Splenic Macrophage Activation and Disordered Heme–Iron Metabolism in a Mouse Model of Acute Hepatic Encephalopathy

Hepatic encephalopathy is a severe complication of liver failure, traditionally investigated through brain–liver interactions; however, the involvement of extrahepatic organs remains poorly understood. This study examined splenic histopathological changes in a mouse model of acute hepatic encephalopathy induced by ammonium acetate administration, focusing on iron metabolism and macrophage activation. Although conventional hematoxylin and eosin staining revealed no overt structural abnormalities, unstained spleen sections demonstrated abundant black deposits, predominantly in the red pulp. Prussian blue staining confirmed a significant increase in hemosiderin-positive cells; however, a subset of black deposits was iron-negative. Immunohistochemical analyses revealed that these iron-negative pigments were localized within F4/80-positive macrophages and colocalized with heme oxygenase-1 (HO-1), suggesting enhanced heme degradation. Ultrastructural observations further identified electron-dense granules consistent with hematin accumulation in splenic macrophages. Hematological analyses revealed significant reductions in red blood cell count and hemoglobin levels, indicating accelerated erythrocyte destruction. Collectively, these findings demonstrate that acute hepatic encephalopathy induces splenic macrophage activation, accompanied by disordered iron metabolism and hematin accumulation. This study highlights the spleen as a previously underappreciated extrahepatic organ involved in the pathophysiology of hepatic encephalopathy and suggests that splenic heme–iron handling may represent a novel therapeutic target.