Lactate dehydrogenase A exhibits sorbitol/fructose-related catalytic activity and contributes to polyol pathway metabolism in tumor cells.

Introduction: Cancer cells undergo metabolic reprogramming to support survival under stress conditions. Although the polyol pathway has been extensively studied in diabetes, its role in tumor metabolism remains incompletely understood. This study investigated whether lactate dehydrogenase A (LDHA), a key glycolytic enzyme, contributes to hypoxia-associated sorbitol/fructose metabolism in U87MG tumor cells with relatively low sorbitol dehydrogenase (SDH) expression. Methods: Intracellular metabolites in normoxic and hypoxic U87MG cells were analyzed by mass spectrometry. Recombinant SDH and LDHA were expressed in Escherichia coli, purified, and subjected to comparative kinetic analysis at 25°C and 37°C. LDHA knockdown and overexpression were performed to evaluate intracellular sorbitol and fructose levels, ROS accumulation, and cell viability under hypoxia. Results: Metabolomic analysis showed marked fructose accumulation in hypoxic U87MG cells. Both recombinant SDH and LDHA catalyzed sorbitol oxidation and fructose reduction in vitro, and LDHA showed measurable catalytic turnover at 37°C. Cellular analysis showed that LDHA was readily detectable and increased under hypoxia, whereas SDH remained relatively low. LDHA knockdown reduced intracellular fructose levels, increased sorbitol accumulation, elevated ROS levels, and decreased cell viability under hypoxia, whereas LDHA overexpression showed the opposite trend. Discussion: These findings provide biochemical and cellular evidence that LDHA contributes to hypoxia-associated sorbitol/fructose metabolism and links this metabolic activity to redox balance and cell viability in U87MG cells.