y+ cationic amino acid transport of arginine in packed red blood cells

Abstract

Background: Transfusion of packed red blood cells (PRBCs) is associated with morbidity and mortality. The mechanisms are not fully understood. Packed red blood cells deplete extracellular arginine and possess transporters for arginine, an amino acid essential for normal immunity. We hypothesize that the membrane y+ amino acid transporter contributes to arginine depletion in PRBCs.

Materials and methods: We titrated PRBCs to a 10% hematocrit with phosphate-buffered saline, blocked PRBC y+ transporters using n-ethylmaleimide (0.2 mM), and measured arginine and ornithine levels using liquid chromatography-mass spectroscopy. We added radiolabeled L-arginine [4,5-(3)H] (10 μmol/L) added to similar culture conditions and measured arginine uptake in counts per minute (CPM). We examined storage periods of 6-9 d, 1-4 wk, and 6 wk, and correlated donor demographics with arginine uptake.

Results: n-Ethylmaleimide blockade of y+ transporters impaired PRBC arginine depletion from culture media (117.6 ± 8.6 μM versus 76.9 ± 5.8 μM; P < 0.001) and reduced intracellular L-arginine (7,574 ± 955 CPM versus 18,192 ± 1,376 CPM; P < 0.01). Arginine depletion increased with storage duration (1 wk versus 6 wk; P < 0.002). With n-ethylmaleimide treatment, 6-wk-old PRBCs preserved more culture arginine (P < 0.008) than at shorter durations. Nine-day storage duration increased L-arginine uptake compared with 6- to 8-day storage (n = 77, R = 0.225, P < 0.05). Extracellular arginine depletion and extracellular ornithine synthesis varied among donors and correlated inversely (R = -0.5, P = 0.01).

Conclusions: Membrane y+ transporters are responsible for arginine depletion by PRBCs. Membrane y+ activity increases with storage duration. Arginine uptake varies among donors. Membrane biology of RBCs may have a role in the negative clinical effects associated with PRBC transfusion.