Pathways of glutamine and glutamate metabolism in resting and proliferating rat thymocytes: Comparison between free and peptide‐bound glutamine

Abstract

Pathways of glutamine metabolism in resting and proliferating rat thymocytes were evaluated by in vitro incubations of freshly prepared or 60-h cultured cells for 1-2 h with [U14C]glutamine. Complete recovery of glutamine carbons utilized in products allowed quantification of the pathways of glutamine metabolism under the experimental conditions. Partial oxidation of glutamine via 2-oxoglutarate in a truncated citric acid cycle to CO2 and oxaloacetate, which then was converted to aspartate, accounted for 76 and 69%, respectively, of the glutamine metabolized beyond the stage of glutamate by resting and proliferating thymocytes. Complete oxidation to CO2 in the citric acid cycle via 2-oxoglutarate dehydrogenase and isocitrate dehydrogenase accounted for 25 and 7%, respectively. In proliferating cells a substantial amount of glutamine carbons was also recovered in pyruvate, alanine, and especially lactate. The main route of glutamine and glutamate entrance into the citric acid cycle via 2-oxoglutarate in both cells is transamination by aspartate aminotransferase rather than oxidative deamination by glutamate dehydrogenase. In the presence of glucose as second substrate, glutamine utilization and aspartate formation markedly decreased, but complete oxidation of glutamine carbons to CO2 increased to 37 and 23%, respectively, in resting and proliferating cells. The dipeptide, glycyl-L-glutamine, which is more stable than free glutamine, can substitute for glutamine in thymocyte cultures at higher concentrations.

In vitro effect of extracellular AMP on MCF‐7 breast cancer cells: Inhibition of glycolysis and cell proliferation

“…In this way, the decrease in glycolytic energy production is nearly compensated by a n increase in glutaminolytic energy production. In accordance with the increase in glutaminolysis, there is an increase in the enzymes of glutamate degradation and the malate-aspartate shuttle (Table 3) (McKeehan, 1982;Brand et al, 1987;Matsuno, 1987).…”

“…Adenosine derivatives and its analogs massively influence the intracellular levels of GTP, UTP, CTP, NAD, and NADP (Green and Chan, 1973;Snyder et al, 1978;Bernofsky, 1980;Rapaport, 1980Rapaport, , 1983Rapaport, ,1988Schweinsberg et al, 1981;Nord et al, 1989). The reduction of NADP and NAD can affect several metabolic pathways like glycolysis, glutaminolysis, and the oxidative pentose-phosphate pathway, all of which are essential for cell proliferation and tumor formation (Lopez-Alarcon et al, 1979;Chapman et al, 1981;McKeehan, 1982;Groelke and Amos, 1984;Eigenbrodt et al, 1985;Lanks et al, 1986;Matsuno, 1987;Brand et al, 1987). All three pathways have been employed as targets for chemotherapeutic agents.…”

Comparison between transport and degradation of leucine and glutamine by peripheral human lymphocytes exposed to concanavalin A

“…First, in our study glutamine was tested at physiological concentration (0.4 mM), compared with 2.0 mM in the other reports. Second, in the study of Brand et al (19871, there is a problem with the controls. Accumulation rates from cells incubated for 60 hours with ConA were compared with those from freshly isolated thymocytes, but not with those from cells incubated for 60 hours in the absence of the mitogen.…”

Substitution of Glutamine by Pyruvate To Reduce Ammonia Formation and Growth Inhibition of Mammalian Cells

“…To overcome the dilemma of on one hand requiring glutamine for maximum yields and on the other hand generating more inhibiting ammonia at the same time has been subject of many different investigations that have been summarized in the review by Schneider et al (5). Strategies to reduce the chemical decomposition of glutamine are, for example, the addition of glutamine just prior to the use of the medium or the addition of glutamine as a derivative, e.g., glycyl‐glutamine (6) or GlutaMax (Invitrogen). Also the substitution of glutamine by glutamate, other amino acids, or α‐ketoglutarate has been tried (7 – 8).…”