Magnetofection is a

transfection Transfection is the process of deliberately introducing naked or purified nucleic acids into eukaryotic cells. It may also refer to other methods and cell types, although other terms are often preferred: " transformation" is typically used to des ...

method that uses magnetic fields to concentrate particles containing vectors to target cells in the body. Magnetofection has been adapted to a variety of vectors, including

nucleic acids Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main cl ...

, non-viral transfection systems, and

viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...

. This method offers advantages such as high transfection efficiency and

biocompatibility Biocompatibility is related to the behavior of biomaterials in various contexts. The term refers to the ability of a material to perform with an appropriate host response in a specific situation. The ambiguity of the term reflects the ongoing de ...

which are balanced with limitations.

Mechanism

Principle

The term magnetofection, currently

trademarked A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign, design, or expression that identifies products or services from a particular source and distinguishes them from others. ...

by the company OZ Biosciences, combines the words magnetic and transfection. Magnetofection uses nucleic acids associated with

magnetic nanoparticles Magnetic nanoparticles are a class of nanoparticle that can be manipulated using magnetic fields. Such particles commonly consist of two components, a magnetic material, often iron, nickel and cobalt, and a chemical component that has functionali ...

. These molecular complexes are then concentrated and transported into cells using an applied magnetic field.

Synthesis

The

are typically made from iron oxide, which is fully biodegradable, using methods such as

coprecipitation In chemistry, coprecipitation (CPT) or co-precipitation is the carrying down by a precipitate of substances normally soluble under the conditions employed. Analogously, in medicine, coprecipitation is specifically the precipitation of an unbound " ...

microemulsion Microemulsions are clear, thermodynamically stable isotropic liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. The aqueous phase may contain salt(s) and/or other ingredients, and the "oil" may actually be ...

. The nanoparticles are then combined with gene vectors ( DNA,

siRNA Small interfering RNA (siRNA), sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded RNA at first non-coding RNA molecules, typically 20-24 (normally 21) base pairs in length, similar to miRNA, and operating ...

, ODN,

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...

, etc.). One method involves linking viral particles to magnetic particles using an avidin- biotin interaction. Viruses can also bind to the nanoparticles via

hydrophobic interaction In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, t ...

. Another synthesis method involves coating magnetic nanoparticles with cationic lipids or polymers via salt-induced aggregation. For example, nanoparticles may be conjugated with the polyethylenimine (PEI), a positively charged polymer used commonly as a transfection agent. The PEI solution must have a high pH during synthesis to encourage high gene expression. The positively charged nanoparticles can then associate with negatively charged nucleic acids via

electrostatic Electrostatics is a branch of physics that studies electric charges at rest ( static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amb ...

interaction. Magnetofection with labels

Cellular uptake

Magnetic particles loaded with vectors are concentrated on the target cells by the influence of an external magnetic field. The cells then take up genetic material naturally via endocytosis and

pinocytosis In cellular biology, pinocytosis, otherwise known as fluid endocytosis and bulk-phase pinocytosis, is a mode of endocytosis in which small molecules dissolved in extracellular fluid are brought into the cell through an invagination of the cell ...

. Consequently, membrane architecture and structure stays intact, in contrast to other physical transfection methods such as

electroporation Electroporation, or electropermeabilization, is a microbiology technique in which an electrical field is applied to cells in order to increase the permeability of the cell membrane, allowing chemicals, drugs, electrode arrays or DNA to be introd ...

gene gun In genetic engineering, a gene gun or biolistic particle delivery system is a device used to deliver exogenous DNA (transgenes), RNA, or protein to cells. By coating particles of a heavy metal with a gene of interest and firing these micro-proje ...

s that damage the cell membrane. The nucleic acids are then released into the

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

by different mechanisms depending upon the formulation used: # the proton sponge effect caused by cationic polymers coated on the nanoparticles that promote

endosome Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membrane can ...

osmotic swelling, disruption of the

membrane and intracellular release of DNA form, # the destabilization of endosome by cationic

lipids Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

coated on the particles that release the nucleic acid into cells by flip-flop of cell negative lipids and charge neutralization and # the viral infection mechanism. Magnetofection works with cells that are not dividing or slowly dividing, meaning that the genetic materials can go to the cell nucleus without

cell division Cell division is the process by which a parent cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there ar ...

Applications

Magnetofection has been tested on a broad range of

cell lines An immortalised cell line is a population of cells from a multicellular organism which would normally not proliferate indefinitely but, due to mutation, have evaded normal cellular senescence and instead can keep undergoing division. The cells ...

, hard-to-transfect and primary cells. Several optimized and efficient magnetic nanoparticle formulations have been specifically developed for several types of applications such as DNA, siRNA, and primary neuron transfection as well as viral applications. Magnetofection research is currently in the preclinical stage. This technique has primarily been tested in vivo using plasmid DNA in mouse, rat, and rabbit models for applications in the hippocampus, subcutaneous tumors, lungs, spinal cord, and muscle.

Some applications include: * Delivery of GFP gene into primary

neural stem cell Neural stem cells (NSCs) are self-renewing, multipotent cells that firstly generate the radial glial progenitor cells that generate the neurons and glia of the nervous system of all animals during embryonic development. Some neural progenitor ste ...

s, which are typically difficult to transfect, with 18% efficacy with a static magnetic field and 32% efficacy with an oscillating field. * Delivery of oligodesoxynucleotides (ODN) into human umbilical vein endothelial cells with 84% efficiency. * Delivery of siRNA to HeLa cells to knock down luciferase reporter gene. * Delivery of adenoviral vectors to primary human peripheral blood lymphocytes.

Advantages

Magnetofection attempts to unite the advantages of biochemical (cationic

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...

s or polymers) and physical (

) transfection methods. It allows for local delivery with high transfection efficiency, faster incubation time, and biocompatibility.

Transfection efficiency

Coupling magnetic nanoparticles to gene vectors results in hundreds-fold increase of the uptake of these vectors on a time scale of minutes, thus leading to high transfection efficiency. Gene vector and magnetic nanoparticle complexes are transfected into cells after 10–15 minutes, which is faster than the 2–4 hours that other transfection methods require. After 24, 48 or 72 hours, most of the particles are localized in the

, in

vacuoles A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...

(membranes surrounded structure into cells) and occasionally in the cell nucleus.

Biocompatibility

Magnetic nanoparticles do not aggregate easily once the magnet is removed, and therefore are unlikely to block

capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...

or cause

thrombosis Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (t ...

. In addition, iron oxide is biodegradable, and the iron can be reused in hemoglobin or iron metabolism pathways.

Disadvantages

Particle variability

Magnetic nanoparticle synthesis can sometimes lead to a wide range of differently sized particles. The size of particles can influence their usefulness. Specifically, nanoparticles that are less than 10 nm or greater than 200 nm in size tend to be cleared from the body more quickly.

Localization in vivo

While magnets can be used to localize magnetic nanoparticles to desired cells, this mechanism may be difficult to maintain in practice. The nanoparticles can be concentrated in 2D space such as on a culture plate or at the surface of the body, but it can be more difficult to localize them in the 3D space of the body. Magnetofection does not work well for organs or blood vessels far from the surface of the body, since the magnetic field weakens as distance increases. In addition, the user must consider the frequency and timing of applying the magnetic field, as the particles will not necessarily stay in the desired location once the magnet is removed.

Cytotoxicity

While iron oxide used to make nanoparticles is biodegradable, the toxicity of magnetic nanoparticles is still under investigation. Some research has found no signs of damage to cells, while others claim that small (< 2 nm) nanoparticles can diffuse across cell membranes and disrupt organelles. In addition, very high concentrations of iron oxide can disrupt homeostasis and lead to

iron overload Iron overload or hemochromatosis (also spelled ''haemochromatosis'' in British English) indicates increased total accumulation of iron in the body from any cause and resulting organ damage. The most important causes are hereditary haemochromatos ...

, which can damage or alter DNA, affect cellular responses, and kill cells. Lysosymes can also digest the nanoparticles and release free iron which can react with hydrogen peroxide to form free radicals, leading to cytotoxic, mutagenic, and carcinogenic effects.