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

https://www.mdpi.com/2218-273X/10/6/958/pdf

The Hyperoxic-Hypoxic Paradox

Hyperbaric oxygen (HBO) therapy has been reported to be beneficial for treating many conditions of inflammation-associated bone loss. The aim of this work was to in vitro investigate the effect of HBO in the course of osteogenesis of human Mesenchymal Stem Cells (MSCs) grown in a simulated pro-inflammatory environment. Cells were cultured with osteogenic differentiation factors in the presence or not of the pro-inflammatory cytokine Tumor Necrosis Factor-α (TNF-α), and simultaneously exposed daily for 60 min, and up to 21 days, at 2,4 atmosphere absolute (ATA) and 100% O2. To elucidate osteogenic differentiation-dependent effects, cells were additionally pre-committed prior to treatments. Cell metabolic activity was evaluated by means of the MTT assay and DNA content quantification, whereas osteogenic and vasculogenic differentiation was assessed by quantification of extracellular calcium deposition and gene expression analysis. Metabolic activity and osteogenic properties of cells did not differ between HBO, high pressure (HB) alone, or high oxygen (HO) alone and control if cells were pre-differentiated to the osteogenic lineage. In contrast, when treatments started contextually to the osteogenic differentiation of the cells, a significant reduction in cell metabolic activity first, and in mineral deposition at later time points, were observed in the HBO-treated group. Interestingly, TNF-α supplementation determined a significant improvement in the osteogenic capacity of cells subjected to HBO, which was not observed in TNF-α-treated cells exposed to HB or HO alone. This study suggests that exposure of osteogenic-differentiating MSCs to HBO under in vitro simulated inflammatory conditions enhances differentiation towards the osteogenic phenotype, providing evidence of the potential application of HBO in all those processes requiring bone regeneration.

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Hyperbaric Oxygen Therapy Improves the Osteogenic and Vasculogenic Properties of Mesenchymal Stem Cells in the Presence of Inflammation In Vitro.

Stroke continues to be an extremely prevalent disease and poses a great challenge in developing safe and effective therapeutic options. Hyperbaric oxygen therapy (HBOT) has demonstrated significant pre-clinical effectiveness for the treatment of acute ischemic stroke, and limited potential in treating chronic neurological deficits. Reported benefits include reductions in oxidative stress, inflammation, neural apoptosis, and improved physiological metrics such as edema and oxygen perfusion, all of which contribute to improved functional recovery. This pre-clinical evidence has failed to translate into an effective evidence-based therapy, however, due in large part to significant inconsistencies in treatment protocols and design of clinical studies. While the medical community works to standardize clinical protocols in an effort to advance HBOT for acute stroke, pre-clinical investigations continue to probe novel applications of HBOT in an effort to optimize stroke neuroprotection. One such promising strategy is HBOT preconditioning. Based upon the premise of mild oxidative stress priming the brain for tolerating the full-blown oxidative stress inherent in stroke, HBOT preconditioning has displayed extensive efficacy. Here, we first review the pre-clinical and clinical evidence supporting HBOT delivery following ischemic stroke and then discuss the scientific basis for HBOT preconditioning as a neuroprotective strategy. Finally, we propose the innovative concept of stem cell preconditioning, in tandem with brain preconditioning, as a promising regenerative pathway for maximizing the application of HBOT for ischemic stroke treatment.

A Dual Role for Hyperbaric Oxygen in Stroke Neuroprotection: Preconditioning of the Brain and Stem Cells.

Introduction Aging is characterized by the progressive loss of physiological capacity. At the cellular level, two key hallmarks of the aging process include telomere length (TL) shortening and cellular senescence. Repeated intermittent hyperoxic exposures, using certain hyperbaric oxygen therapy (HBOT) protocols, can induce regenerative effects which normally occur during hypoxia. The aim of the current study was to evaluate whether HBOT affects TL and senescent cell concentrations in a normal, non-pathological, aging adult population. Methods Thirty-five healthy independently living adults, aged 64 and older, were enrolled to receive 60 daily HBOT exposures. Whole blood samples were collected at baseline, at the 30th and 60th session, and 1-2 weeks following the last HBOT session. Peripheral blood mononuclear cells (PBMCs) telomeres length and senescence were assessed. Results Telomeres length of T helper, T cytotoxic, natural killer and B cells increased significantly by over 20% following HBOT. The most significant change was noticed in B cells which increased at the 30th session, 60th session and post HBOT by 25.68%±40.42 (p=0.007), 29.39%±23.39 (p=0.0001) and 37.63%±52.73 (p=0.007), respectively. There was a significant decrease in the number of senescent T helpers by -37.30%±33.04 post-HBOT (P

Hyperbaric oxygen therapy increases telomere length and decreases immunosenescence in isolated blood cells: a prospective trial.

Nucleus pulposus-derived mesenchymal stem cells (NP-MSCs) are suitable cell candidates for intervertebral disc (IVD) regeneration. However, little work has been done to determine the proliferation and chondrogenic differentiation of NP-MSCs in the hyperosmotic microenvironment of IVD. This study aimed to investigate the influence of the hyperosmolarity of IVD on the proliferation and chondrogenic differ-entiation of NP-MSCs. NP-MSCs were cultured in media of 300, 400, 430, and 500 mOsm/L, mimicking the osmotic pressures of serious degenerative, moderately degenerative, and healthy IVD. Cell proliferation was measured by CCK-8 assay. The expression of aggrecan, collagen I, and collagen II were measured by gene and protein expression analysis. Alcian blue and dimethylmethylene blue assay were used to investigate the accumulation of sulfate glycosaminoglycan. The regulation role of extracellular signal-regulated kinase (ERK) pathway was also analyzed. The results showed that, compared to 300 mOsm/L, hyperosmolarity of healthy IVD (430 and 500 mOsm/L) inhibited the proliferation and chondrogenic differentiation of NP-MSCs. The relative hypoosmotic condition of moderately degenerative IVD (400 mOsm/L) led to great proliferation and chondrogenic differentiation capacity. The ERK pathway was activated by the hyperosmolarity; inhibition of the ERK pathway abolished the difference in cell proliferation between the 300 mOsm/L and the hyperosmotic conditions, and enhanced chondrogenic differentiation. In conclusion, hyperosmolarity of IVD had a significant impact on the proliferation and chondrogenic differentiation of NP-MSCs. The ERK pathway was involved in the inhibition of proliferation and chondrogenic differentiation of NP-MSCs by the hyperosmolarity of IVD. The relative hypo-osmotic condition prevailing in degenerative discs offers a more permissive microenvironment for NP-MSCs.

The Influence of Hyperosmolarity in the Intervertebral Disc on the Proliferation and Chondrogenic Differentiation of Nucleus Pulposus-Derived Mesenchymal Stem Cells.

Hyperbaric oxygen (HBO) therapy and neural stem cell (NSC) transplantation can improve traumatic brain injury (TBI) clinically This study aimed to investigate the mechanism of HBO promoting NSC proliferation and neurological recovery after TBI Twenty-four Sprague-Dawley rats were divided randomly into three groups: a sham group, a TBI group (constructed using Feeney's free-fall method), and an HBO-treated TBI group Neurological function was evaluated by Neurological Severity Scores on days 1, 3, and 7, and we found that TBI-induced poor neurological function was improved by HBO On day 7 after TBI, we observed that TBI promoted NSC proliferation, migration to the lesion area, and the levels of vascular endothelial growth factor (VEGF), VEGFR2, Raf-1, MEK1/2, and phospho-extracellular signal-regulated kinase (ERK) 1/2 protein, which were further boosted by HBO, from immunohistochemistry, immunofluorescence, and Western blot experiments In vitro, cell injury was applied to NSCs isolated from neonatal Sprague-Dawley rats by the Cell Injury Controller II system Moreover, data from the BrdU Kit and Western blot showed that in-vitro HBO significantly accelerated NSC proliferation and the levels of proteins related to cell cycle and the VEGF/ERK pathway after cell injury, which was suppressed by the VEGFR2 inhibitor Taken together, this study indicated that HBO may promote NSC proliferation by activating VEGF/ERK signaling and play a crucial role in neuroprotection after TBI

Hyperbaric oxygen promotes neural stem cell proliferation by activating vascular endothelial growth factor/extracellular signal-regulated kinase signaling after traumatic brain injury.

Cardiovascular disease leads to the highest morbidity worldwide. There is an urgent need to solve the lack of a viable arterial graft for patients requiring coronary artery bypass surgery. The current gold standard is to use the patient's own blood vessel, such as a saphenous vein graft. However, some patients do not have appropriate vessels to use because of systemic disease or secondary surgery. On the other hand, there is no commercially available synthetic vascular graft available on the market for small diameter (<6 mm) blood vessels like coronary, carotid, and peripheral popliteal arteries. Tissue‐engineered vascular grafts (TEVGs) are studied in recent decades as a promising alternative to synthetic arterial prostheses. Yet only a few studies have proceeded to a clinical trial. Recent studies have uncovered that the host immune response can be directed toward increasing the success of a TEVG by shedding light on ways to modulate the macrophage response and improve the tissue regeneration outcome. In this review, the basic concepts of vascular tissue engineering and immunoengineering are considered. The state‐of‐art of TEVGs is summarized and the role of macrophages in TEVG regeneration is analyzed. Current immunomodulatory strategies based on biomaterials are also discussed.

Immunomodulation Strategies for the Successful Regeneration of a Tissue‐Engineered Vascular Graft

Background Chlorogenic acid (CGA) is a polyphenolic compound with antioxidant and anti-inflammatory properties. CGA has been shown to improve neuroinflammation. This study is aimed at elucidating the exact mechanism by which CGA reduces neuroinflammation. Methods Oxygen and glucose deprivation (OGD) was utilized to treat BV2 microglia and HT-22 hippocampal neurons to engineer an in vitro model of hypoxic ischemia reperfusion. The levels of inflammatory factors (IL-1β, IL-6, TNF-α, IL-4, and IL-10) and oxidative stress factors (MDA, SOD, and GSH-PX) in microglia were determined by ELISA kits. The neuron proliferation was assessed by CCK-8 assay, and LDH kit was used to determine LDH release in neurons. The fluorescent dye DCF-DA was employed to measure ROS levels in neurons. Correlation of MIR497HG, miR-29b-3p, and SIRT1/NF-κB in neurons and microglia was determined by qRT-PCR. Expressions of inflammatory proteins (COX2, iNOS), oxidative stress pathways (Nrf2, HO-1), and apoptosis-related proteins (Bcl-2, Bax, caspase3, caspase8, and caspase9) in microglia or neurons were determined by western blot. The interactions between MIR497HG and miR-29b-3p, as well as between miR-29b-3p and SIRT1, were determined by dual luciferase assay and RIP assay. Results CGA attenuated OGD-mediated inflammation and oxidative stress in microglia and inhibited microglia-mediated neuronal apoptosis. CGA increased the levels of MIR497HG and SIRT1 and suppressed the levels of miR-29b-3p in BV2 and HT-22 cells. MIR497HG knockdown, miR-29b-3p upregulation, and SIRT1 inhibition inhibited CGA-mediated anti-inflammatory and neuronal protective functions. There is a targeting correlation between MIR497HG, miR-29b-3p, and Sirt1. MIR497HG sponges miR-29b-3p to regulate SIRT1 expression in an indirect manner. Conclusion CGA upregulates MIR497HG to curb miR-29b-3p expression, hence initiating the SIRT1/NF-κB signaling pathway and repressing OGD-elicited inflammation, oxidative stress, and neuron apoptosis.

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Chlorogenic Acid Prevents Microglia-Induced Neuronal Apoptosis and Oxidative Stress under Hypoxia-Ischemia Environment by Regulating the MIR497HG/miR-29b-3p/SIRT1 Axis

Abstract Context Chlorogenic acid (CGA) has good antioxidant effects, but its explicit mechanism in cerebral ischaemia-reperfusion injury is still uncertain. Objective We studied the effect of CGA in human brain microvascular endothelial cells (HBMECs) under OGD/R damage. Materials and methods HBMECs in 4 groups were treated with oxygen-glucose deprivation/re-oxygenation (OGD/R) (4 + 24 h), normal no CGA treatment and different concentrations (20, 40 or 80 μM) of CGA. Male C57BL/6J mice were classified as sham, middle cerebral artery occlusion (MCAO), and MCAO + CGA (30 mg/kg/day) groups. Mice in the sham group were not subjected to MCAO. Cell viability, apoptosis, angiogenesis and related protein levels were investigated by CCK-8, flow cytometry, TUNEL staining, tube formation and western blot assays. Infarct volume of brain tissues was analyzed by TTC staining. Results CGA curbed apoptosis (from 32.87% to 13.12% in flow cytometry; from 34.46% to 17.8% in TUNEL assay) but accelerated cell angiogenesis of HBMECs with OGD/R treatment. Moreover, CGA augmented activation of the PI3K-Akt signalling (p-PI3K/PI3K level, from 0.39 to 0.49; p-Akt/Akt level, from 0.52 to 0.81), and the effect of CGA on apoptosis and angiogenesis was abolished by an inhibitor of PI3K-Akt signalling. Furthermore, CGA attenuated infarct (from 41.26% to 22.21%) and apoptosis and promoted angiogenesis and activation of the PI3K/Akt signalling in MCAO-induced mice. Conclusions CGA effectively repressed apoptosis and promoted angiogenesis in OGD/R-treated HBMECs and MCAO-treated mice by modulating PI3K-Akt signalling. Our research provides a theoretical basis for the use of CGA in the treatment of ischaemic stroke.

https://www.tandfonline.com/doi/pdf/10.1080/13880209.2022.2110599?needAccess=true

Fan Zhang

Papers

Hyperbaric oxygen promotes neural stem cell proliferation by activating vascular endothelial growth factor/extracellular signal-regulated kinase signaling after traumatic brain injury.

Immunomodulation Strategies for the Successful Regeneration of a Tissue‐Engineered Vascular Graft

Chlorogenic Acid Prevents Microglia-Induced Neuronal Apoptosis and Oxidative Stress under Hypoxia-Ischemia Environment by Regulating the MIR497HG/miR-29b-3p/SIRT1 Axis

Chlorogenic acid promotes angiogenesis and attenuates apoptosis following cerebral ischaemia-reperfusion injury by regulating the PI3K-Akt signalling