Studies on erythrocyte glycolysis. I. Determination of the glycolytic intermediates in human erythrocytes

Erythrocyte metabolism

Our aim is to present an updated overview of the erythrocyte metabolism highlighting its richness and complexity. We have manually collected and connected the available biochemical pathways and integrated them into a functional metabolic map. The focus of this map is on the main biochemical pathways consisting of glycolysis, the pentose phosphate pathway, redox metabolism, oxygen metabolism, purine/nucleoside metabolism, and membrane transport. Other recently emerging pathways are also curated, like the methionine salvage pathway, the glyoxalase system, carnitine metabolism, and the lands cycle, as well as remnants of the carboxylic acid metabolism. An additional goal of this review is to present the dynamics of erythrocyte metabolism, providing key numbers used to perform basic quantitative analyses. By synthesizing experimental and computational data, we conclude that glycolysis, pentose phosphate pathway, and redox metabolism are the foundations of erythrocyte metabolism. Additionally, the erythrocyte can sense oxygen levels and oxidative stress adjusting its mechanics, metabolism, and function. In conclusion, fine-tuning of erythrocyte metabolism controls one of the most important biological processes, that is, oxygen loading, transport, and delivery.

Tumor microenvironment-activated cancer cell membrane-liposome hybrid nanoparticle-mediated synergistic metabolic therapy and chemotherapy for non-small cell lung cancer

BACKGROUND

Biomimetic nanotechnology-based RNA interference (RNAi) has been successful in improving theranostic efficacy in malignant tumors. Its integration with hybrid biomimetic membranes made of natural cell membranes fused with liposomal membranes is mutually beneficial and extends their biofunctions. However, limited research has focused on engineering such biomimetics to endow them with unique properties and functions, in particular, those essential for a "smart" drug delivery system, such as a tumor microenvironment (TME)-activated multifunctional biomimetic nanoplatform.

RESULTS

Herein, we utilized an integrated hybrid nanovesicle composed of cancer cell membranes (Cm) and matrix metallopeptidase 9 (MMP-9)-switchable peptide-based charge-reversal liposome membranes (Lipm) to coat lipoic acid-modified polypeptides (LC) co-loaded with phosphoglycerate mutase 1 (PGAM1) siRNA (siPGAM1) and DTX. The nanovesicle presented a negatively charged coating (citraconic anhydride-grafted poly-L-lysine, PC) in the middle layer for pH-triggered charge conversion functionalization. The established chemotherapeutic drug (DTX) co-delivery system CLip-PC@CO-LC nanoparticles (NPs) have a particle size of ~ 193 nm and present the same surface proteins as the Cm. Confocal microscopy and flow cytometry results indicated a greater uptake of MMP-9-treated CLip-PC@CO-LC NPs compared with that of the CLip-PC@CO-LC NPs without MMP-9 pretreatment. The exposure to MMP-9 activated positively charged cell-penetrating peptides on the surface of the hybrid nanovesicles. Moreover, pH triggered membrane disruption, and redox triggered DTX and siRNA release, leading to highly potent target-gene silencing in glycolysis and chemotherapy with enhanced antiproliferation ability. The biodistribution results demonstrated that the CLip-PC@LC-DiR NPs accumulated in the tumor owing to a combination of long blood retention time, homologous targeting ability, and TME-activated characteristics. The CLip-PC@CO-LC NPs led to more effective tumor growth inhibition than the DTX and free siPGAM1 formulations.

CONCLUSIONS

TME-activated cancer cell membrane-liposome integrated hybrid NPs provide an encouraging nanoplatform that combines RNAi with chemotherapy for precise treatment of non-small cell lung cancer.

Nucleic Acid Delivery with Red-Blood-Cell-Based Carriers

Gene therapy has the potential to become a staple of 21st-century medicine. However, to overcome the limitations of existing gene-delivery therapies, that is, poor stability and inefficient and delivery and accumulation of nucleic acids (NAs), safe drug-delivery systems (DDSs) allowing the prolonged circulation and expression of the administered genes in vivo are needed. In this review article, the development of DDSs over the past 70 years is briefly described. Since synthetic DDSs can be recognized and eliminated as foreign substances by the immune system, new approaches must be found. Using the body's own cells as DDSs is a unique and exciting strategy and can be used in a completely new way to overcome the critical limitations of existing drug-delivery approaches. Among the different circulatory cells, red blood cells (RBCs) are the most abundant and thus can be isolated in sufficiently large quantities to decrease the complexity and cost of the treatment compared to other cell-based carriers. Therefore, in the second part, this article describes 70 years of research on the development of RBCs as DDSs, covering the most important RBC properties and loading methods. In the third part, it focuses on RBCs as the NA delivery system with advantages and drawbacks discussed to decide whether they are suitable for NA delivery in vivo.

Proton Transport Chains in Glucose Metabolism: Mind the Proton

The Embden-Meyerhof-Parnas (EMP) pathway comprises eleven cytosolic enzymes interacting to metabolize glucose to lactic acid [CH3CH(OH)COOH]. Glycolysis is largely considered as the conversion of glucose to pyruvate (CH3COCOO-). We consider glycolysis to be a cellular process and as such, transporters mediating glucose uptake and lactic acid release and enable the flow of metabolites through the cell, must be considered as part of the EMP pathway. In this review, we consider the flow of metabolites to be coupled to a flow of energy that is irreversible and sufficient to form ordered structures. This latter principle is highlighted by discussing that lactate dehydrogenase (LDH) complexes irreversibly reduce pyruvate/H+ to lactate [CH3CH(OH)COO-], or irreversibly catalyze the opposite reaction, oxidation of lactate to pyruvate/H+. However, both LDH complexes are considered to be driven by postulated proton transport chains. Metabolism of glucose to two lactic acids is introduced as a unidirectional, continuously flowing pathway. In an organism, cell membrane-located proton-linked monocarboxylate transporters catalyze the final step of glycolysis, the release of lactic acid. Consequently, both pyruvate and lactate are discussed as intermediate products of glycolysis and substrates of regulated crosscuts of the glycolytic flow.

The platelet isoform of phosphofructokinase contributes to metabolic reprogramming and maintains cell proliferation in clear cell renal cell carcinoma

Metabolic alterations underlying clear cell renal cell carcinoma (ccRCC) progression include aerobic glycolysis, increased pentose phosphate pathway activity and reduced oxidative phosphorylation. Phosphofructokinase (PFK), a key enzyme of the glycolytic pathway, has L, M, and P isoforms with different tissue distributions. The mRNA level of the platelet isoform of phosphofructokinase (PFKP) is reported to be up-regulated in ccRCC patients. However, it remains unclear whether PFKP plays an important role in promoting aerobic glycolysis and macromolecular biosynthesis to support cell proliferation in ccRCC. Here we found that the up-regulated PFKP became the predominant isoform of PFK in human ccRCC. Suppression of PFKP not only impaired cell proliferation by inducing cell cycle arrest and apoptosis, but also led to decreased glycolysis, pentose phosphate pathway and nucleotide biosynthesis, accompanied by activated tricarboxylic acid cycle in ccRCC cells. Moreover, we found that p53 activation contributed to cell proliferation and metabolic defects induced by PFKP knockdown in ccRCC cells. Furthermore, suppression of PFKP led to reduced ccRCC tumor growth in vivo. Our data indicate that PFKP not only is required for metabolic reprogramming and maintaining cell proliferation, but also may provide us with a valid target for anti-renal cancer pharmaceutical agents.

Metabolomic Studies of Oral Biofilm, Oral Cancer, and Beyond

Oral diseases are known to be closely associated with oral biofilm metabolism, while cancer tissue is reported to possess specific metabolism such as the ‘Warburg effect’. Metabolomics might be a useful method for clarifying the whole metabolic systems that operate in oral biofilm and oral cancer, however, technical limitations have hampered such research. Fortunately, metabolomics techniques have developed rapidly in the past decade, which has helped to solve these difficulties. In vivo metabolomic analyses of the oral biofilm have produced various findings. Some of these findings agreed with the in vitro results obtained in conventional metabolic studies using representative oral bacteria, while others differed markedly from them. Metabolomic analyses of oral cancer tissue not only revealed differences between metabolomic profiles of cancer and normal tissue, but have also suggested a specific metabolic system operates in oral cancer tissue. Saliva contains a variety of metabolites, some of which might be associated with oral or systemic disease; therefore, metabolomics analysis of saliva could be useful for identifying disease-specific biomarkers. Metabolomic analyses of the oral biofilm, oral cancer, and saliva could contribute to the development of accurate diagnostic, techniques, safe and effective treatments, and preventive strategies for oral and systemic diseases.

Flux Control in Glycolysis Varies Across the Tree of Life

Biochemical thought posits that rate-limiting steps (defined here as points of flux control) are strongly selected as points of pathway regulation and control and are thus expected to be evolutionarily conserved. Conversely, population genetic thought based upon the concepts of mutation-selection-drift balance at the pathway level might suggest variation in flux controlling steps over evolutionary time. Glycolysis, as one of the most conserved and best characterized pathways, was studied to evaluate its evolutionary conservation. The flux controlling step in glycolysis was found to vary over the tree of life. Further, phylogenetic analysis suggested at least 60 events of gene duplication and additional events of putative positive selection that might alter pathway kinetic properties. Together, these results suggest that even with presumed largely negative selection on pathway output on glycolysis, the co-evolutionary process under the hood is dynamic.

Phosphoglycerate mutase 1 coordinates glycolysis and biosynthesis to promote tumor growth

It is unclear how cancer cells coordinate glycolysis and biosynthesis to support rapidly growing tumors. We found that the glycolytic enzyme phosphoglycerate mutase 1 (PGAM1), commonly upregulated in human cancers due to loss of TP53, contributes to biosynthesis regulation in part by controlling intracellular levels of its substrate, 3-phosphoglycerate (3-PG), and product, 2-phosphoglycerate (2-PG). 3-PG binds to and inhibits 6-phosphogluconate dehydrogenase in the oxidative pentose phosphate pathway (PPP), while 2-PG activates 3-phosphoglycerate dehydrogenase to provide feedback control of 3-PG levels. Inhibition of PGAM1 by shRNA or a small molecule inhibitor PGMI-004A results in increased 3-PG and decreased 2-PG levels in cancer cells, leading to significantly decreased glycolysis, PPP flux and biosynthesis, as well as attenuated cell proliferation and tumor growth.

Enzymatic and metabolic characterization of the phosphoglycerate kinase deficiency associated with chronic hemolytic anemia caused by the PGK-Barcelona mutation

Recently, we reported a new mutation of phosphoglycerate kinase (PGK), called PGK-Barcelona, which causes chronic hemolytic anemia associated with progressive neurological impairment. We found a 140T→A substitution that produces an Ile46Asn change located at the N-domain of the enzyme and we suggested that the decrease of the PGK activity is probably related to a loss of enzyme stability. In this paper, by analyzing whole hemolysates and cloned enzymes, we show that both enzymes possess similar kinetic properties (although some differences are observed in the Km values) and the same electrophoretic mobility. However, PGK-Barcelona has higher thermal instability. Therefore, we confirm that the decrease of the red blood cell (RBC) PGK activity caused by the PGK-Barcelona mutation is more closely related to a loss of enzyme stability than to a decrease of enzyme catalytic function. Furthermore, we have measured the levels of glycolytic metabolites and adenine nucleotides in the RBC from controls and from the patient. The increase of 2,3-bisphosphoglycerate and the decrease of ATP RBC levels are the only detected metabolic changes that could cause hemolytic anemia.

Metabolomics of supragingival plaque and oral bacteria

Dental caries is initiated by demineralization of the tooth surface through acid production by sugar metabolism of supragingival plaque microflora. To elucidate the sugar metabolic system, we used CE-MS to perform metabolomics of the central carbon metabolism, the EMP pathway, the pentose-phosphate pathway, and the TCA cycle in supra- gingival plaque and representative oral bacteria, Streptococcus and Actinomyces. Supragingival plaque contained all the targeted metabolites in the central carbon metabolism, except erythrose 4-phosphate in the pentose-phosphate pathway. After glucose rinse, glucose 6-phosphate, fructose 6-phosphate, fructose 1,6-bisphosphate, dihydroxyacetone phosphate, and pyruvate in the EMP pathway and 6-phosphogluconate, ribulose 5-phosphate, and sedoheptulose 7-phosphate in the pentose-phosphate pathway, and acetyl CoA were increased. Meanwhile, 3-phosphoglycerate and phosphoenolpyruvate in the EMP pathway and succinate, fumarate, and malate in the TCA cycle were decreased. These pathways and changes in metabolites observed in supragingival plaque were similar to the integration of metabolite profiles in Streptococcus and Actinomyces.

Difference in the xylitol sensitivity of acid production among Streptococcus mutans strains and the biochemical mechanism

Xylitol inhibits the glycolysis and growth of Streptococcus mutans, but to different degrees among strains. Thus, we studied the biochemical mechanism through which the inhibition varies, using S. mutans strains ATCC 31989, NCTN 10449, and NCIB 11723, which are highly sensitive, moderately sensitive, and resistant to xylitol, respectively, under strictly anaerobic conditions such as those found in deep layers of dental plaque. Xylitol (30 mM) decreased the rate of acid production from glucose (10 mM) in ATCC 31989, NCTC 10449, and NCIB 11723 by 86, 26, and 0%, respectively. The activities of the xylitol : phosphoenolpyruvate phosphotransferase system (PEP-PTS) relative to those of glucose : PEP-PTS were 120, 16, and 3%, respectively. In ATCC 31989 and NCTC 10449, intracellular accumulation of xylitol 5-phosphate and decreases of fructose 1,6-bisphosphate and glucose 6-phosphate were observed. Furthermore, in the presence of xylitol (30 mM), glucose : PEP-PTS activities decreased by 34, 17, and 0%, respectively. These findings indicated that the higher the xylitol : PEP-PTS activity was and the more effectively xylitol decreased glucose : PEP-PTS activity, the more sensitive the strain was to xylitol. These results suggest that the following inhibitory mechanisms are active in the xylitol-sensitive mutans streptococci: direct inhibition of glycolytic enzymes by xylitol 5-phosphate derived from xylitol : PEP-PTS and, possibly, indirect inhibition through competition for the phosphoryl donor, HPr-P, between glucose and xylitol : PEP-PTSs.

Triosephosphate isomerase deficiency: consequences of an inherited mutation at mRNA, protein and metabolic levels

Triosephosphate isomerase (TPI) deficiency is a unique glycolytic enzymopathy coupled with neurodegeneration. Two Hungarian compound heterozygote brothers inherited the same TPI mutations (F240L and E145Stop), but only the younger one suffers from neurodegeneration. In the present study, we determined the kinetic parameters of key glycolytic enzymes including the mutant TPI for rational modelling of erythrocyte glycolysis. We found that a low TPI activity in the mutant cells (lower than predicted from the protein level and specific activity of the purified recombinant enzyme) is coupled with an increase in the activities of glycolytic kinases. The modelling rendered it possible to establish the steady-state flux of the glycolysis and metabolite concentrations, which was not possible experimentally due to the inactivation of the mutant TPI and other enzymes during the pre-steady state. Our results showed that the flux was 2.5-fold higher and the concentration of DHAP (dihydroxyacetone phosphate) and fructose 1,6-bisphosphate increased 40- and 5-fold respectively in the erythrocytes of the patient compared with the control. Although the rapid equilibration of triosephosphates is not achieved, the energy state of the cells is not 'sick' due to the activation of key regulatory enzymes. In lymphocytes of the two brothers, the TPI activity was also lower (20%) than that of controls; however, the remaining activity was high enough to maintain the rapid equilibration of triosephosphates; consequently, no accumulation of DHAP occurs, as judged by our experimental and computational data. Interestingly, we found significant differences in the mRNA levels of the brothers for TPI and some other, apparently unrelated, proteins. One of them is the prolyl oligopeptidase, the activity decrease of which has been reported in well-characterized neurodegenerative diseases. We found that the peptidase activity of the affected brother was reduced by 30% compared with that of his neurologically intact brother.

Xylitol inhibition of anaerobic acid production by Streptococcus mutans at various pH levels

Xylitol inhibits the glycolysis and growth of Streptococcus mutans. We studied the inhibitory effect of xylitol on the acid production of S. mutans at several pH levels under the strictly anaerobic conditions found in the deep layer of dental plaque. Xylitol inhibited the rate of acid production from glucose and changed the profile of acidic end products to formate-acetate dominance, with a decrease in the intracellular level of fructose 1,6-bisphosphate and an intracellular accumulation of xylitol 5-phosphate (X5P). These results were notable at pH 5.5-7.0, but were not evident at pH 5.0. Since the activity of phosphoenolpyruvate phosphotransferase for xylitol was greater at higher pH, it is suggested that xylitol could be incorporated more efficiently at higher pH and that the resultant accumulation of X5P could inhibit the glycolysis of S. mutans more effectively.

Combined glucose-6-phosphate dehydrogenase and glucosephosphate isomerase deficiency can alter clinical outcome

Glucosephosphate isomerase (GPI) deficiency in humans is an autosomal recessive disorder, which results in nonspherocytic hemolytic anemia of variable clinical expression. A 4-year-old female with severe congenital hemolytic anemia had low red cell GPI activity of 15.5 IU/g Hb (50% of normal mean) indicating GPI deficiency. Subsequent DNA sequence analysis revealed a novel homozygous 921C to G mutation in the GPI gene sequence, predicting a Phe307 to Leu replacement. Strikingly, the red cell GPI activity in this patient was higher than that found in a second patient expressing the same GPI variant, with a more severe clinical phenotype. We propose that the hemolysis in the first patient may be modified by an accompanying deficiency of glucose-6-phosphate dehydrogenase (G6PD). The proband's red cell G6PD activity was reduced at 4.5 IU/g Hb (50% of normal mean) and molecular studies revealed heterozygosity for the G6PD Viangchan mutation and a skewed pattern of X-chromosome inactivation, producing almost exclusive expression of the mutated allele. The G6PD Viangchan variant is characterised by severe enzyme deficiency, but not chronic hemolysis. This study suggests that the metabolic consequences of a combined deficiency of GPI and G6PD might be responsible for a different clinical outcome than predicted for either defect in isolation.

Inhibitory effect of sorbitol on sugar metabolism of Streptococcus mutans in vitro and on acid production in dental plaque in vivo

This study was conducted to find out whether sorbitol inhibits the sugar metabolism of Streptococcus mutans in vitro and the acid production in dental plaque in vivo. S. mutans NCIB 11723 was anaerobically grown in sorbitol-containing medium. The rate of acid production from sugars was estimated with a pH stat. The rate of acid production from glucose or sucrose was not changed at various concentrations of oxygen. By the addition of sorbitol to sugar, however, the acid production was decreased with increasing levels of oxygen. Intracellular NADH/NAD+ ratio and (dihydroxyacetone-phosphate+glyceraldehyde-phosphate)/3-phosphoglycerate ratio were high whenever the acid production was inhibited by sorbitol. Sorbitol also inhibited the acid production in dental plaque in vivo. These results suggest that the increased NADH/NAD+ ratio during sorbitol metabolism through the inactivation of pyruvate formate-lyase by oxygen inhibited glyceraldehyde-phosphate dehydrogenase and then the acid production of S. mutans and the one in dental plaque.

Congenital lactic acidosis: evaluation of the properties of the a199t natural variant of human pyruvate dehydrogenase e1alpha by in vitro mutation

One cause of congenital lactic acidosis is a mutation in the E1 alpha-subunit of the pyruvate dehydrogenase multienzyme complex. Little is known about the consequences of these mutations at the enzymatic level. Here we study the A199T mutation by expressing the protein in Escherichia coli. The specific activity is 25% of normal and the K(m) for pyruvate is elevated by 10-fold. Inhibitors of lactate dehydrogenase might be a useful therapy for patients with such mutations.

The time-course of acid excretion, levels of fluorescence dependent on cellular nicotinamide adenine nucleotide and glycolytic intermediates of Streptococcus mutans cells exposed and not exposed to air in the presence of glucose and sorbitol

The aim of this study was to examine glucose and sorbitol metabolism in Streptococcus mutans cells exposed and not exposed to air at the coexistence of these compounds by measuring acid excretion, levels of fluorescence dependent on cellular NADH and glycolytic intermediates. An aliquot of bacterial cells grown under strictly anaerobic conditions (anaerobic cells) was exposed temporarily to air (aerobic cells). When glucose was added to the anaerobic cells metabolizing sorbitol, the acid excretion was increased. The level of NADH decreased initially and then increased to the higher plateau level than that during glucose metabolism. The aerobic cells neither metabolized sorbitol nor contained glycolytic intermediates. However, 2 min after glucose was added in the presence of sorbitol, the acid excretion was started slowly and the intermediates appeared. The level of NADH was decreased at first and then increased. These results suggested that the anaerobic S. mutans cells metabolized glucose and sorbitol simultaneously, and that in the presence of sorbitol the aerobic cells could start to metabolize glucose 2 min after glucose was added, as the intermediates (phosphoenopyruvate potential) for the glucose transport were accumulated.

Rate-limiting steps of glucose and sorbitol metabolism in Streptococcus mutans cells exposed to air

It has been supposed that rate of sorbitol metabolism in the air-exposed streptococcal cells could be limited by the low capacity to regenerate nicotinamide adenine dinucleotide (NAD) from reduced NAD (NADH) following inactivation of pyruvate formate-lyase by oxygen. The rate-limiting steps, however, have not been identified. The aim of this study was to examine the effect of temporary exposure of the streptococcal cells to air on the intracellular flux of glucose and sorbitol metabolism by measuring acid excretion, fluorescence dependent on cellular level of NADH, glycolytic intermediates and enzyme activities. The exposure of cells to air decreased the acid excretions during glucose and sorbitol metabolism. The analysis of the glycolytic intermediates and the fluorescence suggested that the reduced level of acid excretion in the air-exposed glucose metabolizing cells resulted from the decrease in pyruvate catabolism. In the presence of sorbitol, the decreased acid production resulted from the reduced rates of the reactions catalyzed by sorbitol-phosphoenolpyruvate phosphotransferase and sorbitol 6-phosphate dehydrogenase because of shortage of substrates for these enzymes in addition to the decrease in pyruvate catabolism.

Functions of two types of NADH oxidases in energy metabolism and oxidative stress of Streptococcus mutans

We have previously identified two distinct NADH oxidases corresponding to H(2)O(2)-forming oxidase (Nox-1) and H(2)O-forming oxidase (Nox-2) induced in Streptococcus mutans. Sequence analyses indicated a strong similarity between Nox-1 and AhpF, the flavoprotein component of Salmonella typhimurium alkyl hydroperoxide reductase; an open reading frame upstream of nox-1 also showed homology to AhpC, the direct peroxide-reducing component of S. typhimurium alkyl hydroperoxide reductase. To determine their physiological functions in S. mutans, we constructed knockout mutants of Nox-1, Nox-2, and/or the AhpC homologue; we verified that Nox-2 plays an important role in energy metabolism through the regeneration of NAD(+) but Nox-1 contributes negligibly. The Nox-2 mutant exhibited greatly reduced aerobic growth on mannitol, whereas there was no significant effect of aerobiosis on the growth on mannitol of the other strains or growth on glucose of any of the strains. Although the Nox-2 mutants grew well on glucose aerobically, the end products of glucose fermentation by the Nox-2 mutant were substantially shifted to higher ratios of lactic acid to acetic acid compared with wild-type cells. The resistance to cumene hydroperoxide of Escherichia coli TA4315 (ahpCF-defective mutant) transformed with pAN119 containing both nox-1 and ahpC genes was not only restored but enhanced relative to that of E. coli K-12 (parent strain), indicating a clear function for Nox-1 as part of an alkyl hydroperoxide reductase system in vivo in combination with AhpC. Surprisingly, the Nox-1 and/or AhpC deficiency had no effect on the sensitivity of S. mutans to cumene hydroperoxide and H(2)O(2), implying that the existence of some other antioxidant system(s) independent of Nox-1 in S. mutans compensates for the deficiency.

Red blood cell enzymes and their clinical application

Red blood cell enzyme activities are measured mainly to diagnose hereditary nonspherocytic hemolytic anemia associated with enzyme anomalies. At least 15 enzyme anomalies associated with hereditary hemolytic anemia have been reported. Some nonhematologic disease can also be diagnosed by the measurement of red blood cell enzyme activities in the case in which enzymes of red blood cells and the other organs are under the same genetic control. Progress in molecular biology has provided a new perspective. Techniques such as the polymerase chain reaction and single-strand conformation polymorphism analysis have greatly facilitated the molecular analysis of erythroenzymopathies. These studies have clarified the correlation between the functional and structural abnormalities of the variant enzymes. In general, the mutations that induce an alteration of substrate binding site and/or enzyme instability might result in markedly altered enzyme properties and severe clinical symptoms.

Influence of aging or left ventricular hypertrophy on the human heart: contents of phosphorus metabolites measured by 31P MRS

Although both aging and hypertrophy are extremely important factors for cardiac performance, their influence on cardiac metabolism, especially that of high-energy phosphates, has not been fully elucidated as yet. Quantitative measurements of high-energy phosphates were attempted by comparing myocardial 31P NMR spectra with an external reference using depth-resolved surface-coil spectroscopy. The voxel size of the region of interest (ROI) was disk-shaped with 15-cm diameter and 25-mm thickness, but the left ventricular weight actually involved in the ROI was estimated to be between 22 and 66 g using MRI. Myocardial phosphocreatine (PCr) content and adenosine triphosphate (ATP) content for the 30 normal volunteers showed significant age dependence since both decreased in relation to increasing age. Myocardial PCr content and ATP content in patients with hypertension did not differ significantly from the age-matched control group. PCr content (6.1 +/- 2.2 micromol/g wet tissue, n = 10) and ATP content (4.1 +/- 1.3 micromol/g wet tissue) in patients with hypertrophic cardiomyopathy were less than the age-matched control group (n = 15; PCr: 9.7 +/- 2.5 micromol/g wet tissue, P < 0.01; ATP: 6.4 +/- 1.8 micromol/g wet tissue, P < 0.05), respectively. These results indicate that quantitative 31P MRS may be valuable in the assessment of changes in high-energy phosphate metabolism caused by aging or hypertrophy.

Expression and enzymatic characterization of human glucose phosphate isomerase (GPI) variants accounting for GPI deficiency

To elucidate the structure-function relationships in glucose phosphate isomerase (GPI), we established an expression system for human GPI as a fusion protein with glutathione S-transferase (GST) in E. coli. The GST-GPI fusion protein showed affinities for the substrates glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P) similar to those of the native enzyme purified from human red blood cells (RBC). We expressed GPI cDNAs with four distinct disease-causing mutations and examined their enzymatic characteristics. Although each mutation caused reduced thermal stability, an amino acid substitution Thr-5-->Ile (T5I) exhibited marked thermal instability, suggesting that the amino-terminal of GPI is important for enzymatic stability. Thr-224 seemed not to be an essential residue, since the amino acid substitution Thr-224-->Met (T224M) showed normal substrate affinity in spite of a slight decrease in both specific activity and thermostability. Gln-343 and Asp-539 have been shown to be in close proximity to the putative catalytic sites, and the present study showed that both Gln-343-->Arg (Q343R) and Asp-539-->Asn (D539N) caused impaired substrate affinity; Q343R showed high Km for both G6P and F6P, whereas D539N showed significantly decreased affinity only for F6P. These results suggest that not only reduced enzymatic stability but also impaired kinetics may disturb RBC metabolism of the GPI variants associated with hereditary hemolytic anemia.

Mechanism of inhibition of acid production in Streptococcus mutans by sodium ions under strictly anaerobic conditions

Acids excreted and intracellular levels of glycolytic intermediates during glucose metabolism in streptococcus mutans NCTC 10449 under strictly anaerobic conditions were quantified in an attempt to understand the effect of sodium ions on bacterial acid production. In the presence of NaCl (0.15-0.30 M), the total amount of individual carboxylic acids excreted was inhibited by up to 31%. The intracellular level of fructose 1,6-bisphosphate increased by 58% and levels of 3-phosphoglycerate and pyruvate decreased by 46% and 12%, respectively. Sodium ions directly inhibited the activities of fructose 1,6-phosphate aldolase and triose phosphate isomerase. This indicated that the glycolytic enzymes responsible for the catalysis of fructose 1,6-bisphosphate to 3-phosphoglycerate were inhibited. However, in spite of the expected reduction in acid production intracellularly, the intracellular pH actually decreased in the presence of sodium ions. It is possible that the low intracellular pH inhibits the activity of the glycolytic enzymes involved in the breakdown of fructose 1,6-bisphosphate to 3-phosphoglycerate.

Frame Shift Mutation, Exon Skipping, and a Two-Codon Deletion Caused by Splice Site Mutations Account for Pyruvate Kinase Deficiency

Three novel splice site mutations and two novel missense mutations were identified by molecular analysis of pyruvate kinase (PK) deficiency associated with hereditary nonspherocytic hemolytic anemia. A Nepalese PK variant, PK Kowloon, was found to have a homozygous transversion at the 5′-splice site of the seventh intervening sequence (IVS) of the L-type PK gene (Ivs7[+1]gt → tt). Using a reverse transcription polymerase chain reaction (RT-PCR) assay, we showed that the R-type PK mRNA in the proband's reticulocytes included the seventh IVS between the seventh and eighth exon, introducing a stop codon 3 nucleotides downstream of the mutated site. Consequently, the translational product may lack 44% of the R-PK polypeptide. A transition at the last nucleotide of exon 9 (1269GCG → GCA) was found in a Japanese PK variant, PK ‘Kamata.’ The mutation did not alter the amino acid sequence, but caused skipping of the ninth exonic sequence in the R-PK transcripts. As a result, the affected R-type PK lost 51 amino acid residues (373Met-423Ala del). A transversion at the splice acceptor site of the third IVS (Ivs 3[-2]ag → tg) was identified in PK ‘Aomori.’ The mutation resulted in aberrant splicing at a cryptic splice site within exon 4, causing deletion of two codons in the aberrant R-PK transcript (95 Gly-96 Pro → del). Both PK ‘Kamata’ and PK ‘Aomori’ had a missense mutation on the other allele, 1044AAG → AAT (348Lys → Asn) and 1075CGC → TGC (359Arg → Cys), respectively. Although both 348Lys and 359Arg were located in the sixth loop of A domain (β/α)8 barrel, which has been shown to contain the substrate and cation binding sites, the degree of anemia was much more severe in PK ‘Kamata’ than PK ‘Aomori,’ possibly because the 51 amino acid deletion of PK ‘Kamata’ but the 2 amino-acid deletion of PK ‘Aomori’ may abolish PK catalytic activity.

Congenital 6-phosphogluconate dehydrogenase (6PGD) deficiency associated with chronic hemolytic anemia in a Spanish family

Clinical and metabolic studies were performed in four members of a Spanish family with partial (50%) 6 phosphogluconate dehydrogenase (6PGD) deficiency. In all cases the activities of 6 phosphogluconolactone (6PGL) and glutathione reductase (GR) were normal, and the molecular characterization performed in the partially purified 6PGD from the propositus showed normal kinetic and electrophoretic patterns. Two females (the propositus and her sister) suffered from a well-compensated chronic nonspherocytic hemolytic anemia (CNSHA) and exhibited decreased RBC glutathione (GSH) stability with increased oxidative susceptibility, defined by enhanced malonyldialdehyde (MDA) generation "in vitro." The other two members of the family (the propositus's mother and brother) were clinically asymptomatic. In the propositus and her sister, RBC metabolism exhibited a markedly abnormal concentration of glycolytic intermediates, mainly characterized by striking increases in fructose 1,6 bisphosphate (50-fold), dihydroxiacetone-phosphate (20-fold) and glyceraldehyde 3-phosphate (tenfold). Although the precise mechanism of the hemolysis in the two patients is unknown, the enhanced oxidative threat observed in their RBCs may interfere in some way with the glycolytic pathway function, leading to a marked increase in certain metabolic intermediates located before the glyceraldehyde 3 phosphate dehydrogenase (GA3PD) step. Since it seems that GA3PD half-life is modulated by fluctuations of the cytosolic redox status, an "in situ" approach was simulated by using permeabilized RBCs. In these conditions, GA3PD activity was significantly lower in the propositus and her sister than in the asymptomatic members of the family and the simultaneous normal control.

Effect of glucagon on the xylitol-induced increase in the plasma concentration and urinary excretion of purine bases

To investigate whether glucagon affects the xylitol-induced increase in the production of purine bases (hypoxanthine, xanthine, and uric acid), the present study was performed with five healthy subjects. Intravenous administration of 300 mL 10% xylitol increased the plasma concentration and urinary excretion of purine bases, erythrocyte concentrations of adenosine monophosphate (AMP) and adenosine diphosphate (ADP), and blood concentrations of glyceraldehyde-3-phosphate (GA3P) + dihydroxyacetone phosphate (DHAP), fructose-1,6-bisphosphate (FBP), and lactic acid; it decreased the blood concentration of pyruvic acid and the plasma concentration and urinary excretion of inorganic phosphate. However, intravenous administration of 1 mg glucagon together with xylitol reduced the xylitol-induced changes in oxypurines, pyruvic acid, GABP + DHAP, and FBP, whereas it promoted the xylitol-induced increase in the urinary excretion of total purine bases and did not affect the xylitol-induced increase in the plasma concentration of total purine bases. In addition, in vitro study demonstrated that sodium pyruvate prevented the xylitol-induced degradation of adenine nucleotides in erythrocytes. These results suggested that gluconeogenesis due to glucagon increased the production of pyruvic acid, accelerated the conversion of NADH to NAD, and thereby prevented both the xylitol-induced degradation of adenine nucleotides in organs similar to erythrocytes and the inhibition of xanthine dehydrogenase in the liver and small intestine, resulting in decreases in the plasma concentration and urinary excretion of oxypurines. However, it was also suggested that in the liver storing glycogen, glucagon-induced glycogenolysis accumulated sugar phosphates, resulting in purine degradation, since the xylitol-induced increase in the NADH/NAD ratio partially blocked glycolysis at the level of GABP dehydrogenase. Therefore, administration of glucagon together with xylitol may synergistically increase purine degradation more than xylitol alone, despite decreases in the plasma concentration and urinary excretion of oxypurines.

Alteration of erythrocyte membrane Na, K-ATPase in children with borderline or essential hypertension

The aim of this study was to evaluate the substrate (ATP) kinetics of erythrocyte membrane Na, K-ATPase in children with borderline or essential hypertension. Although the activity of Na, K-ATPase in the presence of in vivo concentrations of ATP was not significantly altered, kinetic studies showed an obvious inhibition of enzyme activity in the erythrocyte membrane of children with borderline or essential hypertension. Hanes plot analysis revealed a decrease of V(max) from 7.19 in erythrocytes from control subjects to 4.93 and 3.33 in those from children with borderline or essential hypertension, respectively. A mean value of the K(m) decreased from 0.10 in the control to 0.08 and 0.02 in children with borderline or essential hypertension, respectively. The energy status of erythrocytes, estimated by ATP, ADP and AMP levels, ATP/ADP ratio, and adenylate energy charge (AEC) was not significantly changed in the cells from hypertensive children. The use of a free radical-generating system (FeSO4/ascorbate) in vitro significantly reduced enzyme activity in the control erythrocytes while in those from hypertensive children it was abolished completely. The level of lipid peroxides was considerably higher (+ 37 per cent) in the plasma, while that of reduced glutathione was significantly lower both in the erythrocytes and the plasma of children with essential hypertension than in healthy children. These results indicate significant alterations of the antioxidant status which could be the cause of the inhibited Na, K-ATPase activity in erythrocyte membranes from hypertensive children.

Human cardiac high-energy phosphate metabolite concentrations by 1D-resolved NMR spectroscopy

We have developed a method that can measure high-energy phosphate metabolite concentrations in humans with 1D resolved surface-coil NMR spectroscopy. The metabolites are measured by phosphorus (31P) NMR spectroscopy, and the tissue water proton (1H) resonance from the same volume serves as an internal concentration reference. The method requires only the additional acquisition of a 1H data set, and a simple calibration, performed separately, to determine the ratio of the signal per proton to the signal per phosphorus nucleus. The quantification method is particularly useful for human cardiac spectroscopy, where it eliminates image-based tissue volumetry and the corrections for signal sensitivity and phase nonuniformity necessary in prior approaches. Corrections are introduced to account for blood and fat contributions to the spectra. The method was validated on phantoms of phosphate of varying concentrations and on the human calf muscle. In calf, the adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrations were 5.6 +/- 1.6 (mean +/- SD) and 26 +/- 4 mmol/kg wet wt, respectively. In normal heart, [ATP] was 5.8 +/- 1.6 and [PCr] was 10 +/- 2 mmol/kg wet wt. These values are in excellent agreement with prior NMR studies and biopsy data. The protocol is easily accommodated within existing 1D cardiac patient protocols, and the same approach is advantageous for eliminating tissue volumetry and sensitivity corrections when measuring concentrations by 2D and 3D resolved spectroscopy.

Mechanism of inhibition of glycolysis in Streptococcus mutans NCIB 11723 by chlorhexidine

Inhibition of the rate of acid production from glucose by the cells of Streptococcus mutans NCIB 11723 was directly related to the concentrations of 0.075 to 0.20 mM chlorhexidine. Lactate production was inhibited to a greater extent than acetate and formate. Quantification of glycolytic intermediates revealed that the steps in glycolysis inhibited by chlorhexidine were the reactions catalyzed by phosphofructokinase and glyceraldehyde 3-phosphate dehydrogenase and/or phosphoglycerate kinase. However, the activities of these enzymes were not decreased in cells treated with the inhibitor. It was demonstrated that chlorhexidine caused leakage of metabolites from the cells. Our results indicate that the decreased rate of glycolysis caused by chlorhexidine is due to the leakage of metabolic intermediates and not to direct effects on enzymes involved in glycolysis by S. mutans NCIB 11723.

Circulation of red blood cells having high levels of 2,3-bisphosphoglycerate protects rat brain from ischemic metabolic changes during hemodilution

BACKGROUND AND PURPOSE

We designed the present study to examine the effects of red blood cell oxygen-delivering capacity on ischemic brain metabolism during hemodilution with respect to red blood cell 2,3-bisphosphoglycerate content.

METHODS

A modification of red blood cell 2,3-bisphosphoglycerate content was achieved by an exchange transfusion of blood in which red blood cells were treated with either phospho(enol)pyruvate or inorganic phosphate in spontaneously hypertensive rats. Hematocrit values of circulating blood were varied from 30% to 20% during transfusion. Brain ischemia was produced in rats by bilateral carotid artery occlusion lasting 60 minutes. The concentrations of ATP and 2,3-bisphosphoglycerate in the blood and the ATP, phosphocreatine, and lactate concentrations in the brain were estimated by an enzymatic method.

RESULTS

Red blood cell 2,3-bisphosphoglycerate concentration increased to 200% of the pretransfusion level after the transfusion in which red blood cells were treated with phospho(enol)pyruvate, whereas the concentration decreased to 80% after the transfusion in which red blood cells were treated with phosphate. Red blood cell ATP content did not differ significantly between the phospho(enol)pyruvate- and phosphate-treated groups after transfusion. When hematocrit was approximately 30%, the ischemic brain ATP and lactate contents did not differ between the nonischemic and ischemic groups. However, as hematocrit was reduced to less than 25% the ischemic brain ATP content remarkably decreased and the lactate content substantially increased in the 2,3-bisphosphoglycerate-subnormal red blood cell group. In contrast, the ischemic brain ATP and phosphocreatine contents in the 2,3-bisphosphoglycerate-enriched red blood cell group were preserved and as high as those in the nonischemic group under the same conditions.

CONCLUSIONS

Cerebral ischemia was compensated with the increment of cerebral blood flow as a result of the reduction of hematocrit to optimal levels, but the extreme hemodilution induced insufficient oxygen supply to the brain tissue, resulting in a more marked impairment of brain metabolism despite an increase in cerebral blood flow. However, even in extreme hemodilution conditions the 2,3-bisphosphoglycerate-enriched red blood cells in circulating blood protected the brain from ischemic metabolic changes. These results suggest that the 2,3-bisphosphoglycerate-enriched red blood cells in the circulating blood may thus compensate for the insufficient oxygen supply in extremely anemic conditions by providing a sufficient supply of oxygen in the face of ischemic insult.

3D 31P spectroscopic imaging of the human heart at 4.1 T

High field (4 Tesla) spectroscopic imaging offers the advantages of increased signal-to-noise ratio and the possibility of acquiring high resolution metabolite images. We have applied a three dimensional spectroscopic imaging sequence using a sparse Gaussian sampling method to acquire phosphocreatine (PCr) images of the human heart with 8-cc voxels. PCr images enabled observation of the septum, left ventricular free wall, apex, and skeletal muscle. Quantitative evaluation of the 50 myocardial voxels acquired from 10 studies of healthy adults revealed a PCr/adenosine triphosphate (ATP) ratio of 1.80 +/- 0.32 after correction for saturation effects. Due to the small size of the voxels and the ability to choose the location of the volumes to minimize inclusion of blood, no correction for blood pool ATP was required. The calculated PCr/ATP ratio is in agreement with other studies at 1.5 and 4.0 T.

Energy metabolism of reticulocytes: two different sources of energy for Na+K(+)-ATPase activity

Total energy production in rabbit reticulocytes amounted to 136.52 +/- 6.50 mumol ATP h-1 ml-1 of reticulocytes: 88.3 per cent was provided by oxidative phosphorylation, whereas only 11.7 per cent by aerobic glycolysis. Na+K(+)-ATPase accounted for 23 per cent, i.e. 27.65 +/- 2.55 mumol ATP h-1ml-1 of reticulocytes, in the overall energy consumption in reticulocytes of rabbits. Under basal conditions ATP for Na+K(+)-ATPase activity was derived exclusively from oxidative phosphorylation. However, when the activity of Na+K(+)-ATPase was increased due to the stimulation of adenylate cyclase by (-)-isoprenaline, the additional energy required was provided by aerobic glycolysis. These results indicate that two different compartments, one cytosolic and the other mitochondrial, provide energy for Na+K(+)-ATPase activity in reticulocytes.

P-31 MR spectroscopy of skeletal and cardiac muscle metabolism in patients with systemic sclerosis: a multiple case study

Three-dimensionally localized proton-decoupled phosphorus-31 magnetic resonance (MR) spectroscopy of skeletal and cardiac muscle was performed in six patients with systemic sclerosis. Cardiac (n = 9) and skeletal (n = 6) spectra were also obtained in healthy volunteers. Metabolite ratios and intracellular pH were determined from the spectra of skeletal and cardiac muscle. The phosphocreatine-to-adenosine triphosphate ratio was normal for both skeletal and cardiac muscle in patients with systemic sclerosis. The pH values of skeletal muscle were similar in patients and control subjects (7.13 +/- 0.02 vs 7.12 +/- 0.01, respectively). In skeletal muscle, the inorganic phosphate-to-phosphocreatine ratio in patients was increased relative to that of control subjects (0.106 +/- 0.014 vs 0.086 +/- 0.006, respectively; P = .02). P-31 MR spectroscopy showed no abnormalities in the myocardium of patients with systemic sclerosis. Assessment of the inorganic phosphate-to-phosphocreatine ratio in peripheral skeletal muscle may be helpful for assessing disease activity.

Hereditary triosephosphate isomerase (TPI) deficiency: two severely affected brothers one with and one without neurological symptoms

A 13-year-old Hungarian boy (B.J.Jr.) with congenital haemolytic anaemia (CHA) and hyperkinetic torsion dyskinesia was found to have severe triose-phosphate isomerase (TPI) deficiency. One of his two brothers (A.J.), a 23-year-old amateur wrestler, has CHA as well, but no neurological symptoms. Both have less than 10% TPI activity and a highly increased dihydroxyacetone phosphate (DHAP) level in their red blood cells. Their TPI had a slow electrophoretic mobility and was heat unstable. Both parents and a third brother are healthy heterozygous carriers of the defect. A.J. represents a unique phenotype from the point of view that all published "homozygotes" had severe neurological alterations from infancy or early childhood except one infant who died at 11 months, probably too young for neurological symptoms to be noted. In contrast to the two affected Hungarian brothers all but one "homozygote" has died before the age of 6 years. The striking difference in the clinical course of the defect between the two brothers with the same severe red blood cell enzyme deficiency may originate from unusual differences between two double heterozygous brothers resulting inter alia in different levels of TPI expression in various tissues. Significantly lower TPI activities were found in both the T- and B-cells of the propositus as compared to the respective cells of the neurologically symptom-free brother.

Effect of ethanol ingestion on nucleotides and glycolytic intermediates in erythrocytes and purine bases in plasma and urine: acetaldehyde-induced erythrocyte purine degradation

The effect of ethanol on nucleotides and glycolytic intermediates in erythrocytes and purine bases in plasma and urine was investigated. Ethanol ingestion (0.45 mL/kg body weight) increased plasma concentrations and urinary excretion of oxypurines (hypoxanthine and xanthine) and concentrations of adenosine monophosphate (AMP), adenosine diphosphate (ADP), and glyceraldehyde 3-phosphate+dihydroxyacetonephosphate in erythrocytes. In an in vitro incubation study using erythrocytes, acetaldehyde increased the concentrations of AMP, ADP, and glyceraldehyde 3-phosphate+dihydroxyacetonephosphate in erythrocytes as well as the concentration of hypoxanthine in the incubation medium. These results suggest that acetaldehyde (a metabolite of ethanol) induces an increase in purine degradation by erythrocytes and then contributes to the ethanol-induced enhanced purine degradation in vivo.

Cadmium-induced changes of antioxidant and metabolic status in red blood cells of rats: in vivo effects

Chronic exposure of adult rats to dietary intake of cadmium (15 mg CdCl2/day/kg for 30 days) leads to development of anemia and thrombocytosis. Anemia is characterized by significant reticulocytosis (13.1 +/- 1.0%), anysocytosis, poikilocytosis, iron deficiency and marked alterations of antioxidant and metabolic status of red blood cells. Activities of SOD, catalase, GPx and GR were significantly increased in red blood cells of cadmium-treated rats. In treated animals cadmium induced an increase of red cell reduced and oxidized glutathione with no changes of GSSG/GSH ratio. However, significant reduction of lipid peroxidation was found. Plasma levels of tocopherol and ascorbate, as well as activity of glutathione-S-transferase, were all significantly increased in cadmium-treated rats. The energy metabolism of red blood cells was deeply altered in cadmium-treated rats. The levels of ATP, ADP, AMP and TAN were significantly increased while ATP/ADP ratio and adenylate energy charge (AEC) were significantly reduced. The level of 2,3-BPG was somewhat lower, but 2,3-BPG/Hb ratio was considerably higher, in red blood cells of cadmium-treated rats.

Acute episodic hemolysis in the African black rhinoceros as an analogue of human glucose-6-phosphate dehydrogenase deficiency

Sudden episodes of massive hemolysis have become the most common cause of death among captive black rhinoceroses, and there is evidence that they occur in the wild as well. We have observed radically unique enzyme and metabolite profiles in normal rhinoceros erythrocytes compared to humans and other mammals, including marked deficiencies of intracellular adenosine triphosphate (ATP), catalase, adenosine deaminase, and other enzymes involved in glycolysis, glutathione cycling, and nucleotide metabolism. Minimal concentrations of ATP appear to impair effective acceleration of hexosemonophosphate shunt activity in response to oxidants by restricting substrate generation at the hexokinase step. Antioxidant defenses are further compromised by catalase deficiency, which may be a general characteristic of rhinoceros erythrocytes, perhaps related to the common occurrence of severe mucocutaneous ulcerative disease. It is proposed that erythrocyte ATP deficiency in rhinoceroses may be an evolutionary adaptation conferring selective advantage against common hemic parasites, comparable to the role of human glucose-6-phosphate dehydrogenase (G-6-PD) deficiency in falciparum malaria.

31P magnetic resonance spectroscopy in dilated cardiomyopathy and coronary artery disease. Altered cardiac high-energy phosphate metabolism in heart failure

BACKGROUND

The purpose of this work was to further define the value of cardiac 31P magnetic resonance (MR) spectroscopy for patients with coronary artery disease and dilated cardiomyopathy.

METHODS AND RESULTS

Blood-corrected and T1-corrected 31P MR spectra of anteroseptal myocardium were obtained at rest using image-selected in vivo spectroscopy localization, a selected volume of 85 +/- 12 cm3, and a field strength of 1.5 T. Nineteen volunteers had a creatine phosphate (CP)/ATP ratio of 1.95 +/- 0.45 (mean +/- SD) and a PDE/ATP ratio of 1.06 +/- 0.53; in four patients with left anterior descending coronary artery (LAD) stenosis, six patients with chronic anterior wall infarction, and four patients with chronic posterior wall infarction, CP/ATP and phosphodiester (PDE)/ATP ratios did not differ from those in volunteers. Twenty-five measurements of 19 patients with dilated cardiomyopathy yielded a CP/ATP of 1.78 +/- 0.51 and a PDE/ATP of 0.98 +/- 0.56 (p = NS versus volunteers). When these patients were grouped according to the severity of heart failure, however, CP/ATP was 1.94 +/- 0.43 in mild (p = NS versus volunteers) and 1.44 +/- 0.52 in severe DCM (p < 0.05), respectively. No correlation was found between CP/ATP and left ventricular ejection fraction or fractional shortening, but correlation of CP/ATP with the New York Heart Association (NYHA) class was significant (r = 0.60, p < 0.005). Six patients with dilated cardiomyopathy were studied repeatedly before and after 12 +/- 6 weeks of drug treatment leading to clinical recompensation with improvement of the NYHA status by 0.8 +/- 0.3 classes. Concomitantly, CP/ATP increased from 1.51 +/- 0.32 to 2.15 +/- 0.27 (p < 0.01), whereas PDE/ATP did not change significantly.

CONCLUSIONS

Cardiac high-energy phosphate metabolism at rest is normal in LAD stenosis and chronic myocardial infarction in the absence of heart failure. The CP/ATP ratio has low specificity for the diagnosis of dilated cardiomyopathy. However, CP/ATP correlated with the clinical severity of heart failure and may improve during clinical recompensation.

Cardiac metabolism in patients with dilated and hypertrophic cardiomyopathy: assessment with proton-decoupled P-31 MR spectroscopy

Proton-decoupled phosphorus-31 heart spectroscopy was performed in healthy subjects (n = 9) and patients with dilated cardiomyopathy (DCM, n = 9) or hypertrophic cardiomyopathy (HCM, n = 8). The phosphocreatine (PCr)-to-adenosine triphosphate ratio (+/- one standard deviation) after correction for blood contribution and partial saturation was significantly lower in HCM patients relative to the control subjects (1.32 +/- 0.29 vs 1.65 +/- 0.26, P < .05) but not in DCM patients (1.52 +/- 0.58 vs 1.65 +/- 0.26). The inorganic phosphate (Pi) peak was resolved only in patients with the highest spectral quality. Myocardial pH was lower in HCM patients (n = 6) relative to control subjects (n = 4) (7.07 +/- 0.07 vs 7.15 +/- 0.03, P < .05). The Pi/PCr ratio was higher in DCM (n = 3) and HCM (n = 6) patients relative to control subjects (n = 4) (0.29 +/- 0.06 and 0.20 +/- 0.04, respectively, vs 0.14 +/- 0.06; P < .05). Elevated phosphodiester signal in DCM patients correlated with 2,3-diphosphoglycerate signal (r = .94), reflecting blood pool contamination. P-31 spectroscopy enabled detection of abnormalities in cardiac metabolism and determination of pH in patients with HCM and DCM.

Erythrocyte pyruvate kinase deficiency: relations of residual enzyme activity, altered regulation of defective enzymes and concentrations of high-energy phosphates with the severity of clinical manifestation

The defective enzymes of 54 patients with pyruvate kinase (PK) deficiency were characterized according to the recommendations of the International Committee for Standardization in Haematology (ICSH). The erythrocyte PK activity in whole blood was calculated considering the 16-fold higher activity of the reticulocyte enzyme (AR) compared to the erythrocyte enzyme (AE). The following parameters turned out to give a good correlation to the degree of haemolytic anaemia and can therefore serve as a prognostic tool: All patients with a severe course of the disease had residual erythrocyte PK activities less than 33% of the normal enzymes (percentage activity), and patients with mild haemolytic anaemia exhibited residual activity values below and above this threshold value. Studies of enzyme cooperative showed that positive cooperative or mixed cooperative phosphoenolpyruvate (PEP) binding with a predominant positive cooperative part appeared in all cases with a mild clinical course, and about one-third of the severe ones. Negative cooperativity or mixed cooperativity with predominant negative cooperative part was observed only with severe haemolytic anaemia. Furthermore, the determination of glucose-6-phosphate (G-6-P) turned out to be a good prognostic criterion, i.e. all patients with mild clinical course exhibited G-6-P-concentrations lower than 0.11 mumol/l red blood cells. In the case of patients with severe haemolytic anaemia, about 80% showed values higher than 0.11 mumol/l RBC.

Preservation of metabolic activity in lyophilized human erythrocytes

Normal human erythrocytes (RBC) were freeze-dried under conditions that caused minimal modification in normal RBC metabolic activities. Because of the known effects of long-term storage on metabolic activities, we studied the effects of our lyophilization process on RBC metabolism. Of all the metabolic enzymes studied, only triosephosphate isomerase (D-glyceraldehyde-3-phosphate ketol-isomerase, EC 5.3.1.1), enolase (2-phospho-D-glyceratehydro-lyase, EC 4.2.1.11), and pyruvate kinase (ATP:pyruvate O2-phosphotransferase, EC 2.7.1.40) were decreased when compared with fresh control nonlyophilized RBC. The activities of these enzymes did not differ significantly from those of blood bank RBC. Concentrations of high-energy intermediates, ATP, and 2,3-diphosphoglycerate, along with lactate and ATP production were decreased in lyophilized RBC. No enzymes of the pentose phosphate shunt were altered during lyophilization. In addition, our data show that lyophilized RBC possess an intact capacity to (i) synthesize adenine nucleotides and (ii) reduce MetHb to Hb and, thus, maintain the Hb in a functional physiologic state similar to fresh nonlyophilized RBC. The present study demonstrates the possibility of lyophilizing RBC in a manner that maintains normal metabolic and enzymatic function upon rehydration.

Rapid and simple gas chromatographic measurement of lactic acid in red blood cells, plasma, and tumor cells after hyperthermia

The content of lactic acid in red blood cells, plasma, and Ehrlich ascites tumor cells were measured by a gas-liquid chromatography using a column with a terephtalic acid support coated with polyethylene glycol-6000. The lactic acid contents were directly determined in aqueous samples, because they were converted to a volatile derivative in the column. The method was rapid and simple, compared with previous methods which need time-consuming conversion of lactic acid to volatile derivatives. Our measurements showed the increase in the contents of intra- and extracellular lactic acid after hyperthermia.

Effect of TPA on fructose 2,6-bisphosphate levels and protein kinase C activity in B-chronic lymphocytic leukemia (B-CLL)

Normal B lymphocytes and peripheral mononuclear blood cells from B-chronic lymphocytic leukemia (B-CLL) patients were incubated in the presence of the tumor promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). In normal B lymphocytes and lymphocytes from five patients with B-CLL, TPA stimulation increased lymphocyte fructose 2,6-bisphosphate (fructose 2,6-P2) content and activity of 6-phosphofructo 2-kinase (PFK-2), which is the enzyme that catalyzes the synthesis of fructose 2,6-P2. This effect was evident after 6 h and maximal after 12-24 h of TPA exposure. In three patients, lymphocytes seemed to be refractory to TPA stimulation in the conditions described here. Lymphocyte stimulation by TPA was associated with the translocation of protein kinase C (PKC) from the soluble to the particulate membrane fraction, except in B-CLL lymphocytes refractory to the TPA effect. These results give further support to the existence within B-CLL of subsets of cells which are refractory to the stimulation by TPA and demonstrate that the tumor promoter TPA induces important metabolic changes in lymphocytes of some patients with B-CLL.

Altered myocardial high-energy phosphate metabolites in patients with dilated cardiomyopathy

Myocardial high-energy phosphate metabolism in patients with dilated cardiomyopathy (DCM) of ischemic or idiopathic etiology was assessed at rest by one-dimensional phase-encoded 31P-nuclear magnetic resonance (NMR) spectroscopy studies performed in conjunction with 1H imaging in 20 patients with DCM and in 12 normal volunteers. The measured values of anterior myocardial phosphocreatine/beta-adenosine triphosphate (PCr/beta-ATP), corrected for partial saturation and contamination of the spectra by blood metabolites, averaged 1.80 +/- 0.06 (mean +/- SE) in normal volunteers and 1.46 +/- 0.07 in the patients overall, a highly significant (p less than 0.001) decrease. In patients with DCM accompanied by coronary artery disease (n = 9), the PCr/beta-ATP ratio averaged 1.53 +/- 0.07, while in those with DCM alone it was 1.41 +/- 0.12 (n = 11), a value that was not significantly different. There was no significant correlation (r = 0.34) between myocardial PCr/ATP ratio and left ventricular ejection fraction in patients. These studies demonstrate that myocardial PCr/ATP ratios are reduced at rest in human ischemic and idiopathic dilated cardiomyopathy.

Heterozygous pyruvate kinase deficiency and severe hemolytic anemia in a pregnant woman with concomitant, glucose-6-phosphate dehydrogenase deficiency

The aim of this paper is to describe the clinical and hematological characteristics of a 32-year-old woman with concomitant heterozygous pyruvate kinase (PK) and glucose-6-phosphate dehydrogenase (G6PD) deficiencies and severe hemolytic anemia during pregnancy. In 1964, Oski et al. described a family in which a clinically healthy woman was heterozygous for both PK and G6PD deficiencies. To our knowledge, the present case is the first described in which the same condition is associated with hemolysis. A heterozygous condition for both enzymopathies was clearly demonstrated by family study criteria, and all other causes of hemolytic anemia were eliminated. No evidence of genetic relationship between the two disorders was demonstrated. Since late onset of hemolysis in heterozygous PK-deficient women has been observed in association with pregnancy and the molecular characteristics of the concomitant deficient G6PD enzyme were kinetically favorable, partial PK deficiency is suggested as the major cause of hemolysis in this patient.

Intracellular xylitol-phosphate hydrolysis and efflux of xylitol in Streptococcus sobrinus

The parental strain Streptococcus sobrinus (Streptococcus mutans ATCC 27352), which is known to transport, phosphorylate and accumulate xylitol intracellularly as nonmetabolizable xylitol-phosphate (xylitol-sensitive (XS) strain) and its xylitol-resistant (XR) spontaneous mutant were used to further investigate the inhibitory action of xylitol on oral streptococci. Fructose-grown XR cells did not accumulate xylitol-phosphate, indicating that the inducible fructose PTS is incapable of transporting the pentitol. The intracellularly accumulated pentitol-phosphate by the XS cells did not prevent the subsequent uptake and degradation of glucose or fructose, despite a drop in the PEP pool and a 50% inhibition of the glucose but not the fructose catabolism. Intracellular dephosphorylation of the pentitol-phosphate and release of xylitol in the extracellular medium resulted in a rapid decrease of the intracellular level of this nonmetabolizable product. A Mg(++)- or Mn(++)-independent sugar-phosphate hydrolysing activity capable of splitting xylitol-phosphate was demonstrated in both XS and XR strains. Preincubation in the presence of N1-ethylmaleimide (NEM) and xylitol or NEM and fructose resulted in the subsequent inhibition of both xylitol uptake and efflux. The efflux kinetic at various temperatures is compatible with a facilitated diffusion by the phosphotransferase system EIIfru without, however, excluding the existence of an additional exit route, but it excludes a simple diffusion exit process. The results are consistent with the existence of a xylitol futile cycle contributing to the growth inhibition of S. sobrinus by the pentitol without excluding a toxic effect of xylitol-phosphate. Discrepancies in the literature on the action of xylitol on S. mutans could be explained in the light of the evidence presented.