Direct Metabolic Actions Research Articles

Kisspeptins centrally modulate food intake and locomotor activity in mice independently of gonadal steroids in a sexually dimorphic manner.

Kisspeptins are essential regulators of the reproductive axis, with capacity to potently activate gonadotropin-releasing hormoneneurons, acting also as central conduits for the metabolic regulation of fertility. Recent evidence suggests that kisspeptins per se may also modulate several metabolic parameters, including body weight, food intake or energy expenditure, but their actual roles and site(s) of action remain unclear. We present herein a series of studies addressing the metabolic effects of central and peripheral administration of kisspeptin-10 (Kp-10; 1 nmol and 3 nmol daily, respectively) for 11 days in mice of both sexes. To assess direct metabolic actions of Kp-10 versus those derived indirectly from its capacity to modulate gonadal hormone secretion, kisspeptin effects were tested in adult male and female mice gonadectomized and supplemented with fixed, physiological doses of testosterone or 17β-estradiol, respectively. Central administration of Kp-10 decreased food intake in male mice, especially during the dark phase (~50%), which was accompanied by a reduction in total and nocturnal energy expenditure (~16%) and locomotor activity (~70%). In contrast, opposite patterns were detected in female mice, with an increase in total and nocturnal locomotor activity (>65%), despite no changes in food intake or energy expenditure. These changes were independent of body weight, as no differences were detected in mice of both sexes at the end of Kp-10 treatments. Peripheral administration of Kp-10 failed to alter any of the metabolic parameters analyzed, except for a decrease in locomotor activity in male mice and a subtle increase in 24 h food intake in female mice, denoting a predominant central role of kisspeptins in the control of energy metabolism. Finally, glucose tolerance and insulin sensitivity were not significantly affected by central or peripheral treatment with Kp-10. In conclusion, our data reveal a potential role of kisspeptins in the control of key metabolic parameters, including food intake, energy expenditure and locomotor activity, with a preferential action at central level, which is sex steroid-independent but sexually dimorphic.

Protein digestibility and bioavailability in an F2 mouse cross between the selected fat mouse line and an M2 congenic line carrying the anti-obesity and anti-diabetic Tst allele.

The study was performed to investigate protein digestibility and utilization in an F2 cross (M2-F2 cross) between the selected Fat (F) line and an M2 congenic line. The congenic M2line carried the Fob3b2 quantitative trait locus (QTL) from the selected Lean (L) line previously shown to contain the Tst gene with leanness, anti-diabetic and resistance to diet-induced obesity effects. The main objective of the study was to test if some of the effects on leanness and obesity resistance of the L-line Fob3b2 could also be due to the effect of this QTL on nutrient digestibility and bioavailability. The F2littermates carrying either the Fat line segment within the Fob3b2 region or the L-line were compared when fed the high-fat diet. Eleven mice per genotype were individually housed in metabolic cages. In 5-day experimental period, body mass and diet intake were measured. The part of study was done on the F and L line and tested the difference in apparent protein digestibility on low-fat (LFD) and high-fat (HFD) diet. The nitrogen content was determined in the diet, faeces, and urine based on which, the apparent protein digestibility, apparent protein biological value and apparent net protein utilization were calculated There were no significant differences in any of these parameters on congenic line, confirming that the phenotypic effect on adiposity between the genotypes in the M2-F2 population was not due to the differential effect of the Fob3b2locus carrying the Tst gene on protein utilization. We conclude that the observed phenotypic effects of this gene region are due to direct metabolic actions rather than the effects on nutrient absorption and nitrogen utilization since there were no differences in apparent protein digestibility between L and F lines, irrespective to HFD or LFD. The age of animals had significant effect on the level of digestibility.

Endothelial dysfunction due to selective insulin resistance in vascular endothelium: insights from mechanistic modeling.

Previously, we have used mathematical modeling to gain mechanistic insights into insulin-stimulated glucose uptake. Phosphatidylinositol 3-kinase (PI3K)-dependent insulin signaling required for metabolic actions of insulin also regulates endothelium-dependent production of the vasodilator nitric oxide (NO). Vasodilation increases blood flow that augments direct metabolic actions of insulin in skeletal muscle. This is counterbalanced by mitogen-activated protein kinase (MAPK)-dependent insulin signaling in endothelium that promotes secretion of the vasoconstrictor endothelin-1 (ET-1). In the present study, we extended our model of metabolic insulin signaling into a dynamic model of insulin signaling in vascular endothelium that explicitly represents opposing PI3K/NO and MAPK/ET-1 pathways. Novel NO and ET-1 subsystems were developed using published and new experimental data to generate model structures/parameters. The signal-response relationships of our model with respect to insulin-stimulated NO production, ET-1 secretion, and resultant vascular tone, agree with published experimental data, independent of those used for model development. Simulations of pathological stimuli directly impairing only insulin-stimulated PI3K/Akt activity predict altered dynamics of NO and ET-1 consistent with endothelial dysfunction in insulin-resistant states. Indeed, modeling pathway-selective impairment of PI3K/Akt pathways consistent with insulin resistance caused by glucotoxicity, lipotoxicity, or inflammation predict diminished NO production and increased ET-1 secretion characteristic of diabetes and endothelial dysfunction. We conclude that our mathematical model of insulin signaling in vascular endothelium supports the hypothesis that pathway-selective insulin resistance accounts, in part, for relationships between insulin resistance and endothelial dysfunction. This may be relevant for developing novel approaches for the treatment of diabetes and its cardiovascular complications.

Adiponectin improves insulin sensitivity via activation of autophagic flux.

Skeletal muscle insulin resistance is known to play an important role in the pathogenesis of diabetes, and one potential causative cellular mechanism is endoplasmic reticulum (ER) stress. Adiponectin mediates anti-diabetic effects via direct metabolic actions and by improving insulin sensitivity, and we recently demonstrated an important role in stimulation of autophagy by adiponectin. However, there is limited knowledge on crosstalk between autophagy and ER stress in skeletal muscle and in particular how they are regulated by adiponectin. Here, we utilized the model of high insulin/glucose (HIHG)-induced insulin resistance, determined by measuring Akt phosphorylation (T308 and S473) and glucose uptake in L6 skeletal muscle cells. HIHG reduced autophagic flux measured by LC3 and p62 Western blotting and tandem fluorescent RFP/GFP-LC3 immunofluorescence (IF). HIHG also induced ER stress assessed by thioflavin T/KDEL IF, pIRE1, pPERK, peIF2α and ATF6 Western blotting and induction of a GRP78-mCherry reporter. Induction of autophagy by adiponectin or rapamycin attenuated HIHG-induced ER stress and improved insulin sensitivity. The functional significance of enhanced autophagy was validated by demonstrating a lack of improved insulin sensitivity in response to adiponectin in autophagy-deficient cells generated by overexpression of dominant negative mutant of Atg5. In summary, adiponectin-induced autophagy in skeletal muscle cells alleviated HIHG-induced ER stress and insulin resistance.

Testosterone and obesity.

Testosterone is a key hormone in the pathology of metabolic diseases such as obesity. Low testosterone levels are associated with increased fat mass (particularly central adiposity) and reduced lean mass in males. These morphological features are linked to metabolic dysfunction, and testosterone deficiency is associated with energy imbalance, impaired glucose control, reduced insulin sensitivity and dyslipidaemia. A bidirectional relationship between testosterone and obesity underpins this association indicated by the hypogonadal-obesity cycle and evidence weight loss can lead to increased testosterone levels. Androgenic effects on enzymatic pathways of fatty acid metabolism, glucose control and energy utilization are apparent and often tissue specific with differential effects noted in different regional fat depots, muscle and liver to potentially explain the mechanisms of testosterone action. Testosterone replacement therapy demonstrates beneficial effects on measures of obesity that are partially explained by both direct metabolic actions on adipose and muscle and also potentially by increasing motivation, vigour and energy allowing obese individuals to engage in more active lifestyles. The degree of these beneficial effects may be dependent on the treatment modality with longer term administration often achieving greater improvements. Testosterone replacement may therefore potentially be an effective adjunctive treatment for weight management in obese men with concomitant hypogonadism.

Abstract 469: Influences of Dietary Weight Reduction on the Atrial Natriuretic Peptide System in Obese Subjects

In obese individuals, reduced atrial natriuretic peptide (ANP) bioavailability appears to promote arterial hypertension and type 2 diabetes likely through direct metabolic actions. Mid-regional pro-ANP is cleaved off during ANP processing, thus, serving as ANP release marker. We hypothesized that dietary weight reduction improves ANP release. In 75 overweight and obese women and men who had lost >5% body weight during six months hypocaloric dieting (-9.1±3.8 kg), we analyzed venous mid-regional pro-ANP and natriuretic peptide receptor (NPR) expression in abdominal subcutaneous adipose tissue before and after the intervention. Participants underwent ambulatory blood pressure (ABPM) monitoring and cardiac magnetic resonance imaging. ABPM decreased from 118±9/73±7 to 115±9/71±6 mm Hg and left ventricular mass from 92±20 to 86±19 g (p<0.05 for all). End-diastolic and end-systolic volumes remained unchanged. Mid-regional pro-ANP plasma concentrations did not respond to weight loss (before: 51±24 pmol/; after 53± 24 pmol/l) and increased similarly during exercise testing. Adipose NPR-A mRNA expression remained unchanged whereas NPR-C receptor mRNA decreased from 1.2±0.7 to 1.0±0.5 (p<0.05). Our data suggest that dietary weight loss does not augment ANP release in overweight and obese subjects. However, weight loss could improve ANP bioavailability through decreased clearance. Possible mechanisms are reduced fat mass and reduced expression of adipose tissue ANP scavenger receptor NPR-C.

Improvement of environmental remediation by on-site phytoremediating greenhouses.

such as climatic conditions, soil properties, abiotic stress,or multipollution combinations (polycyclic aromatic hydro-carbons, solvents, explosives, pesticides, heavy metals). We wishto argue that there are important cases where difficulties ofapplying efficient phytoremediation protocols in the field couldbe lifted by the reversed approach of on-site installation of phy-toremediating greenhouses.Plant phenotypic plasticity is an important leverage for meet-ing phytoremediation challenges. As integrators of nutrition,development and stress responses, endogenous soluble carbo-hydrates have major positive effects on physiological pro-perties that are essential for phytoremediation: root growth,root-microorganisms interactions, growth of aerial organs, leaf-microorganisms interactions, pollutant uptake, stress tolerance,defense against oxidative stress, tolerance of pollutant accumu-lation, and pollutant chelation, conjugation or detoxification.These effects stem from direct metabolic action of carbohy-drates,

Effects of vandetanib on body composition in patients with advanced medullary thyroid carcinomas: Results from a placebo-controlled study.

5569 Background: Muscle (MT) and adipose tissue (AT) share common intra cellular pathways with tumor, thus it is not surprising to observe metabolic consequences with targeted therapies. The aim of the study was to assess the effects of vandetanib, a tyrosine kinase inhibitor (TKI) which demonstrated efficacy for the treatment of advanced medullary thyroid carcinoma (MTC), on MT and AT. Methods: 33 patients (25 men and 8 women, mean age of 54 years) with metastatic MTC received vandetanib 300 mg/d (n=23) or placebo (n=10) in the setting of the ZETA study. Cross-sectional areas (cm2) of visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT) and MT were assessed by computed tomography imaging at 3rd lumbar vertebra and were indexed for height (cm2/m2). Comparisons between treatment and placebo were made at 3 months, and long-term evolution was evaluated over 12 months. Results: At 3 months, compared to baseline, patients treated with vandetanib gained 1.5 kg, 1.3 cm2/m2 of MT, 5.1 cm2/m2 of VAT and 4.5 cm2/m2 of SAT. In contrast, patients under placebo lost 1.5 kg (p=0.02), 1.0 cm2/m2 of MT (p=0.009), 5.5 cm2/m2 of SAT (p=0.004) and gained significantly less VAT (0.6 cm2/m2) (p=0.02). At 12 months, compared to baseline, patients treated with vandetanib gained 2 kg (NS), lost 0.3 cm2/m2 MT (NS), gained 3.4 cm2/m2 of VAT (NS) and 8.7 cm2/m2 of SAT (95% CI, 1.1 to 16.2). A significant decrease of calcitonin (defined as ≤50% compared to baseline) was associated with higher weight (p=0.01), VAT (p=0.01), and total adipose tissue (p=0.02). Conclusions: Beyond its proved efficacy in MTC treatment, and despite common intracellular pathways, vandetanib is the only studied TKI to preserve MT and to restore AT. Further research is needed to explore whether the relationship between changes of VAT and vandetanib treatment results from a direct metabolic action of vandetanib or is a consequence of biochemical tumor control.

The igf System in Carcinogenesis and Its Implication for Cancer Therapy

The discovery of the insulin-like growth factor (igf) system occurred half a century ago, in a series of experiments showing that the growth hormone itself exercises no direct metabolic action on skeletal tissues, but rather acts through secondary substances[...].

Acute exposure to rosiglitazone does not affect glucose transport in intact human skeletal muscle

Thiazolidinediones (TZDs) such as rosiglitazone are widely used as antidiabetic drugs. Animal studies suggest that TZDs may have direct metabolic actions in skeletal muscle. Here, we examined if acute exposure to rosiglitazone stimulates glucose transport rate and affects proximal insulin signaling in isolated skeletal muscle strips from nondiabetic men. Open muscle biopsies were obtained from musculus vastus lateralis from 15 nondiabetic men (50 ± 3 years old, 26.9 ± 1.1 kg/m 2). Skeletal muscle strips were isolated and exposed to rosiglitazone (1 or 10 μmol/L), 5-aminoimidazole-4-carboxamide 1- β- d-ribonucleoside (1 mmol/L), insulin (120 nmol/L), or a combination of insulin (120 nmol/L) and rosiglitazone (10 μmol/L) in vitro for 1 hour. Glucose transport was analyzed by accumulation of intracellular 3- O-methyl [ 3H] glucose; phosphorylation of Akt-Ser 473 and Akt-Thr 308 and phosphorylation of acetyl coenzyme A carboxylase β were determined using phosphospecific antibodies. 5-Aminoimidazole-4-carboxamide 1- β- d-ribonucleoside and insulin increased glucose transport rate 1.5-fold ( P < .05) and 1.7-fold ( P < .01) in isolated muscle strips, respectively. Exposure to rosiglitazone transiently increased phosphorylation of acetyl coenzyme A carboxylase β, with a maximum effect at 15 minutes and return to baseline at 60 minutes. However, rosiglitazone did not affect basal or insulin-stimulated glucose transport rate, or phosphorylation of Akt-Ser 473 or Akt-Thr 308 in isolated muscle strips. In conclusion, acute exposure to rosiglitazone does not affect glucose transport in human skeletal muscle.

Acute effect of leptin on hepatic glycogenolysis and gluconeogenesis in perfused rat liver.

Leptin circulates in blood and is involved in body weight control primarily via hypothalamic receptors. To examine its direct metabolic action, effects of short-term portal leptin infusion: 1) on postprandial basal and epinephrine-stimulated glycogenolysis; and 2) on postabsorptive lactate-stimulated gluconeogenesis were studied in isolated perfused rat livers. Incremental epinephrine (150 pmol x min-1 x g-1 liver)-stimulated glucose release (in micromol/g liver within 30 minutes; control: 28.3 +/- 2.8) was suppressed (P <.05) by 44% (15.8 +/- 1.6), by 48% (14.6 +/- 4.1), and by 53% (13.3 +/- 2.1) during insulin (3 pmol x min-1 x g-1 liver), leptin (30 pmol x min-1 x g-1 liver), and simultaneous leptin + insulin infusion. Perfusate cyclic adenosine monophosphate increased approximately twofold during epinephrine stimulation in all groups. Neither leptin nor insulin affected hepatic lactate production, bile flow, or portal pressure in the fed state. In the postabsorptive state (20-hour fasting), rates of lactate (10 mmol/L)-dependent hepatic glucose release (in micromol. min-1 x g-1 liver; control: 0.12 +/- 0.01) were increased (P <.01) to 0.35 +/- 0.02 and to 0.24 +/- 0.01 by glucagon (3 pmol x min-1 x g-1 liver) and by leptin (15 pmol x min-1 x g-1 liver), respectively. In parallel, lactate uptake rates (in micromol x min-1 x g-1 liver) were higher in the presence of both glucagon (0.90 +/- 0. 03) and leptin (0.84 +/- 0.02) compared with control (0.68 +/- 0.04). In conclusion, leptin modulates hepatic glucose fluxes and may contribute to direct humoral regulation of liver glycogen stores in the fasted as well as in the fed state.

Effect of follicle‐stimulating hormone on metabolism and maturation in Bufo arenarum oocytes

In the fully grown Bufo arenarum oocyte, carbohydrate breakdown during the autumn-winter season is accomplished mainly through the glycolytic pathway followed by the Krebs cycle. During the breeding season (spring-summer), carbohydrates are used mainly through the pentose phosphate cycle and through the variant of the Krebs cycle known as the glutamic aspartic cycle. The metabolism operating in the oocytes was determined using the following parameters: 1) the capacity of isolated mitochondria to oxidize citrate and fumarate; 2) the enzymatic activities of phosphofructokinase (PFK) and glucose-6-phosphate dehydrogenase (G-6-PDH); and 3) citrate and ATP compartmentalization. The present paper shows that follicle-stimulating hormone (FSH) would be one of the factors responsible for summer metabolism, since ovary fractions obtained from winter specimens treated with the hormone acquired the metabolic characteristics corresponding to oocytes obtained from breeding-season animals. From dose-response, and response in the function of time curves, it could be assumed that the optimum doses and times were 0.1 micrograms FSH/ml of incubation medium and 30 min treatment, respectively. The metabolic effect of FSH upon oocytes could be mediated by the adenylate cyclase-cAMP system, since treatment of ovaric fractions with cAMP 10(-3) M reproduced the effects obtained with the hormone. In addition, 0.02 mg/ml tetracycline proved to block the effect of FSH. A direct metabolic action of FSH on body cavity oocytes (without follicle cells) was observed when submitting these oocytes to the same hormonal treatment.

Metabolic actions of glucagon-family hormones in liver

This review addresses direct and indirect metabolic actions of hormones co-encoded in the preproglucagon gene of fishes. Emphasis is placed on a critical analysis of the effects of glucagon and glucagon-like peptide (GLP) and the current knowledge of the respective modes of action is reviewed. In mammals GLPs exert no direct metabolic actions. In fish liver, GLP and glucagon act on similar targets of intermediary metabolism by enhancing flux through glycogenolysis, lipolysis and gluconeogenesis. Increases in substrate oxidation are not uniform. Hormonal activation of glycogen phosphorylase and triglyceride lipase and inhibition of pyruvate kinase are implicated in these actions. Hormone-dependent hyperglycemia, depletion of hepatic glycogen and increases in free fatty acids are noticeablein vivo. Glucagon also activates hepatic amino acid uptake and ammonia excretion.Glucagon actions are accompanied by large increases in hepatic cAMP and increased phosphorylation of pyruvate kinase. Metabolic effects measured after GLP administration are associated with minor, if any, increases in cAMP and effects on pyruvate kinase are variable. We hypothesize that different hepatic receptors with differing modes of intracellular message transduction are involved in glucagon and GLP actions while targetting identical metabolic routes. Responses of different species of fish cover a wide spectrum, and variation of response with the circannual cycle of experimental animals makes comparisons of results, even within one species, difficult.

Fatty acid oxidation and glucose utilization interact to control food intake in rats.

To determine whether glucose and fat metabolism interact to control food intake, rats were administered 2-deoxyglucose (2-DG), which inhibits glucose utilization, and methyl palmoxirate (MP), which inhibits fatty acid oxidation. Combined treatment with 2-DG and MP increased food intake in a synergistic fashion. This synergistic effect was observed even at doses of the two agents that alone did not increase food intake, and it was expressed by either an initiation of eating or a prolonged bout of eating, depending on the testing conditions. Metabolic measures of circulating substrates, liver glycogen, and gastric contents confirmed that the drugs had their intended metabolic effects and revealed no evidence that one drug enhanced the direct metabolic action of the other. The results provide direct evidence that glucose and fat metabolism exert a coordinated control over feeding behavior and suggest the existence of a common integrative mechanism in that control.

Evidence for a Beneficial Effect of Intravenous Glucose on the Hemodynamic Response to Acute Asphyxia

Anesthetized rabbits were subjected to two 4-min periods of asphyxia with a 15-min recovery period intervening. During the recovery period animals received an iv infusion of either isotonic glucose or mannitol. Results indicated that glucose had a beneficial effect on systolic blood pressure during the second period of asphyxia. A direct metabolic action of glucose on the myocardium is favored as the explanation, but other possibilities include peripheral or neurohumoral effects.

The effects of isoprenaline and phenylephrine on oxygen consumption in isolated smooth muscle.

1. Simultaneous measurements of oxygen consumption and mechanical activity have been made in isolated preparations of guinea-pig taenia coli, rabbit abdominal aorta and the longitudinal muscle of rabbit duodenum.2. Mean resting oxygen consumption was greater in mechanically-active preparations (taenia coli and duodenum) than in the aorta which showed no spontaneous activity.3. The relaxation produced by isoprenaline in guinea-pig taenia coli and rabbit duodenum was accompanied by a dose-dependent fall in oxygen consumption.4. The relaxation produced by phenylephrine in guinea-pig taenia coli was accompanied by a dose-dependent fall in oxygen consumption whereas, in the rabbit duodenum, the transient fall in tension was not accompanied by any significant change in oxygen consumption.5. The increase in tension produced by phenylephrine in rabbit abdominal aorta was accompanied by an increase in oxygen consumption.6. Changes in mechanical activity and oxygen consumption produced by isoprenaline and phenylephrine were antagonized by propranolol and phentolamine respectively.7. It is concluded that the variations in oxygen consumption associated with spontaneous or drug-induced mechanical changes are simple reflections of altered mechanical activity. The possibility of additional direct metabolic actions of isoprenaline and phenylephrine is discussed.

Effects of Feeding Low-Level Chlortetracycline to a Dairy Herd Continuously for One Year

Summary The effects of feeding chlortetracycline at the low level (0.1mg. per pound of body weight, or 0.2 p.p.m.) were studied for a continuous period of 12 mo. on 34 pairs of Guernsey cows in one herd. Under the conditions of this experiment, the incidence of diseases such as foot rot, bloat, metritis, and milk fever was low in both treated and untreated groups. There was a moderate number of mastitis cases in both groups, with no significant difference between them. Differences found in the production of milk, fat, 4% FCM, 4% FCM-ME, fat percentage, persistency of lactation level, daily peak production, or average yield per month were statistically not significant. A comparison of the initial 15 cow pairs showed tendencies in milk, fat percentage, and 4% FCM production in favor of the chlortetracycline treatment, but differences were statistically significant only for fat and 4% FCM production. This experiment with lactating cows and a low-level oral dosage of chlortetracycline did not seem to add new support to a concept of direct metabolic action by chlortetracycline, on the basis of the criteria used for evaluation, even though there was a tendency for the chlortetracycline-fed cows to have an increased fat content in the milk.