Insulin at the intersection of thermoregulation and glucose homeostasis

Mammals are protected from changes in environmental temperature by altering energetic processes that modify heat production. Insulin is the dominant stimulus of glucose uptake and metabolism, which are fundamental for thermogenic processes. The purpose of this work was to determine the interaction of ambient temperature induced changes in energy expenditure (EE) on the insulin sensitivity of glucose fluxes. Short-term and adaptive responses to thermoneutral temperature (TN, ∼28 °C) and room (laboratory) temperature (RT, ∼22 °C) were studied in mice. This range of temperature does not cause detectable changes in circulating catecholamines or shivering and postabsorptive glucose homeostasis is maintained. We tested the hypothesis that a decrease in EE that occurs with TN causes insulin resistance and that this reduction in insulin action and EE is reversed upon short term (<12h) transition to RT. Insulin-stimulated glucose disposal (Rd) and tissue-specific glucose metabolic index were assessed combining isotopic tracers with hyperinsulinemic-euglycemic clamps. EE and insulin-stimulated Rd are both decreased (∼50%) in TN-adapted vs RT-adapted mice. When RT-adapted mice are switched to TN, EE rapidly decreases and Rd is reduced by ∼50%. TN-adapted mice switched to RT exhibit a rapid increase in EE, but whole-body insulin-stimulated Rd remains at the low rates of TN-adapted mice. In contrast, whole body glycolytic flux rose with EE. This higher EE occurs without increasing glucose uptake from the blood, but rather by diverting glucose from glucose storage to glycolysis. In addition to adaptations in insulin action, 'insulin-independent' glucose uptake in brown fat is exquisitely sensitive to thermoregulation. These results show that insulin action adjusts to non-stressful changes in ambient temperature to contribute to the support of body temperature homeostasis without compromising glucose homeostasis.

Insulin at the Intersection of Thermoregulation and Glucose Homeostasis

Mammals are protected from changes in environmental temperature by altering energetic processes that modify heat production. Insulin is the dominant stimulus of glucose uptake and metabolism, which are fundamental for thermogenic processes. The purpose of this work was to determine the interaction of ambient temperature induced changes in energy expenditure (EE) on the insulin sensitivity of glucose fluxes. Short-term and adaptive responses to thermoneutral temperature (TN, ~28°C) and room (laboratory) temperature (RT, ~22°C) were studied in mice. This range of temperature does not cause detectable changes in circulating catecholamines or shivering and postabsorptive glucose homeostasis is maintained. We tested the hypothesis that a decrease in EE that occurs with TN causes insulin resistance and that this reduction in insulin action and EE is reversed upon short term (<12h) transition to RT. Insulin-stimulated glucose disposal (Rd) and tissue specific glucose uptake were assessed combining isotopic tracers with hyperinsulinemic-euglycemic clamps. EE and insulin-stimulated Rd are both decreased (~50%) in TN-adapted vs RT-adapted mice. When RT-adapted mice are switched to TN, EE rapidly decreases and Rd is reduced by ~50%. TN-adapted mice switched to RT exhibit a rapid increase in EE, but whole body insulin-stimulated Rd remains at the low rates of TN-adapted mice. In contrast, whole body glycolytic flux rose with EE. This higher EE occurs without increasing glucose uptake from the blood, but rather by diverting glucose from glucose storage to glycolysis. In addition to adaptations in insulin action, 'insulin-independent' glucose uptake in brown fat is exquisitely sensitive to thermoregulation. These results show that insulin action adjusts to non-stressful changes in ambient temperature to contribute to the support of body temperature homeostasis without compromising glucose homeostasis.

Deletion of complement factor 5 amplifies glucose intolerance in obese male but not female mice

Complement factor 5 of the innate immune system generates C5a and C5b ligands, which initiate inflammatory and cell lysis events, respectively. C5 activation has been linked with obesity-associated metabolic disorders; however, whether it has a causative role is unclear. We generated a C5 null (C5-/-) mouse using CRISPR-Cas9 gene editing to determine whether loss of C5 improves obesity-linked metabolic dysfunction. Generation of a new mouse model was prompted in part by the observation of off-target gene mutations in commercially available C5-/- lines. Male and female wild-type (WT), heterozygous (Het), and C5-/- mice were fed low-fat diet (LFD) or high-fat diet (HFD) for 22 wk. Body weight gain did not differ between genotypes on LFD or HFD. In lean animals, male C5-/- mice had similar glucose tolerance compared with WT controls; however, in obese conditions, glucose tolerance was worsened in C5-/- compared with controls. In contrast, female mice did not exhibit differences in glucose tolerance between genotypes under either dietary paradigm. Fasting insulin was not different between genotypes, whereas diet-induced obese male C5-/- mice had lower fed insulin concentrations compared with WT controls. No differences in adipose tissue inflammation or adipocyte size were identified between groups. Similarly, susceptibility to fatty liver and hepatic inflammation was similar between WT and C5-/- mice. However, the systemic cytokine response to acute endotoxin exposure was decreased in C5-/- mice. Together, these data suggest that loss of C5 worsens glucose tolerance in obese male but not female mice. Additional work is required to pinpoint the mechanisms by which loss of C5 amplifies glucose intolerance in obesity.NEW & NOTEWORTHY We generated a new mouse model of complement factor 5 deficiency. This work was prompted by a need for improved transgenic mouse lines of C5, due to off-target gene mutations. We find that loss of C5 worsens glucose tolerance in a sex-dependent manner. Though the mechanisms evoking glucose intolerance are not clear, we are confident this model will be useful in interrogating complement activation in obesity-associated diseases.

Temporal optimization of exercise to lower fasting glucose levels

Exercise stimulates glucose uptake and increases insulin sensitivity acutely. Temporally optimizing exercise timing may minimize the nocturnal rise in glucose levels. This study examined the effect of exercise timing on evening and overnight glucose concentrations in individuals who were non-obese with normal fasting glucose levels (Non-Ob; n = 18) and individuals with obesity (OB) with impaired fasting glucose levels (OB+IFG) and without (n = 16 and n = 18, respectively). Subjects were studied on three occasions (no exercise (NOEX)), morning exercise (AMEX; 0700 h) and evening exercise (PMEX; 2000 h). The evening meal was provided (1800 h) and blood samples were taken from 1740 to 0700 h and morning endogenous glucose production (EGP) was measured. Glucose and insulin concentrations increased with the dinner meal with peak concentrations being higher in OB+IFG than in OB and Non-Ob (P = 0.04). In OB+IFG, evening glucose concentrations rose above baseline levels at about 2300 h, with the glucose concentrations staying somewhat lower with AMEX and PMEX until ∼0500 h than with NOEX. In OB+IFG, insulin concentrations decreased following the dinner meal and waned throughout the night, despite the rising glucose concentrations. In the OB and Non-Ob individuals following the dinner meal, no increase in glucose concentrations occurred in the evening period and insulin levels mirrored this. No difference was observed in the morning fasting glucose levels between study days or between groups. Regardless of time of day, exercise delays the evening rise in glucose concentrations in adults with OB+IFG but does not lower morning fasting glucose levels or improve the synchrony between glucose and insulin concentrations. KEY POINTS: Insulin resistance and type 2 diabetes have been linked to disturbances of the core clock, and glucose tolerance demonstrates a diurnal rhythm in healthy humans with better glucose tolerance in the morning than in the afternoon and evening. Skeletal muscle is a primary site for insulin resistance in people with impaired glucose tolerance. In individuals with obesity and impaired fasting glucose levels (OB+IFG), following a dinner meal, glucose concentrations started to rise and continues throughout the night, resulting in elevated glucose levels, while concomitantly, insulin levels are waning. Exercise, regardless of the time of day, suppressed the rise in glucose levels in OB+IFG for many hours during the night but did not lower morning fasting glucose levels. Morning exercise was not quite as effective as evening exercise.

The miR-23-27-24 clusters drive lipid-associated macrophage proliferation in obese adipose tissue

Identifying molecular circuits that control adipose tissue macrophage (ATM) function is necessary to understand how ATMs contribute to tissue homeostasis and obesity-induced insulin resistance. In this study, we find that mice with a myeloid-specific knockout of the miR-23-27-24 clusters of microRNAs (miRNAs) gain less weight on a high-fat diet but exhibit worsened glucose and insulin tolerance. Analysis of ATMs from these mice shows selectively reduced numbers and proliferation of a recently reported subset of lipid-associated CD9+Trem2+ ATMs (lipid-associated macrophages [LAMs]). Leveraging the role of miRNAs to control networks of genes, we use RNA sequencing (RNA-seq), functional screens, and biochemical assays to identify candidate target transcripts that regulate proliferation-associated signaling. We determine that miR-23 directly targets the mRNA of Eif4ebp2, a gene that restricts protein synthesis and proliferation in macrophages. Altogether, our study demonstrates that control of proliferation of a protective subset of LAMs by noncoding RNAs contributes to protection against diet-induced obesity metabolic dysfunction.

Weight Cycling Impairs Pancreatic Insulin Secretion but Does Not Perturb Whole-Body Insulin Action in Mice With Diet-Induced Obesity

In the setting of obesity and insulin resistance, glycemia is controlled in part by β-cell compensation and subsequent hyperinsulinemia. Weight loss improves glycemia and decreases hyperinsulinemia, whereas weight cycling worsens glycemic control. The mechanisms responsible for weight cycling-induced deterioration in glucose homeostasis are poorly understood. Thus, we aimed to pinpoint the main regulatory junctions at which weight cycling alters glucose homeostasis in mice. Using in vivo and ex vivo procedures we show that despite having worsened glucose tolerance, weight-cycled mice do not manifest impaired whole-body insulin action. Instead, weight cycling reduces insulin secretory capacity in vivo during clamped hyperglycemia and ex vivo in perifused islets. Islets from weight-cycled mice have reduced expression of factors essential for β-cell function (Mafa, Pdx1, Nkx6.1, Ucn3) and lower islet insulin content, compared with those from obese mice, suggesting inadequate transcriptional and posttranscriptional response to repeated nutrient overload. Collectively, these data support a model in which pancreatic plasticity is challenged in the face of large fluctuations in body weight resulting in a mismatch between glycemia and insulin secretion in mice.

Exon 2-mediated deletion of Trem2 does not worsen metabolic function in diet-induced obese mice

Triggering receptor expressed on myeloid cells 2 (Trem2) is highly expressed on myeloid cells and is involved in cellular lipid homeostasis and inflammatory processes. Trem2 deletion in mice (Trem2-/- ) evokes adipose tissue dysfunction, but its role in worsening obesity-induced metabolic dysfunction has not been resolved. Here we aimed to determine the causal role of Trem2 in regulating glucose homeostasis and insulin sensitivity in mice. Nine-week-old male and female littermate wild-type (WT) and Trem2-/- mice were fed a low- or high-fat diet for 18 weeks and phenotyped for metabolic function. Diet-induced weight gain was similar between genotypes, irrespective of sex. Consistent with previous reports, we find that loss of Trem2 causes massive adipocyte hypertrophy and an attenuation in the lipid-associated macrophage transcriptional response to obesity. In contrast to published data, we find that loss of Trem2 does not worsen metabolic function in obese mice. No differences in intraperitoneal glucose tolerance (ipGTT), oral GTT or mixed meal substrate control, including postprandial glucose, non-esterified fatty acids, insulin or triglycerides, were found between WT and Trem2-/- animals. Similarly, no phenotypic differences existed when animals were challenged with stressors on metabolic demand (i.e. acute exercise or environmental temperature modulation). Collectively, we report a disassociation between adipose tissue remodelling caused by loss of Trem2 and whole-body metabolic homeostasis in obese mice. The complementary nature of experiments conducted gives credence to the conclusion that loss of Trem2 is unlikely to worsen glucose homeostasis in mice.

Multiomics reveals persistence of obesity-associated immune cell phenotypes in adipose tissue during weight loss and weight regain in mice

Within adipose tissue (AT), immune cells and parenchymal cells closely interact creating a complex microenvironment. In obesity, immune cell derived inflammation contributes to insulin resistance and glucose intolerance. Diet-induced weight loss improves glucose tolerance; however, weight regain further exacerbates the impairment in glucose homeostasis observed with obesity. To interrogate the immunometabolic adaptations that occur in AT during murine weight loss and weight regain, we utilized cellular indexing of transcriptomes and epitopes by sequencing (CITEseq) in male mice. Obesity-induced imprinting of AT immune cells persisted through weight-loss and progressively worsened with weight regain, ultimately leading to impaired recovery of type 2 regulatory cells, activation of antigen presenting cells, T cell exhaustion, and enhanced lipid handling in macrophages in weight cycled mice. This work provides critical groundwork for understanding the immunological causes of weight cycling-accelerated metabolic disease. For further discovery, we provide an open-access web portal of diet-induced AT immune cell imprinting: https://hastylab.shinyapps.io/MAIseq .

Recruitment and remodeling of peridroplet mitochondria in human adipose tissue

Beige adipocyte mitochondria contribute to thermogenesis by uncoupling and by ATP-consuming futile cycles. Since uncoupling may inhibit ATP synthesis, it is expected that expenditure through ATP synthesis is segregated to a disparate population of mitochondria. Recent studies in mouse brown adipocytes identified peridroplet mitochondria (PDM) as having greater ATP synthesis and pyruvate oxidation capacities, while cytoplasmic mitochondria have increased fatty acid oxidation and uncoupling capacities. However, the occurrence of PDM in humans and the processes that result in their expansion have not been elucidated. Here, we describe a novel high-throughput assay to quantify PDM that is successfully applied to white adipose tissue from mice and humans. Using this approach, we found that PDM content varies between white and brown fat in both species. We used adipose tissue from pheochromocytoma (Pheo) patients as a model of white adipose tissue browning, which is characterized by an increase in the capacity for energy expenditure. In contrast with control subjects, PDM content was robustly increased in the periadrenal fat of Pheo patients. Remarkably, bioenergetic changes associated with browning were primarily localized to PDM compared to cytoplasmic mitochondria (CM). PDM isolated from periadrenal fat of Pheo patients had increased ATP-linked respiration, Complex IV content and activity, and maximal respiratory capacity. We found similar changes in a mouse model of re-browning where PDM content in whitened brown adipose tissue was increased upon re-browning induced by decreased housing temperature. Taken together, this study demonstrates the existence of PDM as a separate functional entity in humans and that browning in both mice and humans is associated with a robust expansion of peri-droplet mitochondria characterized by increased ATP synthesis linked respiration.

Myeloid-specific deletion of ferroportin impairs macrophage bioenergetics but is disconnected from systemic insulin action in adult mice

Tissue iron overload is associated with insulin resistance and mitochondrial dysfunction in rodents and humans; however, the mechanisms or cell types that mediate this phenotype are not completely understood. Macrophages (Mɸs) are known to contribute to iron handling; thus, we hypothesized that perturbed iron handling by Mɸs impairs mitochondrial energetics and evokes systemic insulin resistance in mice. Male and female mice with myeloid-targeted (LysMCre) deletion of the canonical iron exporter, ferroportin (Fpn, encoded by Slc40a1), floxed littermates, and C57BL/6J wild-type mice were used to test our hypotheses. Myeloid-targeted deletion of Fpn evoked multitissue iron accumulation and reduced mitochondrial respiration in bone marrow-derived Mɸs, liver leukocytes, and Mɸ-enriched populations from adipose tissue (AT). In addition, a single bolus of exogenous iron administered to C57BL/6J mice phenocopied the loss of Fpn, resulting in a reduction in maximal and mitochondrial reserve capacity in Mɸ-enriched cellular fractions from liver and AT. In vivo exogenous iron chelation restored mitochondrial reserve capacity in liver leukocytes from Fpn LysMCre mice, but had no effect in AT myeloid populations. However, despite the impairments in mitochondrial respiration, neither loss of myeloid-specific Fpn nor exogenous iron overload perturbed glucose homeostasis or systemic insulin action in lean or obese mice, whereas aging coupled with lifelong loss of Fpn unmasked glucose intolerance. Together these data demonstrate that iron handling is critical for the maintenance of macrophage mitochondrial function, but perturbing myeloid iron flux via the loss of Fpn action is not sufficient to evoke systemic insulin resistance in young adult mice. These findings also suggest that if Mɸs are capable of storing iron properly, they have a pronounced ability to withstand iron excess without evoking overt collateral damage and associated insulin resistance that may be age dependent.NEW & NOTEWORTHY We used myeloid-specific knockout of ferroportin to determine whether macrophage iron enrichment alters systemic metabolism. We found that macrophages in several tissues showed mitochondrial defects such as a reduction in mitochondrial reserve capacity. However, insulin action in the mice was preserved. These findings also suggest that Mɸs have a pronounced ability to withstand iron excess without evoking overt collateral damage and associated insulin resistance, which appears to be age dependent.

Exercise and Adipose Tissue Immunity: Outrunning Inflammation

Chronic inflammation is considered a precipitating factor and possibly an underlying cause of many noncommunicable diseases, including cardiovascular disease, metabolic diseases, and some cancers. Obesity, which manifests in more than 650 million people worldwide, is the most common chronic inflammatory condition, with visceral adiposity thought to be the major inflammatory hub that links obesity and chronic disease. Adipose tissue (AT) inflammation is triggered or heightened in large part by (1) accelerated immune cell recruitment, (2) reshaping of the AT stromal-immuno landscape (e.g., immune cells, endothelial cells, fibroblasts, adipocyte progenitors), and (3) perturbed AT immune cell function. Exercise, along with diet management, is a cornerstone in promoting weight loss and preventing weight regain. This review focuses on evidence that increased physical activity reduces AT inflammation caused by hypercaloric diets or genetic obesity. The precise cell types and mechanisms responsible for the therapeutic effects of exercise on AT inflammation remain poorly understood. This review summarizes what is known about obesity-induced AT inflammation and immunomodulation and highlights mechanisms by which aerobic exercise combats inflammation by remodeling the AT immune landscape. Furthermore, key areas are highlighted that require future exploration and novel discoveries into the burgeoning field of how the biology of exercise affects AT immunity.

The Tailgate Study: Differing metabolic effects of a bout of excessive eating and drinking

INTRODUCTION

Excess energy intake by spectators at a sporting event (i.e., a tailgate) might cause acute negative health effects. However, limited data exist regarding the effects of overeating and alcohol consumption on lipid metabolism and the potential to gain intrahepatic triacylglycerols (IHTG). We tested the hypothesis that overconsumption of food and alcohol would significantly increase both hepatic de novo lipogenesis (DNL) and IHTG.

METHODS

Eighteen males (mean ± SD, age: 31.4 ± 7.3 years, BMI: 32.1 ± 5.9 kg/m²) were given alcoholic drinks to elevate blood alcohol for 5 h, while highly palatable food was presented. Blood samples were collected and DNL in TG-rich lipoproteins (TRL) was measured by GC/MS, IHTG was measured via MRS (n = 15), and substrate oxidation was measured via indirect calorimetry.

RESULTS

Subjects consumed 5087 ± 149 kcal (191 ± 25% excess of total daily energy needs including 171 ± 24 g alcohol), which increased plasma insulin, glucose, TG, and decreased NEFA (ANOVA p ≤ 0.003 for all). Both DNL and TRL-TG increased (p < 0.001), while IHTG did not change in the group as a whole (p = 0.229). Individual subject data revealed remarkably differing responses for IHTG (nine increased, five decreased, one did not change). Despite maintaining equal breath alcohol levels, subjects with IHTG elevations exhibited higher DNL, consumed 90% less alcohol (p = 0.048), tended to consume more carbohydrates, and exhibited lower whole-body fat oxidation (not significant) compared to those whose IHTG was reduced.

DISCUSSION

This study demonstrates that acute excess energy intake may have differing effects on an individual's DNL and IHTG, and dietary carbohydrate may influence DNL more than alcohol.

Regulation of tissue iron homeostasis: the macrophage "ferrostat"

Iron is an essential element for multiple fundamental biological processes required for life; yet iron overload can be cytotoxic. Consequently, iron concentrations at the cellular and tissue level must be exquisitely governed by mechanisms that complement and fine-tune systemic control. It is well appreciated that macrophages are vital for systemic iron homeostasis, supplying or sequestering iron as needed for erythropoiesis or bacteriostasis, respectively. Indeed, recycling of iron through erythrophagocytosis by splenic macrophages is a major contributor to systemic iron homeostasis. However, accumulating evidence suggests that tissue-resident macrophages regulate local iron availability and modulate the tissue microenvironment, contributing to cellular and tissue function. Here, we summarize the significance of tissue-specific regulation of iron availability and highlight how resident macrophages are critical for this process. This tissue-dependent regulation has broad implications for understanding both resident macrophage function and tissue iron homeostasis in health and disease.

Post Meal Exercise May Lead to Transient Hypoglycemia Irrespective of Glycemic Status in Humans

During exercise, there is coordination between various hormonal systems to ensure glucoregulation. This study examined if hypoglycemia occurs during moderate-intensity exercise in non-obese and obese individuals with and without type 2 diabetes (T2D). Eighteen non-obese, 18 obese, and 10 obese with T2D completed 2 study days that included a meal at 1,800 h followed by rest (NOEX) or exercise (PMEX; 45 min/55% of VO₂ max 2 h post meal). Glucose, insulin, and glucagon concentrations were measured throughout this 5.5 h period. Subjects with T2D had elevated glucose responses to the meal on both study days, compared to non-obese and obese subjects (P < 0.05). During evening exercise (PMEX), subjects with T2D had a greater drop in glucose concentration (-98.4 ± 13.3 mg/dL) compared to obese (-44.8 ± 7.1 mg/dL) and non-obese (-39.3 ± 6.1 mg/dL; P < 0.01) subjects. Glucose levels decreased more so in females than males in both conditions (P < 0.01). Nadir glucose levels <70 mg/dL were observed in 33 subjects during NOEX and 39 subjects during PMEX. Obese males had a larger exercise-induced insulin drop than obese females (P = 0.01). During PMEX, peak glucagon concentrations were elevated compared to NOEX (P < 0.001). Male participants with T2D had an increased glucagon response during NOEX and PMEX compared to females (P < 0.01). In conclusion, in individuals with varying glucose tolerance, there is a dramatic drop in glucose levels during moderate-intensity exercise, despite appropriate insulin concentrations prior to exercise, and glucagon levels rising during exercise. Moderate-intensity exercise can result in low glucose concentrations (<60 mg/dL), and yet many of these individuals will be asymptomatic.

Global estrogen receptor-α knockout has differential effects on cortical and cancellous bone in aged male mice

Estrogen receptor-α knockout (ERKO) in female rodents results in bone loss associated with increased osteocyte sclerostin expression; whether this also occurs in males is unknown. Here, we examined the effects of ERKO on femoral cortical geometry, trabecular microarchitecture, and osteocyte sclerostin expression of the femur and lumbar vertebrae. At 14 months of age, male ERKO and wild-type (WT) littermates ( n = 6 per group) were sacrificed, and femora and vertebra were collected. Cortical geometry and trabecular microarchitecture were assessed via micro-computed tomography; osteocyte sclerostin expression was assessed via immunohistochemistry. ANCOVA with body weight was used to compare ERKO and WT for cortical geometry; t-tests were used for all other outcomes. Regardless of skeletal site, ERKO mice had greater trabecular bone volume and trabecular number and decreased trabecular separation compared with WT. In the femoral diaphysis, ERKO had lower total area, cortical area, and cortical thickness compared with WT. The percentage of sclerostin+ osteocytes was increased in ERKO animals in cortical bone but not in cancellous bone of the femur or the lumbar vertebrae. In conclusion, ERKO improved trabecular microarchitecture in aged male mice, but negatively altered femoral cortical geometry associated with a trend towards increased cortical sclerostin expression.

Metabolic Implications of Diet and Energy Intake during Physical Inactivity

PURPOSE

Physical inactivity is associated with disruptions in glucose metabolism and energy balance, whereas energy restriction may blunt these adverse manifestations. During hypocaloric feeding, higher-protein intake maintains lean mass which is an important component of metabolic health. This study determined whether mild energy restriction preserves glycemic control during physical inactivity and whether this preservation is more effectively achieved with a higher-protein diet.

METHODS

Ten adults (24 ± 1 yr) consumed a control (64% carbohydrate, 20% fat, 16% protein) and higher-protein diet (50% carbohydrate, 20% fat, 30% protein) during two 10-d inactivity periods (>10,000 → ~5000 steps per day) in a randomized crossover design. Energy intake was decreased by ~400 kcal·d to account for reduced energy expenditure associated with inactivity. A subset of subjects (n = 5) completed 10 d of inactivity while consuming 35% excess of their basal energy requirements, which served as a positive control condition (overfeeding+inactivity).

RESULTS

Daily steps were decreased from 12,154 ± 308 to 4275 ± 269 steps per day (P < 0.05) which was accompanied by reduced V˙O2max (-1.8 ± 0.7 mL·kg·min, P < 0.05), independent of diet conditions. No disruptions in fasting or postprandial glucose, insulin, and nonesterified fatty acids in response to 75 g of oral glucose were observed after inactivity for both diet conditions (P > 0.05). Overfeeding+inactivity increased body weight, body fat, homeostasis model assessment of insulin resistance, and 2-h postprandial glucose and insulin concentrations (P < 0.05), despite no changes in lipid concentrations.

CONCLUSIONS

We show that independent of diet (normal vs higher-protein), mild energy restriction preserves metabolic function during short-term inactivity in healthy subjects. That is, metabolic deterioration with inactivity only manifests in the setting of energy surplus.

A Thermogenic-Like Brown Adipose Tissue Phenotype Is Dispensable for Enhanced Glucose Tolerance in Female Mice

The prevailing dogma is that thermogenic brown adipose tissue (BAT) contributes to improvements in glucose homeostasis in obesogenic animal models, though much of the evidence supporting this premise is from thermostressed rodents. Determination of whether modulation of the BAT morphology/function drives changes in glucoregulation at thermoneutrality requires further investigation. We used loss- and gain-of-function approaches including genetic manipulation of the lipolytic enzyme Pnpla2, change in environmental temperature, and lifestyle interventions to comprehensively test the premise that a thermogenic-like BAT phenotype is coupled with enhanced glucose tolerance in female mice. In contrast to this hypothesis, we found that 1) compared to mice living at thermoneutrality, enhanced activation of BAT and its thermogenic phenotype via chronic mild cold stress does not improve glucose tolerance in obese mice, 2) silencing of the Pnpla2 in interscapular BAT causes a brown-to-white phenotypic shift accompanied with inflammation but does not disrupt glucose tolerance in lean mice, and 3) exercise and low-fat diet improve glucose tolerance in obese mice but these effects do not track with a thermogenic BAT phenotype. Collectively, these findings indicate that a thermogenic-like BAT phenotype is not linked to heightened glucose tolerance in female mice.

Overproduction of endothelin-1 impairs glucose tolerance but does not promote visceral adipose tissue inflammation or limit metabolic adaptations to exercise

Endothelin-1 (ET-1) is a potent vasoconstrictor and proinflammatory peptide that is upregulated in obesity. Herein, we tested the hypothesis that ET-1 signaling promotes visceral adipose tissue (AT) inflammation and disrupts glucose homeostasis. We also tested if reduced ET-1 is a required mechanism by which exercise ameliorates AT inflammation and improves glycemic control in obesity. We found that 1) diet-induced obesity, AT inflammation, and glycemic dysregulation were not accompanied by significantly increased levels of ET-1 in AT or circulation in wild-type mice and that endothelial overexpression of ET-1 and consequently increased ET-1 levels did not cause AT inflammation yet impaired glucose tolerance; 2) reduced AT inflammation and improved glucose tolerance with voluntary wheel running was not associated with decreased levels of ET-1 in AT or circulation in obese mice nor did endothelial overexpression of ET-1 impede such exercise-induced metabolic adaptations; 3) chronic pharmacological blockade of ET-1 receptors did not suppress AT inflammation in obese mice but improved glucose tolerance; and 4) in a cohort of human subjects with a wide range of body mass indexes, ET-1 levels in AT, or circulation were not correlated with markers of inflammation in AT. In aggregate, we conclude that ET-1 signaling is not implicated in the development of visceral AT inflammation but promotes glucose intolerance, thus representing an important therapeutic target for glycemic dysregulation in conditions characterized by hyperendothelinemia. Furthermore, we show that the salutary effects of exercise on AT and systemic metabolic function are not contingent on the suppression of ET-1 signaling.

Impaired insulin signaling in the B10.D2-Hc0 H2d H2-T18c/oSnJ mouse model of complement factor 5 deficiency

Given the chemoattractant potential of complement factor 5 (C5) and its increased expression in adipose tissue (AT) of obese mice, we determined whether this protein of the innate immune system impacts insulin action. C5 control (C5cont) and spontaneously C5-deficient (C5def, B10.D2-Hc0 H2d H2-T18c/oSnJ) mice were placed on low- and high-fat diets to investigate their inflammatory and metabolic phenotypes. Adenoviral delivery was used to evaluate the effects of exogenous C5 on systemic metabolism. C5def mice gained less weight than controls while fed a high-fat diet, accompanied by reduced AT inflammation, liver mass, and liver triglyceride content. Despite these beneficial metabolic effects, C5def mice demonstrated severe glucose intolerance and systemic insulin resistance, as well as impaired insulin signaling in liver and AT. C5def mice also exhibited decreased expression of insulin receptor (INSR) gene and protein, as well as improper processing of pro-INSR. These changes were not due to the C5 deficiency alone as other C5-deficient models did not recapitulate the INSR processing defect; rather, in addition to the mutation in the C5 gene, whole genome sequencing revealed an intronic 31-bp deletion in the Insr gene in the B10.D2-Hc0 H2d H2-T18c/oSnJ model. Irrespective of the genetic defect, adenoviral delivery of C5 improved insulin sensitivity in both C5cont and C5def mice, indicating an insulin-sensitizing function of C5.

Glycemic effects following the consumption of mixed soy protein isolate and alginate beverages in healthy adults

This study examined whether the consumption of beverages containing mixed soy protein isolate (SPI) and fiber, alginate (ALG), would affect postprandial glucose and insulin responses or appetite in healthy adults. Following an overnight fast, twelve healthy subjects were asked to consume six standardized breakfast beverages in a randomized order: a 122 kcal sugar beverage (CONT), a 122 kcal sugar beverage with ALG, a 172 kcal sugar beverage with SPI at pH 7 (SPI-7) or 6 (SPI-6), and a 172 kcal sugar beverage with mixed SPI and alginate at pH 7 (SPI + ALG-7) or 6 (SPI + ALG-6). Subjects consumed one of the beverages at time 0. Blood samples were drawn at -15, 0, 15, 30, 45, 60, 90 and 120 min and questionnaires were completed immediately following the blood drawing at each time point. The results showed that, compared to CONT, the consumption of SPI-7, SPI-6, SPI + ALG-7 and SPI + ALG-6 significantly lowered (P < 0.05) the peak plasma glucose concentration (33.4%, 36.3%, 53.2%, and 58.5%, respectively), 120 min incremental area under the curve (AUC), and peak insulin concentration. SPI + ALG-6 and SPI + ALG-7 exhibited a significant reduction in the peak glucose concentration compared to SPI without alginate (P < 0.05). No significant effect on appetite was found in any conditions. Electrostatic interactions between the protein and alginate during digestion and formation of intragastric gel could play an important role in influencing the postprandial glucose response. This study indicates that the consumption of mixed SPI and ALG beverages was the most effective in attenuating the postprandial glycemic excursion in healthy adult subjects.

Estrogen receptor-α signaling maintains immunometabolic function in males and is obligatory for exercise-induced amelioration of nonalcoholic fatty liver

The role of estrogen receptor-α (ERα) signaling in immunometabolic function is established in females. However, its necessity in males, while appreciated, requires further study. Accordingly, we first determined whether lower metabolic function in male mice compared with females is related to reduced ERα expression. ERα protein expression in metabolically active tissues was lower in males than in females, and this lower expression was associated with worse glucose tolerance. Second, we determined whether ERα is required for optimal immunometabolic function in male mice consuming a chow diet. Despite lower expression of ERα in males, its genetic ablation (KO) caused an insulin-resistant phenotype characterized by enhanced adiposity, glucose intolerance, hepatic steatosis, and metaflammation in adipose tissue and liver. Last, we determined whether ERα is essential for exercise-induced metabolic adaptations. Twelve-week-old wild-type (WT) and ERα KO mice either remained sedentary (SED) or were given access to running wheels (WR) for 10 wk while fed an obesogenic diet. Body weight and fat mass were lower in WR mice regardless of genotype. Daily exercise obliterated immune cell infiltration and inflammatory gene transcripts in adipose tissue in both genotypes. In the liver, however, wheel running suppressed hepatic steatosis and inflammatory gene transcripts in WT but not in KO mice. In conclusion, the present findings indicate that ERα is required for optimal immunometabolic function in male mice despite their reduced ERα protein expression in metabolically active tissues. Furthermore, for the first time, we show that ERα signaling appears to be obligatory for exercise-induced prevention of hepatic steatosis.

Increased susceptibility to OVX-associated metabolic dysfunction in UCP1-null mice

Premenopausal females are protected against adipose tissue inflammation and insulin resistance, until loss of ovarian hormone production (e.g., menopause). There is some evidence that females have greater brown adipose tissue (BAT) thermogenic capacity. Because BAT mass correlates inversely with insulin resistance, we hypothesized that increased uncoupling protein 1 (UCP1) expression contributes to the superior metabolic health of females. Given that UCP1 transiently increases in BAT following ovariectomy (OVX), we hypothesized that UCP1 may 'buffer' OVX-mediated metabolic dysfunction. Accordingly, female UCP1-knockout (KO) and WT mice received OVX or sham (SHM) surgeries at 12 weeks of age creating four groups (n = 10/group), which were followed for 14 weeks and compared for body weight and adiposity, food intake, energy expenditure and spontaneous physical activity (metabolic chambers), insulin resistance (HOMA-IR, ADIPO-IR and glucose tolerance testing) and adipose tissue phenotype (histology, gene and protein expression). Two-way ANOVA was used to assess the main effects of genotype (G), OVX treatment (O) and genotype by treatment (GxO) interactions, which were considered significant when P ≤ 0.05. UCP1KO mice experienced a more adverse metabolic response to OVX than WT. Whereas OVX-induced weight gain was not synergistically greater for KO compared to WT (GxO, NS), OVX-induced insulin resistance was significantly exacerbated in KO compared to WT (GxO for HOMA-IR, P < 0.05). These results suggest UCP1 is protective against metabolic dysfunction associated with loss of ovarian hormones and support the need for more research into therapeutics to selectively target UCP1 for prevention and treatment of metabolic dysfunction following ovarian hormone loss.

Endothelial dysfunction occurs independently of adipose tissue inflammation and insulin resistance in ovariectomized Yucatan miniature-swine

In rodents, experimentally-induced ovarian hormone deficiency increases adiposity and adipose tissue (AT) inflammation, which is thought to contribute to insulin resistance and increased cardiovascular disease risk. However, whether this occurs in a translationally-relevant large animal model remains unknown. Herein, we tested the hypothesis that ovariectomy would promote visceral and perivascular AT (PVAT) inflammation, as well as subsequent insulin resistance and peripheral vascular dysfunction in female swine. At sexual maturity (7 months of age), female Yucatan mini-swine either remained intact (control, n = 9) or were ovariectomized (OVX, n = 7). All pigs were fed standard chow (15-20 g/kg), and were euthanized 6 months post-surgery. Uterine mass and plasma estradiol levels were decreased by ∼10-fold and 2-fold, respectively, in OVX compared to control pigs. Body mass, glucose homeostasis, and markers of insulin resistance were not different between control and OVX pigs; however, OVX animals exhibited greater plasma triglycerides and triglyceride:HDL ratio. Ovariectomy enhanced visceral adipocyte expansion, although this was not accompanied by brachial artery PVAT adipocyte expansion, AT inflammation in either depot, or increased systemic inflammation assessed by plasma C-reactive protein concentrations. Despite the lack of AT inflammation and insulin resistance, OVX pigs exhibited depressed brachial artery endothelial-dependent vasorelaxation, which was rescued with blockade of endothelin receptor A. Together, these findings indicate that in female Yucatan mini-swine, increased AT inflammation and insulin resistance are not required for loss of ovarian hormones to induce endothelial dysfunction.

Energy-matched moderate and high intensity exercise training improves nonalcoholic fatty liver disease risk independent of changes in body mass or abdominal adiposity - A randomized trial

BACKGROUND AND PURPOSE

Exercise training is commonly prescribed for individuals diagnosed with nonalcoholic fatty liver disease (NAFLD); however, consensus regarding the volume and intensity of exercise for optimal benefits is lacking. Thus, we determined whether high intensity interval exercise training (HIIT) produced greater reductions in intrahepatic lipid (IHL) content and NAFLD risk factors compared with energy-matched moderate intensity continuous exercise training (MICT) in obese adults with liver steatosis.

METHODS

Eighteen obese adults were randomized to either 4weeks of HIIT (4min 80% VO₂peak/3min, 50% VO₂peak) or MICT (55% VO₂peak, ~60min), matched for energy expenditure (~400kcal/session) and compared to five non-exercising age-matched control subjects. IHL was measured by ¹H-MRS and frequent blood samples were analyzed for glucose, insulin, c-peptide, and NEFA levels during a liquid meal test (180min) to characterize metabolic phenotype.

RESULTS

Baseline body weight, visceral abdominal adiposity, and fasting insulin concentrations were greater in the MICT vs HIIT group (P<0.05), while IHL was tightly matched between MICT and HIIT subjects (P>0.05), albeit higher than control subjects (P<0.01). Visceral abdominal adiposity, body mass, liver aminotransferases (ALT, AST), and hepatic apoptotic/inflammatory markers (cytokeratin 18 and fetuin a) were not reduced with either exercise training intervention (P>0.05). Both HIIT and MICT lowered IHL (HIIT, -37.0±12.4%; MICT, -20.1±6.6%, P<0.05); however, the reduction in IHL was not statistically different between exercise intensities (P=0.25). Furthermore, exercise training decreased postprandial insulin, c-peptide, and lipid peroxidation levels (iAUC, P<0.05).

CONCLUSIONS

Collectively, these findings indicate that energy-matched high intensity and moderate intensity exercise are effective at decreasing IHL and NAFLD risk that is not contingent upon reductions in abdominal adiposity or body mass.

Removal of interscapular brown adipose tissue increases aortic stiffness despite normal systemic glucose metabolism in mice

Brown adipose tissue (BAT) is considered protective against obesity and related cardiometabolic dysfunction. Indeed, activation of BAT improves glucose homeostasis and attenuates cardiovascular disease development. However, whether a reduction in BAT mass perturbs metabolic function and increases risk for cardiovascular disease remains largely unknown. To address this question, C57BL/6J male mice underwent a sham procedure or surgical bilateral excision of interscapular BAT (iBATx) and were fed a normal chow or a Western diet for 18 wk, creating four groups ( n = 10/group). Mice were housed at 25°C. As expected, the Western diet increased final body weight and adiposity; however, contrary to our hypothesis, iBATx did not potentiate adiposity independent of diet. Furthermore, iBATx did not affect indexes of glycemic control (HbA_1c, fasting glucose and insulin, and glucose area under the curve during a glucose tolerance test) and produced minimal-to-no effects on lipid homeostasis. The absence of metabolic disturbances with iBATx was not attributed to regrowth of iBAT or a "browning" or proliferative compensatory response of other BAT depots. Notably, iBATx caused an increase in aortic stiffness in normal chow-fed mice only, which was associated with an increase in aortic uncoupling protein-1. Collectively, we demonstrated that, at 25°C (i.e., limited thermal stress conditions), a substantial reduction in BAT mass via iBATx does not disrupt systemic glucose metabolism, challenging the current dogma that preservation of BAT is obligatory for optimal metabolic function. However, iBATx caused aortic stiffening in lean mice, hence supporting the existence of an interplay between iBAT and aortic stiffness, independent of alterations in glucose homeostasis.

Anti-inflammatory effects of exercise training in adipose tissue do not require FGF21

Exercise enhances insulin sensitivity; it also improves adipocyte metabolism and reduces adipose tissue inflammation through poorly defined mechanisms. Fibroblast growth factor 21 (FGF21) is a pleiotropic hormone-like protein whose insulin-sensitizing properties are predominantly mediated via receptor signaling in adipose tissue (AT). Recently, FGF21 has also been demonstrated to have anti-inflammatory properties. Meanwhile, an association between exercise and increased circulating FGF21 levels has been reported in some, but not all studies. Thus, the role that FGF21 plays in mediating the positive metabolic effects of exercise in AT are unclear. In this study, FGF21-knockout (KO) mice were used to directly assess the role of FGF21 in mediating the metabolic and anti-inflammatory effects of exercise on white AT (WAT) and brown AT (BAT). Male FGF21KO and wild-type mice were provided running wheels or remained sedentary for 8 weeks (n = 9-15/group) and compared for adiposity, insulin sensitivity (i.e., HOMA-IR, Adipo-IR) and AT inflammation and metabolic function (e.g., mitochondrial enzyme activity, subunit content). Adiposity and Adipo-IR were increased in FGF21KO mice and decreased by EX. The BAT of FGF21KO animals had reduced mitochondrial content and decreased relative mass, both normalized by EX. WAT and BAT inflammation was elevated in FGF21KO mice, reduced in both genotypes by EX. EX increased WAT Pgc1alpha gene expression, citrate synthase activity, COX I content and total AMPK content in WT but not FGF21KO mice. Collectively, these findings reveal a previously unappreciated anti-inflammatory role for FGF21 in WAT and BAT, but do not support that FGF21 is necessary for EX-mediated anti-inflammatory effects.

Deletion of UCP1 enhances ex vivo aortic vasomotor function in female but not male mice despite similar susceptibility to metabolic dysfunction

Females are typically more insulin sensitive than males, which may be partly attributed to greater brown adipose tissue (BAT) activity and uncoupling protein 1 (UCP1) content. Accordingly, we tested the hypothesis that UCP1 deletion would abolish sex differences in insulin sensitivity and that whitening of thoracic periaortic BAT caused by UCP1 loss would be accompanied with impaired thoracic aortic function. Furthermore, because UCP1 exerts antioxidant effects, we examined whether UCP1 deficiency-induced metabolic dysfunction was mediated by oxidative stress. Compared with males, female mice had lower HOMA- and AT-insulin resistance (IR) despite no significant differences in BAT UCP1 content. UCP1 ablation increased HOMA-IR, AT-IR, and whitening of BAT in both sexes. Expression of UCP1 in thoracic aorta was greater in wild-type females compared with males. Importantly, deletion of UCP1 enhanced aortic vasomotor function in females only. UCP1 ablation did not promote oxidative stress in interscapular BAT. Furthermore, daily administration of the free radical scavenger tempol for 8 wk did not abrogate UCP1 deficiency-induced increases in adiposity, hyperinsulinemia, or liver steatosis. Collectively, we report that 1) in normal chow-fed mice housed at 25°C, aortic UCP1 content was greater in females than males and its deletion improved ex vivo aortic vasomotor function in females only; 2) constitutive UCP1 content in BAT was similar between females and males and loss of UCP1 did not abolish sex differences in insulin sensitivity; and 3) the metabolic disruptions caused by UCP1 ablation did not appear to be contingent upon increased oxidative stress in mice under normal dietary conditions.

Plasma Irisin Modestly Increases during Moderate and High-Intensity Afternoon Exercise in Obese Females

BACKGROUND AND PURPOSE

Irisin is an exercise-responsive myokine that has been proposed to exert anti-obesity benefits; yet its response during exercise in obese women is not described. This study characterized plasma irisin levels during a single bout of afternoon isocaloric-exercise of different intensities (moderate- vs high-intensity) in obese females.

METHODS

Eleven obese females participated in 3 randomized study days beginning at 1600h: 1) no exercise (NoEx), 2) moderate exercise (ModEx; 55%VO2max) and 3) high intensity interval exercise (IntEx; 4 min (80%VO2max)/3 min (50% VO2max). Frequent blood samples were analyzed for glucose and lactate (whole-blood), and insulin, c-peptide, glucagon, and irisin (plasma) throughout 190 min of testing.

RESULTS

Plasma irisin increased above baseline during ModEx and IntEx (P<0.05), but not NoEx (P>0.05). Peak irisin levels during ModEx and IntEx exercise were 11.9± 3.4% and 12.3 ± 4.1% relative to baseline (P<0.05), respectively, with no differences between exercise intensities (P>0.05). Irisin levels remained elevated above resting for 125 minutes post-exercise during ModEx, whereas levels returned to baseline within 15 minutes post-exercise during IntEx. Similarly, no associations were found between plasma irisin levels and circulating lactate, glucose, insulin, c-peptide, or glucagon among study days (P>0.05). However, there was an inverse association between basal irisin and lean mass (r = -0.70, P = 0.01).

CONCLUSION

A single bout of moderate and high intensity afternoon exercise induces modest increases in circulating irisin concentrations during exercise; however the regulation post-exercise appears to be dimorphic between exercise intensity in obese females. Future studies are needed to compare morning and afternoon exercise on irisin secretion.

Loss of UCP1 exacerbates Western diet-induced glycemic dysregulation independent of changes in body weight in female mice

We tested the hypothesis that female mice null for uncoupling protein 1 (UCP1) would have increased susceptibility to Western diet-induced "whitening" of brown adipose tissue (AT) and glucose intolerance. Six-week-old C57BL/6J wild-type (WT) and UCP1 knockout (UCP1^-/-) mice, housed at 25°C, were randomized to either a control diet (10% kcal from fat) or Western diet (45% kcal from fat and 1% cholesterol) for 28 wk. Loss of UCP1 had no effect on energy intake, energy expenditure, spontaneous physical activity, weight gain, or visceral white AT mass. Despite similar susceptibility to weight gain compared with WT, UCP1^-/- exhibited whitening of brown AT evidenced by a striking ~500% increase in mass and appearance of large unilocular adipocytes, increased expression of genes related to inflammation, immune cell infiltration, and endoplasmic reticulum/oxidative stress (P < 0.05), and decreased mitochondrial subunit protein (COX I, II, III, and IV, P < 0.05), all of which were exacerbated by Western diet (P < 0.05). UCP1^-/- mice also developed liver steatosis and glucose intolerance, which was worsened by Western diet. Collectively, these findings demonstrate that loss of UCP1 exacerbates Western diet-induced whitening of brown AT, glucose intolerance, and induces liver steatosis. Notably, the adverse metabolic manifestations of UCP1^-/- were independent of changes in body weight, visceral adiposity, and energy expenditure. These novel findings uncover a previously unrecognized metabolic protective role of UCP1 that is independent of its already established role in energy homeostasis.

Prior exercise does not alter the incretin response to a subsequent meal in obese women

Prior research has shown an increase in GLP-1 concentrations during exercise but this exercise bout was conducted postprandially. The purpose of this study was to examine the incretin response to a meal following an exercise bout of different intensities in obese subjects. Eleven women (BMI>37.3±7.0kg/m(2); Age 24.3±4.6year) participated in 3 counter- balanced study days, where a standardized meal was preceded by: (1) No exercise (NoEx), (2) ModEx (55% VO2max), and (3) IntEx (4min (80% VO2max)/3min (50% VO2max). Frequent blood samples were analyzed for glucose, lactate, insulin, glucagon, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and C-peptide concentrations throughout 280min of testing. Glucose concentrations were not different between conditions during exercise or meals. There were no differences between conditions in insulin levels during exercise and recovery, but postprandial insulin incremental area under the curve was lower in ModEx vs. NoEx (p<0.01). GIP and GLP-1 levels were not different between conditions during exercise, but during exercise recovery, GLP-1 concentrations were higher in ModEx vs. NoEx (p=0.03). The meal increased the incretin responses (p<0.01) but this response was not affected by prior exercise. Glucagon concentrations increased with exercise (p<0.05) and continued to be elevated during recovery, with the greatest increase with IntEx compared with NoEx (p<0.05). No differences between conditions were detected for hepatic insulin extraction, insulin secretion, or insulin sensitivity. Exercise prior to an evening meal has no impact on the incretin response to the subsequent meal, yet insulin concentrations were lower during the meals that followed exercise. Exercise intensity had no impact on this response.

Postdinner resistance exercise improves postprandial risk factors more effectively than predinner resistance exercise in patients with type 2 diabetes

Abnormally elevated postprandial glucose and triacylglycerol (TAG) concentrations are risk factors for cardiovascular disease in type 2 diabetes. The most effective time to exercise to lower postprandial glucose and TAG concentrations is unknown. Thus the aim of this study was to determine what time is more effective, either pre- or postdinner resistance exercise (RE), at improving postprandial risk factors in patients with type 2 diabetes. Thirteen obese patients with type 2 diabetes completed three trials in a random order in which they consumed a dinner meal with 1) no RE (NoRE), 2) predinner RE (RE → M), and 3) postdinner RE beginning 45 min after dinner (M → RE). Clinical outcome measures included postprandial glucose and TAG concentrations. In addition, postprandial acetaminophen (gastric emptying), endocrine responses, free fatty acids, and β-cell function (mathematical modeling) were measured to determine whether these factors were related to changes in glucose and TAG. The TAG incremental area under the curve (iAUC) was ∼92% lower (P ≤ 0.02) during M → RE compared with NoRE and RE → M, an effect due in part to lower very-low-density lipoprotein-1 TAG concentrations. The glucose iAUC was reduced (P = 0.02) by ∼18 and 30% during the RE → M and M → RE trials, respectively, compared with NoRE, with no difference between RE trials. RE → M and M → RE reduced the insulin iAUC by 35 and 48%, respectively, compared with NoRE (P < 0.01). The glucagon-like peptide-1 iAUC was ∼50% lower (P ≤ 0.02) during M → RE compared with NoRE and RE → M. Given that predinner RE only improves postprandial glucose concentrations, whereas postdinner RE improves both postprandial glucose and TAG concentrations, postdinner RE may lower the risk of cardiovascular disease more effectively.

Postdinner resistance exercise improves postprandial risk factors more effectively than predinner resistance exercise in patients with type 2 diabetes

Abnormally elevated postprandial glucose and triacylglycerol (TAG) concentrations are risk factors for cardiovascular disease in type 2 diabetes. The most effective time to exercise to lower postprandial glucose and TAG concentrations is unknown. Thus the aim of this study was to determine what time is more effective, either pre- or postdinner resistance exercise (RE), at improving postprandial risk factors in patients with type 2 diabetes. Thirteen obese patients with type 2 diabetes completed three trials in a random order in which they consumed a dinner meal with 1) no RE (NoRE), 2) predinner RE (RE → M), and 3) postdinner RE beginning 45 min after dinner (M → RE). Clinical outcome measures included postprandial glucose and TAG concentrations. In addition, postprandial acetaminophen (gastric emptying), endocrine responses, free fatty acids, and β-cell function (mathematical modeling) were measured to determine whether these factors were related to changes in glucose and TAG. The TAG incremental area under the curve (iAUC) was ∼92% lower (P ≤ 0.02) during M → RE compared with NoRE and RE → M, an effect due in part to lower very-low-density lipoprotein-1 TAG concentrations. The glucose iAUC was reduced (P = 0.02) by ∼18 and 30% during the RE → M and M → RE trials, respectively, compared with NoRE, with no difference between RE trials. RE → M and M → RE reduced the insulin iAUC by 35 and 48%, respectively, compared with NoRE (P < 0.01). The glucagon-like peptide-1 iAUC was ∼50% lower (P ≤ 0.02) during M → RE compared with NoRE and RE → M. Given that predinner RE only improves postprandial glucose concentrations, whereas postdinner RE improves both postprandial glucose and TAG concentrations, postdinner RE may lower the risk of cardiovascular disease more effectively.

Moderate amounts of fructose- or glucose-sweetened beverages do not differentially alter metabolic health in male and female adolescents

BACKGROUND

Adolescents consume more sugar-sweetened beverages than do individuals in any other age group, but it is unknown how the type of sugar-sweetened beverage affects metabolic health in this population.

OBJECTIVE

The objective was to compare the metabolic health effects of short-term (2-wk) consumption of high-fructose (HF) and high-glucose (HG)-sweetened beverages in adolescents (15-20 y of age).

DESIGN

In a counterbalanced, single-blind fashion, 40 male and female adolescents completed two 2-wk trials that included 1) an HF trial in which they consumed 710 mL of a sugar-sweetened beverage/d (equivalent to 50 g fructose/d and 15 g glucose/d) for 2 wk and 2) an HG trial in which they consumed 710 mL of a sugar-sweetened beverage/d (equivalent to 50 g glucose/d and 15 g fructose/d) for 2 wk in addition to their normal ad libitum diet. In addition, the participants maintained similar physical activity levels during each trial. The day after each trial, insulin sensitivity and resistance [assessed via Quantitative Insulin Sensitivity Check Index (QUICKI) and homeostatic model assessment of insulin resistance (HOMA-IR) index] and fasting and postprandial glucose, lactate, lipid, cholesterol, insulin, C-peptide, insulin secretion, and clearance responses to HF or HG mixed meals were assessed.

RESULTS

Body weight, QUICKI (whole-body insulin sensitivity), HOMA-IR (hepatic insulin resistance), and fasting lipids, cholesterol, glucose, lactate, and insulin secretion or clearance were not different between trials. Fasting HDL- and HDL₃-cholesterol concentrations were ∼10-31% greater (P < 0.05) in female adolescents than in male adolescents. Postprandial triacylglycerol, HDL-cholesterol, HDL₃-cholesterol, and glucose concentrations were not different between HF and HG trials. The lactate incremental area under the curve was ∼3.7-fold greater during the HF trial (P < 0.05), whereas insulin secretion was 19% greater during the HG trial (P < 0.05).

CONCLUSIONS

Moderate amounts of HF- or HG-sweetened beverages for 2 wk did not have differential effects on fasting or postprandial cholesterol, triacylglycerol, glucose, or hepatic insulin clearance in weight-stable, physically active adolescents.