Role of Na+-K+-ATPase in insulin-induced lactate release by skeletal muscle.

Hyperinsulinemia increases lactate release by various organs and tissues. Whereas it has been shown that aerobic glycolysis is linked to Na+-K+-ATPase activity, we hypothesized that stimulation by insulin of skeletal muscle Na+-K+-ATPase is responsible for increased muscle lactate production. To test this hypothesis, we assessed muscle lactate release in healthy volunteers from the [13C]lactate concentration in the effluent dialysates of microdialysis probes inserted into the tibialis anterior muscles on both sides and infused with solutions containing 5 mmol/l [U-13C]glucose. On one side, the microdialysis probe was intermittently infused with the same solution additioned with 2.10(-5) M ouabain. In the basal state, [13C]lactate concentration in the dialysate was not affected by ouabain. During a euglycemic-hyperinsulinemic clamp, [13C]lactate concentration increased by 135% in the dialysate without ouabain, and this stimulation was nearly entirely reversed by ouabain (56% inhibition compared with values in the dialysate collected from the contralateral probe). These data indicate that insulin stimulates muscle lactate release by activating Na+-K+-ATPase in healthy humans

Hepatic de novo lipogenesis after liver transplantation.

BACKGROUND: The liver can synthesize fatty acids from carbohydrate (de novo lipogenesis [DNL]). We hypothesized that stimulation of this process may be involved in the development of obesity and dyslipidemia, 2 conditions frequently encountered after liver transplantation. METHODS: Hepatic fractional DNL and glucose metabolism were measured in 2 groups of 5 patients (age 36.8 +/- [SD] 14.9 years, BMI 26.3+/-5.3 kg/M2) 1 to 5 years after liver transplantation and 8 healthy subjects (age 28.1+/-5.3 years, BMI 27.2+/-4.5 kg/M2). Subjects were studied while receiving an isoenergetic nutrition (based on 1.1 x their basal energy expenditure) as hourly oral liquid formula during 10 hours. Their hepatic DNL was measured by infusing 1-13C acetate and measuring tracer incorporation in VLDL-palmitate. Their glucose metabolism was assessed by means of 6,6-2H2 glucose and indirect calorimetry. RESULTS: Two liver transplant recipients and 4 healthy subjects were obese, as defined by a BMI > 27 kg/M2. Fractional hepatic DNL was not different in the 2 groups of subjects: liver transplant recipients 3.1+/-1.7% vs 3.2+/-2.1% in healthy subjects. In both groups, DNL increased in proportion to BMI. When both groups were analyzed together, BMI was positively correlated with DNL (DNL = 0.28 x BMI - 4.28, r2 = .445, p < .05). Whole body glucose turnover was 15.0+/-4.4 micromol/kg per minute in liver transplant recipients and 15.8+/-4.1 micromol/kg per minute in healthy subjects (NS). Net carbohydrate oxidation tended to be lower in liver transplant recipients (8.1+/-2.6 micromol/kg per minute) than in healthy subjects (10.4+/-2.4 micromol/kg per minute; NS). Net nonoxidative glucose disposal (4.0+/-2.7 in liver transplant recipients vs 1.9+/-1.8 in healthy subjects, NS) and energy expenditure (0.065+/-0.01 vs 0.065+/-0.01 kJ/kg per minute) were similar in both groups. CONCLUSIONS: These results indicate that fractional hepatic DNL is not altered by liver transplantation during near continuous nutrition. The disposal of orally administered carbohydrate is also essentially unchanged. This strongly argues against a role of hepatic DNL in the pathogenesis of obesity and dyslipidemia after liver transplantation

Doxorubicin-induced cardiotoxicity — A key role of altered protein kinase signaling in the response to energetic, oxidative and genotoxic stress

Doxorubicin is one of the most powerful drugs used in chemotherapy of a large number of cancers. However, its anti-tumor effects are associated with serious cardiotoxicity, which can lead to heart failure. So far, mechanisms responsible for cardiotoxicity are not fully understood. Here we provide evidence that persistent alterations in protein kinase cell signaling may play a key role in the etiology of cardiotoxicity. In this study, we apply targeted analysis of key protein kinase pathways as well as non-biased analysis of the entire cardiac phosphoproteome in two different model systems: isolated perfused rat heart, and heart from doxorubicin-treated rats. Although doxorubicin induces energetic, oxidative and genotoxic stress in the heart, activity of the energy stress sensor AMP-activated protein kinase is paradoxically down-regulated. Pro-survival MAPK and Akt pathways are activated, the latter via DNA damage sensed by DNA-PK. This is at least partially responsible for low AMPK activity, since Akt inhibition can restore AMPK activation. Combined inhibition of AMPK and activation of Akt and MAPKs also leads to activation of growth-stimulating mTOR signaling. Such signalling increases cellular energy deficits and, via active mTOR signaling, also contributes to the pathological cardiac phenotype. Cardiac phosphoproteomics based on 2D-gels and mass spectrometry revealed further alterations of phosphorylation and dephosphorylation events that are associated with the early response to doxorubicin. Some candidate phosphoproteins with putative functions in cardiotoxicity are currently under investigation. This study emphasizes the importance of cell signaling for our understanding of doxorubicin cardiotoxicity

Tissue specificity of mitochondrial adaptations in rats after 4 weeks of normobaric hypoxia

Purpose Exposure to hypoxia has been suggested to activate multiple adaptive pathways so that muscles are better able to maintain cellular energy homeostasis. However, there is limited research regarding the tissue specificity of this response. The aim of this study was to investigate the influence of tissue specificity on mitochondrial adaptations of rat skeletal and heart muscles after 4 weeks of normobaric hypoxia (FiO2: 0.10). Methods Twenty male Wistar rats were randomly assigned to either normobaric hypoxia or normoxia. Mitochondrial respiration was determined in permeabilised muscle fibres from left and right ventricles, soleus and extensorum digitorum longus (EDL). Citrate synthase activity and the relative abundance of proteins associated with mitochondrial biogenesis were also analysed. Results After hypoxia exposure, only the soleus and left ventricle (both predominantly oxidative) presented a greater maximal mass-specific respiration (+48 and +25%, p \u3c 0.05) and mitochondrial-specific respiration (+75 and +28%, p \u3c 0.05). Citrate synthase activity was higher in the EDL (0.63 ± 0.08 vs 0.41 ± 0.10 μmol min− 1 μg− 1) and lower in the soleus (0.65 ± 0.17 vs 0.87 ± 0.20 μmol min− 1 μg− 1) in hypoxia with respect to normoxia. There was a lower relative protein abundance of PGC-1α (−25%, p \u3c 0.05) in the right ventricle and a higher relative protein abundance of PGC-1β (+43%, p \u3c 0.05) in the left ventricle of rats exposed to hypoxia, with few differences for protein abundance in the other muscles. Conclusion Our results show a muscle-specific response to 4 weeks of normobaric hypoxia. Depending on fibre type, and the presence of ventricular hypertrophy, muscles respond differently to the same degree of environmental hypoxia