The role of reactive oxygen intermediates in neutrophil pathophysiology

PadmaKumar Narayanan, Purdue University

Abstract

The neutrophil is a rapid response element in host defense, being recruited from the circulation as a result of host tissue injury or infection. Neutrophils respond to these stimuli by producing reactive oxygen species superoxide anion and hydrogen peroxide by a process termed respiratory burst. Defective oxidative burst is associated with an increased rate of infections and mortalities. Although tremendous progress has been achieved in studying neutrophil physiology in counteracting infectious pathogens, few studies have been conducted to investigate the effect of xenobiotics, especially polychlorinated biphenyls on reactive cells such as human peripheral blood neutrophils. Human neutrophils isolated from the peripheral blood was monitored after exposure to different types of polychlorinated biphenyl mixtures and congeners. Abnormalities in the oxidative burst pathway of neutrophils subsequent to interactions in vitro were detected using fluorescent probes. Hydroethidine and $2\sp\prime,7\sp\prime$-dichlorofluorescin diacetate were used to monitor intracellular generation of superoxide and hydrogen peroxide in neutrophils via the fluorescent products, ethidium bromide and $2\sp\prime,7\sp\prime$-dichlorofluorescein respectively. This abnormality was a result of the decreased ability of the antioxidant enzyme superoxide dismutase to breakdown superoxide to hydrogen peroxide. Since an abnormality in superoxide dismutase function coupled with inactivation of glutathione peroxidase was detected, we hypothesized that downregulation of this crucial antioxidant system would hasten the onset of apoptosis in neutrophils. A direct relationship between apoptosis and intracellular hydrogen peroxide production was demonstrated in aging neutrophils. A significant decrease in intracellular hydrogen peroxide production was observed in aging neutrophils at 12, 24, and 48 hours. Intracellular superoxide anion production on the other hand was preserved up to 24 hours, implying some retention of intracellular signaling pathways relevant to its production. A significant decrease in the cytoplasmic content and activity of superoxide dismutase was responsible for the observed decrease in intracellular hydrogen peroxide production in apoptotic neutrophils. Exposure to these toxicants accelerated the onset of apoptosis as early as 4 hours in human neutrophils. The ability to accentuate existing downregulation of superoxide dismutase in apoptotic neutrophils may contribute partly to the observed quickening in the onset of apoptosis in polychlorinated biphenyl-treated neutrophils.

Degree

Ph.D.

Advisors

Robinson, Purdue University.

Subject Area

Anatomy & physiology|Animals|Immunology|Pathology|Toxicology

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