Cell-cell communications in the brain of hepatic encephalopathy: The neurovascular unit

Many patients with liver diseases are exposed to the risk of hepatic encephalopathy (HE). The incidence of HE in liver patients is high, showing various symptoms ranging from mild symptoms to coma. Liver transplantation is one of the ways to overcome HE. However, not all patients can receive liver transplantation. Moreover, patients who have received liver transplantation have limitations in that they are vulnerable to hepatocellular carcinoma, allograft rejection, and infection. To find other therapeutic strategies, it is important to understand pathological factors and mechanisms that lead to HE after liver disease. Oxidative stress, inflammatory response, hyperammonaemia and metabolic disorders seen after liver diseases have been reported as risk factors of HE. These are known to affect the brain and cause HE. These peripheral pathological factors can impair the blood-brain barrier, cause it to collapse and damage the neurovascular unit component of multiple cells, including vascular endothelial cells, astrocytes, microglia, and neurons, leading to HE. Many previous studies on HE have suggested the impairment of neurovascular unit and cell-cell communication in the pathogenesis of HE. This review focuses on pathological factors that appear in HE, cell type-specific pathological mechanisms, miscommunication/incorrect relationships, and therapeutic candidates between brain cells in HE. This review suggests that regulating communications and interactions between cells may be important in overcoming HE.