Adenylate degradation products release from the human myocardium during open heart surgery

Oxypurine and purine nucleoside concentrations in renal vein of allograft are potential markers of energy status of renal tissue

BACKGROUND

Impairment of organ function derived from ischemia-reperfusion injury is an important problem in solid organ transplantation. Cell alterations induced by ischemia prime the tissue for subsequent damage that occurs during the reperfusion phase. Purine nucleosides and oxypurines are products of adenine nucleotides degradation. Reperfusion and reoxygenation are accompanied by production of reactive oxygen species and free radicals, which lead to damage of graft tissue. The aim of this study was to measure concentrations of adenine nucleotides and their metabolites in renal allograft vein as well as in recipient's peripheral veins during the reperfusion period and to evaluate their usefulness as markers of tissue metabolism in kidney allografts.

METHODS

The study enrolled 20 renal transplant recipients. The first blood sample was taken from the recipient's ulnar vein before anastomosing of the kidney graft's vessels with recipient's iliac vessels. Samples were then taken from the renal allograft and ulnar veins 5 min after total graft reperfusion measured with an infrared camera. High-performance liquid chromatography (HPLC) was performed to measure whole blood and plasma concentrations of adenosine triphosphate (ATP), adenosine monophosphate (AMP), guanosine (Guo), inosine (Ino), hypoxanthine (Hyp), xanthine (Xan), uric acid (UA), and uridine (Urd).

RESULTS

Hyp and Xan concentrations were significantly increased in renal allograft vein after reperfusion as compared with peripheral vein during the pre- and post-reperfusion periods.

CONCLUSIONS

The results of the present study suggest that differences in Hyp and Xan concentrations between renal and peripheral veins reflect metabolic alterations in renal tissue during reperfusion and may be useful for graft function monitoring during reperfusion.

Oxypurine and nucleoside concentrations in renal veins during reperfusion are predictors of early graft function

OBJECTIVE

To examine whether purine and pyrimidine nucleoside concentrations as well as oxypurine concentrations in renal and peripheral veins during reperfusion correlate with graft function parameters.

MATERIAL AND METHODS

The study population comprised 25 recipients of cadaver kidney transplant. A first blood sample was taken from the recipient's peripheral vein before anastomosing the kidney allograft vessels with the recipient's iliac vessels. Subsequent samples were taken from the allograft renal vein and the recipient's peripheral vein 5 min after beginning reperfusion. High-performance liquid chromatography was done to measure plasma concentrations of the oxypurines hypoxanthine (Hyp), xanthine (Xan) and uric acid and the nucleosides guanosine, inosine (Ino) and uridine (Urd).

RESULTS

Concentrations of Hyp, Xan and Ino were significantly higher in the renal than the peripheral vein. The differences between the Xan, Hyp, Ino and Urd plasma concentrations in the renal and peripheral veins before and 5 min after reperfusion correlated positively and significantly with serum creatinine concentrations 24 and 72 h after graft transplantation. Moreover, the concentrations of Hyp were significantly increased in renal transplant recipients with delayed graft function.

CONCLUSION

The results of this study suggest that the concentration of Hyp in the kidney allograft vein can be a useful predictor of early graft function.

Hypoxanthine as a graft ischemia marker stimulates catalase activity in the renal vein during reperfusion in humans

BACKGROUND

The impairment of organ function derived from ischemia-reperfusion injury is still an important problem in solid organ transplantation. Cell alterations induced by ischemia prime the tissue for subsequent damage occurring during the reperfusion phase. Purine nucleotides and oxypurines are products of adenine nucleotide degradation. Reperfusion and reoxygenation are characterized by great production of reactive oxygen species and free radicals. On the contrary, superoxide dismutase, catalase, glutathione, and glutathione peroxidase are involved in protecting against free radicals. The aim of the study was to examine the correlation between concentrations of ischemia markers (hypoxanthine or inosine) and the activity of erythrocyte superoxide dismutase, catalase, or glutathione peroxidase.

PATIENTS AND METHODS

The study included 40 renal transplant recipients. Before anastomosis of the kidney vessels with the recipient's iliac vessels, a "0" blood sample was taken from the iliac vein. Then, after anastomosis, the renal vein of the graft was cannulated and blood samples I, II, and III were obtained. The reperfusion of the transplanted kidney was measured with a thermovision camera ThermaCAM SC500.

RESULTS

The plasma concentrations of hypoxanthine and inosine increased in statistically significant fashion immediately after total tissue reperfusion (P < .0001). Catalase activity at 4 minutes after total tissue reperfusion correlated positively with hypoxanthine concentrations immediately after total tissue reperfusion (Rs = +0.49), 2 minutes after total tissue reperfusion (Rs = +0.47), and 4 minutes after total tissue reperfusion (Rs = +0.46). There were no statistically significant correlations between hypoxanthine or inosine concentrations or superoxide dismutase or glutathione peroxidase activities.

CONCLUSIONS

The results of the present study suggest that catalase activity may correlate with the concentration of hypoxanthine in the graft renal vein and other mediators of oxidative stress.

Myocardial and coronary sinus purines as indicators of pig heart energy metabolism during reperfusion after extracorporeal circulation

AIM

The precise understanding of myocardial metabolism is crucial for the optimization of cardiosurgical procedures. We attempted to gain a comprehensive insight into the purine metabolism of the porcine heart during reperfusion by measuring concentrations of nucleotides, nucleosides and oxypurines simultaneously in the myocardium and coronary sinus.

METHODS

Twenty-five pigs were subjected to sham cardiosurgery with extracorporeal circulation and cold cardioplegic arrest of 60 min. Myocardial biopsies, as well as coronary sinus and arterial blood samples were taken before aortic clamping and at 5, 20, 60 and 120 min of reperfusion. HPLC was used to measure concentrations of 17 purines in the bioptates and of 5 in plasma.

RESULTS

Reperfusion rapidly normalized the ischaemic decrease in the adenylate energy charge of the myocardium, but during 120 min failed to restore the reduced adenylate pool, because of irreversible loss of nucleosides by cardiomyocytes. Low adenylate energy charge and depletion of the adenylate pool were accompanied by analogous changes in the guanylates and growing deficit of NAD and NADP. Reperfusion was marked by significant release of inosine and guanosine from the heart, without any noticeable effect on hypoxanthine and xanthine.

CONCLUSIONS

Coronary sinus concentrations of purines provide only a limited insight into the metabolism of the porcine heart. Repeated biopsies of the heart muscle and HPLC determinations of purine profiles represent a comprehensive and unique method for the study of purine metabolism during ischaemia and reperfusion. Future research on myocardial metabolism in disease and during cardiosurgical procedures should additionally be oriented to deficits in guanine and pyridine nucleotides.

In vitro adenine nucleotide catabolism in African catfish spermatozoa

It has been shown recently that African catfish (Clarias gariepinus) spermatozoa possess relatively low ATP content and low adenylate energy charge (AEC). One of the possible explanations for this phenomenon is that the spermatozoa actively catabolize adenine nucleotides. A relatively high rate of such catabolism could then contribute to the low ATP concentration and low adenylate energy charge observed in the spermatozoa in vitro. To check this hypothesis, we investigated ATP content and adenine nucleotide catabolism in African catfish spermatozoa stored at 4 degrees C in the presence of glycine as an energetic substrate. Our results indicate that the storage of African catfish sperm at 4 degrees C in the presence of glycine causes time-dependent ATP depletion. In contrast to ATP, the AMP content increases significantly during the same period of sperm storage, while the ADP increases only slightly. Moreover, a significant increase of inosine and hypoxanthine content was also found. Hypoxanthine was accumulated in the storage medium, but xanthine was found neither in spermatozoa nor in the storage medium. It indicates that hypoxanthine is not converted to xanthine, probably due to lack of xanthine oxidase activity in catfish spermatozoa. Present results suggest that adenine nucleotides may be converted to hypoxanthine according to the following pathway: ATP-->ADP-->AMP (adenosine/IMP)-->inosine-->hypoxanthine. Moreover, hypoxanthine seems to be the end product of adenine nucleotide catabolism in African catfish spermatozoa. In conclusion, our results suggest that a relatively high rate of adenine nucleotide catabolism contributes to the low ATP concentration and low adenylate energy charge observed in African catfish spermatozoa in vitro.

Kinetics of adenylate metabolism in human and rat myocardium

Pathways producing and converting adenosine have hardly been investigated in human heart, contrasting work in other species. We compared the kinetics of enzymes associated with purine degradation and salvage in human and rat heart cytoplasm assaying for adenosine deaminase, nucleoside phosphorylase, xanthine oxidoreductase, AMP deaminase, AMP- and IMP-specific 5'-nucleotidases, adenosine kinase and hypoxanthine guanine phosphoribosyltransferase (HGPRT). Xanthine oxidoreductase was not detectable in human heart. The Km-values of the AMP-catabolizing enzymes were 2-5 times higher in human heart; the substrate affinity of the other enzymes was in the same order of magnitude in both species. The maximal activity (Vmax) of adenosine kinase was the same in both species, but HGPRT in man was only 12% of that in the rat. For human heart the Vmax-values of adenosine deaminase, nucleoside phosphorylase, AMP- and IMP-specific 5'-nucleotidases, and AMP deaminase were 25-50% of those for rat heart. We conclude that human heart is less geared to purine catabolism than rat heart as is evident from the lower activities of the catabolic enzymes. Maintenance of the nucleotide pool may thus play a more important role in human heart.

Hyperthyroidism increases adenosine transport and metabolism in the rat heart

Hyperthyroidism induces a number of metabolic and physiological changes in the heart including hypertrophy, increase in inotropic status, and alterations of myocardial energy metabolism. The effects of hyperthyroidism on adenosine metabolism which is intimately involved in the control of many aspects of myocardial energetics, have not been clarified. The aim of this study was thus to evaluate the potential role of adenosine in the altered physiology of the hyperthyroid heart. Transport of adenosine was studied in cardiomyocytes isolated from hyperthyroid and euthyroid rats. Activities of different enzymes of purine metabolism were studied in heart homogenates and concentrations of nucleotide and creatine metabolites were determined in hearts freeze-clamped in situ. Both transport of adenosine into cardiomyocytes and the rate of intracellular phosphorylation were higher in the hyperthyroid rat. At 10 microM concentration, adenosine transport rates were 275 and 197 pmol/min/mg protein in hyperthyroid and euthyroid cardiomyocytes respectively whilst rates of adenosine phosphorylation were 250 and 180 pmol/min/mg prot. An even more pronounced difference was observed if values were expressed per number of cells due to cardiomyocyte enlargement. Hyperthyroidism was associated with a 20% increase in adenosine kinase, 30% decrease in membrane 5'-nucleotidase and 15% decrease in adenosine deaminase activities measured in heart homogenates. In addition there was a substantial depletion in the total creatine pool from 63.7 to 41.6 mumol/g dry wt, a small decrease in the adenylate pool (from 27.2 to 24.3 mumol/g dry wt) and an elevation of the guanylate pool (from 1.22 to 1.36). These results show that adenosine transport and phosphorylation capacity is enhanced in hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)

High performance liquid chromatographic determination of methacrylate in blood serum

Methacrylic acid is a hydrolytic breakdown product of methylmethacrylate which is widely used in orthopaedic surgery, dentistry and in the chemical industry for fabrication of acrylic resins. Information on the toxicity of methacrylic acid and its metabolism is limited. To facilitate studies in this field we developed a liquid chromatographic procedure allowing determination of methacrylate in blood serum. The procedure was based on reversed-phase HPLC using a gradient elution with UV detection at 210 or 240 nm. The method was linear up to 5 mM concentration with a detection limit of 0.5 microM. The procedure was applied to determination of methacrylate in rat blood serum after administration of sodium methacrylate solution into the stomach. A peak of this compound was demonstrated in the chromatogram 10 min after administration which disappeared after 60 min, confirming suitability of the method for biological applications.

Distribution of xanthine oxidoreductase activity in human tissues — a histochemical and biochemical study

Localization of the activity of both the dehydrogenase and oxidase forms of xanthine oxidoreductase were studied in biopsy and postmortem specimens of various human tissues with a recently developed histochemical method using unfixed cryostat sections, poly-(vinyl alcohol) as tissue stabilizator, 1-methoxyphenazine methosulphate as intermediate electron acceptor and Tetranitro BT as final electron acceptor. High enzyme activity was found only in the liver and jejunum, whereas all the other organs studied showed no activity. In the liver, enzyme activity was found in sinusoidal cells and both in periportal and pericentral hepatocytes. In the jejunum, enterocytes and goblet cells, as well as the lamina propria beneath the basement membrane showed activity. The oxidase activity and total dehydrogenase and oxidase activity of xanthine oxidoreductase, as determined biochemically, were found in the liver and jejunum, but not in the kidney and spleen. This confirmed the histochemical results for these organs. Autolytic rat livers several hours after death were studied to exclude artefacts due to postmortem changes in the human material. These showed loss of activity both histochemically and biochemically. However, the percentage activity of xanthine oxidase did not change significantly in these livers compared with controls. The findings are discussed with respect to the possible function of the enzyme. Furthermore, the low conversion rate of xanthine dehydrogenase into xanthine oxidase during autolysis is discussed in relation to ischemia-reperfusion injury.

Liquid chromatographic evaluation of purine production in the donor human heart during transplantation

A reversed phase high performance liquid chromatographic technique is presented allowing purine catabolite determination in a whole blood extract without a prior purification step. The method was applied to determine the timing and the profile of myocardial nucleotide catabolite release during reperfusion of the transplanted human heart. Samples of arterial and coronary sinus blood collected at various times within 1 h after aortic declamping during heart or heart-lung transplantations were used for nucleotide catabolite determination. Massive release of inosine and hypoxanthine from the heart was demonstrated. Production of adenosine was also shown but there was no liberation of xanthine or uric acid. Nucleotide catabolite release was greatest in the first 5 min (coronary sinus-arterial difference = 15-20 microM), but was still significant after 30 min of reperfusion. The determination of inosine and hypoxanthine--major catabolites released--was found to be reproducible in coronary sinus blood (coefficient of variation < 10%). However, immediate protein precipitation afer blood sample collection was necessary, as rapid metabolism of both exogenous and endogenous adenosine and inosine was demonstrated.

Acetate-induced changes of adenine nucleotide levels in rat liver

The changes in adenine nucleotide concentration induced by acetate were investigated in rat liver in situ and in isolated rat hepatocytes. Adenosine monophosphate (AMP) concentration increased approximately threefold within 15 minutes after intraperitoneal injection of sodium acetate. A small but significant decrease in adenosine triphosphate (ATP) concentration also occurred. Consequently, the ATP/AMP ratio decreased from approximately 14 (the value found in control or sodium chloride-injected rats) to approximately 3 (the value found in sodium acetate-injected rats). Adenosine diphosphate (ADP) concentration increased slightly, but this was statistically nonsignificant. Total adenine nucleotide concentrations after acetate injection remained essentially the same as those in control rats. Adenylate energy charge decreased after acetate administration. No significant changes in nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate (NADP) concentrations were found after sodium acetate injection. Similar patterns of changes in adenine nucleotide concentrations were found in isolated rat hepatocytes incubated in the presence of acetate. These data indicate that acetate, which appears in human blood either during hemodialysis with acetate-containing solution or after ethanol consumption, may alter energy equilibrium of adenine nucleotides in the liver. This is due to the conversion of ATP to AMP in the course of acetate to acetyl-coenzyme A (CoA) activation. It is therefore possible that accelerated ATP turnover in the liver may contribute both to the "intolerance to acetate" in patients subjected to dialysis with the sodium acetate-containing solution and to the pathogenesis of gout associated with excessive ethanol consumption.

Adenosine alters glucose use during ischemia and reperfusion in isolated rat hearts

BACKGROUND

Adenosine possesses marked cardioprotective properties, but the mechanisms for this beneficial effect are unclear. The objective of this study was to determine the effect of adenosine given before ischemia or at reperfusion on mechanical function, glucose oxidation, glycolysis, and metabolite levels in isolated, paced (280 beats per minute) working rat hearts.

METHODS AND RESULTS

Hearts were perfused with Krebs-Henseleit buffer containing 11 mM glucose, 1.2 mM palmitate, and 500 microU.mL-1 insulin at an 11.5 mm Hg left atrial preload and 80 mm Hg aortic afterload. Adenosine (100 microM) pretreatment or adenosine (100 microM) at reperfusion markedly increased the recovery of mechanical function (from 44% to 81% and 96%, respectively) after 60 minutes of low-flow ischemia (coronary flow, 0.5 mL.min-1). Glucose oxidation (mumol.min-1 x g dry wt-1) was inhibited during ischemia (from 0.44 +/- 0.04 to 0.12 +/- 0.01), and this was not altered by adenosine (100 microM). During reperfusion, glucose oxidation recovered (to 0.38 +/- 0.02) and adenosine (100 microM), given at reperfusion, further increased glucose oxidation (to 0.52 +/- 0.06). The rate of glycolysis (mumol.min-1 x g dry wt-1), which was unaffected by ischemia per se, was inhibited by adenosine pretreatment (from 4.7 +/- 0.3 to 2.6 +/- 0.3). During reperfusion, glycolysis was also inhibited by adenosine relative to control (3.9 +/- 0.8) either when present during ischemia (2.6 +/- 0.6) or during reperfusion (1.4 +/- 0.4). These effects of adenosine on glucose metabolism reduced the calculated rate of H+ production attributable to glucose metabolism during the ischemic and reperfusion periods. Tissue lactate levels (mumol.g dry wt-1), which increased during ischemia (from 9.3 +/- 1.1 to 87.4 +/- 10.3) and then declined during reperfusion (to 26.2 +/- 3.7), were depressed further by adenosine pretreatment (to 19.7 +/- 4.1) and by adenosine at reperfusion (to 13.6 +/- 2.1). ATP levels (mumol.g dry wt-1), which were depressed by ischemia (from 18.1 +/- 1.1 to 10.6 +/- 1.3) and tended to be further depressed during reperfusion (to 7.1 +/- 0.7), were increased by adenosine pretreatment (to 14.1 +/- 1.2) and by adenosine at reperfusion (to 15.6 +/- 2.4).

CONCLUSIONS

The effects of adenosine on glucose metabolism that would tend to decrease cellular acidosis and hence, Ca2+ overload, may explain the beneficial effects of adenosine on mechanical function observed in these hearts during reperfusion after ischemia.

Oxygen partial pressure and free intracellular adenosine of isolated cardiomyocytes

Adenosine formation by the heart is known to critically depend on the ratio of oxygen supply to oxygen demand, but the sensitivity of cardiomyocytes to defined changes in PO2 is not known. Isolated metabolically stable rat cardiomyocytes were incubated up to 45 min at constant PO2 values ranging from 0.1 to 100 mmHg using a feedback-controlled incubation system (oxystat system). Changes of the free intracellular adenosine concentration were measured after trapping of adenosine by cytosolic S-adenosylhomocysteine (SAH) hydrolase in the presence of 200 microM L-homocysteine thiolactone. Rate of SAH formation was constant at a PO2 between 3 and 100 mmHg and gradually increased at PO2 less than 3 mmHg. Cellular ATP decreased only at PO2 less than 1 mmHg, and this was accompanied by a decline of oxygen consumption. Treatment of cells with 5.5 mM deoxyglucose and 4 micrograms/ml oligomycin increased SAH formation 60-fold and was associated with elevated intra- and to a lesser extent extracellular adenosine levels. Inhibition of nucleoside transport with 20 microM S-(p-nitrobenzyl)-6-thioinosine steepened the transmembrane adenosine gradient. Our findings suggest that the cardiomyocyte responds to metabolic poisoning and oxygen deprivation with an enhanced formation of adenosine. This adenosine is mainly formed intracellularly and reaches the extracellular space by diffusion. Threshold for adenosine formation is as low as 3 mmHg.

Purines, lactate and phosphate release from child and adult heart during cardioplegic arrest

The release of lactate, phosphate and purine catabolites from the heart in adult and children undergoing cardiac surgery was recorded. The compounds were determined in the coronary effluent collected during subsequent infusions of cardioplegic solution into the coronary root. As compared to the infusion just after onset of ischemia, both in adults and children manifold increase of the release was observed during subsequent infusions. The rates of release of lactate, phosphate and purines (adenosine + inosine + hypoxanthine) were 1.5 to 2.5 times higher in children than in adult hearts during the second cardioplegic infusion and 3 to 7 times higher during the third cardioplegic infusion in spite of a more frequent infusion of cardioplegic solution in children. A much greater increase of the release of lactate, phosphate and purines provides evidence for more severe metabolic injury during cardioplegic arrest to the heart in children than in adults.

Xanthine oxidoreductase activity in perfused hearts of various species, including humans

Oxygen free radicals generated by xanthine oxidase have been implicated in cardiac damage. The activity of xanthine oxidase/reductase in adult rat heart is considerable. Its assay gives controversial results for other species, for example, rabbits and humans. Therefore, we perfused isolated hearts of various species, including explanted human hearts, to measure the conversion of exogenous hypoxanthine to xanthine and urate. We assayed these purines with high-performance liquid chromatography. The apparent xanthine oxidoreductase activities, calculated as release of xanthine plus 2x urate, were (milliunits per gram wet weight, mean +/- SEM) mice 33 +/- 3 (n = 5), rats 28.5 +/- 1.4 (n = 9), guinea pigs 14.4 +/- 1.0 (n = 5), rabbits 0.59 +/- 0.09 (n = 5), pigs less than 0.1 (n = 6), humans 0.31 +/- 0.04 (n = 7), and cows 3.7 +/- 0.8 (n = 4). In rabbit heart the conversion of hypoxanthine to xanthine was slow, and that of xanthine to urate was even slower. On the other hand, guinea pig and human heart released little xanthine, indicating that xanthine breakdown exceeds its formation. We conclude that isolated perfused mouse, rat, guinea pig, and also bovine hearts show considerable xanthine oxidoreductase activity, contrasting rabbit, porcine, and diseased human hearts.

Myocardial protection by intravenous diltiazem during angioplasty of single-vessel coronary artery disease

The possible cardioprotective effect of diltiazem during ischemia caused by percutaneous transluminal coronary angioplasty was tested. Electrocardiograms and myocardial lactate, hypoxanthine and urate production were determined in 26 patients with a stenosis in the left anterior descending artery without angiographically demonstrable collaterals. Measurements took place before angioplasty, after each of 4 occlusions and 15 minutes after the last balloon inflation. Patients were randomly given placebo or DL-diltiazem (0.4 mg/kg as a bolus intravenously, followed by an infusion of 15 mg/hr). During angioplasty the ST-segment elevation for the anterior wall leads V2, V4 and V6, and the intracoronary lead was similar for both groups, as was lactate release. Diltiazem significantly reduced cardiac hypoxanthine release immediately after angioplasty from 63 to 88% (p less than 0.05). The drug diminished urate production after the last dilatation by 82% (p less than 0.05). In conclusion, intravenous infusion of diltiazem reduced cardiac adenosine triphosphate breakdown during angioplasty as shown by diminished hypoxanthine and urate production. In contrast, diltiazem was unable to attenuate ST-segment elevation and lactate release.