Differential effects of TNF-α and IL-1β on the control of metal metabolism and cadmium-induced cell death in chronic inflammation

Objective Interleukin-1-beta (IL-1 beta) and tumour necrosis factor-alpha (TNF-alpha) are both monocyte-derived cytokines. Both cytokines have been previously described to exert a role in rheumatoid arthritis (RA) pathogenesis synergizing with other pro-inflammatory mediators, such as interleukin-17 (IL-17) on target cells, for the perpetuation of the inflammatory response (e.g. IL-6 production). In the context of experimental RA, Cd addition has an anti-proliferative and anti-inflammatory effect when associated to IL-17/TNF-alpha stimulation, due to its accumulation in synoviocytes. The aim of this work was to evaluate if IL-1 beta interaction with IL-17 also contributes to metal-import mechanisms and its effects on cell viability and inflammation. Methods IL-17 and IL-1 beta were added to synoviocyte cultures with or without exogenous Cd addition (0.1 ppm, 0.89 mu M). IL-6 production, Cd import kinetics, gene expression of ZIP-8 importer and metallothioneins (MTs) and cell viability were evaluated by ELISA, inductively-coupled mass spectrometry (ICP-MS), q-RT-PCR and viability assays (neutral red and annexin V) respectively. Results IL-17 and IL-1 beta acted in synergy on synoviocytes to induce IL-6 production similarly to the IL-17/TNF-alpha combination. Metal import was lower with IL17/IL-1 beta in comparison to IL-17/ TNF-alpha exposed-synoviocytes, as the expression of ZIP-8 and MT-1F was less induced. Monocyte and PBMCs exposure to Cd resulted in a reduced production of IL-1 beta and an increased production of TNF-alpha and this result was confirmed in co-cultures of synoviocytes and PBMCs. The IL-17/IL-1 beta combination with Cd slightly reduced cell viability in comparison to the IL-17/TNF-alpha combination and resulted in a strong induction of IL-6 production. Conclusion IL-17/TNF-alpha combination but not IL-17/IL-1 beta combination mainly drives the accumulation of Cd in synoviocytes and its effects on cell viability and inflammation.