Scientists have identified that etanercept can restore responsiveness to the pain-relieving effects of morphine in rats that have developed morphine tolerance.
The experimental results suggest that etanercept-which blocks the inflammatory cytokine tumor necrosis factor (TNF)-alpha-could provide a useful new approach to "extend the effectiveness" of morphine and related drugs (opioids) for pain control.
The authors led by Chih-Shung Wong of Cathay General Hospital, Taipei, Taiwan, designed an experiment to evaluate the effects of etanercept in rats that had been made morphine tolerant.
When these animals were treated with etanercept, it restored up to 60 percent of their responsiveness to morphine.
Morphine tolerance was associated with changes in the levels of certain inflammation-promoting proteins, called cytokines.
When the animals were treated with etanercept, expression of the inflammatory cytokines was significantly reduced, in particular Tumor necrosis factor-alpha, often called TNF.
These changes were accompanied by reduced levels of activation of specialized spinal cord immune cells, called microglia.
Because of its ability to block TNF-?, etanercept is an effective treatment for rheumatoid arthritis and other inflammatory autoimmune diseases.
The new results show that etanercept can restore much of the pain-relieving effect of morphine in morphine-tolerant rats.
Etanercept treatment also reduces expression of inflammation-promoting cytokines, as well as activation of the microglia.
The study appeared in the February issue of Anesthesia and Analgesia, official journal of the International Anesthesia Research Society (IARS).