SENSITIVITY TO THIAMINE-DEFICIENCY IN CULTURED HUMAN-CELLS IS DEPENDENT ON CELL-TYPE AND IS ENHANCED IN CELLS FROM THIAMINE-RESPONSIVE MEGALOBLASTIC-ANEMIA PATIENTS

To address tissue-specific variation in sensitivity to thiamine defici ency, three human cell types were grown in medium with various thiamin e concentrations. The activity of a cytosolic and a mitochondrial thia mine diphosphate-dependent enzyme was examined. Each cell type display ed a unique response to thiamine depletion with respect to alpha-ketog lutamate dehydrogenase and transketolase activity and to inhibition of cell growth. Loss of alpha-ketoglutarate dehydrogenase activity was s imilar in lymphoblasts and fibroblasts, whereas loss of activity in ne uroblastoma cells tvas significantly more resistant to thiamine deplet ion. Transketolase activity in neuroblastoma cells was only moderately resistant to thiamine depletion, with the activity in fibroblasts bei ng the most and in lymphoblasts the least resistant. Total transketola se activity was 33% higher in fibroblasts than in lymphoblasts and neu roblastoma cells, indicating a differential requirement for production and maintenance of transketolase activity in this cell type. Compared with normal lymphoblasts, those derived from patients with thiamine-r esponsive megaloblastic anemia were 100 to 1000 times more sensitive t o thiamine depletion. Although fibroblasts from these patients also de monstrated a 1000-fold increase in sensitivity with respect To transke tolase activity, alpha-ketoglutarate dehydrogenase activity demonstrat ed no enhanced sensitivity. The results indicate a complex, cell-type dependent regulation of intracellular pools of thiamine and its phosph orylated derivatives ill response to fluctuating extracellular thiamin e levels. (C) Elsevier Science Inc. 1998.