Prolonged fasting induces peripheral insulin resistance, which is not ameliorated by high-dose salicylate

Thrifty energy phenotype predicts weight regain in postmenopausal women with overweight or obesity and is related to FGFR1 signaling

BACKGROUND&AIMS

Long term improvement of body weight and metabolism is highly requested in obesity. The specific impact of weight loss associated temporary negative energy balance or modified body composition on metabolism and weight regain is unclear.

METHODS

We randomly assigned 80 post-menopausal women (BMI 33.9 (32.2-36.8)kg/m²) to an intervention (IG) or control group (CG). IG underwent a dietary three month-weight loss intervention followed by a four week-weight maintenance period without negative energy balance. The CG was instructed to keep their weight stable. Phenotyping was performed at baseline (M0), after weight loss (M3), the maintenance period (M4) and 24-month follow-up (M24). Co-primary outcomes were changes of insulin sensitivity (ISI_Clamp) and lean body mass (LBM). Energy metabolism and adipose gene expression were secondary endpoints.

RESULTS

Between March 2012 and July 2015, 479 subjects were screened for eligibility. 80 subjects were randomly assigned to IG (n = 40) or CG (n = 40). The total number of dropouts was 18 (IG: n = 13, CG: n = 5). LBM and ISI_Clamp were stable in the CG between M0 and M3, but were changed in the IG at M3 (LBM: -1.4 (95%CI -2.2-(-0.6)) kg and ISI_Clamp: +0.020 (95%CI 0.012-0.028) mg·kg^-1·min^-1/(mU·l^-1)) (p < 0.01 and p < 0.05 for IG vs. CG, respectively). Effects on LBM, ISI_Clamp, FM and BMI were preserved until M4. Lower resting energy expenditure per LBM (REE_LBM) at M3 and stronger difference of REE_LBM between M3 and M4 (ΔREE_LBM-M3M4), which indicates a thrifty phenotype, were positively associated with FM regain at M24 (p = 0.022 and p = 0.044, respectively). Gene set enrichment analysis revealed a relationship of this phenotype to weight loss-induced adaption of adipose FGFR1 signaling.

CONCLUSION

Negative energy balance had no additional effect on insulin sensitivity. FGFR1 signaling might be involved in the adaption of energy expenditure to temporary negative energy balance, which indicates a thrifty phenotype susceptible to weight regain.

TRIAL REGISTRATION

ClinicalTrials.gov number: NCT01105143, https://clinicaltrials.gov/ct2/show/NCT01105143, date of registration: April 16th, 2010.

Effects of 10-Day Complete Fasting on Physiological Homeostasis, Nutrition and Health Markers in Male Adults

Fasting shows great potential in preventing chronic diseases and has to be surmounted under some extraordinary circumstances. This study aimed to investigate the safety, time effects of metabolic homeostasis and health indexes during prolonged fasting. Thirteen participants were recruited to conduct a 10-day complete fasting (CF) in a controlled health research building under medical supervision including 3-day Baseline (BL), 10-day CF, 4-day calorie restriction (CR) and 5-day full recovery (FR). Body healthy status was assessed by surveying pulse, blood pressure, body weight (BW), blood glucose and ketones, body composition and nutritional and biochemistry indexes at different times. BW declined about 7.28 kg (−9.8%) after 10-day CF, accompanied by increased pulse and decreased systolic blood pressure, but there were no changes to the myocardial enzymogram. Body composition analysis showed fat mass was constantly lost, but lean mass could recover after CR. The energy substrate switch from glucose to ketone occurred and formed a stable dynamic balance between 3–6 days of CF. The lipid metabolism presented increased total cholesterol, LDL-C, ApoA1 and almost no changes to TG and HDL-C. Prolonged CF did not influence liver function, but induced a slight decrease of kidney function. The interesting results came from the marked increase of lipid-soluble vitamins and a significant decrease of sodium and chlorine. Adults could well tol-erate a 10-day CF. A new metabolic homeostasis was achieved. No vitamins but NaCl supplement should be considered. These findings provide evidence to design a new fasting strategy for clinical practice.

Impact of Dietary Carbohydrate Restriction versus Energy Restriction on Exogenous Carbohydrate Oxidation during Aerobic Exercise

Individuals with high physical activity levels, such as athletes and military personnel, are likely to experience periods of low muscle glycogen content. Reductions in glycogen stores are associated with impaired physical performance. Lower glycogen stores in these populations are likely due to sustained aerobic exercise coupled with sub-optimal carbohydrate or energy intake. Consuming exogenous carbohydrate during aerobic exercise may be an effective intervention to sustain physical performance during periods of low glycogen. However, research is limited in the area of carbohydrate recommendations to fuel performance during periods of sub-optimal carbohydrate and energy intake. Additionally, the studies that have investigated the effects of low glycogen stores on exogenous carbohydrate oxidation have yielded conflicting results. Discrepancies between studies may be the result of glycogen stores being lowered by restricting carbohydrate or restricting energy intake. This narrative review discusses the influence of low glycogen status resulting from carbohydrate restriction versus energy restriction on exogenous carbohydrate oxidation and examines the potential mechanism resulting in divergent responses in exogenous carbohydrate oxidation. Results from this review indicate that rates of exogenous carbohydrate oxidation can be maintained when glycogen content is lower following carbohydrate restrictions, but may be reduced following energy restriction. Reductions in exogenous carbohydrate oxidation following energy restriction appear to result from lower insulin sensitivity and glucose uptake. Exogenous carbohydrate may thus be an effective intervention to sustain performance following short-term energy adequate carbohydrate restriction, but may not be an effective ergogenic aid when glycogen stores are low due to energy restriction.

Brain insulin signalling in metabolic homeostasis and disease

Insulin signalling in the central nervous system regulates energy homeostasis by controlling metabolism in several organs and by coordinating organ crosstalk. Studies performed in rodents, non-human primates and humans over more than five decades using intracerebroventricular, direct hypothalamic or intranasal application of insulin provide evidence that brain insulin action might reduce food intake and, more importantly, regulates energy homeostasis by orchestrating nutrient partitioning. This Review discusses the metabolic pathways that are under the control of brain insulin action and explains how brain insulin resistance contributes to metabolic disease in obesity, the metabolic syndrome and type 2 diabetes mellitus.

Impact of prolonged fasting on insulin secretion, insulin action, and hepatic versus whole body insulin secretion disposition indices in healthy young males

The extent to which reduced insulin secretion during prolonged fasting reflects failure to compensate for whole body insulin resistance or a normal adjustment to potentially increased hepatic insulin action is unknown. We examined the effects of 36- versus 12-h fasting on insulin secretion and whole body versus hepatic insulin action in 13 healthy young males. Hepatic glucose production and insulin action were studied using stable isotopes, whereas whole body insulin action and insulin secretion were studied using an intravenous glucose tolerance test (IVGTT) and minimal modeling. Insulin, glucose, and lipid profiles were subsequently measured during a refeeding meal test. Prolonged fasting caused a minor reduction of first-phase insulin secretion in a context of improved hepatic insulin action, contrasting an increase in whole body insulin resistance. Accordingly, prolonged fasting was associated with opposite-directed effects on hepatic versus whole body insulin secretion disposition indices. Thirty-six-hour fasting compared with 12-h fasting was associated with increased serum insulin levels during the refeeding meal test. In conclusion, reduced insulin secretion during prolonged fasting may represent a healthy response to improved hepatic insulin action. Use of insulin secretion disposition indices without taking organ-specific insulin action into account may lead to erroneous conclusions.NEW & NOTEWORTHY Thirty-six-hour prolonged, compared with 12-h overnight fasting, is associated with slightly reduced first-phase insulin secretion in the face of opposite-directed changes in hepatic versus whole body insulin action in healthy young males. The paradoxical finding of increased hepatic versus decreased whole body insulin secretion disposition indices during prolonged fasting challenges the physiological understanding and validity of insulin secretion disposition indices not taking organ-specific insulin action into account.

SDF-1 Is an Autocrine Insulin-Desensitizing Factor in Adipocytes

Insulin desensitization occurs not only under the obese diabetic condition but also in the fasting state. However, little is known about the common secretory factor(s) that are regulated under these two insulin-desensitized conditions. Here, using database analysis and in vitro and in vivo experiments, we identified stromal derived factor-1 (SDF-1) as an insulin-desensitizing factor in adipocytes, overexpressed in both fasting and obese adipose tissues. Exogenously added SDF-1 induced extracellular signal-regulated kinase signal, which phosphorylated and degraded IRS-1 protein in adipocytes, decreasing insulin-mediated signaling and glucose uptake. In contrast, knockdown of endogenous SDF-1 or inhibition of its receptor in adipocytes markedly increased IRS-1 protein levels and enhanced insulin sensitivity, indicating the autocrine action of SDF-1. In agreement with these findings, adipocyte-specific ablation of SDF-1 enhanced insulin sensitivity in adipose tissues and in the whole body. These results point to a novel regulatory mechanism of insulin sensitivity mediated by adipose autocrine SDF-1 action and provide a new insight into the process of insulin desensitization in adipocytes.

Plasma acylcarnitine concentrations reflect the acylcarnitine profile in cardiac tissues

Increased plasma concentrations of acylcarnitines (ACs) are suggested as a marker of metabolism disorders. The aim of the present study was to clarify which tissues are responsible for changes in the AC pool in plasma. The concentrations of medium- and long-chain ACs were changing during the fed-fast cycle in rat heart, muscles and liver. After 60 min running exercise, AC content was increased in fasted mice muscles, but not in plasma or heart. After glucose bolus administration in fasted rats, the AC concentrations in plasma decreased after 30 min but then began to increase, while in the muscles and liver, the contents of medium- and long-chain ACs were unchanged or even increased. Only the heart showed a decrease in medium- and long-chain AC contents that was similar to that observed in plasma. In isolated rat heart, but not isolated-contracting mice muscles, the significant efflux of medium- and long-chain ACs was observed. The efflux was reduced by 40% after the addition of glucose and insulin to the perfusion solution. Overall, these results indicate that during fed-fast cycle shifting the heart determines the medium- and long-chain AC profile in plasma, due to a rapid response to the availability of circulating energy substrates.

Thyroid Hormone Regulation and Insulin Resistance: Insights From Animals Naturally Adapted to Fasting

The contribution of thyroidal status in insulin signaling and glucose homeostasis has been implicated as a potential pathophysiological factor in humans, but the specific mechanisms remain largely elusive. Fasting induces changes in both thyroid hormone secretion and insulin signaling. Here, we explore how mammals that undergo natural, prolonged bouts of fasting provide unique insight into evolved physiological adaptations that allow them to tolerate such conditions despite intermittent states of reversible insulin resistance. Such insights from nature may provide clues to better understand the basis of thyroidal involvement in insulin dysregulation in humans.

Ketone bodies mimic the life span extending properties of caloric restriction

The extension of life span by caloric restriction has been studied across species from yeast and Caenorhabditis elegans to primates. No generally accepted theory has been proposed to explain these observations. Here, we propose that the life span extension produced by caloric restriction can be duplicated by the metabolic changes induced by ketosis. From nematodes to mice, extension of life span results from decreased signaling through the insulin/insulin-like growth factor receptor signaling (IIS) pathway. Decreased IIS diminishes phosphatidylinositol (3,4,5) triphosphate (PIP₃ ) production, leading to reduced PI3K and AKT kinase activity and decreased forkhead box O transcription factor (FOXO) phosphorylation, allowing FOXO proteins to remain in the nucleus. In the nucleus, FOXO proteins increase the transcription of genes encoding antioxidant enzymes, including superoxide dismutase 2, catalase, glutathione peroxidase, and hundreds of other genes. An effective method for combating free radical damage occurs through the metabolism of ketone bodies, ketosis being the characteristic physiological change brought about by caloric restriction from fruit flies to primates. A dietary ketone ester also decreases circulating glucose and insulin leading to decreased IIS. The ketone body, d-β-hydroxybutyrate (d-βHB), is a natural inhibitor of class I and IIa histone deacetylases that repress transcription of the FOXO3a gene. Therefore, ketosis results in transcription of the enzymes of the antioxidant pathways. In addition, the metabolism of ketone bodies results in a more negative redox potential of the NADP antioxidant system, which is a terminal destructor of oxygen free radicals. Addition of d-βHB to cultures of C. elegans extends life span. We hypothesize that increasing the levels of ketone bodies will also extend the life span of humans and that calorie restriction extends life span at least in part through increasing the levels of ketone bodies. An exogenous ketone ester provides a new tool for mimicking the effects of caloric restriction that can be used in future research. The ability to power mitochondria in aged individuals that have limited ability to oxidize glucose metabolites due to pyruvate dehydrogenase inhibition suggests new lines of research for preventative measures and treatments for aging and aging-related disorders. © 2017 The Authors IUBMB Life published by Wiley Periodicals, Inc. on behalf of International Union of Biochemistry and Molecular Biology, 69(5):305-314, 2017.

β-Hydroxybutyrate: A signaling metabolite in starvation response?

Ketone bodies β-hydroxybutyrate (BHB) and acetoacetate are important metabolic substrates for energy production during prolonged fasting. However, BHB also has signaling functions. Through several metabolic pathways or processes, BHB modulates nutrient utilization and energy expenditure. These findings suggest that BHB is not solely a metabolic intermediate, but also acts as a signal to regulate metabolism and maintain energy homeostasis during nutrient deprivation. We briefly summarize the metabolism and emerging physiological functions of ketone bodies and highlight the potential role for BHB as a signaling molecule in starvation response.

High dose of aspirin moderates diabetes-induced changes of heart glycogen/glucose metabolism in rats

Aspirin (ASA), as a multifunctional drug has been used as a hypoglycaemic agent in the treatment of diabetes and severe hyperglycaemia and has been established as a secondary strategy which may prevent many cardiovascular events. In this study we investigated high dose (100 mg/kg b.w./i.p) and time-dependent (2, 7 and 14 days) effects of ASA on the heart key enzymes and substrates from glycogen/glucose metabolism in control and diabetic rats. The results accomplished demonstrated that ASA significantly potentiates glycogen accumulation, as well as decreased blood glucose level and heart glycolytic potential in control rats. The treatment of diabetic rats with ASA caused moderation of the diabetic complication-significant inhibition of glycogen accumulation, lowering of blood glucose, as well as elevation of glycolytic potential. In conclusion, we propose that use of high-dose of ASA has anabolic effects in control rats and reduces heart glycogen glucose complications in diabetic rats. The moderation of diabetes-induced changes is time-dependent and involves reduction of glycogenogenesis and inhibited depression of glycolysis, with a tendency to maintenance control values.

Variability in HOMA-IR, lipoprotein profile and selected hormones in young active men

Resistance to insulin actions is contributing to many metabolic disturbances. Such factors as age, sex, nutrition, body fat, and physical activity determine body insulin resistance. Present study attempted to asses insulin resistance and its metabolic effects with respect to energy intake in young, lean, and active men. A total of 87 men aged 18-23 participated in the study. Plasma levels of glucose, insulin, lipoproteins, cortisol, and TSH were determined. Insulin resistance was expressed as Homeostasis Model Assessment for Insulin Resistance (HOMA-IR) and calculated using homeostatic model. The median value of HOMA-IR (1.344) was used to divide subjects into two groups. Men did not differ in anthropometric parameters, daily physical activity, and plasma TSH and cortisol levels. However, in men with higher HOMA-IR significantly lower daily energy intake was observed concomitantly with higher TG, TC, and HDL-C concentrations in plasma versus their counterparts with lower HOMA-IR. Exclusively in subjects with higher HOMA-IR significant and positive correlation was noted between HOMA-IR and TC and LDL-C. We concluded that despite a normal body weight and physical activity, a subset of young men displayed unfavorable changes in insulin sensitivity and lipid profile, probably due to insufficient energy intake.

Insulin and GLP-1 infusions demonstrate the onset of adipose-specific insulin resistance in a large fasting mammal: potential glucogenic role for GLP-1

Prolonged food deprivation increases lipid oxidation and utilization, which may contribute to the onset of the insulin resistance associated with fasting. Because insulin resistance promotes the preservation of glucose and oxidation of fat, it has been suggested to be an adaptive response to food deprivation. However, fasting mammals exhibit hypoinsulinemia, suggesting that the insulin resistance-like conditions they experience may actually result from reduced pancreatic sensitivity to glucose/capacity to secrete insulin. To determine whether fasting results in insulin resistance or in pancreatic dysfunction, we infused early- and late-fasted seals (naturally adapted to prolonged fasting) with insulin (0.065 U/kg), and a separate group of late-fasted seals with low (10 pmol/L per kg) or high (100 pmol/L per kg) dosages of glucagon-like peptide-1 (GLP-1) immediately following a glucose bolus (0.5 g/kg), and measured the systemic and cellular responses. Because GLP-1 facilitates glucose-stimulated insulin secretion, these infusions provide a method to assess pancreatic insulin-secreting capacity. Insulin infusions increased the phosphorylation of insulin receptor and Akt in adipose and muscle of early- and late-fasted seals; however, the timing of the signaling response was blunted in adipose of late-fasted seals. Despite the dose-dependent increases in insulin and increased glucose clearance (high dose), both GLP-1 dosages produced increases in plasma cortisol and glucagon, which may have contributed to the glucogenic role of GLP-1. Results suggest that fasting induces adipose-specific insulin resistance in elephant seal pups, while maintaining skeletal muscle insulin sensitivity, and therefore suggests that the onset of insulin resistance in fasting mammals is an evolved response to cope with prolonged food deprivation.

A randomised trial of salsalate for insulin resistance and cardiovascular risk factors in persons with abnormal glucose tolerance

AIMS/HYPOTHESIS

Chronic sub-acute inflammation contributes to the pathogenesis of type 2 diabetes mellitus and cardiovascular disease. High doses of salicylate reduce inflammation, glucose and triacylglycerols, and may improve insulin sensitivity, suggesting therapeutic potential in impaired fasting glucose and/or impaired glucose tolerance. This trial aimed to evaluate the effect of salsalate vs placebo on insulin resistance and glycaemia in impaired fasting glucose and/or impaired glucose tolerance.

METHODS

We conducted a 12 week, two-centre, randomised, placebo-controlled study to evaluate the effect of salsalate (up to 4 g/day) vs placebo on systemic glucose disposal. Secondary objectives included treatment effects on glycaemia, inflammation and cardiovascular risk factors. Seventy-eight participants with impaired fasting glucose and/or impaired glucose tolerance from two VA healthcare systems were enrolled. Randomisation assignment was provided by the coordinating center directly to site pharmacists, and participants and research staff were blinded to treatment assignment.

RESULTS

Seventy-one individuals were randomised to placebo (n = 36) or salsalate (n = 35). Glucose disposal did not change in either group (salsalate 1% [95% CI -39%, 56%]; placebo 6% [95% CI -20%, 61%], p = 0.3 for placebo vs salsalate). Fasting glucose was reduced by 6% during the study by salsalate (p = 0.006) but did not change with placebo. Declines in glucose were accompanied by declines in fasting C-peptide with salsalate. Insulin clearance was reduced with salsalate. In the salsalate group, triacylglycerol levels were lower by 25% (p = 0.01) and adiponectin increased by 53% (p = 0.02) at the end of the study. Blood pressure, endothelial function and other inflammation markers did not differ between groups. Adipose tissue nuclear factor κB (NF-κB) activity declined in the salsalate group compared with placebo (-16% vs 42%, p = 0.005), but was not correlated with metabolic improvements. The frequency of tinnitus was low but tended to be higher with salsalate therapy (n = 4 vs n = 2).

CONCLUSIONS/INTERPRETATION

In summary, salsalate therapy was well tolerated, lowered fasting glucose, increased adiponectin and reduced adipose tissue NF-κB activity. These changes were not related to changes in peripheral insulin sensitivity, suggesting additional mechanisms for metabolic improvement.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00330733.

FUNDING

Office of Research and Development, Medical Research Service, Department of Veterans Affairs and NIH K24 DK63214.

Adaptive reciprocity of lipid and glucose metabolism in human short-term starvation

The human organism has tools to cope with metabolic challenges like starvation that are crucial for survival. Lipolysis, lipid oxidation, ketone body synthesis, tailored endogenous glucose production and uptake, and decreased glucose oxidation serve to protect against excessive erosion of protein mass, which is the predominant supplier of carbon chains for synthesis of newly formed glucose. The starvation response shows that the adaptation to energy deficit is very effective and coordinated with different adaptations in different organs. From an evolutionary perspective, this lipid-induced effect on glucose oxidation and uptake is very strong and may therefore help to understand why insulin resistance in obesity and type 2 diabetes mellitus is difficult to treat. The importance of reciprocity in lipid and glucose metabolism during human starvation should be taken into account when studying lipid and glucose metabolism in general and in pathophysiological conditions in particular.

Mechanisms for insulin resistance: common threads and missing links

Insulin resistance is a complex metabolic disorder that defies explanation by a single etiological pathway. Accumulation of ectopic lipid metabolites, activation of the unfolded protein response (UPR) pathway, and innate immune pathways have all been implicated in the pathogenesis of insulin resistance. However, these pathways are also closely linked to changes in fatty acid uptake, lipogenesis, and energy expenditure that can impact ectopic lipid deposition. Ultimately, these cellular changes may converge to promote the accumulation of specific lipid metabolites (diacylglycerols and/or ceramides) in liver and skeletal muscle, a common final pathway leading to impaired insulin signaling and insulin resistance.

Acute changes in blood glucose do not alter blood glutathione synthesis in adolescents with poorly controlled type 1 diabetes mellitus

Depletion of blood glutathione (GSH), a key antioxidant, is associated with type 1 diabetes mellitus (T1D) and contributes to the pathophysiology of diabetes complications. The aim of the current study was to determine whether acute normalization of blood glucose would restore GSH kinetics in adolescents with poorly controlled T1D. Ten 16.9 ± 1.5-year-old (SE) adolescents who had had T1D for 8.5 ± 1.9 years and were free of complications but were in poor control (hemoglobin A(1c), 9.2% ± 0.5%) received two 5-hour intravenous infusions of L-[3,3-(2)H(2)]cysteine in the postabsorptive state on 2 separate days after blood glucose had been maintained overnight at 246 ± 24 mg/dL (hyperglycemia) or 118 ± 23 mg/dL (euglycemia) using intravenous insulin infusion. Blood GSH fractional synthesis rates were determined by mass spectrometry from (2)H(2)-cysteine incorporation into GSH. Neither blood GSH (551 ± 169 vs 541 ± 232 μmol/L, P = .629) nor GSH fractional synthesis rate (84% ± 30% vs 82% ± 33% d(-1), P = .965) was altered by the short-term change in glycemic control. This finding suggests that, in adolescents with poorly controlled T1D, either (a) blood glucose per se does not regulate GSH metabolism or (b) GSH may only respond to sustained, more chronic changes in blood glucose level.

Glucose supplementation does not interfere with fasting-induced protection against renal ischemia/reperfusion injury in mice

BACKGROUND

Preoperative fasting induces robust protection against renal ischemia/reperfusion (I/R) injury in mice but is considered overcautious and possibly detrimental for postoperative recovery in humans. Furthermore, fasting seems to conflict with reported benefits of preoperative nutritional enhancement with carbohydrate-rich drinks. Here, we investigated whether preoperative ingestion of a glucose solution interferes with fasting-induced protection against renal I/R injury.

METHODS

Mice were randomized into the following groups: fasted for 3 days with access to water (fasted) or a glucose solution (fasted+glc) and fed ad libitum with water (fed) or a glucose solution (fed+glc). After induction of bilateral renal I/R injury, all animals had free access to food and water. Calorie intake, body weight, insulin sensitivity, kidney function, and animal survival were determined.

RESULTS

Fed+glc mice had a comparable daily calorie intake as fed mice, but 50% of those calories were obtained from the glucose solution. Fasted+glc mice had a daily calorie intake of approximately 75% of the intake of both fed groups. This largely prevented the substantial body weight loss seen in fasted animals. Preoperative insulin sensitivity was significantly improved in fasted+glc mice versus fed mice. After I/R injury, kidney function and animal survival were superior in both fasted groups.

CONCLUSIONS

The benefits of fasting and preoperative nutritional enhancement with carbohydrates are not mutually exclusive and may be a clinically feasible regimen to protect against renal I/R injury.

Erythrocyte glutathione concentration and production during hyperinsulinemia, hyperglycemia, and endotoxemia in healthy humans

In diabetes mellitus and sepsis, low erythrocyte glutathione (GSH) concentrations are found. Whether this is caused by lowered GSH production has not been clarified. To obtain insight in the relationship between erythrocyte GSH concentrations and GSH production, GSH kinetics were measured in healthy male volunteers during 4 different clamps (low-dose or medium-dose insulin [100 or 400 pmol/L] and euglycemia or hyperglycemia [5 or 12 mmol/L]) in a control setting (n = 6; all 4 clamps in the same subject) or after systemic administration of lipopolysaccharide (to mimic sepsis) (4 groups of n = 6; each clamp in a different subject). Hyperinsulinemia decreased erythrocyte GSH concentration (P = .042), but did not affect fractional synthetic rate (FSR) of GSH. Hyperglycemia did not affect erythrocyte GSH concentration, but decreased FSR of GSH (P = .025). Lipopolysaccharide decreased erythrocyte GSH concentration (P < .001), but increased FSR of erythrocyte GSH (P = .035). Depending on the metabolic circumstances, we found either stable GSH concentrations with lower production rates or decreased levels with either no change or an increase in production rate. Based upon these data, it seems inappropriate to infer conclusions about changes in synthesis rate of GSH from changes in its concentration.

Glut4 is upregulated despite decreased insulin signaling during prolonged fasting in northern elephant seal pups

Postprandial cellular glucose uptake is dependent on an insulin-signaling cascade in muscle and adipose tissue, resulting in the translocation of the insulin-dependent glucose transporter 4 (Glut4) into the plasma membrane. Additionally, extended food deprivation is characterized by suppressed insulin signaling and decreased Glut4 expression. Northern elephant seals are adapted to prolonged fasts characterized by high levels of plasma glucose. To address the hypothesis that the fasting-induced decrease in insulin is associated with reduced insulin signaling in prolonged fasted seals, we compared the adipose protein levels of the cellular insulin-signaling pathway, Glut4 and plasma glucose, insulin, cortisol, and adiponectin concentrations between Early (n = 9; 2-3 wks postweaning) and Late (n = 8; 6-8 wks postweaning) fasted seals. Plasma adiponectin (230 ± 13 vs. 177 ± 11 ng/ml), insulin (2.7 ± 0.4 vs. 1.0 ± 0.1 μU/ml), and glucose (9.8 ± 0.5 vs. 8.0 ± 0.3 mM) decreased, while cortisol (124 ± 6 vs. 257 ± 30 nM) doubled with fasting. Glut4 increased (31%) with fasting despite the significant decreases in the cellular content of phosphatidylinositol 3-kinase as well as phosphorylated insulin receptor, insulin receptor substrate-1, and Akt2. Increased Glut4 may have contributed to the decrease in plasma glucose, but the decrease in insulin and insulin signaling suggests that Glut4 is not insulin-dependent in adipose tissue during prolonged fasting in elephant seals. The reduction of plasma glucose independent of insulin may make these animals an ideal model for the study of insulin resistance.

FoxO1 links hepatic insulin action to endoplasmic reticulum stress

Forkhead box O1 (FoxO1) is a transcription factor that mediates the inhibitory effect of insulin on target genes in hepatic metabolism. Hepatic FoxO1 activity is up-regulated to promote glucose production during fasting and is suppressed to limit postprandial glucose excursion after meals. Increased FoxO1 activity augments the expression of insulin receptor (IR) and IR substrate (IRS)2, which in turn inhibits FoxO1 activity in response to reduced insulin action. To address the underlying physiology of such a feedback loop for regulating FoxO1 activity, we delivered FoxO1-ADA by adenovirus-mediated gene transfer into livers of adult mice. FoxO1-ADA is a constitutively active allele that is refractory to insulin inhibition, allowing us to determine the metabolic effect of a dislodged FoxO1 feedback loop in mice. We show that hepatic FoxO1-ADA production resulted in significant induction of IR and IRS2 expression. Mice with increased FoxO1-ADA production exhibited near glycogen depletion. Unexpectedly, hepatic FoxO1-ADA production elicited a profound unfolded protein response, culminating in the induction of hepatic glucose-regulated protein 78 (GRP78) expression. These findings were recapitulated in primary human and mouse hepatocytes. FoxO1 targeted GRP78 gene for trans-activation via selective binding to an insulin responsive element in the GRP78 promoter. This effect was counteracted by insulin. Our studies underscore the importance of an IR and IRS2-dependent feedback loop to keep FoxO1 activity in check for maintaining hepatic glycogen homeostasis and promoting adaptive unfolded protein response in response to altered metabolism and insulin action. Excessive FoxO1 activity, resulting from a dislodged FoxO1 feedback loop in insulin resistant liver, is attributable to hepatic endoplasmic reticulum stress and metabolic abnormalities in diabetes.

Potential role of salicylates in type 2 diabetes

OBJECTIVE

To review the evidence base supporting the use of salicylates for glucose level control in patients with type 2 diabetes and provide a comprehensive review of available information describing the potential role of salicylates and, in particular, salsalate, for glucose control in type 2 diabetes prevention and treatment.

DATA SOURCES

A literature search using MEDLINE (1966-March 2010), PubMed, and Google Scholar was conducted using the search terms salicylates, salicylic acid, aspirin, salsalate, acetylsalicylic acid, insulin, glucose, glycemic control, diabetes, hyperglycemia, and nuclear factor. The bibliographies of identified articles were reviewed for additional citations.

STUDY SELECTION AND DATA EXTRACTION

All relevant English-language information on the pharmacology, efficacy, and safety of salicylates for glucose control related to insulin resistance or diabetes prevention were reviewed. Preclinical data, clinical trials, and case reports were identified, evaluated, and included in this systematic review.

DATA SYNTHESIS

Treatment of inflammation may be a potential novel strategy in prevention and treatment of type 2 diabetes, in which the body is resistant to the effects of insulin. Previous and recent studies reveal a possible relationship between inflammation and obesity. The chronic activation of the immune system due to low-grade inflammation was found in several studies to be associated with obesity, and this, in turn, can promote development of insulin resistance and impaired glucose tolerance. Administration of salicylates was shown over a century ago to lower glucose levels in patients with diabetes. Many in vitro and in vivo pharmacologic studies have demonstrated a glucose-lowering effect of salicylates. Salicylates, especially salsalate, were found in several clinical studies and case reports to be potential agents for diabetes treatment with a favorable safety profile. Although these studies had inherent limitations, such as small numbers of patients and short duration, the vast majority showed significant glucose-lowering effects. A large randomized trial, the National Institute of Diabetes and Digestive and Kidney Diseases-sponsored Targeting Inflammation with Salsalate in Type 2 Diabetes (TINSAL-T2D) trial, recently concluded that salsalate lowers hemoglobin A(1c) levels and improves glycemic control in patients with type 2 diabetes.

CONCLUSIONS

Salicylates, especially salsalate, appear to be a promising treatment option for prevention or treatment of diabetes by lowering glucose levels. More extensive studies are needed to confirm the mechanisms involved and whether the effects are sustainable with continued administration of these agents. Further studies are warranted.

A single night of partial sleep deprivation induces insulin resistance in multiple metabolic pathways in healthy subjects

BACKGROUND

Subsequent nights with partial sleep restriction result in impaired glucose tolerance, but the effects on insulin sensitivity have not been characterized.

OBJECTIVE

The aim of this study was to evaluate the effect of a single night of partial sleep restriction on parameters of insulin sensitivity.

RESEARCH DESIGN AND METHODS

Nine healthy subjects (five men, four women) were studied once after a night of normal sleep duration (sleep allowed from 2300 to 0730 h), and once after a night of 4 h of sleep (sleep allowed from 0100 to 0500 h). Sleep characteristics were assessed by polysomnography. Insulin sensitivity was measured by hyperinsulinemic euglycemic clamp studies (from 1130 to 1430 h) with infusion of [6,6-(2)H(2)]glucose.

RESULTS

Sleep duration was shorter in the night with sleep restriction than in the unrestricted night (226 +/- 11 vs. 454 +/- 9 min; P< 0.0001). Sleep restriction did not affect basal levels of glucose, nonesterified fatty acids, insulin, or endogenous glucose production. Sleep restriction resulted in increased endogenous glucose production during the hyperinsulinemic clamp study compared to the unrestricted night (4.4 +/- 0.3 vs. 3.6 +/- 0.2 micromol x kg lean body mass(-1) x min(-1); P = 0.017), indicating hepatic insulin resistance. In addition, sleep restriction decreased the glucose disposal rate during the clamp (32.5 +/- 3.6 vs. 40.7 +/- 5.1 micromol x kg lean body mass(-1) x min(-1); P = 0009), reflecting decreased peripheral insulin sensitivity. Accordingly, sleep restriction decreased the rate of glucose infusion by approximately 25% (P = 0.001). Sleep restriction increased plasma nonesterified fatty acid levels during the clamp study (68 +/- 5 vs. 57 +/- 4 micromol/liter; P = 0.005).

CONCLUSIONS

Partial sleep deprivation during only a single night induces insulin resistance in multiple metabolic pathways in healthy subjects. This physiological observation may be of relevance for variations in glucoregulation in patients with type 1 and type 2 diabetes.

Combined effects of ghrelin and higher food intake enhance skeletal muscle mitochondrial oxidative capacity and AKT phosphorylation in rats with chronic kidney disease

Skeletal muscle mitochondrial dysfunction and insulin resistance occur in chronic kidney disease. Ghrelin is a gastric hormone previously shown to enhance muscle mitochondrial enzyme activities and AKT-mediated insulin signaling independent of food intake in healthy rats. Here we determined the impact of ghrelin treatment on anorexia, skeletal muscle mitochondrial oxidative capacity, AKT phosphorylation as a measure of insulin signaling, and lean body mass in a rat model of chronic kidney disease. Ghrelin infusion promoted higher food intake and lean body mass. Further, although muscle mitochondrial enzyme activities were low in the rats with CKD (chronic kidney disease), they normalized with ghrelin treatment, a change that was consistent with the increase in the transcript levels of regulators of mitochondrial biogenesis and lipid metabolism. This was associated with a lower muscle triglyceride content and higher AKT phosphorylation. Pair-feeding showed that mitochondrial effects of ghrelin are independent of changes in food intake, whereas combined ghrelin treatment and higher food intake were needed to enhance AKT phosphorylation. Thus, ghrelin-induced muscle mitochondrial changes and lower tissue triglycerides could favor insulin action and muscle anabolism in the presence of improvement in food intake. Our study shows that combined effects of ghrelin on appetite and muscle mitochondria improve muscle metabolic and nutritional alterations in chronic kidney disease. This could have potential beneficial impact on patient morbidity and survival.

Inflammatory effects of nutritional stimuli: further support for the need for a big picture approach to tackling obesity and chronic disease

The discovery of a form of low-grade systemic inflammation (called 'metaflammation'), and the close evolutionary link between the immune and metabolic systems, poses questions about the supposed antigens (inducers) of such an immune reaction. Initially, this was thought to be mediated through obesity. However, we have identified a number of lifestyle or environmentally related inducers that may cause metaflammation, even in the absence of obesity. In this paper, the third of a series linking obesity with broad environmental and evolutionary factors, we identify nutritional stimuli with evidence of an involvement in metaflammation. From this we propose that components of certain foods and beverages with which humans have not evolved, are more often the inducers of an inflammatory effect in the body than those with which humans have become more familiar, and to which a neutral, or anti-inflammatory response may be expected to have developed. The implications of such a finding are considered in relation to broader aspects of the environment, economic growth, policy change and current global financial issues.

Intermittent fasting does not affect whole-body glucose, lipid, or protein metabolism

BACKGROUND

Intermittent fasting (IF) was shown to increase whole-body insulin sensitivity, but it is uncertain whether IF selectively influences intermediary metabolism. Such selectivity might be advantageous when adapting to periods of food abundance and food shortage.

OBJECTIVE

The objective was to assess effects of IF on intermediary metabolism and energy expenditure.

DESIGN

Glucose, glycerol, and valine fluxes were measured after 2 wk of IF and a standard diet (SD) in 8 lean healthy volunteers in a crossover design, in the basal state and during a 2-step hyperinsulinemic euglycemic clamp, with assessment of energy expenditure and phosphorylation of muscle protein kinase B (AKT), glycogen synthase kinase (GSK), and mammalian target of rapamycine (mTOR). We hypothesized that IF selectively increases peripheral glucose uptake and lowers proteolysis, thereby protecting protein stores.

RESULTS

No differences in body weight were observed between the IF and SD groups. Peripheral glucose uptake and hepatic insulin sensitivity during the clamp did not significantly differ between the IF and SD groups. Likewise, lipolysis and proteolysis were not different between the IF and SD groups. IF decreased resting energy expenditure. IF had no effect on the phosphorylation of AKT but significantly increased the phosphorylation of glycogen synthase kinase. Phosphorylation of mTOR was significantly lower after IF than after the SD.

CONCLUSIONS

IF does not affect whole-body glucose, lipid, or protein metabolism in healthy lean men despite changes in muscle phosphorylation of GSK and mTOR. The decrease in resting energy expenditure after IF indicates the possibility of an increase in weight during IF when caloric intake is not adjusted. This study was registered at www.trialregister.nl as NTR1841.

Obesity and chronic disease: always offender or often just accomplice?

Over a decade ago, the finding of a form of low-grade systemic inflammation ('metaflammation') associated with obesity, insulin resistance and chronic disease proffered a causal explanation for the latter. However, recent work has shown that metaflammation is also associated with several modern lifestyle-related and environmental inducers, with or without obesity. Here, we present accumulating data to show a link between metaflammation and a number of non-microbial environmental and lifestyle stimulants, both with and without obesity. This implies that obesity may often be an accomplice to, as much as an offender in, major metabolic disease. The real (albeit distal) cause of such a disease appears to lie in aspects of the modern techno-industrial environment driving unhealthy lifestyle behaviours. If true, this suggests that while individual weight loss may be a component of chronic disease management, it may be neither 'necessary' nor 'sufficient' to reduce the problem at a population level. Greater multidisciplinary and policy input is needed to modify the economic and political drivers of the modern, obesogenic environment.

Should obesity be the main game? Or do we need an environmental makeover to combat the inflammatory and chronic disease epidemics?

There is a link between obesity and chronic disease. However, the causal relationship is complicated. Some forms of obesity are associated with low-level systemic inflammation, which is linked to disease. But lifestyle behaviours that may not necessarily cause obesity (poor diet, inadequate sleep, smoking, etc.) can independently cause inflammation and consequent disease. It is proposed here that it is the environment driving modern lifestyles, which is the true cause of much chronic disease, rather than obesity per se, and that obesity may be a marker of environmental derangement, rather than the primary cause of the problem. Attempts to clinically manage obesity alone on a large scale are therefore unlikely to be successful at the population level without significant lifestyle or environmental change. Environmental factors influencing obesity and health have now also been implicated in ecological perturbations such as climate change, through the shift to positive energy balance in humans caused by the exponential use of fossil fuels in such areas as transport, and consequent rises in carbon emissions into the atmosphere. It is proposed therefore that a more policy-based approach to dealing with obesity, which attacks the common causes of both biological and ecological 'dis-ease', could have positive effects on both chronic disease and environmental problems. A plea is thus made for a greater health input into discussions on environmental regulation for chronic disease control, as well as climate change.

The effect of salsalate on insulin action and glucose tolerance in obese non-diabetic patients: results of a randomised double-blind placebo-controlled study

AIM/HYPOTHESIS

Low-grade inflammation may contribute to obesity-related insulin resistance and has been associated with increased risk of type 2 diabetes mellitus. The present study evaluated whether treatment with salsalate, a traditional anti-inflammatory medication, would improve insulin action in obese non-diabetic individuals.

METHODS

The study was a randomised, double-blind, placebo-controlled, parallel trial conducted at the inpatient clinical research unit of the NIDKK (Phoenix, AZ, USA). Participants were 54 adults (18 to 45 years of age) with BMI >or= 30 kg/m(2). The intervention was salsalate (3 g/day, n = 28) or identical placebo (n = 26) for 7 days. The allocation was kept concealed by giving the investigator only a number corresponding to a vial of placebo or salsalate sequentially randomised in blocks by sex. Main outcomes were changes in insulin action assessed as rate of glucose disposal (R (d)) by euglycaemic-hyperinsulinaemic clamp (insulin infusion rate 40 mU m(-2) min(-1)) and glucose tolerance by 75 g OGTT.

RESULTS

The study was completed by 47 participants, of which 40 were analysed (salsalate n = 22, placebo n = 18). Salsalate treatment resulted in decreased fasting plasma glucose concentration (mean [SD]; 4.83 [0.28] vs 5.11 [0.33] mmol/l, p = 0.001) and glucose AUC during the OGTT (p = 0.01), and in increased R (d) (20 [8] vs 18 [6] micromol [kg estimated metabolic body size](-1) min(-1), p = 0.002), while there was no significant change in these variables with placebo (p > 0.3 for all). The effect of salsalate on R (d) disappeared (p = 0.9) after normalising to increased insulin concentrations (701 [285] vs 535 [201] pmol/l, p < 0.0001) measured during the clamp. No side effects of salsalate were observed during the study.

CONCLUSIONS/INTERPRETATION

The glucose-lowering potential of salicylates appears to be due to effects on insulin concentration rather than improved insulin action. Salicylate-based compounds may be useful for the treatment and prevention of type 2 diabetes.

Muscle adaptation to short-term fasting in healthy lean humans

CONTEXT

It has been demonstrated repeatedly that short-term fasting induces insulin resistance, although the exact mechanism in humans is unknown to date. Intramyocellular sphingolipids (i.e. ceramide) have been suggested to induce insulin resistance by interfering with the insulin signaling cascade in obesity.

OBJECTIVE

Our objective was to study peripheral insulin sensitivity together with muscle ceramide concentrations and protein kinase B/AKT phosphorylation after short-term fasting. MAIN OUTCOME MEASURES AND DESIGN: After 14- and 62-h fasting, glucose fluxes were measured before and after a hyperinsulinemic euglycemic clamp. Muscle biopsies were performed in the basal state and during the clamp to assess muscle ceramide and protein kinase B/AKT.

RESULTS

Insulin-mediated peripheral glucose uptake was significantly lower after 62-h fasting compared with 14-h fasting. Intramuscular ceramide concentrations tended to increase during fasting. During the clamp the phosphorylation of protein kinase B/AKT at serine(473) in proportion to the total amount of protein kinase B/AKT was significantly lower. Muscle ceramide did not correlate with plasma free fatty acids.

CONCLUSIONS

Fasting for 62 h decreases insulin-mediated peripheral glucose uptake with lower phosphorylation of AKT at serine(473). AKT may play a regulatory role in fasting-induced insulin resistance. Whether the decrease in AKT can be attributed to the trend to higher muscle ceramide remains unanswered.