| 1. |
- Escher, Sylvia E., et al.
(author)
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Integrate mechanistic evidence from new approach methodologies (NAMs) into a read-across assessment to characterise trends in shared mode of action
- 2022
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In: Toxicology in Vitro. - : Elsevier. - 0887-2333 .- 1879-3177. ; 79
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Journal article (peer-reviewed)abstract
- Read-across approaches often remain inconclusive as they do not provide sufficient evidence on a common mode of action across the category members. This read-across case study on thirteen, structurally similar, branched aliphatic carboxylic acids investigates the concept of using human-based new approach methods, such as in vitro and in silico models, to demonstrate biological similarity.Five out of the thirteen analogues have preclinical in vivo studies. Three out of them induced lipid accumulation or hypertrophy in preclinical studies with repeated exposure, which leads to the read-across hypothesis that the analogues can potentially induce hepatic steatosis.To confirm the selection of analogues, the expression patterns of the induced differentially expressed genes (DEGs) were analysed in a human liver model. With increasing dose, the expression pattern within the tested analogues got more similar, which serves as a first indication of a common mode of action and suggests differences in the potency of the analogues.Hepatic steatosis is a well-known adverse outcome, for which over 55 adverse outcome pathways have been identified. The resulting adverse outcome pathway (AOP) network, comprised a total 43 MIEs/KEs and enabled the design of an in vitro testing battery. From the AOP network, ten MIEs, early and late KEs were tested to systematically investigate a common mode of action among the grouped compounds.The targeted testing of AOP specific MIE/KEs shows that biological activity in the category decreases with side chain length. A similar trend was evident in measuring liver alterations in zebra fish embryos. However, activation of single MIEs or early KEs at in vivo relevant doses did not necessarily progress to the late KE “lipid accumulation”. KEs not related to the read-across hypothesis, testing for example general mitochondrial stress responses in liver cells, showed no trend or biological similarity.Testing scope is a key issue in the design of in vitro test batteries. The Dempster-Shafer decision theory predicted those analogues with in vivo reference data correctly using one human liver model or the CALUX reporter assays.The case study shows that the read-across hypothesis is the key element to designing the testing strategy. In the case of a good mechanistic understanding, an AOP facilitates the selection of reliable human in vitro models to demonstrate a common mode of action. Testing DEGs, MIEs and early KEs served to show biological similarity, whereas the late KEs become important for confirmation, as progression from MIEs to AO is not always guaranteed.
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| 2. |
- Koymans, Kirsten J, et al.
(author)
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The TLR2 Antagonist Staphylococcal Superantigen-Like Protein 3 Acts as a Virulence Factor to Promote Bacterial Pathogenicity in vivo
- 2017
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In: Journal of Innate Immunity. - : S. Karger AG. - 1662-811X .- 1662-8128. ; 9, s. 561-573
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Journal article (peer-reviewed)abstract
- Toll-like receptor (TLR) signaling is important in the initiation of immune responses and subsequent instigation of adaptive immunity. TLR2 recognizes bacterial lipoproteins and plays a central role in the host defense against bacterial infections, including those caused by Staphylococcus aureus. Many studies have demonstrated the importance of TLR2 in murine S. aureus infection. S. aureus evades TLR2 activation by secreting two proteins, staphylococcal superantigen-like protein 3 (SSL3) and 4 (SSL4). In this study, we demonstrate that antibodies against SSL3 and SSL4 are found in healthy individuals, indicating that humans are exposed to these proteins during S. aureus colonization or infection. To investigate the TLR2-antagonistic properties of SSL3 and SSL4, we compared the infection with wild-type and SSL3/4 knockout S. aureus strains in an intravenous murine infection model. Direct evaluation of the contribution of SSL3/4 to infection pathogenesis was hindered by the fact that the SSLs were not expressed in the murine system. To circumvent this limitation, an SSL3-overproducing strain (pLukM-SSL3) was generated, resulting in constitutive expression of SSL3. pLukM-SSL3 exhibited increased virulence compared to the parental strain in a murine model that was found to be TLR2 dependent. Altogether, these data indicate that SSL3 contributes to S. aureus virulence in vivo.
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| 3. |
- Loof, Torsten, et al.
(author)
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Aberrant Inflammatory Response to Streptococcus pyogenes in Mice Lacking Myeloid Differentiation Factor 88.
- 2010
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In: American Journal of Pathology. - : Elsevier BV. - 1525-2191 .- 0002-9440. ; 176, s. 754-763
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Journal article (peer-reviewed)abstract
- Several in vitro studies have emphasized the importance of toll-like receptor/myeloid differentiation factor 88 (MyD88) signaling in the inflammatory response to Streptococcus pyogenes. Since the extent of inflammation has been implicated in the severity of streptococcal diseases, we have examined here the role of toll-like receptor/MyD88 signaling in the pathophysiology of experimental S. pyogenes infection. To this end, we compared the response of MyD88-knockout (MyD88(-/-)) after subcutaneous inoculation with S. pyogenes with that of C57BL/6 mice. Our results show that MyD88(-/-) mice harbored significantly more bacteria in the organs and succumbed to infection much earlier than C57BL/6 animals. Absence of MyD88 resulted in diminished production of inflammatory cytokines such as interleukin-12, interferon-gamma, and tumor necrosis factor-alpha as well as chemoattractants such as monocyte chemotactic protein-1 (MCP-1) and Keratinocyte-derived chemokine (KC), and hampered recruitment of effector cells involved in bacterial clearance (macrophages and neutrophils) to the infection site. Furthermore, MyD88(-/-) but not C57BL/6 mice exhibited a massive infiltration of eosinophils in infected organs, which can be explained by an impaired production of the regulatory chemokines, gamma interferon-induced monokine (MIG/CXCL9) and interferon-induced protein 10 (IP-10/CXCL10), which can inhibit transmigration of eosinophils. Our results indicate that MyD88 signaling targets effector cells to the site of streptococcal infection and prevents extravasation of cells that can induce tissue damage. Therefore, MyD88 signaling may be important for shaping the quality of the inflammatory response elicited during infection to ensure optimal effector functions.
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| 4. |
- Loof, Torsten, et al.
(author)
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Staphylococcus aureus induced clotting of plasma is an immune evasion mechanism to persist within the fibrin network.
- 2014
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In: Microbiology. - : Microbiology Society. - 1465-2080 .- 1350-0872.
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Journal article (peer-reviewed)abstract
- Recent work has shown that coagulation and innate immunity are tightly interwoven host responses that help eradicate an invading pathogen. Some bacterial species including Staphylococcus aureus secrete pro-coagulant factors that in turn can modulate these immune reactions. Such mechanisms may not only protect the microorganism from a lethal attack, but also promote bacterial proliferation and the establishment of the infection. Our data show that coagulase positive S. aureus bacteria promote clotting of plasma which was not seen when a coagulase-deficient mutant strain was used. Further in vitro studies show that this ability constitutes a mechanism that supports the aggregation, survival, and persistence of the microorganism within the fibrin network. These findings were also confirmed when agglutination and persistence of coagulase-positive S. aureus bacteria at the local focus of infection were studied in a subcutaneous murine infection model. In contrast, the coagulase-deficient S. aureus strain which was not able to induce clotting failed to aggregate and to persist in vivo. In conclusion our data suggest that coagulase positive S. aureus have evolved mechanisms that prevent their elimination within a fibrin clot.
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