Adenosine metabolism and its effect on methylation potential in cultured cells: methodological considerations.

Cell culture models are frequently used to study the role of adenosine in several physiological and pathological processes. In the present study, we have shown that adenosine deaminase activity in medium supplemented with calf serum significantly reduces adenosine concentration in culture medium. In the presence of HepG2 cells, the adenosine concentration in culture medium is decreased much faster, because a large amount of exogenous adenosine is metabolized by cellular enzyme. In order to measure intracellular adenosine, inosine, adenine nucleotides, S-adenosylhomocysteine (AdoHcy) and Sadenosylmethionine (AdoMet) contents, two methods for cell harvesting were compared. First, cells were removed with trypsin/EDTA, second, cells were lysed in cell culture dishes immediately after removing culture medium. Our results show that exact determination of adenosine metabolites requires immediate inactivation of metabolism by cell lysis in culture dishes. Application of adenosine (1mM) resulted in a time-dependent increase in intracellular adenosine, inosine, AMP, ATP, AdoHcy and AdoMet concentration. Since AdoHcy levels increased to a larger extent than AdoMet, the methylation potential, expressed as the ratio of AdoMet/AdoHcy, was reduced from 51.8 (control) to 2.9 (adenosine 1 mM, 2 hrs), suggesting that AdoMet-dependent methylation reactions might be impaired. In conclusion our data demonstrate that extracellular adenosine concentration and intracellular metabolite concentration strongly depend on the methods used to culture and harvest the cells.

Insulin effects on myocardial function and bioenergetics in L-bupivacaine toxicity in the isolated rat heart.

BACKGROUND AND OBJECTIVES: A positive effect of insulin-glucose-potassium infusion in severe bupivacaine-induced cardiovascular collapse has been described in vivo. It has been speculated that an antagonistic influence of insulin on sodium channel inhibition, transient outward potassium current, calcium-dependent adenosine triphosphatase or even improved myocardial energetics may be responsible for this effect. Using an isolated heart model, we therefore sought to further elucidate insulin effects in l-bupivacaine-induced myocardial depression. METHODS: An isolated rat heart constant-pressure perfused, non-recirculating Langendorff preparation was used. Hearts were exposed to l-bupivacaine 5 microg mL(-1) and insulin 10 mIU mL(-1). Heart rate, systolic pressure, the first derivative of left ventricular pressure (+dP/dt), coronary flow, double product, PR and QRS intervals were recorded. Hearts were freeze-clamped and high-performance liquid chromatography measurement of the total adenine nucleotide pool was performed. RESULTS: l-Bupivacaine led to a significant decrease in heart rate, +dP/dt, systolic pressure, coronary flow and double product, and to an increase in PR and QRS. Insulin exerted a positive inotropic effect, significantly augmenting +dP/dt and systolic pressure in both l-bupivacaine-treated and control hearts. Heart rate, coronary flow, total adenine nucleotides, PR and QRS were not significantly changed by the insulin intervention. CONCLUSION: Insulin did not have a significant effect on total adenine nucleotides in controls and in l-bupivacaine-treated hearts. However, it does exert a positive inotropic action in bupivacaine-induced myocardial depression. We conclude that the positive effect of insulin application lies in positive inotropic action and not in changes in total adenine nucleotides.

The dual effects of nitric oxide synthase inhibitors on ischemia-reperfusion injury in rat hearts.

OBJECTIVE: Nitric oxide (NO) is known to act as a mediator of tissue injury as well as being a potent endogenous vasodilator. The functional and metabolic effects of NO on ischemia-reperfusion injury are still controversial. The aim of this study was to clarify the relationship between the degree of NO synthase (NOS) inhibition and the effects on ischemia-reperfusion injury. METHODS AND RESULTS: Langendorff-perfused rat hearts were subjected to 30 minutes of global ischemia followed by 30 minutes of reperfusion. The recovery of left ventricular developed pressure (LVDP), creatine kinase (CK) release, and myocardial high energy phosphates were measured in hearts perfused with or without NOS inhibitors, L-N(G)-monomethyl arginine (L-NMMA) or N(G)nitro-L-arginine methylester (L-NAME). NOS inhibitors exerted different effects on the recovery of LVDP and CK release depending on the concentration. The low dose of L-NMMA improved the recovery of LVDP, decreased the CK release during reperfusion, and preserved the myocardial adenosine triphosphate content after reperfusion. In contrast, the high dose of L-NMMA had adverse effects. L-NMMA reduced NO release in coronary effluent in a dose-dependent fashion. Both effects of L-NMMA were abolished by excessive co-administration of L-arginine and the same doses of D-N(G)-monomethyl arginine (D-NMMA) showed no effect on ischemia-reperfusion injury. Therefore, both effects were due to NOS inhibition. In addition, L-NMMA suppressed the myocardial malondialdehyde accumulation, an indicator of oxidative stress, which might be attributed to the beneficial effects by partial NOS inhibition. On the other hand, the high dose L-NMMA significantly decreased coronary fl ow during aerobic perfusion and reperfusion. Therefore, it is conceivable that the vasoactive NOS inhibition contributes to the harmful effects, which might exceed the beneficial effects due to a decrease in oxidative stress. CONCLUSION: The present results showed that NO inhibitors had dual effects on mechanical function and energy metabolism depending on the concentration. Non-vasoactive inhibition of NOS had beneficial effects due to the suppression of oxidative injury. However, strong vasoactive inhibition of NOS exacerbated the ischemia-reperfusion injury.

Glutamine administration during total parenteral nutrition protects liver adenosine nucleotides during and after subsequent hemorrhagic shock.

BACKGROUND: Glutamine supplementation of total parenteral nutrition (TPN) in stressed patients has been advocated. To determine whether glutamine supplementation affects the host response to conditions of stress, animals were given TPN with or without glutamine for 7 days. They were then subjected to the acute stress of hemorrhagic shock, which results in marked loss of hepatic adenosine triphosphate (ATP) and adenosine diphosphate (ADP), with accumulation of adenosine monophosphate (AMP) and the metabolites adenosine, inosine, hypoxanthine, and xanthine. This loss of ATP and accumulation of metabolites contributes to subsequent tissue damage. The hypothesis of the study was that glutamine supplementation would significantly improve restoration of hepatic adenosine nucleotides before and after hemorrhagic shock. METHODS: Sprague-Dawley rats were given TPN for 7 days. One half of the animals (n = 8) received TPN supplemented with glutamine, while one half received TPN with an isonitrogenous mixture of alanine and glycine. Animals were subjected to hemorrhagic shock for 30 minutes and then resuscitated using only heparinized shed blood. Liver biopsies were taken pre- and post-shock, and at 30 and 60 minutes after resuscitation. ATP, ADP, AMP, and their metabolites were measured using gradient high-performance liquid chromatography. RESULTS: After 7 days of TPN, baseline values of ATP, ADP, AMP, and metabolites were similar between the 2 groups before the initiation of shock. Glutamine-treated animals manifested a 40% decrease in ATP level immediately after shock and recovered to 90% of baseline within 60 minutes. By contrast, the control animals manifested a 66% decrease in ATP level after the shock period and recovered only to 60% of baseline at 1 hour postresuscitation. Similar changes were observed in ADP levels and were accompanied by corresponding changes in AMP and adenosine metabolites, all of which rose during shock and fell after resuscitation. CONCLUSIONS: Glutamine supplementation significantly protected the liver from tissue damage caused by hemorrhagic shock. ATP levels remained higher during shock and recovered more rapidly after resuscitation. Glutamine supplementation may help to protect cellular energy stores in the stressed organism and may offer opportunities for therapeutic intervention during and after stress.

Methylation demand and homocysteine metabolism: effects of dietary provision of creatine and guanidinoacetate.

S-adenosylmethionine, formed by the adenylation of methionine via S-adenosylmethionine synthase, is the methyl donor in virtually all known biological methylations. These methylation reactions produce a methylated substrate and S-adenosylhomocysteine, which is subsequently metabolized to homocysteine. The methylation of guanidinoacetate to form creatine consumes more methyl groups than all other methylation reactions combined. Therefore, we examined the effects of increased or decreased methyl demand by these physiological substrates on plasma homocysteine by feeding rats guanidinoacetate- or creatine-supplemented diets for 2 wk. Plasma homocysteine was significantly increased (~50%) in rats maintained on guanidinoacetate-supplemented diets, whereas rats maintained on creatine-supplemented diets exhibited a significantly lower (~25%) plasma homocysteine level. Plasma creatine and muscle total creatine were significantly increased in rats fed the creatine-supplemented or guanidinoacetate-supplemented diets. The activity of kidney L-arginine:glycine amidinotransferase, the enzyme catalyzing the synthesis of guanidinoacetate, was significantly decreased in both supplementation groups. To examine the role of the liver in mediating these changes in plasma homocysteine, isolated rat hepatocytes were incubated with methionine in the presence and absence of guanidinoacetate and creatine, and homocysteine export was measured. Homocysteine export was significantly increased in the presence of guanidinoacetate. Creatine, however, was without effect. These results suggest that homocysteine metabolism is sensitive to methylation demand imposed by physiological substrates.

Effect of creatine supplementation on sprint exercise performance and muscle metabolism.

The aim of the present study was to examine the effect of creatine supplementation (CrS) on sprint exercise performance and skeletal muscle anaerobic metabolism during and after sprint exercise. Eight active, untrained men performed a 20-s maximal sprint on an air-braked cycle ergometer after 5 days of CrS [30 g creatine (Cr) + 30 g dextrose per day] or placebo (30 g dextrose per day). The trials were separated by 4 wk, and a double-blind crossover design was used. Muscle and blood samples were obtained at rest, immediately after exercise, and after 2 min of passive recovery. CrS increased the muscle total Cr content (9.5 +/- 2.0%, P < 0.05, mean +/- SE); however, 20-s sprint performance was not improved by CrS. Similarly, the magnitude of the degradation or accumulation of muscle (e.g., adenine nucleotides, phosphocreatine, inosine 5'-monophosphate, lactate, and glycogen) and plasma metabolites (e.g. , lactate, hypoxanthine, and ammonia/ammonium) were also unaffected by CrS during exercise or recovery. These data demonstrated that CrS increased muscle total Cr content, but the increase did not induce an improved sprint exercise performance or alterations in anaerobic muscle metabolism.

Dietary nucleotides accelerate intestinal recovery after food deprivation in old rats.

Previous studies in very young rats have shown that dietary nucleotides improve small intestine repair after injury or malnutrition. To investigate the potential effect of nucleotides in old rats, which have a diminished capability for intestinal repair, 17-mo-old rats were deprived of food for 5 d and then fed a nucleotide-free diet or a nucleotide-supplemented diet for 3 or 6 d. Intestinal jejunal and ileal mucosal weight, protein and DNA were evaluated as intestinal growth markers, and brush-border maltase, sucrase, lactase and aminopeptidase activities were evaluated as intestinal differentiation markers. The adenine nucleotide pool and the adenylate energy charge were also evaluated as indices of nucleotide availability. Food deprivation significantly decreased mucosal growth markers as well as differentiation markers in both jejunum and ileum. The ATP pool was also significantly depressed, but the adenylate energy charge was not significantly altered. To a certain extent, refeeding restored the losses, but in the rats that were fed the nucleotide-free diet, the restoration of the jejunum was significantly slower and the restoration of the ileum differentiation markers was incomplete compared with the rats fed the nucleotide-supplemented diet. The results suggest that dietary nucleotide intake in the elderly may accelerate the normal physiological intestinal response to refeeding after food deprivation.

Effects of acute alcohol intoxication on gluconeogenesis and its hormonal responsiveness in isolated, perfused rat liver.

Rats were acutely administered ethanol as a primed constant infusion in order to produce sustained blood ethanol levels of 8-12 or 55-65 mM. At the end of ethanol infusion the livers were either freeze-clamped in vivo or isolated and perfused for metabolic studies. The rate of gluconeogenesis and its responsiveness to phenylephrine (10 microM), prostaglandin F2 alpha (5 microM) and glucagon (10 nM), as well as the redox state of the cytosolic NAD(+)-NADH system were assessed in livers isolated from acutely ethanol-treated rats, and subsequently perfused without ethanol. For liver clamped in vivo, high- but not low-ethanol treatment decreased the ATP content by 31% and slightly increased ADP and AMP content, resulting in a decreased energy charge (11%). Glutamate and aspartate content was also increased in high-dose ethanol-infused rats with no changes in malate and 2-oxoglutarate content. Gluconeogenesis with saturating concentrations of lactate (4 mM)+pyruvate (0.4 mM) was delayed in reaching a plateau in the livers of high-dose ethanol-treated rats and its response to all three stimulators was impaired. Low-dose ethanol treatment only decreased the liver response to phenylephrine. While the perfused livers of low-dose ethanol-treated rats displayed no changes in adenine nucleotide content, the livers of high-dose ethanol-treated rats had a decreased ATP (35%) and an increased AMP (77%) content, paralleled by a fall in the total adenine nucleotides (14%) and energy charge (14%). No differences were observed between the saline- and ethanol-treated rats with respect to malate-aspartate shuttle intermediate concentration in perfused livers. Also, the livers of high-, but not low-dose ethanol-treated rats had a more negative value of NAD(+)-NADH redox state as compared to the livers of control rats. The data suggest that acute ethanol intoxication produces changes in liver metabolism and its responsiveness to hormones/agonists that are demonstrable for at least 2 hr after isolation and perfusion of the liver.

Changes in gastric mucosal content of adenosine, xanthine and hypoxanthine induced by restrained water immersion stress: antiulcer effects of tetraprenylacetone.

The purpose of this study was to clarify the involvement of adenine nucleotide metabolism and substrates of the xanthine-xanthine oxidase system as the source of oxygen free radicals in a rat model of restrained water immersion stress ulceration. The gastric mucosal concentrations of adenine-5'-triphosphate (ATP), adenine-5'-diphosphate (ADP), adenine-5'-monophosphate (AMP) and thiobarbituric-acid (TBA)-reactant substances were measured after 4, 8 and 12 h restrained water immersion stress. The gastric mucosal concentrations of the nucleoside adenosine, the purine bases xanthine and hypoxanthine, and the final metabolic product uric acid, were measured after 4 h of restrained water immersion stress. The concentrations of ATP diminished significantly after 4, 8 and 12 h of restrained water immersion stress. However, the observed stress-induced changes in ADP were not significant. AMP concentrations increased significantly after 4, 8 and 12 h of stress. The adenylate pool (ATP + ADP + AMP) dropped significantly from the prestress value after 4, 8 and 12 h of stress, and the concomitant energy charge (EC = ATP + 0.5 ADP/ATP + ADP + AMP) decreased significantly after 4 and 8 h of stress compared with the prestress value. Gastric mucosal concentrations of TBA-reactant substances displayed a significant increase after 4 h of stress, and remained unchanged after 8 and 12 h of stress from the level after 4 h. Four hours of restrained water immersion stress induced an increase in adenosine and uric acid concentrations and a decrease in the hypoxanthine concentration of the gastric mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of dimephosphon on the adenine nucleotide system]. / Vliianie dimefosfona na sistemu adenilovykh nukleotidov.

The effect of a single injection of dimephosphon (1 mM/kg) on adenine nucleotide system in the liver of healthy and chlorophos-poisoned (a mean lethal dose) rats was studied. It was shown that in healthy rats dimephosphon decreased the levels of all components of adenylate system without changing the energy charge of adenylates. The treatment of the poisoned animals with dimephosphon normalized the parameters of energy metabolism disturbed by chlorophos intoxication.

A 31P nuclear magnetic resonance in vivo study of cerebral ischaemia in the gerbil.

We have used the noninvasive method of 31phosphorus nuclear magnetic resonance (31P NMR) in vivo to follow changes in phosphorous metabolite concentrations and the intracellular pH in the right and left hemispheres and in the cerebellum of gerbil brains after the occlusion of the right carotid artery. Spatial resolution over the brain was possible using surface coils. Ligation, which is know to cause ischaemia in this species in the ipsilateral hemisphere, resulted in the diminution of phosphocreatine and adenine nucleotides and a decrease in tissue pH. Less acidification occurred in the contralateral hemisphere and in the cerebellum. The high-energy metabolite concentrations, phosphocreatine and adenosine triphosphate (ATP), declined in unison in the ischaemic region, in marked contrast to the sequence of events in skeletal muscle, in which phosphocreatine buffers against an immediate fall in ATP concentration. In a separate series of gerbils, 31P NMR spectra were followed for exactly 1 h after carotid ligation. The animals were then sacrificed and brain grey matter specific gravity was rapidly measured to assess the development of oedema. There was a clear correlation between abnormality of spectra and the presence of oedema. It cannot, however, be confidently asserted that a normal spectrum is never seen in oedematous gerbil brains. 31P NMR spectra specific gravity and histological changes shown by light microscopy have been correlated and show that useful signals are received from a depth of at least 4 mm or more from the 10-mm diameter coil.

Needle biopsy for muscle chemistry.

Needle biopsy can readily provide samples of human skeletal muscle for biochemical analysis. Muscle metabolites are measured by enzymic microanalytical techniques and electrolytes by neutron-activation analysis. This paper summarises the methods of analysis, gives the normal ranges for muscle contents of metabolites and electrolytes, and reviews the reported changes in a number of neuromuscular and metabolic disorders. Muscle is a fairly homogeneous tissue in health, but replacement with fat and fibrous tissue in myopathies causes error in analyses unless metabolites are referred to a reliable standard. It is recommended that needle-biopsy samples to be freeze-dried and dissected to remove connective tissue before analysis. Total creatine (phosphorylcreatine+free creatine) total adenosine+inosine nucleotides, and potassium and phosphorus separtely correlated very highly with sample dry weight after dissection, suggesting that these may be used as standards. When assessing whether a given metabolite is present in an abnormal amount, it is probaby advisable to check the content with reference to more than one standard, since one or more of these may be changed in disease.