Dietary troglitazone decreases oxidative stress in early stage type II diabetic rats

Oxidative stress is involved in the initiation and development of atherosclerosis in diabetes. We tested the hypothesis that oxidative stress is already increased in early stage type II diabetes, and that troglitazone may prevent the increase. Three groups of 20 week old rats were studied: untreated Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as an animal model of type II diabetes, OLETF rats treated with troglitazone, and control Long-Evans Tokushima Otsuka (LETO) rats. Plasma lipid hydroperoxides (LOOH) concentration, as an indication of lipid peroxidation, and superoxide dismutase (SOD) activity in the thoracic aorta were measured. Plasma LOOH concentration was significantly higher in non-treated OLETF rats compared to LETO rats and treatment with troglitazone completely prevented this increase. SOD activity was significantly decreased in non-treated OLETF rats compared to LETO rats and troglitazone attenuated the diminution of it. These observations demonstrate oxidative stress is already increased in the early stage of type II diabetes and we confirmed troglitazone has the effect of an antioxidant in vivo.     

Exercise training increases oxidative capacity and attenuates exercise-induced ultrastructural damage in skeletal muscle of aged horses.

Exercise training improves functional capacity in aged individuals. Whether such training reduces the severity of exercise-induced muscle damage is unknown. The purpose of the present study was to determine the effect of 10 wk of treadmill exercise training on skeletal muscle oxidative capacity and exercise-induced ultrastructural damage in six aged female Quarter horses (>23 yr of age). The magnitude of ultrastructural muscle damage induced by an incremental exercise test before and after training was determined by electron microscopic examination of samples of triceps, semimembranosus, and masseter (control) muscles. Maximal aerobic capacity increased 22% after 10 wk of exercise training. The percentage of type IIa myosin heavy chain increased in semimembranosus muscle, whereas the percentage of type IIx myosin heavy chain decreased in triceps muscle. After training, triceps muscle showed significant increases in activities of both citrate synthase and 3-hydroxyacyl-CoA-dehydrogenase. Attenuation of exercise-induced ultrastructural muscle damage occurred in the semimembranosus muscle at both the same absolute and the same relative workloads after the 10-wk conditioning period. We conclude that aged horses adapt readily to intense aerobic exercise training with improvements in endurance, whole body aerobic capacity, and muscle oxidative capacity, and heightened resistance to exercise-induced ultrastructural muscle cell damage. However, adaptations may be muscle-group specific.     

Exercise protects against doxorubicin-induced oxidative stress and proteolysis in skeletal muscle

Doxorubicin (Dox) is a potent antitumor agent used in cancer treatment. Unfortunately, Dox is myotoxic and results in significant reductions in skeletal muscle mass and function. Complete knowledge of the mechanism(s) by which Dox induces toxicity in skeletal muscle is incomplete, but it is established that Dox-induced toxicity is associated with increased generation of reactive oxygen species and oxidative damage within muscle fibers. Since muscular exercise promotes the expression of numerous cytoprotective proteins (e.g., antioxidant enzymes, heat shock protein 72), we hypothesized that muscular exercise will attenuate Dox-induced damage in exercise-trained muscle fibers. To test this postulate, Sprague-Dawley rats were randomly assigned to the following groups: sedentary, exercise, sedentary with Dox, or exercise with Dox. Our results show increased oxidative stress and activation of cellular proteases (calpain and caspase-3) in skeletal muscle of animals treated with Dox. Importantly, our findings reveal that exercise can prevent the Dox-induced oxidative damage and protease activation in the trained muscle. This exercise-induced protection against Dox-induced toxicity may be due, at least in part, to an exercise-induced increase in muscle levels of antioxidant enzymes and heat shock protein 72. Together, these novel results demonstrate that muscular exercise is a useful countermeasure that can protect skeletal muscle against Dox treatment-induced oxidative stress and protease activation in skeletal muscles.     

Elevated expression and activity of protein-tyrosine phosphatase 1B in skeletal muscle of insulin-resistant type II diabetic Goto-Kakizaki rats

We investigated the cellular mechanism(s) of insulin resistance associated with non-insulin dependent diabetes mellitus (NIDDM) using skeletal muscles isolated from non-obese, insulin resistant type II diabetic Goto-Kakizaki (GK) rats, a well known genetic rat model for type II diabetic humans. Relative to non-diabetic control rats (WKY), insulin-stimulated insulin receptor (IR) autophosphorylation and insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation were significantly inhibited in GK skeletal muscles. This may be due to increased dephosphorylation by a protein tyrosine phosphatase (PTPase). Therefore, we measured skeletal muscle total PTPase and PTPase 1B activities in the skeletal muscles isolated from control rats (WKY) and diabetic Goto-Kakizaki (GK) rats. PTPase activity was measured using a synthetic phosphopeptide, TRDIY(P)ETDY(P)Y(P)RK, as the substrate. Basal PTPase activity was 2-fold higher (P < 0.001) in skeletal muscle of GK rats when compared to WKY. Insulin infusion inhibited skeletal muscle PTPase activity in both control (26.20% of basal, P < 0.001) and GK (25.35% of basal, P < 0.001) rats. However, PTPase activity in skeletal muscle of insulin-stimulated GK rats was 200% higher than hormone-treated WKY controls (P < 0.001). Immunoprecipitation of PTPase 1B from skeletal muscle lysates and analysis of the enzyme activity in immunoprecipitates indicated that both basal and insulin-stimulated PTPase 1B activities were significantly higher (twofold, P < 0.001) in skeletal muscle of diabetic GK rats when compared to WKY controls. The increase in PTPase 1B activity in diabetic GK rats was associated with an increased expression of the PTPase 1B protein. We concluded that insulin resistance of GK rats is accompanied atleast by an abnormal regulation of PTPase 1B. Elevated PTPase 1B activity through enhanced tyrosine dephosphorylation of the insulin receptor and its substrates, may lead to impaired glucose tolerance and insulin resistance in GK rats.     

Taurine supplementation decreases oxidative stress in skeletal muscle after eccentric exercise

Infrequent exercise, typically involving eccentric actions, has been shown to cause oxidative stress and to damage muscle tissue. High taurine levels are present in skeletal muscle and may play a role in cellular defences against free radical‐mediated damage. This study investigates the effects of taurine supplementation on oxidative stress biomarkers after eccentric exercise (EE). Twenty‐four male rats were divided into the following groups (n = 6): control; EE; EE plus taurine (EE + Taurine); EE plus saline (EE + Saline). Taurine was administered as a 1‐ml 300 mg kg^?1 per body weight (BW) day^?1 solution in water by gavage, for 15 consecutive days. Starting on the 14th day of supplementation, the animals were submitted to one 90‐min downhill run session and constant velocity of 1·0 km h^?1. Forty‐eight hours after the exercise session, the animals were killed and the quadriceps muscles were surgically removed. Production of superoxide anion, creatine kinase (CK) levels, lipoperoxidation, carbonylation, total thiol content and antioxidant enzyme were analysed. Taurine supplementation was found to decrease superoxide radical production, CK, lipoperoxidation and carbonylation levels and increased total thiol content in skeletal muscle, but it did not affect antioxidant enzyme activity after EE. The present study suggests that taurine affects skeletal muscle contraction by decreasing oxidative stress, in association with decreased superoxide radical production. Copyright © 2010 John Wiley & Sons, Ltd.     

Exercise training prevents oxidative stress and ubiquitin-proteasome system overactivity and reverse skeletal muscle atrophy in heart failure

Background

Heart failure (HF) is known to lead to skeletal muscle atrophy and dysfunction. However, intracellular mechanisms underlying HF-induced myopathy are not fully understood. We hypothesized that HF would increase oxidative stress and ubiquitin-proteasome system (UPS) activation in skeletal muscle of sympathetic hyperactivity mouse model. We also tested the hypothesis that aerobic exercise training (AET) would reestablish UPS activation in mice and human HF.

Methods/Principal Findings

Time-course evaluation of plantaris muscle cross-sectional area, lipid hydroperoxidation, protein carbonylation and chymotrypsin-like proteasome activity was performed in a mouse model of sympathetic hyperactivity-induced HF. At the 7^th month of age, HF mice displayed skeletal muscle atrophy, increased oxidative stress and UPS overactivation. Moderate-intensity AET restored lipid hydroperoxides and carbonylated protein levels paralleled by reduced E3 ligases mRNA levels, and reestablished chymotrypsin-like proteasome activity and plantaris trophicity. In human HF (patients randomized to sedentary or moderate-intensity AET protocol), skeletal muscle chymotrypsin-like proteasome activity was also increased and AET restored it to healthy control subjects’ levels.

Conclusions

Collectively, our data provide evidence that AET effectively counteracts redox imbalance and UPS overactivation, preventing skeletal myopathy and exercise intolerance in sympathetic hyperactivity-induced HF in mice. Of particular interest, AET attenuates skeletal muscle proteasome activity paralleled by improved aerobic capacity in HF patients, which is not achieved by drug treatment itself. Altogether these findings strengthen the clinical relevance of AET in the treatment of HF.     

Chromium picolinate attenuates hyperglycemia-induced oxidative stress in streptozotocin-induced diabetic rats

Chromium picolinate is advocated as an anti-diabetic agent for impaired glycemic control. It is a transition metal that exists in various oxidation states and may thereby act as a pro-oxidant. The present study has been designed to examine the effect of chromium picolinate supplementation on hyperglycemia-induced oxidative stress. Diabetes was induced in male Wistar rats by a single intraperitoneal injection of streptozotocin (50 mg/kg body weight) and chromium was administered orally as chromium picolinate (1 mg/kg body weight) daily for a period of four weeks after the induction of diabetes. As is characteristic of diabetic condition, hyperglycemia was associated with an increase in oxidative stress in liver in terms of increased lipid peroxidation and decreased glutathione levels. The activity of antioxidant enzymes like superoxide dismutase, catalase and glutathione reductase were significantly reduced in liver of diabetic animals. Levels of α-tocopherol and ascorbic acid were found to be considerably lower in plasma of diabetic rats. Chromium picolinate administration on the other hand was found to have beneficial effect in normalizing glucose levels, lipid peroxidation and antioxidant status. The results from the present study demonstrate potential of chromium picolinate to attenuate hyperglycemia-induced oxidative stress in experimental diabetes.     

Heat stress attenuates skeletal muscle atrophy in hindlimb-unweighted rats.

This study tested the hypothesis that elevation of heat stress proteins by whole body hyperthermia is associated with a decrease in skeletal muscle atrophy induced by reduced contractile activity (i.e. , hindlimb unweighting). Female adult rats (6 mo old) were assigned to one of four experimental groups (n = 10/group): 1) sedentary control (Con), 2) heat stress (Heat), 3) hindlimb unweighting (HLU), or 4) heat stress before hindlimb unweighting (Heat+HLU). Animals in the Heat and Heat+HLU groups were exposed to 60 min of hyperthermia (colonic temperature approximately 41.6 degrees C). Six hours after heat stress, both the HLU and Heat+HLU groups were subjected to hindlimb unweighting for 8 days. After hindlimb unweighting, the animals were anesthetized, and the soleus muscles were removed, weighed, and analyzed for protein content and the relative levels of heat shock protein 72 (HSP72). Compared with control and HLU animals, the relative content of HSP72 in the soleus muscle was significantly elevated (P < 0.05) in both the Heat and Heat+HLU animals. Although hindlimb unweighting resulted in muscle atrophy in both the HLU and Heat+HLU animals, the loss of muscle weight and protein content was significantly less (P < 0.05) in the Heat+HLU animals. These data demonstrate that heat stress before hindlimb unweighting can reduce the rate of disuse muscle atrophy. We postulate that HSP70 and/or other stress proteins play a role in the control of muscle atrophy induced by reduced contractile activity.     

Exercise training increases ERK2 activity in skeletal muscle of obese Zucker rats.

Acute exercise and training increase insulin action in skeletal muscle, but the mechanism responsible for this effect is unknown. Activation of the insulin receptor initiates signaling through both the phosphatidylinositol (PI) 3-kinase and the mitogen-activated protein kinase [MAPK, also referred to as extracellular signal-regulated kinases (ERK1/2)] pathways. Acute exercise has no effect on the PI3-kinase pathway signaling elements but does activate the MAPK pathway, which may play a role in the adaptation of muscle to exercise. It is unknown whether training produces a chronic effect on basal activity or insulin response of the MAPK pathway. The present study was undertaken to determine whether exercise training improves the activity of the MAPK pathway or its response to insulin in obese Zucker rats, a well-characterized model of insulin resistance. To accomplish this, obese Zucker rats were studied by using the hindlimb perfusion method with or without 7 wk of treadmill training. Activation of the MAPK pathway was determined in gastrocnemius muscles exposed in situ to insulin. Compared with lean Zucker rats, untrained obese Zucker rats had reduced basal and insulin-stimulated activities of ERK2 and its downstream target p90 ribosomal S6 kinase (RSK2). Seven weeks of training significantly increased basal and insulin-stimulated ERK2 and RSK2 activities, as well as insulin stimulation of MAPK kinase activity. This effect was maintained for at least 96 h in the case of ERK2. The training-induced increase in basal ERK2 activity was correlated with the increase in citrate synthase activity. Therefore, 7 wk of training increases basal and insulin-stimulated ERK2 activity. The increase in basal ERK2 activity may be related to the response of muscle to training.     

Exercise training increases branched-chain oxoacid dehydrogenase kinase content in human skeletal muscle

The branched-chain oxoacid dehydrogenase complex (BCOAD) is rate determining for the oxidation of branched-chain amino acids (BCAAs) in skeletal muscle. Exercise training blunts the acute exercise-induced activation of BCOAD (BCOADa) in human skeletal muscle (McKenzie S, Phillips SM, Carter SL, Lowther S, Gibala MJ, Tarnopolsky MA. Am J Physiol Endocrinol Metab 278: E580-E587, 2000); however, the mechanism is unknown. We hypothesized that training would increase the muscle protein content of BCOAD kinase, the enzyme responsible for inactivation of BCOAD by phosphorylation. Twenty subjects [23 +/- 1 yr; peak oxygen uptake (.VO(2peak)) = 41 +/- 2 ml.kg(-1).min(-1)] performed 6 wk of either high-intensity interval or continuous moderate-intensity training on a cycle ergometer (n = 10/group). Before and after training, subjects performed 60 min of cycling at 65% of pretraining .VO(2peak), and needle biopsy samples (vastus lateralis) were obtained before and immediately after exercise. The effect of training was demonstrated by an increased .VO(2peak), increased citrate synthase maximal activity, and reduced muscle glycogenolysis during exercise, with no difference between groups (main effects, P < 0.05). BCOADa was lower after training (main effect, P < 0.05), and this was associated with a approximately 30% increase in BCOAD kinase protein content (main effect, P < 0.05). We conclude that the increased protein content of BCOAD kinase may be involved in the mechanism for reduced BCOADa after exercise training in human skeletal muscle. These data also highlight differences in models used to study the regulation of skeletal muscle BCAA metabolism, since exercise training was previously reported to increase BCOADa during exercise and decrease BCOAD kinase content in rats (Fujii H, Shimomura Y, Murakami T, Nakai N, Sato T, Suzuki M, Harris RA. Biochem Mol Biol Int 44: 1211-1216, 1998).     

Ganoderma lucidum polysaccharides supplementation attenuates exercise-induced oxidative stress in skeletal muscle of mice

The present study was designed to determine the effects of Ganoderma lucidum polysaccharides (GL-PS) on exhaustive exercise-induced oxidative stress in skeletal muscle tissues of mice. The mice were divided into four groups (three GL-PS administered groups and the control group). The control group was administered with distilled water and GL-PS administered groups were administered with GL-PS (50, 100 and 200 mg/kg body weight per day). After 28 days, the mice performed an exhaustive swimming exercise, along with the determination of superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT) activities and malondialdehyde (MDA) levels in the skeletal muscle of mice. The results showed that GL-PS could increase antioxidant enzymes activities and decrease the MDA levels in the skeletal muscle of mice. This study provides strong evidence that GL-PS supplementation possessed protective effects against exhaustive exercise-induced oxidative stress.     

Hepatic expression of cytochrome P450 in type 2 diabetic Goto-Kakizaki rats

Although hepatic expression of cytochrome P450 (CYP) changes markedly in diabetes, the role of ketone bodies in the regulation of CYP in diabetes is controversial. The present study was performed to determine the expression and activity of CYP in non-obese type II diabetic Goto-Kakizaki (GK) rats with normal levels of ketone bodies. In the present study, basal serum glucose levels increased 1.95-fold in GK rats, but acetoacetate and β-hydroxybutyrate levels were not significantly different. Hepatic expression of CYP reductase and CYP3A2 was up-regulated in the GK rats, and consequently, activities of CYP reductase and midazolam 4-hydroxylase, mainly catalyzed by CYP3A2, increased. In contrast, hepatic expression of CYP1A2 and CYP3A1 was down-regulated and the activities of 7-ethoxyresorufin-O-deethylase and 7-methoxyresorufin-O-demethylase, mainly catalyzed by CYP1A, also decreased in GK rats. Hepatic levels of microsomal protein and total CYP and hepatic expression of cytochrome b(5), CYP1B1, CYP2B1 and CYP2C11 were not significantly different between the GK rats and normal Wistar rats. Moreover, the expression and activity of CYP2E1, reported to be up-regulated in diabetes with hyperketonemia, were not significantly different between GK rats and control rats, suggesting that elevation of ketone bodies plays a critical role in the up-regulation of hepatic CYP2E1 in diabetic rats. Our results showed that the expression of hepatic CYP is regulated in an isoform-specific manner. The present results also show that the GK rat is a useful animal model for the pathophysiological study of non-obese type II diabetes with normal ketone body levels.     

Shikonin increases glucose uptake in skeletal muscle cells and improves plasma glucose levels in diabetic Goto-Kakizaki rats

Background

There is considerable interest in identifying compounds that can improve glucose homeostasis. Skeletal muscle, due to its large mass, is the principal organ for glucose disposal in the body and we have investigated here if shikonin, a naphthoquinone derived from the Chinese plant Lithospermum erythrorhizon, increases glucose uptake in skeletal muscle cells.

Methodology/Principal Findings

Shikonin increases glucose uptake in L6 skeletal muscle myotubes, but does not phosphorylate Akt, indicating that in skeletal muscle cells its effect is medaited via a pathway distinct from that used for insulin-stimulated uptake. Furthermore we find no evidence for the involvement of AMP-activated protein kinase in shikonin induced glucose uptake. Shikonin increases the intracellular levels of calcium in these cells and this increase is necessary for shikonin-mediated glucose uptake. Furthermore, we found that shikonin stimulated the translocation of GLUT4 from intracellular vesicles to the cell surface in L6 myoblasts. The beneficial effect of shikonin on glucose uptake was investigated in vivo by measuring plasma glucose levels and insulin sensitivity in spontaneously diabetic Goto-Kakizaki rats. Treatment with shikonin (10 mg/kg intraperitoneally) once daily for 4 days significantly decreased plasma glucose levels. In an insulin sensitivity test (s.c. injection of 0.5 U/kg insulin), plasma glucose levels were significantly lower in the shikonin-treated rats. In conclusion, shikonin increases glucose uptake in muscle cells via an insulin-independent pathway dependent on calcium.

Conclusions/Significance

Shikonin increases glucose uptake in skeletal muscle cells via an insulin-independent pathway dependent on calcium. The beneficial effects of shikonin on glucose metabolism, both in vitro and in vivo, show that the compound possesses properties that make it of considerable interest for developing novel treatment of type 2 diabetes.