A 45-year-old woman is brought to the emergency department by a neighbor because of confusion and disorientation for 1 day. She has a sweet and sour body odor. She appears drowsy. Physical examination shows jaundice, spider angiomata, hepatomegaly, and flapping tremors of the extremities. Laboratory studies show a prolonged prothrombin time, anemia, hyperbilirubinemia, hyperammonemia, and hypoalbuminemia. Test of the stool for occult blood is positive. Which of the following mechanisms is the most likely cause of the encephalopathy in this patient?
A) Decreased concentration of y-aminobutyric acid in the central nervous system
B) Decreased concentration of glycine in the central nervous system
C) Decreased dietary intake of protein
D) Excessive bilirubin deposition in the central nervous system
E) Shunting of portal venous blood into the systemic circulation