Differential influence ofStreptococcus mitison host response to metals in reconstructed human skin and oral mucosa

Abstract

Background: Skin and oral mucosa are continuously exposed to potential metal sensitizers while hosting abundant microbes, which may influence the host response to sensitizers. This host response may also be influenced by the route of exposure that is skin or oral mucosa, due to their different immune properties. Objective: Determine how commensal Streptococcus mitis influences the host response to nickel sulfate (sensitizer) and titanium(IV) bis(ammonium lactato) dihydroxide (questionable sensitizer) in reconstructed human skin (RHS) and gingiva (RHG). Methods: RHS/RHG was exposed to nickel or titanium, in the presence or absence of S. mitis for 24 hours. Histology, cytokine secretion, and Toll-like receptors (TLRs) expression were assessed. Results: S. mitis increased interleukin (IL)-6, CXCL8, CCL2, CCL5, and CCL20 secretion in RHS but not in RHG; co-application with nickel further increased cytokine secretion. In contrast, titanium suppressed S. mitis-induced cytokine secretion in RHS and had no influence on RHG. S. mitis and metals differentially regulated TLR1 and TLR4 in RHS, and predominantly TLR4 in RHG. Conclusion: Co-exposure of S. mitis and nickel resulted in a more potent innate immune response in RHS than in RHG, whereas titanium remained inert. These results indicate the important influence of commensal microbes and the route of exposure on the host's response to metals.

A Multi-Organ-on-Chip Approach to Investigate How Oral Exposure to Metals Can Cause Systemic Toxicity Leading to Langerhans Cell Activation in Skin

“…However, exposure to nickel sulfate did not result in increased levels of pro-inflammatory cytokines IL-6, IL-8, and IL-18. For IL-18, this is in-line with previous research where we show that metal salts do not result in increased IL-18 levels in reconstructed human epidermis (RHE, ( Gibbs et al, 2018 )) and RHG ( Shang et al, 2020 ). Notably, RHG and RHS are able to produce increased levels of general inflammatory mediators IL-6 and IL-8 upon exposure to nickel sulfate when compared to the vehicle ( Kosten et al, 2015b ; Shang et al, 2020 ) although higher concentrations of nickel sulfate were applied previously than those in this study (20 vs 10 mM, respectively).…”

“…For IL-18, this is in-line with previous research where we show that metal salts do not result in increased IL-18 levels in reconstructed human epidermis (RHE, ( Gibbs et al, 2018 )) and RHG ( Shang et al, 2020 ). Notably, RHG and RHS are able to produce increased levels of general inflammatory mediators IL-6 and IL-8 upon exposure to nickel sulfate when compared to the vehicle ( Kosten et al, 2015b ; Shang et al, 2020 ) although higher concentrations of nickel sulfate were applied previously than those in this study (20 vs 10 mM, respectively). Although in this study we did not include the assessment of pro-inflammatory cytokines, it is most probable that these are released at low concentrations within the RHG and RHS-LC and immediately removed from the circulating culture supernatant by the keratinocyte and fibroblasts within the tissue constructs.…”

Metal Allergy: State-of-the-Art Mechanisms, Biomarkers, Hypersensitivity to Implants

“…Ni-mediated cytokine secretion IL-6, CXCL8, C-C motif ligand (CCL2), CCL5, and CCL20 is enriched by Streptococcus mitis in reconstructed human skin (RHS) but not in the gingiva (RHG), while Ti suppresses cytokines induced by S. mitis in RHS. Moreover, the co-application of metal and S. mitis differentially regulate Toll-like receptors (TLR)1 and 4 expressions [ 78 ].…”

Stable reconstructed human gingiva–microbe interaction model: Differential response to commensals and pathogens

“…In the past, we have developed a reconstructed human gingiva (RHG) consisting of a stratified and differentiated gingival epithelium on a fibroblast-populated collagen hydrogel which functions as the lamina propria ( Kosten et al., 2015 ). RHG is cultured exposed to the air from above with culture medium being supplied from below, which enables topical application of chemicals and bacteria similar to the in vivo situation ( Shang et al., 2020 ). Using this RHG model, we have investigated host TLR expression and cytokine secretion in response to saliva-derived multi-species biofilms ( Buskermolen et al., 2018 ; Shang et al., 2019 ), as well as to an oral resident bacterium Streptococcus mitis in combination with metal sensitizers related to oral allergy ( Shang et al., 2020 ).…”

“…RHG is cultured exposed to the air from above with culture medium being supplied from below, which enables topical application of chemicals and bacteria similar to the in vivo situation ( Shang et al., 2020 ). Using this RHG model, we have investigated host TLR expression and cytokine secretion in response to saliva-derived multi-species biofilms ( Buskermolen et al., 2018 ; Shang et al., 2019 ), as well as to an oral resident bacterium Streptococcus mitis in combination with metal sensitizers related to oral allergy ( Shang et al., 2020 ). Even though this co-culture model represents complex host-microbe interactions in comparison to conventional 2D monolayer models, it still has the major limitation in that bacterial cells were no longer viable after 24 hours.…”