Metformin severely impairs in vivo muscle oxidative capacity in a rat model of type 2 diabetes

Objective: To investigate the effects of metformin on in vivo and in vitro skeletal muscle mitochondrial function in Zucker diabetic fatty (ZDF) rats using 31P magnetic resonance spectroscopy (MRS) and high-resolution respirometry (HRR), respectively. Methods: 12-week old healthy (fa/+) and diabetic (fa/fa) ZDF rats were treated with metformin (0, 30, 100 or 300 mg/kg body weight/day) for 15 days by oral gavage. At day 14, in vivo31P MRS was performed on the tibialis anterior (TA) muscle to measure PCr recovery. At day 15, animals were killed and TA muscles were excised for in vitro HRR measurements. Results: Metformin treatment decreased PCr recovery rates in a dose-dependent manner in both healthy fa/+ and diabetic fa/fa rats. Whereas, the clinical dose of 30 mg/kg/day had no significant effect, PCr recovery rates were ~22% and ~47% decreased at 100 and 300 mg/kg/day. HRR measurements showed a similar, but less pronounced effect of metformin on in vitro mitochondrial function

Obesity and type 2 diabetes : a systems biology perspective of a molecular mechanism

People who have excess body weight have a higher risk of insulin resistance and type 2 diabetes, because fat interferes with the body's ability to make and use insulin. Insulin, a hormone released by pancreatic beta-cells, is needed to move diet-derived glucose from blood into fat and muscle cells where it is used to produce energy. The precise ways of how fat interferes with insulin action are not yet known. Our hypothesis is that accumulation of fatty acids (break down product of fats) in these cells leads to increased levels of activated fatty acids, so called fatty acyl-CoA esters. The latter may impair cellular energy metabolism and stimulate the production of reactive oxygen species (ROS) due to inhibition of mitochondrial adenine nucleotide translocator (ANT) leading to impaired cell function, for example impaired insulin release from pancreatic beta-cells. In agreement with our hypothesis we have shown that addition of fatty acyl-CoA esters to mitochondria isolated from livers of normal rats leads to decreased activity of the ANT, decreased levels of extramitochondrial ATP and increased production of ROS. The effect of saturated fatty acyl-CoA ester (palmitoyl-CoA) was stronger than the effect of unsaturated fatty acyl-CoA ester (oleoyl-CoA). Interestingly, the observed effects depended on the working condition of these mitochondria. Next we showed, that long-term high fat diet feeding leads to higher blood glucose levels, as well as to oxidative stress and accumulation of fatty acyl-CoA esters in rat livers. However, long-term high fat diet feeding does not cause adaptive changes that would improve mitochondrial ability to deal with these challenges. This indicates that fatty acyl-CoA may exert same effects in intact liver as the ones observed in isolated mitochondria. Similarly to rat livers, long-term exposure of human endothelial cells (cells that line interior surface of blood vessels) to high levels of fatty acids leads to accumulation of fatty acyl-CoA ester and lower levels of ATP in these cells. This negatively affects the ability of these cells to survive and grow. Again, the effect of saturated fatty acid palmitate is stronger that the effect of unsaturated fatty acid oleate. In summary, our data indicate that the proposed mechanism linking obesity and type 2 diabetes (i.e. inhibition of the ANT by fatty acy-CoA esters) may indeed occur in cells leading to impaired cell function characteristic to type 2 diabetes.Heine, R.J. [Promotor]Westerhoff, H.V. [Promotor]Bakker, S.J.L. [Copromotor]Krab, K. [Copromotor

An in vivo magnetic resonance spectroscopy study of the effects of caloric and non-caloric sweeteners on liver lipid metabolism in rats

We aimed to elucidate the effects of caloric and non-caloric sweeteners on liver lipid metabolism in rats using in vivo magnetic resonance spectroscopy (MRS) and to determine their roles in the development of liver steatosis. Wistar rats received normal chow and either normal drinking water, or solutions containing 13% (w/v) glucose, 13% fructose, or 0.4% aspartame. After 7 weeks, in vivo hepatic dietary lipid uptake and de novo lipogenesis were assessed with proton-observed, carbon-13-edited MRS combined with13C-labeled lipids and13C-labeled glucose, respectively. The molecular basis of alterations in hepatic liver metabolism was analyzed in detail ex vivo using immunoblotting and targeted quantitative proteomics. Both glucose and fructose feeding increased adiposity, but only fructose induced hepatic lipid accumulation. In vivo MRS showed that this was not caused by increased hepatic uptake of dietary lipids, but could be attributed to an increase in de novo lipogenesis. Stimulation of lipogenesis by fructose was confirmed by a strong upregulation of lipogenic enzymes, which was more potent than with glucose. The non-caloric sweetener aspartame did not significantly affect liver lipid content or metabolism. In conclusion, liquid fructose more severely affected liver lipid metabolism in rats than glucose, while aspartame had no effect.</p

Western-style diet does not negatively affect the healthy aging benefits of lifelong restrictive feeding

BACKGROUND: Lifelong consumption of a Western-style diet is a risk factor for developing metabolic disorders and therefore impairs healthy aging. Dietary restriction (DR) could delay the onset of age-related diseases and prolong life span, however, the extent to which this depends on diet type is poorly understood. OBJECTIVE: To study whether feeding a Western-style diet affects the healthy aging benefits of DR. METHODS: Mice fed a Western-style diet (ad libitum and DR) were compared to those fed a standard healthy diet (ad libitum and DR). Survival and several metabolic and endocrine parameters were analyzed. RESULTS: Lifelong consumption of a Western-style diet resulted in increased adiposity, elevated triglyceride levels in plasma, higher homeostatic model assessment-insulin resistance and higher resting metabolic rate in mice compared to the standard diet group. This was accompanied by reduced survival in the Western-style diet group. DR irrespective of diet type improved abovementioned parameters. CONCLUSIONS: Lifelong restricted consumption of Western-style diet led to improved metabolic and endocrine parameters, and increased survival compared to the ad libitum Western-style diet group. Interestingly, the survival was comparable in restricted Western-style and standard diet groups, suggesting that reduced food intake rather than diet composition play more important role in promoting longevity/survival

An In Vivo Magnetic Resonance Spectroscopy Study of the Effects of Caloric and Non-Caloric Sweeteners on Liver Lipid Metabolism in Rats

We aimed to elucidate the effects of caloric and non-caloric sweeteners on liver lipid metabolism in rats using in vivo magnetic resonance spectroscopy (MRS) and to determine their roles in the development of liver steatosis. Wistar rats received normal chow and either normal drinking water, or solutions containing 13% (w/v) glucose, 13% fructose, or 0.4% aspartame. After 7 weeks, in vivo hepatic dietary lipid uptake and de novo lipogenesis were assessed with proton-observed, carbon-13-edited MRS combined with C-13-labeled lipids and C-13-labeled glucose, respectively. The molecular basis of alterations in hepatic liver metabolism was analyzed in detail ex vivo using immunoblotting and targeted quantitative proteomics. Both glucose and fructose feeding increased adiposity, but only fructose induced hepatic lipid accumulation. In vivo MRS showed that this was not caused by increased hepatic uptake of dietary lipids, but could be attributed to an increase in de novo lipogenesis. Stimulation of lipogenesis by fructose was confirmed by a strong upregulation of lipogenic enzymes, which was more potent than with glucose. The non-caloric sweetener aspartame did not significantly affect liver lipid content or metabolism. In conclusion, liquid fructose more severely affected liver lipid metabolism in rats than glucose, while aspartame had no effect

Organ-specific responses during brain death:increased aerobic metabolism in the liver and anaerobic metabolism with decreased perfusion in the kidneys

Hepatic and renal energy status prior to transplantation correlates with graft survival. However, effects of brain death (BD) on organ-specific energy status are largely unknown. We studied metabolism, perfusion, oxygen consumption, and mitochondrial function in the liver and kidneys following BD. BD was induced in mechanically-ventilated rats, inflating an epidurally-placed Fogarty-catheter, with sham-operated rats as controls. A 9.4T-preclinical MRI system measured hourly oxygen availability (BOLD-related R2*) and perfusion (T1-weighted). After 4 hrs, tissue was collected, mitochondria isolated and assessed with high-resolution respirometry. Quantitative proteomics, qPCR, and biochemistry was performed on stored tissue/plasma. Following BD, the liver increased glycolytic gene expression (Pfk-1) with decreased glycogen stores, while the kidneys increased anaerobic- (Ldha) and decreased gluconeogenic-related gene expression (Pck-1). Hepatic oxygen consumption increased, while renal perfusion decreased. ATP levels dropped in both organs while mitochondrial respiration and complex I/ATP synthase activity were unaffected. In conclusion, the liver responds to increased metabolic demands during BD, enhancing aerobic metabolism with functional mitochondria. The kidneys shift towards anaerobic energy production while renal perfusion decreases. Our findings highlight the need for an organ-specific approach to assess and optimise graft quality prior to transplantation, to optimise hepatic metabolic conditions and improve renal perfusion while supporting cellular detoxification

Protection against the Metabolic Syndrome by Guar Gum-Derived Short-Chain Fatty Acids Depends on Peroxisome Proliferator-Activated Receptor. and Glucagon-Like Peptide-1

The dietary fiber guar gum has beneficial effects on obesity, hyperglycemia and hypercholesterolemia in both humans and rodents. The major products of colonic fermentation of dietary fiber, the short-chain fatty acids (SCFAs), have been suggested to play an important role. Recently, we showed that SCFAs protect against the metabolic syndrome via a signaling cascade that involves peroxisome proliferator-activated receptor (PPAR) γ repression and AMP-activated protein kinase (AMPK) activation. In this study we investigated the molecular mechanism via which the dietary fiber guar gum protects against the metabolic syndrome. C57Bl/6J mice were fed a high-fat diet supplemented with 0% or 10% of the fiber guar gum for 12 weeks and effects on lipid and glucose metabolism were studied. We demonstrate that, like SCFAs, also guar gum protects against high-fat diet-induced metabolic abnormalities by PPARγ repression, subsequently increasing mitochondrial uncoupling protein 2 expression and AMP/ATP ratio, leading to the activation of AMPK and culminating in enhanced oxidative metabolism in both liver and adipose tissue. Moreover, guar gum markedly increased peripheral glucose clearance, possibly mediated by the SCFA-induced colonic hormone glucagon-like peptide-1. Overall, this study provides novel molecular insights into the beneficial effects of guar gum on the metabolic syndrome and strengthens the potential role of guar gum as a dietary-fiber intervention

Whole-body vibration partially reverses aging-induced increases in visceral adiposity and hepatic lipid storage in mice

At old age, humans generally have declining muscle mass and increased fat deposition, which can increase the risk of developing cardiometabolic diseases. While regular physical activity postpones these age-related derangements, this is not always possible in the elderly because of disabilities or risk of injury. Whole-body vibration (WBV) training may be considered as an alternative to physical activity particularly in the frail population. To explore this possibility, we characterized whole-body and organ-specific metabolic processes in 6-month and 25-month old mice, over a period of 14 weeks of WBV versus sham training. WBV training tended to increase blood glucose turnover rates and stimulated hepatic glycogen utilization during fasting irrespective of age. WBV was effective in reducing white fat mass and hepatic triglyceride content only in old but not in young mice and these reductions were related to upregulation of hepatic mitochondrial uncoupling of metabolism (assessed by high-resolution respirometry) and increased expression of uncoupling protein 2. Because these changes occurred independent of changes in food intake and whole-body metabolic rate (assessed by indirect calorimetry), the liver-specific effects of WBV may be a primary mechanism to improve metabolic health during aging, rather than that it is a consequence of alterations in energy balance

Distal lower limb strength is reduced in subjects with impaired glucose tolerance and is related to elevated intramuscular fat level and vitamin D deficiency.

AIM: To quantify muscle strength and size in subjects with impaired glucose tolerance (IGT) in relation to intramuscular non-contractile tissue, the severity of neuropathy and vitamin D level. METHODS: A total of 20 subjects with impaired glucose tolerance and 20 control subjects underwent assessment of strength and size of knee extensor, flexor and ankle plantar and dorsi-flexor muscles, as well as quantification of intramuscular non-contractile tissue and detailed assessment of neuropathy and serum 25-hydroxy vitamin D levels. RESULTS: In subjects with impaired glucose tolerance, proximal knee extensor strength (P=0.17) and volume (P=0.77), and knee flexor volume (P=0.97) did not differ from those in control subjects. Ankle plantar flexor strength was significantly lower (P=0.04) in the subjects with impaired glucose tolerance, with no difference in ankle plantar flexor (P=0.62) or dorsiflexor volume (P=0.06) between groups. Intramuscular non-contractile tissue level was significantly higher in the ankle plantar flexors and dorsiflexors (P=0.03) of subjects with impaired glucose tolerance compared with control subjects, and it correlated with the severity of neuropathy. Ankle plantar flexor muscle strength correlated significantly with corneal nerve fibre density (r= 0.53; P=0.01), a sensitive measure of small fibre neuropathy, and was significantly lower in subjects with vitamin D deficiency (P=0.02). CONCLUSIONS: People with impaired glucose tolerance have a significant reduction in distal but not proximal leg muscle strength, which is not associated with muscle atrophy, but with increased distal intramuscular non-contractile tissue, small fibre neuropathy and vitamin D deficiency. This article is protected by copyright. All rights reserved