Animal models of muscle diseases, Part III: Compilation of therapeutic trials for hereditary muscular dystrophy

Therapeutic trial of isaxonine in Duchenne muscular dystrophy

A randomized double-blind therapeutic trial of isaxonine was completed over a 2-year period for 20 ambulant boys with Duchenne muscular dystrophy aged 5 1/2-10 years. The effect of the drug was monitored by measurement of walking times over 28 and 150 ft, motor ability score, MRC score based on 32 muscle groups, and myometry of 7 muscle groups. The drug had no significant effect on the progression of the disease. The trial had statistical power comparable to previous larger-scale multicenter trials. This reflected the low variability in the patients in relation to the magnitude of the overall deterioration. Measurements of muscle force (myometry and MRC score) had much greater statistical power than measurements of function (motor ability score and walking times) as analyzed by our methods. These observations have important implications for the design of future trials.

Ultrastructural changes in the cardiomyopathy of dystrophic hamsters and mice

Changes in the ultrastructure of the cardiac muscle cells have been followed in dystrophic mice and hamsters (22-40 weeks of age) and in both species a severe cardiomyopathy accompanies the cellular damage of the skeletal muscle. The degradative changes of the myofilament apparatus of the heart cells and the specific changes in mitochondrial ultrastructure (including swelling, septation and apparent division) are characteristic of the cellular damage of both the dystrophic skeletal muscle and of normal cardiac muscle in which [Ca]i has been experimentally raised, confirming the suggestions that (i) the same gene is responsible for the myopathy of skeletal and cardiac muscle in animal dystrophy and (ii) that changes in [Ca]i are implicated in the degradative changes of muscle cells.

Chicken muscle aldose reductase: purification, properties and relationship to other chicken aldo/keto reductases

An enzyme that catalyzes the NADPH-dependent reduction of a wide range of aromatic and hydroxy-aliphatic aldehydes was purified from chicken breast muscle. This enzyme shares many properties with mammalian aldose reductases including molecular weight, relative substrate specificity, Michaelis constants, an inhibitor specificity. Therefore, it seems appropriate to call this enzyme an aldose reductase (EC 1.1.1.21). Chicken muscle aldose reductase appears to be kinetically identical to an aldose reductase that has been purified from chicken kidney (Hara et al., Eur. J. Biochem. 133, 207-214) and to hen muscle L-glycol dehydrogenase (Bernado et al., Biochim. biophys. Acta 659, 189-198). The association of this aldose reductase with muscular dystrophy in the chick is discussed.

Inhibition studies on chicken muscle aldose reductase

Several compounds that are known to inhibit mammalian aldose reductases were examined for their effects on chicken muscle aldose reductase (EC 1.1.1.21). Sorbinil was the most effective compound tested. Alrestatin and phenobarbital were effective inhibitors of the enzyme although their IC50 values were 10-fold more than that of Sorbinil. Indomethacin, diphenylhydantoin, phenacetin, and valproate were also inhibitors of chicken muscle aldose reductase but were less effective. These compounds are all non-competitive inhibitors with respect to substrate. Menadione bisulfite, a watersoluble analog of Vitamin K3 which is a substrate for carbonyl reductase but not aldose reductase, was a competitive inhibitor of chicken aldose reductase with respect to substrate. This observation is discussed with reference to the possible treatment of muscular dystrophy with specific inhibitor of aldose reductases.

In vivo effects of three calcium blockers on chickens with inherited muscular dystrophy

Genetically homozygous Line 413 dystrophic chickens were given in separate trials daily i.p. injections of aqueous solutions of the calcium blocker drugs, diltiazem, verapamil, or nifedipine. At a dosage of 20 mg/kg/day, drug therapy in each case significantly prolonged the functional ability of the dystrophic chickens as quantitated regularly by a standardized test for righting ability. Enhanced functional ability, however, was not generally accompanied by a decrease in the usually high plasma creatine kinase activity. In addition, there was no change in the pectoralis muscle mass or protein with any of the drug treatments. Moreover, no significant reduction in the abnormally high total muscle calcium was found with calcium blocker treatment. Also, there was no marked change in the histopathology of muscle from the drug-treated dystrophic chickens. We concluded that drugs with calcium entry blocker activity offer only limited benefit in retarding dystrophic symptoms expressed in the chicken (viz., short-term enhancement in righting ability).

Drugs in muscular dystrophy of the chicken: corticosterone-21-acetate

In a previous series of 22-day evaluations of 31 compounds, only corticosterone-21-acetate (C-21-A) increased righting ability of genetically dystrophic chickens to a greater extent than the standard of comparison, methysergide maleate. In the present study, C-21-A was subjected to longer-term trials of up to 48 days, and additional signs of the myopathy were examined. The highest doses of C-21-A increased righting ability for the duration of the trials, decreased the typically elevated plasma levels of creatine kinase (CK) activity by more than 80%, and improved morphology of the dystrophic pectoralis major muscle at the light microscopic level. The major adverse effect of C-21-A, reduction of body weight, was consistently observed at the relatively high doses needed to increase righting ability. That alone, however, could not account for increased righting ability, and plasma CK activity was decreased even at doses that did not reduce body weight. The results show that C-21-A is the most effective compound yet tested in this system and, perhaps more significantly, provides the first evidence that it is possible to identify compounds that improve muscle morphology in a hereditary myopathy using a short-term, step-wise system.