A novel method for determination of ATP, ADP, and AMP contents of a single pancreatic islet before transplantation

Assessment of islet viability before transplantation is mandatory for successful clinical transplantation. ATP content or energy charge (EC) of islets may represent a good parameter to assess viability. We have introduced a novel bioluminescent enzymatic cycling assay using synthetic firefly luciferase, pyruvate kinase) (PK), and pyruvate orthophosphate dikinase (PPDK) to determine adenine nucleotides (AN) in isolated islets. A complete assay requires several minutes. The ATP contents of 1, 3, 10, 30 or 100 islets each with a diameter of 150 microm were 9.95 +/- 0.03, 28.3 +/- 1.18, 89.5 +/- 1.48, 282 +/- 10.2, and 673 +/- 27.1 pmol, respectively, showing a relatively constant ATP content per 30 islets (9.95, 9.42, 8.95, and 9.41 pmol/IEQ). ECs of each group were 0.74 +/- 0.02, 0.74 +/- 0.02, 0.75 +/- 0.02, 0.74 +/- 0.02, and 0.65 +/- 0.01, respectively, a value that was quite constant up to 30 islets. The quantity of ATP and EC in a single islet can be measured quickly and reproducibly, offering a new method to determine viability of isolated islets prior to transplantation.

[High performance liquid chromatogram (HPLC) determination of adenosine phosphates in rat myocardium]

OBJECTIVE

To establish method for the quantitative determination of adenosine phosphates in rat myocardium by optimized high performance liquid chromatogram (HPLC).

METHODS

ODS HYPERSIL C(18) column and a mobile phase of 50 mmol/L tribasic potassium phosphate buffer solution (pH 6.5), with UV detector at 254 nm were used.

RESULTS

The average recovery rates of myocardial adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP) were 99%-107%, 96%-104% and 95%-119%, respectively; relative standard deviations (RSDs) of within-day and between-days were less than 1.5% and 5.1%, respectively.

CONCLUSION

The method is simple, rapid and accurate, and can be used to analyse the adenosine phosphates in myocardium.

Constitutive UCP3 overexpression at physiological levels increases mouse skeletal muscle capacity for fatty acid transport and oxidation

Uncoupling protein 3 (UCP3) expression is directly correlated to fatty acid oxidation in skeletal muscle. UCP3 has been hypothesized to facilitate high rates of fatty acid oxidation, but evidence thus far is lacking. Our aim was to investigate the effects of UCP3 overexpression and ablation on fatty acid uptake and metabolism in muscle of mice having congenic backgrounds. In mice constitutively expressing the UCP3 protein (human form) at levels just over twofold higher than normal (230% of wild-type levels), indirect calorimetry demonstrated no differences in total energy expenditure (VO2), but a shift toward increased fat oxidation compared with wild-type (WT) mice. Metabolic efficiency (gram weight gain/kcal ingested) was similar between Ucp3 overexpressors, WT and Ucp3 (-/-) mice. In muscle of Ucp3-tg mice, plasma membrane fatty acid binding protein (FABPpm) content was increased compared with WT mice. Although hormone-sensitive lipase activity was unchanged across the genotypes, there were increases in carnitine palmitoyltransferase I, beta-hydroxyacylCoA dehydrogenase, and citrate synthase activities and decreases in intramuscular triacylglycerol in muscle of Ucp3-tg mice. There were no differences in muscle mitochondrial content. High-energy phosphates and total muscle carnitine and CoA were also greater in Ucp3-tg compared with WT mice. Taken together, the findings demonstrate an increased capacity for fat oxidation in the absence of significant increases in thermogenesis in Ucp3-tg mice. Findings from Ucp3 (-/-) mice revealed few differences compared with WT mice, consistent with the possibility of compensatory mechanisms. In conjunction with our observed increases in CoA and carnitine in muscle of Ucp3 overexpressors, the findings support the hypothesized role for Ucp3 in facilitating fatty acid oxidation in muscle.

Decreased UCP2 mRNA expression in rat stomach following vagotomy: novel role for UCP2 as free radical scavenger in the stomach?

Uncoupling protein 2 (UCP2) is a protein, located in the inner mitochondrial membrane, which dissipates the proton gradient of this membrane and uncouples respiration from oxidative phosphorylation. We found, by in situ hybridisation, UCP2 mRNA to be located in the proliferating zone of the mucous neck cells in the fundus part of the rat stomach. We also found that UCP2 expression in fundus was significantly decreased after seven days of vagotomy. Furthermore, we found manganese-containing superoxide dismutase (SOD2), in fundus, to be down-regulated in a way similar to UCP2. The amount of ATP was significantly decreased following vagotomy. It is concluded that UCP2 in the gastro-intestinal tract is regulated through vagal innervation and suggested to act as a free radical scavenger.

Uniformly oriented bacterial F0F1-ATPase immobilized on a semi-permeable membrane: a step towards biotechnological energy transduction

The immobilization of F(0)F(1)-ATPase in uniform orientation is reported. The biotinylated and histidine-tagged subunits of the bacterial F(0)F(1)-ATPase complex were used for immobilization of the complex on artificial semi-permeable membranes resulting in 88+/-7.8 and 72+/-5.2% coupling of the enzymes. The immobilized enzymes retained over 90% activity. The immobilized ATPase/synthase was used for generation of ATP from ADP and P(i) at the expense of electrochemical potential energy. The re-usability, ratio of amount of enzyme immobilized to enzymic activity conferred on the membranes, ATP synthesized by assembled system and suitability of ATP generated for use in coupled enzymic reactions were determined.

ADP-specific sensors enable universal assay of protein kinase activity

Two molecular sensors that specifically recognize ADP in a background of over 100-fold molar excess of ATP are described. These sensors are nucleic-acid based and comprise a general method for monitoring protein kinase activity. The ADP-aptamer scintillation proximity assay is configured in a single-step, homogeneous format while the allosteric ribozyme (RiboReporter) sensor generates a fluorescent signal upon ADP-dependent ribozyme self-cleavage. Both systems perform well when configured for high-throughput screening and have been used to rediscover a known protein kinase inhibitor in a high-throughput screening format.

Polynucleotide phosphorylase-based photometric assay for inorganic phosphate

Polynucleotide phosphorylase is a prokaryotic enzyme that catalyzes phosphorolysis of polynucleotides with release of nucleotide diphosphates. By taking advantage of this property, we developed a photometric assay for inorganic phosphate. In the presence of polyadenylic acid, phosphate is converted into adenosine 5'-diphosphate (ADP) by this enzyme. ADP then reacts with phosphoenolpyruvate in a pyruvate kinase-catalyzed reaction, thus giving rise to adenosine 5'-triphosphate and pyruvate. Finally, pyruvate oxidizes reduced nicotinamide adenine dinucleotide (NADH) through the action of L-lactate dehydrogenase, with concomitant decrease in absorbance at 340 nm. As expected, in this detection system 1 mol of NADH was oxidized per mole of phosphate. The assay showed an excellent reproducibility, as the standard deviations never exceeded 5%. It also was shown to be unaffected by several compounds that are regarded as major interferents of the traditional colorimetric assays. Absence of interference was also demonstrated when determining phosphate content in different biological samples, such as human serum and perchloric acid extracts from Escherichia coli, yeast, and bovine liver. An E. coli strain overexpressing His-tagged polynucleotide phosphorylase developed in our laboratories allowed quick and straightforward purification of enzyme, making the assay feasible and convenient. Since all other reagents required are inexpensive, the assay represents a cheaper alternative to commercially available phosphate assay kits.

Cloning, function, and expression of sanS: a gene essential for nikkomycin biosynthesis of Streptomyces ansochromogenes

A 2-kb SmaI DNA fragment was cloned from the cosmid library of Streptomyces ansochromogenes. This DNA fragment contains a complete open reading frame which is 1275 bp in length, designated sanS (GenBank accession no. AF322179). The deduced SanS protein consists of 424 amino acids and belongs to a superfamily of enzymes with an unusual ATP-grasp fold. The disruption and complementation of sanS indicated that sanS is essential for nikkomycin biosynthesis in Streptomyces ansochromogenes. The sanS gene was subcloned into expression vector pET23b and overexpressed in E. coli BL21 (DE3). The protein was then purified and showed ATPase activity.

Microanalysis for MDR1 ATPase by high-performance liquid chromatography with a titanium dioxide column

MDR1 is clinically important because it is involved in multidrug resistance of cancer cells and affects the pharmacokinetics of various drugs. Because MDR1 harnesses adenosine 5'-triphosphate (ATP) hydrolysis for transporting drugs, examining the effect on ATPase activity is imperative for understanding the interactions between drugs and MDR1. However, conventional assay systems for ATPase activity are not sensitive enough for screening drugs using purified MDR1. Here we report a novel method to measure ATPase activity of MDR1 using high-performance liquid chromatography equipped with a titanium dioxide column. The amount of adenosine 5'-diphosphate (ADP) produced by the ATPase reaction was determined within 2 min with a titanium dioxide column (4.6 mm ID x 100 mm). The relationship between ADP amount and chromatogram peak area was linear from 5 pmol to 10 nmol. This method made it possible to reduce the amount of purified MDR1 required for a reaction to 0.5 ng, about 1/20th of the conventional colorimetric inorganic phosphate detection assay. This method is sensitive enough to detect any subtle changes in ATPase activity of MDR1 induced by drugs and can be applied to measure ATPase activity of any protein.

Determination of mitochondrial function and site-specific defects in electron transport in duodenal mitochondria in broilers with low and high feed efficiency

Duodenal mitochondria were isolated from broiler breeder males with high (0.79+/-0.01, n = 9) and low (0.63+/-0.02, n = 9) feed efficiency (FE) to assess relationships of FE with duodenal mitochondrial function and site-specific defects in electron transport. Sequential additions of adenosine diphosphate (ADP) resulted in 1) higher respiratory control ratio (RCR; an index of respiratory chain coupling) in high FE mitochondria provided succinate, and 2) higher ADP to oxygen ratio (ADP:O; an index of oxidative phosphorylation) in low FE mitochondria provided NADH-linked substrates (malate, pyruvate, or both). Basal electron leak, measured as H2O2 production, was greater in low FE mitochondria provided succinate (P = 0.08) or NADH-linked substrates. As H2O2 levels were elevated in low FE compared with high FE mitochondria by complex I (P+/-0.07) and complex II inhibition, the higher basal electron leak in low FE mitochondria was apparently due to site-specific defects in electron transport at complexes I and II. Elevations in H2O2 above basal levels indicated that high FE mitochondria may also exhibit electron transport defects at complexes I and III. Despite an ability to produce adenosine triphosphate (ATP) that was equal or superior to that demonstrated in high FE duodenal mitochondria, low FE mitochondria exhibited a greater inherent degree of electron leak. The results provide insight into the role that duodenal mitochondria play in the phenotypic expression of FE in broilers.

Brain to blood efflux transport of adenosine: blood-brain barrier studies in the rat

The blood-brain barrier (BBB) efflux transport of [(14)C] adenosine was studied using the brain efflux index (BEI) technique. BEI increased linearly over the first 2 min after injection, with deviation from linearity thereafter; 90.12 +/- 1.5% of the injected [(14)C] radioactivity remained within the brain after 20 min. The remaining tracer appears to be mainly intracellular, trapped by phosphorylation, as an almost linear increase of BEI over 20 min was observed after intracerebral injection of [(14)C] adenosine together with 5-iodo tubercidin. The BBB efflux clearance of [(14)C] radioactivity was estimated to be 27.62 +/- 5.2 micro L/min/g, almost threefold higher than the BBB influx clearance estimated by the brain uptake index technique. High-performance liquid chromatography (HPLC) analysis of blood plasma collected from the jugular vein after the intracerebral injection revealed metabolic breakdown of [(14)C] adenosine into nucleobases. The BBB efflux transport was saturable with apparent K(m) = 13.22 +/- 1.75 micro m and V(max) = 621.07 +/- 71.22 pmole/min/g, which indicated that BBB efflux in vivo is 6.2-12p mole/min/g, negligible when compared to the reported rate of adenosine uptake into neurones/glia. However, these kinetic parameters also suggest that under conditions of elevated ISF adenosine in hypoxia/ischaemia, BBB efflux transport could increase up to 25% of the uptake into neurones/glia and become an important mechanism to oppose the rise in ISF concentration. HPLC-fluorometry detected 93.6 +/- 5.25 nm of adenosine in rat plasma, which is 17- to 220-fold lower than the reported K(m) of adenosine BBB influx in rat. Together with the observed rapid degradation inside endothelial cells, this indicated negligible BBB influx of intact adenosine under resting conditions. Cross-inhibition studies showed that unlabelled inosine, adenine and hypoxanthine caused a decrease in BBB efflux of [(14)C] radioactivity in a concentration-dependent manner, with K(i) of 16.7 +/- 4.88, 65.1 +/- 14.1 and 71.1 +/- 16.9 micro m, respectively. This could be due to either competition of unlabelled molecules with [(14)C] adenosine or competition with its metabolites hypoxanthine and adenine for the same transport sites.

Role of uncoupling protein-2 up-regulation and triglyceride accumulation in impaired glucose-stimulated insulin secretion in a beta-cell lipotoxicity model overexpressing sterol regulatory element-binding protein-1c

Triglyceride (TG) accumulation in pancreatic beta-cells is thought to be associated with impaired insulin secretory response to glucose (lipotoxicity). To better understand the mechanism of the impaired insulin secretory response to glucose in beta-cell lipotoxicity, we overexpressed a constitutively active form of the sterol regulatory element-binding protein- 1c (SREBP-1c), a master transcriptional factor of lipogenesis, in INS-1 cells with an adenoviral vector. This treatment was associated with strong activation of transcription of the genes involved in fatty acid biosynthesis, increased cellular TG content, severely blunted glucose-stimulated insulin secretion, and enhanced expression of the uncoupling protein-2 (UCP-2), which supposedly dissipates the mitochondrial electrochemical potential. To decrease the up-regulated UCP-2 expression, small interfering RNA for UCP-2 was used. Introduction of the small interfering RNA increased the ATP/ADP ratio and partially rescued the glucose-stimulated insulin secretion in the cells overexpressing SREBP-1c, but did not affect the cellular TG content. Next, the effect of the AMP-activated protein kinase (AMPK) agonist, 5-amino-4-imidazolecarboxamide riboside, was examined in the lipotoxicity model. Exposure of the cells with lipotoxicity to 5-amino-4-imidazolecarboxamide riboside increased free fatty acid oxidation, partially reversed the TG accumulation, phosphorylated AMPK and acetyl-coenzyme A carboxylase, and improved the impaired glucose-stimulated insulin secretion. These results suggest that UCP-2 down-regulation and AMPK activation could be candidate targets for releasing beta-cells from lipotoxicity.

Single dose of glutamine enhances myocardial tissue metabolism, glutathione content, and improves myocardial function after ischemia-reperfusion injury

BACKGROUND

Myocardial ischemia and reperfusion (I/R) injury causes significant morbidity and mortality. Protection against I/R injury may occur via preservation of tissue metabolism and ATP content, preservation of reduced glutathione, and stimulation of heat shock protein (HSP) synthesis. Supplementation with glutamine (GLN) has been reported to have beneficial effects on all of these protective pathways. Thus, we hypothesized that GLN pretreatment given to the rat in vivo would protect the myocardium against I/R-induced dysfunction.

METHODS

GLN (0.52 g/kg, intraperitoneally, given as alanine-glutamine dipeptide), alanine alone (0.23 g/kg), or a Ringer's lactate solution (control) was administered to Sprague-Dawley rats 18 hours before heart excision, perfusion, exposure to global ischemia (15 minutes) and reperfusion (1 hour). Tissue metabolites were analyzed via magnetic resonance spectroscopy.

RESULTS

In control and alanine-treated animals, I/R injury resulted in cardiac dysfunction, indicated by a decrease in cardiac output. Administration of GLN 18 hours before I/R injury preserved cardiac output after reperfusion. Metabolic analysis of the myocardial tissue revealed that [/R injury led to significant diminution of myocardial tissue glutamate, ATP content, accumulation of myocardial lactate, and a reduction in reduced glutathione content in control animals. GLN significantly reduced the deleterious changes in myocardial metabolism and improved reduced glutathione content. No changes in pre- or post-I/R injury HSP expression were observed after GLN administration.

CONCLUSIONS

These observations demonstrate that remote in vivo administration of GLN before cardiac I/R injury can improve post-I/R cardiac function. This effect may be mediated via improved myocardial metabolism and enhanced reduced glutathione content.

Progressive sensorimotor impairment is not associated with reduced dopamine and high energy phosphate donors in a model of ataxia-telangiectasia

Ataxia-telangiectasia (A-T) is a genetic disease, associated with progressive motor impairment and a lack of functional ATM protein. It has been reported that immunoreactive tyrosine hydroxylase and dopamine transporter are reduced in an Atm-/- mouse model of A-T. These observations led to a hypothesis that A-T is associated with loss of nigrostriatal dopamine and prompted the launch of clinical trials to evaluate a therapeutic utility of the anti-parkinsonian drug, l-DOPA. To test for dopamine depletion more directly, we measured regional levels of monoamines and their metabolites in the Atm-/- mouse brain. We also measured levels of NAD+, a cofactor for dopamine biosynthesis and substrate of the DNA damage surveillance enzyme, poly(ADP-ribose) polymerase (PARP). Constitutive activation of PARP has been posited to cause NAD+ depletion. We observed no reduction in monoamine transmitters and no depletion of NAD+, or other high energy phosphate donors in the adult Atm-/- cerebellum, striatum, or ventral mesencephalon. However, our studies did reveal a progressive sensorimotor impairment in Atm-/- mice that may serve as a relevant proxy for progressive neurological impairment in the human disease. Our results call into question the involvement of dopamine in A-T and the therapeutic strategy of enhancing dopaminergic function with l-DOPA.

On selectivity and sensitivity of synthetic multifunctional pores as enzyme sensors: discrimination between ATP and ADP and comparison with biological pores

This report delineates scope and limitation of the selectivity of synthetic multifunctional pores as enzyme sensors using glycolytic enzymes as example (G. Das, P. Talukdar, and S. Matile, Science, 2002, Vol. 298, pp. 1600-1602). Unproblematic detectability of hexokinase and phosphofructokinase demonstrates that the selectivity of synthetic multifunctional pore (SMPs) sensors suffices to sense ATP in mixed analytes containing ADP, whereas detection of the isomerization of glucose 6-phosphate into fructose 6-phosphate by phosphoglucose isomerase is not possible with confidence. The sensitivity of SMP sensors is sufficient for end-point detection of one picomole poly-L-glutamate hydrolyzed by papain in unoptimized assay format; the sensitivity of melittin as representative biological pore of similar charge and aggregation number to detect the same reaction is more than four orders of magnitude inferior.

[Determination of creatine, phosphocreatine and adenosinephosphates in experimental hydrocephalus tissue by reversed-phase high performance liquid chromatography]

OBJECTIVE

To investigate the state of impaired cerebral energy metabolism of the hydrocephalus tissue.

METHODS

Adult male dogs were used for establishing the model of kaolin-induced hydrocephalus. A simple and rapid method for the simultaneous determination of creatine (Cr), phosphocreatine (Crp), and adenosinephosphates (AMP, ADP, ATP) in different stages of experimental hydrocephalus tissue by reversed-phase high performance liquid chromatography (RP-HPLC) has been established. The chromatographic conditions were as follows: Inertsil ODS-3 C18 column (4.6 mm x 250 mm i.d. 5 microns), the mobile phase being composed of KH2PO4 buffer (330 mmol/L)-acetonitrile-TBA (45 mmol/L) (94:5.5:0.5) (pH = 6.27) and detector at 210 nm.

RESULTS

The calibration curve showed a good linearity in the mass concentration range of 5.69-3640.50 mumol/L (r = 0.9993) for Cr, 3.47-555.50 mumol/L (r = 0.9999) for Crp, 2.69-1723.00 mumol/L (r = 0.9993) for AMP, 2.66-1704.00 mumol/L (r = 0.9999) for ADP and 2.94-1883.50 mumol/L (r = 0.9999) for ATP. The recoveries ranged from 90.10% to 107.00% with relative standard deviations from 1.58% to 3.88%. The detection limits of this method were 3.55-5.84 mumol/L. By means of this method, the Cr, Crp, AMP, ADP and ATP in different stages of 16 dogs experimental hydrocephalus tissue were determined with satisfactory results.

CONCLUSION

This method is rapid, precise, accurate and suitable for the determination of the high energy nucleotides in hydrocephalus tissues.

Mid-infrared spectroscopic measurement of ionic dissociative materials in the metabolic pathway

We determine the pH dependency of the mid-infrared spectra in aqueous solution of the organic dissociative materials in the metabolic pathway: saccharide phosphates (G6P, F6P), adenosine, and its phosphates (ATP, ADP, AMP). The series of molar absorbance spectra for these reagents were obtained in a pH range of about 2 to 11 with a Fourier transform infrared (FT-IR) spectrometer equipped with a horizontal diamond attenuated total reflection (ATR) sampling accessory. We also provide a method of infrared spectral extraction of ionic dissociative materials by performing a linear least-square fitting utilizing the formulas of ionic dissociation equilibrium shift, and we obtain the infrared spectrum of each ionic species of the dissociative materials: G6P-, G6P2-; F6P-, F6P2-; ATP2-, ATP3-, ATP4-; ADP-, ADP2-, ADP3-; AMP, AMP-, AMP2-; and adenosine+, adenosine0. The infrared spectral structure of each ionic species of the dissociative materials in the metabolic pathway are discussed. Additionally, the possibility for a quantification system of the concentrations of the organic dissociative materials in varying pH is suggested.

Sepsis-induced failure of hepatic energy metabolism

HYPOTHESIS

Recent evidence suggests that sepsis may induce an uncoupling of oxidative phosphorylation. The purpose of this study was to quantify temporal changes in hepatic oxygen consumption and cellular energy state with increasing severity of sepsis and thus assess the interrelationship of these parameters as either primary defect or compensatory response.

MAIN OUTCOME MEASURES

Pseudomonas aeruginosa was infused intravenously in eight instrumented anesthetized swine inducing a progressive severity of sepsis to shock. Eight other animals served as instrumented controls. Hepatic blood flow, oxygen use, and concentrations of ATP, ADP, AMP, NAD(+), and NADH were measured at baseline and then sequentially during the study.

RESULTS

Except for an increase in heart rate, there were no temporal changes in measured values for the control animals. For swine receiving P. aeruginosa, hepatic oxygen delivery and consumption increased with early sepsis whereas there were no alterations in the concentrations of adenine nucleotides or NAD(+)/NADH within liver. Septic shock was notable for a decrease in oxygen delivery yet oxygen consumption remained elevated because of an increase in percent oxygen extraction. The hepatic concentrations of ATP and NADH decreased during septic shock.

CONCLUSIONS

These findings suggest that any sepsis-induced limitation in phosphorylation may be initially compensated by an increase in oxygen use. This study also suggests that decreases in NADH availability may be a principal factor in the decompensation of sepsis to shock.

Permeability transition in rat liver mitochondria is modulated by the ATP-Mg/Pi carrier

Mitochondrial permeability transition, due to opening of the permeability transition pore (PTP), is triggered by Ca2+ in conjunction with an inducing agent such as phosphate. However, incubation of rat liver mitochondria in the presence of low micromolar concentrations of Ca2+ and millimolar concentrations of phosphate is known to also cause net efflux of matrix adenine nucleotides via the ATP-Mg/Pi carrier. This raises the possibility that adenine nucleotide depletion through this mechanism contributes to mitochondrial permeability transition. Results of this study show that phosphate-induced opening of the mitochondrial PTP is, at least in part, secondary to depletion of the intramitochondrial adenine nucleotide content via the ATP-Mg/Pi carrier. Delaying net adenine nucleotide efflux from mitochondria also delays the onset of phosphate-induced PTP opening. Moreover, mitochondria that are depleted of matrix adenine nucleotides via the ATP-Mg/Pi carrier show highly increased susceptibility to swelling induced by high Ca2+ concentration, atractyloside, and the prooxidant tert-butylhydroperoxide. Thus the ATPMg/Pi carrier, by regulating the matrix adenine nucleotide content, can modulate the sensitivity of rat liver mitochondria to undergo permeability transition. This has important implications for hepatocytes under cellular conditions in which the intramitochondrial adenine nucleotide pool size is depleted, such as in hypoxia or ischemia, or during reperfusion when the mitochondria are exposed to increased oxidative stress.

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.

Ischaemic preconditioning alters the energy metabolism and protects the ischaemic myocardium in a stepwise fashion

AIMS AND METHODS

Recently it was suggested that ischaemic preconditioning (IP) protects the myocardium in a graded pattern as assessed by myocardial infarct size estimation. Using tissue biopsies we investigated the impact of the proposed graded pattern of protection on myocardial energy state in an open-chest porcine model of IP with either one (1xIP) or four (4xIP) episodes of preconditioning. Furthermore, we evaluated the relationship between interstitial energy-related metabolite levels obtained by the microdialysis technique and the degree of subsequent ischaemic insult.

RESULTS

During the long ischaemia the difference between pre-ischaemic and post-ischaemic total adenylate pools and the sum of adenylate breakdown products (adenosine, inosine and hypoxanthine) as well as tissue lactate levels appeared as follows: non-IP > 1xIP > 4xIP (P < 0.05). Moreover interstitial peak levels of lactate, hypoxanthine and taurine displayed a graded pattern analogous to the development of ischaemic damage, where non-IP > 1xIP > 4xIP.

CONCLUSIONS

We present for the first time concordant energy metabolic and morphometric data in support of IP being a stepwise phenomenon for protection of the ischaemic myocardium. Furthermore, IP resulted in proportionally higher levels of hypoxanthine (relative to inosine) in the ischaemic myocardium, suggesting a different handling of adenine nucleotide breakdown products in the IP myocardium.

Cellular energetics in hemorrhagic shock: restoring adenosine triphosphate to the cells

BACKGROUND

This is a review of studies with two agents, glutamine and crocetin, which have been found to enhance recovery of cellular adenosine triphosphate (ATP) and adenosine diphosphate after hemorrhagic shock.

METHODS

The studies used a sublethal (30 minutes) reservoir shock model in 300- to 350-g, male, Sprague-Dawley rats, using either ketamine-xylazine or isoflurane anesthesia. Glutamine was given as a 3% (21 mmol/L) solution in Ringer's lactate (630 mg/kg). Crocetin was given as a 500 nmol/L solution in Ringer's lactate (2 mg/kg).

RESULTS

Both glutamine and crocetin caused recovery of ATP to baseline levels (9.0 micromol/g) within 60 to 120 minutes after resuscitation. Xanthine levels returned more rapidly to baseline (0.1 micromol/g). Both agents prevented the elevation in apoptosis seen in controls at 24 and 48 hours.

CONCLUSION

Glutamine is a metabolic substrate and a precursor of ATP synthesis. Crocetin enhances oxygen diffusivity in plasma. Both agents restore cellular energy stores to normal after hemorrhagic shock and produce a marked diminution in the extent of apoptosis postshock. Their mechanism of action probably involves prevention of mitochondrial damage.

A spectrophotometric method to quantify linear DNA

A spectrophotometric method for quantification of linear DNA is described. The assay measures ADP produced following digestion of linear DNA by an ATP-dependent deoxyribonuclease. Cleavage of the phosphodiester bond of the DNA substrate is proportional to ADP formed in the reaction which follows typical Michaelis-Menten kinetics (K(m) of 0.6 microM, and a V(max) of 30 nmol/min/mg). The enzyme requires Mg(2+)-ATP and Mg(2+)-DNA as substrates, although the results suggest a requirement for yet another metal ion which may be enzyme bound. Both single-stranded and double-stranded linear DNA are substrates, as demonstrated by comparable initial velocity measurements. However, covalently closed circular (CCC) and nicked open circular DNA are not substrates for the enzyme. The rate of hydrolysis of ATP is not inhibited by 1 microg RNA or covalently closed circular DNA. The product (ADP) formed in the reaction is coupled to NADH oxidation using pyruvate kinase and lactate dehydrogenase. NAD formed in the reaction is monitored spectrophotometrically as a loss in absorbance at 340 nm. This assay directly measures the amount of linear DNA present in preparations of supercoiled (CCC) plasmid DNA, and has direct utility for monitoring the quality of plasmid preparations for gene therapy.

Effects of epinephrine and norepinephrine on hemodynamics, oxidative metabolism, and organ energetics in endotoxemic rats

OBJECTIVE

To determine whether epinephrine increases lactate concentration in sepsis through hypoxia or through a particular thermogenic or metabolic pathway.

DESIGN

Prospective, controlled experimental study in rats.

SETTING

Experimental laboratory in a university teaching hospital.

INTERVENTIONS

Three groups of anesthetized, mechanically ventilated male Wistar rats received an intravenous infusion of 15 mg/kg Escherichia coli O127:B8 endotoxin. Rats were treated after 90 min by epinephrine ( n=14), norepinephrine ( n=14), or hydroxyethyl starch ( n=14). Three groups of six rats served as time-matched control groups and received saline, epinephrine, or norepinephrine from 90 to 180 degrees min. Mean arterial pressure, aortic, renal, mesenteric and femoral blood flow, arterial blood gases, lactate, pyruvate, and nitrate were measured at baseline and 90 and 180 min after endotoxin challenge. At the end of experiments biopsy samples were taken from the liver, heart, muscle, kidney, and small intestine for tissue adenine nucleotide and lactate/pyruvate measurements.

MEASUREMENTS AND RESULTS

Endotoxin induced a decrease in mean arterial pressure and in aortic, mesenteric, and renal blood flow. Plasmatic and tissue lactate increased with a high lactate/pyruvate (L/P) ratio. ATP decreased in liver, kidney, and heart. The ATP/ADP ratio did not change, and phosphocreatinine decreased in all organs. Epinephrine and norepinephrine increased mean arterial pressure to baseline values. Epinephrine increased aortic blood flow while renal blood low decreased with both drugs. Plasmatic lactate increased with a stable L/P ratio with epinephrine and did not change with norepinephrine compared to endotoxin values. Nevertheless epinephrine and norepinephrine when compared to endotoxin values did not change tissue L/P ratios or ATP concentration in muscle, heart, gut, or liver. In kidney both drugs decreased ATP concentration.

CONCLUSIONS

Our data demonstrate in a rat model of endotoxemia that epinephrine-induced hyperlactatemia is not related to cellular hypoxia.

Once again about the functional coupling between mitochondrial creatine kinase and adenine nucleotide translocase

The synthesis of creatine phosphate (CP) by mitochondrial creatine kinase during oxidative phosphorylation was terminated when the mass action ratio of the creatine kinase reaction Gamma = [ADP]*[CP]/[ATP]*[Cr] became equal to the apparent equilibrium constant (K(eq)(app))of this reaction. Subsequent excess of Gamma over the K(eq)(app) was due to an increase in the ADP concentration in the medium. A comparable increase in the ADP concentration also occurred in the absence of creatine (Cr) in the incubation medium. Increase in the ADP concentration was shown to be associated with a decrease in the rate of oxidative phosphorylation and with a relative increase in the ATPase activity of mitochondria during the incubation. A low concentration of ADP (<30 micro M) and relatively high concentrations (1-6 mM) of other components of the creatine kinase reaction prevented the detection of the reverse reaction within 10 min after Gamma exceeded the K(eq)(app), but the reverse reaction became evident on more prolonged incubation. The reverse reaction was accompanied by a further increase in Gamma. Low ADP concentration in the medium was also responsible for the lack of an immediate conversion of the excess creatine phosphate added although Gamma > K(eq)(app). The findings are concluded to be in contradiction with the concept of microcompartment formation between mitochondrial creatine kinase and adenine nucleotide translocase.

Hypoxia differentially regulates nutrient transport in rat jejunum regardless of luminal nutrient present

Aggressive enteral nutrition and poor intestinal perfusion are hypothesized to play an important pathogenic role in nonocclusive small bowel necrosis. This study tests the hypothesis that glucose and glutamine transport are differentially regulated during hypoxia regardless of the luminal nutrient present. Sprague-Dawley rats (247 +/- 3 g; n = 16) were randomized to receive 1 h of intestinal hypoxia or serve as normoxic controls. During this hour, jejunal loops were randomized to receive in situ perfusions of mannitol, glucose, or glutamine. When compared with normoxic groups, glucose but not glutamine transport was impaired (P < 0.001) during hypoxia. Messenger RNA abundance of the sodium glucose cotransporter sodium-dependent glucose cotransporter-1 (SGLT-1) and neutral basic amino acid transporter B(o) did not differ with hypoxia or nutrient perfused. Jejunal brush-border SGLT-1 abundance was decreased (P = 0.039) with hypoxia; however, total cellular SGLT-1 protein abundance did not differ among treatment groups. These data indicate that SGLT-1 activity is regulated during hypoxia at the posttranslational level. Additional information regarding the mechanisms regulating nutrient transport in the hypoperfused intestine is critical for optimizing the composition of enteral nutrient formulas.

Extracellular metabolisation of NADH by blood cells correlates with intracellular ATP levels

A new assay allowing quantitation of extracellular NADH metabolisation by intact blood cells was compared with the intracellular ATP/ADP ratio of these cells. The sensitivity, reproducibility and NADH specificity of this assay were determined. The diagnostic potential of this test was examined in a study with highly conditioned athletes. NADH consumption was measured before and immediately after maximum aerobic performance as well as 1 day later and was compared with the ATP/ADP level in these blood cells. A significant decline of cellular energy after aerobic performance was detected with both approaches to a similar extent (P<0.01). However, the extracellular NADH metabolisation assay (ENMA) is more convenient to perform than the determination of intracellular ATP/ADP. Due to its easy and versatile handling, a huge array of possible applications like monitoring the training efficiency of athletes, the fitness of senior citizens or the recovery from disease may be envisioned.

[Peculiarities of metabolism of the microsporidia Nosema grylli during the intracellular development]

A long adaptation of Microsporidia to intracellular development supposes the host-derived ATP dependence of merogony and sporogony stages. To prove this assumption the activities of ten carbohydrate and energy metabolism enzymes were compared in the microsporidia Nosema grylli intracellular stages and mature spores. This species infects the fat body of crickets Gryllus bimaculatus. We have demonstrated lower activities of glycolytic enzymes, phosphoglucomutase and glucose-6-PhDH in the metabolically active meronts and sporonts than in the dormant mature spores. Low glycolysis level indicates that carbohydrate catabolism is not a principal mechanism of ATP supply in the N. grylli intracellular stages. Furthermore, we have not revealed a preferable expenditure of glycogen in comparison with triglycerides in infected cricket fat bodies. The N. grylli infection causes an equal reduction of glycogen and lipid content approximately in 2-3 times. Microsporidia have not mitochondria, Krebs cycle and electron-transport chain. Therefore they are not able to utilise fat reserves for ATP production. It seems to be proposed that microsporidia consume exogenous ATP which is produced by host cell metabolic system. The N. grylli infection provokes an increase of ATP content and ratio of ATP/ADP concentrations in cricket fat bodies approximately in 4 times. These data indicates a rise of host cell energy metabolism rate during the infection.

Role of extracellular ATP metabolism in regulation of platelet reactivity

Extracellular adenosine triphosphate (ATP) regulates platelet reactivity by way of direct action on platelet purinergic receptors or by hydrolysis to adenosine diphosphate (ADP). Subsequent metabolism of ATP and ADP to adenosine monophosphate (AMP) and adenosine inhibits platelet aggregation. Endothelial cell membrane-bound ecto-ATP/ADPase (CD39, E-NTPDase1) is thought to be the main regulator of platelet responsiveness. However, the findings in studies of CD39-knockout mice imply that nucleotidase(s) in plasma regulates circulating adenine nucleotides levels. Understanding extracellular ATP metabolism by CD39 and plasma nucleotidases is therefore important. In this study, alpha-phosphorus 32- and gamma-phosphorus 32-labeled ATP were rapidly metabolized directly to AMP and pyrophosphate in human plasma at pH 7.4, suggesting the presence of pyrophosphatase/phosphodiesterase-like activity. A specific phosphodiesterase substrate, p-nitrophenol-5'-TMP (p-Nph-5'-TMP), was readily hydrolyzed in human plasma. The antiaggregatory action of beta,gamma-methylene-ATP (AMPPCP) (5 micromol/L) was blocked by DMPX, an adenosine-receptor antagonist, suggesting that in plasma, AMPPCP was metabolized to AMP and adenosine. Recombinant soluble CD39 (solCD39) was used to assess the role of CD39 in ATP metabolism. As little as 0.25 microg/mL of solCD39 inhibited ADP-induced platelet aggregation. However, in the presence of ADP-free ATP (10 micromol/L), solCD39 induced platelet aggregation in a dose-dependent manner. Because AMPPCP could not substitute for ATP in solCD39-stimulated platelet aggregation, it is likely that ADP formation from ATP was required. Endogenous CD39 may thus have a hemostatic function by promoting ADP formation from released ATP, in addition to its antiaggregatory properties. A plasma nucleotidase hydrolyzes ATP directly to AMP. This prevents ADP accumulation and generates adenosine, a potent, locally acting inhibitor of platelet reactivity. The presence of both endothelial CD39 and plasma nucleotidase appears to be important in the maintenance of normal hemostasis and prevention of excessive platelet responsiveness.

Direct measurement of enzyme activity with infrared spectroscopy

A direct approach to enzyme activity measurements is presented. Vibrational spectroscopy can monitor the progress of enzymatic reactions because the vibrational spectrum of substrates and products usually differs. This is demonstrated by the example of ATP hydrolysis by Ca(2+)-ATPase: The substrate concentration can be followed using the infrared absorption of the alpha- and beta-PO(2)(-) phosphate groups of ATP, and the product concentration can be followed using the PO(3)(2-) absorption of P(i) and of the beta-phosphate of ADP. The results of the infrared spectroscopic measurement of ATPase activity and of an independent activity assay agree very well. The main advantage of the infrared method is that it observes the reaction of interest directly--that is, no activity assay that converts the progress of the reaction into an observable quantity is required.

High-performance liquid chromatographic technique for detection of a fluorescent analogue of ADP-ribose in isolated blood vessel preparations

Analysis of endogenous nucleotides in biologic media is hampered by rapid degradation and low final concentrations that are difficult to detect. A reversed-phase high-performance liquid chromatographic (HPLC) technique is described that efficiently detects a stable fluorescence derivative of adenosine 5'-diphosphoribose (ADPR), 1,N6-etheno-ADPR (epsilon-ADPR), at low femtomolar concentration range in vascular tissue superfusates. epsilon-ADPR was formed by the reaction of ADPR with chloroacetaldehyde at 80 degrees C and pH 4.0. Gradient elution with 0.1 M KH2PO4 (pH 6.0), increasing methanol (0-35% over 18 min), and a 25-cm by 4.5-mm (5 microm) silica ODS-AM column were employed. epsilon-ADPR was detected by fluorescence at an excitation wavelength of 230 nm and an emission wavelength of 410 nm. The detection sensitivity for epsilon-ADPR was approximately 10 fmol. Linearity of the HPLC detection method was demonstrated in the range from 0.0125 to 1 pmol epsilon-ADPR. The method was validated in terms of within-day and between-day reproducibility of retention times and peak areas of standard nucleotide. Matrix-assisted laser desorption/ionization mass spectrometry measurements confirmed the presence of an etheno ring after reaction of ADPR with chloroacetaldehyde. The method was applied to quantitate the overflow of ADPR upon electrical field stimulation (8 Hz, 0.3 ms, 15 V, 1-2 min) of both canine and guinea-pig isolated mesenteric artery segments.

On-column enzyme-catalyzed microreactions using capillary electrophoresis: quantitative studies

Capillary electrophoresis and on-column enzyme-catalyzed microreactor techniques were used to quantitate the reaction projects resulting from three model systems: i) the conversion of nicotinamide adenine dinucleotide (NAD) to nicotinamide adenine dinucleotide, reduced form (NADH) in the oxidation of glucose-6-phosphate (glc-6-p) to 6-phosphogluconate by glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49); ii) the conversion of adenosine triphosphate (ATP) to adenosine diphosphate (ADP) and adenosine monophosphate (AMP) by hexokinase (HK, EC 2.7.1.1) and apyrase (APY, EC 3.6.1.5), respectively, in the conversion of glucose to glucose-6-phosphate and inorganic phosphate, respectively, and; iii) the conversion of fructose-1,6-bisphosphate to dihydroxyacetone phosphate and glyceraldehyde-3-phosphate by fructose-biphosphate aldolase (ALD, EC 4.1.2.13). Single and double microreactor techniques employing direct or indirect detection were used to follow the conversion of substrate to product(s). In addition, electrophoresis conditions including voltage, enzyme concentration, and mixing time of the reaction, were correlated to product distribution profiles.

An increase in the myocardial PCr/ATP ratio in GLUT4 null mice

ATP and creatine phosphate (PCr) are prime myocardial high-energy phosphates. Their relative concentrations are conserved among mammalian species and across a range of physiologic cardiac workloads. The cardiac PCr/ATP ratio is decreased with several pathologic conditions, such as ischemia and heart failure, but there are no reports of an increase in the cardiac PCr/ATP ratio in any species or with interventions. We studied the in vivo energetics in transgenic mice lacking expression of the glucose transport protein GLUT4 (G4N) and observed a significant 60% increase in the myocardial PCr/ATP ratio in G4N that was confirmed in three different experimental settings including intact animals. The higher PCr/ATP in G4N is cardiac-specific and is due to higher total cardiac creatine (CR) concentrations in G4N than in wild-type (WT). However, [ATP], [ADP], and -DG(-ATP) did not differ between the strains. Expression of the creatine transport protein (CreaT) that is responsible for creatine uptake in myocytes was preserved in G4N cardiac tissue. These observations demonstrate, for the first time to our knowledge, that G4N manifest a unique increase in the cardiac PCr/ATP ratio, which suggests a novel genetic strategy for increasing myocardial creatine levels.

A quantitative study of bioenergetics in skeletal muscle lacking utrophin and dystrophin

Muscle energetics and function were investigated in the hindlimb of mice lacking dystrophin (mdx), utrophin and dystrophin (utr-dys) and controls (C57Bl/10) using 31P and 1H magnetic resonance techniques, electrical nerve stimulation and direct biochemical analysis. At rest, [adenosine triphosphate] and [total creatine] were lowest in utr-dys, while [inorganic phosphate] was elevated. Calculated [adenosine diphosphate] was 3-fold higher in mdx and 5-fold higher in utr-dys than in controls, consistent with an increased adenosine triphosphate requirement for ion pump activity. During stimulation, force production was low only in utr-dys, and this was reflected in the bioenergetic changes. Initial recovery rates of [phosphocreatine] and [adenosine diphosphate] after stimulation were rapid in all groups, indicative of normal mitochondrial adenosine triphosphate production in utr-dys and mdx. Recovery of pH was slow in utr-dys. The data indicate that the severe abnormalities which are present in the absence of utrophin and dystrophin leave basic muscle energetics intact and appear confined to processes involving the sarcolemma.

Effect of tributyltin on adenylate content and enzyme activities of teleost sperm: a biochemical approach to study the mechanisms of toxicant reduced spermatozoa motility

The effects of tributyltin (TBT) on the energy metabolism and motility of fish spermatozoa were investigated in vitro in African catfish and common carp. A significant (P<0.05) decrease of the duration and the intensity of motility was observed in catfish spermatozoa exposed to 0.27 microg/l TBT for 24 h. Exposure of catfish spermatozoa to 2.7-27 microg/l TBT caused an instant decrease in ATP content. In the presence of 27 microg/l TBT approximately 55% of the initial ATP concentration in catfish semen was lost after 60 min incubation while AMP concentrations increased and the total adenine nucleotide (TAN) pool remained unchanged. The reduction in sperm ATP levels could not be attributed to cell death since viability decreased only slightly over the period of exposure. In carp by contrast, none of the adenylates concentrations studied (ATP, ADP and AMP) were affected by TBT exposure at any experimental condition. However, carp sperm motility was significantly reduced by exposure to 2.7 microg/l TBT. Among the enzymes investigated only lactate dehydrogenase (LDH) in catfish sperm was significantly (P<0.01) affected by 27 microg/l TBT treatment with a reduction in activity of approximately 75%. Compared with carp sperm before TBT exposure, that of catfish had lower adenylate contents and overall lower enzymatic activities; this explains its slower sperm velocity and shorter duration of movement as measured by computer assisted sperm analysis (CASA). The present in vitro study shows that catfish spermatozoa are more sensitive to TBT exposure (and probably to other toxicants) than those of carp.

2001 Harry M. Vars Research Award. Enteral nutrients alter enterocyte function within an in vitro model similar to an acute in vivo rat model during hypoxia

BACKGROUND

Early enteral nutrition in patients following traumatic injury is an important intervention. However, after shock-resuscitation, intestinal hypoperfusion persists despite adequate systemic resuscitation. Our previous in vivo rat studies indicate that hypoperfusion impairs mucosal function in the small intestine. Therefore, the current study sought to improve previous in vitro models by the following means: (1) We used Caco-2 monolayers stably transfected with the brush-border sodium-glucose co-transporter (SGLT-1); and (2) we created an environment that mimicked the physiologic enterocyte environment. We hypothesized that hypoxic alterations of epithelial function in an in vitro model are comparable to those of an in vivo rat model.

METHODS

After 21 days, monolayers were randomized to receive 24 hours of incubation in a normoxic or hypoxic environment. Cells were further randomized to receive 1 of 4 nutrient treatments: mannitol (an osmotic control), glucose (uses SGLT-1 and is metabolized), 3-O-methylglucose (3-O-mg; uses SGLT-1 and is not metabolized), or fructose (does not use SGLT-1 but can be metabolized).

RESULTS

Transepithelial resistance (p = .007) and short-circuit current (p = .05) were lower in hypoxic groups. When compared with normoxic groups, hypoxic groups had significantly impaired glucose (p < .001) but not glutamine transport, irrespective of nutrient treatment. Additionally, adenosine triphosphate/adenosine diphosphate ratio was reduced (p = .01) and lactate concentration was increased (p < .001) during hypoxia.

CONCLUSIONS

In summary, results from this in vitro study using Caco-2BBe cells stably transfected with SGLT-1 correspond to results obtained in the in vivo rat model. Therefore, this is an appropriate in vitro model in which to study cellular alterations caused by the hypoxic small intestine, with the goal of ensuring safe early enteral nutrition following traumatic injury.

Mechanism of amino acid-induced skeletal muscle insulin resistance in humans

Plasma concentrations of amino acids are frequently elevated in insulin-resistant states, and a protein-enriched diet can impair glucose metabolism. This study examined effects of short-term plasma amino acid (AA) elevation on whole-body glucose disposal and cellular insulin action in skeletal muscle. Seven healthy men were studied for 5.5 h during euglycemic (5.5 mmol/l), hyperinsulinemic (430 pmol/l), fasting glucagon (65 ng/l), and growth hormone (0.4 microg/l) somatostatin clamp tests in the presence of low (approximately 1.6 mmol/l) and increased (approximately 4.6 mmol/l) plasma AA concentrations. Glucose turnover was measured with D-[6,6-(2)H(2)]glucose. Intramuscular concentrations of glycogen and glucose-6-phosphate (G6P) were monitored using (13)C and (31)P nuclear magnetic resonance spectroscopy, respectively. A approximately 2.1-fold elevation of plasma AAs reduced whole-body glucose disposal by 25% (P < 0.01). Rates of muscle glycogen synthesis decreased by 64% (180--315 min, 24 plus minus 3; control, 67 plus minus 10 micromol center dot l(-1) center dot min(-1); P < 0.01), which was accompanied by a reduction in G6P starting at 130 min (DeltaG6P(260--300 min), 18 plus minus 19; control, 103 plus minus 33 micromol/l; P < 0.05). In conclusion, plasma amino acid elevation induces skeletal muscle insulin resistance in humans by inhibition of glucose transport/phosphorylation, resulting in marked reduction of glycogen synthesis.

Heart design: free ADP scales with absolute mitochondrial and myofibrillar volumes from mouse to human

Our aim was to estimate a number of bioenergetic parameters in the beating mouse, rat and guinea pig heart in situ and compare the values to those in hearts of mammals over a 2000-fold range in body mass. For the mouse, rat and guinea pig heart, we report a phosphorylation ratio of 1005+/-50 (n=16), 460+/-32 (n=10) and 330+/-22 (n=5) mM(-1) and a free cytosolic [ADP] concentration of 13, 18 and 22 microM, respectively. When each parameter was plotted against body mass, they scaled closely to the quarter power (-0.28, r=0.99 and -0.23, r=0.97). A similar regression slope was found when the inverse of free [ADP] was plotted against absolute mitochondrial (slope=-0.26, r=0.99) and myofibrillar volumes (slope=-0.24, r=0.99). The similar slopes indicate that the ratio of absolute mitochondria and myofibrillar volumes in the healthy mammalian heart is a constant, and independent of body size. In conclusion, our study supports the hypothesis that the mammalian heart has a number of highly conserved thermodynamic and kinetic parameters that obey quarter-power laws linking the phosphorylation ratio, ATP turnover rates, free [ADP] and absolute mitochondrial volumes to body size. The results are discussed in terms of possible mechanisms and potential deviations from these laws in some disease states.

Is glutamine beneficial in ischemic heart disease?

OBJECTIVE

Glutamine enhances recovery from acute normothermic ischemia in isolated rat heart by a dose-dependent effect (Khogali et al. J Mol Cell Cardiol 1998;30:819). We compared the cardioprotective effects of equimolar concentrations of glutamine, glutamate, and aspartate in isolated rat heart. We also explored the potential cardioprotective effects of glutamine in patients with chronic stable angina.

METHODS

The isolated perfused working rat heart was subjected to ischemia, followed by reperfusion with or without an amino acid (2.5 mM). Patients with chronic stable angina received a single oral dose of glutamine (80 mg/kg) or placebo in a double-blind, random fashion 40 min before a standard Bruce exercise test.

RESULTS

Postischemic reperfusion of isolated rat heart with glutamine (but not with glutamate or aspartate) resulted in full recovery of cardiac output. Only glutamine prevented the decrease in the myocardial ratio between adenosine triphosphate to adenosine diphosphate and significantly enhanced the myocardial ratio of reduced to oxidized glutathione. A single oral dose of glutamine given to patients with chronic stable angina significantly increased plasma glutamine concentration from 419 to 649 microM and delayed time to onset of more than 1.0 mm of ST segment depression on the ECG by 38 s.

CONCLUSION

Glutamine may be cardioprotective in patients with coronary heart disease.

Evaluation of toxicity of pesticides and their biodegradation products using human cells

Juvenoids are biologically active compounds, of relatively low toxicity to humans, that efficiently inhibit the fertility of insects. However, little attention has been paid to the stability and toxicity of products that may be generated by their biodegradation in the ecosystem. This study describes a simple comparison of the toxicity of the active compound and its degradation products generated by aerobic soil microbial isolates. Surprisingly we have found that toxicity of a biologically active carbamate juvenoid N-[2-[4-(2,2-ethylenedioxy-1-cyclohexylmethyl)-phenoxylethyl]carbamate (W328) was comparable with that of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT). The toxic effect was evaluated using the determination of the ATP/ADP content and viability of HeLa S3 cells exposed to various concentrations of the chemicals tested for various durations. DDT was used as a reference compound. Its toxicity was compared with two juvenile hormone analogs. The original compound, W328, was found to be the most toxic. The major product (W329) generated both by yeast isolates and the mixture of moulds lost its activity on reproduction of the tested insect. Its toxicity towards human cells was also decreased. Another two W328 degradation HPLC fractions exhibited significantly reduced toxicity compared to W328.

Chronic exposure to high leucine impairs glucose-induced insulin release by lowering the ATP-to-ADP ratio

Exposure of rat pancreatic islets to 20 mM leucine for 24 h reduced insulin release in response to glucose (16.7 and 22.2 mM). Insulin release was normal when the same islets were stimulated with leucine (40 mM) or glyburide (1 microM). To investigate the mechanisms responsible for the different effect of these secretagogues, we studied several steps of glucose-induced insulin secretion. Glucose utilization and oxidation rates in leucine-precultured islets were similar to those of control islets. Also, the ATP-sensitive K(+) channel-independent pathway of glucose-stimulated insulin release, studied in the presence of 30 mM K(+) and 250 microM diazoxide, was normal. In contrast, the ATP-to-ADP ratio after stimulation with 22.2 mM glucose was reduced in leucine-exposed islets with respect to control islets. The decrease of the ATP-to-ADP ratio was due to an increase of ADP levels. In conclusion, prolonged exposure of pancreatic islets to high leucine levels selectively impairs glucose-induced insulin release. This secretory abnormality is associated with (and might be due to) a reduced ATP-to-ADP ratio. The abnormal plasma amino acid levels often present in obesity and diabetes may, therefore, affect pancreatic islet insulin secretion in these patients.

The in-vitro characterization of induced apoptosis in placental cytotrophoblasts and syncytiotrophoblasts

Placental trophoblasts undergo apoptosis as part of normal epithelial turnover and placental ageing. Classically, the induction of apoptosis in in vitro preparations has utilized the cytokines TNFalpha and IFNgamma and has been measured using the TUNEL technique. The aim of this study was to compare apoptotic susceptibility of mononucleated and differentiated trophoblasts using a range of cytotoxic agents. To achieve this, an in vitro model of syncytialization was used, along with isolated placental cytotrophoblasts and an extravillous cytotrophoblast derived cell line (SGHPL-4). Cytotrophoblasts from term placentae (n=12), syncytiotrophoblasts (n=12) and SGHPL-4s (n=8) were cultured under reduced oxygen or with TNFalpha/IFNgamma, dexamethasone or staurosporine. Apoptosis assessments were made using TUNEL, Annexin V binding, fluorescence microscopy and ATP/ADP measurements. Each cytotoxic agent increased apoptosis in all three cell populations. For untreated cells, cytotrophoblasts showed the greatest levels of apoptosis in culture. With stimulation, these levels were significantly elevated using dexamethasone, TNFalpha/IFNgamma and staurosporine and further raised under hypoxic conditions. SGHPL-4 cells showed similar trends to those of cytotrophoblasts, however the syncytiotrophoblasts, although responsive to dexamethasone and TNFalpha/IFNgamma, showed lower levels of apoptosis with staurosporine and hypoxia. ADP : ATP measurements gave similar results to the other techniques and ratios of less than 1.0 were correlated with Annexin V measurements on the flow cytometer (P< 0.001). The typical morphological features of apoptosis i.e. chromatin margination, membrane blebbing and apoptotic body formation were detected in cytotrophoblasts and SGHPL-4 cells. However, only chromatin condensation could be recognized in syncytiotrophoblast preparations. Necrotic cell numbers were also increased under all cytotoxic conditions. Although elevated with dexamethasone, staurosporine and hypoxia, these levels were markedly raised in cytotrophoblasts and SGHPL-4 cells following incubations with TNFalpha/IFNgamma. These observations show variations in apoptosis between mononuclear trophoblasts and differentiated multinucleated syncytiotrophoblasts. Differential effects of stimuli may suggest disparate apoptotic pathways. These variations may reflect functional differences between placental cellular and syncytial components and may highlight the importance of exogenous stimulation in various stages of placental development.

The catabolic capacity of Saccharomyces cerevisiae is preserved to a higher extent during carbon compared to nitrogen starvation

A comparison of catabolic capacity was made between S. cerevisiae cells subjected to 24 h carbon or nitrogen starvation. The cells were shifted to starvation conditions at the onset of respiratory growth on ethanol in aerobic batch cultures, using glucose as the carbon and energy source. The results showed that the catabolic capacity was preserved to a much larger extent during carbon compared to nitrogen starvation. Nitrogen starvation experiments were made in the presence of ethanol (not glucose) to exclude the effect of glucose transport inactivation (Busturia and Lagunas, 1986). Hence, the difference in catabolic capacity could not be attributed to differences in glucose transport capacity during these conditions. In order to understand the reason for this difference in starvation response, measurement of protein composition, adenine nucleotides, inorganic phosphate, polyphosphate and storage carbohydrates were performed. No clear correlation between any of these variables and catabolic capacity after starvation could be obtained. However, there was a positive correlation between total catabolic activity and intracellular ATP concentration when glucose was added to starved cells. The possible mechanism for this correlation, as well as what determines the ATP level, is discussed.

Mechanisms of the deleterious effects of tamoxifen on mitochondrial respiration rate and phosphorylation efficiency

Tamoxifen (TAM), the widely prescribed drug in the prevention and therapy of breast cancer, is a well-known modulator of estrogen receptor (ER) that also inhibits the proliferation of different cell types that lack the ER. However, the ER-independent action mechanisms of TAM and its side effects have not been yet clarified. Mitochondria are essential in supporting the energy-dependent regulation of cell functions. Changes in mitochondria result in bioenergetic deficits leading to the loss of vital functions to cell survival. Therefore, this study describes the effects of TAM on mitochondrial bioenergetics, contributing to a better understanding of the biochemical mechanisms underlying the multiple antiproliferative and toxic effects of this drug. TAM at concentrations above 20 nmol/mg protein, preincubated with isolated rat liver mitochondria at 25 degrees C for 3 min, significantly depresses, in a dose-dependent manner, the phosphorylation efficiency of mitochondria as inferred from the decrease in the respiratory control and ADP/O ratios, the perturbations in mitochondrial transmembrane potential (DeltaPsi), the fluctuations associated with mitochondrial energization, and the phosphorylative cycle induced by ADP. Furthermore, TAM at up to 40 nmol/mg protein stimulates the rate of state 4 respiration and at higher concentrations it strongly inhibits state 3 and uncouples the mitochondrial respiration. The stimulation of state 4 respiration parallels the decrease of DeltaPsi as a consequence of proton permeability. The TAM-stimulatory action of ATPase is also observed in intact mitochondria, suggesting that TAM promotes extensive permeability to protons due to destructive effects in the structural integrity of the mitochondrial inner membrane. These multiple effects of TAM on mitochondrial bioenergetic functions, causing changes in the respiration, phosphorylation efficiency, and membrane structure, may explain the cell death induced by this drug in different cell types, its anticancer activity in ER-negative cells, and its side effects.

Mitochondrial ATPase and high-energy phosphates in failing hearts

This study examined high-energy phosphates (HEP) and mitochondrial ATPase protein expression in hearts in which myocardial infarction resulted in either compensated left ventricular remodeling (LVR) or congestive heart failure (CHF). The response of HEP (measured via (31)P magnetic resonance spectroscopy) to a modest increase in the cardiac work state produced by dobutamine-dopamine infusion and pacing (if needed) was examined in 17 pigs after left circumflex coronary artery ligation (9 with LVR and 8 with CHF) and compared with 7 normal pigs. In hearts with LVR, the baseline phosphocreatine (PCr)-to-ATP ratio decreased, and calculated ADP increased; these changes were most severe in hearts with CHF. HEP levels did not change in normal or LVR hearts during dobutamine-dopamine infusion. However, in hearts with CHF, the PCr-to-ATP ratio decreased further, and free ADP increased. The mitochondrial protein levels of the F(0)F(1)-ATPase subunits were normal in hearts with compensated LVR. However, in failing hearts, the alpha-subunit decreased by 36%, the beta-subunit decreased by 16%, the oligomycin sensitivity-conferring protein subunit decreased by 40%, and the initiation factor 1 subunit decreased by 41%. Thus in failing hearts, reductions in mitochondrial F(0)F(1)-ATPase protein expression are associated with increased myocardial free ADP.

Effects of chronic alcohol consumption on regulation of myocardial protein synthesis

Heart disease represents an important etiology of mortality in chronic alcoholics. The purpose of the present study was to examine potential mechanisms for the inhibitory effect of chronic alcohol exposure (16 wk) on the regulation of myocardial protein metabolism. Chronic alcohol feeding resulted in a lower heart weight and 25% loss of cardiac protein per heart compared with pair-fed controls. The loss of protein mass resulted in part from a diminished (30%) rate of protein synthesis. Ethanol exerted its inhibition of protein synthesis through diminished translational efficiency rather than lower RNA content. Chronic ethanol administration decreased the abundance of eukaryotic initiation factor (eIF)4G associated with eIF4E in the myocardium by 36% and increased the abundance of the translation response protein (4E-BP1) associated with eIF4E. In addition, chronic alcohol feeding significantly reduced the extent of p70S6 kinase (p70(S6K)) phosphorylation. The decreases in the phosphorylation of 4E-BP1 and p70(S6K) did not result from a reduced abundance of mammalian target of rapamycin (mTOR). These data suggest that a chronic alcohol-induced impairment in myocardial protein synthesis results in part from inhibition in peptide chain initiation secondary to marked changes in eIF4E availability and p70(S6K) phosphorylation.

Impaired muscular contractile performance and adenine nucleotide handling in creatine kinase-deficient mice

Creatine kinase (CK) forms a small family of isoenzymes playing an important role in maintaining the concentration of ATP and ADP in muscle cells. To delineate the impact of a lack of CK activity, we studied contractile performance during a single maximal tetanic contraction and during 12 repeated tetanic contractions of intact dorsal flexors of CK knockout (CK(-/-)) mice. To investigate the effect on ATP regeneration, muscular high-energy phosphate content was determined at rest, immediately after the contraction series, and after a 60-s recovery period. Maximal torque of the dorsal flexors was significantly lower in CK(-/-) mice than in wild-type animals, i.e., 23.7 +/- 5.1 and 33.3 +/- 6.8 mN. m. g(-1) wet wt, respectively. Lower muscle ATP (20.1 +/- 1.4 in CK(-/-) vs. 28.0 +/- 2.1 micromol/g dry wt in controls) and higher IMP (1.2 +/- 0.5 in CK(-/-) vs. 0.3 +/- 0.1 micromol/g dry wt in controls) levels at the onset of contraction may contribute to the declined contractility in CK(-/-) mice. In contrast to wild-type muscles, ATP levels could not be maintained during the series of 12 tetanic contractions of dorsal flexors of CK(-/-) mice and dropped to 15.5 +/- 2.4 micromol/g dry wt. The significant increase in tissue IMP (2.4 +/- 1.1 micromol/g dry wt) content after the contraction series indicates that ATP regeneration through adenylate kinase was not capable of fully compensating for the lack of CK. ATP regeneration via the adenylate kinase pathway is a likely cause of reduced basal adenine nucleotide levels in CK(-/-) mice.

Pathogenetic analysis of three cases with a bleeding disorder characterized by defective platelet aggregation induced by Ca2+ ionophores

We report three cases of platelet dysfunction characterized by defective Ca2+ ionophore-induced platelet aggregation without impaired production of thromboxane A2 (TXA2). The patients had mild to moderate bleeding tendencies, and their platelet aggregation and secretion induced by ADP, collagen, arachidonic acid, stable TXA2 (STA2) and Ca2+ ionophore A23187 was defective or much reduced. However, ristocetin- or thrombin-induced platelet aggregation was normal. The analysis of second messenger formation showed that inositol 1,4,5-triphosphate formation or Ca2+ mobilization induced by thrombin, STA2 or A23187 was normal. Furthermore, the phosphorylation of 47 kDa protein (pleckstrin) and 20 kDa protein (myosin light chain, MLC) in response to those agonists was normal. These findings suggest that the defective site in the patients' platelets lies in the process distal to or independent of protein kinase C activation, Ca2+ mobilization and MLC phosphorylation.

Successful nonfreezing, subzero preservation of rat liver with 2,3-butanediol and type I antifreeze protein

BACKGROUND

Organ cryopreservation is hindered by ice inflicted damage. Nonfreezing preservation of livers at subzero temperatures might offer advantages over current preservation.

METHODS

Sprague-Dawley rats were divided into three groups. UW livers (n = 6) were stored in University of Wisconsin (UW) solution at +4 degrees C. UWB livers (n = 6) were perfused ex vivo with UW + 10% 2,3-butanediol at < or =7 degrees C and stored at -4 degrees C. AFP livers (n = 4) were preserved identical to UWB livers, except for addition of 1 mg/ml of type I antifreeze protein. After 24 h livers were perfused with Krebs-Henseleit buffer (37 degrees C) for 60 min. Bile production, O(2) consumption (O(2)C), taurocholate extraction, and lactate dehydrogenase (LDH) release during perfusion and liver adenine nucleotide content and energy charge at the end of perfusion were measured. Cell membrane integrity was determined by trypan blue infusion.

RESULTS

Ice formation was prevented in all livers stored at -4 degrees C. Bile production, O(2)C, and taurocholate extraction were similar among three groups. Livers stored at -4 degrees C contained significantly more adenine nucleotides than livers stored at +4 degrees C but the energy charge was similar. LDH release was significantly greater (P < 0.05) in the AFP group vs UWB and UW (63 vs 28 and 21 mU/min/g liver, respectively). Hepatocyte and sinusoidal cell trypan blue uptake was similar in all three groups.

CONCLUSIONS

Butanediol with or without AFP was effective in preventing ice formation up to 24 h in rat livers stored at -4 degrees C. Although as effective as current +4 degrees C protocols, subzero preservation for longer periods needs to be achieved prior to clinical application.

A 1.8 A resolution structure of pig muscle 3-phosphoglycerate kinase with bound MgADP and 3-phosphoglycerate in open conformation: new insight into the role of the nucleotide in domain closure

3-phosphoglycerate kinase (PGK) is a typical kinase with two structural domains. The domains each bind one of the two substrates, 3-phosphoglycerate (3-PG) and MgATP. For the phospho-transfer reaction to take place the substrates must be brought closer by a hinge-bending domain closure. Open and closed structures of the enzyme with different relative domain positions have been determined from different species, but a comprehensive description of this conformational transition is yet to be attained. Crystals of pig muscle PGK in complex with MgADP and 3-phosphoglycerate were grown under the conditions which have previously resulted in crystals of the closed, catalytically competent conformation of Trypanosoma brucei PGK. The X-ray structure of the pig muscle ternary complex was determined at 1.8 A and the model was refined to R=20.8% and Rfree=24.1%. Contrary to expectation, however, it represents an essentially open conformation compared to that of T. brucei PGK. In addition, the beta-phosphate group of ADP is mobile in the new structure, in contrast to its well-defined position in T. brucei PGK. An extensive comparison of the ternary complexes from these remote species has been carried out in order to establish general differences between the two conformations and is reported here. A second pair of the open and closed structures was also compared. These analyses have made it possible to define several characteristic changes which accompany the structural transition, in addition to those identified previously: (1) the operation of a hinge at beta-strand L in the inter-domain region which greatly affects the relative domain positions; (2) the rearrangement and movement of helix 8, regulated through the interactions with the nucleotide phosphate; and (3) the existence of another hinge between helix 14 and the rest of the C-terminal part of the chain, which allows fine adjustment of the N-domain position. The main hinge at beta-strand L acts in concert with the C-terminal hinge at helix 7 described previously. Simultaneous interactions of the nucleotide phosphate groups with the loop that precedes helix 8, beta-strand J and the N terminus of helix 13 are required for propagation of the nucleotide effect towards the beta-strand L molecular hinge. A detailed description of the role of nucleotide binding in the hinge operation is presented.