L-leucine stimulation of glucose uptake and utilization involves modulation of glucose - lipid metabolic switch and improved bioenergetic homeostasis in isolated rat psoas muscle ex vivo.

The antidiabetic effect of l-leucine has been attributed to its modulatory effect on glucose uptake and lipid metabolism in muscles. However, there is a dearth on its effect on glucose metabolism in muscles. Thus, the present study investigated the effect of l-leucine - stimulated glucose uptake on glucose metabolism, dysregulated lipid metabolic pathways, redox and bioenergetic homeostasis, and proteolysis in isolated psoas muscle from Sprague Dawley male rats. Isolated psoas muscles were incubated with l-leucine (30-240 µg/mL) in the presence of 11.1 mMol glucose at 37 ˚C for 2 h. Muscles incubated in only glucose served as the control, while muscles not incubated in l-leucine and/or glucose served as the normal control. Metformin (6.04 mM) was used as the standard antidiabetic drug. Incubation with l-leucine caused a significant increase in muscle glucose uptake, with an elevation of glutathione levels, superoxide dismutase, catalase, E-NTPDase and 5'nucleotidase activities. It also led to the depletion of malondialdehyde and nitric oxide levels, ATPase, chymotrypsin, acetylcholinesterase, glycogen phosphorylase, glucose-6-phosphatase, fructose-1,6-bisphosphatase and lipase activities. There was an alteration in lipid metabolites, with concomitant activation of glycerolipid metabolism, fatty acid metabolism, and fatty acid elongation in mitochondria in the glucose-incubated muscle (negative control). Incubation with l-leucine reversed these alterations, and concomitantly deactivated the pathways. These results indicate that l-leucine-enhanced muscle glucose uptake involves improved redox and bioenergetic homeostasis, with concomitant suppressed proteolytic, glycogenolytic and gluconeogenetic activities, while modulating glucose - lipid metabolic switch.

Modulatory effects of Caralluma fimbriata extract against high-fat diet induced abnormalities in carbohydrate metabolism in Wistar rats.

The present study was aimed to evaluate the modulatory effects of hydroalcoholic extract of Caralluma fimbriata (CFE) by assaying the activities of key enzymes of carbohydrate metabolism and changes in glycogen content (liver and muscle) in high-fat (HF) diet-induced diabetic rats. In vitro glucose uptake studies were carried out in both psoas muscle and adipose tissue. The inhibitory effect of the extract on α-amylase was determined in in vitro studies. Male Wistar rats of body weight around 180g were divided into five groups (n=8), two of these groups were fed with standard pellet diet and the other three groups were fed with HF- (60%) diet. CFE (200mg/kg body weight/day) was administered through oral route to each group of standard pellet diet rats and HF-fed rats and Metformin (Met) (20mg/kg body weight/day) was administered through oral route to HFD+Met group for 90 days. At the end of the experimental period, biochemical parameters related to glycogen content in liver and muscle, and intestinal disaccharidases like maltase, sucrase and lactase were assayed. Alterations in the activities of enzymes of glucose metabolism (hexokinase, phosphorfructoki nase, pyruvate kinase, glucose-6-phosphatase, fructose-1,6-bisphosphatase, and glucose-6-phosphate dehydrogenase), intestinal disaccharidases and glycogen content as observed in the high fat diet-fed rats were prevented with CFE/Met administration. From this study, we observed that CFE/Met could significantly restore the levels of glycogen in liver and muscle and key enzymes of carbohydrate metabolism to near normal in groups-HFD+CFE and HFD+Met. The skeletal muscle of HF-diet fed rats showed degenerative changes of muscle myofibers with fat deposition. These changes were attenuated in the HFD group treated with CFE/Met and retained their normal structure appearance. It can be concluded from these results that CFE might be of value in reducing the alterations related to carbohydrate metabolism under high calorie diet consumption.

Myo-inositol inhibits intestinal glucose absorption and promotes muscle glucose uptake: a dual approach study.

The present study investigated the effects of myo-inositol on muscle glucose uptake and intestinal glucose absorption ex vivo as well as in normal and type 2 diabetes model of rats. In ex vivo study, both intestinal glucose absorption and muscle glucose uptake were studied in isolated rat jejunum and psoas muscle respectively in the presence of increasing concentrations (2.5 % to 20 %) of myo-inositol. In the in vivo study, the effect of a single bolus dose (1 g/kg bw) of oral myo-inositol on intestinal glucose absorption, blood glucose, gastric emptying and digesta transit was investigated in normal and type 2 diabetic rats after 1 h of co-administration with 2 g/kg bw glucose, when phenol red was used as a recovery marker. Myo-inositol inhibited intestinal glucose absorption (IC50 = 28.23 ± 6.01 %) and increased muscle glucose uptake, with (GU50 = 2.68 ± 0.75 %) or without (GU50 = 8.61 ± 0.55 %) insulin. Additionally, oral myo-inositol not only inhibited duodenal glucose absorption and reduced blood glucose increase, but also delayed gastric emptying and accelerated digesta transit in both normal and diabetic animals. Results of this study suggest that dietary myo-inositol inhibits intestinal glucose absorption both in ex vivo and in normal or diabetic rats and also promotes muscle glucose uptake in ex vivo condition. Hence, myo-inositol may be further investigated as a possible anti-hyperglycaemic dietary supplement for diabetic foods and food products.

Antihyperglycemic activity of Caralluma tuberculata in streptozotocin-induced diabetic rats.

The current study aimed at evaluating the potential and mechanisms of the antidiabetic activity of the methanolic extract (ME) of Caralluma tuberculata as well as its chloroform (CF), n-butanol (BF) and the remaining water fractions (RFs) in streptozotocin-induced diabetic rats. The antidiabetic activity was evaluated through assessing fasting blood glucose (FBG), insulin levels, oral glucose tolerance test (OGTT), glucose utilization by isolated rat psoas muscle, gut glucose absorption and G-6-Pase activity in isolated rat liver microsomes. Both ME and RF showed the highest potency, where ME had superior activity. The mechanism underlying the observed antihyperglycemic activity of ME could be attributed, at least in part, to enhanced skeletal muscle utilization of glucose, inhibition of hepatic gluconeogenesis and stimulation of insulin secretion. ME was standardized through LC-MS analysis for its major pregnanes.

Resistance exercise combined with essential amino acid supplementation improved walking ability in elderly people.

We investigated the effects of resistance exercise combined with essential amino acid supplementation on psoas major muscle (PMM) hypertrophy and walking ability in elderly individuals. Twenty-nine healthy elderly individuals were assigned to 3 groups: (1) E (exercise), (2) A3 (exercise combined with 3.0 g of essential amino acid supplementation), and (3) A6 (exercise combined with 6.0 g of essential amino acid supplementation). To evaluate walking ability, the participants underwent the following 3 types of tests: the (1) 10-meter walk (10-W), (2) 10-meter walk involving crossing of obstacles (10-W + O), and (3) 6-minute walk (6M-W) tests. The 6-month training program resulted in significant PMM hypertrophy in all groups independent of amino acid supplementation. The extent of hypertrophy in the participants who took amino acids was dose-dependent, although the differences were not significant. Groups A3 and A6 demonstrated improvements in the 10-W and 10-W + O tests, whereas no improvement was observed in group E, regardless of PMM hypertrophy. Furthermore, group A6 showed an improvement in the 6M-W test. These results suggest that our training program causes PMM hypertrophy, whereas the training program combined with essential amino acid supplementation improves walking ability.

Mechanisms of the antihyperglycemic activity of Retama raetam in streptozotocin-induced diabetic rats.

Retama raetam (RR) fruits are used in Saudi traditional medicine for the treatment of diabetes. Current study aimed at evaluating the potential and mechanisms of the antidiabetic activity of the RR methanolic extract in streptozotocin-induced diabetic rats. Oral LD(50) of the extract was found to be 1995 mg/kg. The extract was administered once orally to STZ-diabetic rats at three dose levels; 100, 250 or 500 mg/kg/day for 4 consecutive weeks. RR extract at 250 or 500 mg/kg significantly lowered blood glucose levels at the 3rd and 1st week of treatment, respectively. Meanwhile, oral glucose tolerance test indicated that the same two doses significantly lowered glucose levels at 30 and 60 min after glucose challenge. Administration of RR extract at 500 mg/kg/day for 4 consecutive weeks significantly increased serum insulin level. In vitro studies indicated that the extract significantly inhibits glucose absorption by rat isolated intestine. The extract neither altered glucose uptake by rat isolated psoas muscle nor the activity of hepatic microsomal glucose-6-phosphatase. In conclusion, the methanolic extract of RR improves STZ-induced diabetes in rats. This can be attributed, at least partly, to stimulating pancreatic insulin release and reducing intestinal glucose absorption.

Antioxidative and oxidative status in muscles of pigs fed rapeseed oil, vitamin E, and copper.

The susceptibility of a given muscle tissue to lipid oxidation may not only depend on the presence of unsaturated fatty acids and the balance between antioxidants and prooxidants, but also on the composition of the skeletal muscle. In the present study, the effects of dietary supplementation of vitamin E (dl-alpha-tocopheryl acetate) and copper in combination with a high level of monounsaturated fatty acids were examined with regard to the antioxidant concentration and the susceptibility to lipid oxidation of two muscles, longissimus (LD) and psoas major (PM), representing different oxidative capacity. In addition, fatty acid profiles of the backfat and the intramuscular lipids, as well as fresh meat quality traits, were studied. Pigs were allotted to a 3x3 factorial experiment with three levels of dl-alpha-tocopheryl acetate (0, 100, and 200 mg/kg of feed) and three levels of copper (0, 35, and 175 mg/kg of feed) added to a diet containing 6% rapeseed oil. A basal diet (without rapeseed oil) was added to the experimental design, giving a total of 10 dietary treatments. Muscle alpha-tocopherol concentrations increased (P<.001) with increasing dl-alpha-tocopheryl acetate in the feed. The antioxidative status was higher in PM than in LD, when considering the concentration of alpha-tocopherol (P<.001) and the activity of antioxidant enzymes (superoxide dismutase, P<.001; glutathione peroxidase, P = .06). Supplemental copper did not give rise to any deposition of copper in muscle tissue or backfat, but the antioxidant status of PM increased. The susceptibility to lipid oxidation was reduced in LD with increasing dietary dl-alpha-tocopheryl acetate and in PM with increasing dietary copper. Supplemental dl-alpha-tocopherol acetate improved the water-holding capacity of LD (P = .005) and PM (P = .003). The fatty acid composition of the backfat and the triglyceride fraction of the intramuscular fat became more unsaturated with the addition of rapeseed oil to the feed. Higher intakes of monounsaturated fatty acids due to the rapeseed oil were also reflected in the phospholipid fraction of the intramuscular fat, but no influence on the proportion of saturated fatty acids was seen. The susceptibility to lipid oxidation of PM was lower for pigs on the rapeseed oil-based diet than for those on the basal diet. The energy metabolic status of the muscles and the accumulation of calcium by the sarcoplasmic reticulum were not influenced by the dietary treatments, but there were differences between muscle types. The addition of rapeseed oil to the diet reduced the muscular content of glycogen (LD, P = .02; PM, P = .06) and elevated the plasma concentration of free fatty acids (P = .05). Overall, dietary fat, dl-alpha-tocopherol acetate, and copper affected the oxidative status of pig muscles, and the results differed depending on muscle type.

Effects of alpha-tocopherol on metmyoglobin formation and reduction in beef from cattle fed soybean or cottonseed meal diets.

Hereford-Angus crossbred heifers were fed a cottonseed meal-based diet containing gossypol (14 mg free gossypol x kg body wt(-1) x d(-1); CSM), a soybean meal-based diet (SBM), or alpha-tocopherol-supplemented diets (4,036 IU vitamin E x heifer(-1) x d(-1) for 90 d; CSM+E and SBM+E). The effects of diet on color stability and aerobic metmyoglobin reducing ability of beef longissimus lumborum (LL) and psoas major (PM) were evaluated. The CSM containing gossypol did not affect alpha-tocopherol concentration, a* value, or hue angle value of beef muscles obtained from control or vitamin E-supplemented cattle compared to their SBM counterparts. Vitamin E supplementation increased endogenous alpha-tocopherol concentrations and color stability in LL and PM muscles compared with controls from either diet (P < .05). In the aerobic metmyoglobin reducing ability study, LL and PM muscles were stored in 1% O2:99% N2 (a pigment-oxidizing atmosphere) for 48 h and subsequently stored aerobically for an additional 48 h. Within the LL, alpha-tocopherol supplementation delayed metmyoglobin formation in LL exposed to 1% O2 (P < .05). Within the PM, no differences in metmyoglobin formation were found between controls and vitamin E treatments in SBM or CSM diets. Relative aerobic metmyoglobin reduction was the same (P > .05) in LL and PM muscles within SBM or CSM diets for control and vitamin E treatments. Alpha-tocopherol did not seem to affect metmyoglobin aerobic reducing ability in LL and PM muscles.

Crossbridge scheme and the kinetic constants of elementary steps deduced from chemically skinned papillary and trabecular muscles of the ferret.

Elementary steps of the crossbridge cycle in chemically skinned ferret myocardium were investigated with sinusoidal analysis. The muscle preparations were activated at pCa 4.82 and an ionic strength of 200 mM, and the effects of the change in the MgATP (S) and phosphate (Pi) concentrations on three exponential processes were studied at 20 degrees C. Results are consistent with the following crossbridge scheme: [formula: see text] where A is actin, M is myosin, D is MgADP, and Det includes all detached states (MS and MDP) and weakly attached states (AMS and AMDP). From our studies, we obtained K1a = 0.99 mM-1 (MgATP association), k1b = 270 s-1 (ATP isomerization), k-1b = 280 s-1 (reverse isomerization), K1b = k1b/k-1b = 0.95, k2 = 48 s-1 (crossbridge detachment), k-2 = 14 s-1 (reverse detachment), K2 = 3.5, k4 = 11 s-1 (crossbridge attachment), k-4 = 107 s-1 (reverse attachment), K4 = 0.11, and K5 = 0.06 mM-1 (Pi association). K6 is the rate-limiting step, and it is the slowest forward reaction in the cycle, which results in the rigor-like AM state. K1a (MgATP binding) is four times that of rabbit psoas, and K5 (Pi binding) is 0.3 times that of psoas, demonstrating that crossbridges in myocardium bind MgATP more and Pi less than psoas. The rate constants of ATP isomerization (k1b, k-1b), crossbridge detachment (k2, k-2), and crossbridge attachment (k4) steps are generally an order of magnitude slower than rabbit psoas. The reverse attachment step (k-4) is similar to that in psoas, indicating that this step may occur irrespective of the myosin type and possibly spontaneously. The above scheme with the deduced kinetic constants predicts the following crossbridge distributions at 5 mM MgATP2- and 8 mM Pi:AM (3%), AM S (15%), AM*S (14%), Det (50%), AM*DP (6%), and AM*D (12%). The actual number of attached crossbridges was measured to be 51 +/- 4% by the stiffness ratio during activation and after rigor induction, and a strong correlation was seen with the prediction. Our results are consistent with the hypothesis that force generation occurs at the Det-->AM*DPi transition, and the same force is maintained after the release of Pi.

Influence of ionic strength on contractile force and energy consumption of skinned fibers from mammalian and crustacean striated muscle.

Increased ionic strength decreases maximal calcium-activated force (Fmax) of skinned muscle fibers via mechanisms that are incompletely understood. In detergent-skinned fibers from either rabbit (psoas) or lobster (leg or abdomen), Fmax in KCl-containing solutions was less than in potassium methanesulfonate (KMeSO3), which we showed previously was the least deleterious salt for adjusting ionic strength. In either salt, lobster fibers were considerably less sensitive to elevated ionic strength than rabbit fibers. Trimethylamine N-oxide (TMAO, a zwitterionic osmolyte found in high concentration in cells of salt-tolerant animals) increased Fmax, especially in high KCl solutions. In this regard, TMAO was more effective than a variety of other natural or synthetic zwitterions. In rabbit fibers, increasing ionic strength decreases Fmax but has little effect on contractile ATPase rate measured simultaneously using a linked-enzyme assay. Thus high salt increases the tension-cost of contraction (i.e. ratio ATPase/Fmax). At both high and low salt, TMAO decreases tension-cost. Given a simple two-state model of the cross-bridge cycle, these data indicate that ionic strength and TMAO affect the apparent detachment rate constant. High ionic strength KCl solutions extract myosin heavy- and light-chains, and troponin C from rabbit fibers. This extraction is virtually abolished by TMAO. Natural zwitterions, such as TMAO, have been shown to protect proteins against destabilization by high salt or other denaturatants. Our data indicate that, even in the best of salts, destabilization of the actomyosin complex may play a role in the effect of high ionic strength on the contractile process.