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Kappa-opioid modulation of human microglial cell superoxide anion generation
1Institute for Brain and Immune Disorders, Minneapolis Medical Research Foundation and the University of Minnesota Medical School, 55404, USA.
Abstract:
Opioids have been postulated to play an immunomodulatory role in the CNS. Recently, we found that priming microglia with interferon (IFN)-gamma or tumor necrosis factor (TNF)-alpha resulted in an enhanced production of superoxide anion, a reactive oxygen intermediate that may be pathogenic during brain inflammation. In the present study, we investigated the effects of trans-3,4-dichloro-N-methyl-N[2-(1-pyrolidinyl)cyclohexyl]benze neaceamide methanesulfonate (U50,488), a selective kappa-opioid ligand, on microglial cell superoxide production when cells were primed with cytokines or stimulated with phorbol myristate acetate. While treatment of microglial cells with U50,488 had little effect on nonstimulated or stimulated superoxide production, this opioid inhibited (by >70%) the priming effects of cytokines. Maximal inhibition of microglial cell superoxide generation by U50,488 was observed at 10 nM for the priming effect of interferon-gamma and at 1 microM for tumor necrosis factor-alpha. Pretreatment of microglial cell cultures for 30 min with an equal concentration of the selective kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI) completely blocked the inhibitory effect of U50,488. The results of this study suggest that kappa-opioids may have therapeutic potential in inflammatory diseases of the CNS involving reactive oxygen intermediates produced by activated microglia.
Insights
Kappa-opioids, like U50,488, can significantly reduce superoxide production in primed microglia. This suggests potential therapeutic applications for central nervous system inflammatory diseases involving reactive oxygen species.
Area of Science:
- Neuroimmunology
- Pharmacology
Background:
- Microglia play a key role in central nervous system (CNS) inflammation.
- Priming microglia with cytokines like interferon-gamma (IFN-γ) or tumor necrosis factor-alpha (TNF-α) enhances superoxide anion production.
- Superoxide anion is a reactive oxygen intermediate implicated in neuropathology.
Purpose of the Study:
- To investigate the effect of a selective kappa-opioid ligand, U50,488, on microglial superoxide production.
- To determine if U50,488 modulates cytokine-induced priming or phorbol myristate acetate (PMA) stimulation of microglia.
- To explore the potential therapeutic role of kappa-opioids in CNS inflammatory conditions.
Main Methods:
- Primary microglial cell cultures were used.
- Cells were primed with IFN-γ or TNF-α, or stimulated with PMA.
- Superoxide production was measured.
- The effects of U50,488 and the kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI) were assessed.
Main Results:
- U50,488 showed minimal effect on non-stimulated or PMA-stimulated superoxide production.
- U50,488 significantly inhibited (>70%) the priming effect of IFN-γ and TNF-α on superoxide production.
- Maximal inhibition by U50,488 occurred at 10 nM for IFN-γ and 1 µM for TNF-α.
- Pretreatment with nor-BNI completely blocked the inhibitory effect of U50,488, confirming kappa-opioid receptor involvement.
Conclusions:
- Kappa-opioid receptor activation inhibits cytokine-induced superoxide production in microglia.
- This inhibitory effect is mediated via kappa-opioid receptors.
- Kappa-opioids may represent a novel therapeutic strategy for CNS inflammatory diseases characterized by microglial-derived reactive oxygen intermediates.