The interest in brown adipose tissue (BAT) as a target to combat metabolic disease has recently been renewed with the discovery of functional BAT in humans. In rodents, BAT can be activated by bile ...acids, which activate type 2 iodothyronine deiodinase (D2) in BAT via the G-coupled protein receptor TGR5, resulting in increased oxygen consumption and energy expenditure. Here we examined the effects of oral supplementation of the bile acid chenodeoxycholic acid (CDCA) on human BAT activity. Treatment of 12 healthy female subjects with CDCA for 2 days resulted in increased BAT activity. Whole-body energy expenditure was also increased upon CDCA treatment. In vitro treatment of primary human brown adipocytes derived with CDCA or specific TGR5 agonists increased mitochondrial uncoupling and D2 expression, an effect that was absent in human primary white adipocytes. These findings identify bile acids as a target to activate BAT in humans.
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•The bile acid CDCA increases human BAT activity•CDCA increases mitochondrial uncoupling in human primary adipocytes derived from BAT•CDCA promotes mitochondrial uncoupling via TGR5
While cold is an effective strategy to activate brown fat, alternative approaches are warranted. Broeders et al. show that the bile acid chenodeoxycholic acid (CDCA) promotes mitochondrial uncoupling via TGR5 in human brown adipocytes and increases brown fat activity and energy expenditure in women.
Circadian misalignment, such as in shift work, has been associated with obesity and type 2 diabetes. However, direct effects of circadian misalignment on skeletal muscle insulin sensitivity and the ...muscle molecular circadian clock have never been studied in humans. Here, we investigated insulin sensitivity and muscle metabolism in 14 healthy young lean men age 22.4 ± 2.8 years; body mass index (BMI) 22.3 ± 2.1 kg/m2 (mean ± SD) after a 3-d control protocol and a 3.5-d misalignment protocol induced by a 12-h rapid shift of the behavioral cycle. We show that short-term circadian misalignment results in a significant decrease in muscle insulin sensitivity due to a reduced skeletal muscle nonoxidative glucose disposal (rate of disappearance: 23.7 ± 2.4 vs. 18.4 ± 1.4 mg/kg per minute; control vs. misalignment; P = 0.024). Fasting glucose and free fatty acid levels as well as sleeping metabolic rate were higher during circadian misalignment. Molecular analysis of skeletal muscle biopsies revealed that the molecular circadian clock was not aligned to the inverted behavioral cycle, and transcriptome analysis revealed the human PPAR pathway as a key player in the disturbed energy metabolism upon circadian misalignment. Our findings may provide a mechanism underlying the increased risk of type 2 diabetes among shift workers.
Nicotinamide riboside (NR) is an NAD+ precursor that boosts cellular NAD+ concentrations. Preclinical studies have shown profound metabolic health effects after NR supplementation.
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.
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.
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.
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
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.
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 (
H-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
H-MRS methodology, is a measure of DNL and suggest that specifically the SFA fraction may hamper hepatic insulin sensitivity.
Recent preclinical studies showed the potential of nicotinamide adenine dinucleotide (NAD(+)) precursors to increase oxidative phosphorylation and improve metabolic health, but human data are ...lacking. We hypothesize that the nicotinic acid derivative acipimox, an NAD(+) precursor, would directly affect mitochondrial function independent of reductions in nonesterified fatty acid (NEFA) concentrations. In a multicenter randomized crossover trial, 21 patients with type 2 diabetes (age 57.7 ± 1.1 years, BMI 33.4 ± 0.8 kg/m(2)) received either placebo or acipimox 250 mg three times daily dosage for 2 weeks. Acipimox treatment increased plasma NEFA levels (759 ± 44 vs. 1,135 ± 97 μmol/L for placebo vs. acipimox, P < 0.01) owing to a previously described rebound effect. As a result, skeletal muscle lipid content increased and insulin sensitivity decreased. Despite the elevated plasma NEFA levels, ex vivo mitochondrial respiration in skeletal muscle increased. Subsequently, we showed that acipimox treatment resulted in a robust elevation in expression of nuclear-encoded mitochondrial gene sets and a mitonuclear protein imbalance, which may indicate activation of the mitochondrial unfolded protein response. Further studies in C2C12 myotubes confirmed a direct effect of acipimox on NAD(+) levels, mitonuclear protein imbalance, and mitochondrial oxidative capacity. To the best of our knowledge, this study is the first to demonstrate that NAD(+) boosters can also directly affect skeletal muscle mitochondrial function in humans.
Non-alcoholic fatty liver (NAFL) is an independent risk factor for the development of type 2 diabetes (T2DM). We examined metabolic perturbations in patients with NAFL, patients with T2DM, and ...control (CON) subjects with normal intrahepatic lipid (IHL) content.A two-step (10 mU/m
/min; 40 mU/m
/min) hyperinsulinemic-euglycemic clamp was performed in 11 NAFL, 13 T2DM, and 11 CON subjects, all matched for BMI, and aerobic fitness. IHL content was measured using proton magnetic resonance spectroscopy. Because of high IHL content variability in T2DM patients, this group was separated into a high IHL content group (IHL ≥ 5.0%, T2DM+NAFL) and a normal IHL content group (IHL < 5.0%, T2DM-non-NAFL) for further analysis.IHL content was increased in NAFL and T2DM+NAFL subjects (
<0.050 versus CON and T2DM-non-NAFL subjects). Adipose tissue insulin sensitivity index (Adipo-IR
) was higher in NAFL (
<0.050 versus CON and T2DM-non-NAFL subjects) and in T2DM+NAFL subjects (
=0.055 versus CON subjects,
<0.050 versus T2DM-non-NAFL subjects). Suppression of plasma-free fatty acids (
=0.046) was lower in NAFL compared with CON subjects, with intermediate values for T2DM-non-NAFL, and T2DM+NAFL subjects. Suppression of endogenous glucose production (EGP) and insulin-stimulated glucose disposal (Δ
) was comparable between NAFL, T2DM-non-NAFL, and T2DM+NAFL subjects (all
>0.05), and was lower in comparison with CON subjects (all
<0.01). Metabolic flexibility was lower in T2DM-non-NAFL subjects (
=0.047) and NAFL subjects (
=0.059) compared with CON subjects. Adipo-IR
(
=0.652,
<0.001), hepatic insulin resistance index (HIR
) (
=0.576,
=0.001), and Δ
(
=-0.653,
<0.001) correlated with IHL content.Individuals with NAFL suffer from metabolic perturbations to a similar degree as T2DM patients. NAFL is an important feature leading to severe insulin resistance and should be viewed as a serious health threat for the development of T2DM. ClinicalTrials.gov: NCT01317576.
Thyroid hormone receptors are present on brown adipose tissue (BAT), indicating a role for thyroid hormone in the regulation of BAT activation. The objective of this study was to examine the effect ...of thyroid hormone withdrawal followed by thyroid hormone in TSH-suppressive dosages, on energy expenditure and brown adipose tissue activity.
This study was a longitudinal study in an academic center, with a follow-up period of 6 months. Ten patients with well-differentiated thyroid carcinoma eligible for surgical treatment and subsequent radioactive iodine ablation therapy were studied in a hypothyroid state after thyroidectomy and in a subclinical hyperthyroid state (TSH-suppression according to treatment protocol). Paired two-tailed t-tests and linear regression analyses were used.
Basal metabolic rate (BMR) was significantly higher after treatment with synthetic thyroid hormone (levothyroxine) than in the hypothyroid state (BMR 3.8 ± 0.5 kJ/min versus 4.4 ± 0.6 kJ/min, P = 0.012), and non-shivering thermogenesis (NST) significantly increased from 15 ± 10% to 25 ± 6% (P = 0.009). Mean BAT activity was significantly higher in the subclinical hyperthyroid state than in the hypothyroid state (BAT standard uptake value (SUVMean) 4.0 ± 2.9 versus 2.4 ± 1.8, P = 0.039).
Our study shows that higher levels of thyroid hormone are associated with a higher level of cold-activated BAT.
ClinicalTrials.gov NCT02499471.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract Objective A disturbed day-night rhythm is associated with metabolic perturbations that can lead to obesity and type 2 diabetes mellitus (T2DM). In skeletal muscle, a reduced oxidative ...capacity is also associated with the development of T2DM. However, whether oxidative capacity in skeletal muscle displays a day-night rhythm in humans has so far not been investigated. Methods Lean, healthy subjects were enrolled in a standardized living protocol with regular meals, physical activity and sleep to reflect our everyday lifestyle. Mitochondrial oxidative capacity was examined in skeletal muscle biopsies taken at five time points within a 24-hour period. Results Core-body temperature was lower during the early night, confirming a normal day-night rhythm. Skeletal muscle oxidative capacity demonstrated a robust day-night rhythm, with a significant time effect in ADP-stimulated respiration (state 3 MO, state 3 MOG and state 3 MOGS, p < 0.05). Respiration was lowest at 1 PM and highest at 11 PM (state 3 MOGS: 80.6 ± 4.0 vs. 95.8 ± 4.7 pmol/mg/s). Interestingly, the fluctuation in mitochondrial function was also observed in whole-body energy expenditure, with peak energy expenditure at 11 PM and lowest energy expenditure at 4 AM (p < 0.001). In addition, we demonstrate rhythmicity in mRNA expression of molecular clock genes in human skeletal muscle. Conclusions Our results suggest that the biological clock drives robust rhythms in human skeletal muscle oxidative metabolism. It is tempting to speculate that disruption of these rhythms contribute to the deterioration of metabolic health associated with circadian misalignment.
Abstract
Objective:
Multiple endocrine neoplasia type 1 (MEN1) is associated with an early-onset elevated breast cancer risk. This finding potentially has implications for breast cancer screening for ...women with MEN1, and therefore it is necessary to assess whether other risk factors are involved to identify those at greatest risk.
Design:
A cross-sectional case control study was performed using the Dutch MEN1 cohort, including >90% of the adult Dutch MEN1 population. All women with a confirmed MEN1 mutation received a questionnaire regarding cancer family history and breast cancer–related endocrine and general cancer risk factors.
Results:
A total of 138 of 165 (84%) eligible women with MEN1 completed the questionnaire. Eleven of the 138 women had breast cancer. Another 34 relatives with breast cancer were identified in the families of the included women, of whom 11 were obligate MEN1 carriers, 14 had no MEN1 mutation, and 9 had an unknown MEN1 status. The median age at breast cancer diagnosis of women with MEN1 (n = 22) was 45 years (range, 30 to 80 years), in comparison with 57.5 years (range, 40 to 85 years) in female relatives without MEN1 (n = 14; P = 0.03) and 61.2 years in the Dutch reference population. Known endocrine risk factors and general risk factors were not different for women with and without breast cancer.
Conclusion:
The increased breast cancer risk in MEN1 carriers was not related to other known breast cancer risk factors or familial cancer history, and therefore breast cancer surveillance from the age of 40 years for all women with MEN1 is justifiable.
MEN1 is associated with an early-onset elevated breast cancer risk and is not related to other breast cancer risk factors. Early breast cancer surveillance is justified for all women with MEN1.
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