Life Under Hypoxia Lowers Blood Glucose Independently of Effects on Appetite and Body Weight in Mice

Blood glucose and the prevalence of diabetes are lower in mountain than lowland dwellers, which could among other factors be due to reduced oxygen availability. To investigate metabolic adaptations to life under hypoxia, male mice on high fat diet (HFD) were continuously maintained at 10% O2. At variance to preceding studies, the protocol was designed to dissect direct metabolic effects from such mediated indirectly via hypoxia-induced reductions in appetite and weight gain. This was achieved by two separate control groups on normal air, one with free access to HFD, and one fed restrictedly in order to obtain a weight curve matching that of hypoxia-exposed mice. Comparable body weight in restrictedly fed and hypoxic mice was achieved by similar reductions in calorie intake (−22%) and was associated with parallel effects on body composition as well as on circulating insulin, leptin, FGF-21, and adiponectin. Whereas the effects of hypoxia on the above parameters could thus be attributed entirely to blunted weight gain, hypoxia improved glucose homeostasis in part independently of body weight (fasted blood glucose, mmol/l: freely fed control, 10.2 ± 0.7; weight-matched control, 8.0 ± 0.3; hypoxia, 6.8 ± 0.2; p < 0.007 each; AUC in the glucose tolerance test, mol/l*min: freely fed control, 2.54 ± 0.15; weight-matched control, 1.86 ± 0.08; hypoxia, 1.67 ± 0.05; p < 0.05 each). Although counterintuitive to lowering of glycemia, insulin sensitivity appeared to be impaired in animals adapted to hypoxia: In the insulin tolerance test, hypoxia-treated mice started off with lower glycaemia than their weight-matched controls (initial blood glucose, mmol/l: freely fed control, 11.5 ± 0.7; weight-matched control, 9.4 ± 0.3; hypoxia, 8.1 ± 0.2; p < 0.02 each), but showed a weaker response to insulin (final blood glucose, mmol/l: freely fed control, 7.0 ± 0.3; weight-matched control, 4.5 ± 0.2; hypoxia, 5.5 ± 0.3; p < 0.01 each). Furthermore, hypoxia weight-independently reduced hepatic steatosis as normalized to total body fat, suggesting a shift in the relative distribution of triglycerides from liver to fat (mg/g liver triglycerides per g total fat mass: freely fed control, 10.3 ± 0.6; weight-matched control, 5.6 ± 0.3; hypoxia, 4.0 ± 0.2; p < 0.0004 each). The results show that exposure of HFD-fed mice to continuous hypoxia leads to a unique metabolic phenotype characterized by improved glucose homeostasis along with evidence for impaired rather than enhanced insulin sensitivity

Effects of prolonged hypoxia and treatment with Metformin on glucose metabolism of obese mice

Dem geringen Sauerstoffpartialdruck in Höhenlagen sowie dem Medikament Metformin, das die Zellatmung hemmen kann, werden sowohl Appetitreduktion als auch anti-diabetische Wirkung zugeschrieben, wobei die Wirkmechanismen unklar sind. In zahllosen Studien zur Wirkung von Hypoxie und Metformin wurde jedoch nicht berücksichtigt, ob und wie weit ein Absinken der Blutglukose nur die naheliegende Folge von Appetit- und Gewichtsverlust ist. Hier wurde diese wichtige Frage an fettreich gefütterten, adipösen Mäuse untersucht, die über ein bis drei Monate unter Hypoxie gehalten oder mit Metformin behandelt wurden. Vergleich mit KontrolItieren, die durch reduzierte Fütterung das gleiche Körpergewicht hatten, schloss den indirekten Einfluss von Gewichtsunterschieden aus. Haltung unter einer normobaren Atmosphäre von 10% O2 senkte die Basalglykämie und verbesserte die Glukosetoleranz, was auf direkte anti-hyperglykämische Wirkung von Hypoxie hinweist, die mehr als die triviale Folge eines Appetitverlusts ist. Die verbesserte Homöostase der Blutglukose wurde in den adipösen Mäusen jedoch von keinerlei Hinweis auf reduzierte Insulinresistenz begleitet. Bessere Glukosehomöostase ohne einen begleitenden Anstieg der Insulinsensitivität ist ungewöhnlich und lässt vermuten, dass Hypoxie den Glukosestoffwechsel über bisher unbekannte Mechanismen moduliert. In Experimenten an Knock-out-Mäusen konnte der Fibroblast Growth Factor 21 allerdings als essentieller Vermittler der Hypoxiewirkung auf den Glukosestoffwechsel ausgeschlossen werden. Die Wirkung von Metformin wurde entlang verschiedener Protokolle untersucht, die in vorangehenden Nagerstudien Anwendung gefunden hatten (tägliche intraperitoneale Injektionen, Beimischung ins Trinkwasser). Bei Ausschluss indirekter Effekte über Appetit- und Gewichtsverlust zeigte Metformin jedoch unter keinem dieser Protokolle blutglukosesenkende Wirkung, sondern führte vielmehr zu einem weiteren Entgleisen der Glukosehomöostase. Insbesondere kam es zu einem Anstieg der Insulinresistenz, was in krassem Gegensatz zur den positiven Effekten von Metformin in der Klinik steht. Weitere Experimente zur Pharmakokinetik und zu direkten Metformineffekten am isolierten Skelettmuskel von Ratte und Maus wiesen auf eine mögliche Bedeutung langfristig-kontinuierlicher Metforminexposition für anti-diabetische Effekte hin. Kontinuierliche Metformininfusion über intraperitoneale Minipumpen konnte in den adipösen Mäusen jedoch auch kein gewichtsunabhängiges Absinken der Blutglukose bewirken. Insgesamt betonen die Ergebnisse die besondere Notwendigkeit bei metabolischen Untersuchungen indirekte Wirkungen durch Gewichtsänderungen zu berücksichtigen. Darüber hinaus wird gezeigt, dass in der präklinischen Forschung über die Wirkungen von Metformin auch mögliche Einflussfaktoren wie Akkumulation in intrazellulären Sub-Kompartimenten, die Interaktion von Dosis und Expositionszeit, sowie Speziesunterschiede in Betracht gezogen werden müssen.Low partial oxygen pressure at high altitude as well as metformin, a drug known to inhibit cell respiration, have been associated with both, reduced appetite and anti-diabetic action, but the involved metabolic and molecular mechanisms are still incompletely understood. In countless studies on hypoxia and metformin it has never been consequently dissected, to what extent the lowering of blood glucose is a direct specific effect or just an indirect consequence of reduced calorie consumption and weight loss. Here, this unanswered question was tackled using obese mice fed high fat diet, which were subjected to continuous hypoxia or regular treatment with metformin for a period of one to three months. Indirect effects via weight loss were excluded by control animals that were weight matched due to restricted feeding. Life under a normobaric atmosphere containing 10% O2 markedly lowered basal blood glucose and improved glucose tolerance in obese mice, indicating anti-hyperglycemic activity of hypoxia that cannot be entirely explained by a spoilt appetite. However, better glucose homeostasis was not accompanied by any evidence for increased insulin sensitivity. This surprising dissociation of improvement of glucose homeostasis from improvement of insulin sensitivity suggests that glucose lowering under hypoxia could rely on unique and previously unknown mechanisms. A parallel study on knock out mice did not deliver any evidence that fibroblast growth factor 21 is an essential mediator of these effects of hypoxia on glucose metabolism. The effects of metformin were examined in obese mice subjected to several treatment regimens as used in preceding studies on experimental rodents (daily intraperitoneal injections, admixture to drinking water). When indirect action via loss of appetite and body weight was excluded, metformin failed to exhibit a beneficial effect on blood glucose under any of these chronic treatment regimens. Rather, metformin treatment led to further derangement of glucose homeostasis and, in particular, to worsening of insulin resistance, which contrasted with its established beneficial actions in diabetic patients. Further experiments on metformin dealt with pharmacokinetics and with direct effects on isolated rat and mouse skeletal muscle. The results suggested that prolonged and continuous exposure to metformin might be essential to unmask its beneficial potential. Hence, several groups of mice were implanted with intraperitoneal osmotic mini-pumps for continuous metformin infusion, but weight independent lowering of blood glucose was not obtained under this treatment regimen either. In summary, the results emphasize the often neglected importance of considering potential indirect actions via weight changes in metabolic research. Beyond this, it is shown that preclinical research dealing with metformin action must account not only for indirect actions via appetite and weight, but also for potential accumulation of the drug in deep intracellular compartments, for a complex interdependence of dose and exposure time, as well as for species differences.submitted by Mairam KaplanianAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersMedizinische Universität Wien, Diss., 2018(VLID)336062

Life Under Hypoxia Lowers Blood Glucose Independently of Effects on Appetite and Body Weight in Mice

Blood glucose and the prevalence of diabetes are lower in mountain than lowland dwellers, which could among other factors be due to reduced oxygen availability. To investigate metabolic adaptations to life under hypoxia, male mice on high fat diet (HFD) were continuously maintained at 10% O2. At variance to preceding studies, the protocol was designed to dissect direct metabolic effects from such mediated indirectly via hypoxia-induced reductions in appetite and weight gain. This was achieved by two separate control groups on normal air, one with free access to HFD, and one fed restrictedly in order to obtain a weight curve matching that of hypoxia-exposed mice. Comparable body weight in restrictedly fed and hypoxic mice was achieved by similar reductions in calorie intake (22%) and was associated with parallel effects on body composition as well as on circulating insulin, leptin, FGF-21, and adiponectin. Whereas the effects of hypoxia on the above parameters could thus be attributed entirely to blunted weight gain, hypoxia improved glucose homeostasis in part independently of body weight (fasted blood glucose, mmol/l: freely fed control, 10.2 0.7; weight-matched control, 8.0 0.3; hypoxia, 6.8 0.2; p < 0.007 each; AUC in the glucose tolerance test, mol/l*min: freely fed control, 2.54 0.15; weight-matched control, 1.86 0.08; hypoxia, 1.67 0.05; p < 0.05 each). Although counterintuitive to lowering of glycemia, insulin sensitivity appeared to be impaired in animals adapted to hypoxia: In the insulin tolerance test, hypoxia-treated mice started off with lower glycaemia than their weight-matched controls (initial blood glucose, mmol/l: freely fed control, 11.5 0.7; weight-matched control, 9.4 0.3; hypoxia, 8.1 0.2; p < 0.02 each), but showed a weaker response to insulin (final blood glucose, mmol/l: freely fed control, 7.0 0.3; weight-matched control, 4.5 0.2; hypoxia, 5.5 0.3; p < 0.01 each). Furthermore, hypoxia weight-independently reduced hepatic steatosis as normalized to total body fat, suggesting a shift in the relative distribution of triglycerides from liver to fat (mg/g liver triglycerides per g total fat mass: freely fed control, 10.3 0.6; weight-matched control, 5.6 0.3; hypoxia, 4.0 0.2; p < 0.0004 each). The results show that exposure of HFD-fed mice to continuous hypoxia leads to a unique metabolic phenotype characterized by improved glucose homeostasis along with evidence for impaired rather than enhanced insulin sensitivity.(VLID)470109

Emodin : a compound with putative antidiabetic potential, deteriorates glucose tolerance in rodents

Emodin is found in remedies from Traditional Chinese Medicine. Since antihyperglycaemic action was observed in rodents, non-scientific sources advertise emodin intake as a natural cure for diabetes. Emodin was admixed to high fat-food of obese mice at two doses (2 and 5 g/kg; daily emodin uptake 103 and 229 mg/kg). Comparison was made to ad libitum fed and to food restricted control groups, the latter showing the same weight gain as the corresponding emodin-treated groups. Emodin blunted food intake by 6% and 20% for the low and high dose, which was accompanied by proportionate reductions in weight gain. Emodin reduced blood glucose relative to freely feeding controls, but comparison to weight-matched controls unmasked deterioration, rather than improvement, of basal glycaemia (mmol/l: fed ad libitum, 9.5±0.4; low emodin, 9.4±0.3, weight-matched, 8.2±0.3; high emodin, 7.2±0.4, weight-matched, 6.1±0.3; P<0.01, emodin vs weight-matched) and glucose tolerance (area under the curve, min*mol/l: fed ad libitum, 2.01±0.08; low emodin, 1.97±0.12, weight-matched, 1.75±0.03; high emodin, 1.89±0.07, weight-matched, 1.65±0.05; P<0.0002, emodin vs weight-matched). An insulin tolerance test suggested insulin desensitisation by prolonged emodin treatment. Furthermore, a single oral emodin dose did not affect glucose tolerance in obese mice, whereas intravenous injection in rats suggested a potential of emodin to acutely impair insulin release. Our results show that the antihyperglycaemic action of emodin as well as associated biochemical alterations could be the mere consequences of a spoilt appetite. Published claims of antidiabetic potential via other mechanisms evoke the danger of misuse of natural remedies by diabetic patients