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Ketolytic and glycolytic enzymatic expression profiles in malignant gliomas: implication for ketogenic diet therapy
Howard T Chang1, Lawrence Karl Olson, Kenneth A Schwartz
1Department of Neurology and Ophthalmology, Michigan State University, East Lansing, MI, 48824, USA. howard.chang@ht.msu.edu.
Background:
Recent studies in animal models, based on the hypothesis that malignant glioma cells are more dependent on glycolysis for energy generation, have shown promising results using ketogenic diet (KD) therapy as an alternative treatment strategy for malignant glioma, effectively starving glioma cells while providing ketone bodies as an energy source for normal neurons and glial cells. In order to test this treatment strategy in humans, we investigated the relative expression of several key enzymes involved in ketolytic and glycolytic metabolism in human anaplastic glioma (WHO grade III) and glioblastoma (GBM, WHO grade IV).
Methods:
Immunohistochemistry was performed on formalin fixed paraffin embedded sections from 22 brain biopsies (17 GBM, 3 anaplastic astrocytoma and 2 anaplastic oligoastrocytoma) using antibodies raised against glycolytic and ketolytic enzymes. The glycolytic enzymes included hexokinase-II (HK2) and pyruvate kinase M2 isoform (PKM2). The ketone body metabolic enzymes included: succinyl CoA: 3-oxoacid CoA transferase (OXCT1), 3-hydroxybutyrate dehydrogenase 1 and 2 (BDH1 and BDH2), and acetyl-CoA acetyltransferase 1 (ACAT1). The immunoreactivities were graded using a semi-quantitative scale based on the percentage of positive cells: POS (>20%), LOW (5-20%), and very low (VLOW) (<5%). Focal non-neoplastic "normal" brain tissue within the biopsy specimens served as internal controls.
Results:
The rate limiting mitochondrial ketolytic enzymes (OXCT1 and BDH1) were either LOW or VLOW, concordantly in 14 of the 17 GBMs and in 1 of 5 anaplastic gliomas, whereas at least one of the glycolytic enzymes was POS in 13 of these 17 GBMs and all 5 anaplastic gliomas. Cytosolic BDH2 and mitochondrial ACTAT1 were, surprisingly, POS in most of these tumors.
Conclusion:
Our results showing that malignant gliomas have differential expression of ketolytic and glycolytic enzymes are consistent with previous studies that have shown that these are genetically heterogeneous tumors. It seems reasonable to hypothesize that patients with low or very low expression of key ketolytic enzymes in their malignant gliomas may respond better to the KD therapy than those patients with positive expression of these enzymes. Further studies in animal models and/or a large-scale clinical trial would be needed to test this hypothesis.
Insights
Ketogenic diet (KD) therapy shows promise for malignant glioma. This study found that gliomas have varied expression of key metabolic enzymes, suggesting patients with low ketolytic enzyme expression may benefit most from KD therapy.
Area of Science:
- Neuro-oncology
- Metabolic research
- Cancer metabolism
Background:
- Malignant gliomas exhibit high glycolytic rates, suggesting potential vulnerability to metabolic therapies.
- Ketogenic diet (KD) therapy, which utilizes ketone bodies for energy, is being explored as an alternative treatment for malignant glioma.
- Animal models indicate KD may starve glioma cells while sparing normal brain cells.
Purpose of the Study:
- To investigate the expression of key glycolytic and ketolytic enzymes in human anaplastic glioma and glioblastoma (GBM).
- To assess the potential of KD therapy in human malignant glioma based on metabolic enzyme profiles.
Main Methods:
- Immunohistochemistry was performed on 22 brain tumor biopsies (17 GBM, 5 anaplastic gliomas).
- Antibodies were used to detect glycolytic enzymes (HK2, PKM2) and ketolytic enzymes (OXCT1, BDH1, BDH2, ACAT1).
- Enzyme immunoreactivity was semi-quantitatively graded as POS (>20%), LOW (5-20%), or VLOW (<5%).
Main Results:
- Rate-limiting mitochondrial ketolytic enzymes (OXCT1, BDH1) were LOW or VLOW in most GBMs and anaplastic gliomas.
- At least one glycolytic enzyme was POS in the majority of GBMs and all anaplastic gliomas.
- Surprisingly, cytosolic BDH2 and mitochondrial ACAT1 were POS in most tumors.
Conclusions:
- Malignant gliomas display differential expression of ketolytic and glycolytic enzymes, consistent with their genetic heterogeneity.
- Patients with low or very low expression of key ketolytic enzymes may respond better to KD therapy.
- Further research in animal models and clinical trials is warranted to validate these findings and the efficacy of KD therapy.
