Herpes simplex virus mediated nerve growth factor expression in bladder and afferent neurons: Potential treatment for diabetic bladder dysfunction

Purpose: Diabetic cystopathy resulting from sensory neuropathy may potentia lly be treated by direct gene therapy. It has been suggested that nerve gro wth factor (NGF) has an ameliorative effect in preventing the death in diab etes of efferent dorsal root ganglion neurons, which control bladder functi on. We investigated NGF gene transfer to the bladder and bladder afferent p athways for treating diabetic cystopathy. We used replication competent and replication defective herpes simplex virus type 1 (HSV-1) vectors that exp ress a functionally active form of the beta -subunit of mouse NGF (beta -NG F) to examine the level and duration of therapeutic, gene expression after administration of the vectors. Materials and Methods: NGF expression during acute (3 days) and latent (21 days) infections was assessed by enzyme-linked immunosorbent assay (ELISA) and immunohistochemical testing after the injection of 1 x 10(6) to 1 x 10( 8) pfu HSV-NGF expression vectors into the bladder wall of adult rats. Results: HSV vectors with the strong human cytomegalovirus immediate early promoter used to drive beta -NGF gene expression exhibited increased NGF 3 days after infection in the bladder and L6 to S1 dorsal root ganglia, where bladder afferent neurons are located, ELISA analysis revealed that NGF in the bladder tissue and dorsal rest ganglia was increased 7 to 9 and 2 to 4- fold, respectively, over the control vector. Increased NGF expression in L6 to S1 dorsal root ganglia neurons was also detected by immunohistochemical staining with antiNGF antibodies. Extended NGF expression was detected by ELISA 21 days after injection. Replication defective vectors containing HSV -1 latency promoter (LAP-2) driving NGF expressed NGF in the bladder and do rsal root ganglia 21 days after bladder injection. ELISA analysis confirmed an approximate 2 to 3-fold increase of NGF expression in the bladder and L 6 to S1 dorsal 1 root ganglia. Conclusions: The NGF gene may be transferred and expressed in the bladder a nd bladder afferent pathways using HSV vectors. To our knowledge our study represents the first demonstration of the effectiveness of gene therapy for altering neurotrophic expression in visceral sensory neurons. This techniq ue of gene transfer may be useful for treating certain types of neurogenic bladder dysfunction, such as, diabetic cystopathy, in which decreased NGF t ransport may be a causative factor.