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

Changes of nucleotide patterns in liver, muscle and blood during the growth of Ehrlich ascites cells: application of the reversed-phase and ion-pair reversed-phase high-performance liquid chromatography with radial compression column

The pool of purine compounds was analysed in liver, skeletal muscle and blood of mice during the growth of Ehrlich ascites tumour cells. Three fast isocratic high-performance liquid chromatographic methods were used. (1) Determination of nucleotides by an isocratic ion-pair reversed-phase chromatography with a 10 mM ammonium phosphate buffer containing acetonitrile and tetrabutylammonium phosphate. (2) Separation of nucleosides and nucleobases in cell extracts by a reversed-phase system with methanol and 50 mM potassium phosphate buffer as eluent. (3) Nucleosides and nucleobases in body fluids were analysed by a reversed-phase system with 10 mM potassium phosphate containing methanol. These methods allow the rapid determination of purine compounds in small biological samples from various cell types and body fluids, with high accuracy and sensitivity. The pool of cellular nucleotides increased during the exponential phase of tumour growth. Adenosine accumulated significantly in all tissues in the stationary phase of tumour growth.

Muscle ATP loss and lactate accumulation at different work intensities in the exercising Thoroughbred horse

The effect of 2 min treadmill exercise, at speeds of 6-12 m.s-1 on an incline of 5 degrees, upon muscle adenine nucleotide loss and lactate accumulation was studied in six Thoroughbred horses. Minimal change occurred in the adenosine triphosphate (ATP) content of the middle gluteal muscle at speeds of 10 m.s-1 or less, but significant loss (up to 47%) had occurred in all horses by 12 m.s-1. The decline in ATP significantly correlated with the accumulation of muscle lactate, beginning shortly after the accumulation of 40 mmol.kg-1 dry muscle lactate. Decline in muscle ATP was mirrored closely by the appearance of ammonia, and to a lesser extent, hypoxanthine and uric acid in plasma. The results suggest that peak accumulation of any of these, or simply the concentration at a specified recovery time, may be used as a measure of ATP loss in the musculature as a whole. This was not so in the case of xanthine, which may also be formed from the degradation of guanidine nucleotides. An In-In plot of plasma ammonia against treadmill speed indicated a break point in accumulation between 8 and 9 m.s-1. The kinetics of ammonia accumulation with speed differed from those of lactate.

The pathogenesis of the Lesch-Nyhan syndrome: ATP use is positively related to hypoxanthine supply to hypoxanthine guanine phosphoribosyltransferase

In order to explain features of severe hypoxanthine guanine phosphoribosyltransferase (HPRT) deficiency, the Lesch-Nyhan syndrome, a continuous supply of substrate, hypoxanthine, for the enzyme must be generated. This supply must be increased in association with increased ATP turnover. We have shown that ATP turnover continuously supplies hypoxanthine for recycling by the enzyme HPRT and that this supply increases curvilinearly with increasing ATP turnover. The effects of increasing exercise on ATP turnover were examined using a Latin square experimental design. The outputs of hypoxanthine, xanthine, urate and creatinine were measured. The data were then examined statistically.

Adenine nucleotide depletion from endothelial cells exposed to xanthine oxidase

Hypoxia causes breakdown of cellular nucleotides, accumulation of hypoxanthine (HX), and conversion of xanthine dehydrogenase into xanthine oxidase (XO). Upon reoxygenation, the HX-XO reaction generates free radicals, one potential mechanism of tissue damage. Because endothelial cells contain XO and are exposed to circulating HX, they are a likely target for damage. We studied the effect of XO and/or HX at physiologically relevant concentrations on nucleotide metabolism of cultured endothelial cells from human umbilical veins. Cells were labeled with [14C]adenine and incubated for up to 6 h with HX, XO, or both, in the absence or presence of serum. Adenine nucleotides from cell extracts and nucleotide breakdown products (HX, xanthine, and urate) from the medium were separated and counted. HX alone had no effect. XO (80 mU/ml) alone caused a 70% (no serum) or 40% (with serum) fall in adenine nucleotides and an equivalent increase of xanthine and urate. The combination of HX and XO caused a 90% (no serum) or 70% (with serum) decrease in nucleotides, decrease in energy charge, and detachment of cells from the culture plate. Nucleotide depletion was not accounted for by proteolytic activity in the XO preparation. Albumin was only half as effective as serum in preventing nucleotide loss. Thus exogenous XO, in the presence of endogenous HX, triggers adenine nucleotide catabolism, but endogenous XO activity is too low to influence nucleotide levels even at high exogenous HX concentrations. Serum limits the catabolic effect of XO and thus protects cells from free radical damage.

Erythrocyte nucleotide stability and plasma hypoxanthine concentrations: improved ATP stability with short-term storage at room temperature

We have measured erythrocyte nucleotide concentrations at timed intervals over 24 h in heparinised blood stored at 4 degrees C, room temperature, or 37 degrees C. The objective was to determine whether the grossly altered NAD concentrations found in the erythrocytes of patients with two different inherited purine disorders could be related to altered stability or turnover rates. An unexpected finding was the improved stability of all erythrocyte nucleotides in blood stored at room temperature compared with 4 degrees C. Not only was the breakdown of ATP greater at 4 degrees C compared with room temperature, higher hypoxanthine concentrations were present in the plasma associated with a fictitious increment in inosine. NAD and NADP, by contrast, showed remarkable stability in both control and patient erythrocytes, irrespective of their original value. Although these studies failed to establish an explanation for the altered NAD levels in the patients, the superior ATP stability in blood stored at room temperature in the erythrocytes from both patients and controls suggests that current practices of storing blood on ice for short-term studies require re-evaluation.

Plasma and blood assay of xanthine and hypoxanthine by gas chromatography-mass spectrometry: physiological variations in humans

Plasma and blood xanthine and hypoxanthine levels were assayed using a sensitive and specific method involving gas chromatography-mass spectrometry, associated with an optimized sample preparation procedure. Physiological variation was studied in 224 subjects with no purine metabolism disorders. An age dependency for both compounds was found, comparable with that known for uric acid. The mean plasma levels for the 224 subjects were 0.65 +/- 0.24 microM for xanthine and 1.65 +/- 0.78 microM for hypoxanthine. Corresponding mean blood levels were 0.59 +/- 0.21 microM for xanthine and 1.72 +/- 0.74 microM for hypoxanthine. Plasma and blood levels were significantly different, by ca. 10%. Rapid in vitro release of hypoxanthine from erythrocytes and continuation of intraerythrocytal metabolism lead to overestimation exceeding 10% within half an hour after sample blood collection. Hence samples must be deproteinized promptly. Blood can therefore be conveniently used for oxypurine assay instead of plasma when prompt spinning of samples is difficult to manage, as is usually encountered in clinical practice.

Identification of hypoxanthine and inosine in brain dialyzable fraction as stimulators for growth of porcine aortic endothelial cells in response to fibroblast growth factor in either dialyzed serum media or low serum media

The rate of proliferation of porcine aortic endothelial cells (PAEC) in response to fibroblast growth factor (FGF) was largely retarded when incubated in Dulbecco's modified Eagle's medium (DMEM) supplemented with either 1% fetal bovine serum (FBS) or 10% dialyzed FBS in place of 10% FBS. Proliferation of endothelial cells in low serum media in response to FGF was enhanced to the level of media containing FGF plus 10% FBS by the addition of the dialyzable fraction from bovine brain homogenates. From the bovine brain dialyzable fraction, two active components were purified and identified as hypoxanthine and inosine. Either hypoxanthine or inosine, at a dose of 5 microM in DMEM with 1% FBS, maximally increased the incorporation of [3H]thymidine into DNA of PAEC in low serum media in the presence of FGF. However, no additive effect was observed when hypoxanthine and inosine were added simultaneously. The present data indicate that the proliferative action of FGF on PAEC can be potentiated by hypoxanthine and inosine.

Release of purine and pyrimidine nucleosides and their catabolites from the perfused rat hindlimb in response to noradrenaline, vasopressin, angiotensin II and sciatic-nerve stimulation

Uric acid and uracil were released at constant rates (0.95 and 0.4 nmol/min per g respectively) by the perfused rat hindlimb. Noradrenaline, vasopressin or angiotensin II further increased the release of these substances 2-5-fold, coinciding with increases in both perfusion pressure (vasoconstriction) and O2 uptake. The hindlimb also released, but in lesser amounts, uridine, hypoxanthine, xanthine, inosine and guanosine, and all but hypoxanthine and guanosine were increased during intense vasoconstriction. Uric acid and uracil releases were increased by noradrenaline in a dose-dependent manner. However, the release of these substances did not fully correspond with the dose-dependent increase in O2 uptake and perfusion pressure, where changes in the latter occurred at lower doses of noradrenaline. Sciatic-nerve stimulation (skeletal-muscle contraction) did not increase the release of uracil, uric acid or uridine, but instead increased the release of inosine (7-fold) and hypoxanthine (2-fold). Since the UTP content as well as the UTP/ATP ratio are higher in smooth muscle than in skeletal muscle, it is proposed that release of uric acid and uracil arises from increased metabolism of the respective adenosine and uridine nucleotides during intense constriction of smooth muscle.

Hypoxanthine phosphoribosyltransferase activity in tissues and hypoxanthine concentrations in plasma and CSF of the horse in comparison with other species

1. Plasma hypoxanthine and xanthine concentrations are very low in the horse and low in rat, mouse and greyhound compared to concentrations in beagles, man, sheep and rabbit. 2. Activities in erythrocytes of the main enzyme metabolizing hypoxanthine, hypoxanthine phosphori-bosyltransferase, show a similar pattern (Tax et al., 1976, Comp. Biochem. Physiol. 54B, 209-212); thus low activities have been found where plasma concentrations were low. 3. Hypoxanthine phosphoribosyltransferase activities in horse tissue other than erythrocytes are similar to those in man and rabbit with high activities in brain; this enzyme may therefore be functionally important in equine brain.

Retention of in vivo antipyrimidine effects of Brequinar sodium (DUP-785; NSC 368390) in murine liver, bone marrow and colon cancer

Brequinar sodium (DUP-785) is a potent inhibitor of the pyrimidine de novo enzyme, dihydroorotic acid dehydrogenase (DHO-DH). In order to determine whether in vitro data could be extrapolated to the in vivo situation we investigated antipyrimidine effects of DUP-785 in mice bearing colon cancer. Two tumor models were used, Colon 26 and Colon 38, resistant and moderately sensitive to DUP-785, respectively. DUP-785 at 50 mg/kg caused a depletion of plasma uridine in mice, and depleted tissue uridine levels in Colon 38 down to 10%, which was retained for several days; in Colon 26 the decrease was less and tissue uridine levels recovered rapidly. In livers of these mice no significant effect on uridine was observed. DUP-785 depleted UTP in bone marrow cells within 2 hr to 25% of control levels, after 4 days normal levels were found. In livers of both Balb-c mice (bearing Colon 26) and C57Bl/6 mice (bearing Colon 38) a small decrease of uridine nucleotide pools was found. In Colon 26 DUP-785 increased uridine nucleotide pools to 170% after 2 hr, at 1 day normal levels were observed, but after 2 days again an increase was found. In Colon 38 DUP-785 decreased the uridine nucleotide pool by 50% after 1 and 2 days. DUP-785 did not affect cytidine nucleotide pools of livers and of Colon 26 and Colon 38. The ratio between uridine nucleotides and cytidine nucleotides decreased from 2.2 to 0.90 in Colon 38, in the other tissues the decrease was less. DHO-DH was measured in bone marrow cells and Colon 26 and 38 before and after treatment. Basal levels of DHO-DH were 3 times higher in Colon 26 than in Colon 38. In treated tumors DHO-DH was initially inhibited by more than 90%, after 7 days enzyme activity in Colon 26 was 50% and in Colon 38 about 200% of basal levels. In bone marrow cells DHO-DH was also rapidly inhibited but recovered within 4 days. It is concluded that the retention of antipyrimidine effects of DUP-785 in Colon 38 were more pronounced than in Colon 26, which is in agreement with the better antitumor effect of DUP-785 in Colon 38.

Fibroblast growth factor-stimulated growth of porcine aortic endothelial cells depends on hypoxanthine in fetal bovine serum in culture media

The rate of proliferation of porcine aortic endothelial cells (PAEC) in response to stimulation of fibroblast growth factors (FGFs) was largely retarded in media supplemented with 10% dialyzed fetal bovine serum (FBS) in place of nondialyzed FBS. This inhibition was overcome by supplement of dialyzable fraction, and hypoxanthine was purified from the dialyzable fraction as the active compound which stimulated the basal and FGF-dependent growth rates of dialyzed FBS-treated PAEC. Addition of hypoxanthine (5 microM) to media with 10% dialyzed FBS containing FGFs (10 ng/ml) markedly increased the rate of both cell proliferation and DNA synthesis of PAEC, and their maximal levels were comparable to those attained by cells in media with 10% nondialyzed FBS. Hypoxanthine changed the spindle-like morphology of dialyzed FBS-treated PAEC even in the presence of FGFs into the cobblestone-like morphology of regular PAEC in media with 10% FBS.