The total amount of cellular mitochondrial DNA (mtDNA) varies widely and seems to be related to the nature and metabolic state of tissues and cells in culture. It is not known, however, whether this variation has any significance in vivo, and to which extent it regulates energy production. To better understand the importance of the cellular mtDNA level, we studied the influence of a gradual reduction of mtDNA copy number on oxidative phosphorylation in two models: (a) a control human cell line treated with different concentrations of 2', 3'-dideoxycytidine, a nucleoside analogue that inhibits mtDNA replication by interfering with mitochondrial DNA polymerase gamma, and (b) a cell line derived from a patient presenting mtDNA depletion. The two models were used to construct biochemical and phenotypic threshold curves. Our results show that oxidative phosphorylation activities are under a tight control by the amount of mtDNA in the cell, and that the full complement of mtDNA molecules are necessary to maintain a normal energy production level.

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The aim of this study was to determine if it was possible to decrease the number of boluses of indomethacin for the treatment of patent ductus arteriosus. This retrospective study included 46 preterm neonates (<34 weeks’ GA) who had had an ultrasound diagnosis predictive of subsequent symptomatic patent ductus arteriosus. All patients had received a daily intravenous doses of indomethacin, 0.1 mg/kg. Mean age at initiation of treatment was 4.5 ± 3.1 days. Patency of the ductus arteriosus was controlled echocardiographically each day and treatment was discontinued as soon as the ductus arteriosus was closed. The initial success rate was 84.7%, of which 6.5% reopened. The mean cumulative dose of indomethacin was 0.35 mg/kg. There was no correlation between gestational age or birth weight and total cumulative dose. Overall tolerance was satisfactory with only one case of transient acute renal failure. A weak correlation between the cumulative dose of indomethacin and natremia (r = –0.43) or weight gain (r = 0.35) was noted, and none with serum creatinine or blood urea nitrogen levels. We confirm that lower indomethacin treatment of patent ductus arteriosus in premature neonates are as effective as standard protocols.

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