OBJECTIVE— Blockade of angiotensin (Ang) II has been shown to prevent new-onset type 2 diabetes. We focused on the effects of AngII on muscle mitochondria, especially on their biogenesis, as an underlining mechanism of type 2 diabetes. RESEARCH DESIGN AND METHODS— C2C12 cells and C57bl/6 mice were used to examine roles for AngII in the regulation of muscle mitochondria and to explore whether the effect was mediated by type 1 AngII receptor (AT1R) or type 2 receptor (AT2R). RESULTS— C2C12 cells treated with 10 −8 –10 −6 mol/l AngII reduced the mitochondrial content associated with downregulation of the genes involved in mitochondrial biogenesis. The action of AngII was diminished by blockade of AT2R but not AT1R, whereas overexpression of AT2R augmented the effect. AngII increased mitochondrial ROS and decreased mitochondrial membrane potential, and these effects of AngII were significantly suppressed by blockade of either AT1R or AT2R. Chronic AngII infusion in mice also reduced muscle mitochondrial content in association with increased intramuscular triglyceride and deteriorated glycemic control. The AngII-induced reduction in muscle mitochondria in mice was partially, but significantly, reversed by blockade of either AT1R or AT2R, associated with increased fat oxidation, decreased muscle triglyceride, and improved glucose tolerance. Genes involved in mitochondrial biogenesis were decreased via AT2R but not AT1R under these in vivo conditions. CONCLUSIONS— Taken together, these findings imply the novel roles for AngII in the regulation of muscle mitochondria and lipid metabolism. AngII reduces mitochondrial content possibly through AT1R-dependent augmentation of their degradation and AT2R-dependent direct suppression of their biogenesis.

Statins are cholesterol-lowering drugs widely used in the prevention of cardiovascular diseases; however, they are associated with various types of myopathies. Statins inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase and thus decrease biosynthesis of low-density lipoprotein cholesterol and may also reduce ubiquinones, essential coenzymes of a mitochondrial electron transport chain, which contain isoprenoid residues, synthesized through an HMG-CoA reductase-dependent pathway. Therefore, we hypothesized that statin treatment might influence physical performance through muscular mitochondrial dysfunction due to ubiquinone deficiency. The effect of two statins, atorvastatin and pravastatin, on ubiquinone content, mitochondrial function, and physical performance was examined by using statin-treated mice. Changes in energy metabolism in association with statin treatment were studied by using cultured myocytes. We found that atorvastatin-treated mice developed muscular mitochondrial dysfunction due to ubiquinone deficiency and a decrease in exercise endurance without affecting muscle mass and strength. Meanwhile, pravastatin at ten times higher dose of atorvastatin had no such effects. In cultured myocytes, atorvastatin-related decrease in mitochondrial activity led to a decrease in oxygen utilization and an increase in lactate production. Conversely, coenzyme Q(10) treatment in atorvastatin-treated mice reversed atorvastatin-related mitochondrial dysfunction and a decrease in oxygen utilization, and thus improved exercise endurance. Atorvastatin decreased exercise endurance in mice through mitochondrial dysfunction due to ubiquinone deficiency. Ubiquinone supplementation with coenzyme Q(10) could reverse atorvastatin-related mitochondrial dysfunction and decrease in exercise tolerance.

Recently, sarcopenia has attracted attention as therapeutic target because it constitutes a risk factor for metabolic and cardiovascular diseases. We focused 5-aminolevulinic acid (ALA) which act as electron carriers in the mitochondrial electron transport system. The mice that received ALA for 8 weeks gained muscle strength and endurance, and exhibited increased muscle mass and mitochondrial amount. Administration of ALA to sarcopenia mice aged 100 weeks and chronic kidney disease (CKD) model mice also increased muscle mass and improved physical performance. Metabolome analysis revealed increased branched-chain amino acids (BCAAs) levels in the skeletal muscle of ALA-treated mice. Quantitative PCR analysis revealed decreased expression levels in branched-chain amino acid transaminases (BCATs) that degrade BCAAs and other muscle-degrading factors, and increased levels of mitochondria-activating factors. We also studied in cultured myocytes and obtained compatible results. ALA-treated mice tended to increase body weight, but reduced blood glucose level. These suggested that ALA treatment not only activated muscle mitochondria but also enhanced muscle mass through an increase in BCAAs contents, as to improve muscle strength, endurance and glucose tolerance in mice. In these ways, muscle mitochondrial activation with ALA is suggested to be useful for the treatment of sarcopenia and glucose intolerance.

Because a physical decline correlates with an increased risk of a wide range of disease and morbidity, an improvement of physical performance is expected to bring significant clinical benefits. The primary cause of physical decline in 5/6 nephrectomized (5/6Nx) chronic kidney disease model mice has been regarded as a decrease in muscle mass; however, our recent study showed that a decrease in muscle mitochondria plays a critical role. In the present study, we examined the effects of a gastric hormone ghrelin, which has been reported to promote muscle mitochondrial oxidation, on the physical decline in the chronic kidney disease model mice, focusing on the epigenetic modulations of a mitochondrial activator gene, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). Ghrelin treatment improved a decline in exercise endurance of 5/6Nx mice, associated with an increase in both of the muscle mass and mitochondrial amount. The expression level of PGC-1α was decreased in the skeletal muscle of 5/6Nx mice, which was associated with an increase in the methylation ratio of the cytosine residue at 260 base pairs upstream of the initiation point. Conversely, ghrelin treatment de-methylated the cytosine residue and increased the expression of PGC-1α. A representative muscle anabolic factor, IGF-1, did not affect the expression of PGC-1α and muscle mitochondrial amount, although it increased muscle mass. As a result, IGF-1 treatment in 5/6Nx mice did not increase the decreased exercise endurance as effectively as ghrelin treatment did. These findings indicate an advantage of ghrelin treatment for a recovery of physical decline.

UnfortUnately suicidal insulin overdose often occurs in patients with mental illness [1]. Insulin overdose results in prolonged hypoglycemia. Since there is no appropriate marker to estimate the recovery time from hypoglycemia, prolonged hypoglycemia often persists after stopping glucose supplementation. Here we hypothesized that if a huge amount of insulin is injected, the duration of hypoglycemia depends on the dose of insulin rather than the type of insulin, and provide an equation for the correlation between insulin dose and recovery time from hypoglycemia. research Design and MethodsWe conducted a literature review of Japanese cases of insulin overdose using PubMed and Ichushi web (Japana Centra Revuo Medicina). We identified 43 cases of insulin overdose. Among them, we excluded 9 cases in which the injected insulin dose and/or recovery time from hypoglycemia was not available. We also excluded 2 cases that had been receiving hemodi- abstract. Insulin overdose results in prolonged hypoglycemia. We hypothesized that if a huge amount of insulin is subcutaneously injected, the duration of hypoglycemia depends on the dose of insulin rather than the type of insulin. We conducted a literature review of insulin overdose and 33 cases were included in this study. We assessed the correlation between recovery time from hypoglycemia and insulin dose. As a result, there was a significant correlation between recovery time from hypoglycemia and insulin dose (r = 0.88, p <0.0001) and this correlation was expressed as y = 0.045x; where y is time (h) and x is insulin dose (U), corresponding to that if 1000 U insulin is injected, hypoglycemia will persist for ~45 h. This equation may be useful to predict the duration of glucose supplementation for treatment of insulin overdose.

Mitsuishi M, Miyashita K, Muraki A, Tamaki M, Tanaka K, Itoh H. Dietary protein decreases exercise endurance through rapamycin-sensitive suppression of muscle mitochondria. Am J Physiol Endocrinol Metab 305: E776 -E784, 2013. First published July 23, 2013; doi:10.1152/ajpendo.00145.2013.-Loss of physical performance is linked not only to decreased activity in daily life but also to increased onset of cardiovascular diseases and mortality. A highprotein diet is recommended for aged individuals in order to preserve muscle mass; however, the regulation of muscle mitochondria by dietary protein has not been clarified. We investigated the long-term effects of a high-protein diet on muscle properties, focusing especially on muscle mitochondria. Mice were fed a high-protein diet from the age of 8 wk and examined for mitochondrial properties and exercise endurance at the ages of 20 and 50 wk. Compared with normal chow, a high-protein diet significantly decreased the amount of muscle mitochondria, mitochondrial activity, and running distance at 50 wk, although it increased muscle mass and grip power. Inhibition of TORC1-dependent signal pathways by rapamycin from 8 wk suppressed the decline in mitochondria and exercise endurance observed when mice were fed the high-protein diet in association with preserved AMPK activity. Collectively, these findings suggest a role for dietary protein as a suppressor of muscle mitochondria and indicate that the age-associated decline in exercise endurance might be accelerated by excessive dietary protein through rapamycin-sensitive suppression of muscle mitochondria. skeletal muscle mass; muscle mitochondria; physical performance; exercise endurance; TORC1; AMPK; rapamycin MAINTENANCE OF PHYSICAL PERFORMANCE is essential for a healthy life, especially among the elderly. The loss of muscle mass associated with aging, termed sarcopenia, is known to predict a wide range of diseases and morbidity. Sarcopenic individuals suffer from increased risk of falls and fractures and, as a result, a 1.5 to 4.6-fold higher risk of loss of independence compared with those with a normal volume of muscle mass (19,35). Moreover, inactive individuals are at higher risk of coronary heart diseases and all-cause mortality (4,5,7,22,33,38), and the relative risk for coronary heart diseases is reported to be similar between inactivity and smoking, hypertension, or dyslipidemia (16).The age-associated change in muscle is not limited to a decrease in muscle volume; the amount of muscle mitochondria decreases with aging (30, 37). Because skeletal muscle consumes 40% of total energy intake and plays a vital role in whole body energy homeostasis (12, 47), the age-associated reduction in mitochondrial amount and function in skeletal muscle is likely to contribute to an age-associated decline in physical activity, and the development of obesity and diabetes in the elderly, through dysregulation of energy homeostasis (31, 32, 34). Unlike obesity or osteoporosis, however, muscle aging is not recognized as a pathological ...

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