THIAMINE-DEFICIENCY IN CULTURED NEUROBLASTOMA-CELLS - EFFECT ON MITOCHONDRIAL-FUNCTION AND PERIPHERAL BENZODIAZEPINE RECEPTORS

When neuroblastoma cells were transferred to a medium of low (6 nM) th iamine concentration, a 16-fold decrease in total intracellular thiami ne content occurred within 8 days. Respiration and ATP levels were onl y slightly affected, but addition of a thiamine transport inhibitor (a mprolium) decreased ATP content and increased lactate production. Oxyg en consumption became low and insensitive to oligomycin and uncouplers . At least 25% of mitochondria were swollen and electron translucent, Cell mortality increased to 75% within 5 days. [H-3]PK 11195, a specif ic ligand of peripheral benzodiazepine receptors (located in the outer mitochondrial membrane) binds to the cells with high affinity (K-D = 1.4 +/- 0.2 nM). Thiamine deficiency leads to an increase in both B-ma x and K-D. Changes in binding parameters for peripheral benzodiazepine receptors may be related to structural or permeability changes in mit ochondrial outer membranes. In addition to the high-affinity (nanomola r range) binding site for peripheral benzodiazepine ligands, there is a low-affinity (micromolar range) saturable binding for PK 11195. At m icromolar concentrations, peripheral benzodiazepines inhibit thiamine uptake by the cells. Altogether, our results suggest that impairment o f oxidative metabolism, followed by mitochondrial swelling and disorga nization of cristae, is the main cause of cell mortality in severely t hiamine-deficient neuroblastoma cells.