Reverse phase partition HPLC for determination of plasma purines and pyrimidines in subjects with gout and renal failure

Separation of ribonucleotides, deoxynucleotides, cyclic nucleotides and deoxycyclic nucleotides by reversed-phase high-performance liquid chromatography

A reversed-phase gradient elution system with methanol-triethylammonium phosphate buffer (83.3 mM, pH 6.0) as eluent on C(18)-bonded silica is described for the separation of 38 ribonucleotides, deoxynucleotides, cyclic nucleotides and deoxycyclic nucleotides in less than 33 min. The retention of the nucleotides can be precisely controlled by adjusting the pH, buffer concentration and methanol content in the mobile phase. The system is especially useful for the analysis of low levels of cyclic nucleotides in cells and tissues.

Physiological concentrations of purines and pyrimidines

The concentrations of bases, nucleosides, and nucleosides mono-, di- and tri-phosphate are compared for about 600 published values. The data are predominantly from mammalian cells and fluids. For the most important ribonucleotides, average concentrations +/- SD (microM) are: ATP, 3,152 +/- 1,698; GTP, 468 +/- 224; UTP, 567 +/- 460 and CTP, 278 +/- 242. For deoxynucleosides-triphosphate (dNTP), the concentrations in dividing cells are: dATP, 24 +/- 22; dGTP, 5.2 +/- 4.5; dCTP, 29 +/- 19 and dTTP 37 +/- 30. By comparison, dUTP is usually about 0.2 microM. For the 4 dNTPs, tumor cells have concentrations of 6-11 fold over normal cells, and for the 4 NTPs, tumor cells also have concentrations 1.2-5 fold over the normal cells. By comparison, the concentrations of NTPs are significantly lower in various types of blood cells. The average concentration of bases and nucleosides in plasma and other extracellular fluids is generally in the range of 0.4-6 microM; these values are usually lower than corresponding intracellular concentrations. For phosphate compounds, average cellular concentrations are: Pi, 4400; ribose-1-P, 55; ribose-5-P, 70 and P-ribose-PP, 9.0. The metal ion magnesium, important for coordinating phosphates in nucleotides, has values (mM) of: free Mg2+, 1.1; complexed-Mg, 8.0. Consideration of experiments on the intracellular compartmentation of nucleotides shows support for this process between the cytoplasm and mitochondria, but not between the cytoplasm and the nucleus.

Quantitation of hypoxanthine in plasma from patients with ischemic heart disease: adaption of a high-performance liquid chromatographic method

A high-performance liquid chromatographic method is described for the separation and quantitation of several purine compounds, including hypoxanthine. The isocratic separation of a standard mixture of nine compounds is achieved within 20 min on a reversed-phase Nucleosil 100-5C18 column, with a mobile phase of KH2PO4 (300 mM, pH 4.0)-methanol-acetonitrile-tetrahydrofuran (97.9:1:1:0.1, v/v). Uric acid, guanine, hypoxanthine, uridine, xanthine, allopurinol, inosine, guanosine and 7-methylxanthine were almost completely baseline-separated, with detection limits in the range 0.5-1.2 pmol per injection. The influence of the concentrations of buffer and tetrahydrofuran on the quality of separation are described. The within-day and the day-to-day precision were satisfactory (e.g. coefficients of variation of less than 1.5 and ca. 6.0%, respectively, for peak heights). The recovery of [3H]hypoxanthine added to samples was 86 +/- 1%. Hypoxanthine was quantified in human plasma samples obtained at various times during coronary artery bypass grafting. The hypoxanthine levels measured immediately after release of the aortic cross-clamp were significantly higher than those determined under control conditions (18.8 +/- 7.0 and 3.4 +/- 1.0 microM, respectively).

A novel mechanism for the generation of superoxide anions in hematoporphyrin derivative-mediated cutaneous photosensitization. Activation of the xanthine oxidase pathway

Prior studies, both in vitro and in vivo, have suggested that cutaneous porphyrin photosensitization requires the generation of superoxide anion (.O2-) and various other reactive oxygen metabolites. No unifying concept has emerged, however, that unequivocally demonstrates the source of generation of these species. Since xanthine oxidase is known to generate .O2- in reperfused ischemic tissue and in certain inflammatory disorders, we attempted to assess its role in porphyrin photosensitization. C3H mice were rendered photosensitive by the intraperitoneal administration of dihematoporphyrin ether (DHE) (5 mg/kg) followed by irradiation with visible light. Murine ear swelling was used as a marker of the acute photosensitization response and involvement of oxygen radicals was evaluated using electron spin resonance (ESR) spectroscopy. The administration of allopurinol, a potent inhibitor of xanthine oxidase, afforded 90% protection against DHE-mediated acute photosensitivity in vivo. Furthermore, xanthine oxidase activity was twofold higher in the skin of photosensitized mice than in unirradiated animals. ESR spectra of 5,5-dimethyl-1-pyrroline N-oxide-trapped radicals from the skin of photosensitized mice verified the presence of .O2- and .OH, while neither of these species was detected in the skin of control mice or mice receiving allopurinol. The administration of a soybean trypsin inhibitor or verapamil before irradiation also partially blocked the photosensitivity response, suggesting that calcium-dependent proteases play a role in the activation of xanthine oxidase in this photodynamic process. These data provide in vivo evidence for the involvement of .O2- in DHE-mediated cutaneous photosensitization and suggest that these radicals are generated through the activation of the xanthine oxidase pathway. The administration of allopurinol and calcium channel blockers may thus offer new approaches for the treatment of cutaneous porphyrin photosensitization.

The excretion of oxypurines in normal subjects

Reverse phase high performance liquid chromatography was used for the determination of urinary hypoxanthine and xanthine in normal subjects. The values observed in normal subjects agree with those reported by other authors. Excretion of hypoxanthine and xanthine was not related to sex. Urinary oxypurines were related to age, and, when corrected for body surface area (1.73 m2), they were significantly higher in normal children under 15 years of age than in adults.

Renal excretion of hypoxanthine and xanthine in primary gout

PURPOSE

The renal excretion of uric acid is usually diminished in primary gout with respect to increased serum urate levels. To determine whether the renal excretion of uric acid precursors, hypoxanthine and xanthine, is also abnormal in primary gout, the concentrations of these purines were measured in plasma and 24-hour urine samples in normal subjects, in patients with primary gout and uric acid underexcretion, and in patients with enzyme deficiencies that are known to result in over-production of uric acid.

SUBJECTS AND METHODS

Three groups of subjects were studied: Group I consisted of 10 ambulatory healthy normal men; Group II consisted of 15 patients in whom primary gout was diagnosed; and Group III consisted of 10 patients with various enzyme defects known to produce an excessive synthesis of uric acid. In each subject, plasma and 24-hour urinary uric acid, hypoxanthine, xanthine, and creatinine concentrations were measured and the mean of three consecutive determinations was used. The fractional excretion of purine compounds was calculated from a formula. Hypoxanthine phosphoribosyltransferase, adenine phosphoribosyltransferase, and hemoglobin were also measured in each subject.

RESULTS

Plasma hypoxanthine and xanthine were increased in the two groups of patients compared with the control subjects. Urinary hypoxanthine and xanthine levels were reduced in gouty patients compared with control subjects, whereas levels were increased in patients with uric acid overproduction. A positive correlation was found between the renal clearances of uric acid, hypoxanthine, and xanthine.

CONCLUSION

The results indicate that the renal excretion of hypoxanthine and xanthine is severely impaired in most patients with primary gout.

Hypoxanthine, xanthine and uridine in body fluids, indicators of ATP depletion

Measurements of hyp, xan and urd in body fluids can provide evidence of energy, ATP, depletion in the body, in organs or in cells. Such information is clinically useful in the many diseases in which cellular energy supplies cannot be maintained like perinatal asphyxia, hydrocephalus and vascular insufficiency in brain, heart, limbs, kidneys or other organs. Similar HPLC methods using reversed-phase C18 columns and quantitation by UV absorption have been employed in a variety of centres to yield almost identical results. These have been assembled in this review to form a series of reference values. The current analytical problems are reviewed. Since concentrations of hyp and xan may alter independently situations are discussed in which separate measurements rather than their summed, total oxypurine concentrations are needed. The biochemistry and physiology underlying the use of such analyses is examined to guide sampling of the appropriate body fluid at a relevant time and to avoid oversimplified interpretation of results as well as unnecessary arguments. Specifically: (1) Intracellular concentrations of hyp and xan are inversely related to adenylate energy change and therefore to the energy currency of the cell ATP. Uridine in tissues is similarly 'controlled'. (2) There is extensive evidence that large increases in hyp, xan and urd in body fluids indicate ATP depletion. (3) Small changes in hyp probably reflect alterations of ATP turnover. (4) Xanthine arises mainly from guanine and can change independently of hyp. (5) Clinically useful information is obtainable from hyp and xan concentrations in CSF, amniotic fluid, urine and plasma. Extensive clinical correlations are reviewed. At present we are in a development phase for which HPLC is ideal but the most efficient way to perform and use such analyses in routine clinical practice remains to be established.

Effects of chronic allopurinol therapy on purine metabolism in Duchenne muscular dystrophy

Adenine, adenosine, inosine, hypoxanthine, xanthosine, xanthine, guanine and guanosine blood levels in 11 Duchenne muscular dystrophy patients treated with allopurinol, 10 untreated patients and 8 healthy controls, were determined by HPLC. Serum ADA, PNP and 5'-NT were also determined. Untreated patients showed lower adenine (p less than 0.001) and higher adenosine, xanthine, ADA and PNP levels (p less than 0.01) than controls. Treated patients had lower adenine and higher xanthine levels (p less than 0.001), but higher hypoxanthine, xanthosine and guanine levels (p less than 0.001), than controls, with normal ADA and PNP. The changes observed in ADA and PNP levels suggest an involvement of these enzymes in accelerated degradation of purines in Duchenne dystrophy.

Micellar liquid chromatography for the analysis of nucleosides and bases

A new high-performance liquid chromatographic method for the analysis of nucleosides and bases was developed in which a micellar mobile phase is used. Separation was achieved on a polyvinyl alcohol (PVA) column by isocratic elution with micellar sodium dodecyl sulfate (SDS) as the mobile phase. The retention behavior of the nucleosides and bases was significantly different from that obtained by reversed-phase chromatography. Effect of pH, temperature, and concentration of SDS and the counter ion (Na+) on retention behavior were investigated. With the PVA column, the best conditions for an isocratic separation were 0.01 M SDS (pH 3.4) and a flow-rate of 2 ml/min at ambient temperature. Mechanisms for the retention of the nucleosides and bases on the PVA column with a micellar mobile phase were proposed and an application of the separation was demonstrated by the analysis of human serum.

High-performance liquid chromatographic profiling of nucleic acid components in physiological samples

The papers reviewed represent recent progress in HPLC profiling of nucleic acid components in physiological samples. Each method was designed for a particular application and possesses certain inherent advantages and/or disadvantages. Many methods are simply modifications of previous procedures. Although some methodologies appear to be superior to others, there is no "best" method for universal usage. The analyst must use the procedure which is best suited for the particular application at hand. This review is meant to be a starting point for the chromatographer who is comparing and evaluating HPLC methods for a given application.

Reversed-phase high-performance liquid chromatographic investigation of mucosal nucleosides and bases and urinary modified nucleosides of gastrointestinal cancer patients

Reversed-phase high-performance liquid chromatography (HPLC) was used to determine the levels of nucleosides, bases and their metabolites in perchloric acid extracts of gastrointestinal mucosa. By comparing the levels of these compounds in the normal portion with the neoplastic portion of mucosa resected from malignant cancer patients, it was found that there was significant elevation of the uracil level in the neoplastic mucosa of all eight patients with colorectal cancer (2.7-fold in normal mucosa), but only in the neoplastic mucosa of one out of four patients with gastric cancer. The levels of hypoxanthine and uridine in the colorectal cancer mucosa samples and the inosine in gastric cancer samples were also significantly higher than those in normal mucosa. The urinary modified nucleosides were prefractionated with a boronate affinity gel column, and their levels were determined by the same HPLC method. There was no significant difference in the concentrations of pseudouridine, 1-methylguanosine N2-methylguanosine and N2,N2-dimethylguanosine between urine samples taken before and after surgery from eight patients with malignant colorectal cancer. Contrary to other reports, no significant differences in modified nucleoside levels were observed between urine samples from patients with colorectal cancer and those from normal subjects.

Fluorometric determination of hypoxanthine and xanthine in biological fluids by high-performance liquid chromatography using enzyme reactors

A selective and sensitive assay of hypoxanthine and xanthine in biological fluids by high-performance liquid chromatography coupled with immobilized-enzyme reactors was developed. The separations were achieved by reversed-phase liquid chromatography. Hydrogen peroxide produced from hypoxanthine and xanthine by immobilized xanthine oxidase was determined fluorometrically using immobilized peroxidase and p-hydroxyphenylacetic acid. Immobilized enzymes were prepared by intermolecular cross-linking to controlled-pore glass. Assay of allopurinol was also possible by the present method. The method was applied to serum and urine. The detection limits of hypoxanthine and xanthine were approximately 50 and 120 pg per injection, respectively.

Alterations in purine salvage and hypoxanthine levels in granulation tissue during skin wound repair

We report the levels of hypoxanthine in rabbit skin granulation tissue, harvested at different postwound intervals and from various locations within the wounds. The effect of full-thickness autogenous skin grafts on hypoxanthine levels has also been examined. The levels of inosine, xanthine, adenosine 5'-monophosphate, and inosine 5'-monophosphate are reported as well. The correlation between the level of these compounds and the healing process suggests they may be useful indicators of the extent of tissue damage.

Oxypurines in cerebrospinal fluid as indices of disturbed brain metabolism. A clinical study of ischemic brain diseases

Using a HPLC method the concentrations of oxypurines were simultaneously measured in CSF of patients with acute cerebrovascular lesions (CVL) and global cerebral ischemia (GCI) in an attempt to study disturbed brain metabolism during cerebral oxygen deprivation. In cerebral infarction both hypoxanthine and xanthine gradually increased from normal levels at admission to pathologically increased on the fourth day from onset of symptoms. There was no correlation between these substances and the clinical score but the maximum CSF-hypoxanthine concentration was significantly correlated to the maximum lesion volume determined by computerized tomography. In GCI the hypoxanthine-xanthine concentrations were considerably increased less than 20 hours from onset of unconsciousness but the initial levels did not predict the final outcome. These findings suggest that the end products of nucleotide degradation accumulate rapidly in acute cerebral hypoxia but more gradually in CVL probably due to growing local edema with subsequent local hypoxia. In controls and patients with CVL the CSF-urate concentrations were positively correlated to those of CSF-albumin. However, in CVL the increase of urate was relatively much more pronounced than the increase of albumin indicating that urate is a sensitive marker of dysfunction of blood-brain barrier.

Hypoxanthine and xanthine levels determined by high-performance liquid chromatography in plasma, erythrocyte, and urine samples from healthy subjects: the problem of hypoxanthine level evolution as a function of time

The levels of hypoxanthine and xanthine are determined in plasma, erythrocyte, and urine samples by a reverse-phase high-performance liquid chromatographic (HPLC) method. The hypoxanthine concentration increases in erythrocyte and plasma samples when whole blood is stored at room temperature between sampling and centrifugation. Furthermore, the hypoxanthine concentration increases in erythrocyte samples when they are kept apart at room temperature before analysis, whereas the plasma hypoxanthine level remains constant. This result proves an endogenous formation of hypoxanthine in erythrocytes with time, at room temperature. These studies show the necessity of rigorous conditions for the collection, transport, and treatment of blood samples. In order to achieve accurate results, the blood must be centrifuged immediately after collection. The erythrocyte and plasma samples must be stored frozen until deproteinization and HPLC analysis. Under these conditions, the concentrations of hypoxanthine and xanthine in plasma are 2.5 +/- 1 and 1.4 +/- 0.7 microM, respectively. In erythrocyte samples, hypoxanthine concentration reaches 8.0 +/- 6.2 microM.

High-performance liquid chromatographic determination of hypoxanthine and xanthine in biological fluids

A rapid and selective reversed-phase high-performance liquid chromatographic method for the simultaneous determination of hypoxanthine and xanthine in biological fluids was developed. The identification of hypoxanthine and xanthine was confirmed by xanthine oxidase reaction. This method was applied to the investigation of purine metabolism in subjects with xanthine oxidase deficiency or gout. Hypoxanthine concentrations three to ten times higher than those determined in plasma were found in erythrocyte samples from normal subjects and from patients with xanthine oxidase deficiency or hyperuricemia under allopurinol therapy.

HPLC analysis of aromatic amino acids, nucleosides, and bases in plasma of acute lymphocytic leukemia on chemotherapy

Plasma chromatograms--obtained by the reversed-phase mode of high performance liquid chromatography (HPLC)--of 19 subjects with acute lymphocytic leukemia (ALL) were compared to those of 19 normal individuals. ALL patients were in remission and on a methotrexate and 6-mercaptopurine maintenance regimen. The concentrations of the aromatic amino acids L-phenylalanine and L-tyrosine, the nucleosides uridine, adenosine, inosine, and guanosine, as well as the bases hypoxanthine and xanthine, were elevated in the leukemic in comparison to the normal chromatograms. Highest inosine levels corresponded to leukemic subjects whose condition severely deteriorated with time. Patients with lower inosine levels are still in continuous remission.

Hypoxanthine production by ischemic heart demonstrated by high pressure liquid chromatography of blood purine nucleosides and oxypurines

An isocratic high pressure liquid chromatographic system was developed for the estimation of purine nucleosides and oxypurines in blood. Use was made of a reversed-phase column. Nucleotides derived from erythrocytes affected the separation; these compounds were removed with A12O3. The recovery of the whole clean-up procedure exceeded 75%, and the lower detection limit of the assay for blood metabolites was 0.1 mumol/l. In 6 healthy volunteers, non-resting, the following blood concentrations (mean values +/- S.D. in mumol/l) were observed: adenosine (less than 0.1), inosine (0.2 +/- 0.1), hypoxanthine (2.2 +/- 1.3) and xanthine (0.2 +/- 0.1). In plasma and serum the total amount of these compounds was 1.9 and 5.4 times higher, respectively, presumably due to nucleotide breakdown during blood processing. The myocardial arterial-venous differences of blood purine nucleosides, oxypurines and lactate were subsequently measured in blood samples from 13 patients with angiographically documented ischemic heart disease, undergoing an atrial pacing stress test. No significant release of adenosine, inosine and xanthine by the heart was detectable in this study. The myocardial arterial-venous difference of lactate changed from 0.01 +/- 0.03 mmol/l (mean +/- SEM) at rest, to -0.10 +/- 0.04 mmol/l during pacing (p less than 0.002). Relatively larger changes were observed for hypoxanthine: pacing increased the arterial-venous difference from -0.01 +/- 0.05 to -0.51 +/- 0.17 mumol/l (p less than 0.02). We conclude that the high pressure liquid chromatographic assay of blood hypoxanthine is a useful tool in the diagnosis of ischemic heart disease.