Stimulated human neutrophils limit iron-catalyzed hydroxyl radical formation as detected by spin-trapping techniques

The molecular biology of selected phagocyte defects

Advances in molecular genetic understanding of disease processes has been extended to a number of phagocytic disorders. Most of these disorders were extensively characterized at the functional and protein level prior to cloning of the relevant genes. Nucleotide sequence data has been essential for establishing the mechanism and mode of inheritance of genetically transmitted phagocyte disorders. Such data provides insights into the functionally important regions of affected proteins and information regarding regulation of these genes and homologies to other known proteins. From such data it is also possible to determine the evolutionary history of these genes. Chronic granulomatous disease, a phenotypic classification of a heterogeneous group of defects in oxidative metabolism, has now been defined in terms of specific molecular defects. Cloning of the two subunits of cytochrome b558 has led the way to characterization of the X-linked form and one of the autosomal recessive forms of this disease and confirmed the importance of this protein in the phagocyte oxidative burst. The absence of lactoferrin associated with hereditary specific granule deficiency is a result of decreased transcription of the lactoferrin gene in myeloid cells. Myeloperoxidase deficiency is likely a result of a mutation of the gene coding for myeloperoxidase. More precise understanding of expression of the lactoferrin and myeloperoxidase genes may be important in elucidating some of the underlying mechanisms in the pathogenesis of myeloid malignancies. A rare disorder, leukocyte adhesion deficiency, has provided a model for establishing the relationship between the several distinct alpha subunits and the shared common beta subunit of leukocyte adhesion proteins. These proteins have been shown to be genetically related to the superfamily of extracellular matrix receptors termed 'integrins'. Because these proteins have been highly conserved at the genetic level across a variety of species, comparison of nucleotide sequence data has illuminated some of the evolutionary history of these genes as they arose from ancestral genes. Studies of these adhesion protein genes may contribute new information in the broader context of how the functions of these genes evolved.

Aromatic hydroxylation of phenylalanine as an assay for hydroxyl radicals: application to activated human neutrophils and to the heme protein leghemoglobin

Attack of hydroxyl radical (.OH), generated by a Fenton system at physiological pH, upon L-phenylalanine produces three isomeric tyrosines, o-tyrosine (2-hydroxyphenylalanine), m-tyrosine (3-hydroxyphenylalanine), and p-tyrosine (4-hydroxyphenylalanine). These may be separated by high-performance liquid chromatography and measured using an electrochemical detector. Since L-phenylalanine is relatively nontoxic, it is proposed that generation of these three tyrosines from phenylalanine can be used as an assay for .OH in biological systems. The use of the assay to measure .OH production by leghemoglobin (plus H2O2) and by activated human neutrophils is described. No .OH production by activated human neutrophils was observed unless a source of iron ions was added to the reaction mixture, which suggests that these cells do not release an iron "promoter" of .OH generation from superoxide and hydrogen peroxide.

Detection of phagocyte-derived free radicals with spin trapping techniques: effect of temperature and cellular metabolism

Human neutrophils activated with either particulate or soluble stimuli generate oxygen-centered free radicals which are detected by spin trapping in conjunction with electron spin resonance (ESR) spectroscopy. We investigated the effect of temperature on ESR spectra resulting from stimulation of human neutrophils with phorbol myristate acetate (PMA) or opsonized zymosan in the presence of the spin trap, 5,5-dimethyl-1-pyrroline 1-oxide (DMPO). At 20 degrees C with either stimuli, neutrophil superoxide production was manifested predominantly as the superoxide spin-trapped adduct, 5,5-dimethyl-5-hydroperoxy-1-pyrrolidinyloxy (DMPO-OOH). In contrast, at 37 degrees C, the hydroxyl spin-trapped adduct, 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxy (DMPO-OH) was dominant. No evidence of hydroxyl radical (defined as the methyl spin-trapped adduct, 2,2,5-trimethyl-1-pyrrolidinyloxy, DMPO-CH3) was observed, suggesting that elevated temperatures increased the rate of DMPO-OOH conversion to DMPO-OH. In addition, the elevated temperature activated a neutrophil reductase which accelerated the rate of DMPO-OH reduction to its corresponding hydroxylamine, 2,2-dimethyl-5-hydroxy-1-hydroxypyrrolidine. This bioreduction was dependent upon the presence of both superoxide and a phagocyte-derived factor (possibly a thiol) released into the surrounding media.

Do humans neutrophils form hydroxyl radical? Evaluation of an unresolved controversy

Hydroxyl radical is a potent oxidizing agent of potential importance in human pathobiology. Since neutrophilic phagocytes make superoxide and hydrogen peroxide during phagocytosis, it has been proposed that hydroxyl radical is also formed. In this paper we review the literature which supports or refutes formation of hydroxyl radical by neutrophils and the mechanism(s) by which this radical might be formed. We conclude that there is no definitive proof for hydroxyl radical formation by neutrophils. In fact, neutrophil release of lactoferrin and myeloperoxidase appears to limit formation of this radical. Future studies are likely to determine whether superoxide released by neutrophils interacts with target substrates to allow formation of hydroxyl radical.

Spin trapping: ESR parameters of spin adducts

Spin trapping has become a valuable tool for the study of free radicals in biology and medicine. The electron spin resonance hyperfine splitting constants of spin adducts of interest in this area are tabulated. The entries also contain a brief comment on the source of the radical trapped.