Galactose 1‐phosphate accumulates to high levels in galactose‐treated cells due to low GALT activity and absence of product inhibition of GALK.

Classic Galactosaemia is a genetic disorder, characterised by galactose intolerance in newborns. It occurs due to recessive mutations in the galactose‐1‐phosphate uridylyltransferase (GALT) gene. One of the main alterations caused by GALT deficiency is the accumulation of galactose 1‐phosphate (Gal‐1P) in cells. Studies have suggested that Gal‐1P exerts cellular toxicity, possibly by inhibiting cellular metabolism. However, the exact significance of Gal‐1P in disease pathogenesis remains unclear. In this study, we tested the hypothesis that Gal‐1P inhibits cellular glucose utilisation by competing with substrates in the glycolytic pathway. We also investigated the metabolism of both galactose and glucose in GALT‐expressing HEK293T and 143B cells to identify critical reactions steps contributing to the metabolic toxicity of galactose. Notably, we found that galactose‐treated HEK293T and 143B cells, which express endogenous GALT, accumulate markedly high intracellular Gal‐1P concentrations. Despite very high intracellular Gal‐1P concentrations, no inhibition of cellular glucose uptake and no significant changes in the intracellular concentrations of glycolytic metabolites were observed. This indicates that Gal‐1P does not exert an inhibitory effect on glycolysis in cells and rules out one potential hypothesis for cellular Gal‐1P toxicity. We also investigated the mechanism responsible for the observed Gal‐1P accumulation. Our results suggest that Gal‐1P accumulation is a result of both low GALT activity and the absence of product inhibition by Gal‐1P on galactokinase (GALK1), the enzyme responsible for phosphorylating galactose to Gal‐1P. These findings provide a better understanding of the disease mechanisms underlying Classic Galactoaemia. [ABSTRACT FROM AUTHOR]