Morphine inhibits the TRPM2 signaling pathways in microglia cells, reducing the increases in oxidative stress, cytokines, and cell death caused by lipopolysaccharide.

Background: Microglia are brain resident cells that control neural network maintenance, damage healing, and brain development. Microglia undergo apoptosis, cytokine production, and reactive free radicals of oxygen (ROS) in response to lipopolysaccharide (LPS) stimulation. TRPM2 is activated by LPS-induced oxidative stress, but it is inhibited by carvacrol (CARV) and N-(p-amylcinnamoyl)anthranilic acid (ACA). Morphine (MRP), an opioid ligand, has the potential to be both an anesthetic and an antioxidant.

Objective: We investigated how MRP changed the TRPM2 signaling pathways to protect murine BV-2 microglia cells from LPS-induced ROS, cytokine production, and death.

Materials and methods: We generated five primary groups in the cultured BV-2 cells: Control, MRP (50 μM for 24h), LPS (1 μg/ml for 24h), LPS + MRP, and LPS + TRPM2 blockers (ACA or CARV).

Results: The incubation of LPS increased the amounts of apoptosis, cell death (propidium iodide positive cell number), oxidants (ROS and lipid peroxidation), mitochondrial dysfunction, apoptotic markers (caspase -3, -8, and -9), cytokines (TNF-α, IL-1β, and IL-6), death cell waste (debris), cytosolic free Ca²⁺, Zn²⁺, and ADP-ribose-induced TRPM2 current densities, while the treatments of MRP and TRPM2 blockers reduced their amounts. The LPS-induced reductions in BV-2 viability percentage, BV-2 number, glutathione peroxidase activity, and glutathione levels were increased by the treatments.

Conclusions: MRP reduced the levels of LPS-induced oxidative stress, inflammatory cytokines, and apoptosis via inhibiting TRPM2 in the BV-2 cells. One possible treatment option for oxidative microglia damage and neurological disorders induced by LPS could be the MRP.