Sustained correction of OTC deficiency in spf( ash) mice using optimized self-complementary AAV2/8 vectors

Area of Science:

• Biochemistry
• Genetics
• Molecular Biology

Background:

• Ornithine transcarbamylase deficiency (OTCD) is a prevalent genetic disorder of urea synthesis, often leading to fatal hyperammonemic coma in newborns.
• Current treatments for OTCD include dialysis, stimulating alternative nitrogen clearance pathways, and liver transplantation, with gene therapy offering a potential novel approach.

Purpose of the Study:

• To evaluate the efficacy of adeno-associated virus (AAV) vector-based gene therapy for ornithine transcarbamylase deficiency (OTCD).
• To investigate the therapeutic potential of a self-complementary (sc) AAV2/8 vector expressing the murine OTC (mOTC) gene in a mouse model of OTCD.

Main Methods:

• An AAV2/8-based self-complementary (sc) vector encoding the murine OTC (mOTC) gene under a liver-specific promoter was developed.
• The vector's therapeutic effects were assessed in spf(ash) mice, a genetic model of OTCD, following a single intravenous injection.
• Vector efficacy was further enhanced by incorporating Kozak or Kozak-like sequences into the mOTC cDNA.

Main Results:

• A single intravenous injection of the AAV vector normalized urinary orotic acid levels in treated mice within seven days, indicating restored OTC activity.
• Optimization of the vector with Kozak sequences increased OTC activity by two- to fivefold.
• Sustained correction of orotic aciduria was observed for up to 7 months in treated mice.

Conclusions:

• Adeno-associated virus (AAV) vector-based gene therapy is a viable strategy for treating ornithine transcarbamylase deficiency (OTCD).
• Vector optimization significantly enhances gene therapy efficacy, leading to sustained therapeutic benefits in a preclinical model.
• This study demonstrates the potential of optimized AAV gene therapy to address urea cycle disorders.