Adenine Nucleotide Degradation Research Articles

The limits of cardiac preservation with University of Wisconsin solution

Previous studies from this institution have suggested that University of Wisconsin solution is preferred for prolonged cardiac storage and preserves high-energy phosphates better than other storage fluids. University of Wisconsin solution contains adenosine (5 mmol/L), which may maintain the concentration of myocardial adenine nucleotides. Cultures of human adult myocytes were grown from left ventricular biopsy specimens obtained from patients undergoing coronary bypass procedures. Cells (seven to nine dishes per group) were rinsed of culture medium and stored at 0 °C in University of Wisconsin solution. Cells were analyzed for adenine nucleotide content after 1, 6,12, and 24 hours of storage by high-performance liquid chromatography (units = nmol/μg DNA) and compared with control samples (0 hour). Adenosine concentration increased from 0.03 ± 0.02 (mean ± standard deviation) to 1.77 ± 1.03 by 1 hour ( p < 0.0001, analysis of variance) and remained increased thereafter. Adenosine was largely degraded to inosine (0 hours, 0.03 ± 0.03; 6 hours, 0.88 ± 0.56; p < 0.001) and hypoxanthine (0 hours, 0.01 ± 0.01; 6 hours, 0.15 ± 0.09; p = 0.004). Measured levels of xanthine and uric acid were extremely low at all time intervals. Adenosine triphosphate levels were maintained at 1 hour (0 hours, 0.64 ± 0.38; 1 hour, 0.67 ± 0.45) but declined thereafter (6 hours, 0.21 ± 0.21; 12 hours, 0.11 ± 0.09; 24 hours, 0.04 ± 0.03; p < 0.0001). Levels of adenosine diphosphate ( p = 0.007) and adenosine monophosphate ( p < 0.05) decreased to approximately 25% of original values by 24 hours. University of Wisconsin solution does not prevent the degradation of adenine nucleotides during hypothermic storage and may not permit adequate cardiac preservation beyond the present limits.

Adenine Nucleotide Degradation in Modified Atmosphere Chill‐stored Fresh Fish

ABSTRACTEffects of carbon dioxide modified atmospheres on degradation of adenine nucleotides in chill‐stored whitefish (Coregonus clupeafor‐mis) and rainbow trout (Salmo gairdneri) were studied. K values were determined during storage up to 26 days. Results indicated CO2 atmospheres did not alter K values compared to those observed for aerobically held fish. However, both CO2 atmospheres and potassium sorbate‐dipping of fillets caused decreases in hypoxanthine concentrations compared to untreated aerobically held samples.

Mechanism of peroxide‐induced cellular injury in cultured adult cardiac myocytes

Reactive oxygen species contribute to the tissue injury seen after reperfusion of ischemic myocardium. We propose that toxicity originates from the effect that mitochondrial peroxide metabolism has on substrate entry into oxidative pathways. To support our contention, cultured adult rat cardiomyocytes were incubated with physiological concentrations of peroxide. The cellular extract and incubation medium were analyzed for adenine nucleotides and purines by reverse-phase high-pressure liquid chromatography. Cellular glutathione efflux was determined by enzymatic analysis of the incubation medium. Pyruvate dehydrogenase (PDH) activity was determined in the cultured myocytes as well as in freshly isolated cardiac mitochondria using [1-C14]pyruvate. Extracellular glutathione rose 3.3-fold in response to small doses of peroxide (approximately 108 nmol/mg protein). Likewise, small quantities of peroxide reduced total cellular adenine nucleotides to 50-60% of control values with only a modest (0.95-0.91) reduction in energy charge [ATP + 1/2 ADP)/(ATP + ADP + AMP]. Peroxide-treated myocytes selectively release inosine and adenosine, as only these two purine degradation products were detected in the incubation medium. The most dramatic response was a peroxide dose-dependent inhibition of PDH activity in cultured myocytes as well as freshly isolated mitochondria; just 65 and 30 nmol peroxide/mg protein induced a 50% reduction in cellular and mitochondrial PDH activity, respectively. In conclusion, physiological quantities of peroxide potently inhibit PDH in cultured cardiomyocytes and isolated cardiac mitochondria. PDH inhibition blocks the aerobic oxidation of glucose and inhibits the oxidative phosphorylation of ADP, which in turn leads to cellular adenine nucleotide degradation.

Adenine nucleotide degradation in human myocardium during heart and heart-lung transplantation

Adenine nucleotide degradation in human myocardium during heart and heart-lung transplantation

14 Adenine Nucleotide Metabolism In Contracting Skeletal Muscle

During steady-state muscle contractions, ATP production and utilization are well matched. When the rate of ATP hydrolysis exceeds the capacity of a given muscle fiber to phosphorylate ADP, the ADPf and AMPf concentrations rise, first leading to the deamination of adenylates and subsequently to the dephosphorylation of AMP or IMP, or both, to their respective nucleosides and bases. Several proposed roles for the purine nucleotide cycle in skeletal muscle have been reviewed and evaluated. The deaminating limb of the purine nucleotide cycle is most important; it maintains the ATP/ADP ratio and lessens adenine nucleotide degradation. Regulation of glycolytic pathway enzymes by the products of AMP deamination (IMP and NH4+) does not seem likely. During reamination there is a net production of fumarate, with the branch-chain amino acids potentially supplying a significant fraction of the amine; reamination, however, is probably not concurrent with a high rate of deamination. Evidence from some studies of AMP deaminase-deficient persons suggests that an intact purine nucleotide cycle is required for normal muscle function during intense exercise; the issue is clouded, however, by the occurrence of asymptomatic AMP deaminase deficiency. Skeletal muscle is capable of extensive adenine nucleotide degradation during severe, energy-depleting conditions. Purine nucleosides and bases not reincorporated by the salvage pathway must be synthesized de novo. The capacity for de novo synthesis differs among fiber types, being highest in muscle with the highest oxidative capacity.

Functional and metabolic effects of uridine and UTP on the skeletal muscle of the rat submitted to exercise

Twenty millimolar and 2 mM uridine triphosphate and 2 mM uridine were injected intra-arterially into rat leg muscles during a 20 min period of intense exercise and during the recovery phase (20 min). Administration of 20 mM uridine triphosphate during exercise, provoked a complete depression of muscle contractility. On the contrary, supply of 2 mM uridine triphosphate or 20 mM uridine induced a reduction in the decrease of muscular developed tension during the exercise period of time and favoured functional recovery. This positive effect of pyrimidine compounds on muscular functional parameters did not seem to be correlated with metabolic effects. Indeed, 2 mM uridine supply did not modify the evolution of intramuscular glycogen and lactate concentrations and made worsened the adenine nucleotide degradation induced by exercise.

Plasma accumulation of hypoxanthine, uric acid and creatine kinase following exhausting runs of differing durations in man

During exhausting exercise adenylate kinase in the muscle cells is activated and a degradation of adenosine 5'-diphosphate occurs. Consequently, degradation products of adenosine 5'-monophosphate including hypoxanthine and uric acid, accumulate in plasma. The aim of this study was to compare the concentration changes of hypoxanthine and uric acid in plasma following running of varying duration and intensity. In addition, plasma creatine kinase activity was measured to assess the possible relationship between metabolic stress and protein release. Four groups of competitive male runners ran 100 m (n = 7), 800 m (n = 11), 5000 m (n = 7) and 42,000 m (n = 7), respectively, at an exhausting pace. Subsequent to the 100 m event (mean running time 11 s) plasma concentrations of hypoxanthine and uric acid increased by 364% and 36% respectively (P less than 0.05), indicating a very high rate of adenine nucleotide degradation during the event. Following the 800-m event (mean running time 125 s), hypoxanthine and uric acid concentrations had increased by 1598% and 66%, respectively (P less than 0.05). Both the events of longer duration, 5000 m and 42,000 m, also caused a significant increase in plasma concentration of hypoxanthine (742% and 237% respectively, P less than 0.05) and plasma uric acid (54% and 34% respectively, P less than 0.05). Plasma activities of creatine kinase were significantly increased at 24 h only following the 5000 m and 42,000 m events (64% and 1186% respectively, P less than 0.05). Changes in plasma creatine kinase activity showed no correlation with changes in plasma concentration of either hypoxanthine or uric acid for the 5000 m and 42,000 m events (r = 0.00-0.45, P greater than 0.05).

Adenine Nucleotide Degradation in Striated Muscle

Adenine nucleotides play a central role in cellular processes involving the transduction of energy. Among striated muscles, the management of adenine nucleotide catabolism differs greatly. These differences can be understood by considering the distribution, activity, and kinetic characteristics of degradative enzymes. When these factors are weighed in light of the differing energetic demands faced by heart and skeletal muscle fiber types, a coherent picture emerges. Our analysis suggests that, as the routine energy demand of a particular muscle rises in relation to the tissue's capacity for oxidative metabolism, the pattern of adenine nucleotide degradation shifts toward increased rates of AMP deamination along with lessened rates of dephosphorylation.

Ischemic preconditioning slows energy metabolism and delays ultrastructural damage during a sustained ischemic episode.

We have shown previously that preconditioning myocardium with four 5-minute episodes of ischemia and reperfusion dramatically limited the size of infarcts caused by a subsequent 40-minute episode of sustained ischemia. The current study was undertaken to assess whether the same preconditioning protocol slowed the loss of high energy phosphates, limited catabolite accumulation, and/or delayed ultrastructural damage during a sustained ischemic episode. Myocardial metabolites and ultrastructure in the severely ischemic subendocardial regions were compared between control and preconditioned canine hearts. Hearts (four to 10 per group) were excised after 0, 5, 10, 20, or 40 minutes of sustained ischemia. All groups had comparable collateral blood flow. Preconditioned hearts developed ultrastructural injury more slowly than controls; evidence of irreversible injury was observed after 20 minutes in controls but not until 40 minutes in preconditioned hearts. Furthermore, after 40 minutes of ischemia, irreversible injury was homogeneous in controls but only focal in preconditioned myocardium. Preconditioning reduced starting levels of ATP by 29%. Nevertheless, it also slowed the rate of ATP depletion during the episode of sustained ischemia, so that after 10 minutes of ischemia, preconditioned hearts had more ATP than controls. However, after 40 minutes, ATP contents were not significantly different between groups. Preservation of ATP resulted from reduced ATP utilization and was not due to increased ATP production. Accumulation of purine nucleosides and bases (products of adenine nucleotide degradation) was limited in preconditioned myocardium. Accumulation of glucose-1-phosphate, glucose-6-phosphate, and lactate also was reduced markedly by preconditioning, due to reduced rates of glycogen breakdown and and anaerobic glycolysis. We propose that preconditioning reduces myocardial energy demand during ischemia, which results in a reduced rate of high energy phosphate utilization and a reduced rate of anaerobic glycolysis. Either preservation of ATP or reduction of the cellular load of catabolites may be responsible for delaying ischemic cell death.

The catabolism of endogenous adenine nucleotides in rat liver mitochondria

The degradation of intramitochondrial adenine nucleotides to nucleosides and bases was investigated by incubating isolated rat liver mitochondria at 37 degrees C under non-phosphorylating conditions in the presence of oligomycin and carboxyatractyloside. Within 30 min the adenine nucleotides were degraded by about 25 per cent. The main products formed were adenosine and inosine the contents of which increased five- to sevenfold. Compartmentation studies revealed that about 50 to 60 per cent of the adenosine formed remained inside the organelles whereas inosine was almost completely released into the surrounding medium. Outside the mitochondria only very small amounts of adenine nucleotides were detected. Similar incubations in the presence of [14C]-adenosine yielded no [14C]-inosine ruling out extramitochondrial adenosine deamination. It is concluded that endogenous adenine nucleotides can be degraded in mitochondria via AMP dephosphorylation and subsequent adenosine deamination. A purine nucleoside transport system mediating at least the efflux of inosine from the mitochondria is suggested.

Adenine nucleotide degradation in slow-twitch red muscle

The catabolism of adenine nucleotides (AdN) in rat soleus muscle (predominantly slow twitch) is very different from that in fast-twitch muscle. AMP deaminase is highly inhibited during brief (3 min) intense (120 tetani/min) in situ stimulation, resulting in little inosine 5'-monophosphate (IMP) accumulation (0.21 mumol/g). Even with ligation of the femoral artery during the same brief intense contraction conditions there is surprisingly little increase in IMP (0.37 mumol/g), although AdN depletion is evident (-1.30 mumol/g). We have tested the hypothesis that accumulation of purine nucleosides and bases accounts for the AdN depletion by measuring purine degradation products using high-performance liquid chromatography. There was no stoichiometric accumulation of purine degradation products to account for the observed AdN depletion even though metabolite recovery was essentially quantitative. We hypothesis that under these conditions AdN are converted to a form different from purine nucleoside and base degradation products. In contrast to the inhibition of AMP deamination seen during brief ischemia, slow-twitch muscle depletes a substantial fraction (28%) of muscle AdN (1.75 mumol/g) that can be accounted for stoichiometrically as purine degradation products during an extended 10-min ischemic period of mild (12 tetani/min) contraction conditions. IMP accumulation (1 mumol/g) is most prominent with inosine, accounting for 23% (0.4 mumol/g) of the depleted AdN, showing that slow-twitch red muscle is capable of both AMP deamination and the subsequent production of purine nucleosides during an extended period of ischemic contractions. The present results indicate that AdN metabolism in the soleus muscle is complex, yielding expected degradation products or a loss of total purines, depending on contraction conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycolytic support of adenine nucleotides in rat liver flush-preserved with UW or Collins' II. Importance of donor nutritional status.

Correlation of hepatocellular adenine nucleotides in donor liver with clinical posttransplant outcome has recently been reported. Our earlier work with rats has shown that pretreatment of donors with glucose effectively retards hepatocellular ATP losses in livers preserved in Collins' II solution through potentiation of their glycolytic capacity. The primary substrate--i.e., endogenous or exogenous glucose--was not identified. The current study was undertaken to compare the relative efficacy of the University of Wisconsin (UW) solution, which is devoid of glucose, with Collins' II in the support of adenine nucleotides through anaerobic glycolysis in flush-preserved rat liver. Adult rats were either pretreated with 25% dextrose or fasted prior to liver harvesting and preservation in either UW or Collins' II. Adenine nucleotide degradation and lactate production during preservation were assessed. For a given dietary pretreatment, losses of ATP and adenylate energy charge and lactate production were similar for UW- and Collins' II-preserved livers. Donor pretreatment with dextrose resulted in significantly higher ex vivo liver ATP, energy charge, and lactate regardless of the preservation solution. Salvageable nucleotide degradates were increased significantly in UW livers, presumably through the effects of allopurinol. These results demonstrate that effective support of adenine nucleotides by glycolysis in flush-preserved liver is independent of the presence of exogenous glucose but dependent upon the nutritional status of the donor prior to liver procurement.

Delayed Myocardial Metabolic Recovery After Blood Cardioplegia

Previous studies have demonstrated that both myocardial metabolism and ventricular function were depressed after blood cardioplegic arrest for elective coronary artery bypass grafting. To evaluate the etiology of this metabolic defect, we measured the levels of adenine nucleotides and their precursors in 29 patients undergoing elective coronary revascularization. Myocardial biopsy specimens were obtained at 37 degrees C before cardioplegic arrest, immediately after 74 +/- 4 minutes of cardioplegic arrest, and after 30 minutes of reperfusion. Biopsy specimens were analyzed for levels of adenine nucleotides and their precursors by high-performance liquid chromatography. Adenosine triphosphate concentrations decreased with cardioplegic arrest and with reperfusion. Adenosine monophosphate concentrations increased after cardioplegic arrest and remained nearly twice the initial values after reperfusion. The ratio of adenosine monophosphate to adenosine triphosphate doubled after reperfusion, suggesting defective conversion of adenosine monophosphate to adenosine triphosphate. Levels of adenine nucleotide degradation products (adenosine, inosine, and hypoxanthine) increased after cardioplegia and decreased with reperfusion, suggesting a washout of soluble precursors. This study suggests that improvements in myocardial protection should attempt to stimulate mitochondrial energy production and preserve adenine nucleotide precursors.

Adenosine formation by isolated rat kidney mitochondria

Isolated rat kidney mitochondria are able to generate extraordinary amounts of adenosine. About one-third of the adenosine formed only results from the degradation of adenine nucleotides. Pyridine nucleotides may contribute to adenosine formation. Nevertheless, there must be an additional, as yet unidentified, acid-insoluble compound in mitochondria which is able to form a significant portion of adenosine.

Embryonic versus adult myocardium: Adenine nucleotide degradation during ischemia

Neonatal myocardium demonstrates better recovery from ischemia than does adult tissue. We tested the hypothesis that developmental differences in adenine nucleotide degradation might facilitate recovery by quantitating depletion of high-energy phosphates in nine-day-old embryonic (n = 9) and 15-month-old adult (n = 14) chicken hearts at 15-, 30-, 45-, and 60-minute intervals of normothermic ischemia in vitro. Nucleotides adenosine triphosphate, adenosine diphosphate, and adenosine monopnosphate and nucleosides adenosine, inosine, hypoxanthine, and xanthine were determined by highperformance liquid chromatography. Several observations in metabolite degradative response to ischemia were noted. The embryonic myocardium maintained higher adenosine triphosphate and adenosine monophosphate levels over the course of the investigation than did mature myocardium. Moreover, the adult group showed an increase in diffusible nucleoside pool metabolites. Relative immaturity of enzymes responsible for nucleotide degradation may facilitate postiachemic recovery by preserving nondiffusible high-energy phosphate precursors to participate in salvage resynthesis of adenosine triphosphate.

Degradation of adenine nucleotides in ischemic and reperfused rat heart

Complete cessation of flow in isolated rat hearts for 90 min resulted in a gradual breakdown of ATP and concomitant accumulation of degradation products, such as adenosine, inosine (major break-down product), hypoxanthine, and, to a lesser extent, xanthine. After 45 min of ischemia, the content and relative composition of purines hardly changed, whereas the AMP content continued to rise. This finding points to constraints on AMP degradation and flux through the degradation pathway from adenosine to uric acid in the ischemic heart. In myocardial preparations, the cells of which were deliberately disrupted by freezing and thawing before anoxic incubation, AMP did not accumulate and was finally converted to hypoxanthine. These results indicate that compartmentalization of substrates and enzymes is responsible for the observed preferential accumulation of AMP and inosine in the ischemic heart. Inhibition of hypoxanthine degradation is explained by the absence of oxygen. Restoration of flow and oxygen supply abolished the inhibition of metabolic flux. Accumulated purines were released into the coronary effluent and, concomitantly, further metabolized. Comparison of tissue levels of hypoxanthine, xanthine, and uric acid before reperfusion and the amounts released during reperfusion indicates that in rat myocardium substantial amounts of potentially hazardous xanthine oxidase-derived reactive oxygen species are likely to be formed during the early reperfusion phase.

Adenine nucleotide degradation in human skeletal muscle during prolonged exercise.

Eight healthy men cycled at a work load corresponding to approximately 70% of maximal O2 uptake (VO2max) to fatigue (exercise I). Exercise to fatigue at the same work load was repeated after 75 min of rest (exercise II). Exercise duration averaged 65 and 21 min for exercise I and II, respectively. Muscle (quadriceps femoris) content of glycogen decreased from 492 +/- 27 to 92 +/- 20 (SE) mmol/kg dry wt and from 148 +/- 17 to 56 +/- 17 (SE) mmol/kg dry wt during exercise I and II, respectively. Muscle and blood lactate were only moderately increased during exercise. The total adenine nucleotide pool (TAN = ATP + ADP + AMP) decreased and inosine 5'-monophosphate (IMP) increased in the working muscle during both exercise I (P less than 0.001) and II (P less than 0.01). Muscle content of ammonia (NH3) increased four- and eight-fold during exercise I and II, respectively. The working legs released NH3, and plasma NH3 increased progressively during exercise. The release of NH3 at the end of exercise II was fivefold higher than that at the same time point in exercise I (P less than 0.001, exercise I vs. II). It is concluded that submaximal exercise to fatigue results in a breakdown of the TAN in the working muscle through deamination of AMP to IMP and NH3. The relatively low lactate levels demonstrate that acidosis is not a necessary prerequisite for activation of AMP deaminase. It is suggested that the higher average rate of AMP deamination during exercise II vs. exercise I is due to a relative impairment of ATP resynthesis caused by the low muscle glycogen level.

Exercise- induced alteration of erythrocyte glycolysis -Its relation to accelerated degradation of muscular adenine nucleotides

Exercise- induced alteration of erythrocyte glycolysis -Its relation to accelerated degradation of muscular adenine nucleotides

Purine degradation in contracting fast and slow muscles of rats.

We previously reported that hyperuricemia found in patients with glycogenosis types III, V, and VII was caused by excess purine degradation due to impaired ATP generation in muscles (myogenic hyperuricemia)(Kono et al., 1986, 1987; Mineo et al., 1987). Even minimal or mild exercise leads to elevated levels of blood inosine and hypoxanthine in patients with metabolic myopathy (Bertorini et al., 1985; Brooke et al., 1983; Hara et al., 1987; Kono et al., 1986; Mineo et al., 1985). Inosine and hypoxanthine serve as precursors of uric acid in the liver. When ATP is utilized during strenuous contraction of skeletal muscle, AMP is deaminated to IMP by AMP deaminase (EC. 3.5.4.6). AMP and IMP are broken down into adenosine and inosine, respectively, by 5′-nucleotidase (EC. 3.1.3.5). It has been reported that regulation of adenine nucleotide degradation is different between fast and slow muscles. Bookman et al. (1983) reported that nucleosides increased in proportion to an increase in lactate in cat slow muscles but not in fast muscles. Meyer et al. (1979) reported that large amount of IMP was produced in fast muscles but there was no significant increase in IMP in slow muscles during ischemic contraction, while Whitlock et al. (1987) showed adenine nucleotide deamination to IMP could occur in slow muscles under specific contraction conditions. However, difference in purine degradation between fast and slow muscles is still controversial. This study was designed to clarify overall purine degradation and its regulation in different types of rat skeletal muscles during ischemic contraction.

Propranolol enhances adenine nucleotide degradation in human muscle during exercise.

Eight healthy men cycled to exhaustion [4.1 +/- 0.3 (SE) min] during beta-adrenoceptor blockade (beta B) with propranolol. The exercise was repeated on another day with the same power output and duration but without propranolol (control). The total adenine nucleotide (TAN) content in muscle (quadriceps femoris) decreased during exercise, and the decrease was more pronounced during beta B (delta TAN = 4.8 +/- 1.0 mmol/kg dry wt) than during control (delta TAN = 2.8 +/- 0.9; P less than 0.01, beta B vs. control). The decrease in TAN corresponded with a similar increase in inosine 5'-monophosphate (IMP). The increase in IMP was more pronounced during beta B (delta IMP = 5.1 +/- 1.2 mmol/kg dry wt) than during control (delta IMP = 2.8 +/- 0.7; P less than 0.05, beta B vs. control). Similarly, the increase in the content of NH3 in muscle was twice as high during beta B vs. control (P less than 0.01). The increase in muscle lactate and the decrease in phosphocreatine during exercise were similar between treatments, but postexercise hexose phosphates were approximately twofold higher (P less than 0.05) during control than during beta B. It is concluded that beta B enhances the degradation of TAN and the production of NH3 and IMP in muscle during intense exercise. This indicates that the imbalance between the rates of utilization and resynthesis of ATP is more pronounced during beta B possibly because of a decreased O2 transport to the contracting muscle and a diminished activation of glycolysis by the hexose phosphates.(ABSTRACT TRUNCATED AT 250 WORDS)