Selective analysis for adenosine using reversed-phase high-pressure liquid chromatography

Highly Sensitive Real-Time Monitoring of Adenosine Receptor Activities in Nonsmall Cell Lung Cancer Cells Using Carbon Nanotube Field-Effect Transistors

Adenosine metabolism through adenosine receptors plays a critical role in lung cancer biology. Although recent studies showed the potential of targeting adenosine receptors as drug targets for lung cancer treatment, conventional methods for investigating receptor activities often suffer from various drawbacks, including low sensitivity and slow analysis speed. In this study, adenosine receptor activities in nonsmall cell lung cancer (NSCLC) cells were monitored in real time with high sensitivity through a carbon nanotube field-effect transistor (CNT-FET). In this method, we hybridized a CNT-FET with NSCLC cells expressing A2A and A2B adenosine receptors to construct a hybrid platform. This platform could detect adenosine, an endogenous ligand of adenosine receptors, down to 1 fM in real time and sensitively discriminate adenosine among other nucleosides. Furthermore, we could also utilize the platform to detect adenosine in complicated environments, such as human serum. Notably, our hybrid platform allowed us to monitor pharmacological effects between adenosine and other drugs, including dipyridamole and theophylline, even in human serum samples. These results indicate that the NSCLC cell-hybridized CNT-FET can be a practical tool for biomedical applications, such as the evaluation and screening of drug-candidate substances.

Analysis of submicromolar concentrations of adenosine in plasma using reversed phase high-performance liquid chromatography

A method is described for the determination of adenosine in small samples of plasma (< 1 ml) using reversed-phase high-performance liquid chromatography (HPLC) in either a simple isocratic or a gradient elution system which gives a clear separation of adenosine from other plasma constituents. Acetone is used to deproteinize plasma and chloroform to remove unwanted lipid soluble material prior to HPLC. 6-Methyladenosine is used as an internal standard for making corrections for changes in concentration during sample processing. Adenosine in plasma could be reliably detected at concentrations lower than its minimum effector concentration as a vasodilator (4 x 10(-8) Mol l(-1) using the isocratic system and 1.9 x 10(-8) Mol l(-1) with gradient elution). The recoveries of adenosine added to blood at concentrations ranging from 2 x 10(-8) Mol l(-1) to 1.4 x 10(-6) Mol l(-1) were from 101.4 +/- 16.9% (n = 4) to 100.0 +/- 3.6% (n = 5). The present method provides a simple, sensitive and selective assay for submicromolar concentrations of adenosine in plasma with good recovery.

Enzymatic repair of 5-formyluracil. II. Mismatch formation between 5-formyluracil and guanine during dna replication and its recognition by two proteins involved in base excision repair (AlkA) and mismatch repair (MutS)

5-Formyluracil (fU), a major methyl oxidation product of thymine, forms correct (fU:A) and incorrect (fU:G) base pairs during DNA replication. In the accompanying paper (Masaoka, A., Terato, H., Kobayashi, M., Honsho, A., Ohyama, Y., and Ide, H. (1999) J. Biol. Chem. 274, 25136-25143), it has been shown that fU correctly paired with A is recognized by AlkA protein (Escherichia coli 3-methyladenine DNA glycosylase II). In the present work, mispairing frequency of fU with G and cellular repair protein that specifically recognized fU:G mispairs were studied using defined oligonucleotide substrates. Mispairing frequency of fU was determined by incorporation of 2'-deoxyribonucleoside 5'-triphosphate of fU opposite template G using DNA polymerase I Klenow fragment deficient in 3'-5' exonuclease. Mispairing frequency of fU was dependent on the nearest neighbor base pair in the primer terminus and 2-12 times higher than that of thymine at pH 7.8 and 2.6-6.7 times higher at pH 9.0 with an exception of the nearest neighbor T(template):A(primer). AlkA catalyzed the excision of fU placed opposite G, as well as A, and the excision efficiencies of fU for fU:G and fU:A pairs were comparable. In addition, MutS protein involved in methyl-directed mismatch repair also recognized fU:G mispairs and bound them with an efficiency comparable to T:G mispairs, but it did not recognize fU:A pairs. Prior complex formation between MutS and a heteroduplex containing an fU:G mispair inhibited the activity of AlkA to fU. These results suggest that fU present in DNA can be restored by two independent repair pathways, i.e. the base excision repair pathway initiated by AlkA and the methyl-directed mismatch repair pathway initiated by MutS. Biological relevance of the present results is discussed in light of DNA replication and repair in cells.

Application of high-performance liquid chromatography and thermospray high-performance liquid chromatography-mass spectrometry to the analysis and identification of 2',3'-dideoxyadenosine and its metabolite in biological media

Reversed-phase high-performance liquid chromatographic (HPLC) procedures are described for determining the stability of 2',3'-dideoxyadenosine (DDA) in biological fluids at therapeutic dosages. The validated methodology uses both direct injection and solid-phase extraction techniques. Deamination of DDA to 2',3'-dideoxyinosine (DDI) in plasma by adenosine deaminase was monitored by HPLC, and the identification of DDI verified by thermospray HPLC-mass spectrometry. This methodology should prove useful in future studies concerning the stability and metabolism of dideoxynucleosides.

Plasma adenosine levels: measurement in humans and relationship to the anxiogenic effects of caffeine

The effects of caffeine on plasma adenosine were examined in eight healthy normal volunteers. Subjects were randomly administered on 4 separate days, in a double-blind fashion, either placebo or three different doses of caffeine (240, 480, and 720 mg). Adenosine concentrations, measured by high performance liquid chromatography, were in the micromolar range when samples were drawn into tubes containing dipyridamole to prevent adenosine reuptake by red blood cells. Plasma adenosine levels did not change after caffeine administration. The effects of caffeine on anxiety were related to changes in plasma caffeine but not plasma adenosine levels. The potential interest of caffeine as a chemical model of anxiety is discussed.

Optimization of a high-performance liquid chromatographic method for the determination of nucleosides and their catabolites. Application to cat and rabbit heart perfusates

A high-performance liquid chromatographic method is described for the separation of nucleosides and related compounds in a single isocratic run. The separation of a standard mixture of at least thirteen compounds is achieved within 15 min on a new type of reversed-phase column 25 cm long, filled with 5-micron particles of Select B. Pre-treatment of the silica particles before silanization has given this type of reversed-phase material unique characteristics for basic and acidic compounds. Chromatograms are shown to compare the effectiveness of the Select B column for the separation of nucleosides with that of other C18 and C8 phases. The separation is achieved with 0.3 M ammonium dihydrogen phosphate (pH 4.00) and a mixture of methanol, acetonitrile and tetrahydrofuran. Detection is carried out with a variable-wavelength UV detector at 254 nm. Sample preparation and the influence of the organic solvents, pH and buffer concentration are described. To illustrate the applicability of the method, representative chromatograms are shown of perfusates of Langendorff preparations and the working hearts of cats and rabbits. Remarkable differences were obtained before and after ischaemia and before and after treatment with a nucleoside transport inhibitor. Baseline separation of cytosine, orotic acid, cytidine, uracil, uric acid, hypoxanthine, xanthine, inosine, guanosine, xanthosine, allopurinol, thymine and adenosine was achieved. The detection limit for these compounds was less than 1 ng per injection.

The mechanism of adenosine release from hypoxic rat liver cells

Uptake of [14C]-adenosine into freshly dispersed rat hepatocytes was inhibited 44% by dipyridamole (50 microM) and 60% by nitrobenzylthioinosine (NBTI, 20 microM). The results are consistent with the known ability of these drugs to inhibit adenosine transport in other cell types. The nucleotide analogue, alpha, beta-methylene adenosine diphosphate (AOPCP, 50 microM), inhibited by 84% the degradation of exogenous 5' AMP that occurred rapidly when this substrate alone was presented to isolated hepatocytes. This confirms the ecto-5'-nucleotidase inhibitory properties of this analogue in isolated hepatocytes. During hypoxic incubation, isolated hepatocytes released adenosine, which accumulated in the extracellular volume. Dipyridamole and NBTI each markedly attenuated this extracellular adenosine accumulation. In contrast, AOPCP had no inhibitory effect on net hypoxic adenosine release. It is concluded that hypoxic rat hepatocytes produce adenosine intracellularly and that this adenosine is released via facilitated diffusion to the extracellular space, based on the inhibition observed with the transport inhibitors. The plasma membrane enzyme ecto-5'-nucleotidase does not appear to participate in hypoxic adenosine release from these cells as indicated by the lack of effect of the nucleotidase inhibitor, AOPCP.

A radioenzymatic assay for plasma adenosine

A method for analysis of plasma adenosine which combines the principles of radioisotope dilution and enzymatic catalysis is presented. Plasma from venous heparinized blood containing the adenosine deaminase inhibitor 2'-deoxycoformycin is mixed with a small amount of [3H]adenosine and extracted with perchloric acid. Using highly purified enzyme and [gamma-32P]GTP as the phosphate donor, the neutralized extract then serves as substrate for adenosine kinase, and the AMP product is purified by high-performance liquid chromatography. Adenosine concentrations in plasma are linearly proportional to 32P/3H ratios in the enzymatically synthesized AMP and are calculated from a standard curve. The advantages of the method are: ease of sample preparation; sensitivity of 20 nM in as little as 0.3 ml plasma; 20 samples per day can be analyzed by a single operator. Care must be used when obtaining plasma since cellular contamination will affect results. Using this assay, human plasma adenosine levels are 0.121 +/- 0.054 microM for males and 0.101 +/- 0.067 microM for females.

Development of a chromatographic method for the quantitative determination of minor ribonucleosides in physiological fluids. Characterization and quantitative determination of minor ribonucleosides in physiological fluids, Part I

We describe an on-line multi-column high performance liquid chromatographic method for the selective clean-up and analysis of major and minor ribonucleosides in physiological fluids. Quantitative data obtained for the determination of some methylated ribonucleosides in human urines are compared with those obtained with the traditional off-line method. The on-line technique developed in our laboratory is distinguished from the off-line method by the following features: Sample clean-up and analysis of the target-compounds can easily be automatized, Total time of analysis, for example of urinary ribonucleosides, is decreased to 35 minutes, Laborious and error-prone evaporation and redissolution steps are avoided, Reliability of the overall analytical system can be controlled with ease, Small sample-volumes can be applied directly, Sensitive samples can be processed very rapidly under mild conditions, Results obtained with the on-line and off-line-techniques compare well.

Intracellular adenosine in isolated rat liver cells

Our objective was to determine whether a non-extracellular pool of adenosine exists in mammalian cells. Rat liver cells were dispersed by a collagenase perfusion technique and suspended in buffered salt solution. The adenosine content of these suspensions rose during hypoxia. Exogenous adenosine deaminase prevented or reversed the hypoxic increment but failed to reduce suspension adenosine levels to zero. This residual adenosine pool (average size = 85 +/- 10 pmol/mg protein) was not located in the extracellular medium, on surface adenosine receptors or in solution in the cytoplasm. A likely locus is the adenine-analog binding protein which has been described for liver and other tissues. Thus, our study supports the existence of an intracellular adenosine pool in isolated rat liver cells which is a large fraction of the total tissue adenosine. This situation may exist in other cell types as well, based on the ubiquity of the adenosine binding protein. Tissue adenosine content may not, therefore, accurately reflect interstitial adenosine concentration; thus, such measurements must be interpreted cautiously. It is not clear what, if any, functional role this putative, intracellular, bound adenosine pool plays in local vasoregulation.

Quantification without purification of blood and tissue adenosine by radioimmunoassay

Highly specific anti-adenosine antibodies were produced in rabbits by the injection of N6-carboxymethyl adenosine-methylated serum albumin conjugates. They were used to develop a radioimmunoassay allowing the quantitation of adenosine in the range 0.1-10 pmol per sample. Inosine did not interfere except at 300 times higher concentrations, while AMP (ATP) did not displace the [3H]adenosine tracer even at 10(5) (10(6) ) times higher amounts. Due to the high specificity of the anti-adenosine antibodies, determination of blood and tissue adenosine levels could be performed directly from perchloric acid extracts. Values for human peripheral venous blood from various donors obtained with this procedure varied between 46 and 148 pmol/ml blood. The procedure was also applied to HeLa cultures with low and high intracellular adenosine. The reliability of the method was demonstrated by comparative analyses using HPLC purification of adenosine prior to the radioimmunoassay.

Determination of ribonucleosides, deoxyribonucleosides, and purine and pyrimidine bases in adult rabbit cerebrospinal fluid and plasma

Purine and pyrimidine base and nucleoside levels were measured in adult rabbit cisternal CSF and plasma by reversed-phase high-performance liquid chromatography. The concentrations of bases, nucleosides, and nucleoside phosphates were similar in plasma and CSF except for the adenosine phosphates and uracil which were higher in the plasma. In plasma and CSF, adenosine levels were low (0.12 microM) and guanosine, deoxyadenosine, deoxyguanosine, and deoxyinosine were not detectable (less than 0.1 microM); inosine and xanthine concentrations were 1-2 microM and hypoxanthine concentrations were approximately 5 microM; uridine (approximately 8 microM), cytidine (2-3 microM), and thymidine, deoxyuridine, and deoxycytidine (0.5-1.4 microM) were easily detectable. In both plasma and CSF, guanine, and thymine were undetectable (less than 0.1 microM), adenine and cytosine were less than 0.2 microM, but uracil was present (greater than 1 microM). Adenosine, inosine, and guanosine phosphates were also detectable at low concentrations in CSF and plasma. These results are consistent with the hypothesis that purine deoxyribonucleosides are synthesized in situ in the adult rabbit brain. In contrast, pyrimidine deoxyribonucleosides and ribonucleosides, and purine and pyrimidine bases are available in the CSF for use by the brain.

Highly sensitive method for determination of esterase activity of alpha-chymotrypsin and alpha-chymotrypsin-like enzymes using micro high-performance liquid chromatography

A new substrate, Dns-L-phenylalanine ethyl ester, with high UV absorption has been developed for the determination of the esterase activity of alpha-chymotrypsin and alpha-chymotrypsin-like enzymes. The product, generated by the enzyme action, Dns-L-phenylalanine, was clearly separated from the ester substrate by micro reversed-phase high-performance liquid chromatography. The substrate was highly stable under the enzyme assay conditions used. As little as 0.15 ng of alpha-chymotrypsin and 1.49 ng of subtilisin BPN' could be detected when a long reaction time was employed. Hydrolyses of the substrate by alpha-chymotrypsin and alpha-chymotrypsin-like enzymes were blocked by specific inhibitors of the enzymes.

Formulation of a stable vidarabine infusion fluid

Decomposition of vidarabine in a 5% glucose infusion fluid after steam sterilization was measured by HPLC and TLC analysis. After sterilization for 60 minutes at 100 degrees C and 20 minutes at 120 degrees C no degradation could be observed. A slight but significant degradation was observed after sterilization for 60 minutes at 120 degrees C followed by storage for eight months. Assuming 5% loss of content to be acceptable, it was concluded that a vidarabine infusion fluid can be sterilized for 20 minutes at 120 degrees C and stored at room temperature for at least eight months afterwards.

Chronic caffeine consumption potentiates the hypotensive action of circulating adenosine

Mean arterial blood pressure was correlated with arterial plasma adenosine levels during intravenous adenosine infusion in unanesthetized, unrestrained rats. Elevation of plasma adenosine to 5 to 6 microM (normal range 1.6 to 4.6 microM) depressed mean arterial pressure by 20 to 30 percent: this was blocked by a single caffeine injection (15 mg/kg). In contrast, caffeine consumption for 3 weeks, followed by a 1-day washout, markedly potentiated responses to adenosine, plasma levels in the 2 to 4 microM range causing 30 to 40 percent reductions in mean arterial pressure. These observations suggest that chronic occupancy of cardiovascular adenosine receptors by caffeine can enhance tissue responsiveness to adenosine, and that endogenous adenosine might act as a circulating hormone.

Current high-performance liquid chromatographic methodology in analysis of nucleotides, nucleosides, and their bases. I

This review of HPLC technology is presented in two parts. An introduction to chromatography, sample preparation, and basic information on chromatographic theory and terminology, modes, and instrumentation is presented here. A discussion of stationary and mobile phase parameters which can be varied to optimize separations is also presented here. The second part of the review, which will appear in the next issue, will cover peak identification, quantification, and selected applications. The applications include short discussions of applications of HPLC for metabolic profiling, for assays of adenosine and cyclic nucleotides in studies of disease processes, and for enzyme assays. The paper concludes with a short discussion of future trends for HPLC in biomedical research and clinical chemistry.

High-performance liquid chromatographic methods for base and nucleoside analysis in extracellular fluids and in cells

High-performance liquid chromatography based methods for the study of the metabolism of purine and pyrimidine bases and nucleosides have been developed. These methods, using 200--50 microliter samples of extracellular fluids and employing isocratic separations, can measure a wide range of compounds. Hypoxanthine, xanthine and uridine concentrations in plasma from normal men are relatively stable. Species differences have been detected: concentrations of cytidine are higher in rat and mouse serum than in man, since the concentrations of uridine are similar; purine/pyrimidine ratios may be different. Fetal calf serum used for tissue culture contains about a 40 times higher concentration of hypoxanthine than the less-effective calf serum. Use of the methods appears to be justified in the assessment of the metabolic damage due to severe hypoxia and/or ischaemia.

The release of adenosine and inosine from canine subcutaneous adipose tissue by nerve stimulation and noradrenaline

1. Plasma and adipose tissue purine nucleosides were assayed by reversed phase high-performance liquid chromatography after purification of the samples on phenylboronate affinity gel. 2. The adenosine content of unstimulated subcutaneous adipose tissue was close to 1 n-mole/g. The concentrations of adenosine and inosine in canine arterial plasma were 0.26 +/- 0.03 and 0.16 +/- 0.03 microM, respectively. In venous plasma from the canine subcutaneous adipose tissue the corresponding values were 0.32 +/- 0.04 and 0.28 +/- 0.06 microM under basal conditions. The arterio-venous concentration difference of adenosine was linearly dependent upon the arterial adenosine concentration. At arterial concentrations below 0.3 microM there was a net production of adenosine; above 0.3 microM there was a net extraction of approximately 77% of the adenosine. Adenosine was extensively eliminated in blood. The major part of this elimination could be accounted for by metabolism to inosine, hypoxanthine and uric acid. 3. Following sympathetic nerve stimulation (4 Hz for 20 min) the rate of adenosine outflow from adipose tissue increased from 0.33 +/- 0.22 to a peak value of 1.2 +/- 0.26 n-mole/min. This corresponds to a net release of 8.7 +/- 3.0 n-mole/100 g tissue. Inosine outflow rose from 0.64 +/- 0.37 to 5.3 +/- 1.4 n-mole/min, corresponding to a net release of 24.6 4/- 8.7 n-mole/100 g. Nerve stimulation also increased the release of [3H]purines from [3H]adenine pre-labelled adipose tissue. The fractional release increased 15-fold after stimulation. The radioactivity was mainly in the form of hypoxanthine, inosine and uric acid while adenosine was a minor component. When metabolism in blood was inhibited by dipyridamole and an adenosine deaminase inhibitor nerve-stimulation-induced release of [3H]purines was mainly in the form of adenosine. 4. Noradrenaline injection also induced a release of radioactive purines and of inosine. On the other hand, the outflow of endogenous adenosine was very small. 5. The present results demonstrate that under basal conditions adenosine is present in arterial and venous canine plasma. The free extracellular tissue level may be similar to the basal arterial adenosine concentration. Sympathetic nerve stimulation and noradrenaline induces a marked release of adenosine which is rapidly metabolized in the tissue and blood stream to inosine, hypoxanthine and uric acid. In adipose tissue the levels of adenosine reached after adrenergic stimulation appear high enough to be of physiological relevance.

Quantitative high-performance liquid chromatography of nucleosides and bases in human plasma

A reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the estimation of purines, pyrimidines and their congeners in biological fluids. An initial HPLC separation allowed the collection of a number of effluent fractions, each of which contained a single component of interest. The re-application of these fractions to a second HPLC separation permitted the resolution and quantification of nanogram amounts of these components. Isocratic elution with volatile buffers renders the samples amenable to automatic sampling procedures or lyophilisation. Data are presented on the application of the method to the analysis of nucleosides and bases in human plasma.

High-performance liquid chromatographic assay for acid and alkaline phosphatase in serum

High-performance liquid chromatography was used to assay serum acid and alkaline phosphatase. Samples were incubated with adenosine-5'-monophosphoric acid (AMP) in a buffer of required pH, 5'-nucleotidase was inhibited with Ni2+ ions, and the phosphatase activity was determined by measuring the concentration of the reaction product, adenosine. The analysis time, after the incubation is terminated, is short (7 min), and the assay is quantitative and reproducible. Complete separation of the reaction product from the substrate and the naturally occurring serum constituents and the high sensitivity of the ultraviolet detection system eliminate some of the problems commonly encountered in spectrophotometric assays.

Radioimmunoassay for adenosine in biological samples

A sensitive and specific radioimmunoassay for adenosine has been developed. Antibodies directed against adenosine (titer 1:400--1:700) were obtained by immunizing rabbits with adenosine, conjugated via its vicinal hydroxyl groups to bovine serum albumin (periodate oxidation). Interfering adenosine deaminase activity was removed from the antisera by treatment with DEAE-cellulose. Free and antibody bound 3H-adenosine was separated by either the "second antibody" precipitation method or by a simple filtration step. The sensitivity and assay range for adenosine was 1--100 pmoles per assay tube. Structurally related purine compounds (adenine nucleotides, adenine) crossreacted with adenosine binding and were removed by a single chromatographic step. Analysis of the adenosine content in normoxic guinea pig hearts yielded 2.53 nmoles/g, a value which was confirmed by spectrophotometric analysis.