Enhanced carbon tetrachloride-induced liver fibrosis in mice lacking adiponectin

Induction of TLR tolerance in human macrophages by adiponectin: does LPS play a role?

Obesity is regarded as a pro-inflammatory state. It is associated with low circulating levels of the adipokine, adiponectin, which is considered to be an anti-inflammatory. However, adiponectin knockout mice do not consistently demonstrate pro-inflammatory phenotypes, suggesting more complexity in the in vivo immunomodulatory effects of adiponectin than originally anticipated. Moreover, adiponectin exerts pro-inflammatory effects in some experimental systems. This contradiction has been resolved by hypothesizing that adiponectin induces tolerance to inflammatory stimuli, notably Toll-like receptor (TLR) ligands. We noticed that this effect resembled lipopolysaccharide (LPS) tolerance and therefore tested adiponectin from a variety of sources for LPS contamination. All adiponectin tested carried low levels of LPS in the range of 1-30 pg/microg of adiponectin, sufficient to produce final LPS concentrations in the pg/ml range under experimental conditions. We found that induction of tolerance to TLR ligands by adiponectin in human monocyte-derived macrophages could be reproduced by such LPS concentrations. Moreover, the LPS antagonist, polymixin B, substantially inhibited induction of tolerance by adiponectin. Furthermore, polymixin B and a naturally occurring antagonist LPS were able to partially attenuate induction of tumour necrosis factor-alpha and interleukin-6 in human monocyte-derived macrophages by adiponectin. Polymixin B also inhibited nuclear factor-kappaB and mitogen-activated protein kinase signalling elicited by adiponectin. We therefore propose that some of adiponectin's immunomodulatory effects, in particular, its TLR-tolerising actions in human monocyte-derived macrophages, may be confounded by induction of tolerance by contaminating LPS.

Prevention of steatohepatitis by pioglitazone: implication of adiponectin-dependent inhibition of SREBP-1c and inflammation

BACKGROUND/AIMS

Peroxisome proliferator-activated receptor gamma (PPARgamma) agonist drugs, like pioglitazone (PGZ), are proposed as treatments for steatohepatitis. Their mechanisms of action remain ill-clarified.

METHODS

To test the hypothesis that PGZ improves steatohepatitis through adiponectin-dependent stimulation of AMPK and/or PPARalpha, mice lacking adiponectin (Adipo(-/-)) or the AMPKalpha1 catalytic subunit (AMPKalpha1(-/-)) or wild-type (Wt) mice were fed the methionine and choline deficient (MCD) diet, supplemented or not with PGZ.

RESULTS

In Wt mice, PGZ increased circulating levels of adiponectin and reduced the severity of MCD-induced steatohepatitis but there was no evidence of activation of AMPK or PPARalpha and their downstream targets. By contrast, PGZ completely repressed nuclear translocation of SREBP-1c, a key transcription factor for de novo lipogenesis. This effect was lacking in Adipo(-/-) mice in which PGZ failed to prevent steatohepatitis. Surprisingly, AMPKalpha1(-/-) mice were resistant to MCD-induced steatohepatitis, a status also associated with repression of SREBP-1c.

CONCLUSIONS

The preventive effect of PGZ on MCD-induced steatohepatitis depends on adiponectin upregulation but apparently does not involve AMPK or PPARalpha activation. The inhibition of SREBP-1c and dependent repression of lipogenesis are likely to participate in this effect. The mechanisms by which PGZ and adiponectin control SREBP-1c and inflammation remain to be elucidated.

Obesity-induced insulin resistance and hepatic steatosis are alleviated by omega-3 fatty acids: a role for resolvins and protectins

Omega-3-polyunsaturated fatty acids (omega-3-PUFAs) have well-documented protective effects that are attributed not only to eicosanoid inhibition but also to the formation of novel biologically active lipid mediators (i.e., resolvins and protectins). In this study, we examined their effects on ob/ob mice, an obesity model of insulin resistance and fatty liver disease. Dietary intake of omega-3-PUFAs had insulin-sensitizing actions in adipose tissue and liver and improved insulin tolerance in obese mice. Genes involved in insulin sensitivity (PPARgamma), glucose transport (GLUT-2/GLUT-4), and insulin receptor signaling (IRS-1/IRS-2) were up-regulated by omega-3-PUFAs. Moreover, omega-3-PUFAs increased adiponectin, an anti-inflammatory and insulin-sensitizing adipokine, and induced AMPK phosphorylation, a fuel-sensing enzyme and a gatekeeper of the energy balance. Concomitantly, hepatic steatosis was alleviated by omega-3-PUFAs. A lipidomic analysis with liquid chromatography/mass spectrometry/mass spectrometry revealed that omega-3-PUFAs inhibited the formation of omega-6-PUFA-derived eicosanoids, while triggering the formation of omega-3-PUFA-derived resolvins and protectins. Moreover, representative members of these lipid mediators, namely resolvin E1 and protectin D1, mimicked the insulin-sensitizing and antisteatotic effects of omega-3-PUFAs and induced adiponectin expression to a similar extent that of rosiglitazone, a member of the thiazolidinedione family of antidiabetic drugs. Taken together, these findings uncover beneficial actions of omega-3-PUFAs and their bioactive lipid autacoids in preventing obesity-induced insulin resistance and hepatic steatosis.

Adipocytokines and liver disease

Adipose tissue is a massive source of bioactive substances known as adipocytokines, including tumor necrosis factor (TNF)-alpha, resistin, leptin, and adiponectin. Recent advances in medical research view obesity as a chronic low-grade inflammatory state. Hypertrophied adipocytes in obesity release chemokines that induce macrophage accumulation in adipose tissue. Accumulated macrophages in obese adipose tissue produce proinflammatory cytokines and nitric oxide, and these inflammatory changes induce adipocytokine dysregulation. The latter is characterized by a decrease in insulinsensitizing and anti-inflammatory adipocytokines, and an increase in proinflammatory adipocytokines. Adipocytokine dysregulation induces obesity-related metabolic disorders, the so-called metabolic syndrome. Metabolic syndrome is a cluster of metabolic abnormalities, including diabetes mellitus, hypertension, hyperlipidemia, and nonalcoholic steatohepatitis (NASH). Recent studies have revealed that obesity is an independent risk factor for chronic liver diseases, such as NASH, alcoholic liver disease, chronic hepatitis C, and hepatocellular carcinoma. A common mechanism underlying these hepatic clinical states is thought to be adipocytokine dysregulation. In this review, we discuss the association of adipocytokines, especially leptin, adiponectin, TNF-alpha, and resistin, with liver diseases.

Expression of adiponectin and its receptors in livers of morbidly obese patients with non-alcoholic fatty liver disease

BACKGROUND AND AIM

Obesity is one of the risk factors for non-alcoholic fatty liver disease (NAFLD) and a common disease that comprises simple steatosis and non-alcoholic steatohepatitis (NASH), and can eventually lead to liver cirrhosis. Adiponectin is an adipocyte-derived protein that has anti-obesity, antidiabetic and anti-inflammatory properties, and is considered to possess a hepatoprotective function. Its role in the development and progression of NAFLD in morbidly obese patients is unknown. In this study, we examined the expression levels of adiponectin and its receptors in liver biopsies of morbidly obese patients and then determined whether there was an association with the disease severity.

METHODS

Liver biopsies from 30 morbidly obese patients (18 NASH vs 12 steatosis) were analyzed. The needle core biopsies were subjected to routine histological examination and stained immunohistochemically for adiponectin, adiponectin receptor I (adipoRI) and receptor II (adipoRII).

RESULTS

The two groups were comparable with respect to body mass index, age and gender distribution. The expression of adiponectin decreased in liver biopsies with NASH as compared to those with simple steatosis (1.61 +/- 0.70 vs 2.25 +/- 0.75, P = 0.028). Spearman's rank correlation coefficient analysis showed that the staining intensity of adiponectin negatively correlated with the grade of inflammation (r = -0.368, P = 0.045) and stage of fibrosis (r = -0.380, P = 0.038). There was no significant difference in expression of adipoRI and adipoRII between the two groups.

CONCLUSION

These findings indicate that decreased liver adiponectin expression may play a role in the development and progression of NAFLD, from simple steatosis to NASH, in morbidly obese patients.

Adiponectin inhibits steatotic CD95/Fas up-regulation by hepatocytes: therapeutic implications for hepatitis C

BACKGROUND/AIMS

Steatosis may trigger hepatocytes to up-regulate CD95/Fas thereby increasing susceptibility to apoptosis, inflammation and fibrosis. We investigated this concept and potential roles of adiponectin and its receptors (AdipoR1; AdipoR2) in chronically HCV-infected patients.

METHODS

In 98 HCV+ patients and 20 controls, sera were tested for HCV genotypes, FFAs, adiponectin and the M30 apoptosis indicator, and biopsies were evaluated for steatosis/inflammation/fibrosis, CD95/Fas (mRNA/protein), adiponectin (mRNA/protein), AdipoR1/-R2 (mRNA) and M30 (protein). We also questioned whether adiponectin protects HepG2 hepatoblastoma cells from FFA-triggered CD95/Fas up-regulation and apoptosis.

RESULTS

Patients [HCV clades 1 (78%), 2 (3%) and 3 (19%)] revealed increased FFA and adiponectin serum levels (p = .005). Hepatocyte CD95/Fas up-regulation correlated with steatosis, inflammation and fibrosis (p = .004). Advanced fibrosis correlated significantly (p = .05) with serum M30. Liver adiponectin correlated with steatosis (p = .016), CD95/Fas (p < .001) and inflammation/fibrosis. Hepatocyte AdipoR2 mRNA specifically correlated with serum adiponectin and steatosis (p = .003), while hepatocyte AdipoR1 mRNA dropped in pronounced fibrosis (p = .060). Finally, adiponectin protected HepG2 cells from FFA-triggered CD95/Fas expression and induction of apoptosis (p = .0396).

CONCLUSIONS

In chronic HCV infection, steatosis up-regulates hepatocyte CD95/Fas and thus increases apoptosis, which facilitates inflammation and fibrosis. The physiologic countermeasure of adiponectin up-regulation may offer clues for future therapeutic intervention.

High serum adiponectin correlates with advanced liver disease in patients with chronic hepatitis B virus infection

PURPOSE

Adiponectin possesses anti-inflammatory and insulin-sensitizing properties. Little is known about the role of adiponectin in hepatitis B-related liver disease.

METHODS

Serum adiponectin and hepatitis B viral factors were cross-sectionally assayed in 280 patients with chronic hepatitis B virus (HBV) infection including 120 patients with chronic HBV infection, 40 patients with cirrhosis, and 120 patients with hepatocellular carcinoma (HCC); 116 healthy adults were used as controls. The dynamics of serum adiponectin level was also studied longitudinally in 25 patients with hepatitis B e antigen (HBeAg) seroconversion (SC).

RESULTS

We found that serum adiponectin level in patients with chronic HBV infection was similar to that in healthy controls and was significantly lower than patients with cirrhosis and HCC. In univariate analysis, high serum adiponectin level significantly correlated with the presence of HBV-related cirrhosis or HCC, abnormal serum ALT level, and HBV genotype C. Multivariate analysis revealed that high serum adiponectin level significantly correlated with the development of HCC. Serum adiponectin levels remained stationary in patients experiencing HBeAg SC.

CONCLUSIONS

Our findings suggest that HBV infection itself does not affect adiponectin levels. Serum adiponectin level correlates with the progression of HBV-related liver diseases but not with the development of HBeAg SC.

New concepts in the pathogenesis of alcoholic liver disease

Alcoholic liver disease still represents an important cause for death and disability in most well-developed countries and is becoming a leading cause of disease in developing countries. It is now increasingly clear that, besides the formation of acetaldehyde, alcohol effects on the liver include oxidative stress, disturbances in methionine metabolism, endoplasmic reticulum stress, inflammatory/immune responses and adipokine imbalances. This article will discuss the most recent findings on the mechanisms by which alcohol abuse causes hepatic steatosis and steatohepatitis, and now it contributes to the progression of fibrosis. Although still incomplete, these data shed new light on the multifactorial pathogenesis of alcoholic liver disease and open new possibilities in the understanding of how gender and genetic factors can influence disease progression.

Advances in antifibrotic therapy

Sustained progress in defining the molecular pathophysiology of hepatic fibrosis has led to a comprehensive framework for developing antifibrotic therapies. Indeed, the single greatest limitation in bringing new drugs to the clinical setting is a lack of clarity regarding clinical trial and treatment end points, not a lack of promising agents. A range of treatments, including those developed for other indications, as well as those specifically developed for hepatic fibrosis, are nearing or in clinical trials. Most are focused on attacking features of either hepatic injury and/or activated stellate cells and myofibroblasts, which are the primary sources of extracellular matrix (scar) proteins. Thus, features of injury and stellate cell activation provide a useful template for classifying these emerging agents and point to a new class of therapies for patients with fibrosing liver disease.

Delayed liver regeneration after partial hepatectomy in adiponectin knockout mice

We previously demonstrated that adiponectin has anti-fibrogenic and anti-inflammatory effects in the liver of mouse models of various liver diseases. However, its role in liver regeneration remains unclear. The aim of this study was to determine the role of adiponectin in liver regeneration. We assessed liver regeneration after partial hepatectomy in wild-type (WT) and adiponectin knockout (KO) mice. We analyzed DNA replication and various signaling pathways involved in cell proliferation and metabolism. Adiponectin KO mice exhibited delayed DNA replication and increased lipid accumulation in the regenerating liver. The expression levels of peroxisome proliferator-activated receptor (PPAR) alpha and carnitine palmitoyltransferase-1 (CPT-1), a key enzyme in mitochondrial fatty acid oxidation, were decreased in adiponectin KO mice, suggesting possible contribution of altered fat metabolism to these phenomena. Collectively, the present results highlight a new role for adiponectin in the process of liver regeneration.

Disease-specific mechanisms of fibrosis: hepatitis C virus and nonalcoholic steatohepatitis

Our mechanistic understanding of liver fibrosis has increased dramatically in recent years for all liver diseases and for hepatitis C and nonalcoholic steatohepatitis (NASH) in particular. Hepatitis C causes liver injury and fibrosis through direct cytopathic means, direct and indirect interactions with hepatic stellate cells, and activation of the immune system. Steatosis and insulin resistance, which are intrinsic deficits in NASH, are also of great importance in hepatitis C and may be induced by viral or host metabolic factors. For NASH, the key mediators of damage include oxidative stress, fat compartmentalization, visceral fat, apoptosis, and adipokine derangement. This article explores in depth the disease-specific mechanisms of fibrosis in hepatitis C and NASH, with a focus on recent developments.

Fibrosis and cirrhosis reversibility - molecular mechanisms

The concept that liver fibrosis is a dynamic process with potential for regression as well as progression has emerged in parallel with clinical evidence for remodeling of fibrotic extracellular matrix in patients who can be effectively treated for their underlying cause of liver disease. This article reviews recent discoveries relating to the cellular and molecular mechanisms that regulate fibrosis regression, with emphasis on studies that have used experimental in vivo models of liver disease. Apoptosis of hepatic myofibroblasts is discussed. The functions played by transcription factors, receptor-ligand interactions, and cell-matrix interactions as regulators of the lifespan of hepatic myofibroblasts are considered, as are the therapeutic opportunities for modulating these functions. Growth factors, proteolytic enzymes, and their inhibitors are discussed in detail.

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Cytokines and renin-angiotensin system signaling in hepatic fibrosis

Hepatic fibrosis is the result of a complex interplay between resident hepatic cells, infiltrating inflammatory cells, and a number of locally acting peptides called cytokines. Key mediators include transforming growth factor b1, vasoactive substances, adipokines, inflammatory cytokines and chemokines. Angiotensin II, the main effector of the renin-angiotensin system, is a true cytokine that plays a major role in liver fibrosis. Angiotensin II is locally synthesized in the injured liver and induces profibrogenic actions in hepatic stellate cells. Drugs blocking the renin-angiotensin system are promising antifibrotic agents. There are multiple signal transduction pathways involved in cytokine signaling. Drugs interfering intracellular pathways involved in increased collagen production are potential therapies for liver fibrosis.

Pattern of expression of adiponectin receptors in human liver and its relation to nonalcoholic steatohepatitis

BACKGROUND

Adiponectin has antisteatosis-anti-inflammatory properties and its circulating levels are reduced in nonalcoholic steatohepatitis (NASH).

METHODS

To assess the role of adiponectin in NASH, we measured expression of adiponectin gene (APM1) and receptors (AdipoR1/AdipoR2) in liver and subcutaneous and visceral fat in subjects with biopsy-proven NASH or pure steatosis (PS). In 103 subjects undergoing gastric bypass or elective abdominal surgery (17 with normal liver histology (C), 52 with PS, and 34 with NASH), RNA was extracted from tissue samples, and quantification of APM1, AdipoR1, and AdipoR2 was carried out by real-time polymerase chain reaction.

RESULTS

In NASH vs C, circulating adiponectin levels (3.6[2.4] vs 5.3[4.3] microg/ml, median[interquartile range], p < 0.05) and adiponectin concentrations, APM1, AdipoR1, and AdipoR2 expression in visceral fat were all reduced (p < or = 0.03). These differences disappeared when adjusting for obesity. In contrast, liver AdipoR1 (1.40 [0.46] vs 1.00 [0.32] of controls) and AdipoR2 expression (1.20 [0.41] vs 0.78 [0.43]) were increased in NASH, and group differences were statistically significant (p < 0.0001 for AdipoR1 and p = 0.0001 for AdipoR2). Results for PS were generally intermediate between NASH and C. Liver receptor expression was reciprocally related to circulating adiponectin (rho = -0.42, p < 0.003 for AdipoR1 and rho = -0.26, p < 0.009 for AdipoR2). In multivariate models adjusting for sex, age, fasting plasma glucose, and obesity, liver enzymes levels were directly related to both AdipoR1 and AdipoR2 expression in liver.

CONCLUSION

In obese patients with NASH, adiponectin receptors are underexpressed in visceral fat-as a likely correlate of obesity-but overexpressed in liver, possibly as a compensatory response to hypoadiponectinemia, and positively associated with liver damage.

Bezafibrate prevents hepatic stellate cell activation and fibrogenesis in a murine steatohepatitis model, and suppresses fibrogenic response induced by transforming growth factor-beta1 in a cultured stellate cell line

AIM

The aim of this study was to investigate the preventive actions of bezafibrate against non-alcoholic steatohepatitis (NASH), the activation of hepatic stellate cells (HSC), and fibrogenesis by using a model of NASH and an in vitro model.

METHODS

Male KK-A(y)/TaJcl (KK-A(y)) mice were fed a methionine and choline-deficient (MCD) diet or a MCD diet containing bezafibrate or pioglitazone for 7 weeks, after which biochemical parameters, pathological changes, and hepatic mRNA levels were assessed. An in vitro HSC model was designed by using a previously described RI-T cell line stimulated by transforming growth factor-beta1 (TGF-beta1).

RESULTS

MCD diet-fed KK-A(y) mice developed hepatic steatosis, oxidative stress, inflammation, and hepatic fibrosis. Bezafibrate markedly decreased the hepatic content of triglyceride accumulation of fatty droplets within hepatocytes, and increased the expression of hepatic fatty acid beta-oxidative genes in MCD diet-fed KK-A(y) mice. Bezafibrate markedly inhibited the increases in the plasma alanine aminotransferase level and hepatic content of thiobarbituric acid-reactive substances in this model. Moreover, it dramatically reduced hepatic inflammatory changes and fibrosis concomitantly with marked reductions in the mRNA levels for inflammatory cytokine, chemokine, and profibrogenic genes. Importantly, both bezafibrate and pioglitazone markedly reduced the mRNA levels of profibrogenic and fibrogenic genes in TGF-beta1-stimulated cells.

CONCLUSION

Bezafibrate improved hepatic steatosis and potently prevented inflammation, oxidative stress, HSC activation, and fibrogenesis in the liver. Moreover, this study was the first to demonstrate that bezafibrate directly inhibits hepatic fibrogenic response induced by TGF-beta1 in vitro. Hence bezafibrate may be a new therapeutic strategy against NASH and hepatic fibrosis.

Association of ADIPOR2 with liver function tests in type 2 diabetic subjects

OBJECTIVE

Adiponectin protects against liver dysfunction in insulin-resistant states such as obesity and type 2 diabetes (T2DM), but the role of adiponectin receptors in this disorder is largely unknown. We studied whether common single-nucleotide polymorphisms (SNPs) in ADIPOR1 and ADIPOR2 are associated with liver function tests (LFTs) in human subjects with various degrees of insulin resistance.

METHODS AND PROCEDURES

Serum alanine (ALT) and aspartate (AST) aminotransferases, homeostasis model assessment of insulin resistance (HOMA-IR), -8503 G/A (rs6666089) and +5843 C/T (rs1342387) SNPs in ADIPOR1, -64,241 T/G (rs1029629) and +33447 C/T (rs1044471) SNPs in ADIPOR2 were assessed in 700 white subjects from a population-based study.

RESULTS

In nondiabetic subjects, the at-risk alleles for the common -64,241 T/G and +33447 C/T SNPs in ADIPOR2 were associated with increased circulating adiponectin (P < 0.05 to P < 0.005), but not with LFT. Conversely, in T2DM subjects (who are at risk for liver dysfunction), the same alleles were associated with increased serum ALT and AST (P < 0.05 to P < 0.0001), but not with circulating adiponectin. No significant associations with these parameters were evident for the common -8503 G/A and +5843 C/T SNPs in ADIPOR1. In a replication study, the -64,241 T/G and +33447 C/T SNPs in ADIPOR2 were associated with ALT and AST (P < 0.05 to P < 0.0001) in pooled obese and T2DM subjects.

DISCUSSION

Common SNPs in ADIPOR2 are associated with LFT in T2DM subjects, which suggests a possible role of this receptor in liver dysfunction associated with insulin resistance.

Mitochondrial dysfunction contributes to the increased vulnerabilities of adiponectin knockout mice to liver injury

Adiponectin is an adipocyte-derived hormone with a wide range of beneficial effects on obesity-related medical complications. Numerous epidemiological investigations in diverse ethnic groups have identified a lower adiponectin level as an independent risk factor for nonalcoholic fatty liver diseases and liver dysfunctions. Animal studies have demonstrated that replenishment of adiponectin protects against various forms of hepatic injuries, suggesting it to be a potential drug candidate for the treatment of liver diseases. This study was designed to investigate the cellular and molecular mechanisms underlying the hepatoprotective effects of adiponectin. Our results demonstrated that in adiponectin knockout (ADN-KO) mice, there was a preexisting condition of hepatic steatosis and mitochondrial dysfunction that might contribute to the increased vulnerabilities of these mice to secondary liver injuries induced by obesity and other conditions. Adenovirus-mediated replenishment of adiponectin depleted lipid accumulation, restored the oxidative activities of mitochondrial respiratory chain (MRC) complexes, and prevented the accumulation of lipid peroxidation products in ADN-KO mice but had no obvious effects on mitochondrial biogenesis. The gene and protein levels of uncoupling protein 2 (UCP2), a mitochondrial membrane transporter, were decreased in ADN-KO mice and could be significantly up-regulated by adiponectin treatment. Moreover, the effects of adiponectin on mitochondrial activities and on protection against endotoxin-induced liver injuries were significantly attenuated in UCP2 knockout mice.

CONCLUSION

These results suggest that the hepatoprotective properties of adiponectin are mediated at least in part by an enhancement of the activities of MRC complexes through a mechanism involving UCP2.

Circulating adiponectin levels in patients with atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) characterized by atrial remodeling occurs with obesity-related conditions. Adiponectin, an adipose tissue-derived hormone exerts beneficial effects on ventricular remodeling, so in the present study the potential association between circulating adiponectin levels and atrial remodeling in patients with AF was investigated.

METHODS AND RESULTS

The levels of plasma adiponectin, serum carboxy-terminal telopeptide of collagen type I (CITP), as a collagen type I degradation marker, and serum type III procollagen-N-peptide (PIIINP), as a collagen type III synthesis marker, were measured in 304 consecutive patients (162 paroxysmal AF, 46 persistent AF, 96 paroxysmal supra-ventricular tachycardia [controls]). Plasma adiponectin levels were significantly higher in patients with persistent AF than in those with paroxysmal AF or the control patients (p<0.05). Serum CITP levels, but not serum PIIINP levels, were higher in patients with persistent AF compared with the paroxysmal AF and control patients (p<0.05). In addition, there was a positive correlation between adiponectin levels and CITP levels in patients with persistent AF (r=0.39, p<0.005).

CONCLUSIONS

High plasma adiponectin levels are associated with the presence of persistent AF, which is accompanied by increased CITP levels. Thus, measurement of plasma adiponectin could be useful for assessment of AF.

Targeting liver myofibroblasts: a novel approach in anti-fibrogenic therapy

Chronic liver disease results in a liver-scarring response termed fibrosis. Excessive scarring leads to cirrhosis, which is associated with high morbidity and mortality. The only treatment for liver cirrhosis is liver transplantation; therefore, much attention has been directed toward therapies that will slow or reverse fibrosis. Although anti-fibrogenic therapies have been shown to be effective in experimental animal models, licensed therapies have yet to emerge. A potential problem for any anti-fibrogenic therapy in the liver is the existence of the body’s major drug metabolising cell (the hepatocyte) adjacent to the primary fibrosis-causing cell, the myofibroblast. This article reviews the development of a human recombinant single-chain antibody (scAb) that binds to the surface of myofibroblasts. This antibody binds specifically to myofibroblasts in fibrotic mouse livers. When conjugated with a compound that stimulates myofibroblast apoptosis, the antibody directs the specific apoptosis of myofibroblasts with greater specificity and efficacy than the free compound. The antibody also reduces the adverse effect of liver macrophage apoptosis and—in contrast to the free compound—reversed fibrosis in the sustained injury model used. These data suggest that specifically stimulating the apoptosis of liver myofibroblasts using a targeting antibody has potential in the treatment of liver fibrosis.

Hepatic fibrogenesis in response to chronic liver injury: novel insights on the role of cell-to-cell interaction and transition

Hepatic fibrosis represents the wound-healing response process of the liver to chronic injury, independently from aetiology. Advanced liver fibrosis results in cirrhosis that can lead to liver failure, portal hypertension and hepatocellular carcinoma. Currently, no effective therapies are available for hepatic fibrosis. After the definition of hepatic stellate cells (HSCs) as the main liver extracellular matrix-producing cells in the 1980s, the subsequent decade was dedicated to determine the role of specific cytokines and growth factors. Fibrotic progression of chronic liver diseases can be nowadays considered as a dynamic and highly integrated process of cellular response to chronic liver injury. The present review is dedicated to the novel mechanisms of cellular response to chronic liver injury leading to hepatic myofibroblasts' activation. The understanding of the cellular and molecular pathways regulating their function is crucial to counteract therapeutically the organ dysfunction caused by myofibroblasts' activation.

Plasma adiponectin levels in primary biliary cirrhosis: a novel perspective for link between hypercholesterolemia and protection against atherosclerosis

INTRODUCTION

Hypercholesterolemia is a common finding in primary biliary cirrhosis (PBC), but the risk of cardiovascular events in PBC patients is not increased in respect to the general population. High serum adiponectin levels appear to play a protective role in the development of either metabolic syndrome or cardiovascular disease.

AIM

To investigate factors potentially preventing atherosclerosis in PBC patients.

METHODS

Circulating levels of adiponectin, resistin, leptin, and tumor necrosis factor-alpha (TNF-alpha) were measured in 137 consecutive PBC patients (125 women, 12 men; mean age 61.6 +/- 12.3 yr), 137 sex- and age-matched healthy controls, and 30 female patients with nonalcoholic steatohepatitis (NASH) and associated metabolic syndrome.

RESULTS

The body mass index (BMI) was comparable in the three groups, whereas total cholesterol was significantly higher in both PBC and NASH cases than in controls (221.6 +/- 50.5 mg/dL in PBC vs 221.7 +/- 39.7 mg/dL in NASH vs 209.8 +/- 39.2 mg/dL in controls, P < 0.05). Serum concentrations of adiponectin, resistin, and leptin were significantly higher in PBC patients than in either NASH cases or controls (P < 0.05). Among the PBC patients, only adiponectin correlated positively with histological progression of the disease (P= 0.001) and negatively with BMI (P= 0.01). Logistic regression analysis revealed that adiponectin correlated independently with age, BMI, Mayo score, and gamma-glutamyl transpeptidase.

CONCLUSIONS

The high adiponectin concentrations observed in PBC patients should be regarded as a possible protective factor against atherogenesis. The search for further protective factors should be encouraged.

Hepatic fibrosis -- overview

The study of hepatic fibrosis, or scarring in response to chronic liver injury, has witnessed tremendous progress in the past two decades. Clarification of the cellular sources of scar, and emergence of hepatic stellate cells not only as a fibrogenic cell type, but also as a critical immunomodulatory and homeostatic regulator are among the most salient advances. Activation of hepatic stellate cells remains a central event in fibrosis, complemented by evidence of additional sources of matrix-producing cells including bone marrow, portal fibroblasts, and epithelial-mesenchymal transition from both hepatocytes and cholangiocytes. A growing range of cytokines and their receptors and inflammatory cell subsets have further expanded our knowledge about this dynamic process. Collectively, these findings have laid the foundation for continued elucidation of underlying mechanisms, and more importantly for the implementation of rationally based approaches to limit fibrosis, accelerate repair and enhance liver regeneration in patients with chronic liver disease.

The role of adipokines in liver fibrosis

Liver fibrosis is a dynamic process consisting of the chronic activation of the wound healing reaction in response to reiterated liver damage, leading to the excessive deposition of fibrillar extracellular matrix into the liver and eventually, if the cause of injury is not removed, to liver cirrhosis. The term "adipokines" identifies a group of polypeptide molecules secreted primarily by adipose tissue, which exert local, peripheral and/or central actions. Additionally to their well-established role in controlling adipose tissue physiology, adipokines have been shown to be involved in different obesity-related diseases, such as hypertension, atherosclerosis and type 2 diabetes. Accumulating data demonstrate that obesity and insulin resistance are associated with a more severe and faster progression of the fibrogenic process in different chronic liver diseases. Therefore, numerous recent studies have analyzed the role played by adipokines in the hepatic wound healing process, identifying novel roles as modulators of liver pathophysiology. This review summarizes the more significant and recent findings concerning the role played by adipocyte-derived molecules, such as leptin, adiponectin and resistin, in the liver fibrogenic process. The actions of different adipokines on the biology of liver resident cells, as well as their effects in different animal models of liver injury are discussed. The variations in the circulating levels and in the intrahepatic expression of these molecules occurring in patients with different chronic liver diseases will be also analyzed.

Adiponectin and left ventricular structure and function in healthy adults

CONTEXT

Adiponectin inhibits protein synthesis in cardiac myocytes, thereby opposing the effect of cardiac workload and trophic factors (in particular, insulin) on left ventricular (LV) mass and wall thickness (WT).

OBJECTIVE

We tested whether adiponectin and its isoforms are related to LV mass, WT, and function independently of metabolic factors.

DESIGN

This was a cross-sectional study.

SUBJECTS

The study included 77 healthy volunteers (42 men) aged 30-59 yr with normal LV structure and function.

MAIN OUTCOME MEASURES

Insulin response and insulin sensitivity were assessed by oral glucose tolerance test and euglycemic hyperinsulinemic clamp. LV mass, WT, stroke work, chamber function, and myocardial longitudinal function were evaluated by standard Doppler echocardiography and tissue Doppler imaging. Total and molecular isoforms of adiponectin were measured in plasma.

RESULTS

By multivariate analysis, independent factors affecting LV mass were sex, body mass index, stroke work, and current smoking (R(2) = 0.66). Independent correlates of LV WT were age, stroke work, and plasma adiponectin (standardized r = 0.28, 0.41, and -0.26, P at least < 0.005, R(2) = 0.48). LV longitudinal late diastolic velocity was independently related to age, body mass index, and adiponectin (standardized r = 0.20, 0.26, -0.33, P at least < 0.05, R(2) = 0.30). High-molecular-weight adiponectin (47% of total), but not lower molecular-weight isoforms, insulin sensitivity, or other metabolic factors, was inversely and independently related to WT (standardized r = -0.27, P < 0.01) and myocardial longitudinal late diastolic velocity (standardized r = -0.28, P < 0.05).

CONCLUSION

In healthy subjects, circulating total and high-molecular-weight adiponectin are related to LV WT and diastolic function, independently of age and metabolic factors.

Hepatic triglyceride synthesis and nonalcoholic fatty liver disease

PURPOSE OF REVIEW

Nonalcoholic fatty liver disease is a spectrum of diseases ranging from simple steatosis to cirrhosis. The hallmark of nonalcoholic fatty liver disease is hepatocyte accumulation of triglycerides. We will review the role of triglyceride synthesis in nonalcoholic fatty liver disease progression and summarize recent findings about triglyceride synthesis inhibition and prevention of progressive disease.

RECENT FINDINGS

Attempts to inhibit triglyceride synthesis in animal models have resulted in improvement in hepatic steatosis. Studies in animal models of nonalcoholic fatty liver disease demonstrate that inhibition of acyl-coenzyme A:diacylglycerol acyltransferase, the enzyme that catalyzes the final step in triglyceride synthesis, results in improvement in hepatic steatosis and insulin sensitivity. We recently confirmed that hepatic specific inhibition of acyl-coenzyme A:diacylglycerol acyltransferase with antisense oligonucleotides improves hepatic steatosis in obese, diabetic mice but, unexpectedly, exacerbated injury and fibrosis in that model of progressive nonalcoholic fatty liver disease. When hepatocyte triglyceride synthesis was inhibited, free fatty acids accumulated in the liver, leading to induction of fatty acid oxidizing systems that increased hepatic oxidative stress and liver damage. These findings suggest that the ability to synthesize triglycerides may, in fact, be protective in obesity.

SUMMARY

Nonalcoholic fatty liver disease is strongly associated with obesity and peripheral insulin resistance. Peripheral insulin resistance increases lipolysis in adipose depots, promoting increased free fatty acid delivery to the liver. In states of energy excess, such as obesity, the latter normally triggers hepatic triglyceride synthesis. When hepatic triglyceride synthesis is unable to accommodate increased hepatocyte free fatty acid accumulation, however, lipotoxicity results. Thus, rather than being hepatotoxic, liver triglyceride accumulation is actually hepato-protective in obese, insulin-resistant individuals.

Mechanisms of hepatic fibrogenesis

Substantial improvements in the treatment of chronic liver disease have accelerated interest in uncovering the mechanisms underlying hepatic fibrosis and its resolution. Activation of resident hepatic stellate cells into proliferative, contractile, and fibrogenic cells in liver injury remains a dominant theme driving the field. However, several new areas of rapid progress in the past 5-10 years also have taken root, including: (1) identification of different fibrogenic populations apart from resident stellate cells, for example, portal fibroblasts, fibrocytes, and bone-marrow-derived cells, as well as cells derived from epithelial mesenchymal transition; (2) emergence of stellate cells as finely regulated determinants of hepatic inflammation and immunity; (3) elucidation of multiple pathways controlling gene expression during stellate cell activation including transcriptional, post-transcriptional, and epigenetic mechanisms; (4) recognition of disease-specific pathways of fibrogenesis; (5) re-emergence of hepatic macrophages as determinants of matrix degradation in fibrosis resolution and the importance of matrix cross-linking and scar maturation in determining reversibility; and (6) hints that hepatic stellate cells may contribute to hepatic stem cell behavior, cancer, and regeneration. Clinical and translational implications of these advances have become clear, and have begun to impact significantly on the management and outlook of patients with chronic liver disease.

Hypoadiponectinemia plays a crucial role in the development of nonalcoholic fatty liver disease in patients with type 2 diabetes mellitus independent of visceral adipose tissue

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver injury. The spectrum of NAFLD is broad, extending from simple steatosis through nonalcoholic steatohepatitis (NASH). Insulin resistance has been found to increase the risk of NASH, and obesity, and decreased levels of adiponectin are important factors in determining the severity of insulin resistance. Recent evidence has indicated that hypoadiponectinemia is involved in hepatic steatosis and NASH.

METHODS

To investigate whether hypoadiponectinemia causes hepatic steatosis in type 2 diabetes mellitus (DM) patients independently of visceral adipose tissue, we measured the plasma adiponectin concentration, hepatic fat content based on the liver-to-spleen ratio (L/S ratio) according to computed tomography (CT) attenuation values, and the amount of visceral adipose tissue and subcutaneous adipose tissue by CT in 248 type 2 DM patients. We also investigated the relationship between the serum level of adiponectin and hepatic fibrosis.

RESULTS

Significant correlations were observed between the L/S ratios and aspartate aminotransferase, alanine aminotransferase, visceral adipose tissue, subcutaneous adipose tissue, and serum adiponectin values (r=0.300, p=0.0007), and there was a highly significant inverse correlation between the visceral adipose tissue values and the serum adiponectin levels (r=-0.327, p<0.0002). The subcutaneous adipose tissue values, however, were not correlated with the serum adiponectin levels. Multiple regression analysis was used to quantify the impact of measured variables on the L/S ratio. After adjustment for age, gender, and visceral adipose tissue, the serum adiponectin levels were still significantly correlated with the L/S ratios (p=0.0064). And there was a stepwise decrease in the serum adiponectin in parallel to the severity of hepatic fibrosis.

CONCLUSIONS

Hypoadiponectinemia is concluded to be involved in the etiology of hepatic steatosis independently of visceral adipose tissue content, and is considered to be an important factor in the progression of fibrosis; further studies will be necessary to elucidate the exact physiological role of adiponectin and its contribution to the progression of NASH.

Liver fibrosis

Liver damage leads to an inflammatory response and to the activation and proliferation of mesenchymal cell populations within the liver which remodel the extracellular matrix as part of an orchestrated wound-healing response. Chronic damage results in a progressive accumulation of scarring proteins (fibrosis) that, with increasing severity, alters tissue structure and function, leading to cirrhosis and liver failure. Efforts to modulate the fibrogenesis process have focused on understanding the biology of the heterogeneous liver fibroblast populations. The fibroblasts are derived from sources within and out with the liver. Fibroblasts expressing alpha-smooth muscle actin (myofibroblasts) may be derived from the transdifferentiation of quiescent hepatic stellate cells. Other fibroblasts emerge from the portal tracts within the liver. At least a proportion of these cells in diseased liver originate from the bone marrow. In addition, fibrogenic fibroblasts may also be generated through liver epithelial (hepatocyte and biliary epithelial cell)-mesenchymal transition. Whatever their origin, it is clear that fibrogenic fibroblast activity is sensitive to (and may be active in) the cytokine and chemokine profiles of liver-resident leucocytes such as macrophages. They may also be a component driving the regeneration of tissue. Understanding the complex intercellular interactions regulating liver fibrogenesis is of increasing importance in view of predicted increases in chronic liver disease and the current paucity of effective therapies.

Dietary phosphatidylinositol prevents the development of nonalcoholic fatty liver disease in Zucker (fa/fa) rats

Recent studies have shown that dietary phospholipids, especially phosphatidylcholine and phosphatidylserine, have various beneficial biological effects. However, there are not enough data concerning the physiological function of dietary phosphatidylinositol (PI). The metabolic syndrome, a cluster of metabolic abnormalities such as dyslipidemia, diabetes mellitus, and hypertension, is a widespread and increasingly prevalent disease in industrialized countries. Nonalcoholic fatty liver disease (NAFLD) is often associated with features of the metabolic syndrome. NAFLD describes the spectrum of liver damage ranging from hepatic steatosis to steatohepatitis, liver fibrosis, and cirrhosis, and it is emerging as the most common liver disease worldwide. The present study examined whether dietary PI protects Zucker ( fa/ fa) rats from the metabolic syndrome. For 4 weeks, rats were fed semisynthetic diets containing either 7% soybean oil or 5% soybean oil plus 2% PI. Dietary PI markedly prevented the development of hepatomegaly and hepatic steatosis and lowered hepatic injury markers in serum. Additionally, hyperinsulinemia was relieved by the feeding of dietary PI in Zucker rats. These effects were attributable to an increase in serum adiponectin, enhancement of fatty acid beta-oxidation, and suppression of mRNA expression of inflammatory genes in the liver. This is the first report that dietary PI increases serum adiponectin level and prevents the development of NAFLD in a rat model of the metabolic syndrome.

Bioconjugation of oligonucleotides for treating liver fibrosis

Liver fibrosis results from chronic liver injury due to hepatitis B and C, excessive alcohol ingestion, and metal ion overload. Fibrosis culminates in cirrhosis and results in liver failure. Therefore, a potent antifibrotic therapy is urgently needed to reverse scarring and eliminate progression to cirrhosis. Although activated hepatic stellate cells (HSCs) remain the principle cell type responsible for liver fibrosis, perivascular fibroblasts of portal and central veins as well as periductular fibroblasts are other sources of fibrogenic cells. This review will critically discuss various treatment strategies for liver fibrosis, including prevention of liver injury, reduction of inflammation, inhibition of HSC activation, degradation of scar matrix, and inhibition of aberrant collagen synthesis. Oligonucleotides (ODNs) are short, single-stranded nucleic acids, which disrupt expression of target protein by binding to complementary mRNA or forming triplex with genomic DNA. Triplex forming oligonucleotides (TFOs) provide an attractive strategy for treating liver fibrosis. A series of TFOs have been developed for inhibiting the transcription of alpha1(I) collagen gene, which opens a new area for antifibrotic drugs. There will be in-depth discussion on the use of TFOs and how different bioconjugation strategies can be utilized for their site-specific delivery to HSCs or hepatocytes for enhanced antifibrotic activities. Various insights developed in individual strategy and the need for multipronged approaches will also be discussed.

Evidence-Based Efficacy of Kampo Formulas in a Model of Non Alcoholic Fatty Liver

Data on the efficacy of herbal compounds are often burdened by the lack of appropriate controls or a limited statistical power. Treatments to prevent the progression of non alcoholic fatty liver disease (NAFLD) to steatohepatitis (NASH) remain unsatisfactory. A total of 56 rabbits were arrayed into 7 groups fed with standard rabbit chow (SRC), SRC with 1% cholesterol, or each of the five experimental treatments (Kampo formulas 1% keishibukuryogan [KBG], 1% orengedokuto [OGT], and 1% shosaikoto [SST]; vitamin E [VE]; or pioglitazone [PG]) in a 1% cholesterol SRC. We analyzed changes after 12 weeks in plasma and liver lipid profiles, glucose metabolism, adipocytokines, oxidative stress, and liver fibrosis. Data demonstrated that all five treatments were associated with significant amelioration of lipid profiles, oxidative stress, and liver fibrosis compared to no supplementation. KBG was superior to VE and PG in the reduction of liver total cholesterol ( P < 0.01) and lipid peroxidase levels ( P < 0.05), urinary 8-hydroxy-2′-deoxyguanosine ( P < 0.05), hepatic α-smooth muscle actin positive areas ( P < 0.01) and activated stellate cells ( P < 0.01). In conclusion, there was a statistically significant benefit of Kampo formulas (KBG in particular) on a dietary model of NAFLD/NASH. Future studies need to be directed at the mechanisms in the treatment of NASH.

Adiponectin and cardiovascular inflammatory responses

Obesity is recognized as a cause of many metabolic and cardiovascular disorders through its ability to promote chronic systemic inflammation. Recent studies have found that adipose tissues secrete numerous cytokines that are referred to as adipokines. Although most adipokines induce inflammation, adiponectin inhibits inflammatory reactions and protects against metabolic and cardiovascular diseases. This review focuses on the anti-inflammatory properties of adiponectin in various experimental systems, especially with respect to cardiovascular diseases.

Role of adiponectin and PBEF/visfatin as regulators of inflammation: involvement in obesity-associated diseases

Obesity and obesity-related disorders play an important role in clinical medicine. Adipose tissue, with its soluble mediators called adipocytokines, has emerged as a major endocrine organ. These adipocytokines comprise many mediators such as adiponectin, PBEF (pre-B-cell-enhancing factor)/visfatin, leptin, resistin, retinol-binding protein-4 and others. They play major roles in key aspects of metabolism, such as insulin resistance, fatty acid oxidation, inflammation and immunity. Adiponectin, a prototypic adipocytokine, is of importance in the regulation of insulin resistance, as circulating levels are decreased in obesity and diseases associated with insulin resistance. Besides its major role in regulation of insulin sensitivity, recent evidence suggests potent anti-inflammatory functions for adiponectin. These effects are paralleled by other immune-regulatory properties, such as regulation of endothelial cell function. The in vitro effects of adiponectin have been corroborated by several studies demonstrating potent in vivo anti-inflammatory effects. Many other adipocytokines, such as PBEF/visfatin, leptin, resistin or retinol binding protein-4, are involved in the physiology and pathophysiology of adipocytes, adipose tissue and related diseases. PBEF/visfatin, another recently characterized adipocytokine, has been linked to several inflammatory disease states beyond insulin resistance, such as acute lung injury or inflammatory bowel diseases. It has been recognized for many decades that obesity is accompanied by an increase in cancer and potentially some immune-mediated diseases. Understanding this new exciting world of adipocytokines will be of importance in the development of novel therapies for obesity-associated diseases.

Roles of adipokines in liver injury and fibrosis

Adipose tissue is now recognized as the largest endocrine organ in the body, secreting over 100 proteins termed adipokines that influence energy homeostasis, lipid physiology, inflammation, immune function and wound healing. Some of these proteins, such as TNFalpha, have important proinflammatory effects, but during hepatic injury are principally secreted at a local level within the liver. Their role in liver injury and fibrosis is beyond the scope of this review. However, circulating adipose-derived proteins such as leptin, adiponectin and resistin have important systemic effects, including the modulation of injury and fibrosis. The activities of these adipokines in the pathogenesis of liver injury and fibrosis will be the topic of this review.

Serum retinol binding protein 4 and nonalcoholic fatty liver disease in patients with type 2 diabetes mellitus

Retinol binding protein 4 (RBP4) is a protein secreted by adipocytes, and closely associated with insulin resistance. Whereas RBP4 is also mainly expressed in hepatocytes as the principal transport protein for retinol (vitamin A) in the circulation, and its pathophysiological role in liver remain unclear. The aim of this paper was to investigate the association between RBP4 and nonalcoholic fatty liver disease (NAFLD) in patients with type 2 diabetes mellitus (T2DM). Serum RBP4 and adiponectin concentrations were measured by radioimmunoassay in 52 diabetic patients who had NAFLD and 50 sex- and age-matched diabetic patients without any clinical features of liver diseases who had normal liver ultrasonic appearance and normal liver function. Serum RBP4 levels were elevated in diabetic patients with NAFLD (32.0+/-8.9 microg/ml vs. 41.3+/-9.8 microg/ml, p<0.001), while adiponectin decreased (17.4+/-9.3 microg/ml vs. 13.8+/-7.0 microg/ml, p=0.032). Male diabetic patients had higher serum RBP4 concentration and lower serum adiponectin concentration than female diabetic patients (38.5+/-9.9 microg/ml vs. 34.0+/-10.7 microg/ml, p=0.031 and 12.7+/-5.7 microg/ml vs. 20.23+/-9.8 microg/ml, p<0.001, respectively). Multiple logistic regression analysis revealed RBP4 and triglyceride as independent association factors for NAFLD, while the association between serum adiponectin and NAFLD was not significant. Increasing concentrations of RBP4 were independently and significantly associated with NAFLD in diabetic patients. In multiple linear regression analysis, alanine aminotransferase, fasting serum insulin and adiponectin were independent factors for serum RBP4 level. The study demonstrates that retinol binding protein 4 might contribute to the pathogenesis of nonalcoholic fatty liver disease.

Adenosine monophosphate-activated protein kinase modulates the activated phenotype of hepatic stellate cells

Adiponectin limits the development of liver fibrosis and activates adenosine monophosphate-activated protein kinase (AMPK). AMPK is a sensor of the cellular energy status, but its possible modulation of the fibrogenic properties of hepatic stellate cells (HSCs) has not been established. In this study, we investigated the role of AMPK activation in the biology of activated human HSCs. A time-dependent activation of AMPK was observed in response to a number of stimuli, including globular adiponectin, 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR), or metformin. All these compounds significantly inhibited platelet-derived growth factor (PDGF)-stimulated proliferation and migration of human HSCs and reduced the secretion of monocyte chemoattractant protein-1. In addition, AICAR limited the secretion of type I procollagen. Knockdown of AMPK by gene silencing increased the mitogenic effects of PDGF, confirming the negative modulation exerted by this pathway on HSCs. AMPK activation did not reduce PDGF-dependent activation of extracellular signal-regulated kinase (ERK) or Akt at early time points, whereas a marked inhibition was observed 24 hours after addition of PDGF, reflecting a block in cell cycle progression. In contrast, AICAR blocked short-term phosphorylation of ribosomal S6 kinase (p70(S6K)) and 4E binding protein-1 (4EBP1), 2 downstream effectors of the mammalian target of rapamycin (mTOR) pathway, by PDGF. The ability of interleukin-a (IL-1) to activate nuclear factor kappa B (NF-kappaB) was also reduced by AICAR.

CONCLUSION

Activation of AMPK negatively modulates the activated phenotype of HSCs.

High molecular weight adiponectin inhibits proliferation of hepatic stellate cells via activation of adenosine monophosphate-activated protein kinase

Adiponectin is an adipocyte-derived, antidiabetic, antiatherogenic adipocytokine that is present in serum as 3 isoforms. Decreased plasma adiponectin levels are closely associated with the severity of nonalcoholic fatty liver diseases. This study was designed to elucidate a role of adiponectin and its mediator adenosine monophosphate-activated protein kinase (AMPK) on proliferation of activated hepatic stellate cells (HSCs), the key cells promoting fibrosis. Immortalized human HSC line hTERT and primary rat HSCs were stimulated with platelet-derived growth factor (PDGF) with or without pretreatment with AMPK activator 5-aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR), metformin, or high molecular weight (HMW) adiponectin. HMW adiponectin dose-dependently suppressed PDGF-induced HSC proliferation. Adenoviral transduction with dominant-negative AMPK (DN-AMPK) abolished the suppressive effect of adiponectin in HSCs. AICAR, metformin, or transduction of constitutively active AMPK attenuated PDGF-induced [(3)H]thymidine incorporation, which was abolished by either a chemical AMPK inhibitor or transduction of DN-AMPK, consistent with an antiproliferative effect of AMPK. The suppressive effect of AMPK on HSC proliferation is mediated through multiple mechanisms, including (1) an inhibition of the AKT pathway, (2) inhibition of NADPH oxidase-dependent reactive oxygen species (ROS) production via induction of antioxidant enzymes, and (3) an increase in the expression of the cyclin-dependent kinase inhibitors p27(kip1) and p21(cip1).

CONCLUSION

Adiponectin inhibits HSC proliferation via activation of AMPK. AMPK activation by AICAR or metformin inhibits HSC proliferation via suppression of ROS production and subsequent inhibition of AKT pathway. Thus, adiponectin and AMPK inhibit HSC proliferation and hepatic fibrosis via multiple molecular mechanisms.

High hepatitis C viral load is associated with insulin resistance in patients with chronic hepatitis C

BACKGROUND AND AIMS

Although insulin resistance affects liver fibrosis progression and treatment response in chronic hepatitis C (CHC), the relationship between chronic hepatitis C virus (HCV) infection and insulin resistance (IR) remains to be firmly established. We thus studied the impact of host, metabolic and viral factors on IR in CHC patients.

METHODS

A total of 162 CHC patients with complete clinical data were enrolled. Among them, 94 received histological examinations. Quantitative HCV RNA was assayed by a real-time polymerase chain reaction (PCR) assay. Genotyping was performed by reverse transcription PCR with type-specific primers. The pretreatment IR index was determined using homeostasis model assessment (HOMA), and an index value of more than 2.4 was designated IR. Unadjusted and adjusted association of the HCV RNA level and IR was further analysed.

RESULTS

In multivariate linear regression analysis, a dose-response relationship was observed between the log(10) HCV RNA level and the presence of IR. IR was positively correlated with body mass index, triglyceride, HCV RNA and alanine aminotransferase levels, but negatively correlated with adiponectin level. Subgroup analysis stratified by HCV genotype showed that there was a trend towards a higher HOMR-IR index value and lower adiponectin levels in genotype 1 patients. Histological analysis showed that IR was positively associated with the severity of hepatic steatosis.

CONCLUSIONS

Our data indicate that higher HCV RNA levels are associated with the presence of IR in CHC patients. Further studies are needed to clarify the interplays between HCV infection, IR and adiponectin in an attempt to develop new adjuvant therapy for CHC.

Molecular basis and mechanisms of progression of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH), a cause of cirrhosis and hepatocellular carcinoma, is characterized by fatty infiltration of the liver, inflammation, hepatocellular damage and fibrosis. Progress has been made in understanding the molecular and cellular mechanisms implicated in the pathogenesis of this condition, therefore, we here review recent developments regarding the basic mechanisms of NASH development. Accumulation of triglycerides in the hepatocytes is the result of increased inflow of free fatty acids and de novo lipogenesis. Steatosis leads to lipotoxicity, which causes apoptosis, necrosis, generation of oxidative stress and inflammation. The resulting chronic injury activates a fibrogenic response that leads eventually to end-stage liver disease. A better understanding of these mechanisms is crucial for the design of novel diagnostic and therapeutic strategies.

Influence of cannabis use on severity of hepatitis C disease

BACKGROUND & AIMS

Complications of HCV infection are primarily related to the development of advanced fibrosis and whether cannabis use is a risk factor for more severe fibrosis is controversial.

METHODS

Baseline data from a prospective cohort study of 204 persons with chronic HCV infection were used for analysis. The outcome was fibrosis score on biopsy, and the primary predictor evaluated was daily cannabis use.

RESULTS

The median age of the cohort was 46.8 years, 69.1% were male, 49.0% were white, and the presumed route of infection was injection drug use in 70.1%. The median lifetime duration and average daily use of alcohol were 29.1 years and 1.94 drink equivalents per day, respectively. Cannabis use frequency (within prior 12 months) was daily in 13.7%, occasional in 45.1%, and never in 41.2%. Fibrosis stage, assessed by the Ishak method, was F0, F1-2, and F3-6 in 27.5%, 55.4%, and 17.2% of subjects, respectively. Daily compared with non-daily cannabis use was significantly associated with moderate to severe fibrosis (F3-6 vs F1-2) in univariate (odds ratio [OR], 3.21; 95% confidence interval [CI], 1.20-8.56, P = .020) and multivariate analyses (OR, 6.78; 95% CI, 1.89-24.31, P = .003). Other independent predictors of F3-6 were >or=11 portal tracts (compared with <5, OR, 6.92; 95% CI, 1.34-35.7, P = .021) and lifetime duration of moderate to heavy alcohol use (OR per decade, 1.72; 95% CI, 1.02-2.90, P = .044).

CONCLUSIONS

Daily cannabis use is strongly associated with moderate to severe fibrosis, and HCV-infected individuals should be counseled to reduce or abstain from cannabis use.

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.

Expression of adiponectin during hepatic stellate cell (HSC) activation and the effect of adiponectin on expression of matrix metalloproteinase-13 in primary HSCs

AIM: To study trends in the expression of adiponectin during hepatic stellate cell (HSC) activation and the effects of adiponectin on mRNA and protein expression of matrix metalloproteinase-13 (MMP-13), which was closely related to liver fibrosis in primary HSCs.

METHODS: We isolated primary HSCs through improved two-step liver in situ perfusion, and investigated changes in expression of adiponectin during activation of primary HSCs. MTT was used to study the effect of adiponectin on proliferation of activated HSCs. We chose proper concentration of adiponectin and then divided primary HSCs into five groups according to the concentration of adiponectin. Real-time PCR was used to detect the difference of a-smooth muscle actin, adiponectin and MMP-13 expression between the groups. Enzyme linked immunosorbent assay (ELISA) was used to detect the quantity of MMP-13 protein secreted into the medium.

RESULTS: The survival rate of HSCs showed a linear correlation with adiponectin concentration (OR = 0.828). Expression of adiponectin was down-regulated during HSC activation. Adiponectin was able to inhibit the proliferation of HSCs. When the concentration of adiponectin was 500 mg/L, MMP-13 mRNA expression, in contrast with that in the control group, increased by 5.54 times. MMP-13 protein expression in adiponectin-treated cells increased significantly in contrast with that in the control group (30.951 mg/L vs 24.127 mg/L).

CONCLUSION: Expression of adiponectin was decreased during HSC activation. As a member of the adipokines, adiponectin can exert its potential anti-fibrotic activity through inhibition of HSC proliferation and up-regulation of expression of MMP-13 in primary HSCs.

Regulation of adiponectin receptor expression in human liver and a hepatocyte cell line

Nonalcoholic fatty liver disease (NAFLD) is closely associated with obesity. An adipocyte-derived hormone, adiponectin, may play a role in the pathophysiology of NAFLD through insulin-sensitizing and antifibrotic effects. We found that hepatic expression of adiponectin receptor AdipoR2, but not AdipoR1, was down-regulated in 14 patients with NAFLD compared with 7 patients with a normal liver (P < .05). To investigate the significance of the adiponectin system in obesity and NAFLD, we examined the regulation of AdipoR2 expression in a nonmalignant human hepatocyte cell line, the THLE-5b cells. Insulin down-regulated the levels of AdipoR2 messenger RNA (mRNA) and protein, whereas an adipocytokine, tumor necrosis factor alpha, up-regulated them. A thiazolidinedione, pioglitazone, up-regulated the expression of AdipoR2 mRNA and protein in THLE-5b cells. The AdipoR2 mRNA level was decreased in fatty THLE-5b cells induced by coincubating with fatty acids. These findings suggest that down-regulation of AdipoR2 in the liver caused by hyperinsulinemia and steatosis may play a role in the development of NAFLD.

Nonalcoholic fatty liver disease as a complication of insulin resistance

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