Involvement of d-lactate and lactic acid racemase in the metabolism of glucose by Selenomonas ruminantium

Selenomonas ruminantium HD4 produced significant quantities of d- and l-lactate from glucose in batch culture. Both isomers also supported growth if fumarate was present. In glucose-limited continuous culture, d-lactate was detected in the medium only at fast dilution rates. In continuous-culture-grown cells, only a cytoplasmic NAD-dependent l-lactate dehydrogenase (LDH) and a membrane-associated NAD-independent l-LDH were detected; activity of the soluble enzyme was twice as high at the fast dilution rate as at the slow dilution rate. Lactate racemase was also detected; its activity was 4-fold higher at the fast dilution rate. The presence of racemase explains why d-lactate was made and used by this organism.     

Stimulation of glucose utilization and lactate production in cultured human fibroblasts by thyroid hormone

Human dermal fibroblasts were obtained by harvesting outgrowing cells from the dermal tissue explants and cultured in Dulbecco's modified Eagle medium containing 10% fetal calf serum. After the cells reached confluency, culture was continued in the medium containing calf serum which was deprived of thyroid hormone by the treatment with activated charcoal. These fibroblasts were responsive to exogeneously added thyroid hormone (triiodothyronine) at physiological concentrations, resulting in enhanced utilization of glucose and production of lactate. This stimulation by thyroid hormone was dependent upon the length of exposure to the hormone and its concentration.The hormone did not show any effects on cellular DNA and protein content. The experimental system described above seems to be easy to reconstitute and should be useful for the elucidation of the mechanism of thyroid hormone action.     

Dynamic changes in glucose and lactate in the cortex of the freely moving rat monitored using microdialysis

These experiments for the first time examine simultaneous changes in glucose and lactate in unanaesthetised animals during moderate hypoxia. Unanaesthetised rats were exposed to moderate hypoxia for a period of 15 min by reducing inspired oxygen to 8%. Changes in glucose and lactate were monitored in rat cortex using microdialysis and a novel dual enzyme-based assay. Samples of dialysate collected at 3-min intervals were assayed for both glucose and lactate. There was an early rapid rise of lactate that reached a peak at the end of the period of hypoxia followed by a steep decline. Glucose showed a very much smaller delayed increase that started during the period of hypoxia and continued beyond it. The origin of the rise in glucose is discussed, using the temporal relationship between the lactate and glucose changes.     

Glucose uptake and lactate production by the autotransplanted ovary of the ewe during the luteal and follicular phases of the oestrous cycle

Two experiments were carried out on ewes with ovarian autotransplants to estimate the ovarian uptake of glucose and production of lactate. The first was carried out in the luteal phase of the oestrous cycle. Samples of carotid arterial, ovarian venous and jugular venous blood were collected simultaneously for glucose analysis. The arterial concentration of glucose (58.0 ± 5.0 mg/dL; Mean ± SEM) was significantly higher than the ovarian venous concentration (42.3 ± 2.4 mg/dL; P < 0.001). Next, a second more complete experiment was carried out in the luteal and follicular phases of the oestrous cycle. The oestrous cycle was synchronised and samples of carotid arterial, ovarian venous and jugular venous blood were collected simultaneously for glucose and lactate analysis. There were significant positive arterio-venous differences in the concentration of glucose in the luteal (5.6 ± 1.2 mg/dL, mean ± SEM; P = 0.001), early (3.1 ± 0.82 mg/d; P = 0.003) and late follicular (6.4 ± 1.3 mg/dL; P = 0.001) phases of the oestrous cycle. There was a significant negative arterio-ovarian venous difference in the concentration of lactate in only the luteal phase (-2.2 ± 0.96 mg/dL; P = 0.043).The results show significant removal of glucose from the arterial circulation during its passage through the ovary in the luteal, early follicular and late follicular phases of the oestrous cycle. Furthermore, there was lactate production in the luteal phase but not in the follicular phase suggesting that in the luteal phase of the oestrous cycle, ovarian metabolism can be anaerobic.     

宫内和出生后早期发育环境对成年期糖代谢影响的中枢调控作用机制

目前有大量证据表明早期不良的发育环境对成年期增加代谢性疾病的易感性起着决定性的作用。另外,随着人们对中枢胰岛素抵抗的认识增加,中枢对调控外周葡萄糖稳态起着极其重要的作用,越来越多的研究表明这可能是一种表观遗传学机制。表观遗传学是研究在没有DNA序列变化的情况下,引起基因表达可遗传性的改变。它能特异性地调节相关组织的基因表达,从而诱导物质代谢长期的改变。本文着重探讨早期发育环境对成年期糖代谢影响的中枢调控作用的表观遗传学机制。     

Aerobic glucose metabolism of Saccharomyces kluyveri: growth, metabolite production, and quantification of metabolic fluxes.

The growth and product formation of Saccharomyces kluyveri was characterized in aerobic batch cultivation on glucose. At these conditions it was found that ethyl acetate was a major overflow metabolite in S. kluyveri. During the exponential-growth phase on glucose ethyl acetate was produced at a constant specific rate of 0.12 g ethyl acetate per g dry weight per hour. The aerobic glucose metabolism in S. kluyveri was found to be less fermentative than in S. cerevisiae, as illustrated by the comparably low yield of ethanol on glucose (0.08 +/- 0.02 g/g), and high yield of biomass on glucose (0.29 +/- 0.01 g/g). The glucose metabolism of S. kluyveri was further characterized by the new and powerful techniques of metabolic network analysis. Flux distributions in the central carbon metabolism were estimated for respiro-fermentative growth in aerobic batch cultivation on glucose and respiratory growth in aerobic glucose-limited continuous cultivation. It was found that in S. kluyveri the flux into the pentose phosphate pathway was 18.8 mmole per 100 mmole glucose consumed during respiratory growth in aerobic glucose-limited continuous cultivation. Such a low flux into the pentose phosphate pathway cannot provide the cell with enough NADPH for biomass formation which is why the remaining NADPH will have to be provided by another pathway. During batch cultivation of S. kluyveri the tricarboxylic acid cycle was working as a cycle with a considerable flux, that is in sharp contrast to what has previously been observed in S. cerevisiae at the same growth conditions, where the tricarboxylic acid cycle operates as two branches. This indicates that the respiratory system was not significantly repressed in S. kluyveri during batch cultivation on glucose.     

Crosstalk between xenobiotics metabolism and circadian clock

Many aspects of physiology and behavior in organisms from bacteria to man are subjected to circadian regulation. Indeed, the major function of the circadian clock consists in the adaptation of physiology to daily environmental change and the accompanying stresses such as exposition to UV-light and food-contained toxic compounds. In this way, most aspects of xenobiotic detoxification are subjected to circadian regulation. These phenomena are now considered as the molecular basis for the time-dependence of drug toxicities and efficacy. However, there is now evidences that these toxic compounds can, in turn, regulate circadian gene expression and thus influence circadian rhythms. As food seems to be the major regulator of peripheral clock, the possibility that food-contained toxic compounds participate in the entrainment of the clock will be discussed.     

The recycling of carbon in glucose,lactate and alanine in sheep

Pregnant ewes with catheters implanted in an artery and the uterine and recurrent tarsal veins were infused at a constant rate with U−¹⁴C-labelled glucose, alanine or bicarbonate. Measurements were made of the overall and local fractional contribution of glucose and alanine to CO₂ production and of the extent of interconversion of these metabolites. In the whole animal, by coupling the results with the authors’ previous study of lactate metabolism, a solution was obtained to an open unrestricted 4-compartment model of the exchange of carbon between glucose, lactate, alanine and CO₂. A more limited study was made with non-pregnant sheep because complete data for lactate interactions with alanine were not available. Our analysis of glucose/lactate/alanine/CO₂ interactions in pregnant sheep suggests that about two-thirds of the glycogenic carbon was oxidised fairly directly to CO₂. There was relatively little recycling of glucose carbon through lactate and alanine so that most of the remaining glycogenic carbon was stored as product with relatively long turnover time. It is possible that much of this was in the form of muscle glycogen, and analysis of glycogenic carbon exchange across the hind limb muscle was consistent with this conclusion. In non-pregnant ewes, the findings, although incomplete, suggested that there were no great differences from the findings in pregnant ewes.     

Organ-specific fuel rewiring in acute and chronic hypoxia redistributes glucose and fatty acid metabolism

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Bone and glucose metabolism: A two-way street

Evidence from rodent models indicates that undercarboxylated osteocalcin (ucOC), a product of osteoblasts, is a hormone affecting insulin production by the pancreas and insulin sensitivity in peripheral tissues, at least in part through enhanced secretion of adiponectin from adipocytes. Clinical research to test whether this relationship is found in humans is just beginning to emerge. Cross-sectional studies confirm associations between total osteocalcin (OC), ucOC and glucose metabolism but cannot distinguish causality. To date, longitudinal studies have not provided a consistent picture of the effects of ucOC or OC on fasting glucose and insulin sensitivity. Further exploration into the physiological and mechanistic effects of ucOC and OC, in rodent models and clinical studies, is necessary to determine to what extent the skeleton regulates energy metabolism in humans.     

A dynamic model linking cell growth to intracellular metabolism and extracellular by-product accumulation

Mathematical modeling of animal cell growth and metabolism is essential for the understanding and improvement of the production of biopharmaceuticals. Models can explain the dynamic behavior of cell growth and product formation, support the identification of the most relevant parameters for process design, and significantly reduce the number of experiments to be performed for process optimization. Few dynamic models have been established that describe both extracellular and intracellular dynamics of growth and metabolism of animal cells. In this study, a model was developed, which comprises a set of 33 ordinary differential equations to describe batch cultivations of suspension AGE1.HN.AAT cells considered for the production of α1-antitrypsin. This model combines a segregated cell growth model with a structured model of intracellular metabolism. Overall, it considers the viable cell concentration, mean cell diameter, viable cell volume, concentration of extracellular substrates, and intracellular concentrations of key metabolites from the central carbon metabolism. Furthermore, the release of metabolic by-products such as lactate and ammonium was estimated directly from the intracellular reactions. Based on the same set of parameters, this model simulates well the dynamics of four independent batch cultivations. Analysis of the simulated intracellular rates revealed at least two distinct cellular physiological states. The first physiological state was characterized by a high glycolytic rate and high lactate production. Whereas the second state was characterized by efficient adenosine triphosphate production, a low glycolytic rate, and reactions of the TCA cycle running in the reverse direction from α-ketoglutarate to citrate. Finally, we show possible applications of the model for cell line engineering and media optimization with two case studies.     

Blood glucose responses in humans mirror lactate responses for individual anaerobic threshold and for lactate minimum in track tests

The equilibrium point between blood lactate production and removal (La-(min)) and the individual anaerobic threshold (IAT) protocols have been used to evaluate exercise. During progressive exercise, blood lactate [La-]b, catecholamine and cortisol concentrations, show exponential increases at upper anaerobic threshold intensities. Since these hormones enhance blood glucose concentrations [Glc]b, this study investigated the [Glc] and [La-]b responses during incremental tests and the possibility of considering the individual glucose threshold (IGT) and glucose minimum (Glc(min)) in addition to IAT and La-(min) in evaluating exercise. A group of 15 male endurance runners ran in four tests on the track 3000 m run (v3km); IAT and IGT - 8 x 800 m runs at velocities between 84% and 102% of v3km; La-(min) and Glc(min) - after lactic acidosis induced by a 500-m sprint, the subjects ran 6 x 800 m at intensities between 87% and 97% of v3km; endurance test (ET) - 30 min at the velocity of IAT. Capillary blood (25 microl) was collected for [La-]b and [Glc]b measurements. The IAT and IGT were determined by [La-]b and [Glc]b kinetics during the second test. The La-(min) and Glc(min) were determined considering the lowest [La-] and [Glc]b during the third test. No differences were observed (P < 0.05) and high correlations were obtained between the velocities at IAT [283 (SD 19) and IGT 281 (SD 21) m. x min(-1); r = 0.096; P < 0.001] and between La-(min) [285 (SD 21)] and Glc(min) [287 (SD 20) m. x min(-1) r = 0.77; P < 0.05]. During ET, the [La-]b reached 5.0 (SD 1.1) and 5.3 (SD 1.0) mmol x l(-1) at 20 and 30 min, respectively (P > 0.05). We concluded that for these subjects it was possible to evaluate the aerobic capacity by IGT and Glc(min) as well as by IAT and La-(min).     

Metabolic effects of acetate in perfused rat liver studies on ketogenesis,glucose output,lactate uptake and lipogenesis

1. Livers from fed male rats were perfused in situ in a non-recirculating system with whole rat blood containing acetate at six concentrations, from 0.04 to 1.5 μmol/ml, to cover the physiological range encountered in the hapatic portal venous blood in vivo. 2. Below a concentration of 0.25 μmol/ml there was net production of acetate by the liver, while above it there was ner uptake with a fractional extraction of 40%. 3.No relationship was observed between blood [acetate] and hepatic ketogenesis, the ration [3-hydroxybutyrate]/[acetoacetate] or glucose output, either at low fatty acid concentration s or during oleate infusion. 4. Following the increase in serum fatty acid concentration, induced by oleate infusion, there were suquential incresase in ketogenesis and the ratio of [3-hydroxybutyrate]/[acetoacetate] while glucose output rose and lactate uptake fell significantly after in redox state. 5. There was a highly significant negative correlation between blood [acetate] and hepatic lactate uptake during oleate infusion. At the highest acetate concentration of 1.5 μmol/ml there was a small net hepatic lactate output. After oleate infusion ceased, lactate uptake increased, but the negative correlation between blood [acetate] and hepatic lactate uptake persisted. 6. Livers were also perfused with iether [1-¹⁴C]acetate or [U-¹⁴C]lactate at a concentration of acetate of either 0.3 or 1.3 μmol/ml of blood. With [1-¹⁴C]acetate, most of the radioactivity was recovered as fatty acids at the lower concentration of blood acetate. At the higher blood [acetate] a considerably smaller proportion of the radioactivity was recovered in lipids. With [U-¹⁴C]lactate the reverse pattern obtained i.e., recovery was greater at the high concentration of acetate and fell at the low concentration. Fatty acid biosynthesis, measured with ³H₂O, was stimulated from 2.4 to 6.6 μmol of fatty acid/g of liver per h by high blood [acetate] although the contribution of (acetate+lactate) to synthesis remained constant at 33–38% of the total. 7. These results emphasize the important role of the liver in regulating blood acetate concentrations and indicate that it can be major hepatic substrate. Acetate taken up by the liver appeared to compete directly with lactate, for lipogenesis and metabolism and acetate uptake was inhibited by raised bloodd [lactate].     

Low salt medium for lactate and ethanol production by recombinant Escherichia coli B

Individual nutrient salts were experimentally varied to determine the minimum requirements for efficient l(+)-lactate production by recombinant strains of Escherichia coli B. Based on these results, AM1 medium was formulated with low levels of alkali metals (4.5 mM and total salts (4.2 g l⁻¹). This medium was equally effective for ethanol production from xylose and lactate production from glucose with average productivities of 18–19 mmol l⁻¹ h⁻¹ for both (initial 48 h of fermentation).     

Lactate carbon does not enter the sugars of lipopolysaccharide when gonococci are grown in a medium containing glucose and lactate: implications in vivo

In media containing glucose, lactate stimulates the metabolism of gonococci at concentrations that simulate conditions in vivo. Nuclear magnetic resonance (NMR) spectroscopy of (13)C-labelled lipids obtained from gonococci grown in a synthetic medium with (13)C-labelled lactate and unlabelled glucose (culture A), (13)C-labelled glucose alone (culture B) or (13)C-labelled glucose and unlabelled lactate (culture C) showed lactate carbon was not present in glycerol/ethanolamine residues of lipids from culture A. This indicated that, in the presence of glucose, lactate gluconeogenesis is shut down. Hence, the stimulation of metabolism could result from the production of extra energy because lactate is used solely for conversion to acetyl-CoA, the precursor of fatty acid synthesis and the components of the tricarboxylic acid cycle. In this paper, additional evidence for lack of gluconeogenesis has been sought using a different approach. The carbohydrate moieties of lipopolysaccharide (LPS) have been examined for lactate carbon after gonococci were grown with lactate and glucose. Two methods were used: NMR spectroscopy of (13)C-labelled lipopolysaccharide purified from the three cultures described above showed that, in the presence of glucose, lactate carbon, in contrast to glucose carbon, was not in the carbohydrate moiety. Also, (14)C-labelled lactate was added to a culture containing unlabelled glucose and lactate (culture A) and [(14)C]glucose to cultures containing unlabelled glucose without unlabelled lactate (culture B) and with unlabelled lactate (culture C). When LPS samples purified from these cultures were subjected to hydrazinolysis, the ratio of the radioactivity of water-soluble products (carbohydrate moieties) to those of chloroform-soluble products (fatty acids) was much lower when [(14)C]lactate was used in culture A, than when [(14)C]glucose was used in cultures B and C. Thus, in the presence of glucose, lactate carbon, unlike glucose carbon, is incorporated predominantly into fatty acids of LPS, not into its carbohydrate moieties. There is no doubt, therefore, that gluconeogenesis is shut off when lactate is present with glucose and there is a consequent stimulation of metabolism. This probably occurs in vivo on mucous surfaces, where gonococci are surrounded by a mixture of glucose and lactate in the secretions.     

Glucose production, gluconeogenesis, and hepatic tricarboxylic acid cycle fluxes measured by nuclear magnetic resonance analysis of a single glucose derivative

A triple-tracer method was developed to provide absolute fluxes contributing to endogenous glucose production and hepatic tricarboxylic acid (TCA) cycle fluxes in 24-h-fasted rats by (2)H and (13)C nuclear magnetic resonance (NMR) analysis of a single glucose derivative. A primed, intravenous [3,4-(13)C(2)]glucose infusion was used to measure endogenous glucose production; intraperitoneal (2)H(2)O (to enrich total body water) was used to quantify sources of glucose (TCA cycle, glycerol, and glycogen), and intraperitoneal [U-(13)C(3)] propionate was used to quantify hepatic anaplerosis, pyruvate cycling, and TCA cycle flux. Plasma glucose was converted to monoacetone glucose (MAG), and a single (2)H and (13)C NMR spectrum of MAG provided the following metabolic data (all in units of micromol/kg/min; n = 6): endogenous glucose production (40.4+/-2.9), gluconeogenesis from glycerol (11.5+/-3.5), gluconeogenesis from the TCA cycle (67.3+/-5.6), glycogenolysis (1.0+/-0.8), pyruvate cycling (154.4+/-43.4), PEPCK flux (221.7+/-47.6), and TCA cycle flux (49.1+/-16.8). In a separate group of rats, glucose production was not different in the absence of (2)H(2)O and [U-(13)C]propionate, demonstrating that these tracers do not alter the measurement of glucose turnover.     

Fasting modifies Aroclor 1254 impact on plasma cortisol,glucose and lactate responses to a handling disturbance in Arctic charr

Integrated effects of polychlorinated biphenyl (PCB) and nutritional status on responses to handling disturbance were investigated in the Arctic charr (Salvelinus alpinus). The fish were orally contaminated with Aroclor 1254 and held either with or without food for 5 months before they were subjected to a 10-min handling disturbance. Food-deprived fish were given 0, 1, 10 or 100 mg PCB kg(-1) and the fed fish 0 or 100 mg PCB kg(-1). Plasma cortisol, glucose and lactate levels were measured at 0 (pre-handling), 1, 3, 6 and 23 h after the handling disturbance. Food-deprived control fish had elevated plasma cortisol levels compared with fed fish before handling. These basal cortisol levels were suppressed by PCB in food-deprived fish, and elevated by PCB in fed fish. The immediate cortisol and glucose responses to handling disturbance were suppressed by PCB in a dose-dependent way in food-deprived fish. Although these responses were also lowered by PCB in the fed fish, the effect was much less pronounced than in food-deprived fish. There were only minor effects on plasma lactate responses. Our findings suggest that the stress responses of the Arctic charr are compromised by PCB and that the long-term fasting, typical of high-latitude fish, makes these species particularly sensitive to organochlorines such as PCB.     

The emerging role and targetability of the TCA cycle in cancer metabolism

The tricarboxylic acid (TCA) cycle is a central route for oxidative phosphorylation in cells, and fulfills their bioenergetic, biosynthetic, and redox balance requirements. Despite early dogma that cancer cells bypass the TCA cycle and primarily utilize aerobic glycolysis, emerging evidence demonstrates that certain cancer cells, especially those with deregulated oncogene and tumor suppressor expression, rely heavily on the TCA cycle for energy production and macromolecule synthesis. As the field progresses, the importance of aberrant TCA cycle function in tumorigenesis and the potentials of applying small molecule inhibitors to perturb the enhanced cycle function for cancer treatment start to evolve. In this review, we summarize current knowledge about the fuels feeding the cycle, effects of oncogenes and tumor suppressors on fuel and cycle usage, common genetic alterations and deregulation of cycle enzymes, and potential therapeutic opportunities for targeting the TCA cycle in cancer cells. With the application of advanced technology and in vivo model organism studies, it is our hope that studies of this previously overlooked biochemical hub will provide fresh insights into cancer metabolism and tumorigenesis, subsequently revealing vulnerabilities for therapeutic interventions in various cancer types.     

Partitioning of CO2 Production Between Glucose and Lactate in Excised Sympathetic Ganglia, with Implications for Brain

Abstract: Chains of lumbar sympathetic ganglia from 15-day-old chicken embryos were incubated for 4 h at 36°C in a bicarbonate-buffered salt solution equilibrated with 5% CO₂-95% O₂. Glucose (1–10 m M ), lactate (1–10 m M ), [U-¹⁴C]glucose, [1-¹⁴C]glucose, [6-¹⁴C]glucose, and [U-¹⁴C]lactate were added as needed. ¹⁴CO₂ output was measured continuously by counting the radioactivity in gas that had passed through the incubation chamber. Lactate reduced the output of CO₂ from [U-¹⁴C]glucose, and glucose reduced that from [U-¹⁴C]lactate. When using uniformly labeled substrates in the presence of 5.5 m M glucose, the output of CO₂ from lactate exceeded that from glucose when the lactate concentration was >2 m M . The combined outputs at each concentration tested were greater than those from either substrate alone. The ¹⁴CO₂ output from [1-¹⁴C]glucose always exceeded that from [6-¹⁴C]glucose, indicating activity of the hexose monophosphate shunt. Lactate reduced both of these outputs, with the maximum difference between them during incubation remaining constant as the lactate concentration was increased, suggesting that lactate may not affect the shunt. Modeling revealed many details of lactate metabolism as a function of its concentration. Addition of a blood-brain barrier to the model suggested that lactate can be a significant metabolite for brain during hyperlactemia, especially at the high levels reached physiologically during exercise.