A comparative study of the efficiency of mitochondria-targeted antioxidants MitoTEMPO and SKQ1 under oxidative stress

MitoTEMPO (MT) and Visomitin (SKQ1) are regareded as mitochondria-targeted antioxidants, which inhibit production of mitochondrial reactive oxygen species (ROS). However, the differences in function between MT and SKQ1 remain unexplored. Herein, we investigated the differential potency of MT and SKQ1 in mitigating oxidative stress under different conditions. The results indicated that high levels of SKQ1 induced cell death. The appropriate concentrations of MT and SKQ1 can prevent or rescue cell damage triggered by hydrogen peroxide (H2O2) and menadione (MEN). MT and SKQ1 reduced ROS levels and reversed the down-regulation of antioxidant defence genes and enzymes. These effects can alleviate the damage to lipids, proteins, and deoxyribonucleic acid (DNA) caused by oxidative stress and restore adenosine 5' triphosphate (ATP) generation. Subsequently, we found that MT administration in ischemic reperfusion kidney injury in mice provided superior renal protection compared to SKQ1, as evidenced by reduced plasma levels of kidney injury markers, improved renal morphology, decreased apoptosis, restored mitochondrial function, and enhanced antioxidant capacity. Overall, our findings suggest that MT is safer and has greater potential than SKQ1 as a therapeutic agent to mitigate oxidative stress damage or oxidative renal injury.

DNA of neutrophil extracellular traps promote NF-κB-dependent autoimmunity via cGAS/TLR9 in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterised by persistent airway inflammation even after cigarette smoking cessation. Neutrophil extracellular traps (NETs) have been implicated in COPD severity and acute airway inflammation induced by short-term cigarette smoke (CS). However, whether and how NETs contribute to sustained airway inflammation in COPD remain unclear. This study aimed to elucidate the immunoregulatory mechanism of NETs in COPD, employing human neutrophils, airway epithelial cells (AECs), dendritic cells (DCs), and a long-term CS-induced COPD mouse model, alongside cyclic guanosine monophosphate-adenosine monophosphate synthase and toll-like receptor 9 knockout mice (cGAS--/-, TLR9-/-); Additionally, bronchoalveolar lavage fluid (BALF) of COPD patients was examined. Neutrophils from COPD patients released greater cigarette smoke extract (CSE)-induced NETs (CSE-NETs) due to mitochondrial respiratory chain dysfunction. These CSE-NETs, containing oxidatively-damaged DNA (NETs-DNA), promoted AECs proliferation, nuclear factor kappa B (NF-κB) activation, NF-κB-dependent cytokines and type-I interferons production, and DC maturation, which were ameliorated/reversed by silencing/inhibition of cGAS/TLR9. In the COPD mouse model, blocking NETs-DNA-sensing via cGAS-/- and TLR9-/- mice, inhibiting NETosis using mitoTEMPO, and degrading NETs-DNA with DNase-I, respectively, reduced NETs infiltrations, airway inflammation, NF-κB activation and NF-κB-dependent cytokines, but not type-I interferons due to IFN-α/β receptor degradation. Elevated NETs components (myeloperoxidase and neutrophil elastase activity) in BALF of COPD smokers correlated with disease severity and NF-κB-dependent cytokine levels, but not type-I interferon levels. In conclusion, NETs-DNA promotes NF-κB-dependent autoimmunity via cGAS/TLR9 in long-term CS exposure-induced COPD. Therefore, targeting NETs-DNA and cGAS/TLR9 emerges as a potential strategy to alleviate persistent airway inflammation in COPD.

The current insights of mitochondrial hormesis in the occurrence and treatment of bone and cartilage degeneration

It is widely acknowledged that aging, mitochondrial dysfunction, and cellular phenotypic abnormalities are intricately associated with the degeneration of bone and cartilage. Consequently, gaining a comprehensive understanding of the regulatory patterns governing mitochondrial function and its underlying mechanisms holds promise for mitigating the progression of osteoarthritis, intervertebral disc degeneration, and osteoporosis. Mitochondrial hormesis, referred to as mitohormesis, represents a cellular adaptive stress response mechanism wherein mitochondria restore homeostasis and augment resistance capabilities against stimuli by generating reactive oxygen species (ROS), orchestrating unfolded protein reactions (UPRmt), inducing mitochondrial-derived peptides (MDP), instigating mitochondrial dynamic changes, and activating mitophagy, all prompted by low doses of stressors. The varying nature, intensity, and duration of stimulus sources elicit divergent degrees of mitochondrial stress responses, subsequently activating one or more signaling pathways to initiate mitohormesis. This review focuses specifically on the effector molecules and regulatory networks associated with mitohormesis, while also scrutinizing extant mechanisms of mitochondrial dysfunction contributing to bone and cartilage degeneration through oxidative stress damage. Additionally, it underscores the potential of mechanical stimulation, intermittent dietary restrictions, hypoxic preconditioning, and low-dose toxic compounds to trigger mitohormesis, thereby alleviating bone and cartilage degeneration.

Oleoylethanolamide protects mesenchymal stem/stromal cells (MSCs) from oxidative stress and reduces adipogenic related genes expression in adipose-derived MSCs undergoing adipocyte differentiation

BACKGROUND

Human mesenchymal stem/stromal cells (hMSCs) are known for their pronounced therapeutic potential; however, they are still applied in limited clinical cases for several reasons. ROS-mediated oxidative stress is among the chief causes of post-transplantation apoptosis and death of hMSCs. It has been reported that a strategy to protect hMSCs against ROS is to pretreat them with antioxidants. Oleoylethanolamide (OEA) is a monounsaturated fatty acid derived from oleic acid and it has many protective properties, including anti-obesity, anti-inflammatory, and antioxidant effects. OEA is also used as a weight loss supplement; due to its high affinity for the PPAR-α receptor, OEA increases the fat metabolism rate.

METHODS AND RESULTS

This study hence assessed the effects of OEA pretreatment on the in vitro survival rate and resistance of hMSCs under oxidative stress as well as the cellular and molecular events in the biology of stem/stromal cells affected by oxidative stress and free radicals. Considering the role of MSCs in adipogenesis and obesity, the expression of the main genes involved in adipogenesis was also addressed in this study. Results revealed that OEA increases the in vitro proliferation of MSCs and inhibits cell apoptosis by reducing the induction of oxidative stress. The results also indicated that OEA exerts its antioxidant properties by both activating the Nrf2/NQO-1/HO-1 signaling pathway and directly combating free radicals. Moreover, OEA can reduce adipogenesis through reducing the expression of PPARγ, leptin and CEBPA genes in hMSCs undergoing adipocyte differentiation.

CONCLUSIONS

Thus, OEA protects hMSCs from oxidative stress and reduces adipogenic related genes expression and can be regarded as a therapeutic agent for this purpose.

Mitochondrial reactive oxygen species modify extracellular vesicles secretion rate

Extracellular vesicle (EV) secretion rate is stimulated by hypoxia that causes increased reactive oxygen species (ROS) production by the mitochondrial electron transport chain (ETC) and hypoxia-induced factor (HIF)-1 signaling; however, their contribution to the increased EV secretion rate is unknown. We found that the EV marker secretion rate in our EV reporter cell line CD9truc-EGFP was unaffected by the HIF-1α stabilizer roxadustat; yet, ETC stimulation by dichloroacetic acid (DCA) significantly increased EV secretion. The DCA-induced EV secretion was blocked by the antioxidant TEMPO and rotenone, an inhibitor of the ETC's Complex I. Under hypoxic conditions, the limited oxygen reduction impedes the ETC's Complex III. To mimic this, we inhibited Complex III with antimycin A, which increased ROS-dependent EV secretion. The electron transport between Complex I and III is accomplished by coenzyme Q created by the mevalonate pathway and tyrosine metabolites. Blocking an early step in the mevalonate pathway using pitavastatin augmented the DCA-induced EV secretion, and 4-nitrobenzoate-an inhibitor of the condensation of the mevalonate pathway with tyrosine metabolites-increased ROS-dependent EV secretion. Our findings indicate that hypoxia-mimetics targeting the ETC modify EV secretion and that ROS produced by the ETC is a potent stimulus for EV secretion.

Mito-TEMPO, a Mitochondria-Targeted Antioxidant, Improves Cognitive Dysfunction due to Hypoglycemia: an Association with Reduced Pericyte Loss and Blood-Brain Barrier Leakage

Hypoglycemia is associated with cognitive dysfunction, but the exact mechanisms have not been elucidated. Our previous study found that severe hypoglycemia could lead to cognitive dysfunction in a type 1 diabetes (T1D) mouse model. Thus, the aim of this study was to further investigate whether the mechanism of severe hypoglycemia leading to cognitive dysfunction is related to oxidative stress-mediated pericyte loss and blood-brain barrier (BBB) leakage. A streptozotocin T1D model (150 mg/kg, one-time intraperitoneal injection), using male C57BL/6J mice, was used to induce hypoglycemia. Brain tissue was extracted to examine for neuronal damage, permeability of BBB was investigated through Evans blue staining and electron microscopy, reactive oxygen species and adenosine triphosphate in brain tissue were assayed, and the functional changes of pericytes were determined. Cognitive function was tested using Morris water maze. Also, an in vitro glucose deprivation model was constructed. The results showed that BBB leakage after hypoglycemia is associated with excessive activation of oxidative stress and mitochondrial dysfunction due to glucose deprivation/reperfusion. Interventions using the mitochondria-targeted antioxidant Mito-TEMPO in both in vivo and in vitro models reduced mitochondrial oxidative stress, decreased pericyte loss and apoptosis, and attenuated BBB leakage and neuronal damage, ultimately leading to improved cognitive function.

Nesting and fate of transplanted stem cells in hypoxic/ischemic injured tissues: The role of HIF1α/sirtuins and downstream molecular interactions

The nesting mechanisms and programming for the fate of implanted stem cells in the damaged tissue have been critical issues in designing and achieving cell therapies. The fracture site can induce senescence or apoptosis based on the surrounding harsh conditions, hypoxia, and oxidative stress (OS). Respiration deficiency, disruption in energy metabolism, and consequently OS induction change the biophysical, biochemical, and cellular components of the native tissue. Additionally, the homeostatic molecular players and cell signaling might be changed. Despite all aforementioned issues, in the native stem cell niche, physiological hypoxia is not toxic; rather, it is vitally required for homing, self-renewal, and differentiation. Hence, the key macromolecular players involved in the support of stem cell survival and re-adaptation to a new dysfunctional niche must be understood for managing the cell therapy outcome. Hypoxia-inducible factor 1-alpha is the master transcriptional regulator, involved in the cell response to hypoxia and the adaptation of stem cells to a new niche. This protein is regulated by interaction with sirtuins. Sirtuins are highly conserved NAD+-dependent enzymes that monitor the cellular energy status and modulate gene transcription, genome stability, and energy metabolism in response to environmental signals to modulate the homing and fate of stem cells. Herein, new insights into the nesting of stem cells in hypoxic-ischemic injured tissues were provided and their programming in a new dysfunctional niche along with the involved complex macromolecular players were critically discussed.

Mitohormesis and mitochondrial dynamics in the regulation of stem cell fate

The ability of stem cells for self-renewing, differentiation, and regeneration of injured tissues is believed to occur via the hormetic modulation of nuclear/mitochondrial signal transductions. The evidence now indicates that in damaged tissues, the mitochondria set off the alarm under oxidative stress conditions, hence they are the central regulators of stem cell fate decisions. This review aimed to provide an update to a broader concept of stem cell fate in stress conditions of damaged tissues, and insights for the mitochondrial hormesis (mitohormesis), including the integrated stress response (ISR), mitochondrial dynamics, mitochondria uncoupling, unfolded protein response, and mitokines, with implications for the control of stem cells programing in a successful clinical cell therapy.

An evaluation of a new high-sensitivity PrestoBlue assay for measuring cell viability and drug cytotoxicity using EA.hy926 endothelial cells

INTRODUCTION

Commercially-available resazurin-based reagents used for cell viability assessment contain varying amounts of resorufin; these may contribute to differences in autofluorescence, signal-to-background (S/B) ratio and the dynamic range of the assay.

OBJECTIVES

This in vitro study compares the sensitivity of a new, high-sensitivity PrestoBlue (hs-PB) assay with standard PrestoBlue (PB) in assessing the efficacy of valinomycin and antimycin A in human vascular endothelial EA.hy926 cells, as well as cell viability.

METHODS

The metabolic activity of EA.hy926 was evaluated based on resorufin fluorescence or formazan absorbance.

RESULTS

The hs-PB assay demonstrated lower resorufin autofluorescence than the PB, resulting in a ≥ 1.4-fold increase in S/B ratio in hs-PB compared to PB. Valinomycin was more potent cytotoxic agent than antimycin A. The hs-PB, PB and MTT produced similar IC₅₀ values for valinomycin. Antimycin A demonstrated significantly higher potency in the MTT than in the resazurin-based assays. The EA.hy926 cells demonstrated higher metabolic activity in the presence of the antimycin A solvent - DMSO.

CONCLUSION

All the examined methods may be used interchangeably to analyze drug cytotoxicity. Any differences in drug cytotoxicity observed between the assays may be due to relatively low drug potency and/or the influence of solvent on metabolism of assay reagent. The hs-PB assay appears to more effectively detect cell viability and produce a stronger signal than its conventional counterpart.

Strategies to protect against age-related mitochondrial decay: Do natural products and their derivatives help?

Mitochondria serve vital roles critical for overall cellular function outside of energy transduction. Thus, mitochondrial decay is postulated to be a key factor in aging and in age-related diseases. Mitochondria may be targets of their own decay through oxidative damage. However, treating animals with antioxidants has been met with only limited success in rejuvenating mitochondrial function or in increasing lifespan. A host of nutritional strategies outside of using traditional antioxidants have been devised to promote mitochondrial function. Dietary compounds are under study that induce gene expression, enhance mitochondrial biogenesis, mitophagy, or replenish key metabolites that decline with age. Moreover, redox-active compounds may now be targeted to mitochondria which improve their effectiveness. Herein we review the evidence that representative dietary effectors modulate mitochondrial function by stimulating their renewal or reversing the age-related loss of key metabolites. While in vitro evidence continues to accumulate that many of these compounds benefit mitochondrial function and/or prevent their decay, the results using animal models and, in some instances human clinical trials, are more mixed and sometimes even contraindicated. Thus, further research on optimal dosage and age of intervention are warranted before recommending potential mitochondrial rejuvenating compounds for human use.

Designing robust chitosan-based hydrogels for stem cell nesting under oxidative stress

Introduction: Hydrogels are unique candidates for a wide range of biomedical applications including drug delivery and tissue engineering. The present investigation was designed to consider the impact of chitosan-based hydrogels as a scaffold on the proliferation of human bone marrow mesenchymal stem cells (hBM-MSCs) besides neutralization of oxidative stress in hBM-MSCs. Methods: Chitosan (CS) and CS-gelatin hydrogels were fabricated through ionic crosslinking using β-glycerophosphate. The hBM-MSCs were cultured on the prepared matrices and their proliferation was evaluated using DAPI staining and MTT assay. Furthermore, the effect of hydrogels on oxidative stress was assessed by measuring the expression of NQO1, Nrf2, and HO-1 genes using real-time PCR. Results: The developed hydrogels indicated a porous structure with high water content. The toxicity studies showed that the prepared hydrogels have a high biocompatibility/cytocompatibility. The expression of intracellular antioxidant genes was studied to ensure that stress is not imposed by the scaffold on the nested cells. The results showed that Nrf2 as a super transcription factor of antioxidant genes and its downstream antioxidant gene, NQO1 were downregulated. Unexpectedly, the upregulation of HO-1 was detected in the current study. Conclusion: The prepared CS-based hydrogels with desired properties including porous structure, high swelling ability, and cytocompatibility did not show oxidative stress for the nesting of stem cells. Therefore, they could be attractive scaffolds to support stem cells for successful tissue engineering purposes.

Ionomycin-induced mouse oocyte activation can disrupt preimplantation embryo development through increased reactive oxygen species reaction and DNA damage

Oocyte activation induced by calcium oscillations is an important process in normal fertilization and subsequent embryogenesis. In the clinical-assisted reproduction, artificial oocyte activation (AOA) is an effective method to improve the clinical outcome of patients with null or low fertilization rate after ICSI. However, little is known about the effect of AOA on preimplantation embryo development in cases with normal fertilization by ICSI. Here, we used ionomycin at different concentrations to activate oocytes after ICSI with normal sperm and evaluated energy metabolism and preimplantation embryo development. We found that a high concentration of ionomycin increased the frequency and amplitude of calcium oscillation patterns, affecting the balance of mitochondrial energy metabolism, leading to increased reactive oxygen species (ROS) and decreased ATP. Eventually, it increases DNA damage and decreases blastocyst formation. In addition, the addition of vitamin C to the culture medium ameliorated the increase in ROS and DNA damage and rescued the abnormal embryo development caused by excessive ionomycin activation. This study provides a perspective that the improper application of AOA may have adverse effects on preimplantation embryo development. Thus, clinical AOA treatment should be cautiously administered.

Parkin-mediated mitochondrial quality control protects against aluminum-induced liver damage in mice

Aluminum (Al) is known to be hepatotoxic. Oxidative stress is the main mechanism of liver injury caused by Al, and can also lead to mitochondrial damage. Mitochondrial damage is a prerequisite for mitochondrial quality control (MQC) dysregulation. Parkin can activate MQC and maintain mitochondrial homeostasis. However, the role of Parkin-mediated MQC in Al-induced liver damage has not been elucidated. In this study, forty male wild type (WT) C57BL/6N mice were treated with 0, 44.825, 89.65 or 179.3 mg/kg body weight AlCl₃ in drinking water for 90 days, respectively. We found that Al induced mitophagy and disrupted mitochondrial dynamics and mitochondrial biogenesis. Then, twenty male WT C57BL/6N mice and twenty male Parkin knockout (Parkin^-/-) C57BL/6N mice were divided into four groups and treated with 0, 89.65, 0, 89.65 mg/kg body weight AlCl₃ in drinking water for 90 days, respectively. We found that Parkin^-/- inhibited mitophagy and further disrupted mitochondrial dynamics and mitochondrial biogenesis. These results indicated that Parkin-mediated MQC could be disrupted by Al and protected against Al-induced liver damage.

Astaxanthin protects mesenchymal stem cells from oxidative stress by direct scavenging of free radicals and modulation of cell signaling

Recent evidence has shown that mesenchymal stem cells (MSCs) play vital roles in cell therapy of ischemia/hypoxia damaged tissues. However, after the transplantation, they might undergo apoptosis due to oxidative stress. Thus, some strategies have been developed to support stem cells in harsh conditions, including pre-treatment of the cells with antioxidants. Of various antioxidants, in this study, astaxanthin (ATX) was used to protect adipose-derived MSCs against oxidative stress. The MSCs were exposed to different doses of hydrogen peroxide, and then the expression of key genes involved in the redox signaling pathway was studied, including nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and NADPH quinine oxidoreductase 1 (NQO1). The balance of intracellular reactive oxygen species was detected with the H2DCFDA molecular probe. Additionally, for the detection of apoptosis and protective effect of ATX, the DAPI/Phallacidin and annexin V cell staining were performed. The results of cellular studies revealed that ATX reduced the H₂O₂-induced cell apoptosis and oxidative stress. Furthermore, after the induction of oxidative stress, the cells' native antioxidants (HO-1 and NQO1) were overexpressed but they were modulated with ATX treatments (p < 0.023). Based on our findings, ATX could increase the expression of Nrf2 as a key transcription factor of antioxidant enzymes (p < 0.05). These findings support the notion that ATX can act as an effective antioxidant in the pre-treatment of MSCs before cell therapy. Thus, to enhance the viability of stem cells during the transplantation in harsh conditions, the concurrent use of ATX in cell therapy modalities is proposed.