Effect of systemic high dose enzyme replacement therapy on the improvement of CNS defects in a mouse model of mucopolysaccharidosis type II.

Abstract

BACKGROUND: Mucopolysaccharidosis type II (MPS II, Hunter syndrome), is caused by a deficiency of iduronate-2-sulfatase (IDS). Despite the therapeutic effect of intravenous enzyme replacement therapy (ERT), the central nervous system (CNS) defects persist because the enzyme cannot cross the blood-brain barrier (BBB). There have been several trials of direct infusion to the cerebrospinal space showing promising results; however, this approach may have limitations in clinical situations such as CNS infection. The objective of this study was to improve the CNS defect with systemic high-dose ERT.

METHODS: Systemic ERT was performed using three doses (1, 5, and 10 mg/kg weekly) of IDS for three different durations (1, 3, and 6 months) in IDS knock out (KO) mice of two age groups (2 months, 8 months). GAG measurement in tissues, brain pathology, and behavioral assessment were analyzed.

RESULTS: Brain IDS activities increased in parallel with the concentrations of IDS injected. The glycosaminoglycan (GAG) level and histopathology in the brains of the young mice improved in a dose- and duration-dependent manner; however, those were not improved in the old mice, even at higher doses of IDS. The spontaneous alternation behavior was recovered in young KO mice treated with ≥ 5 mg/kg IDS; however, no significant improvement was observed in old KO mice.

CONCLUSIONS: These results suggest that high-dose ERT given to mice of earlier ages may play a role in preventing GAG accumulation and preventing CNS damage in IDS KO mice. Therefore, ERT above the present standard dose, starting in early childhood, could be a promising treatment regimen for reducing neurological impairment in Hunter syndrome.