Determination of adenosine and deoxyadenosine in urine by high-performance liquid chromatography with column switching

An in-tube aptamer/gold nanoparticles coated capillary solid-phase microextraction for separation of adenosine in serum and urine samples

As an endogenous nucleoside, adenosine was significant for the diagnosis and treatment of some diseases, such as schizophrenia. However, due to the complicated matrix interference, it was difficult to monitor trace or ultra-trace adenosine directly in bio-samples. In this contribution, a novel in-tube SPME technique based on aptamer/Au nanoparticles coated open tubular fused-silica capillary was established to separate and enrich adenosine in bio-samples with high affinity. Therefore, a uniform and dense AuNPs layer was coated on the inner surface of the open tubular capillary, and then adenosine aptamer was immobilized on AuNPs with a high capacity of 2.44 μg per 27-cm capillary. As a result, the capillary shown high selectivity to adenosine with a selectivity factor of 14.4 when compared with the scrambled aptamer/AuNPs coated capillary. Also, the extraction amount of adenosine was 2.8-24.8 times higher than those of its structural analogs and contrast, such as guanosine, uridine, cytidine, thymidine, and toluic acid. After the optimization of extraction conditions, the aptamer/AuNPs coated in-tube SPME-HPLC method was developed for the adenosine assay with the linear range of 0.002-0.100 μg mL^-1 and the detection limit of 0.45 ng mL^-1. Subsequently, the approach was applied for trace adenosine monitoring in human serum and urine samples. It showed a strong performance of reducing matrix interference and improving sensitivity, and the spiking recoveries of 89.9-92.6% and 91.1-94.5% were achieved respectively.

Surface-enhanced Raman spectroscopy and MCR-ALS for the selective sensing of urinary adenosine on filter paper

Adenosine is a purine nucleoside that is present in all human cells and is essential for regulating certain physiological activities in tissues and organs. Since adenosine is considered to be a potential cancer biomarker in urine, its determination may be crucial for the early diagnosis and non-invasive monitoring of cancer. Herein, we present a label-free method to quantify urinary adenosine using surface-enhanced Raman spectroscopy (SERS) and multivariate curve resolution-alternating least squares (MCR-ALS). Ring-oven preconcentration and direct deposition of monodisperse gold nanoparticles on filter paper were employed to improve the sampling efficiency. Further, MCR-ALS (assessed with and without a correlation constraint), the standard addition method and pH controls were combined to compensate for the matrix effect and to address overlapping bands in the analysis of human urine samples. As a result, the proposed method showed to be sensitive (LOD varying between 3.8 and 4.9 µmol L^-1, S/R = 3), reproducible (RSD less than ± 15%), and selective over other nucleosides (guanosine, cytidine, thymidine and uridine) and unknown interferences (second-order advantage). This is the first report of a SERS-chemometric method applied to urinary adenosine sensing at physiologically relevant concentrations, with minimal sample preparation, and has strong potential to be a valuable tool in cancer research.

Urinary adenosine excretion in type 1 diabetes

In experimental models of diabetes, augmented sodium-glucose cotransport-2 (SGLT2) activity diminishes sodium (Na+) delivery at the macula densa. As a result, less vasoconstrictive adenosine is generated, leading to afferent arteriolar vasodilatation and hyperfiltration. The measurement and significance of urinary adenosine in humans has not been examined extensively in states of renal hemodynamic impairment like that of diabetes. Our aim was to validate a method for urine adenosine quantification in humans and perform an exploratory post hoc analysis to determine whether urinary adenosine levels change dynamically in response to natriuresis in patients with type 1 diabetes (T1D) before and after treatment with the SGLT2 inhibitor (SGLT2i) empagliflozin. We hypothesized that SGLT2i, which reduces renal hyperfiltration through increased Na+delivery to the macula densa, would increase urinary adenosine excretion. Urine adenosine corrected for creatinine was measured using our validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in 40 healthy participants and 40 patients with T1D. In the T1D cohort, measurements were performed during clamped euglycemic and hyperglycemic conditions before and following 8 wk of SGLT2i therapy. Urinary adenosine was detectable in healthy subjects (0.32 ± 0.11 µmol/mmol Cr) and patients with T1D. In response to SGLT2i, urine adenosine increased during clamped hyperglycemia (0.40 ± 0.11 vs. 0.45 ± 0.12 µmol/mmol Cr, P = 0.005). Similar trends were observed during clamped euglycemia ( P = 0.08). In conclusion, SGLT2i increases urinary adenosine excretion under clamped hyperglycemic conditions in patients with T1D. The potentially protective role of SGLT2i against glomerular hyperfiltration and its mediation by adenosine in diabetes merits further study.

Simple Pretreatment and HILIC Separation for LC-ESI-MS/MS Determination of Adenosine in Human Plasma

A simple pretreatment method and separation mode for the LC-ESI-MS/MS determination of adenosine in human plasma have been developed. Deproteinization by acetonitrile and ultrafiltration followed by chromatographic separation with a hydrophilic interaction chromatographic (HILIC) column give a highly sensitive MS/MS response without ionic suppression caused by the matrix compounds in human plasma. In addition, the presence of ammonium acetate in the mobile phase contributes to high sensitivity in MS/MS detection, facilitating the ionization of adenosine. This method seems to be amenable to the treatment of many samples in clinical practice.

A carbon ion beam irradiated MWCNT/AuNPs composite sensor for a sensitive assay of purine-nucleosides of DNA

Sensor for purine nucleosides has been developed using irradiation with high energy carbon ion beam.

Development and application of a LC-MS/MS method to quantify basal adenosine concentration in human plasma from patients undergoing on-pump CABG surgery

A sensitive and robust LC-MS/MS method was developed to quantify basal adenosine concentrations in human plasma of patients undergoing on-pump coronary artery bypass grafting (CABG) surgery. A strong cation exchange (SCX) monolithic cartridge was used to enrich analyte, improve robustness, and reduce biological complexity. A simple modifier-free mobile phase was employed to improve sensitivity and reproducibility. This method exhibits consistent precision and accuracy, and the RSDs or REs of all the intraday and interday determinations were within 10%. The calibration curve was linear across the examined dynamic range from 1nM to 500nM (r(2)=0.996). LOD and LOQ were determined to be 0.257nM and 0.857nM respectively, while LLOQ was below 10nM. This method was used to monitor changes of adenosine levels in patient plasma drawn intraoperatively during on-pump CABG surgery. The analysis of 84 patients revealed that the mean concentration of adenosine in coronary sinus plasma after cardiopulmonary bypass (CPB) is higher than that in coronary sinus before CPB (p=0.0024; two-tailed t-test) and that in radial artery plasma after CPB (p=0.0409; two-tailed t-test). These findings suggest that the equilibrium between adenosine production and elimination has favored the elevation of adenosine basal level during on-pump CABG surgery and the change is specific to heart tissues. Evaluation of adenosine with a sensitive and robust analytical method has important implications on providing consistent results and meaningful insights into adenosine regulation, as well as its steady state and sustained action on the heart. Relating patient characteristics or clinical outcomes with basal adenosine concentration can be used to optimize the CABG-CPB maneuver by regulating adenosine level via pharmacological intervention, and differentiating adenosine's contribution to cardioprotection from other modulatory factors.

Quantitative analysis of adenosine using liquid chromatography/atmospheric pressure chemical ionization-tandem mass spectrometry (LC/APCI-MS/MS)

Adenosine-secreting cellular brain implants constitute a promising therapeutic approach for the treatment of epilepsy. To engineer neural stem cells for therapeutic adenosine delivery, a reliable and fast analytical method is necessary to quantify cell-based adenosine release. Here we describe the development, optimization and validation of adenosine measurement using liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (LC-APCI-MS/MS). LC-MS/MS in positive ion mode used selected reaction monitoring at m/z of 268.2/136.1 and 302.2/170.0 for adenosine and the internal standard, respectively. The bias was within 15% of the nominal value and evaluation of precision showed a relative standard deviation lower than 15% for all measured concentrations. The lower limit of quantification of adenosine was 15.6 ng/ml. Freeze and thaw stability and processed sample stability also fulfilled the acceptance criteria. Evaluation of the matrix effect showed that the method is not affected by relative matrix effects. The major advantages of this method are the absence of an extraction phase and the combination of the high selectivity and sensitivity characteristic for the LC-MS/MS technique, with a short run time of 4.5 min. These results demonstrate that this method is a useful tool to measure adenosine concentrations in culture medium released from stem cells in vitro.

Analysis of modified nucleosides in the urine of patients with malignant cancer by liquid chromatography/electrospray ionization mass spectrometry

As modified nucleosides reflect altered tRNA turnover which seems to be impaired in the body of cancer patients, they have been evaluated as potential tumor markers. High-performance liquid chromatography/electrosprary ionization quadrupole time-of-flight mass spectrometry (HPLC/ESI-Q-TOFMS) was used to identify nucleosides purified from urine in positive ionization mode. Potential nucleosides were assessed by their evident UV absorbance in HPLC and then further examined by mass spectrometric techniques. In this manner, 21 nucleosides were detected in the urine of a patient with lymphoid cancer including three modified nucleosides 5'-dehydro-2-deoxyinosine, N1,N2,N7-trimethylguanosine and N1-methyl-N2-ethylguanosine, which had never been reported previously.

Simple and rapid determination of adenosine in human synovial fluid with high performance liquid chromatography-mass spectrometry

A simple, fast, sensitive and selective reversed-phase high performance liquid chromatography-mass spectrometry coupling with an electrospray ionization (ESI) interface method is described for the determination of adenosine in human synovial fluid. This method involved the use of the [M + H](+)ions of adenosine and 2-chloroadenosine (internal standard for the assay) at m/z 268 and 302 in positive ion mode with selective ion monitoring (SIM). Separation was carried out on a 2.0 x 150 mm Shimadzu VP-ODS column by using an isocratic elution with a mobile phase consisting of water (94%),methanol (5%) and formic acid (1%). No interference with the components of the biological matrix was observed in the determination conditions. The calibration curve was linear in the range of 0.2-140 microgml(-1). The limits of quantification (LOQ) and detection (LOD) were 0.2 and 0.03 microgml(-1), respectively. The standard recoveries were between 93.3 and 104.0%. The method was successfully applied to determination of adenosine in some synovial fluids of patients affected by rheumatoid arthritis.

Simultaneous determination of six adenyl purines in human plasma by high-performance liquid chromatography with fluorescence derivatization

A sensitive method was developed for the simultaneous determination of six adenyl purines in human plasma by high-performance liquid chromatography. The adenyl purines (adenine, adenosine, AMP, ADP, ATP and cyclic AMP) were derivatized using 2-chloroacetaldehyde for fluorescence detection, and the reaction and separation conditions were reinvestigated to improve sensitivity for small volume sample analysis. Each derivatized purine was separated on a Capcell Pack SG120A column with mobile phase consisting of 0.05 M citric acid-0.1 M dipotassium hydrogen phosphate (pH 4.0)-methanol (97+3). The detection limits were 100-1000 fmol/ml by fluorescence detection, some 500 times better than previous reports. The proposed method was applied to determine adenyl purines in human plasma. The purine levels were as follows: ATP (9.2-22.2 pmol/ml), ADP (5.5-22.2 pmol/ml), AMP (0.8-3.2 pmol/ml). Other purines, adenine, adenosine, cAMP were lower than 0.1 pmol/ml.