Lactate Gradient Research Articles

P-265 A low-lactate undisturbed culture medium protocol provides an increase in usable blastocysts on day 5 vs. day 6

Abstract Study question Does a culture medium with more physiological concentrations of lactate provide more usable blastocysts on day 5 vs day 6 compared to higher lactate medium. Summary answer 1mm lactate medium supports a noticeable trend for more usable blastocysts on day 5 compared to day 6. What is known already Previous studies have shown that blastocyst utilization and normal embryo ploidy are more significant when a low lactate (1mM) culture medium is utilized in the laboratory compared to higher lactate (5-10mM) concentrations. It is presumed that a lactate gradient (from high to low) provides a more optimal embryo growth environment; However, it can be debated that lower lactate concentrations are more physiological and less disruptive to embryo metabolism, particularly at the blastocyst stage. Study design, size, duration From January through March 2020, a split sibling oocyte study was performed on 50 patient cycles, each with a minimum of 9 oocytes retrieved. Oocytes were divided between low-lactate Continuous Single Culture Medium-NX and the laboratory’s current culture system of higher lactate Continuous Single Culture Medium following aspiration, thus resulting in 276 oocytes and 257 oocytes, respectively. The resulting zygotes were subsequently cultured from fertilization events to the blastocyst stage in their corresponding medium. Participants/materials, setting, methods The study was undertaken in a private IVF laboratory. No consideration was given to the patient age, stimulation protocol, or diagnosis indication. Comparative parameters for analysis included fertilization success and usable blastocysts through day 6 culture. Usable blastocysts were defined as any blastocyst transferred in a fresh cycle, or vitrified for future use. The denominator for such determination was the total normal 2PNs at fertilization check. Main results and the role of chance Our data demonstrates the potential advantages of culturing embryos in an undisturbed culture medium with a 1mM lactate concentration as opposed to a more traditional, higher lactate concentration. The overall blastocyst utilization rate (BUR) on day 5 was 27% in low lactate vs. 20% in high lactate and 12% vs 15% for day 6, thus resulting in more usable blastocysts on day 5, as well as overall, in low lactate culture. When stratified by patient age, embryos cultured in low lactate showed an increase in BUR on day 5 across all age groups. In patients 35-37 years old, a 13% increase in usable blastocysts on day 5 was observed, followed by patients 41-42 which had a 12% BUR increase in low lactate versus higher lactate. 38-40 year olds had a 7% increase in low lactate and <35 increased by 3% on day 5. Interestingly, our data also shows a significant increase in normal fertilization outcomes, both by ICSI and overall with conventional insemination, in low lactate vs higher lactate (79% vs 71% respectively at p < 0.05). Limitations, reasons for caution Need for increased n to determine significance along with further studies to understand the metabolic pathways which lead to earlier blastocyst development on day 5 vs. day 6. Additionally, there needs to be more investigative studies into the role a lower lactate concentration plays in normal fertilization outcome improvement. Wider implications of the findings A low lactate culture medium supports an increase in the availability of usable blastocysts on day 5. This finding can improve laboratory workflow efficiency through patient scheduling for fresh day 5 embryo transfers as well as allocate resources to accommodate more embryo vitrification on the 5th day of embryo culture. Trial registration number NA

P-267 A continuous culture medium with a lower concentration of lactate has a pronounced effect on the percentage of usable blastocysts on day 5

Abstract Study question Does Continuous Single Culture Medium NX, an embryo culture medium containing 1mM lactate, support increased blastocyst development over high lactate Vitrolife G1/G2 Series sequential culture? Summary answer There is a statistically significant increase in day 5 usable blastocysts in low lactate culture medium compared to the one with high lactate medium. What is known already Studies have shown that day 5 is the most desirable day to obtain blastocysts that are of an expansion, grade and quality to be utilized for transfer and/or vitrification procedures as those result in the highest success of clinical pregnancy,as compared to day 6/ 7 blastocysts, that do not meet criteria. Moreover, recent studies have indicated that there is an increase in chromosomal correctness of embryos cultured in a 1mM lactate environment as opposed to the higher 6-10mM lactate concentrations that have historically been believed necessary for successful blastocyst culture and resulting pregnancy. Study design, size, duration A prospective split sibling oocytes study was performed on 50 ICSI and IMSI cycles from October 2020 through April 2021. Oocytes were divided into the low lactate medium and high lactate gradient medium immediately following ICSI/IMSI and thereafter cultured in those medium until the final day of blastocyst culture. All patient ages were included in the sample population. Participants/materials, setting, methods This study was carried out in a private clinic. All patient stimulation protocol information and diagnosis’ were recorded; however, there was no restriction on participation. The endpoint was to analyse the resulting usable blastocyst rates on day 5 and day 6 in both arms of the study, using a denominator of normal 2PN fertilization. If a blastocyst was transferred or cryopreserved on day 5 or day 6, it was determined to be usable. Main results and the role of chance The resulting data was stratified not only by day 5 and day 6 usable blastocyst rates but also by patient age. It illustrates a statistically significant improvement in day 5 usable blastocysts for patients <35 in CSCM-NXC vs G1/G2 at 56% and 42%, respectively, a 14% increase (p < .05). The overall day 5 usable blastocyst rate was also statistically significant in CSCM-NXC (47%) as compared to G1/G2 (36%), (p < .05) with all ages considered. Additionally, on day 5, there was a higher percentage of usable blastocysts demonstrated in low lactate vs high in patients aged 35-37 (65% vs 42%, respectively) and 41-42 (41% vs 15%). Statistical significance was reversed in patients <35 on day 6, with G1/G2 having 24% usable blasts and CSCM-NXC 10% (p < .05). Interestingly, though not significant, G1/G2 had an increase in usable blastocyst percentage on day 5 in patients >42 (20% vs 11%), but overall, CSCM-NXC saw an increase in that same age group by 16%. Limitations, reasons for caution Though statistical significance was found in this study, a greater number will help to bolster the statistical power of the observations. Additionally, more studies are needed in order to ascertain if low lactate has an effect on the development prior to ICSI and resulting culture. Wider implications of the findings The mechanism of action that leads to the successful embryo development in low lactate embryo culture medium is vastly unknown, so further studies are required in order to understand the complexities and the impact of the observations provided. Trial registration number not applicable.

Patient-specific apparent diffusion maps used to model nutrient availability in degenerated intervertebral discs.

IntroductionIn this study, magnetic resonance imaging data was used to (1) model IVD‐specific gradients of glucose, oxygen, lactate, and pH; and (2) investigate possible effects of covariate factors (i.e., disc geometry, and mean apparent diffusion coefficient values) on the IVD’s microenvironment. Mathematical modeling of the patient’s specific IVD microenvironment could be important when selecting patients for stem cell therapy due to the increased nutrient demand created by that treatment.Materials and MethodsDisc geometry and water diffusion coefficients were extracted from MRIs of 37 patients using sagittal T1‐weighted images, T2‐weighted images, and ADC Maps. A 2‐D steady state finite element mathematical model was developed in COMSOL Multiphysics® 5.4 to compute concentration maps of glucose, oxygen, lactate and pH.ResultsConcentration of nutrients (i.e., glucose, and oxygen) dropped with increasing distance from the cartilaginous endplates (CEP), whereas acidity levels increased. Most discs experienced poor nutrient levels along with high acidity values in the inner annulus fibrosus (AF). The disc’s physiological microenvironment became more deficient as degeneration progressed. For example, minimum glucose concentration in grade 4 dropped by 31.1% compared to grade 3 (p < 0.0001). The model further suggested a strong effect of the following parameters: disc size, AF and CEP diffusivities, metabolic reactions, and cell density on solute concentrations in the disc (p < 0.05).ConclusionThe significance of this work implies that the individual morphology and physiological conditions of each disc, even among discs of the same Pfirrmann grade, should be evaluated when modeling IVD solute concentrations.

Monitoring of the Progression of the Perioperative Serum Lactate Concentration Improves the Accuracy of the Prediction of Acute Mesenteric Ischemia Development After Cardiovascular Surgery

To examine the sensitivity and specificity of perioperative lactate gradients for the prediction of subsequent acute mesenteric ischemia development in patients undergoing cardiovascular surgery. Retrospective, single-center, case-control study. University hospital. The study comprised 108 (1.15%) patients with acute mesenteric ischemia who were selected from 9,385 patients who underwent cardiovascular surgery and were matched to 324 control patients by age and surgery type. None. Univariate and logistic regression analyses were used to examine intraoperative and early postoperative lactate levels in patients with and without mesenteric ischemia after cardiac surgery. Late intraoperative lactate concentrations were significantly greater in patients who subsequently developed mesenteric ischemia (p < 0.001). Patients with lactate levels >3 mmol/L had a four-fold increased risk of mesenteric ischemia development (odds ratio [OR] 4.2, 95% confidence interval [CI] 2.4-7.5; area under the curve [AUC] 0.597; p < 0.002). Patients whose lactate levels remained >3 mmol/L on the first postoperative day had a nearly eight-fold increased risk (OR 7.8, 95% CI 4.6-13.3; AUC 0.68; p < 0.001), indicating that mesenteric ischemia developed at an early stage in almost every second patient (p < 0.001). For patients with normal or less elevated lactate levels, similar results were obtained for a >200% increase between the intraoperative and early postoperative periods (OR 4.1, 95% CI 2.4-6.8; AUC 0.62; p < 0.001). Late intraoperative and early postoperative lactate levels >3 mmol/L and increases >200%, even when remaining within the normal range, should raise the suspicion of subsequent mesenteric ischemia development.

Negative central venous to arterial lactate gradient in patients receiving vasopressors is associated with higher ICU 30-day mortality: a retrospective cohort study

BackgroundSerum lactate has long been used to evaluate hypoxia and predict prognosis in critically ill patients, however, discrepancy in lactate measurements between different sites have not been recognized as a useful tool for monitoring hypoxia and evaluating outcome.MethodsData were obtained from the clinical information system of the intensive care unit (ICU) in a tertiary academic hospital for 1582 ICU patients with vasoactive drug requirement and valid paired blood gas. The mortality rates were compared between patients with sustained negative venous to arterial lactate gradient (VALac) and the others using the Cox proportional hazard model. Predictive factors associated with negative VALac were searched.ResultsA sustained negative VALac was significantly associated with higher 30 day ICU mortality [Adjusted hazard ratio (HR) = 2.31, 95% confidence interval (CI), 1.07–4.99; p = 0.032. Propensity score- weighted HR: 2.57; 95% CI, 1.17–5.64; p = 0.010]. Arterial lactate in the first blood gas pair, 24-h arterial lactate clearance, use of epinephrine, mean positive end-expiratory pressure level, and extracorporeal membrane oxygenation initiation showed statistically significant association with sustained negative VALac during the first 24 h.ConclusionThe sustained negative VALac in the early stage of treatment may suggest additional information about tissue hypoxia than arterial lactate alone. Critical care physicians should pay more attention to the lactate discrepancy between different sites in their clinical practice.

The effect of blood-flow-restricted interval training on lactate and H+ dynamics during dynamic exercise in man.

To assess how blood-flow-restricted (BFR) interval-training affects the capacity of the leg muscles for pH regulation during dynamic exercise in physically trained men. Ten men (age: 25±4y; : 50±5mL∙kg-1 ∙min-1 ) completed a 6-wk interval-cycling intervention (INT) with one leg under BFR (BFR-leg; ~180mmHg) and the other without BFR (CON-leg). Before and after INT, thigh net H+ -release (lactate-dependent, lactate-independent and sum) and blood acid/base variables were measured during knee-extensor exercise at 25% (Ex25) and 90% (Ex90) of incremental peak power output. A muscle biopsy was collected before and after Ex90 to determine pH, lactate and density of H+ -transport/buffering systems. After INT, net H+ release (BFR-leg: 15±2; CON-leg: 13±3; mmol·min-1 ; Mean±95% CI), net lactate-independent H+ release (BFR-leg: 8±1; CON-leg: 4±1; mmol·min-1 ) and net lactate-dependent H+ release (BFR-leg: 9±3; CON-leg: 10±3; mmol·min-1 ) were similar between legs during Ex90 (P>.05), despite a ~142% lower muscle intracellular-to-interstitial lactate gradient in BFR-leg (-3±4 vs 6±6mmol·L-1 ; P<.05). In recovery from Ex90, net lactate-dependent H+ efflux decreased in BFR-leg with INT (P<.05 vs CON-leg) owing to lowered muscle lactate production (~58% vs CON-leg, P<.05). Net H+ gradient was not different between legs (~19%, P>.05; BFR-leg: 48±30; CON-leg: 44±23; mmol·L-1 ). In BFR-leg, NHE1 density was higher than in CON-leg (~45%; P<.05) and correlated with total-net H+ -release (r=0.71; P=.031) and lactate-independent H+ release (r=0.74; P=.023) after INT, where arterial [ ] and standard base excess in Ex25 were higher in BFR-leg than CON-leg. Compared to a training control, BFR-interval training increases the capacity for pH regulation during dynamic exercise mainly via enhancement of muscle lactate-dependent H+ -transport function and blood H+ -buffering capacity.

Lactate Attenuates Synaptic Transmission and Affects Brain Rhythms Featuring High Energy Expenditure.

SummaryLactate shuttled from blood, astrocytes, and/or oligodendrocytes may serve as the major glucose alternative in brain energy metabolism. However, its effectiveness in fueling neuronal information processing underlying complex cortex functions like perception and memory is unclear. We show that sole lactate disturbs electrical gamma and theta-gamma oscillations in hippocampal networks by either attenuation or neural bursts. Bursting is suppressed by elevating the glucose fraction in substrate supply. By contrast, lactate does not affect electrical sharp wave-ripple activity featuring lower energy use. Lactate increases the oxygen consumption during the network states, reflecting enhanced oxidative ATP synthesis in mitochondria. Finally, lactate attenuates synaptic transmission in excitatory pyramidal cells and fast-spiking, inhibitory interneurons by reduced neurotransmitter release from presynaptic terminals, whereas action potential generation in the axon is regular. In conclusion, sole lactate is less effective and potentially harmful during gamma-band rhythms by omitting obligatory ATP delivery through fast glycolysis at the synapse.

The use of atomized purified condensed smoke (PCS) in cold-smoke processing of Atlantic salmon - Effects on quality and microbiological stability of a lightly salted product

A novel technology for smoking of muscle foods is atomization of purified condensed smoke (PCS). The use of PCS is supported by the European Union and is considered healthier than traditional smoke-processing and is nowadays widely used in meat processing. However, scant information regarding the potential of PCS-processing of seafood is available. The aim of the present study was to study PCS-processing of lightly salted salmon added a gradient of potassium lactate (KL), and its effect on product quality. As a reference, traditionally cold smoked salmon (CSS) smoked with beech chips was used. The study stated that PCS-processing inhibit bacterial growth (aerobic plate count, and lactic acid bacteria) and thereby has potential to enhance the shelf life of CSS. Combination of barriers such as decreased water activity (aw) and pH were of highly importance, whereas the effect of phenolic compounds and added KL were minor. PCS-processed salmon was moreover firmer, darker, and slightly less reddish and yellowish compared to those smoked traditionally. Fillet appearance and firmness were both found related to muscle aw, showing the importance of optimizing the ratio between drying and atomization to obtain a PCS processed high-quality CSS.

The circadian clock regulates RPE-mediated lactate transport via SLC16A1 (MCT1)

Multiple retinal cells harbor a circadian oscillator, including retinal pigment epithelial cells (RPE). However, little is known about the functions that are regulated by the RPE clock. The aim of this study was to investigate whether the circadian clock in the RPE regulates the transport of glucose and its glycolytic metabolic by-product - lactate. To that end, we first characterized the mRNA expression profile of glucose and monocarboxylate transporters in ARPE-19 cells. We found that SLC2A1 and SLC16A1 were, respectively, the most abundantly expressed glucose and lactate (monocarboxylate) transporters. We further observed that the protein products of SLC2A1 (encoding GLUT1) and SLC16A1 (encoding MCT1) localize on the apical membrane of ARPE-19 monolayers. In a subsequent time-course experiment, we found that SLC2A1 and SLC16A1 mRNA oscillated in ARPE-19 monolayers, but not in dispersed cells, suggesting that monolayer cellular organization is necessary for rhythmic regulation of these transporters. In these monolayers, we found that MCT1 proteins varied over time, in contrast to GLUT1 proteins which did not vary over time. Spectrophotometric measurements of supernatants sampled from ARPE-19 monolayer cultures revealed that glucose concentrations did not significantly differ between apical (Api) supernatants and basolateral (BL) ones. In addition, we did not find rhythms in Api or BL glucose concentrations. Conversely, we found higher lactate concentrations in Api supernatants than BL ones. Further, we found that Api lactate concentrations were rhythmic. Pearson's r revealed that the concentration gradients (Api - BL) of glucose and lactate correlated with the gene expression of respective SLC2A1 and SLC16A1 transporters. Incubation with photoreceptor outer segments (POS) affected the mRNA expression of SLC16A1 and SLC2A1 in ARPE-19 monolayers in a time-dependent manner, thus suggesting that the retina might modulate the RPE clock-controlled expression of transporters via interactions with POS. In conclusion, this work provides evidence that the transport of lactate is regulated by the circadian clock in the RPE.

Biomarker Guided Diagnosis of Septic Peritonitis in Dogs

Septic peritonitis (SP) is common in dogs and is associated with high mortality. Early recognition is essential to maximizing survival and may be aided by biomarker measurement. The present study aimed to evaluate the ability of biomarkers to discriminate septic peritonitis from non-septic ascites (NSA). Eighteen dogs with SP and 19 age-matched controls with NSA were enrolled. Contemporaneous blood and peritoneal effusion samples were obtained. Concentrations of cell-free DNA (cfDNA), cytokines, glucose, lactate, N-terminal pro-C-type natriuretic peptide (NT-proCNP), nucleosomes, and procalcitonin (PCT) were measured using commercial reagents and assays. Paired biomarker concentrations were compared with the Wilcoxon matched-pairs signed rank test, and biomarker concentrations between groups were compared with the Mann-Whitney U-test. P-values were adjusted for multiple comparisons using the Bonferroni correction. Receiver operating characteristic curves were generated to assess the ability of the above biomarkers to discriminate SP from NSA. Dogs with SP had significantly greater blood CCL2 concentrations than dogs with NSA (P = 0.032). Dogs with SP had significantly greater effusion CCL2, IL-6, IL-10, and lactate concentrations than dogs with NSA (P ≤ 0.0121). Blood-effusion concentration gradients of CCL2, glucose, IL-6, IL-10, and lactate were significantly different in dogs with SP compared to dogs with NSA (P ≤ 0.0165). Effusion lactate concentration had the highest AUROC value (0.866, 95% CI 0.751–0.980, P = 0.0001), although other biomarkers performed similarly. An effusion lactate concentration of 4.2 mmol/L was 72.2% (95% CI 46.5–90.3%) sensitive and 84.2% (95% CI 60.4–96.6%) specific for the diagnosis of SP.

Elevated arterial lactate delays recovery of intracellular muscle pH after exercise.

We evaluated muscle proton elimination following similar exercise in the same muscle group following two exercise modalities. Seven rowers performed handgrip or rowing exercise for ~ 5min. The intracellular response of the wrist flexor muscles was evaluated by 31P nuclear magnetic resonance spectroscopy, while arterial and venous forearm blood was collected. Rowing and handgrip reduced intracellular pH to 6.3 ± 0.2 and 6.5 ± 0.1, arterial pH to 7.09 ± 0.03 and 7.40 ± 0.03 and venous pH to 6.95 ± 0.06 and 7.20 ± 0.04 (P < 0.05), respectively. Arterial and venous lactate increased to 17.5 ± 1.6 and 20.0 ± 1.6mM after rowing while only to 2.6 ± 0.8 and 6.8 ± 0.8mM after handgrip exercise. Arterio-venous concentration difference of bicarbonate and phosphocreatine recovery kinetics (T50% rowing 1.5 ± 0.7min; handgrip 1.4 ± 1.0min) was similar following the two exercise modalities. Yet, intramuscular pH recovery in the forearm flexor muscles was 3.5-fold slower after rowing than after handgrip exercise (T50% rowing of 2 ± 0.1 vs. 7 ± 0.3min for handgrip). Rowing delays intracellular-pH recovery compared with handgrip exercise most likely because rowing, as opposed to handgrip exercise, increases systemic lactate concentration. Thus the intra-to-extra-cellular lactate gradient is small after rowing. Since this lactate gradient is the main driving force for intracellular lactate removal in muscle and, since pHi normalization is closely related to intracellular lactate removal, rowing results in a slower pHi recovery compared to handgrip exercise.

Vasopressin and nitroglycerin decrease portal and hepatic venous pressure and hepato-splanchnic blood flow.

Various methods are used to reduce venous blood pressure in the hepato-splanchnic circulation, and hence minimise blood loss during liver surgery. Previous studies show that combination of vasopressin and nitroglycerin reduces portal pressure and flow in patients with portal hypertension, and in this study we investigated this combination in patients with normal portal pressure. In all, 13 patients were studied. Measurements were made twice to confirm baseline (C1 and BL), during vasopressin infusion 4.8 U/h (V), and during vasopressin infusion combined with nitroglycerin infusion (V + N). Portal venous pressure (PVP), hepatic venous pressure (HVP), central haemodynamics and arterial and venous blood gases were obtained at each measuring point, and portal (splanchnic) and hepato-splanchnic blood flow changes were calculated. Vasopressin alone did not affect PVP, whereas HVP increased slightly. In combination with nitroglycerin, PVP decreased from 10.1 ± 1.6 to 8.9 ± 1.3 mmHg (P < 0.0001), and HVP decreased from 7.9 ± 1.9 to 6.2 ± 1.3 mmHg (P = 0.001). Vasopressin reduced portal blood flow by 47 ± 19% and hepatic venous flow by 11 ± 18%, respectively. Addition of nitroglycerin further reduced portal- and hepatic flow by 55 ± 13% and 30 ± 13%, respectively. Vasopressin alone had minor effects on central haemodynamics, whereas addition of nitroglycerin reduced cardiac index (3.2 ± 0.7 to 2.7 ± 0.5; P < 0.0001). The arterial-portal vein lactate gradient was unaffected. The combination of vasopressin and nitroglycerin decreases portal pressure and hepato-splanchnic blood flow, and could be a potential treatment to reduce bleeding in liver resection surgery.

Brain metabolism in health, aging, andneurodegeneration.

Brain cells normally respond adaptively to bioenergetic challenges resulting from ongoing activity in neuronal circuits, and from environmental energetic stressors such as food deprivation and physical exertion. At the cellular level, such adaptive responses include the "strengthening" of existing synapses, the formation of new synapses, and the production of new neurons from stem cells. At the molecular level, bioenergetic challenges result in the activation of transcription factors that induce the expression of proteins that bolster the resistance of neurons to the kinds of metabolic, oxidative, excitotoxic, and proteotoxic stresses involved in the pathogenesis of brain disorders including stroke, and Alzheimer's and Parkinson's diseases. Emerging findings suggest that lifestyles that include intermittent bioenergetic challenges, most notably exercise and dietary energy restriction, can increase the likelihood that the brain will function optimally and in the absence of disease throughout life. Here, we provide an overview of cellular and molecular mechanisms that regulate brain energy metabolism, how such mechanisms are altered during aging and in neurodegenerative disorders, and the potential applications to brain health and disease of interventions that engage pathways involved in neuronal adaptations to metabolic stress.

Simulating Heterogeneous Tumor Cell Populations.

Certain tumor phenomena, like metabolic heterogeneity and local stable regions of chronic hypoxia, signify a tumor’s resistance to therapy. Although recent research has shed light on the intracellular mechanisms of cancer metabolic reprogramming, little is known about how tumors become metabolically heterogeneous or chronically hypoxic, namely the initial conditions and spatiotemporal dynamics that drive these cell population conditions. To study these aspects, we developed a minimal, spatially-resolved simulation framework for modeling tissue-scale mixed populations of cells based on diffusible particles the cells consume and release, the concentrations of which determine their behavior in arbitrarily complex ways, and on stochastic reproduction. We simulate cell populations that self-sort to facilitate metabolic symbiosis, that grow according to tumor-stroma signaling patterns, and that give rise to stable local regions of chronic hypoxia near blood vessels. We raise two novel questions in the context of these results: (1) How will two metabolically symbiotic cell subpopulations self-sort in the presence of glucose, oxygen, and lactate gradients? We observe a robust pattern of alternating striations. (2) What is the proper time scale to observe stable local regions of chronic hypoxia? We observe the stability is a function of the balance of three factors related to O2—diffusion rate, local vessel release rate, and viable and hypoxic tumor cell consumption rate. We anticipate our simulation framework will help researchers design better experiments and generate novel hypotheses to better understand dynamic, emergent whole-tumor behavior.

Development of TRACER: tissue roll for analysis of cellular environment and response

The tumour microenvironment is heterogeneous and consists of multiple cell types, variable extracellular matrix (ECM) composition, and contains cell-defined gradients of small molecules, oxygen, nutrients and waste. Emerging in vitro cell culture systems that attempt to replicate these features often fail to incorporate design strategies to facilitate efficient data collection and stratification. The tissue roll for analysis of cellular environment and response (TRACER) is a novel strategy to assemble layered, three-dimensional tumours with cell-defined, graded heterogeneous microenvironments that also facilitates cellular separation and stratification of data from different cell populations from specific microenvironments. Here we describe the materials selection and development of TRACER. We find that cellulose fibre scaffolding is an ideal support to generate tissue constructs having homogenous cell seeding and consistent properties. We explore ECM remodeling and long-term cell growth in the scaffold, and characterize the tumour microenvironment in assembled TRACERs using multiple established analysis methods. Finally, we confirm that TRACERs replicate small molecule gradients of glucose and lactate, and explore cell phenotype associated with these gradients using confocal microscopy, flow cytometry, and quantitative PCR analysis. We envision this technology will provide a platform to create complex, yet controlled tumour microenvironments that can be easily disassembled for snapshot analysis of cell phenotype and response to therapy in relation to microenvironment properties.

Lactate recovery kinetics in response to high-intensity exercises.

The aim of this study was to investigate lactate recovery kinetics after high-intensity exercises. Six competitive middle-distance runners performed 500-, 1000-, and 1500-m trials at 90% of their current maximal speed over 1500m. Each event was followed by a passive recovery to obtain blood lactate recovery curves (BLRC). BLRC were fitted by the bi-exponential time function: La(t)=La(0)+A 1(1-e (-γ1t) )+A 2(1-e (-γ2t) ), where La(0) is the blood lactate concentration at exercise completion, and γ 1 and γ 2 enlighten the lactate exchange ability between the previously active muscles and the blood and the overall lactate removal ability, respectively. Applications of the model provided parameters related to lactate release, removal and accumulation rates at exercise completion, and net amount of lactate released during recovery. The increase of running distance was accompanied by (1) a continuous decrease in γ 1 (p<0.05), (2) a primary decrease (p<0.05) and then a stabilization of γ 2, and (3) a constant increase in blood concentrations (p<0.05) and whole body accumulation of lactate (p<0.05). Estimated net lactate release, removal and accumulation rates at exercise completion, as well as the net amount of lactate released during recovery were not significantly altered by distance. Alterations of lactate exchange and removal abilities have presumably been compensated by an increase in muscle-to-blood lactate gradient and blood lactate concentrations, respectively, so that estimated lactate release, removal and accumulation rates remained almost stable as distance increased.

Vasopressin‐induced changes in splanchnic blood flow and hepatic and portal venous pressures in liver resection

To minimize blood loss during hepatic surgery, various methods are used to reduce pressure and flow within the hepato-splanchnic circulation. In this study, the effect of low- to moderate doses of vasopressin, a potent splanchnic vasoconstrictor, on changes in portal and hepatic venous pressures and splanchnic and hepato-splanchnic blood flows were assessed in elective liver resection surgery. Twelve patients were studied. Cardiac output (CO), stroke volume (SV), mean arterial (MAP), central venous (CVP), portal venous (PVP) and hepatic venous pressures (HVP) were measured, intraoperatively, at baseline and during vasopressin infusion at two infusion rates (2.4 and 4.8 U/h). From arterial and venous blood gases, the portal (splanchnic) and hepato-splanchnic blood flow changes were calculated, using Fick's equation. CO, SV, MAP and CVP increased slightly, but significantly, while systemic vascular resistance and heart rate remained unchanged at the highest infusion rate of vasopressin. PVP was not affected by vasopressin, while HVP increased slightly. Vasopressin infusion at 2.4 and 4.8 U/h reduced portal blood flow (-26% and -37%, respectively) and to a lesser extent hepato-splanchnic blood flow (-9% and -14%, respectively). The arterial-portal vein lactate gradient was not significantly affected by vasopressin. Postoperative serum creatinine was not affected by vasopressin. Short-term low to moderate infusion rates of vasopressin induced a splanchnic vasoconstriction without metabolic signs of splanchnic hypoperfusion or subsequent renal impairment. Vasopressin caused a centralization of blood volume and increased cardiac output. Vasopressin does not lower portal or hepatic venous pressures in this clinical setting.

Are Astrocytes the Pressure-Reservoirs of Lactate in the Brain?

The role of lactate in the brain has been controversial. In this issue, Mächler et al. (2015) present data from in vivo experiments suggesting that there is a downward gradient of lactate in the brain. They provide a mechanistic basis for the proposed export of lactate from astrocytes to neurons.

In Vivo Evidence for a Lactate Gradient from Astrocytes to Neurons

Investigating lactate dynamics in brain tissue is challenging, partly because in vivo data at cellular resolution are not available. We monitored lactate in cortical astrocytes and neurons of mice using the genetically encoded FRET sensor Laconic in combination with two-photon microscopy. An intravenous lactate injection rapidly increased the Laconic signal in both astrocytes and neurons, demonstrating high lactate permeability across tissue. The signal increase was significantly smaller in astrocytes, pointing to higher basal lactate levels in these cells, confirmed by a one-point calibration protocol. Trans-acceleration of the monocarboxylate transporter with pyruvate was able to reduce intracellular lactate in astrocytes but not in neurons. Collectively, these data provide in vivo evidence for a lactate gradient from astrocytes to neurons. This gradient is a prerequisite for a carrier-mediated lactate flux from astrocytes to neurons and thus supports the astrocyte-neuron lactate shuttle model, in which astrocyte-derived lactate acts as an energy substrate for neurons.

The 11th International Conference on Brain Energy Metabolism "how energy metabolism shapes brain function". Preface.

The 11th International Conference on Brain Energy Metabolism "how energy metabolism shapes brain function". Preface.