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Dynorphin and related opioid peptides enhance tumoricidal activity mediated by murine peritoneal macrophages
Abstract:
The influence of dynorphin A (DYN) and related opioid peptides on the tumoricidal function of activated murine peritoneal exudate macrophages (PEM) was investigated. Addition of DYN to macrophage cultures previously activated with mixed alpha + beta-interferon (IFN-alpha/beta) and bacterial lipopolysaccharide (LPS) significantly enhanced their ability to lyse P815 murine mastocytoma cells in a 16 hr chromium-release assay. The effects of DYN were dependent on prior macrophage activation. Peptide subfragments of DYN were effective in a manner similar to that of the 17-amino-acid parent molecule, indicating that peptide interaction with either kappa or delta-opioid receptors on the effector cell is effective in potentiating lytic function. The involvement of opiate receptors was confirmed by inhibition of the effects of DYN and leucine enkephalin by the opioid receptor antagonist naloxone. Finally, in addition to IFN-alpha/beta-primed macrophages, DYN also augmented tumoricidal function in PEM primed for cytotoxicity by either gamma-interferon (IFN-gamma) or the calcium ionophore A23187, indicating that DYN potentiates function in activated macrophages independent of the specific mode of activation.
Insights
Dynorphin A (DYN) enhances the tumor-killing ability of activated macrophages. This effect involves opioid receptors and occurs regardless of how macrophages are activated, suggesting a broad therapeutic potential.
Area of Science:
- Immunology
- Neuroscience
- Pharmacology
Background:
- Macrophages are key immune cells involved in tumor surveillance and destruction.
- Opioid peptides, like dynorphin A (DYN), can modulate immune cell function.
- Understanding these interactions is crucial for developing novel cancer therapies.
Purpose of the Study:
- To investigate the impact of dynorphin A (DYN) on the tumoricidal activity of activated macrophages.
- To determine the role of opioid receptors in mediating DYN's effects.
- To assess if DYN's influence is specific to certain activation pathways.
Main Methods:
- Murine peritoneal exudate macrophages (PEM) were activated using combinations of interferons (IFN-alpha/beta, IFN-gamma) and lipopolysaccharide (LPS) or calcium ionophore A23187.
- Macrophage tumoricidal function was assessed using a 16-hour chromium-release assay against P815 murine mastocytoma cells.
- The effects of DYN and its subfragments were evaluated in the presence and absence of the opioid receptor antagonist naloxone.
Main Results:
- Dynorphin A (DYN) significantly enhanced the lysis of tumor cells by activated macrophages.
- DYN's potentiating effect was observed in macrophages activated by various stimuli, including IFN-alpha/beta, IFN-gamma, LPS, and A23187.
- The effects of DYN were blocked by naloxone, confirming the involvement of opioid receptors.
- DYN subfragments also demonstrated efficacy, suggesting interaction with kappa or delta-opioid receptors.
Conclusions:
- Dynorphin A (DYN) is a potent enhancer of macrophage-mediated tumoricidal function.
- DYN's mechanism involves opioid receptors and is independent of the specific macrophage activation pathway.
- These findings highlight the potential of DYN as an immunomodulatory agent in cancer therapy.