Long‐term uninterrupted enzyme replacement therapy prevents liver disease in murine model of severe homocystinuria

Classical homocystinuria (HCU) is an inborn error of metabolism caused by loss of cystathionine β‐synthase (CBS) activity with the concomitant buildup of homocysteine. In knockout (KO) mice, a mouse model of HCU, complete lack of CBS is neonatally lethal. Administration of OT‐58, an enzyme therapy for HCU, during the first 5 weeks of life rescued KO mice survival by preventing liver disease. Here, we studied the impact of a long‐term uninterrupted OT‐58 treatment or its absence beyond the neonatal period on liver pathology and metabolism. Plasma and liver metabolites of KO mice on OT‐58 treatment were substantially improved or normalized compared with those receiving vehicle. Increased plasma activities of alanine aminotransferase and aspartate aminotransferase of vehicle‐injected KO mice suggested the progression of liver damage with age and lack of treatment. At 3 months of age, liver histology showed no signs of hepatopathy in both vehicle‐ and OT‐58‐treated KO mice. However, moderate to severe liver disease, characterized by steatosis, hepatocellular necroses, disorganized endoplasmic reticulum, and swollen mitochondria, developed in 6‐month‐old vehicle‐injected KO mice. KO mice on OT‐58 treatment remained asymptomatic and were indistinguishable from age‐matched healthy controls. Long‐term uninterrupted OT‐58 treatment was essential to prevent severe liver disease in the KO mouse model of HCU.