Relationship between gluconeogenesis and glutathione redox state in rabbit kidney-cortex tubules.
The intracellular glutathione redox state and the rate of glucose formation were studied in rabbit kidney-cortex tubules. In the presence of substrates effectively utilized for glucose formation, ie, aspartate + glycerol + octanoate, alanine + glycerol + octanoate, malate, or pyruvate, the intracellular reduced glutathione/oxidized glutathione (GSH/GSSG) ratios were significantly higher than those under conditions of negligible glucose production. Changes in the intracellular GSH/GSSG ratio corresponded to those in glucose-6-phosphate content and reduced nicotinamide adenine dinucleotide phosphate/oxidized nicotinamide adenine dinucleotide phosphate (NADPH/NADP(+)) ratio obtained from malate/pyruvate measurements. Gluconeogenesis stimulation by extracellular adenosine triphosphate (ATP) or inosine caused an elevation of the intracellular GSH/GSSG and NADPH/NADP(+) ratios, as well as glucose-6-phosphate level. Surprisingly, in the presence of 5 mmol/L glucose, both the intracellular GSH/GSSG and NADPH/NADP(+) ratios and glucose-6-phosphate content were almost as low as under conditions of negligible glucose synthesis. L-buthionine sulfoximine (BSO)-induced decline in both the intracellular glutathione level and redox state resulted in inhibition of gluconeogenesis accompanied by accumulation of phosphotrioses and a decrease in fructose-1,6-bisphosphate content, while cysteine precursors altered neither GSH redox state nor the rate of glucose formation. In view of the data, it seems likely that: (1) intensive gluconeogenesis rather than extracellular glucose is responsible for maintaining a high intracellular GSH/GSSG ratio due to effective glucose-6-phosphate delivery for NADPH generation via the pentose phosphate pathway; (2) a decline in the intracellular glutathione level and/or redox state causes a decrease in glucose synthesis resulting from a diminished flux through aldolase; (3) induced by cysteine precursors, elevation of the intracellular GSH level does not affect the rate of glucose formation, probably due to no changes in the intracellular GSH/GSSG ratio.
Winiarska
Katarzyna
K
Institute of Biochemistry, Warsaw University, Warsaw, Poland.
Drozak
Jakub
J
Wegrzynowicz
Michał
M
Jagielski
Adam K
AK
Bryła
Jadwiga
J
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005943:Gluconeogenesis / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D007672:Kidney Cortex; D007684:Kidney Tubules / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction / Q000187:drug effects; D011761:Pyrrolidonecarboxylic Acid; D011817:Rabbits; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines
D004791:Enzyme Inhibitors; D013844:Thiazoles; D053778:Thiazolidines; D019328:Buthionine Sulfoximine; D005978:Glutathione; D011761:Pyrrolidonecarboxylic Acid; D000111:Acetylcysteine; C029536:2-oxothiazolidine-4-carboxylic acid