Non-invasive monitoring of redox status in mice with dextran sodium sulphate-induced colitis

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.

Emerging role of mitochondrial DAMPs, aberrant mitochondrial dynamics and anomalous mitophagy in gut mucosal pathogenesis

Gastroduodenal inflammation and ulcerative injuries are increasing due to expanding socio-economic stress, unhealthy food habits-lifestyle, smoking, alcoholism and usage of medicines like non-steroidal anti-inflammatory drugs. In fact, gastrointestinal (GI) complications, associated with the prevailing COVID-19 pandemic, further, poses a challenge to global healthcare towards safeguarding the GI tract. Emerging evidences have discretely identified mitochondrial dysfunctions as common etiological denominators in diseases. However, it is worth realizing that mitochondrial dysfunctions are not just consequences of diseases. Rather, damaged mitochondria severely aggravate the pathogenesis thereby qualifying as perpetrable factors worth of prophylactic and therapeutic targeting. Oxidative and nitrosative stress due to endogenous and exogenous stimuli triggers mitochondrial injury causing production of mitochondrial damage associated molecular patterns (mtDAMPs), which, in a feed-forward loop, inflicts inflammatory tissue damage. Mitochondrial structural dynamics and mitophagy are crucial quality control parameters determining the extent of mitopathology and disease outcomes. Interestingly, apart from endogenous factors, mitochondria also crosstalk and in turn get detrimentally affected by gut pathobionts colonized during luminal dysbiosis. Although mitopathology is documented in various pre-clinical/clinical studies, a comprehensive account appreciating the mitochondrial basis of GI mucosal pathologies is largely lacking. Here we critically discuss the molecular events impinging on mitochondria along with the interplay of mitochondria-derived factors in fueling mucosal pathogenesis. We specifically emphasize on the potential role of aberrant mitochondrial dynamics, anomalous mitophagy, mitochondrial lipoxidation and ferroptosis as emerging regulators of GI mucosal pathogenesis. We finally discuss about the prospect of mitochondrial targeting for next-generation drug discovery against GI disorders.

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.

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

In ulcerative colitis, an inflammatory bowel disease of unknown cause, diagnosis of the degree and location of colitis at an early stage is required to control the symptoms. Changes in redox status, including the production of reactive oxygen and nitrogen species (RONS), have been associated with ulcerative colitis in humans and dextran sodium sulfate (DSS)-induced colitis in rodents. In this study, the in vivo redox status of colons of DSS-induced colitis mice were monitored by Overhauser-enhanced magnetic resonance imaging (OMRI), and the relationship between redox status and colitis development was investigated. Colitis was induced by administering 5% DSS in drinking water to male Slc:ICR mice, which are a strain classified as closed colony outbred mice (5-week-old, 25-30 g). On the 3rd day of the DSS challenge, when no symptoms of colitis were displayed, the contrast decays of ¹⁵N-CmP and ¹⁴N-CxP tended to show enhancement in the whole colon and were not altered by DMSO. On the 5th day of the DSS challenge, with histological damage of the rectum being displayed, the contrast decay of ¹⁵N-CmP was significantly enhanced not only in the rectum, but also in the proximal colon, and this was suppressed by DMSO. On the 7th day of the DSS challenge, with the mice displaying severe colitis symptoms, the image contrasts of ¹⁵N-labeled 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (¹⁵N-CmP) and ¹⁴N-labeled 3-carboxyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (¹⁴N-CxP) showed much faster decay than those of healthy mice, while the increased decays of both probes were restored by the membrane-permeable reactive oxygen species (ROS) scavenger dimethyl sulfoxide (DMSO). Image differencing between the decay rate images of ¹⁵N-CmP and ¹⁴N-CxP showed the DSS-induced redox imbalance spreading over the whole colon, and a histogram of the difference image showed a smaller peak and broader distribution with the DSS treatment. These data indicate that ROS are produced intracellularly in the distal and proximal colon in the initiation stage of DSS-induced colitis, and that ROS are produced intracellularly and extracellularly in the advanced stage of DSS-induced colitis.

In Vivo Imaging of the Intra- and Extracellular Redox Status in Rat Stomach with Indomethacin-Induced Gastric Ulcers Using Overhauser-Enhanced Magnetic Resonance Imaging

AIMS

Repeated use of nonsteroidal anti-inflammatory drugs can induce changes in the redox status, including production of reactive oxygen species (ROS), but the specific details of these changes remain unknown. Overhauser-enhanced magnetic resonance imaging (OMRI) has been used in vivo to monitor the redox status in several diseases and map tissue oxygen concentrations. We monitored the intra- and extracellular redox status in the stomach of rats with indomethacin-induced gastric ulcers using OMRI and investigated the relationship with gastric mucosal damage.

RESULTS

One hour after oral administration of indomethacin (30 mg/kg), OMRI measurements in the stomach were made following nitroxyl probe administration. OMRI with the membrane-permeable nitroxyl probe, 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPOL), demonstrated a redox change toward oxidation, which was reversed by a membrane-permeable antioxidant. Conversely, imaging with the impermeable probe, 4-trimethylammonium-2,2,6,6-tetramethyl-piperidine-1-oxyl (CAT-1), demonstrated little redox change. Redox imbalance imaging of a live rat stomach with indomethacin-induced gastric ulcers was produced by dual imaging of ¹⁵N-labeled TEMPOL and ¹⁴N-labeled CAT-1, in addition to imaging with another membrane-permeable ¹⁵N-labeled probe, 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL), and ¹⁴N-labeled CAT-1. Pretreatment with MC-PROXYL suppressed gastric mucosal damage, whereas pretreatment with CAT-1 did not suppress ulcer formation.

INNOVATION

OMRI combined with a dual probe is a less invasive imaging technique for evaluation of intracellular ROS production contributing to the formation of gastric ulcers in the stomach of indomethacin-treated rats, which cannot be done with other methods.

CONCLUSION

This method may be a very powerful tool for characterizing the pathogenesis of various diseases and may have medical applications.

Reactivity of redox sensitive paramagnetic nitroxyl contrast agents with reactive oxygen species

The reactivity of nitroxyl free radicals, 4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl (CmP), with reactive oxygen species (ROS) were compared as typical 6-membered and 5-membered ring nitroxyl compounds, respectively. The reactivity of the hydroxylamine forms of both these nitroxyl radicals (TEMPOL-H and CmP-H) was also assessed. Two free radical species of ROS, hydroxyl radical (^•OH) and superoxide (O₂^•−), were subjected to a competing reaction. ^•OH was generated by UV irradiation from an aqueous H₂O₂ solution (H₂O₂-UV system), and O₂^•− was generated by a reaction between hypoxanthine and xanthine oxidase (HX-XO system). ^•OH and O₂^•− generated by the H₂O₂-UV and HX-XO systems, respectively, were measured by electron paramagnetic resonance (EPR) spin-trapping, and the amount of spin adducts generated by each system was adjusted to be equal. The time courses of the one-electron oxidation of TEMPOL, CmP, TEMPOL-H, and CmP-H in each ROS generation system were compared. A greater amount of TEMPOL was oxidized in the HX-XO system compared with the H₂O₂-UV system, whereas the reverse was observed for CmP. Although the hydroxylamine forms of the tested nitroxyl radicals were oxidized evenly in the H₂O₂-UV and HX-XO systems, the amount of oxidized CmP-H was approximately 3 times greater compared with TEMPOL-H.

Involvement of nitric oxide with activation of Toll-like receptor 4 signaling in mice with dextran sodium sulfate-induced colitis

Ulcerative colitis is an inflammatory bowel disease characterized by acute inflammation, ulceration, and bleeding of the colonic mucosa. Its cause remains unknown. Increases in adhesion molecules in vascular endothelium, and activated neutrophils releasing injurious molecules such as reactive oxygen species, are reportedly associated with the pathogenesis of dextran sodium sulfate (DSS)-induced colitis. Nitric oxide (NO) production derived from inducible NO synthase (iNOS) via activation of nuclear factor κB (NF-κB) has been reported. It is also reported that stimulation of Toll-like receptor 4 (TLR4) by lipopolysaccharide can activate NF-κB. In this study, we investigated the involvement of NO production in activation of the TLR4/NF-κB signaling pathway in mice with DSS-induced colitis. The addition of 5% DSS to the drinking water of male ICR mice resulted in increases in TLR4 protein in colon tissue and NF-κB p65 subunit in the nuclear fraction on day 3, increases in colonic tumor necrosis factor-α on day 4, and increases in P-selectin, intercellular adhesion molecule-1, NO2(-)/NO3(-), and nitrotyrosine in colonic mucosa on day 5. These activated inflammatory mediators and pathology of colitis were completely suppressed by treatment with a NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, as well as an iNOS inhibitor, aminoguanidine. Conversely, a NO-releasing compound, NOC-18, increased TLR4 levels and nuclear translocation of NF-κB p65 and exacerbated mucosal damage induced by DSS challenge. These data suggest that increases in TLR4 expression induced by drinking DSS-treated water might be directly or indirectly associated with NO overproduction.

The detrimental effect of nitric oxide on tissue is associated with inflammatory events in the vascular endothelium and neutrophils in mice with dextran sodium sulfate-induced colitis

Nitric oxide (NO) is thought to be a key molecule in the progression of ulcerative colitis and experimental colitis induced by dextran sodium sulfate (DSS). However, the detrimental effect of DSS-induced NO production on the colonic mucosa is incompletely understood. Increases in the expression of adhesion molecules in the vascular endothelium and activated neutrophils (thereby releasing injurious molecules such as reactive oxygen species) are reportedly associated with the pathogenesis of DSS-induced colitis. We investigated if the detrimental effect of NO production on the colonic mucosa was attributable to the activation of neutrophil infiltration by NO in mice with DSS-induced colitis. NO(2)(-)/NO(3)(-) content in the middle and distal colon was increased on days 5 and 7, but alterations in the proximal colon were not observed. Myeloperoxidase (MPO) activity and expression of P-selectin and intercellular adhesion molecule-1 (ICAM-1) were significantly increased in the entire colon, whereas TNF-α levels were significantly increased only in the middle and distal colon on day 7. The pathology of colitis and increases in colonic MPO activity, P-selectin, ICAM-1, and TNF-α levels were suppressed by the inducible NO synthase (iNOS)-specific inhibitor aminoguanidine and NO scavenger c-PTIO, whereas all but TNF-α levels were increased by the non-specific NOS inhibitor L-NAME. These findings suggest that iNOS-derived NO increases TNF-α levels in the middle and distal colon and increased TNF-α levels induce expression of P-selectin and ICAM-1, thereby promoting the infiltration of activated neutrophils, which leads to damage to colonic tissue.

Nitroxyl radical-containing nanoparticles for novel nanomedicine against oxidative stress injury

This article discusses the preparation and characterization of pH-sensitive nitroxyl radical-containing nanoparticles (RNPs) possessing nitroxyl radicals in the core and reactive groups on the periphery, and its biomedical application. The RNPs prepared by a self-assembling amphiphilic block copolymers composed of a hydrophilic poly(ethylene glycol) (PEG) segment and a hydrophobic poly(chloromethylstyrene) (PCMS) segment in which the chloromethyl groups were converted to 2,2,6,6-tetramethylpiperidinyloxyls (TEMPOs) via an amination of PEG-b-PCMS block copolymer with 4-amino-TEMPO are initially described. The cumulant average diameter of an RNP is approximately 40 nm, and the RNP has intense electron paramagnetic resonance signals. RNPs show a prolonged blood circulation time by the compartmentalization of nitroxyl radicals into the hydrophobic core, and disintegrate in response to a low pH environment, such as ischemic tissue, resulting in effectively scavenging reactive oxygen species due to an exposure of nitroxyl radicals from the RNP core. Thus, the RNP prepared was found to be effective for cerebral ischemia–reperfusion injury. Therefore, RNPs are promising as high-performance therapeutic nanomedicine for oxidative stress injuries.

Oral nitrite ameliorates dextran sulfate sodium-induced acute experimental colitis in mice

Inflammatory bowel diseases (IBDs) such as Crohn's disease and ulcerative colitis are chronic inflammatory disorders of the intestinal tract with excessive production of cytokines, adhesion molecules, and reactive oxygen species. Although nitric oxide (NO) is reported to be involved in the onset and progression of IBDs, it remains controversial as to whether NO is toxic or protective in experimental colitis. We investigated the effects of oral nitrite as a NO donor on dextran sulfate sodium (DSS)-induced acute colitis in mice. Mice were fed DSS in their drinking water with or without nitrite for up to 7days. The severity of colitis was assessed by disease activity index (DAI) observed over the experimental period, as well as by the other parameters, including colon lengths, hematocrit levels, and histological scores at day 7. DSS treatment induced severe colitis by day 7 with exacerbation in DAI and histological scores. We first observed a significant decrease in colonic nitrite levels and increase in colonic TNF-alpha expression at day 3 after DSS treatment, followed by increased colonic myeloperoxidase (MPO) activity and increased colonic expressions of both inducible NO synthase (iNOS) and heme oxygenase-1 (HO-1) at day 7. Oral nitrite supplementation to colitis mice reversed colonic nitrite levels and TNF-alpha expression to that of normal control mice at day 3, resulting in the reduction of MPO activity as well as iNOS and HO-1 expressions in colonic tissues with clinical and histological improvements at day 7. These results suggest that oral nitrite inhibits inflammatory process of DSS-induced experimental colitis by supplying nitrite-derived NO instead of impaired colonic NOS activity.