Ventricular CSF proteomic profiles and predictors of surgical treatment outcome in chronic hydrocephalus

BACKGROUND

By applying an unbiased proteomic approach, we aimed to search for cerebrospinal fluid (CSF) protein biomarkers distinguishing between obstructive and communicating hydrocephalus in order to improve appropriate surgical selection for endoscopic third ventriculostomy vs. shunt implants. Our second study purpose was to look for potential CSF biomarkers distinguishing between patients with adult chronic hydrocephalus benefitting from surgery (responders) vs. those who did not (non-responders).

METHODS

Ventricular CSF samples were collected from 62 patients with communicating hydrocephalus and 28 patients with obstructive hydrocephalus. CSF was collected in relation to the patients' surgical treatment. As a control group, CSF was collected from ten patients with unruptured aneurysm undergoing preventive surgery (vascular clipping).

RESULTS

Mass spectrometry-based proteomic analysis of the samples identified 1251 unique proteins. No proteins differed significantly between the communicating hydrocephalus group and the obstructive hydrocephalus group. Four proteins were found to be significantly less abundant in CSF from communicating hydrocephalus patients compared to control subjects. A PCA plot revealed similar proteomic CSF profiles of obstructive and communicating hydrocephalus and control samples. For obstructive hydrocephalus, ten proteins were found to predict responders from non-responders.

CONCLUSION

Here, we show that the proteomic profile of ventricular CSF from patients with hydrocephalus differs slightly from control subjects. Furthermore, we find ten predictors of response to surgical outcome (endoscopic third ventriculostomy or ventriculo-peritoneal shunt) in patients with obstructive hydrocephalus.

Effect of aerobic exercise training on the fat fraction of the liver in persons with chronic hepatitis B and hepatic steatosis: Trial protocol for a randomized controlled intervention trial- The FitLiver study

BACKGROUND

The global prevalence of chronic hepatitis B is more than 300 million people, and in Denmark, 17,000 people are estimated to have chronic hepatitis B. Untreated, chronic hepatitis B can lead to the development of liver cirrhosis and liver cancer. There is no curable therapy. In persons with obesity and chronic hepatitis B infection, the development of hepatic steatosis imposes a double burden on the liver, leading to an increased risk of cirrhosis and liver cancer. In patients without chronic hepatitis B, exercise interventions have shown beneficial effects on hepatic steatosis through improvements in fat fraction of the liver, insulin resistance, fatty acid metabolism, and glucose metabolism, as well as activation of liver-induced regulatory protein secretion (hepatokines) after the exercise intervention.

OBJECTIVE

To investigate in persons with chronic hepatitis B and hepatic steatosis: Primary: Whether exercise will decrease the fat fraction of the liver. Secondary: If exercise will affect hepatokine secretion and if it will improve lipid- and glucose metabolism, liver status, markers of inflammation, body composition, and blood pressure.

METHODS

A randomized, controlled, clinical intervention trial consisting of 12 weeks of aerobic exercise training or no intervention. Thirty persons with chronic hepatitis B and hepatic steatosis will be randomized 1:1. Before and after the intervention, participants will undergo an MRI scan of the liver, blood sampling, oral glucose tolerance test, fibroscan, VO2_max test, DXA scan, blood pressure measurements, and optional liver biopsy. Lastly, a hormone infusion test with somatostatin and glucagon to increase the glucagon/insulin ratio for stimulating secretion of circulating hepatokines will be performed. The training program includes three weekly training sessions of 40 min/session over 12 weeks.

DISCUSSION

This trial, investigating high-intensity interval training in persons with chronic hepatitis B and hepatic steatosis, is the first exercise intervention trial performed on this group of patients. If exercise reduces hepatic steatosis and induces other beneficial effects of clinical markers in this group of patients, there might be an indication to recommend exercise as part of treatment. Furthermore, the investigation of the effect of exercise on hepatokine secretion will provide more knowledge on the effects of exercise on the liver.

TRIAL REGISTRATION

Danish Capital Regions committee on health research ethics reference: H-21034236 (version 1.4 date: 19-07-2022) and ClinicalTrials.gov: NCT05265026.

Lowered muscle glycogen reduces body mass with no effect on short-term exercise performance in men

Performance in short-duration sports is highly dependent on muscle glycogen, but the total degradation is only moderate and considering the water-binding property of glycogen, unnecessary storing of glycogen may cause an unfavorable increase in body mass. To investigate this, we determined the effect of manipulating dietary carbohydrates (CHO) on muscle glycogen content, body mass and short-term exercise performance. In a cross-over design twenty-two men completed two maximal cycle tests of either 1-min (n = 10) or 15-min (n = 12) duration with different pre-exercise muscle glycogen levels. Glycogen manipulation was initiated three days prior to the tests by exercise-induced glycogen-depletion followed by ingestion of a moderate (M-CHO) or high (H-CHO) CHO-diet. Subjects were weighed before each test, and muscle glycogen content was determined in biopsies from m. vastus lateralis before and after each test. Pre-exercise muscle glycogen content was lower following M-CHO than H-CHO (367 mmol · kg^-1 DW vs. 525 mmol · kg^-1 DW, P < 0.00001), accompanied by a 0.7 kg lower body mass (P < 0.00001). No differences were observed in performance between diets in neither the 1-min (P = 0.33) nor the 15-min (P = 0.99) test. In conclusion, pre-exercise muscle glycogen content and body mass was lower after ingesting moderate compared with high amounts of CHO, while short-term exercise performance was unaffected. This demonstrates that adjusting pre-exercise glycogen levels to the requirements of competition may provide an attractive weight management strategy in weight-bearing sports, particularly in athletes with high resting glycogen levels.

Impact of Aging and Lifelong Exercise Training on Mitochondrial Function and Network Connectivity in Human Skeletal Muscle

Aging is associated with metabolic decline in skeletal muscle, which can be delayed by physical activity. Moreover, both lifelong and short-term exercise training have been shown to prevent age-associated fragmentation of the mitochondrial network in mouse skeletal muscle. However, whether lifelong endurance exercise training exerts the same effects in human skeletal muscle is still not clear. Therefore, the aim of the present study was to examine the effect of volume-dependent lifelong endurance exercise training on mitochondrial function and network connectivity in older human skeletal muscle. Skeletal muscle complex I+II-linked mitochondrial respiration per tissue mass was higher, but intrinsic complex I+II-linked mitochondrial respiration was lower in highly trained older subjects than in young untrained, older untrained, and older moderately trained subjects. Mitochondrial volume and connectivity were higher in highly trained older subjects than in untrained and moderately trained older subjects. Furthermore, the protein content of the ADP/ATP exchangers ANT1 + 2 and VDAC was higher and of the mitophagic marker parkin lower in skeletal muscle from the highly trained older subjects than from untrained and moderately trained older subjects. In contrast, H2O2 emission in skeletal muscle was not affected by either age or exercise training, but SOD2 protein content was higher in highly trained older subjects than in untrained and moderately trained older subjects. This suggests that healthy aging does not induce oxidative stress or mitochondrial network fragmentation in human skeletal muscle, but high-volume exercise training increases mitochondrial volume and network connectivity, thereby increasing oxidative capacity in older human skeletal muscle.

Validation of a novel automated system, Fluispotter®, for serial sampling of dried blood spots

Repeated blood sampling is required in certain clinical and research settings, which is currently performed by drawing blood from venous catheters requiring manual handling of each sample at time of collection. A novel body-worn device for repeated serial samples, Fluispotter®, with automated extraction, collection and storage of up to 20 venous dried blood spot samples over the course of 20 hours may overcome problems with current methods for serial sampling. The purpose of this study was to assess the performance and safety of Fluispotter for the first time in healthy subjects. Fluispotter consists of a cartridge with tubing, reservoir for flushing solution, pumps and filter-paper and a multi-lumen catheter placed in the brachial vein. We recruited healthy subjects for testing in an in-hospital setting. Fluispotter was attached by an anesthesiologist to 22 healthy subjects of which 9/22 (40.9 %) participants had all 20 samples taken, which was lower than the goal of complete sampling in 80 % of the subjects (p = 0.02). The main reason for sample failure was clogging of blood flow which was observed in 11/22 (50 %) of the participants. No serious adverse events occurred, and the participants rated the pain from insertion and removal of catheter as very low. A cortisol profile showed nadir values at midnight and highest values at 5 a.m. Although full sampling was not successful in all participants, the Fluispotter technology proved safe and highly acceptable to the participants producing the expected cortisol profile without the requirement of staff during sample collection.

Differential proteomic profile of lumbar and ventricular cerebrospinal fluid

BACKGROUND

Pathological cerebral conditions may manifest in altered composition of the cerebrospinal fluid (CSF). Although diagnostic CSF analysis seeks to establish pathological disturbances in the brain proper, CSF is generally sampled from the lumbar compartment for reasons of technical ease and ethical considerations. We here aimed to compare the molecular composition of CSF obtained from the ventricular versus the lumbar CSF compartments to establish a relevance for employing lumbar CSF as a proxy for the CSF bathing the brain tissue.

METHODS

CSF was collected from 46 patients with idiopathic normal pressure hydrocephalus (iNPH) patients during their diagnostic workup (lumbar samples) and in connection with their subsequent CSF diversion shunt surgery (ventricular samples). The mass-spectrometry-based proteomic profile was determined in these samples and in addition, selected biomarkers were quantified with ELISA (S100B, neurofilament light (NfL), amyloid-β (Aβ₄₀, Aβ₄₂), and total tau (T-tau) and phosphorylated tau (P-tau) forms). The latter analysis was extended to include paired porcine samples obtained from the lumbar compartment and the cerebromedullary cistern closely related to the ventricles.

RESULTS

In total 1231 proteins were detected in the human CSF. Of these, 216 distributed equally in the two CSF compartments, whereas 22 were preferentially (or solely) present in the ventricular CSF and four in the lumbar CSF. The selected biomarkers of neurodegeneration and Alzheimer's disease displayed differential distribution, some with higher (S100B, T-tau, and P-tau) and some with lower (NfL, Aβ₄₀, Aβ₄₂) levels in the ventricular compartment. In the porcine samples, all biomarkers were most abundant in the lumbar CSF.

CONCLUSIONS

The overall proteomic profile differs between the ventricular and the lumbar CSF compartments, and so does the distribution of clinically employed biomarkers. However, for a range of CSF proteins and biomarkers, one can reliably employ lumbar CSF as a proxy for ventricular CSF if or a lumbar/cranial index for the particular molecule has been established. It is therefore important to verify the compartmental preference of the proteins or biomarkers of interest prior to extrapolating from lumbar CSF to that of the ventricular fluid bordering the brain.

DPYD genotyping and dihydropyrimidine dehydrogenase (DPD) phenotyping in clinical oncology. A clinically focused minireview

BACKGROUND

In clinical oncology, systemic 5-fluorouracil (5-FU) and its oral pro-drugs are used to treat a broad group of solid tumours. Patients with dihydropyrimidine dehydrogenase (DPD) enzyme deficiency are at elevated risk of toxicity if treated with standard doses of 5-FU. DPYD genotyping and measurements of plasma uracil concentration (DPD phenotyping) can be applied as tests for DPD deficiency. In April 2020, the European Medicines Agency recommended pre-treatment DPD testing to reduce the risk of 5-FU-related toxicity.

OBJECTIVES

The objective of this study is to present the current evidence for DPD testing in routine oncological practice.

METHODS

Two systematic literature searches were performed following the PRISMA guidelines. We identified studies examining the possible benefit of DPYD genotyping or DPD phenotyping on the toxicity risk.

FINDINGS

Nine and 12 studies met the criteria for using DPYD genotyping and DPD phenotyping, respectively.

CONCLUSIONS

The evidence supporting either DPYD genotyping or DPD phenotyping as pre-treatment tests to reduce 5-FU toxicity is poor. Further evidence is still needed to fully understand and guide clinicians to dose by DPD activity.

Acute effects on glucose tolerance by neprilysin inhibition in patients with type 2 diabetes

AIMS

Sacubitril/valsartan is a neprilysin-inhibitor/angiotensin II receptor blocker used for the treatment of heart failure. Recently, a post-hoc analysis of a 3-year randomized controlled trial showed improved glycaemic control with sacubitril/valsartan in patients with heart failure and type 2 diabetes. We previously reported that sacubitril/valsartan combined with a dipeptidyl peptidase-4 inhibitor increases active glucagon-like peptide-1 (GLP-1) in healthy individuals. We now hypothesized that administration of sacubitril/valsartan with or without a dipeptidyl peptidase-4 inhibitor would lower postprandial glucose concentrations (primary outcome) in patients with type 2 diabetes via increased active GLP-1.

METHODS

We performed a crossover trial in 12 patients with obesity and type 2 diabetes. A mixed meal was ingested following five respective interventions: (a) a single dose of sacubitril/valsartan; (b) sitagliptin; (c) sacubitril/valsartan + sitagliptin; (d) control (no treatment); and (e) valsartan alone. Glucose, gut and pancreatic hormone responses were measured.

RESULTS

Postprandial plasma glucose increased by 57% (incremental area under the curve 0-240 min) (p = .0003) and increased peak plasma glucose by 1.7 mM (95% CI: 0.6-2.9) (p = .003) after sacubitril/valsartan compared with control, whereas postprandial glucose levels did not change significantly after sacubitril/valsartan + sitagliptin. Glucagon, GLP-1 and C-peptide concentrations increased after sacubitril/valsartan, but insulin and glucose-dependent insulinotropic polypeptide did not change.

CONCLUSIONS

The glucose-lowering effects of long-term sacubitril/valsartan treatment reported in patients with heart failure and type 2 diabetes may not depend on changes in entero-pancreatic hormones. Neprilysin inhibition results in hyperglucagonaemia and this may explain the worsen glucose tolerance observed in this study.

CLINICALTRIALS

gov (NCT03893526).

Amino Acid Metabolism and Protein Turnover in Lean and Obese Humans During Exercise-Effect of IL-6 Receptor Blockade

CONTEXT

Interleukin-6 (IL-6) is implicated in skeletal muscle wasting and in regulating skeletal muscle hypertrophy in the healthy state.

OBJECTIVE

This work aimed to determine the role of IL-6 in regulating systemic protein and amino acid metabolism during rest, exercise, and recovery in lean and obese humans.

METHODS

In a nonrandomized, single-blind design, 12 lean and 9 obese individuals were infused first with 0.9% saline (Saline), secondly with the IL-6 receptor antibody tocilizumab (Acute IL-6R ab), and 21 days later with saline while still under tocilizumab influence (Chronic IL-6R ab). Outcome measures were determined before, during, and after 90 minutes of exercise at 40% Wattmax by isotope dilution technique, using primed continuous infusion of L-[ring-D5]phenylalanine and L-[D2]tyrosine. Main outcomes measures included systemic protein turnover and plasma amino acid concentrations.

RESULTS

We saw no effect of acute or chronic IL-6 receptor blockade on protein turnover. In lean individuals, chronic IL-6 receptor blockade increased plasma concentrations of total amino acids (rest Δ + 186 μmol/L; 95% CI, 40-332; recovery Δ + 201 μmol/L; 95% CI, 55-347) and essential amino acids (rest Δ + 43 μmol/L; 95% CI, 12-76; recovery Δ + 45 μmol/L; 95% CI, 13-77) independently of exercise but had no such effect in obese individuals (total amino acids rest Δ + 63 μmol/L; 95% CI, -170 to 295, recovery Δ - 23 μmol/L, 95% CI, -256 to 210; essential amino acids rest Δ + 26 μmol/L; 95% CI, -21 to 73, recovery Δ + 11 μmol/L; 95% CI, -36 to 58).

CONCLUSION

IL-6 receptor blockade has no effect on protein turnover in fasting lean and obese humans during rest, exercise, and recovery. Chronic IL-6 receptor blockade increases total and essential amino acid concentrations only in lean individuals.

GDF15 is an exercise-induced hepatokine regulated by glucagon and insulin in humans

OBJECTIVE

Growth differentiation factor (GDF)-15 is implicated in regulation of metabolism and circulating GDF15 increases in response to exercise. The source and regulation of the exercise-induced increase in GDF15 is, however not known.

METHOD

Plasma GDF15 was measured by ELISA under the following conditions: 1) Arterial-to-hepatic venous differences sampled before, during, and after exercise in healthy male subjects (n=10); 2) exogenous glucagon infusion compared to saline infusion in resting healthy subjects (n=10); 3) an acute exercise bout with and without a pancreatic clamp (n=6); 4) healthy subjects for 36 hours (n=17), and 5) patients with anorexia nervosa (n=25) were compared to healthy age-matched subjects (n=25). Tissue GDF15 mRNA content was determined in mice in response to exhaustive exercise (n=16).

RESULTS

The splanchnic bed released GDF15 to the circulation during exercise and increasing the glucagon-to-insulin ratio in resting humans led to a 2.7-fold (P<0.05) increase in circulating GDF15. Conversely, inhibiting the exercise-induced increase in the glucagon-to-insulin ratio blunted the exercise-induced increase in circulating GDF15. Fasting for 36 hours did not affect circulating GDF15, whereas resting patients with anorexia nervosa displayed elevated plasma concentrations (1.4-fold, P<0.05) compared to controls. In mice, exercise increased GDF15 mRNA contents in liver, muscle, and adipose tissue.

CONCLUSION

In humans, GDF15 is a "hepatokine" which increases during exercise and is at least in part regulated by the glucagon-to-insulin ratio. Moreover, chronic energy deprivation is associated with elevated plasma GDF15, which supports that GDF15 is implicated in metabolic signalling in humans.

Ameliorating effects of lifelong physical activity on healthy aging and mitochondrial function in human white adipose tissue

Growing old is patently among the most prominent risk factors for lifestyle related diseases and deterioration in physical performance. Aging in particular affects mitochondrial homeostasis and maintaining a well-functioning mitochondrial pool is imperative in order to avoid age-associated metabolic decline. White adipose tissue (WAT) is a key organ in energy balance and impaired mitochondrial function in adipocytes has been associated with increased low-grade inflammation, altered metabolism, excessive ROS production and an accelerated aging phenotype. Exercise training improves mitochondrial health but whether lifelong exercise training can sufficiently maintain WAT mitochondrial function is currently unknown. Therefore, to dissect the role and dose-dependence of lifelong exercise training on aging WAT metabolic parameters and mitochondrial function, young and older untrained, as well as moderately and highly exercise trained older male subjects were recruited and abdominal subcutaneous (s)WAT biopsies and venous blood samples were obtained to measure mitochondrial function and key metabolic factors in WAT and plasma. Mitochondrial intrinsic respiratory capacity was lower in sWAT from older than in young subjects. In spite of this, maximal mitochondrial respiration per wet weight, markers of oxidative capacity, and mitophagic capacity were increased in sWAT from lifelong highly exercise trained than all other groups. Furthermore, ROS emission was generally lower in sWAT from lifelong highly exercise trained than older untrained subjects. Taken together, aging reduces intrinsic mitochondrial respiration in human sWAT, but lifelong high volume exercise training increases oxidative capacity by increasing mitochondrial volume likely contributing to healthy aging.

The Regulation of Circulating Hepatokines by Fructose Ingestion in Humans

Context

Fibroblast growth factor 21 (FGF21), follistatin, angiopoietin-like 4 (ANGPTL4), and growth differential factor 15 (GDF15) are regulated by energy metabolism. Recent findings in humans demonstrate that fructose ingestion increases circulating FGF21, with increased response in conditions of insulin resistance.

Objective

This study examines the acute effect of fructose and somatostatin on circulating FGF21, follistatin, ANGPTL4, and GDF15 in humans.

Methods

Plasma FGF21, follistatin, ANGPTL4, and GDF15 concentrations were measured in response to oral ingestion of 75 g of fructose in 10 young healthy males with and without a 15-minute infusion of somatostatin to block insulin secretion. A control infusion of somatostatin was also performed in the same subjects.

Results

Following fructose ingestion, plasma FGF21 peaked at 3.7-fold higher than basal concentration (P < 0.05), and it increased 4.9-fold compared with basal concentration (P < 0.05) when somatostatin was infused. Plasma follistatin increased 1.8-fold after fructose ingestion (P < 0.05), but this increase was blunted by concomitant somatostatin infusion. For plasma ANGPTL4 and GDF15, no increases were obtained following fructose ingestion. Infusion of somatostatin alone slightly increased plasma FGF21 and follistatin.

Conclusion

Here we show that in humans (1) the fructose-induced increase in plasma FGF21 was enhanced when somatostatin was infused, suggesting an inhibitory role of insulin on the fructose-induced FGF21 increase; (2) fructose ingestion also increased plasma follistatin, but somatostatin infusion blunted the increase; and (3) fructose ingestion had no stimulating effect on ANGPTL4 and GDF15 levels, demonstrating differences in the hepatokine response to fructose ingestion.

Neprilysin Inhibition Increases Glucagon Levels in Humans and Mice With Potential Effects on Amino Acid Metabolism

Context

Inhibitors of the protease neprilysin (NEP) are used for treating heart failure, but are also linked to improvements in metabolism. NEP may cleave proglucagon-derived peptides, including the glucose and amino acid (AA)-regulating hormone glucagon. Studies investigating NEP inhibition on glucagon metabolism are warranted.

Objective

This work aims to investigate whether NEP inhibition increases glucagon levels.

Methods

Plasma concentrations of glucagon and AAs were measured in eight healthy men during a mixed meal with and without a single dose of the NEP inhibitor/angiotensin II type 1 receptor antagonist, sacubitril/valsartan (194 mg/206 mg). Long-term effects of sacubitril/valsartan (8 weeks) were investigated in individuals with obesity (n = 7). Mass spectrometry was used to investigate NEP-induced glucagon degradation, and the derived glucagon fragments were tested pharmacologically in cells transfected with the glucagon receptor (GCGR). Genetic deletion or pharmacological inhibition of NEP with or without concomitant GCGR antagonism was tested in mice to evaluate effects on AA metabolism.

Results

In healthy men, a single dose of sacubitril/valsartan significantly increased postprandial concentrations of glucagon by 228%, concomitantly lowering concentrations of AAs including glucagonotropic AAs. Eight-week sacubitril/valsartan treatment increased fasting glucagon concentrations in individuals with obesity. NEP cleaved glucagon into 5 inactive fragments (in vitro). Pharmacological NEP inhibition protected both exogenous and endogenous glucagon in mice after an AA challenge, while NEP-deficient mice showed elevated fasting and AA-stimulated plasma concentrations of glucagon and urea compared to controls.

Conclusion

NEP cleaves glucagon, and inhibitors of NEP result in hyperglucagonemia and may increase postprandial AA catabolism without affecting glycemia.

Glycogen supercompensation is due to increased number, not size, of glycogen particles in human skeletal muscle

NEW FINDINGS

What is the central question of this study? Glycogen supercompensation after glycogen-depleting exercise can be achieved by consuming a carbohydrate-enriched diet, but the associated effects on the size, number and localization of intramuscular glycogen particles are unknown. What is the main finding and its importance? Using transmission electron microscopy to inspect individual glycogen particles visually, we show that glycogen supercompensation is achieved by increasing the number of particles while keeping them at submaximal sizes. This might be a strategy to ensure that glycogen particles can be used fast, because particles that are too large might impair utilization rate.

ABSTRACT

Glycogen supercompensation after glycogen-depleting exercise can be achieved by consuming a carbohydrate-enriched diet, but the associated effects on the size, number and localization of intramuscular glycogen particles are unknown. We investigated how a glycogen-loading protocol affects fibre type-specific glycogen volume density, particle diameter and numerical density in three subcellular pools: between (intermyofibrillar) or within (intramyofibrillar) the myofibrils or beneath the sarcolemma (subsarcolemmal). Resting muscle biopsies from 11 physically active men were analysed using transmission electron microscopy after mixed (MIX), LOW or HIGH carbohydrate consumption separated by glycogen-lowering cycling at 75% of maximal oxygen consumption until exhaustion. After HIGH, the total volumetric glycogen content was 40% [95% confidence interval 16, 68] higher than after MIX in type I fibres (P < 0.001), with little to no difference in type II fibres (9% [95% confidence interval -9, 27]). Median particle diameter was 22.5 (interquartile range 20.8-24.7) nm across glycogen pools and fibre types, and the numerical density was 61% [25, 107] and 40% [9, 80] higher in the subsarcolemmal (P < 0.001) and intermyofibrillar (P < 0.01) pools of type I fibres, respectively, with little to no difference in the intramyofibrillar pool (3% [-20, 32]). In LOW, total glycogen was in the range of 21-23% lower, relative to MIX, in both fibre types, reflected in a 21-46% lower numerical density across pools. In comparison to MIX, particle diameter was unaffected by other diets ([-1.4, 1.3] nm). In conclusion, glycogen supercompensation after prolonged cycling is exclusive to type I fibres, predominantly in the subsarcolemmal pool, and involves an increase in the numerical density rather than the size of existing glycogen particles.

Quantification of biotin in plasma samples by column switching liquid chromatography - tandem mass spectrometry

Biotin (or Vitamin B7) is a vitamin where deficiency can be caused by inadequate intake. Biotin deficiency is rare, as most people get enough biotin from diet, since many foods contain biotin. In addition to biotin from food, intestinal bacteria can synthesize biotin, which can then be absorbed by the body. Supplementation with biotin has been advocated, mainly due to proposed beneficial effects on skin, nail and hair growth. There is no evidence that high biotin intakes are toxic, but a high intake may interfere with diagnostic assays that use biotin-streptavidin technology. These tests are commonly used to measure plasma concentrations of a wide range of hormones. Erroneous results may lead to misdiagnosis of various endocrine disorders. Supplementation with high-dose biotin has been used experimental for the treatment of diseases (e.g. multiple sclerosis) and high doses are used to obtain effect on nail and hair growth. On this background a demand for tests to determine if there is a risk of obtaining false test results when using biotin-streptavidin based tests have appeared. In this paper we present a method based on column switching liquid chromatography tandem mass spectrometry for the quantification of biotin in plasma and serum and explore the effects of biotin on an immunoassay based on biotin strept(avidin) chemistry.

S100B and brain derived neurotrophic factor in monozygotic twins with, at risk of and without affective disorders

BACKGROUND

The calcium binding protein S100B and brain derived neurotrophic factor (BDNF) are both biomarkers implicated in neuronal processes in the central nervous system and seem to be associated with affective disorders. Here we investigated both markers in a sample of monozygotic (MZ) twins with, at risk of and without affective disorders, aiming to evaluate whether these markers have a role as causal factors- or trait markers for affective disorders.

METHOD

We measured serum S100B and plasma BDNF levels in 204 monozygotic twins (MZ) with unipolar or bipolar disorder in remission or partial remission (affected), their unaffected co-twins (high-risk) and twins with no personal or family history of affective disorder (low-risk).

RESULTS

No significant group differences in S100B and BDNF levels were found between the three groups. Exploratory analysis revealed that higher S100B levels were correlated with lower cognitive performance.

LIMITATIONS

The cross-sectional design cannot elucidate the two neuronal biomarkers role as causal factors. We would have preferred a higher sample size in the high- and low-risk groups.

CONCLUSION

The present result did not support a role for S100B and BDNF as neither causal factors nor trait markers for affective disorders. Elevated S100B levels may associate with impaired cognition, but further studies are warranted.

Effect of insulin on natriuretic peptide gene expression in porcine heart

Gut hormones affect cardiac function and contractility. In this study, we examined whether insulin affects the cardiac atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) gene expression and release of proANP-derived peptides in pigs. Anaesthetized pigs were included in an experimental study comparing the effect of hyperinsulinemia in 15 pigs submitted to two different protocols versus 11 control pigs receiving saline infusion. Phosphorylation of Akt on Thr308 was determined by western blotting with a pAkt-Thr308 antibody. The mRNA contents of ANP and BNP were determined with real-time PCR; plasma and cardiac tissue proANP was measured with an immunoluminometric assay targeted against the mid-region of the propeptide and a processing-independent assay. Insulin stimulation increased phosphorylation of Akt Thr308 in both left atrium and left ventricle of porcine hearts (p < 0.005). No change was observed in ANP and BNP mRNA contents in the right or left atrium. BNP mRNA contents in the left ventricle, however, decreased 3-fold (p = 0.02) compared to control animals, whereas the BNP mRNA content in the right ventricle as well as ANP mRNA content in the right and left ventricle did not change following hyperinsulinemia. Moreover, the peptide contents did not change in the four cardiac chambers. Finally, proANP concentrations in plasma did not change during the insulin infusion compared to the control animals. These results suggest that insulin does not have direct effect on atrial natriuretic peptide expression but may have a role in the left ventricle.

Heterogeneity in subcellular muscle glycogen utilisation during exercise impacts endurance capacity in men

KEY POINTS

When muscle biopsies first began to be used routinely in research on exercise physiology five decades ago, it soon become clear that the muscle content of glycogen is an important determinant of exercise performance. Glycogen particles are stored in distinct pools within the muscles, but the role of each pool during exercise and how this is affected by diet is unknown. Here, the effects of diet and exercise on these pools, as well as their relation to endurance during prolonged cycling were examined. We demonstrate here that an improved endurance capacity with high carbohydrate loading is associated with a temporal shift in the utilisation of the distinct stores of glycogen pools and is closely linked to the content of the glycogen pool closest to actin and myosin (intramyofibrillar glycogen). These findings highlight the functional importance of distinguishing between different subcellular microcompartments of glycogen in individual muscle fibres.

ABSTRACT

In muscle cells, glycogen is stored in three distinct subcellular pools: between or within myofibrils (inter- and intramyofibrillar glycogen, respectively) or beneath the sarcolemma (subsarcolemmal glycogen) and these pools may well have different functions. Here, we investigated the effect of diet and exercise on the content of these distinct pools and their relation to endurance capacity in type 1 and 2 muscle fibres. Following consumption of three different diets (normal, mixed diet = MIX, high in carbohydrate = HIGH, or low in carbohydrate = LOW) for 72 h, 11 men cycled at 75% of V ̇ O 2 max until exhaustion. The volumetric content of the glycogen pools in muscle biopsies obtained before, during, and after exercise were quantified by transmission electron micrographs. The mean (SD) time to exhaustion was 150 (30), 112 (22), and 69 (18) minutes in the HIGH, MIX and LOW trials, respectively (P < 0.001). As shown by multiple regression analyses, the intramyofibrillar glycogen content in type 1 fibres, particularly after 60 min of exercise, correlated most strongly with time to exhaustion. In the HIGH trial, intramyofibrillar glycogen was spared during the initial 60 min of exercise, which was associated with levels and utilisation of subsarcolemmal glycogen above normal. In all trials, utilisation of subsarcolemmal and intramyofibrillar glycogen was more pronounced than that of intermyofibrillar glycogen in relative terms. In conclusion, the muscle pool of intramyofibrillar glycogen appears to be the most important for endurance capacity in humans. In addition, a local abundance of subsarcolemmal glycogen reduces the utilisation of intramyofibrillar glycogen during exercise.

Are remitted affective disorders and familial risk of affective disorders associated with metabolic syndrome, inflammation and oxidative stress? - a monozygotic twin study

BACKGROUND

Metabolic syndrome (MetS) is associated with reduced life expectancy in patients with affective disorders, however, whether MetS also plays a role before the onset of affective disorder is unknown. We aimed to investigate whether MetS, inflammatory markers or oxidative stress act as risk factors for affective disorders, and whether MetS is associated with increased inflammation and oxidative stress.

METHODS

We conducted a high-risk study including 204 monozygotic (MZ) twins with unipolar or bipolar disorder in remission or partial remission (affected), their unaffected co-twins (high-risk) and twins with no personal or family history of affective disorder (low-risk). Metabolic Syndrome was ascertained according to the International Diabetes Federation (IDF) criteria. Inflammatory markers and markers of oxidative stress were analyzed from fasting blood and urine samples, respectively.

RESULTS

The affected and the high-risk group had a significantly higher prevalence of MetS compared to the low-risk group (20% v. 15% v. 2.5%, p = 0.0006), even after adjusting for sex, age, smoking and alcohol consumption. No differences in inflammatory and oxidative markers were seen between the three groups. Further, MetS was associated with alterations in inflammatory markers, and oxidative stress was modestly correlated with inflammation.

CONCLUSION

Metabolic syndrome is associated with low-grade inflammation and may act as a risk factor and a trait marker for affective disorders. If confirmed in longitudinal studies, this suggests the importance of early intervention and preventive approaches targeted towards unhealthy lifestyle factors that may contribute to later psychopathology.

Identification and regulation of the xenometabolite derivatives cis- and trans-3,4-methylene-heptanoylcarnitine in plasma and skeletal muscle of exercising humans

Little is known about xenometabolites in human metabolism, particularly under exercising conditions. Previously, an exercise-modifiable, likely xenometabolite derivative, cis-3,4-methylene-heptanoylcarnitine, was reported in human plasma. Here, we identified trans-3,4-methylene-heptanoylcarnitine, and its cis-isomer, in plasma and skeletal muscle by liquid chromatography-mass spectrometry. We analyzed the regulation by exercise and the arterial-to-venous differences of these cyclopropane ring-containing carnitine esters over the hepatosplanchnic bed and the exercising leg in plasma samples obtained in three separate studies from young, lean and healthy males. Compared with other medium-chain acylcarnitines, the plasma concentrations of the 3,4-methylene-heptanoylcarnitine isomers only marginally increased with exercise. Both isomers showed a more than twofold increase in the skeletal muscle tissue of the exercising leg; this may have been due to the net effect of fatty acid oxidation in the exercising muscle and uptake from blood. The latter idea is supported by a more than twofold increased net uptake in the exercising leg only. Both isomers showed a constant release from the hepatosplanchnic bed, with an increased release of the trans-isomer after exercise. The isomers differ in their plasma concentration, with a four times higher concentration of the cis-isomer regardless of the exercise state. This is the first approach studying kinetics and fluxes of xenolipid isomers from tissues under exercise conditions, supporting the hypothesis that hepatic metabolism of cyclopropane ring-containing fatty acids is one source of these acylcarnitines in plasma. The data also provide clear evidence for an exercise-dependent regulation of xenometabolites, opening perspectives for future studies about the physiological role of this largely unknown class of metabolites.

Sacubitril/valsartan increases postprandial gastrin and cholecystokinin in plasma

AIMS

Neprilysin degrades natriuretic peptides in circulation and is also suggested to degrade the gut hormones gastrin and cholecystokinin. Neprilysin inhibition has become a therapeutic strategy and thus a regimen in need of further testing in terms of other hormonal axes besides natriuretic peptides. The aim of this study was to examine whether acute inhibition of neprilysin affects meal-induced responses in gastrin and cholecystokinin concentrations in healthy individuals.

METHODS AND RESULTS

Nine healthy young men were included in an open-labelled, randomized cross-over clinical trial. The participants received a standardized meal (25 g fat, 26 g protein, 42 g carbohydrate) on two separate days with or without a one-time dosage of sacubitril ((194 mg)/valsartan (206 mg)). Blood pressure, heart rate and blood samples were measured and collected during the experiment. Statistical differences between groups were assessed using area under the curve together with an ANOVA with a Bonferroni post hoc test. Sacubitril/valsartan increased the postprandial plasma concentrations of both gastrin and cholecystokinin (80% (AUC0-270 min, P = 0.004) and 60% (AUC0-270 min, P = 0.003), respectively) compared with the control meal. No significant hemodynamic effects were noted (blood pressure, AUC0-270 min, P = 0.86, heart rate, AUC0-270 min, P = 0.96).

CONCLUSION

Our study demonstrates that sacubitril/valsartan increases the postprandial plasma concentrations of gastrin and cholecystokinin in healthy individuals. The results thus suggest that neprilysin-mediated degradation of gastrin and cholecystokinin is physiologically relevant and may have a role in heart failure patients treated with sacubitril/valsartan.

Muscle-Liver Substrate Fluxes in Exercising Humans and Potential Effects on Hepatic Metabolism

CONTEXT

The liver is crucial to maintain energy homeostasis during exercise. Skeletal muscle-derived metabolites can contribute to the regulation of hepatic metabolism.

OBJECTIVE

We aim to elucidate which metabolites are released from the working muscles and taken up by the liver in exercising humans and their potential influence on hepatic function.

METHODS

In two separate studies, young healthy men fasted overnight and then performed an acute bout of exercise. Arterial-to-venous differences of metabolites over the hepato-splanchnic bed and over the exercising and resting leg were investigated by capillary electrophoresis- and liquid chromatography-mass spectrometry metabolomics platforms. Liver transcriptome data of exercising mice were analyzed by pathway analysis to find a potential overlap between exercise-regulated metabolites and activators of hepatic transcription.

RESULTS

During exercise, hepatic O2 uptake and CO2 delivery were increased two-fold. In contrast to all other free fatty acids (FFA), those FFA with 18 or more carbon atoms and a high degree of saturation showed a constant release in the liver vein and only minor changes by exercise. FFA 6:0 and 8:0 were released from the working leg and taken up by the hepato-splanchnic bed. Succinate and malate showed a pronounced hepatic uptake during exercise and were also released from the exercising leg. The transcriptional response in the liver of exercising mice indicates the activation of HIF-, NRF2-, and cAMP-dependent gene transcription. These pathways can also be activated by succinate.

CONCLUSION

Metabolites circulate between working muscles and the liver and may support the metabolic adaption to exercise by acting both as substrates and as signaling molecules.

Early Life Exposures to Perfluoroalkyl Substances in Relation to Adipokine Hormone Levels at Birth and During Childhood

BACKGROUND

Birth cohort studies have linked exposure to perfluoroalkyl substances (PFASs) with child anthropometry. Metabolic hormone dysregulation needs to be considered as a potential adverse outcome pathway. We examined the associations between PFAS exposures and concentrations of adipokine hormones from birth to adolescence.

METHODS

We studied 80 mother-child pairs from a Faroese cohort born in 1997 to 2000. Five PFASs were measured in maternal pregnancy serum and in child serum at ages 5, 7, and 13 years. Leptin, adiponectin, and resistin were analyzed in cord serum and child serum at the same ages. We fitted multivariable-adjusted generalized estimating equations to assess the associations of PFASs at each age with repeated adipokine concentrations at concurrent and subsequent ages.

RESULTS

We observed tendencies of inverse associations between PFASs and adipokine hormones specific to particular ages and sex. Significant associations with all adipokines were observed for maternal and child 5-year serum PFAS concentrations, whereas associations for PFASs measured at ages 7 to 13 years were mostly null. The inverse associations with leptin and adiponectin were seen mainly in females, whereas the inverse PFAS associations with resistin levels were seen mainly in males. Estimates for significant associations (P value <0.05) suggested mean decreases in hormone levels (range) by 38% to 89% for leptin, 16% to 70% for adiponectin, and 33% to 62% for resistin for each twofold increase in serum PFAS concentration.

CONCLUSIONS

These findings suggest adipokine hormone dysregulation in early life as a potential pathway underlying PFAS-related health outcomes and underscore the need to further account for susceptibility windows and sex-dimorphic effects in future investigations.

Sacubitril/valsartan augments postprandial plasma concentrations of active GLP-1 when combined with sitagliptin in men

CONTEXT

Combined inhibition of neprilysin and dipeptidyl peptidase 4 (DPP-4) has been shown to augment plasma concentrations of glucagon-like peptide-1(GLP-1) in animal models, but whether this occurs in humans is unknown.

OBJECTIVE

To investigate the effects of inhibition of neprilysin by sacubitril/valsartan alone or in combination with a DPP-4 inhibitor (sitagliptin) on plasma concentrations of GLP-1 in healthy men.

DESIGN

Two open-labeled crossover studies were performed in human subjects.

SETTING

General community.

PARTICIPANTS

Nine and 10 healthy young males were included in study 1 and study 2, respectively.

INTERVENTION

Study participants received a standardized meal (34% carbohydrates, 45% fat, 21% protein, total caloric content of 2106kJ) combined with a prior dose of either sacubitril/valsartan (194/206mg) or control in study 1, and in study 2, with a prior dose of sitagliptin (2x100mg, given ∼10 hours apart) either alone or with sacubitril/valsartan (194/206mg).

MAIN OUTCOME MEASURES

Plasma concentrations of total and intact GLP-1.

RESULTS

Sacubitril/valsartan increased postprandial plasma concentrations of total GLP-1 by 67% (tAUC0-240min: 3929±344 vs. 2348±181 min × pmol/L P=0.0023), and increased concentrations of intact GLP-1 plasma concentrations more than sitagliptin alone (tAUC0-240min: 1021±114 vs. 660±80 min × pmol/L, P=0.01). Plasma concentrations of glucose, insulin, and GIP were not significantly (P>0.10) changed upon sacubitril/valsartan treatment.

CONCLUSIONS

Sacubitril/valsartan combined with a DPP-4 inhibitor lead to markedly higher concentrations of intact GLP-1 than DPP-4 inhibition alone, supporting a role for both neprilysin and DPP-4 in the metabolism of GLP-1 in humans, a finding which may have therapeutic implications.

Nasal insulin administration does not affect hepatic glucose production at systemic fasting insulin levels

AIMS

To evaluate the effects of brain insulin on endogenous glucose production in fasting humans, with a focus on hepatic glucose release by performing a randomized, placebo-controlled, blinded, crossover experiment.

MATERIALS AND METHODS

On two separate days, ² H₂ -glucose was infused to nine healthy lean men, and blood was sampled from the hepatic vein and a radial artery. On day 1, participants received 160 U human insulin through nasal spray, and on day 2 they received placebo spray, together with an intravenous insulin bolus to mimic spillover of nasal insulin to the circulation. Hepatic glucose fluxes and endogenous glucose production were calculated.

RESULTS

Plasma insulin concentrations were similar on the two study days, and no differences in whole-body endogenous glucose production or hepato-splanchnic glucose turnover were detected.

CONCLUSIONS

Nasal administration of insulin does not influence whole-body or hepatic glucose production in fasting humans. By contrast, pharmacological delivery of insulin to the brain might modulate insulin effectiveness in glucose-producing tissue when circulating insulin levels are elevated; therefore, the metabolic consequences of brain insulin action appear to be dependent on metabolic prandial status.

Training state and skeletal muscle autophagy in response to 36 h of fasting

The present study aimed at investigating fasting-induced responses in regulators and markers of autophagy in vastus lateralis muscle from untrained and trained human subjects. Untrained and trained subjects (based on maximum oxygen uptake, muscle citrate synthase activity, and oxidative phosphorylation protein level) fasted for 36 h with vastus lateralis muscle biopsies obtained at 2, 12, 24, and 36 h after a standardized meal. Fasting reduced ( P < 0.05) skeletal muscle microtubule-associated protein-1A/1B light chain 3 (LC3)I, LC3II, and adaptor protein sequestosome 1/p62 protein content in untrained subjects only. Moreover, skeletal muscle RAC-alpha serine/threonine-protein kinase (AKT)Thr308, AMP-activated protein kinase (AMPK)Thr172, and Unc-51-like autophagy-activating kinase-1 (ULK1)Ser555 phosphorylation state, as well as Bcl-2-interacting coiled-coil protein-1 (Beclin1) and ULK1Ser757 phosphorylation, was lower ( P < 0.05) in trained than untrained subjects during fasting. In addition, the plasma concentrations of several amino acids were higher ( P < 0.05) in trained than untrained subjects, and the plasma concentration profile of several amino acids was different in untrained and trained subjects during fasting. Taken together, these findings suggest that 36-h fasting has effects on some mediators of autophagy in untrained human skeletal muscle and that training state influences the effect of fasting on autophagy signaling and on mediators of autophagy in skeletal muscle.

NEW & NOTEWORTHY This study showed that skeletal muscle autophagy was only modestly affected in humans by 36 h of fasting. Hence, 36-h fasting has effects on some mediators of autophagy in untrained human skeletal muscle, and training state influences the effect of fasting on autophagy signaling and on mediators of autophagy in skeletal muscle.

Hepatokines-a novel group of exercise factors

Regular physical activity not only improves the exercise capacity of the skeletal muscle performing the contractions, but it is beneficial for the whole body. An extensive search for "exercise factors" mediating these beneficial effects has been going on for decades. Particularly skeletal muscle tissue has been investigated as a source of circulating exercise factors, and several myokines have been identified. However, exercise also has an impact on other tissues. The liver is interposed between energy storing and energy utilising tissues and is highly active during exercise, maintaining energy homeostasis. Recently, a novel group of exercise factors-termed hepatokines-has emerged. These proteins (fibroblast growth factor 21, follistatin, angiopoietin-like protein 4, heat shock protein 72, insulin-like growth factor binding protein 1) are released from the liver and increased in the bloodstream during or in the recovery after an exercise bout. In this narrative review, we evaluate this new group of exercise factors focusing on the regulation and potential function in exercise metabolism and adaptations. These hepatokines may convey some of the beneficial whole-body effects of exercise that could ameliorate metabolic diseases, such as obesity or type 2 diabetes.

Cardiac procholecystokinin expression during haemodynamic changes in the mammalian heart

Cardiac myocytes express the cholecystokinin gene (CCK) at propeptide level. We recently reported that cardiac CCK expression is acutely regulated by isoprenaline in a porcine model. The regulation of CCK expression after myocardial infarction, in exercise, and in severe heart failure is, however, unknown. Cardiac tissue was obtained from healthy new-born and adolescent farm pigs. Myocardial infarction was induced by coronary artery occlusion in adult minipigs. Healthy male subjects performed a 3-hour exercise test, and patients with severe heart failure referred for right heart catheterization were included. Extracts of porcine cardiac tissue and human plasma were analysed with specific proCCK radioimmunoassays. Cardiac proCCK expression shifted from the right atrium in new-born piglets to include the left atrium in adolescent pigs. Regional proCCK expression in the adolescent pig heart was mainly confined to the atria without different expression in sinus node tissue. In adult minipigs with myocardial infarction, no changes in overall left ventricular function or proCCK expression were observed after 8 weeks. In healthy adults, proCCK in circulation increased markedly during exercise in parallel with pro-B-type natriuretic peptide. Finally, patients with severe heart failure displayed markedly increased proCCK - but not CCK - concentrations in plasma. Taken together, our data shows that regional proCCK expression reflects haemodynamic changes in the mammalian heart. The data supports the notion that cardiac CCK expression resembles that of cardiac natriuretic peptides in atria. The ventricular content of proCCK, however, differs from natriuretic peptides and suggests a distinct secretory pathway in ventricular cardiomyocytes.

Changes in metabolism but not myocellular signaling by training with CHO-restriction in endurance athletes

Carbohydrate (CHO) restricted training has been shown to increase the acute training response, whereas less is known about the acute effects after repeated CHO restricted training. On two occasions, the acute responses to CHO restriction were examined in endurance athletes. Study 1 examined cellular signaling and metabolic responses after seven training-days including CHO manipulation (n = 16). The protocol consisted of 1 h high-intensity cycling, followed by 7 h recovery, and 2 h of moderate-intensity exercise (120SS). Athletes were randomly assigned to low (LCHO: 80 g) or high (HCHO: 415 g) CHO during recovery and the 120SS. Study 2 examined unaccustomed exposure to the same training protocol (n = 12). In Study 1, muscle biopsies were obtained at rest and 1 h after 120SS, and blood samples drawn during the 120SS. In Study 2, substrate oxidation and plasma glucagon were determined. In Study 1, plasma insulin and proinsulin C-peptide were higher during the 120SS in HCHO compared to LCHO (insulin: 0 min: +37%; 60 min: +135%; 120 min: +357%, P = 0.05; proinsulin C-peptide: 0 min: +32%; 60 min: +52%; 120 min: +79%, P = 0.02), whereas plasma cholesterol was higher in LCHO (+15-17%, P = 0.03). Myocellular signaling did not differ between groups. p-AMPK and p-ACC were increased after 120SS (+35%, P = 0.03; +59%, P = 0.0004, respectively), with no alterations in p-p38, p-53, or p-CREB. In Study 2, glucagon and fat oxidation were higher in LCHO compared to HCHO during the 120SS (+26-40%, P = 0.03; +44-76%, P = 0.01 respectively). In conclusion, the clear respiratory and hematological effects of CHO restricted training were not translated into superior myocellular signaling after accustomization to CHO restriction.

Regulation of apoptosis and autophagy in mouse and human skeletal muscle with aging and lifelong exercise training

Exercise training has been reported to prevent the age-induced decline in muscle mass and fragmentation of mitochondria, as well as to affect autophagy and mitophagy. The interaction between these pathways during aging as well as the similarity between such changes in human and mouse skeletal muscle is however not fully understood. Therefore the aim of the present study was to test the hypothesis that cellular degradation pathways, including apoptosis, autophagy and mitophagy are coordinately regulated in mouse and human skeletal muscle during aging and lifelong exercise training through a PGC-1α-p53 axis. Muscle samples were obtained from young untrained, aged untrained and aged lifelong exercise trained men, and from whole-body PGC-1α knockout mice and their littermate controls that were either lifelong exercise trained or sedentary young and aged. Lifelong exercise training prevented the aging-induced reduction in PGC-1α, p53 and p21 mRNA as well as the increase in LC3II and BNIP3 protein in mouse skeletal muscle, while aging decreased the BAX/Bcl-2 ratio, LC3I and BAX protein in mouse skeletal muscle without effects of lifelong exercise training. In humans, aging was associated with reduced PGC-1α mRNA as well as decreased p62 and p21 protein in skeletal muscle, while lifelong exercise training increased BNIP3 protein and decreased p53 mRNA. In conclusion, there was a divergent regulation of autophagy and apoptosis in mouse muscle with aging and lifelong exercise training, whereas healthy aged human skeletal muscle seemed rather robust to changes in apoptosis, autophagy and mitophagy markers compared with mouse muscle at the investigated age.

Angiogenin and Osteoprotegerin are type II muscle specific myokines protecting pancreatic beta-cells against proinflammatory cytokines

Tissue cross-talk is emerging as a determinant way to coordinate the different organs implicated in glucose homeostasis. Among the inter-organ communication factors, muscle-secreted myokines can modulate the function and survival of pancreatic beta-cells. Using primary human myotubes from soleus, vastus lateralis and triceps brachii muscles, we report here that the impact of myokines on beta-cells depends on fiber types and their metabolic status. We show that Type I and type II primary myotubes present specific mRNA and myokine signatures as well as a different sensitivity to TNF-alpha induced insulin resistance. Finally, we show that angiogenin and osteoprotegerin are triceps specific myokines with beta-cell protective actions against proinflammatory cytokines. These results suggest that type I and type II muscles could impact insulin secretion and beta-cell mass differentially in type 2 diabetes through specific myokines secretion.

Quality Control of Serum and Plasma by Quantification of (4E,14Z)-Sphingadienine-C18-1-Phosphate Uncovers Common Preanalytical Errors During Handling of Whole Blood

BACKGROUND

Nonadherence to standard operating procedures (SOPs) during handling and processing of whole blood is one of the most frequent causes affecting the quality of serum and plasma. Yet, the quality of blood samples is of the utmost importance for reliable, conclusive research findings, valid diagnostics, and appropriate therapeutic decisions.

METHODS

UHPLC-MS-driven nontargeted metabolomics was applied to identify biomarkers that reflected time to processing of blood samples, and a targeted UHPLC-MS analysis was used to quantify and validate these biomarkers.

RESULTS

We found that (4E,14Z)-sphingadienine-C18-1-phosphate (S1P-d18:2) was suitable for the reliable assessment of the pronounced changes in the quality of serum and plasma caused by errors in the phase between collection and centrifugation of whole blood samples. We rigorously validated S1P-d18:2, which included the use of practicality tests on >1400 randomly selected serum and plasma samples that were originally collected during single- and multicenter trials and then stored in 11 biobanks in 3 countries. Neither life-threatening disease states nor strenuous metabolic challenges (i.e., high-intensity exercise) affected the concentration of S1P-d18:2. Cutoff values for sample assessment were defined (plasma, ≤0.085 μg/mL; serum, ≤0.154 μg/mL).

CONCLUSIONS

Unbiased valid monitoring to check for adherence to SOP-dictated time for processing to plasma or serum and/or time to storage of whole blood at 4 °C is now feasible. This novel quality assessment step could enable scientists to uncover common preanalytical errors, allowing for identification of serum and plasma samples that should be excluded from certain investigations. It should also allow control of samples before long-term storage in biobanks.

No Superior Adaptations to Carbohydrate Periodization in Elite Endurance Athletes

PURPOSE

The present study investigated the effects of periodic carbohydrate (CHO) restriction on endurance performance and metabolic markers in elite endurance athletes.

METHODS

Twenty-six male elite endurance athletes (maximal oxygen consumption (V˙O2max), 65.0 mL O2·kg·min) completed 4 wk of regular endurance training while being matched and randomized into two groups training with (low) or without (high) CHO manipulation 3 d·wk. The CHO manipulation days consisted of a 1-h high-intensity bike session in the morning, recovery for 7 h while consuming isocaloric diets containing either high CHO (414 ± 2.4 g) or low CHO (79.5 ± 1.0 g), and a 2-h moderate bike session in the afternoon with or without CHO. V˙O2max, maximal fat oxidation, and power output during a 30-min time trial (TT) were determined before and after the training period. The TT was undertaken after 90 min of intermittent exercise with CHO provision before the training period and both CHO and placebo after the training period. Muscle biopsies were analyzed for glycogen, citrate synthase (CS) and β-hydroxyacyl-coenzyme A dehydrogenase (HAD) activity, carnitine palmitoyltransferase (CPT1b), and phosphorylated acetyl-CoA carboxylase (pACC).

RESULTS

The training effects were similar in both groups for all parameters. On average, V˙O2max and power output during the 30-min TT increased by 5% ± 1% (P < 0.05) and TT performance was similar after CHO and placebo during the preload phase. Training promoted overall increases in glycogen content (18% ± 5%), CS activity (11% ± 5%), and pACC (38% ± 19%; P < 0.05) with no differences between groups. HAD activity and CPT1b protein content remained unchanged.

CONCLUSIONS

Superimposing periodic CHO restriction to 4 wk of regular endurance training had no superior effects on performance and muscle adaptations in elite endurance athletes.

Impact of training state on fasting-induced regulation of adipose tissue metabolism in humans

Recruitment of fatty acids from adipose tissue is increased during fasting. However, the molecular mechanisms behind fasting-induced metabolic regulation in human adipose tissue and the potential impact of training state in this are unknown. Therefore the aim of the present study was to investigate 1) fasting-induced regulation of lipolysis and glyceroneogenesis in human adipose tissue as well as 2) the impact of training state on basal oxidative capacity and fasting-induced metabolic regulation in human adipose tissue. Untrained [maximal oxygen uptake (V̇o_2max) < 45 ml·min^-1·kg^-1] and trained subjects (V̇o_2max > 55 ml·min^-1·kg^-1) fasted for 36 h, and abdominal subcutaneous adipose tissue biopsies were obtained 2, 12, 24, and 36 h after a standardized meal. Adipose tissue oxidative phosphorylation complexes, phosphoenolpyruvate carboxykinase, and pyruvate dehydrogenase (PDH)-E1α protein as well as PDH kinase (PDK) 2, PDK4, and PDH phosphatase 2 mRNA content were higher in trained subjects than in untrained subjects. In addition, trained subjects had higher adipose tissue hormone-sensitive lipase Ser660 phosphorylation and adipose triglyceride lipase protein content as well as higher plasma free fatty acid concentration than untrained subjects during fasting. Moreover, adipose tissue PDH phosphorylation increased with fasting only in trained subjects. Taken together, trained subjects seem to possess higher basal adipose tissue oxidative capacity as well as higher capacity for regulation of lipolysis and for providing substrate for glyceroneogenesis in adipose tissue during fasting than untrained subjects. NEW & NOTEWORTHY This study shows for the first time higher protein content of lipolytic enzymes and higher oxidative phosphorylation protein in adipose tissue from trained subjects than from untrained subjects during fasting. Furthermore, trained subjects had higher capacity for adipose tissue glyceroneogenesis than untrained subjects.

The extent of B-cell activation and dysfunction preceding lymphoma development in HIV-positive people

OBJECTIVES

B-cell dysfunction and activation are thought to contribute to lymphoma development in HIV-positive people; however, the mechanisms are not well understood. We investigated levels of several markers of B-cell dysfunction [free light chain (FLC)-κ, FLC-λ, immunoglobulin G (IgG), IgA, IgM and IgD] prior to lymphoma diagnosis in HIV-positive people.

METHODS

A nested matched case-control study was carried out within the EuroSIDA cohort, including 73 HIV-positive people with lymphoma and 143 HIV-positive lymphoma-free controls. Markers of B-cell dysfunction were measured in prospectively stored serial plasma samples collected before the diagnosis of lymphoma (or selection date in controls). Marker levels ≤ 2 and > 2 years prior to diagnosis were investigated.

RESULTS

Two-fold higher levels of FLC-κ [odds ratio (OR) 1.84; 95% confidence interval (CI) 1.19, 2.84], FLC-λ (OR 2.15; 95% CI 1.34, 3.46), IgG (OR 3.05; 95% CI 1.41, 6.59) and IgM (OR 1.46; 95% CI 1.01, 2.11) were associated with increased risk of lymphoma > 2 years prior to diagnosis, but not ≤ 2 years prior. Despite significant associations > 2 years prior to diagnosis, the predictive accuracy of each marker was poor, with FLC-λ emerging as the strongest candidate with a c-statistic of 0.67 (95% CI 0.58, 0.76).

CONCLUSIONS

FLC-κ, FLC-λ and IgG levels were higher > 2 years before lymphoma diagnosis, suggesting that B-cell dysfunction occurs many years prior to lymphoma development. However, the predictive value of each marker was low and they are unlikely candidates for risk assessment for targeted intervention.

Effects of training status on PDH regulation in human skeletal muscle during exercise

Pyruvate dehydrogenase (PDH) is the gateway enzyme for carbohydrate-derived pyruvate feeding into the TCA cycle. PDH may play a central role in regulating substrate shifts during exercise, but the influence of training state on PDH regulation during exercise is not fully elucidated. The purpose of this study was to investigate the impact of training state on post-translational regulation of PDHa activity during submaximal and exhaustive exercise. Eight untrained and nine endurance exercise-trained healthy male subjects performed incremental exercise on a cycle ergometer: 40 min at 50% incremental peak power output (IPPO), 10 min at 65% (IPPO), followed by 80% (IPPO) until exhaustion. Trained subjects had higher (P < 0.05) PDH-E1α, PDK1, PDK2, PDK4, and PDP1 protein content as well as PDH phosphorylation and PDH acetylation. Exercising at the same relative intensity led to similar muscle PDH activation in untrained and trained subjects, whereas PDHa activity at exhaustion was higher (P < 0.05) in trained than untrained. Furthermore, exercise induced similar PDH dephosphorylation in untrained and trained subjects, while PDH acetylation was increased (P < 0.05) only in trained subjects. In conclusion, PDHa activity and PDH dephosphorylation were well adjusted to the relative exercise intensity during submaximal exercise. In addition, higher PDHa activity in trained than untrained at exhaustion seemed related to differences in glycogen utilization rather than differences in PDH phosphorylation and acetylation state, although site-specific contributions cannot be ruled out.

Angiopoietin-like protein 4 is an exercise-induced hepatokine in humans, regulated by glucagon and cAMP

Objective

Angiopoietin-like protein-4 (ANGPTL4) is a circulating protein that is highly expressed in liver and implicated in regulation of plasma triglyceride levels. Systemic ANGPTL4 increases during prolonged fasting and is suggested to be secreted from skeletal muscle following exercise.

Methods

We investigated the origin of exercise-induced ANGPTL4 in humans by measuring the arterial-to-venous difference over the leg and the hepato-splanchnic bed during an acute bout of exercise. Furthermore, the impact of the glucagon-to-insulin ratio on plasma ANGPTL4 was studied in healthy individuals. The regulation of ANGPTL4 was investigated in both hepatic and muscle cells.

Results

The hepato-splanchnic bed, but not the leg, contributed to exercise-induced plasma ANGPTL4. Further studies using hormone infusions revealed that the glucagon-to-insulin ratio is an important regulator of plasma ANGPTL4 as elevated glucagon in the absence of elevated insulin increased plasma ANGPTL4 in resting subjects, whereas infusion of somatostatin during exercise blunted the increase of both glucagon and ANGPTL4. Moreover, activation of the cAMP/PKA signaling cascade let to an increase in ANGPTL4 mRNA levels in hepatic cells, which was prevented by inhibition of PKA. In humans, muscle ANGPTL4 mRNA increased during fasting, with only a marginal further induction by exercise. In human muscle cells, no inhibitory effect of AMPK activation could be demonstrated on ANGPTL4 expression.

Conclusions

The data suggest that exercise-induced ANGPTL4 is secreted from the liver and driven by a glucagon-cAMP-PKA pathway in humans. These findings link the liver, insulin/glucagon, and lipid metabolism together, which could implicate a role of ANGPTL4 in metabolic diseases.

•

Release of Angiopoietin-like Protein 4 from the hepato-splanchnic bed is induced by exercise.

•

It is regulated by the glucagon-to-insulin ratio in vivo in humans.

•

In vitro in hepatocytes Angiopoietin-like Protein 4 is stimulated by cAMP.

•

Angiopoietin-like Protein 4 is not released from the exercising nor resting leg.

Do diabetes and obesity affect the metabolic response to exercise?

PURPOSE OF REVIEW

Exercise is recommended as therapeutic intervention for people at risk to develop type 2 diabetes to prevent or treat the disease. Recent studies on the influence of obesity and type 2 diabetes on the outcome of exercise programs are discussed.

RECENT FINDINGS

Poor glycemic control before an intervention can be a risk factor of reduced therapeutic benefit from exercise. But the acute metabolic response to exercise and the transcriptional profile of the working muscle is similar in healthy controls and type 2 diabetic patients, including but not limited to intact activation of skeletal muscle AMP-activated kinase signaling, glucose uptake and expression of peroxisome proliferator-activated receptor gamma coactivator 1α. The increase in plasma acylcarnitines during exercise is not influenced by type 2 diabetes or obesity. The hepatic response to exercise is dependent on the glucagon/insulin ratio and the exercise-induced increase in hepatokines such as fibroblast growth factor 21 and follistatin is impaired in type 2 diabetes and obesity, but consequences for the benefit from exercise are unknown yet.

SUMMARY

Severe metabolic dysregulation can reduce the benefit from exercise, but the intact response of key metabolic regulators in exercising skeletal muscle of diabetic patients demonstrates the effectiveness of exercise programs to treat the disease.

Liver and Muscle Contribute Differently to the Plasma Acylcarnitine Pool During Fasting and Exercise in Humans

BACKGROUND

Plasma acylcarnitine levels are elevated by physiological conditions such as fasting and exercise but also in states of insulin resistance and obesity.

AIM

To elucidate the contribution of liver and skeletal muscle to plasma acylcarnitines in the fasting state and during exercise in humans.

METHODS

In 2 independent studies, young healthy males were fasted overnight and performed an acute bout of exercise to investigate either acylcarnitines in skeletal muscle biopsies and arterial-to-venous plasma differences over the exercising and resting leg (n = 9) or the flux over the hepato-splanchnic bed (n = 10).

RESULTS

In the fasting state, a pronounced release of C2- and C3-carnitines from the hepato-splanchnic bed and an uptake of free carnitine by the legs were detected. Exercise further increased the release of C3-carnitine from the hepato-splanchnic bed and the uptake of free carnitine in the exercising leg. In plasma and in the exercising muscle, exercise induced an increase of most acylcarnitines followed by a rapid decline to preexercise values during recovery. In contrast, free carnitine was decreased in the exercising muscle and quickly restored thereafter. C8-, C10-, C10:1-, C12-, and C12:1-carnitines were released from the exercising leg and simultaneously; C6, C8, C10, C10:1, C14, and C16:1 were taken up by the hepato-splanchnic.

CONCLUSION

These data provide novel insight to the organo-specific release/uptake of acylcarnitines. The liver is a major contributor to systemic short chain acylcarnitines, whereas the muscle tissue releases mostly medium chain acylcarnitines during exercise, indicating that other tissues are contributing to the systemic increase in long chain acylcarnitines.

Local depletion of glycogen with supramaximal exercise in human skeletal muscle fibres

KEY POINTS

Glycogen is stored in local spatially distinct compartments within skeletal muscle fibres and is the main energy source during supramaximal exercise. Using quantitative electron microscopy, we show that supramaximal exercise induces a differential depletion of glycogen from these compartments and also demonstrate how this varies with fibre types. Repeated exercise alters this compartmentalized glycogen depletion. The results obtained in the present study help us understand the muscle metabolic dynamics of whole body repeated supramaximal exercise, and suggest that the muscle has a compartmentalized local adaptation to repeated exercise, which affects glycogen depletion.

ABSTRACT

Skeletal muscle glycogen is heterogeneously distributed in three separated compartments (intramyofibrillar, intermyofibrillar and subsarcolemmal). Although only constituting 3-13% of the total glycogen volume, the availability of intramyofibrillar glycogen is of particular importance to muscle function. The present study aimed to investigate the depletion of these three subcellular glycogen compartments during repeated supramaximal exercise in elite athletes. Ten elite cross-country skiers (aged 25 ± 4 years, V̇O2 max : 65 ± 4 ml kg^-1  min^-1 ; mean ± SD) performed four ∼4 min supramaximal sprint time trials (STT 1-4) with 45 min of recovery. The subcellular glycogen volumes in musculus triceps brachii were quantified from electron microscopy images before and after both STT 1 and 4. During STT 1, the depletion of intramyofibrillar glycogen was higher in type 1 fibres [-52%; (-89:-15%)] than type 2 fibres [-15% (-52:22%)] (P = 0.02), whereas the depletion of intermyofibrillar glycogen [main effect: -19% (-33:0%), P = 0.006] and subsarcolemmal glycogen [main effect: -35% (-66:0%), P = 0.03] was similar between fibre types. By contrast, only intermyofibrillar glycogen volume was significantly reduced during STT 4, in both fibre types [main effect: -31% (-50:-11%), P = 0.002]. Furthermore, for each of the subcellular compartments, the depletion of glycogen during STT 1 was associated with the volumes of glycogen before STT 1. In conclusion, the depletion of spatially distinct glycogen compartments differs during supramaximal exercise. Furthermore, the depletion changes with repeated exercise and is fibre type-dependent.

Circulating follistatin in relation to energy metabolism

Recently, substantial evidence has emerged that the liver contributes significantly to the circulating levels of follistatin and that circulating follistatin is tightly regulated by the glucagon-to-insulin ratio. Both observations are based on investigations of healthy subjects. These novel findings challenge the present view of circulating follistatin in human physiology, being that circulating follistatin is a result of spill-over from para/autocrine actions in various tissues and cells. Follistatin as a liver-derived protein under the regulation of glucagon-to-insulin ratio suggests a relation to energy metabolism. In this narrative review, we attempt to reconcile the existing findings on circulating follistatin with the novel concept that circulating follistatin is a liver-derived molecule regulated by the glucagon-to-insulin ratio. The picture emerging is that conditions associated with elevated levels of circulating follistatin have a metabolic denominator with decreased insulin sensitivity and/or hyperglucagoneimia.

Impaired Follistatin Secretion in Cirrhosis

CONTEXT

Follistatin is a liver-derived inhibitor of the muscle-growth inhibitor myostatin. Reduction in acute follistatin release may help explain muscle loss in liver cirrhosis.

OBJECTIVE

The study aimed to investigate the capacity of acute follistatin release in patients with liver cirrhosis compared to healthy control participants.

DESIGN, SETTING, AND PARTICIPANTS

To experimentally increase the glucagon-insulin ratio (mimicking the hormonal effect of exercise), we infused glucagon/somatostatin (to inhibit insulin secretion) and compared the acute follistatin increase in eight male cirrhosis patients with eight healthy control participants. Patients and controls received 1-hour glucagon/somatostatin and saline infusions on 2 separate days.

MAIN OUTCOME MEASURE

Follistatin was measured during and 5 hours after termination of infusions.

RESULTS

The peak follistatin change was significantly decreased in patients with liver cirrhosis compared to healthy control participants (1.9 (interquartile range, 1.4-2.5) versus 3.6 (interquartile range, 3.0-4.0), respectively; P = .003). Patients with liver cirrhosis demonstrated significantly decreased amounts of appendicular lean mass compared to healthy controls (27.6 ± 3.8 vs 34.5 ± 2.9%, respectively; P = .001).

CONCLUSIONS

Patients with cirrhosis show impaired capacity to acutely secrete follistatin. The decrease in acute follistatin release may contribute to the loss of muscle mass in liver cirrhosis.

Exercise-Induced Secretion of FGF21 and Follistatin Are Blocked by Pancreatic Clamp and Impaired in Type 2 Diabetes

CONTEXT

Hepatokines have emerged as liver-derived hormone-like factors. Plasma fibroblast growth factor (FGF)-21 and follistatin increase with a high glucagon to insulin ratio and exercise, and resting levels are elevated in patients with type 2 diabetes (T2D).

OBJECTIVE

The objective of the study was to investigate the regulatory roles of glucagon to insulin ratio and T2D on exercise-induced FGF21 and follistatin secretion. Design /Interventions: Young healthy males performed a 2-hour bicycle exercise bout followed by 5 hours of rest in supine position with and without a pancreatic clamp blocking the increase in the glucagon to insulin ratio. In addition, we evaluated exercise-induced plasma FGF21 and follistatin in patients with T2D compared with healthy controls in response to 1 hour of bicycle exercise followed by a 3-hour recovery period.

RESULTS

In healthy individuals, we observed a 10-fold (P < .002) increase in the glucagon to insulin ratio during exercise, which was abolished by the pancreatic clamp. Exercise with the pancreatic clamp completely blunted the exercise-induced increase in FGF21 (P = .007), whereas the induction of follistatin was approximately 50% reduced (P = .04). Exercise-induced FGF21 secretion was completely absent in patients with T2D, whereas the exercise-induced follistatin increase was impaired.

CONCLUSIONS/INTERPRETATION

Exercise-induced increases in plasma FGF21 and follistatin are attenuated by the pancreatic clamp, indicating important roles for glucagon and insulin as upstream regulators. For follistatin, an additional regulatory mechanism must exist. Our data further show that exercise-induced FGF21 and follistatin secretion are impaired in patients with T2D. The magnitude of changes in glucagon and insulin or the sensitivity to these hormones seems central in the regulation of FGF21 and follistatin in humans.

Circulating Follistatin Is Liver-Derived and Regulated by the Glucagon-to-Insulin Ratio

CONTEXT

Follistatin is a plasma protein recently reported to increase under conditions with negative energy balance, such as exercise and fasting in humans. Currently, the perception is that circulating follistatin is a result of para/autocrine actions from various tissues. The large and acute increase in circulating follistatin in response to exercise suggests that it may function as an endocrine signal.

OBJECTIVE

We assessed origin and regulation of circulating follistatin in humans.

DESIGN/INTERVENTIONS

First, we assessed arterial-to-venous difference of follistatin over the splanchnic bed at rest and during exercise in healthy humans. To evaluate the regulation of plasma follistatin we manipulated glucagon-to-insulin ratio in humans at rest as well as in cultured hepatocytes. Finally, the impact of follistatin on human islets of Langerhans was assessed.

RESULTS

We demonstrate that in humans the liver is a major contributor to circulating follistatin both at rest and during exercise. Glucagon increases and insulin inhibits follistatin secretion both in vivo and in vitro, mediated via the secondary messenger cAMP in the hepatocyte. Short-term follistatin treatment reduced glucagon secretion from islets of Langerhans, whereas long-term follistatin treatment prevented apoptosis and induced proliferation of rat β cells.

CONCLUSIONS

In conclusion, in humans, the liver secretes follistatin at rest and during exercise, and the glucagon-to-insulin ratio is a key determinant of circulating follistatin levels. Circulating follistatin may be a marker of the glucagon-to-insulin tone on the liver.

Type 2 diabetes alters metabolic and transcriptional signatures of glucose and amino acid metabolism during exercise and recovery

AIMS/HYPOTHESIS

The therapeutic benefit of physical activity to prevent and treat type 2 diabetes is commonly accepted. However, the impact of the disease on the acute metabolic response is less clear. To this end, we investigated the effect of type 2 diabetes on exercise-induced plasma metabolite changes and the muscular transcriptional response using a complementary metabolomics/transcriptomics approach.

METHODS

We analysed 139 plasma metabolites and hormones at nine time points, and whole genome expression in skeletal muscle at three time points, during a 60 min bicycle ergometer exercise and a 180 min recovery phase in type 2 diabetic patients and healthy controls matched for age, percentage body fat and maximal oxygen consumption (VO2).

RESULTS

Pathway analysis of differentially regulated genes upon exercise revealed upregulation of regulators of GLUT4 (SLC2A4RG, FLOT1, EXOC7, RAB13, RABGAP1 and CBLB), glycolysis (HK2, PFKFB1, PFKFB3, PFKM, FBP2 and LDHA) and insulin signal mediators in diabetic participants compared with controls. Notably, diabetic participants had normalised rates of lactate and insulin levels, and of glucose appearance and disappearance, after exercise. They also showed an exercise-induced compensatory regulation of genes involved in biosynthesis and metabolism of amino acids (PSPH, GATM, NOS1 and GLDC), which responded to differences in the amino acid profile (consistently lower plasma levels of glycine, cysteine and arginine). Markers of fat oxidation (acylcarnitines) and lipolysis (glycerol) did not indicate impaired metabolic flexibility during exercise in diabetic participants.

CONCLUSIONS/INTERPRETATION

Type 2 diabetic individuals showed specific exercise-regulated gene expression. These data provide novel insight into potential mechanisms to ameliorate the disturbed glucose and amino acid metabolism associated with type 2 diabetes.