Cellular glutathione in fatty liver in vitro models

Plasma cystine/methionine ratio is associated with left ventricular diastolic function in patients with heart disease

Elevated circulating homocysteine (Hcy) is a well-known risk factor for cardiovascular diseases (CVDs), including coronary artery disease (CAD) and heart failure (HF). It remains unclear how Hcy and its derivatives relate to left ventricular (LV) diastolic function. The aim of the present study was to investigate the relationship between plasma Hcy-related metabolites and diastolic dysfunction (DD) in patients with heart disease (HD). A total of 62 HD patients with preserved LV ejection fraction (LVEF ≥ 50%) were enrolled. Plasma Hcy and its derivatives were measured by liquid chromatography‒mass spectrometry (LC-MS/MS). Spearman's correlation test and multiple linear regression models were used to analyze the associations between metabolite levels and LV diastolic function. The cystine/methionine (CySS/Met) ratio was positively correlated with LV diastolic function, which was defined from the ratio of mitral inflow E and mitral e' annular velocities (E/e') (Spearman's r = 0.43, p < 0.001). When the subjects were categorized into two groups by E/e', the high-E/e' group had a significantly higher CySS/Met ratio than the low-E/e' group (p = 0.002). Multiple linear regression models revealed that the CySS/Met ratio was independently associated with E/e' after adjustment for age, sex, body mass index (BMI), diabetes mellitus, hypertension, chronic kidney disease (CKD),　hemoglobin, and lipid peroxide (LPO) {standardized β (95% CI); 0.14 (0.04-0.23); p = 0.005}. Hcy, CySS, and Met did not show a significant association with E/e' in the same models. A high plasma CySS/Met ratio reflected DD in patients with HD.

Differential effects of bariatric surgery and caloric restriction on hepatic one-carbon and fatty acid metabolism

Weight loss interventions, including dietary changes, pharmacotherapy, or bariatric surgery, prevent many of the adverse consequences of obesity, and may also confer intervention-specific benefits beyond those seen with decreased weight alone. We compared the molecular effects of different interventions on liver metabolism to understand the mechanisms underlying these benefits. Male rats on a high-fat, high-sucrose diet underwent sleeve gastrectomy (SG) or intermittent fasting with caloric restriction (IF-CR), achieving equivalent weight loss. The interventions were compared to ad-libitum (AL)-fed controls. Analysis of liver and blood metabolome and transcriptome revealed distinct and sometimes contrasting metabolic effects between the two interventions. SG primarily influenced one-carbon metabolic pathways, whereas IF-CR increased de novo lipogenesis and glycogen storage. These findings suggest that the unique metabolic pathways affected by SG and IF-CR contribute to their distinct clinical benefits, with bariatric surgery potentially influencing long-lasting changes through its effect on one-carbon metabolism.

Beneficial Effects of Standardized Extracts from Wastes of Red Oranges and Olive Leaves

The awareness of the large amount of waste produced along the food chain, starting in the agricultural sector and continuing across industrial transformation to the domestic context, has in recent years also aroused strong concern amongst the public, who are ing about the possible consequences that this could have on environmental sustainability, resource waste and human health. The aim of the present research is the recovery of substances with high added value from waste and by-products typical of the Mediterranean area, such as the residue from the industrial processing of red oranges, called pastazzo (peels, pulps and seeds), which is particularly rich in anthocyanins, flavanones and hydroxycinnamic acids, and has numerous nutraceutical properties, as well as the olive leaves coming from olive-tree pruning, which are rich in substances such as oleuropein, elenolic acid, hydroxytyrosol, tyrosol and rutin. The effect of Red Orange Extract (ROE) and Olive Leaf Extract (OLE) on HepG2 fatty storage capacity was assessed performing Oil Red O’ staining, and antioxidant properties of the extracts were evaluated following the steatosis model onset. Based on the results obtained, the preparation of natural extracts that are derived from these waste products can be useful for preventing, counteracting or delaying the onset of the complications of fatty liver disease, such as hepatic steatosis.

In Vitro Hepatoprotective and Human Gut Microbiota Modulation of Polysaccharide-Peptides in Pleurotus citrinopileatus

Pleurotus citrinopileatus, a golden oyster mushroom, is popular in Asia and has pharmacological functions. However, the effects of polysaccharide-peptides extracted from Pleurotus citrinopileatus and underlying mechanism on digestive systme have not yet been clarified. Here, we determined the composition of two polysaccharide-peptides (PSI and PSII) from P. citrinopileatus and investigated the protective effects of on hepatoprotective and gut microbiota. The results showed that PSI and PSII were made up of similar monosaccharide moieties, except for the varying ratios. Furthermore, PSI and PSII showed that they have the hepatoprotective effects and significantly increased the viabilities and cellular total superoxide dismutase activities increased significantly in HepG2 cells. Intracellular triglyceride content and extracellular alanine aminotransferase and aspartate transaminase contents markedly decreased following treatment with 40 and 50 μg/mL PSI and PSII, respectively. Moreover, PSI and PSII activated the adiponectin pathway and reduced lipid accumulation in liver cells. PSI and PSII elevated short-chain fatty acid concentrations, especially butyric and acetic acids. 16S rRNA gene sequencing analysis showed that PSI promoted the relative abundances of Bifidobacteria, Lactobacillus, Faecalibacterium, as well as Prevotella generas in the gut. PSII markedly suppressed the relative abundances of Escherichia-Shigella and Bacteroides generas. We speculate that the PSI and PSII play a role through liver-gut axis system. Polysaccharide-peptides metabolize by gut microbiota to produce short-chain fatty acids (SCFAs) and in turn influence liver functions.

In vitro models for non-alcoholic fatty liver disease: Emerging platforms and their applications

Non-alcoholic fatty liver disease (NAFLD) represents a global healthcare challenge, affecting 1 in 4 adults, and death rates are predicted to rise inexorably. The progressive form of NAFLD, non-alcoholic steatohepatitis (NASH), can lead to fibrosis, cirrhosis, and hepatocellular carcinoma. However, no medical treatments are licensed for NAFLD-NASH. Identifying efficacious therapies has been hindered by the complexity of disease pathogenesis, a paucity of predictive preclinical models and inadequate validation of pharmacological targets in humans. The development of clinically relevant in vitro models of the disease will pave the way to overcome these challenges. Currently, the combined application of emerging technologies (e.g., organ-on-a-chip/microphysiological systems) and control engineering approaches promises to unravel NAFLD biology and deliver tractable treatment candidates. In this review, we will describe advances in preclinical models for NAFLD-NASH, the recent introduction of novel technologies in this space, and their importance for drug discovery endeavors in the future.

The Role of the Transsulfuration Pathway in Non-Alcoholic Fatty Liver Disease

The prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing and approximately 25% of the global population may have NAFLD. NAFLD is associated with obesity and metabolic syndrome, but its pathophysiology is complex and only partly understood. The transsulfuration pathway (TSP) is a metabolic pathway regulating homocysteine and cysteine metabolism and is vital in controlling sulfur balance in the organism. Precise control of this pathway is critical for maintenance of optimal cellular function. The TSP is closely linked to other pathways such as the folate and methionine cycles, hydrogen sulfide (H₂S) and glutathione (GSH) production. Impaired activity of the TSP will cause an increase in homocysteine and a decrease in cysteine levels. Homocysteine will also be increased due to impairment of the folate and methionine cycles. The key enzymes of the TSP, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), are highly expressed in the liver and deficient CBS and CSE expression causes hepatic steatosis, inflammation, and fibrosis in animal models. A causative link between the TSP and NAFLD has not been established. However, dysfunctions in the TSP and related pathways, in terms of enzyme expression and the plasma levels of the metabolites (e.g., homocysteine, cystathionine, and cysteine), have been reported in NAFLD and liver cirrhosis in both animal models and humans. Further investigation of the TSP in relation to NAFLD may reveal mechanisms involved in the development and progression of NAFLD.

Baicalin attenuates hepatic injury in non-alcoholic steatohepatitis cell model by suppressing inflammasome-dependent GSDMD-mediated cell pyroptosis

Baicalin (BA), a flavone glycoside, is the constituent of Scutellaria baicalensis, a Chinese herbal medicine used to treat non-alcoholic steatohepatitis (NASH). However, the mechanism of BA on NASH is still not clear. Here, the improving effect of BA on hepatocyte through inhibition of pyroprosis was investigated in vitro. With a cell model of NASH exposing HepG2 cells in free fatty acids (FFA), we revealed that BA could improve hepatocyte from FFA-induced morphological damage and death. And then through transcriptomes screening, a significant down-regulation of NLR pyrin domain containing 3 (Nlrp3), gasdermin D (Gsdmd), andinterleukin-1 beta (IL-1β) expression were found after BA treatment. Further analysis confirmed that BA could decrease the levels of NLRP3 and GSDMD, as well as the release of IL-1β and IL-18, resulting in the reduction of pyroptosis. Moreover, the improving effect of BA could be attenuated by Gsdmd knockdown. In conclusion, BA can reduce pyroptosis of hepatocyte by blocking NLRP3-GSDMD signaling in vitro.

CYP4A11 is involved in the development of nonalcoholic fatty liver disease via ROS‑induced lipid peroxidation and inflammation

Nonalcoholic fatty liver disease (NAFLD) is a fat metabolism disorder that occurs in liver cells. The development of NAFLD is considered to be associated with hepatic oxidative stress. The present study aimed to investigate the role of cytochrome P450 4A11 (CYP4A11) in the pathogenesis of NAFLD. The levels of plasma CYP4A11 and lipid peroxidation products levels exhibited a high correlation, and were increased significantly compared with those from normal subjects. Further in vitro studies demonstrated that the expression levels of CYP4A11 and the content of reactive oxygen species (ROS) were increased in free fatty acid (FFA)-stimulated HepG2 cells. Clofibrate, a CYP4A11 inducer, aggravated cell damage. Opposite results were observed for the CYP4A11 inhibitor HET0016, which attenuated apoptosis in FFA-treated cells. Furthermore, CYP4A11 gene overexpression and silencing were used to investigate the effects on inflammatory cytokine secretion. The data demonstrated that CYP4A11 promoted an increase in the mRNA expression of tumor necrosis factor α, interleukin (IL)-1β and IL-6 in response to FFA. In addition, western blot analysis highlighted that CYP4A11 caused an upregulation of phosphorylated p65 levels and therefore affected the NF-κB signaling pathway. The data demonstrated that CYP4A11 may metabolize fatty acids to promote the production of ROS and accelerate the progression of NAFLD.

Water Extract of Curcuma longa L. Ameliorates Non-Alcoholic Fatty Liver Disease

Our aim was to investigate whether hot water extract (CLW) of Curcuma longa L. could prevent non-alcoholic fatty liver disease (NAFLD). HepG2 cells were treated with free fatty acid (FFA) mixture (oleic acid: palmitic acid, 2:1) for 24 h to stimulate in vitro fatty liver. In addition, C57BL/6 mice were fed 60 kcal% high-fat (HF) diet for eight weeks to induce fatty liver in vivo. Intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) productions were increased by FFA and HF-diet, but supplementation with CLW significantly decreased these levels. CLW treatment ameliorated antioxidant activities that were suppressed by exposure to the FFA and HF-diet. Cluster of differentiation 36 (CD36) and fatty acid transport proteins (FATP2 and FATP5) were increased in HF-diet groups, while CLW suppressed their expression levels. Moreover, sterol regulatory element-binding protein-1c (SREBP-1c), acetyl-coenzyme A carboxylase (ACC), and fatty acid synthase (FAS) expression levels were down-regulated in the CLW groups compared to HF-diet groups. On the other hand, 5′ adenosine monophosphate-activated protein kinase (AMPK), Peroxisome proliferator-activated receptor alpha (PPAR-α), and carnitine palmitoyltransferase 1 (CPT-1) expressions were up-regulated in the CLW groups. HF-diet fed mice showed high hepatic triglycerides (TG) content compared to the normal diet mice. However, the administration of CLW restored the hepatic TG level, indicating an inhibitory effect against lipid accumulation by CLW. These results suggest that CLW could be a potentially useful agent for the prevention of NAFLD through modulating fatty acid uptake.

First demonstration of protective effects of purified mushroom polysaccharide-peptides against fatty liver injury and the mechanisms involved

Fatty liver (FLD) disease is a consequence of metabolic syndrome, which is a health problem worldwide with a phenomenal rise in prevalence. In this study, two hepatoprotective polysaccharide-peptides were extracted from the mushroom Auricularia polytricha followed by chromatographic fractionation of the extract on the ion exchanger DEAE-cellulose and gel filtration on Sephadex-200 to yield two purified fractions: APPI and APPII. The monosaccharide compositions, FT-IR, N-terminal sequences, internal peptide sequences and molecular weights of the two fractions were determined. Furthermore, their hepatoprotective effect on human hepatoma HepG2 cells in vitro and in an animal model of fatty liver disease was evidenced by the findings that APPI and APPII diminished lipid deposit in cells, blood and the liver, increased cellular antioxidant activity and viability, and protected the liver against injury. The mechanistic study revealed that APPI and APPII activated the adiponectin pathway, up-regulated expression of genes controlling free fatty acid (FFA) oxidation, such as AMPK, CPTl, ACOX1 and PPARα genes, enhanced lipid metabolism, preserved hepatic function, promoted the antioxidant defense system and reduced lipid peroxidation. Hence the bioactive compounds of A. polytricha could serve as therapeutic agents in the food and pharmaceutical industries.

Chemokine (C-C motif) ligand 2 gene ablation protects low-density lipoprotein and paraoxonase-1 double deficient mice from liver injury, oxidative stress and inflammation

The risk of non-alcoholic fatty liver disease increases with obesity. Vulnerability to oxidative stress and/or inflammation represents a crucial step in non-alcoholic fatty liver disease progression through abnormal metabolic responses. In this study, we investigated the role of CCL2 gene ablation in mice that were double deficient in low density lipoprotein receptor and in paraoxonase-1. Mass spectrometry methods were used to assess the liver metabolic response in mice fed either regular chow or a high-fat diet. Dietary fat caused liver steatosis, oxidative stress and the accumulation of pro-inflammatory macrophages in the livers of double deficient mice. We observed alterations in energy metabolism-related pathways and in metabolites associated with the methionine cycle and the glutathione reduction pathway. This metabolic response was associated with impaired autophagy. Conversely, when we established CCL2 deficiency, histologic features of fatty liver disease were abrogated, hepatic liver oxidative stress decreased, and anti-inflammatory macrophage marker expression levels increased. These changes were associated with the normalization of metabolic disturbances and increased lysosome-associated membrane protein 2, expression, which suggests enhanced chaperone-mediated autophagy. This study demonstrates that CCL2 is a key molecule for the development of metabolic and histological alterations in the liver of mice sensitive to the development of hyperlipidemia and hepatic steatosis, a finding with potential to identify new therapeutic targets in liver diseases.

A Pathophysiological Model of Non-Alcoholic Fatty Liver Disease Using Precision-Cut Liver Slices

Non-alcoholic fatty liver disease (NAFLD) is a common liver disorder closely related to metabolic syndrome. NAFLD can progress to an inflammatory state called non-alcoholic steatohepatitis (NASH), which may result in the development of fibrosis and hepatocellular carcinoma. To develop therapeutic strategies against NAFLD, a better understanding of the molecular mechanism is needed. Current in vitro NAFLD models fail to capture the essential interactions between liver cell types and often do not reflect the pathophysiological status of patients. To overcome limitations of commonly used in vitro and in vivo models, precision-cut liver slices (PCLSs) were used in this study. PCLSs, prepared from liver tissue obtained from male Wistar rats, were cultured in supraphysiological concentrations of glucose, fructose, insulin, and palmitic acid to mimic metabolic syndrome. Accumulation of lipid droplets was visible and measurable after 24 h in PCLSs incubated with glucose, fructose, and insulin, both in the presence and absence of palmitic acid. Upregulation of acetyl-CoA carboxylase 1 and 2, and of sterol responsive element binding protein 1c, suggests increased de novo lipogenesis in PCLSs cultured under these conditions. Additionally, carnitine palmitoyltransferase 1 expression was reduced, which indicates impaired fatty acid transport and disrupted mitochondrial β-oxidation. Thus, steatosis was successfully induced in PCLSs with modified culture medium. This novel ex vivo NAFLD model could be used to investigate the multicellular and molecular mechanisms that drive NAFLD development and progression, and to study potential anti-steatotic drugs.

Attenuation of diethylnitrosamine (DEN) - Induced hepatic cancer in experimental model of Wistar rats by Carissa carandas embedded silver nanoparticles

OBJECTIVE

Hepatic cancer is well known, and leading cancer around the world and remain asymptomatic diseases. Carissa carandas possess anti-proliferative, antioxidant, hepatoprotective property and used in hepatic cancer. The current study deals to evaluate the chemoprotective and therapeutic property of Carissa carandas embedded silver nanoparticles (CCAgNPs) against diethylnitrosamine (DEN) -induced hepatic cancer.

MATERIAL AND METHOD

Wistar rats were divided into six groups and hepatic cancer was induced with diethylnitrosamine at the dose of 200 mg/kg BW. The animals were gastrogavaged with standard drug and CCAgNPs for 16 weeks. Serum biomarkers, haematological profile, antioxidants enzymes, inflammatory markers and membrane bound enzymes were assessed to find the anti-proliferative potential of silver nanoparticles. Histological evaluation and microscopic characterizations were also performed to authenticate the outcomes of the present work.

RESULTS

Biosynthesized CCAgNPs significantly down-regulated the serum marker enzymes of hepatic and non-hepatic parameter, elevated the levels of enzymatic and non-enzymatic antioxidant profile, elevation in membrane bound enzymes and diminish the levels of inflammatory markers (IL-6, TNF-α, and IL-1β) via NF-κB pathway. Histopathological features also showed recovery of a hepatic architecture in cancer-induced rats in a dose-dependent manner.

CONCLUSION

Our consequences established that such plant mediated silver nanoparticles shown a defensive impact against DEN-induced hepatocarcinogenesis, and serves as a better option to ameliorate the clinical results against hepatocellular carcinoma.

Steroidogenic acute regulatory protein (StAR) overexpression attenuates HFD-induced hepatic steatosis and insulin resistance

Non-alcoholic fatty liver disease (NAFLD) covers a wide spectrum of liver pathology. Intracellular lipid accumulation is the first step in the development and progression of NAFLD. Steroidogenic acute regulatory protein (StAR) plays an important role in the synthesis of bile acid and intracellular lipid homeostasis and cholesterol metabolism. We hypothesize that StAR is involved in non-alcoholic fatty liver disease (NAFLD) pathogenesis. The hypothesis was identified using free fatty acid (FFA)-overloaded NAFLD in vitro model and high-fat diet (HFD)-induced NAFLD mouse model transfected by recombinant adenovirus encoding StAR (StAR). StAR expression was also examined in pathology samples of patients with fatty liver by immunohistochemical staining. We found that the expression level of StAR was reduced in the livers obtained from fatty liver patients and NAFLD mice. Additionally, StAR overexpression decreased the levels of hepatic lipids and maintained the hepatic glucose homeostasis due to the activation of farnesoid x receptor (FXR). StAR overexpression attenuated the impairment of insulin signaling in fatty liver. This protective role of StAR was owing to a reduction of intracellular diacylglycerol levels and the phosphorylation of PKCε. Furthermore, FXR inactivation reversed the observed beneficial effects of StAR. The present study revealed that StAR overexpression can reduce hepatic lipid accumulation, regulate glucose metabolism and attenuate insulin resistance through a mechanism involving the activation of FXR. Our study suggests that StAR may be a potential therapeutic target for NAFLD.

A Western diet induced NAFLD in LDLR(-/)(-) mice is associated with reduced hepatic glutathione synthesis

Oxidative stress plays a key role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Glutathione is the major anti-oxidant involved in cellular oxidative defense, however there are currently no simple non-invasive methods for assessing hepatic glutathione metabolism in patients with NAFLD. As a primary source of plasma glutathione, liver plays an important role in interorgan glutathione homeostasis. In this study, we have tested the hypothesis that measurements of plasma glutathione turnover could be used to assess the hepatic glutathione metabolism in LDLR(-/)(-) mice, a mouse model of diet-induced NAFLD. Mice were fed a standard low fat diet (LFD) or a high fat diet containing cholesterol (a Western type diet (WD)). The kinetics of hepatic and plasma glutathione were quantified using the (2)H2O metabolic labeling approach. Our results show that a WD leads to reduced fractional synthesis rates (FSR) of hepatic (25%/h in LFD vs. 18%/h in WD, P<0.05) and plasma glutathione (43%/h in LFD vs. 21%/h in WD, P<0.05), without any significant effect on their absolute production rates (PRs). WD-induced concordant changes in both hepatic and plasma glutathione turnover suggest that the plasma glutathione turnover measurements could be used to assess hepatic glutathione metabolism. The safety, simplicity, and low cost of the (2)H2O-based glutathione turnover approach suggest that this method has the potential for non-invasive probing of hepatic glutathione metabolism in patients with NAFLD and other diseases.

S-Propargyl-cysteine Exerts a Novel Protective Effect on Methionine and Choline Deficient Diet-Induced Fatty Liver via Akt/Nrf2/HO-1 Pathway

This study investigated the antioxidative effect of S-propargyl-cysteine (SPRC) on nonalcoholic fatty liver (NAFLD) by treating mice fed a methionine and choline deficient (MCD) diet with SPRC for four weeks. We found that SPRC significantly reduced hepatic reactive oxygen species (ROS) and methane dicarboxylic aldehyde (MDA) levels. Moreover, SPRC also increased the superoxide dismutase (SOD) activity. By Western blot, we found that this protective effect of SPRC was importantly attributed to the regulated hepatic antioxidant-related proteins, including protein kinase B (Akt), heme oxygenase-1 (HO-1), nuclear factor erythroid 2-related factor 2 (Nrf2), and cystathionine γ-lyase (CSE, an enzyme that synthesizes hydrogen sulfide). Next, we examined the detailed molecular mechanism of the SPRC protective effect using oleic acid- (OA-) induced HepG2 cells. The results showed that SPRC significantly decreased intracellular ROS and MDA levels in OA-induced HepG2 cells by upregulating the phosphorylation of Akt, the expression of HO-1 and CSE, and the translocation of Nrf2. SPRC-induced HO-1 expression and Nrf2 translocation were abolished by the phosphoinositide 3-kinase (PI3K) inhibitor LY294002. Moreover, the antioxidative effect of SPRC was abolished by CSE inhibitor DL-propargylglycine (PAG) and HO-1 siRNA. Therefore, these results proved that SPRC produced an antioxidative effect on NAFLD through the PI3K/Akt/Nrf2/HO-1 signaling pathway.

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.

Reduced oxidative stress contributes to the lipid lowering effects of isoquercitrin in free fatty acids induced hepatocytes

Oxidative stress interferes with hepatic lipid metabolism at various levels ranging from benign lipid storage to so-called second hit of inflammation activation. Isoquercitrin (IQ) is widely present flavonoid but its effects on hepatic lipid metabolism remain unknown. We used free fatty acids (FFA) induced lipid overload and oxidative stress model in two types of liver cells and measured cell viability, intracellular lipids, and reactive oxygen species (ROS) within hepatocytes. In addition, Intracellular triglycerides (TG), superoxide dismutase (SOD), and malondialdehyde (MDA) were examined. A novel in vitro model was used to evaluate correlation between lipid lowering and antioxidative activities. Furthermore, 34 major cytokines and corresponding ROS levels were analyzed in FFA/LPS induced coculture model between hepatocytes and Kupffer cells. At molecular level AMPK pathway was elucidated. We showed that IQ attenuated FFA induced lipid overload and ROS within hepatocytes. Further, IQ reversed FFA induced increase in intracellular TG SOD and MDA. It was shown that antioxidative activity of IQ correlates with its lipid lowering potentials. IQ reversed major proinflammatory cytokines and oxidative stress in FFA/LPS induced coculture model. Finally, AMPK pathway was found responsible for metabolic benefits at molecular level. IQ strikingly manifests antioxidative and related lipid lowering activities in hepatocytes.

Antioxidant properties of proanthocyanidins attenuate carbon tetrachloride (CCl4)-induced steatosis and liver injury in rats via CYP2E1 regulation

Liver steatosis is characterized by lipid dysregulation and fat accumulation in the liver and can lead to oxidative stress in liver. Since proanthocyanidins are present in plant-based foods and have powerful antioxidant properties, we investigated whether proanthocyanidins can prevent oxidative stress and subsequent liver injury. Carbon tetrachloride (CCl4) treatment can cause steatosis in rats that models both alcoholic and non-alcoholic fatty liver disease in humans. We pre-treated rats by oral administration of proanthocyanidins extracted from grape seeds 7 days prior to intragastrically administering CCl4. Proanthocyanidin treatment continued for an additional 2 weeks, after which time liver and serum were harvested, and mediators of liver injury, oxidative stress, and histological features were evaluated. CCl4-treated rats exhibited significant increases in the following parameters as compared to non-treated rats: fat droplets in the liver, liver injury (ALT, AST), and DNA damage (8-OHdG). Additionally, CCl4 treatment decreased antioxidant enzymes SOD, GSH, GPX, and CAT in the liver due to their rapid depletion after battling against oxidative stress. Compared to CCl4-treated rats, treatment with proanthocyanidins effectively suppressed lipid accumulation, liver injury, DNA damage, as well as restored antioxidant enzyme levels. Further investigation revealed that proanthocyanidins treatment also inhibited expression of CYP2E1 in liver, which prevented the initial step of generating free radicals from CCl4. The data presented here show that treatment with orally administered proanthocyanidins prevented liver injury in the CCl4-induced steatosis model, likely through exerting antioxidant actions to suppress oxidative stress and inhibiting the free radical-generating CYP2E1 enzyme.

The effect of tert-butyl hydroperoxide-induced oxidative stress on lean and steatotic rat hepatocytes in vitro

Oxidative stress and mitochondrial dysfunction play an important role in the pathogenesis of nonalcoholic fatty liver disease and toxic liver injury. The present study was designed to evaluate the effect of exogenous inducer of oxidative stress (tert-butyl hydroperoxide, tBHP) on nonfatty and steatotic hepatocytes isolated from the liver of rats fed by standard and high-fat diet, respectively. In control steatotic hepatocytes, we found higher generation of ROS, increased lipoperoxidation, an altered redox state of glutathione, and decreased ADP-stimulated respiration using NADH-linked substrates, as compared to intact lean hepatocytes. Fatty hepatocytes exposed to tBHP exert more severe damage, lower reduced glutathione to total glutathione ratio, and higher formation of ROS and production of malondialdehyde and are more susceptible to tBHP-induced decrease in mitochondrial membrane potential. Respiratory control ratio of complex I was significantly reduced by tBHP in both lean and steatotic hepatocytes, but reduction in NADH-dependent state 3 respiration was more severe in fatty cells. In summary, our results collectively indicate that steatotic rat hepatocytes occur under conditions of enhanced oxidative stress and are more sensitive to the exogenous source of oxidative injury. This confirms the hypothesis of steatosis being the first hit sensitizing hepatocytes to further damage.

Precision-cut liver slices from diet-induced obese rats exposed to ethanol are susceptible to oxidative stress and increased fatty acid synthesis

Oxidative stress from fat accumulation in the liver has many deleterious effects. Many believe that there is a second hit that causes relatively benign fat accumulation to transform into liver failure. Therefore, we evaluated the effects of ethanol on ex vivo precision-cut liver slice cultures (PCLS) from rats fed a high-fat diet resulting in fatty liver. Age-matched male Sprague-Dawley rats were fed either high-fat (obese) (45% calories from fat, 4.73 kcal/g) or control diet for 13 mo. PCLS were prepared, incubated with 25 mM ethanol for 24, 48, and 72 h, harvested, and evaluated for ethanol metabolism, triglyceride production, oxidative stress, and cytokine expression. Ethanol metabolism and acetaldehyde production decreased in PCLS from obese rats compared with age-matched controls (AMC). Increased triglyceride and smooth muscle actin production was observed in PCLS from obese rats compared with AMC, which further increased following ethanol incubation. Lipid peroxidation, measured by thiobarbituric acid reactive substances assay, increased in response to ethanol, whereas GSH and heme oxygenase I levels were decreased. TNF-α and IL-6 levels were increased in the PCLS from obese rats and increased further with ethanol incubation. Diet-induced fatty liver increases the susceptibility of the liver to toxins such as ethanol, possibly by the increased oxidative stress and cytokine production. These findings support the concept that the development of fatty liver sensitizes the liver to the effects of ethanol and leads to the start of liver failure, necrosis, and eventually cirrhosis.

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

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

Oxidative stress rather than triglyceride accumulation is a determinant of mitochondrial dysfunction in in vitro models of hepatic cellular steatosis

BACKGROUND/AIMS

There is still debate about the relationship between fat accumulation and mitochondrial function in nonalcoholic fatty liver disease. It is a critical question as only a small proportion of individuals with steatosis progress to steatohepatitis. In this study, we focused on defining (i) the effects of triglyceride accumulation and reactive oxygen species (ROS) on mitochondrial function (ii) the contributions of triglyceride, ROS and subsequent mitochondrial impairment on the metabolism of energy substrates.

METHODS

Human hepatoblastoma C3A cells, were treated with various combinations of oleate, octanoate, lactate (L), pyruvate (P) and ammonia (N) acutely or for 72 h, before measurements of triglyceride concentration, cell respiration, ROS production, mitochondrial membrane potential, ketogenesis and gluconeogenesis, TCA cycle metabolite analysis and electron microscopy.

RESULTS

Acutely, LPON treatment enhanced mitochondrial respiration and ROS formation. After 72 h, despite the similarities in triglyceride accumulation, LPON treatment, but not oleate, dramatically affected mitochondrial function as evidenced by decreased respiration, increased mitochondrial membrane potential and ROS formation with concomitant enhanced ketogenesis. By comparison, respiration and ROS formation remained unperturbed with oleate. Importantly, this was accompanied by an increased gluconeogenesis and ketogenesis. The addition of the antioxidant N-acetyl-L-cysteine prevented mitochondrial dysfunction and reversed metabolic changes seen with LPON, strongly suggesting ROS involvement in mediating mitochondrial impairment.

CONCLUSIONS

Our data indicate that ROS formation, rather than cellular steatosis per se, impairs mitochondrial function. Thus, reduction in cellular steatosis may not always be the desired outcome without concomitant improvement in mitochondrial function and/or reducing of ROS formation.

Effect of intracellular lipid accumulation in a new model of non-alcoholic fatty liver disease

Background

In vitro exposure of liver cells to high concentrations of free fatty acids (FFA) results in fat overload which promotes inflammatory and fibrogenic response similar to those observed in patients with Non-Alcoholic Fatty Liver Disease (NAFLD) and Non-Alcoholic Steatohepatitis (NASH). Since the mechanisms of this event have not been fully characterized, we aimed to analyze the fibrogenic stimuli in a new in vitro model of NASH.

Methods

HuH7 cells were cultured for 24 h in an enriched medium containing bovine serum albumin and increasing concentrations of palmitic and oleic acid at a molar ratio of 1:2 (palmitic and oleic acid, respectively). Cytotoxic effect, apoptosis, oxidative stress, and production of inflammatory and fibrogenic cytokines were measured.

Results

FFA induces a significant increment in the intracellular content of lipid droplets. The gene expression of interleukin-6, interleukin-8 and tumor necrosis factor alpha was significantly increased. The protein level of interleukin-8 was also increased. Intracellular lipid accumulation was associated to a significant up-regulation in the gene expression of transforming growth factor beta 1, alpha 2 macroglobulin, vascular endothelial growth factor A, connective tissue growth factor, insulin-like growth factor 2, thrombospondin 1. Flow cytometry analysis demonstrated a significant increment of early apoptosis and production of reactive oxygen species.

Conclusions

The exposure of hepatocytes to fatty acids elicits inflammation, increase of oxidative stress, apoptosis and production of fibrogenic cytokines. These data support a primary role of FFA in the pathogenesis of NAFLD and NASH.

Glutathione-deficient mice are susceptible to TCDD-Induced hepatocellular toxicity but resistant to steatosis

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) generates both hepatocellular injury and steatosis, processes that involve oxidative stress. Herein, we evaluated the role of the antioxidant glutathione (GSH) in TCDD-induced hepatotoxicity. Glutamate-cysteine ligase (GCL), comprising catalytic (GCLC) and modifier (GCLM) subunits, is rate limiting in de novo GSH biosynthesis; GCLM maintains GSH homeostasis by optimizing the catalytic efficiency of GCL holoenzyme. Gclm(-/-) transgenic mice exhibit 10-20% of normal tissue GSH levels. Gclm(-/-) and Gclm(+/+) wild-type (WT) female mice received TCDD for 3 consecutive days and were then examined 21 days later. As compared with WT littermates, Gclm(-/-) mice were more sensitive to TCDD-induced hepatocellular toxicity, exhibiting lower reduction potentials for GSH, lower ATP levels, and elevated levels of plasma glutamic oxaloacetic transaminase (GOT) and γ-glutamyl transferase (GGT). However, the histopathology showed that TCDD-mediated steatosis, which occurs in WT mice, was absent in Gclm(-/-) mice. This finding was consistent with cDNA microarray expression analysis, revealing striking deficiencies in lipid biosynthesis pathways in Gclm(-/-) mice; qrt-PCR analysis confirmed that Gclm(-/-) mice are deficient in expression of several lipid metabolism genes including Srebp2, Elovl6, Fasn, Scd1/2, Ppargc1a, and Ppara. We suggest that whereas GSH protects against TCDD-mediated hepatocellular damage, GSH deficiency confers resistance to TCDD-induced steatosis due to impaired lipid metabolism.