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Triacylglycerol infusion improves exercise endurance in patients with mitochondrial myopathy due to complex I deficiency^1,2,3

¹ From the Department of Pediatric Gastroenterology (MJR) and the Laboratory for Metabolic Diseases (HWHCS, MB, and RB), the University Children's Hospital, Utrecht, Netherlands; the Department of Clinical Chemistry, Vrije Universiteit Medical Center, Amsterdam (KM); the Laboratory for Metabolic Diseases, the Department of Pediatrics, the University Hospital Groningen, Groningen, Netherlands (D-JR); and the Robert Schwartz, MD, Center for Metabolism and Nutrition, MetroHealth Medical Center, Case Western Reserve University School of Medicine, Cleveland (SCK).

Background: A high-fat diet has been recommended for the treatment of patients with mitochondrial myopathy due to complex I (NADH dehydrogenase) deficiency (CID).

Objective: This study evaluated the effects of intravenous infusion of isoenergetic amounts of triacylglycerol or glucose on substrate oxidation, glycolytic carbohydrate metabolism, and exercise endurance time and energy state of muscle in CID patients.

Design: Four CID patients and 15 control subjects were infused with triacylglycerol (3.7 mg·kg^-1·min^-1) or glucose (10 mg·kg^-1·min^-1) during low-intensity leg exercise. Respiratory calorimetry was used to evaluate mitochondrial substrate oxidation. The concentration and rate of appearance of plasma lactate (from dilution of [1-¹³C]lactate) were used to evaluate glycolytic carbohydrate metabolism. ³¹P magnetic resonance spectroscopy was used to determine ratios of phosphocreatine to inorganic o-phosphate in forearm muscle during exercise.

Results: In 3 patients, leg exercise endurance time was better during the triacylglycerol infusion than during the glucose infusion. In all 4 patients, whole-body oxygen consumption rates during exercise were higher during triacylglycerol infusion than during the glucose infusion. In 3 patients, the concentration and rate of appearance of plasma lactate were lower during triacylglycerol infusion than during the glucose infusion. Ratios of phosphocreatine to inorganic o-phosphate during exercise were not significantly different between the 2 infusion studies or between the patients and control subjects.

Conclusions: Triacylglycerol infusion is associated with a greater oxidation of substrates, lower rates of appearance and concentrations of plasma lactate, and greater leg exercise endurance time in myopathic CID patients than is glucose infusion. The energy state of muscle during exercise, however, was not significantly different after infusion of triacylglycerol or glucose.

Key Words: Complex I deficiency • exercise • triacylglycerol infusion • mitochondrial myopathy • stable isotopes • ³¹P magnetic resonance spectroscopy

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