Metabolic pathway of 4-pyridone-3-carboxamide-1β-d-ribonucleoside and its effects on cellular energetics

Synthesis, Detection, and Metabolism of Pyridone Ribosides, Products of NAD Overoxidation

Pyridone-containing adenine dinucleotides, ox-NAD, are formed by overoxidation of nicotinamide adenine dinucleotide (NAD+) and exist in three distinct isomeric forms. Like the canonical nucleosides, the corresponding pyridone-containing nucleosides (PYR) are chemically stable, biochemically versatile, and easily converted to nucleotides, di- and triphosphates, and dinucleotides. The 4-PYR isomer is often reported with its abundance increasing with the progression of metabolic diseases, age, cancer, and oxidative stress. Yet, the pyridone-derived nucleotides are largely under-represented in the literature. Here, we report the efficient synthesis of the series of ox-NAD and pyridone nucleotides and measure the abundance of ox-NAD in biological specimens using liquid chromatography coupled with mass spectrometry (LC-MS). Overall, we demonstrate that all three forms of PYR and ox-NAD are found in biospecimens at concentrations ranging from nanomolar to midmicromolar and that their presence affects the measurements of NAD(H) concentrations when standard biochemical redox-based assays are applied. Furthermore, we used liver extracts and 1H NMR spectrometry to demonstrate that each ox-NAD isomer can be metabolized to its respective PYR isomer. Together, these results suggest a need for a better understanding of ox-NAD in the context of human physiology since these species are endogenous mimics of NAD+, the key redox cofactor in metabolism and bioenergetics maintenance.

Elevated Plasma Concentration of 4-Pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR) Highlights Malignancy of Renal Cell Carcinoma

Nicotinamide (NA) derivatives play crucial roles in various biological processes, such as inflammation, regulation of the cell cycle, and DNA repair. Recently, we proposed that 4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR), an unusual derivative of NA, could be classified as an oncometabolite in bladder, breast, and lung cancer. In this study, we investigated the relations between NA metabolism and the progression, recurrence, metastasis, and survival of patients diagnosed with different histological subtypes of renal cell carcinoma (RCC). We identified alterations in plasma NA metabolism, particularly in the clear cell RCC (ccRCC) subtype, compared to papillary RCC, chromophobe RCC, and oncocytoma. Patients with ccRCC also exhibited larger tumor sizes and elevated levels of diagnostic serum biomarkers, such as hsCRP concentration and ALP activity, which were positively correlated with the plasma 4PYR. Notably, 4PYR levels were elevated in advanced stages of ccRCC cancer and were associated with a highly aggressive phenotype of ccRCC. Additionally, elevated concentrations of 4PYR were related to a higher likelihood of mortality, recurrence, and particularly metastasis in ccRCC. These findings are consistent with other studies, suggesting that NA metabolism is accelerated in RCC, leading to abnormal concentrations of 4PYR. This supports the concept of 4PYR as an oncometabolite and a potential prognostic factor in the ccRCC subtype.

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.

4-Pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR)—A Novel Oncometabolite Modulating Cancer-Endothelial Interactions in Breast Cancer Metastasis

The accumulation of specific metabolic intermediates is known to promote cancer progression. We analyzed the role of 4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR), a nucleotide metabolite that accumulates in the blood of cancer patients, using the 4T1 murine in vivo breast cancer model, and cultured cancer (4T1) and endothelial cells (ECs) for in vitro studies. In vivo studies demonstrated that 4PYR facilitated lung metastasis without affecting primary tumor growth. In vitro studies demonstrated that 4PYR affected extracellular adenine nucleotide metabolism and the intracellular energy status in ECs, shifting catabolite patterns toward the accumulation of extracellular inosine, and leading to the increased permeability of lung ECs. These changes prevailed over the direct effect of 4PYR on 4T1 cells that reduced their invasive potential through 4PYR-induced modulation of the CD73-adenosine axis. We conclude that 4PYR is an oncometabolite that affects later stages of the metastatic cascade by acting specifically through the regulation of EC permeability and metabolic controls of inflammation.

An unusual nicotinamide derivative, 4-pyridone-3-carboxamide ribonucleoside (4PYR), is a novel endothelial toxin and oncometabolite

Our recent studies identified a novel pathway of nicotinamide metabolism that involves 4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR) and demonstrated its endothelial cytotoxic effect. This study tested the effects of 4PYR and its metabolites in experimental models of breast cancer. Mice were divided into groups: 4T1 (injected with mammary 4T1 cancer cells), 4T1 + 4PYR (4PYR-treated 4T1 mice), and control, maintained for 2 or 21 days. Lung metastasis and endothelial function were analyzed together with blood nucleotides (including 4PYR), plasma amino acids, nicotinamide metabolites, and vascular ectoenzymes of nucleotide catabolism. 4PYR metabolism was also evaluated in cultured 4T1, MDA-MB-231, MCF-7, and T47D cells. An increase in blood 4PYR in 4T1 mice was observed at 2 days. 4PYR and its metabolites were noticed after 21 days in 4T1 only. Higher blood 4PYR was linked with more lung metastases in 4T1 + 4PYR vs. 4T1. Decreased L-arginine, higher asymmetric dimethyl-L-arginine, and higher vascular ecto-adenosine deaminase were observed in 4T1 + 4PYR vs. 4T1 and control. Vascular relaxation caused by flow-dependent endothelial activation in 4PYR-treated mice was significantly lower than in control. The permeability of 4PYR-treated endothelial cells was increased. Decreased nicotinamide but enhanced nicotinamide metabolites were noticed in 4T1 vs. control. Reduced N-methylnicotinamide and a further increase in Met2PY were observed in 4T1 + 4PYR vs. 4T1 and control. In cultured breast cancer cells, estrogen and progesterone receptor antagonists inhibited the production of 4PYR metabolites. 4PYR formation is accelerated in cancer and induces metabolic disturbances that may affect cancer progression and, especially, metastasis, probably through impaired endothelial homeostasis. 4PYR may be considered a new oncometabolite.

Levels of a metabolite of nicotinamide, a form of vitamin B₃, found in the blood and urine of cancer patients may provide a useful biomarker indicating the likelihood of metastasis. Disruption to the lining of blood vessels (endothelium) enables cancer cells to infiltrate the bloodstream and migrate to other organs. Research suggests that increased levels of 4PYR, a derivative of nicotinamide metabolism, may induce metabolic disturbances that favor cancer progression. Ewa Slominska and co-workers at the Medical University of Gdansk, Poland, examined 4PYR in mouse models injected with breast cancer cells and found increased levels in the blood only two days after injection. Mice with the highest 4PYR levels had enhanced lung metastases after three weeks. The team believes 4PYR activity may increase the permeability of the endothelium, but further investigation is needed.

The Biochemical Pathways of Nicotinamide-Derived Pyridones

As catabolites of nicotinamide possess physiological relevance, pyridones are often included in metabolomics measurements and associated with pathological outcomes in acute kidney injury (AKI). Pyridones are oxidation products of nicotinamide, its methylated form, and its ribosylated form. While they are viewed as markers of over-oxidation, they are often wrongly reported or mislabeled. To address this, we provide a comprehensive characterization of these catabolites of vitamin B3, justify their nomenclature, and differentiate between the biochemical pathways that lead to their generation. Furthermore, we identify an enzymatic and a chemical process that accounts for the formation of the ribosylated form of these pyridones, known to be cytotoxic. Finally, we demonstrate that the ribosylated form of one of the pyridones, the 4-pyridone-3-carboxamide riboside (4PYR), causes HepG3 cells to die by autophagy; a process that occurs at concentrations that are comparable to physiological concentrations of this species in the plasma in AKI patients.

Increased plasma concentration of 4-pyridone-3-carboxamide-1-ß-D-ribonucleoside (4PYR) in lung cancer. Preliminary studies

4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR) is a new nicotinamide derivative, which is potentially toxic to the endothelium. Dysfunction of the endothelium promotes cancer cell proliferation, invasiveness, and inflammatory signaling. The aim of this study was to analyze 4PYR concentration in the plasma of lung cancer patients and its relationship to other known biochemical parameters associated with the endothelium function. The concentration of 4PYR, nicotinamide, 1-methylnicotinamide (MNA), amino acids, and their derivatives were measured in samples obtained from patients with primary squamous cell carcinoma (n = 48) and control group (n = 100). The concentration of 4PYR and 4PYR/MNA ratio were significantly higher in lung cancer patients as compared to controls (0.099 ± 0.009 vs. 0.066 ± 0.006 µmol/L and 1.10 ± 0.08 vs. 1.97 ± 0.15, respectively). The plasma arginine/asymmetric dimethylarginine (Arg/ADMA) ratio was considerably lower in lung cancer patients (253 ± 17 vs. 369 ± 19) as well as plasma MNA (0.057 ± 0.004 vs. 0.069 ± 0.003 µmol/L). There was no difference in the plasma concentrations of nicotinamide and nicotinamide riboside in both groups (0.116 ± 0.019 vs. 0.131 ± 0.014 and 0.102 ± 0.006 vs. 0.113 ± 0.011, respectively). In this study, a higher 4PYR concentration was observed for the first time in patients with squamous cell carcinoma. This change may be related to the endothelial dysfunction that promote cancer progression since 4PYR and its derivatives are known to disrupt glycolytic pathway.

Metabolism of 4-pyridone-3-carboxamide-1β-d-ribonucleoside (4PYR) in primary murine brain microvascular endothelial cells (mBMECs)

4-pyridone-3-carboxamide-1β-D-ribonucleoside (4PYR) is a derivative of nicotinamide found physiologically in human body fluids that can be metabolized to mono-, di- or triphosphate derivatives (4PYMP, 4PYDP and 4PYTP respectively) and an analogue of NAD - the 1-β-D-ribonucleoside-4-pyridone-3-carboxamide adenine dinucleotide (4PYRAD) in human cells. The European Uremic Toxin Work Group (EUTox) has classified 4PYR as a uremic toxin that adversely affects endothelium. This study aimed to investigate the metabolism of 4PYR in murine brain microvascular endothelial cells (mBMECs). Incubation of mBMECs with 4PYR was carried out for 0, 24, 48 or 72 h. After incubation, a medium was removed and cellular concentrations of ATP, ADP, NAD, 4PYMP and 4PYRAD were analyzed using reversed-phase HPLC. 4PYR was metabolized by mBMECs to 4PYMP and 4PYRAD that reached concentrations of 2 ± 0.7 and 0.6 ± 0.2 nmol/mg protein (mean ± SEM), respectively, after 72 h incubation. However, unlike with endothelial cells studied so far this process has no effect on energy balance in the cell as indicated by maintained ATP/ADP ratio and adenine and nicotinamide intracellular pools. Further studies are required to explain whether the difference in 4PYR metabolism is related to differences between species or organs.

Characterization of adenine nucleotide metabolism in the cellular model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder that is caused by expanded CAG repeats within the exon-1 of the huntingtin (HTT) gene. It has been shown that HTT interacts with the proteins involved in the gene transcription, endocytosis and metabolism, nevertheless the biochemical pathways by which mutant HTT causes a cellular dysfunction remain unclear. Thus, this study aimed to establish the role of mutant HTT expansion in energy and nucleotide metabolism deteriorations. We examined HEK 293 T cell line transfected with plasmids expressing wild-type (control) or mutant exon 1 of the HTT gene (HD). Analysis of intracellular concentration of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD⁺), as well as activities of intra- and extracellular enzymes of nucleotide catabolism (such as adenine monophosphate deaminase (AMPD), adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP) and ectonucleoside triphosphate diphosphohydrolase (eNTPD), ecto-5'-nucleotidase (e5NT), ecto-adenosine deaminase (eADA) were performed with high pressure liquid chromatography. Protein concentration was measured with Bradford method. We found diminished intracellular ATP concentration (22.5 ± 1.7 in HD; 29.3 ± 1.4 nmol/mg protein in control), increased ADA activity (27.9 ± 1.0 in HD; 21.1 ± 1.6 nmol/min/mg protein in control) and reduced activities of eNTPD (2.4 ± 0.5 in HD; 5.8 ± 0.7 nmol/min/mg protein in control), e5NT (0.1 ± 0.01 in HD; 0.2 ± 0.01 nmol/min/mg protein in control) and eADA (0.3 ± 0.03 in HD; 0.4 ± 0.04 nmol/min/mg protein in control) while NAD⁺ concentration, AMPD and PNP activities remained unchanged. This study highlights that the mutant HTT expansion resulted in depletion of cellular ATP concentration and reduced rates of extracellular nucleotide breakdown. In conclusion, such changes may contribute to the pathology of HD.

The chemistry of the vitamin B3 metabolome

The functional cofactors derived from vitamin B3 are nicotinamide adenine dinucleotide (NAD⁺), its phosphorylated form, nicotinamide adenine dinucleotide phosphate (NADP⁺) and their reduced forms (NAD(P)H). These cofactors, together referred as the NAD(P)(H) pool, are intimately implicated in all essential bioenergetics, anabolic and catabolic pathways in all forms of life. This pool also contributes to post-translational protein modifications and second messenger generation. Since NAD⁺ seats at the cross-road between cell metabolism and cell signaling, manipulation of NAD⁺ bioavailability through vitamin B3 supplementation has become a valuable nutritional and therapeutic avenue. Yet, much remains unexplored regarding vitamin B3 metabolism. The present review highlights the chemical diversity of the vitamin B3-derived anabolites and catabolites of NAD⁺ and offers a chemical perspective on the approaches adopted to identify, modulate and measure the contribution of various precursors to the NAD(P)(H) pool.

Optimal Xeno-free Culture Condition for Clinical Grade Stem Cells from Human Exfoliated Deciduous Teeth

Background and Objectives

Stem cells from human exfoliated deciduous teeth (SHED) are a promising clinical resource for various tissue defects, including lumbar spondylosis, neural compression, and cleft palate. Use of media containing animal-derived serum carries potential risk of infectious diseases and unwanted immunogenicity. To increase the potential utility of SHED for clinical application, SHED was adapted to xeno-free conditions.

Methods

Define xeno-free culture media were compared with the conventional serum containing media in the culture of SHED. Cultured SHED in different media were further characterized through proliferative capacities, cellular phenotype, and differentiation potential.

Results

Selected xeno-free media were capable of supporting the growth of SHED. MSCGM-CD Bulletkit medium greatly increased the number and proliferate capacity of colony-forming unit-fibroblast than SHED cultured in other media. In addition, the characteristic surface markers expression and multipotent differentiation potential of SHED in the MSCGM-CD Bulletkit medium were comparable to those observed with serum-containing medium.

Conclusions

The xeno-free medium described herein has the potential to be further used for the safe expansion and to determine efficient way to produce clinical grade dental stem cells for therapeutic applications.