Encapsulated genetically engineered fibroblasts: release of nerve growth factor and effects in vivo on recovery of cholinergic markers after devascularizing cortical lesions

Genetically engineered rat fibroblasts producing nerve growth factor (NGF) were encapsulated in alginate-polylysine-alginate gels with the objective to produce viable "minifactories" continuously producing and secreting NGF into the rat brain. Microencapsulated fibroblasts (NGF secretors and NGF non-secretors) were placed onto the surface of the lesioned rat cortex (unilateral devascularizing lesion) and animals were sacrificed 30 days after surgery. Fibroblasts NGF-non secreters normally produce tumors after implantation, therefore, they were irradiated prior to encapsulation. Three other experimental groups were studied in parallel: non-lesioned (controls), lesioned rats receiving "empty" alginate spheres and lesioned animals without treatment and microspheres. Biochemical analysis of microdissected brain tissues of lesioned animals treated with encapsulated NGF-secretor fibroblasts showed a significant increase in choline acetyltransferase (ChAT) activity in cortices adjacent to the lesion but not far from it (entorhinal cortex). This may indicate a gradient of concentration of the released NGF and/or differential responsivity of lesioned vs non-lesioned target tissue. ChAT enzymatic activity in the microdissected nucleus basalis magnocellularis (NBM) was significantly decreased (P < 0.05) in all lesioned animals treated with spheres without fibroblasts and those with fibroblasts not secreting NGF. Morphometric analysis of ChAT-IR and low affinity NGF-receptor IR cholinergic neurons in the middle portion of the NBM shows a prevention of neuronal shrinkage and extensive neuropil in animals treated with microencapsulated NGF-secretor fibroblasts. The results of this study demonstrate that NGF from encapsulated genetically engineered fibroblasts can be secreted for at least long enough to prevent degenerative changes of cholinergic neurons in the NBM.