Nicotinamide N-Methyltransferase: More Than a Vitamin B3 Clearance Enzyme

Identification of nicotinamide N-methyltransferase as a promising therapeutic target for sarcopenia

Sarcopenia is a significant geriatric syndrome that involves the loss of skeletal muscle mass and strength. Due to its substantial endocrine role, the metabolic microenvironment of skeletal muscle undergoes changes with age. Examining the pathogenesis of sarcopenia through focusing on metabolic dysregulation could offer insights for developing more effective intervention strategies. In this study, we analyzed the transcriptomics data to identify specific genes involved in the regulation of metabolism in skeletal muscle during the development of sarcopenia. Three machine learning algorithms were employed to screen key target genes exhibiting strong correlations with metabolism, which were further validated using RNA-sequencing data and publicly accessible datasets. Among them, the metabolic enzyme nicotinamide N-methyltransferase (NNMT) was elevated in sarcopenia, and predicted sarcopenia with an area under the curve exceeding 0.7, suggesting it as a potential therapeutic target for sarcopenia. As expected, inhibition of NNMT improved the grip strength in aging mice and alleviated age-related decline in the mass index of the quadriceps femoris muscles and whole-body lean mass index. Additionally, the NNMTi treatment increased the levels of nicotinamide adenine dinucleotide (NAD+) content, as well as PGC1α and p-AMPK expression in the muscles of both the D-galactose-treated mouse model and naturally aging mouse model. Overall, this work demonstrates NNMT as a promising target for preventing age-related decline in muscle mass and strength.

Targeting nicotinamide N-methyltransferase decreased aggressiveness of osteosarcoma cells

BACKGROUND

Osteosarcoma (OS) is a primary bone malignancy that mostly affects young people, characterized by high metastatic potential, and a marked chemoresistance that is responsible for disease relapse in most patients. Therefore, it is necessary to identify novel molecules to setup targeted strategies to improve the clinical outcome. The enzyme nicotinamide N-methyltransferase (NNMT) catalyses the N-methylation of nicotinamide and other analogs, playing a crucial role in the biotransformation of drugs and xenobiotics. NNMT overexpression was reported in a wide variety of cancers, and several studies demonstrated that is able to promote cell proliferation, migration and resistance to chemotherapy. The aim of this study was to explore the potential involvement of NNMT in OS.

METHODS

Immunohistochemical analyses have been performed to evaluate NNMT expression in selected OS and healthy bone tissue samples. Subsequently, OS cell lines have been transfected with vectors targeting NNMT mRNA (shRNAs) and the impact of this downregulation on migration, cell proliferation, and response to chemotherapeutic treatment was also analysed by wound healing, MTT, SRB and Trypan blue assays, respectively.

RESULTS

Results showed that OS samples display a significantly higher NNMT expression compared with healthy tissue. Preliminary results suggest that NNMT silencing in OS cell lines is associated to a decrease of cell proliferation and migration, as well as to enhanced sensitivity to chemotherapy. Data obtained showed that NNMT may represent an interesting marker for OS detection and a promising target for effective anti-cancer therapy.

Knockdown of nicotinamide N-methyltransferase suppresses proliferation, migration, and chemoresistance of Merkel cell carcinoma cells in vitro

Merkel cell carcinoma (MCC) is an aggressive skin cancer, with a propensity for early metastasis. Therefore, early diagnosis and the identification of novel targets become fundamental. The enzyme nicotinamide N-methyltransferase (NNMT) catalyzes the reaction of N-methylation of nicotinamide and other analogous compounds. Although NNMT overexpression was reported in many malignancies, the significance of its dysregulation in cancer cell phenotype was partly clarified. Several works demonstrated that NNMT promotes cancer cell proliferation, migration, and chemoresistance. In this study, we investigated the possible involvement of this enzyme in MCC. Preliminary immunohistochemical analyses were performed to evaluate NNMT expression in MCC tissue specimens. To explore the enzyme function in tumor cell metabolism, MCC cell lines have been transfected with plasmids encoding for short hairpin RNAs (shRNAs) targeting NNMT mRNA. Preliminary immunohistochemical analyses showed elevated NNMT expression in MCC tissue specimens. The effect of enzyme downregulation on cell proliferation, migration, and chemosensitivity was then evaluated through MTT, trypan blue, and wound healing assays. Data obtained clearly demonstrated that NNMT knockdown is associated with a decrease of cell proliferation, viability, and migration, as well as with enhanced sensitivity to treatment with chemotherapeutic drugs. Taken together, these results suggest that NNMT could represent an interesting MCC biomarker and a promising target for targeted anti-cancer therapy.

Lactobacillus rhamnosus GG Stimulates Dietary Tryptophan-Dependent Production of Barrier-Protecting Methylnicotinamide

BACKGROUND & AIMS

Lacticaseibacillus rhamnosus GG (LGG) is the world's most consumed probiotic but its mechanism of action on intestinal permeability and differentiation along with its interactions with an essential source of signaling metabolites, dietary tryptophan (trp), are unclear.

METHODS

Untargeted metabolomic and transcriptomic analyses were performed in LGG monocolonized germ-free mice fed trp-free or -sufficient diets. LGG-derived metabolites were profiled in vitro under anaerobic and aerobic conditions. Multiomic correlations using a newly developed algorithm discovered novel metabolites tightly linked to tight junction and cell differentiation genes whose abundances were regulated by LGG and dietary trp. Barrier-modulation by these metabolites were functionally tested in Caco2 cells, mouse enteroids, and dextran sulfate sodium experimental colitis. The contribution of these metabolites to barrier protection is delineated at specific tight junction proteins and enterocyte-promoting factors with gain and loss of function approaches.

RESULTS

LGG, strictly with dietary trp, promotes the enterocyte program and expression of tight junction genes, particularly Ocln. Functional evaluations of fecal and serum metabolites synergistically stimulated by LGG and trp revealed a novel vitamin B3 metabolism pathway, with methylnicotinamide (MNA) unexpectedly being the most robust barrier-protective metabolite in vitro and in vivo. Reduced serum MNA is significantly associated with increased disease activity in patients with inflammatory bowel disease. Exogenous MNA enhances gut barrier in homeostasis and robustly promotes colonic healing in dextran sulfate sodium colitis. MNA is sufficient to promote intestinal epithelial Ocln and RNF43, a master inhibitor of Wnt. Blocking trp or vitamin B3 absorption abolishes barrier recovery in vivo.

CONCLUSIONS

Our study uncovers a novel LGG-regulated dietary trp-dependent production of MNA that protects the gut barrier against colitis.

Fibroblast regulates angiogenesis in assembled oral cancer organoid: A possible role of NNMT

OBJECTIVE

Tumour angiogenesis is affected by various cell types in the tumour microenvironment (TME), including cancer cells and cancer-associated fibroblasts (CAFs). Here, an assembled organoid model was generated to investigate the mechanism by which the TME regulates angiogenesis in oral squamous cell carcinoma (OSCC).

MATERIALS AND METHODS

Secretion of vascular endothelial growth factor-A (VEGFA) was analysed to compare the proangiogenic properties of OSCC cells and corresponding CAFs. Cell aggregates consisting of endothelial cells (ECs), CAFs and cancer cells were generated to construct assembled organoids. Nicotinamide N-methyltransferase (NNMT) was pharmacologically or genetically inhibited to block the activation of CAFs. ATAC-seq was employed to test the transcriptional network of fibroblasts overexpressing NNMT.

RESULTS

Compared with cancer cells, CAFs secreted more VEGFA. Coculture with CAFs more effectively promoted the sprouting of ECs. Blockade of CAF activation via inhibition of NNMT drastically reduced the expression of CD31 in the assembled organoids. Overexpression of NNMT enhanced the transcription of genes related to angiogenesis in fibroblasts. Specifically, NNMT orchestrated the enrichment of the transcription factor JUNB at the promoter of VEGFA.

CONCLUSIONS

We clarify that stromal NNMT enables the steady reproduction of angiogenesis in assembled oral cancer organoids, providing a novel target for exploiting antiangiogenic therapy.

Impact of Pregnancy on the Pharmacokinetics and Metabolism of Nicotinamide in Humans

In pre-eclampsia models, nicotinamide (NAM) has protective effects in pre-eclampsia and is being evaluated as a therapeutic nutraceutical in clinical studies. NAM undergoes extensive hepatic metabolism by NAM N-methyltransferase to methylnicotinamide (MNA), which is subsequently metabolized to methyl-2-pyridone-5-carboxamide (M2PY) by aldehyde oxidase. However, the pharmacokinetics of NAM and its major metabolites has never been studied in pregnant individuals. Blood samples were collected before and 1, 2, 4, 8, and 24 hours after single 1 g oral NAM dose in healthy pregnant (gestational age 24-33 weeks) and nonpregnant female volunteers (n = 6/group). Pooled urine was collected from 0 to 8 hours. NAM, MNA, and M2PY area under the concentration-time curve (AUC) data were analyzed by noncompartmental analysis. No difference in the plasma AUC0→24 of NAM (median (25%-75%): 463 (436-576) vs. 510 (423, 725) μM*hour, P = 0.430) and its intermediate metabolite MNA (89.1 (60.4, 124.4) vs. 83.8 (62.7, 93.7) μM*hour, P = 0.515) was observed in pregnant and nonpregnant volunteers, respectively; however, the terminal metabolite M2PY AUC0 → 24 was significantly lower in pregnant individuals (218 (188, 254) vs. 597 (460, 653) μM*hour, P < 0.001). NAM renal clearance (CLR ; P = 0.184), MNA CLR (P = 0.180), and total metabolite formation clearance (P = 0.405) did not differ across groups; however, M2PY CLR was significantly higher in pregnant individuals (10.5 (9.3-11.3) vs. 7.5 (6.4-8.5) L/h, P = 0.002). These findings demonstrate that the PK of NAM and systemic exposure to its intermediate metabolite MNA are not significantly altered during pregnancy, and systemic exposure to NAM's major metabolite M2PY was reduced during pregnancy due to increased renal elimination.

Inhibitors of NAD+ Production in Cancer Treatment: State of the Art and Perspectives

The addiction of tumors to elevated nicotinamide adenine dinucleotide (NAD+) levels is a hallmark of cancer metabolism. Obstructing NAD+ biosynthesis in tumors is a new and promising antineoplastic strategy. Inhibitors developed against nicotinamide phosphoribosyltransferase (NAMPT), the main enzyme in NAD+ production from nicotinamide, elicited robust anticancer activity in preclinical models but not in patients, implying that other NAD+-biosynthetic pathways are also active in tumors and provide sufficient NAD+ amounts despite NAMPT obstruction. Recent studies show that NAD+ biosynthesis through the so-called "Preiss-Handler (PH) pathway", which utilizes nicotinate as a precursor, actively operates in many tumors and accounts for tumor resistance to NAMPT inhibitors. The PH pathway consists of three sequential enzymatic steps that are catalyzed by nicotinate phosphoribosyltransferase (NAPRT), nicotinamide mononucleotide adenylyltransferases (NMNATs), and NAD+ synthetase (NADSYN1). Here, we focus on these enzymes as emerging targets in cancer drug discovery, summarizing their reported inhibitors and describing their current or potential exploitation as anticancer agents. Finally, we also focus on additional NAD+-producing enzymes acting in alternative NAD+-producing routes that could also be relevant in tumors and thus become viable targets for drug discovery.

Enhancing nicotinamide N-methyltransferase bisubstrate inhibitor activity through 7-deazaadenosine and linker modifications

Nicotinamide N-methyltransferase (NNMT) catalyzes the transfer of a methyl group from S-adenosylmethionine (SAM) to nicotinamide (NAM) and other pyridine-related compounds and is involved in various metabolic processes in the human body. In addition, abnormal expression of NNMT occurs under various pathological conditions such as cancer, diabetes, metabolic disorders, and neurodegenerative diseases, making it a promising drug target worthy of in-depth research. Small-molecule NNMT inhibitors with high potency and selectivity are necessary chemical tools to test biological hypotheses and potential therapies. In this study, we developed a series of highly active NNMT inhibitors by modifying N7 position of adenine. Among them, compound 3-12 (IC50 = 47.9 ± 0.6 nM) exhibited potent inhibitory activity and also had an excellent selectivity profile over a panel of human methyltransferases. We showed that the N7 position of adenine in the NNMT bisubstrate inhibitor was a modifiable site, thus offering insights into the development of NNMT inhibitors.

N1-methylnicotinamide impairs gestational glucose tolerance in mice

N1-methylnicotinamide (MNAM), a product of methylation of nicotinamide through nicotinamide N-methyltransferase, displays antidiabetic effects in male rodents. This study aimed to evaluate the ameliorative potential of MNAM on glucose metabolism in a gestational diabetes mellitus (GDM) model. C57BL/6N mice were fed with a high-fat diet (HFD) for 6 weeks before pregnancy and throughout gestation to establish the GDM model. Pregnant mice were treated with 0.3% or 1% MNAM during gestation. MNAM supplementation in CHOW diet and HFD both impaired glucose tolerance at gestational day 14.5 without changes in insulin tolerance. However, MNAM supplementation reduced hepatic lipid accumulation as well as mass and inflammation in visceral adipose tissue. MNAM treatment decreased GLUT4 mRNA and protein expression in skeletal muscle, where NAD+ salvage synthesis and antioxidant defenses were dampened. The NAD+/sirtuin system was enhanced in liver, which subsequently boosted hepatic gluconeogenesis. GLUT1 protein was diminished in placenta by MNAM. In addition, weight of placenta, fetus weight, and litter size were not affected by MNAM treatment. The decreased GLUT4 in skeletal muscle, boosted hepatic gluconeogenesis and dampened GLUT1 in placenta jointly contribute to the impairment of glucose tolerance tests by MNAM. Our data provide evidence for the careful usage of MNAM in treatment of GDM.

Control of NAD+ homeostasis by autophagic flux modulates mitochondrial and cardiac function

Impaired autophagy is known to cause mitochondrial dysfunction and heart failure, in part due to altered mitophagy and protein quality control. However, whether additional mechanisms are involved in the development of mitochondrial dysfunction and heart failure in the setting of deficient autophagic flux remains poorly explored. Here, we show that impaired autophagic flux reduces nicotinamide adenine dinucleotide (NAD+) availability in cardiomyocytes. NAD+ deficiency upon autophagic impairment is attributable to the induction of nicotinamide N-methyltransferase (NNMT), which methylates the NAD+ precursor nicotinamide (NAM) to generate N-methyl-nicotinamide (MeNAM). The administration of nicotinamide mononucleotide (NMN) or inhibition of NNMT activity in autophagy-deficient hearts and cardiomyocytes restores NAD+ levels and ameliorates cardiac and mitochondrial dysfunction. Mechanistically, autophagic inhibition causes the accumulation of SQSTM1, which activates NF-κB signaling and promotes NNMT transcription. In summary, we describe a novel mechanism illustrating how autophagic flux maintains mitochondrial and cardiac function by mediating SQSTM1-NF-κB-NNMT signaling and controlling the cellular levels of NAD+.

Urine and serum metabolomic analysis of endometrial cancer diagnosis and classification based on ultra-performance liquid chromatography mass spectrometry

OBJECTIVE

This study aimed to reveal the urinary and serum metabolic pattern of endometrial cancer (EC) and establish diagnostic models to identify EC from controls, high-risk from low-risk EC, and type II from type I EC.

METHOD

This study included 146 EC patients (comprising 79 low-risk and 67 high-risk patients, including 124 type I and 22 type II) and 59 controls. The serum and urine samples were analyzed using ultraperformance liquid chromatography mass spectrometry. Analysis was used to elucidate the distinct metabolites and altered metabolic pathways. Receiver operating characteristic (ROC) analyses were employed to discover and validate the potential biomarker models.

RESULTS

Serum and urine metabolomes displayed significant differences between EC and controls, with metabolites related to amino acid and nicotinamide metabolisms. The serum and urine panels distinguished these two groups with Area Under the Curve (AUC) of 0.821 and 0.902, respectively. The panel consisting of serum and urine metabolites demonstrated the best predictive ability (AUC = 0.953 and 0.976 in discovering and validation group). In comparing high-risk and low risk EC, differential metabolites were enriched in purine and glutamine metabolism. The AUC values for serum and urine panels were 0.818, and 0.843, respectively. The combined panel exhibited better predictive accuracy (0.881 in discovering group and 0.936 in external validation). In the comparison between type I and type II group, altered folic acid metabolism was identified. The serum, urine and combined panels discriminated these two groups with the AUC of 0.829, 0.913 and 0.922, respectively.

CONCLUSION

The combined urine and serum metabolome effectively revealed the metabolic patterns in EC patients, offering valuable diagnostic models for EC diagnosis and classification.

NAD+ Metabolism-Related Gene Profile Can Be a Relevant Source of Squamous Cell Carcinoma Biomarkers

Poor survival rates of squamous cell carcinomas (SCCs) are associated with high recurrence, metastasis, and late diagnosis, due in part to a limited number of reliable biomarkers. Thus, the identification of signatures improving the diagnosis of different SCC types is mandatory. Considering the relevant role of NAD+ metabolism in SCC chemoprevention and therapy, the study aimed at identifying new biomarkers based on NAD+ metabolism-related gene (NMRG) expression. Gene expression of 18 NMRGs and clinical-pathological information for patients with head and neck SCC (HNSCC), lung SCC (LuSCC), and cervix SCC (CeSCC) from The Cancer Genome Atlas (TCGA) were analyzed by several bioinformatic tools. We identified a 16-NMRG profile discriminating 3 SCCs from 3 non-correlated tumors. We found several genes for HNSCC, LuSCC, and CeSCC with high diagnostic power. Notably, three NMRGs were SCC-type specific biomarkers. Furthermore, specific signatures displayed high diagnostic power for several clinical-pathological characteristics. Analyzing tumor-infiltrating immune cell profiles and PD-1/PD-L1 levels, we found that NMRG expression was associated with suppressive immune microenvironment mainly in HNSCC. Finally, the evaluation of patient survival identified specific genes for HNSCC, LuSCC, and CeSCC with potential prognostic power. Therefore, our analyses indicate NAD+ metabolism as an important source of SCC biomarkers and potential therapeutic targets.

NAD+, Axonal Maintenance, and Neurological Disease

Significance: The remarkable geometry of the axon exposes it to unique challenges for survival and maintenance. Axonal degeneration is a feature of peripheral neuropathies, glaucoma, and traumatic brain injury, and an early event in neurodegenerative diseases. Since the discovery of Wallerian degeneration (WD), a molecular program that hijacks nicotinamide adenine dinucleotide (NAD+) metabolism for axonal self-destruction, the complex roles of NAD+ in axonal viability and disease have become research priority. Recent Advances: The discoveries of the protective Wallerian degeneration slow (WldS) and of sterile alpha and TIR motif containing 1 (SARM1) activation as the main instructive signal for WD have shed new light on the regulatory role of NAD+ in axonal degeneration in a growing number of neurological diseases. SARM1 has been characterized as a NAD+ hydrolase and sensor of NAD+ metabolism. The discovery of regulators of nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) proteostasis in axons, the allosteric regulation of SARM1 by NAD+ and NMN, and the existence of clinically relevant windows of action of these signals has opened new opportunities for therapeutic interventions, including SARM1 inhibitors and modulators of NAD+ metabolism. Critical Issues: Events upstream and downstream of SARM1 remain unclear. Furthermore, manipulating NAD+ metabolism, an overdetermined process crucial in cell survival, for preventing the degeneration of the injured axon may be difficult and potentially toxic. Future Directions: There is a need for clarification of the distinct roles of NAD+ metabolism in axonal maintenance as contrasted to WD. There is also a need to better understand the role of NAD+ metabolism in axonal endangerment in neuropathies, diseases of the white matter, and the early stages of neurodegenerative diseases of the central nervous system. Antioxid. Redox Signal. 39, 1167-1184.

A cane toad (Rhinella marina) N-methyltransferase converts primary indolethylamines to tertiary psychedelic amines

Psychedelic indolethylamines have emerged as potential medicines to treat several psychiatric pathologies. Natural sources of these compounds include 'magic mushrooms' (Psilocybe spp.), plants used to prepare ayahuasca, and toads. The skin and parotid glands of certain toads accumulate a variety of specialized metabolites including toxic guanidine alkaloids, lipophilic alkaloids, poisonous steroids, and hallucinogenic indolethylamines such as DMT, 5-methoxy-DMT, and bufotenin. The occurrence of psychedelics has contributed to the ceremonial use of toads, particularly among Mesoamerican peoples. Yet, the biosynthesis of psychedelic alkaloids has not been elucidated. Herein, we report a novel indolethylamine N-methyltransferase (RmNMT) from cane toad (Rhinella marina). The RmNMT sequence was used to identify a related NMT from the common toad, Bufo bufo. Close homologs from various frog species were inactive, suggesting a role for psychedelic indolethylamine biosynthesis in toads. Enzyme kinetic analyses and comparison with functionally similar enzymes showed that recombinant RmNMT was an effective catalyst and not product inhibited. The substrate promiscuity of RmNMT enabled the bioproduction of a variety of substituted indolethylamines at levels sufficient for purification, pharmacological screening, and metabolic stability assays. Since the therapeutic potential of psychedelics has been linked to activity at serotonergic receptors, we evaluated binding of derivatives at 5-HT1A and 5-HT2A receptors. Primary amines exhibited enhanced affinity at the 5-HT1A receptor compared with tertiary amines. With the exception of 6-substituted derivatives, N,N-dimethylation also protected against catabolism by liver microsomes.

Histone methyltransferase activity affects metabolism in human cells independently of transcriptional regulation

The N-terminal tails of eukaryotic histones are frequently posttranslationally modified. The role of these modifications in transcriptional regulation is well-documented. However, the extent to which the enzymatic processes of histone posttranslational modification might affect metabolic regulation is less clear. Here, we investigated how histone methylation might affect metabolism using metabolomics, proteomics, and RNA-seq data from cancer cell lines, primary tumour samples and healthy tissue samples. In cancer, the expression of histone methyltransferases (HMTs) was inversely correlated to the activity of NNMT, an enzyme previously characterised as a methyl sink that disposes of excess methyl groups carried by the universal methyl donor S-adenosyl methionine (SAM or AdoMet). In healthy tissues, histone methylation was inversely correlated to the levels of an alternative methyl sink, PEMT. These associations affected the levels of multiple histone marks on chromatin genome-wide but had no detectable impact on transcriptional regulation. We show that HMTs with a variety of different associations to transcription are co-regulated by the Retinoblastoma (Rb) tumour suppressor in human cells. Rb-mutant cancers show increased total HMT activity and down-regulation of NNMT. Together, our results suggest that the total activity of HMTs affects SAM metabolism, independent of transcriptional regulation.

Nitrogen-15 dynamic nuclear polarization of nicotinamide derivatives in biocompatible solutions

Dissolution dynamic nuclear polarization (dDNP) increases the sensitivity of magnetic resonance imaging by more than 10,000 times, enabling in vivo metabolic imaging to be performed noninvasively in real time. Here, we are developing a group of dDNP polarized tracers based on nicotinamide (NAM). We synthesized 1-15N-NAM and 1-15N nicotinic acid and hyperpolarized them with dDNP, reaching (13.0 ± 1.9)% 15N polarization. We found that the lifetime of hyperpolarized 1-15N-NAM is strongly field- and pH-dependent, with T1 being as long as 41 s at a pH of 12 and 1 T while as short as a few seconds at neutral pH and fields below 1 T. The remarkably short 1-15N lifetime at low magnetic fields and neutral pH drove us to establish a unique pH neutralization procedure. Using 15N dDNP and an inexpensive rodent imaging probe designed in-house, we acquired a 15N MRI of 1-15N-NAM (previously hyperpolarized for more than an hour) in less than 1 s.

Structure-Activity Relationship Studies on Cell-Potent Nicotinamide N-Methyltransferase Bisubstrate Inhibitors

Nicotinamide N-methyltransferase (NNMT) is a metabolic enzyme implicated in multiple diseases, making it a promising therapeutic target. Building upon our recently reported NNMT inhibitor II399, we systematically investigate the structure-activity relationship by designing and synthesizing a series of analogues. Among them, two top inhibitors II559 (Ki = 1.2 nM) and II802 (Ki = 1.6 nM) displayed over 5000-fold selectivity for NNMT over closely related methyltransferases. Moreover, II559 and II802 showed enhanced cellular inhibition, with a cellular IC50 value of approximately 150 nM, making them the most cell-potent bisubstrate inhibitors reported to date. Furthermore, both inhibitors reduced the cell viability with a GI50 value of ∼10 μM and suppressed the migration of aggressive clear cell renal cancer cell carcinoma cell lines. Overall, II559 and II802 would serve as valuable probes to investigate the enzymatic function of NNMT in health and diseases.

Nicotinamide N-Methyl Transferase as a Predictive Marker of Tubular Fibrosis in CKD

Purpose

Chronic kidney disease (CKD) progression is complex. There are not standardized methods for predicting the prognosis of CKD. Nicotinamide N-methyltransferase (NNMT) has been shown to be associated with renal fibrosis. This study aimed to validate NNMT as a prognostic biomarker of progressive CKD.

Patients and Methods

We explored the relationship between NNMT expression and CKD-related outcome variables using the NephroseqV5 and GEO databases. Additionally, a validation set of 37 CKD patients was enrolled to measure the correlation between NNMT expression levels and CKD outcomes. Furthermore, single-cell RNA sequencing data and the Human Protein Atlas were reanalyzed to investigate the expression specificity of NNMT in the kidney. Finally, to detect the status of NNMT expression with tubular fibrosis in vivo, we constructed a unilateral ureteral obstruction (UUO) mouse treated with an NNMT inhibitor.

Results

Analyzing the datasets showed that NNMT was expressed mainly in proximal tubule compartments. And patients with high NNMT expression levels had a significantly lower overall survival rate compared to those with low NNMT expression levels (P = 0.013). NNMT was independent of prognosis factors in the multivariate Cox regression model, and the AUCs for CKD progression at 1, 3, and 5 years were 0.849, 0.775, and 0.877, respectively. Pathway enrichment analysis indicated that NNMT regulates the biological processes of tubulointerstitial fibrosis (TIF). In the validation group, NNMT levels were significantly higher in the CKD group combined with interstitial fibrosis. In vivo, NNMT was a high expression in the UUO group, peaking at postoperative day 21. Treatment with an NNMT inhibitor improved renal tubular interstitial fibrosis, and expression levels of FN, α-SMA, VIM, and TGF-β1 were decreased compared with UUO (P < 0.05).

Conclusion

NNMT was expressed mainly in tubular renal compartments, and associated with CKD prognosis. It holds potential as a diagnostic biomarker for tubular fibrosis in CKD.

Defining NAD(P)(H) Catabolism

Dietary vitamin B3 components, such as nicotinamide and nicotinic acid, are precursors to the ubiquitous redox cofactor nicotinamide adenine dinucleotide (NAD⁺). NAD⁺ levels are thought to decline with age and disease. While the drivers of this decline remain under intense investigation, strategies have emerged seeking to functionally maintain NAD⁺ levels through supplementation with NAD⁺ biosynthetic intermediates. These include marketed products, such as nicotinamide riboside (NR) and its phosphorylated form (NMN). More recent developments have shown that NRH (the reduced form of NR) and its phosphorylated form NMNH also increases NAD⁺ levels upon administration, although they initially generate NADH (the reduced form of NAD⁺). Other means to increase the combined levels of NAD⁺ and NADH, NAD(H), include the inhibition of NAD⁺-consuming enzymes or activation of biosynthetic pathways. Multiple studies have shown that supplementation with an NAD(H) precursor changes the profile of NAD(H) catabolism. Yet, the pharmacological significance of NAD(H) catabolites is rarely considered although the distribution and abundance of these catabolites differ depending on the NAD(H) precursor used, the species in which the study is conducted, and the tissues used for the quantification. Significantly, some of these metabolites have emerged as biomarkers in physiological disorders and might not be innocuous. Herein, we review the known and emerging catabolites of the NAD(H) metabolome and highlight their biochemical and physiological function as well as key chemical and biochemical reactions leading to their formation. Furthermore, we emphasize the need for analytical methods that inform on the full NAD(H) metabolome since the relative abundance of NAD(H) catabolites informs how NAD(H) precursors are used, recycled, and eliminated.

Nicotinamide N-methyltransferase sustains a core epigenetic program that promotes metastatic colonization in breast cancer

Metastatic colonization of distant organs accounts for over 90% of deaths related to solid cancers, yet the molecular determinants of metastasis remain poorly understood. Here, we unveil a mechanism of colonization in the aggressive basal-like subtype of breast cancer that is driven by the NAD+ metabolic enzyme nicotinamide N-methyltransferase (NNMT). We demonstrate that NNMT imprints a basal genetic program into cancer cells, enhancing their plasticity. In line, NNMT expression is associated with poor clinical outcomes in patients with breast cancer. Accordingly, ablation of NNMT dramatically suppresses metastasis formation in pre-clinical mouse models. Mechanistically, NNMT depletion results in a methyl overflow that increases histone H3K9 trimethylation (H3K9me3) and DNA methylation at the promoters of PR/SET Domain-5 (PRDM5) and extracellular matrix-related genes. PRDM5 emerged in this study as a pro-metastatic gene acting via induction of cancer-cell intrinsic transcription of collagens. Depletion of PRDM5 in tumor cells decreases COL1A1 deposition and impairs metastatic colonization of the lungs. These findings reveal a critical activity of the NNMT-PRDM5-COL1A1 axis for cancer cell plasticity and metastasis in basal-like breast cancer.

Nicotinamide N-methyltransferase upregulation contributes to palmitate-elicited peroxisome proliferator-activated receptor transactivation in hepatocytes

Peroxisome proliferator-activated receptor γ (PPARγ) plays a pivotal role in regulating lipid metabolism and hepatic PPARγ transactivation contributes to fatty liver development. Fatty acids (FAs) are well-known endogenous ligands for PPARγ. Palmitate, a 16-C saturated FA (SFA) and the most abundant SFA in human circulation, is a strong inducer of hepatic lipotoxicity, a central pathogenic factor for various fatty liver diseases. In this study, using both alpha mouse liver 12 (AML12) and primary mouse hepatocytes, we investigated the effects of palmitate on hepatic PPARγ transactivation and underlying mechanisms, as well as the role of PPARγ transactivation in palmitate-induced hepatic lipotoxicity, all of which remain ambiguous currently. Our data revealed that palmitate exposure was concomitant with both PPARγ transactivation and upregulation of nicotinamide N-methyltransferase (NNMT), a methyltransferase catalyzing the degradation of nicotinamide, the predominant precursor for cellular NAD+ biosynthesis. Importantly, we discovered that PPARγ transactivation by palmitate was blunted by NNMT inhibition, suggesting that NNMT upregulation plays a mechanistic role in PPARγ transactivation. Further investigations uncovered that palmitate exposure is associated with intracellular NAD+ decline and NAD+ replenishment with NAD+-enhancing agents, nicotinamide and nicotinamide riboside, obstructed palmitate-induced PPARγ transactivation, implying that cellular NAD+ decline resulted from NNMT upregulation represents a potential mechanism behind palmitate-elicited PPARγ transactivation. At last, our data showed that the PPARγ transactivation marginally ameliorated palmitate-induced intracellular triacylglycerol accumulation and cell death. Collectively, our data provided the first-line evidence supporting that NNMT upregulation plays a mechanistic role in palmitate-elicited PPARγ transactivation, potentially through reducing cellular NAD+ contents.NEW & NOTEWORTHY Hepatic PPARγ transactivation contributes to fatty liver development. Saturated fatty acids (SFAs) induce hepatic lipotoxicity. Here, we investigated whether and how palmitate, the most abundant SFA in the human blood, affects PPARγ transactivation in hepatocytes. We reported for the first time that upregulation of nicotinamide N-methyltransferase (NNMT), a methyltransferase catalyzing the degradation of nicotinamide, the predominant precursor for cellular NAD+ biosynthesis, plays a mechanistic role in regulating palmitate-elicited PPARγ transactivation through reducing intracellular NAD+ contents.

Urinary Exosomal Metabolites: Overlooked Clue for Predicting Cardiovascular Risk

Over the last decade, increasing research has focused on urinary exosomes (UEs) in biological fluids and their relationship with physiological and pathological processes. UEs are membranous vesicles with a size of 40-100 nm, containing a number of bioactive molecules such as proteins, lipids, mRNAs, and miRNAs. These vesicles are an inexpensive non-invasive source that can be used in clinical settings to differentiate healthy patients from diseased patients, thereby serving as potential biomarkers for the early identification of disease. Recent studies have reported the isolation of small molecules called exosomal metabolites from individuals' urine with different diseases. These metabolites could utilize for a variety of purposes, such as the discovery of biomarkers, investigation of mechanisms related to disease development, and importantly prediction of cardiovascular diseases (CVDs) risk factors, including thrombosis, inflammation, oxidative stress, hyperlipidemia as well as homocysteine. It has been indicated that alteration in urinary metabolites of N1-methylnicotinamide, 4-aminohippuric acid, and citric acid can be valuable in predicting cardiovascular risk factors, providing a novel approach to evaluating the pathological status of CVDs. Since the UEs metabolome has been clearly and precisely so far unexplored in CVDs, the present study has specifically addressed the role of the mentioned metabolites in the prediction of CVDs risk factors.

Metabolomic and transcriptomic analyses of Fmo5-/- mice reveal roles for flavin-containing monooxygenase 5 (FMO5) in NRF2-mediated oxidative stress response, unfolded protein response, lipid homeostasis, and carbohydrate and one-carbon metabolism

Flavin-containing monooxygenase 5 (FMO5) is a member of the FMO family of proteins, best known for their roles in the detoxification of foreign chemicals and, more recently, in endogenous metabolism. We have previously shown that Fmo5-/- mice display an age-related lean phenotype, with much reduced weight gain from 20 weeks of age. The phenotype is characterized by decreased fat deposition, lower plasma concentrations of glucose, insulin and cholesterol, higher glucose tolerance and insulin sensitivity, and resistance to diet-induced obesity. In the present study we report the use of metabolomic and transcriptomic analyses of livers of Fmo5-/- and wild-type mice to identify factors underlying the lean phenotype of Fmo5-/- mice and gain insights into the function of FMO5. Metabolomics was performed by the Metabolon platform, utilising ultrahigh performance liquid chromatography-tandem mass spectroscopy. Transcriptomics was performed by RNA-Seq and results analysed by DESeq2. Disruption of the Fmo5 gene has wide-ranging effects on the abundance of metabolites and expression of genes in the liver. Metabolites whose concentration differed between Fmo5-/- and wild-type mice include several saturated and monounsaturated fatty acids, complex lipids, amino acids, one-carbon intermediates and ADP-ribose. Among the genes most significantly and/or highly differentially expressed are Apoa4, Cd36, Fitm1, Hspa5, Hyou1, Ide, Me1 and Mme. The results reveal that FMO5 is involved in upregulating the NRF2-mediated oxidative stress response, the unfolded protein response and response to hypoxia and cellular stress, indicating a role for the enzyme in adaptation to oxidative and metabolic stress. FMO5 also plays a role in stimulating a wide range of metabolic pathways and processes, particularly ones involved in lipid homeostasis, the uptake and metabolism of glucose, the generation of cytosolic NADPH, and in one-carbon metabolism. The results predict that FMO5 acts by stimulating the NRF2, XBP1, PPARA and PPARG regulatory pathways, while inhibiting STAT1 and IRF7 pathways.

Enzymatic Fluoromethylation Enabled by the S-Adenosylmethionine Analog Te-Adenosyl-L-(fluoromethyl)homotellurocysteine

Fluoromethyl, difluoromethyl, and trifluoromethyl groups are present in numerous pharmaceuticals and agrochemicals, where they play critical roles in the efficacy and metabolic stability of these molecules. Strategies for late-stage incorporation of fluorine-containing atoms in molecules have become an important area of organic and medicinal chemistry as well as synthetic biology. Herein, we describe the synthesis and use of Te-adenosyl-L-(fluoromethyl)homotellurocysteine (FMeTeSAM), a novel and biologically relevant fluoromethylating agent. FMeTeSAM is structurally and chemically related to the universal cellular methyl donor S-adenosyl-L-methionine (SAM) and supports the robust transfer of fluoromethyl groups to oxygen, nitrogen, sulfur, and some carbon nucleophiles. FMeTeSAM is also used to fluoromethylate precursors to oxaline and daunorubicin, two complex natural products that exhibit antitumor properties.

Source of nicotinamide governs its metabolic fate in cultured cells, mice, and humans

Metabolic routing of nicotinamide (NAM) to NAD⁺ or 1-methylnicotinamide (MeNAM) has impacts on human health and aging. NAM is imported by cells or liberated from NAD⁺. The fate of ²H₄-NAM in cultured cells, mice, and humans was determined by stable isotope tracing. ²H₄-NAM is an NAD⁺ precursor via the salvage pathway in cultured A549 cells and human PBMCs and in A549 cell xenografts and PBMCs from ²H₄-NAM-dosed mice and humans, respectively. ²H₄-NAM is a MeNAM precursor in A549 cell cultures and xenografts, but not isolated PBMCs. NAM released from NAD⁺ is a poor MeNAM precursor. Additional A549 cell tracer studies yielded further mechanistic insight. NAMPT activators promote NAD⁺ synthesis and consumption. Surprisingly, NAM liberated from NAD⁺ in NAMPT activator-treated A549 cells is also routed toward MeNAM production. Metabolic fate mapping of the dual NAM sources across the translational spectrum (cells, mice, humans) illuminates a key regulatory node governing NAD⁺ and MeNAM synthesis.

Identification of novel human nicotinamide N-methyltransferase inhibitors: a structure-based pharmacophore modeling and molecular dynamics approach

Human nicotinamide N-methyltransferase (hNNMT) is a cytosolic enzyme associated in the phase-II metabolism, belonging to the S-adenosyl-L-methionine (SAM)-dependent methyltransferases family. Overexpression of hNNMT was observed in diseases such as metabolic disorders and different types of cancers, which suggest NNMT as a prospective therapeutic target. In this study we propose a structure-based pharmacophore model to understand the structural features responsible for the pharmacological activity. The generated model was validated using the ROC curve (AUC), goodness of hit score (GH), specificity, sensitivity and enrichment factor (EF). The pharmacophore was employed to retrieve active molecules from the ZINC database, followed by virtual-screening and molecular docking. Six molecules with the best pharmfit score, binding energy and ADMET properties were identified in this study. A 150 ns molecular dynamics simulation was performed on the selected molecules complexed with hNNMT protein to validate the results. The molecules ZINC35464499, ZINC13311192, ZINC31159282, ZINC14650833, ZINC14819515 and ZINC00303881 were identified, which could be act as the potential hNNMT inhibitors and can also be used as direct hits for developing novel hNNMT antagonists.Communicated by Ramaswamy H. Sarma.

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.

NAD+ Homeostasis and NAD+-Consuming Enzymes: Implications for Vascular Health

Nicotinamide adenine dinucleotide (NAD⁺) is a ubiquitous metabolite that takes part in many key redox reactions. NAD⁺ biosynthesis and NAD⁺-consuming enzymes have been attracting markedly increasing interest since they have been demonstrated to be involved in several crucial biological pathways, impacting genes transcription, cellular signaling, and cell cycle regulation. As a consequence, many pathological conditions are associated with an impairment of intracellular NAD⁺ levels, directly or indirectly, which include cardiovascular diseases, obesity, neurodegenerative diseases, cancer, and aging. In this review, we describe the general pathways involved in the NAD⁺ biosynthesis starting from the different precursors, analyzing the actual state-of-art of the administration of NAD⁺ precursors or blocking NAD⁺-dependent enzymes as strategies to increase the intracellular NAD⁺ levels or to counteract the decline in NAD⁺ levels associated with ageing. Subsequently, we focus on the disease-related and age-related alterations of NAD⁺ homeostasis and NAD⁺-dependent enzymes in endothelium and the consequent vascular dysfunction, which significantly contributes to a wide group of pathological disorders.

Metabolomics study of ribavirin in the treatment of orthotopic lung cancer based on UPLC-Q-TOF/MS

Ribavirin is a common antiviral drug, especially for patients with hepatitis C. Our recent studies demonstrated that ribavirin showed anti-tumor activity in colorectal cancer and hepatocellular carcinoma, but its effects on lung cancer remains unclear. This study aimed to evaluate the anti-tumor activity of ribavirin against lung cancer and elucidate the underlying mechanism. We established orthotopic mouse model of lung cancer (LLC and GLC-82) and employed an ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS)-based metabolomics approach. We found that ribavirin significantly inhibited the proliferation and colony formation of lung cancer cells. Tumor sizes of orthotopic lung cancer in ribavirin-treated groups were also significantly lower than those in control groups. Metabolomics analysis revealed that ribavirin mainly affected 5 metabolic pathways in orthotopic lung tumor models, taurine and hypotaurine metabolism, nicotinate and nicotinamide metabolism, linoleic acid metabolism, arginine biosynthesis and arachidonic acid metabolism. Furthermore, we identified 5 upregulated metabolites including β-nicotinamide adenine dinucleotide (NAD⁺), nicotinamide (NAM), taurine, ornithine and citrulline, and 7 downregulated metabolites including 1-methylnicotinamide (MNAM), S-adenosyl-l-homocysteine (SAH), N1-Methyl-2-pyridone-5-carboxamide (2PY), homocysteine (Hcy), linoleic acid, arachidonic acid (AA) and argininosuccinic acid in ribavirin-treated groups. These results provide new insight into the anti-tumor mechanism of ribavirin for lung cancer.

Correlation of NNMT and DKK1 Protein Expression With Clinicopathological Characteristics and Prognosis of Breast Cancer

Background

Nicotinamide N-methyltransferase (NNMT) and Dickkopf-1 (DKK1) play an important role in the development of breast cancer, and the purpose of this study was designed to examine the clinical and prognostic significance of NNMT and DKK1 in breast cancer.

Methods

The GEPIA2 database was used to evaluate the expression and survival of NNMT mRNA and DKK1 mRNA of breast cancer. Then an immunohistochemical study was carried out on 374 cases of breast tissue to identify the protein expression and significance of NNMT and DKK1. Next, the prognostic significance of DKK1 in breast cancer was explored by COX and Kaplan-Meier models.

Results

Protein NNMT expression was correlated with lymph node metastasis and histological grade (P < .05) while protein DKK1 expression was related to tumor size, pT stage, histological grade, and Ki-67 (P < .05). Protein DKK1 was related to disease-specific survival (DSS), and low DKK1 expression indicated a poor prognosis of breast cancer patients (P < .05). Combined expression of protein NNMT and protein DKK1 predicted different prognosis of DSS (P < .05).

Conclusions

Nicotinamide N-methyltransferase and DKK1 were linked to breast cancer malignancy and invasion. Breast cancer patients with low DKK1 expression had a worse prognosis. Oncotypes of NNMT and DKK1 expression predicted patient outcomes.

Importance of NAD+ Anabolism in Metabolic, Cardiovascular and Neurodegenerative Disorders

The role of nicotinamide adenine dinucleotide (NAD+) in ageing has emerged as a critical factor in understanding links to a wide range of chronic diseases. Depletion of NAD+, a central redox cofactor and substrate of numerous metabolic enzymes, has been detected in many major age-related diseases. However, the mechanisms behind age-associated NAD+ decline remains poorly understood. Despite limited conclusive evidence, supplements aimed at increasing NAD+ levels are becoming increasingly popular. This review provides renewed insights regarding the clinical utility and benefits of NAD+ precursors, namely nicotinamide (NAM), nicotinic acid (NA), nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), in attenuating NAD+ decline and phenotypic characterization of age-related disorders, including metabolic, cardiovascular and neurodegenerative diseases. While it is anticipated that NAD+ precursors can play beneficial protective roles in several conditions, they vary in their ability to promote NAD+ anabolism with differing adverse effects. Careful evaluation of the role of NAD⁺, whether friend or foe in ageing, should be considered.

Nicotinamide riboside kinases regulate skeletal muscle fiber-type specification and are rate-limiting for metabolic adaptations during regeneration

Nicotinamide riboside kinases (NRKs) control the conversion of dietary Nicotinamide Riboside (NR) to NAD+, but little is known about their contribution to endogenous NAD+ turnover and muscle plasticity during skeletal muscle growth and remodeling. Using NRK1/2 double KO (NRKdKO) mice, we investigated the influence of NRKs on NAD+ metabolism and muscle homeostasis, and on the response to neurogenic muscle atrophy and regeneration following muscle injury. Muscles from NRKdKO animals have altered nicotinamide (NAM) salvage and a decrease in mitochondrial content. In single myonuclei RNAseq of skeletal muscle, NRK2 mRNA expression is restricted to type IIx muscle fibers, and perturbed NAD+ turnover and mitochondrial metabolism shifts the fiber type composition of NRKdKO muscle to fast glycolytic IIB fibers. NRKdKO does not influence muscle atrophy during denervation but alters muscle repair after myofiber injury. During regeneration, muscle stem cells (MuSCs) from NRKdKO animals hyper-proliferate but fail to differentiate. NRKdKO also alters the recovery of NAD+ during muscle regeneration as well as mitochondrial adaptations and extracellular matrix remodeling required for tissue repair. These metabolic perturbations result in a transient delay of muscle regeneration which normalizes during myofiber maturation at late stages of regeneration via over-compensation of anabolic IGF1-Akt signaling. Altogether, we demonstrate that NAD+ synthesis controls mitochondrial metabolism and fiber type composition via NRK1/2 and is rate-limiting for myogenic commitment and mitochondrial maturation during skeletal muscle repair.

Identification of Biological Functions and Prognostic Value of NNMT in Oral Squamous Cell Carcinoma

BACKGROUND

Nicotinamide N-methyltransferase (NNMT) is a metabolic enzyme that catalyzes the methylation of nicotinamide (NAM) to generate 1-methyl nicotinamide (MNAM). Although previous studies have shown that NNMT is frequently dysregulated to promote the onset and progression of many malignancies, its expression profile, prognostic value and function in oral squamous cell carcinoma (OSCC) are still unknown.

METHODS

We used untargeted metabolomics based on mass spectrometry to analyze potential metabolite differences between tumors and matched adjacent normal tissues in 40 OSCC patients. Immunohistochemistry (IHC) was used to analyze the NNMT expression profile in OSCC, and the diagnostic and prognostic values of NNMT were evaluated. Next, qPCR and Western blot were used to compare the expression of NNMT in five OSCC cell lines. Stable transfected cell lines were constructed, and functional experiments were carried out to elucidate the effects of NNMT on the proliferation and migration of OSCC cells. Finally, gene set enrichment analysis (GSEA) was performed using The Cancer Genome Atlas (TCGA) data to investigate the potential functional mechanisms of NNMT in OSCC.

RESULTS

We found that the nicotinamide metabolic pathway was abnormally activated in OSCC tumor tissues compared with normal tissues. NNMT was expressed ubiquitously in tumor cells (TCs) and fibroblast-like cells (FLCs) but was absent in tumor-infiltrating lymphocytes (TILs). OSCC patients with highly expressed NNMT in TCs had higher risk of lymph node metastasis and showed a worse pattern of invasion (POI). Moreover, patients with highly expressed NNMT were also susceptible to postoperative recurrence. Highly expressed NNMT can independently predict shorter disease-free survival and recurrence-free survival. Functionally, we demonstrated that the ectopic expression of NNMT promoted OSCC tumor cell proliferation and migration in vitro. Conversely, silencing exerted significantly opposite effects in vitro. In addition, GSEA showed that highly expressed NNMT was mainly enriched in the epithelial-mesenchymal transformation (EMT) pathway, which displayed a significant positive correlation with the six classic EMT markers.

CONCLUSIONS

Our study uncovered that NNMT may be a critical regulator of EMT in OSCC and may serve as a prognostic biomarker for OSCC patients. These findings might provide novel insights for future research in NNMT-targeted OSCC metastasis and recurrence therapy.

Novel tricyclic small molecule inhibitors of Nicotinamide N-methyltransferase for the treatment of metabolic disorders

Nicotinamide N-methyltransferase (NNMT) is a metabolic regulator that catalyzes the methylation of nicotinamide (Nam) using the co-factor S-adenosyl-L-methionine to form 1-methyl-nicotinamide (MNA). Overexpression of NNMT and the presence of the active metabolite MNA is associated with a number of diseases including metabolic disorders. We conducted a high-throughput screening campaign that led to the identification of a tricyclic core as a potential NNMT small molecule inhibitor series. Elaborate medicinal chemistry efforts were undertaken and hundreds of analogs were synthesized to understand the structure activity relationship and structure property relationship of this tricyclic series. A lead molecule, JBSNF-000028, was identified that inhibits human and mouse NNMT activity, reduces MNA levels in mouse plasma, liver and adipose tissue, and drives insulin sensitization, glucose modulation and body weight reduction in a diet-induced obese mouse model of diabetes. The co-crystal structure showed that JBSNF-000028 binds below a hairpin structural motif at the nicotinamide pocket and stacks between Tyr-204 (from Hairpin) and Leu-164 (from central domain). JBSNF-000028 was inactive against a broad panel of targets related to metabolism and safety. Interestingly, the improvement in glucose tolerance upon treatment with JBSNF-000028 was also observed in NNMT knockout mice with diet-induced obesity, pointing towards the glucose-normalizing effect that may go beyond NNMT inhibition. JBSNF-000028 can be a potential therapeutic option for metabolic disorders and developmental studies are warranted.

NNMT contributes to high metastasis of triple negative breast cancer by enhancing PP2A/MEK/ERK/c-Jun/ABCA1 pathway mediated membrane fluidity

Elucidating the mechanism for high metastasis capacity of triple negative breast cancers (TNBC) is crucial to improve treatment outcomes of TNBC. We have recently reported that nicotinamide N-methyltransferase (NNMT) is overexpressed in breast cancer, especially in TNBC, and predicts poor survival of patients undergoing chemotherapy. Here, we aimed to determine the function and mechanism of NNMT on metastasis of TNBC. Additionally, analysis of public datasets indicated that NNMT is involved in cholesterol metabolism. In vitro, NNMT overexpression promoted migration and invasion of TNBCs by reducing cholesterol levels in the cytoplasm and cell membrane. Mechanistically, NNMT activated MEK/ERK/c-Jun/ABCA1 pathway by repressing protein phosphatase 2A (PP2A) activity leading to cholesterol efflux and membrane fluidity enhancement, thereby promoting the epithelial-mesenchymal transition (EMT) of TNBCs. In vivo, the metastasis capacity of TNBCs was weakened by targeting NNMT. Collectively, our findings suggest a new molecular mechanism involving NNMT in metastasis and poor survival of TNBC mediated by PP2A and affecting cholesterol metabolism.

NNMT promotes the progression of intrahepatic cholangiocarcinoma by regulating aerobic glycolysis via the EGFR-STAT3 axis

Nicotinamide N-methyltransferase (NNMT), a member of the N-methyltransferase family, plays an important role in tumorigenesis. However, its expression and biological functions in intrahepatic cholangiocarcinoma (iCCA) remain to be established. In our study, we identified NNMT as an oncogene in iCCA and provided mechanistic insights into the roles of NNMT in iCCA progression. High NNMT expression in iCCA tissues was identified using western blotting and immunohistochemistry (IHC). We identified a significantly higher NNMT expression level in human iCCA tissues than that in adjacent normal tissues. Increased NNMT expression promoted iCCA cell proliferation and metastasis in vitro and in vivo. Mechanistically, NNMT inhibited the level of histone methylation in iCCA cells by consuming the methyl donor S-adenosyl methionine (SAM), thereby promoting the expression of epidermal growth factor receptor (EGFR). EGFR may activate the aerobic glycolysis pathway in iCCA cells by activating the STAT3 signaling pathway. In conclusion, we identified NNMT as an oncogene in iCCA and provided mechanistic insights into the roles of NNMT in iCCA progression.

RNA Modification in Inflammatory Bowel Diseases

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder characterized by damage to the intestinal mucosa, which is caused by a combination of factors. These include genetic and epigenetic alterations, environmental influence, microorganism interactions, and immune conditions. Some populations with IBD show a cancer-prone phenotype. Recent studies have provided insight into the involvement of RNA modifications in the specific pathogenesis of IBD through regulation of RNA biology in epithelial and immune cells. Studies of several RNA modification-targeting reagents have shown preferable outcomes in patients with colitis. Here, we note a new awareness of RNA modification in the targeting of IBD and related diseases, which will contribute to early diagnosis, disease monitoring, and possible control by innovative therapeutic approaches.

Qing-Wen-Jie-Re Mixture Ameliorates Poly (I:C)-Induced Viral Pneumonia Through Regulating the Inflammatory Response and Serum Metabolism

Qing-Wen-Jie-Re mixture (QWJR) has been used in the treatment of the coronavirus disease 2019 (COVID-19) in China. However, the protective mechanisms of QWJR on viral pneumonia remain unclear. In the present study, we first investigated the therapeutic effects of QWJR on a rat viral pneumonia model established by using polyinosinic-polycytidylic acid (poly (I:C)). The results indicated that QWJR could relieve the destruction of alveolar-capillary barrier in viral pneumonia rats, as represented by the decreased wet/dry weight (W/D) ratio in lung, total cell count and total protein concentration in bronchoalveolar lavage fluid (BALF). Besides, QWJR could also down-regulate the expression of inflammatory factors such as tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β and IL-6. More M1-type macrophage polarization was detected by calculating CD86⁺ cells and CD206⁺ cells and validated by the decline of inducible nitric oxide synthase (iNOS) and elevated arginase-1 (Arg-1) in lung. Finally, serum untargeted metabolomics analysis demonstrated that QWJR might take effect through regulating arginine metabolism, arachidonic acid (AA) metabolism, tricarboxylic acid (TCA) cycle, nicotinate and nicotinamide metabolism processes.

Remote solid cancers rewire hepatic nitrogen metabolism via host nicotinamide-N-methyltransferase

Cancers disrupt host homeostasis in various manners but the identity of host factors underlying such disruption remains largely unknown. Here we show that nicotinamide-N-methyltransferase (NNMT) is a host factor that mediates metabolic dysfunction in the livers of cancer-bearing mice. Multiple solid cancers distantly increase expression of Nnmt and its product 1-methylnicotinamide (MNAM) in the liver. Multi-omics analyses reveal suppression of the urea cycle accompanied by accumulation of amino acids, and enhancement of uracil biogenesis in the livers of cancer-bearing mice. Importantly, genetic deletion of Nnmt leads to alleviation of these metabolic abnormalities, and buffers cancer-dependent weight loss and reduction of the voluntary wheel-running activity. Our data also demonstrate that MNAM is capable of affecting urea cycle metabolites in the liver. These results suggest that cancers up-regulate the hepatic NNMT pathway to rewire liver metabolism towards uracil biogenesis rather than nitrogen disposal via the urea cycle, thereby disrupting host homeostasis.

The presence of cancer can induce systemic disruption of the host homeostasis. Here, the authors show that different solid tumours remotely increase hepatic nicotinamide-Nmethyltransferase disrupting the host urea cycle metabolism in the liver.

Nicotinamide N-Methyltransferase: A Promising Biomarker and Target for Human Cancer Therapy

Cancer cells typically exhibit a tightly regulated program of metabolic plasticity and epigenetic remodeling to meet the demand of uncontrolled cell proliferation. The metabolic-epigenetic axis has recently become an increasingly hot topic in carcinogenesis and offers new avenues for innovative and personalized cancer treatment strategies. Nicotinamide N-methyltransferase (NNMT) is a metabolic enzyme involved in controlling methylation potential, impacting DNA and histone epigenetic modification. NNMT overexpression has been described in various solid cancer tissues and even body fluids, including serum, urine, and saliva. Furthermore, accumulating evidence has shown that NNMT knockdown significantly decreases tumorigenesis and chemoresistance capacity. Most importantly, the natural NNMT inhibitor yuanhuadine can reverse epidermal growth factor receptor tyrosine kinase inhibitor resistance in lung cancer cells. In this review, we evaluate the possibility of NNMT as a diagnostic biomarker and molecular target for effective anticancer treatment. We also reveal the exact mechanisms of how NNMT affects epigenetics and the development of more potent and selective inhibitors.

Renal Transporter-Mediated Drug-Biomarker Interactions of the Endogenous Substrates Creatinine and N1 -Methylnicotinamide: A PBPK Modeling Approach

Endogenous biomarkers for transporter-mediated drug-drug interaction (DDI) predictions represent a promising approach to facilitate and improve conventional DDI investigations in clinical studies. This approach requires high sensitivity and specificity of biomarkers for the targets of interest (e.g., transport proteins), as well as rigorous characterization of their kinetics, which can be accomplished utilizing physiologically-based pharmacokinetic (PBPK) modeling. Therefore, the objective of this study was to develop PBPK models of the endogenous organic cation transporter (OCT)2 and multidrug and toxin extrusion protein (MATE)1 substrates creatinine and N¹ -methylnicotinamide (NMN). Additionally, this study aimed to predict kinetic changes of the biomarkers during administration of the OCT2 and MATE1 perpetrator drugs trimethoprim, pyrimethamine, and cimetidine. Whole-body PBPK models of creatinine and NMN were developed utilizing studies investigating creatinine or NMN exogenous administration and endogenous synthesis. The newly developed models accurately describe and predict observed plasma concentration-time profiles and urinary excretion of both biomarkers. Subsequently, models were coupled to the previously built and evaluated perpetrator models of trimethoprim, pyrimethamine, and cimetidine for interaction predictions. Increased creatinine plasma concentrations and decreased urinary excretion during the drug-biomarker interactions with trimethoprim, pyrimethamine, and cimetidine were well-described. An additional inhibition of NMN synthesis by trimethoprim and pyrimethamine was hypothesized, improving NMN plasma and urine interaction predictions. To summarize, whole-body PBPK models of creatinine and NMN were built and evaluated to better assess creatinine and NMN kinetics while uncovering knowledge gaps for future research. The models can support investigations of renal transporter-mediated DDIs during drug development.

COVID-19: Are We Facing Secondary Pellagra Which Cannot Simply Be Cured by Vitamin B3?

Immune response to SARS-CoV-2 and ensuing inflammation pose a huge challenge to the host’s nicotinamide adenine dinucleotide (NAD⁺) metabolism. Humans depend on vitamin B3 for biosynthesis of NAD⁺, indispensable for many metabolic and NAD⁺-consuming signaling reactions. The balance between its utilization and resynthesis is vitally important. Many extra-pulmonary symptoms of COVID-19 strikingly resemble those of pellagra, vitamin B3 deficiency (e.g., diarrhoea, dermatitis, oral cavity and tongue manifestations, loss of smell and taste, mental confusion). In most developed countries, pellagra is successfully eradicated by vitamin B3 fortification programs. Thus, conceivably, it has not been suspected as a cause of COVID-19 symptoms. Here, the deregulation of the NAD⁺ metabolism in response to the SARS-CoV-2 infection is reviewed, with special emphasis on the differences in the NAD⁺ biosynthetic pathway’s efficiency in conditions predisposing for the development of serious COVID-19. SARS-CoV-2 infection-induced NAD⁺ depletion and the elevated levels of its metabolites contribute to the development of a systemic disease. Acute liberation of nicotinamide (NAM) in antiviral NAD⁺-consuming reactions potentiates “NAM drain”, cooperatively mediated by nicotinamide N-methyltransferase and aldehyde oxidase. “NAM drain” compromises the NAD⁺ salvage pathway’s fail-safe function. The robustness of the host’s NAD⁺ salvage pathway, prior to the SARS-CoV-2 infection, is an important determinant of COVID-19 severity and persistence of certain symptoms upon resolution of infection.

Complex roles of nicotinamide N-methyltransferase in cancer progression

Nicotinamide N-methyltransferase (NNMT) is an intracellular methyltransferase, catalyzing the N-methylation of nicotinamide (NAM) to form 1-methylnicotinamide (1-MNAM), in which S-adenosyl-l-methionine (SAM) is the methyl donor. High expression of NNMT can alter cellular NAM and SAM levels, which in turn, affects nicotinamide adenine dinucleotide (NAD⁺)-dependent redox reactions and signaling pathways, and remodels cellular epigenetic states. Studies have revealed that NNMT plays critical roles in the occurrence and development of various cancers, and analysis of NNMT expression levels in different cancers from The Cancer Genome Atlas (TCGA) dataset indicated that NNMT might be a potential biomarker and therapeutic target for tumor diagnosis and treatment. This review provides a comprehensive understanding of recent advances on NNMT functions in different tumors and deciphers the complex roles of NNMT in cancer progression.

Techniques to detect epitranscriptomic marks

Similar to epigenetic DNA modification, RNA can be methylated and altered for stability and processing. RNA modifications, i.e., epitranscriptomes involve three functions, that is, writing, erasing, and reading of marks. Methods for measurement and position detection are useful for the assessment of cellular function and human disease biomarkers. Since the first detection of pyrimidine 5-methylcytosine hundred years ago, numerous techniques have been developed to study the modifications of nucleotides, including RNAs. Recent studies focused on high throughput and direct measurements to investigate the precise function of epitranscriptomes, including the characterization of SARS-CoV-2. The current work presents an overview of the development of detection techniques for epitranscriptomic marks and updates recent progress on the related field.

Metabolic adaptation of ovarian tumors in patients treated with an IDO1 inhibitor constrains antitumor immune responses

To uncover underlying mechanisms associated with failure of indoleamine 2,3-dioxygenase 1 (IDO1) blockade in clinical trials, we conducted a pilot, window-of-opportunity clinical study in 17 patients with newly diagnosed advanced high-grade serous ovarian cancer before their standard tumor debulking surgery. Patients were treated with the IDO1 inhibitor epacadostat, and immunologic, transcriptomic, and metabolomic characterization of the tumor microenvironment was undertaken in baseline and posttreatment tumor biopsies. IDO1 inhibition resulted in efficient blockade of the kynurenine pathway of tryptophan degradation and was accompanied by a metabolic adaptation that shunted tryptophan catabolism toward the serotonin pathway. This resulted in elevated nicotinamide adenine dinucleotide (NAD⁺), which reduced T cell proliferation and function. Because NAD⁺ metabolites could be ligands for purinergic receptors, we investigated the impact of blocking purinergic receptors in the presence or absence of NAD⁺ on T cell proliferation and function in our mouse model. We demonstrated that A2a and A2b purinergic receptor antagonists, SCH58261 or PSB1115, respectively, rescued NAD⁺-mediated suppression of T cell proliferation and function. Combining IDO1 inhibition and A2a/A2b receptor blockade improved survival and boosted the antitumor immune signature in mice with IDO1 overexpressing ovarian cancer. These findings elucidate the downstream adaptive metabolic consequences of IDO1 blockade in ovarian cancers that may undermine antitumor T cell responses in the tumor microenvironment.

The CD38 glycohydrolase and the NAD sink: implications for pathological conditions

Nicotinamide adenine dinucleotide (NAD) acts as a cofactor in several oxidation-reduction (redox) reactions and is a substrate for a number of nonredox enzymes. NAD is fundamental to a variety of cellular processes including energy metabolism, cell signaling, and epigenetics. NAD homeostasis appears to be of paramount importance to health span and longevity, and its dysregulation is associated with multiple diseases. NAD metabolism is dynamic and maintained by synthesis and degradation. The enzyme CD38, one of the main NAD-consuming enzymes, is a key component of NAD homeostasis. The majority of CD38 is localized in the plasma membrane with its catalytic domain facing the extracellular environment, likely for the purpose of controlling systemic levels of NAD. Several cell types express CD38, but its expression predominates on endothelial cells and immune cells capable of infiltrating organs and tissues. Here we review potential roles of CD38 in health and disease and postulate ways in which CD38 dysregulation causes changes in NAD homeostasis and contributes to the pathophysiology of multiple conditions. Indeed, in animal models the development of infectious diseases, autoimmune disorders, fibrosis, metabolic diseases, and age-associated diseases including cancer, heart disease, and neurodegeneration are associated with altered CD38 enzymatic activity. Many of these conditions are modified in CD38-deficient mice or by blocking CD38 NADase activity. In diseases in which CD38 appears to play a role, CD38-dependent NAD decline is often a common denominator of pathophysiology. Thus, understanding dysregulation of NAD homeostasis by CD38 may open new avenues for the treatment of human diseases.

N1-Methylnicotinamide: Is It Time to Consider as a Dietary Supplement for Athletes?

Abstract:

Exercise is considered to be a “medicine” due to its modulatory roles in metabolic disorders such as diabetes and obesity. The intensity and duration of exercise determine the mechanism of energy production by various tissues of the body, especially by muscles, in which the requirement for adenosine triphosphate (ATP) increases by as much as 100-fold. Naturally, athletes try to improve their exercise performance by dietary supplementation with, e.g., vitamins, metabolites, and amino acids. MNAM, as a vitamin B3 metabolite, reduces serum levels and liver contents of triglycerides, and cholesterol and induces lipolysis. It stimulates gluconeogenesis and prohibits liver cholesterol and fatty acid synthesis through the expression of sirtuin1 (SIRT1). It seems that MNAM is not responsible for the actions of NNMT in the adipose tissues as MNAM inhibits the activity of NNMT in the adipose tissue and acts like inhibitors of its activity. NNMT-MNAM axis is more activated in the muscles of participants who were undergoing the high-volume-low-intensity exercise and caloric restriction. Therefore, MNAM could be an important myokine during exercise and fasting where it provides the required energy for muscles through the induction of lipolysis and gluconeogenesis in the liver and adipose tissues, respectively. Increased levels of MNAM in exercise and fasting led us to propose that the consumption of MNAM during training especially endurance training could boost exercise capacity and improves performance. Therefore, in this review, we shed light on the potential of MNAM as a dietary supplement in sports medicine.

Novel insights from a multiomics dissection of the hayflick limit

The process wherein dividing cells exhaust proliferative capacity and enter into replicative senescence has become a prominent model for cellular aging in vitro. Despite decades of study, this cellular state is not fully understood in culture and even much less so during aging. Here, we revisit Leonard Hayflick’s original observation of replicative senescence in WI-38 human lung fibroblasts equipped with a battery of modern techniques including RNA-seq, single-cell RNA-seq, proteomics, metabolomics, and ATAC-seq. We find evidence that the transition to a senescent state manifests early, increases gradually, and corresponds to a concomitant global increase in DNA accessibility in nucleolar and lamin associated domains. Furthermore, we demonstrate that senescent WI-38 cells acquire a striking resemblance to myofibroblasts in a process similar to the epithelial to mesenchymal transition (EMT) that is regulated by t YAP1/TEAD1 and TGF-β2. Lastly, we show that verteporfin inhibition of YAP1/TEAD1 activity in aged WI-38 cells robustly attenuates this gene expression program.

Nicotinamide N-methyltransferase ameliorates renal fibrosis by its metabolite 1-methylnicotinamide inhibiting the TGF-β1/Smad3 pathway

Chronic kidney disease (CKD), a disease involving damage to the kidney structure and function, is a global public health problem. Tubulointerstitial fibrosis (TIF) is both an inevitable pathological change in individuals with CKD and a driving force in the progression of renal fibrosis. Nicotinamide N-methyltransferase (NNMT) and its metabolite 1-methylnicotinamide (MNAM) have been shown to protect against lipotoxicity-induced kidney tubular injury. However, the biological roles of NNMT and MNAM in regulating TIF remain elusive. This study aimed to investigate the protective effect of NNMT and MNAM on TIF and the mechanisms involved. We explored the functions and mechanisms of NNMT and MNAM in TIF, as well as the interaction between NNMT and MNAM, using unilateral ureteral obstruction (UUO) mice and cultured mouse tubular epithelial cells (mTECs) stimulated with transforming growth factor-β1 (TGF-β1). Several important findings were obtained as follows: (1) NNMT expression was upregulated in the kidneys of UUO mice and TGF-β1-induced mTECs, and this upregulation was proposed to be a protective compensatory response to TIF. (2) MNAM was a potentially effective antifibrotic and anti-inflammatory medication in UUO mice. (3) The antifibrotic effect of NNMT overexpression was exerted by increasing the concentration of MNAM. (4) The renoprotective role of MNAM depended on the selective blockade of the interaction of Smad3 with TGFβ receptor I. Overall, our study shows that NNMT is involved in the development and progression of CKD and that its metabolite MNAM may be a novel inhibitor of the TGF-β1/Smad3 pathway with great therapeutic potential for CKD.