Discovery of Novel Nicotinamide Derivatives by a Two-Step Strategy of Azo-Incorporating and Bioisosteric Replacement.

Azobenzene moieties can serve as active fragments in antimicrobials and exert trans/cis conversions of molecules. Herein, a series of novel nicotinamide derivatives (NTMs) were developed by employing a two-step strategy, including azo-incorporating and bioisosteric replacement. Azo-incorporation can conveniently provide compounds that can be easily optically interconverted between trans/cis isomers, enhancing the structural diversity of azo compounds. It is noteworthy that the replacement of the azo bond with a 1,2,4-oxadiazole motif through further bioisosteric replacement led to the discovery of a novel compound, NTM18, which made a breakthrough in preventing rice sheath blight disease. A control effect value of 94.44% against Rhizoctonia solani could be observed on NTM18, while only 11.11% was determined for boscalid at 200 mg·L-1. Further mechanism validations were conducted, and the molecular docking analysis demonstrated that compound NTM18 might have a tight binding with SDH via an extra π-π interaction between the oxadiazole ring and residue of D_Y586. This work sets up a typical case for the united applications of azo-incorporating and bioisosteric replacement in fungicide design, posing an innovative approach in structural diversity-based development of pesticides.

The Rate of NAD+ Breakdown Is Maintained Constant against Deletion or Overexpression of NAD+-Degrading Enzymes in Mammalian Cells.

Cellular NAD+ is continuously degraded and synthesized under resting conditions. In mammals, NAD+ synthesis is primarily initiated from nicotinamide (Nam) by Nam phosphoribosyltransferase, whereas poly(ADP-ribose) polymerase 1 (PARP1) and 2 (PARP2), sirtuin1 (SIRT1), CD38, and sterile alpha and TIR motif containing 1 (SARM1) are involved in NAD+ breakdown. Using flux analysis with 2H-labeled Nam, we found that when mammalian cells were cultured in the absence of Nam, cellular NAD+ levels were maintained and NAD+ breakdown was completely suppressed. In the presence of Nam, the rate of NAD+ breakdown (RB) did not significantly change upon PARP1, PARP2, SIRT1, or SARM1 deletion, whereas stable expression of CD38 did not increase RB. However, RB in PARP1-deleted cells was much higher compared with that in wild-type cells, in which PARP1 activity was blocked with a selective inhibitor. In contrast, RB in CD38-overexpressing cells in the presence of a specific CD38 inhibitor was much lower compared with that in control cells. The results indicate that PARP1 deletion upregulates the activity of other NADases, whereas CD38 expression downregulates the activity of endogenous NADases, including PARP1 and PARP2. The rate of cellular NAD+ breakdown and the resulting NAD+ concentration may be maintained at a constant level, despite changes in the NAD+-degrading enzyme expression, through the compensatory regulation of NADase activity.

Preparation of a multiple interacting magnetic fluid for rapid and sensitive simultaneous extraction of ß-nicotinamide mononucleotide metabolites in biological samples.

BACKGROUND: ß-nicotinamide mononucleotide stands out as an essential breakthrough in "anti-aging" and consistently leads the list of top-selling nutritional supplements in terms of quantity. As the metabolites of ß-nicotinamide mononucleotide, the detection of nicotinamide and N1-methylnicotinamide is of great significance for evaluating the nutritional effect of dietary supplements of ß-nicotinamide mononucleotide. However, due to the extremely low concentration of nicotinamide and N1-methylnicotinamide in vivo and the serious matrix interference in biological samples, there is an increasing demand for materials and methods of pre-treatment. RESULTS: In this study, Fe3O4@hydroxypropyl methyl cellulose@dodecylbenzenesulfonic acid magnetic fluid was synthesized for the first time, and it was used as pretreatment material to detect nicotinamide and N1- methylnicotinamide in urine samples by high performance liquid chromatography. Compared with other adsorption materials, Fe3O4@hydroxypropyl methyl cellulose@dodecylbenzenesulfonic acid nanoparticles are a kind of uniform magnetic fluid. Furthermore, they have more types and quantities of interaction sites (electrostatic interactions, hydrophobic interactions, hydrogen bonding interactions, and π-π interactions), so they own greater adsorption capacity. When the pH of the solution is 4, they can be adsorbed quickly within 10 s. The method successfully detected trace nicotinamide and N1-methylnicotinamide in urine samples in the linear range of 0.1-80 µg mL-1, the low detection limits were 0.30 ng mL-1 and 1.5 ng mL-1 respectively, and the quantification limits were 1.0 ng mL-1 and 5.0 ng mL-1, respectively. At the same time, the standard urine samples of nicotinamide and N1-methylnicotinamide showed satisfactory recovery rate 94.50-109.1 %. The results indicated that the established method can accurately and quantitatively determine trace nicotinamide and N1-methylnicotinamide in urine samples. SIGNIFICANCE: Consequently, low concentration of ß-nicotinamide mononucleotide metabolites can be detected simultaneously, and the interference can be eliminated during the detection process, which provides an efficient and convenient pretreatment method and a rapid and sensitive detection method for the analysis of ß-nicotinamide mononucleotide metabolites. What's more, it has a wide application prospect in the analysis of other similar metabolites in biological samples.

Cardiac NAD+ depletion in mice promotes hypertrophic cardiomyopathy and arrhythmias prior to impaired bioenergetics.

Nicotinamide adenine dinucleotide (NAD+) is an essential co-factor in metabolic reactions and co-substrate for signaling enzymes. Failing human hearts display decreased expression of the major NAD+ biosynthetic enzyme nicotinamide phosphoribosyltransferase (Nampt) and lower NAD+ levels, and supplementation with NAD+ precursors is protective in preclinical models. Here we show that Nampt loss in adult cardiomyocytes caused depletion of NAD+ along with marked metabolic derangements, hypertrophic remodeling and sudden cardiac deaths, despite unchanged ejection fraction, endurance and mitochondrial respiratory capacity. These effects were directly attributable to NAD+ loss as all were ameliorated by restoring cardiac NAD+ levels with the NAD+ precursor nicotinamide riboside (NR). Electrocardiograms revealed that loss of myocardial Nampt caused a shortening of QT intervals with spontaneous lethal arrhythmias causing sudden cardiac death. Thus, changes in NAD+ concentration can have a profound influence on cardiac physiology even at levels sufficient to maintain energetics.

Phages reconstitute NAD+ to counter bacterial immunity.

Bacteria defend against phage infection through a variety of antiphage defence systems1. Many defence systems were recently shown to deplete cellular nicotinamide adenine dinucleotide (NAD+) in response to infection, by cleaving NAD+ into ADP-ribose (ADPR) and nicotinamide2-7. It was demonstrated that NAD+ depletion during infection deprives the phage of this essential molecule and impedes phage replication. Here we show that a substantial fraction of phages possess enzymatic pathways allowing reconstitution of NAD+ from its degradation products in infected cells. We describe NAD+ reconstitution pathway 1 (NARP1), a two-step pathway in which one enzyme phosphorylates ADPR to generate ADPR pyrophosphate (ADPR-PP), and the second enzyme conjugates ADPR-PP and nicotinamide to generate NAD+. Phages encoding NARP1 can overcome a diverse set of defence systems, including Thoeris, DSR1, DSR2, SIR2-HerA and SEFIR, all of which deplete NAD+ as part of their defensive mechanism. Phylogenetic analyses show that NARP1 is primarily encoded on phage genomes, suggesting a phage-specific function in countering bacterial defences. A second pathway, NARP2, allows phages to overcome bacterial defences by building NAD+ using metabolites different from ADPR-PP. Our findings reveal a unique immune evasion strategy in which viruses rebuild molecules depleted by defence systems, thus overcoming host immunity.

A Supramolecular Biosensor for Rapid and High-Throughput Quantification of a Disease-Associated Niacin Metabolite.

Metabolic abnormalities play a pivotal role in various pathological conditions, necessitating the quantification of specific metabolites for diagnosis. While mass spectrometry remains the primary method for metabolite measurement, its limited throughput underscores the need for biosensors capable of rapid detection. Previously, we reported that pillar[6]arene with 12 carboxylate groups (P6AC) forms host-guest complexes with 1-methylnicotinamide (1-MNA), which is produced in vivo by nicotinamide N-methyltransferase (NNMT). P6AC acts as a biosensor by measuring the fluorescence quenching caused by photoinduced electron transfer upon 1-MNA binding. However, the low sensitivity of P6AC makes it impractical for detecting 1-MNA in unpurified biological samples. In this study, we found that P6A with 12 sulfonate groups (P6AS) is a specific and potent supramolecular host for 1-MNA interactions even in biological samples. The 1-MNA binding affinity of P6AS in water was found to be (5.68 ± 1.02) × 106 M-1, which is approximately 700-fold higher than that of P6AC. Moreover, the 1-MNA detection limit of P6AS was determined to be 2.84 × 10-7 M, which is substantially lower than that of P6AC. Direct addition of P6AS to culture medium was sufficient to quantify 1-MNA produced by cancer cells. Furthermore, this sensor was able to specifically detect 1-MNA even in unpurified human urine. P6AS therefore enables rapid and high-throughput quantification of 1-MNA, and further improvement of our strategy will contribute to the establishment of high-throughput screening of NNMT inhibitors, diagnosis of liver diseases, and imaging of human cancer cells in vivo.

Time-restricted feeding ameliorates non-alcoholic fatty liver disease through modulating hepatic nicotinamide metabolism via gut microbiota remodeling.

Non-alcoholic fatty liver disease (NAFLD) has emerged as a global health concern, lacking specific therapeutic strategies. Time-restricted feeding (TRF) regimen demonstrated beneficial effects in NAFLD; however, the underlying mechanisms remain unclear. In this study, we established a NAFLD mouse model through a high-fat diet (HFD) and implemented the 16:8 TRF regimen for a duration of 6 weeks. We demonstrated that TRF remarkably alleviated hepatic steatosis in HFD mice. Of note, aldehyde oxidase 1 (AOX1), a key enzyme in hepatic nicotinamide (NAM) catabolism, exhibited apparent upregulation in response to HFD, leading to abnormal accumulation of N-Methyl-6-pyridone-3-carboxamide (N-Me-6-PY, also known as 2PY) and N-Methyl-4-pyridone-5-carboxamide (N-Me-4-PY, also known as 4PY), whereas it was almost restored by TRF. Both N-Me-6-PY and N-Me-4-PY promoted de novo lipogenesis and fatty acid uptake capacities in hepatocyte, and aggravated hepatic steatosis in mice either fed chow diet or HFD. In contrast, pharmacological inhibition of AOX1 was sufficient to ameliorate the hepatic steatosis and lipid metabolic dysregulation induced by HFD. Moreover, transplantation of fecal microbiota efficiently mimicked the modulatory effect of TRF on NAM metabolism, thus mitigating hepatic steatosis and lipid metabolic disturbance, suggesting a gut microbiota-dependent manner. In conclusion, our study reveals the intricate relationship between host NAM metabolic modification and gut microbiota remodeling during the amelioration of NAFLD by TRF, providing promising insights into the prevention and treatment of NAFLD.

Urine Metabolites Changes in Acute Myocardial Infarction Rats via Metabolomic Analysis.

OBJECTIVES: To screen biomarkers for forensic identification of acute myocardial infarction (AMI) by non-targeted metabolomic studies on changes of urine metabolites in rats with AMI. METHODS: The rat models of the sham surgery group, AMI group and hyperlipidemia + acute myocardial infarction (HAMI) group were established. Ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) was used to analyze the changes of urine metabolic spectrometry in AMI rats. Principal component analysis, partial least squares-discriminant analysis, and orthogonal partial least squares-discriminant analysis were used to screen differential metabolites. The MetaboAnalyst database was used to analyze the metabolic pathway enrichment and access the predictive ability of differential metabolites. RESULTS: A total of 40 and 61 differential metabolites associated with AMI and HAMI were screened, respectively. Among them, 22 metabolites were common in both rat models. These small metabolites were mainly concentrated in the niacin and nicotinamide metabolic pathways. Within the 95% confidence interval, the area under the curve (AUC) values of receiver operator characteristic curve for N8-acetylspermidine, 3-methylhistamine, and thymine were greater than 0.95. CONCLUSIONS: N8-acetylspermidine, 3-methylhistamine, and thymine can be used as potential biomarkers for AMI diagnosis, and abnormal metabolism in niacin and nicotinamide may be the main causes of AMI. This study can provide reference for the mechanism and causes of AMI identification.

Evaluation of NAD+ precursors for improved metabolism and productivity of antibody-producing CHO cell.

In the previous study, the culture medium was treated with nicotinamide adenine dinucleotide (NAD+) under the hypothesis that NAD+ regeneration is a major factor causing excessive lactate accumulation in Chinese hamster ovary (CHO) cells. The NAD+ treatment improved metabolism by not only reducing the Warburg effect but also enhancing oxidative phosphorylation, leading to enhanced antibody production. Building on this, four NAD+ precursors - nicotinamide mononucleotide (NMN), nicotinic acid (NA), nicotinamide riboside (NR), and nicotinamide (NAM) - were tested to elevate intracellular NAD+ levels more economically. First, the ability of CHO cells to utilize both the salvage and Preiss-Handler pathways for NAD+ biosynthesis was verified, and then the effect of NAD+ precursors on CHO cell cultures was evaluated. These precursors increased intracellular NAD+ levels by up to 70.6% compared to the non-treated group. Culture analysis confirmed that all the precursors induced metabolic changes and that NMN, NA, and NR improved productivity akin to NAD+ treatment, with comparable integral viable cell density. Despite the positive effects such as the increase in the specific productivity and changes in cellular glucose metabolism, none of the precursors surpassed direct NAD+ treatment in antibody titer, presumably due to the reduction in nucleoside availability, as evidenced by the decrease in ATP levels in the NAD+ precursor-treated groups. These results underscore the complexity of cellular metabolism as well as the necessity for further investigation to optimize NAD+ precursor treatment strategies, potentially with the supplementation of nucleoside precursors. Our findings suggest a feasible approach for improving CHO cell culture performances by using NAD+ precursors as medium and feed components for the biopharmaceutical production.

Regulation of and challenges in targeting NAD+ metabolism.

Nicotinamide adenine dinucleotide, in its oxidized (NAD+) and reduced (NADH) forms, is a reduction-oxidation (redox) co-factor and substrate for signalling enzymes that have essential roles in metabolism. The recognition that NAD+ levels fall in response to stress and can be readily replenished through supplementation has fostered great interest in the potential benefits of increasing or restoring NAD+ levels in humans to prevent or delay diseases and degenerative processes. However, much about the biology of NAD+ and related molecules remains poorly understood. In this Review, we discuss the current knowledge of NAD+ metabolism, including limitations of, assumptions about and unappreciated factors that might influence the success or contribute to risks of NAD+ supplementation. We highlight several ongoing controversies in the field, and discuss the role of the microbiome in modulating the availability of NAD+ precursors such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), the presence of multiple cellular compartments that have distinct pools of NAD+ and NADH, and non-canonical NAD+ and NADH degradation pathways. We conclude that a substantial investment in understanding the fundamental biology of NAD+, its detection and its metabolites in specific cells and cellular compartments is needed to support current translational efforts to safely boost NAD+ levels in humans.

High-efficient preparation of ß-nicotinamide mononucleotides by crude enzymes cascade catalytic reaction.

ß-nicotinamide mononucleotide (ß-NMN) is a key precursor of nicotinamide adenine dinucleotide, and becomes attractive in the nutrition and health care fields, but its enzymatic synthesis is expensive. In this study, a six-enzyme cascade catalytic system was constructed to produce ß-NMN. Using D-ribose and nicotinamide as substrates, the ß-NMN yield reached 97.5 % catalyzed by purified enzymes. Then, after knocking out the genes encoding proteins that consume ß-NMN in E. coli BL21(DE3), the similar ß-NMN yield, 97.2 %, using the crude enzymes could be also obtained. After that, ß-NMN synthesis was performed under increased substrate concentration, and 'modular' crude enzymes cascade catalytic reaction system was proposed to reduce the inhibition of polyphosphate on ribose-phosphate diphosphokinase activity, and the ß-NMN yield reached 78.4 % at 10 mM D-ribose, which is 1.82 times of that in 'one-pot' reaction and represents the highest ß-NMN preparation level with phosphoribosylpyrophosphate as the core reported till now.

Structure-Function Insights into the Dual Role in Nucleobase and Nicotinamide Metabolism and a Possible Use in Cancer Gene Therapy of the URH1p Riboside Hydrolase.

The URH1p enzyme from the yeast Saccharomyces cerevisiae has gained significant interest due to its role in nitrogenous base metabolism, particularly involving uracil and nicotinamide salvage. Indeed, URH1p was initially classified as a nucleoside hydrolase (NH) with a pronounced preference for uridine substrate but was later shown to also participate in a Preiss-Handler-dependent pathway for recycling of both endogenous and exogenous nicotinamide riboside (NR) towards NAD+ synthesis. Here, we present the detailed enzymatic and structural characterisation of the yeast URH1p enzyme, a member of the group I NH family of enzymes. We show that the URH1p has similar catalytic efficiencies for hydrolysis of NR and uridine, advocating a dual role of the enzyme in both NAD+ synthesis and nucleobase salvage. We demonstrate that URH1p has a monomeric structure that is unprecedented for members of the NH homology group I, showing that oligomerisation is not strictly required for the N-ribosidic activity in this family of enzymes. The size, thermal stability and activity of URH1p towards the synthetic substrate 5-fluoruridine, a riboside precursor of the antitumoral drug 5-fluorouracil, make the enzyme an attractive tool to be employed in gene-directed enzyme-prodrug activation therapy against solid tumours.

Exploring nicotinamide adenine dinucleotide precursors across biosynthesis pathways: Unraveling their role in the ovary.

Natural Nicotinamide Adenine Dinucleotide (NAD+) precursors have attracted much attention due to their positive effects in promoting ovarian health. However, their target tissue, synthesis efficiency, advantages, and disadvantages are still unclear. This review summarizes the distribution of NAD+ at the tissue, cellular and subcellular levels, discusses its biosynthetic pathways and the latest findings in ovary, include: (1) NAD+ plays distinct roles both intracellularly and extracellularly, adapting its distribution in response to requirements. (2) Different precursors differs in target tissues, synthetic efficiency, biological utilization, and adverse effects. Importantly: tryptophan is primarily utilized in the liver and kidneys, posing metabolic risks in excess; nicotinamide (NAM) is indispensable for maintaining NAD+ levels; nicotinic acid (NA) constructs a crucial bridge between intestinal microbiota and the host with diverse functions; nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) increase NAD+ systemically and can be influenced by delivery route, tissue specificity, and transport efficiency. (3) The biosynthetic pathways of NAD+ are intricately intertwined. They provide multiple sources and techniques for NAD+ synthesis, thereby reducing the dependence on a single molecule to maintain cellular NAD+ levels. However, an excess of a specific precursor potentially influencing other pathways. In addition, Protein expression analysis suggest that ovarian tissues may preferentially utilize NAM and NMN. These findings summarize the specific roles and potential of NAD+ precursors in enhancing ovarian health. Future research should delve into the molecular mechanisms and intervention strategies of different precursors, aiming to achieve personalized prevention or treatment of ovarian diseases, and reveal their clinical application value.

Novel insight into nicotinamide adenine dinucleotide and related metabolites in cancer patients undergoing surgery.

Nicotinamide adenine dinucleotide (NAD +) plays a pivotal role in numerous cellular functions. Reduced NAD + levels are postulated to be associated with cancer. As interest in understanding NAD + dynamics in cancer patients with therapeutic applications in mind grows, there remains a shortage of comprehensive data. This study delves into NAD + dynamics in patients undergoing surgery for different digestive system cancers. This prospective study enrolled 99 patients with eight different cancers. Fasting blood samples were obtained during the perioperative period. The concentrations of NAD + , nicotinamide mononucleotide (NMN), and nicotinamide riboside were analyzed using tandem mass spectrometry. After erythrocyte volume adjustment, NAD + remained relatively stable after surgery. Meanwhile, NMN decreased the day after surgery and displayed a recovery trend. Interestingly, liver and pancreatic cancer patients exhibited poor postoperative NMN recovery, suggesting a potential cancer type-specific influence on NAD + metabolism. This study illuminated the behavior of NAD + in surgically treated cancer patients. We identified which cancer types have particularly low levels and at what point depletion occurs during the perioperative period. These insights suggest the need for personalized NAD + supplementation strategies, calibrated to individual patient needs and treatment timelines. Clinical trial registration jRCT1020210066.

H3K56 acetylation affects Candida albicans morphology and secreted soluble factors interacting with the host.

In recent years, epigenetics has been revealed as a mechanism able to modulate the expression of virulence traits in diverse pathogens, including Candida albicans. Indeed, epigenetic regulation can sense environmental changes, leading to the rapid and reversible modulation of gene expression with consequent adaptation to novel environments. How epigenetic changes can impact expression and signalling output, including events associated with mechanisms of morphological transition and virulence, is still poorly studied. Here, using nicotinamide as a sirtuin inhibitor, we explored how the accumulation of the H3K56 acetylation, the most prominent histone acetylation in C. albicans, might affect its interaction with the host. Our experiments demonstrate that H3K56 acetylation profoundly affects the production and/or secretion of soluble factors compromising actin remodelling and cytokine production. ChIP- and RNA-seq analyses highlighted a direct impact of H3K56 acetylation on genes related to phenotypic switching, biofilm formation and cell aggregation. Direct and indirect regulation also involves genes related to cell wall protein biosynthesis, ß-glucan and mannan exposure, and hydrolytic secreted enzymes, supporting the hypothesis that the fluctuations of H3K56 acetylation in C. albicans might impair the macrophage response to the yeast and thus promote the host-immune escaping.

Thiophenyl Derivatives of Nicotinamide Are Metabolized by the NAD Salvage Pathway into Unnatural NAD Derivatives That Inhibit IMPDH and Are Toxic to Peripheral Nerve Cancers.

N-Pyridinylthiophene carboxamide (compound 21) displays activity against peripheral nerve sheath cancer cells and mouse xenografts by an unknown mechanism. Through medicinal chemistry, we identified a more active derivative, compound 9, and found that only analogues with structures similar to nicotinamide retained activity. Genetic screens using compound 9 found that both NAMPT and NMNAT1, enzymes in the NAD salvage pathway, are necessary for activity. Compound 9 is metabolized by NAMPT and NMNAT1 into an adenine dinucleotide (AD) derivative in a cell-free system, cultured cells, and mice, and inhibition of this metabolism blocked compound activity. AD analogues derived from compound 9 inhibit IMPDH in vitro and cause cell death by inhibiting IMPDH in cells. These findings nominate these compounds as preclinical candidates for the development of tumor-activated IMPDH inhibitors to treat neuronal cancers.

Photocatalytic regeneration of nicotinamide cofactor biomimetics drives biocatalytic reduction by Old Yellow enzymes.

A key approach in developing green chemistry involves converting solar energy into chemical energy of biomolecules through photocatalysis. Photocatalysis can facilitate the regeneration of nicotinamide cofactors during redox processes. Nicotinamide cofactor biomimetics (NCBs) are economical substitutes for natural cofactors. Here, photocatalytic regeneration of NADH and reduced NCBs (NCBsred) using graphitic carbon nitride (g-C3N4) was developed. The process involves g-C3N4 as the photocatalyst, Cp*Rh(bpy)H2O2+ as the electron mediator, and Triethanolamine as the electron donor, facilitating the reduction of NAD+ and various oxidative NCBs (NCBsox) under light irradiation. Notably, the highest reduction yield of 48.32 % was achieved with BANA+, outperforming the natural cofactor NAD+. Electrochemical analysis reveals that the reduction efficiency and capacity of cofactors relies on their redox potentials. Additionally, a coupled photo-enzymatic catalysis system was explored for the reduction of 4-Ketoisophorone by Old Yellow Enzyme XenA. Among all the NCBsox and NAD+, the highest conversion ratio of over 99 % was obtained with BANA+. After recycled for 8 times, g-C3N4 maintained over 93.6 % catalytic efficiency. The photocatalytic cofactor regeneration showcases its outstanding performance with NAD+ as well as NCBsox. This work significantly advances the development of photocatalytic cofactor regeneration for artificial cofactors and its potential application.

Biosynthesis of vitamin B3 and NAD+: incubating HepG2 cells with the alkaloid myosmine.

BACKGROUND: In the kynurenine pathway, it is reported that the essential amino acid tryptophan forms nicotinic acid (NA, vitamin B3) in biological systems. This pathway is part of the de novo pathway to perform nicotinamide adenine dinucleotide (NAD+) biosynthesis. Additionally, biosynthesis of NAD+ via the Preiss-Handler pathway involves NA and its analogue nicotinamide, both designated as niacin. Previous attempts were successful in converting myosmine (MYO) by organic synthesis to NA, and the assumption was that the alkaloid MYO, which is taken in from food, can be converted into NA by biological oxidation. RESULT: Incubation of HepG2 cells with MYO yielded NA. Moreover, a significant increase of NAD+ compared with the control has been found. CONCLUSION: Hence, MYO could be assumed to be the hitherto unknown origin of an alternative NA biosynthesis additionally influencing NAD+ biosynthesis positively. This novel MYO pathway may open new perspectives to improve knowledge and relevance of NA and NAD+ biosynthesis and bioactivation in cells and, moreover, in food staples, food, and diet. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.