Glutamine and α‐ketoglutarate as glutamate sources for glutathione synthesis in human erythrocytes

Abstract

Glutathione (GSH) is an intracellular antioxidant synthesized from glutamate, cysteine and glycine. The human erythrocyte (red blood cell, RBC) requires a continuous supply of glutamate to prevent the limitation of GSH synthesis in the presence of sufficient cysteine, but the RBC membrane is almost impermeable to glutamate. As optimal GSH synthesis is important in diseases associated with oxidative stress, we compared the rate of synthesis using two potential glutamate substrates, a-ketoglutarate and glutamine. Both substrates traverse the RBC membrane rapidly relative to many other metabolites. In whole RBCs partially depleted of intracellular GSH and glutamate, 10 mM extracellular a-ketoglutarate, but not 10 mM glutamine, significantly increased the rate of GSH synthesis (0.85 ± 0.09 and 0.61 ± 0.18 lmolAE(L RBC) , while the initial rate for 0.8 mM a-ketoglutarate was 0.97 lmolAE(L RBC) )1 AEmin )1. However, with normal plasma concentrations, the calculated rate of GSH synthesis was higher with glutamine than with a-ketoglutarate (0.31 and 0.25 lmolAE(L RBC) )1 AEmin)1 , respectively), due to the substantially higher plasma concentration of glutamine. Thus, a potential protocol to maximize the rate of GSH synthesis would be to administer a cysteine precursor plus a source of a-ketoglutarate and ⁄ or glutamine. DatabaseThe mathematical models described here have been submitted to the Online Cellular Systems Modelling Database and can be accessed at http://jjj.biochem.sun.ac.za/database/Whillier/ index.html free of charge.

Dietary alpha-ketoglutarate increases cold tolerance in Drosophila melanogaster and enhances protein pool and antioxidant defense in sex-specific manner

“…The low molecular mass thiols are represented mainly by glutathione and increased level of L-SH could result either from enhanced level of precursors of glutamine or enhanced expression of key enzymes of glutathione biosynthesis (Lushchak, 2011(Lushchak, , 2012. Given that the ability of AKG to serve as a glutamate precursor for glutathione biosynthesis was shown earlier in human erythrocytes (Whillier et al, 2011), we suppose that in our experiments externally added AKG could be used for glutathione biosynthesis resulting in increased L-SH level.…”

“…We expected that AKG supplement would influence amino acid level and redox homeostasis of adult flies, as it was observed in other model organisms (Lambert et al, 2006;Whillier et al, 2011;Niemiec et al, 2011;Yao et al, 2012). To test this suggestion, we determined respective biochemical parameters in flies reared on control food and food supplemented with 10 mM AKG, a concentration which showed the most protective effect in chill coma recovery test.…”

“…Involvement of AKG in amino acid metabolism is well known, in particular AKG was found to serve as a precursor for biosynthesis of such amino acids as glutamate, glutamine, and proline (Lambert et al, 2006;Whillier et al, 2011). The ability of AKG to enhance protein synthesis in intestinal porcine epithelial cells was also demonstrated recently (Yao et al, 2012).…”

“…Previously, we and others showed that dietary AKG beneficially affected energy status and physical performance of pigs Harrison and Pierzynowski, 2008;Hou et al, 2011), which could be connected to its role as a precursor for biosynthesis of certain amino acids such as glutamate, glutamine, and proline, and eventually protein biosynthesis (Lambert et al, 2006;Whillier et al, 2011;Niemiec et al, 2011;Yao et al, 2012). In addition, dietary AKG was found to modulate the activity of antioxidant enzymes and to stabilize redox homeostasis in older mice (Niemiec et al, 2011).…”

Microsomal Triglyceride Transfer Protein Inhibition Induces Endoplasmic Reticulum Stress and Increases Gene Transcription via Ire1α/cJun to Enhance Plasma ALT/AST

“…The RBC membrane is impermeable to glutamate and, thus, requires exogenous ␣-ketoglutarate to synthesize glutamate (33). Plasma glutamate is elevated in metabolic disorders such as NAFLD (34,35).…”