ELSEVIER Life Sciences, Vol. 58, NO. 8, PP.691-699, 1996 Cqyright 0 1996 Elsevier Science Inc. Printed in the USA. All rights reserved 0024-3205(95)02338-O 0024-3205/% $15.00 t .oo INCREASE OF BLOOD NAD+ AND ATTENUATION OF LACTACIDEMIA DURING NICOTINAMIDE TREATMENT OF A PATIENT WITH THE MELAS SYNDROME Kari Majamaa,‘.* Harri Rusanen,’ Anne M. Remes,2 Juhani Pyhtinen,’ and Ilmo E. Hassinen,2 From the ‘Department of Neurology, 2Medical Biochemistry, and ‘Radiology, University of Oulu, Oulu, Finland (Received in final form December 7, 1995) Summary Decreased activity of complex I (NAD:ubiquinone oxidoreductase) is the most frequent biochemical finding associated with the mutation at the base pair 3243 of the mitochondrial DNA. The mutation has been previously shown to lead to a defective translation. We hypothesized that due to an imperfect assembly of complex I subunits the substrate affinity of this enzyme may be lowered and this may be counteracted by increasing the mitochondrial NAD+NADH concentration. Therefore, we studied the effect and mechanism of action of nicotinamide treatment in a MELAS patient with the base pair 3243 mutation. Nicotinamide treatment was initiated after his first stroke-like episode. The blood NAD concentration (representing the intracellular concentration in erythrocytes) increased linearly being 24-fold at 6 weeks of treatment. Blood lactate and pyruvate concentration decreased by 50 % within three days and 24 h urine lactate content within 2 weeks and we observed a clinical improvement together with a decrease in the lesion volume in magnetic resonance imaging within the first month. The cellular NAD increase upon nicotinamide administration was probably universal, because it occurred in a time and dose-dependent manner in cultured fibroblasts from both the patient and the controls. Alleviation of the lactate accumulation during the nicotinamide treatment suggests that an increase in the cellular NAD+NADH concentration leads to enhancement of the oxidation of reducing equivalents. However, the Km of complex I for NADH in skeletal muscle from the patient was similar to that of controls. This may indicate that physiologically mitochondrial complex I operates at non-saturating substrate concentration, and this may explain the effect of nicotinamide treatment. Key Words: mitochondrial encephalomyopathy, point mutation, complex 1 activity, skin fibroblast culture, lactate, vitamin E therapy * Corresponding author: Dr. Kari Majamaa, Department of Neurology, University of Oulu, Kajaanintie 52 A, FIN-90220 Oulu, Finland. Tel: +358-8 1-3 15 4521, fax: +358-8 1-3 15 4544