[Muscle energy metabolism in children with progressive muscular dystrophy type Duchenne. Metabolites of the Embden-Meyerhof pathway, the citric acid cycle and high energy phosphates and enzyme activity of alpha-glycerol-oxidase, succinate-dehydrogenase and 6-phospho-gluconate-dehydrogenase (author's transl)]

Altered allosteric properties of cytoskeleton-bound phosphofructokinase in muscle from mice with X chromosome-linked muscular dystrophy (mdx)

Intracellular distribution of cytoskeleton-bound and soluble phosphofructokinase (PFK) (the rate-limiting enzyme in glycolysis) in mdx dystrophic muscle was the same as in control nondystrophic muscle. However, the allosteric activity of both bound and soluble PFK was reduced in mdx muscle, accompanied by a decrease in ATP level. In contrast to normal muscle, the cytoskeleton-bound PFK in mdx muscle was sensitive to allosteric regulation, like the soluble enzyme. This change in the properties of cytoskeletal PFK in mdx mice may result from the absence of dystrophin, believed to reside in the cytoskeleton. The findings that cytoskeletal PFK in mdx muscle, although altered, remains bound to cytoskeleton may play a role in muscle structure and function and the mild clinical symptoms in mdx mice.

The pentose phosphate pathway in skeletal muscle under patho-physiological conditions. A combined histochemical and biochemical study

Over the last 30 years, research into the neuromuscular apparatus, has expanded greatly. Multidisciplinary investigations have rapidly advanced our understanding both of diseases and of the basic neuromuscular mechanisms. The mode of pathological reaction of the neuromuscular apparatus is now quite well understood. The most notable aspect of the reaction of the injured neuromuscular apparatus is the remarkably stereotyped character of the resulting pathological changes as demonstrated by a wide variety of harmful causes, producing surprisingly similar effects. The findings of our combined histochemical and biochemical investigations presented in this monograph, are in complete harmony with the stereotyped character of the pathological changes. For example, it is particularly striking that many affected muscle fibres of patients with muscular dystrophies, congenital myopathies, inflammatory myopathies, metabolic myopathies, endocrine myopathies, or with diseases of the lower motor neuron, display an enhanced activity of both oxidative enzymes of the pentose phosphate pathway. Likewise, we found that experimental animals with disordered skeletal muscles, provoked by different types of agents or treatments, reveal the same marked rise in activity of GPDH and PGDH in the muscle fibres, with a positive correlation between the activity of both enzymes. Other findings of our investigations point to a positive correlation between the activity of GPDH and PGDH on the one hand and that of the non-oxidative enzymes of the pentose phosphate pathway, the enzymes TA, TK, RPI and RPE on the other hand. The rise in activity of PGDH and, in particular, of GPDH is regulated by two different mechanisms. The first represents a rapid control mechanism based on the stimulation of both oxidative enzymes of the pentose phosphate pathway by NADP+ and on their inhibition by NADPH. The other mechanism represents a long-term effect directed at the synthesis of the enzymes. It is this type of mechanism which is responsible for the rise in activity of GPDH and PGDH we observed. The findings obtained with the applied enzyme histochemical techniques clearly demonstrated that the rise in activity of both enzymes is not homogeneously distributed in the disordered skeletal muscles of man and experimental animals. For that reason, in order to obtain reliable quantitative information about enzyme activities in the muscle fibres themselves, the application of biochemical assays on a micro-scale was indispensable. The biochemical assay of enzyme activities was performed on histologically and histochemically selected dissected muscle specimens.(ABSTRACT TRUNCATED AT 400 WORDS)

Ketogenic effects of carnitine in patients with muscular dystrophy and cytochrome oxidase deficiency

The effects of a single oral dose of carnitine on fasting-induced ketosis was investigated in four normal individuals, five patients with muscular dystrophy, and one patient with a generalized cytochrome c oxidase deficiency. Plasma carnitine, free fatty acids, glucose, insulin, and glucagon were also measured. Normal individuals showed an average 0.09 mM increase in blood beta-hydroxybutyrate concentration during a 12- to 18-hr period of fasting and carnitine administration did not affect this response (average: 0.12 mM). Muscular dystrophy patients showed a greater fasting-induced elevation in beta-hydroxybutyrate (average 0.29 mM) and carnitine administration greatly enhanced this ketogenic response (average 0.84 mM). The cytochrome c oxidase deficient patient showed an even larger increase in beta-hydroxybutyrate with fasting (1.67 mM) and carnitine further augmented this ketotic effect (3.78 mM). Plasma free fatty acids were also elevated in patients that showed enhanced ketosis. Plasma glucagon concentration did not change, but insulin levels decreased during the 12- to 18-hr period of fasting; no major differences were found between controls and patients. These results indicate that some patients with muscular dystrophy and cytochrome c oxidase deficiency are more prone to develop ketosis than normal individuals and that carnitine administration enhances this response. Since both muscular dystrophy patients and the patient with cytochrome c oxidase deficiency had similar ketogenic responses, the data suggest that ketone body utilization may be impaired in these patients. The ability of L-carnitine to be ketogenic should be considered in the treatment of these patients.

Effect of denervation on adenine nucleotides in skeletal muscle from normal and dystrophic mice

The effect of denervation on the adenine nucleotide content of fast- and slow-twitch skeletal muscle of the C57BL mouse was studied by high-performance liquid chromatography. From the adenine nucleotide content the energy charge, a measure of high-energy phosphate available to the cell, was calculated. The energy charge of the extensor digitorum longus muscle was significantly higher than that of the same muscle from dystrophic mice (C57BL/6J dy2j/dy2j) and on denervation decreased to the values found in the innervated muscle from dystrophic animals. Denervation of the muscle in dystrophic mice did not change the energy charge of that muscle. The energy charge of the soleus muscle from both normal and dystrophic mice was similar and did not change on denervation. It is proposed that in the dystrophic process a functional denervation of skeletal muscle occurs which preferentially affects fast-twitch muscle, leading to a reduction in the energy charge.

Duchenne muscular dystrophy: normal ATP turnover in cultured cells

We examined ATP metabolism in cultured muscle cells and fibroblasts from patients with Duchenne dystrophy. ATP and ADP levels were the same in cultured cells from normal subjects and patients and there was no difference in ATP synthesis or degradation. Although there was a significant decrease in radioactively labelled ATP after incubation with deoxyglucose in Duchenne muscle cells, there was no difference in ATP concentration or ADP metabolism.

An in vivo study of muscle phosphate metabolism in Becker's dystrophy by 31P NMR spectroscopy

The forearm flexor muscles of five patients with Becker's dystrophy were examined by the painless and noninvasive technique of high resolution phosphorus nuclear magnetic resonance spectroscopy. In the mildly affected cases, the ratios of the signals of phosphocreatine to ATP and to inorganic phosphate were normal but they were reduced in the patients with advanced disease. Absolute quantitation under the conditions of the study was not feasible, but it was probable that whereas in advanced Becker's dystrophy the intramyocellular concentration of phosphocreatine was reduced, that of ATP was unchanged. The intramyocellular pH was normal in three of the four patients in whom this could be measured and an additional unidentified signal between those of phosphocreatine and inorganic phosphate was recorded in two patients. This study emphasizes some metabolic similarities between Becker's and Duchenne type muscular dystrophy and suggests that nuclear magnetic resonance spectroscopy may be a useful and objective technique with which to investigate the biochemistry of these and other muscle diseases.

Clinical trials of allopurinol in Duchenne muscular dystrophy

A wide range of different disturbances characteristic of Duchenne muscular dystrophy (DMD) can be attributed to a fundamental chronic shortage of intracellular adenosine 5'-triphosphate (ATP), in turn arising from a basic lack of total adenylate. Purine conservation by the hypoxanthine isomer allopurinol, which promotes salvage and inhibits catabolism, greatly increases muscle ATP and total adenylate, with corresponding clinical benefit. Among subsequent confirmatory clinical trials some gave positive results, while others provided no information. Reasons given why these latter proved uninformative include asking questions either irrelevant and/or incapable of being answered, not least in older boys with too much shrinking fibrous tissue infiltrating too little remaining muscle. Informative results from any metabolic intervention can be expected only where sufficient muscle is left to respond, and this age-linked effect is everywhere evident in the positive trials. Thus, if an effect of allopurinol now seems apparent, and since it is extremely safe and does not enter the genetic material, it is suggested that it be administered shortly after birth before irreversible pathological changes occur. This implies neo-natal male mass screening, easily accomplished by a simple dried-blood spot test, and already carried out successfully elsewhere.

Topical magnetic resonance for the study of muscle metabolism in human myopathy

The role of changes in energy metabolism are obvious in the myopathies with described enzyme defects, but the ability afforded by topical magnetic resonance spectroscopy to study these changes repeatedly and non-invasively helps provide an understanding of the alterations in energy metabolism seen in muscle complaints of which the aetiologies are still unclear. Attention is focused on interpreting the findings with particular regard to Duchenne muscular dystrophy.

Increased rates of myofibrillar protein breakdown in muscle-wasting diseases

The excretion of endogenous creatinine and 3-methylhistidine by subjects with muscle diseases has been measured in order to assess muscle mass and fractional rates of myofibrillar protein degradation. Increases in the rates of myofibrillar protein breakdown were observed in all subjects with Duchenne, Becker, autosomal recessive Duchenne-like, and limb-girdle muscular dystrophy; dystrophia myotonica; myotonia congenita; peroneal muscular atrophy; myasthenia gravis; and central core disease; in some cases of spinal muscular atrophy; but in no cases of facioscapulohumeral muscular dystrophy of dystonia musculorum deformans. All increases in myofibrillar protein breakdown were associated with reductions in muscle proportion below the normal. Muscle-wasting diseases may respond to therapy directed towards an inhibition of muscle protease activity; the efficacy of such therapy can be monitored by the 3-methylhistidine-to-creatinine excretion ratio.

Hypoxanthine-guanine phosphoribosyltransferase activity of blood and muscle in Duchenne dystrophy

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity was measured in red cells and in skeletal muscles of normal and Duchenne subjects. [8-14C] hypoxanthine was used as substrate, and 5-phospho-alpha-D-ribose 1-diphosphate (PRPP) was used as the ribose-5-phosphate donor. The [8-14C] inosine monophosphate (IMP) formed was separated by high-voltage electrophoresis, and radioactivity was measured by lipid scintillation counting. HGPRT activity in Duchenne and normal red-cell hemolysates was similar, but such activity was significantly higher in Duchenne than in normal muscle homogenates. Red cells of both normal and Duchenne subjects had significantly higher enzyme activity than did skeletal muscles. It is suggested that increased HGPRT activity may be involved in enhancing protein synthesis by increasing intracellular levels of purine ribonucleotides.

The levels of cyclic GMP and glucose 1,6-diphosphate, and the activity of phosphofructokinase, in muscle from normal and dystrophic mice

A striking reduction in the levels of glucose 1,6-diphosphate and an increase in cyclic GMP were found in muscle from dystrophic mice. Concomitant to these changes, the allosteric activity of phosphofructokinase was found to be markedly reduced. These findings could offer an explanation for the observed reduction in glycolysis in the dystrophic muscle.

X-linked recessive (Duchenne) muscular dystrophy (DMD) and purine metabolism: effects of oral allopurinol and adenylate

Data are presented which suggest that Duchenne muscular dystrophy (DMD) may have some origin in a severe deficiency of total muscle adenine nucleotides. Using double-blind techniques, this possibility was tested in 16 DMD patients by giving oral allopurinol, a synthetic inhibitor of the purine catabolic enzyme xanthine oxidase. Sublingual procaine adenylate was also briefly tested. Instances of clinical improvement quickly occurred which were statistically significant; they were accompanied by a significant increase in physical strength. These improvements have been maintained for more than 6 mo by administration of a small amount of allopurinol daily. Procaine adenylate had little effect. These results support the above view of DMD and seem to indicate that existing purines, retained and recycled after allopurinol, can sustain such improvement, and that additional adenylate is unnecessary.

Studies on the carrier state in X-linked recessive (Duchenne) muscular dystrophy

Observations in 12 normal women and 12 female carriers of X-linked recessive Duchenne muscular dystrophy (DMD), of whom 4 had symptoms and 8 had none, were compared between all 4 groups and with those in 2 DMD boys, one active and one crippled. Carrier symptoms were readily ascertained by systematic examination. Measurement of both lower legs in all 24 women showed neither calf enlargement nor asymmetry in carriers beyond normal variation. Two DMD carrier daughters were noted of the same DMD carrier mother but by different fathers. Whole body counting showed the biological half-life of previously administered 86Rb to be much reduced in DMD, but no differences were found between normal women and any group of carriers. The test is thus valueless for carrier detection, and reasons are given why it should be so. Simultaneous measurement of total body K+, with subsequent determination by isotope dilution of total body water as 3H2O space and extracellular water as NH4 82Br space, showed increased intracellular water and reduced intracellular K+ concentration in all carriers, as if due to osmotic causes, with actual loss of muscle mass and slight diminution of serum K+ in the 4 symptomatic carriers only. Because of diurnal and other variations, the means and standard deviations for six serum enzymes from six fortnightly assays in all subjects were used to measure precise individual status. Their coefficients of variation were abnormal only in symptomatic carriers and ambulant DMD, easily overtexed by even accustomed exertion. This is shown to support previous propositions on the pathogenesis of DMD and the escape of muscle cell content into the circulation.