Determination of 8-oxoguanine in human plasma and urine by high-performance liquid chromatography with electrochemical detection

Analysis of four alkaloids of Coptis chinensis in rat plasma by high performance liquid chromatography with electrochemical detection

A sensitive and precise high performance liquid chromatography (HPLC)-electrochemical detection (ECD) method has been developed for the simultaneous determination of four isoquinoline alkaloids including berberine, jatrorrhizine, coptisine and palmatine in Chinese medicine Coptis chinensis. The typical HPLC analysis was performed on WondaSil(®) C18-WR column (250×4.6 mm, 5 μm) with the mobile phase comprising 40 mM phosphate buffer (pH 7.0)-acetonitrile (40:60, v/v) at the flow rate of 0.8 mL min(-1). The electrochemical detection employed a three electrode system with a bare glassy carbon electrode at +1.3 V versus the Ag/AgCl reference electrode. The limits of detection (LODs) of four alkaloids ranged from 0.01 to 0.03 μmol L(-1) and the LOD of berberine was 80 times lower than LOD obtained by UV detection. The rat plasma samples were assayed after oral administration of the traditional Chinese medicine Coptis chinensis by the proposed HPLC-ECD method. The recoveries of this method were ranging from 88.0 to 116%, with the relative standard deviation lower than 3.1% for intra-day precision and 5.7% for inter-day precision. These results show that HPLC-ECD is a useful tool for the quality control of herbal medicine Coptis chinensis and also for pharmacokinetic studies.

Beneficial effect of coenzyme Q10 on increased oxidative and nitrative stress and inflammation and individual metabolic components developing in a rat model of metabolic syndrome

Metabolic syndrome (MetS) is a group of cardiovascular risk factors, including visceral obesity, glucose intolerance, hypertension, and dyslipidemia. Increased oxidative and nitrative stress and inflammation and decreased endothelial function occur in an animal model of metabolic syndrome, SHR/NDmcr-cp (SHR/cp) rats. The present study investigated the effects of coenzyme Q10 (CoQ10), one of the important antioxidants, on the abnormal oxidative condition and characteristic components of metabolic syndrome in SHR/cp rats by maintaining them on a diet supplemented with 0.07% - 0.7% CoQ10 for 26 weeks. We determined serum levels of oxidatively modified low-density lipoprotein (Ox-LDL) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) as oxidative stress markers, 3-nitrotyrosine as a nitrative stress marker, 3-chlorotyrosine as a marker of myeloperoxidase (MPO)-catalyzed oxidation and high-sensitivity C-reactive protein (hsCRP) as an inflammatory marker. The administration of CoQ10 significantly attenuated the increase of oxidative and nitrative stress markers and inflammatory markers in a dose-dependent manner. CoQ10 prevented the elevated serum insulin levels, although it did not affect the elevated glucose level and dyslipidemia. CoQ10 also reduced elevated blood pressure, but did not affect body weight gain. In addition, CoQ10 improved endothelial dysfunction in the mesenteric arteries. These findings suggest that the antioxidant properties of CoQ10 can be effective for ameliorating cardiovascular risk in MetS.

Oxidants in the Gas Phase of Cigarette Smoke Pass Through the Lung Alveolar Wall and Raise Systemic Oxidative Stress

Cigarette smoking-induced oxidative stress plays a key role in the pathogenesis of atherosclerosis in smokers. Aqueous cigarette smoke extract (CSE) contains stable oxidants, peroxynitrite-like reactants, which have the ability to oxidize and nitrate low-density lipoprotein (LDL). We examined whether oxidants in CSE can penetrate into the blood through the lung alveolar wall and cause oxidative vascular injury. The oxidants in CSE and sodium peroxynitrite could easily pass through the reconstituted basement membrane. When CSE or sodium peroxynitrite solution was infused into the alveolar air space of an isolated rat lung mounted in tyrosine solution, CSE gradually increased the 3-nitrotyrosine levels in the external tyrosine solution while sodium peroxynitrite caused a rapid increase. CSE did not activate the rat alveolar macrophages. When rats were acutely exposed to the gas phase of cigarette smoke from which tar and nicotine had been removed, both serum levels of 3-nitrotyrosine and 8-hydroxy-2'-deoxyguanine, oxidative stress markers, rapidly increased. Our results demonstrate that relatively stable oxidants in CSE can pass through the pulmonary alveolar wall into the blood and induce systemic oxidative stress, which most likely facilitates oxidative modification of LDL and endothelial dysfunction, explaining early key events in the development of atherosclerosis.

Elevated circulating levels of markers of oxidative-nitrative stress and inflammation in a genetic rat model of metabolic syndrome

Metabolic syndrome is a cluster of metabolic diseases that in essence greatly promotes progression of atherosclerosis. We used a genetic model of the metabolic syndrome, the SHR/NDmcr-cp (SHR/cp) rat, from 6 to 40 weeks of age to investigate whether systemic oxidative stress, a major cause of atherosclerosis, increases in this syndrome. Nine-week-old male rats already showed manifestations of metabolic syndrome, including heavier body weight, higher blood pressure and higher levels of serum glucose, insulin and various lipids compared to the age-matched Wistar Kyoto (WKY) rats used as a genetic control. These metabolic parameters gradually progressed with age. Likewise, the serum levels of oxidative stress markers, including lipid peroxides, which oxidatively modify low-density lipoprotein (LDL) and 8-hydroxydeoxyguanosine (8-OHdG), gradually increased in SHR/cp rats. The serum levels of 3-nitrotyrosine and 3-chlorotyrosine also persistently increased, indicating the involvement of peroxynitrite or myeloperoxidase-catalyzed oxidation. In addition, high-sensitivity C-reactive protein (hsCRP), an early marker of inflammation, temporarily increased in SHR/cp rats compared to WKY rats. These findings suggest that oxidative stress, as well as nitrative stress and inflammation, increases in the metabolic syndrome, which may contribute to the development of atherosclerosis.

Corosolic acid prevents oxidative stress, inflammation and hypertension in SHR/NDmcr-cp rats, a model of metabolic syndrome

Corosolic acid (CRA), a constituent of banaba leaves, has been reported to have anti-inflammatory and hypoglycemic activities. The aim of this study was to determine the effects of CRA on metabolic risk factors including obesity, hypertension, hyperinsulinemia, hyperglycemia, and hyperlipidemia together with oxidative stress and inflammation, all of which are characteristic of the SHR/NDmcr-cp (cp/cp) (SHR-cp) rat, an animal model of metabolic syndrome. Six-week-old male SHR-cp rats were fed a high fat diet containing 0.072% CRA for 14 weeks. Treatment with CRA lowered blood pressure, which was elevated in control animals, by 10% after 8 weeks, and serum free fatty acids by 21% after 2 weeks. CRA treatment resulted in decreases in the levels of the oxidative stress markers thiobarbituric acid-reactive substances and 8-hydroxydeoxyguanosine by 27% and 59%, respectively, after 2 weeks. CRA treatment also reduced the levels of myeloperoxidase markers, 3-nitrotyrosine and 3-chlorotyrosine by 38% and 39%, respectively, after 10 weeks, and tended to decrease the levels of high sensitivity C-reactive protein, a marker of inflammation, after 6 weeks. However, CRA had no effect on weight gain or hyperglycemia. These results demonstrate that CRA can ameliorate hypertension, abnormal lipid metabolism, and oxidative stress as well as the inflammatory state in SHR-cp rats. This implies that CRA can be beneficial for preventing atherosclerosis-related diseases that are an increasing health care problem worldwide.

Facilitated nitration and oxidation of LDL in cigarette smokers

BACKGROUND

Cigarette smoking increases the risk of developing atherosclerosis and ischaemic heart disease. Smoking-induced oxidative stress is considered to favour oxidation of low-density lipoprotein (LDL) and subsequently promotes the atherogenic process. We investigated whether peroxynitrite, a reaction product of cigarette smoke, is involved in facilitated oxidation of LDL in smokers.

MATERIALS AND METHODS

Plasma LDL was obtained from 10 healthy asymptomatic cigarette smokers and 10 healthy nonsmokers. The state of enhanced oxidative stress in the plasma was assessed by LDL subfraction assay using anion-exchange high-performance liquid chromatography (AE-HPLC) and measurements of thiobarbituric acid-reactive substances (TBARS), 8-hydroxydeoxyguanosine (8-OHdG), vitamin E, 3-nitrotyrosine and 3-chlorotyrosine.

RESULTS

Smokers showed a significantly higher level of TBARS and 8-OHdG as well as a significantly lower level of vitamin E than nonsmokers, even after stopping smoking for 10 h or more. The LDL subfraction assay demonstrated an increase in oxidatively modified LDL, as expressed by lower levels of LDL1 and higher levels of LDL2. The 3-nitrotyrosine levels in apolipoprotein B in LDL were significantly higher in smokers than nonsmokers, while the 3-chlorotyrosine levels remained unchanged. In addition, these changes observed in the smokers were further accelerated within 30 min after resumption of cigarette smoking when compared with the levels before smoking resumption.

CONCLUSION

The present study suggests that peroxynitrite plays a significant role in oxidative modification of plasma LDL induced by cigarette smoking.

High dietary intake of sodium selenite induces oxidative DNA damage in rat liver

One mechanism for the cancer-chemopreventive effects of high selenium (Se) intake is hypothesized to be antioxidant protection of DNA. In this work we examine DNA oxidation in whole animals as a function of dietary Se intake and carcinogen administration. Weanling male Sprague-Dawley rats were fed a basal, Torula yeast-based, Se-deficient diet supplemented with 0, 0.15, or 2.0 ppm Se as sodium selenite for 10 wk. They were then injected with 0, 0.1, or 10 mg /kg body weight of the pro-oxidant carcinogen N-nitrosodiethylamine. High levels of carcinogen and high levels of selenite intake each increased concentration of 8-hydroxy-2'-deoxyguanosine in liver DNA. Se-dependent glutathione peroxidase I gene expression and enzyme activity were dramatically reduced by dietary Se deficiency but were unaffected by carcinogen administration. There were no significant main or interactive effects of Se or carcinogen on activity or gene expression of the DNA repair enzyme 8-oxoguanine glycosylase I. These results do not support the hypothesis that high Se intake may be cancer-preventive by inhibiting oxidative DNA damage. Rather than inhibiting oxidative DNA damage, these findings suggest that high dietary intake of inorganic Se may promote in vivo DNA oxidation.

Quantification of 8-oxo-guanine and guanine as the nucleobase, nucleoside and deoxynucleoside forms in human urine by high-performance liquid chromatography-electrospray tandem mass spectrometry

Oxidative DNA damage, linked pathogenically to a variety of diseases such as cancer and ageing, can be investigated by measuring specific DNA repair products in urine. Within the last decade, since it was established that such products were excreted into urine, progress in their analysis in urine has been limited. Guanine is the DNA base most prone to oxidation. We present a method for determination of the urinary 8-hydroxylated species of guanine, based on direct injection of urine onto a high-performance liquid chromatography (HPLC)-tandem mass spectrometry system. The analysis covers the 8-hydroxylated base, ribonucleoside and deoxynucleoside, and the corresponding non-oxidised species. Without pre-treatment of urine the detection limits for the nucleobases are approximately 2 nM (50 fmol injected) and for the nucleosides approximately 0.5 nM (12.5 fmol injected). Previously, liquid chromatography of the nucleobases has been problematic but is made possible by low-temperature reverse-phase C18 chromatography, a method that increases retention on the column. In the case of the nucleosides, retention was almost total and provides a means for on-column concentration of larger urine samples and controlled high peak gradient elution. The total excretion of 8-hydroxylated guanine species was 212 nmol/24 h. The oxidised base accounted for 64%, the ribonucleoside for 23% and the deoxynucleoside for 13%, indicating substantial oxidation of RNA in humans. In rat urine, excretion of the oxidised base was more dominant, the percentages of the oxidised base, ribonucleoside and deoxynucleosides being 89, 8 and 3%. This finding is at odds with previous reports using immunoaffinity pre-purification and HPLC-electrochemical detection analysis. The developed method now makes it possible to measure oxidative nucleic acid stress to both RNA and DNA in epidemiological and intervention settings, and our findings indicate a substantial RNA oxidation in addition to DNA oxidation. The small volume needed also makes the method applicable to small experimental animals.

Longitudinal study of urinary 8-hydroxy-2'-deoxyguanosine excretion in healthy adults

Numerous studies have investigated the urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a biomarker for the assessment of oxidative DNA damage in humans. In this study, we performed six consecutive series of measurement of urinary levels of 8-OHdG in 68 healthy probands, in order to provide information on the intra- and inter-individual variability of 8-OHdG and to estimate the influence of smoking, age, sex, body weight and body mass index (BMI) on the excretion of 8-OHdG. The intra-individual coefficient of variation (CV) of urinary 8-OHdG/24 h ranged from 0.18 to 1.06 (mean CV = 0.48). Women excreted significantly lower amounts of 8-OHdG/24 h than men, but the difference lost its significance when the body weight or urinary creatinine were used as covariates. By multiple linear regression analysis significant correlations between the mean individual levels of 8-OHdG/24 h excretion and urinary creatinine (rp = 0.61), and cotinine (rp = 0.27) have been observed, whereas no statistically significant effect of age, body weight and BMI was found. The 8-OHdG/creatinine ratio was found to be significantly increased in 23 smokers (1.95 +/- 0.40 mumol/mol) opposed to 45 non-smoking probands (1.62 +/- 0.50 mumol/mol), which is in good agreement with previously published data. No effect of passive smoking on the excretion of 8-OHdG was found. From our data we conclude that the intra-individual variability of urinary 8-OHdG excretion has been underestimated so far, indicating that values of 8-OHdG measured by single spot monitoring are not representative for individual base levels.

Measurement of 8-oxo-2'-deoxyguanosine and 8-oxo-2'-deoxyadenosine in DNA and human urine by high performance liquid chromatography-electrospray tandem mass spectrometry

A method for the determination of 8-oxo-2'-deoxyguanosine and 8-oxo-2'-deoxyadenosine in DNA and urine by High Performance Liquid Chromatography (HPLC)-Tandem Mass Spectrometry is described. For the urine samples there is no sample preparation except for addition of buffer and internal standards followed by redissolvation of precipitate containing 8-oxo-2'-deoxyguanosine and a centrifugation step before the samples are injected onto the HPLC column. The detection limit for 8-oxo-2'-deoxyguanosine and 8-oxo-2'-deoxyadenosine is approximately 0.3 nM corresponding to 7.5 fmol injected. Long runs, that is, > 50 samples, can be analyzed with only minimal loss of sensitivity. The concentrations excreted into urine samples from humans are between 1 and 100 nM for 8-oxo-2'-deoxyguanosine and below 0.3 nM for 8-oxo-2'-deoxyadenosine. In calf thymus DNA levels down to about 1 oxidized guanosine and adenosine per 10(6) unmodified bases can be detected. High levels of 8-oxo-2'-deoxyguanosine were found, 30 per 10(6) 2'-deoxyguanosine, levels of 8-oxo-2'-deoxyadenosine are at or below the detection limit. These findings indicate that High Performance Liquid Chromatography-Tandem Mass Spectrometry is a highly sensitive and specific method for analysis of oxidative DNA modifications in tissue as well as for analysis of excretion of oxidized nucleotides into urine that ensures a minimum artifact formation.

Debenzylation of O(6)-benzyl-8-oxoguanine in human liver: implications for O(6)-benzylguanine metabolism

O(6)-Benzylguanine (BG) effectively inactivates the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase, and enhances the effectiveness of 1,3-bis(2-chloroethyl)-1-nitrosourea in cells in culture and tumor-bearing animals. BG is presently in phase II clinical trials. In humans, BG is converted to O(6)-benzyl-8-oxoguanine (8-oxoBG), a longer-lived, yet equally potent inactivator. We have isolated and identified the debenzylated product, 8-oxoguanine, in plasma and urine of patients following administration of BG. The purpose of this work was to determine the human liver enzymes responsible for the debenzylation of 8-oxoBG. Therefore, 8-oxoBG was incubated with human liver microsomes and cytosol, and the concentration of 8-oxoguanine was determined. No appreciable product was formed in the cytosol; however, increasing amounts of 8-oxoguanine were formed with increasing concentrations of pooled human liver microsomes. The amount of 8-oxoguanine formed increased with time and substrate concentration. Co-incubation of human liver microsomes with 8-oxoBG and various cytochrome P450 isoform-selective inhibitors suggested the possible involvement of CYP1A2, 2E1, and/or 2A6 in this reaction. Incubation of 8-oxoBG with baculovirus cDNA-overexpressed CYP1A2, 2E1, 2A6, and 3A4 demonstrated that formation of 8-oxoguanine was due mainly to CYP1A2. Debenzylation of 8-oxoBG complied with Michaelis-Menten kinetics with K(m) and V(max) values of 35.9 microM and 0.59 pmol/min/pmol of CYP1A2, respectively. CYP1A2 appears to be mainly responsible for the debenzylation of 8-oxoBG in human liver.

Phase I trial of carmustine plus O6-benzylguanine for patients with recurrent or progressive malignant glioma

PURPOSE

The major mechanism of resistance to alkylnitrosourea therapy involves the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT), which removes chloroethylation or methylation damage from the O(6) position of guanine. O(6)-benzylguanine (O(6)-BG) is an AGT substrate that inhibits AGT by suicide inactivation. We conducted a phase I trial of carmustine (BCNU) plus O(6)-BG to define the toxicity and maximum-tolerated dose (MTD) of BCNU in conjunction with the preadministration of O(6)-BG with recurrent or progressive malignant glioma.

PATIENTS AND METHODS

Patients were treated with O(6)-BG at a dose of 100 mg/m(2) followed 1 hour later by BCNU. Cohorts of three to six patients were treated with escalating doses of BCNU, and patients were observed for at least 6 weeks before being considered assessable for toxicity. Plasma samples were collected and analyzed for O(6)-BG, 8-oxo-O(6)-BG, and 8-oxoguanine concentration.

RESULTS

Twenty-three patients were treated (22 with glioblastoma multiforme and one with anaplastic astrocytoma). Four dose levels of BCNU (13.5, 27, 40, and 55 mg/m(2)) were evaluated, with the highest dose level being complicated by grade 3 or 4 thrombocytopenia and neutropenia. O(6)-BG rapidly disappeared from plasma (elimination half-life = 0. 54 +/- 0.14 hours) and was converted to a longer-lived metabolite, 8-oxo-O(6)-BG (elimination half-life = 5.6 +/- 2.7 hours) and further to 8-oxoguanine. There was no detectable O(6)-BG 5 hours after the start of the O(6)-BG infusion; however, 8-oxo-O(6)-BG and 8-oxoguanine concentrations were detected 25 hours after O(6)-BG infusion. The mean area under the concentration-time curve (AUC) of 8-oxo-O(6)-BG was 17.5 times greater than the mean AUC for O(6)-BG.

CONCLUSION

These results indicate that the MTD of BCNU when given in combination with O(6)-BG at a dose of 100 mg/m(2) is 40 mg/m(2) administered at 6-week intervals. This study provides the foundation for a phase II trial of O(6)-BG plus BCNU in nitrosourea-resistant malignant glioma.