P-1858. Exploring the Role of Fatty acid synthase (FASN) Inhibition in Interferon Gamma Mediated Killing of <i>Histoplasma capsulatum</i>

Abstract Background Histoplasma capsulatum (Hc) is the leading cause of fungal respiratory infections in the US. Most cases are mild but 20% require hospitalization. Immunosuppression is a major risk factor for disseminated histoplasmosis. The cytokine Interferon gamma (IFN)-γ is crucial for host resistance to Hc. The absence of IFN-γ or its failure to signal affects the host immune response. Activated CD4+ T cells release IFN-γ to arm macrophages(MΦ) to kill intracellular yeasts. Immunometabolism is a key element in the function of MΦ and fatty acid synthase (FASN) regulates inflammatory responses by these cells. FASN is a large multi-enzyme complex comprised of 6 separate enzymatic grooves that work together to produce 16-carbon chain saturated fatty acid (FA), palmitate, from acetyl-coenzyme A (CoA) and malonyl-CoA(Figure 1). The influence of FASN in the IFN-γ-mediated activation of MΦ remains unclear. Key inhibitor targets in FASN complex Methods Figure 1 shows key inhibitor targets in FASN complex. Bone marrow derived Mφ were used in all experiments with a 2 to 1 yeast to Mφ ratio. IFN-γ induced killing of Hc in mouse Mφ require 48h. We used the tetrazolium salt XTT to assess the Hc viability as this correlates with the colony counts. Controls (Hc in Mφ) are set to 100 %. Toxicity of each inhibitor to Hc and Mφ was studied first. Mφ were treated with IFN-γ 4hrs before infection and then treated with graded amounts of FASN inhibitors C 75 (inhibits ketoacyl synthase), orlistat (inhibits thioesterase), and TVB-3166 or GSK2194069 (both inhibit ketoacyl synthase) 2hrs before infection with 2x Hc for 48hrs. Intracellular yeast survival at 48hrs was assessed. Effect of FASN inhibitors on IFN- γ mediated killing of Hc at 48 hrs. n= 3-10 , mean ±SEM Results Pretreatment with the FASN inhibitor C75 reversed the killing activity of IFN- γ. Neither orlistat or inhibitors of ketoacyl reductase modified the impact of IFN-γ. (Figure 2) Conclusion The FASN inhibitor C75 reversed the activity of IFN-γ in killing Hc. These results suggest that cholesterol synthesis may be involved in the action of IFN- γ. Disclosures All Authors: No reported disclosures