Impact of ageing on female metabolic flexibility: a cross-sectional pilot study in over-60 active women

Background Ageing influences the metabolic flexibility, albeit the physical status could determine this relationship. This cross-sectional study aims to describe and analyse the metabolic flexibility/inflexibility in a group of active older women, together with the impact of ageing and physical status on their oxidation rates and maximal fat oxidation (MFO). Methods Fifteen volunteers (69.00±6.97 years) from 24 women, completed an incremental cycling test until the second ventilatory threshold. Intensity increased 10W each 3min–15sec, starting at 30W. Gas exchange, heart rate, rate of perceived effort, pain scale and muscle power were registered, together with lactate. VO2 and VCO2 were considered for Fat and CHO oxidation (FATox & CHOox; Frayn’s equation) at the intensities 60%, 80% and 100% from the peak of power in the test (P100). Psychophysiological parameters were compared at MFO/FATmax and P100, together with the main correlation analyses, with and without P100 and VO2 as covariates. Results FATox was low at MFO (0.13; 95%CI [0.09-0.17] g·min−1·kg; 5.61 [3.59-7.63] g·min−1·kg FFM), with a shifting down and leftward of a short oxidation-rate curves. CHOox and FATox were both low for a reduced power with age (77.14±18.58 W & 39.29±9.17 W at P100 and MFO respectively), pointing to metabolic inflexibility in older women despite being active. Notwithstanding, the negative correlation between age and MFO (r=-0.54, p=0.04; R2=0.29) disappeared when normalized with P100 (r=-0.17, p=0.53), which was in turn strongly and negatively associated to age (r=-0.85, p<0.005; R2=0.72). P100 was also positive and moderately associated to MFO (r=0.71, p=0.01; R2=0.50). Conclusions Despite the inflexibility with age, physical status (i.e., larger muscular power) suggest a key role in the preservation of the metabolic health with aging in active women.

Feeding Tolerance, Glucose Availability, and Whole-Body Total Carbohydrate and Fat Oxidation in Male Endurance and Ultra-Endurance Runners in Response to Prolonged Exercise, Consuming a Habitual Mixed Macronutrient Diet and Carbohydrate Feeding During Exercise

Using metadata from previously published research, this investigation sought to explore: (1) whole-body total carbohydrate and fat oxidation rates of endurance (e.g., half and full marathon) and ultra-endurance runners during an incremental exercise test to volitional exhaustion and steady-state exercise while consuming a mixed macronutrient diet and consuming carbohydrate during steady-state running and (2) feeding tolerance and glucose availability while consuming different carbohydrate regimes during steady-state running. Competitively trained male endurance and ultra-endurance runners (n = 28) consuming a balanced macronutrient diet (57 ± 6% carbohydrate, 21 ± 16% protein, and 22 ± 9% fat) performed an incremental exercise test to exhaustion and one of three 3 h steady-state running protocols involving a carbohydrate feeding regime (76–90 g/h). Indirect calorimetry was used to determine maximum fat oxidation (MFO) in the incremental exercise and carbohydrate and fat oxidation rates during steady-state running. Gastrointestinal symptoms (GIS), breath hydrogen (H2), and blood glucose responses were measured throughout the steady-state running protocols. Despite high variability between participants, high rates of MFO [mean (range): 0.66 (0.22–1.89) g/min], Fatmax [63 (40–94) % V̇O2max], and Fatmin [94 (77–100) % V̇O2max] were observed in the majority of participants in response to the incremental exercise test to volitional exhaustion. Whole-body total fat oxidation rate was 0.8 ± 0.3 g/min at the end of steady-state exercise, with 43% of participants presenting rates of ≥1.0 g/min, despite the state of hyperglycemia above resting homeostatic range [mean (95%CI): 6.9 (6.7–7.2) mmol/L]. In response to the carbohydrate feeding interventions of 90 g/h 2:1 glucose–fructose formulation, 38% of participants showed breath H2 responses indicative of carbohydrate malabsorption. Greater gastrointestinal symptom severity and feeding intolerance was observed with higher carbohydrate intakes (90 vs. 76 g/h) during steady-state exercise and was greatest when high exercise intensity was performed (i.e., performance test). Endurance and ultra-endurance runners can attain relatively high rates of whole-body fat oxidation during exercise in a post-prandial state and with carbohydrate provisions during exercise, despite consuming a mixed macronutrient diet. Higher carbohydrate intake during exercise may lead to greater gastrointestinal symptom severity and feeding intolerance.

Tissue specific responses that constrain glucose oxidation and increase lactate production with the severity of hypoxemia in fetal sheep

Fetal hypoxemia decreases insulin and increases cortisol and norepinephrine concentrations and may restrict growth by decreasing glucose utilization and altering substrate oxidation. Specifically, we hypothesized that hypoxemia would decrease fetal glucose oxidation and increase lactate and pyruvate production. We tested this by measuring whole-body glucose oxidation and lactate production, and molecular pathways in liver, muscle, adipose, and pancreas tissues of fetuses exposed to maternal hypoxemia for 9 days (HOX) compared with control fetal sheep (CON) in late gestation. Fetuses with more severe hypoxemia had lower whole-body glucose oxidation rates, and HOX fetuses had increased lactate production from glucose. In muscle and adipose tissue, expression of the glucose transporter GLUT4 was decreased. In muscle, pyruvate kinase (PKM) and lactate dehydrogenase B (LDHB) expression was decreased. In adipose tissue, LDHA and lactate transporter (MCT1) expression was increased. In liver, there was decreased gene expression of PKLR and MPC2 and phosphorylation of PDH, and increased LDHA gene and protein abundance. LDH activity, however, was decreased only in HOX skeletal muscle. There were no differences in basal insulin signaling across tissues, nor differences in pancreatic tissue insulin content, beta cell area, or genes regulating beta cell function. Collectively, these results demonstrate coordinated metabolic responses across tissues in the hypoxemic fetus that limit glucose oxidation and increase lactate and pyruvate production. These responses may be mediated by hypoxemia induced endocrine responses including increased norepinephrine and cortisol, which inhibit pancreatic insulin secretion resulting in lower insulin concentrations and decreased stimulation of glucose utilization.

Effects of simulated high altitude on blood glucose levels during exercise in individuals with Type 1 Diabetes

Context Current exercise guidelines for individuals with type 1 diabetes (T1D) do not consider the impact that high altitude may have on blood glucose levels (BGL) during exercise. Objective To investigate the effect of acute hypoxia (simulated high altitude) on BGL and carbohydrate oxidation rates during moderate intensity exercise in individuals with T1D. Methods Using a counterbalanced, repeated measures study design, 7 individuals with T1D completed two exercise sessions; normoxia and hypoxia (~4,200m simulated altitude). Participants cycled for 60min on an ergometer at 45% of their sea-level V̇O2peak, and then recovered for 60min. Before, during and after exercise, blood samples were taken to measure glucose, lactate and insulin levels. Respiratory gases were collected to measure carbohydrate oxidation rates. Results Early during exercise (&lt;30min), there was no fall in BGL in either condition. After one hour of exercise and during recovery, BGL were significantly lower under the hypoxic condition compared to both pre-exercise levels (p=0.008) and the normoxic condition (p=0.027). Exercise in both conditions resulted in a significant rise in carbohydrate oxidation rates, which returned to baseline levels post-exercise. Before, during and after exercise, carbohydrate oxidation rates were higher under the hypoxic compared with the normoxic condition (p&lt;0.001). Conclusions The greater decline in BGL during and after exercise performed under acute hypoxia suggests that exercise during acute exposure to high altitude may increase the risk of hypoglycemia in individuals with T1D. Future guidelines may have to consider the impact altitude has on exercise-mediated hypoglycemia.

Protein folding stabilities are a major determinant of oxidation rates for buried methionine residues

The oxidation of protein-bound methionines to form methionine sulfoxides has a broad range of biological ramifications, making it important to delineate factors that influence methionine oxidation rates within a protein. This is especially important for biopharmaceuticals, where oxidation can lead to deactivation and degradation. Previously, neighboring residue effects and solvent accessibility (SA) have been shown to impact the susceptibility of methionine residues to oxidation. In this study, we provide proteome-wide evidence that oxidation rates of buried methionine residues are also strongly influenced by the thermodynamic folding stability of proteins. We surveyed the E. coli proteome using several proteomic methodologies and globally measured oxidation rates of methionines in the presence and absence of tertiary structure, as well as folding stabilities of methionine containing domains. The data indicate that buried methionines have a wide range of protection factors against oxidation which correlate strongly with folding stabilities. Concordantly, we show that in comparison to E. coli, the proteome of the thermophile T. thermophilus is significantly more stable and thus more resistant to methionine oxidation. These results indicate that oxidation rates of buried methionines from the native state of proteins can be used as a metric of folding stability. To demonstrate the utility of this correlation, we used native methionine oxidation rates to survey the folding stabilities of E. coli and T. thermophilus proteomes at various temperatures and suggest a model that relates the temperature dependence of the folding stabilities of these two species to their optimal growth temperatures.

Continuous cultivation of the lithoautotrophic nitrate-reducing Fe(II)-oxidizing culture KS in a chemostat bioreactor

Laboratory-based studies on microbial Fe(II) oxidation are commonly performed over just a few weeks in small volumes with high substrate concentrations, resulting in geochemical gradients and volumetric effects caused by sampling. We used a chemostat to enable uninterrupted supply of medium, and investigated autotrophic growth of the nitrate-reducing Fe(II)-oxidizing culture KS for 24 days. We analysed Fe- and N-speciation, cell-mineral associations, and the identity of minerals. Results were compared to different batch systems (50 and 700 ml – static/shaken). The Fe(II) oxidation rate was highest in the chemostat with 7.57 mM Fe(II) d-1, while the extent was similar (averaged 92% of all Fe(II)). Short-range ordered Fe(III) phases, presumably ferrihydrite, precipitated and later goethite was detected in the chemostat. 1 mM solid phase Fe(II) remained in the chemostat, up to 15 µM of reactive nitrite was measured, and 42% of visualized cells were partially or completely mineral-encrusted, likely caused by abiotic oxidation of Fe(II) by nitrite. Despite (partial) encrustation, cells were still viable. Our results show that even with similar oxidation rates as in batch cultures, cultivating Fe(II)-oxidizing microorganisms under continuous conditions reveals mechanistic insights on the role of reactive intermediates for Fe(II) oxidation, mineral formation and cell-mineral interactions.

Intermittent maternofetal oxygenation during late gestation improved birthweight, neonatal growth, body symmetry, and muscle metabolism in intrauterine growth-restricted lambs

In humans and animals, intrauterine growth restriction (IUGR) results from fetal programming responses to poor intrauterine conditions. Chronic fetal hypoxemia elevates circulating catecholamines, which reduces skeletal muscle β2 adrenoceptor content and contributes to growth and metabolic pathologies in IUGR-born offspring. Our objective was to determine whether intermittent maternofetal oxygenation during late gestation would improve neonatal growth and glucose metabolism in IUGR-born lambs. Pregnant ewes were housed at 40°C from the 40 th to 95 th d of gestational age (dGA) to produce IUGR-born lambs (n = 9). A 2 nd group of IUGR-born lambs received prenatal O2 supplementation via maternal O2 insufflation (100% humidified O2, 10 L/min) for 8 h/d from dGA 130 to parturition (IUGR+O2, n = 10). Control lambs (n = 15) were from pair-fed thermoneutral ewes. All lambs were weaned at birth, hand-reared, and fitted with hindlimb catheters at d 25. Glucose-stimulated insulin secretion (GSIS) and hindlimb hyperinsulinemic-euglycemic clamp (HEC) studies were performed at d 28 and 29, respectively. At d 30, lambs were euthanized and ex vivo HEC studies were performed on isolated muscle. Without maternofetal oxygenation, IUGR lambs were 40% lighter (P &lt; 0.05) at birth and maintained slower (P &lt; 0.05) growth rates throughout the neonatal period compared to controls. At 30 d of age, IUGR lambs had lighter (P &lt; 0.05) hindlimbs and flexor digitorum superficialis (FDS) muscles. IUGR+O2 lambs exhibited improved (P &lt; 0.05) birthweight, neonatal growth, hindlimb mass, and FDS mass compared to IUGR lambs. Hindlimb insulin-stimulated glucose utilization and oxidation rates were reduced (P &lt; 0.05) in IUGR but not IUGR+O2 lambs. Ex vivo glucose oxidation rates were less (P &lt; 0.05) in muscle from IUGR but not IUGR+O2 lambs. Surprisingly, β2 adrenoceptor content and insulin responsiveness were reduced (P &lt; 0.05) in muscle from IUGR and IUGR+O2 lambs compared to controls. In addition, glucose-stimulated insulin secretion was reduced (P &lt; 0.05) in IUGR lambs and only modestly improved (P &lt; 0.05) in IUGR+O2. Insufflation of O2 also increased (P &lt; 0.05) acidosis and hypercapnia in dams, perhaps due to the use of 100% O2 rather than a gas mixture with a lesser O2 percentage. Nevertheless, these findings show that intermittent maternofetal oxygenation during late gestation improved postnatal growth and metabolic outcomes in IUGR lambs without improving muscle β2 adrenoceptor content.

Isotopic and Chemical Assessment of the Dynamics of Methane Sources and Microbial Cycling during Early Development of an Oil Sands Pit Lake

Water-capped tailings technology (WCTT) is a key component of the reclamation strategies in the Athabasca oil sands region (AOSR) of northeastern Alberta, Canada. The release of microbial methane from tailings emplaced within oil sands pit lakes, and its subsequent microbial oxidation, could inhibit the development of persistent oxygen concentrations within the water column, which are critical to the success of this reclamation approach. Here, we describe the results of a four-year (2015–2018) chemical and isotopic (δ13C) investigation into the dynamics of microbial methane cycling within Base Mine Lake (BML), the first full-scale pit lake commissioned in the AOSR. Overall, the water-column methane concentrations decreased over the course of the study, though this was dynamic both seasonally and annually. Phospholipid fatty acid (PLFA) distributions and δ13C demonstrated that dissolved methane, primarily input via fluid fine tailings (FFT) porewater advection, was oxidized by the water column microbial community at all sampling times. Modeling and under-ice observations indicated that the dissolution of methane from bubbles during ebullition, or when trapped beneath ice, was also an important source of dissolved methane. The addition of alum to BML in the fall of 2016 impacted the microbial cycling in BML, leading to decreased methane oxidation rates, the short-term dominance of a phototrophic community, and longer-term shifts in the microbial community metabolism. Overall, our results highlight a need to understand the dynamic nature of these microbial communities and the impact of perturbations on the associated biogeochemical cycling within oil sands pit lakes.

Substantial oxygen consumption by aerobic nitrite oxidation in oceanic oxygen minimum zones

Oceanic oxygen minimum zones (OMZs) are globally significant sites of biogeochemical cycling where microorganisms deplete dissolved oxygen (DO) to concentrations <20 µM. Amid intense competition for DO in these metabolically challenging environments, aerobic nitrite oxidation may consume significant amounts of DO and help maintain low DO concentrations, but this remains unquantified. Using parallel measurements of oxygen consumption rates and 15N-nitrite oxidation rates applied to both water column profiles and oxygen manipulation experiments, we show that the contribution of nitrite oxidation to overall DO consumption systematically increases as DO declines below 2 µM. Nitrite oxidation can account for all DO consumption only under DO concentrations <393 nM found in and below the secondary chlorophyll maximum. These patterns are consistent across sampling stations and experiments, reflecting coupling between nitrate reduction and nitrite-oxidizing Nitrospina with high oxygen affinity (based on isotopic and omic data). Collectively our results demonstrate that nitrite oxidation plays a pivotal role in the maintenance and biogeochemical dynamics of OMZs.