Hyperbaric oxygen therapy ameliorates pathophysiology of 3xTg-AD mouse model by attenuating neuroinflammation

Hyperbaric oxygen preconditioning rescues prolonged underwater exercise-induced hippocampal dysfunction by regulating microglia activation and polarization

Underwater exercise is becoming increasingly prevalent, during which brain function is necessary but is also at risk. However, no study has explored how prolonged exercise affect the brain in underwater environment. Previous studies have indicated that excessive exercise in common environment causes brain dysfunction but have failed to provide appropriate interventions. Numerous evidence has indicated the neuroprotective effect of hyperbaric oxygen preconditioning (HBO-PC). The objective of this study was to investigate the cognitive effect of prolonged underwater exercise (PUE) and to explore the potential neuroprotective effect of HBO-PC in underwater environment. Rats swimming for 3 h in a simulated hyperbaric chamber (2.0 ATA) was used to establish the PUE animal model and HBO-PC (2.5 ATA for 1, 3,5 times respectively) was administrated before PUE. The results demonstrated that PUE triggers anxiety-like behaviors, cognitive impairment accompanied by hippocampal dysfunction, microglia activation and neuroinflammation. Conversely, 3 HBO-PC rescued anxiety-like behaviors and cognitive impairment. Mechanistically, 3 HBO-PC reduced microglia activation and switched the activated microglia from a pro-inflammatory to neuroprotective phenotype. These findings illustrated that PUE induces anxiety-like behaviors and cognitive impairment and HBO-PC of proper frequency may provide an appropriate and less invasive intervention for protecting the brain in underwater exercise.

Hyperbaric Oxygen Therapy as an Alternative Therapeutic Option for Radiation-Induced Necrosis Following Radiotherapy for Intracranial Pathologies

BACKGROUND

Radiotherapy (RT) is a feasible adjuvant therapeutic option for managing intracranial pathologies. One of the late complications of RT that frequently develops within months following RT is radiation necrosis (RN). Corticosteroids are the first-line therapeutic option for RNs; however, in case of unfavorable outcomes or intolerability, several other options, including bevacizumab, laser interstitial thermal therapy, surgery, and hyperbaric oxygen therapy (HBOT). Our goal was to investigate the feasibility and efficacy of the application of HBOT in RNs following RT and help physicians make decisions based on the latest data in the literature.

METHODS

We provide a comprehensive review of the literature on the current issues of utilization of HBOT in RNs.

RESULTS

We included 11 studies with a total of 46 patients who underwent HBOT. Most of the cases were diagnosed with brain tumors or arteriovenous malformations. Improvement was achieved in most of the cases.

DISCUSSION

HBOT is a noninvasive therapeutic intervention that can play a role in adjuvant therapy concurrent with RT and chemotherapy and treating RNs. HBOT resolves the RN through 3 mechanisms, including angiogenesis, anti-inflammatory modulation, and cellular repair. Previous studies demonstrated that HBOT is a feasible and well-tolerated therapeutic option that has shown promising results in improving clinical and radiological outcomes in intracranial RNs. Complications of HBOT are usually mild and reversible.

CONCLUSIONS

HBOT is a feasible and effective therapeutic option in steroid-refractory RNs and is associated with favorable outcomes and a low rate of side effects.

Hyperbaric Oxygen Therapy Attenuated the Motor Coordination and Cognitive Impairment of Polyglutamine Spinocerebellar Ataxia SCA17 Mice

Spinocerebellar ataxias (SCAs) are a large and diverse group of autosomal-dominant neurodegenerative diseases. No drugs have been approved for these relentlessly progressive and fatal SCAs. Our previous studies indicate that oxidative stress, neuroinflammation, and neuronal apoptosis are elevated in the SCA17 mice, which are the main therapeutic targets of hyperbaric oxygen treatment (HBOT). HBOT is considered to be an alternative and less invasive therapy for SCAs. In this study, we evaluated the HBOT (2.2 ATA for 14 days) effect and the persistence for the management of SCA17 mice and their wild-type littermates. We found HBOT attenuated the motor coordination and cognitive impairment of SCA17 mice and which persisted for about 1 month after the treatment. The results of several biochemistry and liver/kidney hematoxylin and eosin staining show the HBOT condition has no obvious toxicity in the mice. Immunostaining analyses show that the neuroprotective effect of HBOT could be through the promotion of BDNF production and the amelioration of neuroinflammation. Surprisingly, HBOT executes different effects on the male and female SCA17 mice, including the reduction of neuroinflammation and activation of CaMKII and ERK. This study suggests HBOT is a potential alternative therapeutic treatment for SCA17. Accumulated findings have revealed the similarity in disease pathomechanisms and possible therapeutic strategies in polyQ diseases; therefore, HBOT could be an optional treatment as well as the other polyQ diseases.

Therapeutic effects of long-term HBOT on Alzheimer's disease neuropathologies and cognitive impairment in APPswe/PS1dE9 mice

Alzheimer's disease (AD) is the most common neurodegenerative disorder with the pathological hallmarks of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain. Although there is a hope that anti-amyloid monoclonal antibodies may emerge as a new therapy for AD, the high cost and side effect is a big concern. Non-drug therapy is attracting more attention and may provide a better resolution for the treatment of AD. Given the fact that hypoxia contributes to the pathogenesis of AD, hyperbaric oxygen therapy (HBOT) may be an effective intervention that can alleviate hypoxia and improve AD. However, it remains unclear whether long-term HBOT intervention in the early stage of AD can slow AD progression and ultimately prevent cognitive impairment in this disease. In this study we applied consecutive 3-month HBOT interventions on 3-month-old APPswe/PS1dE9 AD mice which represent the early stage of AD. When the APPswe/PS1dE9 mice at 9-month-old which represent the disease stage we measured cognitive function, 24-h blood oxygen saturation, Aβ and tau pathologies, vascular structure and function, and neuroinflammation in APPswe/PS1dE9 mice. Our results showed that long-term HBOT can attenuate the impairments in cognitive function observed in 9-month-old APPswe/PS1dE9 mice. Most importantly, HBOT effectively reduced the progression of Aβ plaques deposition, hyperphosphorylated tau protein aggregation, and neuronal and synaptic degeneration in the AD mice. Further, long-term HBOT was able to enhance blood oxygen saturation level. Besides, long-term HBOT can improve vascular structure and function, and reduce neuroinflammation in AD mice. This study is the first to demonstrate that long-term HBOT intervention in the early stage of AD can attenuate cognitive impairment and AD-like pathologies. Overall, these findings highlight the potential of long-term HBOT as a disease-modifying approach for AD treatment.

Glitches in the brain: the dangerous relationship between radiotherapy and brain fog

Up to approximately 70% of cancer survivors report persistent deficits in memory, attention, speed of information processing, multi-tasking, and mental health functioning, a series of symptoms known as "brain fog." The severity and duration of such effects can vary depending on age, cancer type, and treatment regimens. In particular, every year, hundreds of thousands of patients worldwide undergo radiotherapy (RT) for primary brain tumors and brain metastases originating from extracranial tumors. Besides its potential benefits in the control of tumor progression, recent studies indicate that RT reprograms the brain tumor microenvironment inducing increased activation of microglia and astrocytes and a consequent general condition of neuroinflammation that in case it becomes chronic could lead to a cognitive decline. Furthermore, radiation can induce endothelium reticulum (ER) stress directly or indirectly by generating reactive oxygen species (ROS) activating compensatory survival signaling pathways in the RT-surviving fraction of healthy neuronal and glial cells. In particular, the anomalous accumulation of misfolding proteins in neuronal cells exposed to radiation as a consequence of excessive activation of unfolded protein response (UPR) could pave the way to neurodegenerative disorders. Moreover, exposure of cells to ionizing radiation was also shown to affect the normal proteasome activity, slowing the degradation rate of misfolded proteins, and further exacerbating ER-stress conditions. This compromises several neuronal functions, with neuronal accumulation of ubiquitinated proteins with a consequent switch from proteasome to immunoproteasome that increases neuroinflammation, a crucial risk factor for neurodegeneration. The etiology of brain fog remains elusive and can arise not only during treatment but can also persist for an extended period after the end of RT. In this review, we will focus on the molecular pathways triggered by radiation therapy affecting cognitive functions and potentially at the origin of so-called "brain fog" symptomatology, with the aim to define novel therapeutic strategies to preserve healthy brain tissue from cognitive decline.

Enriched oxygen improves age-related cognitive impairment through enhancing autophagy

Age-related cognitive impairment represents a significant health concern, with the understanding of its underlying mechanisms and potential interventions being of paramount importance. This study aimed to investigate the effects of hyperbaric oxygen therapy (HBOT) on cognitive function and neuronal integrity in aged (22-month-old) C57BL/6 mice. Male mice were exposed to HBOT for 2 weeks, and spatial learning and memory abilities were assessed using the Morris water maze. We employed transcriptome sequencing and Gene Ontology (GO) term enrichment analysis to examine the effects of HBOT on gene expression profiles, with particular attention given to synapse-related genes. Our data indicated a significant upregulation of postsynapse organization, synapse organization, and axonogenesis GO terms, likely contributing to improved cognitive performance. Moreover, the hyperphosphorylation of tau, a hallmark of many neurodegenerative diseases, was significantly reduced in the HBO-treated group, both in vivo and in vitro. Transmission electron microscopy revealed significant ultrastructural alterations in the hippocampus of the HBOT group, including an increase in the number of synapses and the size of the active zone, a reduction in demyelinated lesions, and a decreased number of "PANTHOS." Furthermore, Western blot analyses confirmed the upregulation of PSD95, BDNF, and Syn proteins, suggesting enhanced synaptic plasticity and neurotrophic support. Moreover, HBOT increased autophagy, as evidenced by the elevated levels of Beclin-1 and LC3 proteins and the reduced level of p62 protein. Finally, we demonstrated that HBOT activated the AMPK-mTOR signaling pathway, a critical regulator of autophagy. Notably, our findings provide novel insights into the mechanisms by which HBOT ameliorates age-related cognitive impairment, suggesting the potential therapeutic value of this approach.

Hyperbaric oxygen alleviates selective domains of cognitive and motor deficits in female 5xFAD mice

Treatment of Alzheimer's disease (AD) has been limited to managing of symptoms or anti-amyloid therapy with limited results and uncertainty. Seeking out new therapies that can reverse the effects of this devastating disease is important. Hyperbaric oxygen (HBO) therapy could be such a candidate as it has been shown to improve brain function in certain neurological conditions. Furthermore, the role sex plays in the vulnerability/resilience to AD remains equivocal. An understanding of what makes one sex more vulnerable to AD could unveil new pathways for therapy development. In this study, we investigated the effects of HBO on cognitive, motor, and affective function in a mouse model of AD (5xFAD) and assessed protein oxidation in peripheral tissues as a safety indicator. The motor and cognitive abilities of 5xFAD mice were significantly impaired. HBO therapy improved cognitive flexibility and associative learning of 5xFAD females but not males, but HBO had no effect other aspects of cognition. HBO also reversed AD-related declines in balance but had no impact on gait and anxiety-like behavior. HBO did not affect body weights or oxidative stress in peripheral tissues. Our study provides further support for HBO therapy as a potential treatment for AD and emphasizes the importance of considering sex as a biological variable in therapeutic development. Further investigations into the underlying mechanisms of HBO's sex-specific responses are warranted, as well as optimizing treatment protocols for maximum benefits.

HIF-1α serves as a co-linker between AD and T2DM

Alzheimer's disease (AD)-related brain deterioration is linked to the type 2 diabetes mellitus (T2DM) features hyperglycemia, hyperinsulinemia, and insulin resistance. Hypoxia as a common risk factor for both AD and T2DM. Hypoxia-inducible factor-1 alpha (HIF-1α) acts as the main regulator of the hypoxia response and may be a key target in the comorbidity of AD and T2DM. HIF-1α expression is closely related to hyperglycemia, insulin resistance, and inflammation. Tissue oxygen consumption disrupts HIF-1α homeostasis, leading to increased reactive oxygen species levels and the inhibition of insulin receptor pathway activity, causing neuroinflammation, insulin resistance, abnormal Aβ deposition, and tau hyperphosphorylation. HIF-1α activation also leads to the deposition of Aβ by promoting the abnormal shearing of amyloid precursor protein and inhibiting the degradation of Aβ, and it promotes tau hyperphosphorylation by activating oxidative stress and the activation of astrocytes, which further exasperates AD. Therefore, we believe that HIF-α has great potential as a target for the treatment of AD. Importantly, the intracellular homeostasis of HIF-1α is a more crucial factor than its expression level.

Oxygen metabolism abnormality and Alzheimer's disease: An update

Oxygen metabolism abnormality plays a crucial role in the pathogenesis of Alzheimer's disease (AD) via several mechanisms, including hypoxia, oxidative stress, and mitochondrial dysfunction. Hypoxia condition usually results from living in a high-altitude habitat, cardiovascular and cerebrovascular diseases, and chronic obstructive sleep apnea. Chronic hypoxia has been identified as a significant risk factor for AD, showing an aggravation of various pathological components of AD, such as amyloid β-protein (Aβ) metabolism, tau phosphorylation, mitochondrial dysfunction, and neuroinflammation. It is known that hypoxia and excessive hyperoxia can both result in oxidative stress and mitochondrial dysfunction. Oxidative stress and mitochondrial dysfunction can increase Aβ and tau phosphorylation, and Aβ and tau proteins can lead to redox imbalance, thus forming a vicious cycle and exacerbating AD pathology. Hyperbaric oxygen therapy (HBOT) is a non-invasive intervention known for its capacity to significantly enhance cerebral oxygenation levels, which can significantly attenuate Aβ aggregation, tau phosphorylation, and neuroinflammation. However, further investigation is imperative to determine the optimal oxygen pressure, duration of exposure, and frequency of HBOT sessions. In this review, we explore the prospects of oxygen metabolism in AD, with the aim of enhancing our understanding of the underlying molecular mechanisms in AD. Current research aimed at attenuating abnormalities in oxygen metabolism holds promise for providing novel therapeutic approaches for AD.

Effect of hyperbaric oxygen therapy combined with repetitive transcranial magnetic stimulation on vascular cognitive impairment: a randomised controlled trial protocol

INTRODUCTION

Vascular cognitive impairment (VCI) has an increasing prevalence worldwide, accounting for at least 20%-40% of all diagnoses of dementia. The decline in cognitive function seriously impairs patients' activities of daily living and social participation and reduces their quality of life. However, there is still a lack of advanced, definitive rehabilitation programmes for VCI. Hyperbaric oxygen therapy (HBOT) and repetitive transcranial magnetic stimulation (rTMS) are recognised treatments for improving cognitive impairment. The former can restore oxygen supply in the brain by increasing oxygen partial pressure in brain tissue, while the latter can enhance neuronal excitability and promote synaptic plasticity. However, no studies have explored the effect of HBO combined with rTMS on VCI.

METHODS AND ANALYSIS

This study is designed as a single-centre, assessor-blind, randomised controlled clinical trial with four parallel arms. A total of 72 participants will be recruited and randomly assigned to the control group, HBOT group, rTMS group and HBOT combined with rTMS group at a ratio of 1:1:1:1. All enrolled participants will receive conventional treatment. The entire intervention period is 4 weeks, with a 3-week follow-up. Outcomes will be measured at baseline (T0), after a 4-week intervention (T1) and after an additional 3-week follow-up period (T2). The primary endpoint is the Montreal Cognitive Assessment score. The secondary endpoints are Mini-Mental State Examination score, Modified Barthel Index score, latency and amplitude of P300, cerebral cortical oxygenated haemoglobin (HbO2) and deoxygenated haemoglobin (HbR) concentrations as measured by task-state functional near-infrared spectroscopy.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the West China Hospital Clinical Trials and Biomedical Ethics Committee of Sichuan University (ethics reference: 2022 (1972)). The findings will be published in peer-reviewed journals and disseminated through scientific conferences and seminars.

TRIAL REGISTRATION NUMBER

ChiCTR2300068242.

COVID-19 and Alzheimer's Disease Share Common Neurological and Ophthalmological Manifestations: A Bidirectional Risk in the Post-Pandemic Future

A growing body of evidence indicates that a neuropathological cross-talk takes place between the coronavirus disease 2019 (COVID-19) -the pandemic severe pneumonia that has had a tremendous impact on the global economy and health since three years after its outbreak in December 2019- and Alzheimer's Disease (AD), the leading cause of dementia among human beings, reaching 139 million by the year 2050. Even though COVID-19 is a primary respiratory disease, its causative agent, the so-called Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2), is also endowed with high neuro-invasive potential (Neurocovid). The neurological complications of COVID-19, resulting from the direct viral entry into the Central Nervous System (CNS) and/or indirect systemic inflammation and dysregulated activation of immune response, encompass memory decline and anosmia which are typically associated with AD symptomatology. In addition, patients diagnosed with AD are more vulnerable to SARS-CoV-2 infection and are inclined to more severe clinical outcomes. In the present review, we better elucidate the intimate connection between COVID-19 and AD by summarizing the involved risk factors/targets and the underlying biological mechanisms shared by these two disorders with a particular focus on the Angiotensin-Converting Enzyme 2 (ACE2) receptor, APOlipoprotein E (APOE), aging, neuroinflammation and cellular pathways associated with the Amyloid Precursor Protein (APP)/Amyloid beta (Aβ) and tau neuropathologies. Finally, the involvement of ophthalmological manifestations, including vitreo-retinal abnormalities and visual deficits, in both COVID-19 and AD are also discussed. Understanding the common physiopathological aspects linking COVID-19 and AD will pave the way to novel management and diagnostic/therapeutic approaches to cope with them in the post-pandemic future.

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 Mechanisms of Action of Hyperbaric Oxygen in Restoring Host Homeostasis during Sepsis

The perception of sepsis has shifted over time; however, it remains a leading cause of death worldwide. Sepsis is now recognized as an imbalance in host cellular functions triggered by the invading pathogens, both related to immune cells, endothelial function, glucose and oxygen metabolism, tissue repair and restoration. Many of these key mechanisms in sepsis are also targets of hyperbaric oxygen (HBO2) treatment. HBO2 treatment has been shown to improve survival in clinical studies on patients with necrotizing soft tissue infections as well as experimental sepsis models. High tissue oxygen tension during HBO2 treatment may affect oxidative phosphorylation in mitochondria. Oxygen is converted to energy, and, as a natural byproduct, reactive oxygen species are produced. Reactive oxygen species can act as mediators, and both these and the HBO2-mediated increase in oxygen supply have the potential to influence the cellular processes involved in sepsis. The pathophysiology of sepsis can be explained comprehensively through resistance and tolerance to infection. We argue that HBO2 treatment may protect the host from collateral tissue damage during resistance by reducing neutrophil extracellular traps, inhibiting neutrophil adhesion to vascular endothelium, reducing proinflammatory cytokines, and halting the Warburg effect, while also assisting the host in tolerance to infection by reducing iron-mediated injury and upregulating anti-inflammatory measures. Finally, we show how inflammation and oxygen-sensing pathways are connected on the cellular level in a self-reinforcing and detrimental manner in inflammatory conditions, and with support from a substantial body of studies from the literature, we conclude by demonstrating that HBO2 treatment can intervene to maintain homeostasis.

The potential of hyperbaric oxygen as a therapy for neurodegenerative diseases

The World Health Organization estimates that by the year 2040, neurodegenerative diseases will be the second leading cause of death in developed countries, overtaking cancer-related deaths and exceeded only by cardiovascular disease-related death. The search for interventions has therefore become paramount to alleviate some of this burden. Based on pathways affected in neurodegenerative diseases, hyperbaric oxygen treatment (HBOT) could be a good candidate. This therapy has been used for the past 50 years for conditions such as decompression sickness and wound healing and has been shown to have promising effects in conditions associated with neurodegeneration and functional impairments. The goal of this review was to explore the history of hyperbaric oxygen therapy, its uses, and benefits, and to evaluate its effectiveness as an intervention in treating neurodegenerative diseases. Additionally, we examined common mechanisms underlying the effects of HBOT in different neurodegenerative diseases, with a special emphasis on epigenetics.

The neuroprotective effects of oxygen therapy in Alzheimer’s disease: a narrative review

Alzheimer’s disease (AD) is a degenerative neurological disease that primarily affects the elderly. Drug therapy is the main strategy for AD treatment, but current treatments suffer from poor efficacy and a number of side effects. Non-drug therapy is attracting more attention and may be a better strategy for treatment of AD. Hypoxia is one of the important factors that contribute to the pathogenesis of AD. Multiple cellular processes synergistically promote hypoxia, including aging, hypertension, diabetes, hypoxia/obstructive sleep apnea, obesity, and traumatic brain injury. Increasing evidence has shown that hypoxia may affect multiple pathological aspects of AD, such as amyloid-beta metabolism, tau phosphorylation, autophagy, neuroinflammation, oxidative stress, endoplasmic reticulum stress, and mitochondrial and synaptic dysfunction. Treatments targeting hypoxia may delay or mitigate the progression of AD. Numerous studies have shown that oxygen therapy could improve the risk factors and clinical symptoms of AD. Increasing evidence also suggests that oxygen therapy may improve many pathological aspects of AD including amyloid-beta metabolism, tau phosphorylation, neuroinflammation, neuronal apoptosis, oxidative stress, neurotrophic factors, mitochondrial function, cerebral blood volume, and protein synthesis. In this review, we summarized the effects of oxygen therapy on AD pathogenesis and the mechanisms underlying these alterations. We expect that this review can benefit future clinical applications and therapy strategies on oxygen therapy for AD.

Toward Prevention and Reduction of Alzheimer's Disease

Different investigations lead to the urgent need to generate validated clinical protocols as a tool for medical doctors to orientate patients under risk for a preventive approach to control Alzheimer's disease. Moreover, there is consensus that the combined effects of risk factors for the disease can be modified according to lifestyle, thus controlling at least 40% of cases. The other fraction of cases are derived from candidate genes and epigenetic components as a relevant factor in AD pathogenesis. At this point, it appears to be of critical relevance the search for molecular biomarkers that may provide information on probable pathological events and alert about early detectable risks to prevent symptomatic events of the disease. These precocious detection markers will then allow early interventions of non-symptomatic subjects at risk. Here, we summarize the status and potential avenues of prevention and highlight the usefulness of biological and reliable markers for AD.

Hyperbaric Oxygen Therapy Promotes Hearing Gain with Increases in Serum IGF-1 and HSP70 in Patients with Idiopathic Sudden Sensorineural Hearing Loss

Objective

Hyperbaric oxygen therapy (HBOT) has been recommended for the initial and salvage treatment of patients with idiopathic sudden sensorineural hearing loss (ISSHL), but its underlying mechanisms remain unclear. In this study, we investigated whether HBOT alters serum levels of insulin-like growth factor 1 (IGF-1) and heat shock protein 70 (HSP70) in patients with ISSHL. Then, we identified the relationship between hearing recovery and changes in serum IGF-1 and HSP70 levels.

Methods

Moderately severe to profound unilateral ISSHL patients (n = 70) and healthy control participants (n = 30) were enrolled. The ISSHL patients were randomly assigned to receive medical therapy alone (MT group, n = 35) or both HBOT and medical therapy (HBOT + MT group, n = 35). Audiometric testing was performed before and after treatment. Serum IGF-1 and HSP70 levels were assessed by ELISA in ISSHL patients pre-and posttreatment and healthy controls.

Results

Before treatment, compared with the healthy controls, serum IGF-1 and HSP70 were lower in ISSHL patients. After treatment, serum IGF-1 and HSP70 increased in both the HBOT + MT and MT groups, although they were significantly higher in the HBOT + MT group (p < 0.01). In the HBOT + MT group, these increases were associated with hearing gains. In addition, IGF-1 was strongly associated with HSP70 (r = 0.621, p = 0.001). No such association was found in the MT group (p = 0.757).

Conclusion

Administering HBOT in addition to medical therapy can improve the hearing of patients with moderately severe to profound unilateral ISSHL. The improvement is related to the upregulation of IGF-1 and HSP70.

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.

SMAD 3, Integrin and VEGF Expression in a Periodontal Ligament During Orthodontic Tooth Movement Induced by Hyperbaric Oxygen Therapy and Stichopus hermanii

Purpose

The aim of this study is to analyze SMAD 3, integrin and VEGF expressions in the periodontal ligament during orthodontic tooth movement induced by hyperbaric oxygen therapy and Stichopus hermanii.

Materials and Methods

Thirty Cavia cobaya were divided into 5 groups, namely, a normal control group (KN) without installation of helical springs or administration of HBOT and Stichopus hermanii gel. The negative control K(-) had helical spring without administration of HBOT and Stichopus hermanii gel for 14 days, while P1 had helical spring for 14 days then on day 3–14, Stichopus hermanii gel was added. Also, the helical spring was installed in P2 for 14 days then on day 8–14, HBOT 2.4 ATA was added 3 × 30 minutes a day, while P3 had helical spring for 14 days then on day 3–14, the gel was applied, and on day 8–14, HBOT 2.4 ATA was administered 3 × 30 minutes a day. Furthermore, SMAD3, integrin, and VEGF expressions were examined using immunohistochemical staining.

Results

SMAD3, integrins, and VEGF expressions showed significant differences within the groups. The combination of HBOT and Stichopus hermanii increased the expression of SMAD3 and VEGF compared to the single administration of Stichopus hermanii. The combination treatment also decreased integrin expression compared to a single HBOT administration.

Conclusion

The combination of HBOT and Stichopus hermanii increases the expression of SMAD3, integrins, and VEGF compared to control but did not show significant differences compared to single HBOT treatment.

Impact of Hyperbaric Oxygen Therapy on Cognitive Functions: a Systematic Review

Hyperbaric oxygen therapy (HBOT) is a modality of treatment in which patients inhale 100% oxygen inside a hyperbaric chamber pressurised to greater than 1 atmosphere. The aim of this review is to discuss neuropsychological findings in various neurological disorders treated with HBOT and to open new perspectives for therapeutic improvement. A literature search was conducted in the MEDLINE (via PubMed) database from the inception up 10 May 2020. Eligibility criteria included original articles published in English. Case studies were excluded. Full-text articles were obtained from the selected studies and were reviewed on the following inclusion criteria (1) performed cognitive processes assessment (2) performed HBOT with described protocol. Two neuropsychologists independently reviewed titles, abstracts, full texts and extracted data. The initial search retrieved 1024 articles, and a total of 42 studies were finally included after applying inclusion and exclusion criteria. The search yielded controversial results with regard to the efficiency of HBOT in various neurological conditions with cognitive disturbance outcome. To the best of our knowledge this is the first state-of-the art, systematic review in the field. More objective and precise neuropsychological assessment methods are needed to exact evaluation of the efficacy of HBOT for neuropsychological deficits. Future studies should widen the assessment of HBOT effects on different cognitive domains because most of the existing studies have focussed on a single process. Finally, there is a need for further longitudinal studies.

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.

Scavenger Receptor A1 Signaling Pathways Affecting Macrophage Functions in Innate and Adaptive Immunity

First discovered on macrophages by Goldstein and Brown in 1979, Scavenger Receptors have since been shown to participate in a diverse number of cell functions; equally diverse are their structures and the ligands they bind. Macrophage activation is crucial in the outcome of an immune response. SR-A1 is highly abundant on macrophages and recognizes both host- and microorganism-derived molecules that impact processes that are initiated, perpetuated, or modified. This review summarizes the involvement of SR-A1 in both inflammatory and anti-inflammatory responses, the multiple-ligand internalization mechanisms and the diversity of signaling pathways that impact macrophage function and activation. Engagement of SR-A1 results in the stimulation of differential signaling pathways and patterns of cytokine expression, kinetics, magnitude of response and activation status. SR-A1 plays essential roles in phagocytosis and efferocytosis, interacting with other receptors and promoting tolerance in response to apoptotic cell uptake. In cell adhesion, tissue remodeling, and cell migration, SR-A1 signals through different pathways engaging different cytoplasmic motifs. We describe the role of SR-A1 during innate and adaptive immune responses, such as participation in macrophage polarization and interaction with other innate receptors, as well as in antigen uptake, processing, and presentation, regulating T and B cell activation. The dichotomous contribution of SR-A1 on macrophage functions is discussed. A better understanding of the role SR-A1 plays through molecular mechanisms and crosstalk with other receptors may provide insights into developing novel therapeutic strategies to modulate immune responses and immunopathologies.

Differences in Immune-Related Genes Underlie Temporal and Regional Pathological Progression in 3xTg-AD Mice

The prevalence of Alzheimer’s disease (AD), the most common cause of age-associated dementia, is estimated to increase over the next decades. Evidence suggests neuro-immune signaling deregulation and risk genes beyond the amyloid-β (Aβ) deposition in AD pathology. We examined the temporal profile of inflammatory mediators and microglia deactivation/activation in the brain cortex and hippocampus of 3xTg-AD mice at 3- and 9-month-old. We found upregulated APP processing, decreased expression of CD11b, CX3CR1, MFG-E8, TNF-α, IL-1β, MHC-II and C/EBP-α and increased miR-146a in both brain regions in 3-month-old 3xTG-AD mice, suggestive of a restrictive regulation. Enhanced TNF-α, IL-1β, IL-6, iNOS, SOCS1 and Arginase 1 were only present in the hippocampus of 9-month-old animals, though elevation of HMGB1 and reduction of miR-146a and miR-124 were common features in the hippocampus and cortex regions. miR-155 increased early in the cortex and later in both regions, supporting its potential as a biomarker. Candidate downregulated target genes by cortical miR-155 included Foxo3, Runx2 and CEBPβ at 3 months and Foxo3, Runx2 and Socs1 at 9 months, which are implicated in cell survival, but also in Aβ pathology and microglia/astrocyte dysfunction. Data provide new insights across AD state trajectory, with divergent microglia phenotypes and inflammatory-associated features, and identify critical targets for drug discovery and combinatorial therapies.

Age dependence of retinal vascular plexus attenuation in the triple transgenic mouse model of Alzheimer's disease

The influence of Alzheimer's disease (AD) progression and severity on the structural and functional integrity of the cerebral vasculature is well recognized. The retina is an extension of the brain; thus, changes in retinal vascular features may serve as markers of AD cerebrovascular pathologies. However, differentiating normal aging-versus AD-induced retinal vascular changes is unresolved. Therefore, we compared and quantified changes in superficial (SVP), intermediate (IVP), and deep (DVP) retinal vascular plexuses in young, middle-age, and old triple transgenic mouse model of AD (3xT-AD) to the changes that occur in age-matched controls (C57BL/6j). We used immunostaining combined with a novel tissue optical clearing approach along with a computational tool for quantitative analysis of vascular network alterations (vessel length and density) in SVP, IVP, and DVP. All three layers had comparable structural features and densities in young 3xTg-AD and control animals. In controls, IVP and DVP densities decreased with aging (-14% to -32% change from young to old, p < 0.05), while no changes were observed in SVP. In contrast, vascular parameters in the transgenic group decreased in all three layers with aging (-12% to -49% change from young to old, p < 0.05). Furthermore, in the old group, SVP and DVP vascular parameters were lower in the transgenics compared to age-matched controls (p < 0.05). Our analysis demonstrates that normal aging and progression of AD lead to various degrees of vascular alterations in the retina. Specifically, compared to normal aging, changes in vascular features of SVP and DVP regions of the retina are accelerated during AD progression. Considering recent advances in the field of depth-resolved imaging of retinal capillary network and microangiography, noninvasive quantitative monitoring of changes in retinal vascular network parameters of SVP and DVP may serve as markers for diagnosis and staging of Alzheimer's disease and discriminating AD-induced vascular attenuation from age-related vasculopathy.

Intermittent hypoxia treatment alleviates memory impairment in the 6-month-old APPswe/PS1dE9 mice and reduces amyloid beta accumulation and inflammation in the brain

Background

Alzheimer’s disease (AD) is a progressive, degenerative, and terminal disease without cure. There is an urgent need for a new strategy to treat AD. The aim of this study was to investigate the effects of intermittent hypoxic treatment (IHT) on cognitive functions in a mouse model of AD and unravel the mechanism of action of IHT.

Methods

Six-month-old APPswe/PS1dE9 (APP/PS1) male mice were exposed to hypoxic environment (14.3% O₂) 4 h/day for 14 days or 28 days. Cognitive functions were measured by Morris water maze test after either 14 days or 42 days of interval. Thereafter the distribution of amyloid plaque and microglial activation were determined by mouse brain immunohistochemistry, while the amyloid beta (Aβ) and inflammatory cytokines were measured by ELISA and Western Blot. Microarray was used for studying gene expressions in the hippocampus.

Results

IHT for 14 days or 28 days significantly improved the spatial memory ability of the 6-month-old APP/PS1 mice. The memory improvement by 14 days IHT lasted to 14 days, but not to 42 days. The level of Aβ plaques and neurofilament accumulations was reduced markedly after the IHT exposure. IHT reduced the pro-inflammatory cytokines IL-1β, IL-6 levels, and β-secretase cleavage of APP processing which implies reduced Aβ production. Microarray analysis revealed a large number of genes in the hippocampus were significantly altered which are known to be metabolism-regulated genes.

Conclusions

This study provides evidence of the beneficial effect of IHT on the progression of AD by alleviating memory impairment, reducing Aβ accumulation and inflammation in the brain. IHT can be developed as a novel measure to relieve the progression of AD by targeting multiple pathways in the AD pathogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00935-z.

Hyperbaric Oxygen Treatment-From Mechanisms to Cognitive Improvement

Hyperbaric oxygen treatment (HBOT)—the medical use of oxygen at environmental pressure greater than one atmosphere absolute—is a very effective therapy for several approved clinical situations, such as carbon monoxide intoxication, incurable diabetes or radiation-injury wounds, and smoke inhalation. In recent years, it has also been used to improve cognition, neuro-wellness, and quality of life following brain trauma and stroke. This opens new avenues for the elderly, including the treatment of neurological and neurodegenerative diseases and improvement of cognition and brain metabolism in cases of mild cognitive impairment. Alongside its integration into clinics, basic research studies have elucidated HBOT’s mechanisms of action and its effects on cellular processes, transcription factors, mitochondrial function, oxidative stress, and inflammation. Therefore, HBOT is becoming a major player in 21st century research and clinical treatments. The following review will discuss the basic mechanisms of HBOT, and its effects on cellular processes, cognition, and brain disorders.

Integrative Role of Hyperbaric Oxygen Therapy on Healthspan, Age-Related Vascular Cognitive Impairment, and Dementia

Growing life expectancy will contribute to the on-going shift towards a world population increasingly comprised of elderly individuals. This demographic shift is associated with a rising prevalence of age-related diseases, among all age-related pathologies it has become crucial to understand the age-associated cognitive changes that remain a major risk factor for the development of vascular cognitive impairment and dementia (VCID). Furthermore, age-related Alzheimer's disease and other neurogenerative diseases with vascular etiology are the most prominent contributing factors for the loss of cognitive function observed in aging. Hyperbaric Oxygen Therapy (HBOT) achieves physiologic effects by increasing oxygen tension (PO2), raising oxygen tissue levels, decreasing intracranial pressure and relieving cerebral edema. Many of the beneficial effects of HBOT exert their protective effects at the level of the microcirculation. Furthermore, the microcirculation's exquisite pervasive presence across every tissue in the body, renders it uniquely able to influence the local environment of most tissues and organs, including the brain. As such, treatments aimed at restoring aging-induced functional and structural alterations of the cerebral microcirculation may potentially contribute to the amelioration of a range of age-related pathologies including vascular cognitive impairment, Alzheimer's disease, and vascular dementias. Despite the presented evidence, the efficacy and safety of HBOT for the treatment of age-related vascular cognitive impairment and dementia remains understudied. The present review aims to examine the existing evidence indicative of a potential therapeutic role for HBOT-induced hyperoxia against age-related cerebromicrovascular pathologies contributing to cognitive impairment, dementia and decreased healthspan in the elderly.

Hyperbaric oxygen treatment on keloid tumor immune gene expression

Background:

Hyperbaric oxygen treatment (HBOT) has been demonstrated to influence the keloid recurrence rate after surgery and to relieve keloid symptoms and other pathological processes in keloids. To explore the mechanism of the effect of HBOT on keloids, tumor immune gene expression and immune cell infiltration were studied in this work.

Methods:

From February 2021 to April 2021, HBOT was carried out on keloid patients four times before surgery. Keloid tissue samples were collected and divided into an HBOT group (keloid with HBOT before surgery [HK] group, n = 6) and a non-HBOT group (K group, n = 6). Tumor gene expression was analyzed with an Oncomine Immune Response Research Assay kit. Data were mined with R package. The differentially expressed genes between the groups were compared. Hub genes between the groups were determined and verified with Quantitative Real-time PCR. Immune cell infiltration was analyzed based on CIBERSORT deconvolution algorithm analysis of gene expression and verified with immunohistochemistry (IHC).

Results:

Inflammatory cell infiltration was reduced in the HK group. There were 178 upregulated genes and 217 downregulated genes. Ten hub genes were identified, including Integrin Subunit Alpha M (ITGAM), interleukin (IL)-4, IL-6, IL-2, Protein Tyrosine Phosphatase Receptor Type C (PTPRC), CD86, transforming growth factor (TGF), CD80, CTLA4, and IL-10. CD80, ITGAM, IL-4, and PTPRC with significantly downregulated expression were identified. IL-10 and IL-2 were upregulated in the HK group but without a significant difference. Infiltration differences of CD8 lymphocyte T cells, CD4 lymphocyte T-activated memory cells, and dendritic resting cells were identified with gene CIBERSORT deconvolution algorithm analysis. Infiltration levels of CD4 lymphocyte T cell in the HK group were significantly higher than those of the K group in IHC verification.

Conclusion:

HBOT affected tumor gene expression and immune cell infiltration in keloids. CD4 lymphocyte T cell, especially activated memory CD4⁺T, might be the key regulatory immune cell, and its related gene expression needs further study.

Oxygen Sensing and Signaling in Alzheimer's Disease: A Breathtaking Story!

Oxygen sensing and homeostasis is indispensable for the maintenance of brain structural and functional integrity. Under low-oxygen tension, the non-diseased brain has the ability to cope with hypoxia by triggering a homeostatic response governed by the highly conserved hypoxia-inducible family (HIF) of transcription factors. With the advent of advanced neuroimaging tools, it is now recognized that cerebral hypoperfusion, and consequently hypoxia, is a consistent feature along the Alzheimer's disease (AD) continuum. Of note, the reduction in cerebral blood flow and tissue oxygenation detected during the prodromal phases of AD, drastically aggravates as disease progresses. Within this scenario a fundamental question arises: How HIF-driven homeostatic brain response to hypoxia "behaves" during the AD continuum? In this sense, the present review is aimed to critically discuss and summarize the current knowledge regarding the involvement of hypoxia and HIF signaling in the onset and progression of AD pathology. Importantly, the promises and challenges of non-pharmacological and pharmacological strategies aimed to target hypoxia will be discussed as a new "hope" to prevent and/or postpone the neurodegenerative events that occur in the AD brain.

Hyperbaric oxygen therapy alleviates vascular dysfunction and amyloid burden in an Alzheimer's disease mouse model and in elderly patients

Vascular dysfunction is entwined with aging and in the pathogenesis of Alzheimer's disease (AD) and contributes to reduced cerebral blood flow (CBF) and consequently, hypoxia. Hyperbaric oxygen therapy (HBOT) is in clinical use for a wide range of medical conditions. In the current study, we exposed 5XFAD mice, a well-studied AD model that presents impaired cognitive abilities, to HBOT and then investigated the therapeutical effects using two-photon live animal imaging, behavioral tasks, and biochemical and histological analysis. HBOT increased arteriolar luminal diameter and elevated CBF, thus contributing to reduced hypoxia. Furthermore, HBOT reduced amyloid burden by reducing the volume of pre-existing plaques and attenuating the formation of new ones. This was associated with changes in amyloid precursor protein processing, elevated degradation and clearance of Aß protein and improved behavior of 5XFAD mice. Hence, our findings are consistent with the effects of HBOT being mediated partially through a persistent structural change in blood vessels that reduces brain hypoxia. Motivated by these findings, we exposed elderly patients with significant memory loss at baseline to HBOT and observed an increase in CBF and improvement in cognitive performances. This study demonstrates HBOT efficacy in hypoxia-related neurological conditions, particularly in AD and aging.

Current Alzheimer disease research highlights: evidence for novel risk factors

Alzheimer disease (AD) is the most common type of dementia characterized by the progressive cognitive and social decline. Clinical drug targets have heavily focused on the amyloid hypothesis, with amyloid beta (Aβ), and tau proteins as key pathophysiologic markers of AD. However, no effective treatment has been developed so far, which prompts researchers to focus on other aspects of AD beyond Aβ, and tau proteins. Additionally, there is a mounting epidemiologic evidence that various environmental factors influence the development of dementia and that dementia etiology is likely heterogenous. In the past decades, new risk factors or potential etiologies have been widely studied. Here, we review several novel epidemiologic and clinical research developments that focus on sleep, hypoxia, diet, gut microbiota, and hearing impairment and their links to AD published in recent years. At the frontiers of AD research, these findings and updates could be worthy of further attention.

Hyperoxygenation Treatment Reduces Beta-amyloid Deposition via MeCP2-dependent Upregulation of MMP-2 and MMP-9 in the Hippocampus of Tg-APP/PS1 Mice

Recently we reported that hyperoxygenation treatment reduces amyloid-beta accumulation and rescues cognitive impairment in the Tg-APP/PS1 mouse model of Alzheimer’s disease. In the present study, we continue to investigate the mechanism by which hyperoxygenation reduces amyloid-beta deposition in the brain. Hyperoxygenation treatment induces upregulation of matrix metalloproteinase-2 (MMP-2), MMP-9, and tissue plasminogen activator (tPA), the endopeptidases that can degrade amyloid-beta, in the hippocampus of Tg-APP/PS1 mice. The promoter regions of the three proteinase genes all contain potential binding sites for MeCP2 and Pea3, which are upregulated in the hippocampus after hyperoxygenation. Hyperoxygenation treatment in HT22 neuronal cells increases MeCP2 but not Pea3 expression. In HT22 cells, siRNA-mediated knockdown of Mecp2 decreases Mmp-9 expression and to a lesser extent, Mmp-2 and tPA expression. In mice, siRNA-mediated Mecp2 knockdown in the hippocampus reduces Mmp-9 expression, but not significantly Mmp-2 and tPA expression. The ChIP assay indicates that hyperoxygenation treatment in Tg-APP/PS1 mice increases MeCP2 binding to the promoter regions of Mmp-2, Mmp-9 and tPA genes in the hippocampus. Together, these results suggest that hyperoxygenation increases the expression of MMP-2, MMP-9, and tPA, of which MMP-9 is upregulated via MeCP2 in neuronal cells, and MMP-2 and tPA are upregulated through MeCP2 and other nuclear factors.

Linagliptin, a DPP-4 inhibitor, ameliorates Aβ (1-42) peptides induced neurodegeneration and brain insulin resistance (BIR) via insulin receptor substrate-1 (IRS-1) in rat model of Alzheimer's disease

Alzheimer's disease (AD) is the most devastating neurodegenerative disorder, accounting over 46 million cases of dementia globally. Evidence supports that Brain Insulin Resistance (BIR) due to serine phosphorylation of Insulin Receptor Substrate-1 (IRS-1) has an association with AD. GLP-1 an incretin hormone, rapidly degraded by Dipeptidyl Peptidase-4 (DPP-4) has also confirmed its efficacious role in AD. Linagliptin, a DPP-4 inhibitor is hypothesized to increase GLP-1 level, which then crosses Blood Brain Barrier (BBB), decreases Amyloid-beta (Aβ) and insulin resistance in hippocampus. Thus, the present study was designed to evaluate Linagliptin in Aβ (1-42) peptides induced rat model of AD. Following 1 week of induction, rats were administered with Linagliptin (0.513 mg/kg, 3 mg/kg, and 5 mg/kg) orally for 8 weeks and donepezil (5 mg/kg) as a reference standard. At the end of scheduled treatment neurobehavioral parameters were assessed. After this, rats were sacrificed, hippocampus was isolated from the whole brain for histopathological analysis and biochemical parameters estimation. Linagliptin dose-dependently and significantly reversed motor and cognitive impairment, assessed through locomotor activity (LA) and Morris water maze (MWM) test respectively. Moreover, Linagliptin augmented GLP-1 level and attenuated soluble Aβ (1-42), IRS-1 (s307), GSK-3β, TNF-α, IL-1β, IL-6, AchE and oxidative/nitrosative stress level in hippocampus. H&E and Congo red staining also exhibited neuroprotective and anti-amylodogenic effect respectively. Our study findings implies the significant effect of Linagliptin in reversing the behavioural and biochemical deficits by altering Aβ (1-42) and BIR via IRS-1 confirming one of the mechanism underlying the pathophysiology of AD.

A Review of the Application of Hyperbaric Oxygen Therapy in Alzheimer's Disease

Alzheimer's disease (AD) is considered as the most common cause of dementia in elderly population. While the exact mechanism of AD has not been discovered, hyperbolic oxygen therapy (HBOT) has been proven to be effective in the treatment of this degenerative disease. The objectives of this article are to review the literature available on molecular and physiological mechanisms underlying HBOT and its efficacy in treating AD and to review the effectiveness of HBOT as an alternate treatment intervention in both human and animal models. 391 full text articles were included in the review after literature search between 1980-2021 from two online data base (ScienceDirect and PubMed). The following key words were used: 'hyperbaric oxygen therapy' and 'Alzheimer disease.' Based on the outcomes of clinical and experimental studies, this review advocates the use of HBOT for the treatment of AD. This review explores future directions and recommends further research into a treatment protocol that will maintain long-term cognitive health of AD patients.

Hyperbaric oxygen therapy restores cognitive function and hippocampal pathologies in both aging and aging-obese rats

The population of obese-elderly has increased prominently around the world. Both aging and obesity are major factors of neurodegeneration. The present study hypothesizes that HBOT attenuates metabolic disturbance, cognitive decline, hippocampal pathologies in aging and aging-obese model. Sixty Wistar rats were separated into 2 groups to receive normal-diet (ND) or high-fat diet (HFD) for 22 weeks. At week 13, ND rats were divided into two subgroups to receive vehicle (0.9 % NSS, s.c) or d-gal (150 mg/kg/d, s.c) for total 10 weeks. HFD rats were injected only d-gal (150 mg/kg/d, s.c; HFDD) for total 10 weeks. At week 20, rats in each subgroup were given sham-treatment (1ATA, 80 L/min, 80 min/day), or HBOT (2ATA, pure O₂, 250 L/min, 80 min/day) for 14 days. Novel object location test, metabolic parameters, and hippocampal pathologies were determined after HBOT. d-gal induced insulin resistance, increased oxidative stress, autophagy impairment, microglial hyperactivation, apoptosis, synaptic dysplasticity which resulted in cognitive impairment. d-gal-treated HFD-fed rats had the highest levels of oxidative stress, apoptosis, dendritic spine loss. HBOT attenuated insulin resistance, cognitive impairment, hippocampal aging and pathologies in both models. These findings suggest that HBOT restored insulin sensitivity, hippocampal functions, cognition in aging and aging-obese models.

A review on the neuroprotective effects of hyperbaric oxygen therapy

Hyperbaric oxygen therapy, intermittent breathing of 100% oxygen at a pressure upper than sea level, has been shown to be some of the neuroprotective effects and used therapeutically in a wide range of neurological disorders. This review summarizes current knowledge about the neuroprotective effects of hyperbaric oxygen therapy with their molecular mechanisms in different models of neurological disorders.

Hyperbaric Oxygen Therapy Attenuates Burn-Induced Denervated Muscle Atrophy

Background: Neuronal apoptosis and inflammation in the ventral horn of the spinal cord contribute to denervated muscle atrophy post-burn. Hyperbaric oxygen therapy (HBOT) exerts anti-inflammation and neuroprotection. Furthermore, hypoxia-inducible factor (HIF)-1α has been reported to promote inflammation and apoptosis. We investigated the therapeutic potential of HBOT and the role of HIF-1α post-burn. Methods: Sprague-Dawley rats were divided into three groups: a control group, an untreated burn group receiving burn and sham treatment, and a HBOT group receiving burn injury and HBOT. The burn injury was induced with 75ºC ± 5ºC at the right hindpaw. HBOT (100% oxygen at 2.5 atmosphere, 90 min/day) and sham HBOT (21% oxygen at 1 atmosphere, 90 min/day) was started on day 28 after burn injury and continued for 14 treatments (days 28-41). Incapacitance (hind limb weight bearing) testing was conducted before burn and weekly after burn. At day 42 post-burn, the gastrocnemius muscle and the spinal cord ventral horn were analyzed. Results: HBOT improved burn-induced weight bearing imbalance. At day 42 post-burn, less gastrocnemius muscle atrophy and fibrosis were noted in the HBOT group than in the untreated burn group. In the ventral horn, HBOT attenuated the neuronal apoptosis and glial activation post-burn. The increases in phosphorylated AKT/mTOR post-burn were reduced after HBOT. HBOT also inhibited HIF-1α signaling, as determined by immunofluorescence and western blot. Conclusions: HBOT reduces burn-induced neuronal apoptosis in the ventral horn, possibly through HIF-1α signaling.

Molecular and Therapeutic Aspects of Hyperbaric Oxygen Therapy in Neurological Conditions

In hyperbaric oxygen therapy (HBOT), the subject is placed in a chamber containing 100% oxygen gas at a pressure of more than one atmosphere absolute. This treatment is used to hasten tissue recovery and improve its physiological aspects, by providing an increased supply of oxygen to the damaged tissue. In this review, we discuss the consequences of hypoxia, as well as the molecular and physiological processes that occur in subjects exposed to HBOT. We discuss the efficacy of HBOT in treating neurological conditions and neurodevelopmental disorders in both humans and animal models. We summarize by discussing the challenges in this field, and explore future directions that will allow the scientific community to better understand the molecular aspects and applications of HBOT for a wide variety of neurological conditions.

Combined Therapy With Hyperbaric Oxygen and Melatonin Effectively Reduce Brain Infarct Volume and Preserve Neurological Function After Acute Ischemic Infarct in Rat

This study tested the hypothesis that combined hyperbaric oxygen (HBO) and melatonin (Mel) was superior to either one for protecting the brain functional and parenchymal integrity from acute ischemic stroke (IS) injury. Adult-male Sprague-Dawley rats were divided into groups 1 (sham-operated control), 2 (IS), 3 (IS + HBO), 4 (IS + Mel), and 5 (IS + HBO-Mel). By day 28 after IS, the brain infarct area (BIA) was lowest in group 1, highest in group 2, significantly higher in groups 3 and 4 than in group 5, but not different between groups 3 and 4. The neurological function at day 7, 14, and 28 exhibited an opposite pattern to BIA among the 5 groups. The protein expressions of inflammatory (IL-1β/IL-6/iNOS/TNF-α/p-NF-κB), apoptotic (cleaved-caspase3/cleaved-PARP/mitochondrial Bax), mitochondrial/DNA-damaged (cytochrome-C/γ-H2AX), oxidative stress (NOX-1/NOX-2), and autophagy (i.e. ratio of CL3B-II/CL3B-I) biomarkers displayed an identical pattern of BIA among 5 groups. Cellular expressions of inflammation (F4/80+/GFAP+) and DNA-damaged biomarker (γ-H2AX+) exhibited an identical pattern, whereas the integrities of myelin sheath/neuron (MPB+/NeuN+), endothelial cell (CD31+/vWF+), and number of small vessels exhibited an opposite pattern of BIA among the 5 groups. Combined HBO-Mel therapy offered an additional benefit in protecting the brain against IS injury.

Hyperbaric oxygen ameliorates cognitive impairment in patients with Alzheimer's disease and amnestic mild cognitive impairment

INTRODUCTION

It has been reported that environmental factors such as hypoxia could contribute to the pathogenesis of Alzheimer's disease (AD). Therapeutics like hyperbaric oxygen treatment, which improves tissue oxygen supply and ameliorates hypoxic conditions in the brain, may be an alternative therapy for AD and amnestic mild cognitive impairment (aMCI). The present work aims to investigate the potential therapeutic effect of hyperbaric oxygen treatment for AD and aMCI.

METHODS

We recruited 42 AD, 11 aMCI, and 30 control AD patients in this study. AD and aMCI patients were treated with 40 minutes of hyperbaric oxygen once a day for 20 days and assessed by neuropsychiatric assessments including Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), and Activities of Daily Living (ADL) scale before and at 1-, 3-, and 6-month follow-up after treatment. Control AD patients who were not given hyperbaric oxygen treatment had similar clinical profile as hyperbaric oxygen treated AD. We examined 10 of the AD/aMCI patients with fluorodeoxyglucose positron emission tomography.

RESULTS

In self-comparison study, one course of hyperbaric oxygen treatment significantly improved the cognitive function assessed by MMSE and MoCA in AD patients after 1-month follow-up; such treatment also significantly improved MMSE score at 3-month follow-up and MoCA score at 1- and 3-month follow-up in aMCI patients. The ADL scale was significantly improved in AD patients after 1- and 3-month follow-up. Compared to the control AD patients, the MMSE and MoCA in hyperbaric oxygen treated AD patients were significantly improved after 1-month follow-up. Hyperbaric oxygen treatment also ameliorated the reduced brain glucose metabolism in some of the AD and aMCI patients.

CONCLUSION

Based on previous studies and our recent findings, we propose that hyperbaric oxygen treatment may be a promising alternative therapy for AD and aMCI.

Enhanced Cerebral Blood Volume under Normobaric Hyperoxia in the J20-hAPP Mouse Model of Alzheimer's Disease

Early impairments to neurovascular coupling have been proposed to be a key pathogenic factor in the onset and progression of Alzheimer's disease (AD). Studies have shown impaired neurovascular function in several mouse models of AD, including the J20-hAPP mouse. In this study, we aimed to investigate early neurovascular changes using wild-type (WT) controls and J20-hAPP mice at 6 months of age, by measuring cerebral haemodynamics and neural activity to physiological sensory stimulations. A thinned cranial window was prepared to allow access to cortical vasculature and imaged using 2D-optical imaging spectroscopy (2D-OIS). After chronic imaging sessions where the skull was intact, a terminal acute imaging session was performed where an electrode was inserted into the brain to record simultaneous neural activity. We found that cerebral haemodynamic changes were significantly enhanced in J20-hAPP mice compared with controls in response to physiological stimulations, potentially due to the significantly higher neural activity (hyperexcitability) seen in the J20-hAPP mice. Thus, neurovascular coupling remained preserved under a chronic imaging preparation. Further, under hyperoxia, the baseline blood volume and saturation of all vascular compartments in the brains of J20-hAPP mice were substantially enhanced compared to WT controls, but this effect disappeared under normoxic conditions. This study highlights novel findings not previously seen in the J20-hAPP mouse model, and may point towards a potential therapeutic strategy.

Multi-target PET evaluation in APP/PS1/tau mouse model of Alzheimer's disease

Positron emission tomography (PET) has great benefits for developing therapeutics and quantifying pathological markers in neuropsychiatric disorders. This study aimed to firstly demonstrate the feasibility of PET imaging for glucagon-like peptide-1 receptor (GLP-1R) in Alzheimer's disease (AD) and evaluate the GLP-1R expression. Besides, microglial activation, dopamine D2 receptor (D2R) expression, and glucose metabolism in the brain of APP/PS1/tau transgenic model of AD (3×Tg-AD) were also investigated by PET. [¹⁸F]FBEM-Cys³⁹-exendin-4, [¹⁸F]DPA-714, [¹⁸F]fallypride, and [¹⁸F]FDG were prepared and PET imaging acquisitions for 3×Tg-AD mice and wild-type (WT) mice were performed at 15, 30, and 60 min post-injection. Fifteen regions of interest (ROIs) were selected and %ID/g was calculated. The results showed that the uptake of [¹⁸F]FBEM-Cys³⁹-exendin-4 in 10 ROIs of 3×Tg-AD mice at 60 min post-injection was significantly lower than that of WT mice (p < 0.05). Besides, 3×Tg-AD mice showed significantly higher [¹⁸F]DPA-714 uptake in 7 ROIs and lower [¹⁸F]fallypride uptake in 4 ROIs compared to WT mice. [¹⁸F]FDG PET showed no significant differences in any ROIs between the two groups. A positive correlation between the uptake of [¹⁸F]fallypride and [¹⁸F]FBEM-Cys³⁹-exendin-4 could be found in the whole brain. In summary, these results validated the feasibility of GLP-1R PET in AD and demonstrated the reduced GLP-1R and D2R expression as well as increased microglial activation caused by AD.

Modulation of neuroinflammation by cysteinyl leukotriene 1 and 2 receptors: implications for cerebral ischemia and neurodegenerative diseases

Neuroinflammation is a complex biological process and has been known to play an important role in age-related cerebrovascular and neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease, and Parkinson's disease. Cysteinyl leukotrienes (CysLTs) are potent inflammatory lipid mediators that exhibit actions mainly through activating type 1 and type 2 CysLT receptors (CysLT1 and CysLT2). Accumulating evidence shows that CysLT1 and CysLT2 are activated at different stages of pathological process in various cell types in the brain such as vascular endothelial cells, astrocytes, microglia, and neurons in response to insults. However, the precise roles and mechanisms of CysLT1 and CysLT2 in regulating the pathogenesis of cerebral ischemia, Alzheimer's disease, and Parkinson's disease are not fully understood. In this article, we focus on current advances that link activation of CysLT1 and CysLT2 to the pathological process during brain ischemia and neurodegeneration and discuss mechanisms by which CysLT1 and CysLT2 mediate inflammatory process and brain injury. Multitarget anti-inflammatory potentials of CysLT1 and CysLT2 antagonism for neuroinflammation and brain injury will also be reviewed.

Microglial priming of antigen presentation and adaptive stimulation in Alzheimer's disease

The prominent pathological consequences of Alzheimer's disease (AD) are the misfolding and mis-sorting of two cellular proteins, amyloid-β and microtubule-associated protein Tau. The accumulation of toxic phosphorylated Tau inside the neurons induces the increased processing of amyloid-β-associated signaling cascade and vice versa. Neuroinflammation-driven synaptic depletion and cognitive decline are substantiated by the cross talk of activated microglia and astroglia, leading to neuron degeneration. Microglia are the brain-resident immune effectors that prove their diverse functions in maintaining CNS homeostasis via collaboration with astrocytes and T lymphocytes. Age-related senescence and chronic inflammation activate microglia with increased pro-inflammatory markers, oxidative damage and phagocytosis. But the improper processing of misfolded protein via lysosomal pathway destines the spreading of 'seed' constituents to the nearby healthy neurons. Primed microglia process and present self-antigen such as amyloid-β and modified Tau to the infiltrated T lymphocytes through MHC I/II molecules. After an effective conversation with CD4+ T cells, microglial phenotype can be altered from pro-active M1 to neuro-protective M2 type, which corresponds to the tissue remodeling and homeostasis. In this review, we are focusing on the change in functionality of microglia from innate to adaptive immune response in the context of neuroprotection, which may help in the search of novel immune therapy in AD.

KCa3.1 deficiency attenuates neuroinflammation by regulating an astrocyte phenotype switch involving the PI3K/AKT/GSK3β pathway

Neuroinflammation may induce a phenotype switch to reactive astrogliosis in neurodegenerative disorders. The calcium-activated potassium channel (KCa3.1) is active in the phenotypic switch that occurs during astrogliosis in Alzheimer's disease and ischemic stroke. Here, transcriptome sequencing (RNA-Seq), immunohistochemistry, western blotting, pharmacological blockade, and calcium imaging were used to investigate astrocyte KCa3.1 activity in neuroinflammation, Tau accumulation, and insulin signaling deficits in male wild-type C57BL/6 and KCa3.1^-/- knockout (KO) mice, and in primary astrocyte cultures. KCa3.1 deficiency in KO mice decreased lipopolysaccharide (LPS)-induced memory deficits, neuronal loss, glial activation, Tau phosphorylation, and insulin signaling deficits in vivo. KCa3.1 expression in astrocytes was associated with LPS-induced upregulation of the Orai1 store-operated Ca²⁺ channel protein. The KCa3.1 channel was found to regulate store-operated Ca²⁺ overload through an interaction with Orai1 in LPS-induced reactive astrocytes. The LPS-induced effects on KCa3.1 and Orai1 indirectly promoted astrogliosis-related changes via the PI3K/AKT/GSK3β and NF-κB signaling pathways in vitro. Unbiased evaluation of RNA-Seq results for actively translated RNAs confirmed that substantial astrocyte diversity was associated with KCa3.1 deficiency. Our results suggest that KCa3.1 regulated astrogliosis-mediated neuroinflammation, Tau accumulation, and insulin signaling deficiency via PI3K/AKT/GSK3β and NF-κB signaling pathways, and contributing to neuronal loss and memory deficits in this neuroinflammation mouse model.

Protective Effect of Hyperbaric Oxygen Therapy on Cognitive Function in Patients with Vascular Dementia

Recent studies have shown that hyperbaric oxygen (HBO) has a therapeutic effect on vascular dementia (VD); however, the exact mechanism remains unclear. This article aims to reveal the protective effects and underlying mechanisms of HBO on VD. A total of 158 patients with VD were prospectively included in the study and were randomly divided into control group and HBO group. The control group was given conventional treatment and the HBO group was treated with HBO in addition to conventional treatment. The following HBO protocol was practiced: 5 days per week, 60 min each, 100% oxygen at 2 standard atmospheric pressures for 12 weeks. The Mini-Mental State Examination (MMSE) scores and serum Humanin levels were detected before and after treatments in both groups. The baseline characteristics were not different dramatically between groups (p > 0.05). There was no significant difference in MMSE scores and serum Humanin levels between the two groups before treatment (p > 0.05). After treatment, compared with the control group, the MMSE scores and serum Humanin levels in the HBO group were significantly increased (p < 0.05). Spearman correlation analysis showed that the serum Humanin levels were positively correlated with MMSE scores (r = 0.409, p < 0.05) and this correlation was independent of baseline characteristics (β = 0.312, p < 0.05). HBO therapy can improve cognitive function in patients with VD, and its mechanism may be related to elevated serum Humanin levels.

Pathological Impacts of Chronic Hypoxia on Alzheimer's Disease

Chronic hypoxia is considered as one of the important environmental factors contributing to the pathogenesis of Alzheimer's disease (AD). Many chronic hypoxia-causing comorbidities, such as obstructive sleep apnea syndrome (OSAS) and chronic obstructive pulmonary disease (COPD), have been reported to be closely associated with AD. Increasing evidence has documented that chronic hypoxia may affect many pathological aspects of AD including amyloid β (Aβ) metabolism, tau phosphorylation, autophagy, neuroinflammation, oxidative stress, endoplasmic reticulum (ER) stress, and mitochondrial and synaptic dysfunction, which may collectively result in neurodegeneration in the brain. In this Review, we briefly summarize the effects of chronic hypoxia on AD pathogenesis and discuss the underlying mechanisms. Since chronic hypoxia is common in the elderly and may contribute to the pathogenesis of AD, prospective prevention and treatment targeting hypoxia may be helpful to delay or alleviate AD.

Hyperbaric oxygen therapy for Alzheimer's dementia with positron emission tomography imaging: a case report

A 58-year-old female was diagnosed with Alzheimer's dementia (AD) which was rapidly progressive in the 8 months prior to initiation of hyperbaric oxygen therapy (HBOT). ¹⁸Fluorodeoxyglucose (¹⁸FDG) positron emission tomography (PET) brain imaging demonstrated global and typical metabolic deficits in AD (posterior temporal-parietal watershed and cingulate areas). An 8-week course of HBOT reversed the patient's symptomatic decline. Repeat PET imaging demonstrated a corresponding 6.5-38% regional and global increase in brain metabolism, including increased metabolism in the typical AD diagnostic areas of the brain. Continued HBOT in conjunction with standard pharmacotherapy maintained the patient's symptomatic level of function over an ensuing 22 months. This is the first reported case of simultaneous HBOT-induced symptomatic and ¹⁸FDG PET documented improvement of brain metabolism in AD and suggests an effect on global pathology in AD.

Ameliorative effect of alendronate against intracerebroventricular streptozotocin induced alteration in neurobehavioral, neuroinflammation and biochemical parameters with emphasis on Aβ and BACE-1

Alzheimer's disease (AD) is the most prevalent age related neurodegenerative disorder manifested by progressive cognitive decline and neuronal loss in the brain, yet precise etiopathology of majority of sporadic or late-onset AD cases is unknown. AD is associated with various pathological events such as Aβ deposition due to BACE-1 induced cleavage of APP, neuroinflammation, increased cholesterol synthesis, cholinergic deficit and oxidative stress. It was found that bone drug, alendronate (ALN) that cross blood brain barrier inhibits brain cholesterol synthesis and AChE enzyme activity. As cholesterol modifying agents have been supposed to alter AD like pathologies, the current study was designed to investigate the possible neuroprotective and therapeutic potential of ALN against ICV STZ induced experimental sporadic AD (SAD) in mice in a non-cholesterol dependent manner, using donepezil (5 mg/kg) as a reference standard. The preliminary study was done by molecular modelling to identify the binding affinity of ALN with BACE-1 in silico. The prevention of cognitive impairment in mice induced by ICV STZ (3 mg/kg) infused on first and third day, by ALN (1.76 mg/kg p.o.) administered for 15 consecutive days was assessed through Spontaneous Alternation Behavior (SAB) and Morris water maze (MWM) test. Additionally, the protective effect of ALN was also observed by the reversal of altered levels of Aβ_1-42, BACE-,1 neuroinflammatory cytokines, AChE activity and oxidative stress markers (except TBARS) in ICV-STZ infused mice. However, the findings of the present study imply the therapeutic potential of ALN against SAD-like complications.