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

The Normobaric Oxygen Paradox-Hyperoxic Hypoxic Paradox: A Novel Expedient Strategy in Hematopoiesis Clinical Issues

Hypoxia, even at non-lethal levels, is one of the most stressful events for all aerobic organisms as it significantly affects a wide spectrum of physiological functions and energy production. Aerobic organisms activate countless molecular responses directed to respond at cellular, tissue, organ, and whole-body levels to cope with oxygen shortage allowing survival, including enhanced neo-angiogenesis and systemic oxygen delivery. The benefits of hypoxia may be evoked without its detrimental consequences by exploiting the so-called normobaric oxygen paradox. The intermittent shift between hyperoxic-normoxic exposure, in addition to being safe and feasible, has been shown to enhance erythropoietin production and raise hemoglobin levels with numerous different potential applications in many fields of therapy as a new strategy for surgical preconditioning aimed at frail patients and prevention of postoperative anemia. This narrative review summarizes the physiological processes behind the proposed normobaric oxygen paradox, focusing on the latest scientific evidence and the potential applications for this strategy. Future possibilities for hyperoxic-normoxic exposure therapy include implementation as a synergistic strategy to improve a patient's pre-surgical condition, a stimulating treatment in critically ill patients, preconditioning of athletes during physical preparation, and, in combination with surgery and conventional chemotherapy, to improve patients' outcomes and quality of life.

Integrated analysis reveals effects of bioactive ingredients from Limonium Sinense (Girard) Kuntze on hypoxia-inducible factor (HIF) activation

Limonium Sinense (Girard) Kuntze is a traditional Chinese medicinal herb, showing blood replenishment, anti-tumour, anti-hepatitis, and immunomodulation activities amongst others. However, the mechanism of its pharmacological activities remains largely unknown. Here, we investigated the effects of bioactive ingredients from Limonium Sinense using an integrated approach. Water extracts from Limonium Sinense (LSW) showed a strong growth inhibitory effect on multiple cells in both 2D and 3D cultures. Global transcriptomic profiling and further connectivity map (CMap) analysis identified several similarly acting therapeutic candidates, including Tubulin inhibitors and hypoxia-inducible factor (HIF) modulators. The effect of LSW on the cell cycle was verified with flow cytometry showing a G2/M phase arrest. Integrated analysis suggested a role for gallic acid in mediating HIF activation. Taken together, this study provides novel insights into the bioactive ingredients in Limonium Sinense, highlighting the rich natural resource and therapeutic values of herbal plants.

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.

Oxygen: A Stimulus, Not “Only” a Drug

Depending on the oxygen partial pressure in a tissue, the therapeutic effect of oxygenation can vary from simple substance substitution up to hyperbaric oxygenation when breathing hyperbaric oxygen at 2.5–3.0 ATA. Surprisingly, new data showed that it is not only the oxygen supply that matters as even a minimal increase in the partial pressure of oxygen is efficient in triggering cellular reactions by eliciting the production of hypoxia-inducible factors and heat-shock proteins. Moreover, it was shown that extreme environments could also interact with the genome; in fact, epigenetics appears to play a major role in extreme environments and exercise, especially when changes in oxygen partial pressure are involved. Hyperbaric oxygen therapy is, essentially, “intermittent oxygen” exposure. We must investigate hyperbaric oxygen with a new paradigm of treating oxygen as a potent stimulus of the molecular network of reactions.

Effects of high versus low inspiratory oxygen fraction on postoperative clinical outcomes in patients undergoing surgery under general anesthesia: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVES

To determine whether high perioperative inspired oxygen fraction (FiO₂) compared with low FiO₂ has more deleterious postoperative clinical outcomes in patients undergoing non-thoracic surgery under general anesthesia.

DESIGN

Meta-analysis of randomized controlled trials.

SETTING

Operating room, postoperative recovery room and surgical ward.

PATIENTS

Surgical patients under general anesthesia.

INTERVENTION

High perioperative FiO₂ (≥0.8) vs. low FiO₂ (≤0.5).

MEASUREMENTS

The primary outcome was mortality within 30 days. Secondary outcomes were pulmonary outcomes (atelectasis, pneumonia, respiratory failure, postoperative pulmonary complications [PPCs], and postoperative oxygen parameters), intensive care unit (ICU) admissions, and length of hospital stay. A subgroup analysis was performed to explore the treatment effect by body mass index (BMI).

MAIN RESULTS

Twenty-six trials with a total 4991 patients were studied. The mortality in the high FiO₂ group did not differ from that in the low FiO₂ group (risk ratio [RR] 0.91, 95% confidence interval [CI] 0.42-1.97, P = 0.810). Nor were there any significant differences between the groups in such outcomes as pneumonia (RR 1.19, 95% CI 0.74-1.92, P = 0.470), respiratory failure (RR 1.29, 95% CI 0.82-2.04, P = 0.270), PPCs (RR 1.05, 95% CI 0.69-1.59, P = 0.830), ICU admission (RR 0.94, 95% CI 0.55-1.60, P = 0.810), and length of hospital stay (mean difference [MD] 0.27 d, 95% CI -0.28-0.81, P = 0.340). The high FiO₂ was associated with postoperative atelectasis more often (risk ratio 1.27, 95% CI 1.00-1.62, P = 0.050), and lower postoperative arterial partial oxygen pressure (MD -5.03 mmHg, 95% CI -7.90- -2.16, P < 0.001)_. In subgroup analysis of BMI >30 kg/m², these parameters were similarly affected between the groups.

CONCLUSIONS

The use of high FiO₂ compared to low FiO₂ did not affect the short-term mortality, although it may increase the incidence of atelectasis in adult, non-thoracic patients undergoing surgical procedures. Nor were there any significant differences in other secondary outcomes.

Supplemental Intraoperative Oxygen and Long-term Mortality: Subanalysis of a Multiple Crossover Cluster Trial

BACKGROUND

Whether supplemental oxygen worsens long-term mortality remains unclear, with contradictory trial results. The authors therefore tested the hypothesis that supplemental oxygen (80% vs. 30%) increases the hazard for long-term mortality.

METHODS

The authors conducted a post hoc analysis of a large multiple crossover cluster trial in which more than 5,000 colorectal surgeries on 4,088 adults were allocated to receive either 30% or 80% inspired oxygen during general anesthesia. The authors assessed the effect of 80% versus 30% target-inspired oxygen on long-term mortality and calculated Kaplan-Meier survival estimates. Analysis was restricted to patients with a home address in Ohio because the authors could obtain reliable vital status information from the Ohio Department of Health (Columbus, Ohio) for them.

RESULTS

A total of 3,471 qualifying colorectal surgeries performed in 2,801 patients were analyzed, including 1,753 (51%) surgeries in 1,577 patients given 80% oxygen and 1,718 surgeries in 1,551 patients given 30% oxygen. The observed incidence of death after a median of 3 yr was 13% (234 of 1,753) in the 80% oxygen group and 14% (245 of 1,718) in the 30% oxygen group. The estimated hazard ratio for mortality was 0.94 (95% CI, 0.78 to 1.13; P = 0.493).

CONCLUSIONS

In this post hoc analysis of a large, controlled trial, supplemental oxygen did not increase postoperative mortality.

EDITOR’S PERSPECTIVE

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.

Hyperoxia Alters Ultrastructure and Induces Apoptosis in Leukemia Cell Lines

Oxygenation conditions are crucial for growth and tumor progression. Recent data suggests a decrease in cancer cell proliferation occurring after exposure to normobaric hyperoxia. Those changes are associated with fractal dimension. The purpose of this research was to study the impact of hyperoxia on apoptosis and morphology of leukemia cell lines. Two hematopoietic lymphoid cancer cell lines (a T-lymphoblastoid line, JURKAT and a B lymphoid line, CCRF-SB) were tested under conditions of normobaric hyperoxia (FiO₂ > 60%, ± 18h) and compared to a standard group (FiO₂ = 21%). We tested for apoptosis using a caspase-3 assay. Cell morphology was evaluated by cytospin, microphotography after coloration, and analysis by a fractal dimension calculation software. Our results showed that exposure of cell cultures to transient normobaric hyperoxia induced apoptosis (elevated caspase-3) as well as significant and precocious modifications in cell complexity, as highlighted by increased fractal dimensions in both cell lines. These features are associated with changes in structure (pycnotic nucleus and apoptosis) recorded by microscopic analysis. Such morphological alterations could be due to several molecular mechanisms and rearrangements in the cancer cell, leading to cell cycle inhibition and apoptosis as shown by caspase-3 activity. T cells seem less resistant to hyperoxia than B cells.

Hydrogen Gas in Cancer Treatment

Gas signaling molecules (GSMs), composed of oxygen, carbon monoxide, nitric oxide, hydrogen sulfide, etc., play critical roles in regulating signal transduction and cellular homeostasis. Interestingly, through various administrations, these molecules also exhibit potential in cancer treatment. Recently, hydrogen gas (formula: H₂) emerges as another GSM which possesses multiple bioactivities, including anti-inflammation, anti-reactive oxygen species, and anti-cancer. Growing evidence has shown that hydrogen gas can either alleviate the side effects caused by conventional chemotherapeutics, or suppress the growth of cancer cells and xenograft tumor, suggesting its broad potent application in clinical therapy. In the current review, we summarize these studies and discuss the underlying mechanisms. The application of hydrogen gas in cancer treatment is still in its nascent stage, further mechanistic study and the development of portable instruments are warranted.

Diving physiopathology: the end of certainties? Food for thought

Our understanding of decompression physiopathology has slowly improved during this last decade and some uncertainties have disappeared. A better understanding of anatomy and functional aspects of patent foramen ovale (PFO) have slowly resulted in a more liberal approach toward the medical fitness to dive for those bearing a PFO. Circulating vascular gas emboli (VGE) are considered the key actors in development of decompression sickness and can be considered as markers of decompression stress indicating induction of pathophysiological processes not necessarily leading to occurrence of disease symptoms. During the last decade, it has appeared possible to influence post-dive VGE by a so-called "preconditioning" as a pre-dive denitrogenation, exercise or some pharmacological agents. In the text we have deeply examined all the scientific evidence about this complicated but challenging theme. Finally, the role of the "normobaric oxygen paradox" has been clarified and it is not surprising that it could be involved in neuroprotection and cardioprotection. However, the best level of inspired oxygen and the exact time frame to achieve optimal effect is still not known. The aim of this paper was to reflect upon the most actual uncertainties and distil out of them a coherent, balanced advice towards the researchers involved in gas-bubbles-related pathologies.

Gaseous signaling molecules and their application in resistant cancer treatment: from invisible to visible

Multidrug resistance (MDR) in cancer remains a critical obstacle for efficient chemotherapy. Many MDR reversal agents have been discovered but failed in clinical trials due to severe toxic effects. Gaseous signaling molecules (GSMs), such as oxygen, nitric oxide, hydrogen sulfide and carbon monoxide, play key roles in regulating cell biological function and MDR. Compared with other toxic chemosensitizing agents, GSMs are endogenous and biocompatible molecules with little side effects. Research show that GSM modulators, including pharmaceutical formulations of GSMs (combined with conventional chemotherapeutic drugs) and GSM-donors (small molecules with GSMs releasing property), can overcome or reverse MDR. This review discusses the roles of these four GSMs in modulating MDR, and summarizes GSMs modulators in treating cancers with drug resistance.

Effects of Hyperoxia on Oxygen-Related Inflammation with a Focus on Obesity

Several studies have shown a pathological oxygenation (hypoxia/hyperoxia) on the adipose tissue in obese subjects. Additionally, the excess of body weight is often accompanied by a state of chronic low-degree inflammation. The inflammation phenomenon is a complex biological response mounted by tissues to combat injurious stimuli in order to maintain cell homeostasis. Furthermore, it is believed that the abnormal oxygen partial pressure occurring in adipose tissue is involved in triggering inflammatory processes. In this context, oxygen is used in modern medicine as a treatment for several diseases with inflammatory components. Thus, hyperbaric oxygenation has demonstrated beneficial effects, apart from improving local tissue oxygenation, on promoting angiogenesis, wound healing, providing neuroprotection, facilitating glucose uptake, appetite, and others. Nevertheless, an excessive hyperoxia exposure can lead to deleterious effects such as oxidative stress, pulmonary edema, and maybe inflammation. Interestingly, some of these favorable outcomes occur under high and low oxygen concentrations. Hereby, we review a potential therapeutic approach to the management of obesity as well as the oxygen-related inflammation accompanying expanded adipose tissue, based on elevated oxygen concentrations. To conclude, we highlight at the end of this review some areas that need further clarification.

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.

Rational use of oxygen in medical disease and anesthesia

PURPOSE OF REVIEW

Supplemental oxygen is often administered during anesthesia and in critical illness to treat hypoxia, but high oxygen concentrations are also given for a number of other reasons such as prevention of surgical site infection (SSI). The decision to use supplemental oxygen is, however, controversial, because of large heterogeneity in the reported results and emerging reports of side-effects. The aim of this article is to review the recent findings regarding benefits and harms of oxygen therapy in anesthesia and acute medical conditions.

RECENT FINDINGS

Large randomized trials have not found significant reductions in SSI with 80% oxygen during and after abdominal surgery and cesarean section. There is no documented benefit of hyperbaric oxygen treatment for acute ischemic stroke, and there is emerging data to suggest increased mortality with normobaric supplemental oxygen for myocardial infarction without heart failure. Survival and neurologic outcome seem to be adversely affected by hyperoxia in patients with return of spontaneous circulation after cardiac arrest.

SUMMARY

The benefits of supplemental oxygen are not yet confirmed, and new findings suggest that potential side-effects should be considered if the inspired oxygen concentration is increased above what is needed to maintain normal arterial oxygen saturation.

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.