Role of mitochondrial hydrogen peroxide induced by intermittent hypoxia in airway epithelial wound repair in vitro

Far-infrared radiation and its therapeutic parameters: A superior alternative for future regenerative medicine?

In future regenerative medicine, far-infrared radiation (FIR) may be an essential component of optical therapy. Many studies have confirmed or validated the efficacy and safety of FIR in various diseases, benefiting from new insights into FIR mechanisms and the excellent performance of many applications. However, the lack of consensus on the biological effects and therapeutic parameters of FIR limits its practical applications in the clinic. In this review, the definition, characteristics, and underlying principles of the FIR are systematically illustrated. We outline the therapeutic parameters of FIR, including the wavelength range, power density, irradiation time, and distance. In addition, the biological effects, potential molecular mechanisms, and preclinical and clinical applications of FIR are discussed. Furthermore, the future development and applications of FIR are described in this review. By applying optimal therapeutic parameters, FIR can influence various cells, animal models, and patients, eliciting diverse underlying mechanisms and offering therapeutic potential for many diseases. FIR could represent a superior alternative with broad prospects for application in future regenerative medicine.

Glutamine Metabolism Is Required for Alveolar Regeneration during Lung Injury

(1) Background: Abnormal repair after alveolar epithelial injury drives the progression of idiopathic pulmonary fibrosis (IPF). The maintenance of epithelial integrity is based on the self-renewal and differentiation of alveolar type 2 (AT2) cells, which require sufficient energy. However, the role of glutamine metabolism in the maintenance of the alveolar epithelium remains unclear. In this study, we investigated the role of glutamine metabolism in AT2 cells of patients with IPF and in mice with bleomycin-induced fibrosis. (2) Methods: Single-cell RNA sequencing (scRNA-seq), transcriptome, and metabolomics analyses were conducted to investigate the changes in the glutamine metabolic pathway during pulmonary fibrosis. Metabolic inhibitors were used to stimulate AT2 cells to block glutamine metabolism. Regeneration of AT2 cells was detected using bleomycin-induced mouse lung fibrosis and organoid models. (3) Results: Single-cell analysis showed that the expression levels of catalytic enzymes responsible for glutamine catabolism were downregulated (p < 0.001) in AT2 cells of patients with IPF, suggesting the accumulation of unusable glutamine. Combined analysis of the transcriptome (p < 0.05) and metabolome (p < 0.001) revealed similar changes in glutamine metabolism in bleomycin-induced pulmonary fibrosis in mice. Mechanistically, inhibition of the key enzymes involved in glucose metabolism, glutaminase-1 (GLS1) and glutamic-pyruvate transaminase-2 (GPT2) leads to reduced proliferation (p < 0.01) and differentiation (p < 0.01) of AT2 cells. (4) Conclusions: Glutamine metabolism is required for alveolar epithelial regeneration during lung injury.

Therapeutic candidates for keloid scars identified by qualitative review of scratch assay research for wound healing

The scratch assay is an in vitro technique used to analyze cell migration, proliferation, and cell-to-cell interaction. In the assay, cells are grown to confluence and then ‘scratched’ with a sterile instrument. For the cells in the leading edge, the resulting polarity induces migration and proliferation in attempt to ‘heal’ the modeled wound. Keloid scars are known to have an accelerated wound closure phenotype in the scratch assay, representing an overactivation of wound healing. We performed a qualitative review of the recent literature searching for inhibitors of scratch assay activity that were already available in topical formulations under the hypothesis that such compounds may offer therapeutic potential in keloid treatment. Although several shortcomings in the scratch assay literature were identified, caffeine and allicin successfully inhibited the scratch assay closure and inflammatory abnormalities in the commercially available keloid fibroblast cell line. Caffeine and allicin also impacted ATP production in keloid cells, most notably with inhibition of non-mitochondrial oxygen consumption. The traditional Chinese medicine, shikonin, was also successful in inhibiting scratch closure but displayed less dramatic impacts on metabolism. Together, our results partially summarize the strengths and limitations of current scratch assay literature and suggest clinical assessment of the therapeutic potential for these identified compounds against keloid scars may be warranted.

Adiponectin ameliorates lung injury induced by intermittent hypoxia through inhibition of ROS-associated pulmonary cell apoptosis

PURPOSE

Obstructive sleep apnea hypopnea syndrome has been reported to be associated with pulmonary hypertension (PH). Adiponectin (Ad) has many protective roles in the human body, including its function as an anti-inflammatory and an anti-oxidant, as well as its role in preventing insulin resistance and atherosclerosis. This study aimed to investigate the molecular mechanism of chronic intermittent hypoxia (CIH)-induced pulmonary injury and the protective role of Ad in experimental rats.

METHODS

Thirty male Sprague-Dawley rats were randomly divided into three groups with 10 rats in each group: normal control (NC) group, CIH group, and CIH + Ad group. Rats in the NC group were kept breathing room air for 12 weeks. Rats in the CIH group were intermittently exposed to a hypoxic environment for 8 h/day for 12 weeks. Rats in the CIH + Ad group received 10 μg Ad twice weekly via intravenous injection. After 12 weeks of CIH exposure, we detected the pulmonary function, pulmonary artery pressure, lung histology, pulmonary cell apoptosis, pulmonary artery endothelial cell apoptosis, mitochondrial membrane potential (MMP), and reactive oxygen species (ROS) level. We also analyzed expression proteins involved in the mitochondria-, endoplasmic reticulum (ER) stress-, and Fas receptor-associated pulmonary apoptosis pathways, as well as the SIRT3/SOD2 pathway.

RESULTS

CIH exposure for 12 weeks did not lead to abnormal pulmonary function, PH, or pulmonary artery endothelial cell apoptosis. However, we observed a significant increase in the rate of pulmonary cell apoptosis, the expression of proteins involved in mitochondria-, ER stress-, and Fas receptor-associated pulmonary apoptosis pathways, and the generation of ROS in the CIH group compared with the NC group. In contrast, the MMP and protein expressions of SIRT3/SOD2 pathway were significantly decreased in the CIH group compared with the NC group. Ad supplementation in the CIH + Ad group partially improved these changes induced by CIH.

CONCLUSION

Even though CIH did not cause abnormal pulmonary function or PH, early lung injury was detected at the molecular level in rats exposed to CIH. Treatment with Ad ameliorated the pulmonary injury by activating the SIRT3/SOD2 pathway, reducing ROS generation, and inhibiting ROS-associated lung cell apoptosis.

Mitochondrial DNA: A Key Regulator of Anti-Microbial Innate Immunity

During the last few years, mitochondrial DNA has attained much attention as a modulator of immune responses. Due to common evolutionary origin, mitochondrial DNA shares various characteristic features with DNA of bacteria, as it consists of a remarkable number of unmethylated DNA as 2′-deoxyribose cytidine-phosphate-guanosine (CpG) islands. Due to this particular feature, mitochondrial DNA seems to be recognized as a pathogen-associated molecular pattern by the innate immune system. Under the normal physiological situation, mitochondrial DNA is enclosed in the double membrane structure of mitochondria. However, upon pathological conditions, it is usually released into the cytoplasm. Growing evidence suggests that this cytosolic mitochondrial DNA induces various innate immune signaling pathways involving NLRP3, toll-like receptor 9, and stimulator of interferon genes (STING) signaling, which participate in triggering downstream cascade and stimulating to produce effector molecules. Mitochondrial DNA is responsible for inflammatory diseases after stress and cellular damage. In addition, it is also involved in the anti-viral and anti-bacterial innate immunity. Thus, instead of entire mitochondrial importance in cellular metabolism and energy production, mitochondrial DNA seems to be essential in triggering innate anti-microbial immunity. Here, we describe existing knowledge on the involvement of mitochondrial DNA in the anti-microbial immunity by modulating the various immune signaling pathways.

Detecting the limits of the biological effects of far-infrared radiation on epithelial cells

Far-infrared radiation (FIR) exerts numerous beneficial effects on health and cell physiology. Recent studies revealed that the biological effects of FIR are independent of thermal effects. There is no proper method for measuring the parameters of the non-thermal biological effects of FIR, which limits its biomedical application. In this study, we established a cell detection platform using epithelial cell migration to measure the limits of the biological effects of FIR. FIR promoted the migration of rat renal tubular epithelial cells as revealed by our standardized detection method. We defined the ratio of the FIR-promoted migration area to the migration area of the control group as the FIR biological index (FBI). An increase of the FBI was highly associated with FIR-promoted mitochondrial function. Through FBI detection, we revealed the limits of the biological effects of FIR, including effective irradiation time, wavelengths, and temperature. FBI detection can be used to clarify important parameters of the biological effects of FIR in biomedical studies and health industry applications.

Hydrogen peroxide inhibits neurons in the paraventricular nucleus of the hypothalamus via potassium channel activation

The paraventricular nucleus (PVN) of the hypothalamus is an important homeostatic and reflex center for neuroendocrine, respiratory, and autonomic regulation, including during hypoxic stressor challenges. Such challenges increase reactive oxygen species (ROS) to modulate synaptic, neuronal, and ion channel activity. Previously, in the nucleus tractus solitarius, another cardiorespiratory nucleus, we showed that the ROS H₂O₂ induced membrane hyperpolarization and reduced action potential discharge via increased K⁺ conductance at the resting potential. Here, we sought to determine the homogeneity of influence and mechanism of action of H₂O₂ on PVN neurons. We recorded PVN neurons in isolation and in an acute slice preparation, which leaves neurons in their semi-intact network. Regardless of preparation, H₂O₂ hyperpolarized PVN neurons and decreased action potential discharge. In the slice preparation, H₂O₂ also decreased spontaneous excitatory postsynaptic current frequency, but not amplitude. To examine potential mechanisms, we investigated the influence of the K⁺ channel blockers Ba²⁺, Cs⁺, and glibenclamide on membrane potential, as well as the ionic currents active at resting potential and outward K⁺ currents (I_K) upon depolarization. The H₂O₂ hyperpolarization was blocked by K⁺ channel blockers. H₂O₂ did not alter currents between -50 and -110 mV. However, H₂O₂ induced an outward I_K at -50 mV yet, at potentials more positive to 0 mV H₂O₂, decreased I_K. Elevated intracellular antioxidant catalase eliminated H₂O₂ effects. These data indicate that H₂O₂ alters synaptic and neuronal properties of PVN neurons likely via membrane hyperpolarization and alteration of I_K, which may ultimately alter cardiorespiratory reflexes.

Mitochondrial DNA Leakage Caused by Streptococcus pneumoniae Hydrogen Peroxide Promotes Type I IFN Expression in Lung Cells

Streptococcus pneumoniae (S. pn), the bacterial pathogen responsible for invasive pneumococcal diseases, is capable of producing substantial amounts of hydrogen peroxide. However, the impact of S. pn-secreted hydrogen peroxide (H₂O₂) on the host immune processes is not completely understood. Here, we demonstrated that S. pn-secreted H₂O₂ caused mitochondrial damage and severe histopathological damage in mouse lung tissue. Additionally, S. pn-secreted H₂O₂ caused not only oxidative damage to mitochondrial deoxyribonucleic acid (mtDNA), but also a reduction in the mtDNA content in alveolar epithelia cells. This resulted in the release of mtDNA into the cytoplasm, which subsequently induced type I interferons (IFN-I) expression. We also determined that stimulator of interferon genes (STING) signaling was probably involved in S. pn H₂O₂-inducing IFN-I expression in response to mtDNA damaged by S. pn-secreted H₂O₂. In conclusion, our study demonstrated that H₂O₂ produced by S. pn resulted in mtDNA leakage from damaged mitochondria and IFN-I production in alveolar epithelia cells, and STING may be required in this process, and this is a novel mitochondrial damage mechanism by which S. pn potentiates the IFN-I cascade in S. pn infection.

Vulpinic acid, a lichen metabolite, emerges as a potential drug candidate in the therapy of oxidative stress–related diseases, such as atherosclerosis

Vulpinic acid, a lichen compound, has been shown to have many beneficial effects and its medicinal value increases day by day. As in atherosclerosis, endothelial damage is the basis of many diseases. The aim of this study is to investigate the effects of vulpinic acid against oxidative stress damage induced by hydrogen peroxide (H2O2) in endothelial cells. In order to find the IC50 of H2O2 and the protective dose of vulpinic acid, methyl thiazolyldiphenyl tetrazolium bromide (MTT) assays were performed. The amount of reactive oxygen species (ROS) induced by H2O2 and the protective effects of vulpinic acid against ROS were examined by fluorometric DCF-DA kit. The effects of H2O2 and vulpinic acid on actin filaments were determined by tetramethyl rhodamine (TRITC)-phalloidin fluorescence staining. Expression of Tie2 proteins was immunocytochemically analyzed in H2O2- and vulpinic acid-treated cells. After 24 h, the IC50 was found to be 215 μM in HUVECs treated with H2O2. The most effective dose of vulpinic acid against H2O2-associated damage was found to be 15 μM. Vulpinic acid pretreatment was shown to reduce H2O2-induced ROS production significantly ( p < 0.05). It was shown that 215 μM of H2O2 caused actin fragmentation, cell shrinkage, and decrease in actin florescence intensity while vulpinic acid protected the cells from these damages. It was found that Tie2 immunoreactivity was decreased in H2O2-treated groups and vulpinic acid pretreatment reduced the expression of this protein. In conclusion, vulpinic acid decreases H2O2-induced oxidative stress and oxidative stress–related damages in HUVECs. It may be drug candidate in the therapy of atherosclerosis.

Overcoming sleep disordered breathing and ensuring sufficient good sleep time for a healthy life expectancy

Recent advances in basic and clinical medicine have resulted in major improvements in human health. Currently sleep has been considered an essential factor in maintaining and promoting a healthy life expectancy. Sleep disorders include more than 60 diseases. Sleep disordered breathings (SDB) have 17 disorders, including sleep apnea. SDB usually induces hypoxemia and hypercapnia, which would have significant effects on cells, organs, and the whole body. We have investigated SDB for nearly 35 years. We found that SDB has significant associations with humoral factors, including coagulation systems, the body's protective factors against diseases, and metabolic and organ diseases. Currently we have been giving attention to the associations among SDB, short sleep duration, and obesity. In addition, SDB is important not only in the home but under critical care such as in the perioperative stage. In this review, I would like to describe several aspects of SDB in relation to systemic diseases and overall health based mainly on our published reports.