WO1995031220A1

WO1995031220A1 - Contrast medium for magnetic resonance imaging

Info

Publication number: WO1995031220A1
Application number: PCT/JP1995/000894
Authority: WO
Inventors: Kazuo Yagi; Junji Nakamura
Original assignee: Otsuka Pharmaceutical Co., Ltd.
Priority date: 1994-05-12
Filing date: 1995-05-10
Publication date: 1995-11-23
Also published as: AU2419695A

Abstract

A contrast medium for magnetic resonance imaging (MRI contrast medium) comprising fine magnetic iron oxide particles having an average particle diameter of 2-20 nm and the properties of a single magnetic domain as the core, with its surface being coated with a polysaccharide having functional groups selected from the group consisting of sulfone, ketone, amino, carboxyl and alkyl groups. When injected into the blood vessel in magnetic resonance angiography, this medium enhances the signal intensity of the blood vessel to thereby give a white image. It can be used also in the liver as the MRI contrast medium, because it can lower the signal intensity of the liver after the lapse of a given time from the injection. The medium is easy to inject and has high stability and safety as a pharmaceutical preparation. In addition, it can reside in the blood vessel for long and does not exude therefrom, so that it enables contrast enhancement in the blood vessel and facilitates the setting of a proper inspection time.

Description

Specification

Magnetic resonance contrast agent

Technical field

The present invention relates to a magnetic resonance imaging (MRI) of a living body and a magnetic resonance contrast agent improved in its usefulness for diagnosis (hereinafter referred to as an MRI contrast agent), and particularly to an MRI contrast agent useful as an MR angiographic agent Agent.

Background art

Magnetic iron oxide fine particles having magnetism such as ferrite have attracted attention as MRI contrast agents because of their superparamagnetic properties.

However, ordinary magnetic iron oxide fine particles have a much larger spin-spin relaxation time (hereinafter, referred to as T2) than the spin-lattice relaxation time (hereinafter, referred to as T1) in MRI, and converge on relaxation. Because of the time required, the local magnetic field in the area where the iron oxide particles were present was disturbed, the signal intensity was reduced, and images were missing or the images of surrounding organs became black, making diagnosis difficult.

In addition, the magnetic iron oxide fine particles were hardly soluble as they were and had extremely high toxicity in intravenous administration, so that they could not be used for living bodies for medical purposes. Therefore, an MRI contrast agent in which magnetic iron oxide is coated with dextran or a dextran derivative is known. For example, magnetic iron oxide contrast agents such as "AM 1-25" manufactured by Advansed Magnetics Co., Ltd. exhibit superparamagnetic effects, and it has been known that coating with dextran reduces toxicity. I have.

However, conventional dextran-based magnetic iron oxide contrast agents cannot stay in the circulatory system (vascular system) for a long time and are rapidly taken up by the liver or spleen. In addition, since the particle size is as large as 150 to 300 m, there are side effects such as hypotensive shock and allergic reaction. For example, when an intravenous drip infusion is performed and an MRI image of the liver is taken one hour later, it is confirmed that a decrease in blood pressure, shock, and pulsation occurs during that time, and in some cases, death may occur. In addition, the conventional contrast agent simply coats magnetic iron oxide with dextran, so that the bond between iron oxide and dextran is weak, and therefore, it is easily dissociated in blood, and the stability during heat sterilization is low. The stability over time was also poor. In addition, conventional magnetic iron oxide contrast agents are rapidly absorbed from blood into organs such as the liver and spleen and cannot stay in blood vessels for a long time, making it very difficult to use them as MRI angiography agents. there were.

The main object of the present invention is to enhance the signal intensity of intravascular blood flow, which is originally no signal on MR images, to image the blood flow, thereby enabling blood, heart, cerebral vascular system, abdominal vascular system, An object of the present invention is to provide an MRI contrast agent that enables imaging of circulatory organs and organs such as lymphatic vessels, thereby facilitating diagnosis of lesions, and has high safety and stability.

Another object of the present invention is to provide a blood vessel which has a long residence time in a blood vessel, does not exude from a blood vessel to a tissue unlike conventional Gd-DTPA contrast agents, and makes the contrast between the blood vessel part and the tissue clear. It is to provide an MRI contrast agent for angiography.

Disclosure of the invention

The present inventors have conducted intensive research to solve the above-mentioned problems, and as a result, by using magnetic iron oxide fine particles as a core and coating this with a polysaccharide as an outer shell, MRI of cardiac and vascular systems, cine MR We have found the surprising fact that a T 1 -weighted image with the effect of increasing T 1 and decreasing T 2 in I is obtained. In addition, in the formulation, the use of a polysaccharide having a specific functional group as a coating agent for the magnetic iron oxide fine particles increases the affinity of the iron oxide fine particles with water, which increases the biological affinity. The adverse effects of long-term residence in blood vessels are reduced, the load on the living body is reduced, the safety is increased, and the specific functional groups of the outer polysaccharide are magnetic iron oxide fine particles. It shows high resilience and stability over a long period of time because it reacts with and binds tightly.

In particular, the present inventors have synthesized a magnetic iron oxide fine particle having an ultimate single domain structure, thereby producing a contrast agent for MRI in which fine particles having the property of a superparamagnetic material can be used as a strong paramagnetic material. succeeded in. In the region where the magnetic iron oxide fine particles are present, the NMR signal intensity is enhanced, and, for example, the heart, cerebral vascular system, abdominal vascular system, etc. can be imaged in white. Therefore, the MRI contrast agent of the present invention can be used as a T1 enhancer that enhances the T1 signal intensity by shortening the T1 relaxation time of a hydrogen atom in a living body. Conventionally, iron oxide fine particles with a single domain structure have not existed. It was created for the first time.

That is, the MRI contrast agent of the present invention has magnetic iron oxide fine particles having an average particle diameter of 2 to 20 nm and a single magnetic domain structure as a core, and the surface of the core is formed of a sulfone group (sulfate group), a ketone group, It is characterized by being coated with a polysaccharide having a functional group selected from the group consisting of an amino group, a carboxyl group and an alkyl group.

That is, since the MRI contrast agent of the present invention coats single-domain iron oxide fine particles with a polysaccharide, it is difficult for the fine particles to change over time together with the superparamagnetic effect, and is used for imaging heart and vascular organs with blood flow. That is, it can be suitably used as an MRI contrast agent for angiography.

In addition, since the iron oxide fine particles are coated with the polysaccharide, problems of biological reactions and toxicity are solved, and affinity with blood and the like is further improved. In addition, the MRI contrast agent of the present invention has an advantage in that absorption into organs such as the liver and spleen is delayed, so that it can stay in blood vessels for a long time. Furthermore, since the average particle size of the magnetic iron oxide fine particles used in the present invention is as fine as 2 to 20 nm, even if they stay in the blood vessel for a long time, there is no adverse effect such as a decrease in blood pressure and shock, and they are safe for living organisms. High in nature.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory diagram showing an MRI contrast agent of the present invention in which magnetic iron oxide fine particles are coated with a polysaccharide,

FIG. 2 is a graph showing the magnetization curve of the chondroitin sulfate-monomagnetic iron oxide composite obtained in Production Example 1.

Fig. 3 is a transmission electron micrograph (TEM, magnification: 100,000 times) of the chondroitin sulfate-magnetic iron oxide complex obtained in Production Example 1.

Fig. 4 is a photograph showing MR angiography images near the heart and aorta of a rabbit taken under the same conditions using different contrast agents.The right side of the photograph is an angiography image of the MRI contrast agent of the present invention, and the left side is an image. Shows an angiographic image of a conventional Gd-DTPA, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

Examples of the magnetic iron oxide fine particles in the present invention include, for example, a general formula

(MO) _m · F e ₂ 〇 ₃ (In the formula, M represents a divalent metal atom, and m is a number of 0 m 1.)

Ferrite represented by Examples of the divalent metal atom include magnesium, calcium, manganese, iron, nickel, cobalt, copper, zinc, strontium, and barium. Especially M is a divalent magnetic iron oxide in the case of iron (e.g. magnetite F e ₃ 〇 _{_{4, 7 - F e 2 0}} 3 , etc.) it is preferably used in the present invention. The magnetic iron oxide fine particles in the present invention include those containing water of crystallization.

The magnetic iron oxide fine particles in the present invention have an average particle size of 2 to 20 nm, preferably 3 to 8 nm.

The single magnetic domain structure of the magnetic iron oxide fine particles refers to a structure having no magnetic domain wall and having only one magnetic domain like a normal magnetic material. The reason for having no magnetic domain wall is that the average particle size of the magnetic iron oxide is extremely small to the molecular level as described above. In such a single-domain structure, the residual magnetization shown in a typical magnetic hysteresis curve generated by the movement of the domain wall when an external magnetic field is applied as in a normal magnetic body does not appear (see the later-described embodiment). In Figure 2). Accordingly, the magnetic iron oxide fine particles having such a single magnetic domain structure act as a superparamagnetic substance or a strong paramagnetic substance, and thus can be suitably used as a T1 enhancer.

As the polysaccharide having a specific functional group in the present invention, a water-soluble polysaccharide is preferable, and examples thereof include chondroitin 4-monosulfate, chondroitin 6-sulfate, hyaluronic acid, chitin, and heno. Examples include polysaccharides or mucopolysaccharides such as phosphorus, sialic acid, neuraminic acid, acetylhexosamine, inulin, agarose, dextransulfonic acid, and N-cetylglycosamine derivatives. Furthermore, a sulfone group substituted, amino Moto置conversion, an alkyl group substituted or ketone group (e.g., _{_{- CH 2 -C0-CH 2 CH}} 3,

A dextrin substituted with —CH ₂ —0C0—N ₂ or the like can also be suitably used.

Examples of the alkyl group include an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a t-butyl group, a pentyl group and a hexyl group.

Suitably, these polysaccharides have a number average molecular weight in the range of about 500 to 300,000, preferably about 1000 to 50,000, more preferably about 150 to 30,000. is there. Also The polysaccharide may be used as a mixture with various oligosaccharides (such as glucose, maltose, lactose, cellobiose, maltotriose, and melibiose) and pullulan.

In addition, a function as a therapeutic agent can be imparted to the polysaccharide by containing various receptors having specificity for accumulation in abnormal cells such as tumor cells. Examples of the receptor include, for example, various monoclonal antibodies, various proteins, and immune-related agents (immune cell activation and activation materials). This is useful, for example, in diagnosing and treating tumors, as well as inducing killer cells.

In the production of the MRI contrast agent of the present invention, first, an aqueous sol consisting only of magnetic iron oxide fine particles is prepared and then reacted with a polysaccharide, and the first method is a one-step synthesis in the presence of the polysaccharide. There are two ways.

In the first method, an aqueous bull made of only magnetic iron oxide fine particles is prepared. Examples of the method for preparing the aqueous sol include a co-precipitation method with a zinc ion exchange resin method and the like.

In the alkaline coprecipitation method, for example, ferrous and ferric salts are mixed at a molar ratio of 1: 3

To 2:. About 0 includes in the order of one ratio and the 1-2 moles of aqueous, N a OH, then mixed as KOH, NH ₄ 〇 ^ 1 like base and a 11 is about 7 to 1 2, If necessary, heat and ripen.Then, the magnetic iron oxide formed is separated, washed with water, redispersed in water, and a mineral acid such as hydrochloric acid is added until the pH of the solution becomes about 1 to 3. A magnetic iron oxide aqueous solution can be obtained.

On the other hand, in the ion-exchange resin method, for example, an about 0.1 to 2 mol aqueous solution containing a ferrous salt and a ferric salt in a molar ratio of about i: 2 is stirred into a strongly basic exchange resin slurry. After the addition while maintaining the pH at about 8 to 9, a mineral acid such as hydrochloric acid is added until the pH becomes about 1 to 3, and then the resin is filtered off to obtain a magnetic iron oxide aqueous solution. it can.

These aqueous sols may be purified or reduced by filtration, ultrafiltration, centrifugation or the like as necessary.

The reaction between the aqueous magnetic iron oxide aqueous solution and the polysaccharide is usually performed by mixing these at a predetermined ratio and heating. The ratio of the magnetic iron oxide aqueous sol to the polysaccharide is about 1 by weight. : 1 to 1: About 6 is sufficient. The reaction may be carried out at a temperature from room temperature to about 120 ° C. for about 10 minutes to 10 hours, and usually, heating and refluxing for about 1 hour is sufficient. The concentration of the magnetic iron oxide in the reaction solution is usually about 0.1 to 1 OwZv%, preferably about 1 to 5 w / v% as iron.

After the reaction, a purification operation for separating unreacted polysaccharides and low molecular weight compounds is performed by using a known means such as ultrafiltration to obtain an aqueous solution having a predetermined purity and concentration. To this, a solvent such as methanol, ethanol, or acetone is added to preferentially precipitate and precipitate the magnetic iron oxide fine particle-polysaccharide complex, which is separated, and then the precipitate is re-dissolved in water, and The mixture is dialyzed and, if necessary, concentrated under reduced pressure to obtain an aqueous solution of the above complex. Then, if necessary, centrifugation, filtration, pH adjustment and the like may be performed. The MRI contrast agent of the present invention obtained by caulking has an average particle size of about 30 to 200 nm, and the magnetic iron oxide fine particles as the core have an average particle size of about 2 to 20 nm. These particle sizes are measured by the dynamic light scattering method. The magnetization of the MRI contrast agent at 1 Tesla is usually in the range of about 20 to 150 emu / g of iron.

A second method for preparing the MRI contrast agent of the present invention comprises, in the presence of a polysaccharide having a specific functional group, a mixed aqueous solution of a ferrous salt of iron (III) and a salt of iron (III) and an aqueous solution of a base. These are mixed and reacted. The order of adding the polysaccharide, the mixed iron salt aqueous solution and the base aqueous solution is not particularly limited.

The mixed iron salt aqueous solution is prepared by dissolving a ferrous salt and a ferric salt in a molar ratio of about 1: 4 to 3: 1, preferably about 1: 3 to 1: 1, in an aqueous medium. Can be obtained by: The concentration of the aqueous iron salt solution is usually about 0.1 to 3 mol, preferably about 0.5 to 2 mol.

Examples of iron salts include salts with mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid. Examples of the base include alkali metal hydroxides such as Na〇H and K〇H, and amines such as ammonium nitrate, triethylamine, and trimethylamine.If necessary, a mixture of two or more kinds may be used. You can.

The amount of polysaccharide used should be about 1 to 15 times, preferably 3 to 10 times, based on the weight of the iron salt used.

The addition and mixing of each aqueous solution is performed while heating from room temperature to about 100 ° C with stirring. ― I―

After adjusting the pH by adding a base or an acid as necessary, the mixture is heated at a temperature of about 60 to 120 ° C. for about 分 0 to 5 hours, preferably for about 1 hour. The reaction is caused by flowing. The obtained reaction solution is purified in the same manner as in the first method, and if necessary, pH adjustment, concentration, and filtration are performed.

In these methods, the particle size of the magnetic iron oxide fine particles to be generated is set to 2 to

To adjust within the range of 20 nm, the following synthesis conditions must be satisfied.

(1) Ferrous chloride and ferric chloride are reacted at high temperature and high pH to form an aqueous solution.

(2) Polysaccharides are added at a high pH, and the pH is rapidly lowered while maintaining a high temperature.

(3) Perform the reaction in an inert gas (eg, argon) atmosphere to prevent oxidation. (4) Remove coarse particles by centrifugation.

(5) Adjust the particle size with a membrane filter.

(6) Perform dialysis in pure water for at least 20 hours.

Further, the particle size of the formed composite can be controlled by adjusting the reaction time and the reaction temperature.

The ratio of the polysaccharide to the magnetic iron oxide fine particles is not particularly limited, but generally, the polysaccharide is about 0.1 to 5 parts by weight, preferably 0 to 5 parts by weight per 1 part by weight of iron in the magnetic iron oxide. It can be contained in the range of 2 to 3 parts by weight.

In any of the first and second methods, 50 mol% or less of the ferrous salt is used as another divalent metal salt such as magnesium, calcium, manganese, niggel, cobalt, copper, or the like. It can be replaced with one or more salts, such as zinc.

The polysaccharide and the magnetic iron oxide fine particles react with each other by the above-described method to form a compound bonded to each other. Specifically, it has a form in which magnetic iron oxide fine particles are used as a core, and the surface thereof is firmly covered with a polysaccharide. This means that, for example, when the reaction product is fractionated on a gel column, an elution peak is observed on the higher polymer side than the elution position of the polysaccharide, and both sugar and iron are detected by analyzing the force and the peak. ing.

T 1 relaxation ability of the MR I contrast agents of the invention, one crotch about ^{2~5 0 (sec - mM) 1} , is good Mashiku is about ^{3~3 O (sec 'mM) _} 1. In addition, the T2 mitigation capacity is generally about 3 ~

30 O (sec-m), preferably about 6 to 30 (sec · mM). Preferably, the MRI contrast agent of the present invention is used in the form of an aqueous sol. The concentration of the magnetic iron oxide fine particle-polysaccharide complex in the aqueous sol can be set as appropriate in consideration of the dosage to the living body, etc. Approximately 90 ax mol / ^ to 20 ^ mol (90 nmol / to 720 nmol / m), preferably about 180 / ^ to 360 mol / ^ is sufficient. In preparing the aqueous sol, for example, inorganic salts such as sodium chloride, monosaccharides such as glucose, sugar alcohols such as mannite, sorbitol, and organic acid salts such as acetate, lactate, citrate, and tartaric acid , A phosphate buffer, a Tris buffer and the like can be appropriately added.

The MRI contrast agent of the present invention uses magnetic iron oxide in the form of ultrafine particles, and the outer shell polysaccharide has a specific functional group. Accordingly, it can be used as a powerful paramagnetic T1 contrast agent.

According to electron microscopic observation, the outer shell polysaccharide has an elastic structure in the form of hair balls or coils, and if it is elongated, it has a very long molecular structure. It is not easily degraded even in the living body and can exist as a saccharide in blood for a long time. That is, as shown in FIG. 1, the MRI contrast agent of the present invention has magnetic iron oxide fine particles 1 as a core, and a large number of polysaccharide chains 2 are firmly attached to the surface of the magnetic iron oxide fine particles 1 so as to cover the surface. Is bound to. Therefore, the iron oxide fine particles 1 and the polysaccharide chains 2 are not easily dissociated in blood, and can be present in blood for a long time.

Therefore, a paramagnetic effect is exhibited by administration of a very small amount, and it can be suitably used as a blood vessel contrast agent or a T1 tissue relaxation contrast agent. Therefore, the amount of the MRI contrast agent of the present invention is about 1-2 cc Zkg by intravenous administration in the case of an aqueous sol having an iron equivalent concentration of 180 to 360 mol ^. Is appropriate. A typical dose in terms of iron is about 5 ^ moI to 40 \ / i, preferably about 10 mol Z ^ to 20 mol Z, in terms of iron.

Suitable administration methods include intravenous, intraarterial, intravesical, intramuscular, and subcutaneous injection and injection, but oral administration and intestinal administration are also possible.

The MRI contrast agent of the present invention has a characteristic that it stays in the bloodstream for a long time and is hardly absorbed by organs such as the liver and 陴, and can stay in the vasculature, which is a characteristic of the sugar agent, for a long time. That During recognition, polysaccharides surface sulfonic group is an outer shell by the presence of certain functional groups, such as (one S 0 ₃ H, sulphate group), a ketone group, a saccharification coalescing recognition of biological defense mechanisms And delay the decomposition and absorption of magnetic iron oxide. In addition, it is estimated that a relatively long time is required for decomposition and absorption in vivo due to the outer shell structure of the polysaccharide due to the reaction with the magnetic iron oxide. The chains are not easily broken). Therefore, there is an advantage that MRI imaging can be suitably performed even for an organ that requires a relatively long time to reach the contrast agent, and that an examination time can be easily set. Blood vessels are mainly targeted as organs to be imaged. Unlike conventional Gd-chelate contrast agents, they do not penetrate blood vessels and are suitable for enhancing contrast between blood vessels and surrounding tissues. In addition, the liver, lymph vessels, brain, spleen, and digestive tract can be imaged.

At that time, the MRI contrast agent of the present invention has safety such as being able to inject a bolus intravenously without causing a decrease in blood pressure or shock.

In particular, the MRI contrast agent of the present invention can make the T1 relaxation ability larger than the T2 relaxation ability by making the particle size of magnetic iron oxide extremely fine to the size of the ultimate single domain fine particles. As a result, in the imaging of the circulatory system and the vascular system, which could not be imaged with the conventional magnetic iron oxide fine particles, the presence site of the magnetic iron oxide fine particles becomes a high signal, and the region can be photographed in white. Has characteristics. Therefore, the MRI contrast agent of the present invention is extremely effective in the latest equipment such as high-speed MRI imaging, and greatly facilitates the diagnosis of myocardial infarction, cerebral infarction, cancer and vascular lesions. The effect can be expected.

Industrial applicability

When the MRI contrast agent of the present invention is administered intravascularly, it can enhance the signal intensity of the vascular part in MR angiodara phylla and cause white contrast. It can also be used as a liver MRI contrast agent since it reduces the liver signal after a certain period of time after administration.

In addition, the MRI contrast agent of the present invention can be easily administered, has high stability as a preparation, and has high safety. Furthermore, the MRI contrast agent of the present invention has a long residence time in a blood vessel and has no exudation outside the blood vessel, so that the blood vessel can be contrasted and the examination time is long. Is easy to set.

Example

Production Example 1

(Production of chondroitin sulfate monomagnetic iron oxide composite)

29. 86 g0F e C a l ₃ · 6Η ₂ 〇 was dissolved in distilled water 80 m 1, after A r substitution for 10 minutes, F under Ar eC l _₂ · 4Η ₂ 〇 a 5. 49 g The solution was added and completely dissolved, and heated to 80 to 100 ° C. to accelerate the reaction. The total amount of iron charged was 0.13 mol, and Fe ²⁺ / Fe ³⁺ was 1Z4.

On the other hand, an aqueous solution in which 43 g of chondroitin sulfate was dissolved in 12 Oml of distilled water was heated to 80 ° C under an Ar atmosphere, and the above iron chloride solution was added at a stretch.

While maintaining the temperature at 80 ± 5′C, the pH was adjusted to 11 by dropwise addition of 3 N sodium hydroxide with stirring. Then, 6N hydrochloric acid was added dropwise to adjust the pH to 6.9. In this state, the temperature of the solution was kept at 100 ° C., heated for 1 hour, and then cooled to 2 (TC, and then centrifuged at 3000 rpm for 30 minutes to separate a supernatant.

To 414 ml of the supernatant, 262 ml of methanol was added and centrifuged at 3000 rpm for 11 minutes to obtain a precipitate of the complex. This precipitate was dissolved in 150 ml of water, the pH was adjusted to 8 with 3N sodium hydroxide, and dialyzed with running water for about 20 hours. The dialysate was adjusted to pH 8 with 3N7] sodium oxide and concentrated under reduced pressure to obtain an aqueous sol of chondroitin sulfate-magnetic iron oxide complex.

The magnetic measurement result of the obtained chondroitin sulfate monomagnetic iron oxide complex is shown. A hysteresis curve was drawn using a sample vibrating magnetometer (VMS: Vibrating Sample magnetometer) manufactured by Toei Kogyo Co., Ltd., and the saturation magnetization was determined from this curve. As the measurement sample, a sample (S1 to S5) randomly sampled from the fine powder particles obtained by drying the aqueous bull was used and packed in a measurement capsule, and the result was converted to the value per 1 g of the sample. did. Iron oxide fine particles (S6) not coated with chondroitin sulfate were similarly measured and compared. FIG. 2 shows the magnetization curves of the samples S1 to S5. Table 1 shows the saturation magnetization of samples S1 to S6. table 1

FIG. 2 clearly shows that the resulting composite is a superparamagnetic material. In other words, this magnetization curve follows the same locus with respect to the reversal of the external magnetic field, indicating that the obtained iron oxide fine particles have a single magnetic domain structure. Specifically, iron oxide fine particles having the same initial magnetization curve, demagnetization curve, and magnetization curve are considered to have no magnetic anisotropy while being a superparamagnetic material, and have no remanent magnetization and a low coercive force. Not observed at all In addition, the particle size of the chondroitin sulfate-magnetic iron oxide complex was measured by a dynamic light scattering method using a dynamic light scattering light intensity system, and the particle size distribution was determined by histogram method analysis. The results are shown in Table 2.

Table 2

Fig. 3 shows a transmission electron micrograph (TEM, magnification: × 1,000) of the chondroitin sulfate-monomagnetic iron oxide complex. In the same figure, each black lump indicates a chondroitin sulfate-magnetic iron oxide complex.

The analysis results of the above aqueous bull are shown below.

Iron concentration: 31.6mg / m1

Chondroitin sulfate concentration: 43.5mg / m1

pH: 7.0

Average core particle size: 4.1 nm

Magnetization at 1 Tesla (10K) 21.3 emu / 1 g iron

T 1 mitigation ability: 3.3 (s e c · πιΜ)

Τ2 Mitigation ability: 6.0 (sec-mM) "

Overall average particle size: 42 nm

Production Example 2

(Production of chondroitin sulfate monomagnetic iron oxide composite) 29. 86 g of F eC 13 - 6H ₂ 〇 soluble _ construed in distilled water 8 OML a, after the A r substituted 10 minutes, 5. 49 g added FeC 1 _₂ · 4Η ₂ 0 under Ar And completely dissolved. All iron content were charged is 0.1 to 3 mol, Fe ²⁺ ZFe ^{3 +} was 1Z 4.

On the other hand, an aqueous solution in which 43 g of chondroitin sulfate was dissolved in 120 ml of distilled water was heated to 80 ° C under an Ar atmosphere, and the above iron chloride solution was added at a stretch.

While maintaining the temperature at 80 ± 5 ° C, the pH was adjusted to 11 by dropwise addition of 3 N sodium hydroxide with stirring. Then, 6 N hydrochloric acid was added dropwise to adjust the pH to 6.9. In this state, the solution was heated for 1.5 hours while keeping the temperature of the solution at 100, and then cooled to 14, and then centrifuged at 3000 rpm for 30 minutes to separate a supernatant. 310 ml of acetone was added to 400 ml of the supernatant, and centrifuged at 2000 rpm to obtain a precipitate of the complex. The precipitate was dissolved in 120 ml of water, adjusted to pH 8 with 3 N sodium hydroxide, and dialyzed with running water for about 15 hours. The pH of the eluate was adjusted to 8 with 3 N sodium hydroxide, filtered through a 0.45 m membrane filter, concentrated under reduced pressure, and concentrated under reduced pressure to obtain an aqueous sol of chondroitin sulfate-magnetic iron oxide complex. I got The analysis results of this aqueous sol are shown below. Iron concentration: 56.5 mg / m 1

Chondroitin sulfate concentration: 71.2 mg / m 1

pH: 6.9

Average core particle size: 6.3 nm

Magnetization at 1 Tesla (1 OK): 32.6 emuZl g iron

T 1 relaxation ability: 4.4 (sec-mM)

T 2 relaxation ability: 9. 8 (sec · mM) one ¹

Overall average particle size: 69 nm

Test example 1 (in vivo MR imaging)

After anesthesia by injecting 0.25 cc of Nembutal into the abdominal cavity of a rat (Wistar, 3 weeks old, weighing 300 g), a spin echo (Spin Echo) method was performed on the liver, kidney and muscle site before injection of the contrast agent. Slice in axial direction 3 mm thick T1-weighted image (repetition time: 60 Oms, echo time: 15 ms), T2-weighted image (repetition time: 200 Oms, echo time: 9 Oms) and proton density (PD) image (repetition Time: 200 Oms, echo time: 15 ms) was taken as the control image.

Then, after administering 0.3 cc (concentration: 13.0 M) of the complex (contrast agent) obtained in Production Example 1 to the tail vein, the same spin echo as described above was performed within about 15 to 30 minutes. T1-weighted image (repetition time: 600 ms, echo time: 15 ms) and proton density (PD) image (repetition time: 2000 ms, echo time: 15 ms) ) Was imaged, and the change in signal intensity was compared with the control image before administration of the contrast agent. The values of the signal strength of the image were set for the mouth (region of interest) on the CRT (display) screen, and the average value was calculated. Tables 3 and 4 show the results. A clinical MR device (Magnetom (trade name, SIEMENS), static magnetic field strength: 1.5 T) was used as the imaging device.

Table 3 shows the T1-weighted image, and Table 4 shows the signal intensity for each concentration when the proton density-weighted image was captured.

Table 3 s ^ (τ ι: 6oo / i5. 6 minutes after administration) Control 10 mol / g 20 mol / Kg 40 Lord 1 / g 80 / zmol / Kg Blood 462 ± 34 686 ± 40 876 ± 37 1340 ± 51 1301 ± 52 Liver 646 ± 38 418 ± 46 375 ± 41 242 ± 50 215 ± 68

575 ± 66 637 ± 55 667 ± 65 718 ± 74 719 ± 81

516 ± 48 624 ± 46 597 ± 49 π9 ± 68 786 ± 51 Spleen 5 ± 63 345 ± 38 50 is 37 316 ± 62 269 ± 89 Skeletal muscle 394 ± 54 431 ± 35 380 ± 33 413 ± 38 427 ± 40 heart Muscle 470 ± 45 577 ± 71 667 ± 54 578 ± 28 58 is 16 Table 4 ^ sm ^. (Proton density: 2500/15. 6 o min after administration)

From Tables 3 and 4, it can be seen that the signal intensity of the renal cortex and renal medulla, which is rich in blood flow and blood, is increased at the Τ1-weighted and proton density, and conversely, the signal is decreased in the liver. That is, the signal intensity of the blood vessel was enhanced. A similar effect was obtained when the complex (contrast agent) 0.4 CC (concentration: 8.8 Μ) obtained in Production Example 2 was administered to the tail vein of a rat in the same manner as described above.

Test example 2 (in vivo MR imaging)

FIG. 4 shows an MR angiography image around the rabbit heart and aorta in comparison with the MRI contrast agent of the present invention and Gd-DTPA. The right of the photograph is an image obtained by using the MRI contrast agent of the present invention (contrast agent obtained in Production Example 1), and the left is an image obtained by using a conventional Gd-DTPA (trade name: Magnepist, manufactured by Schering AG).

The test conditions are as follows.

3D-FLASH s e qu e n c e,

Model used: Magnetom 1.5 made by Siemens

TR: 40 ms e c. TE: 10 ms e c.

f l i p a n g 1 e: 20 degr e e s

As is evident from Fig. 4, the blood vessels near the rabbit heart and aorta are clearly imaged. Therefore, the MRI contrast agent of the present invention can clearly display a blood vessel image that cannot be seen with a normal contrast agent, and its contribution to future medical treatment is immeasurable.

Claims

The scope of the claims .

1) Magnetic iron oxide fine particles having an average particle size of 2 to 20 nm and having a single magnetic domain structure are used as a core, and the surface of this core is composed of a sulfone group, a ketone group, an amino group, a carboxyl group, and an alkyl group. A magnetic resonance contrast agent characterized by being coated with a polysaccharide having a functional group selected from the group.

2. The magnetic resonance contrast agent according to claim 1, wherein the magnetic iron oxide fine particles are ferrite particles.

3. The polysaccharide is chondroitin 4-sulfate, chondroitin 6-sulfate, hyaluronic acid, chitin, heparin, sialic acid, neuraminic acid, acetylhexosamine, inulin, agarose, dextransulfonic acid, and N-acetylglycosamine. 2. The magnetic resonance contrast agent according to claim 1, which is selected from the group consisting of derivatives.

4. The magnetic resonance contrast agent according to claim 1, wherein the average particle size is 30 to 200 nm.