Lipid Peroxidation in Bariatric Candidates with Nonalcoholic Fatty Liver Disease (NAFLD) – Preliminary Findings

The emerging significance of mitochondrial targeted strategies in NAFLD treatment

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease worldwide, ranging from liver steatosis to nonalcoholic steatohepatitis, which ultimately progresses to fibrosis, cirrhosis, and hepatocellular carcinoma. Individuals with NAFLD have a higher risk of developing cardiovascular and extrahepatic cancers. Despite the great progress being made in understanding the pathogenesis and the introduction of new pharmacological targets for NAFLD, no drug or intervention has been accepted for its management. Recent evidence suggests that NAFLD may be a mitochondrial disease, as mitochondrial dysfunction is involved in the pathological processes that lead to NAFLD. In this review, we describe the recent advances in our understanding of the mechanisms associated with mitochondrial dysfunction in NAFLD progression. Moreover, we discuss recent advances in the efficacy of mitochondria-targeted compounds (e.g., Mito-Q, MitoVit-E, MitoTEMPO, SS-31, mitochondrial uncouplers, and mitochondrial pyruvate carrier inhibitors) for treating NAFLD. Furthermore, we present some medications currently being tested in clinical trials for NAFLD treatment, such as exercise, mesenchymal stem cells, bile acids and their analogs, and antidiabetic drugs, with a focus on their efficacy in improving mitochondrial function. Based on this evidence, further investigations into the development of mitochondria-based agents may provide new and promising alternatives for NAFLD management.

Oxidative Stress in Non-Alcoholic Fatty Liver Disease

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

Dual Regulation of Tank Binding Kinase 1 by BRG1 in Hepatocytes Contributes to Reactive Oxygen Species Production

Excessive accumulation of reactive oxygen species (ROS) is considered a major culprit for the pathogenesis of non-alcoholic fatty liver disease (NAFLD). We have previously shown that deletion of Brahma related gene 1 (BRG1) mitigated NAFLD in mice in part by attenuating ROS production in hepatocyte. Here we report that BRG1 deletion led to simultaneous down-regulation in expression and phosphorylation of tank binding kinase 1 (TBK1) in vivo and in vitro. On the one hand, BRG1 interacted with AP-1 to bind to the TBK1 promoter and directly activated TBK1 transcription in hepatocytes. On the other hand, BRG1 interacted with Sp1 to activate the transcription of c-SRC, a tyrosine kinase essential for TBK1 phosphorylation. Over-expression of c-SRC and TBK1 corrected the deficiency in ROS production in BRG1-null hepatocytes whereas depletion of TBK1 or c-SRC attenuated ROS production. In conclusion, our data suggest that dual regulation of TBK1 activity, at the transcription level and the post-transcriptional level, by BRG1 may constitute an important mechanism underlying excessive ROS production in hepatocytes.

Oxidative Stress Linked Organ Lipid Hydroperoxidation and Dysregulation in Mouse Model of Nonalcoholic Steatohepatitis: Revealed by Lipidomic Profiling of Liver and Kidney

Nonalcoholic steatohepatitis (NASH) is a prevalent disease related to lipid metabolism disorder and oxidative stress. Lipid hydroperoxidation is known to be a critical driving force of various disorders and diseases. However, the combination of both intact and hydroperoxidized lipids in NASH has not yet been studied. In this work, the liver and kidney samples from NASH-model mice were comprehensively investigated by using the LC/MS-based lipidomic analysis. As a result, triglycerides showed the amount accumulation and the profile alteration for the intact lipids in the NASH group, while phosphatidylethanolamines, lysophosphatidylethanolamines, plasmalogens, and cardiolipins largely depleted, suggesting biomembrane damage and mitochondria dysfunction. Notably, the lipid hydroperoxide species of triglyceride and phosphatidylcholine exhibited a significant elevation in both the liver and the kidney of the NASH group and showed considerable diagnostic ability. Furthermore, the relationship was revealed between the lipid metabolism disturbance and the lipid hydroperoxide accumulation, which played a key role in the vicious circle of NASH. The present study suggested that the omics approach to the lipid hydroperoxide profile might be the potential diagnostic marker of NASH and other oxidative stress-related diseases, as well as the evaluative treatment index of antioxidants.

Impact of vitamin E on redox biomarkers in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disorder in Western nations and characterized by excessive accumulation of lipids in the liver. In this narrative review, we summarize the evidence from human trials that free radical-induced oxidation of macromolecules, in particular of lipids, is a characteristic feature of NAFLD and non-alcoholic steatohepatitis (NASH). We further synthesize the data in the scientific literature describing the impact of vitamin E (mainly α-tocopherol) on concentrations of redox biomarkers in liver biopsies from patients with NAFLD as well as animal experiments. In summary, the available evidence from clinical trials suggests that reactive species-mediated damage to macromolecules, predominantly lipids, occurs in NAFLD and NASH and that daily supplementation with at least 200 I.U. α-tocopherol may alleviate oxidative stress in the liver of NAFLD patients. We propose α-tocopherol as a useful model substance to identify and validate suitable redox biomarkers that may be employed in future clinical trials of new therapeutics for NAFLD.

The Interplay between Angiopoietin-Like Proteins and Adipose Tissue: Another Piece of the Relationship between Adiposopathy and Cardiometabolic Diseases?

Angiopoietin-like proteins, namely ANGPTL3-4-8, are known as regulators of lipid metabolism. However, recent evidence points towards their involvement in the regulation of adipose tissue function. Alteration of adipose tissue functions (also called adiposopathy) is considered the main inducer of metabolic syndrome (MS) and its related complications. In this review, we intended to analyze available evidence derived from experimental and human investigations highlighting the contribution of ANGPTLs in the regulation of adipocyte metabolism, as well as their potential role in common cardiometabolic alterations associated with adiposopathy. We finally propose a model of ANGPTLs-based adipose tissue dysfunction, possibly linking abnormalities in the angiopoietins to the induction of adiposopathy and its related disorders.

Role of oxidative stress in the pathogenesis of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most common chronic liver disease worldwide and is strongly associated with the presence of oxidative stress. Disturbances in lipid metabolism lead to hepatic lipid accumulation, which affects different reactive oxygen species (ROS) generators, including mitochondria, endoplasmic reticulum, and NADPH oxidase. Mitochondrial function adapts to NAFLD mainly through the downregulation of the electron transport chain (ETC) and the preserved or enhanced capacity of mitochondrial fatty acid oxidation, which stimulates ROS overproduction within different ETC components upstream of cytochrome c oxidase. However, non-ETC sources of ROS, in particular, fatty acid β-oxidation, appear to produce more ROS in hepatic metabolic diseases. Endoplasmic reticulum stress and NADPH oxidase alterations are also associated with NAFLD, but the degree of their contribution to oxidative stress in NAFLD remains unclear. Increased ROS generation induces changes in insulin sensitivity and in the expression and activity of key enzymes involved in lipid metabolism. Moreover, the interaction between redox signaling and innate immune signaling forms a complex network that regulates inflammatory responses. Based on the mechanistic view described above, this review summarizes the mechanisms that may account for the excessive production of ROS, the potential mechanistic roles of ROS that drive NAFLD progression, and therapeutic interventions that are related to oxidative stress.

Nutrition and physical activity in Asian Indians with non-alcoholic fatty liver: A case control study

AIM

We tested the hypothesis that Asian Indians with non-alcoholic fatty liver disease (NAFLD) would have imbalanced diets and lower intensity of physical activity than those without NAFLD.

METHODS

We studied dietary intake, intensity of physical activity and anthropometric and metabolic profiles in subjects with NAFLD and in healthy controls. Complete clinical, biochemical, dietary and physical activity profiles were studied for 169 cases and 173 controls in a prospective manner. Bivariate and multivariate analyses were carried out to identify the predictors of NAFLD [odds ratio (OR) and 95% confidence intervals (95%CI)].

RESULTS

The mean dietary intakes of total energy, carbohydrate, protein, total fat, saturated fat and total cholesterol were significantly higher, while intake of monounsaturated fatty acids and polyunsaturated fatty acids was significantly lower in cases as compared to controls (p < 0.01 for all). Further, mean physical activity in a day (expressed as MET.Minutes) and total energy expenditure were significantly lower in cases than in controls (33.3 ± 3.6 vs.36.2 ± 0.5, p = 0.001 and 2707.6 ± 505.6 vs. 2904.3 ± 690.3, p = 0.02, respectively). On multivariate analysis, percentage dietary total fat intake (OR: 13.4; 95% CI: 4.6-39.3, p = 0.001), homeostatis model assessment for insulin resistance (OR: 6.9; 95% CI: 3.2-14.8, p = 0.001) abdominal obesity (OR: 2.7; 95% CI: 1.5-5.0, p = 0.001) and high serum triglycerides (OR: 2.1; 95%CI: 1.2-3.8, p = 0.007) were associated with an increased risk for development of NAFLD.

CONCLUSION

Decrease in intake of total dietary fats and improvement of insulin resistance, abdominal obesity and blood triglycerides should be important measures for management of NAFLD in Asian Indians in north India.

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

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

Evolution of Liver Steatosis Quantified by MR Imaging and MR Spectroscopy, in Morbidly Obese Patients Undergoing Sleeve Gastrectomy: Short-Term Outcomes

BACKGROUND

Currently, the standard procedure used to evaluate hepatic steatosis is the liver biopsy. This is an invasive practice that presents inherent risks. Increasing evidence suggests that magnetic resonance imaging (MRI) and MR spectroscopy (MRS) may represent an accurate method to determine the hepatic lipid content. The aim of this study was to evaluate the effect of sleeve gastrectomy on liver steatosis, quantified by MRI and MRS.

PATIENTS AND METHODS

A prospective observational study of patients undergoing laparoscopic sleeve gastrectomy was performed. All patients underwent a MRI and a MRS study 2 weeks before the intervention and 6 months after the surgery. Anthropometric, biochemical, and radiological parameters were analyzed.

RESULTS

Twenty-three patients were included, 21 females and 2 males, with a mean age of 47.6 ± 10.6 years and mean pre-op BMI 47.6 ± 6.7 Kg/m². Six months after surgery, mean BMI was 32.2 ± 5.1 Kg/m², with a mean excess weight loss of 68.2 ± 18.6%. Mean preoperative hepatic volume was 1999.9 ± 436.2 ml and 6 months after surgery it decreased to 1568 ± 170.3 ml (p = 0.005). Mean preoperative percentage of lipid content was 14.2 ± 15.4% and 6 months after surgery, it decreased to 4.3 ± 3.2% (p = 0.007). A significant reduction of steatosis grade was observed, with disappearance of preoperative steatosis in 54.9% of the patients.

CONCLUSION

Six months after sleeve gastrectomy, a significant reduction of liver steatosis is observed, as demonstrated by reduction in the percentage of intrahepatocitary lipids and liver volume, determined by MRS and MRI. These imaging techniques can be considered as noninvasive, accurate methods for monitoring liver steatosis in morbidly obese patients undergoing bariatric surgery.

The effects of bariatric surgeries on nonalcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and is associated with obesity. Bariatric surgery has been shown to be the most effective method for weight reduction. However, no conclusive data exists on the effects of weight reduction surgery on NAFLD. This study aimed to characterize liver histology, metabolic status, and liver function changes in patients who underwent bariatric surgery, before and after the weight-reduction procedure. This is a phase 1 report of a prospective cohort study of patients who underwent bariatric surgery. Biopsies were obtained at baseline (intraoperatively) and 3 months postoperatively. Clinical characteristics, biochemical profile, and histopathological data [steatosis, NAFLD activity score (NAS), hepatocyte ballooning, lobular inflammation, and degree of fibrosis] were obtained at each time point. Twenty-seven patients were included (9 men and 18 women), and the median age was 35 ± 8 years old. At baseline, 3 patients had dyslipidemia, 4 had diabetes, and 5 patients had hypertension, which did not change at follow-up. The average body mass index decreased from 44.6 ± 7.8 to 34.2 ± 6.3 kg/m² at follow-up (P < 0.001). On histopathology, 12 of the 18 patients with preoperative steatosis (median score 2) had reduced steatosis scores postoperatively (P = 0.025); fibrosis (median score 1) was also reduced in 17 patients (P = 0.012), and NAS was decreased from 4 (3-5) to 2 (1-3) (P = 0.004). The changes in lobular inflammation and hepatocyte ballooning were not statistically significant on follow-up. The phase 1 results of this study described the histopathological changes following weight reduction surgery and suggested that hepatic steatosis, fibrosis, and NAFLD activity score were reduced 3 months after surgery. This clinical trial is financially supported by the National Plan for Science, Technology and Innovation Program grant number (11-MED1910-02).

Strategies, models and biomarkers in experimental non-alcoholic fatty liver disease research

Non-alcoholic fatty liver disease encompasses a spectrum of liver diseases, including simple steatosis, steatohepatitis, liver fibrosis and cirrhosis and hepatocellular carcinoma. Non-alcoholic fatty liver disease is currently the most dominant chronic liver disease in Western countries due to the fact that hepatic steatosis is associated with insulin resistance, type 2 diabetes mellitus, obesity, metabolic syndrome and drug-induced injury. A variety of chemicals, mainly drugs, and diets is known to cause hepatic steatosis in humans and rodents. Experimental non-alcoholic fatty liver disease models rely on the application of a diet or the administration of drugs to laboratory animals or the exposure of hepatic cell lines to these drugs. More recently, genetically modified rodents or zebrafish have been introduced as non-alcoholic fatty liver disease models. Considerable interest now lies in the discovery and development of novel non-invasive biomarkers of non-alcoholic fatty liver disease, with specific focus on hepatic steatosis. Experimental diagnostic biomarkers of non-alcoholic fatty liver disease, such as (epi)genetic parameters and '-omics'-based read-outs are still in their infancy, but show great promise. In this paper, the array of tools and models for the study of liver steatosis is discussed. Furthermore, the current state-of-art regarding experimental biomarkers such as epigenetic, genetic, transcriptomic, proteomic and metabonomic biomarkers will be reviewed.

The effect of bariatric surgeries on nonalcoholic fatty liver disease

A review of published data addressing hepatic histopathological, metabolical, and functional changes following gastric banding, sleeve gastrectomy, gastric bypass surgery, and biliopancreatic with duodenal switch surgeries on nonalcoholic fatty liver disease (NAFLD). NAFLD is currently the most common chronic liver disease. Owing to the strong relationship between obesity and NAFLD, the idea of weight reduction as a method to treat NAFLD has rapidly emerged. Bariatric surgery has proved to be the most efficient method for weight reduction; hence, their beneficial effects on NAFLD have been evaluated by several studies. A literature review of published data was performed during the years 2012-2014 using PubMed with the following key words: Bariatric, NAFLD, steatosis, sleeve gastrectomy, gastric bypass, gastric banding, biliopancreatic diversion with duodenal switch, obesity, and insulin resistance (IR). Exclusion criteria were non-English articles and inherited NAFLD, pregnancy-induced NAFLD, and children. The majority of published data are in favor of indicating that bariatric surgeries improve the histologic and metabolic changes associated with NAFLD. The suggested mechanisms are: The reversal of IR, reduction of inflammatory markers, and improved histological features of NAFLD. Accordingly, bariatric surgeries are potentially one of the future methods in treating patients with morbid obesity and NAFLD. However, some questions remain unanswered, such as whether timing of surgery, type of surgery most effective, and whether bariatric surgeries are capable of curing the disease. Long-term and well-designed prospective studies are needed to address these issues.

Involvement of free radicals and oxidative stress in NAFLD/NASH

Non-alcoholic fatty liver disease (NAFLD) is now the most common liver disease affecting high proportion of the population worldwide. NAFLD encompasses a large spectrum of conditions ranging from fatty liver to non-alcoholic steatohepatitis (NASH), which can progress to cirrhosis and cancer. NAFLD is considered as a multifactorial disease in relation to the pathogenic mechanisms. Oxidative stress has been implicated in the pathogenesis of NAFLD and NASH and the involvement of reactive oxygen species (ROS) has been suggested. Many studies show the association between the levels of lipid oxidation products and disease state. However, often neither oxidative stress nor ROS has been characterized, despite oxidative stress is mediated by multiple active species by different mechanisms and the same lipid oxidation products are produced by different active species. Further, the effects of various antioxidants have been assessed in human and animal studies, but the effects of drugs are determined by the type of active species, suggesting the importance of characterizing the active species involved. This review article is focused on the role of free radicals and free radical-mediated lipid peroxidation in the pathogenesis of NAFLD and NASH, taking characteristic features of free radical-mediated oxidation into consideration. The detailed analysis of lipid oxidation products shows the involvement of free radicals in the pathogenesis of NAFLD and NASH. Potential beneficial effects of antioxidants such as vitamin E are discussed.

Quercetin decreases liver damage in mice with non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a frequent condition in obese patients that may progress to end-stage liver disease. This study was designed to evaluate the modulation of this condition by use of quercetin (Q), a flavonoid largely found in vegetable foods, with known anti-inflammatory and antioxidant properties, in the experimental model of non-alcoholic steatohepatitis (NASH) using a diet deficient in methionine and choline (MCD). Male C57BL6 mice were divided into four groups (n = 16): (i) Control plus vehicle (control ration plus carboxymethylcellulose 1% used as vehicle, CO + V); (ii) Control ration plus Q 50 mg/kg (CO + Q); (iii) MCD diet plus vehicle (NASH + V); and (iv) MCD diet plus Q (NASH + Q). Diets were administered for 4 weeks. At the end of the experimental period, liver alterations, bioindicators of oxidative stress and DNA damage were assessed. NASH was diagnosed in 100% of the mice that were fed the MCD diet. In addition, a significant increase in DNA damage in liver tissue from NASH + V group was observed in comparison with CO + V. The group NASH + Q showed a significant decrease in hepatic damage enzymes, lipoperoxidation, DNA damage and a lower degree of macrovesicular steatosis, ballooning and inflammatory process. These findings suggest that Q may have protective effects by improving liver integrity in NASH.

Misregulation of PPAR Functioning and Its Pathogenic Consequences Associated with Nonalcoholic Fatty Liver Disease in Human Obesity

Nonalcoholic fatty liver disease in human obesity is characterized by the multifactorial nature of the underlying pathogenic mechanisms, which include misregulation of PPARs signaling. Liver PPAR-α downregulation with parallel PPAR-γ and SREBP-1c up-regulation may trigger major metabolic disturbances between de novo lipogenesis and fatty acid oxidation favouring the former, in association with the onset of steatosis in obesity-induced oxidative stress and related long-chain polyunsaturated fatty acid n-3 (LCPUFA n-3) depletion, insulin resistance, hypoadiponectinemia, and endoplasmic reticulum stress. Considering that antisteatotic strategies targeting PPAR-α revealed that fibrates have poor effectiveness, thiazolidinediones have weight gain limitations, and dual PPAR-α/γ agonists have safety concerns, supplementation with LCPUFA n-3 appears as a promising alternative, which achieves both significant reduction in liver steatosis scores and a positive anti-inflammatory outcome. This latter aspect is of importance as PPAR-α downregulation associated with LCPUFA n-3 depletion may play a role in increasing the DNA binding capacity of proinflammatory factors, NF-κB and AP-1, thus constituting one of the major mechanisms for the progression of steatosis to steatohepatitis.

Obstructive sleep apnea and non-alcoholic Fatty liver disease: is the liver another target?

Obstructive sleep apnea (OSA) is recurrent obstruction of the upper airway during sleep leading to intermittent hypoxia (IH). OSA has been associated with all components of the metabolic syndrome as well as with non-alcoholic fatty liver disease (NAFLD). NAFLD is a common condition ranging in severity from uncomplicated hepatic steatosis to steatohepatitis (NASH), liver fibrosis, and cirrhosis. The gold standard for the diagnosis and staging of NAFLD is liver biopsy. Obesity and insulin resistance lead to liver steatosis, but the causes of the progression to NASH are not known. Emerging evidence suggests that OSA may play a role in the progression of hepatic steatosis and the development of NASH. Several cross-sectional studies showed that the severity of IH in patients with OSA predicted the severity of NAFLD on liver biopsy. However, neither prospective nor interventional studies with continuous positive airway pressure treatment have been performed. Studies in a mouse model showed that IH causes triglyceride accumulation in the liver and liver injury as well as hepatic inflammation. The mouse model provided insight in the pathogenesis of liver injury showing that (1) IH accelerates the progression of hepatic steatosis by inducing adipose tissue lipolysis and increasing free fatty acids (FFA) flux into the liver; (2) IH up-regulates lipid biosynthetic pathways in the liver; (3) IH induces oxidative stress in the liver; (4) IH up-regulates hypoxia inducible factor 1 alpha and possibly HIF-2 alpha, which may increase hepatic steatosis and induce liver inflammation and fibrosis. However, the role of FFA and different transcription factors in the pathogenesis of IH-induced NAFLD is yet to be established. Thus, multiple lines of evidence suggest that IH of OSA may contribute to the progression of NAFLD but definitive clinical studies and experiments in the mouse model have yet to be done.

Transcriptome analysis of anti-fatty liver action by Campari tomato using a zebrafish diet-induced obesity model

BACKGROUND

High dietary intake of vegetable products is beneficial against obesity and its related diseases such as dyslipidemia, nonalcoholic fatty liver disease, and cancer. We previously developed a diet-induced obesity model of zebrafish (DIO-zebrafish) that develops visceral adiposity, dyslipidemia, and liver steatosis. Zebrafish is a polyphagous animal; thus we hypothesized that DIO-zebrafish could be used for transcriptome analysis of anti-obesity effects of vegetables.

RESULTS

Each vegetable exhibited different effects against obesity. We focused on "Campari" tomato, which suppressed increase of body weight, plasma TG, and lipid droplets in livers of DIO-zebrafish. Campari tomato decreased srebf1 mRNA by increase of foxo1 gene expression, which may depend on high contents of β-carotene in this strain.

CONCLUSIONS

Campari tomato ameliorates diet-induced obesity, especially dyslipidemia and liver steatosis via downregulation of gene expression related to lipogenesis. DIO-zebrafish can discriminate the anti-obesity effects of different strains of vegetables, and will become a powerful tool to assess outcomes and find novel mechanisms of anti-obesity effects of natural products.

Oxidative stress in chronic liver disease: relationship between peripheral and hepatic measurements

INTRODUCTION

Oxidative stress plays an important role in the pathogenesis of many liver diseases. Investigators often measure markers of oxidative stress in peripheral veins as a reflection of hepatic oxidative stress as it is not always feasible to measure oxidative stress in liver tissue. However, it is unknown whether markers of oxidative stress measured from peripheral sites accurately reflect hepatic tissue oxidative stress. The aim of this study is to examine the relationship of oxidative stress marker among hepatic tissue, hepatic and peripheral veins and urine.

METHODS

Malondialdehyde (MDA), a marker of oxidative stress was measured in hepatic vein, peripheral vein and urine samples from 26 consecutive patients undergoing transjugular liver procedures. In 19 patients undergoing liver biopsies, we measured MDA by immunohistochemical staining of paraffin-embedded liver tissue.

RESULTS

Peripheral venous MDA levels showed significant correlation with hepatic venous MDA levels (r = 0.62, P = 0.02), but they did not correlate with hepatic tissue MDA content (r = 0.22, P = 0.4). Hepatic venous MDA levels did not correlate with hepatic tissue MDA content (r = -0.01, P = 0.9). Subgroup analysis of patients without portal hypertension showed a positive correlation between hepatic venous and hepatic tissue MDA levels, but this was not statistically significant (r = 0.45, P = 0.22). Urinary MDA did not correlate with MDA from any other sampling location.

CONCLUSION

Oxidative stress measured from the peripheral venous samples is poorly reflective of hepatic tissue oxidative stress. Hepatic venous sampling might be suitable for assessing hepatic tissue oxidative stress in patients without portal hypertension, but a larger study is needed to examine this possibility.

The importance of the long-chain polyunsaturated fatty acid n-6/n-3 ratio in development of non-alcoholic fatty liver associated with obesity

Non-alcoholic fatty liver disease (NAFLD) is the most important cause of chronic liver disease that is characterized by hepatocyte triacylglycerol accumulation (steatosis), which can progress to inflammation, fibrosis, and cirrhosis (steatohepatitis). Overnutrition triggers the onset of oxidative stress in the liver due to higher availability and oxidation of fatty acids (FA), with development of hyperinsulinemia and insulin resistance (IR), and n-3 long-chain polyunsaturated FA (n-3 LCPUFA) depletion, with enhancement in the n-6/n-3 LCPUFA ratio favouring a pro-inflammatory state. These changes may lead to hepatic steatosis by different mechanisms, namely, (i) IR-dependent higher peripheral lipolysis and FA flux to the liver, (ii) n-3 LCPUFA depletion-induced changes in DNA binding activity of sterol regulatory element-binding protein 1c (SREBP-1c) and peroxisome proliferator-activated receptor α (PPAR-α) favouring lipogenesis over FA oxidation, and (iii) hyperinsulinemia-induced activation of lipogenic factor PPAR-γ. Supplementation with n-3 LCPUFA appears to reduce nutritional hepatic steatosis in adults, however, other histopathologic features of NAFLD remain to be studied.

Metabolic surgery and cancer: protective effects of bariatric procedures

The worldwide epidemic of obesity and the global incidence of cancer are both increasing. There is now epidemiological evidence to support a correlation between obesity, weight gain, and some cancers. Metabolic or bariatric surgery can provide sustained weight loss and reduced obesity-related mortality. These procedures can also improve the metabolic profile to decrease cardiovascular risk and resolve diabetes in morbidly obese patients. The operations offer several physiological steps, the so-called BRAVE effects: 1) bile flow alteration, 2) reduction of gastric size, 3) anatomical gut rearrangement and altered flow of nutrients, 4) vagal manipulation and 5) enteric gut hormone modulation. Metabolic operations are also associated with a significant reduction of cancer incidence and mortality. The cancer-protective role of metabolic surgery is strongest for female obesity-related tumors; however, the underlying mechanisms may involve both weight-dependent and weight-independent effects. These include the improvement of insulin resistance with attenuation of the metabolic syndrome as well as decreased oxidative stress and inflammation in addition to the beneficial modulation of sex steroids, gut hormones, cellular energetics, immune system, and adipokines. Elucidating the precise metabolic mechanisms of cancer prevention by metabolic surgery can increase our understanding of how obesity, diabetes, and metabolic syndrome are associated with cancer. It may also offer novel treatment strategies in the management of tumor generation and growth.

Clerodendron glandulosum.Coleb extract ameliorates high fat diet/fatty acid induced lipotoxicity in experimental models of non-alcoholic steatohepatitis

This study evaluates the protective role of Clerodendron glandulosum.Coleb (CG) aqueous extract against high fat diet/fatty acid induced lipotoxicity in experimental models of non-alcoholic steatohepatitis (NASH). Supplementation of NASH mice with CG extract (1% and 3% in high fat diet for 16 weeks) prevented high fat diet induced elevation in liver enzymes, plasma and hepatic lipids, mitochondrial oxidative stress and compromised enzymatic and non-enzymatic antioxidant status and histopathological damage to hepatocytes. Furthermore, results from in vitro study indicates, addition of CG extract (20-200 μg/ml for 24h) to HepG2 cells minimizes oleic acid induced lipid accumulation, higher lipid peroxidation, cytotoxicity and reduced cell viability. These in vivo and in vitro studies suggest that CG extract has the potential of preventing high fat/fatty acid induced NASH.

Association of polymorphisms of glutamate-cystein ligase and microsomal triglyceride transfer protein genes in non-alcoholic fatty liver disease

BACKGROUND AND AIMS

Although the metabolic risk factors for non-alcoholic fatty liver disease (NAFLD) progression have been recognized, the role of genetic susceptibility remains a field to be explored. The aim of this study was to examine the frequency of two polymorphisms in Brazilian patients with biopsy-proven simple steatosis or non-alcoholic steatohepatitis (NASH): -493 G/T in the MTP gene, which codes the protein responsible for transferring triglycerides to nascent apolipoprotein B, and -129 C/T in the GCLC gene, which codes the catalytic subunit of glutamate-cystein ligase in the formation of glutathione.

METHODS

One hundred and thirty-one biopsy-proven NAFLD patients (n = 45, simple steatosis; n = 86, NASH) and 141 unrelated healthy volunteers were evaluated. Genomic DNA was extracted from peripheral blood cells, and the -129 C/T polymorphism of the GCLC gene was determined by restriction fragment length polymorphism (RFLP). The -493 G/T polymorphism of the MTP gene was determined by direct sequencing of the polymerase chain reaction products.

RESULTS

The presence of at least one T allele in the -129 C/T polymorphism of the GCLC gene was independently associated with NASH (odds ratio 12.14, 95% confidence interval 2.01-73.35; P = 0.007), whereas, the presence of at least one G allele in the -493 G/T polymorphism of the MTP gene differed slightly between biopsy-proven NASH and simple steatosis.

CONCLUSION

This difference clearly warrants further investigation in larger samples. These two polymorphisms could represent an additional factor for consideration in evaluating the risk of NAFLD progression. Further studies involving a larger population are necessary to confirm this notion.

Liver enzymes and histology in obese patients with obstructive sleep apnea

BACKGROUND AND AIMS

Recent studies have shown an association between obstructive sleep apnea (OSA) and elevated liver enzymes in patients with nonalcoholic fatty liver disease (NAFLD). The aim of the current study was to compare biochemical and histologic findings in patients with NAFLD as a function of OSA status.

METHODS

Subjects consisted of 85 patients who had a sleep study followed by a liver biopsy performed at the time of obesity surgery. The diagnosis of OSA was based on an apnea hypopnea index of >/=15. Demographic and laboratory data were collected retrospectively. Liver biopsies were systematically evaluated for features of NAFLD including degree of steatosis, inflammation, and fibrosis.

RESULTS

All but one patient had histologic evidence of NAFLD and 51% of the study population had OSA. A higher proportion of patients with OSA had elevated alanine aminotransferase levels (13/39) compared with those without OSA (3/34) (P=0.01). Only 19% of subjects had fibrosis on liver biopsy and still fewer (5%) had bridging fibrosis or cirrhosis. There was a trend toward a higher prevalence of OSA in patients with evidence of progressive liver disease, as indicated by inflammation plus fibrosis (11/15), compared with those with inflammation alone (22/48) (P=0.06).

CONCLUSIONS

In obese patients with NAFLD, OSA was associated with elevated alanine aminotransferase levels and a trend toward histologic evidence of progressive liver disease.

Nonalcoholic fatty liver disease as a complication of insulin resistance

Nonalcoholic fatty liver disease (NAFLD) refers to a spectrum of liver damage ranging from simple steatosis to nonalcoholic steatohepatitis, advanced fibrosis, and rarely, progression to cirrhosis. The pathogenesis of NAFLD is thought to be related to insulin resistance and oxidant stress. Truncal obesity, dyslipidema, hypertension, and hyperglycemia are strongly associated with NAFLD; therefore, management of NAFLD entails identification and treatment of metabolic risk factors, improving insulin sensitivity, and increasing antioxidant defenses in the liver. This article briefly summarizes advances in our understanding of the relationship between NAFLD and the insulin resistance (metabolic) syndrome, its prevalence, natural history, and treatment.

Oxidative stress and potential interventions to reduce oxidative stress in overweight and obesity

PURPOSE

Obesity may be a state of chronic oxidative stress. Oxidative stress may be the mechanism underlying the development of co-morbidities in obesity. This review provides a summary of the available evidence regarding systemic oxidative stress in young, older and clinical obese populations.

METHODS

Medline was searched for all available articles published between 1975 and 2006 that evaluated oxidative stress biomarkers in resting conditions or following various interventions in overweight and obese humans.

RESULTS

Obesity elevates oxidative stress in young, old and clinical populations as shown by elevations in lipid peroxidation (malondialdehyde, hydroperoxides, 4-hydroxynonenal, isoprostanes, conjugated dienes) or protein oxidation (8-hydroxy-deoxyguanosine). Lipid peroxidation is associated with several indices of adiposity and a low systemic antioxidant defence (i.e. antioxidant enzymes, tissue dietary antioxidants, glutathione). Oxidative stress may be exacerbated with acute exercise, advancing age or co-existing clinical conditions and may be corrected by improving antioxidant defences through fat volume reduction via surgery, pharmacological agents, exercise and/or dietary modification.

CONCLUSION

Oxidative stress is related to chronic disease in obesity, but is reversible with one or more interventions described above.

Chronic intermittent hypoxia causes hepatitis in a mouse model of diet-induced fatty liver

Obstructive sleep apnea (OSA) causes chronic intermittent hypoxia (CIH) during sleep. OSA is associated with nonalcoholic steatohepatitis (NASH) in obese individuals and may contribute to progression of nonalcoholic fatty liver disease from steatosis to NASH. The purpose of this study was to examine whether CIH induces inflammatory changes in the liver in mice with diet-induced hepatic steatosis. C57BL/6J mice (n = 8) on a high-fat, high-cholesterol diet were exposed to CIH for 6 mo and were compared with mice on the same diet exposed to intermittent air (control; n = 8). CIH caused liver injury with an increase in serum ALT (461 +/- 58 U/l vs. 103 +/- 16 U/l in the control group; P < 0.01) and AST (637 +/- 37 U/l vs. 175 +/- 13 U/l in the control group; P < 0.001), whereas alkaline phosphatase and total bilirubin levels were unchanged. Histology revealed hepatic steatosis in both groups, with mild accentuation of fat staining in the zone 3 hepatocytes in mice exposed to CIH. Animals exposed to CIH exhibited lobular inflammation and fibrosis in the liver, which were not evident in control mice. CIH caused significant increases in lipid peroxidation in serum and liver tissue; significant increases in hepatic levels of myeloperoxidase and proinflammatory cytokines IL-1beta, IL-6, and CXC chemokine MIP-2; a trend toward an increase in TNF-alpha; and an increase in alpha1(I)-collagen mRNA. We conclude that CIH induces lipid peroxidation and inflammation in the livers of mice on a high-fat, high-cholesterol diet.

Comparative review of diets for the metabolic syndrome: implications for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a significant health problem and affects 70 million adults in the United States (30% of the adult population), and an estimated 20% of these individuals have the most severe form of NAFLD-nonalcoholic steatohepatitis (NASH). The mechanisms underlying disease development and progression are awaiting clarification. Insulin resistance and obesity-related inflammation, among other possible genetic, dietary, and lifestyle factors, are thought to play a key role. A program targeting gradual weight reduction and physical exercise continues to be the gold standard of treatment for all forms of NAFLD. Even though weight loss and dietary and lifestyle changes are recommended as primary treatment for fatty liver, little to no scientific evidence is available on diet and NAFLD. This article reviews the implications of current dietary approaches, including national guidelines and popular weight-loss diets, with a focus on determining the optimal diet to prescribe for NAFLD and NASH patients. The effects of macronutrient content (carbohydrate, fat, and protein ratios) and specific food components, such as soluble fiber, n-3 fatty acids, and fructose, are discussed. The premises, effects, barriers, and issues related to current dietary guidelines and specific diets are discussed, and the question, "Will it work for the pathogenesis of NAFLD and NASH? ", is addressed.

Effects of bariatric surgery on nonalcoholic fatty liver disease: preliminary findings after 2 years

BACKGROUND AND AIM

Although nonalcoholic fatty liver disease (NAFLD) is very common among morbidly obese patients, the effect of weight loss after bariatric surgery on inflammation and fibrosis related to NAFLD is still a matter of debate. The aim of this study was to evaluate the impact of Roux-en-Y gastric bypass (RYGB) surgery on NAFLD with a follow up of 2 years.

METHODS

Eighteen consecutive NAFLD patients with body mass index >40 kg/m(2) undergoing gastroplasty with RYGB were enrolled, and wedge liver biopsy was obtained at the operation. After 2 years, these patients underwent percutaneous liver biopsy.

RESULTS

At baseline, 67% of patients had nonalcoholic steatohepatitis (NASH) and 33% had steatosis, according to the NASH Clinical Research Network Scoring System (NAS) for biopsy. Cirrhosis was present in 5.5% of the patients with NASH. After a mean excess weight loss of 60%, steatosis disappeared in 84% and fibrosis disappeared in 75% of the patients. Hepatocellular ballooning disappeared in 50%. A slight lobular inflammatory infiltrate remained in 81%, apparently unrelated to fatty degeneration. As liver biochemical variables had been found within normal limits in 92.3% of patients at initial biopsy, no difference was found 2 years later. Lipid profile and blood sugar plasma concentration were closer to normal in all patients after 2 years (P < 0.05).

CONCLUSIONS

Aspects of NAFLD including steatohepatitis improved significantly with massive weight loss at 2 years after RYGB surgery. No patient in this series had progression of hepatic fibrosis.