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Defects in intracellular oxidative metabolism of neutrophils undergoing apoptosis
P K Narayanan1, K Ragheb, G Lawler
1Department of Basic Medical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, Indiana, USA.
Abstract:
Apoptosis permits neutrophil recognition by macrophages, thereby not only limiting potential cytotoxicity but also promoting resolution of inflammation. A direct relationship between apoptosis and intracellular hydrogen peroxide (H2O2) production was observed in phorbol 12-myristate 13-acetate (PMA) -stimulated neutrophils aged in culture. A significant decrease in intracellular H2O2 production was observed in aging neutrophils at 12, 24, and 48 h. However, intracellular superoxide anion production in response to PMA stimulation was preserved up to 24 h, implying retention of intracellular signaling pathways leading to NADPH oxidase stimulation. A significant decrease in the cytoplasmic content and activity of Cu,Zn superoxide dismutase was responsible for the observed decline in intracellular H2O2 production in apoptotic neutrophils. Intracellular glutathione content also decreased concomitantly with H2O2 production. These observations indicate that onset of apoptosis in neutrophils is in part mediated by oxidative stress resulting from the down-regulation of key antioxidant defense systems of the cell, namely superoxide dismutase and glutathione.
Insights
Neutrophil apoptosis, a key process in inflammation resolution, is linked to reduced hydrogen peroxide (H2O2) production. This decrease is caused by lower levels of antioxidant enzymes like superoxide dismutase and glutathione.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Neutrophil apoptosis is crucial for resolving inflammation and preventing tissue damage.
- Oxidative stress plays a role in cellular processes, including programmed cell death.
Purpose of the Study:
- To investigate the relationship between neutrophil apoptosis and intracellular hydrogen peroxide (H2O2) production.
- To identify the mechanisms underlying changes in H2O2 production during neutrophil aging and apoptosis.
Main Methods:
- Neutrophils were stimulated with phorbol 12-myristate 13-acetate (PMA) and aged in culture.
- Intracellular H2O2 and superoxide anion production were measured over time.
- Levels and activity of antioxidant enzymes, including Cu,Zn superoxide dismutase and glutathione, were assessed.
Main Results:
- A significant decrease in intracellular H2O2 production was observed in aging neutrophils at 12, 24, and 48 hours.
- Superoxide anion production remained preserved up to 24 hours, indicating intact signaling pathways.
- Reduced cytoplasmic content and activity of Cu,Zn superoxide dismutase and glutathione correlated with decreased H2O2 production.
Conclusions:
- Neutrophil apoptosis is associated with a decline in H2O2 production.
- Down-regulation of antioxidant systems, specifically superoxide dismutase and glutathione, contributes to oxidative stress during neutrophil apoptosis.
- Oxidative stress, mediated by reduced antioxidant capacity, is a factor in initiating neutrophil apoptosis.