Tissue Expressions of Regulatory Enzymes of the Krebs Cycle in Low- and High-grade Gliomas

AIM: To compare tissue levels of the regulatory enzymes related to the Krebs cycle between low, and high-grade supratentorial gliomas. MATERIAL and METHODS: Forty patients who underwent surgery for supratentorial gliomas (19 with low-grade and 21 with high-grade gliomas) were evaluated. The regulatory enzymes directly involved in the Krebs cycle, namely pyruvate dehydrogenase, citrate synthase, alpha-ketoglutarate dehydrogenase, and isocitrate dehydrogenase, and two enzymes that indirectly regulate the Krebs cycle, namely glutamate dehydrogenase and glutaminase, were quantitatively studied in tumor tissues using ELISA. The results were compared between the two groups. RESULTS: The levels of all enzymes were higher in the high-grade glioma group but only pyruvate dehydrogenase, citrate synthase, and isocitrate dehydrogenase levels showed statistical significance. Moreover, all enzymes showed higher tissue levels in grade -II compared to grade-I gliomas, but only two enzymes, glutamate dehydrogenase and glutaminase, reached significantly higher levels. In the high-grade glioma group, all enzymes again showed higher tissue levels in grade-IV gliomas than in grade-III gliomas, but none showed statistical significance. CONCLUSION: Regulatory enzymes of the Krebs cycle are increased in high-grade gliomas compared to low-grade gliomas. Glutaminolysis enzymes, namely glutamate dehydrogenase and glutaminase, which are required for resupplying the Krebs cycle, are also increased in order to meet the high energy demand in high-grade gliomas.