Chronic losartan administration reduces mortality and preserves cardiac but not skeletal muscle function in dystrophic mice

Duchenne muscular dystrophy (DMD) is a degenerative disorder affecting skeletal and cardiac muscle for which there is no effective therapy. Angiotension receptor blockade (ARB) has excellent therapeutic potential in DMD based on recent data demonstrating attenuation of skeletal muscle disease progression during 6–9 months of therapy in the mdx mouse model of DMD. Since cardiac-related death is major cause of mortality in DMD, it is important to evaluate the effect of any novel treatment on the heart. Therefore, we evaluated the long-term impact of ARB on both the skeletal muscle and cardiac phenotype of the mdx mouse. Mdx mice received either losartan (0.6 g/L) (n = 8) or standard drinking water (n = 9) for two years, after which echocardiography was performed to assess cardiac function. Skeletal muscle weight, morphology, and function were assessed. Fibrosis was evaluated in the diaphragm and heart by Trichrome stain and by determination of tissue hydroxyproline content. By the study endpoint, 88% of treated mice were alive compared to only 44% of untreated (p = 0.05). No difference in skeletal muscle morphology, function, or fibrosis was noted in losartan-treated animals. Cardiac function was significantly preserved with losartan treatment, with a trend towards reduction in cardiac fibrosis. We saw no impact on the skeletal muscle disease progression, suggesting that other pathways that trigger fibrosis dominate over angiotensin II in skeletal muscle long term, unlike the situation in the heart. Our study suggests that ARB may be an important prophylactic treatment for DMD-associated cardiomyopathy, but will not impact skeletal muscle disease.

Complement 3 deficiency and oral prednisolone improve strength and prolong survival of laminin alpha2-deficient mice

Complement deposition and macrophages are common in biopsies of children with muscular dystrophy. While the presumed roles of complement and macrophages have been those of scavenger to remove and clear necrotic fibers, there is some evidence that they play a primary role in the pathogenesis of these diseases. Here, we explore the role of complement in the pathogenesis of the most severe animal model of congenital dystrophy, the dy-/- mouse, which is laminin alpha2-deficient. We generated animals deficient in both C3 and laminin alpha2. C3 is the third component of the complement cascade and is required for activation of either the classical or alternative pathways. Thirty-three percent of the dy-/-:C3+ mice (n=59) died before 24 weeks while only 14% of the dy-/-:C3-/- (n=29) mice died (p=0.04). Absolute forepaw strength was 25-30% greater for the dy-/-:C3-/- mice up to 20 weeks of age (p<0.05 compared to complement-sufficient). Forepaw strength adjusted for weight also showed significant differences with C3-/- mice being stronger up to 20 weeks (p<0.05). However, by 24 weeks, the two groups did not differ for strength. Next, we treated 20 mice with twice weekly oral prednisolone. Survival at 24 weeks for the prednisolone treated dy-/- mice (C3-/- or C3+) was 90% (p=0.04). This work shows that complement insufficiency and weekly prednisone prolong survival and improve strength of the laminin alpha2-deficient mouse. This work suggests that the complement system may contribute directly to the pathogenesis of this form of dystrophy. Because complement activity may be modified pharmacologically, this work may have implications for treatment of children with congenital muscular dystrophy secondary to laminin alpha2 deficiency.

Mutual interference of myotonia and muscular dystrophy in the mouse: a study on ADR-MDX double mutants

For Duchenne muscular dystrophy (DMD, dystrophin deficiency) and Thomsen/Becker myotonia (muscular chloride channel deficiency) genetically homologous mouse models are available, the dystrophin-deficient MDX mouse and the myotonic ADR mouse. Whereas the latter shows more severe symptoms than human myotonia patients, the MDX mouse, in contrast to DMD patients, is only mildly affected. We have introduced, by appropriate breeding, the defect leading to myotonia (Clc1 null mutation, adr allele) into MDX mice, thus creating ADR-MDX double mutants. The expectation was that, due to mechanical stress during myotonic cramps, the ADR status should symptomatically aggravate the muscle fibre necrosis caused by the dystrophin deficiency. The overall symptoms of the double mutants were dominated by myotonia. Weight reduction and premature death rate were higher in ADR-MDX than in ADR mice. Sarcolemmal ruptures as indicated by influx into muscle fibres of serum globulins and injected Evans blue were found with great inter-individual variation in MDX and in ADR-MDX muscles. Affected fibres were found mainly in large groups in MDX but single or in small clusters in ADR-MDX leg muscles. The symptoms of myotonia (aftercontractions, shift towards oxidative fibres) were less pronounced in ADR-MDX than in ADR muscles. Conversely, numbers of damaged fibres as well as the percentage of central nuclei (an indicator of fibre regeneration) were significantly lower in ADR-MDX than in MDX skeletal muscles. Thus it appears that, at the level of the muscle fibre, myotonia and muscular dystrophy attenuate each other.

Examining potential drug therapies for muscular dystrophy utilising the dy/dy mouse: I. Clenbuterol

As a potent promoter of muscle growth, clenbuterol has been proposed as a treatment for muscle wasting diseases. Thus, the effects of clenbuterol on dystrophic skeletal muscle was examined. Male dystrophic (dy/dy) mice aged 4-5 weeks were treated with clenbuterol for 3 weeks, and the isometric contractile, fatigue and histochemical properties of the slow-twitch soleus and fast-twitch plantaris muscles measured. Muscles of dystrophic animals produced lower forces, contracted more slowly and exhibited greater fatigue resistance than age-matched normal animals. Dystrophic soleus muscles also had higher proportions of type I fibres than normal mice. Clenbuterol significantly reduced the natural death rate of dystrophic mice, as 3 of 11 untreated animals died prior to completion of the 3-week experimental period, whereas none of the 9 clenbuterol-treated animals died. Clenbuterol treatment significantly increased the relative mass (P<0.001) and relative tetanic force production (P<0.01) of the soleus of dystrophic animals, most likely due to increases in protein accretion and improved regeneration. The plantaris of clenbuterol-treated dystrophic animals also exhibited higher mass (P<0.05) and higher absolute forces than untreated mice. The results from this study show that clenbuterol could be a valuable adjunct to treatments of muscle wasting diseases such as muscular dystrophy.

Beneficial effect of new thiol protease inhibitors, epoxide derivatives, on dystrophic mice

We studied the effect of E-64, a new thiol protease inhibitor derived from Aspergillus japonicus TPR-64, and of its synthesized analogue, E-64-d, on dystrophic mice (C57BL/6J-dy). The locomotor activity of normal mice increased markedly, reaching a plateau at 8 weeks of age. In dystrophic mice, it increased until they were 7 weeks old, thereafter, it decreased gradually. This decrease reflected the degradation of the hind legs. Serum activities of creatine phosphokinase were significantly greater in dystrophic than in normal mice. When 3-week-old dystrophic mice were injected with E-64 (1 mg/kg, i.p.) or E-64-d (40 to 60 mg/kg, p.o.), the decrease in their locomotor activity was retarded and their serum enzyme activities decreased significantly. In addition, the survival time of treated dystrophic mice was prolonged. The locomotor activity of normal mice and their serum enzyme levels were not affected by the administration of E-64-d. We posit that the new thiol protease inhibitors we tested retard the progression of dystrophy in mice.

Exercise effect on contractile properties of skeletal muscle in mouse muscular dystrophy

The purpose of this study was to determine the effect of a high repetitive exercise program, treadmill running, on the tetanic tension and rate of tension development of the slow twitch soleus muscle of normal plus dystrophic mice and their littermates. The exercise program used would be considered to be of mild intensity since it failed to produce any detectable histochemical or biochemical changes. In the noninvolved normal and littermate mice, there was no difference in maximum tetanic tension between the exercised and nonexercised control groups. In the normal mice (eight weeks of age), there was a significant decrease in rate of tension development for those exercised for five weeks compared to nonexercised controls. In littermate mice (seven weeks old) exercised for a four-week period, there was also a significantly lower rate of tension development compared to their nonexercised controls. In dystrophic mice (seven weeks old) exercised for only one to two weeks, there was significantly lower tension as well as rate of tension developed for the exercised mice when compared to nonexercised dystrophic mice. In dystrophic mice (six weeks old) exercised for one to two weeks, there was no difference in tension or rate of tension development when compared to nonexercised controls. In both six and seven-week-old littermate mice, also exercised for one to two weeks, this reduction in tension and rate of tension development did not occur. The average life span for the dystrophic mice used in this study is about 30 weeks. Of the nine exercised dystrophic mice scheduled for study at eight weeks, only one survived, suggesting that even the mild exercise used might have shortened their life expectancy.

Selenium-responsive myopathy in broiler breeder hens in Queensland

A syndrome characterised by bilateral paralysis and associated with degenerative changes in skeletal musculature, has been noted in adult breeder hens, and their progeny broilers, in a commercial poultry organisation in Queensland. Paralysis occurred between the ages of 24 to 63 weeks in broiler breeder hens and at approximately 6 weeks in the broiler chickens. Onset is slow, taking up to 2-3 days from the time leg weakness if first noticed until paralysis was complete. Other than the paralysis the birds appeared normal. Histopathological and experimental observations indicate that the muscular dystrophy is caused by a selenium deficiency. Supplementation of the diet with selenium at a level of 0.1 ppm completely alleviated the symptoms such that the birds may be returned to the mating pens.

Relationship between selenium content of forage, blood and organs of sheep, and lamb mortality rate

The investigation comprised 12 herds, totalling 660 sheep, in the counties of Stockholm and Uppsala. The selenium content of specimens of forage, whole blood, muscle, liver, and kidney was determined by a fluorimetric method. Data on the number of born and dead lambs were collected 4—5 months after lambing. Dead and sick lambs were subjected to necropsy and to clinico-chemical analyses, respectively.

The selenium content of hay and corn was lower than 60 ng per g, which some authors regard as the minimum level of Se requirement for protection against white muscle disease in sheep. The analyses of forage mixtures containing oil concentrates and beet pulp showed selenium levels that were about 2—5 times as high as this minimum level.

In herds in which the animals had not been treated with selenium preparations prior to sampling, there was a significant positive correlation between the selenium content of the forage and that of whole blood. A relationship was also noted between the selenium content of forage and of organs.

In 9 out of the 12 herds the selenium concentrations in whole blood were on the level that is considered to be representative of white muscle disease.

A high mortality rate was recorded for lambs whose mothers had low selenium levels in their blood.

Prophylactic and curative treatment with selenium plus vitamin E orally and/or parenterally probably reduced lamb mortality rate in the herds fed a low-selenium diet.