Insulin-like effects of visfatin on human osteoblasts

Characterization of the visfatin gene and its expression pattern and effect on 3T3-L1 adipocyte differentiation in chickens

Visfatin is a newly identified adipocytokine that plays an important role in the determination of fat traits. In this study, we investigated the characterization of visfatin and the relationship between gene expression and chicken development to provide a theoretical basis for studying visfatin functions. The main results are summarized as follows: The 1482-bp full coding sequence of the visfatin gene of silky fowl was obtained and found to encode 493 amino acids. This gene contains 26 phosphorylation sites and a conserved domain of the NAPRTase family but no signal peptide sequence. It exhibits six functional motifs, including an amidation site. In chickens, visfatin is a highly conserved protein. The highest expression of visfatin was found in breast muscle and the lowest in bone marrow. There was no difference in expression between visceral fat and subcutaneous fat. However, the expression of visfatin in the bone marrow, liver, kidneys, and subcutaneous and visceral fat of broiler chickens was significantly higher than that in silky fowl (P<0.05). Visfatin mRNA levels in the bone marrow decreased with development (P<0.05) but increased in the liver and leg muscle. Visfatin gene expression in the liver, heart and bone marrow did not differ in silky fowl according to sex. A visfatin fusion protein caused a significant increase in the expression of adipocyte differentiation markers (PPARγ, aP2, C/EBPα, and FAS) compared with the control group and a decrease compared with the insulin group. Taken together, the results of the present study contribute to a better understanding of the expression and role of the visfatin gene in chickens.

Resistin promotes the abnormal Type I collagen phenotype of subchondral bone in obese patients with end stage hip osteoarthritis

The purpose of this study was to determine the effect of adiposity on the architecture and composition of hip OA subchondral bone, and to examine the pathological role of adipokines. Femoral heads were collected from normal-weight or over-weight/obese patients with hip OA. Structural parameters of subchondral bone were determined by MicroCT and type I collagen α1/α2 ratio was determined by SDS PAGE and by qRT-PCR in ex-vivo bone explants. The serum concentration of adipokines was determined by Luminex. The effect of resistin on primary OA osteoblasts was determined by analysis of Wnt pathway signal transduction, bone nodule formation, and osteoblast metabolic activity. Subchondral bone from over-weight/obese hip OA patients exhibited reduced trabecular thickness, increased bone surface/bone volume ratio, and an increase in the Type I collagen α1/α2, compared to normal-weight hip OA patients. The serum concentration of resistin was higher in overweight/obese OA patients, compared to normal-weight OA patients. Stimulation of normal-weight bone explant with recombinant resistin increased the Type I collagen α1/α2 ratio. Stimulation of primary OA osteoblasts with recombinant resistin increased Wnt signalling activation, osteoblast metabolic activity, and bone nodule formation. Increased adiposity in hip OA patients is associated with altered subchondral bone architecture and type I collagen composition.

Novel bone metabolism-associated hormones: the importance of the pre-analytical phase for understanding their physiological roles

The endocrine function of bone is now a recognized feature of this tissue. Bone-derived hormones that modulate whole-body homeostasis, are being discovered as for the effects on bone of novel and classic hormones produced by other tissues become known. Often, however, the data regarding these last generation bone-derived or bone-targeting hormones do not give about a clear picture of their physiological roles or concentration ranges. A certain degree of uncertainty could stem from differences in the pre-analytical management of biological samples. The pre-analytical phase comprises a series of decisions and actions (i.e., choice of sample matrix, methods of collection, transportation, treatment and storage) preceding analysis. Errors arising in this phase will inevitably be carried over to the analytical phase where they can reduce the measurement accuracy, ultimately, leading discrepant results. While the pre-analytical phase is all important, in routine laboratory medicine, it is often not given due consideration in research and clinical trials. This is particularly true for novel molecules, such as the hormones regulating the endocrine function of bone. In this review we discuss the importance of the pre-analytical variables affecting the measurement of last generation bone-associated hormones and describe their, often debated and rarely clear physiological roles.

Epigenetic regulation of Runx2 transcription and osteoblast differentiation by nicotinamide phosphoribosyltransferase

BACKGROUND

Bone degenerative disorders like osteoporosis may be initiated by age-related shifts in anabolic and catabolic responses that control bone homeostasis. Although there are studies suggesting that metabolic changes occur with stem cell differentiation, the molecular mechanisms governing energy metabolism and epigenetic modification are not understood fully. Here we reported the key role of nicotinamide phosphoribosyltransferase (Nampt), which is the rate-limiting enzyme in the salvage pathway of NAD biosynthesis from nicotinamide, in the osteogenic differentiation of bone marrow stromal cells.

RESULTS

Differentiated bone marrow stromal cells isolated from Nampt^+/- mice presented with diminished osteogenesis, as evaluated by alkaline phosphatase (ALP) staining, ALP activity and osteoblast-mediated mineralization, compared to cells from Nampt^+/+ mice. Similar results were observed in differentiated Nampt-deficient C3H/10T1/2 and MC3T3-E1 cells. Further studies showed that Nampt promotes osteoblast differentiation through increased function and expression of Runx2 as tested by luciferase reporter assay, RT-PCR, and Western Blotting. Our data also demonstrated that Nampt regulates Runx2 transcription in part through epigenetic modification of H3-Lys9 acetylation.

CONCLUSION

Our study demonstrated that Nampt plays a critical role in osteoblast differentiation through epigenetic augmentation of Runx2 transcription. NAMPT may be a potential therapeutic target of aging-related osteoporosis.

Bone marrow adipose tissue as an endocrine organ: close to the bone?

White adipose tissue (WAT) is a major endocrine organ, secreting a diverse range of hormones, lipid species, cytokines and other factors to exert diverse local and systemic effects. These secreted products, known as 'adipokines', contribute extensively to WAT's impact on physiology and disease. Adipocytes also exist in the bone marrow (BM), but unlike WAT, study of this bone marrow adipose tissue (MAT) has been relatively limited. We recently discovered that MAT contributes to circulating adiponectin, an adipokine that mediates cardiometabolic benefits. Moreover, we found that MAT expansion exerts systemic effects. Together, these observations identify MAT as an endocrine organ. Additional studies are revealing further secretory functions of MAT, including production of other adipokines, cytokines and lipids that exert local effects within bone. These observations suggest that, like WAT, MAT has secretory functions with diverse potential effects, both locally and systemically. A major limitation is that these findings are often based on in vitro approaches that may not faithfully recapitulate the characteristics and functions of BM adipocytes in vivo. This underscores the need to develop improved methods for in vivo analysis of MAT function, including more robust transgenic models for MAT targeting, and continued development of techniques for non-invasive analysis of MAT quantity and quality in humans. Although many aspects of MAT formation and function remain poorly understood, MAT is now attracting increasing research focus; hence, there is much promise for further advances in our understanding of MAT as an endocrine organ, and how MAT impacts human health and disease.

Implications of exercise-induced adipo-myokines in bone metabolism

Physical inactivity has been recognized, by the World Health Organization as the fourth cause of death (5.5 % worldwide). On the contrary, physical activity (PA) has been associated with improved quality of life and decreased risk of several diseases (i.e., stroke, hypertension, myocardial infarction, obesity, malignancies). Bone turnover is profoundly affected from PA both directly (load degree is the key determinant for BMD) and indirectly through the activation of several endocrine axes. Several molecules, secreted by muscle (myokines) and adipose tissues (adipokines) in response to exercise, are involved in the fine regulation of bone metabolism in response to the energy availability. Furthermore, bone regulates energy metabolism by communicating its energetic needs thanks to osteocalcin which acts on pancreatic β-cells and adipocytes. The beneficial effects of exercise on bone metabolism depends on the intermittent exposure to myokines (i.e., irisin, IL-6, LIF, IGF-I) which, instead, act as inflammatory/pro-resorptive mediators when chronically elevated; on the other hand, the reduction in the circulating levels of adipokines (i.e., leptin, visfatin, adiponectin, resistin) sustains these effects as well as improves the whole-body metabolic status. The aim of this review is to highlight the newest findings about the exercise-dependent regulation of these molecules and their role in the fine regulation of bone metabolism.

An association of serum vistafin level and number of circulating endothelial progenitor cells in type 2 diabetes mellitus patients

BACKGROUND

The decreased number and impaired functions of endothelial progenitor cells (EPCs) may associate with cardiovascular disease (CV) including atherosclerosis. However, the role of vistafin in regulation of angiogenic EPC subset maturation in T2DM patients without known atherosclerosis is still not fully understood.

THE AIM OF THE STUDY

To investigate an association of serum vistafin level and number of circulating EPCs in T2DM patients beyond known CV disease.

METHODS

This case-control observational investigation was evolved 54 subjects with T2DM and 35 healthy volunteers. The flow cytometry was used for predictably distinguishing cell subsets, which depend on expression of CD45, CD34, CD14, Tie-2, and VEGFR2. Biomarkers were measured at baseline of the study.

RESULTS

All T2DM patients were divided depending median of vistafin level (5.88ng/mL) in to two cohorts with low vistafin level (<5.88ng/mL; n=29) and high vistafin level (≥5.88ng/mL; n=25) respectively. Logistic regression analysis has shown that visfatin, hs-CRP, age and BMI were the best variables in the prediction of EPC number labeled as CD14⁺CD309⁺ and CD14⁺CD309⁺Tie²⁺ cells. After adjustment of the model to age and BMI elevated visfatin level remained the best predictor for both CD14⁺CD309⁺ and CD14⁺CD309⁺Tie²⁺ EPCs (OR 0.92, 95% CI: 0.88-0.95; P=0.001 and OR 0.90, 95% CI: 0.87-0.96; P=0.001 respectively).

CONCLUSION

We found that elevated level of vistafin was an independent predictor for declined numerous of non-classical EPCs labeled as CD14⁺CD309⁺ and CD14⁺CD309⁺Tie²⁺, whereas CD34⁺ subsets of EPCs did not associate with vistafin level in T2DM individuals.

Serum Concentrations of Leptin and Adiponectin in Dogs with Myxomatous Mitral Valve Disease

Background

The concentrations of circulating adipokines in dogs with myxomatous mitral valve disease (MMVD) have not been investigated in detail.

Objectives

To determine whether serum concentrations of adipokines differ between healthy dogs and dogs with MMVD and whether circulating concentrations depend on the severity of heart failure resulting from MMVD.

Animals

In the preliminary study, 30 healthy dogs and 17 client‐owned dogs with MMVD, and in the subsequent study, 30 healthy dogs and 46 client‐owned dogs with MMVD.

Methods

Prospective case‐controlled observational study. In the preliminary study, serum concentrations of leptin, adiponectin, resistin, visfatin, interleukin (IL)‐1β, IL‐6, IL‐10, IL‐18, and tumor necrosis factor‐α were measured. In the subsequent study, MMVD dogs were divided into three groups according to the International Small Animal Cardiac Health Council (ISACHC) classification, and serum concentrations of leptin and adiponectin were measured.

Results

In the preliminary study, serum leptin and adiponectin concentrations differed significantly between dogs with MMVD and healthy dogs. Serum leptin (P = .0013) concentrations were significantly higher in dogs with MMVD than in healthy dogs, whereas adiponectin (P = .0009) concentrations were significantly lower in dogs with MMVD. However, we observed no significant differences in the other variables. In the subsequent study, dogs classified as ISACHC class 3 had higher serum concentrations of leptin (P = .0022) than healthy dogs but ISACHC class 1 or 2 dogs did not. Serum adiponectin concentrations were significantly lower in ISACHC class 1 (P < .0001) dogs than in healthy dogs, whereas adiponectin concentrations in ISACHC class 3 dogs were significantly higher than in ISACHC class 1 dogs (P = .0081).

Conclusions and Clinical Importance

Circulating concentrations of leptin and adiponectin might be altered in dogs with MMVD.

Chemerin, visfatin, and vaspin serum levels in relation to bone mineral density in patients with inflammatory bowel disease

BACKGROUND

There is evidence that fat mass is correlated with bone mineral density (BMD) in inflammatory bowel disease (IBD), but data on the role of adipokines on this association are limited. The aim of this study was to investigate the serum levels of chemerin, visfatin, and vaspin, hormones that act as adipokines, in relation to BMD in patients with ulcerative colitis (UC) and Crohn's disease (CD).

PATIENTS AND METHODS

Serum from 120 IBD patients (68 CD, 52 UC) and 98 matched healthy controls (HC) was collected. Chemerin, visfatin, and vaspin levels were assessed using an enzyme-linked immunosorbent assay. BMD was determined for the lumbar spine and the proximal femur using dual-energy X-ray absorptiometry. Full-body composition scans were analyzed using enCORE software based on the absorptiometry system.

RESULTS

Serum chemerin was higher in IBD patients than HC [CD 13.67.1±5.8, UC 13.9±4.3 vs. HC 7.8±2.6 ng/ml, odds ratio (OR): 0.95, 95% confidence interval (CI) 0.93-0.98, P<0.0001]. Serum visfatin levels in CD patients were significantly higher than those in UC patients (9.3±14.01 vs. 6.5±7.2 ng/ml, OR: 0.86, 95% CI 0.80-0.92, P=0.039). In multivariate logistic regression analysis, a significant independent association of osteoporosis (T-score ≤2.5 SD) with age (OR: 1.04, 95% CI 1.01-1.08, P=0.02), visfatin (OR: 0.78, 95% CI 0.63-0.97, P=0.02), and chemerin levels (OR: 0.83, 95% CI 0.70-0.98, P=0.03), but not with BMI or body composition, was found.

CONCLUSION

Serum visfatin and chemerin levels are associated with the development of osteoporosis in IBD. These results suggest a role of visfatin and chemerin in the pathophysiology of osteoporosis in IBD.

The Role of Nicotinamide Phosphoribosyltransferase in Cerebral Ischemia

As recombinant tissue plasminogen activator is the only drug approved for the clinical treatment of acute ischemic stroke, there is an urgent unmet need for novel stroke treatments. Endogenous defense mechanisms against stroke may hold the key to new therapies for stroke. A large number of studies suggest that nicotinamide phosphoribosyl-transferase (NAMPT is an attractive candidate to improve post-stroke recovery. NAMPT is a multifunctional protein and plays important roles in immunity, metabolism, aging, inflammation, and stress responses. NAMPT exists in both the intracellular and extracellular space. As a rate-limiting enzyme, the intracellular form (iNAMPT catalyzes the first step in the biosynthesis of nicotinamide adenine dinucleotide (NAD from nicotinamide. iNAMPT closely regulates energy metabolism, enhancing the proliferation of endothelial cells, inhibiting apoptosis, regulating vascular tone, and stimulating autophagy in disease conditions such as stroke. Extracellular NAMPT (eNAMPT is also known as visfatin (visceral fat-derived adipokine and has pleotropic effects. It is widely believed that the diverse biological functions of eNAMPT are attributed to its NAMPT enzymatic activity. However, the effects of eNAMPT on ischemic injury are still controversial. Some authors have argued that eNAMPT exacerbates ischemic neuronal injury non-enzymatically by triggering the release of TNF-α from glial cells. In addition, NAMPT also participates in several pathophysiological processes such as hypertension, atherosclerosis, and ischemic heart disease. Thus, it remains unclear under what conditions NAMPT is beneficial or destructive. Recent work using in vitro and in vivo genetic/ pharmacologic manipulations, including our own studies, has greatly improved our understanding of NAMPT. This review focuses on the multifaceted and complex roles of NAMPT under both normal and ischemic conditions.

Obesity and Cardiovascular Risk: Variations in Visfatin Gene Can Modify the Obesity Associated Cardiovascular Risk. Results from the Segovia Population Based-Study. Spain

Objectives

Our aim was to investigate if genetic variations in the visfatin gene (SNPs rs7789066/ rs11977021/rs4730153) could modify the cardiovascular-risk (CV-risk) despite the metabolic phenotype (obesity and glucose tolerance). In addition, we investigated the relationship between insulin sensitivity and variations in visfatin gene.

Material and Methods

A population-based study in rural and urban areas of the Province of Segovia, Spain, was carried out in the period of 2001–2003 years. A total of 587 individuals were included, 25.4% subjects were defined as obese (BMI ≥30 Kg/m²).

Results

Plasma visfatin levels were significantly higher in obese subjects with DM2 than in other categories of glucose tolerance. The genotype AA of the rs4730153 SNP was significantly associated with fasting glucose, fasting insulin and HOMA-IR (Homeostasis model assessment-insulin resistance) after adjustment for gender, age, BMI and waist circumference.

The obese individuals carrying the CC genotype of the rs11977021 SNP showed higher circulating levels of fasting proinsulin after adjustment for the same variables.

The genotype AA of the rs4730153 SNP seems to be protective from CV-risk either estimated by Framingham or SCORE charts in general population; and in obese and non-obese individuals. No associations with CV-risk were observed for other studied SNPs (rs11977021/rs7789066).

Conclusions

In summary, this is the first study which concludes that the genotype AA of the rs4730153 SNP appear to protect against CV-risk in obese and non–obese individuals, estimated by Framingham and SCORE charts. Our results confirm that the different polymorphisms in the visfatin gene might be influencing the glucose homeostasis in obese individuals.

Vaspin regulates the osteogenic differentiation of MC3T3-E1 through the PI3K-Akt/miR-34c loop

Vaspin (visceral adipose tissue-derived serine protease inhibitor) is a newly discovered adipokine that widely participates in diabetes mellitus, polycystic ovarian syndrome and other disorders of metabolism. However, the effect of vaspin on the regulation of osteogenesis and the mechanism responsible are still unclear. Here, we found that vaspin can attenuate the osteogenic differentiation of the preosteoblast cell line MC3T3-E1 in a dose-dependent way; also, during this process, the expression of miRNA-34c (miR-34c) was significantly increased. Down-regulation of the expression of miR-34c in MC3T3-E1 diminished the osteogenic inhibitory effect of vaspin, while the up-regulation of miR-34c increased this effect through its target gene Runx2. Meanwhile, we found that vaspin could also activate the PI3K-Akt signalling pathway. Blocking the PI3K-Akt signalling pathway with specific inhibitors could decrease the osteogenic inhibitory effect of vaspin as well as the expression level of miR-34c. Furthermore, knock-down of miR-34c could promote the activation of Akt, which was probably realised by targeting c-met expression. Thus, PI3K-Akt and miR-34c constituted a modulation loop and controlled the expression of each other. Taken together, our study showed that vaspin could inhibit the osteogenic differentiation in vitro, and the PI3K-Akt/miR-34c loop might be the underlying mechanism.

Determinants of visfatin in type 2 diabetes patients with diabetic kidney disease: Relationship to inflammation, adiposity and undercarboxylated osteocalcin

BACKGROUND

Visfatin is a proinflammatory molecule with possible actions on glucose metabolism. Interactions to bone metabolism and undercarboxylated osteocalcin (uOC) in diabetic patients (T2DP) with diabetic kidney disease (DKD) have not been reported.

MATERIALS AND METHODS

We included 51 incident T2DP with DKD. History, laboratory evaluation, anthropometry, visfatin, uOC were obtained. Fifteen T2DP without DKD were used as controls.

RESULTS

Visfatin was similar in DKD patients and controls: 1.56(0.97-3.03) versus 2.04(1.08-3.21) ng/mL, p = 0.51. In controls, visfatin positively correlated with diabetes duration (r = 0.63, p = 0.01) and negatively with uOC (r = -0.57, p = 0.03). In multivariate regression, diabetes duration remained significant (p = 0.01). In patients with DKD, visfatin was positively linked to C reactive protein (r = 0.27, p = 0.05), tricipital skin fold (TSF) (r = 0.41, p = 0.004) and leukocytes (r = 0.37, p = 0.01); the latter two parameters predicted visfatin in multivariate model (p = 0.001). In normoalbuminuric patients, visfatin was linked to body mass index (r = 0.32, p = 0.04), waist circumference (r = 0.42, p < 0.0001), LDL cholesterol (r = 0.33, p = 0.03), serum glucose (r = 0.36, p = 0.03) and glycated hemoglobin (r = 0.41, p = 0.007); there was a trend towards negative correlation to uOC (r = -0.28, p = 0.07); only glycaemia remained significant in multivariate analysis (p = 0.04). Albuminuric patients displayed a positive correlation of visfatin to waist to hip ratio (r = 0.41, p = 0.04) and leukocytes (r = 0.56, p = 0.04); the latter remained significant in multivariate regression (p = 0.005).

CONCLUSION

The main determinant of visfatin in T2D patients with DKD is inflammation; in normoalbuminuric patients, a positive link to adiposity and altered glycemic control and a trend towards a negative correlation to uOC was observable; the latter relationship was evident in patients without DKD.

VISFATIN (NAMPT) Improves In Vitro IGF1-Induced Steroidogenesis and IGF1 Receptor Signaling Through SIRT1 in Bovine Granulosa Cells

VISFATIN is a novel adipokine, also known as a nicotinamide phosphorybosyltransferase (NAMPT), that is able to modulate different processes, including lipid and glucose metabolism, oxidative stress, inflammation, and insulin resistance. Recent data suggest that it also plays a role in reproductive function in rats, humans, and chickens. Here we identified VISFATIN in the bovine ovary and investigated the in vitro effects of this hormone on granulosa cell steroidogenesis and proliferation and oocyte maturation. By RT-PCR, immunoblotting, and immunohistochemistry, we found VISFATIN in various ovarian cells, including granulosa and theca cells, corpus luteum, and oocytes. In cultured bovine granulosa cells, we showed that IGF1 (10(-8) M) and VISFATIN (10 and 100 ng/ml) but not FSH (10(-8) M) increased mRNA expression levels of NAMPT after 48 h of stimulation. Moreover, we observed that human recombinant VISFATIN (hVisf, 10 ng/ml, 48 h) increased the release of progesterone and estradiol secretion, and this was associated with an increase in the protein level of STAR, the HSD3B activity, and the phosphorylation levels of IGF1R and MAPK ERK1/2 in the presence or absence of IGF1 (10(-8) M). All these effects were abolished when NAMPT was knocked down and when the sirtuin pharmacological inhibitors CHIC-35 (60 nM) and EX-527 (0.5 μM) were preincubated in bovine granulosa cells. Thus, in cultured bovine granulosa cells, VISFATIN improves basal and IGF1-induced steroidogenesis and IGF1 receptor signaling through SIRT1.

Adipokines and their receptors: potential new targets in cardiovascular diseases

Adipose tissue is an 'endocrine organ' that influences diverse physiological and pathological processes via adipokines secretion. Strong evidences suggest that epicardial and perivascular adipose tissue can directly regulate heart and vessels' structure and function. Indeed, in obesity there is a shift toward the secretion of adipokines that promote a pro-inflammatory status and contribute to obesity cardiomyopathy. The prospect of modulating adipokines and/or their receptors represents an attractive perspective to the treatment of cardiovascular diseases. In this paper, we described the most important actions of certain adipokines and their receptors that are capable of influencing cardiovascular physiology as well as their possible use as therapeutic targets.

The role of visfatin (PBEF/Nampt) in pregnancy complications

Visfatin (PBEF/Nampt) is an adipocytokine that exerts pleiotropic effects within the human body, particularly affecting its metabolism and immunity. Visfatin was originally identified as being secreted by peripheral blood lymphocytes acting as a pre-B-cell colony-enhancing factor (PBEF). However, it was subsequently reported to be expressed in almost every tissue of the human body, with visceral fat deposits being the main source of visfatin. In addition to its secreted form, visfatin may also be found intracellularly where it functions as a nicotinamide phosphoribosyltransferase (Nampt). Visfatin maternal plasma concentrations increase during pregnancy, suggesting its important role in this complicated process. Alterations in visfatin level also take place in patients during pregnancy complications. This review focuses on the ones that most commonly occur in connection with visfatin: preterm labor, pre-eclampsia and gestational diabetes mellitus. The review aims to provide a better understanding of the role of visfatin during pregnancy and the causes of its alteration in maternal plasma, highlighting the potential use of visfatin as a diagnostic marker of pregnancy complications in the future.

Physiological and pathophysiological roles of NAMPT and NAD metabolism

Nicotinamide phosphoribosyltransferase (NAMPT) is a regulator of the intracellular nicotinamide adenine dinucleotide (NAD) pool. NAD is an essential coenzyme involved in cellular redox reactions and is a substrate for NAD-dependent enzymes. In various metabolic disorders and during ageing, levels of NAD are decreased. Through its NAD-biosynthetic activity, NAMPT influences the activity of NAD-dependent enzymes, thereby regulating cellular metabolism. In addition to its enzymatic function, extracellular NAMPT (eNAMPT) has cytokine-like activity. Abnormal levels of eNAMPT are associated with various metabolic disorders. NAMPT is able to modulate processes involved in the pathogenesis of obesity and related disorders such as nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) by influencing the oxidative stress response, apoptosis, lipid and glucose metabolism, inflammation and insulin resistance. NAMPT also has a crucial role in cancer cell metabolism, is often overexpressed in tumour tissues and is an experimental target for antitumour therapies. In this Review, we discuss current understanding of the functions of NAMPT and highlight progress made in identifying the physiological role of NAMPT and its relevance in various human diseases and conditions, such as obesity, NAFLD, T2DM, cancer and ageing.

Bone mass and bone metabolic indices in male master rowers

The purpose of this study was to assess bone mass and bone metabolic indices in master athletes who regularly perform rowing exercises. The study was performed in 29 men: 14 master rowers and 15 non-athletic, body mass index-matched controls. Dual-energy X-ray absorptiometry measurements of the areal bone mineral density (aBMD) were performed for the total body, regional areas (arms, total forearms, trunk, thoracic spine, pelvis, and legs), lumbar spine (L1-L4), left hip (total hip and femoral neck), and forearm (33 % radius of the dominant and nondominant forearm). Serum concentrations of osteocalcin, collagen type I cross-linked C-telopeptide, visfatin, resistin, insulin, and glucose were determined. Comparative analyses showed significantly lower levels of body fat and higher lean body mass values in the rowers compared to the control group. The rowers also had significantly higher values of total and regional (left arm, trunk, thoracic spine, pelvis, and leg) BMD, as well as higher BMD values for the lumbar spine and the left hip. There were significant differences between the groups with respect to insulin, glucose, and the index of homeostasis model assessment insulin resistance. In conclusion, the systematic training of master rowers has beneficial effects on total and regional BMD and may be recommended for preventing osteoporosis.

Visfatin, a novel adipokine, stimulates glucose uptake through the Ca2 +-dependent AMPK-p38 MAPK pathway in C2C12 skeletal muscle cells

Visfatin is a novel adipocytokine produced by visceral fat. In the present study, visfatin increased AMP-activated protein kinase (AMPK) phosphorylation in mouse C2C12 skeletal muscle cells. It also increased phosphorylation of the insulin receptor, whose knockdown blocked visfatin-induced AMPK phosphorylation and glucose uptake. Visfatin stimulated glucose uptake in differentiated skeletal muscle cells. However, inhibition of AMPKα2 with an inhibitor or with knockdown of AMPKα2 using siRNA blocked visfatin-induced glucose uptake, which indicates that visfatin stimulates glucose uptake through the AMPKα2 pathway. Visfatin increased the intracellular Ca(2) (+) concentration. STO-609, a calmodulin-dependent protein kinase kinase inhibitor, blocked visfatin-induced AMPK phosphorylation and glucose uptake. Visfatin-mediated activation of p38 MAPK was AMPKα2-dependent. Furthermore, both inhibition and knockdown of p38 MAPK blocked visfatin-induced glucose uptake. Visfatin increased glucose transporter type 4 (GLUT4) mRNA and protein levels. In addition, visfatin stimulated the translocation of GLUT4 to the plasma membrane, and this effect was suppressed by AMPKα2 inhibition. The present results indicate that visfatin plays an important role in glucose metabolism via the Ca(2) (+)-mediated AMPK-p38 MAPK pathway.

Expression and effect of NAMPT (visfatin) on progesterone secretion in hen granulosa cells

In mammals, nicotinamide phosphoribosyltransferase (NAMPT) is an adipokine produced by adipose tissue that is found in intracellular and extracellular compartments. The intracellular form of NAMPT is a nicotinamide phosphoribosyltransferase, whereas the extracellular form is considered an adipokine. In humans, NAMPT regulates energy metabolism and reproductive functions, such as ovarian steroidogenesis. To date, no study has investigated the role of NAMPT in hen ovaries. We investigated whether NAMPT is present in hen ovarian follicles and its role in granulosa cells. Using RT-PCR, western blotting and immunocytochemistry, we detected mRNA transcripts and proteins related to NAMPT in theca and granulosa cells from pre-ovulatory follicles. Using RT-PCR, we demonstrated that mRNA NAMPT levels were higher in granulosa cells than they were in theca cells and that during follicle development, theca cell levels decreased, whereas levels remained unchanged in granulosa cells. NAMPT protein quantities were significantly higher in theca cells than they were in granulosa cells, but they were unchanged during follicular development. Plasma NAMPT levels, as determined by ELISA and immunoblotting, were significantly lower in adult hens than they were in juveniles. In vitro, treatment with human recombinant NAMPT (100 ng/ml, 48 h) halved basal and IGF1-induced progesterone secretion, and this was associated with a reduction in STAR and HSD3B protein levels and MAPK3/1 phosphorylation levels in granulosa cells. These effects were abolished by the addition of FK866, a specific inhibitor of NAMPT enzymatic activity. Moreover, NAMPT had no effect on granulosa cell proliferation. In conclusion, NAMPT is present in hen ovarian cells and inhibits progesterone production in granulosa cells.

Serum adipokine levels in patients with ankylosing spondylitis and their relationship to clinical parameters and radiographic spinal progression

OBJECTIVE

Adipokines have metabolic and inflammatory functions but can also affect bone metabolism. The purpose of this study was to determine the relationship between serum levels of adiponectin, resistin, and visfatin and markers of inflammation, disease activity, and radiographic spinal progression in patients with ankylosing spondylitis (AS).

METHODS

Levels of adiponectin, resistin, and visfatin in the serum of 86 AS patients and 25 healthy controls were measured by enzyme-linked immunosorbent assay at baseline. Radiographic spinal progression was determined by the scoring of radiographs of the spine obtained at baseline and after 2 years.

RESULTS

Mean (±SD) baseline levels of resistin and visfatin were significantly higher in AS patients than in healthy controls (11.6 ± 10.6 ng/ml versus 6.6 ± 3.2 ng/ml [P = 0.01] for resistin, and 20.9 ± 48.3 ng/ml versus 3.4 ± 2.6 ng/ml [P = 0.001] for visfatin). Adipokine serum levels did not correlate with disease activity or functional indices. Only resistin serum levels correlated with markers of inflammation. Baseline levels of visfatin, but not resistin or adiponectin, were significantly higher in patients with worsening of the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) by ≥2 units after 2 years (n = 19) as compared to patients without mSASSS worsening (37.7 ± 57.8 ng/ml versus 16.1 ± 44.6 ng/ml; P = 0.029) and in patients with syndesmophyte formation/progression (n = 22) as compared to patients without such progression (37.1 ± 55.3 ng/ml versus 15.3 ± 44.8 ng/ml; P = 0.023). Visfatin levels of >8 ng/ml at baseline were predictive of subsequent radiographic spinal progression (adjusted odds ratio 3.6 for mSASSS progression and 5.4 for syndesmophyte formation/progression).

CONCLUSION

Serum levels of resistin and visfatin are elevated in AS patients. Elevated visfatin levels at baseline are predictive of subsequent progression of radiographic damage in AS patients.

Expression of Leptin and Visfatin in Gingival Tissues of Chronic Periodontitis With and Without Type 2 Diabetes Mellitus: A Study Using Enzyme-Linked Immunosorbent Assay and Real-Time Polymerase Chain Reaction

BACKGROUND

The aim of this study is to investigate the protein and gene expression of leptin and visfatin in gingival tissue from patients with chronic periodontitis (CP), patients with CP and type 2 diabetes mellitus (T2DM), and healthy individuals.

METHODS

The study includes 50 individuals: 10 healthy individuals, 20 patients with CP, and 20 patients with CP and T2DM. Plaque index, gingival index, probing depth, and clinical attachment loss were measured, and gingival biopsies were obtained. Leptin and visfatin protein expression in gingival tissues was determined using enzyme-linked immunosorbent assay, and messenger RNA (mRNA) expression was measured via real-time polymerase chain reaction.

RESULTS

The highest leptin mRNA and protein expression was observed in the control group and was significantly (P ≤0.05) different from the CP and CP+T2DM groups. Gingival tissues from patients with CP and T2DM had a significant increase in visfatin and a decrease in leptin gene and protein expression (P <0.05) compared with both controls and patients with CP.

CONCLUSION

Expression of leptin and visfatin in the gingival tissues suggests a possible role for these adipokines in the pathogenesis of CP and T2DM.

Effect of Non-surgical Periodontal Therapy on Serum and Salivary Concentrations of Visfatin in Patients with Chronic Periodontitis

Background and aims. Visfatin, mainly secreted by visceral adipose tissue, especially by macrophages, plays an important role in regulating the defense and immune functions, and functions as a growth factor, a cytokine, an enzyme and more importantly as a proinflammatory mediator. The aim of the present study was to evaluate the effect of non-surgical periodontal treatment on serum and salivary levels of visfatin in patients with generalized moderate-to-severe chronic periodontitis. Materials and methods. Eighteen patients with generalized moderate-to-severe chronic periodontitis were selected based on periodontal parameters of gingival index (GI), probing pocket depth (PPD), clinical attachment level (CAL) and radiographic parameters. Serum and salivary samples were collected at baseline and one month following non-surgical periodontal therapy (scaling and root planing ([SRP]). Visfatin levels were measured using an ELISA kit. Data were analyzed by SPSS 15, using paired t-test and Pearson's correlation coefficient. Results. Mean salivary and serum levels of visfatin significantly decreased after non-surgical periodontal treatment (P<0.05). Changes in salivary visfatin levels were more prominent. Conclusion. According to the findings of this study it seems that there is a direct relationship between periodontal tissue inflammation and disease activity with salivary and serum visfatin levels.

Serum visfatin concentration in acutely ill and weight-recovered patients with anorexia nervosa

Visfatin is a recently described protein that is thought to regulate the process of adipocyte differentiation. Findings suggest that visfatin may be actively involved in the control of weight regulatory networks. However, to what extent and which role it plays in eating disorders is still poorly understood, as mixed results have been reported. The aim of the current study was to investigate serum visfatin concentrations on a cross sectional sample between acute anorexia nervosa patients (n=44), weight recovered patients (n=13) and healthy controls (n=46) and a longitudinal sample of acute patients (n=57) during weight recovery at three different time-points. Results did not show significant differences in visfatin between the three groups; however, acute patients showed a higher visfatin/BMI-SDS ratio than controls and recovered patients. Longitudinal results revealed an increase of visfatin levels during therapy. Our results suggest that high ratios of visfatin/BMI-SDS could be a state marker in acute anorexia nervosa, displaying a compensatory mechanism of the individual to maintain normal visfatin levels under malnourished conditions.

The role of adipocytokines in the pathogenesis of knee joint osteoarthritis

Osteoarthritis (OA) is one of the most common causes of musculoskeletal disability in the world. Traditionally, it has been thought that obesity contributes to the development and progression of OA by increased mechanical load of the joint structures. Nevertheless, studies have shown that adipose tissue-derived cytokines (adipocytokines) are a possible link between obesity and OA. Furthermore, according to recent findings, not only articular cartilage may be the main target of these cytokines but also the synovial membrane, subchondral bone and infrapatellar fat pad may be encompassed in the process of degradation. This review presents the most recent reports on the contribution of adipocytokines to the knee joint cartilage degradation, osteophyte formation, infrapatellar fat pad alterations and synovitis.

Pre-B cell colony enhancing factor induces Nampt-dependent translocation of the insulin receptor out of lipid microdomains in A549 lung epithelial cells

Pre-B cell colony-enhancing factor (PBEF) is a highly conserved pleiotropic protein reported to be an alternate ligand for the insulin receptor (IR). We sought to clarify the relationship between PBEF and insulin signaling by evaluating the effects of PBEF on the localization of the IRβ chain to lipid rafts in A549 epithelial cells. We isolated lipid rafts from A549 cells and detected the IR by immunoprecipitation from raft fractions or whole cell lysates. Cells were treated with rPBEF, its enzymatic product nicotinamide adenine dinucleotide (NAD), or the Nampt inhibitor daporinad to study the effect of PBEF on IRβ movement. We used coimmunoprecipitation studies in cells transfected with PBEF and IRβ constructs to detect interactions between PBEF, the IRβ, and caveolin-1 (Cav-1). PBEF was present in both lipid raft and nonraft fractions, whereas the IR was found only in lipid raft fractions of resting A549 cells. The IR-, PBEF-, and Cav-1-coimmunoprecipitated rPBEF treatment resulted in the movement of IRβ- and tyrosine-phosphorylated Cav-1 from lipid rafts to nonrafts, an effect that could be blocked by daporinad, suggesting that this effect was facilitated by the Nampt activity of PBEF. The addition of PBEF to insulin-treated cells resulted in reduced Akt phosphorylation of both Ser⁴⁷³ and Thr³⁰⁸. We conclude that PBEF can inhibit insulin signaling through the IR by Nampt-dependent promotion of IR translocation into the nonraft domains of A549 epithelial cells. PBEF-induced alterations in the spatial geometry of the IR provide a mechanistic explanation for insulin resistance in inflammatory states associated with upregulation of PBEF.

The bone and fat connection in inflammatory bowel diseases

Osteopenia and osteoporosis are common manifestations in inflammatory bowel diseases (IBD) but the pathogenetic mechanism of bone loss in IBD is only partially understood. There is evidence that fat mass is an important determinant of the bone mineral density and adipose-derived factors seem to play an important role for the association between fat mass and bone mass. The association between adiposity and low bone density is rather poorly studied in IBD, but emerging data on adipokines in IBD in relation to osteoporosis provide a novel pathophysiological concept that may shed light on the etiology of bone loss in IBD. It could be suggested that adipokines interfere in bone metabolism by altering the sensitive balance between osteoblasts and osteoclasts although further studies in this setting are needed.

Muscle-bone and fat-bone interactions in regulating bone mass: do PTH and PTHrP play any role?

Metabolic bone disease occurs when there is a net loss in bone density. Osteoporosis, the most common metabolic bone disease, is a devastating problem and an increasingly major public health issue. A substantial body of evidence in the elderly population indicates that a relationship exists between the components of body weight and various measures of bone/mass, density, and function. Both muscle and fat contribute to the body's total weight and the intimate associations of muscle, fat, and bone are known. But the close functional interactions between muscle and bone or fat and bone are largely unidentified and have drawn much attention in recent years. Each of these tissues not only responds to afferent signals from traditional hormone systems and the central nervous systems but also secretes factors with important endocrine functions. Studies suggest that during growth, development, and aging, the relationship of muscle and fat with the skeleton possibly governs bone homeostasis and turnover. A better understanding of the endocrine function and the cellular and molecular mechanisms and pathways linking muscle or adipose tissues with bone anabolism and catabolism is a new avenue for novel pathways for anabolic drug discovery. These in turn will likely lead to more rational therapy toward increasingly prevalent disorders like osteoporosis. In this review, some of the recent works on the interaction of bone with muscle and fat are highlighted, and in so doing the role of parathyroid hormone (PTH), and PTH-related peptide (PTHrP) is surveyed.

Relationship between circulating visfatin/NAMPT, nutritional status and insulin resistance in an elderly population - results from the PolSenior substudy

BACKGROUND

Circulating visfatin/nicotinamide phosphoribosyltransferase (visfatin/NAMPT) levels according to some studies are related to nutritional status and insulin resistance. These associations have not been studied in large elderly populations. Therefore, the aim of our study was to assess the relationships between circulating visfatin/NAMPT levels, nutritional status, and insulin resistance in a large population of the elderly.

MATERIALS AND METHODS

Concentrations of glucose, albumin, creatinine, CRP, interleukin-6, insulin, and visfatin/NAMPT (by ELISA) were assessed, and HOMA-IR calculated in 3050 elderly participants of the PolSenior study.

RESULTS

The highest plasma visfatin/NAMPT levels were observed in obese, as well as in non-diabetic insulin resistant subjects; however there were only significant differences found in women. The regression models showed that plasma visfatin/NAMPT levels decline with age and increased with waist circumference, BMI, and hs-CRP. Waist circumference was better correlated than BMI for visfatin/NAMPT levels in statistical models not adjusted by sex, and just the opposite in models which were. We demonstrated a 0.023ng/mL increase of Visfatin/NAMPT levels for 1mg/L increase of hs-CRP, and a 0.007ng/mL decline for each year of age.

CONCLUSION

Our study revealed that in elderly subjects, circulating visfatin/NAMPT levels are related to age, nutritional status, especially visceral obesity, and inflammation.

Visfatin: an adipokine activator of rat hepatic stellate cells

The present study was conducted to investigate the effects of visfatin on the activation of hepatic stellate cells (HSC) and the possible underlying mechanism. HSC were isolated from the livers of Sprague‑Dawley rats by in situ perfusion of collagenase and pronase and a single‑step density Nycodenz gradient. The culture‑activated cells were serum‑starved and incubated with different concentrations of recombinant visfatin (0, 25, 50, 100 or 200 ng/ml) for 24 h. The expression of α‑smooth muscle actin (α‑SMA), collagen types I and III and connective tissue growth factor (CTGF) were then measured by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blot analysis. The results demonstrated that 100 and 200 ng/ml concentrations of visfatin induced the expression of α‑SMA in culture‑activated rat HSC, which was accompanied by a significant increase in collagen types I and III, as confirmed by western blot and RT‑qPCR analyses. In addition, treatment of the HSC with certain concentrations of visfatin upregulated the expression of CTGF. These findings suggested that visfatin activated HSC and induced the production of collagen types I and III.

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.

Adipokines: Biomarkers for osteoarthritis?

Osteoarthritis (OA) is one of the most common degenerative joint diseases in aging population. Obesity is an important risk factor for initiation and progression of OA. It is accepted that excess body weight may lead to cartilage degeneration by increasing the mechanical forces across weight-bearing joints. However, emerging data suggest that additional metabolic factors released mainly by white adipose tissue may also be responsible for the high prevalence of OA among obese people. Adipocyte-derived molecules ‘‘adipokines’’ have prompt much interest in OA pathophysiological research over the past decade since they play an important role in cartilage and bone homeostasis. Therefore, the aim of this review is to summarize the current knowledge on the role of adipokines including leptin, adiponectin, visfatin and resistin in OA and their potential to be used as biomarkers for earlier diagnosis, classifying disease severity, monitoring disease progression, and testing pharmacological interventions for OA. In OA patients, leptin, visfatin and resistin showed increased production whereas adiponectin showed decreased production. Leptin and adiponectin are far more studied than visfatin and resistin. Importantly, altered adipokine levels also contribute to a wide range of diseases. Further experiments are still crucial for understanding the relationship between adipokines and OA.

Visfatin is involved in TNFα-mediated insulin resistance via an NAD(+)/Sirt1/PTP1B pathway in 3T3-L1 adipocytes

Tumor necrosis factor α (TNFα) is a well-known mediator of inflammation in the context of obesity in adipose tissue. Its action appears to be directly linked to perturbations of the insulin pathway, leading to the development of insulin resistance. Visfatin has been suspected to be linked to insulin sensitivity, but the mechanism involved is still partly unknown. The aim of this study was to evaluate the role of visfatin in the impairment of the insulin pathway by TNFα activity in 3T3-L1 adipocytes and to unveil the mechanisms involved in such impairment.

We demonstrated in 3T3-L1 adipocytes that visfatin was involved in TNFα-mediated insulin resistance in adipocytes. Indeed, after TNFα treatment in 3T3-L1 cells, visfatin was downregulated, leading to decreased nicotinamide adenine dinucleotide (NAD⁺) concentrations in cells. This decrease was followed by a decrease in Sirt1 activity, which was linked to an increase in PTP1B expression. The modulation of PTP1B by visfatin was likely responsible for the observed decreases in glucose uptake and Akt phosphorylation in 3T3-L1 adipocytes.

Here, we demonstrated a complete pathway involving visfatin, NAD⁺, Sirt1, and PTP1B that led to the perturbation of insulin signaling by TNFα in 3T3-L1 adipocytes.

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.

MAPK pathway mediates the induction of visfatin in neonatal SD rat cardiomyocytes pretreated with glucose

The protein visfatin is an insulin mimetic that has been shown to reduce plasma glucose levels, increase cytokine production and induce angiogenesis. However, few studies have focused on visfatin expression in cardiomyocytes at the cellular level. Therefore, the aim of the present study was to investigate visfatin expression and its potential mechanisms in cultured neonatal rat cardiomyocytes exposed to high-glucose concentrations. Primary cultures of 2-to 3-day-old Sprague Dawley (SD) rat cardiomyocytes were pretreated with increasing concentrations of glucose. P38 mitogen-activated protein kinase (MAPK) pathway inhibitor SB203580, extra cellular signal-regulated kinase (ERK1/2) pathway inhibitor PD098059 and c-Jun NH 2-terminal kinase (JNK) pathway inhibitor SP600125 were used to block the effect of glucose on visfatin expression. Cell viability following each glucose treatment was determined using the MTT assay. Expression of visfatin was detected using RT-PCR and western blot analysis. Increased glucose concentration directly correlated with an increased expression of visfatin mRNA and protein in neonatal rat cardiomyocytes. Following high doses of glucose, visfatin mRNA and protein expression peaked after 24 h with no significant change thereafter. Increased visfatin expression was blocked by the P38 MAPK inhibitor SB203580, suggesting a potential mechanism not yet identified. Expression of visfatin in cardiomyocytes was increased through the P38 MAPK pathway in the presence of high-glucose concentrations.

The impact of bone marrow adipocytes on osteoblast and osteoclast differentiation

Throughout life, bone is constantly remodeled through the complementary processes of bone resorption and bone formation. Highly coordinated regulation of these activities is essential for maintaining consistent bone quality and quantity. Normally, the development and function of bone-forming (osteoblast) and bone-resorbing (osteoclast) cells are tightly regulated by signaling molecules secreted by these two cell types. Within the bone marrow microenvironment, osteoblasts arise from mesenchymal stem cells (MSCs), which are in close contact with the hematopoietic stem cell (HSC) precursors that differentiate into mature osteoclasts. Signaling molecules secreted by osteoblasts (e.g., receptor activator of nuclear factor kappa B ligand and osteoprotegerin) and osteoclasts (e.g., bone morphogenetic protein 6, wingless-type MMTV integration site family member 10B, sphingosine-1-phosphate, and ephrin-B2) play a key role in bone remodeling by guiding the differentiation, localization, and function of bone cells. In addition to osteoblasts, bone marrow MSCs can also differentiate into adipocytes that affect bone remodeling by competitively suppressing intracellular osteogenic signals, including runt-related transcription factor 2, osterix, and beta-catenin, while simultaneously promoting the secretion of adipogenic signaling molecules such as leptin, adiponectin, chemerin, omentin-1, resistin, and visfatin. Secreted adipogenic factors have also been shown to affect the osteoclastogenic differentiation of HSCs. Herein, we discuss the impact of bone marrow adipocytes on the coupling of osteoblast and osteoclast differentiation, and the relevance to bone-loss disorders such as osteoporosis. © 2014 IUBMB Life, 66(3):147-155, 2014.

Cytokines and Hormones That Contribute to the Positive Association between Fat and Bone

The positive association between body weight and bone density has been established in numerous laboratory and clinical studies. Apart from the direct effect of soft tissue mass on bone through skeletal loading, a number of cytokines and hormones contribute to the positive association between adipose and bone tissue, acting either locally in sites where cells of the two tissues are adjacent to each other or systemically through the circulation. The current review describes the effects of such local and systemic factors on bone physiology. One class of factors are the adipocyte-secreted peptides (adipokines), which affect bone turnover through a combination of direct effects in bone cells and indirect mechanisms mediated by the central nervous system. Another source of hormones that contribute to the coupling between fat and bone tissue are beta cells of the pancreas. Insulin, amylin, and preptin are co-secreted from pancreatic beta cells in response to increased glucose levels after feeding, and are also found in high circulating levels in obesity. A number of peptide hormones secreted from the gastrointestinal tract in response to feeding affect both fat and bone cells and thus can also act as mediators of the association between the two tissues. The current review focuses on results of laboratory studies investigating possible mechanism involved in the positive association between fat mass and bone mass.

Increased visfatin in hemodialysis patients is associated with decreased demands for recombinant human erythropoietin

BACKGROUND

Studies detected an association between visfatin and markers of iron metabolism in patients with insulin resistance. In this study, such a relation was evaluated in hemodialysis (HD) patients. Also relations between visfatin and hepcidin, demands for recombinant human erythropoietin (rHuEpo), inflammation, and situations characterized by insulin resistance were evaluated.

METHODS

After a four-week washout period from iron treatment, 33 HD patients and 20 healthy volunteers enrolled in the study. Serum visfatin, hepcidin, and interleukin-6 (IL-6) were assessed by means of enzyme-linked immunosorbent assay. Hemoglobin, serum iron, ferritin, and transferrin saturation (TSAT) were also measured.

RESULTS

Visfatin was markedly increased in HD patients. Visfatin levels did not differ between diabetics and non-diabetics. No relation was detected between visfatin and body mass index or IL-6 in HD patients. From the markers of iron metabolism, the hepcidin included, visfatin was related only to TSAT. A strong positive relation was revealed between visfatin and hemoglobin, whereas visfatin was inversely related to rHuEpo dose. Resistance to rHuEpo index was inversely and independently of TSAT related to visfatin.

CONCLUSION

Visfatin is increased in HD patients and it is associated with decreased demands for rHuEpo.

The interrelationship between bone and fat: from cellular see-saw to endocrine reciprocity

The number of mature osteoblasts and marrow adipocytes in bone is influenced by the differentiation of the common mesenchymal progenitor cell towards one phenotype and away from the other. Consequently, factors which promote adipogenesis not only lead to fatty marrow but also inhibit osteoblastogenesis, resulting in decreased osteoblast numbers, diminished bone formation and, potentially, inadequate bone mass and osteoporosis. In addition to osteoblast and bone adipocyte numbers being influenced by this skewing of progenitor cell differentiation towards one phenotype, mature osteoblasts and adipocytes secrete factors which may evoke changes in the cell fate and function of each other. This review examines the endogenous factors, such as PPAR-γ2, Wnt, IGF-1, GH, FGF-2, oestrogen, the GP130 signalling cytokines, vitamin D and glucocorticoids, which regulate the selection between osteoblastogenesis and adipogenesis and the interrelationship between fat and bone. The role of adipokines on bone, such as adiponectin and leptin, as well as adipose-derived oestrogen, is reviewed and the role of bone as an energy regulating endocrine organ is discussed.

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.