R. Cazzola et al., PH SENSITIVITY AND PLASMA STABILITY OF LIPOSOMES CONTAINING N-STEAROYLCYSTEAMINE, Biochimica et biophysica acta. Biomembranes, 1329(2), 1997, pp. 291-301
In this study, we investigated the pH sensitivity of different liposom
al formulations containing 10 mol% N-stearoylcys-teamine, as pH sensit
ive molecule. Liposome stability was monitored by determining the rele
ase of different entrapped water soluble molecules, 5,6-carboxyfluores
cein (CF) being the marker of leakage mainly used. Small unilamellar v
esicles composed of egg phosphatidylcholine (EPC) and N-stearoylcystea
mine (9:1 molar ratio) incubated at 20 degrees C in citrate phosphate
buffer released, at pH 6.8, 2.5 fold the amount of CF released at pH 7
.4. The addition of plasma to the incubation medium and an increase of
temperature to 37 degrees C led to significantly increased the CF rel
ease from EPC/N-stearoylcysteamine SUV, both at pH 7.4 and 6.8, The ad
dition of cholesterol had a stabilizing effect on liposomal vesicles w
ith respect to both temperature and plasma, without affecting pH sensi
tivity. In fact, at 37 degrees C and in 25% plasma the ternary mixture
showed the highest CF release, as a consequence of the moderate acidi
fication of the medium from 7.4 to 6.8. Thus, these liposome formulati
ons are potentially a useful tool for specific drug delivery to pathol
ogical tissues such as tumours, inflammation sites and ischemic areas
where it is known that a lowering of the pH can occur. (C) 1997 Elsevi
er Science B.V.