Increased levels of plasma nucleotides in patients with rheumatoid arthritis.

Novel biomarkers of rheumatoid arthritis (RA), in addition to antibodies against cyclic citrullinated peptides, are required. Metabolome analysis is a promising approach to identify metabolite biomarkers for clinical diagnosis. We adopted a comprehensive non-targeted metabolomics approach combining capillary electrophoresis time-of-flight mass spectrometry (TOFMS) and liquid chromatography TOFMS. We constructed metabolomics profiling of 286 plasma samples of a Japanese population [92 RA patients, 13 systemic lupus erythematosus (SLE) patients and 181 healthy controls). RA case-control association tests showed that seven metabolites exhibited significantly increased levels in RA samples compared with controls (P < 1.0 × 10-4; UTP, ethanolamine phosphate, ATP, GDP, ADP, 6-aminohexanoic acid and taurine), whereas one exhibited a decreased level (xanthine). The plasma levels of these eight metabolites were not significantly different between seropositive and seronegative RA patients (P > 0.05; n = 68 and 24, respectively). The four nucleotide levels (UTP, ATP, GDP and ADP) were significantly higher in the non-treatment patients in comparison between patients with and without treatment (P < 0.014; n = 57 and 35, respectively). Furthermore, we found that none of the four nucleotide levels showed significant differences in SLE case-control association tests (P > 0.2; 13 patients with SLE and the 181 shared controls) and psoriatic arthritis (PsA) case-control association tests (P > 0.11; 42 patients with PsA and 38 healthy controls), indicating disease specificity in RA. In conclusion, our large-scale metabolome analysis demonstrated the increased plasma nucleotide levels in RA patients, which could be used as potential clinical biomarkers of RA, especially for seronegative RA.

Phase I pharmacological study of continuous chronomodulated capecitabine treatment.

PURPOSE: Capecitabine is an oral pre-pro-drug of the anti-cancer drug 5-fluorouracil (5-FU). The biological activity of the 5-FU degrading enzyme, dihydropyrimidine dehydrogenase (DPD), and the target enzyme thymidylate synthase (TS), are subject to circadian rhythmicity in healthy volunteers. The aim of this study was to determine the maximum tolerated dose (MTD), dose-limiting toxicity (DLT), safety, pharmacokinetics (PK) and pharmacodynamics (PD) of capecitabine therapy adapted to this circadian rhythm (chronomodulated therapy). METHODS: Patients aged ≥18 years with advanced solid tumours potentially benefitting from capecitabine therapy were enrolled. A classical dose escalation 3 + 3 design was applied. Capecitabine was administered daily without interruptions. The daily dose was divided in morning and evening doses that were administered at 9:00 h and 24:00 h, respectively. The ratio of the morning to the evening dose was 3:5 (morning: evening). PK and PD were examined on treatment days 7 and 8. RESULTS: A total of 25 patients were enrolled. The MTD of continuous chronomodulated capecitabine therapy was established at 750/1250 mg/m2/day, and was generally well tolerated. Circadian rhythmicity in the plasma PK of capecitabine, dFCR, dFUR and 5-FU was not demonstrated. TS activity was induced and DPD activity demonstrated circadian rhythmicity during capecitabine treatment. CONCLUSION: The MTD of continuous chronomodulated capecitabine treatment allows for a 20% higher dose intensity compared to the approved regimen (1250 mg/m2 bi-daily on day 1-14 of every 21-day cycle). Chronomodulated treatment with capecitabine is promising and could lead to improved tolerability and efficacy of capecitabine.

Intracellular pharmacokinetics of gemcitabine, its deaminated metabolite 2',2'-difluorodeoxyuridine and their nucleotides.

AIMS: Gemcitabine (2',2'-difluoro-2'-deoxycytidine; dFdC) is a prodrug that has to be phosphorylated within the tumour cell to become active. Intracellularly formed gemcitabine diphosphate (dFdCDP) and triphosphate (dFdCTP) are considered responsible for the antineoplastic effects of gemcitabine. However, a major part of gemcitabine is converted into 2',2'-difluoro-2'-deoxyuridine (dFdU) by deamination. In the cell, dFdU can also be phosphorylated to its monophosphate (dFdUMP), diphosphate (dFdUDP) and triphosphate (dFdUTP). In vitro data suggest that these dFdU nucleotides might also contribute to the antitumour effects, although little is known about their intracellular pharmacokinetics (PK). Therefore, the objective of the present study was to gain insight into the intracellular PK of all dFdC and dFdU nucleotides formed during gemcitabine treatment. METHODS: Peripheral blood mononuclear cell (PBMC) samples were collected from 38 patients receiving gemcitabine, at multiple time points after infusion. Gemcitabine, dFdU and their nucleotides were quantified in PBMCs. In addition, gemcitabine and dFdU plasma concentrations were monitored. The individual PK parameters in plasma and in PBMCs were determined. RESULTS: Both in plasma and in PBMCs, dFdU was present in higher concentrations than gemcitabine [mean intracellular area under the concentration-time curve from time zero to 24 h (AUC0-24 h ) 1650 vs. 95 µM*h]. However, the dFdUMP, dFdUDP and dFdUTP concentrations in PBMCs were much lower than the dFdCDP and dFdCTP concentrations. The mean AUC0-24 h for dFdUTP was 312 µM*h vs. 2640 µM*h for dFdCTP. CONCLUSIONS: The study provides the first complete picture of all nucleotides that are formed intracellularly during gemcitabine treatment. Low intracellular dFdU nucleotide concentrations were found, which calls into question the relevance of these nucleotides for the cytotoxic effects of gemcitabine.

Strain differences in mice highlight the role of DNA damage in neoplasia induced by low dietary folate.

In earlier work, we showed that low dietary folate induced intestinal tumors in BALB/c mice. In this study, our goal was to examine the effect of the same diets on a strain that is more resistant to tumorigenesis (C57Bl/6). We also questioned whether supplementation of the folate-deficient diet (FD) with betaine, an alternate methyl donor, would influence tumor formation. C57Bl/6 mice were fed the same diets [control diet (CD) with 2 mg folate/kg diet and FD with 0.3 mg folate/kg diet] as those in our previous study for 1 y, but they did not develop tumors. We also fed BALB/c mice the FD or FD supplemented with betaine for 1 y, but there was no change in tumor incidence. To determine the relative contributions of DNA damage and altered methylation patterns, we measured intestinal dUTP:dTTP ratios, phosphorylated histone H2AX (p-H2AX) staining, and global DNA methylation in both strains. Only BALB/c mice showed changes due to diet in dUTP:dTTP (from 2.19 +/- 0.20 in CD to 2.77 +/- 0.18 in FD; P = 0.05) and in p-H2AX staining (from 14.10 +/- 3.59% in CD to 22.40 +/- 2.65% in FD; P = 0.054). In BALB/c mice only, FD tended to have less (P = 0.06) global DNA methylation than CD. Although the FD increased plasma homocysteine and the betaine-supplemented FD lowered plasma homocysteine, the latter diet did not reduce tumor incidence. We conclude that plasma homocysteine is not likely to be associated with tumorigenesis in our model. However, DNA damage plays a critical role in initiating tumorigenesis when dietary folate is low and methylation changes may also be contributory.

Uridine triphosphate (UTP) is released during cardiac ischemia.

BACKGROUND: Extracellular uridine triphosphate (UTP) stimulates vasodilatation, automaticity in ventricular myocytes and release of tissue-plasminogen activator (t-PA), indicating that UTP may be important in cardiac regulation. We took advantage of a recently developed quantitative assay for UTP to test the hypothesis that UTP is released in the circulation during cardiac ischemia. METHODS: In ten pigs, a balloon catheter in the left anterior descending artery was introduced to induce ischemia. Samples were collected from the coronary sinus. Blood flow in the coronary sinus was assessed by a Doppler velocity transducer. RESULTS: Plasma UTP levels increased early during ischemia and early after reperfusion (by 257+/-100 and 247+/-72%, p<0.05). Cardiac blood flow, ventricular arrhythmias and t-PA release were markedly increased at the same time points. In contrast, after 30 min, a second period of ischemia did not result in any significant increase of UTP or blood flow. Furthermore, ventricular arrhythmias were less frequent. UTP levels correlated with ventricular arrhythmia and blood flow. Similar results were found for ATP. CONCLUSION: For the first time we have shown that UTP is released during cardiac ischemia. UTP released during ischemia may stimulate blood flow, arrhythmia and t-PA release.

Evidence that most high-affinity ATP binding sites on aortic endothelial cells and membranes do not correspond to P2 receptors.

It has recently been demonstrated that two types of ATP receptors, the P2Y and P2U receptors, are coexpressed on bovine aortic endothelial cells. The aim of the present study was to characterize directly P2Y and P2U subtypes on intact bovine aortic endothelial cells and on membranes prepared from these cells using adenosine 5'-0-(3-thio[35S]triphosphate) ([35S]ATP gamma S), [alpha-32P]ATP and [alpha-32P]UTP as radioligands. [35S]ATP gamma S binding to bovine aortic endothelial cell membranes was saturable and apparently involved a single class of high-affinity binding sites (Kd: 14 +/- 11 nM. Bmax 1.6 +/- 0.7 pmol/mg protein; mean +/- S.D.). A similar class of high-affinity binding sites was identified with [alpha-32P]ATP (Kd: 14 +/- 9 nM; Bmax: 1.7 +/- 1.1 pmol/mg protein; mean +/- S.D.). Competition experiments showed that only one third of these sites bound 2-methylthio-ATP (2-MeSATP) with high affinity (Ki: 21 +/- 5 and 14 +/- 10 nM, mean +/- S.D., for [35S]ATP gamma S and [alpha-32P]ATP, respectively) and might therefore represent the P2Y receptors. UTP did not compete with [35S]ATP gamma S or [alpha-32P]ATP for binding at the remaining sites, indicating that they are not the P2U receptors. No high-affinity UTP binding sites could be detected using [alpha-32P]UTP. [35S]ATP gamma S binding to intact bovine aortic endothelial cells was competed by ATP gamma S (Kd: 1.0 +/- 0.5 microM; mean +/- S.D.), but not by 2-MeSATP and UTP, indicating that these binding sites are neither the P2Y nor the P2U receptors.

Distribution of erythrocyte nucleotides in pyrimidine 5'-nucleotidase deficiency.

In pyrimidine 5'-nucleotidase deficiency, erythrocytes contain elevated levels of pyrimidine nucleotides. The composition of this nucleotide pool was examined by ion exchange chromatography on Dowex formate columns using a linear ammonium formate elution gradient. In contradistinction to normal erythrocytes, adenine nucleotides accounted for only 32% of the nucleotide pool. The remainder consisted of 50% cytidine and 16% uridine nucleotides. The remaining 2% was not identified. The most abundant compound appeared to be UDP glucose whilst high levels of CTP, CMP and an unidentified cytidine compound less polar than CMP accounted for most of the cytidine nucleotide pool. The possibility that the abnormal nucleotides were due to an elevated reticulocyte count was excluded and it was also shown that erythrocytes from subjects heterozygous for pyrimidine 5'-nucleotidase deficiency did not have detectable levels of the abnormal nucleotides.

NTP pattern of avian embryonic red cells: role of RNA degradation and AMP deaminase/5'-nucleotidase activity.

During terminal erythroid differentiation, degradation of RNA is a potential source for nucleotide triphosphates (NTPs) that act as allosteric effectors of hemoglobin. In this investigation, we assessed the developmental profile of RNA and purine/pyrimidine trinucleotides in circulating embryonic chick red blood cells (RBC). Extensive changes of the NTP pattern are observed which differ significantly from what is observed for adult RBC. The biochemical mechanisms have not been identified yet. Therefore, we studied the role of AMP deaminase and IMP/GMP 5'-nucleotidase, which are key enzymes for the regulation of the purine nucleotide pool. Finally, we tested the effect of major NTPs on the oxygen affinity of embryonic/adult hemoglobin. The results are as follows. 1) Together with ATP, UTP and CTP serve as allosteric effectors of hemoglobin. 2) Degradation of erythroid RNA is apparently a major source for NTPs. 3) Developmental changes of nucleotide content depend on the activities of key enzymes (AMP deaminase, IMP/GMP 5'-nucleotidase, and pyrimidine 5'-nucleotidase). 4) Oxygen-dependent hormonal regulation of AMP deaminase adjusts the red cell ATP concentration and therefore the hemoglobin oxygen affinity.

Platelet P1, P4-Di (adenosine-51) tetraphosphate (AP4A) in migraine patients before and during beta-adrenoceptor blockade.

P1,P4-Di(adenosine-51) tetraphosphate (AP4A) is a metabolically inactive nucleotide which can be released from platelet dense granules. This study was designed firstly, to investigate whether platelet content of AP4A was decreased in patients with classical migraine and secondly, whether the content of AP4A was changed by beta-adrenoceptor blockade. No significant difference in platelet dense granule content of AP4A, was observed between 10 migraine patients and 10 normal controls. Both metoprolol, a beta 1-selective blocker and propranolol, a non-selective beta-blocker significantly decreased the migraine attack rate. However, while propranolol significantly reduced the platelet content of AP4A, metoprolol did not. Therefore, the present data suggest that platelet dense granule release, as estimated by the content of AP4A is not of major importance in migraine.

Inhibition of RNA synthesis by deoxyadenosine plus deoxycoformycin in resting lymphocytes.

Deoxyadenosine has been implicated in the lymphocytopenia that occurs in immunodeficient children with an inherited deficiency of adenosine deaminase (ADA) and in leukemic patients treated with the ADA inhibitor deoxycoformycin. The recent reports of deoxyadenosine toxicity to nondividing lymphocytes indicates a challenge to the mechanism for deoxyadenosine toxicity, which involves the inhibition of ribonucleotide reductase by dATP, leading to the inhibition of DNA synthesis. This study provides evidence for the inhibition of transcription by deoxyadenosine as an alternative mechanism of toxicity. The incubation of resting peripheral blood lymphocytes with deoxyadenosine plus deoxycoformycin led to an inhibition of uridine incorporation. The extent of inhibition increased with the increasing time of incubation and concentration of deoxyadenosine. Replacement of deoxyadenosine with other nucleosides, adenosine or deoxyguanosine, had no effect, suggesting that deoxyadenosine-induced inhibition was not due to the reduced transport of uridine. Separation of DNA from RNA by differential alkaline hydrolysis showed that the reduction of uridine incorporation was primarily in the RNA fraction. The time sequence of the reduction in uridine incorporation coincided with that of the accumulation of dATP, but preceded that of ATP depletion and cell lysis. The phosphorylation of uridine into UTP was slightly reduced by deoxyadenosine, but this could not entirely account for the reduced incorporation of uridine into RNA. Finally, the direct measurement of RNA synthesis by the incorporation of UTP into isolated nuclei showed that RNA synthesis was inhibited to 88% and 41% of control values in lymphocytes preincubated with 20 microM deoxyadenosine for 3 and 15 hr, respectively. These findings demonstrate that deoxyadenosine plus deoxycoformycin inhibits RNA synthesis in resting lymphocytes.