Hyperbaric oxygen therapy effects on pulmonary functions: a prospective cohort study

Translational medicine for acute lung injury

Acute lung injury (ALI) is a complex disease with numerous causes. This review begins with a discussion of disease development from direct or indirect pulmonary insults, as well as varied pathogenesis. The heterogeneous nature of ALI is then elaborated upon, including its epidemiology, clinical manifestations, potential biomarkers, and genetic contributions. Although no medication is currently approved for this devastating illness, supportive care and pharmacological intervention for ALI treatment are summarized, followed by an assessment of the pathophysiological gap between human ALI and animal models. Lastly, current research progress on advanced nanomedicines for ALI therapeutics in preclinical and clinical settings is reviewed, demonstrating new opportunities towards developing an effective treatment for ALI.

Effects of hyperbaric oxygen therapy on human psychomotor performance: A review

Psychomotor performance is the coordination of a sensory or ideational (cognitive) process and a motor activity. All sensorimotor processes involved in planning and execution of voluntary movements need oxygen supply and seem to be significantly disrupted in states of hypoxia. Hyperbaric oxygen therapy has become a widely used treatment in routine medicine and sport medicine due to its beneficial effects on different aspects of human physiology and performance. This paper presents state-of-the-art data on the effects of hyperbaric oxygen therapy on different aspects of human psychomotor function. The therapy's influence on musculoskeletal properties and motor abilities as well as the effects of hyperbaric oxygenation on cognitive, myocardial and pulmonary functions are presented. In this review the molecular and physiological processes related to human psychomotor performance in response to hyperbaric oxygen are discussed to contribute to this fast-growing field of research in integrative medicine. Please cite this article as: Olex-Zarychta D. Effects of hyperbaric oxygen therapy on human psychomotor performance: A review. J Integr Med. 2023; 21(5): 430-440.

The pulmonary oxygen toxicity index

Pulmonary oxygen toxicity (POT) is a major risk in diving while breathing hyperoxic gas and is also considered in clinical hyperbaric oxygen treatment. The POTindex calculated by the power equation K = t² × PO₂^4.57 with the recovery form Ktr = Ke × e ^{- [- 0.42 + 0.384 × (PO}₂⁾_ex^{] × tr} which are based on chemical and physiological principles, have a better prediction power than other suggested approaches. Reduction of vital capacity as well as incidence of POT are well predicted by the POTindex. Both the cumulative pulmonary toxic effect and concomitant recovery were suggested to operate at the lower toxic range of PO₂ used in saturation diving K = t² × PO₂^4.57 × e^{-0.0135 × t}, and further experimental support is supplied. The recovery time constant for the full range of PO₂ is presented. POTindex is suggested to replace the old method of UPTD for safe diving. Many diving clubs and diving institutes already adopted the POTindex.

Pulmonary function following hyperbaric oxygen therapy: A longitudinal observational study

Hyperbaric oxygen therapy (HBOT) is known to be associated with pulmonary oxygen toxicity. However, the effect of modern HBOT protocols on pulmonary function is not completely understood. The present study evaluates pulmonary function test changes in patients undergoing serial HBOT. We prospectively collected data on patients undergoing HBOT from 2016-2021 at a tertiary referral center (protocol registration NCT05088772). Patients underwent pulmonary function testing with a bedside spirometer/pneumotachometer prior to HBOT and after every 20 treatments. HBOT was performed using 100% oxygen at a pressure of 2.0-2.4 atmospheres absolute (203-243 kPa) for 90 minutes, five times per week. Patients' charts were retrospectively reviewed for demographics, comorbidities, medications, HBOT specifications, treatment complications, and spirometry performance. Primary outcomes were defined as change in percent predicted forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and forced mid-expiratory flow (FEF25-75), after 20, 40, and 60 HBOT sessions. Data was analyzed with descriptive statistics and mixed-model linear regression. A total of 86 patients were enrolled with baseline testing, and the analysis included data for 81 patients after 20 treatments, 52 after 40 treatments, and 12 after 60 treatments. There were no significant differences in pulmonary function tests after 20, 40, or 60 HBOT sessions. Similarly, a subgroup analysis stratifying the cohort based on pre-existing respiratory disease, smoking history, and the applied treatment pressure did not identify any significant changes in pulmonary function tests during HBOT. There were no significant longitudinal changes in FEV1, FVC, or FEF25-75 after serial HBOT sessions in patients regardless of pre-existing respiratory disease. Our results suggest that the theoretical risk of pulmonary oxygen toxicity following HBOT is unsubstantiated with modern treatment protocols, and that pulmonary function is preserved even in patients with pre-existing asthma, chronic obstructive lung disease, and interstitial lung disease.

Protocol of HOTFy: randomised clinical trial to hyperbaric oxygen therapy in fibromyalgia

INTRODUCTION

Fibromyalgia is a polysymptomatic syndrome with a prevalence between 0.2% and 13% of the population and causes work disabilities in approximately half of affected patients. Several treatments to fibromyalgia have been proposed with partial improvement. This study aims to evaluate the efficacy of hyperbaric oxygen therapy and when it should be introduced to fibromyalgia.

METHODS AND ANALYSIS

This is a protocol for an open-label, crossover, randomised clinical trial comparing treatment with hyperbaric oxygen therapy and standardised treatment to fibromyalgia. In the proposed study, 56 individuals with fibromyalgia will be randomised in a 1:1 ratio into a single, fixed, random block, in which one group will receive hyperbaric oxygen therapy and another will receive standard treatment. Subsequently, the groups will be crossed. Participants will be evaluated at baseline, eight and 16 weeks based on functional impairment assessed with the Fibromyalgia Impact Questionnaire-Brazilian Portuguese version, psychopathological symptoms questionnaire and short-form quality of life questionnaire. The improvement of symptoms concerning the moment of therapy used will be compared between groups. For sample size calculation, a moderate effect size, 80% power and 95% CI will be estimated, in a total of 46 patients. Considering a dropout of 20%, 56 patients should be recruited.

ETHICS AND DISSEMINATION

The study was approved by the Universidade Federal de Juiz de Fora Teaching Hospital ethics committee and assigned the number 53058421.9.0000.5133 (version 3). The results will be disseminated via publications in peer-reviewed journals and presentations in medical meetings.

TRIAL REGISTRATION NUMBER

RBR-6prps8g)/UTN U1111-1278-3224.

Addition of hyperbaric oxygen therapy versus usual care alone for inflammatory bowel disease: A systematic review and meta-analysis

Objective

Inflammatory bowel disease (IBD) is a chronic idiopathic inflammatory disease that includes ulcerative colitis (UC) and Crohn's disease (CD). Hyperbaric oxygen therapy (HBOT) involves breathing pure oxygen in a pressurized environment. Existing literature suggests that HBOT may be an effective therapy for IBD, but a quantitative analysis is lacking. This study aims to estimate the adjunctive role of HBOT in treating IBD and lowering its recurrence rate.

Design

Systematic review and meta-analysis.

Methods

The Cochrane Library, EMBASE, PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), China Science and Technology Journal Database (VIP), and Wanfang databases were systematically searched by two reviewers independently. Meta-analyses were performed using Review Manager (RevMan, version 5.3). A random-effects model was applied due to the heterogeneity between studies.

Results

Twenty-nine out of the initially identified 606 articles were covered in this review, with a total of 2151 patients (2071 for UC and 80 for CD). No randomized data of HBOT for CD were included. Among UC patients, usual care plus HBOT were more likely to achieve a clinical response than usual care alone (risk ratio [RR], 1.24; 95% confidence interval (CI), 1.17 to 1.31; P < 0.001). Subgroup analysis showed that the number of HBOT sessions had no statistically significant effect on overall efficacy (P > 0.05). The pooled data showed a lower recurrence rate in the usual care plus HBOT group (RR, 0.35; 95% CI, 0.24 to 0.53; P < 0.001). The standardized mean difference in the serum tumor necrosis factor level between HBOT and non-HBOT groups was -2.13 (95% CI, -3.09 to -1.18; P < 0.001). No severe adverse events of HBOT were observed.

Conclusions

HBOT might be an effective and safe adjunctive treatment for IBD. Further studies are required to investigate the optimal protocol of HBOT in IBD treatment.

Hyperbaric oxygen therapy for healthy aging: From mechanisms to therapeutics

Hyperbaric oxygen therapy (HBOT), a technique through which 100% oxygen is provided at a pressure higher than 1 atm absolute (ATA), has become a well-established treatment modality for multiple conditions. The noninvasive nature, favorable safety profile, and common clinical application of HBOT make it a competitive candidate for several new indications, one of them being aging and age-related diseases. In fact, despite the conventional wisdom that excessive oxygen accelerates aging, appropriate HBOT protocols without exceeding the toxicity threshold have shown great promise in therapies against aging. For one thing, an extensive body of basic research has expanded our mechanistic understanding of HBOT. Interestingly, the therapeutic targets of HBOT overlap considerably with those of aging and age-related diseases. For another, pre-clinical and small-scale clinical investigations have provided validated information on the efficacy of HBOT against aging from various aspects. However, a generally applicable protocol for HBOT to be utilized in therapies against aging needs to be defined as a subsequent step. It is high time to look back and summarize the recent advances concerning biological mechanisms and therapeutic implications of HBOT in promoting healthy aging and shed light on prospective directions. Here we provide the first comprehensive overview of HBOT in the field of aging and geriatric research, which allows the scientific community to be aware of the emerging tendency and move beyond conventional wisdom to scientific findings of translational value.

Volatile Organic Compounds Frequently Identified after Hyperbaric Hyperoxic Exposure: The VAPOR Library

Diving or hyperbaric oxygen therapy with increased partial pressures of oxygen (pO₂) can have adverse effects such as central nervous system oxygen toxicity or pulmonary oxygen toxicity (POT). Prevention of POT has been a topic of interest for several decades. One of the most promising techniques to determine early signs of POT is the analysis of volatile organic compounds (VOCs) in exhaled breath. We reanalyzed the data of five studies to compose a library of potential exhaled markers for the early detection of POT. GC-MS data from five hyperbaric hyperoxic studies were collected. Wilcoxon signed-rank tests were used to compare baseline- and postexposure measurements; all ion fragments that significantly varied were compared by similarity using the National Institute of Standards and Technology (NIST) library. All identified molecules were cross-referenced with open-source databases and other scientific publications on VOCs to exclude compounds that occurred as a result of contamination, and to identify the compounds most likely to occur due to hyperbaric hyperoxic exposure. After identification and removal of contaminants, 29 compounds were included in the library. This library of hyperbaric hyperoxic-related VOCs can help to advance the development of an early noninvasive marker of POT. It enables validation by others who use more targeted MS-related techniques, instead of full-scale GC-MS, for their exhaled VOC research.

Hyperbaric oxygen treatment for long coronavirus disease-19: a case report

BACKGROUND

The coronavirus disease 2019 pandemic has resulted in a growing population of individuals who experience a wide range of persistent symptoms referred to as "long COVID." Symptoms include neurocognitive impairment and fatigue. Two potential mechanisms could be responsible for these long-term unremitting symptoms: hypercoagulability, which increases the risk of blood vessel occlusion, and an uncontrolled continuous inflammatory response. Currently, no known treatment is available for long COVID. One of the options to reverse hypoxia, reduce neuroinflammation, and induce neuroplasticity is hyperbaric oxygen therapy. In this article, we present the first case report of a previously healthy athletic individual who suffered from long COVID syndrome treated successfully with hyperbaric oxygen therapy.

CASE PRESENTATION

A previously healthy 55-year-old Caucasian man presented 3 months after severe coronavirus disease 2019 infection with long COVID syndrome. His symptoms included a decline in memory, multitasking abilities, energy, breathing, and physical fitness. After evaluation that included brain perfusion magnetic resonance imaging, diffusion tensor imaging, computerized cognitive tests, and cardiopulmonary test, he was treated with hyperbaric oxygen therapy. Each session included exposure to 90 minutes of 100% oxygen at 2 atmosphere absolute pressure with 5-minute air breaks every 20 minutes for 60 sessions, 5 days per week. Evaluation after completing the treatment showed significant improvements in brain perfusion and microstructure by magnetic resonance imaging and significant improvement in memory with the most dominant effect being on nonverbal memory, executive functions, attention, information procession speed, cognitive flexibility, and multitasking. The improved cognitive functions correlated with the increased cerebral blood flow in brain regions as measured by perfusion magnetic resonance imaging. With regard to physical capacity, there was a 34% increase in the maximum rate of oxygen consumed during exercise and a 44% improvement in forced vital capacity. The improved physical measurements correlated with the regain of his pre-COVID physical capacity.

CONCLUSIONS

We report the first case of successfully treated long COVID symptoms with hyperbaric oxygen therapy with improvements in cognition and cardiopulmonary function. The beneficial effects of hyperbaric oxygen shed additional light on the pathophysiology of long COVID. As this is a single case report, further prospective randomized control studies are needed.

Potential Advances of Adjunctive Hyperbaric Oxygen Therapy in Infective Endocarditis

Patients with infective endocarditis (IE) form a heterogeneous group by age, co-morbidities and severity ranging from stable patients to patients with life-threatening complications with need for intensive care. A large proportion need surgical intervention. In-hospital mortality is 15-20%. The concept of using hyperbaric oxygen therapy (HBOT) in other severe bacterial infections has been used for many decades supported by various preclinical and clinical studies. However, the availability and capacity of HBOT may be limited for clinical practice and we still lack well-designed studies documenting clinical efficacy. In the present review we highlight the potential beneficial aspects of adjunctive HBOT in patients with IE. Based on the pathogenesis and pathophysiological conditions of IE, we here summarize some of the important mechanisms and effects by HBOT in relation to infection and inflammation in general. In details, we elaborate on the aspects and impact of HBOT in relation to the host response, tissue hypoxia, biofilm, antibiotics and pathogens. Two preclinical (animal) studies have shown beneficial effect of HBOT in IE, but so far, no clinical study has evaluated the feasibility of HBOT in IE. New therapeutic options in IE are much needed and adjunctive HBOT might be a therapeutic option in certain IE patients to decrease morbidity and mortality and improve the long-term outcome of this severe disease.

Effects of Hyperoxia on Aging Biomarkers: A Systematic Review

The effects of short-term hyperoxia on age-related diseases and aging biomarkers have been reported in animal and human experiments using different protocols; however, the findings of the studies remain conflicting. In this systematic review, we summarized the existing reports in the effects of short-term hyperoxia on age-related diseases, hypoxia-inducible factor 1α (HIF-1α), and other oxygen-sensitive transcription factors relevant to aging, telomere length, cellular senescence, and its side effects. This review was done as described in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. A systematic search was done in PubMed, Google Scholar, and Cochrane Library and from the references of selected articles to identify relevant studies until May 2021. Of the total 1,699 identified studies, 17 were included in this review. Most of the studies have shown significant effects of short-term hyperoxia on age-related diseases and aging biomarkers. The findings of the studies suggest the potential benefits of short-term hyperoxia in several clinical applications such as for patients undergoing stressful operations, restoration of cognitive function, and the treatment of severe traumatic brain injury. Short-term hyperoxia has significant effects in upregulation or downregulation of transcription factors relevant to aging such as HIF-1α, nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-kB), and nuclear factor (erythroid-derived 2)-like 2 (NRF2) among others. Short-term hyperoxia also has significant effects to increase antioxidant enzymes, and increase telomere length and clearance of senescent cells. Some of the studies have also reported adverse consequences including mitochondrial DNA damage and nuclear cataract formation depending on the dose and duration of oxygen exposure. In conclusion, short-term hyperoxia could be a feasible treatment option to treat age-related disease and to slow aging because of its ability to increase antioxidant enzymes, significantly increase telomere length and clearance of senescent cells, and improve cognitive function, among others. The reported side effects of hyperoxia vary depending on the dose and duration of exposure. Therefore, it seems that additional studies for better understanding the beneficial effects of short-term hyperoxia and for minimizing side effects are necessary for optimal clinical application.

Autocatalytic oncotherapy nanosystem with glucose depletion for cascade amplification of hypoxia-activated chemotherapy and H2O2-dependent chemodynamic therapy

Hypoxia-activated prodrug is an appealing oncotherapy strategy, but limited by insufficient tumor hypoxia. Moreover, standalone prodrug fails to treat tumor satisfactorily due to tumor complexity. Herein, a nanosystem (TPZ@FeMSN-GOX) was...

Liberal or conservative oxygen therapy for ventilated patients in the ICU: a meta-analysis of randomized controlled trials

Background

The acknowledgment that conservative oxygen therapy (COT) was related to better prognosis in the intensive care unit (ICU) was challenged recently. We conducted an updated meta-analysis aimed to determine whether liberal oxygen therapy (LOT) or COT is associated with better improve clinical outcomes.

Methods

We systematically searched the electronic databases (PubMed, Web of Science and Embase) up to May 2021 for randomized controlled trials (RCTs). The primary outcome was the mortality of the final follow-up time and secondary outcomes were ICU mortality, the ICU length of stay and the number of ventilator-free days.

Results

A total of 7 RCTs were included, with 2166 patients admitted to the ICU. There was no significant difference in the primary outcome between the LOT and COT. Additionally, LOT could not significantly increase ICU mortality and the ICU length of stay compared with COT.

Conclusions

The present study showed that COT was not significantly superior to LOT in clinical outcomes. Therefore, additional high-quality studies with novel designs are required to further elucidate this controversy.

A General Overview on the Hyperbaric Oxygen Therapy: Applications, Mechanisms and Translational Opportunities

Hyperbaric oxygen therapy (HBOT) consists of using of pure oxygen at increased pressure (in general, 2-3 atmospheres) leading to augmented oxygen levels in the blood (Hyperoxemia) and tissue (Hyperoxia). The increased pressure and oxygen bioavailability might be related to a plethora of applications, particularly in hypoxic regions, also exerting antimicrobial, immunomodulatory and angiogenic properties, among others. In this review, we will discuss in detail the physiological relevance of oxygen and the therapeutical basis of HBOT, collecting current indications and underlying mechanisms. Furthermore, potential areas of research will also be examined, including inflammatory and systemic maladies, COVID-19 and cancer. Finally, the adverse effects and contraindications associated with this therapy and future directions of research will be considered. Overall, we encourage further research in this field to extend the possible uses of this procedure. The inclusion of HBOT in future clinical research could be an additional support in the clinical management of multiple pathologies.

The effects of hyperbaric oxygen therapy (HBOT) on coronavirus disease-2019 (COVID-19): a systematic review

Background

Oxygenation serves as a cornerstone in the treatment of COVID-19, and several methods have been extensively studied so far. Herein, we aimed to systematically review the studies discussing hyperbaric oxygen therapy (HBOT) to examine its reported efficacy and adverse events in patients with COVID-19.

Methods

We systematically searched and retrieved the relevant articles using keywords on the online databases, including PubMed, Scopus, Embase, Web of Science, and Cochrane databases up to April 11th, 2021. The retrieved records underwent a two-step title/abstract and full-text screening process, and the eligible papers were identified. National Institutes of health (NIH) quality assessment tool was used for this study. This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) with ID CRD42021269821.

Results

Eight articles from three countries were included. All the included studies had good and fair quality scores, with no poor studies included in this systematic review (Good: n = 5, Fair: n = 3). Studies were divided into clinical trials and case reports/series. Most of the studies used HBOT less than 1.5–2 absolute atmospheres (ATA) for 90 min sessions and thereafter sessions were decreased to 60 min. Trials demonstrated most of the patients recovered after receiving HBOT, and blood oxygen saturation increased after several sessions of HBOT.

Conclusion

Overall, HBOT seems to be a safe and effective oxygenation method in patients with COVID-19. However, there is limited knowledge and evidence regarding the effects and mechanism of HBOT in COVID-19 treatment, and further evaluations require extensive well-designed studies.

Hyperbaric hyperoxemia as a risk factor for ventilator-acquired pneumonia?

OBJECTIVES

Ventilator-acquired pneumonia (VAP) is the leading cause of serious associated infections in Intensive Care Units (ICU) and is associated with significant morbidity. The use of hyperbaric oxygen therapy (HBOT) in patients on mechanical ventilation may increase exposure to certain risk factors such as hyperoxemia and the need for multiple transfers. The aim of our study was to assess the relationship between HBOT and VAP.

METHOD

This retrospective observational study was performed from March 2017 to March 2018 in a 10-bed ICU using HBOT. All patients receiving mechanical ventilation (MV) for more than 48 hours were eligible. VAP was defined using clinical and radiological criteria. Data collection was carried out via digital medical records. Risk factors for VAP were determined by univariate and multivariate analysis.

RESULTS

Forty-two (23%) of the 182 patients enrolled developed at least one episode of VAP. One hundred and twenty-four (68%) patients received HBOT. The incidence rate of VAP was 34 per 1000 ventilator days. The occurrence of VAP was significantly associated with immunosuppression (p<0.029), MV duration (5 [3-7] vs 8 [5-11.5] days, p<0.0001), length of stay (8 [5-13] vs 19.5 [13-32] days, p<0.0001), reintubation (p<0.0001), intra-hospital transport (p = 0.001), use of paralytic agents (p = 0.013), tracheotomy (p = 0.003) and prone position (p = 0.003). The use of HBOT was not associated with the occurrence of VAP. Multivariate analysis identified reintubation (OR: 8.3 [2.6-26.6]; p<0.0001), intra-hospital transport (OR: 3.5 [1.3-9.2]; p = 0.011) and the use of paralytic agents (OR: 3.3 [1.3-8.4]; p = 0.014) as independent risk factors for VAP.

CONCLUSION

Known risk factors for VAP are to be found within our ICU population. HBOT, however, is not an extra risk factor for VAP within this group. Further experimental and clinical investigations are needed to understand the impact of HBOT on the occurrence of VAP and on physiological microbiome.

Hyperbaric Oxygen Ameliorates Bleomycin-Induced Pulmonary Fibrosis in Mice

The prevalence of pulmonary fibrosis is increasing with an aging population and its burden is likely to increase following COVID-19, with large financial and medical implications. As approved therapies in pulmonary fibrosis only slow disease progression, there is a significant unmet medical need. Hyperbaric oxygen (HBO) is the inhaling of pure oxygen, under the pressure of greater than one atmosphere absolute, and it has been reported to improve pulmonary function in patients with pulmonary fibrosis. Our recent study suggested that repetitive HBO exposure may affect biological processes in mice lungs such as response to wounding and extracellular matrix. To extend these findings, a bleomycin-induced pulmonary fibrosis mouse model was used to evaluate the effect of repetitive HBO exposure on pulmonary fibrosis. Building on our previous findings, we provide evidence that HBO exposure attenuates bleomycin-induced pulmonary fibrosis in mice. In vitro, HBO exposure could reverse, at least partially, transforming growth factor (TGF)-β-induced fibroblast activation, and this effect may be mediated by downregulating TGF-β-induced expression of hypoxia inducible factor (HIF)-1α. These findings support HBO as a potentially life-changing therapy for patients with pulmonary fibrosis, although further research is needed to fully evaluate this.

The herbicide paraquat-induced molecular mechanisms in the development of acute lung injury and lung fibrosis

The herbicide paraquat (PQ; 1,1'-dimethyl-4,4'-bipyridylium dichloride) is a highly toxic organic heterocyclic herbicide that has been widely used in agricultural settings. Since its commercial introduction in the early 1960s, numerous cases of fatal PQ poisonings attributed to accidental and/or intentional ingestion of PQ concentrated formulations have been reported. The clinical manifestations of the respiratory system during the acute phase of PQ poisoning mainly include acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), followed by pulmonary fibrosis in a later phase. The focus of this review is to summarize the most recent publications related to PQ-induced lung toxicity as well as the underlying molecular mechanisms for PQ-mediated pathologic processes. Growing sets of data from in vitro and in vivo models have demonstrated the involvement of the PQ in regulating lung oxidative stress, inflammatory response, epigenetics, apoptosis, autophagy, and the progression of lung fibrosis. The article also summarizes novel therapeutic avenues based on a literature review, which can be explored as potential means to combat PQ-induced lung toxicity. Finally, we also presented clinical studies on the association of PQ exposure with the incidence of lung injury and pulmonary fibrosis.

An Ethacrynic Acid-Brominated BODIPY Photosensitizer (EA-BPS) Construct Enhances the Lethality of Reactive Oxygen Species in Hypoxic Tumor-Targeted Photodynamic Therapy

Despite being a clinically approved intervention for cancer, photodynamic therapy (PDT) still suffers from limitations. Prime among these is a therapeutic response that is mostly oxygen dependent. This limits the utility of PDT in treating hypoxic tumors since lower levels of cytotoxic reactive oxygen species (ROS) are generated in regions of low oxygen tension. Glutathione-pi (GST-pi) is a key enzyme that militates against ROS-mediated apoptosis. We report herein a new construct, EA-BPS, that contains both a brominated BODIPY photosensitizer (BPS) and an ethacrynic acid (EA) GST-pi inhibitor. Photoirradiation of EA-BPS induces a synergistic antitumor effect that results from the combination of ROS production and GST-pi inhibition. Relative to BPS alone, an enhanced cell-killing effect is seen under hypoxic conditions both in vitro and in vivo. We conclude that by making better use of the available oxygen in tumor environments, improved therapeutic PDT outcomes should be achievable even under hypoxic conditions.

The Hyperoxic-Hypoxic Paradox

Effective metabolism is highly dependent on a narrow therapeutic range of oxygen. Accordingly, low levels of oxygen, or hypoxia, are one of the most powerful inducers of gene expression, metabolic changes, and regenerative processes, including angiogenesis and stimulation of stem cell proliferation, migration, and differentiation. The sensing of decreased oxygen levels (hypoxia) or increased oxygen levels (hyperoxia), occurs through specialized chemoreceptor cells and metabolic changes at the cellular level, which regulate the response. Interestingly, fluctuations in the free oxygen concentration rather than the absolute level of oxygen can be interpreted at the cellular level as a lack of oxygen. Thus, repeated intermittent hyperoxia can induce many of the mediators and cellular mechanisms that are usually induced during hypoxia. This is called the hyperoxic-hypoxic paradox (HHP). This article reviews oxygen physiology, the main cellular processes triggered by hypoxia, and the cascade of events triggered by the HHP.

The Hyperoxic-Hypoxic Paradox

Effective metabolism is highly dependent on a narrow therapeutic range of oxygen. Accordingly, low levels of oxygen, or hypoxia, are one of the most powerful inducers of gene expression, metabolic changes, and regenerative processes, including angiogenesis and stimulation of stem cell proliferation, migration, and differentiation. The sensing of decreased oxygen levels (hypoxia) or increased oxygen levels (hyperoxia), occurs through specialized chemoreceptor cells and metabolic changes at the cellular level, which regulate the response. Interestingly, fluctuations in the free oxygen concentration rather than the absolute level of oxygen can be interpreted at the cellular level as a lack of oxygen. Thus, repeated intermittent hyperoxia can induce many of the mediators and cellular mechanisms that are usually induced during hypoxia. This is called the hyperoxic-hypoxic paradox (HHP). This article reviews oxygen physiology, the main cellular processes triggered by hypoxia, and the cascade of events triggered by the HHP.

The Role of Hyperbaric Oxygen Treatment for COVID-19: A Review

The recent coronavirus disease 2019 (COVID-19) pandemic produced high and excessive demands for hospitalizations and equipment with depletion of critical care resources. The results of these extreme therapeutic efforts have been sobering. Further, we are months away from a robust vaccination effort, and current therapies provide limited clinical relief. Therefore, several empirical oxygenation support initiatives have been initiated with intermittent hyperbaric oxygen (HBO) therapy to overcome the unrelenting and progressive hypoxemia during maximum ventilator support in intubated patients, despite high FiO2. Overall, few patients have been successfully treated in different locations across the globe. More recently, less severe patients at the edge of impending hypoxemia were exposed to HBO preventing intubation and obtaining the rapid resolution of symptoms. The few case descriptions indicate large variability in protocols and exposure frequency. This summary illustrates the biological mechanisms of action of increased O₂ pressure, hoping to clarify more appropriate protocols and more useful application of HBO in COVID-19 treatment.