Mitochondrial Reactive Oxygen Species: Double-Edged Weapon in Host Defense and Pathological Inflammation During Infection

Roles of mitochondrial DNA in dynamics of the immune response to COVID-19

Mitochondria dynamics have a pivotal role in many aspects of immune function. Viral infections affect mitochondrial dynamics and trigger the release of mitochondrial DNA (mtDNA) in host cells. Released mtDNA guides the immune response towards an inflammatory response against pathogens. In addition, circulating cell-free mtDNA (ccf-mtDNA) is considered an invaluable indicator for the prognosis and severity of infectious diseases. This study provides an overview of the role of mtDNA in the dynamics of the immune response to COVID-19. We focused on the possible roles of mtDNA in inducing the signaling pathways, and the inflammasome activation and regulation in SARS-CoV-2. Targeting mtDNA-related pathways can provide critical insights into therapeutic strategies for COVID-19.

Platelet CD40L Expression Response to Mixing of pRBCs and Washed Platelets but no Causality Association between Platelet ROS Generation and CD40L Expression: An In Vitro Study

Platelets play a role in transfusion reaction via reactive oxygen species (ROS) generation and CD40 ligand (CD40L) expression. In this study, we aimed to test the hypothesis that the mixing of packed red blood cells (pRBCs) and washed platelets has a causal effect on platelet ROS generation and CD40L expression. Thus, a better understanding of this causality relationship may help interrupt the chain of events and avoid an uncontrollable transfusion reaction. We simulated transfusion in vitro by mixing pRBCs and washed platelets. Donor cross-matched stored pRBCs) from our blood bank and recipient whole blood from patients undergoing coronary artery bypass graft surgery prepared into washed platelets were used. Briefly, donor pRBCs were added to washed recipient platelets to form 1%, 5%, or 10% (v/v) mixtures. The mixed blood sample was used to determine platelet ROS generation (dichlorofluorescein fluorescence levels) and CD40L expression. The effect of antioxidants (20 mM glutamine and 20 mM dipeptiven) on ROS generation and CD40L expression was also evaluated. Platelet ROS generation was not significantly associated with the mixing of pRBCs and washed platelets (p = 0.755), glutamine treatment (p = 0.800), or dipeptiven treatment (p = 0.711). The expression of CD40L by platelets increased significantly (p < 0.001), and no significant difference was noted after treatment with glutamine (p = 0.560) or dipeptiven (p = 0.618). We observed that the mixing pRBCs and washed platelets had no effect via ROS, whereas CD40L could directly induce transfusion reactions. Furthermore, platelets did not causally express ROS or CD40L after being mixed with pRBCs. Although antioxidants are more accessible than anti-CD40L antibodies, platelet ROS may not serve as a therapeutic target for antioxidants. Nevertheless, CD40L expression may be a valuable therapeutic target for managing transfusion reactions.

Antifungal activity of dexamethasone against fluconazole-resistant Candida albicans and its activity against biofilms

Objective: The present study investigated the antifungal action of dexamethasone disodium phosphate (Dex). Methodology: Susceptibility testing was performed using the Clinical & Laboratory Standards Institute protocol; M27-A3, checkerboard test and biofilm were evaluated with two isolates of Candida albicans, hyphal production test, molecular docking analysis and flow cytometry analysis. Result: Dex and fluconazole (FLC) together had a synergistic effect. Mature biofilm was reduced when treated with Dex alone or in combination. Dex and FLC promoted a decrease in the production of hyphae and changes in the level of mitochondrial depolarization, increased generation of reactive oxygen species, loss of membrane integrity, increased phosphatidylserine externalization and molecular docking; there was interaction with ALS3 and SAP5 targets. Conclusion: Dex showed antifungal activity against FLC-resistant C. albicans strains.

Intrinsic Radical Species Scavenging Activities of Tea Polyphenols Nanoparticles Block Pyroptosis in Endotoxin-Induced Sepsis

Sepsis, a life-threating illness caused by deregulated host immune responses to infections, is characterized by overproduction of multiple reactive oxygen and nitrogen species (RONS) and excessive pyroptosis, leading to high mortality. However, there is still no approved specific molecular therapy to treat sepsis. Here we reported drug-free tea polyphenols nanoparticles (TPNs) with intrinsic broad-spectrum RONS scavenging and pyroptosis-blocking activities to treat endotoxin (LPS)-induced sepsis in mice. The RONS scavenging activities originated from the polyphenols-derived structure, while the pyroptosis blockage was achieved by inhibiting gasdermin D (GSDMD) mediating the pore formation and membrane rupture, showing multifunctionalities for sepsis therapy. Notably, TPNs suppress GSDMD by inhibiting the oligomerization of GSDMD rather than the cleavage of GSDMD, thus displaying high pyroptosis-inhibition efficiency. As a result, TPNs showed an excellent therapeutic efficacy in sepsis mice model, as evidenced by survival rate improvement, hypothermia amelioration, and the organ damage protection. Collectively, TPNs present biocompatible candidates for the treatment of sepsis.

mtROS Induced via TLR-2-SOCE Signaling Plays Proapoptotic and Bactericidal Role in Mycobacterium fortuitum-Infected Head Kidney Macrophages of Clarias gariepinus

The mechanisms underlying Mycobacterium fortuitum-induced mycobacteriosis remain unexplored. Using head kidney macrophages (HKM) from catfish (Clarias gariepinus), we report that Ca²⁺ surge across mitochondrial-Ca²⁺ uniporter (MICU), and consequent mitochondrial ROS (mtROS) production, is imperative for mycobactericidal activity. Inhibition of mtROS alleviated HKM apoptosis and enhanced bacterial survival. Based on RNA interference (RNAi) and inhibitor studies, we demonstrate that the Toll-like receptor (TLR)-2–endoplasmic reticulum (ER) stress–store-operated calcium entry (SOCE) axis is instrumental for activating the mt-Ca²⁺/mtROS cascade in M. fortuitum-infected HKM. Additionally, pharmacological inhibition of mtROS attenuated the expression of CHOP, STIM1, and Orai1, which suggests a positive feedback loop between ER-stress-induced SOCE and mtROS production. Elevated tumor necrosis factor alpha (TNF-α) levels and caspase-8 activity were observed in HKM consequent to M. fortuitum infection, and our results implicate that mtROS is crucial in activating the TNF-mediated caspase-8 activation. Our results for the first time demonstrate mitochondria as an innate immune signaling center regulating mycobacteriosis in fish. We conclude that M. fortuitum-induced persistent SOCE signaling leads to mtROS production, which in turn activates the TNF-α/caspase-8 axis culminating in HKM apoptosis and bacterial clearance.

Comparative Study of the Characterisation and Extraction Techniques of Polyphenolic Compounds from Acacia seyal gum

Abstract

Acacia seyal gum is an abundant source of natural polyphenolic compounds (NPPCs) and antioxidant activity with numerous benefits and is often used in cancer treatment. The type of extraction technique can significantly impact the yield and isolation of NPPCs from Acacia seyal gum (ASG). The traditional use of maceration extraction reportedly yields fewer NPPCs.

Objectives

This study investigates five extraction techniques for NPPCs and ASG antioxidant activity, namely: homogenisation, shaking, ultrasonication, magnetic stirring, and maceration.

Materials and Methods

The evaluation of the antioxidant activity (AoA) of the extracted NPPCs from ASG used five assays, namely: Total Flavonoids Content (TFC), Folin-Ciocalteu index (FCI), 2,2-Diphenyl-1-Picrylhydrazyl radical scavenging activity (DPPH), Ferric Reducing Antioxidant Power (FRAP), and Cupric Reducing Antioxidant Capacity (CUPRAC).

Results

To minimise the dataset dimensionality requires Principal Component Analysis. The ultrasonic and maceration techniques were the best techniques to extract NPPCs and examine the AoA of ASG, with a high correlation between the NPPCs and AoA. However, the maceration process was slow (12 h) compared to ultrasonication (1 h). Slow extraction can result in a decline of the NPPCs due to polyphenol oxidase-enzyme and impact productivity.

Conclusions

These findings provide an essential guide for the choice of extraction techniques for the effective extraction of NPPCs from ASG and other plant materials.

Cellular Organelles Involved in Hepatitis E Virus Infection

Hepatitis E virus (HEV), a major cause of acute hepatitis worldwide, infects approximately 20 million individuals annually. HEV can infect a wide range of mammalian and avian species, and cause frequent zoonotic spillover, increasingly raising public health concerns. To establish a successful infection, HEV needs to usurp host machineries to accomplish its life cycle from initial attachment to egress. However, relatively little is known about the HEV life cycle, especially the functional role(s) of cellular organelles and their associated proteins at different stages of HEV infection. Here, we summarize current knowledge regarding the relation of HEV with the different cell organelles during HEV infection. Furthermore, we discuss the underlying mechanisms by which HEV infection is precisely regulated in infected cells and the modification of host cell organelles and their associated proteins upon HEV infection.

The mitochondria-targeting antioxidant MitoQ alleviated lipopolysaccharide/ d-galactosamine-induced acute liver injury in mice

The mitochondria are the primary source of reactive oxygen species (ROS) under pathological condition, but the significance of mitochondrial ROS in the development of Lipopolysaccharide (LPS)/D-galactosamine (D-Gal)-induced acute liver injury remains unclear. In the present study, the level of mitochondrial ROS in LPS/D-Gal has been determined by MitoSox staining and the potential roles of mitochondrial ROS in LPS/D-Gal-induced liver injury have been investigated by using the mitochondria-targeting antioxidant MitoQ. The results indicated that LPS/D-Gal exposure induced the generation of mitochondrial ROS while treatment with MitoQ reduced the level of mitochondrial ROS. Treatment with MitoQ ameliorated LPS/D-Gal-induced histopathologic abnormalities, suppressed the elevation of AST and ALT, and increased the survival rate of the experimental animals. Treatment with MitoQ also suppressed LPS/D-Gal-induced production of tumor necrosis factor α (TNF-α), inhibited the activities of caspase-3, caspase-8 and caspase-9, decreased the level of cleaved caspase-3 and reduced the counts of TUNEL positive cells. These results indicate that mitochondrial ROS is involved in the development of LPS-induced acute liver injury and the mitochondria-targeting antioxidant MitoQ might have potential value for the treatment of inflammation-based acute liver injury.

Paeonol alleviates lipopolysaccharide‑induced hepatocytes injury through alteration of mitochondrial function and NF‑κB translocation

Sepsis is a severe disease, with high mortality. Permanent organ damage caused by sepsis reduces the quality of life of surviving patients. The liver is an easily damaged organ in sepsis and sepsis-associated liver injury foretells a poor prognosis. Unfortunately, there are no effective treatments or drugs to solve this problem. Therefore, strategies or novel drugs are urgently required to protect against liver dysfunction in sepsis. In the present study, lipopolysaccharide (LPS) was used to establish a model of liver injury in vitro. The data demonstrated that pretreatment of L02 human normal hepatocytes with paeonol (PAE) alleviated LPS-induced cell injury and decreased the levels of alanine aminotransferase and aspartate transaminase, indicating a protective effect of PAE. Further experiments demonstrated that PAE increased LPS-decreased L02 cell viability, the levels of superoxide dismutase and Bcl-2 expression. PAE decreased LPS-increased cell apoptosis, intracellular reactive oxygen species and the expression levels of Bax and cleaved-caspase-3. PAE decreased LPS-promoted mitochondrial depolarization and nuclear translocation of NF-κB. In conclusion, PAE alleviated LPS-induced liver injury via alteration of mitochondrial function and NF-κB translocation. Therefore, PAE has potential for the treatment of sepsis.

Porcine circovirus 2 manipulates PERK-ERO1α axis of endoplasmic reticulum in favor of its replication by derepressing viral DNA from HMGB1 sequestration within nuclei

Porcine circovirus type 2 (PCV2) causes several disease syndromes in grower pigs. PCV2 infection triggers endoplasmic reticulum (ER) stress, autophagy and oxidative stress, all of which support PCV2 replication. We have recently reported that nuclear HMGB1 is an anti-PCV2 factor by binding to viral genomic DNA. However, how PCV2 manipulates host cell responses to favor its replication has not been explored. Here, we demonstrate that PCV2 infection increased expression of ERO1α, generation of ROS and nucleocytoplasmic migration of HMGB1 via PERK activation in PK-15 cells. Inhibition of PERK or ERO1α repressed ROS production in PCV2-infected cells and increased HMGB1 retention within nuclei. These findings indicate that PCV2-induced activation of the PERK-ERO1α axis would lead to enhanced generation of ROS sufficient to decrease HMGB1 retention in the nuclei, thus derepressing viral DNA from HMGB1 sequestration. The viral Rep and Cap proteins were able to induce PERK-ERO1α-mediated ROS accumulation. Cysteine residues 107 and 305 of Rep or 108 of Cap played important roles in PCV2-induced PERK activation and distribution of HMGB1. Of the mutant viruses, only the mutant PCV2 with substitution of all three cysteine residues failed to activate PERK with reduced ROS generation and decreased nucleocytoplasmic migration of HMGB1. Collectively, this study offers novel insight into the mechanism of enhanced viral replication in which PCV2 manipulates ER to perturb its redox homeostasis via the PERK-ERO1α axis and the ER-sourced ROS from oxidative folding is sufficient to reduce HMGB1 retention in the nuclei, hence the release of HMGB1-bound viral DNA for replication. IMPORTANCE Considering the fact that clinical PCVAD mostly results from activation of latent PCV2 infection by confounding factors such as co-infection or environmental stresses, we propose that such confounding factors might impose oxidative stress to the animals where PCV2 in infected cells might utilize the elevated ROS to promote HMGB1 migration out of nuclei in favor of its replication. An animal infection model with a particular stressor could be approached with or without antioxidant treatment to examine the relationship among the stressor, ROS level, HMGB1 distribution in target tissues, virus replication and severity of PCVAD. This will help decide the use of antioxidants in the feeding regime on pig farms that suffer from PCVAD. Further investigation could examine if similar strategies are employed by DNA viruses, such as PCV3 and BFDV and if there is cross-talk among ER stress, autophagy/mitophagy and mitochondria-sourced ROS in favor of PCV2 replication.

Non-Coding RNAs and Reactive Oxygen Species–Symmetric Players of the Pathogenesis Associated with Bacterial and Viral Infections

Infections can be triggered by a wide range of pathogens. However, there are few strains of bacteria that cause illness, but some are quite life-threatening. Likewise, viral infections are responsible for many human diseases, usually characterized by high contagiousness. Hence, as bacterial and viral infections can both cause similar symptoms, it can be difficult to determine the exact cause of a specific infection, and this limitation is critical. However, recent scientific advances have geared us up with the proper tools required for better diagnoses. Recent discoveries have confirmed the involvement of non-coding RNAs (ncRNAs) in regulating the pathogenesis of certain bacterial or viral infections. Moreover, the presence of reactive oxygen species (ROS) is also known as a common infection trait that can be used to achieve a more complete description of such pathogen-driven conditions. Thus, this opens further research opportunities, allowing scientists to explore infection-associated genetic patterns and develop better diagnosis and treatment methods. Therefore, the aim of this review is to summarize the current knowledge of the implication of ncRNAs and ROS in bacterial and viral infections, with great emphasis on their symmetry but, also, on their main differences.

Oxidative Stress and Mitochondrial Damage in Dry Age-Related Macular Degeneration Like NFE2L2/PGC-1α -/- Mouse Model Evoke Complement Component C5a Independent of C3

Aging-associated chronic oxidative stress and inflammation are known to be involved in various diseases, e.g., age-related macular degeneration (AMD). Previously, we reported the presence of dry AMD-like signs, such as elevated oxidative stress, dysfunctional mitophagy and the accumulation of detrimental oxidized materials in the retinal pigment epithelial (RPE) cells of nuclear factor erythroid 2-related factor 2, and a peroxisome proliferator-activated receptor gamma coactivator 1-alpha (NFE2L2/PGC1α) double knockout (dKO) mouse model. Here, we investigated the dynamics of inflammatory markers in one-year-old NFE2L2/PGC1α dKO mice. Immunohistochemical analysis revealed an increase in levels of Toll-like receptors 3 and 9, while those of NOD-like receptor 3 were decreased in NFE2L2/PGC1α dKO retinal specimens as compared to wild type animals. Further analysis showed a trend towards an increase in complement component C5a independent of component C3, observed to be tightly regulated by complement factor H. Interestingly, we found that thrombin, a serine protease enzyme, was involved in enhancing the terminal pathway producing C5a, independent of C3. We also detected an increase in primary acute phase C-reactive protein and receptor for advanced glycation end products in NFE2L2/PGC1α dKO retina. Our main data show C5 and thrombin upregulation together with decreased C3 levels in this dry AMD-like model. In general, the retina strives to mount an orchestrated inflammatory response while attempting to maintain tissue homeostasis and resolve inflammation.

The signaling pathway PI3K/Akt/Nrf2/HO-1 plays a role in the mitochondrial protection promoted by astaxanthin in the SH-SY5Y cells exposed to hydrogen peroxide

The mitochondria are the major source of reactive species in the mammalian cells. Hydrogen peroxide (H₂O₂) is a potent inducer of redox impairment by a mechanism, at least in part, dependent on its ability to impair mitochondrial function. H₂O₂ plays an important role in several pathological conditions, including neurodegeneration and cardiovascular diseases. Astaxanthin (AST) is a xanthophyll that may be found in microalgae, crustaceans, and salmon and exhibits antioxidant and anti-inflammatory effects in different cell types. Even though there is evidence pointing to a role for AST as mitochondrial protectant agent, it was not clearly demonstrated how this xanthophyll attenuates mitochondrial stress. Therefore, we investigated here whether and how AST would be able to prevent the H₂O₂-induced mitochondrial dysfunction in the human neuroblastoma SH-SY5Y cells. We found that AST (20 μM) prevented the H₂O₂-induced loss of mitochondrial membrane potential (MMP) and decrease in the activity of the Complexes I and V. AST pretreatment blocked the mitochondria-related pro-apoptotic effects elicited by H₂O₂. AST upregulated the enzyme heme oxygenase-1 (HO-1) and the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) by a mechanism dependent on the phosphoinositide 3-kinase/Akt (PI3K/Akt) signaling pathway. Inhibition of the PI3K/Akt or of the HO-1 enzyme abolished the AST-induced mitochondrial protection in cells challenged with H₂O₂. Silencing of Nrf2 caused similar effects. Thus, we suggest that AST promotes mitochondrial protection by a mechanism dependent on the PI3K/Akt/Nrf2/HO-1 signaling pathway in SH-SY5Y cells exposed to H₂O₂.

High fat suppresses SOD1 activity by reducing copper chaperone for SOD1 associated with neurodegeneration and memory decline

High fat consumption leads to reactive oxygen species (ROS) which is associated with age-progressive neurological disorders. Cu/Zn superoxide dismutase (SOD1) is a critical enzyme against ROS. However, the relationship between SOD1 and the high-fat-induced ROS and neurodegeneration is poorly known. Here we showed that, upon treatment with a saturated fatty acid palmitic acid (PA), the SOD1 activity was decreased in mouse neuronal HT-22 cell line accompanied by elevation of ROS, but not in mouse microglial BV-2 cell line. We further showed that PA decreased the levels of copper chaperone for SOD1 (CCS) in HT-22 cells, which promoted the nuclear import of SOD1 and decreased its activity. We demonstrated that the reduction of CCS is involved in the PA-induced decrease of SOD1 activity and elevation of ROS. In addition, compared with the adult mice fed with a standard diet, the high-fat-diet adult mice presented an increase of plasma free fatty acids, reduction of hippocampal SOD1 activity and CCS, mitochondrial degeneration and long-term memory decline. Taken together, our findings suggest that the high-fat-induced lower CCS level is essential for SOD1 suppression which may be associated with neurodegeneration and cognitive decline.

Protective Effect of Mitochondria-Targeted Antioxidants against Inflammatory Response to Lipopolysaccharide Challenge: A Review

Lipopolysaccharide (LPS), the major component of the outer membrane of Gram-negative bacteria, is the most abundant proinflammatory agent. Considerable evidence indicates that LPS challenge inescapably causes oxidative stress and mitochondrial dysfunction, leading to cell and tissue damage. Increased mitochondrial reactive oxygen species (mtROS) generation triggered by LPS is known to play a key role in the progression of the inflammatory response. mtROS at excessive levels impair electron transport chain functioning, reduce the mitochondrial membrane potential, and initiate lipid peroxidation and oxidative damage of mitochondrial proteins and mtDNA. Over the past 20 years, a large number of mitochondria-targeted antioxidants (mito-AOX) of different structures that can accumulate inside mitochondria and scavenge free radicals have been synthesized. Their protective role based on the prevention of oxidative stress and the restoration of mitochondrial function has been demonstrated in a variety of common diseases and pathological states. This paper reviews the current data on the beneficial application of different mito-AOX in animal endotoxemia models, in either in vivo or in vitro experiments. The results presented in our review demonstrate the promising potential of approaches based on mito-AOX in the development of new treatment strategies against Gram-negative infections and LPS per se.

The involvement of autophagy in the maintenance of endothelial homeostasis: The role of mitochondria

Endothelial mitochondria play important signaling roles critical for the regulation of various cellular processes, including calcium signaling, ROS generation, NO synthesis or inflammatory response. Mitochondrial stress or disturbances in mitochondrial function may participate in the development and/or progression of endothelial dysfunction and could precede vascular diseases. Vascular functions are also strictly regulated by properly functioning degradation machinery, including autophagy and mitophagy, and tightly coordinated by mitochondrial and endoplasmic reticulum responses to stress. Within this review, current knowledge related to the development of cardiovascular disorders and the importance of mitochondria, endoplasmic reticulum and degradation mechanisms in vascular endothelial functions are summarized.

Fate of Hematopoiesis During Aging. What Do We Really Know, and What are its Implications?

There is an ongoing shift in demographics such that older persons will outnumber young persons in the coming years, and with it age-associated tissue attrition and increased diseases and disorders. There has been increased information on the association of the aging process with dysregulation of hematopoietic stem (HSC) and progenitor (HPC) cells, and hematopoiesis. This review provides an extensive up-to date summary on the literature of aged hematopoiesis and HSCs placed in context of potential artifacts of the collection and processing procedure, that may not be totally representative of the status of HSCs in their in vivo bone marrow microenvironment, and what the implications of this are for understanding aged hematopoiesis. This review covers a number of interactive areas, many of which have not been adequately explored. There are still many unknowns and mechanistic insights to be elucidated to better understand effects of aging on the hematopoietic system, efforts that will take multidisciplinary approaches, and that could lead to means to ameliorate at least some of the dysregulation of HSCs and HPCs associated with the aging process. Graphical Abstract.