Monomeric eNAMPT in the development of experimental diabetes in mice: a potential target for type 2 diabetes treatment

NAD World 3.0: the importance of the NMN transporter and eNAMPT in mammalian aging and longevity control

Over the past five years, systemic NAD+ (nicotinamide adenine dinucleotide) decline has been accepted to be a key driving force of aging in the field of aging research. The original version of the NAD World concept was proposed in 2009, providing an integrated view of the NAD+-centric, systemic regulatory network for mammalian aging and longevity control. The reformulated version of the concept, the NAD World 2.0, was then proposed in 2016, emphasizing the importance of the inter-tissue communications between the hypothalamus and peripheral tissues including adipose tissue and skeletal muscle. There has been significant progress in our understanding of the importance of nicotinamide mononucleotide (NMN), a key NAD+ intermediate, and nicotinamide phosphoribosyltransferase (NAMPT), particularly extracellular NAMPT (eNAMPT). With these exciting developments, the further reformulated version of the concept, the NAD World 3.0, is now proposed, featuring multi-layered feedback loops mediated by NMN and eNAMPT for mammalian aging and longevity control.

Pathobiochemistry of Aging and Neurodegeneration: Deregulation of NAD+ Metabolism in Brain Cells

NAD+ plays a pivotal role in energy metabolism and adaptation to external stimuli and stressful conditions. A significant reduction in intracellular NAD+ levels is associated with aging and contributes to the development of chronic cardiovascular, neurodegenerative, and metabolic diseases. It is of particular importance to maintain optimal levels of NAD+ in cells with high energy consumption, particularly in the brain. Maintaining the tissue level of NAD+ with pharmacological tools has the potential to slow down the aging process, to prevent the development of age-related diseases. This review covers key aspects of NAD+ metabolism in terms of brain metabolic plasticity, including NAD+ biosynthesis and degradation in different types of brain cells, as well as its contribution to the development of neurodegeneration and aging, and highlights up-to-date approaches to modulate NAD+ levels in brain cells.

Adipokines and their potential impacts on susceptibility to myocardial ischemia/reperfusion injury in diabetes

Coronary artery disease has a high mortality rate and is a striking public health concern, affecting a substantial portion of the global population. On the early onset of myocardial ischemia, thrombolytic therapy and coronary revascularization could promptly restore the bloodstream and nutrient supply to the ischemic tissue, efficiently preserving less severely injured myocardium. However, the abrupt re-establishment of blood flow triggers the significant discharge of previously accumulated oxidative substances and inflammatory cytokines, leading to further harm referred to as ischemia/reperfusion (I/R) injury. Diabetes significantly raises the vulnerability of the heart to I/R injury due to disrupted glucose and lipid processing, impaired insulin sensitivity and metabolic signaling, and increased inflammatory responses. Numerous studies have indicated that adipokines are crucial in the etiology and pathogenesis of obesity, diabetes, hyperlipidemia, hypertension, and coronary artery disease. Adipokines such as adiponectin, adipsin, visfatin, chemerin, omentin, and apelin, which possess protective properties against inflammatory activity and insulin resistance, have been shown to confer myocardial protection in conditions such as atherosclerosis, myocardial hypertrophy, myocardial I/R injury, and diabetic complications. On the other hand, adipokines such as leptin and resistin, known for their pro-inflammatory characteristics, have been linked to elevated cardiac lipid deposition, insulin resistance, and fibrosis. Meteorin-like (metrnl) exhibits opposite effects in various pathological conditions. However, the data on adipokines in myocardial I/R, especially in diabetes, is still incomplete and controversial. This review focuses on recent research regarding the categorization and function of adipokines in the heart muscle, and the identification of different signaling pathways involved in myocardial I/R injury under diabetic conditions, aiming to facilitate the exploration of therapeutic strategies against myocardial I/R injury in diabetes.

Impact of Lipids on Insulin Resistance: Insights from Human and Animal Studies

Insulin resistance (IR) is a complex pathological condition central to metabolic diseases such as type 2 diabetes mellitus (T2DM), cardiovascular disease, non-alcoholic fatty liver disease, and polycystic ovary syndrome (PCOS). This review evaluates the impact of lipids on insulin resistance (IR) by analyzing findings from human and animal studies. The articles were searched on the PubMed database using two keywords: (1) "Role of Lipids AND Insulin Resistance AND Humans" and (2) "Role of Lipids AND Insulin Resistance AND Animal Models". Studies in humans revealed that elevated levels of free fatty acids (FFAs) and triglycerides (TGs) are closely associated with reduced insulin sensitivity, and interventions like metformin and omega-3 fatty acids show potential benefits. In animal models, high-fat diets disrupt insulin signaling and increase inflammation, with lipid mediators such as diacylglycerol (DAG) and ceramides playing significant roles. DAG activates protein kinase C, which eventually impairs insulin signaling, while ceramides inhibit Akt/PKB, further contributing to IR. Understanding these mechanisms is crucial for developing effective prevention and treatment strategies for IR-related diseases.

NAMPT, IL-6, and vaspin gene expressions and serum protein levels in type 2 diabetes mellitus and related complication

Background/aim

Type 2 diabetes mellitus (T2DM) is the most common type of diabetes and occurs due to insufficient insulin secretion or inability to use existing insulin and the effects of environmental factors. Although there are many studies on the pathophysiology of T2DM, the mechanisms contributing to the pathogenesis of insulin resistance and pancreatic beta-cell dysfunction have not been completely elucidated. Some adipokines secreted from adipose tissue, which are the primary regulators of insulin resistance, affect immune and inflammatory functions. Altered adipokine profiles have been observed in obesity and T2DM, leading to severe metabolic risks and changes in insulin sensitivity.

Materials and methods

This study used quantitative PCR and ELISA techniques to analyze samples from individuals without diabetes (control group) and with T2DM (macrovascular and microvascular complications and without complications) for at least 10 years.

Results

The mRNA expression and protein levels of NAMPT, IL-6, and vaspin genes were determined. While there was no significant difference in NAMPT, IL-6, and vaspin mRNA expression levels between diabetic groups, there was a significant decrease between the patient and control groups (p < 0.001). For serum protein levels, NAMPT protein levels decreased significantly in the uncomplicated group, while IL-6 and vaspin protein levels increased significantly in both microvascular and macrovascular complication groups (p < 0.001).

Conclusion

The correlations between gene expressions, clinical parameters, and protein levels are crucial to understanding the implications of the findings.

Pathogenic role of NAMPT in the perivascular regions after ischemic stroke in mice with type 2 diabetes mellitus

Ischemic stroke in patients with abnormal glucose tolerance results in poor outcomes. Nicotinamide phosphoribosyltransferase (NAMPT), an adipocytokine, exerts neuroprotective effects. However, the pathophysiological role of NAMPT after ischemic stroke with diabetes and the relationship of NAMPT with cerebrovascular lesions are unclear. The purpose of this study was to clarify the pathophysiological role of NAMPT in cerebral ischemia with diabetes, using db/db mice as a type 2 diabetes animal model. The number of degenerating neurons increased after middle cerebral artery occlusion and reperfusion (MCAO/R) in db/db mice compared with the degenerating neurons in db/+ mice. Extracellular NAMPT (eNAMPT) levels, especially monomeric eNAMPT, increased significantly in db/db MCAO/R mice but not db/+ mice in isolated brain microvessels. The increased eNAMPT levels were associated with increased expression of inflammatory cytokine mRNA. Immunohistochemical analysis demonstrated that NAMPT colocalized with GFAP-positive cells after MCAO/R. In addition, both dimeric and monomeric eNAMPT levels increased in the conditioned medium of primary cortical astrocytes under high glucose conditions subsequent oxygen/glucose deprivation. Our findings are the first to demonstrate the ability of increased monomeric eNAMPT to induce inflammatory responses in brain microvessels, which may be located near astrocyte foot processes.

Extracellular nicotinamide phosphoribosyltransferase: role in disease pathophysiology and as a biomarker

Nicotinamide phosphoribosyltransferase (NAMPT) plays a central role in mammalian cell metabolism by contributing to nicotinamide adenine dinucleotide biosynthesis. However, NAMPT activity is not limited to the intracellular compartment, as once secreted, the protein accomplishes diverse functions in the extracellular space. Extracellular NAMPT (eNAMPT, also called visfatin or pre-B-cell colony enhancing factor) has been shown to possess adipocytokine, pro-inflammatory, and pro-angiogenic activities. Numerous studies have reported the association between elevated levels of circulating eNAMPT and various inflammatory and metabolic disorders such as obesity, diabetes, atherosclerosis, arthritis, inflammatory bowel disease, lung injury and cancer. In this review, we summarize the current state of knowledge on eNAMPT biology, proposed roles in disease pathogenesis, and its potential as a disease biomarker. We also briefly discuss the emerging therapeutic approaches for eNAMPT inhibition.

SARS-CoV-2 infection dysregulates NAD metabolism

Introduction

Severe COVID-19 results initially in pulmonary infection and inflammation. Symptoms can persist beyond the period of acute infection, and patients with Post-Acute Sequelae of COVID (PASC) often exhibit a variety of symptoms weeks or months following acute phase resolution including continued pulmonary dysfunction, fatigue, and neurocognitive abnormalities. We hypothesized that dysregulated NAD metabolism contributes to these abnormalities.

Methods

RNAsequencing of lungs from transgenic mice expressing human ACE2 (K18-hACE2) challenged with SARS-CoV-2 revealed upregulation of NAD biosynthetic enzymes, including NAPRT1, NMNAT1, NAMPT, and IDO1 6 days post-infection.

Results

Our data also demonstrate increased gene expression of NAD consuming enzymes: PARP 9,10,14 and CD38. At the same time, SIRT1, a protein deacetylase (requiring NAD as a cofactor and involved in control of inflammation) is downregulated. We confirmed our findings by mining sequencing data from lungs of patients that died from SARS-CoV-2 infection. Our validated findings demonstrating increased NAD turnover in SARS-CoV-2 infection suggested that modulating NAD pathways may alter disease progression and may offer therapeutic benefits. Specifically, we hypothesized that treating K18-hACE2 mice with nicotinamide riboside (NR), a potent NAD precursor, may mitigate lethality and improve recovery from SARS-CoV-2 infection. We also tested the therapeutic potential of an anti- monomeric NAMPT antibody using the same infection model. Treatment with high dose anti-NAMPT antibody resulted in significantly decreased body weight compared to control, which was mitigated by combining HD anti-NAMPT antibody with NR. We observed a significant increase in lipid metabolites, including eicosadienoic acid, oleic acid, and palmitoyl carnitine in the low dose antibody + NR group. We also observed significantly increased nicotinamide related metabolites in NR treated animals.

Discussion

Our data suggest that infection perturbs NAD pathways, identify novel mechanisms that may explain some pathophysiology of CoVID-19 and suggest novel strategies for both treatment and prevention.

Involvement of eNAMPT/TLR4 inflammatory signaling in progression of non-alcoholic fatty liver disease, steatohepatitis, and fibrosis

Although the progression of non-alcoholic fatty liver disease (NAFLD) from steatosis to steatohepatitis (NASH) and cirrhosis remains poorly understood, a critical role for dysregulated innate immunity has emerged. We examined the utility of ALT-100, a monoclonal antibody (mAb), in reducing NAFLD severity and progression to NASH/hepatic fibrosis. ALT-100 neutralizes eNAMPT (extracellular nicotinamide phosphoribosyltransferase), a novel damage-associated molecular pattern protein (DAMP) and Toll-like receptor 4 (TLR4) ligand. Histologic and biochemical markers were measured in liver tissues and plasma from human NAFLD subjects and NAFLD mice (streptozotocin/high-fat diet-STZ/HFD, 12 weeks). Human NAFLD subjects (n = 5) exhibited significantly increased NAMPT hepatic expression and significantly elevated plasma levels of eNAMPT, IL-6, Ang-2, and IL-1RA compared to healthy controls, with IL-6 and Ang-2 levels significantly increased in NASH non-survivors. Untreated STZ/HFD-exposed mice displayed significant increases in NAFLD activity scores, liver triglycerides, NAMPT hepatic expression, plasma cytokine levels (eNAMPT, IL-6, and TNFα), and histologic evidence of hepatocyte ballooning and hepatic fibrosis. Mice receiving the eNAMPT-neutralizing ALT-100 mAb (0.4 mg/kg/week, IP, weeks 9 to 12) exhibited marked attenuation of each index of NASH progression/severity. Thus, activation of the eNAMPT/TLR4 inflammatory pathway contributes to NAFLD severity and NASH/hepatic fibrosis. ALT-100 is potentially an effective therapeutic approach to address this unmet NAFLD need.

Extracellular Nicotinamide Phosphoribosyltransferase Is a Component of the Senescence-Associated Secretory Phenotype

Cellular senescence is a stress or damage response by which a cell adopts of state of essentially permanent proliferative arrest, coupled to the secretion of a number of biologically active molecules. This senescence-associated secretory phenotype (SASP) underlies many of the degenerative and regenerative aspects of cellular senescence - including promoting wound healing and development, but also driving diabetes and multiple age-associated diseases. We find that nicotinamide phosphoribosyltransferase (NAMPT), which catalyzes the rate-limiting step in nicotinamide adenine dinucleotide (NAD) biosynthesis, is elevated in senescent cells without a commensurate increase in NAD levels. This elevation is distinct from the acute DNA damage response, in which NAD is depleted, and recovery of NAD by NAMPT elevation is AMPK-activated protein kinase (AMPK)-dependent. Instead, we find that senescent cells release extracellular NAMPT (eNAMPT) as part of the SASP. eNAMPT has been reported to be released as a catalytically active extracellular vesicle-contained dimer that promotes NAD increases in other cells and extends lifespan, and also as free monomer that acts as a damage-associated molecular pattern and promotes conditions such as diabetes and fibrosis. Senescent cells released eNAMPT as dimer, but surprisingly eNAMPT appeared in the soluble secretome while being depleted from exosomes. Finally, diabetic mice showed elevated levels of eNAMPT, and this was lowered by treatment with the senolytic drug, ABT-263. Together, these data reveal a new SASP factor with implications for NAD metabolism.

Visfatin exacerbates hepatic inflammation and fibrosis in a methionine-choline-deficient diet mouse model

BACKGROUND AND AIM

Non-alcoholic fatty liver disease (NAFLD) ranges from simple steatosis to non-alcoholic steatohepatitis, which is characterized by hepatic inflammation that can progress to fibrosis, cirrhosis, and hepatocellular carcinoma. Visfatin, an adipocytokine, was reported to induce pro-inflammatory cytokines and can be associated with liver fibrosis. We investigated the role of visfatin on hepatic inflammation and fibrosis in a methionine-choline-deficient (MCD)-diet-induced steatohepatitis mouse model.

METHODS

Eight-week-old male C57BL/6 J mice were randomly assigned into one of three groups: (1) saline-injected control diet group; (2) saline-injected MCD diet group; and (3) visfatin-injected MCD diet group (n = 8 per group). Mice were administered intravenous saline or 10 μg/kg of recombinant murine visfatin for 2 weeks. Histologic assessment of liver and biochemical and molecular measurements of endoplasmic reticulum (ER) stress, reactive oxidative stress (ROS), inflammation, and fibrosis were performed in livers from these animals.

RESULTS

Visfatin injection aggravated hepatic steatosis and increased plasma alanine aminotransferase and aspartate aminotransferase concentrations. Visfatin increased inflammatory cell infiltration (as indicated by F4/80, CD68, ly6G, and CD3 mRNA expression) and expression of chemokines in the liver. Visfatin also increased the expression of pro-inflammatory cytokines (IL-1β, TNF-α, and IL-6) and activated fibrosis markers (CTGF, TIMP1, collagen 1α2, collagen 3α2, αSMA, fibronectin, and vimentin) in liver. Livers of visfatin-injected mice showed upregulation of ER stress and ROS and activation of JNK signaling.

CONCLUSIONS

These results suggest that visfatin aggravates hepatic inflammation together with induction of ER and oxidative stress and exacerbates fibrosis in an MCD-diet-fed mouse model of NAFLD.

The Peculiar Trialogue between Pediatric Obesity, Systemic Inflammatory Status, and Immunity

Pediatric obesity is not only an energetic imbalance, but also a chronic complex multisystem disorder that might impair both the life length and quality. Its pandemic status should increase worldwide awareness regarding the long-term life-threatening associated complications. Obesity related complications, such as cardiovascular, metabolic, or hepatic ones, affect both short and long-term wellbeing, and they do not spare pediatric subjects, defined as life-threatening consequences of the systemic inflammatory status triggered by the adipose tissue. The energetic imbalance of obesity clearly results in adipocytes hypertrophy and hyperplasia expressing different degrees of chronic inflammation. Adipose tissue might be considered an immune organ due to its rich content in a complex array of immune cells, among which the formerly mentioned macrophages, neutrophils, mast cells, but also eosinophils along with T and B cells, acting together to maintain the tissue homeostasis in normal weight individuals. Adipokines belong to the class of innate immunity humoral effectors, and they play a crucial role in amplifying the immune responses with a subsequent trigger effect on leukocyte activation. The usefulness of complete cellular blood count parameters, such as leukocytes, lymphocytes, neutrophils, erythrocytes, and platelets as predictors of obesity-triggered inflammation, was also proved in pediatric patients with overweight or obesity. The dogma that adipose tissue is a simple energy storage tissue is no longer accepted since it has been proved that it also has an incontestable multifunctional role acting like a true standalone organ resembling to endocrine or immune organs.

NAD+ oscillation and hypothalamic neuronal functions

A substantial body of evidence shows the importance of nicotinamide adenine dinucleotide (NAD⁺) biosynthesis and its regulation in a wide range of cellular metabolism. The expression of nicotinamide phosphoribosyltransferase (NAMPT) is regulated in a circadian manner by the core clock mechanism and NAD⁺-dependent sirtuins, producing the circadian oscillation of NAD⁺. The hypothalamus is a critical center for the homeostatic regulation of metabolism, circadian rhythm, and age-associated physiology. The dysfunction of systemic NAD⁺ biosynthesis over age affects the functions of hypothalamic neurons, causing age-associated metabolic pathophysiologies, including obesity and age-associated diseases. These recent studies suggest that NAD⁺ oscillation contributes to the hypothalamic function, and its disruption produces circadian and aging-related metabolic disorders. Furthermore, new studies have demonstrated a novel intertissue NAD⁺-dependent communication as a potential target for preventing and treating such disorders and for extending the health span of humans.

NAD+ metabolism and its roles in cellular processes during ageing

Nicotinamide adenine dinucleotide (NAD+) is a coenzyme for redox reactions, making it central to energy metabolism. NAD+ is also an essential cofactor for non-redox NAD+-dependent enzymes, including sirtuins, CD38 and poly(ADP-ribose) polymerases. NAD+ can directly and indirectly influence many key cellular functions, including metabolic pathways, DNA repair, chromatin remodelling, cellular senescence and immune cell function. These cellular processes and functions are critical for maintaining tissue and metabolic homeostasis and for healthy ageing. Remarkably, ageing is accompanied by a gradual decline in tissue and cellular NAD+ levels in multiple model organisms, including rodents and humans. This decline in NAD+ levels is linked causally to numerous ageing-associated diseases, including cognitive decline, cancer, metabolic disease, sarcopenia and frailty. Many of these ageing-associated diseases can be slowed down and even reversed by restoring NAD+ levels. Therefore, targeting NAD+ metabolism has emerged as a potential therapeutic approach to ameliorate ageing-related disease, and extend the human healthspan and lifespan. However, much remains to be learnt about how NAD+ influences human health and ageing biology. This includes a deeper understanding of the molecular mechanisms that regulate NAD+ levels, how to effectively restore NAD+ levels during ageing, whether doing so is safe and whether NAD+ repletion will have beneficial effects in ageing humans.

Role of secreted extracellular nicotinamide phosphoribosyltransferase (eNAMPT) in prostate cancer progression: Novel biomarker and therapeutic target

BACKGROUND

There remains a serious need to prevent the progression of invasive prostate cancer (PCa). We previously showed that secreted extracellular nicotinamide phosphoribosyltransferase (eNAMPT) is a multifunctional innate immunity regulator via TLR4 ligation which has been implicated in PCa progression. Here we investigate the role of eNAMPT as a diagnostic biomarker and therapeutic target in the progression of PCa.

METHODS

Tumor NAMPT expression and plasma eNAMPT level were evaluated in human subjects with various PCa tumor stages and high risk subjects followed-up clinically for PCa. The genetic regulation of NAMPT expression in PCa cells and the role of eNAMPT in PCa invasion were investigated utilizing in vitro and in vivo models.

FINDINGS

Marked NAMPT expression was detected in human extraprostatic-invasive PCa tissues compared to minimal expression of organ-confined PCa. Plasma eNAMPT levels were significantly elevated in PCa subjects compared to male controls, and significantly greater in subjects with extraprostatic-invasive PCa compared to subjects with organ-confined PCa. Plasma eNAMPT levels showed significant predictive value for diagnosing PCa. NAMPT expression and eNAMPT secretion were highly upregulated in human PCa cells in response to hypoxia-inducible factors and EGF. In vitro cell culture and in vivo preclinical mouse model studies confirmed eNAMPT-mediated enhancement of PCa invasiveness into muscle tissues and dramatic attenuation of PCa invasion by weekly treatment with an eNAMPT-neutralizing polyclonal antibody.

INTERPRETATION

This study suggests that eNAMPT is a potential biomarker for PCa, especially invasive PCa. Neutralization of eNAMPT may be an effective therapeutic approach to prevent PCa invasion and progression.

Visfatin and Rheumatoid Arthritis: Pathogenetic Implications and Clinical Utility

Objective:

Analysis and generalization of data related to visfatin involvement in the pathogenesis of inflammation at various stages of rheumatoid arthritis.

Data Synthesis:

Visfatin is an adipocytokine which has also been identified in non-adipose tissues. It influences directly on the maturation of B cells, which are involved in autoantibody production and T cell activation. Visfatin can promote inflammation via regulation of pro-inflammatory cytokines including TNF, IL-1β and IL-6. The concentration of circulating visfatin in rheumatoid arthritis patients is higher compared to healthy individuals. Several studies suggest that visfatin level is associated with rheumatoid arthritis activity, and its elevation may precede clinical signs of the relapse. In murine collagen-induced arthritis, visfatin levels were also found to be elevated both in inflamed synovial cells and in joint vasculature. Visfatin blockers have been shown to confer fast and long-term attenuation of pathological processes; however, most of their effects are transient. Other factors responsible for hyperactivation of the immune system can participate in this process at a later stage. Treatment of rheumatoid arthritis with a combination of these blockers and inhibitors of other mediators of inflammation can potentially improve treatment outcomes compared to current therapeutic strategies. Recent advances in the treatment of experimental arthritis in mice as well as the application of emerging treatment strategies obtained from oncology for rheumatoid arthritis management could be a source of novel adipokine-mediated anti-rheumatic drugs.

Conclusion:

The ongoing surge of interest in anticytokine therapy makes further study of visfatin highly relevant as it may serve as a base for innovational RA treatment.

Anthocyanins regulate serum adipsin and visfatin in patients with prediabetes or newly diagnosed diabetes: a randomized controlled trial

BACKGROUND

Epidemiological studies have suggested that adipsin and visfatin are associated with the development of type 2 diabetes. This is the first study to investigate the effects of supplementation with purified anthocyanins on serum adipsin and visfatin in patients with prediabetes or newly diagnosed diabetes.

METHODS

A total of 160 participants with prediabetes or newly diagnosed diabetes (40-75 years old) were given 320 mg anthocyanins or placebo daily for 12 weeks in a randomized trial. Serum adipsin, serum visfatin, lipids and glycated hemoglobin A1c (HbA1c) were measured. The areas under the curve (AUCs) for glucose, insulin and C-peptide were determined before-and after-treatment by a standard 3-h 75 g oral glucose tolerance test (OGTT).

RESULTS

Relatively significant increases in serum adipsin (net change 0.15 µg/mL [0.03, 0.27], p = 0.018) and decreases in visfatin (-3.5 ng/mL [-6.69, -0.31], p = 0.032) were observed between the anthocyanins and placebo groups. We also observed significant improvements in HbA1c (-0.11% [-0.22, -0.11], p = 0.033), apolipoprotein A-1 (apo A-1) (0.12 g/L [0.03, 0.21], p = 0.012) and apolipoprotein B (apo B) (-0.07 g/L [-0.14, -0.01], p = 0.033) in response to the anthocyanins intervention.

CONCLUSION

Purified anthocyanins supplementation for 12 weeks increased serum adipsin and decreased serum visfatin in patients with prediabetes or newly diagnosed diabetes. Trial registration ClinicalTrials.gov, identifier: NCT02689765.

Visfatin associated with major adverse cardiovascular events in patients with acute myocardial infarction

BACKGROUND

Visfatin is an adipokine that related with the inflammation in atherosclerosis and the destabilization of atherosclerotic plaque. The aim of this study was to observe the relationship between visfatin and major adverse cardiovascular events (MACEs) in acute myocardial infarction (AMI) patients.

METHODS

We enrolled a total of 238 patients (183 AMI and 55 control) who underwent coronary angiography. Patients with AMI were followed for an average of 19.3 months and 159 patients were finally included in the study.

RESULTS

It was observed patients with AMI had higher serum visfatin levels than controls. The total incidence of MACEs was 11.32% (18/159) in AMI patients. After calculation of the Youden index, the best cut-off value of visfatin on the curve of receiver-operating characteristic was 8.799 ng/mL for predicting the occurrence of MACEs. The occurrence of MACEs was elevated in high-visfatin group (≥8.799 ng/mL) compared with low-visfatin group (≤8.799 ng/mL). The time to MACEs was correlated with visfatin (HR = 1.235, 95%CI 1.051-1.451, P = 0.01) and high-visfatin group had an earlier time to MACEs and a shorter time of cumulative survival.

CONCLUSIONS

Increased serum visfatin levels were observed in AMI patients, and correlated with an earlier onset and higher incidence of MACEs.

Structure-functional changes in eNAMPT at high concentrations mediate mouse and human beta cell dysfunction in type 2 diabetes

AIMS/HYPOTHESIS

Progressive decline in functional beta cell mass is central to the development of type 2 diabetes. Elevated serum levels of extracellular nicotinamide phosphoribosyltransferase (eNAMPT) are associated with beta cell failure in type 2 diabetes and eNAMPT immuno-neutralisation improves glucose tolerance in mouse models of diabetes. Despite this, the effects of eNAMPT on functional beta cell mass are poorly elucidated, with some studies having separately reported beta cell-protective effects of eNAMPT. eNAMPT exists in structurally and functionally distinct monomeric and dimeric forms. Dimerisation is essential for the NAD-biosynthetic capacity of NAMPT. Monomeric eNAMPT does not possess NAD-biosynthetic capacity and may exert distinct NAD-independent effects. This study aimed to fully characterise the structure-functional effects of eNAMPT on pancreatic beta cell functional mass and to relate these to beta cell failure in type 2 diabetes.

METHODS

CD-1 mice and serum from obese humans who were without diabetes, with impaired fasting glucose (IFG) or with type 2 diabetes (from the Body Fat, Surgery and Hormone [BodyFatS&H] study) or with or at risk of developing type 2 diabetes (from the VaSera trial) were used in this study. We generated recombinant wild-type and monomeric eNAMPT to explore the effects of eNAMPT on functional beta cell mass in isolated mouse and human islets. Beta cell function was determined by static and dynamic insulin secretion and intracellular calcium microfluorimetry. NAD-biosynthetic capacity of eNAMPT was assessed by colorimetric and fluorescent assays and by native mass spectrometry. Islet cell number was determined by immunohistochemical staining for insulin, glucagon and somatostatin, with islet apoptosis determined by caspase 3/7 activity. Markers of inflammation and beta cell identity were determined by quantitative reverse transcription PCR. Total, monomeric and dimeric eNAMPT and nicotinamide mononucleotide (NMN) were evaluated by ELISA, western blot and fluorometric assay using serum from non-diabetic, glucose intolerant and type 2 diabetic individuals.

RESULTS

eNAMPT exerts bimodal and concentration- and structure-functional-dependent effects on beta cell functional mass. At low physiological concentrations (~1 ng/ml), as seen in serum from humans without diabetes, eNAMPT enhances beta cell function through NAD-dependent mechanisms, consistent with eNAMPT being present as a dimer. However, as eNAMPT concentrations rise to ~5 ng/ml, as in type 2 diabetes, eNAMPT begins to adopt a monomeric form and mediates beta cell dysfunction, reduced beta cell identity and number, increased alpha cell number and increased apoptosis, through NAD-independent proinflammatory mechanisms.

CONCLUSIONS/INTERPRETATION

We have characterised a novel mechanism of beta cell dysfunction in type 2 diabetes. At low physiological levels, eNAMPT exists in dimer form and maintains beta cell function and identity through NAD-dependent mechanisms. However, as eNAMPT levels rise, as in type 2 diabetes, structure-functional changes occur resulting in marked elevation of monomeric eNAMPT, which induces a diabetic phenotype in pancreatic islets. Strategies to selectively target monomeric eNAMPT could represent promising therapeutic strategies for the treatment of type 2 diabetes.

New Insights into Adipokines as Potential Biomarkers for Type-2 Diabetes Mellitus

A large number of studies have been focused on investigating serum biomarkers associated with risk or diagnosis of type-2 diabetes mellitus. In the last decade, promising studies have shown that circulating levels of adipokines could be used as a relevant biomarker for diabetes mellitus progression as well as therapeutic future targets. Here, we discuss the possible use of recently described adipokines, including apelin, omentin-1, resistin, FGF-21, neuregulin-4 and visfatin, as early biomarkers for diabetes. In addition, we also include recent findings of other well known adipokines such as leptin and adiponectin. In conclusion, further studies are needed to clarify the pathophysiological significance and clinical value of these biological factors as potential biomarkers in type-2 diabetes and related dysfunctions.

Nicotinamide phosphoribosyltransferase aggravates inflammation and promotes atherosclerosis in ApoE knockout mice

Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme of nicotinamide adenine dinucleotide (NAD) salvage biosynthesis in mammals, and is involved in fundamental physiological processes and pathophysiology of many diseases. Thus far, however, the role of Nampt in atherosclerosis development is still in debate. In this study, we crossed global Nampt transgenic mice (Nampt-Tg) with a well-established atherosclerosis animal model (ApoE knockout mice, ApoE-/-) to generate ApoE-/-;Nampt-Tg mice and investigated the effects of Nampt overexpression on atherosclerosis development in ApoE-/- mice. Both ApoE-/- and ApoE-/-;Nampt-Tg mice were fed with a pro-atherosclerotic high-fat diet (HFD) for 16 weeks. Their serum lipid contents and atherosclerotic lesion were assessed. The results showed that there was no significant difference in body weight or serum levels of glucose, total cholesterol, triglycerides, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol between the two strains of mice, but ApoE-/-;Nampt-Tg mice had a significantly higher level of serum non-esterified fatty acid. Compared with ApoE-/- mice, ApoE-/-;Nampt-Tg mice displayed significantly increased atherosclerotic lesion area and thickness, lower collagen content, decreased collagen I/III ratio (collagen immaturation), increased number of apoptotic cells, and enhanced activities of caspase-3, caspase-8, and caspase-9. Moreover, macrophage infiltration (F4/80 staining), tumor necrosis factor signaling, and chemokines expression (ICAM-1 and CXCR-4) were all activated in aortic atherosclerotic plaque of ApoE-/-;Nampt-Tg mice compared with ApoE-/- mice. Our results provide in vivo evidence that Nampt transgene aggravates atherosclerotic inflammation and promotes atherosclerosis development in ApoE-/- mice.

The endocrine function of adipose tissues in health and cardiometabolic disease

In addition to their role in glucose and lipid metabolism, adipocytes respond differentially to physiological cues or metabolic stress by releasing endocrine factors that regulate diverse processes, such as energy expenditure, appetite control, glucose homeostasis, insulin sensitivity, inflammation and tissue repair. Both energy-storing white adipocytes and thermogenic brown and beige adipocytes secrete hormones, which can be peptides (adipokines), lipids (lipokines) and exosomal microRNAs. Some of these factors have defined targets; for example, adiponectin and leptin signal through their respective receptors that are expressed in multiple organs. For other adipocyte hormones, receptors are more promiscuous or remain to be identified. Furthermore, many of these hormones are also produced by other organs and tissues, which makes defining the endocrine contribution of adipose tissues a challenge. In this Review, we discuss the functional role of adipose tissue-derived endocrine hormones for metabolic adaptations to the environment and we highlight how these factors contribute to the development of cardiometabolic diseases. We also cover how this knowledge can be translated into human therapies. In addition, we discuss recent findings that emphasize the endocrine role of white versus thermogenic adipocytes in conditions of health and disease.

Adipocytokines in Rheumatoid Arthritis: The Hidden Link between Inflammation and Cardiometabolic Comorbidities

Rheumatoid arthritis is a chronic autoimmune disease affecting typically synovial joints and leading to progressive articular damage, disability, and reduced quality of life. Despite better recent therapeutic strategies improving long-term outcomes, RA is associated with a high rate of comorbidities, infections, malignancies, and cardiovascular disease (CVD). Remarkably, some well-known pathogenic proinflammatory mediators in RA, such as interleukin-1β (IL-1β) and tumor necrosis factor (TNF), may play a pivotal role in the development of CVD. Interestingly, different preclinical and clinical studies have suggested that biologic agents commonly used to treat RA patients may be effective in improving CVD. In this context, the contribution of adipocytokines has been suggested. Adipocytokines are pleiotropic molecules, mainly released by white adipose tissue and immune cells. Adipocytokines modulate the function of different tissues and cells, and in addition to energy homeostasis and metabolism, amplify inflammation, immune response, and tissue damage. Adipocytokines may contribute to the proinflammatory state in RA patients and development of bone damage. Furthermore, they could be associated with the occurrence of CVD. In this study, we reviewed available evidence about adipocytokines in RA, because of their involvement in disease activity, associated CVD, and possible biomarkers of prognosis and treatment outcome and because of their potential as a possible new therapeutic target.

The emergence of the nicotinamide riboside kinases in the regulation of NAD+ metabolism

The concept of replenishing or elevating NAD+ availability to combat metabolic disease and ageing is an area of intense research. This has led to a need to define the endogenous regulatory pathways and mechanisms cells and tissues utilise to maximise NAD+ availability such that strategies to intervene in the clinical setting are able to be fully realised. This review discusses the importance of different salvage pathways involved in metabolising the vitamin B3 class of NAD+ precursor molecules, with a particular focus on the recently identified nicotinamide riboside kinase pathway at both a tissue-specific and systemic level.

Cyanidin-3-O-β-glucoside regulates the activation and the secretion of adipokines from brown adipose tissue and alleviates diet induced fatty liver

AIM

Cyanidin-3-O-β-glucoside (Cy-3-G) the most abundant monomer of anthocyanins has multiple protective effects on many diseases. To date, whether Cy-3-G could regulate the function of brown adipose tissue (BAT) is still unclear and whether this regulation could influence the secretion of adipokines from BAT to prevent non-alcoholic fatty liver disease (NAFLD) indirectly remains to be explored. In this study we investigated the effect of Cy-3-G on BAT and the potential role of Cy-3-G to prevent fatty liver through regulating the secretion of BAT.

METHODS

Male C57BL/6 J mice were fed with a high fat high cholesterol (HFC) diet with or without 200 mg/kg B.W Cy-3-G for 8 weeks. In in vitro experiments, the differentiated brown adipocytes (BAC) and C3H10T1/2 clone8 cells were treated with 0.2 mM palmitate with or without Cy-3-G for 72 or 96 h. Then the culture media of C3H10T1/2 clone8 cells were collected for measuring the adipokines secretion by immunoblot assay and were applied to culture HepG2 cells or LO2 cells for 24 h. Lipid accumulation in HepG2 cells or LO2 cells were evaluated by oil red O staining.

RESULTS

Here we found that Cy-3-G regulated the activation of BAT and the expression of adipokines in BAT which were disrupted by HFC diet and alleviated diet induced fatty liver in mice. In in vitro experiments, Cy-3-G inhibited the release of adipokines including extracellular nicotinamide phosphoribosyltransferase (eNAMPT) and fibroblast growth factor 21 (FGF21) from differentiated C3H10T1/2 clone8 cells induced by palmitate, which was accompanied by a reduction of lipid accumulation in HepG2 cells and LO2 cells cultured by the corresponding collected media of C3H10T1/2 clone8 cells.

CONCLUSIONS

These results indicate that Cy-3-G can regulate the thermogenic and secretory functions of BAT. Furthermore, our data suggest that the protective effect of Cy-3-G on hepatic lipid accumulation is probably via regulating the secretion of adipokines from BAT.

Nesfatin-1 and visfatin expression is associated with reduced atherosclerotic disease risk in patients with rheumatoid arthritis

Nesfatin is an anti-inflammatory molecule that reduces atherosclerotic cardiovascular risk. By contrast, visfatin has pro-inflammatory properties and is pro-atherogenic. We examined the potential impact of nesfatin and visfatin on atherosclerotic disease in 232 (113 black and 119 white) consecutive rheumatoid arthritis (RA) patients from 2 centers. Independent relationships of nesfatin and visfatin concentrations with metabolic risk factors, endothelial activation, carotid atherosclerosis and altered plaque stability were determined in multivariable regression models. Rheumatoid factor (RF) positivity was associated with both nesfatin (β = 0.650, p < 0.0001) and visfatin levels (β = 0.157, p = 0.03). Visfatin concentrations were related to increased diastolic blood pressure (β = 4.536, p = 0.01) and diabetes prevalence (β = 0.092, p = 0.04). Nesfatin levels were associated with reduced carotid intima-media thickness (β = -0.017, p = 0.008). Nesfatin (β = 0.116, p = 0.001) and visfatin concentrations (β = 0.234, p = 0.001) were related to those of matrix metalloproteinase-2 (MMP-2), a plaque stability mediator. Nesfatin and visfatin concentrations were directly correlated (Spearman's rho = 0.516). The nesfatin-MMP-2 and visfatin-MMP-2 relations were both stronger in RF negative compared to RF positive patients (interaction p = 0.01 and p = 0.04, respectively). Nesfatin is associated with reduced atherosclerosis and increased plaque stability mediator levels in RA. Visfatin is related to adverse cardio-metabolic risk in RA. Increased MMP-2 expression in relation to visfatin may represent a compensatory mechanism aimed at reducing cardiovascular risk in RA.

NAD+ Intermediates: The Biology and Therapeutic Potential of NMN and NR

Research on the biology of NAD+ has been gaining momentum, providing many critical insights into the pathogenesis of age-associated functional decline and diseases. In particular, two key NAD+ intermediates, nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), have been extensively studied over the past several years. Supplementing these NAD+ intermediates has shown preventive and therapeutic effects, ameliorating age-associated pathophysiologies and disease conditions. Although the pharmacokinetics and metabolic fates of NMN and NR are still under intensive investigation, these NAD+ intermediates can exhibit distinct behavior, and their fates appear to depend on the tissue distribution and expression levels of NAD+ biosynthetic enzymes, nucleotidases, and presumptive transporters for each. A comprehensive concept that connects NAD+ metabolism to the control of aging and longevity in mammals has been proposed, and the stage is now set to test whether these exciting preclinical results can be translated to improve human health.

Can the skin make you fat? A role for the skin in regulating adipose tissue function and whole-body glucose and lipid homeostasis

Prevalence of obesity and related complications such as type 2 diabetes (T2D) has increased dramatically in recent decades. Metabolic complications of obesity arise in part due to subcutaneous adipose tissue (SAT) dysfunction. However, it is currently unclear why some obese individuals develop insulin resistance and T2D and others do not. In this review, we discuss the role of the skin in regulating SAT function, and whether presence of inflammatory skin diseases such as psoriasis represent a novel risk mechanism mediating development of obesity-related complications.

NAD+ : A key metabolic regulator with great therapeutic potential

Nicotinamide adenine dinucleotide (NAD⁺ ) is a ubiquitous metabolite that serves an essential role in the catabolism of nutrients. Recently, there has been a surge of interest in NAD⁺ biology, with the recognition that NAD⁺ influences many biological processes beyond metabolism, including transcription, signalling and cell survival. There are a multitude of pathways involved in the synthesis and breakdown of NAD⁺ , and alterations in NAD⁺ homeostasis have emerged as a common feature of a range of disease states. Here, we provide an overview of NAD⁺ metabolism and summarise progress on the development of NAD⁺ -related therapeutics.