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PurposeThe recovery of muscle oxygen consumption (m\\[V\\]O2) after exercise provides a measure of skeletal muscle mitochondrial capacity, as more and better-functioning mitochondria will be able to restore m\\[V\\]O2 faster to the pre-exercise state. The aim was to measure muscle mitochondrial capacity using near-infrared spectroscopy (NIRS) within a healthy, normally active population and relate this to parameters of aerobic fitness, investigating the applicability and relevance of using NIRS to assess muscle mitochondrial capacity non-invasively.MethodsMitochondrial capacity was analysed in the gastrocnemius and flexor digitorum superficialis (FDS) muscles of eight relatively high-aerobic fitness (\\[V\\]O2peak ≥ 57 mL/kg/min) and eight relatively low-aerobic fitness male subjects (\\[V\\]O2peak ≤ 47 mL/kg/min). Recovery of whole body \\[V\\]O2, i.e. excess post-exercise oxygen consumption (EPOC) was analysed after a cycling protocol.ResultsMitochondrial capacity, as analysed using NIRS, was significantly higher in high-fitness individuals compared to low-fitness individuals in the gastrocnemius, but not in the FDS (p = 0.0036 and p = 0.20, respectively). Mitochondrial capacity in the gastrocnemius was significantly correlated with \\[V\\]O2peak (R2 = 0.57, p = 0.0019). Whole body \\[V\\]O2 recovery was significantly faster in the high-fitness individuals (p = 0.0048), and correlated significantly with mitochondrial capacity in the gastrocnemius (R2 = 0.34, p = 0.028).ConclusionNIRS measurements can be used to assess differences in mitochondrial muscle oxygen consumption within a relatively normal, healthy population. Furthermore, mitochondrial capacity correlated with parameters of aerobic fitness (\\[V\\]O2peak and EPOC), emphasising the physiological relevance of the NIRS measurements.

Sepsis is associated with high rates of multiorgan failure and mortality. Altered mitochondrial function is an essential component of the early sepsis syndrome. However, its progression over time in peripheral blood mononuclear cells (PBMCs) is thus far unclear. Our purpose was to investigate this in the early phase of sepsis in ICU patients. A single-centre prospective observational cohort study was conducted in sepsis patients and compared with age- and sex-matched controls. Mitochondrial function was measured in PBMCs thrice during the first ICU week. RT-qPCR was used for semi-quantitative analysis of expression of genes involved in oxidative phosphorylation. Secondary endpoints included associations between mitochondrial function and (I) sepsis severity and (II) clinical outcomes, including 3-month mortality. Basal, ATP-linked, maximal and proton leak associated respiration were increased in sepsis patients (n = 25) compared to matched controls (n = 24) at all time points. This was associated with increased expression of SDBH (complex II) and ATP5F1A (complex V). Increased basal respiration was associated with 3-month mortality (HR 3.794, 95% CI 1.018–14.149, p  = 0.047). No differences were observed in other secondary outcomes. PBMC mitochondria were shown to have an increased respiratory rate during the first week of sepsis. Moreover, a progressive increase was negatively associated with 3-month survival.

Biomarkers are important in the assessment of health and disease, but are poorly studied in still healthy individuals with a (potential) different risk for metabolic disease. This study investigated, first, how single biomarkers and metabolic parameters, functional biomarker and metabolic parameter categories, and total biomarker and metabolic parameter profiles behave in young healthy female adults of different aerobic fitness and, second, how these biomarkers and metabolic parameters are affected by recent exercise in these healthy individuals. A total of 102 biomarkers and metabolic parameters were analysed in serum or plasma samples from 30 young, healthy, female adults divided into a high-fit (V̇O2peak ≥ 47 mL/kg/min, N = 15) and a low-fit (V̇O2peak ≤ 37 mL/kg/min, N = 15) group, at baseline and overnight after a single bout of exercise (60 min, 70% V̇O2peak). Our results show that total biomarker and metabolic parameter profiles were similar between high-fit and low-fit females. Recent exercise significantly affected several single biomarkers and metabolic parameters, mostly related to inflammation and lipid metabolism. Furthermore, functional biomarker and metabolic parameter categories corresponded to biomarker and metabolic parameter clusters generated via hierarchical clustering models. In conclusion, this study provides insight into the single and joined behavior of circulating biomarkers and metabolic parameters in healthy females, and identified functional biomarker and metabolic parameter categories that may be used for the characterisation of human health physiology.

Background Due to the interaction between skeletal muscle ageing and lifestyle factors, it is often challenging to attribute the decline in muscle mass and quality to either changes in lifestyle or to advancing age itself. Because many of the physiological factors affecting muscle mass and quality are modulated by physical activity and physical activity declines with age, the aim of this study is to better understand the effects of early ageing on muscle function by comparing a population of healthy older and young males with similar physical activity patterns. Methods Eighteen older (69 ± 2.0 years) and 20 young (22 ± 2.0 years) males were recruited based on similar self‐reported physical activity, which was verified using accelerometry measurements. Gene expression profiles of vastus lateralis biopsies obtained by RNA sequencing were compared, and key results were validated using quantitative polymerase chain reaction and western blot. Results Total physical activity energy expenditure was similar between the young and old group (404 ± 215 vs. 411 ± 189 kcal/day, P = 0.11). Three thousand seven hundred ninety‐seven differentially expressed coding genes (DEGs) were identified (adjusted P‐value cut‐off of <0.05), of which 1891 were higher and 1906 were lower expressed in the older muscle. The matrisome, innervation and inflammation were the main upregulated processes, and oxidative metabolism was the main downregulated process in old compared with young muscle. Lower protein levels of mitochondrial transcription factor A (TFAM, P = 0.030) and mitochondrial respiratory Complexes IV and II (P = 0.011 and P = 0.0009, respectively) were observed, whereas a trend was observed for Complex I (P = 0.062), in older compared with young muscle. Protein expression of Complexes I and IV was significantly correlated to mitochondrial capacity in the vastus lateralis as measured in vivo (P = 0.017, R2 = 0.42 and P = 0.030, R2 = 0.36). A trend for higher muscle‐specific receptor kinase (MUSK) protein levels in the older group was observed (P = 0.08). Conclusions There are clear differences in the transcriptome signatures of the vastus lateralis muscle of healthy older and young males with similar physical activity levels, including significant differences at the protein level. By disentangling physical activity and ageing, we appoint early skeletal muscle ageing processes that occur despite similar physical activity. Improved understanding of these processes will be key to design targeted anti‐ageing therapies.

Background Physical weakness is a key component of frailty, and is highly prevalent in older adults. While females have a higher prevalence and earlier onset, sex differences in the development of frailty-related physical weakness are hardly studied. Therefore, we investigated the intramuscular changes that differentiate between fit and weak older adults for each sex separately. Methods Male ( n  = 28) and female ( n  = 26) older adults (75 + years) were grouped on the basis of their ranks according to three frailty-related physical performance criteria. Muscle biopsies taken from vastus lateralis muscle were used for transcriptome and histological examination. Pairwise comparisons were made between the fittest and weakest groups for each sex separately, and potential sex-specific effects were assessed. Results Weak females were characterized by a higher expression of inflammatory pathways and infiltration of NOX2-expressing immune cells, concomitant with a higher VCAM1 expression. Weak males were characterized by a smaller diameter of type 2 (fast) myofibers and lower expression of PRKN . In addition, weakness-associated transcriptome changes in the muscle were distinct from aging, suggesting that the pathophysiology of frailty-associated physical weakness does not necessarily depend on aging. Conclusions We conclude that physical weakness-associated changes in muscle are sex-specific and recommend that sex differences are taken into account in research on frailty, as these differences may have a large impact on the development of (pharmaceutical) interventions against frailty. Trial registration number: The FITAAL study was registered in the Dutch Trial Register, with registration code NTR6124 on 14-11-2016 ( https://trialsearch.who.int/Trial2.aspx?TrialID=NTR6124  ). Highlights • In female, but not male older adults, physical weakness was associated with a higher expression of intramuscular markers for inflammation. • In male, but not female older adults, physical weakness was associated with a smaller diameter of type 2 (fast) myofibers and lower PRKN expression. • Fit older adults (of both sexes) maintained expression levels comparable to young participants of weakness related genes, differing from frail participants.

The recovery of muscle oxygen consumption (mV˙O2) after exercise measured using near‐infrared spectroscopy (NIRS) provides a measure of skeletal muscle mitochondrial capacity. Nevertheless, due to sex differences in factors that can influence scattering and thus penetration depth of the NIRS signal in the tissue, e.g., subcutaneous adipose tissue thickness and intramuscular myoglobin and hemoglobin, it is unknown whether results in males can be extrapolated to a female population. Therefore, the aim of this study was to measure skeletal muscle mitochondrial capacity in females at different levels of aerobic fitness to test whether NIRS can measure relevant differences in mitochondrial capacity. Mitochondrial capacity was analyzed in the gastrocnemius muscle and the wrist flexors of 32 young female adults, equally divided in relatively high (V˙O2peak ≥ 47 ml/kg/min) and relatively low aerobic fitness group (V˙O2peak ≤ 37 ml/kg/min). mV˙O2 recovery was significantly faster in the high‐ compared to the low‐fitness group in the gastrocnemius, but not in the wrist flexors (p = 0.009 and p = 0.0528, respectively). Furthermore, V˙O2peak was significantly correlated to mV˙O2 recovery in both gastrocnemius (R2 = 0.27, p = 0.0051) and wrist flexors (R2 = 0.13, p = 0.0393). In conclusion, NIRS measurements can be used to assess differences in mitochondrial capacity within a female population and is correlated to V˙O2peak. This further supports NIRS assessment of muscle mitochondrial capacity providing additional evidence for NIRS as a promising approach to monitor mitochondrial capacity, also in an exclusively female population.

Fructose consumption has been linked to obesity and increased hepatic de novo lipogenesis (DNL). Excessive caloric intake often confounds the results of fructose studies, and experimental diets are generally low‐fat diets, not representative for westernized diets. Here, we compared the effects of dietary fructose with those of dietary glucose, in adult male and female mice on a starch‐containing moderate high–fat (HF) diet. After 5 weeks fattening on a HF high‐glucose (HF‐G) diet, mice were stratified per sex and assigned to one of the three intervention diets for 6 weeks: HF high fructose (HF‐F), HF with equimolar glucose and fructose (HF‐GF), or HF‐G. Bodyweight (BW) and food intake were measured weekly. Indirect calorimetry was performed on week 5; animals were sacrificed in food‐deprived state on week 6. Data were analyzed within sex. BW gain was similar among animals on the HF‐G, HF‐GF, and HF‐F diets. Cumulative food intake was slightly lower in HF‐F animals (both sexes). However, energy expenditure was not affected, or were circulating insulin and glucose concentrations, and hepatic triglyceride levels at endpoint. Hepatic gene expression analysis showed only minor alterations in hexokinase and glycolysis‐related expression in males, and no alterations in sugar transporters, or DNL‐related enzymes. In females, no consistent alterations in hepatic or small intestine gene expression were seen. Concluding, partial or complete replacement of dietary glucose with fructose does not increase caloric intake, and does not affect BW, hepatic triglyceride levels, or insulin concentrations in male and female mice on a moderate high–fat diet. Effects of dietary fructose are compared with those of dietary glucose and of dietary glucose and fructose in equimolar amounts. The study was performed in adult male and female mice on a starch‐containing moderate high–fat (HF) diet. The partial or complete replacement of dietary glucose with fructose did not increase caloric intake, and did not affect BW, hepatic triglyceride levels, or insulin concentrations in male and female mice on a moderate high–fat diet.

Background The role of dietary protein in short term satiety is of interest with respect to body weight regulation. Aim To compare the effects of a high versus a normal soyprotein breakfast on satiety and subsequent energy intake (EI), including 'satiety' hormones and plasma amino acid responses. Methods Twenty-five healthy subjects (mean ± SEM, BMI: 23.9 ± 0.3 kg/m²; age: 22 ± 1 years) received a subject-specific standardized breakfast: a custard with soy as single protein type with either 10/55/35 (normal-protein) or 25/55/20 (high-protein) En% protein/carbohydrate/fat in a randomized, single-blind design. Appetite profile (Visual Analogue Scale, VAS), plasma glucose, insulin, Glucagon-like Peptide 1, ghrelin, and amino acid concentrations were determined for 4 h, determining the sensitive time point to assess EI. Since at 180 min glucose and insulin concentrations still were significantly different, in a second set of experiments subjects received an ad lib lunch at 180 min after the breakfasts; EI was assessed. Results Overall the 25 En% soy-custard was rated as being more satiating than the 10 En% soy-custard (P < 0.01) and there was a difference at 20 min after breakfast (64 ± 5 vs. 52 ± 5 mmVAS, P < 0.05), related to higher postprandial taurine concentrations (P < 0.05). Insulin response was increased more after the 25 En% than after the 10 En% soy-custard (AUC: 7,520 ± 929 vs. 4,936 ± 468 mU/l h, P < 0.001). There was no difference in EI (25 En%: 3,212 ± 280 kJ vs. 10 En%: 3,098 ± 286 kJ, ns). Conclusion A high soyprotein breakfast is more satiating than a normal soyprotein breakfast related to elevated taurine and insulin concentrations.

Sex differences in muscle aging are poorly understood, but could be crucial for the optimization of sarcopenia-related interventions. To gain insight into potential sex differences in muscle aging, we recruited young (23 ± 2 years, 13 males and 13 females) and old (80 ± 3.5 years, 28 males and 26 females) participants. Males and females in both groups were highly matched, and vastus lateralis muscle parameters of old versus young participants were compared for each sex separately, focusing on gene expression. The overall gene expression profiles separated the sexes, but similar gene expression patterns separated old from young participants in males and females. Genes were indeed regulated in the same direction in both sexes during aging; however, the magnitude of differential expression was sex specific. In males, oxidative phosphorylation was the top-ranked differentially expressed process, and in females, this was cell growth mediated by AKT signaling. Findings from RNA-seq data were studied in greater detail using alternative approaches. In addition, we confirmed our data using publicly available data from three independent human studies. In conclusion, top-ranked pathways differ between males and females, but were present and altered in the same direction in both sexes. We conclude that the same processes are associated with skeletal muscle aging in males and females, but the differential expression of those processes in old vs. young participants is sex specific.

Energy metabolism at whole body and cellular, and even organelle (i [...]