A Web-Based Mobile App (INTERACCT App) for Adolescents Undergoing Cancer and Hematopoietic Stem Cell Transplantation Aftercare to Improve the Quality of Medical Information for Clinicians: Observational Study

Background

A growing number of cancer and hematopoietic stem cell transplant (HSCT) survivors require long-term follow-up with optimal communication schemes, and patients' compliance is crucial. Adolescents have various unmet needs. Regarding self-report of symptoms and health status, users of mobile apps showed enhanced compliance. Currently, HSCT aftercare at the HSCT outpatient clinic of the St. Anna Children’s Hospital in Vienna, Austria, is based on handwritten diaries, carrying various disadvantages. Recently, we developed the prototype of a web-based, self-monitoring gamified mobile app tailored for adolescents: the INTERACCT (Integrating Entertainment and Reaction Assessment into Child Cancer Therapy) app.

Objective

This observational, prospective study evaluated the usability of the INTERACCT app for tracking real-time self-reported symptoms and health status data in adolescent HSCT patients and a healthy matched control group. The primary outcome of the study was the quality of the self-reported medical information. We hypothesized that the mobile app would provide superior medical information for the clinicians than would the handwritten diaries.

Methods

Health data were reported via paper diary and mobile app for 5 consecutive days each. The quality of medical information was rated on a 5-point scale independently and blinded by two HSCT clinicians, and the duration of use was evaluated. A total of 52 participant questionnaires were assessed for gaming patterns and device preferences, self-efficacy, users’ satisfaction, acceptability, and suggestions for improvement of the mobile app. Interrater reliability was calculated with the intraclass correlation coefficient, based on a two-way mixed model; one-way repeated-measures analysis of variance and t tests were conducted post hoc. Descriptive methods were used for correlation with participants’ demographics. For users’ satisfaction and acceptability of the mobile app, the median and the IQR were calculated.

Results

Data from 42 participants—15 patients and 27 healthy students—with comparable demographics were evaluated. The results of our study indicated a superiority of the quality of self-reported medical data in the INTERACCT app over traditional paper-and-pencil assessment (mobile app: 4.14 points, vs paper-based diary: 3.77 points, P=.02). The mobile app outperformed paper-and-pencil assessments mainly among the patients, in particular among patients with treatment-associated complications (mobile app: 4.43 points, vs paper-based diary: 3.73 points, P=.01). The mobile app was used significantly longer by adolescents (≥14 years: 4.57 days, vs ≤13 years: 3.14 days, P=.03) and females (4.76 days for females vs 2.95 days for males, P=.004). This corresponds with a longer duration of use among impaired patients with comorbidities. User satisfaction and acceptability ratings for the mobile app were high across all groups, but adherence to entering a large amount of data decreased over time. Based on our results, we developed a case vignette of the target group.

Conclusions

Our study was the first to show that the quality of patient-reported medical information submitted via the INTERACCT app embedded in a serious game is superior to that submitted via a handwritten diary. In light of these results, a refinement of the mobile app supported by a machine learning approach is planned within an international research project.

Evidence that the multiflorine-derived substituted quinazolidine 55P0251 augments insulin secretion and lowers blood glucose via antagonism at α2 -adrenoceptors in mice

AIMS

To investigate the mechanism of action of 55P0251, a novel multiflorine-derived substituted quinazolidine that augments insulin release and lowers blood glucose in rodents, but does not act via mechanisms addressed by any antidiabetic agent in clinical use.

MATERIALS AND METHODS

Using male mice, we determined the effects of 55P0251 on glucose tolerance, insulin secretion from isolated islets and blood oxygen saturation, including head-to-head comparison of 55P0251 to its inverted enantiomer 55P0250, as well as to other anti-hyperglycaemic multiflorine derivatives discovered in our programme.

RESULTS

55P0251 was clearly superior to its inverted enantiomer in the glucose tolerance test (area under the curve: 11.3 mg/kg 55P0251, 1.19 ± 0.04 min*mol/L vs 55P0250, 1.80 ± 0.04 min*mol/L; P < .0001). For insulin release in vitro, this superiority became visible only under concomitant adrenergic background stimulation (glucose-stimulated insulin release, fmol*islet^-1 *30 min^-1 : without α₂ -adrenoceptor agonist: 500 μmol/L 55P0251, 390 ± 34, vs 55P0250, 459 ± 40, nonsignificant; with α₂ -adrenoceptor agonist: 250 μmol/L 55P0251, 138 ± 9, vs 55P0250, 21 ± 6; P < .0001). Since receptor binding assays suggested antagonism at α_2A -adrenoceptors as a potential mechanism of action, we measured oxygen saturation in capillary blood from the tail as a surrogate of vasoconstriction, which supported α₂ -antagonistic action in vivo (90 mg/kg 55P0251, 83 ± 3%, vs 55P0250, 57 ± 3%; P < .0001). Lack of association between glucose-lowering activities and α_2A -adrenoceptor binding affinity arising from comparison of multiflorine derivatives was attributed to differences in their pharmacokinetic properties.

CONCLUSIONS

Our findings suggest that 55P0251 and related multiflorine derivatives are to be categorized as α₂ -adrenoceptor antagonists with potential to lower blood glucose by blocking α_2A -adrenoceptors on pancreatic β cells.

Survey on paediatric tumour boards in Europe: current situation and results from the ExPo-r-Net project

BACKGROUND

Under the ExPO-r-NeT project (European Expert Paediatric Oncology Reference Network for Diagnostics and Treatment), we aimed to identify paediatric oncology tumour boards in Europe to investigate the kind of technologies and logistics that are in place in different countries and to explore current differences between regions.

METHODS

A 20-question survey regarding several features of tumor boards was designed. Data collected included infrastructure, organization, and clinical decision-making information from the centres. The survey was distributed to the National Paediatric Haematology and Oncology Societies that forwarded the survey to the sites. For comparative analysis, respondents were grouped into four geographical regions.

RESULTS

The questionnaire was distributed amongst 30 countries. Response was obtained from 23 (77%) that altogether have 212 paediatric oncology treating centres. A total of 121 institutions answered (57%). Ninety-one percent of the centres hold multidisciplinary boards; however, international second consultations are performed in 36% and only 15% participate on virtual tumor boards. Videoconferencing facilities and standard operational procedures (SOPs) are available in 49 and 43% of the centres, respectively. There were statistically significant differences between European regions concerning meeting infrastructure and organization/logistics: specific room, projecting equipment, access to medical records, videoconferencing facilities, and existence of SOPs.

CONCLUSION

Paediatric tumor boards are a common feature in Europe. To reduce inequalities and have equal access to healthcare, a virtual network is needed. Important differences on the functioning and access to technology between regions in Europe have been observed and need to be addressed.

Preclinical characterization of 55P0251, a novel compound that amplifies glucose-stimulated insulin secretion and counteracts hyperglycaemia in rodents

AIMS

55P0251 is a novel compound with blood glucose lowering activity in mice, which has been developed from a molecular backbone structure found in herbal remedies. We here report its basic pharmacological attributes and initial progress in unmasking the mode of action.

MATERIALS AND METHODS

Pharmacokinetic properties of 55P0251 were portrayed in several species. First efforts to elucidate the glucose lowering mechanism in rodents included numerous experimental protocols dealing with glucose tolerance, insulin secretion from isolated pancreatic islets and comparison to established drugs.

RESULTS

A single oral dose of 55P0251 improved glucose tolerance in mice with an ED₅₀ between 1.5 and 2 mg/kg (reductions in areas under the curve, 1 mg/kg, -18%; 5 mg/kg, -30%; 27 mg/kg, -47%). Pharmacokinetic studies revealed attractive attributes, including a plasma half-life of approximately 3 hours and a bioavailability of approximately 58% in rats. 55P0251 amplified glucose stimulated insulin release from isolated mouse islets and improved glucose tolerance via increased insulin secretion in rats (increase in area under the insulin curve, +184%). Unlike sulfonylureas and glinides, 55P0251 hardly stimulated insulin release under basal conditions and did not induce hypoglycaemia in vivo, but it amplified the secretory response to glucose and other insulinotropic stimuli (KCl, glucagon-like peptide-1). Comparison to established anti-diabetic agents and examination of interaction with molecular targets (K_ATP channel, dipeptidyl peptidase-4, glucagon-like peptide-1 receptor) excluded molecular mechanisms addressed by presently marketed drugs.

CONCLUSIONS

55P0251 is a novel compound that potently counteracts hyperglycaemia in rodents via amplification of glucose-stimulated insulin release.

Interoperability Architecture for a Paediatric Oncology European Reference Network

With the Directive 2011/24/EU on patients' rights in cross-border healthcare and the related delegated decisions, the European Commission defined a legal framework on how healthcare shall be organised by European Union (EU) member states (MS) where patients can move beyond the borders of their home country. Among other aspects, Article 12 of the directive is concerned with supporting MS with the development of so called European Reference Networks (ERN), dedicated to the treatment of "patients with a medical condition requiring a particular concentration of expertise in medical domains where expertise is rare". In the "European Expert Paediatric Oncology Reference Network for Diagnostics and Treatment" (ExPO-r-Net) project, the establishment of such an ERN in the domain of Paediatric Oncology is currently piloted. The present paper describes the high level use cases, the main requirements and a corresponding interoperability architecture capable to serve as the necessary IT platform to facilitate cross-border health data exchange.

55P0110, a Novel Synthetic Compound Developed from a Plant Derived Backbone Structure, Shows Promising Anti-Hyperglycaemic Activity in Mice

Starting off with a structure derived from the natural compound multiflorine, a derivatisation program aimed at the discovery and initial characterisation of novel compounds with antidiabetic potential. Design and discovery of the structures was guided by oral bioactivities obtained in oral glucose tolerance tests in mice. 55P0110, one among several new compounds with distinct anti-hyperglycaemic activity, was further examined to characterise its pharmacology and mode of action. Whereas a single oral dose of 55P0110 did not affect basal glycaemia, it markedly improved the glucose tolerance of healthy and diabetic mice (peak blood glucose in glucose tolerance test, mmol/l: healthy mice with 90 mg/kg 55P0110, 17.0 ± 1.2 vs. 10.1 ± 1.1; diabetic mice with 180 mg/kg 55P0110, 23.1 ± 0.9 vs. 11.1 ± 1.4; p<0.001 each). Closer examination argued against retarded glucose resorption from the gut, increased glucose excretion in urine, acute insulin-like or insulin sensitising properties, and direct inhibition of dipeptidyl peptidase-4 as the cause of glucose lowering. Hence, 55P0110 seems to act via a target not exploited by any drug presently approved for the treatment of diabetes mellitus. Whereas the insulinotropic sulfonylurea gliclazide (16 mg/kg) distinctly increased the circulating insulin-per-glucose ratio under basal conditions, 55P0110 (90 mg/kg) lacked such an effect (30 min. after dosing, nmol/mol: vehicle, 2.49 ± 0.27; 55P0110, 2.99 ± 0.35; gliclazide, 8.97 ± 0.49; p<0.001 each vs. gliclazide). Under an exogenous glucose challenge, however, 55P0110 increased this ratio to the same extent as gliclazide (20 min. after glucose feeding: vehicle, 2.53 ± 0.41; 55P0110, 3.80 ± 0.46; gliclazide, 3.99 ± 0.26; p<0.05 each vs. vehicle). By augmenting the glucose stimulated increase in plasma insulin, 55P0110 thus shows distinct anti-hyperglycaemic action in combination with low risk for fasting hypoglycaemia in mice. In summary, we have discovered a novel class of fully synthetic substituted quinazolidines with an attractive pharmacological profile that recommends the structures for further evaluation as candidates for the treatment of diabetes mellitus.

Mechanisms of antihyperglycaemic action of efaroxan in mice: time for reappraisal of α2A-adrenergic antagonism in the treatment of type 2 diabetes?

AIMS/HYPOTHESIS

Inspired by recent speculation about the potential utility of α(2A)-antagonism in the treatment of type 2 diabetes, the study examined the contribution of α(2)-antagonism vs other mechanisms to the antihyperglycaemic activity of the imidazoline (±)-efaroxan.

METHODS

Effects of the racemate and its pure enantiomers on isolated pancreatic islets and beta cells in vitro, as well as on hyperglycaemia in vivo, were investigated in a comparative manner in mice.

RESULTS

In isolated perifused islets, the two enantiomers of efaroxan were equally potent in counteracting inhibition of insulin release by the ATP-dependent K(+) (K(ATP)) channel-opener diazoxide but (+)-efaroxan, the presumptive carrier of α(2)-antagonistic activity, was by far superior in counteracting inhibition of insulin release by the α(2)-agonist UK14,304. In vivo, (+)-efaroxan improved oral glucose tolerance at 100-fold lower doses than (-)-efaroxan and, in parallel with observations made in vitro, was more effective in counteracting UK14,304-induced than diazoxide-induced hyperglycaemia. The antihyperglycaemic activity of much higher doses of (-)-efaroxan was associated with an opposing pattern (i.e. with stronger counteraction of diazoxide-induced than UK14,304-induced hyperglycaemia), which implicates a different mechanism of action.

CONCLUSIONS/INTERPRETATION

The antihyperglycaemic potency of (±)-efaroxan in mice is almost entirely due to α(2)-antagonism, but high doses can also lower blood glucose via another mechanism. Our findings call for reappraisal of the possible clinical utility of α(2A)-antagonistic compounds in recently identified subpopulations of patients in which a congenitally higher level of α(2A)-adrenergic activation contributes to the development and pathophysiology of type 2 diabetes.

Lipophilicity as a determinant of thiazolidinedione action in vitro: findings from BLX-1002, a novel compound without affinity to PPARs

The pharmacology of thiazolidinediones (TZDs) seems to be driven not only by activation of peroxisome proliferator-activated receptor-γ (PPARγ), but also by PPARγ-independent effects on mitochondrial function and cellular fuel handling. This study portrayed such actions of the novel hydrophilic TZD compound BLX-1002 and compared them to those of conventional TZDs. Mitochondrial function and fuel handling were examined in disrupted rat muscle mitochondria, intact rat liver mitochondria, and specimens of rat skeletal muscle. BLX-1002 was superior to most other TZDs as an inhibitor of respiratory complex 1 in disrupted mitochondria, but had less effect than any other TZD on oxygen consumption by intact mitochondria and on fuel metabolism by intact tissue. The latter finding was obviously related to the hydrophilic properties of BLX-1002, because high potentials of individual TZDs to shift muscle fuel metabolism from the aerobic into the anaerobic pathway were associated with high ClogP values indicative of high lipophilicity and low hydrophilicity (e.g., % increase in lactate release induced by 10 μmol/l of respective compound: BLX-1002, ClogP 0.39, +10 ± 8%, not significant; pioglitazone, ClogP 3.53, +68 ± 12%, P < 0.001; troglitazone, ClogP 5.58, +157 ± 14%, P < 0.001). The observed specific properties of BLX-1002 could result from relatively strong direct affinity to an unknown mitochondrial target, but limited access to this target. Results suggest 1) that impairment of mitochondrial function and increased anaerobic fuel metabolism are unlikely to account for PPARγ-independent glucose lowering by BLX-1002, and 2) that higher lipophilicity of an individual TZD is associated with stronger acceleration of anaerobic glycolysis.

The effects of amino acids on glucose metabolism of isolated rat skeletal muscle are independent of insulin and the mTOR/S6K pathway

Two mechanisms have been proposed for the modulation of skeletal muscle glucose metabolism by amino acids. Whereas studies on humans and cultured cells suggested acute insulin desensitization via mammalian target of rapamycin (mTOR) and its downstream target p70 S6 kinase (S6K), investigations using native specimens of rat muscle hinted at impairment of glucose oxidation by competition for mitochondrial oxidation. To better understand these seemingly contradictory findings, we explored the effects of high concentrations of mixed amino acids on fuel metabolism and S6K activity in freshly isolated specimens of rat skeletal muscle. In this setting, increasing concentrations of amino acids dose-dependently reduced the insulin-stimulated rates of CO(2) production from glucose and palmitate (decrease in glucose oxidation induced by addition of 5.5, 11, 22, and 44 mmol/l amino acids:--16 +/- 3, -25 +/- 7, -44 +/- 4, -62 +/- 4%; P < 0.02 each). This effect could not be attributed to insulin desensitization, because it was not accompanied by any reduction of insulin-stimulated glucose transport [+12 +/- 16, +17 +/- 22, +21 +/- 33, +13 +/- 12%; all nonsignificant (NS)] or glycogen synthesis (+1 +/- 6, -5 +/- 6, -9 +/- 8, +6 +/- 5%; all NS) and because it persisted without insulin stimulation. Abrogation of S6K activity by the mTOR blocker rapamycin failed to counteract amino acid-induced inhibition of glucose and palmitate oxidation, which therefore was obviously independent of mTOR/S6K signaling (decrease in glucose oxidation by addition of 44 mmol/l amino acids: without rapamycin, -60 +/- 4%; with rapamycin, -50 +/- 13%; NS). We conclude that amino acids can directly affect muscle glucose metabolism via two mechanisms, mTOR/S6K-mediated insulin desensitization and mitochondrial substrate competition, with the latter predominating in isolated rat muscle.

Age-dependent development of metabolic derangement and effects of intervention with pioglitazone in Zucker diabetic fatty rats

Zucker diabetic fatty (ZDF) rats are a standard animal model for the study of type 2 diabetes and for pharmacological characterization of insulin-sensitizing drugs. To analyze the age-dependent development of their metabolic derangements and the associated changes in their responses to treatment with the insulin sensitizer pioglitazone, groups of 7, 10.5, or 15.5-week-old ZDF rats were treated orally with vehicle or pioglitazone (12 mg/kg/day). Metabolic parameters including circulating concentrations of glucose, insulin, lipids, and adiponectin as well as body weight, tissue glycogen content, and the activity of p70S6 kinase in skeletal muscle were determined. Blood glucose of ZDF rats rose steeply from 5.9 +/- 0.4 to 23.7 +/- 0.5 mM between 7 and 13 weeks of age and then reached a new steady state, which was associated with increased tissue glycogen content (in 15-week-old ZDF rats versus lean littermates: skeletal muscle, 18.0 +/- 0.9 versus 10.5 +/- 1.4 micromol/g; liver, 181 +/- 6 versus 109 +/- 14 micromol/g; both p < 0.001). Early intervention with pioglitazone at 7 weeks of age fully prevented the development of hyperglycemia (blood glucose, 6.4 +/- 0.4 versus 18.7 +/- 1.5 mM after 5.5 weeks of treatment), which was accompanied by a 40% (p = 0.01) reduction of the activity of p70S6 kinase in skeletal muscles. These beneficial effects of pioglitazone were progressively lost, if treatment was initiated at later stages of disease development. Thus, ZDF rats are suitable for preclinical characterization of insulin-sensitizing thiazolidinediones in many aspects, but several important differences versus human type 2 diabetes exist and are to be considered in the use of this animal model.

Progesterone impairs cell respiration and suppresses a compensatory increase in glucose transport in isolated rat skeletal muscle: a non-genomic mechanism contributing to metabolic adaptation to late pregnancy?

AIMS/HYPOTHESIS

The aim of the study was to gain better insight into the mechanisms responsible for impaired glucose metabolism during late pregnancy. We explored the direct effects of progesterone on glucose metabolism of skeletal muscle.

METHODS

Specimens of skeletal muscle from untreated rats were incubated with progesterone and rates of substrate fluxes through the various pathways of glucose metabolism were analysed.

RESULTS

Progesterone dose-dependently reduced the rates of glucose and pyruvate oxidation (insulin-stimulated rates after 5 h of exposure to 1 and 10 mumol/l progesterone: glucose oxidation, -6 +/- 4%, NS, and -39 +/- 4%, p < 0.001; pyruvate oxidation, -28 +/- 2% and -55 +/- 4%, p < 0.001 each) and increased lactate release (+28 +/- 4% and +58 +/- 9%, p < 0.005 each), which indicated inhibition of mitochondrial respiratory function. Impairment of cell respiration, e.g. by the specific inhibitor rotenone, is known to trigger a compensatory increase in glucose transport, but this response was blunted in the case of progesterone (change of glucose transport in response to 10 mumol/l progesterone vs 60 nmol/l rotenone, both causing a reduction in glucose oxidation by -39%: progesterone, +14 +/- 8% vs rotenone, +84 +/- 23%, p < 0.03). Further experiments dealt with the underlying mechanisms and revealed a rapid mode of action (50 mumol/l progesterone, reduction in insulin-stimulated glucose oxidation after 30 min: -29 +/- 7%, p < 0.01) not affected by blockers of gene expression or the nuclear progesterone receptor.

CONCLUSIONS/INTERPRETATION

Progesterone inhibits cell respiration and at the same time suppresses a compensatory increase in glucose transport, causing cellular carbohydrate deficiency in isolated rat skeletal muscle. This effect is mediated by a direct, rapid and non-genomic mechanism and could contribute to pregnancy-associated changes in glucose homeostasis.

Effects of free fatty acids on carbohydrate metabolism and insulin signalling in perfused rat liver

BACKGROUND

Elevated circulating free fatty acids (FFAs) induce insulin resistance and play a crucial role in the development of type 2 diabetes, in which fasting hepatic glucose production (HGP) is increased. However, direct effects of FFAs on fasting HGP are still unclear because indirect endocrine and metabolic effects contribute to FFA action. Thus, we aimed to investigate acute direct effects of specific FFAs on fasting HGP, lactate uptake, and insulin signalling.

MATERIALS AND METHODS

Isolated livers obtained from 20 h fasted rats were perfused with albumin-bound palmitate or oleate (200 micromol L(-1) each) or vehicle (control) for 180 min (n = 5-7/group).

RESULTS

Compared to control, hepatic lactate uptake was increased by palmitate and oleate (~+40%; P < 0.05), while HGP from lactate (~3 mmol L(-1)) and liver glycogen content were similar. Tyrosine phosphorylation (pY) of insulin-receptor-substrate-(IRS)-2 and p70S6-kinase phosphorylation were not affected by FFAs. Palmitate decreased insulin-receptor-beta pY, IRS-1 pY and phosphoinositol-3-kinase expression by 46 +/- 16%, 46 +/- 11% and 20 +/- 9%, respectively (P < 0.03), while oleate reduced Akt phosphorylation by 85 +/- 7% (P < 0.006).

CONCLUSIONS

Isolated liver perfusion with saturated or unsaturated FFAs reduced insulin signalling protein phosphorylation at different sites and increased lactate uptake without affecting HGP or glycogen content. These results suggest that at fasting, both saturated and unsaturated FFAs increase hepatic glucose precursor uptake and may, independently of insulin's presence, accelerate protein dephosphorylation of the insulin signalling cascade at different sites.

Insulin does not regulate glucose transport and metabolism in human endothelium

BACKGROUND

Although endothelial cells express insulin receptors, it is controversially discussed whether the endothelium represents an insulin-responsive tissue. Since available data are primarily restricted to animal endothelial cells, this study tested (i) whether insulin affects glucose metabolism in human endothelium; (ii) whether insulin sensitivity is different in micro- versus macrovascular endothelial cells; and (iii) whether glucose concentration in the incubation medium affects the cells' response to insulin.

MATERIALS AND METHODS

Human umbilical vein endothelial cells (HUVECs), human adult saphenous vein endothelial cells (HAVECs), human aortic endothelial cells (HAEC), and human retinal endothelial cells (HRECs) as well as human smooth muscle cells were incubated with/without insulin (0.3 nmol L(-1) or 1 micromol L(-1)). Glucose transport, glycogen synthesis, glycogen content, lactate release, and expression of phospho-Akt, Akt, and endothelial nitric oxide synthase (eNOS) were determined.

RESULTS

In HUVECs and HRECs, insulin (1 micromol L(-1)) increased (P < 0.05) eNOS expression by ~70% and doubled Akt phosphorylation, but the latter was by far more pronounced in human smooth muscle cells (+1093 +/- 500%, P < 0.05). In human smooth muscle cells, insulin (1 micromol L(-1)) stimulated glycogen synthesis by 67 +/- 11% (P < 0.01). In human micro- (HRECs) and macrovascular endothelial cells (HUVECs, HAVECs and HAECs), insulin, however, failed to stimulate glucose transport, glycogen synthesis, glycogen content, or lactate release under various conditions, i.e. after glucose deprivation or in medium with normal (5.5 mmol L(-1)) or high glucose (30 mmol L(-1)).

CONCLUSIONS

Insulin stimulated glycogen synthesis and Akt phosphorylation in human smooth muscle cells. In human micro- and macrovascular endothelial cells, insulin, however, failed to affect glucose uptake and metabolism under all experimental conditions applied, whereas it increased Akt phosphorylation and eNOS expression.

The Mammalian target of rapamycin pathway regulates nutrient-sensitive glucose uptake in man

The nutrient-sensitive kinase mammalian target of rapamycin (mTOR) and its downstream target S6 kinase (S6K) are involved in amino acid-induced insulin resistance. Whether the mTOR/S6K pathway directly modulates glucose metabolism in humans is unknown. We studied 11 healthy men (29 years old, BMI 23 kg/m(2)) twice in random order after oral administration of 6 mg rapamycin, a specific mTOR inhibitor, or placebo. An amino acid mixture was infused to activate mTOR, and somatostatin-insulin-glucose clamps created conditions of low peripheral hyperinsulinemia (approximately 100 pmol/l, 0-180 min) and prandial-like peripheral hyperinsulinemia (approximately 450 pmol/l, 180-360 min). Glucose turnover was assessed using d-[6,6-(2)H(2)]glucose infusion (n = 8). Skeletal muscle biopsies were performed at baseline and during prandial-like peripheral hyperinsulinemia (n = 3). At low peripheral hyperinsulinemia, whole-body glucose uptake was not affected by rapamycin. During prandial-like peripheral hyperinsulinemia, rapamycin increased glucose uptake compared with placebo by 17% (R(d 300-360 min), 75 +/- 5 vs. 64 +/- 5 micromol x kg(-1) x min(-1), P = 0.0008). Rapamycin affected endogenous glucose production neither at baseline nor during low or prandial-like peripheral hyperinsulinemia. Combined hyperaminoacidemia and prandial-like hyperinsulinemia increased S6K phosphorylation and inhibitory insulin receptor substrate-1 (IRS-1) phosphorylation at Ser312 and Ser636 in the placebo group. Rapamycin partially inhibited this increase in mTOR-mediated S6K phosphorylation and IRS-1 Ser312 and Ser636 phosphorylation. In conclusion, rapamycin stimulates insulin-mediated glucose uptake in man under conditions known to activate the mTOR/S6K pathway.

Peroxisome proliferator-activated receptor-delta, a regulator of oxidative capacity, fuel switching and cholesterol transport

Synthetic agonists of peroxisome proliferator-activated receptor (PPAR)-delta have shown a promising pharmacological profile in preclinical models of metabolic and cardiovascular disease. At present, the pharmaceutical development of these drugs exploits the potential to raise plasma HDL-cholesterol in animals and their insulin-sensitising and glucose-lowering properties. PPAR-delta agonists have also proven to be powerful research tools that have provided insights into the role of fatty acid metabolism in human physiology and disease. Activation of PPAR-delta induces the expression of genes important for cellular fatty acid combustion and an associated increase in whole-body lipid dissipation. The predominant target tissue in this regard is skeletal muscle, in which PPAR-delta activation regulates the oxidative capacity of the mitochondrial apparatus, switches fuel preference from glucose to fatty acids, and reduces triacylglycerol storage. These changes counter the characteristic derangements of insulin- resistant skeletal muscle but resemble the metabolic adaptation to regular physical exercise. Apart from effects on fuel turnover, there is evidence for direct antiatherogenic properties, because PPAR-delta activation increases cholesterol export and represses inflammatory gene expression in macrophages and atherosclerotic lesions. Whereas conclusions about the full potential of PPAR-delta as a drug target await the result of large scale clinical testing, ongoing investigation of this nuclear receptor has greatly improved our knowledge of the physiological regulation of whole-body fuel turnover and the interdependence of mitochondrial function and insulin sensitivity.

Activation of PPAR-delta in isolated rat skeletal muscle switches fuel preference from glucose to fatty acids

AIMS/HYPOTHESIS

GW501516, an agonist of peroxisome proliferator-activated receptor-delta (PPAR-delta), increases lipid combustion and exerts antidiabetic action in animals, effects which are attributed mainly to direct effects on skeletal muscle. We explored such actions further in isolated rat skeletal muscle.

MATERIALS AND METHODS

Specimens of rat skeletal muscle were pretreated with GW501516 (0.01-30 mumol/l) for 0.5, 4 or 24 h and rates of fuel metabolism were then measured. In addition, effects on mitochondrial function were determined in isolated rat liver mitochondria.

RESULTS

At concentrations between 0.01 and 1 mumol/l, GW501516 dose-dependently increased fatty acid oxidation but reduced glucose utilisation in isolated muscle. Thus after 24 h of preincubation with 1 mumol/l GW501516, palmitate oxidation increased by +46+/-10%, and the following decreased as specified: glucose oxidation -46+/-8%, glycogen synthesis -42+/-6%, lactate release -20+/-2%, glucose transport -15+/-6% (all p<0.05). Reduction of glucose utilisation persisted independently of insulin stimulation or muscle fibre type, but depended on fatty acid availability (the effect on glucose transport in the absence of fatty acids was an increase of 30+/-9%, p<0.01), suggesting a role for the glucose-fatty acid cycle. At higher concentrations, GW501516 uncoupled oxidative phosphorylation by direct action on isolated mitochondria.

CONCLUSIONS/INTERPRETATION

GW501516-induced activation of PPAR-delta reduces glucose utilisation by skeletal muscle through a switch in mitochondrial substrate preference from carbohydrate to lipid. High concentrations of GW501516 induce mitochondrial uncoupling independently of PPAR-delta.

Expression of uncoupling protein-3 mRNA in rat skeletal muscle is acutely stimulated by thiazolidinediones: an exercise-like effect?

AIMS/HYPOTHESIS

We examined whether thiazolidinediones (TZDs) acutely affect uncoupling protein-3 ( UCP-3) expression in skeletal muscle and plasma NEFA in Sprague-Dawley rats.

METHODS

Expression of UCP-3 mRNA in hindlimb muscles and plasma NEFA were measured after a single intraperitoneal injection of TZDs in healthy male rats.

RESULTS

Independent of which TZD was injected (50 micromol/kg), UCP-3 expression in gastrocnemius muscle was distinctly increased after 6 h (increase vs vehicle-injected control: pioglitazone, 10.3+/-3.2-fold, p=0.03; rosiglitazone, 8.7+/-1.2-fold, p=0.001; RWJ241947, 9.5+/-2.7-fold, p=0.03). This was accompanied by elevated plasma NEFA (control 158+/-13 micromol/l; pioglitazone, 281+/-40 micromol/l, p=0.03; rosiglitazone, 276+/-27 micromol/l, p=0.005; RWJ241947, 398+/-51 micromol/l, p=0.004). The increase in plasma NEFA could in part have mediated TZD-induced UCP-3 expression, but increased UCP-3 mRNA was also found in isolated muscle after 2 h of TZD exposure in vitro (25 micromol/l pioglitazone, 1.7+/-0.3-fold, p=0.046), suggesting that TZDs act directly and independently of NEFA on skeletal muscle.

CONCLUSIONS/INTERPRETATION

In healthy rats, a single dose of TZDs rapidly increases UCP-3 mRNA in skeletal muscle and plasma NEFA. This effect resembles the acute response to a bout of exercise.

Fenofibrate Impairs Rat Mitochondrial Function by Inhibition of Respiratory Complex I

Fibrates are used for the treatment of dyslipidemia and known to affect mitochondrial function in vitro. To better understand the mechanisms underlying their mitochondrial effects, fibrate actions on complex I of the respiratory chain and cell respiration were studied in vitro. In homogenates of rat skeletal muscle, fenofibrate, and to a lesser extent clofibrate, reduced the activity of complex I (10, 30, and 100 microM fenofibrate: -41 +/- 7%, -70 +/- 2%, and -78 +/- 4%; 100 microM clofibrate: -27 +/- 7%; p < 0.005 each). Inhibition of complex I by fenofibrate (100 microM) was confirmed by reduced state 3 respiration of isolated mitochondria consuming glutamate + malate as substrates for complex I (-33 +/- 4%; p < 0.0005), but not of such consuming succinate as substrate for complex II (-8 +/- 4%; NS). In isolated rat muscle, 24-h fenofibrate exposure (25, 50, and 100 microM) decreased CO(2) production from palmitate (-15 +/- 7%, -23 +/- 8%, and -22 +/- 7%; p < 0.05 each) and increased lactate release (+15 +/- 5%, +14 +/- 5%, and + 17 +/- 6%; p < 0.02 each) indicating impaired cell respiration. Ciprofibrate and gemfibrocil (but not bezafibrate) impaired cell respiration without any inhibition of complex I. Our findings support the notion that individual fibrates induce mitochondrial dysfunction via different molecular mechanisms and show that fenofibrate predominantly acts by inhibition of complex I of the respiratory chain.

Thiazolidinediones, like metformin, inhibit respiratory complex I: a common mechanism contributing to their antidiabetic actions?

Metformin and thiazolidinediones (TZDs) are believed to exert their antidiabetic effects via different mechanisms. As evidence suggests that both impair cell respiration in vitro, this study compared their effects on mitochondrial functions. The activity of complex I of the respiratory chain, which is known to be affected by metformin, was measured in tissue homogenates that contained disrupted mitochondria. In homogenates of skeletal muscle, metformin and TZDs reduced the activity of complex I (30 mmol/l metformin, -15 +/- 2%; 100 micromol/l rosiglitazone, -54 +/- 7; and 100 micromol/l pioglitazone, -12 +/- 4; P < 0.05 each). Inhibition of complex I was confirmed by reduced state 3 respiration of isolated mitochondria consuming glutamate + malate as substrates for complex I (30 mmol/l metformin, -77 +/- 1%; 100 micromol/l rosiglitazone, -24 +/- 4; and 100 micromol/l pioglitazone, -18 +/- 5; P < 0.05 each), whereas respiration with succinate feeding into complex II was unaffected. In line with inhibition of complex I, 24-h exposure of isolated rat soleus muscle to metformin or TZDs reduced cell respiration and increased anaerobic glycolysis (glucose oxidation: 270 micromol/l metformin, -30 +/- 9%; 9 micromol/l rosiglitazone, -25 +/- 8; and 9 micromol/l pioglitazone, -45 +/- 3; lactate release: 270 micromol/l metformin, +84 +/- 12; 9 micromol/l rosiglitazone, +38 +/- 6; and 9 micromol/l pioglitazone, +64 +/- 11; P < 0.05 each). As both metformin and TZDs inhibit complex I activity and cell respiration in vitro, similar mitochondrial actions could contribute to their antidiabetic effects.

Differences in troglitazone action on glucose metabolism in freshly isolated vs long-term incubated rat skeletal muscle

1. Exposure of isolated skeletal muscle to troglitazone has resulted in inconsistent findings ranging from inhibition to stimulation of fuel oxidation and the glycogenic pathway. To better understand such variation in outcome, the present study used isolated rat soleus muscle strips to examine the interdependent influences of prolonged maintenance in vitro and of troglitazone exposure. 2. If freshly isolated muscle strips were exposed to troglitazone (1 micro mol l(-1)) for 24 h, glucose oxidation was markedly reduced (-26+/-1%, P<0.0001), whereas glycogen synthesis remained unaffected (+9+/-7%, n.s.). 3. In contrast, extended exposure to troglitazone for 72 h increased both glucose oxidation (+65+/-28%, P<0.05) and glycogen synthesis (+46+/-11%, P<0.005), and a similar stimulatory effect was also observed in muscles exposed to troglitazone only during the last 24 h of their 72 h preincubation period (glucose oxidation: +61+/-15%, P<0.001; glycogen synthesis: +43+/-15%, P<0.01). 4. Troglitazone thus stimulated glucose utilization in long-term incubated muscle independent of the duration of exposure (24 or 72 h), whereas it inhibited glucose utilization in freshly isolated muscle. 5. The observed differences in troglitazone action on freshly isolated vs long-term incubated muscle suggest that findings on muscle tissue subject to prolonged maintenance in vitro cannot be extrapolated to native muscle in vivo.

Thiazolidinediones influence plasma steroids of male obese Zucker rats

Insulin sensitizing thiazolidinediones (TZDs) inhibit steroidogenic enzyme activities in vitro and affect plasma steroids in women with polycystic ovary syndrome. This study was to examine TZD action on circulating steroids in male genetically obese Zucker rats (fa/fa), which were treated with troglitazone or rosiglitazone (0.3% and 0.01% food admixture, respectively) and were compared to untreated obese and lean littermates. After 36 days of TZD administration, obesity- associated derangement of carbohydrate metabolism was ameliorated (e.g., insulin-stimulated glucose oxidation by isolated soleus muscle, nmol/g/h: lean controls, 1049 +/- 100; obese controls, 518 +/- 30; troglitazone-treated obese, 672 +/- 43; rosiglitazone-treated obese, 761 +/- 77; p < 0.01 each vs. obese controls). While plasma pregnenolone and testosterone were neither affected by obesity nor by TZDs, a marked reduction of 17-hydroxyprogesterone in obese vs. lean controls (27 +/- 3 vs. 58 +/- 10 ng/dl; p < 0.01) was partially reversed by TZD treatment (46 +/- 5 and 48 +/- 9 ng/dl for troglitazone and rosiglitazone, respectively; p < 0.02 each vs. untreated obese). Plasma 5-alpha-dihydrotestosterone, in contrast, was not reduced by obesity (76 +/- 9 vs. 59 +/- 7 ng/dl in obese vs. lean controls; n.s.) but blunted by TZD treatment of obese rats (38 +/- 4 and 44 +/- 3 ng/dl for troglitazone and rosiglitazone, respectively; p < 0.05 each vs. untreated obese). We conclude that (i) oral TZD treatment influences circulating steroid concentrations of male obese Zucker rats, and (ii) these effects are at least in part mediated via mechanisms other than those underlying TZD-induced insulin sensitization.

Direct thiazolidinedione action on isolated rat skeletal muscle fuel handling is independent of peroxisome proliferator-activated receptor-gamma-mediated changes in gene expression

Thiazolidinediones (TZDs) are believed to induce insulin sensitization by modulating gene expression via agonistic stimulation of the nuclear peroxisome proliferator-activated receptor-gamma (PPAR-gamma). We have shown earlier that the TZD troglitazone inhibits mitochondrial fuel oxidation in isolated rat skeletal muscle. In the present study, rat soleus muscle strips were exposed to TZDs to examine whether the inhibition of fuel oxidation is mediated by PPAR-gamma activation. Our findings consistently indicated direct, acute, and PPAR-gamma-independent TZD action on skeletal muscle fuel metabolism. Rapid stimulation of lactate release by 20 micromol/l troglitazone within 30 min suggested that direct TZD action on skeletal muscle in vitro does not rely on changes in gene expression rates (12.6 +/- 0.6 [control] vs. 16.0 +/- 0.8 micromol. g(-1). h(-1) [troglitazone]; P < 0.01). This conclusion was supported by the failure of actinomycin D and cycloheximide to block the effects of troglitazone. Mitochondrial fuel oxidation was consistently inhibited by six different TZDs (percent inhibition of CO(2) production from palmitate after 25 h: troglitazone, -61 +/- 2%; pioglitazone, -43 +/- 7%; rosiglitazone, -22 +/- 6%; BM13.1258, -47 +/- 9%; BM15.2054, -51 +/- 4%; and T-174, -59 +/- 4% [P < 0.005 each]), but not by PPAR-gamma agonistic compounds not belonging to the TZD class (JTT-501, -5 +/- 7% [NS]; prostaglandin J(2), 17 +/- 7% [P < 0.05]), which further argues against dependence on PPAR-gamma activation. In summary, our findings provided good evidence that direct inhibition of mitochondrial fuel oxidation in isolated skeletal muscle is a group-specific effect of TZDs and is independent of PPAR-gamma-mediated gene expression.

Metabolic response to anisoosmolarity of rat skeletal muscle in vitro

Isolated rat hepatocytes exhibit an insulin-like anabolic response to hypoosmotic incubation and a glucagon-like catabolic response to hyperosmotic incubation. Recently, a distinct glycogenic response to hypoosmotic treatment was likewise reported for cultured rat myotubes. The present study examines the effects of anisoosmolar exposure on glucose metabolism in freshly isolated rat soleus muscle strips. Under the same experimental conditions as used for cultured myotubes, hypoosmolarity reduced net glycogen synthesis to 52%, while hyperosmolarity stimulated glycogen storage to 231% of isoosmolar control (nmol glucose incorporated into glycogen g(-1) x h(-1): hypoosmolar, 34+/-3; isoosmolar, 65+/-8; hyperosmolar, 150+/-11; p<0.01 each vs. isoosmolar). The responses of native skeletal muscle to anisoosmolarity are therefore in opposition to what has been described for hepatocytes and cultured myotubes. Further experiments on rat skeletal muscle revealed that the observed lack of a glycogenic response to hypoosmolarity persisted independent of medium composition, specifically with regard to prevailing glucose and K+ concentrations. In conclusion, hypoosmotic exposure inhibits glycogen synthesis in isolated rat soleus muscle, which clearly argues against the hypothesis that osmotic changes and cell swelling may be physiologically relevant stimulators of muscle glycogen synthesis.

Troglitazone directly inhibits CO(2) production from glucose and palmitate in isolated rat skeletal muscle

Troglitazone is a nuclear peroxisome proliferator-activated receptor-gamma agonist with insulin-sensitizing properties that has been introduced for the treatment of type 2 diabetes. To further elucidate its mechanism of action, this study examined direct troglitazone effects on glucose and palmitate utilization in isolated rat soleus muscle. Exposure of muscle specimens for 25 h to 5 micromol/liter troglitazone resulted in the distinct inhibition of insulin-stimulated mitochondrial fuel oxidation as indicated by decreased rates of CO(2) produced from glucose (glucose converted to CO(2), nanomoles per gram per hour: control, 1461 +/- 192 versus troglitazone, 753 +/- 80, P <.0001) and palmitate (palmitate converted to CO(2), nanomoles per gram per hour: control, 75 +/- 5 versus troglitazone, 20 +/- 2, P <.0001). Blunted fuel oxidation was accompanied by increased rates of anaerobic glycolysis (lactate release, micromoles per gram per hour: control, 17.3 +/- 1.0 versus troglitazone, 49.2 +/- 2.7, P <.0001) and glucose transport ([(3)H]2-deoxyglucose transport, cpm per milligram per hour: control, 540 +/- 46 versus troglitazone, 791 +/- 61, P <.0001), as well as by decreased rates of glycogen synthesis (glucose incorporation into glycogen, micromoles per gram per hour: control, 2.00 +/- 0.26 versus troglitazone, 1.02 +/- 0.13, P <.001). Such shift toward anaerobic glucose utilization also was seen in the absence of insulin and with short-term troglitazone exposure for 90 min, indicating an underlying mechanism that is rapid and independent of concomitant insulin stimulation. The results demonstrate direct and acute inhibition of fuel oxidation to CO(2) by troglitazone in rat skeletal muscle in vitro.

Chronic and acute effects of thiazolidinediones BM13.1258 and BM15.2054 on rat skeletal muscle glucose metabolism

1 New thiazolidinediones BM13.1258 and BM15.2054 were studied with regard to their PPARgamma-agonistic activities and to their acute and chronic effects on glucose metabolism in soleus muscle strips from lean and genetically obese rats. 2 Both BM13.1258 and BM15.2054 revealed to be potent PPARgamma-activators in transient transfection assays in vitro. 3 In insulin-resistant obese rats, but not in lean rats, 10 days of oral treatment with either compound increased the stimulatory effect of insulin on muscle glycogen synthesis to a similar extent (insulin-induced increment in micromol glucose incorporated into glycogen g-1 h-1: control, +1.19+/-0.28; BM13.1258, +2.50+/-0.20; BM15.2054, +2.55+/-0.46; P<0.05 vs control each). 4 In parallel to insulin sensitization, mean glucose oxidation increased insulin-independently in response to BM13.1258 (to 191 and 183% of control in the absence and presence of insulin, respectively; P<0.01 each), which was hardly seen in response to BM15.2054 (to 137 and 124% of control, respectively; ns). 5 Comparable effects on PPARgamma activation and on amelioration of insulin resistance by BM13.1258 and BM15.2054 were therefore opposed by different effects on glucose oxidation. 6 In contrast to chronic oral treatment, acute exposure of muscles to BM13.1258 or BM15.2054 in vitro elicited a distinct catabolic response of glucose metabolism in specimens from both lean and obese rats. 7 The results provide evidence that BM13.1258 and BM15.2054 can affect muscle glucose metabolism via more than one mechanism of action. 8 Further efforts are required to clarify, to what extent other mechanisms besides insulin sensitization via the activation of PPARgamma are involved in the antidiabetic actions of thiazolidinediones.

Failure of leptin to affect basal and insulin-stimulated glucose metabolism of rat skeletal muscle in vitro

Studies on different isolated tissues have provided evidence that leptin may directly modulate cellular glucose handling. The present study was performed to elucidate leptin's action on basal and insulin-stimulated glucose metabolism in native muscle tissue, which under physiological circumstances is the quantitatively most important target tissue of insulin. Isolated rat soleus muscle strips were incubated for 1 h in the absence or presence of leptin (0, 1, 10, or 100 nmol/l) under basal or insulin-stimulated conditions (10 nmol/l). No effects of leptin were found on the rates of 3H-2-deoxy-glucose transport (basal: control, 314+/-14; 1 nmol/l leptin, 320+/-17; 10 nmol/l leptin, 314+/-13; 100 nmol/l leptin, 322+/-16; insulin-stimulated: control, 690+/-33; 1 nmol/l leptin, 691+/-29; 10 nmol/l leptin, 665+/-26; 100 nmol/l leptin, 664+/-27; cpm x mg(-1) x h(-1); NS vs respective control) and on net glucose incorporation into glycogen (basal: control, 1.75+/-0.18; 1 nmol/l leptin, 2.01+/-0.13; 10 nmol/l leptin, 1.92+/-0.11; 100 nmol/l leptin, 1.81+/-0.13; insulin-stimulated: control, 5.98+/-0.40; 1 nmol/l leptin, 5.93+/-0.30; 10 nmol/l leptin, 5.46+/-0.25; 100 nmol/l leptin, 5.85+/-0.30; micromol x g(-1) x h(-1); NS vs respective control). In parallel, leptin failed to affect rates of aerobic and anaerobic glycolysis as well as muscle glycogen content. Further experiments revealed that the inability of leptin to directly affect muscle glucose handling prevailed independently of muscle fiber type (soleus and epitrochlearis muscle), of ambient insulin concentrations (0-30 nmol/l), and of leptin exposure time (1 h or 6 h). Thus, our findings fail to support speculations about a physiological role of direct insulin-mimetic or insulin-desensitizing effects of leptin on skeletal muscle tissue.