Effects of sinomenine on the proliferation, cytokine production, and regulatory T-cell frequency in peripheral blood mononuclear cells of rheumatoid arthritis patients.

Sinomenine (SN) is a plant-derived alkaloid isolated from Caulis Sinomenii. It has been approved by the State Food and Drug Administration of China for treating rheumatoid arthritis (RA) nearly 20 years ago. To investigate the anti-RA mechanism of SN, a lot of scholars reported the immunosuppressive effect of SN on T lymphocytes. We continued to evaluate the suppressive function of SN by using human peripheral blood mononuclear cells (PBMCs) isolated from RA patients. As the positive control, 10 ng/ml of methylprednisolone (MP) showed the antiproliferation effect on mitogen-activated PBMCs of RA patients significantly (*p < .05). Meanwhile, MP decreased the frequency of CD4+ CD25+ T cells and suppressed the secretion of inflammatory Th1/Th2/Th17 cytokines such as IL-4, IL-6, IL-10, IL-17, IFN-γ, and TNF-α. However, SN at concentrations of 0.3-30 μM, showed little suppressive effects on the proliferation of PBMCs of RA patients. We did not observe any suppressive effects of SN on percentages of CD4+ T cells and CD4+ CD25+ T cells in the mitogen-activated PBMCs of RA patients. The influence of SN on the percentage of CD4+ CD25+ Foxp3+ T cells was also limited. Finally, even 30 μM of SN did not influence the secretion of Th1/Th2/Th17 cytokine significantly. The present study provided evidence that anti-RA mechanism of SN seems not to be related with the suppressive effects on peripheral T cells.