Metabolic consequences of lactate dehydrogenase inhibition by oxamate in hyperglycemic proximal tubular cells

Diabetic kidney disease (DKD) is associated with altered metabolic patterns, leading to increased lactate production even in the presence of sufficient oxygen supply. Studies have shown hyperglycemia to be an important factor in determining development of DKD. Here we explore the metabolic consequences of lactate dehydrogenase (LDH) inhibition exerted by the LDH inhibitor, oxamate, in the isolated rat renal proximal tubular cells (NRK-52E) under hyperglycemic conditions. Cells treated with oxamate (100 mM) for 24 h, with or without high D-glucose (25 mM) load, were investigated with hyperpolarized [1-13C]pyruvate in a 1T NMR system. Respiratory measurements using an oxygen microsensor system was conducted. Oxamate treatment of cells with or without the presences of high D-glucose, reduced the lactate production/accumulation with 36.5% or 22.5% respectively. Reduced proliferation, hypertrophic effects, as well as elevated vascular endothelial growth factor (VEGF) expression in the NRK-52E cells were found. The increased glycolytic flux in high D-glucose cultured NRK-52E cells resulted in an upregulation of the cellular oxygen consumption rate upon treatment with oxamate. Our findings suggested that in vitro cultured NRK-52E cells exposed to hyperglycemic conditions, could redirect the glycolytic flux towards oxidative phosphorylation by LDH inhibition. This link between aerobic and anaerobic metabolism may be determined by the redox balance (NAD+/NADH ratio). In conclusion, hyperglycemic conditions and oxamate treatment alters the metabolic phenotype of NRK-52E cells towards increased oxygen utilization mediated by a decreased NAD+/NADH ratio, which in turn decreases cell proliferation/survival.