LC-APCI-MS/MS analysis of urinary 8-hydroxy-2'-deoxyguanosine

A system consisting of cation-exchange chromatography, combined surface-activated chemical and electrospray ionization, and ion-trap analysis for the analysis of 8-oxo-7,8-dihydro-2'-deoxyguanosine in urine

RATIONALE

8-Hydroxy-2'-deoxyguanosine has served as a biomarker for oxidative damage to DNA from different types of biological samples, and various techniques have been used to analyze it. In particular, liquid chromatography coupled to mass spectrometry has been used to identify 8-hydroxy-2'-deoxyguanosine in urine samples. Usually, a triple quadrupole analyzer and multiple reaction monitoring have been employed for its detection. Only a few studies have used a less expensive ion-trap analyzer instead.

METHODS

We have developed a new liquid chromatography/mass spectrometry procedure that incorporates cation-exchange chromatography in conjunction with surface-activated and electrospray ionization with an ion trap analyzer for the mass spectral step.

RESULTS

The combination of two ionization sources reduced the matrix effect arising from in-source reactions, thus increasing the sensitivity to levels comparable with those obtained by triple quadrupole analyzers.

CONCLUSIONS

This new method for 8-hydroxy-2'-deoxyguanosine detection provided increased sensitivity and reduced chemical noise, using a less expensive, stable and accurate mass spectrometric technology.

Capillary electrophoretic determination of DNA damage markers: content of 8-hydroxy-2'-deoxyguanosine and 8-nitroguanine in urine

A sensitive and low-cost analytical method has been developed to determine 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 8-nitroguanine (8-NO(2)Gua) based on capillary electrophoresis with amperometric detection (CE-AD) after solid phase extraction (SPE). Under optimized condition, these two markers were well separated from other components coexisting in urine, exhibiting a linear calibration over the concentration range of 0.1-50.0 μg/mL with the detection limits ranging from 0.02 to 0.06 μg/mL. The relative standard deviations (RSDs) were in the range of 0.1-2.1% for peak area, 0.1-1.5% for migration time, respectively. The average recovery and RSD were within the range of 100.0-108.0% and 0.1-1.7%, respectively. It was found that the urinary contents of 8-OHdG and 8-NO(2)Gua in cancer patients were significantly higher than those in healthy ones.

Urine 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a specific marker of oxidative stress, using direct, isocratic LC-MS/MS: Method evaluation and application in study of biological variation in healthy adults

BACKGROUND

Urine 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) is a specific biomarker of oxidative stress. We evaluated a modified LC-MS/MS assay for urine 8-oxodG and determined biological variation in healthy adults.

METHOD

Untreated urine was injected into an isocratic LC-MS/MS system (positive-ion MRM mode). Urine 8-oxodG in 51 healthy volunteers was measured; within- and between-day variations in 23 healthy volunteers were investigated.

RESULTS

Dose-response was linear to 452 nmol/l; limit of detection=2.3 nmol/l; within-run and between-run CVs were <3.0% and <4.7%, respectively; recovery=97%-101%; accuracy=97.7-103.5%. Urine 8-oxodG (median, mean [SD]): 1.70, 1.70[0.60]nmol/mmol creatinine (n=51). Men had higher (p=0.027) concentrations than women matched for age and body mass index: mean [SD]: 1.90[1.60]; n=26 vs. 1.50[0.55]; n=25. Within- and between-day variations were wide but random. No significant differences were seen overall across time-points within 1 day or at the same time-point across 5 consecutive days.

CONCLUSIONS

The method has advantages of speed and relative simplicity as it does not require sample pre-treatment for 8-oxodG extraction, the use of internal standard or gradient LC elution and has high linearity, specificity, precision and recovery. Biological variation in urine 8-oxodG is wide, but no within- or between-day differences at the group concentration were seen in healthy adults.

Analysis of DNA-bound advanced glycation end-products by LC and mass spectrometry

Sugars and sugar degradation products readily react in vitro with guanine derivatives, resulting in the formation of DNA-bound advanced glycation end-products (DNA-AGEs). The two diastereomers of N(2)-(1-carboxyethyl)-2'-deoxyguanosine (CEdG(A,B)) and the cyclic adduct of methylglyoxal and 2'-deoxyguanosine (mdG) (N(2)-7-bis(1-hydroxy-2-oxopropyl)-2'-deoxyguanosine have also been detected in cultured cells and/or in vivo. LC-MS/MS methods have been developed to analyze sensitively DNA adducts in vitro and in vivo. In this paper, the chemical structures of possible DNA-AGEs and the application of LC-MS/MS to measure DNA-AGEs are reviewed.

Chromatographic and electrophoretic methods for the analysis of biomarkers of oxidative damage to macromolecules (DNA, lipids, and proteins)

Free radicals and other reactive species can cause oxidative damage to biomolecules when oxidant species exceed the antioxidant defences in the body, resulting in oxidative stress. Oxidatively damaged products have been associated with aging as well as with the development of pathologies like cancer, cardiovascular disease, neurodegenerative disorders, diabetes, inflammation, etc. Reliable measurements of biomarkers of oxidative damage to macromolecules would afford information on the pre-disposition and prognosis of certain pathologies, being of utmost importance in evaluation of the effect of intervention with antioxidants on the incidence of diseases associated to oxidative stress. This review will present and compare different analytical methods, especially those involving chromatographic and electrophoretic techniques, commonly used for the analysis of biomarkers of oxidative damage to the three main macromolecules, namely oxidised DNA, lipid peroxidation products, and protein carbonyls.

Quantitation of 8-hydroxydeoxyguanosine in DNA by liquid chromatography/positive atmospheric pressure photoionization tandem mass spectrometry

A methodology has been developed and validated for quantifying 8-hydroxydeoxyguanosine (8-OHdG) in both commercial DNA and DNA isolated from livers of male Sprague-Dawley rats by liquid chromatography/positive atmospheric pressure photoionization tandem mass spectrometry. The analytical method conditions, including conditions for stabilizing 8-OHdG during complex nuclease P1 enzymatic digestion, were also evaluated. The limit of detection for 8-OHdG was 1.0 ng/mL (17.6 fmol on-column), and the linearity of the calibration curve was greater than 0.998 from 1.0 to 500 ng/mL. The intraday assay precision relative standard deviation (RSD) value for quality control (QC) samples was < or =5.59% with accuracies ranging from 91.84 to 117.61%. The interday assay precision (RSD) value was < or =1.76% with accuracies ranging from 91.84 to 116.67%. This method, combined with the LC/UV analysis of deoxyguanosine (dG), was used for determination of the levels of 8-OHdG/10(6) dG in DNA nuclease P1 enzymatic hydrolysates from both commercial DNA and rat liver DNA.

A method for routine quantitation of urinary 8-hydroxy-2'-deoxyguanosine based on solid-phase extraction and micro-high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

8-Hydroxy-2'-deoxyguanosine (8OHdG), one of the major oxidative DNA lesions induced by radical agents, is commonly used as a biomarker for oxidative stress, nowadays preferably in urine. In the absence of a commercially available internal standard a micro-high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (micro-HPLC/ESI-MS/MS) method, suitable for routine analysis of 8OHdG in human urine using external calibration, was developed. Evaluation of the matrix effect showed that the method allows highly sensitive and accurate quantitation despite the absence of an internal standard. HPLC analysis was performed using gradient elution at a flow rate of 10 microL min(-1) using a capillary reversed-phase column and an injection volume of 0.5 microL, with detection of 8OHdG in positive multiple reaction monitoring (MRM) mode. The absolute limit of detection was 0.35 fmol using m/z 168 as a quantifier (fragment) ion. A linear (R2> 0.999) calibration curve in urine was obtained over a range 0.2-10 ng mL(-1). This method is about 20 times more sensitive than previously described procedures, and is characterized by high accuracy (mean 90%) and good reproducibility (RSD <10%). The optimized method was applied to determination of 8OHdG in 18 urinary samples derived from three healthy volunteers. 8OHdG urinary excretion ranged from 3.0-7.9 microg/day, and a large intra-individual variation was found. This method, which effectively circumvents the need for isotopically labeled 8OHdG (internal standard), is suitable for routine monitoring of exposure to DNA-damaging factors in a large number of subjects.