Effect of an acute dose of omega-3 fish oil following exercise-induced muscle damage.

PURPOSE: The purpose of this double-blind, placebo-controlled study was to examine the effect of two fish oil supplements, one high in EPA (750 mg EPA, 50 mg DHA) and one low in EPA (150 mg EPA, 100 mg DHA), taken acutely as a recovery strategy following EIMD. METHODS: Twenty-seven physically active males (26 ± 4 year, 1.77 ± 0.07 m, 80 ± 10 kg) completed 100 plyometric drop jumps to induce muscle damage. Perceptual (perceived soreness) and functional (isokinetic muscle strength at 60° and 180° s-1, squat jump performance and countermovement jump performance) indices of EIMD were recorded before, and 1, 24, 48, 72, and 96h after the damaging protocol. Immediately after the damaging protocol, volunteers ingested either a placebo (Con), a low-EPA fish oil (Low EPA) or a high-EPA fish oil (High EPA) at a dose of 1 g per 10 kg body mass. RESULTS: A significant group main effect was observed for squat jump, with the High EPA group performing better than Con and Low EPA groups (average performance decrement, 2.1, 8.3 and 9.8%, respectively), and similar findings were observed for countermovement jump performance, (average performance decrement, 1.7, 6.8 and 6.8%, respectively, p = 0.07). Significant time, but no interaction main effects were observed for all functional and perceptual indices measured, although large effect sizes demonstrate a possible ameliorating effect of high dose of EPA fish supplementation (effect sizes ≥0.14). CONCLUSION: This study indicates that an acute dose of high-EPA fish oil may ameliorate the functional changes following EIMD.

A systematic review of the effectiveness of community-based interventions aimed at improving health literacy of parents/carers of children.

AIM: The aim of this systematic review was to examine the effectiveness of community-based health literacy interventions in improving the health literacy of parents. METHODS: A systematic review of six databases - MEDLINE, PsycINFO, CINAHL, Cochrane Library, Embase, and Education Source - was conducted to identify relevant articles. Risk of bias was assessed using version two of the Cochrane risk of bias tool for randomised controlled trials or the Cochrane collaboration risk of bias in non-randomised studies of interventions. The study findings were grouped and synthesised following the synthesis without meta-analysis framework. RESULTS: Eleven community-based health literacy interventions for parents were identified. Study design included randomised controlled trials (n = 4), non-randomised studies with comparison group (n = 4), and non-randomised studies without a comparison group (n = 3). Interventions were delivered digitally, in person or a combination of the two. The risk of bias was high in over half the studies (n = 7). The main findings of the studies showed some potential for both in person and digital interventions to increase parental health literacy. Studies were heterogeneous preventing a meta-analysis. CONCLUSION: Community-based, health literacy interventions have been identified as potential methods for enhancing parental health literacy. Due to the small number of included studies and their potential for bias, these results must be interpreted with caution. This study emphasises the need for additional theory and evidence-based research on the long-term effects of community interventions.

Prediction of peak oxygen uptake from ratings of perceived exertion during arm exercise in able-bodied and persons with poliomyelitis.

STUDY DESIGN: Each participant completed an arm-crank ramp exercise test to volitional exhaustion. OBJECTIVE: To assess the utility of the rating of perceived exertion (RPE) to predict peak oxygen uptake (VO(2)peak) during arm ergometry in able-bodied participants and those with poliomyelitis. SETTING: University of Jordan, Amman, Jordan. PARTICIPANTS: In all, 16 able-bodied and 15 participants with poliomyelitis completed an arm-crank ramp exercise test to volitional exhaustion. MAIN OUTCOME MEASURES: The prediction of VO(2)peak is calculated by extrapolating the sub-maximal RPE and VO(2) values by linear regression to RPE 20. RESULTS: For the able-bodied participants, there were no significant differences between measured and predicted VO(2)peak from the three sub-maximal ranges of the RPE (RPEs before and including RPE 13, 15 and 17, P > 0.05). For the participants with poliomyelitis, the VO(2)peak predicted from RPEs before and including RPE 13 was significantly higher than measured VO(2)max (P < 0.05). The 95% limits of agreement of able-bodied participants for RPE 13, 15 and 17 (-3 ± 14, -1 ± 10 & 0 ± 8 ml kg(-1) min(-1), respectively) were lower than those observed for poliomyelitis participants (6 ± 19, 2 ± 12 and 1 ± 9 ml kg(-1) min(-1), respectively). CONCLUSION: This study has shown that the estimation of VO(2)peak from submaximal RPE during arm ergometry is generally more accurate in able-bodied participants in comparison with those with poliomyelitis.

Assembly of the dystrophin-associated protein complex does not require the dystrophin COOH-terminal domain.

Dystrophin is a multidomain protein that links the actin cytoskeleton to laminin in the extracellular matrix through the dystrophin associated protein (DAP) complex. The COOH-terminal domain of dystrophin binds to two components of the DAP complex, syntrophin and dystrobrevin. To understand the role of syntrophin and dystrobrevin, we previously generated a series of transgenic mouse lines expressing dystrophins with deletions throughout the COOH-terminal domain. Each of these mice had normal muscle function and displayed normal localization of syntrophin and dystrobrevin. Since syntrophin and dystrobrevin bind to each other as well as to dystrophin, we have now generated a transgenic mouse deleted for the entire dystrophin COOH-terminal domain. Unexpectedly, this truncated dystrophin supported normal muscle function and assembly of the DAP complex. These results demonstrate that syntrophin and dystrobrevin functionally associate with the DAP complex in the absence of a direct link to dystrophin. We also observed that the DAP complexes in these different transgenic mouse strains were not identical. Instead, the DAP complexes contained varying ratios of syntrophin and dystrobrevin isoforms. These results suggest that alternative splicing of the dystrophin gene, which naturally generates COOH-terminal deletions in dystrophin, may function to regulate the isoform composition of the DAP complex.

Transgenic mdx mice expressing dystrophin with a deletion in the actin-binding domain display a "mild Becker" phenotype.

The functional significance of the actin-binding domain of dystrophin, the protein lacking in patients with Duchenne muscular dystrophy, has remained elusive. Patients with deletions of this domain (domain I) typically express low levels of the truncated protein. Whether the moderate to severe phenotypes associated with such deletions result from loss of an essential function, or from reduced levels of a functional protein, is unclear. To address this question, we have generated transgenic mice that express wild-type levels of a dystrophin deleted for the majority of the actin-binding domain. The transgene derived protein lacks amino acids 45-273, removing 2 of 3 in vitro identified actin interacting sites and part of hinge 1. Examination of the effect of this deletion in mice lacking wild-type dystrophin (mdx) suggests that a functional domain I is not essential for prevention of a dystrophic phenotype. However, in contrast to deletions in the central rod domain and to full-length dystrophin, both of which are functional at only 20% of wild-type levels, proteins with a deletion in domain I must be expressed at high levels to prevent a severe dystrophy. These results are also in contrast to the severe dystrophy resulting from truncation of the COOH-terminal domain that links dystrophin to the extracellular matrix. The mild phenotype observed in mice with domain I-deletions indicates that an intact actin-binding domain is not essential, although it does contribute to an important function of dystrophin. These studies also suggest the link between dystrophin and the subsarcolemmal cytoskeleton involves more than a simple attachment of domain I to actin filaments.

Progressive muscular dystrophy in alpha-sarcoglycan-deficient mice.

Limb-girdle muscular dystrophy type 2D (LGMD 2D) is an autosomal recessive disorder caused by mutations in the alpha-sarcoglycan gene. To determine how alpha-sarcoglycan deficiency leads to muscle fiber degeneration, we generated and analyzed alpha-sarcoglycan- deficient mice. Sgca-null mice developed progressive muscular dystrophy and, in contrast to other animal models for muscular dystrophy, showed ongoing muscle necrosis with age, a hallmark of the human disease. Sgca-null mice also revealed loss of sarcolemmal integrity, elevated serum levels of muscle enzymes, increased muscle masses, and changes in the generation of absolute force. Molecular analysis of Sgca-null mice demonstrated that the absence of alpha-sarcoglycan resulted in the complete loss of the sarcoglycan complex, sarcospan, and a disruption of alpha-dystroglycan association with membranes. In contrast, no change in the expression of epsilon-sarcoglycan (alpha-sarcoglycan homologue) was observed. Recombinant alpha-sarcoglycan adenovirus injection into Sgca-deficient muscles restored the sarcoglycan complex and sarcospan to the membrane. We propose that the sarcoglycan-sarcospan complex is requisite for stable association of alpha-dystroglycan with the sarcolemma. The Sgca-deficient mice will be a valuable model for elucidating the pathogenesis of sarcoglycan deficient limb-girdle muscular dystrophies and for the development of therapeutic strategies for this disease.

Muscle fiber regeneration after transplantation: prediction of structure and physiology from electromyograms.

Digitized electromyographic activity of transplanted extensor digitorum longus (EDL) muscles in cats differs from that of control EDL and anterior tibialis muscles lying adjacent to transplanted EDL muscles. In autotransplanted muscles, the cross-sectional area of the fibers shows a negative correlation with mean spike frequency and a positive correlation with mean amplitude. The mean frequency-amplitude products correlate with isometric tetanic tensions.

Free radical generation by skeletal muscle of adult and old mice: effect of contractile activity.

Oxidative modification of cellular components may contribute to tissue dysfunction during aging. In skeletal muscle, contractile activity increases the generation of reactive oxygen and nitrogen species (ROS). The question of whether contraction-induced ROS generation is further increased in skeletal muscle of the elderly is important since this influences recommendations on their exercise participation. Three different approaches were used to examine whether aging influences contraction-induced ROS generation. Hind limb muscles of adult and old mice underwent a 15-min period of isometric contractions and we examined ROS generation by isolated skeletal muscle mitochondria, ROS release into the muscle extracellular fluid using microdialysis techniques, and the muscle glutathione and protein thiol contents. Resting skeletal muscle of old mice compared with adult mice showed increased ROS release from isolated mitochondria, but no changes in the extracellular levels of superoxide, nitric oxide, hydrogen peroxide, hydroxyl radical activity or muscle glutathione and protein thiol contents. Skeletal muscle mitochondria isolated from both adult and old mice after contractile activity showed significant increases in hydrogen peroxide release compared with pre-contraction values. Contractions increased extracellular hydroxyl radical activity in adult and old mice, but had no significant effect on extracellular hydrogen peroxide or nitric oxide in either group. In adult mice only, contractile activity increased the skeletal muscle release of superoxide. A similar decrease in muscle glutathione and protein thiol contents was seen in adult and old mice following contractions. Thus, contractile activity increased skeletal muscle ROS generation in both adult and old mice with no evidence for an age-related exacerbation of ROS generation.

Sarcospan-deficient mice maintain normal muscle function.

Sarcospan is an integral membrane component of the dystrophin-glycoprotein complex (DGC) found at the sarcolemma of striated and smooth muscle. The DGC plays important roles in muscle function and viability as evidenced by defects in components of the DGC, which cause muscular dystrophy. Sarcospan is unique among the components of the complex in that it contains four transmembrane domains with intracellular N- and C-terminal domains and is a member of the tetraspan superfamily of proteins. Sarcospan is tightly linked to the sarcoglycans, and together these proteins form a subcomplex within the DGC. Stable expression of sarcospan at the sarcolemma is dependent upon expression of the sarcoglycans. Here we describe the generation and analysis of mice carrying a null mutation in the Sspn gene. Surprisingly, the Sspn-deficient muscle maintains expression of other components of the DGC at the sarcolemma, and no gross histological abnormalities of muscle from the mice are observed. The Sspn-deficient muscle maintains sarcolemmal integrity as determined by serum creatine kinase and Evans blue uptake assays, and the Sspn-deficient muscle maintains normal force and power generation capabilities. These data suggest either that sarcospan is not required for normal DGC function or that the Sspn-deficient muscle is compensating for the absence of sarcospan, perhaps by utilizing another protein to carry out its function.

Genetic modification of the manganese superoxide dismutase/glutathione peroxidase 1 pathway influences intracellular ROS generation in quiescent, but not contracting, skeletal muscle cells.

Increased amounts of reactive oxygen species (ROS) are generated by skeletal muscle during contractile activity, but their intracellular source is unclear. The oxidation of 2',7'-dichlorodihydrofluorescein (DCFH) was examined as an intracellular probe for reactive oxygen species in skeletal muscle myotubes derived from muscles of wild-type mice and mice that were heterozygous knockout for manganese superoxide dismutase (Sod2(+/-)), homozygous knockout for glutathione peroxidase 1 (GPx1(-/-)), or MnSOD transgenic overexpressors (Sod2-Tg). Myoblasts were stimulated to fuse and loaded with DCFH 5-7 days later. Intracellular DCF epifluorescence was measured and myotubes were electrically stimulated to contract for 15 min. Quiescent myotubes with decreased MnSOD or GPx1 showed a significant increase in the rate of DCFH oxidation whereas those with increased MnSOD did not differ from wild type. Following contractions, myotubes from all groups showed an equivalent increase in DCF fluorescence. Thus the oxidation of DCFH in quiescent skeletal muscle myotubes is influenced by the content of enzymes that regulate mitochondrial superoxide and hydrogen peroxide content. In contrast, the increase in DCFH oxidation following contractions was unaffected by reduced or enhanced MnSOD or absent GPx1, indicating that reactive oxygen species produced by contractions were predominantly generated by nonmitochondrial sources.

Free radical activity following contraction-induced injury to the extensor digitorum longus muscles of rats.

The purpose of the study was to investigate the role of free radicals in the injury induced by a protocol of repeated pliometric (lengthening) contractions to the extensor digitorum longus (EDL) muscle in situ in rats. Previous data have indicated that prior treatment with the antioxidant polyethylene glycol-superoxide dismutase reduced the damage that was apparent at 3 days following this type of exercise. Three hours and 3 days following the protocol, the magnitude of the semiquinone-derived free radical signal observed by electron spin resonance spectroscopy (ESR) was not different for exercised and non-exercised skeletal muscles. A reduction in the protein thiol content of muscle was evident at 3 h, and was still apparent at 3 days. Three hours after the protocol, the total muscle glutathione content and the percentage in the oxidized form were unchanged, but by 3 days the percentage of muscle glutathione present in the oxidized form was elevated. The susceptibility of muscle to lipid peroxidation in vitro was reduced 3 days after the pliometric contractions. These data indicate that oxidation of protein thiols and glutathione may be involved in the secondary damage following pliometric contractions, but provide no evidence that the species involved were derived from mitochondrial semiquinone radicals.

Force and power output of diaphragm muscle strips from mdx and control mice after clenbuterol treatment.

Based on its anabolic properties, treatment with the beta(2)-adrenoceptor agonist, clenbuterol, has been proposed as a strategy for ameliorating the symptoms of muscular dystrophy. In the dystrophic mdx mouse, only the diaphragm muscle exhibits progressive and severe degeneration in muscle structure and function similar to that observed in Duchenne muscular dystrophy. We tested the hypothesis that 20 weeks of clenbuterol treatment ( approximately 1.5-2 mg kg(-1)day(-1)) would increase the force and power output of diaphragm muscle strips of 6-month-old mdx and control mice. At this age, the diaphragm muscles of mdx mice show extensive degeneration and impaired contractility compared with control mice. Clenbuterol treatment did not increase the normalized force or power output of diaphragm strips from either mdx or control mice. The degeneration and necrosis within the diaphragm muscle of mdx mice was also not ameliorated by clenbuterol treatment. The results indicate that clenbuterol treatment does not improve the structure or function of diaphragm muscles from mdx mice.

Clinical conference in pulmonary disease. Factors influencing upper airway closure.

The factors which produce closure of the upper airway (UAW) in patients with the sleep apnea syndrome are still poorly understood. A distinction should be made between the factors which induce closure and those which reopen the UAW. Neurologic factors include arousal phenomena, the magnitude and timing of various motor outputs, and postsynaptic inhibition. Mechanical factors include the anatomy of the UAW, especially that above the tongue, the position of the neck and jaw, and mucosal adherence once occlusion has occurred. Muscle factors include the type of myosin isozyme, the forces generated by the large number of UAW muscles and the diaphragm, and the possibility of high-frequency fatigue occurring during occlusion. Hypoxia and acidosis probably play a critical role in making the UAW less stable. Currently, the best method to prevent UAW closure is by nasal CPAP. Patients with life-threatening arrhythmias due to sleep apnea should have a tracheostomy. The role of drugs is controversial. Respiratory or muscle stimulants should probably be avoided; oxygen, medroxyprogesterone, and protriptyline may be useful adjuncts.

Functional development of engineered skeletal muscle from adult and neonatal rats.

A myooid is a three-dimensional skeletal muscle construct cultured from mammalian myoblasts and fibroblasts. The purpose was to compare over several weeks in culture the morphology, excitability, and contractility of myooids developed from neonatal and adult rat cells. The hypotheses tested were as follows: (1) baseline forces of myooids correlate with the cross-sectional area (CSA) of the myooids composed of fibroblasts, and (2) peak isometric tetanic forces normalized by total CSA (specific P(o)) of neonatal and adult rat myooids are not different. Electrical field stimulation was used to measure the excitability and peak tetanic forces. The proportion of the CSA composed of fibroblasts was greater for neonatal (40%) than adult (17%) myooids. For all myooids the baseline passive force normalized by fibroblast CSA (mean = 5.5 kPa) correlated with the fibroblast CSA (r(2) = 0.74). A two-element cylindrical model was analyzed to determine the contributions of fibroblasts and myotubes to the baseline force. At each measurement period, the specific P(o) of the adult myooids was greater than that of the neonatal myooids. The specific P(o) of the adult myooids was approximately 1% of the control value for adult muscles and did not change with time in culture, while that of neonatal myooids increased.

The regeneration of noninnervated muscle grafts and marcaine-treated muscles in young and old rats.

Free grafts of the extensor digitorum longus (EDL) muscle in 4-month-old rats regenerate 2-3 times better than in 24-month-old rats. Based on these data, we formulated the working hypothesis that deficient reinnervation is one of the most important age-related environmental factors within the host that might account for the poor regeneration. In the present experiments, we compared the regeneration of EDL muscles in two groups of young and old rats: (a) 21-day grafts, with fibers regenerating in the absence of nerves, and (b) Marcaine-treated muscle with fibers regenerating in the presence of uninterrupted innervation. The specific hypothesis was that, under each of these circumstances, reinnervation was not involved and age-related differences in regeneration would not be seen. Differences were assessed by measurements of mass and maximum isometric force normalized to values for age-matched control muscles. In the absence of nerves, the degree of regeneration in 21-day noninnervated EDL grafts was not significantly different between young and old rats. Similarly, when EDL muscles were damaged by Marcaine and regenerated in the presence of uninterrupted innervation, no differences were noted between young and old rats. These data support the working hypothesis that a deficiency in reinnervation with increasing age accounts, at least in part, for the poorer success of muscle regeneration in grafts in old compared with young rats.

Muscle regeneration in young and old rats: effects of motor nerve transection with and without marcaine treatment.

We tested the hypothesis that after skeletal muscle regeneration in old compared with young rats damage to the motor nerve rather than damage to muscle fibers determines the magnitude of the deficits in muscle mass and maximum force (Po). The mass and Po of extensor digitorum longus (EDL) muscles of young (4 months) and old (24 months) male rats were compared two months following (i) Marcaine treatment plus simultaneous motor nerve transection, (ii) motor nerve transection alone, and (iii) Marcaine treatment alone (from data compiled previously). In both the nerve transection-only and Marcaine with nerve transection groups the recovery of mass and Po was significantly greater in young than in old rats. This is in contrast to our previous data showing that in the absence of nerve damage Marcaine-treated muscle in old rats regenerates as well as that in young rats. Our hypothesis was supported, and we conclude that impaired axonal regeneration, re-establishment of nerve-muscle contact, or both, is the critical component in the impaired regeneration of muscle grafts in old as compared with young rats.

Muscle atrophy and weakness with aging: contraction-induced injury as an underlying mechanism.

In old compared with young animals, muscle mass is decreased by 30% to 40%, and maximum force and power are decreased to an even greater extent. The age-related declines in muscle mass and muscle function are similar to those that occur with decreased physical activity. Despite the similarities, we conclude that the losses in muscle mass, force, and power are not due solely to old animals being less active, but rather accrue from intrinsic age-related changes in muscles and in muscle fibers that appear to be immutable and irreversible. The intrinsic changes are associated with denervation of fast fatigable fibers and motor units and motor unit remodeling, which may be initiated by contraction-induced injury. The mechanisms remain unresolved for the weakness, the fatigability, the high susceptibility to contraction-induced injury, and the impaired recovery from injury demonstrated by the skeletal muscles of old animals.

Conditioning of skeletal muscles in adult and old mice for protection from contraction-induced injury.

The purpose of this study was to design a conditioning program that protected muscles in both adult and old mice from a protocol of contractions that previously caused a significant number of damaged fibers and a deficit in force. Hind-limb dorsiflexor muscles of adult (7 months) and old (22 months) female B6D2F1 mice were exposed once a week to a protocol of repeated forced stretches while maximally activated in vivo. By week 4, muscles of adult, but not old, mice showed no force deficit. Conditioning was continued for 6 weeks, when both age groups showed no force deficit for two consecutive weeks. Three days after the sixth contraction protocol, when morphological damage and force deficits are most severe, the numbers of damaged fibers in muscles of adult and old mice were not different from those in uninjured control muscles and the force deficits were reduced dramatically compared with unconditioned muscles. We conclude that muscles of both adult and old mice conditioned successfully, but muscles of old mice conditioned more slowly than those of adult mice.

Skeletal muscle regeneration in very old rats.

This study was undertaken to assess the regenerative capacity of skeletal muscle in rats near the end of their normal life span. Two experiments were performed. In the first, extensor digitorum longus (EDL) muscles were cross-age transplanted from 32-month-old male inbred Wistar (WI/HicksCar) rats in place of an EDL muscle in 4-month-old hosts. The other EDL muscle in the hosts was autotransplanted. After 60 days, the old-into-young muscle transplants regenerated as well as the young-into-young autotransplants. In the second experiment, EDL muscles in young adult (4 months) and old rats (32 and 34 months) of WI/HicksCar and Brown Norway (BN) were injected with a local anesthetic, bupivacaine, and allowed to regenerate for 41 days. In all cases, the masses and absolute maximum tetanic force of the regenerates equaled or exceeded those of untouched contralateral control muscles. These experiments showed that under appropriate conditions, very old muscles can regenerate to equal or exceed the contralateral control values, which in old rats are much less than those in muscles of young rats.

Motor unit properties of nerve-intact extensor digitorum longus muscle grafts in young and old rats.

Impaired reinnervation has been implicated as the cause of the threefold disparity in the recovery of maximum force (P0) of standard muscle grafts in old compared with young rats. The specific, null hypothesis of this study is that compared with age-matched control extensor digitorum longus (EDL) muscles, nerve-intact EDL muscle grafts in young and old rats show no evidence of an age-related impairment in reinnervation. Nerve-intact grafts were performed in 3-month-old and 23-month-old rats and were evaluated 60 days postoperatively. Compared with age-matched control EDL muscles, nerve-intact grafts in young and old rats showed no difference in muscle mass or motor unit numbers. The mean motor unit P0 for nerve-intact graft muscles in both age groups was significantly lower than that of age-matched control muscles. These data support our hypothesis that if axons are allowed to regenerate in an endoneurial environment, there is no evidence of an age-related impairment in muscle reinnervation.