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.     

Metabolic engineering of Ralstonia eutropha for the biosynthesis of 2-hydroxyacid-containing polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are bio-based and biodegradable polyesters synthesized by numerous microorganisms. PHAs containing 2-hydroxyacids as monomer units have attracted much attention, but their production has not been efficient. Here, we metabolically engineered Ralstonia eutropha strains for the in vivo synthesis of PHAs containing 2-hydroxyacids as monomers. This was accomplished by replacing the R. eutropha phaC gene in the chromosome with either the R. eutropha phaC S506G A510K gene, which contains two point mutations, or the Pseudomonas sp. MBEL 6–19 phaC1437 gene. In addition, the R. eutropha phaAB genes in the chromosome were replaced with the Clostridium propionicum pct540 gene. All of the engineered R. eutropha strains produced PHAs containing 2-hydroxyacid monomers, including lactate and 2-hydroxybutyrate (2HB), along with 3-hydroxybutyrate (3HB) and/or 3-hydroxyvalerate (3HV), when they were cultured in nitrogen-free medium containing 5 g/L lactate or 4 g/L 2HB and 20 g/L glucose as carbon sources. Expression of the Escherichia coli ldhA gene in engineered R. eutropha strains allowed production of poly(3-hydroxybutyrate-co-lactate) [P(3HB-co-LA)] from glucose as the sole carbon source. This is the first report on the production of 2-hydroxyacid-containing PHAs by metabolically engineered R. eutropha.     

Metal Cu(II) and Zn(II) bipyridyls as inhibitors of lactate dehydrogenase

Metal complex–protein interaction is an evolving concept for determining cellular targets of metallodrugs. Lacatate dehydrogenase (LDH) is critically implicated in tumor growth and therefore, considered to be an important target protein for anti-tumor metal complexes. Due to efficient biocompatibility of copper (Cu²⁺) and zinc (Zn²⁺), we synthesized CubpyAc₂ · H₂O (Cu-bpy) and ZnbpyAc₂ · H₂O (Zn-bpy; where bpy = 2,2′ bipyridine, Ac = CH₃COO⁻) complexes and evaluated their interaction with and modulation of LDH in mouse tissues. The increasing concentration of both the complexes showed a significant shift in UV–Vis spectra of LDH. The binding constant data (Kc = 1 × 10³ M⁻¹ for Cu-bpy and 7 × 10⁶ M⁻¹ for Zn-bpy) suggested that Zn-bpy-LDH interaction is stronger than that of Cu-bpy-LDH. LDH modulating potential of the complexes were monitored by perfusing the mice tissues with non-toxic doses of Cu-bpy and Zn-bpy followed by activity measurement and analysis of LDH isozymes on non-denaturing polyacrylamide gel electrophoresis (PAGE). As compared to the control sets, Cu-bpy caused a significant decline (P < 0.05–0.001) in the activity of LDH in all the tissues studied. However, Zn-bpy showed inhibition of LDH only in liver (P < 0.01), kidney (P < 0.001) and heart (P < 0.01), but with no effect in spleen, brain and skeletal muscle tissues. PAGE analysis suggested that all the five LDH isozymes are equally sensitive to both the complexes in the respective tissues. The results suggest that Cu- and Zn-bpy are able to interact with and inhibit LDH, a tumor growth supportive target protein at tissue level.     

Electromyogram as an indicator of neuromuscular fatigue during incremental exercise

This study analysed the changes in the electromyographic activity (EMG) of the vastus lateralis muscle (VL) during an incremental maximal oxygen uptake test on a treadmill. A breakpoint in the integrated electromyogram (iEMG)-velocity relationship has already been interpreted in two ways: either as a sign of neuromuscular fatigue or as an expression of the iEMG-velocity relationship characteristics. The aim of this study was to test a method of distinguishing fatigue effects from those due to increases in exercise power. Eight well-trained male runners took part in the study. They completed a running protocol consisting of 4-min stages of increments in power output. Between each stage (about 15 s after the start of a minute at rest), the subjects had to maintain a standard effort: a 10-s isometric leg extension contraction [50% isometric maximal voluntary contraction (IMVC)]. The EMG was recorded during the running and isometric protocols, a change in the EMG signal during the isometric exercise being considered as the sign of fatigue. The iEMG-velocity relationships were strongly fitted by a second-order polynomial function for data taken at both the start (r = 0.98) and the end (r = 0.98) of the stage. Based on the stability of the 50%IMVC-iEMG relationship noted between stages, the start-iEMG has been identified as expressing the iEMG-velocity relationship without fatigue. The stage after which end-iEMG increased significantly more steeply than start-iEMG was considered as the iEMG threshold and was simultaneous with the ventilatory equivalent for carbon dioxide threshold. The parallel changes of minute ventilation and iEMG would suggest the existence of common regulation stimuli linked either to effort intensity and/or to metabolic conditions. The fall in intracellular [K⁺] has been discussed as being one of the main factors in regulating ventilation. Accepted: 16 December 1997     

Lactate modeling and its application to endurance training

1. 1. In this short review, previous studies regarding the modeling of lactate (La) response to exercise and its application to endurance training have been summarized.

2. 2. Additionally the result of a recent study by the present authors are shown.

3. 3. Several models for La response to step and ramp exercise are already proposed and deductions derived from them are used for practical purposes such as the prediction of race performance in middle-and long-distance runners as well as for construction of their training regimens.

4. 4. Only a limited number of models however have tried to quantify whole body La kinetics to exercise in humans concomitantly with describing physiological mechanisms underlying the observed phenomenon.

5. 5. In a recent study described further in this paper a 2 compartment model was used for the purpose of clarifying the current “La production vs degradation” controversy during La adaptation to training.

6. 6. It was determined from this investigation that the La metabolic clearance rate during recovery is enhanced by the endurance training.

7. 7. This is in accordance with another recent observation of an increased La metabolic clearance rate at high absolute work rates and all relative work rates during exercise.

Relationship between plasma ammonia and blood lactate concentrations after maximal treadmill exercise in circumpubertal girls and boys

The purpose of the study was to define a relationship between plasma ammonia [NH3]pl and blood lactate concentrations [la-]b after exercise in children and to find out whether the [NH3]pl, determined during laboratory treadmill tests, may be useful as a predictor of the children's sprint running ability. A group of 20 girls and 14 boys trained in athletics or swimming and 8 untrained boys, aged 13.2 to 13.7 years, participated in the study. Their [NH3]pl and [la-]b were measured before and after incremental maximal treadmill exercise. In addition, the subjects' running performance was tested in 30-, 60- and 600- or 1000-m runs under field conditions. The [NH3]pl during the treadmill runs increased by 20.1 (SD 17.3), 24 (SD 16.7) and 10 (SD 4.3) mumol.l-1 in the girls, the trained boys and the untrained boys, respectively. The postexercise [NH3]pl correlated positively with [la-]b (r = 0.565 in the girls and 0.812 in the boys) and treadmill speed attained during the test (r = 0.489 in the girls and 0.490 in the boys). Significant correlations were also found between [NH3]pl obtained during the treadmill test and the times of 30- and 60-m runs (r = -0.676 and -0.648, respectively) in the boys but not in the girls. A comparison of the present data with those reported previously in adults showed that increases in [NH3]pl during maximal exercise in children would seem to be lower than in adult subjects both in absolute values and in relation to [la-]b.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lactate dehydrogenase in the cyanobacterium Microcystis PCC7806

Abstract The cyanobacterium Microcystis PCC7806 was found to possess an NAD-dependent lactate dehydrogenase (EC 1.1.1.27) which catalyzes the reduction of pyruvate to l-lactate. The enzyme required fructose 1,6-bisphosphate for activity and displayed positive cooperativity towards pyruvate. Lactate was not formed during fermentation by cell suspensions, possibly due to low intracellular concentrations of fructose 1,6-bisphosphate and/or pyruvate.     

NDRG3-mediated lactate signaling in hypoxia

Hypoxia is associated with many pathological conditions as well as the normal physiology of metazoans. We identified a lactate-dependent signaling pathway in hypoxia, mediated by the oxygen- and lactate-regulated protein NDRG family member 3 (NDRG3). Oxygen negatively regulates NDRG3 expression at the protein level via the PHD2/VHL system, whereas lactate, produced in excess under prolonged hypoxia, blocks its proteasomal degradation by binding to NDRG3. We also found that the stabilized NDRG3 protein promotes angiogenesis and cell growth under hypoxia by activating the Raf-ERK pathway. Inhibiting cellular lactate production abolishes NDRG3-mediated hypoxia responses. The NDRG3-Raf-ERK axis therefore provides the genetic basis for lactate-induced hypoxia signaling, which can be exploited for the development of therapies targeting hypoxia-induced diseases in addition to advancing our understanding of the normal physiology of hypoxia responses. [BMB Reports 2015; 48(6): 301-302]     

血S100B蛋白和尿乳酸/肌酐比值对门静脉高压症术后肝性脑病发生的早期预测价值

目的评价血S100B蛋白和尿乳酸/肌酐对乙肝肝硬化门脉高压症术后肝性脑病发生的早期预测价值。方法回顾性分析65例乙肝肝硬化门脉高压症患者的临床资料,动态检测术后24、48和72h的血S100B蛋白和尿乳酸/肌酐比值水平,根据是否发生术后肝性脑病将受试者分为肝性脑病组与非肝性脑病组,并对肝性脑病组患者进行临床分度。结果乙肝肝硬化门脉高压症患者术后发生肝性脑病组72h内血S100B蛋白含量和24 h内尿乳酸/肌酐比值水平明显高于非肝性脑病组(P<0.001);72h内血S100B蛋白含量和24 h内尿乳酸/肌酐比值之间及与肝性脑病的临床分度呈正相关(P<0.001);当血S100B水平在28ng/L,尿乳酸/肌酐比值在0.47时,单独检测72h血S100B蛋白的敏感度、特异度分别为91.2%、93.6%;尿乳酸/肌酐比值预测肝性脑病的敏感度和特异性度以术后24h最高,分别为89.3%和91.7%;如检测72h血S100B蛋白的同时监测术后24h尿乳酸/肌酐比值可显著提高肝性脑病诊断的准确性,联合应用两项指标进行检测,诊断的敏感度和特异度分别为95.7%和98.6%,较两种方法单独应用敏感度和特异度均提高。结论对门静脉高压症患者术后以临床表现为基础,同时监测72h内血S100B蛋白和24h尿乳酸/肌酐比值,对提高术后肝性脑病的早期诊断和临床分度具有一定应用价值。