Ligand bound structure of a 6-hydroxynicotinic acid 3-monooxygenase provides mechanistic insights.

6-Hydroxynicotinic acid 3-monooxygenase (NicC) is a bacterial enzyme involved in the degradation of nicotinic acid. This enzyme is a Class A flavin-dependent monooxygenase that catalyzes a unique decarboxylative hydroxylation. The unliganded structure of this enzyme has previously been reported and studied using steady- and transient-state kinetics to support a comprehensive kinetic mechanism. Here we report the crystal structure of the H47Q NicC variant in both a ligand-bound (solved to 2.17 Å resolution) and unliganded (1.51 Å resolution) form. Interestingly, in the liganded form, H47Q NicC is bound to 2-mercaptopyridine (2-MP), a contaminant present in the commercial stock of 6-mercaptopyridine-3-carboxylic acid(6-MNA), a substrate analogue. 2-MP binds weakly to H47Q NicC and is not a substrate for the enzyme. Based on kinetic and thermodynamic characterization, we have fortuitously captured a catalytically inactive H47Q NicC•2-MP complex in our crystal structure. This complex reveals interesting mechanistic details about the reaction catalyzed by 6-hydroxynicotinic acid 3-monooxygenase.

Effect of nicotinic acid supplementation on digestion, metabolism, microbiome, and production in late-lactation Holstein cows.

The purpose of this experiment was to determine if nicotinic acid (NA) effects on dairy cows and rumen microbial characteristics are forage-type dependent (corn silage, CS; grass silage, GS). Four late-lactation (DIM = 225 ± 12 d) Holstein cows were used in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. The main effects were a CS (66.10% CS) based diet or a GS (79.59%) based diet with or without 12 g/d NA. Each experimental period lasted for 28 d. Milk production and milk components, blood metabolites, apparent total-tract nutrient digestibilities, minutes rumen pH were below 5.8 as an indicator of ruminal acidosis, and body temperature changes were analyzed as indicators of heat stress. Nicotinic acid supplementation did not improve apparent total-tract nutrient digestibility. Feeding a GS-based diet improved NDF and hemicellulose digestibility. Feeding a CS-based diet increased the apparent total-tract digestibility of fat, and minutes rumen pH below 5.8 for a greater proportion of the time. The CS-based diet also improved milk yield, milk fat and protein yields, and ECM yield; however, somatic cell count and BHB were also increased. Supplementing NA tended to decrease nonesterified fatty acids, especially when combined with GS where DMI was low. There was a trend for the total protozoa population to increase when GS and NA were fed but decreased when CS and NA were fed. Nicotinic acid tended to decrease rumen protozoal populations of Dasytricha, but increased populations of Ophryoscolex and Diplodiniinae with GS diets and decreased with CS diets. Entodiniinae were increased with CS but NA had no effect. Body temperature was increased when a CS-based diet was fed when compared with a GS-based diet. More research is needed to determine how NA can affect rumen microbial protein synthesis and what kind of diets will provide the optimum effect.

Nicotinic Acid Adenine Dinucleotide Phosphate (NAADP)-Mediated Calcium Signaling Is Active in Memory CD4+ T Cells.

Nicotinic acid adenine dinucleotide phosphate (NAADP), identified as one of the most potent calcium-mobilizing second messengers, has been studied in different eukaryotic cell types, including lymphocytes. Although aspects of NAADP-mediated calcium release in lymphocytes are still under debate, the organelles pertaining to NAADP-mediated calcium release are often characterized as acidic and related to lysosomes. Although NAADP-mediated calcium release in different subsets of T cells, including naïve, effector and natural regulatory T cells, has been studied, it has not been widely studied in memory CD4+ T cells, which show a different calcium flux profile. Using a pharmacological approach, the effect of Ned-19, an NAADP pathway antagonist, on the involvement of NAADP in TCR activation in murine memory CD4+ T cells and their downstream effector functions, such as proliferation and cytokine production, was studied. According to this study, Ned-19 inhibited TCR-mediated calcium flux and its downstream effector functions in primary memory CD4+ T cells. The study also revealed that both extracellular and intracellular calcium stores, including endoplasmic reticulum and lysosome-like acidic calcium stores, contribute to the TCR-mediated calcium flux in memory CD4+ T cells. NAADP-AM, a cell permeable analogue of NAADP, was shown to release calcium in memory CD4+ T cells and calcium flux was inhibited by Ned-19.

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.

Identification of structural determinants of nicotinamide phosphoribosyl transferase (NAMPT) activity and substrate selectivity.

NAD homeostasis in mammals requires the salvage of nicotinamide (Nam), which is cleaved from NAD+ by sirtuins, PARPs, and other NAD+-dependent signaling enzymes. Nam phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step in vitamin B3 salvage, whereby Nam reacts with phosphoribosyl pyrophosphate (PRPP) to form nicotinamide mononucleotide. NAMPT has a high affinity towards Nam, which is further enhanced by autophosphorylation of His247. The mechanism of this enhancement has remained unknown. Here, we present high-resolution crystal structures and biochemical data that provide reasoning for the increased affinity of the phosphorylated NAMPT for its substrate. Structural and kinetic analyses suggest a mechanism that includes Mg2+ coordination by phospho-His247, such that PRPP is stabilized in a position highly favorable for catalysis. Under these conditions, nicotinic acid (NA) can serve as a substrate. Moreover, we demonstrate that a stretch of 10 amino acids, present only in NAMPTs from deuterostomes, facilitates conformational plasticity and stabilizes the chemically unstable phosphorylation of His247. Thereby the apparent substrate affinity is considerably enhanced compared to prokaryotic NAMPTs. Collectively, our study provides a structural basis for the important function of NAMPT to recycle Nam into NAD biosynthesis with high affinity.

Activation of HCA2 regulates microglial responses to alleviate neurodegeneration in LPS-induced in vivo and in vitro models.

BACKGROUND: Previous studies have shown a close association between an altered immune system and Parkinson's disease (PD). Neuroinflammation inhibition may be an effective measure to prevent PD. Recently, numerous reports have highlighted the potential of hydroxy-carboxylic acid receptor 2 (HCA2) in inflammation-related diseases. Notably, the role of HCA2 in neurodegenerative diseases is also becoming more widely known. However, its role and exact mechanism in PD remain to be investigated. Nicotinic acid (NA) is one of the crucial ligands of HCA2, activating it. Based on such findings, this study aimed to examine the effect of HCA2 on neuroinflammation and the role of NA-activated HCA2 in PD and its underlying mechanisms. METHODS: For in vivo studies, 10-week-old male C57BL/6 and HCA2-/- mice were injected with LPS in the substantia nigra (SN) to construct a PD model. The motor behavior of mice was detected using open field, pole-climbing and rotor experiment. The damage to the mice's dopaminergic neurons was detected using immunohistochemical staining and western blotting methods. In vitro, inflammatory mediators (IL-6, TNF-α, iNOS and COX-2) and anti-inflammatory factors (Arg-1, Ym-1, CD206 and IL-10) were detected using RT-PCR, ELISA and immunofluorescence. Inflammatory pathways (AKT, PPARγ and NF-κB) were delineated by RT-PCR and western blotting. Neuronal damage was detected using CCK8, LDH, and flow cytometry assays. RESULTS: HCA2-/- increases mice susceptibility to dopaminergic neuronal injury, motor deficits, and inflammatory responses. Mechanistically, HCA2 activation in microglia promotes anti-inflammatory microglia and inhibits pro-inflammatory microglia by activating AKT/PPARγ and inhibiting NF-κB signaling pathways. Further, HCA2 activation in microglia attenuates microglial activation-mediated neuronal injury. Moreover, nicotinic acid (NA), a specific agonist of HCA2, alleviated dopaminergic neuronal injury and motor deficits in PD mice by activating HCA2 in microglia in vivo. CONCLUSIONS: Niacin receptor HCA2 modulates microglial phenotype to inhibit neurodegeneration in LPS-induced in vivo and in vitro models.

"Cap-Pair" Effect as the Reason of the Catalytic Properties of Nicotinic Acid: Experimental and Theoretical Studies.

The influence of nicotinic acid (NC) on the kinetics and the mechanism of electroreduction of Zn2+ ions in the acetate buffer (pH=6.0) was investigated using electrochemical methods (EIS, CV, SWV and DC). It was shown that the anions of NC catalyze the electrode reaction (cap-pair effect) by adsorbing on the surface of the mercury electrode. The catalytic activity of NC is due to its ability to form active NC-Zn2+ complexes on the electrode surface, facilitating the electron transfer process. However, no evidence of the formation of such complexes in the solution was found using classical molecular dynamics. Moreover, it was proved that the electroreduction of Zn2+ ions in the presence of NC is a two-stage process. The first stage involves the transfer of the first electron, preceded by the partial loss of the hydration shell by the Zn2+ ions and formation of the active complex. Moreover, it was shown that in the range of lower concentrations, c≤1.10-2  mol.dm-3 , the nicotinic acid shows weaker catalytic abilities than another form of vitamin B3 - nicotinamide. In the range of its higher concentrations, the nicotinic acid is a more effective catalyst for the electroreduction of Zn2+ ions.

Comparative effects of vitamin and mineral supplements in the management of type 2 diabetes in primary care: A systematic review and network meta-analysis of randomized controlled trials.

Medical nutrition treatment can manage diabetes and slow or prevent its complications. The comparative effects of micronutrient supplements, however, have not yet been well established. We aimed at evaluating the comparative effects of vitamin and mineral supplements on managing glycemic control and lipid metabolism for type 2 diabetes mellitus (T2DM) to inform clinical practice. Electronic and hand searches for randomized controlled trials (RCTs) were performed until June 1, 2022. We selected RCTs enrolling patients with T2DM who were treated with vitamin supplements, mineral supplements, or placebo/no treatment. Data were pooled via frequentist random-effects network meta-analyses. A total of 170 eligible trials and 14223 participants were included. Low to very low certainty evidence established chromium supplements as the most effective in reducing fasting blood glucose levels and homeostasis model assessment of insulin resistance (SUCRAs: 90.4% and 78.3%, respectively). Vitamin K supplements ranked best in reducing glycated hemoglobin A1c and fasting insulin levels (SUCRAs: 97.0% and 82.3%, respectively), with moderate to very low certainty evidence. Vanadium supplements ranked best in lowering total cholesterol levels with very low evidence certainty (SUCRAs:100%). Niacin supplements ranked best in triglyceride reductions and increasing high-density lipoprotein cholesterol levels with low to very low evidence certainty (SUCRAs:93.7% and 94.6%, respectively). Vitamin E supplements ranked best in reducing low-density lipoprotein cholesterol levels with very low evidence certainty (SUCRAs:80.0%). Our analyses indicated that micronutrient supplements, especially chromium, vitamin E, vitamin K, vanadium, and niacin supplements, may be more efficacious in managing T2DM than other micronutrients. Considering the clinical importance of these findings, new research is needed to get better insight into this issue.

Blood levels of nicotinic acid negatively correlate with hearing ability in healthy older men.

BACKGROUND: Age-related hearing loss (ARHL) is a common phenomenon observed during aging. On the other hand, the decrease in Nicotinamide adenine dinucleotide (NAD +) levels is reported to be closely related to the age-related declines in physiological functions such as ARHL in animal studies. Moreover, preclinical studies confirmed NAD + replenishment effectively prevents the onset of age-related diseases. However, there is a paucity of studies on the relationship between NAD+ metabolism and ARHL in humans. METHODS: This study was analyzed the baseline results of our previous clinical trial, in which nicotinamide mononucleotide or placebo was administered to 42 older men (Igarashi et al., NPJ Aging 8:5, 2022). The correlations between blood levels of NAD+-related metabolites at baseline and pure-tone hearing thresholds at different frequencies (125, 250, 500, 1000, 2000, 4000, and 8000 Hz) in 42 healthy Japanese men aged > 65 years were analyzed using Spearman's rank correlation. Multiple linear regression analysis was performed with hearing thresholds as the dependent variable and age and NAD+-related metabolite levels as independent variables. RESULTS: Positive associations were observed between levels of nicotinic acid (NA, a NAD+ precursor in the Preiss-Handler pathway) and right- or left-ear hearing thresholds at frequencies of 1000 Hz (right: r = 0.480, p = 0.001; left: r = 0.422, p = 0.003), 2000 Hz (right: r = 0.507, p < 0.001, left: r = 0.629, p < 0.001), and 4000 Hz (left: r = 0.366, p = 0.029). Age-adjusted multiple linear regression analysis revealed that NA was an independent predictor of elevated hearing thresholds (1000 Hz (right): p = 0.050, regression coefficient (ß) = 1610; 1000 Hz (left): p = 0.026, ß = 2179; 2000 Hz (right): p = 0.022, ß = 2317; 2000 Hz (left): p = 0.002, ß = 3257). Weak associations of nicotinic acid riboside (NAR) and nicotinamide (NAM) with hearing ability were observed. CONCLUSIONS: We identified negative correlations between blood concentrations of NA and hearing ability at 1000 and 2000 Hz. NAD+ metabolic pathway might be associated with ARHL onset or progression. Further studies are warranted. TRIAL REGISTRATION: The study was registered at UMIN-CTR (UMIN000036321) on 1st June 2019.

Exogenously applied nicotinic acid alleviates drought stress by enhancing morpho-physiological traits and antioxidant defense mechanisms in wheat.

Across the globe, the frequent occurrence of drought spells has significantly undermined the sustainability of modern high-input farming systems, particularly those focused on staple crops like wheat. To ameliorate the deleterious impacts of drought through a biologically viable and eco-friendly approach, a study was designed to explore the effect of nicotinic acid on different metabolic, and biochemical processes, growth and yield of wheat under optimal moisture and drought stress (DS). The current study was comprised of different levels of nicotinic acid applied as foliar spray (0 g L-1, 0.7368, 1.477, 2.2159 g L-1) and fertigation (0.4924, 0.9848, and 1.4773 g L-1) under normal conditions and imposed drought by withholding water at anthesis stage. The response variables were morphological traits such as roots and shoots characteristics, yield attributes, grain and biological yields along with biosynthesis of antioxidants. The results revealed that nicotinic acid dose of 2.2159 g L-1 out-performed rest of treatments under both normal and DS. The same treatment resulted in the maximum root growth (length, fresh and dry weights, surface area, diameter) and shoot traits (length, fresh and dry weights) growth. Additionally, foliar applied nicotinic acid (2.2159 g L-1) also produced as the highest spike length, grains spike-1, spikelet's spike-1 and weight of 1000 grains. Moreover, these better yield attributes led to significantly higher grain yield and biological productivity of wheat. Likewise in terms of physiological growth of wheat under DS, the same treatment remained superior by recording the highest SPAD value, relative water content, water potential of leaves, leaf area, stomatal conductance (292 mmolm-2S-1), internal carbon dioxide concentration, photosynthesis and transpiration rate. Interestingly, exogenously applied nicotinic acid remained effective in triggering the antioxidant system of wheat by recording significantly higher catalase, peroxidase, superoxide dismutase and ascorbate peroxidase.

Synthesis of novel nicotinic acid derivatives of potential antioxidant and anticancer activity.

This study comprises the design and synthesis of novel nicotinic acid-based cytotoxic agents with selective inhibitory efficacy against the vascular endothelial growth factor receptor-2 (VEGFR-2). Screening of novel compounds for cytotoxicity was assessed against 60 human cancer cell lines. The two most active compounds, 5b and 5c, and the reference drugs sorafenib and doxorubicin were investigated against HCT-15, PC-3, and CF-295 cancer cell lines. Compound 5c exhibited the highest cytotoxic potential compared to doxorubicin against the HCT-15 and PC-3 tumor cell lines. Moreover, it exhibited higher cytotoxic potential and selectivity toward the HCT-15 cell panel compared with sorafenib. Compound 5c demonstrated promising VEGFR-2 inhibition (concentration needed to inhibit cell viability by 50%, IC50 = 0.068 µM) and superior VEGFR-2 selectivity over the epidermal growth factor receptor and platelet-derived growth factor receptor-ß enzymes. It also reduced the total and phosphorylated VEGFR-2 and induced apoptosis, as evidenced by a 4.3-fold rise in caspase-3 levels. The antioxidant potential of the new compounds was determined via measuring the superoxide dismutase (SOD) levels, among which compound 5c exhibited an SOD level almost comparable to ascorbic acid. These results suggested that compound 5c exhibited dual cytotoxic and antioxidant activities. Docking of 5c into the VEGFR-2 pocket showed a similar binding mode to sorafenib. Moreover, the ADME (absorption, distribution, metabolism, and excretion) profile of 5c outlined drug-likeness. Finally, The density functional theory calculations displayed an increased binding affinity of 5c to the target enzyme.

Test for abnormal niacin response syndrome in schizophrenia: reclaiming the oral route / Prueba de síndrome de respuesta a niacina anormal en pacientes con diagnóstico de esquizofrenia: reivindicando la vía oral.

Introduction: Although there is an abnormal presentation of Niacin Response Syndrome (ANRS) in schizophrenic patients (SZ) compared to subjects with other psychiatric illnesses and with healthy individuals. However, most of the literature is based on studies that have used tests of niacin topical administration, observing, on the other hand, less scientific production of its oral administration. The objective was to determine the sensitivity of the oral niacin test as a method of detecting ASRN in EZ. Methods: A non-randomized clinical trial was carried out. Two groups were formed, the experimental or SZ, with 21 patients diagnosed with schizophrenia according to DSM-IV-TR SZ or schizoaffective disorder, and the HC group, made up of 20 healthy controls. Both groups were exposed to an oral niacin test and clinical-semiological tools were applied to evaluate the NRS. Results: 90.5% of the SZ group presented ANRS. In contrast, no participant in the HC group presented ANRS (0%). Conclusions: Oral niacin administration was sensitive to the detection of ASRN in schizophrenia. Likewise, ASRN could be a gradual phenomenon and its prevalence could be dose-dependent, being lower the lower the dose of oral niacin used. Further trials with larger and randomized samples will be needed.

Introducción: En pacientes esquizofrénicos (EZ) existe un síndrome de respuesta a niacina (ASRN) anormal en comparación con sujetos con otras enfermedades psiquiátricas y con individuos sanos. Sin embargo, la mayor parte de la literatura se basa en estudios que han utilizado pruebas de niacina por vía tópica, observándose, en cambio, menor cantidad de ensayos utilizando su administración por vía oral, a pesar de existir algunas ventajas comparativas con el uso de esta última vía. El objetivo fue determinar la sensibilidad de la prueba de niacina por vía oral como método de detección del ASRN en EZ. Metodología: Se realizó un ensayo clínico no aleatorizado, conformando dos grupos, el grupo experimental o EZ, con 21 pacientes con diagnóstico de esquizofrenia según DSM-IV-TR SZ o trastorno esquizoafectivo, y el grupo CS, constituido por 20 controles sanos. Ambos grupos fueron expuestos a la prueba de niacina por vía oral y se aplicaron herramientas clínico-semiológicas para evaluar el SRN. Resultados: La prevalencia de ASRN fue del 90,5% en el grupo EZ, mientras que en el grupo CS fue nula (0%). Conclusiones: La administración oral de niacina fue sensible a la detección de ASRN en la esquizofrenia. Asimismo, la ASRN podría ser un fenómeno gradual y su prevalencia podría ser dosis-dependiente, siendo menor cuanto menor sea la dosis de niacina oral utilizada. Se necesitarán ensayos adicionales con muestras de mayor tamaño y aleatorizadas.

Synthesis of Silver Nanoparticles from the Polysaccharide of Farfarae Flos and Uncovering Its Anticancer Mechanism Based on the Cell Metabolomic Approach.

In this study, the polysaccharide of Farfarae Flos (FFP) was utilized as a reducing agent to the green synthesis of FFP@AgNPs, and the anticancer activity was evaluated using the HT29 cells. The results showed that the FFP@AgNPs could significantly decrease proliferation ability, inhibit migration, and promote cell apoptosis of HT29 cells, which suggested that the FFP@AgNPs showed significant, strong cytotoxicity against HT29 cells. The cell metabolomic analysis coupled with the heatmap showed an obvious metabolome difference for the cells with and without FFP@AgNPs treatment, which was related to 51 differential metabolites. Four metabolic pathways were determined as the key pathways, and the representative functional metabolites and metabolic pathways were validated in vitro. Nicotinic acid (NA) was revealed as the key metabolite relating with the effect of FFP@AgNPs, and it was interesting that NA supplementation could inhibit the proliferation ability of HT29 cells in vitro, lead to mitochondrial dysfunction, reduce intracellular ATP, and damage the integrity of the cell membrane, which exhibited a similar effect as FFP@AgNPs. In conclusion, this study not only revealed the anticancer mechanism of FFP@AgNPs against the HT29 cells but also provided the important reference that NA shows a potential role in the development of a therapy for colorectal cancer.

Design, synthesis and properties of peptide inhibitors based on BRCA1856-871.

Overexpression of RAD51 protein was found to increase drug resistance in breast cancer cells. Breast cancer susceptibility gene 1 (BRCA1) protein can specifically bind to RAD51 protein and regulate the expression level of RAD51 protein. Based on previous studies, eight modified peptides were obtained by modifying the N-terminus of the key peptide segment 856-871 of BRCA1 with nicotinic acid (NA) and its derivatives. The interaction of BRCA1856-871 and modified peptides with the RAD51158-180 target peptide was investigated by fluorescence and circular dichroism spectroscopies. The results showed that the binding ability of 2-TFM-NA-PP to RAD51158-180 was significantly enhanced. BRCA1856-871 and modified peptides were studied by in vitro cell experiments. The results showed that the antitumor activity of 5-TFM-NA-PP was significantly enhanced compared with BRCA1856-871.

High Density Lipoproteins: Is There a Comeback as a Therapeutic Target?

Low plasma levels of High Density Lipoprotein (HDL) cholesterol (HDL-C) are associated with increased risks of atherosclerotic cardiovascular disease (ASCVD). In cell culture and animal models, HDL particles exert multiple potentially anti-atherogenic effects. However, drugs increasing HDL-C have failed to prevent cardiovascular endpoints. Mendelian Randomization studies neither found any genetic causality for the associations of HDL-C levels with differences in cardiovascular risk. Therefore, the causal role and, hence, utility as a therapeutic target of HDL has been questioned. However, the biomarker "HDL-C" as well as the interpretation of previous data has several important limitations: First, the inverse relationship of HDL-C with risk of ASCVD is neither linear nor continuous. Hence, neither the-higher-the-better strategies of previous drug developments nor previous linear cause-effect relationships assuming Mendelian randomization approaches appear appropriate. Second, most of the drugs previously tested do not target HDL metabolism specifically so that the futile trials question the clinical utility of the investigated drugs rather than the causal role of HDL in ASCVD. Third, the cholesterol of HDL measured as HDL-C neither exerts nor reports any HDL function. Comprehensive knowledge of structure-function-disease relationships of HDL particles and associated molecules will be a pre-requisite, to test them for their physiological and pathogenic relevance and exploit them for the diagnostic and therapeutic management of individuals at HDL-associated risk of ASCVD but also other diseases, for example diabetes, chronic kidney disease, infections, autoimmune and neurodegenerative diseases.

Exploring GPR109A Receptor Interaction with Hippuric Acid Using MD Simulations and CD Spectroscopy.

Previous research has indicated that various metabolites belonging to phenolic acids (PAs), produced by gut microflora through the breakdown of polyphenols, help in promoting bone development and protecting bone from degeneration. Results have also suggested that G-protein-coupled receptor 109A (GPR109A) functions as a receptor for those specific PAs such as hippuric acid (HA) and 3-(3-hydroxyphenyl) propionic acid (3-3-PPA). Indeed, HA has a molecular structural similarity with nicotinic acid (niacin) which has been shown previously to bind to GPR109A receptor and to mediate antilipolytic effects; however, the binding pocket and the structural nature of the interaction remain to be recognized. In the present study, we employed a computational strategy to elucidate the molecular structural determinants of HA binding to GPR109A and GPR109B homology models in understanding the regulation of osteoclastogenesis. Based on the docking and molecular dynamics simulation studies, HA binds to GPR109A similarly to niacin. Specifically, the transmembrane helices 3, 4 and 6 (TMH3, TMH4 and TMH6) and Extracellular loop 1 and 2 (ECL1 and ECL2) residues of GRP109A; R111 (TMH3), K166 (TMH4), ECL2 residues; S178 and S179, and R251 (TMH6), and residues of GPR109B; Y87, Y86, S91 (ECL1) and C177 (ECL2) contribute for HA binding. Simulations and Molecular Mechanics Poisson-Boltzmann solvent accessible area (MM-PBSA) calculations reveal that HA has higher affinity for GPR109A than for GPR109B. Additionally, in silico mutation analysis of key residues have disrupted the binding and HA exited out from the GPR109A protein. Furthermore, measurements of time-resolved circular dichroism spectra revealed that there are no major conformational changes in the protein secondary structure on HA binding. Taken together, our findings suggest a mechanism of interaction of HA with both GPR109A and GPR109B receptors.

Design, Synthesis and Fungicidal Activity of N-(thiophen-2-yl) Nicotinamide Derivatives.

Based on the modification of natural products and the active substructure splicing method, a series of new N-(thiophen-2-yl) nicotinamide derivatives were designed and synthesized by splicing the nitrogen-containing heterocycle natural molecule nicotinic acid and the sulfur-containing heterocycle thiophene. The structures of the target compounds were identified through 1H NMR, 13C NMR and HRMS spectra. The in vivo bioassay results of all the compounds against cucumber downy mildew (CDM, Pseudoperonospora cubensis (Berk.et Curt.) Rostov.) in a greenhouse indicated that compounds 4a (EC50 = 4.69 mg/L) and 4f (EC50 = 1.96 mg/L) exhibited excellent fungicidal activities which were higher than both diflumetorim (EC50 = 21.44 mg/L) and flumorph (EC50 = 7.55 mg/L). The bioassay results of the field trial against CDM demonstrated that the 10% EC formulation of compound 4f displayed excellent efficacies (70% and 79% control efficacies, respectively, each at 100 mg/L and 200 mg/L) which were superior to those of the two commercial fungicides flumorph (56% control efficacy at 200 mg/L) and mancozeb (76% control efficacy at 1000 mg/L). N-(thiophen-2-yl) nicotinamide derivatives are significant lead compounds that can be used for further structural optimization, and compound 4f is also a promising fungicide candidate against CDM that can be used for further development.

pH-Responsive Inorganic/Organic Nanohybrids System for Controlled Nicotinic Acid Drug Release.

Although nicotinic acid (NA) has several clinical benefits, its potency cannot be fully utilized due to several undesirable side effects, including cutaneous flushing, GIT-associated symptoms, etc. To overcome such issues and improve the NA efficacy, a new inorganic-organic nanohybrids system was rationally designed. For making such a hybrid system, NA was intercalated into LDH through a coprecipitation technique and then coated with Eudragit® S100 to make the final drug delivery system called Eudragit® S100-coated NA-LDH. The as-made drug delivery system not only improved the NA release profile but also exhibited good bio-compatibility as tested on L929 cells. Such an inorganic-organic nanohybrid drug delivery agent is expected to reduce the undesirable side effects associated with NA and hopefully improve the pharmacological effects without inducing any undesirable toxicity.

Hydrolysis kinetics of the prodrug myristyl nicotinate.

Myristyl nicotinate is a prodrug of nicotinic acid. In this research, the kinetics of hydrolysis for myristyl nicotinate was studied in an aqueous phosphate buffer solution within a 5-10 pH range and constant ionic strength at a high temperature which was 80 °C to perform accelerated hydrolysis experiments. The effect of temperature, ionic strength, buffer concentrations, and buffer type was studied. The degradation was monitored using a validated HPLC method. The kinetics of hydrolysis of myristyl nicotinate was also studied in skin and liver homogenates. The hydrolysis was found to follow pseudo-first-order kinetics. The rate constant was calculated from the slope of a linear plot of Ln transformation (Ln) of the remaining parent prodrug concentration versus time. The hydrolysis was found pH- dependent, and a pH rate profile was constructed. Moreover, the hydrolysis rate of the prodrug was found to be buffer species dependent. Carbonate buffer has the most catalytic effect over borate and phosphate buffers. The effect of temperature on the kinetics of hydrolysis of myristyl nicotinate in phosphate buffer at pH 9 at 343, 348, 353, and 358°K was studied. The hydrolysis was found to follow the Arrhenius equation. From the Arrhenius plot, the half-life at 25 °C, and the activation energy were calculated and were found to be 466.5 days and 24.57 kcal mol-1, respectively. The hydrolysis of the prodrug was faster in liver and skin homogenates than those in aqueous buffer solutions. The pseudo-first-order rate constants were found to be 0.012, 0.028 min-1 for myristyl nicotinate in the liver, and skin homogenates, respectively.

Overexpression of nicotinamidase 3 (NIC3) gene and the exogenous application of nicotinic acid (NA) enhance drought tolerance and increase biomass in Arabidopsis.

KEY MESSAGE: Overexpressing Nicotinamidase 3 gene, and the exogenous application of its metabolite nicotinic acid (NA), enhance drought stress tolerance and increase biomass in Arabidopsis thaliana. With progressive global climatic changes, plant productivity is threatened severely by drought stress. Deciphering the molecular mechanisms regarding genes responsible for balancing plant growth and stress amelioration could imply multiple possibilities for future sustainable goals. Nicotinamide adenine dinucleotide (NAD) biosynthesis and recycling/ distribution is a crucial feature for plant growth. The current study focuses on the functional characterization of nicotinamidase 3 (NIC3) gene, which is involved in the biochemical conversion of nicotinamide (NAM) to nicotinic acid (NA) in the salvage pathway of NAD biosynthesis. Our data show that overexpression of NIC3 gene enhances drought stress tolerance and increases plant growth. NIC3-OX plants accumulated more NA as compared to WT plants. Moreover, the upregulation of several genes related to plant growth/stress tolerance indicates that regulating the NAD salvage pathway could significantly enhance plant growth and drought stress tolerance. The exogenous application of nicotinic acid (NA) showed a similar phenotype as the effect of overexpressing NIC3 gene. In short, we contemplated the role of NIC3 gene and NA application in drought stress tolerance and plant growth. Our results would be helpful in engineering plants with enhanced drought stress tolerance and increased growth potential.