Anti-Apoptotic Effect of Hyperbaric Oxygen Preconditioning on a Rat Model of Myocardial Infarction

Hyperbaric Oxygen Upregulates Mst1 to Activate Keap1/Nrf2/HO-1 Pathway Resisting Oxidative Stress in a Rat Model of Acute Myocardial Infarction

This study aimed to investigate the protective effects and mechanisms of hyperbaric oxygen (HBO) preconditioning in a rat model of acute myocardial infarction (MI) established by ligation of the left anterior descending (LAD) coronary artery. Microarray, real-time PCR, and western blotting (WB) results demonstrated that the Mst1 gene was downregulated in the heart tissue of the MI rat model. HBO preconditioning significantly increased Mst1 expression in cardiac tissues of rats after MI modeling. Lentiviral infection was used to silence the Mst1 gene in rats treated with HBO to probe the effect of Mst1 on HBO cardioprotection. HBO preconditioning decreased heart infarct size and ameliorated cardiac function in MI rats, whereas Mst1 silencing reversed the effect of HBO administration, as indicated after heat infarct size determination via TTC staining, histological examination via HE staining, and measurements of cardiac function. HBO preconditioning reduced oxidative stress and inflammation in cardiac tissue of MI rat model, evidenced by alteration of malondialdehyde (MDA), 8-hydroxy-2-deoxyguanosine (8-OHdG), and protein carbonyl contents, as well as production of inflammation-associated myeloperoxidase (MPO), IL-1β, and TNF-α. These findings provide a new signaling mechanism through which HBO preconditioning can protect against acute MI injury through the Mst1-mediating Keap1/Nrf2/HO-1-dependent antioxidant defense system.

Diversity and Isolation of Endophytic Fungi in Panax japonicus and Biotransformation Activity on Saponins

OBJECTIVE

This study reports the diversity and community structure differences of the endophytic fungi of Panax japonicus of different ages to obtain novel endophytic fungi with glycoside hydrolytic activity for rare saponins production.

METHODS

This study used the high-throughput sequencing method to analyze the diversity and community structure of endophytic fungi of P. japonicus. The endophytic fungi were processed by traditional isolation, culture, conservation, and ITS rDNA sequence analyses. Then the total saponins of P. japonicus were used as the substrate to evaluate the glycoside hydrolytic activity.

RESULTS

The composition analysis of the community structure showed that the abundance, evenness, and diversity of endophytic fungi of nine-year-old P. japonicus were the best among all samples. A total of 210 endophytic fungi were isolated from P. japonicus samples and further annotated by sequencing the internal transcribed spacer. Then the biotransformation activity of obtained strains was further examined on total saponins of P. japonicus (TSPJ), with a strain identified as Fusarium equiseti (No.30) from 7-year-old P. japonicus showing significant glycoside hydrolytic activity on TSPJ, including ginsenoside Ro→zinglbroside R1, pseudoginsenoside RT1→pseudoginsenoside RP1, chikusetsusaponin IV→tarasaponin VI and chikusetsusaponin IVa →calenduloside E.

CONCLUSION

These results reveal the diversity and community structure differences of the endophytic fungi of P. japonicus with different ages and establish a resource library of endophytic fungi of P. japonicus. More importantly, we identified a valuable endophytic fungus with glycoside hydrolytic activity and provided a promising convenient microbial transformation approach to produce minor deglycosylated ginsenosides.

Hyperbaric oxygen-induced long non-coding RNA MALAT1 exosomes suppress MicroRNA-92a expression in a rat model of acute myocardial infarction

Hyperbaric oxygen (HBO) improves angiogenesis. The effect of HBO on metastasis‐associated lung adenocarcinoma transcript 1 (MALAT1), a pro‐angiogenic long non‐coding RNA, in cardiac myocyte‐derived exosomes and acute myocardial infarction (AMI) is unknown. We aimed to investigate whether MALAT1 is altered in cardiac myocyte‐derived exosomes in response to HBO as well as the molecular regulatory mechanisms of MALAT1 in cardiac myocytes treated with HBO. Cardiac myocytes were cultured, and HBO was applied at 2.5 atmosphere absolute in a hyperbaric chamber. Exosomes were extracted from the culture media. A rat model of AMI generated by the ligation of the left anterior descending artery was used. HBO significantly increased MALAT1 expression in cardiac myocytes and HBO‐induced MALAT1 and exosomes attenuated miR‐92a expression after myocardial infarction. Expression of krüppel‐like factor 2 (KLF2) and CD31 was significantly decreased after infarction and HBO‐induced exosomes significantly reversed the expression. Silencing of MALAT1 using MALAT1‐locked nucleic acid GapmeR significantly attenuated KLF2 and CD31 protein expression after infarction induced by HBO‐induced exosomes. HBO‐induced exosomes also decreased infarct size significantly. HBO‐induced exosomes from cardiac myocytes up‐regulate MALAT1 to suppress miR‐92a expression and counteract the inhibitory effect of miR‐92a on KLF2 and CD31 expression in left ventricular myocardium after myocardial infarction to enhance neovascularization.

Alterations in glutathione, nitric oxide and 3-nitrotyrosine levels following exercise and/or hyperbaric oxygen treatment in mice with diet-induced diabetes

Oxidative stress is involved in the development of diabetes. Nitric oxide (NO) contributes to oxidative stress, affects the synthesis of glutathione (GSH) in tissues and also regulates important physiological processes. The levels of nitrosative stress, assessed by measuring the levels of 3-nitrotirosina (3NT) as well as the bioavailability of NO are modulated by exercise and hyperbaric oxygenation (HBO). The aim of the present study was to evaluate the effects of exercise and HBO on the levels of NO, 3NT and GSH in tissues of various organs obtained from diabetic mice. Female mice were fed a high-fat/high-fructose diet to induce diabetes. Mice with diabetes were subjected to exercise and/or HBO. Initial and final concentrations of NO, 3NT and GSH were assessed in the muscle, liver, kidney, heart, spleen, lung, brain, visceral adipose, thoracic aorta and small intestine. Diabetes did not affect initial values of NO, although it significantly increased the levels of 3NT. The basal level of GSH in the diabetic group was lower than or comparable to that of the control group in the majority of the organs assessed. A negative correlation was observed between 3NT and GSH levels in the initial values of all tissues of the control group only, whereas all pathological tissues showed a positive correlation between NO and GSH. There was an increase or a stabilization of GSH levels in the majority of the organs in all treated mice despite the increase in nitrosative stress.

Hyperbaric oxygen preconditioning inhibits skin flap apoptosis in a rat ischemia-reperfusion model

BACKGROUND

Hyperbaric oxygen (HBO) improves skin flap function and inhibits partial necrosis induced by ischemia-reperfusion (I/R) injury. Our study aimed to evaluate the mechanism underlying HBO regulation of the antiapoptosis factors associated with I/R injury of skin flaps.

METHODS

The rats were divided into sham surgery, I/R, and HBO groups. Rats from the HBO group received HBO preconditioning followed by I/R surgery. Blood perfusion of the skin flaps was measured with laser Doppler flowmeters. Tissue morphology and apoptosis were subsequently assessed based on hematoxylin-eosinhe and terminal deoxynucleotidyl transferase dUTP nick-end labeling staining. Protein expression of phosphorylated apoptosis signal-regulating kinase 1 (pASK-1), phosphorylated c-Jun N-terminal kinase (pJNK), B-cell lymphoma-2 (Bcl-2), and Bcl2-associated X protein (Bax) was examined by immunodetection, and Bcl-2 messenger RNA expression was detected by quantitative polymerase chain reaction. In addition, caspase-3 activity was also measured.

RESULTS

The result of microcirculation analysis showed that the survival and blood perfusion rates significantly increased in the skin flap after HBO exposure. Terminal deoxynucleotidyl transferase dUTP nick-end labeling staining revealed that cell apoptosis was significantly attenuated in the HBO group. Furthermore, HBO preconditioning increased the expression of Bcl-2 and inhibited pASK-1, pJNK, and Bax expression as determined by both immunohistochemistry and Western blot. Caspase-3 activity and the Bax/Bcl-2 ratio declined in the HBO group.

CONCLUSIONS

HBO preconditioning effectively ameliorates I/R injury by regulating the apoptosis signal-regulating kinase 1 and/or c-Jun N-terminal kinase pathway and anti- and proapoptosis factors.

Hyperbaric oxygen therapy (HBOT) suppresses biomarkers of cell stress and kidney injury in diabetic mice

The disease burden from diabetic kidney disease is large and growing. Effective therapies are lacking, despite an urgent need. Hyperbaric oxygen therapy (HBOT) activates Nrf2 and cellular antioxidant defenses; therefore, it may be generally useful for treating conditions that feature chronic oxidative tissue damage. Herein, we determined how periodic exposure to oxygen at elevated pressure affected type 2 diabetes mellitus-related changes in the kidneys of db/db mice. Two groups of db/db mice, designated 2.4 ATA and 1.5 ATA, were treated four times per week with 100 % oxygen at either 1.5 or 2.4 ATA (atmospheres absolute) followed by tests to assess kidney damage and function. The sham group of db/db mice and the Hets group of db/+ mice were handled but did not receive HBOT. Several markers of kidney damage were reduced significantly in the HBOT groups including urinary biomarkers neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C (CyC) along with significantly lower levels of caspase-3 activity in kidney tissue extracts. Other stress biomarkers also showed trends to improvement in the HBOT groups, including urinary albumin levels. Expressions of the stress response genes NRF2, HMOX1, MT1, and HSPA1A were reduced in the HBOT groups at the end of the experiment, consistent with reduced kidney damage in treated mice. Urinary albumin/creatinine ratio (ACR), a measure of albuminuria, was significantly reduced in the db/db mice receiving HBOT. All of the db/db mouse groups had qualitatively similar changes in renal histopathology. Glycogenated nuclei, not previously reported in db/db mice, were observed in these three experimental groups but not in the control group of nondiabetic mice. Overall, our findings are consistent with therapeutic HBOT alleviating stress and damage in the diabetic kidney through cytoprotective responses. These findings support an emerging paradigm in which tissue oxygenation and cellular defenses effectively limit damage from chronic oxidative stress more effectively than chemical antioxidants.

Hyperbaric oxygen therapy in China

Hyperbaric oxygen therapy (HBOT) is defined as a treatment in which a patient intermittently breathes 100% oxygen while the treatment chamber is pressurized to a pressure greater than sea level (1.0 atmosphere absolute, ATA). In China, for nearly 50 years, HBOT has been used as a primary or adjuvant therapy to treat a variety of diseases. This article mainly reviewed the indications and contraindications of HBOT, as well as the status of clinical and experimental HBOT research in China. At the same time, there is a brief introduction of hyperbaric oxygen preconditioning (HBO-PC) in China.

The medical use of oxygen: a time for critical reappraisal

Oxygen treatment has been a cornerstone of acute medical care for numerous pathological states. Initially, this was supported by the assumed need to avoid hypoxaemia and tissue hypoxia. Most acute treatment algorithms, therefore, recommended the liberal use of a high fraction of inspired oxygen, often without first confirming the presence of a hypoxic insult. However, recent physiological research has underlined the vasoconstrictor effects of hyperoxia on normal vasculature and, consequently, the risk of significant blood flow reduction to the at-risk tissue. Positive effects may be claimed simply by relief of an assumed local tissue hypoxia, such as in acute cardiovascular disease, brain ischaemia due to, for example, stroke or shock or carbon monoxide intoxication. However, in most situations, a generalized hypoxia is not the problem and a risk of negative hyperoxaemia-induced local vasoconstriction effects may instead be the reality. In preclinical studies, many important positive anti-inflammatory effects of both normobaric and hyperbaric oxygen have been repeatedly shown, often as surrogate end-points such as increases in gluthatione levels, reduced lipid peroxidation and neutrophil activation thus modifying ischaemia-reperfusion injury and also causing anti-apoptotic effects. However, in parallel, toxic effects of oxygen are also well known, including induced mucosal inflammation, pneumonitis and retrolental fibroplasia. Examining the available 'strong' clinical evidence, such as usually claimed for randomized controlled trials, few positive studies stand up to scrutiny and a number of trials have shown no effect or even been terminated early due to worse outcomes in the oxygen treatment arm. Recently, this has led to less aggressive approaches, even to not providing any supplemental oxygen, in several acute care settings, such as resuscitation of asphyxiated newborns, during acute myocardial infarction or after stroke or cardiac arrest. The safety of more advanced attempts to deliver increased oxygen levels to hypoxic or ischaemic tissues, such as with hyperbaric oxygen therapy, is therefore also being questioned. Here, we provide an overview of the present knowledge of the physiological effects of oxygen in relation to its therapeutic potential for different medical conditions, as well as considering the potential for harm. We conclude that the medical use of oxygen needs to be further examined in search of solid evidence of benefit in many of the current clinical settings in which it is routinely used.

Hyperbaric oxygen preconditioning protects skin from UV-A damage

Hyperbaric oxygen therapy (HBOT) is used for a number of applications, including the treatment of diabetic foot ulcers and CO poisoning. However, we and others have shown that HBOT can mobilize cellular antioxidant defenses, suggesting that it may also be useful under circumstances in which tissue protection from oxidative damage is desired. To test the protective properties of hyperbaric oxygen (HBO) on a tissue level, we evaluated the ability of a preconditioning treatment regimen to protect cutaneous tissue from UV-A-induced oxidative damage. Three groups of hairless SKH1-E mice were exposed to UV-A 3 days per week for 22 weeks, with two of these groups receiving an HBO pretreatment either two or four times per week. UV-A exposure increased apoptosis and proliferation of the skin tissue, indicating elevated levels of epithelial damage and repair. Pretreatment with HBO significantly reduced UV-A-induced apoptosis and proliferation. A morphometric analysis of microscopic tissue folds also showed a significant increase in skin creasing following UV-A exposure, which was prevented by HBO pretreatment. Likewise, skin elasticity was found to be greatest in the group treated with HBO four times per week. The effects of HBO were also apparent systemically as reductions in caspase-3 activity and expression were observed in the liver. Our findings support a protective function of HBO pretreatment from a direct oxidative challenge of UV-A to skin tissue. Similar protection of other tissues may likewise be achievable.

In vivo hyperoxic preconditioning protects against rat-heart ischemia/reperfusion injury by inhibiting mitochondrial permeability transition pore opening and cytochrome c release

In vivo hyperoxic preconditioning (PC) has been shown to protect against ischemia/reperfusion (I/R) myocardial damage. Mitochondrial permeability transition pore (MPTP) opening is an important event in cardiomyocyte cell death occurring during I/R and therefore a possible target for cardioprotection. We tested the hypothesis that in vivo hyperoxic PC, obtained by mechanical ventilation of animals, could protect heart against I/R injury by inhibiting MPTP opening and cytochrome c release from mitochondria. Mechanically ventilated rats were first exposed to a short period of hyperoxia and isolated hearts were subsequently subjected to I/R in a Langendorff apparatus. Hyperoxic PC significantly improved the functional recovery of hearts on reperfusion, reduced the infarct size, and decreased necrotic damage as shown by the reduced release of lactate dehydrogenase. Mitochondria from hyperoxic PC hearts were less sensitive than mitochondria from reperfused heart to MPTP opening. In addition, hyperoxic PC prevented mitochondrial NAD(+) depletion, an indicator of MPTP opening, and cytochrome c release as well as cardiolipin oxidation/depletion associated with I/R. Together, these results demonstrate that hyperoxic PC protects against heart I/R injury by inhibiting MPTP opening and cytochrome c release. Thus, in vivo hyperoxic PC may represent a useful strategy for the treatment of cardiac I/R injury and could have potential applications in clinical practice.