Studies on the NADPH oxidase of phagocytes

Characterization of neutrophil NADPH oxidase activity reconstituted in a cell-free assay using specific monoclonal antibodies raised against cytochrome b558

The immunochemical characterization of NADPH oxidase activity of cytochrome b558 purified from human neutrophils was determined after reconstitution in a cell-free assay using the native hemoprotein and recombinant purified cytosolic activating factors. The oxidase activity showed a strict dependence on the heme content at each step of the hemoprotein purification process. The immunochemical properties of the reconstituted oxidase made use of monoclonal antibodies raised against membrane-bound and octyl-glucoside-extracted cytochrome b. From nine specific monoclonal antibodies reacting with gp91-phox cytochrome b558, two were selected, both of which were found to bind to the beta subunit of cytochrome b558 and to inhibit superoxide formation in the oxidase reconstituted cell-free assay. The extent of inhibition was dependent on the phospholipid environment. Neutrophil membrane extracts from X-linked chronic granulomatous disease patients did not produce O2- in the reconstituted system and did not bind to the antibodies.

Free radicals and other reactive oxygen metabolites in inflammatory bowel disease: cause, consequence or epiphenomenon?

Oxygen-derived free radicals and other reactive oxygen metabolites have emerged as a common pathway of tissue injury in a wide variety of otherwise disparate disease processes. This has given rise to the hope that efforts directed towards the pharmacologic control of free radical-mediated tissue injury (Reilly, P.M., Schiller, H. J. and Bulkley, G. B. (1991) Pharmacologic approach to tissue injury mediated by free radicals and other reactive oxygen metabolites. Am. J. Surg. 161: 488-503) may have particular application to patients suffering from Crohn's disease and/or ulcerative colitis. However, because tissue injury by any mechanism, even direct mechanical trauma, can elicit an inflammatory response which entails the secondary generation of toxic oxidants by neutrophils and tissue macrophages, it is important that the evidence for this association be examined critically, so as to discriminate the possibility of an etiologic role for these toxic compounds from their presence as a reflection of injury caused primarily by other agents. Similarly, in considering the therapeutic potential of free radical ablation for the treatment of patients with IBD it is important to distinguish between interventions that might specifically block the fundamental injury mechanism from those which would act in a more nonspecific, anti-inflammatory role.

A monoclonal antibody against peripheral benzodiazepine receptor activities the human neutrophil NADPH-oxidase

A murine monoclonal antibody, mAb 8523, raised against whole human pro-monocytic U937 cells recognizes an 18 kDa antigen in human neutrophils (PMN), as determined by immunoprecipitation and by immunodetection on Western blots of SDS-PAGE of PMN membrane fractions. That is 18 kDa antigen corresponds to the phagocyte peripheral benzodiazepine receptor (PBZDR) is evidenced by its co-migration with the 18 kDa covalently labeled PBZDR, detected by autoradiography, and their co-modulation upon phorbol-myristate-acetate activation of PMN. Purified mAb 8523 (IgG2b) is able to dose-dependently and specifically stimulate both the basal and the FMLP-induced oxidative burst of intact human PMN, assessed by luminol-amplified chemiluminescence. This property of the first described monoclonal antibody against PBZDR supports the implication of this receptor in NADPH-oxidase activation and consequently in phagocyte-dependent host defense mechanisms.

Pharmacologic approach to tissue injury mediated by free radicals and other reactive oxygen metabolites

Highly toxic metabolites of oxygen are generated normally by aerobic metabolism in most cells, and this generation is often greatly increased in pathologic conditions. When this oxidant flux exceeds the capability of the multiple endogenous antioxidant mechanisms, tissue injury ensues. The pharmacologic modification of this injury process, with agents that scavenge these reactive oxygen metabolites, block their generation, or enhance the endogenous antioxidant capability, has shown great promise in animal models of common clinical conditions, and has already been successfully applied in controlled clinical trials. This approach represents an interruption of tissue injury at its most basic level.

Inhibition by aminoacyl-chloromethane protease inhibitors of superoxide anion production by phorbol-ester-stimulated human neutrophils. The labeled target is a membrane protein

In a previous paper, we described the kinetic characteristics of the inhibition exerted by the protease inhibitors tosylphenylalanyl and tosyllysyl chloromethanes on superoxide production by human polymorphonuclear leukocytes when stimulated by phorbol esters [E. C. Conseiller & F. Lederer (1989) Eur. J. Biochem. 183, 107-114]. The results suggested the existence of a specific target which was affinity labeled by the inhibitors. The target appeared to be neither a protease, nor intracellular enzymes which can be inhibited in vitro by the chloromethanes (protein kinase C, hexokinase and enzymes of the hexose monophosphate shunt). In the present work, using the cell-free reconstitution assay for superoxide production, we substantiate the hypothesis that the chloromethanes, target is on the plasma membrane. We have radiolabeled the membranes of cells inactivated before or after phorbol ester stimulation, using either [3H]KBH4 reduction after reaction with unlabeled inactivator, or tritiated tosylphenylalanyl chloromethane. In all cases, besides a certain background of non-specific labeling, a radioactive band of Mr 15,000 can be observed upon SDS/PAGE of radiolabeled membranes. We suggest that it is the chemical modification of this protein which is responsible for inactivation of superoxide production. Its identity and its role in the oxidative burst remain to be determined.

The generation of reactive oxygen-derived species by phagocytes

The generation of reactive oxygen-derived species is one main constituent of the microbicidal activity of professional phagocytes. This process is known as the respiratory or the oxidative burst. It is initiated by a cyanide- and azide-insensitive increase in O2-consumption and the concomitant generation of superoxide radicals catalyzed by a membrane-localized NADPH oxidase which is triggered by an appropriate stimulation of the cells. The generated O2 is converted to hydrogen peroxide, hydroxyl radicals and other reactive products of oxygen which, if released extracellularly (for example in connection with frustrated phagocytosis), are potentially harmful to the tissue. The oxidative burst is not necessarily dependent on phagocytosis, nor is it necessarily associated with degranulation. Therefore, the process constitutes an important independent variable of phagocyte activity, and researches aiming to characterize various forms of airway inflammation may derive valuable information from an examination of the oxidative burst.

Genetic Defects of Phagocyte Nadph Oxidase Activity and Activation

NADPH oxidase is the key enzyme of the free radical-generating oxidative matabolism of phagocytes. Work from our and other's laboratories has recently established that the oxidase is not a single molecular entity, but it is a multicomponent system including a NADPH-binding protein, a flavoprotein, a b-type cytochrome and other unidentified factors. A working model of the molecular nature and of the activation mechanism of phagocyte NADPH oxidase is here proposed. This model is suitable for the study and the classification of the molecular pathology of the oxidase system. The various genetic defects of the NADPH oxidase, that are the cause of chronic granulomatous disease, (CGD) are here presented and discussed.