Catecholamine-containing biodegradable microsphere implants as a novel approach in the treatment of CNS neurodegenerative disease. A review of experimental studies in DA-lesioned rats

Biodegradable controlled-release microsphere systems made with the biocompatible biodegradable polyester excipient poly(DL-lactide-co-glycolide) constitute an exciting new technology for drug delivery to the central nervous system (CNS). Implantable controlled-release microspheres containing dopamine (DA) or norepinephrine (NE) provide a novel means to compare DA- or NE -induced restitution of function in unilateral 6-hydroxydopamine lesioned rats. A suspension of 3 microL of DA- or NE-containing microspheres or empty microspheres was implanted in 2 sites of the DA denervated striatum of rats previously unilaterally lesioned with 6-hydroxydopamine. Contralateral-rotational behavior induced by apomorphine was used as an index of lesion success and, following implantation of the microspheres, also as an index of functional recovery. Interestingly, both DA- and NE-microsphere-implanted rats displayed a 30-50% reduction in the number of apomorphine-induced rotations up to 8 wk postimplantation. Rats implanted with empty microspheres did not demonstrate significant changes in contralateral rotational behavior. Behavioral studies following implantation of a mixture of DA and NE microspheres revealed an 80% decrease in the number of apomorphine induced rotations up to 4 wk. On conclusion of the studies, immunocytochemical examination revealed growth of DA and tyrosine hydroxylase immunoreactive fibers in the striatum of DA and NE microsphere-implanted rats. Functional behavior appeared to correlate with the degree of fiber growth. Preliminary electron microscopic studies showed signs of axonal sprouting in the vicinity of the implanted microspheres. No growth was noted in rats implanted with empty microspheres. This report reviews the abilities of both microencapsulated NE and DA to assure functional recovery and to promote DA fiber (re)growth in parkinsonian rats. This novel means to deliver these substances to the central nervous system could be of therapeutic usefulness in Parkinson's disease.