2.3 Liposomes and Lipoplexes
Negatively charged DNA can also be condensed by cationic lipids. Further, cationic
lipids can form clusters of aggregated vesicles (liposomes) to encapsulate the DNA
within a lipid bilayer to form a lipoplex. Because liposomes can interact and fuse
with the cell membrane, DNA can be delivered directly across the plasma membrane. Consequently, liposome-mediated gene delivery (lipofection) has become a
common protocol for gene delivery in a variety of cell types, and several commercial products are now available on the market. Cationic liposomes can be formed
from a variety of cationic lipids including N-[1-(2,3-dioleoyloxy)propyl]-N,N,Ntrimethylammonium-methyl sulfate (DOTAP) and N-[1-(2,3-dioleoyloxy) propyl]N,N,N-trimethylammonium chloride (DOTMA). A neutral lipid such as
1,2,-dioleoyl-3-phosphatidylethanolamine (DOPE) is often included in the formulation to facilitate membrane fusion and to destabilize the liposomes for DNA
release in the cytoplasm.
Liposomes and lipoplexes are usually self-assembling, easy to prepare and
biodegradable. They allow increased uptake of naked DNA and DNA NPs. They
can also be combined with polycations to form lipid–DNA NPs. Caracciola et al.
[8] observed that lipid–protamine–DNA (LPD) NPs were more efficient than
lipoplexes for gene delivery in CHO (Chinese hamster ovary cells), HEK293
(human embryonic kidney cells), NIH 3T3 (mouse embryonal cells) and A17
(murine cancer cells) cells. Unfortunately, cationic liposomes exhibit significant
variability in gene delivery efficiency and are often toxic to cells.
2.4 NP-Based Gene Delivery
Gene delivery NPs can be formulated from diverse materials with unique
architectures and loaded with DNA by condensation, encapsulation, surface attachment or entrapment. They offer multifold advantages over other methods of gene
delivery:
– Due to their small size, NPs can efficiently penetrate across the cell membrane
barrier to increase the efficiency of gene delivery.
– NPs can modify the condensation and physico-chemical state of the loaded DNA
to protect them against cytoplasmic nuclease.
– Unlike many viral vectors, use of NPs is not limited by DNA size. They are
capable of delivering large-sized DNA having multiple regulatory sequences.
They can also be used to deliver multiple genes simultaneously.
– Functionality of the NPs can be tailored for specific or multiple bioactivities,
such as controlled release of genes, cell-type-specific gene delivery and environmentally sensitive degradability, etc. Use of NPs may also allow the delayed
release of DNA into cells until the cells enter mitosis and dissolve their nuclear
Nanoparticles for Gene Delivery into Stem Cells and Embryos
55
Negatively charged DNA can also be condensed by cationic lipids. Further, cationic
lipids can form clusters of aggregated vesicles (liposomes) to encapsulate the DNA
within a lipid bilayer to form a lipoplex. Because liposomes can interact and fuse
with the cell membrane, DNA can be delivered directly across the plasma membrane. Consequently, liposome-mediated gene delivery (lipofection) has become a
common protocol for gene delivery in a variety of cell types, and several commercial products are now available on the market. Cationic liposomes can be formed
from a variety of cationic lipids including N-[1-(2,3-dioleoyloxy)propyl]-N,N,Ntrimethylammonium-methyl sulfate (DOTAP) and N-[1-(2,3-dioleoyloxy) propyl]N,N,N-trimethylammonium chloride (DOTMA). A neutral lipid such as
1,2,-dioleoyl-3-phosphatidylethanolamine (DOPE) is often included in the formulation to facilitate membrane fusion and to destabilize the liposomes for DNA
release in the cytoplasm.
Liposomes and lipoplexes are usually self-assembling, easy to prepare and
biodegradable. They allow increased uptake of naked DNA and DNA NPs. They
can also be combined with polycations to form lipid–DNA NPs. Caracciola et al.
[8] observed that lipid–protamine–DNA (LPD) NPs were more efficient than
lipoplexes for gene delivery in CHO (Chinese hamster ovary cells), HEK293
(human embryonic kidney cells), NIH 3T3 (mouse embryonal cells) and A17
(murine cancer cells) cells. Unfortunately, cationic liposomes exhibit significant
variability in gene delivery efficiency and are often toxic to cells.
2.4 NP-Based Gene Delivery
Gene delivery NPs can be formulated from diverse materials with unique
architectures and loaded with DNA by condensation, encapsulation, surface attachment or entrapment. They offer multifold advantages over other methods of gene
delivery:
– Due to their small size, NPs can efficiently penetrate across the cell membrane
barrier to increase the efficiency of gene delivery.
– NPs can modify the condensation and physico-chemical state of the loaded DNA
to protect them against cytoplasmic nuclease.
– Unlike many viral vectors, use of NPs is not limited by DNA size. They are
capable of delivering large-sized DNA having multiple regulatory sequences.
They can also be used to deliver multiple genes simultaneously.
– Functionality of the NPs can be tailored for specific or multiple bioactivities,
such as controlled release of genes, cell-type-specific gene delivery and environmentally sensitive degradability, etc. Use of NPs may also allow the delayed
release of DNA into cells until the cells enter mitosis and dissolve their nuclear
Nanoparticles for Gene Delivery into Stem Cells and Embryos
55