Xanthine Oxidase Contributes to Host Defense againstBurkholderia cepaciain the p47^phox−/−Mouse Model of Chronic Granulomatous Disease

Abstract

Chronic granulomatous disease (CGD) is an inherited disorder of the NADPH oxidase in which phagocytes are defective in generating superoxide and downstream microbicidal reactive oxidants, leading to recurrent life-threatening bacterial and fungal infections. Xanthine oxidase (XO) is another enzyme known to produce superoxide in many tissues. Using the p47phox؊/؊ mouse model of CGD, we evaluated the residual antibacterial activity of XO. Clearance of Burkholderia cepacia, a major pathogen in CGD, was reduced in p47 phox؊/؊ mice compared to that in wild-type mice and was further inhibited in p47 phox؊/؊ mice by pretreatment with the specific XO inhibitor allopurinol. Hepatic B. cepacia burden was similar in the two genotypes, but allopurinol significantly reduced net hepatic killing and killing efficiency only in p47 phox؊/؊ mice. Clearance and killing of intravenous Escherichia coli was intact in p47 phox؊/؊ mice and was unaffected by pretreatment with allopurinol. In CGD, XO may contribute to host defense against a subset of reactive oxidant-sensitive pathogens.Chronic granulomatous disease (CGD) is an inherited disorder of the NADPH oxidase complex in which phagocytes are defective in generating superoxide anion and the downstream reactive oxidant products, hydrogen peroxide, hypohalous acid, and hydroxyl radical (2,10,30,37,38). As a result of the defect in this key host defense pathway, CGD patients suffer from recurrent life-threatening infections caused by catalase-positive bacteria and fungi (1,27,31,33,35).NADPH oxidase is localized on the membranes of secondary granules in neutrophils and can be displayed on the phagocytic vacuoles and plasma membranes of myeloid cells (neutrophils, monocytes, and eosinophils). In response to phagocytosis and the chemoattractants interleukin 8, leukotriene B 4 , C5a, and platelet-activating factor, as well as nonphysiologic stimuli such as phorbol myristate acetate or the calcium ionophore A23817, a rapid and dramatic increase in oxygen consumption, termed the "respiratory burst," whereby molecular oxygen is reduced to superoxide, occurs.Xanthine oxidase (XO) is a ubiquitous enzyme involved in purine catabolism that, when activated from its constitutively expressed precursor, xanthine dehydrogenase, generates superoxide anion under certain circumstances. Moreover, in the presence of Fe 3ϩ , XO can generate a highly potent oxidant that behaves like the hydroxyl anion, via a Fenton reduction (13,20). The role of XO in host defense has been supported by in vitro studies using isolated macrophages and Kupffer cells (28, 36) and by exacerbations of experimental infections in which animals received XO inhibitors (39, 40). However, the relative role of XO in superoxide generation has been difficult to determine because the NADPH oxidase system usually generates much more superoxide from phagocytes.We hypothesized that in the absence of a functional NADPH oxidase, the role of XO in host defense against certain pathogens might be revealed. We have generated a knockout mouse model...

Exuberant Inflammation in Nicotinamide Adenine Dinucleotide Phosphate-Oxidase-Deficient Mice After Allogeneic Marrow Transplantation

“…Although our results show decreased oxidative burst and nitrative stress by the majority of monocytes/macrophages of mice lacking NADPH-oxidase, we cannot rule out in vivo formation of oxidative stress via endothelial cell-derived xanthine oxidase and nonphagocytic NADPH-oxidase (42). However, CGD mice are unable to clear infections, presumably because of inadequate generation of in vivo oxidative stress (43). Taken together, we favor the hypothesis that the exuberant inflammatory response in NADPH-oxidase-deficient mice is the main culprit responsible for abolishing the potentially tissue-protective effects of decreased macrophage/monocyte-dependent oxidants.…”

Role of KatG catalase‐peroxidase in mycobacterial pathogenesis: countering the phagocyte oxidative burst

“…Here, we show that, although KatG catalase-peroxidase was important for survival of MTB in wild-type C57Bl/6 mice and in NOS2 -/-mice, which are capable of generating an oxidative burst, it was dispensable for survival in gp91 Phox-/-mice, which cannot produce an oxidative burst. The lack of a discernible phenotype for KatG-deficient MTB in gp91 Phox-/-mice suggests that other potential sources of bactericidal peroxides in vivo, such as p47-dependent/gp91-independent NADPH oxidase (Schaper et al, 2003) and xanthine oxidase (Segal et al, 2000b), cannot compensate for loss of the phagocyte NADPH oxidase. Similar phenotypes have been reported for attenuated ROS-hypersusceptible mutants of Salmo- A and B.…”

Role of NADPH Oxidase in the Mechanism of Lung Neutrophil Sequestration and Microvessel Injury Induced by Gram-Negative Sepsis: Studies in p47phox−/− and gp91phox−/− Mice

“…In addition, we addressed whether the sequestered PMN may be involved in the mechanism of lung microvascular injury, an important feature of sepsis-induced acute lung injury. To study the in vivo role of NADPH oxidase-derived superoxide, we used p47 phoxϪ/Ϫ and gp91 phoxϪ/Ϫ mice in which the phagocytic cells are incapable of the respiratory burst (11,37). We observed that E. coli challenge of control mice resulted in increases in lung tissue PMN sequestration and migration from 1 to 6 h after the challenge, whereas these responses in the null mice were augmented; for example, transalveolar PMN migration was 40 -50% greater in the NADPH oxidase-defective mice after E. coli challenge than in control mice.…”