A method for coating an object, i.e. a particle, with two sheets of lipid film having a space formed there between. In the method for coating a particle having a positive electrostatic-charging property with two sheets of lipid film, the particle having a positive electrostatic-charging property is brought into contact with a plurality of SUV type liposomes having a negative electrostatic-charging property to form a complex having a negative electrostatic-charging property containing the particle having a positive electrostatic-charging property and the SUV type liposomes having a negative electrostatic-charging property coupled electrostatically with the particle having a positive electrostatic-charging property, and then the complex having a negative electrostatic-charging property is treated with cation.

Description of the Invention

TECHNICAL FIELD

The present invention relates to a method for coating a particle with lipid membranes.

BACKGROUND ART

In recent years, developments of vectors for delivering drugs, nucleic acids, peptides, proteins, sugars and the like certainly to target sites have been actively carried out. For example, for gene therapy, viral vectors such as retrovirus, adenovirus, adeno-associated virus and the like have been developed as vectors for introducing a desired gene to a target cell. However, since the viral vectors have problems such as difficulties in mass production, antigenicity, toxicity and the like, liposome vectors, which suffer less from such problems, have attracted attention. The liposome vectors have an advantage that the directivity to a target site can be enhanced by introducing functional molecules such as antibodies, proteins, sugar chains and the like to the surface of the liposome vectors.

As a method for preparing liposomes, for example, there is known a lipid film hydration method. According to the lipid film hydration method, multilamellar liposomes encapsulating an object material can be prepared by hydrating a lipid membrane in the presence of the object material such as genes (see Non-Patent Document 1). New lipid membranes can be further laminated on the external side of the multilamellar liposomes by repeatedly applying the lipid film hydration method to the multilamellar liposomes thus prepared. As such, by repeating the lipid film hydration method, the number of the lipid membranes included in the multilamellar liposomes can be increased. [Non-Patent Document 1] Kogure, et al., Journal of Controlled Release, Vol. 98, pp. 317-323 (2004)

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, in the conventional methods such as the lipid film hydration method, since the lipid membranes are laminated non-uniformly, it was difficult to control the number of the lipid membranes to be included in multilamellar liposomes. Furthermore, in the conventional methods such as the lipid film hydration method and the like, lipid membranes can only be piled up onto any layer as in the case of geological strata, and thus it has been difficult to form a space in between the lipid membranes.

Therefore, it is an object of the present invention to provide a method for coating a subject particle with two sheets of lipid membrane having a space formed there between, and liposomes obtained by coating a subject particle with two sheets of lipid membrane by the method.

Means for Solving the Problems

A first method of the present invention is a method for coating a positively charged particle with two sheets of lipid membrane, comprising contacting the positively charged particle with a plurality of negatively charged SUV type liposomes to form a negatively charged complex containing the positively charged particle and the negatively charged SUV type liposomes that are electrostatically bound to the positively charged particle, and treating the negatively charged complex with cations.

According to the first method of the present invention, a positively charged particle can be coated with two sheets of lipid membrane having a space formed there between. In the liposome obtained by coating a positively charged particle by the first method of the present invention, there is formed a space between the two sheets of lipid membrane which coat the positively charged particle (the first lipid membrane formed on the external side of the positively charged particle, and the second lipid membrane formed on the external side of the first lipid membrane), and a desired material can be retained in this space.

According to the first method of the present invention, it is preferable that the positively charged particle is an aggregate of the object material. In this case, a bilamellar liposome encapsulating an aggregate of an object material and having a space formed between the two sheets of lipid membrane which coat the aggregate of object material, can be produced.

According to the first method of the present invention, it is preferable that the positively charged particle is a positively charged n-lamellar liposome, wherein n is an integer of 1 or greater. In this case, a (n+2)-lamellar liposome having a space formed between two sheets of lipid membranes that coat the positively charged n-lamellar liposome, can be produced.

According to the first method of the present invention, it is preferable that the positively charged particle has a zeta potential of 20 to 30 mV, while the negatively charged SUV type liposome has a zeta potential of -20 to -30 mV. In this case, a negatively charged complex containing a positively charged particle and a plurality of negatively charged SUV type liposomes that are electrostatically bound to the positively charged particle, can be efficiently formed.

According to the first method of the present invention, it is preferable that the positively charged particle has a particle diameter of 50 nm or larger. In this case, a negatively charged complex containing a positively charged particle and a plurality of negatively charged SUV type liposomes that are electrostatically bound to the positively charged particle, can be efficiently formed.

The second method of the present invention is a method for coating a negatively charged particle with two sheets of lipid membrane, comprising contacting the negatively charged particle with a plurality of positively charged SUV type liposomes to form a positively charged complex containing the negatively charged particle and the positively charged SUV type liposomes that are electrostatically bound to the negatively charged particle, and treating the positively charged complex with anions.

According to the second method of the present invention, the negatively charged particle can be coated with two sheets of lipid membrane having a space formed there between. In the liposome obtained by coating a negatively charged particle by the second method of the present invention, there is formed a space between the two sheets of lipid membrane which coat the negatively charged particle (the first lipid membrane formed on the external side of the negatively charged particle, and the second lipid membrane formed on the external side of the first lipid membrane), and a desired material can be retained in this space.

According to the second method of the present invention, it is preferable that the negatively charged particle is an aggregate of the desired material. In this case, a bilamellar liposome encapsulating an aggregate of an object material and having a space formed between the two sheets of lipid membrane which coat the aggregate of object material, can be produced.

According to the second method of the present invention, it is preferable that the negatively charged particle is a negatively charged n-lamellar liposome, wherein n is an integer of or greater. In this case, an (n+2)-lamellar liposome having a space formed between two sheets of lipid membrane that coat a negatively charged n-lamellar liposome, can be produced.

According to the second method of the present invention, it is preferable that the negatively charged particle has a zeta potential of -20 to -30 mV, while the positively charged SUV type liposome has a zeta potential of 20 to 30 mV. In this case, a positively charged complex containing a negatively charged particle and a plurality of positively charged SUV type liposomes that are electrostatically bound to the negatively charged particle, can be efficiently formed.

According to the second method of the present invention, it is preferable that the negatively charged particle has a particle diameter of 50 nm or larger. In this case, a positively charged complex containing a negatively charged particle and a plurality of positively charged SUV type liposomes that are electrostatically bound to the negatively charged particle can be efficiently formed.

Effects of the Invention

According to the method of the present invention, the subject particle for coating can be coated with two sheets of lipid membrane having a space formed there between. Therefore, if an aggregate of an object material is used as the subject particle for coating, a bilamellar liposome encapsulating the aggregate of object material and having a space formed between the two sheets of lipid membranes which coat the aggregate of object material can be produced; while if an n-lamellar liposome, wherein n is an integer of 1 or greater, is used as the subject particle for coating, an (n+2)-lamellar liposome having a space formed between two sheets of lipid membrane that coat the n-lamellar liposome, can be produced. In the liposome obtained by coating a positively charged particle or a negatively charged particle by the method of the present invention, there is formed a space between the two sheets of lipid membrane that coat the positively charged particle or negatively charged particle, and a desired material can be retained in this space.

BEST MODE FOR CARRYING OUT THE INVENTION

In the first method of the present invention, first, a positively charged particle is contacted with a plurality of negatively charged SUV type liposomes to form a negatively charged complex containing the positively charged particle and the negatively charged SUV type liposomes that are electrostatically bound to the positively charged particle.

In the second method of the present invention, first, a negatively charged particle is contacted with a plurality of positively charged SUV type liposomes to form a positively charged complex containing the negatively charged particle and the positively charged SUV type liposomes that are electrostatically bound to the negatively charged particle.

The zeta potential of the positively charged particle is not particularly limited as long as the value is positive, but the value is usually 10 to 60 mV, preferably 20 to 50 mV, and more preferably 20 to 30 mV. The zeta potential of the negatively charged particle is not particularly limited as long as the value is negative, but the value is usually -10 to -60 mV, preferably -20 to -50 mV, and more preferably -20 to -30 mV. The conditions for the measurement of zeta potential are not particularly limited, but the temperature condition is usually 25.degree. C.

The particle diameter of the positively charged particle and the negatively charged particle is not particularly limited, but the lower limit value of the particle diameter is preferably 50 nm, and more preferably 70 nm, while the upper limit value of the particle diameter is preferably 500 nm, more preferably 200 nm. If the particle diameter of the positively charged particle is within the above-mentioned range, the positively charged particle can be efficiently coated with two sheets of lipid membrane when the negatively charged SUV type liposomes that are electrostatically bound to the positively charged particle are treated with cations. Further, if the particle diameter of the negatively charged particle is within the above-mentioned range, the negatively charged particle can be efficiently coated with two sheets of lipid membrane when the positively charged SUV type liposomes that are electrostatically bound to the negatively charged particle are treated with an ions.

The positively charged particle may contain a neutral material and/or an anionic material in addition to a cationic material, as long as the particle is positively charged as a whole. The negatively charged particle may contain a neutral material and/or a cationic material, in addition to an anionic material, as long as the particle is negatively charged as a whole.

As the positively charged or negatively charged particle, for example, an aggregate of an object material (for example, a material to be delivered into a cell or a nucleus) can be used. In the case of using an aggregate of an object material as the positively charged or negatively charged particle, a bilamellar liposome encapsulating the object material can be produced by coating the positively charged or negatively charged particle with two sheets of lipid membrane. The aggregate of object material may be consisted of the object material alone, or alternatively may include materials other than the object material (for example, a carrier retaining the object material).

In the case where the object material is positively charged, an aggregate of the object material can be prepared, for example, by allowing the object material to be electrostatically bound to an anionic material to form a complex. In the case where the object material is negatively charged, an aggregate of the object material can be prepared, for example, by allowing the object material to be electrostatically bound to a cationic material to form a complex. If the object material is charged neither negatively nor positively, an aggregate of the object material can be prepared by allowing the object material to be bound to a cationic material by any appropriate manner (for example, physical adsorption, hydrophobic bonding, chemical bonding and the like) to form a complex. Upon the formation of the complex, an aggregate of the object material which is either positively or negatively charged as a whole can be prepared, by adjusting the mixing ratio between the object material and a cationic material or an anionic material.

The object material is not particularly limited, and examples thereof include nucleic acid, peptide, protein, drug, sugar, complexes thereof, and the like. In addition, the term "nucleic acid" includes DNA or RNA, as well as analogues or derivatives thereof (for example, peptide nucleic acid (PNA), phosphorothioate DNA). Also, the nucleic acid may be of a single strand or a double strand, and may be either linear or cyclic.

If the object material is a nucleic acid, an aggregate of the nucleic acid can be prepared by allowing the nucleic acid to be electrostatically bound to a cationic material to form a complex. Upon the formation of the complex, an aggregate of nucleic acid which is either positively or negatively charged as a whole can be prepared, by adjusting the mixing ratio between the nucleic acid and the cationic material.

The cationic material used for preparing the aggregate of object material is not particularly limited as long as it is a material having a cationic group in the molecule. Examples of the cationic material that can be used include cationic lipids (for example, Lipofectamine (Invitrogen, Inc.)); polymers having cationic groups; homopolymers or copolymers of basic amino acids such as polylysine, polyarginine, copolymers of lysine and arginine, or derivatives thereof (for example, stearylated derivatives); polycationic polymers such as polyethyleneimine, poly(arylamine), poly(diaryldimethylammonium chloride), glucosamine; protamine sulfate; and the like. The number of cationic groups carried by the cationic material is not particularly limited, but the number is preferably two or more. The cationic group is not particularly limited as long as it can be positively charged, and examples thereof include an amino group; a monoalkylamino group such as a methylamino group, an ethylamino group; a dialkylamino group such as a dimethylamino group, a diethylamino group; an imino group; a guanidine group; and the like.

The anionic material that is used for preparing the aggregate of object material is not particularly limited as long as it is a material having an anionic group in the molecule. Examples of the anionic material that can be used include anionic lipids; polymers having anionic groups; homopolymers or copolymers of acidic amino acid such as polyaspartic acid, or derivatives thereof; polyanionic polymers such as xanthane gum, carboxyvinyl polymers, carboxymethylcellulose polystyrenesulfonic acid salts, polysaccharides, carrageenan; and the like. The number of anionic groups carried by the anionic material is not particularly limited, but the number is preferably two or more. The anionic group is not particularly limited as long as it can be negatively charged, and examples thereof include a functional group having a terminal carboxyl group (for example, a succinic acid residue, a malonic acid residue, etc.), a phosphate group, a sulfate group, and the like.

As the positively charged or negatively charged particle, for example, a positively charged or negatively charged n-lamellar liposome, wherein n is an integer of 1 or greater), can be used. In the case of using the n-lamellar liposome as the positively charged or negatively charged particle, a (n+2)-lamellar liposome can be produced by coating the positively charged or negatively charged particle with two sheets of lipid membrane. The positively charged or negatively charged n-lamellar liposome may or may not encapsulate an object material (for example, a material to be delivered into a cell or a nucleus) inside the liposome. The positively charged n-lamellar liposome may contain a neutral material and/or an anionic material in addition to a cationic material, as long as the liposome is positively charged as a whole. The negatively charged n-lamellar liposome may contain a neutral material and/or a cationic material in addition to an anionic material, as long as the liposome is negatively charged as a whole.

The n-lamellar liposome can be produced using known methods such as, for example, a hydration method, an ultrasonication method, an ethanol injection method, an ether injection method, a reverse phase evaporation method, a surfactant method, a freeze-thawing method. The n-lamellar liposome can also be prepared by coating a positively charged or negatively charged particle with two sheets of lipid membrane using the method of the present invention.

The positively charged or negatively charged n-lamellar liposome can be produced by adjusting the type and content of the material constituting the n-lamellar liposome (for example, the lipid membrane-constituting component, the material being encapsulated inside the liposome). Furthermore, a positively charged n-lamellar liposome can be produced by modifying the surface of a negatively charged n-lamellar liposome or a neutral n-lamellar liposome with a cationic material, while a negatively charged n-lamellar liposome can be produced by modifying the surface of a positively charged n-lamellar liposome or a neutral n-lamellar liposome with an anionic material.

The n-lamellar liposome can be produced by, for example, a hydration method as follows. Components of lipid membrane are dissolved in an organic solvent, and then the organic solvent is removed by evaporation to obtain a lipid membrane. Here, the organic solvent may be exemplified by a hydrocarbon such as pentane, hexane, heptane, cyclohexane; a halogenated hydrocarbon such as methylene chloride, chloroform; an aromatic hydrocarbon such as benzene, toluene; a lower alcohol such as methanol, ethanol; an ester such as methyl acetate, ethyl acetate or the like; a ketone such as acetone; or the like, and these can be used individually or in combination of two or more species. Subsequently, the lipid membrane is hydrated, and agitated or ultrasonicated, thereby converting the lipid membrane to multilamellar liposomes. The conversion of multilamellar liposome to unilamellar liposome, or the conversion of unilamellar liposome to multilamellar liposome can be carried out according to known methods. When n-lamellar liposomes are passed through a filter having a predetermined pore size, n-lamellar liposomes having a constant particle size distribution can be obtained.

When the object material is water-soluble, the object material can be encapsulated in the aqueous phase inside a liposome by adding the object material or aggregates thereof to the aqueous solvent used in hydrating a lipid membrane during the preparation of the n-lamellar liposome. When the object material is lipid-soluble, the object material can be encapsulated in the lipid membranes of a liposome by adding the object material or aggregates thereof to the organic solvent used during the preparation of the n-lamellar liposome.

When the surface of a negatively charged n-lamellar liposome or neutral n-lamellar liposome is modified with a cationic material, for example, a cationic material having a hydrophobic group is added to the liquid outside the negatively charged n-lamellar liposome or neutral n-lamellar liposome. In this way, the hydrophobic group is inserted into the lipid membrane such that the cationic material is exposed from the lipid membrane, and thus the cationic material can be introduced into the surface of the negatively charged liposome or neutral n-lamellar liposome.

When the surface of a positively charged n-lamellar liposome or neutral n-lamellar liposome is modified with an anionic material, for example, an anionic material having a hydrophobic group is added to the liquid outside the positively charged n-lamellar liposome or neutral n-lamellar liposome. In this way, the hydrophobic group is inserted into the lipid membrane such that the anionic material is exposed from the lipid membrane, and thus the anionic material can be introduced into the surface of the positively charged liposome or neutral n-lamellar liposome.

The hydrophobic group is not particularly limited as long as it can be inserted into the lipid membrane. Examples of the hydrophobic group include saturated or unsaturated fatty acid groups such as stearyl group, sterol residues such as cholesterol residue, phospholipid residues, glycolipid residues, long chain aliphatic alcohol residues (for example, phosphatidylethanolamine residue), polyoxypropylenealkyl group, glycerin fatty acid ester residues, and the like, and among these, fatty acid groups having 10 to 20 carbon atoms (for example, a palmitoyl group, an oleyl group, a stearyl group, an arachidoyl group, etc.) are particularly preferred.

The lipid membrane component for the n-lamellar liposome is not particularly limited as long as the component does not inhibit the formation of lipid bilayer, and examples of the lipid membrane component include lipids, membrane-stabilizing agents, antioxidants, charged materials, membrane proteins and the like.

The type and content of the lipid membrane component for a positively charged n-lamellar liposome are controlled such that the n-lamellar liposome is positively charged as a whole, while the type and content of the lipid membrane component for a negatively charged n-lamellar liposome are controlled such that the n-lamellar liposome is negatively charged as a whole. Examples of the lipid membrane component which imparts a positive charge include cationic lipids, cationic membrane-stabilizing agents and the like, while examples of the lipid membrane component which imparts a negative charge include an ionic lipids, anionic membrane-stabilizing agents and the like. Moreover, in the case where a predetermined material (for example, an aggregate of the object material) is encapsulated inside the n-lamellar liposome, the type and content of the lipid membrane component in the n-lamellar liposome are controlled in consideration of the overall charge of the material encapsulated inside the n-lamellar liposome.

An SUV (small unilamellar vesicle) type liposome is a unilamellar liposome having a particle size (diameter) of 100 nm or less. The particle size (diameter) of the SUV type liposome is not particularly limited as long as it is of 100 nm or less, but the size is typically 30 to 100 nm, preferably 30 to 70 nm, and more preferably 30 to 50 nm.

Since a multilamellar liposome (MLV) and a unilamellar liposome other than SUV (for example, LUV (large unilamellar vesicle), GUV (giant unilamellar vesicle), etc.) have a particle diameter of 100 nm or greater (in general, a lipid membrane having a particle diameter of 100 nm or greater is considered as a planar membrane), the curvature and surface energy of the membrane are small, and aggregation between liposomes is hard to occur. In this regard, since a SUV type liposome has a particle diameter of less than 100 nm, the curvature and surface energy of the membrane are large, and aggregation between liposomes readily occurs. Therefore, when negatively charged SUV type liposomes that are electrostatically bound to a positively charged particle are treated with cations, it is possible to efficiently induce membrane fusion between the negatively charged SUV type liposomes. Further, when positively charged SUV type liposomes which are electrostatically bound to a negatively charged particle are treated with anions, it is possible to efficiently induce membrane fusion between the positively charged SUV type liposomes.

SUV type liposomes can be produced, for example, by an ultrasonication method as follows. The lipid membrane components are dissolved in an organic solvent, and then the organic solvent is removed by evaporation to obtain a lipid membrane. Here, the organic solvent may be exemplified by a hydrocarbon such as pentane, hexane, heptane, cyclohexane; a halogenated hydrocarbon such as methylene chloride, chloroform; an aromatic hydrocarbon such as benzene, toluene; a lower alcohol such as methanol, ethanol; an ester such as methyl acetate, ethyl acetate; a ketone such as acetone; or the like, and these can be used individually or in combination of two or more species. Subsequently, the lipid membrane is hydrated, and agitated or ultrasonicated using an ultrasonic bath, thereby producing multilamellar liposomes. The resulting multilamellar liposomes are further ultrasonicated by means of a probe type ultrasonicator, and thus SUV type liposomes which are small unilamellar liposomes can be prepared.

The lipid membrane component for the SUV type liposome is not particularly limited as long as the component does not inhibit the formation of lipid bilayer, and examples of the lipid membrane component include lipids, membrane stabilizing agents, antioxidants, charged materials, membrane proteins.

The type and content of the lipid membrane component in the positively charged SUV type liposome are controlled such that the SUV type liposome is positively charged as a whole, while the type and content of the lipid membrane component in the negatively charged SUV type liposome are controlled such that the SUV type liposome is negatively charged as a whole. Examples of the lipid membrane component which imparts a positive charge include cationic lipids, cationic membrane-stabilizing agents and the like, while examples of the lipid membrane component which imparts a negative charge include anionic lipids, anionic membrane-stabilizing agents and the like. The positively charged SUV type liposome may contain a lipid membrane component which imparts a negative charge and/or a neutral lipid membrane component, in addition to the lipid membrane component which imparts a positive charge, as long as the liposome is positively charged as a whole. The negatively charged SUV type liposome may contain a lipid membrane component which imparts a positive charge and/or a neutral lipid membrane component, in addition to the lipid membrane component which imparts a negative charge, as long as the liposome is negatively charged as a whole.

When the positively charged SUV type liposome contains a cationic lipid as the lipid membrane component which imparts a positive charge, the blending amount of the cationic lipid is usually 5 to 30% (molar ratio), preferably 10 to 20% (molar ratio), and more preferably 10 to 15% (molar ratio), based on the total blending amount of lipids.

When the negatively charged SUV type liposome contains an anionic lipid as the lipid membrane component which imparts a negative charge, the blending amount of the anionic lipid is usually 5 to 30% (molar ratio), preferably 10 to 20% (molar ratio), and more preferably 10 to 15% (molar ratio), based on the total compounding amount of lipids.

The zeta potential of the positively charged SUV type liposome is not particularly limited as long as it is positive, but the zeta potential is usually 10 to 60 mV, preferably 20 to 50 mV, and more preferably 20 to 30 mV. The zeta potential of the negatively charged SUV type liposome is not particularly limited as long as it is negative, but the zeta potential is usually 10 to 60 mV, preferably 20 to 50 mV, and more preferably 20 to 30 mV. The conditions for the measurement of zeta potential are not particularly limited, but the temperature condition is usually 25.degree. C.

With regard to the n-lamellar liposome or SUV type liposome, lipids are the essential component of the lipid membrane, and the blending amount is usually 30 to 100% (molar ratio), preferably 50 to 100% (molar ratio), and more preferably 70 to 100% (molar ratio), based on the total blending amount of the lipid membrane components.

Examples of the lipid include phospholipids, glycolipids, sterols, saturated or unsaturated fatty acids, and the like. Examples of the phospholipids include phosphatidylcholine (for example, dioleoylphosphatidylcholine, dilauroylphosphatidylcholine, dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine, distearoylphosphatidylcholine, etc.), phosphatidylglycerol (for example, dioleoylphosphatidylglycerol, dilauroylphosphatidylglycerol, dimyristoylphosphatidylglycerol, dipalmitoylphosphatidylglycerol, distearoylphosphatidylglycerol, etc.), phosphatidylethanolamine (for example, dioleoylphosphatidylethanolamine, dilauroylphosphatidylethanolamine, dimyristoylphosphatidylethanolamine, dipalmitoylphosphatidylethanolamine, distearoylphosphatidylethanolamine, etc.), phosphatidylserine, phosphatidylinositol, phosphatidic acid, cardiolipin, sphingomyelin, egg yolk lecithin, soybean lecithin, hydrogenation products thereof, and the like. Examples of the glycolipids include glyceroglycolipid (for example, sulfoxyribosyl glyceride, diglycosyl diglyceride, digalactosyl diglyceride, galactosyl diglyceride, and glycosyl diglyceride), sphingoglycolipid (for example, galactosyl cerebroside, lactosyl cerebroside and ganglioside), and the like. Examples of the sterols include animal-derived sterols (for example, cholesterol, cholesterol succinate, lanosterol, dihydrolanosterol, desmosterol and dihydrocholesterol), plant-derived sterols (phytosterol) (for example, stigmasterol, sitosterol, campesterol and brassicasterol), microorganism-derived sterols (for example, thymosterol and ergosterol), and the like. Examples of the saturated or unsaturated fatty acids include saturated or unsaturated fatty acids having 12 to 20 carbon atoms, such as palmitic acid, oleic acid, stearic acid, arachidonic acid, myristic acid.

The lipids are classified into neutral lipids, cationic lipids and anionic lipids. Examples of the neutral lipids include diacylphosphatidylcholine, diacylphosphatidylethanolamine, cholesterol, ceramide, sphingomyelin, cephalin, cerebroside and the like; examples of the cationic lipids include DODAC (dioctadecyldimethylammonium chloride), DOTMA (N-(2,3-dioleyloxy)propyl-N,N,N-trimethylammonium), DDAB (didodecylammonium bromide), DOTAP (1,2-dioleoyloxy-3-trimethylammonio propane), DC-Chol (3.beta.-N--(N',N'-dimethyl-aminoethane)-carbamol cholesterol), DMRIE (1,2-dimyristoyloxypropyl-3-dimethylhydroxyethylammonium), DOSPA (2,3-dioleyloxy-N-[2-(sperminecarboxamido)ethyl]-N,N-dimethyl-1-propanami- nium trifluoroacetate), and the like; and examples of the anionic lipids include cardiolipin, diacylphosphatidylserine, diacylphosphatidic acid, N-succinylphosphatidylethanolamine (N-succinyl-PE), phosphatidic acid, phosphatidylinositol, phosphatidylglycerol, phosphatidylethylene glycol, cholesterol succinate, and the like.

With regard to the n-lamellar liposome or SUV type liposome, the membrane-stabilizing agent is any component that is added to physically or chemically stabilize the lipid membrane, or to control the fluidity of the lipid membrane, and the blending amount is usually 10 to 50% (molar ratio), preferably 20 to 50% (molar ratio), and more preferably 30 to 50% (molar ratio), based on the total blending amount of the lipid membrane components.

Examples of the membrane-stabilizing agent include sterols, glycerin or its fatty acid esters. Specific examples of the sterol include those mentioned above, while examples of the fatty acid esters of glycerin include triolein, trioctanoin and the like.

With regard to the n-lamellar liposome or SUV type liposome, the antioxidant is any component that is added to prevent oxidation of the lipid membrane, and the blending amount is usually 5 to 30% (molar ratio), preferably 10 to 30% (molar ratio), and more preferably 20 to 30% (molar ratio), based on the total blending amount of the lipid membrane components.

Examples of the antioxidant include tocopherol, propyl gallate, ascorbyl palmitate, butylated hydroxytoluene and the like.

With regard to the n-lamellar liposome or SUV type liposome, the charged material is any component that is added to impart a positive charge or a negative charge to the lipid membrane, and the blending amount is usually 5 to 30% (molar ratio), preferably 10 to 20% (molar ratio), and more preferably 10 to 15% (molar ratio), based on the total blending amount of the lipid membrane component.

Examples of the charged material which imparts a positive charge include saturated or unsaturated aliphatic amines such as stearylamine, oleylamine; saturated or unsaturated cationic synthetic lipids such as dioleoyltrimethylammoniumpropane; and the like. Examples of the charged material which imparts a negative charge include dicetyl phosphate, cholesterol succinate, phosphatidylserine, phosphatidylinositol, phosphatidic acid, and the like.

With regard to the n-lamellar liposome or SUV type liposome, the membrane protein is any component that is added to maintain the structure of the lipid membrane, or to impart any functionality to the lipid membrane, and the blending amount is usually 0.1 to 2% (molar ratio), preferably 0.5 to 2% (molar ratio), and more preferably 1 to 2% (molar ratio), based on the total blending amount of the lipid membrane components.

Examples of the membrane protein include surface membrane proteins, inner membrane proteins and the like.

The conditions for contacting the negatively charged or positively charged SUV type liposomes with the positively charged or negatively charged particle, respectively, are not particularly limited, but the temperature is usually 10 to 40.degree. C., and preferably 20 to 30.degree. C.; the pH is usually 6.5 to 8.0, and preferably 7.0 to 7.5; and the time is usually 1 to 20 minutes, and preferably 5 to 10 minutes. The solvent used for the contacting is not particularly limited, but for example, HEPES buffer solution, physiological saline, sucrose solution and the like can be used. The amount of the negatively charged or positively charged SUV type liposomes dispersed in the solvent is usually an excess against the positively charged or negatively charged particle, and for example, the amount is 2- to 4-fold the amount of the negatively charged or positively charged SUV type liposomes that is theoretically required at minimum for the encapsulation of the positively charged or negatively charged particle.

When negatively charged SUV type liposomes are contacted with a positively charged particle, the positively charged particle and the negatively charged SUV type liposomes bind through electrostatic interaction, and the surface of the positively charged particle is covered with a plurality of negatively charged SUV type liposomes. Then, a negatively charged complex containing the positively charged particle and a plurality of negatively charged SUV type liposomes electrostatically bound to the positively charged particle is formed. Here, it is preferable that a negatively charged complex having a zeta potential of 20 to 50 mV is formed, and it is more preferable that a negatively charged complex having a zeta potential of 20 to 30 mV is formed. Then, the negatively charged SUV type liposomes that are electrostatically bound to the positively charged particle can be efficiently treated with cations. The zeta potential of the negatively charged complex can be controlled by controlling the zeta potential, particle diameter and the like of the positively charged particle and the negatively charged SUV type liposome.

When positively charged SUV type liposomes are contacted with a negatively charged particle, the negatively charged particle and the positively charged SUV type liposomes bind through electrostatic interaction, and the surface of the negatively charged particle is covered with a plurality of the positively charged SUV type liposomes. Then, a positively charged complex containing the negatively charged particle and a plurality of positively charged SUV type liposomes that are electrostatically bound to the negatively charged particle, is formed. Here, it is preferable that a positively charged complex having a zeta potential of 20 to 50 mV is formed, and it is more preferable that a positively charged complex having a zeta potential of 20 to 30 mV is formed. Then, the positively charged SUV type liposomes that are electrostatically bound to the negatively charged particle can be efficiently treated with anions. The zeta potential of the positively charged complex can be controlled by controlling the zeta potential, particle diameter and the like of the negatively charged particle and the positively charged SUV type liposomes.

In the first method of the present invention, the formed negatively charged complex is subsequently treated with cations.

In the second method of the present invention, the formed positively charged complex is subsequently treated with anions.

The cation is not particularly limited, and for example, a monovalent cation such as H.sup.+; a divalent cation such as Ca.sup.2+, Mg.sup.2+; a trivalent cation such as Al.sup.3+; and the like may be mentioned. Examples of the material generating H.sup.+ include acids such as hydrochloric acid, acetic acid; examples of the material generating Ca.sup.2+ include calcium chloride and the like; examples of the material generating Mg.sup.2+ include magnesium chloride and the like; and examples of the material generating Al.sup.3+ include aluminum chloride and the like.

The anion is not particularly limited, and for example, OH.sup.-, SO.sub.4.sup.2-, PO.sub.4.sup.3-, dissociative short chain fatty acids may be mentioned. Examples of the material generating OH.sup.- include sodium hydroxide and the like; examples of the material generating SO.sub.4.sup.2- include sodium sulfate and the like; examples of the material generating PO.sub.4.sup.3- include sodium phosphate and the like; and examples of the material generating dissociative short chain fatty acid include caprylic acid (CH.sub.3(CH.sub.2).sub.6COOH) and the like.

The conditions for treating the negatively charged complex with cations are not particularly limited, but the temperature is usually 10 to 40.degree. C., and preferably 20 to 30.degree. C.; the pH is usually 6.5 to 8.0, and preferably 7.0 to 7.5; and the time is usually 1 to 20 minutes, and preferably 5 to 10 minutes. The solvent used for the cation treatment is not particularly limited as long as it is an aqueous solution, and for example, HEPES buffer solution and the like can be used. The amount of the cation to be added to the solvent can be appropriately controlled depending on the properties of the cation and the like, but the amount is typically 50-fold the amount of the lipid (moles of cation/moles of lipid) or greater.

The conditions for treating the positively charged complex with anions are not particularly limited, but the temperature is usually 10 to 40.degree. C., and preferably 20 to 30.degree. C.; the pH is usually 6.5 to 8.0, and preferably 7.0 to 7.5; and the time is usually 1 to 20 minutes, and preferably 5 to 10 minutes. The solvent used for the anion treatment is not particularly limited as long as it is an aqueous solution, and for example, HEPES buffer solution and the like can be used. The amount of the anion to be added to the solvent can be appropriately controlled depending on the properties of the anion and the like, but the amount is typically 50-fold the amount of the lipid (moles of anion/moles of lipid) or greater.

When the negatively charged complex is treated with cations, the negative charge on the surface of the negatively charged SUV type liposomes that are electrostatically bound to the positively charged particle is lost, and the hydrophobicity of the surface of the negatively charged SUV type liposomes increases, thus leading to membrane fusion between adjacent negatively charged SUV type liposomes, and the positively charged particle being coated with two sheets of lipid membrane. Also, when the positively charged complex is treated with anions, the positive charge on the surface of the positively charged SUV type liposomes that are electrostatically bound to the negatively charged particle is lost, and the hydrophobicity of the surface of the positively charged SUV type liposomes increases, thus resulting in membrane fusion between adjacent positively charged SUV type liposomes, and the negatively charged particle being coated with two sheets of lipid membrane. Thus, two sheets of lipid membrane coating the positively charged or negatively charged particle are newly formed on the external side of the positively charged or negatively charged particle, but at this time, the two sheets of lipid membrane are formed such that a space is formed therebetween.

When an aggregate of an object material is used as the positively charged or negatively charged particle, a bilamellar liposome encapsulating the aggregate of object material and having a space formed between the two sheets of lipid membrane which coat the aggregate of object material is produced. When an n-lamellar liposome, wherein n is an integer of 1 or greater, is used as the positively charged or negatively charged particle, an (n+2)-lamellar liposome having a space formed between the two sheets of lipid membrane which coat the n-lamellar liposome is produced.

The liposome obtained by coating a positively charged particle with two sheets of lipid membrane using the first method of the present invention is typically negatively charged. However, depending on the magnitude of the zeta potential of the negatively charged complex, type of the cation or the like, it is conceived that the liposome could be positively charged. The liposome obtained by coating a negatively charged particle with two sheets of lipid membrane using the second method of the present invention is typically positively charged. However, depending on the magnitude of the zeta potential of the positively charged complex, type of the anion or the like, it is conceived that the liposome could be negatively charged.

When a positively charged liposome is obtained by coating a positively charged or negatively charged particle with two sheets of lipid membrane using the first or second method of the present invention, the resulting positively charged liposome can be used as the positively charged particle for the first method of the present invention. When a negatively charged liposome or neutral liposome is obtained, the surface of the resulting negatively charged liposome or neutral liposome is modified with a cationic material to prepare a positively charged liposome, and the prepared positively charged liposome can be used as the positively charged particle for the first method of the present invention. As such, by repeatedly performing the first and/or second method of the present invention, a multilamellar liposome can be produced while controlling the number of lipid membranes.

When a negatively charged liposome is obtained by coating a positively charged or negatively charged particle with two sheets of lipid membrane using the first or second method of the present invention, the resulting negatively charged liposome can be used as the negatively charged particle for the second method of the present invention. When a positively charged liposome or neutral liposome is obtained, the surface of the resulting positively charged liposome or neutral liposome is modified with an anionic material to prepare a negatively charged liposome, and the prepared negatively charged liposome can be used as the negatively charged particle for the second method of the present invention. As such, by repeatedly performing the first and/or second method of the present invention, two sheets of lipid membrane can be newly formed on the external side of the two sheets of lipid membrane that have been already formed, and a multilamellar liposome can be produced while controlling the number of lipid membranes. Additionally, when two sheets of lipid membrane are newly formed on the external side of the two sheets of lipid membrane that have been already formed, the space formed between the two sheets of lipid membrane that have been already formed and the corresponding two sheets of lipid membranes is retained.

The liposome obtained by coating a positively charged or negatively charged particle with two sheets of lipid membrane according to the first or second method of the present invention preferably encapsulates an object material. If the object material is a material (for example, nucleic acid, peptide, protein, drug, sugar, complex thereof, etc.) to be delivered into a cell or a nucleus, the liposome encapsulating the object material can be used as a vector for delivering the object material into the cell or the nucleus. The liposome encapsulating the object material can be obtained by using an aggregate of the object material as the positively charged or negatively charged particle, or by using an n-lamellar liposome encapsulating the object material as the positively charged or negatively charged particle. Furthermore, such liposome can be obtained by retaining the object material between the two sheets of lipid membrane that are newly formed on the external side of the positively charged or negatively charged particle (for example, by retaining a liquid containing the object material).

The organism species from which the cell to deliver the object material is derived is not particularly limited, and may be any of animals, plants, microorganisms and the like. However, the organism species is preferably an animal, and more preferably a mammal. Examples of the mammal include human, monkey, cattle, sheep, goat, horse, pig, rabbit, dog, cat, rat, mouse, guinea pig and the like. Furthermore, the type of the cell to deliver the object material is not particularly limited, and for example, a somatic cell, a reproductive cell, a stem cell, cultured cells thereof, and the like may be mentioned.

The liposome encapsulating the object material can be used, for example, in a state of dispersion liquid. For the dispersion solvent, for example, a buffer solution such as physiological saline, phosphate buffer solution, citrate buffer solution, acetate buffer solution, or the like can be used. The dispersion liquid may contain additives such as, for example, sugars, polyhydric alcohols, water-soluble polymers, nonionic surfactants, antioxidants, pH adjusting agents, hydration promoters.

The liposome encapsulating the object material can be used either in vivo or in vitro. In the case of using the liposome in vivo, the route of administration may be administration by injection such as, for example, intravenous, intraperitoneal, subcutaneous, trans nasal or the like, and the dosage and frequency of administration can be appropriately controlled depending on the type or amount of the object material encapsulated in the liposome, or the like.

Claim 1 of 4 Claims

1. A method for coating a positively charged particle with two sheets of lipid membrane, the method comprising contacting the positively charged particle with a plurality of negatively charged SUV type liposomes, forming a negatively charged complex containing the positively charged particle and the negatively charged SUV type liposomes that are electrostatically bound to the positively charged particle, and treating the negatively charged complex with cations; wherein the positively charged particle is a positively charged n-lamellar liposome, wherein n is an integer of 1 or greater.

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