The aims of the studies undertaken were to investigate the physiological and serum biochemical changes associated with muscle damage, and to test possible treatments for this condition. Initial studies examined the effects of walking 37 km daily for 4 days and of running 21.1 km and 25.6 km road race events in different groups of subjects. Prolonged walking produced little soreness, but daily increases in serum creatine kinase (CK) activity were recorded. In the two running studies, delayed increases in the serum activity of the enzymes CK, lactate dehydrogenase (LD) and aspartate transaminase (AST) were observed, as were changes in the CK and LD isoenzyme pattern. In a further study, the CK-MM isoform response to a maximal eccentric arm exercise was studied in 8 subjects. Although total CK activity continued to increase for 5 days after exercise, the CK MM1:MM3 ratio peaked at 48 h after exercise, when muscle soreness also peaked. Two non-steroidal anti-inflammatory drugs were assessed for their effectiveness in the muscle soreness condition. Diclofenac and ibuprofen were tested in double-blind crossover studies in which drug or placebo were administered before and after two bouts of 45 minutes downhill running. Neither drug proved effective in reducing muscle soreness or serum enzyme changes after the eccentric exercise. The effect of prior vitamin C supplementation on the same parameters was assessed, but this treatment also proved ineffective. A final study examined the effect of exercise during the period of muscle soreness and damage. In this study, a light eccentric exercise bout was performed 24 h after a heavy eccentric bout, using the same arm muscles. Performance of the light bout did not alter the symptoms of muscle soreness, but did effect serum CK activity changes and resistance to muscle fatigue during later eccentric exercise.

No description available.

No description available.

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No description available.

Altered apoptotic signaling in skeletal muscle has been observed in a number of disease states associated with skeletal muscle atrophy. Therefore, understanding the mechanisms that lead to increased skeletal muscle apoptosis may help to prevent the atrophy associated with various diseases. Apoptosis repressor with caspase recruitment domain (ARC) is a potent anti-apoptotic protein that is able to inhibit apoptosis mediated by both the death-receptor and mitochondrial pathways. In addition, ARC has a unique distribution pattern and is highly expressed in terminally differentiated tissue such as skeletal muscle. To characterize the role of ARC in skeletal muscle morphology and apoptosis, soleus and plantaris muscles of 18 week-old ARC-deficient mice were excised and compared to those of age-matched wild-type littermates. While no differences were seen in muscle weights between genotypes, in the ARC KO animals, the cross-sectional area (CSA) of the soleus was smaller, while the CSA of the plantaris was larger. With respect to fiber type distribution, both muscles demonstrated a shift towards a faster myosin heavy chain expression pattern. For example, soleus muscles of ARC KO animals had significantly less type I fibers and more IIa fibers, while plantaris muscles had significantly less type IIa fibers, and more IIb fibers. In ARC KO animals, type I and IIa fibers were significantly smaller in the soleus, while type IIb fibers were larger in the plantaris. DNA fragmentation (a hallmark of apoptosis) was increased in the soleus, but not plantaris muscles of ARC KO animals. Surprisingly, activity of the proteolytic enzymes caspase-2, -3, -8, and -9, as well as calpains, was not different in either soleus or plantaris muscles. To determine whether a lack of ARC protein affects apoptotic signaling in skeletal muscle, the total expression of pro- and anti-apoptotic proteins were also assessed. In the soleus, no changes were observed in whole tissue AIF, cytochrome c, EndoG, and Smac. In the plantaris, there was no change in total muscle AIF; however, there were trends towards decreased cytochrome c, and increased Smac, as well as a significant decrease in EndoG ARC KO animals. No changes were observed in Bcl-2 and XIAP in the soleus; however, there were significant reductions in FLIP(s) and HSP70 content. In the plantaris, no changes were observed in anti-apoptotic protein content. Subcellular fractionation of red quadriceps for ARC KO mice revealed an increased Bax:Bcl-2 ratio in the isolated mitochondrial fractions. Furthermore, in cytosolic fractions of red quadriceps, AIF protein content was significantly increased in ARC KO animals. Conversely, no changes in apoptotic-related protein content were observed in any fractions from white quadriceps between groups. In agreement with these findings, isolated mitochondria from ARC-deficient animals were more susceptible to calcium induced swelling, as well as membrane potential loss compared to controls. Taken together, these results suggest that in slow-oxidative skeletal muscle of ARC-deficient mice there is increased apoptosis due to caspase-independent, mitochondrial-mediated apoptotic signaling. Furthermore, this study is the first to show ARC plays an important role in skeletal muscle morphology, as ARC KO mice have an altered skeletal muscle phenotype and morphology.

Statins are the mainstay of cholesterol-lowering therapy and are taken by millions of people worldwide. These drugs are generally well-tolerated but can cause myopathy ranging from mild muscle pain to fatal rhabdomyolysis. The mechanism of statin-induced myopathy (SIM) is not fully understood and there is currently no convenient and reliable marker of SIM, but mitochondrial dysfunction has been implicated. We sought to investigate the effect of statins on mitochondrial DNA (mtDNA) levels in order to gain information on the mechanism of SIM and to explore the possibility of utilizing changing mtDNA levels as a marker of SIM. Several approaches were used. First, mtDNA levels were quantified in skeletal muscle biopsies collected from a previously published 8-week clinical trial of high-dose simvastatin or atorvastatin versus placebo. Forty-eight hypercholesterolemic subjects were randomly assigned to receive placebo (N=16), high dose atorvastatin 40mg/day (N=16), or high dose simvastatin 80mg/day (N=16) for 8 weeks. Muscle mtDNA content was assessed by real-time PCR atbaseline and after 8-weeks on statin treatment and found to be significantly reduced in the groupreceiving simvastatin (P=0.005) but not the other two. In addition, a significant positive correlation was observed between mtDNA and muscle ubiquinone in all groups (R=0.63, P<0.01), with the strongest association found in the simvastatin-treated subjects (R=0.75, P=0.002). Next, in an attempt to determine whether statin-induced muscle pain may be associated with muscle mtDNA depletion, archived muscle biopsies collected from statin users with muscle complaints were sought through a review of a muscle biopsy database and possible study samples were identified; however, this was put on hold as too much information was missing from the pathology reports. Third, a series of cell culture experiments were carried out in which human skeletal muscle myotubes were exposed to various concentrations of simvastatin or atorvastatin, in order to determine an appropriate dose range for subsequent mitochondrial toxicity experiments. Lastly, mtDNA content and expression was quantified in skeletal muscle biopsies collected from 10 patients with statin-induced rhabdomyolysis (SIR) and compared to 8 healthy controls to investigate whether muscle mtDNA is altered in rhabdomyolysis. No differences in mtDNA content or expression were observed between the two study groups, but this may have been be due to the SIR subjects' marked heterogeneity. Statin therapy can be associated with considerable alterations in mtDNA content, which may play a role in the aetiology of SIM. MtDNA levels alterations with statin exposure should be investigated further to explore the involvement of mitochondrial alterations in the mechanism of SIM, and determine whether these may represent a useful clinical tool for assessing statin-induced muscle toxicity.

Thesis (MAppSc in Physiotherapy)--University of South Australia, 1995

Thesis (MPhysio)--University of South Australia, 1998