Nicotinamide phosphoribosyltransferase inhibitor ameliorates mouse aging-induced cognitive impairment

Ablation of NAMPT in dopaminergic neurons leads to neurodegeneration and induces Parkinson's disease in mouse

Nicotinamide phosphoribosyltransferase (NAMPT) is the key enzyme in the salvaging synthesize pathway of nicotinamide adenine dinucleotide (NAD). The neuroprotective roles of NAMPT on neurodegeneration have been explored in aging brain and Alzheimer's Disease. However, its roles in Parkinson's Disease (PD) remain to be elucidated. We found that the dopaminergic neurons in substantia nigra expressed higher levels of NAMPT than the other types of neurons. Using conditional knockout of the Nampt gene in dopaminergic neurons and utilizing a NAMPT inhibitor in the substantia nigra of mice, we found that the NAMPT deficiency triggered the time-dependent loss of dopaminergic neurons, the impairment of the dopamine nigrostriatal pathway, and the development of PD-like motor dysfunction. In the rotenone-induced PD mouse model, nicotinamide ribose (NR), a precursor of NAD, rescued the loss of dopaminergic neurons, the impairment of dopamine nigrostriatal pathway, and mitigated PD-like motor dysfunction. In SH-SY5Y cells, NAD suppression induced the accumulation of reactive oxygen species (ROS), mitochondrial impairment, and cell death, which was reversed by N-acetyl cysteine, an antioxidant and ROS scavenger. Rotenone decreased NAD level, induced the accumulation of ROS and the impairment of mitochondria, which was reversed by NR. In summary, our findings show that the ablation of NAMPT in dopaminergic neurons leads to neurodegeneration and contributes to the development of PD. The NAD precursors have the potential to protect the degeneration of dopaminergic neurons, and offering a therapeutic approach for the treatment of PD.

The function of nicotinamide phosphoribosyl transferase (NAMPT) and its role in diseases

Nicotinamide phosphoribosyl transferase (NAMPT) is a rate-limiting enzyme in the mammalian nicotinamide adenine dinucleotide (NAD) salvage pathway, and plays a vital role in the regulation of cell metabolic activity, reprogramming, aging and apoptosis. NAMPT synthesizes nicotinamide mononucleotide (NMN) through enzymatic action, which is a key protein involved in host defense mechanism and plays an important role in metabolic homeostasis and cell survival. NAMPT is involved in NAD metabolism and maintains intracellular NAD levels. Sirtuins (SIRTs) are a family of nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylases (HDACs), the members are capable of sensing cellular NAD+ levels. NAMPT-NAD and SIRT constitute a powerful anti-stress defense system. In this paper, the structure, biological function and correlation with diseases of NAMPT are introduced, aiming to provide new ideas for the targeted therapy of related diseases.

eNAMPT is a novel therapeutic target for mitigation of coronary microvascular disease in type 2 diabetes

AIMS/HYPOTHESIS

Individuals with diabetes are at high risk of cardiovascular complications, which significantly increase morbidity/mortality. Coronary microvascular disease (CMD) is recognised as a critical contributor to the increased cardiac mortality observed in people with diabetes. Therefore, there is an urgent need for treatments that are specific to CMD. eNAMPT (extracellular nicotinamide phosphoribosyltransferase) is a damage-associated molecular pattern and TLR4 ligand, whose plasma levels are elevated in people with diabetes. This study was thus designed to investigate the pathogenic role of intracellular nicotinamide phosphoribosyltransferase (iNAMPT) and eNAMPT in promoting the development of CMD in a preclinical murine model of type 2 diabetes.

METHODS

An inducible type 2 diabetic mouse model was generated by a single injection of low-dose streptozocin (75 mg/kg, i.p.) combined with a high-fat diet for 16 weeks. The in vivo effects of i/eNAMPT inhibition on cardiac endothelial cell (CEC) function were evaluated by using Nampt+/- heterozygous mice, chronic administration of eNAMPT-neutralising monoclonal antibody (mAb) or use of an NAMPT enzymatic inhibitor (FK866).

RESULTS

As expected, diabetic wild-type mice exhibited significantly lower coronary flow velocity reserve (CFVR), a determinant of coronary microvascular function, compared with control wild-type mice. eNAMPT plasma levels or expression in CECs were significantly greater in diabetic mice than in control mice. Furthermore, in comparison with diabetic wild-type mice, diabetic Nampt+/- heterozygous mice showed markedly improved CFVR, accompanied by increased left ventricular capillary density and augmented endothelium-dependent relaxation (EDR) in the coronary artery. NAMPT inhibition by FK866 or an eNAMPT-neutralising mAb significantly increased CFVR in diabetic mice. Furthermore, administration of the eNAMPT mAb upregulated expression of angiogenesis- and EDR-related genes in CECs from diabetic mice. Treatment with either eNAMPT or NAD+ significantly decreased CEC migration and reduced EDR in coronary arteries, partly linked to increased production of mitochondrial reactive oxygen species.

CONCLUSIONS/INTERPRETATION

These data indicate that increased i/eNAMPT expression contributes to the development of diabetic coronary microvascular dysfunction, and provide compelling support for eNAMPT inhibition as a novel and effective therapeutic strategy for CMD in diabetes.

Preoperative plasma visfatin may have a dual effect on the occurrence of postoperative delirium

BACKGROUND

Visfatin is considered to be a "novel pro-inflammatory cytokine." Neuroinflammatory response is one of the important mechanisms of postoperative delirium (POD). The relationship between preoperative plasma visfatin and POD is unclear.

OBJECTIVE

To investigate the relationship between preoperative plasma visfatin concentrations and POD (primary outcome) in older hip fracture patients and to explore whether it affects POD through inflammatory factors.

MATERIALS AND METHODS

This prospective cohort study enrolled 176 elderly patients who were scheduled for hip fracture surgery. Preoperative plasma was collected on the morning of surgery, and visfatin levels were measured. Interleukin (IL)-1 and IL-6 were measured using patients' plasma collected on the first day after surgery. We used the 3-min diagnostic interview for Confusion Assessment Method-defined delirium (3D-CAM) twice daily within the 2 days after surgery to assess whether POD had occurred. Restricted cubic splines and piecewise regression were used to explore the relationship between preoperative plasma visfatin concentrations and POD, and further mediation analysis was used to verify whether visfatin plays a role in POD through regulating inflammatory factors.

RESULTS

The incidence of POD was 18.2%. A J-shaped association was observed between preoperative plasma visfatin levels and POD. The risk of POD decreased within the lower visfatin concentration range up to 37.87 ng/ml, with a hazard ratio of 0.59 per 5 ng/ml [odds ratio (OR) = 0.59, 95% confidence interval (CI) = 0.37-0.95], but the risk increased above this concentration (P for non-linearity < 0.001, with a hazard ratio of 1.116 per 10 ng/ml; OR = 1.10, 95% CI = 1.02-1.23). Mediation effect analysis showed that when the plasma visfatin concentration was higher than 37.87 ng/ml, the effect of visfatin on POD was mediated by IL-6 (p < 0.01). A significant indirect association with postoperative plasma IL-6 was observed between preoperative plasma visfatin and POD (adjusted β = 0.1%; 95% CI = 4.8∼38.9%; p < 0.01).

CONCLUSION

Visfatin is the protective factor in POD when the preoperative plasma visfatin concentration is below 37.87 ng/ml, but when it exceeds 37.87 ng/ml, the visfatin concentration is a risk factor for POD, which is mediated by postoperative plasma IL-6. The results suggest that preoperative visfatin may have a dual effect on the POD occurrence.

CLINICAL TRIAL REGISTRATION

[www.ClinicalTrials.gov], identifier [ChiCTR21 00052674].

From Rate-Limiting Enzyme to Therapeutic Target: The Promise of NAMPT in Neurodegenerative Diseases

Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme in the nicotinamide adenine dinucleotide (NAD) salvage pathway in mammals. It is of great significance in the metabolic homeostasis and cell survival via synthesizing nicotinamide mononucleotide (NMN) through enzymatic activities, serving as a key protein involved in the host's defense mechanism. The NAMPT metabolic pathway connects NAD-dependent sirtuin (SIRT) signaling, constituting the NAMPT-NAD-SIRT cascade, which is validated as a strong intrinsic defense system. Neurodegenerative diseases belong to the central nervous system (CNS) disease that seriously endangers human health. The World Health Organization (WHO) proposed that neurodegenerative diseases will become the second leading cause of human death in the next two decades. However, effective drugs for neurodegenerative diseases are scant. NAMPT is specifically highly expressed in the hippocampus, which mediates cell self-renewal and proliferation and oligodendrocyte synthesis by inducing the biosynthesis of NAD in neural stem cells/progenitor cells. Owing to the active biological function of NAMPT in neurogenesis, targeting NAMPT may be a powerful therapeutic strategy for neurodegenerative diseases. This study aims to review the structure and biological functions, the correlation with neurodegenerative diseases, and treatment advance of NAMPT, aiming to provide a novel idea for targeted therapy of neurodegenerative diseases.

mTOR-mediated autophagy in the hippocampus is involved in perioperative neurocognitive disorders in diabetic rats

Introduction

Perioperative neurocognitive disorders (PND) are common neurological complications after surgery. Diabetes mellitus (DM) has been reported to be an independent risk factor for PND, but little is known about its mechanism of action. Mammalian target of rapamycin (mTOR) signaling is crucial for neuronal growth, development, apoptosis, and autophagy, but the dysregulation of mTOR signaling leads to neurological disorders. The present study investigated whether rapamycin can attenuate PND by inhibiting mTOR and activating autophagy in diabetic rats.

Methods

Male diabetic Sprague‐Dawley rats underwent tibial fracture surgery under isoflurane anesthesia to establish a PND model. Cognitive functions were examined using the Morris water maze test. The levels of phosphorylated mTOR (p‐mTOR), phosphorylated tau (p‐tau), autophagy‐related proteins (Beclin‐1, LC3), and apoptosis‐related proteins (Bax, Bcl‐2, cleaved caspase‐3) in the hippocampus were examined on postoperative days 3, 7, and 14 by Western blot. Hippocampal amyloid β (Aβ) levels were examined by immunohistochemistry.

Results

The data showed that surgical trauma and/or DM impaired cognitive function, induced mTOR activation, and decreased Beclin‐1 levels and the LC3‐II/I ratio. The levels of Aβ and p‐tau and the hippocampal apoptotic responses were significantly higher in diabetic or surgery‐treated rats than in control rats and were further increased in diabetic rats subjected to surgery. Pretreatment of rats with rapamycin inhibited mTOR hyperactivation and restored autophagic function, effectively decreasing tau hyperphosphorylation, Aβ deposition, and apoptosis in the hippocampus. Furthermore, surgical trauma‐induced neurocognitive disorders were also reversed by pretreatment of diabetic rats with rapamycin.

Conclusion

The results demonstrate that mTOR hyperactivation regulates autophagy, playing a critical role in the mechanism underlying PND, and reveal that the modulation of mTOR signaling could be a promising therapeutic strategy for PND in patients with diabetes.