Correction of the UDP-glucuronosyltransferase gene defect in the Gunn rat model of Crigler-Najjar syndrome type I with a chimeric oligonucleotide

Crigler-Najjar syndrome type I is characterized by unconjugated hyperbiliru binemia resulting from an autosomal recessive inherited deficiency of hepat ic UDP-glucuronosyltransferase (UGT) 1A1 activity. The enzyme is essential for glucuronidation and biliary excretion of bilirubin, and its absence can be fatal. The Gunn rat is an excellent animal model of this disease, exhib iting a single guanosine (G) base deletion within the UGT1A1 gene. The defe ct results in a frameshift and a premature stop codon, absence of enzyme ac tivity, and hyperbilirubinemia. Here, we show permanent correction of the U GT1A1 genetic defect in Gunn rat liver with site-specific replacement of th e absent G residue at nucleotide 1206 by using an RNA/DNA oligonucleotide d esigned to promote endogenous repair of genomic DNA, The chimeric oligonucl eotide was either complexed with polyethylenimine or encapsulated in anioni c liposomes, administered i.v,, and targeted to the hepatocyte via the asia loglycoprotein receptor. G insertion was determined by PCR amplification, c olony lift hybridizations, restriction endonuclease digestion, and DNA sequ encing, and confirmed by genomic Southern blot analysis. DNA repair was spe cific, efficient, stable throughout the 6-month observation period, and ass ociated with reduction of serum bilirubin levels. Our results indicate that correction of the UGT1A1 genetic lesion in the Gunn rat restores enzyme ex pression and bilirubin conjugating activity, with consequent improvement in the metabolic abnormality.