JPH07145038A - Constituent component for membrane of small closed cell - Google Patents

Abstract

PURPOSE:To obtain a constituent component for the membrane of a small closed cell, having a hydrophilic region containing one or more cationic residues and one or more hydrophilic groups at one end of the molecule and a hydrophobic region at the other end, and a medical carrier containing this component and including a medicine for diagnosing and improving an injured part of the vascular endothelium therein. CONSTITUTION:This constituent component for the membrane of a small closed cell, e.g. palmitic acid glucamine ester of the formula has a hydrophilic region containing one or more cationic residues and one or more hydrophilic groups incapable of being recognized by a sugar chain-recognizing receptor, enzyme and lectin-like protein at one end of the molecule and a hydrophobic region at the other end. The constituent component gives a small closed cell an effect, e.g. for improving targeting properties to an injured part of the vascular endothelium. The component is low toxic and a medical carrier containing this constituent component is excellent in inclusion ratio of a neutral or anionic substance and remarkably excellent in safety. For example, in the case heparin as a polysaccharide or its sulfate is included, it is useful as a preventive agent for vascular thickening, capable of inhibiting wandering of smooth muscle cells in an injured part of the vascular endothelium.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a closed vesicle membrane constituent. In addition, the present invention contains the closed vesicle membrane constituent component, and diagnoses a site of vascular endothelium damage therein.
The present invention relates to a drug carrier characterized by encapsulating a drug for treatment.

[0002]

2. Description of the Related Art In recent years, studies have been actively conducted to apply closed vesicles such as liposomes, emulsions and lipid microspheres to drug delivery systems as drug carriers. These closed vesicles are generally prepared using phospholipids or derivatives thereof, sterols and lipids other than phospholipids as basic membrane constituents. However, with only these basic components,
It was not possible to overcome various difficulties in practical application such as aggregation of closed vesicles and reduction of retention in the body. Furthermore, it has been extremely difficult to actually allow the drug to reach the target site as a DDS preparation.

[0003]

DISCLOSURE OF THE INVENTION As a result of intensive studies, the present inventors have found that when a surface of a closed vesicle retains a positively charged residue in a physiological pH range, the vascular endothelium of the closed vesicle is retained. It has been found that the accumulation property on the damaged site is dramatically improved. In addition, when a hydrophilic polymer is bound to the surface of a vesicle to which a positively charged residue is bound, even if such a polymer binds to the surface, the accumulation of closed vesicles on the vascular endothelial damage site However, it was found that the stability of the closed vesicles in the blood can be secured by preventing the aggregation of the closed vesicles in the blood and that the retention in the blood can be improved by avoiding the RES supplement. .

However, until now, stearylamine, glucosamine derivatives, and the like have been disclosed as membrane constituents having a residue having a positive charge, but stearylamine is highly toxic, and such a compound is not disclosed. It is difficult to use as a material, while when using a natural sugar chain such as glucosamine or galactosamine as a residue having such a positive charge, a living body specifically recognizes such sugar chain, an enzyme, an enzyme, Since it has a lectin-like protein, etc., especially when these constituents are designed so that these residues are sufficiently exposed on the surface of the endoplasmic reticulum, the interaction with these various receptors, enzymes, lectin-like proteins, etc. Therefore, there is a possibility that the in vivo kinetics will be influenced and the induction to the target site may not be performed sufficiently. Therefore, it is required to supply a practical cationic membrane component that can bring a high positive zeta potential to the closed endoplasmic reticulum, has low toxicity, and is not recognized by specific receptors, enzymes, lectin-like proteins, etc. It

Therefore, the object of the present invention is to bring a positive charge to the surface of the membrane of closed vesicles, to improve the encapsulation rate of the drug in the closed vesicles, and to improve the targeting property of the closed vesicles to the damaged site of vascular endothelium. The present invention is to supply closed vesicle membrane constituents that exert the above-mentioned effect, have low toxicity, and are not recognized by receptors and enzymes that recognize sugar chains, and lectin-like proteins. Another object of the present invention is to provide a drug carrier characterized by containing the above-mentioned closed vesicle membrane constituents and encapsulating a drug for diagnosing / treating a vascular endothelial damage site therein.

[0006]

The above object can be solved by the present invention described below. (1) Hydrophilicity that has one or more cationic residues and one or more hydrophilic groups at one end in one molecule and that is not recognized by receptors and enzymes or lectin-like proteins that recognize sugar chains A closed vesicle membrane constituent having a portion and a hydrophobic portion at the other end. (2) The above-mentioned cationic residue is one or more aliphatic first,
The closed vesicle membrane constituent according to (1) above, which is a secondary amino group, an amidino group, or an aromatic primary or secondary amino group. (3) The closed vesicle membrane constituent according to (1) above, wherein the hydrophilic group is a hydroxyl group. (4) The closed vesicle membrane constituent according to (1) above, wherein the hydrophobic portion is a long chain fatty acid, a long chain aliphatic alcohol, a sterol, a polyoxypropylene alkyl, or a glycerin fatty acid ester.

(5) The closed vesicle membrane component according to (1) above is contained, and the site of vascular endothelial damage is diagnosed therein.
A drug carrier, which is encapsulated with a drug for treatment. (6) The drug carrier according to (5) above, which comprises fine particles having a particle size of 0.02 to 250 μm. (7) The drug carrier is a macromolecule, a fine aggregate, a fine particle,
The drug carrier according to (5) above, which comprises at least one of microspheres, nanospheres, liposomes, and emulsions. (8) The drug carrier is phospholipid or a derivative thereof,
The drug carrier according to (5) above, which contains a lipid or a derivative thereof other than a phospholipid, and / or a stabilizer, and / or an antioxidant, and / or another surface modifier.

(9) The drug carrier according to the above (5), wherein the drug for diagnosing / treating the vascular endothelial damage site is electrically neutral or anionic. (10) The drug for diagnosing / treating the vascular endothelial injury site is an anti-inflammatory agent, anti-cancer agent, enzyme agent, antibiotic, antioxidant, lipid uptake inhibitor, hormone agent, angiotensin converting enzyme inhibitor, smooth muscle Cell growth / migration inhibitors,
The drug carrier according to (5) above, which is a platelet aggregation inhibitor, a chemical mediator release inhibitor, or a vascular endothelial cell proliferation or inhibitor. (11) The drug carrier according to (5) above, wherein the drug for diagnosing / treating the vascular endothelial damage site is glycosaminoglycan and a derivative thereof. (12) The drug carrier according to (5) above, wherein the drug for diagnosing / treating the vascular endothelial damage site is an oligo- or polysaccharide and a derivative thereof. (13) The drug for diagnosing / treating the vascular endothelial damage site is an X-ray contrast agent, a radioisotope-labeled compound which is a nuclear medicine diagnostic agent, or a diagnostic agent for magnetic resonance diagnosis and derivatives thereof. The drug carrier according to (5) above.

[0009] The present inventors have been investigating cationic closed vesicles highly accumulating at the site of vascular endothelium damage, mainly by means of modification with sugar chains such as amino sugars. At the same time, the accumulating property to a specific organ by the bio-recognition mechanism based on it became an unavoidable problem. In order to further improve the property of accumulating on the vascular endothelium damage site, while conducting various studies on the above-mentioned components with minimal affinity to organs, a sufficient positive charge was given to the surface of the closed vesicle membrane and A compound which is toxic and which is not recognized by various receptors, has a hydrophilic part having one or more cationic residues at one end and one or more hydrophilic groups, and a hydrophobic part at the other end. Found and completed the present invention.

Therefore, the present invention in line with the above object is recognized by a receptor, an enzyme and a lectin-like protein which have one or more cationic residues and one or more hydrophilic groups at one end and recognize sugar chains. It is a constituent component of a closed vesicle membrane, which has a hydrophilic portion that does not exist and a hydrophobic portion at the other end. Further, it is a drug carrier containing the closed vesicle membrane constituent and encapsulating a drug for diagnosing / treating a vascular endothelial damage site therein.

The structure of the closed vesicle membrane component of the present invention has a structure in which one or more cationic residues and one or more
It has a hydrophilic part having one or more hydrophilic groups and a hydrophobic part at the other end. The hydrophobic portion and the cationic hydrophilic portion are most preferably covalently bonded.

The cationic residue is not particularly limited as long as it has a positive charge in the physiological pH range and does not impair the stability of the structure of the drug carrier. Examples thereof include an aliphatic primary and secondary amino group, an amidino group, an aromatic primary and secondary amino group, and the like. The physiological pH range is a pH range in the living body, mainly in blood, in the cytoplasm and inside the organelles present therein, and specifically, pH 4 to 1
0, preferably pH 6-8. The hydrophilic group is also not particularly limited, but a hydroxyl group is preferable.

The hydrophobic part is not particularly limited as long as it does not impair the structural stability of the drug carrier. Various structures can be considered as the structure of the hydrophobic portion, and examples thereof include long-chain aliphatic alcohol, sterol, polyoxypropylene alkyl, and glycerin fatty acid ester. In the case of a chain structure, the chain length and the number of chains are appropriately selected in combination with the hydrophilic part having the above-mentioned cationic residue.

The drug carrier using the closed vesicle membrane constituent of the present invention has a particle size of 0.02 to 250 μm, especially 0.05.
It is preferably about 0.4 μm. In addition, although various structures are conceivable, in particular, one or more macromolecules, microaggregates, microparticles, microspheres, or nano-small particles having a potential function capable of encapsulating a drug therein at a high concentration can be formed. Most preferred are spheres, liposomes and emulsions. Further, each is manufactured by a conventional method.

In this form, the constituents other than these are not particularly limited to the composition as long as they form closed vesicles, but the safety and the drug carrier stable in vivo are provided. From the viewpoint, it is desirable to add phospholipids or their derivatives, lipids other than phospholipids or their derivatives, stabilizers, antioxidants and the like. Further, it is naturally possible to add a hydrophilic polymer derivative having no positive charge, if necessary.

The substance contained inside the drug carrier is not particularly limited, but in consideration of the targeting property of the drug carrier having a cationic property to the site of vascular endothelial damage, diagnosis of the site of vascular endothelial damage is considered. It is most desirable to use a pharmaceutically acceptable pharmacologically active substance, physiologically active substance or diagnostic substance depending on the therapeutic purpose. As a property of the substance to be encapsulated, any substance is basically acceptable, but due to the characteristic that the surface of the drug carrier has a positive charge, a substance that is electrically neutral or anionic is expected to have a higher encapsulation rate. it can.

The type of substance to be encapsulated is not particularly limited as long as it does not impair the formation of closed vesicles, and drugs or blood vessels that suppress various reactions at the site of vascular endothelial damage and induce normal vascular tissue. Any drug can be used without any limitation as long as it can image and diagnose the endothelial damage site.
Examples include anti-inflammatory agents, anti-cancer agents, enzyme agents, antibiotics,
Antioxidants, lipid uptake inhibitors, hormones, angiotensin converting enzyme inhibitors, smooth muscle cell proliferation / migration inhibitors, platelet aggregation inhibitors, chemical mediator release inhibitors, vascular endothelial cell growth promoters or inhibitors Alternatively, a blood vessel contrast agent or the like may be considered. In particular, sulfated glycosaminoglycans such as heparin, oligo- and polysaccharides and their derivatives are effective as substances that inhibit the proliferation and migration of smooth muscle cells, which is the cause of vascular hypertrophy, at the site of vascular endothelial damage.

However, since the drug carrier of the present invention basically has the property of accumulating at the site of vascular endothelial damage,
There is no limitation in selecting the most suitable drug according to the characteristics of the disease at the site. Particularly at the injury site, platelet activation is likely to occur, and accumulation of various leukocytes is observed, and various chemical mediators are released to cause an inflammatory reaction. It is also well known that lipid peroxidation and enhancement of lipid uptake occur in these tissues, and it is considered that these reactions progress in a complex manner to cause arteriosclerotic lesions. Since the contribution of these phenomena to lesion formation is expected to differ from case to case, it goes without saying that all drugs corresponding to these conditions can be targeted by this drug carrier.

Further, prior to treatment, various compounds for in-vivo diagnosis that can reveal the existence of these vascular lesions and their sites, sizes, etc., such as X-ray contrast agents and radioactive materials which are nuclear medicine diagnostic agents, can be used. It goes without saying that an isotope-labeled compound, a diagnostic agent for magnetic resonance diagnosis, a derivative thereof, or the like can be the target of the present drug carrier.

[0020]

EXAMPLES Next, the present invention will be described more specifically by showing examples and test examples. (Example 1) Synthesis of palmitic acid glucamine ester N-Z reaction of D-glucamine D-glucamine 3.62 g (20.0 mmol) was dissolved in a mixed solvent of 20 ml of water and 20 ml of tetrahydrofuran, and potassium carbonate 3. 31 g (24.0 mmol) was added and dissolved. The reaction vessel was kept at 0 ° C., a solution of 2.86 ml (20.0 mmol) of benzyloxycarbonyl chloride (ZCl) in 10 ml of tetrahydrofuran was added dropwise over 15 minutes, and the mixture was stirred for 3 hours as it was. The deposited precipitate was collected by suction filtration and washed twice with 3 ml of tetrahydrofuran, and then N-benzyloxycarbonylglucamine was obtained using methanol-chloroform as a recrystallization solvent.

Yield: 5.72 g (about 90.8%) IR (νcm ^-1 ): 3500-3200 (OH), 34
50 (N-H) 1650 ( C = O) 1 H-NMR (δppm): 3.3 (bs, N-CH 2 - ×
2) 3.5-4.0 (m, HO- CH- × 8) 5.1 (s, Ar-CH 2 - × 2) 7.9 (s, Ar-H- × 5)

Primary Selective Esterification Reaction Using N-Z Glucamine and Palmitoyl Chloride 3.15 g (10.0 mmol) of N-Z glucamine was dissolved in 50 ml of pyridine, and 2.80 g of palmitoyl chloride was stirred while cooling with ice. (10.2 mmol) was slowly added dropwise over 10 minutes. After reacting for 3 hours, dilute with 500 ml of water, neutralize the solution with 4N hydrochloric acid, and then add chloroform 15
Extract 3 times with 0 ml. The extracts are combined and saturated saline solution 10
It was washed twice with 0 ml and the organic layer was dried over anhydrous sodium sulfate. After the solvent was distilled off, the residue was recrystallized from a methanol-chloroform solvent to obtain palmitic acid NZ-glucamine ester.

Yield: 4.63 g (about 83.6%) IR (νcm ^-1 ): 3500-3200 (OH), 34
50 (N−H) 1730 (C═O), 1650 (C═O) ¹ H-NMR (δppm): 1.2 (s, —CH ₂ − × 2) 3.3-4.2 (m, HO-CH- × 8) 5.1 ( s, Ar-CH 2 - × 2) 7.4 (s, Ar-H- × 5)

Synthesis of glucamine palmitate ester N-Z glucamine ester of palmitate 4.0 g
(7.23 mmol) methanol: chloroform = 10: 1
It was dissolved in 100 ml of the solution, 1 g of palladium carbon (10%) (manufactured by Nacalai Tesque, Inc.) was added, and hydrogenation was carried out for one day. After the reaction, the solvent was filtered and the solvent was distilled off from the filtrate to obtain palmitic glucamine ester having the structure shown in the following formula 1.

[0025]

[Chemical 1]

Yield: 4.63 g (about 83.6%) IR (νcm ^-1 ): 3500-3200 (OH), 33
80 (N-H) 3180 (N-H), 1730 (C = O) ¹ H-NMR (δppm): 1.2 (s, -CH ₂ -x 2) 2.8 (bs, NH ₂ -x). 2) 3.3-4.2 (m, HO-CH-x8)

(Example 2) Glucamine palmitate
Preparation of Liposomes Containing Tell as a Membrane Constituent Component The following three types of membrane constituent components were added as chloroform solutions to a round-bottomed flask having a volume of 50 ml and mixed.・ Phosphatidylcholine (concentration 100 mM): 840μ
l-Cholesterol (concentration 100 mM): 240 μl-Glucamine palmitate (10 mM): 120
0 μl

Further, 10 ml of chloroform was added. After the chloroform was distilled off, it was vacuum dried overnight to form a lipid thin film on the inner wall of the flask. Then 100μ
300 mM sorbitol in which g of heparin was dissolved / 1
4 ml of 0 mM Tris-HCl buffer was added to the flask, and the mixture was shaken and stirred vigorously to give liposomes (ML
V) A dispersion was obtained.

The dispersion was centrifuged (120,000).
g, 70 minutes). The supernatant was decanted and the unencapsulated heparin was removed to obtain a liposome pellet. Add this pellet to 300 mM sorbitol /
By dispersing in 10 mM Tris-HCl, the above-mentioned liposome dispersion retaining heparin was obtained.

(Test Example) Next, a test example conducted for investigating the effect of the present invention will be shown. (Test Example 1) Measurement of encapsulation rate <Method> The encapsulation rate of heparin used in Example 2 in liposomes was determined as follows. First, the amount of heparin in the supernatant after centrifugation was determined by the carbazole method to determine the amount of heparin not encapsulated in the liposome. By comparing this with the total amount of heparin that was first added to the liposome preparation,
The encapsulation rate of heparin in the liposome was determined. For comparison, a liposome dispersion prepared by the same method as in Example 2 was prepared without using palmitic acid glucamine ester. Then, the encapsulation rate of heparin was determined by the same method as described above.

<Results> The results are shown in Table 1.

[0032]

[Table 1]

As is clear from the above results, the drug carrier containing the components of the closed vesicle membrane of the present invention showed a higher encapsulation rate of heparin as compared with the neutral drug carrier not containing the same.

(Test Example 2) Pharmacokinetics (1) <Method> From the femoral vein of SD male rat anesthetized with urethane, 100 mM carboxyflurescin (Carboxyfluorescein) prepared according to Example 2 was encapsulated. 500 μl of liposome dispersion was injected intravenously. Blood was collected in Eppendorf tubes over time. Pharmacokinetics was measured by measuring the fluorescence intensity of the collected blood. For comparison, the pharmacokinetics of the liposome dispersion prepared according to Example 2 above without using glutamine palmitate was measured by the same method as above.

<Results> The results are shown in FIG. As is clear from the above results, it was confirmed that the drug carrier containing the closed vesicle membrane constituent of the present invention has higher blood retention than a drug carrier not containing it.

(Test Example 3) Pharmacokinetics (2) <Method> A 2-French balloon catheter was inserted from the femoral artery of an SD male rat anesthetized with urethane, and the carotid artery was rubbed 5 times to damage the vascular endothelium. I created a model. 10 prepared according to Example 2 from the femoral vein
Liposome dispersion containing 0 mM Carboxyfluorescein
500 μl was injected intravenously. After 3 hours, the carotid artery of the rat was collected. Extract Carboxyfluorescein from the collected carotid artery,
The distribution of liposomes to the carotid artery was measured by measuring the fluorescence intensity.

Furthermore, with regard to a rat in which the carotid artery was not scraped, it was prepared from the femoral vein according to Example 2.
Liposome dispersion containing 0 mM Carboxyfluorescein
After intravenous injection of 500 μl, the distribution of liposomes to the carotid artery was measured by the same method as above. For comparison, the distribution of liposomes to the carotid artery was measured in the same manner as above for the liposome dispersion prepared according to Example 2 without using palmitate glucamine ester.

<Results> The results are shown in FIG. As is clear from the above results, the drug carrier of the present invention containing the closed vesicle membrane constituent of the present invention as a membrane constituent is more likely to accumulate at the site of vascular endothelial damage than a drug carrier not containing it. Is high, and when the vascular endothelium is not damaged, the degree of accumulation is similar to that of the comparative control. Therefore, the drug carrier of the present invention is excellent in targeting property to the site of vascular endothelial damage.

(Test Example 4) Organ distribution (3) <Method> 100 mM Carboxyfl prepared according to Example 2 from the femoral vein of SD male rat anesthetized with urethane.
500 μl of a liposome dispersion liquid enclosing uorescein was injected intravenously. The liver was removed 3 hours later. Carboxyfluorescein was extracted from the excised organs and the distribution of liposomes in the liver was measured by measuring the fluorescence intensity.
For comparison, the liposome dispersion prepared according to Example 4 above using 6-o-palmityl-methyl-D-galactosaminide, the structure of which is shown in Formula 2 below, in place of glucamine palmitate was described above. The distribution of liposomes to the liver was measured in the same manner as in.

[0040]

[Chemical 2]

<Results> The results are shown in FIG. As is clear from the above results, the drug carrier of the present invention containing the closed vesicle membrane constituent of the present invention as a membrane constituent is compared with the case of containing the membrane constituent having a sugar chain structure. , It can be seen that the amount of distribution to the liver is kept low. Furthermore, when the hydrophilic polymer is contained in the molecule, the distribution amount is further reduced. This is considered to indicate that, as the surface structure of the membrane component, the effect of avoiding the receptor of the liver by not having a sugar chain structure and the effect of avoiding by having the hydrophilic polymer are exhibited, Therefore, the drug carrier containing the membrane constituent of the present invention is not recognized by a specific receptor, and when it contains a hydrophilic polymer, it is more excellent in RES avoidance.

Test Example 5 Acute Toxicity The purpose of this test is to find out the degree of toxicity of the drug carrier of the present invention as compared with that of conventional ones. For that purpose, a lethal toxicity test for rats was carried out for each of the drug carrier of the present invention prepared without drug encapsulation and the conventional drug carrier.

<Preparation of test liquid> Liposome dispersion of the present invention containing palmitate glucamine ester A liposome containing glutamine palmitate was prepared in the same manner as in Example 4 except that heparin was not added. A dispersion was obtained. This was concentrated using an ultrafiltration membrane and further diluted with sterile distilled water for injection to obtain a test solution. Conventional Liposome Dispersion Liquid For comparison, a neutral liposome dispersion liquid was obtained in the same manner as in Example 2 without using glutamine palmitate. This was concentrated using an ultrafiltration membrane and further diluted with sterile distilled water for injection to obtain a test solution.

<Method> Quarantined 5-week-old SD male rats were divided into 3 groups per group, and 2.0 ml of the above test solution was intraperitoneally administered once. On the other hand, as a solvent control group, 2.0 ml of sterile distilled water was administered. After the administration of the test solution, the general condition was carefully observed at least once a day for 16 days, and toxicity signs and mortality were recorded. <Results> Table 2 shows.

[0045]

[Table 2]

The symbols in the column of the test substance in the table are as follows. Glucamine ester palmitate-containing liposome Conventional neutral liposome dispersion solvent control (saline)

As shown in the above test results, there were no deaths during the observation period for the drug carrier of the present invention. In addition, there were no deaths during the observation period for the drug carrier using the cationic membrane material and the hydrophilic polymer derivative separately.
However, in the conventional drug carriers, the body weight drastically decreased from the first day after the start of administration, and most of them died by the 15th day as shown in the table. This is due to subsequent organ findings, and in conventional drug carriers, aggregates are formed in blood by association with blood cell components or the like in blood or association between liposomes,
It was confirmed that the cause was the formation of an embolus in the lungs and the like. From these results, it can be said that the drug carrier containing the closed vesicle membrane constituent of the present invention has extremely low toxicity and high safety.

[0048]

INDUSTRIAL APPLICABILITY As described above in detail, the drug carrier containing the constituent component of the closed vesicle membrane of the present invention is the same as when the cationic membrane material and the hydrophilic polymer derivative are used individually. The encapsulation rate of neutral or anionic substances is high, and the targeting property to the site of vascular endothelial damage is very high. It is also very safe. Due to such characteristics, the novel drug carrier of the present invention in which a pharmaceutically acceptable pharmacologically active substance, physiologically active substance or diagnostic substance is encapsulated is used for the purpose of diagnosis and treatment at the site of vascular endothelial damage. Very effective. For example, when heparin, a polysaccharide, and a sulfated product thereof are encapsulated, they are useful as a blood vessel thickening preventive agent that suppresses smooth muscle cell migration at a site where the vascular endothelium is damaged.

[Brief description of drawings]

FIG. 1 shows the results of pharmacokinetic test in Test Example 2. The retention property in blood of the drug carrier of the present invention is shown.

FIG. 2 shows the results of pharmacokinetic test in Test Example 3. The vascular endothelial damage site accumulation property of the drug carrier of the present invention is shown.

FIG. 3 shows the results of pharmacokinetic test in Test Example 4. 3 shows distribution of the drug carrier of the present invention to the liver.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inoue Tetsuro Kawanishi, Inoguchi, Nakai-cho, Ashigagami-gun, Kanagawa 1500 Terumo Co., Ltd.

Claims (1)

[Claims] 1. A receptor which has one or more cationic residues and one or more hydrophilic groups at one end in one molecule, and which is not recognized by a receptor that recognizes a sugar chain, an enzyme, or a lectin-like protein. A closed vesicle membrane constituent having a hydrophilic portion and a hydrophobic portion at the other end.