Effects of fatty acids and ketone bodies on cytochromes P450 2B, 4A, and 2E1 expression in primary cultured rat hepatocytes

Effects of ammonia and roxithromycin exposure on skin mucus microbiota composition and immune response of juvenile yellow catfish Pelteobagrus fulvidraco

As an inevitable factor in aquaculture, ammonia plays a critical role in macrolide antibiotic resistance, leading to accumulating of antibiotic-resistant bacteria in fish skin mucus. In this study, four experimental groups were implemented to test the effects of ammonia alone or in combination with roxithromycin for 28 days on skin mucus microbial composition and the immune response of yellow catfish: CON (control), AN (50.00 mg L-1 total ammonia nitrogen, TA-N), ROX (100 μg L-1 roxithromycin), and HR (50.00 mg L-1 TA-N, 100 μg L-1 ROX). This study demonstrated that ammonia or roxithromycin exposure resulted in increased plasma ammonia content and decreased total antioxidant capacity. Compared with AN group, the combined exposure of ammonia and roxithromycin inhibited the skin mucus immune response. Microbial composition analysis showed that combined exposure of ammonia and roxithromycin had no significant effect on skin mucus α-diversity as compared with CON group. The abundance of Cetobacterium, Rhizobiales_Incertae_Sedis_uncultured and Acinetobacter was increased significantly with the combined effect of ammonia and roxithromycin, these bacteria may be potentially antibiotic-resistant. As compared with CON group, the combined exposure of ammonia and roxithromycin did not affect skin goblet cell counts. This study suggests that combined exposure to ammonia and ROX increases the risk of the emergence of antibiotic-resistant bacteria.

Detoxification Cytochrome P450s (CYPs) in Families 1-3 Produce Functional Oxylipins from Polyunsaturated Fatty Acids

This manuscript reviews the CYP-mediated production of oxylipins and the current known function of these diverse set of oxylipins with emphasis on the detoxification CYPs in families 1-3. Our knowledge of oxylipin function has greatly increased over the past 3-7 years with new theories on stability and function. This includes a significant amount of new information on oxylipins produced from linoleic acid (LA) and the omega-3 PUFA-derived oxylipins such as α-linolenic acid (ALA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA). However, there is still a lack of knowledge regarding the primary CYP responsible for producing specific oxylipins, and a lack of mechanistic insight for some clinical associations between outcomes and oxylipin levels. In addition, the role of CYPs in the production of oxylipins as signaling molecules for obesity, energy utilization, and development have increased greatly with potential interactions between diet, endocrinology, and pharmacology/toxicology due to nuclear receptor mediated CYP induction, CYP inhibition, and receptor interactions/crosstalk. The potential for diet-diet and diet-drug/chemical interactions is high given that these promiscuous CYPs metabolize a plethora of different endogenous and exogenous chemicals.

Progressive Liver Fibrosis in Non-Alcoholic Fatty Liver Disease

Non-alcoholic steatohepatitis (NASH) is a chronic and progressive form of non-alcoholic fatty liver disease. Its global incidence is increasing and makes NASH an epidemic and a public health threat. Non-alcoholic fatty liver disease is associated with major morbidity and mortality, with a heavy burden on quality of life and liver transplant requirements. Due to repeated insults to the liver, patients are at risk for developing hepatocellular carcinoma. The progression of NASH was initially defined according to a two-hit model involving an initial development of steatosis, followed by a process of lipid peroxidation and inflammation. In contrast, current evidence proposes a "multi-hit" or "multi-parallel hit" model that includes multiple pathways promoting progressive fibrosis and oncogenesis. This model includes multiple cellular, genetic, immunological, metabolic, and endocrine pathways leading to hepatocellular carcinoma development, underscoring the complexity of this disease.

CYP2E1 in Alcoholic and Non-Alcoholic Liver Injury. Roles of ROS, Reactive Intermediates and Lipid Overload

CYP2E1 is one of the fifty-seven cytochrome P450 genes in the human genome and is highly conserved. CYP2E1 is a unique P450 enzyme because its heme iron is constitutively in the high spin state, allowing direct reduction of, e.g., dioxygen, causing the formation of a variety of reactive oxygen species and reduction of xenobiotics to toxic products. The CYP2E1 enzyme has been the focus of scientific interest due to (i) its important endogenous function in liver homeostasis, (ii) its ability to activate procarcinogens and to convert certain drugs, e.g., paracetamol and anesthetics, to cytotoxic end products, (iii) its unique ability to effectively reduce dioxygen to radical species causing liver injury, (iv) its capability to reduce compounds, often generating radical intermediates of direct toxic or indirect immunotoxic properties and (v) its contribution to the development of alcoholic liver disease, steatosis and NASH. In this overview, we present the discovery of the enzyme and studies in humans, 3D liver systems and genetically modified mice to disclose its function and clinical relevance. Induction of the CYP2E1 enzyme either by alcohol or high-fat diet leads to increased severity of liver pathology and likelihood to develop ALD and NASH, with subsequent influence on the occurrence of hepatocellular cancer. Thus, fat-dependent induction of the enzyme might provide a link between steatosis and fibrosis in the liver. We conclude that CYP2E1 has many important physiological functions and is a key enzyme for hepatic carcinogenesis, drug toxicity and liver disease.

Natural Progression of Non-Alcoholic Steatohepatitis to Hepatocellular Carcinoma

Non-alcoholic steatohepatitis (NASH) is a chronic and progressive form of non-alcoholic fatty liver disease (NAFLD). Its global incidence is increasing which makes NASH an epidemic and a public health threat. Due to repeated insults to the liver, patients are at risk for developing hepatocellular carcinoma (HCC). The progression of NASH to HCC was initially defined according to a two-hit model which involved the development of steatosis, followed by lipid peroxidation and inflammation. However, current research defines a "multi-hit" or "multi-parallel hit" model which synthesizes several contributing pathways involved in progressive fibrosis and oncogenesis. This perspective considers the effects of cellular, genetic, immunologic, metabolic, and endocrine pathways leading up to HCC which underscores the complexity of this condition. This article will provide an updated review of the pathogenic mechanisms leading from NASH to HCC as well as an exploration of the role of biomarkers and screening.

Comparison of the severity of non-alcoholic fatty liver disease in diabetic and non-diabetic obese patients

INTRODUCTION

nonalcoholic fatty liver disease presents a broad spectrum of histopathological alterations, from steatosis to liver cirrhosis. Patients with diabetes mellitus (DM) present increased incidence and severity of NAFLD.

OBJECTIVE

determine the prevalence and severity of NAFLD in diabetic and non-diabetic obese patients undergoing bariatric surgery.

METHOD

the evaluation of liver biopsies was carried out through NAFLD activity score (NAS) in order to evaluate degree of hepatic steatosis, presence of ballooning, inflammatory activity and degree of fibrosis.

RESULTS

a total of 154 patients who have undergone bariatric surgery with intraoperative biopsy were observed and divided into two BMI ranges: from 35 to 44.9 and from 45 to 54.9. 32 (20.8%) from 154 patients were diabetic and 122 (79.2%) were non-diabetic. Patients with DM were significantly older than patients without the disease, presenting 41.29 ± 9.40 years vs 36.71 ± 10.13 years in the group with BMI of 35 to 44.9 (p=0.049); and 45.13 ± 7.10 years vs 37.00 ± 9.24 years in the group with BMI of 45 to 54.9 (p=0.024). In the histological evaluation, patients with DM from the BMI group of 35 to 44.9 had a strong association with higher prevalence and severity of steatosis, balloning, inflammation, fibrosis and steatohepatitis.

CONCLUSION

the present study confirms the high prevalence of NAFLD in patients with Morbid Obesity. Prevalence and severity increase proportionally to BMI and who have DM as comorbidity.

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.

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.

Review article: drug-induced liver injury in the context of nonalcoholic fatty liver disease - a physiopathological and clinical integrated view

BACKGROUND

Nonalcoholic fatty disease (NAFLD) is the most common liver disease, since it is strongly associated with obesity and metabolic syndrome pandemics. NAFLD may affect drug disposal and has common pathophysiological mechanisms with drug-induced liver injury (DILI); this may predispose to hepatoxicity induced by certain drugs that share these pathophysiological mechanisms. In addition, drugs may trigger fatty liver and inflammation per se by mimicking NAFLD pathophysiological mechanisms.

AIMS

To provide a comprehensive update on (a) potential mechanisms whereby certain drugs can be more hepatotoxic in NAFLD patients, (b) the steatogenic effects of drugs, and (c) the mechanism involved in drug-induced steatohepatitis (DISH).

METHODS

A language- and date-unrestricted Medline literature search was conducted to identify pertinent basic and clinical studies on the topic.

RESULTS

Drugs can induce macrovesicular steatosis by mimicking NAFLD pathogenic factors, including insulin resistance and imbalance between fat gain and loss. Other forms of hepatic fat accumulation exist, such as microvesicular steatosis and phospholipidosis, and are mostly associated with acute mitochondrial dysfunction and defective lipophagy, respectively. Drug-induced mitochondrial dysfunction is also commonly involved in DISH. Patients with pre-existing NAFLD may be at higher risk of DILI induced by certain drugs, and polypharmacy in obese individuals to treat their comorbidities may be a contributing factor.

CONCLUSIONS

The relationship between DILI and NAFLD may be reciprocal: drugs can cause NAFLD by acting as steatogenic factors, and pre-existing NAFLD could be a predisposing condition for certain drugs to cause DILI. Polypharmacy associated with obesity might potentiate the association between this condition and DILI.

Production of chlorzoxazone glucuronides via cytochrome P4502E1 dependent and independent pathways in human hepatocytes

CYP2E1 activity is measured in vitro and in vivo via hydroxylation of the Chlorzoxazone (CHZ) producing the 6-hydroxychlorzoxazone (OH-CHZ) further metabolized as a glucuronide excreted in urine. Thus, the quantification of the OH-CHZ following enzymatic hydrolysis of CHZ-derived glucuronide appears to be a reliable assay to measure the CYP2E1 activity without direct detection of this glucuronide. However, OH-CHZ hydrolyzed from urinary glucuronide accounts for less than 80% of the CHZ administrated dose in humans leading to postulate the production of other unidentified metabolites. Moreover, the Uridine 5'-diphospho-glucuronosyltransferase (UGT) involved in the hepatic glucuronidation of OH-CHZ has not yet been identified. In this study, we used recombinant HepG2 cells expressing CYP2E1, metabolically competent HepaRG cells, primary hepatocytes and precision-cut human liver slices to identify metabolites of CHZ (300 μM) by high pressure liquid chromatography-UV and liquid-chromatography-mass spectrometry analyses. Herein, we report the detection of the CHZ-O-glucuronide (CHZ-O-Glc) derived from OH-CHZ in culture media but also in mouse and human urine and we identified a novel CHZ metabolite, the CHZ-N-glucuronide (CHZ-N-Glc), which is resistant to enzymatic hydrolysis and produced independently of CHZ hydroxylation by CYP2E1. Moreover, we demonstrate that UGT1A1, 1A6 and 1A9 proteins catalyze the synthesis of CHZ-O-Glc while CHZ-N-Glc is produced by UGT1A9 specifically. Together, we demonstrated that hydrolysis of CHZ-O-Glc is required to reliably quantify CYP2E1 activity because of the rapid transformation of OH-CHZ into CHZ-O-Glc and identified the CHZ-N-Glc produced independently of the CYP2E1 activity. Our results also raise the questions of the contribution of CHZ-N-Glc in the overall CHZ metabolism and of the quantification of CHZ glucuronides in vitro and in vivo for measuring UGT1A activities.

Sphingolipid metabolism in non-alcoholic fatty liver diseases

Non-alcoholic fatty liver disease (NAFLD) involves a panel of pathologies starting with hepatic steatosis and continuing to irreversible and serious conditions like steatohepatitis (NASH) and hepatocarcinoma. NAFLD is multifactorial in origin and corresponds to abnormal fat deposition in liver. Even if triglycerides are mostly associated with these pathologies, other lipid moieties seem to be involved in the development and severity of NAFLD. That is the case with sphingolipids and more particularly ceramides. In this review, we explore the relationship between NAFLD and sphingolipid metabolism. After providing an analysis of complex sphingolipid metabolism, we focus on the potential involvement of sphingolipids in the different pathologies associated with NAFLD. An unbalanced ratio between ceramides and terminal metabolic products in the liver and plasma promotes weight gain, inflammation, and insulin resistance. In the etiology of NAFLD, some sphingolipid species such as ceramides may be potential biomarkers for NAFLD. We review the clinical relevance of sphingolipids in liver diseases.

1-Aminobenzotriazole: A Mechanism-Based Cytochrome P450 Inhibitor and Probe of Cytochrome P450 Biology

1-Aminobenzotriazole (1-ABT) is a pan-specific, mechanism-based inactivator of the xenobiotic metabolizing forms of cytochrome P450 in animals, plants, insects, and microorganisms. It has been widely used to investigate the biological roles of cytochrome P450 enzymes, their participation in the metabolism of both endobiotics and xenobiotics, and their contributions to the metabolism-dependent toxicity of drugs and chemicals. This review is a comprehensive evaluation of the chemistry, discovery, and use of 1-aminobenzotriazole in these contexts from its introduction in 1981 to the present.

Streptozotocin diabetes increases mRNA expression of ketogenic enzymes in the rat heart

BACKGROUND

Diabetic cardiomyopathy develops in insulin-dependent diabetic patients who have no hypertension, cardiac hypertrophy or vascular disease. Diabetes increases cardiac fatty acid oxidation, but cardiac hypertrophy limits fatty acid oxidation. Here we examined effects of diabetes on gene expression in rat hearts.

METHODS

We used oligonucleotide microarrays to examine effects of insulindependent diabetes in the rat heart. RTQ PCR confirmed results of microarrays. Specific antibodies were used to examine changes in the mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2).

RESULTS

A surprising result of diabetes was increased mRNA encoding all enzymes of the ketone body synthesis pathway. Increased mRNA expression for these enzymes was confirmed by RTQ PCR. The mRNA encoding HMGCS2, the rate-controlling enzyme, was 27 times greater in diabetic hearts. Total HMGCS2 protein increased 8-fold in diabetic hearts, but no difference was found in HMGCS2 protein in control vs. diabetic liver.

CONCLUSIONS

Insulin-dependent diabetes induced the enzymes of ketone body synthesis in the heart, including HMGCS2, as well as increasing enzymes of fatty acid oxidation.

GENERAL SIGNIFICANCE

The mammalian heart does not export ketone bodies to other tissues, but rather is a major consumer of ketone bodies. Induction of HMGCS2, which is normally expressed only in the fetal and newborn heart, may indicate an adaptation by the heart to combat "metabolic inflexibility" by shifting the flux of excess intramitochondrial acetyl-CoA derived from elevated fatty acid oxidation into ketone bodies, liberating free CoA to balance the acetyl-CoA/CoA ratio in favor of increased glucose oxidation through the pyruvate dehydrogenase complex.

Nonalcoholic fatty liver disease in severe obese patients, subjected to bariatric surgery

CONTEXT

Nonalcoholic fatty liver disease encompasses a spectrum of histopathological changes that range from simple steatosis to nonalcoholic steatohepatitis. Works suggest that iron (Fe) deposits in the liver are involved in the physiopathology of nonalcoholic steatohepatitis.

OBJECTIVE

The aim of this study was to determine the prevalence of simple steatosis and nonalcoholic steatohepatitis in patients with morbid obesity, subjected to bariatric surgery and to establish a correlation of the anatomopathological findings with the presence of liver fibrosis.

METHODS

A total of 250 liver biopsies were conducted in the transoperation of the surgeries.

RESULTS

Steatosis was present in 226 (90.4%) of the samples, 76 (30.4%) being classified as mild; 71 (28.4%) as moderate and 79 (31.6%) as intense. Nonalcoholic steatohepatitis was diagnosed in 176 (70.4%) cases, where 120 (48.4%) were mild; 50 (20%) were moderate, and 6 (2.4%) cases were intense. Fibrosis was referred to in 108 (43.2%) biopsies, 95 of which (38%) were mild; 2 (0.8%) were moderate; 7 (2.8%) were intense, and cirrhosis was diagnosed in 4 (1.6%) cases. There was a correlation between the degree of steatosis and the level of inflammatory activity (rs = 0.460; P<0.001) and between the degree of this activity and the degree of fibrosis (rs = 0.583; P<0.001). Only 13 (5.2%) samples showed Fe deposits.

CONCLUSION

There is a high prevalence of nonalcoholic steatohepatitis in these patients and a positive correlation of the degrees of nonalcoholic steatohepatitis with the intensity of fibrosis. The low prevalence of Fe deposits found makes it questionable that the presence of this ion has any participation in the physiopathogeny of nonalcoholic fatty liver disease.

Markers in nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD), the most common liver disorder worldwide, encompasses a spectrum of abnormal liver histology ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) and cirrhosis. Population studies show that NAFLD is strongly associated with insulin resistance, obesity, type 2 diabetes mellitus, and lipid abnormalities. In the context of hepatic steatosis, factors that promote cell injury, inflammation, and fibrosis include oxidative stress, early mitochondrial dysfunction, endoplasmic reticulum stress, iron accumulation, apoptosis, adipocytokines, and stellate cell activation. The exact NASH prevalence is unknown because of the absence of simple noninvasive diagnostic tests. Although liver biopsy is the "gold standard" for the diagnosis of NASH, other tests are needed to facilitate the diagnosis and greatly reduce the requirement for invasive liver biopsy. In addition, the development of new fibrosis markers in NASH is needed to facilitate the assessment of its progression and the effectiveness of new therapies. The aim of this chapter, which is overview of biomarkers in NASH, is to establish a systematic approach to laboratory findings of the disease.

The effect of selegiline on total scavenger capacity and liver fat content: a preliminary study in an animal model

Selegiline is a selective irreversible inhibitor of the B-type of monoamine oxidase (MAO-B). The spectrum of its pharmacological activity is wide, possesses antioxidant, antiapoptotic and neuroprotective properties and, additionally, we found it is effective on the total scavenger capacity (TSC), and the regulation of fat content in rat liver kept on lipid-rich diet. Our aim was to clarify whether the oral treatment with selegiline is protective on oxidative damage of Sprague-Dawley adult rats in vivo. Four groups of rats (five animals in a group) were examined: (1) lipid-rich diet, (2) normal rat food, (3) lipid-rich diet + selegiline and (4) normal rat food + selegiline. Selegiline solution (2.5 µg/ml) was supplied with the drinking water, which was freely available for the animals. Regarding the drinking habit of the rats (20-30 ml/day), the daily dose was roughly equal with that used in the human therapy (5-10 mg/day). TSC was determined both at the beginning (0 day) and at the end of the study (28 days), when the blood samples were taken for chemiluminometric assay. Fat content of the liver was determined in the freshly frozen tissue by Sudan staining. TSC was increased in both the selegiline-treated groups. Selegiline treatment prevented the increase of liver fat in the group fed with lipid-rich diet. Our results led us to the conclusion that prolonged selegiline administration can raise the antioxidant capacity of the animals and prevents the accumulation of fat in their livers.

Effect of dietary monosodium glutamate on HFCS-induced hepatic steatosis: expression profiles in the liver and visceral fat

It has previously been shown that patients with nonalcoholic fatty liver disease (NAFLD) exhibit alterations in both hepatic and adipose tissue metabolism, and the dietary factors that contribute to the pathogenesis of NAFLD are likely to be multifactorial. Using C57BL/6J mice, we examined whether chronic exposure to low-dose dietary monosodium glutamate (MSG), high-fructose corn syrup (HFCS), or a combination of the two, vs. control would affect metabolism and hepatic and visceral fat gene expression in adult male progeny. A maternal diet containing 20% HFCS and/or dietary MSG (97.2 +/- 6.3 mg/kg body weight (bw), provided in the drinking water) was offered ad libitum from 3 weeks before mating, and continued throughout gestation and weaning until the progeny reached 32 weeks of age. Liver and abdominal fat gene expression was compared with control animals fed isocaloric standard chow under identical conditions. HFCS induced hepatic steatosis and increased the expression of genes involved in carbohydrate and lipid metabolism. Conversely, dietary MSG elevated serum free fatty acids (FFAs), triglycerides (TGs), high-density lipoprotein-cholesterol (HDL-C), and insulin, together with the expression of hepatic genes involved in lipid metabolism and bile synthesis. The HFCS+MSG combination elevated hepatic TGs, serum FFAs, and TG levels. In visceral white adipose tissue, both MSG and HFCS diets increased the expression of transcription factor Srebf2 and decreased expression of Ppargc1a, while downregulating the expression of mitochondrial respiratory chain components. MSG increased the expression of several genes implicated in adipocytes differentiation. We hypothesize that HFCS may promote hepatic steatosis, whereas dietary MSG induces dyslipidemia and markers of insulin resistance.

[Molecular bases of diabetic nephropathy]

The determinant of the diabetic nephropathy is hyperglycemia, but hypertension and other genetic factors are also involved. Glomerulus is the focus of the injury, where mesangial cell proliferation and extracellular matrix occur because of the increase of the intra- and extracellular glucose concentration and overexpression of GLUT1. Sequentially, there are increases in the flow by the poliol pathway, oxidative stress, increased intracellular production of advanced glycation end products (AGEs), activation of the PKC pathway, increase of the activity of the hexosamine pathway, and activation of TGF-beta1. High glucose concentrations also increase angiotensin II (AII) levels. Therefore, glucose and AII exert similar effects in inducing extracellular matrix formation in the mesangial cells, using similar transductional signal, which increases TGF-beta1 levels. In this review we focus in the effect of glucose and AII in the mesangial cells in causing the events related to the genesis of diabetic nephropathy. The alterations in the signal pathways discussed in this review give support to the observational studies and clinical assays, where metabolic and antihypertensive controls obtained with angiotensin-converting inhibitors have shown important and additive effect in the prevention of the beginning and progression of diabetic nephropathy. New therapeutic strategies directed to the described intracellular events may give future additional benefits.

Hepatic oxidant/antioxidant status in cholesterol-fed rabbits: Effects of garlic extract

AIM

The investigation of oxidant/antioxidant status in hepatic tissues from cholesterol-fed rabbits and the establishment of possible protective effects of aqueous garlic extract on cholesterol-induced hepatic steatosis.

METHODS

Twenty-two of 31 white New Zealand rabbits were given cholesterol (0.5 g/kg/day) for 4 months. Seven of them were then killed (cholesterol group). The remaining 15 animals were divided into two groups. Seven were fed on a normal laboratory diet (normal diet group) and the others (extract group) on a normal diet plus garlic extract (1.5 ml/kg/day) for an additional 3 months. Superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT) enzyme activities, antioxidant potential (AOP) value, malondialdehyde (MDA), cholesterol and triglyceride levels in the liver tissues and total cholesterol and triglyceride levels in serum samples were measured. An histological evaluation was also done.

RESULTS

An impaired antioxidant system, reduced antioxidant defence potential and increased peroxidation were found in hepatic steatotic tissues from cholesterol-fed animals. Treatment with garlic extract caused a significant increase in antioxidant potential and partly eliminated peroxidation damage in the hepatic tissue. Additionally, the extract caused significant reductions in the cholesterol levels of blood and hepatic tissues. The histological evaluations were in accordance with these results.

CONCLUSION

The results suggest that cholesterol-induced steatosis leads to a weakened antioxidant defence system and causes peroxidation in the hepatic tissue. Treatment with garlic extract may contribute to significant amelioration in the hepatic steatosis and peroxidation processes.

Focus on the intermediate state: immature mRNA of cytochromes P450--methods and insights

The scattered and limited data on hnRNAs (pre-mRNAs) of cytochromes P450 (CYP) are compiled and discussed for the first time. The methods for determination and quantification of hnRNAs are compared. In most cases, CYP hnRNA levels were determined as a parameter of transcriptional activity. It is known, however, that some CYPs, in particular CYP2E1, are in addition specifically and extensively regulated by post-transcriptional processes. Obviously, these processes also influence the processing of CYP hnRNAs so that their levels cannot be considered a mere result of transcription. The underlying mechanisms of post-transcriptional CYP hnRNA and mRNA regulation are not well understood. It is our aim therefore to bring together available data on CYP hnRNA and to discuss them in the light of recent advances in knowledge concerning pre-mRNA processing and interactions between RNA and low molecular weight interfering RNAs. By doing this, we hope to drive research in a direction which appears promising in providing some long-awaited answers with respect to mechanisms of post-transcriptional CYP regulation.

Identification and hepatic expression profiles of cytochrome P450 1–4 isozymes in common minke whales (Balaenoptera acutorostrata)

Full-length cDNA sequences of cytochrome P450 (CYP) 2C78, 2E1, 3A72, 4A35 and 4V6 isozymes were isolated from a hepatic cDNA library of common minke whale (Balaenoptera acutorostrata). The deduced amino acid sequences of minke whale CYP2C78, 2E1, 3A72, 4A35 and 4V6 showed high identities with cattle CYP2C86 (83%), pig CYP2E1 (85%), sheep CYP3A24 (82%), pig CYP4A21 (80%), and human CYP4V2 (76%), respectively. To investigate whether or not these CYP expression levels are altered by contamination of organochlorine contaminants (OCs), mRNA levels of these CYPs in the liver of common minke whale were measured using a quantitative real-time RT-PCR method, and the quantified mRNA levels were employed for the statistical analysis with the residue levels of OCs including PCBs, DDTs (p,p'-DDT, p,p'-DDD and p,p'-DDE), chlordanes (cis-chlordane, trans-chlordane, cis-nonachlor, trans-nonachlor and oxychlordane), HCHs (alpha-, beta- and gamma-isomers) and hexachlorobenzene that have already been reported elsewhere. Spearman's rank correlation analyses showed no significant correlation between CYP expression levels and each OC level in the common minke whale liver, implying that these environmental chemicals have no potential to alter the expression levels of these CYPs or the residue levels encountered in the whale livers may not reach their transcriptional regulation levels. This suggests that the expression of individual CYPs in the whale liver may be at basal level. Relationships among hepatic mRNA expression levels of these CYP2-4 isozymes together with CYP1A1 and CYP1A2 were also examined. Significant positive correlations were detected among mRNA expression levels of individual CYP isozymes in most cases. These associations indicate that the transcriptional regulation of these CYPs examined in this study may be reciprocally related. CYP1A1 levels showed a positive correlation with CYP1A2 levels (r=0.64, p<0.01) indicating that both CYP isozymes were regulated by aryl hydrocarbon receptor activated by endogenous ligands. A strong positive correlation between CYP2C78 and 3A72 (r=0.90, p<0.001) suggests that expression of these CYP isozymes may be under a regulation mechanism of cross-talk in which specific nuclear receptors such as constitutive androstane receptor and pregnane X receptor are involved. The present study indicates that minke whale from the North Pacific may be a model species to investigate the mechanism of basal regulation of these CYPs.

A physiological role of AMP-activated protein kinase in phenobarbital-mediated constitutive androstane receptor activation and CYP2B induction

CAR (constitutive androstane receptor) is a nuclear receptor that regulates the transcription of target genes, including CYP (cytochrome P450) 2B and 3A. The transactivation by CAR is regulated by its subcellular localization; however, the mechanism that governs nuclear translocation has yet to be clarified. It has been reported recently that AMPK (AMP-activated protein kinase) is involved in phenobarbital-mediated CYP2B induction in a particular culture system. We therefore investigated in vivo whether AMPK is involved in the activation of CAR-dependent gene expression. Immunoblot analysis using an antibody which recognizes Thr-172-phosphorylated AMPKalpha1/2 revealed phenobarbital-induced AMPK activation in rat and mouse livers as well. Phenobarbital, however, failed to increase the liver phospho-AMPK level of tumour-bearing rats in which CAR nuclear translocation had been impaired. In in vivo reporter gene assays employing PBREM (phenobarbital-responsive enhancer module) from CYP2B1, an AMPK inhibitor 8-bromo-AMP abolished phenobarbital-induced transactivation. In addition, Cyp2b10 gene expression was attenuated by 8-bromo-AMP. Forced expression of a dominant-negative mutant and the wild-type of AMPKalpha2 in the mouse liver suppressed and further enhanced phenobarbital-induced PBREM-reporter activity respectively. Moreover, the AMPK activator AICAR (5-amino-4-imidazolecarboxamide riboside) induced PBREM transactivation and an accumulation of CAR in the nuclear fraction of the mouse liver. However, AICAR and metformin, another AMPK activator, failed to induce hepatic CYP2B in mice and rats. These observations suggest that AMPK is at least partly involved in phenobarbital-originated signalling, but the kinase activation by itself is not sufficient for CYP2B induction in vivo.

Genome-wide analysis of phenobarbital-inducible genes in Drosophila melanogaster

An oligoarray analysis was conducted to determine the differential expression of genes due to phenobarbital exposure in Drosophila melanogaster (w(1118) strain) third instar larvae. Seventeen genes were observed to be induced with increased expression by a statistical analysis of microarrays approach with a q < or = 0.05. At q < or = 0.12, four more genes (Cyp12d1, DmGstd4, and two genes with unknown function) were found to be up-regulated, and 11 genes with unknown function were found to be down-regulated. Fifteen of these genes, Cyp4d14, Cyp6a2, Cyp6a8, Cyp12d1, Cyp6d5, Cyp6w1, CG2065, DmGstd6, DmGstd7, Amy-p/Amy-d, Ugt86Dd, GC5724, Jheh1, Jheh2 and CG11893, were verified using quantitative real time polymerase chain reaction. Some of these genes have been shown to be over-transcribed in metabolically DDT-resistant Drosophila strains.

Transcriptional profile reveals altered hepatic lipid and cholesterol metabolism in hyposulfatemic NaS1 null mice

Sulfate plays an essential role in human growth and development, and its circulating levels are maintained by the renal Na+-SO42- cotransporter, NaS1. We previously generated a NaS1 knockout (Nas1-/-) mouse, an animal model for hyposulfatemia, that exhibits reduced growth and liver abnormalities including hepatomegaly. In this study, we investigated the hepatic gene expression profile of Nas1-/- mice using oligonucleotide microarrays. The mRNA expression levels of 92 genes with known functional roles in metabolism, cell signaling, cell defense, immune response, cell structure, transcription, or protein synthesis were increased (n = 51) or decreased (n = 41) in Nas1-/- mice when compared with Nas1+/+ mice. The most upregulated transcript levels in Nas1-/- mice were found for the sulfotransferase genes, Sult3a1 (approximately 500% increase) and Sult2a2 (100% increase), whereas the metallothionein-1 gene, Mt1, was among the most downregulated genes (70% decrease). Several genes involved in lipid and cholesterol metabolism, including Scd1, Acly, Gpam, Elov16, Acsl5, Mvd, Insig1, and Apoa4, were found to be upregulated (> or = 30% increase) in Nas1-/- mice. In addition, Nas1-/- mice exhibited increased levels of hepatic lipid (approximately 16% increase), serum cholesterol (approximately 20% increase), and low-density lipoprotein (approximately 100% increase) and reduced hepatic glycogen (approximately 50% decrease) levels. In conclusion, these data suggest an altered lipid and cholesterol metabolism in the hyposulfatemic Nas1-/- mouse and provide new insights into the metabolic state of the liver in Nas1-/- mice.

High glucose stimulates hepatic stellate cells to proliferate and to produce collagen through free radical production and activation of mitogen-activated protein kinase

BACKGROUND

Nonalcoholic steatohepatitis is a clinicopathologic condition that may progress to liver fibrosis. Hyperglycemia is supposed to be one of the factors inducing hepatic fibrogenesis, but the mechanism has not been fully clarified. Oxidative stress is increasingly found in patients with diabetes/hyperglycemia in which conditions reactive oxygen species (ROS) are produced.

METHODS

We performed experiments using hepatic stellate cells (HSCs) in culture in order to confirm the effect of high glucose concentrations on cell proliferation, type I collagen production, ROS production and activation of mitogen-activated protein (MAP) kinase pathway.

RESULTS

High glucose stimulated cell growth of HSCs and up-regulated the levels of activated/phosphorylated extracellular signal-regulated kinase 1/2 and free radical production in HSCs. The MAP kinase phosphorylation and cell proliferation were suppressed by diphenylene iodonium chloride, an NADPH oxidase inhibitor, and by calphostin C, a protein kinase C (PKC)-specific inhibitor. Increased type I collagen mRNA and protein levels were also observed in HSCs at high glucose concentrations.

CONCLUSIONS

Our findings indicate that high glucose concentrations may stimulate ROS production through PKC-dependent activation of NADPH oxidase, and induce MAP kinase phosphorylation subsequent to proliferation and type I collagen production by HSCs.

Acetoacetate induces CYP2E1 protein and suppresses CYP2E1 mRNA in primary cultured rat hepatocytes

The ketone body acetoacetate (AA) in the absence of insulin or in the presence of diabetic insulin levels decreases CYP2E1 mRNA expression in a concentration- and time-dependent manner in primary cultured rat hepatocytes. AA activates p70 ribosomal S6 kinase (p70S6K) and protein kinase C (PKC) by approximately 2- to 2.5-fold, respectively, following 6-h treatment. The AA-mediated activation of p70S6K, but not PKC, was abolished by inhibition of PI 3-K with LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one] or wortmannin, in agreement with p70S6K being downstream of phosphatidylinositol 3-kinase (PI 3-K). Inhibition of PI 3-K, mTOR with rapamycin, or PKC with bisindolylmaleimide ameliorated the AA-mediated down-regulation of CYP2E1 mRNA expression. Neither the mitogen-activated protein kinase kinase inhibitor PD98059 (2'-amino-3'-methoxyflavone) nor the p38 mitogen-activated protein kinase inhibitor SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole] ameliorated the AA-mediated suppression of CYP2E1 mRNA expression. Heterogeneous nuclear RNA analysis revealed that AA suppressed CYP2E1 gene transcription by approximately 50% and that inhibition of PI 3-K and PKC diminished this AA-mediated effect on transcription. CYP2E1 mRNA half-life slightly increased from approximately 24 h in untreated hepatocytes to approximately 32 h in AA-treated cells. Interestingly, AA increased CYP2E1 protein levels by approximately 2- and 2.5-fold at 24 and 48 h, respectively. DL-beta-hydroxybutyrate was without effect. Polysomal distribution studies revealed that AA increased the proportion of RNA associated with the actively translated polysomal fractions versus the 40S to 60S untranslated fractions by approximately 40%. CYP2E1 protein half-life increased from approximately 8 h in untreated hepatocytes to approximately 24 in AA-treated cells. These data show that AA decreases CYP2E1 mRNA expression through inhibition of gene transcription while simultaneously elevating CYP2E1 protein levels through increased translation and decreased protein degradation.

Non-alcoholic fatty liver disease in young adult severely obese non-diabetic patients in South Italy

BACKGROUND/AIMS

In the absence of other causes, obesity increases the risk of liver disease. We evaluated the prevalence and degree of metabolic and hepatic abnormalities associated with non-alcoholic fatty liver disease (NAFLD) in type II-III obesity in a metropolitan area of South Italy.

METHODS

187 (81 M, 106 F) young adult non-diabetic obese patients, age range 18-50 years (mean 31.9 +/- 8.8), body mass index (BMI) > or =30 (mean 47.5 +/- 9.6), consecutively admitted from January 2000 to April 2003 to the Obesity Outpatients Clinic entered into the study. Patients were divided into two groups: (1) BMI 30.0-39.9, and (2) BMI> or =40. Ultrasound detected liver steatosis was classified as: (I) mild; (II) moderate, and (III) severe.

RESULTS

All patients, except 4, showed a variable degree of steatosis: mild was more frequent among females, severe steatosis present only in grade III obesity, with higher prevalence in males than in females (p < 0.001). Mean serum transaminases, in particular alanine aminotransferase (ALT), increased according to BMI and degree of steatosis. Homeostasis Model Assessment (HOMA) index, ferritin and fibrinogen levels increased with BMI, particularly in severe steatosis. In group 2, patients with BMI> or =40 showed a positive correlation between ferritin, aspartate aminotransferase (AST) (r = 0.46, p < 0.018), ALT (r = 0.41, p < 0.036) and gamma-glutamyltransferase (gammaGT) (r = 0.51, p < 0.007), between serum triglycerides (TG) and AST (r = 0.28, p < 0.036), ALT (r = 0.30, p < 0.02) and between HOMA and ALT (r = 0.30, p < 0.03) and gammaGT (r = 0.35, p < 0.012). In group 2 patients with severe steatosis the prevalence of metabolic syndrome according to Adult Treatment Panel III (ATP III) was 40%.

CONCLUSION

These data suggest that, in young adult non-diabetic grade III obese patients, fatty liver is always present and strictly related to insulin resistance which, in the presence of severe liver steatosis, is also related to serum ferritin.

Regulation and inhibition of arachidonic acid omega-hydroxylases and 20-HETE formation

Cytochrome P450-catalyzed metabolism of arachidonic acid is an important pathway for the formation of paracrine and autocrine mediators of numerous biological effects. The omega-hydroxylation of arachidonic acid generates significant levels of 20-hydroxyeicosatetraenoic acid (20-HETE) in numerous tissues, particularly the vasculature and kidney tubules. Members of the cytochrome P450 4A and 4F families are the major omega-hydroxylases, and the substrate selectivity and regulation of these enzymes has been the subject of numerous studies. Altered expression and function of arachidonic acid omega-hydroxylases in models of hypertension, diabetes, inflammation, and pregnancy suggest that 20-HETE may be involved in the pathogenesis of these diseases. Our understanding of the biological significance of 20-HETE has been greatly aided by the development and characterization of selective and potent inhibitors of the arachidonic acid omega-hydroxylases. This review discusses the substrate selectivity and expression of arachidonic acid omega-hydroxylases, regulation of these enzymes during disease, and the application of enzyme inhibitors to study 20-HETE function.

Ontogeny of drug metabolizing enzymes in the neonate

Fetal exposure to xenobiotics is modulated to a considerable degree by the metabolic capabilities of the mother and the placenta. However, once liberated from the uterine environment the neonate is instantly exposed to a wide array of new macromolecules in the form of byproducts of cellular metabolism, dietary constituents, environmental toxins and pharmacologic agents. The rapid and efficient biotransformation of these compounds by Phase I and Phase II drug-metabolizing enzymes is an essential process if the infant is to avoid the accumulation of reactive compounds that could produce cellular injury or tissue dysfunction. Genetic polymorphisms and environmental factors are known to contribute dramatically to individual variation in the activity of drug-metabolizing enzymes. More recently, it has become apparent that programmed, developmental, regulatory events occur - independent of genotype - which further add to individual variation in drug metabolism. An appreciation of the impact of ontogeny on the expression and functional activity of the major drug-metabolizing enzymes enables the practicing clinician to predict the ultimate consequence of drug administration in the neonate to help guide optimal drug therapy.

AMP-activated Protein Kinase Mediates Phenobarbital Induction of CYP2B Gene Expression in Hepatocytes and a Newly Derived Human Hepatoma Cell Line

Phenobarbital (PB) administration is known to trigger pleiotropic responses, including liver hypertrophy, tumor promotion, and induction of genes encoding drug-metabolizing enzymes. The induction of human CYP2B6 and the rat (CYP2B1) and mouse (Cyp2b10) homologues by PB is mediated by the nuclear receptor constitutive androstane receptor (CAR). The study of CYP2B gene regulation and CAR activity by PB has been difficult due to the lack of a cellular model. In this study, we describe a novel differentiated human hepatoma cell line (WGA), derived from HepG2, which expresses CYP2B6 and CAR. WGA cells represent a powerful system to study the regulation of CYP2B6 gene expression by PB. There is evidence that CAR activity is regulated by phosphorylation and that regulation of some CYP genes depends on the nutritional status of cells. The AMP-activated protein kinase (AMPK) functions as an energy sensor and is activated when cells experience energy-depleting stresses. In this report, we show that addition of 5-amino-imidazole carboxamide riboside, an AMPK activator, to WGA and human hepatocytes induces CYP2B6 gene expression. Expression of a constitutively active form of AMPK mimics the PB induction of CYP2B6 and CYP2B1 gene expression. Conversely, the expression of a dominant negative form of AMPK inhibits the induction of these genes by PB. Finally, we demonstrate, for the first time, that AMPK activity increases in cells cultured with PB. Our data strongly support a role for AMPK in the PB induction of CYP2B gene expression and provide new insights into the regulation of gene expression by barbiturate drugs.

Oxidative stress and depletion of hepatic long-chain polyunsaturated fatty acids may contribute to nonalcoholic fatty liver disease

Human nonalcoholic fatty liver disease (NAFLD) associated with obesity is characterized by depletion of hepatic n-3 long-chain polyunsaturated fatty acids (LCPUFA), with lower LCPUFA product/precursor ratios and higher 18:1n-9 trans levels in adipose tissue, both in patients with steatosis and in those with steatohepatitis. These changes point to modification of gene expression, with decreased fatty acid oxidation and triacylglycerol export and enhanced lipid synthesis, thereby leading to fat accumulation in the liver. Changes in oxidative stress-related parameters indicate a moderate enhancement in the pro-oxidant status of the liver in steatosis, which is further exacerbated in steatohepatitis. It is proposed that oxidative stress plays a dual role in NAFLD by contributing to steatosis due to higher peroxidation of LCPUFA, in addition to defective fatty acid desaturation and diet imbalance, and by promoting progression of steatosis to steatohepatitis, features that might involve changes in the activity of transcriptional mediators.

Nonalcoholic fatty liver disease and nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a well-recognized form of chronic liver disease affecting both children and adults that has gained increased recognition. Recently NAFLD has been associated with insulin resistance and its incidence and prevalence is likely increasing, paralleling the rise in obesity and diabetes mellitus in the United States. The article includes current thoughts on the natural history and pathogenesis of NAFLD and describes current trends in the diagnosis and treatment of this condition.

Relationship between genetic polymorphism of cytochrome P450IIE1 and fatty liver

AIM: To study the correlation between genetic polymorphism of cytochrome P450IIE1 (CYPIIE1) and fatty liver.

METHODS: Peripheral blood mononuclear cells were collected in 56 patients with fatty liver, 26 patients without fatty liver and 20 normal controls. Then PCR-RFLP was used to analyze genetic polymorphism of CYPIIE1 in monocytes on the region of Pst I and Rsa I.

RESULTS: The frequency of homozygotic C1 gene in patients with alcoholic fatty liver (28.6%), obese fatty liver (38.5%), or diabetic fatty liver (33.3%) was significantly lower than that of the corresponding patients without fatty liver (100%, 100% and 80% respectively), while the frequency of C2 genes, including C1/C2 and C2/C2, was significantly higher (71.4%/0%, 61.5%/0%, and 66.7%/20%) (P < 0.01). The frequency distribution of the above genes of non-fatty liver patients (100%/0, 100%/0, and 80%/20%) was not significantly different from that of the normal controls (85%/15%) (P > 0.05).

CONCLUSION: The genetic polymorphism of CYPIIE1 on the position of Pst I and Rsa I is related to the susceptibility of fatty liver. Besides, C2 gene may play a key role in the pathogenesis of fatty liver.

The effects of diabetes with hyperlipidemia on P450 expression in APA hamster livers

The effect of chronic hyperglycemia and hyperlipidemia induced by streptozotocin (SZ) on the expression of P450 in the liver of APA hamsters was studied in this experiment. No effect on the total activity of P450 was seen in SZ-induced diabetic hamsters throughout the experimental period. At 1 and 6 months after SZ-injection, the levels of CYP1A, 2C6, and 3A of SZ-injected hamsters were much lower than those of age-matched control hamsters. CYP2B expression tended to decrease and CYP2E1 and 4A expression tended to increase in SZ-injected hamsters, although the results were not significant. At 3 months after SZ-injection, however, no significant difference between SZ-injected and normal hamsters was seen in these P450 isozymes. On the other hand, CYP2C11 expression was slightly depressed in SZ1M and SZ6M, and almost equivalent to control hamsters in SZ3M. Immunohistochemistry by the use of each isozyme antibody revealed that SZ-induced diabetes affected the localization of CYP2C6, 3A, and 4A in the hepatic acinus. The expression of CYP2C6 and 3A was depressed mainly in the periportal region of the acinus, and CYP4A expression was induced mainly in the perivenous region by SZ-induced diabetes. On the other hand, the expression pattern of CYP1A, 2B, 2C11, and 2E1 were not affected. These results demonstrate that the effects of SZ-induced diabetes on hepatic P450 differ for each isozyme in APA hamsters and also differ from those of other experimental diabetic animals, including golden hamsters.

Advances in the Understanding and Treatment of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a well recognised form of chronic liver disease that has recently gained greater recognition. Originally described in the late 1950s, NAFLD is currently considered the leading cause of abnormal liver enzyme levels in the US, closely paralleling the increase in obesity and diabetes mellitus. NAFLD has a worldwide distribution, affecting both adults and children, and typically is seen in association with obesity, diabetes, hypertension and hypertriglyceridaemia. Most patients are asymptomatic and usually present with mild elevations in aminotransferases. The natural history of NAFLD is not clearly defined but progression to cirrhosis and end-stage liver disease is well recognised in some patients. The accumulation of hepatic steatosis is thought to occur initially, primarily through hepatic and peripheral insulin resistance, which leads to altered glucose and free fatty acid metabolism. The progression from simple fatty liver to more severe forms of NAFLD (nonalcoholic steatohepatitis and cirrhosis) is much less clear but evidence suggests that oxidative stress may preferentially enhance proinflammatory cytokines, which leads to cellular adaptations and dysfunction followed by development of inflammation, necrosis and fibrosis. Therapeutic modalities remain limited and are largely focused on correcting the underlying insulin resistance or reducing oxidative stress. However, at the present time, there are several limitations to the current potential therapies, mainly because of the lack of large-scale, prospective, randomised studies, as well as clearly defined histological endpoints. Ultimately, the future for potential therapeutic modalities to treat this disease are quite promising, but further research is needed to clearly demonstrate which therapy or therapies will be effective at eliminating fatty liver disease and its potential complications.

Nonalcoholic steatohepatitis: what we know in the new millennium

Nonalcoholic steatohepatitis (NASH) is a liver disease characterized by diffuse fatty infiltration and inflammation. The exact prevalence of NASH is unclear, but it is becoming more evident that the disease is much more common than previously thought. Although generally a benign, indolent process, it can progress to advanced liver disease in approximately 15-20% of patients. Clinical characteristics associated with NASH include obesity, hyperlipidemia, diabetes mellitus, and hypertension, all of which have been associated with underlying insulin resistance. Typically, this disease becomes evident in the fourth or fifth decade of life with an equal sex predilection. NASH is thought to be caused, in part, by impaired insulin signaling, leading to elevated circulating insulin levels and subsequent altered lipid homeostasis. This process is likely multifactorial and includes both genetic and environmental factors. Treatment options to date are limited and are based on very small clinical trials. Current investigations are focusing on improving the underlying insulin resistance that has been associated with NASH as well as other therapies that decrease oxidative stress or improve hepatocyte survival.

Effect of hyperinsulinemia and type 2 diabetes-like hyperglycemia on expression of hepatic cytochrome p450 and glutathione s-transferase isoforms in a New Zealand obese-derived mouse backcross population

In subgroups of a New Zealand obese mouse-derived backcross population with defined aberrations of glucose homeostasis, a comprehensive study of the hepatic expression of cytochrome P450 and glutathione S-transferase was performed. Three patterns of alterations in response to insulin resistance (normoglycemia/hyperinsulinemia) or diabetes (hyperglycemia/hypoinsulinemia) were observed: mRNA levels of Cyp2b9, Cyp3a16, Cyp4a14, and Gstt2 as assessed by Northern- and dot-blot analysis were increased markedly in liver from diabetic mice with no or only a slight increase in insulin resistant mice. Western-blot analysis detected the corresponding changes of the CYP2B and CYP4A proteins. In contrast, expression of Cyp2c22, Cyp2c29, and Cyp2c40 was reduced in diabetic, but normal in insulin resistant mice. These alterations were correlated with changes in serum free fatty acid levels and, therefore, seem to be mediated by the peroxisome proliferator activated receptor-alpha. Furthermore, expression of Cyp1a2, Cyp7b1, Gstm3, and Gstm6 was reduced in both diabetic and insulin resistant mice. Because this third pattern was not correlated with the alterations of serum free fatty acid levels, it seems to reflect an early alteration in the course of the disease, and may be related to the progression of the syndrome from insulin resistance to the type 2-like diabetes.

Insulin signaling in the transcriptional and posttranscriptional regulation of CYP2E1 expression

Diabetes has been reported to increase the expression of cytochrome P450 (CYP) 2E1 messenger RNA (mRNA) and protein several-fold, and enhanced expression has been associated with elevated ketone bodies. Primary cultured rat hepatocytes were used to explore ketone body and insulin regulation of CYP2E1 expression. Hydroxybutyrate and acetoacetate (AC), alone or in combination, either failed to affect or decreased CYP2E1 mRNA levels by up to 90% relative to untreated hepatocytes. Insulin produced a concentration-dependent decrease in CYP2E1 mRNA levels, and insulin receptor immunoprecipitation showed a correspondence between receptor phosphorylation and the decrease in CYP2E1 mRNA levels at physiologic levels of insulin. Phosphatase inhibitors decreased CYP2E1 mRNA levels by greater than 95%. The phosphatidylinositol 3-kinase (PI3-kinase) inhibitors wortmannin or LY294002 and rapamycin, an inhibitor of p70 S6 kinase phosphorylation, ameliorated the insulin-mediated decrease in CYP2E1 mRNA levels. Geldanamycin, which inhibits Src kinase, also abrogated the insulin-mediated decrease in CYP2E1 mRNA levels. In contrast, the protein kinase C (PKC) inhibitor bisindolylmaleimide, the mitogen-activated protein kinase kinase (MEK) inhibitor PD98059, and the p38 mitogen-activated protein (MAP) kinase inhibitor SB202190 did not affect the insulin-mediated decrease in CYP2E1. CYP2E1 mRNA half-life decreased from approximately 48 hours in the absence of insulin to approximately 15 hours at 10 nmol/L insulin, and this decrease was prevented by wortmannin. The half-life of CYP2B mRNA was increased by insulin, whereas that of CYP3A was unaffected. Analysis of CYP2E1 gene transcription using heterogeneous nuclear RNA (hnRNA) showed that insulin suppressed CYP2E1 transcription. In conclusion, these data show involvement of transcriptional and posttranscriptional mechanisms in the insulin-mediated regulation of CYP2E1 and implicate PI3-kinase, p70 S6 kinase, and Src kinase in mediating these effects.

Mechanisms of circadian rhythmicity of carbon tetrachloride hepatotoxicity

The toxicity of carbon tetrachloride (CCl(4)) and certain other chemicals varies over a 24-h period. Because the metabolism of some drugs follows a diurnal rhythm, it was decided to investigate whether the hepatic metabolic activation of CCl(4) was rhythmic and coincided in time with maximum susceptibility to CCl(4) hepatotoxicity. A related objective was to test the hypothesis that abstinence from food during the sleep cycle results in lipolysis and formation of acetone, which participates in induction of liver microsomal cytochrome P450IIE1 (CYP2E1), resulting in a diurnal increase in CCl(4) metabolic activation and acute liver injury. Groups of fed and fasted male Sprague-Dawley rats were given a single oral dose of 800 mg of CCl(4)/kg at 2- to 4-h intervals over a 24-h period. Serum enzyme activities, measured 24 h post dosing as indices of acute liver injury, exhibited distinct maxima in both fed and fasted animals dosed with CCl(4) near the beginning of their dark/active cycle. Blood acetone, hepatic CYP2E1 activity, and covalent binding of (14)CCl(4)/metabolites to hepatic microsomal proteins in untreated rats fed ad libitum followed circadian rhythms similar to that of susceptibility to CCl(4). Parallel fluctuations of greater amplitude were seen in rats fasted for 24 h. Hepatic glutathione levels were lowest at the time of greatest susceptibility to CCl(4). Acetone dose-response experiments showed high correlations between blood acetone levels, CYP2E1 induction, and CCl(4)-induced liver injury. Pretreatment with diallyl sulfide suppressed CYP2E1 and abolished the circadian rhythmicity of susceptibility to CCl(4). These findings provide additional support for acetone's physiological role in CYP2E1 induction and for CYP2E1's role in modulating CCl(4) chronotoxicity in rats.

Long-term maintenance of cytochrome P450 activities by rat hepatocyte/3T3 cell co-cultures in heparinized human plasma

Little information on the effect of plasma on hepatocyte cytochrome P450 (CYP) activities is currently available. We characterized the effect of plasma on CYPs of hepatocyte-mesenchymal cell co-cultures, which exhibit stable liver specific functions and may be potentially useful for bioartificial liver design. Rat hepatocyte-mouse 3T3-J2 cell co-cultures were maintained for 6 days in medium, and then switched to heparinized human plasma containing 3-methylcholanthrene (3MC; 2 microM), phenobarbital (PB; 1 mM), or no inducer for up to 7 days. CYP activities were measured in situ based on the o-dealkylation of ethoxy- (EROD), methoxy- (MROD), pentoxy- (PROD), or benzyloxy- (BROD) resorufin. Plasma alone increased PROD/BROD but not EROD/MROD. The endogenous inducer was in the high molecular weight fraction (>5 kD) of plasma and inhibited by >5 nM okadaic acid and >10 microM dibutyryl cyclic AMP, two inhibitors of PB-inducible CYPs. Furthermore, plasma increased CYP1A1 and CYP2B1/2 mRNA levels. In plasma, 3MC induced EROD/MROD to about 60% of the level induced in culture medium while PB induced PROD/BROD that were three- to 10-fold above levels induced in medium. CYP activities decreased between days 2 and 7 of plasma exposure, but were enhanced by plasma supplementation with amino acids, insulin, glucagon, and hydrocortisone.

Nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a condition characterized by hepatomegaly, elevated serum aminotransferase levels, and a histologic picture similar to alcoholic hepatitis in the absence of alcohol abuse. Most patients with NASH are obese women, and many have diabetes mellitus, hypercholesterolemia, or hypertriglyceridemia. NASH has also been associated with a number of metabolic conditions, surgical procedures, and drug treatments. Most patients are asymptomatic. The most common sign of NASH is hepatomegaly. Stigmata of chronic liver disease are rare. Laboratory abnormalities include a 2-4-fold elevation of serum aminotransferase levels; other liver function test results are usually normal. Histologically, there is moderate to severe macrovesicular steatosis and lobular hepatitis with necrosis or ballooning degeneration and/or fibrosis. The pathogenesis of NASH is poorly understood, but lipid peroxidation and oxidative stress are the leading culprits. The natural history of NASH is unknown, but NASH seems to be a stable disease in most patients. Treatment of NASH is unproven, but weight reduction is recommended in obese patients. Small pilot studies of several drugs have shown promise, but large randomized clinical trials are awaited. Orthotopic liver transplantation is the treatment of choice for end-stage liver disease secondary to NASH.

The effects of food restriction in man on hepatic metabolism of acetaminophen

BACKGROUND

Recent reports have suggested that food deprivation may contribute to acetaminophen hepatotoxicity by shunting drug detoxification from the conjugative to the potentially toxic oxidative pathways.

METHODS

This study assessed this concept in a prospective study of food restriction of 500 calories/day over 5 days and also of 1000 calories/day over 13 days. Obese, otherwise normal, individuals received 2 g acetaminophen orally at the start and again after food restriction. Sequential liver tests, as well as serum and urine acetaminophen and its derivatives were measured.

RESULTS

In both food-restricted groups there was no evidence of any change in the elimination or in the metabolic pattern of acetaminophen removal. Liver tests remained normal. The average weight loss was about 6 pounds.

CONCLUSIONS

Our data, with this brief, but major degree of food restriction, and this load of acetaminophen (half-maximal daily dose), do not demonstrate an effect of caloric restriction on acetaminophen disposition.

Characterization of pathogenic and prognostic factors of nonalcoholic steatohepatitis associated with obesity

BACKGROUND/AIMS

Nonalcoholic steatohepatitis is an emerging clinical problem among the obese population. However, risk factors of progression to advanced forms of liver disease in this particular group of patients remain to be defined.

METHODS

The demographics and clinical and histologic features of 46 obese patients were evaluated. The intrahepatic immunological phenotype was assessed in all liver biopsy samples by immunohistochemistry.

RESULTS

Histologic findings of nonalcoholic steatohepatitis were observed in 69.5% of the obese population studied and significant fibrosis was evident in 41% of patients with nonalcoholic steatohepatitis. Age (p=0.003), degree of steatosis (p=0.000002), and grade of inflammation (p=0000) at liver biopsy were independent variables positively associated with fibrosis. Intrahepatic expression levels of several immunologic markers of inflammation as well as nitric oxide derivatives were significantly higher in the severe forms of nonalcoholic steatohepatitis than in the mildest forms.

CONCLUSIONS

Obese persons with higher age, with greater degrees of hepatic steatosis, and specially those with increased grades of intrahepatic inflammation have the greatest risk for progression to fibrotic liver disease. An oxidative stress-triggered intrahepatic inflammatory response appears to be important in the pathogenesis of nonalcoholic steatohepatitis in obesity.

Lipid metabolism as a target for potassium channel effectors

K(+) channel effectors are widely used in the treatment of various diseases, including diabetes mellitus type II, hypertension, and cardiac arrhythmia. In addition, a constantly growing body of literature reveals that some of these substances, despite their direct effect on K(+) channels, may influence cellular lipid metabolism. As a result, membrane lipid content and cellular concentrations of lipid messengers are changed. Due to the dependence of K(+) channel activity on membrane lipids, these observations seem to be of particular importance not only to characterize secondary effects of K(+) channel effectors but also to understand the long-term effects of these agents on K(+) channel activity.

The alcohol-inducible form of cytochrome P450 (CYP 2E1): role in toxicology and regulation of expression

Cytochrome P450 (CYP) 2E1 catalyzes the metabolism of a wide variety of therapeutic agents, procarcinogens, and low molecular weight solvents. CYP2E1-catalyzed metabolism may cause toxicity or DNA damage through the production of toxic metabolites, oxygen radicals, and lipid peroxidation. CYP2E1 also plays a role in the metabolism of endogenous compounds including fatty acids and ketone bodies. The regulation of CYP2E1 expression is complex, and involves transcriptional, post-transcriptional, translational, and post-translational mechanisms. CYP2E1 is transcriptionally activated in the first few hours after birth. Xenobiotic inducers elevate CYP2E1 protein levels through both increased translational efficiency and stabilization of the protein from degradation, which appears to occur primarily through ubiquitination and proteasomal degradation. CYP2E1 mRNA and protein levels are altered in response to pathophysiologic conditions by hormones including insulin, glucagon, growth hormone, and leptin, and growth factors including epidermal growth factor and hepatocyte growth factor, providing evidence that CYP2E1 expression is under tight homeostatic control.

Localization and age-related changes in cytochrome P450 expression in APA hamster livers

To establish the baseline data, age-related changes and the regional expression of the hepatic P450 isozymes in Syrian hamsters of the APA strain at 3, 6, 12, 18 months old were examined by immunological techniques. Immunohistochemical analysis of liver serial sections revealed that the midzonal and perivenous regions (zones 2 and 3, respectively) were stained with the anti-rat CYP1A1/2, 2B1/2 and 2E1 antibodies. These three antibodies most intensely stained the hepatocytes around the central vein. An anti-rat CYP3A2 staining section had a staining pattern with equally intense reactions in zones 2 and 3. On the other hand, CYP2C6, 2C11 and 4A1 were distributed diffusely throughout the hepatic acinus. There was no age-related difference in the expression pattern of any of the P450 isozymes examined. Total P450 content had a peak at 6 months of age and decreased to 60% of that level thereafter. Western-blot analysis revealed that the peak expressions of the isozymes detected with anti-rat CYP1A1/2, 2C6, 2E1 and 3A2 antibodies were observed in 6-month-old hamsters and declined in older ones. The CYP2B and 2C11 content reached the maximum at the age of 6 months and maintained almost the same level thereafter. The CYP4A level did not change from 3 to 6 months, and then declined to about 40% of the younger level at 12 and 18 months of age. These results suggest that the hepatic P450 isozymes of APA hamsters have region-specific expressions and most isozymes have their peaks of expression at 6 months of age, which differs from the patterns for rat P450.

Altered expression of hepatic CYP2E1 and CYP4A in obese, diabetic ob/ob mice, and fa/fa Zucker rats

Hepatic levels of the cytochrome P450 (CYP) proteins 2E1 and 4A are often increased in obesity, diabetes and fasting. In such states of nutritional imbalance, CYPs 2E1 and 4A may play a more significant role in fatty acid oxidation. In order to more fully characterize the regulation of CYP2E1 and CYP4A in obesity and obesity-related (type II) diabetes, we analyzed the hepatic expression of CYP2E1 and CYP4A in ob/ob mice which are leptin deficient, and fa/fa Zucker rats which have defective leptin receptor function. CYP2E1 protein and mRNA were either unchanged or reduced in both models. Conversely, expression of murine Cyp4a10 and 4a14 in the obese mice, and 4A2 in the male fatty Zucker rat, were greatly increased. The levels of other CYP4As were either unchanged or reduced. These results show that CYP2E1 is not inevitably increased by obesity and diabetes and indicate differential regulation of CYP4A subfamily genes in rodent models. Further, they implicate leptin receptor signaling as a factor that may modulate expression of CYP gene products involved in fatty acid oxidation.

Cytochrome P450 2E1 activity in diabetic and obese patients as assessed by chlorzoxazone hydroxylation

Cytochrome P450 2E1 (CYP2E1) is a phase I detoxification enzyme, which is induced by chronic alcohol consumption. It is involved in the activation of numerous carcinogens and in the production of free radicals. As it has previously been shown to be induced in diabetic and obese rats, the aim of this study was to investigate its induction level in poorly-controlled diabetics and in obese patients (Body Mass Index > 30 kg/m2). CYP2E1 activity was determined in 35 diabetic and 17 obese patients by using the in vivo chlorzoxazone hydroxylation test. Even though the glucidic parameters were highly disturbed (mean fasting glycemia > 7.9 mmol/L, post prandial glycemia > 12.2 mmol/L and fructosamine > 326 mumol/L), CYP2E1 activity was not enhanced either in insulin-dependent diabetics (IDDs, n = 7) nor in non-obese non-insulin-dependent diabetics (NIDDs, n = 15) when compared to controls (n = 42) (0.21 +/- 0.03, 0.33 +/- 0.03 and 0.30 +/- 0.02, respectively, mean +/- SEM). However, this activity was lower in IDDs when compared to NIDDs (P < 0.05). In obese patients, with (n = 13) or without (n = 17) NIDD mellitus, CYP2E1 activity was increased by a mean of 40% when compared to controls. In addition, positive correlations were found in all subjects (controls or patients, n = 74) between CYP2E1 activity and serum cholesterol (r = 0.42, P < 0.0001), triglycerides (r = 0.44, P < 0.0001) and BMI (r = 0.36, P < 0.001). Accordingly, subjects with cholesterol and/or triglyceride serum levels above 6.4 and 1.8 mmol/L, respectively, displayed a mean increase of 40% of their CYP2E1 activity vs subjects within the above values. It is believed that individuals with increased CYP2E1 activity are more susceptible to the adverse effects of CYP2E1-mediated activation of toxins and carcinogens.