Morphine decreases the function of primary human natural killer cells by both TLR4 and opioid receptor signaling.

BACKGROUND: Opioids are commonly used to provide analgesia for cancer pain, and functional opioid receptors have been identified on natural killer (NK) cells, the lymphocytes responsible for surveillance and elimination of cancer cells. Opioids also bind to other lymphocyte receptors, such as Toll-like receptor (TLR)-4. Here, we characterized the effects of morphine on primary human NK cell cytotoxicity and mediator release, which occur through classical opioid receptor or TLR4 signaling. METHODS: Purified primary human NK cells were pretreated with inhibitors of opioid receptors or TLR4 before being cultured with target tumor cell line K562 in the presence or absence of morphine. Apoptosis of K562 cells in each treatment condition was measured with an Annexin V flow cytometry-based assay and compared to that of K562 cells cultured with NK cells alone. Supernatant concentrations of 13 cytokines and cytotoxic mediators were measured with a multiplex bead-based flow cytometry assay. RESULTS: Exposure of NK cells to morphine decreased their ability to induce apoptosis in K562 cells. Pretreating the NK cells with either naloxone, a mu- and kappa-opioid receptor antagonist, or TAK-242, a selective inhibitor of TLR4 signaling, prevented this effect. Paradoxically, morphine increased the concentration of interleukin-6, granzyme A, and granzyme B in cell supernatants. Pretreatment of NK cells with TAK-242 prevented the morphine-induced increase in interleukin-6, whereas pretreatment with naloxone inhibited the morphine-induced increase in granzymes A and B. CONCLUSIONS: Both classical opioid receptors and TLR4 participate in morphine-induced suppression of NK cell cytotoxic activity. These studies have important implications for maintenance of immune function during management of cancer pain.

Suppression of Human Natural Killer Cells by Different Classes of Opioids.

BACKGROUND: The use of regional and other opioid-sparing forms of anesthesia has been associated with a decrease in the recurrence of certain malignancies. Direct suppression of human natural killer cells by opioids has been postulated to explain this observation. However, the effect of different classes of opioids on suppression of natural killer cell cytotoxicity has not been systematically characterized. METHODS: After confirming that freshly isolated natural killer cells from peripheral human blood express opioid receptors, cells were incubated with increasing concentrations of clinically used or receptor-specific opioid agonists. We also evaluated the effect of pretreatment with receptor-specific antagonists or naloxone. Treated natural killer cells were then coincubated with a carboxyfluorescein succinimidyl ester-labeled target tumor cell line, K562. Annexin V staining was used to compare the percent of tumor cell apoptosis in the presence of opioid-pretreated and untreated natural killer cells. Treated samples were compared to untreated samples using Kruskal-Wallis tests with a post hoc Dunn correction. RESULTS: Morphine, methadone, buprenorphine, loperamide, [D-Ala2, N-MePhe4, Gly-ol]-enkephalin, and U-50488 significantly decreased natural killer cell cytotoxicity. When natural killer cells were pretreated with naloxone, cyprodime, and nor-binaltorphimine before exposure to morphine, there was no difference in natural killer cytotoxicity, compared to the amount observed by untreated natural killer cells. Fentanyl, O-desmethyltramadol, and [D-Pen2,D-Pen5] enkephalin did not change natural killer cell cytotoxicity compare to untreated natural killer cells. CONCLUSIONS: Incubation of isolated natural killer cells with certain opioids causes a decrease in activity that is not observed after naloxone pretreatment. Suppression of natural killer cell cytotoxicity was observed with µ- and κ-receptor agonists but not δ-receptor agonists. These data suggest that the effect is mediated by µ- and κ-receptor agonism and that suppression is similar with many clinically used opioids.