Liposomal Formulations of Tacrolimus and Rapamycin Increase Graft Survival and Fiber Outgrowth of Dopaminergic Grafts

Abstract

The immunosuppressive drugs tacrolimus (TAC) and rapamycin (RAPA) have both been found to have neuroprotective effects on dopaminergic neurons. The purpose of the present study was to investigate whether liposomal formulations of these drugs administered directly into the brain improve cell survival and fiber outgrowth. Rats with unilateral 6-hydroxydopamine lesions were transplanted with 800,000 fetal rat ventral mesencephalic cells and randomly divided to one of four groups. Group 1 received a transplant containing cells only; group 2 received a cell suspension containing 0.68 µM liposomal RAPA (LRAPA); group 3 received a cell suspension containing 2.0 µM liposomal TAC (LTAC); and group 4 received a cell suspension containing a liposomal formulation of both 0.68 µM RAPA and 2.0 µM TAC (LRAPATAC). Rats were sacrificed after 6 weeks, and cell survival and fiber outgrowth were assessed using tyrosine hydroxylase (TH) immunohistochemistry. The animals receiving a cell suspension containing either LTAC or LRAPATAC were found to have significantly more surviving TH-immunoreactive (TH-ir) cells than the control group receiving cells only. The group receiving LTAC had significantly longer fibers, the group receiving LRAPA had significantly more fibers close to the graft, and the group receiving LRAPATAC had significantly more fibers at all distances. This study shows the feasibility of using liposomal formulations of neuroimmunophilins directly in the brain at the time of implantation to improve graft survival and fiber outgrowth. Furthermore, we have shown that the combination of LTAC and LRAPA has a synergistic effect. These compounds may play an important role in optimizing graft survival and host reinnervation in cellmediated brain repair strategies for the treatment of neurological conditions. Key words: Transplantation; Parkinson's disease; Tacrolimus; Rapamycin; Liposomes INTRODUCTION(16), to increase the length of tyrosine hydroxylaseimmunoreactive (TH-ir) neurites extending from embryNeural transplantation is a promising restorative stratonic DA neuron cultures (8,9), and to increase the suregy for the treatment of Parkinson's disease (PD). Howvival of cultured and grafted rat embryonic DA neurons ever, survival of transplanted cells is limited. It has been (6). Rapamycin (RAPA) is another neuroimmunophilin estimated that between 3% and 20% of grafted cells acligand that also binds FKBPs. RAPA has also been found tually survive in the host brain (5). Fiber outgrowth is to have neurotrophic effects in cultures of PC12 cells also of concern, as it has been postulated that a critical and sensory ganglia (16), as well as increasing the numthreshold of reinnervation to the host must be met to ber of neurites extending from PC12 cell culture (6) and achieve functional effects from a dopaminergic graft (15). from embryonic DA neuron culture (9). Various agents, such as neurotrophic factors, haveIn recent years liposomal formulations of the neuroimbeen employed to increase the survival rate of grafted munophilin liga...

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Survival of Neural Progenitors Allografted into the CNS of Immunocompetent Recipients is Highly Dependent on Transplantation Site

“…A high dose of cyclophosphamide administered early after transplantation is able to kill lymphocytes that proliferate in response to graft injection, prolonging graft survival(29). Protection of intracerebral grafts by local immune suppression has also been shown to be effective(1). Microchimerism has also been reported to increase graft tolerance under very specific conditions, but, on the contrary, may also sensitize the host to the graft(12,27).…”

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“…<150 nm). Other immunosuppressive drugs, such as tacrolimus [64] and rapamycin [65], have also demonstrated similar effective results when encapsulated within liposomes. For example, rapamycin demonstrated optimal results when encapsulated within micelles.…”