Oxygen breathing may be a cheaper and safer alternative to exogenous erythropoietin (EPO)

Varying Oxygen Partial Pressure Elicits Blood-Borne Microparticles Expressing Different Cell-Specific Proteins-Toward a Targeted Use of Oxygen?

Oxygen is a powerful trigger for cellular reactions, but there are few comparative investigations assessing the effects over a large range of partial pressures. We investigated a metabolic response to single exposures to either normobaric (10%, 15%, 30%, 100%) or hyperbaric (1.4 ATA, 2.5 ATA) oxygen. Forty-eight healthy subjects (32 males/16 females; age: 43.7 ± 13.4 years, height: 172.7 ± 10.07 cm; weight 68.4 ± 15.7 kg) were randomly assigned, and blood samples were taken before and 2 h after each exposure. Microparticles (MPs) expressing proteins specific to different cells were analyzed, including platelets (CD41), neutrophils (CD66b), endothelial cells (CD146), and microglia (TMEM). Phalloidin binding and thrombospondin-1 (TSP), which are related to neutrophil and platelet activation, respectively, were also analyzed. The responses were found to be different and sometimes opposite. Significant elevations were identified for MPs expressing CD41, CD66b, TMEM, and phalloidin binding in all conditions but for 1.4 ATA, which elicited significant decreases. Few changes were found for CD146 and TSP. Regarding OPB, further investigation is needed to fully understand the future applications of such findings.

Physiological and Clinical Impact of Repeated Inhaled Oxygen Variation on Erythropoietin Levels in Patients After Surgery

The “Normobaric Oxygen Paradox” (NOP) is a physiologic mechanism that induces an increase of endogenous erythropoietin (EPO) production by creating a state of relative hypoxia in subjects previously exposed to hyperoxia, followed by a rapid return to normoxia. Oxygen exposure duration and inspired oxygen fraction required to observe a significant increase in EPO or hemoglobin are not clearly defined. Consequently, we here study the effect of one model of relative hypoxia on EPO, reticulocytes and hemoglobin stimulation in patients after surgery. Patients were prospectively randomized in two groups. The O₂ group (n = 10) received 100% oxygen for 1 h per day for eight consecutive days, via a non-rebreathing mask. The control group (n = 12) received no oxygen variation. Serum EPO, hemoglobin and reticulocyte count were measured on admission and postoperatively on days seven and nine. Percentage EPO at day nine with respect to the baseline value was significantly elevated within the groups [O₂ group: 323.7 (SD ± 139.0); control group: 365.6 (SD± 162.0)] but not between them. No significant difference was found between the groups in terms of reticulocytes count and hemoglobin. Our NOP model showed no difference on EPO increase between the two groups. However, both groups expressed separately significant EPO elevation.

Increasing Oxygen Partial Pressures Induce a Distinct Transcriptional Response in Human PBMC: A Pilot Study on the "Normobaric Oxygen Paradox"

The term “normobaric oxygen paradox” (NOP), describes the response to the return to normoxia after a hyperoxic event, sensed by tissues as oxygen shortage, and resulting in up-regulation of the Hypoxia-inducible factor 1α (HIF-1α) transcription factor activity. The molecular characteristics of this response have not been yet fully characterized. Herein, we report the activation time trend of oxygen-sensitive transcription factors in human peripheral blood mononuclear cells (PBMCs) obtained from healthy subjects after one hour of exposure to mild (MH), high (HH) and very high (VHH) hyperoxia, corresponding to 30%, 100%, 140% O₂, respectively. Our observations confirm that MH is perceived as a hypoxic stress, characterized by the activation of HIF-1α and Nuclear factor (erythroid-derived 2)-like 2 (NRF2), but not Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-κB). Conversely, HH is associated to a progressive loss of NOP response and to an increase in oxidative stress leading to NRF2 and NF-kB activation, accompanied by the synthesis of glutathione (GSH). After VHH, HIF-1α activation is totally absent and oxidative stress response, accompanied by NF-κB activation, is prevalent. Intracellular GSH and Matrix metallopeptidase 9 (MMP-9) plasma levels parallel the transcription factors activation pattern and remain elevated throughout the observation time. In conclusion, our study confirms that, in vivo, the return to normoxia after MH is sensed as a hypoxic trigger characterized by HIF-1α activation. On the contrary, HH and VHH induce a shift toward an oxidative stress response, characterized by NRF2 and NF-κB activation in the first 24 h post exposure.

Need (more than) two to Tango: Multiple tools to adapt to changes in oxygen availability

Oxygen is a fundamental element for the life of a large number of living organisms allowing an efficient energetic utilization of substrates. Organisms relying on oxygen evolved complex structures for oxygen delivery and biochemical machineries dealing with its safe utilization and the ability to overcome the potentially harmful consequences of changes in oxygen availability. On fact, cells composing complex Eukaryotic organisms are set to live within an optimum narrow range of oxygen, quite specific for each cell type. Minute modifications of oxygen availability, either positive or negative, induce the expression of specific genes, the major actors of this responses being the transcription factors HIF and Nrf2 that control the attempt to cope with low oxygen (hypoxia) or to either high oxygen or to an oxygen "overflow," respectively. This review describes the interaction between these two transcription factors and their interaction with the transcription factor NF-κB acting as a pivotal determinant of final cell response. © 2018 BioFactors, 44(3):207-218, 2018.

Can the normobaric oxygen paradox (NOP) increase reticulocyte count after traumatic hip surgery?

STUDY OBJECTIVE

To determine if the normobaric oxygen paradox (NOP) was effective in increasing reticulocyte count and reducing postoperative requirements for allogeneic red blood cell transfusion after traumatic hip surgery.

DESIGN

Prospective, randomized, double blinded, multi-center study.

SETTING

Surgical wards of two academic hospitals.

PATIENTS

85 ASA physical status 1 and 2 patients undergoing surgery for traumatic hip fracture.

INTERVENTIONS

Patients were randomly assigned to receive 30 minutes of air [air group (control); n = 40] or 30 minutes of 100% oxygen (O2 group; n = 14) at 15 L/min every day from the first postoperative day (POD 1) until discharge.

MEASUREMENTS

Venous blood samples were taken at admission and after surgery on POD 1, POD 3, and POD 7. Hemoglobin (Hb), hematocrit (Hct), reticulocytes, hemodynamic variables, and transfusion requirements were recorded, as were hospital length of stay (LOS) and mortality.

MAIN RESULTS

Full analysis was obtained for 80 patients. On hospital discharge, the mean increase in reticulocyte count was significantly higher in the O2 group than the air group. Percent variation also increased: 184.9% ± 41.4% vs 104.7% ± 32.6%, respectively; P < 0.001. No difference in Hb or Hct levels was noted at discharge. Allogeneic red blood cell transfusion was 7.5% in the O2 group versus 35% in the air group (P = 0.0052). Hospital LOS was significantly shorter in the O2 group than the air group (7.2 ± 0.7 days vs 7.8 ± 1.6 days, respectively; P < 0.05).

CONCLUSIONS

Transient O2 administration increases reticulocyte count after traumatic hip surgery. Hospital LOS also was shorter in the O2 group than the control group. Allogeneic red blood cell transfusion was reduced in the O2 group but it was not due to the NOP mechanism.

Pulsed high oxygen induces a hypoxic-like response in human umbilical endothelial cells and in humans

It has been proposed that relative changes of oxygen availability, rather than steady-state hypoxic or hyperoxic conditions, play an important role in hypoxia-inducible factor (HIF) transcriptional effects. According to this hypothesis describing the "normobaric oxygen paradox", normoxia following a hyperoxic event is sensed by tissues as an oxygen shortage, upregulating HIF-1 activity. With the aim of confirming, at cellular and at functional level, that normoxia following a hyperoxic event is "interpreted" as a hypoxic event, we report a combination of experiments addressing the effects of an intermittent increase of oxygen concentration on HIF-1 levels and the activity level of specific oxygen-modulated proteins in cultured human umbilical vein endothelial cells and the effects of hemoglobin levels after intermittent breathing of normobaric high (100%) and low (15%) oxygen in vivo in humans. Our experiments confirm that, during recovery after hyperoxia, an increase of HIF expression occurs in human umbilical vein endothelial cells, associated with an increase of matrix metalloproteinases activity. These data suggest that endothelial cells "interpret" the return to normoxia after hyperoxia as a hypoxic stimulus. At functional level, our data show that breathing both 15 and 100% oxygen 30 min every other day for a period of 10 days induces an increase of hemoglobin levels in humans. This effect was enhanced after the cessation of the oxygen breathing. These results indicate that a sudden decrease in tissue oxygen tension after hyperoxia may act as a trigger for erythropoietin synthesis, thus corroborating the hypothesis that "relative" hypoxia is a potent stimulator of HIF-mediated gene expressions.

Long-term intermittent hyperoxic exposures do not enhance erythropoiesis

BACKGROUND

Based on a report of a marked increase in the erythropoietin concentration ([EPO]) a few hours after the cessation of a single 2-h session of O(2) breathing, short periods of O(2) administration have been advocated as a therapy for anaemia. Accordingly, the purpose of the present study was to evaluate this theory by investigating the effect of 10 daily short-term exposures to normobaric O(2) over a 2-week period on the plasma [EPO] in healthy individuals.

MATERIAL AND METHODS

Twenty men were assigned to either an experimental (NBO(2)) or to a control (AIR) group. The NBO(2) group breathed 100% normobaric O(2) for 2 h every weekday over a 2-week period. The AIR group breathed air within the same time protocol. Blood samples were collected at the pre-, mid- and post-intervention periods to determine [EPO].

RESULTS

[EPO] of the NBO(2) group was significantly lower than that of the AIR group during the mid- and post-periods (P < 0·001). [EPO] of the NBO(2) group showed a slight, albeit statistically nonsignificant, decrease during the mid (∼11%)- and post (∼16%)-periods.

CONCLUSIONS

Daily short-term exposures to normobaric hyperoxia do not increase the [EPO] in healthy individuals. The increased O(2) tension suppresses [EPO]. Hence, administration of pure O(2) to enhance erythropoiesis is not warranted.

Acute short-term hyperoxia followed by mild hypoxia does not increase EPO production: resolving the "normobaric oxygen paradox"

Recent findings suggest that besides renal tissue hypoxia, relative decrements in tissue oxygenation, using a transition of the breathing mixture from hyperoxic to normoxic, can also stimulate erythropoietin (EPO) production. To further clarify the importance of the relative change in tissue oxygenation on plasma EPO concentration [EPO], we investigated the effect of a consecutive hyperoxic and hypoxic breathing intervention. Eighteen healthy male subjects were assigned to either IHH (N = 10) or CON (N = 8) group. The IHH group breathed pure oxygen (F(i)O(2) ~ 1.0) for 1 h, followed by a 1-h period of breathing a hypoxic gas mixture (F(i)O(2) ~ 0.15). The CON group breathed a normoxic gas mixture (F(i)O(2) ~ 0.21) for the same duration (2 h). Blood samples were taken just before, after 60 min, and immediately after the 2-h exposure period. Thereafter, samples were taken at 3, 5, 8, 24, 32, and 48 h after the exposure. During the breathing interventions, subjects remained in supine position. There were significant increases in absolute [EPO] within groups at 8 and 32 h in the CON and at 32 h only in the IHH group. No significant differences in absolute [EPO] were observed between groups following the intervention. Relative (∆[EPO]) levels were significantly lower in the IHH than in the CON group, 5 and 8 h following exposure. The tested protocol of consecutive hyperoxic-hypoxic gas mixture breathing did not induce [EPO] synthesis stimulation. Moreover, the transient attenuation in ∆[EPO] in the IHH group was most likely due to a hyperoxic suppression. Hence, our findings provide further evidence against the "normobaric O(2) paradox" theory.

Acute normobaric hyperoxia transiently attenuates plasma erythropoietin concentration in healthy males: evidence against the 'normobaric oxygen paradox' theory

AIM

The purpose of the present study was to evaluate the 'normobaric oxygen paradox' theory by investigating the effect of a 2-h normobaric O(2) exposure on the concentration of plasma erythropoietin (EPO).

METHODS

Ten healthy males were studied twice in a single-blinded counterbalanced crossover study protocol. On one occasion they breathed air (NOR) and on the other 100% normobaric O(2) (HYPER). Blood samples were collected Pre, Mid and Post exposure; and thereafter, 3, 5, 8, 24, 32, 48, 72 and 96 h, and 1 and 2 weeks after the exposure to determine EPO concentration.

RESULTS

The concentration of plasma erythropoietin increased markedly 8 and 32 h after the NOR exposure (approx. 58% and approx. 52%, respectively, P ≤ 0.05) as a consequence of its natural diurnal variation. Conversely, the O(2) breathing was followed by approx. 36% decrement of EPO 3 h after the exposure (P ≤ 0.05). Moreover, EPO concentration was significantly lower in HYPER than in the NOR condition 3, 5 and 8 h after the breathing intervention (P ≤ 0.05).

CONCLUSION

In contrast to the 'normobaric oxygen paradox' theory, the present results indicate that a short period of normobaric O(2) breathing does not increase the EPO concentration in aerobically fit healthy males. Increased O(2) tension suppresses the EPO concentration 3 and 5 h after the exposure; thereafter EPO seems to change in a manner consistent with natural diurnal variation.

Effect of N-acetyl-cysteine and hyperoxia on erythropoietin production

Previous studies in healthy subjects have shown an increase in erythropoietin (EPO) production after administration of N-acetyl-cysteine (NAC). These authors hypothesized that NAC increases intracellular reduced glutathione, decreasing reactive oxygen species and enabling EPO production. We investigated if EPO production could be stimulated with a single dose of NAC, after 90 min of pure oxygen breathing. Thirty-eight healthy volunteers were randomized into either the control (C) group or the NAC group, which received 600 mg NAC PO dissolved in a glass of orange juice, 60 min before breathing 15 L/min of 100% normobaric oxygen. Orange juice was administered to both groups. Blood samples for EPO measurement were taken at T0, before the orange juice administration, and T1, T2, T3 and T4, respectively, 8, 24, 32 and 48 h after the orange juice. The EPO concentrations of the NAC group decreased significantly at T1, followed by a significant increase compared to baseline, which was obvious until T4. The EPO concentrations of the C group did not show any significant variations. In this study, a significant increase of EPO production was observed after a short-term hyperoxic stimulus only when preceded with the administration of a single dose of NAC.

Hyperoxia may be beneficial

The current practice of mechanical ventilation comprises the use of the least inspiratory O2 fraction associated with an arterial O2 tension of 55 to 80 mm Hg or an arterial hemoglobin O2 saturation of 88% to 95%. Early goal-directed therapy for septic shock, however, attempts to balance O2 delivery and demand by optimizing cardiac function and hemoglobin concentration, without making use of hyperoxia. Clearly, it has been well-established for more than a century that long-term exposure to pure O2 results in pulmonary and, under hyperbaric conditions, central nervous O2 toxicity. Nevertheless, several arguments support the use of ventilation with 100% O2 as a supportive measure during the first 12 to 24 hrs of septic shock. In contrast to patients without lung disease undergoing anesthesia, ventilation with 100% O2 does not worsen intrapulmonary shunt under conditions of hyperinflammation, particularly when low tidal volume-high positive end-expiratory pressure ventilation is used. In healthy volunteers and experimental animals, exposure to hyperoxia may cause pulmonary inflammation, enhanced oxidative stress, and tissue apoptosis. This, however, requires long-term exposure or injurious tidal volumes. In contrast, within the timeframe of a perioperative administration, direct O2 toxicity only plays a negligible role. Pure O2 ventilation induces peripheral vasoconstriction and thus may counteract shock-induced hypotension and reduce vasopressor requirements. Furthermore, in experimental animals, a redistribution of cardiac output toward the kidney and the hepato-splanchnic organs was observed. Hyperoxia not only reverses the anesthesia-related impairment of the host defense but also is an antibiotic. In fact, perioperative hyperoxia significantly reduced wound infections, and this effect was directly related to the tissue O2 tension. Therefore, we advocate mechanical ventilation with 100% O2 during the first 12 to 24 hrs of septic shock. However, controlled clinical trials are mandatory to test the safety and efficacy of this approach.

The normobaric oxygen paradox: a novel way to administer oxygen as an adjuvant treatment for cancer?

The "normobaric oxygen paradox" is a dual mechanism by which oxygen regulates the expression of the Hypoxia Inducible Factor 1 alpha (HIF-1α). The HIF-1α-depending gene regulation is responsible for many different genetic expressions including EPO and VEGF that are usually expressed in parallel. First, VEGF under-expression could decrease tumor angiogenesis leading to a decrease in tumor growth or even apoptosis of cancer cells. Second, induction of EPO-expression can provide cytoprotection. Altogether, this could be deleterious for cancer cells while helping non-malignant cells (at least neural and cardiac) cells to be protected from the side effects of chemotherapy. Eventually, HIF induction could boost immune response by inflammatory cells, increasing their antitumor activity.