Retraction

Beijing ambient particle exposure accelerates atherosclerosis in ApoE knockout mice by upregulating visfatin expression

Ambient particulate matter (PM) exposure has been associated with atherosclerosis. However, research on the effect of real-world exposure to ambient PM in regulating visfatin expression in an animal model is very limited. The objective is to investigate whether Beijing ambient PM exposure could accelerate atherosclerosis in ApoE knockout (ApoE(-/-)) mice by upregulating visfatin expression. Forty male ApoE(-/-) mice were exposed to untreated ambient air (PM group, n = 20) or filtered air (FA group, n = 20), 24 h/day, 7 days/week, for 2 months. During the exposure, the mass concentrations of PM2.5 and PM10 in the two groups were continuously monitored. Moreover, a receptor source apportionment model was applied to apportion sources of PM2.5. At the end of the exposure, visfatin in plasma and aorta, biomarkers of inflammation, oxidative stress and lipid metabolism in blood samples, and bronchoalveolar lavage fluid (BALF) were determined, and the plaque area of the atherosclerosis lesions was quantified. PM-exposed mice were significantly higher than FA-exposed mice in terms of plasma visfatin, OxLDL, MDA, serum TC, LDL, TNF-α as well as IL-6, TNF-α, OxLDL, and MDA in BALF, while SOD and GSH-Px activities in plasma and BALF were reduced in PM-exposed mice. Pathological analysis of the aorta demonstrated that the plaque area and visfatin protein in the PM group increased significantly compared to the FA group. Our findings indicate that ambient PM exposure could accelerate atherosclerosis, which is related to visfatin upregulation, as well as the activation of inflammation and oxidative stress.

Effect of simvastatin treatment on plasma visfatin levels in obese women

AIMS

Obesity is one of the major concerns in the world currently, its prejudicial effect is exerted by proteins secreted by adipose tissue, among them visfatin was demonstrated to be related with BMI and cardiovascular diseases. The HMG-CoA reductase inhibitors are known to minimize the cardiovascular risk in hyperlipidemic patients and recently the discovery of various pleiotropic effects has made the statins evidencing among others anti-inflammatory effect. Our objective in this study was to determinate if simvastatin treatment may modulate visfatin levels in obese women without any other metabolic disorder.

METHODS

We recruited 25 obese women without any other metabolic disorder and treated with simvastatin for 6 weeks 20 mg/day.

RESULTS

The levels of plasma visfatin were similar before and after treatment (22 ± 20 versus 27 ± 14 ng/mL, p > 0.05) and correlated with BMI before treatment (p = 0.001). We also found correlations among visfatin and insulin levels (p = 0.015) and HOMA-IR (p = 0.025) only after treatment.

CONCLUSION

These findings suggest that visfatin is not modulated by simvastatin treatment in this group but the treatment may interfere on the relation among visfatin, BMI, insulin and HOMA-IR.

Visfatin -948G/T and resistin -420C/G polymorphisms in Egyptian type 2 diabetic patients with and without cardiovascular diseases

Diabetes mellitus is one of the main threats to human health in the 21st century. Visfatin/Nampt and resistin are novel adipokines that have been implicated in the pathogenesis of type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD) complication. Several genetic studies have shown inconsistent results regarding association of visfatin/Nampt gene (NAMPT) and resistin gene (RETN) polymorphisms with T2DM and CVD complications. Here, we investigate whether NAMPT -948G/T and RETN -420C/G polymorphisms are associated with T2DM, its CVD complications, and serum adipokines levels in 90 Egyptian diabetic patients (44 without CVD and 46 with CVD) along with 60 healthy control subjects. Higher frequencies of NAMPT -948G/G and RETN -420G/G were observed among T2DM patients compared with controls. Furthermore, the frequencies of these genotypes were significantly higher in T2DM patients with CVD than those without CVD. Both NAMPT -948G/G and RETN -420G/G genotypes and G alleles were significantly associated with T2DM and CVD in Egyptian diabetic patients. Moreover, serum visfatin/Nampt and resistin levels were markedly elevated in T2DM patients, with the highest values observed in G/G genotypes among T2DM patients with CVD. In addition, positive correlations were observed between plasma adipokines levels and CVD risk factors. In conclusion, our data suggests that genetic variations in NAMPT -948G/T and RETN -420C/G may contribute to the disposition for T2DM and its CVD complications in Egyptian patients. However, further studies with greater sample size should be performed to verify these results.

Bone metabolism and adipokines: are there perspectives for bone diseases drug discovery?

INTRODUCTION

Over the past 20 years, the idea that white adipose tissue (WAT) is simply an energy depot organ has been radically changed. Indeed, present understanding suggests WAT to be an endocrine organ capable of producing and secreting a wide variety of proteins termed adipokines. These adipokines appear to be relevant factors involved in a number of different functions, including metabolism, immune response, inflammation and bone metabolism.

AREAS COVERED

In this review, the authors focus on the effects of several adipose tissue-derived factors in bone pathophysiology. They also consider how the modification of the adipokine network could potentially lead to promising treatment options for bone diseases.

EXPERT OPINION

There are currently substantial developments being made in the understanding of the interplay between bone metabolism and the metabolic system. These insights could potentially lead to the development of new treatment strategies and interventions with the aim of successful outcomes in many people affected by bone disorders. Specifically, future research should look into the intimate mechanisms regulating peripheral and central activity of adipokines as it has potential for novel drug discovery.

Adipose tissue and its role in organ crosstalk

The discovery of adipokines has revealed adipose tissue as a central node in the interorgan crosstalk network, which mediates the regulation of multiple organs and tissues. Adipose tissue is a true endocrine organ that produces and secretes a wide range of mediators regulating adipose tissue function in an auto-/paracrine manner and important distant targets, such as the liver, skeletal muscle, the pancreas and the cardiovascular system. In metabolic disorders such as obesity, enlargement of adipocytes leads to adipose tissue dysfunction and a shift in the secretory profile with an increased release of pro-inflammatory adipokines. Adipose tissue dysfunction has a central role in the development of insulin resistance, type 2 diabetes, and cardiovascular diseases. Besides the well-acknowledged role of adipokines in metabolic diseases, and the increasing number of adipokines being discovered in the last years, the mechanisms underlying the release of many adipokines from adipose tissue remain largely unknown. To combat metabolic diseases, it is crucial to better understand how adipokines can modulate adipose tissue growth and function. Therefore, we will focus on adipokines with a prominent role in auto-/paracrine crosstalk within the adipose tissue such as RBP4, HO-1, WISP2, SFRPs and chemerin. To depict the endocrine crosstalk between adipose tissue with skeletal muscle, the cardiovascular system and the pancreas, we will report the main findings regarding the direct effects of adiponectin, leptin, DPP4 and visfatin on skeletal muscle insulin resistance, cardiovascular function and β-cell growth and function.

Visfatin and its genetic variants are associated with obesity-related morbidities and cardiometabolic risk in severely obese children

BACKGROUND

Visfatin is an adipokine, associated with obesity and possibly glucose regulation.

OBJECTIVE

The aim of this study was to examine the association of visfatin and its genetic variants with adiposity, cardiometabolic risk factors and obesity-related morbidities in obese children.

METHODS

Anthropometric measurements, dual energy X-ray absorptiometry scan, fasting blood samples and oral glucose tolerance tests were performed for 243 obese children. We screened the visfatin gene of 24 obese subjects and then performed genotyping of identified genetic variants in other 219 obese children through direct DNA sequencing.

RESULTS

Fasting serum visfatin correlated with measures of obesity and liver enzymes and was elevated in obese children with abnormal glucose tolerance and non-alcoholic fatty liver disease. The two upstream single nucleotide polymorphisms, -3187G>A (rs11977021) and -1537C>T (rs61330082), were at complete linkage disequilibrium. The AA genotype of -3187G>A was associated with higher serum visfatin (6.17 ± 0.76 ng mL(-1) vs. 3.92 ± 0.44 ng mL(-1)) and higher triglyceride (1.39 ± 0.08 mmol L(-1) vs. 1.19 ± 0.07 mmol L(-1)) as compared with the GG genotype. There was also a significant linear increase in serum visfatin across GG to GA to AA genotype of -3187G>A, indicating possible additive effect of A allele. The dominant GA + AA genotype model of +21426G>A (rs2302559) was associated with lower serum visfatin (3.83 ± 0.56 ng mL(-1) vs. 5.13 ± 0.34 ng mL(-1)) and lower plasma glucose (4.37 ± 0.08 mmol L(-1) vs. 4.77 ± 0.12 mmol L(-1)) as compared with the GG genotype.

CONCLUSION

Visfatin and its genetic variants were associated with adiposity, obesity-related morbidities and adverse cardiometabolic parameters. This supported our hypothesis that visfatin plays a significant role in the development of obesity-related morbidities and cardiometabolic risk.

Resveratrol differentially regulates NAMPT and SIRT1 in Hepatocarcinoma cells and primary human hepatocytes

Resveratrol is reported to possess chemotherapeutic properties in several cancers. In this study, we wanted to investigate the molecular mechanisms of resveratrol-induced cell cycle arrest and apoptosis as well as the impact of resveratrol on NAMPT and SIRT1 protein function and asked whether there are differences in hepatocarcinoma cells (HepG2, Hep3B cells) and non-cancerous primary human hepatocytes. We found a lower basal NAMPT mRNA and protein expression in hepatocarcinoma cells compared to primary hepatocytes. In contrast, SIRT1 was significantly higher expressed in hepatocarcinoma cells than in primary hepatocytes. Resveratrol induced cell cycle arrest in the S- and G2/M- phase and apoptosis was mediated by activation of p53 and caspase-3 in HepG2 cells. In contrast to primary hepatocytes, resveratrol treated HepG2 cells showed a reduction of NAMPT enzymatic activity and increased p53 acetylation (K382). Resveratrol induced NAMPT release from HepG2 cells which was associated with increased NAMPT mRNA expression. This effect was absent in primary hepatocytes where resveratrol was shown to function as NAMPT and SIRT1 activator. SIRT1 inhibition by EX527 resembled resveratrol effects on HepG2 cells. Furthermore, a SIRT1 overexpression significantly decreased both p53 hyperacetylation and resveratrol-induced NAMPT release as well as S-phase arrest in HepG2 cells. We could show that NAMPT and SIRT1 are differentially regulated by resveratrol in hepatocarcinoma cells and primary hepatocytes and that resveratrol did not act as a SIRT1 activator in hepatocarcinoma cells.

Mechanisms linking excess adiposity and carcinogenesis promotion

Obesity constitutes one of the most important metabolic diseases being associated to insulin resistance development and increased cardiovascular risk. Association between obesity and cancer has also been well established for several tumor types, such as breast cancer in post-menopausal women, colorectal, and prostate cancer. Cancer is the first death cause in developed countries and the second one in developing countries, with high incidence rates around the world. Furthermore, it has been estimated that 15-20% of all cancer deaths may be attributable to obesity. Tumor growth is regulated by interactions between tumor cells and their tissue microenvironment. In this sense, obesity may lead to cancer development through dysfunctional adipose tissue and altered signaling pathways. In this review, three main pathways relating obesity and cancer development are examined: (i) inflammatory changes leading to macrophage polarization and altered adipokine profile; (ii) insulin resistance development; and (iii) adipose tissue hypoxia. Since obesity and cancer present a high prevalence, the association between these conditions is of great public health significance and studies showing mechanisms by which obesity lead to cancer development and progression are needed to improve prevention and management of these diseases.

Salivary visfatin concentrations in patients with chronic periodontitis

BACKGROUND

Visfatin, also known as pre-B-cell colony-enhancing factor, is secreted from a variety of cells and is thought to have some proinflammatory and immunomodulating effects. It is indicated that serum/plasma levels of visfatin increase in a number of inflammatory disorders. The present study aims to evaluate salivary concentrations of visfatin in patients with chronic periodontitis (CP).

METHODS

Twenty patients with CP and 20 periodontally healthy individuals were enrolled in this study. For each patient, the values of clinical parameters, such as bleeding index, plaque index, probing depth, and clinical attachment level (CAL), were recorded. Whole saliva samples were collected, and concentrations of visfatin were evaluated using standard enzyme-linked immunosorbent assay. Statistical analysis was performed using statistical software.

RESULTS

Visfatin was detectable in all samples. Salivary visfatin concentrations were significantly higher in the periodontitis group. In addition, there was a positive significant relationship between salivary visfatin concentrations and CAL in the periodontitis group. However, no significant association was observed between salivary visfatin levels and other periodontal parameters or body mass index.

CONCLUSION

These results indicate that there is a relationship between salivary visfatin and CP; however, further studies are needed to confirm this finding.

Association of plasma visfatin with risk of colorectal cancer: An observational study of Chinese patients

AIM

To investigate the association between plasma visfatin levels and risk of early and advanced colorectal cancer (CRC).

METHODS

In total, 358 CRC patients and 286 controls were enrolled. According to the T factor of the TNM system. cancer patients were divided into two subgroups: early and advanced cancer. Levels of visfatin, anthropometric and metabolic parameters, which were classified as low, medium, and high, based on the tertile distributions in the control group, were determined.

RESULTS

The visfatin levels in patients with advanced and early cancer were higher than in controls (least significant difference test, P = 0.004 and 0.013, respectively). The patients in the highest tertile of visfatin concentration presented significantly higher odds for early and advanced CRC, adjusted for potential confounding factors (odds ratio 3.37; 95% CI, 1.93-8.37; P = 0.011; odds ratio 2.38; 95% CI: 1.82-8.35; P = 0.015, respectively). The visfatin level correlated significantly with waist:hip ratio (P < 0.05 for all) among case and control participants. Plasma visfatin levels in early and advanced CRC yielded a receiver operating characteristic curve area of 72 and 86%, respectively. The optimal sensitivity and specificity were 73% and 57% in discriminating between early CRC and normal controls while they were 76% and 68% in discriminating between advanced CRC and normal controls.

CONCLUSION

An increased level of visfatin was a strong risk factor for both early and advanced CRC in Chinese patients. Plasma visfatin levels might be a potential biomarker for CRC detection.

Hormones of adipose tissue and their biologic role in lung cancer

INTRODUCTION

Adipose tissue secretes numerous bioactive peptides, collectively termed "adipocytokines" or "adipokines". Adipokines act in a paracrine, autocrine, or endocrine manner and regulate several physiological and pathological processes. Increasing evidence indicates that adipokines are implicated also in several malignancies, including lung cancer as well.

AIM

The aim of this study is to summarize data concerning adipokines in lung cancer pathogenesis, prognosis and survival; the role of adipokines in lung cancer cachexia is also examined.

MATERIALS AND METHODS

A systematic literature search was performed in the electronic database of Medline. Several studies and review articles met the inclusion criteria.

RESULTS

Leptin and adiponectin are the best studied adipokines. The majority of the relevant studies has investigated the potential correlations mainly between leptin, adiponectin, and sometimes also resistin, and nutritional status, systemic inflammation of lung cancer or lung cancer cachexia and have also assessed their prognostic significance. Few other studies have studied genetic variations in leptin, leptin receptor and adiponectin genes and their association with lung cancer susceptibility and prognosis. The ongoing list of adipokines associated with lung cancer also includes resistin, chemerin, and visfatin.

CONCLUSIONS

Increasing evidence points to the involvement of certain adipocytokines in lung cancer development, progression and prognosis. No conclusive evidence exists so far with regards to the role of adipocytokines in lung cancer cachexia. Future, longitudinal studies are warranted in order to clarify the role of adipocytokines in lung cancer and also uncover adipocytokines as novel therapeutic targets.

Pre-B cell colony enhancing factor (PBEF), a cytokine with multiple physiological functions

Pre-B cell colony enhancing factor (PBEF) is regarded as a proinflammatory cytokine. Named for its first discovered function as a pre-B cell colony enhancing factor, it has since been found to have many other functions relating to cell metabolism, inflammation, and immune modulation. It has also been found to have intracellular and extracellular forms, with the two overlapping in function. Most of the intracellular functions of PBEF are due to its role as a nicotinamide phosphoribosyltransferase (Nampt). It has been found in human endothelial cells, where it is able to induce angiogenesis through upregulation of VEGF and VEGFR and secretion of MCP-1. In human umbilical endothelial cells, PBEF increases levels of the protease MMP 2/9. PBEF has also been found in a variety of immune cells other than B cells and has been shown to inhibit apoptosis of macrophages. Extracellular PBEF has been shown to increase inflammatory cytokines, such as TNF-α, IL-1β, IL-16, and TGF-β1, and the chemokine receptor CCR3. PBEF also increases the production of IL-6, TNF-α, and IL-1β in CD14(+) monocyctes, macrophages, and dendritic cells, enhances the effectiveness of T cells, and is vital to the development of both B and T lymphocytes. The purpose of this review is to summarize the recent advances in PBEF research.

Visfatin/Nampt: an adipokine with cardiovascular impact

Adipose tissue is acknowledged as an endocrine organ that releases bioactive factors termed adipokines. Visfatin was initially identified as a novel adipokine with insulin-mimetic properties in mice. This adipokine was identical to two previously described molecules, namely, pre-B cell colony-enhancing factor (PBEF) and the enzyme nicotinamide phosphoribosyltransferase (Nampt). Enhanced circulating visfatin/Nampt levels have been reported in metabolic diseases, such as obesity and type 2 diabetes. Moreover, visfatin/Nampt circulating levels correlate with markers of systemic inflammation. In cardiovascular diseases, visfatin/Nampt was initially proposed as a clinical marker of atherosclerosis, endothelial dysfunction, and vascular damage, with a potential prognostic value. Nevertheless, beyond being a surrogate clinical marker, visfatin/Nampt is an active player promoting vascular inflammation, and atherosclerosis. Visfatin/Nampt effects on cytokine and chemokine secretion, macrophage survival, leukocyte recruitment by endothelial cells, vascular smooth muscle inflammation and plaque destabilization make of this adipokine an active factor in the development and progression of atherosclerosis. Further research is required to fully understand the mechanisms mediating the cellular actions of this adipokine and to better characterize the factors regulating visfatin/Nampt expression and release in all these pathologic scenarios. Only then, we will be able to conclude whether visfatin/Nampt is a therapeutical target in cardiometabolic diseases.

Medicinal chemistry of nicotinamide phosphoribosyltransferase (NAMPT) inhibitors

Nicotinamide phoshophoribosyltransferase (NAMPT) plays a key role in the replenishment of the NAD pool in cells. This in turn makes this enzyme an important player in bioenergetics and in the regulation of NAD-using enzymes, such as PARPs and sirtuins. Furthermore, there is now ample evidence that NAMPT is secreted and has a role as a cytokine. An important role of either the intracellular or extracellular form of NAMPT has been shown in cancer, inflammation, and metabolic diseases. The first NAMPT inhibitors (FK866 and CHS828) have already entered clinical trials, and a surge in interest in the synthesis of novel molecules has occurred. The present review summarizes the recent progress in this field.

Peripheral signalling involved in energy homeostasis control

The alarming prevalence of obesity has led to a better understanding of the molecular mechanisms controlling energy homeostasis. Regulation of energy intake and expenditure is more complex than previously thought, being influenced by signals from many peripheral tissues. In this sense, a wide variety of peripheral signals derived from different organs contributes to the regulation of body weight and energy expenditure. Besides the well-known role of insulin and adipokines, such as leptin and adiponectin, in the regulation of energy homeostasis, signals from other tissues not previously thought to play a role in body weight regulation have emerged in recent years. The role of fibroblast growth factor 21 (FGF21), insulin-like growth factor 1 (IGF-I), and sex hormone-binding globulin (SHBG) produced by the liver in the regulation of body weight and insulin sensitivity has been recently described. Moreover, molecules expressed by skeletal muscle such as myostatin have also been involved in adipose tissue regulation. Better known is the involvement of ghrelin, cholecystokinin, glucagon-like peptide 1 (GLP-1) and PYY(3-36), produced by the gut, in energy homeostasis. Even the kidney, through the production of renin, appears to regulate body weight, with mice lacking this hormone exhibiting resistance to diet-induced obesity. In addition, the skeleton has recently emerged as an endocrine organ, with effects on body weight control and glucose homeostasis through the actions of bone-derived factors such as osteocalcin and osteopontin. The comprehension of these signals will help in a better understanding of the aetiopathology of obesity, contributing to the potential development of new therapeutic targets aimed at tackling excess body fat accumulation.

Expression and regulation of nampt in human islets

Nicotinamide phosphoribosyltransferase (Nampt) is a rate-limiting enzyme in the mammalian NAD+ biosynthesis of a salvage pathway and exists in 2 known forms, intracellular Nampt (iNampt) and a secreted form, extracellular Nampt (eNampt). eNampt can generate an intermediate product, nicotinamide mononucleotide (NMN), which has been reported to support insulin secretion in pancreatic islets. Nampt has been reported to be expressed in the pancreas but islet specific expression has not been adequately defined. The aim of this study was to characterize Nampt expression, secretion and regulation by glucose in human islets. Gene and protein expression of Nampt was assessed in human pancreatic tissue and isolated islets by qRT-PCR and immunofluorescence/confocal imaging respectively. Variable amounts of Nampt mRNA were detected in pancreatic tissue and isolated islets. Immunofluorescence staining for Nampt was found in the exocrine and endocrine tissue of fetal pancreas. However, in adulthood, Nampt expression was localized predominantly in beta cells. Isolated human islets secreted increasing amounts of eNampt in response to high glucose (20 mM) in a static glucose-stimulated insulin secretion assay (GSIS). In addition to an increase in eNampt secretion, exposure to 20 mM glucose also increased Nampt mRNA levels but not protein content. The secretion of eNampt was attenuated by the addition of membrane depolarization inhibitors, diazoxide and nifedipine. Islet-secreted eNampt showed enzymatic activity in a reaction with increasing production of NAD+/NADH over time. In summary, we show that Nampt is expressed in both exocrine and endocrine tissue early in life but in adulthood expression is localized to endocrine tissue. Enzymatically active eNampt is secreted by human islets, is regulated by glucose and requires membrane depolarization.

Misconduct accounts for the majority of retracted scientific publications

A detailed review of all 2,047 biomedical and life-science research articles indexed by PubMed as retracted on May 3, 2012 revealed that only 21.3% of retractions were attributable to error. In contrast, 67.4% of retractions were attributable to misconduct, including fraud or suspected fraud (43.4%), duplicate publication (14.2%), and plagiarism (9.8%). Incomplete, uninformative or misleading retraction announcements have led to a previous underestimation of the role of fraud in the ongoing retraction epidemic. The percentage of scientific articles retracted because of fraud has increased ∼10-fold since 1975. Retractions exhibit distinctive temporal and geographic patterns that may reveal underlying causes.

Nicotinamide phosphoribosyl-transferase/visfatin: a missing link between overweight/obesity and postmenopausal breast cancer? Potential preventive and therapeutic perspectives and challenges

Worldwide breast cancer (BC) constitutes a significant public health concern. Excess body weight is associated with postmenopausal BC (PBC) risk. Recent studies have shown that the constellation of obesity, insulin resistance and serum adipokine levels are associated with the risk and prognosis of PBC. Nicotinamide phosphoribosyl-transferase (Nampt), also known as visfatin and pre-B-cell-colony-enhancing factor, found in the visceral fat, represents a novel pleiotropic adipokine acting as a cytokine, a growth factor and an enzyme. It plays an important role in a variety of metabolic and stress responses as well as in the cellular energy metabolism, particularly NAD biosynthesis. Nampt exhibits proliferative, anti-apoptotic, pro-inflammatory and pro-angiogenic properties. Nampt's insulin-mimetic function remains a controversial issue. Circulating Nampt levels are increased in obese women. Also, Nampt levels are significantly elevated in women suffering from PBC than in healthy controls independently from known risk factors of BC, anthropometric and metabolic parameters as well as serum concentrations of well known adipokines. High expression of Nampt in BC tissues was reported to be associated with more malignant cancer behavior as well as adverse prognosis. Taking into account the mitogenicity of Nampt as well as its proliferative, anti-apoptotic and pro-angiogenic properties, a novel hypothesis is proposed whereas Nampt may be involved in the etiopathogenesis of PBC and may represent a missing link between overweight/obesity and PBC. Nampt could exert its effects on the normal and neoplastic mammary tissue by endocrine and paracrine mechanisms; Nampt could also be secreted by tumor epithelial cells in an autocrine manner. It could stimulate mammary epithelial cell proliferation, invasion, metastasis, and angiogenesis, which is essential for BC development and progression. Serum Nampt might be a novel risk factor as well as a potential diagnostic and prognostic biomarker in PBC. In addition, pharmacologic agents that neutralize biochemically Nampt or medications that decrease Nampt levels or downregulate signaling pathways downstream of Nampt may prove to be useful anti-cancer agents. The potential harmful effect on PBC risk due to vitamin B3 (nicotinic acid, a natural NAD precursor in the biosynthetic route leading to NAD) intake is speculated for the first time. In this hypothesis, the role of Nampt in BC carcinogenesis and progression is explored as well as the pathophysiological mechanisms that underlie the association between Nampt and PBC in the context of a dysfunctional adipose tissue in obesity. Understanding of these mechanisms may be important for the development of preventive and therapeutic strategies against PBC.

Role of adipokines in atherosclerosis: interferences with cardiovascular complications in rheumatic diseases

Patients with rheumatic diseases have an increased risk of mortality by cardiovascular events. In fact, several rheumatic diseases such as rheumatoid arthritis, osteoarthritis, systemic lupus erythematosus, and ankylosing spondylitis are associated with a higher prevalence of cardiovascular diseases (CVDs). Although traditional cardiovascular risk factors have been involved in the pathogenesis of cardiovascular diseases in rheumatic patients, these alterations do not completely explain the enhanced cardiovascular risk in this population. Obesity and its pathologic alteration of fat mass and dysfunction, due to an altered pattern of secretion of proinflammatory adipokines, could be one of the links between cardiovascular and rheumatic diseases. Indeed, the incidence of CVDs is augmented in obese individuals with rheumatic disorders. Thus, in this paper we explore in detail the relationships among adipokines, rheumatic diseases, and cardiovascular complications by giving to the reader a holistic vision and several suggestions for future perspectives and potential clinical implications.

Elevated serum visfatin/nicotinamide phosphoribosyl-transferase levels are associated with risk of postmenopausal breast cancer independently from adiponectin, leptin, and anthropometric and metabolic parameters

OBJECTIVE

Obesity has been implicated in the etiology of postmenopausal breast cancer (PBC). We hypothesized that altered secretion of visfatin may underlie this association. We thus investigated the association of serum visfatin with PBC risk, taking into account known risk factors including adipokines and anthropometric and metabolic parameters.

METHODS

In a case-control study, we studied 102 postmenopausal women with pathologically confirmed, incident invasive breast cancer and 102 control women matched on age and time of diagnosis between 2003 and 2010 at Army Share Fund Hospital, Veterans' Hospital (NIMTS). Levels of serum visfatin, adiponectin, leptin, metabolic parameters, carcinoembryonic antigen, and CA 15-3 were determined.

RESULTS

The mean serum visfatin level was significantly higher in case than in control participants (P < 0.001). Women in the highest quartile of visfatin concentration presented significantly higher odds for PBC, adjusting for age, date of diagnosis, education, body mass index, waist circumference, years with menstruation, parity/age at first full-term pregnancy, breast-feeding, family history of cancer, use of exogenous hormones, alcohol consumption, smoking status, homeostasis model assessment score, and serum leptin and adiponectin concentrations (odds ratio, 7.93; 95% CI, 2.52-24.9). In case participants, the visfatin level correlated significantly with the tumor marker CA 15-3 (P = 0.03) but not with metabolic and anthropometric variables (P > 0.05).

CONCLUSIONS

Further prospective studies are needed to determine whether an elevated serum visfatin level is implicated in the etiopathogenesis of PBC or reflects changes during PBC progression and could therefore be used as a biomarker for PBC.

The value of visfatin in the prediction of metabolic syndrome: a multi-factorial analysis

We describe the adipokine concentration in patients with metabolic syndrome, stressing the role of visfatin. A cross-sectional single center study on 70 patients with metabolic syndrome plus 76 controls was performed. Patients with metabolic syndrome had higher visfatin levels compared to controls, following adjustments for age, sex, waist/hip circumference, systolic, and diastolic blood pressure, fasting plasma glucose (FPG), HbA1c, body mass index, and homeostasis model assessment of insulin resistance (HOMA-IR) [(5.39 ± 0.29 vs. 3.88 ± 0.32); F(1, 129) = 10.8, P < 0.01]. A logistic regression analysis revealed that circulating visfatin levels and HbA1c were the top variables for predicating metabolic syndrome. In patients with metabolic syndrome, visfatin did not correlate with any of the measured variables, with the single exception of adiponectin; in patients without metabolic syndrome, circulating visfatin levels were significantly associated with FPG, HbA1c, insulin, HOMA-IR, HDL, and triglyceride. These findings may contribute to our current knowledge about visfatin in metabolic syndrome.

Visfatin and its role in obesity development

Visfatin, a product of PBEF gene, is an adipocytokine that harbours strong insulin-mimetic activity and it has been reported previously to associate with obesity. Recent reports also provide evidence that Visfatin has also important intracellular effects as it is homologous with nicotinamide phosphoribosyltransferase (NAMPT). In this review, we summarize the main documented effects of Visfatin on metabolism in humans, with special emphasis put on the pathways associated with obesity.

Visfatin/NAMPT: a multifaceted molecule with diverse roles in physiology and pathophysiology

Visfatin/NAMPT (nicotinamide phosphoribosyltransferase) is a protein with several suggested functions. Although the first discovery of this molecule as a pre-B-cell colony-enhancing factor suggested primarily a cytokine function, its rediscovery as the key enzyme in nicotinamide adenine dinucleotide generation has considerably widened its potential biological activities. Although originally thought to be produced in adipose tissue (i.e., adipocytes and infiltrating macrophages), its production seems to involve other cells and tissues such as skeletal muscle, liver, immune cells, cardiomyocytes, and the brain. Visfatin/NAMPT has both intracellular and extracellular effects influencing several signaling pathways. Its broad spectrum of effects is mirrored by its potential involvement in a wide range of disorders including human immunodeficiency virus infection, septicemia, myocardial failure, atherosclerosis, metabolic disorders, inflammatory diseases, malignancies, and neurodegenerative disorders and aging. Moreover, studies on visfatin/NAMPT in atherosclerotic disorders suggest a rather complex role of this molecule in pathophysiology, potentially mediating both adaptive and maladaptive responses.

Proinflammatory actions of visfatin/nicotinamide phosphoribosyltransferase (Nampt) involve regulation of insulin signaling pathway and Nampt enzymatic activity

Visfatin (also termed pre-B-cell colony-enhancing factor (PBEF) or nicotinamide phosphoribosyltransferase (Nampt)) is a pleiotropic mediator acting on many inflammatory processes including osteoarthritis. Visfatin exhibits both an intracellular enzymatic activity (nicotinamide phosphoribosyltransferase, Nampt) leading to NAD synthesis and a cytokine function via the binding to its hypothetical receptor. We recently reported the role of visfatin in prostaglandin E(2) (PGE(2)) synthesis in chondrocytes. Here, our aim was to characterize the signaling pathways involved in this response in exploring both the insulin receptor (IR) signaling pathway and Nampt activity. IR was expressed in human and murine chondrocytes, and visfatin triggered Akt phosphorylation in murine chondrocytes. Blocking IR expression with siRNA or activity using the hydroxy-2-naphthalenyl methyl phosphonic acid tris acetoxymethyl ester (HNMPA-(AM)(3)) inhibitor diminished visfatin-induced PGE(2) release in chondrocytes. Moreover, visfatin-induced IGF-1R(-/-) chondrocytes released higher concentration of PGE(2) than IGF-1R(+/+) cells, a finding confirmed with an antibody that blocked IGF-1R. Using RT-PCR, we found that visfatin did not regulate IR expression and that an increased insulin release was also unlikely to be involved because insulin was unable to increase PGE(2) release. Inhibition of Nampt activity using the APO866 inhibitor gradually decreased PGE(2) release, whereas the addition of exogenous nicotinamide increased it. We conclude that the proinflammatory actions of visfatin in chondrocytes involve regulation of IR signaling pathways, possibly through the control of Nampt enzymatic activity.

Serum visfatin and vaspin levels in normoglycemic first-degree relatives of Iranian patients with type 2 diabetes mellitus

AIM

To investigate circulating visfatin and vaspin levels in first-degree relatives of subjects with type 2 diabetes mellitus (FDRs) who frequently have higher value of HOMA-IR and beta cell dysfunction.

METHODS

Serum visfatin and vaspin concentrations were measured in 179 Iranian subjects (90 normoglycemic FDRs and 89 age- and sex-matched healthy controls) using enzyme-linked immunosorbent assay (ELISA) methods.

RESULT

Serum visfatin levels were significantly lower in the FDRs when compared to the controls (1.71±0.93 ng/ml versus 2.69±2.02 ng/ml, p=0.0001). However, no significant difference was found in serum vaspin concentrations between the FDRs and the controls (0.452±0.254 ng/ml versus 0.409±0.275 ng/ml, p>0.05). In multiple logistic regression analysis, the FDRs showed a significant association with lower visfatin levels after adjustments for age, sex, Body Mass Index, systolic and diastolic blood pressures, lipid profile, blood glucose levels and HOMA-IR [odds ratios (OR)=1.71, 95% confidence interval (1.30-2.25); p<0.0001].

CONCLUSION

The FDRs showed a significant association with lower visfatin levels. The observed lower circulating visfatin levels in FDRs may suggest a pathophysiological role for visfatin in beta cell dysfunction in this group.

Visfatin impairs endothelium-dependent relaxation in rat and human mesenteric microvessels through nicotinamide phosphoribosyltransferase activity

Visfatin, also known as extracellular pre-B-cell colony-enhancing factor (PBEF) and nicotinamide phosphoribosyltransferase (Nampt), is an adipocytokine whose circulating levels are enhanced in metabolic disorders, such as type 2 diabetes mellitus and obesity. Circulating visfatin levels have been positively associated with vascular damage and endothelial dysfunction. Here, we investigated the ability of visfatin to directly impair vascular reactivity in mesenteric microvessels from both male Sprague-Dawley rats and patients undergoing non-urgent, non-septic abdominal surgery. The pre-incubation of rat microvessels with visfatin (50 and 100 ng/mL) did not modify the contractile response to noradrenaline (1 pmol/L to 30 µmol/L), as determined using a small vessel myograph. However, visfatin (10 to 100 ng/mL) concentration-dependently impaired the relaxation to acetylcholine (ACh; 100 pmol/L to 3 µmol/L), without interfering with the endothelium-independent relaxation to sodium nitroprusside (1 nmol/L to 3 µmol/L). In both cultured human umbilical vein endothelial cells and rat microvascular preparations, visfatin (50 ng/mL) stimulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, as determined by lucigenin-derived chemiluminiscence. The relaxation to ACh impaired by visfatin was restored by the NADPH oxidase inhibitor apocynin (10 µmol/L). Additionally, the Nampt inhibitor APO866 (10 mmol/L to 10 µmol/L), but not an insulin receptor-blocking antibody, also prevented the stimulation of NADPH oxidase and the relaxation impairment elicited by visfatin. Accordingly, the product of Nampt activity nicotinamide mononucleotide (100 nmol/L to 1 mmol/L) stimulated endothelial NADPH oxidase activity and concentration-dependently impaired ACh-induced vasorelaxation. In human mesenteric microvessels pre-contracted with 35 mmol/L potassium chloride, the endothelium-dependent vasodilation to bradykinin (1 nmol/L to 3 µmol/L) was equally impaired by visfatin and restored upon co-incubation with APO866. In conclusion, visfatin impairs endothelium-dependent relaxation through a mechanism involving NADPH oxidase stimulation and relying on Nampt enzymatic activity, and therefore arises as a potential new player in the development of endothelial dysfunction.

Beyond fat mass: exploring the role of adipokines in rheumatic diseases

The cloning of leptin in 1994 by Zhang et al. introduced a novel concept about white adipose tissue (WAT) as a very dynamic organ that releases a plethora of immune and inflammatory mediators, such as adipokines and cytokines, which are involved in multiple diseases. Actually, adipokines exert potent modulatory actions on target tissues involved in rheumatic diseases including cartilage, synovial, bone and immune cells. The goal of this paper is to elucidate the recent findings concerning the involvement of adipokines in rheumatic diseases, such as rheumatoid arthritis (RA), osteoarthritis (OA), and systemic lupus erythematosus (SLE).

Visfatin in overweight/obesity, type 2 diabetes mellitus, insulin resistance, metabolic syndrome and cardiovascular diseases: a meta-analysis and systemic review

There are controversies regarding the association of visfatin with overweight/obesity, type 2 diabetes mellitus, insulin resistance (IR), metabolic syndrome and cardiovascular disease in published articles. A meta-analysis was performed to identify the significance of visfatin in these diseases. We searched for relevant articles in Pubmed, Scopus and SCIE. A total of 1035 articles were surveyed and 46 articles were identified, with 14 reports reporting more than one of our investigated diseases. A total of 13 (n = 644), 19 (n = 2405), 20 (n = 2249), 5 (n = 527) and 5 (n = 851) articles/(participants) were included in each meta-analysis regarding the association of visfatin and overweight/obesity, type 2 diabetes mellitus, insulin resistance, metabolic syndrome and cardiovascular diseases, respectively. Plasma visfatin concentrations were increased in participants diagnosed with overweight/obesity, type 2 diabetes mellitus, metabolic syndrome and cardiovascular diseases, with pooled log odds ratios of 1.164 [95% confidence interval (CI): 0.348 to 1.981, p = 0.005], 1.981 (95% CI: 1.377 to 2.584, p < 0.001), 1.094 (95% CI: 0.678 to 1.511, p < 0.001), and 2.902 (95% CI: 0.924 to 4.879, p < 0.005), respectively. The circulating visfatin level was positively associated with insulin resistance, with a Fisher's z of 0.089 (95% CI: 0.013 to 0.165, p = 0.022). No single study was found to affect the overall result of each analysis by sensitivity testing. No publication bias was found by the Egger test. Our study suggests that the use of visfatin may be promising for predicting obesity, diabetes status, insulin resistance, metabolic syndrome and cardiovascular disease.

Adipokines and osteoarthritis: novel molecules involved in the pathogenesis and progression of disease

Obesity has been considered a risk factor for osteoarthritis and it is usually accepted that obesity contributes to the development and progression of osteoarthritis by increasing mechanical load of the joints. Nevertheless, recent advances in the physiology of white adipose tissue evidenced that fat cells produce a plethora of factors, called adipokines, which have a critical role in the development of ostearthritis, besides to mechanical effects. In this paper, we review the role of adipokines and highlight the cellular and molecular mechanisms at play in osteoarthritis elicited by adipokines. We also emphasize how defining the role of adipokines has broadned our understanding of the diversity of factors involved in the genesis and progression of osteoarthritis in the hope of modifying it to prevent and treat diseases.

Soy food supplementation, dietary fat reduction and peripheral blood gene expression in postmenopausal women--a randomized, controlled trial

SCOPE

The effect of soy food supplementation or dietary fat reduction on gene expression is not well studied.

METHODS AND RESULTS

We evaluated the potential of gene expression profiling in peripheral blood mononuclear cells (PBMCs) collected at baseline and at the completion of an 8-wk controlled dietary intervention. Healthy postmenopausal women were randomized to a very-low-fat diet (VLFD; 11% of energy as fat) (n=21), a Step 1 diet (25% energy as fat) supplemented with soy food (SFD; 50 mg isoflavones per day) (n=20), or a control Step 1 diet (CD; 27% energy as fat) with no SFD (n=18). All diets were prepared at the General Clinical Research Center of the University of Southern California. We did not observe any gene that showed variable response across the three dietary interventions. However, there were notable changes in gene expression associated with the intervention in the VLFD and SFD groups. Our findings suggest that the expression of nicotinamide phosphoribosyltransferase (NAMPT) and genes related to Fc γ R-mediated phagocytosis and cytokine interactions may be significantly altered in association with dietary fat reduction and soy supplementation. Gene expression changes in NAMPT were somewhat dampened with adjustment for weight but changes related to Fc γ R-mediated phagocytosis and cytokine interactions remained largely unchanged.

CONCLUSION

PBMCs can reveal novel gene expression changes in association with controlled dietary intervention.

Visfatin enhances CXCL8, CXCL10, and CCL20 production in human keratinocytes

Psoriasis patients are frequently associated with metabolic syndromes. Such associations are possibly mediated by adipokines. We investigated the in vitro effects of visfatin (an adipokine) on chemokine expression in human keratinocytes. Normal human keratinocytes were incubated with visfatin, and their chemokine production was analyzed by ELISA and RT-PCR. Visfatin enhanced TNF-α-induced CXC chemokine ligand (CXCL) 8, CXCL10, and CC chemokine ligand (CCL) 20 secretion and mRNA expression in keratinocytes, although visfatin alone was ineffective. A small interfering RNA against nuclear factor-κB (NF-κB) p65 suppressed the visfatin-induced production of CXCL8, CXCL10, and CCL20 whereas a small interfering RNA against signal transducer and activator of transcription (STAT) 3 suppressed CXCL8 induction. This indicates the involvement of NF-κB in CXCL8, CXCL10, and CCL20 induction by visfatin and the involvement of STAT3 in CXCL8 induction. Visfatin alone increased the transcriptional activity and tyrosine phosphorylation of STAT3, which was suppressed by Janus kinase (JAK) 2 inhibitor. Visfatin enhanced basal and TNF-α-induced NF-κB activity and inhibitory κB (IκB) α phosphorylation, which was suppressed by IκB kinase inhibitor. Visfatin induced the tyrosine and serine phosphorylation of JAK2 and IκB kinase α/β, respectively. Intraperitoneal injection of visfatin elevated mRNA and protein levels of CXCL1, CXCL10, and CCL20 in murine skin. These results suggest that visfatin enhances CXCL8, CXCL10, and CCL20 production in human keratinocytes and homologous chemokine production in murine skin. Visfatin may induce the infiltration of type 1 or type 17 helper T cells or neutrophils to the skin via chemokine induction and thus link metabolic syndromes to psoriasis.

Lack of downstream insulin-mimetic effects of visfatin/eNAMPT on glucose and fatty acid metabolism in skeletal muscles

AIM

Recent studies regarding downstream effects of visfatin/eNAMPT in skeletal muscles have attracted much attention as the previous reports suggested this adipokine may exert insulin-mimetic effects. However, studies in vivo present conflicting data and are still controversial. In this present work, we sought to investigate whether visfatin/eNAMPT is able to reproduce insulin effects on glucose transport and lipid metabolism.

METHODS

  We have used isolated skeletal muscles with different fibre type composition (Soleus and EDL) to examine glucose transport, GLUT-4 translocation, phosphorylation of insulin signalling pathway proteins, as well as the key parameters for fatty acid metabolism.

RESULTS

We found that, in vitro exposure to visfatin/eNAMPT increased skeletal muscle glucose transport but only in EDL (+20%) and not in Soleus muscle (+5%). Interestingly, classical insulin signalling pathways were not significantly involved in this process. Concomitantly, visfatin/eNAMPT exerted no significant effects on muscle's fatty acids (FA) metabolism as no change in either palmitate oxidation or esterification was observed. Importantly, combined insulin and visfatin effects were not found, suggesting non-additivity.

CONCLUSION

Our data suggest that visfatin/eNAMPT plays a rather limited role in regulating skeletal muscle glucose transport and FA metabolism.

Nampt/visfatin/PBEF affects expression of myogenic regulatory factors and is regulated by interleukin-6 in chicken skeletal muscle cells

Nicotinamide phosphoribosyltransferase (Nampt/visfatin/PBEF) has been identified as a rate-limiting NAD(+) biosynthetic enzyme and an adipokine found in the circulation. Human and chicken skeletal muscles are reported to have the highest level of Nampt expression among various tissues whose functional significance remains undetermined. Expression of Nampt is regulated by interleukin-6 (IL-6), an essential cytokine for postnatal muscle growth in mammals. The objective of the current study was to characterize expression of Nampt in chicken (Gallus gallus) myogenic cells and to determine the effect of Nampt on expression of IL-6, myogenic transcription factors, and glucose uptake. We also sought to determine the effect of IL-6 on Nampt expression in chicken myogenic cells. Nampt mRNA and protein were identified in both myoblasts and myocytes, although expression did not differ between the two cell types. Treatment with recombinant human Nampt was found to decrease myoD and mrf4 expression but to increase myf5 expression in myocytes, while glucose uptake was unaffected. In response to treatment with recombinant Nampt, IL-6 expression in myocytes was increased at 24h but decreased when treated for 48 or 72 h. Forced over-expression of chicken Nampt cDNA significantly decreased myf5 expression in myoblasts. Treatment of myogenic cells with lower levels (1 ng.mL(-1)) of recombinant IL-6 increased Nampt expression, whereas a higher IL-6 concentration (100 ng.mL(-1)) decreased Nampt mRNA abundance. Collectively, these results demonstrate that Nampt, regulated in part by IL-6, alters the expression of key myogenic transcription factors and thereby may influence postnatal myogenesis.

Serum visfatin is associated with type 2 diabetes mellitus independent of insulin resistance and obesity

OBJECTIVE

The aim of this study was to evaluate the association of serum visfatin, adiponectin and leptin with 2 diabetes mellitus (T2DM) in the context of the role of obesity or insulin resistance, which is not well understood.

METHODS

A total of 76 newly-diagnosed T2DM patients and 76 healthy control subjects, matched for age, body mass index (BMI) and sex ratio, were enrolled. Anthropometric parameters, glycemic and lipid profile, insulin resistance (measured by homeostasis model assessment of insulin resistance index [HOMA-IR]), leptin, adiponectin, and visfatin were assessed.

RESULTS

On the contrary to adiponectin, serum leptin and visfatin levels were higher in T2DM patients compared with controls (10.07 ± 4.5, 15.87 ± 16.4, and 5.49 ± 2.4 vs. 12.22 ± 4.9 μg/ml, 8.5 ± 7.8 ng/ml and 3.58 ± 2.2 ng/ml, respectively, P<0.01). Waist circumference and BMI were correlated with leptin and adiponectin but not with visfatin. Leptin, adiponectin and visfatin all were associated with T2DM following adjusting for obesity measures. After controlling for HOMA-IR, visfatin remained as an independent predictor of T2DM (odds ratio=1.32, P<0.05). In a multiple regression analysis to determine visfatin only triglycerides and fasting glucose remained in the model (P<0.05).

CONCLUSION

Elevation of visfatin in T2DM is independent of obesity and insulin resistance and is mainly determined by fasting glucose and triglycerides.

Adipocyte-brain: crosstalk

The initial discovery of leptin, an appetite-suppressing hormone originating from fat tissue, substantially supported the idea that fat-borne factors act on the brain to regulate food intake and energy expenditure. Since then, a growing number of cytokines have been found to be released from adipose tissue, thus acting in an endocrine manner. These adipocytokines include not only, e.g., adiponectin, apelin, resistin, and visfatin, but also inflammatory cytokines and steroid hormones such as estrogens and glucocorticoids. They are secreted from their adipose depots and differ in terms of release stimuli, downstream signaling, and their action on the brain. Clearly, adipocytokines play a prominent role in the central control of body weight, and the deregulation of this circuit may lead to the development of obesity and related disorders. In this chapter, we will focus on crosstalk mechanisms and the deregulation of adipocytokines at the expression level and/or sites of central action that eventually will lead to the development and perpetuation of obesity and diabetes.

Nicotinamide Phosphoribosyltransferase in Human Diseases

Nicotinamide phosphoribosyltransferase (NAMPT) was first reported as a pre-B-cell colony enhancing factor in 1994 with little notice, but it has received increasing attention in recent years due to accumulating evidence indicating that NAMPT is a pleiotropic protein such as a growth factor, a cytokine, an enzyme and a visfatin. Now, NAMPT has been accepted as an official name of this protein. Because of NAMPT's multiple functions in a variety of physiological processes, their dysregulations have been implicated in the pathogenesis of a number of human diseases or conditions such as acute lung injury, aging, atherosclerosis, cancer, diabetes, rheumatoid arthritis and sepsis. This review will cover the current understanding of NAMPT's structure and functions with an emphasis on recent progress of nicotinamide phosphoribosyltransferase's pathological roles in various human diseases and conditions. Future directions on exploring its Terra incognita will be offered in the end.

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).

Visfatin/PBEF/Nampt: A New Cardiovascular Target?

In the last years, a growing interest has emerged toward understanding the role of adipocytokines in the development of cardio-metabolic complications. Five years ago, visfatin/PBEF/Nampt was identified as a novel adipocytokine. In the context of metabolic disorders, extracellular visfatin/PBEF/Nampt was initially claimed as a potentially beneficial molecule due to its insulin-mimetic and glucose-lowering properties. Nevertheless, growing evidence has since then unveiled that visfatin/PBEF/Nampt may rather be a biomarker of inflammation and endothelial damage, and also a direct regulator of the cardiovascular system that modulates cell proliferation and survival, extracellular matrix, vascular reactivity, and inflammation. On one side, the blockade of the deleterious cardiovascular actions of visfatin/PBEF/Nampt is being regarded as a potential approach to prevent and treat, not only cardio-metabolic complications, but also other pathologies implying excessive angiogenesis. Conversely, the administration of visfatin/PBEF/Nampt has shown beneficial effects in different ischemic conditions. Further research is required to evaluate the real value of visfatin/PBEF/Nampt as a pharmacological target.

Membrane raft-lysosome redox signalling platforms in coronary endothelial dysfunction induced by adipokine visfatin

AIMS

The adipokine visfatin, produced during obesity, has been reported to participate in the development of cardiovascular disease associated with metabolic syndrome. The present study was designed to test a hypothesis that visfatin causes coronary endothelial dysfunction through lysosome trafficking and fusion to cell membranes, membrane raft (MR) clustering, and formation of redox signalosomes.

METHODS AND RESULTS

By using confocal microscopy, it was found that visfatin, but not adiponectin, stimulated NADPH oxidase (NOX) subunits, gp91(phox) aggregation in MR clusters and p47(phox) translocation to these MR clusters in bovine coronary arterial endothelial cells (CAECs), leading to activation of NOX with a 2.5-fold increase in O(2)(·-) production. A signalling lipid, ceramide, was found to be enriched in such membrane MR-NOX complexes of CAECs. Lysosomal fluorescent dye (FM1-43) quenching and de-quenching revealed that visfatin induced the fusion of lysosomes to cell membranes and incorporation of acid sphingomyelinase and its product, ceramide, in such MR-NOX signalling platforms. Functionally, visfatin significantly attenuated endothelium-dependent vasodilation in small coronary arteries (by 80%), which was blocked by lysosomal function inhibitor and MR disruptors.

CONCLUSION

These results suggest that lysosome-associated molecular trafficking and consequent ceramide accumulation in cell membrane may mediate the assembly of NOX subunits and their activation in response to adipokine visfatin in CAECs, thereby producing endothelial dysfunction in coronary circulation.

Inflammation, a link between obesity and cardiovascular disease

Obesity, the most common nutritional disorder in industrialized countries, is associated with an increased mortality and morbidity of cardiovascular disease (CVD). Obesity is primarily considered to be a disorder of energy balance, and it has recently been suggested that some forms of obesity are associated with chronic low-grade inflammation. The present paper focuses on the current status of our knowledge regarding chronic inflammation, a link between obesity and CVDs, including heart diseases, vascular disease and atherosclerosis. The paper discusses the methods of body fat evaluation in humans, the endocrinology and distribution of adipose tissue in the genders, the pathophysiology of obesity, the relationship among obesity, inflammation, and CVD, and the adipose tissue-derived cytokines known to affect inflammation. Due to space limitations, this paper focuses on C-reactive protein, serum amyloid A, leptin, adiponectin, resistin, visfatin, chemerin, omentin, vaspin, apelin, and retinol binding protein 4 as adipokines.

Visfatin is induced by peroxisome proliferator-activated receptor gamma in human macrophages

Obesity is a low-grade chronic inflammatory disease associated with an increased number of macrophages (adipose tissue macrophages) in adipose tissue. Within the adipose tissue, adipose tissue macrophages are the major source of visfatin/pre-B-cell colony-enhancing factor/nicotinamide phosphoribosyl transferase. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) exerts anti-inflammatory effects in macrophages by inhibiting cytokine production and enhancing alternative differentiation. In this study, we investigated whether PPARgamma modulates visfatin expression in murine (bone marrow-derived macrophage) and human (primary human resting macrophage, classical macrophage, alternative macrophage or adipose tissue macrophage) macrophage models and pre-adipocyte-derived adipocytes. We show that synthetic PPARgamma ligands increase visfatin gene expression in a PPARgamma-dependent manner in primary human resting macrophages and in adipose tissue macrophages, but not in adipocytes. The threefold increase of visfatin mRNA was paralleled by an increase of protein expression (30%) and secretion (30%). Electrophoretic mobility shift assay experiments and transient transfection assays indicated that PPARgamma induces visfatin promoter activity in human macrophages by binding to a DR1-PPARgamma response element. Finally, we show that PPARgamma ligands increase NAD(+) production in primary human macrophages and that this regulation is dampened in the presence of visfatin small interfering RNA or by the visfatin-specific inhibitor FK866. Taken together, our results suggest that PPARgamma regulates the expression of visfatin in macrophages, leading to increased levels of NAD(+).

Regulation of adipokine secretion by n-3 fatty acids

Obesity leads to several chronic morbidities including type 2 diabetes, dyslipidaemia, atherosclerosis and hypertension, which are major components of the metabolic syndrome. White adipose tissue (WAT) metabolism and WAT-derived factors (fatty acids and adipokines) play an important role in the development of these metabolic disturbances. In fact, dysregulated adipokine secretion from the expanded WAT of obese individuals contributes to the development of systemic low-grade inflammation, insulin resistance and metabolic syndrome. The n-3 PUFA EPA and DHA have been widely reported to have protective effects in a range of chronic inflammatory conditions including obesity. In fact, n-3 PUFA have been shown to ameliorate low-grade inflammation in adipose tissue associated with obesity and up-regulate mitochondrial biogenesis and induce beta-oxidation in WAT in mice. Moreover, the ability of n-3 PUFA to regulate adipokine gene expression and secretion has been observed both in vitro and in vivo in rodents and human subjects. The present article reviews: (1) the physiological role of adiponectin, leptin and pre-B cell colony-enhancer factor/visfatin, three adipokines with immune-modulatory properties involved in the regulation of metabolism and insulin sensitivity and (2) the actions of n-3 PUFA on these adipokines focusing on the underlying mechanisms and the potential relationship with the beneficial effects of these fatty acids on obesity-associated metabolic disorders. It can be concluded that the ability of n-3 PUFA to improve obesity and insulin resistance conditions partially results from the modulation of WAT metabolism and the secretion of bioactive adipokines including leptin, adiponectin and visfatin.

Lack of direct insulin-like action of visfatin/Nampt/PBEF1 in human adipocytes

Visfatin, a protein identified as a secretion product of visceral fat in humans and mice, is also expressed in different anatomical locations, and is known as pre-B cell-colony enhancing factor (PEBF1). It is also an enzyme displaying nicotinamide phosphoribosyltransferase activity (Nampt). The evidence that levels of visfatin correlate with visceral fat mass has been largely debated and widely extended to other regulations in numerous clinical studies and in diverse animal models. On the opposite, the initial findings regarding the capacity of visfatin/Nampt/PEBF1 to bind and to activate the insulin receptor have been scarcely reproduced, and even were contradicted in recent reports. Since the putative insulin mimicking effects of visfatin/Nampt/PEBF1 have never been tested on mature human adipocytes, at least to our knowledge, we tested different human visfatin batches on human fat cells freshly isolated from subcutaneous abdominal fat and exhibiting high insulin responsiveness. Up to 10 nM, visfatin was devoid of clear activatory action on glucose transport in human fat cells while, in the same conditions, insulin increased by more than threefold the basal 2-deoxyglucose uptake. Moreover, visfatin was unable to mimic the lipolysis inhibition induced by insulin. Visfatin definitively cannot be considered as a direct activator of insulin signalling in human fat cells. Nevertheless itsin vivo effects on insulin release and on glucose handling deserve to further study the role of this multifunctional extracellular enzyme in obese and diabetic states.