Ascorbate maintains a low plasma low oxygen level

Abstract

3In human blood, oxygen is mainly transported by red blood cells. Accordingly, 4 the oxygen level in plasma is expected to be limited, although it has not been 5 quantified yet. Here, by developing dedicated methods and tools, we determined 6 that human plasma pO2 = 8.4 mmHg (1.2% O2). Oxygen solubility in plasma was 7 believed to be similar to water. Here we reveal that plasma has an additional 8 ascorbate-dependent oxygen-reduction activity. Plasma oxygenation oxidizes 9 ascorbate (49.5 µM in fresh plasma vs <2 µM in oxidized plasma) and abolishes 10 this capacity, which is restored by ascorbate supplementation. We confirmed 11 these results in vivo, showing that the plasma pO2 is significantly higher in 12 ascorbate-deficient guinea pigs (plasma ascorbate < 2µM), compared to control 13 (plasma ascorbate > 15µM). Plasma low oxygen level preserves the integrity of 14 oxidation-sensitive components such as ubiquinol. Circulating leucocytes are 15 well adapted to these conditions, since the abundance of their mitochondrial 16 network is limited. 17 These results shed a new light on the importance of oxygen exposure on 18 leucocyte biological study, in regards with the reducing conditions they 19 encounter in vivo; but also on the manipulation of blood products to improve 20 their integrity and potentially improve transfusions' efficacy. 21 22