Papers of the Week

Duloxetine, a serotonin-norepinephrine reuptake inhibitor, is currently recommended as a useful medicine to chronic pain including low back pain. However, as the analogy of classical selective serotonin reuptake inhibitors, there is a concern to deteriorate osteoporosis with remaining to clarify the exact mechanism of duloxetine in bone metabolism. We have previously reported that prostaglandin E (PGE) induces the synthesis of both osteoprotegerin (OPG) and interleukin-6 (IL-6), essential regulators of bone metabolism, in osteoblast-like MC3T3-E1 cells. Based upon them, we herein investigated the mechanism whereby the effect of duloxetine on the synthesis of OPG and IL-6 induced by PGE in these cells. Duloxetine enhanced the release from MC3T3-E1 cells of both OPG and IL-6 stimulated by PGE. However, reboxetine, a selective and specific inhibitor of norepinephrine reuptake, failed to affect the PGE-induced release of OPG or IL-6. Oppositely, fluvoxamine and sertraline, agents belonging to the class of selective serotonin reuptake inhibitor, upregulated the PGE-stimulated release of both OPG and IL-6. Duloxetine amplified the expression of OPG mRNA and IL-6 mRNA stimulated by PGE. Duloxetine strengthened the PGE-induced p38 MAP kinase phosphorylation, which was amplified by fluvoxamine as well. SB203880, an inhibitor of p38 MAP kinase, suppressed the amplifying effects by duloxetine or fluvoxamine on the PGE-stimulated release of OPG and IL-6. These results strongly suggest that duloxetine could strengthen osteoblast activation by PGE through the upregulation of p38 MAP kinase, leading to increasing the synthesis of OPG and IL-6.