Plasma levels of PBEF/Nampt/visfatin are decreased in patients with liver cirrhosis

Apolipoprotein B-48 and late graft failure in kidney transplant recipients

Introduction

Transplant vasculopathy resembles atherosclerotic plaque formation and is a major contributor to late graft failure in kidney transplant recipients (KTR). Remnant lipoproteins and associated triglycerides are causal risk factors for atherosclerotic plaques and have been implicated in late kidney graft failure. However, whether remnants derived from liver (containing apolipoprotein [apo] B100) or intestine (containing apoB48) are clinically more important is unclear. The current study investigated the association between baseline fasting apoB48 levels and late kidney graft failure.

Methods

481 KTR with a functioning graft for at least 1 year were included in this retrospective, observational longitudinal single center cohort study. The primary endpoint was death-censored late graft failure, defined as need for initiation of dialysis or re-transplantation. ApoB48 was measured by enzyme-linked immunosorbent assay.

Results

During a median follow-up of 9.5 years, 61 KTR developed graft failure (12.7%). At baseline, KTR with higher apoB48 levels had lower eGFR (P < .001), lower high-density lipoprotein (HDL) cholesterol (P < .001), increased triglycerides (P < .001) and used cyclosporine more frequently (P = .003). Cox regression showed that higher baseline apoB48 was associated with higher risk of late graft failure [hazard ratio (95% confidence interval), 1.59 (1.22, 2.07), P < .001], independent of stepwise adjustment for potential confounders, including age and sex, immunosuppression type and proteinuria, triglycerides, and waist circumference (fully adjusted HR, 1.78 (1.29, 2.47), P < .001].

Conclusion

ApoB48 is strongly associated with late graft failure, independent of potential confounders. Since apoB48-containing lipoproteins originate from the intestine, this study provides a rationale for considering pharmacological interventions targeting lipid absorption to improve graft outcome.

Diagnostic Modalities of Non-Alcoholic Fatty Liver Disease: From Biochemical Biomarkers to Multi-Omics Non-Invasive Approaches

Non-Alcoholic Fatty Liver Disease (NAFLD) is currently the most common cause of chronic liver disease worldwide, and its prevalence is increasing globally. NAFLD is a multifaceted disorder, and its spectrum includes steatosis to steatohepatitis, which may evolve to advanced fibrosis and cirrhosis. In addition, the presence of NAFLD is independently associated with a higher cardiometabolic risk and increased mortality rates. Considering that the vast majority of individuals with NAFLD are mainly asymptomatic, early diagnosis of non-alcoholic steatohepatitis (NASH) and accurate staging of fibrosis risk is crucial for better stratification, monitoring and targeted management of patients at risk. To date, liver biopsy remains the gold standard procedure for the diagnosis of NASH and staging of NAFLD. However, due to its invasive nature, research on non-invasive tests is rapidly increasing with significant advances having been achieved during the last decades in the diagnostic field. New promising non-invasive biomarkers and techniques have been developed, evaluated and assessed, including biochemical markers, imaging modalities and the most recent multi-omics approaches. Our article provides a comprehensive review of the currently available and emerging non-invasive diagnostic tools used in assessing NAFLD, also highlighting the importance of accurate and validated diagnostic tools.

Non-Alcoholic Fatty Liver Disease in HIV/HBV Patients - a Metabolic Imbalance Aggravated by Antiretroviral Therapy and Perpetuated by the Hepatokine/Adipokine Axis Breakdown

Non-alcoholic fatty liver disease (NAFLD) is strongly associated with the metabolic syndrome and is one of the most prevalent comorbidities in HIV and HBV infected patients. HIV plays an early and direct role in the development of metabolic syndrome by disrupting the mechanism of adipogenesis and synthesis of adipokines. Adipokines, molecules that regulate the lipid metabolism, also contribute to the progression of NAFLD either directly or via hepatic organokines (hepatokines). Most hepatokines play a direct role in lipid homeostasis and liver inflammation but their role in the evolution of NAFLD is not well defined. The role of HBV in the pathogenesis of NAFLD is controversial. HBV has been previously associated with a decreased level of triglycerides and with a protective role against the development of steatosis and metabolic syndrome. At the same time HBV displays a high fibrogenetic and oncogenetic potential. In the HIV/HBV co-infection, the metabolic changes are initiated by mitochondrial dysfunction as well as by the fatty overload of the liver, two interconnected mechanisms. The evolution of NAFLD is further perpetuated by the inflammatory response to these viral agents and by the variable toxicity of the antiretroviral therapy. The current article discusses the pathogenic changes and the contribution of the hepatokine/adipokine axis in the development of NAFLD as well as the implications of HIV and HBV infection in the breakdown of the hepatokine/adipokine axis and NAFLD progression.

Tripeptide IRW Upregulates NAMPT Protein Levels in Cells and Obese C57BL/6J Mice

Nicotinamide adenine dinucleotide (NAD⁺) plays a vital role in cellular processes that govern human health and disease. Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in NAD⁺ biosynthesis. Thus, boosting NAD⁺ level via an increase in NAMPT levels is an attractive approach for countering the effects of aging and metabolic disease. This study aimed to establish IRW (Ile-Arg-Trp), a small tripeptide derived from ovotransferrin, as a booster of NAMPT levels. Treatment of muscle (L6) cells with IRW increased intracellular NAMPT protein levels (2.2-fold, p < 0.05) and boosted NAD⁺ (p < 0.01). Both immunoprecipitation and recombinant NAMPT assays indicated the possible NAMPT-activating ability of IRW (p < 0.01). Similarly, IRW increased NAMPT mRNA and protein levels in the liver (2.6-fold, p < 0.01) and muscle tissues (2.3-fold, p < 0.05) of C57BL/6J mice fed with a high-fat diet (HFD). A significantly increased level of circulating NAD⁺ was also observed following IRW treatment (4.7 fold, p < 0.0001). Dosing of Drosophila melanogaster with IRW elevated both D-NAAM (fly NAMPT) and NAD⁺ in vivo (p < 0.05). However, IRW treatment did not boost NAMPT levels in SIRT1 KO cells, indicating a possible SIRT1 dependency for the pharmacological effect. Overall, these data indicate that IRW is a novel small peptide booster of the NAMPT pool.

Serum concentrations of selected adipokines in virus-related liver cirrhosis and hepatocellular carcinoma

Aim of the study

Hepatotropic viruses cause metabolic disturbances such as insulin resistance and hepatosteatosis. Moreover, metabolic factors, such as insulin resistance, obesity, and type 2 diabetes mellitus, increase the risk for hepatocellular carcinoma (HCC) in patients with virus-related liver cirrhosis. Cytokines secreted by the adipose tissue (adipokines) may be implicated in these metabolic disturbances, but there is little evidence regarding the role of adipokines in virus-related cirrhosis and HCC. Thus, we studied whether serum concentrations of selected adipokines were altered in patients with virus-related liver cirrhosis, including patients with HCC.

Material and methods

We included 43 patients with liver cirrhosis due to chronic hepatitis B or chronic hepatitis C. Of these patients, 36 had HCC and 7 did not have any malignant lesions. In addition to routine clinical and laboratory variables, we analyzed serum concentrations of betatrophin, insulin, vaspin, visfatin, and irisin.

Results

Compared with healthy controls, patients with HCC had significantly increased vaspin concentrations and significantly reduced irisin concentrations. Compared with controls, patients with virus-related cirrhosis, with or without HCC, had significantly increased concentrations of insulin and betatrophin. The serum visfatin concentration was non-significantly higher in patients with virus-related cirrhosis than in controls. None of the studied adipokines was a significant predictor of HCC. Serum concentrations of the studied adipokines were not related to cirrhosis severity or HCC stage.

Conclusions

Metabolic parameters, including serum adipokine concentrations, are altered in patients with virus-related liver cirrhosis. Adipokines might be related to the HCC risk in these patients.

Adipokines in Liver Cirrhosis

Liver fibrosis can progress to cirrhosis, which is considered a serious disease. The Child-Pugh score and the model of end-stage liver disease score have been established to assess residual liver function in patients with liver cirrhosis. The development of portal hypertension contributes to ascites, variceal bleeding and further complications in these patients. A transjugular intrahepatic portosystemic shunt (TIPS) is used to lower portal pressure, which represents a major improvement in the treatment of patients. Adipokines are proteins released from adipose tissue and modulate hepatic fibrogenesis. These proteins affect various biological processes that are involved in liver function, including angiogenesis, vasodilation, inflammation and deposition of extracellular matrix proteins. The best studied adipokines are adiponectin and leptin. Adiponectin protects against hepatic inflammation and fibrogenesis, and leptin functions as a profibrogenic factor. These and other adipokines are supposed to modulate disease severity in patients with liver cirrhosis. Consequently, circulating levels of these proteins have been analyzed to identify associations with parameters of hepatic function, portal hypertension and its associated complications in patients with liver cirrhosis. This review article briefly addresses the role of adipokines in hepatitis and liver fibrosis. Here, studies having analyzed these proteins in systemic blood in cirrhotic patients are listed to identify adipokines that are comparably changed in the different cohorts of patients with liver cirrhosis. Some studies measured these proteins in systemic, hepatic and portal vein blood or after TIPS to specify the tissues contributing to circulating levels of these proteins and the effect of portal hypertension, respectively.

Hepatic NAD(+) deficiency as a therapeutic target for non-alcoholic fatty liver disease in ageing

BACKGROUND AND PURPOSE

Ageing is an important risk factor of non-alcoholic fatty liver disease (NAFLD). Here, we investigated whether the deficiency of nicotinamide adenine dinucleotide (NAD(+) ), a ubiquitous coenzyme, links ageing with NAFLD.

EXPERIMENTAL APPROACH

Hepatic concentrations of NAD(+) , protein levels of nicotinamide phosphoribosyltransferase (NAMPT) and several other critical enzymes regulating NAD(+) biosynthesis, were compared in middle-aged and aged mice or patients. The influences of NAD(+) decline on the steatosis and steatohepatitis were evaluated in wild-type and H247A dominant-negative, enzymically-inactive NAMPT transgenic mice (DN-NAMPT) given normal or high-fat diet (HFD).

KEY RESULTS

Hepatic NAD(+) level decreased in aged mice and humans. NAMPT-controlled NAD(+) salvage, but not de novo biosynthesis pathway, was compromised in liver of elderly mice and humans. Given normal chow, middle-age DN-NAMPT mice displayed systemic NAD(+) reduction and had moderate NAFLD phenotypes, including lipid accumulation, enhanced oxidative stress, triggered inflammation and impaired insulin sensitivity in liver. All these NAFLD phenotypes, especially release of pro-inflammatory factors, Kupffer cell accumulation, monocytes infiltration, NLRP3 inflammasome pathway and hepatic fibrosis (Masson's staining and α-SMA staining), deteriorated further under HFD challenge. Oral administration of nicotinamide riboside, a natural NAD(+) precursor, completely corrected these NAFLD phenotypes induced by NAD(+) deficiency alone or HFD, whereas adenovirus-mediated SIRT1 overexpression only partially rescued these phenotypes.

CONCLUSIONS AND IMPLICATIONS

These results provide the first evidence that ageing-associated NAD(+) deficiency is a critical risk factor for NAFLD, and suggest that supplementation with NAD(+) substrates may be a promising therapeutic strategy to prevent and treat NAFLD.

The Correlation Between Serum Adipokines and Liver Cell Damage in Non-Alcoholic Fatty Liver Disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic hepatitis, which can lead to cirrhosis and hepatocellular carcinoma.

OBJECTIVES

The aim of the study was to evaluate the correlation between serum adipocytokines and the histologic findings of the liver in patients with non-alcoholic fatty liver disease (NAFLD).

PATIENTS AND METHODS

This case-control study was performed on those with persistent elevated liver enzymes and with evidence of fatty liver in ultrasonography. After exclusion of patients with other etiologies causing abnormal liver function tests, the resulting patients underwent liver biopsies. NAFLD was diagnosed based on liver histology according to the Brunt scoring system.

RESULTS

Waist circumferences and levels of blood glucose (after fasting), insulin, triglycerides, alanine aminotransferases (ALT), and aspartate aminotransferases (AST) were higher in patients with NAFLD than in those in the control group. ALT, AST, and gamma glutamine transferase (GGT) levels were lower in patients with liver steatosis of a grade of less than 33% than those with higher degrees of steatosis. Serum low-density lipoprotein (LDL), cholesterol, and hepcidin levels were significantly higher in those with lobular inflammation of grade 0 - 1 than in those with inflammation of grade 2 - 3 (Brunt score). Meanwhile, AST was significantly lower in those with lobular inflammation of grade 1 than in those with grade 2-3. Hepcidin and resistin levels were significantly higher in patients with moderate to severe fibrosis than in those with mild fibrosis.

CONCLUSIONS

It seems that surrogate liver function tests and adipocytokine levels were correlated with the histologic findings of the liver.

Prediction of Nonalcoholic Fatty Liver Disease Via a Novel Panel of Serum Adipokines

Considering limitations of liver biopsy for diagnosis of nonalcoholic liver disease (NAFLD), biomarkers' panels were proposed. The aims of this study were to establish models based on serum adipokines for discriminating NAFLD from healthy individuals and nonalcoholic steatohepatitis (NASH) from simple steatosis.This case-control study was conducted in patients with persistent elevated serum aminotransferase levels and fatty liver on ultrasound. Individuals with evidence of alcohol consumption, hepatotoxic medication, viral hepatitis, and known liver disease were excluded. Liver biopsy was performed in the remaining patients to distinguish NAFLD/NASH. Histologic findings were interpreted using "nonalcoholic fatty liver activity score." Control group consisted of healthy volunteers with normal physical examination, liver function tests, and liver ultrasound. Binary logistic regression analysis was applied to ascertain the effects of independent variables on the likelihood that participants have NAFLD/NASH.Decreased serum adiponectin and elevated serum visfatin, IL-6, TNF-a were associated with an increased likelihood of exhibiting NAFLD. NAFLD discriminant score was developed as the following: [(-0.298 × adiponectin) + (0.022 × TNF-a) + (1.021 × Log visfatin) + (0.709 × Log IL-6) + 1.154]. In NAFLD discriminant score, 86.4% of original grouped cases were correctly classified. Discriminant score threshold value of (-0.29) yielded a sensitivity and specificity of 91% and 83% respectively, for discriminating NAFLD from healthy controls. Decreased serum adiponectin and elevated serum visfatin, IL-8, TNF-a were correlated with an increased probability of NASH. NASH discriminant score was proposed as the following: [(-0.091 × adiponectin) + (0.044 × TNF-a) + (1.017 × Log visfatin) + (0.028 × Log IL-8) - 1.787] In NASH model, 84% of original cases were correctly classified. Discriminant score threshold value of (-0.22) yielded a sensitivity and specificity of 90% and 66% respectively, for separating NASH from simple steatosis.New discriminant scores were introduced for differentiating NAFLD/NASH patients with a high accuracy. If verified by future studies, application of suggested models for screening of NAFLD/NASH seems reasonable.

Pyrroloquinoline quinone increases the expression and activity of Sirt1 and -3 genes in HepG2 cells

Sirtuin (Sirt) 1 and Sirt 3 are nicotinamide adenine dinucleotide ((+))-dependent protein deacetylases that are important to a number of mitochondrial-related functions; thus, identification of sirtuin activators is important. Herein, we hypothesize that pyrroloquinoline quinone (PQQ) can act as a Sirt1/Sirt3 activator. In HepG2 cell cultures, PQQ increased the expression of Sirt1 and Sirt3 gene, protein, and activity levels (P < .05). We also observed a significant increase in nicotinamide phosphoribosyltransferase gene expression (as early as 18 hours) and increased NAD(+) activity at 24 hours. In addition, targets of Sirt1 and Sirt3 (peroxisome proliferator-activated receptor γ coactivator 1α, nuclear respiratory factor 1 and 2, and mitochondrial transcription factor A) were increased at 48 hours. This is the first report that demonstrates PQQ as an activator of Sirt1 and Sirt3 expression and activity, making it an attractive therapeutic agent for the treatment of metabolic diseases and for healthy aging. Based on our study and the available data in vivo, PQQ has the potential to serve as a therapeutic nutraceutical, when enhancing mitochondrial function.

Adipokines levels are associated with the severity of liver disease in patients with alcoholic cirrhosis

AIM: To investigate the adipokine levels of leptin, adiponectin, resistin, visfatin, retinol-binding protein 4 (RBP4), apelin in alcoholic liver cirrhosis (ALC).

METHODS: Forty non-diabetic ALC patients [median age: 59 years, males: 35 (87.5%), Child-Pugh (CP) score: median 7 (5-12), CP A/B/C: 18/10/12, Model for End-stage Liver Disease (MELD): median 10 (6-25), follow-up: median 32.5 mo (10-43)] were prospectively included. The serum adipokine levels were estimated in duplicate by ELISA. Somatometric characteristics were assessed with tetrapolar bioelectrical impedance analysis. Pearson’s rank correlation coefficient was used to assess possible associations with adipokine levels. Univariate and multivariate Cox regression analysis was used to determine independent predictors for overall survival.

RESULTS: Body mass index: median 25.9 (range: 20.1-39.3), fat: 23.4% (7.6-42.1), fat mass: 17.8 (5.49-45.4), free fat mass: 56.1 (39.6-74.4), total body water (TBW): 40.6 (29.8-58.8). Leptin and visfatin levels were positively associated with fat mass (P < 0.001/P = 0.027, respectively) and RBP4 with TBW (P = 0.025). Median adiponectin levels were significantly higher in CPC compared to CPA (CPA: 7.99 ± 14.07, CPB: 7.66 ± 3.48, CPC: 25.73 ± 26.8, P = 0.04), whereas median RBP4 and apelin levels decreased across the spectrum of disease severity (P = 0.006/P = 0.034, respectively). Following adjustment for fat mass, visfatin and adiponectin levels were significantly increased from CPA to CPC (both P < 0.001), whereas an inverse correlation was observed for both RBP4 and apelin (both P < 0.001). In the multivariate Cox regression analysis, only MELD had an independent association with overall survival (HR = 1.53, 95%CI: 1.05-2.32; P = 0.029).

CONCLUSION: Adipokines are associated with deteriorating liver function in a complex manner in patients with alcoholic liver cirrhosis.

The role of visfatin in diabetic nephropathy

As a result of the energy overload in obesity, insulin resistance, type 2 diabetes, dyslipidemia, hypertension, and atherosclerosis develop, which together comprise the metabolic syndrome. Although the kidney becomes a victim of hyperglycemia in diabetes mellitus, recent work has shown that the abnormalities of lipid and glucose metabolism in the kidney are similarly important to those in adipose tissue. Interestingly, obesity triggers the release of adipokines such as leptin, resistin, and visfatin, and these can then be associated with the progression of diabetic nephropathy and other vascular complications. These adipokines, which are also synthesized in the kidney, appear to have an important role in renal injury associated with insulin resistance. Our studies found that visfatin is not only a surrogate marker of systemic inflammation in type 2 diabetic patients but is also up-regulated in diabetic kidney through the uptake of glucose into renal cells, which leads to the activation of the intracellular insulin signaling pathway and pro-inflammatory mechanisms. However, we also observed a beneficial effect of visfatin administration to type 2 diabetic mice. Visfatin injection improved diabetic nephropathy in vivo, in contrast to our previous in vitro study of cultured renal mesangial cells. These results suggest the possibility of multiple cross-talk between adipose tissue and kidney in the metabolic syndrome, particularly in diabetic nephropathy. Further study should be undertaken to understand the role of adipose tissue and kidney as major organs in the metabolic syndrome.

A key role for Pre-B cell colony-enhancing factor in experimental hepatitis

Pre-B cell colony-enhancing factor (PBEF), also known as nicotinamide phosphoribosyltransferase or visfatin, plays an important role in metabolic, inflammatory, and malignant diseases. Recent evidence suggests that blocking its enzymatic activity using a specific small-molecule inhibitor (FK866) might be beneficial in acute experimental inflammation. We investigated the role of PBEF in human liver disease and experimental hepatitis. PBEF serum levels and hepatic expression were determined in patients with chronic liver diseases. These studies were followed by in vivo experiments using concanavalin A (ConA) and D-galactosamine/lipopolysaccharide (LPS) models of experimental hepatitis. PBEF was either overexpressed by hydrodynamic perfusion or inhibited by FK866. In vivo findings were corroborated studying inflammatory responses of lentivirally PBEF-silenced or control FL83B mouse hepatocytes. Here, we demonstrate that PBEF serum levels were increased in patients with chronic liver diseases irrespective of disease stage and etiology. In particular, we observed enhanced PBEF expression in hepatocytes. Liver-targeted overexpression of PBEF rendered mice more susceptible to ConA- and D-galactosamine/LPS-induced hepatitis compared with control animals. In contrast, inhibition of PBEF using FK866 protected mice from ConA-induced liver damage and apoptosis. Administration of FK866 resulted in depletion of liver nicotinamide adenine dinucleotide+ levels and reduced proinflammatory cytokine expression. Additionally, FK866 protected mice in the D-galactosamine/LPS model of acute hepatitis. In vitro, PBEF-silenced mouse hepatocytes showed decreased responses after stimulation with LPS, lipoteichoic acid, and tumor necrosis factor α. In primary murine Kupffer cells, FK866 suppressed LPS-induced interleukin (IL)-6 production, whereas incubation with recombinant PBEF resulted in increased IL-6 release.

CONCLUSION

Our data suggest that PBEF is of key importance in experimental hepatitis. Its specific inhibition might be considered a novel treatment option for inflammatory liver diseases.

Potential role of leptin, adiponectin and three novel adipokines--visfatin, chemerin and vaspin--in chronic hepatitis

Chronic hepatitis C (CHC) is generally a slowly progressive disease, but some factors associated with rapid progression have been identified. Steatosis, independently of its metabolic or viral origin, leads to liver injury and fibrosis. It is suggested that hepatitis C virus may contribute to a wide spectrum of metabolic disturbances-namely, steatosis, insulin resistance, increased prevalence of impaired glucose tolerance, type 2 diabetes mellitus and lipid metabolism abnormalities. Adipokines, which are produced mainly by adipose tissue, may influence the inflammatory response and insulin sensitivity and contribute to the development of metabolic abnormalities in CHC and also regulate fibrogenesis and angiogenesis. Visfatin was described as an adipokine with immunomodulating and proinflammatory properties that promotes B-cell maturation and enhances activation of leukocytes, synthesis of adhesion molecules and production of proinflammatory cytokines. Visfatin exerts insulin-mimetic effects, decreases plasma glucose levels and regulates cell energy balance. Chemerin stimulates chemotaxis of dendritic cells, macrophages and natural killer (NK) cells toward the site of inflammation. On the other hand, it inhibits synthesis of proinflammatory mediators and enhances adiponectin production, influences adipocyte differentiation and maturation and regulates glucose uptake in adipocytes. Vaspin expression in human adipose tissue seems to be a compensatory mechanism associated with obesity and insulin resistance. Vaspin suppresses leptin, tumor necrosis factor (TNF)-α and resistin expression. Leptin protects against liver steatosis but accelerates fibrosis progression and exacerbates the inflammatory process. In contrast, adiponectin exerts a hepatoprotective effect. In this report, data indicating a possible role of these adipokines in the pathogenesis of chronic hepatitis are summarized.

Nampt and its potential role in inflammation and type 2 diabetes

Nicotinamide phosphoribosyltransferase Nicotinamide phosphoribosyltransferase (Nampt Nampt ) is a key nicotinamide adenine dinucleotide (NAD) NAD biosynthetic enzyme in mammals, converting nicotinamide nicotinamide into nicotinamide mononucleotide nicotinamide mononucleotide (NMN NMN ), an NAD intermediate. First identified in humans as a cytokine cytokine pre-B-cell colony enhancing factor pre-B cell colony enhancing factor (PBEF PBEF ) and subsequently described as an insulin-mimetic hormone visfatin visfatin , Nampt has recently excited the scientific interest of researchers from diverse fields, including NAD biology, metabolic regulation, and inflammation. As an NAD biosynthetic enzyme, Nampt regulates the activity of NAD-consuming enzymes such as sirtuins sirtuins and influences a variety of metabolic and stress responses. Nampt plays an important role in the regulation of insulin secretion insulin secretion in pancreatic β-cells. Nampt also functions as an immunomodulatory cytokine cytokine and is involved in the regulation of inflammatory responses. This chapter summarizes the various functional aspects of Nampt and discusses its potential roles in diseases, with special focus on type 2 diabetes mellitus (T2DM).

SIRT3 is regulated by nutrient excess and modulates hepatic susceptibility to lipotoxicity

SIRT3 is the primary mitochondrial deacetylase that modulates mitochondrial metabolic and oxidative stress regulatory pathways. However, its role in response to nutrient excess remains unknown. Thus, we investigated SIRT3 regulation of the electron transfer chain and evaluated the role of SIRT3 in hepatic lipotoxic stress. SIRT3-depleted HepG2 cells show diffuse disruption in mitochondrial electron transfer chain functioning, a concurrent reduction in the mitochondrial membrane potential, and excess basal reactive oxygen species levels. As this phenotype may predispose to increased lipotoxic hepatic susceptibility we evaluated the expression of SIRT3 in murine liver after chronic high-fat feeding. In this nutrient-excess model SIRT3 transcript and protein levels are downregulated in parallel with increased hepatic fat storage and oxidative stress. Palmitate was used to investigate lipotoxic susceptibility in SIRT3 knockout mouse primary hepatocytes and SIRT3-siRNA-transfected HepG2 cells. Under SIRT3-deficient conditions palmitate enhances reactive oxygen species and increases hepatocyte death. Reconstitution of SIRT3 levels and/or treatment with N-acetylcysteine ameliorates these adverse effects. In conclusion SIRT3 functions to ameliorate hepatic lipotoxicity, although paradoxically, exposure to high fat downregulates this adaptive program in the liver. This SIRT3-dependent lipotoxic susceptibility is possibly modulated, in part, by SIRT3-mediated control of electron transfer chain flux.

Intracellular nicotinamide phosphoribosyltransferase protects against hepatocyte apoptosis and is down-regulated in nonalcoholic fatty liver disease

CONTEXT

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease in Western and non-Western countries, but its pathogenesis is not fully understood.

OBJECTIVE

Based on the role of nicotinamide phosphoribosyltransferase (NAMPT) in fat and glucose metabolism and cell survival, we hypothesized a role for NAMPT/visfatin in the pathogenesis of NAFLD-related disease.

DESIGN AND SETTING

We conducted clinical studies at a referral medical center in well-characterized NAFLD patients (n = 58) and healthy controls (n = 27). In addition we performed experimental in vitro studies in hepatocytes.

MAIN OUTCOME MEASURES

We examined 1) the hepatic and systemic expression of NAMPT/visfatin in patients with NAFLD and control subjects, 2) the hepatic regulation of NAMPT/visfatin, and 3) the effect of NAMPT/visfatin on hepatocyte apoptosis.

RESULTS

Our main findings were as follows. 1) Patients with NAFLD had decreased NAMPT/visfatin expression both systemically in serum and within the hepatic tissue, with no difference between simple steatosis and nonalcoholic steatohepatitis. 2) By studying the hepatic regulation of NAMPT/visfatin in wild-type and peroxisome proliferators-activated receptor (PPAR)alpha(-/-) mice as well as in hepatocytes, we showed that PPARalpha activation and glucose may be involved in the down-regulation of hepatic NAMPT/visfatin expression in NAFLD. 4) Within the liver, NAMPT/visfatin was located to hepatocytes, and our in vitro studies showed that NAMPT/visfatin exerts antiapoptotic effects in these cells, involving enzymatic synthesis of nicotinamide adenine dinucleotide.

CONCLUSION

Based on these findings, we suggest a role for decreased NAMPT/visfatin levels in hepatocyte apoptosis in NAFLD-related disease.

Splanchnic concentrations and postprandial release of visceral adipokines

No detailed data are available on hepatic clearance, postprandial release, and distribution profile of metabolically active adipokines in splanchnic blood compartments such as portal and hepatic veins. This would be a prerequisite for understanding the role of visceral adipose tissue-derived adipokines in metabolism. Adiponectin, resistin, leptin, and visfatin concentrations were measured by enzyme-linked immunosorbent assay in peripheral veins, arterial blood, hepatic veins, and portal veins in 50 patients with liver cirrhosis undergoing transjugular intrahepatic portosystemic shunt implantation, in 6 patients with normal liver function, and in fasted and fed rats. Adiponectin, leptin, resistin, and visfatin did not differ among blood compartments in normal-weight probands in the fasted state. Adiponectin and leptin levels were similar in patients with and without liver cirrhosis. Systemic visfatin levels were decreased and resistin levels were increased in liver cirrhosis. Visfatin secretion was higher from visceral than from peripheral subcutaneous adipose tissue in liver cirrhosis. There was no hepatic clearance of visfatin. Leptin secretion was higher from peripheral than from visceral adipose tissue. Leptin did not undergo hepatic clearance. Resistin and adiponectin did not differ between blood compartments in liver cirrhosis. Resistin concentrations increased upon feeding in rats, and there was an increase in the postprandial clearance of adiponectin by the liver. A postprandial increase of leptin concentrations was restricted to peripheral adipose tissue in rats. The results give insight into the dynamics of splanchnic adipokine concentrations and help critically interpret data derived from messenger RNA expression studies.

Visfatin is upregulated in type-2 diabetic rats and targets renal cells

Visfatin (also known as pre-B cell colony-enhancing factor) is a newly discovered adipocytokine that is preferentially produced by visceral fat and regulated by cytokines promoting insulin resistance. Here we determined its renal synthesis and physiology in a genetic model of type 2 diabetes in rats. These rats had higher levels of visfatin synthesis in both glomeruli and tubulointerstitium compared to control rats. Plasma visfatin levels were significantly increased in the early stages of diabetic nephropathy and positively correlated with body weight, fasting plasma glucose, and microalbuminuria. Interestingly, visfatin synthesis was found to occur in podocytes and proximal tubular cells, as well as in adipocytes in vitro. Further, in both renal cells, visfatin synthesis was significantly increased by high glucose in the media but not by angiotensin II. Additionally, visfatin treatment induced rapid uptake of glucose and was associated with increased translocation of GLUT-1 to the cellular membrane of both renal cell types. Furthermore, visfatin induced tyrosine phosphorylation of the insulin receptor, activated downstream insulin signaling pathways such as Erk-1, Akt, and p38 MAPK, and markedly increased the levels of TGFbeta1, PAI-1, type I collagen, and MCP-1 in both renal cells. Thus, our results suggest that visfatin is produced by renal cells and has an important paracrine role in the pathogenesis of diabetic nephropathy.

Adipokines in liver diseases

Adipokines are polypeptides secreted in the adipose tissue in a regulated manner. While some of these molecules are expressed only by adipocytes, resident and infiltrating macrophages and components of the vascular stroma markedly contribute to expression of other adipokines. As a result, adipose tissue inflammation is associated with a modification in the pattern of adipokine secretion. Leptin, adiponectin, and resistin are the best-studied molecules in this class, but cytokines such as tumor necrosis factor or interleukin-6 are also secreted at high levels by the adipose tissue. Several other molecules have been recently identified and are actively investigated. Adipokines interfere with hepatic injury associated with fatty infiltration, differentially modulating steatosis, inflammation, and fibrosis. Several studies have investigated plasma levels of adiponectin in patients with nonalcoholic fatty liver disease, to establish correlations with the underlying state of insulin resistance and with the type and severity of hepatic damage. Hepatitis C is another disease where adipokines may represent a link between viral infection, steatosis, and metabolic disturbances. Identification of the mediators secreted by expanded adipose tissue and their pathogenic role is pivotal in consideration of the alarming increase in the prevalence of obesity and of the detrimental role that this condition exerts on the course of liver diseases.