Targeting NAD+ in Metabolic Disease: New Insights Into an Old Molecule

Oxygen-Dependent Interactions between the Ruthenium Cage and the Photoreleased Inhibitor in NAMPT-Targeted Photoactivated Chemotherapy

Photoactivated chemotherapy agents form a new branch of physically targeted anticancer agents with potentially lower systemic side effects for patients. On the other hand, limited information exists on the intracellular interactions between the photoreleased metal cage and the photoreleased anticancer inhibitor. In this work, we report a new biological study of the known photoactivated compound Ru-STF31 in the glioblastoma cancer cell line, U87MG. Ru-STF31 targets nicotinamide phosphoribosyltransferase (NAMPT), an enzyme overexpressed in U87MG. Ru-STF31 is activated by red light irradiation and releases two photoproducts: the ruthenium cage and the cytotoxic inhibitor STF31. This study shows that Ru-STF31 can significantly decrease intracellular NAD+ levels in both normoxic (21% O2) and hypoxic (1% O2) U87MG cells. Strikingly, NAD+ depletion by light activation of Ru-STF31 in hypoxic U87MG cells could not be rescued by the addition of extracellular NAD+. Our data suggest an oxygen-dependent active role of the ruthenium photocage released by light activation.

Hepatic steatosis induced by nicotine plus Coca-Cola™ is prevented by nicotinamide riboside (NR)

Introduction

Cigarettes containing nicotine (Nic) are a risk factor for the development of cardiovascular and metabolic diseases. We reported that Nic delivered via injections or e-cigarette vapor led to hepatic steatosis in mice fed with a high-fat diet. High-fructose corn syrup (HFCS) is the main sweetener in sugar-sweetened beverages (SSBs) in the US. Increased consumption of SSBs with HFCS is associated with increased risks of non-alcoholic fatty liver disease (NAFLD). Nicotinamide riboside (NR) increases mitochondrial nicotinamide adenine dinucleotide (NAD+) and protects mice against hepatic steatosis. This study evaluated if Nic plus Coca-Cola™ (Coke) with HFCS can cause hepatic steatosis and that can be protected by NR.

Methods

C57BL/6J mice received twice daily intraperitoneal (IP) injections of Nic or saline and were given Coke (HFCS), or Coke with sugar, and NR supplementation for 10 weeks.

Results

Our results show that Nic+Coke caused increased caloric intake and induced hepatic steatosis, and the addition of NR prevented these changes. Western blot analysis showed lipogenesis markers were activated (increased cleavage of the sterol regulatory element-binding protein 1 [SREBP1c] and reduction of phospho-Acetyl-CoA Carboxylase [p-ACC]) in the Nic+Coke compared to the Sal+Water group. The hepatic detrimental effects of Nic+Coke were mediated by decreased NAD+ signaling, increased oxidative stress, and mitochondrial damage. NR reduced oxidative stress and prevented mitochondrial damage by restoring protein levels of Sirtuin1 (Sirt1) and peroxisome proliferator-activated receptor coactivator 1-alpha (PGC1) signaling.

Conclusion

We conclude that Nic+Coke has an additive effect on producing hepatic steatosis, and NR is protective. This study suggests concern for the development of NAFLD in subjects who consume nicotine and drink SSBs with HFCS.

Nuclear Nicotinamide Adenine Dinucleotide Deficiency by Nmnat1 Deletion Impaired Hepatic Insulin Signaling, Mitochondrial Function, and Hepatokine Expression in Mice Fed a High-Fat Diet

Metabolic syndrome (MetS) is a worldwide challenge that is closely associated with obesity, nonalcoholic liver disease, insulin resistance, and type 2 diabetes. Boosting nicotinamide adenine dinucleotide (NAD+) presents great potential in preventing MetS. However, the function of nuclear NAD+ in the development of MetS remains poorly understood. In this study, hepatocyte-specific Nmnat1 knockout mice were used to determine a possible link between nuclear NAD+ and high-fat diet (HFD)-induced MetS. We found that Nmnat1 knockout significantly reduced hepatic nuclear NAD+ levels but did not exacerbate HFD-induced obesity and hepatic triglycerides accumulation. Interestingly, loss of Nmnat1 caused insulin resistance. Further analysis revealed that Nmnat1 deletion promoted gluconeogenesis but inhibited glycogen synthesis in the liver. Moreover, Nmnat1 deficiency induced mitochondrial dysfunction by decreasing mitochondrial DNA (mtDNA)-encoded complexes Ⅰ and Ⅳ, suppressing mtDNA replication and mtRNA transcription and reducing mtDNA copy number. In addition, Nmnat1 depletion affected the expression of hepatokines in the liver, particularly downregulating the expression of follistatin. These findings highlight the importance of nuclear NAD+ in maintaining insulin sensitivity and provide insights into the mechanisms underlying HFD-induced insulin resistance.

From bacteria to biomedicine: Developing therapies exploiting NAD+ metabolism

Nicotinamide adenine dinucleotide (NAD+) serves as a critical cofactor in cellular metabolism and redox reactions. Bacterial pathways rely on NAD+ participation, where its stability and concentration govern essential homeostasis and functions. This review delves into the role and metabolic regulation of NAD+ in bacteria, highlighting its influence on physiology and virulence. Notably, we explore enzymes linked to NAD+ metabolism as antibacterial drug targets and vaccine candidates. Moreover, we scrutinize NAD+'s medical potential, offering insights for its application in biomedicine. This comprehensive assessment informs future research directions in the dynamic realm of NAD+ and its biomedical significance.

Effects of NAD+ precursors on blood pressure, C-reactive protein concentration and carotid intima-media thickness: A meta-analysis of randomized controlled trials

BACKGROUND

There are contradictory effects regarding the effect of NAD+ precursor on blood pressure and inflammation. In order to obtain a better viewpoint from them, this study aimed to comprehensively investigate the effects of NAD+ precursor supplementation on blood pressure, C-reactive protein (CRP) and carotid intima-media thickness (CIMT).

METHODS

PubMed/MEDLINE, Web of Science, SCOPUS and Embase databases were searched using standard keywords to identify all controlled trials investigating the effects of NAD+ precursor on blood pressure, CRP and CIMT. Pooled weighted mean difference (WMD) and 95% confidence intervals (95% CI) were achieved by random-effects model analysis for the best estimation of outcomes.

RESULTS

Twenty-nine articles (with 8664 participants) were included in this article. Results from meta-analyses of RCTs from random-effects models indicated a significant reduction in systolic (SBP) (weighted mean difference (WMD): -2.54 mmHg, p < .001) and diastolic blood pressure (DBP) (WMD: -2.15 mmHg, p < .001), as well as in CRP (WMD: -.93 mg/L, 95% CI -1.47 to -.40, p < .001) concentrations and CIMT (WMD: -.01 mm, 95% CI -.02 to -.00, p = .005) with the NAD+ precursors supplementation compared with the control group. In addition, a greater effect of supplementation with NAD+ precursors in reducing blood pressure (BP) were observed with the highest dose (≥2 g) and duration of the intervention (>12 weeks), as well as with NA supplementation when compared to NE.

CONCLUSIONS

Overall, these findings suggest that NAD+ precursor supplementation might have a beneficial effect on cardiovascular risk factors such as BP, CRP concentration and CIMT.

The effects of NAD+ precursor (nicotinic acid and nicotinamide) supplementation on weight loss and related hormones: a systematic review and meta-regression analysis of randomized controlled trials

Background

Despite the fact that obesity and overweight are serious major health problems worldwide, fighting against them is also considered a challenging issue. Several interventional studies have evaluated the potential weight-reduction effect of nicotinamide adenine dinucleotide (NAD+) precursor. In order to obtain a better viewpoint from them, this study aimed to comprehensively investigate the effects of NAD+ precursor supplementation on weight loss, adiponectin, and leptin.

Methods

Scopus, PubMed/Medline, Web of Science, Cochrane, and Embase databases were searched using standard keywords to identify all controlled trials investigating the weight loss and related hormones effects of NAD+ precursor. Pooled weighted mean difference and 95% confidence intervals were achieved by random-effects model analysis for the best estimation of outcomes.

Results

Twenty two treatment arms with 5,144 participants' were included in this systematic review and meta-regression analysis. The pooled findings showed that NAD+ precursor supplementation has an effect on lowering BMI (weighted mean difference (WMD): -0.19 kg/m2, 95% confidence interval (CI): -0.29 to -0.09, p < 0.001) and increasing adiponectin (WMD: 1.59 μg/mL, 95% CI: 0.49 to 2.68, p = 0.004) in humans compared with control groups. However, no significant effect was observed on body weight and leptin. There was a significant relationship between doses of intervention with changes in BMI. In addition, subgroup analysis showed that BMI reduction was greater when receiving nicotinic acid (NA) supplementation than nicotinamide (NE) supplementation.

Conclusion

NAD+ precursor had significant effects on weight management with the reduction of BMI and increasing adiponectin.

Elevation of NAD+ by nicotinamide riboside spares spinal cord tissue from injury and promotes locomotor recovery

Spinal cord injury (SCI)-induced tissue damage spreads to neighboring spared cells in the hours, days, and weeks following injury, leading to exacerbation of tissue damage and functional deficits. Among the biochemical changes is the rapid reduction of cellular nicotinamide adenine dinucleotide (NAD+), an essential coenzyme for energy metabolism and an essential cofactor for non-redox NAD+-dependent enzymes with critical functions in sensing and repairing damaged tissue. NAD+ depletion propagates tissue damage. Augmenting NAD+ by exogenous application of NAD+, its synthesizing enzymes, or its cellular precursors mitigates tissue damage. Nicotinamide riboside (NR) is considered to be one of the most promising NAD+ precursors for clinical application due to its ability to safely and effectively boost cellular NAD+ synthesis in rats and humans. Moreover, various preclinical studies have demonstrated that NR can provide tissue protection. Despite these promising findings, little is known about the potential benefits of NR in the context of SCI. In the current study, we tested whether NR administration could effectively increase NAD+ levels in the injured spinal cord and whether this augmentation of NAD+ would promote spinal cord tissue protection and ultimately lead to improvements in locomotor function. Our findings indicate that administering NR (500 mg/kg) intraperitoneally from four days before to two weeks after a mid-thoracic contusion-SCI injury, effectively doubles NAD+ levels in the spinal cord of Long-Evans rats. Moreover, NR administration plays a protective role in preserving spinal cord tissue post-injury, particularly in neurons and axons, as evident from the observed gray and white matter sparing. Additionally, it enhances motor function, as evaluated through the BBB subscore and missteps on the horizontal ladderwalk. Collectively, these findings demonstrate that administering NR, a precursor of NAD+, increases NAD+ within the injured spinal cord and effectively mitigates the tissue damage and functional decline that occurs following SCI.

Both prolonged high-fat diet consumption and calorie restriction boost hepatic NAD+ metabolism in mice

Hepatic NAD+ homeostasis is essential to metabolic flexibility upon energy balance challenges. The molecular mechanism is unclear. This study aimed to determine how the enzymes involved in NAD+ salvage (Nampt, Nmnat1, Nrk1), clearance (Nnmt, Aox1, Cyp2e1), and consumption pathways (Sirt1, Sirt3, Sirt6, Parp1, Cd38) were regulated in the liver upon energy overload or shortage, as well as their relationships with glucose and lipid metabolism. Male C57BL/6N mice were fed ad libitum with the CHOW diet, high-fat diet (HFD), or subjected to 40% calorie restriction (CR) CHOW diet for 16 weeks respectively. HFD feeding increased hepatic lipids content and inflammatory markers, while lipids accumulation was not changed by CR. Both HFD feeding and CR elevated the hepatic NAD+ levels, as well as gene and protein levels of Nampt and Nmnat1. Furthermore, both HFD feeding and CR lowered acetylation of PGC-1α in parallel with the reduced hepatic lipogenesis and enhanced fatty acid oxidation, while CR enhanced hepatic AMPK activity and gluconeogenesis. Hepatic Nampt and Nnmt gene expression negatively correlated with fasting plasma glucose levels concomitant with positive correlations with Pck1 gene expression. Nrk1 and Cyp2e1 gene expression positively correlated with fat mass and plasma cholesterol levels, as well as Srebf1 gene expression. These data highlight that hepatic NAD+ metabolism will be induced for either the down-regulation of lipogenesis upon over nutrition or up-regulation of gluconeogenesis in response to CR, thus contributing to the hepatic metabolic flexibility upon energy balance challenges.

The TAS1R2 sweet taste receptor regulates skeletal muscle mass and fitness

Muscle fitness and mass deteriorate under the conditions of obesity and aging for reasons yet to be fully elucidated. Herein, we describe a novel pathway linking peripheral nutrient sensing and skeletal muscle function through the sweet taste receptor TAS1R2 and the involvement of ERK2-PARP1-NAD signaling axis. Muscle-specific deletion of TAS1R2 (mKO) in mice produced elevated NAD levels due to suppressed PARP1 activity, improved mitochondrial function, increased muscle mass and strength, and prolonged running endurance. Deletion of TAS1R2 in obese or aged mice also ameliorated the decline in muscle mass and fitness arising from these conditions. Remarkably, partial loss-of-function of TAS1R2 (rs35874116) in older, obese humans recapitulated the healthier muscle phenotype displayed by mKO mice in response to exercise training. Our findings show that inhibition of the TAS1R2 signaling in skeletal muscle is a promising therapeutic approach to preserve muscle mass and function.

A novel magnetic fluid for ultra-fast and highly efficient extraction of N1-methylnicotinamide in urine samples

Among the three pre-treatment materials, Fe3O4@HPMC@DMSA NPs were selected to be the best material and were used to perform MSPE-HPLC-UV.

Nicotinamide adenine dinucleotide reduced (NADH) is a natural UV filter of certain bird lens

In this work, we for the first time report the identification of UV filters in the bird eye lens. We found that lenses of some raptors (black kite, common buzzard) and waterfowl (birds from Podicipedidae family) contain unusually high levels of reduced nicotinamide adenine dinucleotide (NADH)—a compound with high absorption in the UV-A range with a maximum at 340 nm. The lens metabolome of these birds also features an extremely low [NAD +]/[NADH] ratio. Chemometric analysis demonstrates that the differences between the metabolomic compositions of lenses with low and high NADH abundances should be attributed to the taxonomic features of bird species rather to the influence of the low [NAD +]/[NADH] ratio. We attributed this observation to the low metabolic activity in lens fiber cells, which make up the bulk of the lens tissue. Photochemical measurements show that properties of NADH as a UV filter are as good as that of UV filters in the human lens, including strong absorption in the UV-A spectral region, high photostability under both aerobic and anaerobic conditions, low yields of triplet state, fluorescence, and radicals under irradiation. Lenticular UV filters protect the retina and the lens from photo-induced damages and improve the visual acuity by reducing chromatic aberrations; therefore, the results obtained contribute to our understanding of the extremely high acuity of the raptor vision.

Nicotinamide mononucleotide ameliorates adriamycin-induced renal damage by epigenetically suppressing the NMN/NAD consumers mediated by Twist2

The activation of nicotinamide adenine dinucleotide (NAD⁺)-dependent deacetylase, Sirt1, after the administration of nicotinamide mononucleotide (NMN) suppresses many diseases. However, the role of NMN and Sirt1 in focal glomerulosclerosis (FSGS) has not yet been elucidated. This study aimed to assess the protective effect of NMN treatment in mice with adriamycin (ADR)-induced FSGS.　Transient short-term NMN treatment was administered to 8-week-old ADR- or saline-treated BALB/c mice (Cont group) for 14 consecutive days. NMN alleviated the increase in urinary albumin excretion in the ADR-treated mice. NMN treatment mitigated glomerulosclerosis and ameliorated the reduced Sirt1 expression and elevated Claudin-1 expression in the kidneys of the mice. Moreover, this treatment improved the decrease in histone methylation and the expression level of Dnmt1 and increased the concentration of NAD⁺ in the kidney. Dnmt1 epigenetically suppressed the expression of the NMN-consuming enzyme nicotinamide mononucleotide adenyltransferase1 (Nmnat1) by methylating the E-box in the promoter region and repressing the NAD-consuming enzyme PARP1. Additionally, NMN downregulated the expression of Nmnat1 in the ADR-treated mice. Short-term NMN treatment in FSGS has epigenetic renal protective effects through the upregulation of Sirt1 and suppression of the NAD and NMN consumers. The present study presents a novel treatment paradigm for FSGS.

Effects of in ovo injection of nicotinamide riboside on high-yield broiler myogenesis

The objective of this study was to determine the effects of in ovo injection of high-yield broiler embryos with nicotinamide riboside (NR) on pectoralis major muscle (PMM) development, growth, and gene expression. Fertilized Cobb 700 broiler eggs were randomly assigned to one of four treatments within a 2 × 2 factorial design. Factor 1 consisted of NR dose (DOS) with eggs receiving 0 or 2.5 mM NR. Factor 2 consisted of injection location (LOC), with treatments injected into either the yolk sac or albumen. At day 10 of incubation, 100 μL of the assigned NR dose was injected into the yolk sac of the developing embryo and chicks were euthanized within 24 h of hatching. Chick PMM and individual fiber morphometrics, and expression of genes associated with cell cycle progression were analyzed. There were DOS × LOC interactions for hatched chick PM weight and length (P < 0.04). When NR was injected into the albumen, PMM weight decreased (P < 0.05); when NR was injected into the yolk, PMM weight increased (P < 0.05). Pectoralis major length was not affected (P > 0.05) when NR was injected into the albumen but was increased (P < 0.05) when NR was injected into the yolk. There was a DOS × LOC interaction (P = 0.04) for muscle fiber density and tended to be a DOS × LOC interaction (P = 0.07) for muscle fiber CSA. Pectoralis major muscle fiber density was not affected when NR was injected into the albumen (P > 0.05), but density increased when NR was injected into the yolk (P < 0.05). There were DOS × LOC interactions for hatched chick COXII, cyclin D, and SIRT1 expression (P ≤ 0.04), which may indicate NR improves skeletal muscle development and growth by enhancing myoblast proliferation during embryonic development.

Nicotinamide supplementation in diabetic nonalcoholic fatty liver disease patients: randomized controlled trial

Background:

Nicotinamide has been reported to protect against liver steatosis and metabolic imbalances in nonalcoholic fatty liver disease (NAFLD) in animal models.

Objectives:

The objective was to investigate the efficacy and safety of nicotinamide supplementation in diabetic NAFLD patients.

Design:

This is a prospective randomized controlled open label study.

Methods:

Seventy diabetic NAFLD patients were randomly assigned either to the nicotinamide group (n = 35) who received nicotinamide 1000 mg once daily for 12 weeks in addition to their antidiabetic therapy or the control group (n = 35) who received their antidiabetic therapy only. The primary outcome was improvement in steatosis score, while secondary outcomes included assessment of liver stiffness, liver enzymes, lipid profile, insulin resistance, serum malondialdehyde, serum adiponectin, and patients’ quality of life (QOL).

Results:

Only 61 patients completed the study; 31 in the nicotinamide group and 30 in the control group. Comparisons between groups and within groups revealed nonsignificant changes in steatosis and fibrosis scores. However, significant reduction was observed in liver enzymes with a median decrease in alanine transaminase of 26.6% versus 0.74% in nicotinamide and control groups, respectively. After 12 weeks of treatment, the nicotinamide group showed significantly lower levels of low-density lipoprotein cholesterol (p value = 0.004), total cholesterol (p value = 0.006), and insulin resistance marker (p value = 0.005) compared with control. Serum triglycerides, malondialdehyde, and adiponectin levels were all comparable between the two groups. Regarding QOL, a significant improvement was detected in the total scores and the activity and fatigue domains scores.

Conclusion:

Nicotinamide at a dose of 1000 mg daily was tolerable, improved metabolic abnormalities and QOL of diabetic NAFLD patients with no effect on liver fibrosis or steatosis.

Trial Registration:

The study was registered at clinicaltrials.gov and given the ID number: ‘NCT03850886’. https://clinicaltrials.gov/ct2/show/NCT03850886.

Altered Plasma Mitochondrial Metabolites in Persistently Symptomatic Individuals after a GBCA-Assisted MRI

Despite the impressive safety of gadolinium (Gd)-based contrast agents (GBCAs), a small number of patients report the onset of new, severe, ongoing symptoms after even a single exposure—a syndrome termed Gadolinium Deposition Disease (GDD). Mitochondrial dysfunction and oxidative stress have been repeatedly implicated by animal and in vitro studies as mechanisms of Gd/GBCA-related toxicity, and as pathogenic in other diseases with similarities in presentation. Here, we aimed to molecularly characterize and explore potential metabolic associations with GDD symptoms. Detailed clinical phenotypes were systematically obtained for a small cohort of individuals (n = 15) with persistent symptoms attributed to a GBCA-enhanced MRI and consistent with provisional diagnostic criteria for GDD. Global untargeted mass spectroscopy-based metabolomics analyses were performed on plasma samples and examined for relevance with both single marker and pathways approaches. In addition to GDD criteria, frequently reported symptoms resembled those of patients with known mitochondrial-related diseases. Plasma differences compared to a healthy, asymptomatic reference cohort were suggested for 45 of 813 biochemicals. A notable proportion of these are associated with mitochondrial function and related disorders, including nucleotide and energy superpathways, which were over-represented. Although early evidence, coincident clinical and biochemical indications of potential mitochondrial involvement in GDD are remarkable in light of preclinical models showing adverse Gd/GBCA effects on multiple aspects of mitochondrial function. Further research on the potential contributory role of these markers and pathways in persistent symptoms attributed to GBCA exposure is recommended.

Molecular markers of DNA repair and brain metabolism correlate with cognition in centenarians

Oxidative stress is an important factor in age-associated neurodegeneration. Accordingly, mitochondrial dysfunction and genomic instability have been considered as key hallmarks of aging and have important roles in age-associated cognitive decline and neurodegenerative disorders. In order to evaluate whether maintenance of cognitive abilities at very old age is associated with key hallmarks of aging, we measured mitochondrial bioenergetics, mitochondrial DNA copy number and DNA repair capacity in peripheral blood mononuclear cells from centenarians in a Danish 1915 birth cohort (n = 120). Also, the circulating levels of brain-derived neurotrophic factor, NAD⁺ /NADH and carbonylated proteins were measured in plasma of the centenarians and correlated to cognitive capacity. Mitochondrial respiration was well preserved in the centenarian cohort when compared to young individuals (21-35 years of age, n = 33). When correlating cognitive performance of the centenarians with mitochondrial function such as basal respiration, ATP production, reserve capacity and maximal respiration, no overall correlations were observed, but when stratifying by sex, inverse associations were observed in the males (p < 0.05). Centenarians with the most severe cognitive impairment displayed the lowest activity of the central DNA repair enzyme, APE1 (p < 0.05). A positive correlation between cognitive capacity and levels of NAD⁺ /NADH was observed (p < 0.05), which may be because NAD⁺ /NADH consuming enzyme activities strive to reduce the oxidative DNA damage load. Also, circulating protein carbonylation was lowest in centenarians with highest cognitive capacity (p < 0.05). An opposite trend was observed for levels of brain-derived neurotrophic factor (p = 0.17). Our results suggest that maintenance of cognitive capacity at very old age may be associated with cellular mechanisms related to oxidative stress and DNA metabolism.

NAMPT-mediated NAD+ biosynthesis suppresses activation of hepatic stellate cells and protects against CCl4-induced liver fibrosis in mice

Background: Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step in the salvage pathway of mammalian nicotinamide adenine dinucleotide (NAD⁺) biosynthesis. Through its NAD⁺-biosynthetic activity, NAMPT is able to regulate the development of hepatic steatosis and inflammation induced by diet or alcohol. However, the roles NAMPT plays in the development of liver fibrosis remain obscure. Purpose: To investigate the roles of NAMPT-mediated NAD⁺ biosynthesis in hepatic stellate cell (HSC) activation and liver fibrosis. Research Design: Realtime RT-PCR and western blot analyses were performed to analyze the expression of profibrogenic genes. Sirius red staining was conducted to examine the fibrosis in liver. Mouse liver fibrosis was induced by intraperitoneal injection of carbon tetrachloride (CCl₄) 2 times a week for 6 weeks. Adenovirus-mediated NAMPT overexpression or nicotinamide mononucleotide (NMN) administration was carried out to study the effects of elevation of NAD⁺ levels on protecting CCl₄-induced liver fibrosis in mice. LX2 cells or primary HSCs were used to study the role of NAMPT overexpression or NMN treatment in reducing profibrogenic gene expression in vitro. ResultsCCl₄ administration suppresses NAMPT expression in liver and reduces hepatic NAD⁺ content. Tgfβ1 treatment decreases intracellular NAD⁺ levels and NAMPT expression in LX2 cells. Adenovirus-mediated NAMPT overexpression augments liver NAD⁺ levels, inhibits HSC activation and alleviates CCl₄-induced liver fibrosis in mice. Administration of NMN also suppresses HSC activation and protects against CCl₄-induced liver fibrosis in mice. Conclusions: NAMPT-mediated NAD⁺ biosynthesis inhibits HSC activation and protects against CCl₄-induced liver fibrosis.

Vitamin D3 potentiates the nephroprotective effects of vildagliptin-metformin combination in a rat model of metabolic syndrome

The current study was conducted to investigate the nephroprotective effects of vildagliptin-metformin combination in an experimental model of fructose/salt-induced metabolic syndrome (MetS). A major aim was to evaluate the potential capacity of vitamin D3 to potentiate the pleiotropic nephroprotective effects of vildagliptin-metformin combination. MetS was induced in adult male Wistar rats by adding fructose (10%) to everyday drinking water and salt (3%) to the diet for 6 weeks. Along with the same concentrations of fructose/salt feeding, MetS rats were then treated orally with either vildagliptin (10 mg/kg/day)-metformin (200 mg/kg/day) combination, vitamin D3 (10 μg/kg/day), or the triple therapy for a further 6 weeks. The incidence of MetS was confirmed 6 weeks after fructose/salt consumption, when the rats exhibited significant weight gain, dyslipidemia, hyperuricemia, insulin resistance, hyperinsulinemia, and impaired glucose tolerance. At the end of the 12-week experimental period, MetS rats displayed significantly deteriorated renal function, enhanced intrarenal oxidative stress and inflammation together with exaggerated renal histopathological damages and interstitial fibrosis. The study has corroborated antioxidant, anti-inflammatory, and antifibrotic effects of vildagliptin-metformin combination, vitamin D3, and the triple collaborative therapy, conferring renoprotection in the setting of MetS. Due attention has been paid to the crucial role of dipeptidyl peptidase-4 inhibition and sirtuin-1/5' adenosine monophosphate-activated protein kinase activation as novel therapeutic targets to optimize renoprotection. The apparent potentiating effect, evoked upon coadministration of vitamin D3 with vildagliptin-metformin combination, may provide a cornerstone for further clinical investigations.

CD20 as a gatekeeper of the resting state of human B cells

Worldwide about one million patients are given anti-CD20 antibodies such as rituximab (RTX) for the treatment of B cell-associated diseases. Despite the success of this first therapeutic antibody, little is known about the function of its target. The role of CD20 only becomes clear in the context of the nanoscale compartmentalization of the B lymphocyte membrane. We found that CD20 is an organizer of the IgD-class nanocluster on the B cell membrane. The loss of CD20 on human B cells results in a dissolution of the IgD-class nanocluster and a transient B cell activation inducing a B cell-to-PC differentiation. Thus, CD20 is an essential gatekeeper of a membrane nanodomain and the resting state of naive B cells.

CD20 is a B cell-specific membrane protein and represents an attractive target for therapeutic antibodies. Despite widespread usage of anti-CD20 antibodies for B cell depletion therapies, the biological function of their target remains unclear. Here, we demonstrate that CD20 controls the nanoscale organization of receptors on the surface of resting B lymphocytes. CRISPR/Cas9-mediated ablation of CD20 in resting B cells resulted in relocalization and interaction of the IgM-class B cell antigen receptor with the coreceptor CD19. This receptor rearrangement led to a transient activation of B cells, accompanied by the internalization of many B cell surface marker proteins. Reexpression of CD20 restored the expression of the B cell surface proteins and the resting state of Ramos B cells. Similarly, treatment of Ramos or naive human B cells with the anti-CD20 antibody rituximab induced nanoscale receptor rearrangements and transient B cell activation in vitro and in vivo. A departure from the resting B cell state followed by the loss of B cell identity of CD20-deficient Ramos B cells was accompanied by a PAX5 to BLIMP-1 transcriptional switch, metabolic reprogramming toward oxidative phosphorylation, and a shift toward plasma cell development. Thus, anti-CD20 engagement or the loss of CD20 disrupts membrane organization, profoundly altering the fate of human B cells.

Pre-emptive Short-term Nicotinamide Mononucleotide Treatment in a Mouse Model of Diabetic Nephropathy

BACKGROUND

The activation of NAD⁺-dependent deacetylase, Sirt1, by the administration of nicotinamide mononucleotide (NMN) ameliorates various aging-related diseases.

METHODS

Diabetic db/db mice were treated with NMN transiently for 2 weeks and observed for effects on diabetic nephropathy (DN).

RESULTS

At 14 weeks after the treatment period, NMN attenuated the increases in urinary albumin excretion in db/db mice without ameliorating hemoglobin A1c levels. Short-term NMN treatment mitigated mesangium expansion and foot process effacement, while ameliorating decreased Sirt1 expression and increased claudin-1 expression in the kidneys of db/db mice. This treatment also improved the decrease in the expression of H3K9me2 and DNMT1. Short-term NMN treatment also increased kidney concentrations of NAD⁺ and the expression of Sirt1 and nicotinamide phosphoribosyltransferase (Nampt), and it maintained nicotinamide mononucleotide adenyltransferase1 (Nmnat1) expression in the kidneys. In addition, survival rates improved after NMN treatment.

CONCLUSIONS

Short-term NMN treatment in early-stage DN has remote renal protective effects through the upregulation of Sirt1 and activation of the NAD⁺ salvage pathway, both of which indicate NMN legacy effects on DN.

New Crystalline Salts of Nicotinamide Riboside as Food Additives

NR⁺ is a highly effective vitamin B₃ type supplement due to its unique ability to replenish NAD⁺ levels. While NR⁺ chloride is already on the market as a nutritional supplement, its synthesis is challenging, expensive, and low yielding, making it cumbersome for large-scale industrial production. Here we report the novel crystalline NR⁺ salts, d/l/dl-hydrogen tartrate and d/l/dl-hydrogen malate. Their high-yielding, one-pot manufacture does not require specific equipment and is suitable for multi-ton scale production. These new NR⁺ salts seem ideal for nutritional applications due to their bio-equivalence compared to the approved NR⁺ chloride. In addition, the crystal structures of all stereoisomers of NR⁺ hydrogen tartrate and NR⁺ hydrogen malate and a comparison to the known NR⁺ halogenides are presented.

In vitro angiogenesis inhibition with selective compounds targeting the key glycolytic enzyme PFKFB3

Abnormal glycolytic metabolism contributes to angiogenic sprouting involved in atherogenesis. We investigated the potential anti-angiogenic properties of specific 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3) inhibitors in endothelial cells (ECs). ECs were treated with PFKFB3 inhibitors (named PA-1 and PA-2) and their effects on metabolic and functional characteristics of ECs were investigated. The anti-glycolytic compound 3-(pyridinyl)- 1-(4-pyridinyl)- 2-propen-1-one (3PO) was used as reference compound. PFKFB3 expression and activity (IC₅₀ about 3-21 nM) was inhibited upon treatment with both compounds. Glucose uptake and lactate export were measured using commercial assays and showed a partial reduction up to 40%. PFKFB3 inhibition increased intracellular lactate accumulation, and reduced expression of monocarboxylate transporters-1 (MCT1) and MCT4. Furthermore, endothelial cell migration and proliferation assays demonstrated significant reduction upon treatment with both compounds. Matrix- metalloproteinase (MMP) activity, measured by gelatin zymography, and expression was significantly reduced (up to 25%). In addition, PA compounds downregulated the expression of VCAM-1, VE-cadherin, VEGFa, VEGFR2, TGF-β, and IL-1β, in inflamed ECs. Finally, PA-1 and PA-2 treatment impaired the formation of angiogenic sprouts measured by both morphogenesis and spheroid-based angiogenesis assays. Our data demonstrate that the anti-glycolytic PA compounds may affect several steps involved in angiogenesis. Targeting the key glycolytic enzyme PFKFB3 might represent an attractive therapeutic strategy to improve the efficacy of cancer treatments, or to be applied in other pathologies where angiogenesis is a detrimental factor.

Nicotinamide adenine dinucleotide: Biosynthesis, consumption and therapeutic role in cardiac diseases

Nicotinamide adenine dinucleotide (NAD) is an abundant cofactor that plays crucial roles in several cellular processes. NAD can be synthesized de novo starting with tryptophan, or from salvage pathways starting with NAD precursors like nicotinic acid (NA), nicotinamide (NAM) or nicotinamide riboside (NR), referred to as niacin/B₃ vitamins, arising from dietary supply or from cellular NAD catabolism. Given the interconversion between its oxidized (NAD⁺ ) and reduced form (NADH), NAD participates in a wide range of reactions: regulation of cellular redox status, energy metabolism and mitochondrial biogenesis. Plus, NAD acts as a signalling molecule, being a cosubstrate for several enzymes such as sirtuins, poly-ADP-ribose-polymerases (PARPs) and some ectoenzymes like CD38, regulating critical biological processes like gene expression, DNA repair, calcium signalling and circadian rhythms. Given the large number of mitochondria present in cardiac tissue, the heart has the highest NAD levels and is one of the most metabolically demanding organs. In several models of heart failure, myocardial NAD levels are depressed and this depression is caused by mitochondrial dysfunction, metabolic remodelling and inflammation. Emerging evidence suggests that regulating NAD homeostasis by NAD precursor supplementation has therapeutic efficiency in improving myocardial bioenergetics and function. This review provides an overview of the latest understanding of the different NAD biosynthesis pathways, as well as its role as a signalling molecule particularly in cardiac tissue. We highlight the significance of preserving NAD equilibrium in various models of heart diseases and shed light on the potential pharmacological interventions aiming to use NAD boosters as therapeutic agents.

Exposure to high fructose corn syrup during adolescence in the mouse alters hepatic metabolism and the microbiome in a sex-specific manner

KEY POINTS

The prevalence of obesity and non-alcoholic fatty liver disease in children is dramatically increasing at the same time as consumption of foods with a high sugar content. Intake of high fructose corn syrup (HFCS) is a possible aetiology as it is thought to be more lipogenic than glucose. In a mouse model, HFCS intake during adolescence increased fat mass and hepatic lipid levels in male and female mice. However, only males showed impaired glucose tolerance. Multiple metabolites including lipids, bile acids, carbohydrates and amino acids were altered in liver in a sex-specific manner at 6 weeks of age. Some of these changes were also present in adulthood even though HFCS exposure ended at 6 weeks. HFCS significantly altered the gut microbiome, which was associated with changes in key microbial metabolites. These results suggest that HFCS intake during adolescence has profound metabolic changes that are linked to changes in the microbiome and these changes are sex-specific.

ABSTRACT

The rapid increase in obesity, diabetes and fatty liver disease in children over the past 20 years has been linked to increased consumption of high fructose corn syrup (HFCS), making it essential to determine the short- and long-term effects of HFCS during this vulnerable developmental window. We hypothesized that HFCS exposure during adolescence significantly impairs hepatic metabolic signalling pathways and alters gut microbial composition, contributing to changes in energy metabolism with sex-specific effects. C57bl/6J mice with free access to HFCS during adolescence (3-6 weeks of age) underwent glucose tolerance and body composition testing and hepatic metabolomics, gene expression and triglyceride content analysis at 6 and 30 weeks of age (n = 6-8 per sex). At 6 weeks HFCS-exposed mice had significant increases in fat mass, glucose intolerance, hepatic triglycerides (females) and de novo lipogenesis gene expression (ACC, DGAT, FAS, ChREBP, SCD, SREBP, CPT and PPARα) with sex-specific effects. At 30 weeks, HFCS-exposed mice also had abnormalities in glucose tolerance (males) and fat mass (females). HFCS exposure enriched carbohydrate, amino acid, long chain fatty acid and secondary bile acid metabolism at 6 weeks with changes in secondary bile metabolism at 6 and 30 weeks. Microbiome studies performed immediately before and after HFCS exposure identified profound shifts of microbial species in male mice only. In summary, short-term HFCS exposure during adolescence induces fatty liver, alters important metabolic pathways, some of which continue to be altered in adulthood, and changes the microbiome in a sex-specific manner.

The effects of in ovo nicotinamide riboside dose on broiler myogenesis

The objective of this study was to determine the effects of in ovo injection of nicotinamide riboside (NR) on broiler embryonic myogenesis. Fertilized Cobb 500 broiler eggs (N = 240) were sorted by weight and within each strata, randomly assigned to 1 of 4 NR dose treatments (0 mmol, 250 mmol, 500 mmol, or 1 mol; final concentration in yolk of 0, 2.5, 5.0, or 10.0 mmol) of NR. At day 10 of incubation, 100 μL of the assigned NR dose was injected into the yolk sac of the developing embryo, and chicks were euthanized within 24 h of hatching. Pectoralis major muscle (PMM) and individual fiber morphometrics were collected. Chicks injected with NR had greater PMM weight and length (P < 0.01), but did not differ from each other (P > 0.14). Chicks from eggs injected with NR had greater PMM weight and width than control chicks (P < 0.01), but did not differ from each other (P = 0.86). Chicks from eggs injected with 500 mmol NR had greater PMM depth than control and 1M chicks (P < 0.04), which did not differ (P = 0.24) from each other. Chicks from eggs injected with 250 mmol NR did not differ in PMM length compared with all other treatments (P > 0.06). There was no treatment effect (P = 0.20) for PMM fiber cross-sectional area; however, there was a treatment effect (P < 0.01) for muscle fiber density. Chicks from eggs injected with 1 mol NR had greater fiber density than all other treatments (P < 0.01). Chicks injected with 250 and 500 mmol NR had greater fiber density than control chicks (P < 0.01), but did not differ (P < 0.06) from each other. Injecting developing embryos at day 10 of incubation increased hatched chick PMM morphometrics, which were partly because of the NR catalyzed increase in muscle fiber density.

Healthy Lifestyle Recommendations: Do the Beneficial Effects Originate from NAD+ Amount at the Cellular Level?

In this review, we describe the role of oxidized forms of nicotinamide adenine dinucleotide (NAD⁺) as a molecule central to health benefits as the result from observing selected healthy lifestyle recommendations. Namely, NAD⁺ level can be regulated by lifestyle and nutrition approaches such as fasting, caloric restriction, sports activity, low glucose availability, and heat shocks. NAD⁺ is reduced with age at a cellular, tissue, and organismal level due to inflammation, defect in NAMPT-mediated NAD⁺ biosynthesis, and the PARP-mediated NAD⁺ depletion. This leads to a decrease in cellular energy production and DNA repair and modifies genomic signalling leading to an increased incidence of chronic diseases and ageing. By implementing healthy lifestyle approaches, endogenous intracellular NAD⁺ levels can be increased, which explains the molecular mechanisms underlying health benefits at the organismal level. Namely, adherence to here presented healthy lifestyle approaches is correlated with an extended life expectancy free of major chronic diseases.

NAD+-Increasing Strategies to Improve Cardiometabolic Health?

Depleted nicotinamide adenine dinucleotide (NAD+) is a common hallmark of metabolic disorders. Therefore, NAD+-increasing strategies have evolved as a potential therapeutic venue to combat cardiometabolic diseases. Several forms of vitamin B3, i.e., nicotinamide and nicotinamide mononucleotide, and especially nicotinamide riboside, have attracted most interest as potentially safe and efficacious candidates for NAD+ restoration. Herein, we dissected the characteristics of the latest clinical trials testing the therapeutic potential of different vitamin B3 molecules to improve cardiometabolic health, with a special focus on randomized, placebo-controlled clinical trials performed in the context of obesity or other pathologies, mainly linked to cardiovascular system and skeletal muscle functionality. The favorable outcomes via NAD+-increasing strategies found in the different studies were quite heterogeneous. NAD+-increasing interventions improved capacity to exercise, decreased blood pressure, increased the anti-inflammatory profile and insulin-stimulated glucose disposal, and reduced the fat-free mass. Except for the decreased blood pressure, the significant results did not include many hard clinical end points, such as decreases in weight, BMI, fasting glucose, or HbA1c percentage. However, the analyzed trials were short-term interventions. Overall, the accumulated clinical data can be interpreted as moderately promising. Additional and long-term studies will be needed to directly compare the doses and duration of treatments among different vitamin B3 regimes, as well as to define the type of patients, if any, that could benefit from these treatments. In this context, a major point of advancement in delineating future clinical trials would be to identify subjects with a recognized NAD+ deficiency using novel, appropriate biomarkers. Also, confirmation of gender-specific effect of NAD+-increasing treatments would be needed.

Nicotinamide Riboside Augments the Aged Human Skeletal Muscle NAD+ Metabolome and Induces Transcriptomic and Anti-inflammatory Signatures

Nicotinamide adenine dinucleotide (NAD⁺) is modulated by conditions of metabolic stress and has been reported to decline with aging in preclinical models, but human data are sparse. Nicotinamide riboside (NR) supplementation ameliorates metabolic dysfunction in rodents. We aimed to establish whether oral NR supplementation in aged participants can increase the skeletal muscle NAD⁺ metabolome and if it can alter muscle mitochondrial bioenergetics. We supplemented 12 aged men with 1 g NR per day for 21 days in a placebo-controlled, randomized, double-blind, crossover trial. Targeted metabolomics showed that NR elevated the muscle NAD⁺ metabolome, evident by increased nicotinic acid adenine dinucleotide and nicotinamide clearance products. Muscle RNA sequencing revealed NR-mediated downregulation of energy metabolism and mitochondria pathways, without altering mitochondrial bioenergetics. NR also depressed levels of circulating inflammatory cytokines. Our data establish that oral NR is available to aged human muscle and identify anti-inflammatory effects of NR.

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NR supplementation in aged subjects augments the skeletal muscle NAD⁺ metabolome

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NR supplementation does not affect skeletal muscle mitochondrial bioenergetics

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NR supplementation reduces levels of circulating inflammatory cytokines

Resistance to Acetylsalicylic Acid in Patients with Coronary Heart Disease Is the Result of Metabolic Activity of Platelets

Sensitivity to acetylsalicylic acid (ASA) is important in the treatment of patients with coronary heart disease (CHD) after coronary artery bypass grafting (CABG). Patients were divided into ASA sensitive (sASA) and ASA resistant (rASA) by the activity of platelet aggregation induced arachidonic acid (ARA) together with ASA. Induced platelet aggregation activity was studied in sASA and rASA patients with CHD before and after CABG. The level of synthesis of primary and secondary reactive oxygen species (ROS) by platelets was determined using chemiluminescent analysis. The activity of NAD- and NADP-dependent dehydrogenases in platelets was determined by the bioluminescent method. It was found that the aggregation activity of platelets depended on the sensitivity of CHD patients to ASA and decreased during postoperative ASA therapy. The most pronounced differences in metabolic parameters of platelets in sASA and rASA patients were detected by Nox2 activity. The synthesis of secondary ROS by platelets of CHD patients did not depend on the sensitivity of patients to ASA but increased during postoperative treatment with ASA. The activity of NAD(P)-dependent dehydrogenases in platelets did not differ in sASA and rASA patients with CHD.

Metabolic Reprogramming in Immune Response and Tissue Inflammation

Innate and adaptive immunity participate in and regulate numerous human diseases. Increasing evidence implies that metabolic reprogramming mediates immune cell functional changes during immune responses. In this review, we present and discuss our current understanding of metabolic regulation in different immune cells and their subsets in response to pathological stimuli. An interactive biochemical and molecular model was established to characterize metabolic reprogramming and their functional implication in anti-inflammatory, immune resolution, and proinflammatory responses. We summarize 2 major features of metabolic reprogramming in inflammatory stages in innate and adaptive immune cells: (1) energy production and biosynthesis reprogramming, including increased glycolysis and decreased oxidative phosphorylation, to secure faster ATP production and biosynthesis for defense response and damage repair and (2) epigenetic reprogramming, including enhanced histone acetylation and suppressed DNA methylation, due to altered accessibility of acetyl/methyl group donor and metabolite-modulated enzymatic activity. Finally, we discuss current strategies of metabolic and epigenetic therapy in cardiovascular disease and recommend cell-specific metabolic and gene-targeted site-specific epigenetic alterations for future therapies.

Implications of NAD+ Metabolism in the Aging Retina and Retinal Degeneration

Nicotinamide adenine dinucleotide (NAD⁺) plays an important role in various key biological processes including energy metabolism, DNA repair, and gene expression. Accumulating clinical and experimental evidence highlights an age-dependent decline in NAD⁺ levels and its association with the development and progression of several age-related diseases. This supports the establishment of NAD⁺ as a critical regulator of aging and longevity and, relatedly, a promising therapeutic target to counter adverse events associated with the normal process of aging and/or the development and progression of age-related disease. Relative to the above, the metabolism of NAD⁺ has been the subject of numerous investigations in various cells, tissues, and organ systems; however, interestingly, studies of NAD⁺ metabolism in the retina and its relevance to the regulation of visual health and function are comparatively few. This is surprising given the critical causative impact of mitochondrial oxidative damage and bioenergetic crises on the development and progression of degenerative disease of the retina. Hence, the role of NAD⁺ in this tissue, normally and aging and/or disease, should not be ignored. Herein, we discuss important findings in the field of NAD⁺ metabolism, with particular emphasis on the importance of the NAD⁺ biosynthesizing enzyme NAMPT, the related metabolism of NAD⁺ in the retina, and the consequences of NAMPT and NAD⁺ deficiency or depletion in this tissue in aging and disease. We discuss also the implications of potential therapeutic strategies that augment NAD⁺ levels on the preservation of retinal health and function in the above conditions. The overarching goal of this review is to emphasize the importance of NAD⁺ metabolism in normal, aging, and/or diseased retina and, by so doing, highlight the necessity of additional clinical studies dedicated to evaluating the therapeutic utility of strategies that enhance NAD⁺ levels in improving vision.

The 4 D's of Pellagra and Progress

Nicotinamide homeostasis is a candidate common denominator to explain smooth transitions, whether demographic, epidemiological or economic. This 'NAD world', dependent on hydrogen-based energy, is not widely recognised as it is neither measured nor viewed from a sufficiently multi-genomic or historical perspective. Reviewing the importance of meat and nicotinamide balances during our co-evolution, recent history suggests that populations only modernise and age well with low fertility on a suitably balanced diet. Imbalances on the low meat side lead to an excess of infectious disease, short lives and boom-bust demographics. On the high side, meat has led to an excess of degenerative, allergic and metabolic disease and low fertility. A 'Goldilocks' diet derived from mixed and sustainable farming (preserving the topsoil) allows for high intellectual capital, height and good health with controlled population growth resulting in economic growth and prosperity. Implementing meat equity worldwide could lead to progress for future generations on 'spaceship' earth by establishing control over population quality, thermostat and biodiversity, if it is not already too late.

NAD+ /sirtuin metabolism is enhanced in response to cold-induced changes in lipid metabolism in mouse liver

The nicotinamide adenine dinucleotide (NAD⁺ )/Sirtuin (SIRT) system is linked to metabolic adaptation. This study aimed to determine the temporal profile of metabolic responses of the liver to cold exposure and changes in the hepatic NAD⁺ /SIRT system. Eight-week-old male C57BL/6 mice were individually housed in conventional cages under cold exposure (4 °C) for up to 5 days. Cold exposure decreased the hepatic triglyceride level and cholesterol level in mice by 1.7- and 1.6-fold, respectively. Lipogenic gene expression was persistently reduced, while gluconeogenic gene expression was transiently increased. Hepatic NAD⁺ /SIRT metabolism was induced during the 'cold remodeling' phase (days 1-3) and correlated with decreasing lipogenic and increasing gluconeogenic gene expression, contributing to the maintenance of whole-body lipid and glucose homeostasis.

Depot-specific regulation of NAD+/SIRTs metabolism identified in adipose tissue of mice in response to high-fat diet feeding or calorie restriction

Deteriorated nicotinamide adenine dinucleotide (NAD⁺)/sirtuins (SIRTs) metabolism in adipose tissue is implicated in diet-induced obesity, while calorie restriction (CR)-induced beneficial effects require sufficient NAD⁺ biosynthesis. Mechanistic links have not been defined. This study aims to identify changes of specific components of NAD⁺/SIRTs system in white adipose tissue (WAT) and brown adipose tissue (BAT) of mice upon energy imbalance, focusing on key enzymes in NAD⁺ salvage (Nampt, Nmnat1, Nrk1), clearance (Nnmt, Aox1, Cyp2e1) and consumption pathways (Sirt1, Sirt2, Sirt3, Sirt6, Parp1). Male C57BL/6J mice were fed ad libitum with the standard laboratory chow diet, high-fat diet (HFD) or 40% CR diet, respectively. The epididymal and inguinal WAT (eWAT and iWAT) and interscapular BAT (iBAT) were harvested for histological, NAD⁺ assay, gene and protein expression analysis after 16 weeks of dietary regimen. HFD decreased, while CR increased, the NAD⁺ and NADH levels in eWAT, iWAT and iBAT. NAD⁺ content negatively correlated with plasma cholesterol, TNF-α levels and calorie intake, while it positively correlated with plasma adiponectin level. The change trend of SIRT1 is quite the same as that of NAD⁺/NADH ratio. Nmnat1 gene is sensitive to energy imbalance in WAT but not in BAT. Nrk1 gene expression was decreased in eWAT and iWAT but increased in iBAT of HFD mice. Nnmt mRNA and protein abundance was increased in iWAT of HFD mice. Nampt, Cyp2e1 and Sirt3 were the most robust genes responding to energy imbalance. In summary, adipose tissue responds to long-term energy excess or shortage with depot-specific transcriptional activation or repression of NAD⁺/SIRTs metabolic components.

NAD+ precursors protect corneal endothelial cells from UVB-induced apoptosis

Excessive exposure of the eye to ultraviolet B light (UVB) leads to corneal edema and opacification because of the apoptosis of the corneal endothelium. Our previous study found that nicotinamide (NIC), the precursor of nicotinamide adenine dinucleotide (NAD), could inhibit the endothelial-mesenchymal transition and accelerate healing the wound to the corneal endothelium in the rabbit. Here we hypothesize that NIC may possess the capacity to protect the cornea from UVB-induced endothelial apoptosis. Therefore, a mouse model and a cultured cell model were used to examine the effect of NAD⁺ precursors, including NIC, nicotinamide mononucleotide (NMN), and NAD, on the UVB-induced apoptosis of corneal endothelial cells (CECs). The results showed that UVB irradiation caused apparent corneal edema and cell apoptosis in mice, accompanied by reduced levels of NAD⁺ and its key biosynthesis enzyme, nicotinamide phosphoribosyltransferase (NAMPT), in the corneal endothelium. However, the subconjunctival injection of NIC, NMN, or NAD⁺ effectively prevented UVB-induced tissue damage and endothelial cell apoptosis in the mouse cornea. Moreover, pretreatment using NIC, NMN, and NAD⁺ increased the survival rate and inhibited the apoptosis of cultured human CECs irradiated by UVB. Mechanistically, pretreatment using nicotinamide (NIC) recovered the AKT activation level and decreased the BAX/BCL-2 ratio. In addition, the capacity of NIC to protect CECs was fully reversed in the presence of the AKT inhibitor LY294002. Therefore, we conclude that NAD⁺ precursors can effectively prevent the apoptosis of the corneal endothelium through reactivating AKT signaling; this represents a potential therapeutic approach for preventing UVB-induced corneal damage.

Aging and drug discovery

Multiple interventions in the aging process have been discovered to extend the healthspan of model organisms. Both industry and academia are therefore exploring possible transformative molecules that target aging and age-associated diseases. In this overview, we summarize the presented talks and discussion points of the 5th Annual Aging and Drug Discovery Forum 2018 in Basel, Switzerland. Here academia and industry came together, to discuss the latest progress and issues in aging research. The meeting covered talks about the mechanistic cause of aging, how longevity signatures may be highly conserved, emerging biomarkers of aging, possible interventions in the aging process and the use of artificial intelligence for aging research and drug discovery. Importantly, a consensus is emerging both in industry and academia, that molecules able to intervene in the aging process may contain the potential to transform both societies and healthcare.

Significant alteration of liver metabolites by AAV8.Urocortin 2 gene transfer in mice with insulin resistance

INTRODUCTION

Urocortin 2 (Ucn2) is a 38-amino acid peptide of the corticotropin-releasing factor family. Intravenous (IV) delivery of an adeno-associated virus vector serotype 8 encoding Ucn2 (AAV8.Ucn2) increases insulin sensitivity and glucose disposal in mice with insulin resistance.

OBJECTIVE

To determine the effects of Ucn2 on liver metabolome.

METHODS

Six-week-old C57BL6 mice were divided into normal chow (CHOW)-fed and high fat diet (HFD)-fed groups. The animals received saline, AAV8 encoding no gene (AAV8.Empt) or AAV8.Ucn2 (2x1013 genome copy/kg, IV injection). Livers were isolated from CHOW-fed and HFD-fed mice and analyzed by untargeted metabolomics. Group differences were statistically analyzed.

RESULTS

In CHOW-fed mice, AAV8.Ucn2 gene transfer (vs. saline) altered the metabolites in glycolysis, pentose phosphate, glycogen synthesis, glycogenolysis, and choline-folate-methionine signaling pathways. In addition, AAV8.Ucn2 gene transfer increased amino acids and peptides, which were associated with reduced protein synthesis. In insulin resistant (HFD-induced) mice, HFD (vs CHOW) altered 448 (112 increased and 336 decreased) metabolites and AAV8.Ucn2 altered 239 metabolites (124 increased and 115 reduced) in multiple pathways. There are 61 metabolites in 5 super pathways showed interactions between diet and AAV8.Ucn2 treatment. Among them, AAV8.Ucn2 gene transfer reversed HFD effects on 13 metabolites. Finally, plasma Ucn2 effects were determined using a 3-group comparison of HFD-fed mice that received AAV8.Ucn2, AAV.Empt or saline, where 18 metabolites that altered by HFD (15 increased and 3 decreased), but restored levels to that seen in CHOW-fed mice by increased plasma Ucn2.

CONCLUSIONS

Metabolomics study revealed that AAV8.Ucn2 gene transfer, through increased plasma Ucn2, provided counter-HFD effects in restoring hepatic metabolites to normal levels, which could be the underlying mechanisms for Ucn2 effects on increasing glucose disposal and reducing insulin assistance.

Novel NAXE variants as a cause for neurometabolic disorder: implications for treatment

Neurometabolic disorders are often inherited and complex disorders that result from abnormalities of enzymes important for development and function of the nervous system. Recently, biallelic mutations in NAXE (APOA1BP) were found in patients with an infantile, lethal, neurometabolic disease. Here, exome sequencing was performed in two affected sisters and their healthy parents. The best candidate, NAXE, was tested for replication in exome sequencing data from 4351 patients with neurodevelopmental disorders. Quantitative RT-PCR, western blot and form factor analysis were performed to assess NAXE expression, protein levels and to analyze mitochondrial morphology in fibroblasts. Vitamin B3 was administered to one patient. Compound heterozygous missense (c.757G>A: p.Gly253Ser) and splicing (c.665-1G>A) variants in NAXE were identified in both affected sisters. In contrast to the previously reported patients with biallelic NAXE variants, our patients showed a milder phenotype with disease onset in early adulthood with psychosis, cognitive impairment, seizures, cerebellar ataxia and spasticity. The symptoms fluctuated. Additional screening of NAXE identified three novel homozygous missense variants (p.Lys245Gln, p.Asp218Asn, p.Ile214Val) in three patients with overlapping phenotype (fluctuating disease course, respiratory insufficiency, movement disorder). Lastly, patients with the c.665-1G>A splicing variant showed a significant reduction of NAXE expression compared to control fibroblasts and undetectable NAXE protein levels compared to control fibroblasts. Based on the metabolic pathway, vitamin B3 and coenzyme Q treatment was introduced in one patient in addition to antiepileptic treatment. This combination and avoidance of triggers was associated with continuous motor and cognitive improvement. The NAXE variants identified in this study suggest a loss-of-function mechanism leading to an insufficient NAD(P)HX repair system. Importantly, symptoms of patients with NAXE variants may improve with vitamin B3/coenzyme Q administration.

NAD+ Depletion Triggers Macrophage Necroptosis, a Cell Death Pathway Exploited by Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) kills infected macrophages by inhibiting apoptosis and promoting necrosis. The tuberculosis necrotizing toxin (TNT) is a secreted nicotinamide adenine dinucleotide (NAD⁺) glycohydrolase that induces necrosis in infected macrophages. Here, we show that NAD⁺ depletion by TNT activates RIPK3 and MLKL, key mediators of necroptosis. Notably, Mtb bypasses the canonical necroptosis pathway since neither TNF-α nor RIPK1 are required for macrophage death. Macrophage necroptosis is associated with depolarized mitochondria and impaired ATP synthesis, known hallmarks of Mtb-induced cell death. These results identify TNT as the main trigger of necroptosis in Mtb-infected macrophages. Surprisingly, NAD⁺ depletion itself was sufficient to trigger necroptosis in a RIPK3- and MLKL-dependent manner by inhibiting the NAD⁺ salvage pathway in THP-1 cells or by TNT expression in Jurkat T cells. These findings suggest avenues for host-directed therapies to treat tuberculosis and other infectious and age-related diseases in which NAD⁺ deficiency is a pathological factor.

Medicines discovery for auditory disorders: Challenges for industry

Currently, no approved medicines are available for the prevention or treatment of hearing loss. Pharmaceutical industry productivity across all therapeutic indications has historically been disappointing, with a 90% chance of failure in delivering a marketed drug after entering clinical evaluation. To address these failings, initiatives have been applied in the three cornerstones of medicine discovery: target selection, clinical candidate selection, and clinical studies. These changes aimed to enable data-informed decisions on the translation of preclinical observations into a safe, clinically effective medicine by ensuring the best biological target is selected, the most appropriate chemical entity is advanced, and that the clinical studies enroll the correct patients. The specific underlying pathologies need to be known to allow appropriate patient selection, so improved diagnostics are required, as are methodologies for measuring in the inner ear target engagement, drug delivery and pharmacokinetics. The different therapeutic strategies of protecting hearing or preventing hearing loss versus restoring hearing are reviewed along with potential treatments for tinnitus. Examples of current investigational drugs are discussed to highlight key challenges in drug discovery and the learnings being applied to improve the probability of success of launching a marketed medicine.

Nicotinamide phosphoribosyltransferase‑related signaling pathway in early Alzheimer's disease mouse models

Alzheimer's disease (AD) is a neurodegenerative disease of the central nervous system that is characterized by progressive cognitive dysfunction and which ultimately leads to dementia. Studies have shown that energy dysmetabolism contributes significantly to the pathogenesis of a variety of aging-associated diseases and degenerative diseases of the nervous system, including AD. One focus of research thus has been how to regulate the expression of nicotinamide phosphoribosyltransferase (NAMPT) to prevent against neurodegenerative diseases. Therefore, the present study used 6-month-old APPswe/PS1ΔE9 (APP/PS1) transgenic mice as early AD mouse models and sought to evaluate nicotinamide adenine dinucleotide (NAD⁺) and FK866 (a NAMPT inhibitor) treatment in APP/PS1 mice to study NAMPT dysmetabolism in the process of AD and elucidate the underlying mechanisms. As a result of this treatment, the expression of NAMPT decreased, the synthesis of ATP and NAD⁺ became insufficient and the NAD⁺/NADH ratio was reduced. The administration of NAD⁺ alleviated the spatial learning and memory of APP/PS1 mice and reduced senile plaques. Administration of NAD⁺ may also increase the expression of the key protein NAMPT and its related protein sirtuin 1 as well as the synthesis of NAD⁺. Therefore, increasing NAMPT expression levels may promote NAD⁺ production. Their regulation could form the basis for a new therapeutic strategy.

High Dose of Dietary Nicotinamide Riboside Induces Glucose Intolerance and White Adipose Tissue Dysfunction in Mice Fed a Mildly Obesogenic Diet

Nicotinamide riboside (NR) is a nicotinamide adenine dinucleotide (NAD⁺) precursor vitamin. The scarce reports on the adverse effects on metabolic health of supplementation with high-dose NR warrant substantiation. Here, we aimed to examine the physiological responses to high-dose NR supplementation in the context of a mildly obesogenic diet and to substantiate this with molecular data. An 18-week dietary intervention was conducted in male C57BL/6JRccHsd mice, in which a diet with 9000 mg NR per kg diet (high NR) was compared to a diet with NR at the recommended vitamin B3 level (control NR). Both diets were mildly obesogenic (40 en% fat). Metabolic flexibility and glucose tolerance were analyzed and immunoblotting, qRT-PCR and histology of epididymal white adipose tissue (eWAT) were performed. Mice fed with high NR showed a reduced metabolic flexibility, a lower glucose clearance rate and aggravated systemic insulin resistance. This was consistent with molecular and morphological changes in eWAT, including sirtuin 1 (SIRT1)-mediated PPARγ (proliferator-activated receptor γ) repression, downregulated AKT/glucose transporter type 4 (GLUT4) signaling, an increased number of crown-like structures and macrophages, and an upregulation of pro-inflammatory gene markers. In conclusion, high-dose NR induces the onset of WAT dysfunction, which may in part explain the deterioration of metabolic health.

Transcriptome analysis suggests a compensatory role of the cofactors coenzyme A and NAD+ in medium-chain acyl-CoA dehydrogenase knockout mice

During fasting, mitochondrial fatty-acid β-oxidation (mFAO) is essential for the generation of glucose by the liver. Children with a loss-of-function deficiency in the mFAO enzyme medium-chain acyl-Coenzyme A dehydrogenase (MCAD) are at serious risk of life-threatening low blood glucose levels during fasting in combination with intercurrent disease. However, a subset of these children remains asymptomatic throughout life. In MCAD-deficient (MCAD-KO) mice, glucose levels are similar to those of wild-type (WT) mice, even during fasting. We investigated if metabolic adaptations in the liver may underlie the robustness of this KO mouse. WT and KO mice were given a high- or low-fat diet and subsequently fasted. We analyzed histology, mitochondrial function, targeted mitochondrial proteomics, and transcriptome in liver tissue. Loss of MCAD led to a decreased capacity to oxidize octanoyl-CoA. This was not compensated for by altered protein levels of the short- and long-chain isoenzymes SCAD and LCAD. In the transcriptome, we identified subtle adaptations in the expression of genes encoding enzymes catalyzing CoA- and NAD(P)(H)-involving reactions and of genes involved in detoxification mechanisms. We discuss how these processes may contribute to robustness in MCAD-KO mice and potentially also in asymptomatic human subjects with a complete loss of MCAD activity.

Diverse therapeutic efficacies and more diverse mechanisms of nicotinamide

BACKGROUND

Nicotinamide (NAM) is a form of vitamin B3 that, when administered at near-gram doses, has been shown or suggested to be therapeutically effective against many diseases and conditions. The target conditions are incredibly diverse ranging from skin disorders such as bullous pemphigoid to schizophrenia and depression and even AIDS. Similar diversity is expected for the underlying mechanisms. In a large portion of the conditions, NAM conversion to nicotinamide adenine dinucleotide (NAD⁺) may be a major factor in its efficacy. The augmentation of cellular NAD⁺ level not only modulates mitochondrial production of ATP and superoxide, but also activates many enzymes. Activated sirtuin proteins, a family of NAD⁺-dependent deacetylases, play important roles in many of NAM's effects such as an increase in mitochondrial quality and cell viability countering neuronal damages and metabolic diseases. Meanwhile, certain observed effects are mediated by NAM itself. However, our understanding on the mechanisms of NAM's effects is limited to those involving certain key proteins and may even be inaccurate in some proposed cases.

AIM OF REVIEW

This review details the conditions that NAM has been shown to or is expected to effectively treat in humans and animals and evaluates the proposed underlying molecular mechanisms, with the intention of promoting wider, safe therapeutic application of NAM.

KEY SCIENTIFIC CONCEPTS OF REVIEW

NAM, by itself or through altering metabolic balance of NAD⁺ and tryptophan, modulates mitochondrial function and activities of many molecules and thereby positively affects cell viability and metabolic functions. And, NAM administration appears to be quite safe with limited possibility of side effects which are related to NAM's metabolites.

Loss of NAMPT in aging retinal pigment epithelium reduces NAD+ availability and promotes cellular senescence

Retinal pigment epithelium (RPE) performs numerous functions critical to retinal health and visual function. RPE senescence is a hallmark of aging and degenerative retinal disease development. Here, we evaluated the temporal expression of key nicotinamide adenine dinucleotide (NAD⁺)-biosynthetic genes and associated levels of NAD⁺, a principal regulator of energy metabolism and cellular fate, in mouse RPE. NAD⁺ levels declined with age and correlated directly with decreased nicotinamide phosphoribosyltransferase (NAMPT) expression, increased expression of senescence markers (p16^INK4a, p21^Waf/Cip1, ApoJ, CTGF and β-galactosidase) and significant reductions in SIRT1 expression and activity. We simulated in vitro the age-dependent decline in NAD⁺ and the related increase in RPE senescence in human (ARPE-19) and mouse primary RPE using the NAMPT inhibitor FK866 and demonstrated the positive impact of NAD⁺-enhancing therapies on RPE cell viability. This, we confirmed in vivo in the RPE of mice injected sub-retinally with FK866 in the presence or absence of nicotinamide mononucleotide. Our data confirm the importance of NAD⁺ to RPE cell biology normally and in aging and demonstrate the potential utility of therapies targeting NAMPT and NAD⁺ biosynthesis to prevent or alleviate consequences of RPE senescence in aging and/or degenerative retinal diseases in which RPE dysfunction is a crucial element.

Metabolic tracing reveals novel adaptations to skeletal muscle cell energy production pathways in response to NAD + depletion

Background: Skeletal muscle is central to whole body metabolic homeostasis, with age and disease impairing its ability to function appropriately to maintain health. Inadequate NAD + availability is proposed to contribute to pathophysiology by impairing metabolic energy pathway use. Despite the importance of NAD + as a vital redox cofactor in energy production pathways being well-established, the wider impact of disrupted NAD + homeostasis on these pathways is unknown. Methods: We utilised skeletal muscle myotube models to induce NAD + depletion, repletion and excess and conducted metabolic tracing to provide comprehensive and detailed analysis of the consequences of altered NAD + metabolism on central carbon metabolic pathways. We used stable isotope tracers, [1,2-13C] D-glucose and [U- 13C] glutamine, and conducted combined 2D-1H,13C-heteronuclear single quantum coherence (HSQC) NMR spectroscopy and GC-MS analysis. Results: NAD + excess driven by nicotinamide riboside (NR) supplementation within skeletal muscle cells resulted in enhanced nicotinamide clearance, but had no effect on energy homeostasis or central carbon metabolism. Nicotinamide phosphoribosyltransferase (NAMPT) inhibition induced NAD + depletion and resulted in equilibration of metabolites upstream of glyceraldehyde phosphate dehydrogenase (GAPDH). Aspartate production through glycolysis and TCA cycle activity was increased in response to low NAD +, which was rapidly reversed with repletion of the NAD + pool using NR. NAD + depletion reversibly inhibits cytosolic GAPDH activity, but retains mitochondrial oxidative metabolism, suggesting differential effects of this treatment on sub-cellular pyridine pools. When supplemented, NR efficiently reversed these metabolic consequences. However, the functional relevance of increased aspartate levels after NAD + depletion remains unclear, and requires further investigation. Conclusions: These data highlight the need to consider carbon metabolism and clearance pathways when investigating NAD + precursor usage in models of skeletal muscle physiology.

Mitohormesis and metabolic health: The interplay between ROS, cAMP and sirtuins

The key role of mitochondria in oxidative metabolism and redox homeostasis explains the link between mitochondrial dysfunction and the development of metabolic disorders. Mitochondria's highly dynamic nature, based on alterations in biogenesis, mitophagy, fusion and fission, allows adjusting sequential redox reactions of the electron transport chain (ETC) and dissipation of the membrane potential by ATP synthase, to different environmental cues. With reactive oxygen species being an inevitable by-product of oxidative phosphorylation (OXPHOS), alterations on mitochondrial oxidative rate with a consequent excessive load of reactive oxygen species have been traditionally associated with pathological conditions. However, reactive oxygen species have also been suggested as promoters of mitohormesis, a process in which low, non-cytotoxic concentrations of reactive oxygen species promote mitochondrial homeostasis. Therefore, signaling systems involved in the regulation of mitochondrial homeostasis are attractive candidates for drug development for metabolic diseases triggered by mitochondrial dysfunction. Reversible phosphorylation downstream the cyclic AMP (cAMP) signaling cascade and deacetylation mediated by sirtuins are recognized as major mitochondrial regulators.

Nicotinamide and Demographic and Disease transitions: Moderation is Best

Good health and rapid progress depend on an optimal dose of nicotinamide. Too little meat triggers the neurodegenerative condition pellagra and tolerance of symbionts such as tuberculosis (TB), risking dysbioses and impaired resistance to acute infections. Nicotinamide deficiency is an overlooked diagnosis in poor cereal-dependant economies masquerading as 'environmental enteropathy' or physical and cognitive stunting. Too much meat (and supplements) may precipitate immune intolerance and autoimmune and allergic disease, with relative infertility and longevity, via the tryptophan-nicotinamide pathway. This switch favours a dearth of regulatory T (Treg) and an excess of T helper cells. High nicotinamide intake is implicated in cancer and Parkinson's disease. Pro-fertility genes, evolved to counteract high-nicotinamide-induced infertility, may now be risk factors for degenerative disease. Moderation of the dose of nicotinamide could prevent some common diseases and personalised doses at times of stress or, depending on genetic background or age, may treat some other conditions.

Nicotinamide as Independent Variable for Intelligence, Fertility, and Health: Origin of Human Creative Explosions?

Meat and nicotinamide acquisition was a defining force during the 2-million-year evolution of the big brains necessary for, anatomically modern, Homo sapiens to survive. Our next move was down the food chain during the Mesolithic 'broad spectrum', then horticultural, followed by the Neolithic agricultural revolutions and progressively lower average 'doses' of nicotinamide. We speculate that a fertility crisis and population bottleneck around 40 000 years ago, at the time of the Last Glacial Maximum, was overcome by Homo (but not the Neanderthals) by concerted dietary change plus profertility genes and intense sexual selection culminating in behaviourally modern Homo sapiens. Increased reliance on the 'de novo' synthesis of nicotinamide from tryptophan conditioned the immune system to welcome symbionts, such as TB (that excrete nicotinamide), and to increase tolerance of the foetus and thereby fertility. The trade-offs during the warmer Holocene were physical and mental stunting and more infectious diseases and population booms and busts. Higher nicotinamide exposure could be responsible for recent demographic and epidemiological transitions to lower fertility and higher longevity, but with more degenerative and auto-immune disease.

Emissive Synthetic Cofactors: A Highly Responsive NAD+ Analogue Reveals Biomolecular Recognition Features

Apart from its vital function as a redox cofactor, nicotinamide adenine dinucleotide (NAD⁺ ) has emerged as a crucial substrate for NAD⁺ -consuming enzymes, including poly(ADP-ribosyl)transferase 1 (PARP1) and CD38/CD157. Their association with severe diseases, such as cancer, Alzheimer's disease, and depressions, necessitates the development of new analytical tools based on traceable NAD⁺ surrogates. Here, the synthesis, photophysics and biochemical utilization of an emissive, thieno[3,4-d]pyrimidine-based NAD⁺ surrogate, termed N^th AD⁺ , are described. Its preparation was accomplished by enzymatic conversion of synthetic ^th ATP by nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1). The new NAD⁺ analogue possesses useful photophysical features including redshifted absorption and emission maxima as well as a relatively high quantum yield. Serving as a versatile substrate, N^th AD⁺ was reduced by alcohol dehydrogenase (ADH) to N^th ADH and afforded ^th ADP-ribose (^th ADPr) upon hydrolysis by NAD⁺ -nucleosidase (NADase). Furthermore, N^th AD⁺ was engaged in cholera toxin A (CTA)-catalyzed mono(^th ADP-ribosyl)ation, but was found incapable in promoting PARP1-mediated poly(^th ADP-ribosyl)ation. Due to its high photophysical responsiveness, N^th AD⁺ is suited for spectroscopic real-time monitoring. Intriguingly, and as an N7-lacking NAD⁺ surrogate, the thieno-based cofactor showed reduced compatibility (i.e., functional similarity compared to native NAD⁺ ) relative to its isothiazolo-based analogue. The distinct tolerance, displayed by diverse NAD⁺ producing and consuming enzymes, suggests unique biological recognition features and dependency on the purine N7 moiety, which is found to be of importance, if not essential, for PARP1-mediated reactions.