Visfatin: a new player in mesangial cell physiology and diabetic nephropathy

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.

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.

Risk of chronic kidney disease in patients with non-alcoholic fatty liver disease: is there a link?

Non-alcoholic fatty liver disease (NAFLD) has emerged as a growing public health problem worldwide. Increasing recognition of the importance of NAFLD and its association with the features of the metabolic syndrome has stimulated an interest in its putative role in the development and progression of chronic kidney disease (CKD). Accumulating evidence suggests that NAFLD and CKD share many important cardio-metabolic risk factors and common pathogenetic mechanisms and that NAFLD is associated with an increased prevalence and incidence of CKD. This association appears to be independent of obesity, hypertension, and other potentially confounding factors, and it occurs both in patients without diabetes and in those with diabetes. Although further research is needed to establish a definitive conclusion, these observations raise the possibility that NAFLD is not only a marker of CKD but also might play a part in the pathogenesis of CKD, possibly through the systemic release of several pro-inflammatory/pro-coagulant mediators from the steatotic/inflamed liver or through the contribution of NAFLD itself to insulin resistance and atherogenic dyslipidemia. However, given the heterogeneity and small number of observational longitudinal studies, further research is urgently required to corroborate the prognostic significance of NAFLD for the incidence of CKD, and to further elucidate the complex and intertwined mechanisms that link NAFLD and CKD. If confirmed in future large-scale prospective studies, the potential adverse impact of NAFLD on kidney disease progression will deserve particular attention, especially with respect to the implications for screening and surveillance strategies in the growing number of patients with NAFLD.

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.

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 stimulates a cellular renin-angiotensin system in cultured rat mesangial cells

OBJECTIVE

Visfatin is a newly identified proinflammatory adipocytokine whose plasma levels have been reported to be higher in subjects with type 2 diabetes mellitus. Recent studies have shown that visfatin increases the synthesis of profibrotic molecules in mesangial cells (MCs) and thus plays an important role in the pathogenesis of diabetic nephropathy. However, the mechanism by which visfatin induces kidney injury is unknown. The renin-angiotensin system (RAS) plays pivotal roles in renal diseases. Therefore, in this study the effect of visfatin on the regulation of RAS in MCs was examined.

METHODS

Cultured rat MCs were treated with different doses of visfatin. We used real-time polymerase chain reaction to detect mRNA expression of renin, angiotensinogen (AGT), angiotensin-converting enzyme (ACE), angiotensin II (Ang II) type 1 receptor (AT1), and Ang II type 2 receptor (AT2); western blot analysis for expression of ANG and AT1; and radioimmunoassay to measure Ang II production from MCs in the supernatants of culture media.

RESULTS

Visfatin treatments increased renin, angiotensinogen (AGT), AT1 mRNA, and AGT, AT1 protein expression, as well as Ang II levels in a dose-dependent manner but did not affect ACE and AT2 mRNA levels in cultured rat MCs.

CONCLUSIONS

Our findings suggest that visfatin imparts a detrimental effect on diabetic nephropathy at least partly through the activation of intrarenal RAS.

The role of mammalian sirtuins in the regulation of metabolism, aging, and longevity

Ever since the discovery of sirtuins a decade ago, interest in this family of NAD-dependent deacetylases has exploded, generating multiple lines of evidence implicating sirtuins as evolutionarily conserved regulators of lifespan. In mammals, it has been established that sirtuins regulate physiological responses to metabolism and stress, two key factors that affect the process of aging. Further investigation into the intimate connection among sirtuins, metabolism, and aging has implicated the activation of SIRT1 as both preventative and therapeutic measures against multiple age-associated disorders including type 2 diabetes and Alzheimer's disease. SIRT1 activation has clear potential to not only prevent age-associated diseases but also to extend healthspan and perhaps lifespan. Sirtuin activating compounds and NAD intermediates are two promising ways to achieve these elusive goals.

Serum visfatin as a non-traditional biomarker of endothelial dysfunction in chronic kidney disease: an Egyptian study

BACKGROUND

Endothelial dysfunction (ED) is closely linked to cardiovascular disease and outcome in patients with chronic kidney disease (CKD). Visfatin is an adipocytokine that recently generated much interest; however, its role in CKD remains to be clarified. This study aimed to assess visfatin in correlation with markers of ED and inflammation in Egyptian patients with CKD.

METHODS

The study included 40 non-diabetic, clinically stable CKD patients and 20 healthy volunteers. Serum levels of visfatin, markers of ED (intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1)) and markers of inflammation (interleukin-6 (IL-6), and C-reactive protein (CRP)) were measured. Endothelial function was evaluated using brachial artery flow-mediated dilatation (FMD).

RESULTS

Serum visfatin, ICAM-1, VCAM-1, CRP, and IL-6 levels were significantly elevated and FMD% was decreased in CKD patients as compared to controls. Visfatin correlated positively with ICAM-1, VCAM-1, CRP, and IL-6 and negatively with FMD% in CKD patients. In a multiple regression model, visfatin was strongly and independently associated with FMD (Beta=-0.02, P<0.001) in CKD patients.

CONCLUSIONS

Serum visfatin is strongly associated with endothelial adhesion molecules and FMD%, suggesting that visfatin is an important promising biomarker for prediction of ED and future cardiovascular risk in CKD patients. Moreover, the relationship between visfatin and IL-6 indicates that circulating visfatin may reflect the sub-clinical inflammatory status. Thus, visfatin might be involved in the complex interactions between ED, inflammation, and atherosclerosis and their major clinical consequences; however, further prospective studies are required to prove this hypothesis.

Neuronal protective role of PBEF in a mouse model of cerebral ischemia

Pre-B-cell colony-enhancing factor (PBEF) (also known as nicotinamide phosphoribosyltransferase) is a rate-limiting enzyme in the salvage pathway for mammalian biosynthesis of nicotinamide adenine dinucleotide (NAD(+)). By synthesizing NAD(+), PBEF functions to maintain an energy supply that has critical roles in cell survival. Cerebral ischemia is a major neural disorder with a high percentage of mortality and disability. Ischemia leads to energy depletion and eventually neuronal death and brain damage. This study investigated the role of PBEF in cerebral ischemia using a photothrombosis mouse model. Using immunostaining, we initially determined that PBEF is highly expressed in neurons, but not in glial cells in the mouse brain. To study the role of PBEF in ischemia in vivo, we used PBEF knockout heterozygous (Pbef+/-) mice. We showed that these mice have lower PBEF expression and NAD(+) level than do wild-type (WT) mice. When subjected to photothrombosis, Pbef+/- mice have significantly larger infarct volume than do age-matched WT mice at 24 hours after ischemia. Higher density of degenerating neurons was detected in the penumbra of Pbef+/- mice than in WT mice using Fluoro-Jade B staining. Our study shows that PBEF has a neuronal protective role in cerebral ischemia presumably through enhanced energy metabolism.

The changes of visfatin in serum and its expression in fat and placental tissue in pregnant women with gestational diabetes

OBJECTIVES

To elucidate the main source of circulating visfatin and its potential roles in pathogenesis of gestational diabetes mellitus (GDM).

METHODS

We examined serum concentrations of visfatin with ELISA and its expression in subcutaneous adipose tissue, visceral adipose tissue and placenta with RT-PCR and western blot both in women with GDM and normal pregnant controls at term. Moreover, BeWo cells were treated with tumor necrosis factor-alpha (TNF-alpha) and then the intra- and extra-cellular changes of visfatin expression were measured.

RESULTS

Serum visfatin concentrations were significantly higher in women with GDM than controls, which reduced obviously three days after delivery compared with antepartum. Visfatin expressions in placenta were significantly higher in GDM women than controls but there was no difference in its expressions in adipose tissue between the two groups. Moreover, serum visfatin concentrations correlated positively with its expressions in placenta, rather than adipose tissue. We demonstrated that visfatin secretion from BeWo cells was significantly increased but the intracellular expression was decreased at 48h incubation with TNF-alpha in a dose-depended way.

CONCLUSIONS

The oversecretion of visfatin from placenta, probably induced by the elevated TNF-alpha level, contributes to the increased serum visfatin concentrations in women with GDM.

Visfatin-induced lipid raft redox signaling platforms and dysfunction in glomerular endothelial cells

Adipokines have been reported to contribute to glomerular injury during obesity or diabetes mellitus. However, the mechanisms mediating the actions of various adipokines on the kidney remained elusive. The present study was performed to determine whether acid sphingomyelinase (ASM)-ceramide associated lipid raft (LR) clustering is involved in local oxidative stress in glomerular endothelial cells (GECs) induced by adipokines such as visfatin and adiponectin. Using confocal microscopy, visfatin but not adiponectin was found to increase LRs clustering in the membrane of GECs in a dose and time dependent manner. Upon visfatin stimulation ASMase activity was increased, and an aggregation of ASMase product, ceramide and NADPH oxidase subunits, gp91(phox) and p47(phox) was observed in the LR clusters, forming a LR redox signaling platform. The formation of this signaling platform was blocked by prior treatment with LR disruptor filipin, ASMase inhibitor amitriptyline, ASMase siRNA, gp91(phox) siRNA and adiponectin. Corresponding to LR clustering and aggregation of NADPH subunits, superoxide (O(2)(-)) production was significantly increased (2.7 folds) upon visfatin stimulation, as measured by electron spin resonance (ESR) spectrometry. Functionally, visfatin significantly increased the permeability of GEC layer in culture and disrupted microtubular networks, which were blocked by inhibition of LR redox signaling platform formation. In conclusion, the injurious effect of visfatin, but not adiponectin on the glomerular endothelium is associated with the formation of LR redox signaling platforms via LR clustering, which produces local oxidative stress resulting in the disruption of microtubular networks in GECs and increases the glomerular permeability.

Plasma concentration of visfatin is a new surrogate marker of systemic inflammation in type 2 diabetic patients

It is not clear whether plasma visfatin level is related with systemic inflammation or diabetic nephropathy in diabetic patients. In this study, we investigated the relationship between plasma visfatin levels and systemic inflammation or diabetic nephropathy in type 2 diabetic patients. In addition, we examined the physiological action of visfatin in cultured adipocytes in diabetic condition. Plasma visfatin concentrations were significantly higher in the diabetic groups than in the controls. Plasma visfatin levels were positively correlated with systolic blood pressure, body weight, fasting blood glucose, plasma levels of MCP-1, urinary albumin excretion (UAE), and carotid intima-media thickness (IMT), and were inversely correlated with plasma adiponectin, and creatinine clearance. However, plasma visfatin concentrations did not show a significant relationship with HbA1C, BMI or HOMA-IR. Regression analysis showed that plasma levels of MCP-1 and UAE were only independent determinants of plasma visfatin concentration. In cultured adipocytes, high glucose and angiotensin II stimuli markedly increased visfatin synthesis. Exogenous visfatin treatment significantly decreased differentiation of adipocytes and increased NF-kappaB transcriptional activity and pro-inflammatory molecules in adipocytes. These findings suggest that visfatin synthesis is activated from adipose tissue in a diabetic environment, induces NF-kappaB activation and leads to activation of pro-inflammatory cytokines and systemic inflammation.

Sirtuins and their relevance to the kidney

Sirtuins (silent information regulator 2 [Sir2] proteins) belong to an ancient family of evolutionary conserved nicotinamide adenine dinucleotide (NAD)(+)-dependent enzymes with deacetylase and/or mono-ADP-ribosyltransferase activity. They regulate DNA repair and recombination, chromosomal stability, and gene transcription, and most importantly mediate the health-promoting effects of caloric restriction (CR), which includes the retardation of aging. At least seven Sir2 homologs, sirtuins (SIRT) 1 to 7 have been identified in mammals. Mammalian SIRT1, the most extensively studied family member, couples protein deacetylation with NAD(+) hydrolysis and links cellular energy and redox state to multiple signaling and survival pathways. Cell-type and context-specific activation of sirtuins increases resistance to metabolic, oxidative, and hypoxic stress in different tissues. In particular, SIRT1 plays a central role in mediating the beneficial effects of CR, and its activation associates with longevity and the attenuation of metabolic disorders. SIRT1 in the kidney is cytoprotective and participates in the regulation of BP and sodium balance. Here, we review sirtuin biology and discuss how CR-triggered sirtuin-dependent pathways affect renal physiology and the pathogenesis of kidney diseases and related disorders.

Visfatin regulates genes related to lipid metabolism in porcine adipocytes

Visfatin is a visceral adipose tissue-specific adipocytokine that plays a positive role in attenuating insulin resistance by binding to the insulin receptor. Visfatin has been suggested to play a role in the regulation of lipid metabolism and inflammation; however, the mechanism remains unclear. We investigated the effects of visfatin on the regulation of gene expression in cultured porcine preadipocytes and differentiated adipocytes. In preadipocytes, the mRNA abundance of lipoprotein lipase and PPARgamma were significantly increased by visfatin or insulin treatment after 8 d (all P < 0.05). In the presence of insulin, the mRNA abundance of adipocyte fatty acid-binding protein was 24.7-fold greater than in the untreated group (P < 0.05), whereas visfatin alone had no effect on adipocyte fatty acid-binding protein mRNA abundance. Adipocyte differentiation was induced by insulin treatment for 8 d. In differentiated porcine adipocytes, exposure to insulin or visfatin for 24 h increased (P < 0.05) fatty acid synthase mRNA abundance but had no effect on the expression of sterol regulatory element binding-protein 1c mRNA. We also found a 5.8-fold upregulation of IL-6 expression in porcine adipocytes after 24 h of treatment with visfatin (P < 0.05). These results demonstrated that visfatin upregulated lipoprotein lipase expression in preadipocytes, potentially facilitating lipid uptake, and increased the gene expression of fatty acid synthase in differentiated adipocytes to potentially enhance lipogenic activity. Furthermore, visfatin can upregulate IL-6 expression in differentiated porcine adipocytes. The information presented in this study provides insights into the roles of visfatin in lipid metabolism in pigs.

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.

Role of adipocytokines in predicting the development of diabetes and its late complications

Diabetes is an important health problem since the incidence of diabetes is continuously increasing. Early diagnosis is important as type 2 diabetes begins long before we diagnose it, leading to a complicated course of the disease. In order to prevent delay in the diagnosis of type 2 diabetes, novel predictors and pathways for type 2 diabetes are mounting. Diabetic complications are common cause of morbidity and mortality among subjects with diabetes. In the pathogenesis of diabetic complications some factors other than chronic hyperglycemia may be involved. Adipocytokines play important roles in the pathogenesis of diabetes mellitus, insulin resistance, and associated metabolic conditions such as hypertension and dyslipidemia. The investigations on the role of adipocytokines in developing diabetes and its complications have been made. In this review, we discussed the implications of adipocytokines in predicting diabetes and diabetic complications, with particular attention on the roles of adiponectin, leptin, visfatin, and vaspin.

Visfatin induces oxidative stress in differentiated C2C12 myotubes in an Akt- and MAPK-independent, NFkB-dependent manner

Adipose tissue is an important endocrine and metabolic tissue that is actively involved in cross-talk with peripheral organs such as skeletal muscle. It is likely that adipose-derived factors may underlie the development of insulin resistance in muscle. Thus, the cross-talk between adipose and muscle may be important for the propagation of obesity-related diseases. Visfatin (Pre-B-cell colony-enhancing factor 1 homolog/Nampt) is a recently discovered adipokine with pleiotropic functions. The aim of this study was to examine the effect of visfatin on cellular stress responses and signalling pathways in skeletal muscle. Visfatin treatment of differentiated C2C12 myotubes generated reactive oxygen species (ROS) comprising both superoxide and hydrogen peroxide that was dependent on de novo transcription and translation. In differentiated C2C12 myoblasts, visfatin had no effects on insulin-stimulated Akt phosphorylation nor on activation of the Akt signalling pathway. Additionally, visfatin-induced oxidative stress occurred independent of activation of the stress-activated protein kinases (MAPKs) ERK and p38. In contrast, phosphorylation of NFkB was associated with visfatin-mediated generation of ROS and blockade of this pathway via selective IKK inhibition led to a partial reduction in oxidative stress. Furthermore, the generation of ROS following visfatin treatment was highly dependent on both de novo transcription and translation. Taken together, these findings provide novel insights for the unique pathophysiological role of visfatin in skeletal muscle.

Extracellular PBEF/NAMPT/visfatin activates pro-inflammatory signalling in human vascular smooth muscle cells through nicotinamide phosphoribosyltransferase activity

AIMS/HYPOTHESIS

Extracellular pre-B cell colony-enhancing factor/nicotinamide phosphoribosyltransferase/visfatin (ePBEF/NAMPT/visfatin) is an adipocytokine, whose circulating levels are enhanced in metabolic disorders, such as diabetes mellitus and obesity. Here, we explored the ability of ePBEF/NAMPT/visfatin to promote vascular inflammation, as a condition closely related to atherothrombotic diseases. We specifically studied the ability of PBEF/NAMPT/visfatin to directly activate pathways leading to inducible nitric oxide synthase (iNOS) induction in cultured human aortic smooth muscle cells, as well as the mechanisms involved.

METHODS

iNOS levels and extracellular signal-regulated kinase (ERK) 1/2 activity were determined by western blotting. Nuclear factor (NF)-kappaB activity was assessed by electrophoretic mobility shift assay.

RESULTS

ePBEF/NAMPT/visfatin (10-250 ng/ml) induced iNOS in a concentration-dependent manner. At a submaximal concentration (100 ng/ml), ePBEF/NAMPT/visfatin time-dependently enhanced iNOS levels up to 18 h after stimulation. Over this time period, ePBEF/NAMPT/visfatin elicited a sustained activation of NF-kappaB and triggered a biphasic ERK 1/2 activation. By using the respective ERK 1/2 and NF-kappaB inhibitors, PD98059 and pyrrolidine dithiocarbamate, we established that iNOS induction by ePBEF/NAMPT/visfatin required the consecutive upstream activation of ERK 1/2 and NF-kappaB. The pro-inflammatory action of ePBEF/NAMPT/visfatin was not prevented by insulin receptor blockade. However, exogenous nicotinamide mononucleotide, the product of NAMPT activity, mimicked NF-kappaB activation and iNOS induction by ePBEF/NAMPT/visfatin, while the NAMPT inhibitor APO866 prevented the effects of ePBEF/NAMPT/visfatin on iNOS and NF-kappaB.

CONCLUSIONS/INTERPRETATION

Through its intrinsic NAMPT activity, ePBEF/NAMPT/visfatin appears to be a direct contributor to vascular inflammation, a key feature of atherothrombotic diseases linked to metabolic disorders.

Visfatin in gestational diabetes: serum level and mRNA expression in fat and placental tissue

AIMS AND METHODS

In this study we measured: (1) serum visfatin concentrations in pregnant women with normal glucose tolerance (NGT) and gestational diabetes mellitus (GDM) between 26 and 33 weeks of gestation, using two immunoassays: EIA and ELISA; (2) serum visfatin levels (ELISA) and its mRNA expression (quantitative real-time PCR) in subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT) and placental tissue from women with NGT and GDM at term.

RESULTS

Visfatin concentrations (measured by EIA and ELISA) did not differ in the women with GDM and NGT between 26 and 33 weeks of gestation but were significantly lower in GDM than in NGT subjects at term (2.7 [0.7-4.6] vs 5.2 [3.7-5.9]ng/ml, p=0.02). There was no difference in visfatin mRNA expression in fat and placental tissue between the two subgroups. Regression analysis revealed that visfatin mRNA expression was significantly related to interleukin-6 and tumour necrosis factor-alpha mRNA expression in SAT (beta=0.39, p=0.009 and beta=0.47, p=0.002) and placental tissue (beta=0.37, p=0.03 and beta=0.49, p=0.005).

CONCLUSIONS

Circulating visfatin was significantly lower in the GDM than in the NGT subjects at term, although no differences in its mRNA expression in fat and placental tissues were observed.

Nampt: linking NAD biology, metabolism and cancer

Nicotinamide phosphoribosyltransferase (Nampt) converts nicotinamide to nicotinamide mononucleotide (NMN), a key nicotinamide adenine dinucleotide (NAD) intermediate. Previously identified as a cytokine pre-B-cell colony-enhancing factor and controversially claimed as an insulin-mimetic hormone visfatin, Nampt has recently drawn much attention in several fields, including NAD biology, metabolism and inflammation. As a NAD biosynthetic enzyme, Nampt regulates the activity of NAD-consuming enzymes such as sirtuins and influences a variety of metabolic and stress responses. Nampt also plays an important part in regulating insulin secretion in pancreatic beta-cells. Nampt seems to have another function as an immunomodulatory cytokine and, therefore, has a role in inflammation. This review summarizes these various functional aspects of Nampt and discusses its potential roles in diseases, including type 2 diabetes and cancer.

Molecular mechanisms of insulin resistance in obesity and type 2 diabetes mellitus

A zsírszövetben az inzulinreceptor jelátviteli folyamatait auto-, para- és endokrin hatásokkal szabályozó számos fehérje termelődik és szekretálódik. Ezek közül több, így a tumornekrózis-faktor-α és szolúbilis receptor formái, az sTNFR1 és sTNFR2, a rezisztin, retinolkötő fehérje-4, plazminogénaktivátor-inhibitor, lipokain-1 gátolja az inzulin jelátviteli folyamatait és inzulinrezisztenciát okoz, elsősorban a zsírszövetben, a májban, az izomszövetben, az agyban, az endothelsejtekben, valamint a hasnyálmirigy β-sejtjeiben. Más fehérjék, így az adiponektin, visfatin, vaspin, omentin, apelin és chemerin pedig javítják az inzulinreceptor jelátvitelét. Az összefoglalás áttekinti az inzulinreceptor jelátviteli folyamatainak főbb részleteit és kitér az elhízásban, valamint a 2-es típusú cukorbetegségben észlelhető inzulin- és citokinrezisztenciák patomechanizmusában a közelmúltban megismert molekuláris tényezőkre (például a suppressor of cytokine signaling fehérje család).

Nicotinamide phosphoribosyltransferase (Nampt): a link between NAD biology, metabolism, and diseases

New interest in NAD biology has recently been revived, and enzymes involved in NAD biosynthetic pathways have been identified and characterized in mammals. Among them, nicotinamide phosphoribosyltransferase (Nampt) has drawn much attention in several different fields, including NAD biology, metabolism, and immunomodulatory response. The research history of this protein is peculiar and controversial, and its physiological function has been a matter of debate. Nampt has both intra- and extracellular forms in mammals. Intracellular Nampt (iNampt) is an essential enzyme in the NAD biosynthetic pathway starting from nicotinamide. On the other hand, an extracellular form of this protein has been reported to act as a cytokine named PBEF, an insulin-mimetic hormone named visfatin, or an extracellular NAD biosynthetic enzyme named eNampt. This review article summarizes the research history and reported functions of this unique protein and discusses the pathophysiological significance of Nampt as an NAD biosynthetic enzyme vs. a potential inflammatory cytokine in diverse biological contexts.