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Naloxone is an inappropriate antagonist of met-enkephalin-modulated superoxide anion release
1Institute R. Boskovic, Department of Experimental Biology and Medicine, Zagreb, Croatia.
Abstract:
Met-enkephalin (MENK) increased superoxide anion release by human polymorphonuclear cells (PMNs) at a physiological (10(-10) M) concentration and decreased release at a relatively high (10(-8) M) concentration. Surprisingly, naloxone (NAL), used as a specific antagonist in these experiments, displayed immunomodulatory actions of its own, increasing superoxide anion release at 10(-10) and 10(-8) M concentrations. Although both were effective, the dose-response curves were different for NAL and MENK. NAL and MENK also had a combined influence on O2- release. The stimulative effect of 10(-10) M MENK could be abolished by 10(-8) M NAL in seven of eight cases. Unexpectedly, the stimulatory effect of 10(-8) and 10(-10) M NAL could be abrogated by MENK in five of eight cases as well. The fact that NAL and MENK mutually interfere with one another in their effect upon O2- release by human PMNs discredits NAL as an appropriate antagonist in this system.
Insights
Met-enkephalin (MENK) and naloxone (NAL) modulate superoxide anion release by human polymorphonuclear cells (PMNs). Their opposing effects suggest naloxone may not be a suitable antagonist in this immunomodulatory system.
Area of Science:
- Immunology
- Neuroendocrinology
Background:
- Met-enkephalin (MENK) is an endogenous opioid peptide.
- Polymorphonuclear cells (PMNs) are key immune cells involved in inflammation.
- Naloxone (NAL) is typically used as a specific opioid antagonist.
Purpose of the Study:
- To investigate the immunomodulatory effects of MENK and NAL on superoxide anion release by human PMNs.
- To evaluate the potential interference between MENK and NAL in this system.
Main Methods:
- Human PMNs were treated with varying concentrations of MENK and NAL.
- Superoxide anion release was measured to assess cellular response.
- Dose-response relationships and combined effects were analyzed.
Main Results:
- MENK exhibited biphasic effects, increasing superoxide release at 10(-10) M and decreasing it at 10(-8) M.
- NAL also demonstrated immunomodulatory actions, increasing superoxide release at both tested concentrations.
- MENK and NAL showed mutual interference, with each substance affecting the other's influence on superoxide release.
Conclusions:
- Naloxone exhibits unexpected immunomodulatory activity, independent of its antagonist role.
- The mutual interference between MENK and NAL challenges the use of NAL as a specific antagonist in this PMN-based system.
- Further research is needed to elucidate the complex interactions between endogenous opioids and immune cells.