Hydrophobic mixed solvent induced PLGA-based in situ forming systems for smooth long-lasting delivery of Radix Ophiopogonis polysaccharide in rats

Abstract

To overcome the deficient sustained release of bioactive Radix Ophiopogonis polysaccharide (ROP) from hydrophilic solvent-induced PLGA-based in situ forming systems (ISFSs), hydrophobic mixed solvent-induced ISFSs were investigated, including the factors affecting drug release and the anti-myocardial ischemic activity of a representative formulation. The initial release was reduced by 3.7–8.0 times and the plasma level was significantly prolonged from 4 days to 10–15 days as the hydrophilic N-methyl-2-pyrrolidone (NMP) was replaced by the hydrophobic mixed solvent consisting of 90% benzyl benzoate (BB) and 10% co-solvent (benzyl alcohol, triacetin, or NMP). The effect of 10% co-solvent on the phase inversion rate, depot morphology, and ROP release was unexpectedly high, with NMP surprisingly being optimal although having much higher hydrophilicity. Further studies indicated that the release behaviour could be tailored by changing the ratio of BB to NMP, PLGA molecular weight, and PLGA concentration. Linear reductions in C_max and AUC_{0–12 h} were observed with the increase of the ratio (7 : 3 to 9 : 1), PLGA MW (20 to 40 kDa), and PLGA level (20% to 40%), respectively. Moreover, it is possible to achieve nearly zero-order release by different formulation combinations. The bioactivity data suggested that thanks to sustained stable release of ROP, the ISFS studied showed an obvious advantage over aqueous solution in the treatment of myocardial ischemia. Therefore, ISFSs with hydrophobic mixed solvents like BB/NMP appear to be promising and suitable for smooth long-lasting release of herb polysaccharides with low oral bioavailability and short plasma half-life, like ROP.