Linoleic Acid‐Derived Diol 12,13‐DiHOME Modulates THP‐1 Macrophage NLRP3 Inflammasome Activation

While inflammatory dysregulation is a major contributor to cardiac injury and worsened functional recovery, current anti-inflammatory therapies have shown limited success, necessitating studies which identify gaps in our mechanistic understanding of inflammation in the heart. Essential dietary N-3 and N-6 polyunsaturated fatty acids (PUFAs) are metabolized into a family of PUFA epoxides and downstream diols with contrasting effects in cardiac inflammatory disease, suggesting metabolite- and cell-specific roles for these molecules. Previous studies have demonstrated 12,13-dihydroxyoctadecenoic acid (12,13-DiHOME), a linoleic acid-derived diol, mediates mitochondrial damage and inflammation in cardiomyocytes, though its roles in other cardiac cell types are unknown. We hypothesized that 12,13-DiHOME enhances macrophage inflammation by promoting M1 polarization and NLRP3 inflammasome activation. To study macrophage polarization, PMA-differentiated THP1 "M0" macrophages were incubated with vehicle, 12,13-DiHOME (0.5 µM), M1-polarization stimuli (10 ng/mL LPS and 20 ng/mL IFN-gamma) or M1-polarization stimuli + 12,13-DiHOME for 24 hours. Using quantitative real-time PCR we observed that 12,13-DiHOME alone did not induce M1 polarization but M1-associated cytokine TNF gene expression was enhanced in macrophages treated with 12,13-DiHOME alone or M1-polarization stimuli + 12,13-DiHOME. The NLRP3 inflammasome response was activated in THP1 M0 macrophages by first priming with LPS (10 ng/mL) for 4.5h followed by treatment with nigericin (10 µM) for 30min. NLRP3 inflammasome activation was assessed by measuring key markers (NLRP3, caspase-1, interleukin-1β). We observed a concentration-dependent increase in NLRP3 inflammasome activation when 12,13-DiHOME was co-treated with LPS-priming. Next, we used epifluorescence microscopy to assess mitochondrial dysfunction, which is known to modulate macrophage NLRP3 inflammasome activation, by measuring alterations in membrane potential with TMRE (50nM). Time course analyses demonstrated no differences in mitochondrial membrane potential between LPS-primed and LPS+12,13-DiHOME-primed macrophages prior to nigericin-activation. However, LPS+12,13-DiHOME-primed macrophages activated with nigericin had a more rapid decline in membrane potential compared to nigericin-activated macrophages primed with LPS alone, suggesting exaggerated mitochondrial damage. Overall, our data demonstrates 12,13-DiHOME does not trigger macrophage polarization alone but enhances macrophage NLRP3 inflammasome activation potentially by causing mitochondrial injury.