Mitchell Clark

Introduction & Hypothesis: Fusobacterium species, especially F. necrophorum, are the causative pathogens of Lemierre’s Syndrome (LS), which is characterized by disseminated intravascular coagulation and septic emboli.^1,2 First-line treatment consists of aggressive antibiotic cocktails; the use of anticoagulants remains controversial, and might increase mortality by creating surgical complications.^1,2 How Fusobacterium causes thrombosis remains unclear;¹ a better understanding of this mechanism could lead to novel treatments. I propose inflammasome dysregulation as a mechanism for coagulation, and an inhibitor of this mechanism (parabens) as an avenue towards a treatment. Methods: Transcription levels of NLRP3 and AIM2 inflammasomes in human cells were measured after exposure to F. nucleatum using RT-PCR, and expression of interleukin-1-β (IL-1β) was quantified via ELISA.^3,4 Independently, the effects of Fusobacterium infection on both canonical and noncanonical inflammasome pathways were examined by infection of wild-type and caspase-11 knockout cells (murine bone-marrow derived macrophages) with F. nucleatum in the presence and absence of ATP, again measuring IL-1β with ELISA.⁵ In an unrelated experiment, researchers exposed wild-type and knockout mice and murine cells (without caspase-1, caspase-11, or gasdermin-D) to type III secretion system (T3SS) rod proteins and LPS as inflammasome triggers, measuring a series of coagulation markers too numerous to list here.⁶ Additionally, they measured the effects of T3SS and LPS challenge on mice with depleted tissue factor (TF) in microvesicles using an anti-TF antibody.⁶ In the final experiment of note, IL-1β levels were measured after exposure to inflammasome triggers in mice (in vivo) and murine cells (in vitro), and the effects of pre-treatment with ethylparaben and methylparaben on IL-1β levels quantified.⁷ Results: Fusobacterium infection activated inflammasome pathways, increasing IL-1β levels.^3,4 Caspase-11 knockout cells showed significantly attenuated IL-1β levels after exposure to F. nucleatum, demonstrating activation of the non-canonical pathway.⁵ Activation of inflammasome pathways increased all markers of coagulation in mice, and this was dependent on gasdermin-D and pyroptosis.⁶ Parabens inhibited the non-canonical inflammasome pathway in a dose-dependent manner, acting on caspase-11 to prevent cleavage of gasdermin-D.⁷ Discussion: Non-canonical inflammasome activation may drive disseminated intravascular coagulation in LS, and parabens could represent an avenue for treatment of thrombosis by inhibiting this pathway. Several questions remain unanswered: Is the mechanism causing coagulation the same in F. necrophorum and F. nucleatum? Are parabens similarly effective on human orthologs of caspase-11 (caspases 4 and 5)? What are the side effects of paraben administration, and do they outweigh the benefits (if any) in treatment of LS?

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