Interactions of vitamin E and penicillamine in the treatment of hereditary avian muscular dystrophy

Pharmacologic management of Duchenne muscular dystrophy: target identification and preclinical trials

Duchenne muscular dystrophy (DMD) is an X-linked human disorder in which absence of the protein dystrophin causes degeneration of skeletal and cardiac muscle. For the sake of treatment development, over and above definitive genetic and cell-based therapies, there is considerable interest in drugs that target downstream disease mechanisms. Drug candidates have typically been chosen based on the nature of pathologic lesions and presumed underlying mechanisms and then tested in animal models. Mammalian dystrophinopathies have been characterized in mice (mdx mouse) and dogs (golden retriever muscular dystrophy [GRMD]). Despite promising results in the mdx mouse, some therapies have not shown efficacy in DMD. Although the GRMD model offers a higher hurdle for translation, dogs have primarily been used to test genetic and cellular therapies where there is greater risk. Failed translation of animal studies to DMD raises questions about the propriety of methods and models used to identify drug targets and test efficacy of pharmacologic intervention. The mdx mouse and GRMD dog are genetically homologous to DMD but not necessarily analogous. Subcellular species differences are undoubtedly magnified at the whole-body level in clinical trials. This problem is compounded by disparate cultures in clinical trials and preclinical studies, pointing to a need for greater rigor and transparency in animal experiments. Molecular assays such as mRNA arrays and genome-wide association studies allow identification of genetic drug targets more closely tied to disease pathogenesis. Genes in which polymorphisms have been directly linked to DMD disease progression, as with osteopontin, are particularly attractive targets.

Oxidative stress and the pathogenesis of muscular dystrophies

The muscular dystrophies represent a diverse group of diseases differing in underlying genetic basis, age of onset, mode of inheritance, and severity of progression, but they share certain common pathologic features. Most prominent among these features is the necrotic degeneration of muscle fibers. Although the genetic basis of many of the dystrophies has been known for over a decade and new disease genes continue to be discovered, the pathogenetic mechanisms leading to muscle cell death in the dystrophies remain a mystery. This review focuses on the oxidative stress theory, which states that the final common pathway of muscle cell death in these diseases involves oxidative damage.

Lazaroids enhance skeletal myogenesis in primary cultures of dystrophin-deficient mdx mice

Growing evidence suggests a role for free radicals in the degeneration of dystrophin-deficient muscle (as observed in Duchenne muscular dystrophy). We therefore decided to test the action of the lazaroid antioxidant compounds on primary skeletal muscle cell cultures derived from an animal model of Duchenne muscular dystrophy, the mdx mouse. Both vitamin E-derived U-83836E and glucocorticoid-derived U-74389F enhanced myogenesis of dystrophin-deficient cultures as determined by the number of myotubes, the amount of nicotinic acetylcholine receptor, skeletal muscle alpha-actin levels and myosin light chain. U-83836E enhanced myogenesis of control congenic C57BL/10 mouse-derived muscle cultures whereas U-74389F had no detectable effect. This enhanced myogenesis was in most respects similar to the one triggered by alpha-methylprednisolone which is the only drug known to be beneficial in Duchenne muscular dystrophy.

Regulation of membrane-mediated chronic muscle degeneration in dystrophic hamsters by calcium-channel blockers: diltiazem, nifedipine and verapamil

Membrane-mediated excessive intracellular calcium accumulation (EICA) is a fundamental pathogenetic event associated with chronic muscle degeneration in patients with Duchenne muscular dystrophy (DMD), and in animals with hereditary muscular dystrophy (HMD). Because of potential Ca(2+)-channel blocking properties, we investigated the relative efficacies of chronic diltiazem (DTZM) (50 mg/kg/d), nifedipine (NFDN) (6 mg/kg/d), and verapamil (VPML) (25 mg/kg/d) therapies in reducing EICA and improving dystrophic pathobiology beginning in 30-day-old male BIO-14.6 strain dystrophic hamsters (DH). Each agent, and sterile distilled water as vehicle control, was given in a single daily oral dose for 180 days to four groups each of DH and BIO-F1B strain normal hamsters (NH). Plasma [Ca] and [Mg]; plasma aldolase (ALD), creatine kinase (CK), and lactate dehydrogenase (LDH) activities; relative cardiac hypertrophy and relative soleus hypertrophy; tissue [Ca] and [Mg] of the heart and rectus femoris muscle, histology of rectus femoris, and overall mortality rate were quantitated. Muscle Mg was not modified in DH, or by any of these agents. NFDN produced significant edema in the soleus and myocardium. During the 6-month therapeutic trial, 45% DH and 18% NH died on VPML, 27% DH and 9% NH on NFDN, and 20% DH controls on distilled water, but none on DTZM; suggesting that DTZM treated DH lived longer than DH controls. Relative efficacy in regulating EICA in both the cardiac and skeletal muscles; plasma ALD, CK, and LDH; and improving associated dystrophic pathobiology was found to be DTZM >>> NFDN > VPML. DTZM appears to be the most effective and safest agent in mitigating EICA in cardiac and skeletal muscles, efflux of intracellular enzymes, histopathology of dystrophic muscle with sporadic necrosis, and chronic muscle degeneration in DH with HMD. DTZM therapy also halted the high morbidity and mortality associated with the dystrophic pathobiology inherent in DH.

Catalytic mechanism and interactions of NAD+ with glyceraldehyde-3-phosphate dehydrogenase: correlation of EPR data and enzymatic studies

Perdeuterated spin label (DSL) analogs of NAD+, with the spin label attached at either the C8 or N6 position of the adenine ring, have been employed in an EPR investigation of models for negative cooperativity binding to tetrameric glyceraldehyde-3-phosphate dehydrogenase and conformational changes of the DSL-NAD+-enzyme complex during the catalytic reaction. C8-DSL-NAD+ and N6-DSL-NAD+ showed 80 and 45% of the activity of the native NAD+, respectively. Therefore, these spin-labeled compounds are very efficacious for investigations of the motional dynamics and catalytic mechanism of this dehydrogenase. Perdeuterated spin labels enhanced spectral sensitivity and resolution thereby enabling the simultaneous detection of spin-labeled NAD+ in three conditions: (1) DSL-NAD+ freely tumbling in the presence of, but not bound to, glyceraldehyde-3-phosphate dehydrogenase, (2) DSL-NAD+ tightly bound to enzyme subunits remote (58 A) from other NAD+ binding sites, and (3) DSL-NAD+ bound to adjacent monomers and exhibiting electron dipolar interactions (8-9 A or 12-13 A, depending on the analog). Determinations of relative amounts of DSL-NAD+ in these three environments and measurements of the binding constants, K1-K4, permitted characterization of the mathematical model describing the negative cooperativity in the binding of four NAD+ to glyceraldehyde-3-phosphate dehydrogenase. For enzyme crystallized from rabbit muscle, EPR results were found to be consistent with the ligand-induced sequential model and inconsistent with the pre-existing asymmetry models. The electron dipolar interaction observed between spin labels bound to two adjacent glyceraldehyde-3-phosphate dehydrogenase monomers (8-9 or 12-13 A) related by the R-axis provided a sensitive probe of conformational changes of the enzyme-DSL-NAD+ complex. When glyceraldehyde-3-phosphate was covalently bound to the active site cysteine-149, an increase in electron dipolar interaction was observed. This increase was consistent with a closer approximation of spin labels produced by steric interactions between the phosphoglyceryl residue and DSL-NAD+. Coenzyme reduction (DSL-NADH) or inactivation of the dehydrogenase by carboxymethylation of the active site cysteine-149 did not produce changes in the dipolar interactions or spatial separation of the spin labels attached to the adenine moiety of the NAD+. However, coenzyme reduction or carboxymethylation did alter the stoichiometry of binding and caused the release of approximately one loosely bound DSL-NAD+ from the enzyme. These findings suggest that ionic charge interactions are important in coenzyme binding at the active site.

Altered contents of tocopherols in chickens with inherited muscular dystrophy

Oxidative damage has been hypothesized as the basis for some of the changes in enzymatic functions and physical properties of membranes in inherited muscular dystrophy. The contents of alpha- and gamma-tocopherol (vitamin E) and their oxidation products, the tocopheryl quinones, were measured at 1 to 4 weeks after hatching in the muscle and other tissues of chickens with inherited muscular dystrophy. Analyses at these early ages minimized the potential influence of pathological changes on the measured parameters. The affected muscle (pectoralis major) of dystrophic birds contained significantly higher levels of alpha-tocopheryl quinone and a decreased ratio of alpha- to gamma-tocopherol. Consistent changes in these parameters were not observed in other tissues. Although their basis remains unclear, these changes in the tocopherols are suggestive of oxidative stress in dystrophic muscle membranes. Lipid extracts of tissues of normal and dystrophic birds exhibited no significant differences in the content of conjugated dienes or lipofuscins, two other indices of oxidative stress. These data do not consistently support the hypothesis that oxidative stress plays a causal role in damage to dystrophic muscle, although it remains possible that free-radical damage is involved in the secondary alterations associated with muscular dystrophy.

Clinical investigation in Duchenne muscular dystrophy: penicillamine and vitamin E

A double-blind controlled trial of penicillamine and vitamin E against placebo was conducted in 106 boys with Duchenne muscular dystrophy. Nine dropped out of the study after being randomized. Patients were evaluated using an established protocol that measures muscle strength, joint contractures, functional grade, and pulmonary function. The trial lasted for 18 months. The power of the study to detect a 75% slowing of the disease was 0.95 at a P less than 0.05. No therapeutic effect was observed in the patients taking penicillamine and vitamin E as compared with those taking placebo.