Huperzine A Biodegradable Study Of The Long-acting Injectable Microspheres

Huperzine A, a novel, potent, highly reversible and selective acetylcholinesterase inhibitor isolated from Chinese herb Huperzia serrata (Thunb) Trev, is one of the most promising agents for the palliative treatment of several progressive disorders including Alzheimer's disease in which neurons deteriorate. One- or two-month release injectable microspheres containing huperzine A were prepared using specifically end-group uncapped poly (d,l-lactide acid) and poly (d,l-lactide-co-glycolide acid) for the improvement of patients' compliance and the security of therapy.In vitro and in vivo analysis methods were established and the basic physicochemical properties of huperzine A and related properties of the polymers were studied. It was indicated that the in vitro/in vivo analysis method was reliable and simple; the solubility of huperzine A was at least 1mg/mL in different aqueous solutions; the partition coefficient in n-octanol/water system at 25°C was 13.1; huperzine A was very stable in PBS 7.4; the acid number of the end uncapped polymers was decreased with an increased molecular weight.Huperzine A loaded microspheres were successfully prepared from polymer E, F and H (E, F and H-MS) using a simple o/w solvent evaporation method. The effects of formula and preparative parameters on its morphology, size and size distribution, drug loading, encapsulation efficiency and in vitro drug release behavior was studied in detail, based on which the best formulation and preparation conditions was determined. The reproducibility and stability of the best formulation were good. It was found that the terminal group and the inherent viscosity (IV) of the polymers played key role in the drug encapsulation: higher EE was achieved with end-group uncapped and low IV polymers. In vitro drug release from the three kinds of microspheres revealed sustained release of the drug for about 5-6 weeks without significant burst release. A microdialysis method was established to monitor the in vivo drug release from the microspheres and it was found that the in vivo drug release was a litter slower than that of the in vitro one.An accelerated in vitro drug release method was established for the fast evaluation of in vitro drug release and quality control with the amount of drug released under the accelerated conditions comparable to that of the long term release.The in vivo performance of the microspheres was studied. The pharmacokinetic study in rats showed that the microspheres could sustain the drug plasma level for 6-8 week and the IVIVC was good. The cholinesterase inhibition was maintained for 6 weeks after administration of E-MS to mice, and the inhibition percentage was in good relationship to the corresponding drug plasma level. The histology study of the site of injection after subcutaneous injection of the three micropsheres to rats showed that the biocompatibility of the microspheres was good.