The extended effect of adsorbed damage-associated molecular patterns and Toll-like receptor 2 signaling on macrophage-material interactions

Therapeutic Insulin Analogue Concentrations at Infusion Sites Enhanced the Pro-Inflammatory Response and Apoptosis in an In Vitro Macrophage-Material Interaction Model

Continuous subcutaneous insulin infusion for Type 1 diabetes relies upon insulin infusion sets (IIS) to reliably deliver insulin to a subcutaneous depot, where it is absorbed into systemic circulation. However, IIS are plagued by short wear times and high failure rates, due in part to inconsistent insulin absorption that can arise over time. While emerging evidence suggests that the local inflammatory response to the IIS cannula may impact both wear times and unreliable insulin adsorption, the mechanisms are poorly understood. Here, we investigated the effects of local infused insulin concentrations on the biomaterial host response to better understand the underlying factors that limit the IIS performance. We first modeled the insulin concentration for a constant basal infusion rate to select a relevant insulin concentration range of 0.1-10 U/mL within the infusion site. We then examined the influence of a commercial insulin analogue (Humulin-N) using an in vitro macrophage-material model, which uses adsorbed fibroblast lysate (containing damage-associated molecular patterns) to activate macrophages and recapitulates macrophage responses on implanted biomaterials. RAW-Blue macrophages cultured on lysate-adsorbed surfaces had increased nuclear factor-κB (NF-κB) and activating protein 1 (AP-1) activity and intracellular reactive oxygen species (ROS) accumulation compared to control surfaces. Humulin-N concentration (0.5-10 U/mL) enhanced the NF-κB/AP-1 activity and ROS accumulation in macrophages on lysate-adsorbed surfaces. However, Humulin-N had no effect on NF-κB/AP-1 or ROS in the absence of the inflammatory stimulus. Additionally, high insulin concentrations arising from therapeutic doses induced macrophage apoptosis with and without adsorbed lysate. This study contributes to emerging evidence that infused insulin affects the tissue response to IIS.

Cell- and Serum-Derived Proteins Act as DAMPs to Activate RAW 264.7 Macrophage-like Cells on Silicone Implants

Protein adsorption after biomaterial implantation is the first stage of the foreign body response (FBR). However, the source(s) of the adsorbed proteins that lead to damaged associated molecular patterns (DAMPs) and induce inflammation have not been fully elucidated. This study examined the effects of different protein sources, cell-derived (from a NIH/3T3 fibroblast cell lysate) and serum-derived (from fetal bovine serum), which were compared to implant-derived proteins (after a 30 min subcutaneous implantation in mice) on activation of RAW 264.7 cells cultured in minimal (serum-free) medium. Both cell-derived and serum-derived protein sources when preadsorbed to either tissue culture polystyrene or medical-grade silicone induced RAW 264.7 cell activation. The combination led to an even higher expression of pro-inflammatory cytokine genes and proteins. Implant-derived proteins on silicone explants induced a rapid inflammatory response that then subsided more quickly and to a greater extent than the studies with in vitro cell-derived or serum-derived protein sources. Proteomic analysis of the implant-derived proteins identified proteins that included cell-derived and serum-derived, but also other proteinaceous sources (e.g., extracellular matrix), suggesting that the latter or nonproteinaceous sources may help to temper the inflammatory response in vivo. These findings indicate that both serum-derived and cell-derived proteins adsorbed to implants can act as DAMPs to drive inflammation in the FBR, but other protein sources may play an important role in controlling inflammation.

MyD88-dependent Toll-like receptor 2 signaling modulates macrophage activation on lysate-adsorbed Teflon™ AF surfaces in an in vitro biomaterial host response model

The adsorbed protein layer on an implanted biomaterial surface is known to mediate downstream cell-material interactions that drive the host response. While the adsorption of plasma-derived proteins has been studied extensively, the adsorption of damage-associated molecular patterns (DAMPs) derived from damaged cells and matrix surrounding the implant remains poorly understood. Previously, our group developed a DAMP-adsorption model in which 3T3 fibroblast lysates were used as a complex source of cell-derived DAMPs and we demonstrated that biomaterials with adsorbed lysate potently activated RAW-Blue macrophages via Toll-like receptor 2 (TLR2). In the present study, we characterized the response of mouse bone marrow derived macrophages (BMDM) from wildtype (WT), TLR2-/- and MyD88-/- mice on Teflon™ AF surfaces pre-adsorbed with 10% plasma or lysate-spiked plasma (10% w/w total protein from 3T3 fibroblast lysate) for 24 hours. WT BMDM cultured on adsorbates derived from 10% lysate in plasma had significantly higher gene and protein expression of IL-1β, IL-6, TNF-α, IL-10, RANTES/CCL5 and CXCL1/KC, compared to 10% plasma-adsorbed surfaces. Furthermore, the upregulation of pro-inflammatory cytokine and chemokine expression in the 10% lysate in plasma condition was attenuated in TLR2-/- and MyD88-/- BMDM. Proteomic analysis of the adsorbed protein layers showed that even this relatively small addition of lysate-derived proteins within plasma (10% w/w) caused a significant change to the adsorbed protein profile. The 10% plasma condition had fibrinogen, albumin, apolipoproteins, complement, and fibronectin among the top 25 most abundant proteins. While proteins layers generated from 10% lysate in plasma retained fibrinogen and fibronectin among the top 25 proteins, there was a disproportionate increase in intracellular proteins, including histones, tubulins, actins, and vimentin. Furthermore, we identified 7 DAMPs or DAMP-related proteins enriched in the 10% plasma condition (fibrinogen, apolipoproteins), compared to 39 DAMPs enriched in the 10% lysate in plasma condition, including high mobility group box 1 and histones. Together, these findings indicate that DAMPs and other intracellular proteins readily adsorb to biomaterial surfaces in competition with plasma proteins, and that adsorbed DAMPs induce an inflammatory response in adherent macrophages that is mediated by the MyD88-dependent TLR2 signaling pathway.