An Empirical Approach to Derive Water T1 from Multiparametric MR Images Using an Automated Pipeline and Comparison With Liver Stiffness

BACKGROUND

Water T1 of the liver has been shown to be promising in discriminating the progressive forms of fatty liver diseases, inflammation, and fibrosis, yet proper correction for iron and lipid is required.

PURPOSE

To examine the feasibility of an empirical approach for iron and lipid correction when measuring imaging-based T1 and to validate this approach by spectroscopy on in vivo data.

STUDY TYPE

Retrospective.

POPULATION

Next to mixed lipid-iron phantoms, individuals with different hepatic lipid content were investigated, including people with type 1 diabetes (N = 15, %female = 15.6, age = 43.5 ± 14.0), or type 2 diabetes mellitus (N = 21, %female = 28.9, age = 59.8 ± 9.7) and healthy volunteers (N = 9, %female = 11.1, age = 58.0 ± 8.1).

FIELD STRENGTH/SEQUENCES

3 T, balanced steady-state free precession MOdified Look-Locker Inversion recovery (MOLLI), multi- and dual-echo gradient echo Dixon, gradient echo magnetic resonance elastography (MRE).

ASSESSMENT

T1 values were measured in phantoms to determine the respective correction factors. The correction was tested in vivo and validated by proton magnetic resonance spectroscopy (1 H-MRS). The quantification of liver T1 based on automatic segmentation was compared to the T1 values based on manual segmentation. The association of T1 with MRE-derived liver stiffness was evaluated.

STATISTICAL TESTS

Bland-Altman plots and intraclass correlation coefficients (ICCs) were used for MOLLI vs. 1 H-MRS agreement and to compare liver T1 values from automatic vs. manual segmentation. Pearson's r correlation coefficients for T1 with hepatic lipids and liver stiffness were determined. A P-value of 0.05 was considered statistically significant.

RESULTS

MOLLI T1 values after correction were found in better agreement with the 1 H-MRS-derived water T1 (ICC = 0.60 [0.37; 0.76]) in comparison with the uncorrected T1 values (ICC = 0.18 [-0.09; 0.44]). Automatic quantification yielded similar liver T1 values (ICC = 0.9995 [0.9991; 0.9997]) as with manual segmentation. A significant correlation of T1 with liver stiffness (r = 0.43 [0.11; 0.67]) was found. A marked and significant reduction in the correlation strength of T1 with liver stiffness (r = 0.05 [-0.28; 0.38], P = 0.77) was found after correction for hepatic lipid content.

DATA CONCLUSION

Imaging-based correction factors enable accurate estimation of water T1 in vivo.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 1.

Post mortem analysis of hepatic volume and lipid content by magnetic resonance imaging and spectroscopy in fixed murine neonates

Maternal obesity and hyperglycemia are linked to an elevated risk for obesity, diabetes, and steatotic liver disease in the adult offspring. To establish and validate a noninvasive workflow for perinatal metabolic phenotyping, fixed neonates of common mouse strains were analyzed postmortem via magnetic resonance imaging (MRI)/magnetic resonance spectroscopy (MRS) to assess liver volume and hepatic lipid (HL) content. The key advantage of nondestructive MRI/MRS analysis is the possibility of further tissue analyses, such as immunohistochemistry, RNA extraction, and even proteomics, maximizing the data that can be gained per individual and therefore facilitating comprehensive correlation analyses. This study employed an MRI and 1H-MRS workflow to measure liver volume and HL content in 65 paraformaldehyde-fixed murine neonates at 11.7 T. Liver volume was obtained using semiautomatic segmentation of MRI acquired by a RARE sequence with 0.5-mm slice thickness. HL content was measured by a STEAM sequence, applied with and without water suppression. T1 and T2 relaxation times of lipids and water were measured for respective correction of signal intensity. The HL content, given as CH2/(CH2 + H2O), was calculated, and the intrasession repeatability of the method was tested. The established workflow yielded robust results with a variation of ~3% in repeated measurements for HL content determination. HL content measurements were further validated by correlation analysis with biochemically assessed triglyceride contents (R2 = 0.795) that were measured in littermates. In addition, image quality also allowed quantification of subcutaneous adipose tissue and stomach diameter. The highest HL content was measured in C57Bl/6N (4.2%) and the largest liver volume and stomach diameter in CBA (53.1 mm3 and 6.73 mm) and NMRI (51.4 mm3 and 5.96 mm) neonates, which also had the most subcutaneous adipose tissue. The observed effects were independent of sex and litter size. In conclusion, we have successfully tested and validated a robust MRI/MRS workflow that allows assessment of morphology and HL content and further enables paraformaldehyde-fixed tissue-compatible subsequent analyses in murine neonates.

Reproducibility of absolute quantification of adenosine triphosphate and inorganic phosphate in the liver with localized 31 P-magnetic resonance spectroscopy at 3-T using different coils

Concentrations of the key metabolites of hepatic energy metabolism, adenosine triphosphate (ATP) and inorganic phosphate (Pi ), can be altered in metabolic disorders such as diabetes mellitus. 31 Phosphorus (31 P)-magnetic resonance spectroscopy (MRS) is used to noninvasively measure hepatic metabolites, but measuring their absolute molar concentrations remains challenging. This study employed a 31 P-MRS method based on the phantom replacement technique for quantifying hepatic 31 P-metabolites on a 3-T clinical scanner. Two surface coils with different size and geometry were used to check for consistency in terms of repeatability and reproducibility and absolute concentrations of metabolites. Day-to-day (n = 8) and intra-day (n = 6) reproducibility was tested in healthy volunteers. In the day-to-day study, mean absolute concentrations of γ-ATP and Pi were 2.32 ± 0.24 and 1.73 ± 0.26 mM (coefficient of variation [CV]: 7.3% and 8.8%) for the single loop, and 2.32 ± 0.42 and 1.73 ± 0.27 mM (CVs 6.7% and 10.6%) for the quadrature coil, respectively. The intra-day study reproducibility using the quadrature coil yielded CVs of 4.7% and 6.8% for γ-ATP and Pi without repositioning, and 6.3% and 7.1% with full repositioning of the volunteer. The results of the day-to-day data did not differ between coils and visits. Both coils robustly yielded similar results for absolute concentrations of hepatic 31 P-metabolites. The current method, applied with two different surface coils, can be readily utilized in long-term and interventional studies. In comparison with the single loop coil, the quadrature coil also allows measurements at a greater distance between the coil and liver, which is relevant for studying people with obesity.

Analysis of type 2 diabetes heterogeneity with a tree-like representation: insights from the prospective German Diabetes Study and the LURIC cohort

BACKGROUND

Heterogeneity in type 2 diabetes can be represented by a tree-like graph structure by use of reversed graph-embedded dimensionality reduction. We aimed to examine whether this approach can be used to stratify key pathophysiological components and diabetes-related complications during longitudinal follow-up of individuals with recent-onset type 2 diabetes.

METHODS

For this cohort analysis, 927 participants aged 18-69 years from the German Diabetes Study (GDS) with recent-onset type 2 diabetes were mapped onto a previously developed two-dimensional tree based on nine simple clinical and laboratory variables, residualised for age and sex. Insulin sensitivity was assessed by a hyperinsulinaemic-euglycaemic clamp, insulin secretion was assessed by intravenous glucose tolerance test, hepatic lipid content was assessed by 1 H magnetic resonance spectroscopy, serum interleukin (IL)-6 and IL-18 were assessed by ELISA, and peripheral and autonomic neuropathy were assessed by functional and clinical measures. Participants were followed up for up to 16 years. We also investigated heart failure and all-cause mortality in 794 individuals with type 2 diabetes undergoing invasive coronary diagnostics from the Ludwigshafen Risk and Cardiovascular Health (LURIC) cohort.

FINDINGS

There were gradients of clamp-measured insulin sensitivity (both dimensions: p<0·0001) and insulin secretion (pdim1<0·0001, pdim2=0·00097) across the tree. Individuals in the region with the lowest insulin sensitivity had the highest hepatic lipid content (n=205, pdim1<0·0001, pdim2=0·037), pro-inflammatory biomarkers (IL-6: n=348, pdim1<0·0001, pdim2=0·013; IL-18: n=350, pdim1<0·0001, pdim2=0·38), and elevated cardiovascular risk (nevents=143, pdim1=0·14, pdim2<0·00081), whereas individuals positioned in the branch with the lowest insulin secretion were more prone to require insulin therapy (nevents=85, pdim1=0·032, pdim2=0·12) and had the highest risk of diabetic sensorimotor polyneuropathy (nevents=184, pdim1=0·012, pdim2=0·044) and cardiac autonomic neuropathy (nevents=118, pdim1=0·0094, pdim2=0·06). In the LURIC cohort, all-cause mortality was highest in the tree branch showing insulin resistance (nevents=488, pdim1=0·12, pdim2=0·0032). Significant gradients differentiated individuals having heart failure with preserved ejection fraction from those who had heart failure with reduced ejection fraction.

INTERPRETATION

These data define the pathophysiological underpinnings of the tree structure, which has the potential to stratify diabetes-related complications on the basis of routinely available variables and thereby expand the toolbox of precision diabetes diagnosis.

FUNDING

German Diabetes Center, German Federal Ministry of Health, Ministry of Culture and Science of the state of North Rhine-Westphalia, German Federal Ministry of Education and Research, German Diabetes Association, German Center for Diabetes Research, European Community, German Research Foundation, and Schmutzler Stiftung.

Cotadutide promotes glycogenolysis in people with overweight or obesity diagnosed with type 2 diabetes

Cotadutide is a dual glucagon-like peptide 1 and glucagon receptor agonist under development for the treatment of non-alcoholic steatohepatitis and type 2 diabetes mellitus (T2DM) and chronic kidney disease. Non-alcoholic steatohepatitis is a complex disease with no approved pharmacotherapies, arising from an underlying state of systemic metabolic dysfunction in association with T2DM and obesity. Cotadutide has been shown to improve glycaemic control, body weight, lipids, liver fat, inflammation and fibrosis. We conducted a two-part, randomized phase 2a trial in men and women with overweight or obesity diagnosed with T2DM to evaluate the efficacy and safety of cotadutide compared with placebo and liraglutide. The primary endpoints were change from baseline to day 28 of treatment in postprandial hepatic glycogen (part A) and to day 35 of treatment in fasting hepatic glycogen (part B) with cotadutide versus placebo. Secondary endpoints in part B were changes in fasting hepatic glycogen with cotadutide versus the mono glucagon-like peptide 1 receptor agonist, liraglutide, and change in hepatic fat fraction. The trial met its primary endpoint. We showed that cotadutide promotes greater reductions in liver glycogen and fat compared with placebo and liraglutide. Safety and tolerability findings with cotadutide were comparable to those of previous reports. Thus, this work provides evidence of additional benefits of cotadutide that could be attributed to glucagon receptor engagement. Our results suggest that cotadutide acts on the glucagon receptor in the human liver to promote glycogenolysis and improve the metabolic health of the liver. ClinicalTrials.gov registration: NCT03555994 .

Intramyocellular Triglyceride Content During the Early Course of Type 1 and Type 2 Diabetes

Intramyocellular lipid content (IMCL) is elevated in insulin-resistant humans, but it changes over time, and relationships with comorbidities remain unclear. We examined IMCL during the initial course of diabetes and its associations with complications. Participants of the German Diabetes Study (GDS) with recent-onset type 1 (n = 132) or type 2 diabetes (n = 139) and glucose-tolerant control subjects (n = 128) underwent 1H-MRS to measure IMCL and muscle volume, whole-body insulin sensitivity (hyperinsulinemic-euglycemic clamps; M-value), and cycling spiroergometry (VO2max). Subgroups underwent the same measurements after 5 years. At baseline, IMCL was ∼30% higher in type 2 diabetes than in other groups independently of age, sex, BMI, and muscle volume. In type 2 diabetes, the M-value was ∼36% and ∼62% lower compared with type 1 diabetes and control subjects, respectively. After 5 years, the M-value decreased by ∼29% in type 1 and ∼13% in type 2 diabetes, whereas IMCL remained unchanged. The correlation between IMCL and M-value in type 2 diabetes at baseline was modulated by VO2max. IMCL also associated with microalbuminuria, the Framingham risk score for cardiovascular disease, and cardiac autonomic neuropathy. Changes in IMCL within 5 years after diagnosis do not mirror the progression of insulin resistance in type 2 diabetes but associate with early diabetes-related complications.

ARTICLE HIGHLIGHTS

Intramyocellular lipid content (IMCL) can be elevated in insulin-resistant humans, but its dynamics and association with comorbidities remain unclear. Independently of age, sex, body mass, and skeletal muscle volume, IMCL is higher in recent-onset type 2, but not type 1 diabetes, and remains unchanged within 5 years, despite worsening insulin resistance. A degree of physical fitness modulates the association between IMCL and insulin sensitivity in type 2 diabetes. Whereas higher IMCL associates with lower insulin sensitivity in people with lower physical fitness, there is no association between IMCL and insulin sensitivity in those with higher degree of physical fitness. IMCL associates with progression of microalbuminuria, cardiovascular disease risk, and cardiac autonomic neuropathy.

Ectopic lipid deposition in muscle and liver, quantified by proton magnetic resonance spectroscopy

Advances in the development of noninvasive imaging techniques have spurred investigations into ectopic lipid deposition in the liver and muscle and its implications in the development of metabolic diseases such as type 2 diabetes. Computed tomography and ultrasound have been applied in the past, though magnetic resonance-based methods are currently considered the gold standard as they allow more accurate quantitative detection of ectopic lipid stores. This review focuses on methodological considerations of magnetic resonance-based methods to image hepatic and muscle fat fractions, and it emphasizes anatomical and morphological aspects and how these may influence data acquisition, analysis, and interpretation.

The tissue-specific metabolic effects of the PPARα agonist ciprofibrate in insulin-resistant male individuals: a double-blind, randomized, placebo-controlled crossover study

OBJECTIVE

Insulin resistance is characterized by ectopic fat accumulation leading to cardiac diastolic dysfunction and nonalcoholic fatty liver disease. The objective of this study was to determine whether treatment with the peroxisome proliferator-activated receptor-α (PPARα) agonist ciprofibrate has direct effects on cardiac and hepatic metabolism and can improve insulin sensitivity and cardiac function in insulin-resistant volunteers.

METHODS

Ten insulin-resistant male volunteers received 100 mg/d of ciprofibrate and placebo for 5 weeks in a randomized double-blind crossover study. Insulin-stimulated metabolic rate of glucose (MRgluc) was measured using dynamic 18 F-fluorodeoxyglucose-positron emission tomography (18 F-FDG-PET). Additionally, cardiac function, whole-body insulin sensitivity, intrahepatic lipid content, skeletal muscle gene expression, 24-hour blood pressure, and substrate metabolism were measured.

RESULTS

Whole-body insulin sensitivity, energy metabolism, and body composition were unchanged after ciprofibrate treatment. Ciprofibrate treatment decreased insulin-stimulated hepatic MRgluc and increased hepatic lipid content. Myocardial net MRgluc tended to decrease after ciprofibrate treatment, but ciprofibrate treatment had no effect on cardiac function and cardiac energy status. In addition, no changes in PPAR-related gene expression in muscle were found.

CONCLUSIONS

Ciprofibrate treatment increased hepatic lipid accumulation and lowered MRgluc, without affecting whole-body insulin sensitivity. Furthermore, parameters of cardiac function or cardiac energy status were not altered upon ciprofibrate treatment.

The effect of weight loss on whole-body and tissue-specific insulin sensitivity and hepatic lipid content and composition: SWEET substudy

OBJECTIVE

This study (1) investigated the effect of weight loss on whole-body and tissue-specific insulin sensitivity and on intrahepatic lipid (IHL) content and composition and (2) investigated the association between weight-loss-induced changes in insulin sensitivity and IHL content in individuals with overweight or obesity.

METHODS

In this secondary analysis of the European SWEET project, 50 adults (age 18-65 years) with overweight or obesity (BMI ≥ 25 kg/m² ) followed a low-energy diet (LED) for 2 months. At baseline and after the LED, body composition (dual-energy x-ray absorptiometry), IHL content and composition (proton magnetic resonance spectroscopy), whole-body insulin sensitivity (Matsuda index), muscle insulin sensitivity index (MISI), and hepatic insulin resistance index (HIRI) were determined (7-point oral glucose tolerance test).

RESULTS

The LED reduced body weight (p < 0.001). This was accompanied by increased Matsuda index and reduced HIRI (both p < 0.001) but no change in MISI (p = 0.260). Weight loss decreased IHL content (mean [SEM], 3.9% [0.7%] vs. 1.6% [0.5%], p < 0.001) and the hepatic saturated fatty acid fraction (41.0% [1.5%] vs. 36.6% [1.9%], p = 0.039). The reduced IHL content was associated with an improvement in HIRI (r = 0.402, p = 0.025).

CONCLUSIONS

Weight loss decreased IHL content and the hepatic saturated fatty acid fraction. The decrease in IHL content was associated with weight-loss-induced improvement in hepatic insulin sensitivity in individuals with overweight or obesity.

Invasive and noninvasive markers of human skeletal muscle mitochondrial function

Mitochondria are organelles that fuel cellular energy requirements by ATP formation via aerobic metabolism. Given the wide variety of methods to assess skeletal muscle mitochondrial capacity, we tested how well different invasive and noninvasive markers of skeletal muscle mitochondrial capacity reflect mitochondrial respiration in permeabilized muscle fibers. Nineteen young men (mean age: 24 ± 4 years) were recruited, and a muscle biopsy was collected to determine mitochondrial respiration from permeabilized muscle fibers and to quantify markers of mitochondrial capacity, content such as citrate synthase (CS) activity, mitochondrial DNA copy number, TOMM20, VDAC, and protein content for complex I-V of the oxidative phosphorylation (OXPHOS) system. Additionally, all participants underwent noninvasive assessments of mitochondrial capacity: PCr recovery postexercise (by ³¹ P-MRS), maximal aerobic capacity, and gross exercise efficiency by cycling exercise. From the invasive markers, Complex V protein content and CS activity showed the strongest concordance (Rc = 0.50 to 0.72) with ADP-stimulated coupled mitochondrial respiration, fueled by various substrates. Complex V protein content showed the strongest concordance (Rc = 0.72) with maximally uncoupled mitochondrial respiration. From the noninvasive markers, gross exercise efficiency, VO_2max , and PCr recovery exhibited concordance values between 0.50 and 0.77 with ADP-stimulated coupled mitochondrial respiration. Gross exercise efficiency showed the strongest concordance with maximally uncoupled mitochondrial respiration (Rc = 0.67). From the invasive markers, Complex V protein content and CS activity are surrogates that best reflect skeletal muscle mitochondrial respiratory capacity. From the noninvasive markers, exercise efficiency and PCr recovery postexercise most closely reflect skeletal muscle mitochondrial respiratory capacity.

PCr/ATP ratios and mitochondrial function in the heart. A comparative study in humans

Cardiac energy status, measured as phosphocreatine (PCr)/adenosine triphosphate (ATP) ratio with 31P-Magnetic Resonance Spectroscopy (31P-MRS) in vivo, is a prognostic factor in heart failure and is lowered in cardiometabolic disease. It has been suggested that, as oxidative phosphorylation is the major contributor to ATP synthesis, PCr/ATP ratio might be a reflection of cardiac mitochondrial function. The objective of the study was to investigate whether PCr/ATP ratios can be used as in vivo marker for cardiac mitochondrial function. We enrolled thirty-eight patients scheduled for open-heart surgery in this study. Cardiac 31P-MRS was performed before surgery. Tissue from the right atrial appendage was obtained during surgery for high-resolution respirometry for the assessment of mitochondrial function. There was no correlation between the PCr/ATP ratio and ADP-stimulated respiration rates (octanoylcarnitine R² < 0.005, p = 0.74; pyruvate R² < 0.025, p = 0.41) nor with maximally uncoupled respiration (octanoylcarnitine R² = 0.005, p = 0.71; pyruvate R² = 0.040, p = 0.26). PCr/ATP ratio did correlate with indexed LV end systolic mass. As no direct correlation between cardiac energy status (PCr/ATP) and mitochondrial function in the heart was found, the study suggests that mitochondrial function might not the only determinant of cardiac energy status. Interpretation should be done in the right context in cardiac metabolic studies.

Thigh muscles are more susceptible to age-related muscle loss when compared to lower leg and pelvic muscles

BACKGROUND

A key hallmark of aging is the progressive loss of skeletal muscle mass. Due to limitations of the various methods typically applied to assess muscle mass, only limited information is available on age-related differences between various muscle groups. This study assessed differences in individual lower body muscle group volumes between healthy young and older males.

METHODS

Lower body muscle mass assessments were performed in 10 young (age: 27 ± 4 y) and 10 older (age: 71 ± 6 y) healthy, male adults using Dual-energy X-ray Absorptiometry (DXA), single slice (thigh) Computed Tomography (CT), as well as Magnetic Resonance Imaging (MRI). Muscle volumes of all individual muscle groups in the lower body were assessed by MRI.

RESULTS

Leg lean mass, as assessed with DXA, was not significantly different between older (9.2 ± 1.0 kg) and young (10.5 ± 2.0 kg) men (P = 0.075). Thigh muscle cross-sectional area, as assessed with CT, was significantly lower (by 13 %) in the older (137 ± 17 cm²) compared to young (157 ± 24 cm²) participants (P = 0.044). MRI-derived lower body muscle volume was also significantly lower (by 20 %) in older (6.7 ± 0.9 L) compared to young (8.3 ± 1.3 L) men (P = 0.005). This was primarily attributed to substantial differences in thigh (24 %), rather than lower leg (12 %) and pelvis (15 %) muscle volume in the older vs the young. Thigh muscle volume averaged 3.4 ± 0.5 L in older and 4.5 ± 0.7 L in young men (P = 0.001). Of all thigh muscle groups, the quadriceps femoris showed the most profound difference (30 %) between young (2.3 ± 0.4 L) and older (1.6 ± 0.2 L) men (P < 0.001).

CONCLUSIONS

The most profound differences in lower body muscle volume between young and older men are observed in the thigh. Within the thigh muscle groups, the quadriceps femoris shows the largest difference in muscle volume between young and older men. Finally, DXA appears less sensitive when compared to CT and MRI to assess age-related differences in muscle mass.

Timing of physical activity in relation to liver fat content and insulin resistance

AIMS/HYPOTHESIS

We hypothesised that the insulin-sensitising effect of physical activity depends on the timing of the activity. Here, we examined cross-sectional associations of breaks in sedentary time and timing of physical activity with liver fat content and insulin resistance in a Dutch cohort.

METHODS

In 775 participants of the Netherlands Epidemiology of Obesity (NEO) study, we assessed sedentary time, breaks in sedentary time and different intensities of physical activity using activity sensors, and liver fat content by magnetic resonance spectroscopy (n=256). Participants were categorised as being most active in the morning (06:00-12:00 hours), afternoon (12:00-18:00 hours) or evening (18:00-00:00 hours) or as engaging in moderate-to-vigorous-physical activity (MVPA) evenly distributed throughout the day. Most active in a certain time block was defined as spending the majority (%) of total daily MVPA in that block. We examined associations between sedentary time, breaks and timing of MVPA with liver fat content and HOMA-IR using linear regression analyses, adjusted for demographic and lifestyle factors including total body fat. Associations of timing of MVPA were additionally adjusted for total MVPA.

RESULTS

The participants (42% men) had a mean (SD) age of 56 (4) years and a mean (SD) BMI of 26.2 (4.1) kg/m². Total sedentary time was not associated with liver fat content or insulin resistance, whereas the amount of breaks in sedentary time was associated with higher liver fat content. Total MVPA (-5%/h [95% CI -10%/h, 0%/h]) and timing of MVPA were associated with reduced insulin resistance but not with liver fat content. Compared with participants who had an even distribution of MVPA throughout the day, insulin resistance was similar (-3% [95% CI -25%, 16%]) in those most active in morning, whereas it was reduced in participants who were most active in the afternoon (-18% [95% CI -33%, -2%]) or evening (-25% [95% CI -49%, -4%]).

CONCLUSIONS/INTERPRETATION

The number of daily breaks in sedentary time was not associated with lower liver fat content or reduced insulin resistance. Moderate-to-vigorous activity in the afternoon or evening was associated with a reduction of up to 25% in insulin resistance. Further studies should assess whether timing of physical activity is also important for the occurrence of type 2 diabetes.

Effects of the sodium-glucose cotransporter 2 inhibitor dapagliflozin on substrate metabolism in prediabetic insulin resistant individuals: A randomized, double-blind crossover trial

AIMS/HYPOTHESIS

Sodium-glucose cotransporter 2 inhibitor (SGLT2i) treatment in type 2 diabetes mellitus patients results in glucosuria, causing an energy loss, and triggers beneficial metabolic adaptations. It is so far unknown if SGLT2i exerts beneficial metabolic effects in prediabetic insulin resistant individuals, yet this is of interest since SGLT2is also reduce the risk for progression of heart failure and chronic kidney disease in patients without diabetes.

METHODS

Fourteen prediabetic insulin resistant individuals (BMI: 30.3 ± 2.1 kg/m²; age: 66.3 ± 6.2 years) underwent 2-weeks of treatment with dapagliflozin (10 mg/day) or placebo in a randomized, placebo-controlled, cross-over design. Outcome parameters include 24-hour and nocturnal substrate oxidation, and twenty-four-hour blood substrate and insulin levels. Hepatic glycogen and lipid content/composition were measured by MRS. Muscle biopsies were taken to measure mitochondrial oxidative capacity and glycogen and lipid content.

RESULTS

Dapagliflozin treatment resulted in a urinary glucose excretion of 36 g/24-h, leading to a negative energy and fat balance. Dapagliflozin treatment resulted in a higher 24-hour and nocturnal fat oxidation (p = 0.043 and p = 0.039, respectively), and a lower 24-hour carbohydrate oxidation (p = 0.048). Twenty-four-hour plasma glucose levels were lower (AUC; p = 0.016), while 24-hour free fatty acids and nocturnal β-hydroxybutyrate levels were higher (AUC; p = 0.002 and p = 0.012, respectively) after dapagliflozin compared to placebo. Maximal mitochondrial oxidative capacity was higher after dapagliflozin treatment (dapagliflozin: 87.6 ± 5.4, placebo: 78.1 ± 5.5 pmol/mg/s, p = 0.007). Hepatic glycogen and lipid content were not significantly changed by dapagliflozin compared to placebo. However, muscle glycogen levels were numerically higher in the afternoon in individuals on placebo (morning: 332.9 ± 27.9, afternoon: 368.8 ± 13.1 nmol/mg), while numerically lower in the afternoon on dapagliflozin treatment (morning: 371.7 ± 22.8, afternoon: 340.5 ± 24.3 nmol/mg).

CONCLUSIONS/INTERPRETATION

Dapagliflozin treatment of prediabetic insulin resistant individuals for 14 days resulted in significant metabolic adaptations in whole-body and skeletal muscle substrate metabolism despite being weight neutral. Dapagliflozin improved fat oxidation and ex vivo skeletal muscle mitochondrial oxidative capacity, mimicking the effects of calorie restriction.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03721874.

A prolonged fast improves overnight substrate oxidation without modulating hepatic glycogen in adults with and without nonalcoholic fatty liver: A randomized crossover trial

OBJECTIVE

Increasing overnight fasting time seems a promising strategy to improve metabolic health in individuals with nonalcoholic fatty liver (NAFL). Mechanisms underlying the beneficial effects of fasting may be related to larger fluctuations in hepatic glycogen and higher fat oxidation. This study investigated whether prolonging an overnight fast depletes hepatic glycogen stores and improves substrate metabolism in individuals with NAFL and healthy lean individuals.

METHODS

Eleven individuals with NAFL and ten control individuals participated in this randomized crossover trial. After a 9.5-hour or 16-hour fast, hepatic glycogen was measured by using carbon-13 magnetic resonance spectroscopy, and a meal test was performed. Nocturnal substrate oxidation was measured with indirect calorimetry.

RESULTS

Extending fasting time led to lower nocturnal carbohydrate oxidation and higher fat oxidation in both groups (intervention × time, p < 0.005 for carbohydrate and fat oxidation). In both arms, the respiratory exchange ratio measured during the night remained higher in the group with NAFL compared with the control group (population p < 0.001). No changes were observed in hepatic glycogen depletion with a prolonged overnight fast in the group with NAFL or the control group.

CONCLUSIONS

These results suggest that acutely prolonging the overnight fast can improve overnight substrate oxidation and that these alterations are not mediated by changes in hepatic glycogen depletion.

Replacing Foods with a High-Glycemic Index and High in Saturated Fat by Alternatives with a Low Glycemic Index and Low Saturated Fat Reduces Hepatic Fat, Even in Isocaloric and Macronutrient Matched Conditions

BACKGROUND

Current guidelines aim to limit the dietary glycemic index (GI) and intake of saturated fatty acids (SFA). Several studies have shown favorable effects of low-GI or low-SFA diets on intrahepatic lipid content (IHL), but these studies were performed under overfeeding conditions or extreme differences in GI or SFA to maximize the contrast between diets. By combining changes in GI and SFA, we can mimic how people can improve their diet in a realistic setting.

OBJECTIVES

We investigated the effect on liver fat content and substrate metabolism of both reducing GI and replacing SFA with polyunsaturated fat in practically realistic amounts under isocaloric conditions.

DESIGN AND METHODS

In a randomized crossover study, thirteen overweight participants consumed two diets, one high in GI and SFA (high GI/SFA) and one low in GI and SFA (low GI/SFA) with identical macronutrient composition, for two weeks each. Diets were equal in caloric content, consisted of habitual food items, and had a macronutrient composition that can be easily achieved in daily life. At the end of each intervention, IHL content/composition and liver glycogen were measured by magnetic resonance spectroscopy. Additionally, fasted and postprandial hepatic de novo lipogenesis and glycemic and metabolic responses were investigated.

RESULTS

IHL was significantly lower (-28%) after the two-week low-GI/SFA diet (2.4 ± 0.5% 95% CI [1.4, 3.4]) than after the two-week high-GI/SFA diet (3.3 ± 0.6% 95% CI [1.9, 4.7], p < 0.05). Although hepatic glycogen content, hepatic de novo lipogenesis, hepatic lipid composition, and substrate oxidation during the night were similar between the two diets, the glycemic response to the low-GI/SFA diet was reduced (p < 0.05).

CONCLUSIONS

Changes in macronutrient quality can already have drastic effects on liver fat content and postprandial glycemia after two weeks and even when energy content and the percentage of total fat and carbohydrate remains unchanged.

Effects of SGLT2 inhibitor dapagliflozin in patients with type 2 diabetes on skeletal muscle cellular metabolism

OBJECTIVE

SGLT2 inhibitors increase urinary glucose excretion and have beneficial effects on cardiovascular and renal outcomes; the underlying mechanism may be metabolic adaptations due to urinary glucose loss. Here, we investigated the cellular and molecular effects of 5 weeks of dapagliflozin treatment on skeletal muscle metabolism in type 2 diabetes patients.

METHODS

Twenty-six type 2 diabetes mellitus patients were randomized to a 5-week double-blind, cross-over study with 6-8-week wash-out. Skeletal muscle acetylcarnitine levels, intramyocellular lipid (IMCL) content and phosphocreatine (PCr) recovery rate were measured by magnetic resonance spectroscopy (MRS). Ex vivo mitochondrial respiration was measured in skeletal muscle fibers using high resolution respirometry. Intramyocellular lipid droplet and mitochondrial network dynamics were investigated using confocal microscopy. Skeletal muscle levels of acylcarnitines, amino acids and TCA cycle intermediates were measured. Expression of genes involved in fatty acid metabolism were investigated.

RESULTS

Mitochondrial function, mitochondrial network integrity and citrate synthase and carnitine acetyltransferase activities in skeletal muscle were unaltered after dapagliflozin treatment. Dapagliflozin treatment increased intramyocellular lipid content (0.060 (0.011, 0.110) %, p = 0.019). Myocellular lipid droplets increased in size (0.03 μm² (0.01-0.06), p < 0.05) and number (0.003 μm^-2 (-0.001-0.007), p = 0.09) upon dapagliflozin treatment. CPT1A, CPT1B and malonyl CoA-decarboxylase mRNA expression was increased by dapagliflozin. Fasting acylcarnitine species and C4-OH carnitine levels (0.4704 (0.1246, 0.8162) pmoles∗mg tissue^-1, p < 0.001) in skeletal muscle were higher after dapagliflozin treatment, while acetylcarnitine levels were lower (-40.0774 (-64.4766, -15.6782) pmoles∗mg tissue^-1, p < 0.001). Fasting levels of several amino acids, succinate, alpha-ketoglutarate and lactate in skeletal muscle were significantly lower after dapagliflozin treatment.

CONCLUSION

Dapagliflozin treatment for 5 weeks leads to adaptive changes in skeletal muscle substrate metabolism favoring metabolism of fatty acid and ketone bodies and reduced glycolytic flux. The trial is registered with ClinicalTrials.gov, number NCT03338855.

Effect of iron deficiency on skeletal muscle metabolism in heart failure with preserved ejection fraction

Background

Iron deficiency (ID) is suggested to be one of the key comorbidities contributing to heart failure with preserved ejection fraction (HFpEF) and concomitant exercise intolerance, possibly by inducing systemic inflammation and microvascular dysfunction (MVD). ID is associated with poorer prognosis in HFpEF, but its exact impact on exercise capacity in HFpEF patients remains to be further investigated.

Purpose

To evaluate the effect of ID on exercise capacity in HFpEF patients by assessing skeletal muscle metabolism. Additionally, to assess the association between ID and MVD in HFpEF patients.

Methods

This prospective study included patients diagnosed with HFpEF according to the ESC Heart Failure 2016 guidelines between January 2018 and May 2021. Patients were excluded if they were of childbearing potential, had any iron supplementation 6 months or chemotherapy 1 year prior to inclusion, were known with significant peripheral artery disease, or had any contraindication for phosphorus-magnetic resonance spectroscopy (31P-MRS). Iron status was defined as absolute ID (serum ferritin &lt;100μg/L), relative ID (serum ferritin 100–299μg/L and transferrin saturation &lt;20%), and no ID. Skeletal muscle oxidative capacity of the upper leg was evaluated by determining phosphocreatine (PCr) recovery kinetics with 31P-MRS in the vastus lateralis muscle after isometric knee extension exercise. Microvascular function was assessed as heat-induced skin hyperemia using laser-Doppler flowmetry. Clinical data up to 6 months prior to or after inclusion was used.

Results

Twenty-four HFpEF patients without ID and 18 with ID were included, including 14 patients with absolute ID. Clinical characteristics of patients without ID and with ID were comparable: median age 74 [69–79] vs. 77 [69–81] years, 13 (54%) vs. 14 (78%) were females, and 20 (83%) vs. 16 (89%) had a history of hypertension (Table 1). Both groups showed similar halftime of PCr recovery after exercise (29.2 [22.8–33.2] vs. 27.0 [21.1–31.4] seconds, p=0.416), and similar skin hyperaemic flow increase (1142 [576–2247] vs. 1023 [574–1511] %, p=0.554). These measures of skeletal muscle metabolism and microvascular function were not correlated. In a subset of patients (11 without ID and 13 with ID), elevated high-sensitive C-reactive protein (hsCRP) was correlated with PCr recovery halftime in those with ID (R2 0.565, p=0.003). This correlation was not found in patients without ID (R2 0.119, p=0.300) in the original data (Figure 1), but was found after removal of a prominent outlier (R2 0.654, p=0.005).

Conclusion

HFpEF patients without ID showed comparable skeletal muscle oxidative capacity and microvascular skin hyperaemia compared to HFpEF patients with ID. Post-hoc analysis suggests that inflammation affects skeletal muscle metabolism in HFpEF patients, possibly regardless of ID. Future studies on the effects of ID and inflammation on cellular metabolism could suggest therapeutic targets in HFpEF.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): This study was funded by Vifor Pharma. The funder had no influence on the study results.

Three weeks of time-restricted eating improves glucose homeostasis in adults with type 2 diabetes but does not improve insulin sensitivity: a randomised crossover trial

AIMS/HYPOTHESIS

Time-restricted eating (TRE) is suggested to improve metabolic health by limiting food intake to a defined time window, thereby prolonging the overnight fast. This prolonged fast is expected to lead to a more pronounced depletion of hepatic glycogen stores overnight and might improve insulin sensitivity due to an increased need to replenish nutrient storage. Previous studies showed beneficial metabolic effects of 6-8 h TRE regimens in healthy, overweight adults under controlled conditions. However, the effects of TRE on glucose homeostasis in individuals with type 2 diabetes are unclear. Here, we extensively investigated the effects of TRE on hepatic glycogen levels and insulin sensitivity in individuals with type 2 diabetes.

METHODS

Fourteen adults with type 2 diabetes (BMI 30.5±4.2 kg/m², HbA_1c 46.1±7.2 mmol/mol [6.4±0.7%]) participated in a 3 week TRE (daily food intake within 10 h) vs control (spreading food intake over ≥14 h) regimen in a randomised, crossover trial design. The study was performed at Maastricht University, the Netherlands. Eligibility criteria included diagnosis of type 2 diabetes, intermediate chronotype and absence of medical conditions that could interfere with the study execution and/or outcome. Randomisation was performed by a study-independent investigator, ensuring that an equal amount of participants started with TRE and CON. Due to the nature of the study, neither volunteers nor investigators were blinded to the study interventions. The quality of the data was checked without knowledge on intervention allocation. Hepatic glycogen levels were assessed with ¹³C-MRS and insulin sensitivity was assessed using a hyperinsulinaemic-euglycaemic two-step clamp. Furthermore, glucose homeostasis was assessed with 24 h continuous glucose monitoring devices. Secondary outcomes included 24 h energy expenditure and substrate oxidation, hepatic lipid content and skeletal muscle mitochondrial capacity.

RESULTS

Results are depicted as mean ± SEM. Hepatic glycogen content was similar between TRE and control condition (0.15±0.01 vs 0.15±0.01 AU, p=0.88). M value was not significantly affected by TRE (19.6±1.8 vs 17.7±1.8 μmol kg^-1 min^-1 in TRE vs control, respectively, p=0.10). Hepatic and peripheral insulin sensitivity also remained unaffected by TRE (p=0.67 and p=0.25, respectively). Yet, insulin-induced non-oxidative glucose disposal was increased with TRE (non-oxidative glucose disposal 4.3±1.1 vs 1.5±1.7 μmol kg^-1 min^-1, p=0.04). TRE increased the time spent in the normoglycaemic range (15.1±0.8 vs 12.2±1.1 h per day, p=0.01), and decreased fasting glucose (7.6±0.4 vs 8.6±0.4 mmol/l, p=0.03) and 24 h glucose levels (6.8±0.2 vs 7.6±0.3 mmol/l, p<0.01). Energy expenditure over 24 h was unaffected; nevertheless, TRE decreased 24 h glucose oxidation (260.2±7.6 vs 277.8±10.7 g/day, p=0.04). No adverse events were reported that were related to the interventions.

CONCLUSIONS/INTERPRETATION

We show that a 10 h TRE regimen is a feasible, safe and effective means to improve 24 h glucose homeostasis in free-living adults with type 2 diabetes. However, these changes were not accompanied by changes in insulin sensitivity or hepatic glycogen.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03992248 FUNDING: ZonMW, 459001013.

Novel insights in intestinal and hepatic fructose metabolism: from mice to men

PURPOSE OF REVIEW

The rise in fructose consumption in parallel with the current epidemic of obesity and related cardiometabolic disease requires a better understanding of the pathophysiological pathways that are involved.

RECENT FINDINGS

Animal studies have shown that fructose has various effects on the intestines that subsequently affect intrahepatic lipid accumulation and inflammation. Fructose adversely affects the gut microbiome - as a producer of endotoxins and intermediates of de novo lipogenesis - and intestinal barrier function. Furthermore, intestinal fructose metabolism shields fructose away from the liver. Finally, fructose 1-phosphate (F1-P) serves as a signal molecule that promotes intestinal cell survival and, consequently, intestinal absorption capacity. Intervention and epidemiological studies have convincingly shown that fructose, particularly derived from sugar-sweetened beverages, stimulates de novo lipogenesis and intrahepatic lipid accumulation in humans. Of interest, individuals with aldolase B deficiency, who accumulate F1-P, are characterized by a greater intrahepatic lipid content. First phase II clinical trials have recently shown that reduction of F1-P, by inhibition of ketohexokinase, reduces intrahepatic lipid content.

SUMMARY

Experimental evidence supports current measures to reduce fructose intake, for example by the implementation of a tax on sugar-sweetened beverages, and pharmacological inhibition of fructose metabolism to reduce the global burden of cardiometabolic disease.

A randomized placebo-controlled clinical trial for pharmacological activation of BCAA catabolism in patients with type 2 diabetes

Elevations in plasma branched-chain amino acid (BCAA) levels associate with insulin resistance and type 2 diabetes (T2D). Pre-clinical models suggest that lowering BCAA levels improve glucose tolerance, but data in humans are lacking. Here, we used sodium phenylbutyrate (NaPB), an accelerator of BCAA catabolism, as tool to lower plasma BCAA levels in patients with T2D, and evaluate its effect on metabolic health. This trial (NetherlandsTrialRegister: NTR7426) had a randomized, placebo-controlled, double-blind cross-over design and was performed in the Maastricht University Medical Center (MUMC+), the Netherlands, between February 2019 and February 2020. Patients were eligible for the trial if they were 40-75years, BMI of 25-38 kg/m², relatively well-controlled T2D (HbA1C < 8.5%) and treated with oral glucose-lowering medication. Eighteen participants were randomly assigned to receive either NaPB 4.8 g/m²/day and placebo for 2 weeks via controlled randomization and sixteen participants completed the study. The primary outcome was peripheral insulin sensitivity. Secondary outcomes were ex vivo muscle mitochondrial oxidative capacity, substrate oxidation and ectopic fat accumulation. Fasting blood samples were collected to determine levels of BCAA, their catabolic intermediates, insulin, triglycerides, free fatty acids (FFA) and glucose. NaPB led to a robust 27% improvement in peripheral insulin sensitivity compared to placebo (ΔRd:13.2 ± 1.8 vs. 9.6 ± 1.8 µmol/kg/min, p = 0.02). This was paralleled by an improvement in pyruvate-driven muscle mitochondrial oxidative capacity and whole-body insulin-stimulated carbohydrate oxidation, and a reduction in plasma BCAA and glucose levels. No effects were observed on levels of insulin, triglycerides and FFA, neither did fat accumulation in muscle and liver change. No adverse events were reported. These data establish the proof-of-concept in humans that modulating the BCAA oxidative pathway may represent a potential treatment strategy for patients with T2D.

Serum sex hormone-binding globulin levels are reduced and inversely associated with intrahepatic lipid content and saturated fatty acid fraction in adult patients with glycogen storage disease type 1a

PURPOSE

De novo lipogenesis has been inversely associated with serum sex hormone-binding globulin (SHBG) levels. However, the directionality of this association has remained uncertain. We, therefore, studied individuals with glycogen storage disease type 1a (GSD1a), who are characterized by a genetic defect in glucose-6-phosphatase resulting in increased rates of de novo lipogenesis, to assess the downstream effect on serum SHBG levels.

METHODS

A case-control study comparing serum SHBG levels in patients with GSD1a (n = 10) and controls matched for age, sex, and BMI (n = 10). Intrahepatic lipid content and saturated fatty acid fraction were quantified by proton magnetic resonance spectroscopy.

RESULTS

Serum SHBG levels were statistically significantly lower in patients with GSD1a compared to the controls (p = 0.041), while intrahepatic lipid content and intrahepatic saturated fatty acid fraction-a marker of de novo lipogenesis-were significantly higher in patients with GSD1a (p = 0.001 and p = 0.019, respectively). In addition, there was a statistically significant, inverse association of intrahepatic lipid content and saturated fatty acid fraction with serum SHBG levels in patients and controls combined (β: - 0.28, 95% CI: - 0.47;- 0.09 and β: - 0.02, 95% CI: - 0.04;- 0.01, respectively).

CONCLUSION

Patients with GSD1a, who are characterized by genetically determined higher rates of de novo lipogenesis, have lower serum SHBG levels than controls.

Brown adipose tissue activation is not related to hypermetabolism in emphysematous chronic obstructive pulmonary disease patients

BACKGROUND

Brown adipose tissue (BAT) has been primarily researched as a potential target for mitigating obesity. However, the physiological significance of BAT in relation to cachexia remains poorly understood. The objective of this study was to investigate the putative contribution of BAT on different components of energy metabolism in emphysematous chronic obstructive pulmonary disease (COPD) patients.

METHODS

Twenty COPD patients (mean ± SD age 62 ± 6, 50% female, median [range] BMI 22.4 [15.1-32.5] kg/m² and 85% low FFMI) were studied. Basal metabolic rate (BMR) was assessed by ventilated hood, total daily energy expenditure (TDEE) by doubly labelled water and physical activity by triaxial accelerometry. BMR was adjusted for fat-free mass (FFM) as assessed by deuterium dilution. Analysis of BAT and WAT was conducted in a subset of ten patients and six age-matched, gender-matched and BMI-matched healthy controls. BAT glucose uptake was assessed by means of cold-stimulated integrated [18F]FDG positron-emission tomography and magnetic resonance imaging. WAT was collected from subcutaneous abdominal biopsies to analyse metabolic and inflammatory gene expression levels. Lung function was assessed by spirometry and body plethysmography and systemic inflammation by high sensitivity C-reactive protein.

RESULTS

Mean TDEE was 2209 ± 394 kcal/day, and mean BMR was 1449 ± 214 kcal/day corresponding to 120% of predicted. FFM-adjusted BMR did not correlate with lung function or C-reactive protein. Upon cooling, energy expenditure increased, resulting in a non-shivering thermogenesis of (median [range]) 20.1% [3.3-41.3] in patients and controls. Mean BAT glucose uptake was comparable between COPD and controls (1.5 [0.1-6.2] vs. 1.1 [0.7-3.9]). In addition, no correlation was found between BMR adjusted for FFM and BAT activity or between cold-induced non-shivering energy expenditure and BAT activity. Gene expression levels of the brown adipocyte or beige markers were also comparable between the groups. No (serious) adverse events were reported.

CONCLUSIONS

Although COPD patients were hypermetabolic at rest, no correlation was found between BMR or TDEE and BAT activity. Furthermore, both BAT activity and gene expression levels of the brown adipocyte or beige markers were comparable between COPD patients and controls.

Sitting less elicits metabolic responses similar to exercise and enhances insulin sensitivity in postmenopausal women

AIMS/HYPOTHESIS

In our current society sedentary behaviour predominates in most people and is associated with the risk of developing type 2 diabetes. It has been suggested that replacing sitting time by standing and walking could be beneficial for individuals with type 2 diabetes but the underlying mechanisms are unknown and direct comparisons with exercise are lacking. Our objective was to directly compare metabolic responses of either sitting less or exercising, relative to being sedentary.

METHODS

We performed a randomised, crossover intervention study in 12 overweight women who performed three well-controlled 4 day activity regimens: (1) sitting regimen (sitting 14 h/day); (2) exercise regimen (sitting 13 h/day, exercise 1 h/day); and (3) sitting less regimen (sitting 9 h/day, standing 4 h/day and walking 3 h/day). The primary outcome was insulin sensitivity measured by a two-step hyperinsulinaemic-euglycaemic clamp. We additionally performed metabolomics on muscle biopsies taken before the clamp to identify changes at the molecular level.

RESULTS

Replacing sitting time by standing and walking over 4 days resulted in improved peripheral insulin sensitivity, comparable with the improvement achieved by moderate-to-vigorous exercise. Specifically, we report a significant improvement in peripheral insulin sensitivity in the sitting less (~13%) and the exercise regimen (~20%), compared with the sitting regimen. Furthermore, sitting less shifted the underlying muscle metabolome towards that seen with moderate-to-vigorous exercise, compared with the sitting regimen.

CONCLUSIONS/INTERPRETATIONS

Replacing sitting time by standing and walking is an attractive alternative to moderate-to-vigorous exercise for improving metabolic health.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03912922.

Postexercise changes in myocellular lipid droplet characteristics of young lean individuals are affected by circulatory nonesterified fatty acids

Intramyocellular lipid (IMCL) content is an energy source during acute exercise. Nonesterified fatty acid (NEFA) levels can compete with IMCL utilization during exercise. IMCL content is stored as lipid droplets (LDs) that vary in size, number, subcellular distribution, and in coating with LD protein PLIN5. Little is known about how these factors are affected during exercise and recovery. Here, we aimed to investigate the effects of acute exercise with and without elevated NEFA levels on intramyocellular LD size and number, intracellular distribution and PLIN5 coating, using high-resolution confocal microscopy. In a crossover study, 9 healthy lean young men performed a 2-h moderate intensity cycling protocol in the fasted (high NEFA levels) and glucose-fed state (low NEFA levels). IMCL and LD parameters were measured at baseline, directly after exercise and 4 h postexercise. We found that total IMCL content was not changed directly after exercise (irrespectively of condition), but IMCL increased 4 h postexercise in the fasting condition, which was due to an increased number of LDs rather than changes in size. The effects were predominantly detected in type I muscle fibers and in LDs coated with PLIN5. Interestingly, subsarcolemmal, but not intermyofibrillar IMCL content, was decreased directly after exercise in the fasting condition and was replenished during the 4 h recovery period. In conclusion, acute exercise affects IMCL storage during exercise and recovery, particularly in type I muscle fibers, in the subsarcolemmal region and in the presence of PLIN5. Moreover, the effects of exercise on IMCL content are affected by plasma NEFA levels.NEW & NOTEWORTHY Skeletal muscle stores lipids in lipid droplets (LDs) that can vary in size, number, and location and are a source of energy during exercise. Specifically, subsarcolemmal LDs were used during exercise when fasted. Exercising in the fasted state leads to postrecovery elevation in IMCL levels due to an increase in LD number in type I muscle fibers, in subsarcolemmal region and decorated with PLIN5. These effects are blunted by glucose ingestion during exercise and recovery.

Impact of aging and exercise on skeletal muscle mitochondrial capacity, energy metabolism, and physical function

The relationship between the age-associated decline in mitochondrial function and its effect on skeletal muscle physiology and function remain unclear. In the current study, we examined to what extent physical activity contributes to the decline in mitochondrial function and muscle health during aging and compared mitochondrial function in young and older adults, with similar habitual physical activity levels. We also studied exercise-trained older adults and physically impaired older adults. Aging was associated with a decline in mitochondrial capacity, exercise capacity and efficiency, gait stability, muscle function, and insulin sensitivity, even when maintaining an adequate daily physical activity level. Our data also suggest that a further increase in physical activity level, achieved through regular exercise training, can largely negate the effects of aging. Finally, mitochondrial capacity correlated with exercise efficiency and insulin sensitivity. Together, our data support a link between mitochondrial function and age-associated deterioration of skeletal muscle.

Aging is associated with a progressive loss of muscle function. Here the authors characterize mitochondrial capacity and muscle function in young and older adults with similar habitual physical activity and also compared to older adults with exercise training or with physical impairment.

NAD+-Precursor Supplementation With L-Tryptophan, Nicotinic Acid, and Nicotinamide Does Not Affect Mitochondrial Function or Skeletal Muscle Function in Physically Compromised Older Adults

BACKGROUND

Boosting NAD+ via supplementation with niacin equivalents has been proposed as a potential modality capable of promoting healthy aging and negating age-dependent declines of skeletal muscle mass and function.

OBJECTIVES

We investigated the efficacy of NAD+-precursor supplementation (tryptophan, nicotinic acid, and nicotinamide) on skeletal muscle mitochondrial function in physically compromised older adults.

METHODS

A randomized, double-blind, controlled trial was conducted in 14 (female/male: 4/10) community-dwelling, older adults with impaired physical function [age, 72.9 ± 4.0 years; BMI, 25.2 ± 2.3 kg/m2]. Participants were supplemented with 207.5 mg niacin equivalents/day [intervention (INT)] and a control product (CON) that did not contain niacin equivalents, each for 32 days. The primary outcomes tested were mitochondrial oxidative capacity and exercise efficiency, analyzed by means of paired Student's t-tests. Secondary outcomes, such as NAD+ concentrations, were analyzed accordingly.

RESULTS

Following supplementation, skeletal muscle NAD+ concentrations [7.5 ± 1.9 compared with 7.9 ± 1.6 AU, respectively] in INT compared with CON conditions were not significantly different compared to the control condition, whereas skeletal muscle methyl-nicotinamide levels were significantly higher under NAD+-precursor supplementation [INT, 0.098 ± 0.063 compared with CON, 0.025 ± 0.014; P = 0.001], suggesting an increased NAD+ metabolism. Conversely, neither ADP-stimulated [INT, 82.1 ± 19.0 compared with CON, 84.0 ± 19.2; P = 0.716] nor maximally uncoupled mitochondrial respiration [INT, 103.4 ± 30.7 compared with CON, 108.7 ± 33.4; P = 0.495] improved under NAD+-precursor supplementation, nor did net exercise efficiency during the submaximal cycling test [INT, 20.2 ± 2.77 compared with CON, 20.8 ± 2.88; P = 0.342].

CONCLUSIONS

Our findings are consistent with previous findings on NAD+ efficacy in humans, and we show in community-dwelling, older adults with impaired physical function that NAD+-precursor supplementation through L-tryptophan, nicotinic acid, and nicotinamide does not improve mitochondrial or skeletal muscle function. This study was registered at clinicaltrials.gov as NCT03310034.

Effects of the SGLT2 Inhibitor Dapagliflozin on Energy Metabolism in Patients With Type 2 Diabetes: A Randomized, Double-Blind Crossover Trial

OBJECTIVE

SGTL2 inhibitors increase urinary glucose excretion and have beneficial effects on cardiovascular and renal outcomes. The underlying mechanism may involve caloric restriction-like metabolic effects due to urinary glucose loss. We investigated the effects of dapagliflozin on 24-h energy metabolism and insulin sensitivity in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

There were 26 patients with type 2 diabetes randomized to a 5-week double-blind, crossover study with a 6- to 8-week washout. Indirect calorimetry was used to measure 24-h energy metabolism and the respiratory exchange ratio (RER), both by whole-room calorimetry and by ventilated hood during a two-step euglycemic-hyperinsulinemic clamp. Results are presented as the differences in least squares mean (95% CI) between treatments.

RESULTS

Evaluable patients (n = 24) had a mean (SD) age of 64.2 (4.6) years, BMI of 28.1 (2.4) kg/m², and HbA_1c of 6.9% (0.7) (51.7 [6.8] mmol/mol). Rate of glucose disappearance was unaffected by dapagliflozin, whereas fasting endogenous glucose production (EGP) increased by dapagliflozin (+2.27 [1.39, 3.14] μmol/kg/min, P < 0.0001). Insulin-induced suppression of EGP (-1.71 [-2.75, -0.63] μmol/kg/min, P = 0.0036) and plasma free fatty acids (-21.93% [-39.31, -4.54], P = 0.016) was greater with dapagliflozin. Twenty-four-hour energy expenditure (-0.11 [-0.24, 0.03] MJ/day) remained unaffected by dapagliflozin, but dapagliflozin reduced the RER during daytime and nighttime, resulting in an increased day-to-nighttime difference in the RER (-0.010 [-0.017, -0.002], P = 0.016). Dapagliflozin treatment resulted in a negative 24-h energy and fat balance (-20.51 [-27.90, -13.12] g/day).

CONCLUSIONS

Dapagliflozin treatment for 5 weeks resulted in major adjustments of metabolism mimicking caloric restriction, increased fat oxidation, improved hepatic and adipose insulin sensitivity, and improved 24-h energy metabolism.

Metabolic responses to mild cold acclimation in type 2 diabetes patients

Mild cold acclimation for 10 days has been previously shown to markedly improve insulin sensitivity in patients with type 2 diabetes. Here we show in a single-arm intervention study (Trialregister.nl ID: NL4469/NTR5711) in nine patients with type 2 diabetes that ten days of mild cold acclimation (16–17 °C) in which observable, overt shivering was prevented, does not result in improved insulin sensitivity, postprandial glucose and lipid metabolism or intrahepatic lipid content and only results in mild effects on overnight fasted fat oxidation, postprandial energy expenditure and aortic augmentation index. The lack of marked metabolic effects in this study is associated with a lack of self-reported shivering and a lack of upregulation of gene expression of muscle activation or muscle contraction pathways in skeletal muscle and suggests that some form of muscle contraction is needed for beneficial effects of mild cold acclimation.

Cold acclimation has been shown to have beneficial metabolic effects, including improved insulin sensitivity in patients with type 2 diabetes. Here the authors show that a mild cold acclimation regiment during which overt shivering was prevented did not result in improved insulin sensitivity in a small group of patients with type 2 diabetes.

Liver fat storage pathways: methodologies and dietary effects

PURPOSE OF REVIEW

Nonalcoholic fatty liver is the result of an imbalance between lipid storage [from meal, de novo lipogenesis (DNL) and fatty acid (FA) uptake] and disposal (oxidation and VLDL output). Knowledge on the contribution of each of these pathways to liver fat content in humans is essential to develop tailored strategies to prevent and treat nonalcoholic fatty liver. Here, we review the techniques available to study the different storage pathways and review dietary modulation of these pathways.

RECENT FINDINGS

The type of carbohydrate and fat could be of importance in modulating DNL, as complex carbohydrates and omega-3 FAs have been shown to reduce DNL. No effects were found on the other pathways, however studies investigating this are scarce.

SUMMARY

Techniques used to assess storage pathways are predominantly stable isotope techniques, which require specific expertise and are costly. Validated biomarkers are often lacking. These methodological limitations also translate into a limited number of studies investigating to what extent storage pathways can be modulated by diet. Further research is needed to elucidate in more detail the impact that fat and carbohydrate type can have on liver fat storage pathways and content.

A Validated Method for Quantification of Fatty Acids Incorporated in Human Plasma Phospholipids by Gas Chromatography-Triple Quadrupole Mass Spectrometry

Fatty acids (FA) are important mediators of health maintenance and disease risk. Optimal quantification assays of FA in high and low abundance as well the identification of 13C-labeled tracers to monitor FA metabolism are of major interest. The article on hand reports about the development and validation of a gas chromatography (GC)-triple quadrupole mass selective detection (GC-TQMS) method for absolute quantification of FA in human plasma phospholipids (hpPL). The quantification of the calibration solution by GC-flame ionization detection (GC-FID), with the introduction of a correction factor, allows the direct comparison of individual FA concentrations in hpPL by GC-TQMS. Specificity, sensitivity, and reproducibility are achieved by optimized chromatographic separation and employment of GC-TQMS. The inter-method comparison between GC-FID and GC-TQMS concentrations revealed good comparability for 27 FA. A full validation has been performed with linearity over 4 magnitudes, a limit of detection of 0.18-38.3 fmol on column, a recovery of 83.6-109.6%, and intraday and interday precision data meeting the criteria of EMA and FDA guidelines. The method includes the absolute quantification of 58 positional and geometrical (cis/trans) isomeric FA in hpPL in the concentration range of 1-3000 nmol/mL, covering also low abundant positional cis/trans isomers. Results obtained from both methods are highly comparable, and selectivity and sensitivity are improved by using GC-TQMS. Additionally, we show here that calculation of 13C-labeled C16:0 tracer/tracee ratios in hpPL in human isotope enrichment studies is possible.

No evidence for brown adipose tissue activation after creatine supplementation in adult vegetarians

Creatine availability in adipose tissue has been shown to have profound effects on thermogenesis and energy balance in mice. However, whether dietary creatine supplementation affects brown adipose tissue (BAT) activation in humans is unclear. In the present study, we report the results of a double-blind, randomized, placebo-controlled, cross-over trial (NCT04086381) in which 14 young, healthy, vegetarian adults, who are characterized by low creatine levels, received 20 g of creatine monohydrate per day or placebo. Participants were eligible if they met the following criteria: male or female, white, aged 18-30 years, consuming a vegetarian diet (≥6 months) and body mass index 20-25 kg m^-2. BAT activation after acute cold exposure was determined by calculating standard uptake values (SUVs) acquired by [¹⁸F]fluorodeoxyglucose positron emission tomography-magnetic resonance imaging. BAT volume (-31.32 (19.32) SUV (95% confidence interval (CI) -73.06, 10.42; P = 0.129)), SUV_mean (-0.34 (0.29) SUV (95% CI -0.97, 0.28; P = 0.254)) and SUV_max (-2.49 (2.64) SUV (95% CI -8.20, 3.21; P = 0.362)) following acute cold exposure were similar between placebo and creatine supplementation. No side effects of creatine supplementation were reported; one participant experienced bowel complaints during placebo, which resolved without intervention. Our data show that creatine monohydrate supplementation in young, healthy, lean, vegetarian adults does not enhance BAT activation after acute cold exposure.

Effects of fructose restriction on liver steatosis (FRUITLESS); a double-blind randomized controlled trial

BACKGROUND

There is an ongoing debate on whether fructose plays a role in the development of nonalcoholic fatty liver disease.

OBJECTIVES

The aim of this study was to investigate the effects of fructose restriction on intrahepatic lipid (IHL) content in a double-blind randomized controlled trial using an isocaloric comparator.

METHODS

Between March 2017 and October 2019, 44 adult overweight individuals with a fatty liver index ≥ 60 consumed a 6-wk fructose-restricted diet (<7.5 g/meal and <10 g/d) and were randomly assigned to supplementation with sachets of glucose (= intervention group) or fructose (= control group) 3 times daily. Participants and assessors were blinded to the allocation. IHL content, assessed by proton magnetic resonance spectroscopy, was the primary outcome and glucose tolerance and serum lipids were the secondary outcomes. All measurements were conducted in Maastricht University Medical Center.

RESULTS

Thirty-seven participants completed the study protocol. After 6 wk of fructose restriction, dietary fructose intake and urinary fructose excretion were significantly lower in the intervention group (difference: -57.0 g/d; 95% CI: -77.9, -39.5 g/d; and -38.8 μmol/d; 95% CI: -91.2, -10.7 μmol/d, respectively). Although IHL content decreased in both the intervention and control groups (P < 0.001 and P = 0.003, respectively), the change in IHL content was more pronounced in the intervention group (difference: -0.7% point, 95% CI: -2.0, -0.03% point). The changes in glucose tolerance and serum lipids were not significantly different between groups.

CONCLUSIONS

Six weeks of fructose restriction per se led to a small, but statistically significant, decrease in IHL content in comparison with an isocaloric control group.This trial was registered at clinicaltrials.gov as NCT03067428.

Effects of dietary macronutrients on liver fat content in adults: a systematic review and meta-analysis of randomized controlled trials

Dietary macronutrient composition may affect hepatic liver content and its associated diseases, but the results from human intervention trials have been equivocal or underpowered. We aimed to assess the effects of dietary macronutrient composition on liver fat content by conducting a systematic review and meta-analysis of randomized controlled trials in adults. Four databases (PubMed, Embase, Web of Science, and COCHRANE Library) were systematically searched for trials with isocaloric diets evaluating the effect of dietary macronutrient composition (energy percentages of fat, carbohydrates, and protein, and their specific types) on liver fat content as assessed by magnetic resonance techniques, computed tomography or liver biopsy. Data on change in liver fat content were pooled by random or fixed-effects meta-analyses and expressed as standardized mean difference (SMD). We included 26 randomized controlled trials providing data for 32 comparisons on dietary macronutrient composition. Replacing dietary fat with carbohydrates did not result in changes in liver fat (12 comparisons, SMD 0.01 (95% CI -0.36; 0.37)). Unsaturated fat as compared with saturated fat reduced liver fat content (4 comparisons, SMD -0.80 (95% CI -1.09; -0.51)). Replacing carbohydrates with protein reduced liver fat content (5 comparisons, SMD -0.33 (95% CI -0.54; -0.12)). Our meta-analyses showed that replacing carbohydrates with total fat on liver fat content was not effective, while replacing carbohydrates with proteins and saturated fat with unsaturated fat was. More well-performed and well-described studies on the effect of types of carbohydrates and proteins on liver fat content are needed, especially studies comparing proteins with fats.

L-carnitine infusion does not alleviate lipid-induced insulin resistance and metabolic inflexibility

BACKGROUND

Low carnitine status may underlie the development of insulin resistance and metabolic inflexibility. Intravenous lipid infusion elevates plasma free fatty acid (FFA) concentration and is a model for simulating insulin resistance and metabolic inflexibility in healthy, insulin sensitive volunteers. Here, we hypothesized that co-infusion of L-carnitine may alleviate lipid-induced insulin resistance and metabolic inflexibility.

METHODS

In a randomized crossover trial, eight young healthy volunteers underwent hyperinsulinemic-euglycemic clamps (40mU/m2/min) with simultaneous infusion of saline (CON), Intralipid (20%, 90mL/h) (LIPID), or Intralipid (20%, 90mL/h) combined with L-carnitine infusion (28mg/kg) (LIPID+CAR). Ten volunteers were randomized for the intervention arms (CON, LIPID and LIPID+CAR), but two dropped-out during the study. Therefore, eight volunteers participated in all three intervention arms and were included for analysis.

RESULTS

L-carnitine infusion elevated plasma free carnitine availability and resulted in a more pronounced increase in plasma acetylcarnitine, short-, medium-, and long-chain acylcarnitines compared to lipid infusion, however no differences in skeletal muscle free carnitine or acetylcarnitine were found. Peripheral insulin sensitivity and metabolic flexibility were blunted upon lipid infusion compared to CON but L-carnitine infusion did not alleviate this.

CONCLUSION

Acute L-carnitine infusion could not alleviated lipid-induced insulin resistance and metabolic inflexibility and did not alter skeletal muscle carnitine availability. Possibly, lipid-induced insulin resistance may also have affected carnitine uptake and may have blunted the insulin-induced carnitine storage in muscle. Future studies are needed to investigate this.

Pericardial fat and its influence on cardiac diastolic function

Background

Pericardial fat (PF) has been suggested to directly act on cardiomyocytes, leading to diastolic dysfunction. The aim of this study was to investigate whether a higher PF volume is associated with a lower diastolic function in healthy subjects.

Methods

254 adults (40–70 years, BMI 18–35 kg/m², normal left ventricular ejection fraction), with (a)typical chest pain (otherwise healthy) from the cardiology outpatient clinic were retrospectively included in this study. All patients underwent a coronary computed tomographic angiography for the measurement of pericardial fat volume, as well as a transthoracic echocardiography for the assessment of diastolic function parameters. To assess the independent association of PF and diastolic function parameters, multivariable linear regression analysis was performed. To maximize differences in PF volume, the group was divided in low (lowest quartile of both sexes) and high (highest quartile of both sexes) PF volume. Multivariable binary logistic analysis was used to study the associations within the groups between PF and diastolic function, adjusted for age, BMI, and sex.

Results

Significant associations for all four diastolic parameters with the PF volume were found after adjusting for BMI, age, and sex. In addition, subjects with high pericardial fat had a reduced left atrial volume index (p = 0.02), lower E/e (p < 0.01) and E/A (p = 0.01), reduced e′ lateral (p < 0.01), reduced e′ septal p = 0.03), compared to subjects with low pericardial fat.

Conclusion

These findings confirm that pericardial fat volume, even in healthy subjects with normal cardiac function, is associated with diastolic function. Our results suggest that the mechanical effects of PF may limit the distensibility of the heart and thereby directly contribute to diastolic dysfunction.

Trial registration NCT01671930

Nicotinamide riboside supplementation alters body composition and skeletal muscle acetylcarnitine concentrations in healthy obese humans

BACKGROUND

Nicotinamide riboside (NR) is an NAD+ precursor that boosts cellular NAD+ concentrations. Preclinical studies have shown profound metabolic health effects after NR supplementation.

OBJECTIVES

We aimed to investigate the effects of 6 wk NR supplementation on insulin sensitivity, mitochondrial function, and other metabolic health parameters in overweight and obese volunteers.

METHODS

A randomized, double-blinded, placebo-controlled, crossover intervention study was conducted in 13 healthy overweight or obese men and women. Participants received 6 wk NR (1000 mg/d) and placebo supplementation, followed by broad metabolic phenotyping, including hyperinsulinemic-euglycemic clamps, magnetic resonance spectroscopy, muscle biopsies, and assessment of ex vivo mitochondrial function and in vivo energy metabolism.

RESULTS

Markers of increased NAD+ synthesis-nicotinic acid adenine dinucleotide and methyl nicotinamide-were elevated in skeletal muscle after NR compared with placebo. NR increased body fat-free mass (62.65% ± 2.49% compared with 61.32% ± 2.58% in NR and placebo, respectively; change: 1.34% ± 0.50%, P = 0.02) and increased sleeping metabolic rate. Interestingly, acetylcarnitine concentrations in skeletal muscle were increased upon NR (4558 ± 749 compared with 3025 ± 316 pmol/mg dry weight in NR and placebo, respectively; change: 1533 ± 683 pmol/mg dry weight, P = 0.04) and the capacity to form acetylcarnitine upon exercise was higher in NR than in placebo (2.99 ± 0.30 compared with 2.40 ± 0.33 mmol/kg wet weight; change: 0.53 ± 0.21 mmol/kg wet weight, P = 0.01). However, no effects of NR were found on insulin sensitivity, mitochondrial function, hepatic and intramyocellular lipid accumulation, cardiac energy status, cardiac ejection fraction, ambulatory blood pressure, plasma markers of inflammation, or energy metabolism.

CONCLUSIONS

NR supplementation of 1000 mg/d for 6 wk in healthy overweight or obese men and women increased skeletal muscle NAD+ metabolites, affected skeletal muscle acetylcarnitine metabolism, and induced minor changes in body composition and sleeping metabolic rate. However, no other metabolic health effects were observed.This trial was registered at clinicaltrials.gov as NCT02835664.

Application of a BIlinear Rotation Decoupling (BIRD) filter in combination with J-difference editing for indirect 13 C measurements in the human liver

PURPOSE

Recently, we introduced a quantum coherence based method (ge-HSQC) for indirect ¹³ C-MRS in the liver to track ¹³ C-labeled lipids into the hepatic lipid pool in vivo. This approach is more robust in case of respiratory motion, however, inherently leads to a signal loss of 50% when compared with a conventional J-difference editing technique (JDE). Here, we intend to improve the robustness of a regular JDE (STEAM-ACED) with the use of a BIlinear Rotation Decoupling (BIRD) filter to achieve 100% higher signal gain when compared with ge-HSQC.

METHODS

To determine the efficiency of the BIRD filter ¹ H-[¹³ C] lipid spectra were acquired on 3T from a peanut oil phantom, with three different MR sequences: ge-HSQC, STEAM-ACED, and the BIRD filter together with STEAM-ACED (BIRD-STEAM-ACED). Finally, our proposed method is tested in vivo in five healthy volunteers with varying liver fat content. In these subjects we quantified the ¹ H-[¹³ C]-signal from the hepatic lipid pool and determined ¹³ C enrichment, which is expected to be 1.1% according to the natural abundance of ¹³ C.

RESULTS

The application of the proposed BIRD filter reduces the subtraction artifact of ¹ H-[¹² C] lipid signal efficiently in JDE experiments, which leads to a signal gain of 100% of ¹ H-[¹³ C]-lipid signals when compared with the ge-HSQC. Phase distortions in vivo were minimal with the use of BIRD compared with STEAM-ACED, which enabled us to robustly quantify the ¹³ C-enrichment in all five subjects.

CONCLUSION

The BIRD-STEAM-ACED sequence is an efficient and promising tool for ¹³ C-tracking experiments in the human liver in vivo.

No effect of resveratrol supplementation after 6 months on insulin sensitivity in overweight adults: a randomized trial

BACKGROUND

Effects of resveratrol on metabolic health have been studied in several short-term human clinical trials, with conflicting results. Next to dose, the duration of the clinical trials may explain the lack of effect in some studies, but long-term studies are still limited.

OBJECTIVES

The objective of this study was to investigate the effects of 6-mo resveratrol supplementation on metabolic health outcome parameters.

METHODS

Forty-one overweight men and women (BMI: 27-35 kg/m2; aged 40-70 y) completed the study. In this parallel-group, double-blind clinical trial, participants were randomized to receive either 150 mg/d of resveratrol (n = 20) or placebo (n = 21) for 6 mo. The primary outcome of the study was insulin sensitivity, using the Matsuda index. Secondary outcome measures were intrahepatic lipid (IHL) content, body composition, resting energy metabolism, blood pressure, plasma markers, physical performance, quality of life, and quality of sleep. Postintervention differences between the resveratrol and placebo arms were evaluated by ANCOVA adjusting for corresponding preintervention variables.

RESULTS

Preintervention, no differences were observed between the 2 treatment arms. Insulin sensitivity was not affected after 6 mo of resveratrol treatment (adjusted mean Matsuda index: 5.18 ± 0.35 in the resveratrol arm compared with 5.50 ± 0.34 in the placebo arm), although there was a significant difference in postintervention glycated hemoglobin (HbA1c) between the arms (P = 0.007). The adjusted means showed that postintervention HbA1c was lower on resveratrol (35.8 ± 0.43 mmol/mol) compared with placebo (37.6 ± 0.44 mmol/mol). No postintervention differences were found in IHL, body composition, blood pressure, energy metabolism, physical performance, or quality of life and sleep between treatment arms.

CONCLUSIONS

After 6 mo of resveratrol supplementation, insulin sensitivity was unaffected in the resveratrol arm compared with the placebo arm. Nonetheless, HbA1c was lower in overweight men and women in the resveratrol arm. This trial was registered at Clinicaltrials.gov as NCT02565979.

One-leg inactivity induces a reduction in mitochondrial oxidative capacity, intramyocellular lipid accumulation and reduced insulin signalling upon lipid infusion: a human study with unilateral limb suspension

AIMS/HYPOTHESIS

Physical inactivity, low mitochondrial function, increased intramyocellular lipid (IMCL) deposition and reduced insulin sensitivity are common denominators of chronic metabolic disorders, like obesity and type 2 diabetes. Yet, whether low mitochondrial function predisposes to insulin resistance in humans is still unknown.

METHODS

Here we investigated, in an intervention study, whether muscle with low mitochondrial oxidative capacity, induced by one-legged physical inactivity, would feature stronger signs of lipid-induced insulin resistance. To this end, ten male participants (age 22.4 ± 4.2 years, BMI 21.3 ± 2.0 kg/m²) underwent a 12 day unilateral lower-limb suspension with the contralateral leg serving as an active internal control.

RESULTS

In vivo, mitochondrial oxidative capacity, assessed by phosphocreatine (PCr)-recovery half-time, was lower in the inactive vs active leg. Ex vivo, palmitate oxidation to ¹⁴CO₂ was lower in the suspended leg vs the active leg; however, this did not result in significantly higher [¹⁴C]palmitate incorporation into triacylglycerol. The reduced mitochondrial function in the suspended leg was, however, paralleled by augmented IMCL content in both musculus tibialis anterior and musculus vastus lateralis, and by increased membrane bound protein kinase C (PKC) θ. Finally, upon lipid infusion, insulin signalling was lower in the suspended vs active leg.

CONCLUSIONS/INTERPRETATION

Together, these results demonstrate, in a unique human in vivo model, that a low mitochondrial oxidative capacity due to physical inactivity directly impacts IMCL accumulation and PKCθ translocation, resulting in impaired insulin signalling upon lipid infusion. This demonstrates the importance of mitochondrial oxidative capacity and muscle fat accumulation in the development of insulin resistance in humans.

TRIAL REGISTRATION

ClinicalTrial.gov NCT01576250.

FUNDING

PS was supported by a 'VICI' Research Grant for innovative research from the Netherlands Organization for Scientific Research (Grant 918.96.618).

Hepatic saturated fatty acid fraction is associated with de novo lipogenesis and hepatic insulin resistance

Hepatic steatosis is associated with poor cardiometabolic health, with de novo lipogenesis (DNL) contributing to hepatic steatosis and subsequent insulin resistance. Hepatic saturated fatty acids (SFA) may be a marker of DNL and are suggested to be most detrimental in contributing to insulin resistance. Here, we show in a cross-sectional study design (ClinicalTrials.gov ID: NCT03211299) that we are able to distinguish the fractions of hepatic SFA, mono- and polyunsaturated fatty acids in healthy and metabolically compromised volunteers using proton magnetic resonance spectroscopy (¹H-MRS). DNL is positively associated with SFA fraction and is elevated in patients with non-alcoholic fatty liver and type 2 diabetes. Intriguingly, SFA fraction shows a strong, negative correlation with hepatic insulin sensitivity. Our results show that the hepatic lipid composition, as determined by our ¹H-MRS methodology, is a measure of DNL and suggest that specifically the SFA fraction may hamper hepatic insulin sensitivity.

Hepatic steatosis is associated with poor cardiometabolic health, with de novo lipogenesis (DNL) contributing to hepatic steatosis and subsequent insulin resistance. Here, the authors use ¹H-MRS methodology to show hepatic SFA fraction is a measure of DNL and specifically may hamper hepatic insulin sensitivity.

Carnitine supplementation improves metabolic flexibility and skeletal muscle acetylcarnitine formation in volunteers with impaired glucose tolerance: A randomised controlled trial

Background

Type 2 diabetes patients and individuals at risk of developing diabetes are characterized by metabolic inflexibility and disturbed glucose homeostasis. Low carnitine availability may contribute to metabolic inflexibility and impaired glucose tolerance. Here, we investigated whether carnitine supplementation improves metabolic flexibility and insulin sensitivity in impaired glucose tolerant (IGT) volunteers.

Methods

Eleven IGT- volunteers followed a 36-day placebo- and L-carnitine treatment (2 g/day) in a randomised, placebo-controlled, double blind crossover design. A hyperinsulinemic-euglycemic clamp (40 mU/m²/min), combined with indirect calorimetry (ventilated hood) was performed to determine insulin sensitivity and metabolic flexibility. Furthermore, metabolic flexibility was assessed in response to a high-energy meal. Skeletal muscle acetylcarnitine concentrations were measured in vivo using long echo time proton magnetic resonance spectroscopy (¹H-MRS, TE=500 ms) in the resting state (7:00AM and 5:00PM) and after a 30-min cycling exercise. Twelve normal glucose tolerant (NGT) volunteers were included without any intervention as control group.

Results

Metabolic flexibility of IGT-subjects completely restored towards NGT control values upon carnitine supplementation, measured during a hyperinsulinemic-euglycemic clamp and meal test. In muscle, carnitine supplementation enhanced the increase in resting acetylcarnitine concentrations over the day (delta 7:00 AM versus 5:00 PM) in IGT-subjects. Furthermore, carnitine supplementation increased post-exercise acetylcarnitine concentrations and reduced long-chain acylcarnitine species in IGT-subjects, suggesting the stimulation of a more complete fat oxidation in muscle. Whole-body insulin sensitivity was not affected.

Conclusion

Carnitine supplementation improves acetylcarnitine formation and rescues metabolic flexibility in IGT-subjects. Future research should investigate the potential of carnitine in prevention/treatment of type 2 diabetes.

Characterization of BAT activity in rats using invasive and non-invasive techniques

Introduction

Brown adipose tissue (BAT) is considered as a potential target for combating obesity in humans where active BAT metabolizes glucose and fatty acids as fuel resulting in heat production. Prospective studies in humans have been set up to further study the presence and metabolic activity of BAT mostly using Positron Emission Tomography (PET) imaging in cold-stimulated conditions with the radiolabeled glucose derivative [¹⁸F]FDG. However, radiotracers beyond [¹⁸F]FDG have been proposed to investigate BAT activity, targeting various aspects of BAT metabolism. It remains questionable which tracer is best suited to detect metabolic BAT activity and to what extent those results correlate with ex vivo metabolic BAT activity.

Methods

PET and Single Photon Emission Computed Tomography (SPECT) imaging, targeting different aspects of BAT activation such as glucose metabolism, fatty acid metabolism, noradrenergic stimulation, blood perfusion and amino acid transport system, was performed immediately after injection of the tracer in rats under different temperatures: room temperature, acute cold (4 ⁰C for 4 h) or acclimated to cold (4 ⁰C for 6 h per day during 28 days). Furthermore, Magnetic Resonance Spectroscopy (MRS)-derived BAT temperature was measured in control and cold-acclimated rats.

Results

At room temperature, only [¹⁸F]FDG visualized BAT. Glucose metabolism, fatty acid metabolism, noradrenergic stimulation and blood perfusion showed a clear tracer-dependent twofold increase in BAT uptake upon cold exposure. Only the tracer for the amino acid transport system did not show BAT specific uptake under any of the experimental conditions. MRS demonstrated that cold-acclimated animals had BAT with a stronger heat-production compared to control animals.

Conclusion

BAT activity following cold exposure in rats was visualized by several tracers, while only [¹⁸F]FDG was also able to show BAT activity under non-stimulated conditions (room temperature). The variances in uptake of the different tracers should be taken into account when developing future clinical applications in humans.

Gene expression and DNA methylation as mechanisms of disturbed metabolism in offspring after exposure to a prenatal HF diet

Exposure to a prenatal high-fat (HF) diet leads to an impaired metabolic phenotype in mouse offspring. The underlying mechanisms, however, are not yet fully understood. Therefore, this study investigated whether the impaired metabolic phenotype may be mediated through altered hepatic DNA methylation and gene expression. We showed that exposure to a prenatal HF diet altered the offspring’s hepatic gene expression of pathways involved in lipid synthesis and uptake (SREBP), oxidative stress response [nuclear factor (erythroid-derived 2)-like 2 (Nrf2)], and cell proliferation. The downregulation of the SREBP pathway related to previously reported decreased hepatic lipid uptake and postprandial hypertriglyceridemia in the offspring exposed to the prenatal HF diet. The upregulation of the Nrf2 pathway was associated with increased oxidative stress levels in offspring livers. The prenatal HF diet also induced hypermethylation of transcription factor (TF) binding sites upstream of lipin 1 (Lpin1), a gene involved in lipid metabolism. Furthermore, DNA methylation of Lpin1 TF binding sites correlated with mRNA expression of Lpin1. These findings suggest that the effect of a prenatal HF diet on the adult offspring’s metabolic phenotype are regulated by changes in hepatic gene expression and DNA methylation.

Consumption of Alcoholic and Sugar-Sweetened Beverages is Associated with Increased Liver Fat Content in Middle-Aged Men and Women

BACKGROUND

Fatty liver is the leading cause of chronic liver diseases and increases the risk of cardiovascular disease. Besides alcohol consumption, energy-containing nonalcoholic beverages may contribute to liver fat accumulation.

OBJECTIVE

We aimed to study the consumption of alcoholic and nonalcoholic beverages and their mutual replacement in relation to hepatic triglyceride content (HTGC) in middle-aged men and women.

METHODS

In this cross-sectional analysis, HTGC was assessed by proton magnetic resonance spectroscopy. Habitual consumption of alcoholic and nonalcoholic beverages was assessed using a validated food-frequency questionnaire. All beverages were converted to standard servings and to percentage of total energy intake (En%). We performed linear regression to examine the association of alcoholic and nonalcoholic beverages with HTGC, adjusted for age, sex, smoking, education, ethnicity, physical activity, total energy intake, and total body fat. We studied replacement of alcoholic beverages with nonalcoholic beverages per 1 serving/d and per 5 En%/d.

RESULTS

After exclusion of individuals with missing values, 1966 participants (47% men) were analyzed, with a mean ± SD age of 55 ± 6 y, BMI of 26 ± 4 kg/m2, and HTGC of 5.7% ± 7.9%. Each extra alcoholic serving per day was associated with more liver fat (1.09 times; 95% CI: 1.05, 1.12). Replacing 5 En% of alcoholic beverages with milk was associated with less liver fat (0.89 times; 95% CI: 0.81, 0.98), whereas replacement with 5 En% of sugar-sweetened beverages was associated with liver fat to an extent similar to alcoholic beverages (1.00 times; 95% CI: 0.91, 1.09).

CONCLUSION

In a population-based cohort, consumption of each extra daily alcoholic beverage was associated with more liver fat. In isocaloric replacement of alcoholic beverages, milk was associated with less liver fat, whereas sugar-sweetened beverages were equally associated with liver fat. This suggests that intake of alcohol and sugars may contribute to liver fat accumulation. This trial was registered at clinicaltrials.gov as NCT03410316.

Resveratrol improves ex vivo mitochondrial function but does not affect insulin sensitivity or brown adipose tissue in first degree relatives of patients with type 2 diabetes

Objective

Resveratrol supplementation improves metabolic health in healthy obese men, but not in patients with type 2 diabetes (T2D) when given as add-on therapy. Therefore, we examined whether resveratrol can enhance metabolic health in men at risk of developing T2D. Additionally, we examined if resveratrol can stimulate brown adipose tissue (BAT).

Methods

Thirteen male first degree relatives (FDR) of patients with T2D received resveratrol (150 mg/day) and placebo for 30 days in a randomized, placebo controlled, cross-over trial.

Results

Resveratrol significantly improved ex vivo muscle mitochondrial function on a fatty acid-derived substrate. However, resveratrol did not improve insulin sensitivity, expressed as the rate of glucose disposal during a two-step hyperinsulinemic-euglycemic clamp. Also, intrahepatic and intramyocellular lipid content, substrate utilization, energy metabolism, and cold-stimulated ¹⁸F-FDG glucose uptake in BAT (n = 8) remained unaffected by resveratrol. In vitro experiments in adipocytes derived from human BAT confirmed the lack of effect on BAT.

Conclusions

Resveratrol stimulates muscle mitochondrial function in FDR males, which is in concordance with previous results. However, no other metabolic benefits of resveratrol were found in this group. This could be attributed to subject characteristics causing alterations in metabolism of resveratrol and thereby affecting resveratrol's effectiveness.

ClinicalTrials.gov ID

NCT02129595.

•

Resveratrol supplementation improves muscle mitochondrial function.

•

Resveratrol does not improve insulin sensitivity in people at risk of diabetes.

•

Resveratrol does not affect brown adipose tissue in people at risk of diabetes.

Exercise training reduces intrahepatic lipid content in people with and people without nonalcoholic fatty liver

Exercise training reduces intrahepatic lipid (IHL) content in people with elevated liver fat content. It is unclear, however, whether exercise training reduces IHL content in people with normal liver fat content. Here, we measured the effect of exercise training on IHL content in people with and people without nonalcohol fatty liver. We further measured changes in insulin sensitivity and hepatic energy metabolism. Eleven males with nonalcoholic fatty liver (NAFL) and 11 body mass index-matched individuals without nonalcoholic fatty liver (CON) completed a 12-wk supervised exercise training program. IHL content (proton magnetic resonance spectroscopy), maximal oxidative capacity (V̇o_2max, spiroergometry), total muscle strength, body composition, insulin sensitivity (hyperinsulinemic-euglycemic clamp), hepatic ATP-to-total phosphorus ratio, and the hepatic phosphomonoester-to-phosphodiester (PME/PDE) ratio (phosphorus magnetic resonance spectroscopy) were determined. IHL content reduced with exercise training ( P = 0.014) in the whole study population. The relative reduction in IHL content was comparable in NAFL (-34.5 ± 54.0%) and CON (-28.3 ± 60.1%) individuals ( P = 0.800). V̇o_2max ( P < 0.001), total muscle strength ( P < 0.001), and skeletal muscle insulin sensitivity ( P = 0.004) increased, whereas adipose tissue ( P = 0.246) and hepatic ( P = 0.086) insulin sensitivity did not increase significantly. Hepatic ATP-to-total phosphorus ratio ( P = 0.987) and PME/PDE ratio ( P = 0.792) did not change. Changes in IHL content correlated with changes in body weight ( r = 0.451, P = 0.035) and changes in hepatic PME/PDE ratio ( r = 0.569, P = 0.019). In conclusion, exercise training reduced intrahepatic lipid content in people with nonalcoholic fatty liver and in people with normal intrahepatic lipid content, and the percent reduction in intrahepatic lipid content was similar in both groups.