Abstract 1685 Poster Session I, Saturday, 5/1 (poster 123)

Background: Premature newborn infants are often subjected to an oxidant stress caused by their immature antioxidant status. Cysteine availability is a limiting step in the synthesis of glutathione, a key element among antioxidants. The level of glutathione is low in premature infants, with a gender-related difference in favour of the girl. We have previously documented that this difference was not related to glutathione synthetic activity nor the activity of γ-glutamyltransferase responsible for the utilisation of circulating glutathione.

Hypothesis: The gender related difference in levels of glutathione should be associated with the activity of cellular cysteine uptake rather than the limited availability of this substrate caused by the immaturity of hepatic cystathionase.

Methods: The activity of cysteine uptake in leukocytes isolated from cord blood of term newborn infants was compared between girls (n=7) and boys (n=6). Leukocytes were isolated by Ficoll-Paque. The cysteine uptake was evaluated using 35S-cysteine; 250000 cells were incubated 15 minutes at 37°C in presence of 0.5 mM cysteine, 141 mM Na, 4.5 mM K, 5 mM DTT, 0.01% Ca, 0.01% Mg, at pH 7.4. As negative control of the sodium-dependent transport of cysteine, a sample of cells was incubated with choline instead of sodium. Cells washed three times were counted for radioactivity. The glutathione content in erythrocytes of newborn infants (4 males, 26 ± 1 wk gest.; 4 females, 28 ±1 wk gest.) fed intravenously 6 days with amino acid solutions containing (Primene®, Baxter) or not (Travasol®, Baxter) cysteine was measured using the reductase-DTNB technique. The effect of gender was compared by the Students' t test.

Results: Without sodium, the transport of cysteine did not occur. The activity of cysteine uptake was twice as high (p<0.05) in leukocytes derived from girls (161 ± 24 vs 79 ± 12 pmol /15 minutes/ 106 cells). Similarly, levels of glutathione were higher (p<0.05) in erythrocytes from premature girls (5.4 ± 0.3 versus 3.8 ± 0.4 nmol / mg prot.) receiving TPN; the amino acid solutions had no effect.

Discussion: The differences between gender observed in glutathione levels are related to cellular transport of cysteine independently from its presence in amino acid solutions. In order to increase the antioxidant status of premature infants, it remains important to find ways to support glutathione synthesis with appropriate substrates, particularly in baby boys.

Funded by the Medical Research Council and Baxter Canada.