Salicylate hydroxylation as an indicator of hydroxyl radical generation in dextran sulfate-induced colitis

A Novel High-Throughput Approach to Measure Hydroxyl Radicals Induced by Airborne Particulate Matter

Oxidative stress is one of the key mechanisms linking ambient particulate matter (PM) exposure with various adverse health effects. The oxidative potential of PM has been used to characterize the ability of PM induced oxidative stress. Hydroxyl radical (•OH) is the most destructive radical produced by PM. However, there is currently no high-throughput approach which can rapidly measure PM-induced •OH for a large number of samples with an automated system. This study evaluated four existing molecular probes (disodium terephthalate, 3′-p-(aminophenyl)fluorescein, coumarin-3-carboxylic acid, and sodium benzoate) for their applicability to measure •OH induced by PM in a high-throughput cell-free system using fluorescence techniques, based on both our experiments and on an assessment of the physicochemical properties of the probes reported in the literature. Disodium terephthalate (TPT) was the most applicable molecular probe to measure •OH induced by PM, due to its high solubility, high stability of the corresponding fluorescent product (i.e., 2-hydroxyterephthalic acid), high yield compared with the other molecular probes, and stable fluorescence intensity in a wide range of pH environments. TPT was applied in a high-throughput format to measure PM (NIST 1648a)-induced •OH, in phosphate buffered saline. The formed fluorescent product was measured at designated time points up to 2 h. The fluorescent product of TPT had a detection limit of 17.59 nM. The soluble fraction of PM contributed approximately 76.9% of the •OH induced by total PM, and the soluble metal ions of PM contributed 57.4% of the overall •OH formation. This study provides a promising cost-effective high-throughput method to measure •OH induced by PM on a routine basis.

Using exomarkers to assess mitochondrial reactive species in vivo

BACKGROUND

The ability to measure the concentrations of small damaging and signalling molecules such as reactive oxygen species (ROS) in vivo is essential to understanding their biological roles. While a range of methods can be applied to in vitro systems, measuring the levels and relative changes in reactive species in vivo is challenging.

SCOPE OF REVIEW

One approach towards achieving this goal is the use of exomarkers. In this, exogenous probe compounds are administered to the intact organism and are then transformed by the reactive molecules in vivo to produce a diagnostic exomarker. The exomarker and the precursor probe can be analysed ex vivo to infer the identity and amounts of the reactive species present in vivo. This is akin to the measurement of biomarkers produced by the interaction of reactive species with endogenous biomolecules.

MAJOR CONCLUSIONS AND GENERAL SIGNIFICANCE

Our laboratories have developed mitochondria-targeted probes that generate exomarkers that can be analysed ex vivo by mass spectrometry to assess levels of reactive species within mitochondria in vivo. We have used one of these compounds, MitoB, to infer the levels of mitochondrial hydrogen peroxide within flies and mice. Here we describe the development of MitoB and expand on this example to discuss how better probes and exomarkers can be developed. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

Protective role of uncoupling protein-2 against dextran sodium sulfate-induced colitis

BACKGROUND AND AIMS

Uncoupling protein-2 (UCP-2) is a negative regulator of reactive oxygen species (ROS) production. We investigated the effect of UCP-2 on disease progression in a murine dextran sodium sulfate (DSS)-induced colitis model, and the expression and distribution of tight junction (TJ) proteins, such as occludin, zonula-1 (ZO-1), claudin-4, and junctional adhesion molecule-1 (JAM-1).

METHODS

Male UCP-2(-/-) mice and wild-type littermates were divided into four groups: groups I and II, which comprised each type of mouse, were administered 2.5% DSS dissolved in drinking water to create a colitis model. The control groups (groups III and IV, which comprised each type of mouse) were given normal drinking water. Disease progression was evaluated according to colon length and the disease activity index. The distribution of TJ proteins was detected by immunohistochemical analysis.

RESULTS

Compared with wild-type littermates, UCP-2(-/-) mice treated with DSS developed more severe diarrhea, body weight loss (P < 0.01), significantly short colon length, and more inflammatory cell infiltration into the mucosa and submucosa. The level of malondialdehyde in colonic mucosa increased in UCP-2(-/-) mice treated with DSS compared with the wild-type littermates (P < 0.001). The distribution of the ZO-1 and JAM-1 proteins was significantly decreased in the colonic mucosa of UCP-2(-/-) mice compared with the wild-type littermates, whereas occludin and claudin-4 distribution were not different between the UCP-2(-/-) mice and wild-type littermates.

CONCLUSIONS

UCP-2 might reduce intestinal inflammatory response through the negative regulation of ROS, and affects the expression and distribution of TJ proteins.

TRP channels: emerging targets for respiratory disease

The mammalian transient receptor potential (TRP) superfamily of cation channels is divided into six subfamilies based on sequence homology TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPA (ankyrin), TRPP (polycystin) and TRPML (mucolipin). The expression of these channels is especially abundant in sensory nerves, and there is increasing evidence demonstrating their existence in a broad range of cell types which are thought to play a key role in respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD). These ion channels can be activated by a diverse range of chemical and physical stimuli. Physical stimuli include temperature, membrane potential changes and osmotic stress, and some of the more well known chemical stimuli include capsaicin (TRPV1), menthol (TRPM8) and acrolein (TRPA1). There is increasing evidence in this rapidly moving field to suggest that selective blockers of these channels may represent attractive novel strategies to treat characteristic features of respiratory diseases such as asthma and COPD. This review focuses on summarising the evidence that modulation of selected TRP channels may have beneficial effects at targeting key features of these respiratory diseases including airways inflammation, airways hyper-reactivity, mucus secretion and cough.

TRPM2 channel properties, functions and therapeutic potentials

IMPORTANCE OF THE FIELD

Oxidative stress, through production of reactive oxygen species, triggers disturbance in intracellular calcium [Ca(2+)](i) homeostasis, which has been identified as an important causative factor in the pathogenesis of numerous inflammatory, cardiovascular and neurodegenerative diseases.

AREAS COVERED IN THIS REVIEW

Transient receptor potential melastatin 2 (TRPM2) protein forms a Ca(2+)-permeable cationic channel that is activated in response to oxidative stress and therefore acts as a cellular redox sensor. Research over the years has substantially advanced the knowledge of expression and functional properties of the TRPM2 channel, and particularly has accumulated compelling evidence for an important role for TRPM2 channel-mediated extracellular Ca(2+) influx in several physiological and pathophysiological functions exemplified by insulin release from pancreatic beta-cells, production of pro-inflammatory cytokines from immune cells, increased endothelial permeability, microglia activation and cell death. These findings suggest therapeutic potential of the TRPM2 channel as a drug target for combating oxidative-stress-related diseases.

WHAT THE READER WILL GAIN

The current state of knowledge with respect to the TRPM2 channel properties and the roles in oxidant stress signalling and functions.

TAKE HOME MESSAGE

TRPM2 may be a novel therapeutic target for oxidative stress-related diseases.

Polyphenol metabolites from colonic microbiota exert anti-inflammatory activity on different inflammation models

The polyphenols in fruits and vegetables may be partly responsible for the health-promoting effects attributed to fruit and vegetable intake. Although their properties have been relatively well studied, the activity of their metabolites, produced after ingestion, has been poorly investigated. Thus, the aim of this work was to study the potential anti-inflammatory effect of 18 polyphenol metabolites, derived from colon microbiota. They were screened by measuring prostaglandin E(2) (PGE(2)) production by CCD-18 colon fibroblast cells stimulated with IL-1beta. Metabolites that inhibited more than 50% PGE(2) production were hydrocaffeic (HCAF), dihydroxyphenyl acetic (dOHPA), and hydroferulic acid (HFER), that subsequently were tested with the writhing and paw pressure test in rodents where all three compounds showed an anti-inflammatory effect. The effect of HCAF administered orally (50 mg/kg) was also tested in the dextran sodium sulfate (DSS)-induced colitis model. Weight loss and fecal water content were more pronounced in DSS rats than in DSS-HCAF treated rats. HCAF treatment diminished the expression of the cytokines IL-1beta, IL-8, and TNF-alpha, reduced malonyldialdehyde (MDA) levels and oxidative DNA damage (measured as 8-oxo-2'-deoxyguanosine levels) in distal colon mucosa. These results indicate that HCAF, dOHPA, and HFER have anti-inflammatory activity in vitro and in vivo.

Estimation of hydroxyl radical generation by salicylate hydroxylation method in multiple organs of mice exposed to whole-body X-ray irradiation

Appropriate experimental conditions for the estimation of hydroxyl radical generation by salicylate hydroxylation were determined for multiple organs of X-irradiated mice in vivo. The in vitro experiments showed that there were significant correlations between the salicylic acid (SA) concentration, the amount of 2,3-dihydroxy benzoic acid (2,3-DHBA) and the X-ray exposure dose, and we obtained two linear-regression equations to calculate the amounts of hydroxyl radicals generated by the X-irradiation. The optimum dosage of SA and the appropriate sampling time for in vivo experiments was determined, and significant increases in the ratio of 2,3-DHBA to SA were detected in several organs of mice after X-irradiation. The hydroxyl radical equivalents of the 2,3-DHBA increases were also calculated. Our results clearly demonstrated the usefulness of the salicylate hydroxylation method in estimating hydroxyl radical generation in multiple organs in vivo.

TRPM2-mediated Ca2+influx induces chemokine production in monocytes that aggravates inflammatory neutrophil infiltration

Reactive oxygen species (ROS) induce chemokines responsible for the recruitment of inflammatory cells to sites of injury or infection. Here we show that the plasma membrane Ca(2+)-permeable channel TRPM2 controls ROS-induced chemokine production in monocytes. In human U937 monocytes, hydrogen peroxide (H(2)O(2)) evokes Ca(2+) influx through TRPM2 to activate Ca(2+)-dependent tyrosine kinase Pyk2 and amplify Erk signaling via Ras GTPase. This elicits nuclear translocation of nuclear factor-kappaB essential for the production of the chemokine interleukin-8 (CXCL8). In monocytes from Trpm2-deficient mice, H(2)O(2)-induced Ca(2+) influx and production of the macrophage inflammatory protein-2 (CXCL2), the mouse CXCL8 functional homolog, were impaired. In the dextran sulfate sodium-induced colitis inflammation model, CXCL2 expression, neutrophil infiltration and ulceration were attenuated by Trpm2 disruption. Thus, TRPM2 Ca(2+) influx controls the ROS-induced signaling cascade responsible for chemokine production, which aggravates inflammation. We propose functional inhibition of TRPM2 channels as a new therapeutic strategy for treating inflammatory diseases.

Estimation of hydroxyl radical generation by salicylate hydroxylation method in kidney of mice exposed to ferric nitrilotriacetate and potassium bromate

Hydroxyl radical (*OH) generation in the kidney of mice treated with ferric nitrilotriacetate (Fe-NTA) or potassium bromate (KBrO3) in vivo was estimated by the salicylate hydroxylation method, using the optimal experimental conditions we recently reported. Induction of DNA lesions and lipid peroxidation in the kidney by these nephrotoxic compounds was also examined. The salicylate hydroxylation method revealed significant increases in the *OH generation after injection of Fe-NTA or KBrO3 in the kidneys. A significant increase in 8-hydroxy-2'-deoxyguanosine in nuclei of the kidney was detected only in the KBrO3 treated mice, while the comet assay showed that the Fe-NTA and KBrO3 treatments both resulted in significant increases in DNA breakage in the kidney. With respect to lipid peroxidation, the Fe-NTA treatment enhanced lipid peroxidation and ESR signals of the alkylperoxy radical adduct. These DNA breaks and lipid peroxidation mediated by *OH were diminished by pre-treatment with salicylate in vivo. These results clearly demonstrated the usefulness of the salicylate hydroxylation method as well as the comet assay in estimating the involvement of *OH generation in cellular injury induced by chemicals in vivo.

Determination of trace hydroxyl radicals by flow injection spectrofluorometry and its analytical application

On the basis of the fluorescence increase of the reaction of ninhydrin with hydroxyl radicals, a new method for the determination of trace amounts of hydroxyl radicals by flow injection spectrofluorometry is presented. The introduction of flow injection analysis brought better reproducibility and avoided the effect of oxygen and other substances in the environment on the reaction of ninhydrin with hydroxyl radicals. Under optimum experimental conditions, the hydroxylated product of ninhydrin had excitation and emission maxima at 300 and 406 nm, respectively. The linear range was 2.60 x 10(-7) to 4.00 x 10(-5) M, and the limit of detection was 7.91 x 10(-8) M. A high analysis rate of 22 samples per hour was obtained. The proposed method has been applied successfully to the determination of scavenging effects of thiourea and vitamin C on hydroxyl radicals as well as to the evaluation of antioxidant capacities of some natural food.

Acetylsalicylic acid and acetaminophen protect against MPP+-induced mitochondrial damage and superoxide anion generation

The effects of 1-methyl-4-phenylpyridinium (MPP+) has been extensively researched due to its selective toxicity to dopaminergic neurons. Mitochondrial dysfunction which is common in the etiology of Parkinson's disease (PD), has been widely implicated in MPP+-induced toxicity. MPP+-induced mitochondrial dysfunction is believed to result in the generation of free radicals. This study was therefore performed to assess the effect of MPP+ on mitochondrial function and the ability of MPP+ to generate superoxide free radicals. Furthermore, we assessed the ability of the non-narcotic analgesics, acetaminophen and acetylsalicylic acid to prevent any diliterious effects of the potent neurotoxin, MPP+, on mitochondrial function and superoxide anion generation, in vivo. Acetylsalicylic acid and acetaminophen prevented the MPP+-induced inhibition of the electron transport chain and complex I activity. In addition, acetylsalicylic acid and acetaminophen significantly attenuated the MPP+-induced superoxide anion generation. Furthermore the results provide novel data explaining the ability of these agents to prevent MPP+-induced mitochondrial dysfunction and subsequent reactive oxygen species generation. While these findings suggest the usefulness of non-narcotic analgesics in neuroprotective therapy in neurodegenerative diseases, acetylsalicylic acid appears to be a potential candidate in prophylactic as well as in adjuvant therapy in Parkinson's disease.

Evaluation of the probes 2',7'-dichlorofluorescin diacetate, luminol, and lucigenin as indicators of reactive species formation

This study attempts to provide a critical assessment of three different common approaches to identifying teactive species formed in biological systems: the 2',7'-dichlorofluorescin diacetate (DCFH-DA) assay, and the luminol- and lucigenin-amplified chemiluminescence assays. There have been several contradictory reports about the specificity of these methods. Our results show that DCFH is oxidized to the fluorescent compound 2',7'-dichlorofluorescin (DCF) in human neutrophils exposed to the following compounds: Aroclor (A)1242, hydrogen peroxide (H(2)O(2)), nitric oxide (NO), and FeSO(4). Use of a cell-free DCFH system showed increased formation of DCF by peroxynitrite (ONOO(-)), horseradish peroxidase (HRP) alone, and HRP in combination with H(2)O(2), FeSO(4) alone, and a mixture of FeSO(4) and H(2)O(2). The hydroxyl radical (z.rad;OH) scavenger formate and the iron ion chelator deferoxamine reduced the DCF formation induced by FeSO(4) in combination with H(2)O(2). DCFH was insensitive to NO and H(2)O(2) in the cell-free system. In the presence of neutrophils, the A1242-induced luminol chemiluminescence was decreased by the superoxide dismutase inhibitor diethyldithiocarbamic acid (DDC) and the myeloperoxidase inhibitor salicylhydroxamic acid (SHA). Exposure of the neutrophils to NO, FeSO(4), or H(2)O(2) alone did not have any effect. A1242-induced lucigenin chemiluminescence in the neutrophils was increased slightly by DDC, but was not affected by SHA, NO, FeSO(4), or H(2)O(2). In conclusion, we suggest that the DCF assay is only suitable for measurements of ONOO(-), H(2)O(2) in combination with cellular peroxidases, and z.rad;OH. Luminol is sensitive towards HOCl, while lucigenin is oxidized by O(2)z.rad;(-).

Selective destruction of dopaminergic neurons by low concentrations of 6-OHDA and MPP+: protection by acetylsalicylic acid aspirin

We optimized a mesencephalic cell culture system to employ low concentrations of 6-hydroxydopamine (6-OHDA) and 1-methyl-4 phenylpyridinium (MPP+), neurotoxins known to trigger oxidative stress in dopaminergic cells. Both 6-OHDA and MPP(+) at 5 micro M reproducibly reduced the survival of dopaminergic neurons by 50-70% (p<0.02) without affecting the survival of the non-dopaminergic neuronal population. We found that 1mM of the non-steroidal anti-inflammatory drug (NSAID), acetylsalicylic acid (ASA), significantly (p<0.05) increased the survival of dopaminergic neurons exposed to either neurotoxin. The mechanisms underlying neuroprotection by ASA may be of therapeutic import in Parkinson's disease.

Endogenous released ascorbic acid suppresses ethanol-induced hydroxyl radical production in rat striatum

Previous studies have shown that acute systemic administration of ethanol induced ascorbic acid release in the striatum. However, the pharmacological implications of ethanol-induced striatal ascorbic acid release are unclear. In the present study, ethanol-induced extracellular changes of ascorbic acid and hydroxyl radical levels were detected in rat striatum by using brain microdialysis coupled to high-performance liquid chromatography with electrochemical detection. It was found that both in male and female rats, ethanol (3.0 g/kg, i.p.) increased striatal ascorbic acid release in the first 60 min after ethanol administration. Meanwhile, the extracellular hydroxyl radical levels, detected as 2,3- and 2,5-DHBA, were significantly decreased. However, when the ascorbic acid levels returned to the baseline, hydroxyl radical levels rebounded. Administration of DL-fenfluramine (20 mg/kg, i.p.) had no effect on the basal levels of ascorbic acid and hydroxyl radical, but significantly blocked ethanol-induced ascorbic acid release and increased hydroxyl radical levels significantly. Exogenous administration of ascorbic acid (20 mg/kg, s.c.) increased the extracellular levels of ascorbic acid in the striatum, and inhibited the increase of 2,3- and 2,5-DHBA in DL-fenfluramine plus ethanol group. These results provide first evidence that release of endogenous ascorbic acid in the striatum plays an important role in preventing oxidative stress by trapping hydroxyl radical in the central nervous system.

Regulation of murine intestinal inflammation by reactive metabolites of oxygen and nitrogen: divergent roles of superoxide and nitric oxide

Several reports have implicated reactive oxygen and nitrogen metabolites (RONS) in the initiation and/or progression of inflammatory bowel diseases (IBDs). We have investigated the role of three key RONS-metabolizing enzymes (inducible nitric oxide synthase [iNOS], superoxide dismutase [SOD], nicotinamide adenine dinucleotide phosphate [NADPH] oxidase) in a murine model of IBD. Mice genetically deficient ((-/-)) in either iNOS or the p47phox subunit of NADPH oxidase, transgenic (Tg) mice that overexpress SOD, and their respective wild-type (WT) littermates were fed dextran sulfate sodium (DSS) in drinking water for 7 days to induce colitis. In addition, the specific iNOS inhibitor 1400W was used in DSS-treated WT and p47phox(-/-) mice. WT mice responded to DSS feeding with progressive weight loss, bloody stools, elevated serum NO(X) and colonic mucosal injury with neutrophil infiltration. Both the onset and severity of colitis were significantly attenuated in iNOS(-/-) and 1400W-treated WT mice. While the responses to DSS did not differ between WT and p47phox(-/-) mice, enhanced protection was noted in 1400W-treated p47phox(-/-) mice. Interestingly, SOD(Tg) mice exhibited more severe colitis than their WT littermates. These findings reveal divergent roles for superoxide and iNOS-derived NO in intestinal inflammation.

Oxidative stress in brain during experimental bacterial meningitis: differential effects of alpha-phenyl-tert-butyl nitrone and N-acetylcysteine treatment

Antioxidant treatment has previously been shown to be neuroprotective in experimental bacterial meningitis. To obtain quantitative evidence for oxidative stress in this disease, we measured the major brain antioxidants ascorbate and reduced glutathione, and the lipid peroxidation endproduct malondialdehyde in the cortex of infant rats infected with Streptococcus pneumoniae. Cortical levels of the two antioxidants were markedly decreased 22 h after infection, when animals were severely ill. Total pyridine nucleotide levels in the cortex were unaltered, suggesting that the loss of the two antioxidants was not due to cell necrosis. Bacterial meningitis was accompanied by a moderate, significant increase in cortical malondialdehyde. While treatment with either of the antioxidants alpha-phenyl-tert-butyl nitrone or N-acetylcysteine significantly inhibited this increase, only the former attenuated the loss of endogenous antioxidants. Cerebrospinal fluid bacterial titer, nitrite and nitrate levels, and myeloperoxidase activity at 18 h after infection were unaffected by antioxidant treatment, suggesting that they acted by mechanisms other than modulation of inflammation. The results demonstrate that bacterial meningitis is accompanied by oxidative stress in the brain parenchyma. Furthermore, increased cortical lipid peroxidation does not appear to be the result of parenchymal oxidative stress, because it was prevented by NAC, which had no effect on the loss of brain antioxidants.

Different kinds of reactive oxygen and nitrogen species were detected in colon and breast tumors

Several studies have shown the involvement of reactive oxygen species (ROS; O2*-, hypochlorite, hydroxyl radical, hydrogen peroxide) in carcinogenesis. With certain pathologies, nitric oxide (NO) is formed and can interact with superoxide radical (O2*-) resulting in the propagation of the highly reactive species, peroxynitrite. In order to study the molecular mechanisms underlying the ability of reactive oxygen and nitrogen species (RONS) to mediate carcinogenesis, we have measured ROS, NO, and peroxynitrite content of cancerous tissues obtained from colon and breast carcinoma cases by chemiluminescence technique. All ROS were significantly increased in cancerous colon tissues with hypochlorite making the most important contribution and suggesting the role of inflammatory cells. NO was also increased and the peroxynitrite concentration was higher in cancerous samples. For breast carcinoma cases, only O2*- was significantly increased. Hypochlorite was not detected excluding the contribution of inflammatory cells. NO concentrations were not significantly different, therefore, ROS might originate by change in the redox state of the tissue.

Properties of fucoidan from Cladosiphon okamuranus tokida in gastric mucosal protection

To elucidate the anti-ulcer potential of Cladosiphon fucoidan, anti-peptic activity, bFGF stabilizing activity and inflammatory properties of this and related substances were investigated. Anti-peptic activity was observed with this and other sulfated polysaccharides such as dextran sulfate, carrageenan, and Fucus fucoidan. However, non-sulfated polysaccharides such as mannan and dextran did not exert the anti-peptic activity. The loss of bFGF bioactivity was prevented by all sulfated polysaccharides tested except chondroitin sulfate, at pH 7.4 and at pH 4.0. At pH 2.0, only heparin protected the bFGF activity. The generation of superoxide by macrophages and PMNs was stimulated by dextran sulfate, carrageenan, and Fucus fucoidan, whereas Cladosiphon fucoidan, heparin and chondroitin did not. Dextran sulfate, carrageenan, and Fucus fucoidan also stimulated the secretion of TNFalpha from macrophages, while Cladosiphon fucoidan did not. Thus, Cladosiphon fucoidan is a sulfated polysaccharide without inflammatory action. These results suggest that Cladosiphon fucoidan is a safe substance with potential for gastric protection.

Measurement of hydroxyl radical in rat blood vessel by microbore liquid chromatography and electrochemical detection: an on-line microdialysis study

Salicylic acid (0.5 mM) is used as a trapping reagent of hydroxyl radical, and the formed 2,3- and 2,5-dihydroxybenzoic acids were collected via an on-line microdialysis device from the blood vessels. This study revealed the use of a sensitive liquid chromatographic system with electrochemical detection for the determination of 2,3- and 2,5-dihydroxybenzoic acids. Mobile phase consisted of 0.1 M monochloroacetic acid, 10 mM EDTA, 0.5 mM sodium octylsulfate, 20% acetonitrile and 5% tetrahydrofuran in 1 l (pH 3.0 adjusted with 1 M NaOH), and the flow-rate of 0.05 ml/min were found to be optimum. Isocratic separation of these adducts on a microbore column (reversed-phase C18, 150x1 mm I.D., 5 microm) was achieved within 10 min. The optimal applied potential of dihydroxybenzoic acids was set at 750 mV based on a hydrodynamic study. This method has the detection limits of 1.3 pmol/ml (or 0.2 ng/ml) for 2,3- and 2,5-dihydroxybenzoic acids in Ringer solution (at signal-to-noise ratio=3).

Protein carbonyl formation on mucosal proteins in vitro and in dextran sulfate-induced colitis

Reactive oxygen and nitrogen species have been implicated as mediators of mucosal injury in inflammatory bowel disease, but few studies have investigated protein oxidation in the inflamed mucosa. In this study, protein carbonyl formation on colonic mucosal proteins from mice was investigated following in vitro exposure of homogenates to iron/ascorbate, hydrogen peroxide, hypochloric acid (HOCl), or nitric oxide (*NO). Total carbonyl content was measured spectrophotometrically by derivatization with dinitrophenylhydrazine (DNPH), and oxidation of component proteins within the tissue was examined by Western blotting for DNPH-derivatized proteins using anti-dinitrophenyl DNP antibodies. These results were compared with protein carbonyl formation found in the acutely inflamed mucosa from mice with colitis induced by dextran sulfate sodium (DSS) administered at 5% w/v in the drinking water for 7 d. In vitro, carbonyl formation was observed after exposure to iron/ascorbate, HOCl and *NO. Iron/ascorbate (20 microM/20 mM) exposure for 5 h increased carbonyl groups by 80%, particularly on proteins of 48, 75-100, 116, 131, and 142 kDa. Oxidation by 0.1 and 0.5 mM HOCl did not increase total carbonyl levels, but Western blotting revealed carbonyl formation on many proteins, particularly in the 49-95 kDa region. After exposure to 1-10 mM HOCl, total carbonyl levels were increased by 0.5 to 12 times control levels with extensive cross-linking and fragmentation of proteins rich in carbonyl groups observed by Western blotting. In mice with acute colitis induced by DSS, protein carbonyl content of the inflamed mucosa was not significantly different from control mucosa, (7.80 +/- 1.05 vs. 8.43 +/- 0.59 nmo/mg protein respectively, p = .16 n = 8, 10); however, Western blotting analysis indicated several proteins of molecular weight 48, 79, 95, and 131 kDa that exhibited increased carbonyl content in the inflamed mucosa. These proteins corresponded to those observed after in vitro oxidation of normal intestinal mucosa with iron/ ascorbate and HOCl, suggesting that both HOCl and metal ions may be involved in protein oxidation in DSS-induced colitis. Identification and further analysis of the mucosal proteins susceptible to carbonyl modification may lead to a better understanding of the contribution of oxidants to the colonic mucosa tissue injury in inflammatory bowel disease.