In vivo redox imaging of dextran sodium sulfate-induced colitis in mice using Overhauser-enhanced magnetic resonance imaging

BODIPY-Based Ratiometric Fluorescent Probe for Sensing Peroxynitrite in Inflammatory Cells and Tissues

Peroxynitrite (ONOO-) plays an important role in many physiological and pathological processes. Excessive ONOO- in cells leads to oxidative stress and inflammation. However, precise monitoring of ONOO- levels in specific organelles (e.g., mitochondria) is still lacking and urgently needed. Herein, we rationally designed a mitochondria-targeted ratiometric fluorescent probe, MOBDP-I, for imaging of ONOO- in the mitochondria of inflammatory cells and model mice. This probe, MOBDP-I, was synthesized by conjugating a BODIPY fluorophore to a mitochondria-targeting moiety-indole-salt group by a carbon-carbon double bond (C=C). In the presence of ONOO-, the C=C bond between the BODIPY backbone and the indole-salt group was oxidized and broken, leading to an 18-fold enhancement of fluorescence at 510 nm, along with a significant fluorescence decrease at 596 nm. The ratiometric response property bestowed the probe with advantages in the precise quantification of ONOO- in cells, thus allowing estimation of the extent of inflammation in living cells and mouse models of rheumatoid arthritis, peritonitis, and brain inflammation. MOBDP-I could act as an effective molecular tool to study the relationship between ONOO- and the occurrence and development of inflammatory diseases.

Sustained release of 5-aminosalicylic acid from azoreductase-responsive polymeric prodrugs for prolonged colon-targeted colitis therapy

Ulcerative colitis (UC) is a challenging inflammatory gastrointestinal disorder, whose therapies encounter limitations in overcoming insufficient colonic retention and rapid systemic clearance. In this study, we report an innovative polymeric prodrug nanoformulation for targeted UC treatment through sustained 5-aminosalicylic acid (5-ASA) delivery. Amphiphilic polymer-based 13.5 nm micelles were engineered to incorporate azo-linked 5-ASA prodrug motifs, enabling cleavage via colonic azoreductases. In vitro, micelles exhibited excellent stability under gastric/intestinal conditions while demonstrating controlled 5-ASA release over 24 h in colonic fluids. Orally administered micelles revealed prolonged 24-h retention and a high accumulation within inflamed murine colonic tissue. At an approximately 60% dose reduction from those most advanced recent studies, the platform halted DSS colitis progression and outperformed standard 5-ASA therapy through a 77-97% suppression of inflammatory markers. Histological analysis confirmed intact colon morphology and restored barrier protein expression. This integrated prodrug nanoformulation addresses limitations in colon-targeted UC therapy through localized bioactivation and tailored pharmacokinetics, suggesting the potential of nanotechnology-guided precision delivery to transform disease management.

Therapeutic Benefits of Tuna Oil by In Vitro and In Vivo Studies Using a Rat Model of Acetic Acid-Induced Ulcerative Colitis

Ulcerative colitis (UC), an inflammation of the colon lining, represents the main form of inflammatory bowel disease IBD. Nutritional therapy is extremely important in the management of ulcerative colitis. Fish oil contains long-chain omega-3 polyunsaturated fatty acids, which have beneficial effects on health, including anti-inflammatory effects. This study aims to investigate the benefits of bluefin tuna oil extracted by the Soxhlet method in vitro by determining the anti-radical and anti-inflammatory activities and in vivo by evaluating the preventive and curative effects. The experiments were carried out using two doses of oil (100 and 260 mg/kg) and glutamine (400 and 1000 mg/kg) on the acetic acid-induced UC model. UC has been induced in Wistar rats by intrarectal administration of a single dose of 1 mL acetic acid (5% v/v in distilled water). The obtained results indicate that tuna oil and glutamine have a significant anti-free radical effect. Tuna oil has a marked anti-inflammatory power based on membrane stabilization and inhibiting protein denaturation. The reduction of various UC parameters, such as weight loss, disease activity score DAS, and colonic ulceration in rats pre-treated with tuna oil and glutamine, demonstrate that these treatments have a significant effect on UC. Total glutathione GSH, superoxide dismutase SOD, and catalase activities are significantly restored in the tuna oil and glutamine groups, while lipid peroxidation has been markedly reduced.

Role of Mitochondria in Intestinal Epithelial Barrier Dysfunction in Inflammatory Bowel Disease

Abstract

Inflammatory bowel disease (IBD) is widespread in industrial countries with every 20th citizen being affected. Dysregulation of the epithelial barrier function is considered to play a key role in IBD. Permeability of the intestinal epithelium depends mostly on its self-renewal potential and the condition of intercellular junctions. Mitochondria are involved in regulating various intracellular processes in addition to their energy function. Recent data implicate mitochondria in intestinal epithelial barrier regulation and IBD. Mitochondrial dysfunction is possibly one of the factors that underlie the structural abnormalities of tight junctions and the cytoskeleton in intestinal epithelial cells and decrease the self-renewal capacity of the epithelium. The barrier function of the intestinal epithelium is consequently distorted, and IBD develops. The mechanisms of these processes are still unclear and require further research.

A system for in vivo on-demand ultra-low field Overhauser-enhanced 3D-Magnetic resonance imaging

Development of very-low field MRI is an active area of research. It aims at reducing operating costs and improve portability. However, the signal-to-noise issue becomes prominent at ultra-low field (<1 mT), especially for molecular imaging purposes that addresses specific biochemical events. In the context of preclinical molecular MRI of abnormal proteolysis the paper describes a MRI system able to produce Overhauser-enhanced MR images in living rats through in situ Dynamic Nuclear Polarization at 206 µT using stable and non-toxic nitroxides. In parallel conventional images are generated at 206 µT following pre-polarization at 20 mT. Results show that nitroxides are visualized in 3D within a few minutes in the lungs, kidneys and bladder post-administration. This system will be used for molecular imaging of inflammation using protease-specific nitroxide probes.

EPR and Related Magnetic Resonance Imaging Techniques in Cancer Research

Imaging tumor microenvironments such as hypoxia, oxygenation, redox status, and/or glycolytic metabolism in tissues/cells is useful for diagnostic and prognostic purposes. New imaging modalities are under development for imaging various aspects of tumor microenvironments. Electron Paramagnetic Resonance Imaging (EPRI) though similar to NMR/MRI is unique in its ability to provide quantitative images of pO₂ in vivo. The short electron spin relaxation times have been posing formidable challenge to the technology development for clinical application. With the availability of the narrow line width trityl compounds, pulsed EPR imaging techniques were developed for pO₂ imaging. EPRI visualizes the exogenously administered spin probes/contrast agents and hence lacks the complementary morphological information. Dynamic nuclear polarization (DNP), a phenomenon that transfers the high electron spin polarization to the surrounding nuclear spins (¹H and ¹³C) opened new capabilities in molecular imaging. DNP of ¹³C nuclei is utilized in metabolic imaging of 13C-labeled compounds by imaging specific enzyme kinetics. In this article, imaging strategies mapping physiologic and metabolic aspects in vivo are reviewed within the framework of their application in cancer research, highlighting the potential and challenges of each of them.

Research and Development of Preclinical Overhauser-Enhanced Magnetic Resonance Imaging

Significance: Imaging free radicals, including reactive oxygen species and reactive nitrogen species, can be useful for understanding the pathology of diseases in animal disease models, as they are related to various physiological functions or diseases. Among the methods used for imaging free radicals, Overhauser-enhanced magnetic resonance imaging (OMRI) has a short image acquisition time and high spatial resolution. Therefore, OMRI is used to obtain various biological parameters. In this study, we review the methodology for improving the biological OMRI system and its applications. Recent Advances: The sensitivity of OMRI systems has been enhanced significantly to allow the visualization of various biological parameters, such as redox state, partial oxygen pressure, and pH, in different body parts of small animals, using spin probes. Furthermore, both endogenous free radicals and exogenous free radicals present in drugs can be visualized using OMRI. Critical Issues: To acquire accurate biological parameters at a high resolution, it is essential to increase the electron paramagnetic resonance (EPR) excitation efficiency and achieve a high enhancement factor. In addition, the size and magnetic field strength also need to be optimized for the measurement target. Future Directions: The advancement of in vivo OMRI techniques will be useful for understanding the pathology, diagnosis, and evaluation of therapeutic effects of drugs in various disease models. Antioxid. Redox Signal. 37, 1094-1110.

Mitochondria-Targeted Antioxidant SkQ1 Prevents the Development of Experimental Colitis in Mice and Impairment of the Barrier Function of the Intestinal Epithelium

Mitochondria-targeted antioxidants have become promising candidates for the therapy of various pathologies. The mitochondria-targeted antioxidant SkQ1, which is a derivative of plastoquinone, has been successfully used in preclinical studies for the treatment of cardiovascular and renal diseases, and has demonstrated anti-inflammatory activity in a number of inflammatory disease models. The present work aimed to investigate the therapeutic potential of SkQ1 and C12TPP, the analog of SkQ1 lacking the antioxidant quinone moiety, in the prevention of sodium dextran sulfate (DSS) experimental colitis and impairment of the barrier function of the intestinal epithelium in mice. DSS-treated animals exhibited weight loss, bloody stool, dysfunction of the intestinal epithelium barrier (which was observed using FITC-dextran permeability), reduced colon length, and histopathological changes in the colon mucosa. SkQ1 prevented the development of clinical and histological changes in DSS-treated mice. SkQ1 also reduced mRNA expression of pro-inflammatory molecules TNF, IL-6, IL-1β, and ICAM-1 in the proximal colon compared with DSS-treated animals. SkQ1 prevented DSS-induced tight junction disassembly in Caco-2 cells. Pretreatment of mice by C12TPP did not protect against DSS-induced colitis. Furthermore, C12TPP did not prevent DSS-induced tight junction disassembly in Caco-2 cells. Our results suggest that SkQ1 may be a promising therapeutic agent for the treatment of inflammatory bowel diseases, in particular ulcerative colitis.

In Vivo Dynamic Nuclear Polarization Magnetic Resonance Imaging for the Evaluation of Redox-Related Diseases and Theranostics

Significance:In vivo molecular and metabolic imaging is an emerging field in biomedical research that aims to perform noninvasive detection of tissue metabolism in disease states and responses to therapeutic agents. The imbalance in tissue oxidation/reduction (Redox) states is related to the onset and progression of several diseases. Tissue redox metabolism provides biomarkers for early diagnosis and drug treatments. Thus, noninvasive imaging of redox metabolism could be a useful, novel diagnostic tool for diagnosis of redox-related disease and drug discovery. Recent Advances:In vivo dynamic nuclear polarization magnetic resonance imaging (DNP-MRI) is a technique that enables the imaging of free radicals in living animals. DNP enhances the MRI signal by irradiating the target tissue or solution with the free radical molecule's electron paramagnetic resonance frequency before executing pulse sequence of the MRI. In vivo DNP-MRI with redox-sensitive nitroxyl radicals as the DNP redox contrast agent enables the imaging of the redox metabolism on various diseases. Moreover, nitroxyl radicals show antioxidant effects that suppress oxidative stress. Critical Issues: To date, considerable progress has been documented preclinically in the development of animal imaging systems. Here, we review redox imaging of in vivo DNP-MRI with a focus on the recent progress of this system and its uses in patients with redox-related diseases. Future Directions: This technique could have broad applications in the study of other redox-related diseases, such as cancer, inflammation, and neurological disorders, and facilitate the evaluation of treatment response as a theranostic tool. Antioxid. Redox Signal. 36, 172-184.

Redox-Based Theranostics of Gastric Ulcers Using Nitroxyl Radicals

Significance: Redox-based theranostics involves redox monitoring and therapeutics that normalize redox imbalance. It may be a promising approach to markedly improve a patient's quality of life through streamlined treatment. Nitroxyl radicals are useful for both redox monitoring and treating gastric ulcers in rodents. Recent Advances: Redox monitoring using in vivo electron paramagnetic resonance (EPR) spectroscopy in a gastric ulcer rat model showed the production of reactive oxygen species in the whole stomach. A combination of Overhauser-enhanced magnetic resonance imaging (MRI) and nitroxyl radicals provided high-resolution images of redox imbalance in the stomach of rats with a gastric ulcer. Treatment with nitroxyl radicals was effective to treat ulcers that were formed using model experiments of Helicobacter pylori and mental stress as well as nonsteroidal anti-inflammatory drugs. Critical Issues: For redox monitoring using Overhauser-enhanced MRI, the EPR irradiation power that is delivered to subjects must be within the range of the specific absorption rate regulation to protect against microwave damage regardless of a decrease in image contrast. The effect of long-term treatment with a nitroxyl radical in patients with a gastric ulcer remains unclear. Future Directions: Further research on redox-based theranostics in redox-related diseases, including gastric ulcers, would be accelerated by improving the redox imager and by developing functional nitroxyl radicals that localize in the target organ, tissue, or cell and that have specific reactivity for the redox-related biomolecule.

Imaging analysis for multiple paramagnetic agents using OMRI and electrophoresis

Nitroxides have been widely used as a molecular probe for analysis of various diseases models. This article describes an analytical method for separation and semi-quantification of multiple paramagnetic contrast agents with simple procedure combining electrophoresis and Overhauser enhancement magnetic resonance imaging (OMRI) imaging. We used three nitroxides, 3-carbamoyl PROXYL, 3-carboxy PROXYL, and CAT-1, which have different ionic charges in the molecule. In addition, we showed that this method could apply for in vitro measurement using biological sample. The results showed the nitroxides were successfully separated with electrophoresis depending on their charge, and their separation was visualized with OMRI after electrophoresis. Vehicle media such as whole blood did not affect the electrophoresis results and OMRI enhancement factor. Thus, the method can be used to analyze the redox status of biological samples without preprocessing. This analytical method enables in vitro measurement of biological samples to determine the redox status of specific tissue layers using paramagnetic agents, which is helpful for detailed analysis of redox-related diseases.

Development of 20 cm sample bore size dynamic nuclear polarization (DNP)-MRI at 16 mT and redox metabolic imaging of acute hepatitis rat model

Tissue redox metabolism is involved in various diseases, and an understanding of the spatio-temporal dynamics of tissue redox metabolism could be useful for diagnosis of progression and treatment. In in vivo dynamic nuclear polarization (DNP)-MRI, electron paramagnetic resonance (EPR) irradiation at the resonance frequency of nitroxyl radicals administered as a redox probe for induction of DNP, increases the intensity of MRI signals. For electron spin, it is necessary to apply a resonant frequency 658 times higher than that required for nuclear spin because of the higher magnetic moment of unpaired electrons. Previous studies using a disease model of small animals and in vivo DNP-MRI have revealed that an abnormal redox status is involved in many diseases, and that it could be used to visualize the dynamics of alterations in redox metabolism. To use the current methods in clinical practice, the development of a prototype DNP-MRI system for preclinical examinations of large animals is indispensable for clarifying the problems peculiar to the increase in size of the DNP-MRI device. Therefore, we developed a in vivo DNP-MRI system with a sample bore size of 20 cm and a 16-mT magnetic field using a U-shaped permanent magnet. Because the NMR frequency is very low, we adopted a digital radiofrequency transmission/reception system with excellent filter and dynamic range characteristics and equipped with a digital eddy current compensation system to suppress large eddy currents. The pulse sequence was based on the fast spin-echo sequence, which was improved for low frequency and large-eddy current equipment. The in vivo DNP-MRI system developed was used to non-invasively image the redox reaction of a carbamoyl-PROXYL probe in the livers of large rats weighing 800 g. Furthermore, DNP-MRI analysis was able to capture significant changes in redox metabolism in hepatitis-model rats.

Role of Oxidative Stress and Inflammatory Cytokines (TNF-α and IL-6) in Acetic Acid-Induced Ulcerative Colitis in Rats: Ameliorated by Otostegia fruticosa

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) that causes irritation, inflammation, and ulceration in the linings of the colon and rectum. Otostegia fruticosa is traditionally used to treat various disorders in different parts of the Middle East and sub-Saharan Africa. In the present study, we evaluated the ameliorative effects of crude leaves extract of O. fruticosa (OF.Cr) on acetic acid (AA)-induced UC model in Wistar albino rats. Wistar rats were administered orally with either vehicle (10 mL/kg), OF.Cr (200 and 400 mg/kg), or prednisolone (2 mg/kg) once a day for 6 days. On day 6, UC was induced in rats by intrarectal administration of a single dose of 5% AA (1.0 mL). Disease activity index (DAI) was recorded after one day of colitis induction by assessing the symptoms of colitis and then the rats were euthanized by cervical dislocation, and colon tissues were isolated for the histopathological examination and biochemical analysis of oxidative stress parameters and cytokines (Interleukin-6 and Tumor Necrosis Factor-α). OF.Cr pretreatment exhibits significant prevention against UC, as confirmed by a significant decrease of DAI, colonic ulceration, and reduced inflammatory score as compared to the AA-induced colitis rats. Depletion of total glutathione (GSH) levels and catalase (CAT) activities in the colitis group was significantly restored in the OF.Cr treated groups, while increased lipid peroxidation in the colon tissues was significantly reduced. OF.Cr prevented the activation of the IL-6 and TNF-α pathways in the colonic tissues, which were clearly observed by the decreased levels of IL-6 and TNF-α in the OF.Cr treated animals. Hence, OF.Cr could be developed in the future for the treatment of UC.

[Free Radical Production and Production Mechanism in the Early and Advanced Stages of Gastrointestinal Lesions]

Disruption of redox balance due to the overproduction of free radicals and reactive oxygen species (ROS) could cause protein denaturation, lipid peroxidation, and DNA mutation. These lead to an induction of gastrointestinal diseases such as gastric ulcers induced by long-term administration of non-steroidal anti-inflammatory drugs (NSAIDs) and ulcerative colitis. Magnetic resonance technique, which is non-invasive and free of radiation exposure, is a promising tool for evaluating redox status in the living body. This study investigated ROS production in rats with gastric ulcers induced by a typical NSAIDs indomethacin using in vivo ESR/spin probe technique. The ESR signal intensity of membrane-permeable nitroxyl probe in the indomethacin group showed enhanced decay compared with the vehicle group, but the enhancement was not observed in the presence of a membrane-permeable ROS scavenger, suggesting the intracellular ROS production. The imaging analysis using Overhauser-enhanced MRI (OMRI) with dual probes labeled with ¹⁴N and ¹⁵N enabled visualization of ROS production in the glandular stomach of rat with indomethacin-induced gastric ulcers. The intracellular ROS production in the distal and proximal colon in the initiation stage and intra- and extra-cellular ROS production of the advanced stage of colitis induced by dextran sodium sulfate (DSS) using the OMRI/dual-probe technique was observed. Furthermore, nitration of src homology protein tyrosine phosphatase 2 in macrophages might be involved in the activation of Toll-like receptor 4 and NF-κB, inducing infiltration of activated neutrophils into colonic mucosa to produce ROS in DSS-induced colitis mice.

Protective Effect of Bruguiera gymnorrhiza (L.) Lam. Fruit on Dextran Sulfate Sodium-Induced Ulcerative Colitis in Mice: Role of Keap1/Nrf2 Pathway and Gut Microbiota

Bruguiera gymnorrhiza (BG), a medicinal mangrove, and its fruit (a food material) (BGF), have traditionally been used to treat diarrhea (also known as ulcerative colitis) in folk medicine. However, the mechanism of action against colitis remains ambiguous. This study aimed to investigate the potential efficacy and mechanism of BGF on experimental colitis. Colitis was induced by oral intake of dextran sulfate sodium (DSS) and treated with aqueous extract of BGF (25, 50 and 100 mg/kg) for a week. The Disease Activity Index (DAI), colon length, and histological changes of colon were analyzed. The inflammatory and oxidative stress status was explored. The protein expression of Nrf2 and Keap1 in the colon was detected by Western blotting. The mRNA expression of Nrf2 downstream genes (GCLC, GCLM, HO-1 and NQO1) was determined by RT-PCR. Furthermore, the effect on intestinal flora was analyzed. Results indicated that BGF was rich in pinitol, and showed strong antioxidative activity in vitro. Compared with the DSS model, BGF effectively reduced the body weight loss and DAI, restored the colon length, repaired colonic pathological variations, and decreased the histological scores, which was superior to salicylazosulfapyridine (SASP) with smaller dosage. Moreover, BGF not only abated the levels of MDA and inflammatory mediators (TNF-α, IL-6, IL-1β, and IFN-γ), increased the level of IL-10, but also prevented the depletion of SOD and GSH. BGF upregulated the protein level of nuclear Nrf2 and mRNA levels of GCLC, GCLM, HO-1 and NQO1, while significantly inhibited the protein expression of Keap1 and cytosolic Nrf2. Besides, BGF promoted the growth of probiotics (Bifidobacterium, Anaerotruncus, and Lactobacillus) in the gut, and inhibited the colonization of pathogenic bacteria (Bacteroides and Streptococcus), which contributed to the maintenance of intestinal homeostasis. BGF possessed protective effect against DSS-induced colitis. The potential mechanism of BGF may involve the amelioration of inflammatory and oxidative status, activation of Keap1/Nrf2 signaling pathway, and maintenance of micro-ecological balance of the host. This study provides experimental evidence for the traditional application of BGF in the treatment of diarrhea, and indicates that BGF may be a promising candidate against colitis.