QUANTITATIVE-DETERMINATION OF HYDROPHOBIC COMPOUND ENTRAPMENT IN DIPALMITOYLPHOSPHATIDYLCHOLINE LIPOSOMES BY DIFFERENTIAL SCANNING CALORIMETRY

In this paper the feasibility of determing the percentage of drug entr apment (PDE) in dipalmitoylphosphatidylcholine (DPPC) liposomes by usi ng differential scanning calorimetry (DSC) was assessed. Three differe nt lipophilic compounds, namely testosterone, vitamin E acetate and re tinoic acid, were encapsulated in multilamellar liposomes and their PD E values were determined by DSC and by conventional separative techniq ues, such as dialysis and centrifugation. PDE values of testosterone, vitamin E acetate and retinoic acid determined by DSC analysis, applyi ng Van't Hoff equation, were 6.3 +/- 0.1, 68.9 +/- 0.7 and 87.8 +/- 0. 6, respectively. Dialysis was performed at different time intervals, 3 , 6, 9 and 12 h, on DPPC liposomes entrapping the compounds tested. Th e duration of the dialysis process strongly affected the quantificatio n of testosterone incorporated in DPPC liposomes while it slightly inf luenced the determination of vitamin E acetate and retinoic acid PDE v alues. Centrifugation of DPPC liposomes entrapping the compounds teste d was carried out at different rpm (6000, 9000 and 12000 rpm). No sign ificant difference was observed comparing PDE values obtained centrifu gating at different rpm. Comparing PDE values obtained by dialysis (at 9 and 12 h) and centrifugation for each compound with the correspondi ng PDE values determined by DSC, linear relationships were observed. T hese results suggest that DSC analysis could be regarded as a suitable technique for the quantitative determination of the percentage of hyd rophobic compound entrapped in DPPC liposomes.