Changes in blood lactate and pyruvate concentrations and the lactate-to-pyruvate ratio during the lactate minimum speed test

Importance of Michaelis Constants for Cancer Cell Redox Balance and Lactate Secretion-Revisiting the Warburg Effect

Cancer cells metabolize a large fraction of glucose to lactate, even under a sufficient oxygen supply. This phenomenon-the "Warburg Effect"-is often regarded as not yet understood. Cancer cells change gene expression to increase the uptake and utilization of glucose for biosynthesis pathways and glycolysis, but they do not adequately up-regulate the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS). Thereby, an increased glycolytic flux causes an increased production of cytosolic NADH. However, since the corresponding gene expression changes are not neatly fine-tuned in the cancer cells, cytosolic NAD+ must often be regenerated by loading excess electrons onto pyruvate and secreting the resulting lactate, even under sufficient oxygen supply. Interestingly, the Michaelis constants (KM values) of the enzymes at the pyruvate junction are sufficient to explain the priorities for pyruvate utilization in cancer cells: 1. mitochondrial OXPHOS for efficient ATP production, 2. electrons that exceed OXPHOS capacity need to be disposed of and secreted as lactate, and 3. biosynthesis reactions for cancer cell growth. In other words, a number of cytosolic electrons need to take the "emergency exit" from the cell by lactate secretion to maintain the cytosolic redox balance.

Metabolome and lipidome derangements during a severe mast cell activation event in a patient with indolent systemic mastocytosis

BACKGROUND

The number of mast cells in various organs is elevated manifold in individuals with systemic mastocytosis. Degranulation can lead to life-threatening symptomatology. No data about the alterations of the metabolome and lipidome during an attack have been published.

OBJECTIVE

Our aim was to analyze changes in metabolomics and lipidomics during the acute phase of a severe mast cell activation event.

METHODS

A total of 43 metabolites and 11 lipid classes comprising 200 subvariants from multiple plasma samples in duplicate, covering 72 hours of a severe mast cell activation attack with nausea and vomiting, were compared with 2 baseline samples by using quantitative liquid chromatography-mass spectrometry.

RESULTS

A strong enterocyte dysfunction reflected in an almost 20-fold reduction in the functional small bowel length was extrapolated from strongly reduced ornithine and citrulline concentrations and was very likely secondary to severe endothelial cell dysfunction with hypoperfusion and extensive vascular leakage. Highly increased histamine and lactate concentrations accompanied the peak in clinical symptoms. Elevated asymmetric and symmetric dimethylarginine levels combined with reduced arginine levels compromised endothelial nitric oxide synthase activity and nitric oxide signaling. Specific and extensive depletion of many lysophosphatidylcholine variants indicates localized autotaxin activation and lysophosphatidic acid release. A strong correlation of clinical parameters with histamine concentrations and symptom reduction after 100-fold elevated plasma diamine oxidase concentrations implies that histamine is the key driver of the acute phase.

CONCLUSIONS

Rapid elimination of elevated histamine concentrations through use of recombinant human diamine oxidase, supplementation of lysophosphatidylcholine for immunomodulation, inhibition of autotaxin activity, and/or blockade of lysophosphatidic acid receptors might represent new treatment options for life-threatening mast cell activation events.

Accuracy of a Modified Lactate Minimum Test and Reverse Lactate Threshold Test to Determine Maximal Lactate Steady State

Wahl, P, Manunzio, C, Vogt, F, Strütt, S, Volmary, P, Bloch, W, and Mester, J. Accuracy of a modified lactate minimum test and reverse lactate threshold test to determine maximal lactate steady state. J Strength Cond Res 31(12): 3489-3496, 2017-This study evaluated the accuracy of a modified lactate minimum test (mLMT), a modified reverse lactate threshold test (mRLT), compared with 2 established threshold concepts (onset of blood lactate accumulation [OBLA] and modified maximal deviation method [mDmax]) to determine power output at maximal lactate steady state (MLSS) in cycling. Nineteen subjects performed an mLMT, mRLT, graded exercise test (100 W start, +20 W every 3 minutes) and 3 or more constant-load tests of 30 minutes to determine power output at MLSS. The mLMT and mRLT both consisted of an initial lactate priming segment, followed by a short recovery phase. Afterward, the initial load of the subsequent incremental or reverse segment was calculated individually and was increased or decreased by 10 W every 90 seconds, respectively. The mean difference to MLSS was +2 ± 7 W (mLMT), +5 ± 10 W (mRLT), +9 ± 21 W (OBLA), and +6 ± 14 W (mDmax). The correlation between power output at MLSS and mLMT was highest (r = 0.99), followed by mRLT (r = 0.98), mDmax (r = 0.95), and OBLA (r = 0.90). Because of the higher accuracy of the mLMT and the mRLT to determine MLSS compared with OBLA and mDmax, we suggest both tests as valid and meaningful concepts to estimate power output at MLSS in one single test in moderately trained to well-trained athletes. Additionally, our modified tests provide anaerobic data and do not require detailed knowledge of the subjects' training status compared with previous LMT or RLT protocols.

The Lactate Minimum Test: Concept, Methodological Aspects and Insights for Future Investigations in Human and Animal Models

In 1993, Uwe Tegtbur proposed a useful physiological protocol named the lactate minimum test (LMT). This test consists of three distinct phases. Firstly, subjects must perform high intensity efforts to induce hyperlactatemia (phase 1). Subsequently, 8 min of recovery are allowed for transposition of lactate from myocytes (for instance) to the bloodstream (phase 2). Right after the recovery, subjects are submitted to an incremental test until exhaustion (phase 3). The blood lactate concentration is expected to fall during the first stages of the incremental test and as the intensity increases in subsequent stages, to rise again forming a “U” shaped blood lactate kinetic. The minimum point of this curve, named the lactate minimum intensity (LMI), provides an estimation of the intensity that represents the balance between the appearance and clearance of arterial blood lactate, known as the maximal lactate steady state intensity (iMLSS). Furthermore, in addition to the iMLSS estimation, studies have also determined anaerobic parameters (e.g., peak, mean, and minimum force/power) during phase 1 and also the maximum oxygen consumption in phase 3; therefore, the LMT is considered a robust physiological protocol. Although, encouraging reports have been published in both human and animal models, there are still some controversies regarding three main factors: (1) the influence of methodological aspects on the LMT parameters; (2) LMT effectiveness for monitoring training effects; and (3) the LMI as a valid iMLSS estimator. Therefore, the aim of this review is to provide a balanced discussion between scientific evidence of the aforementioned issues, and insights for future investigations are suggested. In summary, further analyses is necessary to determine whether these factors are worthy, since the LMT is relevant in several contexts of health sciences.

Methods of exercise intensity and lactataemia determination of lactate minimum test in rats

The lactate minimum test (LMT) is a useful protocol for determining the intensity corresponding to the maximal lactate steady state. Nevertheless, different methods to determine LMT variables are found in the literature. The aim of this study was to analyse three different methods for determining the effort intensity (LMTi) and lactataemia (LMTLAC) corresponding to LMT. We subjected seventeen rats to LMT in a swimming ergometer, following three steps: (1) acidosis induction phase; (2) recovery of nine minutes; and (3) incremental swimming intensity phase. We determined the LMTi and LMTLAC using three methods: visual inspection (VI - non-mathematic), second order polynomial function (fPOLY - mathematic) and spline function (fSPL - mathematic). Results showed no significant differences between the LMTi or LMTLAC values determined using VI (5.32+0.50% bw and 5.62+0.78 mM, respectively), fPOLY (5.31+0.53% bw and 5.64+0.72 mM, respectively) and fSPL (5.32+0.54% bw and 5.59+0.76 mM, respectively). We found significant correlations between the three methods (P<0.05). We concluded that the determination of the intensity and lactataemia corresponding to LMT are not influenced by mathematic or non-mathematic methods in swimming sedentary rats.

Reverse lactate threshold: a novel single-session approach to reliable high-resolution estimation of the anaerobic threshold

The multisession maximal lactate steady-state (MLSS) test is the gold standard for anaerobic threshold (AnT) estimation. However, it is highly impractical, requires high fitness level, and suffers additional shortcomings. Existing single-session AnT-estimating tests are of compromised validity, reliability, and resolution. The presented reverse lactate threshold test (RLT) is a single-session, AnT-estimating test, aimed at avoiding the pitfalls of existing tests. It is based on the novel concept of identifying blood lactate's maximal appearance-disappearance equilibrium by approaching the AnT from higher, rather than from lower exercise intensities. Rowing, cycling, and running case data (4 recreational and competitive athletes, male and female, aged 17-39 y) are presented. Subjects performed the RLT test and, on a separate session, a single 30-min MLSS-type verification test at the RLT-determined intensity. The RLT and its MLSS verification exhibited exceptional agreement at 0.5% discrepancy or better. The RLT's training sensitivity was demonstrated by a case of 2.5-mo training regimen following which the RLT's 15-W improvement was fully MLSS-verified. The RLT's test-retest reliability was examined in 10 trained and untrained subjects. Test 2 differed from test 1 by only 0.3% with an intraclass correlation of 0.997. The data suggest RLT to accurately and reliably estimate AnT (as represented by MLSS verification) with high resolution and in distinctly different sports and to be sensitive to training adaptations. Compared with MLSS, the single-session RLT is highly practical and its lower fitness requirements make it applicable to athletes and untrained individuals alike. Further research is needed to establish RLT's validity and accuracy in larger samples.

Influence of recovery manipulation after hyperlactemia induction on the lactate minimum intensity

This study analyzed the influence of recovery phase manipulation after hyperlactemia induction on the lactate minimum intensity during treadmill running. Twelve male runners (24.6 +/- 6.3 years; 172 +/- 8.0 cm and 62.6 +/- 6.1 kg) performed three lactate minimum tests involving passive (LMT(P)) and active recoveries at 30%vVO(2max) (LMT(A30)) and 50%vVO(2max) (LMT(A50)) in the 8-min period following initial sprints. During subsequent graded exercise, lactate minimum speed and VO(2) in LMT(A50) (12.8 +/- 1.5 km h(-1) and 40.3 +/- 5.1 ml kg(-1) min(-1)) were significantly lower (P < 0.05) than those in LMT(A30) (13.3 +/- 1.6 km h(-1) and 42.9 +/- 5.3 ml kg(-1) min(-1)) and LMT(P) (13.8 +/- 1.6 km h(-1) and 43.6 +/- 6.1 ml kg(-1) min(-1)). In addition, lactate minimum speed in LMT(A30) was significantly lower (P < 0.05) than that in LMT(P). These results suggest that lactate minimum intensity is lowered by active recovery after hyperlactemia induction in an intensity-dependent manner compared to passive recovery.

Influência da forma de indução à acidose na determinação da intensidade de lactato mínimo em corredores de longa distância

O objetivo principal deste estudo foi verificar se diferentes formas de indução à acidose interferem na determinação da intensidade do lactato mínimo (LACmin) em corredores de longa distância. Desse modo, 14 corredores de provas fundas do atletismo participaram do estudo. Os atletas realizaram três protocolos: 1) teste incremental em esteira rolante, com incrementos de 1km.h-1 a cada três minutos até a exaustão, para a determinação das intensidades de limiar anaeróbio (OBLA), de limiar aeróbio (Laer), consumo máximo de oxigênio (VO2max) e intensidade de consumo máximo de oxigênio (vVO2max); 2) teste de lactato mínimo em pista de atletismo (LACminp), que consistiu de dois esforços máximos de 233m na pista de atletismo com intervalo de um minuto entre cada repetição, com oito minutos de recuperação passiva, seguido de um teste incremental semelhante ao do protocolo 1; e 3) teste de lactato mínimo em esteira rolante (LACmine), constituído de dois esforços máximos de um minuto e 45 segundos com intervalo de um minuto, na intensidade de 120% da vVO2max, seguido dos mesmos procedimentos do protocolo 2. Foram coletadas amostras de sangue do lóbulo da orelha ao final de cada estágio em todos os protocolos e no 7º minuto de recuperação passiva dos testes de LACmine e LACminp. A análise de variância (ANOVA) mostrou que ocorreram diferenças significativas entre as intensidades de LACmine (13,23 ± 1,78km.h-1) e OBLA (14,67 ± 1,44km.h-1). Dessa maneira, a partir dos resultados obtidos no presente estudo, é possível concluir que a determinação da intensidade correspondente ao lactato mínimo é dependente do protocolo utilizado para a indução à acidose. Além disso, o LACmine subestimou a intensidade correspondente ao OBLA, não podendo ser utilizado para a mensuração da capacidade aeróbia de corredores fundistas.

Role for mitochondrial oxidants as regulators of cellular metabolism

Leakage of mitochondrial oxidants contributes to a variety of harmful conditions ranging from neurodegenerative diseases to cellular senescence. We describe here, however, a physiological and heretofore unrecognized role for mitochondrial oxidant release. Mitochondrial metabolism of pyruvate is demonstrated to activate the c-Jun N-terminal kinase (JNK). This metabolite-induced rise in cytosolic JNK1 activity is shown to be triggered by increased release of mitochondrial H(2)O(2). We further demonstrate that in turn, the redox-dependent activation of JNK1 feeds back and inhibits the activity of the metabolic enzymes glycogen synthase kinase 3beta and glycogen synthase. As such, these results demonstrate a novel metabolic regulatory pathway activated by mitochondrial oxidants. In addition, they suggest that although chronic oxidant production may have deleterious effects, mitochondrial oxidants can also function acutely as signaling molecules to provide communication between the mitochondria and the cytosol.