Mitochondrial glutathione depletion by glutamine in growing tumor cells

The effect of L-glutamine (Gln) on mitochondrial glutathione (mtGSH) levels in tumor cells was studied in vivo in Ehrlich ascites tumor (EAT)-bearing mice. Tumor growth was similar in mice fed a Gin-enriched diet (GED; where 30% of the total dietary nitrogen was from Gin) or a nutritionally complete elemental diet (SD). As compared with non-tumor-bearing mice, tumor growth caused a decrease of blood Gin levels in mice fed an SD but not in those f ed a GED. Tumor cells in mice fed a GED showed higher glutaminase and lower Gin synthetase activities than did cells isolated from mice fed an SD. Cyt osolic glutamate concentration was 2-fold higher in tumor cells from mice f ed a GED (similar to4 mM) than in those fed an SD. This increase in glutama te content inhibited GSH uptake by tumor mitochondria and led to a selectiv e depletion of mitochondrial GSH (mtGSH) content (not found in mitochondria of normal cells such as lymphocytes or hepatocytes) to similar to 57% of t he level found in tumor mitochondria of mice fed an SD. In tumor cells of m ice fed a GED, 6-diazo-5-norleucine- or L-glutamate-gamma -hydrazine-induce d inhibition of glutaminase activity decreased cytosolic glutamate content and restored GSH uptake by mitochondria to the rate found in EAT cells of m ice fed an SD. The partial loss of mtGSH elicited by Gin did not affect gen eration of reactive oxygen intermediates (ROIs) or mitochondrial functions (e.g., intracellular peroxide levels, O-2(-.) generation, mitochondrial mem brane potential, mitochondrial size, adenosine triphosphate and adenosine d iphosphate contents, and oxygen consumption were found similar in tumor cel ls isolated from mice fed an SD or a GED); however, mitochondrial productio n ROIs upon TNF-alpha stimulation was increased. Our results demonstrate th at glutamate derived from glutamine promotes an inhibition of GSH transport into mitochondria, which may render tumor cells more susceptible to oxidat ive stress-induced mediators. (C) 2000 Elsevier Science inc.