Isocratic separation of ATP and its degradation products from biological fluids by automated liquid chromatography

Two groups of metabolites (a) IMP, AMP, ADP, ATP, and cAMP in extracts of fibroblasts and erythrocytes and (b) hypoxanthine, xanthine, adenosine, and inosine in plasma and urine have been separated by ion-pairing reversed-phase chromatography on a microBondapak C18 column, with use of the following reagents: 60 mmol/L KH2PO4, 0.45 mmol/L tetrabutylammonium phosphate, and 1.26 mol/L acetonitrile, pH 3.2 (at 23 degrees C) (group a) and 20 mmol/L KH2PO4, 0.45 mmol/L tetrabutylammonium phosphate, and 0.35 mol/L acetonitrile, pH 2.70 (at 24 degrees C) (group b). Under both sets of conditions, the compounds are completely separated in less than 15 min. The separation is isocratic, so the method is easily adaptable to automation.

Isocratic separation of ATP and its degradation products from biological fluids by automated liquid chromatography

Two groups of metabolites (a) IMP, AMP, ADP, ATP, and cAMP in extracts of fibroblasts and erythrocytes and (b) hypoxanthine, xanthine, adenosine, and inosine in plasma and urine have been separated by ion-pairing reversed-phase chromatography on a microBondapak C18 column, with use of the following reagents: 60 mmol/L KH2PO4, 0.45 mmol/L tetrabutylammonium phosphate, and 1.26 mol/L acetonitrile, pH 3.2 (at 23 degrees C) (group a) and 20 mmol/L KH2PO4, 0.45 mmol/L tetrabutylammonium phosphate, and 0.35 mol/L acetonitrile, pH 2.70 (at 24 degrees C) (group b). Under both sets of conditions, the compounds are completely separated in less than 15 min. The separation is isocratic, so the method is easily adaptable to automation.

The arthropathy of Wilson's disease: clinical and pathologic features

Twenty-two patients with Wilson's disease were evaluated for arthropathy with history, examination, and radiographs. Knee arthroscopy with cartilage and synovial biopsies was performed in 4 patients. Radiologic findings were minimal, including osteophytes, subchondral cysts, and joint space narrowing. Chondrocalcinosis was observed in 3 patients. Cartilage and synovial biopsies studied by energy dispersive elemental analysis showed copper and sulfur diffusely throughout cartilage in 2 of 4 patients. No crystals were found. The finding of copper in cartilage biopsies suggests that copper deposition may be a factor in the etiology of arthropathy, although definitive studies remain to be performed.

Deferoxamine induced decreases of lipid peroxides in rheumatoid arthritis

Eleven patients with rheumatoid arthritis (RA) were treated with intraarticular deferoxamine or placebo to test the hypothesis that iron chelation decreased hydroxyl radical mediated lipid peroxidation in RA. Intraarticular administration of deferoxamine 100 mg resulted in predominantly systemic effects with decreased serum ferritin and decreased serum levels of lipid peroxidation products. Similar changes were not detected in synovial fluid at this dose. Iron chelation with deferoxamine may provide a novel approach to preventing tissue injury in RA by inhibiting hydroxyl radical production and lipid peroxidation.

Radiologic features of a pyrophosphate-like arthropathy associated with long-term dialysis

In a series of 28 long-term dialysis patients with musculoskeletal complaints, the radiologic findings in six cases resembled those occurring in the arthropathy of idiopathic calcium pyrophosphate dihydrate deposition (CPPD) disease. These findings included osteophytes, subchondral cysts, and cartilage loss in the metacarpophalangeal joints, patellofemoral joints, wrists, and shoulders. Chondrocalcinosis was present in three of the six cases. There were no significant differences in renal function or levels of serum calcium, phosphorus, iron, ferritin, aluminum, or parathormone between these patients and a control group matched for sex and age. Long-term dialysis may be associated with a metabolic arthritis similar to the arthritis which occurs in CPPD deposition disease. The etiology may include deposition of CPPD crystals, hydroxyapatite, or other calcium-containing substances in joints, or it may be related to a number of dialysis-induced metabolic abnormalities.

Hereditary xanthinuria. Evidence for enhanced hypoxanthine salvage

We tested the hypothesis that there is an enhanced rate of hypoxanthine salvage in two siblings with hereditary xanthinuria. We radiolabeled the adenine nucleotide pool with [8-14C]adenine and examined purine nucleotide degradation after intravenous fructose. The cumulative excretion of radioactivity during a 5-d period was 9.7% and 9.1% of infused radioactivity in the enzyme-deficient patients and 6.0 +/- 0.7% (mean +/- SE) in four normal subjects. Fructose infusion increased urinary radioactivity to 7.96 and 9.16 X 10(6) cpm/g creatinine in both patients and to 4.73 +/- 0.69 X 10(6) cpm/g creatinine in controls. The infusion of fructose increased total urinary purine excretion to a mean of 487% from low-normal baseline values in the patients and to 398 +/- 86% in control subjects. In the enzyme-deficient patients, the infusion of fructose elicited an increase of plasma guanosine from undetectable values to 0.7 and 0.9 microM. With adjustments made for intestinal purine loss, these data support the hypothesis that there is enhanced hypoxanthine salvage in hereditary xanthinuria. Degradation of guanine nucleotides to xanthine bypasses the hypoxanthine salvage pathway and may explain the predominance of this urinary purine compound in xanthinuria.

Increased body fluid purine levels during hypotensive events. Evidence for ATP degradation

Tissue ischemia leads to adenosine triphosphate (ATP) breakdown with elevation of body fluid ATP metabolites. This study tests the hypothesis that there is a direct relationship between periods of hypotension and body fluid uric acid and oxypurine levels in 19 prospectively studied patients. Significant elevations in urine oxypurine/creatinine clearance were found during periods of hypotension as compared with nonhypotensive periods (p less than 0.05). During severe episodes of hypotension, the serum urate level was significantly elevated as well (p less than 0.05). The increase in these body fluid products of ATP degradation may reflect cellular ischemia during hypotensive periods. There was a weak correlation (r = -0.31, p less than 0.001) between the systolic blood pressure and urine oxypurine/creatinine clearance. However, variability in the appearance of body fluid ATP breakdown products during episodes of hypotension suggests the interplay of multiple factors in the degradation of ATP. The use of ATP degradation products to quantitate the physiologic significance of clinical events remains tantalizing but not proved.

Inhibition of guinea-pig oxyntic cell function by adenosine and prostaglandins

Adenosine and prostaglandins (PGs) are known inhibitors of oxyntic cell function. Using quantitative cytochemistry of hydroxyl ion production (HIP) in guinea-pig oxyntic cells, we examined the effects of adenosine and PGs on secretagogue-stimulated HIP. Adenosine (10(-6) M) inhibited the actions of histamine (10(-14) M) and gastrin (2.5 X 10(-12) M) by 69 and 67%, respectively, but not that of dibutyryl cyclic AMP (10(-16) M) or carbachol (10(-9) M). These observations suggest that adenosine does not influence the Ca++-dependent pathway of carbachol action and that the adenosine activity precedes the generation of cyclic AMP. Adenosine and related analogs, N6-L-phenylisopropyladenosine and 5-N-ethylcarboxam-idoadenosine (10(-12) to 10(-14) M), inhibited histamine-stimulated HIP (10(-14) M) in the following order: N6-L-phenylisopropyladenosine greater than 5-N-ethylcarboxamidoadenosine greater than adenosin. The adenosine antagonist, 1,3-diethylphenylxanthine (10(-6) M), reversed the inhibitory effects of adenosine. Exogenous PGE2 (10(-6) M) also inhibited histamine- and gastrin-stimulated HIP by 65 and 55%, respectively. Indomethacin (10(-6) M) and flurbiprofen (10(-6) M), PG synthesis inhibitors, potentiated the action of histamine by 175 and 159%, respectively. Adenosine was incapable of reversing this potentiated effect. These data indicate that adenosine and related analogs are inhibitors of oxyntic cell HIP and suggest that these biological properties are mediated by binding to a cell surface receptor and thereby regulating oxyntic cell adenylate cyclase activity. The more potent properties of N6-L-phenylisopropyladenosine as compared to 5-N-ethylcarboxamidoadenosine are consistent with activity at the high-affinity surface adenosine receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Human placental cytoplasmic 5'-nucleotidase. Kinetic properties and inhibition

The kinetic properties of highly purified human placental cytoplasmic 5'-nucleotidase were investigated. Initial velocity studies gave Michaelis constants for AMP, IMP, and CMP of 18, 30, and 2.2 microM, respectively. The enzyme shows the following relative Vmax values: CMP greater than UMP greater than dUMP greater than GMP greater than AMP greater than dCMP greater than IMP. The activity was magnesium-dependent, and this cation binds sequentially with a Km of 14 microM for AMP and an apparent Km of 6 mM for magnesium. A large variety of purine, pyrimidine, and pyridine compounds exert an inhibitory effect on enzyme activity. IMP, GMP, and NADH produce almost 100% inhibition at 1.0 mM. Nucleoside di- and triphosphates are potent inhibitors. ATP and ADP are competitive inhibitors with respect to AMP and IMP as substrates with Ki values of 100 and 15 microM, respectively. Inorganic phosphate is a noncompetitive inhibitor with Ki values of 19 and 43 mM. Nucleosides and other compounds studied produce only a modest decrease of enzyme activity at 1 mM. Our findings suggest that the enzyme is regulated under physiological conditions by the concentrations of magnesium, nucleoside 5'-monophosphates, and nucleoside di- and triphosphates. The nucleotide pool concentration regulates the enzyme possibly by a mechanism of heterogeneous metabolic pool inhibition. These properties of human placental cytoplasmic 5'-nucleotidase may be related to the control of nucleotide degradation in vivo.

Characteristics of high affinity and low affinity adenosine binding sites in human cerebral cortex

The binding characteristics of human brain cortical membrane fractions were evaluated to test the hypothesis that there are A1 and A2 adenosine binding sites. The ligands used were 2-chloro[8-3H]adenosine and N6-[adenine-2,8-3H]cyclohexyladenosine. Binding of chloroadenosine to human brain cortical membranes was time dependent, reversible and concentration dependent. The Kd calculated for chloroadenosine by Scatchard analysis of equilibrium data was 280 nM, with a Bmax of 1.6 pmoles/mg protein, suggesting a single class of binding sites. The specificity of chloroadenosine binding was assessed by the ability of adenosine analogs to compete for binding sites. Using this approach, the apparent Kd was estimated to be 0.74 microM for 5'-N-ethyl-carboxamideadenosine, 1 microM cyclohexyladenosine, and 13 microM for N6-(L-2-phenylisopropyl)adenosine. Isobutylmethylxanthine and theophylline, receptor antagonists, had apparent Kd values of 84 microM and 105 microM, respectively. Hill slope factors ranged from 0.3 to 0.6. Chloroadenosine binding to human brain cortical membranes approached equilibrium at 90 minutes, with a T1/2 of 10 minutes. The kob was 0.080 min-1 and the k1 was 7.5 X 10(4) min-1 M-1. Reversibility of chloroadenosine binding at equilibrium was completed at approximately 10 minutes with a k2 value of 0.074 min-1. The Kd calculated from the rate constants was 990 nM. Cyclohexyladenosine binding was concentration dependent. The Kd calculated for cyclohexyladenosine via Scatchard analysis of equilibrium data was 5 nM with a Bmax of 0.35 pmoles/mg protein. Cyclohexyladenosine binding was displaced by 3 known receptor agonists: N6-(L-2-phenyliso propyl)adenosine (Kd 4 nM), 2-chloroadenosine (Kd 10 nM) and 5H-N-ethyl-carboxamideadenosine (Kd 6 nM). The apparent Kd values for the agonists were 1 to 3 orders of magnitude lower with this ligand as compared to radioactive chloroadenosine. Binding was also displaced by 2 known antagonists, isobutylmethylxanthine and theophylline, with apparent Kd values of 4 microM and 8 microM, respectively. Hill slope factors ranged from 0.5 to 0.8. Our data support the existence of two adenosine binding sites in human cortex compatible with the low affinity (A2) and high affinity (A1) adenosine receptors.

Regulation of deoxyadenosine and nucleoside analog phosphorylation by human placental adenosine kinase

The enzymes responsible for phosphorylation of adenosine and nucleoside analogs are important in the pathogenesis of adenosine deaminase deficiency and for the activation of specific anticancer and antiviral drugs. We examined the role of adenosine kinase in catalyzing these reactions using an enzyme purified 4000-fold (2.1 umol/min/mg) from human placenta. The Km values of adenosine and ATP are 135 uM and 4 uM, respectively. Adenosine kinase phosphorylates adenine arabinoside with an apparent Km value of 1 mM using adenosine kinase assay conditions. The Km values for 6-methylmercaptopurine riboside and 5-iodotubercidin, substrates for adenosine kinase, are estimated to be 4.5 uM and 2.6 nM, respectively. These data indicate that dadenosine phosphorylation by adenosine kinase is primarily regulated by its Km, and the concentrations of Mg2+, ADP and AMP. The high Km values for phosphorylation of dadenosine and adenine arabinoside suggest that adenosine kinase may be less likely to phosphorylate these nucleosides in vivo than other enzymes with lower Km values. Adenosine kinase appears to be important for adenosine analog phosphorylation where the Michaelis constant is in the low micromolar range.

Duchenne muscular dystrophy: normal ATP turnover in cultured cells

We examined ATP metabolism in cultured muscle cells and fibroblasts from patients with Duchenne dystrophy. ATP and ADP levels were the same in cultured cells from normal subjects and patients and there was no difference in ATP synthesis or degradation. Although there was a significant decrease in radioactively labelled ATP after incubation with deoxyglucose in Duchenne muscle cells, there was no difference in ATP concentration or ADP metabolism.

Regulation of deoxyadenosine and nucleoside analog phosphorylation by human placental adenosine kinase

The enzymes responsible for the phosphorylation of deoxyadenosine and nucleoside analogs are important in the pathogenesis of adenosine deaminase deficiency and in the activation of specific anticancer and antiviral drugs. We examined the role of adenosine kinase in catalyzing these reactions using an enzyme purified 4000-fold (2.1 mumol/min/mg) from human placenta. The Km values of deoxyadenosine and ATP are 135 and 4 microM, respectively. Potassium and magnesium are absolute requirements for deoxyadenosine phosphorylation, and 150 mM potassium and 5 mM MgCl2 are critical for linear kinetics. With only 0.4 mM MgCl2 in excess of ATP levels, the Km for deoxyadenosine is increased 10-fold. ADP is a competitive inhibitor with a Ki of 13 microM with variable MgATP2-, while it is a mixed inhibitor with a Ki and Ki' of 600 and 92 microM, respectively, when deoxyadenosine is variable. AMP is a mixed inhibitor with Ki and Ki' of 177 and 15 microM, respectively, with variable deoxyadenosine; it is a non-competitive inhibitor with a Ki of 17 microM and Ki' of 27 microM with variable ATP. Adenosine kinase phosphorylates adenine arabinoside with an apparent Km of 1 mM using deoxyadenosine kinase assay conditions. The Km values for 6-methylmercaptopurine riboside and 5-iodotubercidin, substrates for adenosine kinase, are estimated to be 4.5 microM and 2.6 nM, respectively. Other nucleoside analogs are potent inhibitors of deoxyadenosine phosphorylation, but their status as substrates remains unknown. These data indicate that deoxyadenosine phosphorylation by adenosine kinase is primarily regulated by its Km and the concentrations of Mg2+, ADP, and AMP. The high Km values for phosphorylation of deoxyadenosine and adenine arabinoside suggest that adenosine kinase may be less likely to phosphorylate these nucleosides in vivo than other enzymes with lower Km values. Adenosine kinase appears to be important for adenosine analog phosphorylation where the Michaelis constant is in the low micromolar range.

Evidence for adenosine triphosphate degradation in critically-ill patients

Alterations of cellular energy metabolism may provide important markers during the clinical course of critically ill patients. To determine whether adenosine triphosphate (ATP) degradation occurs in critically ill patients, we measured levels of adenosine, inosine, hypoxanthine, and xanthine in 18 patients and seven control subjects. The mean concentration of hypoxanthine (3.8 microM) in the critically ill patients was elevated (p less than 0.01) compared to that of our control population (0.1 microM). A subgroup of seven critically ill patients had levels of hypoxanthine, xanthine, or inosine higher than those of any member of the control group. This subgroup was characterized by a lower systolic blood pressure, an increased requirement for vasopressors, and a markedly decreased survival rate when compared to the other critically ill patients. Arterial and mixed venous blood gas values were not helpful in predicting survival and did not correlate with levels of ATP degradation products. In two patients who showed subsequent clinical improvement, the initially elevated levels of hypoxanthine and xanthine returned to normal. This study indicates that critically ill patients have elevated levels of ATP degradation products. These increased levels may indicate cellular hypoxia.

Human placental nucleoside kinase activities

Our studies have indicated that normal human placental cytosol contains a complex mixture of nucleoside kinase enzymes, some of which conform to previously characterized activities. Deoxyadenosine is phosphorylated by deoxycytidine kinase, adenosine kinase, and two as yet uncharacterized activities. Deoxyguanosine phosphorylation is associated with deoxycytidine kinase. More complete and detailed studies will be necessary to characterize these enzymes fully.

Duchenne muscular dystrophy: normal ATP turnover in cultured cells

We examined ATP metabolism in cultured muscle cells and fibroblasts from patients with Duchenne dystrophy. ATP and ADP levels were the same in cultured cells from normal subjects and patients, and there was no difference in ATP synthesis or degradation. Although there was a significant decrease in radioactively labeled ATP after incubation with deoxyglucose in Duchenne muscle cells, there was no difference in ATP concentration or ADP metabolism.

Characteristics of high-affinity and low-affinity adenosine binding sites in human cerebral cortex

The binding characteristics of human brain cortical membrane fractions were evaluated to test the hypothesis that there are A1 and A2 adenosine binding sites. The ligands used were 2-chloro[8-3H]adenosine and N6-[adenine-2,8-3H]cyclohexyladenosine. Binding of chloroadenosine to human brain cortical membranes was time dependent, reversible, and concentration dependent. The dissociation constant (Kd) calculated for chloroadenosine by Scatchard analysis of equilibrium data was 280 nmol/L, with a maximum binding (Bmax) of 1.6 pmol/mg protein, suggesting a single class of binding sites. The specificity of chloroadenosine binding was assessed by the ability of adenosine analogues to compete for binding sites. With this approach, the apparent Kd was estimated to be 0.74 mumol/L for 5'-N-ethylcarboxamideadenosine, 1 mumol/L for cyclohexyladenosine, and 13 mumol/L for N6-(L-2-phenylisopropyl)adenosine. Isobutylmethylxanthine and theophylline, receptor antagonists, had apparent Kd values of 84 mumol/L and 105 mumol/L, respectively. Hill slope factors ranged from 0.3 to 0.6. Chloroadenosine binding to human brain cortical membranes approached equilibrium at 90 minutes, with a t 1/2 of 10 minutes. The kob was 0.080/min, and the k1 was 7.5 X 10(4)/min/mol/L. Reversibility of chloroadenosine binding at equilibrium was completed at approximately 10 minutes, with a k2 value of 0.074/min. The Kd calculated from the rate constants was 990 nmol/L. Cyclohexyladenosine binding was concentration dependent. The Kd calculated for cyclohexyladenosine via Scatchard analysis of equilibrium data was 5 nmol/L with a Bmax of 0.35 pmol/mg protein. Cyclohexyladenosine binding was displaced by three known receptor agonists: N6-(L-2-phenylisopropyl)adenosine (Kd 4 nmol/L), 2-chloroadenosine (Kd 10 nmol/L) and 5'-N-ethylcarboxamideadenosine (Kd 6 nmol/L).(ABSTRACT TRUNCATED AT 250 WORDS)

ATP degradation products after ischemic exercise: hereditary lack of phosphorylase or carnitine palmityltransferase

We measured purine degradation products of ATP in plasma after ischemic exercise in eight normal subjects, one patient with myophosphorylase deficiency (McArdle's disease), and one with carnitine palmityltransferase deficiency. Normal subjects increase hypoxanthine and inosine, but not xanthine. Plasma purine levels were elevated above the normal range after ischemic exercise in McArdle's disease and in carnitine palmityltransferase deficiency after fasting. Those changes implied abnormally accelerated ATP degradation in these two myopathies.

Hyperuricemia and hypertriglyceridemia: metabolic basis for the association

Hypertriglyceridemia has been reported frequently in patients with hyperuricemia and gout. The current studies have evaluated this relationship. To examine whether hypertriglyceridemia leads to hyperuricemia, IV intralipid was given to three gouty patients. Triglycerides increased from 169 to 700 mg/dl for three hours but caused no change in serum urate level or urine uric acid and oxypurine excretion. We next examined whether high carbohydrate intake increases serum urate and triglyceride levels. Four obese patients were placed on a 2000 kcal/d sucrose diet for seven days. The serum urate increased from 6.3 +/- 1.7 to 7.9 +/- 2.0 mg/dL. The percent uric acid clearance to creatinine clearance decreased from 5.9 +/- 1.3 to the lowest mean value of 3.7 +/- 1.2, while serum triglycerides increased from 106 +/- 33 to 252 +/- 57 mg/dL and blood lactate from 607 +/- 227 to 1167 +/- 381 mumol/L. A 3000 kcal/d glucose diet in four other obese subjects produced no change in serum urate levels but increased lactate and triglyceride levels. During an isocaloric sucrose diet in two normal men, the serum urate level increased from 5.3 and 4.0 to peak values of 9.5 and 7.4 mg/dL. The percent uric acid to creatinine clearance decreased from 5.6 and 6.6 to 2.9 and 3.3. The uric acid turnover did not increase. In three gouty patients the mean serum urate increased from 8.5 +/- 1.5 to 10.6 +/- 1.4 mg/dL following an isocaloric sucrose diet. The urine uric acid excretion increased from 0.30 and 0.25 to 0.37 and 0.38 mg/mg creatinine in two patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine triphosphate degradation in specific disease

Two hypotheses concerning adenosine triphosphate (ATP) degradation are examined: The metabolic basis of specific disorders involves ATP degradation, and uric acid and its precursors are measurable body fluid markers of ATP degradation. These hypotheses are examined by discussing human models of ATP degradation, methods for measurement of ATP degradation, and disorders of ATP degradation.

Antihyperuricemic properties of amflutizole in gout

The antihyperuricemic properties of amflutizole were investigated in studies designed to determine its efficacy and mechanisms of action in individuals with gout and hyperuricemia. In a randomized double blind, multiple dose, crossover study of 29 patients, amflutizole caused a significant dose dependent reduction in serum urate concentrations. Mean serum urate concentrations decreased significantly from 9.6 +/- 1.5 mg/dl to 7.2 +/- 1.3 mg/dl with the 500 mg dosage (p less than 0.01). Detailed studies in 5 patients demonstrated evidence for modest xanthine oxidase inhibition. However, the majority of the antihyperuricemic effect was derived from an enhanced renal clearance of uric acid. Although the drug has significant antihyperuricemic properties, these were inadequate to achieve adequate control of the serum urate concentration in hyperuricemia and gout at the doses utilized.