Uracil Concentrations Research Articles

Feasibility of Measuring 5-Fluorouracil Catabolic Potential by Oral Loading

The efficacy of 5-fluorouracil (5-FU) treatment and the incidence of adverse events differ among patients and depend to some extent on individual variations in drug catabolism. This feasibility study aimed to determine the optimum conditions for a 5-FU oral load test, which would allow the simple evaluation of individual differences in 5-FU catabolism. Patients with colon cancer were given oral 5-FU (200 mg/day) for 3 days (n = 36) or a single 100 mg dose (n = 14). Serum concentrations of uracil, dihydrouracil, 5-FU and 5-fluoro-5,6-dihydrouracil were measured before and after 5-FU administration. The results suggested that a decline in 5-FU metabolism was associated with continuous administration and increasing age. We conclude that a continuous load of 5-FU is necessary in order to predict the efficacy and side-effects of the drug. The 3-day regimen, with its ease of administration, merits further study to assess its possible clinical application.

Post mortem degradation of nucleosides in the brain: Comparison of human and rat brains for estimation of in vivo concentration of nucleosides

There is an increasing attention paid for nucleoside metabolism and changes of nucleoside concentrations in human brain because of its pathological and physiological relevance. In order to determine the post mortem degradation of nucleosides and nucleoside metabolites, the concentrations of four nucleosides and three nucleobases were measured in rat and neurosurgical human cerebral cortical samples with 30 s to 24 h post mortem delay. Adenosine degradation coefficient (a multiplying factor for calculating concentrations of investigated substances for the living state) was 0.886 for human brain at 2 h post mortem time, while it was 1.976 for rats. Hypoxanthine, an adenosine degradation product had coefficients 0.564 for human brain and 0.812 for the rat brain. We provide data and degradation coefficients for the concentrations of adenosine, guanosine, inosine, uridine, uracil, hypoxanthine and xanthine with 2, 4, 6 and 24 h post mortem delay. We also report a method how to validate human neurosurgical brain samples in terms of sample preparation and statistical analysis.

Urinary uracil in female patients with ornithine transcarbamylase deficiency

Female patients with ornithine transcarbamylase deficiency (OTCD) show a wide range of clinical severity, from asymptomatic to lethal hyperammonemia. It is important to establish a simple method to distinguish symptomatic from asymptomatic patients. Uracil and orotic acid concentrations were analyzed in three female patients with OTCD at both the hyperammonemia-attack and interval stages. These concentrations were compared with those in asymptomatic female patients reported previously. Uracil concentrations in symptomatic female patients were uniformly higher than those in asymptomatic female patients at both the hyperammonemia-attack and interval stages. Uracil may present a useful index for detecting OTCD female patients who are destined to suffer from hyperammonemia attack. Further data on uracil concentrations are necessary to establish the threshold for distinguishing symptomatic from asymptomatic subjects.

Abstracts of papers presented at the Nordic Drosophila Meeting 1994, sponsored by Nordic Academy for Advanced Study (NorFA) and the University of Copenhagen August 13-16, 1994, Kristiansminde/Sorø, Denmark

Abstracts of papers presented at the Nordic Drosophila Meeting 1994, sponsored by Nordic Academy for Advanced Study (NorFA) and the University of Copenhagen August 13-16, 1994, Kristiansminde/Sorø, Denmark

Quantification of 5,6-dihydrouracil by HPLC-electrospray tandem mass spectrometry.

In humans, the pathway for the catabolism of uracil and thymine consists of three consecutive steps. Dihydropyrimidine dehydrogenase catalyzes the reduction of uracil and thymine to 5,6-dihydrouracil and 5,6-dihydrothymine, respectively. The second step is catalyzed by dihydropyrimidinase and consists of reversible hydrolysis of 5,6-dihydrouracil and 5,6-dihydrothymine to N -carbamyl-β-alanine and N -carbamyl-β-aminoisobutyric acid, respectively. Finally, β-ureidopropionase catalyzes the conversion of N -carbamyl-β-alanine and N -carbamyl-β-aminoisobutyric acid to β-alanine and β-aminoisobutyric acid, respectively, ammonia, and CO2. Patients with a defect in one of the enzymes of the pyrimidine degradation pathway can be diagnosed by an aberrant excretion profile of the pyrimidine bases and their degradation products in urine (1). For example, in patients with a complete deficiency of dihydropyrimidinase, highly increased concentrations of 5,6-dihydrouracil and 5,6-dihydrothymine and moderately increased concentrations of uracil and thymine can be detected in urine. It has also …

Plasma concentrations of 5-fluorouracil and F-beta-alanine following oral administration of S-1, a dihydropyrimidine dehydrogenase inhibitory fluoropyrimidine, as compared with protracted venous infusion of 5-fluorouracil.

The pharmacokinetics and pharmacodynamics of oral S-1, a dihydropyrimidine dehydrogenase (DPD) inhibitory fluoropyrimidine, were compared with those of protracted venous infusion (PVI) of 5-fluorouracil (5-FU). In all, 10 patients with gastric cancer received PVI of 5-FU at a dose of 250 mg m−2 day−1 for 5 days. After a washout period of 9 days, the patients received two divided doses daily for 28 days. S-1 was administered orally at about 0900 and 1900 hours. The daily dose of S-1 in terms of tegafur was 80 mg day−1 in patients with a body surface area (BSA) of <1.25 m2, 100 mg day−1 in those with a BSA of ⩾1.25 m2 to <1.5 m2, and 120 mg day−1 in those with a BSA of ⩾1.5 m2. Plasma concentrations of 5-FU and F-β-alanine (FBAL) were measured for pharmacokinetic analysis, and the plasma uracil concentration was monitored as a surrogate marker of DPD inhibition (pharmacodynamic analysis) in the same patients on days 1–5 of PVI of 5-FU and on days 1–5 of oral S-1. The area under the curve (AUC0–10 h) of 5-FU on day 5 was 728±113 ng h ml−1 for PVI of 5-FU and 1364±374 ng h ml−1 for S-1. The median 5-FU PVI : S-1 ratio of the AUC0–10 h of 5-FU was 1.9. The AUC0–10 h of FBAL on day 5 of PVI of 5-FU was 9465±3225 ng h ml−1, AUC0–10 h, as compared with 1725±605 ng h ml−1 on day 5 of S-1 treatment. The AUC0–10 h of uracil on day 5 was 252±60 ng h ml−1 with PVI of 5-FU and 12 582±3060 ng h ml−1 with S-1. The AUC0–10 h of FBAL was markedly lower and plasma uracil concentrations were significantly higher for S-1 than for PVI of 5-FU, clearly demonstrating the effect of DPD inhibition.

5-Chlorouracil, a Marker of DNA Damage from Hypochlorous Acid during Inflammation: A GAS CHROMATOGRAPHY-MASS SPECTROMETRY ASSAY

Hypochlorous acid (HOCl), generated from H2O2 and Cl- by myeloperoxidase in activated neutrophils, causes tissue damage during inflammation. We have developed a simple, sensitive (approximately 0.2 fmol on column) and specific GC-MS assay for the detection of 5-chlorouracil (5-ClUra), a signature product of HOCl-mediated damage to nucleobases. In this assay, 5-ClUra is released from isolated DNA by a digestion with nuclease P1, alkaline phosphatase, and thymidine phosphorylase (TP), or from chlorinated nucleosides in biological fluids by TP. The freed 5-ClUra is derivatized with 3, 5-bis-(trifluoromethyl)-benzyl bromide, which is detected by negative chemical ionization mass spectrometry. The assay can be used to simultaneously detect other halogenated uracils including bromouracil. Using this assay, we showed that 5-ClUra is generated by the reaction of low micromolar HOCl with (deoxy)cytidine, (deoxy)uridine, and DNA. In cell cultures, an increase of 5-ClUra was detected in DNA when cells were treated with sublethal doses of HOCl and allowed to proliferate. The elevation of 5-ClUra was markedly accentuated when physiologically relevant concentrations of (deoxy)uridine, (deoxy) cytidine, uracil, or cytosine were present in the medium during HOCl treatment. In the carrageenan-induced inflammation model in rats, chlorinated nucleosides was significantly increased, compared with controls, in the exudate fluid isolated from the inflammation site. Our study provides the direct evidence that chlorinated nucleosides are found in the inflammation site and can be incorporated in DNA during cell/tissue proliferation. These findings may be relevant to the carcinogenesis associated with chronic inflammation.

Adsorption kinetics of uracil on bismuth single crystal planes

The electrochemical impedance method has been used for the quantitative study of uracil adsorption kinetics at the bismuth single crystal plane ∣ aqueous Na 2SO 4 solution interface. Analysis of impedance data demonstrates that the adsorption process of uracil is complicated and limited by the mixed kinetics, i.e. by the slow adsorption and diffusion steps. Analysis of the Cole–Cole and other dependences indicates that, at small frequencies and higher uracil concentrations, two-dimensional association of the uracil molecules is possible. Nonlinear regression analysis has been used for fitting the experimental complex plane ( Z″, Z′) plots. The classical Frumkin–Melik-Gaikazyan circuit in the region of higher ac frequencies and lower uracil concentrations ( c uracil≤2×10 −3 M), and the modified Frumkin–Melik-Gaikazyan equivalent circuit (taking into account the inhomogeneous semi-infinite diffusion) at c uracil≥2×10 −3 M fit with a reasonable accuracy the experimental Z″, Z′-plots. It was found that the values of the double layer capacitance, partial charge transfer resistance, adsorption capacitance and Warburg-like diffusion impedance depend noticeably on the electrode potential and concentration of uracil. Other more complicated equivalent circuits have been used for fitting the experimental impedance data.

Modulation of the pharmacokinetics of endogenous plasma uridine by 5-(phenylthio)acyclouridine, a uridine phosphorylase inhibitor: implications for chemotherapy.

The purpose of this investigation was to evaluate the ability of oral PTAU, 5-(phenylthio)acyclouridine, to increase the concentration of endogenous plasma uridine. PTAU is a new potent and specific inhibitor of uridine phosphorylase (UrdPase, EC 2.4.2.3), the enzyme responsible for uridine catabolism. This compound was designed as a lipophilic inhibitor in order to facilitate its access to the liver and intestine, the main organs involved in uridine catabolism. PTAU was administered to mice orally and parenterally. The plasma levels of PTAU as well as those of uridine and its catabolite uracil were measured by HPLC, and pharmacokinetic analysis was performed. PTAU was fully adsorbed after oral administration (over 100% oral bioavailability) and no PTAU metabolites were detected. PTAU administered orally had no apparent toxicity at doses up to 120 mg/kg per day for 5 days. Parenteral administration of PTAU at 30, 45 and 60 mg/kg increased the concentration of endogenous plasma uridine (1.8 +/- 0.2 microM) by approximately six-, seven-, and nine-fold, respectively. Plasma uridine concentration remained higher than control values until 8 h after PTAU administration. Similar results were obtained following oral administration of PTAU. The baseline concentrations of endogenous plasma uridine were increased by approximately six-, seven- and ten-fold by oral administration of PTAU at 30, 45 and 60 mg/kg, respectively, and remained higher than the controls until 8 h after PTAU administration. PTAU did not alter the concentration of endogenous plasma uracil. The effectiveness of the PTAU in elevating and sustaining high plasma uridine concentrations may be useful in rescuing or protecting the host from toxicities of various chemotherapeutic pyrimidine analogues as well as in the management of medical disorders that respond to the administration of uridine.

Adsorption of nucleic acid constituent uracil on copper(II)-loaded, solid peat and soil-derived humic acids

Humic acids (HA) in compost, peats and soils sorb organic compounds selectively. This paper investigates the micro- and macroscopic properties of solid HAs isolated from a German peat (GHA) and a New Hampshire soil (NHA) using tightly bound copper(II) and nucleic acid constituent uracil adsorption as analytical probes. Isotherm measurements at 5.0–35.0°C show that tightly bound Cu(II) decreases the amount of uracil adsorbed by GHA at mM or lower uracil concentrations whereas previous work revealed the opposite effect for bound Hg(II). Site capacity comparisons are consistent with lower coordination numbers for HA-bound Hg(II) than for HA-bound Cu(II). Low coordination numbers leave Hg(II) sites open for uracil binding. Enthalpy and entropy changes for uracil adsorption on GHA, NHA, their Cu(II) and Hg(II)-loaded forms and on compost-derived HA are linearly correlated, indicating that HAs are free energy buffers. Water and bound metals evidently play major roles in HA-solute interactions and in HA aggregation/disaggregation. Key words: Humic acids, metal binding, nucleic acid constituents, uracil, adsorption, isotherms, thermodynamics

Oral uracil and Ftorafur plus leucovorin: pharmacokinetics and toxicity in patients with metastatic cancer.

To assess the pharmacokinetics of Ftorafur (tegafur, FT), 5-fluorouracil (5-FU), and uracil in 31 cancer patients who were enrolled in phase I studies of oral uracil and FT (UFT). The correlation between pharmacokinetic parameters and toxic effects of UFT was evaluated. Uracil and FT were orally administered in a 4:1 molar ratio at FT doses of 200-400 mg/m2 per day. Patients also received leucovorin at 150 mg/day. Daily doses were divided into three doses and administered at 8-h intervals for 28 consecutive days. Plasma FT concentrations were measured by high-performance liquid chromatography, and plasma 5-FU and uracil concentrations were determined using gas chromatography-mass spectrometry. National Institutes of Health Common Toxicity Criteria were used for assessment of toxicity. The concentrations of FT, 5-FU, and uracil showed wide interpatient variations. Maximum plasma concentrations (Cp(max)) of all three compounds were achieved in 0.3 to 4.0 h. At the various study doses, the terminal half-life (t 1/2beta) of FT ranged from 3.9 to 5.9 h, the area under the concentration-versus-time curve (AUC0-6h) ranged from 16,220 to 52,446 (ng/ml)h, the total clearance (ClT) ranged from 100 to 175 ml/min, and the steady-state volume of distribution (Vd(ss)) ranged from 18.3 to 28.7 l. The 5-FU generated from FT had an apparent distribution half-life (t 1/2alpha) and an apparent elimination half-life (t 1/2beta) of 0.3-1.3 h and 4.9-7.0 h, respectively. The AUC0-6h of 5-FU ranged from 120 to 325 (ng/ml)h. Uracil had a t 1/2alpha of 0.2-0.5 h and the level quickly returned to the endogenous level. The AUC0-6h for uracil ranged from 605 to 3764 (ng/ml)h, the ClT ranged from 3225 to 7748 ml/min, and the Vd(ss) ranged from 341 to 1354 l. The Cp(max) and AUC0-6h of both FT and uracil were significantly correlated with FT doses (P-values of 0.0244 and 0.0112) and with uracil doses (P-values of 0.0346 and 0.0083), respectively. In addition to interpatient variations, intrapatient variations were also observed in six patients who had pharmacology studies done on days 1 and 26+/-2 at the same study dose. We found that the repeated treatment with UFT caused cumulative increases in the values of Cp(max), Ctrough, and AUC0-6h of FT and 5-FU. The major toxic effects observed were diarrhea and nausea and vomiting. The occurrence of these toxic effects correlated significantly with the Cp(max) and AUC0-6h of 5-FU. The pharmacology studies showed that FT and uracil were readily absorbed orally and that FT was rapidly converted to 5-FU. The preliminary findings suggest that determination of plasma levels of 5-FU after oral administration of UFT may help predict subsequent toxic effects.

Modulation of plasma uridine concentration by 5-(phenylselenenyl)acyclouridine, an inhibitor of uridine phosphorylase: relevance to chemotherapy.

The purpose of this investigation was to evaluate the efficacy of oral 5-(phenylselenenyl)-acyclouridine (PSAU) in increasing endogenous plasma uridine concentration as well as its ability to improve the bioavailability of oral uridine. PSAU is a new potent and specific inhibitor of uridine phosphorylase (Urd-Pase, EC 2.4.2.3), the enzyme responsible for uridine catabolism. This compound was designed as a lipophilic inhibitor in order to facilitate its access to the liver and intestine, the main organs involved in uridine catabolism. Oral PSAU was administered orally to mice alone or with uridine. The plasma levels of PSAU as well as uridine and its catabolites were measured using high-performance liquid chromatography and pharmacokinetic analysis was performed. PSAU has an oral bioavailability of 100% and no PSAU metabolites were detected. PSAU has no apparent toxicity at high doses. Oral administration of PSAU at 30 and 120 mg/kg increased baseline concentration of endogenous plasma uridine (2.6 +/- 0.7 microM) by 3.2- and 8.7-fold, respectively, and remained three- and six-fold higher, respectively, than the controls for over 8 h. PSAU, however, did not alter the concentration of endogenous plasma uracil. Co-administration of PSAU with uridine elevated the concentration of plasma uridine over that resulting from the administration of either alone, and reduced the peak plasma concentration (C(max)) and area under the curve (AUC) of plasma uracil. Co-administration of PSAU at 30 mg/kg and 120 mg/kg improved the low bioavailability of oral uridine (7.7%) administered at 1,320 mg/kg by 4.8- and 4.2-fold, respectively, and reduced the AUC of plasma uracil from 1,421 to 787 micromol/h x l and 273 micromol/h x l, respectively. Similar results were observed when PSAU was co-administered with lower doses of uridine. Oral PSAU at 30 mg/kg and 120 mg/kg improved the bioavailability of oral 330 mg/kg uridine by 5.2- and 8.9-fold, and that of oral 660 mg/kg uridine by 6.4- and 9.0-fold, respectively. However, the reduction in the AUC values of plasma uracil was less dramatic than that seen when the high dose of 1,320 mg/kg uridine was used. The effectiveness of the PSAU plus uridine combination in elevating and sustaining high plasma uridine concentration may be useful to rescue or protect from host toxicity of various chemotherapeutic pyrimidine analogs as well as in the management of medical disorders that are remedied by administration of uridine.

Effect of TEI-6720, a Xanthine Oxidase Inhibitor, on the Nucleoside Transport in the Lung Cancer Cell Line A549

To examine the effect of 2-(3-cyano-4-isobutoxyphenyl)-4-methyl-5-thiazolecarboxylic acid (TEI-6720), an inhibitor of xanthine oxidase, on purine metabolism in the lung cancer cell line A549, the activities of adenosine deaminase, purine nucleoside phosphorylase, adenine phosphoribosyltransferase, hypoxanthine guanine phosphoribosyltransferase, xanthine oxidase, and guanase together with pyrimidine nucleoside phosphorylase were measured with or without the addition of TEI-6720, and the extracellular concentrations of hypoxanthine, xanthine, inosine, uracil, and uridine were measured after the addition of inosine or uridine to the incubation medium with or without TEI-6720. Moreover, the Na-indepenent nucleoside transport was determined in A549 cells with or without TEI-6720. TEI-6720 inhibited the activity of xanthine oxidase in A549 cells, but did not affect other enzymes. During incubation, TEI-6720 not only prevented a decrease in the inosine concentration in inosine-containing medium, but also a decrease in the uridine concentration in uridine-containing medium. Furthermore, the Na-independent transport of uridine was inhibited by TEI-6720 with a K_i value of 4.1 μmol/l. These results indicate that TEI-6720 is an inhibitor of the Na-independent nucleoside transport of uridine and inosine, as well as xanthine oxidase.

Determination of urinary orotic acid and uracil by capillary zone electrophoresis

We describe a simple method for measuring orotic acid and uracil concentration in urine by capillary zone electrophoresis in 20 m M Na-borate buffer, pH 9.2. The method was applied for studying a patient with HHH (hyperornithinemia, hyperammonemia and homocitrullinuria) syndrome. A high value of uracil excretion was found during periods of relatively low orotic acid excretion and normal ammonemia. The orotic acid level in urine was increased by increasing protein intake.

Severe 5-fluorouracil-related toxicity in a Japanese patient with dihydropyrimidine dehydrogenase deficiency

Dihydropyrimidine dehydrogenase (DPD) is the major enzyme involved in the catabolism of pyrimidines and fluoropyrimidines. Severe 5-fluorouracil (5-FU) toxicity has been reported in patients with DPD deficiency in Western countries. We now report a case of 5-FU-related severe toxicity in a Japanese patient with DPD deficiency. A-44 year-old woman with gastric cancer associated with peritoneal dissemination underwent palliative gastrectomy at the Tochigi Cancer Center. After surgery, she was treated with a combination of mitomycin C (12.5 mg/m2, bolus iv) and 5-FU (312.5 mg/m2 per day, continuous infusion). Eight days after commencement, the chemotherapy was discontinued because of severe gastrointestinal toxicity. On day 12 the patient developed a high fever with granulocytopenia (617.4 granulocytes/μl). DPD-activity in peripheral blood mononuclear cells (PBMC) was extremely low (up to 8.9 pmol/mg protein per min) and serum and urine uracil concentrations were high, at 225.2 ng/ml and 2334.2 ng/mg creatinine, respectively. To our knowledge, this appears to be the first case of 5-FU-related severe toxicity due to DPD deficiency reported in a Japanese patient.

Properties of uracil transport by vegetative mycelium of Trichoderma viride

The transport of radioactively labelled uracil into submerged mycelium of T. viride was measured by means of a membrane filtration technique. It was found to be time-dependent (up to 90 min) and concentration-dependent (up to 8 mmol l −1). Its concentration dependence was biphasic and consisted from the saturatable part (at the uracil concentration below 0.2 mmol l −1) with K M=0.08±0.02 mmol l −1 and V max=1.74±0.3 nmol (mg dry wt.) −1 h −1, and from the region at higher uracil concentration which showed only a weak saturatability with the substrate. The transport measured in the saturatable part of the curve was also pH- and temperature-dependent. The optimal pH was between 5.4 and 6.4 and the optimal temperature was at 37°C. The activation energy of 54 kJ mol −1 and the temperature quotient of Q 10=2.1 could be calculated from the temperature dependence. The entry of uracil was in part inhibited by nucleobases and their analogues, nucleosides, nucleotides and amino acids. The inhibitors had similar inhibitory efficiency about 50% at 0.2 mmol l −1. 3,3′,4′,5-tetrachlorosalicylanilide (TCS), the uncoupling agent, significantly inhibited the uracil transport, but its inhibitory efficiency decreased upon increasing the uracil concentration. Ionophore antibiotics valinomycin and monensin also inhibited the uracil transport. Inhibitors of RNA-polymerase, rifamycin and rifampicin were without effect. The results suggest that at low uracil concentrations (below 0.2 mmol l −1), its transport is mediated by a carrier and is driven by the electrochemical potential of protons. At higher uracil concentrations, the transport may be driven by the concentration difference of uracil with the contribution of the proton-motive force. It is feasible that inhibitors of uracil transport tested exert their inhibition by the dissipation of the driving force rather than by the direct competition with the substrate-binding site.

Properties of uracil transport by vegetative mycelium of Trichoderma viride.

The transport of radioactively labelled uracil into submerged mycelium of T. viride was measured by means of a membrane filtration technique. It was found to be time-dependent (up to 90 min) and concentration-dependent (up to 8 mmol l-1). Its concentration dependence was biphasic and consisted from the saturatable part (at the uracil concentration below 0.2 mmol l-1) with KM = 0.08 +/- 0.02 mmol l-1 and Vmax = 1.74 +/- 0.3 nmol (mg dry wt.)-1 h-1, and from the region at higher uracil concentration which showed only a weak saturatability with the substrate. The transport measured in the saturatable part of the curve was also pH- and temperature-dependent. The optimal pH was between 5.4 and 6.4 and the optimal temperature was at 37 degrees C. The activation energy of 54 kJ mol-1 and the temperature quotient of Q10 = 2.1 could be calculated from the temperature dependence. The entry of uracil was in part inhibited by nucleobases and their analogues, nucleosides, nucleotides and amino acids. The inhibitors had similar inhibitory efficiency about 50% at 0.2 mmol l-1. 3,3',4',5-tetrachlorosalicylanilide (TCS), the uncoupling agent, significantly inhibited the uracil transport, but its inhibitory efficiency decreased upon increasing the uracil concentration. Ionophore antibiotics valinomycin and monensin also inhibited the uracil transport. Inhibitors of RNA-polymerase, rifamycin and rifampicin were without effect. The results suggest that at low uracil concentrations (below 0.2 mmol l-1), its transport is mediated by a carrier and is driven by the electrochemical potential of protons. At higher uracil concentrations, the transport may be driven by the concentration difference of uracil with the contribution of the protonmotive force. It is feasible that inhibitors of uracil transport tested exert their inhibition by the dissipation of the driving force rather than by the direct competition with the substrate-binding site.

Phase I Trial ofU racil-Tegafur (UFT) plus Oral Leucovorin: 28-Day Schedule

UFT [Taiho Pharmaceutical Co. Ltd., Tokyo, Japan; (BMS-200604), Bristol-Myers Squibb, Princeton, NJ], a fluorouracil prodrug, is an oral 4:1 molar concentration of uracil plus tegafur. This study examined the dose-limiting toxic effects and maximum tolerated dose of UFT plus leucovorin administered for 28 consecutive days followed by a 7-day rest period. A course of therapy was repeated every 35 days. UFT dose levels examined were 200 mg/m2/day, with planned escalations to 250, 300, 350, and 400 mg/m2/day; the leucovorin dose remained at 150 mg/day. Three patients were initially enrolled at each UFT dose level. The total daily doses of both UFT and leucovorin were divided into three doses administered every 8 hr. Diarrhea became the dose-limiting toxicity at 400 mg/m2/day UFT, with grade 3 diarrhea noted in 2 of the 3 patients receiving that dose. To further define a phase II UFT starting dose, 3 additional patients were entered at the 350 mg/m2 level; 3 of the 6 patients treated at this level developed grade 3 nonhematological toxic effects. No partial or complete responses were observed. The recommended phase II UFT starting dose is 300 mg/m2/day plus 150 mg/day leucovorin. Since neutropenia, significant mucositis, and “hand-foot syndrome“ were not observed with UFT plus leucovorin, the toxicity profile of this regimen appears favorable compared with that of intravenous regimens of fluorouracil plus leucovorin. This phase I trial of UFT served as the basis for a phase II trial, current phase III trials, and a national adjuvant therapy trial of UFT for high-risk colon cancer patients.

Adsorption of Aqueous Nucleobases, Nucleosides, and Nucleotides on Humic Acids. 3. Adsorption of Uracil, Uridine, and Uridine-5‘-Monophosphate on a German Peat-Derived Humic Acid and Its Tightly Bound Mercury(II) Form

Aqueous nucleic acid constituents uracil, uridine, and uridine-5‘-monophosphate are selectively adsorbed by a solid German peat-derived humic acid (GHA) and its tightly bound mercury(II) form (MGHA). Adsorption isotherms with GHA and MGHA adsorbents were obtained at 19 solute concentrations from 0 to 1.20 mM and seven fixed temperatures from 5.0 to 35.0 °C. Langmuir data analysis indicates that adsorption occurs in sequential steps A, B, and C, depending on the solute and experimental conditions. MGHA very strongly adsorbs low concentrations of uracil and site capacity vA for uracil adsorption on MGHA in step A increases with increasing temperature. The last steps of adsorption of relatively high concentrations of uridine, and uridine-5‘-monophosphate on MGHA are S-curves ascribed to increasing site capacity with increasing solute concentration. Comparison of the new data for adsorbents GHA and MGHA with data for adsorption of uracil, uridine, and uridine-5‘-monophosphate on compost-derived humic acid (CHA) from part 1 reveals similarities and differences. Nevertheless, linear plots of adsorption enthalpies vs entropies in all detected steps with CHA, GHA, and MGHA as adsorbents indicate that selective adsorption of nucleic acid constituents on different HAs is free energy buffered by similar mechanisms.

Urinary uracil concentrations are a useful guide to genetic disorders associated with neurological deficits and abnormal pyrimidine metabolism.

AbstractElevated urinary uracil concentrations are characteristic of genetic deficiencies of enzymes catalysing the first two steps of the pyrimidine degradative pathway (Van Gennip et al 1993), dihydropyrimidine dehydrogenase (DPD) and dihydropyrimidinase (DHP). DPD is rate limiting for the whole pathway. Homozygotes are detected by the raised levels of uracil and thymine in urine. The pyrimidine synthetic route shares a common intermediate. carbamoyl phosphate, with the urea cycle. In urea‐cycle disorders such as ornithine carbamoyltransferase (OCT) deficiency, orotic aciduria resulting from an increased flux through the pathway has been used to detect hemizygotes or carriers following a protein, or more recently, an allopurinol load (Sebesta et al 1994). This paper demonstrates that uracil may be an even more useful guide to OCT carrier status and compares urinary uracil with concentrations found in genetic pyrimidine defects associated with neurological deficits.