Ascorbate maintains a low plasma oxygen level

Abstract

In human blood, oxygen is mainly transported by red blood cells. Accordingly, the dissolved oxygen level in plasma is expected to be limited, although it has not been quantified yet. Here, by developing dedicated methods and tools, we determined that human plasma pO 2 = 8.4 mmHg (1.1% O 2). oxygen solubility in plasma was believed to be similar to water. Here we reveal that plasma has an additional ascorbate-dependent oxygen-reduction activity. Plasma experimental oxygenation oxidizes ascorbate (49.5 μM in fresh plasma vs < 2 μM in oxidized plasma) and abolishes this capacity, which is restored by ascorbate supplementation. We confirmed these results in vivo, showing that the plasma po 2 is significantly higher in ascorbate-deficient guinea pigs (Ascorbate plasma < 2 μM), compared to control (Ascorbate plasma > 15 μM). Plasma low oxygen level preserves the integrity of oxidationsensitive components such as ubiquinol. Circulating leucocytes are well adapted to these conditions, since the abundance of their mitochondrial network is limited. These results shed a new light on the importance of oxygen exposure on leucocyte biological study, in regards with the reducing conditions they encounter in vivo; but also, on the manipulation of blood products to improve their integrity and potentially improve transfusions' efficacy.

The ascorbate-deficient guinea pig model of shigellosis allows the study of the entireShigellalife cycle

“…infection in guinea pigs. We previously reported that Shigella infection induces a significant decrease of plasma ascorbate concentration (22), through a mechanism which remains to be defined. Here, we further investigated in a complementary approach the abundance of ascorbate within the different colonic mucosa layers and its modulation during Shigella infection.…”

“…Following centrifugation for 5 min at 2,000 x g, the plasma was acidified with an equal volume of 10% (w/v) metaphosphoric acid (MPA) containing 2 mmol/L of disodium-EDTA. Ascorbate concentration was quantified by high-performance liquid chromatography with coulometric detection, as described previously (22,34). Results were averaged from dosage performed on at least 4 animals per conditions.…”

Reducing neutrophil exposure to oxygen allows their basal state maintenance

“…We recently determined by direct measurements that the plasma fraction of the blood contains a limited amount of dissolved oxygen (< 1.2% O 2 ). 4 Accordingly, we set up a new method consisting of limiting oxygen exposure during neutrophil culture and compared its impact on the phenotype of neutrophils purified in anoxia or hyperoxia (Figure 1c ). This strategy allowed us to evaluate the respective impact of oxygen exposure during neutrophil purification and culture on their viability and activation.…”

“…Neutrophils differentiate from hematopoietic stem cells (HSCs, CD34 + ) in the bone marrow, in a hypoxic compartment (1.3–4.1% O 2 ) 2 . Under basal conditions, 10% of the mature bone marrow neutrophils are released into the plasma fraction of the blood, containing low amounts of dissolved oxygen (∼0.1–1.2%) 3,4 . In conclusion, neutrophils are adapted to low oxygen concentrations in homeostasis; they face more elevated oxygen tensions only while transmigrating into perfused tissues during inflammation or infection processes.…”

“… 2 Under basal conditions, 10% of the mature bone marrow neutrophils are released into the plasma fraction of the blood, containing low amounts of dissolved oxygen (∼0.1–1.2%). 3 , 4 In conclusion, neutrophils are adapted to low oxygen concentrations in homeostasis; they face more elevated oxygen tensions only while transmigrating into perfused tissues during inflammation or infection processes. Under basal conditions, tissues contain < 10% O 2 (reviewed by Carreau and colleagues), 5 whereas during inflammation and infection the tissues become hypoxic with < 1% O 2 (inflammatory hypoxia and infectious hypoxia).…”