Intrinsic laryngeal muscles share many anatomical and physiological properties with extraocular muscles, which are unaffected in both Duchenne muscular dystrophy and mdx mice. We hypothesized that intrinsic laryngeal muscles are spared from myonecrosis in mdx mice and may serve as an additional tool to understand the mechanisms of muscle sparing in dystrophinopathy. Intrinsic laryngeal muscles and tibialis anterior (TA) muscle of adult and aged mdx and control C57Bl/10 mice were investigated. The percentage of central nucleated fibers, as a sign of muscle fibers that had undergone injury and regeneration, and myofiber labeling with Evans blue dye, as a marker of myofiber damage, were studied. Except for the cricothyroid muscle, none of the intrinsic laryngeal muscles from adult and old mdx mice showed signs of myofiber damage or Evans blue dye labeling, and all appeared to be normal. Central nucleation was readily visible in the TA of the same mdx mice. A significant increase in the percentage of central nucleated fibers was observed in adult cricothyroid muscle compared to the other intrinsic laryngeal muscles, which worsened with age. Thus, we have shown that the intrinsic laryngeal muscles are spared from the lack of dystrophin and may serve as a useful model to study the mechanisms of muscle sparing in dystrophinopathy.

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In the mdx mouse model of Duchenne muscular dystrophy, the lack of dystrophin is associated with increased calcium levels and skeletal muscle myonecrosis. The intrinsic laryngeal muscles (ILM) are protected and do not undergo myonecrosis. We investigated whether this protection is related to an increased expression of calcium-binding proteins, which may protect against the elevated calcium levels seen in dystrophic fibers. The expression of sarcoplasmic-endoplasmic-reticulum Ca(2+)-ATPase and calsequestrin was examined in ILM and in nonspared limb muscles of control and mdx mice using immunofluorescence and immunoblotting. Dystrophic ILM presented a significant increase in the proteins studied when compared to controls. The increase of Ca(2+)-handling proteins in dystrophic ILM may permit better maintenance of calcium homeostasis, with the consequent absence of myonecrosis. The results further support the concept that abnormal Ca(2+)-handling is involved in dystrophinopathies. Muscle Nerve, 2009.

In dystrophin-deficient fibers of mdx mice and in Duchenne muscular dystrophy, inflammation and increased production of tumor necrosis factor alpha (TNF-α) contribute to myonecrosis. We examined the effects of eicosapentaenoic acid (EPA) on dystrophic muscle degeneration. Mdx mice (14 days old) received EPA for 16 days. The sternomastoid, diaphragm and biceps brachii muscles were removed. Control mdx mice received vehicle. EPA decreased creatine kinase and myonecrosis and reduced the levels of TNF-α. These results suggest that EPA plays a protective role in dystrophic muscle degeneration, possibly by reducing TNF-α, and support further investigations of EPA as a potential therapy for dystrophinopathies.

The present study was designed to determine if the more severe copper deficiency in rats fed sucrose and fructose, as compared to starch, is due to a specific effect of the fructose or to a nonspecific effect of any simple carbohydrate. Seventy weanling male rats were fed, for 9 wk, copper-deficient diets or copper-supplemented diets containing either 62% starch, fructose, or glucose. Decreased hematocrit, serum copper, and ceruloplasmin concentrations but increased heart and liver weights, total liver lipid, and hepatic iron concentrations were found in all copper-deficient rats regardless of the dietary carbohydrate. Feeding rats the high glucose diet decreased plasma albumin and liver glycogen but increased blood urea nitrogen when compared to rats fed starch. However, rats fed fructose generally exhibited a more severe copper deficiency as compared to rats fed either starch or glucose. The severity was characterized by lower (p less than 0.05) body weight, liver glycogen, hematocrit, serum copper, and albumin. Conversely, liver and heart weights, blood urea nitrogen, and plasma glutamic oxaloacetic transaminase were higher (p less than 0.05). Plasma cholesterol was increased by copper deficiency only in rats fed fructose or glucose. During the study, 17 of the 40 rats fed copper-deficient diets died; 66% of those fed fructose, 26% fed glucose, and 30% fed starch. These results suggest that the fructose moiety of sucrose is responsible for the increased severity of copper deficiency in rats fed sucrose as compared to starch.

Copper deficiency was induced in rats by feeding sucrose or starch diets deficient in copper. Copper-deprived rats fed either diet exhibited decreased plasma ceruloplasmin concentration and increased plasma cholesterol. Glucose homeostasis and utilization was impaired both in vivo and in vitro. Oral glucose tolerance was impaired, insulin binding decreased, and CO2 formation and lipogenesis from [U-14C]glucose were decreased. Feeding sucrose but not starch diets deficient in copper magnified the copper deficiency and resulted in 60% mortality. Although both deficient diets contained the same concentration of copper, the hepatic copper concentration of rats fed sucrose was reduced nearly threefold compared to rats fed starch. Reduced epididymal fat pad, increased liver weight, reduced blood hemoglobin and a marked hypertrophy of the heart with gross deformities as well as histopathologic changes were noted only in those rats fed the copper-deficient sucrose diet. The biochemical lesions induced by deprivation of copper can be suppressed by feeding diets containing starch or can be magnified by high sucrose intake.

The effects of the interactions between dietary carbohydrates and copper deficiency on superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and their roles in peroxidative pathways were investigated. Weanling rats were fed diets deficient in copper and containing either 62% starch, fructose, or glucose. Decreased activity of SOD was noted in all rats fed the copper-deficient diets regardless of the nature of dietary carbohydrate. However, the decreased activity was more pronouced in rats fed fructose. Feeding the fructose diets decreased the activity of GSH-Px by 25 and 50% in the copper-supplemented and copper-deficient rats, respectively, compared to enzyme activities in rats fed similar diets containing either starch or glucose. The decreased SOD and GSH-Px activities in rats fed the fructose diet deficient in copper were associated with increased tissue per-oxidation and decreased hepatic adenosine triphosphate (ATP). When the fructose in the diet of copper-deficient rats was replaced with either starch or glucose, tissue SOD and GSH-Px activities were increased and these increases in enzyme activity were associated with a tendency toward reduced mitochondrial peroxidation when compared to the corre-sponding values for rats fed fructose throughout the experiment Dietary fructose aggrevated the symptoms associated with copper deficiency, but starch or glucose ameliorated them. The protective effects were more pronounced with starch than with glucose.

Rats were fed copper deficient (0.9 microgram/g) or copper-supplemented diets in which the carbohydrate was either starch, sucrose, or fructose (62% by weight) for 7 wk. Regardless of the nature of the carbohydrate, copper deficiency decreased blood ceruloplasmin activity, hepatic copper and ATP levels, and increased plasma cholesterol and triglycerides. Copper deficiency in rats fed sucrose or fructose, but not those fed starch, significantly lowered blood hematocrit, Hb, and albumin and significantly increased heart and liver weight and the glucose response to a glycemic stress. Hepatic copper level was significantly lower in copper-deficient rats fed sucrose or fructose than in those fed starch. Fasting blood glucose, cholesterol, and triglyceride levels were significantly higher in copper deficient rats fed fructose than in those fed starch. During the study 14 copper-deficient rats died, one of 10 fed starch, six of 20 fed sucrose, and seven of 20 fed fructose. Death was apparently the result of rupture of the heart in the region of the apex. These results indicate that fructose-containing carbohydrates as compared to starch markedly increase the severity of copper deficiency in rats. Whether this effect is due to differences in the nature of the simple carbohydrate (fructose versus glucose) or to molecular size (simple versus complex carbohydrate) remains to be established.