Ariën A, Toulmé-Henry N, Dupuy B
INSERM U. 306, Laboratoire Biophysique, Université de Bordeaux II, France.
Pharm Res. 1995 Sep;12(9):1289-92. doi: 10.1023/a:1016261321011.
The work was performed to obtain a better understanding why the oral administration of calcitonin (CT)-loaded liposomes to rats results in a hypocalcemia, while liposomes are normally disrupted in the gastro-intestinal tract and cannot protect the hormone from enzymatic digestion.
In vitro comparisons between the stability of calcein and CT-loaded liposomes in the presence of cholate solutions led to an interpretation of the results observed. By means of gel filtration, turbidimetry, and fluorescence measurements, the interactions between CT and lipids were studied after sonicated liposomes had been broken down by cholate.
Experiments showed that CT in the external medium of a liposome suspension had no effect on the vesicles. Gel filtration of cholate-treated liposomes loaded with calcein and CT resulted in a total separation of calcein from the lipid fraction for detergent concentrations higher than 4 mM. However, 50% of the CT was reencapsulated even when the cholate-to-phospholipid molar ratio was increased up to 100. Incubation of cholate-solubilized liposomes with 1% trypsin resulted in a partial CT-breakdown.
These results strongly suggest that during membrane solubilization by cholate, lipid-CT complexes are formed which retain most of the CT initially embedded in the liposomal membrane, and which offer some protection to CT under the action of trypsin. The existence of these complexes could be one of the reasons for the reported hypocalcemia in rats after oral administration of CT-loaded liposomes.
开展这项工作是为了更好地理解为何给大鼠口服载有降钙素（CT）的脂质体后会导致血钙过少，而脂质体通常会在胃肠道中被破坏，无法保护该激素免受酶消化。
通过比较钙黄绿素和载有CT的脂质体在胆酸盐溶液存在下的体外稳定性来解释所观察到的结果。借助凝胶过滤、比浊法和荧光测量，在胆酸盐使超声处理后的脂质体分解后，研究CT与脂质之间的相互作用。
实验表明脂质体悬浮液外部介质中的CT对囊泡没有影响。对于高于4 mM的去污剂浓度，对用胆酸盐处理过的载有钙黄绿素和CT的脂质体进行凝胶过滤，可使钙黄绿素与脂质部分完全分离。然而，即使胆酸盐与磷脂的摩尔比增加到100，仍有50%的CT被重新包裹。将用胆酸盐增溶的脂质体与1%的胰蛋白酶一起孵育会导致CT部分分解。
这些结果有力地表明，在胆酸盐使膜增溶的过程中，会形成脂质-CT复合物，这些复合物保留了最初包埋在脂质体膜中的大部分CT，并在胰蛋白酶的作用下为CT提供了一定保护。这些复合物的存在可能是口服载有CT的脂质体后大鼠出现血钙过少现象的原因之一。
