Apolipoprotein synthesis in nonalcoholic steatohepatitis

Reduced hepatic extraction of palmitate in steatosis correlated to lower level of liver fatty acid binding protein

Nonalcoholic fatty liver disease is the most common of all liver diseases. The hepatic disposition [(3)H]palmitate and its low-molecular-weight metabolites in perfused normal and steatotic rat liver were studied using the multiple indicator dilution technique and a physiologically based slow diffusion/bound pharmacokinetic model. The steatotic rat model was established by administration of 17 alpha-ethynylestradiol to female Wistar rats. Serum biochemistry markers and histology of treated and normal animals were assessed and indicated the presence of steatosis in the treatment group. The steatotic group showed a significantly higher alanine aminotransferase-to-aspartate aminotransferase ratio, lower levels of liver fatty acid binding protein and cytochrome P-450, as well as microvesicular steatosis with an enlargement of sinusoidal space. Hepatic extraction for unchanged [(3)H]palmitate and production of low-molecular-weight metabolites were found to be significantly decreased in steatotic animals. Pharmacokinetic analysis suggested that the reduced extraction and sequestration for palmitate and its metabolites was mainly attributed to a reduction in liver fatty acid binding protein in steatosis.

Nonalcoholic fatty liver disease: a review of current understanding and future impact

Nonalcoholic fatty liver disease (NAFLD), already the most common form of liver disease in the United States, can be expected to increase in prevalence and severity in parallel with national epidemics of obesity and type 2 diabetes. NAFLD is frequently associated with insulin resistance. While insulin resistance, and thereby hyperinsulinemia, are, in large part, metabolic consequences of obesity, the basis of diversity in severity and progression of inflammation and fibrosis is not known. Increased susceptibility to oxidative stress is likely to play a role. Several patient characteristics have been associated with more severe histological findings in patients with NAFLD, including type 2 diabetes, hypertension, age over 40 years, and higher transaminases. Liver biopsy is, however, required to accurately grade and stage NAFLD histologically. Although the natural history of NAFLD is relatively poorly defined, NAFLD is increasingly recognized as an important cause of decompensated liver disease. Weight reduction and improved insulin sensitivity are associated with improved biochemical and histological parameters of NAFLD. There are, however, no proven safe and efficacious pharmacological treatments for NAFLD.

Mitochondrial injury in steatohepatitis

Rich diet and lack of exercise are causing a surge in obesity, insulin resistance and steatosis, which can evolve into steatohepatitis. Patients with non-alcoholic steatohepatitis have increased lipid peroxidation, increased tumour necrosis factor-alpha (TNF-alpha) and increased mitochondrial beta-oxidation rates. Their in-vivo ability to re-synthesize ATP after a fructose challenge is decreased, and their hepatic mitochondria exhibit ultrastructural lesions, depletion of mitochondrial DNA and decreased activity of respiratory chain complexes. Although the mechanisms for these effects is unknown, the basal cellular formation of reactive oxygen species (ROS) may oxidize fat deposits to cause lipid peroxidation, which damages mitochondrial DNA, proteins and cardiolipin to partially hamper the flow of electrons within the respiratory chain. This flow may be further decreased by TNF-alpha, which can release cytochrome c from mitochondria. Concomitantly, the increased mitochondrial fatty acid beta-oxidation rate augments the delivery of electrons to the respiratory chain. Due to the imbalance between a high electron input and a restricted outflow, electrons may accumulate within complexes I and III, and react with oxygen to form the superoxide anion radical. Increased mitochondrial ROS formation could in turn directly oxidize mitochondrial DNA, proteins and lipids, enhance lipid peroxidation-related mitochondrial damage, trigger hepatic TNF-alpha formation and deplete antioxidants, thus further blocking electron flow and further increasing mitochondrial ROS formation. Mitochondrial dysfunction plays an important role in liver lesions, through the ROS-induced release of both biologically active lipid peroxidation products and cytokines. In particular, the up-regulation of both TNF-alpha and Fas triggers mitochondrial membrane permeability and apoptosis. The ingestion of apoptotic bodies by stellate cells stimulates fibrogenesis, which is further activated by lipid peroxidation products and high leptin levels. Chronic apoptosis is compensated by increased cell proliferation, which, together with oxidative DNA damage, may cause gene mutations and cancer.

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.

Lipid metabolism in hepatic steatosis

Hepatic steatosis is a consequence of both obesity and ethanol use. Nonalcoholic steatosis (NASH) resemble alcoholic steatosis and steatohepatitis. Both exhibit increased hepatocellular triglycerides(TG), reflecting an increase in long chain fatty acids (LCFA). LCFA enter cells by both facilitated transport and passive diffusion. A driving force for both is the plasma unbound LCFA concentration ([LCFAu]). In both obese rodents and obese patients, adipocyte LCFA uptake via both facilitated transport and diffusion is increased. However, the LCFA uptake Vmax in hepatocytes is not increased in obese animals. Nevertheless, total LCFA uptake in obese rodents is increased ~3-fold, reflecting increased plasma LCFA concentrations. With advancing obesity, resistance to the antilipolytic effects of insulin results in increased lipolysis within the omental fat depot, a consequent further rise in portal venous LCFA, and an even greater rise in portal [LCFAu]. This causes a further increase in hepatocellular LCFA uptake, increased intracellular generation of reactive oxygen species (ROS), and transition from simple steatosis to NASH. By contrast, in rodent hepatocytes and in human hepatoma cell lines, ethanol up-regulates the LCFA uptake Vmax. Consequently, although plasma LCFA are unaltered, hepatocellular LCFA uptake in ethanol-fed rats is also increased~3-fold, leading to increased ROS generation and evolution of alcoholic hepatitis. Thus, while increased hepatic LCFA uptake contributes to the pathogenesis of both NASH and alcoholic hepatitis,the underlying mechanisms differ. Recognizing these mechanistic differences is important in developing strategies for both prevention and treatment of these conditions.

Approach to the pathogenesis and treatment of nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) represents an advanced stage of fatty liver disease developed in the absence of alcohol abuse. Its increasing prevalence in western countries, the diagnostic difficulties by noninvasive tests, and the possibility of progression to advanced fibrosis and even cirrhosis make NASH a challenge for hepatologists. NASH is frequently associated with type 2 diabetes and the metabolic syndrome, and several genetic and acquired factors are involved in its pathogenesis. Insulin resistance plays a central role in the development of a steatotic liver, which becomes vulnerable to additional injuries. Several cyclic mechanisms leading to self-enhancement of insulin resistance and hepatic accumulation of fat have been recently identified. Excess intracellular fatty acids, oxidant stress, tumor necrosis factor-alpha, and mitochondrial dysfunction are causes of hepatocellular injury, thereby leading to disease progression and to the establishment of NASH. Intestinal bacterial overgrowth also plays a role, by increasing production of endogenous ethanol and proinflammatory cytokines. Therapeutic strategies aimed at modulating insulin resistance, normalizing lipoprotein metabolism, and downregulating inflammatory mediators with probiotics have promising potential.

Insulin resistance and the pathogenesis of nonalcoholic fatty liver disease

The prevalence of obesity has reached epidemic proportions in most of the western world. Current estimates suggest that 22.5%of the population of the United States suffers from obesity and is at risk for development of obesity-related complications, including hypertension, coronary artery disease, diabetes, hyperlipidemia,increased predisposition for various cancers, and nonalcoholic fatty liver disease. Fatty liver disease is currently the most common abnormality observed in hepatology practice. Since it was first reported in the 1980s in obese diabetic females, our understanding of nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH) has undergone significant metamorphosis. It is now universally accepted that insulin resistance and subsequent hyperinsulinemia are key factors that lead to both NAFL and NASH.This article reviews the role of insulin resistance in the genesis of these conditions.

Systemic levels of lipid peroxidation and its metabolic and dietary correlates in patients with nonalcoholic steatohepatitis

BACKGROUND AND AIM

Products of systemic lipid peroxidation are important in the pathogenesis of cardiovascular disease. Subjects with NASH have increased hepatic lipid peroxidation, but it is unknown if they have increased oxidative stress and lipid peroxidation systemically. Therefore, we conducted a study to measure the circulating levels of lipid peroxidation products and their metabolic and nutritional correlates in patients with NASH and controls.

METHODS

Systemic lipid peroxidation was assessed by measuring the levels of oxidized LDL (ox-LDL) and thiobarbituric acid-reacting substances (TBARS) in 21 subjects with NASH and 19 controls. Correlations were made between serum lipid peroxidation and nutritional determinants of oxidative stress and defense, serum lipids, insulin resistance, transaminases, and liver histology. The short-term nutrient intake was analyzed by maintaining a 3-wk dietary diary.

RESULTS

The serum levels of ox-LDL were significantly higher in NASH patients compared to controls (56 +/- 16 U/L vs 40 +/- 12 U/L, respectively, p < 0.001). Similarly, serum TBARS were significantly higher in NASH patients compared to controls (3.4 +/- 1.3 vs 1.8 +/- 0.9 nmols/ml, respectively, p= 0.0001). Insulin resistance was independently associated with ox-LDL (p= 0.01) and TBARS levels (p= 0.01). We found no differences in the intake of various macro- and micronutrients between the two groups and there was no association between nutrient intake and ox-LDL or TBARS.

CONCLUSION

Subjects with NASH have significantly higher systemic levels of lipid peroxidation products and this could indicate an increased risk of cardiovascular disease. More studies are needed to evaluate this possibility.

The potential role of genes in nonalcoholic fatty liver disease

Although most people with obesity and type 2 diabetes will have steatosis, only a minority will ever develop nonalcoholic steatohepatitis (NASH), fibrosis, and cirrhosis. Family studies suggest that genetic factors are important in disease progression, although dissecting genetic factors playing a role in NASH and fibrosis from those influencing the development established risk factors is difficult. Several approaches can be used to look for genetic factors playing a role in nonalcoholic fatty liver disease (NAFLD). In the future, genome-wide single nucleotide polymorphism (SNP) scanning of cases and controls may become feasible. To date, however,studies have relied on candidate gene, case control, allele association methodology. Recent, and as yet preliminary, studies have reported associations between steatosis severity, NASH, and fibrosis with genes whose products are involved in lipid metabolism,oxidative stress, and endotoxin-cytokine interactions. If confirmed,these associations will enhance understanding of disease pathogenesis,and accordingly, the ability to design effective therapies.

The ins and outs of mitochondrial dysfunction in NASH

Rich diet and lack of exercise are causing a surge in obesity, insulin resistance and steatosis, which can evolve into steatohepatitis. Steatosis and nonalcoholic steatohepatitis (NASH) can also be induced by drugs such as amiodarone, tamoxifen and some antiretroviral drugs. There is growing evidence that mitochondrial dysfunction, and more specifically respiratory chain deficiency, plays a role in the pathophysiology of NASH whatever its initial cause. In contrast, the B-oxidation of fatty acids can be either increased (as in insulin resistance-associated NASH) or decreased (as in drug-induced NASH). However, in both circumstances, the generation of reactive oxygen species (ROS) by the damaged respiratory chain is augmented, as components of this chain are over-reduced by electrons, which then abnormally react with oxygen to form increased amounts of ROS. Concomitantly, ROS oxidize fat deposits to release lipid peroxidation products that have detrimental effects on hepatocytes and other hepatic cells. In hepatocytes, ROS and lipid peroxidation products further impair the respiratory chain, either directly or indirectly through oxidative damage to the mitochondrial genome. This, in turn, leads to the generation of more ROS and a vicious cycle ensues. Mitochondrial dysfunction can also lead to apoptosis or necrosis depending on the energy status of the cell. ROS and lipid peroxidation products also activate stellate cells, thus resulting in fibrosis. Finally, ROS and lipid peroxidation increase the generation of several cytokines (TNF-alpha, TGF-B, Fas ligand) that play sundry roles in the pathogenesis of NASH. Recent investigations have shown that some genetic polymorphisms can significantly increase the risk of steatohepatitis and that several drugs can prevent or even reverse NASH. For the next decade, reducing the incidence of NASH will be a major challenge for hepatologists.

Dietary saturated fat reduces alcoholic hepatotoxicity in rats by altering fatty acid metabolism and membrane composition

Rats fed a saturated fat diet are protected from experimentally induced alcoholic liver disease, but the molecular mechanisms underlying this phenomenon remain in dispute. We fed male Sprague-Dawley rats intragastrically by total enteral nutrition using diets with or without ethanol. In 1 control and 1 ethanol group, the dietary fat was corn oil at a level of 45% of total energy. In other groups, saturated fat [18:82 ratio of beef tallow:medium-chain triglyceride (MCT) oil] was substituted for corn oil at levels of 10, 20, and 30% of total energy, while keeping the total energy from fat at 45%. After 70 d, liver pathology, serum alanine aminotransferase (ALT), biochemical markers of oxidative stress, liver fatty acid composition, cytochrome P450 2E1 (CYP2E1) expression and activity and cytochrome P450 4A (CYP4A) expression were assessed. In rats fed the corn oil plus ethanol diet, hepatotoxicity was accompanied by oxidative stress. As dietary saturated fat content increased, all measures of hepatic pathology and oxidative stress were progressively reduced, including steatosis (P < 0.05). Thus, saturated fat protected rats from alcoholic liver disease in a dose-responsive fashion. Changes in dietary fat composition did not alter ethanol metabolism or CYP2E1 induction, but hepatic CYP4A levels increased markedly in rats fed the saturated fat diet. Dietary saturated fat also decreased liver triglyceride, PUFA, and total FFA concentrations (P < 0.05). Increases in dietary saturated fat increased liver membrane resistance to oxidative stress. In addition, reduced alcoholic steatosis was associated with reduced fatty acid synthesis in combination with increased CYP4A-catalyzed fatty acid oxidation and effects on lipid export. These findings may be important in the nutritional management and treatment of alcoholic liver disease.

Hepatic steatosis in obese patients: clinical aspects and prognostic significance

Non-alcoholic fatty liver disease is a new clinicopathological condition of emerging importance, now recognized as the most common cause of abnormal liver tests. It is characterized by a wide spectrum of liver damage: simple steatosis may progress to advanced fibrosis and to cryptogenic cirrhosis through steatohepatitis, and ultimately to hepatocellular carcinoma. Obesity is the most significant single risk factor for the development of fatty liver, both in children and in adults; obesity is also predictive of the presence of fibrosis, potentially progressing to advanced liver disease. From a pathogenic point of view, insulin resistance plays a central role in the accumulation of triglycerides within the hepatocytes and in the initiation of the inflammatory cascade. Chronic hepatocellular injury, necroinflammation, stellate cell activation, progressive fibrosis and ultimately, cirrhosis may be initiated by peroxidation of hepatic lipids and injury-related cytokine release. In the last few years, several pilot studies have shown that treatment with insulin-sensitizing agents, anti-oxidants or cytoprotective drugs may be useful, but there is no evidence-based support from randomized clinical trials. Modifications in lifestyle (e.g. diet and exercise) to reduce obesity remain the mainstay of prevention and treatment of a disease, which puts a large number of individuals at risk of advanced liver disease in the near future.

Non-alcoholic steatohepatitis: review of a growing medical problem

Non-alcoholic steatohepatitis (NASH) is a metabolic liver disorder that is seen in 2-6% of the general population. It manifests itself by elevated liver enzymes, frequently without symptoms. The histological findings include steatosis, inflammation, fibrosis, and cirrhosis. Three case reports are presented to illustrate features of NASH. A two-hit model has been proposed in the pathogenesis of NASH. The first hit is hepatic steatosis. A hypercaloric diet with high levels of carbohydrates and saturated fatty acids results in elevated plasma free fatty acids (FFA) and expands the adipose tissue. Insulin resistance develops and augments steatosis. Oxidation of FFA yields toxic free radicals, resulting in lipid peroxidation. They cause the second hits: increased oxidative stress on hepatocytes and induction of pro-inflammatory cytokines. When the antioxidant capacities of the liver are insufficient, mitochondrial dysfunction and tumor necrosis factor alpha (TNF-alpha) cause inflammation and fibrosis. Treatment consists of life style modifications, particularly weight loss and exercise. Many drugs have been tried in the treatment of NASH. The insulin-sensitizing drugs metformin, rosiglitazone, and pioglitazone, and the antioxidant vitamin E show promising results. Further investigation of therapeutic options is needed to direct the choice of therapy in the future.

Steatosis and hepatitis C virus: mechanisms and significance for hepatic and extrahepatic disease

Nonalcoholic fatty liver disease (NAFLD) and hepatitis C virus (HCV)-related liver disease are common in the general population, but their concurrence is 2- to 3-fold higher than would be expected by chance alone. In patients with chronic HCV infection, steatosis is attributable to a variable combination of the mechanisms considered to play a role in the pathogenesis of NAFLD--insulin resistance in the obese and in the lean subject--along with a direct effect of HCV on hepatic lipid metabolism that leads to triglyceride accumulation through inhibition of export proteins that are required for very low density lipoprotein (VLDL) assembly and secretion. Accumulating evidence suggests that steatosis contributes to the progression of fibrosis in HCV-related disease in a pattern similar to that observed in NAFLD. Potential mechanisms of this effect include the increased sensitivity of steatotic livers to oxidative stress and cytokine-mediated injury. Steatosis-related hepatic insulin resistance may also play a role through the profibrogenic effects of the compensatory hyperinsulinemia and provides a potential explanation for the association between HCV and type 2 diabetes mellitus. Indeed, an appreciation of the importance of fat in HCV has recently led to trials of adjuvant therapy for HCV directed at steatosis-associated disease mechanisms, with encouraging results reported for various modalities, including weight loss and antioxidants. Future therapy should be aimed at exploiting the interactions of HCV with host insulin and lipid metabolism, particularly in nonresponders to standard antiviral schedules.

Non-alcoholic fatty liver disease: an emerging pathological spectrum

The spectrum of pathological lesions observed in non-alcoholic fatty liver disease (NAFLD) is wide and strongly resembles that of alcohol-induced liver disease. It ranges from fatty liver to steatohepatitis, progressive fibrosis and cirrhosis. Hepatocellular carcinoma is a possible complication of NAFLD, but whether it is related to frequently associated metabolic disorders (e.g., overweight, diabetes) or to underlying cirrhosis is unclear. This disease is the result of a multi-factorial process in which insulin resistance seems to play a major role in the initial accumulation of fat in the liver, whereas multiple causes of mitochondrial dysfunction and oxidative stress can induce the secondary occurrence of necroinflammatory lesions and fibrosis. Genetic factors might explain why only some patients with simple steatosis will develop steatohepatitis and fibrosis. Due to the increasing prevalence of obesity in Western countries, NAFLD will possibly be a public health problem and the liver disease of the future.

Serum lipids, lipoproteins and apolipoproteins levels in patients with nonalcoholic steatohepatitis

GOALS/BACKGROUND

Nonalcoholic steatohepatitis (NASH) is a form of liver disease that is histologically indistinguishable from alcoholic hepatitis but occurs in persons who do not consume alcohol in excess. The objectives of this study are to measure serum levels of lipids, lipoproteins and apolipoproteins (apo AI, apo B), lipoprotein (a) [Lp (a)] in patients with nonalcoholic steatohepatitis (NASH), and to investigate the relationship with liver histology.

STUDY

The scope of this study is composed of 36 patients (27 males, 9 females) with NASH, diagnosed by biochemical liver function tests, sonographic examination of liver and liver biopsy and 32 healthy adults as a control group (22 males, 10 females). Serum lipids, lipoproteins and apo AI, apo B, and Lp (a) measurements were taken in the study group and controls, and a correlation with histopathologic findings was searched for.

RESULTS

Serum mean levels (+/- SD as mg/dl) of total cholesterol (201.05 +/- 34.48), triglyceride (225.94 +/- 156.50), and LDL-cholesterol (111.77 +/- 19.85) in patients with NASH were significantly higher than those of the control group (170.68 +/- 31.06; 138.81 +/- 49.96; 100.68 +/- 17.98; respectively) and serum HDL-cholesterol level (41.22 +/- 2.47) was less than that of the control group (45.06 +/- 8.32) (P = 0.017). The serum mean level of apo AI (151.54 +/- 30.90) in the study group was lower than that of the controls (160.62 +/- 22.11), but the difference was not significant (P = 0.17). However, the serum apo AI level in patients with liver fibrosis (140.62 +/- 35.62) was significantly lower than that of patients without liver fibrosis (164.57 +/- 25.47) (P = 0.01). The serum mean level of apo B (89.80 +/- 20.62) in the patients was significantly higher than the control group (73.25 +/- 25.39) (P = 0.004), but not correlate with liver histopathology. The serum Lp (a) levels in both the patients (13.09 +/- 9.61) and the controls (12.01 +/- 7.50) were not different (P = 0.61). Hypertriglyceridemia (above 220 mg/dL) had a positive correlation with steatosis of the liver (r = 0.333, P = 0.04) and a negative correlation with liver fibrosis (r = -0.438, P = 0.008). There was a significant negative correlation between apo AI and steatosis (r = -0.360, P = 0.03), inflammation (r = -0.364, P = 0.03) and fibrosis of liver (r = -0.418, P = 0.01). A positive correlation of serum LDL-cholesterol (r = 0.507, P = 0.002) and Lp(a) (r = 0.394, P = 0.01) concentrations with liver fibrosis was also noted.

CONCLUSIONS

Abnormalities of lipid metabolism such as the increase of serum triglyceride, cholesterol and LDL-cholesterol level and decrease of HDL-cholesterol may be the contributing factors in the development of NASH. The decrease in apo AI and the increase in LDL and Lp (a) in patients were correlated with liver fibrosis. Apo AI may be a serum marker for liver fibrosis in patients with NASH.

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Hepatic gene expression in histologically progressive nonalcoholic steatohepatitis

Although the molecular basis for the pathophysiology of nonalcoholic steatohepatitis (NASH) is poorly understood, insulin resistance and mitochondrial dysfunction are physiologic hallmarks of this condition. We sought evidence of a transcriptional or pretranscriptional basis for insulin resistance and mitochondrial dysfunction through measurement of hepatic gene expression (messenger RNA [mRNA]) using high-density synthetic oligonucleotide microarray analysis (Hu6800 GeneChip, Affymetrix, CA). Global hepatic gene expression was determined in snap-frozen liver biopsy specimens from 4 groups: (1) patients with cirrhotic-stage NASH (n = 6), (2) patients with cirrhosis caused by hepatitis C virus (HCV) (n = 6), (3) patients with cirrhosis secondary to primary biliary cirrhosis (PBC) (n = 6), and (4) healthy controls (n = 6). Genes were considered to be expressed differentially in NASH only if there was a greater than 2-fold difference in abundance of mRNA when compared with each of the control groups. Sixteen genes were uniquely differentially expressed (4 overexpressed and 12 underexpressed) in patients with cirrhotic-stage NASH. Genes that were significantly underexpressed included genes important for maintaining mitochondrial function (copper/zinc superoxide dismutase, aldehyde oxidase, and catalase). Glucose 6-phospatase, alcohol dehydrogenase, elongation factor-TU, methylglutaryl coenzyme A (CoA), acyl CoA synthetase, oxoacyl CoA thiolase, and ubiquitin also were underexpressed in NASH. Genes that were overexpressed in NASH included complement component C3 and hepatocyte-derived fibrinogen-related protein, potentially contributing to impaired insulin sensitivity. In conclusion, these studies provide evidence for a transcriptional or pretranscriptional basis for impaired mitochondrial function (attenuated capacity for the dismutation of reactive oxygen species) and diminished insulin sensitivity (increased acute phase reactants) in patients with histologically progressive NASH. Further studies are required to determine the mechanism and the physiologic significance of these findings.

Hepatitis C virus-associated hypobetalipoproteinemia is correlated with plasma viral load, steatosis, and liver fibrosis

OBJECTIVES

A relationship between chronic hepatitis C virus (HCV) infection and lipid metabolism has recently been suggested. The aim of this study was to determine the correlation between lipid profile and virology, histologic lesions, and response to alpha interferon therapy in noncirrhotic, nondiabetic patients with hepatitis C.

METHODS

A total of 109 consecutive untreated chronic hepatitis C patients were studied to assess the following: 1) the effects of HCV genotype, viral load, steatosis, hepatic fibrosis, and body mass index (BMI) on lipid profile; and 2) whether lipid parameters could predict response to antiviral therapy.

RESULTS

The control group showed a significantly higher apolipoprotein B (apoB) concentration compared with patients with chronic hepatitis C. Hypobetalipoproteinemia (apo B <0.7 g/L) was found in 27 (24.7%) chronic HCV patients and in five (5.3%) control subjects (p = 0.0002). Levels of apo B were negatively correlated with steatosis and HCV viral load (r = -0.22; p = 0.03). This last correlation was strong for non-1 genotype and genotype 3 (r = -0.48; p = 0.0005, and r = -0.47; p = 0.007, respectively) but was not found in genotype 1. In multivariate analysis, low apo B concentration was significantly associated with fibrosis grade 2 or 3 versus grade 0 or 1 (p < 0.001), steatosis >5% (p < 0.001), low body mass index (p < 0.001), and high HCV viral load (p < 0.014). No correlation was found in the 76 treated patients between apo B and response to interferon therapy.

CONCLUSIONS

In chronic HCV patients, hypobetalipoproteinemia occurs already in the early stages of HCV infection before the development of liver cirrhosis. The correlation between apo B levels and HCV viral load seems to confirm the interaction between hepatitis C infection and beta-lipoprotein metabolism.

Nonalcoholic steatohepatitis: summary of an AASLD Single Topic Conference

Fatty liver disease that develops in the absence of alcohol abuse is recognized increasingly as a major health burden. This report summarizes the presentations and discussions at a Single Topic Conference held September 20-22, 2002, and sponsored by the American Association for the Study of Liver Diseases. The conference focused on fatty liver disorders. Estimates based on imaging and autopsy studies suggest that about 20% to 30% of adults in the United States and other Western countries have excess fat accumulation in the liver. About 10% of these individuals, or fully 2% to 3% of adults, are estimated to meet current diagnostic criteria for nonalcoholic steatohepatitis (NASH). Sustained liver injury leads to progressive fibrosis and cirrhosis in a fraction, possibly up to one third, of those with NASH, and NASH may be a cause of cryptogenic cirrhosis. NASH is now a significant health issue for obese children as well, leading to cirrhosis in some. The diagnostic criteria for NASH continue to evolve and rely on the histologic findings of steatosis, hepatocellular injury (ballooning, Mallory bodies), and the pattern of fibrosis. Generally recognized indications for biopsy include establishing the diagnosis and staging of the injury, but strict guidelines do not exist. Liver enzymes are insensitive and cannot be used reliably to confirm the diagnosis or stage the extent of fibrosis. Older age, obesity, and diabetes are predictive of fibrosis. The pathogenesis of NASH is multifactorial. Insulin resistance may be an important factor in the accumulation of hepatocellular fat, whereas excess intracellular fatty acids, oxidant stress, adenosine triphosphate (ATP) depletion, and mitochondrial dysfunction may be important causes of hepatocellular injury in the steatotic liver. Efforts are underway to refine the role of insulin resistance in NASH and determine whether improving insulin sensitivity pharmacologically is an effective treatment. An altered lifestyle may be a more effective means of improving insulin sensitivity. The research agenda for the future includes establishing the role of insulin resistance and abnormal lipoprotein metabolism in NASH, determining the pathogenesis of cellular injury, defining predisposing genetic abnormalities, identifying better noninvasive predictors of disease, and defining effective therapy.

Dietary habits and their relations to insulin resistance and postprandial lipemia in nonalcoholic steatohepatitis

The relations of dietary habits to insulin sensitivity and postprandial triglyceride metabolism were evaluated in 25 patients with nonalcoholic steatohepatitis (NASH) and 25 age-, body mass index (BMI)-, and gender-matched healthy controls. After a 7-day alimentary record, they underwent a standard oral glucose tolerance test (OGTT), and the insulin sensitivity index (ISI) was calculated from the OGTT; an oral fat load test was also performed in 15 patients and 15 controls. The dietary intake of NASH patients was richer in saturated fat (13.7% +/- 3.1% vs. 10.0% +/- 2.1% total kcal, respectively, P =.0001) and in cholesterol (506 +/- 108 vs. 405 +/- 111 mg/d, respectively, P =.002) and was poorer in polyunsaturated fat (10.0% +/- 3.5% vs. 14.5% +/- 4.0% total fat, respectively, P =.0001), fiber (12.9 +/- 4.1 vs. 23.2 +/- 7.8 g/d, respectively, P =.000), and antioxidant vitamins C (84.3 +/- 43.1 vs. 144.2 +/- 63.1 mg/d, respectively, P =.0001) and E (5.4 +/- 1.9 vs. 8.7 +/- 2.9 mg/d, respectively, P =.0001). The ISI was significantly lower in NASH patients than in controls. Postprandial total and very low density lipoproteins triglyceride at +4 hours and +6 hours, triglyceride area under the curve, and incremental triglyceride area under the curve were higher in NASH compared with controls. Saturated fat intake correlated with ISI, with the different features of the metabolic syndrome, and with the postprandial rise of triglyceride. Postprandial apolipoprotein (Apo) B48 and ApoB100 responses in NASH were flat and strikingly dissociated from the triglyceride response, suggesting a defect in ApoB secretion. In conclusion, dietary habits may promote steatohepatitis directly by modulating hepatic triglyceride accumulation and antioxidant activity as well as indirectly by affecting insulin sensitivity and postprandial triglyceride metabolism. Our findings provide further rationale for more specific alimentary interventions, particularly in nonobese, nondiabetic normolipidemic NASH patients.

Fatty acid binding protein is a major determinant of hepatic pharmacokinetics of palmitate and its metabolites

Disposition kinetics of [(3)H]palmitate and its low-molecular-weight metabolites in perfused rat livers were studied using the multiple-indicator dilution technique, a selective assay for [(3)H]palmitate and its low-molecular-weight metabolites, and several physiologically based pharmacokinetic models. The level of liver fatty acid binding protein (L-FABP), other intrahepatic binding proteins (microsomal protein, albumin, and glutathione S-transferase) and the outflow profiles of [(3)H]palmitate and metabolites were measured in four experimental groups of rats: 1) males; 2) clofibrate-treated males; 3) females; and 4) pregnant females. A slow-diffusion/bound model was found to better describe the hepatic disposition of unchanged [(3)H]palmitate than other pharmacokinetic models. The L-FABP levels followed the order: pregnant female > clofibrate-treated male > female > male. Levels of other intrahepatic proteins did not differ significantly. The hepatic extraction ratio and mean transit time for unchanged palmitate, as well as the production of low-molecular-weight metabolites of palmitate and their retention in the liver, increased with increasing L-FABP levels. Palmitate metabolic clearance, permeability-surface area product, retention of palmitate by the liver, and cytoplasmic diffusion constant for unchanged [(3)H]palmitate also increased with increasing L-FABP levels. It is concluded that the variability in hepatic pharmacokinetics of unchanged [(3)H]palmitate and its low-molecular-weight metabolites in perfused rat livers is related to levels of L-FABP and not those of other intrahepatic proteins.

Hepatic cytochrome P450 2E1 activity in nondiabetic patients with nonalcoholic steatohepatitis

Cytochrome P450 2E1 (CYP2E1) plays an important role in the pathogenesis of nonalcoholic steatohepatitis (NASH) in animal models, but its role in the pathogenesis of human NASH is unclear. Therefore, we measured hepatic CYP2E1 activity and its correlates in a cohort of nondiabetic patients with NASH (NDN) and controls to explore its role in the pathogenesis of human NASH. Hepatic CYP2E1 activity was assessed using the oral clearance (CL(PO)) of chlorzoxazone (CHZ) in 20 NDN and 17 age, gender, and body mass index (BMI)-matched controls. The relationship between hepatic CYP2E1 activity and demographic and anthropometric variables; fasting levels of insulin, glucose, lipids, and beta-OH butyrate; insulin resistance; and nocturnal hypoxemia was assessed. Furthermore, expression of CYP2E1 in the peripheral lymphocytes was assessed using reverse transcription-polymerase chain reaction (RT-PCR). The CL(PO) of CHZ was significantly (P =.03) greater in NDN (41 +/- 12 L/h) compared with controls (33 +/- 16 L/h). Lymphocyte CYP2E1 messenger RNA was significantly higher in NDN compared with controls (11.5 x 10(3) +/- 10 x 10(3) vs. 2.6 x 10(3) +/- 1.2 x 10(3) molecules/microg total RNA, respectively, P <.001). On univariate analysis, BMI, respiratory quotient, high-density lipoprotein, triglycerides, insulin, insulin resistance, hypoxemia, and beta-OH butyrate significantly correlated with hepatic CYP2E1 activity. However, on stepwise regression analysis, only nocturnal hypoxemia (r = 0.50, P =.009) and beta-OH butyrate (r = 0.37, P =.04) were independent predictors of hepatic CYP2E1 activity. In conclusion, hepatic CYP2E1 activity and lymphocyte CYP2E1 expression are enhanced in NDN. The significant correlations noted between CYP2E1 and hypoxemia and beta-OH butyrate suggest that these factors play a role in increased CYP2E1 activity that is seen in patients with NASH.

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.