Why is the partial oxygen pressure of human tissues a crucial parameter? Small molecules and hypoxia

Abstract

Oxygen supply and diffusion into tissues are necessary for survival. The oxygen partial pressure (pO2), which is a key component of the physiological state of an organ, results from the balance between oxygen delivery and its consumption. In mammals, oxygen is transported by red blood cells circulating in a well-organized vasculature. Oxygen delivery is dependent on the metabolic requirements and functional status of each organ. Consequently, in a physiological condition, organ and tissue are characterized by their own unique ‘tissue normoxia’ or ‘physioxia’ status. Tissue oxygenation is severely disturbed during pathological conditions such as cancer, diabetes, coronary heart disease, stroke, etc., which are associated with decrease in pO2, i.e. ‘hypoxia’. In this review, we present an array of methods currently used for assessing tissue oxygenation. We show that hypoxia is marked during tumour development and has strong consequences for oxygenation and its influence upon chemotherapy efficiency. Then we compare this to physiological pO2 values of human organs. Finally we evaluate consequences of physioxia on cell activity and its molecular modulations. More importantly we emphasize the discrepancy between in vivo and in vitro tissue and cells oxygen status which can have detrimental effects on experimental outcome. It appears that the values corresponding to the physioxia are ranging between 11% and 1% O2 whereas current in vitro experimentations are usually performed in 19.95% O2, an artificial context as far as oxygen balance is concerned. It is important to realize that most of the experiments performed in so-called normoxia might be dangerously misleading.

Rhythmic Oxygen Levels Reset Circadian Clocks through HIF1α

“…Kidney oxygenation was rhythmic, and reached its peak levels during the dark phase ( Figure 1D and 1E). In line with previous reports, the mean daily O2 levels in kidney were ~7% (6.94 ± 1.34%, mean ± SEM, n=5), (Carreau et al, 2011). The range of the rhythmic daily changes in kidney oxygenation was ~3% O2 ( Figure 1F).…”

Concise Review: Wharton's Jelly: The Rich, but Enigmatic, Source of Mesenchymal Stromal Cells

“…The pO 2 of oxygenated blood within the umbilical vein is approximately 20%–30% of that within adult arteries 46, and a lack of microvessels within Wharton's jelly, lead to the hypothesis that the stromal cells within the cord reside in a relatively hypoxic environment, a sentiment that has also been postulated by others 47. It is well established that bone marrow (BM)‐derived MSCs grow faster under hypoxic conditions in vitro and have a greater CFU‐F frequency over normoxic conditions 48, 49.…”

A EuII‐Containing Cryptate as a Redox Sensor in Magnetic Resonance Imaging of Living Tissue

“…This rapid oxidation with elevated oxygen exposure suggests that Eu II -222Fb is oxidized upon clearance from the oxygen-deficient 4T1 necrotic core (pO 2 ≤ 10 mmHg) [12,13] into relatively oxygenated vasculature (pO 2 ≈ 40-100 mmHg). [14] Collectively, the persistence of the +2 oxidation state over a 120 min period, the correlation between necrotic tissue and contrast enhancement, the lack of positive contrast enhancement in organs associated with clearance (bladder, liver, or kidneys), and the rapid oxidation observed in elevated air exposure suggest that Eu II -222Fb persists in the poorly oxygenated necrotic core of the tumors and oxidizes elsewhere.…”