Grafting of genetically modified cells: effects of acetylcholine release in vivo

Nerve growth factor gene therapy in Alzheimer disease

Nervous system growth factors potently stimulate cell function and prevent neuronal death. These broad effects on survival and function arise from direct downstream activation of antiapoptotic pathways, inhibition of proapoptotic pathways, and stimulation of functionally important cellular mechanisms including ERK/MAP kinase and CREB. Thus, as a class, growth factors offer the potential to treat neurodegenerative disorders for the first time by preventing neuronal degeneration rather than compensating for cell loss after it has occurred. Different growth factors affect distinct and specific populations of neurons: the first nervous system growth factor identified, nerve growth factor, potentially stimulates the survival and function of basal forebrain cholinergic neurons, suggesting that nerve growth factor could be a means for reducing the cholinergic component of cell degeneration in Alzheimer disease. This review will discuss the transition of growth factors from preclinical studies to human clinical trials in Alzheimer disease. The implementation of clinical testing of growth factor therapy for neurologic disease has been constrained by the dual need to achieve adequate concentrations of these proteins in specific brain regions containing degenerating neurons, and preventing growth factor spread to nontargeted regions to avoid adverse effects. Gene therapy is one of a limited number of potential methods for achieving these requirements.

Application of in vivo microdialysis to the study of cholinergic systems

The application of in vivo microdialysis to the study of acetylcholine (ACh) release has contributed greatly to our understanding of cholinergic brain systems. This article reviews standard experimental procedures for dialysis probe selection and implantation, perfusion parameters, neurochemical detection, and data analysis as they relate to microdialysis assessments of cholinergic function. Particular attention is focused on the unique methodological considerations that arise when in vivo microdialysis is dedicated expressly to the recovery and measurement of ACh as opposed to other neurotransmitters. Limitations of the microdialysis technique are discussed, as well as methodological adaptations that may prove useful in overcoming these limitations. This is followed by an overview of recent studies in which the application of in vivo microdialysis has been used to characterize the basic pharmacology and physiology of cholinergic neurons. Finally, the usefulness of the microdialysis approach for testing hypotheses regarding the cholinergic systems' involvement in cognitive processes is examined. It can be concluded that, in addition to being a versatile and practical method for studying the neurochemistry of cholinergic brain systems, in vivo microdialysis represents a valuable tool in our efforts to better comprehend ACh's underlying role in a variety of behavioral processes.

Implants of polymer-encapsulated human NGF-secreting cells in the nonhuman primate: rescue and sprouting of degenerating cholinergic basal forebrain neurons

Baby hamster kidney (BHK) cells were genetically modified to secrete high levels of human nerve growth factor (BHK-hNGF). Following polymer encapsulation, these cells were implanted into the lateral ventricle of four cynomolgus monkeys immediately following a unilateral transection/aspiration of the fornix. Three control monkeys received identical implants, with the exception that the BHK cells were not genetically modified to secrete hNGF and thus differed only by the hNGF construct. One monkey received a fornix transection only. All monkeys displayed complete transections of the fornix as revealed by a comprehensive loss of acetylcholinesterase-containing fibers within the hippocampus ipsilateral to the lesion. Control monkeys that were either unimplanted or received BHK-control (non-NGF secreting) cell implants did not differ from each other and displayed extensive losses of choline acetyltransferase and p75 NGF receptor (NGFr)-immunoreactive neurons within the medial septum (MS; 53 and 54%, respectively) and vertical limb of the diagonal band (VLDB; 21 and 30%, respectively) ipsilateral to the lesion. In contrast, monkeys receiving implants of BHK-hNGF cells exhibited a only a modest loss of cholinergic neurons within the septum (19 and 20%, respectively) and VLDB (7%). Furthermore, only implants of hNGF-secreting cells induced a dense sprouting of cholinergic fibers within the septum, which ramified against the ependymal lining of the ventricle adjacent to the transplant site. Examination of the capsules retreived from monkeys just prior to their death revealed an abundance of cells that produced detectable levels of hNGF in a sufficient concentration to differentiate PC12A cells in culture. These findings support the use of polymer-encapsulated cell therapy as a potential treatment for neurodegenerative diseases such as Alzheimer disease where basal forebrain degeneration is a consistent pathological feature. Moreover, this encapsulated xenogeneic system may provide therapeutically effective levels of a number of neurotrophic factors, alone or in combination, to select populations of neurons within the central nervous system.

Microencapsulation of genetically engineered fibroblasts secreting nerve growth factor

We demonstrated that genetically modified fibroblasts can be encapsulated into biocompatible, biodegradable spheres retaining their viability and capacity to continuously secrete nerve growth factor (NGF) for at least two months. Genetically engineered rat fibroblasts producing NGF were encapsulated in an alginate-polylysine gel with the ultimate objective of improving transplantation methodologies. Cultures were suspended in a sodium alginate solution and the suspension was extruded drop-wise into a solution of calcium chloride. Morphological properties of the spheres were assessed by light and electron microscopy. The spheres had a homogenous external membrane, without fibroblasts, protruding from the surface of the capsular membrane. The NGF determinations in culture media showed that encapsulated fibroblasts continued to synthesize NGF for at least 60 days. We also confirmed that secreted NGF was biologically active, by assessing the induction of choline acetyltransferase (ChAT) activity in dissociated embryonic rat septal cultures. These results encourage further studies using in vivo models to determine the value of applying microencapsulated genetically modified cells secreting trophic factors as a therapeutic strategy for central nervous system (CNS) injuries.