OBJECTIVES:Endurance exercise reduces the risk of metabolic diseases by improving skeletal muscle metabolism, particularly in individuals with overweight and obesity. As biological sex impacts glucose and fatty acid handling in skeletal muscle, we hypothesized sex differences at the transcriptomic and proteomic level in the acute response to exercise and after an 8-week exercise intervention. METHODS:We analyzed skeletal muscle biopsies from 25 sedentary subjects (16f/9 m) with overweight and obesity using transcriptomics and proteomics at baseline, after acute exercise, and following an 8-week endurance training program. Regulation of sex-specific differences was studied in primary myotubes from the donors. RESULTS:At baseline, differentially methylated CpG-sites potentially explain up to 59% of transcriptomic and 67% of proteomic sex differences. Differences were dominated by higher abundance of fast-twitch fiber type proteins, and transcripts and proteins regulating glycogen degradation and glycolysis in males. Females showed higher abundance of proteins regulating fatty acid uptake and storage. Acute exercise induced stress-responsive transcripts and serum myoglobin predominantly in males. Both sexes adapted to 8-week endurance training by upregulating mitochondrial proteins involved in TCA cycle, oxidative phosphorylation, and β-oxidation. Training equalized fast-twitch fiber type protein levels, mainly by reducing them in males. In vivo sex differences in autosomal genes were poorly retained in myotubes but partially restored by sex hormone treatment. CONCLUSIONS:Our findings highlight sex-specific molecular signatures that reflect known differences in glucose and lipid metabolism between female and male skeletal muscle. After just 8 weeks of endurance training, these sex differences were attenuated, suggesting a convergence towards a shared beneficial adaptation at the molecular level.

Exercise is a potent skeletal muscle stimulus and one of the most effective strategies to prevent muscle loss and type 2 diabetes. Biological sex-based differences are reported for aerobic capacity, muscle mass, and exercise performance. We aimed to provide a yet missing comprehensive picture of molecular differences between female and male skeletal muscle at baseline, after acute exercise and training. Further we investigated which differences were conserved in vitro. We characterized muscle biopsies from 25 (16f/9m) subjects in a multi-omics approach employing epigenomics, transcriptomics and proteomics at baseline, after acute exercise and 8 weeks of supervised endurance training. Donor matched myoblasts and myotubes were analyzed in vitro. We found differential CpG-site methylation in 16.012 genes, 1.366 differentially expressed genes and 120 proteins at baseline. Differential transcripts were associated with translational regulation, histone methylation, glucose homeostasis and insulin signaling. Type-2 fast-twitch fiber-type proteins were elevated in males, along with proteins regulating glycolysis. Y-linked transcript expression was conserved in vitro, but only a few differences in expression of autosomal genes, e.g. elevated LDHB in females. Acute exercise upregulated oxidative stress-responsive transcripts predominantly in males. After 8-week-training, both sexes had upregulated mitochondrial proteins involved in substrate oxidation and ATP production, while glycolytic fiber marker MYH1 and MYH3 were only reduced in males. Thus, sex specific differences exist in resting skeletal muscle and in exercise adaptation on epigenomic, transcriptomic and proteomic level. The few conserved differences in vitro hint towards hormonal or yet undefined mechanisms. Training might mitigate initially differential responses to exercise. The question remains whether there are sex specific differences within individual fiber-types or whether it is just a matter of composition. Disclosure S.I. Dreher: None. T. Goj: None. C. von Toerne: None. M. Hoene: None. M. Irmler: None. M. Ouni: None. M. Jähnert: None. J. Beckers: None. A. Peter: None. A.L. Birkenfeld: None. A. Schürmann: None. S.M. Hauck: None. C. Weigert: None.

Biological sex has a strong impact on skeletal muscle metabolism and performance. By a comprehensive investigation of epigenetic, transcriptomic and proteomic differences between female and male skeletal muscle of untrained subjects we provide a molecular basis for the sexual dimorphism of glucose and lipid metabolism. The sex-specific multi-OMICs profiles indicate higher degree of glucose turnover and higher abundance of fast-twitch fibers in males and high degree of lipid handling in females. Eight-week endurance training equalized initial differences toward an endurance-trained proteomic profile in both sexes. The untrained muscle of females was more resistant to an acute exercise challenge since stress-responsive transcripts were predominantly upregulated in males. In myotubes from the same donors, transcriptomic differences were hardly conserved, but could be partially restored by treatment with sex hormones. In conclusion, after only 8 weeks training mitigates deeply rooted sex-specific molecular profiles in skeletal muscle toward a common metabolically beneficial response. ### Competing Interest Statement The authors have declared no competing interest.

Aims/hypothesis While physical activity is clearly beneficial in combating type 2 diabetes, the underlying molecular mechanisms are incompletely understood. Moreover, there is a considerable degree of variability in the individual response to exercise-based lifestyle interventions that remains to be explained. We aimed to identify novel exercise-induced metabolites that could mediate the improvement in glycemic control and reduction of obesity and contribute to individual differences in the response to exercise interventions. Methods We studied acute exercise- and training-induced changes in plasma metabolites in sedentary subjects with overweight (8 male, 14 female) participating in an eight-week supervised training program flanked by two acute endurance exercise sessions. Plasma metabolites were quantified using LC- and CE-MS. In a separate study (n=9 lean males), we assessed metabolite fluxes over the leg using arterial and venous catheters. Functional analyses were performed in primary blood mononuclear cells (PBMCs) stimulated with lipopolysaccharide (LPS) or the saturated fatty acid palmitate. Results The amino acid breakdown products 3-phenyllactic acid (PLA), 4-hydroxyphenyllactic acid and indolelactic acid were increased after both acute exercise and training. All three aromatic lactic acids, which so far mainly received attention as bacterial metabolites, exhibited an efflux from the leg. PLA showed the largest increase after both acute exercise and training, of 57% and 20% respectively. The magnitude of the acute exercise-induced increase in PLA correlated with a decrease in subcutaneous adipose tissue volume and an improvement in insulin sensitivity over the course of the intervention. Furthermore, both isomers, D- and L-PLA, counteracted inflammatory cytokine production in PBMCs. Conclusions/interpretation Our findings indicate that PLA is physiologically released from skeletal muscle and can contribute to the anti-inflammatory effects of exercise as well as to individual difference in the response to lifestyle interventions in humans. PLA and potentially, aromatic lactic acids in general may be particularly relevant metabolic regulators because they can be produced both endogenously and by the microbiome. Trial registration ClinicalTrials.gov NCT03151590 ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial NCT03151590 ### Funding Statement This study was supported in part by grants from the Mobility Programme of the Sino-German Center for Research Promotion (M-0257), the Strategic Leading Science and Technology Project B of the Chinese Academy of Sciences (XDB38020200), the German Federal Ministry of Education and Research (BMBF) to the German Centre for Diabetes Research (DZD e.V., 01GI0925) and by grants from the German Diabetes Association (DDG) to MH and AM. AM is currently funded by a clinician scientist program from the medical faculty of the University of Tuebingen. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Written consent was obtained from all participants and the study was approved by the ethics committee of the University of Tuebingen and registered at Clinicaltrials.gov. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes

CONTEXT:One acute bout of exercise leads to a rapid increase in the systemic cytokine concentration. Regular exercise might alter the cytokine response, in particular in beforehand untrained and obese individuals.OBJECTIVE:Using a proximity extension assay, we studied the effects of acute exercise as well as endurance training on a panel of 92 cytokines related to inflammation.METHODS:A total of 22 individuals (30 ± 9 years; peak oxygen uptake [VO2peak] 25.2 ± 4.2 mL/[kg × min]; body mass index [BMI] 31.7 ± 4.4) participated in an 8-week endurance exercise intervention. Blood samples were collected before and immediately after 30 minutes' ergometer exercise at 80% VO2peak.RESULTS:Before and after the training intervention, 40 and 37 cytokines, respectively, were acutely increased more than 1.2-fold (Benjamini-Hochberg [BH]-adjusted P < .05). The exercise intervention did not change the acute increase in cytokines nor the resting cytokine levels, whereas fitness was improved and adiposity reduced. The increase in fitness led to a slight increase in power output when exercising at the same heart rate, which might explain the comparable increase in cytokines before and after the intervention. The largest acute increase was found for OSM, TGFA, CXCL1 and 5, and TNFSF14 (≥ 1.9-fold, BH-adjusted P < .001). The transcript levels of these proteins in whole blood were also elevated, particularly in the trained state. Only the acute increase in IL6 (1.3-fold) was related to the increase in lactate, confirming the lactate-driven secretion of IL6.CONCLUSION:Our comprehensive proteomics approach detected several underexplored serum exerkines with up to now less understood function in the adaptation to exercise.

Background: Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a sensitive method with high specificity. However, its routine use in the clinical laboratory is hampered by its high complexity and lack of automation. Studies demonstrate excellent analytical performance using the first fully automated LC-MS/MS for 25-hydroxy vitamin D and immunosuppressant drugs (ISD) in hospital routine laboratories.Objectives: Our objectives were (1) to verify the suitability of an automated LC-MS/MS in a commercial labo-ratory, which differs from the needs of hospital laboratories, and (2) examine its usability among operators with various professional backgrounds.Methods: We assessed the analytical assay performance for vitamin D and the ISDs cyclosporine A and tacrolimus over five months. The assays were compared to an identical analyzer in a hospital laboratory, to in-house LC-MS/ MS methods, and to chemiluminescent microparticle immunoassays (CMIA). Nine operators evaluated the us-ability of the fully automated LC-MS/MS system by means of a structured questionnaire.Results: The automated system exhibited a high precision (CV < 8%), accuracy (bias < 7%) and good agreement with concentrations of external quality assessment (EQA) samples. Comparable results were obtained with an identical analyzer in a hospital routine laboratory. Acceptable median deviations of results versus an in-house LC-MS/MS were observed for 25-OH vitamin D3 (-10.6%), cyclosporine A (-4.3%) and tacrolimus (-6.6%). The median bias between the automated system and immunoassays was only acceptable for 25-OH vitamin D3 (6.6%). All users stated that they had had a good experience with the fully automated LC-MS/MS system.Conclusions: A fully automated LC-MS/MS can be easily integrated for routine diagnostics in a commercial laboratory.

The gut microbiome is of tremendous relevance to human health and disease, so it is a hot topic of omics-driven biomedical research. However, a valid identification of gut microbiota-associated molecules in human blood or urine is difficult to achieve. We hypothesize that bowel evacuation is an easy-to-use approach to reveal such metabolites. A non-targeted and modifying group-assisted metabolomics approach (covering 40 types of modifications) was applied to investigate urine samples collected in two independent experiments at various time points before and after laxative use. Fasting over the same time period served as the control condition. As a result, depletion of the fecal microbiome significantly affected the levels of 331 metabolite ions in urine, including 100 modified metabolites. Dominating modifications were glucuronidations, carboxylations, sulfations, adenine conjugations, butyrylations, malonylations, and acetylations. A total of 32 compounds, including common, but also unexpected fecal microbiota-associated metabolites, were annotated. The applied strategy has potential to generate a microbiome-associated metabolite map (M3) of urine from healthy humans, and presumably also other body fluids. Comparative analyses of M3 vs. disease-related metabolite profiles, or therapy-dependent changes may open promising perspectives for human gut microbiome research and diagnostics beyond analyzing feces.

Background Physical exercise causes pronounced changes in circulating metabolites that could act as “exerkines” mediating its well-known beneficial effects, such as improvement of chronic low-grade inflammation, glucose homeostasis and insulin sensitivity.

Reliability, robustness, and interlaboratory comparability of quantitative measurements is critical for clinical lipidomics studies. Lipids' different ex vivo stability in blood bears the risk of misinterpretation of data. Clear recommendations for the process of blood sample collection are required. We studied by UHPLC-high resolution mass spectrometry, as part of the "Preanalytics interest group" of the International Lipidomics Society, the stability of 417 lipid species in EDTA whole blood after exposure to either 4°C, 21°C, or 30°C at six different time points (0.5 h–24 h) to cover common daily routine conditions in clinical settings. In total, >800 samples were analyzed. 325 and 288 robust lipid species resisted 24 h exposure of EDTA whole blood to 21°C or 30°C, respectively. Most significant instabilities were detected for FA, LPE, and LPC. Based on our data, we recommend cooling whole blood at once and permanent. Plasma should be separated within 4 h, unless the focus is solely on robust lipids. Lists are provided to check the ex vivo (in)stability of distinct lipids and potential biomarkers of interest in whole blood. To conclude, our results contribute to the international efforts towards reliable and comparable clinical lipidomics data paving the way to the proper diagnostic application of distinct lipid patterns or lipid profiles in the future.

Objective: Endothelin receptor B (ETB) together with ETA mediates cellular effects of endothelin 1 (ET-1), an autocrine and endocrine peptide produced by the endothelium and other cells. It regulates vascular tone and controls kidney function. Metabolic syndrome is due to high caloric intake and is characterized by insulin resistance, dyslipidemia, and white adipose tissue (WAT) accumulation. ETA/ETB antagonism has been demonstrated to favorably influence insulin resistance. Our study explored the role of ETB in metabolic syndrome. Methods: Wild type (etb(+/+)) and rescued ETB-deficient (etb(-/-)) mice were fed a high-fat diet, and energy, glucose, and insulin metabolism were analyzed, and hormones and lipids measured in serum and tissues. Cell culture experiments were performed in HepG2 cells. Results: Compared to etb(+/+) mice, etb(-/-) mice exhibited better glucose tolerance and insulin sensitivity, less WAT accumulation, lower serum triglycerides, and higher energy expenditure. Protection from metabolic syndrome was paralleled by higher hepatic production of fibroblast growth factor 21 (FGF21) and higher serum levels of free thyroxine (fT4), stimulators of energy expenditure. Conclusions: ETB deficiency confers protection from metabolic syndrome by counteracting glucose intolerance, dyslipidemia, and WAT accumulation due to enhanced energy expenditure, effects at least in part dependent on enhanced production of thyroid hormone/FGF21. ETB antagonism may therefore be a novel therapeutic approach in metabolic syndrome. (c) 2023 The Author(s). Published by Elsevier GmbH. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

We present an approach for the visual analysis of multi‐omics data obtained using high‐throughput methods. The term “omics” denotes measurements of different types of biologically relevant molecules like the products of gene transcription (transcriptomics) or the abundance of proteins (proteomics). Current popular visualization approaches often only support analyzing each of these omics separately. This, however, disregards the interconnectedness of different biologically relevant molecules and processes. Consequently, it describes the actual events in the organism suboptimally or only partially. Our visual analytics approach for multi‐omics data provides a comprehensive overview and details‐on‐demand by integrating the different omics types in multiple linked views. To give an overview, we map the measurements to known biological pathways and use a combination of a clustered network visualization, glyphs, and interactive filtering. To ensure the effectiveness and utility of our approach, we designed it in close collaboration with domain experts and assessed it using an exemplary workflow with real‐world transcriptomics, proteomics, and lipidomics measurements from mice.

Flux Sampling (FS) is an unbiased constraint-based modeling method in systems biology that characterizes the admissible metabolic flux space of cells and organisms at a molecular level. It returns information about reaction flux ranges and their probability from a genome-scale metabolic model (GEM), which can be used to predict metabolic phenotypes. FS is particularly beneficial if a cellular objective cannot be easily identified. We present FluxomicsExplorer, a web-based visual analysis application that facilitates a data- and task-driven exploratory analysis of FS results. It was designed together with experts in medicine and systems biology to satisfy their requirements and offers multiple linked views that visualize the standardized scoring of flux differences, flux distributions, and the network of biological pathways to guide the analysis process. Instead of focusing on a subset of known influential reactions for the analysis, it allows users to assess the results as a whole concerning the underlying GEM. The visualizations guide the user to affected reactions, metabolites, and network areas by highlighting relevant changes between two conditions. These flux changes can then be analyzed in detail by visualizing the reaction flux distributions. We show FluxomicsExplorer’s utility using a case study of the red blood cell metabolism in different blood plasma environments.

Background Acute physical exercise leads to rapid changes in blood cytokines. However, the changes are variable and can be influenced by reduced physical fitness and other type 2 diabetes risk factors. We investigated the influence of metabolic parameters and endurance training on the acute release of cytokines in subjects at high risk to develop type 2 diabetes.

BACKGROUNDInsulin resistance of the brain can unfavorably affect long-term weight maintenance and body fat distribution. Little is known if and how brain insulin sensitivity can be restored in humans. We aimed to evaluate the effects of an exercise intervention on insulin sensitivity of the brain and how this relates to exercise-induced changes in whole-body metabolism and behavior.METHODSIn this clinical trial, sedentary participants who were overweight and obese underwent an 8-week supervised aerobic training intervention. Brain insulin sensitivity was assessed in 21 participants (14 women, 7 men; age range 21-59 years; BMI range 27.5-45.5 kg/m2) using functional MRI, combined with intranasal administration of insulin, before and after the intervention.RESULTSThe exercise program resulted in enhanced brain insulin action to the level of a person of healthy weight, demonstrated by increased insulin-induced striatal activity and strengthened hippocampal functional connectivity. Improved brain insulin action correlated with increased mitochondrial respiration in skeletal muscle, reductions in visceral fat and hunger, as well as improved cognition. Mediation analyses suggest that improved brain insulin responsiveness helps mediate the peripheral exercise effects leading to healthier body fat distribution and reduced perception of hunger.CONCLUSIONOur study demonstrates that an 8-week exercise intervention in sedentary individuals can restore insulin action in the brain. Hence, the ameliorating benefits of exercise toward brain insulin resistance may provide an objective therapeutic target in humans in the challenge to reduce diabetes risk factors.TRIAL REGISTRATIONClinicalTrials.gov (NCT03151590).FUNDINGBMBF/DZD 01GI0925.

Aims/Hypothesis Large-scale prediabetes screening is still a challenge since fasting blood glucose and HbA 1c as the long-standing, recommended analytes have only moderate diagnostic sensitivity, and the practicability of the oral glucose tolerance test for population-based strategies is limited. To tackle this issue and to identify reliable diagnostic patterns, we developed an innovative metabolomics-based strategy deviating from common concepts by employing urine instead of blood samples, searching for sex-specific biomarkers, and focusing on modified metabolites. Methods Non-targeted, modification group-assisted metabolomics by liquid chromatography–mass spectrometry (LC-MS) was applied to second morning urine samples of 340 individuals from a prediabetes cohort. Normal ( n = 208) and impaired glucose-tolerant (IGT; n = 132) individuals, matched for age and BMI, were randomly divided in discovery and validation cohorts. ReliefF, a feature selection algorithm, was used to extract sex-specific diagnostic patterns of modified metabolites for the detection of IGT. The diagnostic performance was compared with conventional screening parameters fasting plasma glucose (FPG), HbA 1c , and fasting insulin. Results Female- and male-specific diagnostic patterns were identified in urine. Only three biomarkers were identical in both. The patterns showed better AUC and diagnostic sensitivity for prediabetes screening of IGT than FPG, HbA 1c , insulin, or a combination of FPG and HbA 1c . The AUC of the male-specific pattern in the validation cohort was 0.889 with a diagnostic sensitivity of 92.6% and increased to an AUC of 0.977 in combination with HbA 1c . In comparison, the AUCs of FPG, HbA 1c , and insulin alone reached 0.573, 0.668, and 0.571, respectively. Validation of the diagnostic pattern of female subjects showed an AUC of 0.722, which still exceeded the AUCs of FPG, HbA 1c , and insulin (0.595, 0.604, and 0.634, respectively). Modified metabolites in the urinary patterns include advanced glycation end products (pentosidine-glucuronide and glutamyl-lysine-sulfate) and microbiota-associated compounds (indoxyl sulfate and dihydroxyphenyl-gamma-valerolactone-glucuronide). Conclusions/Interpretation Our results demonstrate that the sex-specific search for diagnostic metabolite biomarkers can be superior to common metabolomics strategies. The diagnostic performance for IGT detection was significantly better than routinely applied blood parameters. Together with recently developed fully automatic LC-MS systems, this opens up future perspectives for the application of sex-specific diagnostic patterns for prediabetes screening in urine.

Physical exercise is a powerful measure to prevent cardiometabolic diseases. However, the individual response to lifestyle interventions is variable and cannot, to date, be predicted. N-Lactoylphenylalanine (Lac-Phe) produced during exercise has recently been shown to mediate weight loss in obese mice. Lac-Phe could also contribute to, and potentially explain differences in, the effectiveness of exercise interventions in humans. Sedentary overweight and obese subjects completed an 8-week supervised endurance exercise intervention (n = 22). Before and after the intervention, plasma levels of Lac-Phe were determined by UHPLC-MS in the resting state and immediately after an acute bout of endurance exercise. Adipose tissue volume was quantified using MRI. Acute exercise caused a pronounced increase in Lac-Phe, both before and after the intervention. Higher levels of Lac-Phe after acute exercise were associated with a greater reduction in abdominal subcutaneous and, to a lower degree, visceral adipose tissue during the intervention. Lac-Phe produced during physical activity could contribute to weight loss by acting as a signaling molecule that regulates food intake, as previously shown in mice. Quantification of Lac-Phe during an exercise test could be employed as a tool to predict and potentially improve the individual response to exercise-based lifestyle interventions in overweight humans and those with obesity.

Regular physical activity is an effective strategy to prevent and ameliorate aging-associated diseases. In particular, training increases muscle performance and improves whole-body metabolism. Since exercise affects the whole organism, it has countless health benefits. The systemic effects of exercise can, in part, be explained by communication between the contracting skeletal muscle and other organs and cell types. While small proteins and peptides known as myokines are the most prominent candidates to mediate this tissue cross-talk, recent investigations have paid increasing attention to metabolites. The purpose of this review is to highlight the potential role of tricarboxylic acid (TCA) metabolites as humoral mediators of exercise adaptation processes. We focus on TCA metabolites that are released from human skeletal muscle in response to exercise and provide an overview of their potential auto-, para- or endocrine health-promoting effects.

From microbes to human beings, nontargeted metabolic profiling by liquid chromatography (LC)-mass spectrometry (MS) has been commonly used to investigate metabolic alterations. Still, a major challenge is the annotation of metabolites from thousands of detected features. The aim of our research was to go beyond coverage of metabolite annotation in common nontargeted metabolomics studies by an integrated multistep strategy applying data-dependent acquisition (DDA)-based ultrahigh-performance liquid chromatography (UHPLC)-high-resolution mass spectrometry (HRMS) analysis followed by comprehensive neutral loss matches for characteristic metabolite modifications and database searches in a successive manner. Using pooled human urine as a model sample for method establishment, we found 22% of the detected compounds having modifying structures. Major types of metabolite modifications in urine were glucuronidation (33%), sulfation (20%), and acetylation (6%). Among the 383 annotated metabolites, 100 were confirmed by standard compounds and 50 modified metabolites not present in common databases such as human metabolite database (HMDB) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were structurally elucidated. Practicability was tested by the investigation of urines from pregnant women diagnosed with gestational diabetes mellitus vs healthy controls. Overall, 83 differential metabolites were annotated and 67% of them were modified metabolites including five previously unreported compounds. To conclude, the systematic modifying group-assisted strategy can be taken as a useful tool to extend the number of annotated metabolites in biological and biomedical nontargeted studies.

Prostate cancer (PCa) is associated with cellular metabolism alterations leading to changes of the metabolome. So far, studies investigating these alterations mainly focused on comparisons of metabolite profiles of PCa patients and healthy controls. In the present study we compared for the first time metabolite profiles in a significant number of paired urine samples collected before and eight weeks after radical prostatectomy (rPX) in 34 patients with PCa. Our comprehensive non-targeted liquid chromatographic-mass spectrometric metabolomics approach covered > 3000 metabolite ion masses. We annotated 23 metabolites showing significant changes eight weeks after rPX. While the levels of uridine and six acylcarnitines in urine were increased before surgery, lower levels were detected for 16 metabolites, like e.g. citrate, phenyl-lactic acid, choline, myo-inositol, emphasizing a relevant pathophysiological role of these biomarkers and the associated metabolic pathways. These results have important implications for potential use of metabolome analyses for detection of prostate cancer and related pathologic and molecular features.

The selection of carbohydrates or fat to generate intracellular energy is thought to be crucial for long-term metabolic health. While most studies assess fuel selection after a metabolic challenge, the determinants of substrate oxidation in the fasted state remain largely unexplored. We therefore assessed the respiratory quotient by indirect calorimetry as a read-out for substrate oxidation following an overnight fast. This cross-sectional analysis consisted of 192 (92 women, 100 men) either lean or obese participants. Following an overnight fast, the respiratory quotient (RQ) was assessed, after which a 5-point 75-g oral glucose tolerance test was performed. Unlike glucose and insulin, fasting free fatty acids (FFA) correlated negatively with fasting RQ ( p < 0.0001). Participants with high levels of the ketone body β-hydroxybutyric acid had significantly lower RQ values. Fasting levels of glucose-dependent insulinotropic polypeptide (GIP) and glicentin were positively associated with fasting RQ (all p ≤ 0.03), whereas GLP-1 showed no significant association. Neither BMI, nor total body fat, nor body fat distribution correlated with fasting RQ. No relationship between the RQ and diabetes or the metabolic syndrome could be observed. In the fasting state, FFA concentrations were strongly linked to the preferentially oxidized substrate. Our data did not indicate any relationship between fasting substrate oxidation and metabolic diseases, including obesity, diabetes, and the metabolic syndrome. Since glicentin and GIP are linked to fuel selection in the fasting state, novel therapeutic approaches that target these hormones may have the potential to modulate substrate oxidation.