William J. Bank

A disorder of muscle lipid metabolism and myoglobinuria. Absence of carnitine palmityl transferase.

Two brothers, 29 and 33 years of age, had recurrent myoglobinuria, renal failure and azotemia, but were otherwise normal, without apparent muscle weakness or exercise intolerance. Ischemic exercise resulted in normal lactate production. Muscle glycogen content and activities of phosphorylase and phosphofructokinase were normal. Plasma triglycerides were elevated (500 mg per deciliter) on a regular diet and rose during fasting. During a 72-hour fast, serum creatine phosphokinase rose more than 10 times, and myoglobin was detected in urine. Plasma ketone production was minimal during fasting, but prompt ketonemia ( a normal response) occurred after ingestion of medium-chain triglycerides. Carnitine palmityl transferase activity was virtually absent in crude muscle extracts and mitochondrial fractions. Lack of this enzyme impairs long-chain fatty acid utilization, reflected in increased content of plasma free fatty acids and plasma triglycerides. Depletion of ATP because of this metabolic block in muscle may account for the attacks of myoglobinuria.

31P NMR studies in Duchenne muscular dystrophy: Age‐related metabolic changes

To evaluate possible progressive metabolic changes in Duchenne muscular dystrophy, we used 31P nuclear magnetic resonance spectroscopy to measure high-energy phosphate compounds and phosphorylated diesters (PDE) in resting gastrocnemius muscle of 14 Duchenne patients and 10 normal boys. The patients had higher inorganic phosphate (Pi), intracellular pH, and PDE; and lower phosphocreatine (PCr) and PCr/Pi ratio; ATP was not significantly different. The patients showed significant age-related decreases in PCr and PCr/Pi, and increases in Pi and PDE, but ATP did not change. In normal boys, ATP increased with age, but PCr and Pi did not. These studies imply progressive metabolic deterioration in Duchenne dystrophy.

Bioenergetic heterogeneity of human mitochondrial myopathies: Phosphorus magnetic resonance spectroscopy study

Twelve adults with mitochondrial myopathies were studied by phosphorus magnetic resonance spectroscopy of muscle. All 12 had abnormal 31P-NMR findings; recovery from exercise was abnormal in 11 patients. At rest, the ratio of phosphocreatine to inorganic phosphate was reduced in 10. Exercise transfer characteristics were abnormal in all five patients who could exercise. Exercise-induced intracellular acidosis was subnormal in nine patients. The range of abnormalities indicates biochemical heterogeneity, with two possible groups: (1) primary defects of energy metabolism with marked 31P-NMR abnormalities, and (2) secondary, less specific 31P-NMR abnormalities.

Effects of thyroid hormones on skeletal muscle bioenergetics. In vivo phosphorus-31 magnetic resonance spectroscopy study of humans and rats.

The pathophysiology of the myopathy in dysthyroid states is poorly understood. We therefore tested the effects of thyroid hormones on muscle bioenergetics in humans and rats, using in vivo 31P NMR. Two hypothyroid patients had: low phosphocreatine to inorganic phosphate ratio (PCr/Pi) at rest, increased PCr depletion during exercise and delayed postexercise recovery of PCr/Pi. Eight thyroidectomized rats did not show abnormalities at rest, but muscle work induced by nerve stimulation resulted in a significantly (P less than 0.0001) lower PCr/Pi (35-45% of control) at each of the three stimulation frequencies tested (0.25, 0.5, and 1.0 Hz). Recovery rate was markedly slowed to one-third of normal values. Thyroxine therapy reversed these abnormalities in both human and rat muscle. Five patients and six rats with hyperthyroidism did not differ from normal controls during rest and exercise but had an unusually rapid recovery after exercise. The bioenergetic abnormalities in hypothyroid muscle suggest the existence of a hormone-dependent, reversible mitochondrial impairment in this disorder. The exercise intolerance and fatigue experienced in hypothyroid muscle may be due to such a bioenergetic impairment. The changes in energy metabolism in hyperthyroid muscle probably do not cause the muscular disease in this disorder.

The use of nuclear magnetic resonance to evaluate muscle injury

Magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) are new and powerful tools to study tissue biochemistry, and to provide precise anatomical visualization of soft tissue structures. This review focuses on the use of these techniques to study exercise-induced muscle injury. MRS measurements show an increase in the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) 1-7 d after eccentric exercise. This increase in Pi/PCr could be due to either increases in extracellular Pi or small increases in resting muscle metabolism. Increased Pi/PCr is also seen during training programs and may indicate persistent muscle injury. Increased resting Pi/PCr with injury was not associated with altered metabolism during exercise. Elevations in resting Pi/PCr have been used to show increased susceptibility of dystrophic muscle to exercise-induced injury. Progressive clinical deterioration in dystrophic dogs is marked by impaired muscle metabolism, and the presence of low oxidative muscle fibers not seen in normal dogs. MRI shows increased proton T2 relaxation times following eccentric exercise that last up to 80 d after injury, and can reflect muscle edema as well as longer lasting changes in the characteristics of cell water. MRI demonstrate precise localization of the injured area, with large differences in both location and degree of injury in different subjects following the same exercise protocol. Thus, MRS can provide information on the metabolic response to injury, while MRI provides information regarding the site and extent of the injury. These tools have promise in helping to understand exercise-induced muscle injury.

Muscle energy metabolism in McArdle's syndrome by in vivo phosphorus magnetic resonance spectroscopy

Five patients with McArdles syndrome were examined by phosphorus magnetic resonance spectroscopy (31P-NMR). Adenosine triphosphate (ATP) levels at rest were reduced by 22%, but did not fall further during exercise or contracture. The slope of work rate versus inorganic phosphate/phosphocreatine (Pi/PCr) was 42 ± 8 joules/min/Pi/PCr in three patients without muscle wasting, compared with 13 and 16 in patients with atrophy (normal, 30 to 50 joules/min/Pi/PCr). Recovery from exercise showed similar rates in patients (postischemic exercise 1.03 ± 0.17, post-aerobic 1.63 ± 0.17 PCr/Pi units per minute) and controls (1.0 ± 0.2 and 1.8 ± 0.2, respectively) independent of intracellular pH. Infusion of glucose improved exercise kinetics by 163 to 190%, but an oral load of protein had no effect. We conclude that (1) muscle mitochondria operate normally in vivo in this glycogenolytic disorder, suggesting a sufficient alternate fuel supply. (2) Blood-borne glucose may serve as one alternate fuel for the “second wind” phenomenon. (3) ATP control mechanisms are altered only at rest. (4) Recovery from exercise is relatively pH-independent.

Atherosclerotic carotid artery disease in patients with retinal ischemic syndromes

The extracranial carotid systems of 105 patients with retinal ischemia were examined using B-mode ultrasonography with integrated pulsed Doppler. Sixty-four patients had amaurosis fugax (AF), 17 central retinal artery occlusions (CRAO), and 21 branch retinal artery occlusions (BRAO). The prevalence of carotid stenosis (≥60%) ipsilateral to the symptomatic eye was low (16%). Eighty-six percent of AF patients had either no plaque or plaque causing less than a 60% stenosis. A significant proportion of subjects with normal duplex scans had alternative explanations for their retinal ischemia (eg, migraine, cardiac embolus). Patients with Hollenhorst plaques were more likely to have stenotic or ulcerated plaque (p = 0.04). The degree of carotid stenosis correlated significantly with the number of vascular risk factors identified in individual patients (p = 0.02). The presence of risk factors was more common in CRAO and BRAO patients compared with the AF group. Combined ultrasound-Doppler investigations of the carotid bifurcation are valuable noninvasive tools for the screening of patients with retinal ischemia.

Near infrared muscle spectroscopy in patients with Friedreich's ataxia

Friedreichs ataxia is a progressive neurodegenerative disorder of the afferent cerebellar pathways associated with mitochondrial dysfunction at the cellular level. We have used noninvasive continuous near infrared muscle spectroscopy (NIRS) to investigate the delivery and utilization of oxygen in response to exercise in this disorder. Patients performed an incremental treadmill walking protocol in which levels of muscle deoxygenation or oxygenation were continuously measured in the medial calf muscle. The kinetics of recovery from exercise‐induced deoxygenation, called the half‐time of recovery (t1/2) were determined. The t1/2 was prolonged in patients with Friedreichs ataxia compared with controls, and the degree of prolongation correlated with the length of the shorter GAA repeat, a genetic measure that correlates with the age of onset of disease. The t1/2 also correlated inversely with patient age and with the maximum treadmill speed attained. Several patients also displayed features consistent with inadequate oxygen utilization by muscle. These results suggest that NIRS may be an effective tool for monitoring the biochemical and functional features of Friedreichs ataxia in parallel.

Biochemical and genetic studies in a family with mitochondrial myopathy.

We present a family with severe exercise intolerance, progressive proximal weakness, and lactic acidemia. Fifteen of 24 family members in five generations were affected. Since the affected males do not have offspring at this time, the family pedigree is consistent with either maternal or autosomal dominant inheritance. Muscle histochemistry showed ragged‐red fibers and electron microscopy showed globular mitochondrial inclusions. Biochemical analysis showed reduced muscle activities of mitochondrial NADH‐cytochrome c reductase (1 of 2 patients), succinate‐cytochrome c reductase (2 patients), and cytochrome c oxidase (2 patients). For 1 patient, sequence analysis of 44% of the muscle mitochondrial DNA including all 22 transfer RNA regions showed no point mutation with pathogenic significance. Southern blot analysis showed no deletion. Six affected members of the family were treated with methylprednisolone (0.25 mg/kg) for 3 months. Muscle strength, serum lactate, and energy metabolism at rest (measured by 31P magnetic resonance spectroscopy) significantly improved with treatment.

Diagnosis of defects in oxidative muscle metabolism by non-invasive tissue oximetry

The dynamics of oxygen delivery and utilization are examined in a variety of mitochondrial disorders during rest, exercise and post exercise. We used a non-invasive optical technique to measure the oxygen consumption in the exercising limb in normal subjects and 5 patients with cytochrome c oxidase deficiency. We also examined 6 patients with MELAS and MERRF syndrome. We measured near-infrared spectra of hemoglobin in the gastrocnemius muscle during treadmill exercise. Normal subjects demonstrated a sustained deoxygenation during exercise, indicating an efficient utilization of delivered oxygen. Patients with cytochrome c oxidase deficiency demonstrated consistent oxygenation during exercise indicating an under utilization of delivered oxygen. Patients with MELAS and MERRF syndrome showed similar under utilization of oxygen during exercise. Non-invasive tissue oximetry during exercise demonstrates specific abnormalities in a variety of mitochondrial disorders, indicating abnormal oxygen utilization, and will be a useful addition to the clinical investigation of such disorders. (Mol Cell Biochem 174: 7–10, 1997)