Simultaneous quantification of 12 different nucleotides and nucleosides released from renal epithelium and in human urine samples using ion-pair reversed-phase HPLC

Advancements in Adenine Nucleotides Extraction and Quantification from a Single Drop of Human Blood

Adenine nucleotides (ANs)-adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), and adenosine 5'-monophosphate (AMP)-are essential for energy transfer and the supply of countless processes within cellular metabolism. Their concentrations can be expressed as adenylate energy charge (AEC), a measure of cellular metabolic energy that directly correlates with the homeostasis of the organism. AEC index has broad diagnostic potential, as reduced ATP levels are associated to various conditions, such as inflammatory diseases, metabolic disorders, and cancer. We introduce a novel methodology for rapid isolation, purification, and quantification of ANs from a single drop of capillary blood. Of all the stationary phases tested, activated carbon proved to be the most efficient for the purification of adenine nucleotides, using an automated micro-solid phase extraction (µ-SPE) platform. An optimized µ-SPE method, coupled with RP-HPLC and a run time of 30 min, provides a reliable analytical framework for adenine nucleotide analysis of diverse biological samples. AN concentrations measured in capillary blood samples were 1393.1 µM, 254.8 µM, and 76.9 µM for ATP, ADP, and AMP molecules aligning with values reported in the literature. Overall, this study presents a streamlined and precise approach for analyzing ANs from microliters of blood, offering promising applications in clinical diagnostics.

An on-line SPE-LC-MS/MS method for quantification of nucleobases and nucleosides present in biological fluids

Solid phase extraction (SPE) and liquid chromatographic (LC) separation of nucleobases and nucleosides are challenging due to the high hydrophilicity of these compounds. Herein we report a novel on-line SPE-LC-MS/MS method for their quantification after pre-column derivatization with chloroacetaldehyde (CAA). The method proposed is selective and sensitive with limits of detection at the nano-molar level. Analysis of urine and saliva samples by using this method is demonstrated. Adenine, guanine, cytosine, adenosine, guanosine, and cytidine were found in the range from 0.19 (guanosine) to 1.83 μM (cytidine) in urine and from 0.015 (guanosine) to 0.79 μM (adenine) in saliva. Interestingly, methylation of cytidine was found to be significantly different in urine from that in saliva. While 5-hydroxymethylcytidine was detected at a very low level (<0.05 μM) in saliva, it was found to be the most prominent methylated cytidine in urine at a high level of 3.33 μM. Since on-line SPE is deployed, the proposed LC-MS/MS quantitative assay is convenient to carry out and offers good assay accuracy and repeatability.

Preparation of restricted-access boronate affinity adsorbent with excellent anti-protein adsorption property for directly extracting small cis-diol molecules from biological matrices

Boronate affinity adsorbents are of great promise in the enrichment of small cis-diol-containing molecules (cis-diols) from biological matrices. This work develops a restricted-access boronate affinity mesoporous adsorbent, in which boronate sites are only distributed on the internal surface of mesopores and the external surface is a strongly hydrophilic layer. The adsorbent has high binding capacities (30.3 mg g-1, 22.9 mg g-1 and 14.9 mg g-1 for dopamine, catechol and adenosine, respectively) in spite of removal of the boronate sites on the external surface of adsorbent. The adsorption specific of adsorbent towards cis-diols was assessed by dispersive solid-phase extraction (d-SPE) method, and the results show that the adsorbent can selectively extract small cis-diols in the biosamples while exclude proteins completely. Under the optimal d-SPE, the nucleosides and cis-diol drugs in human serum were successfully analyzed by coupling d-SPE with high-performance liquid chromatography. Where, the detection limits are between 6.1 and 13.4 ng mL-1 for four nucleosides, and 24.9 and 34.3 ng mL-1 for two cis-diol drugs; the relative recoveries of all the analytes vary from 84.1% to 110.1% (RSDs <13.4%, n = 6). The results indicate that the adsorbent can directly treat the real biosamples without the necessary protein precipitation steps in advance, thus simplifying the analysis process.

Simultaneous enrichment and sequential elution of cis-diol containing molecules and deoxyribonucleotides with bifunctional boronate and titanium (Ⅳ) ion modified-magnetic nanoparticles prior to quantitation by high performance liquid chromatography

Some diseases can cause abnormal concentrations of catecholamines (CAs), nucleosides (NSs) and nucleotides (NTs) in patients. Previous studies normally focused on the detection of the three types of substances separately. In this work, a bifunctional boronate and titanium (Ⅳ) ion affinity magnetic adsorbent with high-capacity was prepared. The adsorbent can simultaneously enrich CAs, NSs and NTs in a single extraction process, and the adsorbed analytes can be sequentially eluted by 1.0% trifluoroacetic acid and 20.0 mmol L-1 Na3PO4. An analytical method of the analytes has been established by coupling the adsorbent with RP-HPLC. The method has low detection limits (0.039-0.708 ng mL-1) and good reproducibility (inter- and intra-day of assay RSDs less than 15.0%). Serum sample from healthy volunteer was successfully quantified for two CAs, four NSs and five NTs. Compared with the reported methods, the proposed method is simpler to operate, consume less samples, and has enough accurate and sensitivity to obtain comprehensive information on the concentrations of analytes in a single extraction process.

Extraction of Nucleotides from Dietary Supplements by Newly Synthesized Adsorbents

The aim of the study was the synthesis and application of novel adsorbents for the extraction of nucleotides from dietary supplements. Three different adsorbents modified with a silane containing two amine groups and various dicarboxylic acids were synthesized and characterized using various instrumental techniques. Next, different solvents were tested for their adsorption and desorption of five nucleotides. The results showed that the efficiency of both processes depends on the conditions used and the type of dicarboxylic acid bound to the surface of the adsorbent. The best results were obtained for succinic acid. The most effective adsorption occurred for water acidified with acetic acid to pH 4.5, while the highest recoveries (85-102%) with high reproducibility were obtained for 10 mM ammonium acetate at pH 9. The nucleotide extraction was performed simply by changing the charge at the adsorbent surface, providing the possibility of electrostatic attraction and repulsion between the adsorbent and nucleotides. Moreover, the sorption capacity of the obtained materials was also determined, which was essential for their use in extracting nucleotides from real samples by dispersive extrusion to the solid phase. The new adsorbents and the developed extraction method were successfully applied to isolate nucleotides from two different dietary supplements with different compositions (one of them with yeast strains). The method is simple and reproducible; no organic solvents or high-concentration inorganic salts are used (it is environmentally friendly). The entire process is performed in one centrifuge tube and is cheaper compared with methods used so far.

Kinetic Characterization and Inhibition of Trypanosoma cruzi Hypoxanthine–Guanine Phosphoribosyltransferases

Chagas disease, caused by the parasitic protozoan Trypanosoma cruzi, affects over 8 million people worldwide. Current antiparasitic treatments for Chagas disease are ineffective in treating advanced, chronic stages of the disease, and are noted for their toxicity. Like most parasitic protozoa, T. cruzi is unable to synthesize purines de novo, and relies on the salvage of preformed purines from the host. Hypoxanthine–guanine phosphoribosyltransferases (HGPRTs) are enzymes that are critical for the salvage of preformed purines, catalyzing the formation of inosine monophosphate (IMP) and guanosine monophosphate (GMP) from the nucleobases hypoxanthine and guanine, respectively. Due to the central role of HGPRTs in purine salvage, these enzymes are promising targets for the development of new treatment methods for Chagas disease. In this study, we characterized two gene products in the T. cruzi CL Brener strain that encodes enzymes with functionally identical HGPRT activities in vitro: TcA (TcCLB.509693.70) and TcC (TcCLB.506457.30). The TcC isozyme was kinetically characterized to reveal mechanistic details on catalysis, including identification of the rate-limiting step(s) of catalysis. Furthermore, we identified and characterized inhibitors of T. cruzi HGPRTs originally developed as transition-state analogue inhibitors (TSAIs) of Plasmodium falciparum hypoxanthine–guanine–xanthine phosphoribosyltransferase (PfHGXPRT), where the most potent compound bound to T. cruzi HGPRT with low nanomolar affinity. Our results validated the repurposing of TSAIs to serve as selective inhibitors for orthologous molecular targets, where primary and secondary structures as well as putatively common chemical mechanisms are conserved.

Development of a retention prediction model in ion-pair reversed-phase HPLC for nucleoside triphosphates used as mRNA vaccine raw materials

The International Conference on Harmonization guidelines for quality on pharmaceutical development recommends a systematic development approach including robustness studies which assure performance of manufacturing and analytical method development of drug product. It was demonstrated that the retention prediction model for nucleoside triphosphates (NTPs) on ion-pair reversed-phase HPLC was developed by a highly accurate Kawabe's model which supports the development of robust HPLC methods. As NTPs and its derivatives are typically used for Messenger ribonucleic acid (mRNA) vaccine production, adenosine-5'-triphosphate (ATP), guanosine-5'-triphosphate (GTP), cytidine-5'-triphosphate (CTP), 5-methylcytidine-5'-triphosphate (m5-CTP), uridine-5'-triphosphate (UTP), 5-methyluridine-5'-triphosphate (m5-UTP), pseudouridine-5'-triphosphate (Ψ-UTP) and N1-methylpseudouridine-5'-triphosphate (m1Ψ-UTP) were applied for prediction model development. By a comparison of the predicted retention factor in eight studied samples with the retention factor measured under six isocratic conditions, the absolute prediction error was 0.075 and also the prediction error (%) was 2.70%. In practical examples, analytical method for residual ATP, GTP, CTP, and m1Ψ-UTP in the commercial mRNA-based drugs and purity method for UTP derivatives were optimized by QbD approach. The design space for the minimum resolution between adjacent peaks was simulated with the models developed to evaluate the robustness of peak separation, and the optimal mobile phase condition was also simulated. As a conclusion, the desired peak was successfully separated under the optimized condition, and we thought that these retention models could optimize the mobile phase condition of the NTP analysis method for applying to various quality tests, such as quantity, purity and identity test for NTPs and its derivates in the mRNA-based drugs.

Application of a HPLC-Q/TOF method with post-column compensation for separation and identification of polar impurities in Cytidine disodium triphosphate for injection

Background:

Cytidine Disodium Triphosphate (CTP-2Na) for injection is mainly used for treating nervous system diseases. Currently, there are few studies focused on the separation and identification of polar impurities in CTP-2Na for injection, which is important for ensuring drug safety and efficacy.

Objective:

The study aimed to establish an HPLC-Q/TOF method for the separation and identification of polar impurities in CTP-2Na for injection.

Methods:

Chromatographic separation was achieved on a Waters Atlantis T3 column using 5 mM aqueous ammonium acetate solution as the mobile phase in an isocratic elution mode. A postcolumn compensation technology was used to improve the ionization efficiency of impurities in the spray chamber.

Results:

Three polar impurities (disodium cytidine tetraphosphate, disodium cytidine diphosphate, disodium cytidine monophosphate) were detected in CTP-2Na for injection. The former one is probably the overreaction product during the production of CTP-2Na, the latter two were reported as degradation products. The fragmentation patterns of cytidine phosphate compounds in negative ion mode are summarized.

Conclusion:

This study provides a good reference for the separation and identification of polar impurities in nucleotide drugs.

Development of a versatile HPLC-based method to evaluate the activation status of small GTPases

Small GTPases cycle between an inactive GDP-bound and an active GTP-bound state to control various cellular events, such as cell proliferation, cytoskeleton organization, and membrane trafficking. Clarifying the guanine nucleotide-bound states of small GTPases is vital for understanding the regulation of small GTPase functions and the subsequent cellular responses. Although several methods have been developed to analyze small GTPase activities, our knowledge of the activities for many small GTPases is limited, partly because of the lack of versatile methods to estimate small GTPase activity without unique probes and specialized equipment. In the present study, we developed a versatile and straightforward HPLC-based assay to analyze the activation status of small GTPases by directly quantifying the amounts of guanine nucleotides bound to them. This assay was validated by analyzing the RAS-subfamily GTPases, including HRAS, which showed that the ratios of GTP-bound forms were comparable with those obtained in previous studies. Furthermore, we applied this assay to the investigation of psychiatric disorder-associated mutations of RHEB (RHEB/P37L and RHEB/S68P), revealing that both mutations cause an increase in the ratio of the GTP-bound form in cells. Mechanistically, loss of sensitivity to TSC2 (a GTPase-activating protein for RHEB) for RHEB/P37L, as well as both decreased sensitivity to TSC2 and accelerated guanine-nucleotide exchange for RHEB/S68P, is involved in the increase of their GTP-bound forms, respectively. In summary, the HPLC-based assay developed in this study provides a valuable tool for analyzing small GTPases for which the activities and regulatory mechanisms are less well understood.

Versatile separation of nucleotides from bacterial cell lysates using strong anion exchange chromatography

Nucleotides exemplify some of the building blocks of life, comprising DNA & RNA, participating in processes such as cell signaling and metabolism, and serving as carriers of metabolic energy. The quantification of these compounds in biological samples is critical for researchers to understand complex systems. Herein, we demonstrate an anion exchange chromatography method utilizing a pH range of 8 to 10, which provides superior resolution and selectivity to previously reported methods and, more importantly, gives the flexibility to shift analyte selectivity if resolution between analytes is not optimal. We have applied the method to study the kinetics of the nucleotide pool in a bacterial cell-free lysate system that is producing RNA. Sample to sample runtimes are less than 18 min and recoveries greater than 96% were observed for all analytes through our methanol quench protocol with day-to-day variabilities less than 5%. This method reliably detects and quantifies all analytes that were expected to be observed in the process and helps lay the groundwork for future nucleotide research.

HPLC method to resolve, identify and quantify guanine nucleotides bound to recombinant ras GTPase

The Ras superfamily of small G proteins play central roles in diverse signaling pathways. Superfamily members act as molecular on-off switches defined by their occupancy with GTP or GDP, respectively. In vitro functional studies require loading with a hydrolysis-resistant GTP analogue to increase the on-state lifetime, as well as knowledge of fractional loading with activating and inactivating nucleotides. The present study describes a method combining elements of previous approaches with new, optimized features to analyze the bound nucleotide composition of a G protein loaded with activating (GMPPNP) or inactivating (GDP) nucleotide. After nucleotide loading, the complex is washed to remove unbound nucleotides then bound nucleotides are heat-extracted and subjected to ion-paired, reverse-phase HPLC-UV to resolve, identify and quantify the individual nucleotide components. These data enable back-calculation to the nucleotide composition and fractional activation of the original, washed G protein population prior to heat extraction. The method is highly reproducible. Application to multiple HRas preparations and mutants confirms its ability to fully extract and analyze bound nucleotides, and to resolve the fractional on- and off-state populations. Furthermore, the findings yield a novel hypothesis for the molecular disease mechanism of Ras mutations at the E63 and Y64 positions.

The cAMP Inducers Modify N-Acetylaspartate Metabolism in Wistar Rat Brain

Neuronal N-acetylaspartate production appears in the presence of aspartate N-acetyltransferase (NAT8L) and binds acetyl groups from acetyl-CoA with aspartic acid. Further N-acetylaspartate pathways are still being elucidated, although they seem to involve neuron-glia crosstalk. Together with N-acetylaspartate, NAT8L takes part in oligoglia and astroglia cell maturation, myelin production, and dopamine-dependent brain signaling. Therefore, understanding N-acetylaspartate metabolism is an emergent task in neurobiology. This project used in in vitro and in vivo approaches in order to establish the impact of maturation factors and glial cells on N-acetylaspartate metabolism. Embryonic rat neural stem cells and primary neurons were maturated with either nerve growth factor, trans-retinoic acid or activators of cAMP-dependent protein kinase A (dibutyryl-cAMP, forskolin, theophylline). For in vivo, adult male Wistar rats were injected with theophylline (20 mg/kg b.w.) daily for two or eight weeks. Our studies showed that the N-acetylaspartate metabolism differs between primary neurons and neural stem cell cultures. The presence of glia cells protected N-acetylaspartate metabolism from dramatic changes within the maturation processes, which was impossible in the case of pure primary neuron cultures. In the case of differentiation processes, our data points to dibutyryl-cAMP as the most prominent regulator of N-acetylaspartate metabolism.

Effect of suramin on urinary excretion of diabetes-induced glomerular and tubular injury parameters in rats

Diabetes mellitus causes changes in metabolism of extracellular nucleotides acting through P2 receptors (P2Rs). This affects renal function and may lead to glomerular and tubular disturbances. We measured urinary excretion of nucleotides (ATP, ADP, AMP, UTP, UDP, UMP) in streptozotocin-induced diabetic rats (65 mg/kg, i.p., day 0) and the effects of P2Rs' blockade by suramin (10 mg/kg, i.p., days +7, +14) on glomerular P2×7R expression and urinary excretion of glomerular (albumin, nephrin) and tubular (KIM-1, NGAL) injury markers, electrolytes, and oxidative stress markers (TBARS, 8-OHdG). Concentrations of nucleotides, specific proteins, electrolytes, and oxidative stress markers in 24-h urine samples collected in metabolic cages at days -1, +6 and +20 were measured using ion-paired reversed-phase HPLC, immunoenzymatic and fluorometric methods, and flame photometry, respectively. Expression of KIM-1 and P2×7R was examined by immunohistochemistry or immunoblotting. Diabetes was associated with increased urinary excretion of ATP, ADP, UTP, UDP and glomerular P2×7R expression. Suramin attenuated P2×7R expression but did not affect urinary excretion of nucleotides. Urinary excretion of albumin, nephrin, NGAL, and 8-OHdG were increased in diabetic rats and were not affected by suramin. TBARS was higher in diabetic rats and suramin attenuated the excretion dynamics in this group. KIM-1 excretion was higher in diabetic rats and suramin further increased excretion of KIM-1 in both diabetic and non-diabetic rats. Furthermore, suramin attenuated the diabetes-induced natriuresis and kaliuresis. It is possible that suramin affects both glomerular and tubular functions in diabetic rats.

An Overview of Pretreatment and Analysis of Nucleotides in Different Samples (Update since 2010)

Nucleotides, which are important low-molecular-weight compounds present in organisms, are precursors of nucleic acids and participate in various regulatory and metabolic functions. Sensitive and valid methods for monitoring and determining nucleotides and nucleosides in different samples are urgently required. Due to the presence of numerous endogenous interferences in complex matrices and the high polarity of the molecules of the phosphate moiety, the determination of nucleotide content is challenging. This review summarizes the pretreatment and analysis methods of nucleotides in different samples. Advanced pretreatment methods, including different microextraction methods, solid-phase extraction based on novel materials, QuEChERS, are clearly displayed, and continuous progress which has been made in LC, LC-MS/MS and capillary electrophoresis methods are discussed. Moreover, the strengths and weaknesses of different methods are discussed and compared. Highlight:Advanced pretreatment and detection methods of nucleotides were critically reviewed.Microextraction technology was one of the trends of nucleotides pretreatment in the future.Applications of novel materials and supercritical fluid were highlighted.The evolution and advance of HRMS analyzers were in detailed.

Acetate and auto-inducing peptide are independent triggers of quorum sensing in Lactobacillus plantarum

The synthesis of plantaricin in Lactobacillus plantarum is regulated by quorum sensing. However, the nature of the extra-cytoplasmic (EC) sensing domain of the histidine kinase (PlnB1) and the ability to recognize the auto-inducing peptide PlnA1 is not known. We demonstrate the key motif Ile-Ser-Met-Leu of auto-inducing peptide PlnA1 binds to the hydrophobic region Phe-Ala-Ser-Gln-Phe of EC loop 2 of PlnB1 via hydrophobic interactions and hydrogen bonding. Moreover, we identify a new inducer, acetate, that regulates the synthesis of plantaricin by binding to a positively charged region (Arg-Arg-Tyr-Ser-His-Lys) in loop 4 of PlnB1 via electrostatic interaction. The side chain of Phe143 on loop 4 determined the specificity and affinity of PlnB1 to recognize acetate. PlnA1 activates quorum sensing in log phase growth and acetate in stationary phase to maintain the synthesis of plantaricin under conditions of reduced growth. Acetate activation of PlnB was also evident in four types of PlnB present in different Lb. plantarum strains. Finally, we proposed a model to explain the developmental regulation of plantaricin synthesis by PlnA and acetate. These results have potential applications in improving food fermentation and bacteriocin production.

Neither Excessive Nitric Oxide Accumulation nor Acute Hyperglycemia Affects the N-Acetylaspartate Network in Wistar Rat Brain Cells

The N-acetylaspartate network begins in neurons with N-acetylaspartate production catalyzed by aspartate N-acetyltransferase from acetyl-CoA and aspartate. Clinical studies reported a significant depletion in N-acetylaspartate brain level in type 1 diabetic patients. The main goal of this study was to establish the impact of either hyperglycemia or oxidative stress on the N-acetylaspartate network. For the in vitro part of the study, embryonic rat primary neurons were treated by using a nitric oxide generator for 24 h followed by 6 days of post-treatment culture, while the neural stem cells were cultured in media with 25–75 mM glucose. For the in vivo part, male adult Wistar rats were injected with streptozotocin (65 mg/kg body weight, ip) to induce hyperglycemia (diabetes model) and euthanized 2 or 8 weeks later. Finally, the biochemical profile, NAT8L protein/Nat8l mRNA levels and enzymatic activity were analyzed. Ongoing oxidative stress processes significantly affected energy metabolism and cholinergic neurotransmission. However, the applied factors did not affect the N-acetylaspartate network. This study shows that reduced N-acetylaspartate level in type 1 diabetes is not related to oxidative stress and that does not trigger N-acetylaspartate network fragility. To reveal why N-acetylaspartate is reduced in this pathology, other processes should be considered.

Development of dried blood spot quality control materials for adenosine deaminase severe combined immunodeficiency and LC-MS/MS method for their characterization

Adenosine deaminase severe combined immunodeficiency (ADA-SCID) is an autosomal recessive disorder in which a lack of ADA enzyme prevents the maturation of T- and B-cells; early intervention is crucial for restoring immune function in affected neonates. ADA is responsible for purine metabolism and-in its absence-adenosine, deoxyadenosine, and S-adenosylhomocysteine build up and can be detected in the blood. Preparing dried blood spot (DBS) quality control (QC) materials for these analytes is challenging because enrichments are quickly metabolized by the endogenous ADA in normal donor blood. Adding an inhibitor, erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), has been previously reported to minimize enzyme activity, although this adds additional cost and complexity. We describe an alternative method using unnatural L-enantiomer nucleosides (L-adenosine and 2'-deoxy-L-adenosine) which eliminates the need for enzyme inhibition. We also present a novel method for characterization of the materials using liquid chromatography mass spectrometry to quantify the analytes of interest.

Simultaneous quantification of 8 nucleotides and adenosine in cells and their medium using UHPLC-HRMS

Purinergic signalling is involved in physiological processes, particularly during ischemia-reperfusion injuries for which it has a protective effect. The purpose of this work was to develop a method for simultaneous quantification of eight nucleotides and adenosine in biological matrices by liquid chromatography coupled with high-resolution mass spectrometry. A method was developed that was sufficiently robust to quantify the targeted analytes in 20 min with good sensitivity. Analysis of extracellular media from cultured endothelial cells detected the release of nucleotides and adenosine during 2 h of hypoxia. The quantification of cylic adenosine monophosphate (cAMP) allowed to establish a dose-response curve after receptor stimulation. Therefore, our method allows us to study the involvement of nucleotides in various processes in both the intracellular and extracellular compartment.

Quantification of serum purine metabolites for distinguishing patients with hepatitis B from hepatocellular carcinoma

Aim: In order to differential diagnosis of chronic hepatitis B (HBV-I) and hepatocellular carcinoma (HCC), a UPLC-MS/MS method for measuring purine metabolites was developed. Methodology & results: serum samples from 26 HBV-I and 35 HCC patients were collected. Ten purine metabolites were simultaneously quantified by UPLC-MS/MS with tubercidin and uric acid-1,3-¹⁵N₂ as internal standards. The method was validated to meet the requirements of clinical sample analysis. A logistic equation was established for differential diagnosis of HBV-I and HCC by combination of xanthosine and guanine with the area under the receiver operating characteristic curve of 0.885. Conclusion: Guanine and xanthosine are intermediates in the metabolism of purine, which play an important role in gene synthesis, and metabolism regulation. The alteration of serum purine metabolite may contribute to differential diagnosis of HBV-I and HCC.

Extracellular Nucleotides and P2 Receptors in Renal Function

The understanding of the nucleotide/P2 receptor system in the regulation of renal hemodynamics and transport function has grown exponentially over the last 20 yr. This review attempts to integrate the available data while also identifying areas of missing information. First, the determinants of nucleotide concentrations in the interstitial and tubular fluids of the kidney are described, including mechanisms of cellular release of nucleotides and their extracellular breakdown. Then the renal cell membrane expression of P2X and P2Y receptors is discussed in the context of their effects on renal vascular and tubular functions. Attention is paid to effects on the cortical vasculature and intraglomerular structures, autoregulation of renal blood flow, tubuloglomerular feedback, and the control of medullary blood flow. The role of the nucleotide/P2 receptor system in the autocrine/paracrine regulation of sodium and fluid transport in the tubular and collecting duct system is outlined together with its role in integrative sodium and fluid homeostasis and blood pressure control. The final section summarizes the rapidly growing evidence indicating a prominent role of the extracellular nucleotide/P2 receptor system in the pathophysiology of the kidney and aims to identify potential therapeutic opportunities, including hypertension, lithium-induced nephropathy, polycystic kidney disease, and kidney inflammation. We are only beginning to unravel the distinct physiological and pathophysiological influences of the extracellular nucleotide/P2 receptor system and the associated therapeutic perspectives.

Metabolic Profiling of Water-Soluble Compounds from the Extracts of Dark Septate Endophytic Fungi (DSE) Isolated from Scots Pine (Pinus sylvestris L.) Seedlings Using UPLC-Orbitrap-MS

Endophytes are microorganisms living inside plant hosts and are known to be beneficial for the host plant vitality. In this study, we isolated three endophytic fungus species from the roots of Scots pine seedlings growing on Finnish drained peatland setting. The isolated fungi belonged to dark septate endophytes (DSE). The metabolic profiles of the hot water extracts of the fungi were investigated using Ultrahigh Performance Liquid Chromatography with Diode Array Detection and Electron Spray Ionization source Mass Spectrometry with Orbitrap analyzer (UPLC-DAD-ESI-MS-Orbitrap). Out of 318 metabolites, we were able to identify 220, of which a majority was amino acids and peptides. Additionally, opine amino acids, amino acid quinones, Amadori compounds, cholines, nucleobases, nucleosides, nucleotides, siderophores, sugars, sugar alcohols and disaccharides were found, as well as other previously reported metabolites from plants or endophytes. Some differences of the metabolic profiles, regarding the amount and identity of the found metabolites, were observed even though the fungi were isolated from the same host. Many of the discovered metabolites have been described possessing biological activities and properties, which may make a favorable contribution to the host plant nutrient availability or abiotic and biotic stress tolerance.

Isotope-dilution mass spectrometry for exact quantification of noncanonical DNA nucleosides

DNA contains not only canonical nucleotides but also a variety of modifications of the bases. In particular, cytosine and adenine are frequently modified. Determination of the exact quantity of these noncanonical bases can contribute to the characterization of the state of a biological system, e.g., determination of disease or developmental processes, and is therefore extremely important. Here, we present a workflow that includes detailed description of critical sample preparation steps and important aspects of mass spectrometry analysis and validation. In this protocol, extraction and digestion of DNA by an optimized spin-column and enzyme-based method are described. Isotopically labeled standards are added in the course of DNA digestion, which allows exact quantification by isotope dilution mass spectrometry. To overcome the major bottleneck of such analyses, we developed a short (~14-min-per-sample) ultra-HPLC (UHPLC) and triple quadrupole mass spectrometric (QQQ-MS) method. Easy calculation of the modification abundance in the genome is possible with the provided evaluation sheets. Compared to alternative methods, the quantification procedure presented here allows rapid, ultrasensitive (low femtomole range) and highly reproducible quantification of different nucleosides in parallel. Including sample preparation and evaluation, quantification of DNA modifications can be achieved in less than a week.

Method for Quantification of Ribonucleotides and Deoxyribonucleotides in Human Cells Using (Trimethylsilyl)diazomethane Derivatization Followed by Liquid Chromatography-Tandem Mass Spectrometry

Investigation into intracellular ribonucleotides (RNs) and deoxyribonucleotides (dRNs) is important for studies of the mechanism of many biological processes, such as RNA and DNA synthesis and DNA repair, as well as metabolic and therapeutic efficacy of nucleoside analogues. However, current methods are still unsatisfactory for determination of nucleotides in complex matrixes. Here we describe a novel method for the determination of RN and dRN pools in cells based on fast derivatization with (trimethylsilyl)diazomethane (TMSD) followed by quantification using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Derivatization was accomplished in 3 min, and each derivatized nucleotide not only had a sufficient retention on reversed-phase column by introduction of methyl groups but also exhibited a unique ion transition which consequently eliminated mutual interference in LC-MS/MS. Chromatographic separation was performed on a C₁₈ column with a simple acetonitrile-water gradient elution system, which avoided contamination and ion suppression caused by ion-pairing reagents. The developed method was fully validated and applied to the analysis of RNs and dRNs in cell samples. Moreover, results demonstrated that the applicability of this method could be extended to nucleoside analogues and their metabolites and could facilitate many applications in future studies.

LC-MS Analysis of Methylated RNA

The detection and quantification of methylated RNA can be beneficial to understand certain cellular regulation processes such as transcriptional modulation of gene expression, immune response, or epigenetic alterations. Therefore, it is necessary to have methods available, which are extremely sensitive and accurate, for instance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Here, we describe the preparation of RNA samples by enzymatic hydrolysis and the subsequent analysis of ribonucleosides by LC-MS/MS via NLS (Neutral loss scan) and DMRM (Dynamic multiple reaction monitoring). Also, we provide variations of these methods including chromatographic techniques and different kinds of quantification.

Altered urothelial ATP signaling in a major subset of human overactive bladder patients with pyuria

Overactive Bladder (OAB) is an idiopathic condition, characterized by urgency, urinary frequency, and urgency incontinence, in the absence of routinely traceable urinary infection. We have described microscopic pyuria (≥10 wbc/μl) in patients suffering from the worst symptoms. It is established that inflammation is associated with increased ATP release from epithelial cells, and extracellular ATP originating from the urothelium following increased hydrostatic pressure is a mediator of bladder sensation. Here, using bladder biopsy samples, we have investigated urothelial ATP signaling in OAB patients with microscopic pyuria. Basal, but not stretch-evoked, release of ATP was significantly greater from the urothelium of OAB patients with pyuria than from non-OAB patients or OAB patients without pyuria (<10 wbc/μl). Basal ATP release from the urothelium of OAB patients with pyuria was inhibited by the P2 receptor antagonist suramin and abolished by the hemichannel blocker carbenoxolone, which differed from stretch-activated ATP release. Altered P2 receptor expression was evident in the urothelium from pyuric OAB patients. Furthermore, intracellular bacteria were visualized in shed urothelial cells from ∼80% of OAB patients with pyuria. These data suggest that increased ATP release from the urothelium, involving bacterial colonization, may play a role in the heightened symptoms associated with pyuric OAB patients.

Analysis of Intra- and Extracellular Levels of Purine Bases, Nucleosides, and Nucleotides in HepG2 Cells by High-performance Liquid Chromatography

To evaluate cellular uptake and purine transport, we developed a high-performance liquid chromatography method for intra- and extracellular purine quantification. Our aim was to develop an effective method for simultaneously quantifying the substrate and metabolites with high sensitivity. C18 columns from different manufacturers were tested for simultaneous quantification of 22 different purine bases, nucleosides, and nucleotides. We used a YMC-Triart C18 column. The analysis conditions, including extraction solutions for the cells and cell culture medium, were optimized to achieve good quantification. Linearity, accuracy, determination limits, and recovery were assessed and showed good performance. The developed HPLC method was successfully applied to the qualitative analysis of 22 different intra- and extracellular purines, demonstrating that it is useful for studying the overall pattern of purine metabolism. This method could also be useful for evaluating metabolic dynamics of purines under a variety of stimulatory conditions of culture cells.

Analysis of RNA modifications by liquid chromatography-tandem mass spectrometry

The analysis of RNA modifications is of high importance in order to address a wide range of biological questions. Therefore, a highly sensitive and accurate method such as liquid chromatography-tandem mass spectrometry (LC-MS/MS) has to be available. By using different LC-MS/MS procedures, it is not only possible to quantify very low amounts of RNA modifications, but also to detect probably unknown modified nucleosides. For these cases the dynamic multiple reaction monitoring and the neutral loss scan are the most common techniques. Here, we provide the whole workflow for analyzing RNA samples regarding their modification content. This includes an equipment list, the preparation of required solutions/enzymes and the creation of an internal standard or nucleoside stocks for internal or external calibration. Furthermore, we describe the preparation of RNA samples for the subsequent LC-MS/MS analysis and the corresponding analysis process.

Adenosine enhances acetylcholine receptor channel openings and intracellular calcium 'spiking' in mouse skeletal myotubes

AIMS

The autocrine activity of the embryonic isoform of the nicotinic acetylcholine receptor is crucial for the correct differentiation and trophism of skeletal muscle cells before innervation. The functional activity of extracellular adenosine and adenosine receptor subtypes expressed in differentiating myotubes is still unknown. In this study, we performed a detailed analysis of the role of adenosine receptor-mediated effects on the autocrine-mediated nicotinic acetylcholine receptor channel openings and the associated spontaneous intracellular calcium 'spikes' generated in differentiating mouse myotubes in vitro.

METHODS

Cell-attached patch-clamp recordings and intracellular calcium imaging experiments were performed in contracting myotubes derived from mouse satellite cells.

RESULTS

The endogenous extracellular adenosine and the adenosine receptor-mediated activity modulated the properties of the embryonic isoform of the nicotinic acetylcholine receptor in myotubes in vitro, by increasing the mean open time and the open probability of the ion channel, and sustaining nicotinic acetylcholine receptor-driven intracellular [Ca(2+) ]i 'spikes'. The pharmacological characterization of the adenosine receptor-mediated effects suggested a prevalent involvement of the A2B adenosine receptor subtype.

CONCLUSION

We propose that the interplay between endogenous adenosine and nicotinic acetylcholine receptors represents a potential novel strategy to improve differentiation/regeneration of skeletal muscle.

Original 2-(3-Alkoxy-1H-pyrazol-1-yl)azines Inhibitors of Human Dihydroorotate Dehydrogenase (DHODH)

Following our discovery of human dihydroorotate dehydrogenase (DHODH) inhibition by 2-(3-alkoxy-1H-pyrazol-1-yl)pyrimidine derivatives as well as 2-(4-benzyl-3-ethoxy-5-methyl-1H-pyrazol-1-yl)-5-methylpyridine, we describe here the syntheses and evaluation of an array of azine-bearing analogues. As in our previous report, the structure-activity study of this series of human DHODH inhibitors was based on a phenotypic assay measuring measles virus replication. Among other inhibitors, this round of syntheses and biological evaluation iteration led to the highly active 5-cyclopropyl-2-(4-(2,6-difluorophenoxy)-3-isopropoxy-5-methyl-1H-pyrazol-1-yl)-3-fluoropyridine. Inhibition of DHODH by this compound was confirmed in an array of in vitro assays, including enzymatic tests and cell-based assays for viral replication and cellular growth. This molecule was found to be more active than the known inhibitors of DHODH, brequinar and teriflunomide, thus opening perspectives for its use as a tool or for the design of an original series of immunosuppressive agent. Moreover, because other series of inhibitors of human DHODH have been found to also affect Plasmodium falciparum DHODH, all the compounds were assayed for their effect on P. falciparum growth. However, the modest in vitro inhibition solely observed for two compounds did not correlate with their inhibition of P. falciparum DHODH.

Activation of P2Y6 Receptors Facilitates Nonneuronal Adenosine Triphosphate and Acetylcholine Release from Urothelium with the Lamina Propria of Men with Bladder Outlet Obstruction

PURPOSE

Deregulation of purinergic bladder signaling may contribute to persistent detrusor overactivity in patients with bladder outlet obstruction. Activation of uridine diphosphate sensitive P2Y6 receptors increases voiding frequency in rats indirectly by releasing adenosine triphosphate from the urothelium. To our knowledge this mechanism has never been tested in the human bladder.

MATERIALS AND METHODS

We examined the role of the uridine diphosphate sensitive P2Y6 receptor on tetrodotoxin insensitive nonneuronal adenosine triphosphate and [(3)H]acetylcholine release from the human urothelium with the lamina propria of control organ donors and patients with benign prostatic hyperplasia.

RESULTS

The adenosine triphosphate-to-[(3)H]acetylcholine ratio was fivefold higher in mucosal urothelium/lamina propria strips from benign prostatic hyperplasia patients than control men. The selective P2Y6 receptor agonist PSB0474 (100 nM) augmented by a similar amount adenosine triphosphate and [(3)H]acetylcholine release from mucosal urothelium/lamina propria strips from both groups of individuals. The facilitatory effect of PSB0474 was prevented by MRS2578 (50 nM) and by carbenoxolone (10 μM), which block P2Y6 receptor and pannexin-1 hemichannels, respectively. Blockade of P2X3 (and/or P2X2/3) receptors with A317491 (100 nM) also attenuated release facilitation by PSB0474 in control men but not in patients with benign prostatic hyperplasia. Immunolocalization studies showed that P2Y6, P2X2 and P2X3 receptors were present in choline acetyltransferase positive urothelial cells. In contrast to P2Y6 staining, choline acetyltransferase, P2X2 and P2X3 immunoreactivity decreased in the urothelium of benign prostatic hyperplasia patients.

CONCLUSIONS

Activation of P2Y6 receptor amplifies mucosal adenosine triphosphate release underlying bladder overactivity in patients with benign prostatic hyperplasia. Therefore, we propose selective P2Y6 receptor blockade as a novel therapeutic strategy to control persistent storage symptoms in obstructed patients.

A novel method for measuring the ATP-related compounds in human erythrocytes

The ATP-related compounds in whole blood or red blood cells have been used to evaluate the energy status of erythrocytes and the degradation level of the phosphorylated compounds under various conditions, such as chronic renal failure, drug monitoring, cancer, exposure to environmental toxics, and organ preservation. The complete interpretation of the energetic homeostasis of erythrocytes is only performed using the compounds involved in the degradation pathway for adenine nucleotides alongside the uric acid value. For the first time, we report a liquid chromatographic method using a diode array detector that measures all of these compounds in a small human whole blood sample (125 μL) within an acceptable time of 20 min. The stability was evaluated for all of the compounds and ranged from 96.3 to 105.1% versus the day zero values. The measurement had an adequate sensitivity for the ATP-related compounds (detection limits from 0.001 to 0.097 μmol/L and quantification limits from 0.004 to 0.294 μmol/L). This method is particularly useful for measuring inosine monophosphate, inosine, hypoxanthine, and uric acid. Moreover, this assay had acceptable linearity (r > 0.990), precision (coefficients of variation ranged from 0.1 to 2.0%), specificity (similar retention times and spectra in all samples) and recoveries (ranged from 89.2 to 104.9%). The newly developed method is invaluable for assessing the energetic homeostasis of red blood cells under diverse conditions, such as in vitro experiments and clinical settings.

Absolute and relative quantification of RNA modifications via biosynthetic isotopomers

In the resurging field of RNA modifications, quantification is a bottleneck blocking many exciting avenues. With currently over 150 known nucleoside alterations, detection and quantification methods must encompass multiple modifications for a comprehensive profile. LC-MS/MS approaches offer a perspective for comprehensive parallel quantification of all the various modifications found in total RNA of a given organism. By feeding (13)C-glucose as sole carbon source, we have generated a stable isotope-labeled internal standard (SIL-IS) for bacterial RNA, which facilitates relative comparison of all modifications. While conventional SIL-IS approaches require the chemical synthesis of single modifications in weighable quantities, this SIL-IS consists of a nucleoside mixture covering all detectable RNA modifications of Escherichia coli, yet in small and initially unknown quantities. For absolute in addition to relative quantification, those quantities were determined by a combination of external calibration and sample spiking of the biosynthetic SIL-IS. For each nucleoside, we thus obtained a very robust relative response factor, which permits direct conversion of the MS signal to absolute amounts of substance. The application of the validated SIL-IS allowed highly precise quantification with standard deviations<2% during a 12-week period, and a linear dynamic range that was extended by two orders of magnitude.

P2Y receptor modulation of ATP release in the urothelium

The release of ATP from the urothelium in response to stretch during filling demonstrates the importance of the purinergic system for the physiological functioning of the bladder. This study examined the effect of P2 receptor agonists on ATP release from two urothelial cell lines (RT4 and UROtsa cells). Hypotonic Krebs was used as a stretch stimulus. Incubation of urothelial cells with high concentrations of the P2Y agonist ADP induced ATP release to a level that was 40-fold greater than hypotonic-stimulated ATP release (P < 0.0011, ADP EC50 1.8 µM). Similarly, an increase in ATP release was also observed with the P2Y agonist, UTP, up to a maximum of 70% of the hypotonic response (EC50 0.62 µM). Selective P2 receptor agonists, αβ -methylene-ATP, ATP- γ -S, and 2-methylthio-ADP had minimal effects on ATP release. ADP-stimulated ATP release was significantly inhibited by suramin (100 µM, P = 0.002). RT4 urothelial cells break down nucleotides (100 µM) including ATP, ADP, and UTP to liberate phosphate. Phosphate liberation was also demonstrated from endogenous nucleotides with approximately 10% of the released ATP broken down during the incubation. These studies demonstrate a role for P2Y receptor activation in stimulation of ATP release and emphasize the complexity of urothelial P2 receptor signalling.

P2Y2 receptor knock-out mice display normal NaCl absorption in medullary thick ascending limb

Local purinergic signals modulate renal tubular transport. Acute activation of renal epithelial P2 receptors causes inhibition of epithelial transport and thus, should favor increased water and salt excretion by the kidney. So far only a few studies have addressed the effects of extracellular nucleotides on ion transport in the thick ascending limb (TAL). In the medullary thick ascending limb (mTAL), basolateral P2X receptors markedly (~25%) inhibit NaCl absorption. Although this segment does express both apical and basolateral P2Y₂ receptors, acute activation of the basolateral P2Y₂ receptors had no apparent effect on transepithelial ion transport. Here we studied, if the absence of the P2Y₂ receptor causes chronic alterations in mTAL NaCl absorption by comparing basal and AVP-stimulated transepithelial transport rates. We used perfused mouse mTALs to electrically measure NaCl absorption in juvenile (<35 days) and adult (>35 days) male mice. Using microelectrodes, we determined the transepithelial voltage (V_te) and the transepithelial resistance (R_te) and thus, transepithelial NaCl absorption (equivalent short circuit current, I'_sc). We find that mTALs from adult wild type (WT) mice have significantly lower NaCl absorption rates when compared to mTALs from juvenile WT mice. This could be attributed to significantly higher R_tevalues in mTALs from adult WT mice. This pattern was not observed in mTALs from P2Y₂ receptor knockout (KO) mice. In addition, adult P2Y₂ receptor KO mTALs have significantly lower V_tevalues compared to the juvenile. No difference in absolute I'_sc was observed when comparing mTALs from WT and KO mice. AVP stimulated the mTALs to similar increases of NaCl absorption irrespective of the absence of the P2Y₂ receptor. No difference was observed in the medullary expression level of NKCC2 in between the genotypes. These data indicate that the lack of P2Y₂ receptors does not cause substantial differences in resting and AVP-stimulated NaCl absorption in mouse mTAL.

Inhibition of pyrimidine biosynthesis pathway suppresses viral growth through innate immunity

Searching for stimulators of the innate antiviral response is an appealing approach to develop novel therapeutics against viral infections. Here, we established a cell-based reporter assay to identify compounds stimulating expression of interferon-inducible antiviral genes. DD264 was selected out of 41,353 compounds for both its immuno-stimulatory and antiviral properties. While searching for its mode of action, we identified DD264 as an inhibitor of pyrimidine biosynthesis pathway. This metabolic pathway was recently identified as a prime target of broad-spectrum antiviral molecules, but our data unraveled a yet unsuspected link with innate immunity. Indeed, we showed that DD264 or brequinar, a well-known inhibitor of pyrimidine biosynthesis pathway, both enhanced the expression of antiviral genes in human cells. Furthermore, antiviral activity of DD264 or brequinar was found strictly dependent on cellular gene transcription, nuclear export machinery, and required IRF1 transcription factor. In conclusion, the antiviral property of pyrimidine biosynthesis inhibitors is not a direct consequence of pyrimidine deprivation on the virus machinery, but rather involves the induction of cellular immune response.

Our therapeutic arsenal to treat viral diseases is extremely limited, and there is a critical need for molecules that could be used against multiple viruses. Among possible strategies, there is a growing interest for molecules stimulating cellular defense mechanisms. We recently developed a functional assay to identify stimulators of antiviral genes, and selected compound DD264 from a chemical library using this approach. While searching for its mode of action, we identified this molecule as an inhibitor of pyrimidine biosynthesis, a metabolic pathway that fuels the cell with pyrimidine nucleobases for both DNA and RNA synthesis. Interestingly, it was recently shown that inhibitors of this metabolic pathway prevent the replication of RNA viruses. Here, we established a functional link between pyrimidine biosynthesis pathway and the induction of antiviral genes, and demonstrated that pyrimidine biosynthesis inhibitors like DD264 or brequinar critically rely on cellular immune response to inhibit virus growth. Thus, pyrimidine deprivation is not directly responsible for the antiviral activity of pyrimidine biosynthesis inhibitors, which rather involves the induction of a metabolic stress and subsequent triggering of cellular defense mechanisms.

Determination of antazoline hydrochloride in rat plasma and excreta by reversed-phase ion-pair chromatography and its application to pharmacokinetics

A reversed-phase ion pair chromatography method with liquid-liquid extraction analytical method was developed and validated for the determination of antazoline hydrochloride in plasma and excreta of rat. The aim of our study was to characterize the preclinical pharmacokinetics and excretion profiles of antazoline hydrochloride in rats after intravenous injection at the dose of 10 mg/kg. Plasma and excreta samples were extracted with ethyl acetate, and phenacetin was used as the internal standard. The result showed that the method is suitable for the quantification of antazoline hydrochloride in plasma and excreta samples. Analysis of accuracy (90.89-112.33%), imprecision (<7.1%) and recovery (>82.5%) showed adequate values. After a single intravenous administration at 10 mg/kg to rats, plasma concentration profile showed a relative fast elimination proceeding with a terminal elimination half-life of 3.53 h. Approximately 61.8 and 14.2% of the administered dose were recovered in urine and bile after 72 and 24 h post-dosing respectively; 5.9% of the administered dose was recovered in feces after 72 h post-dosing. The above results show that the major elimination route is urinary excretion.