NR1H4 and Hyperammonemia: A recent study showed that FXR regulates hepatic amino acid catabolism and the detoxification of ammonium through ureagenesis and glutamine synthesis in mice [60]; FXR activation by OCA treatment increased the expressions of genes involved in amino acid degradation, ureagenesis, and glutamine synthesis, whereas the loss of FXR had opposite effects, suggesting the novel function of FXR in the regulation of hyperammonemia as a common complication in patients with acute and chronic liver diseases.