Where is the glutamine? Intradialytic supplementation may not solve all issues in amino acid balance

CeSSIAM, Guatemala City, Guatemala
University of Bonn, Bonn, Germany
Hohenheim University, Stuttgart, Germany

Dear Sir:

Glutamine is the most abundant amino acid in intra- and extracellular fluid, although the total amount of glutamine in the skeletal muscle pool was recently downwardly revised (1). Our interest in the nutrition and metabolism of this amino acid provoke us to comment on the recent report by Navarro et al (2) on amino acid losses during hemodialysis with polyacrylonitrile membranes and the effect of intradialytic amino acid supplementation. In that article's Table 2, which provided the composition of infused amino acid solution in the supplementation group, all nonessential amino acids were contained in the formulation with the exception of glutamine, taurine, and citrulline. In Table 3, which included data on the hourly losses of individual amino acids during hemodialysis, and Table 4, which provided data on pre- and postdialysis amino acid concentrations, glutamine concentrations were measured and reported. Not unsurprisingly, of the 22 amino acids listed in Table 4, the unsupplemented ones—glutamine, citrulline, and taurine—were the only 3 that had a greater decline in circulating concentrations during dialysis with the amino acid supplementation than during dialysis without supplementation. Glutamine concentrations fell by 13% ± 6% in the former situation and by 9% ± 13% in the latter. In Table 5, in which the net losses of amino acids per dialysis session were shown, glutamine data appeared once again; the wastage of this amino acid during hemodialysis was on the order of 2.3–2.6 g, more than twice that of any companion amino acid. In the final table (Table 6), however, in which the net balance of individual amino acids during dialysis was shown, glutamine again disappeared from the ranks of nonessential (indispensable) amino acids. This is a critical datum, and we wonder why the authors chose to omit reporting it.

Glutamine is sparingly soluble in aqueous solution, with a solubility approaching 35 g/L, and this could be why it was left out of the supplement's formulation. We would remind the authors—and readers—that glutamine dipeptides, such as alanylglutamine, have solubilities of 586 g/L (3) and allow for parenteral nutritional support of patients with glutamine (3–5). Such an approach (ie, using glutamine dipeptides) could be incorporated in intradialytic supplementation. In fact, it seems reasonable to consider the use of glutamine dipeptides in contemporary nephrology because the cumulative and unopposed negatives for glutamine in hemodialysis patients (2) could reduce the total body pool to critically low levels, compromising the functions dependent on this amino acid.

REFERENCES

1. Kuhn KS, Schuhmann K, Stehle P, Darmaun D, Fürst P. Determination of glutamine in muscle protein facilitates accurate assessment of proteolysis and de novo synthesis–derived endogenous glutamine production. Am J Clin Nutr 1999;70:484–9.
2. Navarro JF, Mora C, León C, et al. Amino acid losses during hemodialysis with polyacrylonitrile membranes: effect of intradialytic amino acid supplementation on plasma amino acid concentrations and nutritional variables in nondiabetic patients. Am J Clin Nutr 2000;71:765–73.
3. Fürst P, Albers S, Stehle P. Evidence for a nutritional need for glutamine in catabolic patients. Kidney Int Suppl 1989;27:S287–92.
4. Stehle P, Zander J, Mertes N, et al. Effect of parenteral glutamine peptide on muscle glutamine loss and nitrogen balance after major surgery. Lancet 1989;1:231–3.
5. Fürst P, Pogam K, Stehle P. Glutamine dipeptides in clinical nutrition. Nutrition 1997;13:731–7.