Exercise training-induced effects on brown and white adipose tissue metabolism in humans : positron emission tomography studies in health and insulin resistance

White adipose tissue (WAT) not only serves as a passive energy storage but also has an endocrine role releasing hormones that play a major role in the regulation of whole-body glucose homeostasis and insulin sensitivity. Active brown adipose tissue (BAT) is able to consume lipids and glucose to generate heat. The dysregulation of BAT and WAT may predispose a person to become obese and insulin resistant. Exercise training is established to reduce fat mass and insulin resistance. Some of the exercise-induced benefits may be dose-specific. However, only a few studies exist examining the effects of training on BAT metabolism in humans that are cross-sectional in nature and the results are contradictory. There are no controlled prospective intervention studies that have investigated exercise-induced effects on BAT metabolism directly in humans. Furthermore, there is no clear evidence that exercise improves WAT metabolism. The aim of this thesis was to investigate the effects of short-term (2wks) exercise training with either, sprint interval training (SIT) or moderate intensity continuous training (MICT) on BAT and WAT metabolism in middle-aged sedentary healthy (BMI 26.1±2.4; age 48±5) and insulin resistant (IR) subjects (BMI 30.1±2.5; age 49±4). Further, the effects of longer term (6wks) progressive endurance and resistance exercise training on cold-induced BAT metabolism in healthy men (BMI 23±0.9; age31±7) were studied. BAT and WAT glucose and free fatty acid was determined using positron emission tomography (PET). The results show that modifications after exercise training are not only adipose tissue depot-specific but also the type of exercise (SIT vs MICT) induces different responses. Training decreased insulin stimulated BAT glucose uptake but had no effect on cold stimulated BAT glucose uptake in healthy subjects. At baseline IR had impaired WAT GU compared to healthy subjects which normalized after training. SIT improves WAT insulin resistance while MICT decreases WAT free fatty acid metabolism in IR. This suggests that different adipose tissue depots respond differently to the metabolic demands of exercise training. Moreover, intensity affects different substrate uptake from WAT. This data suggests that changes in adipose tissue metabolism may help whole body insulin action. Overall, exercise-induced BAT and WAT adaptations provide potential therapeutic targets for obesity and type 2 diabetes

Exercise training improves adipose tissue metabolism and vasculature regardless of baseline glucose tolerance and sex

Introduction We investigated the effects of a supervised progressive sprint interval training (SIT) and moderate-intensity continuous training (MICT) on adipocyte morphology and adipose tissue metabolism and function; we also tested whether the responses were similar regardless of baseline glucose tolerance and sex. Research design and methods 26 insulin-resistant (IR) and 28 healthy participants were randomized into 2-week-long SIT (4-6x30 s at maximum effort) and MICT (40-60 min at 60% of maximal aerobic capacity (VO2peak)). Insulin-stimulated glucose uptake and fasting-free fatty acid uptake in visceral adipose tissue (VAT), abdominal and femoral subcutaneous adipose tissues (SATs) were quantified with positron emission tomography. Abdominal SAT biopsies were collected to determine adipocyte morphology, gene expression markers of lipolysis, glucose and lipid metabolism and inflammation. Results Training increased glucose uptake in VAT (pPeer reviewe

Exercise intensity regulates cytokine and klotho responses in men

Background Short-term exercise training programs that consist of moderate intensity endurance training or high intensity interval training have become popular choices for healthy lifestyle modifications, with as little as two weeks of training being shown to improve cardiorespiratory fitness and whole-body glucose metabolism. An emerging concept in exercise biology is that exercise stimulates the release of cytokines and other factors into the blood that contribute to the beneficial effects of exercise on metabolism, but whether these factors behave similarly in response to moderate and high intensity short term training is not known. Here, we determined the effects of two short-term exercise training programs on the concentrations of select secreted cytokines and Klotho, a protein involved in anti-aging. Methods Healthy, sedentary men (n = 22) were randomized to moderate intensity training (MIT) or sprint intensity training (SIT) treatment groups. SIT consisted of 6 sessions over 2 weeks of 6 x 30 s all out cycle ergometer sprints with 4 min of recovery between sprints. MIT consisted of 6 sessions over 2 weeks of cycle ergometer exercise at 60% VO2peak, gradually increasing in duration from 40 to 60 min. Blood was taken before the intervention and 48 h after the last training session, and glucose uptake was measured using [18F]FDG-PET/CT scanning. Cytokines were measured by multiplex and Klotho concentrations by ELISA. Results Both training protocols similarly increased VO2peak and decreased fat percentage and visceral fat (P Conclusion Short-term exercise training at markedly different intensities similarly improves cardiovascular fitness but results in intensity-specific changes in cytokine responses to exercise.</div

Exercise training improves adipose tissue metabolism and vasculature regardless of baseline glucose tolerance and sex

Introduction We investigated the effects of a supervised progressive sprint interval training (SIT) and moderate-intensity continuous training (MICT) on adipocyte morphology and adipose tissue metabolism and function; we also tested whether the responses were similar regardless of baseline glucose tolerance and sex.Research design and methods 26 insulin-resistant (IR) and 28 healthy participants were randomized into 2-week-long SIT (4-6x30 s at maximum effort) and MICT (40-60 min at 60% of maximal aerobic capacity (VO2peak)). Insulin-stimulated glucose uptake and fasting-free fatty acid uptake in visceral adipose tissue (VAT), abdominal and femoral subcutaneous adipose tissues (SATs) were quantified with positron emission tomography. Abdominal SAT biopsies were collected to determine adipocyte morphology, gene expression markers of lipolysis, glucose and lipid metabolism and inflammation.Results Training increased glucose uptake in VAT (pConclusions Short-term training improves adipose tissue metabolism both in healthy and IR participants independently of the sex. Adipose tissue angiogenesis and gene expression was only significantly affected in IR participants.</div

Decreased insulin‐stimulated brown adipose tissue glucose uptake after short‐term exercise training in healthy middle‐aged men

Aims To test the hypothesis that high‐intensity interval training (HIIT) and moderate‐intensity continuous training (MICT) improve brown adipose tissue (BAT) insulin sensitivity. Participants and methods Healthy middle‐aged men (n = 18, age 47 years [95% confidence interval {CI} 49, 43], body mass index 25.3 kg/m2 [95% CI 24.1‐26.3], peak oxygen uptake (VO2peak) 34.8 mL/kg/min [95% CI 32.1, 37.4] ) were recruited and randomized into six HIIT or MICT sessions within 2 weeks. Insulin‐stimulated glucose uptake was measured using 2‐[18F]flouro‐2‐deoxy‐D‐glucose positron‐emission tomography in BAT, skeletal muscle, and abdominal and femoral subcutaneous and visceral white adipose tissue (WAT) depots before and after the training interventions. Results: Training improved VO2peak (P = .0005), insulin‐stimulated glucose uptake into the quadriceps femoris muscle (P = .0009) and femoral subcutaneous WAT (P = .02) but not into BAT, with no difference between the training modes. Using pre‐intervention BAT glucose uptake, we next stratified subjects into high BAT (>2.9 µmol/100 g/min; n = 6) or low BAT (<2.9 µmol/100 g/min; n = 12) groups. Interestingly, training decreased insulin‐stimulated BAT glucose uptake in the high BAT group (4.0 [2.8, 5.5] vs 2.5 [1.7, 3.6]; training*BAT, P = .02), whereas there was no effect of training in the low BAT group (1.5 [1.2, 1.9] vs 1.6 [1.2, 2.0] µmol/100 g/min). Participants in the high BAT group had lower levels of inflammatory markers compared with those in the low BAT group. Conclusions: Participants with functionally active BAT have an improved metabolic profile compared with those with low BAT activity. Short‐term exercise training decreased insulin‐stimulated BAT glucose uptake in participants with active BAT, suggesting that training does not work as a potent stimulus for BAT activation

Exercise and brown adipose tissue activation in humans

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