In vivo detection of free radicals in mouse septic encephalopathy using molecular MRI and immuno-spin trapping

Application of magnetic resonance imaging-related techniques in the diagnosis of sepsis-associated encephalopathy: present status and prospect

Sepsis-associated encephalopathy (SAE) refers to diffuse brain dysfunction secondary to systemic infection without central nervous system infection. The early diagnosis of SAE remains a major clinical problem, and its diagnosis is still exclusionary. Magnetic resonance imaging (MRI) related techniques, such as magnetic resonance spectroscopy (MRS), molecular MRI (mMRI), arterial spin-labeling (ASL), fluid-attenuated inversion recovery (FLAIR), and diffusion-weighted imaging (DWI), currently provide new options for the early identification of SAE. This review collected clinical and basic research and case reports related to SAE and MRI-related techniques in recent years, summarized and analyzed the basic principles and applications of MRI technology in diagnosing SAE, and provided a basis for diagnosing SAE by MRI-related techniques.

In vivo Detection of Macromolecule Free Radicals in Mouse Sepsis-Associated Encephalopathy Using a New MRI and Immunospin Trapping Strategy

INTRODUCTION

Free radicals in oxidative stress are known to play a pathogenic role in sepsis. A major clinical challenge associated with sepsis is sepsis-associated encephalopathy (SAE). The rapid increase of free radicals in the brain promotes SAE progression. Here, macromolecule free radicals in the mouse brain were uniquely detected by immunospin trapping (IST) and magnetic resonance imaging (MRI).

METHODS

The new strategy uses spin trapping agent DEPMPO-biotin to capture macromolecule free radicals in lesions and form biotin-DEPMPO-radical adducts. Then, a targeting MRI probe, avidin-BSA@Gd-ESIO, was used to detect the radical adducts through the highly specific binding of avidin and biotin. The avidin-BSA@Gd-ESIO probe was synthesized and systematically characterized. The detection capability of the new strategy was evaluated in vitro and in vivo using a confocal microscope and a 7T MRI, respectively.

RESULTS

In reactive oxygen species (ROS)-induced microglial cells, the accumulation of the avidin-BSA@Gd-ESIO probe in the DEPMPO-biotin-treated group was significantly higher than that of control groups. In vivo MRI T1 signal intensities were significantly higher within the hippocampus, striatum, and medial cortex of the brain in mice with a mild or severe degree of sepsis compared with the sham control group. Histological analysis validated that the distribution of the avidin-BSA@Gd-ESIO probe in brain tissue slices was consistent with the MRI images. The fluorescence signals of ROS and avidin-BSA@Gd-ESIO probe were overlapped and visualized using immunofluorescent staining. By evaluating the T1 signal changes over time in different areas of the brain, we estimated the optimal MRI detection time to be 30 minutes after the probe administration.

DISCUSSION

This method can be applied specifically to assess the level of macromolecular free radicals in vivo in a simple and stable manner, providing a pathway for a more comprehensive understanding of the role of free radicals in SAE.

Central role of microglia in sepsis-associated encephalopathy: From mechanism to therapy

Sepsis-associated encephalopathy (SAE) is a cognitive impairment associated with sepsis that occurs in the absence of direct infection in the central nervous system or structural brain damage. Microglia are thought to be macrophages of the central nervous system, devouring bits of neuronal cells and dead cells in the brain. They are activated in various ways, and microglia-mediated neuroinflammation is characteristic of central nervous system diseases, including SAE. Here, we systematically described the pathogenesis of SAE and demonstrated that microglia are closely related to the occurrence and development of SAE. Furthermore, we comprehensively discussed the function and phenotype of microglia and summarized their activation mechanism and role in SAE pathogenesis. Finally, this review summarizes recent studies on treating cognitive impairment in SAE by blocking microglial activation and toxic factors produced after activation. We suggest that targeting microglial activation may be a putative treatment for SAE.

A Toolbox to Investigate the Impact of Impaired Oxygen Delivery in Experimental Disease Models

Impaired oxygen utilization is the underlying pathophysiological process in different shock states. Clinically most important are septic and hemorrhagic shock, which comprise more than 75% of all clinical cases of shock. Both forms lead to severe dysfunction of the microcirculation and the mitochondria that can cause or further aggravate tissue damage and inflammation. However, the detailed mechanisms of acute and long-term effects of impaired oxygen utilization are still elusive. Importantly, a defective oxygen exploitation can impact multiple organs simultaneously and organ damage can be aggravated due to intense organ cross-talk or the presence of a systemic inflammatory response. Complexity is further increased through a large heterogeneity in the human population, differences in genetics, age and gender, comorbidities or disease history. To gain a deeper understanding of the principles, mechanisms, interconnections and consequences of impaired oxygen delivery and utilization, interdisciplinary preclinical as well as clinical research is required. In this review, we provide a "tool-box" that covers widely used animal disease models for septic and hemorrhagic shock and methods to determine the structure and function of the microcirculation as well as mitochondrial function. Furthermore, we suggest magnetic resonance imaging as a multimodal imaging platform to noninvasively assess the consequences of impaired oxygen delivery on organ function, cell metabolism, alterations in tissue textures or inflammation. Combining structural and functional analyses of oxygen delivery and utilization in animal models with additional data obtained by multiparametric MRI-based techniques can help to unravel mechanisms underlying immediate effects as well as long-term consequences of impaired oxygen delivery on multiple organs and may narrow the gap between experimental preclinical research and the human patient.

Fluorescent Nanodiamonds for Detecting Free-Radical Generation in Real Time during Shear Stress in Human Umbilical Vein Endothelial Cells

Free-radical generation is suspected to play a key role in cardiovascular diseases. Another crucial factor is shear stress. Human umbilical vein endothelial cells (HUVECS), which form the lining of blood vessels, require a physiological shear stress to activate many vasoactive factors. These are needed for maintaining vascular cell functions such as nonthrombogenicity, regulation of blood flow, and vascular tone. Additionally, blood clots form at regions of high shear stress within a blood vessel. Here, we use a new method called diamond magnetometry which allows us to measure the dynamics of free-radical generation in real time under shear stress. This quantum sensing technique allows free-radical detection with nanoscale resolution at the single-cell level. We investigate radical formation in HUVECs in a microfluidic environment under different flow conditions typically found in veins and arteries. Here, we looked into free-radical formation before, during, and after flow. We found that the free-radical production varied depending on the flow conditions. To confirm the magnetometry results and to differentiate between radicals, we performed conventional fluorescent reactive oxygen species (ROS) assays specific for superoxide, nitric oxide, and overall ROS.

Oklahoma Nathan Shock Aging Center - assessing the basic biology of aging from genetics to protein and function

The Oklahoma Shock Nathan Shock Center is designed to deliver unique, innovative services that are not currently available at most institutions. The focus of the Center is on geroscience and the development of careers of young investigators. Pilot grants are provided through the Research Development Core to junior investigators studying aging/geroscience throughout the USA. However, the services of our Center are available to the entire research community studying aging and geroscience. The Oklahoma Nathan Shock Center provides researchers with unique services through four research cores. The Multiplexing Protein Analysis Core uses the latest mass spectrometry technology to simultaneously measure the levels, synthesis, and turnover of hundreds of proteins associated with pathways of importance to aging, e.g., metabolism, antioxidant defense system, proteostasis, and mitochondria function. The Genomic Sciences Core uses novel next-generation sequencing that allows investigators to study the effect of age, or anti-aging manipulations, on DNA methylation, mitochondrial genome heteroplasmy, and the transcriptome of single cells. The Geroscience Redox Biology Core provides investigators with a comprehensive state-of-the-art assessment of the oxidative stress status of a cell, e.g., measures of oxidative damage and redox couples, which are important in aging as well as many major age-related diseases as well as assays of mitochondrial function. The GeroInformatics Core provides investigators assistance with data analysis, which includes both statistical support as well as analysis of large datasets. The Core also has developed number of unique software packages to help with interpretation of results and discovery of new leads relevant to aging. In addition, the Geropathology Research Resource in the Program Enhancement Core provides investigators with pathological assessments of mice using the recently developed Geropathology Grading Platform.

Neuroinflammation in Sepsis: Molecular Pathways of Microglia Activation

Frequently underestimated, encephalopathy or delirium are common neurological manifestations associated with sepsis. Brain dysfunction occurs in up to 80% of cases and is directly associated with increased mortality and long-term neurocognitive consequences. Although the central nervous system (CNS) has been classically viewed as an immune-privileged system, neuroinflammation is emerging as a central mechanism of brain dysfunction in sepsis. Microglial cells are major players in this setting. Here, we aimed to discuss the current knowledge on how the brain is affected by peripheral immune activation in sepsis and the role of microglia in these processes. This review focused on the molecular pathways of microglial activity in sepsis, its regulatory mechanisms, and their interaction with other CNS cells, especially with neuronal cells and circuits.

Detection and structural analysis of lipid-derived radicals in vitro and in vivo

Lipids can be oxidized by reactive oxygen species, resulting in lipid peroxidation and the formation of reactive metabolites such as lipid-derived electrophiles. These products have been reported to induce inflammation, angiogenesis, and ferroptosis. Lipid peroxidation can produce many different products, each of which performs a different function, and which can be challenging to detect in vivo. The initial products of lipid oxidation are lipid-derived radicals, which can cause extensive chain reactions leading to lipid peroxidation. Hence, the ability to detect lipid radicals may provide information about this important class of molecules and the mechanism by which they cause cellular and tissue damage in a wide range of oxidative conditions. In this review, we report recent scientific advances in the detection of lipid-derived radicals in vitro and in cultured cells. We also introduce the possibility of visualization and structural analysis of lipid-derived radicals generated not only in in cells but also in animal tissue samples from oxidative disease models, using fluorescence-based lipid radicals' detection probes. We anticipate that the various innovative techniques summarized in this paper will be applied and further developed to clarify the role of lipid peroxidation in the pathogenesis of oxidative stress-associated diseases.

In vivo and ex vivo assessment of bladder hyper-permeability and using molecular targeted magnetic resonance imaging to detect claudin-2 in a mouse model for interstitial cystitis

OBJECTIVES

To determine if the URO-MCP-1 mouse model for bladder IC/BPS is associated with in vivo bladder hyper-permeability, as measured by contrast-enhanced MRI (CE-MRI), and assess whether molecular-targeted MRI (mt-MRI) can visualize in vivo claudin-2 expression as a result of bladder hyper-permeability. Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic, painful condition of the bladder that affects primarily women. It is known that permeability plays a substantial role in IC/BPS. Claudins are tight junction membrane proteins that are expressed in epithelia and endothelia and form paracellular barriers and pores that determine tight junction permeability. Claudin-2 is a molecular marker that is associated with increased hyperpermeability in the urothelium.

MATERIALS AND METHODS

CE-MRI was used to measure bladder hyper-permeability in the URO-MCP-1 mice. A claudin-2-specific mt-MRI probe was used to assess in vivo levels of claudin-2. The mt-MRI probe consists of an antibody against claudin-2 conjugated to albumin that had Gd-DTPA (gadolinium diethylenetriamine pentaacetate) and biotin attached. Verification of the presence of the mt-MRI probe was done by targeting the biotin moiety for the probe with streptavidin-horse radish peroxidase (SA-HRP). Trans-epithelial electrical resistance (TEER) was also used to assess bladder permeability.

RESULTS

The URO-MCP-1 mouse model for IC/BPS was found to have a significant increase in bladder permeability, following liposaccharide (LPS) exposure, compared to saline-treated controls. mt-MRI- and histologically-detectable levels of the claudin-2 probe were found to increase with LPS -induced bladder urothelial hyper-permeability in the URO-MCP-1 IC mouse model. Levels of protein expression for claudin-2 were confirmed with immunohistochemistry and immunofluorescence imaging. Claudin-2 was also found to highly co-localize with zonula occlidens-1 (ZO-1), a tight junction protein.

CONCLUSION

The combination of CE-MRI and TEER approaches were able to demonstrate hyper-permeability, a known feature associated with some IC/BPS patients, in the LPS-exposed URO-MCP-1 mouse model. This MRI approach could be clinically translated to establish which IC/BPS patients have bladder hyper-permeability and help determine therapeutic options. In addition, the in vivo molecular-targeted imaging approach can provide invaluable information to enhance our understanding associated with bladder urothelium hyper-permeability in IC/BPS patients, and perhaps be used to assist in developing further therapeutic strategies.

Sepsis and Cerebral Dysfunction: BBB Damage, Neuroinflammation, Oxidative Stress, Apoptosis and Autophagy as Key Mediators and the Potential Therapeutic Approaches

Sepsis-associated cerebral dysfunction is complex pathophysiology, generated from primary infections that are developed elsewhere in the body. The neonates, elderly population and chronically ill and long-term hospitalized patients are predominantly vulnerable to sepsis and related cerebral damage. Generally, electrophysiological recordings, severity and sedation scales, computerized imaging and spectroscopy techniques are used for its detection and diagnosis. About the underlying mechanisms, enhanced blood-brain barrier permeability and metalloprotease activity, tight junction protein loss and endothelial cell degeneration promote the influx of inflammatory and toxic mediators into the brain, triggering cerebrovascular damage. An altered neutrophil count and phenotype further dysregulate the normal neuroimmune responses and neuroendocrine stability via modulated activation of protein kinase C-delta, nuclear factor kappa-B and sphingolipid signaling. Glial activation, together with pro-inflammatory cytokines and chemokines and the Toll-like receptor, destabilize the immune system. Moreover, superoxides and hydroperoxides generate oxidative stress and perturb mitochondrial dynamics and ATP synthesis, propagating neuronal injury cycle. Activated mitochondrial apoptotic pathway, characterized by increased caspase-3 and caspase-9 cleavage and Bax/Bcl2 ratio in the hippocampal and cortical neurons, stimulate neurocognitive impairments. Additionally, altered LC3-II/I and P62/SQSTM1, p-mTOR, p-AMPK1 and p-ULK1 levels and dysregulated autophagosome-lysosome fusion decrease neuronal and glial energy homeostasis. The therapies and procedures for attenuating sepsis-induced brain damage include early resuscitation, cerebral blood flow autoregulation, implantable electric vagus nerve stimulation, antioxidants, statins, glucocorticoids, neuroimmune axis modulators and PKCδ inhibitors. The current review enumerates the pathophysiology of sepsis-induced brain damage, its diagnosis, the role of critical inducers and mediators and, ultimately, therapeutic measures attenuating cerebrovascular degeneration.

Anti-inflammatory agent, OKN-007, reverses long-term neuroinflammatory responses in a rat encephalopathy model as assessed by multi-parametric MRI: implications for aging-associated neuroinflammation

Lipopolysaccharide (LPS)-induced encephalopathy induces neuroinflammation. Long-term neuroinflammation is associated with aging and subsequent cognitive impairment (CI). We treated rats that had LPS-induced neuroinflammation with OKN-007, with an anti-inflammatory agent currently considered an anti-cancer investigational new drug in clinical trials for glioblastoma (GBM). Contrast-enhanced magnetic resonance imaging (MRI) (CE-MRI), perfusion MRI, and MR spectroscopy were used as methods to assess long-term (up to 6 weeks post-LPS) alterations in blood-brain barrier (BBB) permeability, microvascularity, and metabolism, respectively, and the therapeutic effect of OKN-007. A free radical-targeted molecular MRI approach was also used to detect the effect of OKN-007 on brain free radical levels at 24 h and 1 week post-LPS injection. OKN-007 was able to reduce BBB permeability in the cerebral cortex and hippocampus at 1 week post-LPS using CE-MRI. OKN-007 was able to restore vascular perfusion rates by reducing LPS-induced increased relative cerebral blood flow (rCBF) in the cortex and hippocampus regions at all time points studied (1, 3, and 6 weeks post-LPS). OKN-007 was also able to restore LPS-induced brain metabolite depletions. NAA/Cho, Cr/Cho, and Myo-Ins/Cho metabolite ratios at 1, 3, and 6 weeks post-LPS were all restored to normal levels following OKN-007 treatment. OKN-007 also reduced LPS-induced free radical levels at 24 h and 1 week post-LPS, as detected by free radical-targeted MRI. LPS-exposed rats were compared with saline-treated controls and LPS + OKN-007-treated animals. We clearly demonstrated that OKN-007 restores LPS-induced BBB dysfunction, impaired vascularity, and decreased brain metabolites, all long-term neuroinflammatory indicators, as well as decreases free radicals in a LPS-induced neuroinflammation model. OKN-007 should be considered an anti-inflammatory agent for age-associated neuroinflammation.

Immuno-spin trapping of macromolecules free radicals in vitro and in vivo - One stop shopping for free radical detection

The only general technique that allows the unambiguous detection of free radicals is electron spin resonance (ESR). However, ESR spin trapping has severe limitations especially in biological systems. The greatest limitation of ESR is poor sensitivity relative to the low steady-state concentration of free radical adducts, which in cells and in vivo is much lower than the best sensitivity of ESR. Limitations of ESR have led to an almost desperate search for alternatives to investigate free radicals in biological systems. Here we explore the use of the immuno-spin trapping technique, which combine the specificity of the spin trapping to the high sensitivity and universal use of immunological techniques. All of the immunological techniques based on antibody binding have become available for free radical detection in a wide variety of biological systems.

In Vivo and In Situ Detection of Macromolecular Free Radicals Using Immuno-Spin Trapping and Molecular Magnetic Resonance Imaging

SIGNIFICANCE

In vivo free radical imaging in preclinical models of disease has become a reality. Free radicals have traditionally been characterized by electron spin resonance (ESR) or electron paramagnetic resonance (EPR) spectroscopy coupled with spin trapping. The disadvantage of the ESR/EPR approach is that spin adducts are short-lived due to biological reductive and/or oxidative processes. Immuno-spin trapping (IST) involves the use of an antibody that recognizes macromolecular 5,5-dimethyl-pyrroline-N-oxide (DMPO) spin adducts (anti-DMPO antibody), regardless of the oxidative/reductive state of trapped radical adducts. Recent Advances: The IST approach has been extended to an in vivo application that combines IST with molecular magnetic resonance imaging (mMRI). This combined IST-mMRI approach involves the use of a spin-trapping agent, DMPO, to trap free radicals in disease models, and administration of an mMRI probe, an anti-DMPO probe, which combines an antibody against DMPO-radical adducts and an MRI contrast agent, resulting in targeted free radical adduct detection.

CRITICAL ISSUES

The combined IST-mMRI approach has been used in several rodent disease models, including diabetes, amyotrophic lateral sclerosis (ALS), gliomas, and septic encephalopathy. The advantage of this approach is that heterogeneous levels of trapped free radicals can be detected directly in vivo and in situ to pin point where free radicals are formed in different tissues.

FUTURE DIRECTIONS

The approach can also be used to assess therapeutic agents that are either free radical scavengers or generate free radicals. Smaller probe constructs and radical identification approaches are being considered. The focus of this review is on the different applications that have been studied, advantages and limitations, and future directions. Antioxid. Redox Signal. 28, 1404-1415.

Immuno-Spin Trapping-Based Detection of Oxidative Modifications in Cardiomyocytes and Coronary Endothelium in the Progression of Heart Failure in Tgαq*44 Mice

Recent studies suggest both beneficial and detrimental role of increased reactive oxygen species and oxidative stress in heart failure (HF). However, it is not clear at which stage oxidative stress and oxidative modifications occur in the endothelium in relation to cardiomyocytes in non-ischemic HF. Furthermore, most methods used to date to study oxidative stress are either non-specific or require tissue homogenization. In this study, we used immuno-spin trapping (IST) technique with fluorescent microscopy-based detection of DMPO nitrone adducts to localize and quantify oxidative modifications of the hearts from Tgαq*44 mice; a murine model of HF driven by cardiomyocyte-specific overexpression of Gαq* protein. Tgαq*44 mice and age-matched FVB controls at early, transition, and late stages of HF progression were injected with DMPO in vivo and analyzed ex vivo for DMPO nitrone adducts signals. Progressive oxidative modifications in cardiomyocytes, as evidenced by the elevation of DMPO nitrone adducts, were detected in hearts from 10- to 16-month-old, but not in 8-month-old Tgαq*44 mice, as compared with age-matched FVB mice. The DMPO nitrone adducts were detected in left and right ventricle, septum, and papillary muscle. Surprisingly, significant elevation of DMPO nitrone adducts was also present in the coronary endothelium both in large arteries and in microcirculation simultaneously, as in cardiomyocytes, starting from 10-month-old Tgαq*44 mice. On the other hand, superoxide production in heart homogenates was elevated already in 6-month-old Tgαq*44 mice and progressively increased to high levels in 14-month-old Tgαq*44 mice, while the enzymatic activity of catalase, glutathione reductase, and glutathione peroxidase was all elevated as early as in 4-month-old Tgαq*44 mice and stayed at a similar level in 14-month-old Tgαq*44. In summary, this study demonstrates that IST represents a unique method that allows to quantify oxidative modifications in cardiomyocytes and coronary endothelium in the heart. In Tgαq*44 mice with slowly developing HF, driven by cardiomyocyte-specific overexpression of Gαq* protein, an increase in superoxide production, despite compensatory activation of antioxidative mechanisms, results in the development of oxidative modifications not only in cardiomyocytes but also in coronary endothelium, at the transition phase of HF, before the end-stage disease.

Assessing long-term neuroinflammatory responses to encephalopathy using MRI approaches in a rat endotoxemia model

Sepsis-associated encephalopathy (SAE) induces neuroinflammation, which is associated with cognitive impairment (CI). CI is also correlated with aging. We used contrast-enhanced magnetic resonance imaging (MRI), perfusion MRI, and MR spectroscopy to assess long-term alterations in BBB permeability, microvascularity, and metabolism, respectively, in a rat lipopolysaccharide-induced SAE model. Free radical-targeted molecular MRI was used to detect brain radical levels at 24 h and 1 week post-LPS injection. CE-MRI showed increased Gd-DTPA uptake in LPS rat brains at 24 h in cerebral cortex, hippocampus, thalamus, and perirhinal cortex regions. Increased MRI signal intensities were observed in LPS rat brains in cerebral cortex, perirhinal cortex, and hippocampus regions 1 week post-LPS. Long-term BBB dysfunction was detected in the cerebral cortex at 6 weeks post-LPS. Increased relative cerebral blood flow (rCBF) in cortex and thalamus regions at 24 h, decreased cortical and hippocampal rCBF at 6 weeks, decreased cortical rCBF at 3 and 12 weeks, and increased thalamus rCBF at 6 weeks post-LPS, were detected. MRS indicated that LPS-exposed rat brains had decreased: NAA/Cho metabolite ratios at 1, 3, 6, and 12 weeks; Cr/Cho at 1, 3, and 12 weeks; and Myo-Ins/Cho at 1, 3, and 6 weeks post-LPS. Free radical imaging detected increased radical levels in LPS rat brains at 24 h and 1 week post-LPS. LPS-exposed rats were compared to saline-treated controls. We clearly demonstrated BBB dysfunction, impaired vascularity, and decreased brain metabolites, as measures of long-term neuroinflammatory indicators, as well as increased free radicals in a LPS-induced rat SAE model.

Brain Oxidative Stress During Experimental Sepsis Is Attenuated by Simvastatin Administration

During sepsis, brain damage is associated with oxidative stress due to overproduction of reactive oxygen species (ROS). Although there are recent reports about the benefits of statins in experimental sepsis and endotoxemia in peripheral organs, little is known about their effects in the CNS. Here, we investigated the antioxidant properties of simvastatin and its possible neuroprotective role during experimental sepsis. Male Wistar rats (250-300 g) were submitted to cecal ligation and puncture (CLP, n = 34) or remained as non-manipulated (naive, n = 34). Both groups were treated by gavage with simvastatin (20 mg/kg) or an equivalent volume of saline. The animals submitted to CLP were treated 4 days before and 48 h after surgery. One animal group was decapitated and the blood and brain were collected to quantify plasma levels of cytokines and assess astrogliosis and apoptosis in the prefrontal cortex and hippocampus. Another group was perfused with PBS (0.01 M), and the same brain structures were dissected to analyze oxidative damage. The CLP rats treated with simvastatin showed a reduction in nitric oxide (P < 0.05), IL1-β (P < 0.001), IL-6 (P < 0.01), and TBARS levels (P < 0.001) and an increase in catalase activity (P < 0.01), citrate synthase enzyme (P < 0.05), and normalized GSH/GSSG ratio. In addition, the histopathological analysis showed a reduction (P < 0.001) in reactive astrocytes and caspase 3-positive apoptotic cells. The results suggest a possible neuroprotective effect of simvastatin in structures responsible for spatial learning and memory and indicate the need for behavioral studies evaluating the impact on cognitive damage, as frequently seen in patients surviving sepsis.

Measurement of Reactive Oxygen Species, Reactive Nitrogen Species, and Redox-Dependent Signaling in the Cardiovascular System: A Scientific Statement From the American Heart Association

Reactive oxygen species and reactive nitrogen species are biological molecules that play important roles in cardiovascular physiology and contribute to disease initiation, progression, and severity. Because of their ephemeral nature and rapid reactivity, these species are difficult to measure directly with high accuracy and precision. In this statement, we review current methods for measuring these species and the secondary products they generate and suggest approaches for measuring redox status, oxidative stress, and the production of individual reactive oxygen and nitrogen species. We discuss the strengths and limitations of different methods and the relative specificity and suitability of these methods for measuring the concentrations of reactive oxygen and reactive nitrogen species in cells, tissues, and biological fluids. We provide specific guidelines, through expert opinion, for choosing reliable and reproducible assays for different experimental and clinical situations. These guidelines are intended to help investigators and clinical researchers avoid experimental error and ensure high-quality measurements of these important biological species.

Imaging free radicals in organelles, cells, tissue, and in vivo with immuno-spin trapping

The accurate and sensitive detection of biological free radicals in a reliable manner is required to define the mechanistic roles of such species in biochemistry, medicine and toxicology. Most of the techniques currently available are either not appropriate to detect free radicals in cells and tissues due to sensitivity limitations (electron spin resonance, ESR) or subject to artifacts that make the validity of the results questionable (fluorescent probe-based analysis). The development of the immuno-spin trapping technique overcomes all these difficulties. This technique is based on the reaction of amino acid- and DNA base-derived radicals with the spin trap 5, 5-dimethyl-1-pyrroline N-oxide (DMPO) to form protein- and DNA-DMPO nitroxide radical adducts, respectively. These adducts have limited stability and decay to produce the very stable macromolecule-DMPO-nitrone product. This stable product can be detected by mass spectrometry, NMR or immunochemistry by the use of anti-DMPO nitrone antibodies. The formation of macromolecule-DMPO-nitrone adducts is based on the selective reaction of free radical addition to the spin trap and is thus not subject to artifacts frequently encountered with other methods for free radical detection. The selectivity of spin trapping for free radicals in biological systems has been proven by ESR. Immuno-spin trapping is proving to be a potent, sensitive (a million times higher sensitivity than ESR), and easy (not quantum mechanical) method to detect low levels of macromolecule-derived radicals produced in vitro and in vivo. Anti-DMPO antibodies have been used to determine the distribution of free radicals in cells and tissues and even in living animals. In summary, the invention of the immuno-spin trapping technique has had a major impact on the ability to accurately and sensitively detect biological free radicals and, subsequently, on our understanding of the role of free radicals in biochemistry, medicine and toxicology.

In vivo targeted molecular magnetic resonance imaging of free radicals in diabetic cardiomyopathy within mice

Free radicals contribute to the pathogenesis of diabetic cardiomyopathy. We present a method for in vivo observation of free radical events within murine diabetic cardiomyopathy. This study reports on in vivo imaging of protein/lipid radicals using molecular MRI (mMRI) and immuno-spin trapping (IST) in diabetic cardiac muscle. To detect free radicals in diabetic cardiomyopathy, streptozotocin (STZ)-exposed mice were given 5,5-dimethyl-pyrroline-N-oxide (DMPO) and administered an anti-DMPO probe (biotin-anti-DMPO antibody-albumin-Gd-DTPA). For controls, non-diabetic mice were given DMPO (non-disease control), and administered an anti-DMPO probe; or diabetic mice were given DMPO but administered a non-specific IgG contrast agent instead of the anti-DMPO probe. DMPO administration started at 7 weeks following STZ treatment for 5 days, and the anti-DMPO probe was administered at 8 weeks for MRI detection. MRI was used to detect a significant increase (p < 0.001) in MRI signal intensity (SI) from anti-DMPO nitrone adducts in diabetic murine left-ventricular (LV) cardiac tissue, compared to controls. Regional increases in MR SI in the LV were found in the apical and upper-left areas (p < 0.01 for both), compared to controls. The biotin moiety of the anti-DMPO probe was targeted with fluorescently-labeled streptavidin to locate the anti-DMPO probe in excised cardiac tissues, which indicated elevated fluorescence only in cardiac muscle of mice administered the anti-DMPO probe. Oxidized lipids and proteins were also found to be significantly elevated (p < 0.05 for both) in diabetic cardiac muscle compared to controls. It can be concluded that diabetic mice have more heterogeneously distributed radicals in cardiac tissue than non-diabetic mice.

Protracted Oxidative Alterations in the Mechanism of Hematopoietic Acute Radiation Syndrome

The biological effects of high-dose total body ionizing irradiation [(thereafter, irradiation (IR)] are attributed to primary oxidative breakage of biomolecule targets, mitotic, apoptotic and necrotic cell death in the dose-limiting tissues, clastogenic and epigenetic effects, and cascades of functional and reactive responses leading to radiation sickness defined as the acute radiation syndrome (ARS). The range of remaining and protracted injuries at any given radiation dose as well as the dynamics of post-IR alterations is tissue-specific. Therefore, functional integrity of the homeostatic tissue barriers may decline gradually within weeks in the post-IR period culminating with sepsis and failure of organs and systems. Multiple organ failure (MOF) leading to moribundity is a common sequela of the hemotapoietic form of ARS (hARS). Onset of MOF in hARS can be presented as “two-hit phenomenon” where the “first hit” is the underlying consequences of the IR-induced radiolysis in cells and biofluids, non-septic inflammation, metabolic up-regulation of pro-oxidative metabolic reactions, suppression of the radiosensitive hematopoietic and lymphoid tissues and the damage to gut mucosa and vascular endothelium. While the “second hit” derives from bacterial translocation and spread of the bacterial pathogens and inflammagens through the vascular system leading to septic inflammatory, metabolic responses and a cascade of redox pro-oxidative and adaptive reactions. This sequence of events can create a ground for development of prolonged metabolic, inflammatory, oxidative, nitrative, and carbonyl, electrophilic stress in crucial tissues and thus exacerbate the hARS outcomes. With this perspective, the redox mechanisms, which can mediate the IR-induced protracted oxidative post-translational modification of proteins, oxidation of lipids and carbohydrates and their countermeasures in hARS are subjects of the current review. Potential role of ubiquitous, radioresistant mesenchymal stromal cells in the protracted responses to IR and IR-related septicemia is also discussed.