Penicillamine, a cysteine analog with a reduced sulfhydryl group, has been used in this laboratory for the treatment of hereditary avian dystrophy. The drug delays the onset of symptoms and alleviates the debilitating aspects of the disease. To study the mechanism of drug action, the effects of penicillamine on white and red muscles of dystrophic chickens were examined with regard to the specific activities of the soluble enzymes glyceraldehyde-3-phosphate dehydrogenase, acetylphosphatase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glutathione reductase, glutathione preoxidase, superoxide dismutase, and catalase. The sulfhydryl contents of the soluble proteins and the concentration of myoglobin were also determined. In white dystrophic muscle (pectoral), there were large alterations in the various enzymatic activities compared to normal levels. In the DISCUSSION, these changes are related to the pathogenesis of the disease and to the adaptive response for protection of the severely affected fast fibers. Red dystrophic muscles (thigh) were minimally involved, in accordance with the known sparing action of the slow fiber type. The results suggested that the disease process in dystrophic muscle may be due to oxidation of the essential sulfhydryl groups of proteins. Penicillamine may produce therapeutic effects by altering the intracellular redox status, thereby promoting better regulation of enzymatic activity, membrane stability, and improved muscle function.

Penicillamine TreatmentPenicillamine has been used in this laboratory as a therapeutic agent in the treatment of hereditary muscular dystrophy in chickens.' Penicillamine delayed the onset of symptoms and partially alleviated the debilitating aspects of the disease. The drug produced three major improvements: better righting ability when birds were placed on their backs, greater wing flexibility, and suppression of plasma creatine phosphokinase (CPK) activity. The rationale for using penicillamine, a sulfhydryl compound with reducing properties, was an attempt to (1 ) protect essential thiol groups of enzymes and structural proteins against oxidation and to (2) decrease the formation of cross-linked insoluble collagen in muscle and tendon. Penicillamine was selected as a suitable drug for a program with this rationale because it is relatively stable to autoxidation and metabolic degradation.* Moreover, penicillamine blocks collagen cross-linking by inhibiting the formation of Schiff base intermediates and by cleaving intermolecular bonds3 Etfects of Penicillamine on Activities of Various EnzymesAs a continuation of this work, the mechanism of action of peniciliamine is now being investigated at an enzymatic level. Since penicillamine is a cysteine analog with a sulfhydryl group, the beneficial therapeutic effects may be related to changes in the intracellular oxidation-reduction state in dystrophic muscle. It was of interest, therefore, to examine the properties of the enzyme glyceraldehyde-3-phosphate dehydrogenase from dystrophic muscles. This dehydrogenase contains the most reactive cysteine residue in all glycolytic enzymes and is extremely sensitive to inactivation by sulfhydryl inhibitors or oxidants.' Sulfhydryl compounds, such as cysteine, glutathione, and penicillamine, protect the enzyme from inactivation. In muscle metabolism, this enzyme is important because it catalyzes the formation of 1,3-diphosphogIyceric acid, which supplies high-energy phosphate for ATP production during contraction and relaxation (FIGURE 1).In Duchenne human muscular dystrophy, this dehydrogenase has been shown to lose 70% of its activity compared to levels in normal muscle. This :L Supported