Expression and activity of the cytochrome P450 2E1 in patients with nonalcoholic steatosis and steatohepatitis

Gypenoside XLIX alleviates acute liver injury: Emphasis on NF-κB/PPAR-α/NLRP3 pathways

Liver is one of the vital organs in the human body and liver injury will have a very serious impact on human damage. Gypenoside XLIX is a PPAR-α activator that inhibits the activation of the NF-κB signaling pathway. The components of XLIX have pharmacological effects such as cardiovascular protection, antihypoxia, anti-tumor and anti-aging. In this study, we used cecum ligation and puncture (CLP) was used to induce in vivo mice hepatic injury, and lipopolysaccharide (LPS)-induced inflammation in RAW264.7 cells, evaluated whether Gypenoside XLIX could have a palliative effect on sepsis-induced acute liver injury via NF-κB/PPAR-α/NLRP3. In order to gain insight into these mechanisms, six groups were created in vivo: the Contol group, the Sham group, the CLP group, the CLP + XLIX group (40 mg/kg) and the Sham + XLIX (40 mg/kg) group, and the CLP + DEX (2 mg/kg) group. Three groups were created in vitro: Control, LPS, LPS + XLIX (40 μM). The analytical methods used included H&E staining, qPCR, reactive oxygen species (ROS), oil red O staining, and Western Blot. The results showed that XLIX attenuated hepatic inflammatory injury in mice with toxic liver disease through inhibition of the TLR4-mediated NF-κB pathway, attenuated lipid accumulation through activation of PPAR-α, and attenuated hepatic pyroptosis by inhibiting NLRP3 production. Regarding the imbalance between oxidative and antioxidant defenses due to septic liver injury, XLIX reduced liver oxidative stress-related biomarkers (ALT, AST), reduced ROS accumulation, decreased the amount of malondialdehyde (MDA) produced by lipid peroxidation, and increased the levels of antioxidant enzymes such as glutathione (GSH) and catalase (CAT). Our results demonstrate that XLIX can indeed attenuate septic liver injury. This is extremely important for future studies on XLIX and sepsis, and provides a potential pathway for the treatment of acute liver injury.

Pathophysiological Mechanisms and Clinical Associations of Non-Alcoholic Fatty Pancreas Disease

Non-Alcoholic Fatty Pancreas disease (NAFPD), characterized by fat accumulation in pancreatic tissue, is an emerging clinical entity. However, the clinical associations, the underlying molecular drivers, and the pathophysiological mechanisms of NAFPD have not yet been characterized in detail. The NAFPD spectrum not only includes infiltration and accumulation of fat within and between pancreatic cells but also involves several inflammatory processes, dysregulation of physiological metabolic pathways, and hormonal defects. A deeper understanding of the underlying molecular mechanisms is key to correlate NAFPD with clinical entities including non-alcoholic fatty liver disease, metabolic syndrome, diabetes mellitus, atherosclerosis, as well as pancreatic cancer and pancreatitis. The aim of this review is to examine the pathophysiological mechanisms of NAFPD and to assess the possible causative/predictive risk factors of NAFPD-related clinical syndromes.

Insulin Resistance, Obesity, and Lipotoxicity

Lipotoxicity, originally used to describe the destructive effects of excess fat accumulation on glucose metabolism, causes functional impairments in several metabolic pathways, both in adipose tissue and peripheral organs, like liver, heart, pancreas, and muscle. Ectopic lipid accumulation in the kidneys, liver, and heart has important clinical counterparts like diabetic nephropathy in type 2 diabetes mellitus, obesity-related glomerulopathy, nonalcoholic fatty liver disease, and cardiomyopathy. Insulin resistance due to lipotoxicity indirectly lead to reproductive system disorders, like polycystic ovary syndrome. Lipotoxicity has roles in insulin resistance and pancreatic beta-cell dysfunction. Increased circulating levels of lipids and the metabolic alterations in fatty acid utilization and intracellular signaling have been related to insulin resistance in muscle and liver. Different pathways, like novel protein kinase c pathways and the JNK-1 pathway, are involved as the mechanisms of how lipotoxicity leads to insulin resistance in nonadipose tissue organs, such as liver and muscle. Mitochondrial dysfunction plays a role in the pathogenesis of insulin resistance. Endoplasmic reticulum stress, through mainly increased oxidative stress, also plays an important role in the etiology of insulin resistance, especially seen in non-alcoholic fatty liver disease. Visceral adiposity and insulin resistance both increase the cardiometabolic risk, and lipotoxicity seems to play a crucial role in the pathophysiology of these associations.

Advances in Noninvasive Biomarkers for Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) currently represents one of the most common liver diseases worldwide. Early diagnosis and disease staging is crucial, since it is mainly asymptomatic, but can progress to nonalcoholic steatohepatitis (NASH) or cirrhosis or even lead to the development of hepatocellular carcinoma. Over time, efforts have been put into developing noninvasive diagnostic and staging methods in order to replace the use of a liver biopsy. The noninvasive methods used include imaging techniques that measure liver stiffness and biological markers, with a focus on serum biomarkers. Due to the impressive complexity of the NAFLD's pathophysiology, biomarkers are able to assay different processes involved, such as apoptosis, fibrogenesis, and inflammation, or even address the genetic background and "omics" technologies. This article reviews not only the currently validated noninvasive methods to investigate NAFLD but also the promising results regarding recently discovered biomarkers, including biomarker panels and the combination of the currently validated evaluation methods and serum markers.

Pharmacokinetics of obese adults: Not only an increase in weight

Obesity is a pathophysiological state defined by a body mass index > 30 kg/m2 and characterized by an adipose tissue accumulation leading to an important weight increased. Several pathologies named comorbidities such as cardiovascular disease, type 2 diabetes and cancer make obesity the fifth cause of death in the world. Physiological changes impact the four main phases of pharmacokinetics of some drugs and leads to an inappropriate drug-dose. For absorption, the gastrointestinal transit is accelerated, and the gastric empty time is shortened, that can reduce the solubilization and absorption of some oral drugs. The drug distribution is probably the most impacted by the obesity-related changes because the fat mass (FM) increases at the expense of the lean body weight (LBW), leading to an important increase of the volume of distribution for lipophilic drugs and a low or moderately increase of this parameter for hydrophilic drugs. This modification of the distribution may require drug-dose adjustments. By various mechanisms, the metabolism and elimination of drugs are impacted by obesity and should be considered as similar or lower than that non-obese patients. To better understand the necessary drug-dose adjustments in obese patients, a narrative review of the literature was conducted to highlight the main elements to consider in the therapeutic management of adult obese patients.

Acetaminophen-Induced Hepatotoxicity in Obesity and Nonalcoholic Fatty Liver Disease: A Critical Review

The epidemic of obesity, type 2 diabetes and nonalcoholic liver disease (NAFLD) favors drug consumption, which augments the risk of adverse events including liver injury. For more than 30 years, a series of experimental and clinical investigations reported or suggested that the common pain reliever acetaminophen (APAP) could be more hepatotoxic in obesity and related metabolic diseases, at least after an overdose. Nonetheless, several investigations did not reproduce these data. This discrepancy might come from the extent of obesity and steatosis, accumulation of specific lipid species, mitochondrial dysfunction and diabetes-related parameters such as ketonemia and hyperglycemia. Among these factors, some of them seem pivotal for the induction of cytochrome P450 2E1 (CYP2E1), which favors the conversion of APAP to the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). In contrast, other factors might explain why obesity and NAFLD are not always associated with more frequent or more severe APAP-induced acute hepatotoxicity, such as increased volume of distribution in the body, higher hepatic glucuronidation and reduced CYP3A4 activity. Accordingly, the occurrence and outcome of APAP-induced liver injury in an obese individual with NAFLD would depend on a delicate balance between metabolic factors that augment the generation of NAPQI and others that can mitigate hepatotoxicity.

Depression and non-alcoholic fatty liver disease: Association and potential mechanisms

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world, and is closely related to the high incidence of obesity, metabolic syndrome, type 2 diabetes, arteriosclerotic cardiovascular disease, and colorectal tumor. Depression is a common mental disorder that is characterized by high incidence, high recurrence rate, high disability rate, and high suicide rate, which has serious harm to patients' physical and mental health, reduce the quality of life of patients. In recent years, as more and more attention has been paid to mental health of NAFLD patients, the relationship between NAFLD and depression has become one of the hot research topics. Studies have shown that the incidence of depression in NAFLD patients is higher than that in non-NAFLD patients, and the incidence of NAFLD in depressed patients is also higher. Some research results have been published on the mechanism of comorbidity between the two. This paper reviews the research progress on the correlation and common mechanism between NAFLD and depression, aiming to lay a foundation for further research on the comorbidities of NAFLD and depression, and provide a basis and research direction for the diagnosis and treatment of patients with both comorbidities.

Oxidative Stress in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a challenging disease caused by multiple factors, which may partly explain why it still remains an orphan of adequate therapies. This review highlights the interaction between oxidative stress (OS) and disturbed lipid metabolism. Several reactive oxygen species generators, including those produced in the gastrointestinal tract, contribute to the lipotoxic hepatic (and extrahepatic) damage by fatty acids and a great variety of their biologically active metabolites in a “multiple parallel-hit model”. This leads to inflammation and fibrogenesis and contributes to NAFLD progression. The alterations of the oxidant/antioxidant balance affect also metabolism-related organelles, leading to lipid peroxidation, mitochondrial dysfunction, and endoplasmic reticulum stress. This OS-induced damage is at least partially counteracted by the physiological antioxidant response. Therefore, modulation of this defense system emerges as an interesting target to prevent NAFLD development and progression. For instance, probiotics, prebiotics, diet, and fecal microbiota transplantation represent new therapeutic approaches targeting the gut microbiota dysbiosis. The OS and its counter-regulation are under the influence of individual genetic and epigenetic factors as well. In the near future, precision medicine taking into consideration genetic or environmental epigenetic risk factors, coupled with new OS biomarkers, will likely assist in noninvasive diagnosis and monitoring of NAFLD progression and in further personalizing treatments.

Interaction Mechanisms Between Major Depressive Disorder and Non-alcoholic Fatty Liver Disease

Major depressive disorder (MDD), which is highly associated with non-alcoholic fatty liver disease (NAFLD), has complex pathogenic mechanisms. However, a limited number of studies have evaluated the mutual pathomechanisms involved in MDD and NAFLD development. Chronic stress-mediated elevations in glucocorticoid (GC) levels play an important role in the development of MDD-related NAFLD. Elevated GC levels can induce the release of inflammatory factors and changes in gut permeability. Elevated levels of inflammatory factors activate the hypothalamic-pituitary-adrenal (HPA) axis, which further increases the release of GC. At the same time, changes in gut permeability promote the release of inflammatory factors, which results in a vicious circle among the three, causing disease outbreaks. Even though the specific role of the thyroid hormone (TH) in this pathogenesis has not been fully established, it is highly correlated with MDD and NAFLD. Therefore, changing lifestyles and reducing psychological stress levels are necessary measures for preventing MDD-related NAFLD. Among them, GC inhibitors and receptor antagonists may be key in the alleviation of early and mid-term disease progression. However, combination medications may be important in late-stage diseases, but they are associated with various side effects. Traditional Chinese medicines have been shown to be potential therapeutic alternatives for such complex diseases.

Asking the Right Questions With Animal Models: Methionine- and Choline-Deficient Model in Predicting Adverse Drug Reactions in Human NASH

In the past few decades, great conceptual and technological advances have been made in the field of toxicology, but animal model-based research still remains one of the most widely used and readily available tools for furthering our current knowledge. However, animal models are not perfect in predicting all systemic toxicity in humans. Extrapolating animal data to accurately predict human toxicities remains a challenge, and researchers are obligated to question the appropriateness of their chosen animal model. This paper provides an assessment of the utility of the methionine- and choline-deficient (MCD) diet fed animal model in reflecting human nonalcoholic steatohepatitis (NASH) and the potential risks of adverse drug reactions and toxicities that are associated with the disease. As a commonly used NASH model, the MCD model fails to exhibit most metabolic abnormalities in a similar manner to the human disease. The MCD model, on the other hand, closely resembles human NASH histology and reflects signatures of drug transporter alterations in humans. Due to the nature of the MCD model, it should be avoided in studies of NASH pathogenesis, metabolic parameter evaluation, and biomarker identification. But it can be used to accurately predict altered drug disposition due to NASH-associated transporter alterations.

Oxidative Stress and Antioxidant Biomarkers in Clinical and Experimental Models of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a term that covers a range of hepatic disorders involving fat deposits in the liver. NAFLD begins with simple steatosis and progresses into non-alcoholic steatohepatitis (NASH) characterised by inflammation, fibrosis, apoptosis, oxidative stress, lipid peroxidation, mitochondrial dysfunction and release of adipokines and pro-inflammatory cytokines. Oxidative stress and antioxidants are known to play a vital role in the pathogenesis and severity of NAFLD/NASH. A number of oxidative stress and antioxidant markers are employed in the assessment of the pathological state and progression of the disease. In this article, we review several biomarkers of oxidative stress and antioxidants that have been measured at clinical and experimental levels. Also included is a comprehensive description of oxidative stress, sources and contribution to the pathogenesis of NAFLD/NASH.

Molecular pathways of nonalcoholic fatty liver disease development and progression

Nonalcoholic fatty liver disease (NAFLD) is a main hepatic manifestation of metabolic syndrome. It represents a wide spectrum of histopathological abnormalities ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) with or without fibrosis and, eventually, cirrhosis and hepatocellular carcinoma. While hepatic simple steatosis seems to be a rather benign manifestation of hepatic triglyceride accumulation, the buildup of highly toxic free fatty acids associated with insulin resistance-induced massive free fatty acid mobilization from adipose tissue and the increased de novo hepatic fatty acid synthesis from glucose acts as the "first hit" for NAFLD development. NAFLD progression seems to involve the occurrence of "parallel, multiple-hit" injuries, such as oxidative stress-induced mitochondrial dysfunction, endoplasmic reticulum stress, endotoxin-induced, TLR4-dependent release of inflammatory cytokines, and iron overload, among many others. These deleterious factors are responsible for the triggering of a number of signaling cascades leading to inflammation, cell death, and fibrosis, the hallmarks of NASH. This review is aimed at integrating the overwhelming progress made in the characterization of the physiopathological mechanisms of NAFLD at a molecular level, to better understand the factor influencing the initiation and progression of the disease.

Molecular mechanisms of hepatic lipid accumulation in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is currently the world's most common liver disease, estimated to affect up to one-fourth of the population. Hallmarked by hepatic steatosis, NAFLD is associated with a multitude of detrimental effects and increased mortality. This narrative review investigates the molecular mechanisms of hepatic steatosis in NAFLD, focusing on the four major pathways contributing to lipid homeostasis in the liver. Hepatic steatosis is a consequence of lipid acquisition exceeding lipid disposal, i.e., the uptake of fatty acids and de novo lipogenesis surpassing fatty acid oxidation and export. In NAFLD, hepatic uptake and de novo lipogenesis are increased, while a compensatory enhancement of fatty acid oxidation is insufficient in normalizing lipid levels and may even promote cellular damage and disease progression by inducing oxidative stress, especially with compromised mitochondrial function and increased oxidation in peroxisomes and cytochromes. While lipid export initially increases, it plateaus and may even decrease with disease progression, sustaining the accumulation of lipids. Fueled by lipo-apoptosis, hepatic steatosis leads to systemic metabolic disarray that adversely affects multiple organs, placing abnormal lipid metabolism associated with NAFLD in close relation to many of the current life-style-related diseases.

Higher chlorzoxazone clearance in obese children compared with nonobese peers

AIMS

To test the in vivo activity of Cytochrome P450 (CYP) 2E1 in obese children vs. nonobese children, aged 11-18 years. Secondly, whether the activity of CYP2E1 in these patients is associated with NALFD, diabetes or hyperlipidaemia.

METHODS

Seventy children were divided into groups by body mass index (BMI) standard deviation score (SDS). All children received 250 mg oral chlorzoxazone (CLZ) as probe for CYP2E1 activity. Thirteen blood samples and 20-h urine samples were collected per participant.

RESULTS

Obese children had an increased oral clearance and distribution of CLZ, indicating increased CYP2E1 activity, similar to obese adults. The mean AUC_0-∞ value of CLZ was decreased by 46% in obese children compared to nonobese children. The F was was increased twofold in obese children compared to nonobese children, P < 0.0001. Diabetic biomarkers were significantly increased in obese children, while fasting blood glucose and Hba1c levels were nonsignificant between groups. Liver fat content was not associated with CLZ Cl.

CONCLUSION

Oral clearance of CLZ was increased two-fold in obese children vs. nonobese children aged 11-18 years. This indicates an increased CYP2E1 activity of clinical importance, and dose adjustment should be considered for CLZ.

Non-alcoholic fatty liver disease (NAFLD) models in drug discovery

INTRODUCTION

The progressive disease spectrum of non-alcoholic fatty liver disease (NAFLD), which includes non-alcoholic steatohepatitis (NASH), is a rapidly emerging public health crisis with no approved therapy. The diversity of various therapies under development highlights the lack of consensus around the most effective target, underscoring the need for better translatable preclinical models to study the complex progressive disease and effective therapies. Areas covered: This article reviews published literature of various mouse models of NASH used in preclinical studies, as well as complex organotypic in vitro and ex vivo liver models being developed. It discusses translational challenges associated with both kinds of models, and describes some of the studies that validate their application in NAFLD. Expert opinion: Animal models offer advantages of understanding drug distribution and effects in a whole body context, but are limited by important species differences. Human organotypic in vitro and ex vivo models with physiological relevance and translatability need to be used in a tiered manner with simpler screens. Leveraging newer technologies, like metabolomics, proteomics, and transcriptomics, and the future development of validated disease biomarkers will allow us to fully utilize the value of these models to understand disease and evaluate novel drugs in isolation or combination.

Morbidly Obese Patients Exhibit Increased CYP2E1-Mediated Oxidation of Acetaminophen

Introduction

Acetaminophen (paracetamol) is mainly metabolized via glucuronidation and sulphation, while the minor pathway through cytochrome P450 (CYP) 2E1 is held responsible for hepatotoxicity. In obese patients, CYP2E1 activity is reported to be induced, thereby potentially worsening the safety profile of acetaminophen. The aim of this study was to determine the pharmacokinetics of acetaminophen and its metabolites (glucuronide, sulphate, cysteine and mercapturate) in morbidly obese and non-obese patients.

Methods

Twenty morbidly obese patients (with a median total body weight [TBW] of 140.1 kg [range 106–193.1 kg] and body mass index [BMI] of 45.1 kg/m² [40–55.2 kg/m²]) and eight non-obese patients (with a TBW of 69.4 kg [53.4–91.7] and BMI of 21.8 kg/m² [19.4–27.4]) received 2 g of intravenous acetaminophen. Fifteen blood samples were collected per patient. Population pharmacokinetic modelling was performed using NONMEM.

Results

In morbidly obese patients, the median area under the plasma concentration–time curve from 0 to 8 h (AUC_0–8h) of acetaminophen was significantly smaller (P = 0.009), while the AUC_0–8h ratios of the glucuronide, sulphate and cysteine metabolites to acetaminophen were significantly higher (P = 0.043, 0.004 and 0.010, respectively). In the model, acetaminophen CYP2E1-mediated clearance (cysteine and mercapturate) increased with lean body weight [LBW] (population mean [relative standard error] 0.0185 L/min [15 %], P < 0.01). Moreover, accelerated formation of the cysteine and mercapturate metabolites was found with increasing LBW (P < 0.001). Glucuronidation clearance (0.219 L/min [5 %]) and sulphation clearance (0.0646 L/min [6 %]) also increased with LBW (P < 0.001).

Conclusion

Obesity leads to lower acetaminophen concentrations and earlier and higher peak concentrations of acetaminophen cysteine and mercapturate. While a higher dose may be anticipated to achieve adequate acetaminophen concentrations, the increased CYP2E1-mediated pathway may preclude this dose adjustment.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-015-0357-0) contains supplementary material, which is available to authorized users.

Insulin Resistance, Obesity and Lipotoxicity

Lipotoxicity , originally used to describe the destructive effects of excess fat accumulation on glucose metabolism, causes functional impairments in several metabolic pathways, both in adipose tissue and peripheral organs, like liver, heart, pancreas and muscle. Lipotoxicity has roles in insulin resistance and pancreatic beta cell dysfunction. Increased circulating levels of lipids and the metabolic alterations in fatty acid utilization and intracellular signaling, have been related to insulin resistance in muscle and liver. Different pathways, like novel protein kinase c pathways and the JNK-1 pathway are involved as the mechanisms of how lipotoxicity leads to insulin resistance in nonadipose tissue organs, such as liver and muscle. Mitochondrial dysfunction plays a role in the pathogenesis of insulin resistance. Endoplasmic reticulum stress, through mainly increased oxidative stress, also plays important role in the etiology of insulin resistance, especially seen in non-alcoholic fatty liver disease. Visceral adiposity and insulin resistance both increase the cardiometabolic risk and lipotoxicity seems to play a crucial role in the pathophysiology of these associations.

Saikosaponins induced hepatotoxicity in mice via lipid metabolism dysregulation and oxidative stress: a proteomic study

BACKGROUND

Radix Bupleuri (RB) has been popularly used for treating many liver diseases such as chronic hepatic inflammation and viral Hepatitis in China. Increasing clinical and experimental evidence indicates the potential hepatotoxicity of RB or prescriptions containing RB. Recently, Saikosaponins (SS) have been identified as major bioactive compounds isolated from RB, which may be also responsible for RB-induced liver injury.

METHODS

Serum AST, ALT and LDH levels were determined to evaluate SS-induced liver injury in mice. Serum and liver total triglyceride and cholesterol were used to indicate lipid metabolism homeostasis. Liver ROS, GSH, MDA and iNOS were used to examine the oxidative stress level after SS administration. Western blot was used to detect CYP2E1 expression. A 8-Plex iTRAQ Labeling Coupled with 2D LC - MS/MS technique was applied to analyze the protein expression profiles in livers of mice administered with different doses of SS for different time periods. Gene ontology analysis, cluster and enrichment analysis were employed to elucidate potential mechanism involved. HepG2 cells were used to identify our findings in vitro.

RESULTS

SS dose- and time-dependently induced liver injury in mice, indicated by increased serum AST, ALT and LDH levels. According to proteomic analysis, 487 differentially expressed proteins were identified in mice administrated with different dose of SS for different time periods. Altered proteins were enriched in pathways such as lipid metabolism, protein metabolism, macro molecular transportation, cytoskeleton structure and response to stress. SS enhanced CYP2E1 expression in a time and dose dependent manner, and induced oxidative stress both in vivo and in vitro.

CONCLUSION

Our results identified hepatotoxicity and established dose-time course-liver toxicity relationship in mice model of SS administration and suggested potential mechanisms, including impaired lipid and protein metabolism and oxidative stress. The current study provides experimental evidence for clinical safe use of RB, and also new insights into understanding the mechanism by which SS and RB induced liver injury.

Toxicological Implications of Mitochondrial Localization of CYP2E1

Cytochrome P450 2E1 (CYP2E1) metabolizes an extensive array of pollutants, drugs, and other small molecules, often resulting in bioactivation to reactive metabolites. Therefore, it is unsurprising that it has been the subject of decades of research publications and reviews. However, while CYP2E1 has historically been studied in the endoplasmic reticulum (erCYP2E1), active CYP2E1 is also present in mitochondria (mtCYP2E1). Relatively few studies have specifically focused on mtCYP2E1, but there is growing interest in this form of the enzyme as a driver in toxicological mechanisms given its activity and location. Many previous studies have linked total CYP2E1 to conditions that involve mitochondrial dysfunction (fasting, diabetes, non-alcoholic steatohepatitis, and obesity). Furthermore, a large number of reactive metabolites that are formed by CYP2E1 through metabolism of drugs and pollutants have been demonstrated to cause mitochondrial dysfunction. Finally, there appears to be significant inter-individual variability in targeting to the mitochondria, which could constitute a source of variability in individual response to exposures. This review discusses those outcomes, the biochemical properties and toxicological consequences of mtCYP2E1, and highlights important knowledge gaps and future directions. Overall, we feel that this exciting area of research is rich with new and important questions about the relationship between mtCYP2E1, mitochondrial dysfunction, and pathology.

Drug-induced steatohepatitis

INTRODUCTION

Drug induced steatohepatitis (DISH), a form of drug induced liver injury (DILI) is characterized by intracellular accumulation of lipids in hepatocytes and subsequent inflammatory events, in some ways similar to the pathology seen with other metabolic, viral and genetic causes of non alcoholic fatty liver disease and steatohepatitis (NAFLD and NASH). Areas covered: This paper provides a comprehensive review of the main underlying mechanisms by which various drugs cause DISH, and outlines existing preclinical tools to predict it and study underlying pathways involved. The translational hurdles of these models are discussed, with the example of an organotypic liver system designed to address them. Finally, we describe the clinical assessment and management of DISH. Expert Opinion: The complexity of the interconnected mechanistic pathways underlying DISH makes it important that preclinical evaluation of drugs is done in a physiologically and metabolically relevant context. Advanced organotypic tissue models, coupled with translational functional biomarkers and next-generational pan-omic measurements, may offer the best shot at gathering mechanistic knowledge and potential of a drug causing steatohepatitis. Ultimately this information could also help predict, detect or guide the development of specific treatments for DISH, which is an unmet need as of today.

Endoplasmic Reticulum Stress and Associated ROS

The endoplasmic reticulum (ER) is a fascinating network of tubules through which secretory and transmembrane proteins enter unfolded and exit as either folded or misfolded proteins, after which they are directed either toward other organelles or to degradation, respectively. The ER redox environment dictates the fate of entering proteins, and the level of redox signaling mediators modulates the level of reactive oxygen species (ROS). Accumulating evidence suggests the interrelation of ER stress and ROS with redox signaling mediators such as protein disulfide isomerase (PDI)-endoplasmic reticulum oxidoreductin (ERO)-1, glutathione (GSH)/glutathione disuphide (GSSG), NADPH oxidase 4 (Nox4), NADPH-P450 reductase (NPR), and calcium. Here, we reviewed persistent ER stress and protein misfolding-initiated ROS cascades and their significant roles in the pathogenesis of multiple human disorders, including neurodegenerative diseases, diabetes mellitus, atherosclerosis, inflammation, ischemia, and kidney and liver diseases.

A cellular model to study drug-induced liver injury in nonalcoholic fatty liver disease: Application to acetaminophen

Obesity and nonalcoholic fatty liver disease (NAFLD) can increase susceptibility to hepatotoxicity induced by some xenobiotics including drugs, but the involved mechanisms are poorly understood. For acetaminophen (APAP), a role of hepatic cytochrome P450 2E1 (CYP2E1) is suspected since the activity of this enzyme is consistently enhanced during NAFLD. The first aim of our study was to set up a cellular model of NAFLD characterized not only by triglyceride accumulation but also by higher CYP2E1 activity. To this end, human HepaRG cells were incubated for one week with stearic acid or oleic acid, in the presence of different concentrations of insulin. Although cellular triglycerides and the expression of lipid-responsive genes were similar with both fatty acids, CYP2E1 activity was significantly increased only by stearic acid. CYP2E1 activity was reduced by insulin and this effect was reproduced in cultured primary human hepatocytes. Next, APAP cytotoxicity was assessed in HepaRG cells with or without lipid accretion and CYP2E1 induction. Experiments with a large range of APAP concentrations showed that the loss of ATP and glutathione was almost always greater in the presence of stearic acid. In cells pretreated with the CYP2E1 inhibitor chlormethiazole, recovery of ATP was significantly higher in the presence of stearate with low (2.5mM) or high (20mM) concentrations of APAP. Levels of APAP-glucuronide were significantly enhanced by insulin. Hence, HepaRG cells can be used as a valuable model of NAFLD to unveil important metabolic and hormonal factors which can increase susceptibility to drug-induced hepatotoxicity.

Novel insights into the mechanisms whereby isoflavones protect against fatty liver disease

Fatty liver disease (FLD) is a growing public health problem worldwide. There is an urgent requirement for alternative and natural medicine to treat this disease. As phytochemicals, isoflavones have attracted considerable attention for the prevention of FLD. Numerous studies have revealed that isoflavones protect against FLD through various pathways which modulate fatty acid β-oxidation, lipid synthesis, and oxidative stress. Recently, the aldose reductase (AR)/polyol pathway has been reported to be involved in the development of FLD by modulating hepatic fructose production, peroxisome proliferator-activated receptor (PPAR)α activity, cytochrome P450 (CYP)2E1 expression, and gut bacterial endotoxin-induced cytokine release. It has been reported that some isoflavones are potent AR inhibitors. Here, we review the anti-FLD actions of isoflavones and the proposed mechanism whereby isoflavones protect against FLD, with regard to the AR/polyol pathway. We propose that isoflavones block the AR/polyol pathway and in turn reduce fructose production and subsequent fat accumulation in the liver in diabetic or high-glucose-diet mice. In addition, in rodents with alcoholic liver disease or nonalcoholic fatty liver disease/nonalcoholic steatohepatitis, inhibition of AR by isoflavones may improve PPARα-mediated fatty acid oxidation, reduce hepatic steatosis, and attenuate CYP2E1-mediated oxidative stress or AR/gut bacterial endotoxin-mediated cytokine overproduction, to alleviate progression of FLD.

Acetaminophen-induced liver injury in obesity and nonalcoholic fatty liver disease

Although acetaminophen (APAP) is usually considered as a safe drug, this painkiller can lead to acute liver failure after overdoses. Moreover, there is evidence that the maximum recommended dosage can induce hepatic cytolysis in some individuals. Several predisposing factors appear to enhance the risk and severity of APAP-induced liver injury including chronic alcoholic liver disease and nonalcoholic fatty liver disease (NAFLD), which refers to a large spectrum of hepatic lesions linked to obesity. In contrast, obesity by itself does not seem to be associated with a higher risk of APAP-induced liver injury. Since 1987, seven studies dealt with APAP-induced hepatotoxicity in rodent models of NAFLD and five of them found that this liver disease was associated with higher APAP toxicity. Unfortunately, these studies did not unequivocally established the mechanism(s) whereby NAFLD could favour APAP hepatotoxicity, although some investigations suggested that pre-existent induction of hepatic cytochrome P450 2E1 (CYP2E1) could play a significant role by increasing the generation of N-acetyl-p-benzoquinone imine (NAPQI), the toxic metabolite of APAP. Moreover, pre-existent mitochondrial dysfunction associated with NAFLD could also be involved. In contrast, some investigations suggested that factors that could reduce the risk and severity of APAP hepatotoxicity in obesity and NAFLD include higher hepatic APAP glucuronidation, reduced CYP3A4 activity and increased volume of body distribution. Thus, the occurrence and the outcome of APAP-induced liver injury in an obese individual with NAFLD might depend on a delicate balance between metabolic factors that can be protective and others that favour large hepatic levels of NAPQI.

Lipotoxicity in the liver

Obesity due to excessive food intake and the lack of physical activity is becoming one of the most serious public health problems of the 21^st century. With the increasing prevalence of obesity, non-alcoholic fatty liver disease is also emerging as a pandemic. While previously this pathophysiological condition was mainly attributed to triglyceride accumulation in hepatocytes, recent data show that the development of oxidative stress, lipid peroxidation, cell death, inflammation and fibrosis are mostly due to accumulation of fatty acids, and the altered composition of membrane phospholipids. In fact, triglyceride accumulation might play a protective role, and the higher toxicity of saturated or trans fatty acids seems to be the consequence of a blockade in triglyceride synthesis. Increased membrane saturation can profoundly disturb cellular homeostasis by impairing the function of membrane receptors, channels and transporters. However, it also induces endoplasmic reticulum stress via novel sensing mechanisms of the organelle’s stress receptors. The triggered signaling pathways in turn largely contribute to the development of insulin resistance and apoptosis. These findings have substantiated the lipotoxic liver injury hypothesis for the pathomechanism of hepatosteatosis. This minireview focuses on the metabolic and redox aspects of lipotoxicity and lipoapoptosis, with special regards on the involvement of endoplasmic reticulum stress responses.

Is nonalcoholic steatohepatitis associated with a high-though-normal thyroid stimulating hormone level and lower cholesterol levels?

Hypothyroidism is associated with the risk of development of the metabolic syndrome (MS) and hypercholesterolemia. Direct evidence that hypothyroidism might be associated with advanced chronic liver disease via nonalcoholic steatohepatitis (NASH) is limited. We studied the relationship between thyroid hormones, thyroid stimulating hormone (TSH), cholesterol, and NASH. In consecutive euthyroid patients with biopsy-proven nonalcoholic fatty liver disease, TSH and thyroid hormone (FT3 and FT4) concentrations were compared in 25 patients with steatosis and 44 non-cirrhotic NASH patients featuring concurrent ballooning, lobular inflammation and steatosis. The MS was diagnosed according to ATP III criteria. A meta-analysis of previously published studies was performed to evaluate whether NASH, compared to simple steatosis, is associated with lower cholesterol levels. At univariate analysis, compared to those with steatosis, patients with NASH have a wider waist, elevated levels of BMI, ALT, AST, fasting insulin, HOMA-IR, ferritin, TSH and a lower serum cholesterol. At stepwise multivariable logistic regression analysis, the independent predictors of NASH are high HOMA and TSH and lower total cholesterol (Model 1); MS and high TSH (Model 2). At meta-analysis, serum total cholesterol levels are significantly lower in predominantly non-cirrhotic NASH than in simple steatosis. This study provides cross-sectional and meta-analytic evidence that, in euthyroid patients, high-though-normal TSH values are independently associated with NASH. Further work is needed to ascertain the role, if any, of lower cholesterol serum levels in assisting in the diagnosis of NASH.

CYP2E1 and oxidant stress in alcoholic and non-alcoholic fatty liver disease

Alcoholic (ALD) and non-alcoholic fatty liver diseases (NAFLD) are clinical conditions leading to hepatocellular injury and inflammation resulting from alcohol consumption, high fat diet, obesity and diabetes, among others. Oxidant stress is a major contributing factor to the pathogenesis of ALD and NAFLD. Multiple studies have shown that generation of reactive oxygen species (ROS) is key for the progression of fatty liver to steatohepatitis. Cytochrome P450 2E1 (CYP2E1) plays a critical role in ROS generation and CYP2E1 is also induced by alcohol itself. This review summarizes the role of CYP2E1 in ALD and NAFLD.

Relevance of CYP2E1 to non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) and its progression to steatohepatitis (NASH) and cirrhosis is a growing problem in most developed countries. Increased hepatic expression of CYP2E1, which carries out omega hydroxylation of fatty acids, was first shown in a mouse model of NASH and this was later also reported for human NASH, though not all studies agree with this finding and further larger studies are still needed. In view of its role in fatty acid metabolism which leads to increased levels of toxic lipid peroxides and its possible increased expression in NASH, CYP2E1 is an attractive candidate for a role as a genetic risk factor for both NAFLD generally including progression to NASH. Two studies have focused on the variant allele CYP2E1*5, which may be associated with increased CYP2E1 expression. Both reported increased frequencies of this allele in NASH patients, though statistical significance was not achieved because of small sample sizes. Some more indirect data also suggests a relationship between high CYP2E1 activity and progression to NASH. However, three recent genome-wide association studies on NAFLD have failed to find any evidence that single nucleotide polymorphisms in or adjacent to the CYP2E1 gene contribute to susceptibility. Further studies are needed to investigate a possible role in disease progression in addition to susceptibility and the possibility that statistical power in the existing studies was insufficient to detect a relatively small contribution to disease susceptibility.

Effects of dietary inulin, statin, and their co-treatment on hyperlipidemia, hepatic steatosis and changes in drug-metabolizing enzymes in rats fed a high-fat and high-sucrose diet

Background

Rats fed a high-fat and high-sucrose (HF) diet develop hepatic steatosis and hyperlipidemia. There are several reports that a change in nutritional status affects hepatic levels of drug-metabolizing enzymes. Synthetic inulin is a dietary component that completely evades glucide digestion. Supplementing a HF diet with inulin ameliorates hypertriglycemia and hepatic steatosis, but not hypercholesterolemia. This study aimed at distinguishing the effects of synthetic inulin and 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin), which inhibit cholesterol biosynthesis.

Methods

We examined effects of co-treatment with synthetic inulin (5%) and fluvastatin (0, 4, and 8 mg/kg, per os) on body weight, epidydimal white adipose tissue weight, serum and hepatic lipid profiles, and hepatic cytochrome P450 (CYP) mRNA and protein profiles in rats fed a standard diet or a HF diet for 3 weeks.

Results

Treatment with the synthetic inulin (5%) or fluvastatin at 4 mg/kg (lethal dose in rats fed the HF diet, 8 mg/kg) ameliorated the elevation in hepatic triacylglycerol and total cholesterol levels in rats fed the HF diet. Whereas co-treatment with the inulin (5%) and fluvastatin (4 mg/kg) had a tendency to more strongly suppress the elevation in serum levels of very low density lipoprotein triacylglycerol than either treatment alone, no additive or synergistic effect was found in decrease in hepatic lipid levels. Hepatic levels of CYP1A1/2 and CYP2E1 mRNA and protein and methoxyresorufin O-demethylase and ethoxyresorufin O-deethylase activities were reduced in rats fed the HF diet. The synthetic inulin alleviated the reduction in hepatic levels of CYP1A1/2 and CYP2E1 mRNA and protein more strongly than fluvastatin, and no synergistic effects were observed on co-treatment. Furthermore, hepatic levels of aryl hydrocarbon receptor mRNA were decreased in rats fed the HF diet and recovered to near normal values with the intake of dietary inulin, which correlated with change in CYP1A1/2.

Conclusions

Dietary inulin alone was effective to prevent the development of hepatic steatosis, ameliorate nutritional effects, and alleviate the hepatic change in the expression of CYP1A1/2 and CYP2E1, while co-treatment with statin did not have additive or synergistic effects and statin may cause adverse effects in rats fed the HF diet.

Increased expression of cytochrome P450 2E1 in nonalcoholic fatty liver disease: mechanisms and pathophysiological role

Due to the worldwide surge in obesity and type 2 diabetes, the increased incidence of nonalcoholic fatty liver disease (NAFLD) is a major concern for the public health. Indeed, NAFLD encompasses a large spectrum of conditions ranging from fatty liver to nonalcoholic steatohepatitis (NASH), which can progress to cirrhosis in some patients. A better understanding of the mechanisms involved in fatty liver and its progression into NASH is important in order to develop efficient drugs able to alleviate these liver diseases. Although numerous investigations pointed to reactive oxygen species (ROS) as key players in the progression of fatty liver to NASH, their exact source is still uncertain. Besides the mitochondrial respiratory chain, cytochrome P450 2E1 (CYP2E1) has recently emerged as another potentially important cause of ROS overproduction. Indeed, higher hepatic CYP2E1 expression and activity have been frequently observed in the context of obesity and NAFLD. It is currently unknown why CYP2E1 is enhanced in these dysmetabolic diseases, although increased hepatic levels of fatty acids and insulin resistance might play a role. Nonetheless, higher hepatic CYP2E1 could play a significant role in the pathophysiology of NASH by inducing lipid peroxidation and oxidative damage of key cellular components. Moreover, CYP2E1-mediated overproduction of ROS could promote hepatic insulin resistance, which can further aggravate fatty liver. Since a significant amount of CYP2E1 can be located within liver mitochondria, higher levels of CYP2E1 in NAFLD could also have detrimental effects on mitochondrial function. Finally, increased CYP2E1 activity during NAFLD could enhance the susceptibility of some patients to the hepatotoxicity of different xenobiotics through the CYP2E1-mediated generation of harmful reactive metabolites.

The roles of ER stress and P450 2E1 in CCl(4)-induced steatosis

The role of ER stress on hepatic steatosis was investigated in a rat model. We injected CCl(4) into rats and found that CCl(4) could induce hepatic lipid accumulation, confirmed by Oil Red O staining and by measurement of triglyceride and cholesterol. The expression of ApoB, an apolipoprotein, was decreased in plasma and increased in the liver of CCl(4)-treated animals. The ER stress response was also significantly increased by CCl(4). P450 2E1 expression and activity were increased through interactions of P450 2E1 with NADPH-dependent P450 reductase (NPR) under CCl(4)-treated conditions. In HepG2 cells, intracellular lipid accumulation and its signaling were comparable to in vivo results. In order to elucidate the effect of the ER stress response itself, tunicamycin, an N-acetyl-glycosylation inhibitor, was injected into rats, followed by Oil Red O staining, lipid/triglyceride/cholesterol accumulation analysis, and examination of ApoB expression. Additionally, the ER stress response and upregulation of P450 2E1 were also confirmed in the tunicamycin-treated rats. All of the responses were similar to those seen with CCl(4). The P450 2E1 inhibitor diallyl sulphide (DAS), N-acetylcysteine (NAC), and reduced glutathione (GSH) antioxidants also regulated processes, including ApoB expression and lipid accumulation in CCl(4)-treated animals. In the presence of tunicamycin, DAS or NAC/GSH regulated all of the pathological phenomena with the exception of the ER stress response. In summary, CCl(4) induces liver steatosis, a process involving ER stress-induced P450 2E1 activation and ROS production.

Drug metabolism alterations in nonalcoholic fatty liver disease

Drug-metabolizing enzymes play a vital role in the elimination of the majority of therapeutic drugs. The major organ involved in drug metabolism is the liver. Chronic liver diseases have been identified as a potential source of significant interindividual variation in metabolism. Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the United States, affecting between 60 and 90 million Americans, yet the vast majority of NAFLD patients are undiagnosed. NAFLD encompasses a spectrum of pathologies, ranging from steatosis to nonalcoholic steatohepatitis and fibrosis. Numerous animal studies have investigated the effects of NAFLD on hepatic gene expression, observing significant alterations in mRNA, protein, and activity levels. Information on the effects of NAFLD in human patients is limited, though several significant investigations have recently been published. Significant alterations in the activity of drug-metabolizing enzymes may affect the clearance of therapeutic drugs, with the potential to result in adverse drug reactions. With the enormous prevalence of NAFLD, it is conceivable that every drug currently on the market is being given to patients with NAFLD. The current review is intended to present the results from both animal models and human patients, summarizing the observed alterations in the expression and activity of the phase I and II drug-metabolizing enzymes.

Systematic review of performance of non-invasive biomarkers in the evaluation of non-alcoholic fatty liver disease

This systematic review evaluates the many studies carried out to discover and evaluate non-invasive markers of non-alcoholic fatty liver disease (NAFLD). Many different strategies and methods have been used in this task, from the discovery of new markers by global 'shotgun' studies to hypothesis-driven approaches, to the development of algorithm tests based on routinely available clinical and biochemical parameters. We examined the various different approaches, summarising the findings in an attempt to give an overview of the field of non-invasive markers in NAFLD, encompassing markers of steatosis, necro-inflammation and fibrosis. The body of literature surrounding this topic is complex and varied, encompassing not only different methodologies but also different patient characteristics, different disease definitions, as well as different end points. This reflects the heterogeneity of NAFLD, which, however, introduces considerably difficulty when trying to draw a conclusion between studies. We have divided this review into three main chapters based on the characteristics of the studies. The Genomics/Proteomics chapter reviews studies using a non-hypothesis-driven approach to biomarker discovery. Thereafter, we evaluate studies of association - studies that target-specific markers, comparing levels between disease and control groups. Finally, we examine the algorithm tests - mathematical systems developed on the basis of previously described markers and assessed, usually, by receiver operator curve analysis. While radiological examination and investigations offer important diagnostic information, such studies are not discussed in this review - the body of literature surrounding blood and anthropological markers is complex and varied, demanding close attention.

Cytochrome P450 2E1 and hyperglycemia-induced liver injury

Cytochrome P450 2E1 (CYP2E1), a microsomal enzyme involved in xenobiotic metabolism and generation of oxidative stress, has been implicated in promoting liver injury. The review deals with the changes in various cellular pathways in liver linked with the changes in regulation of CYP2E1 under hyperglycemic conditions. Some of the hepatic abnormalities associated with hyperglycemia-mediated induction of CYP2E1 include increased oxidative stress, changes in mitochondrial structure and function, apoptosis, nitrosative stress, and increased ketone body accumulation. Thus, changes in regulation of CYP2E1 are associated with the injurious effects of hyperglycemia in liver.

Hepatic pharmacokinetics of cationic drugs in a high-fat emulsion-induced rat model of nonalcoholic steatohepatitis

The hepatic pharmacokinetics of five selected cationic drugs (propranolol, labetalol, metoprolol, antipyrine, and atenolol) was studied in the liver from control rats and from those with high-fat emulsion-induced nonalcoholic steatohepatitis (NASH). Studies were undertaken using an in situ-perfused rat liver and multiple indicator dilution, and outflow data were analyzed with a physiologically based organ pharmacokinetic model. Hepatic extraction (E) was significantly lower in the NASH model, and lipophilicity was the main solute structural determinant of the observed differences in intrinsic elimination clearance (CL(int)) and permeability-surface area product (PS) with pK(a) defining the extent of sequestration in the liver [apparent distribution ratio (K(v))]. The main pathophysiological determinants were liver fibrosis, leading to a decreased PS, liver fat causing an increase in K(v), and an increase in both total liver cytochrome P450 (P450) concentration and P450 isoform expression for Cyp3a2 and Cyp2d2, causing an increase CL(int) in NASH rat livers compared with control livers. Changes in hepatic pharmacokinetics (PS, K(v), CL(int), and E ratio) as a result of NASH were related to the physicochemical properties of drugs (lipophilicity or pK(a)) and hepatic histopathological changes (fibrosis index, steatosis index, and P450 concentration) by stepwise regression analysis. Thus, it appears that in NASH, counteracting mechanisms to facilitate hepatic removal are created in NASH-induced P450 expression, whereas NASH-induced fibrosis and steatohepatitis inhibit E by decreasing hepatocyte permeability through fibrosis and hepatic sequestration.

Bariatric surgery-induced weight loss reduces hepatic lipid peroxidation levels and affects hepatic cytochrome P-450 protein content

OBJECTIVE

To evaluate the effects of surgical weight loss on hepatic lipid peroxidation levels and cytochrome P-450 protein expression in patients with nonalcoholic fatty liver disease (NAFLD).

SUMMARY BACKGROUND DATA

NAFLD and nonalcoholic steatohepatitis (NASH) affect hepatic cytochrome P-450 (CYP) protein expression and activity, and CYP2E1 may play a role in the pathogenesis of NAFLD and NASH through induction of oxidative stress and lipid peroxidation. NAFLD and NASH are associated with increased systemic lipid peroxidation levels and elevated hepatic CYP2E1 activity, but hepatic CYP3A4/5 activity is decreased.

METHODS

Liver biopsies from 20 patients with NAFLD who underwent bariatric surgery were obtained intraoperatively and at 15 +/- 7 months following surgery. Hepatic malondialdehyde (MDA) levels (a marker of lipid peroxidation), CYP2E1 and CYP3A4/5 protein expression, and steatosis, as a percent of total area, were measured by immunohistochemistry followed by digital image quantitation.

RESULTS

Following weight loss, as reflected by reduced BMI (54 +/- 9 vs. 37 +/- 9 kg/m2; P < 0.001), features of the metabolic syndrome, grade and stage of liver disease, and liver histology were all significantly improved (P < 0.01). Hepatic MDA staining (35 +/- 18% vs. 23 +/- 14%; P = 0.02), CYP2E1 protein content (68 +/- 9% vs. 56 +/- 11%; P < 0.001), and steatosis (17 +/- 7% vs. 2 +/- 3%; P < 0.001) were significantly reduced following weight loss. CYP3A4/5 protein content was unchanged (57 +/- 13% vs. 55 +/- 13%; P = 0.433). The reduction in lipid peroxidation was independently associated with changes in CYP2E1 protein expression after bariatric surgery (r = 0.477; P = 0.033).

CONCLUSION

Elevations in hepatic lipid peroxidation and CYP2E1 expression that are seen in NAFLD improve significantly with weight loss induced by bariatric surgery.

PPAR/RXR Regulation of Fatty Acid Metabolism and Fatty Acid omega-Hydroxylase (CYP4) Isozymes: Implications for Prevention of Lipotoxicity in Fatty Liver Disease

Fatty liver disease is a common lipid metabolism disorder influenced by the combination of individual genetic makeup, drug exposure, and life-style choices that are frequently associated with metabolic syndrome, which encompasses obesity, dyslipidemia, hypertension, hypertriglyceridemia, and insulin resistant diabetes. Common to obesity related dyslipidemia is the excessive storage of hepatic fatty acids (steatosis), due to a decrease in mitochondria β-oxidation with an increase in both peroxisomal β-oxidation, and microsomal ω-oxidation of fatty acids through peroxisome proliferator activated receptors (PPARs). How steatosis increases PPARα activated gene expression of fatty acid transport proteins, peroxisomal and mitochondrial fatty acid β-oxidation and ω-oxidation of fatty acids genes regardless of whether dietary fatty acids are polyunsaturated (PUFA), monounsaturated (MUFA), or saturated (SFA) may be determined by the interplay of PPARs and HNF4α with the fatty acid transport proteins L-FABP and ACBP. In hepatic steatosis and steatohepatitis, the ω-oxidation cytochrome P450 CYP4A gene expression is increased even with reduced hepatic levels of PPARα. Although numerous studies have suggested the role ethanol-inducible CYP2E1 in contributing to increased oxidative stress, Cyp2e1-null mice still develop steatohepatitis with a dramatic increase in CYP4A gene expression. This strongly implies that CYP4A fatty acid ω-hydroxylase P450s may play an important role in the development of steatohepatitis. In this review and tutorial, we briefly describe how fatty acids are partitioned by fatty acid transport proteins to either anabolic or catabolic pathways regulated by PPARs, and we explore how medium-chain fatty acid (MCFA) CYP4A and long-chain fatty acid (LCFA) CYP4Fω-hydroxylase genes are regulated in fatty liver. We finally propose a hypothesis that increased CYP4A expression with a decrease in CYP4F genes may promote the progression of steatosis to steatohepatitis.

Update information on drug metabolism systems--2009, part II: summary of information on the effects of diseases and environmental factors on human cytochrome P450 (CYP) enzymes and transporters

The present paper is an update of the data on the effects of diseases and environmental factors on the expression and/or activity of human cytochrome P450 (CYP) enzymes and transporters. The data are presented in tabular form (Tables 1 and 2) and are a continuation of previously published summaries on the effects of drugs and other chemicals on CYP enzymes (Rendic, S.; Di Carlo, F. Drug Metab. Rev., 1997, 29(1-2), 413-580., Rendic, S. Drug Metab. Rev., 2002, 34(1-2), 83-448.). The collected information presented here is as stated by the cited author(s), and in cases when several references are cited the latest published information is included. Inconsistent results and conclusions obtained by different authors are highlighted, followed by discussion of the major findings. The searchable database is available as an Excel file, for information about file availability contact the corresponding author.

Hepatic cytochrome P450 enzyme alterations in humans with progressive stages of nonalcoholic fatty liver disease

Members of the cytochrome P450 (P450) enzyme families CYP1, CYP2, and CYP3 are responsible for the metabolism of approximately 75% of all clinically relevant drugs. With the increased prevalence of nonalcoholic fatty liver disease (NAFLD), it is likely that patients with this disease represent an emerging population at significant risk for alterations in these important drug-metabolizing enzymes. The purpose of this study was to determine whether three progressive stages of human NALFD alter hepatic P450 expression and activity. Microsomes isolated from human liver samples diagnosed as normal, n = 20; steatosis, n = 11; nonalcoholic steatohepatitis (NASH) (fatty liver), n = 10; and NASH (no longer fatty), n = 11 were analyzed for P450 mRNA, protein, and enzyme activity. Microsomal CYP1A2, CYP2D6, and CYP2E1 mRNA levels were decreased with NAFLD progression, whereas CYP2A6, CYP2B6, and CYP2C9 mRNA expression increased. Microsomal protein expression of CYP1A2, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 tended to decrease with NAFLD progression. Likewise, functional activity assays revealed decreasing trends in CYP1A2 (p = 0.001) and CYP2C19 (p = 0.05) enzymatic activity with increasing NAFLD severity. In contrast, activity of CYP2A6 (p = 0.001) and CYP2C9 (diclofenac, p = 0.0001; tolbutamide, p = 0.004) was significantly increased with NAFLD progression. Increased expression of proinflammatory cytokines tumor necrosis factor alpha and interleukin 1beta was observed and may be responsible for observed decreases in respective P450 activity. Furthermore, elevated CYP2C9 activity during NAFLD progression correlated with elevated hypoxia-induced factor 1alpha expression in the later stages of NAFLD. These results suggest that significant and novel changes occur in hepatic P450 activity during progressive stages of NAFLD.

Effects of ursodeoxycholic acid in combination with vitamin E on adipokines and apoptosis in patients with nonalcoholic steatohepatitis

BACKGROUND/AIMS

Adipokines and hepatocellular apoptosis participate in the pathogenesis of nonalcoholic steatohepatitis (NASH). In a randomized trial ursodeoxycholic acid (UDCA) with vitamin E (VitE) improved serum aminotransferases and hepatic histology. The present work evaluates the effect of this combination on adipokines and hepatocellular apoptosis.

METHODS

Circulating levels of adiponectin, resistin, leptin, interleukin (IL)-6, IL-8, retinol binding protein-4, monocyte chemoattractant protein-1 and tumour necrosis factor-alpha were measured by enzyme-linked immunoassays at the beginning and after 2 years of treatment with either UDCA+VitE, UDCA+placebo (P) or P+P. Apoptosis was assessed by immunohistochemistry for activated caspase-3 and circulating levels of apoptosis-associated cytokeratin 18 fragments (M30).

RESULTS

Levels of adiponectin increased in patients treated with UDCA+VitE, whereas they decreased in the two other groups (P<0.04) and correlated with the improvement of liver steatosis (P<0.04). M30 levels worsened in the P/P group and improved in the other two groups. They correlated with hepatocellular apoptosis (P<0.02) and steatosis (P<0.02) as well as negatively with adiponectin levels (P<0.04).

CONCLUSIONS

UDCA+VitE improves not only aminotransferase levels and liver histology of patients with NASH, but also decreases hepatocellular apoptosis and restores circulating levels of adiponectin. These results suggest that the UDCA+VitE combination has metabolic effects in addition to its beneficial cytoprotective properties.

Risk factors for hyperechogenic pancreas on endoscopic ultrasound: a case-control study

OBJECTIVE

Hyperechogenic pancreas (HP) suggestive of fatty replacement is a common finding during endoscopic ultrasound (EUS). Recent data have implicated pancreatic steatosis as a risk factor for pancreatitis and pancreatic malignancy. Hepatic steatosis has been linked to obesity, increased age, hypertriglyceridemia, hyperglycemia, and hyperinsulinemia. The objective of this study was to evaluate the effect of body mass index (BMI), hepatic steatosis, and other metabolic risk factors on HP seen on EUS.

METHODS

Patients with HP were identified by a review of a structured EUS database. The degree of echogenicity was judged relative to the liver (or spleen if the liver is hyperechogenic) at a similar depth. Various demographic and metabolic risk factors were assessed. Chronic pancreatitis was excluded based on normal findings on prior imaging studies. Each case was age matched and sex matched to 1 control with a normal pancreas on EUS.

RESULTS

By multivariate logistic regression analysis, BMI, hepatic steatosis, and alcohol use in excess of 14 g/wk were highly associated with the presence of HP compared with controls (all P<0.002). Hepatic steatosis was the strongest predictor with an odds ratio of nearly 14-fold.

CONCLUSIONS

Hepatic steatosis, alcohol use, and increased BMI are predictors of HP, which can be a marker for steatosis.

Molecular mechanisms of lipotoxicity in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is characterized by insulin resistance, which results in elevated serum concentration of free fatty acids (FFAs). Circulating FFAs provide the substrate for triacylglycerol formation in the liver, and may also be directly cytotoxic. Hepatocyte apoptosis is a key histologic feature of NAFLD, and correlates with progressive inflammation and fibrosis. The molecular pathways leading to hepatocyte apoptosis are not fully defined; however, recent studies suggest that FFA-induced apoptosis contributes to the pathogenesis of nonalcoholic steatohepatitis. FFAs directly engage the core apoptotic machinery by activating the proapoptotic protein Bax, in a c-jun N-terminal kinase-dependent manner. FFAs also activate the lysosomal pathway of cell death and regulate death receptor gene expression. The role of ER stress and oxidative stress in the pathogenesis of nonalcoholic steatohepatitis has also been described. Understanding the molecular mediators of liver injury should promote development of mechanism-based therapeutic interventions.