During the past several years, work in our laboratory has indicated that the transplantation of adrenal medullary chromaffin cells into CNS pain modulatory regions is a potentially complementary and novel approach in the therapeutic management of pain. Neural transplants may be a means to achieve sustained delivery of pain-reducing neuroactive substances to CNS pain modulatory regions on a long-term basis, reducing or eliminating the need for repeated narcotic administration. Since the encouraging results of these studies has brought this work close to entering clinical trials as a therapy for pain reduction, it is essential to establish optimal conditions for graft selection and handling. The goals of the current proposal are to further characterize the transplants behaviorally, pharmacologically, biochemically, and histologically, to determine optimal graft sources for long term survival and continued production of pain- reducing neuroactive substances, and to develop cell lines for transplantation which can provide a uniform and readily available source of opioid peptides and other agents for the long-term alleviation of chronic pain. Pain reduction over long periods of time will be assessed using acute and chronic pain tests. Biochemical assays and pharmacologic studies will be done to explore the mechanisms of action of the transplants, interactions with other agents, and responses to environmental stimuli. The issues of tolerance and tachyphylaxis will also be addressed. It is possible that the combined release of subeffective levels of pain-reducing neuroactive substances from the transplants can synergize to produce potent analgesia without the development of significant tolerance. Since adrenal medullary allografts are the most likely donor source in the initial clinical phases, it is important to determine the optimal conditions for allograft survival. Short term maintenance in explant culture may improve the survival and transplantability of adrenal medullary allografts. However, the limited availability and non-uniformity of human adrenal medullary tissue reduces its feasibility for widespread use. Thus, another aim of the proposed work is to explore alternative donor sources of chromaffin cells for transplantation. A potentially useful source of chromaffin cells is the bovine adrenal gland since large quantities are readily available. However, the safety and efficacy of such xenografts must be established. One way to immunologically isolate bovine chromaffin cells is to encapsulate them in transplantable permselective membranes. In addition, encapsulation will limit migration of transplanted cells from critical CNS placement sites. Finally, a long term goal of the proposed studies is to develop defined and uniform cells lines for transplantation which are engineered to produce high levels of opioid peptides.
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