Liposomes , as drug carriers, can be administered into the body by several routes e.g. intravenously, intraperitoneally, intramuscularly, intratracheally and topically among others. Radiolabelled markers are suitable to monitor the distribution and elimination of liposomes, but the tissue deposition of intact liposomes, the mode and sites of drug release from the liposomes and liposome-cell interactions cannot be investigated morphologically. Microscopic techniques could provide information regarding the intact state of liposomes and possibly the dynamics of liposomes in tissues provided that they can be identified with certainty in vivo. This is a formidable problem and in spite of several attempts, there is still a lot of work and new ideas needed to overcome this problem.
This paper gives a detailed review of liposome markers used in light and electron microscopy. The use of markers or the technique involved in the identification of liposomes in cells or t issues is discussed.
The feasibility of using colloidal iron, a new electron dense marker, as a marker for intravenously injected liposomes was investigated in mice. Intact multilamellar vesicles containing colloidal iron were identified in the liver, spleen and lung of mice injected with liposomes. The liver and the spleen are organs for the storage of iron containing proteins (ferritin, hemosiderin), therefore studying the disposition of colloidal iron from the liposomes was not possible. However, in organs not containing iron, e.g. lung, the presence of colloidal iron can easily be recognized. The colloidal iron marker may be suitable to label liposomes targeted to the brain , heart or certain tumors
