Neutrophil activation at high-fat high-cholesterol and high-fructose diets induces low-grade inflammation in mice

Nonalcoholic fatty liver disease (NAFLD), which can progress to nonalcoholic steatohepatitis (NASH), is a significant health concern affecting a substantial portion of the population. This study investigates the role of neutrophil extracellular traps (NETs) in liver inflammation induced by high-fat high-cholesterol diet (HFHCD) and high-fructose diet (HFD). The chronic nature of NAFLD involves low-grade inflammation with cytokine elevation. The research aims to visualize neutrophil elastase (NE) activity during HFHCD and HFD representing conditions of low-grade activation and assess neutrophil functional status. The study employs a mouse model subjecting animals to HFHCD, HFD or a standard diet (SD) for six weeks. Various analyses were used including histological evaluations, in vivo imaging of NE activity using a fluorescent probe, fluorescent microscopy, flow cytometry and assessment of neutrophil function through reactive oxygen species (ROS) levels. Mice on HFHCD and HFD display liver damage consistent with NASH, which was validated pathohistologically. NE activity in blood significantly increases after six weeks indicating systemic NETs involvement. In vivo imaging confirms NE activity in multiple organs. Cellular localization reveals NETs persistence even after neutrophil destruction in splenocytes indicating systemic involvement. Neutrophils under HFHCD exhibit a functional phenotype associated with low-grade inflammation, higher basal ROS levels and reduced activation potential. This study establishes the systemic impact of NETs in HFHCD- and HFD-induced liver inflammation, providing insights into the functional state of neutrophils. The findings contribute to understanding the mechanisms underlying chronic liver conditions and may inform future therapeutic strategies. Keywords: high fat diet, in vivo imaging, low-grade inflammation, NASH, neutrophil elastase, neutrophil extracellular traps, neutrophils