Study On Scutellarein Liposomes With Neuroprotective Effect In Cerebral Ischemia Injury

Scutellarin(Scu),a flavonoid glycoside extracted from herb Erigeron breviscapus,has been used in the clinical therapy of ischemia injuries such as cerebral ischemia or stroke for a long history.Scutellariein(Scue)is the aglycone of Scu.Scue shows higher lipophilicity than Scu and more potent neuroprotection effect in animal models.It becomes a promis ing compound for cerebral ischemia therapy.However,the extremely low aqueous solubility(<1μg/ml)and glycoside transformation of Scue in GI tract after oral absorption restrict its in vivo application.In this thes is,we selected PEGylated liposome as the delivery vehicle for Scue and successfully developed a novel intravenous injectable liposome of Scue with much improved bioavailability and good chemical stability.In preformulation study,we measured the solubility and oil-water partition coefficient(logP)of Scue.Scue is insolubled in water(<1μg/ml).It has a log P value of 1.5 at neutral pH.Hydroxypropyl-β-cyclodextrin(HPCD)was selected to increase the solubility of Scue up to 1.8mg/ml.Blank liposomes composed of HSPC/cholesterol/DSPE-PEG2k(3:1:1,w/w)were prepared by ethanol injection and extruded through polycarbonate membranes.Scue was loaded to the liposomes by remote loading method using calcium acetate as the gradient.The pH values of the intraliposomal and extra medium aqueous phases,and the concentrations of calcium acetate inside liposomes were optimized to achieve high encapsulation and good storage stability.HPCD was included ins ide liposomes for further “entrapment” of the intraliposomal Scue.Lipo-Scue had mean diameter of 80-100nm with PDI less than 0.1.The encapsulation efficiency of lipo-Scu was higher than 95% with drug concentration as high as 1mg/ml.The cumulative release percent of Lipo-Scu in saline at 1:20 dilution(v/v)was around 20% at 48hr.Lipo-Scue also kept good storage stability with less than 10% Scue leakage for 90 days at 4 ℃.Lipo-Scue showed long circulation profile and sustained drug release in the healthy SD rats.The half-life of lipo-Scue was 25-35hr,much longer than that of Scue suspension.Meanwhile,bioavailability(AUC)of Scue was significantly increased to 3500-4000μg/ml*h at the dose of 10mg/kg.The results of tissue distribution showed that Scue could be detected in the heart,liver,spleen and kidney at 72 hr after intravenous injection of Lipo-Scue.Lipo-Scue also showed good neuroprotection effect in the middle cerebral artery occlusion(MCAO)rats after administration at the dose of 10mg/kg at 6,24,48,72 and 96hr after reperfus ion.The cerebral infarct area percent in the TTC stained cerebral sections at 120hr treated with Lipo-Scue was very significantly smaller than that of the untreated group(model group,p<0.01)and significantly smaller than that treated with Scu injection(p<0.05)at the same dosage.Positron Emission Tomography/Computer Tomography(PET/CT)of the rats at 72hr after reperfusion also showed good cerebral protection effect of Lipo-Scue.In conclusion,Scue was successfully encapsulated in PEGylated liposomes via calcium acetate gradient,and showed sustained release profiles both in vitro and in SD rats.Lipo-Scue very effectively increased the half-time of Scue and improved its bioavailability.It also showed good neuroprotection effect in MCAO rats.Lipo-Scue makes it feasible for the neuroprotection mechanism study of Scue in vivo.It may also serve as an example for the insoluble compounds liposomes preparation.