LNP mRNA Reduces Storage Material in Selected Brain Regions of Neonatal MPS I-H Mice
Enzyme Deficiency and the Limits of CNS Treatment
An mRNA formulation encapsulated in lipid nanoparticles (LNPs) reduced storage material in selected brain regions and improved behavioral test performance in neonatal mice with mucopolysaccharidosis type I, Hurler syndrome (MPS I-H). This study did not establish therapeutic efficacy in people; the findings apply to repeated dosing in neonatal mice.
MPS I-H is a severe lysosomal storage disorder in which alpha-L-iduronidase (IDUA) deficiency causes glycosaminoglycan (GAG) accumulation. It causes progressive damage to multiple organs, including the central nervous system (CNS). Early hematopoietic stem cell transplantation is a major disease-modifying treatment, but clinical challenges remain. Existing enzyme replacement therapy has limited effects in the CNS because of the blood–brain barrier, and new formulations intended to cross this barrier are being developed.
Results of Repeated Dosing with a Liver-Directed mRNA Formulation
The researchers screened ionizable lipids to develop an LNP optimized for liver delivery. It carried mRNA encoding human IDUA fused to a blood–brain barrier-penetrating melanotransferrin peptide (MTfp). The barrier-penetrating design applied to the fusion enzyme to be produced; the results should not be interpreted as showing that the LNP itself was delivered directly to the brain.
The formulation was administered intravenously to neonatal MPS I-H mice at 1.0 mg/kg every two weeks for four months. The researchers reported significantly increased IDUA enzyme activity in serum and liver. GAG accumulation also decreased in urine and peripheral tissues, with reductions observed in the olfactory bulb, hippocampus, and cerebellum in the brain. This does not mean that storage material was cleared throughout the brain or in all tissues.
Cardiac and skeletal development, assessed by echocardiography and micro-computed tomography, also improved significantly. Performance improved in the Delayed-Matching-to-Place dry maze test, supporting an improvement in cognitive function. However, the abstract did not report effect sizes for individual measures or whether normal levels were restored.
Questions to Resolve Before Application in People
These findings suggest that an mRNA formulation that supplies an enzyme could improve peripheral tissue pathology as well as pathology in selected parts of the CNS and behavioral measures. Whether it outperforms existing treatments or produces similar effects in people remains unconfirmed.
The available material consists of bibliographic information and an abstract from Human Gene Therapy. Sample size, control-group composition, detailed statistics, and safety assessment results are difficult to assess from this material alone. The researchers assessed the formulation’s safety positively, but there is insufficient evidence to extend that assessment to the safety of repeated dosing in people or to conclude that the blood–brain barrier problem has been solved. Further development must evaluate durability of effect, safety with repeated administration, and delivery characteristics suitable for use in people.
Source: Human Gene Therapy article abstract
Mucopolysaccharidosis type I-Hurler (MPS I-H) is a severe lysosomal storage disorder caused by α-L-iduronidase (IDUA) deficiency, leading to glycosaminoglycan (GAG) accumulation and progressive multisystem dysfunction, including the central nervous system (CNS). Early hematopoietic stem cell transplantation remains the primary disease-modifying intervention for MPS I-H despite its clinical challenges. Conventional enzyme replacement therapy (ERT), which has limited CNS efficacy due to blood-brain barrier (BBB) restrictions, is being addressed by the development of novel BBB-penetrating ERT platforms. Recently, mRNA therapy has become a promising treatment option for rare genetic diseases by enabling the production of functional enzymes, such as IDUA, in vivo, using lipid nanoparticles (LNPs) as a delivery system.
This study is significant because it combined a liver-directed mRNA formulation with an enzyme fused to a blood–brain barrier-penetrating peptide to evaluate both peripheral tissues and selected brain regions in MPS I-H. Further development could examine whether changes in enzyme activity and GAG accumulation occur alongside improvements in cardiac, skeletal, and behavioral measures. For example, when assessing dosing conditions for a candidate formulation, this evaluation framework could help determine whether increased serum enzyme activity leads to reduced storage material in brain regions and functional changes. However, results in neonatal mice alone are insufficient to expect improvements in neurological symptoms in pediatric patients or replacement of existing treatments. Evidence on durability of effect, safety with repeated dosing, and comparisons with existing treatments will provide the next basis for assessing use in people.