Vesicular monoamine transporter-2 and aromatic L-amino acid decarboxylase enhance dopamine delivery after L-3,4-dihydroxyphenylalanine administrationin Parkinsonian rats

Medical therapy in Parkinson's disease (PD) is limited by the short-duratio n response and development of dyskinesia that result from chronic L-3,4-dih ydroxyphenylalanine (L-DOPA) therapy. These problems occur partly because t he loss of dopamine storage sites leads to erratic dopamine delivery. Vesic ular monoamine transporter-2 (VMAT-2) plays a critical role in dopamine sto rage by packaging dopamine into synaptic vesicles and regulating sustained release of dopamine. To restore the capacity to produce and store dopamine in parkinsonian rats, primary skin fibroblast cells (PF) were genetically m odified with aromatic L-amino acid decarboxylase (AADC) and VMAT-2 genes. A fter incubation with L-DOPA in culture, the doubly transduced fibroblast ce lls (PFVMAA) produced and stored dopamine at a much higher level than the c ells with either gene alone. PFVMAA cells in culture released dopamine grad ually in a constitutive manner. Genetically modified fibroblast cells were grafted in parkinsonian rat striata, and L-DOPA was systemically administer ed. Higher dopamine levels were sustained for a longer duration in rats gra fted with PFVMAA cells than in those grafted with either control cells or c ells with AADC alone. These findings underscore the importance of dopamine storage capacity in determining the efficacy of L-DOPA therapy and illustra te a novel method of gene therapy combined with precursor administration to overcome the major obstacles of PD treatment.