Delayed functional disability in dystrophic chickens receiving chemotherapy

Abnormal response to calmodulin in vitro of dystrophic chicken muscle membrane Ca2+-ATPase activity

A skeletal muscle membrane fraction enriched in sarcoplasmic reticulum (SR) contained Ca2+-ATPase activity which was stimulated in vitro in normal chickens (line 412) by 6 nM purified bovine calmodulin (33% increase over control, P less than 0.001). In contrast, striated muscle from chickens (line 413) affected with an inherited form of muscular dystrophy, but otherwise genetically similar to line 412, contained SR-enriched Ca2+-ATPase activity which was resistant to stimulation in vitro by calmodulin. Basal levels of Ca2+-ATPase activity (no added calmodulin) were comparable in muscles of unaffected and affected animals, and the Ca2+ optima of the enzymes in normal and dystrophic muscle were identical. Purified SR vesicles, obtained by calcium phosphate loading and sucrose density gradient centrifugation, showed the same resistance of dystrophic Ca2+-ATPase to exogenous calmodulin as the SR-enriched muscle membrane fraction. Dystrophic muscle had increased Ca2+ content compared to that of normal animals (P less than 0.04) and has been previously shown to contain increased levels of immuno- and bioactive calmodulin and of calmodulin mRNA. The calmodulin resistance of the Ca2+-ATPase in dystrophic muscle reflects a defect in regulation of cell Ca2+ metabolism associated with elevated cellular Ca2+ and calmodulin concentrations.

Free radicals: a potential pathogenic mechanism in inherited muscular dystrophy

Despite years of intensive work, the biochemical defect responsible for the pathogenesis of inherited muscular dystrophy has not been identified either in humans or animal models. This review examines evidence in support of the hypothesis that free radicals may be responsible for muscle degeneration in this disorder. A variety of cellular abnormalities noted in dystrophic muscles can be accounted for by free radical mediated damage. In addition, chemical by-products associated with free radical damage are found in dystrophic muscle tissue from humans and animals with this disease. Various enzymatic antioxidant systems can be enhanced as a normal cellular response to oxidative stress, and such changes are seen both in dystrophic muscle cells and certain other tissues of dystrophic animals. An increased level of free radical damage would follow from either: enhanced production of free radical species, or a deficient component of the cellular antioxidant system, such as vitamin E. The free radical hypothesis of muscular dystrophy can account for data supporting several alternative theories of the pathogenesis of this disease, as well as other observations which have not previously been explained.

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.

Limited benefit to genetically dystrophic chickens from a synthetic proteinase inhibitor: Ep475

Chickens with inherited muscular dystrophy (Line 413) were treated in two separate trials with daily intraperitoneal injections of 10% DMSO-water solutions containing the proteinase inhibitors, Ep475 and E64. Drug therapy in each case significantly prolonged the functional ability of the treated chickens. Diluent control chickens around day 35 ex ovo characteristically reached a maximum ability to right from the supine position in a standardized functional test for muscle weakness. Subsequently, the control chickens were found to decline progressively in their ability to right. Treatment with the proteinase inhibitors had no effect on the typically elevated levels of plasma creatine kinase activity. In a histological analysis of the affected pectoralis major muscle, drug treatment had no effect on the relative distribution of degenerating, and vacuolated fibers, inflammatory cells, and abnormal fiber diameters. An exception was seen in decreased necrotic fibers of chickens treated with high doses of Ep475. Moreover, both inhibitors had positive effects on two biochemical abnormalities common to the dystrophic pectoralis muscle: increase in noncollagen protein, and reduction in total calcium.

Chicken muscular dystrophy: an inherited disorder of flight

Dystrophic (University of California, Davis, line 413) and normal control (Davis, 1. 412) chicks (Gallus domesticus) between 7 and 49 days old were tested for flight-related pathology and righting ability. Drop-evoked lateral flight developed in control chicks between 7 and 13 days. Dystrophic chicks never developed lateral flight. Both dystrophic and control chicks showed drop-evoked wing-flapping on the day of hatching. Also, dystrophic chicks had a normal but slightly higher drop-evoked flapping rate than controls at 13 days. Thus, the neural circuits that initiated and generated the rate of drop-evoked wing-flapping, present in dystrophic chicks at birth, were intact at 13 days, when deficiencies in lateral flight and righting ability were already present. The righting behavior of control chicks was superior to that of dystrophic chicks at all ages from 7 to 49 days.

Parenteral branched-chain amino acid treatment and avian dystrophy

Genetically homozygous line 413 dystrophic chickens were given twice-daily intraperitoneal injections of solutions containing branched-chain amino acids (BCCA-leucine, valine, isoleucine) either alone or in combination; and their alpha-ketoacid analogs (alpha-ketoisocaproic and alpha-ketoisovaleric acids). Another trial consisted of an amino acid mixture containing BCAA. Amino acid supplementation in each case significantly prolonged righting ability measured regularly by a standardized flip-test procedure. Enhanced functional ability was not generally accompanied by a decrease in plasma creatine kinase activity. However, a measurable increase in the affected pectoralis major muscle mass and protein content (female chickens in particular) was found with BCAA therapy. Moreover, the increase in muscle bulk was attended in some cases by a reduction in the relative number of degenerating fibers quantitated microscopically. Contrariwise, the amino acid mixture caused a reduction in pectoralis muscle mass. It is concluded that parenteral BCAA therapy offers limited benefit in retarding dystrophic symptoms in the chickens.

Therapeutic trial with protease inhibitor (leupeptin) in chicken muscular dystrophy. A histologic and histochemical study

For the purpose of observing the therapeutic benefit of protease inhibitors for progressive muscular dystrophy, a large quantity of doses of leupeptin of 10 mg/kg/day and 50 mg/kg/day were administered i.p. to male chickens afflicted with hereditary muscular dystrophy (line 413) for 4 months starting on the 7th day ex ovo. No clinical improvement was identified in physical ability as a result of the examination by flip test, and creatine kinase (CK) values. The number of necrotic fibers in the pectoralis superficialis (PS) muscle which is known to be preferentially damaged in dystrophic chicken, did not decrease significantly in the birds treated with 10 mg leupeptin/kg/day (number of necrotic fibers; 47.7/mm2) and 50 mg/kg/day (46.4/mm2) as compared to that of the untreated ones (43.2/mm2). A morphometric analysis of fiber diameter distribution also showed no statistical difference between the treated and untreated birds. In the second group, 10 mg leupeptin/kg and a combination of leupeptin and bestatin of 10 mg/kg each were injected directly into the left lower half of the PS muscle three times a week for 4 months. Necrotic fibers were still present in the injected site, remote area of the left upper PS muscle treated with leupeptin (52.7/mm2), leupeptin and bestatin (52.2/mm2), and contralateral right upper PS muscle (41.6 and 53.5/mm2, respectively). The number of necrotic fibers in treated muscles was again not significantly different from that in untreated dystrophic ones (39.6/mm2). In fiber diameter analysis, no statistical difference was recognized between the treated and untreated dystrophic muscles.

In vivo effects of protease inhibitors on chickens with hereditary muscular dystrophy

Beginning on day 4 ex ovo, and every 3 d thereafter, genetically dystrophic Line 413 chickens were given intraperitoneal injections (4 mg/kg body wt) of a protease inhibitor, leupeptin, pepstatin, or antipain. Experimental chickens received protease inhibitors dissolved in a water:ethanol:dimethyl sulfoxide solution (50:40:10, vol:vol:vol). Control untreated animals received diluent injections. Untreated dystrophic chickens typically reach around day 30 ex ovo a maximum ability to right from the supine position in a standardized functional test for muscle weakness. After day 30 ex ovo, the dystrophic chickens are found to decline progressively in their ability to right, compared with normal, nondystrophic controls, which have an unimpaired ability to right. Concomitantly, dystrophic chickens exhibit characteristically high levels of plasma creatine phosphokinase enzyme activity. In addition, an increased frequency of degenerating, regenerating, and vacuolated myofibers, and inflammatory cells appear in the affected pectoralis major muscles from the dystrophic chicken. Throughout the duration of the trial, there was no major enhancement in the functional righting ability of dystrophic chickens receiving any one of the protease inhibitors tested. However, there was a significant reduction in the abnormally high levels of plasma creatine phosphokinase in the treated chickens. Also, there was an apparent reduction in the mean number of vacuolated fibers in the pectoralis muscle from the protease inhibitor-treated birds. No significant reductions were observed in the relative frequency of degenerating and regenerating myofibers or inflammatory cells. In addition to the plasma creatine phosphokinase decrease, however, therapeutic benefit was seen in 31.0, 30.5, and 14.8% increases in the wet weight (and total noncollagen protein) of pectoralis muscle from dystrophic chickens receiving leupeptin, pepstatin or antipain, respectively.