Evidence of in vivo oxidant-induced injury in inflammatory bowel disease (IBD) is largely indirect. Colon epithelial crypt cells (CEC) from paired specimens of histologically normal and inflamed bowel from IBD patients with active disease were examined for altered protein thiol redox status as an indicator of oxidative damage. When CEC preparations from 22 IBD patients were labeled with the reducedthiol-specific probe [14 C]-iodoacetamide (IAM), there was decreased labeling of a number of proteins indicating oxidation of thiol groups in CEC from inflamed mucosa compared to paired normal mucosa, especially the loss of thiol labeling of a 37-kD protein which was almost completely lost. The loss of reduced protein thiol status for the 37-kD band was paralleled by loss of epithelial cell glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) enzyme activity, an enzyme known to contain an essential reduced cysteine (Cys 149 ) at the active site. The identity of the 37-kD protein as GADPH monomer was confirmed by NH 2 -terminal amino acid sequence analysis.To examine whether this type of in vivo injury could be attributed to biologically relevant oxidants produced by inflammatory cells, CEC prepared from normal mucosa were exposed to H 2 O 2 , OCl

No abstract

DT-diaphorase catalysed the reduction of 1,4-naphthoquinones with hydroxy, methyl, methoxy and glutathionyl substituents at the expense of reducing equivalents from NADPH. The initial rates of quinone reduction did not correlate with either the half-wave reduction potential (E1/2) value (determined by h.p.l.c. with electrochemical detection against an Ag/AgCl reference electrode) or the partition coefficient of the quinones. After their reduction by DT-diaphorase the 1,4-naphthoquinone derivatives autoxidized at distinct rates, the extent of which was influenced by the nature of the substituents. Thus for the 1,4-naphthoquinone series the following order of rate of autoxidation was found: 5-hydroxy-1,4-naphthoquinone greater than 3-glutathionyl-1,4-naphthoquinone greater than 5-hydroxy-3-glutathionyl-1,4-naphthoquinone greater than 1,4-naphthoquinone greater than 2-hydroxy-1,4-naphthoquinone. For the 2-methyl-1,4-naphthoquinone (menadione) series the following order was observed: 5-hydroxy-2-methyl-1,4-naphthoquinone greater than 3-glutathionyl-5-hydroxy-2-methyl-1,4-naphthoquinone greater than 3-glutathionyl-2-methyl-1,4-naphthoquinone greater than 2-methyl-1,4-naphthoquinone greater than 3-hydroxy-2-methyl-1,4-naphthoquinone. The autoxidized naphthohydroquinone derivatives were re-reduced by DT-diaphorase, thus closing a cycle of enzymic reduction in equilibrium autoxidation. This was expressed as an excess of NADPH oxidized over the initial concentration of quinone present as well as H2O2 formation. These findings demonstrate that glutathionyl conjugates of 1,4-naphthoquinone and 2-methyl-1,4-naphthoquinone and those of their respective 5-hydroxy derivatives are able to act as substrates for DT-diaphorase and that they also autoxidize at rates higher than those for the unsubstituted parent compounds. These results are discussed in terms of the cellular role of DT-diaphorase in the reduction of hydroxy- or glutathionyl-substituted naphthoquinones as well as the further conjugation of these hydroquinones with glucuronide or sulphate within the cellular milieu, thereby facilitating their disposal from the cells.

Attempts to establish the presence of oxidant stress and tissue damage in inflammatory bowel disease (IBD) have relied on determining the capacity of peripheral blood inflammatory cells to produce reactive oxygen species (ROS) and other indirect indices. These approaches have failed to address whether or not there are adequate chemical antioxidant defences to prevent oxidative injury in the inflamed mucosa. In this investigation we have determined the mucosal concentrations of reduced and total ascorbic acid and the redox status in paired non-inflamed and inflamed mucosa using colonic biopsies from IBD patients. In inflamed mucosa from Crohn's disease (CD) patients, reduced and total ascorbic acid content decreased by 35% (p = 0.014 and p = 0.009, respectively). In ulcerative colitis (UC) patients, mucosal total ascorbic acid content decreased by 73% (p = 0.069) and reduced ascorbic acid by 41% (p = 0.014). The proportion of total ascorbic acid present in its reduced form in histologically normal mucosa from CD patients was unusually low at approximately 30%. In the paired-inflamed mucosa from CD patients, the redox ratio was also approximately 30% despite the loss of 35% of total ascorbate. In UC patients, the ascorbate redox ratio in the non-inflamed mucosa was 23% which increased to 51% in paired inflamed mucosa. This increase reflected the loss (73%) of total ascorbate. Reduction of dehydroascorbic acid by GSH/NADPH dependent dehydroascorbic acid reductase decreased significantly (p = 0.046) in inflamed mucosa from UC patients, suggesting that the capacity of the inflamed mucosa to maintain the concentration of reduced ascorbic acid is also diminished. HPLC analysis of mucosal preparations for diketogulonic acid, the decomposition product of dehydroascorbic acid, did not account for the loss of total ascorbate in the inflamed mucosa suggesting that ascorbate equivalents underwent further decomposition reactions or were excreted to the colonic lumen. We conclude that the normal luminal environment is strongly oxidising in character and that oxidant stress derived from inflammatory cells contributes to the loss of 35-73% total and reduced ascorbate. In absolute terms, the overall loss of this antioxidant buffering capacity would decrease the capacity of the inflamed mucosa to prevent oxidative tissue damage and hinder recovery of the inflamed mucosa.

As oxidative stress has been implicated in the pathogenesis of certain viral diseases we determined antioxidant and prooxidant parameters in lungs and bronchoalveolar lavage fluid (BALF) of mice infected with a lethal dose of influenza A/PR8/34 virus. Viral infection was characterized by massive infiltration of leukocytes, mainly polymorphonuclear leukocytes, into the alveolar space. The total number of BALF cells increased up to 8-fold (day 3 post-infection) and these cells appeared activated as judged by their increased rates of superoxide anion radical (O2-.) generation upon stimulation. Maximal rates of radical generation by BALF cells during the early stages of infection were 15- or 70-fold higher than those of cells from control animals when expressed per cell or total BALF cells, respectively. At the terminal stages of infection the total capacity of BALF cells to release O2-. declined to approximately 35-fold the control values. Infection also resulted in increased in vivo formation of hydrogen peroxide (H2O2) within the lungs at a time that coincided with the maximal capacity of BALF cells to release O2-.. Whereas pulmonary activities of glutathione peroxidase and reductase remained unaltered, levels of ascorbate in the cell-free BALF decreased significantly during the early stages of the infection and then returned to normal levels and above, late in infection. The oxidation state of the dehydroascorbic acid/ascorbate couple increased concomitantly with the decrease in ascorbate concentrations early in infection and remained elevated throughout the infection. As assessed by the prevention of peroxyl radical-induced loss of phycoerythrin fluorescence, the total antioxidant capacity present in lung tissue homogenate from terminally ill animals was not diminished when compared to that prepared from lungs of control mice. We conclude that although early stages of influenza infection are associated with the presence of oxidative stress in the lung tissue and alveolar fluid lining the epithelial cells, this stress does not appear to overwhelm local antioxidant defenses. The results therefore do not support a direct causative role of oxidative tissue damage in the pathogenesis of influenza virus infection.