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Neutrophil signal transduction in Met-enkephalin modulated superoxide anion release
H Haberstock1, T Marotti, H Banfic
1Rudjer Boskovic Institute, Department of Experimental Biology and Medicine, Zagreb, Croatia.
Abstract:
The present study explored the involvement of signal transduction system(s) in Met-enkephalin (MENK) modulated superoxide anion (O2-) release from human neutrophils. This opioid pentapeptide stimulated the O2- release in all samples if present at 10(-8) M concentration while in lower concentrations the stimulatory concentration was donor-dependent. The most abundant product of MENK degradation, Tyr-Gly-Gly (TGG), suppressed O2- release over a wide range of concentrations (10(-12)-10(-8) M). MENK induced O2- release was associated with a dose-dependent increase of diacylglycerol (DAG) concentration and protein-kinase C (PKC) translocation to the neutrophil membranes, with an increase of cytosolic Ca++, and could be abolished by H7, a PKC inhibitor. On the contrary, the suppressive effect of TGG was not associated with alteration of DAG concentration in neutrophil membranes. Superoxide anion release induced by low concentrations of MENK (10(12)-10(-10) M), could be blocked by NDGA, an inhibitor of the lipoxygenase pathway. We concluded that MENK-induced O2- release results mainly due to DAG/PKC pathway activation, although other secondary messengers might be involved.
Insights
Met-enkephalin (MENK) stimulates superoxide anion release from neutrophils via the diacylglycerol/protein-kinase C pathway. Its degradation product, Tyr-Gly-Gly (TGG), suppresses this release, indicating complex signaling roles.
Area of Science:
- Immunology
- Cellular Signaling
- Pharmacology
Background:
- Neutrophils are key immune cells involved in host defense.
- Superoxide anion (O2-) release is a critical function of neutrophils.
- Opioid peptides can modulate immune cell activity.
Purpose of the Study:
- To investigate the signal transduction pathways involved in Met-enkephalin (MENK)-induced superoxide anion release from human neutrophils.
- To determine the role of MENK degradation products in modulating neutrophil function.
Main Methods:
- Human neutrophils were stimulated with MENK and its degradation product Tyr-Gly-Gly (TGG).
- Superoxide anion release was measured.
- Diacylglycerol (DAG) concentration and protein-kinase C (PKC) translocation were assessed.
- Cytosolic Ca++ levels were monitored.
- Inhibitors of PKC (H7) and the lipoxygenase pathway (NDGA) were used.
Main Results:
- MENK (10(-8) M) stimulated O2- release; lower concentrations were donor-dependent.
- TGG suppressed O2- release across a wide concentration range.
- MENK-induced O2- release correlated with increased DAG, PKC translocation, and cytosolic Ca++.
- PKC inhibition abolished MENK-induced O2- release.
- NDGA blocked O2- release induced by low MENK concentrations.
Conclusions:
- MENK-induced superoxide anion release from neutrophils is primarily mediated by the diacylglycerol/protein-kinase C pathway.
- The lipoxygenase pathway may be involved in MENK-induced O2- release at lower concentrations.
- The MENK degradation product TGG exhibits inhibitory effects on neutrophil O2- release.