Pyruvate metabolism of brain tumors

The glucose metabolism of four patients with brain tumors was examined by means of positronemission computerized tomography (PET) using 11C-Pyruvate. After the intra-venous injection of 11C-Pyruvate, all the patients were found to have a massive accumulation of 11C at the central area of the tumor when compared with the normal state. Since the original observations of Warburg, it had been thought that, in an anaerobic environment, malignant tumor cells produce lactic acid. Under aerobic conditions, the 11C of 11C-Pyruvate may be metabolized to 11CO2, and the transport of 11CO2 from tissue to blood is rapid enough not to be detected in the tissue. However, in tumor cells, the 11C of 11C-Pyruvate cannot be metabolized to 11CO2. Rather, it is converted preferentially to lactic acid. The transport of lactic acid into the blood is relatively slow; consequently, the radioactivity is retained in the tissue for a loger period. In PET, the tumor regions were visualized as positively delineated zones after the injection of 11C-Pyruvate. In fact, the border of a brain tumor is the most important datum for a neurosurgeon. PET using 11C-Pyruvate may thus be a very useful tool for the diagnosis of brain tumors. (author)