An alternative mechanism for the production of hydroxyl radicals by stimulated neutrophils

Role of oxidants in microbial pathophysiology

Reactive oxidant species (superoxide, hydrogen peroxide, hydroxyl radical, hypohalous acid, and nitric oxide) are involved in many of the complex interactions between the invading microorganism and its host. Regardless of the source of these compounds or whether they are produced under normal conditions or those of oxidative stress, these oxidants exhibit a broad range of toxic effects to biomolecules that are essential for cell survival. Production of these oxidants by microorganisms enables them to have a survival advantage in their environment. Host oxidant production, especially by phagocytes, is a counteractive mechanism aimed at microbial killing. However, this mechanism may be contribute to a deleterious consequence of oxidant exposure, i.e., inflammatory tissue injury. Both the host and the microorganism have evolved complex adaptive mechanisms to deflect oxidant-mediated damage, including enzymatic and nonenzymatic oxidant-scavenging systems. This review discusses the formation of reactive oxidant species in vivo and how they mediate many of the processes involved in the complex interplay between microbial invasion and host defense.

Factors affecting the measurement of chemiluminescence in stimulated human polymorphonuclear leucocytes

Optimum conditions were established for the generation and measurement of luminol-dependent chemiluminescence (CL) in human polymorphonuclear leucocytes (PMNL) stimulated with a variety of particulate and soluble agents. Several factors had a particular influence on the kinetics of CL stimulated by the chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP). Two peaks, both azide-sensitive, were observed at 21 degrees C and 25 degrees C, but these increased in magnitude and merged to give a single, early peak when the temperature was increased at 37 degrees C. Pre-exposure of PMNL to a buffer containing calcium was essential for the expression of both phases of fMLP-stimulated CL, while the second peak decreased dramatically if the cells were stored at 4 degrees C for 4 hours before assay. In contrast, storage of PMNL at 4 degrees C for up to 8 hours in a buffer without divalent cations did not alter the kinetics or magnitude of CL induced by other stimuli, and had the benefit of minimizing the rate of cell aggregation. This study confirms that measurement of luminol-dependent CL in stimulated PMNL is a useful analytical tool, but shows that careful attention to experimental design is required to ensure that the observed CL provides a true measure of the parameter under investigation.

Dioxygen-derived radicals in biological systems

Three instances of the involvement of dioxygen-derived radicals in biological systems are considered. The first concerns the formation of radicals in the haemolytic reactions induced by treatment of erythrocytes by phenylhydrazine, as an example of the so-called 'oxidant drugs'. The evidence for the formation of phenyl radicals is considered and their origin in the oxidation of phenylhydrazine by a ferryl derivative of haemoglobin postulated. The relevance to the formation of phenylated iron and porphyrin species is described. It is suspected that many instances of oxidative damage to cellular systems result from the coincidence of unsequestered redox-active metal ions (particularly those of iron and copper), reductants, and dioxygen. As an example, the damage to hepatocytes, grown in a culture medium containing cysteine, is described. The formation of radical species derived from dioxygen during the respiratory burst associated with phagocytosis is discussed. A new electrochemical method of detecting the superoxide ion produced during the respiratory burst is described. Particular emphasis is placed on the relation between the production of radical species such as the hydroxyl radical and the superoxide ion, and the extent of phagocytosis.