Intramyocellular lipid content and insulin sensitivity are increased following a short-term low-glycemic index diet and exercise intervention

Echo time optimization for in-vivo measurement of unsaturated lipid resonances using J-difference-edited MRS

PURPOSE

Measuring lipid composition provides more information than just total lipid content. Hence, the non-invasive measurement of unsaturated lipid protons with both high efficiency and precision is of pressing need. This study was to optimize echo time (TE) for the best resolving of J-difference editing of unsaturated lipid resonances.

METHODS

The TE dependence of J-difference-edited (JDE) MRS was verified in the density-matrix simulation, soybean oil phantom, in-vivo experiments of white adipose tissue (WAT), and skeletal muscles using single-voxel MEGA-PRESS sequence at 3T. The peak SNRs and Cramér-Rao lower bounds (CRLBs) acquired at the proposed TE of 45 ms and previously published TE of 70 ms were compared (eight pairs) in WAT, extramyocelluar lipids (EMCLs), and intramyocellular lipids (IMCLs). The lipid composition in skeletal muscles was compared between healthy males (n = 7) and females (n = 7).

RESULTS

The optimal TE was suggested as 45 ms. Compared to 70 ms, the mean signal gains at TE of 45 ms were 151% in WAT, 168% in EMCL, 204% in IMCL for allylic resonance, and 52% in EMCL for diallylic resonance. CRLBs were significantly reduced at TE of 45 ms in WAT, EMCL, IMCL for allylic resonance and in EMCL for diallylic resonance. With TE of 45 ms, significant gender differences were found in the lipid composition in EMCL pools, while no difference in IMCL pools.

CONCLUSION

The JDE-MRS protocol with TE of 45 ms allows improved quantification of unsaturated lipid resonances in vivo and future lipid metabolism investigations.

Both moderate- and high-intensity exercise training increase intramyocellular lipid droplet abundance and modify myocellular distribution in adults with obesity

Exercise training modifies lipid metabolism in skeletal muscle, but the effect of exercise training on intramyocellular lipid droplet (LD) abundance, size, and intracellular distribution in adults with obesity remains elusive. This study compared high-intensity interval training (HIIT) with more conventional moderate-intensity continuous training (MICT) on intramyocellular lipid content, as well as LD characteristics (size and number) and abundance within the intramyofibrillar (IMF) and subsarcolemmal (SS) regions of type I and type II skeletal muscle fibers in adults with obesity. Thirty-six adults with obesity [body mass index (BMI) = 33 ± 3 kg/m2] completed 12 wk (4 days/wk) of either HIIT (10 × 1 min, 90% HRmax + 1-min active recovery; n = 19) or MICT (45-min steady-state exercise, 70% HRmax; n = 17), while on a weight-maintaining diet throughout training. Skeletal muscle biopsies were collected from the vastus lateralis before and after training, and intramyocellular lipid content and intracellular LD distribution were measured by immunofluorescence microscopy. Both MICT and HIIT increased total intramyocellular lipid content by more than 50% (P < 0.01), which was attributed to a greater LD number per µm2 in the IMF region of both type I and type II muscle fibers (P < 0.01). Our findings also suggest that LD lipophagy (autophagy-mediated LD degradation) may be transiently upregulated the day after the last exercise training session (P < 0.02 for both MICT and HIIT). In summary, exercise programs for adults with obesity involving either MICT or HIIT increased skeletal muscle LD abundance via a greater number of LDs in the IMF region of the myocyte, thereby providing more lipid in close proximity to the site of energy production during exercise.NEW & NOTEWORTHY In this study, 12 wk of either moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT) enhanced skeletal muscle lipid abundance by increasing lipid droplet number within the intramyofibrillar (IMF) region of muscle. Because the IMF associates with high energy production during muscle contraction, this adaptation may enhance lipid oxidation during exercise. Despite differences in training intensity and energy expenditure between MICT and HIIT, their effects on muscle lipid abundance and metabolism were remarkably similar.

Effects of free weight and body mass-based resistance training on thigh muscle size, strength and intramuscular fat in healthy young and middle-aged individuals

NEW FINDINGS

What is the central question of this study? How do free weight resistance training (RT) and body mass-based RT for 8 weeks compare for isometric muscular strength, muscle size and intramuscular fat (IMF) content in the quadriceps femoris? What is the main finding and its importance? Free weight and body mass-based RTs could induce muscle hypertrophy; however, decreased IMF content was observed following the body mass-based RT alone.

ABSTRACT

The objective of this study was to investigate the effects of free weight and body mass-based resistance training (RT) on muscle size and thigh intramuscular fat (IMF) in young and middle-aged individuals. Healthy individuals (aged 30-64 years) were assigned to either a free weight RT group (n = 21) or a body mass-based RT group (n = 16). Both groups performed whole-body resistance exercise twice a week for 8 weeks. Free weight resistance exercises (squats, bench press, deadlift, dumbbell rows and back range) involved 70% one repetition maximum, with three sets of 8-12 repetitions per exercise. The nine body mass-based resistance exercises (leg raise, squats, rear raise, overhead shoulder mobility exercise, rowing, dips, lunge, single-leg Romanian deadlifts and push-ups) included the maximum possible repetitions per session, which were performed in one or two sets. Mid-thigh magnetic resonance images using the two-point Dixon method were taken pre- and post-training. The muscle cross-sectional area (CSA) and IMF content in the quadriceps femoris were measured from the images. Both the groups showed significantly increased muscle CSA post-training (free weight RT group, P = 0.001; body mass-based RT group, P = 0.002). IMF content in the body mass-based RT group significantly decreased (P = 0.036) but did not significantly change in the free weight RT group (P = 0.076). These results suggest that the free weight and body mass-based RTs could induce muscle hypertrophy; however, in healthy young and middle-aged individuals, decreased IMF content was induced following the body mass-based RT alone.

Contribution of skeletal muscle and serum lipids to muscle contraction induced by neuromuscular electrical stimulation in older individuals

Intramyocellular lipids (IMCL) stored in droplets in muscle cells and free fatty acids (FFA) from fat cells in the blood are the main substrates of adenosine triphosphate during continuous muscle contractions of relatively lower intensity. Although it is known that the lipid oxidative capacity decreases with aging, the effect of IMCL and FFA on muscle contraction in older individuals remains unclear. The purpose of this study was to investigate the contribution of skeletal muscle lipids and blood lipids as energy sources for muscle contraction in older individuals. Eighteen older individuals (mean age: 70.4 ± 3.5 years) underwent muscle contraction intervention induced by intermittent neuromuscular electrical stimulation (NMES) to the vastus lateralis for 30 min. Fasting blood samples were obtained and proton magnetic resonance spectroscopy (¹H‐MRS) was performed before and after NMES, and the parameters (including IMCL and extramyocellular lipid [EMCL]) from ¹H‐MRS, along with FFA and adiponectin levels, were analyzed using the blood samples of all participants. Levels of IMCL and EMCL did not change (p > 0.05); however, FFA and adiponectin levels decreased from 1.1 ± 0.5 mEq/L to 0.8 ± 0.2 mEq/L and 12.0 ± 5.3 μg/ml to 11.4 ± 5.0 μg/ml, after NMES (p < 0.05), respectively. These findings indicate that serum lipids, but not skeletal muscle lipids, are the energy substrate utilized during involuntary muscle contraction in older individuals.

β-Hydroxybutyrate is reduced in humans with obesity-related NAFLD and displays a dose-dependent effect on skeletal muscle mitochondrial respiration in vitro

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic fat accumulation and impaired insulin sensitivity. Reduced hepatic ketogenesis may promote these pathologies, but data are inconclusive in humans and the link between NAFLD and reduced insulin sensitivity remains obscure. We investigated individuals with obesity-related NAFLD and hypothesized that β-hydroxybutyrate (βOHB; the predominant ketone species) would be reduced and related to hepatic fat accumulation and insulin sensitivity. Furthermore, we hypothesized that ketones would impact skeletal muscle mitochondrial respiration in vitro. Hepatic fat was assessed by ¹H-MRS in 22 participants in a parallel design, case control study [Control: n = 7, age 50 ± 6 yr, body mass index (BMI) 30 ± 1 kg/m²; NAFLD: n = 15, age 57 ± 3 yr, BMI 35 ± 1 kg/m²]. Plasma assessments were conducted in the fasted state. Whole body insulin sensitivity was determined by the gold-standard hyperinsulinemic-euglycemic clamp. The effect of ketone dose (0.5-5.0 mM) on mitochondrial respiration was conducted in human skeletal muscle cell culture. Fasting βOHB, a surrogate measure of hepatic ketogenesis, was reduced in NAFLD (-15.6%, P < 0.01) and correlated negatively with liver fat (r² = 0.21, P = 0.03) and positively with insulin sensitivity (r² = 0.30, P = 0.01). Skeletal muscle mitochondrial oxygen consumption increased with low-dose ketones, attributable to increases in basal respiration (135%, P < 0.05) and ATP-linked oxygen consumption (136%, P < 0.05). NAFLD pathophysiology includes impaired hepatic ketogenesis, which is associated with hepatic fat accumulation and impaired insulin sensitivity. This reduced capacity to produce ketones may be a potential link between NAFLD and NAFLD-associated reductions in whole body insulin sensitivity, whereby ketone concentrations impact skeletal muscle mitochondrial respiration.

Low-glycemic index diets as an intervention for diabetes: a systematic review and meta-analysis

BACKGROUND

Low-glycemic index (GI) diets are thought to reduce postprandial glycemia, resulting in more stable blood glucose concentrations.

OBJECTIVE

We hypothesized that low-GI diets would be superior to other diet types in lowering measures of blood glucose control in people with type 1 or type 2 diabetes, or impaired glucose tolerance.

METHODS

We searched PubMed, the Cochrane Library, EMBASE, and clinical trials registries for published and unpublished studies up until 1 March, 2019. We included 54 randomized controlled trials in adults or children with impaired glucose tolerance, type 1 diabetes, or type 2 diabetes. Continuous data were synthesized using a random effects, inverse variance model, and presented as standardized mean differences with 95% CIs.

RESULTS

Low-GI diets were effective at reducing glycated hemoglobin (HbA1c), fasting glucose, BMI, total cholesterol, and LDL, but had no effect on fasting insulin, HOMA-IR, HDL, triglycerides, or insulin requirements. The reduction in fasting glucose and HbA1c was inversely correlated with body weight. The greatest reduction in fasting blood glucose was seen in the studies of the longest duration.

CONCLUSIONS

Low-GI diets may be useful for glycemic control and may reduce body weight in people with prediabetes or diabetes.

Local In Vivo Measures of Muscle Lipid and Oxygen Consumption Change in Response to Combined Vitamin D Repletion and Aerobic Training in Older Adults

Intramyocellular (IMCL), extramyocellular lipid (EMCL), and vitamin D deficiency are associated with muscle metabolic dysfunction. This study compared the change in [IMCL]:[EMCL] following the combined treatment of vitamin D and aerobic training (DAT) compared with vitamin D (D), aerobic training (AT), and control (CTL). Male and female subjects aged 60–80 years with a BMI ranging from 18.5–34.9 and vitamin D status of ≤32 ng/mL (25(OH)D) were recruited to randomized, prospective clinical trial double-blinded for supplement with a 2 × 2 factorial design. Cholecalciferol (Vitamin D₃) (10,000 IU × 5 days/week) or placebo was provided for 13 weeks and treadmill aerobic training during week 13. Gastrocnemius IMCL and EMCL were measured with magnetic resonance spectroscopy (MRS) and MRI. Hybrid near-infrared diffuse correlation spectroscopy measured hemodynamics. Group differences in IMCL were observed when controlling for baseline IMCL (p = 0.049). DAT was the only group to reduce IMCL from baseline, while a mean increase was observed in all other groups combined (p = 0.008). IMCL reduction and the corresponding increase in rVO₂ at study end (p = 0.011) were unique to DAT. Vitamin D, when combined with exercise, may potentiate the metabolic benefits of exercise by reducing IMCL and increasing tissue-level VO₂ in healthy, older adults.

Skeletal muscle Nur77 and NOR1 insulin responsiveness is blunted in obesity and type 2 diabetes but improved after exercise training

Obesity and type 2 diabetes (T2DM) are characterized by a blunted metabolic response to insulin, and strongly manifests in skeletal muscle insulin resistance. The orphan nuclear receptors, Nur77 and NOR1, regulate insulin-stimulated nutrient metabolism where Nur77 and NOR1 gene expression is increased with acute aerobic exercise and acute insulin stimulation. Whether Nur77 or NOR1 are associated with the insulin-sensitizing effects of chronic aerobic exercise training has yet to be elucidated. Fourteen lean healthy controls (LHC), 12 obese (OB), and 10 T2DM individuals (T2DM) underwent hyperinsulinemic-euglycemic clamps with skeletal muscle biopsies. Muscle was analyzed for Nur77 and NOR1 gene and protein expression at basal and insulin-stimulated conditions. Furthermore, a subcohort of 18 participants (OB, n = 12; T2DM, n = 6) underwent a 12-week aerobic exercise intervention (85% HRmax , 60 min/day, 5 days/week). In response to insulin infusion, LHC increased protein expression of Nur77 (8.7 ± 3.2-fold) and NOR1 (3.6 ± 1.1-fold), whereas OB and T2DM remained unaffected. Clamp-derived glucose disposal rates correlated with Nur77 (r2  = 0.14) and NOR1 (r2  = 0.12) protein expression responses to insulin, whereas age (Nur77: r2  = 0.22; NOR1: r2  = 0.25) and BMI (Nur77: r2  = 0.22; NOR1: r2  = 0.42) showed inverse correlations, corroborating preclinical data. In the intervention cohort, exercise improved Nur77 protein expression in response to insulin (PRE: -1.2 ± 0.3%, POST: 6.2 ± 1.5%). Also, insulin treatment of primary human skeletal muscle cells increased Nur77 and NOR1 protein. These findings highlight the multifactorial nature of insulin resistance in human obesity and T2DM. Understanding the regulation of Nur77 and NOR1 in skeletal muscle and other insulin-sensitive tissues will create opportunities to advance therapies for T2DM.

Intramyocellular lipid accumulation after sprint interval and moderate-intensity continuous training in healthy and diabetic subjects

The effects of sprint interval training (SIT) on intramyocellular (IMCL) and extramyocellular (EMCL) lipid accumulation are unclear. We tested the effects of SIT and moderate-intensity continuous training (MICT) on IMCL and EMCL accumulation in a randomized controlled setting in two different study populations; healthy untrained men (n 28) and subjects with type 2 diabetes (T2D) or prediabetes (n 26). Proton magnetic resonance spectroscopy (1 H MRS) was used to determine IMCL and EMCL in the Tibialis anterior muscle (TA) before and after a 2-week exercise period. The exercise period comprised six sessions of SIT or MICT cycling on a cycle ergometer. IMCL increased after SIT compared to MICT (P = 0.042) in both healthy and T2D/prediabetic subjects. On EMCL the training intervention had no significant effect. In conclusion, IMCL serves as an important energy depot during exercise and can be extended by high intensity exercise. The effects of high intensity interval exercise on IMCL seem to be similar regardless of insulin sensitivity or the presence of T2D.

Low glycaemic index diets as an intervention for obesity: a systematic review and meta-analysis

OBJECTIVES

Low glycaemic index (GI) diets may aid in weight loss by reducing postprandial blood glucose excursions, leading to more stable blood glucose concentrations and therefore a reduction in hunger. To test this hypothesis, we conducted a systematic review and meta-analysis of randomized controlled trials comparing low GI diets with other diet types.

METHODS

We included 101 studies involving 109 study arms and 8,527 participants. We meta-analysed the studies using a random-effects model and conducted subgroup analyses and meta-regression based on control diet, blood glucose control, baseline BMI and dietary GI.

RESULTS

Low GI diets resulted in small but significant improvements in body weight, BMI, LDL and total cholesterol overall, although no individual control diet was significantly different from low GI diets. Studies in people with normal blood glucose who achieved a difference in GI of 20 points or more resulted in a larger reduction in body weight (SMD = -0.26; 95% CIs [-0.43, -0.09]), and total cholesterol (SMD = -0.24; 95% CIs [-0.42, -0.05]) than studies that only achieved a smaller reduction in GI.

CONCLUSIONS

Low GI diets, especially diets achieving a substantial decrease in GI, were moderately effective in lowering body weight. However, efforts should be made to increase compliance with low GI diets, in order for them to be effective in people with overweight and obesity.

Dicarbonyl Stress and Glyoxalase-1 in Skeletal Muscle: Implications for Insulin Resistance and Type 2 Diabetes

Glyoxalase-1 (GLO1) is a ubiquitously expressed cytosolic protein which plays a role in the natural maintenance of cellular health and is abundantly expressed in human skeletal muscle. A consequence of reduced GLO1 protein expression is cellular dicarbonyl stress, which is elevated in obesity, insulin resistance and type 2 diabetes (T2DM). Both in vitro and pre-clinical models suggest dicarbonyl stress per se induces insulin resistance and is prevented by GLO1 overexpression, implicating a potential role for GLO1 therapy in insulin resistance and type 2 diabetes (T2DM). Recent work has identified the therapeutic potential of novel natural agents as a GLO1 inducer, which resulted in improved whole-body metabolism in obese adults. Given skeletal muscle is a major contributor to whole-body glucose, lipid, and protein metabolism, such GLO1 inducers may act, in part, through mechanisms in skeletal muscle. Currently, investigations examining the specificity of dicarbonyl stress and GLO1 biology in human skeletal muscle are lacking. Recent work from our lab indicates that dysregulation of GLO1 in skeletal muscle may underlie human insulin resistance and that exercise training may impart therapeutic benefits. This minireview will summarize the existing human literature examining skeletal muscle GLO1 and highlight the emerging therapeutic concepts for GLO1 gain-of-function in conditions such as insulin resistance and cardiometabolic disease.

Endurance exercise training and high-fat diet differentially affect composition of diacylglycerol molecular species in rat skeletal muscle

Insulin resistance of peripheral muscle is implicated in the etiology of metabolic syndrome in obesity. Although accumulation of glycerolipids, such as triacylglycerol and diacylglycerol (DAG), in muscle contributes to insulin resistance in obese individuals, endurance-trained athletes also have higher glycerolipid levels but normal insulin sensitivity. We hypothesized that the difference in insulin sensitivity of skeletal muscle between athletes and obese individuals stems from changes in fatty acid composition of accumulated lipids. Here, we evaluated the effects of intense endurance exercise and high-fat diet (HFD) on the accumulation and composition of lipid molecular species in rat skeletal muscle using a lipidomic approach. Sprague-Dawley female rats were randomly assigned to three groups and received either normal diet (ND) in sedentary conditions, ND plus endurance exercise training, or HFD in sedentary conditions. Rats were fed ND or HFD between 4 and 12 wk of age. Rats in the exercise group ran on a treadmill for 120 min/day, 5 days/wk, for 8 wk. Soleus muscle lipidomic profiles were obtained using liquid chromatography/tandem mass spectrometry. Total DAG levels, particularly those of palmitoleate-containing species, were increased in muscle by exercise training. However, whereas the total DAG level in the muscle was also increased by HFD, the levels of DAG molecular species containing palmitoleate were decreased by HFD. The concentration of phosphatidylethanolamine molecular species containing palmitoleate was increased by exercise but decreased by HFD. Our results indicate that although DAG accumulation was similar levels in trained and sedentary obese rats, specific changes in molecular species containing palmitoleate were opposite.

Intramuscular triglyceride synthesis: importance in muscle lipid partitioning in humans

Intramuscular triglyceride (IMTG) concentration is elevated in insulin-resistant individuals and was once thought to promote insulin resistance. However, endurance-trained athletes have equivalent concentration of IMTG compared with individuals with type 2 diabetes, and have very low risk of diabetes, termed the "athlete's paradox." We now know that IMTG synthesis is positively related to insulin sensitivity, but the exact mechanisms for this are unclear. To understand the relationship between IMTG synthesis and insulin sensitivity, we measured IMTG synthesis in obese control subjects, endurance-trained athletes, and individuals with type 2 diabetes during rest, exercise, and recovery. IMTG synthesis rates were positively related to insulin sensitivity, cytosolic accumulation of DAG, and decreased accumulation of C18:0 ceramide and glucosylceramide. Greater rates of IMTG synthesis in athletes were not explained by alterations in FFA concentration, DGAT1 mRNA expression, or protein content. IMTG synthesis during exercise in Ob and T2D indicate utilization as a fuel despite unchanged content, whereas IMTG concentration decreased during exercise in athletes. mRNA expression for genes involved in lipid desaturation and IMTG synthesis were increased after exercise and recovery. Further, in a subset of individuals, exercise decreased cytosolic and membrane di-saturated DAG content, which may help explain insulin sensitization after acute exercise. These data suggest IMTG synthesis rates may influence insulin sensitivity by altering intracellular lipid localization, and decreasing specific ceramide species that promote insulin resistance.

Intramyocellular triacylglycerol accumulation across weight loss strategies; Sub-study of the CENTRAL trial

BACKGROUND

Intramyocellular triacylglycerol (IMTG) is utilized as metabolic fuel during exercise and is linked to insulin resistance, but the long-term effect of weight loss strategies on IMTG among participants with abdominal fat, remain unclear.

METHODS

In an 18-month trial, sedentary participants with abdominal fat/dyslipidemia were randomized to either a low-fat (LF) or Mediterranean/low-carbohydrate (MED/LC) diet (including 28g·day-1 of walnuts). After 6-months, the participants were re-randomized to moderate intense physical activity (PA+) or non-physical activity (PA-). Magnetic resonance imaging (MRI) was used to quantify changes of IMTG, abdominal sub-depots, hepatic and intermuscular fats.

RESULTS

Across the 277 participants [86% men, age = 48 years, body-mass-index (BMI) = 31kg/m2, visceral fat = 33%] 86% completed the 18-m trial. At baseline, women had higher IMTG than men (3.4% vs. 2.3%, p<0.001) and increased IMTG was associated with aging and higher BMI, visceral and intermuscular fats, HbA1c%, HDL-c and leptin(p<0.05), but not with intra-hepatic fat. After 18 month of intervention and a -3 kg mean weight loss, participants significantly increased IMTG by 25%, with a distinct effect in the MED/LCPA+ group as compared to the other intervention groups (57% vs. 9.5-18.5%, p<0.05). Changes in IMTG were associated with visceral and intermuscular fat, metabolic syndrome, insulin and leptin (p<0.05 for all), however, these associations did not remain after adjustment for visceral fat changes.

CONCLUSIONS

Lifestyle strategies differentially affect IMTG accumulation; combination of exercise with decreased carbohydrate/increased unsaturated fat proportion intake greatly increase IMTG. Our findings suggest that increased IMTG during diet-induced moderate weight loss may not be directly related to cardiometabolic risk.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01530724.

Minimal alteration in muscle lipid genes following stabilized weight loss

Variations in skeletal muscle peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), carntine palmitoyltransferase-1 (CPT-1), perilipin protein 2 (PLIN2), and adipose tissue triglyceride lipase (ATGL), and comparative gene identification-58 (CGI-58) have been described as playing important roles in the metabolic regulation of lipid oxidation, and may influence intramyocellular lipid (IMCL) and muscle lipid droplet size (LDS). While acute changes in caloric balance and/or aerobic capacity may affect lipid metabolism, the influence of sustained weight loss derived from caloric restriction with weight loss (CWL) compared with exercise training with weight loss (EWL) on the abovementioned parameters has not been fully elucidated. Using a combination of metabolic feeding and/or supervised exercise training, we evaluated the influence of stabilized weight loss elicited by CWL compared with EWL without the confounding influence of acute alterations in caloric balance on molecular markers of mitochondrial metabolism and lipid droplet size in middle-aged overweight individuals with impaired glucose tolerance. There were no significant changes in PGC-1α, CPT-1, PLIN2, ATGL and, CGI-58 messenger RNA (mRNA) in CWL and EWL. While there were no changes in ATGL mRNA in CWL, there was a strong trend (P = 0.05) for the ΔATGL mRNA in EWL with stabilized weight loss. There were no significant changes in IMCL or LDS within skeletal muscle in CWL or EWL, respectively. In conclusion, under the conditions of chronic caloric balance following dietary or exercise-based interventions, mediators of mitochondrial function, IMCL and LDS, were largely unaffected. Future studies should focus on intervention-based changes in protein expression and/or phosphorylation and the relationship to physiological endpoints.

Resistance training improves skeletal muscle insulin sensitivity in elderly offspring of overweight and obese mothers

AIMS/HYPOTHESIS

Maternal obesity predisposes offspring to adulthood morbidities, including type 2 diabetes. Type 2 diabetes and insulin resistance have been associated with shortened telomere length. First, we aimed to investigate whether or not maternal obesity influences insulin sensitivity and its relationship with leucocyte telomere length (LTL) in elderly women. Second, we tested whether or not resistance exercise training improves insulin sensitivity in elderly frail women.

METHODS

Forty-six elderly women, of whom 20 were frail offspring of lean/normal weight mothers (OLM, BMI ≤26.3 kg/m2) and 17 were frail offspring of overweight/obese mothers (OOM,BMI ≥28.1 kg/m2), were studied before and after a 4 month resistance training (RT) intervention. Muscle insulin sensitivity of glucose uptake was measured using 18F-fluoro-2-deoxyglucose and positron emission tomography with computed tomography during a hyperinsulinaemic–euglycaemic clamp. Muscle mass and lipid content were measured using magnetic resonance and LTL was measured using real-time PCR.

RESULTS

The OOM group had lower thigh muscle insulin sensitivity compared with the OLM group (p=0.048) but similar whole body insulin sensitivity. RT improved whole body and skeletal muscle insulin sensitivity in the OOM group only (p=0.004 and p=0.013, respectively), and increased muscle mass in both groups (p <0 .01). In addition, in the OOM group, LTL correlated with different thigh muscle groups insulin sensitivity (ρ ≥ 0.53; p ≤ 0.05). Individuals with shorter LTL showed a higher increase in skeletal muscle insulin sensitivity after training (ρ ≥ −0.61; p ≤ 0.05).

CONCLUSIONS/INTERPRETATION

Maternal obesity and having telomere shortening were associated with insulin resistance in adult offspring. A resistance exercise training programme may reverse this disadvantage among offspring of obese mothers. Trial registration: ClinicalTrials.gov NCT01931540.

Lipid storage changes in human skeletal muscle during detraining

Exercise training is known to increase intramuscular triglyceride content in both trained and untrained legs. The purpose of the study was to determine the changes of intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) of both trained and untrained legs during detraining. We measured both IMCL and EMCL levels in previously trained vs. untrained legs during 4-weeks of detraining after 6-weeks of strength training. Eight young men (aged 21.4 ± 1.4 years) trained their vastus lateralis muscle in one leg using a dynamometer, whereas the contralateral leg served as untrained control. Muscle cross-sectional area (CSA), IMCL, EMCL, total creatine (creatine + phophocreatine) of extensor (vastus lateralis) muscles were assessed using magnetic resonance imaging (MRI) and proton magnetic resonance spectra (¹H-MRS) before training, 3 days after and 28 days after the last bout of training. CSA was increased in both legs by Day 3 after training, and was still high at Day 28 post-training; IMCL increased in both legs by Day 3 after training, then decreased at Day 28 post-training only in the untrained leg; EMCL shows no significant change by Day 3 after training, but at Day 28 post-training has increased in the trained leg and decreased in the untrained leg; total creatine did not change significantly.

Conclusion: Decreases of IMCL and EMCL storages in previously untrained leg during detraining indicates an ectopic influence on tissue lipid storage by different metabolic demand among tissues in the same human body.

Aberrant REDD1-mTORC1 responses to insulin in skeletal muscle from Type 2 diabetics

The objective of this study was to establish whether alterations in the REDD1-mTOR axis underlie skeletal muscle insensitivity to insulin in Type 2 diabetic (T2D), obese individuals. Vastus lateralis muscle biopsies were obtained from lean, control and obese, T2D subjects under basal and after a 2-h hyperinsulinemic (40 mU·m(-2)·min(-1))-euglycemic (5 mM) clamp. Muscle lysates were examined for total REDD1, and phosphorylated Akt, S6 kinase 1 (S6K1), 4E-BP1, ERK1/2, and MEK1/2 via Western blot analysis. Under basal conditions [(-) insulin], T2D muscle exhibited higher S6K1 and ERK1/2 and lower 4E-BP1 phosphorylation (P < 0.05), as well as elevations in blood cortisol, glucose, insulin, glycosylated hemoglobin (P < 0.05) vs. lean controls. Following insulin infusion, whole body glucose disposal rates (GDR; mg/kg/min) were lower (P < 0.05) in the T2D vs. the control group. The basal-to-insulin percent change in REDD1 expression was higher (P < 0.05) in muscle from the T2D vs. the control group. Whereas, the basal-to-insulin percent change in muscle Akt, S6K1, ERK1/2, and MEK1/2 phosphorylation was significantly lower (P < 0.05) in the T2D vs. the control group. Findings from this study propose a REDD1-regulated mechanism in T2D skeletal muscle that may contribute to whole body insulin resistance and may be a target to improve insulin action in insulin-resistant individuals.

Health benefits of endurance training alone or combined with diet for obese patients over 60: a review

BACKGROUND

The prevalence of obesity is rapidly increasing in older patients and it is ubiquitous in many developed countries. Obesity is related to various negative health outcomes, making it a major public health target for intervention.

PURPOSE

The aim of this study was to explore and summarise the literature that addresses endurance training alone or combined with nutrition interventions to combat obesity in obese patients over age 60.

METHODS

We searched online electronic databases up to September 2014 for original observational and intervention studies published between 1995 and 2014 on the relationship between endurance training alone or combined with a diet in obese patients over 60 regarding health outcomes.

RESULTS

Twenty-six studies examined interventions aimed specifically at promoting endurance training alone or combined with diet for older obese patients over 60. These studies demonstrated a positive effect of this intervention on the primary prevention of cardiovascular disease, and a significant beneficial effect on the lipid profile. Improvement of body composition and insulin sensitivity, and a reduction in blood pressure were also well established.

CONCLUSIONS

Overall, this review demonstrates a positive effect of endurance training alone or combined with diet on health outcomes and metabolic benefits in older adults. Clinicians can now use this evidence to formulate actions to encourage the older obese to profit from the health benefits of endurance training and diet. This will not only help reduce the dramatic increase in the number of older obese but also help prevent sarcopenic obesity, which is a complex challenge for healthcare professionals.

Effect of 1-h moderate-intensity aerobic exercise on intramyocellular lipids in obese men before and after a lifestyle intervention

Intramyocellular lipids (IMCL) are depleted in response to an acute bout of exercise in lean endurance-trained individuals; however, it is unclear whether changes in IMCL content are also seen in response to acute and chronic exercise in obese individuals. We used magnetic resonance spectroscopy in 18 obese men and 5 normal-weight controls to assess IMCL content before and after an hour of cycling at the intensity corresponding with each participant's maximal whole-body rate of fat oxidation (Fatmax). Fatmax was determined via indirect calorimetry during a graded exercise test on a cycle ergometer. The same outcome measures were reassessed in the obese group after a 16-week lifestyle intervention comprising dietary calorie restriction and exercise training. At baseline, IMCL content decreased in response to 1 h of cycling at Fatmax in controls (2.8 ± 0.4 to 2.0 ± 0.3 A.U., -39%, p = 0.02), but not in obese (5.4 ± 2.1 vs. 5.2 ± 2.2 A.U., p = 0.42). The lifestyle intervention lead to weight loss (-10.0 ± 5.4 kg, p < 0.001), improvements in maximal aerobic power (+5.2 ± 3.4 mL/(kg·min)), maximal fat oxidation rate (+0.19 ± 0.22 g/min), and a 29% decrease in homeostasis model assessment score (all p < 0.05). However, when the 1 h of cycling at Fatmax was repeated after the lifestyle intervention, there remained no observable change in IMCL (4.6 ± 1.8 vs. 4.6 ± 1.9 A.U., p = 0.92). In summary, there was no IMCL depletion in response to 1 h of cycling at moderate intensity either before or after the lifestyle intervention in obese men. An effective lifestyle intervention including moderate-intensity exercise training did not impact rate of utilisation of IMCL during acute exercise in obese men.

Excessive Body Weight in Older Adults

The health challenges prompted by obesity in the older adult population are poorly recognized and understudied. A defined treatment of geriatric obesity is difficult to establish, as it must take into account biological heterogeneity, age-related comorbidities, and functional limitations (sarcopenia/dynapenia). This retrospective article highlights the current understanding of the optimal body mass index (BMI) in later life, addressing appropriate recommendations based on BMI category, age, and health history. The findings of randomized control trials of weight loss/maintenance interventions help one to move closer to evidence-based and appropriately individualized recommendations for body weight management in older adults.

Vitamin D status is related to intramyocellular lipid in older adults

Vitamin D and intramyocellular lipid (IMCL) both affect muscle function, but the relationship between vitamin D status and IMCL has not been established. To assess the relationship between vitamin D [measured as 25-hydroxy-vitamin-D (25(OH)D)] and IMCL, 20 community-dwelling adults between the ages of 65 and 85 were recruited. Serum 25(OH)D, and gastrocnemius IMCL and extramyocellular lipid (EMCL) were measured with magnetic resonance spectroscopy and fat ratio segmentation. A lifestyle questionnaire assessed physical activity. Muscle strength (1-repetition maximum) and physical function tests (timed up and go, timed sit to stand, four square step test, and gait speed) were also performed. Mean 25(OH)D was 37.9 ± 13.1 ng/mL with a range of 19-68 ng/mL. Soleus and gastrocnemius IMCL to water ratio was 1.04 ± 0.43 and 0.53 ± 0.22, respectively, but only gastrocnemius IMCL was correlated with 25(OH)D (R (2) = 0.39; p = 0.02). This relationship was independent of body mass index (p > 0.14), physical activity level (p > 0.08), and sex (p > 0.13). 25(OH)D did not correlate with EMCL (R (2) = 0.007; p = 0.78). The four square step test was the only performance or strength test correlated with 25(OH)D (R (2) = 0.26; p = 0.023). Muscle strength and physical function measures were not correlated with IMCL or EMCL. These data suggest that vitamin D status may influence gastrocnemius IMCL content independent of body mass and physical activity. Future studies should consider exploring whether vitamin D has an independent role in affecting muscle lipid metabolism and function.

Subsarcolemmal lipid droplet responses to a combined endurance and strength exercise intervention

Muscle lipid stores and insulin sensitivity have a recognized association although the mechanism remains unclear. We investigated how a 12‐week supervised combined endurance and strength exercise intervention influenced muscle lipid stores in sedentary overweight dysglycemic subjects and normal weight control subjects (n = 18). Muscle lipid stores were measured by magnetic resonance spectroscopy (MRS), electron microscopy (EM) point counting, and direct EM lipid droplet measurements of subsarcolemmal (SS) and intramyofibrillar (IMF) regions, and indirectly, by deep sequencing and real‐time PCR of mRNA of lipid droplet‐associated proteins. Insulin sensitivity and VO₂max increased significantly in both groups after 12 weeks of training. Muscle lipid stores were reduced according to MRS at baseline before and after the intervention, whereas EM point counting showed no change in LD stores post exercise, indicating a reduction in muscle adipocytes. Large‐scale EM quantification of LD parameters of the subsarcolemmal LD population demonstrated reductions in LD density and LD diameters. Lipid droplet volume in the subsarcolemmal LD population was reduced by ~80%, in both groups, while IMF LD volume was unchanged. Interestingly, the lipid droplet diameter (n = 10 958) distribution was skewed, with a lack of small diameter lipid droplets (smaller than ~200 nm), both in the SS and IMF regions. Our results show that the SS LD lipid store was sensitive to training, whereas the dominant IMF LD lipid store was not. Thus, net muscle lipid stores can be an insufficient measure for the effects of training.

We have investigated the muscle storage lipids responses to exercise, finding that subsarcolemmal lipid droplets are reduced 80%. Interestingly, we find that the lipid droplet diameter distribution was skewed, with a marked lack of lipid droplets smaller than 200 nm.

Effect of Hypericum perforatum L. extract on insulin resistance and lipid metabolic disorder in high-fat-diet induced obese mice

Natural product Hypericum perforatum L. has been used in folk medicine to improve mental performance. However, the effect of H. perforatum L. on metabolism is still unknown. In order to test whether H. perforatum L. extract (EHP) has an effect on metabolic syndrome, we treated diet induced obese (DIO) C57BL/6J mice with the extract. The chemical characters of EHP were investigated with thin-layer chromatography, ultraviolet, high-performance liquid chromatography (HPLC), and HPLC-mass spectrometry fingerprint analysis. Oral glucose tolerance test (OGTT), insulin tolerance test (ITT), and the glucose infusion rate (GIR) in hyperinsulinemic–euglycemic clamp test were performed to evaluate the glucose metabolism and insulin sensitivity. Skeletal muscle was examined for lipid metabolism. The results suggest that EHP can significantly improve the glucose and lipid metabolism in DIO mice. In vitro, EHP inhibited the catalytic activity of recombinant human protein tyrosine phosphatase 1B (PTP1B) and reduced the protein and mRNA levels of PTP1B in the skeletal muscle. Moreover, expressions of genes related to fatty acid uptake and oxidation were changed by EHP in the skeletal muscle. These results suggest that EHP may improve insulin resistance and lipid metabolism in DIO mice. © 2014 The Authors. Phytotherapy Research published by John Wiley & Sons Ltd.

Obesity and physical frailty in older adults: a scoping review of lifestyle intervention trials

Many frail older adults are thin, weak, and undernourished; this component of frailty remains a critical concern in the geriatric field. However, there is also strong evidence that excessive adiposity contributes to frailty by reducing the ability of older adults to perform physical activities and increasing metabolic instability. Our scoping review explores the impact of being obese on physical frailty in older adults by summarizing the state of the science for both clinical markers of physical function and biomarkers for potential underlying causes of obesity-related decline. We used the 5-stage methodological framework of Arksey and O'Malley to conduct a scoping review of randomized trials of weight loss and/or exercise interventions for obesity (body mass index ≥ 30 kg/m(2)) in older adults (aged >60 years), examining the outcomes of inflammation, oxidative stress, and lipid accumulation in muscle, as well as direct measures of physical function. Our initial search yielded 212 articles; exclusion of cross-sectional and observational studies, cell culture and animal studies, disease-specific interventions, and articles published before 2001 led to a final result of 21 articles. Findings of these trials included the following major points. The literature consistently confirmed benefits of lifestyle interventions to physical function assessed at the clinical level. Generally speaking, weight loss alone produced a greater effect than exercise alone, and the best outcomes were achieved with a combination of weight loss and exercise, especially exercise programs that combined aerobic, resistance, and flexibility training. Weight loss interventions tended to reduce markers of inflammation and/or oxidative damage when more robust weight reduction was achieved and maintained over time, whereas exercise did not change markers of inflammation. However, participation in a chronic exercise program did reduce the oxidative stress induced by an acute bout of exercise. Weight loss interventions consistently reduced lipid accumulation in the muscle; however, in response to exercise, 3 studies showed an increase and 2 a decrease in muscle lipid infiltration. In summary, this scoping review identified strong clinical evidence that weight reduction and/or exercise interventions can improve physical function and biomarkers of physical dysfunction among overweight/obese older adults, supporting the suggestion that excessive adiposity contributes to physical frailty. However, the evidence also suggests a complexity of metabolic influences, both systemically and within muscle, which has not been elucidated to date. Considerable further study is needed to examine the mechanisms by which lifestyle interventions influence physical frailty before the net impact of such interventions can be fully understood.

The postprandial rise in plasma cortisol in men is mediated by macronutrient-specific stimulation of adrenal and extra-adrenal cortisol production

CONTEXT

Circadian variation is a fundamental characteristic of plasma glucocorticoids, with a postprandial rise in cortisol an important feature. The diurnal rhythm is presumed to reflect alterations in hypothalamic-pituitary-adrenal axis activity; however, cortisol is produced not only by the adrenal glands but also by regeneration from cortisone by the enzyme 11β-hydroxysteroid dehydrogenase type 1, mainly in liver and adipose tissue.

OBJECTIVE

We tested the contribution of peripheral cortisol regeneration to macronutrient-induced circadian variation of plasma cortisol in humans.

DESIGN

This was a randomized, single-blinded, crossover study.

SETTING

The study was conducted at a hospital research facility.

PARTICIPANTS

Eight normal-weight healthy men participated in the study.

INTERVENTIONS

Subjects were given isocaloric energy isodense flavor-matched liquid meals composed of carbohydrate, protein, fat, or low-calorie placebo during infusion of the stable isotope tracer 9,11,12,12-[2H]4-cortisol.

OUTCOME MEASURES AND RESULTS

Plasma cortisol increased similarly after all macronutrient meals (by ∼90 nmol/L) compared with placebo. Carbohydrate stimulated adrenal secretion and extra-adrenal regeneration of cortisol to a similar degree. Protein and fat meals stimulated adrenal cortisol secretion to a greater degree than extra-adrenal cortisol regeneration. The increase in cortisol production by 11β-hydroxysteroid dehydrogenase type 1 was in proportion to the increase in insulin. The postprandial cortisol rise was not accounted for by decreased cortisol clearance.

CONCLUSIONS

Food-induced circadian variation in plasma cortisol is mediated by adrenal secretion and extra-adrenal regeneration of cortisol. Given that the latter has the more potent effect on tissue cortisol concentrations and that effects on adrenal and extra-adrenal cortisol production are macronutrient specific, this novel mechanism may contribute to the physiological interplay between insulin and glucocorticoids and the contrasting effects of certain diets on postprandial metabolism.

Treating Diabetes with Exercise - Focus on the Microvasculature

The rising incidence of diabetes and the associated metabolic diseases including obesity, cardiovascular disease and hypertension have led to investigation of a number of drugs to treat these diseases. However, lifestyle interventions including diet and exercise remain the first line of defense. The benefits of exercise are typically presented in terms of weight loss, improved body composition and reduced fat mass, but exercise can have many other beneficial effects. Acute effects of exercise include major changes in blood flow through active muscle, an active hyperemia that increases the delivery of oxygen to the working muscle fibers. Longer term exercise training can affect the vasculature, improving endothelial health and possibly basal metabolic rates. Further, insulin sensitivity is improved both acutely after a single bout of exercise and shows chronic effects with exercise training, effectively reducing diabetes risk. Exercise-mediated improvements in endothelial function may also reduce complications associated with both diabetes and other metabolic disease. Thus, while drugs to improve microvascular function in diabetes continue to be investigated, exercise can also provide many similar benefits on endothelial function and should remain the first prescription when treating insulin resistance and diabetes. This review will investigate the effects of exercise on the blood vessel and the potential benefits of exercise on cardiovascular disease and diabetes.

A low-glycemic diet lifestyle intervention improves fat utilization during exercise in older obese humans

OBJECTIVE

To determine the influence of dietary glycemic index on exercise training-induced adaptations in substrate oxidation in obesity.

DESIGN AND METHODS

Twenty older, obese individuals undertook 3 months of fully supervised aerobic exercise and were randomized to low- (LoGIX) or high-glycemic (HiGIX) diets. Changes in indirect calorimetry (VO2 ; VCO2 ) were assessed at rest, during a hyperinsulinemic-euglycemic clamp, and during submaximal exercise (walking: 65% VO2 max, 200 kcal energy expenditure). Intramyocellular lipid (IMCL) was measured by (1) H-magnetic resonance spectroscopy.

RESULTS

Weight loss (-8.6 ± 1.1%) and improvements (P < 0.05) in VO2 max, glycemic control, fasting lipemia, and metabolic flexibility were similar for both LoGIX and HiGIX groups. During submaximal exercise, energy expenditure was higher following the intervention (P < 0.01) in both groups. Respiratory exchange ratio during exercise was unchanged in the LoGIX group but increased in the HiGIX group (P < 0.05). However, fat oxidation during exercise expressed in relation to changes in body weight was increased in the LoGIX group (+10.6 ± 3.6%; P < 0.05). Fasting IMCL was unchanged, however, extramyocellular lipid was reduced (P < 0.05) after LoGIX.

CONCLUSIONS

A LoGIX/exercise weight-loss intervention increased fat utilization during exercise independent of changes in energy expenditure. This highlights the potential therapeutic value of low-glycemic foods for reversing metabolic defects in obesity.

Endurance but not resistance training increases intra-myocellular lipid content and β-hydroxyacyl coenzyme A dehydrogenase activity in active elderly men

AIM

Endurance and resistance training (ET and RT, respectively) in older subjects have been proven beneficial against metabolic or cardiovascular disorders and against sarcopaenia respectively. Like ET, RT may also increase muscle oxidative capacities. In addition, it could be questioned whether RT, similarly to ET, is able to increase muscle energetic stores such as intra-myocellular lipids (IMCL) and glycogen contents. To evaluate a possible ET- and RT-induced parallel increase in oxidative capacity and energetic stores, active elderly men (72 ± 2 years) were submitted to a 14-week training programme (three times week(-1) ) combining lower body endurance and upper body resistance.

METHODS

Muscle samples were collected in ET vastus lateralis (VLat) and RT deltoid (Del) muscles before and after training. IMCL and glycogen contents were assessed by histochemistry (Oil Red O and periodic acid-Schiff staining, respectively) and by biochemical assay for glycogen. Citrate synthase (CS, marker of mitochondrial citric acid cycle), β-hydroxyacyl coenzyme A dehydrogenase (β-HAD, beta-oxidation) and phosphofructokinase (PFK, glycolytic pathway) activities were determined and so was the capillary interface index (LC/PF).

RESULTS

Both training regimens significantly increased CS and LC/PF in ET-VLat and RT-Del. IMCL content and β-HAD activity increased (P < 0.05) only in ET-VLat, whereas PFK activity increased (P < 0.05) only in RT-Del. Glycogen content was not significantly altered in response to training in both muscles.

CONCLUSION

Unlike RT, which induced an increase in PFK, ET is able to increase IMCL content and β-oxidation capacity in active elderly men, even though both training may improve CS activity and LC/PF.

The interplay of autoimmunity and insulin resistance in type 1 diabetes

Type 1 diabetes (T1D) is a common chronic disease characterized by selective autoimmune destruction of the pancreatic islet beta cells and subsequent dependence on exogenous insulin. Certain alleles including the high-risk HLA genotype, HLA-DR3-DQ2/DR4-DQ8, place individuals at increased risk of developing T1D. Autoantibodies to beta cell antigens are used in the diagnosis of T1D, and studies have shown that they can be used to predict risk of developing T1D in first degree relatives of probands. The annual global incidence of T1D is increasing by 3-5% per year. Many environmental factors have been implicated in the rising incidence of T1D. Proponents of the accelerator hypothesis argue that T1D and type 2 diabetes (T2D) are the same disorder of insulin resistance, although with different genetic backgrounds. While insulin resistance is a recognized hallmark of T2D, it also appears to play a significant role in the pathogenesis of T1D and its vascular complications. In this article, we will review: 1) immunogenetics of T1D, 2) risk factors for the development of islet autoimmunity and T1D, 3) mechanisms of insulin resistance in T1D, and 4) links between insulin resistance and complications in T1D. Further studies are needed to define environmental factors causing T1D as well as the role of insulin resistance in the pathogenesis of T1D and its complications.

Exercise training with weight loss and either a high- or low-glycemic index diet reduces metabolic syndrome severity in older adults

BACKGROUND

The efficacy of combining carbohydrate quality with exercise on metabolic syndrome risk is unclear. Thus, we determined the effects of exercise training with a low (LoGIx)- or high (HiGIx)-glycemic index diet on the severity of the metabolic syndrome (Z-score).

METHODS

Twenty-one adults (66.2±1.1 years; BMI=35.3±0.9 kg/m2) with the metabolic syndrome were randomized to 12 weeks of exercise (60 min/day for 5 days/week at about 85% HRmax) and provided a LoGIx (n=11) or HiGIx (n=10) diet. Z-scores were determined from: blood pressure, triglycerides (TGs), high-density lipoproteins (HDLs), fasting plasma glucose (FPG), and waist circumference (WC) before and after the intervention. Body composition, aerobic fitness, insulin resistance, and nonesterfied fatty acid (NEFA) suppression were also assessed.

RESULTS

LoGIx and HiGIx diets decreased body mass and insulin resistance and increased aerobic fitness comparably (p<0.05). LoGIx and HiGIx diets decreased the Z-score similarly as each intervention decreased blood pressure, TGs, FPG and WC (p<0.05). The HiGIx diet tended to suppress NEFA during insulin stimulation compared with the LoGIx diet (p=0.06).

CONCLUSIONS

Our findings highlight that exercise with weight loss reduces the severity of the metabolic syndrome whether individuals were randomized to a HiGIx or a LoGIx diet.