Respiratory patterns in human brain tumors

It has been recognized for some time that malignant cells have a diminished respiratory rate coupled with an excessive rate of aerobic glycolysis. Subsequent studies indicated, however, that this pattern was neither unique to malignant tumors nor an essential characteristic of all varieties of cancer. In attempting to synthesize the data on oxygen consumption of human brain tumors, it is difficult to relate activity to malignancy, and the integrity of the mitochondrial electron transport chain has not been systematically examined. In this study, oxygen consumption was measured using a whole cell mixture and subsequently with isolated mitochondria prepared by routine differential centrifugation from a variety of human brain tumors. It is clear from these data that low oxidative respiration is not uniquely characteristic of malignant tumors, but that a number of benign tumors such as meningiomas and pituitary adenomas display very low levels of oxygen consumption. Many of these tumors have normal respiration, with isolated mitochondria using substrates that enter at different points in the electron transport pathway. However, several of the tumors in this series showed defects in respiration at various points in the electron transport pathway. These data suggest that both benign and malignant brain tumors have depressed respiratory capacities secondary to either a decrease in mitochondria per cell or defects in electron transport activities.