Biomedical Engineering Reference
In-Depth Information
Gadolinium was conjugated to a lipid chain and incorporated into the lipo-
somal membrane [31]. h e formulation was shown to possess favorable
relaxivity and stability and thus serves as a good contrast agent for MRI
imaging.
Liposomes have also been successfully used in topical applications.
Recently, a liposomal benzocaine gel was developed as a topical anaes-
thetic [32]. Topical delivery of liposomal colchicine was successfully
evaluated in a rat model [33]. Inhalable liposomal vasoactive intesti-
nal peptide (VIP) has also been shown to be an ef ective approach for
the treatment of various lung diseases [34]. It makes use of a 'peptide
depot' thus allowing for sustained delivery of VIP. Cationic liposomes
have been preferred over conventional/classical liposomes especially in
the i eld of gene delivery because of their positive charge. h is allows
for the ei cient complexing of the genetic cargo further shielding
it from the degrading actions of enzymes in the body. However, they
have known to be less stable than the conventional neutrally charged
liposomes as they are likely to bind the negatively charged proteins in
the blood and increase uptake by MPS. h ey have also been known to
cause toxicity to the cell due to their non-specii c binding. Still, numer-
ous cationic liposomal formulations have been developed for the deliv-
ery of siRNA [35], short hairpin RNA (shRNA) [36], DNA [37-40]
and other oligonucleotides [41-43]. Cationic liposomes encapsulating
siRNA targeting protein kinase N3 was shown to signii cantly inhibit
tumor progression in a murine orthotopic model [44]. Recently, lipo-
somes encapsulating DNA enzymes were shown to ei ciently down-
regulate the target c-jun gene in osteosarcoma cells [45]. h e gene
encoding vascular endothelial growth factor (VEGF) was delivered to
skeletal myoblast cells for the treatment of acute myocardial infarc-
tion [46]. It was further evaluated in a rat model and was found to
signii cantly improve neovascularization and facilitate cardiac repair.
Cationic liposomal formulations have not just been restricted to the
delivery of genes. Recently they have been used for the delivery of anti-
cancer drugs like paclitaxel as well as for photodynamic therapy [47]. By
virtue of their charge-mediated interactions, they have also been very
useful in inducing antigen specii c responses [48].
3.2.2
Polymer-Coated Long-Circulating Liposomes
One of the main drawbacks in using classical liposomes is the fact that
they are very quickly removed from circulation mainly by the liver and
also by the cells of the MPS. Coating of these liposomes prevents this and
