Melatonin Influences Interleukin‐12 and Nitric Oxide Production by Primary Cultures of Rheumatoid Synovial Macrophages and THP‐1 Cells^a

Abstract

Because some of the clinical symptoms related to rheumatoid arthritis (RA) synovitis, such as joint morning stiffness and gelling, might be related to the effects exerted by the diurnal rhythmicity of the neurohormone melatonin (MLT) on synovial immune cell activation, we decided to evaluate the influence of MLT on the production of IL-12 and nitric oxide (NO) on primary cultures of RA synovial macrophages. Synovial macrophages were also prestimulated with lipopolysaccaride (LPS). Results were compared with those obtained on cultured human myeloid monocytic cells (THP-1). A significant increase in IL-12 (p = 0.01) was found in media of MLT-stimulated synovial macrophages versus RMPI-treated synovial macrophage controls. Interestingly, a significant decrease of IL-12 (p < 0.0001) was observed in media of synovial macrophages previously activated with LPS and then treated with MLT, when compared to synovial macrophages treated with LPS alone. A significant increase in NO levels (p = 0.01) was found in MLT-stimulated synovial macrophages versus RMPI-treated synovial macrophage controls. Interestingly, a nonsignificant increase of NO levels was observed in media of synovial macrophages previously activated with LPS and then treated with MLT, when compared to cynovial macrophages treated with LPS alone. Finally, a significant increase in IL-12 (p = 0.03) and NO (p = 0.002) concentrations was observed in media of MLT-stimulated THP-1 cells versus RMPI-treated controls. Our results therefore show that MLT induces IL-12 secretion and NO production by unstimulated cultured RA synovial macrophages and human monocytic myeloid THP-1 cells. The unexpected and opposite effects on IL-12 and NO production in RA synovial macrophages treated with LPS may be related to dose-dependent mechanisms exerted by MLT or to altered cell priming in RA macrophages; these are matters of our further research. This study strongly supports the role of MLT in immune response modulation and in particular suggests a close relationship between diurnal rhythmicity of neuroendocrine pathways, cytokine and reactive oxygen intermediate production by monocyte/macrophages, and synovial arthritis symptomatology, at least in RA.

Circadian rhythms of nocturnal hormones in rheumatoid arthritis: translation from bench to bedside

“…In addition, MLT was found to enhance production of inflammatory cytokines from cultured human monocytes/macrophages, including IL12 and turning the MLT/IL2 connection towards the enhancement of T cell immunity 18. MLT was found to be detectable at high concentration in synovial fluids from patients who had RA, and binding sites for MLT were present in synovial macrophages 19…”

A role for melatonin in maintaining the pro- and anti-inflammatory balance by influencing leukocyte migration and apoptosis in carp

“…Furthermore, melatonin decreased the production of anti-inflammatory IL-10 as well as proinflammatory TNF-a in IL-2 and LPS-stimulated human monocytes (Lissoni et al, 1996;Fjaerli et al, 1999). In human macrophages, a preincubation with LPS led to inhibition of IL-12 production by melatonin (Cutolo et al, 1999). Also, in LPS-stimulated mouse RAW 264.7 cells, melatonin inhibited the expression of TNF-a, IL-1b, IL-6, IL-8 and IL-10 (Xia et al, 2012).…”

Myeloperoxidase-Catalyzed Oxidation of Melatonin by Activated Neutrophils

“…This pineal hormone controls several essential physiological functions associated with circadian and seasonal rhythms (12). Increasing evidence also points to its participation in the immune response, with effects on leukocyte activation, cytokine and nitric oxide production and modulation of vascular permeability having been reported (13)(14)(15)(16). The mechanism of action of this pineal hormone is completely unknown.…”