A novel effect of an opioid receptor antagonist, naloxone, on the production of reactive oxygen species by microglia: a study by electron paramagnetic resonance spectroscopy

• Published in: Brain research 2000-01, Vol.854 (1), p.224-229
• Main Authors: Chang, Raymond C.C, Rota, Cristina, Glover, Richard E, Mason, Ronald P, Hong, Jau-Shyong
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cell Line; Cyclic N-Oxides - metabolism; Electron paramagnetic resonance; Electron Spin Resonance Spectroscopy; Fundamental and applied biological sciences. Psychology; Hydroxyl Radical - metabolism; Iron - antagonists & inhibitors; Iron - metabolism; Isolated neuron and nerve. Neuroglia; Lipopolysaccharides - pharmacology; Mice; Microglia; Microglia - metabolism; Naloxone; Naloxone - pharmacology; Narcotic Antagonists - pharmacology; Nitric Oxide - metabolism; Nitrogen Oxides - antagonists & inhibitors; Nitrogen Oxides - metabolism; Non-heme iron–nitrosyl complex; Reactive Oxygen Species - metabolism; Superoxide; Superoxides - antagonists & inhibitors; Superoxides - metabolism; Tetradecanoylphorbol Acetate - pharmacology; Vertebrates: nervous system and sense organs
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/S0006-8993(99)02267-2

Microglia as the first line of defensive cells in the brain produce free radicals including superoxide and nitric oxide (NO), contributing to neurodegeneration. An opioid receptor antagonist, naloxone, has been considered pharmacologically beneficial to endotoxin shock, experimental cerebral ischemia, and spinal cord injury. However, the mechanisms underlying these beneficial effects of naloxone are still not clear. This study explores the effects of naloxone on the production of superoxide and NO by the murine microglial cell line, BV2, stimulated with lipopolysaccharide (LPS) as measured by electron paramagnetic resonance (EPR). The production of superoxide triggered by phobol-12-myristate-13-acetate (PMA) resulted in superoxide dismutase (SOD)-inhibitable, catalase-uninhibitable 5,5-dimethyl-1-pyrroline N-oxide (DMPO) hydroxyl radical adduct formation. LPS enhanced the production of superoxide and triggered the formation of non-heme iron–nitrosyl complex. Cells pre-treated with naloxone showed significant reduction of superoxide production by 35%. However, it could not significantly reduce the formation of non-heme iron–nitrosyl complex and nitrite. Taken together, the results expand our understanding of the neuroprotective effects of naloxone as it decreases superoxide production by microglia.