Key points• Several biochemical measures of mitochondrial components are used as biomarkers of mitochondrial content and muscle oxidative capacity. However, no studies have validated these surrogates against a morphological measure of mitochondrial content in human subjects.• The most commonly used markers (citrate synthase activity, cardiolipin content, mitochondrial DNA content (mtDNA), complex I-V protein, and complex I-IV activity) were correlated with a measure of mitochondrial content (transmission electron microscopy) and muscle oxidative capacity (respiration in permeabilized fibres).• Cardiolipin content followed by citrate synthase activity and complex I activity were the biomarkers showing the strongest association with mitochondrial content.• mtDNA was found to be a poor biomarker of mitochondrial content.• Complex IV activity was closely associated with mitochondrial oxidative phosphorylation capacity.Abstract Skeletal muscle mitochondrial content varies extensively between human subjects. Biochemical measures of mitochondrial proteins, enzyme activities and lipids are often used as markers of mitochondrial content and muscle oxidative capacity (OXPHOS). The purpose of this study was to determine how closely associated these commonly used biochemical measures are to muscle mitochondrial content and OXPHOS. Sixteen young healthy male subjects were recruited for this study. Subjects completed a graded exercise test to determine maximal oxygen uptake (V O 2 peak ) and muscle biopsies were obtained from the vastus lateralis. Mitochondrial content was determined using transmission electron microscopy imaging and OXPHOS was determined as the maximal coupled respiration in permeabilized fibres. Biomarkers of interest were citrate synthase (CS) activity, cardiolipin content, mitochondrial DNA content (mtDNA), complex I-V protein content, and complex I-IV activity. Spearman correlation coefficient tests and Lin's concordance tests were applied to assess the absolute and relative association between the markers and mitochondrial content or OXPHOS. Subjects had a large range ofV O 2 peak (range 29.9-71.6 ml min −1 kg −1 ) and mitochondrial content (4-15% of cell volume). Cardiolipin content showed the strongest association with mitochondrial content followed by CS and complex I activities. mtDNA was not related to mitochondrial content. Complex IV activity showed the strongest association with muscle oxidative capacity followed by complex II activity. We conclude that cardiolipin content, and CS and complex I activities are the biomarkers that exhibit the strongest association with mitochondrial content, while complex IV activity is strongly associated with OXPHOS capacity in human skeletal muscle.

This study investigates the toxicity of cationic micelles and liposomes utilized as nanocarriers in gene and drug delivery, demonstrating its effects on the lungs, spleen and liver.

Aim/hypothesis The aim of the study was to investigate mitochondrial function, fibre type distribution and substrate oxidation in arm and leg muscle during exercise in patients with type 2 diabetes and in obese and lean controls. Methods Indirect calorimetry was used to calculate fat and carbohydrate oxidation during both progressive arm-cranking and leg-cycling exercises. Muscle biopsies from arm and leg were obtained. Fibre type, as well as O 2 flux capacity of saponin-permeabilised muscle fibres were measured, the latter by high resolution respirometry, in patients with type 2 diabetes, age-and BMI-matched obese controls, and agematched lean controls. Results Fat oxidation was similar in the groups during either arm or leg exercise. During leg exercise at higher intensities, but not during arm exercise, carbohydrate oxidation was lower in patients with type 2 diabetes compared with the other groups. In patients with type 2 diabetes, ADP-stimulated state 3 respiration per mg muscle with parallel electron input from complex I+II was lower in m. vastus lateralis compared with obese and lean controls, whereas no differences between groups were present in m. deltoideus. A higher percentage of type IIX fibres was seen in m. vastus lateralis in patients with type 2 diabetes compared with obese and lean controls, whereas no difference was found in the deltoid muscle. Conclusions/interpretation This study demonstrates similar O 2 flux capacity, fibre type distribution and carbohydrate oxidation in arm muscle in the groups despite the presence of attenuated values in leg muscle in patients with type 2 diabetes compared with obese and lean controls.

Mito increased with 55 ± 9% (P < 0.001), whereas the number of mitochondrial profiles per area of skeletal muscle remained unchanged following training. Citrate synthase activity (CS) increased (44 ± 12%, P < 0.001); however, there were no functional changes in oxidative phosphorylation capacity (OXPHOS, CI+II ) or cytochrome c oxidase (COX) activity. Correlations were found between Mito and CS (P = 0.01; r = 0.58), OXPHOS, CI+CIIP (P = 0.01; R = 0.58) and COX (P = 0.02; R = 0.52) before training; after training, a correlation was found between Mito and CS activity only (P = 0.04; R = 0.49). Intrinsic respiratory capacities decreased (P < 0.05) with training when respiration was normalized to Mito This was not the case when normalized to CS activity although the percentage change was comparable CONCLUSIONS: Mito was increased by inducing mitochondrial enlargement rather than de novo biogenesis. CS activity may be appropriate to track training-induced changes in Mito

The effect of the insulinotropic incretin hormone, glucagon-like peptide-1 (GLP-1), is preserved in typical middle-aged, obese, insulin-resistant type 2 diabetic patients, whereas a defective amplification of the so-called late-phase plasma insulin response (20-120 min) to glucose by the other incretin hormone, glucose-dependent insulinotropic polypeptide (GIP), is seen in these patients. The aim of the present investigation was to evaluate plasma insulin and C-peptide responses to GLP-1 and GIP in five groups of diabetic patients with etiology and phenotype distinct from the obese type 2 diabetic patients. We studied (six in each group): 1) patients with diabetes mellitus secondary to chronic pancreatitis; 2) lean type 2 diabetic patients (body mass index < 25 kg/m(2)); 3) patients with latent autoimmune diabetes in adults; 4) diabetic patients with mutations in the HNF-1alpha gene [maturity-onset diabetes of the young (MODY)3]; and 5) newly diagnosed type 1 diabetic patients. All participants underwent three hyperglycemic clamps (2 h, 15 mM) with continuous infusion of saline, 1 pmol GLP-1 (7-36)amide/kg body weight.min or 4 pmol GIP pmol/kg body weight.min. The early-phase (0-20 min) plasma insulin response tended to be enhanced by both GIP and GLP-1, compared with glucose alone, in all five groups. In contrast, the late-phase (20-120 min) plasma insulin response to GIP was attenuated, compared with the plasma insulin response to GLP-1, in all five groups. Significantly higher glucose infusion rates were required during the late phase of the GLP-1 stimulation, compared with the GIP stimulation. In conclusion, lack of GIP amplification of the late-phase plasma insulin response to glucose seems to be a consequence of diabetes mellitus, characterizing most, if not all, forms of diabetes.