The Danish Centre for Strategic Research in Type 2 Diabetes (DD2) study: expected outcome from the DD2 project and two intervention studies

The overall aim of the Danish Centre for Strategic Research in Type 2 Diabetes (DD2) is to near-normalize metabolic control in newly diagnosed patients with type 2 diabetes (T2D) using an individualized treatment approach. We hypothesize that this will not only prevent complications and improve quality of life for T2D patients but also result in increased cost efficiency compared with current treatment modalities. This paper provides an overview of the expected outcomes from DD2, focusing on the two main intervention studies. The main data for the DD2 project are collected during patient enrollment and stored using the individual civil registration number. This enables subsequent linking to other national databases where supplemental data can be obtained. All data will be used for designing treatment guidelines and continuously monitoring the development of diabetic complications, thereby obtaining knowledge about predictors for the long-term outcome and identifying targets for new interventions. Further data are being collected from two intervention studies. The aim of the first intervention study is to improve T2D treatment using an individualized treatment modality optimizing medication according to individual metabolic responses and phenotypic characteristics. The aim of the second intervention study is to develop an evidence-based training protocol to be implemented as a treatment modality for T2D and used for initiating lifelong changes in physical activity levels in patients with T2D. An initial pilot study evaluating an interval-based walking protocol is ongoing, and preliminary results indicate that this protocol is an optimal “free-living” training intervention. An initial health-economic analysis will also be performed as a basis for analysis of the data collected during the project. A cost-benefit analysis of the two intervention studies will be conducted. The DD2 project is expected to lead to improved treatment modalities and increased knowledge about existing treatment guidelines, and will also provide a solid base for health-economic decision-making.

Glucagon like peptide-1-induced glucose metabolism in differentiated human muscle satellite cells is attenuated by hyperglycemia

BACKGROUND

Glucagon like peptide-1 (GLP-1) stimulates insulin secretion from the pancreas but also has extra-pancreatic effects. GLP-1 may stimulate glucose uptake in cultured muscle cells but the mechanism is not clearly defined. Furthermore, while the pancreatic effects of GLP-1 are glucose-dependent, the glucose-dependency of its extra-pancreatic effects has not been examined.

METHODS

Skeletal muscle satellite cells isolated from young (22.5 ± 0.97 yr), lean (BMI 22.5 ± 0.6 kg/m(2)), healthy males were differentiated in media containing either 22.5 mM (high) or 5 mM (normal) glucose for 7 days in the absence or presence of insulin and/or various GLP-1 concentrations. Myocellular effects of GLP-1, insulin and glucose were assessed by western-blot, glucose uptake and glycogen synthesis.

RESULTS

We firstly show that the GLP-1 receptor protein is expressed in differentiated human muscle satellite cells (myocytes). Secondly, we show that in 5 mM glucose media, exposure of myocytes to GLP-1 results in a dose dependent increase in glucose uptake, GLUT4 amount and subsequently glycogen synthesis in a PI3K dependent manner, independent of the insulin signaling cascade. Importantly, we provide evidence that differentiation of human satellite cells in hyperglycemic (22.5 mM glucose) conditions increases GLUT1 expression, and renders the cells insulin resistant and interestingly GLP-1 resistant in terms of glucose uptake and glycogen synthesis. Hyperglycemic conditions did not affect the ability of insulin to phosphorylate downstream targets, PKB or GSK3. Interestingly we show that at 5 mM glucose, GLP-1 increases GLUT4 protein levels and that this effect is abolished by hyperglycemia.

CONCLUSIONS

GLP-1 increases glucose uptake and glycogen synthesis into fully-differentiated human satellite cells in a PI3-K dependent mechanism potentially through increased GLUT4 protein levels. The latter occurs independently of the insulin signaling pathway. Attenuation of both GLP-1 and insulin-induced glucose metabolism by hyperglycemia is likely to occur downstream of PI3K.

Effects of lipopolysaccharide infusion on arterial levels and transcerebral exchange kinetics of glutamate and glycine in healthy humans

An imbalance between glutamate and glycine signalling may contribute to sepsis-associated encephalopathy by causing neuronal excitotoxicity. In this study, we therefore investigated the transcerebral exchange kinetics of glutamate and glycine in a human-experimental model of systemic inflammation. Cerebral blood flow (CBF) and arterial to jugular venous concentration differences of glutamate and glycine were determined before and after a 4-h intravenous infusion of Escherichia coli lipopolysaccharide (LPS, total dose of 0.3 ng/kg) in 12 healthy volunteers. The global cerebral net exchange was calculated by multiplying CBF with the arterial to jugular venous differences. LPS induced a systemic inflammatory response with fever, neutrocytosis, and elevated arterial levels of tumour necrosis factor-α. This was associated with a decrease in the arterial levels of both glutamate and glycine; however, their transcerebral exchange kinetics were unaffected. Inflammation-induced alterations of the circulating levels of glutamate and glycine, do not affect the global transcerebral exchange kinetics of these amino acids in healthy humans.

Deficient leukemia inhibitory factor signaling in muscle precursor cells from patients with type 2 diabetes

The cytokine leukemia-inhibitory factor (LIF) is expressed by skeletal muscle and induces proliferation of muscle precursor cells, an important feature of skeletal muscle maintenance and repair. We hypothesized that muscle precursor cells from patients with type 2 diabetes had a deficient response to LIF. The mRNA and protein expressions of LIF and its receptor (LIFR) were measured in skeletal muscle biopsies from healthy individuals and patients with type 2 diabetes by use of qPCR and Western blot. LIF signaling and response were studied following administration of recombinant LIF and siRNA knockdown of suppressor of cytokine signaling (SOCS)3 in myoblast cultures established from healthy individuals and patients with type 2 diabetes. Myoblast proliferation rate was assessed by bromodeoxyuridine incorporation. LIF and LIFR proteins were increased in both muscle tissue and cultured myoblasts from diabetic patients. Nonetheless, in the diabetic myoblasts, LIF-induced phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3 was impaired. The deficient response to LIF administration in the diabetic myoblasts was further emphasized by a lack of increase in LIF-stimulated cell proliferation and a decreased LIF-stimulated induction of the proliferation-promoting factors cyclin D1, JunB, and c-myc. SOCS3 protein was upregulated in diabetic myoblasts, and knockdown of SOCS3 rescued LIF-induced gene expression in diabetic myoblasts, whereas neither STAT1 or STAT3 signaling nor proliferation rate was affected. In conclusion, although LIF and LIFR proteins were increased in muscle tissue and myoblasts from diabetic patients, LIF signaling and LIF-stimulated cell proliferation were impaired in diabetic myoblasts, suggesting a novel mechanism by which muscle function is compromised in diabetes.

Independent component analysis in non-hypothesis driven metabolomics: improvement of pattern discovery and simplification of biological data interpretation demonstrated with plasma samples of exercising humans

In a non-hypothesis driven metabolomics approach plasma samples collected at six different time points (before, during and after an exercise bout) were analyzed by gas chromatography-time of flight mass spectrometry (GC-TOF MS). Since independent component analysis (ICA) does not need a priori information on the investigated process and moreover can separate statistically independent source signals with non-Gaussian distribution, we aimed to elucidate the analytical power of ICA for the metabolic pattern analysis and the identification of key metabolites in this exercise study. A novel approach based on descriptive statistics was established to optimize ICA model. In the GC-TOF MS data set the number of principal components after whitening and the number of independent components of ICA were optimized and systematically selected by descriptive statistics. The elucidated dominating independent components were involved in fuel metabolism, representing one of the most affected metabolic changes occurring in exercising humans. Conclusive time dependent physiological changes of the metabolic pattern under exercise conditions were detected. We conclude that after optimization ICA can successfully elucidate key metabolite pattern as well as characteristic metabolites in metabolic processes thereby simplifying the explanation of complex biological processes. Moreover, ICA is capable to study time series in complex experiments with multi-levels and multi-factors.

Soluble CD163: a biomarker linking macrophages and insulin resistance

AIMS/HYPOTHESIS

Soluble CD163 (sCD163) was recently identified as a strong risk marker for developing type 2 diabetes. We hypothesised that sCD163 independently associates with insulin resistance.

METHODS

This cross-sectional study includes 234 participants: 96 with type 2 diabetes, 34 with impaired glucose tolerance (IGT) and 104 with normal glucose tolerance (NGT), matched for sex and BMI. Glucose-lowering medication was paused for 1 week before plasma samples were obtained for determination of sCD163 and other inflammatory and metabolic variables. Insulin resistance was estimated by homeostasis model assessment of insulin resistance (HOMA-IR).

RESULTS

Concentrations of sCD163 were 1.95 mg/l (0.63-6.97) in individuals with type 2 diabetes, 1.64 mg/l (0.58-4.19) in those with IGT, and 1.48 mg/l (0.48-4.11) (median [range]) in those with NGT (p < 0.0001). In univariate analyses, sCD163 correlated significantly with HOMA-IR (R = 0.44), insulin (R = 0.41), glucose (R = 0.30), triacylglycerol (R = 0.29) and HDL-cholesterol (R = -0.34) (all p < 0.0001). All but glucose remained significant when adjusting for age, sex, BMI and glycaemic group. In univariate regression analyses, HOMA-IR was associated with sCD163, C-reactive protein (CRP), TNF-α and IL-6 (all p ≤ 0.0001). An increase of 50% in sCD163 resulted in an estimated increase in HOMA-IR of 36% (95% CI 26, 48; p < 0.0001). In multiple linear regression analyses, sCD163 (p = 0.001) and CRP (p = 0.01) remained independent predictors of HOMA-IR, whereas TNF-α and IL-6 did not.

CONCLUSIONS/INTERPRETATION

Macrophage-specific sCD163 was strongly associated with insulin resistance independently of TNF-α and other predictors. Moreover, sCD163 was associated with well-known variables of the metabolic syndrome.

Plasma and muscle myostatin in relation to type 2 diabetes

Objective

Myostatin is a secreted growth factor expressed in skeletal muscle tissue, which negatively regulates skeletal muscle mass. Recent animal studies suggest a role for myostatin in insulin resistance. We evaluated the possible metabolic role of myostatin in patients with type 2 diabetes and healthy controls.

Design

76 patients with type 2 diabetes and 92 control subjects were included in the study. They were matched for age, gender and BMI. Plasma samples and biopsies from the vastus lateralis muscle were obtained to assess plasma myostatin and expression of myostatin in skeletal muscle.

Results

Patients with type 2 diabetes had higher fasting glucose (8.9 versus 5.1 mmol/L, P<0.001), plasma insulin (68.2 versus 47.2 pmol/L, P<0.002) and HOMA2-IR (1.6 versus 0.9, P<0.0001) when compared to controls. Patients with type 2 diabetes had 1.4 (P<0.01) higher levels of muscle myostatin mRNA content than the control subjects. Plasma myostatin concentrations did not differ between patients with type 2 diabetes and controls. In healthy controls, muscle myostatin mRNA correlated with HOMA2-IR (r = 0.30, P<0.01), plasma IL-6 (r = 0.34, P<0.05) and VO2 max (r = −0.26, P<0.05), however, no correlations were observed in patients with type 2 diabetes.

Conclusions

This study supports the idea that myostatin may have a negative effect on metabolism. However, the metabolic effect of myostatin appears to be overruled by other factors in patients with type 2 diabetes.

Muscles, exercise and obesity: skeletal muscle as a secretory organ

During the past decade, skeletal muscle has been identified as a secretory organ. Accordingly, we have suggested that cytokines and other peptides that are produced, expressed and released by muscle fibres and exert either autocrine, paracrine or endocrine effects should be classified as myokines. The finding that the muscle secretome consists of several hundred secreted peptides provides a conceptual basis and a whole new paradigm for understanding how muscles communicate with other organs, such as adipose tissue, liver, pancreas, bones and brain. However, some myokines exert their effects within the muscle itself. Thus, myostatin, LIF, IL-6 and IL-7 are involved in muscle hypertrophy and myogenesis, whereas BDNF and IL-6 are involved in AMPK-mediated fat oxidation. IL-6 also appears to have systemic effects on the liver, adipose tissue and the immune system, and mediates crosstalk between intestinal L cells and pancreatic islets. Other myokines include the osteogenic factors IGF-1 and FGF-2; FSTL-1, which improves the endothelial function of the vascular system; and the PGC-1α-dependent myokine irisin, which drives brown-fat-like development. Studies in the past few years suggest the existence of yet unidentified factors, secreted from muscle cells, which may influence cancer cell growth and pancreas function. Many proteins produced by skeletal muscle are dependent upon contraction; therefore, physical inactivity probably leads to an altered myokine response, which could provide a potential mechanism for the association between sedentary behaviour and many chronic diseases.

Role of vitamin C and E supplementation on IL-6 in response to training

Vitamin C and E supplementation has been shown to attenuate the acute exercise-induced increase in plasma interleukin-6 (IL-6) concentration. Here, we studied the effect of antioxidant vitamins on the regulation of IL-6 expression in muscle and the circulation in response to acute exercise before and after high-intensity endurance exercise training. Twenty-one young healthy men were allocated into either a vitamin (VT; vitamin C and E, n = 11) or a placebo (PL, n = 10) group. A 1-h acute bicycling exercise trial at 65% of maximal power output was performed before and after 12 wk of progressive endurance exercise training. In response to training, the acute exercise-induced IL-6 response was attenuated in PL (P < 0.02), but not in VT (P = 0.82). However, no clear difference between groups was observed (group × training: P = 0.13). Endurance exercise training also attenuated the acute exercise-induced increase in muscle-IL-6 mRNA in both groups. Oxidative stress, assessed by plasma protein carbonyls concentration, was overall higher in the VT compared with the PL group (group effect: P < 0.005). This was accompanied by a general increase in skeletal muscle mRNA expression of antioxidative enzymes, including catalase, copper-zinc superoxide dismutase, and glutathione peroxidase 1 mRNA expression in the VT group. However, skeletal muscle protein content of catalase, copper-zinc superoxide dismutase, or glutathione peroxidase 1 was not affected by training or supplementation. In conclusion, our results indicate that, although vitamin C and E supplementation may attenuate exercise-induced increases in plasma IL-6 there is no clear additive effect when combined with endurance training.

Increased shelterin mRNA expression in peripheral blood mononuclear cells and skeletal muscle following an ultra-long-distance running event

Located at the end of chromosomes, telomeres are progressively shortened with each replication of DNA during aging. Integral to the regulation of telomere length is a group of proteins making up the shelterin complex, whose tissue-specific function during physiological stress is not well understood. In this study, we examine the mRNA and protein levels of proteins within and associated with the shelterin complex in subjects ( n = 8, mean age = 44 yr) who completed a physiological stress of seven marathons in 7 days. Twenty-two to 24 h after the last marathon, subjects had increased mRNA levels of DNA repair enzymes Ku70 and Ku80 ( P < 0.05) in both skeletal muscle and peripheral blood mononuclear cells (PBMCs). Additionally, the PBMCs displayed an increment in three shelterin protein mRNA levels (TRF1, TRF2, and Pot-1, P < 0.05) following the event. Seven days of ultrarunning did not result in changes in mean telomere length, telomerase activity, hTert mRNA, or hterc mRNAs found in PBMCs. Higher protein concentrations of TRF2 were found in skeletal muscle vs. PBMCs at rest. Mean telomere length in skeletal muscle did not change and did not contain detectable levels of htert mRNA or telomerase activity. Furthermore, changes in the PBMCs could not be attributed to changes in the proportion of subtypes of CD4+ or CD8+ cells. We have provided the first evidence that, in humans, proteins within and associated with the shelterin complex increase at the mRNA level in response to a physiological stress differentially in PBMCs and skeletal muscle.

The role of leptin in human lipid and glucose metabolism: the effects of acute recombinant human leptin infusion in young healthy males

BACKGROUND

Obese and lean humans treated with leptin have not experienced convincing weight-loss results compared with the dramatic weight losses observed in obese rodents.

OBJECTIVE

We sought to investigate the effect of acutely elevating leptin to concentrations observed in obese individuals on muscle and adipose tissue metabolism and muscle signaling in healthy lean males.

DESIGN

Healthy, lean, postabsorptive males were infused with either recombinant human leptin (rhleptin; n = 8) or saline (control; n = 8) for 4 h, which elicited leptin concentrations of ~ 20 and ~ 1 ng/mL, respectively. Systemic, skeletal muscle, and adipose tissue fat and glucose metabolism in vivo were assessed before, during, and 2 h after cessation of the infusion. Skeletal muscle biopsy specimens were obtained to quantify changes in signal transducers and activators of transcription-5'AMP-activated protein kinase (STAT-AMPK) signaling.

RESULTS

During the infusion of rhleptin, no differences in either systemic, skeletal muscle, or adipose tissue glucose or fat metabolism were observed. These observations were made despite increased activation of STAT (~ 17-fold) and AMPK (1.43-fold) after 1 h of rhleptin infusion. After the rhleptin infusion, an increase in systemic palmitate and fat oxidation was observed (P < 0.0003), which likely was caused by a concomitant increase in skeletal muscle palmitate oxidation (P < 0.02). This was observed despite lowered leptin concentrations and basal skeletal muscle STAT-AMPK signaling.

CONCLUSIONS

Elevating circulating leptin concentrations to concentrations comparable with those of obese individuals increases human in vivo skeletal muscle signaling through the AMPK pathway and causes an increase in skeletal muscle fatty acid oxidation. Abdominal adipose tissue was unaffected by the acute physiologic increase in leptin concentrations.

Elevated NF-κB activation is conserved in human myocytes cultured from obese type 2 diabetic patients and attenuated by AMP-activated protein kinase

OBJECTIVE

To examine whether the inflammatory phenotype found in obese and diabetic individuals is preserved in isolated, cultured myocytes and to assess the effectiveness of pharmacological AMP-activated protein kinase (AMPK) activation upon the attenuation of inflammation in these myocytes.

RESEARCH DESIGN AND METHODS

Muscle precursor cells were isolated from four age-matched subject groups: 1) nonobese, normal glucose tolerant; 2) obese, normal glucose tolerant; 3) obese, impaired glucose tolerant; and 4) obese, type 2 diabetes (T2D). The level of inflammation (nuclear factor-κB [NF-κB] signaling) and effect of pharmacological AMPK activation was assessed by Western blots, enzyme-linked immunosorbent assay, and radioactive assays (n = 5 for each subject group).

RESULTS

NF-κB-p65 DNA binding activity was significantly elevated in myocytes from obese T2D patients compared with nonobese control subjects. This correlated to a significant increase in tumor necrosis factor-α concentration in cell culture media. In addition, insulin-stimulated glucose uptake was completely suppressed in myocytes from obese impaired glucose tolerant and T2D subjects. It is interesting that activation of AMPK by A769662 attenuated NF-κB-p65 DNA binding activity in obese T2D cells to levels measured in nonobese myocytes; however, this had no effect on insulin sensitivity of the cells.

CONCLUSIONS

This work provides solid evidence that differentiated human muscle precursor cells maintain in vivo phenotypes of inflammation and insulin resistance and that obesity alone may not be sufficient to establish inflammation in these cells. It is important that we demonstrate an anti-inflammatory role for AMPK in these human cells. Despite attenuation of NF-κB activity by AMPK, insulin resistance in obese T2D cells remained, suggesting factors in addition to inflammation may contribute to the insulin resistance phenotype in muscle cells.

Exercise-induced myokines and their role in chronic diseases

Physical inactivity has recently been identified as a major and independent risk factor for the development of dementia and cognitive decline. In addition to the effect of exercise with regard to protection against neurodegenerative diseases, it is well-established that physical inactivity increases the risk of type 2 diabetes, cardiovascular diseases (CVD), colon cancer and postmenopausal breast cancer. These diseases constitute a network of related diseases, also called "the diseasome of physical inactivity". In this review, physical inactivity is given the central role as an independent and strong risk factor for accumulation of visceral fat and consequently the activation of a network of systemic inflammatory pathways, which promote development of neurodegeneration as well as insulin resistance, atherosclerosis, and tumour growth. The recent finding that muscles produce and release myokines provides a conceptual basis for understanding some of the molecular mechanisms underlying organ cross talk, including muscle-fat cross talk. Accumulating data suggest that contracting skeletal muscles release myokines, which may work in a hormone-like fashion, exerting specific endocrine effects on visceral fat or mediating direct anti-inflammatory effects. Other myokines work locally within the muscle via paracrine mechanisms, exerting their effects on signalling pathways involved in fat oxidation.

Effect of antioxidant supplementation on insulin sensitivity in response to endurance exercise training

While production of reactive oxygen and nitrogen species (RONS) is associated with some of the beneficial adaptations to regular physical exercise, it is not established whether RONS play a role in the improved insulin-stimulated glucose uptake in skeletal muscle obtained by endurance training. To assess the effect of antioxidant supplementation during endurance training on insulin-stimulated glucose uptake, 21 young healthy (age 29 ± 1 y, BMI 25 ± 3 kg/m(2)) men were randomly assigned to either an antioxidant [AO; 500 mg vitamin C and 400 IU vitamin E (α-tocopherol) daily] or a placebo (PL) group that both underwent a supervised intense endurance-training program 5 times/wk for 12 wk. A 3-h euglycemic-hyperinsulinemic clamp, a maximal oxygen consumption (Vo(2max)) and maximal power output (P(max)) test, and body composition measurements (fat mass, fat-free mass) were performed before and after the training. Muscle biopsies were obtained for determination of the concentration and activity of proteins regulating glucose metabolism. Although plasma levels of vitamin C (P < 0.05) and α-tocopherol (P < 0.05) increased markedly in the AO group, insulin-stimulated glucose uptake increased similarly in both the AO (17.2%, P < 0.05) and the PL (18.9%, P < 0.05) group in response to training. Vo(2max) and P(max) also increased similarly in both groups (time effect, P < 0.0001 for both) as well as protein content of GLUT4, hexokinase II, and total Akt (time effect, P ≤ 0.05 for all). Our results indicate that administration of antioxidants during strenuous endurance training has no effect on the training-induced increase in insulin sensitivity in healthy individuals.

IL-6, but not TNF-α, increases plasma YKL-40 in human subjects

Plasma levels of YKL-40 are elevated in patients with systemic infection, inflammatory disorders and cancer. Both monocytes/macrophages, neutrophils, and cancer cells have the capacity to produce YKL-40, but the regulation during the inflammatory response is unknown. To study the possible role of interleukin-6 (IL-6) and tumor necrosis factor (TNF)-α in the regulation of YKL-40 plasma levels, we included healthy men, who received either recombinant human (rh)IL-6 (n=6), rhTNF-α (n=8) or vehicle (n=7) for 3h. The plasma levels of IL-6 and TNF-α reached ∼ 150 and ∼ 18 pg/ml, respectively, during the infusions. Following the IL-6 infusion, the plasma level of YKL-40 increased from ∼ 30 to ∼ 57 ng/ml (p<0.05) at 24h, and returned to normal values after 48 h. The plasma level of YKL-40 did not change during TNF-α infusion or infusion of vehicle. These data demonstrate that IL-6, but not TNF-α, has a key-role in the regulation of plasma YKL-40 levels during inflammation.

Ten questions about systems biology

In this paper we raise 'ten questions' broadly related to 'omics', the term systems biology, and why the new biology has failed to deliver major therapeutic advances for many common diseases, especially diabetes and cardiovascular disease. We argue that a fundamentally narrow and reductionist perspective about the contribution of genes and genetic variants to disease is a key reason 'omics' has failed to deliver the anticipated breakthroughs. We then point out the critical utility of key concepts from physiology like homeostasis, regulated systems and redundancy as major intellectual tools to understand how whole animals adapt to the real world. We argue that a lack of fluency in these concepts is a major stumbling block for what has been narrowly defined as 'systems biology' by some of its leading advocates. We also point out that it is a failure of regulation at multiple levels that causes many common diseases. Finally, we attempt to integrate our critique of reductionism into a broader social framework about so-called translational research in specific and the root causes of common diseases in general. Throughout we offer ideas and suggestions that might be incorporated into the current biomedical environment to advance the understanding of disease through the perspective of physiology in conjunction with epidemiology as opposed to bottom-up reductionism alone.

Muscle specific microRNAs are regulated by endurance exercise in human skeletal muscle

Muscle specific miRNAs, myomiRs, have been shown to control muscle development in vitro and are differentially expressed at rest in diabetic skeletal muscle. Therefore, we investigated the expression of these myomiRs, including miR-1, miR-133a, miR-133b and miR-206 in muscle biopsies from vastus lateralis of healthy young males (n = 10) in relation to a hyperinsulinaemic–euglycaemic clamp as well as acute endurance exercise before and after 12 weeks of endurance training. The subjects increased their endurance capacity, VO2max (l min−1) by 17.4% (P < 0.001), and improved insulin sensitivity by 19% (P < 0.01). While myomiR expression remained stable during a hyperinsulinaemic–euglycaemic clamp, an acute bout of exercise increased mir-1 (P < 0.05) and mir-133a (P < 0.05) expression before, but not after, training. In resting biopsies, endurance training for 12 weeks decreased basal expression of all four myomiRs (P < 0.05). Interestingly, all myomiRs reverted to their pre-training expression levels 14 days after ceasing the training programme. Components of major pathways involved in endurance adaptation such as MAPK and TGF-β were predicted to be targeted by the myomiRs examined. Tested predicted target proteins included Cdc42 and ERK 1/2. Although these proteins were downregulated between post-training period and 2 weeks of cessation, an inverse correlation between myomiR and target proteins was not found. In conclusion, our data suggest myomiRs respond to physiological stimuli, but their role in regulating human skeletal muscle adaptation remains unknown.

Position statement. Part one: Immune function and exercise

An ever-growing volume of peer-reviewed publications speaks to the recent and rapid growth in both scope and understanding of exercise immunology. Indeed, more than 95% of all peer-reviewed publications in exercise immunology (currently >2, 200 publications using search terms "exercise" and "immune") have been published since the formation of the International Society of Exercise and Immunology (ISEI) in 1989 (ISI Web of Knowledge). We recognise the epidemiological distinction between the generic term "physical activity" and the specific category of "exercise", which implies activity for a specific purpose such as improvement of physical condition or competition. Extreme physical activity of any type may have implications for the immune system. However, because of its emotive component, exercise is likely to have a larger effect, and to date the great majority of our knowledge on this subject comes from exercise studies.

Exercise induces a marked increase in plasma follistatin: evidence that follistatin is a contraction-induced hepatokine

Follistatin is a member of the TGF-β super family and inhibits the action of myostatin to regulate skeletal muscle growth. The regulation of follistatin during physical exercise is unclear but may be important because physical activity is a major intervention to prevent age-related sarcopenia. First, healthy subjects performed either bicycle or one-legged knee extensor exercise. Arterial-venous differences were assessed during the one-legged knee extensor experiment. Next, mice performed 1 h of swimming, and the expression of follistatin was examined in various tissues using quantitative PCR. Western blotting assessed follistatin protein content in the liver. IL-6 and epinephrine were investigated as drivers of follistatin secretion. After 3 h of bicycle exercise, plasma follistatin increased 3 h into recovery with a peak of 7-fold. No net release of follistatin could be detected from the exercising limb. In mice performing a bout of swimming exercise, increases in plasma follistatin as well as follistatin mRNA and protein expression in the liver were observed. IL-6 infusion to healthy young men did not affect the follistatin concentration in the circulation. When mice were stimulated with epinephrine, no increase in the hepatic mRNA of follistatin was observed. This is the first study to demonstrate that plasma follistatin is increased during exercise and most likely originates from the liver. These data introduce new perspectives regarding muscle-liver cross talk during exercise and during recovery from exercise.

IL-6 selectively stimulates fat metabolism in human skeletal muscle

Interleukin (IL)-6 is chronically elevated in type 2 diabetes but also during exercise. However, the exact metabolic role, and hence the physiological significance, has not been elucidated. The objective of this study was to investigate the in vivo effect of recombinant human (rh) IL-6 on human fat and glucose metabolism and signaling of both adipose tissue and skeletal muscle. Eight healthy postabsorptive males were infused with either rhIL-6 or saline for 4 h, eliciting IL-6 levels of ∼40 and ∼1 pg/ml, respectively. Systemic, skeletal muscle, and adipose tissue fat and glucose metabolism was assessed before, during, and 2 h after cessation of the infusion. Glucose metabolism was unaffected by rhIL-6. In contrast, rhIL-6 increased systemic fatty acid oxidation approximately twofold after 60 min, and it remained elevated even 2 h after the infusion. The increase in oxidation was followed by an increase in systemic lipolysis. Adipose tissue lipolysis and fatty acid kinetics were unchanged with rhIL-6 compared with saline infusion. Conversely, rhIL-6 infusion caused an increase in skeletal muscle unidirectional fatty acid and glycerol release, indicative of an increase in lipolysis. The increased lipolysis in muscle could account for the systemic changes. Skeletal muscle signaling increased after 1 h of rhIL-6 infusion, indicated by a fourfold increase in the phosphorylated signal transducer and activator of transcription (STAT) 3-to-STAT3 ratio, whereas no changes in phosphorylated AMP-activated protein kinase or acetyl-CoA carboxylase levels could be observed. Our findings suggest that an acute increase in IL-6 at a normophysiological level selectively stimulates lipolysis in skeletal muscle, whereas adipose tissue is unaffected.

Antioxidant supplementation does not alter endurance training adaptation

BACKGROUND

There is a considerable commercial market, especially within the sports community, claiming the need for antioxidant supplementation. One argument for antioxidant supplementation in sports is that physical exercise is associated with increased reactive oxygen and nitrogen species (RONS) production, which may cause cell damage. However, RONS production may also activate redox-sensitive signaling pathways and transcription factors, which subsequently, may promote training adaptation.

PURPOSE

Our aim was to investigate the effects of combined vitamin C and E supplementation to healthy individuals on different measures of exercise performance after endurance training.

METHODS

Using a double-blinded placebo-controlled design, moderately trained young men received either oral supplementation with vitamins C and E (n = 11) or placebo (n = 10) before and during 12 wk of supervised, strenuous bicycle exercise training of a frequency of 5 d x wk(-1). Muscle biopsies were obtained before and after training.

RESULTS

After the training period, maximal oxygen consumption, maximal power output, and workload at lactate threshold increased markedly (P < 0.01) in both groups. Also, glycogen concentration, citrate synthase, and beta-hydroxyacyl-CoA dehydrogenase activity in the muscle were significantly higher in response to training (P < 0.01) in both groups. However, there were no differences between the two groups concerning any of the physiological and metabolic variables measured.

CONCLUSIONS

Our results suggest that administration of vitamins C and E to individuals with no previous vitamin deficiencies has no effect on physical adaptations to strenuous endurance training.

Type 2 diabetes mellitus is associated with impaired cytokine response and adhesion molecule expression in human endotoxemia

PURPOSE

Type 2 diabetes is associated with an increased risk of acquiring infectious diseases and developing sepsis. This may partly be due to immune dysfunction. We investigated the in vivo innate immune response of type 2 diabetic persons to an intravenous injection of E. coli lipopolysaccharide (LPS).

METHODS

After ethics approval, informed consent and a thorough physical examination, 19 type 2 diabetic patients and 23 healthy controls were included. LPS was given as an intravenous bolus injection of 0.3 ng/kg. Physiological variables, white blood cell count, and plasma concentrations of tumour necrosis factor (TNF), interleukin-6 (IL-6), interleukin-1 receptor antagonist (IL-1ra), and the adhesion molecules E-selectin, vascular adhesion molecule (VCAM)-1, and intracellular adhesion molecule (ICAM)-1 were measured hourly for 8 h.

RESULTS

LPS injection induced a systemic inflammatory response with increases in neutrophils, temperature, heart rate and plasma concentrations of cytokines and adhesion molecules in healthy and type 2 diabetic volunteers. Type 2 diabetes was associated with less pronounced LPS-induced increases in TNF, IL-1ra, VCAM-1 and ICAM-1. There was a trend towards an attenuated upregulation of E-selectin in diabetics, even though the plasma concentration tended to be generally higher compared to healthy controls.

CONCLUSIONS

Patients with type 2 diabetes exhibit an attenuated increase in plasma levels of TNF and IL-1ra, as well as an attenuated upregulation of VCAM-1 and ICAM-1 to LPS in vivo. This finding may provide a mechanistic explanation for the adverse outcome seen during infectious diseases in diabetic patients.

Gut microbiota in human adults with type 2 diabetes differs from non-diabetic adults

BACKGROUND

Recent evidence suggests that there is a link between metabolic diseases and bacterial populations in the gut. The aim of this study was to assess the differences between the composition of the intestinal microbiota in humans with type 2 diabetes and non-diabetic persons as control.

METHODS AND FINDINGS

The study included 36 male adults with a broad range of age and body-mass indices (BMIs), among which 18 subjects were diagnosed with diabetes type 2. The fecal bacterial composition was investigated by real-time quantitative PCR (qPCR) and in a subgroup of subjects (N = 20) by tag-encoded amplicon pyrosequencing of the V4 region of the 16S rRNA gene. The proportions of phylum Firmicutes and class Clostridia were significantly reduced in the diabetic group compared to the control group (P = 0.03). Furthermore, the ratios of Bacteroidetes to Firmicutes as well as the ratios of Bacteroides-Prevotella group to C. coccoides-E. rectale group correlated positively and significantly with plasma glucose concentration (P = 0.04) but not with BMIs. Similarly, class Betaproteobacteria was highly enriched in diabetic compared to non-diabetic persons (P = 0.02) and positively correlated with plasma glucose (P = 0.04).

CONCLUSIONS

The results of this study indicate that type 2 diabetes in humans is associated with compositional changes in intestinal microbiota. The level of glucose tolerance should be considered when linking microbiota with metabolic diseases such as obesity and developing strategies to control metabolic diseases by modifying the gut microbiota.

Using molecular classification to predict gains in maximal aerobic capacity following endurance exercise training in humans

A low maximal oxygen consumption (VO2max) is a strong risk factor for premature mortality. Supervised endurance exercise training increases VO2max with a very wide range of effectiveness in humans. Discovering the DNA variants that contribute to this heterogeneity typically requires substantial sample sizes. In the present study, we first use RNA expression profiling to produce a molecular classifier that predicts VO2max training response. We then hypothesized that the classifier genes would harbor DNA variants that contributed to the heterogeneous VO2max response. Two independent preintervention RNA expression data sets were generated (n=41 gene chips) from subjects that underwent supervised endurance training: one identified and the second blindly validated an RNA expression signature that predicted change in VO2max ("predictor" genes). The HERITAGE Family Study (n=473) was used for genotyping. We discovered a 29-RNA signature that predicted VO2max training response on a continuous scale; these genes contained approximately 6 new single-nucleotide polymorphisms associated with gains in VO2max in the HERITAGE Family Study. Three of four novel candidate genes from the HERITAGE Family Study were confirmed as RNA predictor genes (i.e., "reciprocal" RNA validation of a quantitative trait locus genotype), enhancing the performance of the 29-RNA-based predictor. Notably, RNA abundance for the predictor genes was unchanged by exercise training, supporting the idea that expression was preset by genetic variation. Regression analysis yielded a model where 11 single-nucleotide polymorphisms explained 23% of the variance in gains in VO2max, corresponding to approximately 50% of the estimated genetic variance for VO2max. In conclusion, combining RNA profiling with single-gene DNA marker association analysis yields a strongly validated molecular predictor with meaningful explanatory power. VO2max responses to endurance training can be predicted by measuring a approximately 30-gene RNA expression signature in muscle prior to training. The general approach taken could accelerate the discovery of genetic biomarkers, sufficiently discrete for diagnostic purposes, for a range of physiological and pharmacological phenotypes in humans.

Commonly studied polymorphisms in inflammatory cytokine genes show only minor effects on mortality and related risk factors in nonagenarians

Systemic low-grade inflammation is consistently associated with functional status, cognitive functioning, multimorbidity, and survival in oldest olds. If inflammation is either a cause or a consequence of age-related pathology, genetic determinants of late-life survival can reside in cytokine genes polymorphisms, regulating inflammatory responses. The aim of this study was to test associations between commonly studied polymorphisms in interleukin (IL)6, IL10, IL15, and IL18, and tumor necrosis factor-alpha genes and late-life survival in a longitudinal cohort of nonagenarians: the Danish 1905 cohort. Additionally, associations were investigated between inflammatory markers and major predictors of mortality as cognitive and functional status. Modest sex-specific associations were found with survival, cognitive functioning, and handgrip strength. Evaluation of combined genotypes indicated that, in nonagenarian men, the balance of pro- and anti-inflammatory activity at IL18 and IL10 loci is protective against cognitive decline. In conclusion, in this large study with virtually complete follow-up, commonly studied polymorphisms in cytokine genes do not have a major impact on late-life survival or associated risk phenotypes.

A 2-wk reduction of ambulatory activity attenuates peripheral insulin sensitivity

US adults take between approximately 2,000 and approximately 12,000 steps per day, a wide range of ambulatory activity that at the low range could increase risk for developing chronic metabolic diseases. Dramatic reductions in physical activity induce insulin resistance; however, it is uncertain if and how low ambulatory activity would influence peripheral insulin sensitivity. We aimed to explore if healthy, nonexercising subjects who went from a normal to a low level of ambulatory activity for 2 wk would display metabolic alterations including reduced peripheral insulin sensitivity. To do this, ten healthy young men decreased their daily activity level from a mean of 10,501+/-808 to 1,344+/-33 steps/day for 2 wk. Hyperinsulinemic-euglycemic clamps with stable isotopes and muscle biopsies, maximal oxygen consumption (VO2 max) tests, and blood samples were performed pre- and postintervention. A reduced number of daily steps induced a significant reduction of 17% in the glucose infusion rate (GIR) during the clamp. This reduction was due to a decline in peripheral insulin sensitivity with no effect on hepatic endogenous glucose production. The insulin-stimulated ratio of pAktthr308/total Akt decreased after step reduction, with a post hoc analysis revealing the most pronounced effect after 4 h of insulin infusion. In addition, the 2-wk period induced a 7% decline in VO2 max (ml/min; cardiovascular fitness). Lean mass of legs, but not arms and trunk, decreased concurrently. Taken together, one possible biological cause for the public health problem of Type 2 diabetes has been identified. Reduced ambulatory activity for 2 wk in healthy, nonexercising young men significantly reduced peripheral insulin sensitivity, cardiovascular fitness, and lean leg mass.

Edward F. Adolph Distinguished Lecture: Muscle as an endocrine organ: IL-6 and other myokines

Skeletal muscle is an endocrine organ that produces and releases myokines in response to contraction. Some myokines are likely to work in a hormone-like fashion, exerting specific endocrine effects on other organs such as the liver, the brain, and the fat. Other myokines will work locally via paracrine mechanisms, exerting, e.g., angiogenetic effects, whereas yet other myokines work via autocrine mechanisms and influence signaling pathways involved in fat oxidation and glucose uptake. The finding that muscles produce and release myokines creates a paradigm shift and opens new scientific, technological, and scholarly horizons. This finding represents a breakthrough within integrative physiology and contributes to our understanding of why regular exercise protects against a wide range of chronic diseases. Thus the myokine field provides a conceptual basis for the molecular mechanisms underlying, e.g., muscle-fat, muscle-liver, muscle-pancreas, and muscle-brain cross talk.

The diseasome of physical inactivity--and the role of myokines in muscle--fat cross talk

Type 2 diabetes, cardiovascular diseases, colon cancer, breast cancer, dementia and depression constitute a cluster of diseases, which defines 'a diseasome of physical inactivity'. Both physical inactivity and abdominal adiposity, reflecting accumulation of visceral fat mass, are associated with the occurrence of the diseases within the diseasome. Physical inactivity appears to be an independent and strong risk factor for accumulation of visceral fat, which again is a source of systemic inflammation. Chronic inflammation is involved in the pathogenesis of insulin resistance, atherosclerosis, neurodegeneration and tumour growth. Evidence suggests that the protective effect of exercise may to some extent be ascribed to the anti-inflammatory effect of regular exercise, which can be mediated via a reduction in visceral fat mass and/or by induction of an anti-inflammatory environment with each bout of exercise. The finding that muscles produce and release myokines provides a conceptual basis to understand the mechanisms whereby exercise influences metabolism and exerts anti-inflammatory effects. According to our theory, contracting skeletal muscles release myokines, which work in a hormone-like fashion, exerting specific endocrine effects on visceral fat. Other myokines work locally within the muscle via paracrine mechanisms, exerting their effects on signalling pathways involved in fat oxidation.

Role of exercise-induced brain-derived neurotrophic factor production in the regulation of energy homeostasis in mammals

Brain-derived neurotrophic factor (BDNF) has been shown to regulate neuronal development and plasticity and plays a role in learning and memory. Moreover, it is well established that BDNF plays a role in the hypothalamic pathway that controls body weight and energy homeostasis. Recent evidence identifies BDNF as a player not only in central metabolism, but also in regulating energy metabolism in peripheral organs. Low levels of BDNF are found in patients with neurodegenerative diseases, including Alzheimer's disease and major depression. In addition, BDNF levels are low in obesity and independently so in patients with type 2 diabetes. Brain-derived neurotrophic factor is expressed in non-neurogenic tissues, including skeletal muscle, and exercise increases BDNF levels not only in the brain and in plasma, but in skeletal muscle as well. Brain-derived neurotrophic factor mRNA and protein expression was increased in muscle cells that were electrically stimulated, and BDNF increased phosphorylation of AMP-activated protein kinase (AMPK) and acetyl coenzyme A carboxylase-beta (ACCbeta) and enhanced fatty oxidation both in vitro and ex vivo. These data identify BDNF as a contraction-inducible protein in skeletal muscle that is capable of enhancing lipid oxidation in skeletal muscle via activation of AMPK. Thus, BDNF appears to play a role both in neurobiology and in central as well as peripheral metabolism. The finding of low BDNF levels both in neurodegenerative diseases and in type 2 diabetes may explain the clustering of these diseases. Brain-derived neurotrophic factor is likely to mediate some of the beneficial effects of exercise with regard to protection against dementia and type 2 diabetes.

Increased cerebral output of free radicals during hypoxia: implications for acute mountain sickness?

This study examined whether hypoxia causes free radical-mediated disruption of the blood-brain barrier (BBB) and impaired cerebral oxidative metabolism and whether this has any bearing on neurological symptoms ascribed to acute mountain sickness (AMS). Ten men provided internal jugular vein and radial artery blood samples during normoxia and 9-h passive exposure to hypoxia (12.9% O(2)). Cerebral blood flow was determined by the Kety-Schmidt technique with net exchange calculated by the Fick principle. AMS and headache were determined with clinically validated questionnaires. Electron paramagnetic resonance spectroscopy and ozone-based chemiluminescence were employed for direct detection of spin-trapped free radicals and nitric oxide metabolites. Neuron-specific enolase (NSE), S100beta, and 3-nitrotyrosine (3-NT) were determined by ELISA. Hypoxia increased the arterio-jugular venous concentration difference (a-v(D)) and net cerebral output of lipid-derived alkoxyl-alkyl free radicals and lipid hydroperoxides (P < 0.05 vs. normoxia) that correlated with the increase in AMS/headache scores (r = -0.50 to -0.90, P < 0.05). This was associated with a reduction in a-v(D) and hence net cerebral uptake of plasma nitrite and increased cerebral output of 3-NT (P < 0.05 vs. normoxia) that also correlated against AMS/headache scores (r = 0.74-0.87, P < 0.05). In contrast, hypoxia did not alter the cerebral exchange of S100beta and both global cerebral oxidative metabolism (cerebral metabolic rate of oxygen) and neuronal integrity (NSE) were preserved (P > 0.05 vs. normoxia). These findings indicate that hypoxia stimulates cerebral oxidative-nitrative stress, which has broader implications for other clinical models of human disease characterized by hypoxemia. This may prove a risk factor for AMS by a mechanism that appears independent of impaired BBB function and cerebral oxidative metabolism.

Evidence for a release of brain-derived neurotrophic factor from the brain during exercise

Brain-derived neurotrophic factor (BDNF) has an important role in regulating maintenance, growth and survival of neurons. However, the main source of circulating BDNF in response to exercise is unknown. To identify whether the brain is a source of BDNF during exercise, eight volunteers rowed for 4 h while simultaneous blood samples were obtained from the radial artery and the internal jugular vein. To further identify putative cerebral region(s) responsible for BDNF release, mouse brains were dissected and analysed for BDNF mRNA expression following treadmill exercise. In humans, a BDNF release from the brain was observed at rest (P < 0.05), and increased two- to threefold during exercise (P < 0.05). Both at rest and during exercise, the brain contributed 70-80% of circulating BDNF, while that contribution decreased following 1 h of recovery. In mice, exercise induced a three- to fivefold increase in BDNF mRNA expression in the hippocampus and cortex, peaking 2 h after the termination of exercise. These results suggest that the brain is a major but not the sole contributor to circulating BDNF. Moreover, the importance of the cortex and hippocampus as a source for plasma BDNF becomes even more prominent in response to exercise.

Brain-derived neurotrophic factor is produced by skeletal muscle cells in response to contraction and enhances fat oxidation via activation of AMP-activated protein kinase

AIMS/HYPOTHESIS

Brain-derived neurotrophic factor (BDNF) is produced in skeletal muscle, but its functional significance is unknown. We aimed to determine the signalling processes and metabolic actions of BDNF.

METHODS

We first examined whether exercise induced BDNF expression in humans. Next, C2C12 skeletal muscle cells were electrically stimulated to mimic contraction. L6 myotubes and isolated rat extensor digitorum longus muscles were treated with BDNF and phosphorylation of the proteins AMP-activated protein kinase (AMPK) (Thr(172)) and acetyl coenzyme A carboxylase beta (ACCbeta) (Ser(79)) were analysed, as was fatty acid oxidation (FAO). Finally, we electroporated a Bdnf vector into the tibialis cranialis muscle of mice.

RESULTS

BDNF mRNA and protein expression were increased in human skeletal muscle after exercise, but muscle-derived BDNF appeared not to be released into the circulation. Bdnf mRNA and protein expression was increased in muscle cells that were electrically stimulated. BDNF increased phosphorylation of AMPK and ACCbeta and enhanced FAO both in vitro and ex vivo. The effect of BDNF on FAO was AMPK-dependent, since the increase in FAO was abrogated in cells infected with an AMPK dominant negative adenovirus or treated with Compound C, an inhibitor of AMPK. Electroporation of a Bdnf expression vector into the tibialis cranialis muscle resulted in increased BDNF protein production and tropomyosin-related kinase B (TrkB(Tyr706/707)) and extracellular signal-regulated protein kinase (p44/42 Thr(202)/Tyr(204)) phosphorylation in these muscles. In addition, phosphorylation of ACCbeta was markedly elevated in the Bdnf electroporated muscles.

CONCLUSIONS/INTERPRETATION

These data identify BDNF as a contraction-inducible protein in skeletal muscle that is capable of enhancing lipid oxidation in skeletal muscle via activation of AMPK.

Increased urinary orosomucoid excretion: a proposed marker for inflammation and endothelial dysfunction in patients with type 2 diabetes

OBJECTIVE

In a previous study, urinary orosomucoid excretion rate (UOER) independently predicted cardiovascular mortality in patients with type 2 diabetes. The aim of the present study was to determine whether increased UOER is associated with cardiovascular risk factors such as inflammation, impaired left ventricular function and endothelial dysfunction in patients with type 2 diabetes.

MATERIAL AND METHODS

We performed a cross-sectional study of 41 patients with type 2 diabetes (17 patients with normal UOER and 24 with increased UOER) with no history of cardiovascular disease and 21 healthy controls. Urinary orosomucoid was measured using a particle-enhanced immunoturbidimetric assay. Plasma interleukin-6 (IL-6), tissue plasminogen activator (tPA) and soluble intercellular adhesion molecule-1 (sICAM) were measured using ELISA. Endothelial function measured as vasodilatory capacity of the brachial artery and echocardiography were done in all participants.

RESULTS

Patients with diabetes and increased UOER had subclinically increased serum orosomucoid (p<0.001), C-reactive protein (CRP) (p<0.001), IL-6 (p<0.001), tPA (p<0.003) and sICAM (p<0.003) compared with healthy controls. In patients with type 2 diabetes, UOER was independently associated with increasing values of IL-6 (1.43 (1.06-1.93)) and tPA (1.82 (1.20-2.77)). Measurements by echocardiography showed no signs of cardiac dysfunction.

CONCLUSIONS

Asymptomatic patients with type 2 diabetes and increased UOER displayed signs of chronic low-grade inflammation and endothelial dysfunction. UOER was independently related to markers of proinflammation and endothelial dysfunction in patients with type 2 diabetes. The previously shown relation between increased UOER and cardiovascular mortality is proposed to be caused by chronic low-grade inflammation and early endothelial dysfunction.

ROS and myokines promote muscle adaptation to exercise

Physical exercise induces a network of alterations in the transcriptome and proteome of the skeletal muscle, resulting in modifications of the muscle physiology. Intriguingly, exercise also transiently induces the production of both reactive oxygen species (ROS) and some inflammatory cytokines in skeletal muscle. In fact, it seems that exercise-induced ROS are able to stimulate cytokine production from skeletal muscle. Despite the initial view that ROS were potentially cell damaging, it now seems possible that these substances have important roles in the regulation of cell signaling. Muscle-derived cytokines, so-called 'myokines', are distinguished from inflammation and instead possess important anti-inflammatory and metabolic properties. In this opinion piece, we suggest that both ROS and myokines are important players in muscle adaptation to exercise.

RBP-to-retinol ratio, but not total RBP, is elevated in patients with type 2 diabetes

AIM

It was recently reported that serum retinol-binding protein (RBP), also known as retinol-binding protein 4 (RBP4), was positively associated with systemic insulin resistance. We hypothesized that an imbalance between RBP and retinol might be the underlying cause for this association.

METHODS

We studied the ratio between RBP and retinol in 233 humans divided into groups depending on normal glucose tolerance (NGT), impaired glucose tolerance (IGT), type 2 diabetes (T2DM) and presence or absence of obesity.

RESULTS

Plasma RBP and retinol levels were lower in patients with T2DM than in individuals with NGT (p < 0.05 and p < 0.0001 respectively). In contrast, RBP-to-retinol ratio was higher in individuals with T2DM (p < 0.0001) and IGT (p < 0.05). Following multivariate adjustment, RBP and retinol correlated positively with low-density lipoprotein (LDL) and triglycerides (p < 0.0001, except retinol and LDL: p < 0.001). RBP-to-retinol ratio correlated positively with glucose 2 h after an oral glucose tolerance test (p < 0.0001) and with C-reactive protein (p < 0.001). Retinol, RBP and adipose tissue RBP messenger RNA (mRNA) levels shared an inverse relationship with plasma interleukin-6, and adipose tissue RBP mRNA levels correlated positively with plasma tumour necrosis factor-alpha (TNF-alpha) and skeletal muscle TNF-alpha mRNA levels.

CONCLUSIONS

Our results suggest that the excess of RBP relative to retinol, assessed as the RBP-to-retinol ratio, is more indicative of T2DM than RBP itself. Hence, the previously reported insulin resistance in mice induced by overexpression or injection of RBP could be because of higher levels of RBP relative to retinol rather than higher total levels of RBP. Moreover, TNF-alpha may have a role in RBP-mediated adipose to muscle crosstalk.

Residual viraemia in HIV-1-infected patients with plasma viral load <or=20 copies/ml is associated with increased blood levels of soluble immune activation markers

Despite undetectable viral load in conventional assays, probably all human immunodeficiency virus (HIV)-1 infected patients have residual viraemia (RV) detectable by ultra-sensitive assays. To study this issue, this study investigated virologic and immunologic consequences of RV in highly active antiretroviral therapy (HAART)-treated HIV-1-infected patients with plasma HIV-1 RNA <or=20 copies/ml. The study included 32 HAART-treated HIV-1-infected patients with HIV-1 RNA <or=20 copies/ml followed prospectively 6-monthly for 24 months. RV was detected by transcription-mediated amplification (TMA-RV) technique (Procleix HIV-1 Discriminatory Assay; Chiron) and by PCR (PCR-RV, Amplicor HIV-1 Monitor Assay; Roche Diagnostics). The association between RV and proviral-HIV-1-DNA, CD4-count, CD8-count, soluble [soluble tumour necrosis factor receptor (TNFr)-II, beta(2)-microglobulin, immunoglobulins] and cellular (HLA-DR, CD38, CD45RO, CD45RA, CD62L) T-cell markers of immune activation was investigated. In the 24-months study-period, 23 patients had >or=1 episode with TMA-RV whereas 9 patients had undetectable TMA-RV throughout the study-period. Time-points with TMA-RV and PCR-RV were associated with higher circulating sTNFrII (+0.234 ng/ml, P = 0.030) and beta(2)-microglobulin (+22 nmol/l, P = 0.016) and time-points with PCR-RV were also associated with higher IgA (+0.82 micromol/l, P = 0.035) and CD8-count (+1.18-fold, P = 0.001). Patients with TMA-RV in the study-period had higher HIV-1 RNA pre-HAART (P = 0.032). RV was not associated with proviral-HIV-1-DNA, CD4-count, CD4+HLA-DR+, CD8+HLA-DR+CD38+, CD4+CD45RA-CD45RO+, CD8+CD45RA-CD45RO+, CD4+CD45RA+CD62L+, CD8+CD45RA+CD62L+ T cells, IgG or IgM. In conclusion, RV was associated with increased blood levels of soluble immune activation markers in HAART-treated HIV-1-infected patients. The finding that RV was associated with higher pre-HAART plasma viral load suggests that RV is linked to pre-HAART disease progression.