Hydroethidine- and MitoSOX-derived red fluorescence is not a reliable indicator of intracellular superoxide formation: another inconvenient truth

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Singlet Oxygen Photophysics: From Liquid Solvents to Mammalian Cells

Molecular oxygen, O2, has long provided a cornerstone for studies in chemistry, physics, and biology. Although the triplet ground state, O2(X3Σg-), has garnered much attention, the lowest excited electronic state, O2(a1Δg), commonly called singlet oxygen, has attracted appreciable interest, principally because of its unique chemical reactivity in systems ranging from the Earth's atmosphere to biological cells. Because O2(a1Δg) can be produced and deactivated in processes that involve light, the photophysics of O2(a1Δg) are equally important. Moreover, pathways for O2(a1Δg) deactivation that regenerate O2(X3Σg-), which address fundamental principles unto themselves, kinetically compete with the chemical reactions of O2(a1Δg) and, thus, have practical significance. Due to technological advances (e.g., lasers, optical detectors, microscopes), data acquired in the past ∼20 years have increased our understanding of O2(a1Δg) photophysics appreciably and facilitated both spatial and temporal control over the behavior of O2(a1Δg). One goal of this Review is to summarize recent developments that have broad ramifications, focusing on systems in which oxygen forms a contact complex with an organic molecule M (e.g., a liquid solvent). An important concept is the role played by the M+•O2-• charge-transfer state in both the formation and deactivation of O2(a1Δg).

Ten "Cheat Codes" for Measuring Oxidative Stress in Humans

Formidable and often seemingly insurmountable conceptual, technical, and methodological challenges hamper the measurement of oxidative stress in humans. For instance, fraught and flawed methods, such as the thiobarbituric acid reactive substances assay kits for lipid peroxidation, rate-limit progress. To advance translational redox research, we present ten comprehensive "cheat codes" for measuring oxidative stress in humans. The cheat codes include analytical approaches to assess reactive oxygen species, antioxidants, oxidative damage, and redox regulation. They provide essential conceptual, technical, and methodological information inclusive of curated "do" and "don't" guidelines. Given the biochemical complexity of oxidative stress, we present a research question-grounded decision tree guide for selecting the most appropriate cheat code(s) to implement in a prospective human experiment. Worked examples demonstrate the benefits of the decision tree-based cheat code selection tool. The ten cheat codes define an invaluable resource for measuring oxidative stress in humans.

Use of Electron Paramagnetic Resonance (EPR) to Evaluate Redox Status in a Preclinical Model of Acute Lung Injury

PURPOSE

Patients with hyper- vs. hypo-inflammatory subphenotypes of acute respiratory distress syndrome (ARDS) exhibit different clinical outcomes. Inflammation increases the production of reactive oxygen species (ROS) and increased ROS contributes to the severity of illness. Our long-term goal is to develop electron paramagnetic resonance (EPR) imaging of lungs in vivo to precisely measure superoxide production in ARDS in real time. As a first step, this requires the development of in vivo EPR methods for quantifying superoxide generation in the lung during injury, and testing if such superoxide measurements can differentiate between susceptible and protected mouse strains.

PROCEDURES

In WT mice, mice lacking total body extracellular superoxide dismutase (EC-SOD) (KO), or mice overexpressing lung EC-SOD (Tg), lung injury was induced with intraperitoneal (IP) lipopolysaccharide (LPS) (10 mg/kg). At 24 h after LPS treatment, mice were injected with the cyclic hydroxylamines 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine hydrochloride (CPH) or 4-acetoxymethoxycarbonyl-1-hydroxy-2,2,5,5-tetramethylpyrrolidine-3-carboxylic acid (DCP-AM-H) probes to detect, respectively, cellular and mitochondrial ROS - specifically superoxide. Several probe delivery strategies were tested. Lung tissue was collected up to one hour after probe administration and assayed by EPR.

RESULTS

As measured by X-band EPR, cellular and mitochondrial superoxide increased in the lungs of LPS-treated mice compared to control. Lung cellular superoxide was increased in EC-SOD KO mice and decreased in EC-SOD Tg mice compared to WT. We also validated an intratracheal (IT) delivery method, which enhanced the lung signal for both spin probes compared to IP administration.

CONCLUSIONS

We have developed protocols for delivering EPR spin probes in vivo, allowing detection of cellular and mitochondrial superoxide in lung injury by EPR. Superoxide measurements by EPR could differentiate mice with and without lung injury, as well as mouse strains with different disease susceptibilities. We expect these protocols to capture real-time superoxide production and enable evaluation of lung EPR imaging as a potential clinical tool for subphenotyping ARDS patients based on redox status.

Dihydroethidium-derived fluorescence in electrically stressed cells indicates intracellular microenvironment modifications independent of ROS

Intracellular reactive oxygen species (ROS) generation is widely suggested as a trigger for biological consequences of electric field exposures, such as those in electroporation applications. ROS are linked with membrane barrier function degradation, genetic damage, and complex events like immunological cell death. Dihydroethidium (DHE) is commonly used to monitor ROS in cells. DHE is linked to intracellular ROS by a primary oxidation product, Ethidium (Eth+), that shows increased fluorescence upon binding to polynucleotides. We observed changes in DHE-derived fluorescence in Chinese hamster ovary (CHO) cells post 300-ns electric pulse exposures, comparing them to tert-butyl-hydroperoxide (t-BHP) induced oxidative stress. Immediate intracellular fluorescence changes were noted in both cases, but with distinct localization patterns. After electrical stress, cytosolic DHE-derived fluorescence intensity decreases, and nucleolar intensity increases. Conversely, t-BHP exposure increases DHE-derived fluorescence uniformly across the cell. Surprisingly, fluorescence patterns after electrical stress in Eth+-loaded cells is identical to those in DHE-loaded cells, in kinetics and localization patterns. These findings indicate that DHE-derived fluorescence changes after pulsed electric field stress are not due to intracellular ROS generation leading to DHE oxidation, but rather indicate stress-induced intracellular microenvironment alterations affecting Eth+ fluorescence.

Quantum Sensing of Free Radical Generation in Mitochondria of Human Keratinocytes during UVB Exposure

Ultraviolet (UV) radiation is known to cause skin issues, such as dryness, aging, and even cancer. Among UV rays, UVB stands out for its ability to trigger problems within cells, including mitochondrial dysfunction, oxidative stress, and DNA damage. Free radicals are implicated in these cellular responses, but they are challenging to measure due to their short lifetime and limited diffusion range. In our study, we used a quantum sensing technique (T1 relaxometry) involving fluorescent nanodiamonds (FNDs) that change their optical properties in response to magnetic noise. This allowed us to monitor the free radical presence in real time. To measure radicals near mitochondria, we coated FNDs with antibodies, targeting mitochondrial protein voltage-dependent anion channel 2 (anti-VDAC2). Our findings revealed a dynamic rise in radical levels on the mitochondrial membrane as cells were exposed to UVB (3 J/cm2), with a significant increase observed after 17 min.

Increased Prolylcarboxypeptidase Expression Can Serve as a Biomarker of Senescence in Culture

Prolylcarboxypeptidase (PRCP, PCP, Lysosomal Pro-X-carboxypeptidase, Angiotensinase C) controls angiotensin- and kinin-induced cell signaling. Elevation of PRCP appears to be activated in chronic inflammatory diseases [cardiovascular disease (CVD), diabetes] in proportion to severity. Vascular endothelial cell senescence and mitochondrial dysfunction have consistently been shown in models of CVD in aging. Cellular senescence, a driver of age-related dysfunction, can differentially alter the expression of lysosomal enzymes due to lysosomal membrane permeability. There is a lack of data demonstrating the effect of age-related dysfunction on the expression and function of PRCP. To explore the changes in PRCP, the PRCP-dependent prekallikrein (PK) pathway was characterized in early- and late-passage human pulmonary artery endothelial cells (HPAECs). Detailed kinetic analysis of cells treated with high molecular weight kininogen (HK), a precursor of bradykinin (BK), and PK revealed a mechanism by which senescent HPAECs activate the generation of kallikrein upon the assembly of the HK-PK complex on HPAECs in parallel with an upregulation of PRCP and endothelial nitric oxide (NO) synthase (eNOS) and NO formation. The NO production and expression of both PRCP and eNOS increased in early-passage HPAECs and decreased in late-passage HPAECs. Low activity of PRCP in late-passage HPAECs was associated with rapid decreased telomerase reverse transcriptase mRNA levels. We also found that, with an increase in the passage number of HPAECs, reduced PRCP altered the respiration rate. These results indicated that aging dysregulates PRCP protein expression, and further studies will shed light into the complexity of the PRCP-dependent signaling pathway in aging.

Evaluation of nanoplastics-induced redox imbalance in cells, larval zebrafish, and daphnia magna with a superoxide anion radical fluorescent probe

Nanoplastics (NPs) is a novel plastic contaminant that could be taken up by cells and lead to severe biotoxicity toxicity, NPs in cells can cause oxidant damage by inducing reactive oxygen species (ROS) production and lead to acute inflammation. As a major ROS which related to many kinds of physiological and pathological processes, superoxide anion radical (O2•-) could be utilized as a signal of oxidant damage effected by NPs exposure in vivo. To detect the toxic damage mechanism of NPs, a fluorescence probe Bcy-OTf has been developed to monitor O2•- fluctuations content in cells and aquatic organisms after exposure to NPs. The probe has a high sensitivity (LOD = 20 nM) and a rapid responsive time (within 6 min), and it has high selectivity and low cytotoxicity to analysis the levels of the endogenous O2•-. Endogenous O2•- induced by NPs in living cells, Daphnia magna and larval zebrafish were analyzed. Moreover, the results confirmed the key role of MAPK and NF-κB pathway in NPs stimulation mechanisms in cells. This study indicated that Bcy-OTf can precisely assess the fluctuations of endogenous O2•-, which has potential for applying in further analysis mechanisms of NPs biological risks.

Decreased grip strength is associated with paraspinal muscular oxidative stress in female lumbar degenerative disease patients

We aimed to investigate the relationship between superoxide dismutase 2-related oxidative stress in the paraspinal muscles and spinal alignment, clinical skeletal muscle parameters, and mitochondrial function. Multifidus muscle samples from patients who underwent posterior lumbar surgery were analyzed. Patients with diseases affecting oxidative stress and spinal alignment were excluded. The superoxide dismutase 2 redox index was defined as the ratio of reactive oxygen species (superoxide) to antioxidant enzymes (superoxide dismutase 2) and was used as an index of oxidative stress. Patients were divided into two groups based on the superoxide dismutase 2 redox index. Spinal alignment, clinical skeletal muscle parameters, and succinic dehydrogenase (SDH) mean grayscale value were compared between the groups, with analyzes for both sexes. Multiple regression analyzes were used to adjust for the confounding effect of age on variables showing a significant difference between the two groups. Thirty-five patients with lumbar degenerative diseases were included. No significant differences were observed between the two groups for any of the parameters in males; however, females with a higher superoxide dismutase 2 redox index had greater lumbar lordosis, lower grip strength, and higher SDH mean grayscale value than those with a lower index. Multiple regression analyzes revealed that the superoxide dismutase 2 redox index was an independent explanatory variable for lumbar lordosis, grip strength, and SDH mean grayscale value in female patients. In conclusion, superoxide dismutase 2-related oxidative stress in the paraspinal muscles was associated with mitochondrial dysfunction and decreased grip strength in female lumbar degenerative disease patients.

The endogenous antioxidant ability of royal jelly in Drosophila is independent of Keap1/Nrf2 by activating oxidoreductase activity

Royal jelly (RJ) is a biologically active substance secreted by the hypopharyngeal and mandibular glands of worker honeybees. It is widely claimed that RJ reduces oxidative stress. However, the antioxidant activity of RJ has mostly been determined by in vitro chemical detection methods or by external administration drugs that cause oxidative stress. Whether RJ can clear the endogenous production of reactive oxygen species (ROS) in cells remains largely unknown. Here, we systematically investigated the antioxidant properties of RJ using several endogenous oxidative stress models of Drosophila. We found that RJ enhanced sleep quality of aging Drosophila, which is decreased due to an increase of oxidative damage with age. RJ supplementation improved survival and suppressed ROS levels in gut cells of flies upon exposure to hydrogen peroxide or to the neurotoxic agent paraquat. Moreover, RJ supplementation moderated levels of ROS in endogenous gut cells and extended lifespan after exposure of flies to heat stress. Sleep deprivation leads to accumulation of ROS in the gut cells, and RJ attenuated the consequences of oxidative stress caused by sleep loss and prolonged lifespan. Mechanistically, RJ prevented cell oxidative damage caused by heat stress or sleep deprivation, with the antioxidant activity in vivo independent of Keap1/Nrf2 signaling. RJ supplementation activated oxidoreductase activity in the guts of flies, suggesting its ability to inhibit endogenous oxidative stress and maintain health, possibly in humans.

Mitochondria-Targeted Catalase Does Not Suppress Development of Cellular Senescence during Aging

Cellular senescence is a complex stress response marked by stable proliferative arrest and the secretion of biologically active molecules collectively known as the senescence-associated secretory phenotype (SASP). Mitochondria-derived reactive oxygen species (ROS) have been implicated in aging and age-related processes, including senescence. Stressors that increase ROS levels promote both senescence and the SASP, while reducing mitochondrial ROS or mitochondria themselves can prevent senescence or the SASP. Mitochondrially targeted catalase (mCAT), a transgene that reduces mitochondrial levels of ROS, has been shown to extend the lifespan of murine models and protect against the age-related loss of mitochondrial function. However, it remains unclear whether mCAT can prevent senescence or the SASP. In this study, we investigated the impact of mCAT on senescence in cultured cells and aged mice in order to discover if the lifespan-extending activity of mCAT might be due to the reduction in senescent cells or the SASP. Contrary to expectations, we observed that mCAT does not reduce markers of senescence or the SASP in cultured cells. Moreover, mCAT does not prevent the accumulation of senescent cells or the development of the SASP in adipose tissue from aged mice. These results suggest that mitochondrial ROS may not always play a causal role in the development of senescence during natural aging and underscore the need for a nuanced understanding of the intricate relationship between mitochondrial ROS and cellular senescence.

Health position paper and redox perspectives - Disease burden by transportation noise

Transportation noise is a ubiquitous urban exposure. In 2018, the World Health Organization concluded that chronic exposure to road traffic noise is a risk factor for ischemic heart disease. In contrast, they concluded that the quality of evidence for a link to other diseases was very low to moderate. Since then, several studies on the impact of noise on various diseases have been published. Also, studies investigating the mechanistic pathways underlying noise-induced health effects are emerging. We review the current evidence regarding effects of noise on health and the related disease-mechanisms. Several high-quality cohort studies consistently found road traffic noise to be associated with a higher risk of ischemic heart disease, heart failure, diabetes, and all-cause mortality. Furthermore, recent studies have indicated that road traffic and railway noise may increase the risk of diseases not commonly investigated in an environmental noise context, including breast cancer, dementia, and tinnitus. The harmful effects of noise are related to activation of a physiological stress response and nighttime sleep disturbance. Oxidative stress and inflammation downstream of stress hormone signaling and dysregulated circadian rhythms are identified as major disease-relevant pathomechanistic drivers. We discuss the role of reactive oxygen species and present results from antioxidant interventions. Lastly, we provide an overview of oxidative stress markers and adverse redox processes reported for noise-exposed animals and humans. This position paper summarizes all available epidemiological, clinical, and preclinical evidence of transportation noise as an important environmental risk factor for public health and discusses its implications on the population level.

High-Throughput Measure of Mitochondrial Superoxide Levels as a Marker of Coronary Artery Disease to Accelerate Drug Translation in Patient-Derived Endothelial Cells Using Opera Phenix® Technology

Improved human-relevant preclinical models of coronary artery disease (CAD) are needed to improve translational research and drug discovery. Mitochondrial dysfunction and associated oxidative stress contribute to endothelial dysfunction and are a significant factor in the development and progression of CAD. Endothelial colony-forming cells (ECFCs) can be derived from peripheral blood mononuclear cells (PBMCs) and offer a unique potentially personalised means for investigating new potential therapies targeting important components of vascular function. We describe the application of the high-throughput and confocal Opera Phenix® High-Content Screening System to examine mitochondrial superoxide (mROS) levels, mitochondrial membrane potential, and mitochondrial area in both established cell lines and patient-derived ECFCs simultaneously. Unlike traditional plate readers, the Opera Phenix® is an imaging system that integrates automated confocal microscopy, precise fluorescent detection, and multi-parameter algorithms to visualize and precisely quantify targeted biological processes at a cellular level. In this study, we measured mROS production in human umbilical vein endothelial cells (HUVECs) and patient-derived ECFCs using the mROS production probe, MitoSOXTM Red. HUVECs exposed to oxidized low-density lipoprotein (oxLDL) increased mROS levels by 47.7% (p < 0.0001). A pooled group of patient-derived ECFCs from participants with CAD (n = 14) exhibited 30.9% higher mROS levels compared to patients with no CAD when stimulated with oxLDL (n = 14; p < 0.05). When tested against a small group of candidate compounds, this signal was attenuated by PKT-100 (36.22% reduction, p = 0.03), a novel P2X7 receptor antagonist. This suggests the P2X7 receptor as a valid target against excess mROS levels. As such, these findings highlight the potential of the MitoSOX-Opera Phenix technique to be used for drug discovery efforts in CAD.

Sleeve Gastrectomy Provides Cardioprotection from Oxidative Stress In Vitro Due to Reduction of Circulating Myeloperoxidase

Bariatric surgery, including sleeve gastrectomy (SG), improves systolic and diastolic function, which is independent of weight loss in rodent models. The cause of weight loss-independent improvements in cardiac function are unknown but may originate from the gastrointestinal tract. In this study, we investigated whether a circulating blood factor is a mechanism for acute cardioprotection after SG by testing the utility of rodent SG plasma to reduce metabolic stress in vitro. For the initial experiment, obese male Zucker rats underwent SG, ad lib sham, or pair-fed sham surgeries (n = six SG, n = eight SH, n = eight PF). For all other studies, a second group of Zucker rats underwent SG or ad lib sham surgeries (n = eight SH, n = six SG). Six weeks following surgery, plasma was collected from each group, both in the fasting and post-prandial (pp) state. This plasma was then pooled per surgical group and nutrient state and tested in multiple in vitro cell culture and extra-cellular assays to determine the effect of SG on myotubular metabolic stress compared to the sham surgeries. Post-prandial SG plasma (ppSG), but not fasting SG, pp, or fasting sham plasma, reduced the metabolic stress of the H9c2 cells as measured by lactate dehydrogenase (LDH) release (p < 0.01). Unlike SG, weight reduction through pair-feeding did not prevent H9c2 metabolic stress. The PpSG plasma had the slowest rate of extracellular hydrogen peroxide consumption and peroxidatic activity compared to the pp sham, fasting SG, and fasting sham groups. Redox testing of plasma with aminiobenzoic acid hydrazide and edaravone suggested a pattern supporting myeloperoxidase (MPO), or other peroxidases, as the primary component responsible for reduced metabolic stress with ppSG plasma. The PpSG plasma contained 35% less circulating MPO protein as compared to the pp sham and fasting SG plasma. The plasma from an MPO global knockout rat also prevented metabolic stress of the H9c2 cells, compared to the significant increase in LDH release from the plasma of the WT controls (p < 0.01). The MPO global knockout plasma also had a rate of extracellular hydrogen peroxide consumption and peroxidatic activity comparable to the ppSG plasma. These studies suggest that one of the weight loss-independent mechanisms by which SG improves myocellular function could be a reduced pro-oxidative environment due to lower circulating levels of MPO. It appears that the gastrointestinal tract is of critical importance to these findings, as the MPO levels were only lowered after enteral, nutrient stimulation in the SG rats. If this surgical effect is confirmed in humans, SG may be a unique surgical treatment for multiple diseases with a pathogenesis of inflammation and oxidative damage, including obesity-associated heart failure with preserved ejection fraction.

Cigarette Smoke-Induced Reactive Oxygen Species Formation: A Concise Review

Smoking is recognized as a significant risk factor for numerous disorders, including cardiovascular diseases, respiratory conditions, and various forms of cancer. While the exact pathogenic mechanisms continue to be explored, the induction of oxidative stress via the production of excess reactive oxygen species (ROS) is widely accepted as a primary molecular event that predisposes individuals to these smoking-related ailments. This review focused on how cigarette smoke (CS) promotes ROS formation rather than the pathophysiological repercussions of ROS and oxidative stress. A comprehensive analysis of existing studies revealed the following key ways through which CS imposes ROS burden on biological systems: (1) ROS, as well as radicals, are intrinsically present in CS, (2) CS constituents generate ROS through chemical reactions with biomolecules, (3) CS stimulates cellular ROS sources to enhance production, and (4) CS disrupts the antioxidant system, aggravating the ROS generation and its functions. While the evidence supporting these mechanisms is chiefly based on in vitro and animal studies, the direct clinical relevance remains to be fully elucidated. Nevertheless, this understanding is fundamental for deciphering molecular events leading to oxidative stress and for developing intervention strategies to counter CS-induced oxidative stress.

Redox Biology in Adipose Tissue Physiology and Obesity

Reactive oxygen species (ROS), a by-product of mitochondrial oxidative phosphorylation and cellular metabolism, is vital for cellular survival, proliferation, damage, and senescence. In recent years, studies have shown that ROS levels and redox status in adipose tissue are strongly associated with obesity and metabolic diseases. Although it was previously considered that excessive production of ROS and impairment of antioxidant capability leads to oxidative stress and potentially contributes to increased adiposity, it has become increasingly evident that an adequate amount of ROS is vital for adipocyte differentiation and thermogenesis. In this review, by providing a systematic overview of the recent understanding of the key factors of redox systems, endogenous mechanisms for redox homeostasis, advanced techniques for dynamic redox monitoring, as well as exogenous stimuli for redox production in adipose tissues and obesity, the importance of redox biology in metabolic health is emphasized.

Novel NADPH Oxidase-2 Inhibitors as Potential Anti-Inflammatory and Neuroprotective Agents

A family of seven NADPH oxidase enzymes (Nox1-5, Duox1-2) has been implicated in a variety of diseases, including inflammatory lung diseases, neurodegenerative diseases, cardiovascular diseases, and cancer. Here, we report the results of our studies aimed at developing novel brain-permeable Nox2 inhibitors with potential application as neuroprotective agents. Using cell-based assays, we identified a novel Nox2 inhibitor, TG15-132, that prevents PMA-stimulated oxygen consumption and reactive oxygen species (superoxide radical anion and hydrogen peroxide) formation upon acute treatment in differentiated HL60 cells. Long-term treatment with TG15-132 attenuates the induction of genes encoding Nox2 subunits, several inflammatory cytokines, and iNOS in differentiated THP-1 cells. Moreover, TG15-132 shows a relatively long plasma half-life (5.6 h) and excellent brain permeability, with a brain-to-plasma ratio (>5-fold) in rodent models. Additionally, TG15-132 does not cause any toxic effects on vital organs or blood biomarkers of toxicity in mice upon chronic dosing for seven days. We propose that TG15-132 may be used as a Nox2 inhibitor and a potential neuroprotective agent, with possible further structural modifications to increase its potency.

Bioenergetic profile and redox tone modulate in vitro osteogenesis of human dental pulp stem cells: new perspectives for bone regeneration and repair

BACKGROUND

Redox signaling and energy metabolism are known to be involved in controlling the balance between self-renewal and proliferation/differentiation of stem cells. In this study we investigated metabolic and redox changes occurring during in vitro human dental pulp stem cells (hDPSCs) osteoblastic (OB) differentiation and tested on them the impact of the reactive oxygen species (ROS) signaling.

METHODS

hDPSCs were isolated from dental pulp and subjected to alkaline phosphatase and alizarin red staining, q-RT-PCR, and western blotting analysis of differentiation markers to assess achievement of osteogenic/odontogenic differentiation. Moreover, a combination of metabolic flux analysis and confocal cyto-imaging was used to profile the metabolic phenotype and to evaluate the redox tone of hDPSCs.

RESULTS

In differentiating hDPSCs we observed the down-regulation of the mitochondrial respiratory chain complexes expression since the early phase of the process, confirmed by metabolic flux analysis, and a reduction of the basal intracellular peroxide level in its later phase. In addition, dampened glycolysis was observed, thereby indicating a lower energy-generating phenotype in differentiating hDPSCs. Treatment with the ROS scavenger Trolox, applied in the early-middle phases of the process, markedly delayed OB differentiation of hDPSCs assessed as ALP activity, Runx2 expression, mineralization capacity, expression of stemness and osteoblast marker genes (Nanog, Lin28, Dspp, Ocn) and activation of ERK1/2. In addition, the antioxidant partly prevented the inhibitory effect on cell metabolism observed following osteogenic induction.

CONCLUSIONS

Altogether these results provided evidence that redox signaling, likely mediated by peroxide species, influenced the stepwise osteogenic expansion/differentiation of hDPSCs and contributed to shape its accompanying metabolic phenotype changes thus improving their efficiency in bone regeneration and repair.

Association of Apolipoprotein E4-related Microvascular Disease in the Alzheimer's Disease Hippocampal CA1 Stratum Radiatum

Current data suggest a hypothesis of vascular pathogenesis for the development and progression of Alzheimer's disease (AD). To investigate this, we studied the association of apolipoprotein E4 (APOE4) gene on microvessels in human autopsy-confirmed AD with and without APOE4, compared with age/sex-matched control (AC) hippocampal CA1 stratum radiatum. AD arterioles (without APOE4 gene) had mild oxidative stress and loss of vascular endothelial growth factor (VEGF) and endothelial cell density, reflecting aging progression. In AD + APOE4, an increase in strong oxidative DNA damage marker 8-hydroxy-2'-deoxyguanosine (8-OHdG), VEGF, and endothelial cell density were associated with increased diameter of arterioles and perivascular space dilation. In cultured human brain microvascular cells (HBMECs), treatment of ApoE4 protein plus amyloid-β (Aβ) oligomers increased superoxide production and the apoptotic marker cleaved caspase 3, sustained hypoxia inducible factor-1α (HIF-1α) stability that was associated with an increase in MnSOD, VEGF, and cell density. This cell over-proliferation was inhibited with the antioxidants N-acetyl cysteine and MnTMPyP, the HIF-1α inhibitor echinomycin, the VEGFR-2 receptor blocker SU1498, the protein kinase C (PKC) ε knock-down (KD) and the extracellular signal-regulated kinase 1/2 (ERK) inhibitor FR180204. The PKCε KD and echinomycin decreased VEGF and/or ERK. In conclusion, AD capillaries and arterioles in hippocampal CA1 stratum radiatum of non-APOE4 carriers are related with aging, while those in APOE4 carriers with AD are related with pathogenesis of cerebrovascular disease.

Redox-crippled MitoQ potently inhibits breast cancer and glioma cell proliferation: A negative control for verifying the antioxidant mechanism of MitoQ in cancer and other oxidative pathologies

Mitochondria-targeted coenzyme Q10 (Mito-ubiquinone, Mito-quinone mesylate, or MitoQ) was shown to be an effective antimetastatic drug in patients with triple-negative breast cancer. MitoQ, sold as a nutritional supplement, prevents breast cancer recurrence. It potently inhibited tumor growth and tumor cell proliferation in preclinical xenograft models and in vitro breast cancer cells. The proposed mechanism of action involves the inhibition of reactive oxygen species by MitoQ via a redox-cycling mechanism between the oxidized form, MitoQ, and the fully reduced form, MitoQH2 (also called Mito-ubiquinol). To fully corroborate this antioxidant mechanism, we substituted the hydroquinone group (-OH) with the methoxy group (-OCH3). Unlike MitoQ, the modified form, dimethoxy MitoQ (DM-MitoQ), lacks redox-cycling between the quinone and hydroquinone forms. DM-MitoQ was not converted to MitoQ in MDA-MB-231 cells. We tested the antiproliferative effects of both MitoQ and DM-MitoQ in human breast cancer (MDA-MB-231), brain-homing cancer (MDA-MB-231BR), and glioma (U87MG) cells. Surprisingly, DM-MitoQ was slightly more potent than MitoQ (IC50 = 0.26 μM versus 0.38 μM) at inhibiting proliferation of these cells. Both MitoQ and DM-MitoQ potently inhibited mitochondrial complex I-dependent oxygen consumption (IC50 = 0.52 μM and 0.17 μM, respectively). This study also suggests that DM-MitoQ, which is a more hydrophobic analog of MitoQ (logP: 10.1 and 8.7) devoid of antioxidant function and reactive oxygen species scavenging ability, can inhibit cancer cell proliferation. We conclude that inhibition of mitochondrial oxidative phosphorylation by MitoQ is responsible for inhibition of breast cancer and glioma proliferation and metastasis. Blunting the antioxidant effect using the redox-crippled DM-MitoQ can serve as a useful negative control in corroborating the involvement of free radical-mediated processes (e.g., ferroptosis, protein oxidation/nitration) using MitoQ in other oxidative pathologies.

Redox regulation in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the most devastating complications of diabetes mellitus, where currently there is no cure available. Several important mechanisms contribute to the pathogenesis of this complication, with oxidative stress being one of the key factors. The past decades have seen a large number of publications with various aspects of this topic; however, the specific details of redox regulation in DKD are still unclear. This is partly because redox biology is very complex, coupled with a complex and heterogeneous organ with numerous cell types. Furthermore, often times terms such as "oxidative stress" or reactive oxygen species are used as a general term to cover a wide and rich variety of reactive species and their differing reactions. However, no reactive species are the same, and not all of them are capable of biologically relevant reactions or "redox signaling." The goal of this review is to provide a biochemical background for an array of specific reactive oxygen species types with varying reactivity and specificity in the kidney as well as highlight some of the advances in redox biology that are paving the way to a better understanding of DKD development and risk.

Natural Acetogenins, Chatenaytrienins-1, -2, -3 and -4, Mitochondrial Potential Uncouplers and Autophagy Inducers-Promising Anticancer Agents

The present paper details the complete stereoselective synthesis of four natural acetogenins, chatenaytrienins-1, -2, -3 and -4, previously isolated from the roots of fruit trees of the family Annonaceae (A. nutans and A. muricata), as an inseparable mixture. The novel organometallic reactions, developed by the authors, of Ti-catalyzed cross-cyclomagnesiation of O-containing and aliphatic allenes using available Grignard reagents were applied at the key stage of synthesis. We have studied the biological activity of the synthesized individual chatenaytrienins-1, -2, -3 and -4 in vitro, including their cytotoxicity in a panel of tumor lines and their ability to induce apoptosis, affect the cell cycle and mitochondria, and activate the main apoptotic signaling pathways in the cell, applying modern approaches of flow cytometry and multiplex analysis with Luminex xMAP technology. It has been shown that chatenaytrienins affect mitochondria by uncoupling the processes of mitochondrial respiration, causing the accumulation of ROS ions, followed by the initiation of apoptosis. The most likely mechanism for the death of cortical neurons from the consumption of tea from the seeds of Annona fruit is long-term chronic hypoxia, which leads to the development of an atypical form of Parkinson's disease that is characteristic of the indigenous inhabitants of Guam and New Caledonia.

Fluorescence microscopy imaging of mitochondrial metabolism in cancer cells

Mitochondrial metabolism is an important contributor to cancer cell survival and proliferation that coexists with enhanced glycolytic activity. Measuring mitochondrial activity is useful to characterize cancer metabolism patterns, to identify metabolic vulnerabilities and to identify new drug targets. Optical imaging, especially fluorescent microscopy, is one of the most valuable tools for studying mitochondrial bioenergetics because it provides semiquantitative and quantitative readouts as well as spatiotemporal resolution of mitochondrial metabolism. This review aims to acquaint the reader with microscopy imaging techniques currently used to determine mitochondrial membrane potential (ΔΨm), nicotinamide adenine dinucleotide (NADH), ATP and reactive oxygen species (ROS) that are major readouts of mitochondrial metabolism. We describe features, advantages, and limitations of the most used fluorescence imaging modalities: widefield, confocal and multiphoton microscopy, and fluorescent lifetime imaging (FLIM). We also discus relevant aspects of image processing. We briefly describe the role and production of NADH, NADHP, flavins and various ROS including superoxide and hydrogen peroxide and discuss how these parameters can be analyzed by fluorescent microscopy. We also explain the importance, value, and limitations of label-free autofluorescence imaging of NAD(P)H and FAD. Practical hints for the use of fluorescent probes and newly developed sensors for imaging ΔΨm, ATP and ROS are described. Overall, we provide updated information about the use of microscopy to study cancer metabolism that will be of interest to all investigators regardless of their level of expertise in the field.

Ferroptosis-Mediated Cell Death Induced by NCX4040, The Non-Steroidal Nitric Oxide Donor, in Human Colorectal Cancer Cells: Implications in Therapy

Our recent studies show that the treatment of human ovarian tumor cells with NCX4040 results in significant depletions of cellular glutathione, the formation of reactive oxygen/nitrogen species and cell death. NCX4040 is also cytotoxic to several human colorectal cancer (CRC) cells in vitro and in vivo. Here, we examined the ferroptosis-dependent mechanism(s) of cytotoxicity of NCX4040 in HT-29 and K-RAS mutant HCT 116 colon cell lines. Ferroptosis is characterized by the accumulation of reactive oxygen species (ROS) within the cell, leading to an iron-dependent oxidative stress-mediated cell death. However, its relevance in the mechanism of NCX4040 cytotoxicity in CRCs is not known. We found that NCX4040 generates ROS in CRC cells without any depletion of cellular GSH. Combinations of NCX4040 with erastin (ER) or RSL3 (RAS-selective lethal 3), known inducers of ferroptosis, enhanced CRC death. In contrast, ferrostatin-1, an inhibitor of ferroptosis, significantly inhibited NCX4040-induced cell death. Treatment of CRC cells with NCX4040 resulted in the induction of lipid peroxidation in a dose- and time-dependent manner. NCX4040 treatment induced several genes related to ferroptosis (e.g., CHAC1, GPX4 and NOX4) in both cell lines. Metabolomic studies also indicated significant increases in both lipid and energy metabolism following the drug treatment in HT-29 and HCT 116 cells. These observations strongly suggest that NCX4040 causes the ferroptosis-mediated cell death of CRC cells. Furthermore, combinations of NCX4040 and ER or RSL3 may contribute significantly to the treatment of CRC, including those that are difficult to treat due to the presence of Ras mutations in the clinic. NCX4040-induced ferroptosis may also be a dynamic form of cell death for the treatment of other cancers.

SKN-1/Nrf2-dependent regulation of mitochondrial homeostasis modulates transgenerational toxicity induced by nanoplastics with different surface charges in Caenorhabditis elegans

The toxic effects of nanoplastics on transgenerational toxicity in environmental organisms and the involved mechanisms remain poorly comprehended. This study aimed to identify the role of SKN-1/Nrf2-dependent regulation of mitochondrial homeostasis in response to transgenerational toxicity caused by changes in nanoplastic surface charges in Caenorhabditis elegans (C. elegans). Our results revealed that compared with the wild-type control and PS exposed groups, exposure to PS-NH₂ or PS-SOOOH at environmentally relevant concentrations (ERC) of ≥ 1 μg/L caused transgenerational reproductive toxicity, inhibited mitochondrial unfolded protein responses (UPR) by downregulating the transcription levels of hsp-6, ubl-5, dve-1, atfs-1, haf-1, and clpp-1, membrane potential by downregulating phb-1 and phb-2, and promoted mitochondrial apoptosis by downregulating ced-4 and ced-3 and upregulating ced-9, DNA damage by upregulating hus-1, cep-1, egl-1, reactive oxygen species (ROS) by upregulating nduf-7 and nuo-6, ultimately resulting in mitochondrial homeostasis. Additionally, further study indicated that SKN-1/Nrf2 mediated antioxidant response to alleviate PS-induced toxicity in the P0 generation and dysregulated mitochondrial homeostasis to enhance PS-NH₂ or PS-SOOOH-induced transgenerational toxicity. Our study highlights the momentous role of SKN-1/Nrf2 mediated mitochondrial homeostasis in the response to nanoplastics caused transgenerational toxicity in environmental organisms.

Disease-Modifying Effects of Vincamine Supplementation in Drosophila and Human Cell Models of Parkinson's Disease Based on DJ-1 Deficiency

Parkinson's disease (PD) is an incurable neurodegenerative disorder caused by the selective loss of dopaminergic neurons in the substantia nigra pars compacta. Current therapies are only symptomatic and are not able to stop or delay its progression. In order to search for new and more effective therapies, our group carried out a high-throughput screening assay, identifying several candidate compounds that are able to improve locomotor ability in DJ-1β mutant flies (a Drosophila model of familial PD) and reduce oxidative stress (OS)-induced lethality in DJ-1-deficient SH-SY5Y human cells. One of them was vincamine (VIN), a natural alkaloid obtained from the leaves of Vinca minor. Our results showed that VIN is able to suppress PD-related phenotypes in both Drosophila and human cell PD models. Specifically, VIN reduced OS levels in PD model flies. Besides, VIN diminished OS-induced lethality by decreasing apoptosis, increased mitochondrial viability, and reduced OS levels in DJ-1-deficient human cells. In addition, our results show that VIN might be exerting its beneficial role, at least partially, by the inhibition of voltage-gated sodium channels. Therefore, we propose that these channels might be a promising target in the search for new compounds to treat PD and that VIN represents a potential therapeutic treatment for the disease.

Synthetic ditempolphosphatidylcholine liposome-like nanoparticles for anti-oxidative therapy of atherosclerosis

Atherosclerosis (AS), a chronic inflammatory disease, is the leading cause of death worldwide. Anti-oxidative therapy has been developed for AS therapy in light of the critical role of ROS in pathogenesis of AS, but current anti-oxidants have exhibited limited outcomes in the clinic. Herein, new ROS-eliminating liposome-like NPs (Tempol-Lips) were assembled from synthetic lipids that covalently conjugated two Tempol molecules with phosphatidylcholine by esterification reaction. The obtained Tempol-Lips can be efficiently internalized into inflammatory macrophages and attenuated inflammation via scavenging overproduced intracellular ROS. After i.v. administration, Tempol-Lips with nanoscale character accumulated in the plaques of ApoE^-/- mice through passive targeting and significantly inhibited the pathogenesis of AS, compared with those treated with control drugs. The therapeutic benefits of Tempol-Lips primarily are ascribed to the reduced local and systematic oxidative stress and inflammation. Preliminary studies in vivo further demonstrated Tempol-Lips were safe and biocompatible after long-term i.v. injection. Conclusively, Tempol-Lips can be developed as a novel anti-AS nanotherapy with potential translation in the clinic.

Protective Effect of Sulforaphane on Oxidative Stress and Mitochondrial Dysfunction Associated with Status Epilepticus in Immature Rats

The present study aimed to elucidate the effect of sulforaphane (a natural isothiocyanate) on oxidative stress and mitochondrial dysfunction during and at selected periods following status epilepticus (SE) induced in immature 12-day-old rats by Li-pilocarpine. Dihydroethidium was employed for the detection of superoxide anions, immunoblot analyses for 3-nitrotyrosine (3-NT) and 4-hydroxynonenal (4-HNE) levels and respiratory chain complex I activity for evaluation of mitochondrial function. Sulforaphane was given i.p. in two doses (5 mg/kg each), at PD 10 and PD 11, respectively. The findings of the present study indicate that both the acute phase of SE and the early period of epileptogenesis (1 week and 3 weeks following SE induction) are associated with oxidative stress (documented by the enhanced superoxide anion production and the increased levels of 3-NT and 4-HNE) and the persisting deficiency of complex I activity. Pretreatment with sulforaphane either completely prevented or significantly reduced markers of both oxidative stress and mitochondrial dysfunction. Since sulforaphane had no direct anti-seizure effect, the findings suggest that the ability of sulforaphane to activate Nrf2 is most likely responsible for the observed protective effect. Nrf2-ARE signaling pathway can be considered a promising target for novel therapies of epilepsy, particularly when new compounds, possessing inhibitory activity against protein-protein interaction between Nrf2 and its repressor protein Keap1, with less "off-target" effects and, importantly, with an optimal permeability and bioavailability properties, become available commercially.

1,2,4,5-Tetrazine-tethered probes for fluorogenically imaging superoxide in live cells with ultrahigh specificity

Superoxide (O₂^·-) is the primary reactive oxygen species in mammal cells. Detecting superoxide is crucial for understanding redox signaling but remains challenging. Herein, we introduce a class of activity-based sensing probes. The probes utilize 1,2,4,5-tetrazine as a superoxide-responsive trigger, which can be modularly tethered to various fluorophores to tune probe sensitivity and emission color. These probes afford ultra-specific and ultra-fluorogenic responses towards superoxide, and enable multiplexed imaging of various cellular superoxide levels in an organelle-resolved way. Notably, the probes reveal the aberrant superoxide generation in the pathology of myocardial ischemia/reperfusion injury, and facilitate the establishment of a high-content screening pipeline for mediators of superoxide homeostasis. One such identified mediator, coprostanone, is shown to effectively ameliorating oxidative stress-induced injury in mice with myocardial ischemia/reperfusion injury. Collectively, these results showcase the potential of 1,2,4,5-tetrazine-tethered probes as versatile tools to monitor superoxide in a range of pathophysiological settings.

A mechanistic study of gold nanoparticles catalysis of O2 reduction by ascorbate and hydroethidine, investigating reactive oxygen species reactivity

In this work, the mechanism of dioxygen reduction catalysed by gold nanoparticles (AuNPs) by two electron donors was investigated, i.e., by sodium ascorbate and hydroethidine, focusing on potential ROS (reactive oxygen species) formation, such as O₂˙^- and H₂O₂. According to our results, when AuNPs catalyse the reduction of O₂, ROS are formed only as intermediates on the surface of nanoparticles, and they are unavoidably reduced to water, catalysed by the AuNPs. Thus, the statement on ROS production in the presence of AuNPs often reported in the literature is excessive. The AuNPs can catalyze the oxidation of electron donors in the cell, e.g., antioxidants causing oxidative stress. Therefore we propose that when explaining damage in the living cells observed in the presence of AuNP, the catalysis of redox reactions by AuNPs must be considered.

Chronic exposure to di(2-ethylhexyl) phthalate (DEHP) weakens innate immunity and leads to immunosenescence in C. elegans

Di(2-ethylhexyl) phthalate (DEHP), a widespread contaminant, has numerous adverse impacts on human health and ecosystems. Chronic DEHP exposure has been found to accelerate aging; however, its potential threat to age-dependent innate immune decline remains unknown. This study aims to evaluate the effects of chronic DEHP exposure on innate immunosenescence in Caenorhabditis elegans. We show that the length of the exposure period significantly impacts DEHP-induced age-related declines, which is linked to immunosenescence and oxidative stress. We found that the DEHP-caused immunosenescence is accompanied with downregulation of an antimicrobial gene lys-7 as well as an enhancement of the nuclear translocation of HLH-30, an orthologue of mammalian transcription factor EB (TFEB). Moreover, DEHP exposure increases the expression of riok-1, a human RIO kinase homolog, which is associated with DEHP-induced HLH-30/TFEB translocation. Our findings suggest that early-life and chronic exposure to DEHP, mostly due to parent compound rather than its metabolite mono(2-ethylhexyl) phthalate (MEHP), may weaken the innate immunity in C. elegans and may enhance susceptibility to infections or promote immunosenescence in aged populations.

Reactive oxygen species-upregulating nanomedicines towards enhanced cancer therapy

Reactive oxygen species (ROS) play a crucial role in physiological and pathological processes, emerging as a therapeutic target in cancer. Owing to the high concentration of ROS in solid tumor tissues, ROS-based treatments, such as photodynamic therapy and chemodynamic therapy, and ROS-responsive drug delivery systems have been widely explored to powerfully and specifically suppress tumors. However, their anticancer efficacy is still hampered by the heterogeneous ROS levels, and thus comprehensively upregulating the ROS levels in tumor tissues can ensure an enhanced therapeutic effect, which can further sensitize and/or synergize with other therapies to inhibit tumor growth and metastasis. Herein, we review the recently emerging drug delivery strategies and technologies for increasing the H₂O₂, ˙OH, ¹O₂, and ˙O₂^- concentrations in cancer cells, including the efficient delivery of natural enzymes, nanozymes, small molecular biological molecules, and nanoscale Fenton-reagents and semiconductors and neutralization of intracellular antioxidant substances and localized input of mechanical and electromagnetic waves (such as ultrasound, near infrared light, microwaves, and X-rays). The applications of these ROS-upregulating nanosystems in enhancing and synergizing cancer therapies including chemotherapy, chemodynamic therapy, phototherapy, and immunotherapy are surveyed. In addition, we discuss the challenges of ROS-upregulating systems and the prospects for future studies.

Early Detection Is the Best Prevention-Characterization of Oxidative Stress in Diabetes Mellitus and Its Consequences on the Cardiovascular System

Previous studies demonstrated an important role of oxidative stress in the pathogenesis of cardiovascular disease (CVD) in diabetic patients due to hyperglycemia. CVD remains the leading cause of premature death in the western world. Therefore, diabetes mellitus-associated oxidative stress and subsequent inflammation should be recognized at the earliest possible stage to start with the appropriate treatment before the onset of the cardiovascular sequelae such as arterial hypertension or coronary artery disease (CAD). The pathophysiology comprises increased reactive oxygen and nitrogen species (RONS) production by enzymatic and non-enzymatic sources, e.g., mitochondria, an uncoupled nitric oxide synthase, xanthine oxidase, and the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX). Considering that RONS originate from different cellular mechanisms in separate cellular compartments, adequate, sensitive, and compartment-specific methods for their quantification are crucial for early detection. In this review, we provide an overview of these methods with important information for early, appropriate, and effective treatment of these patients and their cardiovascular sequelae.

Inflammatory stimulus worsens the effects of UV-A exposure on J774 cells

UV-A radiation affects skin homeostasis by promoting oxidative distress. Endogenous photosensitizers in the dermis and epidermis of human skin absorb UV-A radiation forming excited states (singlet and triplet) and reactive oxygen species (ROS) producing oxidized compounds that trigger biological responses. The activation of NF-kB induces the expression of pro-inflammatory cytokines and can intensify the generation of ROS. However, there is no studies evaluating the cross talks between inflammatory stimulus and UV-A exposure on the levels of redox misbalance and inflammation. In here, we evaluated the effects of UV-A exposure on J774 macrophage cells previously challenged with LPS in terms of oxidative distress, release of pro-inflammatory cytokines, and activation of regulated cell death pathways. Our results showed that LPS potentiates the dose-dependent UV-A-induced oxidative distress and cytokine release, in addition to amplifying the regulated (autophagy and apoptosis) and non-regulated (necrosis) mechanisms of cell death, indicating that a previous inflammatory stimulus potentiates UV-A-induced cell damage. We discuss these results in terms of the current-available skin care strategies.

An improved method for the detection of myeloperoxidase chlorinating activity in biological systems using the redox probe hydroethidine

Conversion of the redox probe hydroethidine (HE) to 2-chloroethidium (2-Cl-E⁺) by myeloperoxidase (MPO)-derived hypochlorous acid (HOCl) provides comparable specificity and superior sensitivity to measurement of 3-chlorotyrosine (3-Cl-Tyr), the gold standard biomarker for MPO chlorinating activity in biological systems. However, a limitation of the former method is the complex mixture of products formed by the reaction of HE with reagent HOCl, coupled with the difficult purification of 2-Cl-E⁺ from this mixture for analytical purposes. This limitation prompted us to test whether 2-Cl-E⁺ could be formed by reaction of HE with the strong and widely used chlorinating agent, N-chlorosuccinimide (NCS). Unexpectedly, such reaction yielded 2-chlorohydroethidine (2-Cl-HE) as the major product in addition to 2-Cl-E⁺, as assessed by high performance liquid chromatography (HPLC), mass spectrometry (MS), and nuclear magnetic resonance (NMR). 2-Cl-HE was also observed to be the major chlorination product formed from HE with both reagent and enzymatically generated HOCl, just as it was formed ex vivo in different healthy and diseased mouse and human tissues upon incubation with glucose/glucose oxidase to generate a flux of hydrogen peroxide (H₂O₂). Quantification of 2-Cl-HE plus 2-Cl-E⁺ improved the sensitivity of the HE-based method compared with measurement of only 2-Cl-E⁺. Moreover, 2-chlorodimidium (2-Cl-D⁺) was developed as a practical internal standard instead of the previously used internal standard, deuterated 2-Cl-E⁺ (d₅-2-Cl-E⁺). Overall, the present study describes an improved method for the detection of MPO/chlorinating activity in biological systems of health and disease.

In vitro aging of stallion spermatozoa during prolonged storage at 5°C

Artificial insemination with chilled stallion semen is hampered by a limited period of maximum fertility maintenance (24-48 h). This study used multiparametric flow cytometry to simultaneously measure reactive oxygen species (ROS) production, mitochondrial function or [Ca²⁺ ]_i and plasma membrane fluidity in viable, acrosome-intact spermatozoa, with the aim of providing insight into changes in sperm function during storage at 5°C. High proportions of viable and acrosome-intact spermatozoa (71 ± 8%) remained after 96 h of storage demonstrating that the basic integrity of the cells was well preserved (n = 17 stallions). In addition, more than 90% of viable, acrosome-intact spermatozoa had active mitochondria and low intra-cellular or mitochondrial ROS levels. By contrast, the percentage of viable, acrosome-intact sperm with low plasma membrane fluidity and low [Ca²⁺ ]_i decreased over time (1 h: 63 ± 16%, 96 h: 29 ± 18%; p < 0.05). The [Ca²⁺ ]_i in viable sperm rose 3.1-fold (p < 0.05) over the 4 days, and fewer spermatozoa responded to bicarbonate stimulation (1 h: 46 ± 17%, 96 h: 19 ± 12%) with an increase in plasma membrane fluidity following prolonged storage. Overall, prolonged storage of stallion semen at 5°C resulted in disturbed calcium homeostasis and increased plasma membrane fluidity. The decline in fertility of stallion semen during cooled-storage may therefore relate to aspects of in vitro aging (changes in plasma membrane fluidity and intracellular calcium) which impairs capacitation-associated cell functions.

Structure and biological evaluation of Caenorhabditis elegans CISD-1/mitoNEET, a KLP-17 tail domain homologue, supports attenuation of paraquat-induced oxidative stress through a p38 MAPK-mediated antioxidant defense response

CISD-1/mitoNEET is an evolutionarily conserved outer mitochondrial membrane [2Fe-2S] protein that regulates mitochondrial function and morphology. The [2Fe-2S] clusters are redox reactive and shown to mediate oxidative stress in vitro and in vivo. However, there is limited research studying CISD-1/mitoNEET mediation of oxidative stress in response to environmental stressors. In this study, we have determined the X-ray crystal structure of Caenorhabditis elegans CISD-1/mitoNEET homologue and evaluated the mechanisms of oxidative stress resistance to the pro-oxidant paraquat in age-synchronized populations by generating C. elegans gain and loss of function CISD-1 models. The structure of the C. elegans CISD-1/mitoNEET soluble domain refined at 1.70-Å resolution uniquely shows a reversible disulfide linkage at the homo-dimeric interface and also represents the N-terminal tail domain for dimerization of the cognate kinesin motor protein KLP-17 involved in chromosome segregation dynamics and germline development of the nematode. Moreover, overexpression of CISD-1/mitoNEET in C. elegans has revealed beneficial effects on oxidative stress resistance against paraquat-induced reactive oxygen species generation, corroborated by increased activation of the p38 mitogen-activated protein kinase (MAPK) signaling cascade.

Methods for detection of mitochondrial reactive oxygen species in senescent cells

Cellular senescence is a pathophysiological process with multifaceted effects. It is involved in wound healing, aging and age-related diseases as well as cancer. On the one hand, senescence is considered as barrier against tumorigenesis by inducing an irreversible/prolonged cell cycle arrest. On the other hand, it may promote tumorigenesis when senescent cells accumulate genomic instability and bypass this cell cycle arrest. Interestingly, the bystander effects mediate the propagation of the genetic instability from senescent cells to their environment through the SASP (Senescence Associated Secretory Phenotype) including proinflammatory cytokines, proteases, growth factors and Reactive Oxygen Species 'ROS.' From several markers explored to detect senescent cells (β-galactosidase, p16, p21, p53, heterochromatin foci, DNA damage,…), ROS arouse particular interest because of their involvement at the chronic supraphysiological level, in the induction and maintain of DNA damage, inflammation, cell cycle disruption and epigenetic instability. In this context, the choice of methods to detect ROS in senescent cells is of particular interest and must take into account relevant parameters as well as the specificity for each species of ROS and the subcellular localization of ROS production. In this chapter, we introduce senescence and ROS, we briefly discuss the advantages and the shortcomings of methods routinely used to detect ROS. In addition, we describe the protocol to detect ROS at mitochondrial level (using the MitoSOX staining) in the BCPAP cell line (from human papillary thyroid carcinomas) expressing BRAFV600E oncogene known to trigger senescence.

Reactive oxygen species function as signaling molecules in controlling plant development and hormonal responses

Reactive oxygen species (ROS) serve as second messengers in plant signaling pathways to remodel plant growth and development. New insights into how enzymatic ROS-producing machinery is regulated by hormones or localized during development have provided a framework for understanding the mechanisms that control ROS accumulation patterns. Signaling-mediated increases in ROS can then modulate the activity of proteins through reversible oxidative modification of specific cysteine residues. Plants also control the synthesis of antioxidants, including plant-specialized metabolites, to further define when, where, and how much ROS accumulate. The availability of sophisticated imaging capabilities, combined with a growing tool kit of ROS detection technologies, particularly genetically encoded biosensors, sets the stage for improved understanding of ROS as signaling molecules.

SOLUBLE GUANYLYL CYCLASE ACTIVATION RESCUES HYPEROXIA-INDUCED DYSFUNCTION OF VASCULAR RELAXATION

ABSTRACT

Introduction: Perioperative alterations in perfusion lead to ischemia and reperfusion injury, and supplemental oxygen is administered during surgery to limit hypoxic injury but can lead to hyperoxia. We hypothesized that hyperoxia impairs endothelium-dependent and endothelium-independent vasodilation but not the vasodilatory response to heme-independent soluble guanylyl cyclase activation. Methods: We measured the effect of oxygen on vascular reactivity in mouse aortas. Mice were ventilated with 21% (normoxia), 60% (moderate hyperoxia), or 100% (severe hyperoxia) oxygen during 30 minutes of renal ischemia and 30 minutes of reperfusion. After sacrifice, the thoracic aorta was isolated, and segments mounted on a wire myograph. We measured endothelium-dependent and endothelium-independent vasodilation with escalating concentrations of acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, and we measured the response to heme-independent soluble guanylyl cyclase activation with cinaciguat. Vasodilator responses to each agonist were quantified as the maximal theoretical response ( Emax ) and the effective concentration to elicit 50% relaxation (EC 50 ) using a sigmoid model and nonlinear mixed-effects regression. Aortic superoxide was measured with dihydroethidium probe and high-performance liquid chromatography quantification of the specific superoxide product 2-hydroxyethidium. Results: Hyperoxia impaired endothelium-dependent (ACh) and endothelium-independent (SNP) vasodilation compared with normoxia and had no effect on cinaciguat-induced vasodilation. The median ACh Emax was 76.4% (95% confidence interval = 69.6 to 83.3) in the normoxia group, 53.5% (46.7 to 60.3) in the moderate hyperoxia group, and 53.1% (46.3 to 60.0) in the severe hyperoxia group ( P < 0.001, effect across groups), while the ACh EC 50 was not different among groups. The SNP Emax was 133.1% (122.9 to 143.3) in normoxia, 128.3% (118.1 to 138.6) in moderate hyperoxia, and 114.8% (104.6 to 125.0) in severe hyperoxia ( P < 0.001, effect across groups), and the SNP EC 50 was 0.38 log M greater in moderate hyperoxia than in normoxia (95% confidence interval = 0.18 to 0.58, P < 0.001). Cinaciguat Emax and EC 50 were not different among oxygen treatment groups (median range Emax = 78.0% to 79.4% and EC 50 = -18.0 to -18.2 log M across oxygen groups). Aorta 2-hydroxyethidium was 1419 pmol/mg of protein (25th-75th percentile = 1178-1513) in normoxia, 1993 (1831-2473) in moderate hyperoxia, and 2078 (1936-2922) in severe hyperoxia ( P = 0.008, effect across groups). Conclusions: Hyperoxia, compared with normoxia, impaired endothelium-dependent and endothelium-independent vasodilation but not the response to heme-independent soluble guanylyl cyclase activation, and hyperoxia increased vascular superoxide production. Results from this study could have important implications for patients receiving high concentrations of oxygen and at risk for ischemia reperfusion-mediated organ injury.

Mitochondria-Targeted Compounds to Assess and Improve Human Sperm Function

Significance: Currently 10%-15% of couples in reproductive age face infertility issues. More importantly, male factor contributes to 50% of these cases (either alone or in combination with female causes). Among various reasons, impaired sperm function is the main cause for male infertility. Furthermore, mitochondrial dysfunction and oxidative stress due to increased reactive oxygen species (ROS) production, particularly of mitochondrial origin, are believed to be the main contributors. Recent Advances: Mitochondrial dysfunction, particularly due to increased ROS production, has often been linked to impaired sperm function/quality. For decades, different methods and approaches have been developed to assess mitochondrial features that might correlate with sperm functionality. This connection is now completely accepted, with mitochondrial functionality assessment used more commonly as a readout of sperm functionality. More recently, mitochondria-targeted compounds are on the frontline for both assessment and therapeutic approaches. Critical Issues: In this review, we summarize the current methods for assessing key mitochondrial parameters known to reflect sperm quality as well as therapeutic strategies using mitochondria-targeted antioxidants aiming to improve sperm function in various situations, particularly after sperm cryopreservation. Future Directions: Although more systematic research is needed, mitochondria-targeted compounds definitely represent a promising tool to assess as well as to protect and improve sperm function. Antioxid. Redox Signal. 37, 451-480.

Molecular Mechanisms of Cytotoxicty of NCX4040, the Non-Steroidal Anti-Inflammatory NO-Donor, in Human Ovarian Cancer Cells

NCX4040, the non-steroidal anti-inflammatory-NO donor, is cytotoxic to several human tumors, including ovarian tumor cells. We have found that NCX4040 is also cytotoxic against both OVCAR-8 and its adriamycin resistant (NCI/ADR-RES) tumor cell lines. Here, we have examined mechanism(s) for the cytotoxicity of NCX4040 in OVCAR-8 and NCI/ADR-RES cell lines. We found that NCX4040 induced significant apoptosis in both cell lines. Furthermore, NCX4040 treatment caused significant depletion of cellular glutathione, causing oxidative stress due to the formation of reactive oxygen/nitrogen species (ROS/RNS). Significantly more ROS/RNS were detected in OVCAR-8 cells than in NCI/ADR-RES cells which may have resulted from increased activities of SOD, glutathione peroxidase and transferases expressed in NCI/ADR-RES cells. NCX4040 treatment resulted in the formation of double-strand DNA breaks in both cells; however, more of these DNA breaks were detected in OVCAR-8 cells. RT-PCR studies indicated that NCX4040-induced DNA damage was not repaired as efficiently in NCI/ADR-RES cells as in OVCAR-8 cells which may lead to a differential cell death. Pretreatment of OVCAR-8 cells with N-acetylcysteine (NAC) significantly decreased cytotoxicity of NCX4040 in OVCAR-8 cells; however, NAC had no effects on NCX4040 cytotoxicity in NCI/ADR-RES cells. In contrast, FeTPPS, a peroxynitrite scavenger, completely blocked NCX4040-induced cell death in both cells, suggesting that NCX4040-induced cell death could be mediated by peroxynitrite formed from NCX4040 following cellular metabolism.

HIV Promotes Neurocognitive Impairment by Damaging the Hippocampal Microvessels

Current evidence suggests that mild cerebrovascular changes could induce neurodegeneration and contribute to HIV-associated neurocognitive disease (HAND) in HIV patients. We investigated both the quantitative and qualitative impact of HIV infection on brain microvessels, especially on hippocampal microvessels, which are crucial for optimal O2 supply, and thus for maintaining memory and cognitive abilities. The results obtained using cultured human brain microvascular endothelial cells (HBMEC) were reproduced using a suitable mouse model and autopsied human HIV hippocampus. In HBMEC, we found significantly higher oxidative stress-dependent apoptotic cell loss following 5 h of treatment of GST-Tat (1 µg/ml) compared to GST (1 µg/ml) control. We noticed complete recovery of HBMEC cells after 24 h of GST-Tat treatment, due to temporal degradation or inactivation of GST-Tat. Interestingly, we found a sustained increase in mitochondrial oxidative DNA damage marker 8-OHdG, as well as an increase in hypoxia-inducible factor hypoxia-inducible factor-1α (HIF-1α). In our mouse studies, upon short-term injection of GST-Tat, we found the loss of small microvessels (mostly capillaries) and vascular endothelial growth factor (VEGF), but not large microvessels (arterioles and venules) in the hippocampus. In addition to capillary loss, in the post-mortem HIV-infected human hippocampus, we observed large microvessels with increased wall cells and perivascular tissue degeneration. Together, our data show a crucial role of Tat in inducing HIF-1α-dependent inhibition of mitochondrial transcriptional factor A (TFAM) and dilated perivascular space. Thus, our results further define the underlying molecular mechanism promoting mild cerebrovascular disease, neuropathy, and HAND pathogenesis in HIV patients.

Defining roles of specific reactive oxygen species (ROS) in cell biology and physiology

'Reactive oxygen species' (ROS) is a generic term that defines a wide variety of oxidant molecules with vastly different properties and biological functions that range from signalling to causing cell damage. Consequently, the description of oxidants needs to be chemically precise to translate research on their biological effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues associated with identifying the physiological roles of oxidants, focusing on H₂O₂ and O₂^.-. The generic term ROS should not be used to describe specific molecular agents. We also advocate for greater precision in measurement of H₂O₂, O₂^.- and other oxidants, along with more specific identification of their signalling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signalling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiological O₂ levels should be maintained in cell culture to better mimic in vivo redox reactions associated with specific cell types. Use of precise definitions and analytical tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biology.

A new mitochondrial probe combining pyrene and a triphenylphosphonium salt for cellular oxygen and free radical detection via fluorescence lifetime measurements

To improve and diversify the quantification of reactive oxygen species (ROS) in mitochondria of single cells, we connected pyrene derivatives (PB) to a triphenylphosphonium salt (TPP⁺) as a mitochondrial vector forming PB-TPP⁺ probes. Two pyrene isomers with the n-butyltriphenylphosphonium moieties attached at their 1- or 2- positions were synthesized and characterized. Using the long fluorescence lifetime of pyrene, it was possible to monitor the variation of cellular free radicals and oxygen and to follow the reversibility of both quenchers in real-time. We compared the behavior of these new probes to the previously published pyrene-probes, functionalized by a mitochondrial-penetrating peptide, allowing their transfer to the mitochondria (Mito-PB) or to the cytosolic membrane for pyrene butyric acid (PBA). The high cellular uptake of the new probes allows cells to be loaded with an initial concentration 40 times lower than that for Mito-PB probes, without inducing perturbations in cell growth. The variation in free radicals and oxygen levels was monitored within cells under different stress conditions through the fluorescence lifetime of the new TPP⁺-based probes giving comparable results to those obtained for MPP-based probes. However, at a loading concentration as low as 25 nM, our technique allows the detection of increased production of free radicals in the mitochondria in the presence of the TPP⁺ vector, a warning to the user of this well-known vector.

Overview of oxidative stress findings in hepatic encephalopathy: From cellular and ammonium-based animal models to human data

Oxidative stress is a natural phenomenon in the body. Under physiological conditions intracellular reactive oxygen species (ROS) are normal components of signal transduction cascades, and their levels are maintained by a complex antioxidants systems participating in the in-vivo redox homeostasis. Increased oxidative stress is present in several chronic diseases and interferes with phagocytic and nervous cell functions, causing an up-regulation of cytokines and inflammation. Hepatic encephalopathy (HE) occurs in both acute liver failure (ALF) and chronic liver disease. Increased blood and brain ammonium has been considered as an important factor in pathogenesis of HE and has been associated with inflammation, neurotoxicity, and oxidative stress. The relationship between ROS and the pathophysiology of HE is still poorly understood. Therefore, sensing ROS production for a better understanding of the relationship between oxidative stress and functional outcome in HE pathophysiology is critical for determining the disease mechanisms, as well as to improve the management of patients. This review is emphasizing the important role of oxidative stress in HE development and documents the changes occurring as a consequence of oxidative stress augmentation based on cellular and ammonium-based animal models to human data.

Comprehensive Flow-Cytometric Quality Assessment of Ram Sperm Intended for Gene Banking Using Standard and Novel Fertility Biomarkers

Flow cytometry becomes a common method for analysis of spermatozoa quality. Standard sperm characteristics such as viability, acrosome and chromatin integrity, oxidative damage (ROS) etc. can be easily assess in any animal semen samples. Moreover, several fertility-related markers were observed in humans and some other mammals. However, these fertility biomarkers have not been previously studied in ram. The aim of this study was to optimize the flow-cytometric analysis of these standard and novel markers in ram semen. Ram semen samples from Slovak native sheep breeds were analyzed using CASA system for motility and concentration and were subsequently stained with several fluorescent dyes or specific antibodies to evaluate sperm viability (SYBR-14), apoptosis (Annexin V, YO-PRO-1, FLICA, Caspases 3/7), acrosome status (PNA, LCA, GAPDHS), capacitation (merocyanine 540, FLUO-4 AM), mitochondrial activity (MitoTracker Green, rhodamine 123, JC-1), ROS (CM-H2DCFDA, DHE, MitoSOX Red, BODIPY), chromatin (acridine orange), leukocyte content, ubiquitination and aggresome formation, and overexpression of negative biomarkers (MKRN1, SPTRX-3, PAWP, H3K4me2). Analyzed semen samples were divided into two groups according to viability as indicators of semen quality: Group 1 (viability over 60%) and Group 2 (viability under 60%). Significant (p < 0.05) differences were found between these groups in sperm motility and concentration, apoptosis, acrosome integrity (only PNA), mitochondrial activity, ROS production (except for DHE), leukocyte and aggresome content, and high PAWP expression. In conclusion, several standard and novel fluorescent probes have been confirmed to be suitable for multiplex ram semen analysis by flow cytometry as well as several antibodies have been validated for the specific detection of ubiquitin, PAWP and H3K4me2 in ram spermatozoa.

A reversible mitochondrial complex I thiol switch mediates hypoxic avoidance behavior in C. elegans

C. elegans react to metabolic distress caused by mismatches in oxygen and energy status via distinct behavioral responses. At the molecular level, these responses are coordinated by under-characterized, redox-sensitive processes, thought to initiate in mitochondria. Complex I of the electron transport chain is a major site of reactive oxygen species (ROS) production and is canonically associated with oxidative damage following hypoxic exposure. Here, we use a combination of optogenetics and CRISPR/Cas9-mediated genome editing to exert spatiotemporal control over ROS production. We demonstrate a photo-locomotory remodeling of avoidance behavior by local ROS production due to the reversible oxidation of a single thiol on the complex I subunit NDUF-2.1. Reversible thiol oxidation at this site is necessary and sufficient for the behavioral response to hypoxia, does not respond to ROS produced at more distal sites, and protects against lethal hypoxic exposure. Molecular modeling suggests that oxidation at this thiol residue alters the ability for NDUF-2.1 to coordinate electron transfer to coenzyme Q by destabilizing the Q-binding pocket, causing decreased complex I activity. Overall, site-specific ROS production regulates behavioral responses and these findings provide a mechanistic target to suppress the detrimental effects of hypoxia.

Relationship of superoxide dismutase to rotator cuff injury/tear in a rat model

Rotator cuff degeneration is one of the several factors that lead to rotator cuff tears. Oxidative stress and superoxide dismutase have been reported to be related to rotator cuff degeneration; however, the precise mechanism still remains unclear. In this study, we investigated the relationship of oxidative stress and superoxide dismutase to the degeneration of the rotator cuff using rat models. Eighty-four rats were used to create a collagenase-induced rotator cuff injury model (injury model) and a rotator cuff tear model (tear model). The controls were administered saline and had only a deltoid incision, respectively. We evaluated degeneration morphology of the rotator cuff using a degeneration score; dihydroethidium fluorescence intensity, which detects oxidative stress; gene expression; and superoxide dismutase activity. The rotator cuffs in the injury and tear models significantly increased degeneration scores and dihydroethidium fluorescence intensity. On the other hand, gene expression of superoxide dismutase isoform, superoxide dismutase 1, and superoxide dismutase activity were significantly decreased in the injury model but showed no significant difference in the tear model. These findings suggested that superoxide dismutase might not be associated with rotator cuff degeneration after tear but may be involved in degenerative rotator cuff without tear. However, we found that rotator cuff degeneration involves oxidative stress both with and without tear. Based on these findings, it is presumed that different treatments may be appropriate, depending on the state of rotator cuff degeneration, because the mechanisms of the degeneration may be different.