Effects of β-hydroxy-β-methylbutyrate free acid and cold water immersion on post-exercise markers of muscle damage

The aim of the current study was to examine the effects of cold water immersion (CWI) with and without the free acid form of β-hydroxy-β-methylbutyrate (HMB-FA) on markers of muscle damage following acute lower body resistance exercise. Forty recreationally resistance-trained men (22.3 ± 2.4 years) were randomly divided into one of the four groups: (1) Placebo (PL); (2) HMB-FA; (3) HMB-FA-CWI; (4) PL-CWI. HMB-FA groups ingested 3 g day^?1 and CWI groups submersed their lower body into 10–12 °C water for 10-min post-exercise. No differences between groups were observed for CK; however, PL-CWI had significantly greater elevations in myoglobin 30-min post-exercise compared to HMB-FA (p = 0.009) and PL (p = 0.005), and HMB-FA-CWI was significantly greater than HMB-FA (p = 0.046) and PL (p = 0.028). No differences between groups were observed for IL-6 and IL-10, although CRP was significantly greater 24-h post-exercise for PL-CWI compared to HMB-FA-CWI (p = 0.02) and HMB-FA (p = 0.046). Only HMB-FA-CWI showed significantly (p = 0.02) greater improvements in average power per repetition. CWI appeared to elevate myoglobin compared to other groups, while HMB-FA may have attenuated the increase in CRP when combined with CWI. Nevertheless, HMB-FA or CWI treatments did not appear to provide benefit over PL for recovery. Instead, the combination of CWI and HMB-FA improved performance recovery compared to other groups.     

Mechanism of attenuation by β-hydroxy-β-methylbutyrate of muscle protein degradation induced by lipopolysaccharide

The mechanism of the effect of β-hydroxy-β-methylbutyrate (HMB) on protein degradation induced by lipopolysaccharide (LPS) has been evaluated in murine myotubes. HMB (50 μM) completely attenuated total protein degradation induced by LPS (1–100 ng/ml), formation of reactive oxygen species (ROS) and activation of caspase-3/-8. Specific inhibitors of caspase-3/-8 completely attenuated ROS production, total protein degradation and the LPS-induced autophosphorylation of dsRNA-dependent protein kinase (PKR). Protein degradation in response to LPS or ROS production was not seen in myotubes transfected with mutant PKRΔ6, suggesting that PKR was involved in ROS production, which was essential for total protein degradation. This was confirmed using the antioxidant butylated hydroxytoluene (BHT) which completely attenuated protein degradation in response to LPS. The link between PKR activation and ROS production was mediated through p38 mitogen-activated protein kinase (MAPK), which was activated by LPS in myotubes transfected with wild-type PKR, but not PKRΔ6. Both ROS production and protein degradation induced by LPS were completely attenuated by SB203580, a specific inhibitor of p38MAPK. This suggests that LPS induces protein degradation through a signalling cascade involving activation of caspase-3/-8, activation of PKR and production of ROS through p38MAPK, and that this process is attenuated by HMB.     

Does growth hormone treatment alter skeletal muscle mitochondrial respiration in rats?

OBJECTIVE: Growth hormone (GH) has been shown to stimulate lipolysis and enhance lipid oxidation. We investigated whether GH could improve mitochondrial oxidative capacity. METHOD: Fourteen male Wistar rats received 14-day treatment with biosynthetic human GH (10 IU/kg/24 h) or placebo. Mitochondria were isolated from the total muscle of one hind limb of the rat. Mitochondrial oxygen consumption was measured in vitro using a Clark-type electrode with three substrates: palmitoyl-L-carnitine, pyruvate and succinate (+ rotenone). RESULTS: Muscle mitochondrial yield was not significantly different in the GH-treated group from that in controls. Neither the basal nor ADP-stimulated respiratory state reached a significant difference between the 2 groups with palmitoyl-L-carnitine, pyruvate, and succinate. CONCLUSION: GH treatment did not improve the oxidative capacity of skeletal muscle mitochondria.     

Effects of the amino acid derivatives, β-hydroxy-β-methylbutyrate,taurine, and N-methyltyramine,on triacylglycerol breakdown in fat cells

Journal of Physiology and Biochemistry - Various amino acid (AA) metabolites are used as supplements to facilitate metabolic control and enhance responsiveness of insulin-sensitive tissues....     

Effects of long-term taurine supplementation on age-related changes in skeletal muscle function of Sprague–Dawley rats

Taurine (2-aminoethanesulfonic acid) is a free amino acid found abundantly in mammalian tissues. Increasing evidence suggests that taurine plays a role in the maintenance of skeletal muscle function and increase of exercise capacity. Most energy drinks contain this amino acid; however, there is insufficient research on the effects of long-term, low-dose supplementation of taurine. In this study, we investigated the effects of long-term administration of taurine at low doses on aging in rodents. In Experiment 1, we examined age-related changes in aging Sprague–Dawley (SD) rats (32–92 weeks old) that O₂ consumption and spontaneous activity decreased significantly with aging. In Experiment 2, we examined the effects of long-term (21-week) administration of taurine on healthy aging SD rats. SD rats were stabilized for 32–34 weeks and divided into three groups, administrated water (control), 0.5% taurine (25 mg/kg  body weight (BW)/day), or 1% taurine (50 mg/kg  BW/day) from age 34 to 56 weeks (5 days/week, 5 mL/kg BW). Our findings suggest that long-term administration of taurine at relatively low dose could attenuate the age-related decline in O₂ consumption and spontaneous locomotor activity. Upon intestinal absorption, taurine might modulate age-related changes in respiratory metabolism and skeletal muscle function via peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), succinate dehydrogenase (SDH), cytochrome c (Cycs), myocyte enhancer factor 2A (MEF2A), glucose transporter 4 (GLUT4), and myoglobin, which are regulated by the activation of AMP-activated protein kinase (AMPK). This article examines the mechanism underlying the effects of taurine on age-related changes, which may have potential clinical implications.

     

β-Adrenergic receptors in innervated and denervated skeletal muscle

In order to determine if the development of β-adrenergic receptors may explain the catecholamine evoked contracture of denervated mammalian skeletal muscle, the binding capacities and dissociation constants of β-adrenergic receptors of innervated and denervated rat skeletal muscle membrane preparations were determined by using [³H] dihydroalprenolol. The dissociation constants of [³H] dihydroalprenolol binding to innervated and denervated muscle microsomal suspensions were similar. The maximal number of binding sites increased from 27 pmol/g protein to 85 pmol/g protein following 25 days denervation. These results suggest that motor nerve may be involved in part, in the regulation of β-adrenergic receptors in skeletal muscle membrane preparations.     

Epinephrine and AICAR-induced PGC-1α mRNA expression is intact in skeletal muscle from rats fed a high-fat diet

Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) is a master regulator of mitochondrial biogenesis and is controlled, at least in part, through AMP-activated protein kinase and p38-dependent pathways. There is evidence demonstrating that activation of these kinases and induction of PGC-1α in skeletal muscle are regulated by catecholamines. The purpose of the present study was to determine if consumption of a high-fat diet (HFD) impairs epinephrine and 5-aminoimidazole-4-carboxamide-1β-d-ribofuranoside (AICAR) signaling and induction of PGC-1α in rat skeletal muscle. Male Wistar rats were fed chow or a HFD for 6 wk and then given a weight-adjusted bolus injection of epinephrine (20, 10, or 5 μg/100 g body wt sc) or saline, and triceps muscles were harvested 30 min (signaling) or 2 and 4 h (gene expression) postinjection. Despite blunted increases in p38 phosphorylation, the ability of epinephrine to induce PGC-1α was intact in skeletal muscle from HFD-fed rats and was associated with normal increases in activation of PKA and phosphorylation of cAMP response element-binding protein, reputed mediators of PGC-1α expression. The attenuated epinephrine-mediated increase in p38 phosphorylation was independent of increases in MAPK phosphatase 1. At 2 h following AICAR treatment (0.5 g/kg body wt sc), AMP-activated protein kinase and acetyl-CoA carboxylase phosphorylation were similar in skeletal muscle from chow- and HFD-fed rats. Surprisingly, AICAR-induced increases in PGC-1α mRNA levels were greater in skeletal muscle from HFD-fed rats. Our results demonstrate that the ability of epinephrine and AICAR to induce PGC-1α remains intact in skeletal muscle from HFD-fed rats. These results question the existence of reduced β-adrenergic responsiveness in diet-induced obesity and demonstrate that increases in p38 phosphorylation are not required for induction of PGC-1α in muscle from obese rats.     

Produced β-hydroxybutyrate after β-hydroxy-β-methylbutyrate (HMB) administration may contribute HMB function in mice

β-Hydroxy-β-methylbutyrate (HMB) is an intermediate in the metabolism of the branched-chain amino acid leucine. HMB has several demonstrated effects on skeletal muscle function, some of which are contradictory. In addition, the effect of exogenous HMB intake on the levels of intermediate metabolites is not known. Therefore, we investigated changes in HMB metabolites after oral HMB administration in mice. First, ICR mice were treated with either distilled water or HMB (0.215 g/10 mL/kg). Sampling was performed at 0, 1, 6, 12, and 24 h after administration. Next, ICR mice were given distilled water or HMB (0.215 g/10 mL/kg/d) for 10 d. Mice given HMB shown a significant increase in liver β-methylcrotonyl-CoA and increased β-hydroxybutyrate in plasma and the gastrocnemius muscle 1 h after HMB administration. Mice administered HMB for 10 d showed significantly decreased food intake and body weight; however, the relative weight of the gastrocnemius muscle was significantly increased. These results may be attributed to an increase in β-hydroxybutyrate resulting from exogenous HMB, since β-hydroxybutyrate inhibits food intake and suppresses skeletal muscle catabolism. In conclusion, β-hydroxybutyrate, a metabolite of HMB, was found to play an important role in the function of HMB.     

Effects of (−)-epicatechin on molecular modulators of skeletal muscle growth and differentiation

Sarcopenia is a notable and debilitating age-associated condition. Flavonoids are known for their healthy effects and limited toxicity. The flavanol (−)-epicatechin (Epi) enhances exercise capacity in mice, and Epi-rich cocoa improves skeletal muscle structure in heart failure patients. (−)-Epicatechin may thus hold promise as treatment for sarcopenia.We examined changes in protein levels of molecular modulators of growth and differentiation in young vs. old, human and mouse skeletal muscle. We report the effects of Epi in mice and the results of an initial proof-of-concept trial in humans, where muscle strength and levels of modulators of muscle growth were measured. In mice, myostatin and senescence-associated β-galactosidase levels increase with aging, while those of follistatin and Myf5 decrease. (−)-Epicatechin decreases myostatin and β-galactosidase and increases levels of markers of muscle growth. In humans, myostatin and β-galactosidase increase with aging while follistatin, MyoD and myogenin decrease. Treatment for 7 days with (−)-epicatechin increases hand grip strength and the ratio of plasma follistatin/myostatin.In conclusion, aging has deleterious effects on modulators of muscle growth/differentiation, and the consumption of modest amounts of the flavanol (−)-epicatechin can partially reverse these changes. This flavanol warrants its comprehensive evaluation for the treatment of sarcopenia.     

β-Adrenergic inhibition of contractility in L6 skeletal muscle cells

The β-adrenoceptors (β-ARs) control many cellular processes. Here, we show that β-ARs inhibit calcium depletion-induced cell contractility and subsequent cell detachment of L6 skeletal muscle cells. The mechanism underlying the cell detachment inhibition was studied by using a quantitative cell detachment assay. We demonstrate that cell detachment induced by depletion of extracellular calcium is due to myosin- and ROCK-dependent contractility. The β-AR inhibition of L6 skeletal muscle cell detachment was shown to be mediated by the β(2)-AR and increased cAMP but was surprisingly not dependent on the classical downstream effectors PKA or Epac, nor was it dependent on PKG, PI3K or PKC. However, inhibition of potassium channels blocks the β(2)-AR mediated effects. Furthermore, activation of potassium channels fully mimicked the results of β(2)-AR activation. In conclusion, we present a novel finding that β(2)-AR signaling inhibits contractility and thus cell detachment in L6 skeletal muscle cells by a cAMP and potassium channel dependent mechanism.     

Role of fatty acid uptake and fatty acid β-oxidation in mediating insulin resistance in heart and skeletal muscle

Fatty acids are a major fuel source used to sustain contractile function in heart and oxidative skeletal muscle. To meet the energy demands of these muscles, the uptake and β-oxidation of fatty acids must be coordinately regulated in order to ensure an adequate, but not excessive, supply for mitochondrial β-oxidation. However, imbalance between fatty acid uptake and β-oxidation has the potential to contribute to muscle insulin resistance. The action of insulin is initiated by binding to its receptor and activation of the intrinsic protein tyrosine kinase activity of the receptor, resulting in the initiation of an intracellular signaling cascade that eventually leads to insulin-mediated alterations in a number of cellular processes, including an increase in glucose transport. Accumulation of fatty acids and lipid metabolites (such as long chain acyl CoA, diacylglycerol, triacylglycerol, and/or ceramide) can lead to alterations in this insulin signaling pathway. An imbalance between fatty acid uptake and oxidation is believed to be responsible for this lipid accumulation, and is thought to be a major cause of insulin resistance in obesity and diabetes, due to lipid accumulation and inhibition of one or more steps in the insulin-signaling cascade. As a result, decreasing muscle fatty acid uptake can improve insulin sensitivity. However, the potential role of increasing fatty acid β-oxidation in the heart or skeletal muscle in order to prevent cytoplasmic lipid accumulation and decrease insulin resistance is controversial. While increased fatty acid β-oxidation may lower cytoplasmic lipid accumulation, increasing fatty acid β-oxidation can decrease muscle glucose metabolism, and incomplete fatty acid oxidation has the potential to also contribute to insulin resistance. In this review, we discuss the proposed mechanisms by which alterations in fatty acid uptake and oxidation contribute to insulin resistance, and how targeting fatty acid uptake and oxidation is a potential therapeutic approach to treat insulin resistance.     

β-Hydroxy-β-methylbutyrate reduces myonuclear apoptosis during recovery from hind limb suspension-induced muscle fiber atrophy in aged rats

β-Hydroxy-β-methylbutyrate (HMB) is a leucine metabolite shown to reduce protein catabolism in disease states and promote skeletal muscle hypertrophy in response to loading exercise. In this study, we evaluated the efficacy of HMB to reduce muscle wasting and promote muscle recovery following disuse in aged animals. Fisher 344×Brown Norway rats, 34 mo of age, were randomly assigned to receive either Ca-HMB (340 mg/kg body wt) or the water vehicle by gavage (n = 32/group). The animals received either 14 days of hindlimb suspension (HS, n = 8/diet group) or 14 days of unloading followed by 14 days of reloading (R; n = 8/diet group). Nonsuspended control animals were compared with suspended animals after 14 days of HS (n = 8) or after R (n = 8). HMB treatment prevented the decline in maximal in vivo isometric force output after 2 wk of recovery from hindlimb unloading. The HMB-treated animals had significantly greater plantaris and soleus fiber cross-sectional area compared with the vehicle-treated animals. HMB decreased the amount of TUNEL-positive nuclei in reloaded plantaris muscles (5.1% vs. 1.6%, P < 0.05) and soleus muscles (3.9% vs. 1.8%, P < 0.05). Although HMB did not significantly alter Bcl-2 protein abundance compared with vehicle treatment, HMB decreased Bax protein abundance following R, by 40% and 14% (P < 0.05) in plantaris and soleus muscles, respectively. Cleaved caspase-3 was reduced by 12% and 9% (P < 0.05) in HMB-treated reloaded plantaris and soleus muscles, compared with vehicle-treated animals. HMB reduced cleaved caspase-9 by 14% and 30% (P < 0.05) in reloaded plantaris and soleus muscles, respectively, compared with vehicle-treated animals. Although, HMB was unable to prevent unloading-induced atrophy, it attenuated the decrease in fiber area in fast and slow muscles after HS and R. HMB's ability to protect against muscle loss may be due in part to putative inhibition of myonuclear apoptosis via regulation of mitochondrial-associated caspase signaling.     

Hypokalemia modulatesα- andβ-adrenoceptor bindings in rat skeletal muscle

Changes in the population of adrenergic alpha- and beta-receptors were examined in rat soleus muscles during hypokalemia by their direct determination using radiolabeled ligands. Only beta-adrenoceptors were detected in the normal rat muscles. Hypokalemia led to a pronounced decrease in beta-adrenoceptors, the number of [3H]DHA binding sites, by 50%, as compared with that in the normal rats. There was a genesis of alpha 1-adrenoceptors in hypokalemic rat muscles, since the competitive potency of adrenergic drugs against [3H]prazosin binding was in the order prazosin much greater than phentolamine greater than (+/-)-noradrenaline greater than yohimbine much greater than (+/-)-isoproterenol. The reduction of [3H]DHA binding sites was accompanied by an increase of an approximately equal amount in high-affinity [3H]prazosin binding sites. The Kd determined by kinetic analysis of [3H]prazosin binding was calculated from the ratio K-1/K1 that gave a value of 3.05 nM, which generally agreed with the 1.83 nM determined by saturation experiments (Scatchard plot). This phenomenon of a reduction in the beta-adrenoceptors and the occurrence of alpha 1-adrenoceptors in muscles during hypokalemia is discussed. alpha- and beta-adrenoceptors on soleus muscle membrane may play important but opposite roles in modulating potassium release from the muscle cells.     

A 31P-nuclear magnetic resonance study of skeletal muscle metabolism in rats depleted of creatine with the analogue β-guanidinopropionic acid

Rats were fed a diet containing 1% β-guanidinopropionic acid (GPA) for 6–10 weeks to deplete their skeletal muscle of creatine. ³¹P-NMR was used to monitor metabolic changes in the gastrocnemius muscle at rest, during stimulated steady-state isometric contraction at 4 Hz and during recovery from stimulation. In resting muscles, the [creatine phosphate] was reduced to 10% (2.8 μmol·g^?1) and the [ATP] to 50% (3.3 μmol·g^?1) of those found in rats fed a control diet. The concentration of the phosphorylated form of the analogue (PGPA) was 23 μmol·g^?1. There was no significant difference in muscle performance or in the relative changes in the [ATP] during stimulation. Intracellular pH decreased rapidly on stimulation and recovered during the stimulation period to near resting values in both groups. In control rats, the initial decrease in pH was greater and the time to recovery was longer than in GPA-fed rats. The rate at which PGPA supplied energy to the contracting muscle (0.027 mM·s^?1) was insignificant relative to the minimum estimated rate of ATP turnover (1 mM·s^?1). The rate of PGPA resynthesis during recovery (0.018 mM·s^?1) is enzyme-limited and provides an independent estimate of creatine kinase flux during this period (18.9 mM·s^?1). The creatine kinase flux (creatine phosphate → ATP) in the resting muscle of GPA-fed rats was 12-fold less than in control animals, 1.3 vs. 15.7 mM·s^?1. These results demonstrate that neither the [creatine phosphate] nor the activity of creatine kinase is critical for aerobic metabolism. Skeletal muscle appears to adapt to a diminished creatine pool by enhancing its aerobic capacity.