Reduced growth of Ehrlich ascites tumor cells in creatine depleted mice fed β-guanidinopropionic acid

The effect of implantation of Ehrlich ascites tumor (EAT) cells of creatine distribution was investigated. It was also studied how depletion of creatine by feeding creatine-analogue β-guanidinopropionic acid (β-GPA) affects the growth of EAT cells in mice. Enhanced mobilization of creatine from host tissues to EAT cells against a greater concentration gradient was observed. The creatine (but not creatinine) level in blood plasma was lowered to 22% of the normal value by β-GPA feeding alone and assimilation of ¹⁴C-creatine into EAT cells was inhibited. The growth of EAT cells was significantly reduced and the duration of survival of mice after implantation of EAT cells was extended when the creatine concentration was decreased. A decrease in daily food consumption and the degree of muscle atrophy after implantation of EAT cells was less in β-GPA than control groups. In the creatine-depleted mice, the rate of increase in total EAT cell number and the volume of abdominal ascites were approximately half of the control values, and more dead EAT cells were observed. These results suggest that supplementation of β-GPA inhibits creatine transfer to EAT cells and reduces the growth of cancer cells.     

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.     

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.     

Andrographolide reduces cognitive impairment in young and mature AβPPswe/PS-1 mice

Alzheimer’s disease (AD) is a neurodegenerative disorder in which the amyloid-β (Aβ) oligomers are a key factor in synaptic impairment and in spatial memory decline associated with neuronal dysfunction. This impairment includes synaptic failure associated with the loss of synaptic proteins that contribute to AD progression. Interestingly, the use of natural compounds is an emergent conceptual strategy in the search for drugs with therapeutic potentials for treating neurodegenerative disorders. In the present study, we report that andrographolide (ANDRO), which is a labdane diterpene extracted from Andrographis paniculata, increases slope of field excitatory postsynaptic potentials (fEPSP) in the CA1 region of hippocampal slices and inhibits long-term depression (LTD), protecting the long-term potentiation (LTP) against the damage induced by Aβ oligomers in vitro, most likely by inhibiting glycogen synthase kinase-3β (GSK-3β). Additionally, ANDRO prevents changes in neuropathology in two different age groups (7- and 12-month-old mice) of an AβPPswe/PS-1 Alzheimer’s model. ANDRO reduces the Aβ levels, changing the ontogeny of amyloid plaques in hippocampi and cortices in 7-month-old mice, and reduces tau phosphorylation around the Aβ oligomeric species in both age groups. Additionally, we observed that ANDRO recovers spatial memory functions that correlate with protecting synaptic plasticity and synaptic proteins in two different age groups. Our results suggest that ANDRO could be used in a potential preventive therapy during AD progression.     

Influence of β-alanine supplementation on skeletal muscle carnosine concentrations and high intensity cycling capacity

Summary. Muscle carnosine synthesis is limited by the availability of β-alanine. Thirteen male subjects were supplemented with β-alanine (CarnoSyn™) for 4 wks, 8 of these for 10 wks. A biopsy of the vastus lateralis was obtained from 6 of the 8 at 0, 4 and 10 wks. Subjects undertook a cycle capacity test to determine total work done (TWD) at 110% (CCT_110%) of their maximum power (W_max). Twelve matched subjects received a placebo. Eleven of these completed the CCT_110% at 0 and 4 wks, and 8, 10 wks. Muscle biopsies were obtained from 5 of the 8 and one additional subject. Muscle carnosine was significantly increased by +58.8% and +80.1% after 4 and 10 wks β-alanine supplementation. Carnosine, initially 1.71 times higher in type IIa fibres, increased equally in both type I and IIa fibres. No increase was seen in control subjects. Taurine was unchanged by 10 wks of supplementation. 4 wks β-alanine supplementation resulted in a significant increase in TWD (+13.0%); with a further +3.2% increase at 10 wks. TWD was unchanged at 4 and 10 wks in the control subjects. The increase in TWD with supplementation followed the increase in muscle carnosine.     

Effects of β-hydroxy-β-methylbutyrate treatment in different types of skeletal muscle of intact and septic rats

β-Hydroxy-β-methylbutyrate (HMB) is a leucine metabolite that may have a positive effect in protein catabolic conditions. Therefore, we hypothesized that HMB treatment could attenuate the sepsis-induced protein catabolic state. The aims of our study were to elucidate the effect of HMB in healthy and septic animals and to evaluate the differences in the action of HMB in different muscle types. Intact and septic (5 mg endotoxin/kg i.p.) rats were administered with HMB (0.5 g/kg/day) or saline. After 24 h, extensor digitorum longus (EDL) and soleus (SOL) muscles were isolated and used for determination of total and myofibrillar proteolysis, protein synthesis, leucine oxidation, activity of cathepsins B and L, chymotrypsin-like activity, and expression of α-subunits of proteasome. Our results indicate that the catabolic state induced by the endotoxin treatment was caused both by increase in protein breakdown (due to activation of proteasome system) and by attenuation of protein synthesis. The EDL (muscle composed of white, fast-twitch fibers) was more susceptible to these changes than the SOL (muscle composed of red, slow-twitch fibers). The HMB treatment had no effect in healthy animals but counteracted the changes in septic animals. The action of HMB was mediated by attenuation of proteasome activity and protein breakdown, not by stimulation of protein synthesis. More pronounced effect of the HMB treatment on myofibrillar proteolysis was observed in the SOL.     

Gender dependent effects of testosterone and 17β-estradiol on bone growth and modelling in young mice

This study examined the effects of estrogen (17β-estradiol) and testosterone on the growth of long bones in male and female mice, with and without gonadectomy. Weight and nose-to-tail length were determined at 3 weeks of age at time of gonadectomy, 7 days later at the onset of hormone therapy, and throughout the treatment period. Gonadectomized mice exhibited an initial weight gain during the pretreatment period but length was unaffected. Hormone treatment altered weight gain in surgical and intact animals in a gender- and hormone-dependent manner. Estradiol enhanced weight gain in intact mice, but inhibited weight gain in ovariectomized mice. Lower doses of estradiol increased weight gain in orchiectomized mice at early time points. Testosterone increased weight in intact females and males, but not in gonadectomized mice. Estradiol increased nose-to-tail length in intact females at early time points, but inhibited length in ovariectomized females at later times, and it decreased length in intact males. Testosterone increased length in normal females and normal males. Serum Ca was unaffected by ovariectomy, but orchiectomy resulted in decreased levels. Estradiol reduced serum Ca in gonadectomized animals; serum Ca was increased by estradiol treatment in intact females. Changes in tibial bone weight, ash weight and mineral composition, and relative sizes of epiphyseal and metaphyseal bone were gender-, gonadectomy- and hormone-specific. Bone weight was greater in ovariectomized mice. Ash weight per bone was comparable, but there was an increase in Ca and P content with ovariectomy. Estradiol increased bone weight, ash content, and bone Ca and P in ovariectomized and intact females. Orchiectomy alone did not alter bone weight, ash content, or Ca and P, but orchiectomized mice were sensitive to estradiol; all parameters were increased in the orchiectomized animals treated with estradiol. Analysis of the ash content and Ca and P per mg bone, rather than per bone, demonstrated estradiol and testosterone alter net bone formation, but not the amount of mineral per unit bone. Ovariectomy increased hypertrophic cartilage. While estradiol did not alter tibial area in ovariectomized mice, it caused an increase in intact females. The total amount of growth plate cartilage in ovariectomized animals was decreased by estradiol to levels typical of intact animals due to a greater decrease in the hypertrophic cartilage in the ovariectomized mice, as well as a greater increase in metaphyseal bone area. Testosterone had no effect on these parameters in the females. Orchiectomy decreased the amount of growth plate cartilage, but increased the hypertrophic zone. Estradiol increased growth plate cartilage in intact male mice, but decreased it in orchiectomized mice. This difference was also seen in the hypertrophic zone. Total growth plate cartilage and hypertrophic cartilage were increased by testosterone in intact males, whereas metaphyseal and epiphyseal bone area were decreased. The results show for the first time that there is a gender-specific response in both male and female mice to both estradiol and testosterone, whether or not the animals have been gonadectomized. For many parameters, orchiectomized mice behave like females in response to both sex steroids, indicating that the male gonad is needed for mouse bone to exhibit the male phenotypic response to estradiol and testosterone.     

Clenbuterol, a β2-adrenergic agonist, reciprocally alters PGC-1 alpha and RIP140 and reduces fatty acid and pyruvate oxidation in rat skeletal muscle

Clenbuterol, a β2-adrenergic agonist, reduces mitochondrial content and enzyme activities in skeletal muscle, but the mechanism involved has yet to be identified. We examined whether clenbuterol-induced changes in the muscles' metabolic profile and the intrinsic capacity of mitochondria to oxidize substrates are associated with reductions in the nuclear receptor coactivator PGC-1 alpha and/or an increase in the nuclear corepressor RIP140. In rats, clenbuterol was provided in the drinking water (30 mg/l). In 3 wk, this increased body (8%) and muscle weights (12-17%). In red (R) and white (W) muscles, clenbuterol induced reductions in mitochondrial content (citrate synthase: R, 27%; W, 52%; cytochrome-c oxidase: R, 24%; W, 34%), proteins involved in fatty acid transport (fatty acid translocase/CD36: R, 36%; W, 35%) and oxidation [β-hydroxyacyl CoA dehydrogenase (β-HAD): R, 33%; W, 62%], glucose transport (GLUT4: R, 8%; W, 13%), lactate transport monocarboxylate transporter (MCT1: R, 61%; W, 37%), and pyruvate oxidation (PDHE1α, R, 18%; W, 12%). Concurrently, only red muscle lactate dehydrogenase activity (25%) and MCT4 (31%) were increased. Palmitate oxidation was reduced in subsarcolemmal (SS) (R, 30%; W, 52%) and intermyofibrillar (IMF) mitochondria (R, 17%; W, 44%) along with reductions in β-HAD activity (SS: R, 17%; W, 51%; IMF: R, 20%; W, 57%). Pyruvate oxidation was only reduced in SS mitochondria (R, 20%; W, 28%), but this was not attributable solely to PDHE1α, which was reduced in both SS (R, 21%; W, 20%) and IMF mitochondria (R, 15%; W, 43%). These extensive metabolic changes induced by clenbuterol were associated with reductions in PGC-1α (R, 37%; W, 32%) and increases in RIP140 (R, 23%; W, 21%). This is the first evidence that clenbuterol appears to exert its metabolic effects via simultaneous and reciprocal changes in the nuclear receptor coactivator PGC-1α and the nuclear corepressor RIP140.     

Detection and regulation of δ-aminolevulinic acid synthetase activity in rat skeletal muscle

The presence of δ-aminolevulinic acid synthetase (ALAS) in mitochondria obtained from rat skeletal muscles has been observed. Optimal conditions for the meausurement of this activity are described. The activity of skeletal muscle ALAS was investigated under conditions known to affect the activity of this enzyme in other tissues. ALAS activity in skeletal muscle mitochondria was decreased 55% by a 48-h fast. Treatment with dexamethasone did not reverse the effect of starvation on ALAS activity and did not change the activity in the fed controls. ALAS activity was decreased 56% in skeletal muscle mitochondria obtained from rats in which diabetes mellitus had been induced by streptozotocin. Administration of insulin to the diabetic animals partially reversed the effect of diabetes on skeletal muscle ALAS; however, administration of insulin to control animals caused a 21% decrease in skeletal muscle ALAS activity. By contrast, treatment with inducers of hepatic ALAS such as allylisopropylacetamide or 3,5-dicarbethoxy-1,4-dihydrocollidine had no effect on skeletal muscle ALAS. These results confirm our previous suggestion that ALAS activity is regulated in a tissue-specific manner.     

Phenotype and growth behavior of residual β-catenin-positive hepatocytes in livers of β-catenin-deficient mice

Signaling through the Wnt/β-catenin pathway is a crucial determinant of hepatic zonal gene expression, liver development, regeneration, and tumorigenesis. Transgenic mice with hepatocyte-specific knockout of Ctnnb1 (encoding β-catenin) have proven their usefulness in elucidating these processes. We now found that a small number of hepatocytes escape the Cre-mediated gene knockout in that mouse model. The remaining β-catenin-positive hepatocytes showed approximately 25% higher cell volumes compared to the β-catenin-negative cells and exhibited a marker protein expression profile similar to that of normal perivenous hepatocytes or hepatoma cells with mutationally activated β-catenin. Surprisingly, the expression pattern was observed independent of the cell's position within the liver lobule, suggesting a malfunction of physiological periportal repression of perivenously expressed genes in β-catenin-deficient liver. Clusters of β-catenin-expressing hepatocytes lacked expression of the gap junction proteins Connexin 26 and 32. Nonetheless, β-catenin-positive hepatocytes had no striking proliferative advantage, but started to grow out on treatment with phenobarbital, a tumor-promoting agent known to facilitate the formation of mouse liver adenoma with activating mutations of Ctnnb1. Progressive re-population of Ctnnb1 knockout livers with wild-type hepatocytes was seen in aged mice with a pre-cirrhotic phenotype. In these large clusters of β-catenin-expressing hepatocytes, perivenous-specific gene expression was re-established. In summary, our data demonstrate that the zone-specificity of a hepatocyte's gene expression profile is dependent on the presence of β-catenin, and that β-catenin provides a proliferative advantage to hepatocytes when promoted with phenobarbital, or in a pre-cirrhotic environment.     

Loss of ovarian function in mice results in abrogated skeletal muscle PPARδ and FoxO1-mediated gene expression

Menopause, the age-related loss of ovarian hormone production, promotes increased adiposity and associated metabolic pathology, but molecular mechanisms remain unclear. We previously reported that estrogen increases skeletal muscle PPARδ expression in vivo, and transgenic mice overexpressing muscle-specific PPARδ are reportedly protected from diet-induced obesity. We thus hypothesized that obesity observed in ovariectomized mice, a model of menopause, may result in part from abrogated expression of muscle PPARδ and/or downstream mediators such as FoxO1. To test this hypothesis, we ovariectomized (OVX) or sham-ovariectomized (SHM) 10-week old female C57Bl/6J mice, and subsequently harvested quadriceps muscles 12 weeks later for gene expression studies. Compared to SHM, muscle from OVX mice displayed significantly decreased expression of PPARδ (3.4-fold), FoxO1 (4.5-fold), PDK-4 (2.3-fold), and UCP-2 (1.8-fold). Consistent with studies indicating PPARδ and FoxO1 regulate muscle fiber type, we observed dramatic OVX-specific decreases in slow isoforms of the contractile proteins myosin light chain (11.1-fold) and troponin C (11.8-fold). In addition, muscles from OVX mice expressed 57% less myogenin (drives type I fiber formation), 2-fold more MyoD (drives type II fiber formation), and 1.6-fold less musclin (produced exclusively by type II fibers) than SHM, collectively suggesting a shift towards less type I oxidative fibers. Finally, and consistent with changes in PPARδ and FoxO1 activity, we observed decreased expression of atrogin-1 (2.3-fold) and MuRF-1 (1.9-fold) in OVX mice. In conclusion, muscles from ovariectomized mice display decreased PPARδ and FoxO1 expression, abrogated expression of downstream targets involved in lipid and protein metabolism, and gene expression profiles indicating less type I oxidative fibers.     

Effects of creatine and its analog, β-guanidinopropionic acid, on the differentiation of and nucleoli in myoblasts

The effects of supplementation with creatine (Cr) and its analog, β-guanidinopropionic acid (β-GPA), on the differentiation of myoblasts and the numbers of nucleoli were studied in C2C12 cells. The cells were cultured in differentiation medium for 4 d. Then Cr (1 mM) or β-GPA (1 mM) was added to the cells, and the mixture was cultured for an additional 2 d. Although the number of myotubes was not different among the groups, myotube diameters and nuclear numbers in myotubes were increased by Cr and β-GPA treatment respectively. The expression of differentiation marker proteins, myogenin, and the myosine heavy chain, was increased in the β-GPA group. Supplementation with β-GPA also increased the percentage of p21 (inhibitor for cell cycle progression)-positive myoblasts. Supplementation with Cr inhibited the decrease in nucleoli numbers, whereas β-GPA increased nucleolar sizes in the myotubes. These results suggest that β-GPA supplementation stimulated the differentiation of myoblasts into multi-nucleated myotubes through induction of p21 expression.     

Nutritional regulation and role of peroxisome proliferator-activated receptor δ in fatty acid catabolism in skeletal muscle

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors primarily involved in lipid homeostasis. PPARδ displays strong expression in tissues with high lipid metabolism, such as adipose, intestine and muscle. Its role in skeletal muscle remains largely unknown. After a 24-h starvation period, PPARδ mRNA levels are dramatically up-regulated in gastrocnemius muscle of mice and restored to control level upon refeeding. The rise of PPARδ is accompanied by parallel up-regulations of fatty acid translocase/CD36 (FAT/CD36) and heart fatty acid binding protein (H-FABP), while refeeding promotes down-regulation of both genes. To directly access the role of PPARδ in muscle cells, we forced its expression and that of a dominant-negative PPARδ mutant in C2C12 myogenic cells. Differentiated C2C12 cells responds to 2-bromopalmitate or synthetic PPARδ agonist by induction of genes involved in lipid metabolism and increment of fatty acid oxidation. Overexpression of PPARδ enhanced these cellular responses, whereas expression of the dominant-negative mutant exerts opposite effects. These data strongly support a role for PPARδ in the regulation of fatty acid oxidation in skeletal muscle and in adaptive response of this tissue to lipid catabolism.     

Enhanced lipid-but not carbohydrate-supported mitochondrial respiration in skeletal muscle of PGC-1α overexpressing mice

Skeletal muscle mitochondrial dysfunction has been linked to several disease states as well as the process of aging. A possible factor involved is the peroxisome proliferator-activated receptor (PPAR) γ co-activator 1α (PGC-1α), a major player in the regulation of skeletal muscle mitochondrial metabolism. However, it is currently unknown whether PGC-1α, besides stimulating mitochondrial proliferation, also affects the functional capacity per mitochondrion. Therefore, we here tested whether PGC-1α overexpression, besides increasing mitochondrial content, also leads to intrinsic mitochondrial adaptations. Skeletal muscle mitochondria from 10 male, muscle-specific PGC-1α overexpressing mice (PGC-1αTg) and 8 wild-type (WT) mice were isolated. Equal mitochondrial quantities were then analyzed for their oxidative capacity by high-resolution respirometry, fuelled by a carbohydrate-derived (pyruvate) and a lipid (palmitoyl-CoA plus carnitine) substrate. Additionally, mitochondria were tested for reactive oxygen species (superoxide) production and fatty acid (FA)-induced uncoupling. PGC-1αTg mitochondria were characterized by an improved intrinsic mitochondrial fat oxidative capacity as evidenced by pronounced increase in ADP-stimulated respiration (P < 0.001) and maximal uncoupled respiration (P < 0.001) upon palmitoyl-CoA plus carnitine. Interestingly, intrinsic mitochondrial capacity on a carbohydrate-derived substrate tended to be reduced. Furthermore, the sensitivity to FA-induced uncoupling was diminished in PGC-1αTg mitochondria (P = 0.02) and this was accompanied by a blunted reduction in mitochondrial ROS production upon FAs in PGC-1αTg versus WT mitochondria (P = 0.04). Uncoupling protein 3 (UCP3) levels were markedly reduced in PGC-1αTg mitochondria (P < 0.001). Taken together, in addition to stimulating mitochondrial proliferation in skeletal muscle, we show here that overexpression of PGC-1α leads to intrinsic mitochondrial adaptations that seem restricted to fat metabolism.     

Cellular and Physiological Effects of Dietary Supplementation with β-Hydroxy-β-Methylbutyrate (HMB) and β-Alanine in Late Middle-Aged Mice

There is growing evidence that severe decline of skeletal muscle mass and function with age may be mitigated by exercise and dietary supplementation with protein and amino acid ingredient technologies. The purposes of this study were to examine the effects of the leucine catabolite, beta-hydroxy-beta-methylbutyrate (HMB), in C₂C₁₂ myoblasts and myotubes, and to investigate the effects of dietary supplementation with HMB, the amino acid β-alanine and the combination thereof, on muscle contractility in a preclinical model of pre-sarcopenia. In C₂C₁₂ myotubes, HMB enhanced sarcoplasmic reticulum (SR) calcium release beyond vehicle control in the presence of all SR agonists tested (KCl, P<0.01; caffeine, P = 0.03; ionomycin, P = 0.03). HMB also improved C₂C₁₂ myoblast viability (25 μM HMB, P = 0.03) and increased proliferation (25 μM HMB, P = 0.04; 125 μM HMB, P<0.01). Furthermore, an ex vivo muscle contractility study was performed on EDL and soleus muscle from 19 month old, male C57BL/6nTac mice. For 8 weeks, mice were fed control AIN-93M diet, diet with HMB, diet with β-alanine, or diet with HMB and β-alanine. In β-alanine fed mice, EDL muscle showed a 7% increase in maximum absolute force compared to the control diet (202 ± 3vs. 188± 5 mN, P = 0.02). At submaximal frequency of stimulation (20 Hz), EDL from mice fed HMB plus β-alanine showed an 11% increase in absolute force (88.6 ± 2.2 vs. 79.8 ± 2.4 mN, P = 0.025) and a 13% increase in specific force (12.2 ± 0.4 vs. 10.8 ± 0.4 N/cm², P = 0.021). Also in EDL muscle, β-alanine increased the rate of force development at all frequencies tested (P<0.025), while HMB reduced the time to reach peak contractile force (TTP), with a significant effect at 80 Hz (P = 0.0156). In soleus muscle, all experimental diets were associated with a decrease in TTP, compared to control diet. Our findings highlight beneficial effects of HMB and β-alanine supplementation on skeletal muscle function in aging mice.     

Substrate specificity and distribution of acid β-galactosidase activities in seizure-susceptible and non-susceptible strains of mice

The properties and distribution of -galactosidase were studied in the mouse brain using the artificial substrate methylumbelliferyl--galactoside. Enzyme activities were compared between an audiogenic seizure-susceptible mouse strain (DBA/2) and three non-susceptible strains of mice (BALB/c, C3H/He and Swiss A2G). At all ages, DBA/2 mice have significantly lower -galactosidase activity compared with the three other mouse strains: this is attributed to the different alleles present at the Bgs locus. The low activity of -galactosidase is also evident when the natural substrate GMI-ganglioside is hydrolyzed. In contrast to this low GMI-ganglioside--galactosidase activity, there is no difference in the activity of the second form of acid -galactosidase, galactosylceramidase, in DBA/2 mice at 7 and 14 days. However, at 21 and 28 days the activity is significantly lower in DBA/2 mice compared with the other strains of mice. These results on -galactosidase activity in the brain of seizure-susceptible and non-susceptible mice are discussed in relation to published levels of GMI-ganglioside and galactosylceramide present in the developing mouse brain.Dedicated to Henry McIlwain.     

Identification of a novel transforming growth factor-β (TGF-β6) gene in fish: regulation in skeletal muscle by nutritional state

Background  

The transforming growth factor-β (TGF-β) family constitutes of dimeric proteins that regulate the growth, differentiation and metabolism of many cell types, including that of skeletal muscle in mammals. The potential role of TGF-βs in fish muscle growth is not known.