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Inflammatory bowel disease (IBD) patients have an increased risk of developing colitis-associated colon cancer (CAC); however, the basis for inflammation-induced genetic damage requisite for neoplasia is unclear. Several studies have shown that IBD patients have signs of increased oxidative damage, which could be a result of genetic and environmental factors such as an excess in oxidant molecules released during chronic inflammation, mitochondrial dysfunction, a failure in antioxidant capacity, or oxidant promoting diets. It has been suggested that chronic oxidative environment in the intestine leads to the DNA lesions that precipitate colon carcinogenesis in IBD patients. Indeed, several preclinical and clinical studies show that different endogenous and exogenous antioxidant molecules are effective at reducing oxidation in the intestine. However, most clinical studies have focused on the short-term effects of antioxidants in IBD patients but not in CAC. This review article examines the role of oxidative DNA damage as a possible precipitating event in CAC in the context of chronic intestinal inflammation and the potential role of exogenous antioxidants to prevent these cancers.

Graphical abstract, Highlights • Nitric oxide has shown antiviral potential against respiratory viral infections. • Protocols of inhaled nitric oxide against COVID-19 are in current trial. • Current trials might indicate suitable parameters for nitric oxide treatment against COVID-19. • Nitric oxide allied to nanoparticles may improve the antiviral potential., The endogenous free radical nitric oxide (NO) plays a pivotal role in the immunological system. NO has already been reported as a potential candidate for use in the treatment of human coronavirus infections, including COVID-19. In fact, inhaled NO has been used in clinical settings for its antiviral respiratory action, and in the regulation of blood pressure to avoid clot formation. In this mini-review, we discuss recent progress concerning the antivirus activity of NO in clinical, pre-clinical and research settings, and its beneficial effects in the treatment of clinical complications in patients infected with coronaviruses and other respiratory viral diseases, including COVID-19. We also highlight promising therapeutic effects of NO donors allied to nanomaterials to combat COVID-19 and other human coronavirus infections. Nanomaterials can be designed to deliver sustained, localized NO release directly at the desired application site, enhancing the beneficial effects of NO and minimizing the side effects. Challenges and perspectives are presented to open new fields of research.

Recent studies have shown a correlation between COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and the distinct, exaggerated immune response titled “cytokine storm”. This immune response leads to excessive production and accumulation of reactive oxygen species (ROS) that cause clinical signs characteristic of COVID-19 such as decreased oxygen saturation, alteration of hemoglobin properties, decreased nitric oxide (NO) bioavailability, vasoconstriction, elevated cytokines, cardiac and/or renal injury, enhanced D-dimer, leukocytosis, and an increased neutrophil to lymphocyte ratio. Particularly, neutrophil myeloperoxidase (MPO) is thought to be especially abundant and, as a result, contributes substantially to oxidative stress and the pathophysiology of COVID-19. Conversely, melatonin, a potent MPO inhibitor, has been noted for its anti-inflammatory, anti-oxidative, anti-apoptotic, and neuroprotective actions. Melatonin has been proposed as a safe therapeutic agent for COVID-19 recently, having been given with a US Food and Drug Administration emergency authorized cocktail, REGEN-COV2, for management of COVID-19 progression. This review distinctly highlights both how the destructive interactions of HOCl with tetrapyrrole rings may contribute to oxygen deficiency and hypoxia, vitamin B12 deficiency, NO deficiency, increased oxidative stress, and sleep disturbance, as well as how melatonin acts to prevent these events, thereby improving COVID-19 prognosis., Graphical abstract The proposed pathway of SAR-CoV-2 infection associated with an uncontrolled immune response and cytokine storm generating MPO and ROS resulting in decreased NO and vasoconstriction, decreased O2 and hypoxia, and vitamin B12 deficiency through tetrapyrrole ring destruction, and the prevention by melatonin.Unlabelled Image

Methotrexate (MTX) is an immunosuppressant commonly used for the treatment of autoimmune diseases. Recent observations have shown that patients treated with MTX also exhibit a reduced risk for the development of cardiovascular disease (CVD). Although MTX reduces systemic inflammation and tissue damage, the mechanisms by which MTX exerts these beneficial effects are not entirely known. We have previously demonstrated that protein adducts formed by the interaction of malondialdehyde (MDA) and acetaldehyde (AA), known as MAA-protein adducts, are present in diseased tissues of individuals with rheumatoid arthritis (RA) or CVD. In previously reported studies, MAA-adducts were shown to be highly immunogenic, supporting the concept that MAA-adducts not only serve as markers of oxidative stress but may have a direct role in the pathogenesis of inflammatory diseases. Because MAA-adducts are commonly detected in diseased tissues and are proposed to mitigate disease progression in both RA and CVD, we tested the hypothesis that MTX inhibits the generation of MAA-protein adducts by scavenging reactive oxygen species. Using a cell free system, we found that MTX reduces MAA-adduct formation by approximately 6-fold, and scavenges free radicals produced during MAA-adduct formation. Further investigation revealed that MTX directly scavenges superoxide, but not hydrogen peroxide. Additionally, using the Nrf2/ARE luciferase reporter cell line, which responds to intracellular redox changes, we observed that MTX inhibits the activation of Nrf2 in cells treated with MDA and AA. These studies define previously unrecognized mechanisms by which MTX can reduce inflammation and subsequent tissue damage, namely, scavenging free radicals, reducing oxidative stress, and inhibiting MAA-adduct formation., Graphical abstract The production of reactive oxygen species (ROS) can result in lipid peroxidation. Lipid peroxidation can, in turn, result in the formation of malondialdehyde (MDA), which can spontaneously breakdown forming acetaldehyde (AA). Malondialdehyde and acetaldehyde can interact to form the stable hybrid malondialdehyde-acetaldehyde adduct (MAA) on proteins and other macromolecules. Binding of MAA-adducted proteins to cells can lead to expression of pro-inflammatory cytokines, resulting in inflammation. MAA-adducted proteins are also themselves immunogenic and can initiate an inflammatory response. Importantly, methotrexate can scavenge free radicals. This may ameliorate the formation of lipid peroxides and the resulting formation of MDA and AA. Additionally, methotrexate can directly inhibit the formation of MAA-protein adducts. Thus, methotrexate can scavenge free radicals and inhibit the formation of MAA-adducts. These are previously undescribed mechanisms by which methotrexate may reduce inflammation and the tissue damage associated with chronic inflammatory diseases.fx1, Highlights • MTX is commonly used to treat RA and is being tested in CVD patients. • MDA and AA are produced during lipidperoxidation and can interact to form MAA-adducts. • MAA-adducts are found in atheromas and in diseased synovial tissue of RA patients. • MTX scavenges the free radical O2− and prevents the formation of MAA-adducts. • Scavenging O2− may be a mechanism by which MTX reduces inflammation and disease.

Superoxide dismutases play an important role in human health and disease. Three decades of effort have gone into synthesizing SOD mimics for clinical use. The result is the Mn porphyrins which have SOD-like activity. Several clinical trials are underway to test the efficacy of these compounds in patients, particularly as radioprotectors of normal tissue during cancer treatment. However, aqueous chemistry data indicate that the Mn porphyrins react equally well with multiple redox active species in cells including H2O2, O2•-, ONOO-, thiols, and ascorbate among others. The redox potential of the Mn porphyrins is midway between the potentials for the oxidation and reduction of O2•-. This positions them to react equally well as oxidants and reductants in cells. The result of this unique chemistry is that: 1) the species the Mn porphyrins react with in vivo will depend on the relative concentrations of the reactive species and Mn porphyrins in the cell of interest, and 2) the Mn porphyrins will act as catalytic (redox cycling) agents in vivo. The ability of the Mn porphyrins to catalyze protein S-glutathionylation means that Mn porphyrins have the potential to globally modulate cellular redox regulatory signaling networks. The purpose of this review is to summarize the data that indicate the Mn porphyrins have diverse reactions in vivo that are the basis of the observed biological effects. The ability to catalyze multiple reactions in vivo expands the potential therapeutic use of the Mn porphyrins to disease models that are not SOD based., Graphical abstract In step 1 of the catalytic cycle, cationic Mn(III) substituted pyridylporphyrin (MnP) becomes oxidized from Mn(II) to a high-valent, highly oxidizing O=Mn(IV) species with an oxidant such as H2O2. This species closes the catalytic cycle by oxidizing protein cysteines and/or GSH in step 2 and gets ready for another cycle. In step 3 oxidation of the protein and/or glutathione results in protein S-glutathionylation.fx1, Highlights • Mn porphyrins were synthesized as SOD mimics. • The redox potential of the Mn porphyrins makes them equally able to act as oxidants and reductants which in turn allows them to act as catalytic redox cycling agents in vivo. • Mn porphyrins react equally well with H2O2, O2•-, ONOO-; cellular redox environment determines which species react with Mn porphyrins in vivo. • Mn porphyrins catalyze protein S-glutathionylation; global protein S-glutathionylation modulates cellular redox regulatory signaling networks. • Mn porphyrins act as chemo/radiosensitizers of tumor cells, but chemo/radioprotectors of normal tissue in pre-clinical disease models. • Clinical trials are underway to test Mn porphyrin efficacy in patients.

Low-density lipoprotein (LDL) modified by hypochlorous acid (HOCl) produced by myeloperoxidase (MPO) is present in atherosclerotic lesions, where it is implicated in the propagation of inflammation and acceleration of lesion development by multiple pathways, including the induction of endothelial dysfunction. Thiocyanate (SCN-) ions are utilised by MPO to produce the oxidant hypothiocyanous acid (HOSCN), which reacts with LDL in a different manner to HOCl. Whilst the reactivity of HOCl-modified LDL has been previously studied, the role of HOSCN in the modification of LDL in vivo is poorly defined, although emerging evidence suggests that these particles have distinct biological properties. This is important because elevated plasma SCN- is linked with both the propagation and prevention of atherosclerosis. In this study, we demonstrate that both HOSCN- and HOCl-modified LDL inhibit endothelium-mediated vasorelaxation ex vivo in rat aortic ring segments. In vitro experiments with human coronary artery endothelial cells show that HOSCN-modified LDL decreases in the production of nitric oxide (NO•) and induces the loss of endothelial nitric oxide synthase (eNOS) activity. This occurs to a similar extent to that seen with HOCl-modified LDL. In each case, these effects are related to eNOS uncoupling, rather than altered expression, phosphorylation or cellular localisation. Together, these data provide new insights into role of MPO and LDL modification in the induction of endothelial dysfunction, which has implications for both the therapeutic use of SCN- within the setting of atherosclerosis and for smokers, who have elevated plasma levels of SCN-, and are more at risk of developing cardiovascular disease., Highlights • Myeloperoxidase produces HOCl and HOSCN that modify LDL in a distinct manner. • HOSCN- and HOCl-LDL inhibit endothelium-mediated vasorelaxation in aortic rings ex vivo. • HOSCN- and HOCl-LDL decrease endothelial production of nitric oxide in vitro. • Decreased eNOS activity is seen, which associated with enzyme uncoupling. • HOSCN- and HOCl-LDL induce colocalisation of eNOS and caveolin 1.

Mitochondrial toxicity is increasingly being implicated as a contributing factor to many xenobiotic-induced organ toxicities, including skeletal muscle toxicity. This has necessitated the need for predictive in vitro models that are able to sensitively detect mitochondrial toxicity of chemical entities early in the research and development process. One such cell model involves substituting galactose for glucose in the culture media. Since cells cultured in galactose are unable to generate sufficient ATP from glycolysis they are forced to rely on mitochondrial oxidative phosphorylation for ATP generation and consequently are more sensitive to mitochondrial perturbation than cells grown in glucose. The aim of this study was to characterise cellular growth, bioenergetics and mitochondrial toxicity of the L6 rat skeletal muscle cell line cultured in either high glucose or galactose media. L6 myoblasts proliferated more slowly when cultured in galactose media, although they maintained similar levels of ATP. Galactose cultured L6 cells were significantly more sensitive to classical mitochondrial toxicants than glucose-cultured cells, confirming the cells had adapted to galactose media. Analysis of bioenergetic function with the XF Seahorse extracellular flux analyser demonstrated that oxygen consumption rate (OCR) was significantly increased whereas extracellular acidification rate (ECAR), a measure of glycolysis, was decreased in cells grown in galactose. Mitochondria operated closer to state 3 respiration and had a lower mitochondrial membrane potential and basal mitochondrial O2•– level compared to cells in the glucose model. An antimycin A (AA) dose response revealed that there was no difference in the sensitivity of OCR to AA inhibition between glucose and galactose cells. Importantly, cells in glucose were able to up-regulate glycolysis, while galactose cells were not. These results confirm that L6 cells are able to adapt to growth in a galactose media model and are consequently more susceptible to mitochondrial toxicants., Highlights • L6 cells grown in glucose and galactose as model to detect skeletal muscle mitochondrial toxicity. • L6 cells grown in galactose rely on mitochondrial oxidative phosphorylation for ATP production. • Galactose cells are unable to use glycolysis to produce ATP following mitochondrial inhibition.

This article provides a succinct but limited overview of the protective and deleterious effects of reactive oxygen and nitrogen species in a clinical context. Reactive oxygen species include superoxide, hydrogen peroxide, single oxygen and lipid peroxides. Reactive nitrogen species include species derived from nitric oxide. This review gives a brief overview of the reaction chemistry of these species, the role of various enzymes involved in the generation and detoxification of these species in disease mechanisms and drug toxicity and the protective role of dietary antioxidants. I hope that the graphical review will be helpful for teaching both the first year medical and graduate students in the U.S. and abroad the fundamentals of reactive oxygen and nitrogen species in redox biology and clinical medicine., Highlights ► A short course on fundamentals in redox biology of oxyradicals. ► Discusses the good, bad and ugly side of ROS/RNS in biology and medicine. ► Discusses the pathophysiological role of ROS/RNS in drug therapy and clinical medicine.