EVALUATION OF GENE-THERAPY FOR CITRULLINEMIA USING MURINE AND BOVINE MODELS

Citrullinaemia is an autosomal recessive disorder caused by the defici ency of argininosuccinate synthase. The deficiency of this enzyme resu lts In an interruption in the urea cycle and the inability to dispose of excess ammonia derived from the metabolism of protein. The only tre atment for this disorder has been dietary restriction of protein and s upplementation with medications allowing for alternative excretion of excess nitrogen. Gene therapy offers the possibility of a long-term cu re for disorders like citrullinaemia by expressing the deficient gene in the target organ. We have explored the use of adenoviral vectors as a treatment modality for citrullinaemia in two animal models, a natur ally occurring bovine model and a murine model created by molecular mu tagenesis. Mice treated with adenoviral vectors expressing argininosuc cinate synthase lived significantly longer than untreated animals (11 days vs 1 day; however, the animals did not exhibit normal weight gain during the experiment, indicating that the therapeutic effectiveness of the transducing virus was suboptimal. It is speculated that part of the failure to observe better clinical outcome might be due to the de ficiency of arginine. In the bovine model, the use of adenoviral vecto rs did not result in any change in the clinical condition of the anima ls or in the level of plasma ammonia. However, the use of N-15 isotopi c ammonia allowed us to assess the flux of nitrogen through the urea c ycle during the experiment. These studies revealed a significant incre ase in the Bur through the urea cycle following administration of aden oviral vectors expressing argininosuccinate synthase. We conclude that the use of adenoviral vectors in the treatment of citrullinaemia is a viable approach to therapy but that it will be necessary to increase the level of transduction and to increase the level of enzyme produced from the recombinant viral vector. Future experiments will be designe d to address these issues.