Probiotics and antibodies to TNF inhibit inflammatory activity and improve nonalcoholic fatty liver disease

Ob/ob mice, a model for nonalcoholic fatty liver disease (NAFLD), develop intestinal bacterial overgrowth and overexpress tumor necrosis factor alpha (TNF-alpha). In animal models for alcoholic fatty liver disease (AFLD), decontaminating the intestine or inhibiting TNF-alpha improves AFLD. Because AFLD and NAFLD may have a similar pathogenesis, treatment with a probiotic (to modify the intestinal flora) or anti-TNF antibodies (to inhibit TNF-alpha activity) may improve NAFLD in ob/ob mice. To evaluate this hypothesis, 48 ob/ob mice were given either a high-fat diet alone (ob/ob controls) or the same diet + VSL#3 probiotic or anti-TNF antibodies for 4 weeks. Twelve lean littermates fed a high-fat diet served as controls. Treatment with VSL#3 or anti-TNF antibodies improved liver histology, reduced hepatic total fatty acid content, and decreased serum alanine aminotransferase (ALT) levels. These benefits were associated with decreased hepatic expression of TNF-alpha messenger RNA (mRNA) in mice treated with anti-TNF antibodies but not in mice treated with VSL#3. Nevertheless, both treatments reduced activity of Jun N-terminal kinase (JNK), a TNF-regulated kinase that promotes insulin resistance, and decreased the DNA binding activity of nuclear factor kappaB (NF-kappaB), the target of IKKbeta, another TNF-regulated enzyme that causes insulin resistance. Consistent with treatment-related improvements in hepatic insulin resistance, fatty acid beta-oxidation and uncoupling protein (UCP)-2 expression decreased after treatment with VSL#3 or anti-TNF antibodies. In conclusion, these results support the concept that intestinal bacteria induce endogenous signals that play a pathogenic role in hepatic insulin resistance and NAFLD and suggest novel therapies for these common conditions.     

非酒精性脂肪性肝病大鼠肝脏解偶联蛋白2表达及其与能量贮备的关系

目的探讨非酒精性脂肪性肝病(NAFLD)大鼠肝脏线粒体解偶联蛋白2(UCP2)表达及其与能量贮备的关系。方法模型组SD大鼠给予高脂肪高胆固醇饮食饲养,分批于实验第8、12、16、24 周处死,同期设普通饮食饲养大鼠作对照。免疫组织化学和逆转录聚合酶链反应(RT-PCR)检测肝脏UCP2 mRNA转录及其蛋白表达。荧光测定法检测肝脏三磷酸腺苷(ATP)含量。结果模型组大鼠8周呈现单纯性脂肪肝,12-24周从脂肪性肝炎进展为脂肪性肝炎伴肝纤维化。免疫组织化学和RT-PCR显示,随着造模时间延长,模型组肝脏UCP2表达逐渐增强,UCP mRNA转录于24周达高峰,较对照组升高4.2倍, t=16.474,P<0.01;模型组肝脏ATP含量则随造模时间延长而逐渐减低,24周为(1.99±0.66) ×108μmol/g,对照组为(2.97±0.48)×108μmol/g,t=3.248,P<0.01。模型组肝脏UCP2 mRNA 转录的相对数值与其ATP含量呈密切负相关,r=-0.93,P<0.01。结论持续24周高脂饮食成功复制大鼠NAFLD模型,模型大鼠肝脏UCP2表达增强而ATP含量减少,两者之间关系密切。     

Dietary factors alter hepatic innate immune system in mice with nonalcoholic fatty liver disease

Dietary factors promote obesity and obesity-related disorders, such as fatty liver disease. Natural killer T (NKT) cells are components of the innate immune system that regulate proinflammatory (Th-1) and anti-inflammatory (Th-2) immune responses. Previously, we noted that NKT cells are selectively reduced in the fatty livers of obese, leptin-deficient ob/ob mice and demonstrated that this promotes proinflammatory polarization of hepatic cytokine production, exacerbating lipopolysaccharide (LPS) liver injury in these animals. In the current study, we show that hepatic NKT cells are also depleted by diets that induce obesity and fatty livers in wild-type mice, promoting Th-1 polarization of hepatic cytokine production and sensitization to LPS liver injury despite persistent leptin. Adult male C57BL6 mice fed diets containing high amounts of either fat or sucrose, or combined high-fat, high-sucrose, develop increased hepatic NKT cell apoptosis and reduced liver NKT cells. The hepatic lymphocytes are more Th-1 polarized with increased intracellular interferon gamma and tumor necrosis factor alpha. Mice fed high-fat diets also exhibit more liver injury, reflected by 2-fold greater serum alanine aminotransferase (ALT) than control animals after receiving LPS. In conclusion, when otherwise normal mice are fed with high-fat or sucrose diet, they become obese, develop fatty livers, and acquire hepatic innate immune system abnormalities, including increased NKT cell apoptosis. The latter reduces liver NKT cell populations and promotes excessive hepatic production of Th-1 cytokines that promote hepatic inflammation. These diet-induced alterations in the hepatic innate immune system may contribute to obesity-related liver disease.     

Endogenous islet uncoupling protein-2 expression and loss of glucose homeostasis in ob/ob mice

We hypothesized that the loss of glucose homeostasis in ob/ob mice is associated with upregulation of islet uncoupling protein-2 (UCP2) expression, leading to impaired glucose-stimulated insulin secretion (GSIS). Changes in glucose homeostasis in lean and ob/ob mice from 5 to 16 weeks were assessed by fasting blood glucose, plasma insulin, oral glucose tolerance, and tissue insulin sensitivity. In vitro GSIS and ATP content were assayed in isolated islets, while UCP2 expression was determined by quantitative real-time PCR and immunoblotting. Short-term reduction of UCP2 expression was achieved through transfection of islets with specific small interfering RNA. Insulin resistance was detected in 5-week-old ob/ob mice, but GSIS and blood glucose levels remained normal. By 8 weeks of age, ob/ob mice displayed fasting hyperglycemia, hyperinsulinemia and glucose intolerance, and also had elevated non-esterified fatty acid concentration in plasma. In vitro, GSIS and ATP generation were impaired in ob/ob islets. Islet UCP2 expression was elevated at 5 and 8 weeks of age. Short-term knockdown of islet UCP2 increased GSIS in islets of lean mice, but had no effect in islets from ob/ob mice. Loss of glucose homeostasis and impairment of insulin secretion from isolated islets at 8 weeks in ob/ob mice is preceded by an increase in UCP2 expression in islets. Moreover, the glucolipotoxic conditions observed are predicted to increase UCP2 activity, contributing to lower islet ATP and GSIS.     

Uncoupling protein-2 deficiency promotes oxidant stress and delays liver regeneration in mice

The control of liver regeneration remains elusive. Because reactive oxygen species (ROS) are able to mediate cell growth arrest and activate proteins that inhibit the cell cycle, ROS production may have a negative impact on liver regeneration. We examined how liver regeneration is affected by uncoupling protein-2 (UCP2), an inner mitochondrial membrane carrier that senses and negatively regulates superoxide production. Liver regeneration was monitored up to 5 days and was found to be significantly delayed in UCP2(-/-) mice after partial hepatectomy. Apoptosis rates in UCP2(+/+) and UCP2(- /-) liver remnants were similar, while parameters of cell proliferation indicated a diminished response in UCP2(- /-) mice with corresponding changes in the expression of key cell cycle regulatory proteins and prolonged activation of stress-responsive protein kinase p38. Levels of malondialdehyde, a marker of ROS generation and oxidant stress, were elevated in UCP2(- /-) livers at every examined time point. Liver remnants of UCP2(+ /+) mice 48 hours post-hepatectomy showed a fourfold increase in the expression of UCP2 protein primarily detected in hepatocytes. In conclusion, our results suggest that absent or insufficient UCP2 function in the regenerating liver results in increased ROS production and negatively modulates the control of cell cycle.     

Pivotal role of superoxide anion and beneficial effect of antioxidant molecules in murine steatohepatitis

Nonalcoholic fatty liver disease, frequently associated with obesity, can lead to nonalcoholic steatohepatitis (NASH) and cirrhosis. The pathophysiology of NASH is poorly understood, and no effective treatment is available. In view of a potential deleterious role for reactive oxygen species (ROS), we investigated the origin of ROS overproduction in NASH. Mitochondrial production of ROS and its alterations in the presence of antioxidant molecules were studied in livers from ob/ob mice that bear a mutation of the leptin gene and develop experimental NASH. N-acetyl-cysteine and the superoxide dismutase (SOD) mimics ambroxol, manganese [III] tetrakis (5,10,15,20 benzoic acid) (MnTBAP), and copper [II] diisopropyl salicylate (CuDIPS) were used to target different checkpoints of the oxidative cascade to determine the pathways involved in ROS production. Liver mitochondria from ob/ob mice generated more O(2)*- than those of lean littermates (P <.01). Ex vivo, all three SOD mimics decreased O(2)*- generation (P <.001) and totally inhibited lipid peroxidation (P <.001) versus untreated ob/ob mice. Those modifications were associated with in vivo improvements: MnTBAP and CuDIPS reduced weight (P <.02) and limited the extension of histological liver steatosis by 30% and 52%, respectively, versus untreated ob/ob mice. In conclusion, these data demonstrate deleterious effects of superoxide anions in NASH and point at the potential interest of nonpeptidyl mimics of SOD in the treatment of NASH in humans.     

Interleukin 6 alleviates hepatic steatosis and ischemia/reperfusion injury in mice with fatty liver disease

Fatty liver, formerly associated predominantly with excessive alcohol intake, is now also recognized as a complication of obesity and an important precursor state to more severe forms of liver pathology including ischemia/reperfusion injury. No standard protocol for treating fatty liver exists at this time. We therefore examined the effects of 10 days of interleukin 6 (IL-6) injection in 3 murine models of fatty liver: leptin deficient ob/ob mice, ethanol-fed mice, and mice fed a high-fat diet. In all 3 models, IL-6 injection decreased steatosis and normalized serum aminotransferase. The beneficial effects of IL-6 treatment in vivo resulted in part from an increase in mitochondrial beta oxidation of fatty acid and an increase in hepatic export of triglyceride and cholesterol. However, administration of IL-6 to isolated cultured steatotic hepatocytes failed to decrease lipid contents, suggesting that the beneficial effects of IL-6 in vivo do not result from its effects on hepatocytes alone. IL-6 treatment increased hepatic peroxisome proliferator-activated receptor (PPAR) alpha and decreased liver and serum tumor necrosis factor (TNF) alpha. Finally, 10 days of treatment with IL-6 prevented the susceptibility of fatty livers to warm ischemia/reperfusion injury. In conclusion, long-term IL-6 administration ameliorates fatty livers and protects against warm ischemia/reperfusion fatty liver injury, suggesting the therapeutic potential of IL-6 in treating human fatty liver disease.     

Development of steatohepatitis in Ob/Ob mice is dependent on Toll-like receptor 4

Background and aim. The etiology of non-alcoholic fatty liver disease (NAFLD) progression, and why some patients develop non-alcoholic steatohepatitis (NASH) vs. uncomplicated NAFLD, is not well understood. Obesity and NAFLD are thought to be associated with high circulating levels of leptin; however, the role of leptin in NASH has been controversial. Secondly, as ob/ob mice are known to have elevated circulating levels of TLR4-stimulating endotoxin secondary to increased intestinal permeability.Material and methods. We evaluated the long-term effects of steatosis on the livers of aleptinemic (OB) mice and the role of TLR4 in the development of hepatic sequelae in these animals.Results. At 20 weeks of age OB animals displayed grossly steatotic livers, but also features of early stage NASH including hepatocellular ballooning and numerous necroinflammatory foci with associated changes in serum aspartate aminotransferase (AST) and alanine transaminase (ALT). TLR4 KO did not affect the development of obesity or steatosis in ob/ob mice, but protected these animals from hepatitis and liver injury.Conclusions. In conclusion, the data presented here indicate that steatohepatitis develops in the absence of leptin, and that TLR4 is integral to the development NASH secondary to hyperphagia.     

The aggravation of mitochondrial dysfunction in nonalcoholic fatty liver disease accompanied with type 2 diabetes mellitus

Abstract

Objective. Nonalcoholic fatty liver disease (NAFLD) is a mitochondrial disease associated with the metabolic syndrome, but few data are available on the mitochondrial dysfunction of NAFLD after the development of type 2 diabetes mellitus (T2DM). We aimed to identify the changes of mitochondrial function in rat livers when T2DM develops after NAFLD. Material and methods. Rat models of nonalcoholic fatty liver (NAFL) and T2DM were established using high-fat diet and streptozocin. Mitochondria were isolated from the livers. The levels of reactive oxygen species (ROS) and mRNA and protein levels of mitochondrial complex IV (COX IV) and carnitine palmitoyltransferase-1 (CPT-1) were assessed in rat livers. The mitochondrial membrane potential (MP), and the enzyme activities of COX IV and CPT-1 were measured in isolated mitochondria. Results. There were increased ROS, decreased mitochondrial MP, and reduced COX IV and CPT-1 activity in the NAFL and T2DM groups compared with controls (p < 0.05). Compared with NAFL, the T2DM group had higher ROS levels and lower enzyme activity (p < 0.05), but showed no difference in mitochondrial MP. Although COX IV and CPT-1 expression levels in liver decreased in NAFL and T2DM, there was no significant difference between two groups. Conclusion. This study first identified progressively impaired mitochondrial respiratory chain and β-oxidation in NAFLD when T2DM develops, inducing overproduction of ROS, and finally triggering a vicious circle that leads to the aggravation of mitochondrial dysfunction in NAFLD after development of T2DM.     

Reduction of hepatosteatosis and lipid levels by an adipose differentiation-related protein antisense oligonucleotide

BACKGROUND & AIMS: Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive triglyceride accumulation in hepatocytes. Expression of the lipid droplet protein adipose differentiation-related protein (ADRP) is increased in NAFLD, but whether this is causally linked to hepatic lipid metabolism is unclear. We postulated that a reduction in ADRP would ameliorate hepatic steatosis and improve insulin action. METHODS: Leptin deficient Lep(ob/ob) and diet-induced obese (DIO) mice were treated with antisense oligonucleotide (ASO) against ADRP, and effects on hepatic and serum lipids and glucose homeostasis were examined. RESULTS: ADRP ASO specifically decreased ADRP mRNA and protein levels in the livers of Lep(ob/ob) and DIO mice, without altering the levels of other lipid droplet proteins, that is, S3-12 and TIP47. ADRP ASO suppressed expression of lipogenic genes, reduced liver triglyceride content without affecting cholesterol, attenuated triglyceride secretion, and decreased serum triglyceride and alanine aminotransaminase levels. The reduction in hepatic steatosis by ADRP ASO was associated with improvement in glucose homeostasis in both Lep(ob/ob) and DIO mice. CONCLUSIONS: This study demonstrates a crucial role for the lipid droplet protein ADRP in regulation of lipid metabolism. Reduction in hepatic ADRP level using an antisense oligonucleotide reverses hepatic steatosis, hypertriglyceridemia, and insulin resistance in obese mice, suggesting that ADRP may be targeted for the treatment of NAFLD and associated lipid and glucose abnormalities.     

Animal models of steatohepatitis

Animal models of hepatic steatosis and steatohepatitis have improved our understanding of the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Three models, genetically obese ob/ob mice, lipoatrophic mice and normal rats fed choline-deficient, methionine-restricted diets, have been particularly informative. All support the multiple 'hit' hypothesis for NAFLD pathogenesis that suggests that fatty livers are unusually vulnerable to oxidants and develop steatohepatitis when secondary insults generate sufficient oxidants to cause liver cell death and inflammation. Steatohepatitis, in turn, increases sensitivity to other insults that induce hepatic fibrosis, promoting the evolution of cirrhosis. Early during NAFLD pathogenesis, inhibitor kappa kinase beta (IKKbeta), an enzyme that induces tumour necrosis factor alpha (TNFalpha) and other proinflammatory cytokines, is activated and this causes insulin resistance. Inhibition of IKKbeta or TNFalpha improves insulin sensitivity, steatosis and steatohepatitis in animals, suggesting novel strategies to prevent and treat early NAFLD in humans.     

Oval cells compensate for damage and replicative senescence of mature hepatocytes in mice with fatty liver disease

Hepatic steatosis may have a generally benign prognosis, either because most hepatocytes are not significantly injured or mechanisms to replace damaged hepatocytes are induced. To determine the relative importance of these mechanisms, we compared hepatocyte damage and replication in ethanol-fed and ob/ob mice with very indolent fatty liver disease to that of healthy control mice and PARP-1(-/-) mice with targeted disruption of the DNA repair enzyme, poly(ADP-ribose) polymerase. Compared to the healthy controls, both groups with fatty livers had significantly higher serum alanine aminotransferase values, hepatic mitochondrial H(2)O(2) production, and hepatocyte oxidative DNA damage. A significantly smaller proportion of the hepatocytes from fatty livers entered S phase when cultured with mitogens. Moreover, this replicative senescence was not reversed by treating cultured hepatocytes with agents (i.e., betaine or leptin) that improve liver disease in intact ethanol-fed or leptin-deficient mice. Hepatocytes from PARP1(-/-) mice also had more DNA damage and reduced DNA synthesis in response to mitogens. However, neither mice with fatty livers nor PARP-1-deficient mice had atrophic livers. All of the mice with senescent mature hepatocytes exhibited hepatic accumulation of liver progenitor (oval) cells and oval cell numbers increased with the demand for hepatocyte replacement. Therefore, although hepatic oxidant production and damage are generally increased in fatty livers, expansion of hepatic progenitor cell populations helps to compensate for the increased turnover of damaged mature hepatocytes. In conclusion, these results demonstrate that induction of mechanisms to replace damaged hepatocytes is important for limiting the progression of fatty liver disease.     

己酮可可碱对非酒精性脂肪肝大鼠肝组织线粒体解耦联蛋白表达的影响

目的 探讨己酮可可碱(PTX)对非酒精性脂肪肝性肝病(NAFLD)大鼠线粒体解耦联蛋白(UCP)-2 mRNA表达的影响. 方法 SD大鼠60只,正常喂养1周后随机分为3组,每组20只.其中对照组20只,以普通饲料喂养,实验组和干预组各20只,以高脂饲料喂养,干预组高脂饮食4周后,在饮水中加用已酮可可碱(PTX)(100 mg·Kg-1·d-1),于第24周处死,采用反转录聚合酶链反应(RT-PCR)技术检测肝脏UCP-2mRNA的表达. 结果 对照组大鼠肝脏UCP2mRNA呈微量表达(1.2±0.1),实验组大鼠肝脏UCP2mRNA呈强表达(4.0±0.3),干预组大鼠肝脏UCP2mRNA呈弱表达(3.0±0.2),3组间UCP-2mRNA表达差异有统计学意义(F=160.67,P＜0.01). 结论 己酮可可碱可下调NAFLD大鼠肝细胞UCP-2mRNA的表达.     

Rosiglitazone attenuates age- and diet-associated nonalcoholic steatohepatitis in male low-density lipoprotein receptor knockout mice

Nonalcoholic fatty liver disease (NAFLD) is a common complication of obesity that can progress to nonalcoholic steatohepatitis (NASH), a serious liver pathology that can advance to cirrhosis. The mechanisms responsible for NAFLD progression to NASH remain unclear. Lack of a suitable animal model that faithfully recapitulates the pathophysiology of human NASH is a major obstacle in delineating mechanisms responsible for progression of NAFLD to NASH and, thus, development of better treatment strategies. We identified and characterized a novel mouse model, middle-aged male low-density lipoprotein receptor (LDLR)(-/-) mice fed a high-fat diet (HFD), which developed NASH associated with four of five metabolic syndrome (MS) components. In these mice, as observed in humans, liver steatosis and oxidative stress promoted NASH development. Aging exacerbated the HFD-induced NASH such that liver steatosis, inflammation, fibrosis, oxidative stress, and liver injury markers were greatly enhanced in middle-aged versus young LDLR(-/-) mice. Although expression of genes mediating fatty acid oxidation and antioxidant responses were up-regulated in young LDLR(-/-) mice fed HFD, they were drastically reduced in MS mice. However, similar to recent human trials, NASH was partially attenuated by an insulin-sensitizing peroxisome proliferator-activated receptor-gamma (PPARγ) ligand, rosiglitazone. In addition to expected improvements in MS, newly identified mechanisms of PPARγ ligand effects included stimulation of antioxidant gene expression and mitochondrial β-oxidation, and suppression of inflammation and fibrosis. LDLR-deficiency promoted NASH, because middle-aged C57BL/6 mice fed HFD did not develop severe inflammation and fibrosis, despite increased steatosis. Conclusion: MS mice represent an ideal model to investigate NASH in the context of MS, as commonly occurs in human disease, and NASH development can be substantially attenuated by PPARγ activation, which enhances β-oxidation.     

Alleviation of ischemia/reperfusion injury in ob/ob mice by inhibiting UCP-2 expression in fatty liver

AIM： To investigate the protective effect of target suppression of uncoupling protein-2 （UCP-2） on ischemia/ reperfusion （I/R） injury in fatty liver in ob/ob mice. METHODS： Plasmids suppressing UCP-2 expression were constructed, and transfected into fatty liver cells cultured in vitro and the ob/ob mouse I/R injury model. Serum tumor necrosis factor （TNF）-α levels, UCP-2 mRNA expression, alanine aminotransferase （ALT） levels in ob/ob mice were tested, and the pathological changes in fatty liver were observed in experimental and control groups. RESULTS： In ob/ob mouse I/R models, serum TNF-α levels were significantly higher than in normal controls. After the plasmids were transfected into the cultured cells and animal models, expression of UCP-2 rnRNA was significantly reduced as compared with that in the control group （2^1.56± 0.15 vs 2^-0.45± 0.15, p 〈 0.05）. In ob/ob mouse models, in which expression of UCP-2 was suppressed, serum ALT levels were significantly lower than those of other groups, and pathological analysis revealed that injury of liver tissues was significantly alleviated. CONCLUSION： The target suppression of UCP-2 expression in fatty liver can alleviate the I/R injury in the ob/ob mice.     

Current biochemical studies of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis suggest a new therapeutic approach

The study population in this report by Lin et al. was ob/ob mice that have an inherited genetic deficiency of the appetite-suppressing hormone leptin. These mice develop hyperinsulinemia, insulin resistance, and fatty livers. Compared with their lean littermates and wild-type C57BL-6 mice, ob/ob mice have hepatomegaly. In this study, the authors compared three different groups of adult mice (aged 8-10 wk), including male ob/ob C57BL-6 mice, their lean littermates, and wild-type C57BL-6 mice of the same age and sex.The primary purpose of this study was to test the efficacy of metformin for treatment of fatty liver disease in obese, ob/ob mice that develop hyperinsulinemia or insulin resistance and fatty livers. Metformin therapy was found to eliminate fatty liver disease in this model. The potential mechanisms of the action of metformin were the inhibition of hepatic tumor necrosis factor (TNF)alpha and several TNF-inducible responses, which are likely to promote hepatic steatosis and necrosis.In these experiments, ob/ob mice were divided into three treatment groups. Group 1 consisted of eight mice that were treated with metformin and permitted to consume a nutritiously replete liquid mouse diet ad libitum. Mice in group 2 (n = 8) did not receive metformin but were pair-fed the same volume of liquid diet that the mice in the metformin-treated group had consumed on the previous day. Obese ob/ob mice in group 3 (n = 4) and lean mice received no metformin, as with the mice in group 2, but were permitted to consume the liquid diet ad libitum. Liquid diet was given to facilitate accurate daily comparison of food intake among the various treatment groups. All mice were weighed at the beginning of the study and weekly thereafter until killed and then sera, fat, and liver tissues were collected. Tissues were either fixed in buffered formalin and processed from the deceased mice for histology or snap frozen in liquid nitrogen and stored until RNA and proteins were isolated.The feeding protocol was repeated with a second group of 18 ob/ob mice. After 4 wk, hepatocytes were obtained by in situ liver perfusion with collagenase and assayed for cellular adenosine triphosphate (ATP) content. In each experiment, hepatocytes isolated from 3 mice from each treatment group were suspended in a medium and pooled for subsequent analysis to evaluate cell viability, determine the number of obtained cells, and to assay cellular ATP content. These experiments were repeated using another 3 mice from each treatment group, so that analysis of hepatocytes took place from six ob/ob mice in each feeding group.Hepatic steatosis was decreased significantly only in the metformin-treated group. The authors found that metformin's beneficial effect on the fatty liver disease of mice was not due to its ability to constrain hyperphagia, nor due to decreased caloric ingestion, because the daily caloric intakes of the metformin-treated mice and the pair-fed control mice were virtually identical. These caloric intakes were consistently approximately 20% less than that of another obese control group that was permitted to consume diet ad libitum. The authors also observed no significant effect of metformin on serum glucose concentration from fed, ob/ob mice. Metformin is known to reduce hyperinsulinemia by about 40% in both of these obese hyperinsulinemic and insulin-resistant rodent strains. In conclusion, Lin et al. documented that metformin improves fatty liver disease and reverses hepatomegaly, steatosis, and aminotransferase abnormalities in mice. In addition, the authors suggest that metformin might inhibit dieting-induced redistribution of lipid from the liver to adipose tissue depots. In summary, this study identifies a potential treatment for fatty liver disease in humans.     

Sex difference in the liver of hepatocyte-specific Pten-deficient mice: A model of nonalcoholic steatohepatitis

Aim:  Nonalcoholic fatty liver disease (NAFLD) is considered to be a public health problem worldwide. NAFLD is more prevalent in men than in women. Tamoxifen, a potent estrogen receptor antagonist, causes nonalcoholic steatohepatitis (NASH), a severe form of NAFLD. Thus, there may be a sex difference that is dependent on estrogens in NAFLD and NASH. Hepatocyte-specific Pten-deficient mice exhibit hepatic lesions analogous to NASH and are considered to be a clinical model of NASH. We aimed to shed light on any sex differences in the hepatic lesions of Pten-deficient mice and the underlying mechanisms.
Methods:  At 40 weeks, livers from male and female Pten-deficient mice were processed for measuring lipid content, genes expression analysis, and histological examination. Level of serum reactive oxygen species (ROS) was also determined. Seventy-six-week-old mice were used in tumor burden experiments.
Results:  Hepatic steatosis, inflammation, and even carcinogenesis in Pten-deficient mice were attenuated in females compared to males. Attenuated fatty liver in females was ascribed to inactivation of sterol regulatory element binding protein-1c. Hepatic inflammation in females was suppressed via decreased ROS with increased antioxidant gene expression and decreased proinflammatory cytokine production. Anti-cancer effect in female mice was, at least in part, due to the significantly lower ratio of oleic to stearic acid in the liver.
Conclusions:  Hepatic lesions in Pten-deficient mice were attenuated in females compared to males, as were human NAFLD and NASH. Some of the underlying mechanisms in sex difference appeared to be due to the change of gene expression, dependent on estrogens.