Six Dehydrogenase Gatekeepers of Carbohydrate Metabolism: Metabolic Integration in Health and Disease

Dehydrogenases function as metabolic gatekeepers, regulating carbon flux, redox balance, and biosynthetic capacity at critical branch points in cellular metabolism. This narrative review examines six key dehydrogenases, namely glyceraldehyde-3-phosphate dehydrogenase (GAPDH), lactate dehydrogenase (LDH), pyruvate dehydrogenase complex (PDHC), malate dehydrogenase (MDH1/2), isocitrate dehydrogenase (IDH1/2/3), and glucose-6-phosphate dehydrogenase (G6PDH), that collectively orchestrate the partitioning of nutrients among energy production, biosynthesis, and redox homeostasis. These enzymes share common features, including cofactor-dependent catalysis (NAD⁺/NADH or NADP⁺/NADPH), strategic positioning at metabolic nodes, and integration of compartmentalized metabolism between the cytosol and mitochondria. Under physiologic conditions, these dehydrogenases enable metabolic flexibility, allowing cells to adapt nutrient utilization to changing energetic demands and biosynthetic requirements. However, their dysregulation drives pathogenesis across diverse human diseases. In cancer, altered dehydrogenase activity supports metabolic reprogramming, exemplified by the Warburg effect mediated by LDHA, oncometabolite production (mutant IDH1/2), and enhanced biosynthetic capacity associated with G6PDH activity. Metabolic syndrome and diabetes feature PDHC suppression via pyruvate dehydrogenase kinase (PDK) upregulation, contributing to metabolic inflexibility and impaired glucose oxidation. Inherited enzymopathies, including G6PDH and PDHC deficiencies, underscore the essential roles of these enzymes and their tissue-specific requirements. In neurodegenerative disorders, oxidative modification of GAPDH promotes protein aggregation, whereas age-related decline in NAD⁺ compromises the activity of multiple NAD⁺-dependent dehydrogenases in a tissue- and context-dependent manner. The central importance of these enzymes has generated substantial therapeutic interest. Successful clinical translation includes mutant IDH inhibitors that reverse oncometabolite-driven epigenetic reprogramming in cancer. However, targeting essential metabolic enzymes presents challenges, including narrow therapeutic windows, metabolic compensation, and tissue-specific toxicities. Future therapeutic strategies will likely focus on exploiting disease-specific vulnerabilities, developing isoform-selective inhibitors, and combining metabolic interventions with conventional therapies. Understanding these six dehydrogenase gatekeepers provides crucial insights into metabolic regulation and highlights opportunities for precision-medicine approaches targeting the metabolic dependencies of human disease.