Acute exercise reverses starvation-mediated insulin resistance in humans

Elevated heart rate and decreased muscle endothelial nitric oxide synthase in early development of insulin resistance

Insulin resistance (IR) is a risk factor for the development of several major metabolic diseases. Muscle fiber composition is established early in life and is associated with insulin sensitivity. Hence, muscle fiber composition was used to identify early defects in the development of IR in healthy young individuals in the absence of clinical manifestations. Biopsies were obtained from the thigh muscle, followed by an intravenous glucose tolerance test. Indices of insulin action were calculated and cardiovascular measurements, analyses of blood and muscle were performed. Whole body insulin sensitivity (SIgalvin) was positively related to expression of type I muscle fibers (r = 0.49; P < 0.001) and negatively related to resting heart rate (HR, r = -0.39; P < 0.001), which was also negatively related to expression of type I muscle fibers (r = -0.41; P < 0.001). Muscle protein expression of endothelial nitric oxide synthase (eNOS), whose activation results in vasodilation, was measured in two subsets of subjects expressing a high percentage of type I fibers (59 ± 6%; HR = 57 ± 9 beats/min; SIgalvin = 1.8 ± 0.7 units) or low percentage of type I fibers (30 ± 6%; HR = 71 ± 11; SIgalvin = 0.8 ± 0.3 units; P < 0.001 for all variables vs. first group). eNOS expression was 1) higher in subjects with high type I expression; 2) almost twofold higher in pools of type I versus II fibers; 3) only detected in capillaries surrounding muscle fibers; and 4) linearly associated with SIgalvin. These data demonstrate that an altered function of the autonomic nervous system and a compromised capacity for vasodilation in the microvasculature occur early in the development of IR.NEW & NOTEWORTHY Insulin resistance (IR) is a risk factor for the development of several metabolic diseases. In healthy young individuals, an elevated heart rate (HR) correlates with low insulin sensitivity and high expression of type II skeletal muscle fibers, which express low levels of endothelial nitric oxide synthase (eNOS) and, hence, a limited capacity to induce vasodilation in response to insulin. Early targeting of the autonomic nervous system and microvasculature may attenuate development of diseases stemming from insulin resistance.

Fasting for 48 h induced similar glucose intolerance in both sexes despite greater perceived stress and decreased estradiol levels in females

PURPOSE

The purpose of this study was to compare the effects of fasting for 48 h on the evoked insulin and glucose responses in males and females, and to explore factors such as stress and estrogen levels that might influence these responses.

METHODS

Healthy, nonobese male (n = 14) and female (n = 14) subjects underwent 48-h fasting trial. Changes in glucose tolerance and insulin levels in response to the oral glucose tolerance test, subjectively perceived stress and catecholamine concentrations were measured in all participants. Estrogen levels were also measured in the female participants during the 48-h fast.

RESULTS

Glucose area under the curve (AUC) values increased similarly in both sexes after 48-h fasting (P < 0.05), but females displayed a greater rise in insulin AUC values than males (P < 0.05). Fasting increased plasma epinephrine concentrations in both sexes (P < 0.05), whereas plasma norepinephrine concentrations and subjective stress increased only in females (P < 0.05). Plasma 17-β-estradiol concentrations in females decreased after fasting (P < 0.05).

CONCLUSION

Fasting for 48 h induced a similar glucose intolerance in females and males, despite decreased 17-β-estradiol levels and greater psychological and physiological stress in females. These differences represent a plausible explanation for the gender-based differences observed in insulin responses.

TRIAL REGISTRATION

Retrospectively registered on ClinicalTrials.gov (NCT05545943) in September 19, 2022.

Impact of fasting on the AMPK and PGC-1α axis in rodent and human skeletal muscle: A systematic review

Based primarily on evidence from rodent models fasting is currently believed to improve metabolic health via activation of the AMPK-PGC-1α axis in skeletal muscle. However, it is unclear whether the skeletal muscle AMPK-PGC-1α axis is activated by fasting in humans. The current systematic review examined the fasting response in skeletal muscle from 34 selected studies (7 human, 21 mouse, and 6 rat). From these studies, we gathered 38 unique data points related to AMPK and 47 related to PGC-1α. In human studies, fasting mediated activation of the AMPK-PGC-1α axis is largely absent. Although evidence does support fasting-induced activation of the AMPK-PGC-1α axis in rodent skeletal muscle, the evidence is less robust than anticipated. Our findings question the ability of fasting to activate the AMPK-PGC-1α axis in human skeletal muscle and suggest that the metabolic benefits of fasting in humans are associated with caloric restriction rather than the induction of mitochondrial biogenesis. Registration: https://doi.org/10.17605/OSF.IO/KWNQY.

Short-duration cold exposure decreases fasting-induced glucose intolerance but has no effect on resting energy expenditure

The aim of the present study was to investigate whether brief cold exposure can reverse fasting-induced glucose intolerance and insulin resistance, and improve resting energy expenditure (REE). Twelve young non-obese women were randomly assigned to undergo the following conditions: 2 days of fasting with two 10-min whole-body cold-water immersions on separate days (FAST-COLD), 2 days of fasting without cold-water immersions (FAST), 2 days of usual diet with two 10-min whole-body cold-water immersions on separate days (COLD), or 2 days of usual diet without cold-water immersions (CON) in a randomised crossover fashion. Changes in REE and substrate utilisation, and glucose tolerance and insulin sensitivity from the oral glucose tolerance test were examined. The results showed that FAST-COLD and FAST trials increased (P < 0.05) REE and decreased (P < 0.05) respiratory quotient, but these variables did not differ significantly between the FAST-COLD and FAST trials. The glucose and insulin area under the curves (AUCs) were higher (P < 0.05) in the FAST-COLD and FAST trials than in the CON and COLD trials, and these AUCs were lower (P < 0.05) in the FAST-COLD than in the FAST trial. Matsuda index was lower in the FAST trial than in the CON trial (P < 0.05), and tended to be greater after the FAST-COLD trial than after the FAST trial (P = 0.060). In conclusion, cold exposure had no effect on REE but decreased fasting-induced glucose intolerance which was accompanied by a maintained insulin sensitivity.

Prolonged fasting outperforms short-term fasting in terms of glucose tolerance and insulin release: a randomised controlled trial

Fasting is related to glucose intolerance and insulin resistance, but it is unknown whether the duration of fasting influences these factors. We explored whether prolonged fasting increases norepinephrine and ketone concentrations and decreases core temperature to a greater extent than short-term fasting; if so, this should lead to improved glucose tolerance. Forty-three healthy young adult males were randomly assigned to undergo a 2-d fast, 6-d fast or the usual diet. Changes in rectal temperature (TR), ketone and catecholamine concentrations, glucose tolerance and insulin release in response to an oral glucose tolerance test were assessed. Both fasting trials increased ketone concentration, and the effect was larger after the 6-d fast (P < 0·05). TR and epinephrine concentration increased only after the 2-d fast (P < 0·05). Both fasting trials increased the glucose area under the curve (AUC) (P < 0·05), but the AUC remained higher than the baseline value after participants returned to their usual diet in the 2-d fast group (P < 0·05). Neither fasting had an immediate effect on the insulin AUC, although it increased after return to their usual diet in the 6-d fast group (P < 0·05). These data suggest that the 2-d fast elicited residual impaired glucose tolerance, which may be linked to greater perceived stress during short-term fasting, as shown by the epinephrine response and change in core temperature. By contrast, prolonged fasting seemed to evoke an adaptive residual mechanism that is related to improved insulin release and maintained glucose tolerance.

Reduced glucose tolerance and insulin sensitivity after prolonged exercise in endurance athletes

AIM

The purpose of this study was to 1. investigate if glucose tolerance is affected after one acute bout of different types of exercise; 2. assess if potential differences between two exercise paradigms are related to changes in mitochondrial function; and 3. determine if endurance athletes differ from nonendurance-trained controls in their metabolic responses to the exercise paradigms.

METHODS

Nine endurance athletes (END) and eight healthy nonendurance-trained controls (CON) were studied. Oral glucose tolerance tests (OGTT) and mitochondrial function were assessed on three occasions: in the morning, 14 h after an overnight fast without prior exercise (RE), as well as after 3 h of prolonged continuous exercise at 65% of VO2 max (PE) or 5 × 4 min at ~95% of VO2 max (HIIT) on a cycle ergometer.

RESULTS

Glucose tolerance was markedly reduced in END after PE compared with RE. END also exhibited elevated fasting serum FFA and ketones levels, reduced insulin sensitivity and glucose oxidation, and increased fat oxidation during the OGTT. CON showed insignificant changes in glucose tolerance and the aforementioned measurements compared with RE. HIIT did not alter glucose tolerance in either group. Neither PE nor HIIT affected mitochondrial function in either group. END also exhibited increased activity of 3-hydroxyacyl-CoA dehydrogenase activity in muscle extracts vs. CON.

CONCLUSION

Prolonged exercise reduces glucose tolerance and increases insulin resistance in endurance athletes the following day. These findings are associated with an increased lipid load, a high capacity to oxidize lipids, and increased fat oxidation.

Extreme Variations in Muscle Fiber Composition Enable Detection of Insulin Resistance and Excessive Insulin Secretion

CONTEXT

Muscle fiber composition is associated with peripheral insulin action.

OBJECTIVE

We investigated whether extreme differences in muscle fiber composition are associated with alterations in peripheral insulin action and secretion in young, healthy subjects who exhibit normal fasting glycemia and insulinemia.

METHODS

Relaxation time following a tetanic contraction was used to identify subjects with a high or low expression of type I muscle fibers: group 1 (n = 11), area occupied by type I muscle fibers = 61.0 ± 11.8%, and group 2 (n = 8), type I area = 36.0 ± 4.9% (P < 0.001). Biopsies were obtained from the vastus lateralis muscle and analyzed for mitochondrial respiration on permeabilized fibers, muscle fiber composition, and capillary density. An intravenous glucose tolerance test was performed and indices of glucose tolerance, insulin sensitivity, and secretion were determined.

RESULTS

Glucose tolerance was similar between groups, whereas whole-body insulin sensitivity was decreased by ~50% in group 2 vs group 1 (P = 0.019). First-phase insulin release (area under the insulin curve during 10 minutes after glucose infusion) was increased by almost 4-fold in group 2 vs group 1 (P = 0.01). Whole-body insulin sensitivity was correlated with percentage area occupied by type I fibers (r = 0.54; P = 0.018) and capillary density in muscle (r = 0.61; P = 0.005) but not with mitochondrial respiration. Insulin release was strongly related to percentage area occupied by type II fibers (r = 0.93; P < 0.001).

CONCLUSIONS

Assessment of muscle contractile function in young healthy subjects may prove useful in identifying individuals with insulin resistance and enhanced glucose-stimulated insulin secretion prior to onset of clinical manifestations.

Impact of Adenosine Analogue, Adenosine-5'-N-Ethyluronamide (NECA), on Insulin Signaling in Skeletal Muscle Cells

Materials and Methods

Rat L6 skeletal muscle cells were cultured in 25 cm² flasks. These differentiated cells were treated, and then, quantitative reverse transcription-polymerase chain reaction (qRT-PCR) (probe-based) was used to measure the relative mRNA expression level for metabolic, inflammatory, and nuclear receptor genes including peroxisome proliferator-activated receptor gamma (PGC-1α), carnitine palmitoyl transferase 1 beta (CPT1B), long-chain acyl-CoA de hydrogenase (LCAD), acetyl-CoA carboxylase beta (ACCβ), pyruvate dehydrogenase kinase 4 (PDK4), hexokinase II (HKII), phosphofructokinase (PFK), interleukin-6 (IL-6), and nuclear receptor subfamily 4, group A (NR4A) at different treatment conditions.

Results

Adenosine-5′-N-ethyluronamide (NECA), a stable adenosine analogue, significantly stimulate inflammatory mediator (IL-6) (p < 0.001) and nuclear receptors (NR4A) (p < 0.05) and significantly modulate metabolic (PFK, LCAD, PGC-1α, and CPT1B) gene expressions in skeletal muscle cells (p < 0.05, p < 0.05, p < 0.001, and p < 0.01, respectively). This present study shows that there is a noteworthy crosstalk between NECA and insulin at various metabolic levels including glycolysis (HKII), fatty acid oxidation (ACCβ), and insulin sensitivity (PDK4).

Conclusions

A novel crosstalk between adenosine analogue and insulin has been demonstrated for the first time; evidence has been gathered in vitro for the effects of NECA and insulin treatment on intracellular signaling pathways, in particular glycolysis and insulin sensitivity in skeletal muscle cells.

Short-term intensified training temporarily impairs mitochondrial respiratory capacity in elite endurance athletes

The maintenance of healthy and functional mitochondria is the result of a complex mitochondrial turnover and herein quality-control program that includes both mitochondrial biogenesis and autophagy of mitochondria. The aim of this study was to examine the effect of an intensified training load on skeletal muscle mitochondrial quality control in relation to changes in mitochondrial oxidative capacity, maximal oxygen consumption, and performance in highly trained endurance athletes. Elite endurance athletes (n = 27) performed high-intensity interval exercise followed by moderate-intensity continuous exercise 3 days per week for 4 wk in addition to their usual volume of training. Mitochondrial oxidative capacity, abundance of mitochondrial proteins, markers of autophagy, and antioxidant capacity of skeletal muscle were assessed in skeletal muscle biopsies before and after the intensified training period. The intensified training period increased several autophagy markers suggesting an increased turnover of mitochondrial and cytosolic proteins. In permeabilized muscle fibers, mitochondrial respiration was ∼20% lower after training although some markers of mitochondrial density increased by 5%-50%, indicative of a reduced mitochondrial quality by the intensified training intervention. The antioxidative proteins UCP3, ANT1, and SOD2 were increased after training, whereas we found an inactivation of aconitase. In agreement with the lower aconitase activity, the amount of mitochondrial LON protease that selectively degrades oxidized aconitase was doubled. Together, this suggests that mitochondrial respiratory function is impaired during the initial recovery from a period of intensified endurance training whereas mitochondrial quality control is slightly activated in highly trained skeletal muscle.NEW & NOTEWORTHY We show that mitochondrial respiration is temporarily impaired after a period of intensified exercise training in elite athletes. In parallel, proteins involved in the antioxidative response including SOD2, UCP3, and ANT2 were upregulated, whereas mitochondrial biogenesis was slightly activated. Despite the mitochondrial respiratory impairments, physical performance was improved a few days after the intense training period.

The role of glucose homeostasis on immune function in response to exercise: The impact of low or higher energetic conditions

Immune cells are bioenergetically expensive during activation, which requires tightly regulated control of metabolic pathways. Both low and high glycemic conditions can modulate immune function. States of undernourishment depress the immune system, and in the same way, excessive intake of nutrients, such as an obesity state, compromise its functioning. Multicellular organisms depend on two mechanisms to survive: the regulation and ability to store energy to prevent starvation and the ability to fight against infection. Synergic interactions between metabolism and immunity affect many systems underpinning human health. In a chronic way, the breakdown of glycemic homeostasis in the body can influence cells of the immune system and consequently contribute to the onset of diseases such as type II diabetes, obesity, Alzheimer's, and fat and lean mass loss. On the contrary, exercise, recognized as a primary strategy to control hyperglycemic disorders, also induces a coordinated immune-neuro-endocrine response that acutely modulates cardiovascular, respiratory, and muscle functions and the immune response to exercise is widely dependent on the intensity and volume that may affect an immunodepressive state. These altered immune responses induced by exercise are modulated through the "stress hormones" adrenaline and cortisol, which are a threat to leukocyte metabolism. In this context, carbohydrates appear to have a positive acute response as a strategy to prevent depression of the immune system by maintaining plasma glucose concentrations to meet the energy demand from all systems involved during strenuous exercises. Therefore, herein, we discuss the mechanisms through which exercise may promotes changes on glycemic homeostasis in the metabolism and how it affects immune cell functions under higher or lower glucose conditions.

HORMONAL REGULATION OF CARBOHYDRATE AND FAT METABOLISM IN WOMEN WITH DIFFERENT OBESITY TYPES IN THE FOOD DEPRIVATION TEST

CONTEXT

The dominant type of adipose tissue accumulation in the body is associated with the peculiarities of using key substrates in energy metabolism and their hormonal regulation. Hormonal and metabolic parameters were investigated in women with android and gynoid obesity before and after the short-term food deprivation test.

RESULTS

At baseline, at gynoid obesity as compared to android obesity, the women's blood contained lower glucose and insulin levels and higher FFA levels. The reaction to food deprivation manifested by a decrease in glucose level and an increase in FFA level in the blood is less pronounced in women with gynoid obesity than in those with android obesity. At the same time, a similar (though varying in expression) decrease in insulin level and elevated levels of glucagon, growth hormone and thyroxine were revealed in women's blood in both groups. Blood cortisol level increased in women with gynoid obesity and remained unchanged in those with android obesity.

CONCLUSIONS

More pronounced activation of hormonal mechanisms for maintaining blood glucose levels at gynoid obesity as compared to android one suggests that glucose is the preferable substrate for energy metabolism at gynoid obesity in women.

Endocrine responses and food intake in fasted individuals under the influence of glucose ingestion

Introduction

Different metabolic conditions can affect what and how much we eat. Hormones of glucose metabolism and adipokines such as adiponectin take part in the control of these decisions and energy balance of the body. However, a comprehensive understanding of how these endocrine and metabolic factors influence food intake has not been reached. We hypothesised that the amount of food a person consumes differs substantially after a fasting period even after the energy deficit was partially removed by glucose ingestion and endocrine signals like insulin and C-peptide indicated a high glucose metabolic status. Furthermore, the macronutrient composition of the consumed food and a possible association with adiponectin under the influence of glucose ingestion was assessed.

Methods

In a within-subject design, 24 healthy males participated in both a fasting (42 h) and control (non-fasting) condition. A total of 20 blood samples from each subject were collected during each condition to assess serum levels of adiponectin, insulin, C-peptide, cortisol and ACTH. At the end of each condition food intake was measured with an ad libitum buffet after the acute energy deficit was compensated using a carbohydrate-rich drink.

Results

The total amount of caloric intake and single macronutrients was higher after the fasting intervention after replenishment with glucose. All recorded hormone levels, except for adiponectin, were significantly different for at least one of the study intervals. The relative proportions of the macronutrient composition of the consumed food were stable in both conditions under the influence of glucose ingestion. In the non-fasting condition, the relative amount of protein intake correlated with adiponectin levels during the experiment.

Discussion and conclusion

An anabolic glucose metabolism after glucose ingestion following a fasting intervention did not even out energy ingestion compared to a control group with regular food intake and glucose ingestion. Anorexigenic hormones like insulin in this context were not able despite higher levels than in the control condition to ameliorate the drive for food intake to normal or near normal levels. Relative macronutrient intake remains stable under these varying metabolic conditions and glucose influence. Serum adiponectin levels showed a positive association with the relative protein intake in the non-fasting condition under the influence of glucose although adiponectin levels overall did not differ in between the conditions.

Altered Appetite-Mediating Hormone Concentrations Precede Compensatory Overeating After Severe, Short-Term Energy Deprivation in Healthy Adults

BACKGROUND

Adaptive responses of appetite-mediating hormones to negative energy balance are thought to contribute to a counterregulatory response that drives weight regain, but they have not been studied while controlling for reduced diet volume.

OBJECTIVE

In this secondary analysis, we aimed to determine the effects of short-term, severe energy deprivation (ED) on appetite and appetite-mediating hormone concentrations.

METHODS

Twenty-one adults with a mean ± SD age of 21 ± 3 y and body mass index of 25 ± 3 kg/m(2) consumed isovolumetric diets provided over separate 48-h periods while increasing habitual energy expenditure by 1683 ± 329 kcal/d through light- and moderate-intensity exercise. Energy intake was matched to energy expenditure to maintain energy balance (EB) (-44 ± 92 kcal/d) or was <10% of energy expenditure to generate a -3696 ± 742-kcal/d energy deficit. Postprandial appetite, glucose, insulin, acyl ghrelin, peptide YY, pancreatic polypeptide (PP), and glucagon-like peptide-1 (GLP-1) responses and ad libitum energy intake were measured as secondary outcomes after both experimental periods.

RESULTS

Fasting insulin (-56% ± 42%) and acyl ghrelin (-60% ± 17%) concentrations decreased during ED but not during EB (condition-by-time interaction; P-interaction ≤ 0.01), whereas fasting leptin concentrations decreased more during ED compared with during EB (-47% ± 27% compared with -20% ± 27%; P-interaction = 0.05). Postprandial insulin (57% ± 63%; P < 0.001), GLP-1 (14% ± 28%; P = 0.04), and PP (54% ± 52%; P < 0.001) areas under the curve (AUCs) were higher, whereas the acyl ghrelin AUC was lower (-56% ± 13%; P < 0.001) after ED compared with after EB. After ED, self-rated appetite was greater, and ad libitum energy intake was 811 kcal/36 h (95% CI: 184, 1439 kcal/36 h) higher relative to after EB (P = 0.01).

CONCLUSIONS

Short-term, severe ED suppressed acyl ghrelin concentrations and increased postprandial anorexigenic hormone concentrations. These effects preceded compensatory overeating, suggesting that in adults without obesity, altered sensitivity to appetite-mediating hormones may contribute to an adaptive counterregulatory response during the initial stages of negative EB. This trial was registered at clinicaltrials.gov as NCT01603550.

Acute exercise does not decrease liver fat in men with overweight or NAFLD

Elevated hepatic lipid content (IntraHepatic Lipid, IHL) increases the risk of metabolic complications. Although prolonged exercise training lowers IHL, it is unknown if acute exercise has the same effect. Furthermore, hepatic ATP content may be related to insulin resistance and IHL. We aimed to investigate if acute exercise leads to changes in IHL and whether this is accompanied by changes in hepatic ATP. Twenty-one men (age 54.8 ± 7.2 years, BMI 29.7 ± 2.2 kg/m²) performed a 2 h cycling protocol, once while staying fasted and once while ingesting glucose. IHL was determined at baseline, 30 min post-exercise and 4 h post-exercise. Additionally ATP/Total P ratio was measured at baseline and 4 h post-exercise. Compared with baseline values we did not observe any statistically significant changes in IHL within 30 min post-exercise in neither the fasted nor the glucose-supplemented condition. However, IHL was elevated 4 h post-exercise compared with baseline in the fasted condition (from 8.3 ± 1.8 to 8.7 ± 1.8%, p = 0.010), an effect that was blunted by glucose supplementation (from 8.3 ± 1.9 to 8.3 ± 1.9%, p = 0.789). Acute exercise does not decrease liver fat in overweight middle-aged men. Moreover, IHL increased 4 h post-exercise in the fasted condition, an increase that was absent in the glucose-supplemented condition. These data suggest that a single bout of exercise may not be able to lower IHL.

Regulation of glycogen breakdown and its consequences for skeletal muscle function after training

Repeated bouts of physical exercise, i.e., training, induce mitochondrial biogenesis and result in improved physical performance and attenuation of glycogen breakdown during submaximal exercise. It has been suggested that as a consequence of the increased mitochondrial volume, a smaller degree of metabolic stress (e.g., smaller increases in ADP and Pi) is required to maintain mitochondrial respiration in the trained state during exercise at the same absolute intensity. The lower degree of Pi accumulation is believed to account for the diminished glycogen breakdown, since Pi is a substrate for glycogen phosphorylase, the rate-limiting enzyme for glycogenolysis. However, in this review, we present an alternative explanation for the diminished glycogen breakdown. Thus, the lower degree of metabolic stress after training is also associated with smaller increases in AMP (free concentration during contraction at specific intracellular sites) and this results in less activation of phosphorylase b (the non-phosphorylated form of phosphorylase), resulting in diminished glycogen breakdown. Concomitantly, the smaller accumulation of Pi, which interferes with cross-bridge function and intracellular Ca(2+) handling, contributes to the increased fatigue resistance. The delay in glycogen depletion also contributes to enhanced performance during prolonged exercise by functioning as an energy reserve.

Effects of a single bout of aerobic exercise on short-term low-carbohydrate/high-fat intake-induced postprandial glucose metabolism during an oral glucose tolerance test

OBJECTIVE

A single bout of exercise can improve acute postprandial glucose metabolism aggravated by short-term low-carbohydrate/high-fat diet (HFD). The purpose of this study was to investigate the effect of a single bout of aerobic exercise on short-term HFD-induced postprandial glucose and incretin metabolism during an oral glucose tolerance test (OGTT).

MATERIALS/METHODS

Eleven healthy young men (age [mean±SE] 27±1 years; body mass index, 22±1 kg/m(2)) performed three, 3-day interventions in randomized order: (1) a normal diet (ND: ~22% fat), (2) an HFD (~69% fat) and (3) an HFD with a single bout of aerobic exercise (HFDEx). The exercise (50% peak oxygen consumption; ~200 kcal) was performed on the third day in HFDEx. An OGTT was performed after each 3-day dietary intervention.

RESULTS

The incremental area under the curve (iAUC) of plasma glucose levels during the OGTT was significantly higher in the HFD and HFDEx trials than in the ND trial (P=0.001). In addition, the iAUC of glucagon-like peptide-1 (GLP-1) level was significantly higher in the HFD trial than in the ND and HFDEx trials (P=0.04). The first-phase insulin secretion indexes were significantly lower in the HFD (P=0.01 and 0.002) and HFDEx trials (P=0.05 and 0.008) than in the ND trial.

CONCLUSION

A single bout of aerobic exercise did not improve the short-term HFD-induced aggravation of postprandial glucose and insulin metabolism during the OGTT. However, it did normalize the increased postprandial GLP-1 level induced by HFD.

Mitochondrial dysfunction induces formation of lipid droplets as a generalized response to stress

Lipid droplet (LD) formation is a hallmark of cellular stress. Cells attempt to combat noxious stimuli by switching their metabolism from oxidative phosphorylation to glycolysis, sparing resources in LDs for generating cellular reducing power and for anabolic biosynthesis. Membrane phospholipids are also a source of LDs. To elucidate the formation of LDs, we exposed mice to hyperoxia, hypoxia, myocardial ischemia, and sepsis induced by cecal ligation and puncture (CLP). All the above-mentioned stressors enhanced the formation of LDs, as assessed by transmission electron microscopy, with severe mitochondrial swelling. Disruption of mitochondria by depleting mitochondrial DNA ( ρ 0 cells) significantly augmented the formation of LDs, causing transcriptional activation of fatty acid biosynthesis and metabolic reprogramming to glycolysis. Heme oxygenase (HO)-1 counteracts CLP-mediated septic shock in mouse models. In HO-1-deficient mice, LD formation was not observed upon CLP, but a concomitant decrease in "LD-decorating proteins" was observed, implying a link between LDs and cytoprotective activity. Collectively, LD biogenesis during stress can trigger adaptive LD formation, which is dependent on mitochondrial integrity and HO-1 activity; this may be a cellular survival strategy, apportioning energy-generating substrates to cellular defense.