Thioredoxin-binding protein-2 deficiency enhances methionine-choline deficient diet-induced hepatic steatosis but inhibits steatohepatitis in mice

Absence of TXNIP in Humans Leads to Lactic Acidosis and Low Serum Methionine Linked to Deficient Respiration on Pyruvate

Thioredoxin-interacting protein (TXNIP) is an α-arrestin that can bind to and inhibit the antioxidant protein thioredoxin (TXN). TXNIP expression is induced by glucose and promotes β-cell apoptosis in the pancreas, and deletion of its gene in mouse models protects against diabetes. TXNIP is currently studied as a potential new target for antidiabetic drug therapy. In this study, we describe a family with a mutation in the TXNIP gene leading to nondetectable expression of TXNIP protein. Symptoms of affected family members include lactic acidosis and low serum methionine levels. Using patient-derived TXNIP-deficient fibroblasts and myoblasts, we show that oxidative phosphorylation is impaired in these cells when given glucose and pyruvate but normalized with malate. Isolated mitochondria from these cells appear to have normal respiratory function. The cells also display a transcriptional pattern suggestive of a high basal activation of the Nrf2 transcription factor. We conclude that a complete lack of TXNIP in human is nonlethal and leads to specific metabolic distortions that are, at least in part, linked to a deficient respiration on pyruvate. The results give important insights into the impact of TXNIP in humans and thus help to further advance the development of antidiabetic drugs targeting this protein.

Thioredoxin-interacting protein deficiency ameliorates kidney inflammation and fibrosis in mice with unilateral ureteral obstruction

Thioredoxin-interacting protein (TXNIP) is associated with inflammation, tubulointerstitial fibrosis, and oxidative stress in diabetic kidney disease, yet the potential role of TXNIP in nondiabetic renal injury is not well known. This study aimed to investigate the effect of TXNIP on renal injury by creating a unilateral ureteral obstruction (UUO) model in TXNIP knockout (TKO) mice. We performed sham or UUO surgery in 8-week-old TXNIP KO male mice and age and sex-matched wild-type (WT) mice. Animals were killed at 3, 5, 7, or 14 days after surgery, and renal tissues were obtained for RNA, protein, and other analysis. Our results show that the expression of TXNIP was increased in a time-dependent manner in the ligated kidneys. TXNIP deletion reduced renal fibrosis, apoptosis, α-SMA, TGF-β1 and CTGF expression, and activation of Smad3, p38 MAPK, and ERK1/2 in UUO kidneys. We also found UUO-induced renal F4/80+ macrophage infiltration, MCP-1 expression and activation of NF-κB and NLRP3 inflammasome were attenuated in TKO mice. Furthermore, our study revealed that TXNIP deficiency inhibited the expression of 8-OHdG, heme oxygenase-1 (HO-1) and NADPH oxidase 4 (Nox4) in UUO kidney. In summary, our study suggests that TXNIP plays a key role in the renal inflammation and fibrosis induced by UUO. Inhibition of TXNIP may be a strategy to slow the progression of chronic kidney diseases.

TXNIP in Metabolic Regulation: Physiological Role and Therapeutic Outlook

Background & Objective:

Thioredoxin-interacting protein (TXNIP) also known as thioredoxin binding protein-2 is a ubiquitously expressed protein that interacts and negatively regulates expression and function of Thioredoxin (TXN). Over the last few years, TXNIP has attracted considerable attention due to its wide-ranging functions impacting several aspects of energy metabolism. TXNIP acts as an important regulator of glucose and lipid metabolism through pleiotropic actions including regulation of β-cell function, hepatic glucose production, peripheral glucose uptake, adipogenesis, and substrate utilization. Overexpression of TXNIP in animal models has been shown to induce apoptosis of pancreatic β-cells, reduce insulin sensitivity in peripheral tissues like skeletal muscle and adipose, and decrease energy expenditure. On the contrary, TXNIP deficient animals are protected from diet induced insulin resistance and type 2 diabetes.

Summary:

Consequently, targeting TXNIP is thought to offer novel therapeutic opportunity and TXNIP inhibitors have the potential to become a powerful therapeutic tool for the treatment of diabetes mellitus. Here we summarize the current state of our understanding of TXNIP biology, highlight its role in metabolic regulation and raise critical questions that could help future research to exploit TXNIP as a therapeutic target.

Deletion of Thioredoxin-interacting protein ameliorates high fat diet-induced non-alcoholic steatohepatitis through modulation of Toll-like receptor 2-NLRP3-inflammasome axis: Histological and immunohistochemical study

Endemic prevalence of obesity is associated with alarming increases in non-alcoholic steatohepatitis (NASH) with limited available therapeutics. Toll-like receptor2 (TLR2) and Nod-like receptor protein 3 (NLRP3) Inflammasome are implicated in hepatic steatosis, inflammation and fibrosis; the histological landmark stages of NASH. TXNIP, a member of α-arrestin family activates NLRP3 in response to various danger stimuli. The aim of current work was to investigate the effect of TXNIP genetic deletion on histological manifestations of high fat diet-induced steatohepatitis and activation of TLR2-NLRP3-inflammasome axis. Wild-type mice (WT) and TXNIP knock out (TKO) littermates were randomized to normal diet (WT-ND and TKO-ND) or high fat diet (HFD, 60% fat) (WT-HFD and TKO-HFD). After 8-weeks, liver samples from all groups were evaluated by histological, immunohistochemical and western blot analysis. HFD resulted in significant induction of micro and macrovesicular hepatic steatosis, that was associated with increased inflammatory immune cell infiltration in WT-HFD compared with WT-ND and TKO-ND controls, but not in TKO-HFD group. In parallel, WT-HFD group showed significant fibrosis and α-SMA expression; a marker of pro-fibrotic stellate-cell activation, in areas surrounding the central vein and portal circulation, versus all other groups. Western blot revealed increased activation of TLR2-NLRP3 inflammasome pathway and downstream IL-1β and TNFα in WT-HFD group, but not in TKO-HFD group. IL-1β expression coincided within the same areas of steatosis, inflammatory cell infiltration, collagen deposition and α-SMA expression in WT-HFD mice, that was significantly reduced in TKO-HFD mice. In conclusion, TXNIP deletion ameliorates the HFD-induced steatosis, inflammatory and fibrotic response via modulation of TLR2-NLRP3 inflammasome axis. Targeting TXNIP-TLR2-NLRP3 pathway may provide potential therapeutic modalities for NASH treatment.

Thioredoxin-interacting protein regulates lipid metabolism via Akt/mTOR pathway in diabetic kidney disease

Abnormal lipid metabolism contributes to the renal lipid accumulation, which is associated with diabetic kidney disease, but its precise mechanism remains unclear. The growing evidence demonstrates that thioredoxin-interacting protein is involved in regulating cellular glucose and lipid metabolism. Here, we investigated the effects of thioredoxin-interacting protein on lipid accumulation in diabetic kidney disease. In contrast to the diabetic wild-type mice, the physical and biochemical parameters were improved in the diabetic thioredoxin-interacting protein knockout mice. The increased renal lipid accumulation, expression of acetyl-CoA carboxylase, fatty acid synthase and sterol regulatory element binding protein-1, and phosphorylated Akt and mTOR associated with diabetes in wild-type mice was attenuated in diabetic thioredoxin-interacting protein knockout mice. Furthermore, thioredoxin-interacting protein knockout significantly increased the expression of peroxisome proliferator-activated receptor-α, acyl-coenzyme A oxidase 1 and carnitine palmitoyltransferaser 1 in diabetic kidneys. In vitro experiments, using HK-2 cells, revealed that knockdown of thioredoxin-interacting protein inhibited high glucose-mediated lipid accumulation, expression of acetyl-CoA carboxylase, fatty acid synthase and sterol regulatory element binding protein-1, as well as activation of Akt and mTOR. Moreover, knockdown of thioredoxin-interacting protein reversed high glucose-induced reduction of peroxisome proliferator-activated receptor-α, acyl-coenzyme A oxidase 1 and carnitine palmitoyltransferaser 1 expression in HK-2 cells. Importantly, blockade of Akt/mTOR signaling pathway with LY294002, a specific PI3K inhibitor, replicated these effects of thioredoxin-interacting protein silencing. Taken together, these data suggest that thioredoxin-interacting protein deficiency alleviates diabetic renal lipid accumulation through regulation of Akt/mTOR pathway, thioredoxin-interacting protein may be a potential therapeutic target for diabetic kidney disease.

New insights into salvianolic acid A action: Regulation of the TXNIP/NLRP3 and TXNIP/ChREBP pathways ameliorates HFD-induced NAFLD in rats

Salvianolic acid A (SalA), one of the most efficacious polyphenol compounds extracted from Radix Salvia miltiorrhiza (Danshen), has been shown to possess many potential pharmacological activities. This study aimed to investigate whether SalA has hepatoprotective effects against high-fat diet (HFD)-induced non-alcoholic fatty liver disease (NAFLD) and to further explore the mechanism underlying this process. SalA treatment significantly attenuated HFD-induced obesity and liver injury, and markedly decreased lipid accumulation in HFD-fed rat livers. Moreover, SalA treatment ameliorated HFD-induced hepatic inflammation and oxidative stress by decreasing hepatotoxic levels of cytokines, suppressing the overproduction of reactive oxygen species (ROS) and methane dicarboxylic aldehyde (MDA) and preventing the decreased expression of superoxide dismutase (SOD). Importantly, SalA reversed the HFD- or palmitic acid (PA)-induced activation of the NLRP3 inflammasome, the nuclear translocation of ChREBP and the up-regulation of FAS, and these effects were accompanied by TXNIP down-regulation. However, TXNIP siRNA treatment partially abrogated the above-mentioned effects of SalA in PA-treated HepG2 cells. Together, our results demonstrated, for the first time, that SalA protects against HFD-induced NAFLD by ameliorating hepatic lipid accumulation and inflammation, and these protective effects may partially due to regulation of the TXNIP/NLRP3 and TXNIP/ChREBP pathways.

Thioredoxin-interacting protein mediates hepatic lipogenesis and inflammation via PRMT1 and PGC-1α regulation in vitro and in vivo

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is strongly associated with obesity and type 2 diabetes. Thioredoxin-interacting protein (TXNIP) regulates the cellular redox state and metabolism and has been linked to many diseases, including diabetes. Therefore, we examined the role of TXNIP in hepatic steatosis in vitro and in vivo.

METHODS

Lipogenic and inflammatory proteins produced by hepatocytes treated with palmitic acid (PA) or transfected with TXNIP or Txnip siRNA were measured by Western blotting. Lipid accumulation was assessed using Oil Red O staining. Protein interactions were assessed by immunoprecipitation and proximity ligation assay. Hepatic protein levels were measured by Western blotting from wild type or Txnip(-/-) mice fed a high-fat diet (HFD) or chow diet. Livers from NAFLD patients were compared with normal liver by immunohistochemistry.

RESULTS

PA increased TXNIP, and inflammatory and lipogenic proteins in both AML12 and H4IIE cells. It also increased the peroxisome proliferator-activated receptor gamma co-activator-1α (PGC-1α), which mediated the expression of lipogenic markers and lipid accumulation. In addition, PA increased protein arginine methyltransferase-1 (PRMT1) and PRMT1 siRNA abolished the increase in lipogenic markers with PGC-1α. Furthermore, TXNIP interacted with PRMT1 in PA-treated hepatocytes. In vivo, levels of lipogenic proteins, inflammatory molecules, PGC-1α, and PRMT1 were increased in the livers of HFD mice compared with those fed a chow diet, and were ameliorated in HFD Txnip(-/-) mice. Moreover, TXNIP, PRMT1, and PGC-1α were elevated in the livers of human NAFLD patients.

CONCLUSIONS

TXNIP mediates hepatic lipogenesis via PRMT1 and PGC-1α regulation and inflammation in vitro and in vivo, implying that targeting TXNIP and PRMT1 is a potential therapeutic approach for treatment of NAFLD.

Quercetin and allopurinol reduce liver thioredoxin-interacting protein to alleviate inflammation and lipid accumulation in diabetic rats

BACKGROUND AND PURPOSE

Thioredoxin-interacting protein (TXNIP), a regulator of cellular oxidative stress, has been associated with activation of NOD-like receptor 3 (NLRP3) inflammasome, inflammation and lipid metabolism, suggesting it has a role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD) in diabetes. In this study we investigated whether TXNIP is involved in type 1 diabetes-associated NAFLD and whether antioxidants, quercetin and allopurinol, alleviate NAFLD by targeting TXNIP.

EXPERIMENTAL APPROACH

Diabetes was induced in male Sprague-Dawley rats by a single i.p. injection of 55 mg · kg⁻¹ streptozotocin. Quercetin and allopurinol were given p.o. to diabetic rats for 7 weeks. Hepatic function, oxidative stress, inflammation and lipid levels were determined. Rat BRL-3A and human HepG2 cells were exposed to high glucose (30 mM) in the presence and absence of antioxidants, TXNIP siRNA transfection or caspase-1 inhibitor, Ac-YVAD-CMK.

KEY RESULTS

Quercetin and allopurinol significantly inhibited the TXNIP overexpression, activation of NLRP3 inflammasome, down-regulation of PPARα and up-regulation of sterol regulatory element binding protein-1c (SREBP-1c), SREBP-2, fatty acid synthase and liver X receptor α, as well as elevation of ROS and IL-1β in diabetic rat liver. These effects were confirmed in hepatocytes in vitro and it was further shown that TXNIP down-regulation contributed to the suppression of NLRP3 inflammasome activation, inflammation and changes in PPARα and SREBPs.

CONCLUSIONS AND IMPLICATIONS

Inhibition of hepatic TXNIP by quercetin and allopurinol contributes to the reduction in liver inflammation and lipid accumulation under hyperglycaemic conditions. The targeting of hepatic TXNIP by quercetin and allopurinol may have therapeutic implications for prevention of type 1 diabetes-associated NAFLD.

Primary hepatocellular carcinoma and metabolic syndrome: An update

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy. The incidence of hepatocellular carcinoma has increased dramatically by 80% over the past two decades in the United States. Numerous basic science and clinical studies have documented a strong association between hepatocellular carcinoma and the metabolic syndrome. These studies have documented that, in most patients, non-alcoholic fatty liver disease is the hepatic manifestation of the metabolic syndrome, which may progress to hepatocellular carcinoma through the cirrhotic process. However, minority of patients with non-alcoholic fatty liver disease may progress to hepatocellular carcinoma without cirrhosis. This review summarizes the current literature of the link between hepatocellular carcinoma and metabolic syndrome with special emphasis on various components of the metabolic syndrome including risk of association with obesity, diabetes mellitus, hyperlipidemia, and hypertension. Current understanding of pathophysiology, clinical features, treatments, outcomes, and surveillance of hepatocellular carcinoma in the background of metabolic syndrome and non-alcoholic fatty liver disease is reviewed. With the current epidemic of metabolic syndrome, the number of patients with non-alcoholic fatty liver disease is increasing. Subsequently, it is expected that the incidence and prevalence of HCC will also increase. It is very important for the scientific community to shed more light on the pathogenesis of HCC with metabolic syndrome, both with and without cirrhosis. At the same time it is also important to quantify the risk of hepatocellular carcinoma associated with the metabolic syndrome in a prospective setting and develop surveillance recommendations for detection of hepatocellular carcinoma in patients with metabolic syndrome.

Thioredoxin and thioredoxin target proteins: from molecular mechanisms to functional significance

The thioredoxin (Trx) system is one of the central antioxidant systems in mammalian cells, maintaining a reducing environment by catalyzing electron flux from nicotinamide adenine dinucleotide phosphate through Trx reductase to Trx, which reduces its target proteins using highly conserved thiol groups. While the importance of protecting cells from the detrimental effects of reactive oxygen species is clear, decades of research in this field revealed that there is a network of redox-sensitive proteins forming redox-dependent signaling pathways that are crucial for fundamental cellular processes, including metabolism, proliferation, differentiation, migration, and apoptosis. Trx participates in signaling pathways interacting with different proteins to control their dynamic regulation of structure and function. In this review, we focus on Trx target proteins that are involved in redox-dependent signaling pathways. Specifically, Trx-dependent reductive enzymes that participate in classical redox reactions and redox-sensitive signaling molecules are discussed in greater detail. The latter are extensively discussed, as ongoing research unveils more and more details about the complex signaling networks of Trx-sensitive signaling molecules such as apoptosis signal-regulating kinase 1, Trx interacting protein, and phosphatase and tensin homolog, thus highlighting the potential direct and indirect impact of their redox-dependent interaction with Trx. Overall, the findings that are described here illustrate the importance and complexity of Trx-dependent, redox-sensitive signaling in the cell. Our increasing understanding of the components and mechanisms of these signaling pathways could lead to the identification of new potential targets for the treatment of diseases, including cancer and diabetes.

PPARγ and Oxidative Stress: Con(β) Catenating NRF2 and FOXO

Peroxisome-proliferator activator receptor γ (PPARγ) is a nuclear receptor of central importance in energy homeostasis and inflammation. Recent experimental pieces of evidence demonstrate that PPARγ is implicated in the oxidative stress response, an imbalance between antithetic prooxidation and antioxidation forces that may lead the cell to apoptotic or necrotic death. In this delicate and intricate game of equilibrium, PPARγ stands out as a central player devoted to the quenching and containment of the damage and to foster cell survival. However, PPARγ does not act alone: indeed the nuclear receptor is at the point of interconnection of various pathways, such as the nuclear factor erythroid 2-related factor 2 (NRF2), Wnt/β-catenin, and forkhead box proteins O (FOXO) pathways. Here we reviewed the role of PPARγ in response to oxidative stress and its interaction with other signaling pathways implicated in this process, an interaction that emerged as a potential new therapeutic target for several oxidative-related diseases.

Thioredoxin binding protein (TBP)-2/Txnip and α-arrestin proteins in cancer and diabetes mellitus

Thioredoxin binding protein -2/ thioredoxin interacting protein is an α-arrestin protein that has attracted much attention as a multifunctional regulator. Thioredoxin binding protein -2 expression is downregulated in tumor cells and the level of thioredoxin binding protein is correlated with clinical stage of cancer. Mice with mutations or knockout of the thioredoxin binding protein -2 gene are much more susceptible to carcinogenesis than wild-type mice, indicating a role for thioredoxin binding protein -2 in cancer suppression. Studies have also revealed roles for thioredoxin binding protein -2 in metabolic control. Enhancement of thioredoxin binding protein -2 expression causes impairment of insulin sensitivity and glucose-induced insulin secretion, and β-cell apoptosis. These changes are important characteristics of type 2 diabetes mellitus. Thioredoxin binding protein -2 regulates transcription of metabolic regulating genes. Thioredoxin binding protein -2-like inducible membrane protein/ arrestin domain containing 3 regulates endocytosis of receptors such as the β(2)-adrenergic receptor. The α-arrestin family possesses PPXY motifs and may function as an adaptor/scaffold for NEDD family ubiquitin ligases. Elucidation of the molecular mechanisms of α-arrestin proteins would provide a new pharmacological basis for developing approaches against cancer and type 2 diabetes mellitus.

Adipokines and redox signaling: impact on fatty liver disease

Adipokines (adipose tissue cytokines) are polypeptide factors secreted by adipose tissue in a highly regulated manner. The 'classical' adipokines (leptin, adiponectin, and resistin) are expressed only by adipocytes, but other adipokines have been shown to be released by resident and infiltrating macrophages, as well as by components of the vascular stroma. Indeed, adipose tissue inflammation is known to be associated with a modification in the pattern of adipokine secretion. Several studies indicate that adipokines can interfere with hepatic injury associated with fatty infiltration, differentially modulating steatosis, inflammation, and fibrosis. Moreover, plasma levels of adipokines have been investigated in patients with nonalcoholic fatty liver disease in order to establish correlations with the underlying state of insulin resistance and with the type and severity of hepatic damage. In this Forum article, we provide a review of recent data that suggest a significant role for oxidative stress, reactive oxygen species, and redox signaling in mediating actions of adipokines that are relevant in the pathogenesis of nonalcoholic fatty liver disease, including hepatic insulin resistance, inflammation, and fibrosis.

New insights from rodent models of fatty liver disease

Rodent models of fatty liver disease are essential research tools that provide a window into disease pathogenesis and a testing ground for prevention and treatment. Models come in many varieties involving dietary and genetic manipulations, and sometimes both. High-energy diets that induce obesity do not uniformly cause fatty liver disease; this has prompted close scrutiny of specific macronutrients and nutrient combinations to determine which have the greatest potential for hepatotoxicity. At the same time, diets that do not cause obesity or the metabolic syndrome but do cause severe steatohepatitis have been exploited to study factors important to progressive liver injury, including cell death, oxidative stress, and immune activation. Rodents with a genetic predisposition to overeating offer yet another model in which to explore the evolution of fatty liver disease. In some animals that overeat, steatohepatitis can develop even without resorting to a high-energy diet. Importantly, these models and others have been used to document that aerobic exercise can prevent or reduce fatty liver disease. This review focuses primarily on lessons learned about steatohepatitis from manipulations of diet and eating behavior. Numerous additional insights about hepatic lipid metabolism, which have been gained from genetically engineered mice, are also mentioned.

Thioredoxin, thioredoxin-interacting protein and digestive diseases

The thioredoxin system is an antioxidative and redox-regulating system that consists of several small proteins, including thioredoxin (TRX), reduced coenzyme II (NADPH) and thioredoxin reductase (TRX-R). It can function to regulate oxidation-reduction state of cells, resist oxidative stress, activate transcription factors NF-κB and AP-1 to promote the growth and proliferation of cells, and interact with ASK-1 to inhibit apoptosis. Thioredoxin-interacting protein (TXNIP) is a member of the thioredoxin-binding protein family and plays a role in mediating oxidative stress, resisting cell proliferation and inducing apoptosis, acting as a negative regulator of the TRX system. Since oxidative stress and apoptosis are often involved in the pathogenesis of digestive diseases, TRX and TXNIP may play roles in the pathogenesis of digestive diseases. This paper gives an overview of the structure and functions of TRX and TXNIP and reviews the recent advances in understanding the relationship between the two proteins and digestive diseases.

Vitamin D3 up-regulated protein 1 deficiency accelerates liver regeneration after partial hepatectomy in mice

BACKGROUND & AIMS

Liver regeneration is a complicated process involving a variety of interacting factors. Vitamin D3 up-regulated protein 1 (VDUP1) is a potent growth suppressor that, upon over-expression, inhibits tumor cell proliferation and cell-cycle progression. Here, we investigated the function of VDUP1 in liver regeneration following hepatectomy in mice.

METHODS

Liver regeneration after 70% partial hepatectomy (PH) was compared in VDUP1 knockout (KO) and wild-type (WT) mice, and the activities of proliferative- and cell-cycle-related signaling pathways were measured.

RESULTS

Compared with WT mice, liver recovery was significantly accelerated in VDUP1 KO mice during the first day after PH, in association with increased DNA synthesis. Consistent with this observation, the expression levels of key cell-cycle regulatory proteins, including cyclin D, cyclin E, cyclin-dependent kinase 4 (CDK4), p21, and p27, were markedly altered in the livers of VDUP1 KO mice. Induction of growth factors and activation of proliferative signaling pathway components including extracellular signal-regulated kinase 1/2 (ERK1/2), Akt, glycogen synthase kinase 3β (GSK3β), mammalian target of rapamycin (mTOR), and p70S6 kinase (p70(S6K)), occurred much earlier and to a greater extent in VDUP1 KO mouse livers. In addition, primary hepatocytes isolated from VDUP1 KO mice displayed increased activation of ERK1/2 and Akt in response to HGF and TGF-α.

CONCLUSIONS

Our results reveal an important role for VDUP1 in the regulation of proliferative signaling during liver regeneration. Altered activation of genes involved in ERK1/2 and Akt signaling pathways may explain the accelerated growth responses seen in VDUP1 KO mice.

Specific contribution of methionine and choline in nutritional nonalcoholic steatohepatitis: impact on mitochondrial S-adenosyl-L-methionine and glutathione

The pathogenesis and treatment of nonalcoholic steatohepatitis (NASH) are not well established. Feeding a diet deficient in both methionine and choline (MCD) is one of the most common models of NASH, which is characterized by steatosis, mitochondrial dysfunction, hepatocellular injury, oxidative stress, inflammation, and fibrosis. However, the individual contribution of the lack of methionine and choline in liver steatosis, advanced pathology and impact on mitochondrial S-adenosyl-L-methionine (SAM) and glutathione (GSH), known regulators of disease progression, has not been specifically addressed. Here, we examined the regulation of mitochondrial SAM and GSH and signs of disease in mice fed a MCD, methionine-deficient (MD), or choline-deficient (CD) diet. The MD diet reproduced most of the deleterious effects of MCD feeding, including weight loss, hepatocellular injury, oxidative stress, inflammation, and fibrosis, whereas CD feeding was mainly responsible for steatosis, characterized by triglycerides and free fatty acids accumulation. These findings were preceded by MCD- or MD-mediated SAM and GSH depletion in mitochondria due to decreased mitochondrial membrane fluidity associated with a lower phosphatidylcholine/phosphatidylethanolamine ratio. MCD and MD but not CD feeding resulted in increased ceramide levels by acid sphingomyelinase. Moreover, GSH ethyl ester or SAM therapy restored mitochondrial GSH and ameliorated hepatocellular injury in mice fed a MCD or MD diet. Thus, the depletion of SAM and GSH in mitochondria is an early event in the MCD model of NASH, which is determined by the lack of methionine. Moreover, therapy using permeable GSH prodrugs may be of relevance in NASH.