUC by 57.1 and 60.1%, respectively, as compared to control suggesting that reduced formation of CHZ to 6-OHCHZ.

CONCLUSIONS

The results suggest that altered pharmacokinetics of CHZ might be attributed to quercetin-mediated inhibition of CYP2E1 enzyme. Further, the inhibition of CYP2E1 by quercetin may represent a novel therapeutic approach for minimizing the ethanol-induced CYP2E1 enzyme activity and results in reduced hepatotoxicity of ethanol.

Cytotoxicity and cytochrome P450 inhibitory activities of Clinacanthus nutans

BACKGROUND

Clinacanthus nutans Lindau (family: Acanthaceae), also known as "Sabah Snake Grass" or "Belalai Gajah" in Malaysia, has been widely used by Malaysians due to its anticancer property. However, the anticancer activity of C. nutans leaves extract and its safe use need to be further investigated. The objectives of the present study were to evaluate the cytotoxic effects of methanol leaves extract of C. nutans in various human cancer cell lines and to evaluate the in vitro effect of C. nutans leaves on the activity of CYP3A4 and CYP2E1 in human liver microsomes.

METHODS

The cytotoxic effects of methanol extract of C. nutans leaves in various cancer cell lines (Hep-G2, A549, HT-29, MDA-MB-231, MCF-7, and CRL 1739) and normal cells (3T3) were determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell proliferation assay. The activities of CYP3A4 and CYP2E1 were determined using simple spectrophotometric methods.

RESULTS

Results obtained showed that the methanol extract of C. nutans leaves exhibited the highest cytotoxic effect against Hep-G2 cell lines (liver cancer) (IC50=13.33 μg/mL), followed by breast cancer oestrogen negative (MDA-MB-231) (IC50 of 18.67 μg/mL). Methanol leaves extract of C. nutans showed significant inhibition (p<0.05) in CYP3A4 and CYP2E1 activity in human liver microsomes.

CONCLUSIONS

In conclusion, methanol leaves extract of C. nutans exhibited the highest cytotoxic activity against liver cancer cells (Hep-G2). There is a possibility that herb-drug interaction could occur with C. nutans through inhibitory effects on CYP3A4. Additionally, inhibition of C. nutans on CYP2E1 could show anti-carcinogenesis effects in human liver microsomes.

Effect of piperine on CYP2E1 enzyme activity of chlorzoxazone in healthy volunteers

1. The purpose of the present study was to investigate the effect of piperine (PIP) on CYP2E1 enzyme activity and pharmacokinetics of chlorzoxazone (CHZ) in healthy volunteers. 2. An open-label, two period, sequential study was conducted in 12 healthy volunteers. A single dose of PIP 20 mg was administered daily for 10 days during treatment phase. A single dose of CHZ 250 mg was administered during control and after treatment phases under fasting conditions. The blood samples were collected at predetermined time intervals after CHZ dosing and analyzed by HPLC. 3. Treatment with PIP significantly enhanced maximum plasma concentration (C_max) (3.14-4.96 μg/mL)_, area under the curve (AUC) (10.46-17.78 μg h/mL), half life (T_1/2) (1.26-1.82 h) and significantly decreased elimination rate constant (K_el) (0.57-0.41 h ^- 1), apparent oral clearance (CL/F) (24.76-13.65 L/h) of CHZ when compared to control. In addition, treatment with PIP significantly decreased C_max (0.22-0.15 μg/mL), AUC (0.94-0.68 μg h/mL), T_1/2 (2.54-1.68 h) and significantly increased K_el (0.32-0.43 h ^- 1) of 6-hydroxychlorzoxazone (6-OHCHZ) as compared to control. Furthermore, treatment with PIP significantly decreased metabolite to parent (6-OHCHZ/CHZ) ratios of C_max, AUC, T_1/2 and significantly increased K_el ratio of 6-OHCHZ/CHZ, which indicate the decreased formation of CHZ to 6-OHCHZ. 4. The results suggest that altered pharmacokinetics of CHZ might be attributed to PIP mediated inhibition of CYP2E1 enzyme, which indicate significant pharmacokinetic interaction present between PIP and CHZ. The inhibition of CYP2E1 by PIP may represent a novel therapeutic benefit for minimizing ethanol induced CYP2E1 enzyme activity and results in reduced hepatotoxicity of ethanol.

Hepatoprotective effects of hoveniae semen cum fructus extracts in ethanol intoxicated mice

[Purpose]

The objective of this study was to evaluate the hepatoprotective effects of Hoveniae Semen Cum Fructus extract in ethanol induced hepatic damages.

[Methods]

Hepatic damages were induced by oral administration of ethanol and then Hoveniae Semen Cum Fructus extract was administered.

[Results]

Following Hoveniae Semen Cum Fructus extract administration, body and liver weights were increased, while aspartate aminotransferase, alanine aminotransferase, albumin, γ-glutamyl transferase, and triglyceride levels in the serum, triglyceride contents, tumor necrosis factor -α level, cytochrome (CY) P450 2E1 activity in the liver and mRNA expression of hepatic lipogenic genes, and Nitrotyrosine and 4-HNE-immunolabelled hepatocytes were decreased. However, mRNA expression of genes involved in fatty acid oxidation was increased. Also, as a protective mechanism for hepatic antioxidant defense systems, decreased liver MDA contents, increased glutathione contents, increased dismutase and catalase activities were observed when compared to the ethanol control.

[Conclusion]

Hoveniae Semen Cum Fructus extract favorably protected against liver damages, mediated by its potent anti-inflammatory and anti-steatosis properties through the augmentation of the hepatic antioxidant defense system by NF-E2-related factor-2 activation, and down-regulation of the mRNA expression of hepatic lipogenic genes or up-regulation of the mRNA expression of genes involved in fatty acid oxidation.

Resveratrol Pretreatment Affects CYP2E1 Activity of Chlorzoxazone in Healthy Human Volunteers

The purpose of the present study was to investigate the effect of resveratrol (RSV) pretreatment on CYP2E1 enzyme activity and pharmacokinetics of chlorzoxazone (CHZ) in healthy human volunteers. The open-label, two period, sequential study was conducted in 12 healthy human volunteers. A single dose of RSV 500 mg was administered once daily for 10 days during treatment phase. A single dose of CHZ 250 mg was administered during control and after treatment phases under fasting conditions. The blood samples were collected after CHZ dosing at predetermined time intervals and analyzed by HPLC. RSV pretreatment significantly enhanced the maximum plasma concentration (Cmax), area under the curve (AUC) and half life (T1/2) and significantly decreased elimination rate constant (Kel), apparent oral clearance (CL/F) and apparent volume of distribution (Vd/F) of CHZ as compared to that of control. In addition, RSV pretreatment significantly decreased the metabolite to parent (6-OHCHZ/CHZ) ratios of Cmax, AUC and T1/2 and significantly increased the Kel ratio of 6-OHCHZ/CHZ, which indicated the reduced formation of CHZ to 6-OHCHZ. The results suggest that the altered CYP2E1 enzyme activity and pharmacokinetics of CHZ might be attributed to RSV mediated inhibition of CYP2E1 enzyme. Thus, there is a potential pharmacokinetic interaction between RSV and CHZ. The inhibition of CYP2E1 by RSV may provide a novel approach for minimizing the hepatotoxicity of ethanol.

Role of oxidative stress in alcohol-induced liver injury

Reactive oxygen species (ROS) are highly reactive molecules that are naturally generated in small amounts during the body's metabolic reactions and can react with and damage complex cellular molecules such as lipids, proteins, or DNA. Acute and chronic ethanol treatments increase the production of ROS, lower cellular antioxidant levels, and enhance oxidative stress in many tissues, especially the liver. Ethanol-induced oxidative stress plays a major role in the mechanisms by which ethanol produces liver injury. Many pathways play a key role in how ethanol induces oxidative stress. This review summarizes some of the leading pathways and discusses the evidence for their contribution to alcohol-induced liver injury. Special emphasis is placed on CYP2E1, which is induced by alcohol and is reactive in metabolizing and activating many hepatotoxins, including ethanol, to reactive products, and in generating ROS.

CYP2E1 and oxidative liver injury by alcohol

Ethanol-induced oxidative stress seems to play a major role in mechanisms by which ethanol causes liver injury. Many pathways have been suggested to contribute to the ability of ethanol to induce a state of oxidative stress. One central pathway seems to be the induction of cytochrome P450 2E1 (CYP2E1) by ethanol. CYP2E1 metabolizes and activates many toxicological substrates, including ethanol, to more reactive, toxic products. Levels of CYP2E1 are elevated under a variety of physiological and pathophysiological conditions and after acute and chronic alcohol treatment. CYP2E1 is also an effective generator of reactive oxygen species such as the superoxide anion radical and hydrogen peroxide and, in the presence of iron catalysts, produces powerful oxidants such as the hydroxyl radical. This review article summarizes some of the biochemical and toxicological properties of CYP2E1 and briefly describes the use of cell lines developed to constitutively express CYP2E1 and CYP2E1 knockout mice in assessing the actions of CYP2E1. Possible therapeutic implications for treatment of alcoholic liver injury by inhibition of CYP2E1 or CYP2E1-dependent oxidative stress will be discussed, followed by some future directions which may help us to understand the actions of CYP2E1 and its role in alcoholic liver injury.

Silymarin protects against acute ethanol-induced hepatotoxicity in mice

BACKGROUND

Accumulated evidence has demonstrated that both oxidative stress and abnormal cytokine production, especially tumor necrosis factor-alpha (TNF), play important etiological roles in the pathogenesis of alcoholic liver disease (ALD). Agents that have both antioxidant and anti-inflammation properties, particularly anti-TNF production, represent promising therapeutic interventions for ALD. We investigated the effects and the possible mechanism(s) of silymarin on liver injury induced by acute ethanol (EtOH) administration.

METHODS

Nine-week-old mice were divided into 4 groups, control, silymarin treatment, EtOH treatment, and silymarin/EtOH treatment, with 6 mice in each group. Because control and silymarin values were virtually identical, only control treatment is shown for ease of viewing. Ethanol-treated mice received EtOH [5 g/kg body weight (BW)] by gavage every 12 hours for a total of 3 doses. Control mice received an isocalorical maltose solution. In the silymarin/EtOH group, silymarin was dissolved in the EtOH and gavaged simultaneously with EtOH at a dose of 200 mg/kg BW. At 4 hours after the last dosing, the mice were anesthetized and subsequent serum alanine aminotransferase (ALT) level, hepatic lipid peroxidation, enzymatic activity of hepatic cytochrome P450 2E1, hepatic TNF-alpha, and glutathione (GSH) levels were measured. Histopathological change was assessed by hematoxylin and eosin staining.

RESULTS

Acute EtOH administration caused prominent hepatic microvesicular steatosis with mild necrosis and an elevation of serum ALT activity, induced a significant decrease in hepatic GSH in conjunction with enhanced lipid peroxidation, and increased hepatic TNF production. Supplementation with a standardized silymarin attenuated these adverse changes induced by acute EtOH administration.

CONCLUSIONS

Silymarin protects against the liver injury caused by acute EtOH administration. In view of its nontoxic nature, it may be developed as an effective therapeutic agent for alcohol-induced liver disease by its antioxidative stress and anti-inflammatory features.

CYP2E1-dependent oxidative stress and toxicity: role in ethanol-induced liver injury

Ethanol-induced oxidative stress plays a major role in the mechanisms by which ethanol causes liver injury. Many pathways contribute to how ethanol induces a state of oxidative stress. One central pathway appears to be the induction, by ethanol, of the CYP2E1 form of cytochrome P450 enzymes. CYP2E1 is of interest because it metabolises and activates many toxicological substrates, including ethanol, to more reactive products. Levels of CYP2E1 are elevated under a variety of physiological and pathophysiological conditions. CYP2E1 is an effective generator of reactive oxygen species. This review summarises some of the biochemical and toxicological properties of CYP2E1, and briefly describes the use of HepG2 cell lines in assessing the actions of CYP2E1. Future directions, which may help to better understand the actions of CYP2E1 and its role in alcoholic liver injury, are suggested.

Lipopolysaccharide-induced liver injury in rats treated with the CYP2E1 inducer pyrazole

Elevated LPS and elevated cytochrome P-450 2E1 (CYP2E1) in liver are two major independent risk factors in alcoholic liver disease. We investigated possible synergistic effects of the two risk factors in causing oxidative stress and liver injury. Sprague-Dawley rats were injected intraperitoneally with pyrazole (inducer of CYP2E1) for 2 days, and then LPS was injected via tail vein. Other rats were treated with pyrazole alone or LPS alone or saline. Eight hours later, blood was collected and livers were excised. Pathological evaluation showed severe inflammatory responses and necroses only in liver sections from rats in the pyrazole plus LPS group; blood transaminase levels were significantly elevated only in the combination group. Activities of caspase-3 and -9 and positive terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining were highest in the LPS alone and the LPS plus pyrazole group, with no significant difference between the two groups. Lipid peroxidation and protein carbonyls in liver homogenate as well as in situ superoxide production were maximally elevated in the LPS plus pyrazole group. Levels of nitrite plus nitrate and inducible nitric oxide (NO) synthase (iNOS) content were comparably elevated in LPS alone and the LPS plus pyrazole group; however, 3-nitrotyrosine adducts were elevated in the combined group but not the LPS group. It is likely that LPS induction of iNOS, which produces NO, coupled to pyrazole induction of CYP2E1 which produces superoxide, sets up conditions for maximal peroxynitrite formation and production of 3-nitrotyrosine adducts. CYP2E1 activity and content were elevated in the pyrazole and the LPS plus pyrazole groups. Immunohistochemical staining indicated that distribution of CYP2E1 was in agreement with that of necrosis and production of superoxide. These results show that pyrazole treatment enhanced LPS-induced necrosis, not apoptosis. The enhanced liver necrosis appears to involve an increase in oxidative and nitrosative stress generated by the combination of LPS plus elevated CYP2E1 levels.

Phytochemical-induced changes in gene expression of carcinogen-metabolizing enzymes in cultured human primary hepatocytes

1. The naturally occurring compounds curcumin (CUR), 3,3'-diindolylmethane (DIM), isoxanthohumol (IXN), 8-prenylnaringenin (8PN), phenethyl isothiocyanate (PEITC) and sulforaphane (SFN) protect animals against chemically induced tumours. Putative chemoprotective mechanisms include modulated expression of hepatic biotransformation enzymes. However, few, if any, studies have used human primary cells as test models. 2. The present study investigated the effects of these phytochemicals on the expression of four carcinogenesis-relevant enzymes--cytochrome P450 (CYP)1A1 and 1A2, NAD(P)H:quinone oxidoreductase (NQO1) and glutathione S-transferase A1 (GSTA1)--in primary cultures of freshly isolated human hepatocytes. 3. Quantitative RT-PCR analyses demonstrated that CYP1A1 was up-regulated by PEITC and DIM in a dose-dependent manner. CYP1A2 transcription was significantly activated following DIM, IXN, 8PN and PEITC treatments. DIM exhibited a remarkably effective induction response of CYP1A1 (474-, 239- and 87-fold at 50, 25 and 10 microM, respectively) and CYP1A2 (113-, 70- and 31-fold at 50, 25 and 10 microM, respectively), that was semiquantitatively reflected in protein levels. NQO1 expression responded to PEITC (11 x at 25 microM), DIM (4.5 x at 50 microM) and SFN (5 x at 10 microM) treatments. No significant effects on GSTA1 transcription were seen. 4. The findings show novel and unexpected effects of these phytochemicals on the expression of human hepatic biotransformation enzymes that play key roles in chemical-induced carcinogenesis.