Cytokine secretion from monocytes persists differentially after activator removal-One mechanism of long-term biological response to implants

Concomitant activation of P2Y(2) and P2Y(6) receptors on monocytes is required for TLR1/2-induced neutrophil migration by regulating IL-8 secretion

Extracellular nucleotides regulate a variety of cellular responses involved in inflammation via the activation of P2 receptors. Here, we show that nucleotides regulate TLR2-induced neutrophil migration both in vivo and in vitro. The nucleotide scavenger apyrase inhibited neutrophil recruitment in murine air pouches injected with the TLR2 agonist Pam(3)CSK(4). In agreement, the supernatants of either human primary monocytes or monocytic cells (THP-1 and U937) treated with Pam(3)CSK(4) recruited significantly fewer neutrophils when the former cells were treated in the presence of apyrase. As demonstrated with inhibitory Ab, these supernatants induced neutrophil migration due to IL-8 secretion. In addition, IL-8 secretion was markedly diminished by the non-selective P2 receptor antagonists reactive blue 2 and suramin, and by a selective P2Y(6) antagonist, MRS2578. Selective antagonists of P2Y(1) (MRS2500) and P2Y(11) (NF157) did not affect IL-8 release. The knockdown of either P2Y(2) or P2Y(6) with specific shRNA diminished IL-8 secretion from Pam(3)CSK(4)-treated THP-1 cells. Altogether, these results show that extracellular nucleotides, via P2Y(2) and P2Y(6) receptors, regulate neutrophil migration by controlling TLR2-induced IL-8 release from human monocytes. In line with our previous work on TLR4, this study further supports the importance of nucleotides in bacterial-induced neutrophil migration.

Ni(II) ions dysregulate cytokine secretion from human monocytes

Nickel-containing alloys are used in dentistry because of their low cost, but poor corrosion behavior increases their risk of causing adverse biological responses. Intraorally, nickel-containing alloys accumulate bacterial plaque that triggers periodontal inflammation via toxins such as lipopolysaccharide (LPS). Recent evidence suggests that in monocytes, Ni(II) amplifies LPS-induced secretion of several cytokines that mediate periodontal destruction. Thus, we investigated the effects of Ni(II), with or without LPS, on the secretion of a broader array of cytokines from monocytes. We then measured monocytic expression of two proteins, Nrf2 and thioredoxin-1 (Trx1), that influence the regulation of cytokine secretion. Cytokine arrays were used to measure the effects of 0-50 microM Ni(II) on cytokine secretion from human THP1 monocytes, with or without LPS activation. Immunoblots were used to estimate Nrf2 and Trx1 levels. Our results indicate that both Ni(II) alone and Ni(II) with LPS have broad-based effects on cytokine secretion. Ni(II) increased Nrf2 levels by threefold, and LPS amplified the effects of Ni(II) by 10-fold. Trx1 levels did not change under any condition tested. Our results suggest that Ni(II)-induced changes in cytokine secretion by monocytes are diverse and may be influenced by Nrf2 but are not likely influenced by changes in whole-cell Trx1 levels.

Interactions between stainless steel, shear stress, and monocytes

Angioplasty with stent placement is commonly used to treat coronary atherosclerosis. However, 20-40% of stainless steel stents restenose within 6 months via a prolonged inflammatory response mediated by monocytic infiltration and cytokine secretion. In the current study, we tested a hypothesis that blood flow and monocytes interact to alter stent corrosion. We assessed the effects of THP1 monocytes on the corrosion rate of 316L stainless steel (316LSS) under shear stress (0.5-50 dyn/cm(2)). In addition, THP1 cytokine secretion was determined using cytokine arrays and ELISA analyses. Data were compared using ANOVA and Tukey post hoc analysis (alpha = 0.05). Monocytes significantly lowered 316LSS corrosion rates without limiting current density. However, shear stress alone did not alter the corrosion rate of 316LSS. THP1 cells adhered to the 316LSS surface at all flow rates. Exposure to the 316LSS/corrosion test under high fluid flow rates increased (>twofold) the secretion of 7 of the 42 cytokines tested (angeogenin, GRO, I309, interleukin 8, interleukin 6, interleukin 1beta, and macrophage chemoattractant protein-1). Each of these cytokines play a role in wound healing, macrophage differentiation, and cell proliferation, all hallmarks of in-stent restenosis. Furthermore, only IL8 levels were significantly higher than any of the system controls during the 316LSS/corrosion test conditions. The IL8 levels from the 316LSS/corrosion tests were not significantly different from the +LPS control. Together, these data suggest that monocytic cells maybe activated by exposure to 316LSS stents and could contribute to in-stent restenosis and altered corrosion of the stent.