Comparative analysis of the effects of opioids in angiogenesis.

Background Angiogenesis, the formation of blood vessel from pre-existing ones, plays an important role in many pathophysiological diseases, such as cancer. Opioids are often used in clinic for the management of chronic pain in cancer patients at terminal phases. Here, we investigated and compared the effects and mechanisms of four opioids on angiogenesis. Methods We performed angiogenesis assays on human umbilical vein endothelial cells (HUVEC) that represent an in vitro model to assess the toxicity of drugs to endothelium. Results Morphine and oxycodone at 0.1 μM to 100 μM dose-dependently increased endothelial cell tube formation and proliferation. We observed the same in endothelial cells exposed to fentanyl at 0.1 μM to 10 μM but there was a gradual loss of stimulation by fentanyl at 100 μM and 1000 μM. Morphine and fentanyl reduced endothelial cell apoptosis-induced by serum withdrawal whereas oxycodone did not display anti-apoptotic effect, via decreasing Bax level. Oxycodone at the same concentrations was less potent than morphine and fentanyl. Different from other three opioids, codeine at all tested concentrations did not affect endothelial cell tube formation, proliferation and survival. Mechanism studies demonstrated that opioids acted on endothelial cells via μ-opioid receptor-independent pathway. Although we observed the increased phosphorylation of mitogen-activated protein kinase (MAPK) in cells exposed to morphine, fentanyl and oxycodone, the rescue studies demonstrated that the stimulatory effects of morphine but not fentanyl nor oxycodone were reversed by a specific MAPK inhibitor. Conclusion Our work demonstrates the differential effects and mechanisms of opioids on angiogenesis.