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

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

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

Mouse Studies to Shape Clinical Trials for Mitochondrial Diseases: High Fat Diet in Harlequin Mice

BACKGROUND: Therapeutic options in human mitochondrial oxidative phosphorylation (OXPHOS) diseases have been poorly evaluated mostly because of the scarcity of cohorts and the inter-individual variability of disease progression. Thus, while a high fat diet (HFD) is often recommended, data regarding efficacy are limited. Our objectives were 1) to determine our ability to evaluate therapeutic options in the Harlequin OXPHOS complex I (CI)-deficient mice, in the context of a mitochondrial disease with human hallmarks and 2) to assess the effects of a HFD. METHODS AND FINDINGS: Before launching long and expensive animal studies, we showed that palmitate afforded long-term death-protection in 3 CI-mutant human fibroblasts cell lines. We next demonstrated that using the Harlequin mouse, it was possible to draw solid conclusions on the efficacy of a 5-month-HFD on neurodegenerative symptoms. Moreover, we could identify a group of highly responsive animals, echoing the high variability of the disease progression in Harlequin mice. CONCLUSIONS: These results suggest that a reduced number of patients with identical genetic disease should be sufficient to reach firm conclusions as far as the potential existence of responders and non responders is recognized. They also positively prefigure HFD-trials in OXPHOS-deficient patients

Application of modular control analysis to inhibition of the adenine nucleotide translocator by palmitoyl-CoA.

Modular kinetic analysis was used to characterize inhibition of adenine nucleotide translocation by palmitoyl-CoA in isolated rat-liver mitochondria. To this purpose, oxidative phosphorylation has been divided into two modules with the fraction of matrix ATP as linking intermediate. The adenine nucleotide translocator is the matrix ATP-consuming module and the remainder of oxidative phosphorylation (ATP synthesis, respiratory chain and transport of phosphates and respiratory substrate) is the matrix ATP-producing module. We found that palmitoyl-CoA inhibits ATP-consuming module (ANT) and has no effect on ATP-producing module. There were no significant differences between kinetic curves obtained with oligomycin and myxothiazol, inhibitors that have opposite effect on membrane potential, suggesting that the use of the fraction of matrix ATP as the only intermediate is a good approximation. A new method has been used to determine the fraction of ATP in the mitochondrial matrix